Deciphering the alternatively activated (M2) phenotype of macrophages in scleroderma

Nintedanib downregulates the profibrotic M2 phenotype in cultured monocyte-derived macrophages obtained from systemic sclerosis patients affected by interstitial lung disease

BACKGROUND

Systemic sclerosis (SSc) is an autoimmune connective tissue disease characterized by vasculopathy and progressive fibrosis of skin and several internal organs, including lungs. Macrophages are the main cells involved in the immune-inflammatory damage of skin and lungs, and alternatively activated (M2) macrophages seem to have a profibrotic role through the release of profibrotic cytokines (IL10) and growth factors (TGFβ1). Nintedanib is a tyrosine kinase inhibitor targeting several fibrotic mediators and it is approved for the treatment of SSc-related interstitial lung disease (ILD). The study aimed to evaluate the effect of nintedanib in downregulating the profibrotic M2 phenotype in cultured monocyte-derived macrophages (MDMs) obtained from SSc-ILD patients.

METHODS

Fourteen SSc patients, fulfilling the 2013 ACR/EULAR criteria for SSc, 10 SSc patients affected by ILD (SSc-ILD pts), 4 SSc patients non affected by ILD (SSc pts no-ILD), and 5 voluntary healthy subjects (HSs), were recruited at the Division of Clinical Rheumatology-University of Genova, after obtaining Ethical Committee approval and patients' informed consent. Monocytes were isolated from peripheral blood, differentiated into MDMs, and then maintained in growth medium without any treatment (untreated cells), or treated with nintedanib (0.1 and 1µM) for 3, 16, and 24 h. Gene expression of macrophage scavenger receptors (CD204, CD163), mannose receptor-1 (CD206), Mer tyrosine kinase (MerTK), identifying M2 macrophages, together with TGFβ1 and IL10, were evaluated by quantitative real-time polymerase chain reaction. Protein synthesis was investigated by Western blotting and the level of active TGFβ1 was evaluated by ELISA. Statistical analysis was carried out using non-parametric Wilcoxon test.

RESULTS

Cultured untreated SSc-ILD MDMs showed a significant increased protein synthesis of CD206 (p < 0.05), CD204, and MerTK (p < 0.01), together with a significant upregulation of the gene expression of MerTK and TGFβ1 (p < 0.05; p < 0.01) compared to HS-MDMs. Moreover, the protein synthesis of CD206 and MerTK and the gene expression of TGFβ1 were significantly higher in cultured untreated MDMs from SSc-ILD pts compared to MDMs without ILD (p < 0.05; p < 0.01). In cultured SSc-ILD MDMs, nintedanib 0.1 and 1µM significantly downregulated the gene expression and protein synthesis of CD204, CD206, CD163 (p < 0.05), and MerTK (p < 0.01) compared to untreated cells after 24 h of treatment. Limited to MerTK and IL10, both nintedanib concentrations significantly downregulated their gene expression already after 16 h of treatment (p < 0.05). In cultured SSc-ILD MDMs, nintedanib 0.1 and 1µM significantly reduced the release of active TGFβ1 after 24 h of treatment (p < 0.05 vs. untreated cells).

CONCLUSIONS

In cultured MDMs from SSc-ILD pts, nintedanib seems to downregulate the profibrotic M2 phenotype through the significant reduction of gene expression and protein synthesis of M2 cell surface markers, together with the significant reduction of TGFβ1 release, and notably MerTK, a tyrosine kinase receptor involved in lung fibrosis.

Ocular Involvement in Systemic Sclerosis: Updated Review and New Insights on Microvascular Impairment

Systemic sclerosis (SSc) is a chronic multisystemic disease characterized by immunological activation, diffuse vasculopathy, and generalized fibrosis exhibiting a variety of symptoms. A recognized precursor of SSc is Raynaud's phenomenon, which is part of the very early disease of systemic sclerosis (VEDOSS) in combination with nailfold videocapillaroscopy (NVC) impairment. The pathophysiology of ocular involvement, alterations in internal organs, and body integumentary system involvement in SSc patients are complicated and poorly understood, with multiple mechanisms presumptively working together. The most prevalent ocular symptoms of SSc are abnormalities of the eyelids and conjunctiva as well as dry eye syndrome, due to fibroblasts' dysfunction and inflammation of the ocular surface. In particular, lagophthalmos, blepharophimosis limitation of eyelid motion, eyelid telangiectasia, and rigidity or tightening of the lids may affect up to two-third of the patients. In addition, reduction in central corneal thickness, iris defects and higher rates of glaucoma were reported. In the first reports based on retinography or fluorescein angiography, about 50% of SSc patients showed signs of vascular disease: peripheral artery occlusion, thinning of retinal pigment epithelium and choroidal capillaries, ischemic areas surrounded by intraretinal extravasation and microaneurysms, and peripheral capillary non-perfusion. Successively, thanks to the advent of optical coherence tomography angiography (OCTA), several studies highlighted significant impairment of either the choriocapillaris and retinal vascular plexuses, also correlating with NVC involvement and skin disease, even in VEDOSS disease. Given the sensitivity of this technique, ocular micro-vasculopathy may act as a tool for early SSc identification and discriminate between disease stages.

