Mitochondrial dynamics in beta cell function and dysfunction

描述(由申请人提供)：营养诱导的细胞功能障碍和死亡被认为在糖尿病的发展中起着核心作用。对高脂肪和碳水化合物环境(HFC)作出反应的致病和防御机制可能提供有价值的治疗靶点。由这笔赠款支持的研究确定线粒体融合-裂变和自噬是构成线粒体生命周期的相关事件。此外，我们还确定，HFC通过阻止线粒体融合，导致线粒体网络完全断裂，并通过有丝分裂刺激线粒体周转，从而阻止线粒体的生命周期。初步的体内和体外数据表明，断裂是由HFC诱导的线粒体融合蛋白Mfn2的降解所介导的。值得注意的是，我们发现Mfn2在体内的缺失或在体外的敲除会导致解偶联增加，ROS减少，并保护细胞的活力。这些有益的影响是以放松胰岛素分泌为代价的，表现为基础分泌增加，第一时相减少，第二时相增加，振荡模式钝化。我们假设，HFC诱导的胰岛Mfn2的降解和随之而来的网络碎裂作为一种补偿机制，在放松对胰岛素分泌的调控的同时，起到保护细胞存活的作用。我们将通过以下目标解决这一假说：AIM1将确定Mfn2更新在预防细胞丢失中的作用，并将评估Mfn2下调作为糖尿病模型治疗靶点的潜在用途。AIM2将确定Mfn2周转在HFC诱导的胰岛素分泌解除调控中的作用以及Mfn2调节分泌的机制。AIM3将研究Mfn2在细胞内周转的控制机制。我们的初步研究发现了一种新的刺激Mfn2周转的机制，我们已经能够从药物上激活这种机制。我们将评估这一新的治疗靶点作为一种诱导适应的机制。揭示调节Mfn2周转双重影响的途径将允许设计出既保持有利影响又抑制不利影响的干预措施。

DESCRIPTION (provided by applicant): Nutrient-induced ¿-cell dysfunction and death are thought to play a central role in the development of diabetes. Pathogenic and defense mechanisms that respond to a high fat and carbohydrate environment (HFC) may provide valuable therapeutic targets. Research supported by this grant established mitochondrial fusion-fission and autophagy as linked events that form the mitochondrial life cycle. Furthermore we determined that HFC arrests the mitochondrial life cycle by preventing mitochondrial fusion, leading to the complete fragmentation of the mitochondrial network and stimulation of mitochondrial turnover by mitophagy. Preliminary in vivo and in vitro data indicate that fragmentation is mediated by HFC-induced degradation of the mitochondrial fusion protein, Mfn2. Remarkably, we find that in vivo deletion or in vitro knockdown of Mfn2 leads to increased uncoupling, decreased ROS and protection of ¿-cell viability. These beneficial effects come at the expense of deregulated insulin secretion, manifested by increased basal secretion, decreased 1st phase, increased 2nd phase and a blunted oscillatory pattern. We hypothesize that HFC-induced degradation of islet Mfn2 and the ensuing network fragmentation serves to protect ¿-cell viability as a compensatory mechanism while at the same time deregulating insulin secretion. We will address this hypothesis through the following Aims: Aim1 will determine the role of Mfn2 turnover in the prevention of ¿-cell loss and will evaluate the potential use of Mfn2 downregulation as a therapeutic target in diabetic models. Aim2 will determine the contribution of Mfn2 turnover to HFC-induced deregulation of insulin secretion and the mechanism by which Mfn2 modulates secretion. Aim3 will investigate the mechanism by which Mfn2 turnover is controlled in the ¿-cell. Our preliminary studies have identified a novel mechanism for the stimulation of Mfn2 turnover which we have been able to activate pharmacologically. We will evaluate this novel therapeutic target as a mechanism to induce adaptation. Revealing the pathways that mediate the dual effects of Mfn2 turnover will allow for the devise of interventions that will maintain the beneficial effect while suppressing the detrimental.