Zhang Li, Sun Yang, Fei Mingjian, Tan Cheng, Wu Jing, Zheng Jie, Tang Jiqing, Sun Wei, Lv Zhaoliang, Bao Jiandong, Xu Qiang, Yu Huixin
Key Laboratory of Nuclear Medicine; Ministry of Health; Jiangsu Key Laboratory of Molecular Nuclear Medicine; Jiangsu Institute of Nuclear Medicine; Wuxi, Jiangsu China; State Key Laboratory of Pharmaceutical Biotechnology; School of Life Sciences; Nanjing University; Nanjing, Jiangsu China.
State Key Laboratory of Pharmaceutical Biotechnology; School of Life Sciences; Nanjing University; Nanjing, Jiangsu China.
Autophagy. 2014 Jun;10(6):1015-35. doi: 10.4161/auto.28477.
Oxidative stress has been implicated in both normal aging and various neurodegenerative disorders and it may be a major cause of neuronal death. Chaperone-mediated autophagy (CMA) targets selective cytoplasmic proteins for degradation by lysosomes and protects neurons against various extracellular stimuli including oxidative stress. MEF2A (myocyte enhancer factor 2A), a key transcription factor, protects primary neurons from oxidative stress-induced cell damage. However, the precise mechanisms of how the protein stability and the transcriptional activity of MEF2A are regulated under oxidative stress remain unknown. In this study, we report that MEF2A is physiologically degraded through the CMA pathway. In pathological conditions, mild oxidative stress (200 μM H 2O 2) enhances the degradation of MEF2A as well as its activity, whereas excessive oxidative stress (> 400 μM H 2O 2) disrupts its degradation process and leads to the accumulation of nonfunctional MEF2A. Under excessive oxidative stress, an N-terminal HDAC4 (histone deacetylase 4) cleavage product (HDAC4-NT), is significantly induced by lysosomal serine proteases released from ruptured lysosomes in a PRKACA (protein kinase, cAMP-dependent, catalytic, α)-independent manner. The production of HDAC4-NT, as a MEF2 repressor, may account for the reduced DNA-binding and transcriptional activity of MEF2A. Our work provides reliable evidence for the first time that MEF2A is targeted to lysosomes for CMA degradation; oxidative stress-induced lysosome destabilization leads to the disruption of MEF2A degradation as well as the dysregulation of its function. These findings may shed light on the underlying mechanisms of pathogenic processes of neuronal damage in various neurodegenerative-related diseases.
氧化应激与正常衰老和各种神经退行性疾病都有关联，它可能是神经元死亡的主要原因。伴侣介导的自噬（CMA）将选择性的细胞质蛋白靶向溶酶体进行降解，并保护神经元免受包括氧化应激在内的各种细胞外刺激。关键转录因子MEF2A（肌细胞增强因子2A）可保护原代神经元免受氧化应激诱导的细胞损伤。然而，在氧化应激条件下，MEF2A的蛋白质稳定性和转录活性是如何被调控的精确机制仍不清楚。在本研究中，我们报道MEF2A在生理状态下通过CMA途径被降解。在病理条件下，轻度氧化应激（200μM H₂O₂）会增强MEF2A的降解及其活性，而过度氧化应激（>400μM H₂O₂）则会破坏其降解过程，导致无功能的MEF2A积累。在过度氧化应激下，溶酶体破裂释放的溶酶体丝氨酸蛋白酶以不依赖PRKACA（蛋白激酶，cAMP依赖性，催化性，α）的方式显著诱导N端HDAC4（组蛋白脱乙酰基酶4）裂解产物（HDAC4-NT）的产生。作为MEF2的抑制因子，HDAC4-NT的产生可能解释了MEF2A DNA结合和转录活性的降低。我们的工作首次提供了可靠证据，证明MEF2A靶向溶酶体进行CMA降解；氧化应激诱导的溶酶体不稳定导致MEF2A降解的破坏及其功能失调。这些发现可能有助于揭示各种神经退行性相关疾病中神经元损伤致病过程的潜在机制。
