We determined the effect of co-treatment of statins and dexamethasone on macrophage FABP4 expression. Unexpectedly, statins did not block the induction of macrophage FABP4 expression by dexamethasone. In contrast, statins synergized dexamethasone-induced FABP4 expression. In vivo, pitavastatin synergized dexamethasone-induced FABP4 expression in both peritoneal macrophages and adipose tissues. Cholesterol and mevalonate, but not farnesylation and geranylgeranylation, inhibited the synergistic induction. Promoter assay disclosed a putative negative glucocorticoid regulatory element (nGRE) in FABP4 gene. Pitavastatin had little effect on expression of glucocorticoid receptor (GR). However, pitavastatin enhanced dexamethasone-mediated GR nuclear translocation but inhibited the binding of GR with nGRE.
Our study defines an important mechanism involved in the regulation of macrophage FABP4 expression by a glucocorticoid and statins.