Transgenic rat hearts expressing a human cardiac troponin T deletion reveal diastolic dysfunction and ventricular arrhythmias.

OBJECTIVE: Familial hypertrophic cardiomyopathy (FHC) due to mutations of cardiac troponin T (cTnT) is associated with a high frequency of sudden death even in the absence of cardiac hypertrophy. To investigate the causal relationship of cTnT mutations and this particular phenotype, we sought to establish a transgenic rat model for the disease.
METHODS: Transgenic rats were generated expressing human wild-type cTnT or two truncated cTnT molecules (del ex16, del ex15/16), resulting from an intron 15 splice donor site mutation previously observed in FHC patients. Transgenic rat hearts were characterized by histology, immunohistochemistry and in the 'working heart'.
RESULTS: Human wild-type and del ex16 cTnT were stably expressed and incorporated into the sarcomere of transgenic cardiomyocytes. Del ex16 transgenic rats revealed a lower level of expression (4-5%) than human wt cTnT animals (25-40%). In the 'working heart' model del ex16 hearts exhibited significant systolic and diastolic dysfunction without cardiac hypertrophy. In contrast, human wt cTnT hearts showed improved contractile performance and moderate myocardial hypertrophy. After 6 months of daily physical exercise one del ex16 rat died suddenly and three out of five del ex16 hearts revealed ventricular tachycardia/fibrillation. No arrhythmia was observed in human wt cTnT expressors. Myofibrillar disarray was present in del ex16 hearts after training but not in human wild-type cTnT rats or non-transgenic controls.
CONCLUSION: A human cTnT deletion overexpressed in transgenic rats exerts a dominant-negative effect and mimics the phenotype of FHC with diastolic dysfunction and arrhythmias. By contrast, human cTnT wild-type animals reveal a gain of function and cardiac hypertrophy without arrhythmias.