Innate Immunity in Systemic Sclerosis Fibrosis: Recent Advances

Areca nut polysaccharide induces M1 macrophage polarization through the NF-κB and MAPK pathways independent of TLR2 and TLR4 signaling

In this study, the structure of Areca nut polysaccharide (ANP) was characterized, and its effects on macrophage activation and the underlying molecular mechanisms were investigated. ANP was identified as a glucan with a molecular weight of 24.5 kDa, and its structure was analyzed using XRD, SEM, FT-IR, methylation, and NMR techniques. The main chain of ANP is composed of →4)-α-D-Glcp-(1 → and →4,6)-α-D-Glcp-(1→, with a branched α-D-Glcp-(1 → chain. Furthermore, the activation of macrophages by ANP was explored. Stimulation of RAW264.7 cells with ANP in vitro increased the expression of inflammatory cytokines (TNF-α and IL-6) and NO levels. Flow cytometry showed that ANP induced M1 macrophage polarization. RNA-seq and Western blot analyses revealed that ANP activated the NF-κB and MAPK pathways. Importantly, TLR2- and TLR4- specific antibodies did not affect ANP-induced M1 polarization, whereas endocytosis inhibitors reduced the production of inflammatory cytokines in ANP-treated macrophages. In conclusion, ANP engages macrophages without interacting with TLR2 and TLR4 receptors, inducing M1 polarization through the NF-κB and MAPK signaling pathways.

The platelet-mitochondria nexus in autoimmune and musculoskeletal diseases

Platelets are crucial for thrombosis and hemostasis. Importantly, they contain mitochondria that are responsible for energy generation and therefore vital for platelet survival and activation. Activated platelets can release mitochondria that may be free or encapsulated in platelet extracellular vesicles (EVs). Extruded mitochondria are a well-known source of mitochondrial DNA, and mitochondrial antigens that can be targeted by autoantibodies forming immune complexes (IC). Interaction of IC with the platelet cell surface FcγRIIA receptor results in platelet activation and release of platelet granule components. In this review, we summarize how platelets and mitochondria may contribute to the pathogenesis of different autoimmune and musculoskeletal diseases. Targeting key drivers of mitochondrial extrusion may ultimately lead to urgently needed targeted pharmacological interventions for treating inflammation and thrombotic diathesis, and halting organ damage in some of these rheumatological conditions.

Immunogenetics of Systemic Sclerosis

Systemic sclerosis (SSc) is a rare autoimmune connective tissue disorder characterized by massive fibrosis, vascular damage, and immune imbalance. Advances in rheumatology and immunology over the past two decades have led to a redefinition of systemic sclerosis, shifting from its initial perception as primarily a "hyperfibrotic" state towards a recognition of systemic sclerosis as an immune-mediated disease. Consequently, the search for genetic markers has transitioned from focusing on fibrotic mechanisms to exploring immune regulatory pathways. Immunogenetics, an emerging field at the intersection of immunology, molecular biology, and genetics has provided valuable insights into inherited factors that influence immunity. Data from genetic studies conducted thus far indicate that alterations in genetic messages can significantly impact disease risk and progression. While certain genetic variations may confer protective effects, others may exacerbate disease susceptibility. This paper presents a comprehensive review of the most relevant genetic changes that influence both the risk and course of systemic sclerosis. Special emphasis is placed on factors regulating the immune response, recognizing their pivotal role in the pathogenesis of the disease.

PPARγ partial agonist LPSF/GQ-16 prevents dermal and pulmonary fibrosis in HOCl-induced systemic sclerosis (SSc) and modulates cytokine production in PBMC of SSc patients

Thiazolidinediones (TZD) are synthetic molecules that have a range of biological effects, including antifibrotic and anti-inflammatory, and they may represent a promising therapeutic strategy for systemic sclerosis (SSc). The aim of this study was to investigate the immunomodulatory and antifibrotic properties of LPSF/GQ-16, a TZD derivative, in peripheral blood mononuclear cells (PBMC) from SSc patients and in a murine model of SSc HOCl-induced. The PBMC of 20 SSc patients were stimulated with phytohemagglutinin (PHA) and treated with LPSF/GQ-16 for 48 h, later cytokines in the culture supernatants were quantified by sandwich enzyme-linked immunosorbent assay (ELISA) or cytometric bead array (CBA). Experimental SSc was induced by intradermal injections of hypochlorous acid (HOCl) for 6 weeks. HOCl-induced SSc mice received daily treatment with LPSF/GQ-16 (30 mg/kg) through intraperitoneal injections during the same period. Immunological parameters were evaluated by flow cytometry and ELISA, and dermal and pulmonary fibrosis were evaluated by RT-qPCR, hydroxyproline dosage and histopathological analysis. In PBMC cultures, it was possible to observe that LPSF/GQ-16 modulated the secretion of cytokines IL-2 (p < 0.001), IL-4 (p < 0.001), IL-6 (p < 0.001), IL-17A (p = 0.006), TNF (p < 0.001) and IFN-γ (p < 0.001). In addition, treatment with LPSF/GQ-16 in HOCl-induced SSc mice promoted a significant reduction in dermal thickening (p < 0.001), in the accumulation of collagen in the skin (p < 0.001), down-regulated the expression of fibrosis markers in the skin (Col1a1, α-Sma and Tgfβ1, p < 0.001 for all) and lungs (Il4 and Il13, p < 0.001 for both), as well as reduced activation of CD4 + T cells (p < 0.001), B cells (p < 0.001) and M2 macrophages (p < 0.001). In conclusion, LPSF/GQ-16 showed immunomodulatory and antifibrotic properties, demonstrating the therapeutic potential of this molecule for SSc.

Mitochondrial DNA Sensing Pathogen Recognition Receptors in Systemic Sclerosis Associated Interstitial Lung Disease: A Review

Purpose of the review

Systemic sclerosis (SSc) is a condition of dermal and visceral scar formation characterized by immune dysregulation and inflammatory fibrosis. Approximately 90% of SSc patients develop interstitial lung disease (ILD), and it is the leading cause of morbidity and mortality. Further understanding of immune-mediated fibroproliferative mechanisms has the potential to catalyze novel treatment approaches in this difficult to treat disease.

