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high density lipoprotein (HDL)
Classification:
- HDL is usually divided into 2 density classes, HDL2 & HDL3 (precursor of HDL2)
- HDL2 is the larger lipoprotein particle with MW = 360 kD vs. 175 kD for HDL3
- 60% of HDL2 is lipid vs. 45% for HDL3
- another form of HDL, HDLc is thought to develop after ingestion of cholesterol
- HDLc is particularly abundant in apo E, thus binds to LDL receptor
Function:
- HDL plays roles in:
a) returning cholesterol from the periphery to the liver for removal as bile acids
b) scavenging lipids & lipoproteins during catabolism of chylomicrons & VLDL
c) reservoir for plasma apo C2
- HDL may play a role in reducing inflammation [2]
- HDL induces ATF3 in macrophages
- this reduces expression of Toll-like receptor-induced proinflammatory cytokines
Structure:
- ~50% of mass of HDL is protein, with apo A1 & apo A2 constituting 90%
- the A1/A2 ratio is approximately 3:1
- 30% of HDL is phospholipid & 20% cholesterol
- the phospholipid/sphingomyelin ratio is 5:1 & esterified/free cholesterol about 3:1
- some HDL particles contain only apo A1, while others contain apo A1 & apo A2
- HDL particles containing only apo A1 appear to stimulate cholesterol efflux from cells
Expression:
- HDL is secreted by liver & intestine, in the form of a disc-shaped precursor containing apo A1, apo A2, lecithin & free cholesterol
- transformation to the spherical HDL3 depends upon LCAT activity
- little is known of HDL catabolism, although the liver & kidneys are probably involved
Related
cholesterol HDL in serum
scavenger receptor
Specific
high density lipoprotein-2 (HDL-2)
high density lipoprotein-3 (HDL-3)
high density lipoprotein-c (HDL-c)
General
alpha globulin
lipoprotein
macromolecular complex
multisubunit protein
Figures/Diagrams
Figures/diagrams/slides/tables related to high density lipoprotein
Properties
COMPARTMENT: plasma
MISC-INFO: 1/2life 4 DAYS
References
- Tietz Textbook of Clinical Chemistry, 2nd ed.
Burtis CA & Ashwood ER (eds), WB Saunders Co,
Philadelphia PA, 1993, pg 1028
- De Nardo D et al
High-density lipoprotein mediates anti-inflammatory
reprogramming of macrophages via the transcriptional regulator
ATF3.
Nat Immunol. 2013 Dec 8.
PMID: 24317040
http://www.nature.com/ni/journal/vaop/ncurrent/full/ni.2784.html
Components
apolipoprotein A1 (APOA1)
apolipoprotein A2 (APOA2)
apolipoprotein C
apolipoprotein E (APOE)
cholesterol
cholesterol ester
Clusterin; Aging-associated gene 4 protein; apolipoprotein J; apo-J; complement cytolysis inhibitor; CLI; complement-associated protein SP-40,40; Ku70-binding protein 1; NA1/NA2; testosterone-repressed prostate message 2; TRPM-2; contains: Clusterin beta chain; apoJalpha; complement cytolysis inhibitor a chain; contains: Clusterin alpha chain; apoJbeta; complement cytolysis inhibitor b chain (CLU, APOJ, CLI, KUB1, AAG4)
phosphatidylcholine (lecithin)
triglyceride