Stromal cell-derived CCL2 drives neuropathic pain states through myeloid cell infiltration in injured nerve

Immune-cell-mediated tissue engineering strategies for peripheral nerve injury and regeneration

During the process of peripheral nerve repair, there are many complex pathological and physiological changes, including multi-cellular responses and various signaling molecules, and all these events establish a dynamic microenvironment for axon repair, regeneration, and target tissue/organ reinnervation. The immune system plays an indispensable role in the process of nerve repair and function recovery. An effective immune response not only involves innate-immune and adaptive-immune cells but also consists of chemokines and cytokines released by these immune cells. The elucidation of the orchestrated interplay of immune cells with nerve regeneration and functional restoration is meaningful for the exploration of therapeutic strategies. This review mainly enumerates the general immune cell response to peripheral nerve injury and focuses on their contributions to functional recovery. The tissue engineering-mediated strategies to regulate macrophages and T cells through physical and biochemical factors combined with scaffolds are discussed. The dynamic immune responses during peripheral nerve repair and immune-cell-mediated tissue engineering methods are presented, which provide a new insight and inspiration for immunomodulatory therapies in peripheral nerve regeneration.

Roles of Macrophages and Their Interactions with Schwann Cells After Peripheral Nerve Injury

The adult peripheral nervous system has a significant ability for regeneration compared to the central nervous system. This is related to the unique neuroimmunomodulation after peripheral nerve injury (PNI). Unlike the repair of other tissues after injury, Schwann cells (SCs) respond immediately to the trauma and send out signals to precisely recruit macrophages to the injured site. Then, macrophages promote the degradation of the damaged myelin sheath by phagocytosis of local debris. At the same time, macrophages and SCs jointly secrete various cytokines to reconstruct a microenvironment suitable for nerve regeneration. This unique pathophysiological process associated with macrophages provides important targets for the repair and treatment of PNI, as well as an important reference for guiding the repair of other nerve injuries. To understand these processes more systematically, this paper describes the characteristics of macrophage activation and metabolism in PNI, discusses the underlying molecular mechanism of interaction between macrophages and SCs, and reviews the latest research progress of crosstalk regulation between macrophages and SCs. These concepts and therapeutic strategies are summarized to provide a reference for the more effective use of macrophages in the repair of PNI.

Chronic pain accelerates cognitive impairment by reducing hippocampal neurogenesis may via CCL2/CCR2 signaling in APP/PS1 mice

Patients with chronic pain often have cognitive impairment; this is especially true in elderly patients with neurodegenerative diseases such as Alzheimer's disease (AD), but the mechanism underlying this association remains unclear. This was addressed in the present study by investigating the effect of chronic neuropathic pain on hippocampal neurogenesis and cognitive impairment using amyloid precursor protein/presenilin 1 (APP/PS1) double transgenic mice subjected to spared-nerve injury (SNI). The Von Frey test was performed to determine the mechanical threshold of mouse hind limbs after SNI. The Morris water maze test was used to evaluate spatial learning and memory. Doublecortin-positive (DCX+), 5-bromo-2'-deoxyuridine (BrdU)+, BrdU+/neuronal nuclei (NeuN)+, and C-C motif chemokine ligand 2 (CCL2)+ neurons in the dentate gyrus of the hippocampus were detected by immunohistochemistry and immunofluorescence analysis. CCL2 and C-C chemokine receptor type 2 (CCR2) protein levels in the mouse hippocampus were analyzed by western blotting. The results showed that APP/PS1 mice with chronic neuropathic pain induced by SNI had significant learning and memory impairment. This was accompanied by increased CCL2 and CCR2 expression and decreases in the number of DCX+, BrdU+, and BrdU+/NeuN+ neurons. These results suggest that chronic neuropathic pain is associated with cognitive impairment, which may be caused by CCL2/CCR2 signaling-mediated inhibition of hippocampal neurogenesis. Thus, therapeutic strategies that alleviate neuropathic pain can potentially slow cognitive decline in patients with AD and other neurodegenerative diseases.

New insights into irritable bowel syndrome pathophysiological mechanisms: contribution of epigenetics

Irritable bowel syndrome (IBS) is a complex multifactorial condition including alterations of the gut-brain axis, intestinal permeability, mucosal neuro-immune interactions, and microbiota imbalance. Recent advances proposed epigenetic factors as possible regulators of several mechanisms involved in IBS pathophysiology. These epigenetic factors include biomolecular mechanisms inducing chromosome-related and heritable changes in gene expression regardless of DNA coding sequence. Accordingly, altered gut microbiota may increase the production of metabolites such as sodium butyrate, a prominent inhibitor of histone deacetylases. Patients with IBS showed an increased amount of butyrate-producing microbial phila as well as an altered profile of methylated genes and micro-RNAs (miRNAs). Importantly, gene acetylation as well as specific miRNA profiles are involved in different IBS mechanisms and may be applied for future diagnostic purposes, especially to detect increased gut permeability and visceromotor dysfunctions. In this review, we summarize current knowledge of the role of epigenetics in IBS pathophysiology.

Implantation of skin-derived precursor Schwann cells improves erectile function in a bilateral cavernous nerve injury rat model

BACKGROUND

This study was conducted to investigate the therapeutic potential of the skin-derived precursor Schwann cells for the treatment of erectile dysfunction in a rat model of bilateral cavernous nerve injury.

RESULTS

The skin-derived precursor Schwann cells-treatment significantly restored erectile functions, accelerated the recovery of endothelial and smooth muscle tissues in the penis, and promoted nerve repair. The expression of p-Smad2/3 decreased after the treatment, which indicated significantly reduced fibrosis in the corpus cavernosum.

CONCLUSIONS

Implantation of skin-derived precursor Schwann cells is an effective therapeutic strategy for treating erectile dysfunction induced by bilateral cavernous nerve injury.

Targeting the chemokine ligand 2-chemokine receptor 2 axis provides the possibility of immunotherapy in chronic pain

Chronic pain affects patients' physical and psychological health and quality of life, entailing a tremendous public health challenge. Currently, drugs for chronic pain are usually associated with a large number of side effects and poor efficacy. Chemokines in the neuroimmune interface combine with their receptors to regulate inflammation or mediate neuroinflammation in the peripheral and central nervous system. Targeting chemokines and their receptor-mediated neuroinflammation is an effective means to treat chronic pain. In recent years, growing evidence has shown that the expression of chemokine ligand 2 (CCL2) and its main chemokine receptor 2 (CCR2) is involved in its occurrence, development and maintenance of chronic pain. This paper summarises the relationship between the chemokine system, CCL2/CCR2 axis, and chronic pain, and the CCL2/CCR2 axis changes under different chronic pain conditions. Targeting chemokine CCL2 and its chemokine receptor CCR2 through siRNA, blocking antibodies, or small molecule antagonists may provide new therapeutic possibilities for managing chronic pain.

