Stem Cell Therapy for Tendon Regeneration: Current Status and Future Directions.

In adults the healing tendon generates fibrovascular scar tissue and recovers never histologically, mechanically, and functionally which leads to chronic and to degenerative diseases. In this review, the processes and mechanisms of tendon development and fetal regeneration in comparison to adult defect repair and degeneration are discussed in relation to regenerative therapeutic options. We focused on the application of stem cells, growth factors, transcription factors, and gene therapy in tendon injury therapies in order to intervene the scarring process and to induce functional regeneration of the lesioned tissue. Outlines for future therapeutic approaches for tendon injuries will be provided.

Single-Cell Expression Profiling and Proteomics of Primordial Germ Cells, Spermatogonial Stem Cells, Adult Germ Stem Cells, and Oocytes.

The mammalian germ cells, cell assemblies, tissues, and organs during development and maturation have been extensively studied at the tissue level. However, to investigate and understand the fundamental insights at the molecular basis of germ and stem cells, their cell fate plasticity, and determination, it is of most importance to analyze at the large scale on the single-cell level through different biological windows. Here, modern molecular techniques optimized for single-cell analysis, including single fluorescence-activated cell sorting (FACS) and single-cell RNA sequencing (scRNA-seq) or microfluidic high-throughput quantitative real-time polymerase chain reaction (qRT-PCR) for single-cell gene expression and liquid chromatography coupled to tandem mass spectrometry (LC-MSMS) for protein profiling, have been established and are still getting optimized.This review aims on describing and discussing recent single-cell expression profiling and proteomics of different types of human germ cells, including primordial germ cells (PGCs), spermatogonial stem cells (SSCs), human adult germ stem cells (haGSCs), and oocytes.

Generation of pluripotent stem cells from adult human testis.

Human primordial germ cells and mouse neonatal and adult germline stem cells are pluripotent and show similar properties to embryonic stem cells. Here we report the successful establishment of human adult germline stem cells derived from spermatogonial cells of adult human testis. Cellular and molecular characterization of these cells revealed many similarities to human embryonic stem cells, and the germline stem cells produced teratomas after transplantation into immunodeficient mice. The human adult germline stem cells differentiated into various types of somatic cells of all three germ layers when grown under conditions used to induce the differentiation of human embryonic stem cells. We conclude that the generation of human adult germline stem cells from testicular biopsies may provide simple and non-controversial access to individual cell-based therapy without the ethical and immunological problems associated with human embryonic stem cells.

Potential stemness of frozen-thawed testicular biopsies without sperm in infertile men included into the in vitro fertilization programme.

We describe the potential stemness of a small amount of frozen-thawed testicular tissue without sperm obtained by biopsy from six patients undergoing assisted reproductive treatment. The patients were diagnosed with Sertoli Cell-Only Syndrome alone or combined with maturation arrest. Trying to provide the natural stem cell niche for cultured stem cells, all isolated cells from enzymatically degraded biopsies where cultured together in different culture media and the presence of putative mesenchymal and putative pluripotent ES-like stem cells was indicated using different methods. High throughput real-time quantitative PCR followed by multivariate analysis revealed the formation of distinct cell clusters reflecting high degree of similarity and some of these cell clusters expressed the genes characteristic for pluripotent stem cells. In the presence of the follicular fluid, prepared as serum, putative testicular stem cells showed a certain degree of plasticity, and spontaneously differentiated into adipose-like and neuronal-like cells. Additionally, using differentiation protocols putative testicular stem cells were differentiated into neuronal- and pancreatic-like cells. This study shows that in assisted reproduction programmes, testicular tissue with no sperm might be an important source of stem cells, although it is discarded in daily medical practice; this requires further research.

Neogenin mediates the action of repulsive guidance molecule.

