Hepatocyte growth factor is a mitogen for olfactory ensheathing cells

Nasal Placode Development, GnRH Neuronal Migration and Kallmann Syndrome

The development of Gonadotropin releasing hormone-1 (GnRH) neurons is important for a functional reproduction system in vertebrates. Disruption of GnRH results in hypogonadism and if accompanied by anosmia is termed Kallmann Syndrome (KS). From their origin in the nasal placode, GnRH neurons migrate along the olfactory-derived vomeronasal axons to the nasal forebrain junction and then turn caudally into the developing forebrain. Although research on the origin of GnRH neurons, their migration and genes associated with KS has identified multiple factors that influence development of this system, several aspects still remain unclear. This review discusses development of the olfactory system, factors that regulate GnRH neuron formation and development of the olfactory system, migration of the GnRH neurons from the nose into the brain, and mutations in humans with KS that result from disruption of normal GnRH/olfactory systems development.

Semaphorin 3A as an inhibitive factor for migration of olfactory ensheathing cells through cofilin activation is involved in formation of olfactory nerve layer

Olfactory ensheathing cells (OECs) migrate from olfactory epithelium towards olfactory bulb (OB), contributing to formation of the presumptive olfactory nerve layer during development. However, it remains unclear that molecular mechanism of regulation of OEC migration in OB. In the present study, we found that OECs highly expressed the receptors of semaphorin 3A (Sema3A) in vitro and in vivo, whereas Sema3A displayed a gradient expression pattern with higher in inner layer of OB and lower in outer layer of OB. Furthermore, the collapse assays, Boyden chamber migration assays and single-cell migration assays showed that Sema3A induced the collapse of leading front of OECs and inhibited OEC migration. Thirdly, the leading front of OECs exhibited adaptation in a protein synthesis-independent manner, and endocytosis-dependent manner during Sema3A-induced OEC migration. Finally, Sema3A-induced collapse of leading front was required the decrease of focal adhesion and a retrograde F-actin flow in a cofilin activation-dependent manner. Taken together, these results demonstrate that Sema3A as an inhibitive migratory factor for OEC migration through cofilin activation is involved in the formation of olfactory nerve layer.

Human mesenchymal stem cells isolated from olfactory biopsies but not bone enhance CNS myelination in vitro

Spinal cord injury (SCI) is a devastating condition with limited capacity for repair. Cell transplantation is a potential strategy to promote SCI repair with cells from the olfactory system being promising candidates. Although transplants of human olfactory mucosa (OM) are already ongoing in clinical trials, the repair potential of this tissue remains unclear. Previously, we identified mesenchymal-like stem cells that reside in the lamina propria (LP-MSCs) of rat and human OM. Little is known about these cells or their interactions with glia such as olfactory ensheathing cells (OECs), which would be co-transplanted with MSCs from the OM, or endogenous CNS glia such as oligodendrocytes. We have characterized, purified, and assessed the repair potential of human LP-MSCs by investigating their effect on glial cell biology with specific emphasis on CNS myelination in vitro. Purified LP-MSCs expressed typical bone marrow MSC (BM-MSC) markers, formed spheres, were clonogenic and differentiated into bone and fat. LP-MSC conditioned medium (CM) promoted oligodendrocyte precursor cell (OPC) and OEC proliferation and induced a highly branched morphology. LP-MSC-CM treatment caused OEC process extension. Both LP and BM-MSCs promoted OPC proliferation and differentiation, but only myelinating cultures treated with CM from LP and not BM-MSCs had a significant increase in myelination. Comparison with fibroblasts and contaminating OM fibroblast like-cells showed the promyelination effect was LP-MSC specific. Thus LP-MSCs harvested from human OM biopsies may be an important candidate for cell transplantation by contributing to the repair of SCI.

The migration of olfactory ensheathing cells during development and regeneration

The primary olfactory nervous system is unique in that it continuously renews itself and regenerates after injury. These properties are attributed to the presence of olfactory glia, termed olfactory ensheathing cells (OECs). Evidence is now emerging that individual OEC populations exist with distinct anatomical localisations and physiological properties, but their differential roles have not been determined. Unlike other glia, OECs can migrate from the periphery into the central nervous system, and organised OEC migration can enhance axonal extension after injury. Despite this, the mechanisms regulating OEC migration are largely unknown. Here, we provide an overview of the roles of OECs in development and adulthood. We review the latest research describing the differences between individual OEC subpopulations and discuss potential regulatory mechanisms for OEC guidance and migration. Using advanced time lapse techniques, we have obtained novel insights into how OECs behave in a complex multicellular environment which we discuss here with particular focus on cell-cell interactions. Significantly, transplantation of OECs constitutes a promising novel therapy for nerve injuries, but results are highly variable and the method needs improvement. We here review the roles of transplanted OECs in neural repair of damaged neuronal tracts distinct from the primary olfactory nervous system.

