Peripheral nerve extract promotes long-term survival and neurite outgrowth in cultured spinal cord neurons

Role of glypican-1 in the trophic activity on PC12 cells induced by cultured sciatic nerve conditioned medium: identification of a glypican-1-neuregulin complex

Glypican-1 is an extracellular matrix component found by microsequencing in a medium conditioned by cultured rat-sciatic nerves (CM). This CM was concentrated by ultrafiltration and fractionated by quaternary ammonium chromatography, followed by Hi-Trap blue affinity chromatography to obtain the active fraction B1.2. Previously, we have reported a 54 kDa neuregulin (NRG) in the same B1.2 fraction [Villegas et al., Brain Res. 852 (2001) 304]. The effect of Glypican-1 on the neuron-like differentiation of PC12 cells was investigated by immunoprecipitation, Western blot and cellular image analysis. Removal of glypican-1 by immunoprecipitation with increasing concentrations of specific antibodies revealed a gradual decrease of the differentiation activity of fraction B1.2, which paralleled the results obtained by removal of the 54 kDa NRG protein. Colorless native electrophoresis and Western blot analysis was used to identify a glypican-1-NRG protein complex, which could be afterwards separated by sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis into its individual components. Additionally, it was demonstrated that glypican-1, in cooperation with the 54 kDa NRG, is involved in the neuronal-like differentiation of PC12 cells and could play an important role on the regeneration responses of peripheral nerves.

Neuregulin found in cultured-sciatic nerve conditioned medium causes neuronal differentiation of PC12 cells

The present work deals with the search and identification of the molecule or combination of molecules, present in a medium conditioned by cultured rat-sciatic nerves (CM), able to cause neuronal differentiation of PC12 cells. The molecular mass range of the active fraction, as well as the thermostability and heparin affinity of the active component found in previous work, all characteristics shared with neuregulin (NRG) family members, led us to search for a NRG protein in the CM. Nerves were previously cultured for 8 days and the CM collected every 24 h, the following 3 days. The CM was concentrated (30,000 NMWL) and fractionated by quaternary ammonium chromatography and Cibacron blue affinity chromatography. The most active fraction B1.2 was further characterized by heparin affinity chromatography, size exclusion HPLC, Western blotting and immunoprecipitation. Results reveal abundance of NRG mRNA in the cultured nerves, presence of a 54 kDa NRG protein in the CM that increases along fractionation, and progressive diminution of fraction B1.2 differentiation activity on PC12 cells by gradual removal of the NRG protein by immunoprecipitation. The abundance of Schwann cells and the lack of axons in the cultured nerves suggest Schwann cells as the main NRG source, to which fibroblasts and perineurial cells might contribute.

Identity of neurotrophic molecules released from astroglia by vasoactive intestinal peptide

Subnanomolar concentrations of VIP elicit a survival-producing action in CNS cultures composed of both astroglia and neurons. This neurotrophic action is mediated by a complex array of substances released by VIP from astrocytes. Included in this glial protein mixture is a cytokine (interleukin-1 alpha), a serine protease inhibitor (protease nexin I), and an extracellular stress protein (activity-dependent neurotrophic factor). In dissociated spinal cord cultures, all of these substances exhibit neuroprotection from neuronal cell death produced by electrical blockade with tetrodotoxin. All these substances produce neuronal cell death when test cultures are treated with neutralizing antisera to any one of them. They are all apparently necessary for the survival of a subpopulation of neurons that are dependent on spontaneous, excitatory neurotransmission. Our view is that these substances are components of a glia-derived environment that regulates, together with target-derived growth factors, the survival fate of developing neurons. In addition, it is our belief that some of these glia-derived substances will be found to have active roles in the injury response to the CNS or in the regulation of VIP-mediated growth in other tissues. Drugs based on these substances may provide therapeutic agents for the treatment of neurodegeneration and tumor growth.