Total glucosides of paeony alleviates scleroderma by inhibiting type I interferon responses

ETHNOPHARMACOLOGICAL RELEVANCE

Type I interferon (IFN) is believed to play a pathogenic role in systemic sclerosis (SSc, also called scleroderma), which is an autoimmune rheumatic disease. Our previous studies have found that Chinese medicine formula Si-Ni-San (SNS, composed of Glycyrrhiza uralensis Fisch., Bupleurum chinense DC., Paeonia lactiflora Pall., and Citrus aurantium L.) had inhibitory effects on type I IFN responses. Among these herbal products, Paeonia lactiflora Pall. has been traditionally used to treat inflammation-related diseases, yet its therapeutic effects against type I IFN-related diseases and potential bioactive ingredients are not characterized.

AIM OF THE STUDY

We aim to identify bioactive ingredient with anti-type I IFN activity from herbal products in SNS and further elucidate its therapeutic effect against scleroderma and underlying mechanisms.

MATERIALS AND METHODS

We constructed a Gaussia-luciferase (Gluc) reporter assay system to identify ingredients with anti-type I IFN activities from SNS. In RAW264.7 cells, real-time PCR (RT-PCR) and western blotting were used to investigate the induction of type I IFN pathway. Additionally, in a bleomycin (BLM)-induced experimental scleroderma model, the expression of fibrotic genes, type I IFN-related genes, inflammatory cytokines, and cytotoxic granules were measured by RT-PCR, and the histopathological changes were determined by H&E staining, Masson's staining and immunohistochemistry analysis.

RESULTS

Our data demonstrated that total glucosides of paeony (TGP) was the bioactive component of SNS that selectively inhibited TLR3-mediated type I IFN responses and blocked type I IFN-induced downstream JAK-STAT signaling pathways. In the BLM-induced scleroderma mouse model, TGP ameliorated skin fibrosis by inhibiting multiple targets in the upstream and downstream of type I IFN signaling. Further research found that TGP hindered polarization of M2 macrophages and their profibrotic effects and reduced cytotoxic T lymphocytes and their cytotoxic granules by suppressing Cxcl9 and Cxcl10 in the skin tissue of scleroderma mice.

CONCLUSIONS

Our study not only sheds novel lights into the immunoregulative effects of TGP but also provides convincing evidence to develop TGP-based therapies in the treatment of scleroderma and other autoimmune diseases associated with type I IFN signatures.

CLASSIFICATION

Skin.

Adipose-Derived Stem Cells Attenuate Skin Fibrosis and Improve Fat Retention of a Localized Scleroderma Mouse Model

BACKGROUND

Although autologous fat grafting is a feasible surgical technique to improve facial deformity in patients with localized scleroderma, its success is limited by the low graft retention induced by the local inflammatory environment. This study investigated the potential effect of adipose-derived stem cells (ASCs) on skin fibrosis and fat retention in a localized scleroderma mouse model.

METHODS

BALB/C nude mice that were induced by bleomycin to establish a localized scleroderma model were divided randomly into five groups: blank control; fat grafting; and low, moderate, and high doses of ASC-assisted fat grafting. The backs of the mice were subcutaneously injected with phosphate-buffered saline or fat, or fat with low, moderate, and high doses of ASCs (1 × 10 5 /mL, 5 × 10 5 /mL, and 25 × 10 5 /mL, respectively). The skin fibrosis and fat retention were analyzed after 1 month or 3 months, respectively.

RESULTS

Compared to the disease model group, the fat-grafting group, and the low- and moderate-dose ASC-enriched groups, the high-dose ASCs significantly attenuated skin fibrosis, inhibited the production of type III collagen and transforming growth factor-β1, increased fat graft retention, enhanced the expression of angiogenesis-related cytokines and angiogenesis, and increased the expression of adipogenesis-related cytokines.

CONCLUSIONS

The results demonstrated that high-dose ASCs attenuated skin fibrosis and improved fat retention in a localized scleroderma model by reducing inflammation and by promoting angiogenesis and adipogenesis. The authors further demonstrated that ASCs enhanced adipogenesis through the AKT/ERK signaling pathway.

CLINICAL RELEVANCE STATEMENT

Fat grafting has been used to treat localized scleroderma patients but with low fat retention. In this study, ASC attenuated skin fibrosis and improved fat retention in the localized scleroderma model, providing evidence for cell therapy in future application of localized scleroderma treatment.