Repulsive guidance molecule (RGM) is a recently identified protein implicated in both axonal guidance and neural tube closure. The avoidance of chick RGM in the posterior optic tectum by growing temporal, but not nasal, retinal ganglion cell axons is thought to contribute to visual map formation. In contrast to ephrins, semaphorins, netrins and slits, no receptor mechanism for RGM action has been defined. Here, an expression cloning strategy identified neogenin as a binding site for RGM, with a sub-nanomolar affinity. Consistent with selective axonal responsiveness to RGM, neogenin is expressed in a gradient across the chick retina. Neogenin is known to be one of several netrin-binding proteins but only neogenin interacts with RGM. The avoidance of RGM by temporal retinal axons is blocked by the anti-neogenin antibody and the soluble neogenin ectodomain. Dorsal root ganglion axons are unresponsive to RGM but are converted to a responsive state by neogenin expression. Thus, neogenin functions as an RGM receptor.

RGMb controls aggregation and migration of Neogenin-positive cells in vitro and in vivo.

The proliferation, migration and differentiation of dentate gyrus stem and precursor cells have aroused keen interest. Neogenin and RGMb are expressed in non-overlapping compartments of the developing dentate gyrus. While Neogenin is expressed in migrating and proliferating dentate precursors, RGMb is localized in structures bordering the developing dentate, such as cornus ammonis cells and Cajal-Retzius cells in the marginal zone including the hippocampal fissure. Co-immunoprecipitation and binding assays indicate a strong physical interaction. In vitro and in vivo migration of dentate neuroepithelial cells is abolished by RGMb, and cell adhesion is reduced when cells expressing Neogenin comes into contact with cells expressing RGMb. Ectopic expression of RGMb in organotypic slice cultures and after in utero electroporation in the hippocampus modifies precursor cell migration. Our results imply that Neogenin-RGMb interaction might be involved in neuronal migration in the dentate gyrus.

Evaluation of the osteogenic and chondrogenic differentiation capacities of equine adipose tissue-derived mesenchymal stem cells.

OBJECTIVE: To evaluate the proliferative behavior, telomere length, immunophenotype, and differentiation capacity of equine adipose tissue-derived mesenchymal stem cells (AT-MSCs). ANIMALS: 6 adult racing horses treated for articular Injury but otherwise healthy. PROCEDURES: AT-MSCs were Isolated from horses and expanded In Dulbecco modified Eagle medium enriched with fetal bovine serum and antimicrobials. Expression of cell surface antigens and telomere length were Investigated via flow cytometry Differentiation of MSCs Into chondrocytes, osteoblasts, and adipocytes was Induced In vitro by specific stimuli and was evaluated by analyzing marker genes with quantitative reverse transcriptase PCR assays and immunocytochemical and cytologie evaluations. RESULTS: Equine MSCs could be cultured up to the fifth passage before signs of senescence, apoptosis, and detachment Indicated cellular exhaustion. However, the AT-MSCs from 2 of 6 horses survived to later passages with Increased doubling rates and telomere lengths. The cells had a typical phenotype, with expression of CD14, CD73, CD90, CD105, CD140b, and CD164 antigens and a lack of CD34 and CD45 antigens. The cells also had a strong potential to differentiate Into osteoblasts, as characterized by Intense von Kossa and alizarin red staining as well as high Induction of osteopontin. Chondrogenic differentiation was detected via Alelan blue staining and expression of aggrecan and type II collagen Adipogenesis was Induced in AT-MSCs by supplementation of differentiation media with rabbit serum. CONCLUSIONS AND CLINICAL RELEVANCE: Equine AT-MSCs representa suitable cellular source for regenerative treatment of bone or cartilage defects, particularly when expanded In vitro for only a few passages.

The use of clinically approved small particles of iron oxide (SPIO) for labeling of mesenchymal stem cells aggravates clinical symptoms in experimental autoimmune encephalomyelitis and influences their in vivo distribution.