Recent findings

Recent advances have demonstrated the critical role of aberrant innate immune activation mediated by mitochondrial DNA (mtDNA) through interactions with toll-like receptor 9 (TLR9) and cytosolic cyclic guanosine monophosphate-adenosine monophosphate synthase (cGAS).

Summary

In this review, we will discuss how the nature of the mtDNA, whether oxidized or mutated, and its mechanism of release, either intracellularly or extracellularly, can amplify fibrogenesis by activating TLR9 and cGAS, and the novel insights gained by interrogating these signaling pathways. Because the scope of this review is intended to generate hypotheses for future research, we conclude our discussion with several important unanswered questions.

Treatment of Scleroderma-Related Microstomia Using Hyaluronic Acid: An Interventional Study

Systemic sclerosis (SSc) or scleroderma is a rare, systemic, autoimmune connective tissue disease. It causes increased collagen synthesis, leading to multi-organ sclerosis, including the skin and joints. Patients' overall health and quality of life are harmed dramatically. Involvement of the face and, especially, the oral opening can limit patients' ability to speak and eat, oral hygiene, and cosmetic appearance. Profhilo® (NAHYCO®) is an over-the-counter product consisting of pure hyaluronic acid. It is used to improve skin quality by increasing collagen production and adipocyte vitality. This interventional study evaluated the results of perioral injections of hyaluronic acid in terms of improved skin quality, elasticity, and increased oral opening. Patients diagnosed with SSc received an injection of one syringe of Profhilo® (2 mL of hyaluronic acid) at each of two clinic visits at one-month intervals. The oral opening was measured between the upper and lower central incisors before and after treatment. Quality of life was assessed using the modified Rodnan Skin Score and Health Assessment Questionnaire-Disability Index. A total of 14 patients received the first treatment, and 11 received the second treatment. The mean oral opening increased from 31.6 mm (range 17-50 mm) prior to therapy to 35.8 mm (range 21-56) 2 months following the second injection. Statistical analysis showed that there was a significant increase in the oral opening as observed one week (36.2 mm, p = 0.011), one month (36.2 mm, p = 0.007), and three months (31.6 mm, p = 0.023) after the second injection, at the 5-month follow-up. Treatment of SSc patients' perioral area with Profhilo® can result in significant improvements in oral opening and quality of life.

Non-classical circulating monocytes expressing high levels of microsomal prostaglandin E2 synthase-1 tag an aberrant IFN-response in systemic sclerosis

Systemic sclerosis (SSc) is a complex disease that affects the connective tissue, causing fibrosis. SSc patients show altered immune cell composition and activation in the peripheral blood (PB). PB monocytes (Mos) are recruited into tissues where they differentiate into macrophages, which are directly involved in fibrosis. To understand the role of CD14+ PB Mos in SSc, a single-cell transcriptome analysis (scRNA-seq) was conducted on 8 SSc patients and 8 controls. Using unsupervised clustering methods, CD14+ cells were assigned to 11 clusters, which added granularity to the known monocyte subsets: classical (cMos), intermediate (iMos) and non-classical Mos (ncMos) or type 2 dendritic cells. NcMos were significantly overrepresented in SSc patients and showed an active IFN-signature and increased expression levels of PTGES, in addition to monocyte motility and adhesion markers. We identified a SSc-related cluster of IRF7+ STAT1+ iMos with an aberrant IFN-response. Finally, a depletion of M2 polarised cMos in SSc was observed. Our results highlighted the potential of PB Mos as biomarkers for SSc and provided new possibilities for putative drug targets for modulating the innate immune response in SSc.

Enhanced Innate and Acquired Immune Responses in Systemic Sclerosis Primary Peripheral Blood Mononuclear Cells (PBMCs)

Chronic immune activation in systemic sclerosis is supported by the production of a plethora of cytokines with proven regulatory activities of the immune responses. This study aimed to explore PBMCs' cytokine profiles in SSc patients versus controls, as well as to investigate the balance between pro- and anti-inflammatory cytokines in association with disease duration. PBMCs were isolated from 18 SSc patients and 17 controls and further subjected to in vitro stimulation with lipopolysaccharide and heat-killed Candida albicans. Cytokine production was measured after 24 h and 7 days, respectively, using ELISA kits for interleukin (IL)-1β, IL-1 receptor antagonist (IL-1Ra), IL-6, tumor necrosis factor (TNF), IL-10, IL-17, and interferon-gamma (IFN-gamma). IL-1 β, IL-6, and TNF levels were increased in SSc patients compared with healthy volunteers irrespective of the stimulus used. IL-1Ra and Il-17 concentrations were not statistically different between groups, even though a trend toward higher levels in patients compared with their matched controls was also observed. Most cytokines demonstrated a stable course with disease progression, except for IL-10 levels, which declined over time. In conclusion, the results of this pilot study reveal that in patients with SSc a persistently enhanced immune response is established and maintained regardless of stimulus or disease duration.

Fibrosis: Types, Effects, Markers, Mechanisms for Disease Progression, and Its Relation with Oxidative Stress, Immunity, and Inflammation

Most chronic inflammatory illnesses include fibrosis as a pathogenic characteristic. Extracellular matrix (ECM) components build up in excess to cause fibrosis or scarring. The fibrotic process finally results in organ malfunction and death if it is severely progressive. Fibrosis affects nearly all tissues of the body. The fibrosis process is associated with chronic inflammation, metabolic homeostasis, and transforming growth factor-β1 (TGF-β1) signaling, where the balance between the oxidant and antioxidant systems appears to be a key modulator in managing these processes. Virtually every organ system, including the lungs, heart, kidney, and liver, can be affected by fibrosis, which is characterized as an excessive accumulation of connective tissue components. Organ malfunction is frequently caused by fibrotic tissue remodeling, which is also frequently linked to high morbidity and mortality. Up to 45% of all fatalities in the industrialized world are caused by fibrosis, which can damage any organ. Long believed to be persistently progressing and irreversible, fibrosis has now been revealed to be a very dynamic process by preclinical models and clinical studies in a variety of organ systems. The pathways from tissue damage to inflammation, fibrosis, and/or malfunction are the main topics of this review. Furthermore, the fibrosis of different organs with their effects was discussed. Finally, we highlight many of the principal mechanisms of fibrosis. These pathways could be considered as promising targets for the development of potential therapies for a variety of important human diseases.

