Cardiac Transcriptome Remodeling and Impaired Bioenergetics in Single-Ventricle Congenital Heart Disease.

The mechanisms responsible for heart failure in single-ventricle congenital heart disease are unknown. Using explanted heart tissue, we showed that failing single-ventricle hearts have dysregulated metabolic pathways, impaired mitochondrial function, decreased activity of carnitine palmitoyltransferase activity, and altered functioning of the tricarboxylic acid cycle. Interestingly, nonfailing single-ventricle hearts demonstrated an intermediate metabolic phenotype suggesting that they are vulnerable to development of heart failure in the future. Mitochondrial targeted therapies and treatments aimed at normalizing energy generation could represent a novel approach to the treatment or prevention of heart failure in this vulnerable group of patients.

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 remain limited due to lack of a disease model. Our previous study showed that treatment of neonatal rat ventricular myocytes (NRVMs) with serum from nonfailing or DCM pediatric patients 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 miRNAs, promote these pathological changes. Evaluation of the protein secretome showed that midkine (MDK) is upregulated in DCM serum, and NRVM treatment with MDK activates the FGP. Changes in gene expression in serum-treated NRVMs, evaluated by next-generation RNA-Seq, indicated extracellular matrix remodeling and focal adhesion pathways were upregulated in pediatric DCM serum and in DCM 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 promoted pathological changes in gene expression and cellular stiffness, and circulating miRNAs were protective against pathological changes.

Severe thermoregulatory deficiencies in mice with a deletion in the titin gene TTN.

Muscular dystrophy with myositis (mdm) mice carry a deletion in the N2A region of the gene for the muscle protein titin (TTN), shiver at low frequency, fail to maintain body temperatures (Tb) at ambient temperatures (Ta) <34°C, and have reduced body mass and active muscle stiffness in vivo compared with wild-type (WT) siblings. Impaired shivering thermogenesis (ST) could be due to the mutated titin protein causing more compliant muscles. We hypothesized that non-shivering thermogenesis (NST) is impaired. To characterize the response to cold exposure, we measured Tb and metabolic rate (MR) of WT and mdm mice at four nominal temperatures: 20, 24, 29 and 34°C. Subsequently, we stimulated NST with noradrenaline. Manipulation of Ta revealed an interaction between genotype and MR: mdm mice had higher MRs at 29°C and lower MRs at 24°C compared with WT mice. NST capacity was lower in mdm mice than in WT mice. Using MR data from a previous study, we compared MR of mdm mice with MR of Perognathus longimembris, a mouse species of similar body mass. Our results indicated low MR and reduced NST of mdm mice. These were more pronounced than differences between mdm and WT mice owing to body mass effects on MR and capacity for NST. Correcting MR using Q10 showed that mdm mice had lower MRs than size-matched P. longimembris, indicating that mutated N2A titin causes severe thermoregulatory defects at all levels. Direct effects of the titin mutation lead to lower shivering frequency. Indirect effects likely lead to a lower capacity for NST and increased thermal conductance through decreased body size.