Characterization of antibodies to synthetic nerve growth factor (NGF) and proNGF peptides

Imbalance between sympathetic and sensory innervation in peritoneal endometriosis

To investigate possible mechanisms of pain pathophysiology in patients with peritoneal endometriosis, a clinical study on sensory and sympathetic nerve fibre sprouting in endometriosis was performed. Peritoneal lesions (n=40) and healthy peritoneum (n=12) were immunostained and analysed with anti-protein gene product 9.5 (PGP 9.5), anti-substance P (SP) and anti-tyrosine hydroxylase (TH), specific markers for intact nerve fibres, sensory nerve fibres and sympathetic nerve fibres, respectively, to identify the ratio of sympathetic and sensory nerve fibres. In addition, immune cell infiltrates in peritoneal endometriotic lesions were analysed and the nerve growth factor (NGF) and interleukin (IL)-1β expression was correlate with the nerve fibre density. Peritoneal fluids from patients with endometriosis (n=40) and without endometriosis (n=20) were used for the in vitro neuronal growth assay. Cultured chicken dorsal root ganglia (DRG) and sympathetic ganglia were stained with anti-growth associated protein 43 (anti-GAP 43), anti-SP and anti-TH. We could detect an increased sensory and decreased sympathetic nerve fibres density in peritoneal lesions compared to healthy peritoneum. Peritoneal fluids of patients with endometriosis compared to patients without endometriosis induced an increased sprouting of sensory neurites from DRG and decreased neurite outgrowth from sympathetic ganglia. In conclusion, this study demonstrates an imbalance between sympathetic and sensory nerve fibres in peritoneal endometriosis, as well as an altered modulation of peritoneal fluids from patients with endometriosis on sympathetic and sensory innervation which might directly be involved in the maintenance of inflammation and pain.

Characterization and evaluation of NGF antisense oligonucleotides: inhibition of NGF synthesis in transfected COS cells

We present a system for the assessment of the inhibiting capacity of antisense oligonucleotides. The aim of this study was to identify an oligonucleotide that can inhibit chicken nerve growth factor (NGF) synthesis. Five antisense chicken NGF phosphorothioate oligonucleotides, AS1-5, were designed and were tested for their capacity to inhibit NGF expression in COS cells. COS cells that transiently expressed chicken NGF were treated with the oligonucleotides, and NGF expression was analyzed using a bioassay and Western blotting for NGF protein. Two oligonucleotides, AS 1 and AS 5, were more capable than the others of inhibiting expression compared with nonsense oligonucleotide, and they targeted the translational initiation and stop sites. The chicken NGF is expressed at a high level from an adenovirus major late promoter, and AS 1 was capable of inhibiting more than 80% of the NGF expression as determined using the bioassay and Western blotting. Expression of another member of the NGF gene family, neurotrophin-4, was not affected by treatment of the antisense oligonucleotides. A 10-fold lower concentration of the AS 1 oligonucleotide could be used to inhibit NGF synthesis if the cellular uptake was facilitated using lipofectin compared with addition of oligonucleotide directly to the culture medium. The amount of oligonucleotide taken up by the cells was similar in the lipofectin-treated cells as in the cells treated by a 10-fold higher concentration of medium-supplemented nucleotide. This system based on COS cells can facilitate evaluation of the capacity of inhibiting antisense oligonucleotides, particularly targeting those genes in which endogenous products are present in low levels and are difficult to analyze.

