Nyarko, O. O.; Rausch, E.; Goff, J. R. H.; Karimpour-Fard, A.; Conard, C. S.; Hernandez-Lagunas, L.; Burns, M. P. A.; Pena, B.; Miyamoto, S. D.; Stauffer, B. L.; Sucharov, C. C.

Background: Idiopathic dilated cardiomyopathy (iDCM) in children is a life-threatening disease. Little is known about its cellular and transcriptional landscape, and the lack of disease-specific animal models limits our understanding of its mechanisms. We previously demonstrated that pediatric iDCM serum-circulating proteins promote pathologic remodeling in vitro, and that secreted frizzled related protein 1 (sFRP1) increases stiffness in cardiomyocytes. Here we investigated the mechanisms by which sFRP1 contributes to cardiac dysfunction. Methods: The effect of sFRP1 in combination with isoproterenol (ISO) (to recapitulate the increase in circulating catecholamine observed in pediatric DCM patients) was evaluated in neonatal rat ventricular myocytes (in vitro), and in neonatal rats through intraperitoneal injections (in vivo). Function and molecular mechanisms were investigated through echocardiography and next-generation-sequencing respectively. Protein levels and localization were determined by Western blot. Tissue stiffness was measured by Atomic Force Microscopy. In vitro and in vivo data were compared to explanted human heart tissue (ex vivo). Results: We show that ISO+sFRP1 reactivates the fetal gene program in vitro, and promotes cardiac dysfunction, dilation and stiffness in vivo. Importantly, we show stiffness is also increased in pediatric iDCM hearts. We identified co-activation of Notch and WNT signaling in both ISO+sFRP1-treated rats and pediatric iDCM hearts. Mechanistically, in vitro inhibition of Notch or {beta}-catenin prevented pathological remodeling, and Notch inhibition improved cardiac function and reduced ventricular dilation in ISO+sFRP1-treated rats and NRVMs. Conclusion: We identified concordant alterations in Notch and WNT signaling in pediatric iDCM hearts and in our ISO+sFRP1-treated rats. Notch inhibition abrogated pathologic changes in vitro and in vivo. These findings provide novel mechanistic insights and a potential therapeutic target for pediatric iDCM.