Hsp72 (HSPA1A) Prevents Human Islet Amyloid Polypeptide Aggregation and Toxicity: A New Approach for Type 2 Diabetes Treatment

Type 2 diabetes is a growing public health concern and accounts for approximately 90% of all the cases of diabetes. Besides insulin resistance, type 2 diabetes is characterized by a deficit in β-cell mass as a result of misfolded human islet amyloid polypeptide (h-IAPP) which forms toxic aggregates that destroy pancreatic β-cells. Heat shock proteins (HSP) play an important role in combating the unwanted self-association of unfolded proteins. We hypothesized that Hsp72 (HSPA1A) prevents h-IAPP aggregation and toxicity. In this study, we demonstrated that thermal stress significantly up-regulates the intracellular expression of Hsp72, and prevents h-IAPP toxicity against pancreatic β-cells. Moreover, Hsp72 (HSPA1A) overexpression in pancreatic β-cells ameliorates h-IAPP toxicity. To test the hypothesis that Hsp72 (HSPA1A) prevents aggregation and fibril formation, we established a novel C. elegans model that expresses the highly amyloidogenic human pro-IAPP (h-proIAPP) that is implicated in amyloid formation and β-cell toxicity. We demonstrated that h-proIAPP expression in body-wall muscles, pharynx and neurons adversely affects C. elegans development. In addition, we demonstrated that h-proIAPP forms insoluble aggregates and that the co-expression of h-Hsp72 in our h-proIAPP C. elegans model, increases h-proIAPP solubility. Furthermore, treatment of transgenic h-proIAPP C. elegans with ADAPT-232, known to induce the expression and release of Hsp72 (HSPA1A), significantly improved the growth retardation phenotype of transgenic worms. Taken together, this study identifies Hsp72 (HSPA1A) as a potential treatment to prevent β-cell mass decline in type 2 diabetic patients and establishes for the first time a novel in vivo model that can be used to select compounds that attenuate h-proIAPP aggregation and toxicity.

2型糖尿病是日益严峻的公共卫生问题，约占所有糖尿病病例的90%。除胰岛素抵抗外，2型糖尿病的特征还在于β细胞量不足，其诱因是错误折叠的人胰岛淀粉样多肽（human islet amyloid polypeptide, h-IAPP）形成毒性聚集体，破坏胰腺β细胞。热休克蛋白（Heat shock proteins, HSP）在对抗未折叠蛋白的异常自聚集方面发挥重要作用。我们提出假说，Hsp72（HSPA1A）可抑制h-IAPP的聚集与毒性。本研究证实，热应激可显著上调细胞内Hsp72的表达，并抵御h-IAPP对胰腺β细胞的毒性作用。此外，在胰腺β细胞中过表达Hsp72（HSPA1A）可减轻h-IAPP的毒性。为验证Hsp72（HSPA1A）可抑制聚集与原纤维形成这一假说，我们构建了一种新型秀丽隐杆线虫（Caenorhabditis elegans, C. elegans）模型，该模型可表达具有高淀粉样蛋白形成潜力的人源前胰岛淀粉样多肽（human pro-IAPP, h-proIAPP），后者与淀粉样蛋白形成及β细胞毒性密切相关。我们证实，在秀丽隐杆线虫的体壁肌肉、咽部及神经元中表达h-proIAPP会对线虫的发育产生不良影响。此外，我们发现h-proIAPP可形成不溶性聚集体，而在该h-proIAPP秀丽隐杆线虫模型中共表达人源Hsp72，可提高h-proIAPP的溶解度。进一步研究发现，用已知可诱导Hsp72（HSPA1A）表达与释放的ADAPT-232处理转基因h-proIAPP秀丽隐杆线虫，可显著改善转基因线虫的生长迟缓表型。综上，本研究确定Hsp72（HSPA1A）可作为潜在治疗手段，延缓2型糖尿病患者的β细胞量减少，并首次构建了一种新型活体模型，可用于筛选可减轻h-proIAPP聚集与毒性的化合物。