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Invest Ophthalmol Vis Sci. 2020 Jan 23;61(1):1. doi: 10.1167/iovs.61.1.1.
Vacuolar protein sorting 35 (Vps35) mutations and protein dysfunction have been linked to the hyperphosphorylation and accumulation of tau protein in a number of central neurodegenerative disorders. The aims of the present study were to investigate the mechanism underlying the tau hyperphosphorylation caused by Vps35 deficiency.
The cells used in this study were primary retinal ganglion cells (RGCs). The rat retinal glutamate excitotoxicity model was used in vivo. Fresh retinal tissues or eyeballs were collected at different time points. The expression and interactions of Vps35, Cdk5/p35, tau hyperphosphorylation, LAMP1, EEA1 and UBE1 in RGCs were studied by immunofluorescence staining, Western blotting, and immunoprecipitation.
The downregulation and overexpression of Vps35 increased and decreased the expression of p35 and tau hyperphosphorylation, respectively. More important, roscovitine, a Cdk5 inhibitor, could effectively decrease the hyperphosphorylated tau level induced by Vps35 deficiency. Furthermore, this study confirmed that the inhibition of Vps35 could increase the activity of Cdk5/p35 by affecting the lysosomal degradation of p35 and lead to the degeneration of RGCs.
These findings demonstrate the possibility that Cdk5/p35 acts as a "cargo" of Vps35 and provide new insights into the pathogenesis of RGC degeneration caused by hyperphosphorylated tau protein. Vps35 is a potential target for basic research and clinical treatment of RGC degeneration in many ocular diseases such as glaucoma.
空泡蛋白分选 35（Vps35）突变和蛋白功能障碍与多种中枢神经退行性疾病中tau 蛋白的过度磷酸化和积累有关。本研究旨在探讨 Vps35 缺乏引起 tau 过度磷酸化的机制。
本研究使用的细胞是原代视网膜神经节细胞（RGC）。体内使用大鼠视网膜谷氨酸兴奋性毒性模型。在不同时间点采集新鲜的视网膜组织或眼球。通过免疫荧光染色、Western blot 和免疫沉淀研究 Vps35、Cdk5/p35、tau 过度磷酸化、LAMP1、EEA1 和 UBE1 在 RGC 中的表达和相互作用。
下调和过表达 Vps35 分别增加和减少 p35 和 tau 过度磷酸化的表达。更重要的是，Cdk5 抑制剂罗克洛文可有效降低 Vps35 缺乏引起的 tau 过度磷酸化水平。此外，本研究证实抑制 Vps35 可通过影响 p35 的溶酶体降解来增加 Cdk5/p35 的活性，导致 RGC 变性。
这些发现表明 Cdk5/p35 可能作为 Vps35 的“货物”发挥作用，并为 tau 蛋白过度磷酸化引起的 RGC 变性的发病机制提供了新的见解。Vps35 是许多眼部疾病（如青光眼）中 RGC 变性的基础研究和临床治疗的潜在靶点。
