Mutations in MYBPC3 disrupt myosin states of relaxation, and manipulating myosin therapeutically abates the effects of MYBPC3 mutations.

Background—: Inflammation plays a critical role in adverse cardiac remodeling and heart failure. Therefore, approaches geared toward inhibiting inflammation may provide therapeutic benefits. We tested the hypotheses that genetic deletion of interleukin-10 (IL-10), a potent antiinflammatory cytokine, exacerbates pressure overload–induced adverse cardiac remodeling and hypertrophy and that IL-10 therapy inhibits this pathology. Methods and Results—: Cardiac hypertrophy was induced in wild-type and IL-10 knockout mice by isoproterenol (ISO) infusion. ISO-induced left ventricular dysfunction and hypertrophic remodeling, including fibrosis and fetal gene expression, were further exaggerated in knockout mice compared with wild-type mice. Systemic recombinant mouse IL-10 administration markedly improved left ventricular function and not only inhibited but also reversed ISO-induced cardiac remodeling. Intriguingly, a very similar cardioprotective response of IL-10 was found in transverse aortic constriction–induced hypertrophy and heart failure models. In neonatal rat ventricular myocytes and H9c2 myoblasts, ISO activated nuclear factor-κB and inhibited signal transducers and activators of transcription 3 (STAT3) phosphorylation. Interestingly, IL-10 suppressed ISO-induced nuclear factor-κB activation and attenuated STAT3 inhibition. Moreover, pharmacological and genetic inhibition of STAT3 reversed the protective effects of IL-10, whereas ectopic expression of constitutively active STAT3 mimicked the IL-10 responses on the ISO effects, confirming that the IL-10–mediated inhibition of nuclear factor-κB is STAT3 dependent. Conclusion—: Taken together, our results suggest IL-10 treatment as a potential therapeutic approach to limit the progression of pressure overload–induced adverse cardiac remodeling.

The role of cardiac myosin binding protein-C (cMyBP-C) phosphorylation in cardiac physiology or pathophysiology is unclear. To investigate the status of cMyBP-C phosphorylation in vivo, we determined its phosphorylation state in stressed and unstressed mouse hearts. cMyBP-C phosphorylation is significantly decreased during the development of heart failure or pathologic hypertrophy. We then generated transgenic (TG) mice in which the phosphorylation sites of cMyBP-C were changed to nonphosphorylatable alanines (MyBP-C ^AllP− ). A TG line showing &40% replacement with MyBP-C ^AllP− showed no changes in morbidity or mortality but displayed depressed cardiac contractility, altered sarcomeric structure and upregulation of transcripts associated with a hypertrophic response. To explore the effect of complete replacement of endogenous cMyBP-C with MyBP-C ^AllP− , the mice were bred into the MyBP-C ^(t/t) background, in which less than 10% of normal levels of a truncated MyBP-C are present. Although MyBP-C ^AllP− was incorporated into the sarcomere and expressed at normal levels, the mutant protein could not rescue the MyBP-C ^(t/t) phenotype. The mice developed significant cardiac hypertrophy with myofibrillar disarray and fibrosis, similar to what was observed in the MyBP-C ^(t/t) animals. In contrast, when the MyBP-C ^(t/t) mice were bred to a TG line expressing normal MyBP-C (MyBP-C ^WT ), the MyBP-C ^(t/t) phenotype was rescued. These data suggest that cMyBP-C phosphorylation is essential for normal cardiac function.

Rationale:: High-myofilament Ca ²⁺ sensitivity has been proposed as a trigger of disease pathogenesis in familial hypertrophic cardiomyopathy (HCM) on the basis of in vitro and transgenic mice studies. However, myofilament Ca ²⁺ sensitivity depends on protein phosphorylation and muscle length, and at present, data in humans are scarce. Objective:: To investigate whether high myofilament Ca ²⁺ sensitivity and perturbed length-dependent activation are characteristics for human HCM with mutations in thick and thin filament proteins. Methods and Results:: Cardiac samples from patients with HCM harboring mutations in genes encoding thick ( MYH7 , MYBPC3 ) and thin ( TNNT2 , TNNI3 , TPM1 ) filament proteins were compared with sarcomere mutation-negative HCM and nonfailing donors. Cardiomyocyte force measurements showed higher myofilament Ca ²⁺ sensitivity in all HCM samples and low phosphorylation of protein kinase A (PKA) targets compared with donors. After exogenous PKA treatment, myofilament Ca ²⁺ sensitivity was similar ( MYBPC3 _mut , TPM1 _mut , sarcomere mutation-negative HCM), higher ( MYH7 _mut , TNNT2 _mut ), or even significantly lower ( TNNI3 _mut ) compared with donors. Length-dependent activation was significantly smaller in all HCM than in donor samples. PKA treatment increased phosphorylation of PKA-targets in HCM myocardium and normalized length-dependent activation to donor values in sarcomere mutation-negative HCM and HCM with truncating MYBPC3 mutations but not in HCM with missense mutations. Replacement of mutant by wild-type troponin in TNNT2 _mut and TNNI3 _mut corrected length-dependent activation to donor values. Conclusions:: High-myofilament Ca ²⁺ sensitivity is a common characteristic of human HCM and partly reflects hypophosphorylation of PKA targets compared with donors. Length-dependent sarcomere activation is perturbed by missense mutations, possibly via posttranslational modifications other than PKA hypophosphorylation or altered protein–protein interactions, and represents a common pathomechanism in HCM.