Analysis of gene expression following sciatic nerve crush and spinal cord hemisection in the mouse by microarray expression profiling

Therapeutic effects of polydeoxyribonucleotide in an in vitro neuronal model of ischemia/reperfusion injury

Polydeoxyribonucleotide (PDRN) is an agonist that selectively stimulates adenosine A_2A receptor (ADORA2A), which suppresses inflammatory responses. Ischemia/reperfusion (I/R) injury plays a major role in the pathogenesis of ischemic stroke by inducing neuroinflammation. Therefore, this study aimed to investigate the therapeutic effects of PDRN in an in vitro I/R injury model. The in vitro model was established with differentiated Neuro-2a cells under oxygen and glucose deprivation condition. The cells were treated with PDRN for 24 h under reoxygenation condition. As the results of RNA-seq transcriptome analysis, CSF1, IL-6, PTPN6, RAC2, and STAT1 were identified of its relation to the effect of PDRN on inflammatory responses in the model. To further investigate therapeutic effects of PDRN, RT-qPCR, western blotting, LDH assay, and TUNEL assay were performed. PDRN significantly reversed the expression of genes and proteins related to inflammatory responses. The elevated ADORA2A expression by PDRN treatment downregulated JAK/STAT pathway in the model. Furthermore, PDRN inhibited neuronal cell death in the model. Consequently, our results suggested that PDRN alleviated inflammatory responses through inhibition of JAK/STAT pathway by mediating ADORA2A expression and inhibited neuronal cell death in the model. These results provide significant insights into potential therapeutic approaches involving PDRN treatment for I/R injury.

Parasympathetic Effect Induces Cell Cycle Activation in Upper Limbs of Paraplegic Patients with Spinal Cord Injury

The present study aimed to investigate gene expression changes related to cell cycle activation in patients with spinal cord injury (SCI) and to further evaluate the difference between the upper and lower limbs of SCI patients. Fibroblasts were obtained from the upper and lower limbs of SCI patients and healthy subjects. To investigate gene expression profiling in the fibroblasts from SCI patients compared to the healthy subjects, RNA-Seq transcriptome analysis was performed. To validate the parasympathetic effects on cell cycle activation, fibroblasts from upper or lower limbs of SCI patients were treated with the anticholinergic agents tiotropium or acetylcholine, and quantitative RT-PCR and Western blot were conducted. Cell proliferation was significantly increased in the upper limbs of SCI patients compared with the lower limbs of SCI patients and healthy subjects. The pathway and genes involved in cell cycle were identified by RNA-Seq transcriptome analysis. Expression of cell-cycle-related genes CCNB1, CCNB2, PLK1, BUB1, and CDC20 were significantly higher in the upper limbs of SCI patients compared with the lower limbs of SCI patients and healthy subjects. When the fibroblasts were treated with tiotropium the upper limbs and acetylcholine in the lower limbs, the expression of cell-cycle-related genes and cell proliferation were significantly modulated. This study provided the insight that cell proliferation and cell cycle activation were observed to be significantly increased in the upper limbs of SCI patients via the parasympathetic effect.

The alternatively spliced fibronectin CS1 isoform regulates IL-17A levels and mechanical allodynia after peripheral nerve injury

BACKGROUND

Mechanical pain hypersensitivity associated with physical trauma to peripheral nerve depends on T-helper (Th) cells expressing the algesic cytokine, interleukin (IL)-17A. Fibronectin (FN) isoform alternatively spliced within the IIICS region encoding the 25-residue-long connecting segment 1 (CS1) regulates T cell recruitment to the sites of inflammation. Herein, we analyzed the role of CS1-containing FN (FN-CS1) in IL-17A expression and pain after peripheral nerve damage.

