Purification of adult rat sciatic nerve ciliary neuronotrophic factor

Pituitary hyperplasia induced by ectopic expression of nerve growth factor

Nerve growth factor (NGF) cDNA was fused to the rat prolactin promoter to induce its ectopic expression in pituitary lactotrophs of transgenic mice. High-level expression of both RNA and functional protein was achieved in two pedigrees. Pituitary cells from these animals secreted biologically active NGF that was capable of inducing rapid differentiation of cocultured PC12 pheochromocytoma cells. Despite this robust expression, transgenic pituitaries failed to show any detectable increase in neuronal innervation. Unexpectedly, we observed a dramatic hyperplasia of lactotrophs resulting in pituitaries 10-100 times larger than normal. These results suggest that NGF, in addition to its previously described effects, may act as a new class of mitogen, with a potential role in oncogenesis.

Expression cloning of neurotrophic factors using Xenopus oocytes

We have explored the potential for cloning novel neurotrophic factor cDNAs via assay of neurotrophic activities following expression in Xenopus oocytes. In this report, we describe the successful application of the method to tract rat ciliary neurotrophic factor (CNTF) activity from mRNA purified from cultured cells and from mRNA synthesized by in vitro transcription of a cDNA library. Rat C6 glioma cells, which had been previously shown to have CNTF-like activity (Westermann et al., 1988), were used as source material. We tested protein extracts of C6 cells using an in vitro assay of primary neurons from the chick ciliary ganglion (CCG assay) and detected a CNTF-like activity. RNA isolated from C6 cells was shown to direct the synthesis of the activity following microinjection into Xenopus oocytes and one-step fractionation of Xenopus extract. C6 mRNA was size-fractionated, and fractions encoding CNTF-like activity were cloned into a lambda phage vector at a site distal to a T7 promoter. Synthetic RNA transcribed from total library DNA was injected into Xenopus oocytes, and a CNTF-like activity in the oocyte extract was detected by the CCG assay. Further fractionation of library clones narrowed the presence of the clone encoding the CNTF-like activity to a pool containing 20,000 members. The presence of a full-length CNTF cDNA clone in this pool and partial clones in other pools was confirmed by Polymerase Chain Reaction (PCR) using oligonucleotides from the rabbit CNTF cDNA (Lin et al., 1989) as primers.(ABSTRACT TRUNCATED AT 250 WORDS)

The expression of CNTF message and immunoreactivity in the central and peripheral nervous system of the rat

We have examined the temporal and spatial expression of ciliary neurotrophic factor (CNTF) and its messenger RNA (mRNA) by immunocytochemistry and Northern blot analysis. Specific CNTF-like (CNTF-IR) immunoreactivity and CNTF message were detected primarily in sciatic nerve, spinal cord, and optic nerve sections in the adult rat. In the sciatic nerve immunostaining was localized primarily to the Schwann cell cytoplasm. Schwann cells in the dorsal root ganglion and in the spinal motor roots were immunoreactive for CNTF but no CNTF immunoreactivity was detected in Schwann cells associated with unmyelinated sympathetic fibers in the superior cervical ganglion. CNTF-IR was first detected in sciatic nerve sections on postnatal day 8 and increased in intensity until reaching adult levels by postnatal day 21. In the adult rat, optic nerve staining was confined to astrocyte-like cells and their projections, and this pattern of immunoreactivity was first apparent at postnatal day 8. Double labelling experiments suggest that a GFAP-positive cell in the optic nerve synthesizes CNTF. In the spinal cord, CNTF-IR was seen only in white matter non-neuronal cells at all ages studied. Branched oligodendrocyte-like cells appeared stained and the staining was first apparent at postnatal day 8. The data, therefore, suggest that myelinating Schwann cells produce CNTF and demonstrate the presence of CNTF and its messenger RNA at the appropriate time period in tissues previously defined as having biological responses to CNTF.

Effects of ciliary neurotrophic factor (CNTF) and depolarization on neuropeptide expression in cultured sympathetic neurons

We examined the effects of ciliary neurotrophic factor (CNTF) and depolarization, two environmental signals that influence noradrenergic and cholinergic function, on neuropeptide expression by cultured sympathetic neurons. Sciatic nerve extract, a rich source of CNTF, increased levels of vasoactive intestinal peptide (VIP), substance P, and somatostatin severalfold while significantly reducing levels of neuropeptide Y (NPY). No change was observed in the levels of leu-enkephalin (L-Enk). These effects were abolished by immunoprecipitation of CNTF-like molecules from the extract with an antiserum raised against recombinant CNTF, and recombinant CNTF caused changes in neuropeptide levels similar to those of sciatic nerve extract. Alterations in neuropeptide levels by CNTF were dose-dependent, with maximal induction at concentrations of 5-25 ng/ml. Peptide levels were altered after only 3 days of CNTF exposure and continued to change for 14 days. Depolarization of sympathetic neuron cultures with elevated potassium elicited a different spectrum of effects; it increased VIP and NPY content but did not alter substance P, somatostatin, or L-Enk. Depolarization is known to block cholinergic induction in response to heart cell conditioned medium and we found that it blocked the induction of choline acetyltransferase (ChAT) and peptides by recombinant cholinergic differentiation factor/leukemia inhibitory factor (CDF/LIF). In contrast, it did not antagonize the effects of CNTF on either ChAT activity or neuropeptide expression. Thus, while CNTF has effects on neurotransmitter properties similar to those previously reported for CDF/LIF, the actions of these two factors are differentially modulated by depolarization, suggesting that the mechanisms of cholinergic and neuropeptide induction for the two factors differ. In addition, in contrast to CDF/LIF, CNTF did not alter levels of ChAT, VIP, substance P, or somatostatin in cultured dorsal root ganglion neurons. These observations indicate that CNTF and depolarization affect the expression of neuropeptides by sympathetic neurons and provide evidence for an overlapping yet distinct spectrum of actions of the two neuronal differentiation factors, CNTF and CDF/LIF.

