Opposing effects of Toll-like receptors 2 and 4 on synaptic stability in the spinal cord after peripheral nerve injury

Gut Microbiota Protects Listeria monocytogenes-Infected Mice by Reducing the Inflammatory Cytokines Storm and Cell Apoptosis

Gut microbiota (GM) has been proven to resist pathogenic infection through nutritional competition, colonization resistance and promotion of the host immune response. However, in clinical practice, GM is mainly used in intestinal diseases, such as Clostridium difficile infection, and there are few reports on its application in the treatment of pathogenic bacterial infections. In this study, GM from healthy mice was transplanted into mice infected with Listeria monocytogenes using fecal microbiota transplantation (FMT) and the effects were observed. We found that GM from healthy mice could reduce the mortality of infected mice and decrease the counts of L. monocytogenes in their liver and spleen. In addition, FMT inhibited the expression of inflammatory factors in the liver and spleen of infected mice. In vitro cell experiments revealed that GM can reduce the count of L. monocytogenes invading Caco-2 cells and inhibit the L. monocytogenes-caused apoptosis. These results indicate that GM can be used to protect mice infected with L. monocytogenes by eliminating the amount of L. monocytogenes in the host and inhibiting the overexpression of inflammatory factors. Hence, this method can potentially replace antibiotics in the treatment of L. monocytogenes infection.

Embryonic stem cells overexpressing high molecular weight FGF2 isoform enhance recovery of pre-ganglionic spinal root lesion in combination with fibrin biopolymer mediated root repair

BACKGROUND

Spinal ventral root avulsion results in massive motoneuron degeneration with poor prognosis and high costs. In this study, we compared different isoforms of basic fibroblast growth factor 2 (FGF2), overexpressed in stably transfected Human embryonic stem cells (hESCs), following motor root avulsion and repair with a heterologous fibrin biopolymer (HFB).

METHODS

In the present work, hESCs bioengineered to overexpress 18, 23, and 31 kD isoforms of FGF2, were used in combination with reimplantation of the avulsed roots using HFB. Statistical analysis was conducted using GraphPad Prism software with one-way or two-way ANOVA, followed by Tukey's or Dunnett's multiple comparison tests. Significance was set at *p < 0.05, **p < 0.01, ***p < 0.001, and ****p < 0.0001.

RESULTS

For the first set of experiments, rats underwent avulsion of the ventral roots with local administration of HFB and engraftment of hESCs expressing the above-mentioned FGF2 isoforms. Analysis of motoneuron survival, glial reaction, and synaptic coverage, two weeks after the lesion, indicated that therapy with hESCs overexpressing 31 kD FGF2 was the most effective. Consequently, the second set of experiments was performed with that isoform, so that ventral root avulsion was followed by direct spinal cord reimplantation. Motoneuron survival, glial reaction, synaptic coverage, and gene expression were analyzed 2 weeks post-lesion; while the functional recovery was evaluated by the walking track test and von Frey test for 12 weeks. We showed that engraftment of hESCs led to significant neuroprotection, coupled with immunomodulation, attenuation of astrogliosis, and preservation of inputs to the rescued motoneurons. Behaviorally, the 31 kD FGF2 - hESC therapy enhanced both motor and sensory recovery.

CONCLUSION

Transgenic hESCs were an effective delivery platform for neurotrophic factors, rescuing axotomized motoneurons and modulating glial response after proximal spinal cord root injury, while the 31 kD isoform of FGF2 showed superior regenerative properties over other isoforms in addition to the significant functional recovery.

TLR4-MyD88 signaling is involved in the spinal neurons during the full length of recovery from transection of the motor branch of the femoral nerve in mice

This study was designed to see the expression of toll-like receptor 4 (TLR4) and downstream molecules including myeloid differentiation factor 88 (MyD88) and interleukin 1-β (IL-1β) in the spinal cord as peripheral nerve injury recovered in mice. We established a model of femoral nerve injury (FNI) in C57BL/6 mice by transection of the motor branch of the femoral nerve, followed by retrograde labeling to show the according motor neurons in the anterior horn of the spinal cord pars lumbar. We observed the motor function recovery of the injured hind limbs using behavioral tests. The expression of TLR4, MyD88, and IL-1β was examined by immunofluorescent staining and western blot. According to the behavior test, the FNI animals fully recovered within 6-8 weeks. TLR4, MyD88, and IL-1β were expressed in the ventral horn of the spinal cord both at 72 h till 6 weeks after the femoral nerve transection surgery, and these proteins were mostly co-localized with neurons. IL-1β also tended to rise in the same surgery groups, but more intimate with microglia surrounding nearby retrograde labeled neurons. And western blot results were consistent with histological findings. The results indicate that peripheral nerve injury may induce innate immune reactions of the central neurons and critical signaling like TLR4/MyD88 in the spinal cord may reflect the recovery of the injury. These findings suggest that peripheral nerve injury triggered the TLR4/MyD88 signal in the soma of spinal neurons may be involved in function and nerve restoration through neuron-glia crosstalk.

