p21-Activated Kinase 4 and Ischemic Acute Kidney Injury in Mice and Humans

Key Points p21-activated kinase 4 (PAK4) phosphorylates and inactivates GSH peroxidase 3 in the kidney after ischemia-reperfusion. Mice lacking PAK4 or treated with PAK4 proteolysis-targeting chimera were protected from kidney damage caused by ischemia-reperfusion injury. PAK4 expression in kidney tissues post-transplant inversely correlated with kidney function. Background AKI after ischemia-reperfusion remains a substantial perioperative challenge lacking effective treatment. p21-activated kinase 4 (PAK4), a downstream effector of Rho GTPase, has been explored in hepatic ischemia-reperfusion injury, but its role in renal ischemia-reperfusion is unknown. Methods Wild-type and proximal tubule–specific Pak4 knockout mice underwent 25 minutes of ischemia followed by 24 hours of reperfusion injury. Primary tubular cells and human kidney-2 cells were exposed to hypoxia-reoxygenation injury to investigate the in vitro effect of PAK4. Selective degradation of PAK4 was employed using proteolysis-targeting chimera (PROTAC) to ameliorate AKI. Results Post–ischemia-reperfusion, the expression of PAK4 was upregulated through hypoxia-inducible factor 1 α in mouse kidneys. Deletion of PAK4 in proximal tubule cells, but not in myeloid cells, significantly mitigated ischemia-reperfusion–induced AKI, as evidenced by decreased levels of BUN, creatinine, tubular necrosis, apoptosis, macrophage infiltration, and lipid accumulation compared with control mice. Further investigation revealed that PAK4 phosphorylated GSH peroxidase 3 (GPx3) at T47, leading to its proteasomal degradation. In addition, pretreatment of mice with the PAK4 PROTAC preserved GPx3 and enhanced fatty acid β -oxidation, thereby protecting against AKI. In kidney tissues from people with a kidney transplant, elevated levels of PAK4 protein and phosphorylation of GPx3 at T47 were observed. Conclusions Renal tubular PAK4 contributes to tissue damage during ischemia-reperfusion injury, whereas PAK4 PROTAC mitigates ischemia-reperfusion injury by reducing oxidative stress and promoting fatty acid β -oxidation.