Characterization of a neurotrophic factor produced by cultured astrocytes involved in the regulation of subcortical cholinergic neurons

When dissociated subcortical cells were cultured in the presence of conditioned medium of relatively differentiated astrocytes (ACM), a marked increase was observed in the expression of choline acetyltransferase (ChAT), an enzyme required for the synthesis of the neurotransmitter acetylcholine. Astrocytes from the target regions of subcortical neurons, the hippocampus and the cerebral cortex, produced neurotrophic factor consistently more than those derived from the nontarget region, the cerebellum. The production of cholinergic trophic activity was increased with the maturation of astrocytes. Even though, nerve growth factor (NGF) and ciliary neurotrophic factor (CNTF) are known cholinergic trophic compounds produced by astrocytes in vitro, a large part of the neurotrophic activity in our ACM was not related to either of these 2 factors. This is because (i) ACM and NGF produced an additive effect on ChAT activity, (ii) only a small proportion of the cholinergic trophic activity in ACM was abolished by anti-NGF antibody, and (iii) treatment with CNTF had no effect on ChAT activity of basal forebrain cholinergic neurons. On the other hand, when cholinergic neurons are cultured on a preformed layer of astrocytes, addition of basal fibroblast growth factor (bFGF) failed to increase further the ChAT activity. Similarly the effects of ACM and bFGF were not additive. A large proportion of the cholinergic trophic activity in ACM was neutralized by anti-bFGF antibody. These findings would suggest that the trophic activity on septal cholinergic neurons in our ACM was due to bFGF or a bFGF-like compound.

The emerging neuropoietic cytokine family: first CDF/LIF, CNTF and IL-6; next ONC, MGF, GCSF?

CDF/LIF is a polyfunctional cytokine that shares a remarkable overlap with ciliary neurotrophic factor in its actions on neurons, and with interleukin-6 in its actions on other tissues. Moreover, the receptors for this cytokine, as well as those for ciliary neurotrophic factor, share homology with the subunits of the interleukin-6 receptor. The predicted structural similarity of these proteins with oncostatin M, myelomonocytic growth factor and granulocyte colony-stimulating factor, as well as at least a partial overlap in biological activities, is now prompting further examination of their roles in neuronal gene expression.

Platelet-derived growth factor and regulation of Schwann cell proliferation in vivo

To examine the role of platelet-derived growth factor (PDGF) in the in vivo regulation of Schwann cell proliferation, steady-state levels of mRNAs encoding PDGF A and B chains, and PDGF alpha and beta receptors were measured in immature and adult rat sciatic nerves and in cultured rat Schwann cells. PDGF B chain and PDGF beta receptor mRNAs are present in immature rat sciatic nerves and to a lesser extent in adult rat nerves. Short-term cultures of neonatal rat Schwann cells express PDGF beta receptor mRNA, but not PDGF B chain mRNA, and are stimulated to synthesize DNA by addition of PDGF BB to the medium. These data indicate that PDGF BB is a developmentally regulated paracrine growth factor for rat Schwann cells. Very long-term cultures of rat Schwann cells, which have lost normal dependence on exogenous growth factors, express PDGF B chain mRNA as well as mRNAs encoding the PDGF alpha and beta receptors, suggesting that, under these circumstances, PDGF BB also act as an autocrine growth factor. PDGF A chain mRNA is present in both immature and adult rat sciatic nerves and is expressed by primary and secondary cultures of rat Schwann cells as well. However, because the abundance of PDGF alpha receptor mRNA is very low in rat Schwann cells, PDGF AA is not likely to be a significant autocrine growth factor for rat Schwann cells.

Pure Schwann cell suspension grafts promote regeneration of the lesioned septo-hippocampal cholinergic pathway

Regeneration of central nervous system (CNS) axons has been studied in the cholinergic septo-hippocampal system using various 'bridges' able to support fiber growth. In this study, a pure Schwann cell (Sc) suspension labeled with bisbenzimide (Hoechst 33342) was grafted in the lesioned septo-hippocampal pathway. At 2 weeks post-grafting, acetyl-cholinesterase (AChE)-positive fibers invaded the graft and grew in association with the Hoechst-labeled Sc, some of which expressed the low-affinity nerve growth factor receptor (NGF-R). At 2 months and 4 months post-grafting, the dorsal hippocampus was reinnervated with an apparently normal innervation pattern. Analysis of fiber growth in the hippocampus at four months post-grafting revealed a significant increase of reinnervation in the grafted animals (2 mm) compared to the non-grafted ones. No difference was observed in the number of cholinergic septal neurons expressing the NGF-R. These results demonstrate that a Sc suspension grafted into the lesioned septo-hippocampal system, integrates well into the host tissue, and supports axonal CNS outgrowth, implying that Sc by themselves provide an adequate environment for regeneration to occur.

Ciliary neurotrophic factor and its receptor complex

Ciliary neurotrophic factor (CNTF), originally identified for its ability to promote survival of neurons of the ciliary ganglion, is now known to have additional survival and differentiative actions on cells of the nervous system. CNTF is, however, unrelated in structure to the nerve growth factor family of neurotrophic factors. Instead, CNTF is distantly related to, and in fact shares receptor components with, a number of hemopoietic cytokines. This review focuses on the biological actions of CNTF, the shared and unique features of the CNTF receptor complex and signaling pathways, and the distribution of CNTF and its receptor during development, in the adult and in response to injury.

Immunolocalization of ciliary neuronotrophic factor in adult rat sciatic nerve

Two rabbit polyclonal antibodies were raised against synthetic peptides corresponding to residue numbers 45-59 and 181-200 of rat ciliary neuronotrophic factor (CNTF). The resulting antibodies were purified by affinity chromatography and both purified antibodies reacted by enzyme-linked immunoassay (ELISA) and immunoblotting with rat sciatic nerve CNTF. The anti-CNTF peptide antibodies were used to immunostain sections of adult rat sciatic nerve, previously known as the richest tissue source of CNTF. By light microscopy both antibodies appeared to stain exclusively Schwann cells and axons and both did so with the same pattern of specific staining. Immunostaining was eliminated by absorption of the anti-peptide antibodies with either their corresponding peptide or with purified rat nerve CNTF or by using purified nonspecific IgG. Schwann cells were stained and in semi-thin sections this staining appeared to be in the Schwann cell cytoplasm. Axons could be stained in addition to Schwann cells providing higher concentrations of antibodies were used. Epineurial, endoneurial and endothelial cells appeared unstained. Since all Schwann cells and axons appear to contain CNTF and since CNTF is known to act in vitro to support sensory and sympathetic ganglionic and motor neurons, we suggest that Schwann cells may normally provide CNTF to those neurons contributing axons to the peripheral nerve.