Human dental pulp stem cell monolayer and spheroid therapy after spinal motor root avulsion in adult rats

Spinal cord injuries result in severe neurological deficits and neuronal loss, with poor functional recovery. Mesenchymal stem cells have shown promising results; therefore the present objective of this work was to compare motor recovery after treatment with human dental pulp stem cells (hDPSC) cultivated in monolayer (2D) or as spheroids (3D), following avulsion and reimplantation of spinal motor roots in adult rats. Thus, 72 adult female Lewis rats were divided into 4 groups: avulsion (AV); avulsion followed by reimplantation (AR); avulsion associated with reimplant and 2D cell therapy (AR + 2D), and avulsion associated with reimplant and 3D cell therapy (AR + 3D). The application of the cells in 2D and 3D was performed by microsurgery, with subsequent functional assessment using a walking track test (Catwalk system), immunohistochemistry, neuronal survival, and qRT-PCR in 1-, 4-, and 12-weeks post-injury. The animals in the AR + 2D and AR + 3D groups showed the highest neuronal survival rates, and immunofluorescence revealed downregulation of GFAP, and Iba-1, with preservation of synaptophysin, indicating a reduction in glial reactivity, combined with the maintenance of pre-synaptic inputs. There was an increase in anti-inflammatory (IL-4, TGFβ) and a reduction of pro-inflammatory factors (IL-6, TNFα) in animals treated with reimplantation and hDPSC. As for the functional recovery, in all analyzed parameters, the AR + 2D group performed better and was superior to the avulsion alone. Overall, our results indicate that the 2D and 3D cell therapy approaches provide successful immunomodulation and motor recovery, consistent with advanced therapies after spinal cord injury.

Fecal microbiota transplantation reduces mouse mortality from Listeria monocytogenes infection

Listeria monocytogenes (Lm) is a food bacterium with strong pathogenicity which causes infections via the gastrointestinal tract. Mechanisms by which gut microbiota (GM) resist microbial infections have received little attention. Eight-week-old mice were orally inoculated with wild-type Lm EGD-e and fecal microbiota transplantation (FMT) employed. GM richness and diversity of infected mice changed rapidly within 24h. Firmicutes class decreased and Bacteroidetes, Tenericutes and Ruminococcaceae increased significantly. Coprococcus, Blautia and Eubacterium also increased on the 3rd day post-infection. Moreover, GM transplanted from healthy mice reduced mortality of infected mice by approximately 32%. FMT treatment decreased production of TNFα, IFN-γ, IL-1β and IL-6 relative to PBS treatment. In summary, FMT has potential as a treatment against Lm infection and may be used for bacterial resistance management. Further work is required to elucidate the key GM effector molecules.

The Role of Microglia in Neuroinflammation of the Spinal Cord after Peripheral Nerve Injury

Peripheral nerve injuries induce a pronounced immune reaction within the spinal cord, largely governed by microglia activation in both the dorsal and ventral horns. The mechanisms of activation and response of microglia are diverse depending on the location within the spinal cord, type, severity, and proximity of injury, as well as the age and species of the organism. Thanks to recent advancements in neuro-immune research techniques, such as single-cell transcriptomics, novel genetic mouse models, and live imaging, a vast amount of literature has come to light regarding the mechanisms of microglial activation and alluding to the function of microgliosis around injured motoneurons and sensory afferents. Herein, we provide a comparative analysis of the dorsal and ventral horns in relation to mechanisms of microglia activation (CSF1, DAP12, CCR2, Fractalkine signaling, Toll-like receptors, and purinergic signaling), and functionality in neuroprotection, degeneration, regeneration, synaptic plasticity, and spinal circuit reorganization following peripheral nerve injury. This review aims to shed new light on unsettled controversies regarding the diversity of spinal microglial-neuronal interactions following injury.

Weighted gene co-expression network analysis reveals that CXCL10, IRF7, MX1, RSAD2, and STAT1 are related to the chronic stage of spinal cord injury

Background

The process of spinal cord injury involves acute, subacute, and chronic stages; however, the specific pathological mechanism remains unclear. In this study, weighted gene co-expression network analysis (WGCNA) was used to clarify specific modules and hub genes that associated with SCI.

Methods

The gene expression profiles GEO Series (GSE)45006 and GEO Series (GSE)2599 were downloaded, and the co-expression network modules were identified by the WGCNA package. The protein-protein interaction (PPI) network and Venn diagram were constructed to identify hub genes. Quantitative real-time polymerase chain reaction (QRT-PCR) was used to quantify the degree of the top five candidate genes. Correlation analysis was also carried out between hub genes and immune infiltration.

Results

In total, 14,402 genes and seven modules were identified. The brown module was considered to be the most critical module for the chronic stage of SCI, which contained 775 genes that were primarily associated with various biological processes, including extracellular structure organization, lysosome, isoprenoid biosynthesis, response to nutrients, response to wounding, sulfur compound metabolic process, cofactor metabolic process, and ossification. Furthermore, C-X-C motif chemokine ligand 10 (CXCL10), myxovirus (influenza virus) resistance 1 (MX1), signal transducer and activator of transcription 1 (STAT1), interferon regulatory factor 7 (IRF7) and radical S-adenosyl methionine domain containing 2 (RSAD2) were identified as the hub genes in the PPI and Venn diagram network, and verified by qRT-PCR. Immune infiltration analysis revealed that CD8+ T cells, macrophages, neutrophils, plasmacytoid dendritic cells, helper T cells, Th2 cells, and tumor-infiltrating lymphocytes may be involved in the SCI process.

Conclusions

There were significant differences among the five hub genes (CXCL10, IRF7, MX1, RSAD2, and STAT1) of the brown module, which may be potential diagnostic and prognostic markers of SCI, and immune cell infiltration may play an important role in the chronic stage of SCI.