Circulating Soluble CD163, Associations With Cardiovascular Outcomes and Mortality, and Identification of Genetic Variants in Older Individuals: The Cardiovascular Health Study

Background Monocytes/macrophages participate in cardiovascular disease. CD163 (cluster of differentiation 163) is a monocyte/macrophage receptor, and the shed sCD163 (soluble CD163) reflects monocyte/macrophage activation. We examined the association of sCD163 with incident cardiovascular disease events and performed a genome-wide association study to identify sCD163-associated variants. Methods and Results We measured plasma sCD163 in 5214 adults (aged ≥65 years, 58.7% women, 16.2% Black) of the CHS (Cardiovascular Health Study). We used Cox regression models (associations of sCD163 with incident events and mortality); median follow-up was 26 years. Genome-wide association study analyses were stratified on race. Adjusted for age, sex, and race and ethnicity, sCD163 levels were associated with all-cause mortality (hazard ratio [HR], 1.08 [95% CI, 1.04-1.12] per SD increase), cardiovascular disease mortality (HR, 1.15 [95% CI, 1.09-1.21]), incident coronary heart disease (HR, 1.10 [95% CI, 1.04-1.16]), and incident heart failure (HR, 1.18 [95% CI, 1.12-1.25]). When further adjusted (eg, cardiovascular disease risk factors), only incident coronary heart disease lost significance. In European American individuals, genome-wide association studies identified 38 variants on chromosome 2 near MGAT5 (top result rs62165726, P=3.3×10^-18),19 variants near chromosome 17 gene ASGR1 (rs55714927, P=1.5×10^-14), and 18 variants near chromosome 11 gene ST3GAL4. These regions replicated in the European ancestry ADDITION-PRO cohort, a longitudinal cohort study nested in the Danish arm of the Anglo-Danish-Dutch study of Intensive Treatment Intensive Treatment In peOple with screeNdetcted Diabetes in Primary Care. In Black individuals, we identified 9 variants on chromosome 6 (rs3129781 P=7.1×10^-9) in the HLA region, and 3 variants (rs115391969 P=4.3×10^-8) near the chromosome 16 gene MYLK3_. Conclusions Monocyte function, as measured by sCD163, may be predictive of overall and cardiovascular-specific mortality and incident heart failure.

Therapeutic Options for Systemic Sclerosis: Current and Future Perspectives in Tackling Immune-Mediated Fibrosis

Systemic sclerosis (SSc) is a severe auto-immune, rheumatic disease, characterized by excessive fibrosis of the skin and visceral organs. SSc is accompanied by high morbidity and mortality rates, and unfortunately, few disease-modifying therapies are currently available. Inflammation, vasculopathy, and fibrosis are the key hallmarks of SSc pathology. In this narrative review, we examine the relationship between inflammation and fibrosis and provide an overview of the efficacy of current and novel treatment options in diminishing SSc-related fibrosis based on selected clinical trials. To do this, we first discuss inflammatory pathways of both the innate and acquired immune systems that are associated with SSc pathophysiology. Secondly, we review evidence supporting the use of first-line therapies in SSc patients. In addition, T cell-, B cell-, and cytokine-specific treatments that have been utilized in SSc are explored. Finally, the potential effectiveness of tyrosine kinase inhibitors and other novel therapeutic approaches in reducing fibrosis is highlighted.

Scleroderma-like Impairment in the Network of Telocytes/CD34+ Stromal Cells in the Experimental Mouse Model of Bleomycin-Induced Dermal Fibrosis

Considerable evidence accumulated over the past decade supports that telocytes (TCs)/CD34⁺ stromal cells represent an exclusive type of interstitial cells identifiable by transmission electron microscopy (TEM) or immunohistochemistry in various organs of the human body, including the skin. By means of their characteristic cellular extensions (telopodes), dermal TCs are arranged in networks intermingled with a multitude of neighboring cells and, hence, they are thought to contribute to skin homeostasis through both intercellular contacts and releasing extracellular vesicles. In this context, fibrotic skin lesions from patients with systemic sclerosis (SSc, scleroderma) appear to be characterized by a disruption of the dermal network of TCs, which has been ascribed to either cell degenerative processes or possible transformation into profibrotic myofibroblasts. In the present study, we utilized the well-established mouse model of bleomycin-induced scleroderma to gain further insights into the TC alterations found in cutaneous fibrosis. CD34 immunofluorescence revealed a severe impairment in the dermal network of TCs/CD34⁺ stromal cells in bleomycin-treated mice. CD31/CD34 double immunofluorescence confirmed that CD31^-/CD34⁺ TC counts were greatly reduced in the skin of bleomycin-treated mice compared with control mice. Ultrastructural signs of TC injury were detected in the skin of bleomycin-treated mice by TEM. The analyses of skin samples from mice treated with bleomycin for different times by either TEM or double immunostaining and immunoblotting for the CD34/α-SMA antigens collectively suggested that, although a few TCs may transition to α-SMA⁺ myofibroblasts in the early disease stage, most of these cells rather undergo degeneration, and then are lost. Taken together, our data demonstrate that TC changes in the skin of bleomycin-treated mice mimic very closely those observed in human SSc skin, which makes this experimental model a suitable tool to (i) unravel the pathological mechanisms underlying TC damage and (ii) clarify the possible contribution of the TC loss to the development/progression of dermal fibrosis. In perspective, these findings may have important implications in the field of skin regenerative medicine.

