Sex dimorphisms of crossbridge cycling kinetics in transgenic hypertrophic cardiomyopathy mice

Familial hypertrophic cardiomyopathy (HCM) is a disease of the sarcomere and may lead to hypertrophic, dilated, restrictive, and/or arrhythmogenic cardiomyopathy, congestive heart failure, or sudden cardiac death. We hypothesized that hearts from transgenic HCM mice harboring a mutant myosin heavy chain increase the energetic cost of contraction in a sex-specific manner. To do this, we assessed Ca2+ sensitivity of tension and crossbridge kinetics in demembranated cardiac trabeculas from male and female wild-type (WT) and HCM hearts at an early time point (2 mo of age). We found a significant effect of sex on Ca2+ sensitivity such that male, but not female, HCM mice displayed a decrease in Ca2+ sensitivity compared with WT counterparts. The HCM transgene and sex significantly impacted the rate of force redevelopment by a rapid release-restretch protocol and tension cost by the ATPase-tension relationship. In each of these measures, HCM male trabeculas displayed a gain-of-function when compared with WT counterparts. In addition, cardiac remodeling measured by echocardiography, histology, morphometry, and posttranslational modifications demonstrated sex- and HCM-specific effects. In conclusion, female and male HCM mice display sex dimorphic crossbridge kinetics accompanied by sex- and HCM-dependent cardiac remodeling at the morphometric, histological, and cellular level.

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Temporal and mutation-specific alterations in Ca2+ homeostasis differentially determine the progression of cTnT-related cardiomyopathies in murine models

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.01143.2008 ◽

2009 ◽

Vol 297 (2) ◽

pp. H614-H626 ◽

Cited By ~ 38

Author(s):

Pia J. Guinto ◽

Todd E. Haim ◽

Candice C. Dowell-Martino ◽

Nathaniel Sibinga ◽

Jil C. Tardiff

Keyword(s):

Hypertrophic Cardiomyopathy ◽

Ventricular Myocytes ◽

Troponin T ◽

Early Time ◽

Left Ventricular ◽

Familial Hypertrophic Cardiomyopathy ◽

Compensatory Mechanism ◽

Missense Mutations ◽

Tail Domain ◽

Cellular Mechanics

Naturally occurring mutations in cardiac troponin T (cTnT) result in a clinical subset of familial hypertrophic cardiomyopathy. To determine the mechanistic links between thin-filament mutations and cardiovascular phenotypes, we have generated and characterized several transgenic mouse models carrying cTnT mutations. We address two central questions regarding the previously observed changes in myocellular mechanics and Ca2+ homeostasis: 1) are they characteristic of all severe cTnT mutations, and 2) are they primary (early) or secondary (late) components of the myocellular response? Adult left ventricular myocytes were isolated from 2- and 6-mo-old transgenic mice carrying missense mutations at residue 92, flanking the TNT1 NH2-terminal tail domain. Results from R92L and R92W myocytes showed mutation-specific alterations in contraction and relaxation indexes at 2 mo with improvements by 6 mo. Alterations in Ca2+ kinetics remained consistent with mechanical data in which R92L and R92W exhibited severe diastolic impairments at the early time point that improved with increasing age. A normal regulation of Ca2+ kinetics in the context of an altered baseline cTnI phosphorylation suggested a pathogenic mechanism at the myofilament level taking precedence for R92L. The quantitation of Ca2+-handling proteins in R92W mice revealed a synergistic compensatory mechanism involving an increased Ser16 and Thr17 phosphorylation of phospholamban, contributing to the temporal onset of improved cellular mechanics and Ca2+ homeostasis. Therefore, independent cTnT mutations in the TNT1 domain result in primary mutation-specific effects and a differential temporal onset of altered myocellular mechanics, Ca2+ kinetics, and Ca2+ homeostasis, complex mechanisms which may contribute to the clinical variability in cTnT-related familial hypertrophic cardiomyopathy mutations.

