Growth factors and female reproduction in vertebrates

Female reproductive efficiency is influenced by the outcomes of various processes, including folliculogenesis, apoptosis, response to gonadotropin signaling, oocyte maturation, and ovulation. The role of hormones in regulating these processes and other reproductive activities has been well established. It is becoming increasingly evident that in addition to well-characterized hormones, growth factors play vital roles in regulating some of these reproductive activities. Growth factors and their receptors are widely distributed in vertebrate ovaries at different stages of ovarian development, indicating their involvement in intraovarian reproductive functions. In the ovary, cell surface receptors allow growth factors to regulate intraovarian reproductive activities. Understanding these actions in the reproductive axis would provide a tool to target growth factors and/or their receptors to yield desirable reproductive outcomes. These include enrichment of in vitro maturation and fertilization culture media, and management of infertility. This review discusses some widely characterized growth factors belonging to the TGF, EGF, IGF, FGF, and BDNF family of peptides and their role in female reproduction in vertebrates, with a focus on mammals.

Seminal plasma nerve growth factor signaling on the reproductive physiology of female llamas

The ovulation mechanism is one of the fascinating physiological processes in reproductive biology in mammals. From the reproductive point of view, the species have been classified as spontaneous or induced ovulators. Although the release of GnRH followed by the preovulatory LH surge is shared between both types of ovulation, the stimulus to initiate GnRH release varies between both categories. In spontaneous ovulators, ovulation depends on the systemic concentration of ovarian steroids, however, in induced ovulators, different stimuli such as copulation, environmental, and social cues can facilitate or induce ovulation regardless of the increases in systemic estradiol concentration. In this review, we document evidence that a male-derived protein is the main factor responsible for inducing ovulation and also modulating the ovarian function in the domestic South American camelid, the llama. The neurotrophin beta-Nerve Growth Factor (β-NGF) is the principal factor present in the semen of llamas responsible for inducing ovulation in this species. After the intrauterine deposit of semen during mating, β-NGF is absorbed through the endometrium to reach the circulatory system, where it reaches the hypothalamus and stimulates GnRH release. The potential site of action of this neurotrophin at the brain has not been elucidated, however, hypotheses are raised that the factor may cross the blood-brain barrier and stimulate upstream neuronal networks that lead to the stimulation of GnRH-secreting neurons. It is possible that β-NGF could be sensed at the median eminence without crossing the blood-brain barrier. Finally, it has been observed that this factor is not only a powerful stimulator of ovulation but also has a luteotrophic effect, resulting in the development of a corpus luteum capable of secreting more progesterone when compared to other ovulation-stimulating analogues.

Nerve Growth Factor (NGF) and Animal Reproduction

Stimuli that lead to the release of gonadotropin-releasing hormone (GnRH) and pituitary gonadotropins and, consequently, ovulation in mammals fall into two broad categories. In the first, high plasma oestrogen concentrations induce the events that trigger ovulation, a characteristic of spontaneous ovulators. In the second, nerve stimuli occurring during mating reach the hypothalamus and trigger the release of GnRH and ovulation with a neuroendocrine reflex that characterizes induced ovulators.In this review, we will give an overview of the distribution of NGF and its expression in the different tissues of the male accessory sex glands, the main sites of NGF production. Next, we will highlight the role of NGF in sperm function and its potential cryopreserving role in artificial insemination techniques. Finally, we will evaluate the functions of NGF in ovulation, particularly in induced ovulators. Overall, the information obtained so far indicates that NGF is widely distributed in organs that regulate the reproductive activity, in both males and females. In spontaneous ovulators, NGF exerts mainly a luteotrophic action, while, in induced ovulators it is the main ovulation-inducing factor. A better understanding of the role of NGF in reproduction would be of great interest, since it could help finding innovative therapeutic aids to improve mammalian fertility.

Effect of the Camelid's Seminal Plasma Ovulation-Inducing Factor/β-NGF: A Kisspeptin Target Hypothesis

Female mammals are classified into spontaneous and induced ovulators based on the mechanism eliciting ovulation. Ovulation in spontaneous species (e.g., human, sheep, cattle, horse, pigs, and most rodents) occurs at regular intervals and depends upon the circulating estradiol. However, in induced ovulators (e.g., rabbits, ferrets, cats, and camelids), ovulation is associated with coitus. In the later, various factors have been proposed to trigger ovulation, including auditory, visual, olfactory, and mechanic stimuli. However, other studies have identified a biochemical component in the semen of induced ovulators responsible for the induction of ovulation and named accordingly ovulation-inducing factor (OIF). In camelids, intramuscular or intrauterine administration of seminal plasma (SP) was shown to induce the preovulatory luteinizing hormone (LH) surge followed by ovulation and subsequent formation of corpus luteum. Recently, this OIF has been identified from SP as a neurotrophin, the β subunit of nerve growth factor (β-NGF). β-NGF is well known as promoting neuron survival and growth, but in this case, it appears to induce ovulation through an endocrine mode of action. Indeed, β-NGF may be absorbed through the endometrium to be conveyed, via the blood stream, to the central structures regulating the LH preovulatory surge. In this review, we provide a summary of the most relevant results obtained in the field, and we propose a working hypothesis for the central action of β-NGF based on our recent demonstration of the presence of neurons expressing kisspeptin, a potent stimulator of GnRH/LH, in the camel hypothalamus.

