The nerve growth factor 35 years later

K-252a specifically inhibits the survival and morphological differentiation of NGF-dependent neurons in primary cultures of human dorsal root ganglia

We have measured neurofilament protein expression in cultures of human dorsal root ganglia (DRG) grown in both the presence and absence of nerve growth factor (NGF). Cultures established from DRG of 8-13 weeks gestation contained populations of both NGF-dependent and -independent neurofilament-positive cells. A recently described kinase inhibitor named K-252a inhibited NGF-dependent increases in neurofilament protein expression with half-maximal and maximal inhibition apparent at concentrations of 6 and 25 nM. At up to 50 nM, K-252a had no effect on neurofilament protein expression from NGF-independent neurons.

Reorganization of neuronal connections following CNS trauma: principles and experimental paradigms

The present review summarizes how the nervous system responds to trauma. The goal is to provide an introduction to the problems, techniques, experimental paradigms, current issues, and future promise. The review is especially designed for basic scientists and clinicians who are not currently involved in research on CNS reorganization, and for students just entering the field. The review characterizes the secondary degenerative events that occur after trauma, and the types of growth that commonly occur. A standard terminology is set forth with criteria for differentiating between related phenomena. Experimental methods are described that can be used documenting reorganization of circuitry. The principles that determine whether a given process will or will not occur are summarized, and some of the factors that may regulate the nature and extent of growth are considered. Research strategies are outlined that have been used to evaluate whether reorganization of circuitry is functionally significant. Finally, future directions in research and clinical application are discussed, focusing especially on the efforts to facilitate regeneration, and the work on transplants of CNS tissue to facilitate growth of surviving connections, and to replace tissue destroyed by trauma.

NGF in CNS: experimental data and clinical implications

The presence of beta-nerve growth factor (NGF) and its cell surface receptor (NGF-R) in the brain has been well established by a variety of experimental techniques in recent years. In particular, the molecular cloning of NGF and NGF-R as well as the development of sensitive two-site ELISA techniques for determining the levels of NGF and antibodies to NGF-R suitable for immunohistochemistry have led to rapid accumulation of data in this field from many laboratories. A main finding is the function of NGF in the cholinergic neurons of the basal forebrain, expressing NGF receptors and responding to the factor by increased activity of choline acetyltransferase, and the production of NGF in cortical areas and hippocampus comprising terminal areas for the cholinergic projections from the basal forebrain. In addition, findings suggest that additional neurons in the brain and spinal cord may utilize NGF, notably during development and possibly also after lesion of the adult CNS. Moreover, observations indicate that endogenous levels of NGF are lowered in the aged rat brain concomitant with losses of NGF-dependent neurons in the basal forebrain. The involvement of NGF in human neurodegenerative diseases is not established but the application of NGF to degenerating cholinergic neurons in Alzheimer patients may prove useful. A promising approach to achieve this goal is the production of biologically active, recombinant NGF.

NGF primed spleen cells injected in brain of developing rats differentiate into mast cells

The aim of this work was to study the topographic distribution and the morphological behaviour of nerve growth factor (NGF) primed spleen cells injected into the lateral ventricles of developing rat brain. Serial coronal brain sections showed that these transplanted cells acquire phenotypical characteristics similar to those of mast cells (MCs) and that they enhance local neovascularization. These results, together with the observation that these cells are located in proximity to the hippocampus, a brain tissue which contains one of the highest levels of NGF, provide a model for studying the relationship between NGF and MC differentiation and secretion.

Nerve growth factor-like activity in the rat pituitary intermediate lobe

Nerve growth factor (NGF)-like immunoreactivity was demonstrated in the rat pituitary intermediate lobe by indirect immunofluorescence method using antisera specific to beta-NGF isolated from adult male mouse submaxillary salivary gland. Co-culture of frozen or fresh intermediate lobes with newborn rat superior cervical ganglion resulted in marked fiber growth from the ganglion, which was totally inhibited by NGF antiserum, suggesting the presence in situ and secretion in vitro of biologically active pituitary NGF. Pituitary stalk transection caused decrease in both the NGF immunoreactivity and biological activity. These findings suggest that pituitary NGF level is under neural regulation.

