Loss of astrocyte connexin 43 and 30 modulates CNS myelin and inflammation
Lutz, Sarah Elizabeth
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In the mammalian brain, astrocytes express the gap junction (GJ) proteins connexin 43 (Cx43) and Cx30. These form junctions between astrocytes and astrocytes, astrocytes and oligodendrocytes, and astrocytes and myelin. Previous research has shown that loss of oligodendrocyte GJs results in oligodendrocyte and myelin pathology. In this study, we asked whether loss of astrocyte GJs affects oligodendrocytes and myelin. Mice with GFAP-Cre targeted deletion of Cx43 and global loss of Cx30 (double knock-out, dKO) were studied using western blotting, immunohistochemistry, electron microscopy, and functional assays. Commencing around post-natal day 23 and persisting into old age, widespread white matter pathology in dKO mice included oligodendrocyte vacuolation and intramyelinic edema. Astrocytic edema occurred in the CA1 region of the hippocampus. dKO mice had fewer CC1-positive mature oligodendrocytes and reduced myelin basic protein (MBP). In contrast, mice expressing a single allele of either Cx43 or Cx30 exhibited no pathology and normal myelination. Compared with single connexin knock-outs, dKO mice were impaired in rotarod, balance beam and object recognition tasks.;To correlate Cx43 expression with white matter pathology in human disease, we examined multiple sclerosis tissues using western blotting for Cx43 and immunostaining for Cx43, GFAP, aquaporin 4, the Golgi marker GM130, MBP, and DAPI (for inflammation). Chronic active multiple sclerosis lesions showed loss of diffuse Cx43 puncta along astrocytic processes, excessive Cx43 accumulation in perivascular endfeet, and partial retention in the Golgi. Chronic silent lesions had little or no detectable Cx43 protein.;Cx43 is potently downregulated in cultured astrocytes activated with proinflammatory cytokines, a finding that can be replicated in vivo in experimental autoimmune encephalomyelitis (EAE, an animal model for multiple sclerosis). To test if loss of Cx43 might contribute to pathogenesis, we examined susceptibility of astrocyte GJ-deficient mice to MOG35-55 induced EAE. Cx43 single KO and Cx43/Cx30 dKO mice exhibited more severe clinical signs of disease.;We conclude that loss of astrocytic GJ results in white and gray matter pathology, and has functional consequences for physiologic and pathophysiologic processes. Taken together, these data support a role for astrocyte connexins for the proper functioning of glial cell populations.