Non-neuronal TRPA1 encodes mechanical allodynia associated with neurogenic inflammation and partial nerve injury in rats

BACKGROUND AND PURPOSE

The pro-algesic transient receptor potential ankyrin 1 (TRPA1) channel, expressed by a subpopulation of primary sensory neurons, has been implicated in various pain models in mice. However, evidence in rats indicates that TRPA1 conveys nociceptive signals elicited by channel activators, but not those associated with tissue inflammation or nerve injury. Here, in rats, we explored the TRPA1 role in mechanical allodynia associated with stimulation of peptidergic primary sensory neurons (neurogenic inflammation) and moderate (partial sciatic nerve ligation, pSNL) or severe (chronic constriction injury, CCI) sciatic nerve injury.

EXPERIMENTAL APPROACH

Acute nociception and mechanical hypersensitivity associated with neurogenic inflammation and sciatic nerve injury (pSNL and CCI) were investigated in rats with TRPA1 pharmacological antagonism or genetic silencing. TRPA1 presence and function were analysed in cultured rat Schwann cells.

KEY RESULTS

Hind paw mechanical allodynia (HPMA), but not acute nociception, evoked by local injection of capsaicin or allyl isothiocyanate, the TRP vanilloid 1 (TRPV1) or the TRPA1 activators was mediated by CGRP released from peripheral sensory nerve terminals. CGRP-evoked HPMA was sustained by a ROS-dependent TRPA1 activation, probably in Schwann cells. HPMA evoked by pSNL, but not that evoked by CCI, was mediated by ROS and TRPA1 without the involvement of CGRP.

CONCLUSIONS AND IMPLICATIONS

As found in mice, TRPA1 mediates mechanical allodynia associated with neurogenic inflammation and moderate nerve injury in rats. The channel contribution to mechanical hypersensitivity is a common feature in rodents and might be explored in humans.

Pathophysiology of Post-Traumatic Trigeminal Neuropathic Pain

Trigeminal nerve injury is one of the causes of chronic orofacial pain. Patients suffering from this condition have a significantly reduced quality of life. The currently available management modalities are associated with limited success. This article reviews some of the common causes and clinical features associated with post-traumatic trigeminal neuropathic pain (PTNP). A cascade of events in the peripheral and central nervous system function is involved in the pathophysiology of pain following nerve injuries. Central and peripheral processes occur in tandem and may often be co-dependent. Due to the complexity of central mechanisms, only peripheral events contributing to the pathophysiology have been reviewed in this article. Future investigations will hopefully help gain insight into trigeminal-specific events in the pathophysiology of the development and maintenance of neuropathic pain secondary to nerve injury and enable the development of new therapeutic modalities.

Modulation of the Crosstalk between Schwann Cells and Macrophages for Nerve Regeneration: A Therapeutic Strategy Based on a Multifunctional Tetrahedral Framework Nucleic Acids System

Peripheral nerve injury (PNI) is currently recognized as one of the most significant public health issues and affects the general well-being of millions of individuals worldwide. Despite advances in nerve tissue engineering, nerve repair still cannot guarantee complete functional recovery. In the present study, an innovative approach is adopted to establish a multifunctional tetrahedral framework nucleic acids (tFNAs) system, denoted as MiDs, which can integrate the powerful programmability, permeability, and structural stability of tFNAs, with the nerve regeneration potential of microRNA-22 to enhance the communication between Schwann cells (SCs) and macrophages for more effective functional rehabilitation of peripheral nerves. Relevant results demonstrate that MiDs can amplify the ability of SCs to recruit macrophages and facilitate their polarization into the pro-healing M2 phenotype to reconstruct the post-injury microenvironment. Furthermore, MiDs can initiate the adaptive intracellular reprogramming of SCs within a short period to further promote axon regeneration and remyelination. MiDs represent a new possibility for enhancing nerve repair and may have critical clinical applications in the future.

Role of innate immunity in chemotherapy-induced peripheral neuropathy

It has become increasingly clear that the innate immune system plays an essential role in the generation of many types of neuropathic pain including that which accompanies cancer treatment. In this article we review current findings of the role of the innate immune system in contributing to cancer treatment pain at the distal endings of peripheral nerve, in the nerve trunk, in the dorsal root ganglion and in the spinal dorsal horn.

Imaging resident and recruited macrophage contribution to Wallerian degeneration

Wallerian degeneration (WD) is a process of autonomous distal degeneration of axons upon injury. Macrophages (MPs) of the peripheral nervous system (PNS) are the main cellular agent controlling this process. Some evidence suggests that resident PNS-MPs along with MPs of hematogenous origin may be involved, but whether these two subsets exert distinct functions is unknown. Combining MP-designed fluorescent reporter mice and coherent anti–Stokes Raman scattering (CARS) imaging of the sciatic nerve, we deciphered the spatiotemporal choreography of resident and recently recruited MPs after injury and unveiled distinct functions of these subsets, with recruited MPs being responsible for efficient myelin stripping and clearance and resident MPs being involved in axonal regrowth. This work provides clues to tackle selectively cellular processes involved in neurodegenerative diseases.

Dysregulation of Leukocyte Trafficking in Type 2 Diabetes: Mechanisms and Potential Therapeutic Avenues

Type 2 Diabetes Mellitus (T2DM) is a chronic inflammatory disorder that is characterized by chronic hyperglycemia and impaired insulin signaling which in addition to be caused by common metabolic dysregulations, have also been associated to changes in various immune cell number, function and activation phenotype. Obesity plays a central role in the development of T2DM. The inflammation originating from obese adipose tissue develops systemically and contributes to insulin resistance, beta cell dysfunction and hyperglycemia. Hyperglycemia can also contribute to chronic, low-grade inflammation resulting in compromised immune function. In this review, we explore how the trafficking of innate and adaptive immune cells under inflammatory condition is dysregulated in T2DM. We particularly highlight the obesity-related accumulation of leukocytes in the adipose tissue leading to insulin resistance and beta-cell dysfunction and resulting in hyperglycemia and consequent changes of adhesion and migratory behavior of leukocytes in different vascular beds. Thus, here we discuss how potential therapeutic targeting of leukocyte trafficking could be an efficient way to control inflammation as well as diabetes and its vascular complications.

Key role of CCR2-expressing macrophages in a mouse model of low back pain and radiculopathy

Chronic low back pain is a common condition, with high societal costs and often ineffectual treatments. Communication between macrophages/monocytes (MØ) and sensory neurons has been implicated in various preclinical pain models. However, few studies have examined specific MØ subsets, although distinct subtypes may play opposing roles. This study used a model of low back pain/radiculopathy involving direct local inflammation of the dorsal root ganglia (DRG). Reporter mice were employed that had distinct fluorescent labels for two key MØ subsets: CCR2-expressing (infiltrating pro-inflammatory) MØ, and CX3CR1-expressing (resident) macrophages. We observed that local DRG inflammation induced pain behaviors in mice, including guarding behavior and mechanical hypersensitivity, similar to the previously described rat model. The increase in MØ in the inflamed DRG was dominated by increases in CCR2+ MØ, which persisted for at least 14 days. The primary endogenous ligand for CCR2, CCL2, was upregulated in inflamed DRG. Three different experimental manipulations that reduced the CCR2+ MØ influx also reduced pain behaviors: global CCR2 knockout; systemic injection of INCB3344 (specific CCR2 blocker); and intravenous injection of liposomal clodronate. The latter two treatments when applied around the time of DRG inflammation reduced CCR2+ but not CX3CR1+ MØ in the DRG. Together these experiments suggest a key role for the CCR2/CCL2 system in establishing the pain state in this model of inflammatory low back pain and radiculopathy. Intravenous clodronate given after pain was established had the opposite effect on pain behaviors, suggesting the role of macrophages or their susceptibility to clodronate may change with time.