Synaptic Plasticity on Motoneurons After Axotomy: A Necessary Change in Paradigm

Motoneurons axotomized by peripheral nerve injuries experience profound changes in their synaptic inputs that are associated with a neuroinflammatory response that includes local microglia and astrocytes. This reaction is conserved across different types of motoneurons, injuries, and species, but also displays many unique features in each particular case. These reactions have been amply studied, but there is still a lack of knowledge on their functional significance and mechanisms. In this review article, we compiled data from many different fields to generate a comprehensive conceptual framework to best interpret past data and spawn new hypotheses and research. We propose that synaptic plasticity around axotomized motoneurons should be divided into two distinct processes. First, a rapid cell-autonomous, microglia-independent shedding of synapses from motoneuron cell bodies and proximal dendrites that is reversible after muscle reinnervation. Second, a slower mechanism that is microglia-dependent and permanently alters spinal cord circuitry by fully eliminating from the ventral horn the axon collaterals of peripherally injured and regenerating sensory Ia afferent proprioceptors. This removes this input from cell bodies and throughout the dendritic tree of axotomized motoneurons as well as from many other spinal neurons, thus reconfiguring ventral horn motor circuitries to function after regeneration without direct sensory feedback from muscle. This process is modulated by injury severity, suggesting a correlation with poor regeneration specificity due to sensory and motor axons targeting errors in the periphery that likely render Ia afferent connectivity in the ventral horn nonadaptive. In contrast, reversible synaptic changes on the cell bodies occur only while motoneurons are regenerating. This cell-autonomous process displays unique features according to motoneuron type and modulation by local microglia and astrocytes and generally results in a transient reduction of fast synaptic activity that is probably replaced by embryonic-like slow GABA depolarizations, proposed to relate to regenerative mechanisms.

Toll-like receptor 4 (TLR4) influences the glial reaction in the spinal cord and the neural response to injury following peripheral nerve crush

After peripheral axotomy, there is a selective retraction of synaptic terminals in contact with injured motoneurons. This process, which actively involves glial cells, is influenced by the expression of immune-related molecules. Since toll-like receptors (TLRs) are upregulated by astrocytes and microglia following lesions, they might be involved in synaptic plasticity processes. Therefore, we administered lipopolysaccharide (LPS) to enhance TLR4 expression in mice and studied retrograde changes in the spinal cord ventral horn following sciatic nerve crush. To this end, adult C57BL/6J male mice were subjected to unilateral sciatic nerve crush at the mid-thigh level and, after a survival time of seven and forty days (acute and chronic phases, respectively), the spinal cords were paraformaldehyde-fixed and dissected out for immunolabeling for synaptophysin, glial fibrillary acidic protein (GFAP) and ionized calcium-binding adapter molecule 1 (Iba1). The results show that TLR4 upregulation leads to synaptophysin downregulation close to spinal motoneuron cell bodies, indicating increased synaptic elimination. LPS exposure also further increases astrogliosis and microglial reactions in the both ventral and dorsal horns, especially ipsilateral to nerve axotomy, compared to those in untreated mice. Notably, LPS administration to TLR4^-/- mice produces results similar to those observed in untreated wild-type counterparts, reinforcing the role of this receptor in the glial response to injury. Therefore, our results suggest that the overexpression of the TLR4 receptor results in augmented astrogliosis/microglial reactions and the excessive loss of synapses postinjury, which may, in turn, affect the motoneuronal regenerative response and functionality. Additionally, treatment with LPS increases the expression of β2-microglobulin, a subcomponent of MHC I. Importantly, the absence of TLR4 results in imbalanced axonal regeneration, inducing subsequent improvements and setbacks. In conclusion, our results show the involvement of TLR4 in the process of synaptic remodeling, indicating a new target for future research aimed at developing therapies for CNS and PNS repair.

Immune Contributions to Osteoarthritis

PURPOSE OF THE REVIEW

Mounting evidence supports a role of low-grade inflammation in the pathophysiology of osteoarthritis (OA). We review and discuss the role of synovitis, complement activation, cytokines, and immune cell population in OA.

RECENT FINDINGS

Using newer imaging modalities, synovitis is found in the majority of knees with OA. Complement activation and pro-inflammatory cytokines play a significant role in the development of cartilage destruction and synovitis. Immune cell infiltration of OA synovial tissue by sub-populations of T cells and activated macrophages correlates with OA disease progression and pain. The innate and acquired immune system plays a key role in the low-grade inflammation found associated with OA. Targets of these pathways my hold promise for future disease-modifying osteoarthritis drugs (DMOADs).

Deletion of the Fractalkine Receptor, CX3CR1, Improves Endogenous Repair, Axon Sprouting, and Synaptogenesis after Spinal Cord Injury in Mice

Impaired signaling via CX3CR1, the fractalkine receptor, promotes recovery after traumatic spinal contusion injury in mice, a benefit achieved in part by reducing macrophage-mediated injury at the lesion epicenter. Here, we tested the hypothesis that CX3CR1-dependent changes in microglia and macrophage functions also will enhance neuroplasticity, at and several segments below the injury epicenter. New data show that in the presence of inflammatory stimuli, CX3CR1-deficient (CX3CR1^-/-) microglia and macrophages adopt a reparative phenotype and increase expression of genes that encode neurotrophic and gliogenic proteins. At the lesion epicenter (mid-thoracic spinal cord), the microenvironment created by CX3CR1^-/- microglia/macrophages enhances NG2 cell responses, axon sparing, and sprouting of serotonergic axons. In lumbar spinal cord, inflammatory signaling is reduced in CX3CR1^-/- microglia. This is associated with reduced dendritic pathology and improved axonal and synaptic plasticity on ventral horn motor neurons. Together, these data indicate that CX3CR1, a microglia-specific chemokine receptor, is a novel therapeutic target for enhancing neuroplasticity and recovery after SCI. Interventions that specifically target CX3CR1 could reduce the adverse effects of inflammation and augment activity-dependent plasticity and restoration of function. Indeed, limiting CX3CR1-dependent signaling could improve rehabilitation and spinal learning.SIGNIFICANCE STATEMENT Published data show that genetic deletion of CX3CR1, a microglia-specific chemokine receptor, promotes recovery after traumatic spinal cord injury in mice, a benefit achieved in part by reducing macrophage-mediated injury at the lesion epicenter. Data in the current manuscript indicate that CX3CR1 deletion changes microglia and macrophage function, creating a tissue microenvironment that enhances endogenous repair and indices of neuroplasticity, at and several segments below the injury epicenter. Interventions that specifically target CX3CR1 might be used in the future to reduce the adverse effects of intraspinal inflammation and augment activity-dependent plasticity (e.g., rehabilitation) and restoration of function.

