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Am J Physiol Cell Physiol. 2017 Jan 1;312(1):C16-C28. doi: 10.1152/ajpcell.00098.2016. Epub 2016 Oct 26.

Exercise-induced alterations and loss of sarcomeric M-line organization in the diaphragm muscle of obscurin knockout mice.

Author information

1
Molecular Medicine Section, Department of Molecular and Developmental Medicine, University of Siena, Siena, Italy.
2
Venetian Institute of Molecular Medicine, Padua, Italy.
3
Interuniversity Institute of Myology.
4
Center for Research on Ageing and Translational Medicine & Department of Neuroscience, Imaging, and Clinical Sciences, University G. d'Annunzio of Chieti, Chieti, Italy.
5
University of California, San Diego School of Medicine, San Diego, California.
6
Department of Biomedical Sciences, University of Padua, Padua, Italy; and.
7
Molecular Medicine Section, Department of Molecular and Developmental Medicine, University of Siena, Siena, Italy; vincenzo.sorrentino@unisi.it.

Abstract

We recently reported that skeletal muscle fibers of obscurin knockout (KO) mice present altered distribution of ankyrin B (ankB), disorganization of the subsarcolemmal microtubules, and reduced localization of dystrophin at costameres. In addition, these mice have impaired running endurance and increased exercise-induced sarcolemmal damage compared with wild-type animals. Here, we report results from a combined approach of physiological, morphological, and structural studies in which we further characterize the skeletal muscles of obscurin KO mice. A detailed examination of exercise performance, using different running protocols, revealed that the reduced endurance of obscurin KO animals on the treadmill depends on exercise intensity and age. Indeed, a mild running protocol did not evidence significant differences between control and obscurin KO mice, whereas comparison of running abilities of 2-, 6-, and 11-mo-old mice exercised at exhaustion revealed a progressive age-dependent reduction of the exercise tolerance in KO mice. Histological analysis indicated that heavy exercise induced leukocyte infiltration, fibrotic connective tissue deposition, and hypercontractures in the diaphragm of KO mice. On the same line, electron microscopy revealed that, in the diaphragm of exercised obscurin KO mice, but not in the hindlimb muscles, both M-line and H-zone of sarcomeres appeared wavy and less defined. Altogether, these results suggest that obscurin is required for the maintenance of morphological and ultrastructural integrity of skeletal muscle fibers against damage induced by intense mechanical stress and point to the diaphragm as the skeletal muscle most severely affected in obscurin-deficient mice.

KEYWORDS:

contraction; fibrosis; muscular dystrophy; myofibrils; myopathy

PMID:
27784675
PMCID:
PMC5283896
DOI:
10.1152/ajpcell.00098.2016
[Indexed for MEDLINE]
Free PMC Article

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