Mouse HCM Model Expressing E99K ACTC Mutation Reproduces Phenotypes As Found In Human Patients

Abstract

The mutation Gly99lys (E99K) in the cardiac actin (ACTC) gene was reported to cause Hypertrophic Cardiomyopathy in extensive clinical studies. Transgenic (TG) mice expressing 50% E99K mutant cardiac actin in their hearts were generated and studied. The mice show high mortality between 28 and 45 days old (70% females, 34% males).Thin filaments reconstituted with purified mouse f-actin from the survivors and human heart tropomyosin and troponin were studied by in vitro motility assay. The E99K thin filaments were 2.5 ± 0.6 times more Ca2+ sensitive than NTG thin filaments (p = 0.05). E99K actin thin filaments also exhibited a reduced response to troponin dephosphorylation (EC50 E99K/E99KdP = 1.1 ± 0.1 compared with 3.0 ± 0.3 for NTG /NTGdP).7 month-old E99K TG mice (n=9) and their NTG littermates (n=7) were studied using in vivo cine MRI. Abnormal cardiac morphology and significantly lower ejection fractions (56.5 vs. 65.2%) and reduced stroke volumes (26.0 vs. 42.3 μl) were observed in TG mice. Peak LV ejection rates were also reduced (188 ± 41 vs. 252 ± 49 μl/min). LV mass was similar between groups, but septal wall thickness was increased (1.5 vs. 1.0 mm).Left ventricular function of 9 month-old female E99K NTG (n=4) and TG (n=5) mice were studied with an in vivo conductance catheter. In TG mice ejection fraction was 20.2% less, end-diastolic pressure was 39.6% higher and relaxation rate was 50.0% slower.We conclude that the basic effect of E99K mutation is increased Ca2+-sensitivity and blunted response to troponin dephosphorylation and this leads to the high rate of sudden death at early ages, alterations to cardiac function and hypertrophy as observed in patients with hypertrophic cardiomyopathy.Supported by a grant from the British Heart Foundation