Oligodendrocytes exhibit selective expression of suppressor of cytokine signaling genes and signal transducer and activator of transcription 1 independent inhibition of interferon-gamma-induced toxicity in response to leukemia inhibitory factor

hsa-MiR-19a-3p and hsa-MiR-19b-3p Are Associated with Spinal Cord Injury-Induced Neuropathic Pain: Findings from a Genome-Wide MicroRNA Expression Profiling Screen

Neuropathic pain in spinal cord injury (SCI) is associated with inflammation in both the peripheral and central nervous system (CNS), which may contribute to the initiation and maintenance of persistent pain. An understanding of factors contributing to neuroinflammation may lead to new therapeutic targets for neuropathic pain. Moreover, novel circulating biomarkers of neuropathic pain may facilitate earlier and more effective treatment. MicroRNAs (miRNAs) are short, non-coding single-stranded RNA that have emerged as important biomarkers and molecular mediators in physiological and pathological conditions. Using a genome-wide miRNA screening approach, we studied differential miRNA expression in plasma from 68 healthy, community-dwelling adults with and without SCI enrolled in ongoing clinical studies. We detected 2367 distinct miRNAs. Of these, 383 miRNAs were differentially expressed in acute SCI or chronic SCI versus no SCI and 71 were differentially expressed in chronic neuropathic pain versus no neuropathic pain. We selected homo sapiens (hsa)-miR-19a-3p and hsa-miR-19b-3p for additional analysis based on p-value, fold change, and their known role as regulators of neuropathic pain and neuroinflammation. Both hsa-miR-19a-3p and hsa-miR-19b-3p levels were significantly higher in those with chronic SCI and severe neuropathic pain versus those with chronic SCI and no neuropathic pain. In confirmatory studies, both hsa-miR-19a-3p and hsa-miR-19b-3p have moderate to strong discriminative ability to distinguish between those with and without pain. After adjusting for opioid use, hsa-miR-19b-3p levels were positively associated with pain interference with mood. Because hsa-miR-19 levels have been shown to change in response to exercise, folic acid, and resveratrol, these studies suggest that miRNAs are potential targets of therapeutic interventions.

Regulation of Macrophage, Dendritic Cell, and Microglial Phenotype and Function by the SOCS Proteins

Macrophages are innate immune cells of dynamic phenotype that rapidly respond to external stimuli in the microenvironment by altering their phenotype to respond to and to direct the immune response. The ability to dynamically change phenotype must be carefully regulated to prevent uncontrolled inflammatory responses and subsequently to promote resolution of inflammation. The suppressor of cytokine signaling (SOCS) proteins play a key role in regulating macrophage phenotype. In this review, we summarize research to date from mouse and human studies on the role of the SOCS proteins in determining the phenotype and function of macrophages. We will also touch on the influence of the SOCS on dendritic cell (DC) and microglial phenotype and function. The molecular mechanisms of SOCS function in macrophages and DCs are discussed, along with how dysregulation of SOCS expression or function can lead to alterations in macrophage/DC/microglial phenotype and function and to disease. Regulation of SOCS expression by microRNA is discussed. Novel therapies and unanswered questions with regard to SOCS regulation of monocyte-macrophage phenotype and function are highlighted.

SOCS3, a Major Regulator of Infection and Inflammation

In this review, we describe the role of suppressor of cytokine signaling-3 (SOCS3) in modulating the outcome of infections and autoimmune diseases as well as the underlying mechanisms. SOCS3 regulates cytokine or hormone signaling usually preventing, but in some cases aggravating, a variety of diseases. A main role of SOCS3 results from its binding to both the JAK kinase and the cytokine receptor, which results in the inhibition of STAT3 activation. Available data also indicate that SOCS3 can regulate signaling via other STATs than STAT3 and also controls cellular pathways unrelated to STAT activation. SOCS3 might either act directly by hampering JAK activation or by mediating the ubiquitination and subsequent proteasome degradation of the cytokine/growth factor/hormone receptor. Inflammation and infection stimulate SOCS3 expression in different myeloid and lymphoid cell populations as well as in diverse non-hematopoietic cells. The accumulated data suggest a relevant program coordinated by SOCS3 in different cell populations, devoted to the control of immune homeostasis in physiological and pathological conditions such as infection and autoimmunity.