Macrophage: Key player in the pathogenesis of autoimmune diseases

The macrophage is an essential part of the innate immune system and also serves as the bridge between innate immunity and adaptive immune response. As the initiator and executor of the adaptive immune response, macrophage plays an important role in various physiological processes such as immune tolerance, fibrosis, inflammatory response, angiogenesis and phagocytosis of apoptotic cells. Consequently, macrophage dysfunction is a vital cause of the occurrence and development of autoimmune diseases. In this review, we mainly discuss the functions of macrophages in autoimmune diseases, especially in systemic lupus erythematosus (SLE), rheumatic arthritis (RA), systemic sclerosis (SSc) and type 1 diabetes (T1D), providing references for the treatment and prevention of autoimmune diseases.

The Microbiome in Systemic Sclerosis: Pathophysiology and Therapeutic Potential

Systemic sclerosis (SSc), also known as scleroderma, is an autoimmune disease with unknown etiology characterized by multi-organ fibrosis. Despite substantial investigation on SSc-related cellular and molecular mechanisms, effective therapies are still lacking. The skin, lungs, and gut are the most affected organs in SSc, which act as physical barriers and constantly communicate with colonized microbiota. Recent reports have documented a unique microbiome signature, which may be the pathogenic trigger or driver of SSc. Since gut microbiota influences the efficacy and toxicity of oral drugs, evaluating drug-microbiota interactions has become an area of interest in disease treatment. The existing evidence highlights the potential of the microbial challenge as a novel therapeutic option in SSc. In this review, we have summarized the current knowledge about molecular mechanisms of SSc and highlighted the underlying role of the microbiome in SSc pathogenesis. We have also discussed the latest therapeutic interventions using microbiomes in SSc, including drug-microbiota interactions and animal disease models. This review aims to elucidate the pathophysiological connection and therapeutic potential of the microbiome in SSc. Insights into the microbiome will significantly improve our understanding of etiopathogenesis and developing therapeutics for SSc.

Cathepsin B/NLRP3/GSDMD axis-mediated macrophage pyroptosis induces inflammation and fibrosis in systemic sclerosis

BACKGROUND

Pyroptosis is a newly discovered type of programmed cell death associated with inflammatory and fibrotic diseases. Macrophages play an important role in inducing early immune inflammation in systemic sclerosis (SSc).

OBJECTIVE

To investigate the effect of macrophages pyroptosis on fibrosis of SSc.

METHODS

Pyroptosis/inflammatory markers in serum and skin of SSc patients were detected. Bleomycin (BLM) was subcutaneously injected to establish SSc mouse model. The levels of pyroptosis markers, dermal thickness and collagen deposition in skin were assessed before and after the administration of pyroptosis inhibitors, including MCC950, Disulfiram and necrosulfonamide (NSA). Human-derived monocyte-macrophage cell line (THP-1) or mouse bone marrow-derived macrophages (BMDMs) were primed with lipopolysaccharide (LPS) and stimulated by silicon dioxide (SiO₂) to induce cell pyroptosis. Fibroblasts from patients with SSc were co-cultured with pyroptotic THP-1 cells, and the collagen production was assessed.

RESULTS

Pyroptotic/inflammatory proteins, including NLRP3, cleaved-Caspase (CASP)1, GSDMD-N terminal and IL-18 were increased in the serum, and ASC aggregation and GSDMD were elevated in macrophages in the skin of SSc patients. SSc mice showed increased pyroptosis markers, dermal thickness and collagen deposition in skins, which were alleviated by MCC950, Disulfiram and NSA. Pyroptosis of THP-1 cells and BMDMs was induced by LPS/SiO₂, and it was reduced by the inhibitors of Cathepsin B, NLRP3, CASP1 and GSDMD. Co-culture with pyroptotic THP-1 cells increased the fibrotic proteins in fibroblasts, which were alleviated by pyroptosis inhibitors.

CONCLUSIONS

SSc patients and BLM-induced mouse model presented increased pyroptosis. LPS/SiO₂-induced macrophage pyroptosis promoted fibrosis of SSc through Cathepsin B/NLRP3/GSDMD pathway.

Antiviral Innate Immune Responses in Autoimmunity: Receptors, Pathways, and Therapeutic Targeting

Innate immune receptors sense nucleic acids derived from viral pathogens or self-constituents and initiate an immune response, which involves, among other things, the secretion of cytokines including interferon (IFN) and the activation of IFN-stimulated genes (ISGs). This robust and well-coordinated immune response is mediated by the innate immune cells and is critical to preserving and restoring homeostasis. Like an antiviral response, during an autoimmune disease, aberrations of immune tolerance promote inflammatory responses to self-components, such as nucleic acids and immune complexes (ICs), leading to the secretion of cytokines, inflammation, and tissue damage. The aberrant immune response within the inflammatory milieu of the autoimmune diseases may lead to defective viral responses, predispose to autoimmunity, or precipitate a flare of an existing autoimmune disease. Herein, we review the literature on the crosstalk between innate antiviral immune responses and autoimmune responses and discuss the pitfalls and challenges regarding the therapeutic targeting of the mechanisms involved.

Reconstitution of the immune system and clinical correlates after stem cell transplantation for systemic sclerosis

Systemic sclerosis (SSc) is a chronic autoimmune disease that includes fibrosis, diffuse vasculopathy, inflammation, and autoimmunity. Autologous hematopoietic stem cell transplantation (auto-HSCT) is considered for patients with severe and progressive SSc. In recent decades, knowledge about patient management and clinical outcomes after auto-HSCT has significantly improved. Mechanistic studies have contributed to increasing the comprehension of how profound and long-lasting are the modifications to the immune system induced by transplantation. This review revisits the immune monitoring studies after auto-HSCT for SSc patients and how they relate to clinical outcomes. This understanding is essential to further improve clinical applications of auto-HSCT and enhance patient outcomes.

FLT3 functional low-frequency variant rs76428106-C is associated with susceptibility to systemic sclerosis

OBJECTIVES

rs76428106-C, a low frequency polymorphism that affects the splicing of the FLT3 gene, has recently been associated with several seropositive autoimmune diseases. Here, we aimed to evaluate the potential implication of rs76428106-C in the susceptibility to systemic sclerosis (SSc).

METHODS

We analysed a total of 26 598 European ancestry individuals, 9063 SSc and 17 535 healthy controls, to test the association between FLT3 rs76428106-C and SSc and its different subphenotypes. Genotype data of rs76428106 were obtained by imputation of already available genome-wide association study data and analysed by logistic regression analysis.

