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Human biochemistry, Medical Biotechnology, inglese

Programma

ABC transporters
Structure
Mechanism of action
Role in cell physiology
Role in drug resistance

Membrane lipids: architecture, dynamics and biological functions
In/out asymmetry and lateral asymmetry in pathophysiological processes
Aminophospholipids in membrane fusion, cytokinesis clotting, phagocytosis and apoptosis Phosphosinositides: compartimentalization,... Vedi di più

Esame di Human biochemistry docente Prof. P. Viani

Anteprima

ESTRATTO DOCUMENTO

LDL OXIDATION and FOAM CELLS

There!is!no!evidence!of!acetyl;LDL!role!but!there!is! This!is!at!the!basis!of!bad/cholesterol,!that!is!the!cholesterol!associated!to!LDL!(while!HDL!→!

evidence!for!the!physiological!role!of!oxidized!LDL:! good!cholesterol).!

they!are!taken!up!by!scavenger!receptor.!! !

SR;A! and! CD36! are! both! scavenger! receptors! that! Metabolism1of1HDL1

can! recognized! other! molecules,! but! mainly! they! LDL!are!generated!through!the!manipulation!of!VLDL!(there!is!not!a!direct!synthesis!of!LDL),!

are! not! regulated,! so! the! modified! LDL! can! induce! HDL! can! be! assembled! or! be! the! product! of! manipulation! of! the! modification! of! both!

the! foam! cells! formation! because! up! take! is! rapid! chylomicrons!and!VLDL!in!the!bloodstream.!

and! the! scavenger! receptor! aren’t! down;regulated! !

after!the!increase!of!cholesterol!in!the!cell.! HDL!precursors!can!be!synthesized!in!the!liver!and!small!intestine:!they!have!discoidal!shape!

So! modified! LDL! can! be! taken! up! by! the! and!they’re!mainly!formed!by:!

macrophages!through! scavenger! receptors! SR;A! or! ; Phospholipids!

CD36:! both! of! them! can! recognize! also! other! ; Cholesterol!(but!not!cholesterol!esters)!

Rocha & Libby 2009 Nature Reviews Cardiology

molecules/particles! but! they’re! not! regulated:! the! ; ApoA;II!!

Steiberg D 2002 Nature Medicine

oxLDL!can!induce!foam!cell!formation!because!the!uptake!is!rapid!and!the!scavenger!receptor! ; LCAT.!!

isn’t!downregulated!in!response!of!an!increase!in!cholesterol!levels.!! HDL!precursors!are!a!piece!of!membrane,!they’re!flat,!and!they!can!interact!with!extra;hepatic!

incubation of neither monocytes and macrophages nor

On!the!oxLDL!the!recognition!site!for!the!receptor!is!modified!so!the!particle!can!interact!with! tissues.!In!this!interaction!two!ABCs!play!a!role:!the!ABC!stimulate!the/transfer/of/cholesterol/

arterial smooth muscle cells with native LDL, even at

very high concentrations, increases their cell

different! receptors,! but! the! hydrophobic! core! is! the! same,! so! we! have! an! accumulation! of! from/ the/ membrane/ of/ the/ cell/ to/ the/ HDL/ precursor,! and! the! enzyme! LCAT! determines! the!

Metabolism of HDL

cholesterol content substantially

cholesterol!esters.! conversion/ of/ cholesterol/ in/ cholesterol/ esters! (by! using! the! acyl! chain! in! position! 2! of! the!

! phospholipid,!the!product!is!cholesterol!ester!and!lysoPC).!!

acetyl LDL or oxLDL can induce foam-cell formation HDL LCAT

We!can!have!a!potential!oxidation!of!LDL!in!the! When!cholesterol!esters!are!produced!the!hydrophobic!core!can!be!formed:!the!flat!structure!

because uptake is rapid and the scavenger receptors

do not downregulate in response to an increase in

bloodstream! but! it! occurs! in! a! minimum! part! becomes!spherical.!!

cellular cholesterol.

because!the!bloodstream!is!characterized!by!an! da custom medical stock VLDL CM remnants

photo/science photo library

high! level! of! antioxidant! protection:! the!

antioxidant! system! (ascorbate,! glutathione,!

enzymes,! vitamins…)! is! very! concentrated! in!

the!blood!because!the!concentration!of!oxygen!

is!very!high,!so!the!plasma!is!characterized!by!

an! high! barrier! against! oxidative! stress! and!

this!is!associated!to!the!possibility!to!maintain!

the!oxidized!LDL!low.!! !

This!is!not!true!in!the!tonaca/intima:!LDL!particles!can!be!internalized!in!the!sub;endothelial!

space,!where!the!environment!can!determine!an!oxidation!of!LDL!particles,!also!macrophages!

can! act! through! an! oxidative! pathway,! and! this! oxidative! environment! can! generate! oxLDL! !

that!can!be!recognized!by!scavenger!receptors!on!macrophages!which!are!then!converted!into! HDL!are!classified!as:!

foam1cells.! Schematic representation of the effect of OxLDL on ; HDL !→!have!the!LCAT!associated!

3

! macrophages via CD36 scavenger receptor ; HDL !→!have!lost!the!LCAT!because!have!reached!the!maximal!dimension!

2

! They!can!both!be!internalized!by!the!liver.!!

The! interaction! of! oxLDL! with! the! scavenger! !

receptor! is! not! limited! to! the! uptake! of! oxLDL! HDL!precursors!can!be!also!generated!by!the!manipulation!of!VLDL!and!CM:!if!you!remove!all!

apoptosis

but! can! also! act! as! a! signalling/ event:! it! can! triglycerydes! from! VLDL! and! CM,! the! phospholipid! layer! can! associate! proteins! and! it!

induce! a! downstream! activation! of! signalling! represents!the!initial!empty!pocket!of!HDL.!

pathways!that!result!in:! !

; Apoptosis! LCAT/reaction/

; Production/ of/ cytokines! that! can! promote! Cholesterol!is!esterified!using!the!acyl;chain!in!position!2!of!the!phospholipid!producing!the!

apoptosis! cholesterol!ester.!

; Increase/ the/ amount/ of/ CD36/ expressed! in! Cholesterol!+!lecithin!!!Cholesterol!ester!+!Lysolecithin!

the!membrane!→!CD36!has!not!a!negative! This!LCAT!is!different!from!the!one!that!works!in!the!cell,!in!which!we!have!the!ACAT/enzyme/

regulation! so! this! mechanism! induces! a! (AcylOCoaA/ Cholesterol/ Acyl/ Transferase):! into! the! cell! the! acyl! chain! derives! from! acyl;CoA,!

potentiation!of!oxidized!LDL!accumulation.!!

OxLDL bind to CD36 and trigger the activation of transcription factor PPARγ, which leads to while!in!the!HDL!the!only!precursor!of!the!acyl!chain!is!the!phospholipid.!!

an increased presentation of the receptor to the macrophage surface. NFκB is also targeted

by OxLDL stimulation inducing the synthesis of diverse cytokines. OxLDL stimulation in

! 9! ! 10!

macrophages triggers the activation of kinases related to CD36 such as Lyn, MEKK2, JNK1

and JNK2.

So!we!start!form!flat!structures!loaded!with!cholesterol!that!is!then!converted!in!cholesterol! Mechanism/of/function/of/ABCs/

esters,!and!this!occur!in!extra;hepatic!tissues!and!macrophages.!! Two!models!have!been!described!for!ABCA1:/

! 1. ABCA1! is! associated! to! the! membrane! and! act! as! a! receptor! for! the! ApoA;I! with!

The!phospholipid!flat!bilayer!is!stabilized!by!proteins:! affinity;! ABCA1/ act/ as/ a/ cholesterol/ floppase/ and/ accumulates/ cholesterol/ in/ the/ outer/

layer,! and! when! cholesterol! is! associated! to! the! outer! layer! can! exchange! with! the!

Lipid6free1 isolated1 Apo6I! in! the! absence! of! lipid! consists! only! in! an! N! terminal!

• →! ApoA;I! containing! particle! and/so/be/transferred/to/the/lipoprotein.! LCAT! is! associated!

antiparallel!4;helix!bundle!with!2!α;helixes!at!the!C;terminal.!! to! the! lipoproteins,! converts! cholesterol! in! the! cholesterol! esters! and! so! removes!

Truncated1 ApoA6I1 this! structure! lacks! the! first! 43! aa:! the! molecular! shape! of! the!

• →! cholesterol!from!the!equilibrium,!creating!an!efflux!of!cholesterol!in!the!HDL!

protein!is!like!a!ring,!it!has!a!more!open!structure.!This!is!the!conformation!that!intact! cytoplasm cytoplasm

2. ABCA1! is! the! receptor! fro! ApoA;1:! this! structure/ is/ internalized! and! it! works! on!

ApoA;I! can! assume! interacting! with! lipids.! When! the! protein! is! associated! to! cholesterol! rich;domain! inside! the! cell;! ApoA;1! is! loaded! with! cholesterol! inside! the!

phospholipids,! it! assumes! this! conformation,! so! this! protein! can! stabilize! the! cell,!so!the!complex!ApoA;I/ABCA1!is!internalized!and!works!inside!the!cell!and!then!is!

interphase.! release!with!an!exocytotic!mechanism.!

The! evolution! can! be:! from! ApoA1! (a),! adding! cholesterol! and! phospholipids,! the! Extracellular space Extracellular space ABCG1

ABCA1

protein! goes! around! the! bi;layer! (b).! In! a! phospholipid! bilayer,! you! have! a! right!

interaction! of! polar! head! on! the! side,! the! problem! in! the! interface.! The! helixes! are! 1

amphipathic!helixes,!with!hydrophobic!aminoacids!inside!and!hydrophilic!aminoacids! 2

outside.!The!protein!conformation!change!when!the!lipoprotein!structure!change!(c).! LXR/RXR LXR/RXR ABCG1

!

