The machanism of oligodendroglial apoptosis of in the model of the genetic demyelination.

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The twitcher mouse is an authentic model of a human Krabbe disease, which is caused by the deficiency of galactosylceramidase. After postnatal day 30, the number of oligodendroglia progressive decreased with resultant demyelination in the CNS.In this study, we first found out that oligodendroglia in the twitcher cerebrum were depleted by apoptosis judgeby the morphological criteria as well as the presence of TUNEL-positive oligodendroglia and DNA laddering. However, oligodendroglia in the spinal cord was suggested to take a necrotic pathway rather than apoptosis leading to the cell death. Thus, even if thebasic defect is common to all twitcher oligodendroglia, the environmental factors may decide what pathways they take to the eventual death.We also recognized that TNF-α, a well-established apoptotic molecule in vitro, became expressed in concordance with the progression of demyelination in the twitcher brains, whereas TNF-α is not expressed in the age-matched normal controls. Double labeling revealed that TNF-α was expressed in activated microglia/macrophages in the twitcher brains, especially in the cerebellar white matter and the cerebellopontine angle. These sites were severely demyelinated with a lot of apoptotic oligodendrocytes. These lines of evidence indicated that the apoptosis of oligodendroglia in these lesions was progressed via the TNF-α-mediated pathway. We are now investigating the downstream cascade following the TNF-α induction in activated microglia.To know the exact mechanism how oligodendroglia die may make the rational therapy available for this genetic demyelination.