Epithelial Cells Promote Fibroblast Activation via IL-1α in Systemic Sclerosis

Orofacial Complications of the Connective Tissue Disease Systemic Sclerosis

Scleroderma (systemic sclerosis, SSc) is an autoimmune fibrosing connective tissue disease of unknown etiology. SSc patients show increased levels of autoantibodies, profibrotic cytokines, and extracellular matrix remodeling enzymes that collectively cause activated (myo)fibroblasts, the effector cell type of fibrosis. Despite these impacts, no disease-modifying therapy exists; individual symptoms are treated on a patient-to-patient basis. SSc research has been principally focused on symptoms observed in the lung and skin. However, SSc patients display significant oral complications that arise due to fibrosis of the not only skin, causing microstomia, but also the gastrointestinal tract, causing acid reflux, and the oral cavity itself, causing xerostomia and gingival recession. Due to these complications, SSc patients have impaired quality of life, including periodontitis, tooth loss, reduced tongue mobility, and malnutrition. Indeed, due to their characteristic oral presentation, SSc patients are often initially diagnosed by dentists. Despite their clinical importance, the oral complications of SSc are severely understudied; high-quality publications on this topic are scant. However, SSc patients with periodontal complications possess increased levels of matrix metalloproteinase-9 and chemokines, such as interleukin-6 and chemokine (C-X-C motif) ligand-4. Although many unsuccessful clinical trials, mainly exploring the antifibrotic effects of anti-inflammatory agents, have been conducted in SSc, none have used oral symptoms, which may be more amenable to anti-inflammatory drugs, as clinical end points. This review summarizes the current state of knowledge regarding oral complications in SSc with the goal of inspiring future research in this extremely important and underinvestigated area.

Emerging diagnostic and therapeutic challenges for skin fibrosis in systemic sclerosis

Systemic sclerosis (also called scleroderma, SSc) is a chronic autoimmune disorder characterized by excessive collagen deposition leading to skin fibrosis and various internal organ manifestations. The emergent diagnostics and therapeutic strategies for scleroderma focus on early detection and targeted interventions to improve patient outcomes and quality of life. Diagnostics for SSc have evolved significantly in recent years, driven by advancements in serological markers and imaging techniques. Autoantibody profiling, especially antinuclear antibodies (ANA) and specific scleroderma-associated autoantibodies, aids in identifying subsets of scleroderma and predicting disease progression. Furthermore, novel imaging modalities, such as high-frequency ultrasonography and optical coherence tomography, enable early detection of skin fibrosis and internal organ involvement, enhancing the diagnostic precision and allowing for tailored management. Therapeutic strategies for SSc are multifaceted, targeting immune dysregulation, vascular abnormalities, and fibrotic processes. Emerging biologic agents have shown promise in clinical trials, including monoclonal antibodies directed against key cytokines involved in fibrosis, such as transforming growth factor-β (TGF-β) and interleukin-6 (IL-6). Additionally, small-molecule inhibitors that disrupt fibrotic pathways, like tyrosine kinase inhibitors, have exhibited potential in limiting collagen deposition and preventing disease progression. Stem cell therapy, cell ablation and gene editing techniques hold great potential in regenerating damaged tissue and halting fibrotic processes. Early intervention remains crucial in managing SSc, as irreversible tissue damage often occurs in advanced stages. Novel diagnostic methods, such as biomarkers and gene expression profiling, are being explored to identify individuals at high risk for developing progressive severe disease and intervene proactively. Furthermore, patient-tailored therapeutic approaches, employing a combination of immunosuppressive agents and targeted anti-fibrotic therapies, are being investigated to improve treatment efficacy while minimizing adverse effects. The emergent diagnostics and therapeutic strategies in scleroderma are transforming the management of this challenging disease. Nevertheless, ongoing research and clinical trials are needed to optimize the efficacy and safety of these novel approaches in the complex and diverse spectrum of SSc manifestations.

Single-cell epigenomic dysregulation of Systemic Sclerosis fibroblasts via CREB1/EGR1 axis in self-assembled human skin equivalents

Systemic sclerosis (SSc) is an autoimmune disease characterized by skin fibrosis, internal organ involvement and vascular dropout. We previously developed and phenotypically characterized an in vitro 3D skin-like tissue model of SSc, and now analyze the transcriptomic (scRNA-seq) and epigenetic (scATAC-seq) characteristics of this model at single-cell resolution. SSc 3D skin-like tissues were fabricated using autologous fibroblasts, macrophages, and plasma from SSc patients or healthy control (HC) donors. SSc tissues displayed increased dermal thickness and contractility, as well as increased α-SMA staining. Single-cell transcriptomic and epigenomic analyses identified keratinocytes, macrophages, and five populations of fibroblasts (labeled FB1 - 5). Notably, FB1 APOE-expressing fibroblasts were 12-fold enriched in SSc tissues and were characterized by high EGR1 motif accessibility. Pseudotime analysis suggests that FB1 fibroblasts differentiate from a TGF-β1-responsive fibroblast population and ligand-receptor analysis indicates that the FB1 fibroblasts are active in macrophage crosstalk via soluble ligands including FGF2 and APP. These findings provide characterization of the 3D skin-like model at single cell resolution and establish that it recapitulates subsets of fibroblasts and macrophage phenotypes observed in skin biopsies.

