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Sarcolemma-localized nNOS is required to maintain activity after mild exercise


Many neuromuscular conditions are characterized by an exaggerated exercise-induced fatigue response that is disproportionate to activity level. This fatigue is not necessarily correlated with greater central or peripheral fatigue in patients1, and some patients experience severe fatigue without any demonstrable somatic disease2. Except in myopathies that are due to specific metabolic defects, the mechanism underlying this type of fatigue remains unknown2. With no treatment available, this form of inactivity is a major determinant of disability3. Here we show, using mouse models, that this exaggerated fatigue response is distinct from a loss in specific force production by muscle, and that sarcolemma-localized signalling by neuronal nitric oxide synthase (nNOS) in skeletal muscle is required to maintain activity after mild exercise. We show that nNOS-null mice do not have muscle pathology and have no loss of muscle-specific force after exercise but do display this exaggerated fatigue response to mild exercise. In mouse models of nNOS mislocalization from the sarcolemma, prolonged inactivity was only relieved by pharmacologically enhancing the cGMP signal that results from muscle nNOS activation during the nitric oxide signalling response to mild exercise. Our findings suggest that the mechanism underlying the exaggerated fatigue response to mild exercise is a lack of contraction-induced signalling from sarcolemma-localized nNOS, which decreases cGMP-mediated vasomodulation in the vessels that supply active muscle after mild exercise. Sarcolemmal nNOS staining was decreased in patient biopsies from a large number of distinct myopathies, suggesting a common mechanism of fatigue. Our results suggest that patients with an exaggerated fatigue response to mild exercise would show clinical improvement in response to treatment strategies aimed at improving exercise-induced signalling.

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Figure 1: Loss of sarcolemma-localized nNOS leads to skeletal muscle vascular narrowings, decreased capillary perfusion and an exaggerated fatigue response after mild exercise in dystrophic and non-dystrophic mouse models.
Figure 2: Enhancing the cGMP signal resulting from muscle nNOS activation decreases the exaggerated fatigue response to mild exercise.
Figure 3: Treatment with PDE5A inhibitor improves exercised-induced vasomodulation and decreases exercise-induced oedema in mdx mice.
Figure 4: nNOS levels in sarcolemma are decreased in human muscle diseases.


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We thank M. Anderson and M. Henry for comments, and M. M. Kilburg, K. Uppal, B. J. Steinmann and S. Watkins and members of the Campbell laboratory for scientific contributions. This work was supported in part by a Paul D. Wellstone Muscular Dystrophy Cooperative Research Center Grant. Y.M.K. was supported by grants from the University of Iowa Cardiovascular Interdisciplinary Research/ National Research Service Award (NRSA) Fellowship, from an individual NRSA Fellowship from the National Institute of Arthritis and Musculoskeletal and Skin Diseases, from the National Institutes of Health (NIH), and from a Senator Paul D. Wellstone Fellowship. E.P.R. was supported by a Muscular Dystrophy Association Development Grant. R.M.W. was supported by the NIH. K.P.C. is an investigator of the Howard Hughes Medical Institute.

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Correspondence to Kevin P. Campbell.

Supplementary information

Supplementary Information

This file contains Supplementary Additional Methods, Supplementary Figures S1-S9 with Legends, Supplementary Table 1, Supplementary Methods and Supplementary References (PDF 1723 kb)

Movie file S1a

Movie file S1a shows Pre-exercise activity of a C57BL/10 wild-type mouse (MOV 6787 kb)

Movie file S1b

Movie file S1b shows Pre-exercise activity of an mdx mouse (MOV 6763 kb)

Movie file S1c

Movie file S1c shows Pre-exercise activity of a C57BL/6 wild-type mouse (MOV 6729 kb)

Movie file 1d

Movie file 1d shows Pre-exercise activity of an Sgca-null mouse (MOV 6831 kb)

Movie file 2a

Movie file 2a shows Post-exercise activity of a C57BL/10 wild-type mouse. (MOV 6728 kb)

Movie file 2b

Movie file 2b shows Post-exercise activity of an mdx mouse (MOV 6765 kb)

Movie file 2c

Movie file 2c shows Post-exercise activity of a C57BL/6 mouse wild-type mouse (MOV 6777 kb)

Movie file 2d

Movie file 2d shows Post-exercise activity of an Sgca-null mouse (MOV 6947 kb)

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Kobayashi, Y., Rader, E., Crawford, R. et al. Sarcolemma-localized nNOS is required to maintain activity after mild exercise. Nature 456, 511–515 (2008).

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