Angiogenesis and nerve regeneration induced by local administration of plasmid pBud-coVEGF165-coFGF2 into the intact rat sciatic nerve

Vascular endothelial growth factor (VEGF) and fibroblast growth factor 2 (FGF2) are well-known growth factors involved in the regeneration of various tissues and organs, including peripheral nerve system. In the present study, we elucidated the local and systemic effects of plasmid construct рBud-coVEGF165-coFGF2 injected into the epineurium of intact rat sciatic nerve. Results of histological examination of sciatic nerve and multiplex immunoassays of serum showed the absence of immunogenicity and biosafety of plasmid рBud-coVEGF165-coFGF2. Moreover, local administration of plasmid DNA construct resulted in significantly decreased levels of pro-inflammatory cytokines in the peripheral blood, including tumor necrosis factor α (TNFα) and interleukin-12, and significantly increased levels of cytokines and chemokines including Regulated upon Activation, Normal T Cell Expressed and Presumably Secrete (RANTES), epidermal growth factor, interleukin-2, and monocyte chemoattractant protein 1. These changes in the peripheral blood on day 7 after injection of plasmid construct рBud-coVEGF165-coFGF2 show that the plasmid construct has systemic effects and may modulate immune response. At the same time, reverse transcription-polymerase chain reaction revealed transient expression of coFGF2, coVEGF165, ratFGF2 and ratVEGFA with direct transport of transcripts from distal part to proximal part of the sciatic nerve. Immunohistochemical staining revealed prolonged presence of VEGFA in sciatic nerve till 14 days post-injection. These findings suggest that local administration of plasmid construct рBud-coVEGF165-coFGF2 at a concentration of 30 ng/µL results in the formation of pro-angiogenic stimuli and, and the plasmid construct, used as a drug for gene therapy, might potentially facilitate regeneration of the sciatic nerve. The study was approved by the Animal Ethics Committee of Kazan Federal University, procedures were approved by the Local Ethics Committee (approval No. 5) on May 27, 2014.

Characteristics of cytokines in the sciatic nerve stumps and DRGs after rat sciatic nerve crush injury

BACKGROUND

Cytokines are essential cellular modulators of various physiological and pathological activities, including peripheral nerve repair and regeneration. However, the molecular changes of these cellular mediators after peripheral nerve injury are still unclear. This study aimed to identify cytokines critical for the regenerative process of injured peripheral nerves.

METHODS

The sequencing data of the injured nerve stumps and the dorsal root ganglia (DRGs) of Sprague-Dawley (SD) rats subjected to sciatic nerve (SN) crush injury were analyzed to determine the expression patterns of genes coding for cytokines. PCR was used to validate the accuracy of the sequencing data.

RESULTS

A total of 46, 52, and 54 upstream cytokines were differentially expressed in the SNs at 1 day, 4 days, and 7 days after nerve injury. A total of 25, 28, and 34 upstream cytokines were differentially expressed in the DRGs at these time points. The expression patterns of some essential upstream cytokines are displayed in a heatmap and were validated by PCR. Bioinformatic analysis of these differentially expressed upstream cytokines after nerve injury demonstrated that inflammatory and immune responses were significantly involved.

CONCLUSIONS

In summary, these findings provide an overview of the dynamic changes in cytokines in the SNs and DRGs at different time points after nerve crush injury in rats, elucidate the biological processes of differentially expressed cytokines, especially the important roles in inflammatory and immune responses after peripheral nerve injury, and thus might contribute to the identification of potential treatments for peripheral nerve repair and regeneration.

Local Sympathectomy Promotes Anti-inflammatory Responses and Relief of Paclitaxel-induced Mechanical and Cold Allodynia in Mice

BACKGROUND

Patients undergoing cancer treatment often experience chemotherapy-induced neuropathic pain at their extremities, for which there is no U.S. Food and Drug Administration-approved drug. The authors hypothesized that local sympathetic blockade, which is used in the clinic to treat various pain conditions, can also be effective to treat chemotherapy-induced neuropathic pain.

METHODS

A local sympathectomy (i.e., cutting the ipsilateral gray rami entering the spinal nerves near the L3 and L4 dorsal root ganglia) was performed in mice receiving intraperitoneal injections every other day of the chemotherapeutic drug paclitaxel. Sympathectomy effects were then assessed in chemotherapy-induced pain-like behaviors (i.e., mechanical and cold allodynia) and neuroimmune and electrophysiologic responses.

RESULTS

Local microsympathectomy produced a fast recovery from mechanical allodynia (mean ± SD: sympathectomy vs. sham at day 5, 1.07 ± 0.34 g vs. 0.51 ± 0.17g, n = 5, P = 0.030 in male mice, and 1.08 ± 0.28 g vs. 0.62 ± 0.16 g, n = 5, P = 0.036 in female mice) and prevented the development of cold allodynia in both male and female mice after paclitaxel. Mechanistically, microsympathectomy induced transcriptional increases in dorsal root ganglia of macrophage markers and anti-inflammatory cytokines, such as the transforming growth factor-β. Accordingly, depletion of monocytes/macrophages and blockade of transforming growth factor-β signaling reversed the relief of mechanical allodynia by microsympathectomy. In particular, exogenous transforming growth factor-β was sufficient to relieve mechanical allodynia after paclitaxel (transforming growth factor-β 100 ng/site vs. vehicle at 3 h, 1.21 ± 0.34g vs. 0.53 ± 0.14 g, n = 5, P = 0.001 in male mice), and transforming growth factor-β signaling regulated neuronal activity in dorsal root ganglia.

CONCLUSIONS

Local sympathetic nerves control the progression of immune responses in dorsal root ganglia and pain-like behaviors in mice after paclitaxel, raising the possibility that clinical strategies already in use for local sympathetic blockade may also offer an effective treatment for patients experiencing chemotherapy-induced neuropathic pain.

