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

Macrophage polarization in spinal cord injury repair and the possible role of microRNAs: A review

The prevention, treatment, and rehabilitation of spinal cord injury (SCI) have always posed significant medical challenges. After mechanical injury, disturbances in microcirculation, edema formation, and the generation of free radicals lead to additional damage, impeding effective repair processes and potentially exacerbating further dysfunction. In this context, inflammatory responses, especially the activation of macrophages, play a pivotal role. Different phenotypes of macrophages have distinct effects on inflammation. Activation of classical macrophage cells (M1) promotes inflammation, while activation of alternative macrophage cells (M2) inhibits inflammation. The polarization of macrophages is crucial for disease healing. A non-coding RNA, known as microRNA (miRNA), governs the polarization of macrophages, thereby reducing inflammation following SCI and facilitating functional recovery. This study elucidates the inflammatory response to SCI, focusing on the infiltration of immune cells, specifically macrophages. It examines their phenotype and provides an explanation of their polarization mechanisms. Finally, this paper introduces several well-known miRNAs that contribute to macrophage polarization following SCI, including miR-155, miR-130a, and miR-27 for M1 polarization, as well as miR-22, miR-146a, miR-21, miR-124, miR-223, miR-93, miR-132, and miR-34a for M2 polarization. The emphasis is placed on their potential therapeutic role in SCI by modulating macrophage polarization, as well as the present developments and obstacles of miRNA clinical therapy.

Transcription factor network analysis identifies REST/NRSF as an intrinsic regulator of CNS regeneration in mice

The inability of neurons to regenerate long axons within the CNS is a major impediment to improving outcome after spinal cord injury, stroke, and other CNS insults. Recent advances have uncovered an intrinsic program that involves coordinate regulation by multiple transcription factors that can be manipulated to enhance growth in the peripheral nervous system. Here, we use a systems genomics approach to characterize regulatory relationships of regeneration-associated transcription factors, identifying RE1-Silencing Transcription Factor (REST; Neuron-Restrictive Silencer Factor, NRSF) as a predicted upstream suppressor of a pro-regenerative gene program associated with axon regeneration in the CNS. We validate our predictions using multiple paradigms, showing that mature mice bearing cell type-specific deletions of REST or expressing dominant-negative mutant REST show improved regeneration of the corticospinal tract and optic nerve after spinal cord injury and optic nerve crush, which is accompanied by upregulation of regeneration-associated genes in cortical motor neurons and retinal ganglion cells, respectively. These analyses identify a role for REST as an upstream suppressor of the intrinsic regenerative program in the CNS and demonstrate the utility of a systems biology approach involving integrative genomics and bio-informatics to prioritize hypotheses relevant to CNS repair.

The Role of miR-20 in Health and Disease of the Central Nervous System

Current understanding of the mechanisms underlying central nervous system (CNS) injury is limited, and traditional therapeutic methods lack a molecular approach either to prevent acute phase or secondary damage, or to support restorative mechanisms in the nervous tissue. microRNAs (miRNAs) are endogenous, non-coding RNA molecules that have recently been discovered as fundamental and post-transcriptional regulators of gene expression. The capacity of microRNAs to regulate the cell state and function through post-transcriptionally silencing hundreds of genes are being acknowledged as an important factor in the pathophysiology of both acute and chronic CNS injuries. In this study, we have summarized the knowledge concerning the pathophysiology of several neurological disorders, and the role of most canonical miRNAs in their development. We have focused on the miR-20, the miR-17~92 family to which miR-20 belongs, and their function in the normal development and disease of the CNS.

Silencing of miR-324-5p alleviates rat spinal cord injury by Sirt1

MicroRNAs (miRNAs) are implicated in the pathogenesis of spinal cord injury (SCI) as primary regulators. Previous studies have reported that miR-324-5p is involved in the modulation of neural injury, while the underlying mechanisms of miR-324-5p in SCI remain unclear. In a SCI rat model, miR-324-5p was significantly upregulated in the spinal cord tissues after SCI. Downregulation of miR-324-5p via injection of adeno-associated viruses (AAV) expressing miR-324-5p inhibitor relieved animal motor deficits and pathological changes in the tissues. Furthermore, downregulation of miR-324-5p significantly altered the expression of genes regulating neural growth, apoptosis, and the inflammatory and antioxidant response, which are implicated in SCI pathogenesis. In a H₂O₂-induced cell injury model, miR-324-5p silencing rescued the elevated apoptosis of PC12 cells. Finally, miR-324-5p directly targeted the 3'-untranslated region of NAD-dependent protein deacetylase sirtuin-1 (Sirt1) and negatively regulated the levels of Sirt1, an anti-inflammatory protein involved in SCI. Silencing of Sirt1 aggravated SCI and rescued the effects of miR-324-5p downregulation in rats. Overall, our findings indicated that silencing of miR-324-5p alleviates the loss of animal locomotion and concurrently mediates several degenerative processes relevant to the pathogenesis of SCI by Sirt1, which may provide clues for SCI treatment.

Elevated levels of neutrophil gelatinase-associated lipocalin among OCD patients: an exploratory study

BACKGROUND

Obsessive-compulsive disorder (OCD) is a debilitating psychiatric disease that is characterized by its clinical heterogeneity and complex pathophysiology. This complexity comes from the diversity of pathophysiological factors that have been proposed to be involved in the natural history of the disorder. Many theories on OCD pathology support inflammation as a pathophysiological factor, although studies are not consistent on the presence of a pro-inflammatory state among OCD patients. However, some pre-clinical animal studies suggest lipocalin-2 (LCN2), an analogous form of the acute-phase pro-inflammatory protein neutrophil gelatinase-associated lipocalin (NGAL), may be involved in in the regulation of the stress response, which is thought to be disrupted in OCD.

METHODS

Twenty-one OCD patients and 19 healthy subjects participated in this exploratory study. Levels of NGAL were assessed in the peripherous blood of all participants. Severity of disease was assessed using the Yale-Brown Obsessive-Compulsive Scale (Y-BOCS).

RESULTS

OCD patients exhibited significantly higher levels of NGAL when compared to healthy control subjects. No correlation was found between elevated levels of NGAL and severity of symptoms.

CONCLUSIONS

This is the first study to report elevated levels of NGAL among OCD patients, adding evidence for a possible role of immune dysregulation in the pathophysiology of OCD.

MicroRNA-92a-3p enhances functional recovery and suppresses apoptosis after spinal cord injury via targeting phosphatase and tensin homolog

Spinal cord injury (SCI) is a neurological disease commonly caused by traumatic events on spinal cords. MiRNA-92a-3p is reported to be down-regulated after SCI. Our study investigated the effects of up-regulated miR-92a-3p on SCI and the underlying mechanisms. SCI mice model was established to evaluate the functional recovery of hindlimbs of mice through open-field locomotion and scored by Basso, Beattie, and Bresnahan (BBB) locomotion scale. Apoptosis of spinal cord cells was determined by flow cytometry. The effects of miR-92a-3p on SCI were detected by intrathecally injecting miR-92a-3p agomiR (agomiR-92) into the mice prior to the establishment of SCI. Phosphatase and tensin homolog (PTEN) was predicted as a target of miR-29a-3p by TargetScan. We further assessed the effects of agomiR-92 or/and overexpressed PTEN on apoptosis rates and apoptotic protein expressions in SCI mice. Moreover, the activation of protein kinase B (AKT)/mammalian target of rapamycin (mTOR) signaling was determined by Western blot. The results showed that compared with the sham-operated mice, SCI mice had much lower BBB scores, and theapoptosis rate of spinal cord cells was significantly increased. After SCI, the expression of miR-92a-3p was down-regulated, and increased expression of miR-92a-3p induced by agomiR-92 further significantly increased the BBB score and decreased apoptosis. PTEN was specifically targeted by miR-92a-3p. In addition, the phosphorylation levels of Akt and mTOR were up-regulated under the treatment of agomiR-92. Our data demonstrated that the neuroprotective effects of miR-92a-3p on spinal cord safter SCI were highly associated with the activation of the PTEN/AKT/mTOR pathway.