Multiple sclerosis (MS) is an inflammatory and demyelinating disease of the central nervous system (CNS). Mesenchymal stem cells (MSC) have been shown to ameliorate symptoms in experimental autoimmune encephalomyelitis (EAE), a model of MS. Using cloned MSC labeled with clinically approved small particles of iron oxide (SPIO) for treatment of EAE we analyzed the tissue localization of transferred cells. Treatment with unlabeled MSC led to disease amelioration compared to controls. In contrast, treatment with SPIO-labeled MSC lead to increase in disease severity. Treatment with SPIO alone did not alter disease course. After transplantation labeled and nonlabeled MSC were detected in the CNS and the liver with significantly more SPIO-labeled cells present in the CNS. Iron deposition was present in the group treated with SPIO-labeled MSC, indicating that in vivo the initially cell surface-bound iron detached from the MSC. These results could be of great importance for imaging of patients in the clinical setting, indicating that in vivo application of SPIO-labeled MSC needs to be performed with caution because the cell-derived exposure of iron can lead to disease aggravation.

Cell-Biological Requirements for the Generation of Dentate Gyrus Granule Neurons.

The dentate gyrus (DG) receives highly processed information from the associative cortices functionally integrated in the trisynaptic hippocampal circuit, which contributes to the formation of new episodic memories and the spontaneous exploration of novel environments. Remarkably, the DG is the only brain region currently known to have high rates of neurogenesis in adults (Andersen et al., 1966, 1971). The DG is involved in several neurodegenerative disorders, including clinical dementia, schizophrenia, depression, bipolar disorder and temporal lobe epilepsy. The principal neurons of the DG are the granule cells. DG granule cells generated in culture would be an ideal model to investigate their normal development and the causes of the pathologies in which they are involved and as well as possible therapies. Essential to establish such in vitro models is the precise definition of the most important cell-biological requirements for the differentiation of DG granule cells. This requires a deeper understanding of the precise molecular and functional attributes of the DG granule cells in vivo as well as the DG cells derived in vitro. In this review we outline the neuroanatomical, molecular and cell-biological components of the granule cell differentiation pathway, including some growth- and transcription factors essential for their development. We summarize the functional characteristics of DG granule neurons, including the electrophysiological features of immature and mature granule cells and the axonal pathfinding characteristics of DG neurons. Additionally, we discuss landmark studies on the generation of dorsal telencephalic precursors from pluripotent stem cells (PSCs) as well as DG neuron differentiation in culture. Finally, we provide an outlook and comment critical aspects.

RGMa inhibits neurite outgrowth of neuronal progenitors from murine enteric nervous system via the neogenin receptor in vitro.

The enteric nervous system (ENS) in vertebrate embryos is formed by neural crest-derived cells. During development, these cells undergo extensive migration from the vagal and sacral regions to colonize the entire gut, where they differentiate into neurons and glial cells. Guidance molecules like netrins, semaphorins, slits, and ephrins are known to be involved in neuronal migration and axon guidance. In the CNS, the repulsive guidance molecule (RGMa) has been implicated in neuronal differentiation, migration, and apoptosis. Recently, we described the expression of the subtypes RGMa and RGMb and their receptor neogenin during murine gut development. In the present study, we investigated the influence of RGMa on neurosphere cultures derived from fetal ENS. In functional in vitro assays, RGMa strongly inhibited neurite outgrowth of differentiating progenitors via the receptor neogenin. The repulsive effect of RGMa on processes of differentiated enteric neural progenitors could be demonstrated by collapse assay. The influence of the RGM receptor on ENS was also analyzed in neogenin knockout mice. In the adult large intestine of mutants we observed disturbed ganglia formation in the myenteric plexus. Our data indicate that RGMa may be involved in differentiation processes of enteric neurons in the murine gut.

Gene expression of the repulsive guidance molecules/neogenin in the developing and mature mouse visual system: C57BL/6J vs. the glaucoma model DBA/2J.