The CCL2/CCR2 axis is critical to recruiting macrophages into acellular nerve allograft bridging a nerve gap to promote angiogenesis and regeneration

Acellular nerve allografts (ANAs) are increasingly used to repair nerve gaps following injuries. However, these nerve scaffolds have yet to surpass the regenerative capabilities of cellular nerve autografts; improved understanding of their regenerative mechanisms could improve design. Due to their acellular nature, both angiogenesis and diverse cell recruitment is necessary to repopulate these scaffolds to promote functional regeneration. We determined the contribution of angiogenesis to initial cellular repopulation of ANAs used to repair nerve gaps, as well as the signaling that drives a significant portion of this angiogenesis. Wild-type (WT) mice with nerve gaps repaired using ANAs that were treated with an inhibitor of VEGF receptor signaling severely impaired angiogenesis within ANAs, as well as hampered cell repopulation and axon extension into ANAs. Similarly, systemic depletion of hematogenous-derived macrophages, but not neutrophils, in these mice models severely impeded angiogenesis and subsequent nerve regeneration across ANAs suggesting hematogenous-derived macrophages were major contributors to angiogenesis within ANAs. This finding was reinforced using CCR2 knockout (KO) models. As macrophages represented the majority of CCR2 expressing cells, a CCR2 deficiency impaired angiogenesis and subsequent nerve regeneration across ANAs. Furthermore, an essential role for CCL2 during nerve regeneration across ANAs was identified, as nerves repaired using ANAs had reduced angiogenesis and subsequent nerve regeneration in CCL2 KO vs WT mice. Our data demonstrate the CCL2/CCR2 axis is important for macrophage recruitment, which promotes angiogenesis, cell repopulation, and subsequent nerve regeneration and recovery across ANAs used to repair nerve gaps.

Conjunctival Neuropathic and Inflammatory Pain-Related Gene Expression with Contact Lens Wear and Discomfort

Purpose: To identify alterations in neuropathic and inflammatory pain gene expression associated with contact lens (CL) wear and CL discomfort (CLD).Methods: Eight non-wearers, eight asymptomatic CL wearers (CLWs) and eight symptomatic CLWs were included. Conjunctival cells were collected by impression cytology and the mRNA expression levels of 85 genes were analyzed. Differentially expressed genes between non-wearers and CLWs and between asymptomatic and symptomatic CLWs were analyzed. An enrichment analysis was also performed.Results: Twelve genes were upregulated (including IL10, PDYN and PENK) and 28 downregulated (CCL2, IL1A, IL1B, IL2 and NGF) in CLWs (p ≤ 0.050). Eleven genes were upregulated (CCL2, IL1A, IL1B, IL2 and NGF) and nine downregulated (PDYN and PENK) in symptomatic CLWs (p ≤ 0.035). Enriched overrepresented terms were related to pain, neuronal transmission and inflammation.Conclusion: Contact lens wear might produce a desensitization-like mechanism responsible for comfortable CL wear. A malfunction of this mechanism might contribute to CLD.

Decreased miR-325-5p Contributes to Visceral Hypersensitivity Through Post-transcriptional Upregulation of CCL2 in Rat Dorsal Root Ganglia

Chronic visceral hypersensitivity is an important type of chronic pain with unknown etiology and pathophysiology. Recent studies have shown that epigenetic regulation plays an important role in the development of chronic pain conditions. However, the role of miRNA-325-5p in chronic visceral pain remains unknown. The present study was designed to determine the roles and mechanism of miRNA-325-5p in a rat model of chronic visceral pain. This model was induced by neonatal colonic inflammation (NCI). In adulthood, NCI led to a significant reduction in the expression of miRNA-325-5p in colon-related dorsal root ganglia (DRGs), starting to decrease at the age of 4 weeks and being maintained to 8 weeks. Intrathecal administration of miRNA-325-5p agomir significantly enhanced the colorectal distention (CRD) threshold in a time-dependent manner. NCI also markedly increased the expression of CCL2 (C-C motif chemokine ligand 2) in colon-related DRGs at the mRNA and protein levels relative to age-matched control rats. The expression of CXCL12, IL33, SFRS7, and LGI1 was not significantly altered in NCI rats. CCL2 was co-expressed in NeuN-positive DRG neurons but not in glutamine synthetase-positive glial cells. Furthermore, CCL2 was mainly expressed in isolectin B4-binding- and calcitonin gene-related peptide-positive DRG neurons but in few NF-200-positive cells. More importantly, CCL2 was expressed in miR-325-5p-positive DRG neurons. Intrathecal injection of miRNA-325-5p agomir remarkably reduced the upregulation of CCL2 in NCI rats. Administration of Bindarit, an inhibitor of CCL2, markedly raised the CRD threshold in NCI rats in a dose- and time-dependent manner. These data suggest that NCI suppresses miRNA-325-5p expression and enhances CCL2 expression, thus contributing to visceral hypersensitivity in adult rats.

Blue light exposure in vitro causes toxicity to trigeminal neurons and glia through increased superoxide and hydrogen peroxide generation

Today the noxiousness of blue light from natural and particularly artificial (fluorescent tubes, LED panels, visual displays) sources is actively discussed in the context of various ocular diseases. Many of them have an important neurologic component and are associated with ocular pain. This neuropathic signal is provided by nociceptive neurons from trigeminal ganglia. However, the phototoxicity of blue light on trigeminal neurons has not been explored so far. The aim of the present in vitro study was to investigate the cytotoxic impact of various wavebands of visible light (410-630 nm) on primary cell culture of mouse trigeminal neural and glial cells. Three-hour exposure to narrow wavebands of blue light centered at 410, 440 and 480 nm of average 1.1 mW/cm² irradiance provoked cell death, altered cell morphology and induced oxidative stress and inflammation. These effects were not observed for other tested visible wavebands. We observed that neurons and glial cells processed the light signal in different manner, in terms of resulting superoxide and hydrogen peroxide generation, inflammatory biomarkers expression and phototoxic mitochondrial damage. We analyzed the pathways of photic signal reception, and we proposed that, in trigeminal cells, in addition to widely known mitochondria-mediated light absorption, light could be received by means of non-visual opsins, melanopsin (opn4) and neuropsin (opn5). We also investigated the mechanisms underlying the observed phototoxicity, further suggesting an important role of the endoplasmic reticulum in neuronal transmission of blue-light-toxic message. Taken together, our results give some insight into circuit of tangled pain and photosensitivity frequently observed in patients consulting for these ocular symptoms.

Role of macrophages in peripheral nerve injury and repair

Resident and inflammatory macrophages are essential effectors of the innate immune system. These cells provide innate immune defenses and regulate tissue and organ homeostasis. In addition to their roles in diseases such as cancer, obesity and osteoarthritis, they play vital roles in tissue repair and disease rehabilitation. Macrophages and other inflammatory cells are recruited to tissue injury sites where they promote changes in the microenvironment. Among the inflammatory cell types, only macrophages have both pro-inflammatory (M1) and anti-inflammatory (M2) actions, and M2 macrophages have four subtypes. The co-action of M1 and M2 subtypes can create a favorable microenvironment, releasing cytokines for damaged tissue repair. In this review, we discuss the activation of macrophages and their roles in severe peripheral nerve injury. We also describe the therapeutic potential of macrophages in nerve tissue engineering treatment and highlight approaches for enhancing M2 cell-mediated nerve repair and regeneration.

