Hippocampal bone morphogenetic protein signaling mediates behavioral effects of antidepressant treatment.

Many antidepressants stimulate adult hippocampal neurogenesis, but the mechanisms by which they increase neurogenesis and modulate behavior are incompletely understood. Here we show that hippocampal bone morphogenetic protein (BMP) signaling is modulated by antidepressant treatment, and that the changes in BMP signaling mediate effects of antidepressant treatment on neural progenitor cell proliferation and behavior. Treatment with the selective serotonin reuptake inhibitor fluoxetine suppressed BMP signaling in the adult mouse hippocampus both by decreasing levels of BMP4 ligand and increasing production of the BMP inhibitor noggin. Increasing BMP signaling in the hippocampus via viral overexpression of BMP4 blocked the effects of fluoxetine on proliferation in the dentate gyrus and on depressive behavior. Conversely, inhibiting BMP signaling via viral overexpression of noggin in the hippocampus or infusion of noggin into the ventricles exerted antidepressant and anxiolytic activity along with an increase in hippocampal neurogenesis. Similarly, conditional genetic deletion of the type II BMP receptor in Ascl1-expressing cells promoted neurogenesis and reduced anxiety- and depression-like behaviors, suggesting that neural progenitor cells contribute to the effects of BMP signaling on affective behavior. These observations indicate that BMP signaling in the hippocampus regulates depressive behavior, and that decreasing BMP signaling may be required for the effects of some antidepressants. Thus BMP signaling is a new and powerful potential target for the treatment of depression.

Emerging peptide nanomedicine to regenerate tissues and organs.

Peptide nanostructures containing bioactive signals offer exciting novel therapies of broad potential impact in regenerative medicine. These nanostructures can be designed through self-assembly strategies and supramolecular chemistry, and have the potential to combine bioactivity for multiple targets with biocompatibility. It is also possible to multiplex their functions by using them to deliver proteins, nucleic acids, drugs and cells. In this review, we illustrate progress made in this new field by our group and others using peptide-based nanotechnology. Specifically, we highlight the use of self-assembling peptide amphiphiles towards applications in the regeneration of the central nervous system, vasculature and hard tissue along with the transplant of islets and the controlled release of nitric oxide to prevent neointimal hyperplasia. Also, we discuss other self-assembling oligopeptide technology and the progress made with these materials towards the development of potential therapies.

Substance P and somatostatin regulate sympathetic noradrenergic function.

Peptidergic-noradrenergic interactions were examined in explants of rat sympathetic superior cervical ganglia and in cultures of dissociated cells. The putative peptide transmitters substance P and somatostatin each increased the activity of the catecholamine-synthesizing enzyme tyrosine hydroxylase after 1 week of exposure in culture. Maximal increases occurred at 10(-7) molar for each peptide, and either increasing or decreasing the concentration reduced the effects. Similar increases in tyrosine hydroxylase were produced by a metabolically stable agonist of substance P, while a substance P antagonist prevented the effects of the agonist. The data suggest that the increased tyrosine hydroxylase activity was mediated by peptide interaction with specific substance P receptors and that peptides may modulate sympathetic catecholaminergic function.

Substance P in principal sympathetic neurons: regulation by impulse activity.

Regulation of the putative peptide neurotransmitter substance P was examined in the superior cervical sympathetic ganglion of the neonatal rat. Surgical decentralization (denervation) of the superior cervical ganglion increased ganglion substance P content. In cultured ganglia, the amount of substance P increased more than 50-fold after 48 hours, and this rise was dependent on protein and RNA synthesis. Veratridine prevented the increase in substance P in vitro, and tetrodotoxin blocked the veratridine effect; this suggests that sodium influx and membrane depolarization prevent substance P elevation. Immunohistochemical analysis of cultured ganglia indicated that substance P was present in the perikarya of principal sympathetic neurons and in ganglionic nerve processes. Transsynaptic impulses, through the mediation of postsynaptic sodium influx, may decrease substance P in sympathetic neurons.

Translational regulation of somatostatin in cultured sympathetic neurons.

