Iron alters macrophage polarization status and leads to steatohepatitis and fibrogenesis

Abstract

We have previously demonstrated that iron overload in hepatic reticuloendothelial system cells (RES) is associated with severe nonalcoholic steatohepatitis (NASH) and advanced fibrosis in patients with nonalcoholic fatty liver disease (NAFLD). Recruited myeloid‐derived macrophages have gained a pivotal position as drivers of NASH progression and fibrosis. In this study, we used bone marrow‐derived macrophages (BMDM) from C57Bl6 mice as surrogates for recruited macrophages and examined the effect of iron on macrophage polarization. Treatment with iron (ferric ammonium citrate, FAC) led to increased expression levels of M1 markers: CCL2, CD14, iNOS, IL‐1β, IL‐6, and TNF‐α; it also increased protein levels of CD68, TNF‐α, IL‐1β, and IL‐6 by flow cytometry. This effect could be reversed by desferrioxamine, an iron chelator. Furthermore, iron loading of macrophages in the presence of IL‐4 led to the down‐regulation of M2 markers: arginase‐1, Mgl‐1, and M2‐specific transcriptional regulator, KLF4. Iron loading of macrophages with IL‐4 also resulted in reduced phosphorylation of STAT6, another transcriptional regulator of M2 activation. Dietary iron overload of C57Bl6 mice led to hepatic macrophage M1 activation. Iron overload also stimulated hepatic fibrogenesis. Histologic analysis revealed that iron overload resulted in steatohepatitis. Furthermore, NAFLD patients with hepatic RES iron deposition had increased hepatic gene expression levels of M1 markers, IL‐6, IL‐1β, and CD40 and reduced gene expression of an M2 marker, TGM2, relative to patients with hepatocellular iron deposition pattern. We conclude that iron disrupts the balance between M1/M2 macrophage polarization and leads to macrophage‐driven inflammation and fibrogenesis in NAFLD.

Regulation of lipid‐induced macrophage polarization through modulating peroxisome proliferator‐activated receptor‐gamma activity affects hepatic lipid metabolism via a Toll‐like receptor 4/NF‐κB signaling pathway

“…In general, macrophages comprise two main phenotypes, classical M1 activation, and alternative M2 activation phenotypes, which regulate pro‐inflammatory and anti‐inflammatory responses, respectively 32 . An increase in hepatic M1 macrophages or a high M1/M2 ratio was observed in HF diet‐fed mice, triggering inflammatory processes and promoting the progression of NAFLD 33–35 . M2 activation of Kupffer cells by peroxisome proliferator‐activated receptor‐delta ameliorated obesity‐induced insulin resistance and hepatic steatosis 36 .…”

Macrophage Function in the Pathogenesis of Non-alcoholic Fatty Liver Disease: The Mac Attack

“…Hepcidin binds to ferroportin and enhances its degradation. The accumulation of iron promotes "classically" activated macrophage polarization and production of proinflammatory cytokines that enhance the inflammatory response (157,158). Excessive iron accumulation in both KCs and hepatocytes is associated with NAFLD (152).…”

Long non-coding RNA FENDRR regulates IFNγ-induced M1 phenotype in macrophages

“…Iron suppresses M1 polarization in Raw 264.7 macrophages, mouse bone marrow-derived macrophages and THP-1 monocyte-derived macrophages 57 – 59 and promotes M2 polarization in THP-1 monocyte-derived macrophages 59 , 60 . However, one study reported opposite results showing that iron increases M1 macrophage markers, but inhibits IL-4-induced M2 macrophage markers in mouse bone marrow-derived macrophages 61 . Iron decreases STAT1 phosphorylation in IFNγ-treated RAW 246.7 macrophages 57 , which is consistent with the iron-mediated inhibition of M1 macrophage polarization.…”