We used in-situ hybridization to analyze the expression patterns of three known members (a, b and c) of the RGM ("repulsive guidance molecule") gene family and of the RGMa receptor neogenin in a glaucoma mouse model (DBA/2J strain) and the C57BL/6J strain, which served as a control. In order to understand the role of the RGMs and neogenin in glaucoma, we characterized their expression patterns in the developing and mature mouse retina and in the optic nerve. In all investigated stages from post-natal day (P) 0 to 15 months (M) RGMa, RGMb and neogenin expression was detected in the ganglion cell layer (GCL). From P10 to 15M, we found RGMa, RGMb and neogenin expression in the inner nuclear layer (INL) and the outer nuclear layer (ONL). In P10- and older mice, the expression patterns of RGMa and its receptor neogenin were similar, while that of RGMb differed from both. As expected, no specific retinal expression of RGMc was detected in any of the age groups investigated. C57BL/6J mice and DBA/2J mice displayed no differences in the expression pattern of RGMa, RGMb, RGMc and neogenin in the developing retina (gestational age 14.5 days (E14.5), P0 & P10). Interestingly, we found a higher expression of RGMa, RGMb and neogenin in the retinas of all glaucoma-affected mice than in the age-matched control strain. Furthermore, we detected a higher RGMa and RGMb expression in the optic nerves of glaucoma-affected DBA/2J-mice older than 11M than in C57BL/6J mice of the same age.

Spinal cord injury-induced expression of the antiangiogenic endostatin/collagen XVIII in areas of vascular remodelling.

OBJECT: Spinal cord injury (SCI) induces the disruption of neural and vascular structures. In contrast to the emerging knowledge of mechanisms regulating the onset of the postinjury angiogenic response, little is known about counterregulatory signals. METHODS: Using immunohistochemical methods, the authors investigated the expression of the endogenous angiogenic inhibitor endostatin/collagen XVIII during the tissue remodeling response to SCI. RESULTS: After SCI, endostatin/collagen XVIII+ cells accumulated at the lesion site, in pannecrotic regions (especially in areas of cavity formation), at the lesion margin/areas of ongoing secondary damage, and in perivascular Virchow-Robin spaces. In remote areas (> 0.75 cm from the epicenter) a more modest accumulation of endostatin/collagen XVIII+ cells was observed, especially in areas of pronounced Wallerian degeneration. The numbers of endostatin/collagen XVIII+ cells reached their maximum on Day 7 after SCI. The cell numbers remained elevated in both, the lesion and remote regions, compared with control spinal cords for 4 weeks afterwards. In addition to being predominantly confined to ED1+-activated microglia/macrophages within the pannecrotic lesion core, endostatin/collagen XVIII expression was frequently detected by the endothelium/vessel walls. Numbers of lesional endostatin/collagen XVIII+ endothelium/vessel walls were found to increase early by Day 1 postinjury, reaching their maximum on Day 3 and declining subsequently to enhanced (above control) levels 30 days after SCI. CONCLUSIONS: The authors detected that in comparison to the early expression of neoangiogenic factors, there was a postponed lesional expression of the antiangiogenic endostatin/collagen XVIII. Furthermore, the expression of endostatin/collagen XVIII was localized to areas of neovascular pruning and retraction (cavity formation). The expression of endostatin/collagen XVIII by macrophages in a "late" activated phagocytic mode suggests that this factor plays a role in counteracting the preceding "early" neoangiogenic response after SCI.

Effect of single intralesional treatment of surgically induced equine superficial digital flexor tendon core lesions with adipose-derived mesenchymal stromal cells: a controlled experimental trial.

