Function and production of the chemokines CCL2 and CCL7 during brain inflammation

In the brain, recruitment of immune cells to areas of injury or disease can result in increased inflammation and subsequent neurodegeneration. Chemokines are small chemotactic cytokines that mediate recruitment of specific cell types. The chemokines CCL2 and CCL7 have been found upregulated in numerous diseases associated with inflammatory cell infiltrates, and astrocytes are a major source of both chemokines. However, the regulation of CCL2 and CCL7 in astrocytes has not been fully elucidated. Further, the role of CCL2 in mediating peripherally induced brain inflammation is unknown. Therefore, in this dissertation we tested the hypothesis that during brain inflammation, activated astrocytes produce the chemokines CCL2 and CCL7, which leads to recruitment of microglia and other immune cells and increased neuroinflammation. First, we tested the ability of the pro-inflammatory cytokines interleukin (IL)-1beta and tumor necrosis factor (TNF)-alpha to stimulate CCL2 and CCL7 protein production in rat astrocyte cultures, and we examined signaling pathways involved in the cytokine-stimulated chemokine upregulation. We demonstrate that IL-1beta and TNF-alpha upregulate CCL2 and CCL7 production in a dose- and time-dependent manner. These data document for the first time that CCL7 protein production can be stimulated in astrocytes by cytokines. In addition, we show that nuclear factor kappa B (NFkappaB) pathways are important for the cytokine-stimulated CCL2 and CCL7 production, while mitogen activated protein kinase (MAPK) pathways may also contribute but to a lesser degree. Second, we explored the role of the chemokine CCL2 in activation of the brain during acute systemic inflammation. We demonstrate that despite increased peripheral inflammation, CCL2 knockout (KO) mice show reduced upregulation of brain cytokine and chemokine production and lower activation of brain immune cells compared to control mice. These decreased brain responses are correlated with lower serum glucocorticoid levels in the KO mice. These data suggest that although there was an exaggerated inflammatory response in the periphery after LPS injection, the lack of CCL2 prevented this inflammatory signal from being transferred to the brain. These data demonstrate a critical role for CCL2 in regulating brain inflammation and provide a foundation for future studies exploring recruitment of inflammatory cells in the brain.