Effect of GABAA receptor activation on UT-coupled signaling pathways in rat cortical astrocytes

International audienceCultured rat cortical astrocytes express two types of urotensin II (UII) binding sites: a high affinity site corresponding to the UT (GPR14) receptor and a low affinity site that has not been fully characterized. Activation of the high affinity site in astroglial cells stimulates polyphosphoinositide (PIP) turnover and provokes an increase in intracellular calcium concentration. We have hypothesized that the existence of distinct affinity sites for UII in rat cortical astrocytes could be accounted for by a possible cross-talk between UT and the ligand-gated ion channel GABA(A) receptor (GABA A R). Exposure of cultured astrocytes to UII provoked a bell-shaped increase in cAMP production, with an EC50 stimulating value of 0.83+/-0.04 pM, that was totally blocked in the presence of the adenylyl cyclase inhibitor SQ 22,536. In contrast, UII was found to inhibit forskolin-induced cAMP formation. In the presence of the specific PKA inhibitor H89, UII provoked a sustained stimulation of cAMP formation. Inhibition of PKA by H89 strongly reduced the stimulatory effect of UII on PIP metabolism. GABA and the GABA A R agonist isoguvacine provoked a marked inhibition of UII-induced cAMP synthesis and a significant reduction of UII-evoked PIP turnover. These data suggest that functional interaction between UT and GABA(A)R negatively regulates coupling of UT to the classical PLC/IP(3) signaling cascade as well as to the adenylyl cyclase/PKA pathway

[Orn5]URP acts as a pure antagonist of urotensinergic receptors in rat cortical astrocytes

International audienceCultured rat astrocytes, which express functional urotensin II (UII)/UII-related peptide (URP) receptors (UT), represent a very suitable model to investigate the pharmacological profile of UII and URP analogs towards native UT. We have recently designed three URP analogs [D-Trp4]URP, [Orn5]URP and [D-Tyr6]URP, that act as UT antagonists in the rat aortic ring bioassay. However, it has been previously reported that UII/URP analogs capable of inhibiting the contractile activity of UII possess agonistic activity on UT-transfected cells. In the present study, we have compared the ability of URP analogs to compete for [125 I]URP binding and to modulate cytosolic calcium concentration ([Ca2+]c) in cultured rat astrocytes. All three analogs displaced radioligand binding: [D-Trp4]URP and [D-Tyr6]URP interacted with high- and low-affinity sites whereas [Orn5]URP only bound high-affinity sites. [D-Trp4]URP and [D-Tyr6]URP both induced a robust increase in [Ca2+]c in astrocytes while [Orn5]URP was totally devoid of activity. [Orn5]URP provoked a concentration-dependent inhibition of URP- and UII-evoked [Ca2+]c increase and a rightward shift of the URP and UII dose-response curves. The present data indicate that [D-Trp4]URP and [D-Tyr6]URP, which act as UII antagonists in the rat aortic ring assay, behave as agonists in the [Ca2+]c mobilization assay in cultured astrocytes, whereas [Orn5]URP is a pure selective antagonist in both rat aortic ring contraction and astrocyte [Ca2+]c mobilization assays

Beta-amyloid peptide stimulates endozepine release in cultured rat astrocytes through activation of N -formyl peptide receptors

International audienceAstroglial cells synthesize and release endozepines, a family of neuropeptides derived from diazepam-binding inhibitor (DBI). The authors have recently shown that beta-amyloid peptide (Abeta) stimulates DBI gene expression and endozepine release. The purpose of this study was to determine the mechanism of action of Abeta in cultured rat astrocytes. Abeta(25-35) and the N-formyl peptide receptor (FPR) agonist N-formyl-Met-Leu-Phe (fMLF) increased the secretion of endozepines in a dose-dependent manner with EC(50) value of approximately 2 microM. The stimulatory effects of Abeta(25-35) and the FPR agonists fMLF and N-formyl-Met-Met-Met (fMMM) on endozepine release were abrogated by the FPR antagonist N-t-Boc-Phe-Leu-Phe-Leu-Phe. In contrast, Abeta(25-35) increased DBI mRNA expression through a FPR-independent mechanism. Abeta(25-35) induced a transient stimulation of cAMP formation and a sustained activation of polyphosphoinositide turnover. The stimulatory effect of Abeta(25-35) on endozepine release was blocked by the adenylyl cyclase inhibitor somatostatin, the protein kinase A (PKA) inhibitor H89, the phospholipase C inhibitor U73122, the protein kinase C (PKC) inhibitor chelerythrine and the ATP binding cassette transporter blocker glyburide. Taken together, these data demonstrate for the first time that Abeta(25-35) stimulates endozepine release from rat astrocytes through a FPR receptor positively coupled to PKA and PKC

The vasoactive peptides urotensin II and urotensin II-related peptide regulate astrocyte activity through common and distinct mechanisms. Involvement in cell proliferation

International audienceUrotensin II (UII) and its paralog urotensin II-related peptide (URP) are two vasoactive neuropeptides whose respective central actions are currently unknown. Here, we have compared the mechanism of action of URP and UII on cultured astrocytes. Competition experiments performed with [125I]UII showed the presence of very high- and high-affinity binding sites for UII, and a single high-affinity site for URP. Both UII and URP provoked a membrane depolarization accompanied by a decrease of input resistance, stimulated the release of endozepines, neuropeptides specifically produced by astroglial cells, and generated an increase in cytosolic calcium concentration ([Ca2+]c). The UII/URP-induced [Ca2+]c elevation was pertussis toxin (PTX)-insensitive, and was blocked by the PLC inhibitor U73122 or the IP3 channel blocker 2-APB. The addition of Ca2+ chelator EGTA reduced the peak and abolished the plateau phase whereas the T-type calcium channel blocker mibefradil totally inhibited the calcium response evoked by both peptides. However, URP and UII induced a mono- and biphasic dose-dependent increase in [Ca2+]c and provoked short- and long-lasting Ca2+ mobilization, respectively. Similar mono- and biphasic dose-dependent increase in [3H]inositol incorporation into polyphosphoinositides (PIP) in astrocytes was obtained but sole the effect of UII was significantly reduced by PTX, although BRET experiments revealed that both UII and URP recruited Go protein. Finally, UII exerted a dose-dependent mitogenic activity on astrocytes, but not URP. Therefore, we described that URP and UII exert not only similar but also divergent actions on astrocyte activity, UII exhibiting a broader range of activities at physiological peptide concentrations

La recherche à l'Institut Géographique National : activité 1995

Bulletin d'information de l'IGN N°65Ce numéro est consacré aux activités de recherche de I'IGN en 1995. Il dresse le bilan des recherches en traitement d'images, photogrammétrie, instrumentation, SIG, cartographie et géodésie. On traite plus particulièrement des sujets suivants : la mise à jour par SPOT, l'extraction du bâti des prises de vues aériennes, la caméra aéroportée numérique, la télémétrie laser, la précision photogrammétrique, les données multi-échelles, la généralisation cartographique numérique, le système DORIS, le géoïd

La recherche à l'Institut Géographique National : activité 1995

Bulletin d'information de l'IGN N°65Ce numéro est consacré aux activités de recherche de I'IGN en 1995. Il dresse le bilan des recherches en traitement d'images, photogrammétrie, instrumentation, SIG, cartographie et géodésie. On traite plus particulièrement des sujets suivants : la mise à jour par SPOT, l'extraction du bâti des prises de vues aériennes, la caméra aéroportée numérique, la télémétrie laser, la précision photogrammétrique, les données multi-échelles, la généralisation cartographique numérique, le système DORIS, le géoïd