The regulated secretion and vectorial targeting of neurotrophins in neuroendocrine and epithelial cells

The varied roles that neurotrophins play in the development and activity-dependent plasticity of the nervous system presumably require that the sites and quantity of neurotrophin release be precisely regulated. As a step toward understanding how different neurotrophins are sorted and secreted by neurons, we expressed nerve growth factor (NGF), brain-derived neurotrophic factor, and neurotrophin-3 in cell lines used as models for neuronal protein sorting. All three neurotrophins were secreted by a regulated pathway in transfected AtT-20 and PC12 neuroendocrine cells, with a 3-6-fold increase in neurotrophin release in response to 8-bromo-cAMP or depolarization, respectively. To determine if the propeptide directs the intracellular sorting of mature NGF, we examined mutants in which regions spanning the propeptide were deleted. These mutants underwent regulated release in every case in which expression could be detected. Similarly, NGF sorting was not significantly altered by mutations which specifically abolished N-glycosylation or proteolytic processing sites within the NGF precursor. Finally, we found that all three neurotrophins were secreted 65-75% basolaterally by polarized Madin-Darby canine kidney epithelial cells. These findings suggest that the determinants of regulated neurotrophin secretion lie within the mature neurotrophin moiety and that NGF, brain-derived neurotrophic factor, and neurotrophin-3 are likely to be sorted similarly and released in a regulated manner by neurons.

The biosynthesis of neurotrophin heterodimers by transfected mammalian cells

Prompted by the recent discovery that neurotrophins, which are known to be biologically active as noncovalently linked homodimers, can also be induced to form biologically active heterodimers in vitro, we have investigated the biosynthesis of neurotrophin heterodimers by transfected mammalian cells. When COS cells were cotransfected with expression plasmids for nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), or neurotrophin-3 (NT-3), the appropriate heterodimers were detected in the conditioned medium by immunoprecipitation and, in the case of NGF.NT-3, using a two-site enzyme-linked immunosorbent assay. Heterodimer formation occurred predominantly intracellularly and did not require precursor cleavage, because heterodimers containing pro-NGF and pro-BDNF were detected in the conditioned medium. When rat C6 glioma cells or mouse AtT-20 neuroendocrine cells were cotransfected with expression plasmids for NGF and NT-3, NGF.NT-3 heterodimer was detected at levels comparable with those of homodimeric NGF and NT-3, indicating that heterodimer formation can occur at significant levels in a variety of cell types. These data provide evidence that NGF, BDNF, and NT-3 are capable of forming heterodimers when coexpressed in mammalian cells and suggest that such heterodimers are likely to be formed in vivo when a single cell expresses multiple neurotrophins.

Small peptide mimics of nerve growth factor bind TrkA receptors and affect biological responses

Small monomeric cyclic analogs that mimic the beta-turn regions of nerve growth factor (NGF) were designed and synthesized. Potent competitive antagonists were derived from the NGF beta-turn C-D, which inhibited [125I] NGF binding to TrkA receptors and specifically inhibited optimal NGF-mediated neurite outgrowth in PC12 cells. The cyclic beta-turn A'-A" analog also inhibited NGF binding to TrkA receptors but with lower potency. These data indicate that beta-turns C-D and A'-A" are critical for TrkA binding and may confer neurotrophin receptor specificity. Furthermore, structural requirements for binding are absolute, because unconstrained analogs derived from the same regions had no effect. Compounds that mimic NGF will be useful in deciphering the interactions of NGF and its receptors and in rational drug design.

Effects of transferrin receptor antibody-NGF conjugate on young and aged septal transplants in oculo

The purpose of this study was to investigate the effects of nerve growth factor (NGF) conjugated to a monoclonal transferrin receptor antibody (OX-26) on septal transplants in oculo. Three different doses of OX-26-NGF conjugate (0.3, 3, and 50 micrograms/injection) were injected into the tail vein of young adult hosts 2, 4, and 6 weeks following intraocular transplantation of fetal forebrain tissue containing septal nuclei. Intravenous injections of OX-26 alone, NGF alone, and saline served as controls. An increase in intraocular tissue growth, as well as an increase in the intensity of immunoreactivity for p75 receptors and acetylcholinesterase, was observed following peripheral OX-26-NGF administration at the two highest doses tested. In addition, aged host rats with 16-month-old intraocular septal grafts were injected intravenously with OX-26 or OX-26-NGF (10 micrograms NGF/injection) every 2 weeks until the transplants were 24 months old. The intensity of choline acetyltransferase-like (ChAT) staining appeared to be greater and the cell bodies were larger with more processes in aged transplants in hosts treated with the OX-26-NGF conjugate than in aged OX-26-treated subjects. The present results suggest that peripheral OX-26-NGF can deliver biologically active NGF across the blood-brain barrier and have dose-dependent positive effects on both aged and developing cholinergic neurons in septal transplants.

