Matrix metalloproteinase expression in the olfactory epithelium

Effect of intranasal administration of concentrated growth factors on regeneration of the olfactory epithelium in an olfactory dysfunction-induced rat model

OBJECTIVE

The development of treatments that promote the regenerative capacity of the olfactory epithelium (OE) is desirable. This study aimed to evaluate the effects of intranasal administration of concentrated growth factors (CGFs) in a rat model of olfactory dysfunction.

STUDY DESIGN

Animal study.

METHODS

Nineteen male rats were used. Fourteen olfactory dysfunction models were created by intraperitoneal administration of 3-methylindole. We randomly divided the rats from the olfactory dysfunction model after 1 week into the CGF or saline group; CGFs were administered to seven animals and saline to seven animals. Behavioral assessments using the avoidance test were conducted until day 28 after CGF/saline administration. On day 28, histological evaluation was conducted to determine olfactory epithelial thickness and the olfactory marker protein (OMP)-positive cell count. Five animals were intraperitoneally injected with saline as the control group.

RESULTS

The avoidance rate remained decreased until 28 days after CGF/saline administration, and there was no significant difference between the two groups. Olfactory epithelial thicknesses on day 28 were 38.64 ± 3.17 μm and 32.84 ± 4.50 μm in the CGF and saline groups, respectively. OE thickness was significantly thicker in the CGF group than in the saline group (P = 0.013). The numbers of OMP-positive cells were 40.29 ± 9.77/1.0 × 104 μm2 and 31.00 ± 3.69/1.0 × 104 μm2 in the CGF and saline groups, respectively. The number of OMP+ cells in the CGF group was significantly increased compared with that in the saline group (P = 0.009). Both groups showed no improvement compared with the control group (OE thickness: 54.08 ± 3.36 μm; OMP+ cell count: 56.90 ± 9.91/1.0 × 104 μm2).

CONCLUSIONS

The CGF group showed improved olfactory epithelial thickness and OMP-positive cell numbers compared with that in the saline group.

Dynamic Expression of Membrane Type 1-Matrix Metalloproteinase (Mt1-mmp/Mmp14) in the Mouse Embryo

MT1-MMP/MMP14 belongs to a subgroup of the matrix metalloproteinases family that presents a transmembrane domain, with a cytosolic tail and the catalytic site exposed to the extracellular space. Deficient mice for this enzyme result in early postnatal death and display severe defects in skeletal, muscle and lung development. By using a transgenic line expressing the LacZ reporter under the control of the endogenous Mt1-mmp promoter, we reported a dynamic spatiotemporal expression pattern for Mt1-mmp from early embryonic to perinatal stages during cardiovascular development and brain formation. Thus, Mt1-mmp shows expression in the endocardium of the heart and the truncus arteriosus by E8.5, and is also strongly detected during vascular system development as well as in endothelial cells. In the brain, LacZ reporter expression was detected in the olfactory bulb, the rostral cerebral cortex and the caudal mesencephalic tectum. LacZ-positive cells were observed in neural progenitors of the spinal cord, neural crest cells and the intersomitic region. In the limb, Mt1-mmp expression was restricted to blood vessels, cartilage primordium and muscles. Detection of the enzyme was confirmed by Western blot and immunohistochemical analysis. We suggest novel functions for this metalloproteinase in angiogenesis, endocardial formation and vascularization during organogenesis. Moreover, Mt1-mmp expression revealed that the enzyme may contribute to heart, muscle and brain throughout development.

Matrix metalloprotease-mediated cleavage of neural glial-related cell adhesion molecules activates quiescent olfactory stem cells via EGFR