Nerve growth factor increases mRNA levels for the prion protein and the beta-amyloid protein precursor in developing hamster brain

Deposition of amyloid filaments serves as a pathologic hallmark for some neurodegenerative disorders. The prion protein (PrP) is found in amyloid of animals with scrapie and humans with Creutzfeldt-Jakob disease; the beta protein is present in amyloid deposits in Alzheimer disease and Down syndrome patients. These two proteins are derived from precursors that in the brain are expressed primarily in neurons and are membrane bound. We found that gene expression for PrP and the beta-protein precursor (beta-PP) is regulated in developing hamster brain. Specific brain regions showed distinct patterns of ontogenesis for PrP and beta-PP mRNAs. The increases in PrP and beta-PP mRNAs in developing basal forebrain coincided with an increase in choline acetyltransferase activity, raising the possibility that these markers might be coordinately controlled in cholinergic neurons and regulated by nerve growth factor (NGF). Injections of NGF into the brains of neonatal hamsters increased both PrP and beta-PP mRNA levels. Increased PrP and beta-PP mRNA levels induced by NGF were confined to regions that contain NGF-responsive cholinergic neurons and were accompanied by elevations in choline acetyltransferase. It remains to be established whether or not exogenous NGF acts to increase PrP and beta-PP gene expression selectively in forebrain cholinergic neurons in the developing hamster and endogenous NGF regulates expression of these genes.

Developmental and regional expression of beta-nerve growth factor receptor mRNA in the chick and rat

Hybridization probes from the transmembrane region of the chick NGF receptor (NGF-R) that show high homology with the rat NGF-R were used to demonstrate an abundant 4.5 kb NGF-R mRNA in the chick embryo at E3.5. The level remained high until E12 but decreased to adult levels by E18. The highest levels at E8 were in spinal cord, bursa of Fabricius, gizzard, femoralis muscle, and skin. In situ hybridization to E7 embryos showed high expression of the NGF-R gene in spinal cord, particularly the lateral motor column, and in dorsal root, sympathetic, and nodose ganglia. NGF-R mRNA expression was observed throughout brain development and in all regions of the adult brain, with high levels in cerebellum and septum. Lymphoid tissues of chick and rat also expressed the receptor. The complex and widespread expression of NGF-R mRNA in areas not known to be NGF targets suggests broader functions for NGF.

High level of accumulation of a mRNA coding for a precursor-like protein in the submaxillary gland of male rats

NaDodSO4/PAGE analysis of in vitro translation products of rat submaxillary gland (SMG) mRNAs has revealed an important sexual dimorphism. Moreover, most of the rat male-specific major translation products differ in size from those translated from male mouse SMG mRNAs. To characterize proteins accumulated in the rat SMG under androgen control, a cDNA library was constructed. Here we report the nucleotide sequence of a 0.7-kilobase mRNA that is 1000-3000 times more abundant in male rats than in female rats. The predicted corresponding protein, SMR1, has a molecular weight of 16,000 and contains a signal peptide for secretion and potential signals for glycosylation. An interesting feature of SMR1 is the presence, in a hydrophilic region, of the tetrapeptide Gln-His-Asn-Pro surrounded by two pairs of basic residues that represent potential cleavage sites for maturation enzymes. In rats, the tissue distribution of the SMR1 mRNA is restricted to the SMG and the prostate. Only very low amounts of SMR1 mRNA can be detected in the SMG of male or female mice. Southern blot analysis indicates the presence of three genes in rats but only one in mice. Hypotheses on the physiological role of SMR1-derived peptides in male rats are discussed.