Prevention of activity-dependent neuronal death: vasoactive intestinal polypeptide stimulates astrocytes to secrete the thrombin-inhibiting neurotrophic serpin, protease nexin I

Neuronal cell death occurs as a programmed, naturally occurring mechanism and is the primary regressive event in central nervous system development. Death of neurons also occurs on an injury-induced basis after trauma and in human neurodegenerative diseases. Classical neurotrophic factors can reverse this phenomenon in experimental models prompting initiation of clinical trials in conditions such as amyotrophic lateral sclerosis and Alzheimer's disease. The glial-derived protease nexin I (PNI), a known promoter of neurite outgrowth in cell culture and a potent inhibitor of serine proteases, also enhances neuronal cell survival. PNI, in nanomolar concentrations, rescues spinal cord motor neurons from both naturally-occurring programmed cell death in the chick embryo as well as following injury in the neonatal mouse. The potent neuromodulator, vasoactive intestinal polypeptide (VIP), influences neuronal survival through glial-mediated factors and also induces secretion of newly synthesized astrocyte PNI. We now report that subnanomolar amounts of PNI enhance neuronal survival in mixed spinal cord cell culture, especially when neuronal cells were made electrically silent by administration of tetrodotoxin. The mediation of this effect is by inhibition of the multifunctional serine protease, thrombin, because hirudin, a thrombin-specific inhibitor, has the same effect. In addition, spinal cord neurons are exquisitely sensitive to thrombin because picomolar and lower levels of the coagulation factor causes neuronal death. Thus, PNI is an astrocyte-derived, thrombin-inhibiting, activity-dependent neurotrophic agent, enhanced secretion of which by VIP may be one approach to treat neurological disorders.

Neuronal differentiation of PC12 and chick embryo ganglion cells induced by a sciatic nerve conditioned medium: characterization of the neurotrophic activity

The present work deals with the finding and characterization of a neurotrophic factor present in serum-free Dulbecco's modified Eagle's medium in which rat sciatic nerves previously cultured for 9 days were maintained for 24 h. This sciatic nerve conditioned medium (SNCM) produced neuronal differentiation and neurite outgrowth on PC12 cells, as well as survival and differentiation of eight-day old chick embryo dorsal root ganglion (E8-DRG) and ciliary ganglion (E8-CG) neurons. SNCM activity was decreased by dilution, heating and trypsin treatment; it was not inhibited by anti-NGF and anti-bFGF antibodies; and it was not mimicked by CNTF, laminin and fibronectin. By utilizing its neurite-promoting activity on PC12 cells, experiments oriented to purify the factor were carried out. Ultrafiltration, heparin-affinity chromatography and size-exclusion high pressure liquid chromatography (HPLC) were employed. The ability of SNCM to induce PC12 cell, E8-DRG and E8-CG neuronal differentiation, the heparin affinity of the active SNCM protein, and the size-exclusion HPLC elution characteristics of the active protein suggest that the active component of the SNCM is, in all probability, a novel sciatic nerve neurotrophic factor (SNTF).

A serine protease inhibitor, protease nexin I, rescues motoneurons from naturally occurring and axotomy-induced cell death

Protease nexin I (PNI) is a member of the family of serine protease inhibitors (serpins) that have been shown to promote neurite outgrowth in vitro from different neuronal cell types. These include neuroblastoma cells, hippocampal neurons, and sympathetic neurons. Free PNI protein is markedly decreased in various anatomical brain regions, including hippocampus, of patients with Alzheimer disease. Here, we report that PNI rescued spinal motoneurons during the period of naturally occurring (programmed) cell death in the chicken in a dose-dependent fashion. Furthermore, PNI prevented axotomy-induced spinal motoneuron death in the neonatal mouse. The survival effect of PNI on motoneurons during the period of programmed cell death was not associated with increased intramuscular nerve branching. PNI also significantly increased the nuclear size of motoneurons during the period of programmed cell death and prevented axotomy-induced atrophy of surviving motoneurons. These results are consistent with the possible role of PNI as a neurotrophic agent. They also support the idea that serine proteases or, more precisely, the balance of proteases and serpins may be involved in regulating the fate of neuronal cells during development.

