Abstract 20232: Haploinsufficiency of MYBPC3 in the Development of Hypertrophic Cardiomyopathy
Introduction: Mutations in MYBPC3, encoding cardiac myosin binding protein-C (cMyBP-C), account for ~40% of hypertrophic cardiomyopathy (HCM) cases. MYBPC3 mutations are usually encode truncated proteins and are not found in tissue and are typically heterozygous (Het) in humans. Reduced protein levels occur in human HCM patients with these mutations, suggesting haploinsufficiency. However, it is unknown if cMyBP-C reduction causes or results from hypertrophy.
Hypothesis: To test whether haploinsufficiency occurs following cardiac stress and if heterozygous MYBPC3 mice had worsened disease progression.
Methods & Results: Transverse aortic constriction (TAC) was performed on 3 month old wild type (WT) and Het MYBPC3 truncation mutant mice which were allowed to hypertrophy for 4 or 12 weeks. Het TAC mice showed increased hypertrophy 12 weeks post-TAC compared to WT TAC controls. Het TAC hearts showed reduced ejection fraction compared to WT TAC at 4 and 12 weeks. MYBPC3 transcript levels were significantly reduced in sham and TAC Het hearts. cMyBP-C levels decreased in Het sham and TAC at 4 weeks but returned to baseline levels at 12 weeks. Het TAC myocytes showed higher Ca2+ sensitivity at 4 weeks, and impaired maximal force development. Het sham and TAC skinned cardiomyocytes showed reduced length dependent increases in Ca2+ sensitivity and maximal force development. RNA-Seq shows no alterations in proteasome of RNA-degradation pathways which have been suggested to play a role in the pathology of these mutations. Overexpression of WT cMyBP-C in the presence of truncated MYBPC3 rescued the decline in force observed in Het myocytes in the absence of stress.
Conclusions: Heterozygous MYBPC3 truncation mutant carriers develop more profound hypertrophy and dysfunction following stress. Also, increased MYBPC3 expression reverses myocyte deficits in force generation in the presence of truncated alleles.
Author Disclosures: D. Barefield: None. M. Kumar: None. J. Gorham: None. J. Seidman: None. C. Seidman: None. P. de Tombe: None. S. Sadayappan: None.
This research has received full or partial funding support from the American Heart Association.
- © 2014 by American Heart Association, Inc.