Emerging evidence indicates that impaired mitophagy-mediated clearance of defective mitochondria is a critical event in Alzheimer’s disease (AD) pathogenesis. Amyloid-beta (Aβ) metabolism and the microtubule-associated protein tau have been reported to regulate key components of the mitophagy machinery. However, the mechanisms that lead to mitophagy dysfunction in AD are not fully deciphered. We have previously shown that intraneuronal cholesterol accumulation can disrupt the autophagy flux, resulting in low Aβ clearance. In this study, we examine the impact of neuronal cholesterol changes on mitochondrial removal by autophagy. Regulation of PINK1-parkin-mediated mitophagy was investigated in conditions of acute (in vitro) and chronic (in vivo) high cholesterol loading using cholesterol-enriched SH-SY5Y cells, cultured primary neurons from transgenic mice overexpressing active SREBF2 (sterol regulatory element binding factor 2), and mice of increasing age that express the amyloid precursor protein with the familial Alzheimer Swedish mutation (Mo/HuAPP695swe) and mutant presenilin 1 (PS1-dE9) together with active SREBF2. In cholesterol-enriched SH-SY5Y cells and cultured primary neurons, high intracellular cholesterol levels stimulated mitochondrial PINK1 accumulation and mitophagosomes formation triggered by Aβ while impairing lysosomal-mediated clearance. Antioxidant recovery of cholesterol-induced mitochondrial glutathione (GSH) depletion prevented mitophagosomes formation indicating mitochondrial ROS involvement. Interestingly, when brain cholesterol accumulated chronically in aged APP-PSEN1-SREBF2 mice the mitophagy flux was affected at the early steps of the pathway, with defective recruitment of the key autophagy receptor optineurin (OPTN). Sustained cholesterol-induced alterations in APP-PSEN1-SREBF2 mice promoted an age-dependent accumulation of OPTN into HDAC6-positive aggresomes, which disappeared after in vivo treatment with GSH ethyl ester (GSHee). The analyses in post-mortem brain tissues from individuals with AD confirmed these findings, showing OPTN in aggresome-like structures that correlated with high mitochondrial cholesterol levels in late AD stages. Our data demonstrate that accumulation of intracellular cholesterol reduces the clearance of defective mitochondria and suggest recovery of the cholesterol homeostasis and the mitochondrial scavenging of ROS as potential therapeutic targets for AD.

中文翻译：

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胆固醇通过损害阿尔茨海默病中的视神经调节蛋白募集和溶酶体清除来改变线粒体自噬

新出现的证据表明，线粒体自噬介导的缺陷线粒体清除受损是阿尔茨海默病 (AD) 发病机制中的一个关键事件。据报道，淀粉样蛋白-β (Aβ) 代谢和微管相关蛋白 tau 可调节线粒体自噬机制的关键组成部分。然而，导致 AD 线粒体自噬功能障碍的机制尚未完全破译。我们之前已经表明，神经元内胆固醇积累会破坏自噬通量，导致 Aβ 清除率低。在这项研究中，我们检查了神经元胆固醇变化对自噬去除线粒体的影响。使用富含胆固醇的 SH-SY5Y 细胞在急性（体外）和慢性（体内）高胆固醇负荷条件下研究了 PINK1-parkin 介导的线粒体自噬的调节，来自过度表达活性 SREBF2（甾醇调节元件结合因子 2）的转基因小鼠的培养原代神经元，以及表达具有家族性阿尔茨海默氏瑞典突变 (Mo/HuAPP695swe) 和突变早老素 1 (PS1-dE9) 的淀粉样前体蛋白的年龄增加的小鼠具有活性 SREBF2。在富含胆固醇的 SH-SY5Y 细胞和培养的原代神经元中，高细胞内胆固醇水平刺激了 Aβ 触发的线粒体 PINK1 积累和线粒体吞噬体形成，同时损害了溶酶体介导的清除。胆固醇诱导的线粒体谷胱甘肽（GSH）耗竭的抗氧化恢复阻止了线粒体形成，表明线粒体 ROS 参与。有趣的是，当老年 APP-PSEN1-SREBF2 小鼠的脑胆固醇长期积累时，线粒体自噬通量在该途径的早期阶段受到影响，关键自噬受体 optineurin (OPTN) 的募集存在缺陷。APP-PSEN1-SREBF2 小鼠中持续的胆固醇诱导的改变促进了 OPTN 向 HDAC6 阳性聚集体的年龄依赖性积累，在用 GSH 乙酯 (GSHee) 体内处理后消失。对 AD 患者死后脑组织的分析证实了这些发现，表明 OPTN 存在于与 AD 晚期高线粒体胆固醇水平相关的聚集体样结构中。