Programmed Cell Death Protein 1 (PD-1) Regulates Metabolic Activity of Regulatory T Cells in Ischemia-Induced AKI

Background: Immune checkpoint inhibitors (ICPI) targeting PD-1 and its ligands PD-L1 and PD-L2 have revolutionized cancer therapy. However, their use is associated with immune-related adverse events, including nephropathy manifested as acute kidney injury (AKI). AKI, often caused by ischemia-reperfusion injury (IRI), can progress to chronic kidney disease and renal failure if unresolved. Regulatory T cells (Tregs) mitigate IRI-induced damage, with their protective role dependent on PD-1 signaling. Treg stability and function are linked to their metabolic preference for oxidative phosphorylation (OXPHOS) over glycolysis, yet the role of PD-1 in regulating OXPHOS within Tregs remains poorly understood. Methods: We utilized a murine model of IRI-induced AKI to assess the role of PD-1 in Treg-mediated nephroprotection. Global PD-1 knockout (KO) mice were subjected to renal IRI, and kidney function and injury were evaluated. Tregs from wild-type and PD-1 KO mice were analyzed for suppressive function in vitro and examined via transcriptomic profiling. Mitochondrial parameters including mass, membrane potential, biogenesis, and dynamics were assessed to evaluate mitochondrial fitness. Seahorse assay were used to analyze mitochondrial function and electron microscopy was used to observe mitochondrial morphology. Results: PD-1 KO mice exhibited more severe kidney dysfunction and injury following IRI. Despite retaining Foxp3 expression and in vitro suppressive capacity, PD-1-deficient Tregs failed to protect against AKI in vivo. Transcriptomic analysis revealed altered expression of genes associated with Treg function, proliferation, and mitochondrial metabolism in PD-1 KO Tregs. Additionally, these Tregs displayed reduced mitochondrial mass, membrane potential, biogenesis, and altered mitochondrial morphology, indicative of impaired mitochondrial fitness. Conclusion: PD-1 signaling is essential for maintaining mitochondrial integrity and function in Tregs. Loss of PD-1 impairs Treg-mediated protection in AKI through disrupted metabolic homeostasis, specifically by compromising OXPHOS. These findings underscore a critical role for PD-1 in Treg metabolism and kidney protection, with implications for managing ICPI-associated nephrotoxicity. Funding: NIDDK Support