Adipocyte modulation of high-density lipoprotein cholesterol.
BACKGROUND
Adipose harbors a large depot of free cholesterol. However, a role for adipose in cholesterol lipidation of high-density lipoprotein (HDL) in vivo is not established. We present the first evidence that adipocytes support transfer of cholesterol to HDL in vivo as well as in vitro and implicate ATP-binding cassette subfamily A member 1 (ABCA1) and scavenger receptor class B type I (SR-BI), but not ATP-binding cassette subfamily G member 1 (ABCG1), cholesterol transporters in this process.


RESULTS
Cholesterol efflux from wild-type, ABCA1(-/-), SR-BI(-/-), and ABCG1(-/-) adipocytes to apolipoprotein A-I (apoA-I) and HDL3 were measured in vitro. 3T3L1 adipocytes, labeled with (3)H-cholesterol, were injected intraperitoneally into wild-type, apoA-I transgenic, and apoA-I(-/-) mice, and tracer movement onto plasma HDL was monitored. Identical studies were performed with labeled wild-type, ABCA1(-/-), or SR-BI(-/-) mouse embryonic fibroblast adipocytes. The effect of tumor necrosis factor-alpha on transporter expression and cholesterol efflux was monitored during adipocyte differentiation. Cholesterol efflux to apoA-I and HDL3 was impaired in ABCA1(-/-) and SR-BI(-/-) adipocytes, respectively, with no effect observed in ABCG1(-/-) adipocytes. Intraperitoneal injection of labeled 3T3L1 adipocytes resulted in increased HDL-associated (3)H-cholesterol in apoA-I transgenic mice but reduced levels in apoA-I(-/-) animals. Intraperitoneal injection of labeled ABCA1(-/-) or SR-BI(-/-) adipocytes reduced plasma counts relative to their respective controls. Tumor necrosis factor-alpha reduced both ABCA1 and SR-BI expression and impaired cholesterol efflux from partially differentiated adipocytes.


CONCLUSIONS
These data suggest a novel metabolic function of adipocytes in promoting cholesterol transfer to HDL in vivo and implicate adipocyte SR-BI and ABCA1, but not ABCG1, in this process. Furthermore, adipocyte modulation of HDL may be impaired in adipose inflammatory disease states such as type 2 diabetes mellitus.
Zhang
YuZhen
Y
Cardiovascular Institute, University of Pennsylvania School of Medicine, Philadelphia, PA 19104-6160, USA.
McGillicuddy
Fiona C
FC
Hinkle
Christine C
CC
O'Neill
Sean
S
Glick
Jane M
JM
Rothblat
George H
GH
Reilly
Muredach P
MP
D041721:3T3-L1 Cells; D064286:ATP Binding Cassette Transporter 1; D000070998:ATP Binding Cassette Transporter, Subfamily G, Member 1; D018528:ATP-Binding Cassette Transporters / Q000235:genetics / Q000378:metabolism; D017667:Adipocytes / Q000166:cytology / Q000378:metabolism*; D000818:Animals; D016632:Apolipoprotein A-I / Q000235:genetics / Q000378:metabolism; D002454:Cell Differentiation; D002478:Cells, Cultured; D002784:Cholesterol / Q000378:metabolism*; D008076:Cholesterol, HDL / Q000378:metabolism*; D006801:Humans; D007249:Inflammation / Q000378:metabolism; D008074:Lipoproteins / Q000235:genetics / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D008822:Mice, Transgenic; D023421:Models, Animal; D051122:Scavenger Receptors, Class B / Q000235:genetics / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism
C577836:ABCA1 protein, human; C419353:ABCG1 protein, human; C487540:ABCG1 protein, mouse; D064286:ATP Binding Cassette Transporter 1; D000070998:ATP Binding Cassette Transporter, Subfamily G, Member 1; D018528:ATP-Binding Cassette Transporters; D016632:Apolipoprotein A-I; D008076:Cholesterol, HDL; D008074:Lipoproteins; C495124:SCARB1 protein, human; C454739:Scarb1 protein, mouse; D051122:Scavenger Receptors, Class B; D014409:Tumor Necrosis Factor-alpha; D002784:Cholesterol