RAPID COMMUNICATION: Nerve growth factor influences cleavage rate and embryo development in sheep

Recent information about Nerve growth factor (NGF), a protein traditionally associated to the nervous system that regulates survival and maturation of developing neurons, suggests that it may exert action also on different levels in the reproductive system. The aim of this study was to evaluate the effect of NGF added during in vitro oocyte maturation, fertilization or in vitro embryo development in sheep. Nerve growth factor was supplemented to the culture medium at 0, 100, or 1,000 ng/mL, during either in vitro maturation (Exp. 1), in vitro fertilization (Exp. 2), or in vitro culture (Exp. 3). In addition, NGF mRNA expression was determined in cumulus cells and oocytes. Nerve growth factor induced early cleavage when added during oocyte maturation or fertilization, improved embryo development when added during fertilization, and had no significant effect when added during embryo culture. In general, the effect was more evident with 100 rather than 1,000 ng/mL (P < 0.05). Expression of endogenous NGF was not detected in oocytes, and increased in cumulus cells when 1,000 ng/mL of NGF was added during fertilization, but not during maturation and embryo culture. In conclusion, the addition of NGF during oocyte maturation and fertilization affects in vitro cleavage and embryo development in sheep. We suggest a possible effect of this growth factor on oocyte maturation and mainly on the fertilization process.

The nerve of ovulation-inducing factor in semen

A component in seminal fluid elicits an ovulatory response and has been discovered in every species examined thus far. The existence of an ovulation-inducing factor (OIF) in seminal plasma has broad implications and evokes questions about identity, tissue sources, mechanism of action, role among species, and clinical relevance in infertility. Most of these questions remain unanswered. The goal of this study was to determine the identity of OIF in support of the hypothesis that it is a single distinct and widely conserved entity. Seminal plasma from llamas and bulls was used as representative of induced and spontaneous ovulators, respectively. A fraction isolated from llama seminal plasma by column chromatography was identified as OIF by eliciting luteinizing hormone (LH) release and ovulation in llamas. MALDI-TOF revealed a molecular mass of 13,221 Da, and 12-23 aa sequences of OIF had homology with human, porcine, bovine, and murine sequences of β nerve growth factor (β-NGF). X-ray diffraction data were used to solve the full sequence and structure of OIF as β-NGF. Neurite development and up-regulation of trkA in phaeochromocytoma (PC(12)) cells in vitro confirmed NGF-like properties of OIF. Western blot analysis of llama and bull seminal plasma confirmed immunorecognition of OIF using polyclonal mouse anti-NGF, and administration of β-NGF from mouse submandibular glands induced ovulation in llamas. We conclude that OIF in seminal plasma is β-NGF and that it is highly conserved. An endocrine route of action of NGF elucidates a previously unknown pathway for the direct influence of the male on the hypothalamo-pituitary-gonadal axis of the inseminated female.

Nerve growth factor from Vipera lebetina venom

Nerve growth factor was isolated from the Vipera lebetina venom by a four-step procedure including gel filtration, ion exchange, heparin and hydrophobic chromatography. The purified protein is a glycosylated non-covalently bound homodimer with monomeric molecular mass of 14,380 Da. The cDNA encoding NGF is cloned and sequenced. The amino acid sequence translated from the cDNA comprises 117 or 119 amino acids depending on the N-terminus (truncated or not). The recombinant NGF (expressed in Escherichia coli) was used to prepare the anti-NGF antiserum. The antiserum interacted with the wild-type NGF and enabled to localize NGF during the purification procedure in parallel with MALDI-TOF analysis of tryptic peptides. The isolated NGF caused neurite outgrowth from PC12 cells in concentrations beginning from 2.5 ng/ml.

Localization of NGF and nNOS in varicocele-induced rat testis

Nerve growth factor (NGF) is synthesized in male germ cells. The presence of neuronal nitric oxide synthase (nNOS) in Leydig cells is related to its role in the regulation of testosterone release. Varicocele is often characterized by abnormal sperm quality and influences the fertilizing capacity of the haploid gamete. We investigated the localization of NGF and nNOS in testes of adult Wistar rats with experimentally induced varicocele after 9, 11, and 13 weeks, as well as in sham-operated controls by immunohistochemistry and Western blot. In control testis, we detected NGF in nuclei of Sertoli cells and also as small vesicular-like structures in the cytoplasm of primary spermatocytes, and in round and elongating spermatids. Varicocele-induction revealed a slight decrease of NGF at 13 weeks, especially in Sertoli cells. In control tissue, nNOS protein was present mainly in Leydig cells and in Sertoli cell cytoplasm. Additionally, nNOS immunoreactivity was present in the heads of elongated spermatids. Western blot results revealed that the decrease of NGF was not significant in the 13-week varicocele group, moreover, the amount of nNOS was not altered in any of the varicocele groups. In conclusion, NGF and nNOS have important roles for normal gametogenesis and our data for the first time indicates that varicocele induction does not necessarily affect the expression of NGF and nNOS. Thus, these two molecules do not appear to be related to varicocele induction.