Collagen Lattice Model, Populated with Heterogeneous Cancer-Associated Fibroblasts, Facilitates Advanced Reconstruction of Pancreatic Cancer Microenvironment

Pancreatic ductal adenocarcinoma (PDAC) is a solid-tumor malignancy. To enhance the treatment landscape of PDAC, a 3D model optimized for rigorous drug screening is essential. Within the PDAC tumor microenvironment, a dense stroma comprising a large extracellular matrix and cancer-associated fibroblasts (CAFs) is well-known for its vital role in modulating tumor growth, cellular heterogeneity, bidirectional paracrine signaling, and chemoresistance. In this study, we employed a fibroblast-populated collagen lattice (FPCL) modeling approach that has the ability to replicate fibroblast contractility in the collagenous matrix to build dense stroma. This FPCL model allows CAF differentiation by facilitating multifaceted cell-cell interactions between cancer cells and CAFs, with the differentiation further influenced by mechanical forces and hypoxia carried within the 3D structure. Our FPCL models displayed hallmark features, including ductal gland structures and differentiated CAFs with spindle shapes. Through morphological explorations alongside in-depth transcriptomic and metabolomic profiling, we identified substantial molecular shifts from the nascent to mature model stages and potential metabolic biomarkers, such as proline. The initial pharmacological assays highlighted the effectiveness of our FPCL model in screening for improved therapeutic strategies. In conclusion, our PDAC modeling platform mirrors complex tumor microenvironmental dynamics and offers an unparalleled perspective for therapeutic exploration.

Cellular Transdifferentiation: A Crucial Mechanism of Fibrosis in Systemic Sclerosis

Systemic Sclerosis (SSc) is a systemic autoimmune disease of unknown etiology with a highly complex pathogenesis that despite extensive investigation is not completely understood. The clinical and pathologic manifestations of the disease result from three distinct processes: 1) Severe and frequently progressive tissue fibrosis causing exaggerated and deleterious accumulation of interstitial collagens and other extracellular matrix molecules in the skin and various internal organs; 2) extensive fibroproliferative vascular lesions affecting small arteries and arterioles causing tissue ischemic alterations; and 3) cellular and humoral immunity abnormalities with the production of numerous autoantibodies, some with very high specificity for SSc. The fibrotic process in SSc is one of the main causes of disability and high mortality of the disease. Owing to its essentially universal presence and the severity of its clinical effects, the mechanisms involved in the development and progression of tissue fibrosis have been extensively investigated, however, despite intensive investigation, the precise molecular mechanisms have not been fully elucidated. Several recent studies have suggested that cellular transdifferentiation resulting in the phenotypic conversion of various cell types into activated myofibroblasts may be one important mechanism. Here, we review the potential role that cellular transdifferentiation may play in the development of severe and often progressive tissue fibrosis in SSc.

Autoantibodies Which Bind to and Activate Keratinocytes in Systemic Sclerosis

Systemic sclerosis (SSc) is a multisystem connective tissue disease characterised by pathological processes involving autoimmunity, vasculopathy and resultant extensive skin and organ fibrosis. Recent studies have demonstrated activation and aberrant wound healing responses in the epithelial layer of the skin in this disease, implicating the epithelial keratinocytes as a source of pro-fibrotic and inflammatory mediators. In this paper, we investigated the role of Immunoglobulin G (IgG) autoantibodies directed against epithelial cells, as potential initiators and propagators of pathological keratocyte activation and the ensuing SSc fibrotic cascade. A keratinocyte cell-based ELISA is used to evaluate the binding of SSc IgG. SSc skin biopsies were stained by immunofluorescence for the presence of IgG in the keratinocyte layer. Moreover, IgG purified from SSc sera was evaluated for the potential to activate keratinocytes in tissue culture and to induce TLR2 and 3 signalling in reporter cell lines. We demonstrate enhanced binding of SSc IgG to keratinocytes and the activation of these cells leading to the release of IL-1α, representing a potential initiating pathway in this disease.

Cell Cultures as a Versatile Tool in the Research and Treatment of Autoimmune Connective Tissue Diseases

Cell cultures are an important part of the research and treatment of autoimmune connective tissue diseases. By culturing the various cell types involved in ACTDs, researchers are able to broaden the knowledge about these diseases that, in the near future, may lead to finding cures. Fibroblast cultures and chondrocyte cultures allow scientists to study the behavior, physiology and intracellular interactions of these cells. This helps in understanding the underlying mechanisms of ACTDs, including inflammation, immune dysregulation and tissue damage. Through the analysis of gene expression patterns, surface proteins and cytokine profiles in peripheral blood mononuclear cell cultures and endothelial cell cultures researchers can identify potential biomarkers that can help in diagnosing, monitoring disease activity and predicting patient's response to treatment. Moreover, cell culturing of mesenchymal stem cells and skin modelling in ACTD research and treatment help to evaluate the effects of potential drugs or therapeutics on specific cell types relevant to the disease. Culturing cells in 3D allows us to assess safety, efficacy and the mechanisms of action, thereby aiding in the screening of potential drug candidates and the development of novel therapies. Nowadays, personalized medicine is increasingly mentioned as a future way of dealing with complex diseases such as ACTD. By culturing cells from individual patients and studying patient-specific cells, researchers can gain insights into the unique characteristics of the patient's disease, identify personalized treatment targets, and develop tailored therapeutic strategies for better outcomes. Cell culturing can help in the evaluation of the effects of these therapies on patient-specific cell populations, as well as in predicting overall treatment response. By analyzing changes in response or behavior of patient-derived cells to a treatment, researchers can assess the response effectiveness to specific therapies, thus enabling more informed treatment decisions. This literature review was created as a form of guidance for researchers and clinicians, and it was written with the use of the NCBI database.

A randomized clinical trial of bermekimab treatment for clinical improvement of systemic sclerosis

Increased concentrations of interleukin (IL)-1α have been recently described in tissues of patients with systemic sclerosis (SSc) suggesting that IL-1α inhibition may be a target for treatment. We conducted a double-blind, placebo-controlled study to assess the safety and efficacy of the fully humanized IL-1α blocking monoclonal antibody bermekimab in SSc. To evaluate response to treatment, we developed the score of inhibition of progression of SSc which was validated using the CRISS index and the modified CRISS index. The primary endpoint was met in 80% of bermekimab-treated patients vs. 20% of placebo-treated patients (p: 0.023). Most of efficacy was found for increase of carbon monoxide lung diffusion capacity. Production of IL-1α and TNF by circulating mononuclear cells was decreased and the absolute count of CD42/Cd62-platelets was decreased. Results suggest that bermekimab is a promising treatment for SSc.

