MDM2 induces pro-inflammatory and glycolytic responses in M1 macrophages by integrating iNOS-nitric oxide and HIF-1a pathways in mice

M1 macrophages induce protective immunity against infection, but also contribute to metabolic and inflammatory diseases. Here we show that he E3 ubiquitin ligase, MDM2, promotes the glycolytic and inflammatory activities of M1 macrophage by increasing the production of IL-1ß, MCP-1 and nitric oxide (NO). Mechanistically, MDM2 triggers the ubiquitination and degradation of E3 ligase, SPSB2, to stabilize iNOS and increases production of NO, which s-nitrosylates and activates HIF-1a for triggering the glycolytic and pro-inflammatory programs in M1 macrophages. Myeloid-specific haplo-deletion of MDM2 in mice not only blunts LPS-induced endotoxemia and NO production, but also alleviates obesity-induced adipose tissue-resident macrophage inflammation. By contrast, MDM2 haplodeletion induces higher mortality, tissue damage and bacterial burden, and also suppresses M1 macrophage response, in the cecal ligation and puncture-induced sepsis mouse model. Our findings thus identify MDM2 as an activator of glycolytic and inflammatory responses in M1 macrophages by connecting the iNOS-NO and HIF-1a pathways. Overall design: To investigate the role of MDM2 in M1 macrophages, we first isolated bone marrow cells from C57BL/6J mice and differentiated them into bone marrow-derived macrophages (BMDM) using L929-conditioned medium. BMDM were then transfected with siRNA targeting MDM2 (siMdm2) or a scramble control (siScramble) respectively, followed by stimulation with 100 ng/ml lipopolysaccharide (LPS) and 100 ng/ml interferon-gamma (IFNg) for 20 hours.