! PPAR traffic

ABCA1 increase

! For!ABCG1!we!have!a!mechanism!that!it!is!like!the!first!hypothesis!for!ABCA1:!ABCG1/is/not/

T1/2 1-2 h

*Prolin!is!the!amminoacid!that!interrupts!the!α;helix!because!its!N;residue!cannot!be!involved! able/to/recognize/specifically/ApoAOI,! but! in! this! case! cholesterol! is! accumulated! in! the! outer!

degradation is blocked

Calpain-dependent

in!the!bonds!that!stabilize!the!structure!of!the!α;helix.! layer! and! can! be! exchanged! with! the! lipoprotein,! and! LCAT! always! promotes! the! efflux! of!

by apoprotein binding

cytoplasm cytoplasm

by PUFA-induced ser

! Destabilized

cholesterol.!! phosphorylation

! ABCG1/can/work/only/on/HDL,/it/cannot/work/on/the/precursor/of/HDL/that/is/substrate/only/for/

Once!we!have!assembled!HDL,!they!are!able!to!remove!cholesterol!from!cells.!! ABCA1!!! But! the! capacity! to! transfer! cholesterol! by! ABCA1! is! not! enough! to! remove! all! the!

ApoA6I/interacts!with/ABCA1!that!promotes!the!transfer/of/cholesterol/from/the/cell/to/the/HDL! cholesterol,!so!we!also!need!ABCG1.!

Extracellular space Extracellular space

in! the! discoidal! form.! When! the! HDL! is! converted! in! a! real! lipoprotein,! so! when! the! ABCG1

ABCA1

hydrophobic!core!is!formed,!HDL !interacts!also!with!ABCG1!(half!transporter,!so!it!works!as!

3 1

homodimer):!ABCG1!can!transfer!other!free!cholesterol,!LCAT!converts!it!in!cholesterol!esters! 2

(also!for!ABCA1).!!

ABCA1! and! ABCG1! can! transport! only! free/cholesterol! (not! esters)! that! then! is! converted! in!

cholesterol!esters!by!the!LCAT!when!it!is!associated!to!the!HDL.!

The!HDL!is!the!product!of!the!maximal!capacity!of!cholesterol!extraction!from!cells.!!

HDL!can!be!modified!by!the!activity!of!the!Cholesterol/Esters/Transfer/Protein/(CETP)!that!can! !

!

exchange! cholesterol! esters! with! triglycerides! from! triglycerides! rich! particles! (this! occurs! LXR/RXR

!

with!IDL!but!mainly!with!VDLD)!and!move/triglycerides/from/VLDL/to/HDL.!!

The! manipulated/ HDL/ can/ be/ taken/ up/ in/ the/ liver! and! this! can! occur! through! the! The!levels!of!these!proteins!are!under!control!of!transcriptional!factors!such!as!PPARα,!which!

LXR/RXR ABCG1

PPAR traffic

internalization! of! the! particle! and! the/ exchange/ of/ HDL/ cholesterol! with! the! hepatocytes! is!involved!in!the!control!of!lipid!metabolism.!!

ABCA1 increase

through! a! scavenger! receptor! SR6B1;! in! this! case! there! is! the! release/ of/ ApoAOI! that! can! be! ABCA1! is! characterized! by! a! high! turnover! and! that! can! be! blocked! by! the! ApoA;I! binding!

T1/2 1-2 h

associated!to!another!phospholipid!bilayer.!! because!it!blocks!the!calpain;dependent!degradation;!the!same!protein!can!be!destabilized!by!

degradation is blocked

Calpain-dependent

! by apoprotein binding PUFA!which!can!induce!Ser!phosphorylation.!!

by PUFA-induced ser

Destabilized

Why!there!are!two!ABC!transporters!to!remove!cholesterol!from!extra;hepatic!tissues?! There! is! also! a! control! by! LXR/RX! factors:! these! transcriptional! factors! can! be! activated! by!

phosphorylation

ABCG1! can! operate! in! conditions! in! which! ABCA1! is! not! more! able! to! work,! but! ABCG1/can/ retinoic!acids!or!oxysterol!(that!is!a!product!of!cholesterol)!and!they!can!improve!the!system!

operate/only/on/the/products/of/ABCA1/activity.// that! can! remove! cholesterol! from! cells.! So! cholesterol/ increase/ the/ system/ involved/ in/ the/

/ cholesterol/removal! because! cholesterol! is! very! dangerous,! it! can! impact! on! the! flexibility! of!

/ the!membrane.!

! 11! ! 12!

! !

Efflux/of/cholesterol/from/arthery/wall/ 3.2.17!

In! the! first! step! the! precursor! of! HDL! interacts! with! ABCA1;! the! second! step! is! operated! by! Liver 1

ABCG1:!there!is!the!definition!of!the!HDL !that!is!the!final!step!of!HDL!generation.!! The/role/of/liver/in/metabolic/homeostasis/

2

HDL !are!smaller!that!HDL !because!the!hydrophobic!core!is!smaller,!HDL !can!be!charged!of! Liver!has!two!main!traits!that!make!it!central!in!the!process!of!metabolic!homeostasis:!

3 2 3

cholesterol!esters!by!the!activity!of!ABCG1!and!LCAT,!then!they!reach!the!maximal!dimension! ; High/metabolic/capacity/

that!they!can!rich.! ; High/metabolic/flexibility/and/adaptation!

That’s!why!HDL!are!known!as!“good!cholesterol”!because!they!can!remove!cholesterol!from! !

macrophages!and!so!counteract!the!formation!of!foam!cells.! Liver! is! like! a! hub! that! can! receive! from! intestine! monosaccharaides,! aminoacids,! lipids! and!

! bile!but!also!catabolic!intermediates!(like!lactate),!aminoacids,!lipids!and!waste!products!from!

Mature!HDL!can!be!uptaked!in!the!liver!by!SR; the!other!tissues.!These!are!the!possibilities!to!address!to!liver!some!substrates.!!

B1:!cholesterol!than!can!be!associated!to!VLDL! On!the!other!hand!liver!is!crucial!for!the!synthesis!of!plasma!proteins,!Glucose,!lipids,!ketone!

and! be! used! in! the! liver.! Cholesterol/ cannot/ be/ bodies.!!

catabolized,! but! the! only! way! to! eliminate! it! is! The! other! function! of! liver! is! detoxification! that! is! associated! to! the! urea! cycle,! and! also! the!

to! use! it! as! a! precursor! of! bile! salts,! which! are! conversion/of/other/metabolites/in/nonOtoxic/products.!!

synthesized! in! the! liver,! but! part! of! it! can! be! Liver!is!also!the!tissue!that!produces!all!the!components!of!the!bile.!

released! directly! in! the! liver! duct! thanks! to! a! There!are!many!pathway!that!go!from!tissues!to!liver!and!many!processes!that!go!from!liver!

transporter!that!can!accumulate!it!in!the!bile.! to! other! tissues:! all! these! substrates! are! the! way! by! which/liver/can/sustain/the/other/tissues/

! from/an/energetic/point/of/view.!!

Also! ABCG5/8/ are/ involved/ in/ the/ transport/ of/ !

cholesterol/ in/ the/ bile.! In! general! ABCG! are! Since!lipids!can!be!an!energy!supply!for!some!tissues!like!skeletal!muscle,!but!they!can!also!be!

strongly!involved!in!sterol!transport.! addressed! to! the! adipose! tissue,! liver! can! also! contribute! to! the! energy! storage! that! is!

! associated! to! the! accumulation! of! lipids! in! the! adipose! tissue:! the! de/ novo/ synthesis/ of/

! triglycerides/is/more/efficient/in/liver/than/in/adipose/tissue.!!

Pathological/conditions/ Ketone!bodies!can!be!energy!supplier!for!brain!and!muscles.!!

In!the!normal!condition!the!amount!of!cholesterol!inside!the!cell!is!a!balance!of!what!we!can! !

remove! through! ABCA1! and! what! we! assume! through! LDL;R,! and! the! respective! control! of! There!are!two!major!cell!types!in!liver:!

these!two!receptors.!Cellular!cholesterol!inhibits!internalization!on!LDL;R!and!stimulate!the! ; Hepatocytes!→!60;80%!

efflux!on!ABCA1.!But!cholesterol!is!also!associated!to!many!pathologies:!! ; Kupffer!cells!(macrophages)!→!15;30%!

; Familial/hypercholesterolemia!→!if!there!is!defect!in!the!LDL;R:!the!cell!cannot!assume! !

cholesterol!from!outside!but!depends!only!the!cholesterol!biosynthesis,!but!it!has!the! We!can!distinguish!between!processes!that!can!take!place!only!in!hepatocytes!and!processes!

system!to!efflux!cholesterol!through!HDL,!so!there!is!an!accumulation!of!cholesterol!in! that!take!place!mainly!in!hepatocytes.!!

the!bloodstream! Processes! that! take! place! only! in! Processes! that! take! place! mainly! in!

; Tangier/disease!→!the!uptake!of!cholesterol!is!normal,!but!the!remove!of!cholesterol!is! hepatocytes:! hepatocytes:!

inhibited! or! low;! this! is! associated! to! a! defect! in! ABCA1.! The! accumulation! of! ; Synthesis/ketone/bodies/ ; Urea/cycle/

cholesterol!inside!the!cell!is!the!demonstration!that!ABCG1!is!not!able!to!generate!an! ; Synthesis/of/bile/acids/and/pigments/ ; Synthesis/of/uric/acid/

efflux!of!cholesterol!without!the!activity!of!ABCA1.!! ; Synthesis/of/plasma/proteins/ ; Gluconeogenesis/

; Detoxification/processes/ !

!

/

/

LDLR !

Metabolism/of/monosaccharides//

In!liver!there!are!two!specific!enzymes!that!are!not!present!in!other!tissues:!

Galactokinase!

cholesterol Fructokinase!

These!two!enzymes!are!able!to!phosphorylate!Galactose!and!Fructose!in!C1.!!

cell Galactose! and! Fructose! can! also! be! phosphorylated! in! position! C6! by! Hexokinases! in! other!

familial TANGIER disease

Control tissues,!but!phosphorylation/in/C1/occurs/only/in/liver.!

hypercholesterolemia !

! 13! ! 14!

! There!are!two!pathologies!associated!to!a!defect!in!the!activity!of!these!two!enzymes:!

Galactose! ; Fructosuria! leads! to! an! accumulation! of! Fructose! due! to! a! saturation! of!

→!

Galactose;1P! can! be! used! for! the! generation! of! UDP;Galactose! by! the! enzyme! GalactoseO1PO Fructokinase;!Fructose!can!be!anyway!used!because!it!can!be!phosphorylate!in!C6!by!

uridylyltransferase!(GALT).! an!Hexokinase1!(that!has!a!broad!specificity)!!

