The Involvement of Immune Semaphorins in the Pathogenesis of Inflammatory Bowel Diseases (IBDs)

The Involvement of Semaphorins in the Pathogenesis of Skin Diseases

Semaphorins belong to a group of membrane and secretory proteins that act as ligands for several receptor families and are involved in modulating cell signaling pathways. They bind multimeric receptor complexes on the cell membrane to exert their effects and initiate unique intracellular signal transduction cascades. These proteins can influence several processes that are very important for cell function, such as cell division and differentiation. Semaphorins are involved in cell migration, apoptosis, cell adhesion, aggregation, and numerous immune processes due to their immunoregulatory effects. Semaphorins are expressed in keratinocytes, which is why they have become a target for studies on the pathogenesis of skin diseases. Most studies to date on the role of semaphorins in the pathogenesis of skin diseases have been carried out in cellular or animal models, and there are few clinical studies evaluating the role of semaphorins in the pathogenesis and therapy of skin diseases. In this narrative review, we summarized the current state of knowledge on the role of semaphorins in the pathogenesis of skin diseases and their potential importance as targets for therapy. We also tried to present the key findings and weaknesses of previous research in this field. The novelty of this article lies in the comprehensive presentation of the role of semaphorins in the pathogenesis of skin diseases, including the results of studies on cell cultures and animal models, elucidating the mechanisms and signaling pathways through which semaphorins affect the development of skin diseases, as well as on the presentation of the results of existing clinical trials evaluating the role of semaphorins in the pathogenesis of skin diseases, and as potential therapeutic targets.

Class IV semaphorins in disease pathogenesis

Semaphorins are a large family of secreted and/or transmembrane proteins, originally identified as proteins that function in axon guidance during neuronal development. However, semaphorins play crucial roles in other physiological and pathological processes, including immune responses, angiogenesis, maintenance of tissue homeostasis, and cancer progression. Class IV semaphorins may be present as transmembrane and soluble forms and are implicated in the pathogenesis of various diseases. This review discusses recent progress on the roles of class IV semaphorins determined by clinical and experimental pathology studies.

mRNA-engineered mesenchymal stromal cells expressing CXCR2 enhances cell migration and improves recovery in IBD

Mesenchymal stromal cells (MSCs) have shown significant heterogeneity in terms of therapeutic efficacy for inflammatory bowel disease (IBD) treatment, which may be due to an insufficient number of MSCs homing to the damaged tissue of the colon. Engineering MSCs with specific chemokine receptors can enhance the homing ability by lentiviral transduction. However, the unclear specific chemokine profile related to IBD and the safety concerns of viral-based gene delivery limit its application. Thus, a new strategy to modify MSCs to express specific chemokine receptors using mRNA engineering is developed to evaluate the homing ability of MSCs and its therapeutic effects for IBD. We found that CXCL2 and CXCL5 were highly expressed in the inflammatory colon, while MSCs minimally expressed the corresponding receptor CXCR2. Transient expression of CXCR2 in MSC was constructed and exhibited significantly enhanced migration to the inflamed colons, leading to a robust anti-inflammatory effect and high efficacy. Furthermore, the high expression of semaphorins7A on MSCs were found to induce the macrophages to produce IL-10, which may play a critical therapeutic role. This study demonstrated that the specific chemokine receptor CXCR2 mRNA-engineered MSCs not only improves the therapeutic efficacy of IBD but also provides an efficient and safe MSC modification strategy.

Semaphorin 3E Regulates the Response of Macrophages to Lipopolysaccharide-Induced Systemic Inflammation

Semaphorin 3E (Sema3E) is a secreted protein that was initially discovered as a neuronal guidance cue. Recent evidence showed that Sema3E plays an essential role in regulating the activities of various immune cells. However, the exact role of Sema3E in macrophage function, particularly during inflammation, is not fully understood. We studied the impact of Sema3E gene deletion on macrophage function during the LPS-induced acute inflammatory response. We found that Sema3E-deficient (Sema3e^-/- ) mice were better protected from LPS-induced acute inflammation as exemplified by their superior clinical score and effective temperature control compared with their wild-type littermates. This superior control of inflammatory response in Sema3e^-/- mice was associated with significantly lower phosphorylation of ERK1/2, AKT, STAT3, and NF-κB, and a concomitant reduction in inducible NO synthase expression and production of TNF and IL-6 compared with their Sema3e^+/+ littermates. Sema3e^-/- mice also contained significantly higher numbers of activated macrophages compared with their Sema3e^+/+ littermates at both baselines and after LPS challenge. In vivo-specific deletion of the Sema3E high-affinity receptor, plexinD1, on macrophages led to the improvement in clinical disease following exposure to a lethal dose of LPS. Collectively, our data show that Sema3E plays an essential role in dampening the early inflammatory response to LPS by regulating macrophage function, suggesting an essential role of this pathway in macrophage inflammatory response.

