Mediators of Inflammation
Volume 2016 (2016), Article ID 4578230, 9 pages
http://dx.doi.org/10.1155/2016/4578230

Review Article

miRNAs Participate in MS Pathological Processes and Its Therapeutic Response

Ting Wu and Guangjie Chen

Department of Immunology and Microbiology, Shanghai JiaoTong University School of Medicine, Shanghai Institute of Immunology, Shanghai 200025, China

Received 24 November 2015; Accepted 29 February 2016

Academic Editor: Jagadeesh Bayry

Copyright © 2016 Ting Wu and Guangjie Chen. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract.

Multiple sclerosis is the most common autoimmune disease of the central nervous system. It is believed that the increased migration of autoreactive lymphocytes across the blood-brain barrier (BBB) may be responsible for axonal demyelination of neurons. In this review, we discuss microRNAs participating in the pathological processes of MS, including periphery inflammation, blood-brain barrier disruption, and CNS lesions, and in its therapeutic response, in order to find biomarkers of disease severity and to predict the response to therapy of the diseases.

1. Introduction

Multiple sclerosis (MS) is the most common autoimmune disease of the central nervous system (CNS) among young adults and it is more common in women than men [1, 2]. It is widely held that there are different four patterns including relapsing-remitting multiple sclerosis (RRMS), primary progressive multiple sclerosis (PPMS), secondary progressive multiple sclerosis (SPMS), and primary-relapsing multiple sclerosis (PRMS) [3].

Although the etiology and pathogenesis of MS remain unknown, several lines of evidence support that the increased migration of autoreactive lymphocytes across the blood-brain barrier (BBB) may be responsible for axonal demyelination of neurons. It has been demonstrated that autoreactive T cells including IFN-γ-producing Th1 cells and IL-17-producing Th17 cells may mediate autoimmune in CNS leading to axonal degeneration, demyelination, and ultimately irreversible tissue damage of patients with MS [4, 5]. Treg cells that prevent damage to the host by limiting the immune response to pathogens are impaired in MS [6, 7]. The balance between Th17 and Treg is crucial to the development of MS. Moreover, MS pathology and pathogenesis have been concentrated on extensive demyelination and formation of sclerosis plaques in cerebral cortex and spinal cord, which contribute to irreversible neurological injury. Activated macrophages and microglia are always engaged in active lesions [8]. Both extensive accumulation of macrophages and activation of microglia are common occurrences following neurological injury [9–13]. EAE is a mouse model of the human disease multiple sclerosis, characterized by autoimmune inflammation of the CNS associated with microglia activation and infiltration of encephalitogenic T cells and leukocytes from the periphery [14, 15].

MicroRNAs (miRNAs) are small, usually 19–24 nucleotides in length, noncoding RNAs that regulate gene expression at the posttranscriptional level [16]. Several recent studies have detected the involvement of circulating miRNAs in physiological and pathological processes and identified them as potential biomarkers, therapeutic agents, or drug targets. In MS, a number of miRNA species were found to be differentially expressed in patients with MS compared with controls and to have the potential to be used as diagnostic biomarkers or drug-response.

2. miRNAs Involved in Periphery Inflammation

T cell subsets such as Th1 and Th17 accumulate in periphery tissues and mediate adaptive immune response. It is generally believed that Th1 and Th17 cells are key proinflammatory mediators of cellular immunity that are responsible for crucial events during development of EAE. The Th1 lineage cytokine can help Th17 cells invade the brain and spinal, thus triggering EAE [17]. Cytokines produced by DCs may promote CD4⁺ T cell activation and synthesize proinflammatory cytokines.

Several recent studies have examined the involvement of miR-155 in EAE. Besides sustaining inflammatory response by promoting the development of inflammatory Th1 and Th17 cells, miR-155 is critical for the acquisition of phenotypic and functional properties of mature DCs (Figure 1). It is demonstrated that miR-155 modulates IFNγ expression through a mechanism involving repression of Ship1, which promotes IFNγ level in Th1 cells [18]. An early research reported that miR-155 might block c-Maf, a promoter of Th2 cell development, and enhance Th17 cell differentiation [19]. Recently, miR-155 has been implicated in inhibiting the protein suppressor of cytokine signaling 1 (SOCS1) in activated CD4⁺ T cells, which promotes Treg/Th17 cells differentiation and Th17 function by activating IL-2/STAT5 and IL-6/STAT3 signaling pathways. miR-155−/−mice is associated with a decrease in IL-17 and IFN-γ, contributing to a delayed course, decreased EAE clinical severity, and less inflammation in the peripheral lymphoid organs and CNS [20, 21]. Dunand-Sauthier et al. reported that miR155 is required for DC maturation and the ability of DCs to promote antigen-specific CD4⁺ T cell activation by inhibiting c-Fos expression which could dampen TNF-, IL-12p70, IL-6, IFN-, and IL-12p40 secretion by mature BM-DCs [22]. In miR155−/−mices, overexpression of Arg2 in DCs resulted in a selective depletion of arginine which can inhibit T cell responses [23].

Figure 1: Summary of putative mechanisms through which miR-155 could modulate MS. miR-155 could regulate several inflammatory and anti-inflammatory cytokines through different target genes, participating in MS pathological processes such as periphery inflammation, BBB dysfunction, and CNS lesion.

miR-146a is highly expressed in Tregs and suppresses interferon (IFN)γ-dependent Th1 responses and inflammation by inhibition of its gene expression signal transducer and activator of transcription (STAT-1). The deletion of miR-146a in Tregs may increase the production of IFN-γ and develop severe Th1-mediate lesions [24]. Further, miRNA-146a was reported to modulate the signaling proteins involved in the innate immune and inflammatory response, such as complement factor H (CFH) and IRAK-1, and both of them were deficient in MS [25–28].

Overexpression of miR-132 in CD4⁺ T cells from EAE mice downregulated IL-17, IFN-γ, and T cell proliferation [29]. miR-26a was demonstrated to downregulate Th17 and to upregulate Treg cell function through targeting IL-6. In EAE, inhibition of miR26a may result in high level of Th17-related cytokines and aggravate clinical signs of EAE. On the contrary, Treg cell specific transcription factor, Foxp3, was detected to be positively correlated with miR26a expression, contributing to a milder form of EAE [30].

