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Knock-in mice harboring a Ca(2+) desensitizing mutation in cardiac troponin C develop early onset dilated
Bradley K McConnell1, Sonal Singh1, Qiying Fan1
1Department of Pharmacological and Pharmaceutical Sciences, University of Houston Houston, TX, USA.
Abstract:
The physiological consequences of aberrant Ca(2+) binding and exchange with cardiac myofilaments are not clearly understood. In order to examine the effect of decreasing Ca(2+) sensitivity of cTnC on cardiac function, we generated knock-in mice carrying a D73N mutation (not known to be associated with heart disease in human patients) in cTnC. The D73N mutation was engineered into the regulatory N-domain of cTnC in order to reduce Ca(2+) sensitivity of reconstituted thin filaments by increasing the rate of Ca(2+) dissociation. In addition, the D73N mutation drastically blunted the extent of Ca(2+) desensitization of reconstituted thin filaments induced by cTnI pseudo-phosphorylation. Compared to wild-type mice, heterozygous knock-in mice carrying the D73N mutation exhibited a substantially decreased Ca(2+) sensitivity of force development in skinned ventricular trabeculae. Kaplan-Meier survival analysis revealed that median survival time for knock-in mice was 12 weeks. Echocardiographic analysis revealed that knock-in mice exhibited increased left ventricular dimensions with thinner walls. Echocardiographic analysis also revealed that measures of systolic function, such as ejection fraction (EF) and fractional shortening (FS), were dramatically reduced in knock-in mice. In addition, knock-in mice displayed electrophysiological abnormalities, namely prolonged QRS and QT intervals. Furthermore, ventricular myocytes isolated from knock-in mice did not respond to β-adrenergic stimulation. Thus, knock-in mice developed pathological features similar to those observed in human patients with dilated cardiomyopathy (DCM). In conclusion, our results suggest that decreasing Ca(2+) sensitivity of the regulatory N-domain of cTnC is sufficient to trigger the development of DCM.
Insights
Decreasing calcium sensitivity in cardiac troponin C (cTnC) using a D73N mutation in mice led to dilated cardiomyopathy (DCM). This study reveals a direct link between reduced Ca(2+) sensitivity and heart disease development.
Area of Science:
- Cardiovascular Physiology
- Molecular Cardiology
- Biochemistry
Background:
- Aberrant calcium (Ca2+) handling in cardiac myofilaments is implicated in heart disease.
- The precise physiological impact of altered Ca2+ sensitivity in cardiac troponin C (cTnC) remains incompletely understood.
Purpose of the Study:
- To investigate the functional consequences of reduced Ca2+ sensitivity of cTnC on cardiac performance.
- To model aspects of dilated cardiomyopathy (DCM) by engineering a specific mutation in cTnC.
Main Methods:
- Generation of knock-in mice with a D73N mutation in the regulatory N-domain of cTnC.
- Assessment of Ca2+ sensitivity of force development in skinned ventricular trabeculae.
- Longitudinal survival studies, echocardiography, and electrophysiological recordings in mutant mice.
Main Results:
- Heterozygous D73N knock-in mice showed significantly decreased Ca2+ sensitivity of force development.
- Knock-in mice exhibited reduced median survival, impaired systolic function (reduced EF and FS), and cardiac remodeling (increased ventricular dimensions, thinner walls).
- Electrophysiological abnormalities (prolonged QRS and QT intervals) and unresponsiveness to beta-adrenergic stimulation were observed.
Conclusions:
- Reduced Ca2+ sensitivity of the cTnC regulatory N-domain is sufficient to induce DCM.
- The D73N mutation in cTnC recapitulates key pathological features of human DCM.
- This model provides insights into the role of Ca2+ handling in cardiac pathophysiology.