Quiescent stem cells have been found in multiple adult organs, and activation of these stem cells is critical to the restoration of damaged tissues in response to injury or stress. Existing evidence suggests that extrinsic cues from the extracellular matrix or supporting cells of various stem cell niches may interact with intrinsic components to initiate stem cell differentiation, but the molecular and cellular mechanisms regulating their activation are not fully understood. In the present study, we find that olfactory horizontal basal cells (HBCs) are stimulated by neural glial-related cell adhesion molecules (NrCAMs). NrCAM activation requires matrix metalloproteases (MMPs) and epidermal growth factor receptors (EGFRs). Inhibiting MMP activity or EGFR activation not only blocks HBC proliferation in the cultured olfactory organoids, but also severely suppresses HBC proliferation in the olfactory epithelium following methimazole-induced injury, resulting in a delay of olfactory mucosa reconstitution and functional recovery of the injured mice. Both NrCAMs and EGFR are expressed by the HBCs and their expression increases upon injury. Our data indicate that MMP-mediated cleavage of NrCAMs serves as an autocrine or paracrine signal that activates EGFRs on HBCs to trigger HBC proliferation and differentiation to reconstruct the entire olfactory epithelium following injury.

Mild Fluid Percussion Injury Induces Diffuse Axonal Damage and Reactive Synaptic Plasticity in the Mouse Olfactory Bulb

Despite the regenerative capacity of the olfactory bulb (OB), head trauma causes olfactory disturbances in up to 30% of patients. While models of olfactory nerve transection, olfactory receptor neuron (ORN) ablation, or direct OB impact have been used to examine OB recovery, these models are severe and not ideal for study of OB synaptic repair. We posited that a mild fluid percussion brain injury (mFPI), delivered over mid-dorsal cortex, would produce diffuse OB deafferentation without confounding pathology. Wild type FVB/NJ mice were subjected to mFPI and OB probed for ORN axon degeneration and onset of reactive synaptogenesis. OB extracts revealed 3 d postinjury elevation of calpain-cleaved 150-kDa αII-spectrin, an indicator of axon damage, in tandem with reduced olfactory marker protein (OMP), a protein specific to intact ORN axons. Moreover, mFPI also produced a 3-d peak in GFAP+ astrocyte and IBA1+ microglial reactivity, consistent with postinjury inflammation. OB glomeruli showed disorganized ORN axons, presynaptic degeneration, and glial phagocytosis at 3 and 7 d postinjury, all indicative of deafferentation. At 21 d after mFPI, normal synaptic structure re-emerged along with OMP recovery, supporting ORN afferent reinnervation. Robust 21 d postinjury upregulation of GAP-43 was consistent with the time course of ORN axon sprouting and synapse regeneration reported after more severe olfactory insult. Together, these findings define a cycle of synaptic degeneration and recovery at a site remote to non-contusive brain injury. We show that mFPI models diffuse ORN axon damage, useful for the study of time-dependent reactive synaptogenesis in the deafferented OB.

The multifaceted role of metalloproteinases in physiological and pathological conditions in embryonic and adult brains

Matrix metalloproteinases (MMPs) are a large family of ubiquitous extracellular endopeptidases, which play important roles in a variety of physiological and pathological conditions, from the embryonic stages throughout adult life. Their extraordinary physiological "success" is due to concomitant broad substrate specificities and strict regulation of their expression, activation and inhibition levels. In recent years, MMPs have gained increasing attention as significant effectors in various aspects of central nervous system (CNS) physiology. Most importantly, they have been recognized as main players in a variety of brain disorders having different etiologies and evolution. A common aspect of these pathologies is the development of acute or chronic neuroinflammation. MMPs play an integral part in determining the result of neuroinflammation, in some cases turning its beneficial outcome into a harmful one. This review summarizes the most relevant studies concerning the physiology of MMPs, highlighting their involvement in both the developing and mature CNS, in long-lasting and acute brain diseases and, finally, in nervous system repair. Recently, a concerted effort has been made in identifying therapeutic strategies for major brain diseases by targeting MMP activities. However, from this revision of the literature appears clear that MMPs have multifaceted functional characteristics, which modulate physiological processes in multiple ways and with multiple consequences. Therefore, when choosing MMPs as possible targets, great care must be taken to evaluate the delicate balance between their activation and inhibition and to determine at which stage of the disease and at what level they become active in order maximize chances of success.

