Interleukin-1 alpha and vasoactive intestinal peptide: enigmatic regulation of neuronal survival

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

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 oligodeoxynucleotides 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.

Cerebral cortical astroglia from the trisomy 16 mouse, a model for down syndrome, produce neuronal cholinergic deficits in cell culture

Trisomy 21 (Down syndrome) is associated with a high incidence of Alzheimer disease and with deficits in cholinergic function in humans. We used the trisomy 16 (Ts16) mouse model for Down syndrome to identify the cellular basis for the cholinergic dysfunction. Cholinergic neurons and cerebral cortical astroglia, obtained separately from Ts16 mouse fetuses and their euploid littermates, were cultured in various combinations. Choline acetyltransferase activity and cholinergic neuron number were both depressed in cultures in which both neurons and glia were derived from Ts16 fetuses. Cholinergic function of normal neurons was significantly down-regulated by coculture with Ts16 glia. Conversely, neurons from Ts16 animals could express normal cholinergic function when grown with normal glia. These observations indicate that astroglia may contribute strongly to the abnormal cholinergic function in the mouse Ts16 model for Down syndrome. The Ts16 glia could lack a cholinergic supporting factor present in normal glia or contain a factor that down-regulates cholinergic function.

Vasoactive intestinal peptide prevents excitotoxic cell death in the murine developing brain

Excitotoxic damage may be a critical factor in the formation of brain lesions associated with cerebral palsy. When injected at birth, the glutamatergic analog ibotenate induces mouse brain lesions that strikingly mimic human microgyria. When ibotenate is injected at postnatal day 5, it produces transcortical necrosis and white matter cysts that mimic human perinatal hypoxic-like lesions. Vasoactive intestinal peptide (VIP) has potent growth-related actions and neuroprotective properties that influence mitosis and neuronal survival in culture. The goal of this study was to assess the protective role of VIP against excitotoxic lesions induced by ibotenate in developing mouse brain. VIP cotreatment reduced ibotenate-induced microgyric-like cortical lesions and white matter cysts by up to 77 and 85%, respectively. VIP protective effects were reproduced by a peptide derived from activity-dependent neurotrophic factor (ADNF), a trophic factor released by VIP-stimulated astrocytes, and by stearyl norleucine VIP, a specific VIP agonist that does not activate adenylate cyclase. Neither forskolin, an adenylate cyclase activator, nor pituitary adenylate cyclase-activating peptide, provided VIP-like protection. VIP and neurotrophic analogs, acting through a cAMP-independent mechanism and inducing ADNF release, could represent new avenues in the understanding and prevention of human cerebral palsy.

Inhibition of murine embryonic growth by human immunodeficiency virus envelope protein and its prevention by vasoactive intestinal peptide and activity-dependent neurotrophic factor

Intrauterine growth retardation and neurodevelopmental handicaps are common among infants born to HIV-positive mothers and may be due to the actions of virions and/or maternally derived viral products. The viral envelope protein, gp120, is toxic to neurons, induces neuronal dystrophy, and retards behavioral development in neonatal rats. Vasoactive intestinal peptide, a neuropeptide regulator of early postimplantation embryonic growth, and the neuroprotective protein, activity-dependent neurotrophic factor, prevent gp120-induced neurotoxicity. Whole embryo culture of gestational day 9.5 mouse embryos was used to assess the effect of gp120 on growth. Embryos treated with gp120 exhibited a dose-dependent inhibition of growth. gp120-treated embryos (10(-8) M) grew 1.2 somites in the 6-h incubation period, compared with 3.9 somites by control embryos. Embryos treated with gp120 were significantly smaller in cross-sectional area and had significantly less DNA and protein than controls. Growth inhibition induced by gp120 was prevented by cotreatment with vasoactive intestinal peptide or activity-dependent neurotrophic factor. gp120 may play a role in the growth retardation and developmental delays experienced by infants born to HIV-positive mothers. Vasoactive intestinal peptide and related factors may provide a therapeutic strategy in preventing developmental deficits.

Identity of neurotrophic molecules released from astroglia by vasoactive intestinal peptide

Subnanomolar concentrations of VIP elicit a survival-producing action in CNS cultures composed of both astroglia and neurons. This neurotrophic action is mediated by a complex array of substances released by VIP from astrocytes. Included in this glial protein mixture is a cytokine (interleukin-1 alpha), a serine protease inhibitor (protease nexin I), and an extracellular stress protein (activity-dependent neurotrophic factor). In dissociated spinal cord cultures, all of these substances exhibit neuroprotection from neuronal cell death produced by electrical blockade with tetrodotoxin. All these substances produce neuronal cell death when test cultures are treated with neutralizing antisera to any one of them. They are all apparently necessary for the survival of a subpopulation of neurons that are dependent on spontaneous, excitatory neurotransmission. Our view is that these substances are components of a glia-derived environment that regulates, together with target-derived growth factors, the survival fate of developing neurons. In addition, it is our belief that some of these glia-derived substances will be found to have active roles in the injury response to the CNS or in the regulation of VIP-mediated growth in other tissues. Drugs based on these substances may provide therapeutic agents for the treatment of neurodegeneration and tumor growth.