Unravelling morphoea aetiopathogenesis by next-generation sequencing of paired skin biopsies

BACKGROUND

Morphoea can have a significant disease burden. Aetiopathogenesis remains poorly understood, with very limited existing genetic studies. Linear morphoea (LM) may follow Blascho's lines of epidermal development, providing potential pathogenic clues.

OBJECTIVE

The first objective of this study was to identify the presence of primary somatic epidermal mosaicism in LM. The second objective was tTo explore differential gene expression in morphoea epidermis and dermis to identify potential pathogenic molecular pathways and tissue layer cross-talk.

METHODOLOGY

Skin biopsies from paired affected and contralateral unaffected skin were taken from 16 patients with LM. Epidermis and dermis were isolated using a 2-step chemical-physical separation protocol. Whole Genome Sequencing (WGS; n = 4 epidermal) and RNA-seq (n = 5-epidermal, n = 5-dermal) with gene expression analysis via GSEA-MSigDBv6.3 and PANTHER-v14.1 pathway analyses, were performed. RTqPCR and immunohistochemistry were used to replicate key results.

RESULTS

Sixteen participants (93.8% female, mean age 27.7 yrs disease-onset) were included. Epidermal WGS identified no single affected gene or SNV. However, many potential disease-relevant pathogenic variants were present, including ADAMTSL1 and ADAMTS16. A highly proliferative, inflammatory and profibrotic epidermis was seen, with significantly-overexpressed TNFα-via-NFkB, TGFβ, IL6/JAKSTAT and IFN-signaling, apoptosis, p53 and KRAS-responses. Upregulated IFI27 and downregulated LAMA4 potentially represent initiating epidermal 'damage' signals and enhanced epidermal-dermal communication. Morphoea dermis exhibited significant profibrotic, B-cell and IFN-signatures, and upregulated morphogenic patterning pathways such as Wnt.

CONCLUSION

This study supports the absence of somatic epidermal mosaicism in LM, and identifies potential disease-driving epidermal mechanisms, epidermal-dermal interactions and disease-specific dermal differential-gene-expression in morphoea. We propose a potential molecular narrative for morphoea aetiopathogenesis which could help guide future targeted studies and therapies.

Tripterygium wilfordii derivative celastrol, a YAP inhibitor, has antifibrotic effects in systemic sclerosis

OBJECTIVES

Systemic sclerosis (SSc) is characterised by extensive tissue fibrosis maintained by mechanotranductive/proadhesive signalling. Drugs targeting this pathway are therefore of likely therapeutic benefit. The mechanosensitive transcriptional co-activator, yes activated protein-1 (YAP1), is activated in SSc fibroblasts. The terpenoid celastrol is a YAP1 inhibitor; however, if celastrol can alleviate SSc fibrosis is unknown. Moreover, the cell niches required for skin fibrosis are unknown.

METHODS

Human dermal fibroblasts from healthy individuals and patients with diffuse cutaneous SSc were treated with or without transforming growth factor β1 (TGFβ1), with or without celastrol. Mice were subjected to the bleomycin-induced model of skin SSc, in the presence or absence of celastrol. Fibrosis was assessed using RNA Sequencing, real-time PCR, spatial transcriptomic analyses, Western blot, ELISA and histological analyses.

RESULTS

In dermal fibroblasts, celastrol impaired the ability of TGFβ1 to induce an SSc-like pattern of gene expression, including that of cellular communication network factor 2, collagen I and TGFβ1. Celastrol alleviated the persistent fibrotic phenotype of dermal fibroblasts cultured from lesions of SSc patients. In the bleomycin-induced model of skin SSc, increased expression of genes associated with reticular fibroblast and hippo/YAP clusters was observed; conversely, celastrol inhibited these bleomycin-induced changes and blocked nuclear localisation of YAP.

CONCLUSIONS

Our data clarify niches within the skin activated in fibrosis and suggest that compounds, such as celastrol, that antagonise the YAP pathway may be potential treatments for SSc skin fibrosis.

Serum cold-inducible RNA-binding protein levels as a potential biomarker for systemic sclerosis-associated interstitial lung disease

Systemic sclerosis (SSc) is a complex autoimmune disease characterized by fibrotic, inflammatory, and vascular dysfunction. Danger-associated molecular patterns (DAMPs)-mediated inflammasome activation has been reported to be involved in the pathogenesis of SSc. Cold-inducible RNA-binding protein (CIRP) is newly identified as a DAMP. Here we examined the clinical significance of serum levels of CIRP in 60 patients with SSc and 20 healthy control patients (HCs) using an enzyme-linked immunosorbent assay. Serum CIRP levels in diffuse cutaneous SSc (dcSSc) patients were significantly increased compared with limited cutaneous SSc (lcSSc) patients or HCs. When examining the relationship with SSc-specific parameters, serum CIRP levels with the presence of interstitial lung disease (ILD) were higher than those without ILD. In detail, serum CIRP levels correlated negatively with the percent predicted diffusing capacity for carbon monoxide and positively with levels of Krebs von den Lungen-6. In addition, elevated serum CIRP levels declined along with decreased SSc-ILD activity in patients who received immunosuppressive therapy. These results suggest that CIRP may play a role in the development of ILD in SSc. Moreover, CIRP could serve as a useful serological marker of SSc-ILD in terms of disease activity and therapeutic effects.

