Abstract 5291: Mouse Model of Familial Hypertrophic Cardiomyopathy with E99K ACTC Mutation Recapitulates Many Features of Hypertrophic Cardiomyopathy in Patients
The mutation Gly99lys (E99K) in the cardiac actin (ACTC) gene is reported to cause hypertrophic cardiomyopathy (HCM). Transgenic (TG) mice expressing 55% E99K mutant cardiac actin in their hearts were generated and studied. Over 30% male and 70% female E99K mice died between 30 and 45 days, which indicates a phenotype of sudden death at early ages, as found in patients with HCM. An in vitro motility assay was employed to compare the functional properties of actin isolated from the E99K mouse hearts with non-transgenic mouse actin. The sliding speed of pure E99K actin was 8% lower than NTG mouse actin (p = 0.004), whilst the percentage of actin filaments moving was not significantly different. Thin filaments were reconstituted with purified mouse actin (same sequence as human) and tropomyosin and troponin isolated from non-failing human heart muscle. Sliding speed was the same for E99K and NTG, but the E99K thin filaments were 2.5 ± 0.6 times more Ca2+ sensitive than NTG thin filaments (p = 0.05). E99K actin also exhibited a reduced response to troponin dephosphorylation. Thus, at the single filament level E99K actin shows a gain of function phenotype typical of HCM mutations. 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 and reduced stroke volumes were observed in 7 month old TG mice. End-diastolic volume and peak LV ejection rates were also reduced. Left ventricular function of 9 month-old female E99K WT (n=4) and TG (n=5) mice were studied with an in vivo conductance catheter advanced through the apex after an anterior thoracotomy under 1.5% isoflurane. Compared with the NTG mice, the TG mice had significantly reduced ejection fraction (61 ± 2 vs. 77 ± 4 %, p=0.01), increased end-diastolic pressure (14.0 ± 0.9 vs. 8.5 ± 1.7 mmHg, p=0.02), and reduced relaxation rate (Tau g, 21 ± 2 vs. 11 ± 1, p=0.003). We conclude that the high death rate at early ages, alterations to cardiac function, septal thickening, increased Ca2+-sensitivity and progression towards a failing heart phenotype recapitulate many characteristics of hypertrophic cardiomyopathy, as observed in patients with the mutation.
Supported by a grant from the British Heart Foundation