Regulatory T Cells and Their Derived Cytokine, Interleukin-35, Reduce Pain in Experimental Autoimmune Encephalomyelitis

Oligodendrocytes in central nervous system diseases: the effect of cytokine regulation

Cytokines including tumor necrosis factor, interleukins, interferons, and chemokines are abundantly produced in various diseases. As pleiotropic factors, cytokines are involved in nearly every aspect of cellular functions such as migration, survival, proliferation, and differentiation. Oligodendrocytes are the myelin-forming cells in the central nervous system and play critical roles in the conduction of action potentials, supply of metabolic components for axons, and other functions. Emerging evidence suggests that both oligodendrocytes and oligodendrocyte precursor cells are vulnerable to cytokines released under pathological conditions. This review mainly summarizes the effects of cytokines on oligodendrocyte lineage cells in central nervous system diseases. A comprehensive understanding of the effects of cytokines on oligodendrocyte lineage cells contributes to our understanding of central nervous system diseases and offers insights into treatment strategies.

Peroxynitrite reduces Treg cell expansion and function by mediating IL-2R nitration and aggravates multiple sclerosis pathogenesis: One sentence summary: Peroxynitrite-mediated Treg IL-2R nitration impacts on multiple sclerosis

T-helper 17 cells and regulatory T cells (Treg) are critical regulators in the pathogenesis of multiple sclerosis (MS) but the factors affecting Treg/Th17 balance remains largely unknown. Redox balance is crucial to maintaining immune homeostasis and reducing the severity of MS but the underlying mechanisms are unclear yet. Herein, we tested the hypothesis that peroxynitrite, a representative molecule of reactive nitrogen species (RNS), could inhibit peripheral Treg cells, disrupt Treg/Th17 balance and aggravate MS pathology by inducing nitration of interleukin-2 receptor (IL-2R) and down-regulating RAS/JNK-AP-1 signalling pathway. Experimental autoimmune encephalomyelitis (EAE) mouse model and serum samples of MS patients were used in the study. We found that the increases of 3-nitrotyrosine and IL-2R nitration in Treg cells were coincided with disease severity in the active EAE mice. Mechanistically, peroxynitrite-induced IL-2R nitration down-regulated RAS/JNK signalling pathway, subsequently impairing peripheral Treg expansion and function, increasing Teff infiltration into the central nerve system (CNS), aggravating demyelination and neurological deficits in the EAE mice. Those changes were abolished by peroxynitrite decomposition catalyst (PDC) treatment. Furthermore, transplantation of the PDC-treated-autologous Treg cells from donor EAE mice significantly decreased Th17 cells in both axillary lymph nodes and lumbar spinal cord, and ameliorated the neuropathology of the recipient EAE mice. Those results suggest that peroxynitrite could disrupt peripheral Treg/Th17 balance, and aggravate neuroinflammation and neurological deficit in active EAE/MS pathogenesis. The underlying mechanisms are related to induce the nitration of IL-2R and inhibit the RAS/JNK-AP-1 signalling pathway in Treg cells. The study highlights that targeting peroxynitrite-mediated peripheral IL-2R nitration in Treg cells could be a novel therapeutic strategy to restore Treg/Th17 balance and ameliorate MS/EAE pathogenesis. The study provides valuable insights into potential role of peripheral redox balance in maintaining CNS immune homeostasis.

Therapy with regulatory T-cell infusion in autoimmune diseases and organ transplantation: A review of the strengths and limitations

In the last decade, cell therapies have revolutionized the treatment of some diseases, earning the definition of being the "third pillar" of therapeutics. In particular, the infusion of regulatory T cells (Tregs) is explored for the prevention and control of autoimmune reactions and acute/chronic allograft rejection. Such an approach represents a promising new treatment for autoimmune diseases to recover an immunotolerance against autoantigens, and to prevent an immune response to alloantigens. The efficacy of the in vitro expanded polyclonal and antigen-specific Treg infusion in the treatment of a large number of autoimmune diseases has been extensively demonstrated in mouse models. Similarly, experimental work documented the efficacy of Treg infusions to prevent acute and chronic allograft rejections. The Treg therapy has shown encouraging results in the control of type 1 diabetes (T1D) as well as Crohn's disease, systemic lupus erythematosus, autoimmune hepatitis and delaying graft rejection in clinical trials. However, the best method for Treg expansion and the advantages and pitfalls with the different types of Tregs are not fully understood in terms of how these therapeutic treatments can be applied in the clinical setting. This review provides an up-to-date overview of Treg infusion-based treatments in autoimmune diseases and allograft transplantation, the current technical challenges, and the highlights and disadvantages of this therapeutic approaches."

Immune drivers of physiological and pathological pain

Physiological pain serves as a warning of exposure to danger and prompts us to withdraw from noxious stimuli to prevent tissue damage. Pain can also alert us of an infection or organ dysfunction and aids in locating such malfunction. However, there are instances where pain is purely pathological, such as unresolved pain following an inflammation or injury to the nervous system, and this can be debilitating and persistent. We now appreciate that immune cells are integral to both physiological and pathological pain, and that pain, in consequence, is not strictly a neuronal phenomenon. Here, we discuss recent findings on how immune cells in the skin, nerve, dorsal root ganglia, and spinal cord interact with somatosensory neurons to mediate pain. We also discuss how both innate and adaptive immune cells, by releasing various ligands and mediators, contribute to the initiation, modulation, persistence, or resolution of various modalities of pain. Finally, we propose that the neuroimmune axis is an attractive target for pain treatment, but the challenges in objectively quantifying pain preclinically, variable sex differences in pain presentation, as well as adverse outcomes associated with immune system modulation, all need to be considered in the development of immunotherapies against pain.

CD4+CD25+ regulatory T cells ex vivo generated from autologous naïve CD4+ T cells suppress EAE progression

CD4+CD25+ regulatory T cells (Tregs) play an important role in maintaining immune homeostasis in multiple sclerosis (MS). Hence, we aimed to explore the therapeutic efficacy and safety of adoptive cell therapy (ACT) utilizing induced antigen-specific Tregs in an animal model of MS, that is, in an experimental autoimmune encephalomyelitis (EAE) model. B cells from EAE model that were activated with soluble CD40L were used as antigen-presenting cells (APCs) to induce the differentiation of antigen-specific Tregs from naïve CD4 precursors, and then, a stepwise isolation of CD4+CD25highCD127low Tregs was performed using a flow sorter. All EAE mice were divided into Treg-treated group (2 × 104 cells in 0.2 mL per mouse, n = 14) and sham-treated group (0.2 mL normal saline (NS), n = 20), which were observed daily for clinical assessment, and for abnormal appearance for 6 weeks. Afterward, histological analysis, immunofluorescence and real-time PCR were performed. Compared to sham-treated mice, Treg-treated mice exhibited a significant decrease in disease severity scores and reduced inflammatory infiltration and demyelination in the spinal cord. Additionally, Tregs-treated mice demonstrated higher CCN3 protein and mRNA levels than sham-treated mice. The results of this preclinical study further support the therapeutic potential of this ACT approach in the treatment of MS.

