Calcitriol protects against diabetic kidney disease by alleviating ferroptosis in renal tubular epithelial cells via JUN/ATF3 pathway

Ferroptotic renal tubular epithelial cells (RTECs) promote renal fibrosis (RF) by inducing epithelial-to-mesenchymal transition (EMT), thereby aggravating diabetic kidney disease (DKD) progression. Calcitriol has been shown to ameliorate Ferroptosis in neonatal hypoxic-ischemic encephalopathy but not in DKD. Thus, we hypothesized that calcitriol alleviates RF and mitigates DKD by inhibiting Ferroptosis in RTECs and aimed to reveal the underlying molecular mechanism. To test this hypothesis, calcitriol was administered to mice with DKD, whereas calcitriol combined with an inducer of ATF3 or TLR4 was employed in HK-2 cells with simulated DKD. Our latest bioinformatic analysis demonstrated that activating transcription factor 3 (ATF3), Toll-like Receptor 4 (TLR4), gamma-aminobutyric acid receptor-associated protein-like 1 (GABARAPL1), and indoleamine 2,3-dioxygenase 1 (IDO1) are hub genes related to inflammatory response, Ferroptosis, RF, and DKD. Calcitriol and vitamin D receptor (VDR) are closely interrelated with these hub genes, with Jun proto-oncogene (JUN) involved as a key node. Calcitriol effectively alleviated inflammation, Ferroptosis, and EMT in RTECs, and ameliorated RF in DKD and simulated DKD. Calcitriol significantly downregulated JUN, ATF3, and TLR4 but did not significantly affect GABARAPL1 expression in DKD and simulated DKD. Upregulation of ATF3 by supplementing ATF3 inducer counteracted the ameliorative effects of calcitriol on inflammation, Ferroptosis, EMT, and RF in simulated DKD. However, the amelioration of calcitriol in inflammation, Ferroptosis, EMT, and RF in simulated DKD was not significantly impacted by lipopolysaccharides-induced TLR4. Calcitriol alleviates RF and mitigates DKD by inhibiting inflammation and Ferroptosis in RTECs in DKD and simulated DKD via the JUN/ATF3 pathway.