Both type 1 and type 2 diabetes are characterized by deficient insulin secretion and decreased b-cell mass. Thus, regenerative strategies to increase b-cell mass need to be developed. To characterize mechanisms of b-cell plasticity, we studied a model of severe insulin resistance in the adult mouse and defined how b-cells adapt. Chronic corticosterone (CORT) treatment was given to adult mice and led to rapid insulin resistance and adaptive increased insulin secretion. Adaptive and massive increase of b-cell mass was observed during treatment up to 8 weeks. b-Cell mass increase was partially reversible upon treatment cessation and reinduced upon subsequent treatment. b-Cell neogenesis was suggested by an increased number of islets, mainly close to ducts, and increased Sox9 and Ngn3 mRNA levels in islets, but lineagetracing experiments revealed that neoformed b-cells did not derive from Sox9-or Ngn3-expressing cells. CORT treatment after b-cell depletion partially restored b-cells. Finally, b-cell neogenesis was shown to be indirectly stimulated by CORT because serum from CORT-treated mice increased b-cell differentiation in in vitro cultures of pancreatic buds. Altogether, the results present a novel model of b-cell neogenesis in the adult mouse and identify the presence of neogenic factors in the serum of CORT-treated mice.

Non-alcoholic fatty liver disease (NAFLD) is a growing epidemic linked to metabolic disease. The first stage of NAFLD is characterized by lipid accumulation in hepatocytes, but this can progress into non-alcoholic steatohepatitis (NASH), cirrhosis, and hepatocellular carcinoma (HCC). Western diets, high in fats, sugars and cholesterol are linked to NAFLD development. Murine models are often used to study NAFLD; however, there remains debate on which diet-induced model best mimics both human disease progression and pathogenesis. In this study, we performed a side-by-side comparison of two popular diet models of murine NAFLD/NASH and associated HCC: a high fat diet supplemented with 30% fructose water (HFHF) and a western diet high in cholesterol (WDHC), comparing them to a common grain-based chow diet (GBD). Mice on both experimental diets developed liver steatosis, while WDHC-fed mice had greater levels of hepatic inflammation and fibrosis than HFHF-fed mice. In contrast, HFHF-fed mice were more obese and developed more severe metabolic syndrome, with less pronounced liver disease. Despite these differences, WDHC-fed and HFHF-fed mice had similar tumour burdens in a model of diet-potentiated liver cancer. Response to diet and resulting phenotypes were generally similar between sexes, albeit delayed in females. This study shows that modest differences in diet can significantly uncouple glucose homeostasis and liver damage. In conclusion, long-term feeding of either HFHF or WDHC are reliable methods to induce NASH and diet-potentiated liver cancer in mice of both sexes; however, the choice of diet involves a trade-off between severity of metabolic syndrome and liver damage.

Type 2 diabetes is characterized by chronic hyperglycemia associated with impaired insulin action and secretion. Although the heritability of type 2 diabetes is high, the environment, including blood components, could play a major role in the development of the disease. Amongst environmental effects, epitranscriptomic modifications have been recently shown to affect gene expression and glucose homeostasis. The epitranscriptome is characterized by reversible chemical changes in RNA, with one of the most prevalent being the m6A methylation of RNA. Since pancreatic β cells fine tune glucose levels and play a major role in type 2 diabetes physiopathology, we hypothesized that the environment, through variations in blood glucose or blood free fatty acid concentrations, could induce changes in m6A methylation of RNAs in pancreatic β cells. Here we observe a significant decrease in m6A methylation upon high glucose concentration, both in mice and human islets, associated with altered expression levels of m6A demethylases. In addition, the use of siRNA and/or specific inhibitors against selected m6A enzymes demonstrate that these enzymes modulate the expression of genes involved in pancreatic β-cell identity and glucose-stimulated insulin secretion. Our data suggest that environmental variations, such as glucose, control m6A methylation in pancreatic β cells, playing a key role in the control of gene expression and pancreatic β-cell functions. Our results highlight novel causes and new mechanisms potentially involved in type 2 diabetes physiopathology and may contribute to a better understanding of the etiology of this disease.