BACKGROUND: Adipose tissue is a promising source of mesenchymal stromal cells (MSCs) for the treatment of tendon disease. The goal of this study was to assess the effect of a single intralesional implantation of adipose tissue-derived mesenchymal stromal cells (AT-MSCs) on artificial lesions in equine superficial digital flexor tendons (SDFTs). METHODS: During this randomized, controlled, blinded experimental study, either autologous cultured AT-MSCs suspended in autologous inactivated serum (AT-MSC-serum) or autologous inactivated serum (serum) were injected intralesionally 2 weeks after surgical creation of centrally located SDFT lesions in both forelimbs of nine horses. Healing was assessed clinically and with ultrasound (standard B-mode and ultrasound tissue characterization) at regular intervals over 24 weeks. After euthanasia of the horses the SDFTs were examined histologically, biochemically and by means of biomechanical testing. RESULTS: AT-MSC implantation did not substantially influence clinical and ultrasonographic parameters. Histology, biochemical and biomechanical characteristics of the repair tissue did not differ significantly between treatment modalities after 24 weeks. Compared with macroscopically normal tendon tissue, the content of the mature collagen crosslink hydroxylysylpyridinoline did not differ after AT-MSC-serum treatment (p = 0.074) while it was significantly lower (p = 0.027) in lesions treated with serum alone. Stress at failure (p = 0.048) and the modulus of elasticity (p = 0.001) were significantly lower after AT-MSC-serum treatment than in normal tendon tissue. CONCLUSIONS: The effect of a single intralesional injection of cultured AT-MSCs suspended in autologous inactivated serum was not superior to treatment of surgically created SDFT lesions with autologous inactivated serum alone in a surgical model of tendinopathy over an observation period of 22 weeks. AT-MSC treatment might have a positive influence on collagen crosslinking of remodelling scar tissue. Controlled long-term studies including naturally occurring tendinopathies are necessary to verify the effects of AT-MSCs on tendon disease.

Spinal cord injury-induced expression of the immune-regulatory chemokine interleukin-16 caused by activated microglia/macrophages and CD8+ cells.

OBJECT: Spinal cord injury (SCI) elicits a strong inflammatory response that readily participates in lipid oxygenation, edema formation, apoptotic cell death, and tissue remodeling. Because cytokines determine the postinjury inflammatory milieu, the authors analyzed the expression of the immunomodulatory chemokine interleukin- 16 (IL- 16) after SCI. METHODS: The authors detected a highly significant, persistent, lesional accumulation of parenchymal IL-16+ microglia/macrophages, which reached a maximal level 3 days postinjury compared with control rats. The majority of cells that demonstrated positive labeling for IL-16 also had positive labeling for ED1 (> 70%) and OX-8/CD8; these cells exhibited the morphological hallmarks of activated microglia/macrophages and pronounced MHC Class II expression. In contrast to IL-16+ED1+ cells, IL-16+ microglia/macrophages that coexpressed OX-8 were exclusively seen in the pannecrotic lesion core. In addition, clustering of IL-16+ cells was observed in perivascular Virchow-Robin-like spaces in areas of the primary injury (lesion core) and in immediately adjacent areas of secondary injury. Furthermore, on Day 3 postinjury, IL-16+ microglia/macrophages were frequently observed in a perineuronal position. CONCLUSIONS: The early lesional accumulation of IL-16+ microglia/macrophages suggests a role for IL-16 in the early postinjury immune response such as recruitment and activation of immune cells, leading to microvessel clustering and secondary damage progression.

Expression of Genes Related to Germ Cell Lineage and Pluripotency in Single Cells and Colonies of Human Adult Germ Stem Cells.

The aim of this study was to elucidate the molecular status of single human adult germ stem cells (haGSCs) and haGSC colonies, which spontaneously developed from the CD49f MACS and matrix- (collagen-/laminin+ binding-) selected fraction of enriched spermatogonia. Single-cell transcriptional profiling by Fluidigm BioMark system of a long-term cultured haGSCs cluster in comparison to human embryonic stem cells (hESCs) and human fibroblasts (hFibs) revealed that haGSCs showed a characteristic germ- and pluripotency-associated gene expression profile with some similarities to hESCs and with a significant distinction from somatic hFibs. Genome-wide comparisons with microarray analysis confirmed that different haGSC colonies exhibited gene expression heterogeneity with more or less pluripotency. The results of this study confirm that haGSCs are adult stem cells with a specific molecular gene expression profile in vitro, related but not identical to true pluripotent stem cells. Under ES-cell conditions haGSC colonies could be selected and maintained in a partial pluripotent state at the molecular level, which may be related to their cell plasticity and potential to differentiate into cells of all germ layers.

Tracking of autologous adipose tissue-derived mesenchymal stromal cells with in vivo magnetic resonance imaging and histology after intralesional treatment of artificial equine tendon lesions--a pilot study.

