Reciprocal regulation between ER stress and autophagy in renal tubular fibrosis and apoptosis

Shaoqun Shu,Juan Cai,Anqun Chen,Danyi Yang,Zheng Dong,Hui Wang,Zhiwen Liu,Wenwen Wu,Chengyuan Tang,Jiefu Zhu

doi:10.1038/s41419-021-04274-7

Abstract

Both endoplasmic reticulum (ER) stress and autophagy have been implicated in chronic kidney injury and renal fibrosis. However, the relationship and regulatory mechanisms between ER stress and autophagy under this condition remain largely unknown. In this study, we first established a mouse model of ER stress-induced chronic kidney injury by 2 weekly injections of a low dose of tunicamycin (TM), a classical ER stress inducer. This model showed the induction of ER stress, autophagy, fibrosis and apoptosis in kidney tissues. In vitro, TM also induced ER stress, autophagy, fibrosis and apoptosis in HK-2 human kidney proximal tubular cells and BUMPT-306 mouse kidney proximal tubular cells. In these cells, autophagy inhibitor suppressed TM-induced fibrotic changes and apoptosis, suggesting an involvement of autophagy in ER stress-associated chronic kidney injury. PERK inhibitor ameliorated autophagy, fibrotic protein expression and apoptosis in TM-treated cells, indicating a role of the PERK/eIF2α pathway in autophagy activation during ER stress. Similar results were shown in TGF-β1-treated HK-2 cells. Interestingly, in both TM- or TGF-β1-treated kidney proximal tubular cells, inhibition of autophagy exaggerated ER stress, suggesting that autophagy induced by ER stress provides a negative feedback mechanism to reduce the stress. Together, these results unveil a reciprocal regulation between ER stress and autophagy in chronic kidney injury and fibrosis.

Highlights

Endoplasmic reticulum (ER) stress is a cellular state with endoplasmic reticulum (ER) dilatation due to the accumulation of misfolded or unfolded proteins, which results in unfolded protein response (UPR) [1,2,3]
transforming growth factor-β1 (TGF-β1) induces sequential activation of ER stress, autophagy, fibrosis and apoptosis in HK-2 cells We further investigated the relationship of ER stress with autophagy, fibrosis, and apoptosis in HK-2 cells exposed to TGFβ1, a critical factor in renal fibrosis [25]
ER stress and autophagy have been implicated in renal fibrosis and apoptosis in kidney diseases [5, 14,15,16,17,18], but the relationships among ER stress, autophagy, fibrosis, and apoptosis are poorly understood

Summary

INTRODUCTION

Endoplasmic reticulum (ER) stress is a cellular state with ER dilatation due to the accumulation of misfolded or unfolded proteins, which results in unfolded protein response (UPR) [1,2,3]. Fibrotic marker proteins (FN and Collagen I) were induced from 4 h of TGF-β1 treatment (Fig. S7A, B, F–G), while apoptosis was first detected at 8 h after treatment as evidenced by the increases of cleaved caspase-3 levels and TUNELpositive cells (Fig. S7A, B, F, and H) Together, these results suggest that TGF-β1 may trigger a sequential activation of ER stress, autophagy, fibrosis, and apoptosis in HK-2 cells. GSK2656157 reduced apoptosis induced by TGF-β1-treatment as indicated by the reduction of TUNEL -positive cells and cleaved Caspase-3 levels (Fig. 7C–F) Together, these results support a critical role of the PERK-eIF2α pathway in TGF-β1-induced ER stress, autophagy, fibrosis, and apoptosis. These results suggest that following activation, autophagy may provide a negative feedback mechanism to antagonize ER stress

DISCUSSION

MATERIALS AND METHODS

Findings

ETHICS STATEMENT