The Impact of Compression Duration on the RhoA, P75, S100 Expression in Spinal Cord Injury in Rat

Background: Compression of the spinal cord induces alterations in protein expression of neurons and glia cells, which in turn triggers a cascade of pathophysiologic events. It's well-documented that activation of inhibitory proteins following spinal cord injury stimulates activation of the RhoA via neurotrophin receptor p75 (p75NTR), which causes promotion of apoptotic cell death and inhibiting axon outgrowth. Elucidating the underlying factors driving the expressions during sustained compression is important to develop new therapeutic strategies. Objectives: To investigate the impact of compression duration on the RhoA, P75, and S100 expression in spinal cord injury model in rats. Methods: We investigated the impact of compression duration on the expression of RhoA, p75NTR, and S100β in rats with spinal cord injury (SCI). Initially, rats were subjected to SCI using an aneurism clip at the T9 vertebrae lamina for 3 sec or 10 min. Sham group was subjected to laminectomy only. We compared spinal cord histopathology at 3 and 14 days after injury for both short and prolonged compressive surgery groups. At the respective scarify times points, the rats were sacrificed, and the pathology of the injury was studied using light microscopy and immunohistochemistry. Results: We found a greater expression level of p75NTR, S100β, and RhoA in the prolonged compression group compared to the short compression group. The difference was statistically significant, indicating that earlier decompression can prevent the progress of secondary injuries due to higher expression levels of p75NTR, S100, and RhoA. Conclusions: This study demonstrated that early decompression of the spinal cord through the changes in p75NTR, S100β, and RhoA expression may modulate secondary injury events. Besides, it was found that using different inhibitors, especially for RhoA, might improve SCI-induced regeneration.

GDNF rescues the fate of neural progenitor grafts by attenuating Notch signals in the injured spinal cord in rodents

Neural progenitor cell (NPC) transplantation is a promising strategy for the treatment of spinal cord injury (SCI). In this study, we show that injury-induced Notch activation in the spinal cord microenvironment biases the fate of transplanted NPCs toward astrocytes in rodents. In a screen for potential clinically relevant factors to modulate Notch signaling, we identified glial cell-derived neurotrophic factor (GDNF). GDNF attenuates Notch signaling by mediating delta-like 1 homolog (DLK1) expression, which is independent of GDNF's effect on cell survival. When transplanted into a rodent model of cervical SCI, GDNF-expressing human-induced pluripotent stem cell-derived NPCs (hiPSC-NPCs) demonstrated higher differentiation toward a neuronal fate compared to control cells. In addition, expression of GDNF promoted endogenous tissue sparing and enhanced electrical integration of transplanted cells, which collectively resulted in improved neurobehavioral recovery. CRISPR-induced knockouts of the DLK1 gene in GDNF-expressing hiPSC-NPCs attenuated the effect on functional recovery, demonstrating that this effect is partially mediated through DLK1 expression. These results represent a mechanistically driven optimization of hiPSC-NPC therapy to redirect transplanted cells toward a neuronal fate and enhance their integration.

MicroRNA-466c-3p exerts protective effect on neuronal apoptosis and improves functional recovery post spinal cord injury via mitochondrial apoptotic pathway

Spinal cord injury (SCI) is involved with abnormal expression of miRNAs (miRs) which are responsible for some II^ry injury responses which include apoptosis, inflammation and oxidative stress. Mechanisms involving miRs induced apoptosis still needs to be investigated. In the present work we developed a rat model of SCI, followed by microarray analysis for expression of miRs at various time points after SCI. The locomotor activity was assessed by Basso, Beattie and Bresnahan score, lesion volume was analyzed by cresyl violet staining and TUNEL staining for extent of apoptosis at various time points of post SCI. Numbers of miRs were altered after 2 weeks of SCI among which miR-466c-3p was the most significantly down-regulated. Transfection with miR-466c-3p mimics caused overexpression of miR-466c-3p, also improvement in functional recovery, decrease in apoptosis of neuronal cells and lesion size was observed in SCI rats. The Luciferase assay suggested that miR-466c-3p suppressed the expression of Bcl-2 (apoptosis regulator). It was also evidenced that upon restoring the levels of Bcl-2 with the help of pc-DNA3-Bcl-2 halted the attenuating action of miR-466c-3p in hydrogen peroxide exposed N9 microglia cells. The findings suggested that miR-466c-3p may inhibit mitochondrial apoptotic pathway via blocking Bcl-2 and cleaved capase-9/-3in rats after SCI. Altogether, the results suggested that miR-466c-3p may exert attenuating effect on functional recovery and inhibit the apoptosis of neuronal cells via halting the mitochondrial apoptosis cascade in SCI rats indicating that miR-466c-3p can be attractive therapeutic candidate in treating SCI.

miR-142-3p suppresses apoptosis in spinal cord-injured rats

Introduction

Spinal cord injury (SCI) leads to abnormal expression of miRs, leading to secondary responses such as oxidative stress, inflammation and apoptosis. In the present work, we screened the miRs involved and the associated pathway.

Methods

In a rat model of SCI, the microarray analysis for expression of miRs at various time points post-SCI was done. The locomotor analysis was done by Basso, Beattie and Bresnahan score, and Cresyl violet staining was done for lesion volume and TUNEL assay was done for apoptosis in neuronal cells. The expression of apoptotic proteins was done by the western blot study.

Results

It was evidenced that the expression of the number of miRs was altered on the 14th day post-SCI, and miR-142-3p was found to be the most significantly suppressed miR. The results suggested that overexpression of miR-142-3p by its agomir-attenuated functional recovery decreased lesion size and apoptosis of neuronal cells in rats subjected to SCI. The luciferase assay indicated that miR-142-3p blocked the levels of Bax, which is a significant activator of the mitochondrial apoptotic pathway (MAP) via targeting the 3'UTR region of BV-2 cells, and in addition, pc-DNA-Bax restored Bax and inhibited the correcting role of miR-142-3p in hydrogen peroxide-treated BV-2 cells. The findings suggested that miR-142-3p may inhibit the MAP by inhibiting the expression of cleaved-caspase-3/-9 and Bax in SCI rats.

Conclusion

This study concludes that miR-142-3p may attenuate the functional recovery and decrease apoptosis in neuronal cells via inhibiting the MAP in the spinal cord-injured rats, confirming miR-142-3p as a potential therapeutic target in treating SCI.

Novel innovations in cell and gene therapies for spinal cord injury

Spinal cord injury (SCI) leads to chronic and multifaceted disability, which severely impacts the physical and mental health as well as the socio-economic status of affected individuals. Permanent disabilities following SCI result from the failure of injured neurons to regenerate and rebuild functional connections with their original targets. Inhibitory factors present in the SCI microenvironment and the poor intrinsic regenerative capacity of adult spinal cord neurons are obstacles for regeneration and functional recovery. Considerable progress has been made in recent years in developing cell and molecular approaches to enable the regeneration of damaged spinal cord tissue. In this review, we highlight several potent cell-based approaches and genetic manipulation strategies (gene therapy) that are being investigated to reconstruct damaged or lost spinal neural circuits and explore emerging novel combinatorial approaches for enhancing recovery from SCI.

MicroRNA-31 regulating apoptosis by mediating the phosphatidylinositol-3 kinase/protein kinase B signaling pathway in treatment of spinal cord injury

Apoptosis is a highly conservative energy demand program for non-inflammatory cell death, which is extremely significant in normal physiology and disease. There are many techniques used for studying apoptosis. MicroRNA (miRNA) is closely related to cell apoptosis, and especially microRNA-31 (miR-31) is involved in apoptosis by regulating a large number of target genes and signaling pathways. In many neurological diseases, cell apoptosis or programmed cell death plays an important role in the reduction of cell number, including the reduction of neurons in spinal cord injuries. In recent years, the phosphoinositol 3-kinase/AKT (PI3K/AKT) signal pathway, as a signal pathway involved in a variety of cell functions, has been studied in spinal cord injury diseases. The PI3K/AKT pathway directly or indirectly affects whether apoptosis occurs in a cell, thereby affecting a significant intracellular event sequence. This paper reviewed the interactions of miR-31 target sites in the PI3K/AKT signaling pathway, and explored new ways to prevent and treat spinal cord injury by regulating the effect of miR-31 on apoptosis.