METHODS

Mass spectrometry, immunoblotting, and FN-CS1-specific immunofluorescence analyses were employed to examine FN expression after chronic constriction injury (CCI) in rat sciatic nerves. The acute intra-sciatic nerve injection of the synthetic CS1 peptide (a competitive inhibitor of the FN-CS1/α4 integrin binding) was used to elucidate the functional significance of FN-CS1 in mechanical and thermal pain hypersensitivity and IL-17A expression (by quantitative Taqman RT-PCR) after CCI. The CS1 peptide effects were analyzed in cultured primary Schwann cells, the major source of FN-CS1 in CCI nerves.

RESULTS

Following CCI, FN expression in sciatic nerve increased with the dominant FN-CS1 deposition in endothelial cells, Schwann cells, and macrophages. Acute CS1 therapy attenuated mechanical allodynia (pain from innocuous stimulation) but not thermal hyperalgesia and reduced the levels of IL-17A expression in the injured nerve. CS1 peptide inhibited the LPS- or starvation-stimulated activation of the stress ERK/MAPK pathway in cultured Schwann cells.

CONCLUSIONS

After physical trauma to the peripheral nerve, FN-CS1 contributes to mechanical pain hypersensitivity by increasing the number of IL-17A-expressing (presumably, Th17) cells. CS1 peptide therapy can be developed for pharmacological control of neuropathic pain.

Flipping the transcriptional switch from myelin inhibition to axon growth in the CNS

Poor regeneration of severed axons in the central nervous system (CNS) limits functional recovery. Regeneration failure involves interplay of inhibitory environmental elements and the growth state of the neuron. To find internal changes in gene expression that might overcome inhibitory environmental cues, we compared several paradigms that allow growth in the inhibitory environment. Conditions that allow axon growth by axotomized and cultured dorsal root ganglion (DRG) neurons on CNS myelin include immaturity (the first few postnatal days), high levels of cyclic adenosine mono phosphate (cAMP), and conditioning with a peripheral nerve lesion before explant. This shift from inhibition to growth depends on transcription. Seeking to understand the transcriptome changes that allow axon growth in the CNS, we collaborated with the Marie Filbin laboratory to identify several mRNAs that are functionally relevant, as determined by gain- and loss-of-function studies. In this Perspective, we review evidence from these experiments and discuss the merits of comparing multiple regenerative paradigms to identify a core transcriptional program for CNS axon regeneration.

Cell Therapy Augments Functional Recovery Subsequent to Spinal Cord Injury under Experimental Conditions

The spinal cord injury leads to enervation of normal tissue homeostasis ultimately leading to paralysis. Until now there is no proper cure for the treatment of spinal cord injury. Recently, cell therapy in animal spinal cord injury models has shown some progress of recovery. At present, clinical trials are under progress to evaluate the efficacy of cell transplantation for the treatment of spinal cord injury. Different types of cells such as pluripotent stem cells derived neural cells, mesenchymal stromal cells, neural stem cells, glial cells are being tested in various spinal cord injury models. In this review we highlight both the advances and lacuna in the field of spinal cord injury by discussing epidemiology, pathophysiology, molecular mechanism, and various cell therapy strategies employed in preclinical and clinical injury models and finally we discuss the limitations and ethical issues involved in cell therapy approach for treating spinal cord injury.

Genome-wide expression profile of the response to spinal cord injury in Xenopus laevis reveals extensive differences between regenerative and non-regenerative stages

Background

Xenopus laevis has regenerative and non-regenerative stages. As a tadpole, it is fully capable of functional recovery after a spinal cord injury, while its juvenile form (froglet) loses this capability during metamorphosis. We envision that comparative studies between regenerative and non-regenerative stages in Xenopus could aid in understanding why spinal cord regeneration fails in human beings.

Results

To identify the mechanisms that allow the tadpole to regenerate and inhibit regeneration in the froglet, we obtained a transcriptome-wide profile of the response to spinal cord injury in Xenopus regenerative and non-regenerative stages. We found extensive transcriptome changes in regenerative tadpoles at 1 day after injury, while this was only observed by 6 days after injury in non-regenerative froglets. In addition, when comparing both stages, we found that they deployed a very different repertoire of transcripts, with more than 80% of them regulated in only one stage, including previously unannotated transcripts. This was supported by gene ontology enrichment analysis and validated by RT-qPCR, which showed that transcripts involved in metabolism, response to stress, cell cycle, development, immune response and inflammation, neurogenesis, and axonal regeneration were regulated differentially between regenerative and non-regenerative stages.