Effects of castration on the expression of brain-derived neurotrophic factor (BDNF) in the vas deferens and male accessory genital glands of the rat

Brain-derived neurotrophic factor (BDNF) is a growth factor belonging to the family of neurotrophins. Although neurotrophins in the male genital organs have been well documented, their role in the biology of these organs is far from clear. In particular, little is known about the influence of sex hormones on neurotrophin expression. In the present study, using immunohistochemistry and enzyme-linked immunosorbent assay (ELISA), we investigated the distribution and tissue concentration of BDNF in the vas deferens and accessory male genital glands in normal and castrated rats. The expression of BDNF mRNA was also investigated. In normal rats, BDNF immunoreactivity was localized in the musculature of the vas deferens and vesicular gland and in the fibromuscular stromal cells of the prostate. In the ventral prostatic lobes, BDNF immunoreactivity was localized in basal, secretory and neuroendocrine epithelial cells. Innervating ganglia and nerves were immunoreactive in all the examined tracts. After castration, BDNF immunoreactivity increased in the musculature of the vesicular gland and in the fibromuscular stromal cells of both dorsal and ventral prostatic lobes. BDNF immunoreactivity also increased in the nerves. ELISA and reverse transcription/real-time polymerase chain reaction confirmed the findings of the immunohistochemical study. In the accessory glands, castration induced an increase of both BDNF tissue concentration and mRNA expression. These results suggest that BDNF is expressed in the internal male genital organs of the rat and that its expression is downregulated by androgen hormones. We hypothesize that the observed BDNF increases are related to the castration-induced regression of the sympathetic nerves.

Nerve growth factor treatment of adult rats selectively enhances innervation of urinogenital tract rather than vascular smooth muscle

Following treatment of adult rats with nerve growth factor (0.5 mg/rat, three times a week for 3 weeks), the innervation of cardiovascular and urinogenital tract smooth muscle was investigated using immunoassay and immunohistochemical techniques. Substance P and calcitonin gene-related peptide levels were increased in the vas deferens, but not in the atria or femoral artery. Neuropeptide Y and vasoactive intestinal polypeptide levels were unchanged. In penile tissues, there was a marked increase in the density of substance P-, calcitonin gene-related peptide-, neuropeptide Y-, tyrosine hydroxylase- and vasoactive intestinal polypeptide-containing nerves innervating the urethra and in SP-containing nerves in the tunica with little changes in the innervation of the deep dorsal vein and artery and corpus cavernosum. In the bladder, there was increased innervation of the detrusor by neuropeptide Y- and vasoactive intestinal polypeptide-containing nerves, but a decrease in innervation by substance P-containing nerves in the trigone. There were no changes in the density of innervation of the femoral artery after nerve growth factor treatment. Thus, in the mature rat, sensory and sympathetic nerve innervating urinogenital tract smooth muscle appear to be more responsive to exogenous nerve growth factor than those innervating cardiovascular smooth muscle. This may reflect an ongoing requirement of plasticity of innervation in the urinogenital tract of the sexually mature animal.

A heparin-binding protein in porcine seminal plasma stimulates neurite outgrowth on neuroblastoma cells in culture

A protein of neurite outgrowth activity has been identified in porcine seminal plasma after ammonium sulfate precipitation and affinity chromatography on heparin-Sepharose. Upon SDS-PAGE, the polypeptide is shown to have a M(r) of 16,000-18,000. Biologically by induction of neuritic processes on neuroblastoma cells, and immunologically by cross-reaction with specific antisera, this seminal plasma protein differs from acidic fibroblast growth factor (aFGF), basic fibroblast growth factor (bFGF) and nerve growth factor (NGF). The neurite outgrowth activity is relatively stable at pH 3-7 and under denaturing conditions of 8 M urea and beta-mercaptoethanol, but is inactivated by treatment of trypsin. This appears to be a novel protein, enhancing morphological differentiation of neuroblastoma cells in culture.