MicroRNA‑124 improves functional recovery and suppresses Bax‑dependent apoptosis in rats following spinal cord injury

Spinal cord injury (SCI) induces aberrant expression of microRNAs (miRNAs), causing various secondary injury responses, including inflammation, apoptosis and oxidative stress. However, the mechanisms underlying miRNA-mediated apoptosis have not been fully elucidated. In the present study, a rat SCI model was established and a miRNA microarray was analyzed to detect miRNA expression profiles at different times post-SCI. The Basso, Beattie and Bresnahan score, cresyl violet staining and terminal deoxynucleotidyl-transferase-mediated dUTP nick end labeling staining were used to evaluate locomotor activity, lesion volume and neuronal cell apoptosis, respectively, at different time points post-SCI. It was observed that numerous miRNAs were altered at 14 days post-SCI and miR-124 was one of the most notably downregulated miRNAs. The present results demonstrated that overexpression of miR-124 by agomir-124 improves functional recovery, decreases lesion size and suppresses neuronal cell apoptosis in a rat SCI model. Luciferase reporter assay demonstrated that miR-124 inhibited apoptosis regulator BAX (Bax) expression, a key molecule in the activation of the mitochondrial apoptotic pathway, by targeting its 3′-untranslated region in BV-2 cells. Furthermore, restoration of Bax by pc-DNA-Bax inhibits the protective effect of miR-124 in H₂O₂-treated BV-2 cells. Notably, the present results demonstrated that miR-124 may block the mitochondrial apoptotic pathway by inhibiting Bax, cleaved-caspase-9 and cleaved-caspase-3 expression in rats following SCI. Collectively, the present results suggested that miR-124 may improve functional recovery and supress neuronal cell apoptosis by blocking the mitochondrial apoptotic pathway in SCI rats, suggesting that miR-124 may serve as a potential therapeutic target in SCI treatment.

Integrated systems analysis reveals conserved gene networks underlying response to spinal cord injury

Spinal cord injury (SCI) is a devastating neurological condition for which there are currently no effective treatment options to restore function. A major obstacle to the development of new therapies is our fragmentary understanding of the coordinated pathophysiological processes triggered by damage to the human spinal cord. Here, we describe a systems biology approach to integrate decades of small-scale experiments with unbiased, genome-wide gene expression from the human spinal cord, revealing a gene regulatory network signature of the pathophysiological response to SCI. Our integrative analyses converge on an evolutionarily conserved gene subnetwork enriched for genes associated with the response to SCI by small-scale experiments, and whose expression is upregulated in a severity-dependent manner following injury and downregulated in functional recovery. We validate the severity-dependent upregulation of this subnetwork in rodents in primary transcriptomic and proteomic studies. Our analysis provides systems-level view of the coordinated molecular processes activated in response to SCI.

Potential risk of clonally expanded amnion mesenchymal stem cell transplants in contused spinal cords

OBJECTIVE

Mesenchymal stem/stromal cells (MSC) promote recovery after spinal cord injury (SCI) using adult bone marrow MSC (BM-MSC). Newborn tissues are a convenient source of MSC that does not involve an invasive procedure for cell collection. In this study the authors tested the effects of rat amnion MSC clone (rAM-MSC) in SCI.

METHODS

We tested intra-parenchymal injection of a GFP+ rat rAM-MSC clone derived from E18.5 rats in rat SCI and measured behavioral recovery (BBB scores), histology and X-ray opacity. Expression of aggrecan was measured in culture after treatment with TGFß.

RESULTS

Injection of rAM-MSC after SCI did not improve BBB scores compared to control vehicle injections; rather they reduced scores significantly over 6 weeks. Spinal cords injected with rAM-MSC were hard in regions surrounding the SCI site, which was confirmed by X-ray opacity. Whole mount imaging of these cords showed minimal tissue loss in the SCI site that occurred in SCI controls, and persistence of GFP+ rAM-MSC. Mason's Trichrome staining of tissue sections showed more intense staining for extracellular matrix (ECM) surrounding and extending beyond the SCI site with injections of rAM-MSC but not in controls. In response to TGF-ß treatment in culture, chondrogenic aggrecan was expressed at higher levels in rAM-MSC than in rBM-MSC, suggesting that the upregulation of TGF-ß in SCI sites may promote chondrogenic differentiation.

CONCLUSION

Acute injection after SCI of a clonally expanded rAM-MSC resulted in aberrant differentiation towards a chondrocytic phenotype that disrupts the spinal cord and inhibits behavioral recovery after SCI. It will be critical to ensure that injection of extensively expanded neonatal cells do not differentiate aberrantly in traumatic CNS tissue and disrupt recovery.

MicroRNA-494 improves functional recovery and inhibits apoptosis by modulating PTEN/AKT/mTOR pathway in rats after spinal cord injury

Multiple cellular, molecular, and biochemical changes contribute to the etiology and treatment outcome of contusion spinal cord injury (SCI). MicroRNAs (miRNAs) aberrant expression have been found after SCI in recent studies. However, little is known about the functional significance of the unique role of miRNAs in SCI. Here, we established a rat SCI model and performed the miRNA microarray to analyze miRNAs expression at different times post-SCI. Microarray data revealed that 14 miRNAs were upregulated and 46 miRNAs were downregulated by 2 times compared with sham rat spinal cords, and miR-494 was one of the miRNAs being most significantly downregulated. Subsequently, we investigated miR-494 function and found that upregulation of miR-494 by agomir-494 improves functional recovery, reduces lesion size and inhibits apoptotic cell in rats following SCI. Moreover, our data showed that miR-494 suppresses phosphatase and tensin homolog (PTEN), a negative regulator of AKT/mTOR pathway, through directly targeting its 3'-UTR in BV-2 cells. Most importantly, we demonstrated that overexpression of miR-494 activates AKT/mTOR signaling pathway via inhibiting PTEN expression in rat SCI model. These findings suggested that miR-494 harbored the protective effect after SCI by modulating PTEN/AKT/mTOR pathway in rats and it is a potential candidate for SCI therapeutics.

Serum MicroRNAs Reflect Injury Severity in a Large Animal Model of Thoracic Spinal Cord Injury

Therapeutic development for spinal cord injury is hindered by the difficulty in conducting clinical trials, which to date have relied solely on functional outcome measures for patient enrollment, stratification, and evaluation. Biological biomarkers that accurately classify injury severity and predict neurologic outcome would represent a paradigm shift in the way spinal cord injury clinical trials could be conducted. MicroRNAs have emerged as attractive biomarker candidates due to their stability in biological fluids, their phylogenetic similarities, and their tissue specificity. Here we characterized a porcine model of spinal cord injury using a combined behavioural, histological, and molecular approach. We performed next-generation sequencing on microRNAs in serum samples collected before injury and then at 1, 3, and 5 days post injury. We identified 58, 21, 9, and 7 altered miRNA after severe, moderate, and mild spinal cord injury, and SHAM surgery, respectively. These data were combined with behavioural and histological analysis. Overall miRNA expression at 1 and 3 days post injury strongly correlates with outcome measures at 12 weeks post injury. The data presented here indicate that serum miRNAs are promising candidates as biomarkers for the evaluation of injury severity for spinal cord injury or other forms of traumatic, acute, neurologic injury.

Identification of crucial genes associated with rat traumatic spinal cord injury

The aim of the present study was to investigate the key genes associated with traumatic spinal cord injuries (TSCI). The dataset GSE52763 was downloaded from the Gene Expression Omnibus, for which lumbar spinal cord samples were obtained from rats at 1 and 3 weeks following contusive spinal cord injury and 1 week subsequent to a sham laminectomy, and used to identify differentially expressed genes (DEGs). Functional enrichment analysis, co‑expression analysis and transcription factor (TF) identification were performed for DEGs common to the 1 and 3 week injury samples. In total, 234 upregulated and 51 downregulated DEGs were common to the 1 and 3 week injury samples. The upregulated DEGs were significantly enriched in Gene Ontology terms concerning immunity (e.g. Itgal and Ccl2) and certain pathways, including natural killer cell mediated cytotoxicity [e.g. Ras‑related C3 botulinum toxin substrate 2 (Rac2) and TYRO protein tyrosine kinase binding protein (Tyrobp)]. The downregulated DEGs were highly enriched in female gonad development [e.g. progesterone receptor (Pgr)], and the steroid biosynthesis pathway. A total of 139 genes had co‑expression associations and the majority of them were upregulated genes. The upregulated co‑expressed genes were predominantly enriched in biological regulation, including TGFB induced factor homeobox 1 (Tgif1) and Rac2. The downregulated co‑expressed genes were enriched in anatomical structure development (e.g. Dnm3). A total of 92 co‑expressed genes composed the protein‑protein interaction network. Additionally, 9 TFs (e.g. Pgr and Tgif1) were identified from the DEGs. It was hypothesized that the genes including Tgif1, Rac2, Tyrobp, and Pgr may be closely associated with TSCI.

