Function Follows Form: Oriented Substrate Nanotopography Overrides Neurite-Repulsive Schwann Cell-Astrocyte Barrier Formation in an In Vitro Model of Glial Scarring.

Schwann cell (SC) transplantation represents a promising therapeutic approach for traumatic spinal cord injury but is frustrated by barrier formation, preventing cell migration, and axonal regeneration at the interface between grafted SCs and reactive resident astrocytes (ACs). Although regenerating axons successfully extend into SC grafts, only a few cross the SC-AC interface to re-enter lesioned neuropil. To date, research has focused on identifying and modifying the molecular mechanisms underlying such scarring cell-cell interactions, while the influence of substrate topography remains largely unexplored. Using a recently modified cell confrontation assay to model SC-AC barrier formation in vitro, highly oriented poly(ε-caprolactone) nanofibers were observed to reduce AC reactivity, induce extensive oriented intermingling between SCs and ACs, and ultimately enable substantial neurite outgrowth from the SC compartment into the AC territory. It is anticipated that these findings will have important implications for the future design of biomaterial-based scaffolds for nervous tissue repair.

Regulators of G protein signalling as pharmacological targets for the treatment of neuropathic pain.

Neuropathic pain, a specific type of chronic pain resulting from persistent nervous tissue lesions, is a debilitating condition that affects about 7% of the population. This condition remains particularly difficult to treat because of the poor understanding of its underlying mechanisms. Drugs currently used to alleviate this chronic pain syndrome are of limited benefit due to their lack of efficacy and the elevated risk of side effects, especially after a prolonged period of treatment. Although drugs targeting G protein-coupled receptors (GPCR) also have several limitations, such as progressive loss of efficacy due to receptor desensitization or unavoidable side effects due to wide receptor distribution, the identification of several molecular partners that contribute to the fine-tuning of receptor activity has raised new opportunities for the development of alternative therapeutic approaches. Regulators of G protein signalling (RGS) act intracellularly by influencing the coupling process and activity of G proteins, and are amongst the best-characterized physiological modulators of GPCR. Changes in RGS expression have been documented in a range of models of neuropathic pain, or after prolonged treatment with diverse analgesics, and could participate in altered pain processing as well as impaired physiological or pharmacological control of nociceptive signals. The present review summarizes the experimental data that implicates RGS in the development of pain with focus on the pathological mechanisms of neuropathic pain, including the impact of neuropathic lesions on RGS expression and, reciprocally, the influence of modifying RGS on GPCRs involved in the modulation of nociception as well as on the outcome of pain. In this context, we address the question of the relevance of RGS as promising targets in the treatment of neuropathic pain.

Author Correction: Stem cells from human apical papilla decrease neuro­inflammation and stimulate oligodendrocyte progenitor differentiation via activin­A secretion.

In the original publication, sixth author's surname was incorrectly published as "Llyod" instead of "Lloyd". The correct name should read as "Amy Lloyd".

Stem cells from human apical papilla decrease neuro-inflammation and stimulate oligodendrocyte progenitor differentiation via activin-A secretion.

Secondary damage following spinal cord injury leads to non-reversible lesions and hampering of the reparative process. The local production of pro-inflammatory cytokines such as TNF-α can exacerbate these events. Oligodendrocyte death also occurs, followed by progressive demyelination leading to significant tissue degeneration. Dental stem cells from human apical papilla (SCAP) can be easily obtained at the removal of an adult immature tooth. This offers a minimally invasive approach to re-use this tissue as a source of stem cells, as compared to biopsying neural tissue from a patient with a spinal cord injury. We assessed the potential of SCAP to exert neuroprotective effects by investigating two possible modes of action: modulation of neuro-inflammation and oligodendrocyte progenitor cell (OPC) differentiation. SCAP were co-cultured with LPS-activated microglia, LPS-activated rat spinal cord organotypic sections (SCOS), and LPS-activated co-cultures of SCOS and spinal cord adult OPC. We showed for the first time that SCAP can induce a reduction of TNF-α expression and secretion in inflamed spinal cord tissues and can stimulate OPC differentiation via activin-A secretion. This work underlines the potential therapeutic benefits of SCAP for spinal cord injury repair.

