Functional importance of inositol‐1,4,5‐triphosphate‐induced intracellular Ca²⁺ mobilization in galanin‐induced microglial migration

Abstract

J. Neurochem. (2011) 117, 61–70. Abstract Galanin (GAL) is a neuropeptide which is up‐regulated following neuronal axotomy or inflammation. One subtype of GAL receptor (GalR2) is reported to be expressed in the brain’s immune cell population, microglia. In the present study, we investigated the effect of GAL on microglial migration and compared the mechanism with that of bradykinin (BK). GAL significantly increased the migration of rat cultured microglia at 0.1 pM. The GAL‐induced signal cascade was partly similar to that induced by BK. It was not dependent on Gi/o protein but involved activation of protein kinase C, phosphoinositide 3‐kinase and Ca2+‐dependent K+ channels. However, reverse‐mode activation of the Na+/Ca2+‐exchanger 1 was not involved in GAL‐induced microglial migration, unlike BK‐induced migration. Likewise, nominally‐free extracellular Ca2+ inhibited BK‐induced migration but not GAL‐induced migration. An inositol‐1,4,5‐triphosphate receptor antagonist significantly inhibited GAL‐induced migration. GAL‐induced Ca2+ signaling did not induce nitric oxide synthase expression, but up‐regulated class II major histocompatibility complex expression. These results indicate that activation of inositol‐1,4,5‐triphosphate receptor and increase in intracellular Ca2+ are important for GAL‐induced migration and immunoreactivity in microglia. The differences in down‐stream signal transduction induced by GAL and BK suggest that GAL and BK may control distinct microglial functions under pathological conditions.

Physiology, Signaling, and Pharmacology of Galanin Peptides and Receptors: Three Decades of Emerging Diversity

“…Endogenous GAL 2 -induced activation of the MAPK/ERK pathway via PKC has been reported in rodent hippocampal neurons (Hawes et al, 2006;Elliott-Hunt et al, 2007), rat microglial cells (Ifuku et al, 2011), rat PC12 pheochromocytoma cells (Hawes et al, 2006), and human small-cell lung cancer (SCLC) cells (Seufferlein and Rozengurt, 1996), although in the latter, MAPK/ ERK pathway activation can also occur independently of PKC (Wittau et al, 2000). GAL 2 predominantly couples to a G q/11 -type G protein, leading to phospholipase C activation, which stimulates Ca 2+ release via inositol phosphate hydrolysis and opens Ca 2+ -dependent ion channels in a PTXresistant manner, in both GAL 2 -transfected cell lines (Smith et al, 1997b;Borowsky et al, 1998;Fathi et al, 1998;Pang et al, 1998;Wang et al, 1998c) and GAL 2 -expressing rat microglial cells (Ifuku et al, 2011). GAL 2 activation led to a decrease in both Rho and Cdc42 GTPase activity and activation of cofilin in rat PC12 pheochromocytoma cells (Hobson et al, 2013).…”

“…Similarly, intracerebroventricular injection of GALP into Sprague-Dawley rats stimulated production of IL-1a and IL-1b in macrophages and/or microglia in some brain areas (Man and Lawrence, 2008). The BV2 mouse microglia cell line and cultured rat microglial cells solely express GAL 2 (Su et al, 2003;Ifuku et al, 2011), which mediates galanin-induced cell migration and upregulation of class II major histocompatibility complex expression in these innate immune brain cells (Ifuku et al, 2011). Microglial cells also participate in the events leading to multiple sclerosis (Weissert, 2013), and a recent study detected a marked upregulation of galanin expression in microglia associated with multiple sclerosis lesions in postmortem brain tissue from chronic multiple sclerosis patients (Wraith et al, 2009).…”

Galanin System in Human Glioma and Pituitary Adenoma

“…Recently it has been shown that GAL is able to influence immune cell behavior by modulating cytokine expression and release, as demonstrated in human neutrophils, natural killer cells, monocytes and macrophages (7,48,54,55). Furthermore, galanin down-regulates microglial tumor necrosis factor-alpha production and induces microglial migration (56,57). Thus, strategies targeting tumor-supportive myeloid cells represent an encouraging novel therapeutic approach and could also be considered for the GAL system.…”

Calcium ion influx in microglial cells: Physiological and therapeutic significance

“…Galanin (GAL) receptor subtypes, designated as GalR1, GalR2, and GalR3, among which GalR2 is reported to be expressed in rat cultured microglia (Su et al, ), activate PKC‐, PI 3 K‐, and Ca 2+ ‐dependent K + channels. GAL downregulates production of TNF‐α (Su et al, ) and induces microglial migration and upregulation of class II major histocompatibility complex expression in microglial cells (Ifuku et al, ). Complementary receptors are present in mouse cultured microglial cells, and application of complement factors (C5a and C3a) induces [Ca 2+ ] response in in situ and in cultured microglial cells by Ca 2+ release from internal pools and subsequent activation of Ca 2+ entry controlled by the filling state of the intracellular stores (Möller et al, ).…”