The effects of inflammatory cytokines on steroidogenic acute regulatory protein expression in macrophages

Objective: To investigate the expression of steroidogenic acute regulatory protein (StAR) in macrophages and the effects of inflammatory cytokines on StAR expression. Methods: The macrophages isolated from ApoE knockout mice and C57BL/6J mice and RAW264.7 cells (a cell line from mouse macrophage. ATCC Number: TIB-71^TM) were cultured in DMEM containing 10% fetal bovine serum. RAW264.7 cells were treated with different inflammatory cytokines (TNF-α, IFN-γ and TGF-β1) and 8-Br-cAMP, a cAMP analog. RT-PCR and Western blot analysis were applied to evaluate the effects of inflammatory cytokines on StAR expression. Results: RT-PCR and Western blot analysis demonstrated the expression of StAR in the macrophages isolated from ApoE knockout mice, C57BL/6J mice and RAW264.7 cells. Proinflammatory cytokines TNF-α and IFN-γ significantly decreased StAR mRNA and protein levels in RAW264.7 cells. The inhibition was dose- and time-dependent. In contrast, anti-inflammatory cytokine TGF-β1 increased StAR mRNA and protein levels. At 1:15 molecular ratio, TGF-β1 blocked the down-regulation of StAR expression mediated by TNF-α. cAMP also induced StAR expression in RAW264.7 cells. When the cells were co-treated with 8-Br-cAMP and TNF-α, 8-Br-cAMP failed to induce StAR expression. Conclusion: Our results provide interesting evidence that inflammatory cytokines regulate StAR expression in macrophages. Received 12 August 2006; returned for revision 28 September 2006; returned for final revision 28 May 2007; accepted by M. Katori 22 June 2007