Novel Effects of the MuSK System in Muscles of Wild-Type and mdx Mice
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Type
ThesisThesis type
Doctor of PhilosophyAuthor/s
Ban, JoanneAbstract
The agrin/Muscle specific kinase (MuSK)/Rapsyn is the most established signalling pathway promoting the development of the neuromuscular junction. Duchenne muscular dystrophy (DMD) is an X-linked degenerative muscle disorder caused by complete loss of dystrophin protein from muscle ...
See moreThe agrin/Muscle specific kinase (MuSK)/Rapsyn is the most established signalling pathway promoting the development of the neuromuscular junction. Duchenne muscular dystrophy (DMD) is an X-linked degenerative muscle disorder caused by complete loss of dystrophin protein from muscle sarcolemma and destabilisation of dystrophin associated protein complex (DAPC). A recent study reported reduced MuSK expression in the muscle of (dystrophin-deficient) mdx mouse and suggested that this might contribute to the dystrophic phenotype. In this thesis, AAV-MuSK/Rapsyn-GFP was injected into the tibialis anterior muscle of mdx mice to investigate the effects of elevating expression of MuSK or Rapsyn. Short term (3 weeks) overexpression of MuSK or rapsyn partially protected muscles of 8 week old mdx mice against acute eccentric contraction (EC)-induced loss of force. Immunofluorescence analysis showed higher level of β-dystroglycan (β-DG) intensity at the sarcolemma of MuSK overexpressed dystrophic muscle. In addition, the total β-DG protein was markedly elevated in MuSK overexpressed muscle homogenates (Chapter 3). β-DG is known to be a core DAPC that prevents EC-induced loss force, thus the restoration of β-DG may help to explain how MuSK protects dystrophic muscle from EC-induced loss of force. Early injection of AAV-MuSK-GFP into muscles of 3-4 weeks old mdx mice leads to significant reduction muscle mass at 12 weeks, resulting in an increase in specific force production compared to the control muscle. MuSK also caused a modest, but significant, reduction of the percentage of centrally nucleated myofibre (Chapter 4). Another key effect of overexpressing MuSK was a decay of nerve-evoked force during each tetanus. The loss of force increased progressively with the duration of the nerve stimulation train (100 or 150Hz) at 400, 800,1600ms. No decay of force was observed when the same muscle was stimulated directly, ruling out the possibility of muscle fatigue (Chapter 5). These results suggest that overexpressing MuSK can reduce the capacity for neuromuscular transmission, a possible negative-feedback function for MuSK. Together, these findings suggest the additional roles of MuSK in regulating neuromuscular transmission and protecting the extrasynaptic sarcolemma of muscle fibres in mdx mice.
See less
See moreThe agrin/Muscle specific kinase (MuSK)/Rapsyn is the most established signalling pathway promoting the development of the neuromuscular junction. Duchenne muscular dystrophy (DMD) is an X-linked degenerative muscle disorder caused by complete loss of dystrophin protein from muscle sarcolemma and destabilisation of dystrophin associated protein complex (DAPC). A recent study reported reduced MuSK expression in the muscle of (dystrophin-deficient) mdx mouse and suggested that this might contribute to the dystrophic phenotype. In this thesis, AAV-MuSK/Rapsyn-GFP was injected into the tibialis anterior muscle of mdx mice to investigate the effects of elevating expression of MuSK or Rapsyn. Short term (3 weeks) overexpression of MuSK or rapsyn partially protected muscles of 8 week old mdx mice against acute eccentric contraction (EC)-induced loss of force. Immunofluorescence analysis showed higher level of β-dystroglycan (β-DG) intensity at the sarcolemma of MuSK overexpressed dystrophic muscle. In addition, the total β-DG protein was markedly elevated in MuSK overexpressed muscle homogenates (Chapter 3). β-DG is known to be a core DAPC that prevents EC-induced loss force, thus the restoration of β-DG may help to explain how MuSK protects dystrophic muscle from EC-induced loss of force. Early injection of AAV-MuSK-GFP into muscles of 3-4 weeks old mdx mice leads to significant reduction muscle mass at 12 weeks, resulting in an increase in specific force production compared to the control muscle. MuSK also caused a modest, but significant, reduction of the percentage of centrally nucleated myofibre (Chapter 4). Another key effect of overexpressing MuSK was a decay of nerve-evoked force during each tetanus. The loss of force increased progressively with the duration of the nerve stimulation train (100 or 150Hz) at 400, 800,1600ms. No decay of force was observed when the same muscle was stimulated directly, ruling out the possibility of muscle fatigue (Chapter 5). These results suggest that overexpressing MuSK can reduce the capacity for neuromuscular transmission, a possible negative-feedback function for MuSK. Together, these findings suggest the additional roles of MuSK in regulating neuromuscular transmission and protecting the extrasynaptic sarcolemma of muscle fibres in mdx mice.
See less
Date
2018-01-29Licence
The author retains copyright of this thesis. It may only be used for the purposes of research and study. It must not be used for any other purposes and may not be transmitted or shared with others without prior permission.Faculty/School
Faculty of Medicine and Health, School of Medical SciencesDepartment, Discipline or Centre
Discipline of Physiology, Molecular Neurobiology LaboratoryAwarding institution
The University of SydneyShare