Functional enhancement of intrastriatal dopamine-containing grafts by the co-transplantation of sciatic nerve tissue in 6-hydroxydopamine-lesioned rats

Peripheral nerve "bridges" demonstrate the ability to facilitate axonal growth and regenerate adult and fetal central nervous system tissue. The purpose of this study was to determine if co-grafted peripheral nerve tissue could enhance the ability of fetal dopamine (DA) cell transplants to reinnervate host striatum that had been denervated unilaterally. Male Fisher-344 rats were unilaterally lesioned with 6-hydroxydopamine to eliminate the nigrostriatal DA pathway. A total of 31 rats demonstrated a pattern of rotation indicative of a greater than 98% depletion in DA. Rats were kept as nongrafted controls (n = 6), grafted with sciatic nerve (PN) minces (n = 6), grafted with fetal ventral mesencephalon (VM; n = 10), or co-grafted with VM and PN minces (n = 9). All groups were then tested for changes in apomorphine-induced rotational behavior. The PN control group showed no significant differences in rotation when compared to pregrafting levels and to the lesioned nongrafted group. Both the VM-grafted group and the VM-PN co-grafted group showed significant (P less than 0.01, one-way ANOVA) decreases in rotations beginning at 1.5 weeks postgrafting. There was a progressive decrease in rotations up to 12 weeks, the last test point examined. Interestingly, the co-graft group revealed a significantly greater decrease in rotation (P less than 0.05) than the VM group beginning at 5 weeks and continuing out to the 12-week test point. Histological and immunocytochemical studies showed good survival of both PN and VM grafts. The augmented recovery could not be accounted for by increased DA cell survival or host brain DA reinnervation in the co-graft group. Taken together, these findings suggest that PN tissue enhances the ability of fetal VM grafts to reinnervate host brain.

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.

Biological activity of a new neuronal growth factor from injured peripheral nerve

In response to transection injury, the distal nerve segment produces a soluble neurite promoting factor (SN). In this study, the ability to support neuronal survival and differentiation have been studied. Embryonic rat dorsal root ganglion (DRG) neurons were plated out on collagen substrates and incubated in medium containing either SN or nerve growth factor (NGF). The number of surviving neurons was counted after 1, 2, 4, 7, and 15 days in vitro. After fixation and staining, the diameter of the surviving neurons was measured. During the period of observation, 60.8 +/- 5.8% of plated neurons survived in the presence of NGF and 90.5 +/- 12.9% survived with SN (P less than 0.05). The mean of median neuronal cell diameter was 28 +/- 2.7 microns with NGF and 34.2 +/- 3.7 microns with SN, (P less than 0.01). This increased diameter was due to enhanced survival of 30-50 microns diameter neurons. In parallel experiments, the degree of myelination of DRG neurons by Schwann cells was assessed morphometrically. In the presence of SN there was an 86% increased in myelination compared with NGF which indicates that not only is the survival of neurons increased but they are able to become fully differentiated in the presence of SN.

Schwann cell-conditioned medium supports neurite outgrowth and survival of spinal cord neurons in culture

The effect of Schwann cell-conditioned medium (SCM) on the development in vitro of spinal cord neurons was studied. Spinal cord neurons from 18-day-old rat embryos were cultured in serum-free conditioned medium obtained from confluent rat Schwann cells. In cultures fed SCM, the cells developed typical neuronal morphology and were identified by indirect immunofluorescence using a monoclonal antibody to neurofilament protein. SCM stimulated neurite outgrowth and supported survival of spinal cord neurons. Preliminary characterization suggests that the neurotrophic factor in SCM appears to be a protein with a molecular weight greater than 8000 daltons.