Ginsenoside Rg1 promotes proliferation and neurotrophin expression of olfactory ensheathing cells

Transplantation of olfactory ensheathing cells (OECs) is currently considered to be one of the most promising repair strategies for human spinal cord injury. However, the factors that regulate OECs are still poorly understood. Ginsenoside Rg1 (Rg1), the phytosterol from Panax ginseng, is a potent neuroprotective agent that promotes axonal regeneration. The aim of this study is to determine whether Rg1 would influence the biological activity of OECs. Primary cultured OECs from the olfactory bulb of neonatal rats were treated with Rg1 of various concentrations and durations. Using MTT and bromodeoxyuridine assays, we found that Rg1 significantly promoted cell proliferation, with an optimal concentration of 40 mug/ml of Rg1 at 72 h. In addition, RT-PCR and ELISA assays showed that Rg1 could upregulate the mRNA expression and secretion of glial cell-derived neurotrophic factor, brain-derived neurotrophic factor, and nerve growth factor. These results suggest that Rg1 may have a great potential in OEC therapy.

Serum-Free Medium Provides a Clinically Relevant Method to Increase Olfactory Ensheathing Cell Numbers in Olfactory Mucosa Cell Culture

There is much evidence to suggest that transplanted olfactory ensheathing cells may ameliorate the functional deficits associated with injuries to the nervous system, especially the spinal cord. For clinical implementation of this strategy it will be necessary to derive large numbers of these cells from an accessible and, preferably, autologous source, implying that olfactory mucosa would be ideal. Although olfactory ensheathing cells can be derived from olfactory mucosa, in routine culture conditions the proportion of these cells is unacceptably low for clinical purposes. This study compared the effect of culturing dissociated olfactory bulb and olfactory mucosa in two different media: one containing serum and one serum free. The results indicate that olfactory ensheathing cell proportion, and absolute cell numbers, is greatly increased in serum-free conditions. Further analysis suggests that serum-free medium has a differential effect on contaminating fibronectin-positive and p75-positive cells from olfactory bulb and olfactory mucosa. This study demonstrates that serum-free culture conditions provide a simple and useful means of deriving a sufficient number of olfactory ensheathing cells for transplantation and reveals a difference in biological behavior of the cells contained within olfactory bulb and olfactory mucosa.

Culture conditions affect proliferative responsiveness of olfactory ensheathing glia to neuregulins

Olfactory ensheathing glia (OEG) have been used to improve outcome after experimental spinal cord injury and are being trialed clinically. Their rapid proliferation in vitro is essential to optimize clinical application, with neuregulins (NRG) being potential mitogens. We examined the effects of NRG-1beta, NRG-2alpha, and NRG3 on proliferation of p75-immunopurified adult OEG. OEG were grown in serum-containing medium with added bovine pituitary extract and forskolin (added mitogens) or in serum-containing medium (no added mitogens). Cultures were switched to chemically defined medium (no added mitogens or serum), NRG added and OEG proliferation assayed using BrdU. OEG grown initially with added mitogens were not responsive to added NRGs and pre-exposure to forskolin and pituitary extract increased basal proliferation rates so that OEG no longer responded to added NRG. However, NRG promoted proliferation but only if cells were initially grown in mitogen-free medium. Primary OEG express ErbB2, ErbB3, and small levels of ErbB4 receptors; functional blocking indicates that ErbB2 and ErbB3 are the main NRG receptors utilized in the presence of NRG-1beta. The long-term stimulation of OEG proliferation by initial culture conditions raises the possibility of manipulating OEG before therapeutic transplantation.

Comparison of cell populations derived from canine olfactory bulb and olfactory mucosal cultures

OBJECTIVE

To evaluate the numbers and proportions of olfactory ensheathing cells (OECs) in cell cultures derived from the olfactory bulb (OB) and olfactory mucosa of dogs.