Short-Lived Human Umbilical Cord-Blood-Derived Neural Stem Cells Influence the Endogenous Secretome and Increase the Number of Endogenous Neural Progenitors in a Rat Model of Lacunar Stroke

Stroke is the leading cause of severe disability, and lacunar stroke is related to cognitive decline and hemiparesis. There is no effective treatment for the majority of patients with stroke. Thus, stem cell-based regenerative medicine has drawn a growing body of attention due to the capabilities for trophic factor expression and neurogenesis enhancement. Moreover, it was shown in an experimental autoimmune encephalomyelitis (EAE) model that even short-lived stem cells can be therapeutic, and we have previously observed that phenomenon indirectly. Here, in a rat model of lacunar stroke, we investigated the molecular mechanisms underlying the positive therapeutic effects of short-lived human umbilical cord-blood-derived neural stem cells (HUCB-NSCs) through the distinct measurement of exogenous human and endogenous rat trophic factors. We have also evaluated neurogenesis and metalloproteinase activity as cellular components of therapeutic activity. As expected, we observed an increased proliferation and migration of progenitors, as well as metalloproteinase activity up to 14 days post transplantation. These changes were most prominent at the 7-day time point when we observed 30 % increases in the number of bromodeoxyuridine (BrdU)-positive cells in HUCB-NSC transplanted animals. The expression of human trophic factors was present until 7 days post transplantation, which correlated well with the survival of the human graft. For these 7 days, the level of messenger RNA (mRNA) in the analyzed trophic factors was from 300-fold for CNTF to 10,000-fold for IGF, much higher compared to constitutive expression in HUCB-NSCs in vitro. What is interesting is that there was no increase in the expression of rat trophic factors during the human graft survival, compared to that in non-transplanted animals. However, there was a prolongation of a period of increased trophic expression until 14 days post transplantation, while, in non-transplanted animals, there was a significant drop in rat trophic expression at that time point. We conclude that the positive therapeutic effect of short-lived stem cells may be related to the net increase in the amount of trophic factors (rat + human) until graft death and to the prolonged increase in rat trophic factor expression subsequently.

Translational potential of olfactory mucosa for the study of neuropsychiatric illness

The olfactory mucosa (OM) is a unique source of regenerative neural tissue that is readily obtainable from living human subjects and thus affords opportunities for the study of psychiatric illnesses. OM tissues can be used, either as ex vivo OM tissue or in vitro OM-derived neural cells, to explore parameters that have been difficult to assess in the brain of living individuals with psychiatric illness. As OM tissues are distinct from brain tissues, an understanding of the neurobiology of the OM is needed to relate findings in these tissues to those of the brain as well as to design and interpret ex vivo or in vitro OM studies. To that end, we discuss the molecular, cellular and functional characteristics of cell types within the olfactory mucosa, describe the organization of the OM and highlight its role in the olfactory neurocircuitry. In addition, we discuss various approaches to in vitro culture of OM-derived cells and their characterization, focusing on the extent to which they reflect the in vivo neurobiology of the OM. Finally, we review studies of ex vivo OM tissues and in vitro OM-derived cells from individuals with psychiatric, neurodegenerative and neurodevelopmental disorders. In particular, we discuss the concordance of this work with postmortem brain studies and highlight possible future approaches, which may offer distinct strengths in comparison to in vitro paradigms based on genomic reprogramming.

Time dependent integration of matrix metalloproteinases and their targeted substrates directs axonal sprouting and synaptogenesis following central nervous system injury

Over the past two decades, many investigators have reported how extracellular matrix molecules act to regulate neuroplasticity. The majority of these studies involve proteins which are targets of matrix metalloproteinases. Importantly, these enzyme/substrate interactions can regulate degenerative and regenerative phases of synaptic plasticity, directing axonal and dendritic reorganization after brain insult. The present review first summarizes literature support for the prominent role of matrix metalloproteinases during neuroregeneration, followed by a discussion of data contrasting adaptive and maladaptive neuroplasticity that reveals time-dependent metalloproteinase/substrate regulation of postinjury synaptic recovery. The potential for these enzymes to serve as therapeutic targets for enhanced neuroplasticity after brain injury is illustrated with experiments demonstrating that metalloproteinase inhibitors can alter adaptive and maladaptive outcome. Finally, the complexity of metalloproteinase role in reactive synaptogenesis is revealed in new studies showing how these enzymes interact with immune molecules to mediate cellular response in the local regenerative environment, and are regulated by novel binding partners in the brain extracellular matrix. Together, these different examples show the complexity with which metalloproteinases are integrated into the process of neuroregeneration, and point to a promising new angle for future studies exploring how to facilitate brain plasticity.

