Characterization of a Schwann cell neurite-promoting activity that directs motoneuron axon outgrowth

ErbB receptors and PKC regulate PC12 neuronal-like differentiation and sodium current elicitation

Excitability, neurite outgrowth and their specification are very important features in the establishment of neuronal differentiation. We have studied a conditioned medium (CM) from sciatic nerve which is able to induce a neuronal-like differentiation of PC12 cells. Previously, we have demonstrated that supplementing this CM with a generic inhibitor (k252a), which mainly inhibits tropomyosin-related kinase receptors (Trk receptors) and protein kinase C (PKC), caused neurite elongation, sodium current induction and axon development. In the present work, we are showing that the enhancement of neurite length and induction of sodium currents induced by CM+k252a were prevented by ErbB receptor inhibition. Additionally, we demonstrated that specific inhibition of PKC produced a similar effect to that exerted by k252a in CM-treated cells, specifically by increasing the percentage of differentiated cells with long neurites and inducing sodium currents. Moreover, CM changed the mRNA levels for ErbB2 and ErbB3 increasing them 6- and 36-folds respectively compared to their control. The inclusion of k252a with CM changed the ErbB1, ErbB2 and ErbB3 mRNA proportions increasing those eight-, seven- and fivefolds respectively. From this point, it is clear that appropriate ErbB receptor levels and PKC inhibition are necessary to enhance the effect of the CM in inducing the neuronal-like differentiation of PC12 cells. In summary, we demonstrated the involvement of ErbB receptors in the regulation of neurite elongation and sodium current induction in PC12 cells and propose that these processes could be initiated by ErbB receptors followed by a fine regulation of PKC signaling. These findings might implicate a novel interplay between ErbB receptors and PKC in the regulation of these molecular mechanisms.

A real-time quantitative PCR comparative study between rat optic and sciatic nerves: determination of neuregulin-1 mRNA levels

Injured axons from peripheral nervous system (PNS) possess the ability to regenerate. In contrast, regeneration of injured axons does not occur in the central nervous system (CNS) or occurs to a limited extent. Previous works have shown that rat sciatic nerve conditioned medium (CM) produced PC12 cells neuronal-like differentiation and neurite outgrowth. In the present work, we compared the expression of neuregulin-1s (NRG-1s) from rat sciatic and optic nerves as members of the PNS and CNS, respectively. Sciatic nerve CM showed a higher neurotrophic activity on PC12 cells than rat optic nerve CM. RT-PCR analysis verified the presence of all three types of NRG-1 mRNAs and their receptors in both types of nerves. Real-time quantitative PCR (QPCR) assays showed that the relative expression levels of all three types of NRG-1 mRNAs were higher in optic nerves than in sciatic nerves. Eleven-day cultured optic nerves showed an increased in NDF and SMDF when compared to freshly isolated optic nerves, whereas GGF decreased. However, 11-day-cultured sciatic nerves only showed an increase in SMDF mRNA. Western blots corroborated the differences in NRG-1 expression profile for both types of nerves and their CMs. Incubation of both CMs with the anti-pan-NRG-1 antibody showed that the neurotrophic activity of the optic nerve CM increased, whereas the sciatic nerve CM remained unchanged. These results indicated that different NRG-1 levels are expressed upon nerve degeneration and the balance between those levels and other neurotrophic factors could have an important role on nerve regeneration.

Transplantation of Bone Marrow Stromal Cell-Derived Schwann Cells Promotes Axonal Regeneration and Functional Recovery after Complete Transection of Adult Rat Spinal Cord

The aim of this study was to evaluate whether transplantation of Schwann cells derived from bone marrow stromal cells (BMSC-SCs) promotes axonal regeneration and functional recovery in completely transected spinal cord in adult rats. Bone marrow stromal cells (BMSCs) were induced to differentiate into Schwann cells in vitro. A 4-mm segment of rat spinal cord was removed completely at the T7 level. An ultra-filtration membrane tube, filled with a mixture of Matrigel (MG) and BMSC-SCs (BMSC-SC group) or Matrigel alone (MG group), was grafted into the gap. In the BMSC-SC group, the number of neurofilament- and tyrosine hydroxylase-immunoreactive nerve fibers was significantly higher compared to the MG group, although 5-hydroxytryptamine- or calcitonin gene-related peptide-immunoreactive fibers were rarely detectable in both groups. In the BMSC-SC group, significant recovery of the hindlimb function was recognized, which was abolished by retransection of the graft 6 weeks after transplantation. These results demonstrate that transplantation of BMSC-SCs promotes axonal regeneration of lesioned spinal cord, resulting in recovery of hindlimb function in rats. Transplantation of BMSC-SCs is a potentially useful treatment for spinal cord injury.

