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NH2-terminal truncations of cardiac troponin I and cardiac troponin T produce distinct effects on contractility and calcium homeostasis in adult cardiomyocytes. | LitMetric

AI Article Synopsis

  • Cardiac troponin I (TnI) has a special regulatory part that changes during heart stress, and its truncated form (cTnI-ND) improves heart relaxation during diastole.
  • Similarly, cardiac troponin T (TnT) can also be cleaved, with its truncated form (cTnT-ND) leading to slower heart contraction but higher stroke volume.
  • A study showed that cTnI-ND cardiomyocytes had enhanced contractile properties, while both truncated forms of troponins led to faster calcium recombination, highlighting their different roles in heart function.

Article Abstract

Cardiac troponin I (TnI) has an NH2-terminal extension that is an adult heart-specific regulatory structure. Restrictive proteolytic truncation of the NH2-terminal extension of cardiac TnI occurs in normal hearts and is upregulated in cardiac adaptation to hemodynamic stress or β-adrenergic deficiency. NH2-terminal truncated cardiac TnI (cTnI-ND) alters the conformation of the core structure of cardiac TnI similarly to that produced by PKA phosphorylation of Ser(23/24) in the NH2-terminal extension. At organ level, cTnI-ND enhances ventricular diastolic function. The NH2-terminal region of cardiac troponin T (TnT) is another regulatory structure that can be selectively cleaved via restrictive proteolysis. Structural variations in the NH2-terminal region of TnT also alter the molecular conformation and function. Transgenic mouse hearts expressing NH2-terminal truncated cardiac TnT (cTnT-ND) showed slower contractile velocity to prolong ventricular rapid-ejection time, resulting in higher stroke volume. Our present study compared the effects of cTnI-ND and cTnT-ND in cardiomyocytes isolated from transgenic mice on cellular morphology, contractility, and calcium kinetics. Resting cTnI-ND, but not cTnT-ND, cardiomyocytes had shorter length than wild-type cells with no change in sarcomere length. cTnI-ND, but not cTnT-ND, cardiomyocytes produced higher contractile amplitude and faster shortening and relengthening velocities in the absence of external load than wild-type controls. Although the baseline and peak levels of cytosolic Ca(2+) were not changed, Ca(2+) resequestration was faster in both cTnI-ND and cTnT-ND cardiomyocytes than in wild-type control. The distinct effects of cTnI-ND and cTnT-ND demonstrate their roles in selectively modulating diastolic or systolic functions of the heart.

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Source
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4346733PMC
http://dx.doi.org/10.1152/ajpcell.00358.2014DOI Listing

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