Tissue plasminogen activator deficiency promotes early phase regeneration in the olfactory epithelium after bulbectomy

BACKGROUND

Tissue type plasminogen activator (tPA) functions as a fibrinolytic factor in the blood and has unique roles in the nervous system. However, the role of tPA in the olfactory epithelium (OE) is still unclear. Generally, surgical ablation of the olfactory bulb (bulbectomy) triggers degeneration followed by regeneration of OE. In this experimental study, we investigated the role of tPA in OE regeneration.

METHODS

Wild-type (WT) mice and tPA-knockout (tPA(-/-) ) mice were subjected to bulbectomy. Reverse-transcription polymerase chain reaction (RT-PCR), in situ hybridization, and immunohistochemical examination was done to detect tPA expression in the olfactory bulb and OE. Cellular proliferation and apoptosis was also monitored in the OE.

RESULTS

Before bulbectomy, tPA was found to be expressed in the olfactory bulb and OE. OE degenerated to a similar extent in both strains between 0 and 3 days after bulbectomy. However, OE was thicker and contained more cells in tPA(-/-) mice than in WT mice at 7 days after bulbectomy. Moreover, the number of apoptotic bodies was reduced and the number of proliferating cells was increased in the OE of tPA(-/-) mice compared to WT mice, after bulbectomy. Transmission electron microscopy revealed continuous degeneration of the OE for up to 7 days after bulbectomy in WT mice. In contrast, we observed some intact olfactory vesicles and almost normal supporting cells in the OE of tPA(-/-) mice, at 7 days after bulbectomy.

CONCLUSION

The current findings show that the tPA-plasmin system plays an inhibitory role in the regulation of regeneration in the OE.

Matrix rigidity activates Wnt signaling through down-regulation of Dickkopf-1 protein

Cells respond to changes in the physical properties of the extracellular matrix with altered behavior and gene expression, highlighting the important role of the microenvironment in the regulation of cell function. In the current study, culture of epithelial ovarian cancer cells on three-dimensional collagen I gels led to a dramatic down-regulation of the Wnt signaling inhibitor dickkopf-1 with a concomitant increase in nuclear β-catenin and enhanced β-catenin/Tcf/Lef transcriptional activity. Increased three-dimensional collagen gel invasion was accompanied by transcriptional up-regulation of the membrane-tethered collagenase membrane type 1 matrix metalloproteinase, and an inverse relationship between dickkopf-1 and membrane type 1 matrix metalloproteinase was observed in human epithelial ovarian cancer specimens. Similar results were obtained in other tissue-invasive cells such as vascular endothelial cells, suggesting a novel mechanism for functional coupling of matrix adhesion with Wnt signaling.

Morphological assessment of the luminal surface of olfactory epithelium in mice deficient in tissue plasminogen activator following bulbectomy

OBJECTIVE

This study aimed to investigate the function of tissue plasminogen activator in the olfactory epithelium of mice following neural injury.

METHOD

Transmission electron microscopy was used to study the changes in the morphology of the olfactory epithelium 1-7 days after surgical ablation of the olfactory bulb (bulbectomy).

RESULTS

Prior to bulbectomy, a uniformly fine material was observed within some regions of the olfactory epithelium of mice deficient in tissue plasminogen activator. At 2-3 days after bulbectomy, there were degenerative changes in the olfactory epithelium. At 5-7 days after bulbectomy, we noted drastic differences in olfactory epithelium morphology between mice deficient in tissue plasminogen activator and wild-type mice (comparisons were made using findings from a previous study). The microvilli seemed to be normal and olfactory vesicles and receptor neuron dendrites were largely intact in the olfactory epithelium of mice deficient in tissue plasminogen activator.

