Lipoprotein Pathways and Cholesterol Part 2

Question 1

ApoE

Answer 1

Ligand for LP receptors

Binds either of two LP receptors expressed in liver: LDL-R or LRP

Question 2

LPL location

Answer 2

Capillary endothelia in fat and muscle

Question 3

LCAT location

Answer 3

Bound to HDL in blood

Question 4

Exogenous lipoprotein pathway –> CM & CMR

Answer 4

1. Dietary fats digested & taken into enterocytes
2. Enterocytes resynth lipids, then assemble & secrete CMs
   3a. CM acted on by LPL in adipose capillaries until CII is released.
   3b. CII collected by HDL
   3c. CMR generated
3. CMR taken up by apoE binding to either LRP or LDL-R on liver cells
4. CMRs disassembled

Question 5

Endogenous LP pathway - delivering FA to adipose when g:i is low

Answer 5

1. Liver assembles and secretes VLDL in response to liver TG
   2a. LPL acts on VLDL until CII is released, generating IDL
   2b. CII collected by HDL

Question 6

LPL induced in adipose capillaries _____

Answer 6

by insulin, to store FA as TG

Question 7

LPL induced in muscle capillaries _____

Answer 7

during fasting, to use FA for cellular fuel

Question 8

Hepatic Lipase (HL) location

Answer 8

OUter hepatocyte surface

Question 9

HL action

Answer 9

• w/o apo-p

- remove TG from IDL –> FA + glycerol until apoE falls off LP

Question 10

Where does LDL go?

Answer 10

apoB100 binds to LDL-R

1/2 to liver
1/2 to peripheral cells (steroidogenic cells, macrophages)

Question 11

LPL acts on ___ until ___ is released

Answer 11

VLDL

CII

Question 12

Liver secretes ____ in response to liver TG

Answer 12

VLDL

Question 13

Reverse Cholesterol Transport

Answer 13

1. Liver secretes CE-poor HDL
2. Chol is transported from peripheral cells by ABCA1 onto HDL surface
3. LCAT converts surface chol into CE in HDL core –> CE rich HDL
4. CE rich HDL delivers CE back to liver

Question 14

What does liver do with CE rich HDL?

Answer 14

Liver converts chol –> BA (7alpha-OHase) then BA and some chol are secreted into bile.

Question 15

How is Chol removed from body

Answer 15

Only via fecal elim of BA and chol

Question 16

How does insulin resistance increase adipose lipolysis?

Answer 16

Dec inhib of HSL in adipose

Question 17

How does insulin resistance affect FA synth?

Answer 17

Inc FA synth in liver

Question 18

High [VLDL] –> low [HDL

Answer 18

• CETP exchanges VLDL for CE from HDL, normally at insignificant levels
• At high [VLDL], hepatic lipase can act on TG rich HDL and this metab destabilizes them