Molecular mechanisms for generation of neural diversity and specificity: roles of polypeptide factors in development of postmitotic neurons

Development of postmitotic neurons is influenced by two groups of polypeptide factors. Neurotrophic factors promote neuronal survival both in vivo and in vitro. Neuronal differentiation factors influence transmitter phenotypes without affecting neuronal survival. The list of neurotrophic factors is increasing partly because certain growth factors and cytokines have been shown to possess neurotrophic activities and also because new neurotrophic factors including new members of the nerve growth factor (NGF) family have been identified at the molecular level. In vitro assays using recombinant neurotrophic factors and distributions of their mRNAs and proteins have indicated that members of a neurotrophic gene family may play sequential and complementary roles during development and in the adult nervous system. Most of the receptors for neurotrophic factors contain tyrosine kinase domains, suggesting the importance of tyrosine phosphorylation and subsequent signal transduction for their effects. Molecules such as LIF (leukemia inhibitory factor) and CNTF (ciliary neurotrophic factor) have been identified as neuronal differentiation factors in vitro. At the moment, however, it remains to be determined whether or not the receptors for a group of neuronal differentiation factors constitute a gene family or contain domains of kinase or phosphatase activity. Synergetic combinations of neurotrophic and neuronal differentiation factors as well as their receptors may contribute to the generation of neural specificity and diversity.

Ciliary neurotrophic factor prevents neuronal degeneration and promotes low affinity NGF receptor expression in the adult rat CNS

Recombinant human ciliary neurotrophic factor (CNTF) was infused for 2 weeks into the lateral ventricle of fimbria-fornix transected adult rats, and its effects were compared with those of purified mouse nerve growth factor (NGF). We provide evidence that CNTF can prevent degeneration and atrophy of almost all injured medial septum neurons (whereas NGF protects only the cholinergic ones). CNTF is also involved in up-regulation of immunostainable low affinity NGF receptor (LNGFR) in cholinergic medial septum and neostriatal neurons and in a population of lateral septum neurons. In contrast to NGF, CNTF did not stimulate choline acetyltransferase in the lesioned septum and normal neostriatum (pointing to different mechanisms for the regulation of choline acetyltransferase and LNGFR), cause hypertrophy of septal or neostriatal cholinergic neurons, or cause sprouting of LNGFR-positive (cholinergic) septal fibers.

A cell culture model of the blood-brain barrier

Endothelial cells that make up brain capillaries and constitute the blood-brain barrier become different from peripheral endothelial cells in response to inductive factors found in the nervous system. We have established a cell culture model of the blood-brain barrier by treating brain endothelial cells with a combination of astrocyte-conditioned medium and agents that elevate intracellular cAMP. These cells form high resistance tight junctions and exhibit low rates of paracellular leakage and fluid-phase endocytosis. They also undergo a dramatic structural reorganization as they form tight junctions. Results from these studies suggest modes of manipulating the permeability of the blood-brain barrier, potentially providing the basis for increasing the penetration of drugs into the central nervous system.

Co-grafts of embryonic dopamine neurons and adult sciatic nerve into the denervated striatum enhance behavioral and morphological recovery in rats

We have recently demonstrated that a diffusible factor(s) derived from explanted adult rat sciatic nerve can increase the number and neurite outgrowth of embryonic rat dopamine (DA) neurons in culture. The present study extends this finding to compare DA neuron-sciatic nerve co-grafts to grafts of DA-rich neural tissue alone for behavioral and morphological effects in rats with unilateral nigrostriatal lesions of the DA pathway. Our results indicate that the presence of a co-grafted segment of sciatic nerve increased the likelihood of rapid behavioral recovery and promoted complete recovery mediated by small grafts that yielded only modest behavioral changes in the absence of co-grafted nerve. These behavioral effects were accompanied by a modest increase in survival of grafted tyrosine hydroxylase-positive neurons in the striatum and a more pronounced increase in the area and density of striatal reinnervation provided by grafted DA neurons in co-grafted animals. This evidence supports the view that a diffusible product of explanted peripheral nerve acts as a growth-promoting factor for embryonic DA neurons and that the presence of this factor augments the behavioral efficacy of grafted DA neurons.

Neurotropism, frozen muscle grafts and other conduits

Axonal regeneration following nerve transection requires a number of cellular and biochemical phenomena in the axons as well as the nerve cell bodies. The nerve cells must survive the trauma. Since axonal severance means amputation of a large axoplasmic volume from the remaining parts of the nerve cell, the cell body must prepare for increased synthesis of axoplasm to replace the missing parts. A sprouting process must be initiated at the level of transection. Regenerating axonal processes are to regenerate towards peripheral targets, a process regulated by an interaction between genetic mechanisms in the nerve cell body and biochemical information at the molecular level along the pathway.

Neuronal and nonneuronal influences on retinal ganglion cell survival, axonal regrowth, and connectivity after axotomy

In contrast to the abortive regrowth that occurs when axons are interrupted in the adult mammalian CNS, exposure of injured CNS axons to the nonneuronal milieu of a peripheral nerve can lead to extensive axonal elongation. With the application of this experimental approach to the retinocollicular pathway in adult rodents, it has been possible to investigate the influences of neuron-glia and other interactions on the capacity of axotomized CNS neurons to survive injury, to elongate the distances necessary to reach specific targets, and to form connections in the CNS in adult rodents. The results of these investigations indicate that the changed glial environment provided by peripheral nerve grafts permits the guided regeneration of RGC axons to their CNS targets. Back in the CNS glial environment, regenerated axons penetrate their targets for short distances and re-form normal appearing synapses that can excite or inhibit postsynaptic neurons. Further studies will require a better understanding of intrinsic neuronal properties and of the interactions of these neurons with other neurons and with the cellular and noncellular components of the extraneural milieu.

