An increase in tolerogenic dendritic cell and natural regulatory T cell numbers during experimental autoimmune encephalomyelitis in Rras-/- mice results in attenuated disease

Ras family signaling pathway in immunopathogenesis of inflammatory rheumatic diseases

The Ras (rat sarcoma virus) is a GTP-binding protein that is considered one of the important members of the Ras-GTPase superfamily. The Ras involves several pathways in the cell that include proliferation, migration, survival, differentiation, and fibrosis. Abnormalities in the expression level and activation of the Ras family signaling pathway and its downstream kinases such as Raf/MEK/ERK1-2 contribute to the pathogenic mechanisms of rheumatic diseases including immune system dysregulation, inflammation, and fibrosis in systemic sclerosis (SSc); destruction and inflammation of synovial tissue in rheumatoid arthritis (RA); and autoantibody production and immune complexes formation in systemic lupus erythematosus (SLE); and enhance osteoblast differentiation and ossification during skeletal formation in ankylosing spondylitis (AS). In this review, the basic biology, signaling of Ras, and abnormalities in this pathway in rheumatic diseases including SSc, RA, AS, and SLE will be discussed.

Targeting transmembrane-domain-less MOG expression to platelets prevents disease development in experimental autoimmune encephalomyelitis

Multiple sclerosis (MS) is a chronic inflammatory autoimmune disease of the central nervous system with no cure yet. Here, we report genetic engineering of hematopoietic stem cells (HSCs) to express myelin oligodendrocyte glycoprotein (MOG), specifically in platelets, as a means of intervention to induce immune tolerance in experimental autoimmune encephalomyelitis (EAE), the mouse model of MS. The platelet-specific αIIb promoter was used to drive either a full-length or truncated MOG expression cassette. Platelet-MOG expression was introduced by lentivirus transduction of HSCs followed by transplantation. MOG protein was detected on the cell surface of platelets only in full-length MOG-transduced recipients, but MOG was detected in transmembrane-domain-less MOG_1-157-transduced platelets intracellularly. We found that targeting MOG expression to platelets could prevent EAE development and attenuate disease severity, including the loss of bladder control in transduced recipients. Elimination of the transmembrane domains of MOG significantly enhanced the clinical efficacy in preventing the onset and development of the disease and induced CD4⁺Foxp3⁺ Treg cells in the EAE model. Together, our data demonstrated that targeting transmembrane domain-deleted MOG expression to platelets is an effective strategy to induce immune tolerance in EAE, which could be a promising approach for the treatment of patients with MS autoimmune disease.

Crosstalk between dendritic cells and regulatory T cells: Protective effect and therapeutic potential in multiple sclerosis

Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system related to autoimmunity and is characterized by demyelination, neuroinflammation, and neurodegeneration. Cell therapies mediated by dendritic cells (DCs) and regulatory T cells (Tregs) have gradually become accumulating focusing in MS, and the protective crosstalk mechanisms between DCs and Tregs provide the basis for the efficacy of treatment regimens. In MS and its animal model experimental autoimmune encephalomyelitis, DCs communicate with Tregs to form immune synapses and complete a variety of complex interactions to counteract the unbalanced immune tolerance. Through different co-stimulatory/inhibitory molecules, cytokines, and metabolic enzymes, DCs regulate the proliferation, differentiation and function of Tregs. On the other hand, Tregs inhibit the mature state and antigen presentation ability of DCs, ultimately improving immune tolerance. In this review, we summarized the pivotal immune targets in the interaction between DCs and Tregs, and elucidated the protective mechanisms of DC-Treg cell crosstalk in MS, finally interpreted the complex cell interplay in the manner of inhibitory feedback loops to explore novel therapeutic directions for MS.

