Leptomeningeal Cells Transduce Peripheral Macrophages Inflammatory Signal to Microglia in Reponse toPorphyromonas gingivalisLPS
We report here that the leptomeningeal cells transduce inflammatory signals from peripheral macrophages to brain-resident microglia in response toPorphyromonas gingivalis (P.g.)LPS. The expression of Toll-like receptor 2 (TLR2), TLR4, TNF-α, and inducible NO synthase was mainly detected in the gingival macrophages of chronic periodontitis patients. Inin vitrostudies,P.g.LPS induced the secretion of TNF-αand IL-1βfrom THP-1 human monocyte-like cell line and RAW264.7 mouse macrophages. Surprisingly, the mean mRNA levels of TNF-αand IL-1βin leptomeningeal cells after treatment with the conditioned medium fromP.g.LPS-stimulated RAW264.7 macrophages were significantly higher than those after treatment withP.g.LPS alone. Furthermore, the mean mRNA levels of TNF-αand IL-1βin microglia after treatment with the conditioned medium fromP.g.LPS-stimulated leptomeningeal cells were significantly higher than those afterP.g.LPS alone. These observations suggest that leptomeninges serve as an important route for transducing inflammatory signals from macrophages to microglia by secretion of proinflammatory mediators during chronic periodontitis. Moreover, propolis significantly reduced theP.g.LPS-induced TNF-αand IL-1βproduction by leptomeningeal cells through inhibiting the nuclear factor-κB signaling pathway. Together with the inhibitory effect on microglial activation, propolis may be beneficial in preventing neuroinflammation during chronic periodontitis.