Analysis of genes induced in peripheral nerve after axotomy using cDNA microarrays

The effects of Garcinia kola and curcumin on the dorsal root ganglion of the diabetic rat after peripheral nerve transection injury

OBJECTIVE

To test the protective effects of Garcinia kola and curcumin on the ganglion tissues of diabetic rats following the use of autologous vein graft in peripheral nerve transection injury.

METHODS

The sciatic nerve on the right side was transected, and anastomosis was performed between the proximal and distal ends using an autologous vein graft. Curcumin and Garcinia kola seed extract were administered daily by oral gavage. The ganglion tissues were harvested after a 90-day waiting period. Sensory neurons in the dorsal root ganglion at the L4 and L5 levels were used for stereological evaluations. Mean sensory neuron numbers were analyzed using a stereological technique. The size of the light and dark neurons was also estimated, and ultrastructural and immunohistochemical evaluations were performed.

RESULTS

A statistically significant difference in sensory neuron numbers was observed between the groups with and without Garcinia kola and curcumin applications. The immunohistochemical results showed that the s-100 protein is expressed selectively between cell types.

CONCLUSION

The results of this study show that curcumin and Garicinia kola prevented sensory neuron loss in diabetic rats following transection injury to the sciatic nerve.

What happens when Schwann cells are exposed to Mycobacterium leprae - A systematic review

Mycobacterium leprae, the pathogen that causes human leprosy, has a unique affinity for infecting and persisting inside Schwann cells, the principal glia of the peripheral nervous system. Several studies have focused on this intricate host-pathogen interaction as an attempt to advance the current knowledge of the mechanisms governing nerve destruction and disease progression. However, during the chronic course of leprosy neuropathy, Schwann cells can respond to and internalize both live and dead M. leprae and bacilli-derived antigens, and this may result in divergent cellular pathobiological responses. This may also distinctly contribute to tissue degeneration, failure to repair, inflammatory reactions, and nerve fibrosis, hallmarks of the disease. Therefore, the present study systematically searched for published studies on M. leprae-Schwann cell interaction in vitro to summarize the findings and provide a focused discussion of Schwann cell dynamics following challenge with leprosy bacilli.

Effect of necrostatin-1 on sciatic nerve crush injury in rat models

BACKGROUND

Necrostatin-1 (Nec-1) is an inhibitor of the receptor interacting protein (RIP)1 kinase, which acts as an inhibitor of necroptosis, a special form of necrosis. In the present study, the effect of Nec-1 on peripheral nerve injury (PNI) was investigated.

METHODS

The PNI model was established by inducing sciatic nerve injury. Hematoxylin-eosin and immunofluorescence staining techniques were used to assess the extent of injury to nerve fibers and necrosis of Schwann cells (SCs). Western blotting was performed to detect the expression of necroptosis-related factors (RIP1 and RIP3). The concentrations of tumor necrosis factor-α, interleukin (IL)-1β, IL-6, and the oxidative stress-related enzyme malondialdehyde (MDA) were determined to indicate the degree of inflammation and oxidative stress.

RESULTS

Nec-1 could decrease the degree of peripheral nerve lesions after PNI and protect SCs and axons by inhibiting necroptosis. Furthermore, Nec-1 could reduce necroptosis by inhibiting RIP1 and effectively reduce inflammation and reactive oxygen species production at the early stage of PNI.

CONCLUSIONS

Alleviation of necroptosis by Nec-1 may provide new insights into therapies for the early stages of peripheral nerve repair after PNI.

Potential link between the nerve injury-induced protein (Ninjurin) and the pathogenesis of endometriosis

Endometriosis remains a widespread but severe gynecological disease in women of reproductive age, with an unknown etiology and few treatment choices. The menstrual reflux theory is largely accepted as the underlying etiology but does not explain the morbidity or unpleasant pain sensations of endometriosis. The neurological and immune systems are both involved in pain mechanisms of endometriosis, and interlinked through a complex combination of cytokines and neurotransmitters. Numerous pieces of evidence suggest that the nerve injury-inducible protein, Ninjurin, is actively expressed in endometriosis lesions, which contributes to the etiology and development of endometriosis. It may be explored in the future as a novel therapeutic target. The aim of the present review was to elucidate the multifaceted role of Ninjurin. Furthermore, we summarize the association of Ninjurin with the pain mechanism of endometriosis and outline the future research directions. A novel therapeutic pathway can be discovered based on the potential pathogenic variables.

PCL NGCs integrated with urolithin-A-loaded hydrogels for nerve regeneration

Inflammation and oxidative stress are among the leading causes of poor prognosis after peripheral nerve injury (PNI). Urolithin-A (UA), an intermediate product produced by the catabolism of ellagitannins in the gastrointestinal tract, has anti-inflammatory, antioxidant, and immunomodulatory properties for inflammation, oxidative damage, and aging-related diseases. Hence, we prepared UA-loaded hydrogels and embedded them in the lumen of PCL nerve guide conduits (NGCs). The hydrogels continuously released appropriate doses of UA into the microenvironment. Based on in vitro studies, UA facilitates cell proliferation and reduces oxidative damage. Besides, the experimental evaluation revealed good biocompatibility of the materials involved. We implanted NGCs into rat models to bridge the sciatic nerve defects in an in vivo study. The sciatic functional index of the PCL/collagen/UA group was comparable to that of the autograft group. Additionally, the consequences of electrophysiological, gastrocnemius muscle and nerve histology assessment of the PCL/collagen/UA group were better than those in the PCL and PCL/collagen groups and close to those in the autograft group. In this study, UA sustained release via the PCL/collagen/UA NGC was found to be an effective alternative treatment for PNI, validating our hypothesis that UA could promote regeneration of nerve tissue.

Sexual Dimorphism of Early Transcriptional Reprogramming in Dorsal Root Ganglia After Peripheral Nerve Injury

Peripheral nerve injury induces genome-wide transcriptional reprogramming of first-order neurons and auxiliary cells of dorsal root ganglia (DRG). Accumulating experimental evidence suggests that onset and mechanistic principles of post-nerve injury processes are sexually dimorphic. We examined largely understudied aspects of early transcriptional events in DRG within 24 h after sciatic nerve axotomy in mice of both sexes. Using high-depth RNA sequencing (>50 million reads/sample) to pinpoint sexually dimorphic changes related to regeneration, immune response, bioenergy, and sensory functions, we identified a higher number of transcriptional changes in male relative to female DRG. In males, the decline in ion channel transcripts was accompanied by the induction of innate immune cascades via TLR, chemokine, and Csf1-receptor axis and robust regenerative programs driven by Sox, Twist1/2, and Pax5/9 transcription factors. Females demonstrated nerve injury-specific transcriptional co-activation of the actinin 2 network. The predicted upstream regulators and interactive networks highlighted the role of novel epigenetic factors and genetic linkage to sex chromosomes as hallmarks of gene regulation post-axotomy. We implicated epigenetic X chromosome inactivation in the regulation of immune response activity uniquely in females. Sexually dimorphic regulation of MMP/ADAMTS metalloproteinases and their intrinsic X-linked regulator Timp1 contributes to extracellular matrix remodeling integrated with pro-regenerative and immune functions. Lexis1 non-coding RNA involved in LXR-mediated lipid metabolism was identified as a novel nerve injury marker. Together, our data identified unique early response triggers of sex-specific peripheral nerve injury regulation to gain mechanistic insights into the origin of female- and male-prevalent sensory neuropathies.