CONCLUSION

The tissue plasminogen activator plasmin system may inhibit the regeneration of the olfactory epithelium in the early stages following neural injury.

The potential role of metalloproteinases in neurogenesis in the gerbil hippocampus following global forebrain ischemia

BACKGROUND

Matrix metalloproteinases (MMPs) have recently been considered to be involved in the neurogenic response of adult neural stem/progenitor cells. However, there is a lack of information showing direct association between the activation of MMPs and the development of neuronal progenitor cells involving proliferation and/or further differentiation in vulnerable (Cornus Ammoni-CA1) and resistant (dentate gyrus-DG) to ischemic injury areas of the brain hippocampus.

PRINCIPAL FINDINGS

We showed that dynamics of MMPs activation in the dentate gyrus correlated closely with the rate of proliferation and differentiation of progenitor cells into mature neurons. In contrast, in the damaged CA1 pyramidal cells layer, despite the fact that some proliferating cells exhibited antigen specific characteristic of newborn neuronal cells, these did not attain maturity. This coincides with the low, near control-level, activity of MMPs. The above results are supported by our in vitro study showing that MMP inhibitors interfered with both the proliferation and differentiation of the human neural stem cell line derived from umbilical cord blood (HUCB-NSCs) toward the neuronal lineage.

CONCLUSION

Taken together, the spatial and temporal profiles of MMPs activity suggest that these proteinases could be an important component in neurogenesis-associated processes in post-ischemic brain hippocampus.

MMP-2 is involved in synaptic remodeling after cochlear lesion

Lesion-induced neuroplasticity, including fiber degeneration, axonal growth, and synaptogenesis, involves dynamical changes of the extracellular matrix. We discovered that the matrix metalloprotease-2 (MMP-2), a major actor in extracellular matrix recomposition, is changed in distribution and increased in amount in the ventral cochlear nucleus after unilateral cochlear ablation. There was a remarkable coincidence of MMP-2 accumulation and GAP-43 expression in time and space. We obtained evidence indicating that MMP-2 is delivered to regions of emerging GAP-43 positive synaptic endings by postsynaptic neurons as well as by adjoining astrocytes. These results indicate a major role of MMP-2 in lesion-induced remodeling of central auditory networks and suggest a cooperativity with GAP-43-directed axonal outgrowth and synaptogenesis.

Fezf1 is required for penetration of the basal lamina by olfactory axons to promote olfactory development

In the development of the olfactory system, olfactory receptor neurons (ORNs) project their axons from the olfactory epithelium (OE) to the olfactory bulb (OB). The surface of the OB is covered by the central nervous system (CNS) basal lamina. To establish this connection, pioneer axons of the ORNs penetrate the CNS basal lamina at embryonic day 12.5 in mice. The importance of this penetration is highlighted by the Kallmann syndrome. However, little has been known about the molecular mechanism underlying this penetration process. Fezf1 (also called as Fez, Zfp312-like, and 3110069A13Rik) is a C2H2-type zinc-finger gene expressed in the OE and hypothalamic region in mice. In Fezf1-deficient mice, ORN axons (olfactory axons) do not reach the OB. Here we demonstrate that Fezf1-deficient olfactory axons do not penetrate the CNS basal lamina in vivo, and the penetration activity of the axons in Matrigel is impaired in vitro. Coculture experiments using the OE and OB reveal that axonal projection of ORNs is rescued in Fezf1-deficient mice in which the meninges including the CNS basal lamina are removed from the mutant OB. These data indicate that Fezf1 is required for the penetration of olfactory axons through the CNS basal lamina before they innervate the OB.