BACKGROUND: Adipose tissue-derived mesenchymal stromal cells (AT-MSCs) are frequently used to treat equine tendinopathies. Up to now, knowledge about the fate of autologous AT-MSCs after intralesional injection into equine superficial digital flexor tendons (SDFTs) is very limited. The purpose of this study was to monitor the presence of intralesionally injected autologous AT-MSCs labelled with superparamagnetic iron oxide (SPIO) nanoparticles and green fluorescent protein (GFP) over a staggered period of 3 to 9 weeks with standing magnetic resonance imaging (MRI) and histology. METHODS: Four adult warmblood horses received a unilateral injection of 10 × 10(6) autologous AT-MSCs into surgically created front-limb SDFT lesions. Administered AT-MSCs expressed lentivirally transduced reporter genes for GFP and were co-labelled with SPIO particles in three horses. The presence of AT-MSCs in SDFTs was evaluated by repeated examinations with standing low-field MRI in two horses and post-mortem in all horses with Prussian blue staining, fluorescence microscopy and with immunofluorescence and immunohistochemistry using anti-GFP antibodies at 3, 5, 7 and 9 weeks after treatment. RESULTS: AT-MSCs labelled with SPIO particles were detectable in treated SDFTs during each MRI in T2*- and T1-weighted sequences until the end of the observation period. Post-mortem examinations revealed that all treated tendons contained high numbers of SPIO- and GFP-labelled cells. CONCLUSIONS: Standing low-field MRI has the potential to track SPIO-labelled AT-MSCs successfully. Histology, fluorescence microscopy, immunofluorescence and immunohistochemistry are efficient tools to detect labelled AT-MSCs after intralesional injection into surgically created equine SDFT lesions. Intralesional injection of 10 × 10(6) AT-MSCs leads to the presence of high numbers of AT-MSCs in and around surgically created tendon lesions for up to 9 weeks. Integration of injected AT-MSCs into healing tendon tissue is an essential pathway after intralesional administration. Injection techniques have to be chosen deliberately to avoid reflux of the cell substrate injected. In vivo low-field MRI may be used as a non-invasive tool to monitor homing and engraftment of AT-MSCs in horses with tendinopathy of the SDFT.

Derivation of Pluripotent Cells from Mouse SSCs Seems to Be Age Dependent.

Here, we aimed to answer important and fundamental questions in germ cell biology with special focus on the age of the male donor cells and the possibility to generate embryonic stem cell- (ESC-) like cells. While it is believed that spermatogonial stem cells (SSCs) and truly pluripotent ESC-like cells can be isolated from adult mice, it remained unknown if the spontaneous conversion of SSCs to ESC-like cells fails at some age. Similarly, there have been differences in the literature about the duration of cultures during which ESC-like cells may appear. We demonstrate the possibility to derive ESC-like cells from SSC cultures until they reach adolescence or up to 7 weeks of age, but we point out the impossibility to derive these cells from older, mature adult mice. The inability of real adult SSCs to shift to a pluripotent state coincides with a decline in expression of the core pluripotency genes Oct4, Nanog, and Sox2 in SSCs with age. At the same time genes of the spermatogonial differentiation pathway increase. The generated ESC-like cells were similar to ESCs and express pluripotency markers. In vitro they differentiate into all three germ lineages; they form complex teratomas after transplantation in SCID mice and produce chimeric mice.

The repulsive guidance molecule RGMa is involved in the formation of afferent connections in the dentate gyrus.

