Serum circulating proteins from pediatric patients with dilated cardiomyopathy cause pathologic remodeling and cardiomyocyte stiffness

Dilated cardiomyopathy (DCM) is the most common form of cardiomyopathy and main indication for heart transplantation in children. Therapies specific to pediatric DCM remains limited due to lack of a disease model. Our previous study showed that treatment of neonatal rat ventricular myocytes (NRVMs) with non-failing or DCM pediatric patient serum activates the fetal gene program (FGP). Here we show that serum treatment with Proteinase K prevents activation of the FGP, whereas RNase treatment exacerbates it, suggesting that circulating proteins, but not circulating microRNAs, promote these pathological changes. Evaluation of the protein secretome showed that midkine (MDK) is up-regulated in DCM serum, and NRVM treatment with MDK activates the FGP. Changes in gene expression in serum-treated NRVMs, evaluated by next-generation RNA sequencing (RNA-Seq), indicates extracellular matrix remodeling and focal adhesion pathways are upregulated in pediatric DCM serum and serum-treated NRVMs, suggesting alterations in cellular stiffness. Cellular stiffness was evaluated by Atomic Force Microscopy, which showed an increase in stiffness in DCM serum-treated NRVMs. Of the proteins increased in DCM sera, secreted frizzled related protein 1 (sFRP1) was a potential candidate for the increase in cellular stiffness, and sFRP1 treatment of NRVMs recapitulated the increase in cellular stiffness observed in response to DCM-serum treatment. Our results show that serum circulating proteins promote pathological changes in gene expression and cellular stiffness, and circulating miRNAs are protective against pathological changes.