scholarly journals Impact of familial hypertrophic cardiomyopathy-linked mutations in the NH2 terminus of the RLC on β-myosin cross-bridge mechanics

2014 ◽  
Vol 117 (12) ◽  
pp. 1471-1477 ◽  
Author(s):  
Gerrie P. Farman ◽  
Priya Muthu ◽  
Katarzyna Kazmierczak ◽  
Danuta Szczesna-Cordary ◽  
Jeffrey R. Moore
Keyword(s):  
Hypertrophic Cardiomyopathy ◽  
Familial Hypertrophic Cardiomyopathy ◽  
Sarcomeric Proteins ◽  
Motion Generation ◽  
In Vitro Motility Assay ◽  
In Vitro Motility ◽  
Cross Bridge ◽  
Significant Difference ◽  
The Impact

Familial hypertrophic cardiomyopathy (HCM) is associated with mutations in sarcomeric proteins, including the myosin regulatory light chain (RLC). Here we studied the impact of three HCM mutations located in the NH2 terminus of the RLC on the molecular mechanism of β-myosin heavy chain (MHC) cross-bridge mechanics using the in vitro motility assay. To generate mutant β-myosin, native RLC was depleted from porcine cardiac MHC and reconstituted with mutant (A13T, F18L, and E22K) or wild-type (WT) human cardiac RLC. We characterized the mutant myosin force and motion generation capability in the presence of a frictional load. Compared with WT, all three mutants exhibited reductions in maximal actin filament velocity when tested under low or no frictional load. The actin-activated ATPase showed no significant difference between WT and HCM-mutant-reconstituted myosins. The decrease in velocity has been attributed to a significantly increased duty cycle, as was measured by the dependence of actin sliding velocity on myosin surface density, for all three mutant myosins. These results demonstrate a mutation-induced alteration in acto-myosin interactions that may contribute to the pathogenesis of HCM.

scholarly journals Facilitated Cross-Bridge Interactions with Thin Filaments by Familial Hypertrophic Cardiomyopathy Mutations inα-Tropomyosin

2011 ◽  
Vol 2011 ◽  
pp. 1-12 ◽  
Author(s):  
Fang Wang ◽  
Nicolas M. Brunet ◽  
Justin R. Grubich ◽  
Ewa A. Bienkiewicz ◽  
Thomas M. Asbury ◽  
...  
Keyword(s):  
Hypertrophic Cardiomyopathy ◽  
Molecular Mechanisms ◽  
Helical Structure ◽  
Familial Hypertrophic Cardiomyopathy ◽  
Maximum Speed ◽  
Sliding Speed ◽  
Thin Filaments ◽  
In Vitro Motility ◽  
Cardiac Sarcomeres

Familial hypertrophic cardiomyopathy (FHC) is a disease of cardiac sarcomeres. To identify molecular mechanisms underlying FHC pathology, functional and structural differences in three FHC-related mutations in recombinantα-Tm (V95A, D175N, and E180G) were characterized using both conventional and modified in vitro motility assays and circular dichroism spectroscopy. Mutant Tm's exhibited reducedα-helical structure and increased unordered structure. When thin filaments were fully occupied by regulatory proteins, little or no motion was detected at pCa 9, and maximum speed (pCa 5) was similar for all tropomyosins. Ca2+-responsiveness of filament sliding speed was increased either by increasedpCa50(V95A), reduced cooperativityn(D175N), or both (E180G). When temperature was increased, thin filaments with E180G exhibited dysregulation at temperatures ~10°C lower, and much closer to body temperature, than WT. When HMM density was reduced, thin filaments with D175N required fewer motors to initiate sliding or achieve maximum sliding speed.

Differential cross-bridge kinetics of FHC myosin mutations R403Q and R453C in heterozygous mouse myocardium

2004 ◽  
Vol 287 (1) ◽  
pp. H91-H99 ◽  
Author(s):  
Bradley M. Palmer ◽  
David E. Fishbaugher ◽  
Joachim P. Schmitt ◽  
Yuan Wang ◽  
Norman R. Alpert ◽  
...  
Keyword(s):  
Point Mutations ◽  
Force Production ◽  
Calcium Sensitivity ◽  
Isometric Tension ◽  
Familial Hypertrophic Cardiomyopathy ◽  
Maximal Velocity ◽  
In Vitro Motility Assay ◽  
Sinusoidal Analysis ◽  
Cross Bridge

