Mutations in Connexin 30 (Cx30) are known to cause severe congenital hearing impairment; however, the mechanism by which Cx30 mediates homeostasis of endocochlear gap junctions is unclear. We used a gene deletion mouse model to explore the mechanisms of Cx30 in preventing hearing loss. Our results suggest that despite severe loss of the auditory brain response and endocochlear potential at postnatal day 18, Cx30^−/− mice only show sporadic loss of the outer hair cells. This inconsistency in the time course and severity of hearing and hair cell losses in Cx30^−/− mice might be explained in part by an increase in reactive oxygen species generation beginning at postnatal day 10. The expression of oxidative stress genes was increased in Cx30^−/− mice in the stria vascularis, spiral ligament, and organ of Corti. Furthermore, Cx30 deficiency caused mitochondrial dysfunction at postnatal day 18, as assessed by decreased ATP levels and decreased expression of mitochondria Complex I proteins, especially in the stria vascularis. Proteomic analysis further identified 444 proteins that were dysregulated in Cx30^−/− mice, including several that are involved in mitochondria electron transport, ATP synthesis, or ion transport. Additionally, pro-apoptotic proteins, including Bax, Bad and Caspase-3 were upregulated at postnatal day 18, providing a molecular basis to explain the loss of hearing that occurs prior to hair cell loss. Therefore, our results are consistent with an environment of oxidative stress and mitochondrial damage in the cochlea of Cx30^−/− mice that is coincident with hearing loss but precedes hair cell loss.

中文翻译：

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连接蛋白突变小鼠的耳蜗中听力损失和细胞死亡的机制。

已知连接蛋白30（Cx30）中的突变会导致严重的先天性听力障碍；然而，Cx30介导耳蜗间隙连接的稳态的机制尚不清楚。我们使用基因删除小鼠模型来探索Cx30预防听力损失的机制。我们的结果表明，尽管在出生后第18天听觉脑反应和耳蜗内电位严重丧失，但Cx30 ^-/-小鼠仅表现出散发的外毛细胞丧失。这种不一致在CX30听力和毛细胞损失的时间过程和严重性^{- / -}小鼠中可能部分地通过在10日龄开始的氧化应激的基因的表达的增加活性氧产生来解释在CX30增加^{- /-}血管纹，螺旋韧带和Corti器官中的小鼠。此外，Cx30缺乏会在出生后第18天引起线粒体功能障碍，这可以通过降低ATP水平和降低线粒体复合物I蛋白的表达来评估，尤其是在血管纹中。蛋白质组学分析进一步鉴定了444种在Cx30 ^-/-小鼠中失调的蛋白质，包括几种与线粒体电子运输，ATP合成或离子运输有关的蛋白质。此外，促凋亡蛋白，包括Bax，Bad和Caspase-3，在出生后第18天就被上调，这为解释在毛细胞丧失之前发生的听力丧失提供了分子基础。因此，我们的结果与Cx30耳蜗中的氧化应激和线粒体损伤的环境一致^-/-小鼠，与听力丧失同时发生，但先于毛细胞丧失。