Pentylenetetrazol seizures increase pro-nerve growth factor-like immunoreactivity in the reticular thalamic nucleus and nerve growth factor mRNA in the dentate gyrus

Neurotrophins may have a neuroprotective role and are probably involved in the control of axonal sprouting and synaptic plasticity. An antibody raised against a pro-sequence of nerve growth factor (NGF) was tested. In control undisturbed rats, a strong immunoreactivity was detected in scattered cells in and around the pyramidal and granule cell layer of the hippocampus and a moderate labeling was found in the reticular thalamic nucleus. In situ hybridization showed specific expression of NGF mRNA in a similar population of scattered cells in the hippocampal formation but not in the reticular thalamic nucleus. Acute epileptic seizures, induced by a convulsive dose of 50 mg/kg pentylenetetrazol (PTZ), strongly increased NGF mRNA in neurons of the granular layer of the dentate gyrus 3 hr but not 6 hr after the injection. No change in pro-NGF-like immunoreactivity was observed in the hippocampus or reticular thalamic nucleus after acute seizures. Chemical kindling was induced by daily injections of subconvulsive doses (30 mg/kg) of PTZ for 4 weeks. This treatment significantly increased pro-NGF-like immunoreactivity in the reticular thalamic nucleus but did not affect NGF mRNA. These data strengthen a role for the reticular thalamic nucleus and NGF in PTZ kindling.

Function and evolution in the NGF family and its receptors

The gene family of neurotrophins includes nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), and neurotrophin-4 (NT-4). Recently, neurotrophin-5 (NT-5), a possible mammalian homologue to NT-4 described in the frog Xenopus, has been cloned in man and rat. The neurotrophins stimulate survival and differentiation of a range of target neurons by binding to cell surface receptors. The structure of NGF has recently been clarified from crystallographic data. The similarities between the different neurotrophins are substantial with the variable regions, giving specificity to each of the family members, being localized to some exposed loop regions. Low-affinity binding (Kd of 10(-9) M) of all tested neurotrophins is mediated via a 75 K glycoprotein (LNGFR) that has been cloned and characterized. A 140 K tyrosine protein kinase encoded by the proto-oncogene trk has been found to bind NGF with high affinity (Kd of 10(-11) M) and to evoke the cellular neurotrophic responses. In addition, a protein encoded by the trk-related gene trkB has been shown to bind BDNF. Recently, a third member of the trk family, trkC, has been cloned and demonstrated to function as a high-affinity receptor for NT-3. The expression of trk and LNGFR mRNA are co-localized in the rat brain to the medial septal nucleus and the nucleus of Broca's diagonal band containing the NGF-responsive magnocellular cholinergic neurons projecting to hippocampus and cerebral cortex. In sharp contrast, the pattern of expression of trkB is widely spread in many areas of the cortex as well as lateral septum. The trkB protein might serve general functions in large areas of the cortex. Site-directed mutagenesis and expression of recombinant chimaeric neurotrophin proteins have made it possible to localize a likely region for the interaction between NGF and the LNGFR. This region could be altered, resulting in the total loss of LNGFR binding by the mutant NGF protein without affecting the binding to the trk receptor which was sufficient for the full biological activity. Cladistic analysis of likely phylogenies within the neurotrophins shows BDNF and NT-4 to be most closely related whereas NGF may be the sister group to NT-3, BDNF, and NT-4. Neurotrophins offer obvious clinical possibilities for treatment of neurodegenerative diseases.

