Astrocyte-associated axonal damage in pre-onset stages of experimental autoimmune encephalomyelitis

Recent studies of axon-glia and glia-glia communication have emphasized interactivity and interdependence between central nervous system (CNS) components. Concurrently, data from imaging, biochemical, and morphological studies have changed the view of multiple sclerosis (MS) from a neuroinflammatory condition with primary demyelination to one in which cumulative axonal damage drives progression. We therefore studied axonal damage in the context of inflammation and glial responses, from the pre-clinical to onset stage of murine experimental autoimmune encephalomyelitis (EAE), an established MS model. We report three major findings: (1) the first evidence of axonal injury before significant T-cell entry into the parenchyma, (3) coincidence of the earliest manifestation of axonal damage and astrocytic responses, and (3) an association between accumulation of axonal and astrocytic changes and specific forms of MS. These data demonstrate the relationship between the initiation of axonal injury and early inflammation. Significantly, we show that, in common with a growing number of neurodegenerative conditions, the pathology of murine EAE is characterized by early active contribution from astrocytes. This marks a change in the understanding of the role of astrocytes in MS pathogenesis and has important implications for the development of neuroprotective strategies.