The Role of Ninjurin1 and Its Impact beyond the Nervous System

Ninjurin1 (Ninj1) is a double-transmembrane cell surface protein that could promote nerve regeneration in the process of the peripheral nervous system injury and repairment. Nonetheless, the accurate function of Ninj1 in the central nervous system and outside the nervous system is not completely clear. According to the recent studies, we found that Ninj1 is also aberrantly expressed in various pathophysiological processes in vivo, including inflammation, tumorigenesis, and vascular, bone, and muscle homeostasis. These findings suggest that Ninj1 may play an influential role during these pathophysiological processes. Our review summarizes the diverse roles of Ninj1 in multiple pathophysiological processes inside and outside the nervous system. Ninj1 should be considered as an important and novel therapeutic target in certain diseases, such as inflammatory diseases and ischemic diseases. Our study provided a better understanding of Ninj1 in different pathophysiological processes and thereby provided the theoretical support for further research.

Electrophysiological assessment and pharmacological treatment of blast-induced tinnitus

Tinnitus, the phantom perception of sound, often occurs as a clinical sequela of auditory traumas. In an effort to develop an objective test and therapeutic approach for tinnitus, the present study was performed in blast-exposed rats and focused on measurements of auditory brainstem responses (ABRs), prepulse inhibition of the acoustic startle response, and presynaptic ribbon densities on cochlear inner hair cells (IHCs). Although the exact mechanism is unknown, the “central gain theory” posits that tinnitus is a perceptual indicator of abnormal increases in the gain (or neural amplification) of the central auditory system to compensate for peripheral loss of sensory input from the cochlea. Our data from vehicle-treated rats supports this rationale; namely, blast-induced cochlear synaptopathy correlated with imbalanced elevations in the ratio of centrally-derived ABR wave V amplitudes to peripherally-derived wave I amplitudes, resulting in behavioral evidence of tinnitus. Logistic regression modeling demonstrated that the ABR wave V/I amplitude ratio served as a reliable metric for objectively identifying tinnitus. Furthermore, histopathological examinations in blast-exposed rats revealed tinnitus-related changes in the expression patterns of key plasticity factors in the central auditory pathway, including chronic loss of Arc/Arg3.1 mobilization. Using a formulation of N-acetylcysteine (NAC) and disodium 2,4-disulfophenyl-N-tert-butylnitrone (HPN-07) as a therapeutic for addressing blast-induced neurodegeneration, we measured a significant treatment effect on preservation or restoration of IHC ribbon synapses, normalization of ABR wave V/I amplitude ratios, and reduced behavioral evidence of tinnitus in blast-exposed rats, all of which accorded with mitigated histopathological evidence of tinnitus-related neuropathy and maladaptive neuroplasticity.

Cathepsins in neuronal plasticity

Proteases comprise a variety of enzymes defined by their ability to catalytically hydrolyze the peptide bonds of other proteins, resulting in protein lysis. Cathepsins, specifically, encompass a class of at least twenty proteases with potent endopeptidase activity. They are located subcellularly in lysosomes, organelles responsible for the cell’s degradative and autophagic processes, and are vital for normal lysosomal function. Although cathepsins are involved in a multitude of cell signaling activities, this chapter will focus on the role of cathepsins (with a special emphasis on Cathepsin B) in neuronal plasticity. We will broadly define what is known about regulation of cathepsins in the central nervous system and compare this with their dysregulation after injury or disease. Importantly, we will delineate what is currently known about the role of cathepsins in axon regeneration and plasticity after spinal cord injury. It is well established that normal cathepsin activity is integral to the function of lysosomes. Without normal lysosomal function, autophagy and other homeostatic cellular processes become dysregulated resulting in axon dystrophy. Furthermore, controlled activation of cathepsins at specialized neuronal structures such as axonal growth cones and dendritic spines have been positively implicated in their plasticity. This chapter will end with a perspective on the consequences of cathepsin dysregulation versus controlled, localized regulation to clarify how cathepsins can contribute to both neuronal plasticity and neurodegeneration.

PAR2, Keratinocytes, and Cathepsin S Mediate the Sensory Effects of Ciguatoxins Responsible for Ciguatera Poisoning

Ciguatera fish poisoning is caused by the consumption of fish contaminated with ciguatoxins (CTXs). The most distressing symptoms are cutaneous sensory disturbances, including cold dysesthesia and itch. CTXs are neurotoxins known to activate voltage-gated sodium channels, but no specific treatment exists. Peptidergic neurons have been critically involved in ciguatera fish poisoning sensory disturbances. Protease-activated receptor-2 (PAR2) is an itch- and pain-related G protein‒coupled receptor whose activation leads to a calcium-dependent neuropeptide release. In this study, we studied the role of voltage-gated sodium channels, PAR2, and the PAR2 agonist cathepsin S in the cytosolic calcium increase and subsequent release of the neuropeptide substance P elicited by Pacific CTX-2 (P-CTX-2) in rat sensory neurons and human epidermal keratinocytes. In sensory neurons, the P-CTX-2‒evoked calcium response was driven by voltage-gated sodium channels and PAR2-dependent mechanisms. In keratinocytes, P-CTX-2 also induced voltage-gated sodium channels and PAR2-dependent marked calcium response. In the cocultured cells, P-CTX-2 significantly increased cathepsin S activity, and cathepsin S and PAR2 antagonists almost abolished P-CTX-2‒elicited substance P release. Keratinocytes synergistically favored the induced substance P release. Our results demonstrate that the sensory effects of CTXs involve the cathepsin S-PAR2 pathway and are potentiated by their direct action on nonexcitable keratinocytes through the same pathway.

Immunohistochemical localization of nerve injury-induced protein-1 in mouse tissues

Nerve injury-induced protein (Ninjurin)-1 is a cell adhesion molecule that is upregulated in neurons and Schwann cells after transection injury in rats. In this study, we investigated the localization of Ninjurin-1 in various tissues, including the cerebrum, sciatic nerve, spleen, lung, stomach, ileum, colon, liver, pancreas, kidney, testis, and skin in C57BL/6 mice, using Western blotting and immunohistochemistry. Western blot analysis showed that Ninjurin-1 was differentially expressed among organs. Ninjurin-1 was abundant in skin and ileum, weakly expressed in cerebrum, and moderately expressed in the other organs studied. Immunohistochemical analysis largely confirmed the results of the western blot analysis with often localization of Ninjurin-1 in the regions with abundant connective tissues. In addition, Ninjurin-1 was differentially expressed in various cell types in the tissues under the investigation. These findings suggest that Ninjurin-1 may play organ-specific roles in development and homeostasis of many organs.

Pericyte-Specific Ninjurin1 Deletion Attenuates Vessel Maturation and Blood Flow Recovery in Hind Limb Ischemia

Supplemental Digital Content is available in the text.

Objective—

Angiogenesis, entire step from endothelial cells (ECs) sprouts to vascular maturation, is a critical response to ischemia. To form functional mature vessels, interactions between ECs and pericytes are essential. Ninj1 (ninjurin1) is an adhesion molecule that contributes to the pathogenesis of neuroinflammation. We recently demonstrated that Ninj1 is expressed in pericytes during angiogenesis. However, the role of Ninj1 in angiogenesis under pathophysiological ischemic conditions has not yet been elucidated.