Gene expression in the embryonic nervous system of Xenopus laevis

Development of the nervous system in the amphibian embryo is initiated during gastrulation by an inductive interaction between chordamesoderm and dorsal ectoderm. The induced ectoderm forms the neural plate while uninduced ectoderm generates epidermis. We screened for genes activated during gastrulation and expressed specifically in the nervous system of Xenopus laevis in the expectation that clones representing such genes will constitute useful markers for the study of early neurogenesis. Probes were prepared from adult brain RNA by subtraction with RNA from ovary and from different combinations of adult kidney, muscle, and skin; cDNA libraries prepared from early to late neurula embryo RNA were screened with these probes. Six clones were chosen for further study. Three of these clones are not represented in the maternal RNA population but are activated at the late gastrula stage; the other three increase from a maternal base. Expression of five of the genes is restricted to the neural plate during embryogenesis, and all six are restricted to the central nervous system in premetamorphic tadpoles and adults. One of the clones encodes an apparently neurospecific isoform of beta-tubulin; the identity of the other clones is unknown. Expression of all six genes is suppressed in axis-deficient embryos that lack dorsal structures including the brain.

Changes in protein kinase C activities are correlated with the metaplastic transformation of Schwann cell precursors of avian embryos into melanocytes

In previous work, we found that the phorbol ester drug 12-O-tetradecanoyl phorbol acetate (TPA) reverses the developmental restriction of melanogenesis that occurs early in neural crest development, causing Schwann cell precursors to undergo a metaplastic transformation into melanocytes. In this study, we examine whether these effects of TPA may be mediated by changes in endogenous levels of protein kinase C (PKC) activities. We report that low levels of PKC activity are correlated with this adventitious pigmentation in the crest-derived cells of dorsal root ganglia both during normal development and following TPA treatment in culture. These results suggest that regulation of endogenous levels of PKC plays a role in developmental decisions that neural crest cells make during early embryogenesis.

Ciliary neurotrophic factor induces type-2 astrocyte differentiation in culture

We have been studying a population of bipotential glial progenitor cells in the perinatal rat optic nerve and brain in an attempt to understand how cells choose between alternative fates in the developing mammalian central nervous system (CNS). This cell population gives rise initially to oligodendrocytes and then to type-2 astrocytes, both of which apparently collaborate in sheathing axons in the CNS. In vitro studies suggest that oligodendrocyte differentiation is the constitutive pathway of development for the oligodendrocyte-type-2-astrocyte (O-2A) progenitor cell, whereas type-2 astrocyte differentiation depends on a specific inducing protein. This protein is present in the developing optic nerve when type-2 astrocytes are differentiating and can induce O-2A progenitor cells in vitro to express glial fibrillary acidic protein (GFAP), a marker of astrocyte differentiation. Here we show that the type-2-astrocyte-inducing protein is similar or identical to ciliary neutrotrophic factor (CNTF), which promotes the survival of some types of peripheral neurons in vitro, including ciliary ganglion neurons. This suggests that CNTF, in addition to its effect on neurons, may be responsible for triggering type-2 astrocyte differentiation in the developing CNS.

The mode of action of nerve growth factor in PC12 cells

This review deals with the mechanism of nerve growth factor action. In view of the many and diversified effects of this growth factor, and since it could utilize different mechanism(s) in distinct types of cells, we have confined our analysis to the best characterized and more extensively studied target, the clonal cell line PC12. When exposed to NGF in vitro, these neoplastic cells recapitulate the last major steps of neuronal differentiation, i.e., the commitment to become a neuron and the acquisition of the neuronal phenotype. This is characterized by electrically excitable neurites, a display of a highly organized cytoskeleton, and the specific chemical and molecular neuronal properties. These effects are elicited upon the interaction of NGF with a receptor whose gene has been cloned and whose kinetic properties are now relatively well characterized. It is not yet clear, on the contrary, if and which of the several potential second messengers (cAMP, Ca, or phosphoinositides) that undergo marked fluctuations following NGF binding, transduce and amplify the NGF message. Among both the early and late effects of NGF is the modulation of expression of several genes. Some of the products of these genes are mainly restricted to nerve cells and others appear to play a crucial role in regulating the proper assembly of cytoskeletal elements. It is hypothesized that this complex array of chemical, molecular, and ultrastructural changes is triggered by NGF, not through activation of a single pathway, but more likely via combinatorial processes whereby several intracellular signals interplay before the irreversible commitment of becoming a neuron is undertaken.

