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The molecular phenotype of human cardiac myosin associated with hypertrophic obstructive cardiomyopathy.

Jacques AM, Briceno N, Messer AE, Gallon CE, Jalilzadeh S, Garcia E, Kikonda-Kanda G, Goddard J, Harding SE, Watkins H, Esteban MT, Tsang VT, McKenna WJ, Marston SB - Cardiovasc. Res. (2008)

Bottom Line: Failing heart myosin showed 18% reduced motility.One myectomy myosin sample produced a consistently higher sliding speed than donor heart myosin and was identified with a disease-causing heavy chain mutation (V606M).Contractility in myectomy samples resembles the hypocontractile phenotype found in end-stage failing heart muscle irrespective of the primary stimulus, and this phenotype is not a direct effect of the hypertrophy-inducing mutation.

View Article: PubMed Central - PubMed

Affiliation: Cardiac Medicine, National Heart and Lung Institute, Imperial College London, Guy Scadding Building, Dovehouse Street, London, UK.

ABSTRACT

Aim: The aim of the study was to compare the functional and structural properties of the motor protein, myosin, and isolated myocyte contractility in heart muscle excised from hypertrophic cardiomyopathy patients by surgical myectomy with explanted failing heart and non-failing donor heart muscle.

Methods: Myosin was isolated and studied using an in vitro motility assay. The distribution of myosin light chain-1 isoforms was measured by two-dimensional electrophoresis. Myosin light chain-2 phosphorylation was measured by sodium dodecyl sulphate-polyacrylamide gel electrophoresis using Pro-Q Diamond phosphoprotein stain.

Results: The fraction of actin filaments moving when powered by myectomy myosin was 21% less than with donor myosin (P = 0.006), whereas the sliding speed was not different (0.310 +/- 0.034 for myectomy myosin vs. 0.305 +/- 0.019 microm/s for donor myosin in six paired experiments). Failing heart myosin showed 18% reduced motility. One myectomy myosin sample produced a consistently higher sliding speed than donor heart myosin and was identified with a disease-causing heavy chain mutation (V606M). In myectomy myosin, the level of atrial light chain-1 relative to ventricular light chain-1 was 20 +/- 5% compared with 11 +/- 5% in donor heart myosin and the level of myosin light chain-2 phosphorylation was decreased by 30-45%. Isolated cardiomyocytes showed reduced contraction amplitude (1.61 +/- 0.25 vs. 3.58 +/- 0.40%) and reduced relaxation rates compared with donor myocytes (TT(50%) = 0.32 +/- 0.09 vs. 0.17 +/- 0.02 s).

Conclusion: Contractility in myectomy samples resembles the hypocontractile phenotype found in end-stage failing heart muscle irrespective of the primary stimulus, and this phenotype is not a direct effect of the hypertrophy-inducing mutation. The presence of a myosin heavy chain mutation causing hypertrophic cardiomyopathy can be predicted from a simple functional assay.

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Related in: MedlinePlus

Contraction of isolated myocytes from myectomy muscle. (A) Two ventricular myocytes from myectomy samples, showing branched appearance, compared with the more usual rod-shaped appearance of a ventricular myocyte from failing heart. (B) Contraction amplitude (% shortening) and time-to-50% relaxation of ventricular myocytes from myectomy (21 myocytes/10 hearts) and failing (41 myocytes/16 hearts) samples. #P < 0.001, variances significantly different; ***P < 0.001, means significantly different.
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CVN094F1: Contraction of isolated myocytes from myectomy muscle. (A) Two ventricular myocytes from myectomy samples, showing branched appearance, compared with the more usual rod-shaped appearance of a ventricular myocyte from failing heart. (B) Contraction amplitude (% shortening) and time-to-50% relaxation of ventricular myocytes from myectomy (21 myocytes/10 hearts) and failing (41 myocytes/16 hearts) samples. #P < 0.001, variances significantly different; ***P < 0.001, means significantly different.

Mentions: Ventricular myocytes from myectomy samples had a varied morphology, with some cells showing a clear rod-shaped morphology, such as those in samples from non-failing or failing ventricles, but others with a highly branched appearance (Figure 1A). Surprisingly, contraction amplitudes in myocytes from myectomy samples were low, or lower than in those from failing hearts studied during the same period, and relaxation was more impaired. Figure 1B compares myocytes at 2 mmol/L Ca2+, where amplitude was significantly lower in myectomy samples than in failing. Relaxation had a strong tendency to be slower (Figure 1) and was certainly more variable (comparison of variances P < 0.001, comparison of means with Welch's correction for unequal variances, P = 0.058). Relaxation times for myocytes from failing heart shown here were similar to those previously described from this laboratory, where relaxation times were significantly longer than those for non-failing hearts.24 At 4 mmol/L Ca2+, the amplitude difference between myectomy and failing myocytes was reduced (% shortening: myectomy 2.83 ± 0.41%, 34 cells/17 patients, failing 3.28 ± 0.21% 110 cells/40 patients), but the relaxation deficit and high variability was maintained (R90: myectomy, 0.76 ± 0.11 s, failing, 0.51 ± 0.02 s, comparison of variances P < 0.001, comparison of means with Welch's correction for unequal variances, P < 0.05).


