XIAP down-regulation inhibits RIPK2 ubiquitination-mediated insulin resistance

Insulin resistance (IR) is a pathogenic mechanism for type 2 diabetes mellitus (T2DM), and receptor-interacting serine-threonine kinase 2 (RIPK2) participates in mediating IR. To investigate the specific role of RIPK2 in IR, this study utilized bovine serum albumin-conjugated palmitic acid (0.5 mmol/L) to create an IR model in rat L6 myotubes, followed by transfection with/without short hairpin RNA against RIPK2 (shRIPK2)/RIPK2 overexpression plasmid, and X-linked inhibitor of apoptosis (XIAP) overexpression plasmids. The expressions of RIPK2 and XIAP were evaluated using quantitative real-time polymerase chain reaction (qRT-PCR). Oxidative stress markers superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), and malondialdehyde (MDA) were quantified. Western blot was performed to detect the levels of phosphorylation of extracellular signal-regulated kinases 1/2 (p-ERK1/2)/ERK1/2, p-p38/p38, and p-serine/threonine kinase (p-AKT)/AKT, as well as the influence of XIAP on RIPK2 ubiquitination. Glucose absorption was quantified using fluorescent probes (2-NBDG). In the IR model, RIPK2 expression was significantly increased, whereas XIAP expression was reduced. RIPK2 overexpression diminished SOD levels, CAT levels, and GPx levels and elevated MDA levels, accompanied by increased p-ERK1/2/ERK1/2 and p-p38/p38 ratios. Overexpression of RIPK2 lowered glucose absorption and the p-AKT/AKT ratio. RIPK2 was ubiquitinated by XIAP in the IR model. RIPK2 overexpression offset the impact of XIAP overexpression on SOD levels, CAT levels, GPx levels, and MDA levels, p-ERK1/2/ERK1/2 ratios, and p-p38/p38 ratios. XIAP overexpression enhanced glucose absorption and the p-AKT/AKT ratio. Our results demonstrate that XIAP deficiency reduces RIPK2 ubiquitination, thereby mediating IR in T2DM.