Coculture of sympathetic neurons with ganglion nonneuronal cells elevated levels of preprosomatostatin mRNA but did not alter neuronal synthesis, content, or release of somatostatin. Treatment of sympathetic neurons with culture medium conditioned by exposure to ganglion nonneuronal cells similarly elevated preprosomatostatin mRNA. Treatment with conditioned medium elevated somatostatin levels in pure neuronal cultures, but not in neurons cocultured with nonneuronal cells. Conditioned medium also failed to increase peptide levels in neurons cultured on a substratum of killed nonneuronal cells, despite a large increase in preprosomatostatin mRNA. These observations suggest that contact of sympathetic neurons with nonneuronal cell membranes inhibits the increase in peptide synthesis, but not the increase in preprosomatostatin mRNA after treatment with conditioned medium. Thus neuronal interactions with nonneuronal cells regulate somatostatin metabolism at both the mRNA and peptide levels. Regulatory effects on the mRNA and the peptide are separable and do not necessarily occur in parallel, and translational controls may be the rate-limiting factors.

Bone morphogenetic proteins promote astroglial lineage commitment by mammalian subventricular zone progenitor cells.

The epigenetic signals that regulate lineage development in the embryonic mammalian brain are poorly understood. Here we demonstrate that a specific subclass of the transforming growth factor beta superfamily, the bone morphogenetic proteins (BMPs), cause the selective, dose-dependent elaboration of the astroglial lineage from murine embryonic subventricular zone (SVZ) multipotent progenitor cells. The astroglial inductive effect is characterized by enhanced morphological complexity and expression of glial fibrillary acidic protein, with concurrent suppression of neuronal and oligodendroglial cell fates. SVZ progenitor cells express transcripts for the appropriate BMP-specific type I and II receptor subunits and selective BMP ligands, suggesting the presence of paracrine or autocrine developmental signaling pathways (or both). These observations suggest that the BMPs have a selective role in determining the cell fate of SVZ multipotent progenitor cells or their more developmentally restricted progeny.

Cytokine-induced programmed death of cultured sympathetic neurons.

Programmed cell death (PCD) of sympathetic neurons is inhibited by nerve growth factor. However, factors that induce PCD of these cells are unknown. Leukemia inhibitory factor (LIF) and ciliary neurotrophic factor, neuropoietic cytokines known to regulate sympathetic neuron gene expression, were examined for effects on survival of cultured sympathetic neurons. Treatment with LIF or ciliary neurotrophic factor caused neuronal death in a dose-dependent fashion. Inhibition of RNA or protein synthesis, or treatment with potassium, all of which prevent PCD after nerve growth factor deprivation, prevented LIF-induced death. The morphologic and ultrastructural characteristics of the neuronal death induced by LIF and by nerve growth factor deprivation were similar. Furthermore, LIF treatment resulted in DNA fragmentation with a characteristic "ladder" on Southern blot analysis. These observations suggest that neuron numbers may be regulated by factors which initiate PCD, as well as by factors which prevent it.

Hematolymphopoietic and inflammatory cytokines in neural development.

It is now clear that cytokines traditionally viewed as immune modulators participate in inflammatory responses within the adult nervous system. However, in the developing nervous system hematolymphopoietic cytokines also play a role unrelated to neural-immune interactions. Instead, many of these factors subserve primary regulatory functions related both to the morphogenesis and to the cellular maturation of the central and peripheral nervous systems. This article focuses specifically on cytokine actions in neural development.

Bone morphogenetic proteins in the nervous system.

Bone morphogenetic proteins (BMPs) are a rapidly expanding subclass of the transforming growth factor superfamily. BMP ligands and receptor subunits are present throughout neural development within discrete regions of the embryonic brain and within neural crest-derived pre- and post-migratory zones. BMPs initially inhibit the formation of neuroectoderm during gastrulation while, within the neural tube, they act as gradient morphogens to promote the differentiation of dorsal cell types and intermediate cell types throughout co-operative signaling. In the peripheral nervous system, BMPs act as instructive signals for neuronal lineage commitment and promote graded stages of neuronal differentiation. By contrast, within the CNS, these same factors promote astroglial lineage elaboration from embryonic subventricular zone progenitor cells, with concurrent suppression of the neuronal or oligodendroglial lineages, or both. In addition, BMPs act on more lineage-restricted embryonic CNS progenitor cells to promote regional neuronal survival and cellular differentiation. Furthermore, these versatile cytokines induce selective apoptosis of discrete rhombencephalic neural crest-associated cellular populations. These observations suggest that the BMPs exhibit a broad range of cellular and context-specific effects during multiple stages of neural development.