[Understanding chronic ocular pain]

Dry eye disease (DED) is a common chronic condition with multifactorial etiologies that is increasing in prevalence worldwide, up to 20% in the elderly. The economic burden and impact of DED on vision, quality of life, work productivity, psychological and physical impact of pain, are considerable. Chronic ocular pain is the most common symptom of DED and there is currently no topical ocular analgesic therapy available to treat this debilitating disease. Eye pain can be perceived as itch, irritation, dryness, grittiness, burning, aching, and light sensitivity. Ocular pain is triggered by corneal nociceptors (cornea being the most sensory innervated tissue of the body). It was clearly established that repeated direct damage to ocular surface and per se corneal nerves can cause peripheral and central sensitization mechanisms explaining the ocular pain in some patients with DED. However, the brain regions and the neuronal pathways associated with ocular pain are still unclear. Thus, a better characterization of chronic ocular pain and an understanding of the peripheral and central molecular and cellular mechanisms involved are crucial issues for developing effective management and therapeutic strategy to alleviate ocular pain. In this review, we first describe the nociceptive corneal nerve pathways and the classification and the neurochemistry of primary afferents innervating the cornea. Then, an update of the fundamental and clinical studies related to the inflammatory processes linked to ocular pain is detailed. The last part of the review presents the diagnostic tools used in clinic for evaluating corneal sensitivity and corneal inflammation.

Could an endoneurial endothelial crosstalk between Wnt/β-catenin and Sonic Hedgehog pathways underlie the early disruption of the infra-orbital blood-nerve barrier following chronic constriction injury?

Background

Blood–nerve barrier disruption is pivotal in the development of neuroinflammation, peripheral sensitization, and neuropathic pain after peripheral nerve injury. Activation of toll-like receptor 4 and inactivation of Sonic Hedgehog signaling pathways within the endoneurial endothelial cells are key events, resulting in the infiltration of harmful molecules and immunocytes within the nerve parenchyma. However, we showed in a previous study that preemptive inactivation of toll-like receptor 4 signaling or sustained activation of Sonic Hedgehog signaling did not prevent the local alterations observed following peripheral nerve injury, suggesting the implication of another signaling pathway.

Methods

Using a classical neuropathic pain model, the infraorbital nerve chronic constriction injury (IoN-CCI), we investigated the role of the Wnt/β-catenin pathway in chronic constriction injury-mediated blood–nerve barrier disruption and in its interactions with the toll-like receptor 4 and Sonic Hedgehog pathways. In the IoN-CCI model versus control, mRNA expression levels and/or immunochemical detection of major Wnt/Sonic Hedgehog pathway (Frizzled-7, vascular endothelial-cadherin, Patched-1 and Gli-1) and/or tight junction proteins (Claudin-1, Claudin-5, and Occludin) readouts were assessed. Vascular permeability was assessed by sodium fluorescein extravasation.

Results

IoN-CCI induced early alterations in the vascular endothelial-cadherin/β-catenin/Frizzled-7 complex, shown to participate in local blood–nerve barrier disruption via a β-catenin-dependent tight junction protein downregulation. Wnt pathway also mediated a crosstalk between toll-like receptor 4 and Sonic Hedgehog signaling within endoneurial endothelial cells. Nevertheless, preemptive inhibition of Wnt/β-catenin signaling before IoN-CCI could not prevent the downregulation of key Sonic Hedgehog pathway readouts or the disruption of the infraorbital blood–nerve barrier, suggesting that Sonic Hedgehog pathway inhibition observed following IoN-CCI is an independent event responsible for blood–nerve barrier disruption.

Conclusion

A crosstalk between Wnt/β-catenin- and Sonic Hedgehog-mediated signaling pathways within endoneurial endothelial cells could mediate the chronic disruption of the blood–nerve barrier following IoN-CCI, resulting in increased irreversible endoneurial vascular permeability and neuropathic pain development.

The prostaglandin E2 receptor EP3 controls CC-chemokine ligand 2-mediated neuropathic pain induced by mechanical nerve damage

Prostaglandin (PG) E₂ is an important lipid mediator that is involved in several pathophysiological processes contributing to fever, inflammation, and pain. Previous studies have shown that early and continuous application of nonsteroidal anti-inflammatory drugs significantly reduces pain behavior in the spared nerve injury (SNI) model for trauma-induced neuropathic pain. However, the role of PGE₂ and its receptors in the development and maintenance of neuropathic pain is incompletely understood but may help inform strategies for pain management. Here, we sought to define the nociceptive roles of the individual PGE₂ receptors (EP1-4) in the SNI model using EP knockout mice. We found that PGE₂ levels at the site of injury were increased and that the expression of the terminal synthase for PGE₂, cytosolic PGE synthase was up-regulated in resident positive macrophages located within the damaged nerve. Only genetic deletion of the EP3 receptor affected nociceptive behavior and reduced the development of late-stage mechanical allodynia as well as recruitment of immune cells to the injured nerve. Importantly, EP3 activation induced the release of CC-chemokine ligand 2 (CCL2), and antagonists against the CCL2 receptor reduced mechanical allodynia in WT but not in EP3 knockout mice. We conclude that selective inhibition of EP3 might present a potential approach for reducing chronic neuropathic pain.

Proinflammatory Markers, Chemokines, and Enkephalin in Patients Suffering from Dry Eye Disease

Dry eye symptoms are among the leading complaints in ophthalmology. Dry eye disease (DED) is associated with significant pain affecting quality of life. Cellular and molecular mechanisms underlying ocular pain associated with DED are not fully understood. In this study, we investigated the ocular surface of patients with DED using in vivo confocal microscopy (IVCM) to quantify corneal nerve density and its relation with corneal inflammation. Gene expression of the proinflammatory markers HLA-DR, IL-6, CXCL12, and CCL2 and the receptors CXCR4 and CCR2, as well as PENK (enkephalin precursor), was therefore quantified in conjunctival impression cytology specimens. Thirty-two patients with DED and 15 age-matched controls were included. Subbasal nerve density was significantly lower in DED patients compared to controls. IVCM analysis revealed that DED patients had a significantly higher corneal dendritic cell density compared to controls. Conjunctival impression cytology analysis revealed that HLA-DR, IL-6, CXCR4, and CCL2/CCR2 mRNA levels were significantly increased in DED patients compared to controls, whereas PENK mRNA levels were significantly decreased. Similar results were obtained in vitro on immortalized human conjunctiva-derived epithelial cells challenged with osmotic stress that mimics the DED condition. These results demonstrate that proinflammatory molecules and endogenous enkephalin have opposite gene regulation during DED.

A novel interaction between CX3CR1 and CCR2 signalling in monocytes constitutes an underlying mechanism for persistent vincristine-induced pain

BACKGROUND

A dose-limiting side effect of chemotherapeutic agents such as vincristine (VCR) is neuropathic pain, which is poorly managed at present. Chemokine-mediated immune cell/neuron communication in preclinical VCR-induced pain forms an intriguing basis for the development of analgesics. In a murine VCR model, CX₃CR₁ receptor-mediated signalling in monocytes/macrophages in the sciatic nerve orchestrates the development of mechanical hypersensitivity (allodynia). CX₃CR₁-deficient mice however still develop allodynia, albeit delayed; thus, additional underlying mechanisms emerge as VCR accumulates. Whilst both patrolling and inflammatory monocytes express CX₃CR₁, only inflammatory monocytes express CCR₂ receptors. We therefore assessed the role of CCR₂ in monocytes in later stages of VCR-induced allodynia.

