Bai Xiaojing, Wu Junfeng, Zhang Mengqi, Xu Yixuan, Duan Lijie, Yao Kai, Zhang Jianfeng, Bo Jimei, Zhao Yongfei, Xu Guoxiong, Zu Hengbing
Department of Neurology, Jinshan Hospital, Fudan University, Shanghai, China.
The Research Center for Clinical Medicine, Jinshan Hospital, Fudan University, Shanghai, China.
Front Aging Neurosci. 2021 Apr 21;13:513605. doi: 10.3389/fnagi.2021.513605. eCollection 2021.
Accumulating evidences supported that knock-down of DHCR24 is linked to the pathological risk factors of AD, suggesting a potential role of DHCR24 in AD pathogenesis. However, the molecular mechanism link between DHCR24 and tauopathy remains unknown. Here, in order to elucidate the relationship between DHCR24 and tauopathy, we will focus on the effect of DHCR24 on the tau hyperphosphorylation at some toxic sites. In present study, we found that DHCR24 knock-down significantly lead to the hyperphosphorylation of tau sites at Thr181, Ser199, Thr231, Ser262, Ser396. Moreover, DHCR24 knock-down also increase the accumulation of p62 protein, simultaneously decreased the ratio of LC3-II/LC3-I and the number of autophagosome compared to the control groups, suggesting the inhibition of autophagy activity. In contrast, DHCR24 knock-in obviously abolished the effect of DHCR24 knock-down on tau hyperphosphrylation and autophagy. In addition, to elucidate the association between DHCR24 and tauopathy, we further showed that the level of plasma membrane cholesterol, lipid raft-anchored protein caveolin-1, and concomitantly total I class PI3-K (p110α), phospho-Akt (Thr308 and Ser473) were significantly decreased, resulting in the disruption of lipid raft/caveola and inhibition of PI3-K/Akt signaling in silencing DHCR24 SH-SY5Y cells compared to control groups. At the same time, DHCR24 knock-down simultaneously decreased the level of phosphorylated GSK3β at Ser9 (inactive form) and increased the level of phosphorylated mTOR at Ser2448 (active form), leading to overactivation of GSK3β and mTOR signaling. On the contrary, DHCR24 knock-in largely increased the level of membrane cholesterol and caveolin-1, suggesting the enhancement of lipid raft/caveola. And synchronously DHCR24 knock-in also abolished the effect of DHCR24 knock-down on the inhibition of PI3-K/Akt signaling as well as the overactivation of GSK3β and mTOR signaling. Collectively, our data strongly supported DHCR24 knock-down lead to tau hyperphosphorylation and the inhibition of autophagy by a lipid raft-dependent PI3-K/Akt-mediated GSK3β and mTOR signaling. Taking together, our results firstly demonstrated that the decrease of plasma membrane cholesterol mediated by DHCR24 deficiency might contribute to the tauopathy in AD and other tauopathies.
越来越多的证据表明，敲低DHCR24与阿尔茨海默病（AD）的病理风险因素相关，提示DHCR24在AD发病机制中可能发挥作用。然而，DHCR24与tau蛋白病之间的分子机制联系尚不清楚。在此，为了阐明DHCR24与tau蛋白病之间的关系，我们将聚焦于DHCR24对tau蛋白在某些毒性位点过度磷酸化的影响。在本研究中，我们发现敲低DHCR24显著导致tau蛋白在Thr181、Ser199、Thr231、Ser262、Ser396位点的过度磷酸化。此外，与对照组相比，敲低DHCR24还增加了p62蛋白的积累，同时降低了LC3-II/LC3-I的比值和自噬体的数量，提示自噬活性受到抑制。相反，过表达DHCR24明显消除了敲低DHCR24对tau蛋白过度磷酸化和自噬的影响。此外，为了阐明DHCR24与tau蛋白病之间的关联，我们进一步表明，与对照组相比，在沉默DHCR24的SH-SY5Y细胞中，质膜胆固醇水平、脂筏锚定蛋白小窝蛋白-1以及总的I类磷脂酰肌醇-3激酶（p110α）、磷酸化的Akt（Thr308和Ser473）水平显著降低，导致脂筏/小窝的破坏和PI3-K/Akt信号通路的抑制。同时，敲低DHCR24还同时降低了Ser9位点磷酸化的GSK3β（非活性形式）水平，增加了Ser2448位点磷酸化的mTOR（活性形式）水平，导致GSK3β和mTOR信号通路的过度激活。相反，过表达DHCR24大大增加了膜胆固醇和小窝蛋白-1的水平，提示脂筏/小窝增强。并且同步地，过表达DHCR24也消除了敲低DHCR24对PI3-K/Akt信号通路抑制以及GSK3β和mTOR信号通路过度激活的影响。总体而言，我们的数据有力地支持了敲低DHCR24通过脂筏依赖性PI-3K/Akt介导的GSK3β和mTOR信号通路导致tau蛋白过度磷酸化和自噬抑制。综上所述，我们的结果首次证明，DHCR24缺乏介导的质膜胆固醇降低可能导致AD和其他tau蛋白病中的tau蛋白病。