MicroRNA-146a Contributes to SCI Recovery via Regulating TRAF6 and IRAK1 Expression

MicroRNA-146a participates in spinal cord injury (SCI) recovery. Until recently, how miRNA-146a participates in SCI remained unclear. In this study, we tried to explore the roles of miRNA-146a in the recovery of SCI using a rat model. The expression of the probable target genes of miRNA-146a (including IRAK1 and TARF6) as well as proinflammation cytokines were measured until 7 days after surgery in the three groups (sham group, SCI group, and miRNA-146a antagomir injection group). Also, the animals' motivations were estimated using Basso Beattie Bresnahan (BBB) during the whole experiment. A luciferase assay was performed to demonstrate that miRNA-146a could directly target the mRNAs of IRAK1 and TRAF6. Our experiments indicate that miRNA-146a inhibits proinflammatory cytokine secretion by suppressing IRAK1 and TRAF6 expression in the SCI model. In contrast, miRNA-146a may be upregulated by inflammatory mediators via the IRAK1/TRAF6 pathway in the spinal cord. As a negative feedback element, miRNA-146a could make sure that the expression of IRAK1- and TRAF6-mediated genes was under tight control. Thus, miRNA-146a may serve as a novel therapeutic target for SCI interventions.

Cytokine and Growth Factor Activation In Vivo and In Vitro after Spinal Cord Injury

Spinal cord injury results in a life-disrupting series of deleterious interconnected mechanisms encompassed by the primary and secondary injury. These events are mediated by the upregulation of genes with roles in inflammation, transcription, and signaling proteins. In particular, cytokines and growth factors are signaling proteins that have important roles in the pathophysiology of SCI. The balance between the proinflammatory and anti-inflammatory effects of these molecules plays a critical role in the progression and outcome of the lesion. The excessive inflammatory Th1 and Th17 phenotypes observed after SCI tilt the scale towards a proinflammatory environment, which exacerbates the deleterious mechanisms present after the injury. These mechanisms include the disruption of the spinal cord blood barrier, edema and ion imbalance, in particular intracellular calcium and sodium concentrations, glutamate excitotoxicity, free radicals, and the inflammatory response contributing to the neurodegenerative process which is characterized by demyelination and apoptosis of neuronal tissue.

Loss of microRNA-124 expression in neurons in the peri-lesion area in mice with spinal cord injury

MicroRNA-124 (miR-124) is abundantly expressed in neurons in the mammalian central nervous system, and plays critical roles in the regulation of gene expression during embryonic neurogenesis and postnatal neural differentiation. However, the expression profile of miR-124 after spinal cord injury and the underlying regulatory mechanisms are not well understood. In the present study, we examined the expression of miR-124 in mouse brain and spinal cord after spinal cord injury using in situ hybridization. Furthermore, the expression of miR-124 was examined with quantitative RT-PCR at 1, 3 and 7 days after spinal cord injury. The miR-124 expression in neurons at the site of injury was evaluated by in situ hybridization combined with NeuN immunohistochemical staining. The miR-124 was mainly expressed in neurons throughout the brain and spinal cord. The expression of miR-124 in neurons significantly decreased within 7 days after spinal cord injury. Some of the neurons in the peri-lesion area were NeuN(+)/miR-124(-). Moreover, the neurons distal to the peri-lesion site were NeuN(+)/miR-124(+). These findings indicate that miR-124 expression in neurons is reduced after spinal cord injury, and may reflect the severity of spinal cord injury.

Voluntary Exercise Preconditioning Activates Multiple Antiapoptotic Mechanisms and Improves Neurological Recovery after Experimental Traumatic Brain Injury

Physical activity can attenuate neuronal loss, reduce neuroinflammation, and facilitate recovery after brain injury. However, little is known about the mechanisms of exercise-induced neuroprotection after traumatic brain injury (TBI) or its modulation of post-traumatic neuronal cell death. Voluntary exercise, using a running wheel, was conducted for 4 weeks immediately preceding (preconditioning) moderate-level controlled cortical impact (CCI), a well-established experimental TBI model in mice. Compared to nonexercised controls, exercise preconditioning (pre-exercise) improved recovery of sensorimotor performance in the beam walk task, as well as cognitive/affective functions in the Morris water maze, novel object recognition, and tail-suspension tests. Further, pre-exercise reduced lesion size, attenuated neuronal loss in the hippocampus, cortex, and thalamus, and decreased microglial activation in the cortex. In addition, exercise preconditioning activated the brain-derived neurotrophic factor pathway before trauma and amplified the injury-dependent increase in heat shock protein 70 expression, thus attenuating key apoptotic pathways. The latter include reduction in CCI-induced up-regulation of proapoptotic B-cell lymphoma 2 (Bcl-2)-homology 3-only Bcl-2 family molecules (Bid, Puma), decreased mitochondria permeabilization with attenuated release of cytochrome c and apoptosis-inducing factor (AIF), reduced AIF translocation to the nucleus, and attenuated caspase activation. Given these neuroprotective actions, voluntary physical exercise may serve to limit the consequences of TBI.

Acyl-2-aminobenzimidazoles: a novel class of neuroprotective agents targeting mGluR5

Positive allosteric modulators (PAMs) of the metabotropic glutamate receptor 5 (mGluR5) are promising therapeutic agents for treating traumatic brain injury (TBI). Using computational and medicinal methods, the structure-activity relationship of a class of acyl-2-aminobenzimidazoles (1-26) is reported. The new compounds are designed based on the chemical structure of 3,3'-difluorobenzaldazine (DFB), a known mGluR5 PAM. Ligand design and prediction of binding affinities of the new compounds have been performed using the site identification by ligand competitive saturation (SILCS) method. Binding affinities of the compounds to the transmembrane domain of mGluR5 have been evaluated using nitric oxide (NO) production assay, while the safety of the compounds is tested. One new compound found in this study, compound 22, showed promising activity with an IC₅₀ value of 6.4 μM, which is ∼20 fold more potent than that of DFB. Compound 22 represents a new lead for possible development as a treatment for TBI and related neurodegenerative conditions.

Cyclopropyl-containing positive allosteric modulators of metabotropic glutamate receptor subtype 5

Positive allosteric modulators (PAMs) binding to the transmembrane (TM) domain of metabotropic glutamate receptor 5 (mGluR5) are promising therapeutic agents for psychiatric disorders and traumatic brain injury (TBI). Novel PAMs based on a trans-2-phenylcyclopropane amide scaffold have been designed and synthesized. Facilitating ligand design and allowing estimation of binding affinities to the mGluR5 TM domain was the novel computational strategy, site identification by ligand competitive saturation (SILCS). The potential protective activity of the new compounds was evaluated using nitric oxide (NO) production in BV2 microglial cell cultures treated with lipopolysaccharide (LPS), and the toxicity of the new compounds tested using a cell viability assay. One of the new compounds, 3a, indicated promising activity with potency of 30 μM, which is 4.5-fold more potent than its lead compound 3,3'-difluorobenzaldazine (DFB), and showed no detectable toxicity with concentrations as high as 1000 μM. Thus this compound represents a new lead for possible development as treatment for TBI and related neurodegenerative disorders.

DNA methylation temporal profiling following peripheral versus central nervous system axotomy

The regulatory mechanisms responsible for the gene expression pattern associated with axotomy-dependent signaling affecting the neuronal phenotype, including the axonal regenerative program, remain unclear. To further this understanding, we recently performed DNA methylation temporal profiling in lumbar dorsal root ganglia (DRG) after axotomy of the central spinal (non-regenerating) and of the peripheral sciatic nerve (regenerating) axonal branches. DNA methylation microarrays for mouse gene promoters and CpG islands (Roche/NimbleGen) were employed after immunoprecipitation of 5-methylcytosine-DNA. Here we provide a detailed data descriptor of this DNA methylation dataset, which allows in depth evaluation of the experimental design, assessment of data reproducibility and a full interactive operator-based systematic data analysis. In fact, we offer a methylation ‘hit’ scoring map of the whole microarray data in a workable spreadsheet that allows data sorting by genes, conditions or hits of interests that is ready for functional gene annotation and classification. This dataset allows investigators bioinformatic comparison to other epigenetic and gene expression datasets and further experimental characterization of the role of DNA methylation in axotomy-dependent pathways.

