title: Interplay Between the Effects of Dilated Cardiomyopathy Mutation (R206L) and the Protein Kinase C Phosphomimic (T204E) of Rat Cardiac Troponin T Are Differently Modulated by α- and β-Myosin Heavy Chain Isoforms.
abstract: BACKGROUND
  We hypothesized that the functional effects of R206L-a rat analog of the dilated cardiomyopathy (DCM) mutation R205L in human cardiac troponin T (TnT)-were differently modulated by myosin heavy chain (MHC) isoforms and T204E, a protein kinase C (PKC) phosphomimic of TnT. Our hypothesis was based on two observations: (1) α- and β-MHC differentially influence the functional effects of TnT; and (2) PKC isoforms capable of phosphorylating TnT are upregulated in failing human hearts.
  
  
  RESULTS
  We generated 4 recombinant TnT variants: wild type; R206L; T204E; and R206L+T204E. Functional effects of the TnT variants were tested in cardiac muscle fibers (minimum 14 per group) from normal (α-MHC) and propylthiouracil-treated rats (β-MHC) using steady-state and dynamic contractile measurements. Notably, in α-MHC fibers, Ca(2+)-activated maximal tension was attenuated by R206L (≈32%), T204E (≈63%), and R206L+T204E (≈64%). In β-MHC fibers, maximal tension was unaffected by R206L, but was attenuated by T204E (≈33%) and R206L+T204E (≈40%). Thus, β-MHC differentially counteracted the attenuating effects of the TnT variants on tension. However, in β-MHC fibers, R206L+T204E attenuated tension to a greater extent when compared to T204E alone. In β-MHC fibers, R206L+T204E attenuated the magnitude of the length-mediated recruitment of new cross-bridges (≈28%), suggesting that the Frank-Starling mechanism was impaired.
  
  
  CONCLUSIONS
  Our findings are the first (to our knowledge) to demonstrate that the functional effects of a DCM-linked TnT mutation are not only modulated by MHC isoforms, but also by the pathology-associated post-translational modifications of TnT.
authors.affiliation: Department of Integrative Physiology and Neuroscience Washington State University, Pullman, WA.
authors.forename: John Jeshurun
authors.initials: JJ
authors.lastname: Michael
authors.affiliation: Department of Integrative Physiology and Neuroscience Washington State University, Pullman, WA murali@vetmed.wsu.edu.
authors.forename: Murali
authors.initials: M
authors.lastname: Chandra
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism; D000818:Animals; D002311:Cardiomyopathy, Dilated / Q000235:genetics* / Q000378:metabolism* / Q000503:physiopathology; D020022:Genetic Predisposition to Disease; D006352:Heart Ventricles / Q000187:drug effects / Q000201:enzymology* / Q000503:physiopathology; D008297:Male; D009154:Mutation; D009200:Myocardial Contraction; D010766:Phosphorylation; D011441:Propylthiouracil / Q000494:pharmacology; D020033:Protein Isoforms; D011493:Protein Kinase C / Q000378:metabolism*; D011499:Protein Processing, Post-Translational; D017207:Rats, Sprague-Dawley; D013997:Time Factors; D020107:Troponin T / Q000235:genetics* / Q000378:metabolism*; D024723:Ventricular Myosins / Q000378:metabolism*
chemical_list: D020033:Protein Isoforms; D020107:Troponin T; D011441:Propylthiouracil; D011493:Protein Kinase C; D000251:Adenosine Triphosphatases; D024723:Ventricular Myosins
keywords: dilated cardiomyopathy; myosin heavy chain; post‐translational modification; protein kinase C; troponin T