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Maturation-dependent apoptotic cell death of oligodendrocytes in myelin-deficient rats
J B Grinspan1, M Coulalaglou, J S Beesley
1Department of Research Neurology, Children's Hospital of Philadelphia, Pennsylvania 19104, USA. Grinspan@email.chop.edu
Abstract:
Mutations in the proteolipid protein gene (PLP/plp), which encodes the major intrinsic membrane protein in central nervous system (CNS) myelin, cause inherited dysmyelination in mammals. One of these mutants, the myelin-deficient (md) rat, has severe dysmyelination that is associated with oligodendrocyte cell death. Using the terminal deoxynucleotidyl transferase (TdT)-mediated dUTP-biotin nick end-labeling (TUNEL) assay, which labels apoptotic cells, we find that cell death is increased in multiple white matter tracts of md rats. The tracts that myelinate the earliest show the earliest increase in cell death, and cell death persists for at least 22 days, the lifespan of these mutant animals. In all tracts, and at all developmental ages examined, apoptotic cells expressed the markers of mature oligodendrocytes, such as myelin basic protein, myelin-associated glycoprotein, and the Rip antigen, but not chondroitin sulfate proteoglycan, a marker of oligodendrocyte precursors. Mature oligodendrocytes fail to accumulate in md brain because they die before they fully mature.
Insights
Mutations in the proteolipid protein gene cause inherited central nervous system (CNS) dysmyelination. In myelin-deficient rats, mature oligodendrocytes undergo apoptosis, preventing proper myelin development.
Area of Science:
- Neuroscience
- Genetics
- Cell Biology
Background:
- Mutations in the proteolipid protein gene (PLP/plp) lead to inherited dysmyelination in the central nervous system (CNS).
- The myelin-deficient (md) rat model exhibits severe dysmyelination and oligodendrocyte cell death.
Purpose of the Study:
- To investigate the cellular mechanisms underlying oligodendrocyte loss in the myelin-deficient (md) rat.
- To determine if oligodendrocyte cell death contributes to the severe dysmyelination observed in md rats.
Main Methods:
- Utilized the terminal deoxynucleotidyl transferase (TdT)-mediated dUTP-biotin nick end-labeling (TUNEL) assay to detect apoptotic cells.
- Examined cell death in various white matter tracts across different developmental ages in md rats.
- Assessed the expression of mature oligodendrocyte markers (myelin basic protein, myelin-associated glycoprotein, Rip antigen) and precursor markers (chondroitin sulfate proteoglycan) in apoptotic cells.
Main Results:
- Increased apoptotic cell death was observed in multiple white matter tracts of md rats.
- Early-myelinating tracts showed the earliest and most significant increase in cell death, which persisted throughout the animals' lifespan.
- Apoptotic cells consistently expressed markers of mature oligodendrocytes, not oligodendrocyte precursors.
Conclusions:
- Mature oligodendrocytes in md rats die via apoptosis before completing maturation.
- Oligodendrocyte cell death is a primary factor contributing to the failure of myelin accumulation in this model of inherited dysmyelination.