ANIMALS

7 dogs.

PROCEDURES

OB tissue and olfactory mucosa from the nasal cavity and frontal sinus were obtained from euthanatized dogs and prepared for cell culture. At 7, 14, and 21 days of culture in vitro, numbers and proportions of OECs, astrocytes, and fibroblasts were determined via immunocytochemistry. Antibody against the low-affinity nerve growth factor receptor p75 was used to identify OECs, antibody against glial fibrillary acidic protein was used to identify astrocytes, and antibody against fibronectin was used to identify fibroblasts.

RESULTS

Cultured OECs derived from the olfactory mucosa of the nasal cavity and frontal sinus had similar characteristics. However, whereas OECs in the OB cell cultures constituted approximately 50% of the cells at 7 days and approximately 75% at 21 days the proportion of OECs in cultures derived from both mucosal types was much lower, with approximately 40% OECs at 7 days and approximately 25% at 21 days. Analysis of OEC numbers revealed that these changes were accompanied by corresponding decreases and increases in the population of cells with fibronectin receptors.

CONCLUSIONS AND CLINICAL RELEVANCE

Although olfactory mucosal cell cultures yielded a sufficient number of OECs for spinal cord transplantation procedures in dogs, modification of culture conditions would be required to ensure that the derived cell population contained a sufficient proportion of OECs.

Age-related changes in cell density and the proliferation rate of olfactory ensheathing cells in the lamina propria of postnatal mouse olfactory mucosa

We investigated age-related changes in the distribution and proliferation of olfactory ensheathing cells (OECs) in postnatal mouse olfactory mucosa. In contrast to reported data on other glial cell types in the peripheral and central nervous systems, OEC cell density in the olfactory nerve bundles in the lamina propria remained almost constant from 10 days through 16 months of age. Electron microscopy of the nerve bundles revealed that axon packing density also was constant during that period. These findings suggest that the ratio of the number of OECs to the unit length of the olfactory neuron axons ensheathed by them does not change markedly throughout the lifetime of mice in an undisturbed condition. By contrast, OEC proliferative density decreased rapidly in the 10-day to 1-month-old period, showing a significant difference, and for the rest of life remained at low level, similar to previous values reported for other glial cell types.

Neurotrophin 3 promotes purification and proliferation of olfactory ensheathing cells from human nose

Several studies have demonstrated the potential of olfactory ensheathing cells for the repair of central and peripheral nerve injury. However, the majority of these studies have been performed with olfactory ensheathing cells derived from the olfactory bulbs, situated inside the skull. A more clinically relevant source of olfactory ensheathing cells is the olfactory mucosa, located in the nose. To be successful, an autologous transplant of nasal ensheathing glia would require a large number of purified cells. To address this issue, we have focused our research on three neurotrophic factors, namely nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), and neurotrophin 3 (NT3). We show here that their respective receptors, TrkA, TrkB, TrkC, as well as p75(NTR) (the low affinity NGF receptor), are expressed in vitro by the nasal ensheathing cells; the three neurotrophins promote purification and proliferation of these glial cells, with an optimal concentration of 50 ng/ml; and human ensheathing cells can be easily biopsied and highly purified using a serum-free medium supplemented with NT3. This technique opens the door for clinical trials in which nasal ensheathing cells will be autotransplanted in humans suffering from nerve injury.

Lysophosphatidic acid regulates the proliferation and migration of olfactory ensheathing cells in vitro

Olfactory ensheathing cells (OECs) are a unique type of macroglia with axonal growth-promoting properties. However, our understanding of the factors that regulate OECs is at early stages. Lysophosphatidic acid (LPA) is a lipid that influences diverse functions in the nervous system. Recent studies suggest that glial cells, including astrocytes and Schwann cells, are important targets of LPA. However, the influences of LPA on OECs are not known. To address if LPA can influence OECs, we examined effects of LPA on the proliferation and migration of OECs and intracellular effector events. Initially, we observed that OECs expressed the genes for LPA1, LPA2, and LPA3 receptors. When OECs were treated with LPA, we observed stimulated proliferation and migration of OECs. Treatment of OECs with LPA also induced actin cytoskeleton reorganization and focal adhesion assembly. These effects of LPA were blocked by treatment with C3 exoenzyme or Y-27632, which inhibit Rho-GTPase and Rho-associated kinase, respectively. Effects of LPA on OEC proliferation were blocked by the MEK inhibitors PD098059 and U0126 and by the phosphotidylinositol 3-kinase (PI 3-K) inhibitors LY0294002 and wortmannin. These results show that LPA acts via Rho-GTPase, MAPK, and PI 3-K signaling cascades to influence OEC proliferation, migration, and cytoskeleton assembly.