RESULTS

In accordance with that observed in other autoimmune disorders, the FLT3 rs76428106-C allele was significantly increased [P-value = 2.03 × 10-3, odds ratio (OR) = 1.34] in SSc patients compared with healthy controls. A similar risk effect was found when the main SSc clinical and serological subgroups were compared with controls. When comparing SSc patients with and without digital ulcers (DU), the rs76428106-C frequency was significantly increased in DU-positive SSc patients in comparison with DU-negative patients (P-value = 0.036, OR = 2.16).

CONCLUSION

This study is the first to report an association between rs76428176-C and SSc. Our results support the role of FLT3 as a relevant gene in seropositive immune-mediated diseases and a potential biomarker for SSc microangiopathy.

Role of B-Cell in the Pathogenesis of Systemic Sclerosis

Systemic sclerosis (SSc) is a rare multisystem autoimmune disease, characterized by fibrosis, vasculopathy, and autoimmunity. Recent advances have highlighted the significant implications of B-cells in SSc. B-cells are present in affected organs, their subpopulations are disrupted, and they display an activated phenotype, and the regulatory capacities of B-cells are impaired, as illustrated by the decrease in the IL-10+ producing B-cell subpopulation or the inhibitory membrane co-receptor density. Recent multi-omics evidence highlights the role of B-cells mainly in the early stage of SSc and preferentially during severe organ involvement. This dysregulated homeostasis partly explains the synthesis of anti-endothelial cell autoantibodies (AECAs) or anti-fibroblast autoantibodies (AFAs), proinflammatory or profibrotic cytokines (interleukin-6 and transforming growth factor-β) produced by B and plasma cells. That is associated with cell-to-cell interactions with endothelial cells, fibroblasts, vascular smooth muscle cells, and other immune cells, altogether leading to cell activation and proliferation, cell resistance to apoptosis, the impairment of regulatory mechanisms, and causing fibrosis of several organs encountered in the SSc. Finally, alongside these exploratory data, treatments targeting B-cells, through their depletion by cytotoxicity (anti-CD20 monoclonal antibody), or the cytokines produced by the B-cell, or their costimulation molecules, seem interesting, probably in certain profiles of early patients with severe organic damage.

Contributions of Immune Cells and Stromal Cells to the Pathogenesis of Systemic Sclerosis: Recent Insights

Systemic sclerosis (SSc) is a multisystem rheumatic disease characterized by vascular dysfunction, autoimmune abnormalities, and progressive organ fibrosis. A series of studies in SSc patients and fibrotic models suggest that immune cells, fibroblasts, and endothelial cells participate in inflammation and aberrant tissue repair. Furthermore, the growing number of studies on single-cell RNA sequencing (scRNA-seq) technology in SSc elaborate on the transcriptomics and heterogeneities of these cell subsets significantly. In this review, we summarize the current knowledge regarding immune cells and stromal cells in SSc patients and discuss their potential roles in SSc pathogenesis, focusing on recent advances in the new subtypes by scRNA-seq.

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.

Utility of cytokines CXCL4, CXCL8 and GDF15 as biomarkers in systemic sclerosis

BACKGROUND AND OBJECTIVES

Systemic sclerosis (SSc) is an autoinmune disease that can affect several organs and its mortality is fundamentally related to its pulmonary involvement. There are some cytokines with high serum levels of patients with SSc. Our goal is to determine the role of CXCL4, CXCL8 and GDF15 in the physiopathology of SSc and whether they can be considered organic damage biomarkers.

PATIENTS AND METHODS

Observational case-control study of SSc patients (ACR/EULAR 2013 criteria). Demographic, clinical, analytical, activity, severity, health perception, and disability variables were collected. Moreover, Videocapillaroscopy, Echocardiography and Respiratory Function Test were made. Serum levels of CXCL4, CXCL8 and GDF15 were measured both in SSc patients and in healthy controls.

RESULTS

A total of 42 patients were included (95.4% women), with an average age of 59.2 years and a median of 4 years from diagnosis. We also included 42 healthy controls. We found significantly higher levels of GDF15 in SSc patients than in controls (p<0.001), but no higher CXCL4 or CXCL8 levels. GDF15 was associated with Diffuse SSc, pulmonary arterial hypertension, interstitial lung disease, less forced vital capacity, high titles of antiScl70, disease activity, and dilated loops in capillaroscopy. CXCL4 levels were associated to a higher Rodnan punctuation, while CXCL8 was associated to C4 fraction consumption and tortuosities in capillaroscopy.

CONCLUSIONS

GDF15 high levels were associated with diffuse SSc, lung impairment, disease activity and changes in capillaroscopy. Moreover, CXCL4 was only associated with skin impairment, while CXCL8 was not related to organic damage.

The Role of Pro-fibrotic Myofibroblasts in Systemic Sclerosis: from Origin to Therapeutic Targeting

Systemic sclerosis (SSc, scleroderma) is a complex connective tissue disorder characterized by multisystem clinical manifestations resulting from immune dysregulation/autoimmunity, vasculopathy and, most notably, progressive fibrosis of the skin and internal organs. In recent years, it has emerged that the main drivers of SSc-related tissue fibrosis are myofibroblasts, a type of mesenchymal cells with both the extracellular matrix-synthesizing features of fibroblasts and the cytoskeletal characteristics of contractile smooth muscle cells. The accumulation and persistent activation of pro-fibrotic myofibroblasts during SSc development and progression result into elevated mechanical stress and reduced matrix plasticity within the affected tissues and may be ascribed to a reduced susceptibility of these cells to pro-apoptotic stimuli, as well as their increased formation from tissue-resident fibroblasts or transition from different cell types. Given the crucial role of myofibroblasts in SSc pathogenesis, finding the way to inhibit myofibroblast differentiation and accumulation by targeting their formation, function and survival may represent an effective approach to hamper the fibrotic process or even halt or reverse established fibrosis. In this review, we discuss the role of myofibroblasts in SSc-related fibrosis, with a special focus on their cellular origin and the signaling pathways implicated in their formation and persistent activation. Furthermore, we provide an overview of potential therapeutic strategies targeting myofibroblasts that may be able to counteract fibrosis in this pathological condition.

