Epsilon-sarcoglycan in LGMD Type 2D

University Of Iowa, Iowa City IA

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Abstract

DESCRIPTION (provided by applicant): The parent project long-term goal is to explore the therapeutic potential of up-regulating 5-sarcoglycan levels for the treatment of limb-girdle muscular dystrophy type 2D (LGMD2D). Mutations in the 1-sarcoglycan gene cause LGMD2D, and leads to progressive muscle fiber necrosis and weakness. We found that 5-sarcoglycan is able to rescue 1- sarcoglycan deficiency and prevent the muscular dystrophy in a mouse model for LGMD-2D. Despite displaying normal muscle function, these "rescued" mice experienced an exaggerated fatigue response to mild exercise due to deficient sarcolemmal nNOS signaling. Thus, like our rescue mouse, we found that this specific form of fatigue can occur in mouse models that do not have muscle pathology suggesting that deficient sarcolemmal nNOS signaling could be the cause of this form of fatigue in humans that do not have a somatic disease. Significantly, we found that pharmacological treatment with PDE5A inhibitors relieves this form of fatigue by enhancing the nitric oxide signaling from active muscle. In addition, we found that this treatment also improves exercise tolerance and reduces exercised-induced muscle edema in our dystrophic mice. This Competitive Revision focuses on exploring pharmacological treatment strategies encompassing pathways involved in exercise to prevent this form of fatigue as well as prevent exercise-induced muscle edema in our mouse models. The first aim hypothesizes that long-term PDE5A inhibitor treatment will improve the daily activity of our mouse models. Longitudinal characterization of dystrophic and rescue mouse models treated with long-term derivatives of PDE5A inhibitors will test this hypothesis. The second aim hypothesizes that bypassing the nitric oxide dependent pathway is an alternative to increasing exercise-induced signaling. Analysis of mouse models treated with nitric oxide-independent guanylate cyclase activators as well as genetic deletion of soluble guanylate cyclase and PDE5A will test this hypothesis. The final aim hypothesizes that anti-inflammatory treatment will decrease pathology in dystrophic mouse models but also increase activity and reduce exercise-induced muscle edema. Analysis of mouse models treated with various anti-inflammatories will test this hypothesis. The overall results of these experiments will help develop as a synergistic treatment with gene therapy as well as provide insights into exercise-induced fatigue and edema in healthy individuals. PUBLIC HEALTH RELEVANCE: This research will contribute to the mission of NIAMS for biomedical research affecting muscles in terms of addressing exercise-induced fatigue and muscle edema. This proposed research will also contribute to the mission of the ARRA in improving the quality of human life while stimulating the economy by providing hiring opportunities for the project as well as providing increased training for our scientists to improve their marketability as independent biomedical researchers who will start their own laboratories.