Hyperamylinemia in Diabetic Heart Disease: Mechanisms, Responses, and Prevention

描述（由申请人提供）：胰腺β细胞分泌胰淀素增加（高胰淀素血症）在肥胖和胰岛素抵抗患者中很常见，与高胰岛素血症一致，并促进毒性胰淀素低聚物的形成。低聚胰淀素诱导β细胞凋亡，促进2型糖尿病的发展。最近的研究表明，胰淀素低聚物也影响血管系统，肾脏和心脏。我们的数据显示，在肥胖和T2 D患者的衰竭心脏中有大量的低聚胰淀素沉积，但在对照组的心脏中没有。在肌细胞损伤区域发现低聚胰淀素，提示其在损伤机制中的作用。事实上，我们对“人源化”高淀粉血症大鼠模型（HIP大鼠）的初步研究表明，胰淀素低聚物附着于心肌细胞并诱导氧化应激和Ca 2+失调，导致舒张功能障碍和肥大。初步研究还表明，具有抗聚集特性的内源性分子，如纤溶酶和环氧二十烷酸，限制了胰淀素的心脏积聚及其肌病反应。基于这些初步结果，我们的研究计划将测试以下假设：1）低聚胰淀素的心脏积累通过诱导肌膜损伤和氧化应激加速糖尿病心脏损伤，以及2）限制胰淀素在心脏中的沉积可能减少/延迟糖尿病心力衰竭的发作。这些假设将通过使用过表达淀粉样蛋白生成性人胰淀素（HIP大鼠）或非淀粉样蛋白生成性大鼠胰淀素同种型（UCD大鼠）的转基因大鼠模型进行机制评估。具体而言，计划的研究将确定HIP大鼠心脏中寡聚化胰淀素的蓄积如何a）破坏肌膜过程，B）诱导氧化应激和肌细胞Ca 2+失调，以及c）激活Ca 2+介导的CaMKII-HDAC和钙调神经磷酸酶-NFAT肥大信号传导途径。根据我们的初步研究结果，即使在糖尿病前期，HIP大鼠的心功能障碍也会发展，这在人类中经常观察到。相比之下，我们的初步研究预测，年龄和葡萄糖匹配的UCD大鼠，但缺乏心脏胰淀素沉积，可能会显示糖尿病发作后的心脏功能障碍的迹象。我们的研究还将确定在HIP大鼠模型中破坏低聚胰淀素在心脏中的沉积和恢复肌膜完整性是否改善心脏功能。这一创新概念将在使用膜密封剂和循环胰淀素低聚物清除剂的纵向研究中进行探索。因此，我们的研究项目提出胰淀素积累是糖尿病心脏损伤的多因素发病机制的关键因素，并且减轻胰淀素低聚物积累可以延迟糖尿病心力衰竭的发作。如果我们的心脏毒性胰淀素寡聚体的假设得到证实，那么循环胰淀素寡聚体是一个可行的治疗靶点，以减少糖尿病心脏损伤。

DESCRIPTION (provided by applicant): Increased secretion of amylin by pancreatic beta-cells (hyperamylinemia) is common in obese and insulin resistant patients, coincides with hyperinsulinemia, and promotes formation of toxic amylin oligomers. Oligomeric amylin induces beta-cell apoptosis contributing to the development of type-2 diabetes. Recent studies demonstrate that amylin oligomers also affect the vascular system, kidneys, and heart. Our data show large deposits of oligomerized amylin in failing hearts from obese and T2D patients, but not in hearts from controls. Oligomeric amylin was found in myocyte injury areas suggesting a role in the mechanism of injury. Indeed, our pilot study on a "humanized" rat model of hyperamylinemia (the HIP rat) indicates that amylin oligomers attach to cardiac myocytes and induce oxidative stress and Ca2+ dysregulation leading to diastolic dysfunction and hypertrophy. The pilot study also suggests that endogenous molecules with anti-aggregation properties, such as plasmin and epoxyeicosanoids, limit cardiac accumulation of amylin and its myopathic response. Based on these preliminary results, our research proposal will test the hypotheses that 1) cardiac accumulation of oligomerized amylin accelerates diabetic heart injury by inducing sarcolemmal damage and oxidative stress, and 2) limiting amylin deposition in the heart may reduce/ delay the onset of diabetic heart failure. These hypotheses will mechanistically be assessed by using transgenic rat models overexpressing either the amyloido- genic human amylin (HIP rats) or the non-amyloidogenic rat amylin isoform (UCD rats). Specifically, planned studies will determine how accumulation of oligomerized amylin in the HIP rat heart a) disrupts sarcolemmal processes, b) induces oxidative stress and myocyte Ca2+ dysregulation, and c) activates Ca2+-mediated CaMKII-HDAC and calcineurin-NFAT hypertrophy signaling pathways. Based on the results of our pilot study, cardiac dysfunction in HIP rats is expected to develop even in pre-diabetes, as often observed in humans. In contrast, our pilot study predicts that UCD rats matched for age and glucose, but lacking cardiac amylin deposition, may show signs of cardiac dysfunction after the onset of diabetes. Our research will also determine if disrupting deposition of oligomeric amylin in the heart and recovering sarcolemmal integrity improve cardiac function in the HIP rat model. This innovative concept will be explored in longitudinal studies using membrane sealants and scavengers of circulating amylin oligomers. Hence, our research project proposes that amylin buildup is a key contributor to the multifactorial pathogenesis of diabetic heart injury and that mitigating amylin oligomer accumulation could delay the onset of diabetic heart failure. If our hypothesis of cardiotoxic amylin oligomer is proven, then circulating amylin oligomers are a feasible therapeutic target to reduce diabetic heart injury.