The role of uncoupling protein 2 in macrophages and its impact on obesity-induced adipose tissue inflammation and insulin resistance.

The development of a chronic, low-grade inflammation originating from adipose tissue in obese subjects is widely recognized to induce insulin resistance, leading to the development of type 2 diabetes. The adipose tissue microenvironment drives specific metabolic reprogramming of adipose tissue macrophages, contributing to the induction of tissue inflammation. Uncoupling protein 2 (UCP2), a mitochondrial anion carrier, is thought to separately modulate inflammatory and metabolic processes in macrophages, and is upregulated in macrophages in the context of obesity and diabetes. Here, we investigate the role of UCP2 in macrophage activation in the context of obesity-induced adipose tissue inflammation and insulin resistance. Using a myeloid-specific knockout of UCP2 (Ucp2 ΔLysM), we found that Ucp2 deficiency significantly increases glycolysis and oxidative respiration, both unstimulated and after inflammatory conditions. Strikingly, fatty acid loading abolished the metabolic differences between Ucp2 ΔLysM macrophages and their floxed controls. Furthermore, Ucp2 ΔLysM macrophages show attenuated pro-inflammatory responses towards Toll-like receptor-2 and -4 stimulation. To test the relevance of macrophage-specific Ucp2 deletion in vivo, Ucp2 ΔLysM and Ucp2 fl/fl mice were rendered obese and insulin resistant through high-fat feeding. Although no differences in adipose tissue inflammation or insulin resistance was found between the two genotypes, adipose tissue macrophages isolated from diet-induced obese Ucp2 ΔLysM mice showed decreased TNFα secretion after ex vivo LPS stimulation compared to their Ucp2 fl/fl littermates. Together, these results demonstrate that while UCP2 regulates both metabolism and the inflammatory response of macrophages, its activity is not crucial in shaping macrophage activation in the adipose tissue during obesity-induced insulin resistance. Published under license by The American Society for Biochemistry and Molecular Biology, Inc.