Synaptic Failure: Focus in an Integrative View of ALS

From early description by Charcot, the classification of the Amyotrophic Lateral Sclerosis (ALS) is evolving from a subtype of Motor Neuron (MN) Disease to be considered rather a multi-systemic, non-cell autonomous and complex neurodegenerative disease. In the last decade, the huge amount of knowledge acquired has shed new insights on the pathological mechanisms underlying ALS from different perspectives. However, a whole vision on the multiple dysfunctional pathways is needed with the inclusion of information often excluded in other published revisions. We propose an integrative view of ALS pathology, although centered on the synaptic failure as a converging and crucial player to the etiology of the disease. Homeostasis of input and output synaptic activity of MNs has been proved to be severely and early disrupted and to definitively contribute to microcircuitry alterations at the spinal cord. Several cells play roles in synaptic communication across the MNs network system such as interneurons, astrocytes, microglia, Schwann and skeletal muscle cells. Microglia are described as highly dynamic surveying cells of the nervous system but also as determinant contributors to the synaptic plasticity linked to neuronal activity. Several signaling axis such as TNFα/TNFR1 and CX3CR1/CX3CL1 that characterize MN-microglia cross talk contribute to synaptic scaling and maintenance, have been found altered in ALS. The presence of dystrophic and atypical microglia in late stages of ALS, with a decline in their dynamic motility and phagocytic ability, together with less synaptic and neuronal contacts disrupts the MN-microglia dialogue, decreases homeostatic regulation of neuronal activity, perturbs “on/off” signals and accelerates disease progression associated to impaired synaptic function and regeneration. Other hotspot in the ALS affected network system is the unstable neuromuscular junction (NMJ) leading to distal axonal degeneration. Reduced neuromuscular spontaneous synaptic activity in ALS mice models was also suggested to account for the selective vulnerability of MNs and decreased regenerative capability. Synaptic destabilization may as well derive from increased release of molecules by muscle cells (e.g. NogoA) and by terminal Schwann cells (e.g. semaphorin 3A) conceivably causing nerve terminal retraction and denervation, as well as inhibition of re-connection to muscle fibers. Indeed, we have overviewed the alterations on the metabolic pathways and self-regenerative capacity presented in skeletal muscle cells that contribute to muscle wasting in ALS. Finally, a detailed footpath of pathologic changes on MNs and associated dysfunctional and synaptic alterations is provided. The oriented motivation in future ALS studies as outlined in the present article will help in fruitful novel achievements on the mechanisms involved and in developing more target-driven therapies that will bring new hope in halting or delaying disease progression in ALS patients.

The flavivirus dengue induces hypertrophy of white matter astrocytes

Flaviviruses, including Zika and dengue (DENV), pose a serious global threat to human health. Of the 50+ million humans infected with DENV annually, approximately 1-3 % progress to severe disease manifestations, dengue hemorrhagic fever (DHF) or dengue shock syndrome (DSS). Several factors are suspected to mediate the course of infection and pathogenesis of DENV infection. DHF and DSS are associated with vascular leakage and neurological sequelae. Our hypothesis was that altered astrocyte activation and morphology would alter the dynamics of the extracellular space and hence, neuronal and vascular function. We investigated the mechanisms of neuropathogenesis DENV infection in rhesus macaques. There were decreased numbers of GFAP immunopositive astrocytes per unit area, although those that remained had increased arbor length and complexity. This was combined with structural hypertrophy of white matter astrocytes in the absence of increased vascular leakage. Combined, these studies show how even low-grade infection with DENV induces measurable changes within the parenchyma of infected individuals.

Impairment of toll-like receptors 2 and 4 leads to compensatory mechanisms after sciatic nerve axotomy

Background

Peripheral nerve injury results in retrograde cell body-related changes in the spinal motoneurons that will contribute to the regenerative response of their axons. Successful functional recovery also depends on molecular events mediated by innate immune response during Wallerian degeneration in the nerve microenvironment. A previous study in our lab demonstrated that TLR 2 and 4 develop opposite effects on synaptic stability in the spinal cord after peripheral nerve injury. Therefore, we suggested that the better preservation of spinal cord microenvironment would positively influence distal axonal regrowth. In this context, the present work aimed to investigate the influence of TLR2 and TLR4 on regeneration and functional recovery after peripheral nerve injury.

Methods

Eighty-eight mice were anesthetized and subjected to unilateral sciatic nerve crush (C3H/HeJ, n = 22, C3H/HePas, n = 22; C57Bl6/J, n = 22 and TLR2^−/−, n = 22). After the appropriate survival times (3, 7, 14 days, and 5 weeks), all mice were killed and the sciatic nerves and tibialis cranialis muscles were processed for immunohistochemistry and transmission electron microscopy (TEM). Gait analysis, after sciatic nerve crushing, was performed in another set of mice (minimum of n = 8 per group), by using the walking track test (CatWalk system).

Results

TLR4 mutant mice presented greater functional recovery as well as an enhanced p75^NTR and neurofilament protein expression as compared to the wild-type strain. Moreover, the better functional recovery in mutant mice was correlated to a greater number of nerve terminal sprouts. Knockout mice for TLR2 exhibited 30 % greater number of degenerated axons in the distal stump of the sciatic nerve and a decreased p75^NTR and neurofilament protein expression compared to the wild type. However, the absence of TLR2 receptor did not influence the overall functional recovery. End-point equivalent functional recovery in transgenic mice may be a result of enhanced axonal diameter found at 2 weeks after lesion.