Whole genomewide linkage screen for neural tube defects reveals regions of interest on chromosomes 7 and 10.

Neural tube defects (NTDs) are the second most common birth defects (1 in 1000 live births) in the world. Periconceptional maternal folate supplementation reduces NTD risk by 50-70%; however, studies of folate related and other developmental genes in humans have failed to definitively identify a major causal gene for NTD. The aetiology of NTDs remains unknown and both genetic and environmental factors are implicated. We present findings from a microsatellite based screen of 44 multiplex pedigrees ascertained through the NTD Collaborative Group. For the linkage analysis, we defined our phenotype narrowly by considering individuals with a lumbosacral level myelomeningocele as affected, then we expanded the phenotype to include all types of NTDs. Two point parametric analyses were performed using VITESSE and HOMOG. Multipoint parametric and nonparametric analyses were performed using ALLEGRO. Initial results identified chromosomes 7 and 10, both with maximum parametric multipoint lod scores (Mlod) >2.0. Chromosome 7 produced the highest score in the 24 cM interval between D7S3056 and D7S3051 (parametric Mlod 2.45; nonparametric Mlod 1.89). Further investigation demonstrated that results on chromosome 7 were being primarily driven by a single large pedigree (parametric Mlod 2.40). When this family was removed from analysis, chromosome 10 was the most interesting region, with a peak Mlod of 2.25 at D10S1731. Based on mouse human synteny, two candidate genes (Meox2, Twist1) were identified on chromosome 7. A review of public databases revealed three biologically plausible candidates (FGFR2, GFRA1, Pax2) on chromosome 10. The results from this screen provide valuable positional data for prioritisation of candidate gene assessment in future studies of NTDs.

Leukemia inhibitory factor requires concurrent p75LNTR signaling to induce apoptosis of cultured sympathetic neurons.

Apoptosis may result either from positive induction by ligand binding to a plasma membrane receptor or from negative induction attributable to loss of a suppressor signal. For example, apoptosis of developing sympathetic neurons may be induced in culture either by exposure to leukemia inhibitory factor (LIF) or by deprivation of nerve growth factor. This study compared the cell death pathways activated in sympathetic neurons by these two different stimuli. Both types of cell death were developmentally regulated; both were maximal in the immediate postnatal period and disappeared over the next 2 weeks. Both types of cell death were reduced by genetic deletion of Bax or by virally mediated overexpression of Bcl-2. Similarly both were reduced by inhibition of caspase activity or by inhibition of Nedd-2 synthesis with antisense oligonucleotides. Finally, both involved activation of c-Jun N-terminal kinase (JNK) signaling. Nedd-2 expression by sympathetic neurons declined in parallel with the developmental loss of LIF-mediated cell death, suggesting that downregulation of the caspase during development may underlie the loss of cytokine-mediated apoptosis. Treatment of sympathetic neurons with an antibody that blocks the function of the low-affinity neurotrophin receptor (p75(LNTR)) prevented LIF-induced cell death. Similarly genetic deletion of p75(LNTR) prevented apoptosis after LIF treatment. These observations suggest that concurrent p75(LNTR) signaling is necessary for LIF-induced cell death and that cytokine-mediated cell death and growth factor deprivation appear to activate the same intracellular pathways involving JNK signaling.

Multiple roles of bone morphogenetic protein signaling in the regulation of cortical cell number and phenotype.

