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Muscular dystrophy: possible role of mitochondrial deficiency in muscle degeneration processes
B Lucas-Heron1, N Schmitt, B Ollivier
1Laboratoire de Physiologie, UER de Médecine et Unité de Recherche CNRS 1340, Nantes, France.
Abstract:
We isolated mitochondria from fast-twitch (extensor digitorum longus) and slow-twitch (soleus) skeletal muscle of the adult rat in normal conditions and 45 days after denervation as well as from skeletal muscle (gastrocnemius) of control and dystrophic (C57BL6J dy/dy and mdx) mice. We searched for the presence of a calcium-specific mitochondrial protein (calmitine) and measured calcium uptake in mitochondria. Our results indicate a possible correlation between the quantity of calmitine present and calcium entry into mitochondria. Both these parameters were elevated in rat fast-twitch and mouse mixed muscle and very low in slow-twitch muscle. They were also very low in dystrophic mouse muscle (C57BL6J dy/dy) with extensive muscle degeneration, but on the contrary elevated in muscle (mdx) with no important signs of degeneration. Finally, we found a normal calmitine concentration and very low calcium uptake in rat extensor digitorum longus after 45 days of denervation. On the basis of these results, it is hypothesized that calmitine synthesis could be subject to neural influence, thus specific for fast-twitch muscle, and that it could be linked to mitochondrial calcium uptake. A decrease in uptake could disturb certain enzymatic activities related to ATP synthesis and bring about muscle degeneration by inhibiting such synthesis. This would occur in the context of reduced calmitine synthesis in the case of genetic anomalies and of inactivation of calmitine after neural disturbance in the case of denervation.
Insights
Mitochondrial calcium uptake and calmitine levels are higher in fast-twitch muscles. Denervation and muscular dystrophy affect these parameters, impacting ATP synthesis and potentially causing muscle degeneration.
Area of Science:
- Mitochondrial biology
- Skeletal muscle physiology
- Neuroscience
Background:
- Mitochondria play a crucial role in cellular energy production and calcium homeostasis.
- Skeletal muscle exhibits distinct fiber types (fast-twitch and slow-twitch) with differing metabolic and functional characteristics.
- Mitochondrial calcium handling is implicated in muscle function and disease.
Purpose of the Study:
- To investigate the role of calmitine, a calcium-specific mitochondrial protein, in skeletal muscle.
- To determine the relationship between calmitine levels, mitochondrial calcium uptake, and muscle fiber type.
- To examine the impact of denervation and muscular dystrophy on calmitine and mitochondrial calcium uptake.
Main Methods:
- Isolation of mitochondria from rat fast-twitch (extensor digitorum longus) and slow-twitch (soleus) muscles.
- Isolation of mitochondria from control and dystrophic (C57BL6J dy/dy, mdx) mouse skeletal muscles.
- Quantification of calmitine and measurement of mitochondrial calcium uptake.
Main Results:
- Calmitine quantity and mitochondrial calcium uptake were elevated in rat fast-twitch and mouse mixed muscles, but low in slow-twitch muscles.
- In dystrophic mice, calmitine and calcium uptake were very low in C57BL6J dy/dy mice with severe degeneration, but elevated in mdx mice with minimal degeneration.
- Denervation of rat extensor digitorum longus muscle resulted in normal calmitine concentration but very low calcium uptake.
Conclusions:
- Calmitine synthesis may be influenced by neural input, showing specificity for fast-twitch muscles.
- Calmitine is potentially linked to mitochondrial calcium uptake, with implications for ATP synthesis.
- Altered calmitine levels and mitochondrial calcium uptake, due to genetic anomalies or neural disturbances, may contribute to muscle degeneration by affecting energy production.