Human dermal fibroblast-derived exosomes induce macrophage activation in systemic sclerosis

OBJECTIVES

Prior work demonstrates that co-cultured macrophages and fibroblasts from patients with SSc engage in reciprocal activation. However, the mechanism by which these cell types communicate and contribute to fibrosis and inflammation in SSc is unknown.

METHODS

Fibroblasts were isolated from skin biopsies obtained from 7 SSc patients or 6 healthy age and gender-matched control subjects following written informed consent. Human donor-derived macrophages were cultured with exosomes isolated from control or SSc fibroblasts for an additional 48 h. Macrophages were immunophenotyped using flow cytometry, qRT-PCR and multiplex. For mutual activation studies, exosome-activated macrophages were co-cultured with SSc or healthy fibroblasts using Transwells.

RESULTS

Macrophages activated with dermal fibroblast-derived exosomes from SSc patients upregulated surface expression of CD163, CD206, MHC Class II and CD16 and secreted increased levels of IL-6, IL-10, IL-12p40 and TNF compared with macrophages incubated with healthy control fibroblasts (n = 7, P < 0.05). Exosome-stimulated macrophages and SSc fibroblasts engaged in reciprocal activation, as production of collagen and fibronectin was significantly increased in SSc fibroblasts receiving signals from SSc exosome-stimulated macrophages (n = 7, P < 0.05).

CONCLUSION

In this work, we demonstrate for the first time that human SSc dermal fibroblasts mediate macrophage activation through exosomes. Our findings suggest that macrophages and fibroblasts engage in cross-talk in SSc skin, resulting in mutual activation, inflammation, and extracellular matrix (ECM) deposition. Collectively, these studies implicate macrophages and fibroblasts as cooperative mediators of fibrosis in SSc and suggest therapeutic targeting of both cell types may provide maximal benefit in ameliorating disease in SSc patients.

Epidermal Potentiation of Dermal Fibrosis: Lessons from Occlusion and Mucosal Healing

Fibrotic skin conditions, such as hypertrophic and keloid scars, frequently result from injury to the skin and as sequelae to surgical procedures. The development of skin fibrosis may lead to patient discomfort, limitation in range of motion, and cosmetic disfigurement. Despite the frequency of skin fibrosis, treatments that seek to address the root causes of fibrosis are lacking. Much research into fibrotic pathophysiology has focused on dermal pathology, but less research has been performed to understand aberrations in fibrotic epidermis, leading to an incomplete understanding of dermal fibrosis. The literature on occlusion, a treatment modality known to reduce dermal fibrosis, in part through accelerating wound healing and regulating aberrant epidermal inflammation that otherwise drives fibrosis in the dermis, is reviewed. There is a focus on epidermal-dermal crosstalk, which contributes to the development and maintenance of dermal fibrosis, an underemphasized interplay that may yield novel strategies for treatment if understood in more detail.

Contribution of keratinocytes to dermal fibrosis

PURPOSE OF REVIEW

The cellular pathogenesis of fibrotic disorders including systemic sclerosis (SSc) remains largely speculative. Currently, the altered function of endothelial cells and fibroblasts under the influence of an inappropriate immune response are considered central pathogenic events in SSc. Adding to this complexity, novel evidence here reviewed suggests that keratinocytes may concur in the development of skin fibrosis.

RECENT FINDINGS

Epidermal equivalents (EE) generated from primary SSc keratinocytes display a distinct gene expression program when compared to healthy donor (HD) EE. SSc-EE, among others, exhibited enhanced oxidative and metabolic response pathways. Immunohistochemical studies demonstrated similarities between SSc-EE and SSc epidermis including altered keratinocyte differentiation, enhanced expression of activation markers, and reduced rate of basal keratinocytes proliferation. SSc-EE supernatants more than HD-EE modified the inflammatory and extracellular matrix deposition/resorption program of dermal fibroblasts. Further evidence indicated that the relative lack rather than the excess of interleukin-25 in keratinocytes may contribute to enhanced dermal fibrotic changes. Overall, these data support keratinocyte-intrinsic SSc-related modifications.

SUMMARY

Improved methods for engineering epidermal and skin equivalents are helping to address the question whether keratinocyte alterations in SSc are primary and capable to dysregulate dermal homeostasis or secondary following dermal fibrotic changes.

Dermal fibroblasts are the key sensors of aseptic skin inflammation through interleukin 1 release by lesioned keratinocytes

IL-1 plays a crucial role in triggering sterile inflammation following tissue injury. Although most studies associate IL-1 release by injured cells to the recruitment of neutrophils for tissue repair, the inflammatory cascade involves several molecular and cellular actors whose role remains to be specified. In the present study, we identified dermal fibroblasts among the IL-1R1-expressing skin cells as key sensors of IL-1 released by injured keratinocytes. After in vitro stimulation by recombinant cytokines or protein extracts of lysed keratinocytes containing high concentrations of IL-1, we show that dermal fibroblasts are by far the most IL-1-responsive cells compared to keratinocytes, melanocytes and endothelial cells. Fibroblasts have the property to respond to very low concentrations of IL-1 (from 10 fg/ml), even in the presence of 100-fold higher concentrations of IL-1RA, by increasing their expression of chemokines such as IL-8 for neutrophil recruitment. The capacity of IL-1-stimulated fibroblasts to attract neutrophils has been demonstrated both in vitro using cell migration assay and in vivo using a model of superficial epidermal lesion in IL-1R1-deficient mice which harbored reduced expression of inflammatory mediators and neutrophil skin infiltration. Together, our results shed a light on dermal fibroblasts as key relay cells in the chain of sterile inflammation induced after epidermal lesion.