Members of the bone morphogenetic protein (BMP) family have been implicated in multiple aspects of neural development in both the CNS and peripheral nervous system. BMP ligands and receptors, as well as the BMP antagonist noggin, are expressed in the developing cerebral cortex, making the BMPs likely candidates for regulating cortical development. To define the role of these factors in the developing cerebral cortex, we examined the effects of BMP2 and BMP4 on cortical cells in vitro. Cells were cultured from embryonic day 13 (E13) and E16 rat cerebral cortex in the absence or presence of different concentrations of fibroblast growth factor 2, a known regulator of cortical cell proliferation and differentiation. At E13, the BMPs promoted cell death and inhibited proliferation of cortical ventricular zone cells, resulting in the generation of fewer neurons and no glia. At E16, the effects of the BMPs were more complex. Concentrations of BMP2 in the range of 1-10 ng/ml promoted neuronal and astroglial differentiation and inhibited oligodendroglial differentiation, whereas 100 ng/ml BMP2 promoted cell death and inhibited proliferation. Addition of the BMP antagonist noggin promoted oligodendrogliogenesis in vitro, demonstrating that endogenous BMP signaling influences the differentiation of cortical cells in vitro. The distribution of BMP2 and noggin within the developing cortex suggests that local concentrations of ligands and antagonists define gradients of BMP signaling during corticogenesis. Together, these results support the hypothesis that the BMPs and their antagonist noggin co-regulate cortical cell fate and morphogenesis.

Functional properties of channels formed by the neuronal gap junction protein connexin36.

The expression and functional properties of connexin36 (Cx36) were examined in two communication-deficient cell lines (N2A-neuroblastoma and PC-12 cells) transfected with Cx36 and in hippocampal neurons that express the connexin endogenously. Transfected cells expressed the expected 2.9 kb Cx36 transcript and Cx36 immunoreactivity, whereas nontransfected cells were devoid of Cx36. The relationship between steady-state junctional conductance (g(j)) and transjunctional voltage was well described by a two-state Boltzmann equation. The half-inactivation voltage (V(0)), the ratio of minimal to maximal g(j) (g(min)/g(max)), and the equivalent gating charge were +/- 75 mV, 0.55, and 1.75, respectively, indicating that Cx36 exhibits very low voltage sensitivity. Conductance of single Cx36 channels measured with patch pipettes containing 130 mM CsCl was 10-15 pS (n = 15 cell pairs); despite this low unitary conductance, Cx36 channels were permeable to the dye Lucifer yellow. Hippocampal neurons expressed Cx36 both in vivo and in culture. The electrophysiological properties of channels in cultured hippocampal neurons were similar to those of the channels expressed by the transfected cell lines, and the neuronal channels were similarly permeable to Lucifer yellow. The unique combination of weak voltage sensitivity, small unitary conductance, and permeation by anions as large as second messenger molecules endows Cx36 gap junction channels with properties well suited for mediating flexible electrical and biochemical interactions between neurons.

Gating characteristics of a steeply voltage-dependent gap junction channel in rat Schwann cells.

The gating properties of macroscopic and microscopic gap junctional currents were compared by applying the dual whole cell patch clamp technique to pairs of neonatal rat Schwann cells. In response to transjunctional voltage pulses (Vj), macroscopic gap junctional currents decayed exponentially with time constants ranging from < 1 to < 10 s before reaching steady-state levels. The relationship between normalized steady-state junctional conductance (Gss) and (Vj) was well described by a Boltzmann relationship with e-fold decay per 10.4 mV, representing an equivalent gating charge of 2.4. At Vj > 60 mV, Gss was virtually zero, a property that is unique among the gap junctions characterized to date. Determination of opening and closing rate constants for this process indicated that the voltage dependence of macroscopic conductance was governed predominantly by the closing rate constant. In 78% of the experiments, a single population of unitary junctional currents was detected corresponding to an unitary channel conductance of approximately 40 pS. The presence of only a limited number of junctional channels with identical unitary conductances made it possible to analyze their kinetics at the single channel level. Gating at the single channel level was further studied using a stochastic model to determine the open probability (Po) of individual channels in a multiple channel preparation. Po decreased with increasing Vj following a Boltzmann relationship similar to that describing the macroscopic Gss voltage dependence. These results indicate that, for Vj of a single polarity, the gating of the 40 pS gap junction channels expressed by Schwann cells can be described by a first order kinetic model of channel transitions between open and closed states.

Progenitor cell biology: implications for neural regeneration.