The Role of R-Ras Proteins in Normal and Pathologic Migration and Morphologic Change

The contributions that the R-Ras subfamily [R-Ras, R-Ras2/teratocarcinoma 21 (TC21), and M-Ras] of small GTP-binding proteins make to normal and aberrant cellular functions have historically been poorly understood. However, this has begun to change with the realization that all three R-Ras subfamily members are occasionally mutated in Noonan syndrome (NS), a RASopathy characterized by the development of hematopoietic neoplasms and abnormalities affecting the immune, cardiovascular, and nervous systems. Consistent with the abnormalities seen in NS, a host of new studies have implicated R-Ras proteins in physiological and pathologic changes in cellular morphology, adhesion, and migration in the cardiovascular, immune, and nervous systems. These changes include regulating the migration and homing of mature and immature immune cells, vascular stabilization, clotting, and axonal and dendritic outgrowth during nervous system development. Dysregulated R-Ras signaling has also been linked to the pathogenesis of cardiovascular disease, intellectual disabilities, and human cancers. This review discusses the structure and regulation of R-Ras proteins and our current understanding of the signaling pathways that they regulate. It explores the phenotype of NS patients and their implications for the R-Ras subfamily functions. Next, it covers recent discoveries regarding physiological and pathologic R-Ras functions in key organ systems. Finally, it discusses how R-Ras signaling is dysregulated in cancers and mechanisms by which this may promote neoplasia.

Small GTPase RAS in multiple sclerosis - exploring the role of RAS GTPase in the etiology of multiple sclerosis

RAS

signaling is involved in the development of autoimmunity in general. Multiple sclerosis (MS) is a T cell-mediated autoimmune disease of the central nervous system. It is widely recognized that a reduction of Foxp3+ regulatory T (Treg) cells is an immunological hallmark of MS, but the underlying mechanisms are unclear. In experimental autoimmune models, N-Ras and K-Ras inhibition triggers an anti-inflammatory effect up-regulating, via foxp3 elevation, the numbers and the functional suppressive properties of Tregs. Similarly, an increase in natural Tregs number during Experimental Autoimmune Encephalomyelitis (EAE) in R-RAS -/- mice results in attenuated disease. In humans, only KRAS GTPase isoform is involved in mechanism causing tolerance defects in rheumatoid arthritis (RA). T cells from these patients have increased transcription of KRAS (but not NRAS). RAS genes are major drivers in human cancers. Consequently, there has been considerable interest in developing anti-RAS inhibitors for cancer treatment. Despite efforts, no anti-RAS therapy has succeeded in the clinic. The major strategy that has so far reached the clinic aimed to inhibit activated Ras indirectly through blocking its post-translational modification and inducing its mis-localization. The disappointing clinical outcome of Farnesyl Transferase Inhibitors (FTIs) in cancers has decreased interest in these drugs. However, FTIs suppress EAE by downregulation of myelin-reactive activated T-lymphocytes and statins are currently studied in clinical trials for MS. However, no pharmacologic approaches to targeting Ras proteins directly have yet succeeded. The therapeutic strategy to recover immune function through the restoration of impaired Tregs function with the mounting evidences regarding KRAS in autoimmune mediated disorder (MS, SLE, RA, T1D) suggest as working hypothesis the direct targeting KRAS activation using cancer-derived small molecules may be clinically relevant.

ABBREVIATIONS

FTIs: Farnesyl Transferase Inhibitors; MS: Multiple Sclerosis; RRMS: Relapsing Remitting Multiple Sclerosis; PPMS: Primary Progressive Multiple Sclerosis; Tregs: regulatory T-cells; Foxp3: Forkhead box P3; EAE: Experimental Autoimmune Encephalomyelitis; T1D: Type 1 Diabete; SLE: Systemic Lupus Erythematosus; RA: Rheumatoid Arthritis; CNS: Central Nervous System; TMEV: Theiler's murine encephalomyelitis virus; FTS: farnesyl thiosalicylic acid; TCR: T-Cell Receptor; AIA: Adjuvant-induced Arthritis; EAN: experimental autoimmune neuritis; HVR: hypervariable region; HMG-CoA: 3-hydroxy-3-methylglutaryl coenzyme A reductase; PBMC: Peripheral Blood Mononuclear Cells.

