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


CONCLUSIONS
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.
Jacques
Adam M
AM
Cardiac Medicine, National Heart and Lung Institute, Imperial College London, Guy Scadding Building, Dovehouse Street, London, UK.
Briceno
Natalia
N
Messer
Andrew E
AE
Gallon
Clare E
CE
Jalilzadeh
Shapour
S
Garcia
Edwin
E
Kikonda-Kanda
Gaelle
G
Goddard
Jennifer
J
Harding
Sian E
SE
Watkins
Hugh
H
Esteban
M Tomé
MT
Tsang
Victor T
VT
McKenna
William J
WJ
Marston
Steven B
SB
D008841:Actin Cytoskeleton / Q000378:metabolism; D000328:Adult; D024722:Cardiac Myosins / Q000235:genetics / Q000378:metabolism*; D002312:Cardiomyopathy, Hypertrophic / Q000235:genetics / Q000378:metabolism* / Q000503:physiopathology; D005838:Genotype; D006333:Heart Failure / Q000235:genetics / Q000378:metabolism* / Q000503:physiopathology; D006801:Humans; D008875:Middle Aged; D009119:Muscle Contraction; D009154:Mutation; D032383:Myocytes, Cardiac / Q000378:metabolism*; D018995:Myosin Heavy Chains / Q000378:metabolism; D018994:Myosin Light Chains / Q000378:metabolism; D010641:Phenotype; D010766:Phosphorylation; D055815:Young Adult
C501641:MYH7 protein, human; D018994:Myosin Light Chains; C491915:hALC-1 protein, human; C107184:myosin light chain 2; C076659:myosin light chain I; D024722:Cardiac Myosins; D018995:Myosin Heavy Chains