The kinetic effects of the cardiac myosin point mutations R403Q and R453C, which underlie lethal forms of familial hypertrophic cardiomyopathy (FHC), were assessed using isolated myosin and skinned strips taken from heterozygous (R403Q/+ and R453C/+) male mouse hearts. Compared with wild-type (WT) mice, actin-activated ATPase was increased by 38% in R403Q/+ and reduced by 45% in R453C/+, maximal velocity of regulated thin filament ( VRTF) in the in vitro motility assay was increased by 8% in R403Q/+ and was not different in R453C/+, myosin concentration at half-maximal VRTF was reduced by 30% in R403Q/+ and not different in R453C/+, and the characteristic frequency for oscillatory work production ( b frequency), determined by sinusoidal analysis in the skinned strip at maximal calcium activation, was 27% lower in R403Q/+ and 18% higher in R453C/+. The calcium sensitivity for isometric tension in the skinned strip was not different in R403Q/+ (pCa50 5.64 ± 0.02) and significantly enhanced in R453C/+ (5.82 ± 0.03) compared with WT (5.58 ± 0.02). We conclude that isolated myosin and skinned strips of R403Q/+ and R453C/+ myocardium show marked differences in cross-bridge kinetic parameters and in calcium sensitivity of force production that indicate different functional roles associated with the location of each point mutation at the molecular level.

Molecular and phenotypic effects of heterozygous, homozygous, and compound heterozygote myosin heavy-chain mutations

2005 ◽  
Vol 288 (3) ◽  
pp. H1097-H1102 ◽  
Author(s):  
Norman R. Alpert ◽  
Saidi A. Mohiddin ◽  
Dorothy Tripodi ◽  
Jacqueline Jacobson-Hatzell ◽  
Kelly Vaughn-Whitley ◽  
...  
Keyword(s):  
Myosin Heavy Chain ◽  
Heavy Chain ◽  
Mechanical Performance ◽  
Left Ventricular ◽  
Familial Hypertrophic Cardiomyopathy ◽  
In Vitro Motility Assay ◽  
In Vitro Motility ◽  
Common Causes ◽  
Disease Penetrance

Autosomal dominant familial hypertrophic cardiomyopathy (FHC) has variable penetrance and phenotype. Heterozygous mutations in MYH7 encoding β-myosin heavy chain are the most common causes of FHC, and we proposed that “enhanced” mutant actin-myosin function is the causative molecular abnormality. We have studied individuals from families in which members have two, one, or no mutant MYH7 alleles to examine for dose effects. In one family, a member homozygous for Lys207Gln had cardiomyopathy complicated by left ventricular dilatation, systolic impairment, atrial fibrillation, and defibrillator interventions. Only one of five heterozygous relatives had FHC. Leu908Val and Asp906Gly mutations were detected in a second family in which penetrance for Leu908Val heterozygotes was 46% (21/46) and 25% (3/12) for Asp906Gly. Despite the low penetrance, hypertrophy was severe in several heterozygotes. Two individuals with both mutations developed severe FHC. The velocities of actin translocation ( Vactin) by mutant and wild-type (WT) myosins were compared in the in vitro motility assay. Compared with WT/WT, Vactin was 34% faster for WT/D906G and 21% for WT/L908V. Surprisingly Vactin for Leu908Val/Asp906Gly and Lys207Gln/Lys207Gln mutants were similar to WT. The apparent enhancement of mechanical performance with mutant/WT myosin was not observed for mutant/mutant myosin. This suggests that Vactin may be a poor predictor of disease penetrance or severity and that power production may be more appropriate, or that the limited availability of double mutant patients prohibits any definitive conclusions. Finally, severe FHC in heterozygous individuals can occur despite very low penetrance, suggesting these mutations alone are insufficient to cause FHC and that uncharacterized modifying mechanisms exert powerful influences.

Familial hypertrophic cardiomyopathy mutations in troponin I (K183Δ, G203S, K206Q) enhance filament sliding

2003 ◽  
Vol 14 (2) ◽  
pp. 117-128 ◽  
Author(s):  
Jan Köhler ◽  
Ying Chen ◽  
Bernhard Brenner ◽  
Albert M. Gordon ◽  
Theresia Kraft ◽  
...  
Keyword(s):  
Hypertrophic Cardiomyopathy ◽  
Troponin I ◽  
Isometric Force ◽  
Familial Hypertrophic Cardiomyopathy ◽  
In Vitro Assays ◽  
Maximum Speed ◽  
Exchange Method ◽  
In Vitro Motility ◽  
Maximum Isometric Force

A major cause of familial hypertrophic cardiomyopathy (FHC) is dominant mutations in cardiac sarcomeric genes. Linkage studies identified FHC-related mutations in the COOH terminus of cardiac troponin I (cTnI), a region with unknown function in Ca2+ regulation of the heart. Using in vitro assays with recombinant rat troponin subunits, we tested the hypothesis that mutations K183Δ, G203S, and K206Q in cTnI affect Ca2+ regulation. All three mutants enhanced Ca2+ sensitivity and maximum speed ( smax) of filament sliding of in vitro motility assays. Enhanced smax (pCa 5) was observed with rabbit skeletal and rat cardiac (α-MHC or β-MHC) heavy meromyosin (HMM). We developed a passive exchange method for replacing endogenous cTn in permeabilized rat cardiac trabeculae. Ca2+ sensitivity and maximum isometric force did not differ between preparations exchanged with cTn(cTnI,K206Q) or wild-type cTn. In both trabeculae and motility assays, there was no loss of inhibition at pCa 9. These results are consistent with COOH terminus of TnI modulating actomyosin kinetics during unloaded sliding, but not during isometric force generation, and implicate enhanced cross-bridge cycling in the cTnI-related pathway(s) to hypertrophy.