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Abstract 345: R403Q Mutation Increases the Rate of Force Redevelopment in 2 Month Mice

Circulation Research ◽

10.1161/res.113.suppl_1.a345 ◽

2013 ◽

Vol 113 (suppl_1) ◽

Author(s):

Camille Birch ◽

John P Konhilas

Keyword(s):

Steady State ◽

Hypertrophic Cardiomyopathy ◽

Cardiac Tissue ◽

Muscle Length ◽

Familial Hypertrophic Cardiomyopathy ◽

Force Generation ◽

Energetic Cost ◽

Cardiac Pathology ◽

Myofilament Function ◽

Isotonic Shortening

Familial hypertrophic cardiomyopathy is a primary disease of the sarcomere. The R403Q mutation resides at the actin-interaction site on myosin and leads to progressive hypertrophic cardiomyopathy which progresses towards heart failure. Along with deteriorating cardiac function, these hearts experience an overall change in metabolic landscape, suggesting altered energetic function in hearts that express the R403Q mutation. We tested the hypothesis that the R403Q mutation intrinsically increases the energetic cost of contraction. To do this, we determined myofilament function in demembranated cardiac trabeculae from male wild-type (WT) and R403Q mice at 2 months of age, prior to overt signs of cardiac pathology. Firstly, steady-state Ca2+ sensitivity of force generation was not significantly different between male R403Q (n=4) and WT counterparts (n=2) consistent with previous findings. Secondly, the rate of force redevelopment (ktr) in skinned cardiac tissue was measured following unloaded isotonic shortening and a rapid re-stretch to 15% of the original muscle length at a sarcomere length of 2.0μm. R403Q mice display an increased rate of force redevelopment (49.89 s-1 ± 8.13, n = 4) compared to WT counterparts (24.52 ± 4.29, n = 6) at maximal activation indicating an increase in the apparent rates of crossbridges entering and leaving force-generating states (p < 0.05). In conclusion, the R403Q mutation does not impact steady-state Ca2+ sensitivity of force but increases total crossbridge cycling rate suggesting a higher energy cost of force generation. Future studies are aimed at determining the energetic cost of contraction in R403Q hearts and how this increased energetic cost leads to hypertrophic cardiomyopathy.

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Increased Tension Cost in Human Familial Hypertrophic Cardiomyopathy Caused by the MYH7 Mutation R403Q

Biophysical Journal ◽

10.1016/j.bpj.2012.11.881 ◽

2013 ◽

Vol 104 (2) ◽

pp. 156a

Author(s):

E. Rosalie Witjas-Paalberends ◽

Nicoletta Piroddi ◽

Beatrice Scellini ◽

Ger J. Stienen ◽

Chiara Tesi ◽

...

Keyword(s):

Hypertrophic Cardiomyopathy ◽

Familial Hypertrophic Cardiomyopathy ◽

Tension Cost

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Microarray analysis of active cardiac remodeling genes in a familial hypertrophic cardiomyopathy mouse model rescued by a phospholamban knockout

Physiological Genomics ◽

10.1152/physiolgenomics.00023.2013 ◽

2013 ◽

Vol 45 (17) ◽

pp. 764-773 ◽

Cited By ~ 7

Author(s):

Sudarsan Rajan ◽

James R. Pena ◽

Anil G. Jegga ◽

Bruce J. Aronow ◽

Beata M. Wolska ◽

...

