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Troponin T isoform expression in the normal and failing human left ventricle: a correlation with myofibrillar ATPase
P A Anderson1, N N Malouf, A E Oakeley
1Duke University Medical Center, Durham, NC 27710.
Insights
Heart failure involves altered troponin T (TnT) isoform expression, with higher TnT2 levels in failing hearts. These changes may represent an adaptation to abnormal heart function, not a cause of the disease.
Area of Science:
- Biochemistry
- Cardiology
- Molecular Biology
Background:
- Troponin T (TnT) is a critical thin filament regulatory protein in cardiac muscle.
- Altered TnT expression is implicated in various heart conditions.
Purpose of the Study:
- To investigate troponin T isoform expression in normal and failing human left ventricles.
- To determine the relationship between TnT isoform levels and myofibrillar ATPase activity in heart failure.
Main Methods:
- Western blot analysis of myofibrillar proteins from human heart samples.
- Two-dimensional SDS-PAGE to resolve TnT isoforms.
- Alkaline phosphatase treatment to assess post-translational modifications.
- Correlation analysis between TnT2 percentage and myofibrillar ATPase activity.
Main Results:
- Two dominant troponin T isoforms, TnT1 and TnT2, were identified.
- TnT2 expression was significantly elevated in failing ventricles compared to normal hearts (p < 0.004).
- A significant inverse linear relationship was observed between the percentage of TnT2 and myofibrillar ATPase activity (r = 0.7, p < 0.02).
Conclusions:
- Disease-associated changes in troponin T isoform expression, particularly increased TnT2, are present in human heart failure.
- These alterations are proposed to be adaptive responses to abnormal myocardial function rather than causative factors of heart failure.
- Further research is needed to fully elucidate the functional consequences of TnT isoform shifts in cardiac disease.
Abstract:
The expression of troponin T, a thin filament regulatory protein, was examined in normal and failing left ventricles. The samples were obtained from the hearts of patients with severe heart failure who were undergoing cardiac transplantation, and from normal adult hearts that could not be used for transplantation. Western blots of the myofibrillar proteins demonstrated two isoforms, troponin T 1 (TnT1) and troponin T 2 (TnT2). TnT2 is expressed at significantly higher levels in failing hearts (p less than 0.004). Western blots of two-dimension SDS-PAGE gels resolved two dominant spots of TnT1 and of TnT2 and several minor troponin T species. Alkaline phosphatase treatment markedly decreased the sizes of the two acidic spots while increasing the two more basic spots by a comparable amount. Myofibrillar ATPase activity had an inverse and negative linear relationship (r = 0.7, p less than 0.02) with the myofibrillar percentage of total troponin T comprised of TnT2. In that heart failure in these transplant patients had multiple bases, we propose that rather than a cause of heart failure, the disease-associated changes in troponin T isoform expression are an adaptation to abnormal myocardial function.