Transcriptome analysis reveals key genes modulated by ALK5 inhibition in a bleomycin model of systemic sclerosis

Objective

SSc is a rheumatic autoimmune disease affecting roughly 20 000 people worldwide and characterized by excessive collagen accumulation in the skin and internal organs. Despite the high morbidity and mortality associated with SSc, there are no approved disease-modifying agents. Our objective in this study was to explore transcriptomic and model-based drug discovery approaches for SSc.

Methods

In this study, we explored the molecular basis for SSc pathogenesis in a well-studied mouse model of scleroderma. We profiled the skin and lung transcriptomes of mice at multiple timepoints, analysing the differential gene expression that underscores the development and resolution of bleomycin-induced fibrosis.

Results

We observed shared expression signatures of upregulation and downregulation in fibrotic skin and lung tissue, and observed significant upregulation of key pro-fibrotic genes including GDF15, Saa3, Cxcl10, Spp1 and Timp1. To identify changes in gene expression in responses to anti-fibrotic therapy, we assessed the effect of TGF-β pathway inhibition via oral ALK5 (TGF-β receptor I) inhibitor SB525334 and observed a time-lagged response in the lung relative to skin. We also implemented a machine learning algorithm that showed promise at predicting lung function using transcriptome data from both skin and lung biopsies.

Conclusion

This study provides the most comprehensive look at the gene expression dynamics of an animal model of SSc to date, provides a rich dataset for future comparative fibrotic disease research, and helps refine our understanding of pathways at work during SSc pathogenesis and intervention.

Identification of Potential ceRNA Network and Patterns of Immune Cell Infiltration in Systemic Sclerosis-Associated Interstitial Lung Disease

Purpose

Systemic sclerosis-associated interstitial lung disease (SSc-ILD) is one of the most severe complications of systemic sclerosis (SSc) and is the leading cause of SSc-related deaths. However, the precise pathogenesis of pulmonary fibrosis in SSc-ILD remains unknown. This study aimed to evaluate the competing endogenous RNA (ceRNA) regulatory network and immune cell infiltration patterns in SSc-ILD.

Methods

One microRNA (miRNA) and three messenger RNA (mRNA) microarray datasets were obtained from the Gene Expression Omnibus (GEO) database. Then, the differentially expressed miRNAs (DEmiRs) and mRNAs (DEMs) between SSc-ILD patients and normal controls were identified, respectively, followed by the prediction of the target genes and target lncRNAs of DEmiRs. The overlapping genes between DEmiRs target genes and DEMs were identified as core mRNAs to construct the ceRNA network. In addition, the “Cell Type Identification by Estimating Relative Subsets of Known RNA Transcripts (CIBERSORT)” algorithm was used to analyze the composition of infiltrating immune cells in lung tissues of SSc-ILD patients and controls, and differentially expressed immune cells were recognized. The correlation between immune cells and core mRNAs was evaluated by Pearson correlation analysis.

Results

Totally, 42 SSc-ILD lung tissues and 18 normal lung tissues were included in this study. We identified 35 DEmiRs and 142 DEMs and predicted 1,265 target genes of DEmiRs. Then, 9 core mRNAs related to SSc-ILD were recognized, which were the overlapping genes between DEmiRs target genes and DEMs. Meanwhile, 9 DEmiRs related to core mRNAs were identified reversely, and their target lncRNAs were predicted. In total, 9 DEmiRs, 9 core mRNAs, and 51 predicted lncRNAs were integrated to construct the ceRNA regulatory network of SSc-ILD. In addition, 9 types of immune cells were differentially expressed in lung tissues between SSc-ILD patients and controls. Some core mRNAs, such as COL1A1, FOS, and EDN1, were positively or negatively correlated with the number of infiltrating immune cells.

Conclusion

This is the first comprehensive study to construct the potential ceRNA regulatory network and analyze the composition of infiltrating immune cells in lung tissues of SSc-ILD patients, which improves our understanding of the pathogenesis of SSc-ILD.

