Dilated cardiomyopathy mutations in three thin filament regulatory proteins result in a common functional phenotype.
Dilated cardiomyopathy (DCM), characterized by cardiac dilatation and contractile dysfunction, is a major cause of heart failure. Inherited DCM can result from mutations in the genes encoding cardiac troponin T, troponin C, and alpha-tropomyosin; different mutations in the same genes cause hypertrophic cardiomyopathy. To understand how certain mutations lead specifically to DCM, we have investigated their effect on contractile function by comparing wild-type and mutant recombinant proteins. Because initial studies on two troponin T mutations have generated conflicting findings, we analyzed all eight published DCM mutations in troponin T, troponin C, and alpha-tropomyosin in a range of in vitro assays. Thin filaments, reconstituted with a 1:1 ratio of mutant/wild-type proteins (the likely in vivo ratio), all showed reduced Ca(2+) sensitivity of activation in ATPase and motility assays, and except for one alpha-tropomyosin mutant showed lower maximum Ca(2+) activation. Incorporation of either of two troponin T mutants in skinned cardiac trabeculae also decreased Ca(2+) sensitivity of force generation. Structure/function considerations imply that the diverse thin filament DCM mutations affect different aspects of regulatory function yet change contractility in a consistent manner. The DCM mutations depress myofibrillar function, an effect fundamentally opposite to that of hypertrophic cardiomyopathy-causing thin filament mutations, suggesting that decreased contractility may trigger pathways that ultimately lead to the clinical phenotype.
Mirza
Mahmooda
M
National Heart and Lung Institute, Imperial College London, London SW3 6LY, United Kingdom.
Marston
Steven
S
Willott
Ruth
R
Ashley
Christopher
C
Mogensen
Jens
J
McKenna
William
W
Robinson
Paul
P
Redwood
Charles
C
Watkins
Hugh
H
D000818:Animals; D002118:Calcium / Q000502:physiology; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D002311:Cardiomyopathy, Dilated / Q000235:genetics*; D006801:Humans; D008958:Models, Molecular; D018482:Muscle, Skeletal / Q000502:physiology; D009200:Myocardial Contraction / Q000235:genetics; D015879:Myosin Subfragments / Q000737:chemistry / Q000235:genetics*; D010641:Phenotype; D011487:Protein Conformation; D011817:Rabbits; D011994:Recombinant Proteins / Q000378:metabolism; D014335:Tropomyosin / Q000737:chemistry / Q000235:genetics*; D014336:Troponin / Q000235:genetics*; D019209:Troponin C / Q000737:chemistry / Q000235:genetics; D020107:Troponin T / Q000737:chemistry / Q000235:genetics
D015879:Myosin Subfragments; D011994:Recombinant Proteins; D014335:Tropomyosin; D014336:Troponin; D019209:Troponin C; D020107:Troponin T; D000252:Calcium-Transporting ATPases; D002118:Calcium