Altered expression of regulatory molecules in the skin of psoriasis

The presence of T regulatory cells (Tregs) is highly required in normal skin in order to maintain immune tolerance to commensal microbes and to prevent the development of immune-mediated inflammation. Psoriasis is a chronic inflammatory skin disease in which effector T cells, namely, Th17 and their relevant pro-inflammatory cytokines are increased in peripheral blood as well as in the inflamed skin. The status of Tregs in psoriatic skin is continuously studied. In this case, CD4 + CD25high T cells and other regulatory cytokines such as IL-35 are demonstrated to be significantly decreased. Aiming to better characterize Tregs in psoriatic skin and to establish the finding of their abnormal balance, we assessed the expression of semaphorin3A and neuropilin-1 (both reported as biomarkers of Tregs). Semaphorin3A and neuropilin-1 expressing Tregs were found to be significantly decreased in psoriatic skin when compared to normal skin. These findings were supported by demonstrating the downregulation of IL-10 expression in psoriatic skin. Our findings suggest that semaphoring3A may turn to be a new promising therapeutic approach in the process of improving Treg function in psoriasis.

Semaphorin-3E attenuates intestinal inflammation through the regulation of the communication between splenic CD11C+ and CD4+ CD25- T-cells

BACKGROUND AND PURPOSE

An alteration in the communication between the innate and adaptive immune cells is a hallmark of ulcerative colitis (UC). Semaphorin-3E (SEMA3E), a secreted guidance protein, regulates various immune responses.

EXPERIMENTAL APPROACH

We investigated the expression of SEMA3E in colonic biopsies of active UC patients and its mechanisms in Sema3e-/- mice using an experimental model of UC.

KEY RESULTS

SEMA3E level was decreased in active UC patients and negatively correlated with pro-inflammatory mediators. Colonic expression of SEMA3E was reduced in colitic Sema3e+/+ mice, and recombinant (rec-) Plexin-D1 treatment exacerbated disease severity. In vivo rec-SEMA3E treatment restored SEMA3E level in colitic Sema3e+/+ mice. In Sema3e-/- mice, disease severity was increased, and rec-SEMA3E ameliorated these effects. Lack of Sema3e increased the expression of CD11c and CD86 markers. Colitic Sema3e-/- splenocytes and splenic CD11c+ cells produced more IL-12/23 and IFN-γ compared to Sema3e+/+ , and rec-SEMA3E reduced their release as much as NF-κB inhibitors, whereas an NF-κB activator increased their production and attenuated the effect of rec-SEMA3E. Colitic Sema3e-/- splenic CD11c+ /CD4+ CD25- T-cell co-cultures produced higher concentrations of IFN-γ and IL-17 when compared to colitic Sema3e+/+ splenic cell co-cultures, and rec-SEMA3E decreased these effects. In vitro, anti-IL-12p19 and -12p35 antibodies and rec-IL-12 and -23 treatment confirmed the crosstalk between CD11c+ and CD4+ CD25- T-cells.

CONCLUSION AND IMPLICATIONS

SEMA3E is reduced in colitis and modulates colonic inflammation by regulating the interaction between CD11c+ and CD4+ CD25- T-cells via an NF-κB-dependent mechanism. Thus, SEMA3E could be a potential therapeutic target for UC patients.

Aggravated mucosal and immune damage in a mouse model of ulcerative colitis with stress

The aim of the present study was to determine the influence of stress on the colonic mucosa and immune system and to further investigate the association between stress and development and pathogenesis of ulcerative colitis (UC). Mice were treated with 2,4,6-trinitrobenzenesulfonic acid to induce an animal model of UC, and stress was induced by water immersion and restraint. Subsequently, the disease activity index (DAI), secretory immunoglobulin A (sIgA), IgA, interleukin (IL)-6 and -8, tumor necrosis factor-α (TNF-α), complement component (C)3 and C4, and alterations in the colonic mucosa were observed. The DAI scores and the expression levels of IL-6, IL-8 and TNF-α significantly increased in the experimental UC mice compared with the control mice, while the expression levels of IgA and sIgA decreased (all P<0.01). DAI and colonic mucosa damage scores increased in the stress-treated mouse models of UC compared with the untreated mouse models of UC (P<0.05). Expression levels of IgA and sIgA decreased, while IL-6, IL-8 and TNF-α further increased in the stress-treated UC mice (P<0.05). The expression levels of C3 and C4 were not affected by stress or UC (P>0.05). These results indicated that UC may be associated with an immune disorder and that stress can aggravate colonic mucosa injury and alter the immune response. Furthermore, stress and immunity may serve roles in the pathogenesis of UC.

