ARNTL Regulates Endoplasmic Reticulum Stress and Mitochondrial Apoptosis through NRF2 and Plays a Crucial Role in the Development of CKD

Background: The core molecular clock protein, ARNTL, contributes to kidney tubular injury and fibrosis. Endoplasmic reticulum (ER) stress is implicated in the pathogenesis of chronic kidney disease (CKD), yet the interaction between ER stress and circadian clock pathways in kidney tubular cells remains unclear. Methods: In this study, we observed ARNTL expression and ER stress markers in both CKD patients and CKD rats. In vitro experiments involved treating HK2 cells with the ER stress activator tunicamycin (Tm) and the ER stress inhibitor Tauroursodeoxycholic acid (TUDCA). Additionally, ARNTL was silenced using siRNA to assess the effects on ER stress markers and mitochondria-related apoptosis. The regulation of NRF2 by ARNTL was studied through direct E-box binding to the Nrf2 promoter. Results: We found a decrease in ARNTL expression and a significant increase in ER stress markers in both CKD patients and CKD rats. In vitro experiments showed that the ER stress activator tunicamycin (Tm) markedly reduced ARNTL expression, while treatment with Tauroursodeoxycholic acid (TUDCA), an effective ER stress inhibitor, significantly increased ARNTL protein levels and reduced ER stress markers. Silencing ARNTL with siRNA in HK2 cells resulted in the upregulation of ER stress markers and activation of mitochondria-related apoptosis. NRF2 ,crucial in the innate immune response and apoptosis regulation, is shown to be regulated by ARNTL through direct E-box binding to the Nrf2 promoter. Loss of ARNTL diminished NRF2's response to ER stress, leading to increased production of the proinflammatory cytokine IL-1β and subsequent mitochondria-related apoptosis in HK2 cells. Conclusion: These findings underscore the pivotal role of ARNTL in modulating NRF2 activity and the ER stress response in HK2 cells, providing insights into the mechanisms underlying CKD.Our study highlights the importance of ARNTL, ER stress, and NRF2 in the apoptosis and injury of renal tubular cells, contributing to the pathology of CKD. Funding: Private Foundation Support