Rapid axoglial signaling mediated by neuregulin and neurotrophic factors

During peripheral nervous system development, Schwann cells are precisely matched to the axons that they support. This is mediated by axonal neuregulins that are essential for Schwann cell survival and differentiation. Here, we show that sensory and motor axons rapidly release heparin-binding forms of neuregulin in response to Schwann cell-derived neurotrophic factors in a dose-dependent manner. Neuregulin release occurs within minutes, is saturable, and occurs from axons that were isolated using a newly designed chamber slide apparatus. Although NGF and glial cell line-derived neurotrophic factor (GDNF) were the most potent neurotrophic factors to release neuregulin from sensory neurons, GDNF and BDNF were most potent for motor neurons and were the predominant neuregulin-releasing neurotrophic factors produced by cultured Schwann cells. Comparable levels of neuregulin could be released at a similar rate from neurons after protein kinase C activation with the phorbol ester, phorbol 12-myristate 13-acetate, which has also been shown to promote the cleavage and release of neuregulin from its transmembrane precursor. The rapid release of neuregulin from axons in response to Schwann cell-derived neurotrophic factors may be part of a spatially restricted system of communication at the axoglial interface important for proper peripheral nerve development, function, and repair.

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.

AFGF promotes axonal growth in rat spinal cord organotypic slice co-cultures

This study developed a slice culture model system to study axonal regeneration after spinal cord injury. This model was tested in studies of the roles of acidic fibroblast growth factor (aFGF) and peripheral nerve segments in axonal growth between pieces of spinal cord. Transverse sections of P15-P18 Sprague-Dawley rat spinal cord were collected for organotypic slice cultures. Group I consisted of two slices of spinal cord in contact with each other during the culture period. Group II consisted of two slices that were separated by 3 mm and connected by two segments of intercostal nerves. Group III consisted of single slices for studies of neuron survival. Some cultures from each group included aFGF in the culture medium. Bromodeoxyuridine (BrdU) was included in the medium for some cultures. The results showed three principal findings. First, counts of neurofilament-positive cells demonstrated that treatment with aFGF significantly increased the number of surviving neurons in culture. Second, neurofilament immunostaining and DiI tracing demonstrated axons crossing the junction between the two pieces of spinal cord or growing through the intercostal nerve segments, and these axons were seen only in cultures with aFGF treatment. Third, few cells were double stained for neurofilament and BrdU, and these were found only with aFGF treatment. These results demonstrate that (1) organotypic slice cultures present a useful model to study regeneration from spinal cord injury, (2) aFGF rescues neurons and promotes axonal growth in these cultures, and (3) segments of intercostal nerves promote axon growth between slices of spinal cord.

Ionic currents in PC12 cells differentiated into neuron-like cells by a cultured-sciatic nerve conditioned medium

The present work deals with the identification of the ionic currents found in PC12 cells differentiated into neuron-like cells by a 9-11-day cultured-sciatic nerve conditioned medium (CM). PC12 whole-cell currents were measured after chronic exposure to CM. The results obtained in these CM-treated cells reveal that the functional expression of Ca(2+) currents is increased, that Na+ currents are not affected, and that a transient K+ current and a K+ delayed rectifier (K+ dr) current are increased. The combination of nifedipine and omega-conotoxin GVIA (omega-CgTX) does not block completely the increased functional expression of the Ca(2+) current. The remaining current is blocked by omega-agatoxin TK indicating that P/Q-type channels are additionally contributing to the increase in Ca(2+) current. NGF-treated PC12 cells, used as positive controls, confirm that NGF increases the expression of voltage-dependent Na+ currents and of Ca(2+) currents. In addition, we found that NGF also increases a K+ dr-type current in these cells. The results obtained with the CM might be due to a molecule or a mixture of molecules released into the medium by the 9-11-day cultured sciatic nerves.

