Identification of VIP/PACAP receptors on rat astrocytes using antisense oligodeoxynucleotides

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Abstract
Vasoactive intestinal peptide (VIP) has been shown to be a potent promoter of neuronal survival. Pituitary adenylate cyclase-activating peptide (PACAP), a homologous peptide, shares activity and receptor molecules with VIP. The neuroprotective effects of VIP have been shown to be mediated via astroglial-derived molecules. Utilizing a battery of antisense oligodeoxy-nucleotides directed against the multiple cloned VIP-preferring (VIP receptors 1 and 2) or PACAP-preferring receptors (six splice variants derived from the same gene transcript), the authors have demonstrated the existence of a specific PACAP receptor splice variant (PACAP4 or hop2) on astrocytes as well as a VIP type2 receptor. The identification of the receptors was achieved by incubation of the cells in the presence of the specific antisense oligodeoxynucleotide followed by radiolabeled VIP binding and displacement. Polymerase chain reaction (PCR) coupled to direct sequencing identified the expression of the PACAP4-hop2 receptor splice variant in astrocytes. Neuronal survival assays were conducted in mixed neuronal-glial cultures derived from newborn rat cerebral cortex. When these cultures were exposed to the battery of the antisense oligodeoxynucleotides, in serum-free media, only the PACAP-specific ones (e.g., hop2-specific) had an effect in decreasing neuronal cell counts. Thus, the VIP neuronal survival effect is mediated, at least in part, via a specific PACAP receptor (containing a unique insertion of 27 amino acids—the hop2 cassette). These data indicate that a hop2-like PACAP/VIP receptor is the receptor that mediates neurotropism.