title: Cardiomyopathy-related mutation (A30V) in mouse cardiac troponin T divergently alters the magnitude of stretch activation in α- and β-myosin heavy chain fibers.
abstract: The present study investigated the functional consequences of the human hypertrophic cardiomyopathy (HCM) mutation A28V in cardiac troponin T (TnT). The A28V mutation is located within the NH2terminus of TnT, a region known to be important for full activation of cardiac thin filaments. The functional consequences of the A28V mutation in TnT remain unknown. Given how α- and β-myosin heavy chain (MHC) isoforms differently alter the functional effect of the NH2terminus of TnT, we hypothesized that the A28V-induced effects would be differently modulated by α- and β-MHC isoforms. Recombinant wild-type mouse TnT (TnTWT) and the mouse equivalent of the human A28V mutation (TnTA30V) were reconstituted into detergent-skinned cardiac muscle fibers extracted from normal (α-MHC) and transgenic (β-MHC) mice. Dynamic and steady-state contractile parameters were measured in reconstituted muscle fibers. Step-like length perturbation experiments demonstrated that TnTA30Vdecreased the magnitude of the muscle length-mediated recruitment of new force-bearing cross bridges (ER) by 30% in α-MHC fibers. In sharp contrast, TnTA30Vincreased ERby 55% in β-MHC fibers. Inferences drawn from other dynamic contractile parameters suggest that directional changes in ERin TnTA30V+ α-MHC and TnTA30V+ β-MHC fibers result from a divergent impact on cross bridge-regulatory unit (troponin-tropomyosin complex) cooperativity. TnTA30V-mediated effects on Ca2+-activated maximal tension and instantaneous muscle fiber stiffness (ED) were also divergently affected by α- and β-MHC. Our study demonstrates that TnTA30V+ α-MHC and TnTA30V+ β-MHC fibers show contrasting contractile phenotypes; however, only the observations from β-MHC fibers are consistent with the clinical data for A28V in humans.
  The differential impact of α- and β-myosin heavy chain (MHC) on contractile dynamics causes a mutant cardiac troponin T (TnTA30V) to differently modulate cardiac contractile function. TnTA30Vattenuated Ca2+-activated maximal tension and length-mediated cross-bridge recruitment against α-MHC but augmented these parameters against β-MHC, suggesting divergent contractile phenotypes.
authors: Department of Integrative Physiology and Neuroscience, Washington State University, Pullman, Washington.
authors: Alexis V
authors: AV
authors: Mickelson
authors: Department of Integrative Physiology and Neuroscience, Washington State University, Pullman, Washington.
authors: Sampath K
authors: SK
authors: Gollapudi
authors: Department of Integrative Physiology and Neuroscience, Washington State University, Pullman, Washington murali@vetmed.wsu.edu.
authors: Murali
authors: M
authors: Chandra
mesh_terms: D000818:Animals; D015153:Blotting, Western; D002118:Calcium / Q000378:metabolism*; D002312:Cardiomyopathy, Hypertrophic / Q000235:genetics*; D008297:Male; D051379:Mice; D008822:Mice, Transgenic; D009154:Mutation; D009200:Myocardial Contraction / Q000235:genetics* / Q000502:physiology; D032383:Myocytes, Cardiac / Q000378:metabolism* / Q000502:physiology; D018995:Myosin Heavy Chains / Q000235:genetics / Q000378:metabolism*; D020033:Protein Isoforms; D014335:Tropomyosin / Q000378:metabolism*; D014336:Troponin / Q000378:metabolism*; D020107:Troponin T / Q000235:genetics*
chemical_list: C584019:Myh6 protein, mouse; C551613:Myh7 protein, mouse; D020033:Protein Isoforms; D014335:Tropomyosin; D014336:Troponin; D020107:Troponin T; C042260:troponin-tropomyosin complex; D018995:Myosin Heavy Chains; D002118:Calcium
keywords: cross-bridge recruitment; dilated cardiomyopathy; hypertrophic cardiomyopathy; myosin heavy chain; troponin T