抄録
[Background] Rare microduplications at 7q36.3, containing VIPR2, have been known to confer a risk for schizophrenia and autism. VIPR2 encodes VPAC2, a seven transmembrane heterotrimeric G protein-coupled receptor (Gs) that binds two homologous neuropeptides with high affinity, vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP). Lymphocytes from patients with these mutations exhibited higher VIPR2 gene expression and VIP responsiveness, but mechanisms by which overactive VPAC2 signaling may lead to these psychiatric disorders are unknown. We previously found that repeated administration of the selective VPAC2 receptor agonist Ro25-1553 in the mouse during early postnatal development caused cognitive impairment and abnormal dendritic morphology in the prefrontal cortex. In this study, we aimed to clarify the effects of VPAC2 receptor activation on neurite outgrowth in cultured primary mouse cortical neurons.
[Methods] All animal studies were approved by the Animal Care and Use Committee of the Graduate School of Pharmaceutical Sciences, Osaka University. Cerebral cortical neurons were prepared from brains of 16-day-old mouse embryos (strain ICR). For morphological analysis, anti-MAP2 antibody was used for staining dendrites and perikarya of neurons, and anti-phosphoneurofilament antibody was used for staining axons. Axon length, total number of dendrites and total dendritic length were analyzed using Neurolucida software.
[Results] All VIP and PACAP receptors (PAC1, VPAC1 and VPAC2 receptors) were expressed in primary mouse cortical neurons. VIP and Ro25-1553 caused reductions in total numbers and length of neuronal dendrites and length of axon in cortical neurons. These effects were blocked by the VPAC2 receptor antagonist PG99-465 and abolished in VPAC2 receptor-deficient mice. Furthermore, Ro25-1553-induced decreases in axonal and dendritic outgrowth were blocked by the PKA inhibitor H89 and the transcriptional inhibitor actinomycin D. Finally, the atypical antipsychotic clozapine, but not the typical antipsychotic haloperidol, attenuated Ro 25-1553-induced decreases in axonal and dendritic outgrowth.
[Conclusion] These results suggest that activation of the VPAC2 receptor inhibits neurite outgrowth and branching of cortical neurons via a PKA-dependent and transcriptional regulatory mechanism. These findings imply that the VIPR2-linkage to mental health disorders might be due in part to deficits in neuronal maturation and clozapine could affect the VPAC2 receptor signaling pathways.