Effects of ciliary neuronotrophic factor on rat spinal cord neurons in vitro: survival and expression of choline acetyltransferase and low-affinity nerve growth factor receptors

We have studied the effects of ciliary neuronotrophic factor (CNTF) and nerve growth factor (NGF) on cultures of E14 rat spinal cord cells maintained for 7 days. The trophic factors were supplied at the day of seeding and every other day thereafter. Treatments with CNTF (human recombinant or purified from rat sciatic nerve, 100 TU/ml) resulted after 7 days in an increase, relative to control cultures, of: (i) the total number of neurons (identified by neurofilament protein and neuron-specific enolase immunostaining) that were not stained with choline, acetyltransferase (ChAT) and low affinity nerve growth factor receptor (LNGFR) antibodies; (ii) the number of motoneurons (0.5% of the neuronal population) as identified by size (greater than 25 microns), morphology and immunostaining for ChAT and LNGFR; and (iii) a population of small- to medium-sized (less than 25 microns), ChAT- and LNGFR-positive neurons, representing 5-10% of the total neuronal population. NGF treatments (mouse submaxillary beta NGF; 10-3000 TU/ml) were without effect on all 3 neuronal populations. Experiments in which CNTF administration was delayed revealed that the population of ChAT- and LNGFR-negative neurons and the population of motoneurons, were both dependent on CNTF for their survival. The third population, small ChAT and LNGFR-positive neurons, was not dependent on CNTF for survival but was induced by CNTF to express its two markers. These observations indicate that CNTF is a neuronotrophic factor for motoneurons, but that the effect of CNTF is not restricted to that cell population. In addition to its survival promoting effect, CNTF has also a regulatory role on the expression of ChAT and LNGFR for some spinal cord neurons.

Class 1 heparin binding growth factor promotes the differentiation but not the survival of ciliary neurones in vivo

Molecules isolated from target tissues of various neuronal populations have been shown to enable the survival of those innervating neurones. A molecule derived from bovine heart which can support the survival of parasympathetic neurones of the chick embryo ciliary ganglion in vitro has been sequenced and identified as a member of the class 1 heparin binding growth factors (HBGF-1). When injected into developing chick embryos during the period of naturally occurring cell death in the ciliary ganglion, HBGF-1 failed to rescue those neurones which normally die. There was, however, a premature increase in the activity of choline acetyltransferase within the ganglion and a shift to the right in the size distribution of the neurones. We conclude that HBGF-1 may promote the differentiation of some subpopulation of neurones of the ciliary ganglion of the chick embryo but does not act in vivo as a survival molecule.

Cloning and expression of human ciliary neurotrophic factor

Ciliary neurotrophic factor (CNTF) is a survival factor for avian ciliary ganglion neurons and a variety of other neuronal cell types in vitro. We report here the cloning of the entire genomic sequence encoding human CNTF and its primary structure. Biologically active CNTF has been expressed in Chinese hamster ovary cells from a human genomic DNA clone. Human CNTF has no significant sequence similarity to any previously reported protein, although approximately 84% similarity exists compared with rat and rabbit CNTF. The lack of both an N-terminal signal sequence and consensus sequences for glycosylation or hydrophobic regions, and the fact that active CNTF is expressed but not released into the culture medium of transfected cells, argue in favour of human CNTF as a cytosolic protein. These data provide a basis for understanding the role of CNTF in nervous system physiology and pathology.

Expression and characterization of recombinant human ciliary neurotrophic factor from Escherichia coli

The gene for ciliary neurotrophic factor (CNTF) was cloned from a human genomic DNA library by screening with a DNA fragment amplified from human genomic DNA using the polymerase chain reaction. A DNA sequence coding for human CNTF was placed under control of an regulatable promoter in the expression vector pJU1003 and transformed into Escherichia coli strain BL21(DE3). Induction of expression in cultures of this transformant led to the accumulation of approx. 25 mg/l per A600 unit of human CNTF. CNTF was purified to homogeneity from cell lysates via anion-exchange, cation-exchange and Zn(2+)-affinity chromatography. Purified CNTF contained less than 0.1% contaminating E. coli proteins, as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), Western blot analysis and reversed-phase high-pressure liquid chromatography (HPLC). The protein exhibited an ultraviolet absorption maximum at 279 nm with a calculated extinction coefficient of A1%(279) = 9.0. Peptide map and amino acid sequence analyses confirmed that the expressed protein has the amino acid sequence expected for human CNTF, except for the absence of the amino-terminal methionine. High-purified recombinant human CNTF supported the survival of chick embryo parasympathetic, sympathetic and sensory neurons in culture at low picomolar concentrations. These results indicate that the biological activities previously ascribed to impure CNTF preparations indeed reside in one molecule.

von Recklinghausen neurofibroma produces neuronal and glial growth-modulating factors

Two kinds of novel neural trophic factors were currently detected in von Recklinghausen neurofibroma (NF1) extracts. One of the two was a growth factor, neuroblastoma growth factor (Mr less than 5 kDa), which promotes the proliferation of human neuroblastoma cell and survival and neurite-extension of rat cortical neurons, but differently from nerve growth factor (NGF) or NGF-like factors. The other one was a glial growth inhibitor (Mr = 100 kDa), which suppresses the growth of glioma cell lines, astrocytoma, glioblastoma, oligodendroglioma and Schwannoma. These factors do not appear to be previously identified cytokines or growth factors such as interleukins, granulocyte colony-stimulating factor, NGF and fibroblast growth factor. There was also detectable ciliary neurotrophic factor-like activity in the extracts. The primary cause of high contents of these factors in NF1 is not known, but may relate to fundamental mechanisms controlling growth and differentiation of neurons and glias during development of nervous system.

Sequence and structural organization of the human gene encoding ciliary neurotrophic factor

Ciliary neurotrophic factor (CNTF) is a potent polypeptide hormone whose actions appear to be restricted to the nervous system where it promotes survival, neurotransmitter synthesis and neurite outgrowth in certain neuronal populations. We have cloned the gene encoding human CNTF (hCNTF) and have characterized its structure and organization. The hCNTF gene appears to be a unique-copy gene with a simple genetic organization, since only a single intron interrupts the coding domain. The hCNTF gene is located on chromosome 11, as determined using human-hamster somatic cell hybrids. The CNTF protein is highly conserved in evolution. The amino acid (aa) sequences of rat and rabbit CNTF translated from cDNAs display approx. 85% homology with the deduced aa sequence encoding hCNTF.