Thallium Transport and the Evaluation of Olfactory Nerve Connectivity between the Nasal Cavity and Olfactory Bulb

Little is known regarding how alkali metal ions are transported in the olfactory nerve following their intranasal administration. In this study, we show that an alkali metal ion, thallium is transported in the olfactory nerve fibers to the olfactory bulb in mice. The olfactory nerve fibers of mice were transected on both sides of the body under anesthesia. A double tracer solution (thallium-201, (201)Tl; manganese-54, (54)Mn) was administered into the nasal cavity the following day. Radioactivity in the olfactory bulb and nasal turbinate was analyzed with gamma spectrometry. Auto radiographic images were obtained from coronal slices of frozen heads of mice administered with (201)Tl or (54)Mn. The transection of the olfactory nerve fibers was confirmed with a neuronal tracer. The transport of intranasal administered (201)Tl/(54)Mn to the olfactory bulb was significantly reduced by the transection of olfactory nerve fibers. The olfactory nerve transection also significantly inhibited the accumulation of fluoro-ruby in the olfactory bulb. Findings indicate that thallium is transported by the olfactory nerve fibers to the olfactory bulb in mice. The assessment of thallium transport following head injury may provide a new diagnostic method for the evaluation of olfactory nerve injury.

The matrix metalloproteinases and CNS plasticity: an overview

The matrix metalloproteinases (MMPs) are expressed in response to pro-inflammatory stimuli and other triggers. The MMPs cleave numerous substrates including extracellular matrix components, cytokines and growth factors. In the CNS, while most studied in the context of disease, the many physiological functions of the MMPs are now becoming appreciated. This review provides an overview of the growing body of evidence for physiological roles of MMPs both in CNS development and in CNS plasticity in normal brain functioning, including learning and memory, as well as in CNS repair and reorganization as part of the neuroimmune response to injury.

Comparison of in vivo and in vitro gene expression profiles in subventricular zone neural progenitor cells from the adult mouse after middle cerebral artery occlusion

Stroke stimulates neurogenesis in the adult rodent brain. The molecules that mediate stroke-induced neurogenesis are not definitely known. Using microarrays containing approximately 400 known genes associated with stem cell and angiogenesis, we compared transcriptional profiles of subventricular zone (SVZ) tissue with cultured neural progenitor cells isolated from the SVZ 7 days after ischemic stroke in the adult mouse. In SVZ tissue, we found that stroke upregulated 58 genes which are involved in multiple signaling pathways during embryonic development, suggesting that stroke recaptures embryonic molecular signals. In neural progenitor cells cultured in growth medium, 23 gene expressions were increased after stroke and 8 of 23 genes overlapped with upregulated genes in stroke SVZ tissue. Expression alterations of selected genes were confirmed by real-time RT-PCR and immunohistochemistry. These in vivo and in vitro data provide new insight into the genetic program of adult SVZ neural progenitor cells after stroke and demonstrate gene expression differences between SVZ tissue and cultured SVZ cells.

Response of matrix metalloproteinase-9 to olfactory nerve injury

Matrix metalloproteinases function in the remodeling of the extracellular matrix during growth and development as well as in injury and disease processes. We examined the role of matrix metalloproteinase-9 in a model of olfactory nerve injury in mice. We measured changes in matrix metalloproteinase-9 protein levels for up to 60 days following olfactory nerve transection. Matrix metalloproteinase-9 levels increased within hours after injury, peaked at day 1 and were elevated for approximately 2 weeks before returning to control levels over the 60-day time period. The increase in matrix metalloproteinase-9 was temporally associated with the degeneration of olfactory neurons that follows nerve transection and with increased gliosis. Our results demonstrate a temporal relationship between matrix metalloproteinase-9 elevation, degeneration of olfactory neurons and gliosis.