Cloning and mapping of 5' exons from the gene encoding chicken beta nerve growth factor

An NGF cDNA containing the 5' exons of the nerve growth factor (NGF) messenger was obtained from chicken heart mRNA using the anchored polymerase chain reaction technique. Alignment of the chicken with the corresponding murine and human sequences reveals interspecies similarities. A sequence corresponding to an exon found only in the NGF messenger, which is abundant in the submaxillary gland of the male mouse, is present in the chicken NGF cDNA. The first non-coding exons of the NGF gene are much less conserved between chicken and mouse or human than the region of the last exon encoding the mature protein. After the cloning of the chicken NGF gene from a cosmid library, the chicken NGF exons have been located within 20 kb of DNA. The chicken NGF gene is therefore shorter than its murine counterpart which spans more than 43 kb. Furthermore, the organization of the chicken and murine NGF genes markedly differs in their 5' portion.

Disruption of the low affinity receptor-binding site in NGF allows neuronal survival and differentiation by binding to the trk gene product

Nerve growth factor (NGF), like many other growth factors and hormones, binds to two different receptor molecules on responsive cells. The product of the proto-oncogene trk, p140trk, is a tyrosine kinase receptor that has been identified as a signal-transducing receptor for NGF, while the role of the low affinity NGF receptor, p75NGFR, in signal transduction is less clear. The crystal structure of NGF has recently been determined, although structures involved in receptor binding and biological activity are unknown. Here we show that Lys-32, Lys-34, and Lys-95 form a positively charged interface involved in binding to p75NGFR. Simultaneous modification of Lys-32 with either of the two other lysines resulted in loss of binding to p75NGFR. Despite the lack of binding to p75NGFR, these mutants retained binding to p140trk and biological activity, demonstrating a functional dissociation between the two NGF receptors.

Biological and immunological properties of recombinant human, rat, and chicken nerve growth factors: a comparative study

Biological and immunological properties of recombinant human, rat, and chicken nerve growth factors (NGFs) were studied and compared. Recombinant NGF proteins were produced in a transient expression system using COS cells and levels of secreted NGF protein were assessed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of conditioned media from in vivo [35S]cysteine-labeled cell cultures. Antigenic differences among the three NGFs were studied by immunoblotting and immunoprecipitation of secreted cell products using a rabbit polyclonal antiserum against purified mouse NGF, and by a two-site enzyme immunoassay (EIA) with a monoclonal antibody against mouse NGF. Although all three NGFs were recognized equally well in the immunoblotting, only one-third of the chicken NGF protein could be detected by immunoprecipitation or by the EIA as compared to the rat and human NGFs. Thus, changes in the three-dimensional structure of the NGF molecule are most likely responsible for the antigenic differences between avian and mammalian NGFs. The three NGF proteins were also compared in their ability to displace 125I-mouse NGF from low-affinity NGF receptors on rat pheochromocytoma PC12 cells. Similar displacement curves and values were obtained for each NGF protein, indicating that structural differences among these molecules do not affect low-affinity binding to NGF receptors. Biological activities were studied by the ability of the conditioned media to promote neurite outgrowth from explants of E9 chick sympathetic ganglia and from PC12 cells. Although the rat system showed a slight preference for the homologous molecule, the morphological changes, dose-response curves, and maximal stimulation values obtained with the different NGFs were practically indistinguishable in the chicken bioassay.(ABSTRACT TRUNCATED AT 250 WORDS)

Large scale purification and immunological characterization of human placental nerve growth factor

Nerve growth factor (NGF) is a protein which plays a critical role in the development and survival of not only peripheral neurons, but possibly also cholinergic brain neurons. The present study describes a procedure for large scale isolation of human NGF of placental origin, and its immunological characterization. A protein species of approximately 26 kDa was obtained, which cross-reacted with antibodies to mouse NGF. Polyclonal and monoclonal anti-mouse NGF antibodies appeared to recognize different bands within this human NGF preparation. Although these polyclonal antibodies recognized both the dimeric and monomeric forms of mouse NGF, the monoclonal antibody recognized only a band corresponding to the dimeric form of mouse NGF.