Keyword(s):

Hypertrophic Cardiomyopathy ◽

Mouse Model ◽

Microarray Analysis ◽

Cardiac Remodeling ◽

Gene Knockout ◽

Left Ventricular ◽

Familial Hypertrophic Cardiomyopathy ◽

Ventricular Tissue ◽

Microarray Analyses ◽

Insight Into

Familial hypertrophic cardiomyopathy (FHC) is a disease characterized by ventricular hypertrophy, fibrosis, and aberrant systolic and/or diastolic function. Our laboratories have previously developed two mouse models that affect cardiac performance. One mouse model encodes an FHC-associated mutation in α-tropomyosin: Glu → Gly at amino acid 180, designated as Tm180. These mice display a phenotype that is characteristic of FHC, including severe cardiac hypertrophy with fibrosis and impaired physiological performance. The other model was a gene knockout of phospholamban (PLN KO), a regulator of calcium uptake in the sarcoplasmic reticulum of cardiomyocytes; these hearts exhibit hypercontractility with no pathological abnormalities. Previous work in our laboratories shows that when mice were genetically crossed between the PLN KO and Tm180, the progeny (PLN KO/Tm180) display a rescued hypertrophic phenotype with improved morphology and cardiac function. To understand the changes in gene expression that occur in these models undergoing cardiac remodeling (Tm180, PLN KO, PLN KO/Tm180, and nontransgenic control mice), we conducted microarray analyses of left ventricular tissue at 4 and 12 mo of age. Expression profiling reveals that 1,187 genes changed expression in direct response to the three genetic models. With these 1,187 genes, 11 clusters emerged showing normalization of transcript expression in the PLN KO/Tm180 hearts. In addition, 62 transcripts are highly involved in suppression of the hypertrophic phenotype. Confirmation of the microarray analysis was conducted by quantitative RT-PCR. These results provide insight into genes that alter expression during cardiac remodeling and are active during modulation of the cardiomyopathic phenotype.

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N-acetylcysteine reverses diastolic dysfunction and hypertrophy in familial hypertrophic cardiomyopathy

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.00339.2015 ◽

2015 ◽

Vol 309 (10) ◽

pp. H1720-H1730 ◽

Cited By ~ 36

Author(s):

Tanganyika Wilder ◽

David M. Ryba ◽

David F. Wieczorek ◽

Beata M. Wolska ◽

R. John Solaro

Keyword(s):

Hypertrophic Cardiomyopathy ◽

Diastolic Dysfunction ◽

Diastolic Function ◽

Familial Hypertrophic Cardiomyopathy ◽

Cross Bridge ◽

Myosin Binding Protein ◽

Myosin Binding Protein C ◽

Plasmic Reticulum ◽

Extracellular Signal ◽

Tension Cost

S-glutathionylation of cardiac myosin-binding protein C (cMyBP-C) induces Ca2+ sensitization and a slowing of cross-bridge kinetics as a result of increased oxidative signaling. Although there is evidence for a role of oxidative stress in disorders associated with hypertrophic cardiomyopathy (HCM), this mechanism is not well understood. We investigated whether oxidative myofilament modifications may be in part responsible for diastolic dysfunction in HCM. We administered N-acetylcysteine (NAC) for 30 days to 1-mo-old wild-type mice and to transgenic mice expressing a mutant tropomyosin (Tm-E180G) and nontransgenic littermates. Tm-E180G hearts demonstrate a phenotype similar to human HCM. After NAC administration, the morphology and diastolic function of Tm-E180G mice was not significantly different from controls, indicating that NAC had reversed baseline diastolic dysfunction and hypertrophy in our model. NAC administration also increased sarco(endo)plasmic reticulum Ca2+ ATPase protein expression, reduced extracellular signal-related kinase 1/2 phosphorylation, and normalized phosphorylation of phospholamban, as assessed by Western blot. Detergent-extracted fiber bundles from NAC-administered Tm-E180G mice showed nearly nontransgenic (NTG) myofilament Ca2+ sensitivity. Additionally, we found that NAC increased tension cost and rate of cross-bridge reattachment. Tm-E180G myofilaments were found to have a significant increase in S-glutathionylation of cMyBP-C, which was returned to NTG levels upon NAC administration. Taken together, our results indicate that oxidative myofilament modifications are an important mediator in diastolic function, and by relieving this modification we were able to reverse established diastolic dysfunction and hypertrophy in HCM.

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