Approach and Results—

Ninj1 was detected in microvessels, and its expression was enhanced in ischemic tissues after mouse hindlimb ischemia. Knockdown of Ninj1 was performed by injection of biodegradable microspheres releasing Ninj1-small interfering RNA into muscle tissues. Alternatively, pericyte-specific Ninj1 knockout was induced by tamoxifen treatment of NG2-CreERT/Ninj1-flox mice. Ninj1 knockdown/knockout reduced the formation of blood-circulating functional vessels among total CD31⁺ microvessels within ischemic tissues and subsequently attenuated color Doppler–assessed blood flow recovery. Ninj1 overexpression enhanced expression of Anpt (angiopoietin) 1, whereas Ninj1 knockdown enhanced the endogenous Anpt1 antagonist, Anpt2 expression in pericytes and inhibited the association of pericytes with ECs and subsequent formation of capillary-like structure, that is, EC tube surrounded with pericytes in 3-dimensional gel culture.

Conclusions—

Our data demonstrate that Ninj1 is involved in the formation of functional matured vessels through the association between pericytes and ECs, resulting in blood flow recovery from ischemia. These findings further the current our understanding of vascular maturation and may support the development of therapeutics for ischemic diseases.

3D melatonin nerve scaffold reduces oxidative stress and inflammation and increases autophagy in peripheral nerve regeneration

Peripheral nerve defect is a common and severe kind of injury in traumatic accidents. Melatonin can improve peripheral nerve recovery by inhibiting oxidative stress and inflammation after traumatic insults. In addition, it triggers autophagy pathways to increase regenerated nerve proliferation and to reduce apoptosis. In this study, we fabricated a melatonin-controlled-release scaffold to cure long-range nerve defects for the first time. 3D manufacture of melatonin/polycaprolactone nerve guide conduit increased Schwann cell proliferation and neural expression in vitro and promoted functional, electrophysiological and morphological nerve regeneration in vivo. Melatonin nerve guide conduit ameliorated immune milieu by reducing oxidative stress, inflammation and mitochondrial dysfunction. In addition, it activated autophagy to restore ideal microenvironment, to provide energy for nerves and to reduce nerve cell apoptosis, thus facilitating nerve debris clearance and neural proliferation. This innovative scaffold will have huge significance in the nerve engineering.

Regulation of Neuroregeneration by Long Noncoding RNAs

In mammals, neurons in the peripheral nervous system (PNS) have regenerative capacity following injury, but it is generally absent in the CNS. This difference is attributed, at least in part, to the intrinsic ability of PNS neurons to activate a unique regenerative transcriptional program following injury. Here, we profiled gene expression following sciatic nerve crush in mice and identified long noncoding RNAs (lncRNAs) that act in the regenerating neurons and which are typically not expressed in other contexts. We show that two of these lncRNAs regulate the extent of neuronal outgrowth. We then focus on one of these, Silc1, and show that it regulates neuroregeneration in cultured cells and in vivo, through cis-acting activation of the transcription factor Sox11.

It is all about the support - The role of the extracellular matrix in regenerating axon guidance

Although it is known for long time that the peripheral nervous system has the capacity for self-regeneration, the molecular mechanisms by which Schwann cells and extracellular matrix (ECM) guide the injured axons to regrow along their original path, remains a poorly understood process. Due to the importance of ECM molecules during development, constitutive mutant organisms display increased lethality, therefore, conditional or inducible strategies have been used to increase the survival of the organisms and allow the study of the role of ECM proteins. In a recent report published in Neuron, Isaacman-Beck and colleagues (2015) used these pioneering genetic studies on zebrafish combined with in vivo fluorescent imaging, to investigate the micro-environmental conditions required for targeted regeneration of the dorsal motor nerve of zebrafish larvae after laser-transection. A candidate gene approach targeting lh3 basal laminar collagen substrates revealed that the lh3 substrate col4α5 regulates dorsal nerve regeneration by destabilizing misdirected axons. Col4α5 was upregulated in a small population of lh3 expressing Schwann cells located ventrally and ventro-laterally to the injury site and found to co-localize with the molecule slit guidance ligand 1 (slit1a). Capitalizing on the crucial observations of mistargeted regeneration of dorsal nerves in mutant larvae, they put forward a model in which Schwann cells shape an environment that allows and directs axonal regeneration to their original synaptic target. In the light of Isaacman-Beck and colleagues (2015) findings, we will review how their study contributes to the research field, and comment on its potential implications for promoting nerve regeneration after injury.

The Wound Microenvironment Reprograms Schwann Cells to Invasive Mesenchymal-like Cells to Drive Peripheral Nerve Regeneration

Schwann cell dedifferentiation from a myelinating to a progenitor-like cell underlies the remarkable ability of peripheral nerves to regenerate following injury. However, the molecular identity of the differentiated and dedifferentiated states in vivo has been elusive. Here, we profiled Schwann cells acutely purified from intact nerves and from the wound and distal regions of severed nerves. Our analysis reveals novel facets of the dedifferentiation response, including acquisition of mesenchymal traits and a Myc module. Furthermore, wound and distal dedifferentiated Schwann cells constitute different populations, with wound cells displaying increased mesenchymal character induced by localized TGFβ signaling. TGFβ promotes invasion and crosstalks with Eph signaling via N-cadherin to drive collective migration of the Schwann cells across the wound. Consistently, Tgfbr2 deletion in Schwann cells resulted in misdirected and delayed reinnervation. Thus, the wound microenvironment is a key determinant of Schwann cell identity, and it promotes nerve repair through integration of multiple concerted signals. VIDEO ABSTRACT.

Functional Diversity of Neurotrophin Actions on the Oculomotor System

Neurotrophins play a principal role in neuronal survival and differentiation during development, but also in the maintenance of appropriate adult neuronal circuits and phenotypes. In the oculomotor system, we have demonstrated that neurotrophins are key regulators of developing and adult neuronal properties, but with peculiarities depending on each neurotrophin. For instance, the administration of NGF (nerve growth factor), BDNF (brain-derived neurotrophic factor) or NT-3 (neurotrophin-3) protects neonatal extraocular motoneurons from cell death after axotomy, but only NGF and BDNF prevent the downregulation in ChAT (choline acetyltransferase). In the adult, in vivo recordings of axotomized extraocular motoneurons have demonstrated that the delivery of NGF, BDNF or NT-3 recovers different components of the firing discharge activity of these cells, with some particularities in the case of NGF. All neurotrophins have also synaptotrophic activity, although to different degrees. Accordingly, neurotrophins can restore the axotomy-induced alterations acting selectively on different properties of the motoneuron. In this review, we summarize these evidences and discuss them in the context of other motor systems.

Acute appendicitis: transcript profiling of blood identifies promising biomarkers and potential underlying processes

Background

The diagnosis of acute appendicitis can be surprisingly difficult without computed tomography, which carries significant radiation exposure. Circulating blood cells may carry informative changes in their RNA expression profile that would signal internal infection or inflammation of the appendix.