A very recent report has shown that miR-21 promoted Th17 differentiation by decreasing SMAD-7, a negative regulator of TGF-β signaling. Treatment of wild type mice with anti-miR-21 oligonucleotide diminished EAE clinical severity along with decreased Th17 cells [31].

Guan et al. have reported that upregulation of let-7e leads to promote the development of Th1 and Th17 cells and aggravate EAE. Since, overexpression of let-7e repressed IL-13 and IL-10 production and augmented IFN-γ production. Inhibition of let-7e may shift the immune response to a Th2 profile and attenuates the severity of the disease [32].

miR-29ab1 was presented to regulate the Th1 differentiation to affect EAE development by targeting T-bet and IFN-γ [33]. Steiner et al. also found that miR-29 repressed IFN-γ production by direct targeting of both T-bet and Eomes, two transcription factors known to induce IFN-γ production [34]. These results demonstrate that the level of miR-29 can modulate Th1 cell differentiation and reflect the disease severity. A very recent study elucidates that interleukin 6 (IL-6) and RelA (NF-κB subunit) are target genes of miR-291a-3p. Downregulation of miR-291a-3p may indicate oxidative stress at the preonset stage of EAE and upregulation of IL-6 and NF-κB activation to induce proinflammatory pathways by targeting IL-6 and RelA [35].

miR-20b has been reported as a decreased miRNA in blood cells of MS patients. As a negative regulator of EAE, miR-20b suppresses Th17 differentiation in vitro and in vivo and attenuates EAE by targeting RORγt and STAT3. This indicates that miR-20b is involved in pathogenesis of EAE mediated by Th17 [36]. Apart from miR-20b, miR-326 [37], miR-301a [38], and miR-23b [39] are found to be involved in Th17-mediated pathogenesis of EAE by targeting Ets-1, a negative regulator of Th17 cell differentiation, IL-6/23–STAT3 pathway, and TAB2, TAB3, and IKK-a, respectively.

In conclusion, these evidences strongly suggest that circulating miRNAs can be utilized as potential clinical biomarkers that reflect the disease activity and severity in MS (Figure 2).

Figure 2: Different miRNA expression in the pathological processes of MS. The changed level of miRNAs is associated with several pathological processes such as periphery inflammation, BBB dysfunction, and CNS lesion. Dysfunction of immune cells including astrocytes and oligodendrocytes in the CNS and Th1, Th17, and Treg cells in the immune system is characterized by different miRNA expressions that are up- (red) and downregulated (green).

3. miRNAs Involved in Blood-Brain Barrier Dysfunction

Disruption and immune activation of the blood-brain barrier (BBB) are central and early features of MS [40–42], with the characteristic of the increased BBB permeability. Previous studies have shown that BBB breakdown is a fundamental event during the course of MS and that the level of the neurovascular dysfunction in EAE may play an important role in the neurological severity of the disease [43].

In recent years, there are increasing evidences to support that miRNAs may play an important role in neuroinflammatory disorders. Several reports have demonstrated that the interendothelial junctional complex (IJC) and integrin focal adhesion (FA) complexes [44–46] are probably associated with altered expression of tight junction (TJ) proteins in response to proinflammatory cytokines, such as TNF-α and IFN-γ. These cytokines may contribute to increase of brain endothelial cell (BEC) permeability by modulation of its gene expression.

miR-155 is reported as a novel negative regulator of BBB function by modulating BEC cell-to-cell and cell-to-matrix interactions, which contributes to BBB dysfunction in MS. Lopez-Ramirez et al. reported that the putative target genes of miR-155 modulate the alterations in FA and IJC organization that might change the permeability of BEC. There are 4 target genes for miR-155 that have been verified, including 2 components of FAs, DOCK-1 and SDCBP, and 2 components of IJCs, ANXA-2 and CLDN-1, which may modulate BEC permeability and potentially mediate miR-155-induced BBB breakdown during inflammation [47].

During MS, increased permeability and expression of cell-adhesion molecules on the brain endothelium facilitate encephalitogenic T cells and circulating leukocytes infiltrating into the CNS, leading to demyelination and axonal loss [8, 48].

It was recently found that miR-125a-5p may significantly increase BEC barrier function by forming thicker and more continuous junctional complexes of VE-cadherin and zona occludens-1. Overexpression of miR-125a-5p in the brain endothelial cells downregulates TNF-α-mediated ICAM-1 expression, a cell-adhesion molecule involved in vascular permeability and leukocyte infiltration, and reduces the transmigration of monocyte through the brain endothelial cell barrier. Therefore, upregulation of miR-125a-5p could reestablish normal function of the brain vasculature in endothelial cell-based neurological diseases, particularly in MS. miR-101 has been shown to downregulate claudin-5 expression by targeting of VE-cadherin, which demonstrates a new mechanism for the regulation of barrier permeability though posttranscriptional regulation of VE-cadherin [49]. Wu et al. investigated that an increasing level of miR-146a expressed on hCMEC/D3 cells diminished cytokine-stimulated adhesion of T cells to endothelial cells, nuclear translocation of NF-κB, and expression of adhesion molecules [50].

In summary, the mechanism of action of miRNA in the inflamed BBB has still not been systematically studied. It is believed that miRNAs such as miR-125a-5p, miR-155, miR-101, and miR-146a can potentially be regarded as novel biomarkers or therapeutic targets for effective treatment of MS (Figure 2).

4. miRNA Involved in CNS Lesions

Several recent studies have examined the involvement of circulating miRNAs in microglia activation and demyelination.

miR-873 induced by IL-17 is reported to facilitate the production of inflammatory cytokine and aggravate demyelination in EAE through the A20/NF-κB pathway. Inhibiting miR-873 or A20, respectively, decreased or increased the production of inflammatory cytokines and attenuated or aggravated the CNS damage of EAE mice, both in vitro and in vivo [51].

