Sirtuin 1 Inhibition Attenuates Viral Myocarditis by Suppressing the Nuclear Translocation of Pyruvate Kinase M2 to Rebalance Th17/Th9 Differentiation

Sirtuin 1 (SIRT1) regulates CD4 + T cell differentiation, particularly Th17 and Th9 subsets, in various autoimmune and inflammatory diseases, but its role in viral myocarditis (VMC) remains poorly understood. In this study, using a coxsackievirus B3 (CVB3)-induced VMC mouse model, we initially found that Sirt1 mRNA levels in CD4 + T cells peaked at day 7 post-infection, coinciding with maximal myocardial inflammation and Th17/Th9 transcription factors Rorc / Spi1 mRNA levels. Pharmacological inhibition of SIRT1 using EX527 attenuated cardiac inflammation and CVB3 viral load by downregulating SIRT1 expression in CD4 + T cells, leading to decreased Th17 proportions and increased Th9 cell infiltration in both cardiac tissue and spleen of VMC mice. In vitro, EX527 effectively suppressed the mouse CD4 + T cell activation and proliferation, directly inhibiting Th17 cell differentiation while promoting Th9 cell differentiation, and this shift in Th17/Th9 differentiation was also observed in human blood CD4 + T cells. While reduced glycolysis in CD4 + T cells was linked to EX527, a notable reduction in Pyruvate kinase M2 (PKM2) prompted the discovery of a non-metabolic mechanism. Mechanistically, EX527 specifically inhibited PKM2 nuclear translocation and the direct PKM2-STAT3 interaction, resulting in decreased p-STAT3/RORγt and increased p-STAT5/PU.1 levels downstream, while Foxp3 expression remained unchanged. These effects were reversed by SAICAR, an agonist of PKM2 nuclear translocation. Collectively, SIRT1 contributes to the Th17/Th9 imbalance in VMC through PKM2/STAT3/STAT5 signaling pathways, highlighting its potential as a novel therapeutic target.