Suppression of Cutibacterium acnes-Mediated Inflammatory Reactions by Fibroblast Growth Factor 21 in Skin

Cutibacterium acnes (C. acnes) is a common commensal bacterium that is closely associated with the pathogenesis of acne. Fibroblast growth factor 21 (FGF21), as a favorable regulator of glucose and lipid metabolism and insulin sensitivity, was recently shown to exert anti-inflammatory effects. The role and mechanism of FGF21 in the inflammatory reactions induced by C. acnes, however, have not been determined. The present study shows that FGF21 in the dermis inhibits epidermal C. acnes-induced inflammation in a paracrine manner while it functions on the epidermal layer through a receptor complex consisting of FGF receptor 1 (FGFR1) and β-Klotho (KLB). The effects of FGF21 in heat-killed C. acnes-induced HaCaT cells and living C. acnes-injected mouse ears were examined. In the presence of C. acnes, FGF21 largely counteracted the activation of Toll-like receptor 2 (TLR2), the downstream nuclear factor-κB (NF-κB), and mitogen-activated protein kinase (MAPK) signaling pathways induced by C. acnes. FGF21 also significantly reduced the expression of proinflammatory cytokines, including interleukin (IL)-1β, IL-6, IL-8, and tumor necrosis factor (TNF)-α. Taken together, these findings indicate that FGF21 suppresses C. acnes-induced inflammation and might be used clinically in the management and treatment of acne.

IL-25 participates in keratinocyte-driven dermal matrix turnover and is reduced in Systemic Sclerosis epidermis

OBJECTIVES

Evidence shows that dysfunctional SSc keratinocytes contribute to fibrosis by altering dermal homeostasis. Whether interleukin-25 (IL-25), an IL-17 family member regulating many epidermal functions, takes part in skin fibrosis is unknown. Here we address the role of IL-25 in skin fibrosis.

METHODS

The expression of IL-25 was evaluated by immunofluorescence and in situ hybridization in 10 SSc and 7 healthy donors (HD) skin biopsies. Epidermal equivalents (EE) reconstituted by primary HD keratinocytes were used as a model to study transcriptomic changes induced by IL-25 in the epidermis. RNA expression profile in EE was characterized by RNAseq. The conditioned medium (CM) from primary SSc and HD keratinocytes primed with IL-25 was used to stimulate fibroblasts. IL-6, IL-8, MMP-1, type-I collagen (col-I), and fibronectin production by fibroblasts was assessed by ELISA.

RESULTS

SSc epidermis expressed lower levels of IL-25 compared with HD. In EE, IL-25 regulated several molecular pathways related to wound healing and ECM remodeling. Compared with control CM, the CM from IL-25-primed keratinocytes enhanced the fibroblast production of MMP-1, IL-6, IL-8, but not of Col-I nor fibronectin. However, IL-25 significantly reduced the production of Col-I when applied directly to fibroblasts. The activation of keratinocytes by IL-25 was receptor-dependent and evident after a very short incubation time (10 min), largely mediated by IL-1, suggesting enhanced and specific release of preformed mediators.

CONCLUSIONS

These results show that IL-25 participates to skin homeostasis and its decreased expression in SSc may contribute to skin fibrosis by favoring ECM deposition over degradation.

Deficiency of vitamin D receptor in keratinocytes augments dermal fibrosis and inflammation in a mouse model of HOCl-induced scleroderma

Scleroderma, characterized by extensive fibrosis and vascular alterations, involves excessive fibroblast activation, uncontrolled inflammation, and abnormal collagen deposition. Previous studies showed that administrations of either 1,25(OH)2D3 or vitamin D analog effectively decreased or reversed skin fibrosis by regulating the extracellular matrix homeostasis. The actions of 1,25(OH)2D3 are mediated by the vitamin D receptor (VDR), a transcription regulator crucial for skin homeostasis. Although evidence suggests that keratinocyte-fibroblast interaction influences the development of scleroderma, the role of keratinocytes in scleroderma remains unknown. Here, we demonstrated that the ablation of VDR in keratinocytes greatly exacerbated dermal fibrosis in HOCl-induced scleroderma in mice. The deficiency of VDR in the epidermis marked increased dermal thickness, inflammatory cell infiltration, and severe collagen deposition in comparison to the control group in HOCl-treated skin. Moreover, significant elevations in expression levels of mRNA for collagen overproduction (Col1A1, Col1A2, Col3A1, α-SMA, MMP9, TGF-β1) and proinflammatory cytokines (IL-1β, IL-6, CXCL1, CXCL2) were observed in VDR conditional KO versus control mice following HOCl treatment. Collectively, these results suggest that VDR in keratinocytes plays a pivotal role in scleroderma progression, and the interplay between keratinocytes and fibroblasts deserves more attention regarding the exploration of the pathogenesis and treatment for scleroderma.

Changes in tumor suppressors and inflammatory responses during hydrogen peroxide-induced senescence in rat fibroblasts

Cell proliferation and senescence are processes induced by oxidative stress. In this study, we aimed to establish a cellular model of rapid proliferation and senescence of rat tail-tip fibroblasts by hydrogen peroxide(H₂O₂), a well-known oxidant. On this basis, changes in oxidative stress, inflammatory response and cell cycle of fibroblasts were studied. After H₂O₂ treatment, cell counting and flow cytometry results showed that 50μM of H₂O₂ for 12h and 100μM for 8h effectively promoted fibroblast proliferation, while 500μM rapidly led to cell cycle arrest. In addition, stimulation with H₂O₂ at a concentration of 50μM also promoted the inflammatory effects of the cells. At a concentration of 100μM H₂O₂, the cellular antioxidant system began to collapse at 8h and began to affect cellular activity. 500μM of H₂O₂ at 4h the levels of senescence-associated β-galactosidase, a marker of senescence and oxidative stress, were almost positive in fibroblasts. In addition, we found that the risk of fibroblasts carcinogenesis increased with increased H₂O₂ stimulation. The results of this study indicate that H₂O₂ can cause rapid proliferation and senescence of fibroblasts and that its mechanism of action may be mainly through influencing cellular antioxidant systems, cellular inflammatory responses and cell cycle.

