Homocysteine Activates B Cells via Regulating PKM2-Dependent Metabolic Reprogramming

The overactivation of immune cells plays an important role in the pathogenesis of hyperhomocysteinemia (HHcy)-accelerated atherosclerosis. Homocysteine (Hcy) activates B cell proliferation and Ab secretion; however, the underlying mechanisms for these effects remain largely unknown. Metabolic reprogramming is critical for lymphocyte activation and effector function. In this study, we showed that Hcy-activated B cells displayed an increase in both oxidative phosphorylation and glycolysis, with a tendency to shift toward the latter, as well as an accumulation of intermediates in the pentose phosphate pathway, to provide energy and biosynthetic substrates for cell growth and function. Mechanistically, Hcy increased both the protein expression and glycolytic enzyme activity of the pyruvate kinase muscle isozyme 2 (PKM2) in B cells, whereas the PKM2 inhibitor shikonin restored Hcy-induced metabolic changes, as well as B cell proliferation and Ab secretion both in vivo and in vitro, indicating that PKM2 plays a critical role in metabolic reprogramming in Hcy-activated B cells. Further investigation revealed that the Akt-mechanistic target of rapamycin signaling pathway was involved in this process, as the mechanistic target of rapamycin inhibitor rapamycin inhibited Hcy-induced changes in PKM2 enzyme activity and B cell activation. Notably, shikonin treatment effectively attenuated HHcy-accelerated atherosclerotic lesion formation in apolipoprotein E-deficient mice. In conclusion, our results demonstrate that PKM2 is required to support metabolic reprogramming for Hcy-induced B cell activation and function, and it might serve as a critical regulator in HHcy-accelerated initiation of atherosclerosis.