Methods

Genome-wide expression profiling was applied to whole blood RNA of acute appendicitis patients versus patients with other abdominal disorders, in order to identify biomarkers of appendicitis. From a large cohort of emergency patients, a discovery set of patients with surgically confirmed appendicitis, or abdominal pain from other causes, was identified. RNA from whole blood was profiled by microarrays, and RNA levels were filtered by a combined fold-change (>2) and p value (<0.05). A separate set of patients, including patients with respiratory infections, was used to validate a partial least squares discriminant (PLSD) prediction model.

Results

Transcript profiling identified 37 differentially expressed genes (DEG) in appendicitis versus abdominal pain patients. The DEG list contained 3 major ontologies: infection-related, inflammation-related, and ribosomal processing. Appendicitis patients had lower level of neutrophil defensin mRNA (DEFA1,3), but higher levels of alkaline phosphatase (ALPL) and interleukin-8 receptor-ß (CXCR2/IL8RB), which was confirmed in a larger cohort of 60 patients using droplet digital PCR (ddPCR).

Conclusions

Patients with acute appendicitis have detectable changes in the mRNA expression levels of factors related to neutrophil innate defense systems. The low defensin mRNA levels suggest that appendicitis patient’s immune cells are not directly activated by pathogens, but are primed by diffusible factors in the microenvironment of the infection. The detected biomarkers are consistent with prior evidence that biofilm-forming bacteria in the appendix may be an important factor in appendicitis.

Electronic supplementary material

The online version of this article (doi:10.1186/s12920-016-0200-y) contains supplementary material, which is available to authorized users.

Induction of Nerve Injury-Induced Protein 1 (Ninjurin 1) in Myeloid Cells in Rat Brain after Transient Focal Cerebral Ischemia

Nerve injury-induced protein-1 (Ninjurin-1, Ninj1) was initially identified as a novel adhesion molecule in rat sciatic nerve and to be up-regulated in neurons and Schwann cells of distal nerve segments after nerve transection or crush injury. Recently, Ninj1 was found to act as a modulator of cell migration, angiogenesis, and apoptosis. Accumulating evidence indicates that innate immune response plays beneficial and deleterious roles in brain ischemia, and the trans-endothelial migration of blood-derived immune cells is key initiator of this response. In the present study, we examined the expression profile and cellular distribution of Ninj1 in rat brain after transient focal cerebral ischemia. Ninj1 expression was found to be significantly induced in cortical penumbras 1 day after 60 min of middle cerebral artery occlusion (MCAO) and to increase gradually for 8 days and then declined. In infarction cores of cortices, patterns of Ninj1 expression were similar to those observed in cortical penumbras, except induction was maintained for 10 days. At 1 day post-MCAO, Ninj1 inductions were detected mainly in neutrophils and endothelial cells in both infarction cores and penumbras, but reactive macrophages were the major cellular expressers of Ninj1 at 4 days post-MCAO. Expressional induction in reactive macrophages was maintained in infarction cores after 12 days post-MCAO but not in penumbras. These dynamic expressions of Ninj1 in different immune cells at different times suggest that this protein performs various, critical roles in the modulation of acute and delayed immune responses in the postischemic brain.

Sub-Chronic Neuropathological and Biochemical Changes in Mouse Visual System after Repetitive Mild Traumatic Brain Injury

Repetitive mild traumatic brain injury (r-mTBI) results in neuropathological and biochemical consequences in the human visual system. Using a recently developed mouse model of r-mTBI, with control mice receiving repetitive anesthesia alone (r-sham) we assessed the effects on the retina and optic nerve using histology, immunohistochemistry, proteomic and lipidomic analyses at 3 weeks post injury. Retina tissue was used to determine retinal ganglion cell (RGC) number, while optic nerve tissue was examined for cellularity, myelin content, protein and lipid changes. Increased cellularity and areas of demyelination were clearly detectable in optic nerves in r-mTBI, but not in r-sham. These changes were accompanied by a ~25% decrease in the total number of Brn3a-positive RGCs. Proteomic analysis of the optic nerves demonstrated various changes consistent with a negative effect of r-mTBI on major cellular processes like depolymerization of microtubules, disassembly of filaments and loss of neurons, manifested by decrease of several proteins, including neurofilaments (NEFH, NEFM, NEFL), tubulin (TUBB2A, TUBA4A), microtubule-associated proteins (MAP1A, MAP1B), collagen (COL6A1, COL6A3) and increased expression of other proteins, including heat shock proteins (HSP90B1, HSPB1), APOE and cathepsin D. Lipidomic analysis showed quantitative changes in a number of phospholipid species, including a significant increase in the total amount of lysophosphatidylcholine (LPC), including the molecular species 16:0, a known demyelinating agent. The overall amount of some ether phospholipids, like ether LPC, ether phosphatidylcholine and ether lysophosphatidylethanolamine were also increased, while the majority of individual molecular species of ester phospholipids, like phosphatidylcholine and phosphatidylethanolamine, were decreased. Results from the biochemical analysis correlate well with changes detected by histological and immunohistochemical methods and indicate the involvement of several important molecular pathways. This will allow future identification of therapeutic targets for improving the visual consequences of r-mTBI.

Transcriptomic Approaches to Neural Repair

Understanding why adult CNS neurons fail to regenerate their axons following injury remains a central challenge of neuroscience research. A more complete appreciation of the biological mechanisms shaping the injured nervous system is a crucial prerequisite for the development of robust therapies to promote neural repair. Historically, the identification of regeneration associated signaling pathways has been impeded by the limitations of available genetic and molecular tools. As we progress into an era in which the high-throughput interrogation of gene expression is commonplace and our knowledge base of interactome data is rapidly expanding, we can now begin to assemble a more comprehensive view of the complex biology governing axon regeneration. Here, we highlight current and ongoing work featuring transcriptomic approaches toward the discovery of novel molecular mechanisms that can be manipulated to promote neural repair.

SIGNIFICANCE STATEMENT

Transcriptional profiling is a powerful technique with broad applications in the field of neuroscience. Recent advances such as single-cell transcriptomics, CNS cell type-specific and developmental stage-specific expression libraries are rapidly enhancing the power of transcriptomics for neuroscience applications. However, extracting biologically meaningful information from large transcriptomic datasets remains a formidable challenge. This mini-symposium will highlight current work using transcriptomic approaches to identify regulatory networks in the injured nervous system. We will discuss analytical strategies for transcriptomics data, the significance of noncoding RNA networks, and the utility of multiomic data integration. Though the studies featured here specifically focus on neural repair, the approaches highlighted in this mini-symposium will be of broad interest and utility to neuroscientists working in diverse areas of the field.

The transcriptional landscape of dorsal root ganglia after sciatic nerve transection

Following peripheral nerve injury, transcriptional responses are orchestrated to regulate the expression of numerous genes in the lesioned nerve, thus activating the intrinsic regeneration program. To better understand the molecular regulation of peripheral nerve regeneration, we aimed at investigating the transcriptional landscape of dorsal root ganglia (DRGs) after sciatic nerve transection in rats. The cDNA microarray analysis was used to identify thousands of genes that were differentially expressed at different time points post nerve injury (PNI). The results from Euclidean distance matrix, principal component analysis, and hierarchical clustering indicated that 2 nodal transitions in temporal gene expressions could segregate 3 distinct transcriptional phases within the period of 14 d PNI. The 3 phases were designated as “a stress response phase”, “a pre-regeneration phase”, and “a regeneration phase”, respectively, by referring to morphological observation of post-nerve-injury changes. The gene ontology (GO) analysis revealed the distinct features of biological process, cellular component, and molecular function at each transcriptional phase. Moreover, Ingenuity Pathway Analysis suggested that differentially expressed genes, mainly transcription factors and genes associated with neurite/axon growth, might be integrated into regulatory networks to mediate the regulation of peripheral nerve regeneration in a highly cooperative manner.

