Adipophilin is a sensitive marker for lipid loading in human blood monocytes

Adipophilin, a marker of lipid accumulation initially described in adipocyt es, was recently shown to be induced in macrophage roam cells. We found tha t even freshly isolated blood monocytes express adipophilin and that the am ount of adipophilin protein is variable in monocytes from different healthy individuals. However, the physiological expression of adipophilin does not correlate with the levels of free fatty acids, cholesterylesters or free c holesterol. Enzymatically modified low-density lipoprotein (E-LDL) induces rapid foam cell formation in monocytes and upregulates adipophilin mRNA and protein within 2 h of incubation. This rapid induction of adipophilin is a ccompanied by a significant increase of free fatty acids in monocytes incub ated with E-LDL. Adipophilin facilitates the uptake of free fatty acids, an d here we demonstrate that free fatty acids increase is related to the earl y upregulation of adipophilin expression in blood monocytes. Fatty acids ar e ligands for peroxisome proliferator-activated receptor-gamma (PPAR gamma) , and the upregulation of adipophilin mRNA by PPAR gamma agonists like 15d- PGJ(2) and ciglitazone indicates that PPAR gamma may mediate the induction of adipophilin expression in human blood monocytes. (C) 2001 Elsevier Scien ce B.V. All rights reserved.