Age- and strain-related aberrant Ca²⁺release is associated with sudden cardiac death in theACTCE99K mouse model of hypertrophic cardiomyopathy

Abstract

Patients with hypertrophic cardiomyopathy, particularly young adults, can die from arrhythmia, but the mechanism underlying abnormal rhythm formation remains unknown. C57Bl6 × CBA/Ca mice carrying a cardiac actin ( ACTC) E99K (Glu99Lys) mutation reproduce many aspects of human hypertrophic cardiomyopathy, including increased myofilament Ca sensitivity and sudden death in a proportion (up to 40%) of young (28-40 day old) animals. We studied the hearts of transgenic (TG; ACTC E99K) mice and their non-TG (NTG) littermates when they were in their vulnerable period (28-40 days old) and when they were adult (8-12 wk old). Ventricular myocytes were isolated from the hearts of TG and NTG mice at these two time points. We also examined the hearts of mice that died suddenly (SCD). SCD animals had approximately four times more collagen compared with age-matched NTG mice, yet myocyte cell size was normal. Young TG mice had double the collagen content of NTG mice. Contraction and Ca transients were greater in cells from young TG mice compared with their NTG littermates but not in cells from adult mice (TG or NTG). Cells from young TG mice had a greater propensity for Ca waves than NTG littermates, and, despite similar sarcoplasmic reticulum Ca content, a proportion of these cells had larger Ca spark mass. We found that the probability of SCD in young TG mice was increased when the mutation was expressed in animals with a CBA/Ca background and almost eliminated in mice bred on a C57Bl6 background. The latter TG mice had normal cellular Ca homeostasis. NEW & NOTEWORTHY Mice with the actin Glu99Lys hypertrophic cardiomyopathy mutation ( ACTC E99K) are prone to sudden cardiac death around 40 days, associated with increased Ca transients, spark mass, and fibrosis. However, adult survivors have normal Ca transients and spark density accompanied by hypertrophy. Penetrance of the sudden cardiac death phenotype depends on the genetic background of the mouse. Listen to this article's corresponding podcast at http://ajpheart.podbean.com/e/calcium-regulation-in-e99k-mouse-heart/ .

Isogenic Pairs of hiPSC-CMs with Hypertrophic Cardiomyopathy/LVNC-Associated ACTC1 E99K Mutation Unveil Differential Functional Deficits

“…HCM patients can exhibit prolonged Ca 2+ transients ( Lan et al., 2013 ), often attributed to the presence of sarcomeric protein mutations, such as E99K-ACTC1. Indeed, previous models have shown the E99K-ACTC1 mutation to increase Ca 2+ sparks and Ca 2+ transients in young transgenic mice ( Rowlands et al., 2017 ).…”

“…We next investigated whether E99K-ACTC1 mutants showed any difference in arrhythmogenic event frequency, since clinical and animal studies usually show ECG abnormalities and a varying degree of enhanced arrhythmia in mutation carriers ( Arad et al., 2002 , Olson et al., 2000 , Monserrat et al., 2007 , Song et al., 2011 , Rowlands et al., 2017 ). Contraction traces obtained for EHTs clearly highlighted the presence of arrhythmogenic events ( Figure 5 A).…”

Modifications of Sarcoplasmic Reticulum Function Prevent Progression of Sarcomere-Linked Hypertrophic Cardiomyopathy Despite a Persistent Increase in Myofilament Calcium Response

“…Our findings demonstrate that the genetic background of the mice influences the HCM phenotype caused by TnT-R92Q mutation. Moreover, it has been previously presented in two HCM mouse models that mice expressing tropomyosin (Tm-E180G) developed a more pronounced hypertrophic phenotype in FVB/N than in C57BL/6 genetic background (Prabhakar et al, 2001;Michele et al, 2002), and in mice with a mutation in actin (ACTZ E99K), the probability of sudden cardiac death was almost completely eliminated in mice bred on C57/BL6 background (Rowlands et al, 2017). The importance of the mouse genetic background on the basal cardiac function, adaptations to exercise, or stress is also well-documented (Barnabei et al, 2010;Peng et al, 2011;Gibb et al, 2016).…”

“…PLNKO mice used in this project were in FVB/N genetic background (Gaffin et al, 2011). Since it is well-documented that genetic background may have a significant effect on the HCM phenotype (Prabhakar et al, 2001;Michele et al, 2002;Rowlands et al, 2017), we first rederived and characterized TnT-R92Q mice in FVB/N background. We crossed TnT-R92Q heterozygous male with FVB/N female and created F1 generation of mice.…”

The Molecular Mechanisms of Mutations in Actin and Myosin that Cause Inherited Myopathy

“…Finally, the majority of myopathy-causing mutations are heterozygous, indicating one normal and one mutant allele; the extent to which the abnormality is manifested is rather variable and a significant proportion of patients carrying the mutation never show the symptoms of myopathy [ 14 ]. This variable penetrance is itself largely due to a variable genetic background with some patients having compensatory genetic or epigenetic characteristics, as has been shown in mouse models [ 15 , 16 ].…”