Valproate Attenuates Endoplasmic Reticulum Stress-Induced Apoptosis in SH-SY5Y Cells via the AKT/GSK3β Signaling Pathway.

Zhengmao Li,Yuetao Yang,Rui Li,Fenzan Wu,Hongyu Zhang,Daqing Chen,Yi Chai,Xie Zhang,Jiayu Yin,Zhouguang Wang,Xiaokun Li,Hongxue Shi,Kebin Xu,Jian Xiao

doi:10.3390/ijms18020315

Abstract

Endoplasmic reticulum (ER) stress-induced apoptosis plays an important role in a range of neurological disorders, such as neurodegenerative diseases, spinal cord injury, and diabetic neuropathy. Valproate (VPA), a typical antiepileptic drug, is commonly used in the treatment of bipolar disorder and epilepsy. Recently, VPA has been reported to exert neurotrophic effects and promote neurite outgrowth, but its molecular mechanism is still unclear. In the present study, we investigated whether VPA inhibited ER stress and promoted neuroprotection and neuronal restoration in SH-SY5Y cells and in primary rat cortical neurons, respectively, upon exposure to thapsigargin (TG). In SH-SY5Y cells, cell viability was detected by the 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide (MTT) assay, and the expression of ER stress-related apoptotic proteins such as glucose‑regulated protein (GRP78), C/EBP homologous protein (CHOP), and cleaved caspase-12/-3 were analyzed with Western blot analyses and immunofluorescence assays. To explore the pathway involved in VPA-induced cell proliferation, we also examined p-AKT, GSK3β, p-JNK and MMP-9. Moreover, to detect the effect of VPA in primary cortical neurons, immunofluorescence staining of β-III tubulin and Anti-NeuN was analyzed in primary cultured neurons exposed to TG. Our results demonstrated that VPA administration improved cell viability in cells exposed to TG. In addition, VPA increased the levels of GRP78 and p-AKT and decreased the levels of ATF6, XBP-1, GSK3β, p-JNK and MMP-9. Furthermore, the levels of the ER stress-induced apoptosis response proteins CHOP, cleaved caspase-12 and cleaved caspase-3 were inhibited by VPA treatment. Meanwhile, VPA administration also increased the ratio of Bcl-2/Bax. Moreover, VPA can maintain neurite outgrowth of primary cortical neurons. Collectively, the neurotrophic effect of VPA is related to the inhibition of ER stress-induced apoptosis in SH-SY5Y cells and the maintenance of neuronal growth. Collectively, our results suggested a new approach for the therapeutic function of VPA in neurological disorders and neuroprotection.

Highlights

The endoplasmic reticulum (ER), an important subcellular organelle in eukaryotic cells, is the major site for protein folding, synthesis, trafficking and calcium storage, and it plays essential roles in multiple cellular processes that are required for cell survival and normal cellular functions [1]
Activated IRE1 can promote the splicing of X-box-binding protein 1 (XBP-1) messenger RNA, and mature XBP-1 promotes the transcription of unfolded protein response (UPR) target genes such as C/EBP homologous protein (CHOP), leading to apoptosis [11]
When cells are exposed to TG, ER stress can be induced through inhibiting Ca2+-ATPase transporters at the ER membrane [25], which results in apoptosis when the degree of endoplasmic reticulum stress is overwhelming [26]

Summary

Introduction

The endoplasmic reticulum (ER), an important subcellular organelle in eukaryotic cells, is the major site for protein folding, synthesis, trafficking and calcium storage, and it plays essential roles in multiple cellular processes that are required for cell survival and normal cellular functions [1]. Many external factors, such as oxidative stress, protein inclusion bodies, ischemia-reperfusion injury, spinal cord injury, disturbance of calcium homeostasis, and the inhibition of protein glycosylation, can disturb homeostatic ER function, leading to ER stress [2,3,4]. ER stress has been demonstrated to play an important role in neuronal cell death, the correlative mechanism still requires further research

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Conclusion