Elsevier

Neuroscience

Volume 205, 15 March 2012, Pages 29-38
Neuroscience

Cellular and Molecular Neuroscience
Research Paper
Opposite regulation of metabotropic glutamate receptor 3 and metabotropic glutamate receptor 5 by inflammatory stimuli in cultured microglia and astrocytes

https://doi.org/10.1016/j.neuroscience.2011.12.044Get rights and content

Abstract

Metabotropic glutamate receptors (mGluRs) were previously shown to modulate several essential functions in glial cells, including cell proliferation, glutamate uptake, neurotrophic support, and inflammatory responses. As these receptors are regularly proposed as promising targets for the treatment of a wide range of neurological disorders, we herein examined the reciprocal modulation of glial mGluRs by inflammation. Such regulation of mGluRs was also studied in cultures from an experimental model of amyotrophic lateral sclerosis (ALS). Indeed, ALS is characterized by increased neuroinflammation, and glial cell cultures derived from the animal model (rat expressing hSOD1G93A) show enhanced glial reactivity. Within 72 h, the pro-inflammatory cytokines tumor necrosis factor α (TNFα) and interleukin 1β (IL-1β) induced an increase in mGluR3 and a decrease in mGluR5 gene expression. A similar regulation of these receptors was observed in microglia 48 h after an initial 4-h exposure to lipopolysaccharide. In hSOD1G93A-derived glial cultures, the gene up-regulation of mGluR3 (but not the gene down-regulation of mGluR5) was found to be enhanced in both astrocytes and microglia. Together, these results indicate that an inflammatory environment triggers an opposite regulation in the gene expression of the two predominant mGluR subtypes found in glial cells, and that these regulations were particularly robust in hSOD1G93A glial cultures. As neuroinflammation commonly occurs in several nervous diseases, its influence on mGluR expression should be taken into account when considering these receptors as future drug targets.

Highlights

▶mGluR gene expression was examined in primary glial cultures from wild-type or hSOD1G93A rats. ▶Inflammation induces opposite regulations of mGluR5 and mGluR3 in glia from both genotypes. ▶mGluR5 is down-regulated, whereas mGluR3 is up-regulated in activated astrocytes and microglia. ▶mGluR3 up-regulation, but not mGluR5 down-regulation, is enhanced in hSOD1G93A glial cultures. ▶mGluR regulations should be taken into account when considering mGluR ligands for treating neuropathologies.

Section snippets

Materials

Poly-l-lysine, tumor necrosis factor α (TNFα), interleukin 1β (IL-1β), lipopolysaccharide (LPS), and 4',6-diamidino-2-phenylindole (DAPI) were purchased from Sigma (Bornem, Belgium). Culture media, fetal bovine serum, penicillin-streptomycin, fungizone, proline, trypsin-EDTA, and PCR primers were obtained from Invitrogen (Merelbeke, Belgium). TriPure RNA Isolation Reagent was from Roche Diagnostic (Vilvoorde, Belgium). BioRad laboratories (Nazareth, Belgium) provided the iScript cDNA synthesis

Influence of pro-inflammatory stimuli on GFAP and CD11b gene expression and immunoreactivity

The influence of pro-inflammatory cytokines on the astroglial phenotype was examined by comparing the gene expression of GFAP in control cultures or in cells incubated for 72 h with 20 ng/ml of TNFα or 10 ng/ml of IL-1β (Fig. 1A). Quantitative analyses first indicated that GFAP mRNA levels were similar between astrocytes derived from wild-type and transgenic animals maintained in control conditions. Secondly, TNFα was found to decrease GFAP transcript levels in both genotypes, and the amplitude

Discussion

Beside members of the family of glutamate transporters/exchanger and glutamate metabolizing enzymes, glial cells express a variety of mGluRs, which were shown to modulate several activities, including cell proliferation (Ciccarelli et al., 1997, Kanumilli and Roberts, 2006), glutamate uptake (Aronica et al., 2003, Vermeiren et al., 2005b), neurotrophic support (Bruno et al., 1998, Ciccarelli et al., 1999, Viwatpinyo and Chongthammakun, 2009), and inflammatory responses (Byrnes et al., 2009b,

Conclusion

In summary, we herein provide evidence for an opposite regulation of the gene expression of the principal members of family I and II mGluRs in glial cells in response to inflammatory cues. These observations raise questions regarding the relevance of targeting these mGluRs in the treatment of neurological diseases. Also, while the increased gene expression of mGluR3 and the opposite silencing of mGluR5 can be considered as constitutive adaptive processes driving the glial cells into

Acknowledgments

We thank A. Lebbe and R. Lenaert for their excellent technical assistance. This study was supported by the National Fund for Scientific Research (FNRS, Belgium, Conventions des Fonds de la Recherche Scientifique Médicale 3.4560.07 and Crédit au chercheur 1.5.085.10.F and 1.A198.08), by the DIANE research program of the Belgium's Walloon region (DGTRE), and by a grant of Ministry of Scientific Policy (Belgium, ARC 10/15-026). J.V.B. is a Research fellow of the FNRS.

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