Brain-Derived Neurotrophic Factor Induces Sustained Elevation of Intracellular Ca2+ in Rodent Microglia

Abstract

Microglia are intrinsic immune cells that release factors, including proinflammatory cytokines, NO, and neurotrophins, following activation after disturbance in the brain. Elevation of intracellular Ca2+ concentration ([Ca2+]i) is important for microglial functions, such as the release of cytokines and NO from activated microglia. There is increasing evidence suggesting that pathophysiology of neuropsychiatric disorders is related to the inflammatory responses mediated by microglia. Brain-derived neurotrophic factor (BDNF) is a neurotrophin well known for its roles in the activation of microglia as well as in pathophysiology and/or treatment of neuropsychiatric disorders. In this study, we observed that BDNF induced a sustained increase in [Ca2+]i through binding with the truncated tropomyosin-related kinase B receptor, resulting in activation of the PLC pathway and store-operated calcium entry in rodent microglial cells. RT-PCR and immunocytochemical techniques revealed that truncated tropomyosin-related kinase B-T1 receptors were highly expressed in rodent microglial cells. Sustained activation of store-operated calcium entry occurred after brief BDNF application and contributed to the maintenance of sustained [Ca2+]i elevation. Pretreatment with BDNF significantly suppressed the release of NO from activated microglia. Additionally, pretreatment of BDNF suppressed the IFN-γ-induced increase in [Ca2+]i, along with a rise in basal levels of [Ca2+]i in rodent microglial cells. We show direct evidence that rodent microglial cells are able to respond to BDNF, which may be important for the regulation of inflammatory responses, and may also be involved in the pathophysiology and/or the treatment of neuropsychiatric disorders.

Brain-derived Neurotrophic Factor (BDNF) Induces Sustained Intracellular Ca2+ Elevation through the Up-regulation of Surface Transient Receptor Potential 3 (TRPC3) Channels in Rodent Microglia

“…In addition, pretreatment with BDNF suppressed the release of NO from murine microglial cells activated by IFN-␥ (5). To date, BDNF is also well known for its involvement in the pathophysiology of neuropsychiatric disorders (4,5).…”

“…We have reported previously that BDNF induces a sustained increase in intracellular Ca 2ϩ concentration ([Ca 2ϩ ] i ) through the activation of the phospholipase C (PLC) 2 pathway in rodent microglial cells (5). We also tested the effect of 2-aminoethoxydiphenyl borate or SKF-96365, both of which can inhibit canonical transient receptor potential (TRPC) channels (6,7) and showed that sustained activation of TRPC channels occurred after a brief treatment with BDNF and contributed to the maintenance of BDNF-induced sustained intracellular Ca 2ϩ elevation (5).…”

“…We have reported previously that BDNF induces a sustained increase in intracellular Ca 2ϩ concentration ([Ca 2ϩ ] i ) through the activation of the phospholipase C (PLC) 2 pathway in rodent microglial cells (5). We also tested the effect of 2-aminoethoxydiphenyl borate or SKF-96365, both of which can inhibit canonical transient receptor potential (TRPC) channels (6,7) and showed that sustained activation of TRPC channels occurred after a brief treatment with BDNF and contributed to the maintenance of BDNF-induced sustained intracellular Ca 2ϩ elevation (5). In this study, we examined whether TRPC3 channels contribute to the maintenance of BDNF-induced sustained intra-cellular Ca 2ϩ elevation using the pyrazole compound 3 (Pyr3), a selective inhibitor of TRPC3 channels, which does not affect the activity of other TRPC channel members (8,9), in rodent microglial cells.…”

Physiology of Microglia

“…Activation of these receptors by BDNF resulted in sustained [Ca 2ϩ ] i elevation, which was mediated by an initial PLC/InsP 3 -driven Ca 2ϩ release from the ER that followed by a long-lasting activation of the SOCE. Incubation with BDNF also decreased release of NO from the activated microglia (597). LPS-induced activation of microglia can trigger the expression of NGF in cultured microglial cells, which can also be induced by stimulation of A 2 adenosine receptors (366).…”

Calcium signaling in axon guidance

“…In response to a chemotropic factor such as netrin-1, brain-derived neurotrophic factor (BDNF), or nerve growth factor (NGF), phospholipase C (PLC) is activated [24,25], which hydrolyzes phosphatidylinositol 4,5-bisphosphate (PIP 2 ) into IP 3 and diacylglycerol. Once created, IP 3 selectively binds to IP 3 receptors (IP 3 Rs) located on the surface of the endoplasmic reticulum (ER), initiating IICR [26].…”