Circulating Semaphorin 4D as a Marker for Predicting Radiographic Progression in Patients with Rheumatoid Arthritis

Semaphorin 3A (Sema3A) and semaphorin 4D (Sema4D) are molecules which regulate immune responses as well as bone remodeling process. The aim of this study was to evaluate the serum levels of Sema3A and Sema4D and to investigate their clinical significance in rheumatoid arthritis (RA). The serum levels of Sema3A and Sema4D were measured in 130 patients with RA and 65 sex- and age-matched healthy individuals. Circulating levels of biomarkers of RA-related inflammation and bone turnover such as tumor necrosis factor- (TNF-) α, interleukin- (IL-) 6, IL-22, IL-34, osteopontin, Dkk-1, and sclerostin were also measured. Disease activity was determined by the 28-joint disease activity score (DAS28), and radiographic joint damage was assessed by the modified Sharp van der Heijde score (SHS). The serum levels of Sema3A were significantly higher in patients with RA than those in healthy controls (p < 0.001), whereas serum4D levels did not differ between the two groups. The levels of Sema4D showed a positive correlation with C-reactive protein (p = 0.001) and IL-6 (p < 0.001) levels, whereas the levels of Sema3A showed a negative correlation with Dkk-1 (p = 0.007) and TNF-α (p = 0.001). Even though Sema3A and Sema4D levels were comparable between RA patients with DAS28> 3.2 and with DAS28 ≤ 3.2, RA patients with radiographic progression (ΔSHS change/year ≥ 1) had significantly higher baseline levels of Sema4D than those without progression (p = 0.029). Additionally, when RA patients were divided into 3 groups using tertiles of Sema4D levels, the percentage of progressors was significantly increased (p = 0.045). In multivariate logistic regression analysis, serum Sema4D levels were an independent risk factor for radiographic progression. Our results suggest that the baseline levels of Sema4D might be a useful marker to identify RA patients with subsequent radiographic progression and that Sema4D may be an active mediator involved in RA-induced joint damage.

Immunomodulatory effects of probiotics: Can they be used to treat allergies and autoimmune diseases?

As a person ages, physiological, immunological and gut microbiome changes collectively result in an array of chronic conditions. According to the 'hygiene hypothesis' the increasing prevalence of immune-mediated disorders may be related to intestinal dysbiosis, leading to immune dysfunction and associated conditions such as eczema, asthma, allergies and autoimmune diseases. Beneficial probiotic bacteria can be utilized by increasing their abundance within the gastrointestinal lumen, which in turn will modulate immune cells, such as, T helper (Th)-1, Th2, Th17, regulatory T (Treg) cells and B cells, which have direct relevance to human health and the pathogenesis of immune disorders. Here, we describe the cross-talk between probiotics and the gastrointestinal immune system, and their effects in relation to inflammatory bowel disease, multiple sclerosis, allergies and atopic dermatitis.

Guidance Molecules in Vascular Smooth Muscle

Several highly conserved families of guidance molecules, including ephrins, Semaphorins, Netrins, and Slits, play conserved and distinct roles in tissue remodeling during tissue patterning and disease pathogenesis. Primarily, these guidance molecules function as either secreted or surface-bound ligands that interact with their receptors to activate a variety of downstream effects, including cell contractility, migration, adhesion, proliferation, and inflammation. Vascular smooth muscle cells, contractile cells comprising the medial layer of the vessel wall and deriving from the mural population, regulate vascular tone and blood pressure. While capillaries lack a medial layer of vascular smooth muscle, mural-derived pericytes contribute similarly to capillary tone to regulate blood flow in various tissues. Furthermore, pericyte coverage is critical in vascular development, as perturbations disrupt vascular permeability and viability. During cardiovascular disease, smooth muscle cells play a more dynamic role in which suppression of contractile markers, enhanced proliferation, and migration lead to the progression of aberrant vascular remodeling. Since many types of guidance molecules are expressed in vascular smooth muscle and pericytes, these may contribute to blood vessel formation and aberrant remodeling during vascular disease. While vascular development is a large focus of the existing literature, studies emerged to address post-developmental roles for guidance molecules in pathology and are of interest as novel therapeutic targets. In this review, we will discuss the roles of guidance molecules in vascular smooth muscle and pericyte function in development and disease.