Germ cell mitogenic activity is associated with nerve growth factor-like protein(s)

The mitogenicity of germ cell proteins released from round spermatids (RS) and pachytene spermatocytes (PS) was investigated. Germ cells were isolated by centrifugal elutriation from 90-day-old rat testes and incubated in a supplement enriched culture media that lacked exogenous proteins. The conditioned culture media of RS and PS were dialysed/concentrated and lyophilized to prepare RS protein (RSP) and PS protein (PSP). Mitogenic activity of RSP and PSP was determined by 3H-thymidine incorporation into Swiss 3T3 fibroblasts. RSP and PSP stimulated 3H-thymidine incorporation by fibroblasts in a dose-dependent manner. At a higher concentration of RSP (300 micrograms/ml), fibroblast proliferation was stimulated from 6- to 20-fold of control cultures, whereas PSP (300 micrograms/ml) stimulated fibroblast proliferation 2.5-fold of control cultures. Since RSP exhibited substantially greater mitogenic activity than PSP we further investigated the RSP mitogenic substance(s) by immunoneutralization with antibodies against several growth factors. The mitogenic activity of RSP was significantly reduced by treatment with nerve growth factor (NGF) antibody, while neither the treatment of RSP with acidic fibroblast growth factor (aFGF) antibody, nor basic fibroblast growth factor (bFGF) antibody significantly modified the mitogenic activity of RSP. Interestingly, murine NGF-beta, recombinant human NGF-beta, and bovine serum albumin (BSA) did not exhibit mitogenic activity on 3T3 fibroblasts. Nevertheless, the presence of a NGF-like protein in RS and PS was confirmed by indirect immunofluorescence staining with a murine NGF antibody. Subsequently, a Western blot analysis with the NGF antibody identified two immunoreactive bands of 41 +/- 2 kDa and 51 +/- 1 kDa in both RSP and PSP under reduced conditions. These germ cell NGF-like proteins were apparently different from similarly prepared murine and human NGFs (13 kDa) in their molecular weight. Furthermore, neurite outgrowth from pheochromocytoma cells (PC-12), a functional bioassay for NGF-like activity, was stimulated by addition of RSP and PSP to the culture media of the PC-12 cells. These results demonstrate mitogenic activity in germ cell proteins (RSP and PSP) and identify a NGF-like protein(s) which is associated with most of this activity.

Expression of the beta-nerve growth factor gene in male sex organs of the mouse, rat, and guinea pig

Steady-state nerve growth factor (NGF) mRNA levels were estimated in male sex organs of the mouse, rat, and guinea pig by RNA blot hybridization analysis. The abundance of NGF mRNAs was in the order vas deferens greater than epididymis greater than or equal to seminal vesicles much greater than testis. NGF mRNA levels in these organs were compared with those estimated for other rat peripheral tissues and were found to correlate with the density of their sympathetic innervation, with the exception of guinea pig prostate. Castration had no significant effect on NGF mRNA levels in the guinea pig prostate, suggesting that NGF synthesis in this tissue is not under direct androgen control. NGF-like and proNGF-like immunoreactivities were localized by immunohistochemical techniques in the secretory cells of the glandular epithelium of the guinea pig prostate and in germ cells in the seminiferous tubules of the mouse testis.

Structure and biosynthesis of nerve growth factor

Most of our knowledge about NGF comes from extensive study of the mouse submaxillary gland protein. NGF from this source is isolated as a high molecular weight complex consisting of beta-NGF and two subunits, alpha and gamma, belonging to the kallikrein family of serine proteases. There are few other tissues where NGF is found in sufficient quantities for protein purification and study, although new molecular biological techniques have accelerated the study of NGFs from a variety of species and tissues. Mouse submaxillary gland NGF is synthesized as a large precursor that is cleaved at both N- and C-terminals to produce mature NGF. This biologically active molecule can be further cleaved by submaxillary gland proteases. The roles of the alpha and gamma subunits in the processing of the beta-NGF precursor, the modulation of the biological activity of beta-NGF, and the protection of mature beta-NGF from degradation have been well studied in the mouse. However, the apparent lack of alpha and gamma subunits in most other tissues and species and the existence of a large family of murine kallikreins, many of which are expressed in the submaxillary gland, challenge the relevance of murine high molecular weight NGF as a proper model for NGF biosynthesis and regulation. It is important therefore to identify and characterize other NGF complexes and to study their subunit interactions, biosynthesis, processing, and regulation. This review points out a number of other species and tissues in which the study of NGF has just begun. At this time, there exist many more questions than answers regarding the presence and the functions of NGF processing and regulatory proteins. By studying NGF in other species and tissues and comparing the processing and regulation of NGF from several sources, we will discover the unifying concepts governing the expression of NGF biological activity.

Trophic actions of recombinant human nerve growth factor on cultured rat embryonic CNS cells

NGF is a neurotrophic factor for basal forebrain cholinergic neurons and may serve to counteract the cholinergic deficits that are observed in Alzheimer's disease. Prior to the introduction of clinical trials, it is essential that recombinant human NGF (rhNGF) be produced and that its actions on target cells in the CNS be demonstrated. We prepared rhNGF and examined its actions on fetal rat brain neurons in culture including, in particular, the cholinergic neurons of the basal forebrain. rhNGF was more potent in increasing choline acetyltransferase (ChAT) activity in septal cultures than NGF purified from mouse salivary glands (mNGF). ED50s of the beta-NGF dimers were 4.9 pM for rhNGF and 12.4 pM for mNGF. The maximal ChAT activity response was achieved at approximately 35 pM with both NGFs and their efficacies were not significantly different. The two NGFs were not additive in effect. Identical to the results with mNGF, rhNGF strongly enhanced the intensity of ChAT immunostaining in septal cultures. Neither rhNGF nor mNGF affected the appearance of the cultures under phase-contrast illumination. Survival of cells at very low plating density on polyornithine/laminin-coated culture dishes was not affected by rhNGF or mNGF. Protein content and the uptake of GABA were also unaffected. At concentrations of up to 10 micrograms/ml, rhNGF did not significantly increase uptake of dopamine into cultures of ventral mesencephalon. We conclude that rhNGF produces potent and selective actions on cholinergic neurons of the basal forebrain as previously shown for mNGF.