Characterisation of cell-substrate interactions between Schwann cells and three-dimensional fibrin hydrogels containing orientated nanofibre topographical cues.

The generation of complex three-dimensional bioengineered scaffolds that are capable of mimicking the molecular and topographical cues of the extracellular matrix found in native tissues is a field of expanding research. The systematic development of such scaffolds requires the characterisation of cell behaviour in response to the individual components of the scaffold. In the present investigation, we studied cell-substrate interactions between purified populations of Schwann cells and three-dimensional fibrin hydrogel scaffolds, in the presence or absence of multiple layers of highly orientated electrospun polycaprolactone nanofibres. Embedded Schwann cells remained viable within the fibrin hydrogel for up to 7 days (the longest time studied); however, cell behaviour in the hydrogel was somewhat different to that observed on the two-dimensional fibrin substrate: Schwann cells failed to proliferate in the fibrin hydrogel, whereas cell numbers increased steadily on the two-dimensional fibrin substrate. Schwann cells within the fibrin hydrogel developed complex process branching patterns, but, when presented with orientated nanofibres, showed a strong tendency to redistribute themselves onto the nanofibres, where they extended long processes that followed the longitudinal orientation of the nanofibres. The process length along nanofibre-containing fibrin hydrogel reached near-maximal levels (for the present experimental conditions) as early as 1 day after culturing. The ability of this three-dimensional, extracellular matrix-mimicking scaffold to support Schwann cell survival and provide topographical cues for rapid process extension suggest that it may be an appropriate device design for the bridging of experimental lesions of the peripheral nervous system.

Design of Suspended Melt Electrowritten Fiber Arrays for Schwann Cell Migration and Neurite Outgrowth.

In this study, well-defined, 3D arrays of air-suspended melt electrowritten fibers are made from medical grade poly(ɛ-caprolactone) (PCL). Low processing temperatures, lower voltages, lower ambient temperature, increased collector distance, and high collector speeds all aid to direct-write suspended fibers that can span gaps of several millimeters between support structures. Such processing parameters are quantitatively determined using a "wedge-design" melt electrowritten test frame to identify the conditions that increase the suspension probability of long-distance fibers. All the measured parameters impact the probability that a fiber is suspended over multimillimeter distances. The height of the suspended fibers can be controlled by a concurrently fabricated fiber wall and the 3D suspended PCL fiber arrays investigated with early post-natal mouse dorsal root ganglion explants. The resulting Schwann cell and neurite outgrowth extends substantial distances by 21 d, following the orientation of the suspended fibers and the supporting walls, often generating circular whorls of high density Schwann cells between the suspended fibers. This research provides a design perspective and the fundamental parametric basis for suspending individual melt electrowritten fibers into a form that facilitates cell culture.

A novel in vitro assay for peripheral nerve-related cell migration that preserves both extracellular matrix-derived molecular cues and nanofiber-derived topography.

BACKGROUND: Molecular composition and topography of the extracellular matrix (ECM) influence regenerative cell migration following peripheral nerve injury (PNI). Advanced tissue engineering strategies for the repair of neurotmesis-type PNI include the development of nanofiber-containing implantable scaffolds that mimic features of the ECM to orchestrate regenerative growth. Reliable and quantifiable in vitro assays are required to assess the ability of such substrates to influence migration of the cell types of interest. However, most popular migration assays monitor cell migration into a cell exclusion zone (CEZ) but have dubious abilities to preserve the molecular and topographical cues of the substrate. NEW METHOD: Elastic band spacers (EBS), a simple, economical and standardized technique for the generation of well-defined CEZ based on the use of commercially available elastic bands, are introduced. RESULTS: EBS could sufficiently preserve ECM-derived molecular and poly(ε-caprolactone) (PCL) nanofiber-derived topographical cues. The application of EBS in the absence and presence of nanofiber-derived topographical cues was validated using perineurial cells and Schwann cells, both known to play key roles in peripheral nerve regeneration. COMPARISON WITH EXISTING METHODS: In contrast to EBS, commercial silicone inserts and the popular scratch assay caused substantial ECM substrate disruption, thereby preventing these techniques from being included in further investigations employing deposition of PCL nanofibers and cell migration analysis. CONCLUSIONS: EBS represent a useful addition to the existing repertoire of migration assays offering significant benefits in terms of substrate preservation. The simplicity and economy of the approach make it immediately accessible to research groups at minimal extra expense.