Olfactory ensheathing cells of the lamina propria in vivo and in vitro

Olfactory ensheathing cells (OECs) continuously support the regeneration of olfactory receptor neurons (ORNs). In addition, OECs promote regeneration of neurons within the CNS in a number of transplantation paradigms, but details of exactly how they support regeneration remain elusive. The majority of studies using OECs to promote regeneration have thus far focused on understanding the cell biology of OECs purified from the olfactory bulb (OB). Here we show that a population of OECs similar to those obtained from the OB is present in the lamina propria (LP) beneath the olfactory epithelium (OE). These OECs are the first glial cells encountered by the axons of developing ORNs as they exit the OE and display distinct and variable expression of p75, S100beta, GFAP, and O4, characteristic markers of bulb OECs. Once purified in vitro, they display Schwann cell-like and astrocyte-like properties and expand rapidly. In addition to resembling OB-OECs, LP-OECs also express a unique combination of developmentally important proteins-CD 44, beta1 integrin, P200, Notch 3, NG2, VEGF, and PACAP and CREB binding protein (CBP/p300)-not previously reported in OB-OECs. These data suggest that LP-OECs, like OB-OECs, are a developmentally distinct class of glia that are capable of both immature and mature function, depending on environmental stimuli, within the adult nervous system.

Hepatocyte growth factor/scatter factor facilitates migration of GN-11 immortalized LHRH neurons

The molecular cues regulating the migratory process of LHRH neurons from the olfactory placode into the brain are not well known, but gradients of chemotropic and chemorepellent factors secreted by the targets are likely to play a key role in guidance mechanisms. Hepatocyte growth factor/scatter factor (HGF/SF) is a pleiotropic cytokine inducing cell migration. It is involved in a variety of developmental processes through interaction with its receptor c-Met. Here we show that c-Met-antibody labels LHRH migrating neurons in the olfactory mesenchyme of E12 mouse and analyze the potential chemotropic effect of HGF/SF on two immortalized LHRH cell lines, GT1-7 and GN11, isolated from tumors developed in the hypothalamus and in the olfactory bulb, respectively. By RT-PCR analysis, Western blotting, and immunocytochemistry, we provide evidence for a high level of c-Met expression in GN11, but not in GT1-7, cells. In addition, HGF/SF treatment promotes specific migratory activity of GN11 cells, as demonstrated by collagen gel assay, time-lapse video microscopy, and Boyden's chamber experiments. Such promotion is inhibited by the neutralizing antibody. The data reported here represent the first direct evidence of a chemotactic effect of HGF/SF on immortalized LHRH neurons.

Hepatocyte growth factor stimulates the proliferation and migration of oligodendrocyte precursor cells

Hepatocyte growth factor (HGF) was initially identified as a potent mitogen for mature hepatocytes and has since been found to affect a variety of cells. Evidence suggests that HGF may also influence the nervous system, in that HGF stimulates the proliferation of myelin-forming Schwann cells and olfactory ensheathing cells. However, it is not known whether HGF influences oligodendrocytes. To address this issue, oligodendrocyte precursors were obtained from neonatal rat cerebra and cultured. Immunostaining and Western blotting revealed expression of both HGF and the HGF receptor (c-Met) by cultured oligodendrocytes. When the ability of HGF to stimulate oligodendrocyte division and migration was examined, we observed that treatment with HGF (10-50 ng/ml) elicited twofold increases in oligodendrocyte precursor proliferation. HGF also enhanced oligodendrocyte precursor migration, with 2.5-fold increases in rates of migration seen after treatment for 8 hr. HGF also influenced inducing the oligodendrocyte cytoskeleton by altering patterns of F-actin and beta-tubulin distribution and enhanced the expression of actin and beta-tubulin. These observations show that a functional HGF/c-Met system is present in oligodendrocytes, which can influence the growth, development, and cytoskeletal organization of oligodendrocytes.