蛋白质内稳态失衡介导的内皮素受体A上调致肝脏胰岛素抵抗的机制及曲克芦丁干预研究

Hepatic insulin resistance is a key factor in the pathogenesis of systemic insulin resistance and diabetes. Evidence shows that the abnormal expression of endothelin A receptor (ETAR) is associated with the pathogeneses of diabetes and a variety of liver injuries; however, whether the abnormal expression of ETAR plays a role in the regulation of insulin resistance has not been investigated to date. Heat shock factor1 (HSF1) is the major transcription factor required for the maintenance of proteostasis, which may play a role in the regulation of insulin resistance, and its level is downregulated in the livers of diabetic mice. Our pilot studies showed that the expression of ETAR was markedly up-regulated in the livers of diabetic mice. The inhibition of the upregulation of ETAR could restore the HSF1 levels, thereby improving hepatic insulin resistance in the livers of diabetic mice. These results suggested that the HSF1-mediated proteostasis could play a role in the regulation of hepatic insulin resistance induced by the upregulation of ETAR. Our current research aims to explore how the up-regulated expression of ETAR induces hepatic insulin resistance by regulating the HSF1-mediated proteostasis and investigate the molecular mechanism underlying these effects using the mouse models of liver-specific ETAR knockout and RNA interference. We will further investigate the changes in the expression levels and the interaction of the insulin resistance-related signaling molecules and the key target of troxerutin in the intervention of diabetes, which may provide novel insights into the prevention strategy of diabetes.

肝脏胰岛素抵抗是全身胰岛素抵抗及糖尿病病理发展的关键因子。内皮素受体A（ETAR）表达异常与糖尿病相关，并可调控多种肝损伤的病理过程，但其是否调控肝脏胰岛素抵抗，国内外尚未见报道。研究显示，蛋白质内稳态可能参与胰岛素抵抗的调控，热休克因子1（HSF1）是蛋白质内稳态的关键调控因子，其水平在糖尿病小鼠肝脏中显著下降。我们的先期研究显示，糖尿病小鼠肝脏中ETAR水平显著上调，抑制其上调可恢复HSF1水平，并可改善肝脏胰岛素抵抗。这些结果暗示HSF1介导的蛋白质内稳态平衡可能参与ETAR对肝脏胰岛素抵抗的调控。本课题拟建立ETAR肝脏特异性敲除及shRNA干扰小鼠模型，研究ETAR通过调控HSF1介导的蛋白质内稳态平衡致肝脏胰岛素抵抗的病理作用及分子机制，以及曲克芦丁的干预作用及机制，将为糖尿病的防治提供新思路和新靶点。

肝脏胰岛素抵抗在糖尿病的病理发展过程中起关键作用，阐明其发生发展的病理学机制对预防与治疗糖尿病具有重要的指导意义。我们在小鼠肝脏及原代肝细胞、人正常肝细胞L02中研究了蛋白质内稳态失衡介导的ETAR上调致肝脏胰岛素抵抗的机制及曲克芦丁的干预作用。主要发现如下：1）NAD+耗竭/内质网应激及FBXW7下调是蛋白质内稳态失衡介导高脂饮食诱导肝脏胰岛素抵抗的两个重要病理因子，其作用均与激活天然免疫信号介导的代谢炎症有关。其中NAD+耗竭/内质网应激/NLRP3及FBXW7/HMGB1信号轴促发高脂饮食诱导的肝脏胰岛素抵抗属首次报道。2）抑制高脂饮食诱导的ETAR上调可改善肝脏胰岛素抵抗及高血糖，其作用与抑制p66Shc介导的线粒体融合/分裂紊乱及片段化有关。其中ETAR上调导致肝脏胰岛素抵抗及高血糖，以及ETAR导致线粒体融合/分裂紊乱及片段化均未见文献报道，属首次发现。3）曲克芦丁及紫甘薯花青素可有效改善肝脏胰岛素抵抗及高血糖，其作用与抑制NAD+耗竭/内质网应激及天然免疫信号介导的代谢炎症有关。此外紫甘薯花青素可增强SirT1活性而抑制肝脏细胞凋亡，能抑制Src/ERK/C/EBPβ信号通路而改善肝脏脂肪变性，从而改善肝脏胰岛素抵抗。本项目的研究成果将加深对肝脏胰岛素抵抗的分子机制及天然产物干预作用与靶点的理解，并为糖尿病的防治提供新的理论依据。