Conclusions

Altogether, the present results indicate that the lack of TLR2 or the absence of functional TLR4 does affect the nerve regeneration process; however, such changes are minimized through different compensatory mechanisms, resulting in similar motor function recovery, as compared to wild-type mice. These findings contribute to the concept that innate immune-related molecules influence peripheral nerve regeneration by concurrently participating in processes taking place both at the CNS and PNS.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-016-0579-6) contains supplementary material, which is available to authorized users.

Different effects of arginine vasopressin on high-mobility group box 1 expression in astrocytes isolated from stroke-prone spontaneously hypertensive rats and congenic SHRpch1_18 rats

Stroke-prone spontaneously hypertensive rats (SHRSP/Izm) develop severe hypertension and astrocytic oedema following ischaemic stimulation. During ischaemic stress high-mobility group box 1 (Hmgb1) expression in astrocytes is induced, and subsequently potentiates deterioration of the brain due to ischaemic injury, which manifests as both cerebral inflammation and astrocytic oedema. Arginine vasopressin (AVP) induces brain injury and increases astrocytic swelling. After stroke, Hmgb1 and peroxiredoxin (Prx) are released at different times and activate macrophages in the brain via Toll-like receptors (Tlr2s). The purpose of this study was to examine whether AVP and/or hypoxia and reoxygenation (H/R) contribute to Hmgb1 regulation following ischaemic stroke. Thus, Hmgb1, Prx2 and Tlr2 expression levels in astrocytes isolated from Wistar Kyoto rats (WKY/Izm), spontaneously hypertensive rats (SHR/Izm), SHRSP/Izm and congenic rat strain SHRpch1_18 treated with AVP and/or H/R were compared. Gene and protein expression levels were determined by reverse transcriptase-polymerase chain reaction (RT-PCR) and real-time quantitative PCR, and Western blot. mRNA expression of Hmgb1, Prx2 and Tlr2 induced by AVP was dose-dependent, and Hmgb1 and Prx2 expression was higher in SHR/Izm, SHRSP/Izm and SHRch1_18 than in WKY/Izm. Tlr2 expression with AVP was reduced in SHR/Izm compared to WKY/Izm. In SHRpch1_18, Hmgb1 expression increased after AVP plus H/R. AVP-modulated expression of Hmgb1 protein was reduced by the addition of the antioxidant N-acetylcysteine (NAC). These results suggest that oxidative stress by AVP enhanced expression of Hmgb1, Prx2 and Tlr2 in astrocytes. We hypothesize that regulation of Hmgb1 by AVP during H/R might be related to induction of inflammation and stroke in SHRSP/Izm and SHRpch1_18 rats.

Building an RNA Sequencing Transcriptome of the Central Nervous System

The composition and function of the central nervous system (CNS) is extremely complex. In addition to hundreds of subtypes of neurons, other cell types, including glia (astrocytes, oligodendrocytes, and microglia) and vascular cells (endothelial cells and pericytes) also play important roles in CNS function. Such heterogeneity makes the study of gene transcription in CNS challenging. Transcriptomic studies, namely the analyses of the expression levels and structures of all genes, are essential for interpreting the functional elements and understanding the molecular constituents of the CNS. Microarray has been a predominant method for large-scale gene expression profiling in the past. However, RNA-sequencing (RNA-Seq) technology developed in recent years has many advantages over microarrays, and has enabled building more quantitative, accurate, and comprehensive transcriptomes of the CNS and other systems. The discovery of novel genes, diverse alternative splicing events, and noncoding RNAs has remarkably expanded the complexity of gene expression profiles and will help us to understand intricate neural circuits. Here, we discuss the procedures and advantages of RNA-Seq technology in mammalian CNS transcriptome construction, and review the approaches of sample collection as well as recent progress in building RNA-Seq-based transcriptomes from tissue samples and specific cell types.

Synaptic input changes to spinal cord motoneurons correlate with motor control impairments in a type 1 diabetes mellitus model

INTRODUCTION

Hyperglycemia is the main cause of diabetic complications, contributing to a widespread degeneration of the nervous system. Nevertheless, the main focus has been the sensory neurons because of neuropathic pain, while the impairments associated with the spinal cord and motor deficits, mostly of those initiated at early stages of the disease, have been poorly investigated. In this way, the present study used the nonobese diabetic mouse model to evaluate the microenvironment around motoneurons at ventral horn of the spinal cord, following prolonged hyperglycemia.

METHODS

Adult female mice were divided into two groups: spontaneously diabetic (n = 33) and nondiabetic (n = 26). Mice were considered hyperglycemic when blood glucose surpassed 400 mg/dL. Following 2 weeks from that stage, part of the animals was euthanized and the lumbar intumescences were obtained and processed for immunohistochemistry and transmission electron microscopy. For immunohistochemistry, the antibodies used for integrated density of pixels quantification were anti-synaptophysin, anti-GFAP, and anti-Iba1. The functional analysis was monitored with the walking track test (CatWalk system) during 4 weeks.

RESULTS

The results revealed significant motor impairment in diabetic animals in comparison to the control group. Such loss of motor control correlated with a significant reduction in presynaptic terminals apposed to the motoneurons. Nevertheless, there were no significant changes in glial reaction in the spinal cord.

CONCLUSION

Overall, the results herein revealed central nervous system changes at early stages of the disease that may in turn contribute to the motor deficit. Such changes open a new window of investigation in early stages of diabetes to better comprehend motor impairment as a long-term complication of the disease.