B cell depletion inhibits fibrosis via suppressing pro-fibrotic macrophage differentiation in a mouse model of systemic sclerosis

OBJECTIVE

We investigated the effect of B cell depletion on fibrosis in systemic sclerosis (SSc) and its mechanism of action.

METHODS

Bleomycin-induced SSc (BLM-SSc) model mice were treated with anti-CD20 antibody, and skin and lung fibrosis was evaluated histopathologically. T cells and macrophages were co-cultured with B cells, and the effect of B cells on their differentiation was assessed by flow cytometry. We also co-cultured B cells and monocytes from SSc patients and analyzed the correlation between fibrosis and pro-fibrotic macrophage induction by B cells.

RESULTS

B cell depletion inhibited fibrosis in BLM-SSc mice. B cells from BLM-SSc mice increased pro-inflammatory cytokine producing T cells in co-culture. In BLM-SSc mice, B cell depletion before BLM treatment (pre-depletion) inhibited fibrosis more strongly than B cell depletion after BLM treatment (post-depletion). However, the frequencies of pro-inflammatory T cells were lower in the post-depletion group than in the pre-depletion group. This discrepancy suggests that the effect of B cell depletion on fibrosis cannot be explained by its effect on T cell differentiation. On the other hand, pro-fibrotic macrophages were markedly decreased in the pre-depletion group than in the post-depletion group. Furthermore, B cells from BLM-SSc mice increased pro-fibrotic macrophage differentiation in co-culture. In SSc patients, the extent of pro-fibrotic macrophage induction by B cells correlated with the severity of fibrosis.

CONCLUSION

These findings suggest that B cell depletion inhibits tissue fibrosis via suppressing pro-fibrotic macrophage differentiation in BLM-SSc mice, providing a new rationale for B cell depletion therapy in SSc.

Involvement of the myeloid cell compartment in fibrogenesis and systemic sclerosis

Systemic sclerosis (SSc) is an autoimmune fibrotic disease of unknown aetiology that is characterized by vascular changes in the skin and visceral organs. Autologous haematopoietic stem cell transplantation can improve skin and organ fibrosis in patients with progressive disease and a high risk of organ failure, indicating that cells originating in the bone marrow are important contributors to the pathogenesis of SSc. Animal studies also indicate a pivotal function of myeloid cells in the development of fibrosis leading to changes in the tissue architecture and dysfunction in multiple organs such as the heart, lungs, liver and kidney. In this Review, we summarize current knowledge about the function of myeloid cells in fibrogenesis that occurs in patients with SSc. Targeted therapies currently in clinical studies for SSc might affect myeloid cell-related pathways. Therefore, myeloid cells might be used as cellular biomarkers of disease through the application of high-dimensional techniques such as mass cytometry and single-cell RNA sequencing.

Pathophysiology of systemic sclerosis: current understanding and new insights

Introduction: Systemic sclerosis (SSc) is a complex autoimmune connective tissue disease characterized by chronic and progressive tissue and organ fibrosis with broad patient-to-patient variability. Some risk factors are known and include combination of persistent Raynaud's phenomenon, steroid hormone imbalance, selected chemicals, thermal, or other injuries. Endogenous and/or exogenous environmental trigger/risk factors promote epigenetic mechanisms in genetically primed subjects. Disease pathogenesis presents early microvascular changes with endothelial cell dysfunction, followed by the activation of mechanisms promoting their transition into myofibroblasts. A complex autoimmune response, involving innate and adaptive immunity with specific/functional autoantibody production, characterizes the disease. Progressive fibrosis and ischemia involve skin and visceral organs resulting in their irreversible damage/failure. Progenitor circulating cells (monocytes, fibrocytes), together with growth factors and cytokines participate in disease diffusion and evolution. Epigenetic, vascular and immunologic mechanisms implicated in systemic fibrosis, represent major targets for incoming disease modifying therapeutic approaches. Areas covered: This review discusses current understanding and new insights of SSc pathogenesis, through an overview of the most relevant advancements to present aspects and mechanisms involved in disease pathogenesis. Expert opinion: Considering SSc intricacy/heterogeneity, early combination therapy with vasodilators, immunosuppressive and antifibrotic drugs should successfully downregulate the disease progression, especially if started from the beginning.

Vascular Leaking, a Pivotal and Early Pathogenetic Event in Systemic Sclerosis: Should the Door Be Closed?

