Effect of PPARγ-K107 SUMOylation on insulin sensitivity and adiposity in mice

Abstract

Peroxisome Proliferator-Activated Receptor gamma (PPARγ) is a nuclear receptor that plays an essential role in expression of adipocyte-specific genes. The activity of PPARγ is regulated not only by ligand binding, but also by post-transcriptional modifications. In this study, we investigated the physiological function of small ubiquitin-like modifier (SUMO), a suppressive post-transcriptional modification, in PPARγ activity by generating mice with a mutation at the SUMOylation site. 

[Experimental Procedures] Mice with a lysine-to-arginine substitution at codon 107 of PPARγ were generated by homologous recombination (K107R). We challenged with a high-fat diet, K107R mice and their WT littermates, measured their body weights, and performed glucose tolerance test, insulin tolerance test and hyperinsulinemic–euglycemic clamp experiments. We also evaluated gene expression patterns of their adipocytes by RNA sequencing (RNA-seq), and its outcomes were validated by quantitative RT-PCR.

[Results and Discussion] SUMOylated PPARγ levels were virtually undetectable in homozygous K107R adipocytes. We observed mild reduction of body weight gain in K107R mice on high-fat diet, compared with that of WT. In a glucose tolerance test, K107R mice had decreased plasma insulin concentrations compared with WT mice. Our hyperinsulinemic–euglycemic clamp experiments indicate that K107R mice had a doubling in both the glucose infusion rate and whole-body glucose uptake rate. Significant increases were also observed in glucose uptake into gastrocnemius and diaphragm muscle and iWAT and similar trends in soleus muscle and eWAT and iWAT. Our RNA-seq analysis and following quantitative RT-PCR data indicate that genes involved in metabolism were upregulated in K107R adipose tissues. These results demonstrate that SUMO plays a critical role in regulation of PPARγ activity in vivo.