Lipoprotein metabolism continued (metabolism 9)

Question 1

What do chylomicrons transport?

Answer 1

Dietary TAG and cholesterol

Question 2

Nascent chylomicrons

Answer 2

Synthesized in the intestines along with B-48 and A-1

Question 3

What do chylomicrons transiently gain in the blood vessels during transport?

Answer 3

Apo E and C-II from HDL

Question 4

What does the transient C-II activate?

Answer 4

Lipoprotein lipase

Question 5

What happens to the remenant chylomicron?

Answer 5

It is taken up by endocytosis in the liver, which involves apo E (LRP)

Question 6

HDL serves as a repository for __

Answer 6

Apo A-1, C-II, and E

Question 7

What does VLDL transport?

Answer 7

Endogenous TAG and cholesterol

Question 8

Where/with what are VLDLs formed?

Answer 8

In the liver with B-100

Question 9

What does VLDL pick up in circulation from HDL?

Answer 9

Apo C-II and apo E; apo C-II signals for LPL to degrade TAG to glycerol and fatty acids

Question 10

IDL

Answer 10

“VLDL remnant;” formed as VLDL lose fatty acids

Question 11

IDL->LDL

Answer 11

After IDL loses E and C-II, but retains B-100

Question 12

How is LDL removed from circulation?

Answer 12

Binding of B-100 to any cell expressing the receptor (both hepatic and non-hepatic)

Question 13

What happens with elevated cholesterol levels?

Answer 13

There is a down-regulation of the LDL receptors involved with uptake when the cell has adequate cholesterol

Question 14

What other pathway is present even when LDL receptors are down-regulated?

Answer 14

Pinocytosis; it is usually a minor pathway, but can play a big role when LDL levels are too high

Question 15

Why is LDL bad?

Answer 15

LDL can be oxidized and taken up by macrophages, turning them into foam cells. These foam cells will then aggregate, release cytokines that increase smooth muscle, and cause plaques in the arteries.

Question 16

Where/with what are HDLs formed?

Answer 16

In the liver with Apo A-1, LCAT, and phospholipids.

Question 17

Shape change with HDL

Answer 17

They are originally discoidal, but become spherical as they pick up cholesterol from peripheral tissues and other lipoproteins

Question 18

Enzyme mediating transfer of cholesterol and lipids into HDL

Answer 18

ABCA-1

Question 19

CETP

Answer 19

Mediates transfer of cholesterol esters from HDL to VLDLs and IDLs in exchange for TAG.

Question 20

What happens to cholesterol-enriched VLDL and IDL?

Answer 20

They are taken up by the liver by ApoE-dependent binding and LRP.

Question 21

What happens to spherical HDLs?

Answer 21

Taken up by the liver in ApoA1-dependent binding to the scavenger receptor protein B1 (SRPB1)

Question 22

Atheroprotective effects of HDL

Answer 22

1. Contains paroxonase that inhibits oxidation of LDL

2. Increases synthesis of NO