Cell types required to efficiently innervate human muscle cells in vitro

Previous studies carried out in our laboratory have shown that myofibers formed by fusion of muscle satellite cells from donors with spinal muscular atrophy (SMA) type I or II undergo a characteristic degeneration 1.5-3 weeks after innervation with rat embryonic spinal cord explants. The only cells responsible for degeneration of innervated cocultures are SMA muscle satellite cells. In order to study the kinetics of nerve and muscle cell degeneration in nerve-muscle cocultures implicating SMA muscle cells, we attempted to simplify the nervous component of the coculture and identify the nerve cell types necessary for a successful innervation. We demonstrate here that motoneurons alone were unable to innervate myotubes. However, when three cell types (motoneurons, sensory neurons, and Schwann cells) were added onto a reconstituted muscular component consisting of cloned muscle satellite cells and cloned muscular fibroblasts, myotubes contracted, indicating that functional neuromuscular junctions were formed. We concluded that the three cell types were required for a successful innervation. Moreover, we studied the effects of culture medium conditioned by different combinations of nerve cells on innervation; we observed that physical contacts among sensory neurons, motoneurons, and myotubes are required for a successful innervation; in contrast Schwann cells can be replaced by a Schwann-cell-conditioned medium, indicating that these cells produce a putative soluble "innervation-promoting factor." Obviously such a reconstituted system does not reflect the in vivo situation but it allows the formation of functional motor synapses and could therefore allow us to elucidate neuromuscular disease pathogenesis, especially that of spinal muscular atrophy.

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.

Abnormalities in central nervous system development in osteogenesis imperfecta type II

Osteogenesis imperfecta (OI) type II is a perinatally lethal condition resulting from mutations in type I collagen genes. In addition to characteristic skeletal anomalies, OI type II has recently been shown to be associated with neuropathological alterations, specifically perivenous microcalcifications, and impaired neuroblast migration. In light of these findings, and because type I collagen promotes neuritic maturation both in vitro and in vivo, we sought to determine if additional central nervous system (CNS) developmental anomalies could be found in previously autopsied OI type II cases, and if specific abnormalities correlate with OI subtypes. We retrospectively studied brains of nine patients diagnosed with OI. Of these, seven were OI type II: five were OI type IIA, one was type IIB, and one was type IIC. One OI type I specimen and one OI type III brain were included for comparison, as well as five controls. The IIC brain showed hippocampal malrotation, agyria, abnormal neuronal lamination, diffuse hemorrhage, and periventricular leukomalacia (PVL). The IIB brain had white matter gliosis, PVL, and perivascular calcifications, but was normally developed. Of the five type IIA brains, two showed migrational defects with coexisting PVL and gliosis, two were normally developed with similar white matter injuries, and one was grossly normal. These findings support the contention that collagen mutations might negatively impact CNS development.

Cultured sympathetic neurons express functional interleukin-1 receptors

Since recent work has identified an apoptotic pathway in sympathetic neurons that is mediated by autocrine interleukin-1 (IL-1), we investigated whether cultured sympathetic neurons possess functional IL-1 receptors. Cultured sympathetic neurons express levels of IL-1RI and IL-1RAcP mRNAs consistent with signal transduction. Neurons stimulated with IL-1 demonstrate enhanced p65 NF-kappaB nuclear translocation and enhanced NF-kappaB DNA binding activity, with at least p65 and p50 subunits participating in the DNA binding activity. RNA differential display identified several neuronal mRNAs regulated by IL-1, including a member of the reticulon family. We conclude that IL-1 stimulates a potential component of a neuronal secretory pathway.

Removal of retrogradely transported material from rat lumbosacral alpha-motor axons by paranodal axon-Schwann cell networks