Identifying the role of microRNAs in spinal cord injury

Spinal cord injury (SCI) is medically and socioeconomically debilitating, and effective treatments are lacking. The elucidation of the pathophysiological mechanisms underlying SCI is essential for developing effective treatments for SCI. MicroRNAs (miRNAs) are small non-coding RNA molecules (18-24 nucleotides long) that regulate gene expression by interacting with specific target sequences. Recent studies suggest that miRNAs can act as post-transcriptional regulators to inhibit mRNA translation. Bioinformatic analyses indicate that the altered expression of miRNAs has an effect on critical processes of SCI physiopathology, including astrogliosis, oxidative stress, inflammation, apoptosis, and neuroplasticity. Therefore, the study of miRNAs may provide new insights into the molecular mechanisms of SCI. Current studies have also provided potential therapeutic clinical applications that involve targeting mRNAs to treat SCI. This review summarizes the biogenesis and function of miRNAs and the roles of miRNAs in SCI. We also discuss the potential therapeutic applications of miRNA-based interventions for SCI.

Coronin 1A inhibits neurite outgrowth in PC12 cells

Regenerative response to central nervous system damage in mammals is limited because of inhibitor signals which consist of myelin associated inhibitor proteins and chondroitin sulfate proteoglycans. Inhibitor signals mainly affect cytoskeleton elements which are important for axonal sprouting and neurite outgrowth. Coronin 1A is an actin cytoskeleton associated protein. Coronin 1A shows its effect on actin cytoskeleton through binding to the Arp2/3 complex which is a key nucleator of actin polymerization and regulates its activation on actin cytoskeleton. Coronin 1A-Arp2/3 interaction is regulated by phosphorylation of Coronin 1A from the C and N terminal region. Thus, Coronin 1A-Arp2/3 complex is one of the targets of inhibitory signaling cascades. The aim of this study was to investigate the effect of Coronin 1A on neurite outgrowth in PC12 cells in vitro. The results showed that Coronin 1A is expressed in differentiated PC12 cells and localized along axonal sprouting region of the neurites. Other results showed that overexpression of Coronin 1A in PC12 cells effects neurite outgrowth. Neurite lengths of the Coronin 1A overexpressing PC12 cells were lower than the untransfected (p<0.001) and control transfected (p=0.002) PC12 cells. These results indicate that Coronin 1A has an inhibitory effect on neurite outgrowth in vitro.

Analyzing time-series microarray data reveals key genes in spinal cord injury

Although many scholars have utilized high-throughput microarrays to delineate gene expression patterns after spinal cord injury (SCI), no study has evaluated gene changes in raphe magnus (RM) and somatomotor cortex (SMTC), two areas in brain primarily affected by SCI. In present study, we aimed to analyze the differentially expressed genes (DEGs) of RM and SMTC between SCI model and sham injured control at 4, 24 h, 7, 14, 28 days, and 3 months using microarray dataset GSE2270 downloaded from gene expression omnibus and unpaired significance analysis of microarray method. Protein-protein interaction (PPI) network was constructed for DEGs at crucial time points and significant biological functions were enriched using DAVID. The results indicated that more DEGs were identified at 14 days in RM and at 4 h/3 months in SMTC after SCI. In the PPI network for DEGs at 14 days in RM, interleukin 6, glyceraldehyde-3-phosphate dehydrogenase (GAPDH), FBJ murine osteosarcoma viral oncogene homolog (FOS), tumor necrosis factor, and nuclear receptor subfamily 3, group C, member 1 (glucocorticoid receptor) were the top 5 hub genes; In the PPI network for DEGs at 3 months in SMTC, the top 5 hub genes were ubiquitin B, Ras-related C3 botulinum toxin substrate 1 (rho family, small GTP binding protein Rac1), FOS, Janus kinase 2 and vascular endothelial growth factor A. Hedgehog and Wnt signaling pathways were the top 2 significant pathways in RM. These hub DEGs and pathways may be underlying therapeutic targets for SCI.

Time-specific microRNA changes during spinal motoneuron degeneration in adult rats following unilateral brachial plexus root avulsion: ipsilateral vs. contralateral changes

Background

Spinal root avulsion induces multiple pathophysiological events consisting of altered levels of specific genes and proteins related to inflammation, apoptosis, and oxidative stress, which collectively result in the death of the affected motoneurons. Recent studies have demonstrated that the gene changes involved in spinal cord injury can be regulated by microRNAs, which are a class of short non-coding RNA molecules that repress target mRNAs post-transcriptionally. With consideration for the time course of the avulsion-induced gene expression patterns within dying motoneurons, we employed microarray analysis to determine whether and how microRNAs are involved in the changes of gene expression induced by pathophysiological events in spinal cord motoneurons.

Results

The expression of a total of 3,361 miRNAs in the spinal cord of adult rats was identified. Unilateral root-avulsion resulted in significant alterations in miRNA expression. In the ipsilateral half compared to the contralateral half of the spinal cord, on the 3rd day after the injury, 55 miRNAs were upregulated, and 24 were downregulated, and on the 14th day after the injury, 36 miRNAs were upregulated, and 23 were downregulated. The upregulation of miR-146b-5p and miR-31a-3p and the downregulation of miR-324-3p and miR-484 were observed. Eleven of the miRNAs, including miR-21-5p, demonstrated a sustained increase; however, only miR-466c-3p presented a sustained decrease 3 and 14 days after the injury. More interestingly, 4 of the miRNAs, including miR-18a, were upregulated on the 3rd day but were downregulated on the 14th day after injury.

Some of these miRNAs target inflammatory-response genes in the early stage of injury, and others target neurotransmitter transport genes in the intermediate stages of injury. The altered miRNA expression pattern suggests that the MAPK and calcium signaling pathways are consistently involved in the injury response.

Conclusions

This analysis may facilitate the understanding of the time-specific altered expression of a large set of microRNAs in the spinal cord after brachial root avulsion.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2202-15-92) contains supplementary material, which is available to authorized users.

MicroRNA dysregulation in spinal cord injury: causes, consequences and therapeutics

Trauma to the spinal cord causes permanent disability to more than 180,000 people every year worldwide. The initial mechanical damage triggers a complex set of secondary events involving the neural, vascular, and immune systems that largely determine the functional outcome of the spinal cord injury (SCI). Cellular and biochemical mechanisms responsible for this secondary injury largely depend on activation and inactivation of specific gene programs. Recent studies indicate that microRNAs function as gene expression switches in key processes of the SCI. Microarray data from rodent contusion models reveal that SCI induces changes in the global microRNA expression patterns. Variations in microRNA abundance largely result from alterations in the expression of the cells at the damaged spinal cord. However, microRNA expression levels after SCI are also influenced by the infiltration of immune cells to the injury site and the death and migration of specific neural cells after injury. Evidences on the role of microRNAs in the SCI pathophysiology have come from different sources. Bioinformatic analysis of microarray data has been used to identify specific variations in microRNA expression underlying transcriptional changes in target genes, which are involved in key processes in the SCI. Direct evidences on the role of microRNAs in SCI are scarcer, although recent studies have identified several microRNAs (miR-21, miR-486, miR-20) involved in key mechanisms of the SCI such as cell death or astrogliosis, among others. From a clinical perspective, different evidences make clear that microRNAs can be potent therapeutic tools to manipulate cell state and molecular processes in order to enhance functional recovery. The present article reviews the actual knowledge on how injury affects microRNA expression and the meaning of these changes in the SCI pathophysiology, to finally explore the clinical potential of microRNAs in the SCI.

Abundant expression of guidance and synaptogenic molecules in the injured spinal cord

Background

Spinal interneurons have emerged as crucial targets of supraspinal input during post-injury axonal remodelling. For example, lesioned corticospinal projections use propriospinal neurons as relay stations to form intraspinal detour circuits that circumvent the lesion site and contribute to functional recovery. While a number of the molecules that determine the formation of neuronal circuits in the developing nervous system have been identified, it is much less understood which of these cues are also expressed in the injured spinal cord and can thus guide growing collaterals and initiate synaptogenesis during circuit remodelling.

Methodology/Principal Findings

To address this question we characterized the expression profile of a number of guidance and synaptogenic molecules in the cervical spinal cord of healthy and spinal cord-injured mice by in situ hybridization. To assign the expression of these molecules to distinct populations of interneurons we labeled short and long propriospinal neurons by retrograde tracing and glycinergic neurons using a transgenically expressed fluorescent protein. Interestingly, we found that most of the molecules studied including members of slit-, semaphorin-, synCAM-, neuroligin- and ephrin- families as well as their receptors are also present in the adult CNS. While many of these molecules were abundantly expressed in all interneurons examined, some molecules including slits, semaphorin 7a, synCAM4 and neuroligin 1 showed preferential expression in propriospinal interneurons. Overall the expression pattern of guidance and synaptogenic molecules in the cervical spinal cord appeared to be stable over time and was not substantially altered following a midthoracic spinal cord injury.