Emerging role of semaphorin-3A in autoimmune diseases

Autoimmune diseases (ADs) are featured by the body's immune responses being directed against its own tissues, resulting in prolonged inflammation and subsequent tissue damage. Currently, the exact pathogenesis of ADs remains not fully elucidated. Semaphorin-3A (Sema3A), a secreted member of semaphorin family, is a potent immunoregulator during all immune response stages. Sema3A has wide expression, such as in bone, connective tissue, kidney, neurons, and cartilage. Sema3A can downregulate ADs by suppressing the over-activity of both T-cell and B-cell autoimmunity. Moreover, Sema3A shows the ability to enhance T-cell and B-cell regulatory properties that control ADs, including systemic lupus erythematosus, rheumatoid arthritis, multiple sclerosis, and systemic sclerosis. However, it can also induce ADs when overexpressed. Together, these data strongly suggest that Sema3A plays a pivotal role in ADs, and it may be a promising treatment target for these diseases. In the present review, we focus on the immunological functions of Sema3A and summarize recent studies on the involvement of Sema3A in the pathogenesis of ADs; the discoveries obtained from recent findings may translate into novel therapeutic agent for ADs.

Neuroimmune semaphorins as costimulatory molecules and beyond

Several neuronal guidance proteins, known as semaphorin molecules, function in the immune system. This dual tissue performance has led to them being defined as "neuroimmune semaphorins". They have been shown to regulate T cell activation by serving as costimulatory molecules. Similar to classical costimulatory molecules, neuroimmune semaphorins are either constitutively or inducibly expressed on immune cells. In contrast to the classical costimulatory molecule function, the action of neuroimmune semaphorins requires the presence of two signals, the first one provided by TCR/MHC engagement, and the second one provided by B7/CD28 interaction. Thus, neuroimmune semaphorins serve as a "signal three" for immune cell activation and regulate the overall intensity of immune response. The current knowledge on their structures, multiple receptors, specific cell/tissue/organ expression, and distinct functions in different diseases are summarized and discussed in this review.

Decreased Expression of Semaphorin3A/Neuropilin-1 Signaling Axis in Apical Periodontitis

Apical periodontitis (AP) is a chronic infection of endodontic origin accompanied with bone destruction around the apical region. Semaphorin3A (Sema3A) and neuropilin-1 (Nrp1) are regarded as a pair of immune regulators in bone metabolism. In this study, we firstly investigated the expression pattern of Sema3A/Nrp1 in apical periodontitis and its correlation with bone destruction. Using rat animal model, we analysed the level of mandibular bone destruction and the expression of Sema3A/Nrp1 on days 0, 7, 14, 21, 28, and 35 after pulp exposure. In addition, clinical samples from apical periodontitis patients were obtained to analyse the expression of Sema3A/Nrp1. These results indicated that the bone destruction level expanded from days 7 to 35. The number of positive cells and level of mRNA expression of Sema3A/Nrp1 were significantly decreased from days 7 to 35, with a negative correlation with bone destruction. Moreover, expression of Sema3A/Nrp1 in the AP group was reduced compared to the control group of clinical samples. In conclusion, decreased expression of Sema3A/Nrp1 was observed in periapical lesions and is potentially involved in the bone resorption of the periapical area, suggesting that Sema3A/Nrp1 may contribute to the pathological development of apical periodontitis.

Semaphorin3A: A potential therapeutic tool in immune-mediated diseases

The significance of semaphorin3A (sema3A) in regulating immune-mediated inflammation is widely reported. There are multiple mechanisms involved in the process of sema3A-mediated regulation. One of them is the ability of sema3A to maintain a sufficient regulation of both T-cell and B-cell activation. Because it is involved in the pathogenesis of many autoimmune, infectious, and malignant diseases, sema3A turns to be a promising therapeutic tool to be studied and applied in these diseases.

The role of Sema4A in angiogenesis, immune responses, carcinogenesis, and retinal systems

Semaphorins were originally identified as axon guidance cues that regulate the functional activity of axons in the nervous system. In addition, accumulating evidence indicates that semaphorins have multiple functions in physiological and pathogenic processes, including vascular development, tumor progression, and immune responses. Sema4A is a semaphorin expressed in immune cells, and is thus termed an “immune semaphorin.” Sema4A has 4 types of receptors: Plexin D family, Plexin B family, Tim-2, and Nrp-1. Recent studies suggest that Sema4A plays critical roles in many processes including cell–cell interactions, immune-cell activation, differentiation, and migration. In other studies, Sema4A is also associated with carcinogenesis and retinal systems. In this review, we summarize current knowledge regarding the biology of Sema4A in relation to angiogenesis, immune responses, colorectal cancer, and the retina.

Semaphorins 4A and 4D in chronic inflammatory diseases

Long-term inflammatory processes directed at a particular endogenous or exogenous antigen, or sometimes of unknown etiology, form the pathogenetic basis for many debilitating conditions, such as cardiovascular, pulmonary, autoimmune, neurologic diseases, and cancer. Recent discoveries of neuroimmune semaphorins 4A and 4D (Sema4A and Sema4D, respectively) expression and function in the immune system and their key regulatory roles in fine tuning of inflammatory processes made them the molecules of interest for a potential immunotherapy. In this short review, we discuss the current knowledge in the Sema4A and Sema4D actions in chronic inflammation underlying the outlined above diseases.