Conclusions

We identified differences in the timing of the transcriptional response and in the inventory of regulated transcripts and biological processes activated in response to spinal cord injury when comparing regenerative and non-regenerative stages. These genes and biological processes provide an entry point to understand why regeneration fails in mammals. Furthermore, our results introduce Xenopus laevis as a genetic model organism to study spinal cord regeneration.

Extracellular matrix-associated gene expression in adult sensory neuron populations cultured on a laminin substrate

Background

In our previous investigations of the role of the extracellular matrix (ECM) in promoting neurite growth we have observed that a permissive laminin (LN) substrate stimulates differential growth responses in subpopulations of mature dorsal root ganglion (DRG) neurons. DRG neurons expressing Trk and p75 receptors grow neurites on a LN substrate in the absence of neurotrophins, while isolectin B4-binding neurons (IB4⁺) do not display significant growth under the same conditions. We set out to determine whether there was an expression signature of the LN-induced neurite growth phenotype. Using a lectin binding protocol IB4⁺ neurons were isolated from dissociated DRG neurons, creating two groups - IB4⁺ and IB4^-. A small-scale microarray approach was employed to screen the expression of a panel of ECM-associated genes following dissociation (t=0) and after 24 hr culture on LN (t=24LN). This was followed by qRT-PCR and immunocytochemistry of selected genes.

Results

The microarray screen showed that 36 of the 144 genes on the arrays were consistently expressed by the neurons. The array analyses showed that six genes had lower expression in the IB4+ neurons compared to the IB4- cells at t=0 (CTSH, Icam1, Itgβ1, Lamb1, Plat, Spp1), and one gene was expressed at higher levels in the IB4⁺ cells (Plaur). qRT-PCR was carried out as an independent assessment of the array results. There were discrepancies between the two methods, with qRT-PCR confirming the differences in Lamb1, Plat and Plaur, and showing decreased expression of AdamTs1, FN, and Icam in the IB4⁺ cells at t=0. After 24 hr culture on LN, there were no significant differences detected by qRT-PCR between the IB4⁺ and IB4^- cells. However, both groups showed upregulation of Itgβ1 and Plaur after 24 hr on LN, the IB4⁺ group also had increased Plat, and the IB4^- cells showed decreased Lamb1, Icam1 and AdamTs1. Further, the array screen also detected a number of genes (not subjected to qRT-PCR) expressed similarly by both populations in relatively high levels but not detectably influenced by time in culture (Bsg, Cst3, Ctsb, Ctsd, Ctsl, Mmp14, Mmp19, Sparc. We carried out immunohistochemistry to confirm expression of proteins encoded by a number of these genes.

Conclusions

Our results show that 1B4⁺ and IB4^- neurons differ in the expression of several genes that are associated with responsiveness to the ECM prior to culturing (AdamTs1, FN, Icam1, Lamb1, Plat, Plaur). The data suggest that the genes expressed at higher levels in the IB4^- neurons could contribute to the initial growth response of these cells in a permissive environment and could also represent a common injury response that subsequently promotes axon regeneration. The differential expression of several extracellular matrix molecules (FN, Lamb1, Icam) may suggest that the IB4^- neurons are capable of maintaining /secreting their local extracellular environment which could aid in the regenerative process. Overall, these data provide new information on potential targets that could be manipulated to enhance axonal regeneration in the mature nervous system.

Vertebral landmarks for the identification of spinal cord segments in the mouse

Accurate identification of spinal cord segments in relation to vertebral landmarks is essential to surgery aimed at experimental spinal cord injury. We have analyzed a complete series of high-resolution magnetic resonance (MR) images from the mouse spine in order to delineate the boundaries of spinal cord segments in relation to vertebral landmarks. The resulting atlas can be used to plan experimental approaches that require the accurate identification of a target spinal cord segment.

