Activated microglial cells have been implicated in a number of neurodegenerative disorders, including Alzheimer's disease (AD), multiple sclerosis (MS), and HIV dementia. It is well known that inflammatory mediators such as nitric oxide (NO), cytokines, and chemokines play an important role in microglial cell-associated neuron cell damage. Our previous studies have shown that CD40 signaling is involved in pathological activation of microglial cells. Many data reveal that cannabinoids mediate suppression of inflammation in vitro and in vivo through stimulation of cannabinoid receptor 2 (CB₂).

In this study, we investigated the effects of a cannabinoid agonist on CD40 expression and function by cultured microglial cells activated by IFN-γ using RT-PCR, Western immunoblotting, flow cytometry, and anti-CB₂ small interfering RNA (siRNA) analyses. Furthermore, we examined if the stimulation of CB₂ could modulate the capacity of microglial cells to phagocytise Aβ_1–42 peptide using a phagocytosis assay.

We found that the selective stimulation of cannabinoid receptor CB₂ by JWH-015 suppressed IFN-γ-induced CD40 expression. In addition, this CB₂ agonist markedly inhibited IFN-γ-induced phosphorylation of JAK/STAT1. Further, this stimulation was also able to suppress microglial TNF-α and nitric oxide production induced either by IFN-γ or Aβ peptide challenge in the presence of CD40 ligation. Finally, we showed that CB₂ activation by JWH-015 markedly attenuated CD40-mediated inhibition of microglial phagocytosis of Aβ_1–42 peptide. Taken together, these results provide mechanistic insight into beneficial effects provided by cannabinoid receptor CB₂ modulation in neurodegenerative diseases, particularly AD.