PyM Executes Immunosuppressive Activity on Murine T Lymphocytes via Inhibiting CN/NFAT Signaling Pathway

Abstract

Background: Immunosuppressive drugs are critical for managing organ transplantation and autoimmune diseases by targeting aberrant T lymphocyte activation and immune responses. However, existing therapies often cause significant side effects, driving the urgent need for safer alternatives. Natural products, particularly from marine-derived sources like mangrove endophytic fungi, have emerged as promising candidates due to their bioactive diversity and minimal toxicity profiles. Methods: To explore this potential, this study investigated pestalotiopyrone M (PyM), a new pyrone derivative obtained from the endophytic fungus Pestalotiopsis sp. HHL101, which was isolated from the Chinese mangrove plant Rhizophora stylosa. Its immunosuppressive activity targeting calcineurin (CN) was evaluated, and spleen cell viability was tested by CCK-8. The effects of PyM on T cell proliferation were assessed using Con A-induced splenocyte proliferation and unidirectional mixed lymphocyte response (MLR) models. Cell cycle and apoptosis analysis were performed to determine potential cytostatic effects. Additionally, the impact of PyM on NFAT1 dephosphorylation, translocation, and subsequent cytokines secretion (IL-2, IL-4, TNF-α, and IFN-γ) was examined in ConA-stimulated cells. Results: We verified that PyM obviously inhibited Con A-induced splenocyte proliferation and unidirectional MLR. Crucially, it demonstrated markedly reduced cytotoxicity, exhibiting approximately 38-fold lower cytotoxic effects compared to the clinically used drug CsA. It arrested the cell cycle from G1-phase to S-phase and G2-phase. Furthermore, we confirmed that PyM suppressed ConA-stimulated activation of NFAT1 dephosphorylation and blocked NFAT1 translocation in vitro, subsequently inhibiting the transcription and expression of IL-2, IL-4, TNF-α, and IFN-γ. Conclusions: These results indicate that PyM is an efficient inhibitor of the CN/NFAT signaling pathway. It shows promising immunosuppressive activity by targeting T cell activation and proliferation, indicating its potential as a candidate for development into an immunosuppressive agent for treating adverse immune responses.