METHODS

Mechanically evoked hypersensitivity was assessed in VCR-treated CCR₂- or CX₃CR₁-deficient mice. In CX₃CR₁-deficient mice, the CCR₂ antagonist, RS-102895, was also administered. Immunohistochemistry and Western blot analysis were employed to determine monocyte/macrophage infiltration into the sciatic nerve as well as neuronal activation in lumbar DRG, whilst flow cytometry was used to characterise monocytes in CX₃CR₁-deficient mice. In addition, THP-1 cells were used to assess CX₃CR₁-CCR₂ receptor interactions in vitro, with Western blot analysis and ELISA being used to assess expression of CCR₂ and proinflammatory cytokines.

RESULTS

We show that CCR₂ signalling plays a mechanistic role in allodynia that develops in CX₃CR₁-deficient mice with increasing VCR exposure. Indeed, the CCR₂ antagonist, RS-102895, proves ineffective in mice possessing functional CX₃CR₁ receptors but reduces VCR-induced allodynia in CX₃CR₁-deficient mice, in which CCR₂⁺ monocytes are elevated by VCR. We suggest that a novel interaction between CX₃CR₁ and CCR₂ receptors in monocytes accounts for the therapeutic effect of RS-102895 in CX₃CR₁-deficient mice. Indeed, we observe that CCR₂, along with its ligand, CCL₂, is elevated in the sciatic nerve in CX₃CR₁-deficient mice, whilst in THP-1 cells (human monocytes), downregulating CX₃CR₁ upregulates CCR₂ expression via p38 MAP kinase signalling. We also show that the CX₃CR₁-CCR₂ interaction in vitro regulates the release of pronociceptive cytokines TNF-α and IL1β.

CONCLUSIONS

Our data suggests that CCL₂/CCR₂ signalling plays a crucial role in VCR-induced allodynia in CX₃CR₁-deficient mice, which arises as a result of an interaction between CX₃CR₁ and CCR₂ in monocytes.

Schwann cell TRPA1 mediates neuroinflammation that sustains macrophage-dependent neuropathic pain in mice

It is known that transient receptor potential ankyrin 1 (TRPA1) channels, expressed by nociceptors, contribute to neuropathic pain. Here we show that TRPA1 is also expressed in Schwann cells. We found that in mice with partial sciatic nerve ligation, TRPA1 silencing in nociceptors attenuated mechanical allodynia, without affecting macrophage infiltration and oxidative stress, whereas TRPA1 silencing in Schwann cells reduced both allodynia and neuroinflammation. Activation of Schwann cell TRPA1 evoked NADPH oxidase 1 (NOX1)-dependent H2O2 release, and silencing or blocking Schwann cell NOX1 attenuated nerve injury-induced macrophage infiltration, oxidative stress and allodynia. Furthermore, the NOX2-dependent oxidative burst, produced by macrophages recruited to the perineural space activated the TRPA1-NOX1 pathway in Schwann cells, but not TRPA1 in nociceptors. Schwann cell TRPA1 generates a spatially constrained gradient of oxidative stress, which maintains macrophage infiltration to the injured nerve, and sends paracrine signals to activate TRPA1 of ensheathed nociceptors to sustain mechanical allodynia.

Novel pathomechanisms in inflammatory neuropathies

Inflammatory neuropathies are rare autoimmune-mediated disorders affecting the peripheral nervous system. Considerable progress has recently been made in understanding pathomechanisms of these disorders which will be essential for developing novel diagnostic and therapeutic strategies in the future. Here, we summarize our current understanding of antigenic targets and the relevance of new immunological concepts for inflammatory neuropathies. In addition, we provide an overview of available animal models of acute and chronic variants and how new diagnostic tools such as magnetic resonance imaging and novel therapeutic candidates will benefit patients with inflammatory neuropathies in the future. This review thus illustrates the gap between pre-clinical and clinical findings and aims to outline future directions of development.

Identification of key mRNAs and microRNAs in the pathogenesis and progression of osteoarthritis using microarray analysis

Osteoarthritis (OA) is a common type of disease affecting the joints that results from the breakdown of joint cartilage and the underlying bone; currently, its pathogenesis is still unclear. The aim of the present study was to identify key mRNAs and miRNAs involved in the pathogenesis and progression of OA using microarray analysis. The gene expression profile of GSE27492 was downloaded from the Gene Expressed Omnibus database, and included 49 arthritic mouse ankle samples collected at 6 time points (0, 1, 3, 7, 12 and 18 days) following the induction of arthritis via serum transfer. Differentially expressed genes (DEGs) were identified in ankle samples taken on days 1, 3, 7, 12 and 18 following serum transfer compared with day 0 samples, and overlapping DEGs in day 3, 7, 12 and 18 samples were identified. The Database for Annotation, Visualization and Integrated Discovery online tool was used to perform functional and pathway enrichment analyses of the overlapping DEGs. The miRWalk database was used to identify potential micro (mi) RNAs regulating the selected overlapping DEGs, and regulatory miRNA‑target mRNA pairs were obtained. The Cytoscape platform was used to establish and visualize the miRNA‑mRNA regulatory network. The present results revealed that 35, 103, 62 and 75 DEGs were identified in day 3, 7, 12 and 18 samples, respectively. A total of 17 overlapping DEGs were identified among the 4 sample sets, and revealed to be enriched in 14 gene ontology terms and 3 Kyoto Encyclopedia of Genes and Genomes pathways. miRWalk analysis identified 242 potential miRNA‑mRNA regulatory pairs and 211 nodes were revealed to be involved in the miRNA‑mRNA regulatory network. The present study identified potential genes, including C‑type lectin domain family 4 member D, chemokine (C‑X‑C motif) ligand 1 and C‑C motif chemokine ligand, and pathways, including chemokine signaling pathways, cytokine‑cytokine receptor interactions and nucleotide‑binding oligomerization domain‑like receptor signaling pathways, which may be involved in the pathogenesis and progression of OA. These findings may help elucidate the molecular mechanisms underlying OA pathophysiology, and may be useful for the development of novel therapeutic targets for the treatment of patients with OA.

Breaking barriers to novel analgesic drug development

Acute and chronic pain complaints, although common, are generally poorly served by existing therapies. This unmet clinical need reflects a failure to develop novel classes of analgesics with superior efficacy, diminished adverse effects and a lower abuse liability than those currently available. Reasons for this include the heterogeneity of clinical pain conditions, the complexity and diversity of underlying pathophysiological mechanisms, and the unreliability of some preclinical pain models. However, recent advances in our understanding of the neurobiology of pain are beginning to offer opportunities for developing novel therapeutic strategies and revisiting existing targets, including modulating ion channels, enzymes and G-protein-coupled receptors.