The lh3 Glycosyltransferase Directs Target-Selective Peripheral Nerve Regeneration

Functional PNS regeneration requires injured axons to return to their original synaptic targets, yet the mechanisms underlying target-selective regeneration have remained elusive. Using live-cell imaging in zebrafish we find that regenerating motor axons exhibit a strong preference for their original muscle territory and that axons probe both correct and incorrect trajectories extensively before selecting their original path. We show that this process requires the glycosyltransferase lh3 and that post-injury expression of lh3 in Schwann cells is sufficient to restore target-selective regeneration. Moreover, we demonstrate that Schwann cells neighboring the transection site express the lh3 substrate collagen4a5 and that during regeneration collagen4a5 destabilizes axons probing inappropriate trajectories to ensure target-selective regeneration, possibly through the axonal repellant slit1a. Our results demonstrate that selective ECM components match subpopulations of regenerating axons with their original targets and reveal a previously unappreciated mechanism that conveys synaptic target selection to regenerating axons in vivo. VIDEO ABSTRACT.

The calcium-binding proteins S100A8 and S100A9 initiate the early inflammatory program in injured peripheral nerves

To shed light on the early immune response processes in severed peripheral nerves, we performed genome-wide transcriptional profiling and bioinformatics analyses of the proximal (P, regenerating) and distal (D, degenerating) nerve stumps on day 1 in the sciatic nerve axotomy model in rats. Multiple cell death-related pathways were activated in the degenerating D stump, whereas activation of the cytoskeletal motility and gluconeogenesis/glycolysis pathways was most prominent in the P stump of the axotomized nerve. Our bioinformatics analyses also identified the specific immunomodulatory genes of the chemokine, IL, TNF, MHC, immunoglobulin-binding Fc receptor, calcium-binding S100, matrix metalloproteinase, tissue inhibitor of metalloproteinase, and ion channel families affected in both the P and D segments. S100a8 and S100a9 were the top up-regulated genes in both the P and D segments. Stimulation of cultured Schwann cells using the purified S100A8/A9 heterodimer recapitulated activation of the myeloid cell and phagocyte chemotactic genes and pathways, which we initially observed in injured nerves. S100A8/A9 heterodimer injection into the intact nerve stimulated macrophage infiltration. We conclude that, following peripheral nerve injury, an immediate acute immune response occurs both distal and proximal to the lesion site and that the rapid transcriptional activation of the S100a8 and S100a9 genes results in S100A8/A9 hetero- and homodimers, which stimulate the release of chemokines and cytokines by activated Schwann cells and generate the initial chemotactic gradient that guides the transmigration of hematogenous immune cells into the injured nerve.

Characterization of in vitro transcriptional responses of dorsal root ganglia cultured in the presence and absence of blastema cells from regenerating salamander limbs

During salamander limb regeneration, nerves provide signals that induce the formation of a mass of proliferative cells called the blastema. To better understand these signals, we developed a blastema−dorsal root ganglia (DRG) co‐culture model system to test the hypothesis that nerves differentially express genes in response to cues provided by the blastema. DRG with proximal and distal nerve trunks were isolated from axolotls (Ambystoma mexicanum), cultured for 5 days, and subjected to microarray analysis. Relative to freshly isolated DRG, 1541 Affymetrix probe sets were identified as differentially expressed and many of the predicted genes are known to function in injury and neurodevelopmental responses observed for mammalian DRG. We then cultured 5‐day DRG explants for an additional 5 days with or without co‐cultured blastema cells. On day 10, we identified 27 genes whose expression in cultured DRG was significantly affected by the presence or absence of blastema cells. Overall, our study established a DRG−blastema in vitro culture system and identified candidate genes for future investigations of axon regrowth, nerve−blastema signaling, and neural regulation of limb regeneration.

The beneficial effect of ginsenoside Rg1 on Schwann cells subjected to hydrogen peroxide induced oxidative injury

Ginsenoside Rg1 (GRg1) has been considered to have therapeutic potential in promoting peripheral nerve regeneration and functional recovery after sciatic nerve injuries. However, the mechanism underlying the beneficial effect of GRg1 on peripheral nerve regeneration is currently unclear. The possible effect of GRg1 on Schwann cells (SCs), which were subjected to oxidative injury after nerve injury, might contribute to the beneficial effect of GRg1 on nerve regeneration. The present study was designed to investigate the potential beneficial effect of GRg1 on SCs exposed to oxidative injury. The oxidative injury to SCs was induced by hydrogen peroxide. The effect of GRg1 (50 μM) on SCs exposed to oxidative injury was measured by the levels of malondialdehyde (MDA), superoxide dismutase (SOD), glutathione (GSH) and catalase (CAT) in SCs. The cell number and cell viability of SCs were evaluated through fluorescence observation and MTT assay. The apoptosis of SCs induced by oxidative injury was evaluated by an apoptosis assay. The expression and secretion of nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) were evaluated using RT-PCR, Western blotting, and an ELISA method. We found that GRg1 significantly up-regulated the level of SOD, GSH and CAT, and decreased the level of MDA in SCs treated with hydrogen peroxide. In addition, GRg1 has been shown to be able to inhibit the proapoptotic effect of hydrogen peroxide, as well as inhibit the detrimental effect of hydrogen peroxide on cell number and cell viability. Furthermore, GRg1 also increased the mRNA levels, protein levels and secretion of NGF and BDNF in SCs after incubation of hydrogen peroxide. Further study showed that preincubation with H89 (a PKA inhibitor) significantly inhibited the effects induced by hydrogen peroxide, indicating that the PKA pathway might be involved in the antioxidant effect and neurotrophic factors (NTFs) promoting effect of GRg1. In addition, a short-term in vivo study was performed to confirm and validate the antioxidant effect and nerve regeneration-promoting effect of GRg1 in a sciatic crush injury model in rats. We found that GRg1 significantly increased SOD, CAT and GSH, decreased MDA, as well as promoted nerve regeneration after crush injury. In conclusion, the present study showed that GRg1 is capable of helping SCs recover from the oxidative insult induced by hydrogen peroxide, which might account, at least in part, for the beneficial effect of GRg1 on nerve regeneration.

Resetting translational homeostasis restores myelination in Charcot-Marie-Tooth disease type 1B mice

Reduction of the CHOP target Gadd34 restores motor function in P0S63del mice with demyelinating neuropathy.

