A mitochondrial component of neurodegeneration in multiple sclerosis

Neurodegeneration is the main pathological correlate of accumulating disability in progressive stages of Multiple Sclerosis (MS), but both histologic and imaging studies detect significant tissue loss even in early disease. These observations raise the question as to whether neurodegeneration in MS is a primary mechanism or whether it develops secondary to inflammation and demyelination. Recent data suggest that the atrophy of brain and cord is directly linked to inflammation and may partly be independent of demyelination. Released products of both residential and infiltrating immune cells can induce ultrastructural changes and cell-death by multiple mechanism. We propose that the inflammation-induced tissue response is controlled by genetic variations and to some extent involves a mitochondrion-driven mechanism in MS, similar to that described in the final pathway of other neurodegenerative disorders. Current therapeutic strategies primarily target the immune system which results in a successful down-regulation of plaque formation and of relapse rate. However, measures of clinical disability best correlate with the degree of neurodegeneration rather than with the volume of plaques, and these immune-modulating regimens may only incompletely affect the accumulating tissue loss. Considering the need for additional therapeutic strategies, we emphasize the degenerative components, and review a mitochondrial mechanism of tissue loss potentially involved in the process of MS.