Dowling, Paul and Doran, Philip and Ohlendieck, Kay (2004) Drastic reduction of sarcalumenin in Dp427 (dystrophin of 427 kDa)-deficient fibres indicates that abnormal calcium handling plays a key role in muscular dystrophy. Biochemical Journal, 379 (Pt.2). pp. 479-488. ISSN 0264-6021

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Abstract

Although the primary abnormality in dystrophin is the underlying cause for mdx (X-chromosome-linked muscular dystrophy), abnormal Ca2+ handling after sarcolemmal microrupturing appears to be the pathophysiological mechanism leading to muscle weakness. To develop novel pharmacological strategies for eliminating Ca2+-dependent proteolysis, it is crucial to determine the fate of Ca2+-handling proteins in dystrophin-deficient fibres. In the present study, we show that a key luminal Ca2+-binding protein SAR (sarcalumenin) is affected in mdx skeletal-muscle fibres. One- and two-dimensional immunoblot analyses revealed the relative expression of the 160 kDa SR (sarcoplasmic reticulum) protein to be approx. 70% lower in mdx fibres when compared with normal skeletal muscles. This drastic reduction in SAR was confirmed by immunofluorescence microscopy. Patchy internal labelling of SAR in dystrophic fibres suggests an abnormal formation of SAR domains. Differential co-immunoprecipitation experiments and chemical cross-linking demonstrated a tight linkage between SAR and the SERCA1 (sarcoplasmic/endoplasmic-reticulum Ca2+-ATPase 1) isoform of the SR Ca2+-ATPase. However, the relative expression of the fast Ca2+ pump was not decreased in dystrophic membrane preparations. This implies that the reduction in SAR and calsequestrin-like proteins plays a central role in the previously reported impairment of Ca2+ buffering in the dystrophic SR [Culligan, Banville, Dowling and Ohlendieck (2002) J. Appl. Physiol. 92, 435-445]. Impaired Ca2+ shuttling between the Ca2+-uptake SERCA units and calsequestrin clusters via SAR, as well as an overall decreased luminal ion-binding capacity, might indirectly amplify the Ca2+-leak-channel-induced increase in cytosolic Ca2+ levels. This confirms the idea that abnormal Ca2+ cycling is involved in Ca2+-induced myonecrosis. Hence, manipulating disturbed Ca2+ handling might represent new modes of abolishing proteolytic degradation in muscular dystrophy.

Item Type:	Article
Keywords:	calcium handling; Dp427; dystrophin of 427 kDa; dystrophin; muscular dystrophy; sarcalumenin;
Academic Unit:	Faculty of Science and Engineering > Biology
Item ID:	7343
Identification Number:	https://doi.org/10.1042/BJ20031311
Depositing User:	Paul Dowling
Date Deposited:	15 Aug 2016 16:05
Journal or Publication Title:	Biochemical Journal
Publisher:	The Biochemical Society
Refereed:	Yes
Funders:	Enterprise Ireland (EI), Muscular Dystrophy Ireland, European Commission
URI:
Use Licence:	This item is available under a Creative Commons Attribution Non Commercial Share Alike Licence (CC BY-NC-SA). Details of this licence are available here

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