Butyrate Improves Skin/Lung Fibrosis and Intestinal Dysbiosis in Bleomycin-Induced Mouse Models

Systemic sclerosis (SSc) is an autoimmune disorder characterized by fibrosis of the skin and internal organs. Despite several studies on SSc treatments, effective treatments for SSc are still lacking. Since evidence suggests an association between intestinal microbiota and SSc, we focused on butyrate, which has beneficial effects in autoimmune diseases as a bacterial metabolite. Here, we investigated the therapeutic potential of sodium butyrate (SB) using a bleomycin-induced fibrosis mouse model of SSc and human dermal fibroblasts (HDFs). SB attenuated bleomycin-induced dermal and lung fibrosis in mice. SB influenced fecal microbiota composition (phyla Actinobacteria and Bacteroidetes, genera Bifidobacterium and Ruminococcus_g2). SB controlled macrophage differentiation in mesenteric lymph nodes, spleen, and bronchoalveolar lavage cells of mice with bleomycin-induced skin fibrosis. Profibrotic and proinflammatory gene expression was suppressed by SB administration in skin. Furthermore, SB inhibited transforming growth factor β1-responsive proinflammatory expression with increased acetylation of histone 3 in HDFs. Subcutaneous SB application had antifibrogenic effects on the skin. Butyrate ameliorated skin and lung fibrosis by improving anti-inflammatory activity in a mouse model of SSc. Butyrate may exhibit indirect and direct anti-fibrogenic action on fibroblasts by regulating macrophage differentiation and inhibition of histone deacetylase 3. These findings suggest butyrate as an SSc treatment.

Congruent microbiome signatures in fibrosis-prone autoimmune diseases: IgG4-related disease and systemic sclerosis

BACKGROUND

Immunoglobulin G4-related disease (IgG4-RD) and systemic sclerosis (SSc) are rare autoimmune diseases characterized by the presence of CD4+ cytotoxic T cells in the blood as well as inflammation and fibrosis in various organs, but they have no established etiologies. Similar to other autoimmune diseases, the gut microbiome might encode disease-triggering or disease-sustaining factors.

METHODS

The gut microbiomes from IgG4-RD and SSc patients as well as healthy individuals with no recent antibiotic treatment were studied by metagenomic sequencing of stool DNA. De novo assembly-based taxonomic and functional characterization, followed by association and accessory gene set enrichment analysis, were applied to describe microbiome changes associated with both diseases.

RESULTS

Microbiomes of IgG4-RD and SSc patients distinctly separated from those of healthy controls: numerous opportunistic pathogenic Clostridium and typically oral Streptococcus species were significantly overabundant, while Alistipes, Bacteroides, and butyrate-producing species were depleted in the two diseases compared to healthy controls. Accessory gene content analysis in these species revealed an enrichment of Th17-activating Eggerthella lenta strains in IgG4-RD and SSc and a preferential colonization of a homocysteine-producing strain of Clostridium bolteae in SSc. Overabundance of the classical mevalonate pathway, hydroxyproline dehydratase, and fibronectin-binding protein in disease microbiomes reflects potential functional differences in host immune recognition and extracellular matrix utilization associated with fibrosis. Strikingly, the majority of species that were differentially abundant in IgG4-RD and SSc compared to controls showed the same directionality in both diseases. Compared with multiple sclerosis and rheumatoid arthritis, the gut microbiomes of IgG4-RD and SSc showed similar signatures; in contrast, the most differentially abundant taxa were not the facultative anaerobes consistently identified in inflammatory bowel diseases, suggesting the microbial signatures of IgG4-RD and SSc do not result from mucosal inflammation and decreased anaerobism.

CONCLUSIONS

These results provide an initial characterization of gut microbiome ecology in fibrosis-prone IgG4-RD and SSc and reveal microbial functions that offer insights into the pathophysiology of these rare diseases.

Mesenchymal stromal cells for systemic sclerosis treatment

Systemic sclerosis (SSc) is a rare chronic autoimmune disease characterized by vasculopathy, dysregulation of innate and adaptive immune responses, and progressive fibrosis. SSc remains an orphan disease, with high morbity and mortality in SSc patients. The mesenchymal stromal cells (MSC) demonstrate in vitro and in vivo pro-angiogenic, immuno-suppressive, and anti-fibrotic properties and appear as a promising stem cell therapy type, that may target the key pathological features of SSc disease. This review aims to summarize acquired knowledge in the field of :1) MSC definition and in vitro and in vivo functional properties, which vary according to the donor type (allogeneic or autologous), the tissue sources (bone marrow, adipose tissue or umbilical cord) or inflammatory micro-environment in the recipient; 2) preclinical studies in various SSc animal models , which showed reduction in skin and lung fibrosis after MSC infusion; 3) first clinical trials in human, with safety and early efficacy results reported in SSc patients or currently tested in several ongoing clinical trials.

Association Between DNA Damage Response, Fibrosis and Type I Interferon Signature in Systemic Sclerosis

Increased endogenous DNA damage and type I interferon pathway activation have been implicated in systemic sclerosis (SSc) pathogenesis. Because experimental evidence suggests an interplay between DNA damage response/repair (DDR/R) and immune response, we hypothesized that deregulated DDR/R is associated with a type I interferon signature and/or fibrosis extent in SSc. DNA damage levels, oxidative stress, induction of abasic sites and the efficiency of DNA double-strand break repair (DSB/R) and nucleotide excision repair (NER) were assessed in peripheral blood mononuclear cells (PBMCs) derived from 37 SSc patients and 55 healthy controls; expression of DDR/R-associated genes and type I interferon-induced genes was also quantified. Endogenous DNA damage was significantly higher in untreated diffuse or limited SSc (Olive tail moment; 14.7 ± 7.0 and 9.5 ± 4.1, respectively) as well as in patients under cytotoxic treatment (15.0 ± 5.4) but not in very early onset SSc (5.6 ± 1.2) compared with controls (4.9 ± 2.6). Moreover, patients with pulmonary fibrosis had significantly higher DNA damage levels than those without (12.6 ± 5.8 vs. 8.8 ± 4.8, respectively). SSc patients displayed increased oxidative stress and abasic sites, defective DSB/R but not NER capacity, downregulation of genes involved in DSB/R (MRE11A, PRKDC) and base excision repair (PARP1, XRCC1), and upregulation of apoptosis-related genes (BAX, BBC3). Individual levels of DNA damage in SSc PBMCs correlated significantly with the corresponding mRNA expression of type I interferon-induced genes (IFIT1, IFI44 and MX1, r=0.419-0.490) as well as with corresponding skin involvement extent by modified Rodnan skin score (r=0.481). In conclusion, defective DDR/R may exert a fuel-on-fire effect on type I interferon pathway activation and contribute to tissue fibrosis in SSc.

