Astrocytes synthesize and release endozepines, a family of regulatory peptides, including the octadecaneuropeptide (ODN) an endogenous ligand of both central-type benzodiazepine (CBR) and metabotropic receptors. We have recently shown that ODN exerts a protective effect against hydrogen peroxide (H2O2)-induced oxidative stress in astrocytes. The purpose of the present study was to determine the type of receptor and the transduction pathways involved in the protective effect of ODN in cultured rat astrocytes. We have first observed a protective activity of ODN at very low concentrations that was abrogated by the metabotropic ODN receptor antagonist cyclo1–8[DLeu5]OP, but not by the CBR antagonist flumazenil. We have also found that the metabotropic ODN receptor is positively coupled to adenylyl cyclase in astrocytes and that the glioprotective action of ODN upon H2O2-induced astrocyte death is PKA- and MEK-dependent, but PLC/PKC-independent. Downstream of PKA, ODN induced ERK phosphorylation, which in turn activated the expression of the anti-apoptotic gene Bcl-2 and blocked the stimulation by H2O2 of the pro-apoptotic gene Bax. The effect of ODN on the Bax/Bcl-2 balance contributed to abolish the deleterious action of H2O2 on mitochondrial membrane integrity and caspase-3 activation. Finally, the inhibitory effect of ODN on caspase-3 activity was shown to be PKA and MEK-dependent. In conclusion, the present results demonstrate that the potent glioprotective action of ODN against oxidative stress involves the metabotropic ODN receptor coupled to the PKA/ERK-kinase pathway to inhibit caspase-3 activation.

J. Neurochem. (2011) 117, 403–411. Abstract Oxidative stress, associated with a variety of disorders including neurodegenerative diseases, results from accumulation of reactive oxygen species (ROS). Oxidative stress is not only responsible for neuron apoptosis, but can also provoke astroglial cell death. Numerous studies indicate that pituitary adenylate cyclase‐activating polypeptide (PACAP) promotes neuron survival, but nothing is known regarding the action of PACAP on astroglial cell survival. Thus, the purpose of the present study was to investigate the potential glioprotective effect of PACAP on H2O2‐induced astrocyte death. Pre‐treatment of cultured rat astrocytes with nanomolar concentrations of PACAP prevented cell death provoked by H2O2 (300 μM), whereas vasoactive intestinal polypeptide was devoid of protective activity. The effect of PACAP on astroglial cell survival was abolished by the type 1 PACAP receptor antagonist, PACAP6‐38. The protective action of PACAP was blocked by the protein kinase A inhibitor H89, the protein kinase C inhibitor chelerythrine and the mitogen‐activated protein (MAP)‐kinase kinase (MEK) inhibitor U0126. PACAP stimulated glutathione formation, and blocked H2O2‐evoked ROS accumulation and glutathione content reduction. In addition, PACAP prevented the decrease of mitochondrial activity and caspase 3 activation induced by H2O2. Taken together, these data indicate for the first time that PACAP, acting through type 1 PACAP receptor, exerts a potent protective effect against oxidative stress‐induced astrocyte death. The anti‐apoptotic activity of PACAP on astrocytes is mediated through the protein kinase A, protein kinase C and MAPK transduction pathways, and can be accounted for by inhibition of ROS‐induced mitochondrial dysfunctions and caspase 3 activation.

Astroglial cells possess an array of cellular defense mechanisms, including superoxide dismutase (SOD) and catalase antioxidant enzymes, to prevent damages caused by oxidative stress. Nevertheless, astroglial cell viability and functionality can be affected by significant oxidative stress. We have previously shown that pituitary adenylate cyclase-activating polypeptide (PACAP) is a potent glioprotective agent that prevents hydrogen peroxide (H 2 O 2 )-induced apoptosis in cultured astrocytes. The purpose of this study was to investigate the potential protective effect of PACAP against oxidative-generated alteration of astrocytic antioxidant systems.Incubation of cells with subnanomolar concentrations of PACAP inhibited H 2 O 2 -evoked reactive oxygen species accumulation, mitochondrial respiratory burst, and caspase-3 mRNA level increase. PACAP also stimulated SOD and catalase activities in a concentration-dependent manner, and counteracted the inhibitory effect of H 2 O 2 on the activity of these two antioxidant enzymes. The protective action of PACAP against H 2 O 2 -evoked inhibition of antioxidant systems in astrocytes was protein kinase A, PKC, and MAP-kinase dependent. In the presence of H 2 O 2 , the SOD blocker NaCN and the catalase inhibitor 3-aminotriazole, both suppressed the protective effects of PACAP on SOD and catalase