A novel combinational approach of microstimulation and bioluminescence imaging to study the mechanisms of action of cerebral electrical stimulation in mice

Deep brain stimulation (DBS) is used to treat a number of neurological conditions and is currently being tested to intervene in neuropsychiatric conditions. However, a better understanding of how it works would ensure that side effects could be minimized and benefits optimized. We have thus developed a unique device to perform brain stimulation (BS) in mice and to address fundamental issues related to this methodology in the pre-clinical setting. This new microstimulator prototype was specifically designed to allow simultaneous live bioluminescence imaging of the mouse brain, allowing real time assessment of the impact of stimulation on cerebral tissue. We validated the authenticity of this tool in vivo by analysing the expression of toll-like receptor 2 (TLR2), corresponding to the microglial response, in the stimulated brain regions of TLR2-fluc-GFP transgenic mice, which we further corroborated with post-mortem analyses in these animals as well as in human brains of patients who underwent DBS to treat their Parkinson's disease. In the present study, we report on the development of the first BS device that allows for simultaneous live in vivo imaging in mice. This tool opens up a whole new range of possibilities that allow a better understanding of BS and how to optimize its effects through its use in murine models of disease.

The role of innate immunity in osteoarthritis: when our first line of defense goes on the offensive

Although osteoarthritis (OA) has existed since the dawn of humanity, its pathogenesis remains poorly understood. OA is no longer considered a "wear and tear" condition but rather one driven by proteases where chronic low-grade inflammation may play a role in perpetuating proteolytic activity. While multiple factors are likely active in this process, recent evidence has implicated the innate immune system, the older or more primitive part of the body's immune defense mechanisms. The roles of some of the components of the innate immune system have been tested in OA models in vivo including the roles of synovial macrophages and the complement system. This review is a selective overview of a large and evolving field. Insights into these mechanisms might inform our ability to identify patient subsets and give hope for the advent of novel OA therapies.

Modulation of lipopolysaccharide-induced neuronal response by activation of the enteric nervous system

BACKGROUND

Evidence continues to mount concerning the importance of the enteric nervous system (ENS) in controlling numerous intestinal functions in addition to motility and epithelial functions. Nevertheless, little is known concerning the direct participation of the ENS in the inflammatory response of the gut during infectious or inflammatory insults. In the present study we analyzed the ENS response to bacterial lipopolysaccharide, in particular the production of a major proinflammatory cytokine, tumor necrosis factor-alpha (TNF-α).

METHODS

TNF-α expression (measured by qPCR, quantitative Polymerase Chain Reaction) and production (measured by ELISA) were measured in human longitudinal muscle-myenteric plexus (LMMP) and rat ENS primary cultures (rENSpc). They were either treated or not treated with lipopolysaccharide (LPS) in the presence or not of electrical field stimulation (EFS). Activation of extracellular signal-regulated kinase (ERK) and 5'-adenosine monophosphate-activated protein kinase (AMPK) pathways was analyzed by immunocytochemistry and Western blot analysis. Their implications were studied using specific inhibitors (U0126, mitogen-activated protein kinase kinase, MEK, inhibitor and C compound, AMPK inhibitor). We also analyzed toll-like receptor 2 (TLR2) expression and interleukin-6 (IL-6) production after LPS treatment simultaneously with EFS or TNF-α-neutralizing antibody.

RESULTS

Treatment of human LMMP or rENSpc with LPS induced an increase in TNF-α production. Activation of the ENS by EFS significantly inhibited TNF-α production. This regulation occurred at the transcriptional level. Signaling analyses showed that LPS induced activation of ERK but not AMPK, which was constitutively activated in rENSpc neurons. Both U0126 and C compound almost completely prevented LPS-induced TNF-α production. In the presence of LPS, EFS inhibited the ERK and AMPK pathways. In addition, we demonstrated using TNF-α-neutralizing antibody that LPS-induced TNF-α production increased TLR2 expression and reduced IL-6 production.

CONCLUSIONS

Our results show that LPS induced TNF-α production by enteric neurons through activation of the canonical ERK pathway and also in an AMPK-dependent manner. ENS activation through the inhibition of these pathways decreased TNF-α production, thereby modulating the inflammatory response induced by endotoxin.

Synaptic rearrangement following axonal injury: Old and new players

Following axotomy, the contact between motoneurons and muscle fibers is disrupted, triggering a retrograde reaction at the neuron cell body within the spinal cord. Together with chromatolysis, a hallmark of such response to injury is the elimination of presynaptic terminals apposing to the soma and proximal dendrites of the injured neuron. Excitatory inputs are preferentially eliminated, leaving the cells under an inhibitory influence during the repair process. This is particularly important to avoid glutamate excitotoxicity. Such shift from transmission to a regeneration state is also reflected by deep metabolic changes, seen by the regulation of several genes related to cell survival and axonal growth. It is unclear, however, how exactly synaptic stripping occurs, but there is substantial evidence that glial cells play an active role in this process. In one hand, immune molecules, such as the major histocompatibility complex (MHC) class I, members of the complement family and Toll-like receptors are actively involved in the elimination/reapposition of presynaptic boutons. On the other hand, plastic changes that involve sprouting might be negatively regulated by extracellular matrix proteins such as Nogo-A, MAG and scar-related chondroitin sulfate proteoglycans. Also, neurotrophins, stem cells, physical exercise and several drugs seem to improve synaptic stability, leading to functional recovery after lesion. This article is part of a Special Issue entitled 'Neuroimmunology and Synaptic Function'.