Spinal cord trauma and the molecular point of no return

A mechanical trauma to the spinal cord can be followed by the development of irreversible and progressive neurodegeneration, as opposed to a temporary or partially reversible neurological damage. An increasing body of experimental and clinical evidence from humans and animal models indicates that spinal cord injury may set in motion the development of disabling and at times fatal neuromuscular disorders, whose occurrence is not normally associated with any major environmental event. This outcome appears to be dependent on the co-occurrence of a particular form of mechanical stress and of a genetically-determined vulnerability. This increased vulnerability to spinal cord injury may depend on a change of the nature and of the timing of activation of a number of neuroprotective and neurodestructive molecular signals in the injured cord. Among the main determinants, we could mention an altered homeostasis of lipids and neurofilaments, an earlier inflammatory response and the failure of the damaged tissue to rein in oxidative damage and apoptotic cell death. These changes could force injured tissue beyond a point of no return and precipitate an irreversible neurodegenerative process. A better knowledge of the molecular signals activated in a state of increased vulnerability to trauma can inform future treatment strategies and the prediction of the neurological outcome after spinal cord injury.

Molecular target discovery for neural repair in the functional genomics era

A comprehensive understanding of the molecular pathways activated by traumatic neural injury is of major importance for the development of treatments for spinal cord injury (SCI). High-throughput gene expression profiling is a powerful approach to reveal genome-wide changes in gene expression during a specific biological process. Microarray analysis of injured nerves or neurons would ideally generate new hypotheses concerning the progression or deregulation of injury- and repair-related biological processes, such as neural scar formation and axon regeneration. These hypotheses should subsequently be tested experimentally and would eventually provide the molecular substrates for the development of novel therapeutics. Over the last decade, this approach has elucidated numerous extrinsic (mostly neural scar-associated) as well as neuron-intrinsic genes that are regulated following an injury. To date, the main challenge is to translate the observed injury-induced gene expression changes into a mechanistic framework to understand their functional implications. To achieve this, research on neural repair will have to adopt the conceptual advances and analytical tools provided by the functional genomics and systems biology revolution. Based on progress made in bioinformatics, high-throughput and high-content functional cellular screening, and in vivo gene transfer technology, we propose a multistep "roadmap" that provides an integrated strategy for molecular target discovery for repair of the injured spinal cord.

Molecular control of axon growth: insights from comparative gene profiling and high-throughput screening

Axon regeneration in the mammalian adult central nervous system (CNS) is limited by an intrinsically low capacity for axon growth in many CNS neurons. In contrast, embryonic, peripheral, and many nonmammalian neurons are capable of successful regeneration. Numerous studies have compared mammalian CNS neurons to their counterparts in regenerating systems in an effort to identify candidate genes that control regenerative ability. This review summarizes work using this comparative strategy and examines our current understanding of gene function in axon growth, highlighting the emergence of genome-wide expression profiling and high-throughput screening strategies to identify novel regulators of axon growth.

The effect of mechanical strain or hypoxia on cell death in subpopulations of rat dorsal root ganglion neurons in vitro