Differential Effects of Regulatory T Cells in the Meninges and Spinal Cord of Male and Female Mice with Neuropathic Pain

Immune cells play a critical role in promoting neuroinflammation and the development of neuropathic pain. However, some subsets of immune cells are essential for pain resolution. Among them are regulatory T cells (Tregs), a specialised subpopulation of T cells that limit excessive immune responses and preserve immune homeostasis. In this study, we utilised intrathecal adoptive transfer of activated Tregs in male and female mice after peripheral nerve injury to investigate Treg migration and whether Treg-mediated suppression of pain behaviours is associated with changes in peripheral immune cell populations in lymphoid and meningeal tissues and spinal microglial and astrocyte reactivity and phenotypes. Treatment with Tregs suppressed mechanical pain hypersensitivity and improved changes in exploratory behaviours after chronic constriction injury (CCI) of the sciatic nerve in both male and female mice. The injected Treg cells were detected in the choroid plexus and the pia mater and in peripheral lymphoid organs in both male and female recipient mice. Nonetheless, Treg treatment resulted in differential changes in meningeal and lymph node immune cell profiles in male and female mice. Moreover, in male mice, adoptive transfer of Tregs ameliorated the CCI-induced increase in microglia reactivity and inflammatory phenotypic shift, increasing M2-like phenotypic markers and attenuating astrocyte reactivity and neurotoxic astrocytes. Contrastingly, in CCI female mice, Treg injection increased astrocyte reactivity and neuroprotective astrocytes. These findings show that the adoptive transfer of Tregs modulates meningeal and peripheral immunity, as well as spinal glial populations, and alleviates neuropathic pain, potentially through different mechanisms in males and females.

Aryl hydrocarbon receptors improve migraine-like pain behaviors in rats through the regulation of regulatory T cell/T-helper 17 cell-related homeostasis

OBJECTIVE

To investigate the effect of the aryl hydrocarbon receptor (AHR)/regulatory T cell (Treg)/T-helper 17 (Th17) cell pathway on the pathogenesis of migraine.

BACKGROUND

Migraine is a disabling neurovascular disease that imposes an enormous burden on both individuals and society. The pathophysiological mechanisms of migraine remain controversial. Recent studies have suggested that immune dysfunction may be involved in the pathogenesis of migraine. The AHR, a receptor expressed on most immune cells, has been implicated in the occurrence of many autoimmune diseases; however, whether it is involved in the pathogenesis of migraine is unclear.

METHODS

A chronic migraine rat model was established through repeated intraperitoneal injection of nitroglycerin (NTG). The mechanical and thermal pain thresholds were assessed using von Frey filaments and radiant heat. Next, the protein expression levels of AHR in the trigeminal nucleus caudalis (TNC) region of chronic migraine (CM)-like rats were quantified and the changes in Treg/Th17-related transcription factors and inflammatory factors in the TNC were explored. To determine the role of AHR in CM, we examined the effects of the AHR agonist 2-(1'-indole-3'-carbonyl)-thiazole-4-carboxylic acid methyl ester (ITE), and AHR antagonist CH-223191 on pain behavior, c-Fos, calcitonin gene-related peptide (CGRP), AHR, and Treg/Th17-related factor expression in CM-like rats.

RESULTS

Repeated administration of NTG significantly enhanced nociceptive hypersensitivity and increased expression of c-Fos and CGRP in rats, while AHR was significantly decreased in the TNC. In addition, the expression of the transcription factor forkhead box protein P3 and the signal transducer and activator of transcription 5 decreased significantly. In contrast, the expression of the transcription factor retinoic acid receptor-related orphan receptor γ t and signal transducer and activator of transcription 3 were significantly increased. Moreover, the mRNA level of transforming growth factor beta-1 was decreased, while that of interleukin (IL)-10 and IL-22 was increased in the TNC. The AHR agonist ITE alleviated migraine-like pain behaviors in rats, activated the AHR signaling pathway, and improved the imbalance of Treg/Th17-related transcription factors and inflammatory factors. Conversely, the AHR antagonist CH-223191 did not alleviate migraine-like pain behaviors in rats; and even exacerbated them.

CONCLUSIONS

The AHR participates in the development of CM by regulating Treg/Th17-related homeostasis. Therefore, treatments targeting the AHR/Treg/Th17 signaling pathway could be new effective interventions for CM treatment.

Pain-resolving immune mechanisms in neuropathic pain

Interactions between the immune and nervous systems are of central importance in neuropathic pain, a common and debilitating form of chronic pain caused by a lesion or disease affecting the somatosensory system. Our understanding of neuroimmune interactions in pain research has advanced considerably. Initially considered as passive bystanders, then as culprits in the pathogenesis of neuropathic pain, immune responses in the nervous system are now established to underpin not only the initiation and progression of pain but also its resolution. Indeed, immune cells and their mediators are well-established promoters of neuroinflammation at each level of the neural pain pathway that contributes to pain hypersensitivity. However, emerging evidence indicates that specific subtypes of immune cells (including antinociceptive macrophages, pain-resolving microglia and T regulatory cells) as well as immunoresolvent molecules and modulators of the gut microbiota-immune system axis can reduce the pain experience and contribute to the resolution of neuropathic pain. This Review provides an overview of the immune mechanisms responsible for the resolution of neuropathic pain, including those involved in innate, adaptive and meningeal immunity as well as interactions with the gut microbiome. Specialized pro-resolving mediators and therapeutic approaches that target these neuroimmune mechanisms are also discussed.

Mechanisms of acupuncture-electroacupuncture on inflammatory pain

Acupuncture, as a traditional treatment, has been extensively used in China for thousands of years. According to the World Health Organization (WHO), acupuncture is recommended for the treatment of 77 diseases. And 16 of these diseases are related to inflammatory pain. As a combination of traditional acupuncture and modern electrotherapy, electroacupuncture (EA) has satisfactory analgesic effects on various acute and chronic pain. Because of its good analgesic effects and no side effects, acupuncture has been widely accepted all over the world. Despite the increase in the number of studies, the mechanisms via which acupuncture exerts its analgesic effects have not been conclusively established. A literature review of related research is of great significance to elaborate on its mechanisms and to inform on further research directions. We elucidated on its mechanisms of action on inflammatory pain from two levels: peripheral and central. It includes the mechanisms of acupuncture in the periphery (immune cells and neurons, purinergic pathway, nociceptive ion channel, cannabinoid receptor and endogenous opioid peptide system) and central nervous system (TPRV1, glutamate and its receptors, glial cells, GABAergic interneurons and signaling molecules). In this review, we collected relevant recent studies to systematically explain the mechanisms of acupuncture in treating inflammatory pain, with a view to providing direction for future applications of acupuncture in inflammatory pain and promoting clinical development.

Patients With Severe Multiple Sclerosis Exhibit Functionally Altered CD8+ Regulatory T Cells

BACKGROUND AND OBJECTIVES

Multiple sclerosis (MS) is a chronic inflammatory and demyelinating disease of the CNS. Studies of immune dysfunction in MS have mostly focused on CD4⁺ Tregs, but the role of CD8⁺ Tregs remains largely unexplored. We previously evidenced the suppressive properties of rat and human CD8⁺CD45RC^low/neg Tregs from healthy individuals, expressing Forkhead box P3 (FOXP3) and acting through interferon-gamma (IFN-γ), transforming growth factor beta (TGFβ), and interleukin-34 (IL-34). secretions to regulate immune responses and control diseases such as transplant rejection. To better understand CD8⁺CD45RC^low/neg Tregs contribution to MS pathology, we further investigated their phenotype, function, and transcriptome in patients with MS.

METHODS

We enrolled adults with relapsing-remitting MS and age-matched and sex-matched healthy volunteers (HVs). CD8⁺ T cells were segregated based on low or lack of expression of CD45RC. First, the frequency in CSF and blood, phenotype, transcriptome, and function of CD8⁺CD45RC^low and ^neg were investigated according to exacerbation status and secondarily, according to clinical severity based on the MS severity score (MSSS) in patients with nonexacerbating MS. We then induced active MOG_35-55 EAE in C57Bl/6 mice and performed adoptive transfer of fresh and expanded CD8⁺CD45RC^neg Tregs to assess their ability to mitigate neuroinflammation in vivo.

