The precise degradation of dysfunctional mitochondria by mitophagy is essential for maintaining neuronal homeostasis. HTT (huntingtin) can interact with numerous other proteins and thereby perform multiple biological functions within the cell. In this study, we investigated the role of HTT during mitophagy and analyzed the impact of the expansion of its polyglutamine (polyQ) tract. HTT is involved in different mitophagy steps, promoting the physical proximity of different protein complexes during the initiation of mitophagy and recruiting mitophagy receptors essential for promoting the interaction between damaged mitochondria and the nascent autophagosome. The presence of the polyQ tract in mutant HTT affects the formation of these protein complexes and determines the negative consequences of mutant HTT on mitophagy, leading to the accumulation of damaged mitochondria and an increase in oxidative stress. These outcomes contribute to general mitochondrial dysfunction and neurodegeneration in Huntington disease.

Abbreviations: AMPK: AMP-activated protein kinase; ATG13: autophagy related 13; BECN1: beclin 1, autophagy related; BNIP3: BCL2/adenovirus E1B interacting protein 3; BNIP3L/Nix: BCL2/adenovirus E1B interacting protein 3-like; CCCP: carbonyl cyanide 3-chlorophenyl hydrazone; DMEM: Dulbecco’s modified eagle medium; EDTA: ethylene-diamine-tetra-acetic acid; EGFP: enhanced green fluorescent protein; EGTA: ethylene glycol bis(2-aminoethyl ether)tetraacetic acid; FUNDC1: FUN14 domain containing 1; HD: Huntington disease; HRP: horseradish peroxidase; HTT: huntingtin; LC3-II: lipidated form of MAP1LC3/LC3; mtDNA: mitochondrial deoxyribonucleic acid; MTDR: MitoTracker Deep Red; MTOR: mechanistic target of rapamycin kinase; MTORC1: mechanistic target of rapamycin kinase complex 1; NBR1: NBR1, autophagy cargo receptor; CALCOCO2/NDP52: calcium binding and coiled-coil domain 2; OCR: oxygen consumption rate; OPTN: optineurin; OXPHOS: oxidative phosphorylation; PIK3C3/VPS34: phosphatidylinositol 3-kinase catalytic subunit type 3; PIK3R4/VPS15: phosphoinositide-3-kinase regulatory subunit 4; PINK1: PTEN induced putative kinase 1; PLA: proximity ligation assay; PMSF: phenylmethylsulfonyl fluoride; polyQ: polyglutamine; PtdIns3K: phosphatidylinositol 3-kinase; ROS: reactive oxygen species; Rot: rotenone; SDS-PAGE: sodium dodecyl sulfate-polyacrylamide gel electrophoresis; SEM: standard error of the mean; SQSTM1/p62: sequestosome 1; TMRM: tetramethylrhodamine methyl ester; UB: ubiquitin; ULK1: unc-51 like kinase 1.

线粒体自噬对功能失调的线粒体的精确降解对于维持神经元稳态至关重要。HTT（亨廷顿蛋白）可以与许多其他蛋白质相互作用，从而在细胞内发挥多种生物学功能。在本研究中，我们研究了 HTT 在线粒体自噬过程中的作用，并分析了其聚谷氨酰胺 (polyQ) 束扩张的影响。HTT 参与不同的线粒体自噬步骤，在线粒体自噬启动过程中促进不同蛋白质复合物的物理接近，并招募对于促进受损线粒体和新生自噬体之间的相互作用至关重要的线粒体自噬受体。突变型 HTT 中 PolyQ 束的存在影响这些蛋白质复合物的形成，并决定了突变型 HTT 对线粒体自噬的负面影响，导致受损线粒体的积累和氧化应激的增加。这些结果导致亨廷顿病中的一般线粒体功能障碍和神经变性。

缩写：AMPK：AMP 激活蛋白激酶；ATG13：自噬相关13；BECN1：beclin 1，自噬相关；BNIP3：BCL2/腺病毒E1B相互作用蛋白3；BNIP3L/Nix：BCL2/腺病毒E1B相互作用蛋白3样；CCCP：羰基氰3-氯苯腙；DMEM：Dulbecco改良的Eagle培养基；EDTA：乙二胺四乙酸；EGFP：增强型绿色荧光蛋白；EGTA：乙二醇双(2-氨基乙醚)四乙酸；FUNDC1：包含1的FUN14域；HD：亨廷顿病；HRP：辣根过氧化物酶；HTT：亨廷顿蛋白；LC3-II：MAP1LC3/LC3 的脂化形式；mtDNA：线粒体脱氧核糖核酸；MTDR：MitoTracker 深红色；MTOR：雷帕霉素激酶的机制靶点；MTORC1：雷帕霉素激酶复合物 1 的机制靶点；NBR1：NBR1，自噬货物受体；CALCOCO2/NDP52：钙结合和卷曲螺旋结构域 2；OCR：耗氧率；OPTN: 奥替神经氨酸；OXPHOS：氧化磷酸化；PIK3C3/VPS34：磷脂酰肌醇3-激酶催化亚基3型；PIK3R4/VPS15：磷酸肌醇-3-激酶调节亚基4；PINK1：PTEN 诱导的推定激酶 1；PLA：邻近连接测定；PMSF：苯甲基磺酰氟；PolyQ：聚谷氨酰胺；PtdIns3K: 磷脂酰肌醇 3-激酶；ROS：活性氧；腐烂：鱼藤酮；SDS-PAGE：十二烷基硫酸钠-聚丙烯酰胺凝胶电泳；SEM：平均值的标准误差；SQSTM1/p62: 隔离体 1; TMRM：四甲基罗丹明甲酯；UB：泛素；ULK1：unc-51 样激酶 1。