Conclusions

Taken together, our study indicates that many of the guidance and synaptogenic cues that regulate neuronal circuit formation in development are also present in the adult CNS and therefore likely contribute to the remodelling of axonal connections in the injured spinal cord.

Molecular and cellular changes in the lumbar spinal cord following thoracic injury: regulation by treadmill locomotor training

Traumatic spinal cord injury (SCI) often leads to debilitating loss of locomotor function. Neuroplasticity of spinal circuitry underlies some functional recovery and therefore represents a therapeutic target to improve locomotor function following SCI. However, the cellular and molecular mechanisms mediating neuroplasticity below the lesion level are not fully understood. The present study performed a gene expression profiling in the rat lumbar spinal cord at 1 and 3 weeks after contusive SCI at T9. Another group of rats received treadmill locomotor training (TMT) until 3 weeks, and gene expression profiles were compared between animals with and without TMT. Microarray analysis showed that many inflammation-related genes were robustly upregulated in the lumbar spinal cord at both 1 and 3 weeks after thoracic injury. Notably, several components involved in an early complement activation pathway were concurrently upregulated. In line with the microarray finding, the number of microglia substantially increased not only in the white matter but also in the gray matter. C3 and complement receptor 3 were intensely expressed in the ventral horn after injury. Furthermore, synaptic puncta near ventral motor neurons were frequently colocalized with microglia after injury, implicating complement activation and microglial cells in synaptic remodeling in the lumbar locomotor circuitry after SCI. Interestingly, TMT did not influence the injury-induced upregulation of inflammation-related genes. Instead, TMT restored pre-injury expression patterns of several genes that were downregulated by injury. Notably, TMT increased the expression of genes involved in neuroplasticity (Arc, Nrcam) and angiogenesis (Adam8, Tie1), suggesting that TMT may improve locomotor function in part by promoting neurovascular remodeling in the lumbar motor circuitry.

Spatial and temporal expression levels of specific microRNAs in a spinal cord injury mouse model and their relationship to the duration of compression

BACKGROUND CONTEXT

MicroRNAs, a class of small nonprotein-coding RNAs, are thought to control gene translation into proteins. The latter are the ultimate effectors of the biochemical cascade occurring in any physiological and pathological process. MicroRNAs have been shown to change their expression levels during injury of spinal cord in contusion rodent models. Compression is the most frequent mode of damage of neural elements in spinal cord injury. The cellular and molecular changes occurring in the spinal cord during prolonged compression are not very well elucidated. Understanding the underlying molecular events that occur during sustained compression is paramount in building new therapeutic strategies.

PURPOSE

The purpose of our study was to probe the relationship between the expression level changes of different miRNAs and the timing of spinal cord decompression in a mouse model.

STUDY DESIGN

A compression spinal cord injury mouse model was used for the study.

METHODS

A laminectomy was performed in the thoracic spine of C57BL/6 mice. Then, the thecal sac was compressed to create the injury. Decompression was performed early for one group and it was delayed in the second group. The spinal cord at the epicenter of the injury and one level rostral to it were removed at 3, 6, and 24 hours after trauma, and RNA was extracted. Expression levels of six different microRNAs and the relationship to the duration of compression were analyzed. This work was supported in part by the University Research Council Grants Program at the University of Texas Health Science Center San Antonio (Grant 130267). There are no specific conflicts of interest to be disclosed for this work.

RESULTS

Expression levels of microRNAs in the prolonged compression of spinal cord model were significantly different compared with the expression levels in the short duration of compression spinal cord injury model. Furthermore, microRNAs show a different expression pattern in different regions of the injured spinal cord.

CONCLUSIONS

Our findings demonstrate that spinal cord compression causes alterations in the expression of different miRNAs in the acute phase of injury. Their expression is related to the duration of the compression of the spinal cord. These findings suggest that early decompression of the spinal cord may have an important modulating effect on the molecular cascade triggered during secondary injury through the changes in expression levels of specific microRNAs.

Evolution and Controllability of Cancer Networks: A Boolean Perspective

Cancer forms a robust system capable of maintaining stable functioning (cell sustenance and proliferation) despite perturbations. Cancer progresses as stages over time typically with increasing aggressiveness and worsening prognosis. Characterizing these stages and identifying the genes driving transitions between them is critical to understand cancer progression and to develop effective anti-cancer therapies. In this work, we propose a novel model for the `cancer system' as a Boolean state space in which a Boolean network, built from protein-interaction and gene-expression data from different stages of cancer, transits between Boolean satisfiability states by "editing" interactions and "flipping" genes. Edits reflect rewiring of the PPI network while flipping of genes reflect activation or silencing of genes between stages. We formulate a minimization problem min flip to identify these genes driving the transitions. The application of our model (called BoolSpace) on three case studies-pancreatic and breast tumours in human and post spinal-cord injury (SCI) in rats-reveals valuable insights into the phenomenon of cancer progression: (i) interactions involved in core cell-cycle and DNA-damage repair pathways are significantly rewired in tumours, indicating significant impact to key genome-stabilizing mechanisms; (ii) several of the genes flipped are serine/threonine kinases which act as biological switches, reflecting cellular switching mechanisms between stages; and (iii) different sets of genes are flipped during the initial and final stages indicating a pattern to tumour progression. Based on these results, we hypothesize that robustness of cancer partly stems from "passing of the baton" between genes at different stages-genes from different biological processes and/or cellular components are involved in different stages of tumour progression thereby allowing tumour cells to evade targeted therapy, and therefore an effective therapy should target a "cover set" of these genes. A C/C++ implementation of BoolSpace is freely available at: http://www.bioinformatics.org.au/tools-data.

Effects of Tetramethylpyrazine on Microglia Activation in Spinal Cord Compression Injury of Mice

Secondary mechanisms, including inflammation and microglia activation, serve as targets for the development and application of pharmacological strategies in the management of spinal cord injury (SCI). Tetramethylpyrazine (TMP), an active ingredient of Ligusticum wallichii (chuanxiong), has shown anti-inflammatory and neuroprotective effects against SCI. However, it remains uncertain whether the inflammation-suppressive effects of TMP play a modulatory role over microglia activation in SCI. The present study investigated the effects of TMP on microglia activation and pro-inflammatory cytokines in spinal cord compression injury in mice. For a real-time PCR measurement of pro-inflammatory cytokines, SCI was induced in mice by the clip compression method (30 g force, 1 min) and TMP (15 or 30 mg/kg, i.p.) was administered once, 30 minutes before the SCI induction. For immunohistochemistry, TMP (30 mg/kg, i.p.) treatment was given three times during the first 48 hours after the SCI. 30 mg/kg of TMP treatment reduced the up-regulation of TNF-α, IL-1β and COX-2 mRNA in the spinal tissue at four hours after the SCI induction. TMP also significantly attenuated microglia activation and neutrophil infiltration at 48 hours after the SCI induction. In addition, iNOS expression in the spinal tissue was attenuated with TMP treatment. These results suggest that TMP plays a modulatory role in microglia activation and may protect the spinal cord from or potentially delay secondary spinal cord injury.

TrkB.T1 contributes to neuropathic pain after spinal cord injury through regulation of cell cycle pathways

Spinal cord injury (SCI) frequently causes severe, persistent central neuropathic pain that responds poorly to conventional pain treatments. Brain-derived neurotrophic factor (BDNF) signaling appears to contribute to central sensitization and nocifensive behaviors in certain animal models of chronic pain through effects mediated in part by the alternatively spliced truncated isoform of the BDNF receptor tropomyosin-related kinase B.T1 (trkB.T1). Mechanisms linking trkB.T1 to SCI-induced chronic central pain are unknown. Here, we examined the role of trkB.T1 in central neuropathic pain after spinal cord contusion. Genetic deletion of trkB.T1 in mice significantly reduced post-SCI mechanical hyperesthesia, locomotor dysfunction, lesion volumes, and white matter loss. Whole genome analysis, confirmed at the protein level, revealed that cell cycle genes were upregulated in trkB.T1(+/+) but not trkB.T1(-/-) spinal cord after SCI. TGFβ-induced reactive astrocytes from WT mice showed increased cell cycle protein expression that was significantly reduced in astrocytes from trkB.T1(-/-) mice that express neither full-length trkB nor trkB.T1. Administration of CR8, which selectively inhibits cyclin-dependent kinases, reduced hyperesthesia, locomotor deficits, and dorsal horn (SDH) glial changes after SCI, similar to trkB.T1 deletion, without altering trkB.T1 protein expression. In trkB.T1(-/-) mice, CR8 had no effect. These data indicate that trkB.T1 contributes to the pathobiology of SCI and SCI pain through modulation of cell cycle pathways and suggest new therapeutic targets.

