Local effects of recombinant rat interleukin-6 on the peripheral nervous system

Myeloid cells protect corneal nerves against sterile injury through negative-feedback regulation of TLR2-IL-6 axis

BACKGROUND

Mounting evidence suggests that the immune system plays detrimental or protective roles in nerve injury and repair.

MAIN BODY

Herein we report that both CD11b^hiLy6G^hi and CD11b^hiLy6C^hiLy6G^lo myeloid cells are required to protect corneal nerves against sterile corneal injury. Selective depletion of CD11b^hiLy6G^hi or CD11b^hiLy6C^hiLy6G^lo cells resulted in aggravation of corneal nerve loss, which correlated with IL-6 upregulation. IL-6 neutralization preserved corneal nerves while reducing myeloid cell recruitment. IL-6 replenishment exacerbated corneal nerve damage while recruiting more myeloid cells. In mice lacking Toll-like receptor 2 (TLR2), the levels of IL-6 and myeloid cells were decreased and corneal nerve loss attenuated, as compared to wild-type and TLR4 knockout mice. Corneal stromal fibroblasts expressed TLR2 and produced IL-6 in response to TLR2 stimulation.

CONCLUSION

Collectively, our data suggest that CD11b^hiLy6G^hi and CD11b^hiLy6C^hiLy6G^lo myeloid cells confer corneal nerve protection under sterile injury by creating a negative-feedback loop to suppress the upstream TLR2-IL-6 axis that drives corneal nerve loss.

Effect of fasudil on experimental autoimmune neuritis and its mechanisms of action

This study aimed to investigate the therapeutic effect of fasudil on treating experimental autoimmune neuritis (EAN). Twenty-four EAN mice were randomly assigned to fasudil treatment (Fasudil group) or saline treatment (EAN model group) for 28 days. Clinical symptom score was evaluated every other day; inflammatory cell infiltration, demyelination, anti-myelin basic protein (MBP), inflammatory cytokines, inducible nitric oxide synthase (iNOS), and arginase-1 were detected in sciatic nerves at day 28. Th1, Th2, Th17, and Tregs proportions in splenocytes were detected at day 28. Clinical symptom score was found to be attenuated in the Fasudil group compared to the EAN model group from day 12 to day 28. Sciatic nerve inflammatory cell counts by HE staining and demyelination by luxol fast blue staining were both reduced, while MBP was increased in the Fasudil group compared to the EAN model group at day 28. Interferon γ (IFN-γ) and interleukin (IL)-17 were reduced, while IL-4 and IL-10 were elevated in the Fasudil group at day 28. Sciatic nerve M1 macrophages marker iNOS was decreased while M2 macrophages marker arginase-1 was increased in the Fasudil group at day 28. CD4⁺IFN-γ⁺ (Th1) and CD4⁺IL-17⁺ (Th17) cell proportions were both decreased, CD4⁺IL-4⁺ (Th2) cell proportion was similar, while CD25+FOXP3+ (Treg) cell proportion in splenocytes was increased in the Fasudil group. In summary, fasudil presented a good therapeutic effect for treating EAN by attenuating Th1/Th17 cells and promoting Tregs activation as well as M2 macrophages polarization.

Varicella Zoster Virus Alters Expression of Cell Adhesion Proteins in Human Perineurial Cells via Interleukin 6

BACKGROUND

In temporal arteries (TAs) from patients with giant cell arteritis, varicella zoster virus (VZV) is seen in perineurial cells that surround adventitial nerve bundles and form the peripheral nerve-extrafascicular tissue barrier (perineurium). We hypothesized that during VZV reactivation from ganglia, virus travels transaxonally and disrupts the perineurium to infect surrounding cells.

METHODS

Mock- and VZV-infected primary human perineurial cells (HPNCs) were examined for alterations in claudin-1, E-cadherin, and N-cadherin. Conditioned supernatant was analyzed for a soluble factor(s) mediating these alterations and for the ability to increase cell migration. To corroborate in vitro findings, a VZV-infected TA was examined.

RESULTS

In VZV-infected HPNCs, claudin-1 redistributed to the nucleus; E-cadherin was lost and N-cadherin gained, with similar changes seen in VZV-infected perineurial cells in a TA. VZV-conditioned supernatant contained increased interleukin 6 (IL-6) that induced E-cadherin loss and N-cadherin gain and increased cell migration when added to uninfected HPNCs; anti-IL-6 receptor antibody prevented these changes.

CONCLUSIONS

IL-6 secreted from VZV-infected HPNCs facilitated changes in E- and N-cadherin expression and cell migration, reminiscent of an epithelial-to-mesenchymal cell transition, potentially contributing to loss of perineurial cell barrier integrity and viral spread. Importantly, an anti-IL-6 receptor antibody prevented virus-induced perineurial cell disruption.