Nrg1/ErbB signaling-mediated regulation of fibrosis after myocardial infarction

Appropriate fibrotic tissue formation after myocardial infarction (MI) is crucial to the maintenance of the heart's structure. M2-like macrophages play a vital role in post-MI fibrosis by activating cardiac fibroblasts. Because the mechanism by which post-MI cardiac fibrosis is regulated is not fully understood, we investigated, in vitro and in vivo, the cellular and molecular mechanisms of post-MI fibrotic tissue formation, especially those related to the regulation of cellular senescence and apoptosis. CD206⁺ F4/80⁺ CD11b⁺ M2-like macrophages collected from mouse hearts on post-MI day 7 showed increased expression of neuregulin 1 (Nrg1). Nrg1 receptor epidermal growth factor receptors ErbB2 and ErbB4 were expressed on cardiac fibroblasts in the infarct area. M2-like macrophage-derived Nrg1 suppressed both hydrogen peroxide-induced senescence and apoptosis of fibroblasts, whereas blockade of ErbB function significantly accelerated both processes. M2-like macrophage-derived Nrg1/ErbB/PI3K/Akt signaling, shown to be related to anti-senescence, was activated in damaged cardiac fibroblasts. Interestingly, systemic blockade of ErbB function in MI model mice enhanced senescence and apoptosis of cardiac fibroblasts and exacerbated inflammation. Further, increased accumulation of M2-like macrophages resulted in excessive post-MI progression of fibrosis in mice hearts. The molecular mechanism underlying the regulation of fibrotic tissue formation in the infarcted myocardium was shown in part to be attenuation of apoptosis and senescence of cardiac fibroblasts by the activation of Nrg1/ErbB/PI3K/Akt signaling. M2-like macrophage-mediated regulation of Nrg1/ErbB signaling has a substantial effect on fibrotic tissue formation in the infarcted adult mouse heart and is critical for suppressing the progression of senescence and apoptosis of cardiac fibroblasts.

Activation of Age-Related Nuclear Factor-κB Signaling Pathway Leads to Chronic Inflammation and Pituitary Fibrosis

OBJECTIVE

The purpose of the present study was to investigate the mechanism of pituitary fibrosis in elderly people.

METHODS

First, 20 pituitary glands obtained from 11 elderly people and 9 young people were studied using Masson's trichrome staining for fibrosis detection. Second, pituitary glands from 12 male rats, including 6 aged rats (OM group) and 6 young rats (YM group), were also studied. Western blotting was performed to detect collagen 1 and phosphorylation of the nuclear factor (NF)-κB subunit p65 in the OM and YM groups. The levels of 8 proinflammatory cytokines (interleukin [IL]-1α, IL-1β, IL-2, IL-4, IL-6, IL-8, interferon-γ, and tumor necrosis factor-α) in the rat pituitary glands were detected using liquid suspension chip technology. Enzyme-linked immunosorbent assays were performed to detect the growth hormone (GH) levels in the venous blood samples from the rats. Next, 12 aged rats were randomly divided into 2 groups: the QNZ (Q)+OM and normal physiological saline (N)+OM groups. The Q+OM and N+OM groups had undergone intervention by intraperitoneally injection of QNZ and physiological saline (1 mg/kg) for 28 days, respectively. Finally, biochemical and histological examinations were performed, including Masson's trichrome staining for fibrosis, Western blotting for phosphorylation of p65, Millipore multiplex bead arrays (Millipore, Billerica, Massachusetts, USA) for proinflammatory cytokine levels, and enzyme-linked immunosorbent assays for GH secretion.

RESULTS

Fibrosis was detected in the elderly patient group. Collagen 1, phosphorylation of the NF-κB signaling pathway, and the proinflammatory cytokine levels showed a significant increase in the OM group. Compared with the N+OM group, pituitary fibrosis was alleviated in the Q+OM group, with an increase in GH secretion and decreased proinflammatory cytokine levels and NF-κB.

CONCLUSIONS

Pituitary fibrosis was found in the elderly group, and the pathological change was antagonized by decreasing the proinflammatory cytokine levels using QNZ and further increasing GH secretion.

Current Concepts on the Pathogenesis of Systemic Sclerosis

From the clinical standpoint, systemic sclerosis (SSc) is characterized by skin and internal organ fibrosis, diffuse fibroproliferative vascular modifications, and autoimmunity. Clinical presentation and course are highly heterogenous and life expectancy variably affected mostly dependent on lung and heart involvement. SSc touches more women than men with differences in disease severity and environmental exposure. Pathogenetic events originate from altered homeostasis favored by genetic predisposition, environmental cues and a variety of endogenous and exogenous triggers. Epigenetic modifications modulate SSc pathogenesis which strikingly associate profound immune-inflammatory dysregulation, abnormal endothelial cell behavior, and cell trans-differentiation into myofibroblasts. SSc myofibroblasts show enhanced survival and enhanced extracellular matrix deposition presenting altered structure and altered physicochemical properties. Additional cell types of likely pathogenic importance are pericytes, platelets, and keratinocytes in conjunction with their relationship with vessel wall cells and fibroblasts. In SSc, the profibrotic milieu is favored by cell signaling initiated in the one hand by transforming growth factor-beta and related cytokines and in the other hand by innate and adaptive type 2 immune responses. Radical oxygen species and invariant receptors sensing danger participate to altered cell behavior. Conventional and SSc-specific T cell subsets modulate both fibroblasts as well as endothelial cell dysfunction. Beside autoantibodies directed against ubiquitous antigens important for enhanced clinical classification, antigen-specific agonistic autoantibodies may have a pathogenic role. Recent studies based on single-cell RNAseq and multi-omics approaches are revealing unforeseen heterogeneity in SSc cell differentiation and functional states. Advances in system biology applied to the wealth of data generated by unbiased screening are allowing to subgroup patients based on distinct pathogenic mechanisms. Deciphering heterogeneity in pathogenic mechanisms will pave the way to highly needed personalized therapeutic approaches.