In!the!liver!UDP;Galactose!can!be!used!for!the!synthesis!of!Lactate,!Glycoproteins,!Glycolipids! ; Fructosemia!→!Aldolase!B!is!inactive!so!we!have!the!accumulation!of!Fructose;1P!that!

or!it!can!be!converted!into!UDP;Glucose!by!the!UDP;Hexose;4!Epimerase!and!this!addresses! determines!an!impairment!in!the!Glucose!metabolism!because!Fructose;1P!can!affect!

Galactose!to!the!Glucose!metabolism.!! both! gluconeogenesis! and! the! use! of! Glucose! (because! it! can! impair! the! activity! of!

In!the!other!tissues!UDP;Galactose!can!then!be!used!to!synthesize!Lactose!and!in!the!liver!can! Fructokinase)!and!this!results!in!hypoglycaemia.!!

be!used!for!the!synthesis!of!Glycoproteins!and!Glycolipids.!! The!only!way!to!counteract!this!pathology!is!the!removal!of!Fructose!from!diet.!

! 1

All/ the/ monosaccharides/ can/ derive/ from/ Glucose/ and/ can/ be/ converted/ into/ Glucose:! all! 1

saccharides! can! be! produced! starting! from! Glucose! and! can! be! used! as! energy! suppliers! Liver1in1Glucose1homeostasis1

converting!them!into!Glucose.!! The!metabolic!processes!that!take!place!in!the!liver!recapitulate!all!the!biochemistry.!!

The! presence! of! UDP! group! in! UDP;Galactose,! protects! the! position! C1! that! is! the! most! In!the!well6fed1 state1 the!concentration!of!Glucose!in!blood!is!high!as!well!as!the!capacity!of!

reactive! position! in! the! sugar! molecule,! and! then! the! UDP;Hexose;4! Epimerase! can! work! in! liver!to!storage! Glucose!that!is!6mg/Kg/min.!Glucose!can!enter!the!hepatocyte!through!the!

position!C4!leading!to!the!conversion!into!Glucose.!! transporter!GLUT2:!the!internalized!Glucose!is!phosphorylated!to!Glu;6P!that!can!be!used!for!

! the!synthesis!of!Glycogen!or!can!be!addressed!to!the!Glycolysis!to!product!Pyruvate.!!

GALT!is!the!enzyme!defective!in!galactosemia.!! Pyruvate!can!then!be!converted!to!Acetyl;CoA!that!can!be!used!to!produce!energy!for!the!cell,!

When! GALT! is! not! active! there! is! an! alternative! pathway! (only! in! adults)! that! converts! but!the!majority!is!addressed!to!synthesis!of!Fatty!Acids,!and!from!there!obtain!the!substrate!

Galactose;1P! into! Glucose;1P.! This! pathway! performs:! the! synthesis! of! UDP;Glucose,! the! that!needed!to!synthesize!Triglycerides,!that!is!Glycerol;3P.!!

transfer!of!the!UDP;group!from!Glucose!to!Galactose;1P.! Acetyl;CoA! can! be! also! used! for! the! Cholesterol! synthesis,! and! both! Cholesterol! and!

The! enzyme! involved! is! a! Uridylyl! Transferase! enzyme! Triglycerides!can!be!assembled!into!VLDL!to!deliver!them!to!other!tissues.!

that!uses!as!substrate!UDP;Glucose.! !

UDP;Glucose! can! transfer! the! UMP! group! to! the! During!fasting1state!all!these!pathways!are!inactivated!and!liver/produces/Glucose!with!a!rate!

Galactose;1P! giving! rise! to! the! formation! of! UDP; of!2mg/Kg/min,!that!is!lower!than!the!rate!of!Glucose!storage!during!well;fed!state.!!

Galactose!and!Glu;1P.! In! this! condition,! substrates! like! Lactic! Acid,! Aminoacid! and! Glycerol! can! be! converted! into!

UDP;glucose!can!then!transfer!the!UDP!group!to!the!Gal; Glucose! through! Gluconeogenesis,! which! can! occur! thanks! to! the! capacity! of! liver! to! oxides!

1P!giving!rise!to!the!formation!of!two!products:! these!substrates.!Glucose;6P!can!also!derive!from!the!degradation!of!Glycogen.!

; UDPOGalactose!→!can!be!converted!to!UDP;Glucose! In!liver!can!also!occur!the!dephosphorylation!of!Glu;6P!because!Glucose!can!be!transported!

through! the! activity! of! the! UDP;Hexose;4! only!by!GLUT2!in!the!dephosphorylated!form.!

Epimerase! So!also!during!fasting!all!the!pathways!are!activated:!in!the!well;fed!state!they!are!activated!

; GlucoseO1P!→!can!then!be!converted!into!Glu;6P!by! by!insulin,!while!in!the!fasting!state!they’re!activated!by!glucagon.!

the!Phosphoglucomutase.! !

! GLUT2!

UDP;Glucose!+!Galactose!1;phosphate!!!Glucose!1;phosphate!+!UDP;Galactose! The! transport! of! Glucose! is! bidirectional:! all! the! passive! transports! for! Glucose! are!

! bidirectional,!but!if!you!consider!that!liver!has!to!internalize!a!large!amount!of!Glucose!when!

Fructose! it!is!high!in!blood!and!release!a!large!amount!of!Glucose!when!it!is!low!in!blood,!we!have!to!

!Fructose! can! be! phosphorylated! into! Fructose;1P! which! can! be! converted! by! an! Aldolase! B! imagine!the!presence!of!an!high/capacity/and/low/affinity/transport!that!is!operated!by!GLUT2!

(different!from!the!Aldolase!A!active!in!Glycolysis)!into:! (capacity!of!10M),!with!a!passive!transport.!

; DHAP! !

So!GLUT2!is!“the!door”,!than!you!need!something!that!can!trap/release!Glucose!inside!the!cell:!

; Glyceraldehyde! it! is! not! phosphorylated! because!

→! these!functions!are!performed!by!two!liver;specific!enzymes:!

Aldolase/B/works/on/Fructose/when/it/has/just/one/group/

phosphorylated;/ Glyceraldehyde! can! then! be! converted! ; Glucokinase!→!phosphorylates!Glucose!into!Glu;6P!in!the!well;fed!state!

into!Glycerol.! ; GluO6P! Phosphatase! removes! the! P;group! during! fasting! so! that! Glucose! can! be!

→!

So!Fructose;1P!can!be!used!as!an!energy!supply!independently! released.!!

of!the!activity!of!the!enzymes!active!in!Glycolysis!(that’s!why!it!can!be!used!also!by!diabetics).! !

! !

! !

! 1

! 1

! 15! ! 16!

Glucokinase1 Glucose!can!also!regulate!the!subcellular!localization!of!the!enzyme.!!

Glucose!can!enter!the!nucleus:!in!resting!condition!Hexokinase!IV!is!associated!to!the!nucleus!

Glucokinase!(Hexokinase!IV)!is!expressed!in!liver!and!pancreas!β!cells!and!it!has!a!high!Km!(6; because!there!is!a!regulatory!protein!that!traps!it!in!the!nucleus.!!

10mM).! This! enzyme! has! a! high/ capacity/ and/ low/ affinity! because! it! works! when! the! When!Glucose!increases!there!is!the!activation!of!the!transfer!of!Glucokinase!from!the!nucleus!

concentration!of!Glucose!is!very!high;!indeed!the!kinetic! to!the!cytoplasm!where!it!can!be!activated;!the!other!activator!is!FructoseO1P.!

of! Hexokinase! I! (the! enzyme! present! in! all! cells)! and! On!the!contrary!Fructose;6P!determines!a!transport!in!the!opposite!direction.!

Glucokinase!is!very!different:!Hexokinase!I!has!a!classic!

Km,! while! Hexokinase! IV! has! a! kinetics! that! remind! an!

allosteric! behavior,! even! if! it! is! a! monomeric! protein.!

Enzymes! can! have! an! allosteric! behaviour! only! if! they!

have!a!quaternary!structure,!so!in!Hexokinase!IV!there’s!

something!that!gives!rise!to!an!allosteric;like!behaviour!

but!starting!from!a!monomeric!protein.!

! ! !

! !

The!model!hypotisized:!! Many! proteins! have! been! identified! as! regulatory! proteins! for! Hexokinase! 4:! GCKR/

In!Hexokinase!I!there!are!two!domains!that!have!a!connection! (Glucokinase1 Regulatory1 Transfer1 Protein)! has! been! identified! as! involved! in! nuclear!

region:!the!enzyme!can!be!in!the!close/conformation/(active)/or/ sequestration.!

in/the/open/conformation/(not/active).!! In!fasting!condition,!Glucose!inside!the!nucleus!is!almost!zero!and!Glucokinase!is!sequestered!

The! binding/of/Glucose! to! the! enzyme! is! the! driving! force! that! in! the! nucleus! by! the! GCKR! regulator! protein.! When! Glucose! increases! in! cytoplasm,! it! can!

triggers!the!conformation!change!in!the!enzyme!from/the/open/ enter! the! nucleus! and! associate! to! the! enzyme! determining! a! change! in! the! enzyme!

to/the/close/conformation,!so!it!activates!the!enzyme.!! conformation!that!decreases!the!affinity!of!the!protein!for!GCKR,!so!there!is!a!splitting!of!the!

protein!from!its!regulator.!The!binding!of!Glucose!determines!a!change!in!conformation!that!

promotes!the!translocation!to!the!cytoplasm!where!the!enzyme!is!active.!!

GLUCOKINASE no

Fructose;1P! instead! acts! on! the! regulatory! protein:! it! binds! to! the! regulatory! protein! and!

In! the! Glucokinase! there! are! two! conformations:! the! decrease!the!affinity!of!the!GCKR!for!Glucokinase,!permitting!its!detachment!from!the!enzyme.!