Psoriasis and Connective Tissue Diseases

Psoriasis is a chronic systemic inflammatory disease with various co-morbidities, having been recently considered as a comprehensive disease named psoriatic disease or psoriatic syndrome. Autoimmune diseases are one form of its co-morbidities. In addition to the genetic background, shared pathogenesis including innate immunity, neutrophil extracellular trap (NETs), and type I interferon, as well as acquitted immunity such as T helper-17 (Th17) related cytokines are speculated to play a significant role in both psoriasis and connective tissue diseases. On the other hand, there are definite differences between psoriasis and connective tissue diseases, such as their pathomechanisms and response to drugs. Therefore, we cannot expect that one stone kills two birds, and thus caution is necessary when considering whether the administered drug for one disease is effective or not for another disease. In this review, several connective tissue diseases and related diseases are discussed from the viewpoint of their coexistence with psoriasis.

Bi-directional communication: Conversations between fibroblasts and immune cells in systemic sclerosis

Systemic Sclerosis (SSc) is an autoimmune idiopathic connective tissue disease, characterized by aberrant fibro-proliferative and inflammatory responses, causing fibrosis of multiple organs. In recent years the interactions between innate and adaptive immune cells with resident fibroblasts have been uncovered. Cross-talk between immune and stromal cells mediates activation of stromal cells to myofibroblasts; key cells in the pathophysiology of fibrosis. These cells and their cytokines appear to mediate their effects in both a paracrine and autocrine fashion. This review examines the role of innate and adaptive immune cells in SSc, focusing on recent advances that have illuminated our understanding of ongoing bi-directional communication between immune and stromal cells. Finally, we appraise current and future therapies and how these may be useful in a disease that currently has no specific disease modifying treatment.

Role of type I interferons and innate immunity in systemic sclerosis: unbalanced activities on distinct cell types?

PURPOSE OF REVIEW

The role of type I IFNs (IFN-I) in the promotion of autoimmunity has been well established. However, its role in the skin fibrosis of systemic sclerosis (SSc) is less clear. IFN-I can participate to tissue repair, and, here, we will consider the extent to which IFN-I's role in SSc skin fibrosis may reflect in part IFN-I functions during wound healing.

RECENT FINDINGS

Studies are beginning to delineate whether IFN-I has a protective or pathogenic role and how IFN-I affects tissue biology. Recent support for a pathogenic role came from a study depleting plasmacytoid dendritic cells during bleomycin-induced skin fibrosis. The depletion reduced the bleomycin-induced IFN-I-stimulated transcripts and both prevented and reversed fibrosis. Additionally, two recent articles, one identifying SSc endothelial cell injury markers and one showing repressed IFN signaling in SSc keratinocytes, suggest the possibility of unbalanced IFN-I activities on distinct cells types.

SUMMARY

Recent results support a pathogenic role for IFN-I in skin fibrosis, and recent studies along with others suggest a scenario whereby SSc skin damage results from too much IFN-I-activity driving vasculopathy in combination with too little IFN-I-mediated epidermal integrity and antifibrotic fibroblast phenotype.

Arsenic trioxide induces regulatory functions of plasmacytoid dendritic cells through interferon- inhibition

Arsenic trioxide (As₂O₃) is recently found to have therapeutic potential in systemic sclerosis (SSc), a life-threatening multi-system fibrosing autoimmune disease with type I interferon (IFN-I) signature. Chronically activated plasmacytoid dendritic cells (pDCs) are responsible for IFN-I secretion and are closely related with fibrosis establishment in SSc. In this study, we showed that high concentrations of As₂O₃ induced apoptosis of pDCs via mitochondrial pathway with increased BAX/BCL-2 ratio, while independent of reactive oxygen species generation. Notably, at clinical relevant concentrations, As₂O₃ preferentially inhibited IFN-α secretion as compared to other cytokines such as TNF-α, probably due to potent down-regulation of the total protein and mRNA expression, as well as phosphorylation of the interferon regulatory factor 7 (IRF7). In addition, As₂O₃ induced a suppressive phenotype, and in combination with cytokine inhibition, it down-regulated pDCs’ capacity to induce CD4⁺ T cell proliferation, Th1/Th22 polarization, and B cell differentiation towards plasmablasts. Moreover, chronically activated pDCs from SSc patients were not resistant to the selective IFN-α inhibition, and regulatory phenotype induced by As₂O₃. Collectively, our data suggest that As₂O₃ could target pDCs and exert its treatment efficacy in SSc, and more autoimmune disorders with IFN-I signature.

Fli1 Downregulation in Scleroderma Myeloid Cells Has Profibrotic and Proinflammatory Effects

Scleroderma (SSc) is an autoimmune connective tissue disease characterized by immune dysregulation, vasculopathy, and fibrosis. We have previously demonstrated that low Fli1 expression in SSc fibroblasts and endothelial cells plays an important role in SSc pathogenesis. Cells of myeloid and lymphoid origin also express Fli1 and are dysregulated in patients with SSc, playing key roles in disease pathogenesis. However, the role for immune Fli1 in SSc is not yet clear. Our aim was to elucidate whether Fli1 contributes to the immune dysregulation seen in SSc. Comparison of the expression of Fli1 in monocytes, B- and T-cell fractions of PBMCs isolated from SSc patients and healthy controls (HC), showed an increase in Fli1 levels in monocytes. We used siRNA transfected human myeloid cells and mouse peritoneal macrophages obtained from Fli1 flox/flox LysMCre+/+ mice, and found that markers of alternative macrophage activation were increased with Fli1 deletion. Coculture of Fli1-deficient myeloid cells and primary human or mouse fibroblasts resulted in a potent induction of collagen type I, independent of TGFβ upregulation. We next analyzed global gene expression profile in response to Fli1 downregulation, to gain further insight into the molecular mechanisms of this process and to identify differentially expressed genes in myeloid cells. Of relevance to SSc, the top most upregulated pathways were hallmark IFN-γ and IFN-α response. Additionally, several genes previously linked to SSc pathogenesis and fibrosis in general were also induced, including CCL2, CCL7, MMP12, and CXCL10. ANKRD1, a profibrotic transcription co-regulator was the top upregulated gene in our array. Our results show that Fli1-deficient myeloid cells share key features with cells from SSc patients, with higher expression of profibrotic markers and activation of interferon responsive genes, thus suggesting that dysregulation of Fli1 in myeloid cells may contribute to SSc pathogenesis.

