Related Experiment Videos
Functional analyses of troponin T mutations that cause hypertrophic cardiomyopathy: insights into disease
H L Sweeney1, H S Feng, Z Yang
1Department of Physiology, A700 Richards Building, University of Pennsylvania School of Medicine, Philadelphia, PA 19104-6085, USA. lsweeney@mail.med.upenn.edu
Insights
Cardiac troponin T (TnT) mutations can cause hypertrophic cardiomyopathy (HCM) through altered muscle contraction. These TnT mutations impair calcium sensitivity and increase shortening velocity, suggesting a new mechanism for HCM development.
Area of Science:
- Cardiovascular Biology
- Muscle Physiology
- Genetic Diseases
Background:
- Hypertrophic cardiomyopathy (HCM) is often caused by mutations in sarcomeric protein genes.
- Previous research suggested some HCM mutations impair cardiac muscle contractile function.
- A specific troponin T (TnT) mutation was hypothesized to cause hypercontractility, indicating a different pathogenic mechanism.
Purpose of the Study:
- To investigate the functional effects of three HCM-associated cardiac troponin T (TnT) mutations.
- To determine if these TnT mutations alter myotube contractile properties.
- To explore a potential second mechanism for HCM pathogenesis involving TnT.
Main Methods:
- Utilized a myotube expression system to study wild-type and mutant cardiac troponin T (TnT).
- Performed functional analyses on transfected myotubes to assess force production and shortening velocity.
- Investigated the impact of specific TnT mutations (Ile79Asn, Arg92Gln, DeltaGlu160) on calcium sensitivity.
Main Results:
- All three studied cardiac troponin T (TnT) mutations reduced calcium sensitivity in force production.
- Two missense TnT mutations (Ile79Asn and Arg92Gln) significantly increased unloaded shortening velocity.
- The findings indicate TnT's role in modulating myosin cross-bridge detachment rates.
Conclusions:
- The troponin complex plays a more significant role in regulating muscle contraction than previously understood.
- These TnT mutations may lead to HCM by increasing the heart's energetic workload.
- This suggests a distinct pathogenic pathway for hypertrophic cardiomyopathy (HCM) driven by TnT mutations.
Abstract:
Mutations in a number of cardiac sarcomeric protein genes cause hypertrophic cardiomyopathy (HCM). Previous findings indicate that HCM-causing mutations associated with a truncated cardiac troponin T (TnT) and missense mutations in the beta-myosin heavy chain share abnormalities in common, acting as dominant negative alleles that impair contractile performance. In contrast, Lin et al. [Lin, D., Bobkova, A., Homsher, E. & Tobacman, L. S. (1996) J. Clin. Invest. 97, 2842-2848] characterized a TnT point mutation (Ile79Asn) and concluded that it might lead to hypercontractility and, thus, potentially a different mechanism for HCM pathogenesis. In this study, three HCM-causing cardiac TnT mutations (Ile79Asn, Arg92Gln, and DeltaGlu160) were studied in a myotube expression system. Functional studies of wild-type and mutant transfected myotubes revealed that all three mutants decreased the calcium sensitivity of force production and that the two missense mutations (Ile79Asn and Arg92Gln) increased the unloaded shortening velocity nearly 2-fold. The data demonstrate that TnT can alter the rate of myosin cross-bridge detachment, and thus the troponin complex plays a greater role in modulating muscle contractile performance than was recognized previously. Furthermore, these data suggest that these TnT mutations may cause disease via an increased energetic load on the heart. This would represent a second paradigm for HCM pathogenesis.