Iron‐mediated upregulation of M1 and downregulation of M2 programs in macrophages suggests a role for iron in the pathogenesis of non‐alcoholic steatohepatitis (1116.13)

Abstract

Background and Aim: Hepatic reticuloendothelial (RES) iron deposition is associated with nonalcoholic steatohepatitis (NASH) and advanced fibrosis in nonalcoholic fatty liver diseases. We hypothesized that iron loading of macrophages could influence their activation status and contribute to necroinflammation. Methods: Mouse bone marrow derived macrophages (BMDM) were treated with either ferric ammonium citrate (FAC) alone, or cotreated with IL‐4 to determine the effect of iron on proinflammatory or alternative (M2) activation programs. Post treatment, gene expression analysis was performed to assess the status of M1 and M2 markers by qRT‐PCR. Results: BMDMs treated with ferric ammonium citrate (a physiological form of iron) showed increased M1 activation (INOS, TNF‐α, IL‐6, CD14 gene expression) and reduced gene expression of M2 markers (Arginase1, TGF, Mgl1). Further, while cells treated with IL‐4 showed enhanced expression of M2 markers such as Arginase1, Mgl1, Ym1, IL10 and PGC1β, cotreatment with iron abrogated the expression of these M2 markers. Also interestingly, while IL‐4 treatment upregulated the gene expression level of IL‐4 receptor, FAC treatment reduced its expression. Desferrioxamine, an iron chelator, blocked the downregulatory effect of FAC on M2 gene expression. Furthermore, treatment of macrophages with iron led to an elevated expression of hepcidin (p<0.05), the anti‐inflammatory peptide regulating iron homeostasis. Addition of hepcidin to LPS‐treated macrophages resulted in downregulation of TNF‐α (p<0.01), and upregulation of SOCS3 (p=0.05), an anti‐inflammatory mediator. Conclusions: Iron administration causes upregulation of M1 and downregulation of M2 gene expression. We speculate that iron‐induced inflammatory activation may contribute to the necroinflammation, while iron‐mediated downregulation M2 pathway would impact fibrogenesis accompanying NASH. These data provide support for a mechanistic role for iron in NASH.