Abstract Body (Do not enter title and authors here): Background. mRNA modification and degradation can reduce expression of protein leading to heart failure. Cardiac myosin binding protein-C (cMyBPC) with gene (MyBPC3) is a thick filament regulatory protein that modulates contractility and relaxation via its phosphorylation status. Here, we report mutations on cMyBPC phosphorylation sites caused loss of MyBPC3 mRNA leading to heart failure.
Method. cMyBPC knock-in mutations to mimic de-phosphorylation (S273A, S282A, S284A, S302A, S307A: 5SA) and phosphorylation (S273D, S282D, S284D, S302D, S307D:5SD) were created using the traditional homologous recombination technique.
Results. Echocardiogram showed MyBPC3^(5SA/5SA) and MyBPC3^(5SD/5SD) hearts to exhibit hypertrophy, increased chamber size, depressed left ventricular ejection fraction, diastolic dysfunction (slowed e’, increased E/e’ ratio), and abbreviated systolic ejection duration (aortic ejection duration/cycle duration). The heterozygotes trended towards abnormal diastolic dysfunction. These findings resemble cMyBPC deletion. Western blots showed very low level of cMyBPC expression in MyBPC^(5SA/5SA) and MyBPC^(5SD/5SD) hearts. Quantitative polymerase chain reaction (qPCR) showed very low of cMyBPC mRNA copy number with multiple primers targeting different regions from N to C terminus. Further targeted qPCR experiments suggested intron retention about S282A-S284A region likely leading to incomplete assembly followed by degradation.
Conclusion. Mutations in myofilament exon can altered mRNA processing to prevent normal protein production resulting in heart failure.