title: Pituitary Adenylate Cyclase-Activating Polypeptide Receptors Signal via Phospholipase C Pathway to Block Apoptosis in Newborn Rat Retina.
abstract: Glutamate induced cell death mechanisms gained considerable attention lately as excessive release of extracellular glutamate was reported to cause neurodegeneration in brain areas including the retina. Conversely, pituitary adenylate cyclase-activating polypeptide (PACAP) was shown to provide neuroprotection through anti-apoptotic effects in the glutamate-model and also in other degeneration assays. Although PACAP is known to orchestrate complex intracellular signaling primarily through cAMP production, the mechanism that mediates the anti-apoptotic effect in glutamate excitotoxicity remains to be clarified. To study this mechanism we induced retinal neurodegeneration in newborn Wistar rats by subcutaneous monosodium-glutamate injection. 100 pmol PACAP and enzyme inhibitors were administered intravitreally. Levels of caspase 3, 9, and phospho-protein kinase A were assessed by Western blots. Changes in cAMP levels were detected employing a competitive immunoassay. We found that cAMP blockade by an adenylyl-cyclase inhibitor (2',4'-dideoxy-adenosine) did not abrogate the neuroprotective effect of PACAP1-38. We show that following intravitreal PACAP1-38 treatment cAMP was unaltered, consistent with the inhibitor results and phospho-protein kinase A, an effector of the cAMP pathway was also unaffected. On the other hand, blockade of the alternative phosphatidylcholine-specific PLC pathway using an inhibitor (D609CAS) abrogated the neuroprotective effects of PACAP1-38. Our results highlight PACAP1-38 ability in protecting retinal cells against apoptosis through diverse signaling cascades. It seems that at picomolar concentrations, PACAP does not trigger cAMP production, but nonetheless, exerts a significant anti-apoptotic effect through PLC activation. In conclusion, PACAP1-38 may signal via both AC and PLC activation producing the same protective outcome.
authors.affiliation: Department of Experimental Zoology and Neurobiology, University of Pécs, 6 Ifjúság Street, 7601, Pécs, Hungary.
authors.forename: Monika
authors.initials: M
authors.lastname: Lakk
authors.forename: Viktoria
authors.initials: V
authors.lastname: Denes
authors.forename: Robert
authors.initials: R
authors.lastname: Gabriel
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D017209:Apoptosis; D000242:Cyclic AMP / Q000096:biosynthesis / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D004789:Enzyme Activation; D051381:Rats; D017208:Rats, Wistar; D051236:Receptors, Pituitary Adenylate Cyclase-Activating Polypeptide / Q000378:metabolism*; D012160:Retina / Q000166:cytology* / Q000201:enzymology / Q000378:metabolism; D015398:Signal Transduction; D010738:Type C Phospholipases / Q000378:metabolism*
chemical_list: D051236:Receptors, Pituitary Adenylate Cyclase-Activating Polypeptide; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D010738:Type C Phospholipases