Spinal nerves and their associated dorsal root ganglion (DRG) cells can be subject to mechanical deformation and hypoxia associated with pathology such as disc herniation, spinal stenosis and spine trauma. There is very limited information on the response of adult DRG neurons to such stressors. In this study we used an in vitro approach to examine the response of adult DRG cells to (a) mechanical, hypoxic, and combined injuries; and (b) to compare the effects on injury on nociceptive and non-nociceptive neurons, as well as on non-neuronal cells. Mechanical injury (20% tensile strain) led to significant neuronal cell death (assessed by ethidium homodimer-1 labelling), which was proportional to strain duration (5 min, 1 h, 6 h or 18 h). Hypoxia (2% O(2) for 24 h) also promoted death of DRG neurons, and was further enhanced when mechanical strain and hypoxia were combined. Both mechanical strain and hypoxia significantly decreased the maximum neurite length. Conversely, death of non-neuronal cells was only increased by hypoxia and not by mechanical strain. Total cell death in response to mechanical injury or hypoxia was similar in both non-nociceptive (neurofilament, NF-200 immunoreactive) and nociceptive (calcitonin gene-related peptide, CGRP immunoreactive) neurons, but apoptosis (assessed by activated caspase-3 immunostaining) was significantly higher in CGRP than NF-200 neurons. Surprisingly, cell death of non-peptidergic nociceptors (identified by Griffonia simplicifolia IB4 lectin binding) was already high in control cultures, and was not increased further by either mechanical stretch or hypoxia. These results provide detailed information on the response of adult DRG subpopulations to hypoxia and mechanical strain, and describe in vitro models that could be useful for screening potential neuroprotective agents.

Mst3b, an Ste20-like kinase, regulates axon regeneration in mature CNS and PNS pathways

Mammalian sterile 20-like kinase-3b (Mst3b/Stk24) regulates axon outgrowth in embryonic cortical neurons in culture, but its role in vivo and in neural repair is unknown. Here we show that Mst3b mediates the axon-promoting effects of trophic factors in mature rat retinal ganglion cells (RGCs) and dorsal root ganglion (DRG) neurons, and is essential for axon regeneration in vivo. Reducing Mst3b levels using shRNA prevented RGCs and DRG neurons from regenerating axons in response to growth factors in culture, as did expression of a kinase-dead Mst3b mutant. Conversely, expression of constitutively active Mst3b enabled both types of neurons to extend axons without growth factors. In vivo, RGCs lacking Mst3b failed to regenerate injured axons when stimulated by intraocular inflammation. DRG neurons regenerating axons in vivo showed elevated Mst3b activity, and reducing Mst3b expression attenuated regeneration and p42/44 MAPK activation. Thus, Mst3b regulates axon regeneration in both CNS and PNS neurons.

Analysis of gene expression during neurite outgrowth and regeneration

Background

The ability of a neuron to regenerate functional connections after injury is influenced by both its intrinsic state and also by extrinsic cues in its surroundings. Investigations of the transcriptional changes undergone by neurons during in vivo models of injury and regeneration have revealed many transcripts associated with these processes. Because of the complex milieu of interactions in vivo, these results include not only expression changes directly related to regenerative outgrowth and but also unrelated responses to surrounding cells and signals. In vitro models of neurite outgrowth provide a means to study the intrinsic transcriptional patterns of neurite outgrowth in the absence of extensive extrinsic cues from nearby cells and tissues.

Results

We have undertaken a genome-wide study of transcriptional activity in embryonic superior cervical ganglia (SCG) and dorsal root ganglia (DRG) during a time course of neurite outgrowth in vitro. Gene expression observed in these models likely includes both developmental gene expression patterns and regenerative responses to axotomy, which occurs as the result of tissue dissection. Comparison across both models revealed many genes with similar gene expression patterns during neurite outgrowth. These patterns were minimally affected by exposure to the potent inhibitory cue Semaphorin3A, indicating that this extrinsic cue does not exert major effects at the level of nuclear transcription. We also compared our data to several published studies of DRG and SCG gene expression in animal models of regeneration, and found the expression of a large number of genes in common between neurite outgrowth in vitro and regeneration in vivo.

Conclusion

Many gene expression changes undergone by SCG and DRG during in vitro outgrowth are shared between these two tissue types and in common with in vivo regeneration models. This suggests that the genes identified in this in vitro study may represent new candidates worthy of further study for potential roles in the therapeutic regrowth of neuronal connections.

