In inflammatory CNS conditions such as multiple sclerosis (MS),

No abstract

Loss of blood-brain barrier (BBB) integrity is believed to be an early and significant event in lesion pathogenesis in the inflammatory demyelinating disease multiple sclerosis (MS), and understanding mechanisms involved may lead to novel therapeutic avenues for this disorder. Well-differentiated endothelium forms the basis of the BBB, while astrocytes control the balance between barrier stability and permeability via production of factors that restrict or promote vessel plasticity. In this study, we report that the proinflammatory cytokine IL-1β, which is prominently expressed in active MS lesions, causes a shift in the expression of these factors to favor plasticity and permeability. The transcription factor, hypoxia inducible factor-1 (HIF-1), plays a significant role in this switch. Using a microarray-based approach, we found that in human astrocytes, IL-1β induced the expression of genes favoring vessel plasticity, including HIF-1α and its target, vascular endothelial growth factor-A (VEGF-A). Demonstrating relevance to MS, we showed that HIF-1α and VEGF-A were expressed by reactive astrocytes in active MS lesions, while the VEGF receptor VEGFR2/flk-1 localized to endothelium and IL-1 to microglia/macrophages. Suggesting functional significance, we found that expression of IL-1β in the brain induced astrocytic expression of HIF-1α, VEGF-A, and BBB permeability. In addition, we confirmed VEGF-A to be a potent inducer of BBB permeability and angiogenesis, and demonstrated the importance of IL-1β-induced HIF-1α in its regulation. These results suggest that IL-1β contributes to BBB permeability in MS via reactivation of the HIF–VEGF axis. This pathway may represent a potential therapeutic target to restrict lesion formation.

In the developing CNS, Notch1 and its ligand, Jagged1, regulate oligodendrocyte differentiation and myelin formation, but their role in repair of demyelinating lesions in diseases such as multiple sclerosis remains unresolved. To address this question, we generated a mouse model in which we targeted Notch1 inactivation to oligodendrocyte progenitor cells (OPCs) using Olig1Cre and a floxed Notch1 allele, Notch1 12f . During CNS development, OPC differentiation was potentiated in Olig1Cre:Notch1 12f/12f mice. Importantly, in adults, remyelination of demyelinating lesions was also accelerated, at the expense of proliferation within the progenitor population. Experiments in vitro confirmed that Notch1 signaling was permissive for OPC expansion but inhibited differentiation and myelin formation. These studies also revealed that astrocytes exposed to TGF-␤1 restricted OPC maturation via Jagged1-Notch1 signaling. These data suggest that Notch1 signaling is one of the mechanisms regulating OPC differentiation during CNS remyelination. Thus, Notch1 may represent a potential therapeutical avenue for lesion repair in demyelinating disease.autoimmunity ͉ CNS repair ͉ multiple sclerosis ͉ oligodendrocyte progenitor ͉ myelin

No abstract