Expansion of human bone marrow-derived mesenchymal stromal cells: serum-reduced medium is better than conventional medium.

BACKGROUND AIMS: Human mesenchymal stromal cells (hMSC) are of enormous interest for various clinical applications. For the expansion of isolated hMSC to relevant numbers for clinical applications, 10% fetal bovine serum (FBS)-supplemented medium is commonly used. The main critical disadvantage of FBS is the possibility of transmission of infectious agents as well as the possibility of immune rejection of the transplanted cells in response to the bovine serum. Therefore, we tested a commercially available medium, Panserin 401, that was specifically developed for serum-free cell cultivation. METHODS: hMSC were isolated from bone marrow (BM) and expanded in either Dulbecco's modified Eagle medium (DMEM) or Panserin 401 alone, or combined with FBS (2% or 10%), with or without supplementary growth factors. Cell proliferation and cytotoxicity were monitored twice a week for 3 weeks. RESULTS AND CONCLUSIONS: No proliferation was observed in any of the serum-free media. However, DMEM/10% FBS (the conventional culture medium for hMSC) and DMEM/2% FBS with growth factors revealed moderate proliferation. Interestingly, the best proliferation was obtained using Panserin 401 supplemented with 2% FBS and growth factors (as well as with 10% FBS). Analysis of cell growth in Panserin 401 supplemented with 2% FBS only or with growth factors only revealed no proliferation, demonstrating the necessity of the combination of 2% FBS and growth factors. Efficient isolation and expansion of hMSC from cancellous bone could also be performed using Panserin 401 with 2% FBS and growth factors. Furthermore, these isolated cultures maintained multipotency, as demonstrated by adipogenic and osteogenic differentiation.

Growth factor and cytokine expression of human mesenchymal stromal cells is not altered in an in vitro model of tissue damage.

BACKGROUND AIMS: The beneficial effect of human (h) mesenchymal stromal cell (MSC) transplantation in a variety of cell-based intervention strategies is widely believed to be because of paracrine mechanisms. The modification of hMSC cytokine and growth-factor expression patterns were studied following exposure to lipopolysaccharide (LPS) and tissue homogenates (representing tissue debris) from normal and pathologic tissues. METHODS: Human bone marrow-derived MSC were stimulated with LPS or exposed to homogenate from normal or pathologic rat spinal cord or heart. The expression profiles of a number of cytokines and growth factors were investigated using quantitative reverse transcription (RT)-polymerase chain reaction (PCR) with human-specific primers. The effects of tissue homogenates on hMSC proliferation and migratory behavior were also investigated. RESULTS: Stimulation of hMSC with LPS resulted in an up-regulation of interleukin (IL)-1ß, IL-6 and IL-8. However, the pattern of up-regulation varied between donor samples. Furthermore, LPS treatment resulted in a donor-dependent alteration of growth factor expression. Induction of a shift in expression pattern was not observed following exposure to homogenates from either normal or pathologic tissues. Tissue homogenates did stimulate cell proliferation, but not migration. CONCLUSIONS: The hMSC expression pattern is apparently stable, even when cells are confronted by debris from different tissue types. However, treatment of hMSC with LPS is able to change the expression of cytokines and growth factors in a donor-dependent manner that may enhance their potential use in regenerative medicine.

Functionalization of electrospun fibers of poly(epsilon-caprolactone) with star shaped NCO-poly(ethylene glycol)-stat-poly(propylene glycol) for neuronal cell guidance.