P0 glycoprotein is an abundant product of terminal differentiation in myelinating Schwann cells. The mutant P0S63del causes Charcot-Marie-Tooth 1B neuropathy in humans, and a very similar demyelinating neuropathy in transgenic mice. P0S63del is retained in the endoplasmic reticulum of Schwann cells, where it promotes unfolded protein stress and elicits an unfolded protein response (UPR) associated with translational attenuation. Ablation of Chop, a UPR mediator, from S63del mice completely rescues their motor deficit and reduces active demyelination by half. Here, we show that Gadd34 is a detrimental effector of CHOP that reactivates translation too aggressively in myelinating Schwann cells. Genetic or pharmacological limitation of Gadd34 function moderates translational reactivation, improves myelination in S63del nerves, and reduces accumulation of P0S63del in the ER. Resetting translational homeostasis may provide a therapeutic strategy in tissues impaired by misfolded proteins that are synthesized during terminal differentiation.

Whole genome expression profile in neuroblastoma cells exposed to 1-methyl-4-phenylpyridine

Mitochondrial dysfunction and subsequent energy failure is a contributing factor to degeneration of the substantia nigra pars compacta associated with Parkinson's disease (PD). In this study, we investigate molecular events triggered by cell exposure to the mitochondrial toxin 1-methyl-4-phenylpyridine (MPP+) using whole genome-expression microarray, Western Blot and metabolic studies. The data show that MPP+ (500 μM) obstructs mitochondrial respiration/oxidative phosphorylation (OXPHOS) in mouse neuroblastoma Neuro-2a cells, juxtaposing accelerated glucose consumption and production of lactic acid. While additional glucose concentrations restored viability in the presence of MPP+ (500 μM), the loss of OXPHOS was sustained, suggesting that compensatory anaerobic metabolic systems were fulfilling required energy needs. Under these conditions, MPP+ initiated significant changes to the transcription of 439 genes of which 287 DAVID IDs were identified and subsequent functional annotation clusters identified. Prominent changes were as follows; MPP+ initiated loss of mRNA for mitochondrial encoded 3-hydroxybutyratedehydrogenase, type 2(Bdh2), tv1, NADH dehydrogenase 4,5 genes, cytochrome b and NADH dehydrogenase (ubiquinone) flavoprotein 3, concomitant to rise in a mitochondrial fission gene; ganglioside-induced differentiation-associated-protein 1 (GDAP1). The negative changes to OXPHOS components were accompanied by protective forces within the mitochondria espousing elevated ratio of anti/pro-apoptotic processes. These included a loss of apoptotic Bcl-2/adenovirus E1B 19-kDa-interacting protein (BNIP3) and family with sequence similarity 162, member A (FAM162a) and rise of heat shock protein 1 and Lon peptidase 1. There were no changes indicative of free radical damage (e.g. SOD, GSH-Px), rather MPP+ initiated significant elevation in G protein signaling components (which trigger catabolic processes) and anaerobic metabolic systems involving carboxylic acid/transamination reactions (e.g. glutamate oxaloacetate transaminase 1 (GOT1), glutamic pyruvate-alanine transaminase 2 (GPT2), cystathionase and redox proteins such as cytochrome b5 reductase 1 and ferredoxin reductase. Counter-intuitively, the data show reduction of mRNA in glycolytic processes [DAVID enrichment score 9.96 p value 1.90E-19], some corroborated by Western Blot, bringing in to question the sources of lactate observed in the presence of MPP+. Examining this aspect, the data show that diverse carboxylic acids (succinate, oxaloacetate and a-ketoglutarate) are capable of contributing to the lactate pool in addition to phosph(enolpyruvate) or pyruvate in the absence of glucose by this cell line. In conclusion, these findings show that MPP+ negatively affects the transcriptome involved with complex I, but initiated an elevation of G protein signaling and anaerobic metabolic systems involved with nitrogen/carboxylic acid metabolism. Future research will be required to elucidate the survival pathways that drive anaerobic substrate level phosphorylation, and define functional ramification to the loss of mitochondrial FAM162a and BNIP3 proteins.

Drosophila Ninjurin A induces nonapoptotic cell death

Ninjurins are conserved transmembrane proteins that are upregulated across species in response to injury and stress. Their biological functions are not understood, in part because there have been few in vivo studies of their function. We analyzed the expression and function of one of three Drosophila Ninjurins, NijA. We found that NijA protein is redistributed to the cell surface in larval immune tissues after septic injury and is upregulated by the Toll pathway. We generated a null mutant of NijA, which displayed no detectable phenotype. In ectopic expression studies, NijA induced cell death, as evidenced by cell loss and acridine orange staining. These dying cells did not display hallmarks of apoptotic cells including TUNEL staining and inhibition by p35, indicating that NijA induced nonapoptotic cell death. In cell culture, NijA also induced cell death, which appeared to be cell autonomous. These in vivo studies identify a new role for the Ninjurin family in inducing nonapoptotic cell death.

The MMP-9/TIMP-1 axis controls the status of differentiation and function of myelin-forming Schwann cells in nerve regeneration

Background

Myelinating Schwann cells (mSCs) form myelin in the peripheral nervous system. Because of the works by us and others, matrix metalloproteinase-9 (MMP-9) has recently emerged as an essential component of the Schwann cell signaling network during sciatic nerve regeneration.

Methodology/Principal Findings

In the present study, using the genome-wide transcriptional profiling of normal and injured sciatic nerves in mice followed by extensive bioinformatics analyses of the data, we determined that an endogenous, specific MMP-9 inhibitor [tissue inhibitor of metalloproteinases (TIMP)-1] was a top up-regulated gene in the injured nerve. MMP-9 capture followed by gelatin zymography and Western blotting of the isolated samples revealed the presence of the MMP-9/TIMP-1 heterodimers and the activated MMP-9 enzyme in the injured nerve within the first 24 h post-injury. MMP-9 and TIMP-1 co-localized in mSCs. Knockout of the MMP-9 gene in mice resulted in elevated numbers of de-differentiated/immature mSCs in the damaged nerve. Our comparative studies using MMP-9 knockout and wild-type mice documented an aberrantly enhanced proliferative activity and, accordingly, an increased number of post-mitotic Schwann cells, short internodes and additional nodal abnormalities in remyelinated nerves of MMP-9 knockout mice. These data imply that during the first days post-injury MMP-9 exhibits a functionally important anti-mitogenic activity in the wild-type mice. Pharmacological inhibition of MMP activity suppressed the expression of Na_v1.7/1.8 channels in the crushed nerves.

Conclusion/Significance

Collectively, our data established an essential role of the MMP-9/TIMP-1 axis in guiding the mSC differentiation and the molecular assembly of myelin domains in the course of the nerve repair process. Our findings of the MMP-dependent regulation of Na_v channels, which we document here for the first time, provide a basis for therapeutic intervention in sensorimotor pathologies and pain.

Role of transcription factors in peripheral nerve regeneration

Following axotomy, the activation of multiple intracellular signaling cascades causes the expression of a cocktail of regeneration-associated transcription factors which interact with each other to determine the fate of the injured neurons. The nerve injury response is channeled through manifold and parallel pathways, integrating diverse inputs, and controlling a complex transcriptional output. Transcription factors form a vital link in the chain of regeneration, converting injury-induced stress signals into downstream protein expression via gene regulation. They can regulate the intrinsic ability of axons to grow, by controlling expression of whole cassettes of gene targets. In this review, we have investigated the functional roles of a number of different transcription factors - c-Jun, activating transcription factor 3, cAMP response element binding protein, signal transducer, and activator of transcription-3, CCAAT/enhancer binding proteins β and δ, Oct-6, Sox11, p53, nuclear factor kappa-light-chain-enhancer of activated B cell, and ELK3 - in peripheral nerve regeneration. Studies involving use of conditional mutants, microarrays, promoter region mapping, and different injury paradigms, have enabled us to understand their distinct as well as overlapping roles in achieving anatomical and functional regeneration after peripheral nerve injury.

