Shikonin attenuates hyperhomocysteinemia-induced CD4E⁺ T cell inflammatory activation and atherosclerosis in ApoE^−/− mice by metabolic suppression

T cell metabolic activation plays a crucial role in inflammation of atherosclerosis. Shikonin (SKN), a natural naphthoquinone with anti-inflammatory activity, has shown to exert cardioprotective effects, but the effect of SKN on atherosclerosis is unclear. In addition, SKN was found to inhibit glycolysis via targeting pyruvate kinase muscle isozyme 2 (PKM2). In the present study, we investigated the effects of SKN on hyperhomocysteinemia (HHcy)-accelerated atherosclerosis and T cell inflammatory activation in ApoE^−/− mice and the metabolic mechanisms in this process. Drinking water supplemented with Hcy (1.8 g/L) was administered to ApoE^−/− mice for 2 weeks and the mice were injected with SKN (1.2 mg/kg, i.p.) or vehicle every 3 days. We showed that SKN treatment markedly attenuated HHcy-accelerated atherosclerosis in ApoE^−/− mice and significantly decreased inflammatory activated CD4⁺ T cells and proinflammatory macrophages in plaques. In splenic CD4⁺ T cells isolated from HHcy-ApoE^−/− mice, SKN treatment significantly inhibited HHcy-stimulated PKM2 activity, interferon-γ secretion and the capacity of these T cells to promote macrophage proinflammatory polarization. SKN treatment significantly inhibited HHcy-stimulated CD4⁺ T cell glycolysis and oxidative phosphorylation. Metabolic profiling analysis of CD4⁺ T cells revealed that Hcy administration significantly increased various glucose metabolites as well as lipids and acetyl-CoA carboxylase 1, which were reversed by SKN treatment. In conclusion, our results suggest that SKN is effective to ameliorate atherosclerosis in HHcy-ApoE^−/− mice and this is at least partly associated with the inhibition of SKN on CD4⁺ T cell inflammatory activation via PKM2-dependent metabolic suppression.