{alpha}-Tropomyosin mutations Asp175Asn and Glu180Gly affect cardiac function in transgenic rats in different ways

1 Max-Delbrück Center for Molecular Medicine, 13 092 Berlin; 2 Clinic of Internal Medicine, Julius-Maximilians University, 97 080 Würzburg; and 4 Franz Volhard Clinic, Charite of the Humboldt University, 13125 Berlin, Germany; 3 Section on Clinical Pharmacology, Imperial College School of Medicine, Hammersmith Hospital, London W12 ONN; and 5 St. George's Hospital Medical School, London SW17 ORE, United Kingdom Submitted 24 October 2003 ; accepted in final form 8 March 2004 To study the mechanisms by which missense mutations in -tropomyosin cause familial hypertrophic cardiomyopathy, we generated transgenic rats overexpressing -tropomyosin with one of two disease-causing mutations, Asp 175 Asn or Glu 180 Gly, and analyzed phenotypic changes at molecular, morphological, and physiological levels. The transgenic proteins were stably integrated into the sarcomere, as shown by immunohistochemistry using a human-specific anti- -tropomyosin antibody, ARG1. In transgenic rats with either -tropomyosin mutation, molecular markers of cardiac hypertrophy were induced. Ca 2+ sensitivity of cardiac skinned-fiber preparations from animals with mutation Asp 175 Asn, but not Glu 180 Gly, was decreased. Furthermore, elevated frequency and amplitude of spontaneous Ca 2+ waves were detected only in cardiomyocytes from animals with mutation Asp 175 Asn, suggesting an increase in intracellular Ca 2+ concentration compensating for the reduced Ca 2+ sensitivity of isometric force generation. Accordingly, in Langendorff-perfused heart preparations, myocardial contraction and relaxation were accelerated in animals with mutation Asp 175 Asn. The results allow us to propose a hypothesis of the pathogenetic changes caused by -tropomyosin mutation Asp 175 Asn in familial hypertrophic cardiomyopathy on the basis of changes in Ca 2+ handling as a sensitive mechanism to compensate for alterations in sarcomeric structure. familial hypertrophic cardiomyopathy; animal model; calcium transient; cardiac skinned-fiber preparation Address for reprint requests and other correspondence: D. Wernicke, Max-Delbrück-Center for Molecular Medicine, Robert-Roessle-Str. 10, Berlin, 13 092, Germany (E-mail: dwernic{at}mdc-berlin.de )