Related Experiment Videos
Apoptosis is suspended in muscle of mitochondrial encephalomyopathies
Koji Ikezoe1, Masahiro Nakagawa, Chuanzhu Yan
1Department of Neurology, Kyushu Koseinenkin Hospital, Kitakyushu, Fukuoka, 806-8501, Japan.
Abstract:
Over the past few years, many studies have been done on the apoptotic involvement in muscle fiber degeneration in various myopathies, but the occurrence of apoptosis in muscles of mitochondrial encephalomyopathies is still controversial. To confirm whether apoptotic processes are truly related to muscle fiber degeneration in mitochondrial encephalomyopathies, we performed the TUNEL method not only at the light microscopic (LM) but also at the electron microscopic (EM) level for muscles of five MELAS, five CPEO and five MERRF patients and five control muscles. Immunohistochemical studies of Bcl-2, Bax, cytochrome c, Apaf-1, activated caspase-3 and human inhibitor of apoptosis protein XIAP, and immunoblotting of Apaf-1 and XIAP were also carried out. In LM-TUNEL, MELAS, CPEO and MERRF patients had only very small numbers of TUNEL-positive myonuclei: 0.13+/-0.10%, 0.15+/-0.14% and 0.04+/-0.09%, respectively. Almost all of them were seen in ragged-red fibers (RRFs). EM-TUNEL showed no significant increase of DNA fragmentation in RRFs despite mild peripheral chromatin condensation. However, Bax and Apaf-1 expression and cytochrome c release from mitochondria were seen in RRFs. Caspase-3 activation was confirmed in 9.0+/-3.7%, 12.0+/-4.4% and 12.4+/-3.8% of RRFs in MELAS, CPEO and MERRF, respectively, but not in control muscles. Almost all RRFs showed sarcoplasmic expression of XIAP. Thus, there is a possibility that, although apoptotic reactions started in muscles of mitochondrial encephalomyopathies, their execution is rarely completed. Sarcoplasmic expression of XIAP probably leads to the suspension of the apoptotic process in mitochondrial encephalomyopathies.
Insights
Apoptosis involvement in mitochondrial encephalomyopathies muscle degeneration is unclear. While early apoptotic markers are present, the human inhibitor of apoptosis protein XIAP likely halts the process, preventing complete cell death in these muscle diseases.
Area of Science:
- Neurology
- Cell Biology
- Genetics
Background:
- Apoptosis's role in myopathy is studied, but its occurrence in mitochondrial encephalomyopathies remains debated.
- Mitochondrial encephalomyopathies, including MELAS, CPEO, and MERRF, are characterized by muscle fiber degeneration.
Purpose of the Study:
- To investigate the extent and mechanism of apoptosis in muscle fibers of patients with mitochondrial encephalomyopathies.
- To determine if apoptosis execution is completed or inhibited in affected muscle tissues.
Main Methods:
- Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay at light and electron microscopic levels.
- Immunohistochemical analysis of apoptosis-related proteins (Bcl-2, Bax, cytochrome c, Apaf-1, caspase-3, XIAP).
- Immunoblotting for Apaf-1 and XIAP.
Main Results:
- Low percentages of TUNEL-positive myonuclei were observed in MELAS, CPEO, and MERRF patients, primarily in ragged-red fibers (RRFs).
- Electron microscopy showed minimal DNA fragmentation in RRFs, despite signs of early apoptosis like Bax and Apaf-1 expression and cytochrome c release.
- Caspase-3 activation was detected in RRFs of patients but not controls, while XIAP was expressed in the sarcoplasm of almost all RRFs.
Conclusions:
- Apoptotic processes initiate in muscles of mitochondrial encephalomyopathies but are frequently incomplete.
- Sarcoplasmic expression of XIAP likely inhibits the final execution of apoptosis in these conditions.
- This suggests a unique regulatory mechanism of cell death in mitochondrial myopathies.