Loss of <scp>ARNTL</scp> Enhances <scp>ER</scp> Stress and Apoptosis in <scp>CKD</scp> Through Disruption of <scp>NRF2</scp> Signaling

Endoplasmic reticulum (ER) stress is a central driver of tubular cell apoptosis in chronic kidney disease (CKD), though the molecular pathways connecting ER stress to kidney injury remain unclear. In this study, we identify Aryl Hydrocarbon Receptor Nuclear Translocator-Like (ARNTL) as a key regulator of the ER stress response and apoptosis in CKD, with significant implications for disease progression. ARNTL expression is markedly reduced in both CKD patients and CKD model mice, correlating with elevated markers of ER stress and reduced kidney function. In CKD patients, ARNTL expression in the kidney inversely correlates with serum creatinine and blood urea nitrogen levels, suggesting its protective role in maintaining renal health. Single-cell sequencing further reveals that ARNTL is predominantly expressed in proximal tubular cells. In vitro studies demonstrate that the ER stress inducer tunicamycin (Tm) strongly suppresses ARNTL expression, whereas the ER stress inhibitor tauroursodeoxycholic acid (TUDCA) restores ARNTL levels and alleviates ER stress-induced apoptosis, as indicated by reduced cleaved caspase-3 and caspase-9 levels. Notably, ARNTL silencing in HK2 cells intensifies ER stress, triggers mitochondrial apoptosis, promotes ROS production, and disrupts NRF2 activation. Moreover, ARNTL directly binds to the NRF2 promoter region and interacts with NRF2 through protein-protein binding. This study reveals the ARNTL-NRF2 axis as a key protective pathway against stress-induced injury in renal tubular cells, suggesting it as a promising therapeutic target for reducing tubular damage and inflammation in CKD.