Well Fed

Fasting la

superopen!(inactive)!and!the!close!(active)!conformation.!So! Mi

the! structure! is! the! same! as! Hexokinase! I,! but! in! this! case!

there!is!a!close!conformation!state!and!a!second!state!that!is! di

a! more/ open/ state! (compared! to! Hexokinase)! in! which! the!

sites!for!phosphorylation!are!more!distant.!! di

There! is! also! an! intermediate/ state! of! Glucokinase! that! tu

resembles!the!open!one!for!Hexokinase!I.! S

At/ low/ Glucose/ the/ enzyme/ is/ in/ the/ inactive/ superopen/ form,! i

while! upon! the! binding! of! Glucose! it! moves! to! the! gl

intermediate! (open)! state.! Then! it! moves! in! the! close! form! ! de

where!it!associates!ATP:!ATP!induces!the!phosphorylation!of! So!one!of!the!main!controls!of!Glucokinase!activity!is!the!compartimentalization/of/the/enzyme/

Glucose,!so!the!enzyme!goes!back!to!the!initial!conformation.! that/is/regulated/by/the/Glucose/levels./ tà

! ! si

! There!is!also!a!transcriptional!control!of!the!enzyme,!that!is!promoted!by:!

er

! ; PI3K! Transcriptional control

iv

This!cycle!is!slow,!but!when!you!increase!the!Glucose!concentration,!it!traps!the!enzyme!in!the! ; HIF;1α!

open! form! so! that! it! can! make! fast! cycle! because! the! enzyme! doesn’t! reach! the! superopen! Un

! Glucagon

Insulin

form:! And!it!is!inhibited/by/glucagon.!!

open/form/with/Glucose/bound/ /close/form/ /close/form/active/ ht

→ → ! PI3K/Akt

! / rig

This!can!justify!the!allosteric!behaviour!of!the!protein.!! HIF-1

/ SREBP 1c ?

! py

/ Increased gene expression

! 1 Co

! 1

! 17! ! 18!

metabolism from degradation to synthesis

la

i

M

Glu

glucose is the signal to swhitch the glycogen

activity no

i

Glycogen sinthase

metabolism from degradation to synthesis

d

Enzymatic la

di

Mi

Glucose66P1Phosphatase1 So!Glucose!can!control!Glycogen!metabolism!and!Glycogen/Phosphorylase/can/be/considered/as/

tu

Glu

The! phosphorylation! of! Glucose! in! position! C6! is! needed! for! all! the! metabolic! pathways! a/Glucose/sensor:!how!can!it!be!regulated!by!Glucose?!!

activity Glycogen phosphorylase

di

S

Glycogen sinthase

related!to!Glucose.!! In! fasting! condition! the! enzyme! is! in! the! form! Phosphorylase1 a! that! is! phosphorylated/and/

min

2 4 6 8 10

Enzymatic

Glucose!is!converted!into!Glucose;6P!to!be!converted!into!Glycogen,!to!enter!the!Krebs!cycle! active:!the!binding!of!Glucose!to!an!allosteric!site!induces!a!conformational!change!that!causes!

di

i

l

or!the!shunt.! the!exposition!of!two!phosphorylated!Ser!residues!that!are!rendered!available!for!the!activity!

eg

tu

Glucose;6P!produced!by!gluconeogenesis!or!by!glycogenolysis!must!be!converted!into!Glucose! of!the!Protein/Phosphatase/1!(PP1)!that!removes!the!P!group!giving!the!form!Phosphorylase1

Glycogen phosphorylase

S

(if!Glucose!has!to!move!from!liver!to!other!tissues)!by!GlucoseO6P/phosphatase.!! b!that!is!the!less/active/form/of/the/enzyme.! d

Glucose inhibits glycogen phosphorylase and facilitates

 min

2 4 6 8 10

i

! ! protein phosphatase activity gl

This!enzyme!is!associated!to!the!ER,!it!has!a!Km!for!Glucose;6P!of!2;3!mM.! de

si

Glucose;6P!concentration!in!the!cell!can!vary!between!0,05;1!mM,!and!the!first!control!of!the! Glucose inhibits glycogen phosphorylase and facilitates

enzyme! is! on! the! concentration! of! its! substrate:! only! when! Glucose! reaches! 1mM! Glu;6P! protein phosphatase activity

er

Phosphatase!can!work!at!its!high!maximum!capacity.!! si

iv

The!structure!is!characterized!by!the!presence!of!His!and!Arg!residues!in!the!catalytic!domain! PP1

er

that!faces/the/luminal/environment.!The!enzyme!has!also!a!TM!domain!and!the!N;terminal!is! Un !

luminal!while!the!C;terminal!cytoplasmic.! ! iv PP1

! After! the! dephosphorylation,! PP1! can! exert! its! activity! on! Glycogen! Synthase:! PP1! removes!

Un

t

The!enzyme!works!with!a!covalent/modification:!! the! P! group! on! the! Glycogen1 Synthase1 b! (inactive/form)! and! converts! it! into! the! Glycogen1

gh PP1

1. Transfer!of!the!P!on!His! Synthase1a!(active/form)!determining!the!activation!of!the!enzyme.!!

ht

2. Hydrolysis!of!the!P!group!from!His!that!is!then!transferred!to!Arg! PP1

yri

rig

op

py Glycogen Glycogen

synthase b synthase a

C

Co Glycogen Glycogen

synthase b synthase a !

!

Regulation/of/Glycogen/metabolism/

How!can!these!activities!be!coordinated?!The!coordination!and!the!sequential!activity!of!PP1!

!

For!the!activity!of!Glucose;6P!Phosphatase!in!the!ER!the!cell!need!a!transporter!for!Glu;6P,!for! and! the! two! enzymes! depends! on! the! structure! of! the! Glycogen/ granule:! all! the! proteins!

Glucose!and!for!the!P!group.! involved!in!Glycogen!metabolism!are!strictly!associated!to!Glycogen!granules!and!organized!in!

The!enzyme!is!regulated!by:!glucocorticoids/and/cAMP!and!it!is!negatively!regulated!by!insulin.! super!protein!complexes!containing:!

The! main! regulation! of! the! enzyme! is! based! on! the! substrate/concentration! (a! part! from! the! ; Glycogen/Phosphorylase/

transcriptional!regulation).! ; Glycogen/Synthase/

! ; Protein/Phosphatase/1/

6.2.17! ; Adaptor/protein/G /

M

Well6fed1state:1Glucose1storage16mg/Kg/min1 So! PP1! can! work! on! Glycogen! Phosphorylase! and! once! dephosphorylated! it,! it! can! work! on!

The!amount!of!hepatic!Glycogen!is!about!70gr!in!an!adult!male!of!about!70Kg,!if!you!consider! Glycogen! Synthase! and! the! organization! of! the! protein! complex! allows! this! sequential! PP1!

that!liver!is!about!1,5Kg!the!concentration/of/Glycogen/in/liver/is/the/higher/in/the/body,!while!in! activity.!

muscles!is!less!than!in!liver!even!if!the!total!amount!of!muscle!Glycogen!is!higher.! !

Liver/Glycogen/concentration/undergoes/in/vary/rapid/changing/from/the/concentration/of/10gr/ Insulin! can! promote! to! the! phosphorylation! of! the! two! enzymes! because! it! can! activate! an!

glucose is the signal to swhitch the glycogen

per/100gr/in/the/wellOfed/state/to/0,3/0,5gr/per/100gr/in/fasting/condition! and/during/exercise,! insulin;sensitive!kinase!which!can!phosphorylates!the!adaptor!protein!G .!

no M

metabolism from degradation to synthesis

because!liver!Glycogen!can!support!the!activity!of!skeletal!muscles.!! G !has!two!sites!of!phosphorylation!that!can!be!phosphorylated!by!two!different!proteins:!

M

ila

! Insulin6sensitive1kinase!→!Insulin!binds!to!its!receptor!and!induces!the!activation!of!

M How!can!this!variation!be!regulated?!Glucose!represents! a!kinase!that!phosphorylates!G .!

Glu M

the! signal! to! switch! the! Glycogen! metabolism! from!

activity G ;P!maintains!the!architecture!of!the!complex!and!thus!stimulates/the/activity/of/PP1.!!

i

Glycogen sinthase M

d degradation! to! synthesis:! in! the! graph! you! can! see! that! PKA! the! PKA! can! be! activated! by! Glucagon:! the! further! phosphorylation! (2P)!

Enzymatic • →!

i

ud the! enzymatic! capacity! of! Glycogen! Phosphorylase! induces!the!detachment!of!G !from!the!complex.!This!allows!the!release!of!PP1!that!is!

M

decreases! when! Glucose! in! the! liver! increases,! and! only! no! more! active! on! the! enzymes! (PP1! is! active! only! when! associated! to! the! complex)!

St

Glycogen phosphorylase when!Glycogen!Phosphorylase!activity!is!at!the!minimum! thus!promoting!the!phosphorylation!of!the!two!enzymes.!!

min

2 4 6 8 10

i there!is!a!sharp!increase!in!Glycogen!synthesis.!! !

gl

! de

Glucose inhibits glycogen phosphorylase and facilitates

 protein phosphatase activity

! 19! ! 20!

si

er

iv PP1

Un During! fasting/ condition! PKA! determines! also! the!

phosphorylation! of! inhibitor1 1! a! scaffold! protein!

that! maintains! PP1! far! from! the! granules! when! it! is!

phosphorylated.!!

!

!

!

Glycogen! Synthase! can! be! phosphorylated! by!

different! kinases,! in! particular! GSK3! (Glycogen/

Regulation of glycogen metabolism

Synthase/ Kinase/ 3):! GSK3! can! phosphorylate! the! o

Glycogen!Synthase!inhibiting!it.! n !

GSK3! can! be! inactivated/ by/ Insulin! through! the!

ila !

PI3K! pathway! that! activates! PKB! (Akt):! PKB! can! Glucose!is!phosphorylated!in!Glu;6P!that!can!be!used!to!restore!Glycogen!in!the!liver.!

M

phosphorylate!GSK3!inactivating!it.!! Than!Glu;6P!can!be!addressed!to!glycolysis!and!produce!Pyruvate!which!can!be!internalized!

So! when! GSK3;P! is! inactive,! PP1! is! active! and! in!the!mitochondria!where!it!is!converted!into!Acetyl;CoA.!

i

d

Glycogen!Synthase!can!be!activated.! Acetyl;CoA!is!condensed!with!Oxaloacetate!giving!rise!to!the!formation!of!Citrate.!!

! di Citrate!has!two!possibilities:!

! tu ; Be!converted!in!the!Krebs!cycle!

! ; The!amount!of!Citrate!over!the!possibility!of!Krebs!cycle!moves!from!the!mitochondria!

S

! to! the! cytoplasm:! Citrate! is! converted! into! Acetyl;CoA! and! this! is! the! way! to! transfer!

Glucose! and! Glu;6P! stimulate! the! activity! of! PP1;! in! particular! Glu;6P! acts! as! an! allosteric!

i

gl Acetyl;CoA!to!the!cytoplasm!(and!this!is!the!condition!active!in!the!liver!during!well;

regulator!which!binds!to!Glycogen!and!promotes!its!dephosphorylation!by!PP1.! fed!state).!!

de

Glucagon!and!epinephrine!act!exactly!in!the!opposite!way:!they!block!the!activity!of!PP1!on! Citrate!is!then!activated!into!Malonil;CoA!that!is!used!to!synthetize!Acyl;CoA!that!can!