Dose-dependent responses to nerve growth factor by adult rat cholinergic medial septum and neostriatum neurons

This study describes the relationship between the concentration of intraventricularly infused nerve growth factor (NGF) and several responses by axotomized cholinergic medial septum neurons and normal cholinergic neostriatal neurons of the adult rat. NGF infused for 14 days starting either immediately after a unilateral fimbria-fornix transection or after a 2-week delay period elicited similar dose-response relationships for the maintenance or restoration of ChAT and NGF receptor positivity and cell body size and for intraseptal 'sprouting' of the axotomized medial septum neurons. Thus, in the medial septum it appears that the expression of 'marker' molecules, cell body size and the induction of 'sprouting' are regulated by virtually the same concentrations of NGF in the two treatment strategies. This suggests that NGF has a general regulatory role and injured but untreated neurons remain fully susceptible to NGF at least up to 2 weeks after the lesion. A 14-day infusion with NGF also induced an above-normal cell body size (hypertrophy) both in axotomized medial septum and in intact striatal cholinergic neurons. The hypertrophic response of normal striatal neurons required less NGF than did that of medial septum neurons. Since the striatal response began to be detectable at a similar concentration as that required for the full maintenance or restoration of ChAT and NGF receptor positivity it could be seen as an unwanted side-effect. The definition of a sub-optimal dose with which a significant, but not maximal response can be elicited will allow future evaluations of potentially additive or synergistic actions by other agents.

Adrenal medulla and substantia nigra co-grafts in peripheral nerve: chromaffin cells survive for long time periods and prevent degeneration of nigral neurons

A series of degenerative cytoskeletal changes characterize grafts of embryonic substantia nigra when isolated for long time periods in the peripheral nervous system. This study was designed to determine whether the adrenal medulla could modulate the cytoskeletal changes in the substantia nigra when co-grafted within peripheral nerves. The sciatic nerves of young adult rats received single transplants of embryonic day 15 substantia nigra or co-transplants of substantia nigra plus young adult adrenal medulla in close proximity. Immunocytochemistry was used to examine the expression of tyrosine hydroxylase, phosphorylated (RT97) and non-phosphorylated (SMI-32) neurofilament proteins in the grafts. Single substantia nigra grafts, examined after 1 month, consisted of numerous neurons and fibers that expressed the epitope for tyrosine hydroxylase. Normal spatial distributions of the phosphorylated and non-phosphorylated neurofilament subunits were observed. In contrast, single 1-year-old nigral transplants were shrunken, contained significantly fewer tyrosine hydroxylase positive neurons and displayed abnormal neurofilaments staining patterns including swollen axons, a reduction in the density of labeled axons and perikaryal accumulation of the phosphorylated neurofilament subunit. When co-grafted with the adrenal medulla, the nigral transplants did not show the degenerative cytoskeletal aspects evident in the single 1-year-old grafts. The loss of neurons was prevented and the neurofilament immunolabeling was indistinguishable from the young substantia nigra preparations. In addition, all the 1-year-old adrenal medulla grafts were viable within the peripheral nerves, consisting of hundreds of cells identified by immunoreactivity to tyrosine hydroxylase and the rat beta-nerve growth factor receptor (192-IgG). The experiments illustrate a strong protective effect by the adrenal medulla on neurons of the substantia nigra in the peripheral nerve environment. It is suggested that a catecholaminergic trophic source and/or neural interactions with the adrenal medulla may be important factors in the long-term survival of neurons and maintenance of normal cytoskeletal characteristics in the grafted substantia nigra neurons under these experimental circumstances.

Nerve growth factor (NGF) induces sprouting of specific neurons of the snail, Lymnaea stagnalis

Nerve growth factor (NGF) was examined for its ability to elicit sprouting by adult molluscan neurons. Motoneurons and interneurons (but not neurosecretory cells) from Lymnaea exhibited a sprouting response to murine 2.5S NGF in defined medium with a half-maximal response at about 150 ng/mL. Furthermore, an NGF antiserum blocked sprouting by all normally responsive neurons. We tested whether an NGF-like molecule is a component of conditioned medium (CM) by attempting to preabsorb its sprout-inducing activity with NGF antiserum. Treatment of CM with immune (but not nonimmune) serum largely blocked the response of motoneurons, but not that of neurosecretory cells, to CM. We conclude that NGF exerts neurotrophic activity on specific adult Lymnaea neurons, and suggest the possibility that an NGF-like molecule may exist in the molluscan nervous system.

A ciliary neuronotrophic factor from peripheral nerve and smooth muscle which is not retrogradely transported

We have found that a CNTF-like molecule which supports ciliary and sympathetic neurons is not retrogradely transported in either sympathetic or parasympathetic nerves. The factor has an apparent Mr of 21 kDa, a pI of 4.9, and is present in peripheral nerves and smooth muscle of the chick. Our experiments indicate that CNTF-like activity does not accumulate on the distal side of ligated chick expansor nerves. In contrast, there is a clear accumulation of NGF. The activity further differs from NGF in that it is not removed from a smooth muscle of the chick wing by innervating sympathetic fibers. Transection of these fibers does not lead to an accumulation of ciliary activity in the expansor secundariorum muscle, suggesting that neurons do not actively deplete the muscle of factor by retrograde transport. Finally, recombinant CNTF or semi-purified preparations of CNTF-like activity labelled with 125I were not transported to the ciliary ganglion of chicks following injection of biologically active material into the eye. Our results suggest either that endogenous CNTF does not act as a survival factor in vivo, or that retrograde transport is not a property inherent to all neuronotrophic molecules.

Synthesis, purification, and characterization of human ciliary neuronotrophic factor from E. coli

The cDNA for human ciliary neuronotrophic factor (CNTF) has been cloned into an expression vector under the control of the T7 promoter. The BL21 strain of E. coli was transformed with this vector. Human CNTF accounted for about 30% of the total bacterial protein after induction with isopropyl-B-D-thiogalactopyranoside. This human CNTF was purified to homogeneity from inclusion bodies by a combination of ion exchange chromatography and reverse-phase high performance liquid chromatography. The amino-terminal amino acid sequence of the purified protein was identical to the deduced amino acid sequence; however, the methionyl residue has been removed. On SDS-PAGE gels, human CNTF displayed a molecular weight of about 24 kDa, in accord with its deduced molecular mass; a pI of 5.8 indicates the acidic nature of the molecule. A proposed structure for human CNTF includes major alpha helical regions. The ED50 of purified human CNTF was approximately 30 pM, using cultured embryonic day 10 chicken dorsal root ganglion neurons; no activity was observed with neurons from embryonic day 8 ganglia. Polyclonal antibodies prepared against both a synthetic peptide of CNTF and the entire human CNTF protein recognized a single 24 kDa band on Western blots, corresponding to human CNTF. However, only the antibodies against intact CNTF blocked its biological activity. This represents the first molecular expression and purification of human CNTF.