Traumatic brain injury, neuroinflammation, and post-traumatic headaches

Concussions following head and/or neck injury are common, and although most people with mild injuries recover uneventfully, a subset of individuals develop persistent post-concussive symptoms that often include headaches. Post-traumatic headaches vary in presentation and may progress to become chronic and in some cases debilitating. Little is known about the pathogenesis of post-traumatic headaches, although shared pathophysiology with that of the brain injury is suspected. Following primary injury to brain tissues, inflammation rapidly ensues; while this inflammatory response initially provides a defensive/reparative function, it can persist beyond its beneficial effect, potentially leading to secondary injuries because of alterations in neuronal excitability, axonal integrity, central processing, and other changes. These changes may account for the neurological symptoms often observed after traumatic brain injury, including headaches. This review considers selected aspects of the inflammatory response following traumatic brain injury, with an emphasis on the role of glial cells as mediators of maladaptive post-traumatic inflammation.

Therapeutic potential of LIF in multiple sclerosis

Therapies for multiple sclerosis (MS) reduce the relapse rate but are unable to stop neurological decline. Here, we evaluate the potential of leukemia inhibitory factor (LIF) as a novel therapeutic in diseases with a neurodegenerative and inflammatory component, such as MS. LIF, which can be a proinflammatory cytokine, can also modulate the immune response in a beneficial way. Recent evidence demonstrates a crucial role of LIF in neuroprotection and axonal regeneration as well as the prevention of demyelination. Finally, LIF is an important survival factor for stem cells and neuronal precursors. Therefore, we propose that LIF is a potential therapeutic candidate for MS.

Pathological and protective roles of glia in chronic pain

Glia have emerged as key contributors to pathological and chronic pain mechanisms. On activation, both astrocytes and microglia respond to and release a number of signalling molecules, which have protective and/or pathological functions. Here we review the current understanding of the contribution of glia to pathological pain and neuroprotection, and how the protective, anti-inflammatory actions of glia are being harnessed to develop new drug targets for neuropathic pain control. Given the prevalence of chronic pain and the partial efficacy of current drugs, which exclusively target neuronal mechanisms, new strategies to manipulate neuron-glia interactions in pain processing hold considerable promise.

Leukemia inhibitory factor induces an antiapoptotic response in oligodendrocytes through Akt-phosphorylation and up-regulation of 14-3-3

Leukemia inhibitory factor (LIF) promotes the survival of oligodendrocytes (OLG) both in vitro and in an animal model of multiple sclerosis. Here, we show that LIF protects mature rat OLG cultures selectively against the combined insult of the proinflammatory cytokines interferon-gamma and tumor necrosis factor-alpha, but it does not protect against oxidative stress nor against staurosporine induced apoptosis. We further demonstrate that LIF activates the janus kinase (JAK)/signal transducer and activator of transcription 3 (STAT3) and the phosphatidylinositol 3 kinase/Akt pathway in mature OLG. We show that LIF protection is independent of suppressors of cytokine signaling and Bcl-2 mRNA expression levels. To gain further insight into the protective mechanism, a quantitative proteomic approach (DIGE) was applied to identify differentially expressed proteins in LIF-treated OLG. Our results indicate that LIF induces a shift in the cellular machinery toward a prosurvival execution program, illustrated by an enhanced expression of isoforms of the antiapoptotic molecule 14-3-3. These data provide further insight into the mechanisms of LIF-mediated protection of mature OLGs.

Interferon-gamma-oligodendrocyte interactions in the regulation of experimental autoimmune encephalomyelitis

Experimental autoimmune encephalomyelitis (EAE) is an animal model of the human demyelinating disorder multiple sclerosis (MS). The immune cytokine interferon-gamma (IFN-gamma) is believed to participate in disease pathogenesis in both EAE and MS. In the present study, we examined the significance of IFN-gamma-oligodendrocyte interactions in the course of EAE. For the purpose of our study, we used the previously described [proteolipid protein/suppressor of cytokine signaling 1 (PLP/SOCS1)] transgenic mouse line that displays suppressed oligodendrocyte responsiveness to IFN-gamma. PLP/SOCS1 mice developed EAE with an accelerated onset associated with enhanced early inflammation and markedly increased oligodendrocyte apoptosis. Moreover, we found that IFN-gamma pretreatment of mature oligodendrocytes in vitro had a protective effect against oxidative stress and the inhibition of proteasome activity and resulted in upregulation in expression of a number of chemokines, including CXCL10 (IP10), CCL2 (MCP-1), CCL3 (MCP-1alpha), and CCL5 (RANTES). These results suggest that IFN-gamma-oligodendrocyte interactions are of significance to the clinical and pathological aspects of EAE. In addition, the present study suggests that oligodendrocytes are not simply targets of inflammatory injury but active participants of the neuroimmune network operating during the course of EAE.