PTPN2 mutations affect islet beta cell susceptibility in T1D

点击翻译按钮获取中文摘要

Type 1 diabetes (T1D) is characterized by the destruction of pancreatic beta cells by an individual’s own immune system. Although T1D is primarily viewed as a disease of the immune system, there is mounting evidence to suggest that insulin-producing β cells may actively contribute to their destruction. Furthermore, recent genome-wide association studies (GWAS) have suggested that although significant genetic predisposition to T1D is conferred by the human leukocyte antigen (HLA) complex, many single nucleotide polymorphisms (SNPs) in non-HLA loci also contribute to the disease {Floyel, 2015 #2}. Importantly, many of these non-HLA variants occur in genes expressed in both immune cell lineages as well as in the targeted β cells. Knowledge of how these minor gene variants affect function of islet b cells will allow us to develop novel therapies that could be effective in preventing progression of T1D. In this proposal, we will use transgenic mice and human b cell models to explore how mutations in the T1D risk allele Protein tyrosine phosphatase N2 (PTPN2), also known as T cell protein tyrosine phosphatase (TC-PTP), affect islet β cell function in the context of T1D and/or T1D mimicking conditions. In mice and humans, PTPN2 is broadly expressed in several tissues, including T cells and islet β cells, however mutations of PTPN2 have predominantly been studied in the T cell context. In mice, PTPN2 has been show to modulate inflammatory signaling in T cells by acting as a negative regulator of JAK/STAT signaling, downstream of a cytokine response. However, there is evidence that PTPN2-mediated autoimmunity cannot be fully explained by T cell dysfunction. T-cell specific inactivation of PTPN2 caused less severe autoimmune phenotypes than observed in global knockout mice. Indeed, in the pancreas, constitutive inactivation of PTPN2 impaired glucose stimulated insulin secretion in mice fed a high fat diet {Xi, 2015 #20}. The function of PTPN2 in β cells has not yet been examined in the context of T1D; however, PTPN2 is upregulated in mouse and human β cells upon treatment with proinflammatory cytokines or double stranded viral RNA, again suggesting an additional role for PTPN2 in islets. To parse out the β cell-specific contribution of PTPN2 mutations to T1D, we have generated a β cell-specific knockout of Ptpn2 (PTPN2-bKO). Our preliminary data indicate that metabolic pathways are altered in PTPN2-bKO islets under T1D mimicking stress conditions. Consistently, we have identified pyruvate kinase M2 (PKM2), an important glycolytic enzyme in the β cell to be a direct target of PTPN2. In addition, we have generated hPSCs deleted for PTPN2 and collected tissue samples from T1D individuals carrying mutations in PTPN2. In this proposal, we will test the hypothesis that disrupted function of PTPN2 in the β cell promotes the development of T1D by compromising β cell metabolic function and survival. In SA1 we will determine the beta cell defects associated with deletion of PTPN2 in basal and autoimmune-mediated conditions. In SA2 we will determine the molecular pathways regulated by PTPN2 in basal and autoimmune-mediated conditions.