α-Tropomyosin mutations Asp175Asn and Glu180Gly affect cardiac function in transgenic rats in different ways
Wernicke D., Thiel C., Duja-Isac CM., Essin KV., Spindler M., Nunez DJR., Plehm R., Wessel N., Hammes A., Edwards R-J., Lippoldt A., Zacharias U., Strömer H., Neubauer S., Davies MJ., Morano I., Thierfelder L.
<jats:p> To study the mechanisms by which missense mutations in α-tropomyosin cause familial hypertrophic cardiomyopathy, we generated transgenic rats overexpressing α-tropomyosin with one of two disease-causing mutations, Asp<jats:sup>175</jats:sup>Asn or Glu<jats:sup>180</jats:sup>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-α-tropomyosin antibody, ARG1. In transgenic rats with either α-tropomyosin mutation, molecular markers of cardiac hypertrophy were induced. Ca<jats:sup>2+</jats:sup> sensitivity of cardiac skinned-fiber preparations from animals with mutation Asp<jats:sup>175</jats:sup>Asn, but not Glu<jats:sup>180</jats:sup>Gly, was decreased. Furthermore, elevated frequency and amplitude of spontaneous Ca<jats:sup>2+</jats:sup> waves were detected only in cardiomyocytes from animals with mutation Asp<jats:sup>175</jats:sup>Asn, suggesting an increase in intracellular Ca<jats:sup>2+</jats:sup> concentration compensating for the reduced Ca<jats:sup>2+</jats:sup> sensitivity of isometric force generation. Accordingly, in Langendorff-perfused heart preparations, myocardial contraction and relaxation were accelerated in animals with mutation Asp<jats:sup>175</jats:sup>Asn. The results allow us to propose a hypothesis of the pathogenetic changes caused by α-tropomyosin mutation Asp<jats:sup>175</jats:sup>Asn in familial hypertrophic cardiomyopathy on the basis of changes in Ca<jats:sup>2+</jats:sup> handling as a sensitive mechanism to compensate for alterations in sarcomeric structure. </jats:p>