The early phase of systemic sclerosis (SSc) presents edema as one of the main features: this is clinically evident in the digital swelling (puffy fingers) as well as in the edematous skin infiltration of the early active diffuse subset. Other organs could be affected by this same disease process, such as the lung (with the appearance of ground glass opacities) and the heart (with edematous changes on cardiac magnetic resonance imaging). The genesis of tissue edema is tightly linked to pathological changes in the endothelium: various reports demonstrated the effect of transforming growth factor β, vascular endothelial growth factor and hypoxia-reperfusion damage with reactive oxygen species generation in altering vascular permeability and extravasation, in particular in SSc. This condition has an alteration in the glycocalyx thickness, reducing the protection of the vessel wall and causing non-fibrotic interstitial edema, a marker of vascular leak. Moreover, changes in the junctional adhesion molecule family and other adhesion molecules, such as ICAM and VCAM, are associated with an increased myeloid cells' extravasation in the skin and increased myofibroblasts transformation with further vascular leak and cellular migration. This mini-review examines current knowledge on determinants of vascular leak in SSc, shedding light on the role of vascular protection. This could enhance further studies in the light of drug development for early treatment, suggesting that the control of vascular leakage should be considered in the same way that vasodilation and inflammation reduction, as potential therapeutic targets.

Black, White, and Gray: Macrophages in Skin Repair and Disease

PURPOSE OF REVIEW

Macrophages alter their responses during the temporal stages of wound healing. During the inflammatory phase macrophages perform phagocytosis. During neovascularization macrophages activate angiogenesis. In the proliferation phase of wound healing, macrophages deposit extracellular matrix and during wound resolution macrophages phagocytize excessive cellular components. This review addresses how these changing phenotypes affect skin repair and disease.

RECENT FINDINGS

Macrophages can determine the outcome of repair and can shift the normal wound healing response into fibrosis or chronic wounds. Emerging single cell technologies for the first time provide us with tools to uncover macrophage origin, heterogeneity and function.

SUMMARY

Macrophages may exist as one population where all cells alter their phenotype in response to signals from the microenvironment. Alternatively, macrophages may exist as distinct subsets that can control wound outcomes. A clarified understanding will strengthen our knowledge of skin biology and aid in the development of wound healing therapies.

Leflunomide prevents ROS-induced systemic fibrosis in mice

Systemic sclerosis (SSc) is a connective tissue disorder characterized by fibrosis of the skin and inner organs, vasculopathy and immunological abnormalities. Recent insights into the polarization of macrophages in scleroderma and into the implication of STAT6 and KLF4 in this process have prompted us to investigate the effects of the inhibition of STAT6 signaling pathway by leflunomide in mice. SSc was induced in BALB/c mice by daily subcutaneous injections of hypochlorous acid (HOCl) or bleomycin. Mice were treated (or not) every other day, for 4 or 6 weeks, by leflunomide. Skin and lung fibrosis as well as immunological features were studied. Mice exposed to HOCl developed a diffuse cutaneous SSc with pulmonary fibrosis and anti-DNA topoisomerase 1 auto-antibodies. STAT6 pathway was hyperactivated and KLF4 was overexpressed in the skin and the lungs of diseased mice. Their inhibition by leflunomide prevented skin and lung fibrosis. Moreover, the hyperproliferative and pro-oxidative phenotype of skin and lung fibroblasts was reversed by leflunomide. Beneficial immunological effects of leflunomide were associated with decreased activation of CD4+ and CD8+ T cells, B cell activation, decreased auto-antibodies production and restored polarization of macrophages in the spleen. The improvement provided by leflunomide in both mouse models of SSc provides a rationale for the evaluation of this immunomodulating drug in the management of patients affected by this disease.

The role of endothelial cells in the vasculopathy of systemic sclerosis: A systematic review

INTRODUCTION

Systemic sclerosis (SSc) is an autoimmune connective tissue disorder characterized by fibroproliferative vasculopathy, immunological abnormalities and progressive fibrosis of multiple organs including the skin. In this study, all English speaking articles concerning the role of endothelial cells (ECs) in SSc vasculopathy and representing biomarkers are systematically reviewed and categorized according to endothelial cell (EC) (dys)function in SSc.

METHODS

A sensitive search on behalf of the EULAR study group on microcirculation in Rheumatic Diseases was developed in Pubmed, The Cochrane Library and Web of Science to identify articles on SSc vasculopathy and the role of ECs using the following Mesh terms: (systemic sclerosis OR scleroderma) AND pathogenesis AND (endothelial cells OR marker). All selected papers were read and discussed by two independent reviewers. The selection process was based on title, abstract and full text level. Additionally, both reviewers further searched the reference lists of the articles selected for reading on full text level for supplementary papers. These additional articles went through the same selection process.