RESULTS

Thirty-one untreated patients with relapsing-remitting MS were compared with 40 age-matched and sex-matched HVs. We demonstrated no difference of CSF CD8⁺CD45RC^low and CD8⁺CD45RC^neg proportions, but blood CD8⁺CD45RC^low frequency was lower in patients with MS exacerbation when compared with that in HVs. CD8⁺CD45RC^neg Tregs but not CD8⁺CD45RC^low showed higher suppressive capacities in vitro in MS patients with exacerbation than in patients without acute inflammatory attack. In vitro functional assays showed a compromised suppression capacity of CD8⁺CD45RC^low Tregs in patients with nonexacerbating severe MS, defined by the MSSS. We then characterized murine CD8⁺CD45RC^neg Tregs and demonstrated the potential of CD45RC^neg cells to migrate to the CNS and mitigate experimental autoimmune encephalomyelitis in vivo.

DISCUSSION

Altogether, these results suggest a defect in the number and function of CD8⁺CD45RC^low Tregs during MS relapse and an association of CD8⁺CD45RC^low Tregs dysfunction with MS severity. Thus, CD8⁺CD45RC^low/neg T cells might bring new insights into the pathophysiology and new therapeutic approaches of MS.

Infiltration Profile of Regulatory T Cells in Osteoarthritis-Related Pain and Disability

Emerging evidence indicates that regulatory T cells (Treg) intervene in the inflammatory processes that drive osteoarthritis (OA). However, whether polarized Tregs affect clinical features of the disease in the short- or long-term, and if so, what their role in OA-related pain and functional disability really is, remains elusive. Thus, the aim of the current study was to characterize the infiltration profile of Tregs in systemic (peripheral blood) and joint-derived (synovial fluid and synovial membrane) samples from patients with knee OA in relation to OA-induced symptoms. To this end, Treg infiltration (CD4⁺CD25^+/high CD127^low/−) was analyzed in matched samples of peripheral blood (PB), synovial fluid (SF) and synovial membrane (SM) from a total of 47 patients undergoing elective knee arthroplasty using flow cytometry. At the same time, knee pain and function were assessed and correlated with Treg proportions in different compartments (PB, SF, SM). Interestingly, matched-pair analysis revealed significantly higher Treg proportions in joint-derived samples than in PB, which was mainly attributed to the high Treg frequency in SF. Moreover, we found significant associations between infiltrating Tregs and OA-related symptoms which indicate that lower Treg proportions—especially in the SM—are related to increased pain and functional disability in knee OA. In conclusion, this study highlights the importance of local cellular inflammatory processes in OA pathology. Intra-articular Treg infiltration might play an important role not only in OA pathogenesis but also in the development of OA-related symptoms.

Low-dose interleukin-2 reverses chronic migraine-related sensitizations through peripheral interleukin-10 and transforming growth factor beta-1 signaling

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Low-dose interleukin-2 treatment increases the levels of cytokine IL-10 and TGFβ1.

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Peripheral IL-10 and TGFβ1 signaling mediate the therapeutic effects of interleukin-2.

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IL-10 and TGFβ1 directly reverses chronic migraine-related peripheral sensitization.

Low-dose interleukin-2 (LD-IL-2) treatment has been shown to effectively reverse chronic migraine-related behaviors and the sensitization of trigeminal ganglion (TG) neurons through expansion and activation of peripheral regulatory T cells (Tregs) in mice. In this study, we investigated the molecular mechanisms underlying the effects of LD-IL-2 and Treg cells. LD-IL-2 treatment increases the production of cytokines interleukin-10 (IL-10) and transforming growth factor beta-1 (TGFβ1) in T cells, especially Treg cells, suggesting that they may mediate the therapeutic effect of LD-IL-2. Indeed, neutralizing antibodies against either IL-10 or TGFβ completely blocked the effects of LD-IL-2 on the facial mechanical hypersensitivity as well as the sensitization of TG neurons resulting from repeated nitroglycerin (NTG, a reliable trigger of migraine in patients) administration in mice, indicating that LD-IL-2 and Treg cells engage both peripheral IL-10 and TGFβ signaling pathways to reverse chronic-migraine related sensitizations. In an in vitro assay, incubation of TG culture with exogenous IL-10 or TGFβ1 fully reversed NTG-induced sensitization of TG neurons, suggesting that the IL-10 and TGFβ1 signaling in TG neurons contribute to LD-IL-2′s therapeutic effects. Collectively, these results not only elucidate the molecular mechanisms through which LD-IL-2 and Treg cells reverse chronic-migraine related sensitizations, but also suggest that the IL-10 and TGFβ1 signaling pathways in TG neurons are potential targets for chronic migraine therapy.

Transient receptor potential ankyrin 1 mediates headache-related cephalic allodynia in a mouse model of relapsing-remitting multiple sclerosis

ABSTRACT

Primary headache conditions are frequently associated with multiple sclerosis (MS), but the mechanism that triggers or worsens headaches in patients with MS is poorly understood. We previously showed that the proalgesic transient receptor potential ankyrin 1 (TRPA1) mediates hind paw mechanical and cold allodynia in a relapsing-remitting experimental autoimmune encephalomyelitis (RR-EAE) model in mice. Here, we investigated the development of periorbital mechanical allodynia (PMA) in RR-EAE, a hallmark of headache, and if TRPA1 contributed to this response. RR-EAE induction by injection of the myelin oligodendrocyte peptide fragment35-55 (MOG35-55) and Quillaja A adjuvant (Quil A) in C57BL/6J female mice elicited a delayed and sustained PMA. The PMA at day 35 after induction was reduced by the calcitonin gene-related peptide receptor antagonist (olcegepant) and the serotonin 5-HT1B/D receptor agonist (sumatriptan), 2 known antimigraine agents. Genetic deletion or pharmacological blockade of TRPA1 attenuated PMA associated with RR-EAE. The levels of oxidative stress biomarkers (4-hydroxynonenal and hydrogen peroxide, known TRPA1 endogenous agonists) and superoxide dismutase and NADPH oxidase activities were increased in the trigeminal ganglion of RR-EAE mice. Besides, the treatment with antioxidants (apocynin or α-lipoic acid) attenuated PMA. Thus, the results of this study indicate that TRPA1, presumably activated by endogenous agonists, evokes PMA in a mouse model of relapsing-remitting MS.

Differential Role of p53 in Oligodendrocyte Survival in Response to Various Stresses: Experimental Autoimmune Encephalomyelitis, Cuprizone Intoxication or White Matter Stroke

Promoting oligodendrocyte viability has been proposed as a therapeutic strategy for alleviating many neuronal diseases, such as multiple sclerosis and stroke. However, molecular pathways critical for oligodendrocyte survival under various stresses are still not well known. p53 is a strong tumor suppressor and regulates cell cycle, DNA repair and cell death. Our previous studies have shown that p53 plays an important role in promoting neuronal survival after insults, but its specific role in oligodendrocyte survival is not known. Here, we constructed the mice with oligodendrocyte-specific p53 loss by crossing TRP53^flox/flox mice and CNP-cre mice, and found that p53 was dispensable for oligodendrocyte differentiation and myelin formation under physiological condition. In the experimental autoimmune encephalomyelitis (EAE) model, p53 loss of function, specifically in oligodendrocytes, did not affect the EAE disease severity and had no effect on demyelination in the spinal cord of the mice. Interestingly, p53 deficiency in oligodendrocytes significantly attenuated the demyelination of corpus callosum and alleviated the functional impairment of motor coordination and spatial memory in the cuprizone demyelination model. Moreover, the oligodendrocyte-specific loss of p53 provided protection against subcortical white matter damage and mitigated recognition memory impairment in mice in the white matter stroke model. These results suggest that p53 plays different roles in the brain and spinal cord or in response to various stresses. Thus, p53 may be a therapeutic target for oligodendrocyte prevention in specific brain injuries, such as white matter stroke and multiple sclerosis.