Glycogen sinthase is a substrate for different kinases

Glycogen!Synthase,!inactivating!it.! then!be!used!for!the!synthesis!of!Triglycerides.!!

! !

si Glycolysis! can! also! produce! Glycerol;3P! through! the! reduction! of! Glyceraldheyde;3P,! a!

r glycolysis! intermediate.! Glycerol! that! reaches! the! liver! from! the! adipose! tissue! can! also! be!

ve phosphorylated! by! a! Glycerol! Kinase! in! the! liver;! so! we! have! the! possibility! to! synthesize!

i Triglycerides.!

Un For!the!biosynthesis!of!Acyl;CoA!we!also!need!reducing!equivalents:!the!reducing!equivalents!

are!generated!by!the!oxidation!of!Glucose;6P!in!the!Pentose!pathway.!!

ht So!the!two!pathways!are!integrated!because!the!main!aim!of!Pentose!pathway!is!to!produce!

ig NADPH!(in!this!condition!we!don’t!need!Ribose;5P).!

yr !

How!these!two!pathways!can!be!controlled!in!the!wellOfed/state?!

p The! fundamental! steps! that! control! glycolysis! are! the! reactions! driven! by!

Co ! Phosphofructokinase!(PFK!I)!and!Pyruvate!kinase.!

! !

In! the! well;fed! condition! Glycogen! Synthase! is! activated! and! Glycogen! Phosphorylase! is! !

inhibited.! !

The! first! event! in! this! switching! is! due! to! the! action! of! Glu;6P,! but! there! are! two! other! !

metabolic!pathways!that!are!activated!in!the!storage!of!Glucose:! !

; Pentose/ pathway→! associated! to! the! production! of! the! reducing/ equivalents! for! the! !

Fatty!Acids!synthesis! !

; Glycolysis!→!more!strictly!assessed!to!the!synthesis!of!Fatty!Acids!because!the!goal!is!to! !

generate!Pyruvate!and!then!Acetyl;CoA!that!is!largely!used!for!the!synthesis!of!FA.!

! 21! ! 22!

! The!positive/control!is!exerted!by!F1,6BP!that!is!an!upstream!substrate!of!the!enzyme!which!!

Phosphofructokinase611 can! give! a! message! of! the! need! of! an! increase! in! the! Pyruvate! kinase! activity.! All! these!

Phosphofructokinase I

The! most! important! regulatory! molecule! for! PFK! I! is! mechanism!are!active!in!all!glycolytic!tissues!including!liver.!

o

Fructose62,66BP:! this! molecule! activates! the! PFK;1! and! !

n

inhibits! the! FPBase;1! (that! is! the! enzyme! of! But! there! is! a! mechanism! specific/ for/ liver,! in! which! the! enzyme! can! be! inhibited! by!

la

gluconeogenesis),!exerting!an!opposite!effect.! phosphorylation.!The!isoenzyme!Pyruvate!kinase!L!present!in!the!liver!is!inactive!in!its!P;form!

When! Fructose;2,6;BP! increases,! glycolysis! is! activated! and!the!phosphorylation!can!be!achieved!by!the!activity!of!PKA;!the!removal!of!the!P;group!by!

Mi

and! gluconeogenesis! is! inhibited,! so! the! control! depends! the! phosphatases! PP1! or! PP2A! can! convert! Pyruvate! kinase! in! the! active! form!

on!the!levels!of!Fructose;2,6;bP! (dephosphorylated!).!!

di

! When/ Insulin/ is/ high,/ PP1/ is/ active/ and/ the/ enzyme/ is/ dephosphorylated/ and/ active;/ when/

! Glucagon/is/high,/the/enzyme/is/phosphorylated/and/so/inactive.//

di

! !

The! enzyme! activities! that! regulate! the! level! of! Fatty1Acids1biosynthesis1

tu

F2,6BP!are!in!the!same!protein:!it!is!a!Kinase!that! Glycolysis!can!increase!the!level!of!Acetyl;CoA!that!is!then!used!for!the!synthesis!of!FA.!!

S

works!on!position!2!of!the!Fructose;6P,!but!it!also! Which!are!the!proteins!involved!in!this!Fatty!Acids!biosynthesis?!

has! a! Phosphatase! activity! on! the! same! group! The! first! one! is! the! enzyme! that! activates! Acetyl;CoA! to! the! condensation! step:! Acetyl6CoA1

i

(while!PFK1!phosphorylates!in!position!1,!it!is!the! Carboxylase! is! an! ATP! and! biotinOdependent! enzyme! that! catalyses! the! carboxylation! of!

gl

+

enzyme!active!in!glycolysis).! Acetyl;CoA!determining!a!change!in!the!reactivity!of!the!methylene!group!that!becomes!more!

Xilulose-5P de

So! PFK62! and! PFBase62! are! domains/ of/ the/ same/ reactive!to!the!condensation.!The/product/of/the/reaction/is/MalonylOCoA.! Fatty acid biosynth

protein,!the!two!enzymatic!activities!are!present!in!

the!same!protein.! tà

! The acetyl-CoA carboxylase reaction

si

Piruvate kinase

Insulin,! promoting! the! dephosphorylation! of! the! protein,! determines! an! inactivation/ of/ the/

phosphatase/ and/ activation/ of/ the/ kinase/ activity:! in! the! dephosphorylated! form,! the! protein!

er

has!a!kinase!domain!active!and!the!phosphatase!catalytic!domain!inactive.!!

iv

Glucagon! through! the! activation! of! PKA! can! induce! the! phosphorylation! of! the! protein,!

activating/the/phosphatase/activity.! Un !

Moreover!XilusoseO5P!can!activate!a!phosphatase!able!to!remove!the!P!group!and!so!activating/ !

the/PKFO2./ This! enzyme! is! the! starting! point:! FA! synthesis! needs! one! molecule! of! Acetyl;CoA! and! 7!

biotin Malony

ht

! molecules!of!Malonyl;CoA!because!it!works!by!sequential!condensation!steps.!

Acetyl CoA

Xilulose;5P!is!produced!in!the!Pentose!shunt,!and!it!is!able!to!activate!glycolysis!that!induces! When!the!amount!of!Malonyl;CoA!and!Acetyl;CoA!is!balanced,!the!FA1Synthase!can!work:!it!is!

rig

the!production!of!Acetyl;CoA.! a!single!protein!in!which!are!represented!all/the/enzyme/activities/needed!for!the!biosynthetic!

Fatty acid synthase reaction

F2,6BP/ is/ the/ main/ regulatory/ control/ in/ the/ liver/ for/ the/ switch/ from/ glycolysis/ to/ process.!

py

gluconeogenesis.// The!biosynthesis!starts!from!the!loading!of!the!protein!with!the! t

! substrates,! Acetyl;CoA! and! Malonyl;CoA;! the! loading! of! the! S

Co

Pyruvate1kinase1 protein!determines!the!formation!of:!

The! last! step! of! glycolysis! is! i

; AcetylOthiol!→!associated!through!an!SH!group!of!the!Cys! gl

performed!by!the!Pyruvate!kinase:/ in!the!protein!

The! negative/ control! can! be! exerted! ; MalonylOACP!→!Malonyl!fragment!is!associated!to!ACP!! de

by!allosteric!regulators:!! !

; LongOchain/Fatty/Acids/ When! the! protein! is! charged! with! the! two! substrates! the! condensation! step! is! possible! and!

; AcetylOCoA/! there!is!the!formation!of!Ketoacyl!derivatives.! tà

; Alanine! it! represents! the! After!the!condensation!step!all!the!other!steps!are!associated!to!the!reduction!of!the!Ketoacyl!

→!

excess! of! substrates! that! can! be! si

derivatives!using!2!NADPH!molecules.!!

converted!into!aminoacids! ! er

! The! enzyme! performs! 7! cycles! to! reach! the! maximal! dimension! of! the! acyl! chain! that! is!

! PalmitoylOCoA!(16C!molecules)./ iv

! For!this!process!you!need!both!ATP!and!NADPH.!

All!these!elements!are!representative!of!an!excess/of/substrates.!! Un

! 23! ! 24! ht

rig

Fatty! Acids! are! a! storage! mechanism:! in! the! well;fed! state! we! can! accumulate! energy! as! FA! ; To! be! converted! into! Malate! that! can! be! converted! into! Pyruvate! by! Malic! enzyme!

from! the! excess! of! energy! from! Glucose! because! FA! are! the! more! reliable! molecules! for! the! generating!NADPH;!then!Pyruvate!can!be!transported!to!the!mitochondria.!!

storage!of!energy.!! The!conversion!of!Malate!in!the!cytoplasm!generates!NADPH!but!also!carbonate!ions!

How!are!these!enzymes!regulated!in!liver!and!in!the!condition!in!which!we!are!operating?! that!can!be!used!to!the!activation!of!Malonyl;CoA.!This!is!a!very!active!reaction!in!the!

There! are! three! types! of! regulation:! a! short;term! and! long;term! regulation! and! a! Glucose; liver!in!this!condition!because!it!recovers!tricarbons!for!the!energetic!metabolism!but!

based!transcriptional!control.! generates!NADPH!and!carbonate!ions!that!are!needed!for!the!FA!biosynthesis.!!

1 /

(1)1Short6term!regulation!! Insulin/increases/the/levels/of/both/proteins!(Glucose;6P!dehydrogenase,!Malic!enzyme)./

Acetyl;CoA!carboxylase!is!the!only!enzyme!that!has!a!short;term!regulation!mechanism!both! All! these! enzymes! are! fundamental! for! the! production! of! the! right! amount! of! NADPH:! Malic!

by!allosteric!and!covalent!regulation:! enzyme!can!give!rise!only!for!half!of!the!NADPH!needed!(for!one!Acetyl;CoA!transported!there!

is!the!production!of!one!NADPH,!but!for!one!Acetyl;CoA!condensed!we!need!two!NADPH).!

Covalent/mechanism! the! enzyme! is! active/in/the/dephosphorylated/form,! while! it! is!

