PTPN2 mutations affect islet beta cell susceptibility in T1D

1型糖尿病（T1 D）的特征是胰腺β细胞被个体自身的免疫系统破坏。虽然T1 D主要被视为免疫系统疾病，但越来越多的证据表明，产生胰岛素的β细胞可能积极促进其破坏。此外，最近的全基因组关联研究（GWAS）表明，尽管人类白细胞抗原（HLA）复合物赋予了T1 D的显著遗传易感性，但非HLA基因座中的许多单核苷酸多态性（SNP）也导致了该疾病{Floyel，2015 #2}。重要的是，这些非HLA变体中的许多发生在免疫细胞谱系以及靶向β细胞中表达的基因中。了解这些微小基因变异如何影响胰岛B细胞的功能将使我们能够开发出有效预防T1 D进展的新疗法。在本提案中，我们将使用转基因小鼠和人类B细胞模型来探索T1 D风险等位基因蛋白酪氨酸磷酸酶N2（PTPN 2）（也称为T细胞蛋白酪氨酸磷酸酶（TC-PTP））突变如何在T1 D和/或T1 D模拟条件下影响胰岛β细胞功能。在小鼠和人类中，PTPN 2在几种组织中广泛表达，包括T细胞和胰岛β细胞，然而PTPN 2的突变主要在T细胞背景下研究。在小鼠中，PTPN 2已显示通过充当细胞因子应答下游的JAK/STAT信号传导的负调节剂来调节T细胞中的炎症信号传导。然而，有证据表明PTPN 2介导的自身免疫不能完全解释T细胞功能障碍。PTPN 2的T细胞特异性失活引起的自身免疫表型比在全基因敲除小鼠中观察到的要轻。事实上，在胰腺中，PTPN 2的组成性失活损害了高脂肪饮食喂养的小鼠中的葡萄糖刺激胰岛素分泌{Xi，2015 #20}。尚未在T1 D的背景下检查PTPN 2在β细胞中的功能;然而，在用促炎细胞因子或双链病毒RNA处理后，PTPN 2在小鼠和人β细胞中上调，再次表明PTPN 2在胰岛中的额外作用。为了解析PTPN 2突变对T1 D的β细胞特异性贡献，我们产生了Ptpn 2的β细胞特异性敲除（PTPN 2-bKO）。我们的初步数据表明，在T1 D模拟应激条件下，PTPN 2-bKO胰岛中的代谢途径发生了改变。因此，我们已经鉴定了丙酮酸激酶M2（PKM 2），其是β细胞中的重要糖酵解酶，是PTPN 2的直接靶点。此外，我们已经产生了PTPN 2缺失的hPSC，并从携带PTPN 2突变的T1 D个体中收集了组织样品。在本提案中，我们将检验β细胞中PTPN 2功能受损通过损害β细胞代谢功能和存活促进T1 D发展的假设。在SA 1中，我们将确定在基础和自身免疫介导的条件下与PTPN 2缺失相关的β细胞缺陷。在SA 2中，我们将确定PTPN 2在基础和自身免疫介导的条件下调节的分子途径。

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.