Genomic and proteomic microglial profiling: pathways for neuroprotective inflammatory responses following nerve fragment clearance and activation

Microglia, a primary immune effector cell of the central nervous system (CNS) affects homeostatic, neuroprotective, regenerative and degenerative outcomes in health and disease. Despite these broad neuroimmune activities linked to specific environmental cues, a precise cellular genetic profile for microglia in the context of disease and repair has not been elucidated. To this end we used nucleic acid microarrays, proteomics, immunochemical and histochemical tests to profile microglia in neuroprotective immune responses. Optic and sciatic nerve (ON and SN) fragments were used to stimulate microglia in order to reflect immune consequences of nervous system injury. Lipopolysaccharide and latex beads-induced microglial activation served as positive controls. Cytosolic and secreted proteins were profiled by surface enhanced laser desorption ionization-time of flight (SELDI-TOF) ProteinChip, 1D and 2D difference gel electrophoresis. Proteins were identified by peptide sequencing with tandem mass spectrometry, ELISA and western blot tests. Temporal expression of pro-inflammatory cytokines, antioxidants, neurotrophins, and lysosomal enzyme expression provided, for the first time, a unique profile of secreted microglia proteins with neuroregulatory functions. Most importantly, this molecular and biochemical signature supports a broad range of microglial functions for debris clearance and promotion of neural repair after injury.

Gene expression profiling reveals that peripheral nerve regeneration is a consequence of both novel injury-dependent and reactivated developmental processes

One of the most striking features of the injured mature peripheral nervous system is the ability to regenerate. The lesioned peripheral nervous system displays stereotypic histopathological reactions indicating the activation of a co-ordinated lesion-induced gene expression programme. Previous research has already identified molecular components of this axonal switch from a mature transmitting to a regenerative growth mode. The observed alterations in gene expression within the lesioned distal nerve stump were largely attributed to recapitulated developmental processes. However, to our knowledge, this hypothesis has not been proven systematically. Most of the stereotypic molecular and cellular reactions during nerve development and repair can be assigned to specific time windows. Consequently, we have compared gene expression profiles of both paradigms at six different time-points each by means of cDNA array hybridization. Our data identified injury-specific molecular reactions and revealed to what extent developmental mechanisms are reactivated in response to nerve lesion. Ninety-one genes (47% of the regeneration-associated genes) were found to be significantly regulated in both paradigms, suggesting that regeneration only partially recapitulates development and that approximately half of the regulated genes are part of a regeneration-dependent programme. Interestingly, mainly genes encoding signal transducers or factors involved in processes such as cell death, immune response, transport and transcriptional regulation showed injury-specific gene expression.

Proteome analysis of up-regulated proteins in the rat spinal cord induced by transection injury

The inability of the CNS to regenerate in adult mammals propels us to reveal associated proteins involved in the injured CNS. In this paper, either thoracic laminectomy (as sham control) or thoracic spinal cord transection was performed on male adult rats. Five days after surgery, the whole spinal cord tissue was dissected and fractionated into water-soluble (dissolved in Tris buffer) and water-insoluble (dissolved in a solution containing chaotropes and surfactants) portions for 2-DE. Protein identification was performed by MS and further confirmed by Western blot. As a result, over 30 protein spots in the injured spinal cord were shown to be up-regulated no less than 1.5-fold. These identified proteins possibly play various roles during the injury and repair process and may be functionally categorized as several different groups, such as stress-responsive and metabolic changes, lipid and protein degeneration, neural survival and regeneration. In particular, over-expression of 11-zinc finger protein and glypican may be responsible for the inhibition of axonal growth and regeneration. Moreover, three unknown proteins with novel sequences were found to be up-regulated by spinal cord injury. Further characterization of these molecules may help us come closer to understanding the mechanisms that underlie the inability of the adult CNS to regenerate.

