DOMINANT-NEGATIVE EFFECT OF A MUTANT CARDIAC TROPONIN-T ON CARDIAC STRUCTURE AND FUNCTION IN TRANSGENIC MICE

Hypertrophic cardiomyopathy (HCM) is a disease of sarcomeric proteins. The mechanism by which mutant sarcomeric proteins cause HCM is unknow n. The leading hypothesis proposes that mutant sarcomeric proteins exe rt a dominant-negative effect on myocyte structure and function. To te st this, we produced transgenic mice expressing low levels of normal o r mutant human cardiac troponin T (cTnT). We constructed normal (cTnT- Arg(92)) and mutant (cTnT-Gln(92)) transgenes, driven by a murine cTnT promoter, and produced three normal and five mutant transgenic lines, which were identified by PCR and Southern blotting. Expression levels of the transgene proteins, detected using a specific antibody, ranged from 1 to 10% of the total cTnT pool. M-mode and Doppler echocardiogr aphy showed normal left ventricular dimensions and systolic function, but diastolic dysfunction in the mutant mice evidenced by a 50% reduct ion in the E/A ratio of mitral inflow velocities. Histological examina tion showed cardiac myocyte disarray in the mutant mice, which amounte d to 1-15% of the total myocardium, and a twofold increase in the myoc ardial interstitial collagen content. Thus, the mutant cTnT-Gln(92), r esponsible for human HCM, exerted a dominant-negative effect on cardia c structure and function leading to disarray, increased collagen synth esis, and diastolic dysfunction in transgenic mice.