Lipoproteins and Lipid Transport

How are lipids transported?

As triglycerides or cholesteryl esters

Apolipoproteins

Structural component for most lipoproteins, cofactor for enzymes, ligand for cell-surface receptor

ApoB

Present on all lipoproteins except HDL

Classes of lipoprotein

Chylomicron, VLDL, LDL, HDL

Which lipoproteins are rich in triglycerides?

Chylomicrons and VLDL

Which lipoproteins are rich in cholesterol?

LDL

Which lipoproteins are rich in proteins?

HDL

Where are chylomicrons synthesized?

Small intestine

Chylomicron function

Carries dietary triglycerides from intestines to other tissues

Maturation of chylomicron

HDL donates ApoCll and ApoE -> convert to mature chylomicron

Lipoprotein Lipase (LPL)

Hydrolyzes triglycerides in chylomicron and VLDL, releases fatty acid and glycerol to cells

ApoCII

Activates LPL

Where is VLDL synthesized?

In the liver

VLDL function

Transports Triglycerides synthesized in the liver to peripheral tissues

How is LDL synthesized?

Derived from VLDL

LDL function

Main carrier of cholesterol in plasma

Where is HDL synthesized?

Liver and small intestine

HDL function

Takes up cholesterol from non-hepatic tissues

ApoAl

Activates LCAT in HDL

Degradation of Chylomicron

Chylomicron donates its ApoCll back to HDL and returns to liver via receptor-mediated endocytosis

VLDL degradation

LPL is activated by ApoCll and releases fatty acid + glycerol from VLDL → becomes IDL

Fates of IDL

Returns ApoCll to HDL and returns to liver via endocytosis or turns into LDL

HDL degradation

Reverse cholesterol transport

LDL degradation

Internalized by liver via LDL receptors

Familial Hypercholesterolaemia

Non-functional LDL receptors in the liver

Which lipoproteins have apoB?

Chylomicron, VLDL, LDL

Which lipoproteins have apoE?

Chylomicron, VLDL, HDL

Which lipoproteins have apoCII?

Chylomicron, VLDL, HDL

Which lipoprotein has apoAI and LCAT?

HDL