Blot and culture analysis of neuronotrophic factors in nerve regeneration chamber fluids

The fluid accumulating in silicone nerve regeneration chambers implanted between the cut ends of rat sciatic nerve contains neuronotrophic activities towards embryonic chick ciliary and sympathetic neurons. The blot and culture technique of Carnow et al. was used to determine if part of the neuronotrophic activities is due to ciliary neuronotrophic factor, which supports the survival of both types of neurons in vitro. The technique involves separating the fluid proteins by SDS-polyacrylamide gel electrophoresis, Western transfer, and then culturing of purified neurons on the nitrocellulose blots. After 24 hr surviving neurons are restricted to regions of the blot where neuronotrophic factor is present. Analysis of 1 and 2 day fluids showed that a multitude of factors are present, particularly in the 19-30 kD molecular weight range, with discrete peaks of activity at molecular weights consistent with those reported for ciliary neuronotrophic factor. There were several other peaks of activity present in the fluids in addition to these.

The changing scene of neurotrophic factors

The purification of brain-derived neurotrophic factor (BDNF), the elucidation of its primary structure, and the subsequent identification of neurotrophin-3 (NT-3) ended the monopoly of NGF as the only well-characterized, target-derived neurotrophic molecule. NGF, BDNF and NT-3 are members of a gene family called neurotrophins. They have strictly conserved domains that determine their basic structure. However, they also have distinctly variable domains that determine their different neuronal specificity mediated by different high affinity receptors, and that share a common low affinity subunit. These similarities and dissimilarities between the members of the neurotrophin gene family are also reflected by their regional distribution, cellular localization and developmental regulation. In this article the neurotrophins are compared with ciliary neurotrophic factor (CNTF), which is a representative of the category of neurotrophic molecules that, according to their regional distribution, developmental expression and cellular localization, do not fulfil the criteria of a target-derived neurotrophic molecule. The physiological and pathophysiological functions of neurotrophins and CNTF are discussed in the context of their potential use for the treatment of traumatic and degenerative diseases of the peripheral and central nervous systems.

Control of embryonic motoneuron survival in vivo by ciliary neurotrophic factor

During development of the nervous system, neurons in many regions are overproduced by proliferation, after which the excess cells are eliminated by cell death. The survival of only a proportion of neurons during normal development is thought to be regulated by the limited availability of neurotrophic agents. One such putative trophic agent is ciliary neurotrophic factor (CNTF), a polypeptide that promotes the survival of ciliary, sensory, and sympathetic neurons in vitro. In contrast to the results of in vitro studies, however, the daily treatment of chick embryos in vivo with purified human recombinant CNTF failed to rescue any of these cell populations from cell death, whereas CNTF did promote the in vivo survival of spinal motoneurons. Thus, CNTF may not act as a neurotrophic agent in vivo for those embryonic neurons (especially ciliary neurons) on which it acts in vitro. Rather, CNTF may be required for in vivo survival of motoneurons.

Degenerative and regenerative responses of injured neurons in the central nervous system of adult mammals

In adult mammals, the severing of the optic nerve near the eye is followed by a loss of retinal ganglion cells (RGCs) and a failure of axons to regrow into the brain. Experimental manipulations of the non-neuronal environment of injured RGCs enhance neuronal survival and make possible a lengthy axonal regeneration that restores functional connections with the superior colliculus. These effects suggest that injured nerve cells in the mature central nervous system (CNS) are strongly influenced by interactions with components of their immediate environment as well as their targets. Under these conditions, injured CNS neurons can express capacities for growth and differentiation that resemble those of normally developing neurons. An understanding of this regeneration in the context of the cellular and molecular events that influence the interactions of axonal growth cones with their non-neuronal substrates and neuronal targets should help in the further elucidation of the capacities of neuronal systems to recover from injury.

Promotion of neuronal survival in vitro by thermal proteins and poly(dicarboxylic)amino acids

Evaluating molecules for their ability to promote survival and growth of neurons, we tested thermal proteins on cultures of dissociated fetal rat forebrain neurons. (Thermal proteins are polyamino acids formed when mixtures of amino acids with minimal proportions of glutamic or aspartic acid are heated.) Thermal proteins, added to low-density cultures in serum-free medium, stimulated neurite outgrowth and induced the formation of neuronal networks which survived for 6-10 days. Neurons in control cultures failed to grow and degenerated completely within 2-4 days. Effective concentrations (EC50) of thermal proteins ranged from 3 to 100 micrograms/ml. They were equally effective when present in the medium during the culture time or after precoating of the culture dishes. A single preparation which contained only aspartic and glutamic acid was effective, and similar survival promoting actions were then found for polyglutamic acid and mixed polyamino acids containing glutamic or aspartic acid. Thermal proteins and polyglutamic acid acted in a specific manner since, under the same experimental conditions, many control peptides, proteins and growth hormones failed to promote survival of neurons. Furthermore, their effects were antagonized by heparin, but not heparan sulfate nor chondroitin sulfate. These findings suggest that sequences of successive dicarboxylic amino acid residues are able to promote survival and neurite elongation of cultured neurons and that such sequences are responsible for the survival promoting action of thermal proteins. They invite the speculation that sequences of successive dicarboxylic amino acids, while occur in many proteins and show a high degree of evolutionary conservation, may have functional role in molecular recognition processes during neuronal development.

Target dependence of motoneuronal survival: the current status

The concept that target-derived molecules are essential for the maintenance of motoneuronal survival has now received considerable support from different sources. One source of information arises from the target-related motoneuron death that occurs naturally at early developmental stages. Another source of information arises from axotomy-induced motoneuron death in adulthood. During development, the survival of motoneurons is initially target-independent. Its target dependence is expressed at a certain embryonic stage and, subsequently, motoneuronal survival becomes less dependent upon the target. It is not known how the state-switch of motoneurons is induced during development. Also, it is not certain whether naturally occurring motoneuron death during development and axotomy-induced motoneuron death in adulthood are based on the same mechanisms. Axotomy induces injury-associated disturbance in the motoneurons, in addition to elimination of the target-derived trophic supply. At present, there is no direct evidence that axotomy-induced motoneuron death in adulthood results solely from the deprivation of trophic factors from the target. The survival of motoneurons in adulthood appears to be maintained by multiple mechanisms. Some of the tropic factors that are involved in the maintenance of neuronal phenotypic expression are distinct from those involved in the maintenance of neuronal survival. There are multiple target-derived trophic factors for a given neuron.