R-Ras1 and R-Ras2 Are Essential for Oligodendrocyte Differentiation and Survival for Correct Myelination in the Central Nervous System

Rapid and effective neural transmission of information requires correct axonal myelination. Modifications in myelination alter axonal capacity to transmit electric impulses and enable pathological conditions. In the CNS, oligodendrocytes (OLs) myelinate axons, a complex process involving various cellular interactions. However, we know little about the mechanisms that orchestrate correct myelination. Here, we demonstrate that OLs express R-Ras1 and R-Ras2. Using female and male mutant mice to delete these proteins, we found that activation of the PI3K/Akt and Erk1/2-MAPK pathways was weaker in mice lacking one or both of these GTPases, suggesting that both proteins coordinate the activity of these two pathways. Loss of R-Ras1 and/or R-Ras2 diminishes the number of OLs in major myelinated CNS tracts and increases the proportion of immature OLs. In R-Ras1^-/- and R-Ras2^-/--null mice, OLs show aberrant morphologies and fail to differentiate correctly into myelin-forming phenotypes. The smaller OL population and abnormal OL maturation induce severe hypomyelination, with shorter nodes of Ranvier in R-Ras1^-/- and/or R-Ras2^-/- mice. These defects explain the slower conduction velocity of myelinated axons that we observed in the absence of R-Ras1 and R-Ras2. Together, these results suggest that R-Ras1 and R-Ras2 are upstream elements that regulate the survival and differentiation of progenitors into OLs through the PI3K/Akt and Erk1/2-MAPK pathways for proper myelination.SIGNIFICANCE STATEMENT In this study, we show that R-Ras1 and R-Ras2 play essential roles in regulating myelination in vivo and control fundamental aspects of oligodendrocyte (OL) survival and differentiation through synergistic activation of PI3K/Akt and Erk1/2-MAPK signaling. Mice lacking R-Ras1 and/or R-Ras2 show a diminished OL population with a higher proportion of immature OLs, explaining the observed hypomyelination in main CNS tracts. In vivo electrophysiology recordings demonstrate a slower conduction velocity of nerve impulses in the absence of R-Ras1 and R-Ras2. Therefore, R-Ras1 and R-Ras2 are essential for proper axonal myelination and accurate neural transmission.

Experimental Autoimmune Encephalomyelitis Is Successfully Controlled by Epicutaneous Administration of MOG Plus Vitamin D Analog

Multiple sclerosis (MS) is an inflammatory and demyelinating disorder of the central nervous system (CNS). Experimental autoimmune encephalomyelitis (EAE) has been widely employed to evaluate new strategies to control MS, including procedures to induce immunological tolerance. Considering that skin exposure to protein antigens can induce tolerance and that vitamin D analogs conserve immunomodulatory potential and are less toxic, we investigated the efficacy of epicutaneous application of a myelin oligodendrocyte glycoprotein peptide (MOG_35–55) associated with paricalcitol (PARI) on EAE development. Three and 11 days after EAE induction, C57BL/6 mice were treated with an occlusive patch containing MOG plus PARI. Clinical parameters were daily assessed, whereas immunological and histological evaluations were performed during the acute EAE phase. MOG and MOG + PARI significantly controlled disease development reducing weight loss and clinical score. Moreover, MOG and MOG + PARI reduced the inflammatory process and preserved the myelin sheath in the CNS. High percentages of Foxp3⁺ regulatory T cells (Tregs) and lower MHCII fluorescence intensity in dendritic cells in draining lymph nodes were concomitantly observed. MOG + PARI association was, however, more efficient being able to reduce disease incidence and clinical scores more significantly than MOG or PARI alone. This experimental group also displayed a higher ratio between mRNA expression for Foxp3 and RORc and a higher percentage of Foxp3⁺ cells in the CNS. Modulation of activation markers observed in microglial cells eluted from EAE treated mice were confirmed by in vitro studies with the BV-2 microglial cell line. The results show that MOG + PARI association applied by an epicutaneous route controlled EAE development. Protective involved mechanisms include mainly a higher proportion of Tregs and also a direct immunomodulatory effect of PARI on microglial cells.

