ACTIVATION OF GROUP II METABOTROPIC GLUTAMATE RECEPTORS MODULATES NITRIC OXIDE-INDUCED APOPTOSIS IN ASTROCYTES

DURAND DANIELA; PÉREZ MARÍA DE LA CRUZ; CARUSO CARLA; LASAGA MERCEDES

Toronto, Canadá

Congreso; The Endocrine Society`s 89th Annual Meeting; 2007

The Endocrine Society

Astrocytes play a neuroprotective role in the central nervous system (CNS) in pathological conditions and have an essential function in neuroendocrine regulation. Thus, strategies to improve astrocyte survival may provide therapeutic benefit. Astrocytes express metabotropic glutamate receptors (mGluRs) and this expression changes in response to growth factors. mGluRs regulate proliferation, differentiation and apoptosis in the CNS and much evidence suggests a neuroprotective role of several mGluRs subtypes. Here, we investigated the effect of specific group II mGluR agonists on inducible nitric oxide synthase (iNOS) gene expression induced by lipopolysaccharide (LPS) + interferon- gamma (IFN-gamma ) and nitric oxide (NO)-induced apoptosis in rat astrocyte primary cultures. LPS (1 mg/ml) + IFN-gamma (50 ng/ml) treatment for 24hs iNOS gene expression whereas iNOS expression was not detectable in the control group (assayed by RT-PCR). The presence of selective group II mGluR agonists (Ly 379268 and LCCG-I at 100 mM and 1 mM) diminished this effect by 75% (p0.05). NO is the major cytotoxic mediator of apoptosis in astrocytes. We investigated apoptosis by determining DNA fragmentation with the TUNEL method. Exposure for 48 h to DETA/NO 1 mM (a NO donor) increased the percentage of TUNEL-positive astrocytes by 28.5% (p0.05). This increase was significantly attenuated by the presence both group II mGluR agonists by 18% (p0.05). The agonists per se did not modify the percentage of TUNEL-positive astrocytes. We tested whether the expression of pro- and anti-apoptotic members of the Bcl-2 family were involved in the protective action of mGluR group II agonists. NO significantly (p0.001) diminished the protein levels of anti-apoptotic factor Bcl-2 by 85%, while these levels were recovered by 20% (p0.05) in the presence of group II mGluR agonists (determined by Western-blot analysis). However, we observed no variations in the pro-apoptotic Bax protein levels. On the other hand, NO-induced cell death could proceed by a caspase-3 independent mechanism, since NO induced no changes in caspase-3 activation. Moreover, we found no differences in its activity in any experimental condition. Our results suggest that selective group II mGluR activation could play a modulatory role on inflammatory and apoptotic processes in astrocytes, probably through regulation of iNOS and Bcl-2 expression, effects that may depend neither on changes in protein levels of Bax nor on caspase-3 activity.