Microfibers produced with electrospinning have recently been used in tissue engineering. In the development of artificial implants for nerve regeneration they are of particular interest as guidance structures for cell migration and axonal growth. Using electrospinning we produced parallel-orientated biocompatible fibers in the submicron range consisting of poly(epsilon-caprolactone) (PCL) and star shaped NCO-poly(ethylene glycol)-stat-poly(propylene glycol) (sPEG). Addition of the bioactive peptide sequence glycine-arginine-glycine-aspartate-serine (GRGDS) or the extracellular matrix protein fibronectin to the electrospinning solution resulted in functionalized fibers. Surface characteristics and biological properties of functionalized and non-functionalised fibers were investigated. Polymer solutions and electrospinning process parameters were varied to obtain high quality orientated fibers. A polymer mixture containing high molecular weight PCL, PCL-diol, and sPEG permitted a chemical reaction between hydroxyl groups of the diol and isocyanante groups of the sPEG. Surface analysis demonstrated that sPEG at the fiber surface minimized protein adhesion. In vitro experiments using dorsal root ganglia explants showed that the cell repellent property of pure PCL/sPEG fibers was overcome by functionalization either with GRGDS peptide or fibronectin. In this way cell migration and axonal outgrowth along fibers were significantly increased. Thus, functionalized electrospun PCL/sPEG fibers, while preventing non-specific protein adsorption, are a suitable substrate for biological and medical applications.

A bench-top molding method for the production of cell-laden fibrin micro-fibers with longitudinal topography.

Tissue-engineered constructs have great potential in many intervention strategies. In order for these constructs to function optimally, they should ideally mimic the cellular alignment and orientation found in the tissues to be treated. Here we present a simple and reproducible method for the production of cell-laden pure fibrin micro-fibers with longitudinal topography. The micro-fibers were produced using a molding technique and longitudinal topography was induced by a single initial stretch. Using this method, fibers up to 1 m in length and with diameters of 0.2-3 mm could be produced. The micro-fibers were generated with embedded endothelial cells, smooth muscle cell/fibroblasts or Schwann cells. Polarized light and scanning electron microscopy imaging showed that the initial stretch was sufficient to induce longitudinal topography in the fibrin gel. Cells in the unstretched control micro-fibers elongated randomly in both the floating and encapsulated environments, whereas the cells in the stretched micro-fibers responded to the introduced topography by adopting a similar orientation. Proof of concept bottom-up tissue engineering (TE) constructs are shown, all displaying various anisotropic organization of cells within. This simple, economical, versatile and scalable approach for the production of highly orientated and cell-laden micro-fibers is easily transferrable to any TE laboratory.

Dense fibroadhesive scarring and poor blood vessel-maturation hamper the integration of implanted collagen scaffolds in an experimental model of spinal cord injury.

Severe spinal cord injury (SCI) results in permanent functional deficits, which despite pre-clinical advances, remain untreatable. Combinational approaches, including the implantation of bioengineered scaffolds are likely to promote significant tissue repair. However, this critically depends on the extent to which host tissue can integrate with the implant. In the present paper, blood vessel formation and maturation were studied within and around implanted micro-structured type-I collagen scaffolds at 10 weeks post implantation in adult rat mid-cervical spinal cord lateral funiculotomy injuries. Morphometric analysis revealed that blood vessel density within the scaffold was similar to that of the lateral white matter tracts that the implant replaced. However, immunohistochemistry for zonula occludens-1 (ZO-1) and endothelial barrier antigen revealed that scaffold microvessels remained largely immature, suggesting poor blood-spinal cord barrier (BSB) reformation. Furthermore, a band of intense ZO-1-immunoreactive fibroblast-like cells isolated the implant. Spinal cord vessels outside the ZO-1-band demonstrated BSB-formation, while vessels within the scaffold generally did not. The formation of a double-layered fibrotic and astroglial scar around the collagen scaffold might explain the relatively poor implant-host integration and suggests a mechanism for failed microvessel maturation. Targeted strategies that improve implant-host integration for such biomaterials will be vital for future tissue engineering and regenerative medicine approaches for traumatic SCI.

