Reactivation of Pax2 in Proximal Tubular Epithelial Cells May Be Involved in the Directivity of Programmed Cell Death in Acute Tubular Necrosis

Background: Acute Tubular Necrosis (ATN) is a severe kidney injury, posing a critical issue due to its high mortality rate and the risk of progression to chronic kidney disease (CKD). In ATN, Paired box 2 (Pax2) reactivation in injured tubular epithelial cells has been known to occur. Pax2 is a transcription factor essential for kidney development and is reactivated in proximal tubular epithelial cells during recovery from injury. Previously, we reported that Pax2 reactivation is necessary to regenerate cells via cyclin-dependent kinase 4 (CDK4) in injured proximal tubules using a unilateral renal ischemia-reperfusion injury model. However, it is unclear whether the reactivation of Pax2 is an essential factor in the biological defense against ATN. Therefore, we hypothesized that inadequate Pax2 reactivation leads to exacerbating kidney injury and mortality. Methods: To test our hypothesis, we conducted experiments using 8-week-old male mice with proximal tubule-specific Pax2 knockout (Pax2 KO mice) under endogenous androgen control. We administered aristolochic acid (AA) at a dose of 5 mg/kg intraperitoneally for three consecutive days. As a control group, we used C57BL/6 mice. Mice were sacrificed on days 1, 4, 7, and 42 after the end of AA administration. To evaluate the impact on mortality, we administered a single intraperitoneal dose of AA at 15 mg/kg. Results: On the first and fourth days, the two groups showed no significant difference in kidney function. However, on the seventh day, serum creatinine levels increased in the Pax2 KO group (p=0.025). Kidney histological analysis revealed a clear obstruction of the Henle loop in the Pax2 KO group. In addition, TUNEL-positive cells were observed in both groups, while the number of Cleaved caspase 3-positive cells decreased in the cKO group (p=0.001). Instead, the number of p-Mlkl-positive cells increased (p=0.001 ). The experiment evaluating mortality showed a significant exacerbation in the Pax2 KO group (p=0.01). Conclusion: Pax2 reactivation was shown to be protective against kidney injury and mortality. Our results suggest that non-apoptotic cell death is increased in tubular epithelial cells with inadequate Pax2 reactivation and may affect mortality and kidney function by inducing maladaptive cell death. Funding: Government Support – Non-U.S.