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.

Survival of purified embryonic chick retinal ganglion cells in the presence of neurotrophic factors

In a search for neurotrophic factors (NTFs) regulating retinal ganglion cell (RGC) death in the chick embryo we have used purified and cultured RGCs. Purification of RGCs from embryonic day 10 was achieved by employing the "panning" method (Silverstein and Chun: Soc Neurosci Abstr 13:1054, 1987). The obtained neuron population consisted of 97% RGCs as demonstrated by retrograde labeling with a fluorescence dye. RGCs were cultured at low density in a chemically defined medium and short-term survival (24 hr) was determined. In the absence of NTFs, less than 3% of the RGCs survived. In the presence of various crude or purified NTFs (eye, brain, and tectum extracts; glial-conditioned medium; ciliary neurotrophic factor [CNTF]; nerve growth factor [NGF]) 31% to 52% of the RGCs were maintained. The effects of NGF and CNTF were not additive. Neither acidic nor basic fibroblast growth factor was able to maintain RGCs in culture. Our results, obtained with a culture system which allowed the analysis of direct trophic actions, suggest that NGF and CNTF may be NTFs for overlapping subpopulations of chick RGCs.

Spatial and temporal patterns of neurotrophic activities in rat adrenal medulla and cortex

We have studied the spatial distribution and temporal pattern of expression of neurotrophic factor (NTF) activity present in the rat adrenal gland. Tissue extracts of the densely innervated medulla and sparsely innervated cortex from adult and various developmental stages were assayed for their ability to promote the in vitro survival of embryonic chick ciliary (CG), dorsal root ganglia (DRG) and ventral spinal cord (SC) neurons. NTF activity was found in medulla but not in cortex extracts. NTF activity became first detectable at postnatal day (P) 12. At this developmental stage the cholinergic adrenomedullary innervation becomes functional. Specific activity successively increased in medulla extracts from P16 to P30 as revealed by the CG-assay. No further changes occurred during adulthood. In contrast, activity addressing SC neurons present in P16 and P30 medulla extracts could not be detected in adult stages P90 or P120. In DRG-assays, NTF activity could not be blocked by the addition of anti-NGF antibodies to medulla extracts. The activity was sensitive to heat and protease treatment suggesting its proteinaceous nature. At high concentrations cortex extracts had neurotoxic effects that were also seen when 10 microM of dexamethasone were added to saturated amounts of medulla extract. However, gel filtration of cortex material to remove low molecular components including corticosteroid hormones failed to reveal any NTF activity in these preparations. Adrenal NTF activity therefore appears to be restricted to the densely innervated medullary tissue. Moreover, our results also suggest a distinct temporal pattern of NTF activity in the adrenal gland.

Basic fibroblast growth factor promotes in vitro survival and cholinergic development of rat septal neurons: comparison with the effects of nerve growth factor

The effects of basic fibroblast growth factor and nerve growth factor on survival and transmitter expression of cultured rat embryonic (E18) septal neurons were studied. Two different culture media were used: (i) a horse serum-containing Leibowitz L-15 medium and (ii) a serum-free N1-supplemented Dulbecco's modified Eagle's medium. Addition of basic fibroblast growth factor to either culture medium enhanced neuronal survival in low density cultures after 4 days. The effects of basic fibroblast growth factor were dose-dependent and blocked by anti-basic fibroblast growth factor antibodies. In serum-containing L-15 medium nerve growth factor also promoted neuronal survival. Basic fibroblast growth factor and nerve growth factor supported neurons comprised both cholinergic and GABAergic subpopulations. The effects of basic fibroblast growth factor and nerve growth factor were not additive. In high density cultures using serum-containing L-15 medium survival of septal neurons was four times higher than in low density cultures after 4 days. Addition of basic fibroblast growth factor or nerve growth factor did not further augment neuronal survival in high density cultures. Maintenance of septal neurons at high density was not affected by antibodies to basic fibroblast growth factor and/or nerve growth factor. Addition of basic fibroblast growth factor or nerve growth factor to serum-containing L-15 medium at high cell density significantly enhanced choline acetyltransferase activity 3- and 7.5-fold, respectively, without affecting cell survival. In conclusion, next to nerve growth factor, basic fibroblast growth factor, which has been located in the hippocampal target area of septal neurons, appears to be another potent trophic factor for septal neurons.