Biomarkers of Guillain-Barré Syndrome: Some Recent Progress, More Still to Be Explored

Guillain-Barré syndrome (GBS), the axonal subtype of which is mainly triggered by C. jejuni with ganglioside-mimicking lipooligosaccharides (LOS), is an immune-mediated disorder in the peripheral nervous system (PNS) accompanied by the disruption of the blood-nerve barrier (BNB) and the blood-cerebrospinal fluid barrier (B-CSF-B). Biomarkers of GBS have been extensively explored and some of them are proved to assist in the clinical diagnosis and in monitoring disease progression as well as in assessing the efficacy of immunotherapy. Herein, we systemically review the literature on biomarkers of GBS, including infection-/immune-/BNB, B-CSF-B, and PNS damage-associated biomarkers, aiming at providing an overview of GBS biomarkers and guiding further investigations. Furthermore, we point out further directions for studies on GBS biomarkers.

Gene network revealed involvements of Birc2, Birc3 and Tnfrsf1a in anti-apoptosis of injured peripheral nerves

Crush injury or axotomy of peripheral nerves results in the rapid production of the inflammatory cytokines, which were confirmed in various models, to some extent, to be noxious to the myelin sheath or Schwann cells (SCs). TNF-α is one of the primary initiators of the inflammatory cascade and exerts pleiotropic functions in the physiological conditions by binding to its receptors, type I (TNFRI) and type II (TNFRII). The pathway molecules TNFRI, Birc2 and Birc3 play key roles during the activation of the signaling. Injured peripheral nerves, preventing them from TNF-α-mediated destruction and proceeding to successful regeneration, might initiate an anti-apoptotic mechanism. To identity the exact functions of TNFRI, Birc2 and Birc3, as well as its involved pathways in the cellular events, we inferred a dynamic gene regulatory network from short time-series measurements of the proximal nerve segment cDNA microarray following rat sciatic nerve transection. TNFRI family member Tnfrsf1a, Birc2 and Birc3 were mined out integrating as master regulators to mediate inflammatory responses. Experiments revealed that Tnfrsf1a, Birc2 and Birc3 proteins colocalized with S100 in the rat peripheral nerve tissues, and the expression levels increased with the time extension. Knockdown of the proteins induced the apoptotic formation of primary cultured SCs by upregulation of caspase 3 and caspase 6. Our systematic analysis indicated that Tnfrsf1a, Birc2 and Birc3 of SCs, not originally regarded as XIAP, were mainly responsible for the inflammation-mediated anti-apoptosis of peripheral nerves. Birc2 and Birc3 might be the most potential targets for anti-apoptotic protection mediated by inflammatory cytokines.

Acute injury in the peripheral nervous system triggers an alternative macrophage response

BACKGROUND

The activation of the immune system in neurodegeneration has detrimental as well as beneficial effects. Which aspects of this immune response aggravate the neurodegenerative breakdown and which stimulate regeneration remains an open question. To unravel the neuroprotective aspects of the immune system we focused on a model of acute peripheral nerve injury, in which the immune system was shown to be protective.

METHODS

To determine the type of immune response triggered after axotomy of the sciatic nerve, a model for Wallerian degeneration in the peripheral nervous system, we evaluated markers representing the two extremes of a type I and type II immune response (classical vs. alternative) using real-time quantitative polymerase chain reaction (RT-qPCR), western blot, and immunohistochemistry.

RESULTS

Our results showed that acute peripheral nerve injury triggers an anti-inflammatory and immunosuppressive response, rather than a pro-inflammatory response. This was reflected by the complete absence of classical macrophage markers (iNOS, IFN γ, and IL12p40), and the strong up-regulation of tissue repair markers (arginase-1, Ym1, and Trem2). The signal favoring the alternative macrophage environment was induced immediately after nerve damage and appeared to be established within the nerve, well before the infiltration of macrophages. In addition, negative regulators of the innate immune response, as well as the anti-inflammatory cytokine IL-10 were induced. The strict regulation of the immune system dampens the potential tissue damaging effects of an over-activated response.

CONCLUSIONS

We here demonstrate that acute peripheral nerve injury triggers an inherent protective environment by inducing the M2 phenotype of macrophages and the expression of arginase-1. We believe that the M2 phenotype, associated with a sterile inflammatory response and tissue repair, might explain their neuroprotective capacity. As such, shifting the neurodegeneration-induced immune responses towards an M2/Th2 response could be an important therapeutic strategy.

The role of cytokines in Guillain-Barré syndrome

Cytokines play an important role in the pathogenesis of autoimmune diseases including Guillain-Barré syndrome (GBS) and its animal model experimental autoimmune neuritis (EAN). In this article, we reviewed the current knowledge of the role of cytokines such as TNF-α, IFN-γ, IL-1β, IL-6, IL-12, IL-18, IL-23, IL-17, IL-10, IL-4 and chemokines in GBS and EAN as unraveled by studies both in the clinic and the laboratory. However, these studies occasionally yield conflicting results, highlighting the complex role that cytokines play in the disease process. Efforts to modulate cytokine function in GBS and other autoimmune disease have shown efficiency indicating that cytokines are important therapeutic targets.

