Neonatal cardiomyopathy in mice homozygous for the Arg403Gln mutation in the α cardiac myosin heavy chain gene

Abstract

Familial hypertrophic cardiomyopathy (FHC) is inherited as an autosomal dominant trait that is characterized by unexplained hypertrophy of the ventricular myocardium with histologic evidence of myocyte and myofibrillar disarray. Myocyte loss and replacement fibrosis are often prominent features, which can contribute to arrhythmias and altered myocardial hemodynamics in FHC. Molecular genetic studies have demonstrated that FHC is caused by mutations in genes encoding cardiac sarcomere proteins; these defects are most commonly found in the β cardiac myosin heavy chain (MHC) gene (1, 2). The mechanism(s) by which mutated sarcomere proteins cause the clinical features of FHC is largely unknown.We have developed a mouse model for FHC by introducing a missense mutation identified in humans (β cardiac MHC Arg403Gln; ref. 1) into the murine α cardiac MHC gene using homologous recombination (3). In humans, the Arg403Gln mutation causes marked histopathology, ventricular dysfunction, and a high incidence of sudden death (4). Heterozygous α cardiac MHC mutant mice (α-MHC 403/+ ) develop myocardial histologic abnormalities similar to human FHC by 15 weeks of age. Sedentary α-MHC 403/+ mice have a normal life span. Homozygous α cardiac MHC mice (α-MHC 403/403 ) were generated to examine the consequences of complete replacement of normal myosin by mutant peptide. α-MHC 403/403 pups were liveborn, but, unlike their heterozygous littermates, they all died within one week.We report studies of cardiac structure and function in normal and α-MHC 403/403 mice using a new high-frequency (45 MHz) echocardiographic technique (5, 6). Our data provide the first demonstration that high-quality images can be obtained by 45-MHz echocardiography for in vivo assessment of myocardial size and contractility in neonatal mice. Markedly abnormal physiology and pathology were found in α-MHC 403/403 hearts. These data explain the neonatal lethality of homozygous mutants and provide insights into a potential etiology for myocyte death in human FHC. MethodsAnimals. Details of the targeting construct and homologous recombination procedures used in the generation of α-MHC 403/+ mice have been described previously (3). α-MHC 403/403 , α- Heterozygous mice bearing an Arg403Gln missense mutation in the α cardiac myosin heavy chain gene (α-MHC 403/+ ) exhibit the histopathologic features of human familial hypertrophic cardiomyopathy. Surprisingly, homozygous α-MHC 403/403 mice die by postnatal day 8. Here we report that neonatal lethality is caused by a fulminant dilated cardiomyopathy characterized by myocyte dysfunction and loss. Heart tissues from neonatal wild-type and α-MHC 403/403 mice demonstrate equivalent switching of MHC isoforms; α isoforms in each increase from 30% at birth to 70% by day 6. Cardiac dimensions and function, studied for the first time in neonatal mice by high frequency (45 MHz) echocardiography, were normal at birth. Between days 4 and 6, α-MHC 403/403 mice developed a rapidly progressive cardiomyopathy with left ventricular dilat...

Dilated cardiomyopathy in mice deficient for the lysosomal cysteine peptidase cathepsin L

“…To elucidate further the pathophysiology of the disease, gain-of-function and loss-of-function mouse lines for the respective genes have been generated. Some of these lines, e.g., deletions of ␦-sarcoglycan and the actin-associated muscle LIM protein MLP or a R403N point mutation in the cardiac myosin heavy chain, resemble the phenotype of human hereditary DCM (8)(9)(10). On the other hand, multiple genetically altered mouse lines developing hereditary DCM are currently lacking human counterparts, e.g., overexpression of tumor necrosis factor ␣ or retinoic receptor ␣, inactivation of the cAMP response elementbinding protein, and deletion of the bradikinin B2 receptor and the mitochondrial transcription factor A (Tfam; [11][12][13][14][15][16][17].…”

Multimodal imaging of mouse development: Tools for the postgenomic era

“…Since the initial study of mouse embryos in utero (Turnbull et al, 1995a), ultrasonography has been used for imaging and staging early postimplantation embryos in utero (Turnbull, 1999;Chang et al, 2003), and both transcutaneous and transuterine UBM has become a standard method for assessing normal and defective cardiovascular development in mice (Srinivasan et al, 1998;Fatkin et al, 1999;Phoon et al, 2000Phoon et al, , 2002Phoon et al, , 2004Ji et al, 2003;Phoon and Turnbull, 2003;Lickert et al, 2004;Mai et al, 2004;Ji and Phoon, 2005). Many of these studies have also used Doppler echocardiography, a highly sensitive method for measuring the direction and velocity of blood flow (see Phoon and Turnbull, 2003, for review).…”

Hypertrophic cardiomyopathy: from gene defect to clinical disease

“…In both myosin heavy chain and myo- sin-binding protein C mouse models, homozygosity leads to a dilated cardiomyopathy (DCM), i.e. dilatation of heart chambers with reduced contractile function [67], [68]. In the Arg403Gln homozygote mice, DCM occurs in neonates and all mice die of heart failure by age 7 days [67].…”

“…dilatation of heart chambers with reduced contractile function [67], [68]. In the Arg403Gln homozygote mice, DCM occurs in neonates and all mice die of heart failure by age 7 days [67]. In contrast, homozygous myosin-buding protein c mice develop DCM by age 3 weeks, but subsequently develop compensatory hypertrophy and indeed have a normal lifespan [68].…”

“…In addition, recent studies in a myosin-binding protein C mouse model of HCM show that while these mice may exhibit very mild disease based on cardiac function studies and histopathology analysis, electrophysiological testing suggests that there is a significantly increased vulnerability to ventricular arrhythmias, and therefore sudden death [70]. M-mode and two-dimensional echocardiography in mice has also enabled accurate assessment of left ventricular hypertrophy, changes in cardiac dimensions, and systolic function (fractional shortening) [62,[66][67][68]. More recently application of magnetic resonance imaging (MRI) has enabled detailed assessment of heart structure and even congenital malformations (e.g.…”