High glucose stimulates macrophage SR-BI expression and induces a switch in its activity from cholesterol efflux to cholesterol influx.
OBJECTIVE
Diabetes is associated with atherogenesis and macrophage-foam cell formation, due in part to a decrease in HDL-mediated cholesterol efflux from macrophages. This study examined the expression of proteins involved in cholesterol transport, i.e. ABCA1 and SR-BI, under diabetic conditions.


RESULTS
ABCA1 expression was similar, whereas SR-BI expression (mRNA and protein) was significantly increased in mouse peritoneal macrophages (MPM) harvested from C57Bl/6 diabetic mice, compared to MPM from control non-diabetic mice. Similar results were obtained in vitro in J-774A.1 macrophage-like cell line incubated with high (30 mM) vs. low (5mM) glucose concentrations. Accordingly, association and internalization of HDL to MPM from diabetic mice, or to J-774A.1 macrophages grown under diabetic conditions was significantly higher compared to control cells. Unexpectedly, however, increased macrophage SR-BI expression was associated with a substantial reduction in HDL-mediated cholesterol efflux from the macrophages. Moreover, total cellular cholesterol content was increased by 28% in macrophages incubated with HDL under high glucose concentrations, compared to low glucose concentrations. This effect was abolished by a rabbit polyclonal anti-SR-BI, which blocks binding to the receptor, or alternatively by using BLT1, a specific inhibitor of lipid transport via the SR-BI.


CONCLUSIONS
Diabetes stimulates the expression of SR-BI in macrophages and leads to a shift in its activity from HDL-mediated cholesterol efflux to HDL-mediated cholesterol influx. These effects may lead to increased foam cell formation and atherosclerosis development.
Gantman
Anna
A
The Lipid Research Laboratory, Technion Faculty of Medicine, The Rappaport Family Institute for Research in the Medical Sciences, and Rambam Medical Center, Haifa, Israel.
Fuhrman
Bianca
B
Aviram
Michael
M
Hayek
Tony
T
D064286:ATP Binding Cassette Transporter 1; D018528:ATP-Binding Cassette Transporters / Q000096:biosynthesis; D000818:Animals; D050197:Atherosclerosis / Q000209:etiology; D008076:Cholesterol, HDL / Q000378:metabolism*; D003517:Cyclopentanes / Q000494:pharmacology; D003921:Diabetes Mellitus, Experimental / Q000150:complications / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism* / Q000494:pharmacology; D006943:Hyperglycemia / Q000150:complications / Q000378:metabolism*; D017737:Macrophages, Peritoneal / Q000187:drug effects / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D051122:Scavenger Receptors, Class B / Q000037:antagonists & inhibitors / Q000096:biosynthesis*; D013882:Thiosemicarbazones / Q000494:pharmacology
C526651:2-hexyl-1-cyclopentanone thiosemicarbazone; D064286:ATP Binding Cassette Transporter 1; D018528:ATP-Binding Cassette Transporters; D008076:Cholesterol, HDL; D003517:Cyclopentanes; C454739:Scarb1 protein, mouse; D051122:Scavenger Receptors, Class B; D013882:Thiosemicarbazones; D005947:Glucose