Activation of microglial cells triggers a release of brain-derived neurotrophic factor (BDNF) inducing their proliferation in an adenosine A(2A) receptor-dependent manner: A(2A) receptor blockade prevents BDNF release and proliferation of microglia

BACKGROUND: Brain-derived neurotrophic factor (BDNF) has been shown to control microglial responses in neuropathic pain. Since adenosine A(2A) receptors (A(2A)Rs) control neuroinflammation, as well as the production and function of BDNF, we tested to see if A(2A)R controls the microglia-dependent secretion of BDNF and the proliferation of microglial cells, a crucial event in neuroinflammation. METHODS: Murine N9 microglial cells were challenged with lipopolysaccharide (LPS, 100 ng/mL) in the absence or in the presence of the A(2A)R antagonist, SCH58261 (50 nM), as well as other modulators of A(2A)R signaling. The BDNF cellular content and secretion were quantified by Western blotting and ELISA, A(2A)R density was probed by Western blotting and immunocytochemistry and cell proliferation was assessed by BrdU incorporation. Additionally, the A(2A)R modulation of LPS-driven cell proliferation was also tested in primary cultures of mouse microglia. RESULTS: LPS induced time-dependent changes of the intra- and extracellular levels of BDNF and increased microglial proliferation. The maximal LPS-induced BDNF release was time-coincident with an LPS-induced increase of the A(2A)R density. Notably, removing endogenous extracellular adenosine or blocking A(2A)R prevented the LPS-mediated increase of both BDNF secretion and proliferation, as well as exogenous BDNF-induced proliferation. CONCLUSIONS: We conclude that A(2A)R activation plays a mandatory role controlling the release of BDNF from activated microglia, as well as the autocrine/paracrine proliferative role of BDNF.