Toll-like receptors in central nervous system injury and disease: a focus on the spinal cord

Toll-like receptors (TLRs) are best known for recognizing pathogens and initiating an innate immune response to protect the host. However, they also detect tissue damage and induce sterile inflammation upon the binding of endogenous ligands released by stressed or injured cells. In addition to immune system-related cells, TLRs have been identified in central nervous system (CNS) neurons and glial subtypes including microglia, astrocytes and oligodendrocytes. Direct and indirect effects of TLR ligands on neurons and glial subtypes have been documented in vitro. Likewise, the effects of TLR ligands have been demonstrated in vivo using animal models of CNS trauma and disease including spinal cord injury (SCI), amyotrophic lateral sclerosis (ALS) and neuropathic pain. The indirect effects are most likely mediated via microglia or immune system cells that infiltrate the diseased or injured CNS. Despite considerable progress over the past decade, the role of TLRs in the physiological and pathological function of the spinal cord remains inadequately defined. Published reports collectively highlight TLRs as promising targets for therapeutic interventions in spinal cord pathology. The findings also underscore the complexity of TLR-mediated mechanisms and the necessity for further research in this field. The goals of the current review are to recapitulate the studies that investigated the role of TLRs in the spinal cord, to discuss potential future research directions, and to examine some of the challenges associated with pre-clinical studies pertinent to TLRs in the injured or diseased spinal cord.

Retrograde response in axotomized motoneurons: nitric oxide as a key player in triggering reversion toward a dedifferentiated phenotype

The adult brain retains a considerable capacity to functionally reorganize its circuits, which mainly relies on the prevalence of three basic processes that confer plastic potential: synaptic plasticity, plastic changes in intrinsic excitability and, in certain central nervous system (CNS) regions, also neurogenesis. Experimental models of peripheral nerve injury have provided a useful paradigm for studying injury-induced mechanisms of central plasticity. In particular, axotomy of somatic motoneurons triggers a robust retrograde reaction in the CNS, characterized by the expression of plastic changes affecting motoneurons, their synaptic inputs and surrounding glia. Axotomized motoneurons undergo a reprograming of their gene expression and biosynthetic machineries which produce cell components required for axonal regrowth and lead them to resume a functionally dedifferentiated phenotype characterized by the removal of afferent synaptic contacts, atrophy of dendritic arbors and an enhanced somato-dendritic excitability. Although experimental research has provided valuable clues to unravel many basic aspects of this central response, we are still lacking detailed information on the cellular/molecular mechanisms underlying its expression. It becomes clear, however, that the state-switch must be orchestrated by motoneuron-derived signals produced under the direction of the re-activated growth program. Our group has identified the highly reactive gas nitric oxide (NO) as one of these signals, by providing robust evidence for its key role to induce synapse elimination and increases in intrinsic excitability following motor axon damage. We have elucidated operational principles of the NO-triggered downstream transduction pathways mediating each of these changes. Our findings further demonstrate that de novo NO synthesis is not only "necessary" but also "sufficient" to promote the expression of at least some of the features that reflect reversion toward a dedifferentiated state in axotomized adult motoneurons.

Influence of delivery method on neuroprotection by bone marrow mononuclear cell therapy following ventral root reimplantation with fibrin sealant

The present work compared the local injection of mononuclear cells to the spinal cord lateral funiculus with the alternative approach of local delivery with fibrin sealant after ventral root avulsion (VRA) and reimplantation. For that, female adult Lewis rats were divided into the following groups: avulsion only, reimplantation with fibrin sealant; root repair with fibrin sealant associated with mononuclear cells; and repair with fibrin sealant and injected mononuclear cells. Cell therapy resulted in greater survival of spinal motoneurons up to four weeks post-surgery, especially when mononuclear cells were added to the fibrin glue. Injection of mononuclear cells to the lateral funiculus yield similar results to the reimplantation alone. Additionally, mononuclear cells added to the fibrin glue increased neurotrophic factor gene transcript levels in the spinal cord ventral horn. Regarding the motor recovery, evaluated by the functional peroneal index, as well as the paw print pressure, cell treated rats performed equally well as compared to reimplanted only animals, and significantly better than the avulsion only subjects. The results herein demonstrate that mononuclear cells therapy is neuroprotective by increasing levels of brain derived neurotrophic factor (BDNF) and glial derived neurotrophic factor (GDNF). Moreover, the use of fibrin sealant mononuclear cells delivery approach gave the best and more long lasting results.

Form follows function: astrocyte morphology and immune dysfunction in SIV neuroAIDS

Cortical function is disrupted in neuroinflammatory disorders, including HIV-associated neurocognitive disorders (HAND). Astrocyte dysfunction includes retraction of foot processes from the blood-brain barrier and decreased removal of neurotransmitters from synaptic clefts. Mechanisms of astrocyte activation, including innate immune function and the fine neuroanatomy of astrocytes, however, remain to be investigated. We quantified the number of glial fibrillary acidic protein (GFAP)-labeled astrocytes per square millimeter and the proportion of astrocytes immunopositive for Toll-like receptor 2 (TLR2) to examine innate immune activation in astrocytes. We also performed detailed morphometric analyses of gray and white matter astrocytes in the frontal and parietal lobes of rhesus macaques infected with simian immunodeficiency virus (SIV), both with and without encephalitis, an established model of AIDS neuropathogenesis. Protoplasmic astrocytes (gray matter) and fibrous astrocytes (deep white matter) were imaged, and morphometric features were analyzed using Neurolucida. Gray matter and white matter astrocytes showed no change in cell body size in animals infected with SIV regardless of encephalitic status. In SIV-infected macaques, both gray and white matter astrocytes had shorter, less ramified processes, resulting in decreased cell arbor compared with controls. SIV-infected macaques with encephalitis showed decreases in arbor length in white matter astrocytes and reduced complexity in gray matter astrocytes compared to controls. These results provide the first evidence that innate immune activation of astrocytes is linked to altered cortical astrocyte morphology in SIV/HIV infection. Here, we demonstrate that astrocyte remodeling is correlated with infection. Perturbed neuron-glia signaling may be a driving factor in the development of HAND.

