Pyruvate kinase M2 (PKM2), a glycolytic enzyme, is required to maintain vascular barrier function
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RATIONALE - Metabolic enzymes, like pyruvate kinase M2 (PKM2), play an essential role in altering endothelial cell (EC) phenotypes and behavior. Extensive research has elucidated the function of PKM2, a rate-limiting glycolytic enzyme, in the context of cancer cells and in activated immune cells, but its role in EC biology is only newly emerging. Recent findings show PKM2 acts as a key regulator of angiogenesis. Where exogenous circulating PKM2 induces EC cell proliferation leading to increased tumor angiogenesis and growth. Also, PKM2 deficient ECs exhibit decreased proliferation and migration. The relevance of PKM2 in modulating vascular barrier function is yet to be defined. OBJECTIVE -This study attempts to elucidate the role of PKM2 in regulating vascular barrier function. METHODS AND RESULTS - In vivo, EC specific deletion of PKM2 promotes increased vascular permeability in pulmonary capillary vessels and increased VEGF-induced acute vessel permeability in mouse dermal vessels. Similarly, in vitro, PKM2 deficient ECs exhibit decreased electrical resistance, disrupted VE-cadherin junctions and gap formations (illustrated via florescent VE-cadherin staining and phosphorylation of VE- cadherin protein at tyrosine residue Y658). Mechanistically, the deletion of PKM2 in ECs leads to increased angiopoietin-2 (Ang-2) expression, a well-known modulator of vascular permeability. Also, deletion of Ang-2 was sufficient to attenuate vascular leakage in PKM2 deficient endothelium, indicating that vascular leaky phenotype observed in PKM2 deficient endothelium is mediated by increased Ang-2 expression. CONCLUSIONS - PKM2, by modulating Ang-2 expression, plays a vital role in maintaining vascular barrier function.