A recent study has shown that miR-572 are increased in MS patients [52]. The expression level of miR-572 was varied between patients with different patterns of MS. The serum concentration of miR-572 was lowest in PPMS and it was significantly increased in SPMS. Since a putative target for miR-572 is the neuronal cell-adhesion molecule (NCAM), a protein involved in the maturation of the nervous system [53], the decreased level of miR-572 can promote remyelination in CNS.

It has been generally accepted that the capacity of microglia to phagocytose degenerated myelin can be altered by environmental inflammatory mediators, such as IFN-γ, TNF-α, IL-4, and IL-10. TNF-α was shown to increase the phagocytic activity of microglia. IL-4 and IL-10 exerted a role of upregulating phagocytosis in macrophages/microglia, while accompanied by a reduction of inflammatory response [54].

miR-155 is widely considered as a proinflammatory miRNA. It can target anti-inflammatory proteins in microglia, such as the suppressor of SOCS-1, leading to the upregulation of several inflammatory cytokines, including the inducible nitrogen synthase (iNOS), IL-6, and TNF-α related to the M1 phenotype [55]. As a feedback mechanism to control the immune response, it can also upregulate IFN-β which increase the expression of SOCS-1 and IL-10, two important anti-inflammatory mediators [56, 57]. In addition, miR-155 can also target M2-associated genes, such as SMAD2, a protein involved in the TGF-β pathway [58] and CEBPβ, a transcription factor critical for the expression of IL-10, arginase-1, and CD206 [59]. Therefore, miR-155 has a positive effect in promoting inflammatory response and upregulating phagocytosis in microglia.

ARK1C1 and ARK1C2 are different isoforms of an enzyme encoding a 3-α-hydroxysteroid dehydrogenase activity that is necessary to the synthesis of neurosteroids in the brain. These genes are experimentally validated to be downregulated by miR-155 and miR-338, which can reduce the production of neurosteroids synthesis [60, 61].

Miller and Streit recently demonstrated that decreasing CD47 which is regarded as a protein that inhibits macrophage phagocytosis may promote phagocytosis of myelin in a SIRP-α-dependent mechanism [62]. Besides, miR-155-mediated downregulation of CD47 is thought to release macrophages inhibition and thereby promote myelin breakdown [63].

The overexpression of MiR-101 responses to several TLR ligands in macrophages will downregulate MAPK phosphatase 1 (MPK-1), promoting the activation of MAPK and the level of M1-associated proinflammatory cytokines, such as IL-6, TNF-α, and IL-1 [64]. Chaudhuri and colleagues reported an increased miR-125b in M1 macrophage activation, with upregulation of MHC class II, CD40, CD80, and CD86. The potential reason is that interferon regulatory factor 4 (IRF4) is targeted by miR-125b and makes macrophages polarize to M1 cytotoxic phenotype [65].

Cui et al. reported that miR-146a-mediated downregulation of IRAK1 is associated with the reinforcement of IRAK2-induced activation of NF-κβ and a sustained inflammatory response in human astroglial cells [26]. Interestingly, significant amounts of miRNA-146a that have been found in glial cells are responsible for axonal myelination [66–68]. In inactive MS lesions, miR-219 are the most downregulated miRNAs [63]. The enzyme ELOVL7 regulated by miR-219 is essential for myelin maintenance and axonal integrity in the adult mouse CNS [69].

In recent years, there are increasing evidences to support that some miRNAs are engaged in building beneficial environment for remyelination and axon regeneration. For instance, two studies described that miR-214 is upregulated in oligodendrocytes during differentiation and miR-23a overexpression promotes oligodendrocyte differentiation by downregulating lamin B. The increased level of miR-214 and miR-23a in MS lesions may reflect ongoing remyelination [70, 71]. The microglia in CNS are the main macrophages participating in phagocytosis in the early stage of demyelination, while in the late stage, a number of infiltrated blood-borne macrophages contribute to axon debris clearance.

miR-124 is reported as a key regulator of microglia quiescence in the CNS and as a new modulator of monocyte and macrophage activation in the periphery during EAE. miR-124 has been reported to contribute to the M2 phenotype of macrophages and microglia, since its overexpression led to the downregulation of M1-associated markers, such as IL-6, TNF-α, and iNOS, and an increase of proteins associated with the M2 phenotype, such as TGF-β, arginase-1, and FIZZ1 [72], which are crucial for the suppression of EAE. In EAE, Zhu et al. have experimentally validated TAB2, TAB3, and IKK-α as miR-23b targets. These genes are upregulated during EAE and modulate IL-17, TNF-α, and IL-1β induced activation of NF-κβ. These findings indicate that miR-23b overexpression can delay the onset of EAE and alleviates disease severity [39] (Figure 2).

5. miRNA Involved in MS Therapeutic Response

Natalizumab is a recombinant humanized monoclonal antibody which binds to α4β1 and α4β7 integrins and suppresses their interaction with vascular cell-adhesion molecules-1 (VCAM-1) so as to impair leucocyte adhesion and transmigrate across the BBB into the central nervous system, with a reduction of proinflammatory cytokines [73].

Ingwersen et al. reported that five miRNAs (miR-18a, miR-20b, miR-29a, miR-103, and miR-326) were regulated by natalizumab, which were the opposite of the miRNA results in MS patients prior to natalizumab therapy compared to healthy controls. Four of them (miR-18a, miR-20b, miR-29a, and miR-103) were upregulated, while miR-326b is downregulated after natalizumab treatment [74]. As mentioned above, the targets of miR-20b and miR-326, including RORγt, stat3, vegfa, and Ets-1 [37, 74–76], play an important role in regulating Th17 immune responses and BBB breakdown [77, 78]. Further, miR-29a was shown to modulate the differentiation of proinflammatory Th1 immune responses [33].