Prior voluntary wheel running attenuates neuropathic pain

Exercise is known to exert a systemic anti-inflammatory influence, but whether its effects are sufficient to protect against subsequent neuropathic pain is underinvestigated. We report that 6 weeks of voluntary wheel running terminating before chronic constriction injury (CCI) prevented the full development of allodynia for the ∼3-month duration of the injury. Neuroimmune signaling was assessed at 3 and 14 days after CCI. Prior exercise normalized ipsilateral dorsal spinal cord expression of neuroexcitatory interleukin (IL)-1β production and the attendant glutamate transporter GLT-1 decrease, as well as expression of the disinhibitory P2X4R-BDNF axis. The expression of the macrophage marker Iba1 and the chemokine CCL2 (MCP-1), and a neuronal injury marker (activating transcription factor 3), was attenuated by prior running in the ipsilateral lumbar dorsal root ganglia. Prior exercise suppressed macrophage infiltration and/or injury site proliferation, given decreased presence of macrophage markers Iba1, iNOS (M1), and Arg-1 (M2; expression was time dependent). Chronic constriction injury-driven increases in serum proinflammatory chemokines were suppressed by prior running, whereas IL-10 was increased. Peripheral blood mononuclear cells were also stimulated with lipopolysaccharide ex vivo, wherein CCI-induced increases in IL-1β, nitrite, and IL-10 were suppressed by prior exercise. Last, unrestricted voluntary wheel running, beginning either the day of, or 2 weeks after, CCI, progressively reversed neuropathic pain. This study is the first to investigate the behavioral and neuroimmune consequences of regular exercise terminating before nerve injury. This study suggests that chronic pain should be considered a component of "the diseasome of physical inactivity," and that an active lifestyle may prevent neuropathic pain.

Interleukin-1β pre-treated bone marrow stromal cells alleviate neuropathic pain through CCL7-mediated inhibition of microglial activation in the spinal cord

Although neuropathic pain is one of the most intractable diseases, recent studies indicate that systemic or local injection of bone marrow stromal cells (BMSCs) decreases pro-inflammatory cytokines release and alleviates neuropathic pain. However, it is still not clear whether pre-treated BMSCs have a strong anti-inflammatory and/or analgesia effect. Using the spinal nerve ligation model of neuropathic pain, IL-1β pre-treated BMSCs (IL-1β-BMSCs) were injected into rats followed by SNL in order to determine possible effects. Results indicated that IL-1β-BMSCs were more efficacious in both amelioration of neuropathic pain and inhibition of microglia activation. Specifically, microglia inhibition was found to be mediated by chemokine C-C motif ligand 7 (CCL7) but not CCL2. Results also showed that IL-1β-BMSCs had a stronger inhibitory effect on astrocyte activation as well as CCL7 release, which was found to be mediated by IL-10 not transforming growth factor-β1. In addition, we also found directional migration of IL-1β-BMSCs was mediated by inceased C-X-C motif chemokine ligand (CXCL) 13 expression following SNL. In conclusion, our results indicated IL-1β-BMSCs could inhibit microglia activation and neuropathic pain by decreasing CCL7 level in spinal cord.

Early alterations of Hedgehog signaling pathway in vascular endothelial cells after peripheral nerve injury elicit blood-nerve barrier disruption, nerve inflammation, and neuropathic pain development

Changes in the nerve's microenvironment and local inflammation resulting from peripheral nerve injury participate in nerve sensitization and neuropathic pain development. Taking part in these early changes, disruption of the blood-nerve barrier (BNB) allows for infiltration of immunocytes and promotes the neuroinflammation. However, molecular mechanisms engaged in vascular endothelial cells (VEC) dysfunction and BNB alterations remain unclear. In vivo, BNB permeability was assessed following chronic constriction injury (CCI) of the rat sciatic nerve (ScN) and differential expression of markers of VEC functional state, inflammation, and intracellular signaling was followed from 3 hours to 2 months postinjury. Several mechanisms potentially involved in functional alterations of VEC were evaluated in vitro using human VEC (hCMEC/D3), then confronted to in vivo physiopathological conditions. CCI of the ScN led to a rapid disruption of endoneurial vascular barrier that was correlated to a decreased production of endothelial tight-junction proteins and an early and sustained alteration of Hedgehog (Hh) signaling pathway. In vitro, activation of Toll-like receptor 4 in VEC downregulated the components of Hh pathway and altered the endothelial functional state. Inhibition of Hh signaling in the ScN of naive rats mimicked the biochemical and functional alterations observed after CCI and was, on its own, sufficient to evoke local neuroinflammation and sustained mechanical allodynia. Alteration of the Hh signaling pathway in VEC associated with peripheral nerve injury, is involved in BNB disruption and local inflammation, and could thus participate in the early changes leading to the peripheral nerve sensitization and, ultimately, neuropathic pain development.

Hedgehog Pathway-Mediated Vascular Alterations Following Trigeminal Nerve Injury

Whereas neurovascular interactions in spinal neuropathic pain models have been well characterized, little attention has been given to such neurovascular interactions in orofacial neuropathic pain models. This study investigated in male Sprague-Dawley rats the vascular changes following chronic constriction injury (CCI) of the infraorbital nerve (IoN), a broadly validated preclinical model of orofacial neuropathic pain. Following IoN-CCI, an early downregulation of tight junction proteins Claudin-1 and Claudin-5 was observed within the endoneurium and perineurium, associated with increased local accumulation of sodium fluorescein (NaFlu) within the IoN parenchyma, as compared with sham animals. These events were evidence of local blood-nerve barrier disruption and increased vascular permeability. A significant upregulation of immunocytes (CD3, CD11b) and innate immunity (TLR2, TLR4) mRNA markers was also observed, suggestive of increased local inflammation. Finally, a significant downregulation of Hedgehog pathway readouts Patched-1 and Gli-1 was observed within the IoN after CCI and local injections of cyclopamine, a Hedgehog pathway inhibitor, replicated in naïve rats the molecular, vascular, and behavioral changes observed following IoN-CCI. These results suggest a major role of Hedgehog pathway inhibition in mediating local increased endoneurial and perineurial vascular permeability following trigeminal nerve injury, thus facilitating immunocytes infiltration, neuroinflammation development, and neuropathic pain-like aversive behavior.

Upregulation of CCL2 via ATF3/c-Jun interaction mediated the Bortezomib-induced peripheral neuropathy

Bortezomib (BTZ) is a frequently used chemotherapeutic drug for the treatment of refractory multiple myeloma and hematological neoplasms. The mechanism by which the administration of BTZ leads to painful peripheral neuropathy remains unclear. In present study, we found that application of BTZ at 0.4 mg/kg for consecutive 5 days significantly increased the expression of CCL2 in DRG, and intrathecal administration of neutralizing antibody against CCL2 inhibited the mechanical allodynia induced by BTZ. We also found an increased expression of c-Jun in DRG, and that inhibition of c-Jun signaling prevented the CCL2 upregulation and mechanical allodynia in the rats treated with BTZ. Furthermore, the results with luciferase assay in vitro and ChIP assay in vivo showed that c-Jun might be essential for BTZ-induced CCL2 upregulation via binding directly to the specific position of the ccl2 promoter. In addition, the present results showed that an upregulated expression of ATF3 was co-expressed with c-Jun in the DRG neurons, and the enhanced interaction between c-Jun and ATF3 was observed in DRG in the rats treated with BTZ. Importantly, pretreatment with ATF3 siRNA significantly inhibited the recruitment of c-Jun to the ccl2 promoter in the rats treated with BTZ. Taken together, these findings suggested that upregulation of CCL2 resulting from the enhanced interaction between c-Jun and ATF3 in DRG contributed to BTZ-induced mechanical allodynia.