A few brief years ago, damage to the central nervous system was generally perceived to be irreparable, and loss of neurons was largely viewed as an irreversible process. However, major advances in the study of neural progenitor cells have altered these perceptions, and rational approaches to the repair of the damaged nervous system using transplanted progenitor cells now seem feasible. This review will discuss the basic biology of neural progenitor cells, the mechanisms regulating the generation of neurons and glia from these cells, and the techniques that are available for preparing such cells for transplantation into the nervous system. The potential uses for these cells in treating neurologic disease will then be reviewed, and the theoretical and technical problems that may be encountered will be discussed.

Homovanillic acid transport by the spinal cord.

Spinal subarachnoid perfusions of rhesus monkeys were performed to study spinal transport of homovanillic acid in control and probenecid-treated animals. Homovanillic acid enters capillaries within spinal tissue throughout the spinal cord. The mean capillary exchange half-time for homovanillic acid was 19.2+/-2.8 minutes; probenecid did not affect this value significantly. Despite its polar nature, homovanillic acid crosses cell boundaries easily and equilibrates in a distribution volume (55 percent) approaching the total water space. The spinal cord clears homovanillic acid from 21+/-4 mul per minute of cerebrospinal fluid. The rate of clearance after probenecid administration was not significantly different. The apparent diffusion coefficient in tissue of homovanillic acid approximated the diffusion coefficient in water (8.0 X 10(-6) cm2 per second). The data show that homovanillic acid is transported by capillaries throughout spinal tissue by a mechanism largely insensitive to inhibition by probenecid. Lumbar cerebrospinal fluid concentrations of homovanillic acid even after probenecid administration therefore reflect only part of the total dopamine metabolism.

Recombinant human nerve growth factor in the treatment of diabetic polyneuropathy. NGF Study Group.

BACKGROUND: Preclinical studies have demonstrated that nerve growth factor may prevent or reverse peripheral neuropathy. We have therefore tested the effects of recombinant human nerve growth factor in patients with diabetic polyneuropathy. METHODS: A total of 250 patients with symptomatic diabetic polyneuropathy randomly received either placebo or one of two doses of recombinant human nerve growth factor for 6 months. Patients were assessed for symptoms and signs of polyneuropathy before and after treatment. RESULTS: Compared with placebo, recombinant human nerve growth factor led to significant improvement after 6 months of treatment, as measured by the sensory component of the neurologic examination, two quantitative sensory tests, and the impression of most subjects that their neuropathy had improved. Three prospectively identified multiple endpoint analyses indicated improvements in the nerve growth factor treatment groups over the placebo group in all three analyses (p = 0.032; p = 0.008; p = 0.005). Recombinant human nerve growth factor was well tolerated, with injection site discomfort reported as the most frequent adverse event. CONCLUSIONS: Recombinant human nerve growth factor appears to be safe and shows preliminary evidence of efficacy in patients with symptomatic diabetic polyneuropathy.

Differential regulation of peptide and catecholamine characters in cultured sympathetic neurons.

Mechanisms regulating peptidergic, noradrenergic and cholinergic development were compared in dissociated cell cultures of neonatal rat sympathetic ganglia. The majority of cultured neurons contained at least two neurotransmitters and many neurons contained three or more. These studies were undertaken to determine whether co-existing transmitters were co-ordinately regulated by the environment. Co-culture of sympathetic neurons with ganglion non-neuronal cells increased substance P and choline acetyltransferase activity but decreased somatostatin and tyrosine hydroxylase activity. Conversely, elimination of non-neuronal cells virtually abolished neuronal expression of substance P and choline acetyltransferase and increased somatostatin and tyrosine hydroxylase. Consequently, under these conditions, somatostatin and tyrosine hydroxylase were similarly regulated, whereas substance P was associated with choline acetyltransferase. By contrast, stimulation of adenylate cyclase or treatment with membrane-permeable adenosine 3',5'-phosphate analogs increased tyrosine hydroxylase and decreased choline acetyltransferase, but had no effect on substance P or somatostatin levels. Moreover, potassium- or veratridine-induced membrane depolarization increased tyrosine hydroxylase but decreased substance P, somatostatin and norepinephrine levels. However, inhibition of neurotransmitter release with magnesium or calcium-free medium prevented the decrease in norepinephrine levels but not the decrease in substance P and somatostatin. Consequently, the effects of membrane depolarization on peptide levels cannot be ascribed to release and subsequent depletion of substance P and somatostatin and must result from decreased net synthesis (synthesis minus catabolism) of the transmitters. Nerve growth-factor treatment also differentially regulated transmitter metabolism; nerve growth factor increased protein-specific activities of tyrosine hydroxylase and choline acetyltransferase but did not increase the protein-specific content of substance P and somatostatin. Quantitative transmitter expression was also influenced by neuron density; increasing density elevated substance P and choline acetyltransferase activity but decreased somatostatin and tyrosine hydroxylase activity per neuron. Finally, culture of sympathetic neurons in a defined (serum-free) medium also altered some but not all traits, decreasing substance P, somatostatin and choline acetyltransferase without any change in tyrosine hydroxylase.(ABSTRACT TRUNCATED AT 400 WORDS)