Petrocca et al. demonstrated that natalizumab may downregulate miR-17 expression and upregulate the level of miR-106b. Both miR-106b and miR-17 have been identified as important modulators of TGF-β signaling [79] and have been found to regulate CD4⁺ T cell immune responses by targeting TGFBR2 [80]. The TGF-β pathway is necessary for maintaining peripheral Foxp3-expressing regulatory T cells [81]. Inhibition of TGFBR2 resulted in severe inflammatory responses associated with T cell activation and differentiation in mice [82].

In line with decreased miR-17 in natalizumab treated patients, we found an increase in PTEN mRNA, which plays an important role in the regulation of T cell homeostasis and self-tolerance [83, 84]. In addition, downregulation of miR-17 was associated with upregulation of a proapoptotic member of the Bcl-2 family, BIM, the cyclin-dependent kinase inhibitor 1, p21, and a transcription factor controlling the G1-S transition, E2F1 [85].

These targets reverted by natalizumab therapy may alter peripheral immune cells during EAE and negatively associate with disease severity. So the influences of natalizumab on the expression of miRNA can help us to understand long-term effects of natalizumab and functions in the process of MS pathogenesis.

Interferon-beta (IFN-β) therapy is widely used in patients with MS. Besides its effects on immunomodulatory system and metalloproteinase 9 [29], it has been shown to have an effect on neuroprotection against the toxicity induced by activated microglia and inhibiting the production of glutamate and superoxide by activated microglia [86, 87]. It has been reported that the expression level of miR-26a-5p was significantly changed in response to INF-β treatment in MS patients during different stages. It was much higher in IFN-β treated RRMS patients at 3 months’ treatment and kept stable at 6 months’ treatments in all patients. In contrast, postsynaptic density protein 95 (DLG4), a key player in neuronal signaling, decreased after 3 months’ treatment, showing an inverse relation to miR-26a-5p expression [88].

Moreover, it has been reported that 20 miRNAs may play an important role in the mechanisms of therapy of IFN-β. Interestingly, seven of them, including miR-16-5p, miR-342-5p, miR-346, miR-518b, miR-760, let-7a-5p, and let-7b-5p, were increased, whereas 13 miRNAs, including miR-27a-5p, miR-29a-3p, miR-29b-1-5p, miR-29c-3p, miR-95, miR-149-5p, miR-181c-3p, miR-193a-3p, miR-193-5p, miR-423-5p, miR-532-5p, miR-708-5p, and miR-874, were decreased in PBMCs from MS patients in response to IFN-β treatment. Particularly, some of the 20 miRNAs, such as members of the mir-29 family, are associated with apoptosis and are involved in IFN signaling feedback loops and others like hsa-miR-532-5p and hsa-miR-16-5p are demonstrated to have relations with IFN-responsive genes [89]. This information can be served as a novel biomarker to predict the effects of IFN-beta therapy and be applied to develop a novel therapy for MS patients.

Glatiramer acetate (GA), an immunomodulation drug, was approved as a first-line therapy in MS [90]. GA treatment may downregulate miR-146a and miR-142-3p level in the PBMCs of MS patients. The mechanisms by which GA influences the expression of miR-142-3p may attribute to an expansion of T regulatory cells and changes in the composition of the T cell compartment [76]. Downregulation of miR-146a in the glatiramer acetate treatment group may improve disease status of MS patients by inducing a Th1 to Th2 shift and inhibiting monocyte reactivity [91–93].

The GSK3β inhibitors were shown as beneficial drugs in preclinical trials in stroke and Huntington’s and amyotrophic lateral sclerosis, with functions of increasing BBB tightness under physiologic conditions, decreasing inflammatory factors secreted in brain microvascular endothelial cells and protecting against BBB disruption by reducing monocyte adhesion to/migration across the BBB [94, 95]. Rom et al. discovered that the GSK3β inhibitor may upregulate miR-98 and let-7 so as to attenuate leukocyte adhesion/migration into the BBB and diminished BBB permeability in both in vitro and in vivo models. Overexpression of miR-98 and let-7 in brain endothelium may also contribute to inhibiting expression of proinflammatory mediators, such as CCL2 and CCL5 [96]. Table 1 summarized miRNA biomarkers involved in the therapeutic response in multiple sclerosis.

Table 1: MiRNA biomarkers of therapeutic response in multiple sclerosis (MS).

Drug treatment
Increased miRNA
Decreased miRNA

NatalizumAb
miR-18a, 20b, 29a, 103
miR-326, 17

INF-β
miR-26-5p, 16-5p, 342-5p, 346, 518b, 760, let-7a-5p, 7b-5p
miR-27a-5p, 29a-3p, 29b-1-5p, 29c-3p, -95, 149-5p, 181c-3p, 193a-3p, -193-5p, 423-5p, 532-5p, 708-5p, 874

GA

miR-146a, miR-142-3p

GSK3β inhibitors

miR-98 and let-7g

6. Conclusion

MS is a chronic and systemic autoimmune disease with different disease stages. Different patterns of patients with MS undergo several disease processes including periphery inflammation and blood-brain barrier damage and CNS lesions. Without timely and adequate treatment, these patients will suffer chronic demyelination and axonal loss, for unclear reasons, leading to irreversible disability. The discovery of MS biomarkers may extremely improve the diagnosis and management of MS. The current miRNA profiles offer an opportunity to indicate disease progression and the therapeutic effect. Some of the biomarkers are related to an altered biological process and a treatment targeting this process. Understanding the complexity of miRNA network may open up a new vista to find individual biomarkers in clinical diagnosis and monitor the efficacy of therapy.

Competing Interests

The authors declare that they have no competing interests.

Acknowledgments

This work was supported by grants from National Nature Science Foundation of China (81373208), Shanghai Commission of Science and Technology (11JC1411602), Shanghai Municipal Education Commission (12ZZ103), and Shanghai Board of Health Foundation (2011177).

References

A. Compston and A. Coles, “Multiple sclerosis,” The Lancet, vol. 359, no. 9313, pp. 1221–1231, 2002.

R. Milo and E. Kahana, “Multiple sclerosis: geoepidemiology, genetics and the environment,” Autoimmunity Reviews, vol. 9, no. 5, pp. A387–A394, 2010.

