Modulation of Mitofusin Activity to Treat Heart Disease

线粒体“连接”和线粒体内质/肌浆网（ER/SR）“接近” 通过多种机制增强线粒体介导的代谢和坏死。线粒体融合素 (MFN) 1 和 2 是大 GTP 酶，在线粒体连接和线粒体 ER/SR 中发挥关键作用 接近。 MFN1 和 MFN2 位于线粒体外膜，在那里它们介导线粒体 融合。 MFN2（但不是 MFN1）也存在于 ER/SR 膜中，它将 ER/SR 与线粒体相连 通过与线粒体定位的 MFN1 或 MFN2 相互作用。 MFN1 或 MFN2 的缺失会降低心肌 缺血/再灌注 (I/R) 期间的梗塞 (MI) 大小。相反，MFN1 和 MFN2 过度表达会增强 新陈代谢。考虑到这一信息，治疗性抑制 MFN 有望减少梗塞面积 在 MI 期间，治疗性激活 MFN 可能会通过增强新陈代谢来减轻心力衰竭 (HF)。 面临的挑战是找到一种方法来操纵内源性最惠国待遇的活动。与合作 其他，我们创造了第一个调节 MFN1 和 MFN2 构象的肽和小分子， 描述了这些影响的潜在结构基础。我们之前报道过最惠国激活剂增加， 当MFN抑制剂减少时，线粒体融合。这些是需要这些试剂结合的直接效应 到 MFN1 或 MFN2。我们在这里提供的新数据显示 MFN 激活剂增加，而 MFN 抑制剂增加 减少，线粒体-ER/SR 接近度和 Ca2 转移到线粒体。此外，我们观察到最惠国待遇 激活剂会加剧心肌 I/R 期间的梗塞面积，而 MFN 抑制剂会减少双心梗塞面积 和大脑 I/R 模型。有趣的是，激活剂的这些作用取决于 MFN2，而不是 MFN1， 表明线粒体-ER/SR 接近的重要性，但不排除 MFN2- 线粒体连接性和形状的依赖性变化也有贡献。此外，最惠国待遇激活剂 促进心肌细胞代谢。该项目的目标是了解最惠国待遇的机制 调节剂影响心肌细胞死亡和代谢，并测试这些药物是否可能提供新的 MI 和 HF 的治疗策略。我们建议： 1. 将 MFN 激活/抑制的变化与 成人线粒体连接、线粒体-ER/SR 邻近性、Ca2 转移、细胞死亡和代谢 心肌细胞。 2. 描述线粒体连接和线粒体的个体贡献 ER/SR 接近体内心肌细胞的细胞死亡和代谢。 3. 评估线粒体融合蛋白是否 调节剂为 MI 和 HF 提供了新的治疗策略。该项目在定义 MFN 调节剂影响心肌细胞死亡和代谢的机制以及 MFN 是否提供 针对 MI 和 HF 的新疗法的可行目标。

Mitochondrial “connectivity” and mitochondrial-endoplasmic/sarcoplasmic reticulum (ER/SR) “proximity” each potentiate mitochondrial-mediated metabolism and necrosis through a variety of mechanisms. Mitofusins (MFN) 1 and 2 are large GTPases that play critical roles in mitochondrial connectivity and mitochondrial-ER/SR proximity. MFN1 and MFN2 reside in the outer mitochondrial membrane where they mediate mitochondrial fusion. MFN2, but not MFN1, also resides in the ER/SR membrane, where it tethers ER/SR to mitochondria through interactions with mitochondrial-localized MFN1 or MFN2. Deletion of MFN1 or MFN2 reduces myocardial infarct (MI) size during ischemia/reperfusion (I/R). Conversely, MFN1 and MFN2 overexpression augment metabolism. Given this information, therapeutic inhibition of MFNs would be expected to reduce infarct size during MI, while therapeutic activation of MFNs might attenuate heart failure (HF) by augmenting metabolism. The challenge has been to find a means to manipulate the activities of endogenous MFNs. In collaboration with others, we created the first peptides and small molecules that modulate conformations of MFN1 and MFN2 and delineated the underlying structural basis for these effects. We reported previously that MFN activators increase, while MFN inhibitors decrease, mitochondrial fusion. These are direct effects that require binding of these agents to either MFN1 or MFN2. We present here new data showing that MFN activators increase, while MFN inhibitors decrease, mitochondrial-ER/SR proximity and Ca2+ transfer to mitochondria. Moreover, we observed that MFN activators exacerbate infarct size during myocardial I/R, while MFN inhibitors reduce infarct size in both heart and brain I/R models. Interestingly, these effects of the activators are dependent on MFN2, but not MFN1, suggesting the importance of mitochondrial-ER/SR proximity but not excluding the possibility that MFN2- dependent changes in mitochondrial connectivity and shape also contribute. Additionally, MFN activators promote cardiomyocyte metabolism. The goals of this project are to understand the mechanisms by which MFN modulators impact cardiomyocyte death and metabolism and to test whether these agents might provide novel therapeutic strategies for MI and HF. We propose: 1. To correlate changes in MFN activation/inhibition with mitochondrial connectivity, mitochondrial-ER/SR proximity, Ca2+ transfer, cell death, and metabolism in adult cardiomyocytes. 2. To delineate the individual contributions of mitochondrial connectivity and mitochondrial- ER/SR proximity to cell death and metabolism in cardiomyocytes in vivo. 3. To assess whether mitofusin modulators provide novel therapeutic strategies for MI and HF. This project breaks new ground in defining the mechanisms by which MFN modulators impact cardiomyocyte death and metabolism and whether MFNs provide an actionable target for novel therapies directed against MI and HF.