Ciliary neuronotrophic factor stimulates choline acetyltransferase activity in cultured chicken retina neurons

It has been demonstrated that cultured cholinergic retinal neurons from 8-day-old chicken embryos respond to a polypeptide factor present in retinal cell-conditioned medium (RCM) and in retinal extracts. Compared with control cultures, the activity of acetyl-CoA:choline O-acetyltransferase (EC 2.3.1.6; ChAT) is enhanced more than twofold in neuronal retinal cultures grown for 7 days in the presence of RCM. The present study demonstrates that both ciliary neuronotrophic factor (CNTF), which is characterized by its trophic activity on parasympathetic ciliary neurons, and RCM exhibit identical stimulatory effects on ChAT activity in retinal monolayer cultures. Similarly, RCM supports the in vitro survival of ciliary neurons to the same extent as CNTF. The active species in RCM has a molecular weight (20,900 +/- 1,000) identical to that of CNTF, as determined by preparative sodium dodecyl sulfate gel electrophoresis. The results indicate that cholinergic retinal neurons represent a central neuronal target for CNTF or a closely related protein.

Neuronotrophic factors released by C6 glioma cells

Glial cells have been shown previously to release factors that promote survival of central and peripheral neurons [neuronotrophic factors (NTFs)]. We have investigated the release of NTFs by C6 cells, a rat glioma cell line, under different modes of conditioning. Media conditioned in the presence or absence of serum [C6 cell conditioned media (C6CMs)] were analyzed using biological, biochemical, and immunological assays. We report that (a) nuclear and cytoskeletal proteins were not present in C6CMs, indicating that C6CM proteins result from release by C6 cells rather than from cell death; (b) C6CM contained 1-3 micrograms protein/ml, corresponding to a secretion rate of about 0.5 pg protein per cell and day; (c) C6CM contained the neurite-promoting factor laminin and low amounts of nerve growth factor; (d) the presence of fetal calf serum in the culture medium was essential for synthesis and release of NTFs; and (e) our C6CM contained at least three NTFs differing by their temporal secretory patterns and three NTFs differing by biochemical properties, indicating that C6 cells produce and secrete six different NTFs. Within these, nerve growth factor seems to be the only established NTF.

Survival, morphology, and catecholamine storage of chromaffin cells in serum-free culture: evidence for a survival and differentiation promoting activity in medium conditioned by purified chromaffin cells

Adult bovine and young rat chromaffin cells cultured in serum-free medium were examined for their survival and differentiation following exposure to various additives, trophic agents and conditioned media. Adrenal chromaffin cells dissociated from 8 day old rats were maintained by dexamethasone, NGF and CNTF or without any additives in an N1-supplemented medium in similar numbers as in serum-containing medium for up to 6 days. Neuritic growth elicited by NGF or CNTF was enhanced in the absence of serum. Medium conditioned by purified bovine chromaffin cells improved cell survival and caused neurite outgrowth in a dose-dependent manner. The activiti(es) was sensitive to heat and trypsin and not blocked by the addition of anti-NGF antibodies. Bovine chromaffin cell survival was reduced by 30% when cells were maintained for one week in the absence as compared to the presence of serum. Addition of insulin, the N1 supplement, dexamethasone or dbcAMP single or in combinations improved the survival to different extents. A combination of insulin (5 micrograms/ml) and dexamethasone (5 X 10(-6) M) proved to be optimal in this respect. However, these supplements failed to restore the cellular catecholamine, noradrenaline and adrenaline contents to levels seen in the presence of serum. This was also true for a chromaffin cell-conditioned medium, which improved survival without elevating the catecholamine contents. Conditioned medium, however, partly restored a more physiological adrenaline-noradrenaline-ratio.

De novo synthesis of NGF subunits in S-180 mouse sarcoma cell line

It is an accepted hypothesis that the nerve growth factor protein (NGF) plays an important role in the development of vertebrate sympathetic and sensory ganglia and has effects on some central neurons. The best known NGF species is that isolated from mouse submaxillary gland, MSG-NGF. MSG-NGF can be isolated as a subunit containing protein, 7S-NGF, made up of three dissimilar subunits called alpha-, beta-, and gamma-NGF. Beta-NGF is the biologically active subunit and its synthesis in vivo and in vitro has been demonstrated. Less is known about the synthesis of the alpha- and gamma-NGF or the assembly of the subunits into the 7S complex. In order to develop a clonal model system for the study of NGF synthesis, processing and secretion, affinity chromatography techniques were applied to cell extracts of S180 mouse sarcoma, a cell line known to synthesize NGF. After incubating S180 cells in 35S-Methionine, cell extracts were exposed to antibody directed against alpha-NGF, gamma-NGF or beta-NGF covalently bound to Sepharose beads in order to elute and characterize the desired NGF subunits. Parallel experiments using immunoabsorbed [35S]Methionine-beta-NGF were carried out in the presence or absence of excess NGF, in order to demonstrate the specificity of this procedure. Affinity chromatography with a substrate analogue to arginine ester bound to Sepharose beads was also used to isolate de novo synthesized gamma-NGF.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization and partial purification of a novel neuronotrophic factor from bovine seminal vesicle