Neural differentiation potential of human bone marrow-derived mesenchymal stromal cells: misleading marker gene expression.

BACKGROUND: In contrast to pluripotent embryonic stem cells, adult stem cells have been considered to be multipotent, being somewhat more restricted in their differentiation capacity and only giving rise to cell types related to their tissue of origin. Several studies, however, have reported that bone marrow-derived mesenchymal stromal cells (MSCs) are capable of transdifferentiating to neural cell types, effectively crossing normal lineage restriction boundaries. Such reports have been based on the detection of neural-related proteins by the differentiated MSCs. In order to assess the potential of human adult MSCs to undergo true differentiation to a neural lineage and to determine the degree of homogeneity between donor samples, we have used RT-PCR and immunocytochemistry to investigate the basal expression of a range of neural related mRNAs and proteins in populations of non-differentiated MSCs obtained from 4 donors. RESULTS: The expression analysis revealed that several of the commonly used marker genes from other studies like nestin, Enolase2 and microtubule associated protein 1b (MAP1b) are already expressed by undifferentiated human MSCs. Furthermore, mRNA for some of the neural-related transcription factors, e.g. Engrailed-1 and Nurr1 were also strongly expressed. However, several other neural-related mRNAs (e.g. DRD2, enolase2, NFL and MBP) could be identified, but not in all donor samples. Similarly, synaptic vesicle-related mRNA, STX1A could only be detected in 2 of the 4 undifferentiated donor hMSC samples. More significantly, each donor sample revealed a unique expression pattern, demonstrating a significant variation of marker expression. CONCLUSION: The present study highlights the existence of an inter-donor variability of expression of neural-related markers in human MSC samples that has not previously been described. This donor-related heterogeneity might influence the reproducibility of transdifferentiation protocols as well as contributing to the ongoing controversy about differentiation capacities of MSCs. Therefore, further studies need to consider the differences between donor samples prior to any treatment as well as the possibility of harvesting donor cells that may be inappropriate for transplantation strategies.

NG2 and phosphacan are present in the astroglial scar after human traumatic spinal cord injury.

BACKGROUND: A major class of axon growth-repulsive molecules associated with CNS scar tissue is the family of chondroitin sulphate proteoglycans (CSPGs). Experimental spinal cord injury (SCI) has demonstrated rapid re-expression of CSPGs at and around the lesion site. The pharmacological digestion of CSPGs in such lesion models results in substantially enhanced axonal regeneration and a significant functional recovery. The potential therapeutic relevance of interfering with CSPG expression or function following experimental injuries seems clear, however, the spatio-temporal pattern of expression of individual members of the CSPG family following human spinal cord injury is only poorly defined. In the present correlative investigation, the expression pattern of CSPG family members NG2, neurocan, versican and phosphacan was studied in the human spinal cord. METHODS: An immunohistochemical investigation in post mortem samples of control and lesioned human spinal cords was performed. All patients with traumatic SCI had been clinically diagnosed as having "complete" injuries and presented lesions of the maceration type. RESULTS: In sections from control spinal cord, NG2 immunoreactivity was restricted to stellate-shaped cells corresponding to oligodendrocyte precursor cells. The distribution patterns of phosphacan, neurocan and versican in control human spinal cord parenchyma were similar, with a fine reticular pattern being observed in white matter (but also located in gray matter for phosphacan). Neurocan staining was also associated with blood vessel walls. Furthermore, phosphacan, neurocan and versican were present in the myelin sheaths of ventral and dorsal nerve roots axons. After human SCI, NG2 and phosphacan were both detected in the evolving astroglial scar. Neurocan and versican were detected exclusively in the lesion epicentre, being associated with infiltrating Schwann cells in the myelin sheaths of invading peripheral nerve fibres from lesioned dorsal roots. CONCLUSION: NG2 and phosphacan were both present in the evolving astroglial scar and, therefore, might play an important role in the blockade of successful CNS regeneration. Neurocan and versican, however, were located at the lesion epicentre, associated with Schwann cell myelin on regenerating peripheral nerve fibres, a distribution that was unlikely to contribute to failed CNS axon regeneration. The present data points to the importance of such correlative investigations for demonstrating the clinical relevance of experimental data.