Basic fibroblast growth factor and epidermal growth factor exert differential trophic effects on CNS neurons

Epidermal growth factor (EGF) and basic fibroblast growth factor (bFGF) are potent mitogenic proteins capable of inducing cell division in a wide variety of cell types. In addition to their mitogenic properties, both proteins have recently been shown to enhance survival and process outgrowth from neurons of central nervous system origin. The full spectrum of neuronal subtypes responding to these factors has not been elucidated. In the present study, EGF was found to enhance survival and process outgrowth of primary cultures of cerebellar neurons of neonatal rat brain. This effect was dose-dependent and was observed with EGF concentrations as low as 100 pg/ml. In marked contrast, bFGF was ineffective in enhancing survival or neurite elongation from cerebellar neurons when tested in the range of 0.1 to 10.0 ng/ml. However, within this concentration range, bFGF did prove effective in stimulating an increase in [3H]thymidine incorporation into primary cultures of cerebellar astrocytes, demonstrating that bFGF was active and that cells in the cerebellum do respond to bFGF. These results suggest that EGF or an EGF-like peptide may act as a neurite elongation and maintenance factor for cerebellar neurons. EGF has now been shown to support striatal, cortical, and cerebellar neurons, suggesting that this factor may have trophic activity throughout the central nervous system. bFGF, in contrast, appears to exert its effects on limited populations of neurons.

Nerve growth factor binding in aged rat central nervous system: effect of acetyl-L-carnitine

The nerve growth factor protein (NGF) has been demonstrated to affect neuronal development and maintenance of the differentiated state in certain neurons of the peripheral and central nervous system (CNS) of mammals. In the CNS, NGF has sparing effects on cholinergic neurons of the rodent basal forebrain (BF) following lesions where it selectively induces choline acetyltransferase (ChAT). NGF also induces ChAT in the areas to which BF provides afferents. In aged rats, there is a reduction in the NGF-binding capacity of sympathetic ganglia. Here, we wish to report that there is a decrease in the NGF-binding capacity of the hippocampus and basal forebrain of aged (26-month-old) rats as compared to 4-month-old controls but no change in NGF binding in cerebellum. In all instances, equilibrium binding dissociation constants did not differ significantly. Treatment of rats with acetyl-L-carnitine, reported to improve cognitive performance of aged rats, ameliorates these age-related deficits.

Efficient processing and expression of human nerve growth factor receptors in Xenopus laevis oocytes: effects on maturation

The nerve growth factor (NGF) receptor is an integral membrane protein that is phosphorylated and heavily glycosylated. Determination of the amino acid sequence by molecular cloning indicates that the receptor is a cysteine-rich protein which contains a signal peptide sequence and spans the lipid bilayer with a single transmembrane sequence. A single mRNA of 3.8 kilobases was observed for the receptor, of which 1.5 kilobases is coding sequence. We have used microinjection of receptor RNA in Xenopus laevis oocytes to obtain cell surface expression of the receptor. The presence of NGF receptors in oocytes was verified by radioimmunoassay, specific binding of [125I]NGF, and metabolic labeling followed by immunoprecipitation. The NGF receptor protein was rapidly processed in oocytes and displayed extensive glycosylation. Furthermore, the presence of NGF receptors in oocytes potentiates the ability of progesterone to induce maturation.

Activation of phosphoinositide hydrolysis by nerve growth factor and lysophosphatidylserine in rat peritoneal mast cells

Histamine secretion in rat peritoneal mast cells stimulated by nerve growth factor requires a synergistic signal delivered by lysophosphatidylserine. To study the signal-transducing system activated by these compounds, phospholipid metabolism has been investigated in these cells. Phospholipid labeling with 32PO4 reveals a 5-9-fold stimulation of phosphatidic acid, phosphatidylinositol and phosphatidylcholine synthesis. Increased synthesis of phosphatidylinositol is also monitored using [3H]inositol incorporation. When [3H]inositol-labeled mast cells are incubated in the presence of Li+, nerve growth factor and lysophosphatidylserine enhance the accumulation of inositol monophosphate, inositol bisphosphate and inositol trisphosphate. Similar to the induced histamine release, accumulation of inositol phosphates (a) does not occur when the two agonists are added separately; (b) is inhibited when lysophosphatidyl-L-serine is replaced by lysophosphatidyl-D-serine; and (c) is enhanced in the presence of extracellular Ca2+. The data suggest that the interactive stimulus of nerve growth factor and lysophosphatidylserine is transmitted through the polyphosphoinositide-phospholipase C system.

