1199-P: The Oncogene MDM2 Induces M1 Macrophage Polarization and Adipose Tissue Inflammation in Obesity

Obesity is characterized by chronic low-grade inflammation that contributes to the pathogenesis of type 2 diabetes. Adipose tissue macrophages predominantly switch to a pro-inflammatory phenotype known as M1 during obesity. The accumulation of pro-inflammatory M macrophages in obese adipose tissue results in the secretion of a cluster of pro-inflammatory cytokines that instigate adipose tissue inflammation and insulin resistance.

Here we discovered that expression of oncoprotein murine double minute 2 (MDM2) was elevated in obese white adipose tissues. Also, MDM2 protein expression was drastically induced in macrophages activated with lipopolysaccharide (LPS) and interferon-γ (IFNγ). Mice with myeloid cells-specific MDM2 haploinsufficiency (Mye-MDM2 KO mice) were generated and subjected to high-fat-diet (HFD) feeding. After 16 weeks of HFD feeding, obesity-induced glucose intolerance and insulin resistance were alleviated in Mye-MDM2 KO mice with reference to their wild type (WT) controls. Systemic inflammation induced by LPS injection was also reduced in Mye-MDM2 KO mice. In vitro, expression of M1 genes induced by LPS and IFNγ were inhibited in bone marrow-derived macrophages with haplodeficiency of MDM2. Similarly, pharmacological inhibition of MDM2 with the small molecule inhibitor Nutlin-3a attenuates pro-inflammatory cytokines secretion by macrophages. Mechanistically, haplodeletion of MDM2 led to decreased expression of glycolytic genes in BMDM during M1 activation.

Taken together, we demonstrated a novel role of MDM2 in regulating glycolysis and M1 macrophage activation in addition to its role as a negative regulator of p53 tumour suppressor protein, suggesting it as a potential therapeutic target for treating type 2 diabetes.