The Positive Impact of Donor Bone Marrow Cells Transplantation into Immunoprivileged Compartments on the Survival of Vascularized Skin Allografts

Using the vascularized skin allograft (VSA) model, we compared the tolerogenic effects of different allogeneic bone marrow transplantation (BMT) delivery routes into immunoprivileged compartments under a 7-day protocol immunosuppressive therapy. Twenty-eight fully MHC mismatched VSA transplants were performed between ACI (RT1^a) donors and Lewis (RT1¹) recipients in four groups of seven animals each, under a 7-day protocol of alfa/beta TCRmAb/CsA (alpha/beta-TCR monoclonal antibodies/Cyclosporine A therapy). Donor bone marrow cells (BMC) (100 × 106 cells) were injected into three different immunoprivileged compartments: Group 1: Control, without cellular supportive therapy, Group 2: Intracapsular BMT, Group 3: Intragonadal BMT, Group 4: Intrathecal BMT. In Group 2, BMC were transplanted under the kidney capsule. In Group 3, BMC were transplanted into the right testis between tunica albuginea and seminiferous tubules, and in Group 4, cells were injected intrathecally. The assessment included: skin evaluation for signs and grade of rejection and immunohistochemistry for donor cells engraftment into host lymphoid compartments. Donor-specific chimerism for MHC class I (RT1^a) antigens and the presence of CD4⁺/CD25⁺ T cells were assessed in the peripheral blood of recipients. The most extended allograft survival, 50–78 days, was observed in Group 4 after intrathecal BMT. The T cells CD4⁺/CD25⁺ in the peripheral blood were higher after intrathecal BMC injection than other experimental groups at each post-transplant time point. Transplantation of BMC into immunoprivileged compartments delayed rejection of fully mismatched VSA and induction of robust, donor-specific chimerism.

Neural stem cells derived from primitive mesenchymal stem cells reversed disease symptoms and promoted neurogenesis in an experimental autoimmune encephalomyelitis mouse model of multiple sclerosis

Background

Multiple sclerosis (MS) is an autoimmune inflammatory disease of the central nervous system (CNS). MS affects millions of people and causes a great economic and societal burden. There is no cure for MS. We used a novel approach to investigate the therapeutic potential of neural stem cells (NSCs) derived from human primitive mesenchymal stem cells (MSCs) in an experimental autoimmune encephalomyelitis (EAE) mouse model of MS.

Methods

MSCs were differentiated into NSCs, labeled with PKH26, and injected into the tail vein of EAE mice. Neurobehavioral changes in the mice assessed the effect of transplanted cells on the disease process. The animals were sacrificed two weeks following cell transplantation to collect blood, lymphatic, and CNS tissues for analysis. Transplanted cells were tracked in various tissues by flow cytometry. Immune infiltrates were determined and characterized by H&E and immunohistochemical staining, respectively. Levels of immune regulatory cells, Treg and Th17, were analyzed by flow cytometry. Myelination was determined by Luxol fast blue staining and immunostaining. In vivo fate of transplanted cells and expression of inflammation, astrogliosis, myelination, neural, neuroprotection, and neurogenesis markers were investigated by using immunohistochemical and qRT-PCR analysis.

Results

MSC-derived NSCs expressed specific neural markers, NESTIN, TUJ1, VIMENTIN, and PAX6. NSCs improved EAE symptoms more than MSCs when transplanted in EAE mice. Post-transplantation analyses also showed homing of MSCs and NSCs into the CNS with concomitant induction of an anti-inflammatory response, resulting in reducing immune infiltrates. NSCs also modulated Treg and Th17 cell levels in EAE mice comparable to healthy controls. Luxol fast blue staining showed significant improvement in myelination in treated mice. Further analysis showed that NSCs upregulated genes involved in myelination and neuroprotection but downregulated inflammatory and astrogliosis genes more significantly than MSCs. Importantly, NSCs differentiated into neural derivatives and promoted neurogenesis, possibly by modulating BDNF and FGF signaling pathways.

Conclusions

NSC transplantation reversed the disease process by inducing an anti-inflammatory response and promoting myelination, neuroprotection, and neurogenesis in EAE disease animals. These promising results provide a basis for clinical studies to treat MS using NSCs derived from primitive MSCs.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02563-8.

In Vivo Induction of Regulatory T Cells Via CTLA-4 Signaling Peptide to Control Autoimmune Encephalomyelitis and Prevent Disease Relapse

Regulatory T cells play a key role in immune tolerance to self-antigens, thereby preventing autoimmune diseases. However, no drugs targeting Treg cells have been approved for clinical trials yet. Here, a chimeric peptide is generated by conjugation of the cytoplasmic domain of CTLA-4 (ctCTLA-4) with dNP2 for intracellular delivery, dNP2-ctCTLA-4, and evaluated Foxp3 expression during Th0, Th1, Treg, and Th17 differentiation dependent on TGF-β. The lysine motif of ctCTLA-4, not tyrosine motif, is required for Foxp3 expression for Treg induction and amelioration of experimental autoimmune encephalomyelitis (EAE). Transcriptome analysis reveals that dNP2-ctCTLA-4-treated T cells express Treg transcriptomic patterns with properties of suppressive functions. In addition, the molecular interaction between the lysine motif of ctCTLA-4 and PKC-η is critical for Foxp3 expression. Although both CTLA-4-Ig and dNP2-ctCTLA-4 treatment in vivo ameliorated EAE progression, only dNP2-ctCTLA-4 requires Treg cells for inhibition of disease progression and prevention of relapse. Furthermore, the CTLA-4 signaling peptide is able to induce human Tregs in vitro and in vivo as well as from peripheral blood mononuclear cells (PBMCs) of multiple sclerosis patients. These results collectively suggest that the chimeric CTLA-4 signaling peptide can be used for successful induction of regulatory T cells in vivo to control autoimmune diseases, such as multiple sclerosis.

Electroacupuncture Relieves Pain and Attenuates Inflammation Progression Through Inducing IL-10 Production in CFA-Induced Mice

The therapeutic effect of electroacupuncture (EA) on inflammatory pain has been well recognized clinically, but the mechanism is unclear. Interleukin-10 (IL-10), which is produced by regulatory T (Treg) cell, is a key anti-inflammatory cytokine for relieving inflammatory pain. Therefore, the aim of this study is to investigate whether EA could inhibit CFA-induced pain and attenuate inflammation progression by regulating the activation of immunocyte and inducing the expression of IL-10. In this study, mice were treated with EA (2/100 Hz, 2 mA) for five consecutive days after 1 day of CFA injection. The behavioral tests were measured and analyzed after the daily EA treatment; then, hind paw, spinal cord, and spleen tissues were prepared for assessment. The results showed that EA treatment significantly increased the mechanical threshold and thermal latency after CFA injection and boosted the expression of IL-10 in paw and spinal cord tissues. EA treatment promoted Treg cells; suppressed macrophage and neutrophils cells; reduced the expression of IL-1β, NLRP3, and TNF-α; and ultimately relieved inflammatory pain. The findings suggested that the analgesic and anti-inflammatory effect of EA treatment could be partially associated with suppression of pro-inflammatory cytokines mediated by induction of IL-10.

Antigen-Specific Regulatory T Cell Therapy in Autoimmune Diseases and Transplantation

Regulatory T (Treg) cells are a heterogenous population of immunosuppressive T cells whose therapeutic potential for the treatment of autoimmune diseases and graft rejection is currently being explored. While clinical trial results thus far support the safety and efficacy of adoptive therapies using polyclonal Treg cells, some studies suggest that antigen-specific Treg cells are more potent in regulating and improving immune tolerance in a disease-specific manner. Hence, several approaches to generate and/or expand antigen-specific Treg cells in vitro or in vivo are currently under investigation. However, antigen-specific Treg cell therapies face additional challenges that require further consideration, including the identification of disease-relevant antigens as well as the in vivo stability and migratory behavior of Treg cells following transfer. In this review, we discuss these approaches and the potential limitations and describe prospective strategies to enhance the efficacy of antigen-specific Treg cell treatments in autoimmunity and transplantation.