Effect of injury on nerve growth factor uptake by sensory ganglia

The level of the nerve growth factor protein, NGF, in vivo has a profound influence on axonal sprouting by sensory neurons of vertebrate dorsal root ganglia. There is evidence also that NGF may play similar roles in cholinergic central structures in brain. In both instances, retrograde transport of NGF has been demonstrated. Here we examined uptake of NGF by DRG neurons in response to contusion injury of the spinal cord. Under these conditions there was uptake and transport of NGF into large DRG neurons via central processes but no uptake by non-DRG central neurons. Thus, any effects of NGF on spinal neurons or their processes would be secondary to the direct effects of NGF on DRG neurons.

Induction of a neurite-promoting factor in rat brain following injury or deafferentation

Ablation of the entorhinal/occipital cortex in young adult rats caused a several-fold increase in the neurite-promoting activity in extracts of the tissue surrounding the wound and in areas that had been deafferented by the lesion. The time course of induction closely paralleled reactive axon sprouting in the deafferented hippocampus, with maximal levels of neurite-promoting activity reached between 9 and 15 days post-lesion. Aged animals, in which reactive sprouting is deficient, showed no increase in activity by 12 days after deafferentation of the hippocampus. The neurite-promoting activity of brain extracts was non-diffusible, heat-labile, and sensitive to proteolysis. All of the activity bound to diethylaminoethyl (cellulose) and was eluted at 200 mM NaCl. The apparent molecular weight (by gel filtration) of the activity in extracts of uninjured brain was 9-17 kilodaltons, whereas the extracts of injured brain also had peaks or shoulders at 30, 70 and greater than or equal to 200 kilodaltons. These data suggest that the brain neurite-promoting activity resides in one or more proteins. Both the injury-induced and basal activities were different from laminin, nerve growth factor, and polyornithine-bindable neurite-promoting factors. The injury-induced activity was sensitive to repeated freezing and thawing, but this inactivation was reversed by thiol reagents such as glutathione, thioglycerol, and mercaptoethanol. We report a neurite-promoting factor that is induced following brain injury or denervation, and may also be important for reactive axon sprouting after brain injury. The induction of this factor is abnormal in aged animals, as is the reactive sprouting response. The properties of the injury-induced activity distinguish it from the basal activity (found in uninjured brain) and from other characterized neurite-promoting factors.

Peripheral nerve implantation into a penetrating lesion of the eye: stimulation of the damaged retina

A small penetrating incision made through the sclera, choroid and retina of the adult rat eye creates a unique lesion paradigm. More specifically, by one to two weeks after the incision the wound area stabilizes, leaving a clean inflammation-free degeneration gap or 'die-back zone' (200-300 microns wide) between the cut edges of the intact retina. The dependable formation of a small focal retinal lesion makes this an ideal model for the determination of conditions that may stimulate retinal regeneration, wound repair and/or cell survival. In other words, material may be injected or placed into the lesion site and the retina analyzed for responses to such treatments. Accordingly, the placement of a desheathed peripheral nerve implant (PNI) into the lesioned adult rat eye initiated the rescue of retinal tissue that would normally die due to trauma. In addition, the cut edges of the retina just lateral to the PNI actually touched and fused together, thus demonstrating a wound closure or healing phenomenon which was not observed in control situations. Also the thickness and organization of most retinal layers at the site of lesion were maintained at intact control levels in the presence of the PNI. However, controls not containing the PNI exhibited dramatic reductions in total and individual retinal layer thickness for up to approximately 500 microns lateral to the lesion site. Through the use of a double lesion paradigm, it was also determined that the wound repair phenomena could be influenced over a distance by (a) putative diffusable factor(s) elaborated or initiated by the PNI.