The molecular phenotype of human cardiac myosin associated with hypertrophic obstructive cardiomyopathy.

Jacques AM, Briceno N, Messer AE, Gallon CE, Jalilzadeh S, Garcia E, Kikonda-Kanda G, Goddard J, Harding SE, Watkins H, Esteban MT, Tsang VT, McKenna WJ, Marston SB - Cardiovasc. Res. (2008)

Contraction of isolated myocytes from myectomy muscle. (A) Two ventricular myocytes from myectomy samples, showing branched appearance, compared with the more usual rod-shaped appearance of a ventricular myocyte from failing heart. (B) Contraction amplitude (% shortening) and time-to-50% relaxation of ventricular myocytes from myectomy (21 myocytes/10 hearts) and failing (41 myocytes/16 hearts) samples. #P < 0.001, variances significantly different; ***P < 0.001, means significantly different.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2492731&req=5

CVN094F1: Contraction of isolated myocytes from myectomy muscle. (A) Two ventricular myocytes from myectomy samples, showing branched appearance, compared with the more usual rod-shaped appearance of a ventricular myocyte from failing heart. (B) Contraction amplitude (% shortening) and time-to-50% relaxation of ventricular myocytes from myectomy (21 myocytes/10 hearts) and failing (41 myocytes/16 hearts) samples. #P < 0.001, variances significantly different; ***P < 0.001, means significantly different.
Mentions: Ventricular myocytes from myectomy samples had a varied morphology, with some cells showing a clear rod-shaped morphology, such as those in samples from non-failing or failing ventricles, but others with a highly branched appearance (Figure 1A). Surprisingly, contraction amplitudes in myocytes from myectomy samples were low, or lower than in those from failing hearts studied during the same period, and relaxation was more impaired. Figure 1B compares myocytes at 2 mmol/L Ca2+, where amplitude was significantly lower in myectomy samples than in failing. Relaxation had a strong tendency to be slower (Figure 1) and was certainly more variable (comparison of variances P < 0.001, comparison of means with Welch's correction for unequal variances, P = 0.058). Relaxation times for myocytes from failing heart shown here were similar to those previously described from this laboratory, where relaxation times were significantly longer than those for non-failing hearts.24 At 4 mmol/L Ca2+, the amplitude difference between myectomy and failing myocytes was reduced (% shortening: myectomy 2.83 ± 0.41%, 34 cells/17 patients, failing 3.28 ± 0.21% 110 cells/40 patients), but the relaxation deficit and high variability was maintained (R90: myectomy, 0.76 ± 0.11 s, failing, 0.51 ± 0.02 s, comparison of variances P < 0.001, comparison of means with Welch's correction for unequal variances, P < 0.05).

Bottom Line: Failing heart myosin showed 18% reduced motility.One myectomy myosin sample produced a consistently higher sliding speed than donor heart myosin and was identified with a disease-causing heavy chain mutation (V606M).Contractility in myectomy samples resembles the hypocontractile phenotype found in end-stage failing heart muscle irrespective of the primary stimulus, and this phenotype is not a direct effect of the hypertrophy-inducing mutation.

View Article: PubMed Central - PubMed

Affiliation: Cardiac Medicine, National Heart and Lung Institute, Imperial College London, Guy Scadding Building, Dovehouse Street, London, UK.

ABSTRACT

Aim: The aim of the study was to compare the functional and structural properties of the motor protein, myosin, and isolated myocyte contractility in heart muscle excised from hypertrophic cardiomyopathy patients by surgical myectomy with explanted failing heart and non-failing donor heart muscle.

Methods: Myosin was isolated and studied using an in vitro motility assay. The distribution of myosin light chain-1 isoforms was measured by two-dimensional electrophoresis. Myosin light chain-2 phosphorylation was measured by sodium dodecyl sulphate-polyacrylamide gel electrophoresis using Pro-Q Diamond phosphoprotein stain.

Results: The fraction of actin filaments moving when powered by myectomy myosin was 21% less than with donor myosin (P = 0.006), whereas the sliding speed was not different (0.310 +/- 0.034 for myectomy myosin vs. 0.305 +/- 0.019 microm/s for donor myosin in six paired experiments). Failing heart myosin showed 18% reduced motility. One myectomy myosin sample produced a consistently higher sliding speed than donor heart myosin and was identified with a disease-causing heavy chain mutation (V606M). In myectomy myosin, the level of atrial light chain-1 relative to ventricular light chain-1 was 20 +/- 5% compared with 11 +/- 5% in donor heart myosin and the level of myosin light chain-2 phosphorylation was decreased by 30-45%. Isolated cardiomyocytes showed reduced contraction amplitude (1.61 +/- 0.25 vs. 3.58 +/- 0.40%) and reduced relaxation rates compared with donor myocytes (TT(50%) = 0.32 +/- 0.09 vs. 0.17 +/- 0.02 s).

Conclusion: Contractility in myectomy samples resembles the hypocontractile phenotype found in end-stage failing heart muscle irrespective of the primary stimulus, and this phenotype is not a direct effect of the hypertrophy-inducing mutation. The presence of a myosin heavy chain mutation causing hypertrophic cardiomyopathy can be predicted from a simple functional assay.

Show MeSH
Related in: MedlinePlus