Characterization of initiator and effector caspase expressions in dystrophinopathies

Area of Science:

• Molecular Biology
• Cell Biology
• Neuromuscular Disorders

Background:

• Apoptotic cell death mechanisms contribute to muscle fiber loss in dystrophin-deficient muscle.
• Limited knowledge exists regarding the final stages of muscle fiber apoptosis in these conditions.

Purpose of the Study:

• To investigate the expression and role of apoptotic protease cascade members in dystrophinopathies.
• To elucidate the specific caspases involved in muscle fiber degradation.

Main Methods:

• Immunohistochemistry and Western blot analyses were performed on muscle biopsy specimens from 14 patients with dystrophinopathy.
• Expression of APAF-1, caspase-9, caspase-2, caspase-6, and caspase-7 was assessed.

Main Results:

• Caspase-9, -6, and -7 showed upregulation in non-regenerating, atrophic muscle fibers.
• Predominant caspase immunoreactivity was observed in regenerating muscle fibers.
• Western blot analyses confirmed the upregulation of these caspases.

Conclusions:

• Activated caspase-9 initiates a proteolytic cascade involving caspase-6 and -7, leading to muscle fiber degradation in dystrophinopathies.
• The lack of coexpression of APAF-1 suggests alternative pathways for caspase-9 activation, independent of the apoptosome, in these disorders.