Effect of Vitamin D3 on Regulating Human Tenon's Fibroblasts Activity

Purpose

To study the in vitro effect of vitamin D3 on the healing response of human Tenon's fibroblasts (HTF) and its possible role in preventing excessive postoperative subconjunctival fibrosis.

Methods

Effect of vitamin D3 on cytotoxicity and cell survival of primary cultured HTF was measured by lactate dehydrogenase and PrestoBlue assays, respectively. Proliferation and migration of vitamin D3-treated HTF (D3-HTF) was determined by CyQUANT proliferation and scratch assay, respectively. The mRNA expression profiles of control-HTF and D3-HTF from six subjects (three with glaucoma and long-term use of topical medications, three with primary pterygium) were assessed by RNA sequencing analyses to identify potential biomarkers for the inhibitory effect on HTF by vitamin D3. Validation of these biomarkers and their potential pathways were performed by quantitative real-time polymerase chain reaction (qRT-PCR) detection.

Results

Pure monolayers of HTF from controls (retinal detachment or squint surgeries), pterygium, and glaucoma subjects were successfully prepared and passaged. Proliferation and migration of pterygium and glaucoma HTF were inhibited by vitamin D3 in a dose-dependent manner, and without cytotoxicity or decrease in cellular viability with concentrations up to 10 µM. The qRT-PCR results were consistent with the transcriptome analyses, vitamin D3 appears to enhance CYP24A1, SHE, KRT16 but suppresses CILP expression in HTF.

Conclusions

Vitamin D3 can inhibit the in vitro activity of HTF without compromising cellular survivability at concentration up to 10 µM. This has potential clinical application for improving the outcome of pterygium and filtering surgeries.

Translational Relevance

Vitamin D3 can suppress the in vitro proliferation, migration, and transdifferentiation of human Tenon's fibroblasts, without the cytotoxicity of mitomycin-C, the current standard antifibrotic agent in clinical use.

Fli1 deficiency suppresses RALDH1 activity of dermal dendritic cells and related induction of regulatory T cells: a possible role in scleroderma

BACKGROUND

Aldehyde dehydrogenase 1 family member A1 (RALDH1)-producing dermal dendritic cells (DCs), a conventional DC subset regulating skin fibrosis, are decreased in the involved skin of patients with systemic sclerosis (SSc). In this study, we investigated the contribution of Fli1 deficiency, a potential predisposing factor of SSc, to the phenotypical alteration of RALDH1-producing dermal DCs by using SSc model mice and SSc skin samples.

METHODS

Bleomycin (BLM)-induced skin fibrosis was generated with Fli1^+/- and wild-type mice. The proportions of DC and CD4⁺ T cell subsets were determined by flow cytometry in the dermis of BLM-treated mice. Fli1 expression in dermal DCs was evaluated by immunofluorescence with skin samples of SSc and healthy control subjects.

RESULTS

RALDH activity of dermal DCs was significantly decreased in BLM-treated Fli1^+/- mice compared with BLM-treated wild-type mice, whereas the proportion of CD103^-CD11b^- dermal DCs, a major DC subset producing RALDH1 in response to BLM injection, was comparable between groups. Relevant to this finding, the proportion of regulatory T cells (Tregs) in the dermis was decreased in BLM-treated Fli1^+/- mice relative to BLM-treated wild-type mice, while the proportions of Th1, Th2 and Th17 cells were unaltered. In the involved skin of SSc patients, Fli1 was downregulated in CD11c⁺ cells, including dermal DCs.

CONCLUSIONS

Fli1 deficiency inhibits RALDH1 activity of CD103^-CD11b^- dermal DCs and related induction of Tregs in BLM-treated mice. Considering Fli1 reduction in SSc dermal DCs, Fli1deficiency may impair the dermal DC-Treg system, contributing to the development of skin fibrosis in SSc.

Engineering Advanced In Vitro Models of Systemic Sclerosis for Drug Discovery and Development

Systemic sclerosis (SSc) is a complex multisystem disease with the highest case-specific mortality among all autoimmune rheumatic diseases, yet without any available curative therapy. Therefore, the development of novel therapeutic antifibrotic strategies that effectively decrease skin and organ fibrosis is needed. Existing animal models are cost-intensive, laborious and do not recapitulate the full spectrum of the disease and thus commonly fail to predict human efficacy. Advanced in vitro models, which closely mimic critical aspects of the pathology, have emerged as valuable platforms to investigate novel pharmaceutical therapies for the treatment of SSc. This review focuses on recent advancements in the development of SSc in vitro models, sheds light onto biological (e.g., growth factors, cytokines, coculture systems), biochemical (e.g., hypoxia, reactive oxygen species) and biophysical (e.g., stiffness, topography, dimensionality) cues that have been utilized for the in vitro recapitulation of the SSc microenvironment, and highlights future perspectives for effective drug discovery and validation.

Dysfunctional Keratinocytes Increase Dermal Inflammation in Systemic Sclerosis: Results From Studies Using Tissue-Engineered Scleroderma Epidermis

OBJECTIVE

Evidence suggests that keratinocyte-fibroblast interactions are abnormal in systemic sclerosis (SSc). The present study was undertaken to investigate potential epidermal dysfunction in SSc and its effects on dermal homeostasis.

METHODS

Epidermal equivalents (EEs) were generated using keratinocytes from 6 healthy donors and 4 individuals with SSc. Skin and EE expression of markers of proliferation, differentiation, and activation was evaluated by immunohistochemistry. The transcriptomic profile of SSc EEs and healthy donor EEs was identified by RNA sequencing. EE conditioned medium (CM) was used to stimulate fibroblasts, and their production of interleukin-6 (IL-6), IL-8, matrix metalloproteinase 1 (MMP-1), type I collagen, and fibronectin was assessed by enzyme-linked immunosorbent assay.

