Rationale:Obesity-associated cardiomyopathy characterized by hypertrophy and mitochondrial dysfunction. Mitochondrial quality control mechanisms, including mitophagy, are essential for the maintenance of cardiac function in obesity-associated cardiomyopathy. However, autophagic flux peaks at around 6 weeks of high-fat diet (HFD) consumption and declines thereafter.Objective:We investigated whether mitophagy is activated during the chronic phase of cardiomyopathy associated with obesity (obesity cardiomyopathy) after general autophagy is downregulated and, if so, what the underlying mechanism and the functional significance are.Methods and Results:Mice were fed either a normal diet or a HFD (60 kcal% fat). Mitophagy, evaluated using Mito-Keima, was increased after 3 weeks of HFD consumption and continued to increase after conventional mechanisms of autophagy were inactivated, at least until 24 weeks. HFD consumption time-dependently upregulated both Ser555-phosphorylated Ulk1 (unc-51 like kinase 1) and Rab9 (Ras-related protein Rab-9) in the mitochondrial fraction. Mitochondria were sequestrated by Rab9-positive ring-like structures in cardiomyocytes isolated from mice after 20 weeks of HFD consumption, consistent with the activation of alternative mitophagy. Increases in mitophagy induced by HFD consumption for 20 weeks were abolished in cardiac-specific ulk1 knockout mouse hearts, in which both diastolic and systolic dysfunction were exacerbated. Rab9 S179A knock-in mice, in which alternative mitophagy is selectively suppressed, exhibited impaired mitophagy and more severe cardiac dysfunction than control mice following HFD consumption for 20 weeks. Overexpression of Rab9 in the heart increased mitophagy and protected against cardiac dysfunction during HFD consumption. HFD-induced activation of Rab9-dependent mitophagy was accompanied by upregulation of TFE3 (transcription factor binding to IGHM enhancer 3), which plays an essential role in transcriptional activation of mitophagy.Conclusions:Ulk1-Rab9-dependent alternative mitophagy is activated during the chronic phase of HFD consumption and serves as an essential mitochondrial quality control mechanism, thereby protecting the heart against obesity cardiomyopathy.

中文翻译：

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替代线粒体自噬保护心脏免受肥胖相关的心肌病

基本原理：以肥大和线粒体功能障碍为特征的肥胖相关心肌病。线粒体质量控制机制，包括线粒体自噬，对于维持肥胖相关心肌病的心脏功能至关重要。然而，自噬通量在高脂肪饮食 (HFD) 消耗约 6 周时达到峰值，此后下降。目的：我们研究了在一般自噬下调后，在与肥胖相关的心肌病（肥胖性心肌病）慢性期期间，线粒体自噬是否被激活，并且，如果是这样，其潜在机制和功能意义是什么。方法和结果：给小鼠喂食正常饮食或 HFD（60 kcal% 脂肪）。Mitophagy，使用 Mito-Keima 评估，在食用 HFD 3 周后增加，并在常规自噬机制失活后继续增加，至少持续到 24 周。HFD 消耗时间依赖性地上调线粒体部分中的 Ser555 磷酸化 Ulk1（unc-51 样激酶 1）和 Rab9（Ras 相关蛋白 Rab-9）。在消耗 HFD 20 周后，从小鼠分离的心肌细胞中，线粒体被 Rab9 阳性环状结构隔离，这与替代线粒体自噬的激活一致。20 周内由 HFD 消耗引起的线粒体自噬增加在心脏特异性 在消耗 HFD 20 周后，从小鼠分离的心肌细胞中，线粒体被 Rab9 阳性环状结构隔离，这与替代线粒体自噬的激活一致。20 周内由 HFD 消耗引起的线粒体自噬增加在心脏特异性 在消耗 HFD 20 周后，从小鼠分离的心肌细胞中，线粒体被 Rab9 阳性环状结构隔离，这与替代线粒体自噬的激活一致。20 周内由 HFD 消耗引起的线粒体自噬增加在心脏特异性ulk1敲除小鼠心脏，其中舒张和收缩功能障碍均加剧。选择性抑制选择性线粒体自噬的 Rab9 S179A 敲入小鼠在食用 HFD 20 周后表现出线粒体自噬受损和比对照小鼠更严重的心脏功能障碍。Rab9 在心脏中的过度表达增加了线粒体自噬，并在 HFD 消耗期间防止心脏功能障碍。HFD 诱导的 Rab9 依赖性线粒体自噬的激活伴随着 TFE3（与 IGHM 增强子 3 结合的转录因子）的上调，它在线粒体自噬的转录激活中起着重要作用。结论：Ulk1-Rab9 依赖性替代线粒体自噬在慢性HFD 消耗的阶段，并作为重要的线粒体质量控制机制，