Septal deafferentation enhances the neurotrophic effects of rat hippocampus on cultured neural cells from the central nervous system

Neurotrophic effects (NTEs) of various brain regions of 4-week-old rats were examined in primary culture of rat embryonic cerebral hemispheres. Extracts of the hippocampus, brainstem and septal nucleus highly enhanced the survivability of neuronal cells and the division of non-neuronal cells by 9 days. The septohippocampal tract (fimbria fornix) was cut and the effect on the neurotrophic activity in the hippocampus was examined. The NTEs of hippocampal extracts remained unchanged 3 days after septal deafferentation, was significantly increased by 7 days, peaked at 14 days and returned to the basal level by 21 days.

Tissue culture analysis of neurite outgrowth in the presence and absence of serum: possible relevance for central nervous system regeneration

A tissue culture model has been developed to examine the hypothesis that axons can only regenerate when their growing tips are surrounded by extracellular fluid containing proteins derived from the blood. Fetal rat cerebral explants were cultured in serum medium for 10 days, followed by serum-free (SF) medium (from which serum had been removed) until 18 days in vitro (DIV). All explants cultured in serum medium for 0-10 DIV exhibited greater than 77% neurite viability (neurite viability ratio, NVR, 3.10). This degree of neurite viability was maintained for those explants exposed to serum until 18 DIV (NVR 2.82 at 18 DIV). By contrast, explants maintained in SF medium from 10-18 DIV had a much lower NVR, which, by 18 DIV, had declined to 0.30 (7.5% viability). Transmission electron microscopic analysis of explants fixed at 18 DIV confirmed these phase-contrast results and also showed a predominance of axonal profiles within the neurite population. In the center of explants, tissue viability was in excess of 75% in both the serum and SF media, suggesting that serum is of primary importance for axonal extension rather than neuronal survival. These data strengthen the hypothesis that blood-derived proteins may be needed for prolonged regeneration.

Transplants of Schwann cell cultures promote axonal regeneration in the adult mammalian brain

Transplantation of embryonic brain tissue or mature peripheral nerves into the adult mammalian central nervous system promotes axonal regrowth from axotomized central nervous system neurons; however, the cellular origin and molecular nature of the factors promoting axonal growth in vivo are unknown. To further characterize cellular environments that facilitate regeneration of central nervous system axons, we developed a methodology whereby cultured cell preparations can be transplanted into the brain of mature mammals. For this procedure, lesions are produced in the septal-hippocampal system of adult rats, and selected regions from collagen-supported Schwann cell/neuron cultures (consisting of Schwann cells, extracellular matrix, and degenerating neuronal processes and myelin but devoid of neuronal perikarya and fibroblasts) are positioned within the intracephalic cavity so that they bridge the lesion gap (approximately 3 mm) separating the septum and hippocampus. At various time up to 3 weeks after transplantation, specimens were prepared for acetylcholinesterase histochemistry and the immunocytochemical localization of laminin (an extracellular matrix protein) and C-4 (a Schwann cell membrane antigen). All specimens (from uninjured controls and from animals with either acellular collagen or mature Schwann cell/extracellular matrix transplants) contained laminin immunoreactivity associated with the meninges, choroid plexus, ependyma, and cerebral blood vessels. All animals with transplants showed prominent laminin staining on astrocytic processes along the intracephalic cavity, but only the Schwann cell/extracellular matrix transplants exhibited dense laminin and C-4 immunoreactivity within the cellular portion of the transplants. Regeneration of acetylcholinesterase-positive septal fibers occurred only in animals containing Schwann cell/extracellular matrix transplants. By 6 days after transplantation, acetylcholinesterase-positive fibers were observed both on laminin-positive cellular tissue strands connecting the septum and the Schwann cell/extracellular matrix transplants and on the initial portions of the transplants. By day 14, acetylcholinesterase-positive fibers traversed the entire lesion cavity in intimate association with the laminin- and C-4-positive cellular layer of the transplants and reinnervated the host hippocampus. However, cholinergic fibers were not associated with all laminin-containing processes along the lesion cavity nor did they grow along acellular collagen transplants. These results indicate the presence of factors in transplants of cultured Schwann cells and their associated extracellular matrix that promote rapid regeneration of central nervous system cholinergic axons in vivo.