T Cells as Guardians of Pain Resolution

Despite successful research efforts aimed at understanding pain mechanisms, there is still no adequate treatment for many patients suffering from chronic pain. The contribution of neuroinflammation to chronic pain is widely acknowledged. Here, we summarize findings indicating that T cells play a key role in the suppression of pain. An active contribution of the immune system to resolution of pain may explain why immunosuppressive drugs are often not sufficient to control pain. This would also imply that dysregulation of certain immune functions promote transition to chronic pain. Conversely, stimulating the endogenous immune-mediated resolution pathways may provide a potent approach to treat chronic pain.

Cytokines that Modulate the Differentiation of Th17 Cells in Autoimmune Uveitis

Increasing evidence has suggested that T helper 17 (Th17) cells play a central role in the pathogenesis of ocular immune disease. The association between pathogenic Th17 cells and the development of uveitis has been confirmed in experimental and clinical studies. Several cytokines affect the initiation and stabilization of the differentiation of Th17 cells. Therefore, understanding the mechanism of related cytokines in the differentiation of Th17 cells is important for exploring the pathogenesis and the potential therapeutic targets of uveitis. This article briefly describes the structures, mechanisms, and targeted drugs of cytokines-including interleukin (IL)-6, transforming growth factor-β1 (TGF-β1), IL-1β, IL-23, IL-27, IL-35, IL-2, IL-4, IL-21, and interferon (IFN)-γ-which have an important influence on the differentiation of Th17 cells and discusses their potential as therapeutic targets for treating autoimmune uveitis.

Role of Peripheral Immune Cells for Development and Recovery of Chronic Pain

Chronic neuropathic pain (CNP) is caused by a lesion or disease of the somatosensory nervous system. It affects ~8% of the general population and negatively impacts a person's level of functioning and quality of life. Its resistance to available pain therapies makes CNP a major unmet medical need. Immune cells have been shown to play a role for development, maintenance and recovery of CNP and therefore are attractive targets for novel pain therapies. In particular, in neuropathic mice and humans, microglia are activated in the dorsal horn and peripheral immune cells infiltrate the nervous system to promote chronic neuroinflammation and contribute to the initiation and progression of CNP. Importantly, immunity not only controls pain development and maintenance, but is also essential for pain resolution. In particular, regulatory T cells, a subpopulation of T lymphocytes with immune regulatory function, and macrophages were shown to be important contributors to pain recovery. In this review we summarize the interactions of the peripheral immune system with the nervous system and outline their contribution to the development and recovery of pain.

Potential therapeutic effects of interleukin-35 on the differentiation of naïve T cells into Helios+Foxp3+ Tregs in clinical and experimental acute respiratory distress syndrome

Regulatory T lymphocytes are important targets for the treatment of acute respiratory distress syndrome (ARDS). IL-35 is a newly identified IL-12 cytokine family member that plays an important protective role in a variety of immune system diseases by regulating Treg cell differentiation; however, the role of IL-35 in the pathogenesis of ARDS is still unclear. Here, we found that IL-35 was significantly elevated in adult patients with ARDS compared to controls. Additionally, IL-35 was positively and significantly correlated with IL-6, IL-10 and the oxygenation index (PaO2/FiO2 ratio) but negatively correlated with TNF-α, IL-1β and APACHE II score during ARDS. Moreover, the proportion of Treg/CD4⁺ cells in the peripheral blood of ARDS patients and the expression of NF-κB in PMBCs were significantly higher than in healthy individuals. Recombinant IL-35 improved survival in a murine model of CLP-induced ARDS. Additionally, IL-35 administration decreased the inflammatory response, as reflected by lower levels of cytokines (including IL-2, TNF-α, IL-1β and IL-6) and less lung damage in CLP-induced ARDS. Furthermore, recombinant IL-35 reduced the apoptosis of lung tissue and the expression of NF-κB signalling in a CLP-induced ARDS model and increased the proportion of Treg cells in spleen and peripheral blood. In vitro experiments revealed that IL-35 can affect the phosphorylation of STAT5 during differentiation of naïve CD4⁺ T lymphocytes into Foxp3⁺Helios⁺ Tregs. Our findings suggest that IL-35 attenuates ARDS by promoting the differentiation of naïve CD4⁺ T cells into Foxp3⁺Helios⁺ Tregs, thereby providing a novel tool for anti-ARDS therapy.

Administration of CD4+CD25highCD127-FoxP3+ Regulatory T Cells for Relapsing-Remitting Multiple Sclerosis: A Phase 1 Study

BACKGROUND

Multiple sclerosis (MS) is an immune-mediated disease in which autoimmune T conventional (T_conv) cells break the blood-brain barrier and destroy neurons of the central nervous system. It is hypothesized that CD4⁺CD25^highCD127^-FoxP3⁺ T regulatory (T_reg) cells may inhibit this destruction through suppressive activity exerted on T_conv cells.

METHODS

We present the results of a phase 1b/2a, open-label, two-arm clinical trial in 14 patients treated with autologous T_reg cells for relapsing-remitting MS. The patients received either expanded ex vivo T_reg cells intravenously (intravenous [IV] group, n = 11; dose 40 × 10⁶ T_reg cells/kg of body weight) or freshly isolated T_reg cells intrathecally (intrathecal [IT] group, n = 3; dose 1.0 × 10⁶ T_reg cells). Importantly, patients were not treated with any other disease-modifying drugs for at least 6 months before the recruitment and during the follow-up.

RESULTS

No severe adverse events were observed. Self-assessed quality of life (EuroQol-5 Dimensions [EQ-5D] form) did not change and did not differ significantly between the groups. A total of 12 relapses were noted in five intravenously treated patients, who had from one to three attacks per year. Three out of ten participants who completed the trial in the IV group deteriorated more than 1 point on the Expanded Disability Status Scale (EDSS) during the follow-up. At the same time, no patients in the IT group experienced a relapse or such a deterioration in the EDSS. No significant differences were found in the Multiple Sclerosis Functional Composite (MSFC) scale in both the IV and IT groups. Magnetic resonance imaging (MRI) scans revealed a significantly lower change in the T2 lesion volume in the IT group compared to the IV group. The increase in the number of new T2 lesions during the follow-up was significant for the IV group only. There were no significant changes in the level of T_reg cells or T_conv cells in the peripheral blood throughout the follow-up or between the groups. Interestingly, T_reg cells in all patients consisted of two different phenotypes: peripheral T_reg cells Helios(-) (≈ 20%) and thymic T_reg cells Helios(+) (≈ 80%). The analysis of the cytokine pattern revealed higher levels of transforming growth factor-α and proinflammatory factors MCP3, CXCL8, and IL-1RA in the IT group compared with the IV group.

CONCLUSIONS

No serious adverse events were reported in the 14 patients with MS treated with T_reg cells in this study. The results suggest that IT administration is more promising than IV administration. Because of the low number of patients recruited, the statistical results may be underpowered and further studies are necessary to reach conclusions on efficacy and safety.

TRIAL REGISTRATION

EudraCT: 2014-004320-22; registered 18 November 2014.

Regulating the regulators: Is introduction of an antigen-specific approach in regulatory T cells the next step to treat autoimmunity?

