Novel calcium influx pathways in microglia and dorsal root ganglion neurons.

摘要

Ca2+ is critical for cellular signaling, thus the balance between Ca2+ entry and removal from a cell is tightly regulated. In these studies, both pharmacological and genetic techniques were used to study two novel Ca2+ signaling pathways in microglia and dorsal root ganglion (DRG) neurons.; Chemokines initiate activation and migration of microglia. In this initial study, the signal transduction pathway linking activation of the chemokine receptor CCR5 to an elevation in [Ca2+]i in cultured microglia was examined. The CCL5-induced response required Janus kinase (JAK) activity and the stimulation of an inhibitory G protein. Multiple downstream signaling pathways were involved including the lipid kinase, phosphatidylinositol 3-kinase (PI3K), Bruton's tyrosine kinase (Btk) and phospholipase C (PLC)-mediated release of Ca2+ from inositol 1,4,5 triphosphate (IP3 )-sensitive stores. However, the majority of the [Ca2+] i increase was derived from sources activated by NAD metabolites. Cyclic ADP-ribose (cADPR) evoked Ca2+ release from intracellular stores, and ADPR evoked Ca2+ influx via a nimodipine-sensitive channel. Thus, a multistep cascade couples CCRS activation to Ca2+ increases in human microglia.; CCE is an important influx pathway originally discovered in immune cells, recently it was also found in neuronal cells. The presenilins participate in several signal transduction pathways including Ca2+ regulation. Using both genetic and pharmacological approaches, the effects of gamma-secretase inhibition on Ca2+ influx pathways, including CCE, were studied in rat DRG neurons. Expression of a dominant negative presenilin mutant (PS1-D257A) or treatment with the gamma-secretase inhibitor DAPT inhibited gamma-secretase activity and prolonged CCE. Furthermore, capsaicin-induced increases in [Ca 2+]i were prolonged in cells expressing PSl-D257A. This increase in [Ca2+]i resulted from enhanced CCE secondary to capsaicin activation of vanilloid receptors localized to the ER and to an increase in amplitude and impaired inactivation of inward currents following capsaicin application. Thus, gamma-secretase activity modulates the gating of ion channels in sensory neurons highlighting the role of the ER and proteolysis in ion channel regulation.; In summary, these studies identify unique signaling pathways. Because changes in [Ca2+]i affect synaptic transmission, chemotaxis, and gene expression, pharmacologic modulation of Ca2+ signaling pathways may alter inflammatory and degenerative processes in the central nervous system.