Molecular forms of nerve growth factor in mouse submaxillary glands

By use of immunoblot analysis, we demonstrate the presence of a nerve growth factor with a relative molecular mass (Mr) of 53,000 in submaxillary glands of adult male and female mice in addition to the 13,000 form previously discovered in this tissue. Both the Mr 53,000 and 13,000 forms of nerve growth factor are present at equal concentrations in salivary glands of male mice while the Mr 53,000 form is present at a greater concentration than the Mr 13,000 form in the glands of female mice. Testosterone pretreatment, however, specifically augments the Mr 13,000 form of nerve growth factor in the salivary glands of female mice. The existence of nerve growth factor with molecular weight of 53,000, which is higher than the molecular size predicted for the two precursor forms of nerve growth factor, suggest the possibility that one of the nerve growth factor precursors or a product derived from it may undergo post-translational modification in submaxillary glands of mice.

Reduction of naturally occurring motoneuron death in vivo by a target-derived neurotrophic factor

Treatment of chick embryos in ovo with crude and partially purified extracts from embryonic hindlimbs (days 8 to 9) during the normal cell death period (days 5 to 10) rescues a significant number of motoneurons from degeneration. The survival activity of partially purified extract was dose-dependent and developmentally regulated. The survival of sensory, sympathetic, parasympathetic, and a population of cholinergic sympathetic preganglionic neurons was unaffected by treatment with hindlimb extract. The massive motoneuron death that occurs after early target (hindlimb) removal was partially ameliorated by daily treatment with the hindlimb extract. These results indicate that a target-derived neurotrophic factor is involved in the regulation of motoneuron survival in vivo.

Efficient processing and expression of human nerve growth factor receptors in Xenopus laevis oocytes: effects on maturation

The nerve growth factor (NGF) receptor is an integral membrane protein that is phosphorylated and heavily glycosylated. Determination of the amino acid sequence by molecular cloning indicates that the receptor is a cysteine-rich protein which contains a signal peptide sequence and spans the lipid bilayer with a single transmembrane sequence. A single mRNA of 3.8 kilobases was observed for the receptor, of which 1.5 kilobases is coding sequence. We have used microinjection of receptor RNA in Xenopus laevis oocytes to obtain cell surface expression of the receptor. The presence of NGF receptors in oocytes was verified by radioimmunoassay, specific binding of [125I]NGF, and metabolic labeling followed by immunoprecipitation. The NGF receptor protein was rapidly processed in oocytes and displayed extensive glycosylation. Furthermore, the presence of NGF receptors in oocytes potentiates the ability of progesterone to induce maturation.

The melanocytic differentiation pathway in congenital melanocytic nevi: theoretical considerations

It is suggested that the melanocytic series is characterized by a differentiation pathway (MDP) that has four discrete stages during normal development and in postnatal tissue maintenance--nerve sheath precursor (nsp), dermal migratory, junctional migratory, and dendritic--and that congenital melanocytic nevi (CMN) derive from cells in the nsp stage of the MDP. This concept accounts satisfactorily for morphologic variations and clinicopathologic correlations in CMN. It also permits a unified explication of both similarities and differences between congenital and acquired melanocytic nevi (AMN), which are thought to arise by transformation of nsp cells in the MDP during postnatal tissue maintenance. This perspective suggests that answers to many basic questions about CMN may require meticulous study of the interrelations of CMN with peripheral nerve elements. Such research may be necessary to resolve current controversies about optimal criteria for distinguishing small CMN from AMN, thereby permitting an accurate assessment of the risk of malignant melanoma in association with small CMN.