J. H. Noseworthy, C. Lucchinetti, M. Rodriguez, and B. G. Weinshenker, “Multiple sclerosis,” New England Journal of Medicine, vol. 343, no. 13, pp. 938–952, 2000.

A. Compston and A. Coles, “Multiple sclerosis,” The Lancet, vol. 372, no. 9648, pp. 1502–1517, 2008.

S. Ireland and N. Monson, “Potential impact of B cells on T cell function in multiple sclerosis,” Multiple Sclerosis International, vol. 2011, Article ID 423971, 10 pages, 2011.

M. Miyara, G. Gorochov, M. Ehrenstein, L. Musset, S. Sakaguchi, and Z. Amoura, “Human FoxP3⁺ regulatory T cells in systemic autoimmune diseases,” Autoimmunity Reviews, vol. 10, no. 12, pp. 744–755, 2011.

M. Miyara and S. Sakaguchi, “Human FoxP3⁺ CD4⁺ regulatory T cells: their knowns and unknowns,” Immunology and Cell Biology, vol. 89, no. 3, pp. 346–351, 2011.

H. Lassmann, W. Brück, and C. F. Lucchinetti, “The immunopathology of multiple sclerosis: an overview,” Brain Pathology, vol. 17, no. 2, pp. 210–218, 2007.

S. David and A. Kroner, “Repertoire of microglial and macrophage responses after spinal cord injury,” Nature Reviews Neuroscience, vol. 12, no. 7, pp. 388–399, 2011.

M. Prinz, J. Priller, S. S. Sisodia, and R. M. Ransohoff, “Heterogeneity of CNS myeloid cells and their roles in neurodegeneration,” Nature Neuroscience, vol. 14, no. 10, pp. 1227–1235, 2011.

R. M. Ransohoff and A. E. Cardona, “The myeloid cells of the central nervous system parenchyma,” Nature, vol. 468, no. 7321, pp. 253–262, 2010.

K. Saijo and C. K. Glass, “Microglial cell origin and phenotypes in health and disease,” Nature Reviews Immunology, vol. 11, no. 11, pp. 775–787, 2011.

M. B. Graeber, “Changing face of microglia,” Science, vol. 330, no. 6005, pp. 783–788, 2010.

K. C. Williams, E. Ulvestad, and W. F. Hickey, “Immunology of multiple sclerosis,” Clinical Neuroscience, vol. 2, no. 3-4, pp. 229–245, 1994.

K. G. Haanstra, S. A. Jagessar, A.-L. Bauchet et al., “Induction of experimental autoimmune encephalomyelitis with recombinant human myelin oligodendrocyte glycoprotein in incomplete freund's adjuvant in three non-human primate species,” Journal of Neuroimmune Pharmacology, vol. 8, no. 5, pp. 1251–1264, 2013.

E. Lund, S. Güttinger, A. Calado, J. E. Dahlberg, and U. Kutay, “Nuclear export of microRNA precursors,” Science, vol. 303, no. 5654, pp. 95–98, 2004.

A. Reboldi, C. Coisne, D. Baumjohann et al., “C-C chemokine receptor 6-regulated entry of TH-17 cells into the CNS through the choroid plexus is required for the initiation of EAE,” Nature Immunology, vol. 10, no. 5, pp. 514–523, 2009.

T. B. Huffaker, R. Hu, M. C. Runtsch et al., “Epistasis between MicroRNAs 155 and 146a during T cell-mediated antitumor immunity,” Cell Reports, vol. 2, no. 6, pp. 1697–1709, 2012.

T.-H. Thai, D. P. Calado, S. Casola et al., “Regulation of the germinal center response by MicroRNA-155,” Science, vol. 316, no. 5824, pp. 604–608, 2007.

R. M. O'Connell, D. Kahn, W. S. J. Gibson et al., “MicroRNA-155 promotes autoimmune inflammation by enhancing inflammatory T cell development,” Immunity, vol. 33, no. 4, pp. 607–619, 2010.

G. Murugaiyan, V. Beynon, A. Mittal, N. Joller, and H. L. Weiner, “Silencing microRNA-155 ameliorates experimental autoimmune encephalomyelitis,” Journal of Immunology, vol. 187, no. 5, pp. 2213–2221, 2011.

I. Dunand-Sauthier, M.-L. Santiago-Raber, L. Capponi et al., “Silencing of c-Fos expression by microRNA-155 is critical for dendritic cell maturation and function,” Blood, vol. 117, no. 17, pp. 4490–4500, 2011.

I. Dunand-Sauthier, M. Irla, S. Carnesecchi et al., “Repression of arginase-2 expression in dendritic cells by microRNA-155 is critical for promoting T cell proliferation,” The Journal of Immunology, vol. 193, no. 4, pp. 1690–1700, 2014.

L.-F. Lu, M. P. Boldin, A. Chaudhry et al., “Function of miR-146a in controlling Treg cell-mediated regulation of Th1 responses,” Cell, vol. 142, no. 6, pp. 914–929, 2010.

K. D. Taganov, M. P. Boldin, K.-J. Chang, and D. Baltimore, “NF-κB-dependent induction of microRNA miR-146, an inhibitor targeted to signaling proteins of innate immune responses,” Proceedings of the National Academy of Sciences of the United States of America, vol. 103, no. 33, pp. 12481–12486, 2006.

J. G. Cui, Y. Y. Li, Y. Zhao, S. Bhattacharjee, and W. J. Lukiw, “Differential regulation of interleukin-1 receptor-associated kinase-1 (IRAK-1) and IRAK-2 by microRNA-146a and NF-κB in stressed human astroglial cells and in Alzheimer disease,” Journal of Biological Chemistry, vol. 285, no. 50, pp. 38951–38960, 2010.

G. Ingram, S. Loveless, O. W. Howell et al., “Complement activation in multiple sclerosis plaques: an immunohistochemical analysis,” Acta Neuropathologica Communications, vol. 2, article 53, 2014.