Neuroprotective effect of tempol (4 hydroxy-tempo) on neuronal death induced by sciatic nerve transection in neonatal rats

Peripheral nerve injury in newborn rats triggers extensive neuronal death within the spinal cord. Because most neurodegeneration is related to oxidative stress and apoptosis, the use of antioxidants may be of therapeutic interest. Tempol is promising because of its ability to chelate reactive oxygen species and to minimize or even prevent tissue damage. Here, we evaluated neuroprotective effects of tempol following neonatal sciatic nerve transection. Two-day-old pups underwent sciatic nerve axotomy followed by tempol (12, 24 and 48 mg/kg) treatment (i.p.) at 10 min, 6 h, and every 24 h up to 1 week after injury. The rats were then killed for lumbar intumescence analysis. Nissl staining, TUNEL, synaptophysin immunolabeling and qRT-PCR (Caspase 3, Bax and Bcl2) were carried out. The results indicated that tempol treatment, at 24 mg/kg, increased up to 21% spinal cord motoneuron survival (p<0.001), also preserving pre-synaptic terminals in the neuropile. Likewise, the TUNEL-positive cell number decreased in tempol-treated animals. qRT-PCR results indicated differential increase in Caspase 3 (3-fold), Bax (13-fold) and Bcl2 (28-fold) gene expression, after 12 h following axotomy and tempol treatment. In conclusion, tempol administration has proven to be neuroprotective after neonatal nerve injury, leading to improved motoneuron survival, synapse preservation and minimizing apoptosis.

Aerosol-induced brucellosis increases TLR-2 expression and increased complexity in the microanatomy of astroglia in rhesus macaques

Brucella melitensis, a bacterial pathogen and agent of epizootic abortion causes multiple pathologies in humans as well as a number of agriculturally important animal species. Clinical human brucellosis manifests as a non-specific, chronic debilitating disease characterized by undulant fever, arthropathies, cardiomyopathies and neurological sequelae. These symptoms can occur acutely for a few weeks or persist for months to years. Within the brain, endothelial and glial cells can be infected leading to downstream activation events including matrix metalloprotease (MMP) and cytokine secretion and Toll-like receptor (TLR) signaling. These events are likely to lead to tissue remodeling, including morphologic changes in neuronal and glial cells, which are linked to neurological complications including depressive behavior, immune activation and memory loss. Our hypothesis was that B. melitensis infection and neurobrucellosis would lead to activation of astrocytes through upregulation of TLR2 and stimulate concurrent changes in the microanatomy. All six animals were infected via inhalation route. TLR2 expression was approximately doubled in white matter astrocytes of infected rhesus macaques. There was also a 50% increase in the number of astrocytes per unit area in subcortical white matter tracts suggesting increased innate immune activation. This coincided with dramatic increases in the length and complexity of the cell arbor of hypertrophic astrocytes in both cortical gray and white matter. Thus, aerosol-induced brucellosis results in dramatically increased innate immune activation of astrocytes in the absence of widespread neuroinflammation.

TLR2 & Co: a critical analysis of the complex interactions between TLR2 and coreceptors

TLRs play a major role in microbe-host interactions and innate immunity. Of the 10 functional TLRs described in humans, TLR2 is unique in its requirement to form heterodimers with TLR1 or TLR6 for the initiation of signaling and cellular activation. The ligand specificity of TLR2 heterodimers has been studied extensively, using specific bacterial and synthetic lipoproteins to gain insight into the structure-function relationship, the minimal active motifs, and the critical dependence on TLR1 or TLR6 for activation. Different from that for specific well-defined TLR2 agonists, recognition of more complex ligands like intact microbes or molecules from endogenous origin requires TLR2 to interact with additional coreceptors. A breadth of data has been published on ligand-induced interactions of TLR2 with additional pattern recognition receptors such as CD14, scavenger receptors, integrins, and a range of other receptors, all of them important factors in TLR2 function. This review summarizes the roles of TLR2 in vivo and in specific immune cell types and integrates this information with a detailed review of our current understanding of the roles of specific coreceptors and ligands in regulating TLR2 functions. Understanding how these processes affect intracellular signaling and drive functional immune responses will lead to a better understanding of host-microbe interactions and will aid in the design of new agents to target TLR2 function in health and disease.

RNA-seq characterization of spinal cord injury transcriptome in acute/subacute phases: a resource for understanding the pathology at the systems level

Spinal cord injury (SCI) is a devastating neurological disease without effective treatment. To generate a comprehensive view of the mechanisms involved in SCI pathology, we applied RNA-Sequencing (RNA-Seq) technology to characterize the temporal changes in global gene expression after contusive SCI in mice. We sequenced tissue samples from acute and subacute phases (2 days and 7 days after injury) and systematically characterized the transcriptomes with the goal of identifying pathways and genes critical in SCI pathology. The top enriched functional categories include “inflammation response,” “neurological disease,” “cell death and survival” and “nervous system development.” The top enriched pathways include LXR/RXR Activation and Atherosclerosis Signaling, etc. Furthermore, we developed a systems-based analysis framework in order to identify key determinants in the global gene networks of the acute and sub-acute phases. Some candidate genes that we identified have been shown to play important roles in SCI, which demonstrates the validity of our approach. There are also many genes whose functions in SCI have not been well studied and can be further investigated by future experiments. We have also incorporated pharmacogenomic information into our analyses. Among the genes identified, the ones with existing drug information can be readily tested in SCI animal models. Therefore, in this study we have described an example of how global gene profiling can be translated to identifying genes of interest for functional tests in the future and generating new hypotheses. Additionally, the RNA-Seq enables splicing isoform identification and the estimation of expression levels, thus providing useful information for increasing the specificity of drug design and reducing potential side effect. In summary, these results provide a valuable reference data resource for a better understanding of the SCI process in the acute and sub-acute phases.