Extracts from bovine seminal vesicles have been shown to contain high concentrations of nerve growth factor (NGF)-like biological activity and of the NGF protein with properties corresponding to that of NGF from other sources. We now demonstrate that a second neuronotrophic protein, termed seminal vesicle-derived neuronotrophic factor (SVNF), is present in seminal vesicle extracts (SVEs), which could not be distinguished from NGF on the basis of biological activity. SVNF has neuronotrophic activity on NGF target cells like embryonic chicken-sensory and sympathetic neurons, sympathetic neurons, and chromaffin cells from neonatal rats, but it is inactive on embryonic chicken ciliary or neonatal rat nodose ganglion neurons. It also stimulates fiber outgrowth from rat pheochromocytoma (PC 12) cells. In gel filtration chromatography on Biogel A 1.5 m, the activity is eluted with an apparent molecular weight of 40 kilodaltons, and by preparative isoelectric focusing, the isoelectric point was determined to be in the neutral range (6.8-7.8). The biological activity of SVNF, in contrast to that of NGF, is partially retained after preparative sodium dodecyl sulfate-polyacrylamide gel electrophoresis and can be electrophoretically eluted with an apparent molecular weight of 16-20 kilodaltons. Electrophoretically purified SVNF is not inhibited by antisera to mouse NGF, but its activity is increased greater than 10-fold in the presence of very low concentrations of NGF. For partially purified SVNF, a specific activity of 2.9-5.8 X 10(5) biological units/mg of protein was determined in the presence of subthreshold NGF concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

Age-dependent differences in 125I-nerve growth factor binding properties of rat adrenal chromaffin cells

Nerve growth factor (NGF) has been shown to influence survival, morphology, and transmitter phenotype of young postnatal rat chromaffin cells in vitro. Significant differences in NGF responses of chromaffin cells from newborn rats compared to 8-10-day-old ones have been reported. For this reason we studied equilibrium binding and dissociation kinetics of 125I-NGF on newborn (D1) and 10-day-old (D10) rats. Under equilibrium conditions no differences were found between the two cell types, with respect to dissociation constant (approximately 2.5 X 10(-9) M) and receptor number (10-22,000 per cell). In dissociation experiments D10 chromaffin cells exhibited two classes of NGF receptors, similar to those found in other NGF-responsive cells. From fast receptors 125I-NGF was released rapidly both at 4 degrees C and at 37 degrees C, whereas dissociation from "slow" receptors was observed only at 37 degrees C. The slow receptor class was not found on D1 cells. Instead, more than 50% of specifically bound 125I-NGF did not dissociate in the presence of excess unlabeled NGF at 37 degrees C. These age-dependent differences seem to indicate regulatory developmental changes in NGF-binding properties of rat chromaffin cells.

Monoclonal antibody immunoaffinity chromatography of the nerve growth factor from snake venoms

1. Pure monoclonal antibodies to Vipera lebetina venom nerve growth factor have been isolated by affinity chromatography using CNBr-agarose bound antigen. 2. Nerve growth factors from ten snake venoms (Vipera lebetina, Vipera russellii, Vipera berus berus, Vipera ursini, Echis carinatus, Agkistrodon halys, Bungarus caeruleus, Naja naja oxiana, Naja naja, Naja naja atra) were purified using monoclonal antibodies against NGF linked to BrCN-activated agarose.

Neuron-enriched cultures of adult rat dorsal root ganglia: establishment, characterization, survival, and neuropeptide expression in response to trophic factors

It is unknown whether adult dorsal root ganglion (DRG) neurons require trophic factors for their survival and maintenance of neuropeptide phenotypes. We have established and characterized neuron-enriched cultures of adult rat DRGs and investigated their responses to nerve growth factor (NGF), ciliary neuronotrophic factor (CNTF), pig brain extract (PBE, crude fraction of brain-derived neuronotrophic factor, BDNF), and laminin (LN). DRGs were dissected from levels C1 through L6 and dissociated and freed from myelin fragments and most satellite (S-100-immunoreactive) cells by centrifugation on Percoll and preplating. The enriched neurons, characterized by their morphology and immunoreactivity for neuron-specific enolase, constituted a population representative of the in vivo situation with regard to expression of substance P (SP), somatostatin (SOM), and cholecystokinin-8 (CCK) immunoreactivities. In the absence of trophic factors and using polyornithine (PORN) as a substratum, 60-70% of the neurons present initially (0.5 days) had died after 7 days. LN as a substratum did not prevent a 30% loss of neurons up to day 4.5, but it subsequently maintained DRG neurons at a plateau. This behavior might reflect a cotrophic effect of LN and factors provided by non-neuronal cells, whose proliferation between 4.5 and 7 days could not be prevented by addition of mitotic inhibitors of gamma-irradiation. CNTF, but not NGF, slightly enhanced survival at 7 days on either PORN or LN. No neuronal losses were found in non-enriched cultures or when enriched neurons were supplemented with PBE, indicating that non-neuronal cells and PBE provide factor(s) essential for adult DRG neuron survival. Proportions of SP-, SOM-, and CCK-immunoreactive cells were unaltered under any experimental condition, with the exception of a numerical decline in SP cells in 7-day cultures with LN, but not PORN, as the substratum. Our data, considered in the context of recent in vivo and vitro studies, suggest that a combination of trophic factors or an unidentified factor, rather than the established molecules NGF, CNTF, and BDNF, which address embryonic and neonatal DRG neurons, are required for the in vitro maintenance of adult DRG neurons.

