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DNA fragmentation and BCL-2 expression in infantile spinal muscular atrophy
1Division of Neuropathology, Mainz University Medical Center, Germany.
Abstract:
Chromatin cleavage, a hallmark of apoptosis, was identified by in situ labeling in 55 +/- 7% of the muscle fibers in infantile spinal muscular atrophy (ISMA) and, to a lesser extent, in peripheral neuropathy indicating that DNA fragmentation is not specific to ISMA but a common feature in defect innervation. However, as DNA breaks are also known as a temporary process in differentiating myotubes DNA fragmentation may not always proceed to cell death. Therefore, it is currently not certain whether high rates of DNA fragmentation in ISMA are part of delayed muscle maturation due to neuronal defect or part of fibre breakdown. While atrophic muscle fibres in peripheral neuropathy displayed strong expression of bcl-2, a protein delaying onset of apoptosis, only 30% of the ISMA cases revealed weak bcl-2 expression assuming that immature muscle fibers are not able to produce a sufficient level of bcl-2.
Insights
DNA fragmentation is common in infantile spinal muscular atrophy (ISMA) and peripheral neuropathy due to nerve defects. However, its role in ISMA, whether delayed maturation or fiber breakdown, remains uncertain.
Area of Science:
- Neurology
- Cell Biology
- Genetics
Background:
- Chromatin cleavage, a marker of apoptosis, is observed in muscle fibers.
- DNA fragmentation is a common feature in defective innervation, not exclusive to ISMA.
Purpose of the Study:
- To investigate the significance of DNA fragmentation in infantile spinal muscular atrophy (ISMA).
- To differentiate between delayed muscle maturation and fiber breakdown in ISMA.
Main Methods:
- In situ labeling to detect chromatin cleavage in muscle fibers.
- Analysis of bcl-2 protein expression in ISMA and peripheral neuropathy cases.
Main Results:
- 55 +/- 7% of ISMA muscle fibers showed chromatin cleavage.
- DNA fragmentation was also present in peripheral neuropathy.
- Weak bcl-2 expression was found in 30% of ISMA cases, contrasting with strong expression in peripheral neuropathy.
Conclusions:
- DNA fragmentation is a general response to nerve defects, not specific to ISMA.
- The role of DNA fragmentation in ISMA is unclear, potentially linked to delayed maturation or fiber breakdown.
- Immature muscle fibers in ISMA may have insufficient bcl-2 production, impacting apoptosis regulation.