• →! The/fatty/acid/biosynthesis/will/always/depend/on/the/pentose/pathway./

inactive! in! the! phosphorylated! form.! The! activation! occurs! through! the! conversion! !

between!the!monomeric/polymeric!enzyme:!the!monomeric/enzyme/is/inactive/and/the/ (3)1Glucose6based1transcriptional1control1

polymeric/ enzyme/ is/ active! and! the! polymerization! is! due! to! the! aggregation! of! 21! Also! Glucose! can! regulate! these! enzymes,! through! the! formation! of! Xilulose;5P! (X5P)! from!

monomers.! Glu;6P!in!the!Pentose!pathway.!

What! is! the! meaning! of! the! polymerization! mechanism! as! functional! for! this! enzyme! Glu;6P!can!be!addressed!to!the!pentose!pathway!and!produce!XP5:!X5P!can!activate!PP2A!that!

activity?! When! it! is! active! a! big! amount! of! Malonyl;CoA! can! be! produced! and! this! is! can! remove! 2! P;groups! from! the! Carbohydrate6Response6Element1 Binding1 Protein1

functional! to! the! reaction,! because! the! reaction! needs! a! lot! of! Malonyl;CoA! for! one! (ChREBP).1When!the!first!group!is!removed,!ChREBP!translocates!into!the!nucleus!where!X5P!

molecule!of!Acetyl;CoA.!! can!induce!the!removal!of!the!second!P;group;!when!ChREBP!is!totally!dephosphorylated,!it!

It!is!a!capacitive!catalysis,!because!you!start!from!no!Malonyl;CoA!to!21!molecules!of! can! associate! to! the! response! element! and! activate! the! transcription! of! all/ the/ enzymes/

Malonyl;CoA!in!one!single!step.! involved/in/the/FA/biosynthesis./

!

Allosteric/mechanism!→!through!the!regulatory!activity!of!allosteric!factors,!Acetyl;CoA!

• carboxylase!can!be!regulated!by!:!

PalmitoylOCoA! it! negatively! regulates! the! enzyme! because! accumulated!

o →!

Palmitoyl;CoA! in! the! cytoplasm! indicates! that! the! capacity! to! produce! FA! is!

saturated!!

Citrate!→!it!positively!regulates!the!enzyme!because!it!is!an!indication!that!you!

o have!to!synthesize!FA!

These! two! molecules! can! associate! to! the! enzyme! and! convert! it! into! the!

active/inactive!form.!!

!

!

(2)1Long6term!regulation!

Fatty!Acids!synthesis!(FAS)!is!regulated!by!a!transcriptional!mechanism!together!with!other!

enzymes!that!are!crucial!for!this!pathway,!in!particular:!! / no

Glucose based transcriptional control

So!X5P!acts!through!PP2A,!which!activates!ChREBP!that!in!turns!activates:!

Citrate/Lyase!→!allows!the!synthesis!of!Acetyl;CoA!in!cytoplasm!

• la

; Fatty!Acids!Synthase!(FAS)!

AcetylOCoA/Carboxylase/

• Mi

; Acetyl;CoA!Carboxylase!(ACC)!

Enzymes/involved/in/the/synthesis/of/reducing/equivalents,! we! have! an! increase! en! the!

• di

; Acetyl;CoA!Lyase!(ACL)!

amount!of!the!enzymes;!GlucoseO6P/dehydrogenase,/Malic/enzyme!that!is!involved!in!the! di

; Malic!Enzyme!(ME)!!

recovery!of!Oxaloacetate!from!the!cytoplasm!to!the!mitochondria.! tu

; Pyruvate!Kinase!(L;PK)! S

! i

; Enzyme!responsible!for!the!introduction!of!the!double! gl

Citrate!can!move!the!Acetyl!group!from!the!mitochondria!to!the!cytoplasm.!! de

bond!in!the!fatty!acids!

In! the! cytoplasm! Citrate! is! converted! into! Acetyl;CoA! and! Oxaloacetate:! Oxaloacetate! is! a! ! tà

mitochondrial! substrate! so! it! goes! back! to! the! mitochondria,! but! since! there! are! no! si

!

transporters!for!it!in!the!mitochondrial!membrane,!the!possibilities!are!two:!! er

This! Glucose;based! transcriptional! control! is! a! potentiation!

; To! be! converted! into! Malate,! that! goes! back! to! the! mitochondria! because! it! has! a! iv

of! the! regulatory! mechanism! and! it! is! associated! to! the! Un

transporter!on!the!mitochondrial!membrane! Pentose;pathway! activity! because! the! first! condition! is! to!

! ht

have!reducing!equivalents.!! ig

yr

p

! 25! ! 26! Co

Fasting1condition:1Glucose1production12mg/Kg/min1 The!control!derives!from!the!amount/of/substrates!but!there!is!also!a!transcriptional/control.!!

Two!pathways!are!active!in!the!liver!during!the!fasting!state:! Other!enzymes!that!are!regulated!are:!

; Glycogenolysis/ ; Pyruvate/Carboxylase!→!that!is!mainly!controlled!by!the!amount!of!Acetyl;CoA!so!it!is!

; Gluconeogenesis/ active!only!if!there!is!Acetyl;CoA!

The!hierarchy!of!activation!is!in!this!order.!! ; PEP/Carboxykinase/

/ !

Glycogenolysis! is! activated! by! Glucagon,! the! signal! that! So!the!regulation!of!gluconeogenesis!is!the!reciprocal!of!glycolysis.!

controls! the! fasting! condition:! Glucagon! acting! through! GPCR! !

can! activate! the! Adenylate! Cyclase! generating! cAMP! which! !

activates!the!PKA.! There! is! more! than! one! possibility! for! the! conversion! of! Pyruvate! into! PEP;! the! metabolic!

PKA! can! phosphorylate! the! Phosphorylase1 b1 Kinase! pathway!depends!on!the!reducing!power!of!the!cytoplasm,!so!we!have!two!possibilities:!

activating!the!enzyme.! ; Lactate! to! be! addressed! to! gluconeogenesis! it! has!

→!

The! Phosphorylase! b! Kinase! in! the! active! form! to! be! converted! into! Pyruvate! with! an! oxidative! step!

(phosphorylated)! can! phosphorylate! Glycogen! Phosphorylase! that! generates! NADPH! (gluconeogenesis! needs!

b! (inactive! from)! and! convert! it! into! the! Glycogen/ NADPH),! so! there! is! enough! NADPH! for!

Phosphorylase/ a! (active! form)! which! can! work! on! Glycogen:! gluconeogenesis.! Pyruvate! is! then! transferred! to! the!

Glycogen! is! degraded! by! the! removal! of! the! terminal! Glucose! mitochondria,! converted! into! Oxaloacetate! that! is!

residue!in!the!form!of!Glu;1P.! converted!into!PEP!that!can!reach!the!cytoplasm!

Glu;1P!can!then!be!converted!into!Glucose;6P.! !

! ; Alanine! it! can! be! converted! by! Transaminase! into!

→!

/ Pyruvate,! that! is! transferred! to! the! mitochondria!

/ where!it!is!converted!into!Oxaloacetate!(this!step!can!

/ occur! only! in! mitochondria).! Oxaloacetate! is! then!

/ converted! to! Malate! (that! is! more! reduced! that!

/ Oxaloacetate);! Malate! is! transferred! to! the! cytoplasm!

/ where! it! is! converted! to! Oxaloacetate! and! then! into!

Gluconeogenesis! is! the! metabolic! pathway! that! allows! the! PEP.! This! pathway! allow! the! transfer/ of/ reducing/

synthesis! of! Glucose! from! extra;hepatic! substrates:! liver! is! the! equivalents/from/the/mitochondria/to/the/cytoplasm;!so!

collector! of! extra;hepatic! substrates! that! can! be! converted! into! when!you!need!to!move!equivalent!from!mitochondria!to!cytoplasm,!this!is!the!active!

Glucose.!These!substrates!can!be:/ metabolic!pathway.!

; Lactate! !

; Alanine! it! is! the! most! important! aa! involved! in! the! aa! !So! the! possibilities! are! two:! the!Glucose! precursor! is! in! a! reduced! state! and! can! be! used! to!

→!

transport!to!the!liver!together!with!glutamine! generate! reducing! equivalents,! or! it! is! in! an! oxidized! state! and! you! need! to! move! reducing!

; Glycerol! it! is! important! considering! the! relationship! equivalent!from!the!mitochondria!to!the!cytoplasm.!

→!

between! adipose! tissue! and! liver.! Glycerol! mainly! derives! from! !

the! metabolism! of! adipose! tissue! and! can! be! used! for! the! Summary!of!hormonal!control!in!liver:!

synthesis!of!Glucose!in!the!liver.!! Insulin! Glucagon!

! Stimulates! Inhibits! Stimulates! Inhibits!

Gluconeogenesis!shares!many!reactions!with!glycolysis:!the!only! Glycolysis/ Gluconeogenesis/ Gluconeogenesis/ Glycolysis/

ones! that! are! specific! for! the! two! pathways! are! the! irreversible! Glycogenosynthesis/ Glycogenolysis/ Glycogenolysis/ Glycogenosynthesis/

ones!from!a!thermodynamic!point!of!view.!! FA/and/TG/biosynthesis/ Ketogenesis/ Ketogenesis/ FA/and/TG/biosynthesis/

Since!the!irreversible!reactions!of!glycolysis!are:!! NADPH/production! ! ! NADPH/production!

; Phosphorylation!of!Glucose!to!Glu;6P! ! !

; Phosphorylation!of!Fru;6P!to!Fru;1,6BP! !

; Phosphorylation!of!PEP!to!Pyruvate! All!these!pathways!are!activated!in!the!same!time.!

! /

The!irreversible!reactions!of!gluconeogenesis!are:! 1

; Conversion!of!Pyruvate!into!PEP! 1

; Dephosphorylation!of!Fru;1,6BP!to!Fru;6P! 1

; Dephosphorylation!of!Glu;6P!to!Glucose! 1

! 27! ! 28!

Then! we! have! other! elements:! like! Cortisol! that! as! Glucagon! can! upregulate! the! enzymes! of! An! increase! in! Cholesterol! also! stimulates! the! proteolytic! degradation! of! the! enzyme:!

gluconeogenesis,!it!is!the!stimulus!of!a!severe!fasting!condition.! Lanosterol! (an! intermediate! of! Cholesterol! biosynthesis)! can! associate! the! HMG;CoA!

