PRDX1 activates autophagy via the PTEN-AKT signaling pathway to protect against cisplatin-induced spiral ganglion neuron damage

Spiral ganglion neurons (SGNs) are auditory neurons that relay sound signals from the inner ear to the brainstem. The ototoxic drug cisplatin can damage SGNs and thus lead to sensorineural hearing loss (SNHL), and there are currently no methods for preventing or treating this. Macroautophagy/autophagy plays a critical role in SGN development, but the effect of autophagy on cisplatin-induced SGN injury is unclear. Here, we first found that autophagic flux was activated in SGNs after cisplatin damage. The SGN apoptosis and related hearing loss induced by cisplatin were alleviated after co-treatment with the autophagy activator rapamycin, whereas these were exacerbated by the autophagy inhibitor 3-methyladenine, indicating that instead of inducing SGN death, autophagy played a neuroprotective role in SGNs treated with cisplatin both <i>in vitro</i> and <i>in vivo</i>. We further demonstrated that autophagy attenuated reactive oxygen species (ROS) accumulation and alleviated cisplatin-induced oxidative stress in SGNs to mediate its protective effects. Notably, the role of the antioxidant enzyme PRDX1 (peroxiredoxin 1) in modulating autophagy in SGNs was first identified. Deficiency in PRDX1 suppressed autophagy and increased SGN loss after cisplatin exposure, while upregulating PRDX1 pharmacologically or by adeno-associated virus activated autophagy and thus inhibited ROS accumulation and apoptosis and attenuated SGN loss induced by cisplatin. Finally, we showed that the underlying mechanism through which PRDX1 triggers autophagy in SGNs was, at least partially, through activation of the PTEN-AKT signaling pathway. These findings suggest potential therapeutic targets for the amelioration of drug-induced SNHL through autophagy activation. <b>Abbreviations</b>: 3-MA: 3-methyladenine; AAV : adeno-associated virus; ABR: auditory brainstem responses; AKT/protein kinase B: thymoma viral proto-oncogene; Baf: bafilomycin A₁; CAP: compound action potential; COX4I1: cytochrome c oxidase subunit 4I1; Cys: cysteine; ER: endoplasmic reticulum; H₂O₂: hydrogen peroxide; HC: hair cell; MAP1LC3B/LC3B: microtubule-associated protein 1 light chain 3 beta; NAC: N-acetylcysteine; PRDX1: peroxiredoxin 1; PTEN: phosphatase and tensin homolog; RAP: rapamycin; ROS: reactive oxygen species; SGNs: spiral ganglion neurons; SNHL: sensorineural hearing loss; SQSTM1/p62: sequestosome 1; TOMM20: translocase of outer mitochondrial membrane 20; TUNEL: terminal deoxynucleotidyl transferase-mediated dUTP nick-end-labeling; WT: wild type.

螺旋神经节神经元（Spiral ganglion neurons, SGNs）是一类将声音信号从内耳传递至脑干的听觉神经元。耳毒性药物顺铂（cisplatin）可损伤SGNs，进而引发感音神经性听力损失（sensorineural hearing loss, SNHL），目前尚无针对该病症的预防或治疗方案。巨自噬/自噬（Macroautophagy/autophagy）在SGNs发育过程中发挥关键作用，但自噬对顺铂诱导的SGNs损伤的调控效应尚不明确。

本研究首先发现，顺铂损伤后SGNs中的自噬流被激活。联合应用自噬激活剂雷帕霉素（rapamycin）可缓解顺铂诱导的SGNs凋亡及相关听力损失，而自噬抑制剂3-甲基腺嘌呤（3-methyladenine）则会加重上述病理过程，这表明无论在体外（in vitro）还是体内（in vivo）环境中，自噬并未诱导SGNs死亡，反而对顺铂处理的SGNs发挥神经保护作用。

我们进一步证实，自噬可通过减轻活性氧（reactive oxygen species, ROS）积累、缓解顺铂诱导的SGNs氧化应激来介导其保护功效。值得注意的是，本研究首次明确了抗氧化酶PRDX1（过氧化物酶1, peroxiredoxin 1）在调控SGNs自噬中的作用。PRDX1缺失会抑制自噬并增加顺铂暴露后SGNs的丢失；而通过药理学手段或腺相关病毒（adeno-associated virus, AAV）上调PRDX1则可激活自噬，进而抑制ROS积累与细胞凋亡，减轻顺铂诱导的SGNs丢失。

最终我们揭示，PRDX1触发SGNs自噬的潜在分子机制至少部分依赖于PTEN-AKT信号通路的激活。上述研究结果表明，通过激活自噬改善药物性感音神经性听力损失存在潜在治疗靶点。

**缩略词对照表**：
3-MA：3-甲基腺嘌呤；AAV：腺相关病毒；ABR：听觉脑干反应；AKT/蛋白激酶B（protein kinase B，又称胸腺瘤病毒原癌基因）；Baf：巴弗洛霉素A₁；CAP：复合动作电位；COX4I1：细胞色素c氧化酶亚基4I1；Cys：半胱氨酸；ER：内质网；H₂O₂：过氧化氢；HC：毛细胞；MAP1LC3B/LC3B：微管相关蛋白1轻链3β；NAC：N-乙酰半胱氨酸；PRDX1：过氧化物酶1；PTEN：磷酸酶与张力蛋白同源物；RAP：雷帕霉素；ROS：活性氧；SGNs：螺旋神经节神经元；SNHL：感音神经性听力损失；SQSTM1/p62：隔离体1；TOMM20：线粒体外膜转位酶20；TUNEL：末端脱氧核苷酸转移酶介导的dUTP缺口末端标记法；WT：野生型。