Pathogenic Roles of Autoantibodies and Aberrant Epigenetic Regulation of Immune and Connective Tissue Cells in the Tissue Fibrosis of Patients with Systemic Sclerosis

Systemic sclerosis (SSc) is a multi-system autoimmune disease with tissue fibrosis prominent in the skin and lung. In this review, we briefly describe the autoimmune features (mainly autoantibody production and cytokine profiles) and the potential pathogenic contributors including genetic/epigenetic predisposition, and environmental factors. We look in detail at the cellular and molecular bases underlying tissue-fibrosis which include trans-differentiation of fibroblasts (FBs) to myofibroblasts (MFBs). We also state comprehensively the pro-inflammatory and pro-fibrotic cytokines relevant to MFB trans-differentiation, vasculopathy-associated autoantibodies, and fibrosis-regulating microRNAs in SSc. It is conceivable that tissue fibrosis is mainly mediated by an excessive production of TGF-β, the master regulator, from the skewed Th2 cells, macrophages, fibroblasts, myofibroblasts, and keratinocytes. After binding with TGF-β receptors on MFB, the downstream Wnt/β-catenin triggers canonical Smad 2/3 and non-canonical Smad 4 signaling pathways to transcribe collagen genes. Subsequently, excessive collagen fiber synthesis and accumulation as well as tissue fibrosis ensue. In the later part of this review, we discuss limited data relevant to the role of long non-coding RNAs (lncRNAs) in tissue-fibrosis in SSc. It is expected that these lncRNAs may become the useful biomarkers and therapeutic targets for SSc in the future. The prospective investigations in the development of novel epigenetic modifiers are also suggested.

NEK7: a potential therapy target for NLRP3-related diseases

NLRP3 inflammasome plays an essential role in innate immunity, yet the activation mechanism of NLRP3 inflammasome is not clear. In human or animal models, inappropriate NLRP3 inflammasome activation is implicated in many NLRP3-related diseases, such as tumors, inflammatory diseases and autoimmune diseases. Until now, a great number of inhibitors have been used to disturb the related signaling pathways, such as IL-1β blockade, IL-18 blockade and caspase-1 inhibitors. Unfortunately, most of these inhibitors just disturb the signaling pathways after the activation of NLRP3 inflammasome. Inhibitors that directly regulate NLRP3 to abolish the inflammation response may be more effective. NEK7 is a multifunctional kinase affecting centrosome duplication, mitochondrial regulation, intracellular protein transport, DNA repair and mitotic spindle assembly. Researchers have made significant observations on the regulation of gene transcription or protein expression of the NLRP3 inflammasome signaling pathway by NEK7. Those signaling pathways include ROS signaling, potassium efflux, lysosomal destabilization, and NF-κB signaling. Furthermore, NEK7 has been proved to be involved in many NLRP3-related diseases in humans or in animal models. Inhibitors focused on NEK7 may regulate NLRP3 to abolish the inflammation response and NEK7 may be a potential therapeutic target for NLRP3-related diseases.

Toll-like receptors in mediating pathogenesis in systemic sclerosis

Toll-like receptors (TLRs) are evolutionarily conserved receptors essential for the host defence against pathogens. Both immune and non-immune cells can express TLRs, although at different levels. Systemic sclerosis (SSc) is a chronic disease in which autoimmunity, dysregulated profibrotic mediator release and activation of fibroblasts lead to dysregulated collagen deposition and fibrosis. There is now increasing knowledge that the innate immune system and, in particular, TLRs take a part in SSc pathogenesis. The list of endogenous ligands that can stimulate TLRs in SSc is growing: these ligands represent specific danger-associated molecular patterns (DAMPs), involved either in the initiation or the perpetuation of inflammation, and in the release of factors that sustain the fibrotic process or directly stimulate the cells that produce collagen and the endothelial cells. This review reports evidences concerning TLR signalling involvement in SSc. We report the new DAMPs, as well as the TLR-linked pathways involved in disease, with emphasis on type I interferon signature in SSc, the role of plasmacytoid dendritic cells (pDCs) and platelets. The dissection of the contribution of all these pathways to disease, and their correlation with the disease status, as well as their values as prognostic tools, can help to plan timely intervention and design new drugs for more appropriate therapeutic strategies.

The Fibrosis and Immunological Features of Hypochlorous Acid Induced Mouse Model of Systemic Sclerosis

Fibrotic animal models are critical for the pathogenesis investigations and drug explorations in systemic sclerosis (SSc). The bleomycin (BLM)-induced mouse model is the classical and most widely used fibrosis model. However, traditional subcutaneous injection of BLM rarely induced diffuse skin and lung lesions. Hypochlorous acid (HOCl)-induced mice are a more representative model that have diffuse cutaneous lesions, lung fibrosis and renal involvement. However, the fibrotic and immunological features of this model are not fully elucidated. Here, we injected BALB/c mice subcutaneously with HOCl used at different concentrations of HOCl (1:55, 1:70, and 1:110 NaClO: KH2PO4, hereafter named HOCl55, HOCl70, and HOCl110, respectively) for 6 weeks to induce fibrosis, and also used HOCl110 at different time course (4, 5, and 6 weeks). Morphological changes were observed via HE and Masson's trichrome staining. Immunohistochemistry or real-time PCR was used to detect inflammatory infiltrates, important fibrosis pathways and pro-inflammatory mediator expression. Flow cytometry was used to detect the alteration of immune cells in mouse spleen. Skin and lung fibrosis were most obvious in the HOCl55 group compared to lower concentration groups. In the HOCl110 group, dominant inflammatory infiltrates were found after 5 weeks, and significant fibrosis was found after 6 weeks. Then we explored the fibrosis and immunological profiles in the HOCl110 (6 weeks) group. Important fibrosis pathway proteins such as TGF-β, NF-κB, Smad3, p-Smad3, STAT3, and p-STAT3 were significantly elevated at week 6 in the HOCl110 group. Increased infiltration of CD4+T cells, CD8+T cells, CD20+B cells, and myofibroblasts was found both in skin and lung tissues. However, decreased CD4+T cells, CD8+T cells, monocytes and macrophages and increased CD19+B cells were found in the spleen tissues. The mRNA expression of fibrosis mediators such as IL-1β, IL-6, IL-17, IL-33, TNF-α, and CTGF was also upregulated in skin and lung tissues. In conclusion, HOCl induced fibrosis mouse model displayed systemic immune cell infiltration, pro-inflammatory mediator release, vasculopathy and fibrosis, which better mimicked human SSc than BLM-induced mice.

