ITCH-SMAD5新通路介导的细胞自噬与ALS疾病的发生发展的研究

遗传变异或者毒性蛋白引起细胞损伤的状态下，ITCH的会发生相应变化，并被招募到胞质异常聚集体，其参与细胞自噬的分子机制以及是否参与ALS的发生发展尚未有报道。前期研究发现SMAD5为ITCH/AIP4的新底物，其通过自噬系统降解。而高水平的ITCH、SMAD5会明显抑制细胞自噬受体p62胞质溶性，且导致可溶性LC3-II大量累积，从而抑制细胞自噬信号通路，进而引起细胞死亡。检测发现，与8位正常人相比，26位ALS病人的脊髓细胞中ITCH与SMAD5的表达水平变化明显且为大幅度上调。依据这些预实验数据，我们建立一个假设：正常神经细胞中，ITCH依赖的K63-SMAD5通过细胞自噬系统降解；在ALS病人中，ITCH、SMAD5的过量表达，K63-SMAD5带动自噬受体p62变为不可溶，且可溶性LC3-II大量累积，从而抑制遗传突变的毒性蛋白的降解，进而致使运动神经元退行。

ITCH endogenous levels get elevated after various genotoxic and proteotoxic cellular insults and part of the protein are recruited into abnormal cytoplasmic aggregates. However, it is still unclear how, at a molecular level, ITCH regulates the autophagy signal transduction in ALS. Previous studies indicated that SMAD5 is a new substrate of E3 ubiquitin ligase ITCH/AIP4, and it is most probably degraded via the autophagy pathway. The high levels of ITCH and SMAD5 significantly inhibit the p62 solubility, and lead to high level of LC3-II, resulting in the dysfunctional autophagy and cell death. Compared to 8 controls, ITCH and SMAD5 endogenous levels of 26 ALS patients (the spinal cord tissue) were significantly up-regulated. Based on these preliminary data, we established a hypothesis: Under the normal condition, ITCH-dependent K63-SMAD5 is degraded by the autophagy system; in ALS patients, ITCH and SMAD5 are overexpressed, and ITCH-dependent K63-SMAD5 inhibits the formation of autophagosome (p62-LC3-II), resulting in the toxic proteins aggregation, which in turn causes the degeneration of motor neuron.