Ischemia Precondition Attenuates Ischemia-Reperfusion (I/R)-Induced AKI by Activating CLpP

Background: Ischemic preconditioning (IPC) activates endogenous defense mechanisms to protect the kidney from ischemia-reperfusion (I/R) injury, but its protective mechanism is still unclear. The imbalance of mitochondrial protein homeostasis is closely related to the development of acute kidney injury (AKI). Casein hydrolytic protease P (CLPP) is a protease that maintains mitochondrial protein homeostasis by degrading unfolded proteins. In addition, the activation of mitochondrial unfolded protein response (UPRmt) leads to the initiation of integrated stress response (ISR). Various stress factors promote phosphorylation of eukaryotic translation initiation factor 2α (eIF2α), inhibiting overall protein synthesis, and initiating stress response gene expression. However, it remains unclear whether activated eIF2α phosphorylation is involved in renal ischemic tolerance induced by IPC via upregulation of CLPP expression. Methods: In vivo, I/R was used to induce AKI. To investigate the potential effects and mechanisms of different degrees of ischemia on renal injury, C57BL/6J mice underwent bilateral renal artery clamping for 5, 10, and 15 minutes followed by 6 hours of reperfusion to simulate mild, moderate, and severe renal injury. Subsequently, the protective effect of IPC on I/R was studied using ISRIB (ISR inhibitor), or systemic CLPP gene knockout. Results: Moderate IPC significantly alleviates AKI induced by IRI in mice, as evidenced by decreased levels of BUN, Scr, KIM-1, and NGAL mRNA. In addition, IPC notably mitigates the morphological alterations induced by IRI, including loss of brush border, tubular formation, and reduced cell apoptosis. Mechanistically, we propose that IPC activates the ISR, thereby promoting upregulation of CLPP expression and reducing accumulation of unfolded proteins in mitochondria. Inhibition of the eIF2α activity, which is involved in the ISR, abolishes the protective effect of IPC on I/R-induced renal injury. Systemic CLPP gene knockout counteracts the protective effect of IPC on renal injury. Conclusion: Phosphorylation of eIF2α and upregulation of CLPP contribute to the protective effect of IPC on I/R injury. This could offer more possibilities for clinical treatment, thereby improving patient prognosis and quality of life. Funding: Government Support – Non-U.S.