K. H. Stürner, N. Verse, S. Yousef, R. Martin, and M. Sospedra, “Boswellic acids reduce Th17 differentiation via blockade of IL-1β-mediated IRAK1 signaling,” European Journal of Immunology, vol. 44, no. 4, pp. 1200–1212, 2014.

H. Hanieh and A. Alzahrani, “MicroRNA-132 suppresses autoimmune encephalomyelitis by inducing cholinergic anti-inflammation: a new Ahr-based exploration,” European Journal of Immunology, vol. 43, no. 10, pp. 2771–2782, 2013.

R. Zhang, A. Tian, J. Wang, X. Shen, G. Qi, and Y. Tang, “miR26a modulates Th17/Treg balance in the EAE model of multiple sclerosis by targeting IL6,” NeuroMolecular Medicine, vol. 17, no. 1, pp. 24–34, 2015.

G. Murugaiyan, A. P. Da Cunha, A. K. Ajay et al., “MicroRNA-21 promotes Th17 differentiation and mediates experimental autoimmune encephalomyelitis,” Journal of Clinical Investigation, vol. 125, no. 3, pp. 1069–1080, 2015.

H. Guan, D. Fan, D. Mrelashvili et al., “MicroRNA let-7e is associated with the pathogenesis of experimental autoimmune encephalomyelitis,” European Journal of Immunology, vol. 43, no. 1, pp. 104–114, 2013.

K. M. Smith, M. Guerau-de-Arellano, S. Costinean et al., “miR-29ab1 deficiency identifies a negative feedback loop controlling Th1 bias that is dysregulated in multiple sclerosis,” Journal of Immunology, vol. 189, no. 4, pp. 1567–1576, 2012.

D. F. Steiner, M. F. Thomas, J. K. Hu et al., “MicroRNA-29 regulates T-box transcription factors and interferon-γ production in helper T cells,” Immunity, vol. 35, no. 2, pp. 169–181, 2011.

J. Singh, M. Deshpande, H. Suhail, R. Rattan, and S. Giri, “Targeted stage-specific inflammatory microRNA profiling in urine during disease progression in experimental autoimmune encephalomyelitis: markers of disease progression and drug response,” Journal of Neuroimmune Pharmacology, vol. 11, no. 1, pp. 84–97, 2016.

E. Zhu, X. Wang, B. Zheng et al., “MiR-20b suppresses Th17 differentiation and the pathogenesis of experimental autoimmune encephalomyelitis by targeting RORγt and STAT3,” Journal of Immunology, vol. 192, no. 12, pp. 5599–5609, 2014.

C. Du, C. Liu, J. Kang et al., “MicroRNA miR-326 regulates TH-17 differentiation and is associated with the pathogenesis of multiple sclerosis,” Nature Immunology, vol. 10, no. 12, pp. 1252–1259, 2009.

M. P. Mycko, M. Cichalewska, A. Machlanska, H. Cwiklinska, M. Mariasiewicz, and K. W. Selmaj, “MicroRNA-301a regulation of a T-helper 17 immune response controls autoimmune demyelination,” Proceedings of the National Academy of Sciences of the United States of America, vol. 109, no. 20, pp. E1248–E1257, 2012.

S. Zhu, W. Pan, X. Song et al., “The microRNA miR-23b suppresses IL-17-associated autoimmune inflammation by targeting TAB2, TAB3 and IKK-α,” Nature Medicine, vol. 18, no. 7, pp. 1077–1086, 2012.

E. Neuwelt, N. J. Abbott, L. Abrey et al., “Strategies to advance translational research into brain barriers,” The Lancet Neurology, vol. 7, no. 1, pp. 84–96, 2008.

E. A. Neuwelt, B. Bauer, C. Fahlke et al., “Engaging neuroscience to advance translational research in brain barrier biology,” Nature Reviews Neuroscience, vol. 12, no. 3, pp. 169–182, 2011.

B. V. Zlokovic, “The blood-brain barrier in health and chronic neurodegenerative disorders,” Neuron, vol. 57, no. 2, pp. 178–201, 2008.

V. I. Kobrin, M. Manoakh, G. Gol'dberg et al., “Effect of 17-beta-estradiol sulfate on transmembrane potentials of guinea pig heart cardiomyocytes,” Biulleten' Eksperimental'noi Biologii i Meditsiny, vol. 121, no. 4, pp. 370–373, 1996.

M. A. Lopez-Ramirez, D. K. Male, C. Wang, B. Sharrack, D. Wu, and I. A. Romero, “Cytokine-induced changes in the gene expression profile of a human cerebral microvascular endothelial cell-line, hCMEC/D3,” Fluids and Barriers of the CNS, vol. 10, no. 1, article 27, 2013.

N. Schlegel and J. Waschke, “Impaired integrin-mediated adhesion contributes to reduced barrier properties in VASP-deficient microvascular endothelium,” Journal of Cellular Physiology, vol. 220, no. 2, pp. 357–366, 2009.

M. A. Lopez-Ramirez, R. Fischer, C. C. Torres-Badillo et al., “Role of caspases in cytokine-induced barrier breakdown in human brain endothelial cells,” Journal of Immunology, vol. 189, no. 6, pp. 3130–3139, 2012.

M. A. Lopez-Ramirez, D. Wu, G. Pryce et al., “MicroRNA-155 negatively affects blood-brain barrier function during neuroinflammation,” The FASEB Journal, vol. 28, no. 6, pp. 2551–2565, 2014.

C. Larochelle, J. I. Alvarez, and A. Prat, “How do immune cells overcome the blood-brain barrier in multiple sclerosis?” FEBS Letters, vol. 585, no. 23, pp. 3770–3780, 2011.

R. Mishra and S. K. Singh, “HIV-1 Tat C modulates expression of miRNA-101 to suppress VE-cadherin in human brain microvascular endothelial cells,” The Journal of Neuroscience, vol. 33, no. 14, pp. 5992–6000, 2013.

D. Wu, C. Cerutti, M. A. Lopez-Ramirez et al., “Brain endothelial miR-146a negatively modulates T-cell adhesion through repressing multiple targets to inhibit NF-κB activation,” Journal of Cerebral Blood Flow and Metabolism, vol. 35, no. 3, pp. 412–423, 2015.

