Abstract 17166: Hypertrophic Cardiomyopathy - Random Burst-like Transcription of Mutated and Wildtype Alleles as Trigger for Phenotype Development
Mutations in at least 20 different sarcomeric and some non-sarcomeric proteins have been identified in Hypertrophic Cardiomyopathy (HCM). Generally, development of the HCM phenotype is thought to result from functional effects of the respective mutation. Yet, a common mechanism has not yet been identified.
From our previous work we hypothesized that at least for mutations in the beta-myosin heavy chain (β-MyHC, MYH7) contractile imbalance among individual cardiomyocytes due to cell-to-cell variation in the expression of mutated myosin triggers development of HCM-features like myocyte disarray and fibrosis. Stochastic burst-like transcription of the two MYH7-alleles maybe the mechanism leading to this allelic imbalance.
To test this hypothesis we analyzed (i) contractile function of cardiomyocytes of HCM-patients with β-MyHC-mutations Arg723Gly and Ala200Val, (ii) the fraction of mutant MYH7-mRNA in individual cardiomyocytes isolated from the same patients’ samples, (iii) activity of transcription sites in individual cardiomyocytes by FISH (fluorescence in-situ hybridization), and performed (iv) model simulation of burst-like transcription.
For both mutations, altered calcium-sensitivity with significant cell-to-cell variability was found. This was consistent with MYH7-mRNA quantification showing a highly variable fraction of mutated mRNA ranging from cardiomyocytes expressing essentially pure mutant to others with essentially pure wildtype MYH7-mRNA. FISH of cardiomyocytes revealed nuclei with no active transcription sites, inconsistent with continuous transcription of MYH7. Model simulations of independent burst-like transcription of mutant and wildtype alleles showed large cell-to-cell variability in mutant MYH7-mRNA and β-MyHC-protein, just like our cell-by-cell quantifications.
In conclusion, we show that cell-to-cell contractile variability, presumably by variation in mutant mRNA and protein most likely is due to random, independent, burst-like transcription of mutant and wildtype MYH7-alleles. In HCM-patients, the contractile imbalance over time can induce cardiomyocyte distortions, and lead to fibrosis. HCM-mutations in other sarcomeric proteins could have the same underlying disease mechanism.
Author Disclosures: T. Kraft: None. K. Kowalski: None. J. Montag: None. A. Radocaj: None. M. Makul: None. P. Ernstberger: None. A. Perrot: None. A. Francino: None. F. Navarro-Lopez: None. B. Brenner: None.
- © 2016 by American Heart Association, Inc.