Gene expression profiling of experimental traumatic spinal cord injury as a function of distance from impact site and injury severity

Changes in gene expression contribute to pathophysiological alterations following spinal cord injury (SCI). We examined gene expression over time (4 h, 24 h, 7 days) at the impact site, as well as rostral and caudal regions, following mild, moderate, or severe contusion SCI in rats. High-density oligonucleotide microarrays were used that included approximately 27,000 genes/ESTs (Affymetrix RG-U34; A, B and C arrays), together with multiple analyses (MAS 5.0, dChip). Alterations after mild injury were relatively rapid (4 and 24 h), whereas they were delayed and prolonged after severe injury (24 h and 7 days). The number and magnitude of gene expression changes were greatest at the injury site after moderate injury and increased in rostral and caudal regions as a function of injury severity. Sham surgery resulted in expression changes that were similar to mild injury, suggesting the importance of using time-linked surgical controls as well as naive animals for these kinds of studies. Expression of many genes and ESTs was altered; these were classified functionally based on ontology. Overall representation of these functional classes varied with distance from the site of injury and injury severity, as did the individual genes that contributed to each functional class. Different clustering approaches were used to identify changes in neuronal-specific genes and several transcription factors that have not previously been associated with SCI. This study represents the most comprehensive evaluation of gene expression changes after SCI to date. The results underscore the power of microarray approaches to reveal global genomic responses as well as changes in particular gene clusters and/or families that may be important in the secondary injury cascade.

Cellular localization and enzymatic activity of cathepsin B after spinal cord injury in the rat

Mechanical spinal cord injury (SCI) initiates a cascade of pathochemical and pathophysiological events, collectively known as the secondary injury. There has been a long-standing interest in understanding the activation and involvement of proteases in this secondary injury process. Several proteases including the calpains, caspases and matrix metalloproteinases are activated by perturbations to the spinal cord and have been linked to cell death following SCI and in other models of CNS disease and insult. Cathepsin B (Cath B), a potent lysosomal protease, has also been implicated in the pathology of CNS diseases including brain tumors, Alzheimer's disease, amyotrophic lateral sclerosis and stroke. Previously, we reported significant increases in Cath B mRNA and protein expression following contusion-SCI. This characterization of Cath B continues with the experiments reported herein, which were designed to examine Cath B enzymatic activity and cellular localization following contusion-SCI in the rat. Cath B enzymatic activity was significantly increased in the injury epicenter at 5 and 7 days post-injury and was highly correlated with increases in the active forms of the Cath B protein reported earlier. Furthermore, the immunohistochemical analyses revealed that the post-injury increases in expression and enzymatic activity at the injury epicenter were due to the presence of a large and diverse population of inflammatory cells. However, in areas adjacent to the injury epicenter, it appears that parenchymal neurons may also contribute to these increases. Our findings coupled with the documented role of Cath B in other CNS pathologies make this potent protease an attractive candidate for involvement in the tissue destruction associated with the secondary injury cascade following SCI.

Serum Biomarkers for Experimental Acute Spinal Cord Injury: Rapid Elevation of Neuron-specific Enolase and S-100β

OBJECTIVE

We evaluated whether serum levels of neuron-specific enolase (NSE) and S-100beta protein are biomarkers for traumatic injury in an animal model of spinal cord injury (SCI).

METHODS

Enzyme-linked immunosorbent assay serum measurements of NSE and S-100beta and assays of serum protein were compared at 6 and 24 hours after a graded contusive SCI (150 or 200 kdyn IH impactor injury (Infinite Horizons, L.L.C., Lexington, KY) or sham laminectomy at T9 in 30 female Sprague-Dawley rats. Serum from control animals was also analyzed.

RESULTS

Increases in serum levels of NSE were observed for 200-kdyn (3.1-fold, P < 0.001) and 150-kdyn (2.3-fold, P < 0.001) injury groups at 6 hours after injury, which decreased by 73.7% (P < 0.001) and 65.2% (P < 0.001) at 24 hours after SCI, respectively; the levels were still greater than in sham animals (P < 0.001, P = 0.001). The 200- and 150-kdyn injury groups were not different at either time point. S-100beta serum levels increased at 6 hours in the 200-kdyn injury group (P < 0.05), and no differences from sham levels were seen at 24 hours. No differences in total protein concentrations were observed between the injury and control groups.

