The Association of Cardiac Dystrophin with Myofibrils/Z-disc Regions in Cardiac Muscle Suggests a Novel Role in the Contractile Apparatus (*)
- From the (1) Department of Pharmacology, University of Ottawa, Ottawa, Ontario K1H 8M5, Canada, the
- (2) Department of Medicine and Physiology, School of Medicine, University of California, Los Angeles, California 90024-1760, and
- (3) The Montreal Neurological Institute, McGill University, Montreal, Quebec H3A 2B4, Canada
- **Career Investigator of the Heart and Stroke Foundation of Ontario, Canada. To whom correspondence should be addressed: Dept. of Pharmacology, University of Ottawa, 451 Smyth Rd., Ottawa, Ontario K1H 8M5, Canada. Tel.: 613-562-5800 (ext. 8355); Fax: 613-562-5456.
Abstract
Dystrophin serves a variety of roles at the cell membrane through its associations, and defects in the dystrophin gene can give rise to muscular dystrophy and genetic cardiomyopathy. We investigated localization of cardiac dystrophin to determine potential intracellular sites of association. Subcellular fractionation revealed that while the majority of dystrophin was associated with the sarcolemma, about 35% of the 427-kDa form of dystrophin was present in the myofibrils. The dystrophin homolog utrophin was detectable only in the sarcolemmal membrane and was absent from the myofibrils as were other sarcolemmal glycoproteins such as adhalin and the sodium-calcium exchanger. Extraction of myofibrils with KCl and detergents could not solubilize dystrophin. Dystrophin could only be dissociated from the myofibrillar protein complex in 5 M urea followed by sucrose density gradient centrifugation where it co-fractionated with one of two distinctly sedimenting peaks of actin. Immunoelectron microscopy of intracellular regions of cardiac muscle revealed a selective labeling of Z-discs by dystrophin antibodies. In the genetically determined cardiomyopathic hamster, strain CHF 147, the time course of development of cardiac insufficiency correlated with an overall 75% loss of myofibrillar dystrophin. These findings collectively show that a significant pool of the 427-kDa form of cardiac dystrophin was specifically associated with the contractile apparatus at the Z-discs, and its loss correlated with progression to cardiac insufficiency in genetic cardiomyopathy. The loss of distinct cellular pools of dystrophin may contribute to the tissue-specific pathophysiology in muscular dystrophy.
Footnotes
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↵§ Postdoctoral fellow of the Medical Research Council of Canada.
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↵¶ Studentship recipient from the Medical Research Council of Canada.
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↵* This work was supported by grants from the Heart and Stroke Foundation of Ontario and the Medical Research Council of Canada (to B. S. T.), a grant from the National Institutes of Health (to J. F.), and a grant from the Muscular Dystrophy Association of Canada (to P. H.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore by hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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↵(
) The abbreviations used are:
- WGA
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wheat germ agglutinin
- MF
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myofibril
- SL
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sarcolemma
- PAGE
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polyacrylamide gel electrophoresis
- DTT
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dithiothreitol.
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- Received November 20, 1995.
- Revision received February 23, 1996.
- © 1996 by The American Society for Biochemistry and Molecular Biology, Inc.