Characterization of a target-derived neuronal cholinergic differentiation factor

The sympathetic innervation of rat sweat glands undergoes a target-induced switch from a noradrenergic to a cholinergic and peptidergic phenotype during development. Treatment of cultured sympathetic neurons with sweat gland extracts mimics many of the changes seen in vivo. Extracts induce choline acetyltransferase activity and vasoactive intestinal peptide expression in the neurons in a dose-dependent fashion while reducing catecholaminergic properties and neuropeptide Y. The cholinergic differentiation activity appears in developing glands of postnatal day 5 rats and is maintained in adult glands. It is a heat-labile, trypsin-sensitive, acidic protein that does not bind to heparin-agarose. Immunoprecipitation experiments with an antiserum directed against an N-terminal peptide of a cholinergic differentiation factor (CDF/LIF) from heart cells suggest that the sweat gland differentiation factor is not CDF/LIF. The sweat gland activity is a likely candidate for mediating the target-directed change in sympathetic neurotransmitter function observed in vivo.

Soluble and membrane-bound factors together account for target dependence of cultured parasympathetic neurons

The survival of avian ciliary ganglion (CG) neurons in culture depends upon an exogenous supply of trophic factor(s). Skeletal muscle, a normal ganglionic target tissue, is a well documented provider of survival-promoting activity, although the molecular basis for this ability to foster neuronal survival has not been thoroughly investigated. To identify the source of skeletal muscle support, dissociated neurons were plated into microwells containing either: a basal, trophically deficient medium; live pectoral muscle myotubes; medium conditioned by myotubes; membrane remnants of osmotically lysed myotubes; or, membrane remnants and conditioned medium. Neurons remaining in culture were counted after 1, 2, 5, and 7 days. The results reveal that neuronal survival is supported by both muscle conditioned medium and the membrane remnants of cultured myotubes. Each of these alone provides for only partial survival, while both combine to equal the activity of live myotubes. Treatment of the lysed membranes with either 1.5 M NaCl and/or 15 U heparin removed only 50-60% of the activity, suggesting that multiple factors are involved in the neuronal support obtained from lysed myotubes. This is in contrast to fibroblast remnants, which support some neuronal survival, but whose activity is wholly removed by NaCl. Conditioned medium also contains a heparin binding component which accounts for approximately 60% of its activity. These results indicate that full trophic support from the cultured target tissue requires at least two distinct active agents. The experiments further suggest that the target-derived factors responsible for neuronal survival in culture, and perhaps in vivo, are both soluble and membrane-associated molecules.

Diffusible factor(s) from adult rat sciatic nerve increases cell number and neurite outgrowth of cultured embryonic ventral mesencephalic tyrosine hydroxylase-positive neurons

Dissociated embryonic rat ventral mesencephalon containing the developing A8-A10 dopamine (DA) neurons was cultured alone or in the presence of a 10 mm segment of adult rat sciatic nerve that had been explanted and maintained in separate culture for 72 hours prior to introduction to mesencephalic cultures. Nerve segments were contained in a co-culture basket, so that midbrain cells and nerve shared medium but were not in physical contact. The number and morphology of cultured DA neurons was assessed via immunocytochemistry for tyrosine hydroxylase (TH). Co-cultures of ventral midbrain tissue and nerve exhibited an increased number of TH-positive neurons, with larger neuronal perikarya, and increased length and complexity of neurites, than cultures of midbrain tissue alone. Increased number and growth of TH-positive neurons was obtained with as little as 2 days of exposure to nerve. This evidence suggests that a diffusible, soluble factor(s) from sciatic nerve can enhance the number and development of TH-positive neurons detected in cultures of embryonic ventral mesencephalon.

Schwann Cells Secrete a PDGF-like Factor: Evidence for an Autocrine Growth Mechanism involving PDGF

We have investigated the influence of platelet-derived growth factor (PDGF) in peripheral nervous system gliogenesis using two types of Schwann cell cultures. Short-term Schwann cell cultures grow very slowly, but when maintained in culture for several months the division rate of some cells increases, and cell lines can be established. We show that Schwann cells in both short- and long-term culture possess PDGF receptors and synthesize DNA in response to PDGF. Competitive binding experiments show that Schwann cells express mainly PDGF beta-receptors and respond better to PDGF-BB than to PDGF-AA. Conditioned media from short- and long-term Schwann cell cultures contain PDGF-like mitogenic activity, and anti-PDGF immunoglobin partially inhibits DNA synthesis in long-term Schwann cell cultures. Antibody neutralization experiments and Northern blot analyses both indicate that the predominant PDGF isoform in these cultures is PDGF-BB. PDGF-like activity is also detected in extracts of rat sciatic nerve. Taken together, these results suggest that PDGF-BB may stimulate Schwann cell proliferation in an autocrine manner during normal development.

Kinetics of production of a novel growth factor after peripheral nerve injury

In response to transection injury, the distal segment of sciatic nerve produces a soluble factor which stimulates neurite outgrowth from 15 day embryonic rat dorsal root ganglion (DRG) neurons, and PC12 cells. This activity enhances survival of large sensory neurons, promotes myelination and has been designated SN. The expression of SN, undetectable in the perineurium and proximal segments, occurs solely in the endoneurium distal to the site of permanent transection. When the distal portion is removed immediately after transection, homogenized and the supernatant tested, there is little neurite promoting activity in the normal nerve. For the first 10 days after transection the major soluble factor present in the distal segment is NGF. The amount of neurite promoting activity increases after 10 days and appears to plateau at 30-35 days while the proportion that is inhibited by anti-NGF decreases. In a competitive receptor binding assay, SN does not compete with 125I-NGF for receptors on either DRG or PC12 cells. Separation using polyacrylamide-agarose followed by HPLC demonstrates that SN migrates with polypeptides of molecular weights 17.2 and 19.1 kDa.

