PKM2-dependent metabolic reprogramming in CD4+ T cells is crucial for hyperhomocysteinemia-accelerated atherosclerosis

Inflammation mediated by activated T cells plays an important role in the initiation and progression of hyperhomocysteinemia (HHcy)-accelerated atherosclerosis in ApoE−/− mice. Homocysteine (Hcy) activates T cells to secrete proinflammatory cytokines, especially interferon (IFN)-γ; however, the precise mechanisms remain unclear. Metabolic reprogramming is critical for T cell inflammatory activation and effector functions. Our previous study demonstrated that Hcy regulates T cell mitochondrial reprogramming by enhancing endoplasmic reticulum (ER)-mitochondria coupling. In this study, we further explored the important role of glycolysis-mediated metabolic reprogramming in Hcy-activated CD4+ T cells. Mechanistically, Hcy-activated CD4+ T cell increased the protein expression and activity of pyruvate kinase muscle isozyme 2 (PKM2), the final rate-limiting enzyme in glycolysis, via the phosphatidylinositol 3-kinase/AKT/mechanistic target of rapamycin signaling pathway. Knockdown of PKM2 by small interfering RNA reduced Hcy-induced CD4+ T cell IFN-γ secretion. Furthermore, we generated T cell-specific PKM2 knockout mice by crossing LckCre transgenic mice with PKM2fl/fl mice and observed that Hcy-induced glycolysis and oxidative phosphorylation were both diminished in PKM2-deficient CD4+ T cells with reduced glucose and lipid metabolites, and subsequently reduced IFN-γ secretion. T cell-depleted apolipoprotein E-deficient (ApoE−/−) mice adoptively transferred with PKM2-deficient CD4+ T cells, compared to mice transferred with control cells, showed significantly decreased HHcy-accelerated early atherosclerotic lesion formation. In conclusion, this work indicates that the PKM2-dependent glycolytic-lipogenic axis, a novel mechanism of metabolic regulation, is crucial for HHcy-induced CD4+ T cell activation to accelerate early atherosclerosis in ApoE−/− mice.