The aim of this study was to investigate the potential ability of Schwann cells to sequester axonally transported material via so called axon-Schwann cell networks (ASNs). These are entities consisting of sheets of Schwann cell adaxonal plasma membrane that invade the axon and segregate portions of axoplasm in paranodes of large myelinated mammalian nerve fibres. Rat hindlimb alpha-motor axons were examined in the L4-S1 ventral roots using light/fluorescence, confocal laser, and electron microscopy for detection of retrogradely transported red-fluorescent latex nanospheres taken up at a sciatic nerve crush, and intramuscularly injected horseradish peroxidase endocytosed by intact synaptic terminals. Survival times after tracer administration ranged from 27 hours to 4 weeks. During their retrograde transport toward the motor neuron perikarya, organelles carrying nanospheres/peroxidase accumulated at nodes of Ranvier, where they often appeared in close association with the paranodal myelin sheath. Serial section electron microscopy showed that many of the tracer-containing bodies were situated within ASN complexes, thereby being segregated from the main axon. Four weeks after nanosphere administration, several node-paranode regions still showed ASN-associated aggregations of spheres, some of which were situated in the adaxonal Schwann cell cytoplasm. The data establish the ability of Schwann cells to segregate material from motor axons with intact myelin sheaths, using the ASN as mediator. Taken together with our earlier observations that ASNs in alpha-motor axons are also rich in lysosomes, this process would allow a local elimination and secluded degradation of retrogradely transported foreign substances and degenerate organelles before reaching the motor neuron perikarya. In addition, ASNs may serve as sites for disposal of indigestable material.

Quantitative analysis of long-term survival and neuritogenesis in vitro: cochleovestibular ganglion of the chick embryo in BDNF, NT-3, NT-4/5, and insulin

The dynamics of survival and growth were examined for cochleovestibular ganglion (CVG) cells maintained in long-term cultures. CVG cells were explanted from chick embryos after 90 h of incubation into a defined-medium containing BDNF, NT-3, or NT-4/5 and an insulin, transferrin, selenium, and progesterone supplement. Explant survival and neuritogenesis was measured for 23 to 24 days in vitro. All three neurotrophins prolonged CVG survival in a dose-dependent manner although insulin acted as a cofactor. In 0.872 microM insulin-containing medium the ED50 for BDNF and NT-3 was 100 pg/ml, whereas the ED50 for NT-4/5 was 600-1200 pg/ml. However, at later ages in vitro, survival decreased with concentrations of BDNF greater than 2 ng/ml. In insulin-free medium, concentrations of 5-200 ng/ml of BDNF or 30-200 ng/ml of NT-4/5 maintained the survival of explants at a rate that was equivalent to or less than the survival rate of cultures treated with insulin but not with neurotrophin. In contrast, NT-3-treated explants in insulin-free medium did not survive the duration of the experiment. Dose-dependent effects of BDNF and NT-3 on explant neuritogenesis were reflected as an initial delay in outgrowth, whereas NT-4/5 had no effect. Insulin regulation of neuritogenesis was suggested when outgrowth decreased in the presence of an antibody to the insulin receptor. These data suggest that while all three of these neurotrophins protect the CVG from death the long-term consequences of cofactors and certain dose levels should be considered when treating CVG cells in vivo.

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).

Spontaneously immortalized adult mouse Schwann cells secrete autocrine and paracrine growth-promoting activities

We established spontaneously immortalized Schwann cell lines from long-term cultures of adult mouse dorsal root ganglia and peripheral nerves. One of the cell lines, designated IMS32, responded to mitogenic stimuli by platelet-derived growth factor (PDGF)-BB, acidic and basic fibroblast growth factors (aFGF, bFGF), and transforming growth factors (TGF)-beta 1 and -beta 2, as determined by bromodeoxyuridine (BrdU) incorporation and double immunofluorescence for S100 and BrdU. Furthermore, conditioned media (CM) obtained from IMS32 cells showed mitogenic activity for both IMS32 cells and long-term cultured Schwann cells. Western blot analysis revealed TGF-beta-like molecule in the CM, and the activity was absorbed with anti-TGF-beta neutralizing antibody. Reverse transcription followed by polymerase chain reaction (RT-PCR) of IMS32 RNA revealed that these cells expressed TGF-beta 1, -beta 2, and -beta 3 transcripts. When rat pheochromocytoma PC12 cells were incubated with the CM, they developed neurite growth. Coculture of PC12 and IMS32 cells also showed neurite growth of PC12 cells. RNA transcripts of nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT3), ciliary neurotrophic factor (CNTF), and glial cell line-derived neurotrophic factor (GDNF) were detected from IMS32 cells by RT-PCR. In these, we sequenced the mouse GDNF cDNA coding region and observed 97% and 90% homologies to corresponding rat and human cDNA sequences, respectively. These results indicate that the immortalized Schwann cell line mitotically responds to various growth factors and secretes autocrine and paracrine growth-promoting activities in vitro.