In autoimmunity, the important and fragile balance between immunity and tolerance is disturbed, resulting in abnormal immune responses to the body's own tissues and cells. CD4⁺CD25^hiFoxP3⁺ regulatory T cells (Tregs) induce peripheral tolerance in vivo by means of direct cell-cell contact and release of soluble factors, or indirectly through antigen-presenting cells (APC), thereby controlling auto-reactive effector T cells. Based on these unique capacities of Tregs, preclinical studies delivered proof-of-principle for the clinical use of Tregs for the treatment of autoimmune diseases. To date, the first clinical trials using ex vivo expanded polyclonal Tregs have been completed. These pioneering studies demonstrate the feasibility of generating large numbers of polyclonal Tregs in a good manufacturing practices (GMP)-compliant manner, and that infusion of Tregs is well tolerated by patients with no evidence of general immunosuppression. Nonetheless, only modest clinical results were observed, arguing that a more antigen-specific approach might be needed to foster a durable patient-specific clinical cell therapy without the risk for general immunosuppression. In this review, we discuss current knowledge, applications and future goals of adoptive immune-modulatory Treg therapy for the treatment of autoimmune disease and transplant rejection. We describe the key advances and prospects of the potential use of T cell receptor (TCR)- and chimeric antigen receptor (CAR)-engineered Tregs in future clinical applications. These approaches could deliver the long-awaited breakthrough in stopping undesired autoimmune responses and transplant rejections.

Glial cell activation and altered metabolic profile in the spinal-trigeminal axis in a rat model of multiple sclerosis associated with the development of trigeminal sensitization

Trigeminal neuralgia is often an early symptom of multiple sclerosis (MS), and it generally does not correlate with the severity of the disease. Thus, whether it is triggered simply by demyelination in specific central nervous system areas is currently questioned. Our aims were to monitor the development of spontaneous trigeminal pain in an animal model of MS, and to analyze: i) glial cells, namely astrocytes and microglia in the central nervous system and satellite glial cells in the trigeminal ganglion, and ii) metabolic changes in the trigeminal system. The subcutaneous injection of recombinant MOG_1-125 protein fragment to Dark Agouti male rats led to the development of relapsing-remitting EAE, with a first peak after 13 days, a remission stage from day 16 and a second peak from day 21. Interestingly, orofacial allodynia developed from day 1 post injection, i.e. well before the onset of EAE, and worsened over time, irrespective of the disease phase. Activation of glial cells both in the trigeminal ganglia and in the brainstem, with no signs of demyelination in the latter tissue, was observed along with metabolic alterations in the trigeminal ganglion. Our data show, for the first time, the spontaneous development of trigeminal sensitization before the onset of relapsing-remitting EAE in rats. Additionally, pain is maintained elevated during all stages of the disease, suggesting the existence of parallel mechanisms controlling motor symptoms and orofacial pain, likely involving glial cell activation and metabolic alterations which can contribute to trigger the sensitization of sensory neurons.

Regulatory T cells counteract neuropathic pain through inhibition of the Th1 response at the site of peripheral nerve injury

The inflammatory/immune response at the site of peripheral nerve injury participates in the pathophysiology of neuropathic pain. Nevertheless, little is known about the local regulatory mechanisms underlying peripheral nerve injury that counteracts the development of pain. Here, we investigated the contribution of regulatory T (Treg) cells to the development of neuropathic pain by using a partial sciatic nerve ligation model in mice. We showed that Treg cells infiltrate and proliferate in the site of peripheral nerve injury. Local Treg cells suppressed the development of neuropathic pain mainly through the inhibition of the CD4 Th1 response. Treg cells also indirectly reduced neuronal damage and neuroinflammation at the level of the sensory ganglia. Finally, we identified IL-10 signaling as an intrinsic mechanism by which Treg cells counteract neuropathic pain development. These results revealed Treg cells as important inhibitory modulators of the immune response at the site of peripheral nerve injury that restrains the development of neuropathic pain. In conclusion, the boosting of Treg cell function/activity might be explored as a possible interventional approach to reduce neuropathic pain development after peripheral nerve damage.

Novel Analgesics with Peripheral Targets

A limited number of peripheral targets generate pain. Inflammatory mediators can sensitize these. The review addresses targets acting exclusively or predominantly on sensory neurons, mediators involved in inflammation targeting sensory neurons, and mediators involved in a more general inflammatory process, of which an analgesic effect secondary to an anti-inflammatory effect can be expected. Different approaches to address these systems are discussed, including scavenging proinflammatory mediators, applying anti-inflammatory mediators, and inhibiting proinflammatory or facilitating anti-inflammatory receptors. New approaches are contrasted to established ones; the current stage of progress is mentioned, in particular considering whether there is data from a molecular and cellular level, from animals, or from human trials, including an early stage after a market release. An overview of publication activity is presented, considering a IuPhar/BPS-curated list of targets with restriction to pain-related publications, which was also used to identify topics.

Low-dose interleukin-2 reverses behavioral sensitization in multiple mouse models of headache disorders

Headache disorders are highly prevalent and debilitating, with limited treatment options. Previous studies indicate that many proinflammatory immune cells contribute to headache pathophysiology. Given the well-recognized role of regulatory T (Treg) cells in maintaining immune homeostasis, we hypothesized that enhancing Treg function may be effective to treat multiple headache disorders. In a mouse model of chronic migraine, we observed that repeated nitroglycerin (NTG, a reliable trigger of migraine in patients) administration doubled the number of CD3 T cells in the trigeminal ganglia without altering the number of Treg cells, suggesting a deficiency in Treg-mediated immune homeostasis. We treated mice with low-dose interleukin-2 (ld-IL2) to preferentially expand and activate endogenous Treg cells. This not only prevented the development of NTG-induced persistent sensitization but also completely reversed the established facial skin hypersensitivity resulting from repeated NTG administration. The effect of ld-IL2 was independent of mouse sex and/or strain. Importantly, ld-IL2 treatment did not alter basal nociceptive responses, and repeated usage did not induce tolerance. The therapeutic effect of ld-IL2 was abolished by Treg depletion and was recapitulated by Treg adoptive transfer. Furthermore, treating mice with ld-IL2 1 to 7 days after mild traumatic brain injury effectively prevented as well as reversed the development of behaviors related to acute and chronic post-traumatic headache. In a model of medication overuse headache, Ld-IL2 completely reversed the cutaneous hypersensitivity induced by repeated administration of sumatriptan. Collectively, this study identifies ld-IL2 as a promising prophylactic for multiple headache disorders with a mechanism distinct from the existing treatment options.

Qualitative sex differences in pain processing: emerging evidence of a biased literature

Although most patients with chronic pain are women, the preclinical literature regarding pain processing and the pathophysiology of chronic pain has historically been derived overwhelmingly from the study of male rodents. This Review describes how the recent adoption by a number of funding agencies of policies mandating the incorporation of sex as a biological variable into preclinical research has correlated with an increase in the number of studies investigating sex differences in pain and analgesia. Trends in the field are analysed, with a focus on newly published findings of qualitative sex differences: that is, those findings that are suggestive of differential processing mechanisms in each sex. It is becoming increasingly clear that robust differences exist in the genetic, molecular, cellular and systems-level mechanisms of acute and chronic pain processing in male and female rodents and humans.

Tanshinone IIA Ameliorates CNS Autoimmunity by Promoting the Differentiation of Regulatory T Cells

Tanshinone IIA (TSA), an important natural lipophilic diterpene compound from the traditional Chinese herb Salvia miltiorrhiza Bunge, has long been widely used for the prevention and treatment of various diseases because of its anti-inflammatory activities; however, the anti-inflammatory mechanism remains unknown. In the present work, we examined the effects of TSA on experimental autoimmune encephalomyelitis (EAE), a model of autoreactive T/B cell-mediated central nervous system (CNS) autoimmunity. The data showed that TSA significantly attenuates the severity of EAE when administered at the pre-onset and peak of clinical disease. In vivo, the protective effects of TSA on EAE mice are correlated with diminished inflammatory infiltration, demyelination, and GM-CSF-producing CD4+ T cells in the spinal cord and selectively increased regulatory T (Treg) cell frequencies in both the spinal cord and spleen. We further confirm that TSA can promote the polarization of naïve CD4+ T cells into Treg cells both by targeting dendritic cells (DCs) to drive transforming growth factor β1 (TGF-β1) upregulation and by directly targeting naïve CD4+ T cells in vitro. Most importantly, we showed that TSA-induced Treg cells display an effective suppressive activity at a level comparable to TGF-β1-polarized Treg Cells in vitro and in vivo. Taken together, our data provide evidence that TSA can promote Treg cell differentiation, and TSA may have a promising application as a therapeutic agent for the treatment of neuroinflammatory diseases.

