Targeting PPP1R3G to Mitigate Necroptotic Damage in Kidney Transplantation

Background: Graft dysfunction, frequently resulting from injury sustained during transplantation, remains a common complication in kidney transplants. Renal cell death is a major driver of this injury and dysfunction, with necroptosis—regulated by receptor-interacting protein kinase 1 (RIPK1)—emerging as a critical mechanism. Protein phosphatase 1 regulatory subunit 3G (PPP1R3G), known to interact with protein phosphatase 1γ (PP1γ) in modulating kinase activity, has an unclear role in RIPK1 activation and tubular cell death. This study explores the contribution of PPP1R3G to necroptosis during kidney transplantation and assesses the therapeutic potential of a novel sulfono-γ-AApeptide foldamer, PGB-1, designed to disrupt the PPP1R3G/PP1γ interaction to mitigate graft injury. Methods: Hypoxia/reoxygenation was induced in primary proximal tubular cells (PTCs) isolated from both wild-type (WT) and Ppp1r3g knockout (KO) mice. Cell viability, necroptosis, and inflammation were assessed using luminescence assays, fluorescent staining, RT-PCR, and Western blotting. "In vivo, syngeneic kidney transplantation was performed using male mice of both genotypes, or male C57BL/6 mice receiving donor kidneys treated with PGB-1. Graft function, injury, and histological changes were evaluated. Results: PPP1R3G deletion significantly enhanced tubular cell viability and reduced expression of phosphorylated RIPK1, RIPK3, MLKL, and pro-inflammatory markers. In the transplantation model, KO mice exhibited improved graft outcomes, with a 51% reduction in plasma creatinine (1.78 ± 0.16 vs. 0.87 ± 0.18 mg/dL, p < 0.001, n = 5) and a 55% increase in GFR. Histology confirmed reduced necroptosis and tissue injury in KO grafts. Furthermore, treating donor kidneys with PGB-1 during cold storage significantly protected against ischemic injury, reducing post-transplant plasma creatinine by 65% and improving graft function by 73% compared to recipients of untreated donor kidneys. Conclusion: These findings identify PPP1R3G as a critical regulator of necroptosis in kidney transplantation and highlight the therapeutic potential of targeting the PPP1R3G/PP1γ axis to prevent graft injury and improve transplant outcomes. Funding: Other NIH Support - R01, R41, R42