Antiserum to activity-dependent neurotrophic factor produces neuronal cell death in CNS cultures: immunological and biological specificity

Activity-dependent neurotrophic factor (ADNF) is a glia-derived protein that is neuroprotective at femtomolar concentrations. ADNF is released from astroglia after treatment with 0.1 nM vasoactive intestinal peptide (VIP). To further assess the biological role of ADNF, antiserum was produced following sequential injections of purified ADNF into mice. Anti-ADNF ascites fluid (1:10,000) decreased neuronal survival by 45-55% in comparison to untreated cultures or those treated with control ascites. The neuronal death after anti-ADNF treatment was observed in cultures derived from the spinal cord, hippocampus or cerebral cortex at similar IC50's. Using a terminal deoxynucleotidyl transferase in situ assay to estimate apoptosis in cerebral cortical cultures, anti-ADNF was shown to produce a 70% increase in the number of labeled cells in comparison to controls. In spinal cord cultures, anti-ADNF treatment produced a 20% decrease in choline acetyltransferase activity in comparison to controls. Neuronal cell death produced by the antiserum to ADNF was prevented in cultures co-treated with purified ADNF or ADNF-15, an active peptide derived from the parent ADNF. In vitro binding between the anti-ADNF and ADNF-15 was demonstrated with size exclusion chromatography. Comparative studies with other growth factors (insulin-like growth factor-1, platelet-derived growth factor, nerve growth factor, epidermal growth factor, ciliary neurotrophic growth factor, and neurotrophin-3) demonstrated that only ADNF prevented neuronal cell death associated with electrical blockade. These investigations indicated that an ADNF-like substance was present in cultures derived from multiple locations in the central nervous system and that ADNF-15 exhibited both neuroprotection and immunogenicity. ADNF appears to be both a regulator of activity-dependent neuronal survival and a neuroprotectant.

Neurobehavioral development of neonatal mice following blockade of VIP during the early embryonic period

Previous work has shown that blockade of VIP function in the early postimplantation embryo results in growth retardation and microcephaly. In the present work, the neurobehavioral development of neonatal mice was examined following treatment of dams with a VIP antagonist during this period. Inhibition of VIP functions during early embryogenesis impaired the performance of 5 of 10 developmental behaviors. These behaviors included developmental milestones (first appearance of ear twitch and eye opening) and complex motor behaviors (negative geotaxis, surface righting, and air righting). The retardation of neurobehavioral development produced by inhibition of VIP action indicates that this peptide is important to the progression of embryonic development.

Activity-dependent neurotrophic factor (ADNF). An extracellular neuroprotective chaperonin?

To understand and intervene in neuronal cell death, intensive investigations have been directed at the discovery of intracellular and extracellular factors that provide natural neuroprotection. This goal has fundamental importance for both rational strategies for the treatment of neurodegenerative diseases and also the delineation of molecular mechanisms that regulate nervous system differentiation and growth. We have discovered a potential interface among these fields of research with activity-dependent neurotrophic factor (ADNF), a protein containing sequence homologies to intracellular stress proteins that is found in the extracellular milieu of astroglial cells incubated with the neuropeptide vasoactive intestinal peptide (VIP). Femtomolar concentrations of ADNF and a short peptide sequence derived from it (a peptidergic active site) protected neurons from death associated with a broad range of toxins, including those related to Alzheimer's disease, the human immunodeficiency virus, excito-toxicity, and electrical blockade. Because the activity of the protein was mimicked by a short peptide fragment, this peptide is now proposed as a lead compound for drug development against neurodegeneration.

Regulation of VIP gene expression in general. Human lung cancer cells in particular

Vasoactive intestinal peptide (VIP) is a neuropeptide of multiple functions affecting development and aging. In cancer, for example, VIP was found to function as an autocrine growth factor in nonsmall cell lung cancer (NSCLC) promotion. Furthermore, a VIP hybrid antagonist (neurotensin(6-11)-VIP(7-28)) was found to inhibit NSCLC growth. In the present study, the expression of VIP mRNA was studied using human lung cancer cells. RNA prepared from 19 cell lines was fractionated by 1% agarose gel electrophoresis followed by blotting onto nitrocellulose membranes and hybridization to a VIP-specific RNA probe. VIP mRNA was detected in about 50% of the cell lines tested with a greater abundance in NSCLC. Cultures of the NSCLC NCI-H727 cell line were treated with forskolin, an activator of cyclic AMP (cAMP), and separately with the tumor promoter phorbol 12-myristate 13-acetate (PMA). Northern blot hybridization analysis showed an increase in VIP mRNA levels after 4 h treatment with 50 microM forskolin. Incubation with PMA also showed a significant increase in the levels of VIP transcripts. Cultures were then incubated with PMA in the presence of actinomycin D, a transcription blocker. Results indicated that PMA treatment may induce both VIP mRNA synthesis as well as VIP mRNA stabilization, and suggested a 4-5 h half-life for the VIP mRNA in the absence of PMA. Thus, lung cancer tumor proliferation may be regulated, in part, at the level of VIP gene expression.