Growth-modulating molecules are associated with invading Schwann cells and not astrocytes in human traumatic spinal cord injury.

Despite considerable progress in recent years, the underlying mechanisms responsible for the failure of axonal regeneration after spinal cord injury (SCI) remain only partially understood. Experimental data have demonstrated that a major impediment to the outgrowth of severed axons is the scar tissue that finally dominates the lesion site and, in severe injuries, is comprised of connective tissue and fluid-filled cysts, surrounded by a dense astroglial scar. Reactive astrocytes and infiltrating cells, such as fibroblasts, produce a dense extracellular matrix (ECM) that represents a physical and molecular barrier to axon regeneration. In the human situation, correlative data on the molecular composition of the scar tissue that forms following traumatic SCI is scarce. A detailed investigation on the expression of putative growth-inhibitory and growth-promoting molecules was therefore performed in samples of post-mortem human spinal cord, taken from patients who died following severe traumatic SCI. The lesion-induced scar could be subdivided into a Schwann cell dominated domain which contained large neuromas and a surrounding dense ECM, and a well delineated astroglial scar that isolated the Schwann cell/ECM rich territories from the intact spinal parenchyma. The axon growth-modulating molecules collagen IV, laminin and fibronectin were all present in the post-traumatic scar tissue. These molecules were almost exclusively found in the Schwann cell-rich domain which had an apparent growth-promoting effect on PNS axons. In the astrocytic domain, these molecules were restricted to blood vessel walls without a co-localization with the few regenerating CNS neurites located in this region. Taken together, these results favour the notion that it is the astroglial compartment that plays a dominant role in preventing CNS axon regeneration. The failure to demonstrate any collagen IV, laminin or fibronectin upregulation associated with the astroglial scar suggests that other molecules may play a more significant role in preventing axon regeneration following human SCI.

In vitro assessment of axonal growth using dorsal root ganglia explants in a novel three-dimensional collagen matrix.

The goal of this study was the development of a bioartificial nerve guide to induce axonal regeneration in the peripheral nervous system (PNS). In this in vitro study, the ability of a novel, 3-dimensional (3D), highly oriented, cross-linked porcine collagen scaffold to promote directed axonal growth has been studied. Collagen nerve guides with longitudinal guidance channels were manufactured using a series of chemical and mechanical treatments with a patented unidirectional freezing process, followed by freeze-drying (pore sizes 20-50 microm). Hemisected rat dorsal root ganglia (DRG) were positioned such that neural and non-neural elements could migrate into the collagen scaffold. After 21 days, S100-positive Schwann cells (SCs) migrated into the scaffold and aligned within the guidance channels in a columnar fashion, resembling "Bands of Büngner." Neurofilament-positive axons (mean length +/- SD 756 microm +/- 318 microm, maximum 1496 microm) from DRG neurons entered the scaffold where the growth within the guidance channels was closely associated with the oriented SCs. This study confirmed the importance of SCs in the regeneration process (neurotrophic theory). The alignment of SCs within the guidance channels supported directional axonal growth (contact guidance theory). The microstructural properties of the scaffold (open, porous, longitudinal pore channels) and the in vitro data after DRG loading (axonal regeneration along migrated and columnar-aligned SCs resembling "Band of Büngner") suggest that this novel oriented 3D collagen scaffold serves as a basis for future experimental regeneration studies in the PNS.

Mice lacking L1 have reduced CGRP fibre in-growth into spinal transection lesions.