R-Ras deficiency does not affect papain-induced IgE production in mice

Introduction

R‐Ras GTPase has recently been implicated in the regulation of immune functions, particularly in dendritic cell (DC) maturation, immune synapse formation, and subsequent T cell responses.

Methods

Here, we investigated the role of R‐Ras in allergen‐induced immune response (type 2 immune response) in Rras deficient (R‐Ras KO) and wild type (WT) mice.

Results

Initially, we found that the number of conventional DC's in the lymph nodes (LNs) was reduced in R‐Ras KO mice. The expression of co‐stimulatory CD80 and CD86 molecules on these cells was also reduced on DC's from the R‐Ras KO mice. However, there was no difference in papain‐induced immune response between the R‐Ras WT and KO as measured by serum IgE levels after the immunization. Interestingly, neither the DC number nor co‐stimulatory molecule expression was different between WT and R‐Ras KO animals after the immunization.

Conclusions

Taken together, despite having reduced number of conventional DC's in the R‐Ras KO mice and low expression of CD80 on DC's, the R‐Ras KO mice are capable of mounting papain‐induced IgE responses comparable to that of the WT mice. To our knowledge, this is the first report addressing potential differences in in vivo allergen responses regulated by the R‐Ras GTPase.

Inverse correlation of expression of microRNA-140-5p with progression of multiple sclerosis and differentiation of encephalitogenic T helper type 1 cells

The role of microRNA in the regulation of encephalitogenic T-cell development is of interest in understanding the pathogenesis of multiple sclerosis (MS). Direct binding of microRNAs to their target mRNAs usually suppresses gene expression and facilitates mRNA degradation. In this study, we observed that the expression of several microRNAs was significantly altered in patients with MS. Interestingly, the expression of miR-140-5p, among other microRNAs, was significantly decreased in the peripheral blood mononuclear cells of patients with MS, and this microRNA may regulate encephalitogenic T helper type 1 (Th1) cell differentiation. The expression level of miR-140-5p was inversely correlated with disease severity with greater reduction in relapsing disease compared with remitting disease. Transfection of synthetic miR-140-5p in peripheral blood mononuclear cells suppressed encephalitogenic Th1 differentiation. Signal transducer and activator of transcription 1 (STAT1) was the functional target of miR-140-5p - transfection of the synthetic miR-140-5p suppressed activation of STAT1 and the expression of its downstream target, T-bet. Our results suggested that miR-140-5p is probably involved in the regulation of encephalitogenic T cells in the pathogenesis of MS.

Inhibition of myeloperoxidase at the peak of experimental autoimmune encephalomyelitis restores blood-brain barrier integrity and ameliorates disease severity

Oxidative stress is thought to contribute to disease pathogenesis in the central nervous system (CNS) disease multiple sclerosis (MS). Myeloperoxidase (MPO), a potent peroxidase that generates toxic radicals and oxidants, is increased in the CNS during MS. However, the exact mechanism whereby MPO drives MS pathology is not known. We addressed this question by inhibiting MPO in mice with experimental autoimmune encephalomyelitis (EAE) using our non-toxic MPO inhibitor N-acetyl lysyltyrosylcysteine amide (KYC). We found that therapeutic administration of KYC for 5 days starting at the peak of disease significantly attenuated EAE disease severity, reduced myeloid cell numbers and permeability of the blood-brain barrier. These data indicate that inhibition of MPO by KYC restores blood-brain barrier integrity thereby limiting migration of myeloid cells into the CNS that drive EAE pathogenesis. In addition, these observations indicate that KYC may be an effective therapeutic agent for the treatment of MS. We propose that during experimental autoimmune encephalomyelitis (EAE) onset macrophages and neutrophils migrate into the CNS and upon activation release myeloperoxidase (MPO) that promotes disruption of the blood-brain barrier (BBB) and disease progression. KYC restores BBB function by inhibiting MPO activity and in so doing ameliorates disease progression.

