Abstract 14268: PKM2 to PKM1 Isoform Switching in Fibroblasts Attenuates Cardiac Dysfunction in Infarcted Mice

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Introduction: The muscle isoform of pyruvate kinase, PKM, has two splice variants, with PKM2 having important roles in cardiomyocytes during development. The goal of this study was to understand the role of PKM2 in the adult failing heart. Methods: To determine how PKM2 expression changes after myocardial infarction (MI), wild-type (WT) mice were subjected to permanent coronary ligation followed by measurement of PKM2 abundance and localization by Western blotting and immunofluorescence imaging. To delineate the role of PKM2 in fibroblasts after MI, PKM2 fl/fl mice were bred with a fibroblast-specific, tamoxifen-inducible Cre driver (Col1a2-CreER; Cre). The Cre + and Cre - PKM2 fl/fl mice of both sexes were treated with tamoxifen (i.p. 20 mg/kg/d; 5 d), followed by tamoxifen washout and MI surgery. Four weeks after MI, cardiac function was examined by echocardiography. Results: Hearts from infarcted WT mice had 10-fold higher levels of PKM2 compared with sham WT hearts (n=8/gp, p<0.05). Immunofluorescence staining revealed PKM2 localized to areas of replacement fibrosis in infarcted hearts, and immunoblotting of isolated, adult cell populations showed PKM2 expressed in fibroblasts, smooth muscle cells, and endothelial cells, but not in cardiomyocytes. Furthermore, PKM2 levels were higher in cardiac fibroblasts isolated from infarcted mice compared with sham mice (n=3/group; p=0.005). Cardiac fibroblasts isolated from tamoxifen-treated Cre + /PKM2 fl/fl mice had decreased PKM2 expression and increased PKM1 expression. In naïve mice, PKM2 to PKM1 isoform switching did not affect cardiac function for up to 5 wk after tamoxifen administration. Although survival was not different between Cre - and Cre + PKM2 fl/fl mice after MI (n=18-20/gp; p=0.6383), PKM2 to PKM1 switching in Cre + PKM2 fl/fl male mice improved cardiac function compared with Cre - PKM2 fl/fl controls (n=7-12/gp), with a 15% improvement in ejection fraction (p=0.03), a decrease in LVIDd (p=0.04), EDV (p=0.04), and ESV (p=0.03), and an increase in LVPWd (p=0.01) and LVPWs (p=0.01); however, in female mice, PKM isoform switching did not improve cardiac function. Conclusions: Fibroblast-specific switching of PKM2 to PKM1 prior to MI prevents cardiac functional decline in male mice.