Lipoprotein Lecture (Lecture 5)

Question 1

Significant source of cholesterol for peripheral tissues?

Answer 1

LDL

Question 2

Purpose of the reverse cholesterol transport pathway?

Answer 2

Serves to remove excess cholesterol from peripheral tissues and return it to the liver

Question 3

What lipoprotein accomplishes reverse cholesterol transport?

Answer 3

HDL

Question 4

Where are nascent HDL particles derived from?

Answer 4

liver and intestine

Question 5

Apoproteins for HDL?

Answer 5

Apo A-I, A-II, E, and C’s (acquired later)

Question 6

Where are HDL formed?

Answer 6

HDL particles are formed in blood by the addition of lipid to apo A-1

Question 7

Where is Apo A-1 made?

Answer 7

made by the liver and secreted into the blood

Question 8

Name one function of HDL

Answer 8

HDL is a reservoir of apoproteins: HDL particles serve as a circulating reservoir of apoC-II and apoE

Question 9

Purpose of apo E?

Answer 9

apolipoprotein required for the receptor mediated endocytosis of IDLs (VLDL remnants) and chylomicrons

Question 10

Purpose apo C-II?

Answer 10

apolipoprtein transferred to VLDL and chylomicrons, and is an activator of lipoprotein lipase

Question 11

Purpose of A-I?

Answer 11

Activator of LCAT

Question 12

Shape of HDL?

Answer 12

disc-shaped
(“as the discoidal nascent HDL accumulates cholesteryl esters, it first becomes a spherical, relatively cholesteryl ester poor HDL3” … all I mean to say is that it becomes spherical and isn’t always disc-shaped)

Question 13

Purpose of A-II?

Answer 13

activator of hepatic lipase

Question 14

Purpose of LCAT?

Answer 14

bound to HDL; uses a fatty acid from the phospholipid lecithin on a peripheral cell to esterify cholesterol to cholesteryl esters, which are stored inside HDL

Question 15

Purpose of cholesteryl esters?

Answer 15

storage form of cholesterol

Question 16

Overall effect of CETP?

Answer 16

• first, CETP stands for cholesterol ester transfer protein so you can be certain that it’s going to transfer cholesterol esters -
  The overall effect of CETP is a net mass transfer of cholesteryl esters from HDL to VLDL and of triglyceride from VLDL to HDL

Question 17

Consequence of CETP-mediated transfers of cholesteryl esters?

Answer 17

Reduction in cholesterol content and size of HDL particles; “remodeling” of HDL

Question 18

Where is LCAT located?

Answer 18

in the blood

Question 19

Which organ synthesizes LCAT?

Answer 19

liver

Question 20

What is function of LCAT?

Answer 20

esterify cholesterol taken up by HDL

Question 21

What apolipoprotein binds to LCAT?

Answer 21

Apo A-I

Question 22

What is HDL3?

Answer 22

cholesteryl ester poor HDL

Question 23

What is HDL2?

Answer 23

cholesteryl ester-rich HDL

Question 24

HDL3 becomes HDL2, but how?

Answer 24

HDL accumulates cholesteryl esters through activity of LCAT

Question 25

What is the connection between CETP and LCAT

Answer 25

CETP movess some of the cholesteryl esters from HDL to VLDL in exchange for TAG, relieving product inhibition of LCAT

Question 26

What receptor mediates the uptake of cholesteryl esters

Answer 26

SR-B-1; The uptake of cholesteryl esters by the liver is mediated by a cell-surface receptor, SR-B1 (scavenger receptor class B type 1) that binds HDL. The HDL particle itself is not taken up.

Question 27

What enzyme participates in th conversion of HDL2 to HDL3?

Answer 27

Hepatic lipase, with its ability to degrade both TAG and phosphoipids

Question 28

Role of ABCA1 transporter?

Answer 28

enrich discoidal HDL with phosphatidycholine and cholesterol out of plasma membrane, thereby generating discoidal nascent HDL

Question 29

Functions of HDL?

Answer 29

(1) carries “used” cholesterol (as CE) back to the liver

(2) donate some CE to circulating VLDL for redistribution to tissues

Question 30

Where is the ABCA1 transporter found?

Answer 30

peripheral tissues

Question 31

Where is HDL taken up?

Answer 31

HDL is taken up by the liver and degraded. The cholesterol is excreted as bile salts or repackaged in VLDL for distribution to tissue

Question 32

What is “good cholesterol”?

Answer 32

Cholesterol (CE) in HDL

Question 33

What is the function of hepatic lipase in HDL?

Answer 33

conversion of HDL2 to HDL3 (ability to degrade both TAG and phospholipids)