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The heart in Duchenne muscular dystrophy: early detection of contractile performance alteration
Sören Wagner1, Stephan Knipp, Cornelia Weber
1Department of Anesthesiology, University of Heidelberg, Heidelberg, Germany.
Insights
Duchenne muscular dystrophy (DMD) causes cardiomyopathy due to impaired cardiac muscle function. This study reveals early hypertrophy and contractile issues, not just calcium handling problems, contribute to heart failure in DMD.
Area of Science:
- Cardiology
- Molecular Biology
- Biophysics
Background:
- Progressive cardiomyopathy is a leading cause of mortality in Duchenne muscular dystrophy (DMD) patients.
- The interplay between calcium handling and contractile function in dystrophic hearts remains poorly understood.
- It is unclear if cardiac failure in DMD is primarily driven by calcium pathway alterations or the contractile apparatus.
Purpose of the Study:
- To investigate the mechanisms underlying cardiac dysfunction in early-stage Duchenne muscular dystrophy.
- To differentiate the contributions of calcium handling and contractile properties to force deficits in dystrophic hearts.
- To identify early signs of cardiac impairment in a mouse model of DMD.
Main Methods:
- Simultaneous recording of force and calcium transients in field-stimulated papillary muscles from wild-type (wt) and mdx mice.
- Assessment of myofilament calcium sensitivity using pCa-force relations.
- In vitro motility assays to measure myofilament sliding velocities.
- Echocardiography to evaluate cardiac structure and function in vivo.
Main Results:
- Dystrophic (mdx) muscles exhibited a fivefold reduction in force amplitude despite a smaller decrease in calcium transient amplitude.
- Myofibrillar calcium sensitivity was significantly reduced in mdx hearts.
- In vitro motility assays revealed significantly slower myofilament sliding velocities in mdx hearts.
- Echocardiography showed early ventricular wall hypertrophy and enlarged end-diastolic diameter in mdx mice, with preserved fractional shortening.
Conclusions:
- Alterations in the contractile apparatus, including reduced myofilament calcium sensitivity and slower sliding velocities, significantly contribute to force reduction in DMD hearts.
- Early cardiac hypertrophy and functional impairment occur in DMD, with contractile dysfunction playing a key role.
- These findings provide new insights into the mechanisms of cardiac involvement in Duchenne muscular dystrophy.
Abstract:
Progressive cardiomyopathy is a major cause of death in Duchenne muscular dystrophy (DMD) patients. Coupling between Ca(2+) handling and contractile properties in dystrophic hearts is poorly understood. It is also not clear whether developing cardiac failure is dominated by alterations in Ca(2+) pathways or more related to the contractile apparatus. We simultaneously recorded force and Ca(2+) transients in field-stimulated papillary muscles from young (10-14 weeks) wild-type (wt) and dystrophic mdx mice. Force amplitudes were fivefold reduced in mdx muscles despite only 30% reduction in fura-2 ratio amplitudes. This indicated mechanisms other than systolic Ca(2+) to additionally account for force decrements in mdx muscles. pCa-force relations revealed decreased mdx myofibrillar Ca(2+) sensitivity. 'In vitro' motility assays, studied in mdx hearts here for the first time, showed significantly slower sliding velocities. mdx MLC/MHC isoforms were not grossly altered. Dystrophic hearts showed echocardiography signs of early ventricular wall hypertrophy with a significantly enlarged end-diastolic diameter 'in vivo'. However, fractional shortening was still comparable to wt mice. Changes in the contractile apparatus satisfactorily explained force drop in mdx hearts. We give first evidence of early hypertrophy in mdx mice and possible mechanisms for already functional impairment of cardiac muscle in DMD.
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