Lipolysis

What is lipolysis?

Breakdown of stored TAGs

What is the purpose of lipolysis?

Mobilize stored energy

When is lipolysis stimulated?

Fasting

Which hormones stimulate lipolysis?

Glucagon and epinephrine

Which hormone inhibits lipolysis?

Insulin

What is the major fuel source for heart muscle?

Fatty acids

Which tissues rely mainly on glucose during fasting?

Brain and RBCs

Why can't RBCs use fatty acids?

No mitochondria

Where are triacylglycerols mainly stored?

Adipose tissue

What is the major storage form of fat?

Triacylglycerol (TAG)

What are the three major lipases involved in lipolysis?

ATGL, HSL, LAL

What does ATGL stand for?

Adipose triglyceride lipase

What is another name for ATGL?

Desnutrin

What does HSL stand for?

Hormone-sensitive lipase

What does LAL stand for?

Lysosomal acid lipase

What is another name for LAL?

Lipase A

What protects lipid droplets from inappropriate lipolysis?

Perilipin

What surrounds the TAG droplet?

Phospholipid layer

What protein coats the phospholipid layer?

Perilipin

What type of protein is perilipin?

Hydrophobic protein

Which hormone acts through β-adrenergic receptors?

Epinephrine

What second messenger is increased by epinephrine?

cAMP

Which receptor does glucagon bind during lipolysis?

Gs receptor

What enzyme is activated by cAMP?

PKA

What does PKA stand for?

Protein kinase A

What two proteins are phosphorylated by PKA?

Perilipin and HSL

What happens to perilipin after phosphorylation?

Conformational change

What is the effect of phosphorylated perilipin?

Exposes TAG to lipases

What is the effect of phosphorylated HSL?

Activation

What enzyme directly hydrolyzes stored TAGs?

HSL

What are the final products of complete TAG breakdown?

Glycerol and 3 fatty acids

Where does glycerol go after lipolysis?

Liver

How are fatty acids transported in blood?

Bound to albumin

What is the fate of released fatty acids?

Oxidation for energy

Which lipoprotein transports dietary TAGs?

Chylomicrons

Which lipoprotein transports endogenous TAGs?

VLDL

What does VLDL stand for?

Very-low-density lipoprotein

What is the main function of chylomicrons?

Transport dietary TAGs

What is the main function of VLDL?

Transport hepatic TAGs

Which apoprotein is unique to chylomicrons?

Apo B-48

Which apoprotein is unique to LDL?

Apo B-100

What is the function of Apo B-48?

Chylomicron assembly

What is the function of Apo B-100?

LDL receptor binding

Which apoprotein activates lipoprotein lipase?

Apo C-II

Which apoprotein inhibits lipoprotein lipase?

Apo C-III

Which apoprotein mediates hepatic uptake of remnants?

Apo E

Which lipoproteins acquire Apo C-II and Apo E from HDL?

Chylomicrons and VLDL

Which enzyme degrades TAGs in chylomicrons and VLDL?

Lipoprotein lipase

What does LPL stand for?

Lipoprotein lipase

What are the products of LPL action?

Fatty acids and glycerol

What remains after chylomicron TAG removal?

Chylomicron remnant

Where are chylomicron remnants cleared?

Liver

What remains after VLDL TAG removal?

IDL

What does IDL stand for?

Intermediate-density lipoprotein

What is the fate of most IDL?

Converted to LDL

Which lipoprotein carries the most cholesterol?

LDL

What is the main function of LDL?

Deliver cholesterol to tissues

What is the main function of HDL?

Remove cholesterol from tissues

Which lipoprotein is considered "bad cholesterol"?

LDL

Which lipoprotein is considered "good cholesterol"?

HDL

What apoprotein is present on LDL?

Apo B-100

Which receptor binds Apo B-100?

LDL receptor

Can LDL receptors bind Apo E?

Yes

Can LDL receptors bind Apo B-48?

No

What disease results from defective LDL receptors?

Familial hypercholesterolemia

Where is the LDL receptor highly expressed?

Liver

What percentage of LDL cholesterol is cleared by the liver?

70%

What percentage of LDL cholesterol is cleared extrahepatically?

30%

What is the HDL receptor called?

SR-B1

What does SR-B1 stand for?

Scavenger receptor B1

Where is SR-B1 found?

Liver and steroidogenic tissues

Where is HDL synthesized?

Liver and intestine

What form is HDL initially secreted as?

Nascent HDL

What shape is nascent HDL?

Discoid

Which apoproteins are abundant in HDL?

Apo A-I and Apo A-II

What is the function of Apo A-I?

Activates LCAT

What is the function of Apo A-II?

Inhibits LCAT

What does LCAT stand for?

Lecithin cholesterol acyltransferase

What is the role of LCAT?

Esterifies cholesterol

Which apoprotein inhibits CETP?

Apo C-I

What does CETP stand for?

Cholesteryl ester transfer protein

Which apoprotein stimulates lipase activity?

Apo A-II

Which apoprotein is antiatherogenic and activates LCAT?

Apo A-I

Which apoprotein impairs fibrinolysis?

Apo(a)

Which lipoprotein is highly atherogenic due to impaired fibrinolysis?

Lp(a)

Where is Apo(a) produced?

Liver

Which apoprotein activates LPL and clears TAGs?

Apo C-II

Which lipoprotein temporarily stores Apo C-II and Apo E?

HDL

What is the preferred fuel of the heart during fasting?

Fatty acids

Why does the body spare glucose during fasting?

For brain and RBCs

What plasma protein transports free fatty acids?

Albumin

What triggers the cAMP-PKA pathway in adipocytes?

Glucagon and epinephrine

What is the key regulatory protein on lipid droplets?

Perilipin

What is the immediate effect of perilipin phosphorylation?

TAG exposure

What is the immediate effect of HSL phosphorylation?

Lipase activation