Kappa opioid receptors participate in nerve growth factor-induced hyperalgesia.

It has recently been observed that nerve growth factors induces the rapid onset of thermal hyperalgesia, and the more delayed onset of mechanical hyperalgesia when administered to mature rats. Though several mechanisms have been proposed to explain this phenomenon, it is still not well understood. Previous studies have shown that nerve growth factor can directly excite nociceptive sensory ganglion neurons in culture via activation of kappa excitatory opioid receptors. The possible involvement of these excitatory opioid receptors in mediating the hyperalgesia was investigated. Nerve growth factor-induced thermal hyperalgesia in rodents was prevented by co-administration of the non-selective opiate antagonist naloxone, as well as by the kappa-selective antagonist nor-binaltorphimine. Addition of the long-acting opioid antagonist, naltrexone, partially prevented mechanical hyperalgesia. Administration of low dose dynorphin to mice (a selective kappa-receptor agonist) mimicked the hyperalgesia effects of nerve growth factor. Opiate antagonists and anti-nerve growth factor antibody both interfered with Freund's adjuvant-induced inflammatory hyperalgesia. Altogether, these observations suggest that activation of excitatory opioid receptors plays a role in mediating nerve growth factor-induced hyperalgesia and that, in turn, nerve growth factor contributes to the hyperalgesia associated with inflammatory states. Since opioid receptor antagonists are well tolerated clinically, they may be useful for patients receiving nerve growth factor as part of ongoing trials of the factor in peripheral neuropathy.

Substance P and somatostatin metabolism in sympathetic and special sensory ganglia in vitro.

Mechanisms regulating the content of the putative peptide transmitters, substance P and somatostatin, were examined in several neuronal populations in culture. Substance P levels increased more than 25-fold within 48 h in sympathetic neurons in the explanted rat superior cervical ganglion, and remained elevated for 4 weeks. Identity of the peptide was authenticated by combined high pressure liquid chromatography-radioimmunoassay. Veratridine prevented the increase of substance P in vitro, and tetrodotoxin blocked the veratridine effect, suggesting that sodium ion influx and membrane depolarization prevent peptide elevation. Veratridine (or potassium)-induced membrane depolarization released substance P into the culture medium through a calcium-dependent process. Consequently, at least some veratridine effects are attributable to release and subsequent depletion of ganglion peptide. However, the inhibitory effects of veratridine were far greater than could be accounted for by the quantity of peptide released, suggesting a separate influence on net synthesis (synthesis less catabolism) of substance P. Viewed in conjunction with previous in vivo studies, our observations suggest that trans-synaptic impulses, through the mediation of postsynaptic sodium flux, release substance P from sympathetic neurons and also regulate intracellular peptide metabolism. To determine whether the processes regulating substance P in sympathetic neurons reflect generalized mechanisms, a different peptide, somatostatin, was examined in sympathetic neurons; moreover, substance P was examined in a different neuronal population, special sensory neurons in the nodose ganglion. Substance P levels increased significantly in both sympathetic and sensory neurons after explantation, and somatostatin levels increased in sympathetic neurons. In each instance, the increase was dependent upon the presence of the calcium ions. Moreover, these increases were all prevented by veratridine, in a tetrodotoxin-sensitive manner. Our observations suggest that common regulatory mechanisms govern peptide transmitter metabolism in diverse neuronal populations.