Insulin transcriptional control

! Reductase!to!the!system!that!determines!its!ubiquitination!thus!addressing!the!enzyme!to!the!

o

n proteasome;dependent!degradation.!!

la

Mi

di

di

tu

S !

i

gl 1

de 1

1

tà 1

i

rs Ketone1bodies1biosynthesis1

e It!is!a!mitochondrial!process:!when!Acetyl;CoA!

iv ! increases! but! Oxaloacetate! is! not! available!

Un

! enough,!Acetyl;CoA!can!be!recovered!and!used!

Lipid1metabolism1in1the1liver1

ht as! energy! supply! through! the! condensation!

In!the!liver!take!place!the!active!synthesis!of:!

rig two!Acetyl;CoA!and!the!production!of:!

; Triglycerides/ Glucagon Up regulation of ; Acetoacetate!

py

; Phospholipids/ Cortisol Gluconeogenesis enzymes ; Ohydroxybutyrate!

β

; Cholesterol/ Co !

; Lipoproteins!(VLDL,!HDL,!apoCs)! !

! !

Liver!can!use!FA!as!energy!in!the!β;oxidation!and!then!Krebs,!and!it!can!also!operate!partial! These! two! ketone! bodies! can! be! used! for! energy! recover! (the! other! one! is! Acetone! that! is!

o

oxidation!of!FA!leading!to!the!formation!of!Ketone!bodies!using!Acetyl;CoA.! USE OF KETONE BODIES n

present!only!when!we!have!an!excess!of!ketone!bodies,!because!it!cannot!be!used!for!energy!

Synthesis!of!TG!and!Phospholipids!are!mainly!regulated!by!the!substrate!availability:! ila

supply).!

; Dihydroxy;acetonphosphate!and!Glycerol;3P!for!Triglycerides! M

In! healthy! subjects! the! amount! of! Ketone! bodies! is! low! and! range! from! 0,2;2mM/L,! but! in!

; Choline!and!Methionine!for!Phospholipids! Extrahepatic tissues

Liver Blood

fasting!condition!they’re!largely!generated!because!during!fasting!we!have!the!β;oxidation!of!

Cholesterol!biosynthesis!is!controlled!through!the!HMG;CoA!Reductase.! i

d

FA!but!Oxaloacetate!is!addressed!to!Gluconeogenesis.!

/ Acyl coA i CO H O

! d

/ 2 2

tu

!

Regulation/of/Cholesterol/synthesis/through/HMGOCoA/Reductase/ Ketone! bodies! can! be! used! as! energy! source! in! skeletal! muscles!

S

/ Acetyl coA Acetyl coA

and!brain,!nut!not!by!liver.!

HMG;CoA! Reductase! is! activated! by! Insulin! i

gl

Since! liver! can! synthesise! ketone! bodies! but! it! cannot! use! them,!

(dephosphorylated! form)! and! inactivated! by! Glucagon.! de

they! are! transferred! in! the! extra;hepatic! tissues! where! they! can!

acetoacetate

acetoacetate

Insulin!can!also!increase!the!expression!of!the!enzyme.! be!converted!into!Acetyl;CoA!and!used!in!the!Krebs!cycle.!!

The! major! control! of! the! enzyme! is! the! Cholesterol6 ità

!

dependent1 control:! when! Cholesterol! concentration! -Hydroxyibutiyrate -Hydroxyibutiyrate

! rs

increases,!the!activity!of!the!enzyme!is!reduced!through! !

a! control/ on/ the/ level/ of/ the/ protein! (like! the! ve

!

transcriptional! control! of! the! LDL;R)! because! ni

The!two!reactions!that!can!be!involved!in!the!activation!of!acetoacetate!are:!

Cholesterol!can!act!on!the!translocation/of/the/SREBP/in/ U

!

the/nucleus.!! succinylCoA

ht acetoacetate

! CoASH + ATP

! ig

tiophorase

! r

py

succinate AcetoacetylcoA

! !

AMP +PPi !

Co

! 29! ! 30!

7.2.17! There!is!also!the!Beige/adipose/tissue,!which!is!something!that!is!not!constitutively!expressed!

but! it! can! be! induced! by! stimulation! and! it! is! a! differentiation! of! white! adipocytes! in! the!

Adipose1tissue1 direction! of! brown! adipocytes! (number! of! mitochondria! increases! after! stimulation,! the!

! thermogenin!is!expressed!under!stimulation…).!

Energy/balance/in/human/body/ !

The! introduced! energy! is! the! sum! of! consumed! energy! and! storage! energy.! The! energy! Metabolic/profile/of/white/adipocytes/

consumed! is! represented! by! heat! and! biosynthetic! processes;! if! you! introduce! an! higher! We!can!distinguish!two!different!metabolic!profiles!of!adipose!tissue!based!on!the!state!of!the!

energy,! you! have! a! second! element! in! the! equation! that! is! storage! energy;! so! storage! organism.!

metabolites!are!crucial!to!combine!two!elements:! !

; Rate/ of/ energy/ intake! it! strongly! increases! in! some! period! of! the! day! that! do! not!

→! Well6fed1state1

correspond!with!the!periods!of!maximum!consume!of!energy!! The!metabolic!profile!is!addressed!to!Triglycerides/loading.!!

; Rate/of/energy/expenditure// Two!elements!have!to!be!considered:!

This!is!possible!because!we!have!the!possibility!to!store!energy.! ; Glucose/ / it/ is/ high! and! it! can! be! transported! into! adipocytes.! Glucose! undergoes!

! phosphorylation!by!the!Hexokinase!1!(constitutive!enzyme),!and!it!is!mainly!addressed!

In!which!form!can!energy!be!stored?! to!the!synthesis!of!Acetyl;CoA!and!the!production!of!NADPH!and!DHP!for!the!synthesis!

Glucose!cannot!be!stored!as!itself:!it!can!only!guarantee!30min!of!survival.! of!triglycerides.!!

Glycogen!in!the!liver!and!muscles!is!stored!in!the!amount!of!450g!and!it!allows!a!survival!of! ; Free/ FA! they! can! be! taken! by! adipocytes! because! they! are! able! to! regulate! the!

→!

18hours.! expression!of!LPL;!triglycerides!can!also!derive!from!the!hydrolysis!of!VLDL!and!CM.!

Triglycerides!are!more!or!less!15Kg!in!normal!condition!and!allow!a!survival!of!55!days.!

Also!proteins!constitute!an!energy!storage!that!can!last!21!days;!usually!their!function!is!not!

associated!to!the!storage!of!energy!but!we!can!use!them!in!conditions!in!which!all!the!others!

are!eliminated.!

So! triglycerides/ are/ the/ most/ important/ form/ of/ energy/ storage! and! they! represent! also! the!

most!important!source!of!energy!supply.!

!

Why!are!triglycerides!the!chemical!structure!selected!for!this!function?!

Instead!of!carbs,!TG!don’t!need!water!to!be!packaged!in!the!cell!and!this!correspond!to!have!a!

storage!material!that!is!the!highest!possible!for!body!unit.!!

The!chemical!structure!of!triglycerides!is!at!the!basis!of!the!selective!use!of!these!substrates!as!

storage!in!all!animal!kingdoms,!and!we!have!a!specialized!tissue!for!this!that!is!adipose/tissue.! !

/

In!normal!conditions,!adipose!tissue!represents!15;20%!of!body!mass!and!it!is!the!only!tissue! /

that!can!largely!increase!its!mass.! In!the!well;fed!state!the!main!process!occurring!is!lipogenesis.!The!synthesis!of!triglycerides!

The!composition/of/adipose/tissue/is/mainly/represented/by/triglycerides!and!its!functions!are:! can!be:!!

; Energy!storage! ; De/novo!process!→!starting!from!Acyl;CoA!and!Glycerol;3P!!

; Mechanical!protection! ; Recycling/pathway!→!using!the!products!derived!from!VLDL!and!CM!hydrolysis!and!so!

; Thermic!insulation! the!products!that!are!represented!by!Acyl;CoA!and!mono/di;glycerides.!!

; Endocrine!functions!! !

! FA!can!derive!from!lipoproteins!associated!to!triglycerides:!and!the!crucial!role!is!played!by!

We!have!two!different!adipose!tissues:! Lipoprotein!Lipase!(LPL).!

; White/ Adipose/ Tissue/ (WAT)! adipocytes! have! a!

→! The/ synthesis/ of/ LPL/ is/ stimulated/ by/ Insulin! and! other! hormones! (somatotrope! hormone,!

monolocular!droplet!of!lipids!and!few!mitochondria! triiodothyronin)! and! is! inhibited/ by/ cytokines/ and/

; Brown/ Adipose/ Tissue/ (BAT)! adipocytes! have!

→! glucocorticoids! (that! in! particular! are! a! signal! of! stress!

multilocular! droplets,! lots! of! mitochondria,! they! are! and!long!fasting).!!

smaller!than!white!adipocytes.!! Insulin!is!also!able!to!stimulate/the/enzyme/translocation!

The!thermogenin!protein!is!expressed!in!BAT!but!not!in!WAT.! on!the!surface!of!endothelial!cells!where!it!is!expressed!

β;adrenergic!receptors,!are!expressed!in!a!different!way:!β3! facing!the!bloodstream.!!

receptors!are!highly!expressed!in!BAT.! Adipocytes!can!take!up!FA!and!di/mono;acyl;glycerol.!

Moreover!BAT!is!more!vascularized!than!WAT.! !

! !

!

!

! 31! ! 32!

The!other!possibility!is!the!de/novo!synthesis!of!FA!from!Glucose.!! Insulin/acts/on/the/recycling/rate/of/GLUT4!and!this!is!made!through!the!activation!of!PI3K/Akt!

Glucose!can!produce:! pathway.!

; NADPH!during!the!shunt! Akt!pathway!activation!is!the!effector!for!the!vesicle!movement!to!the!plasma!membrane.!Akt!

(PKB)! can! phosphorylate! the! adaptor! protein! AS160! that! phosphorylated! allows! the!

; AcetylOCoA!→!from!Pyruvate! activation!of!a!Rab!protein!involved!in!the!traffic!of!the!specific!vesicles!charged!with!GLUT4.!!

; GlycerolO3P! Glucose! can! be! converted! into! DHP!

→! In!the!dephosphorylated!state!AS160!blocks!Rab!in!the!GTP;binding!form,!so!Rab!is!inhibited!

which!is!then!converted!into!Glycerol;3P! by!AS160.!!