Association between genetic variant on chromosome 12p13 and stroke survival and recurrence: a one year prospective study in Taiwan

BACKGROUND

The association between ischemic stroke and 2 single nucleotide polymorphisms (SNPs) on chromosome 12p13, rs12425791 and rs11833579 appears inconsistent across different samples. These SNPs are close to the ninjurin2 gene which may alter the risk of stroke by affecting brain response to ischemic injury. The purpose of this study was to investigate the association between these two SNPs and ischemic stroke risk, as well as prognostic outcomes in a Taiwanese sample.

METHODS

We examined the relations of these two SNPs to the odds of new-onset ischemic stroke, ischemic stroke subtypes, and to the one year risk of stroke-related death or recurrent stroke following initial stroke in a case-control study. A total of 765 consecutive patients who had first-ever ischemic stroke were compared to 977 stroke-free, age-matched controls. SNPs were genotyped by Taqman fluorescent allelic discrimination assay. The association between ischemic stroke and SNPs were analyzed by multivariate logistic regression. Cox proportional hazard model was used to assess the effect of individual SNPs on stroke-related mortality or recurrent stroke.

RESULTS

There was no significant association between SNP rs12425791 and rs11833579 and ischemic stroke after multiple testing corrections. However, the marginal significant association was observed between SNP rs12425791 and large artery atherosclerosis under recessive model (OR, 2.30; 95%CI, 1.22-4.34; q-value = 0.062). Among the 765 ischemic stroke patients, 59 died or developed a recurrent stroke. After adjustment for age, sex, vascular risk factors and baseline stroke severity, Cox proportional hazard analysis indicated that the hazard ratios were 2.76 (95%CI, 1.34-5.68; q-value, 0.02) and 2.15 (95%CI, 1.15-4.02; q-value, 0.03) for individuals with homozygous variant allele of rs12425791 and rs11833579, respectively.

CONCLUSIONS

This is a precedent study that found genetic variants of rs12425791 and rs11833579 on chromosome 12p13 are independent predictors of stroke-related mortality or stroke recurrence in patients with incident ischemic stroke in Taiwan. Further study is needed to explore the details of the physiological function and the molecular mechanisms underlying the association of this genetic locus with ischemic stroke.

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.

Conditioning lesions before or after spinal cord injury recruit broad genetic mechanisms that sustain axonal regeneration: superiority to camp-mediated effects

Previous studies indicate that peripheral nerve conditioning lesions significantly enhance central axonal regeneration via modulation of cAMP-mediated mechanisms. To gain insight into the nature and temporal dependence of neural mechanisms underlying conditioning lesion effects on central axonal regeneration, we compared the efficacy of peripheral sciatic nerve crush lesions to cAMP elevations (in lumbar dorsal root ganglia) on central sensory axonal regeneration when administered either before or after cervical spinal cord lesions. We found significantly greater effects of conditioning lesions compared to cAMP elevations on central axonal regeneration when combined with cellular grafts at the lesion site and viral neurotrophin delivery; further, these effects persisted whether conditioning lesions were applied prior to or shortly after spinal cord injury. Indeed, conditioning lesions recruited extensively greater sets of genetic mechanisms of possible relevance to axonal regeneration compared to cAMP administration, and sustained these changes for significantly greater time periods through the post-lesion period. We conclude that cAMP-mediated mechanisms account for only a portion of the potency of conditioning lesions on central axonal regeneration, and that recruitment of broader genetic mechanisms can extend the effect and duration of cellular events that support axonal growth.

A biomaterials approach to peripheral nerve regeneration: bridging the peripheral nerve gap and enhancing functional recovery

Microsurgical techniques for the treatment of large peripheral nerve injuries (such as the gold standard autograft) and its main clinically approved alternative--hollow nerve guidance conduits (NGCs)--have a number of limitations that need to be addressed. NGCs, in particular, are limited to treating a relatively short nerve gap (4 cm in length) and are often associated with poor functional recovery. Recent advances in biomaterials and tissue engineering approaches are seeking to overcome the limitations associated with these treatment methods. This review critically discusses the advances in biomaterial-based NGCs, their limitations and where future improvements may be required. Recent developments include the incorporation of topographical guidance features and/or intraluminal structures, which attempt to guide Schwann cell (SC) migration and axonal regrowth towards their distal targets. The use of such strategies requires consideration of the size and distribution of these topographical features, as well as a suitable surface for cell-material interactions. Likewise, cellular and molecular-based therapies are being considered for the creation of a more conductive nerve microenvironment. For example, hurdles associated with the short half-lives and low stability of molecular therapies are being surmounted through the use of controlled delivery systems. Similarly, cells (SCs, stem cells and genetically modified cells) are being delivered with biomaterial matrices in attempts to control their dispersion and to facilitate their incorporation within the host regeneration process. Despite recent advances in peripheral nerve repair, there are a number of key factors that need to be considered in order for these new technologies to reach the clinic.

Differential regulation of the expression of neurotrophin receptors in rat extraocular motoneurons after lesion

Neurotrophins acting through high-affinity tyrosine kinase receptors (trkA, trkB, and trkC) play a crucial role in regulating survival and maintenance of specific neuronal functions after injury. Adult motoneurons supplying extraocular muscles survive after disconnection from the target, but suffer dramatic changes in morphological and physiological properties, due in part to the loss of their trophic support from the muscle. To investigate the dependence of the adult rat extraocular motoneurons on neurotrophins, we examined trkA, trkB, and trkC mRNA expression after axotomy by in situ hybridization. trkA mRNA expression was detectable at low levels in unlesioned motoneurons, and its expression was downregulated 1 and 3 days after injury. Expression of trkB and trkC mRNAs was stronger, and after axotomy a simultaneous, but inverse regulation of both receptors was observed. Thus, whereas a considerable increase in trkB expression was seen about 2 weeks after axotomy, the expression of trkC mRNA had decreased at the same post-lesion period. Injured extraocular motoneurons also experienced an initial induction in expression of calcitonin gene-related peptide and a transient downregulation of cholinergic characteristics, indicating a switch in the phenotype from a transmitter-specific to a regenerative state. These results suggest that specific neurotrophins may contribute differentially to the survival and regenerative responses of extraocular motoneurons after lesion.

Microglial signalling mechanisms: Cathepsin S and Fractalkine

A recent major conceptual advance has been the recognition of the importance of immune system-neuron interactions in the modulation of spinal pain processing. In particular, pro-inflammatory mediators secreted by immune competent cells such as microglia modulate nociceptive function in the injured CNS and following peripheral nerve damage. Chemokines play a pivotal role in mediating neuronal-microglial communication which leads to increased nociception. Here we examine the evidence that one such microglial mediator, the lysosomal cysteine protease Cathepsin S (CatS), is critical for the maintenance of neuropathic pain via cleavage of the transmembrane chemokine Fractalkine (FKN). Both CatS and FKN mediate critical physiological functions necessary for immune regulation. As key mediators of homeostatic functions it is not surprising that imbalance in these immune processes has been implicated in autoimmune disorders including Multiple Sclerosis and Rheumatoid Arthritis, both of which are associated with chronic pain. Thus, impairment of the CatS/FKN signalling pair constitutes a novel therapeutic approach for the treatment of chronic pain.