Peripheral nerve-derived HIV-1 is predominantly CCR5-dependent and causes neuronal degeneration and neuroinflammation

HIV-related peripheral neuropathy is a major neurological complication of HIV infection, although little is known about its pathogenesis. We amplified HIV-1 C2V3 envelope sequences from peroneal nerves obtained from HIV/AIDS patients. Sequence analysis and infectious recombinant viruses containing peripheral nerve-derived C2V3 sequences indicated a predominance of CCR5-dependent and macrophage-tropic HIV-1, although dual tropic viruses using both CCR5 and CXCR4 were identified. The neuropathogenic effects of recombinant HIV-1 clones were investigated using a novel dorsal root ganglion culture system that was comprised of sensory neurons, macrophages and Schwann cells from transgenic rats expressing human CD4 and CCR5 on monocytoid cells. Despite restricted viral replication, HIV-1 infection caused a reduction in the percentage of neurons with neuritic processes together with significant neurite retraction, which was accompanied by induction of IL-1beta and TNF-alpha expression, depending on the individual virus. Our results suggest that HIV-1 infection of the peripheral nervous system causes axonal degeneration, possibly through the induction of pro-inflammatory cytokines.

Receptor for advanced glycation endproduct (RAGE)-mediated nuclear factor-κB activation in vasculitic neuropathy

Binding of ligands to the receptor for advanced glycation endproducts (RAGE) results in activation of the proinflammatory transcription factor nuclear factor-kappaB (NF-kappaB) and subsequent expression of NF-kappaB-regulated cytokines. In order to determine whether engagement of RAGE contributes to the pathogenesis of vasculitic neuropathy, we studied the presence of the RAGE ligand N(epsilon)-(carboxymethyl)lysine (CML), the receptor itself, NF-kappaB, and interleukin-6 (IL-6) in sural nerve biopsies of 12 patients with vasculitic neuropathies and 12 controls. In the patients, CML, RAGE, NF-kappaB, and IL-6 were localized in mononuclear cells, epineurial and endoneurial vessels and the perineurium. CML, RAGE, NF-kappaB, and IL-6 were expressed by CD4(+), CD8(+), and CD68(+) cells invading the nerves. Controls showed only weak staining. These data suggest that the RAGE pathway plays a critical proinflammatory role in vasculitic neuropathy.

A new model of sciatic inflammatory neuritis (SIN): induction of unilateral and bilateral mechanical allodynia following acute unilateral peri-sciatic immune activation in rats

Immune activation near healthy peripheral nerves may have a greater role in creating pathological pain than previously recognized. We have developed a new model of sciatic inflammatory neuritis to assess how such immune activation may influence somatosensory processing. The present series of experiments reveal that zymosan (yeast cell walls) acutely injected around the sciatic nerve of awake unrestrained rats rapidly (within 3h) produces low threshold mechanical allodynia in the absence of thermal hyperalgesia. Low (4 microg) doses of zymosan produce both territorial and extra-territorial allodynia restricted to the ipsilateral hindpaw. Higher (40-400 microg) doses of zymosan again produce both territorial and extra-territorial allodynia. However, allodynia is now expressed both in the ipsilateral as well as contralateral hindpaws. Several lines of evidence are provided that the appearance of this contralateral ('mirror') allodynia reflects local actions of zymosan on the sciatic nerve rather than spread of this immune activator to the general circulation. Since many clinical neuropathies result from inflammation/infection of peripheral nerves rather than frank physical trauma, understanding how immune activation alters pain processing may suggest novel approaches to pain control.

The role of macrophages in immune-mediated damage to the peripheral nervous system

Macrophage-mediated segmental demyelination is the pathological hallmark of autoimmune demyelinating polyneuropathies, including the demyelinating form of Guillain-Barré syndrome and chronic inflammatory demyelinating polyneuropathy. Macrophages serve a multitude of functions throughout the entire pathogenetic process of autoimmune neuropathy. Resident endoneurial macrophages are likely to act as local antigen-presenting cells by their capability to express major histocompatibility complex antigens and costimulatory B7-molecules, and may thus be critical in triggering the autoimmune process. Hematogenous infiltrating macrophages then find their way into the peripheral nerve together with T-cells by the concerted action of adhesion molecules, matrix metalloproteases and chemotactic signals. Within the nerve, macrophages regulate inflammation by secreting several pro-inflammatory cytokines including IL-1, IL-6, IL-12 and TNF-alpha. Autoantibodies are likely to guide macrophages towards their myelin or primarily axonal targets, which then attack in a complement-dependent and receptor-mediated manner. In addition, non-specific tissue damage occurs through the secretion of toxic mediators and cytokines. Later, macrophages contribute to the termination of inflammation by promoting T-cell apoptosis and expressing anti-inflammatory cytokines including TGF-beta1 and IL-10. During recovery, they are tightly involved in allowing Schwann cell proliferation, remyelination and axonal regeneration to proceed. Macrophages, thus, play dual roles in autoimmune neuropathy, being detrimental in attacking nervous tissue but also salutary, when aiding in the termination of the inflammatory process and the promotion of recovery.