NADPH!can!derive!from!the!shunt!(60%)!but!also!from!the! This! is! the! major/step/of/control/in/vesicle/traffic,! but! Insulin! can! also! promote! the! tethering,!

malic!enzyme!activity!(40%).! dock! and! fusion! of! the! vesicle! on! the! membrane.! So! Insulin! controls! the! number! of!

! transporters!present!on!the!membrane.!

These!are!the!only!pathways!that!occur!in!adipocytes!during! !

the!well;fed!state.! !

1

1

1

1

1

1

Fasting1state11

In!the!fasting!state!the!metabolic!profile!is!addressed!to!the!release!of!energy!and!FA!by!the!

hydrolysis!of!TG:!FA!are!released!in!the!bloodstream!and!bind!to!albumin.!

The!hydrolysis!of!TG!also!produces!Glycerol!that!can!be!taken!up!by!the!liver.!! !

!

The! K ! for! Glucose! of! GLUT4! is! in! the! order! of! 5! mM,! like! GLUT1! that! is! the! transporter!

m

expressed!in!all!the!cells.!

!

What!is!the!difference!in!role!of!GLUT2!in!liver!and!GLUT4!in!adipocytes?!

Besides!liver,!the!other!two!important!tissues!in!the!removal!of!Glucose!from!the!bloodstream!

are!adipose!tissue!and!muscles.!

In!adipocytes/muscles!and!liver!Insulin!acts!in!a!different!way:!in!muscles!and!adipose!tissue!

! it! increases! the! number! of! proteins! (GLUT4)! that! can! internalize! Glucose! (capacitive!

! mechanism)! but! the! affinity! of! the! transporter! for! Glucose! is! the! same! than! GLUT1;! while!

In!the!absence!of!Hexokinase!4!(liver;specific)!that!can!be!controlled!by!Insulin,!how!can!the! GLUT2!(liver!specific)!is!a!transporter!characterized!by!high!capacity!because!of!its!high!Km!

uptake!of!Glucose!be!controlled!in!adipocytes?!! for!Glucose,!and!the!checkpoint!for!Insulin!is!Glucokinase!inside!the!cell.!

In! adipocytes! the! control! of! Glucose! uptake! is! linked! to! the! control! of! GLUT4,! the! specific! !

transporter!present!in!adipocytes!and!muscles.!!! /

1 In! the! fasting! state! the! metabolic! pathway! active! is! the!

GLUT4!is!an!InsulinOregulated/Glucose/transporter:!the!rate! degradation! of! TG.! So! we! have! Glucagon! that! binds! its!

of! transport! can! have! 10;100! fold! increase! after! Insulin! receptor,! which! causes! an! increase! in! cAMP! and! the!

stimulation.!! activation!of!PK1!which!can!phosphorylate:!

Insulin! regulates! GLUT4! levels! but! cannot! induce! a! ; Hormone6sensitive1Lipase!→!is!activated.!

transcriptional!regulation!in!adipose!tissue.! It!is!the!only!lipase!that!can!completely!hydrolyse!TG!

In! basal! conditions! GLUT4! is! located! into! the! cytoplasm:! (LPL!and!pancreatic!lipase!cannot).!

Insulin/ stimulates/ GLUT4/ translocation/ to/ the/ plasma/ ; Perilipin! constitutes! the! envelope! of! the! lipid!

membrane/ in/ 15/ minutes! (this! happens! also! in! muscle! →!

droplet! because! it! exposes! hydrophilic! aa! in! the!

cells).! cytoplasm! and! hydrophobic! aa! on! the! other! side!

! allowing! the! compartimentalization! of! TG.! With! the!

The! rate! of! endocytosis! is! very! high:! the! half! time! of! perilipin! phosphorylation,! the! envelope! becomes! less!

endocytosis! is! 3.5! minutes! whereas! the! half! time! of! continuous! and! so! we! have! the! possibility! that! the!

recycling!is!320!minutes.! hormone;sensitive!lipase!can!work!inside!the!droplet.!

!

! 33! ! 34!

FA!are!released!in!the!blood!where!they!bind!albumin!and!are!carried!to!other!tissues!that!can! The/Triacylglycerol/cycle/

use!them,!in!particular!muscles!(not!brain!).!! The!adipocyte!is!empty!during!the!fasting!condition!and!full!in!the!well;fed!state.!!

Also! Glycerol! is! released,! and! from! adipocytes! moves! to! liver! where! it! can! be! converted/into/ But! what! actually! operates! in! adipose! tissue! is! the! Triacylglycerol! cycle! which! means! that!

Glucose/in!the!gluconeogenesis.! about!75%!of!FA!hydrolysed!in!lipolysis!are!re;esterified!to!TG.!

We!are!in!fasting!condition,!so!we!are!set!for!the!maximum!efficiency!of!molecule!recovery:! The!Triacylglycerol!cycle!can!be!divided!in!two!different!cycles:!

Glycerol!is!addressed!to!liver!and!here!it!can!be!converted!in!Glucose!in!the!gluconeogenesis.! Intra6adipocytes1 Triacylglycerol1 cycle!

• →!

At!the!same!time!in!which!you!have!the!regulation!of!triglycerides!in!the!adipocytes!release,! triglycerides! can! be! degraded! to! obtain! FA! that! are!

liver!is!set!to!gluconeogenesis.! partially! released! in! the! blood;stream! but! a!

! significant!amount!are!re;converted!into!TG!

! Triacylglycerol1cycle1between1adipose1tissue1and1

Overview!of!regulation! liver! released! FA! can! be! used! by! tissues! but! a!

→!

part!of!them!go!back!to!the!liver!where!they!can!be!

converted! into! Triacylglycerol! that! can! be!

assembled! into! the! VLDL! and! go! back! into! the!

adipocytes.! This! cycle! occurs! especially! in! fasting!

condition!(but!not!only).!

!

Why!do!we!need!a!so!complicate!condition?!!

Thermogenesis! the! intra;adipocyte! cycle! contributes! to! thermogenesis:! it!

• →!

generates!ATP!during!the!catabolic!part!of!the!cycle!but!the!amount!of!energy!used!in!

the!biosynthetic!process!is!less!than!the!amount!produced!in!the!catabolic!pathway!so!

it!generates/heat!

Pool1 of1 FA! the! cycle! between! adipose! tissue! and! liver! constitutes! a! more! readily!

• →!

available! FA! pool.! Adipocytes! contain! a! huge! amount! of! TG:! having! the! possibility! to!

! move!FA!from!adipocytes!to!the!liver!and!then!come!back!to!the!adipocyte,!creates!a!

! dynamic/pool/of/FA/in/the/bloodOstream/that/is/available/for/the/use/by/tissues.!!

The!mechanism!for!Insulin!activation!of!the!enzymes!involved!in!FA!biosynthesis!is!also!active! !

here.! Glycerogenesis/in/adipose/tissue/

Insulin!stimulates!LPL!and!FA!synthesis,!while!TG!synthesis!depends!on!the!amount!of!Acyl; !

CoA!and!Glycerol;3P.! In! fasting/ condition! we! don’t! have! a!

! source! of! Glycerol;3P! because! it! is!

Insulin! also! stimulates! GLUT4! translocation! and! glycolysis,! so! the! formation! of! Pyruvate! generated! from! Glucose! (that! is! absent)!

because!it!can!act!of!PFK.! and! adipocytes! don’t! express! Glycerol!

! kinase,! so! they! cannot! convert! Glycerol!

Other!hormones!such!as!Glucagon,!Growth!Hormone!and!Adrenalin!act!on!the!cAMP!inducing! into! Glycerol;3P! (as! it! occurs! in! the!

the! inhibition! of! glycolysis! and! the! activation! of! the! Hormone;sensitive! Lipase.! All! these! liver).!

signals!are!associated!to!specific!conditions:!! So! the! synthesis! of! TG! in! adipocytes!

; Glucagon!→!fasting! during! fasting! is! possible! because! in!

; Adrenalin!→!stress! adipocytes! two! enzymes! of! the!

; GH!→!need!of!energy!for!biosynthetic!processes!in!other!tissues.! gluconeogenesis!are!expressed:!

1 ; Pyruvate/Carboxylase/

1 ; PEP/ Carboxykinase! which!

1 produces!PEP!

1 !

1 Adipocytes! don’t! express! Glu;6P!

1 Phosphatase,! so! in! these! cells! there! is!

1 sort! of! truncated/gluconeogenesis! that! is!

1 the! source! of! the! Diidroxyaceton/

1 Phosphate/ (DHP)! that! can! be! converted!

1 into!Glycerol;3P.!

1

! 35! ! 36!


PAGINE

32

PESO

12.54 MB

AUTORE

_ariiel

PUBBLICATO

7 mesi fa


DESCRIZIONE APPUNTO

Programma

ABC transporters
Structure
Mechanism of action
Role in cell physiology
Role in drug resistance

Membrane lipids: architecture, dynamics and biological functions
In/out asymmetry and lateral asymmetry in pathophysiological processes
Aminophospholipids in membrane fusion, cytokinesis clotting, phagocytosis and apoptosis Phosphosinositides: compartimentalization, vesicular traffic and cell signaling
(Glyco)sphingolipids: Lipid Microdomains, signaling platforms, cell-cell communication

Lipids and cell signaling
Lipid mediators in the control of cell proliferation, death and migration: Ceramide , Sphingosine-1-phosphate and Diacylglicerol
“Omics” in lipid signaling

Human biochemistry
Tissue-specific metabolic processes:
Lipoproteins, structure, metabolism, and their role in the regulation of lipid homeostasis. Structural and metabolic alterations of lipoproteins and atherosclerosis.
Liver,
adipose tissue
muscle
metabolic adaptation in physiological conditions (metabolic diseases, aging....)

Biochemistry of the nervous system:
Metabolism and functions: neurons-glia interactions.
Specialized functions of cells of the nervous system
Cell models for the study of biochemical processes in cells of the nervous system

Biochemistry of cancer:
Metabolic processes in the tumor cells
Aberrant glycosylation in the tumor
Cell models


DETTAGLI
Corso di laurea: Corso di laurea magistrale in biotecnologie mediche e medicina molecolare
SSD:
Docente: Viani Paola
Università: Milano - Unimi
A.A.: 2017-2018

I contenuti di questa pagina costituiscono rielaborazioni personali del Publisher _ariiel di informazioni apprese con la frequenza delle lezioni di Human biochemistry e studio autonomo di eventuali libri di riferimento in preparazione dell'esame finale o della tesi. Non devono intendersi come materiale ufficiale dell'università Milano - Unimi o del prof Viani Paola.

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