Patterns of pain: meta-analysis of microarray studies of pain

Existing microarray gene expression profiling studies of tonic/chronic pain were subjected to meta-analysis to identify genes found to be regulated by these pain states in multiple, independent experiments. Twenty studies published from 2002 to 2008 were identified, describing the statistically significant regulation of 2254 genes. Of those, a total of 79 genes were found to be statistically significant "hits" in 4 or more independent microarray experiments, corresponding to a conservative P<0.01 overall. Gene ontology-based functional annotation clustering analyses revealed strong evidence for regulation of immune-related genes in pain states. A multi-gene quantitative real-time polymerase chain reaction experiment was run on dorsal root ganglion (DRG) and spinal cord tissue from rats and mice given nerve (sciatic chronic constriction; CCI) or inflammatory (complete Freund's adjuvant) injury. We independently confirmed the regulation of 43 of these genes in the rat-CCI-DRG condition; the genetic correlates in all other conditions were largely and, in some cases, strikingly, independent. However, a handful of genes were identified whose regulation bridged etiology, anatomical locus, and/or species. Most notable among these were Reg3b (regenerating islet-derived 3 beta; pancreatitis-associated protein) and Ccl2 (chemokine [C-C motif] ligand 2), which were significantly upregulated in every condition in the rat.

miR-107 regulates granulin/progranulin with implications for traumatic brain injury and neurodegenerative disease

Granulin (GRN, or progranulin) is a protein involved in wound repair, inflammation, and neoplasia. GRN has also been directly implicated in frontotemporal dementia and may contribute to Alzheimer's disease pathogenesis. However, GRN regulation expression is poorly understood. A high-throughput experimental microRNA assay showed that GRN is the strongest target for miR-107 in human H4 neuroglioma cells. miR-107 has been implicated in Alzheimer's disease pathogenesis, and sequence elements in the open reading frame-rather than the 3' untranslated region-of GRN mRNA are recognized by miR-107 and are highly conserved among vertebrate species. To better understand the mechanism of this interaction, FLAG-tagged Argonaute constructs were used following miR-107 transfection. GRN mRNA interacts preferentially with Argonaute 2. In vitro and in vivo studies indicate that regulation of GRN by miR-107 may be functionally important. Glucose supplementation in cultured cells that leads to increased miR-107 levels also results in decreased GRN expression, including changes in cell compartmentation and decreased secretion of GRN protein. This effect was eliminated following miR-107 transfection. We also tested a mouse model where miR-107 has been shown to be down-regulated. In brain tissue subjacent to 1.0 mm depth controlled cortical impact, surviving hippocampal neurons show decreased miR-107 with augmentation of neuronal GRN expression. These findings indicate that miR-107 contributes to GRN expression regulation with implications for brain disorders.

Alternation of gene expression in trigeminal ganglion neurons following complete Freund's adjuvant or capsaicin injection into the rat face

The hyperexcitability of trigeminal ganglion (TG) neurons following inflammation or C-fiber stimulation is known to be involved in a variety of changes in gene expression in TG neurons, resulting in pain abnormalities in orofacial regions. We analyzed nocifensive behavior following complete Freund's adjuvant (CFA) or capsaicin injection into the maxillary whisker pad, and gene expression in the TG neurons using microarray analysis. The head-withdrawal latency to capsaicin injection or the head-withdrawal threshold to mechanical stimulation of the whisker pad skin in CFA-treated rats was significantly decreased compared to vehicle-treated rats. Many up-regulated and down-regulated genes in the TG neurons of each model were reported. Genes which have not been linked to peripheral inflammation or C-fiber activation were detected. Moreover, microarray chip containing a number of non-coding sequences was also up-regulated by C-fiber activation. These findings suggest that the diverse gene expressions in TG neurons are differentially involved in the inflammatory chronic pain and the acute pain induced by C-fiber activation, and the hyperexcitation of C-fibers are associated with the activation of certain non-coding RNAs.

Gene expression analysis on anterior temporal neocortex of patients with intractable epilepsy

To elucidate the molecular basis of intractable epilepsy (IE), we used a whole-genome transcriptomic approach to identify genes involved in the pathogenesis of this disease. Using a complementary DNAs microarray representing 4096 human genes, we analyzed differential gene expression in the anterior temporal neocortex (ATN) of IE patients relative to control patients who had an operation to relieve head trauma-related intracranial pressure. The results were validated by real-time fluorescence-quantitative polymerase chain reaction (FQ-PCR) and reverse transcription-PCR (RT-PCR). The expression of 143 genes (3.5%) was significantly altered in IE patients. Thirty-seven genes (26%) were reduced relative to controls, and 106 (74%) were elevated (more than twofold change vs. controls), including genes involved in immunity, signal transduction, apoptosis, stress, synaptic plasticity, structural, and cellular reorganization, among other processes. Results for 13 of the 14 differentially expressed genes tested by FQ-PCR were consistent with the microarray. Twelve abnormally expressed cytoskeletal genes were confirmed by RT-PCR. Expression of 11 was significantly higher in the ATN of IE patients than in controls. Gene products altered in IE, namely HSPBAP1, TRAP220, glycogen synthase kinase-3beta (GSK-3beta), and cyclin-dependent kinase 5 (CDK5), were tested by immunohistochemistry and immunoblotting. GSK-3beta and CDK5 levels were significantly higher in the ATN of IE patients. Our gene chip data are generally in agreement with the published findings on epilepsy. Thus, gene chips may serve as a screening tool to elucidate the pathophysiology of IE. Investigation of some of these newly identified genes should enhance our understanding of the molecular mechanisms of epileptogenesis.

Chapter 27: Neural plasticity after nerve injury and regeneration

Injuries to the peripheral nerves result in partial or total loss of motor, sensory, and autonomic functions in the denervated segments of the body due to the interruption of axons, degeneration of distal nerve fibers, and eventual death of axotomized neurons. Functional deficits caused by nerve injuries can be compensated by reinnervation of denervated targets by regenerating injured axons or by collateral branching of undamaged axons, and remodeling of nervous system circuitry related to the lost functions. Plasticity of central connections may compensate functionally for the lack of adequate target reinnervation; however, plasticity has limited effects on disturbed sensory localization or fine motor control after injuries, and may even result in maladaptive changes, such as neuropathic pain and hyperreflexia. After axotomy, neurons shift from a transmitter to a regenerative phenotype, activating molecular pathways that promote neuronal survival and axonal regeneration. Peripheral nerve injuries also induce a cascade of events, at the molecular, cellular, and system levels, initiated by the injury and progressing throughout plastic changes at the spinal cord, brainstem nuclei, thalamus, and brain cortex. Mechanisms involved in these changes include neurochemical changes, functional alterations of excitatory and inhibitory synaptic connections, sprouting of new connections, and reorganization of sensory and motor central maps. An important direction for research is the development of therapeutic strategies that enhance axonal regeneration, promote selective target reinnervation, and are also able to modulate central nervous system reorganization, amplifying positive adaptive changes that improve functional recovery and also reducing undesirable effects.