Neuronal, stromal, and T-regulatory cell crosstalk in murine skeletal muscle

A distinct population of Foxp3+CD4+ regulatory T (Treg) cells promotes repair of acutely or chronically injured skeletal muscle. The accumulation of these cells depends critically on interleukin (IL)-33 produced by local mesenchymal stromal cells (mSCs). An intriguing physical association among muscle nerves, IL-33+ mSCs, and Tregs has been reported, and invites a deeper exploration of this cell triumvirate. Here we evidence a striking proximity between IL-33+ muscle mSCs and both large-fiber nerve bundles and small-fiber sensory neurons; report that muscle mSCs transcribe an array of genes encoding neuropeptides, neuropeptide receptors, and other nerve-related proteins; define muscle mSC subtypes that express both IL-33 and the receptor for the calcitonin-gene-related peptide (CGRP); and demonstrate that up- or down-tuning of CGRP signals augments or diminishes, respectively, IL-33 production by muscle mSCs and later accumulation of muscle Tregs. Indeed, a single injection of CGRP induced much of the genetic program elicited in mSCs early after acute skeletal muscle injury. These findings highlight neural/stromal/immune-cell crosstalk in tissue repair, suggesting future therapeutic approaches.

Nociception in a Progressive Multiple Sclerosis Model in Mice Is Dependent on Spinal TRPA1 Channel Activation

Central neuropathic pain is a common untreated symptom in progressive multiple sclerosis (PMS) and is associated with poor quality of life and interference with patients' daily activities. The neuroinflammation process and mitochondrial dysfunction in the PMS lesions generate reactive species. The transient potential receptor ankyrin 1 (TRPA1) has been identified as one of the major mechanisms that contribute to neuropathic pain signaling and can be activated by reactive compounds. Thus, the goal of our study was to evaluate the role of spinal TRPA1 in the central neuropathic pain observed in a PMS model in mice. We used C57BL/6 female mice (20-30 g), and the PMS model was induced by the experimental autoimmune encephalomyelitis (EAE) using mouse myelin oligodendrocyte glycoprotein (MOG_35-55) antigen and CFA (complete Freund's adjuvant). Mice developed progressive clinical score, with motor impairment observed after 15 days of induction. This model induced mechanical and cold allodynia and heat hyperalgesia which were measured up to 14 days after induction. The hypersensitivity observed was reduced by the administration of selective TRPA1 antagonists (HC-030031 and A-967079, via intrathecal and intragastric), antioxidants (α-lipoic acid and apocynin, via intrathecal and intragastric), and TRPA1 antisense oligonucleotide (via intrathecal). We also observed an increase in TRPA1 mRNA levels, NADPH oxidase activity, and 4-hydroxinonenal (a TRPA1 agonist) levels in spinal cord samples of PMS-EAE induced animals. In conclusion, these results support the hypothesis of the TRPA1 receptor involvement in nociception observed in a PMS-EAE model in mice.

Neuraxial Cytokines in Pain States

A high-intensity potentially tissue-injuring stimulus generates a homotopic response to escape the stimulus and is associated with an affective phenotype considered to represent pain. In the face of tissue or nerve injury, the afferent encoding systems display robust changes in the input–output function, leading to an ongoing sensation reported as painful and sensitization of the nociceptors such that an enhanced pain state is reported for a given somatic or visceral stimulus. Our understanding of the mechanisms underlying this non-linear processing of nociceptive stimuli has led to our appreciation of the role played by the functional interactions of neural and immune signaling systems in pain phenotypes. In pathological states, neural systems interact with the immune system through the actions of a variety of soluble mediators, including cytokines. Cytokines are recognized as important mediators of inflammatory and neuropathic pain, supporting system sensitization and the development of a persistent pathologic pain. Cytokines can induce a facilitation of nociceptive processing at all levels of the neuraxis including supraspinal centers where nociceptive input evokes an affective component of the pain state. We review here several key proinflammatory and anti-inflammatory cytokines/chemokines and explore their underlying actions at four levels of neuronal organization: (1) peripheral nociceptor termini; (2) dorsal root ganglia; (3) spinal cord; and (4) supraspinal areas. Thus, current thinking suggests that cytokines by this action throughout the neuraxis play key roles in the induction of pain and the maintenance of the facilitated states of pain behavior generated by tissue injury/inflammation and nerve injury.

CD3+ T cells are critical for the resolution of comorbid inflammatory pain and depression-like behavior

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T cells are necessary for resolution of CFA-induced mechanical allodynia and spontaneous pain.

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T cells are required for the resolution of inflammation-induced depression-like behavior.

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T cells did not contribute to onset or severity of indicators of pain and depression-like behavior.

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T cells did not affect cytokine expression in the paw, spinal cord and brain.

Background

Chronic pain and depression often co-occur. The mechanisms underlying this comorbidity are incompletely understood. Here, we investigated the role of CD3⁺ T cells in an inflammatory model of comorbid persistent mechanical allodynia, spontaneous pain, and depression-like behavior in mice.

Methods

C57Bl/6 wt and Rag2^−/− mice were compared in their response to intraplantar administration of complete Freund’s adjuvant (CFA). Mechanical allodynia, spontaneous pain and depression-like behavior were assessed by von Frey, conditioned place preference and forced swim test respectively.

Results

Resolution of mechanical allodynia, spontaneous pain, and depression-like behavior was markedly delayed in Rag2^−/− mice that are devoid of adaptive immune cells. Reconstitution of Rag2^−/− mice with CD3⁺ T cells from WT mice before CFA injection normalized the resolution of indicators of pain and depression-like behavior. T cells did not contribute to onset or severity of indicators of pain and depression-like behavior. The lack of T cells did not affect cytokine expression in the paw, spinal cord and brain, indicating that the delayed resolution was not resulting from prolonged (neuro)inflammation.

Conclusions

Our findings show that T cells are critical for the natural resolution of mechanical allodynia, spontaneous pain, and depression-like behavior after an inflammatory challenge. Dysregulation of this T cell-mediated resolution pathway could contribute to the comorbidity of chronic pain and depression.

Significance

Chronic pain and depression are frequently associated with signs of inflammation. However, general immunosuppression is not sufficient to resolve comorbid pain and depression. Here we demonstrate that T cells are required for resolution of comorbid persistent mechanical allodynia, spontaneous pain, and depression in a model of peripheral inflammation, indicating the immune system can contribute to both onset and resolution of these comorbidities. Enhancing pro-resolution effects of T cells may have a major impact to treat patients with comorbid persistent pain and depression.

High Speed Ventral Plane Videography as a Convenient Tool to Quantify Motor Deficits during Pre-Clinical Experimental Autoimmune Encephalomyelitis

Experimental autoimmune encephalomyelitis (EAE) is the most commonly used multiple sclerosis animal model. EAE mice typically develop motor deficits in a caudal-to-rostral pattern when inflammatory lesions have already developed. However, to monitor more subtle behavioral deficits during lesion development (i.e., pre-clinical phase), more sophisticated methods are needed. Here, we investigated whether high speed ventral plane videography can be applied to monitor early motor deficits during ‘pre-clinical’ EAE. For this purpose, EAE was induced in C57BL/6 mice and gait abnormalities were quantified using the DigiGait™ apparatus. Gait deficits were related to histopathological changes. 10 out of 10 control (100%), and 14 out of 18 (77.8%) pre-clinical EAE mice could be evaluated using DigiGait™. EAE severity was not influenced by DigiGait™-related mice handlings. Most gait parameters recorded from day 6 post-immunization until the end of the experiment were found to be stable in control mice. During the pre-clinical phase, when conventional EAE scorings failed to detect any functional impairment, EAE mice showed an increased Swing Time, increased %Swing Stride, decreased %Stance Stride, decreased Stance/Swing, and an increased Absolute Paw Angle. In summary, DigiGait™ is more sensitive than conventional scoring approaches to study motor deficits during the EAE pre-clinical phase.

