Vascular remodeling driven by the phenotypic switching of vascular smooth muscle cells (VSMCs) poses a significant health risk to astronauts during long-duration spaceflight. While the morphological and molecular changes are well recognized, the underlying metabolic drivers and potential translational countermeasures remain elusive. To investigate the metabolic determinants of VSMCs phenotypic switching, human aortic smooth muscle cells (HASMCs) were subjected to cyclic mechanical stretch, an in vitro model offering indirect mechanistic insights into mechanical loading conditions relevant to spaceflight-associated hemodynamic alterations. An integrated approach combining quantitative proteomics, flux analysis (Seahorse), and functional assays (cell cycle, wound healing, transwell) was used to characterize the accompanying metabolic and phenotypic alterations. Molecular mechanisms were assessed using immunoprecipitation, protein crosslinking, and immunofluorescence. Mechanical stretch triggered a contractile-to-synthetic phenotypic switch in HASMCs, accompanied by a shift from oxidative phosphorylation to aerobic glycolysis. Pyruvate kinase M2 (PKM2) was identified as a central metabolic regulator of this process, its silencing reversed the pro-synthetic phenotype. Notably, lactate, a glycolytic product, was found to exert a self-limiting feedback signal. Exogenous lactate suppressed the synthetic switch in associated with increased PKM2 lactylation. Further analysis indicated that PKM2 lactylation was associated with enhanced stability of its active tetrameric conformation, which was associated with a metabolic shift toward oxidative phosphorylation and restored expression of contractile markers. Although specific lactylation sites on PKM2 were not identified in this study, and direct causality between lactylation and tetramerization remains to be established, these findings identify a previously unrecognized association. This study reveals a novel metabolic regulatory mechanism in which lactate correlates with the suppression of synthetic switching of VSMCs, linked to PKM2 lactylation and tetramer stabilization. The observed lactate-PKM2 axis represents a candidate metabolic node associated with VSMCs phenotype regulation and offers a potential therapeutic target for modulating vascular remodeling. Upon direct validation under relevant conditions in future studies, this mechanism may inform the development of novel therapeutic strategies for managing vascular adaptation during long-duration spaceflight and other aerospace-related physiological challenges.
Li et al. (Sun,) studied this question.