Gene expression changes in the injured spinal cord following transplantation of mesenchymal stem cells or olfactory ensheathing cells

Transplantation of bone marrow derived mesenchymal stromal cells (MSC) or olfactory ensheathing cells (OEC) have demonstrated beneficial effects after spinal cord injury (SCI), providing tissue protection and improving the functional recovery. However, the changes induced by these cells after their transplantation into the injured spinal cord remain largely unknown. We analyzed the changes in the spinal cord transcriptome after a contusion injury and MSC or OEC transplantation. The cells were injected immediately or 7 days after the injury. The mRNA of the spinal cord injured segment was extracted and analyzed by microarray at 2 and 7 days after cell grafting. The gene profiles were analyzed by clustering and functional enrichment analysis based on the Gene Ontology database. We found that both MSC and OEC transplanted acutely after injury induce an early up-regulation of genes related to tissue protection and regeneration. In contrast, cells transplanted at 7 days after injury down-regulate genes related to tissue regeneration. The most important change after MSC or OEC transplant was a marked increase in expression of genes associated with foreign body response and adaptive immune response. These data suggest a regulatory effect of MSC and OEC transplantation after SCI regarding tissue repair processes, but a fast rejection response to the grafted cells. Our results provide an initial step to determine the mechanisms of action and to optimize cell therapy for SCI.

Genome-wide gene expression profiling of stress response in a spinal cord clip compression injury model

Background

The aneurysm clip impact-compression model of spinal cord injury (SCI) is a standard injury model in animals that closely mimics the primary mechanism of most human injuries: acute impact and persisting compression. Its histo-pathological and behavioural outcomes are extensively similar to human SCI. To understand the distinct molecular events underlying this injury model we analyzed global mRNA abundance changes during the acute, subacute and chronic stages of a moderate to severe injury to the rat spinal cord.

Results

Time-series expression analyses resulted in clustering of the majority of deregulated transcripts into eight statistically significant expression profiles. Systematic application of Gene Ontology (GO) enrichment pathway analysis allowed inference of biological processes participating in SCI pathology. Temporal analysis identified events specific to and common between acute, subacute and chronic time-points. Processes common to all phases of injury include blood coagulation, cellular extravasation, leukocyte cell-cell adhesion, the integrin-mediated signaling pathway, cytokine production and secretion, neutrophil chemotaxis, phagocytosis, response to hypoxia and reactive oxygen species, angiogenesis, apoptosis, inflammatory processes and ossification. Importantly, various elements of adaptive and induced innate immune responses span, not only the acute and subacute phases, but also persist throughout the chronic phase of SCI. Induced innate responses, such as Toll-like receptor signaling, are more active during the acute phase but persist throughout the chronic phase. However, adaptive immune response processes such as B and T cell activation, proliferation, and migration, T cell differentiation, B and T cell receptor-mediated signaling, and B cell- and immunoglobulin-mediated immune response become more significant during the chronic phase.

Conclusions

This analysis showed that, surprisingly, the diverse series of molecular events that occur in the acute and subacute stages persist into the chronic stage of SCI. The strong agreement between our results and previous findings suggest that our analytical approach will be useful in revealing other biological processes and genes contributing to SCI pathology.

Anti-apoptotic effect of microRNA-21 after contusion spinal cord injury in rats

Multiple cellular, molecular, and biochemical changes contribute to the etiology and treatment outcome of contusion spinal cord injury (SCI). Dysregulation of microRNAs (miRNAs) has been found following SCI in recent studies. However, little is known about the functional significance of the unique role of miRNAs in SCI. We analyzed the miRNA expression patterns 1 and 3 days following rat SCI using miRNA microarray. Microarray data revealed that nine miRNAs were upregulated and five miRNAs were downregulated 1 day post-injury, and that three miRNAs were upregulated and five miRNAs were downregulated 3 days post-injury, in the sites of contused when compared with sham rat spinal cords. Because miR-21 was one of the miRNAs being most significantly upregulated, we investigated its function. Knockdown of miR-21 by antagomir-21 led to attenuated recovery in hindlimb motor function, increased lesion size, and decreased tissue sparing in rats. Compared with the negative control group, treatment with antagomir-21 significantly increased apoptosis following SCI. Pro-apoptosis genes Fas ligand (FasL), phosphatase and tensin homolog (PTEN), and programmed cell death protein 4 (PDCD4) were proved to be direct targets of miR-21 in many diseases and cell types. In vivo treatment with antagomir-21 increased the expression of FasL and PTEN, but did not affect PDCD4. These results suggested that miR-21 played an important role in limiting secondary cell death following SCI, and that the protective effects of miR-21 might have been the result of its regulation on pro-apoptotic genes. Thus, miR-21 may play an important role in the pathophysiology of SCI.

The emerging roles of microRNAs in CNS injuries

The consequences of injuries to the CNS are profound and persistent, resulting in substantial burden to both the individual patient and society. Existing treatments for CNS injuries such as stroke, traumatic brain injury and spinal cord injury have proved inadequate, partly owing to an incomplete understanding of post-injury cellular and molecular changes. MicroRNAs (miRNAs) are RNA molecules composed of 20-24 nucleotides that function to inhibit mRNA translation and have key roles in normal CNS development and function, as well as in disease. However, a role for miRNAs as effectors of CNS injury has recently emerged. Use of bioinformatics to assess the mRNA targets of miRNAs enables high-order analysis of interconnected networks, and can reveal affected pathways that may not be identifiable with the use of traditional techniques such as gene knock-in or knockout approaches, or mRNA microarrays. In this Review, we discuss the findings of miRNA microarray studies of spinal cord injury, traumatic brain injury and stroke, as well as the use of gene ontological algorithms to discern global patterns of molecular and cellular changes following such injuries. Furthermore, we examine the current state of miRNA-based therapies and their potential to improve functional outcomes in patients with CNS injuries.

Gene expression profiling of liver X receptor α and Bcl-2-associated X protein in experimental transection spinal cord-injured rats

BACKGROUND

Study of molecular responses to central nervous system injury would be helpful for controlling the harmful pathways post-injury and triggering the useful pathways required for the treatment of injury.

OBJECTIVE

To investigate the expression level of liver X receptor α (LXRα) which has anti-inflammatory effects and pro-apoptotic Bcl-2-associated X protein (Bax) upon spinal cord injury (SCI).

DESIGN

To induce SCI, transection was carried out at T9 level of male Wister rats. Approximately 8 mm of rostral, caudal, and epicenter tissues of injured sites in treated rats were chosen for quantitative real-time polymerase chain reaction at the 6, 24, and 72 hours, and 7 and 10 days post-surgery.

RESULTS

Our results showed a complicated temporal and spatial pattern of alteration in LXRα and Bax mRNA expression levels after SCI. LXRα expression level followed a homologues pattern (additive and subtractive wave) with a difference in time at three areas of studied. Rostral, caudal, and epicenter expression patterns of Bax were dissimilar in these areas. Gradual increase in the expression of Bax without any decrease at the rostral area was observed, presumably indicating the active transcription process of this gene, regardless of its protein situation.

CONCLUSION

A time lapse significant change in Bax expression level was observed only in the epicenter of injury, emphasizing that apoptotic responses are limited to this area. Furthermore, an increase in LXRα transcription level was observed first in rostral area and then extended to epicentral and caudal areas, implying that inflammation responses extended from rostral to caudal areas.

Age-dependent modulation of cortical transcriptomes in spinal cord injury and repair

Both injury and aging of the central nervous system reportedly produce profound changes in gene expression. Therefore, aging may interfere with the success of therapeutic interventions which were tailored for young patients. Using genome-scale transcriptional profiling, we identified distinct age-dependent expression profiles in rat sensorimotor cortex during acute, subacute and chronic phases of spinal cord injury (SCI). Aging affects the cortical transcriptomes triggered by transection of the corticospinal tract as there was only a small overlap between the significantly lesion-regulated genes in both age groups. Over-representation analysis of the lesion-regulated genes revealed that, in addition to biological processes in common, such as lipid metabolism, others, such as activation of complement cascade, were specific for aged animals. When a recently developed treatment to suppress fibrotic scarring (anti-scarring treatment AST) was applied to the injured spinal cord of aged (22 months) and young (2 months) rats, we found that the cortical gene expression in old rats was modulated to resemble regeneration-associated profiles of young animals including the up-regulation of known repair promoting growth and transcription factors at 35 dpo. In combination with recent immunohistochemical findings demonstrating regenerative axon growth upon AST in aged animals, the present investigation on the level of gene expression strongly supports the feasibility of a successful AST therapy in elderly patients.