X. Liu, F. He, R. Pang et al., “Interleukin-17 (IL-17)-induced microRNA 873 (miR-873) contributes to the pathogenesis of experimental autoimmune encephalomyelitis by targeting A20 ubiquitin-editing enzyme,” The Journal of Biological Chemistry, vol. 289, no. 42, pp. 28971–28986, 2014.

S. R. Siegel, J. Mackenzie, G. Chaplin, N. G. Jablonski, and L. Griffiths, “Circulating microRNAs involved in multiple sclerosis,” Molecular Biology Reports, vol. 39, no. 5, pp. 6219–6225, 2012.

S. Gnanapavan and G. Giovannoni, “Neural cell adhesion molecules in brain plasticity and disease,” Multiple Sclerosis and Related Disorders, vol. 2, no. 1, pp. 13–20, 2013.

M. E. Smith, “Phagocytosis of myelin in demyelinative disease: a review,” Neurochemical Research, vol. 24, no. 2, pp. 261–268, 1999.

A. L. Cardoso, J. R. Guedes, L. Pereira de Almeida, and M. C. Pedroso de Lima, “miR-155 modulates microglia-mediated immune response by down-regulating SOCS-1 and promoting cytokine and nitric oxide production,” Immunology, vol. 135, no. 1, pp. 73–88, 2012.

E. N. Benveniste and H. Qin, “Type I interferons as anti-inflammatory mediators,” Science's STKE, vol. 416, p. pe70, 2007.

A. Dalpke, K. Heeg, H. Bartz, and A. Baetz, “Regulation of innate immunity by suppressor of cytokine signaling (SOCS) proteins,” Immunobiology, vol. 213, no. 3-4, pp. 225–235, 2008.

F. Louafi, R. T. Martinez-Nunez, and T. Sanchez-Elsner, “MicroRNA-155 targets SMAD2 and modulates the response of macrophages to transforming growth factor-β,” Journal of Biological Chemistry, vol. 285, no. 53, pp. 41328–41336, 2010.

D. Ruffell, F. Mourkioti, A. Gambardella et al., “A CREB-C/EBPβ cascade induces M2 macrophage-specific gene expression and promotes muscle injury repair,” Proceedings of the National Academy of Sciences of the United States of America, vol. 106, no. 41, pp. 17475–17480, 2009.

F. Noorbakhsh, K. K. Ellestad, F. Maingat et al., “Impaired neurosteroid synthesis in multiple sclerosis,” Brain, vol. 134, no. 9, pp. 2703–2721, 2011.

O. Natera-Naranjo, A. Aschrafi, A. E. Gioio, and B. B. Kaplan, “Identification and quantitative analyses of microRNAs located in the distal axons of sympathetic neurons,” RNA, vol. 16, no. 8, pp. 1516–1529, 2010.

K. R. Miller and W. J. Streit, “The effects of aging, injury and disease on microglial function: a case for cellular senescence,” Neuron Glia Biology, vol. 3, no. 3, pp. 245–253, 2007.

A. Junker, M. Krumbholz, S. Eisele et al., “MicroRNA profiling of multiple sclerosis lesions identifies modulators of the regulatory protein CD47,” Brain, vol. 132, no. 12, pp. 3342–3352, 2009.

Q. Y. Zhu, Q. Liu, J.-X. Chen, K. Lan, and B.-X. Ge, “MicroRNA-101 targets MAPK phosphatase-1 to regulate the activation of MAPKs in macrophages,” The Journal of Immunology, vol. 185, no. 12, pp. 7435–7442, 2010.

A. A. Chaudhuri, A. Y.-L. So, N. Sinha et al., “MicroRNA-125b potentiates macrophage activation,” Journal of Immunology, vol. 187, no. 10, pp. 5062–5068, 2011.

Y. Y. Li, J. G. Cui, P. Dua, A. I. Pogue, S. Bhattacharjee, and W. J. Lukiw, “Differential expression of miRNA-146a-regulated inflammatory genes in human primary neural, astroglial and microglial cells,” Neuroscience Letters, vol. 499, no. 2, pp. 109–113, 2011.

P. N. Alexandrov, P. Dua, and W. J. Lukiw, “Up-regulation of miRNA-146a in progressive, age-related inflammatory neurodegenerative disorders of the human CNS,” Frontiers in Neurology, vol. 5, article 181, 2014.

B.-J. Kroesen, N. Teteloshvili, K. Smigielska-Czepiel et al., “Immuno-miRs: critical regulators of T-cell development, function and ageing,” Immunology, vol. 144, no. 1, pp. 1–10, 2015.

D. Shin, J.-Y. Shin, M. T. McManus, L. J. Ptáček, and Y.-H. Fu, “Dicer ablation in oligodendrocytes provokes neuronal impairment in mice,” Annals of Neurology, vol. 66, no. 6, pp. 843–857, 2009.

P. Lau, J. D. Verrier, J. A. Nielsen, K. R. Johnson, L. Notterpek, and L. D. Hudson, “Identification of dynamically regulated microRNA and mRNA networks in developing oligodendrocytes,” The Journal of Neuroscience, vol. 28, no. 45, pp. 11720–11730, 2008.

S.-T. Lin and Y.-H. Fu, “miR-23 regulation of lamin B1 is crucial for oligodendrocyte development and myelination,” DMM Disease Models and Mechanisms, vol. 2, no. 3-4, pp. 178–188, 2009.

E. D. Ponomarev, T. Veremeyko, N. Barteneva, A. M. Krichevsky, and H. L. Weiner, “MicroRNA-124 promotes microglia quiescence and suppresses EAE by deactivating macrophages via the C/EBP-α–PU.1 pathway,” Nature Medicine, vol. 17, no. 1, pp. 64–70, 2011.

T. Derfuss, J. Kuhle, R. Lindberg, and L. Kappos, “Natalizumab therapy for multiple sclerosis,” Seminars in Neurology, vol. 33, no. 1, pp. 26–36, 2013.

