The regulation of utrophin, the autosomal homologue of dystrophin, has been studied in the canine X–linked model of Duchenne muscular dystrophy. Dystrophic muscle has been shown to exhibit abnormal sarcolemmal expression of utrophin, in addition to the normal expression at the neuromuscular junction, in peripheral nerves, vascular tissues and regenerating fibres. To establish whether this abnormal presence of utrophin in dystrophic muscle is a consequence of continued expression following regeneration, or is attributable to a disease related up–regulation, the expression of utrophin was compared immunocytochemically with that of dystrophin, β–spectrin and neonatal myosin in regenerating normal and dystrophic canine muscle, following necrosis induced by the injection of venom from the snake Notechis scutatis. In normal regenerating muscle, sarcolemmal utrophin and dystrophin were detected concomitantly from 2–3 d post–injection, prior to the expression of β–spectrin. Down–regulation of utrophin was apparent in some fibres from 7 d, and it was no longer present on the extra–junctional sarcolemma by 14 d. Neonatal myosin was still present in all fibres at this stage, but dystrophin and β–spectrin had been fully restored. In dystrophic regenerating muscle, downregulation of utrophin occurred from 7 d, although it persisted on some fibres until 28 d, longer than in normal muscle. At 42 d, however, utrophin in dystrophic muscle was only detected in a population of small fibres thought to represent a second cycle of regeneration, with no immunolabelling of mature fibres. The results show that most utrophin is down–regulated in regenerating dystrophic fibres, prior to neonatal myosin, thus abnormal sarcolemmal expression of utrophin in dystrophic muscle is unlikely to be a continuation of the maturational process. Persistence of both utrophin and neonatal myosin, however, suggest a delay in the maturation of dystrophic muscle. In addition, a second cycle of degeneration and regeneration in dystrophic muscle does not occur whilst utrophin is still present, suggesting it may have a protective role against fibre damage and necrosis.
|Number of pages||9|
|Journal||Neuropathology and Applied Neurobiology|
|Publication status||Published - aug. 1994|
ASJC Scopus subject areas
- Pathology and Forensic Medicine
- Clinical Neurology
- Physiology (medical)