In the developing dentate gyrus, afferent fiber projections terminate in distinct laminas. This relies on an accurately regulated spatiotemporal network of guidance molecules. Here, we have analyzed the functional role of the glycosylphosphatidylinositol (GPI)-anchored repulsive guidance molecule RGMa. In situ hybridization in embryonic and postnatal brain showed expression of RGMa in the cornu ammonis and hilus of the hippocampus. In the dentate gyrus, RGM immunostaining was confined to the inner molecular layer, whereas the outer molecular layers targeted by entorhinal fibers remained free. To test the repulsive capacity of RGMa, different setups were used: the stripe and explant outgrowth assays with recombinant RGMa, and entorhino-hippocampal cocultures incubated either with a neutralizing RGMa antibody (Ab) or with the GPI anchor-digesting drug phosphatidylinositol-specific phospholipase C. Entorhinal axons were clearly repelled by RGMa in the stripe and outgrowth assays. After disrupting the RGMa function, the specific laminar termination pattern in entorhino-hippocampal cocultures was lost, and entorhinal axons entered inappropriate hippocampal areas. Our data indicate an important role of RGMa for the layer-specific termination of the perforant pathway as a repulsive signal that compels entorhinal fibers to stay in their correct target zone.

Prolonged lesional expression of RhoA and RhoB following spinal cord injury.

Inhibition of the small GTPase ras homology protein (Rho) or its downstream target, the Rho-associated kinase (ROCK), has been shown to promote axon regeneration and to improve functional recovery following spinal cord injury (SCI) in the adult rat. Here, we have analyzed the expression of RhoA and RhoB following spinal cord injury in order to assess whether Rho is a possible target for late pharmacological intervention. In control spinal cords, RhoA(+) cells were almost absent, whereas RhoB was localized to some ependymal cells, a few microglia, and some dissociated neurons. In injured spinal cords, RhoA(+) and RhoB(+)cells accumulated at perilesional areas and in the developing necrotic core early after injury at day 1. After reaching their maximum levels (RhoA at day 3; RhoB at day 1), RhoA(+) and RhoB(+) cell numbers remained significantly elevated until day 28. In areas remote from the lesion (> or =0.75 mm), a more discrete accumulation of RhoA(+) and RhoB(+) cells was observed, primarily in areas of ongoing Wallerian degeneration. RhoA and RhoB were predominantly expressed by polymorphonuclear granulocytes, ED1(+) microglia/macrophages, oligodendrocytes, some neurons, and swollen axons/neurites. Furthermore, expression was located to lesional, reactive astrocytes and fibroblastoid cells confined to areas of scar formation. Our experiments have determined that most RhoA(+) and RhoB(+) cells (>70%) are of mononuclear origin. The persistent presence of lesional RhoA(+) and RhoB(+) axon/neurite fibers over a period of 4 weeks after injury suggests that Rho inhibition is a putative therapeutic concept also for delayed intervention after SCI.

Central nervous system injury-induced repulsive guidance molecule expression in the adult human brain.

BACKGROUND: The repulsive guidance molecule (RGM) is involved in formation of the central nervous system during development by moderating the repulsion of growing axons. However, the role of RGM in adult central nervous system lesions remains to be clarified. OBJECTIVE: To identify and determine RGM expression in adult brains with focal cerebral ischemia or traumatic brain injury and in neuropathologically unaffected control brains. Patients Twenty-one brains of patients with focal cerebral ischemia, 25 brains after traumatic brain injury, and 4 control brains. Main Outcome Measure Expression of RGM as assessed by immunohistochemical analysis. RESULTS: In normal brains, RGM expression was detected on the perikarya of some neurons, choroid plexus, smooth muscle and endothelial cells, oligodendrocytes, and myelinated white matter fibers. After focal cerebral ischemia and traumatic brain injury, RGM-immunopositive cells accumulated in lesional and perilesional areas. In hemorrhagic lesions, a massive accumulation of RGM-immunopositive cells was observed. During the first week after insult, RGM expression remained confined to neurons, smooth muscle and endothelial cells, and leukocytes infiltrating the lesion. Thereafter, with maturation of the lesion, we observed RGM expression by components of the developing scar tissue, such as fibroblastoid cells, reactive astrocytes, and a pronounced extracellular RGM deposition resembling neo-laminae. CONCLUSIONS: This is the first study of RGM in the human central nervous system. Following central nervous system injury, RGM, a novel, potent axonal growth inhibitor, is present in axonal growth impediments: the mature myelin, choroid plexus, and components of the developing scar.