Repair strategies for spinal cord injury often focus on promoting regeneration of injured axons and stimulating subsequent functional recovery. Although many of these strategies have proven their merits, less is known about potential unwanted side-effects, such as sprouting of nociceptive CGRP immunoreactive axons, which may bring about pain-related behavior. Sprouting of CGRP axons into lesion sites spontaneously occurs after spinal cord injury (SCI). Using L1-deficient mice we show a reduction of such CGRP growth response. This reduction was specific for CGRP axons since the overall neurofilament positive fibre in-growth into the spinal lesion site was not affected. Our results may have important implications on the development and assessment of repair strategies that should not only stimulate functional recovery, but also prevent the development of pain or autonomic dysreflexia.

Matrix metalloproteinases and their inhibitors in human traumatic spinal cord injury.

BACKGROUND: Matrix metalloproteinases (MMPs) are a family of extracellular endopeptidases that degrade the extracellular matrix and other extracellular proteins. Studies in experimental animals demonstrate that MMPs play a number of roles in the detrimental as well as in the beneficial events after spinal cord injury (SCI). In the present correlative investigation, the expression pattern of several MMPs and their inhibitors has been investigated in the human spinal cord. METHODS: An immunohistochemical investigation in post mortem samples of control and lesioned human spinal cords was performed. All patients with traumatic SCI had been clinically diagnosed as having "complete" injuries and presented lesions of the maceration type. RESULTS: In the unlesioned human spinal cord, MMP and TIMP immunoreactivity was scarce. After traumatic SCI, a lesion-induced bi-phasic pattern of raised MMP-1 levels could be found with an early up-regulation in macrophages within the lesion epicentre and a later induction in peri-lesional activated astrocytes. There was an early and brief induction of MMP-2 at the lesion core in macrophages. MMP-9 and -12 expression peaked at 24 days after injury and both molecules were mostly expressed in macrophages at the lesion epicentre. Whereas MMP-9 levels rose progressively from 1 week to 3 weeks, there was an isolated peak of MMP-12 expression at 24 days. The post-traumatic distribution of the MMP inhibitors TIMP-1, -2 and -3 was limited. Only occasional TIMP immuno-positive macrophages could be detected at short survival times. The only clear induction was detected for TIMP-3 at survival times of 8 months and 1 year in peri-lesional activated astrocytes. CONCLUSION: The involvement of MMP-1, -2, -9 and -12 has been demonstrated in the post-traumatic events after human SCI. With an expression pattern corresponding largely to prior experimental studies, they were mainly expressed during the first weeks after injury and were most likely involved in the destructive inflammatory events of protein breakdown and phagocytosis carried out by infiltrating neutrophils and macrophages, as well as being involved in enhanced permeability of the blood spinal cord barrier. Similar to animal investigations, the strong induction of MMPs was not accompanied by an expression of their inhibitors, allowing these proteins to exert their effects in the lesioned spinal cord.

Identification of regeneration-associated genes after central and peripheral nerve injury in the adult rat.

BACKGROUND: It is well known that neurons of the peripheral nervous system have the capacity to regenerate a severed axon leading to functional recovery, whereas neurons of the central nervous system do not regenerate successfully after injury. The underlying molecular programs initiated by axotomized peripheral and central nervous system neurons are not yet fully understood. RESULTS: To gain insight into the molecular mechanisms underlying the process of regeneration in the nervous system, differential display polymerase chain reaction has been used to identify differentially expressed genes following axotomy of peripheral and central nerve fibers. For this purpose, axotomy induced changes of regenerating facial nucleus neurons, and non-regenerating red nucleus and Clarke's nucleus neurons have been analyzed in an intra-animal side-to-side comparison. One hundred and thirty five gene fragments have been isolated, of which 69 correspond to known genes encoding for a number of different functional classes of proteins such as transcription factors, signaling molecules, homeobox-genes, receptors and proteins involved in metabolism. Sixty gene fragments correspond to genomic mouse sequences without known function. In situ-hybridization has been used to confirm differential expression and to analyze the cellular localization of these gene fragments. Twenty one genes (approximately 15%) have been demonstrated to be differentially expressed. CONCLUSIONS: The detailed analysis of differentially expressed genes in different lesion paradigms provides new insights into the molecular mechanisms underlying the process of regeneration and may lead to the identification of genes which play key roles in functional repair of central nervous tissues.