Modeling leukocyte trafficking at the human blood-nerve barrier in vitro and in vivo geared towards targeted molecular therapies for peripheral neuroinflammation

Peripheral neuroinflammation is characterized by hematogenous mononuclear leukocyte infiltration into peripheral nerves. Despite significant clinical knowledge, advancements in molecular biology and progress in developing specific drugs for inflammatory disorders such as rheumatoid arthritis, inflammatory bowel disease, and multiple sclerosis, there are currently no specific therapies that modulate pathogenic peripheral nerve inflammation. Modeling leukocyte trafficking at the blood-nerve barrier using a reliable human in vitro model and potential intravital microscopy techniques in representative animal models guided by human observational data should facilitate the targeted modulation of the complex inflammatory cascade needed to develop safe and efficacious therapeutics for immune-mediated neuropathies and chronic neuropathic pain.

Loss of intraepidermal nerve fiber density during SIV peripheral neuropathy is mediated by monocyte activation and elevated monocyte chemotactic proteins

Background

Peripheral neuropathy (PN) continues to be a major complication of human immunodeficiency virus (HIV) infection despite successful anti-retroviral therapy. Human HIV-PN can be recapitulated in a CD8-depleted, simian immunodeficiency virus (SIV)-infected rhesus macaque animal model, characterized by a loss of intraepidermal nerve fiber density (IENFD) and damage to the dorsal root ganglia (DRG). Increased monocyte traffic to the DRG has previously been associated with severe DRG pathology, as well as a loss in IENFD. Here, we sought to characterize the molecular signals associated with monocyte activation and trafficking to the DRGs.

Methods

Eleven SIV-infected CD8-depleted rhesus macaques were compared to four uninfected control animals. sCD14, sCD163, sCD137, regulated on activation normal T cell expressed and secreted (RANTES), and monocyte chemoattractant protein 1 (MCP-1) were measured in plasma and the latter three proteins were also quantified in DRG tissue lysates. All SIV-infected animals received serial skin biopsies to measure IENFD loss as well as BrdU inoculations to measure monocyte turnover during the course of infection. The number of BrdU+ and CD14+ CD16+ peripheral blood monocytes was determined by flow cytometry. The number of MAC387+, CCR2+, CCR5+, and CD137+ cells in DRG tissue was quantified by immunohistochemistry.

Results

sCD14, sCD163, MCP-1, and sCD137 increased significantly in plasma from pre-infection to necropsy. Plasma sCD163 and RANTES inversely correlated with IENFD. Additionally, sCD137 in DRG tissue lysate was elevated with severe DRG pathology and associated with the recruitment of MAC387+ cells to DRG. Elevated numbers of CCR5+ and CCR2+ satellite cells in the DRG were found, suggesting a chemotactic role of their ligands, RANTES, and MCP-1 in recruiting monocytes to the tissue.

Conclusions

We characterized the role of systemic (plasma) and tissue-specific (DRG) monocyte activation and associated cytokines in the pathogenesis of SIV-PN. We identified sCD163 and RANTES as potential biomarkers for HIV-PN, as these were associated with a loss of IENFD. Additionally, we identified CD137 signaling to play a role in MAC387+ cell traffic to DRG and possibly contribute to severe pathology. These studies highlight the role of monocyte activation and traffic in the pathogenesis of SIV-PN, while identifying specific signaling proteins for future pharmacological blockade.

Role of macrophages in Wallerian degeneration and axonal regeneration after peripheral nerve injury

The peripheral nervous system (PNS) has remarkable regenerative abilities after injury. Successful PNS regeneration relies on both injured axons and non-neuronal cells, including Schwann cells and immune cells. Macrophages are the most notable immune cells that play key roles in PNS injury and repair. Upon peripheral nerve injury, a large number of macrophages are accumulated at the injury sites, where they not only contribute to Wallerian degeneration, but also are educated by the local microenvironment and polarized to an anti-inflammatory phenotype (M2), thus contributing to axonal regeneration. Significant progress has been made in understanding how macrophages are educated and polarized in the injured microenvironment as well as how they contribute to axonal regeneration. Following the discussion on the main properties of macrophages and their phenotypes, in this review, we will summarize the current knowledge regarding the mechanisms of macrophage infiltration after PNS injury. Moreover, we will discuss the recent findings elucidating how macrophages are polarized to M2 phenotype in the injured PNS microenvironment, as well as the role and underlying mechanisms of macrophages in peripheral nerve injury, Wallerian degeneration and regeneration. Furthermore, we will highlight the potential application by targeting macrophages in treating peripheral nerve injury and peripheral neuropathies.

Preliminary expression profile of cytokines in brain tissue of BALB/c mice with Angiostrongylus cantonensis infection

Background

Angiostrongylus cantonensis (A. cantonensis) infection can result in increased risk of eosinophilic meningitis. Accumulation of eosinophils and inflammation can result in the A. cantonensis infection playing an important role in brain tissue injury during this pathological process. However, underlying mechanisms regarding the transcriptomic responses during brain tissue injury caused by A. cantonensis infection are yet to be elucidated. This study is aimed at identifying some genomic and transcriptomic factors influencing the accumulation of eosinophils and inflammation in the mouse brain infected with A. cantonensis.

Methods

An infected mouse model was prepared based on our laboratory experimental process, and then the mouse brain RNA Libraries were constructed for deep Sequencing with Illumina Genome Analyzer. The raw data was processed with a bioinformatics’ pipeline including Refseq genes expression analysis using cufflinks, annotation and classification of RNAs, lncRNA prediction as well as analysis of co-expression network. The analysis of Refseq data provides the measure of the presence and prevalence of transcripts from known and previously unknown genes.

Results

This study showed that Cys-Cys (CC) type chemokines such as CCL2, CCL8, CCL1, CCL24, CCL11, CCL7, CCL12 and CCL5 were elevated significantly at the late phase of infection. The up-regulation of CCL2 indicated that the worm of A. cantonensis had migrated into the mouse brain at an early infection phase. CCL2 could be induced in the brain injury during migration and CCL2 might play a major role in the neuropathic pain caused by A. cantonensis infection. The up-regulated expression of IL-4, IL-5, IL-10, and IL-13 showed Th2 cell predominance in immunopathological reactions at late infection phase in response to infection by A. cantonensis. These different cytokines can modulate and inhibit each other and function as a network with the specific potential to drive brain eosinophilic inflammation. The increase of ATF-3 expression at 21 dpi suggested the injury of neuronal cells at late phase of infection. 1217 new potential lncRNA were candidates of interest for further research.

Conclusions

These cytokine networks play an important role in the development of central nervous system inflammation caused by A. cantonensis infection.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-015-0939-6) contains supplementary material, which is available to authorized users.