RESULTS

In total 193 resulting articles were selected and the identified biomarkers were categorized according to description of EC (dys)function in SSc. The most representing and reliable biomarkers described by the selected articles were adhesion molecules for EC activation, anti-endothelial cell antibodies for EC apoptosis, vascular endothelial growth factor (VEGF), its receptor VEGFR-2 and endostatin for disturbed angiogenesis, endothelial progenitors cells for defective vasculogenesis, endothelin-1 for disturbed vascular tone control, Von Willebrand factor for coagulopathy and interleukin (IL)-33 for EC-immune system communication. Emerging, relatively new discovered biomarkers described in the selected articles, are VEGF₁₆₅b, IL-17A and the adipocytokines. Finally, myofibroblasts involved in tissue fibrosis in SSc can derive from ECs or epithelial cells through a process known as endothelial-to-mesenchymal transition.

CONCLUSION

This systematic review emphasizes the growing evidence that SSc is primarily a vascular disease where EC dysfunction is present and prominent in different aspects of cell survival (activation and apoptosis), angiogenesis and vasculogenesis and where disturbed interactions between ECs and various other cells contribute to SSc vasculopathy.

Inhibition of phosphodiesterase 4 (PDE4) reduces dermal fibrosis by interfering with the release of interleukin-6 from M2 macrophages

OBJECTIVES

To investigate the disease-modifying effects of phosphodiesterase 4 (PDE4) inhibition in preclinical models of systemic sclerosis (SSc).

METHODS

We studied the effects of PDE4 inhibition in a prevention and a treatment model of bleomycin-induced skin fibrosis, in the topoisomerase mouse model as well as in a model of sclerodermatous chronic graft-versus-host disease. To better understand the mode of action of PDE4 blockade in preclinical models of SSc, we investigated fibrosis-relevant mediators in fibroblasts and macrophages from healthy individuals and patients suffering from diffuse-cutaneous SSc on blockade of PDE4.

RESULTS

Specific inhibition of PDE4 by rolipram and apremilast had potent antifibrotic effects in bleomycin-induced skin fibrosis models, in the topoisomerase I mouse model and in murine sclerodermatous chronic graft-versus-host disease. Fibroblasts were not the direct targets of the antifibrotic effects of PDE4 blockade. Reduced leucocyte infiltration in lesional skin on PDE4 blockade suggested an immune-mediated mechanism. Further analysis revealed that PDE4 inhibition decreased the differentiation of M2 macrophages and the release of several profibrotic cytokines, resulting in reduced fibroblast activation and collagen release. Within these profibrotic mediators, interleukin-6 appeared to play a central role.

CONCLUSIONS

PDE4 inhibition reduces inflammatory cell activity and the release of profibrotic cytokines from M2 macrophages, leading to decreased fibroblast activation and collagen release. Importantly, apremilast is already approved for the treatment of psoriasis and psoriatic arthritis. Therefore, PDE4 inhibitors might be further developed as potential antifibrotic therapies for patients with SSc. Our findings suggest that particularly patients with inflammation-driven fibrosis might benefit from PDE4 blockade.

Alternatively Activated (M2) Macrophage Phenotype Is Inducible by Endothelin-1 in Cultured Human Macrophages

Background

Alternatively activated (M2) macrophages are phenotypically characterized by the expression of specific markers, mainly macrophage scavenger receptors (CD204 and CD163) and mannose receptor-1 (CD206), and participate in the fibrotic process by over-producing pro-fibrotic molecules, such as transforming growth factor-beta1 (TGFbeta1) and metalloproteinase (MMP)-9. Endothelin-1 (ET-1) is implicated in the fibrotic process, exerting its pro-fibrotic effects through the interaction with its receptors (ET_A and ET_B). The study investigated the possible role of ET-1 in inducing the transition from cultured human macrophages into M2 cells.

Methods

Cultured human monocytes (THP-1 cell line) were activated into macrophages (M0 macrophages) with phorbol myristate acetate and subsequently maintained in growth medium (M0-controls) or treated with either ET-1 (100nM) or interleukin-4 (IL-4, 10ng/mL, M2 inducer) for 72 hours. Similarly, primary cultures of human peripheral blood monocyte (PBM)-derived macrophages obtained from healthy subjects, were maintained in growth medium (untreated cells) or treated with ET-1 or IL-4 for 6 days. Both M0 and PBM-derived macrophages were pre-treated with ET receptor antagonist (ET_A/BRA, bosentan 10^-5M) for 1 hour before ET-1 stimulation. Protein and gene expression of CD204, CD206, CD163, TGFbeta1 were analysed by immunocytochemistry, Western blotting and quantitative real time polymerase chain reaction (qRT-PCR). Gene expression of interleukin(IL)-10 and macrophage derived chemokine (CCL-22) was evaluated by qRT-PCR. MMP-9 production was investigated by gel zymography.

