AUTHOR=Bai Xiaojing , Wu Junfeng , Zhang Mengqi , Xu Yixuan , Duan Lijie , Yao Kai , Zhang Jianfeng , Bo Jimei , Zhao Yongfei , Xu Guoxiong , Zu Hengbing 

TITLE=DHCR24 Knock-Down Induced Tau Hyperphosphorylation at Thr181, Ser199, Thr231, Ser262, Ser396 Epitopes and Inhibition of Autophagy by Overactivation of GSK3β/mTOR Signaling

JOURNAL=Frontiers in Aging Neuroscience

VOLUME=Volume 13 - 2021

YEAR=2021

URL=https://www.frontiersin.org/journals/aging-neuroscience/articles/10.3389/fnagi.2021.513605

DOI=10.3389/fnagi.2021.513605

ISSN=1663-4365

ABSTRACT=Previous studies showed that DHCR24/Seladin-1 has a  remarkable decline in vulnerable brain areas of patients with AD. Accumulating evidences supported that the downregulation 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, we will focus on the effect of silencing DHCR24 on the tau hyperphosphorylation at some sites, in order to elucidate the relationship between DHCR24 and tauopathy. In present study, the knockdown of DHCR24 was induced by lentivirus-mediated DHCR24-shRNA in SH-SY5Y cells in vitro, the knockdown of DHCR24 significantly induced the hyperphosphorylation of tau sites at Thr181, Ser199, Thr231, and Ser262 by western blot analysis. Additionally, downregulation of DHCR24 simultaneously increase the accumulation of p62 protein, and decreased the ratio of LC3-II/LC3-I and the number of autophagosome compared to the control groups in SH-SY5Y cells. Conversely, upregulation of DHCR24 transfected by lentivirus-mediated DHCR24-cDNA obviously abolished the effect of DHCR24 knockdown on tau hyperphosphrylation and autophagy. To elucidate the mechanisms underlying the association between DHCR24 and tauopathy, we showed that the level of plasma membrane cholesterol, raft structural protein Caveolin-1, total PI3-K (p110α), phospho-Akt (Thr308) and phospho-Akt (Ser473) were significantly decreased, resulting in the inhibition of PI3-K/Akt signaling in silencing DHCR24 SH-SY5Y cells compared to control groups. Concomitantly, silencing DHCR24 simultaneously decreased the level of phosphorylated GSK3β at Ser9 (inactive form) and increased the level of phosphorylated mTOR at Ser2448, leading to overactivation of GSK3β and mTOR signaling. On the contrary, upregulation of DHCR24 obviously abolished the effect of DHCR24 knockdown on the inhibition of PI3-K/Akt signaling and overactivation of GSK3β/mTOR signaling. Collectively, our data strongly supported a critical role of DHCR24 downregulation in tau pathology and autophagy. Very importantly, dysregulation of cholesterol homeostasis in brain mediated by DHCR24 deficiency is likely to become a rational new target to establish a direct link between cholesterol metabolism disturbance and AD. Therefore, we hypothesize that the downregulation of DHCR24 may participate in tau pathology and autophagy.