Recombinant human beta-nerve growth factor (NGF): biological activity and properties in an enzyme immunoassay

Nerve growth factor (NGF) supports sympathetic and sensory neurons in the peripheral nervous system and also functions in the development and maintenance of cholinergic neurons in the basal forebrain. NGF distribution can be studied in the brain of the rat and mouse with the use of a sensitive two-site enzyme immunoassay (EIA) for mouse NGF. It would be of interest to measure the NGF protein also in the human brain, especially against the background that the cholinergic neurons are severely deteriorated in senile dementia of the Alzheimer type. The limited immunological cross-reactivity between NGFs from different species has previously hampered attempts to determine levels of the human NGF. We have now examined the biological activity and immunological properties of human recombinant NGF protein in medium conditioned by COS cells transfected with the human NGF gene. The human NGF behaved similar to mouse NGF in a sympathetic ganglion bioassay. The monoclonal antibody 27/21 to mouse NGF was shown to effectively block the activity of both the human recombinant NGF and mouse native NGF. A two-site EIA using monoclonal antibody 27/21 was optimized. Under the conditions used, the EIA detected the human recombinant NGF with the same sensitivity (1 pg/ml) as shown for the mouse NGF. It should now be possible to test this EIA also on homogenized tissue to examine human NGF in brain samples from Alzheimer patients and age-matched controls.

Immunohistochemical localisation of nerve growth factor in a subpopulation of chick spinal ganglion neurons

We have previously isolated and sequenced the chicken nerve growth factor (NGF) gene and now, from the deduced amino acid sequence, selected and produced peptides suitable for use as antigens. Anti-sera raised against these peptides inhibit the biological activity of a partially purified preparation of native chicken NGF and, when used in immunocytochemical studies, allow the visualisation of sensory neurons accumulating endogenous NGF. Immunoreactive cells form a distinct population of small neurons which may correspond to the well-described neurons generated in the dorsomedial area of spinal ganglia. We conclude that two subpopulations of neurons exist within dorsal root ganglia, whose requirements for, and use of, NGF may be quite distinct.

Testicular atrophy and loss of nerve growth factor-immunoreactive germ cell line in rats exposed to n-hexane and a protective effect of simultaneous exposure to toluene or xylene

Testicular and germ cell line morphology in rats were studied 2 weeks, 10 months and 14 months after cessation of a 61-day inhalation exposure to 1000 ppm n-hexane. Androgen biosynthetic capacity of testis, testosterone blood concentration, vas deferens morphology and noradrenaline (NA) concentration, epididymal sperm morphology, and fertility were also studied. Severe testicular atrophy involving the seminiferous tubules with loss of the nerve growth factor (NGF) immunoreactive germ cell line was found. Total loss of the germ cell line was found in a fraction of animals up to 14 months post-exposure, indicating permanent testicular damage. No impairment of androgen synthesis or androgen dependent accessory organs was observed. Simultaneous administration of 1000 ppm n-hexane and 1000 ppm toluene, or 1000 ppm n-hexane and 1000 ppm xylene, did not cause germ cell line alterations or testicular atrophy. Toluene and xylene were thus found to protect from n-hexane induced testicular atrophy.

Detection of nerve growth factor and its mRNA by separate and combined immunohistochemistry and in situ hybridization in mouse salivary glands

Intense labelling of secretory cells in the male mouse submandibular gland was observed after in situ hybridization using mouse nerve growth factor (NGF) cDNA probes. Under the same conditions, sparse less intensely labelled cells were also found in the sublingual gland. Hybridization to a chicken NGF cDNA probe gave weak labelling on the glands in accordance with a weak cross-hybridization between mouse NGF mRNA and chicken NGF cDNA probes, whereas no labelling was seen using pUC9 DNA as a hybridization probe. A combination of in situ hybridization and immunohistochemistry was also carried out on the same sections of submandibular gland. A good correlation was seen between actively synthesizing and intensely immunoreactive cells in the gland. The technique described here allows the detection of individual cells synthesizing relatively low levels of NGF. The combination of in situ hybridization and immunocytochemistry on the same section should be particularly useful in cases where NGF is transported away from its site of synthesis.