Results

ET-1 significantly increased the expression of M2 phenotype markers CD204, CD206, CD163, IL-10 and CCL-22, and the production of MMP-9 in both cultures of M0 and PBM-derived macrophages compared to M0-controls and untreated cells. In cultured PBM-derived macrophages, ET-1 increased TGFbeta1 protein and gene expression compared to untreated cells. The ET-1-mediated effects were contrasted by ET_A/BRA treatment in both cultured cell types.

Conclusion

ET-1 seems to induce the M2 phenotype in cultured human macrophages, a process apparently contrasted by the action of the ET_A/BRA, suggesting possible clinical implications in those fibrotic diseases characterized by increased ET-1 concentrations, such as systemic sclerosis but also type 2 diabetes.

Platelets Induce Thymic Stromal Lymphopoietin Production by Endothelial Cells: Contribution to Fibrosis in Human Systemic Sclerosis

OBJECTIVE

To investigate the relationship between vascular damage and fibrosis in systemic sclerosis (SSc) by testing the hypothesis that platelets contribute to skin fibrosis via the activation of human dermal microvascular endothelial cells (HDMECs) and subsequent production of profibrotic mediators.

METHODS

A total of 203 SSc patients and 30 healthy donors were prospectively enrolled between 2012 and 2015 at the University Hospital of Bordeaux. Immunohistochemistry and immunofluorescence analyses were performed on skin biopsy sections from 18 SSc patients and 5 healthy donors. Serum thymic stromal lymphopoietin (TSLP) levels were measured by enzyme-linked immunosorbent assay in the entire cohort. HDMECs and fibroblasts were purified from biopsy sections. Extracellular matrix production by cultured fibroblasts was assessed by real-time quantitative polymerase chain reaction.

RESULTS

Serum TSLP levels were significantly increased in SSc patients compared to healthy donors (P < 0.0001) and were associated with a higher frequency of vasculopathy (P = 0.02). The proportion of TSLP-positive dermal cells was increased in the skin of SSc patients compared with healthy donors (P < 0.0001) and was correlated with fibrosis (modified Rodnan skin thickness score) (r = 0.6146, P = 0.0001). In SSc dermis, TSLP was mainly expressed by CD31-positive endothelial cells. In vitro, activated platelets induced TSLP production by HDMECs in an interleukin-1β-dependent manner. SSc fibroblasts responded differently according to their original TSLP environment.

CONCLUSION

Taken together, these results identify HDMECs as contributors to TSLP production in SSc and suggest a potential mechanism by which platelets may profoundly affect the fibrotic process in SSc.

Parallel Aspects of the Microenvironment in Cancer and Autoimmune Disease

Cancer and autoimmune diseases are fundamentally different pathological conditions. In cancer, the immune response is suppressed and unable to eradicate the transformed self-cells, while in autoimmune diseases it is hyperactivated against a self-antigen, leading to tissue injury. Yet, mechanistically, similarities in the triggering of the immune responses can be observed. In this review, we highlight some parallel aspects of the microenvironment in cancer and autoimmune diseases, especially hypoxia, and the role of macrophages, neutrophils, and their interaction. Macrophages, owing to their plastic mode of activation, can generate a pro- or antitumoral microenvironment. Similarly, in autoimmune diseases, macrophages tip the Th1/Th2 balance via various effector cytokines. The contribution of neutrophils, an additional plastic innate immune cell population, to the microenvironment and disease progression is recently gaining more prominence in both cancer and autoimmune diseases, as they can secrete cytokines, chemokines, and reactive oxygen species (ROS), as well as acquire an enhanced ability to produce neutrophil extracellular traps (NETs) that are now considered important initiators of autoimmune diseases. Understanding the contribution of macrophages and neutrophils to the cancerous or autoimmune microenvironment, as well as the role their interaction and cooperation play, may help identify new targets and improve therapeutic strategies.

Update on macrophages and innate immunity in scleroderma

PURPOSE OF REVIEW

In this review of the literature from 2014 through mid-2015, we examine new data that shed light on how macrophages and other innate immune cells and signals contribute to inflammation, vascular dysfunction, and fibrosis in scleroderma.

RECENT FINDINGS

Recent human studies have focused on changes early in scleroderma, and linked macrophages to inflammation in skin and progression of lung disease. Plasmacytoid dendritic cells have been implicated in vascular dysfunction. In mice, several factors have been identified that influence macrophage activation and experimental fibrosis. However, emerging data also suggest that myeloid cells can have differential effects in fibrosis. Sustained signaling through different toll-like receptors can lead to inflammation or fibrosis, and these signals can influence both immune and nonimmune cells.

SUMMARY

There are many types of innate immune cells that can potentially contribute to scleroderma and will be worth exploring in detail. Experimentally dissecting the roles of macrophages based on ontogeny and activation state, and the innate signaling pathways in the tissue microenvironment, may also lead to better understanding of scleroderma pathogenesis.