Cytoprotection and the mechanism of action of a natural product Khellin against ER stress

内质网(ER)应激在越来越多的人类疾病的发病机制中起着重要作用，包括糖尿病、肥胖、动脉粥样硬化和神经退行性疾病。慢性内质网应激通过未折叠蛋白反应(UPR)的过度激活导致细胞功能障碍和死亡，因此被认为是治疗这些疾病的靶点。然而，目前还没有针对内质网应激/UPR诱导的细胞功能障碍和死亡的药物被确定。利用高通量筛选技术，我们已经确定了一种天然产物--呋喃色酮衍生物，它是一种对抗内质网应激的细胞保护分子。我们的初步研究表明：(A)在基于细胞的分析中，呋喃色酮衍生物保护β细胞免受内质网应激、糖毒性和脂毒性诱导的功能障碍和死亡，(B)呋喃色酮改善链脲佐菌素诱导的糖尿病动物的高血糖并保护β细胞的功能和生存，以及(C)呋喃色酮还保护其他类型的细胞免受内质网应激的影响。这些研究首次揭示了这种天然产品对内质网应激具有细胞保护作用。我们的初步研究进一步表明，呋喃色酮衍生物选择性地抑制内质网应激诱导的三个未折叠蛋白反应途径之一的激活，而对另外两个途径：PERK和α没有影响。这些发现导致了我们的中心假设，即该化合物抑制内质网应激诱导的IRE1α过度激活，以提供细胞保护。在这项授权中，我们提出了三个目的来检验这一假设。在目标1中，我们将确定该化合物对IRE1α抑制的作用机制。我们将使用生化分析来确定呋喃色酮衍生物对IRE1a激酶和核糖核酸酶活性及其磷酸化和二聚体/寡聚体状态的影响。在目标2中，我们将确定该化合物是否通过抑制IRE1α而具有细胞保护活性。这些研究将确定其对IRE1α活性的抑制是该化合物细胞保护的分子机制。最后，我们将在已建立的内质网应激相关动物模型中确定该化合物的治疗潜力：两种进行性β细胞丢失的糖尿病模型(秋田鼠和db/db鼠)。综上所述，本工作不仅揭示了天然产物对内质网应激的一种新的细胞保护活性，而且还将阐明其抑制IRE1α活性作为其细胞保护作用的分子机制，从而为呋喃色酮衍生物作为治疗内质网应激相关疾病的新型细胞保护药物的临床开发奠定基础。

Endoplasmic reticulum (ER) stress plays an important role in the pathogenesis of a growing list of human diseases, including diabetes, obesity, atherosclerosis, and neurodegenerative diseases. Chronic ER stress leads to cell dysfunction and death through the hyperactivation of the unfolded protein response (UPR), and hence has been proposed as a therapeutic target for the treatment of these diseases. However, no drugs targeting ER stress/UPR-induced cell dysfunction and death have yet been identified. Using high throughput screen technology, we have identified a natural product, a furanochromone derivative, as a molecule of cytoprotection against ER stress. Our preliminary studies revealed that (a) in cell-based assays, the furanochromone derivative protects β cells against ER stress-, glucotoxicity-, and lipotoxicity-induced dysfunction and death, (b) the furanochromone ameliorates hyperglycemia and protects the function and survival of β cells in streptozotocin-induced diabetic animals, and (c) the furanochromone also protects other cell types against ER stress. These studies revealed for the first time that this natural product exhibits cytoprotection against ER stress. Our pilot studies further indicate that the furanochromone derivative selectively inhibits the ER stress-induced activation of one of three unfolded protein response pathways, IRE1α pathway, with no effect on the other two pathways: PERK and ATF6. These findings led to our central hypothesis that this compound inhibits ER stress-induced IRE1α hyperactivation to confer cytoprotection. In this grant, we propose three aims to test this hypothesis. In aim 1, we will determine the mechanism of action of this compound on IRE1α inhibition. We will use biochemical assays to determine the effects of the furanochromone derivative on IRE1a kinase and RNase activities and its phosphorylation and dimeric/oligomeric statuses. In aim 2, we will determine whether the compound confers cytoprotective activity by inhibiting IRE1α. These studies will establish its inhibition on IRE1α activation as the molecular mechanism of the compound’s cytoprotection. Finally, we will determine therapeutic potential of the compound in well-established ER stress-related animal models: two diabetes models of progressive β cell loss (Akita mice and db/db mice). Together, this work will reveal not only a novel cytoprotective activity of the natural product against ER stress but also elucidate its inhibition of IRE1α activity as the molecular mechanism of action underlying its cytoprotection, thus establishing the foundation for the clinical development of the furanochromone derivatives as novel cytoprotective drugs for ER stress-related diseases.