Identification and distribution of mouse carboxypeptidase A-6

Carboxypeptidase A-6 (CPA6) was recently discovered in the human genome. To gain information regarding the potential function of this novel protein, the mouse homolog of CPA6 was identified using a combination of bioinformatics and reverse transcriptase-polymerase chain reaction (RT-PCR). In addition, homologs in rat, chicken, and frog were identified using a bioinformatics approach. The distribution of CPA6 mRNA in mouse tissues was examined using RT-PCR and in situ hybridization. A strong RT-PCR signal is detectable in olfactory bulb, and much lower levels are present in other regions such as the cerebral cortex, hippocampus, hypothalamus, striatum, and medulla. In peripheral tissues, a moderate RT-PCR signal is present in epididymis, and low levels are detectable in colon and spleen. The high level of CPA6 in adult mouse brain olfactory bulb was confirmed by in situ hybridization. Lower levels of CPA6 mRNA were found to be present in the cingulate cortex, lateral septum, pontine nucleus, and inferior olivary nucleus of the hindbrain. Within the olfactory bulb, CPA6 mRNA is enriched in the mitral and granular layer. A lower level of CPA6 mRNA is present in the internal and external plexiform layers, and no signal is detectable in the olfactory nerve layer. The distribution was also examined in whole embryos at embryonic day 14.5 and CPA6 mRNA was found to be enriched in eye, ear, osteoblasts, stomach, skin, dorsal root ganglia, and throughout the CNS. The presence of CPA6 mRNA in the rectus muscle layer of the eye at embryonic day 14.5 is consistent with the observation that the CPA6 gene is disrupted in a patient with Duane syndrome, a congenital eye defect. Taken together, the distribution of CPA6 suggests a specific role in a limited number of tissues, and it is possible that this role involves an aspect of cell migration.

Genetic expression profile of olfactory ensheathing cells is distinct from that of Schwann cells and astrocytes

Olfactory ensheathing cells (OECs) accompany the axons of olfactory receptor neurons, which regenerate throughout life, from the olfactory mucosa into the olfactory bulb. OECs have shown widely varying efficacy in repairing the injured nervous system. Analysis of the transcriptome of OECs will help in understanding their biology and will provide tools for investigating the mechanisms of their efficacy and interactions with host tissues in lesion models. In this study, we compared the transcriptional profile of cultured OECs with that of Schwann cells (SCs) and astrocytes (ACs), two glial cell types to which OECs have similarities. Two biological replicates of RNA from cultured OECs, SCs, and ACs were hybridized to long oligo rat 5K arrays against a common reference pool of RNA (50% cultured fibroblast RNA and 50% neonatal rat brain RNA). Transcriptional profiles were analyzed by hierarchical clustering, Principal Components Analysis, and the Venn diagram. The three glial cell types had similarly increased or decreased expression of numerous transcripts compared with the reference. However, OECs were distinguishable from both SCs and ACs by a modest number of transcripts, which were significantly enriched or depleted. Furthermore, OECs and SCs were more closely related to each other than to ACs. Expression of selected transcripts not previously characterized in OECs, such as Lyz, Timp2, Gro1 (Cxcl1), Ccl2 (MCP1), Ctgf, and Cebpb, was validated by real-time reverse transcription-polymerase chain reaction (RT-PCR); immunohistochemistry in cultured OECs, SCs, and ACs, and adult tissues was performed to demonstrate their expression at the protein level.

Olfactory horizontal basal cells demonstrate a conserved multipotent progenitor phenotype

Stem cells of adult regenerative organs share a common goal but few established conserved mechanisms. Within the neural stem cell niche of the mouse olfactory epithelium, we identified a combination of extracellular matrix (ECM) receptors that regulate adhesion and mitosis in non-neural stem cells [intercellular adhesion molecule-1 (ICAM-1), beta1, beta4, and alpha-1, -3, and -6 integrins] and on horizontal basal cells (HBCs), candidate olfactory neuro-epithelial progenitors. Using ECM receptors as our guide, we recreated a defined microenvironment in vitro that mimics olfactory basal lamina and, when supplemented with epidermal growth factor, transforming growth factor alpha, and leukemia inhibitory factor, allows us to preferentially expand multiple clonal adherent colony phenotypes from individual ICAM-1+ and ICAM-1+/beta1 integrin+-selected HBCs. The most highly mitotic colony-forming HBCs demonstrate multipotency, spontaneously generating more ICAM-positive presumptive HBCs, a combination of olfactory neuroglial progenitors, and neurons of olfactory and potentially nonolfactory phenotypes. HBCs thus possess a conserved adhesion receptor expression profile similar to non-neural stem cells, preferential self-replication in an in vitro environment mimicking their in vivo niche, and contain subpopulations of cells that can produce multiple differentiated neuronal and glial progeny from within and beyond the olfactory system in vitro.