Effects of pre- and postnatal administration of antibodies to nerve growth factor on the morphological and biochemical development of the rat adrenal medulla: a reinvestigation

Whether or not adrenal medullary (chromaffin) cells which respond to nerve growth factor (NGF) both in vitro and in vivo require NGF for their normal development is controversial. Systemic deprivation of endogenous NGF by injection of anti-NGF antibodies into rat fetuses or by transfer of anti-NGF to the offspring of autoimmunized mothers has provided conflicting results. We have reinvestigated the effects of a specific antiserum to NGF on the morphology, catecholamine (CA) and neuropeptide (Met-enkephalin, Met-ENK; substance P, SP) content, and choline acetyltransferase (ChAT) activity of the rat adrenal medulla. Fetuses were injected with anti-NGF antibodies on day 17 of gestation and postnatally at daily intervals for 7 days. The histological appearance of adrenal medullae of anti-NGF injected animals was not altered as compared to controls. Ultrastructurally, no degenerative changes or developmental retardation of chromaffin cells could be detected. However, numbers of chromaffin granules per micron 2 of cytoplasmic area were greater and the mean diameters of the cores of adrenaline storage granules were smaller in antibody-treated than in control animals. CA and SP content, ratios of adrenaline to noradrenaline and ChAT activities were identical in anti-NGF-treated and control animals. Anti-NGF antibodies caused a reduction of adrenal Met-ENK by 40% as compared to controls. Superior cervical ganglia from the same animals were used to document immunosympathectomy induced by the antiserum. They displayed the well-established structural alterations and a marked reduction of the CA content. We conclude that administration of anti-NGF antibodies to embryonic and early postnatal rats induces only subtle changes in the ultramorphology of chromaffin cells without altering the development of normal CA levels. The small, yet significant effects of anti-NGF antibodies on adrenal Met-ENK, however, may suggest a role for endogenous NGF in the regulation of opioid peptide metabolism in developing chromaffin cells.

Isolation and characterization of nerve growth factor from Vipera berus berus (common viper) venom

Nerve growth factor from Vipera berus berus venom was purified by gel filtration on Sephadex G-100 (superfine), ion-exchange-chromatography on DEAE-Sephadex A-50 and chromatofocusing on PBE 118. The Vipera berus berus venom NGF consists of multiple molecular forms with pls in the interval 9.1-9.7. All isoforms have identical mol. wts approximately 35,000 +/- 3000 (in gel filtration) and 17,000 +/- 2000, 15,000 +/- 2000 (by SDS electrophoresis with beta-mercaptethanol). V. berus berus venom NGF reacted with monoclonal antibodies against Viper lebetina NGF and caused differentiation of pheochromocytoma PC12 cells.

Cellular and subcellular colocalization of nerve growth factor and epidermal growth factor in mouse submandibular glands

Immunocytochemical methods have been used to compare the cellular and subcellular distribution of nerve growth factor (NGF) and epidermal growth factor (EGF) in mouse submandibular glands. Rabbit antisera raised against purified proteins were characterized by immunoblot methods and were used to stain sections of salivary glands embedded in plastic. For light microscopy, antibodies were visualized by indirect immunofluorescence. For electron microscopy, thin sections were treated simultaneously with IgG against NGF and EGF coupled to colloidal gold particles of different size. Data indicate that NGF and EGF are present in all granular convoluted tubule cells and in no other cell type within the salivary gland. Ultrastructural analyses indicate that NGF and EGF are evenly distributed together within mature secretory granules, although a population of small granules was identified that is not immunoreactive for either protein. Taken together, the data suggest that granular convoluted tubule cells are homogeneous in the production and storage of NGF and EGF.

On the immunology of nerve growth factor

We report some experiments on the immunological properties of nerve growth factor from the venom of Heloderma horridum and from bull seminal vesicles. On the basis of these results, taken together with results already in the literature, we propose an operational definition of the term nerve growth factor.

A statistical approach to determine monoclonality after limiting cell plating of a hybridoma clone

One of the standard methods to isolate a hybridoma clone producing a monoclonal antibody requires successive steps of limiting dilution. The probability of obtaining a monoclonal antibody increases with the number of limiting dilution steps. However, without meticulous visual screening monoclonality is hard to prove. Here we describe a statistical analysis, based on Poisson's approximation, which allows one to calculate the number of hybridoma cells at a given plating efficiency so that when seeded a predictable number of mono-, bi-, etc.-clonal cultures are obtained after the first step of limiting cell plating.