J. Ingwersen, T. Menge, B. Wingerath et al., “Natalizumab restores aberrant miRNA expression profile in multiple sclerosis and reveals a critical role for miR-20b,” Annals of Clinical and Translational Neurology, vol. 2, no. 1, pp. 43–55, 2015.

Z. Lei, B. Li, Z. Yang et al., “Regulation of HIF-1α and VEGF by miR-20b tunes tumor cells to adapt to the alteration of oxygen concentration,” PLoS ONE, vol. 4, no. 10, Article ID e7629, 2009.

A. Waschbisch, M. Atiya, R. A. Linker, S. Potapov, S. Schwab, and T. Derfuss, “Glatiramer acetate treatment normalizes deregulated microRNA expression in relapsing remitting multiple sclerosis,” PLoS ONE, vol. 6, no. 9, Article ID e24604, 2011.

A. T. Argaw, B. T. Gurfein, Y. Zhang, A. Zameer, and G. R. John, “VEGF-mediated disruption of endothelial CLN-5 promotes blood-brain barrier breakdown,” Proceedings of the National Academy of Sciences of the United States of America, vol. 106, no. 6, pp. 1977–1982, 2009.

T. J. Harris, J. F. Grosso, H.-R. Yen et al., “Cutting edge: an in vivo requirement for STAT3 signaling in TH17 development and TH17-dependent autoimmunity,” The Journal of Immunology, vol. 179, no. 7, pp. 4313–4317, 2007.

F. Petrocca, A. Vecchione, and C. M. Croce, “Emerging role of miR-106b-25/miR-17-92 clusters in the control of transforming growth factor β signaling,” Cancer Research, vol. 68, no. 20, pp. 8191–8194, 2008.

S. Jiang, C. Li, V. Olive et al., “Molecular dissection of the miR-17-92 cluster's critical dual roles in promoting Th1 responses and preventing inducible Treg differentiation,” Blood, vol. 118, no. 20, pp. 5487–5497, 2011.

L. Xu, A. Kitani, and W. Strober, “Molecular mechanisms regulating TGF-β-induced Foxp3 expression,” Mucosal Immunology, vol. 3, no. 3, pp. 230–238, 2010.

M. O. Li, S. Sanjabi, and R. Flavell, “Transforming growth factor-beta controls development, homeostasis, and tolerance of T cells by regulatory T cell-dependent and -independent mechanisms,” Immunity, vol. 25, no. 3, pp. 455–471, 2006.

A. Suzuki, M. T. Yamaguchi, T. Ohteki et al., “T cell-specific loss of Pten leads to defects in central and peripheral tolerance,” Immunity, vol. 14, no. 5, pp. 523–534, 2001.

R. H. Newton and L. A. Turka, “Regulation of T cell homeostasis and responses by pten,” Frontiers in Immunology, vol. 3, article 151, 2012.

M. Meira, C. Sievers, F. Hoffmann et al., “Unraveling natalizumab effects on deregulated miR-17 expression in CD4⁺ T cells of patients with relapsing-remitting multiple sclerosis,” Journal of Immunology Research, vol. 2014, Article ID 897249, 11 pages, 2014.

M. Yushchenko, M. Mäder, E. Elitok et al., “Interferon-β-1 b decreased matrix metalloproteinase-9 serum levels in primary progressive multiple sclerosis,” Journal of Neurology, vol. 250, no. 10, pp. 1224–1228, 2003.

S. Jin, J. Kawanokuchi, T. Mizuno et al., “Interferon-β is neuroprotective against the toxicity induced by activated microglia,” Brain Research, vol. 1179, no. 1, pp. 140–146, 2007.

B. De Felice, P. Mondola, A. Sasso et al., “Small non-coding RNA signature in multiple sclerosis patients after treatment with interferon-β,” BMC Medical Genomics, vol. 7, article 26, 2014.

M. Hecker, M. Thamilarasan, D. Koczan et al., “MicroRNA expression changes during interferon-beta treatment in the peripheral blood of multiple sclerosis patients,” International Journal of Molecular Sciences, vol. 14, no. 8, pp. 16087–16110, 2013.

S. Messina and F. Patti, “The pharmacokinetics of glatiramer acetate for multiple sclerosis treatment,” Expert Opinion on Drug Metabolism and Toxicology, vol. 9, no. 10, pp. 1349–1359, 2013.

D. Burger, N. Molnarfi, M. S. Weber et al., “Glatiramer acetate increases IL-1 receptor antagonist but decreases T cell-induced IL-1β in human monocytes and multiple sclerosis,” Proceedings of the National Academy of Sciences of the United States of America, vol. 106, no. 11, pp. 4355–4359, 2009.

M. K. Racke and A. E. Lovett-Racke, “Glatiramer acetate treatment of multiple sclerosis: an immunological perspective,” Journal of Immunology, vol. 186, no. 4, pp. 1887–1890, 2011.

M. S. Weber, M. Starck, S. Wagenpfeil, E. Meinl, R. Hohlfeld, and C. Farina, “Multiple sclerosis: glatiramer acetate inhibits monocyte reactivity in vitro and in vivo,” Brain, vol. 127, no. 6, pp. 1370–1378, 2004.

S. H. Ramirez, S. Fan, M. Zhang et al., “Inhibition of glycogen synthase kinase 3beta (GSK3beta) decreases inflammatory responses in brain endothelial cells,” The American Journal of Pathology, vol. 176, no. 2, pp. 881–892, 2010.

S. H. Ramirez, S. Fan, H. Dykstra et al., “Inhibition of glycogen synthase kinase 3β promotes tight junction stability in brain endothelial cells by half-life extension of occludin and claudin-5,” PLoS ONE, vol. 8, no. 2, Article ID e55972, 2013.

S. Rom, H. Dykstra, V. Zuluaga-Ramirez, N. L. Reichenbach, and Y. Persidsky, “miR-98 and let-7g∗ protect the blood-brain barrier under neuroinflammatory conditions,” Journal of Cerebral Blood Flow & Metabolism, vol. 35, no. 12, pp. 1957–1965, 2015.