“脂联素-PPARδ-线粒体”途径在胰高糖素样肽-1受体激动剂改善胰岛功能中的机制研究

Deterioration of pancreatic islet function plays an important role in the progression of type 2 diabetes. Glucagon-like peptide-1 receptor agonist (GLP-1 RA), a class of hypoglycemic agents, has attracted attention recently because of its effect on improving pancreatic islet function in addition to the hypoglycemic efficacy. However, the underlying mechanism of the GLP-1 RA’s protecting effect on pancreatic islet function is to be elucidated. In our previous studies and the preliminary experiments conducted for this project, it has been proved that GLP-1 RA improved pancreatic β-cell function in patients with type 2 diabetes, elevated the serum level of adiponectin, and enhanced the expression and secretion of adiponectin by adipose tissue. The preliminary experiments also confirmed that the elevated adiponectin secreted from adipocytes induced by GLP-1 RA up-regulated PPARδ expression and enhanced mitochondrial function in pancreatic tissue. All the above evidence leads to the hypothesis of this project that ‘adiponectin-PPARδ-mitochondria’ pathway plays an important role in the protective effect of GLP-1 RA on pancreatic islet function. To test and verify this hypothesis, we will further analyze the patients’ data from the previously conducted clinical trial to investigate the association between β-cell function and adiponectin after GLP-1 RA treatment for 48 weeks. Furthermore, adiponectin knockout mice and different cell lines including primary cultured β-cells, MIN-6 cells and 3T3-L1 cells will be utilized, and lentivirus mediated shRNA techniques, Transwell migration assay, etc. will be conducted in this study. The finding of this study contributes to provide some new evidence to reveal the mechanism of the GLP-1 RA’s protecting effect on pancreatic islet function, and offer some new insight on the prevention and treatment of pancreatic islet function deterioration in type 2 diabetes.

胰岛功能减退是2型糖尿病持续进展的重要原因之一。近年研究发现降糖药胰高糖素样肽-1受体激动剂（GLP-1RA）在降糖以外，可改善胰岛功能，但具体机制不详。我们前期研究证实，GLP-1RA可改善2型糖尿病患者胰岛功能，升高血清脂联素；增加脂肪组织脂联素的表达与分泌；GLP-1RA处理后脂肪细胞分泌增多的脂联素可促进胰岛β细胞PPARδ表达及增强线粒体功能。因此我们首次提出假设：脂联素-PPARδ-线粒体途径在GLP-1RA保护胰岛功能中起作用。本课题拟进一步挖掘前期临床研究中人群数据，分析GLP-1RA干预后脂联素与胰岛功能的关系；采用脂联素基因敲除小鼠、原代胰岛β细胞、MIN6胰岛细胞及3T3-L1脂肪细胞，应用shRNA技术、Transwell实验等研究手段，从人群、动物及细胞水平验证课题假设，以期为阐明GLP-1RA保护胰岛功能的机制提供新证据，为防治胰岛功能减退提供新思路及新靶点。

胰岛功能减退是2型糖尿病持续进展的重要原因之一。既往研究发现胰高血糖素样肽-1受体激动剂(GLP-1 RA)具有葡萄糖依赖性促胰岛素分泌作用，但其作用机制仍有待进一步阐明。项目组对申请人单位牵头的多中心前瞻性研究数据进一步分析，发现GLP-1 RA艾塞那肽对不同体重指数的2型糖尿病患者均有明确的降糖疗效，改善胰岛功能，增加血清脂联素水平。动物实验显示，相比于高脂对照组，GLP-1 RA和PPARδ受体激动剂(GW501516)药物干预可明显减轻小鼠体重、改善外周胰岛素抵抗及促进胰岛功能。此外，高脂组小鼠胰岛体积较正常对照组缩小，伴线粒体数量减少、线粒体微结构受损。而GLP-1 RA和PPARδ受体激动剂处理组小鼠的胰岛体积较高脂组增大，并伴线粒体数量增加、体积增大、线粒体嵴面积增加，表明胰岛线粒体功能改善。细胞实验层面，我们进一步发现GLP-1 RA可以促进胰岛细胞株MIN6胰岛增殖相关基因胰十二指肠同源框因子-1（Pdx-1）及B淋巴细胞瘤-2（Bcl-2）的mRNA及蛋白水平，并调节线粒体功能相关基因解偶联蛋白2（Ucp-2）及过氧化物酶体增殖物激活受体γ辅激活因子α（Pgc-1α）的表达。PPARδ激动剂结果与GLP-1 RA一致。而在GLP-1 RA联合PPARδ抑制剂（GSK0660）后，GLP-1 RA下调UCP2的作用明显减弱。以上人群、动物及细胞研究结果均表明，GLP-1 RA可改善2型糖尿病小鼠的胰岛功能，这一机制可能与GLP-1 RA调控PPARδ/Ucp-2通路，从而促进胰岛β细胞线粒体合成与功能有关。