Exogenous activation of tumor necrosis factor receptor 2 promotes recovery from sensory and motor disease in a model of multiple sclerosis

Tumor necrosis factor receptor 2 (TNFR2) is a transmembrane receptor that promotes immune modulation and tissue regeneration and is recognized as a potential therapeutic target for multiple sclerosis (MS). However, TNFR2 also contributes to T effector cell function and macrophage-TNFR2 recently was shown to promote disease development in the experimental autoimmune encephalomyelitis (EAE) model of MS. We here demonstrate that systemic administration of a TNFR2 agonist alleviates peripheral and central inflammation, and reduces demyelination and neurodegeneration, indicating that protective signals induced by TNFR2 exceed potential pathogenic TNFR2-dependent responses. Our behavioral data show that systemic treatment of female EAE mice with a TNFR2 agonist is therapeutic on motor symptoms and promotes long-term recovery from neuropathic pain. Mechanistically, our data indicate that TNFR2 agonist treatment follows a dual mode of action and promotes both suppression of CNS autoimmunity and remyelination. Strategies based on the concept of exogenous activation of TNFR2 therefore hold great promise as a new therapeutic approach to treat motor and sensory disease in MS as well as other inflammatory diseases or neuropathic pain conditions.

T Cells as an Emerging Target for Chronic Pain Therapy

The immune system is critically involved in the development and maintenance of chronic pain. However, T cells, one of the main regulators of the immune response, have only recently become a focus of investigations on chronic pain pathophysiology. Emerging clinical data suggest that patients with chronic pain have a different phenotypic profile of circulating T cells compared to controls. At the preclinical level, findings on the function of T cells are mixed and differ between nerve injury, chemotherapy, and inflammatory models of persistent pain. Depending on the type of injury, the subset of T cells and the sex of the animal, T cells may contribute to the onset and/or the resolution of pain, underlining T cells as a major player in the transition from acute to chronic pain. Specific T cell subsets release mediators such as cytokines and endogenous opioid peptides that can promote, suppress, or even resolve pain. Inhibiting the pain-promoting functions of T cells and/or enhancing the beneficial effects of pro-resolution T cells may offer new disease-modifying strategies for the treatment of chronic pain, a critical need in view of the current opioid crisis.

Interleukin-35 stimulates tumor necrosis factor-α activated osteoblasts differentiation through Wnt/β-catenin signaling pathway in rheumatoid arthritis

Interleukin (IL)-35 plays an important role in the pathogenesis of rheumatoid arthritis (RA), which is characterized by tumor necrosis factor (TNF)-α activated bone loss beginning early and persisting over time. The aim of this study was to explore the effects and signaling pathway of IL-35 on osteoblasts differentiation in MC3T3E1 cells and TNF-α activated MC3T3E1 cells. A microenvironment was established with low concentration and short-term treatment of TNF-α to mimic inflammatory activated osteoblasts of RA in vitro. The role of IL-35 on osteoblasts proliferation and apoptosis were assessed using cell counting kit (CCK)-8 assay and flow cytometry, respectively. Alkaline phosphatase (ALP) activity was measured by p-nitrophenyl phosphate assay. Extracellular matrix mineralization was measured by Alizarin red S staining. Osteoprotegerin (OPG) and receptor activator of nuclear factor-κB ligand (RANKL) in response to IL-35 were investigated using real-time polymerase chain reaction and western blot analysis. Wnt/β-catenin signaling pathway in osteoblasts was investigated. In basal and TNF-α activated osteoblasts, IL-35 promoted proliferation and inhibited apoptosis. Basal and TNF-α activated ALP activity and mineralization in vitro was increased stimulated by IL-35. Furthermore, IL-35 increased the basal and TNF-α activated OPG expression and decreased basal and TNF-α activated RANKL expression. Blocking Wnt/β-catenin signaling pathway with Dickkopf (Dkk)-1 inhibited the osteogenic effects of IL-35. IL-35 stimulates basal and TNF-α activated osteoblasts differentiation through the Wnt/β-catenin signaling pathway, thus highlighting the IL-35 for pharmaceutical and medicinal applications for treating RA bone loss.

Akt3-Mediated Protection Against Inflammatory Demyelinating Disease

Akt is a serine/threonine protein kinase that plays a major role in regulating multiple cellular processes. While the isoforms Akt1 and Akt2 are involved in apoptosis and insulin signaling, respectively, the role for Akt3 remains uncertain. Akt3 is predominantly expressed in the brain, and total deletion of Akt3 in mice results in a reduction in brain size and neurodegeneration following injury. Previously, we found that Akt3-/- mice have a significantly worse clinical course during myelin-oligodendrocyte glycoprotein (MOG)-induced experimental autoimmune encephalomyelitis (EAE), an animal model in which autoreactive immune cells enter the CNS, resulting in inflammation, demyelination, and axonal injury. Spinal cords of Akt3-/- mice are severely demyelinated and have increased inflammation compared to WT, suggesting a neuroprotective role for Akt3 during EAE. To specifically address the role of Akt3 in neuroinflammation and maintaining neuronal integrity, we used several mouse strains with different manipulations to Akt3. During EAE, Akt3 Nmf350 mice (with enhanced Akt3 kinase activity) had lower clinical scores, a lag in disease onset, a delay in the influx of inflammatory cells into the CNS, and less axonal damage compared to WT mice. A significant increased efficiency of differentiation toward FOXP3 expressing iTregs was also observed in Akt3 Nmf350 mice relative to WT. Mice with a conditional deletion of Akt3 in CD4+ T-cells had an earlier onset of EAE symptoms, increased inflammation in the spinal cord and brain, and had fewer FOXP3+ cells and FOXP3 mRNA expression. No difference in EAE outcome was observed when Akt3 expression was deleted in neurons (Syn1-CKO). These results indicate that Akt3 signaling in T-cells and not neurons is necessary for maintaining CNS integrity during an inflammatory demyelinating disease.

Continuous infusion of an agonist of the tumor necrosis factor receptor 2 in the spinal cord improves recovery after traumatic contusive injury

Aim

The activation of the TNFR2 receptor is beneficial in several pathologies of the central nervous system, and this study examines whether it can ameliorate the recovery process following spinal cord injury.

Methods

EHD2‐sc‐mTNF_R2, an agonist specific for TNFR2, was used to treat neurons exposed to high levels of glutamate in vitro. In vivo, it was infused directly to the spinal cord via osmotic pumps immediately after a contusion to the cord at the T9 level. Locomotion behavior was assessed for 6 weeks, and the tissue was analyzed (lesion size, RNA and protein expression, cell death) after injury. Somatosensory evoked potentials were also measured in response to hindlimb stimulation.

Results

The activation of TNFR2 protected neurons from glutamate‐mediated excitotoxicity through the activation of phosphoinositide‐3 kinase gamma in vitro and improved the locomotion of animals following spinal cord injury. The extent of the injury was not affected by infusing EHD2‐sc‐mTNF_R2, but higher levels of neurofilament H and 2′, 3′‐cyclic‐nucleotide 3′‐phosphodiesterase were observed 6 weeks after the injury. Finally, the activation of TNFR2 after injury increased the neural response recorded in the cortex following hindlimb stimulation.

Conclusion

The activation of TNFR2 in the spinal cord following contusive injury leads to enhanced locomotion and better cortical responses to hindlimb stimulation.