A femtomolar-acting neuroprotective peptide

A novel 14-amino acid peptide, with stress-protein-like sequences, exhibiting neuroprotection at unprecedented concentrations, is revealed. This peptide prevented neuronal cell death associated with the envelope protein (GP 120) from HIV, with excitotoxicity (N-methyl d-aspartate), with the beta amyloid peptide (putative cytotoxin in Alzheimer's disease), and with tetrodotoxin (electrical blockade). The peptide was designed to contain a sequence derived from a new neuroprotective protein secreted by astroglial cells in the presence of vasoactive intestinal peptide. The neurotrophic protein was isolated by sequential chromatographic methods combining ion exchange, size separation, and hydrophobic interaction. The protein (mol mass, 14 kD and pI, 8.3 +/- 0.25) was named activity-dependent neurotrophic factor, as it protected neurons from death associated with electrical blockade. Peptide sequencing led to the synthesis of the novel 14-amino acid peptide that was homologous, but not identical, to an intracellular stress protein, heat shock protein 60. Neutralizing antiserum to heat shock protein 60 produced neuronal cell death that could be prevented by cotreatment with the novel protein, suggesting the existence of extracellular stress-like proteins with neuroprotective properties. These studies identify a potent neuroprotective glial protein and an active peptide that provide a basis for developing treatments of currently intractable neurodegenerative diseases.

Maternal vasoactive intestinal peptide and the regulation of embryonic growth in the rodent

Vasoactive intestinal peptide (VIP) has been shown to regulate early postimplantation growth in rodents through central nervous system receptors. However, the source of VIP mediating these effects is unknown. Although VIP binding sites are present prenatally, VIP mRNA was not detected in the rat central nervous system before birth and was detected in the periphery only during the last third of pregnancy. In the present study, the embryonic day (E11) rat embryo/trophoblast was shown to have four times the VIP concentration of the E17 fetus and to have VIP receptors in the central nervous system. However, no VIP mRNA was detected in the E11 rat embryo or embryonic membranes by in situ hybridization or reverse transcriptase-PCR. RIA of rat maternal serum revealed a peak in VIP concentration at days E10-E12 of pregnancy, with VIP rising to levels 6-10-fold higher than during the final third of pregnancy. After intravenous administration of radiolabeled VIP to pregnant female mice, undegraded VIP was found in the E10 embryo. These results suggest that maternal tissues may provide neuroendocrine support for embryonic growth through a surge of VIP during early postimplantation development in the rodent.

A VIP hybrid antagonist: from developmental neurobiology to clinical applications

1. The 28 amino acid vasoactive intestinal peptide, VIP, was originally isolated from the intestine, following a bioassay measuring vasodilating properties. Immunocytochemistry, receptor binding assays and in situ hybridizations have demonstrated VIP abundance in the nervous system, suggesting multiple bioactivities. 2. A pharmacological approach was chosen to dissect VIP activities and a prototype VIP antagonist (Met-Hybrid) consisting of a carboxyl fragment of VIP7-28 and a six amino acid fragment of neurotensin, neurotensin6-11-VIP7-28 was synthesized. 3. This hybrid peptide was designed to maintain the binding capacity of one parent molecule (VIP), while loosing the agonistic properties, representing a classical competitive receptor antagonist. Furthermore, the new molecule exhibited increased specificity to central nervous system VIP receptors. 4. The Met-Hybrid was originally discovered as a potent inhibitor of VIP function in vivo. In the adult rodent, acute administration of the antagonist resulted in blockade of VIP-mediated potentiation of sexual behavior and chronic intracerebroventricular application impaired VIP-associated learning abilities. During ontogeny, chronic injections of the molecule resulted in neuronal damage, disruption of the diurnal rhythmicity of motor behavior, and retardation in the acquisition of neonatal reflexes in the rat. 5. During gestation, severe microcephaly was induced by acute administration of the Met-Hybrid to pregnant mice. The hybrid antagonist inhibited VIP-stimulated mitosis in whole embryo cultures and in a variety of cancer cell lines in vitro and in vivo, suggesting therapeutical potential.