CONCLUSION

Present data suggest that NSE and S-100beta serum levels may be useful experimental tools for the acute measurement of tissue loss after SCI. Despite significant shortcomings, NSE and S-100beta serum measurements in acute SCI patients with clinically defined functional deficits should allow comparisons with well-characterized SCI animal models. Future efforts to develop biomarkers that predict functional outcomes in the acute phase should focus on axon-specific proteins as markers of secondary axonal loss and regeneration.

Strategies for identifying genes that play a role in spinal cord regeneration

A search for genes that promote or block CNS regeneration requires numerous approaches; for example, tests can be made on individual candidate molecules. Here, however, we describe methods for comprehensive identification of genes up- and down-regulated in neurons that can and cannot regenerate after injury. One problem concerns identification of low-abundance genes out of the 30,000 or so genes expressed by neurons. Another difficulty is knowing whether a single gene or multiple genes are necessary. When microchips and subtractive differential display are used to identify genes turned on or off, the numbers are still too great to test which molecules are actually important for regeneration. Candidates are genes coding for trophic, inhibitory, receptor and extracellular matrix molecules, as well as unknown genes. A preparation useful for narrowing the search is the neonatal opossum. The spinal cord and optic nerve can regenerate after injury at 9 days but cannot at 12 days after birth. This narrow window allows genes responsible for the turning off of regeneration to be identified. As a next step, sites at which they are expressed (forebrain, midbrain, spinal cord, neurons or glia, intracellular or extracellular) must be determined. An essential step is to characterize proteins, their levels of expression, and their importance for regeneration. Comprehensive searches for molecular mechanisms represent a lengthy series of experiments that could help in devising strategies for repairing injured spinal cord.

Cathepsin B mRNA and protein expression following contusion spinal cord injury in rats

We provide the first data that cathepsin B (Cath B), a lysosomal cysteine protease, is up-regulated following contusion-spinal cord injury (SCI). Following T12 laminectomy and moderate contusion, Cath B mRNA and protein expression profiles were examined from 2 to 168 h post-injury in rats using real-time PCR and immunoblots, respectively. Contusion injury significantly increased [mRNA]Cath B in the injury site and adjacent segments over sham injury levels. While the largest [mRNA]Cath B induction (20-fold over naive) was seen in the injury site, the caudal segment routinely yielded [mRNA]Cath B levels greater than 10-fold over naive. Interestingly, sham injury animals also experienced mRNA induction at several time points at the injury site and in segments rostral and caudal to the injury site. Contusion injury also significantly elevated levels of Cath B proenzyme protein (37 kDa) over sham injury in the injury site (48, 72 and 168 h post-injury). Furthermore, significant protein increases of single and double chain Cath B (both active forms) occurred at the injury site at 72 and 168 h post-injury. Similar significant increases in Cath B protein levels were seen in areas adjacent to the injury site. The induction of Cath B mRNA and protein expression following contusion injury is previously undescribed and suggests that Cath B may potentially be involved in the secondary injury cascade, perhaps for as long as 1 week post-injury.

Inflammation, degeneration and regeneration in the injured spinal cord: insights from DNA microarrays

GeneChip microarrays have recently been introduced to the field of neurobiology to identify and monitor the expression levels of thousands of genes simultaneously. This powerful technique is now used for studying the pathophysiology of CNS injuries including spinal cord lesions. Early stages after injury are characterized by the strong upregulation of genes involved in transcription and inflammation and a general downregulation of structural proteins and proteins involved in neurotransmission. Later, an increase in the expression of growth factors, axonal guidance factors, extracellular matrix molecules and angiogenic factors reflects the attempts for repair, while upregulation of stress genes and proteases and downregulation of cytoskeletal and synaptic mRNA reflect the struggle of the tissue to survive. DNA microarrays have the potential to aid discovery of new targets for neuroprotective or restorative therapeutic approaches