scholarly journals Cardioinotropic Effects in Subchronic Intoxication of Rats with Lead and/or Cadmium Oxide Nanoparticles

2021 ◽  
Vol 22 (7) ◽  
pp. 3466
Author(s):  
Svetlana V. Klinova ◽  
Boris A. Katsnelson ◽  
Ilzira A. Minigalieva ◽  
Oksana P. Gerzen ◽  
Alexander A. Balakin ◽  
...  
Keyword(s):  
Cadmium Oxide ◽  
Male Rats ◽  
Sliding Velocity ◽  
Muscle Type ◽  
In Vitro Motility Assay ◽  
Thin Filaments ◽  
In Vitro Motility ◽  
Toxic Impact ◽  
Cdo Nanoparticles

Subchronic intoxication was induced in outbred male rats by repeated intraperitoneal injections with lead oxide (PbO) and/or cadmium oxide (CdO) nanoparticles (NPs) 3 times a week during 6 weeks for the purpose of examining its effects on the contractile characteristics of isolated right ventricle trabeculae and papillary muscles in isometric and afterload contractions. Isolated and combined intoxication with these NPs was observed to reduce the mechanical work produced by both types of myocardial preparation. Using the in vitro motility assay, we showed that the sliding velocity of regulated thin filaments drops under both isolated and combined intoxication with CdO–NP and PbO–NP. These results correlate with a shift in the expression of myosin heavy chain (MHC) isoforms towards slowly cycling β–MHC. The type of CdO–NP + PbO–NP combined cardiotoxicity depends on the effect of the toxic impact, the extent of this effect, the ratio of toxicant doses, and the degree of stretching of cardiomyocytes and muscle type studied. Some indices of combined Pb–NP and CdO–NP cardiotoxicity and general toxicity (genotoxicity included) became fully or partly normalized if intoxication developed against background administration of a bioprotective complex.

Worldwide differences in primary prevention implantable cardioverter defibrillator utilization and outcomes in hypertrophic cardiomyopathy

2021 ◽  
Author(s):  
Victor Nauffal ◽  
Peter Marstrand ◽  
Larry Han ◽  
Victoria N Parikh ◽  
Adam S Helms ◽  
...  
Keyword(s):  
Hypertrophic Cardiomyopathy ◽  
Primary Prevention ◽  
Implantable Cardioverter Defibrillator ◽  
Cox Proportional Hazards ◽  
Icd Implantation ◽  
Icd Therapy ◽  
Cardioverter Defibrillator ◽  
Significant Difference ◽  
Implantation Rates ◽  
The Impact

Abstract Aims  Risk stratification algorithms for sudden cardiac death (SCD) in hypertrophic cardiomyopathy (HCM) and regional differences in clinical practice have evolved over time. We sought to compare primary prevention implantable cardioverter defibrillator (ICD) implantation rates and associated clinical outcomes in US vs. non-US tertiary HCM centres within the international Sarcomeric Human Cardiomyopathy Registry. Methods and results We included patients with HCM enrolled from eight US sites (n = 2650) and five non-US (n = 2660) sites and used multivariable Cox-proportional hazards models to compare outcomes between sites. Primary prevention ICD implantation rates in US sites were two-fold higher than non-US sites (hazard ratio (HR) 2.27 [1.89–2.74]), including in individuals deemed at high 5-year SCD risk (≥6%) based on the HCM risk-SCD score (HR 3.27 [1.76–6.05]). US ICD recipients also had fewer traditional SCD risk factors. Among ICD recipients, rates of appropriate ICD therapy were significantly lower in US vs. non-US sites (HR 0.52 [0.28–0.97]). No significant difference was identified in the incidence of SCD/resuscitated cardiac arrest among non-recipients of ICDs in US vs. non-US sites (HR 1.21 [0.74–1.97]). Conclusion  Primary prevention ICDs are implanted more frequently in patients with HCM in US vs. non-US sites across the spectrum of SCD risk. There was a lower rate of appropriate ICD therapy in US sites, consistent with a lower-risk population, and no significant difference in SCD in US vs. non-US patients who did not receive an ICD. Further studies are needed to understand what drives malignant arrhythmias, optimize ICD allocation, and examine the impact of different ICD utilization strategies on long-term outcomes in HCM.

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