Interrelatedness between dysbiosis in the gut microbiota due to immunodeficiency and disease penetrance of colitis

The composition of the microbiome in health and disease has only recently become a major research focus. Although it is clear that an imbalance or dysbiosis in the microbiota is associated with disease, its interrelatedness to disease penetrance is largely unknown. Inflammatory bowel disease (IBD) is an excellent disease in which to explore these questions because of the extensive genetic studies identifying disease susceptibility loci and the ability to easily sample the intestinal microbiota in IBD patients due to the accessibility of stool samples. In addition, mouse models of IBD have contributed to our understanding of the interrelatedness of the gut microbiota and genes associated with IBD. The power of the mouse studies is that multiple colitis models exist that can be used in combination with genetically modified mice that harbour deficiencies in IBD susceptibility genes. Collectively, these studies revealed that bacterial dysbiosis does occur in human IBD and in mouse colitis models. In addition, with an emphasis on immune genes, the mouse studies provided evidence that specific immune regulatory proteins associated with IBD influence the gut microbiota in a manner consistent with disease penetrance. In this review, we will discuss studies in both humans and mice that demonstrate the impact of immunodeficiences in interleukin-10, interleukin-17, nucleotide-binding oligomerization domain (NOD) 2, NOD-like receptor proteins 3 and 6, Toll-like receptor or IgA have on the interrelatedness between the composition of the gut microbiota and disease penetrance of IBD and its mouse models.

Gut Microbial Dysbiosis Due to Helicobacter Drives an Increase in Marginal Zone B Cells in the Absence of IL-10 Signaling in Macrophages

It is clear that IL-10 plays an essential role in maintaining homeostasis in the gut in response to the microbiome. However, it is unknown whether IL-10 also facilitates immune homeostasis at distal sites. To address this question, we asked whether splenic immune populations were altered in IL-10-deficient (Il10(-/-)) mice in which differences in animal husbandry history were associated with susceptibility to spontaneous enterocolitis that is microbiome dependent. The susceptible mice exhibited a significant increase in splenic macrophages, neutrophils, and marginal zone (MZ) B cells that was inhibited by IL-10 signaling in myeloid, but not B cells. The increase in macrophages was due to increased proliferation that correlated with a subsequent enhancement in MZ B cell differentiation. Cohousing and antibiotic treatment studies suggested that the alteration in immune homeostasis in the spleen was microbiome dependent. The 16S rRNA sequencing revealed that susceptible mice harbored a different microbiome with a significant increase in the abundance of the bacterial genus Helicobacter. The introduction of Helicobacter hepaticus to the gut of nonsusceptible mice was sufficient to drive macrophage expansion and MZ B cell development. Given that myeloid cells and MZ B cells are part of the first line of defense against blood-borne pathogens, their increase following a breach in the gut epithelial barrier would be protective. Thus, IL-10 is an essential gatekeeper that maintains immune homeostasis at distal sites that can become functionally imbalanced upon the introduction of specific pathogenic bacteria to the intestinal track.

Resistance of R-Ras knockout mice to skin tumour induction

The R-ras gene encodes a small GTPase that is a member of the Ras family. Despite close sequence similarities, R-Ras is functionally distinct from the prototypic Ras proteins; no transformative activity and no activating mutations of R-Ras in human malignancies have been reported for it. R-Ras activity appears inhibitory towards tumour proliferation and invasion, and to promote cellular quiescence. Contrary to this, using mice with a deletion of the R-ras gene, we found that R-Ras facilitates DMBA/TPA-induced skin tumour induction. The tumours appeared in wild-type (WT) mice on average 6 weeks earlier than in R-Ras knockout (R-Ras KO) mice. WT mice developed almost 6 times more tumours than R-Ras KO mice. Despite strong R-Ras protein expression in the dermal blood vessels, no R-Ras could be detected in the epidermis from where the tumours arose. The DMBA/TPA skin tumourigenesis-model is highly dependent upon inflammation, and we found a greatly attenuated skin inflammatory response to DMBA/TPA-treatment in the R-Ras KO mice in the context of leukocyte infiltration and proinflammatory cytokine expression. Thus, these data suggest that despite its characterised role in promoting cellular quiescence, R-Ras is pro-tumourigenic in the DMBA/TPA tumour model and important for the inflammatory response to DMBA/TPA treatment.