Flashcards in Lipoprotein Lecture (Lecture 5) Deck (33):
Significant source of cholesterol for peripheral tissues?
Purpose of the reverse cholesterol transport pathway?
Serves to remove excess cholesterol from peripheral tissues and return it to the liver
What lipoprotein accomplishes reverse cholesterol transport?
Where are nascent HDL particles derived from?
liver and intestine
Apoproteins for HDL?
Apo A-I, A-II, E, and C's (acquired later)
Where are HDL formed?
HDL particles are formed in blood by the addition of lipid to apo A-1
Where is Apo A-1 made?
made by the liver and secreted into the blood
Name one function of HDL
HDL is a reservoir of apoproteins: HDL particles serve as a circulating reservoir of apoC-II and apoE
Purpose of apo E?
apolipoprotein required for the receptor mediated endocytosis of IDLs (VLDL remnants) and chylomicrons
Purpose apo C-II?
apolipoprtein transferred to VLDL and chylomicrons, and is an activator of lipoprotein lipase
Purpose of A-I?
Activator of LCAT
Shape of HDL?
("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)
Purpose of A-II?
activator of hepatic lipase
Purpose of LCAT?
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
Purpose of cholesteryl esters?
storage form of cholesterol
Overall effect of CETP?
- 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
Consequence of CETP-mediated transfers of cholesteryl esters?
Reduction in cholesterol content and size of HDL particles; "remodeling" of HDL
Where is LCAT located?
in the blood
Which organ synthesizes LCAT?
What is function of LCAT?
esterify cholesterol taken up by HDL
What apolipoprotein binds to LCAT?
What is HDL3?
cholesteryl ester poor HDL
What is HDL2?
cholesteryl ester-rich HDL
HDL3 becomes HDL2, but how?
HDL accumulates cholesteryl esters through activity of LCAT
What is the connection between CETP and LCAT
CETP movess some of the cholesteryl esters from HDL to VLDL in exchange for TAG, relieving product inhibition of LCAT
What receptor mediates the uptake of cholesteryl esters
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.
What enzyme participates in th conversion of HDL2 to HDL3?
Hepatic lipase, with its ability to degrade both TAG and phosphoipids
Role of ABCA1 transporter?
enrich discoidal HDL with phosphatidycholine and cholesterol out of plasma membrane, thereby generating discoidal nascent HDL
Functions of HDL?
(1) carries "used" cholesterol (as CE) back to the liver
(2) donate some CE to circulating VLDL for redistribution to tissues
Where is the ABCA1 transporter found?
Where is HDL taken up?
HDL is taken up by the liver and degraded. The cholesterol is excreted as bile salts or repackaged in VLDL for distribution to tissue
What is "good cholesterol"?
Cholesterol (CE) in HDL