Cross-Disease Innate Gene Signature: Emerging Diversity and Abundance in RA Comparing to SLE and SSc

Overactivation of the innate immune system together with the impaired downstream pathway of type I interferon-responding genes is a hallmark of rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), and systemic sclerosis (SSc). To date, limited data on the cross-disease innate gene signature exists among those diseases. We compared therefore an innate gene signature of Toll-like receptors (TLRs), seven key members of the interleukin (IL)1/IL1R family, and CXCL8/IL8 in peripheral blood mononuclear cells from well-defined patients with active stages of RA (n = 36, DAS28 ≥ 3.2), SLE (n = 28, SLEDAI > 6), and SSc (n = 22, revised EUSTAR index > 2.25). Emerging diversity and abundance of the innate signature in RA patients were detected: RA was characterized by the upregulation of TLR3, TLR5, IL1RAP/IL1R3, IL18R1, and SIGIRR/IL1R8 when compared to SSc (P corr < 0.02) and of TLR2, TLR5, and SIGIRR/IL1R8 when compared to SLE (P corr < 0.02). Applying the association rule analysis, six rules (combinations and expression of genes describing disease) were identified for RA (most frequently included high TLR3 and/or IL1RAP/IL1R3) and three rules for SLE (low IL1RN and IL18R1) and SSc (low TLR5 and IL18R1). This first cross-disease study identified emerging heterogeneity in the innate signature of RA patients with many upregulated innate genes compared to that of SLE and SSc.

Platelets in Skin Autoimmune Diseases

Systemic lupus erythematosus (SLE), systemic sclerosis (SSc), and small vessel vasculitis are three autoimmune diseases frequently manifested in the skin. They share common pathogenic features, including production of autoantibodies, loss of tolerance to self-antigens, tissue necrosis and fibrosis, vasculopathy and activation of the coagulation system. Platelets occupy a central part within the coagulation cascade and are well-recognized for their hemostatic role. However, recent cumulative evidence implicates their additional and multifaceted immunoregulatory functions. Platelets express immune receptors and they store growth factors, cytokines, and chemokines in their granules enabling a significant contribution to inflammation. A plethora of activating triggers such as damage associated molecular patterns (DAMPs) released from damaged endothelial cells, immune complexes, or complement effector molecules can mediate platelet activation. Activated platelets further foster an inflammatory environment and the crosstalk with the endothelium and leukocytes by the release of immunoactive molecules and microparticles. Further insight into the pathogenic implications of platelet activation will pave the way for new therapeutic strategies targeting autoimmune diseases. In this review, we discuss the inflammatory functions of platelets and their mechanistic contribution to the pathophysiology of SSc, ANCA associated small vessel vasculitis and other autoimmune diseases affecting the skin.

Evolving insights into the cellular and molecular pathogenesis of fibrosis in systemic sclerosis

Systemic sclerosis (SSc, scleroderma) is a complex multisystem disease characterized by autoimmunity, vasculopathy, and most notably, fibrosis. Multiple lines of evidence demonstrate a variety of emerging cellular and molecular pathways which are relevant to fibrosis in SSc. The myofibroblast remains the key effector cell in SSc. Understanding the development, differentiation, and function of the myofibroblast is therefore crucial to understanding the fibrotic phenotype of SSc. Studies now show that (1) multiple cell types give rise to myofibroblasts, (2) fibroblasts and myofibroblasts are heterogeneous, and (3) that a large number of (primarily immune) cells have important influences on the transition of fibroblasts to an activated myofibroblasts. In SSc, this differentiation process involves multiple pathways, including well known signaling cascades such as TGF-β and Wnt/β-Catenin signaling, as well as epigenetic reprogramming and a number of more recently defined cellular pathways. After reviewing the major and emerging cellular and molecular mechanisms underlying SSc, this article looks to identify clinical applications where this new molecular knowledge may allow for targeted treatment and personalized medicine approaches.

The Role of Monocytes and Macrophages in Autoimmune Diseases: A Comprehensive Review

Monocytes (Mo) and macrophages (Mϕ) are key components of the innate immune system and are involved in regulation of the initiation, development, and resolution of many inflammatory disorders. In addition, these cells also play important immunoregulatory and tissue-repairing roles to decrease immune reactions and promote tissue regeneration. Several lines of evidence have suggested a causal link between the presence or activation of these cells and the development of autoimmune diseases. In addition, Mo or Mϕ infiltration in diseased tissues is a hallmark of several autoimmune diseases. However, the detailed contributions of these cells, whether they actually initiate disease or perpetuate disease progression, and whether their phenotype and functional alteration are merely epiphenomena are still unclear in many autoimmune diseases. Additionally, little is known about their heterogeneous populations in different autoimmune diseases. Elucidating the relevance of Mo and Mϕ in autoimmune diseases and the associated mechanisms could lead to the identification of more effective therapeutic strategies in the future.

The role of metabolism in the pathogenesis of systemic sclerosis

Systemic sclerosis (SSc) is an immune-mediated autoimmune disease characterized by fibrosis and vascular abnormalities. The cellular and molecular mechanisms remain unclear, and current therapies are limited. Cell metabolism has been shown to play an essential role in cancer survival and tumour invasion as well as in rheumatic diseases such as systemic lupus erythematosus, rheumatoid arthritis and osteoarthritis. Although little is known about SSc, cell metabolism may provide new clues for understanding its pathogenesis. In this review, we summarize recent studies of metabolism in SSc and fibrotic disease, specifically focusing on glycolysis, fatty acid metabolism and oxidative stress. We highlight the role of metabolism in fibroblast differentiation and emphasize its potential therapeutic prospects in SSc.