Enhancement of peripheral nerve regeneration

Numerous factors external to the nerve cell can support and enhance nerve regeneration after injury. The definition of these factors and the elucidation of their mechanisms of action are the central goals of much contemporary neurobiologic research. This research will hopefully lead to the discovery of factors that will prove to be therapeutically beneficial for patients with either peripheral nervous system (PNS) injury or central nervous system (CNS) injury. This article reviews the biology of the regeneration response of the nerve to injury and discusses many of the factors that enhance nerve growth. Finally, the nerve guide or nerve regeneration chamber model for the evaluation of putative nerve regeneration enhancing agents in vivo is also discussed.

Extracellular matrix-associated molecules collaborate with ciliary neurotrophic factor to induce type-2 astrocyte development

O-2A progenitor cells give rise to both oligodendrocytes and type-2 astrocytes in vitro. Whereas oligodendrocyte differentiation occurs constitutively, type-2 astrocyte differentiation requires extracellular signals, one of which is thought to be ciliary neurotrophic factor (CNTF). CNTF, however, is insufficient by itself to induce the development of stable type-2 astrocytes. In this report we show the following: (a) that molecules associated with the extracellular matrix (ECM) cooperate with CNTF to induce stable type-2 astrocyte differentiation in serum-free cultures. The combination of CNTF and the ECM-associated molecules thus mimics the effect of FCS, which has been shown previously to induce stable type-2 astrocyte differentiation in vitro. (b) Both the ECM-associated molecules and CNTF act directly on O-2A progenitor cells and can induce them to differentiate prematurely into type-2 astrocytes. (c) ECM-associated molecules also inhibit oligodendrocyte differentiation, even in the absence of CNTF, but this inhibition is not sufficient on its own to induce type-2 astrocyte differentiation. (d) Whereas the effect of ECM on oligodendrocyte differentiation is mimicked by basic fibroblast growth factor (bFGF), the effect of ECM on type-2 astrocyte differentiation is not. (e) The ECM-associated molecules that are responsible for inhibiting oligodendrocyte differentiation and for cooperating with CNTF to induce type-2 astrocyte differentiation are made by non-glial cells in vitro. (f) Molecules that have these activities and bind to ECM are present in the optic nerve at the time type-2 astrocytes are thought to be developing.

Regulation of neurotransmitter expression by a membrane-derived factor

Cell-cell contact appears to play a critical role in the expression of transmitter traits in developing neurons. We have previously shown that cell membrane contact induces the de novo appearance of choline acetyltransferase (CAT) in virtually pure cultures of dissociated sympathetic neurons. A membrane-associated CAT-inducing factor has been extracted and purified 5000-fold. This factor exerts differential effects on transmitter traits in cultured sympathetic neurons. After 3 days in vitro, neurons exposed to the factor contained 40-fold higher levels of the neuropeptide substance P than controls. Somatostatin exhibited a similar dramatic elevation. In contrast, the factor had no effect on leucine-enkephalin. Further, the specific activity of tyrosine hydroxylase was reduced to 5% of control activity in treated cultures. These effects occurred in the absence of any increases in cell number. Thus, it appears that cell contact via membrane-associated factors may exert differential effects on phenotypic expression.

The cholinergic neuronal differentiation factor from heart cell conditioned medium is different from the cholinergic factors in sciatic nerve and spinal cord

Environmental cues play an important role in determining the transmitter phenotype of developing sympathetic neurons. Several factors have been described which can induce cholinergic function in cultured sympathetic neurons. We have compared certain biological and immunological properties of three of them, cholinergic differentiation factor (CDF), membrane-associated neurotransmitter-stimulating factor (MANS), and ciliary neurotrophic factor (CNTF), to determine whether they are different. As previously reported, all three increased acetylcholine synthesis in cultured sympathetic neurons. In addition, MANS as well as CNTF and CDF decreased catecholamine synthesis. CNTF and MANS, but not CDF, promoted the survival of embryonic chick ciliary neurons. Affinity-purified antibodies raised against a synthetic peptide corresponding to the N-terminal sequence of CDF immunoprecipitated CDF, but not MANS or CNTF. These results indicate that although CDF, MANS, and CNTF have similar effects on transmitter synthesis by cultured sympathetic neurons, CDF lacks the ciliary neurotrophic activity of MANS and CNTF. Further, CDF possesses an N-terminal epitope which is absent from both MANS and CNTF. Thus, CDF is distinct from MANS and CNTF, and at least two factors exist which can alter the transmitter phenotype of sympathetic neurons in vitro.

Neurotrophin-3: a neurotrophic factor related to NGF and BDNF

The development and maintenance of the nervous system depends on proteins known as neurotrophic factors. Although the prototypical neurotrophic factor, nerve growth factor (NGF), has been intensively studied for decades, the discovery and characterization of additional such factors has been impeded by their low abundance. Sequence homologies between NGF and the recently cloned brain-derived neurotrophic factor (BDNF) were used to design a strategy that has now resulted in the cloning of a gene encoding a novel neurotrophic factor, termed neurotrophin-3 (NT-3). The distribution of NT-3 messenger RNA and its biological activity on a variety of neuronal populations clearly distinguish NT-3 from NGF and BDNF, and provide compelling evidence that NT-3 is an authentic neurotrophic factor that has its own characteristic role in vivo.

Purification and characterization of a trophic factor for embryonic peripheral neurons: comparison with fibroblast growth factors

The validation of NGF as a physiologically important neurotrophic factor has led to intense efforts to identify novel polypeptide growth factors for neurons. We report here the details of a greater than 80,000-fold purification of a neurotrophic molecule, referred to as growth-promoting activity (GPA), from chicken sciatic nerves. The final product of the purification migrated as a protein band of 21.5 kd, its apparent pI was approximately 4.8, and the ED50 of the most active preparation was approximately 10 pg/ml. Amino acid sequence of a proteolytic digestion fragment of GPA revealed homology with the recently published sequences for rabbit and rat sciatic nerve CNTF. Thus this molecule may be the chicken form of CNTF. Analysis of the specificity of action of GPA showed that, in addition to E8 ciliary ganglion neurons, the factor was able to support short-term survival of E8 dorsal root ganglion and E12 sympathetic neurons. This range of specificities of biological action was also seen with both acidic and basic FGF in the presence of heparin. The biological activity of GPA differed from that of FGF in that it was not potentiated by heparin and did not stimulate mitogenesis in chick fibroblasts.