SOX2 expression is upregulated in adult spinal cord after contusion injury in both oligodendrocyte lineage and ependymal cells

The upregulation of genes normally associated with development may occur in the adult after spinal cord injury (SCI). To test this, we performed real-time RT-PCR array analysis of mouse spinal cord mRNAs comparing embryonic day (E)14.5 spinal cord with intact adult and adult cord 1 week after a clinically relevant standardized contusion SCI. We found significantly increased expression of a large number of neural development- and stem cell-associated genes after SCI. These included Sox2 (sex determining region Y-box 2), a transcription factor that regulates self-renewal and potency of embryonic neural stem cells and is one of only a few key factors needed to induce pluripotency. In adult spinal cord of Sox2-EGFP mice, Sox2-EGFP was found mainly in the ependymal cells of the central canal. After SCI, both mRNA and protein levels of Sox2 were significantly increased at and near the injury site. By 1 day, Sox2 was upregulated in NG2(+) oligodendrocyte progenitor cells (OPC) in the spared white matter. By 3 days, Sox2-EGFP ependymal cells had increased proliferation and begun to form multiple layers and clusters of cells in the central lesion zone of the cord. Expression of Sox2 by NG2(+) cells had declined by 1 week, but increased numbers of other Sox2-expressing cells persisted for at least 4 weeks after SCI in both mouse and rat models. Thus, SCI upregulates many genes associated with development and neural stem cells, including the key transcription factor Sox2, which is expressed in a pool of cells that persists for weeks after SCI.

Cloning and characterization of SCIRR69: a novel transcriptional factor belonging to the CREB/ATF family

The complete cDNA sequence of a novel gene, SCIRR69 (spinal cord injury and regeneration related no. 69 gene), was obtained by RACE technique. It codes for a protein of 521 amino acid residues homologous to human CREB3l2 (also known as BBF2H7) and mouse CREB3l2. The protein contains a basic DNA binding and leucine zipper dimerization (B-ZIP) motif and a hydrophobic region representing a putative transmembrane domain, similar to the structure of other CREB/ATF transcription factors. Monoclonal antibody against SCIRR69 was developed and could recognize the SCIRR69 protein in both native and denatured forms. Constructing of SCIRR69 fusion proteins with the GAL4 DNA-binding domain disclosed that SCIRR69 functioned as a transcriptional activator and its N-terminal 60 amino acids accounted for the activation ability. SCIRR69 resides in the cytoplasm of primary neurons, whereas neuron damage by incision led to the cleavage and translocation from the cytoplasm to the nucleus. These results suggest that SCIRR69 is activated by proteolytic cleavage at the transmembrane domain in response to neuron damage and its amino-terminal cytoplasmic domain translocates into the nucleus to activate the transcription of target genes.

MicroRNA dysregulation in the spinal cord following traumatic injury

Spinal cord injury (SCI) triggers a multitude of pathophysiological events that are tightly regulated by the expression levels of specific genes. Recent studies suggest that changes in gene expression following neural injury can result from the dysregulation of microRNAs, short non-coding RNA molecules that repress the translation of target mRNA. To understand the mechanisms underlying gene alterations following SCI, we analyzed the microRNA expression patterns at different time points following rat spinal cord injury.

The microarray data reveal the induction of a specific microRNA expression pattern following moderate contusive SCI that is characterized by a marked increase in the number of down-regulated microRNAs, especially at 7 days after injury. MicroRNA downregulation is paralleled by mRNA upregulation, strongly suggesting that microRNAs regulate transcriptional changes following injury. Bioinformatic analyses indicate that changes in microRNA expression affect key processes in SCI physiopathology, including inflammation and apoptosis. MicroRNA expression changes appear to be influenced by an invasion of immune cells at the injury area and, more importantly, by changes in microRNA expression specific to spinal cord cells. Comparisons with previous data suggest that although microRNA expression patterns in the spinal cord are broadly similar among vertebrates, the results of studies assessing SCI are much less congruent and may depend on injury severity. The results of the present study demonstrate that moderate spinal cord injury induces an extended microRNA downregulation paralleled by an increase in mRNA expression that affects key processes in the pathophysiology of this injury.

CCAAT/enhancer binding protein-δ expression by dendritic cells regulates CNS autoimmune inflammatory disease

CCAAT enhancer binding protein-delta (C/EBPδ) is a transcription factor that regulates inflammatory processes mediating bystander neuronal injury and CNS autoimmune inflammatory disease. The mechanism of the involvement of C/EBPδ in these processes remains to be determined. Here, we examined the cellular source(s) and mechanisms by which C/EBPδ may be involved in an animal model of multiple sclerosis. Mice deficient in C/EBPδ expression exhibited less severe clinical disease than wild-type littermates in response to induction of experimental autoimmune encephalomyelitis (EAE) by vaccination with a myelin oligodendrocyte glycoprotein (MOG) fragment. This reduction in EAE severity was associated with a significant alteration in the complement of major CNS T-helper (Th) cell subtypes throughout disease, manifest as reduced ratios of Th17 cells to regulatory T-cells (Tregs). Studies in bone marrow chimeric mice indicated that C/EBPδ expression by peripherally derived immune cells mediates C/EBPδ involvement in EAE. Follow up in vitro and in vivo examination of dendritic cell (DC) mediated Th-cell development suggests that C/EBPδ suppresses DC expression of interleukin-10 (IL-10), favoring Th17 over Treg development. In vitro and in vivo blockade of IL-10 signaling attenuated the effect of reduced C/EBPδ expression by DCs on Th17:Treg ratios. These findings identify C/EBPδ as an important DC transcription factor in CNS autoimmune inflammatory disease by virtue of its capacity to alter the Th17:Treg balance in an IL-10 dependent fashion.

Identification of the role of C/EBP in neurite regeneration following microarray analysis of a L. stagnalis CNS injury model

Background

Neuronal regeneration in the adult mammalian central nervous system (CNS) is severely compromised due to the presence of extrinsic inhibitory signals and a reduced intrinsic regenerative capacity. In contrast, the CNS of adult Lymnaea stagnalis (L. stagnalis), a freshwater pond snail, is capable of spontaneous regeneration following neuronal injury. Thus, L. stagnalis has served as an animal model to study the cellular mechanisms underlying neuronal regeneration. However, the usage of this model has been limited due to insufficient molecular tools. We have recently conducted a partial neuronal transcriptome sequencing project and reported over 10,000 EST sequences which allowed us to develop and perform a large-scale high throughput microarray analysis.

Results

To identify genes that are involved in the robust regenerative capacity observed in L. stagnalis, we designed the first gene chip covering ~15, 000 L. stagnalis CNS EST sequences. We conducted microarray analysis to compare the gene expression profiles of sham-operated (control) and crush-operated (regenerative model) central ganglia of adult L. stagnalis. The expression levels of 348 genes were found to be significantly altered (p < 0.05) following nerve injury. From this pool, 67 sequences showed a greater than 2-fold change: 42 of which were up-regulated and 25 down-regulated. Our qPCR analysis confirmed that CCAAT enhancer binding protein (C/EBP) was up-regulated following nerve injury in a time-dependent manner. In order to test the role of C/EBP in regeneration, C/EBP siRNA was applied following axotomy of cultured Lymnaea PeA neurons. Knockdown of C/EBP following axotomy prevented extension of the distal, proximal and intact neurites. In vivo knockdown of C/EBP postponed recovery of locomotory activity following nerve crush. Taken together, our data suggest both somatic and local effects of C/EBP are involved in neuronal regeneration.

Conclusions

This is the first high-throughput microarray study in L. stagnalis, a model of axonal regeneration following CNS injury. We reported that 348 genes were regulated following central nerve injury in adult L. stagnalis and provided the first evidence for the involvement of local C/EBP in neuronal regeneration. Our study demonstrates the usefulness of the large-scale gene profiling approach in this invertebrate model to study the molecular mechanisms underlying the intrinsic regenerative capacity of adult CNS neurons.

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.