Biophysical Society Thematic Meeting | Canterbury 2023

Towards a More Perfect Union: Multi-Scale Models of Muscle and Their Experimental Validation

Poster Abstracts

27-POS Board 27 MODEL OF TRANSCRIPTIONAL BURSTING EXPLAINS INTERCELLULAR VARIABILITY OBSERVED IN HYPERTROPHIC CARDIOMYOPATHY WITH MUTATIONS IN MYOSIN HEAVY CHAIN OR TROPONIN I Ante Radocaj 1 ; Valentin Burkart 1 ; Kathrin Kowalski 1 ; Judith Montag 1 ; Theresia Kraft 1 ; 1 Hannover Medical School, Institute for Molecular and Cell Physiology, Hannover, Germany Hypertrophic cardiomyopathy (HCM) in most mutation-positive patients is caused by heterozygous mutations in sarcomeric proteins. We observed that HCM is often associated with an increased variability between cardiomyocytes, which is significantly larger than between cardiomyocytes from donors. This variability includes transcriptional activity, mRNA expression and contraction as well as morphological parameters. We hypothesize that the observed variability can be explained by transcription of both, mutated and wildtype alleles, occurring in independent stochastic bursts. We developed a numerical model based on the Euler method which entails (i) the polyploidy of cardiomyocytes, (ii) the stochastic burst-like activation of both alleles, (iii) the synthesis of pre-mRNA, (iv) the splicing of pre-mRNA to mRNA and mRNA degradation, and (v) the synthesis and degradation of the affected protein. We applied the model to two different heterozygous myosin mutations and one heterozygous troponin I mutation. The corresponding rate constants for mRNA and protein synthesis and degradations were taken from the literature. By fitting the distribution of ploidy and the rate constants for activation and inactivation of transcription and for the splicing of pre-mRNA to mRNA, we were able to closely reproduce the observed distributions of active transcription sites in the nuclei, of the absolute mRNA counts, of the mutant to wildtype mRNA ratio, and of the produced force at intermediate calcium concentrations. We conclude that for all three studied HCM mutations the observed phenotypical variations could be associated with the mechanism of stochastic transcriptional bursting.

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