Arsenic, Nrf2 and Autophagy Dysfunction in Type II Diabetes

项目摘要 慢性砷暴露是一个世界性的公共卫生问题，与 罹患某些类型癌症的风险，以及包括II型糖尿病在内的代谢性疾病。 最近，美国人群中出现了与砷相关的II型糖尿病， 墨西哥、加拿大、台湾和孟加拉国。我们之前曾报道过，低、环保 相关剂量的砷会在较晚阶段阻断自噬。自噬是细胞降解的关键 途径和自噬功能障碍被认为是致病变化的组成部分 发生于脂肪细胞、β-胰岛细胞、肝细胞、骨骼肌和肾系膜细胞 糖尿病进展。我们还表明，自噬途径的失调会导致 关键抗氧化剂转录因子核因子红斑狼疮衍生2样蛋白的长时间激活 2(NRF2)。正常情况下，NRF2在胞浆中被Kelch样ECH相关结合和降解 蛋白1(Keap1)在氧化修饰Keap1后在蛋白质水平上调 (Keap1-C151依赖，规范)或通过将Keap1隔离到自噬体内 自噬功能障碍(p62依赖，非典型)。同时通过控制NRF2的激活 典型的机制是保护性的，Nrf2的长期非典型激活导致细胞 功能障碍和组织损伤，表明NRF2的“阴暗面”。因此，我们假设 由于砷介导的自噬通量的阻断，导致Nrf2的长期激活， 对促进II型糖尿病的砷来说是必不可少的。这一假设得到了 以下证据：1)慢性砷暴露降低葡萄糖摄取和胰岛素信号转导 3T3-L1脂肪细胞，2)Keap11kD/Lepob/ob小鼠，一种遗传性糖尿病小鼠模型 NRF2激活，显示脂肪生成受损，以及胰岛素敏感性和血糖下降 与LEPOB/ob对照相比的耐受性，以及3)β细胞特异性敲除ATG7，这是一个关键的自噬 启动蛋白，导致p62和多泛素化蛋白水平增加，伴随着β- 细胞丢失和胰岛素产生减少。 我们已经生成了大量数据，表明砷在 自噬小体-溶酶体融合步骤。三个核心SNARE蛋白Stx17、SNAP29和VAMP8 介导融合，SNAP29介导Stx17与外部自噬小体的相互作用 膜和溶酶体膜上的VAMP8。我们相信这些基因的任何一种消融 三种融合蛋白将阻碍自噬小体-溶酶体融合并导致Nrf2延长 激活，这将模仿砷促进II型糖尿病的效果。因此，我们建议 致： 目的1：确定砷阻断自噬小体的分子机制。 溶酶体融合，导致Nrf2激活时间延长。 目的2：确定Nrf2激活延长是否由自噬功能障碍引起 诱导肌肉、肾脏、胰腺、肝脏和脂肪细胞的代谢重新编程。 目的3：确定自噬功能障碍和延长的Nrf2激活表型 使用II型砷加重胰岛素抵抗、肥胖和糖尿病肾病 SNAP29f/f、Nrf2-/-和SNAP29f/f/Nrf2-/-小鼠的糖尿病模型。 影响：对自噬功能障碍的详细和透彻的理解 在砷诱导的代谢性疾病中激活Nrf2将被证明在生成过程中具有极其重要的价值 预防和治疗策略，以及在识别生物标记物方面， 处于危险中的人口。

Project Summary Chronic arsenic exposure is a worldwide public health concern correlated with an increased risk of developing certain types of cancer, as well as metabolic diseases including type II diabetes. Arsenic-linked type II diabetes has recently been shown among populations in the United States, Mexico, Canada, Taiwan, and Bangladesh. We have previously reported that low, environmentally relevant doses of arsenic block autophagy at a later stage. Autophagy is a key cellular degradation pathway and autophagic dysfunction is thought to be an integral part of pathogenic changes that occur in adipocytes, β-islet cells, hepatocytes, skeletal muscle, and kidney mesangial cells during diabetes progression. We have also shown that dysregulation of the autophagy pathway results in prolonged activation of the key antioxidant transcription factor nuclear factor erytheroid-derived-2-like 2 (Nrf2). Nrf2, which is normally bound and degraded in the cytosol by Kelch-like ECH-associated protein 1 (Keap1), is upregulated at the protein level following oxidative modification of Keap1 (Keap1-C151 dependent, canonical) or by sequestration of Keap1 into autophagosomes during autophagy dysfunction (p62-dependent, non-canonical). While controlled Nrf2 activation through the canonical mechanism is protective, prolonged non-canonical activation of Nrf2 causes cellular dysfunction and tissue damage, indicative of a “dark side” to Nrf2. Therefore, we hypothesize that the prolonged activation of Nrf2, resulting from arsenic-mediated blockage of autophagy flux, is essential for arsenic in promoting type II diabetes. This hypothesis is supported by the following evidence: 1) chronic arsenic exposure decreases glucose uptake and insulin signaling in 3T3-L1 adipocytes, 2) Keap11 KD/Lepob/ob mice, a genetic mouse model for diabetes with persistent Nrf2 activation, display impaired adipogenesis, as well as decreased insulin sensitivity and glucose tolerance compared to Lepob/ob controls, and 3) β-cell specific knockdown of Atg7, a key autophagy initiation protein, results in increased levels of p62 and poly-ubiquitinated proteins, accompanied by β- cell loss and decreased insulin production. We have generated a large amount of data indicating that arsenic blocks autophagy at the autophagosome-lysosome fusion step. Three core SNARE proteins Stx17, SNAP29, and VAMP8 mediate fusion, with SNAP29 mediating the interaction between Stx17 on the outer autophagosomal membrane and VAMP8 on the lysosomal membrane. We believe that genetic ablation of any of these three fusion proteins will hinder autophagosome-lysosome fusion and result in prolonged Nrf2 activation, which will mimic the effect of arsenic in promoting type II diabetes. Therefore, we propose to: Aim 1: Determine the molecular mechanism by which arsenic blocks autophagosome- lysosome fusion, leading to prolonged Nrf2 activation. Aim 2: Determine if prolonged Nrf2 activation resulting from autophagic dysfunction induces metabolic reprogramming in muscle, kidney, pancreas, liver and fat cells. Aim 3: Determine if autophagy dysfunction and prolonged Nrf2 activation phenocopy arsenic in exacerbating insulin resistance, obesity, and diabetic nephropathy using type II diabetes models in SNAP29f/f, Nrf2-/-, and SNAP29f/f/Nrf2-/- mice. Impact: A detailed and thorough understanding of autophagy dysfunction and the prolonged activation of Nrf2 in arsenic-induced metabolic disease will prove extremely valuable in the generation of preventive and therapeutic strategies, as well as in the identification of biomarkers, for the populations at risk.