RESULTS

Compared to healthy donor EEs, SSc EEs exhibited aberrant differentiation, enhanced expression of activation markers, and a lower rate of basal keratinocyte mitosis, reproducing most of the abnormalities observed in SSc epidermis. RNA sequencing analysis revealed that, compared to healthy donor EEs, SSc EEs were characterized by lower expression of homeobox gene family members and by enhanced metabolic and oxidative stress molecular pathways. EE CM enhanced fibroblast production of IL-6, IL-8, MMP-1, type I collagen, and fibronectin (P < 0.05). Except for type I collagen and fibronectin, this effect was 2-fold higher in the presence of CM generated form SSc EEs. IL-1 was responsible, at least in part, for keratinocyte-dependent fibroblast activation.

CONCLUSION

SSc EEs recapitulate the in vivo characteristics of SSc epidermis, demonstrating that SSc keratinocytes have an intrinsically altered differentiation program, possibly due to the dysregulation of genes from the homeobox family. The increased metabolic and oxidative stress associated with SSc epidermis may contribute to chronic inflammation and fibrosis of the dermis.

Interleukin 1α: a comprehensive review on the role of IL-1α in the pathogenesis and treatment of autoimmune and inflammatory diseases

The interleukin (IL)-1 family member IL-1α is a ubiquitous and pivotal pro-inflammatory cytokine. The IL-1α precursor is constitutively present in nearly all cell types in health, but is released upon necrotic cell death as a bioactive mediator. IL-1α is also expressed by infiltrating myeloid cells within injured tissues. The cytokine binds the IL-1 receptor 1 (IL-1R1), as does IL-1β, and induces the same pro-inflammatory effects. Being a bioactive precursor released upon tissue damage and necrotic cell death, IL-1α is central to the pathogenesis of numerous conditions characterized by organ or tissue inflammation. These include conditions affecting the lung and respiratory tract, dermatoses and inflammatory skin disorders, systemic sclerosis, myocarditis, pericarditis, myocardial infarction, coronary artery disease, inflammatory thrombosis, as well as complex multifactorial conditions such as COVID-19, vasculitis and Kawasaki disease, Behcet's syndrome, Sjogren Syndrome, and cancer. This review illustrates the clinical relevance of IL-1α to the pathogenesis of inflammatory diseases, as well as the rationale for the targeted inhibition of this cytokine for treatment of these conditions. Three biologics are available to reduce the activities of IL-1α; the monoclonal antibody bermekimab, the IL-1 soluble receptor rilonacept, and the IL-1 receptor antagonist anakinra. These advances in mechanistic understanding and therapeutic management make it incumbent on physicians to be aware of IL-1α and of the opportunity for therapeutic inhibition of this cytokine in a broad spectrum of diseases.

Serum S100A12 levels: Possible association with skin sclerosis and interstitial lung disease in systemic sclerosis

Damage-associated molecular patterns (DAMPs) have drawn much attention as a member of disease-associated molecules in systemic sclerosis (SSc). In this study, we investigated the potential contribution of S100A12, a member of DAMPs, to the development of SSc by evaluating S100A12 expression in the lesional skin and the clinical correlation of serum S100A12 levels. S100A12 expression was markedly elevated in the epidermis of SSc-involved skin at protein levels and in the bulk skin at mRNA levels. The deficiency of transcription factor Fli1, a predisposing factor of SSc, enhanced S100A12 expression and Fli1 occupied the S100A12 promoter in normal human keratinocytes. Serum S100A12 levels were higher in SSc patients, especially in those with diffuse cutaneous involvement, than in healthy controls and positively correlated with skin score. Furthermore, the presence of interstitial lung disease significantly augmented serum levels of S100A12. Importantly, serum S100A12 levels correlated inversely with both per cent forced vital capacity and per cent diffusing capacity for carbon monoxide and positively with serum levels of KL-6 and surfactant protein-D. Collectively, these results indicate a possible contribution of S100A12 to skin sclerosis and interstitial lung disease associated with SSc, further supporting the critical roles of DAMPs in the pathogenesis of this disease.

microRNA27a-3p mediates reduction of the Wnt antagonist sFRP-1 in systemic sclerosis

Systemic Sclerosis (SSc) is an autoimmune connective tissue disease that leads to skin and lung fibrosis. The Wnt pathway is clearly elevated in SSc and is pro-fibrotic via activation of canonical Wnt signalling. sFRP-1 is a Wnt antagonist that acts as a negative regulator of Wnt signalling. We sought to measure the levels of serum sFRP-1 in early diffuse SSc patients compared to healthy controls and if this is regulated by microRNA27a-3p. Ten early diffuse SSc patients and healthy controls sera were taken and sFRP-1 quantified by ELISA. Skin biopsies were also taken in five SSc patients and controls. Fibroblasts were quantified for microRNA27-3p expression by Taqman qRT-PCR with an internal microRNA to normalize. 3'UTR luciferase assays were performed to confirm direct targets of microRNA27a-3p with microRNA overexpression. Fibroblasts were transfected with microRNA27a mimics or scramble controls and using ELISA sFRP-1 was quantified. Furthermore, Collagen, Axin-2, TIMP-1 and MMP-1 were measured. Serum sFRP-1 was significantly reduced in early diffuse SSc patients. We identified microRNA27a-3p-3p as regulating sFRP-1 in dermal fibroblasts. We found significantly elevated microRNA27a-3p in isolated dermal fibroblasts from SSc patients. We confirmed that sFRP-1 is a direct target of microRNA27a-3p through cloning of the 3'UTR into a luciferase vector. ECM genes were also upregulated by microRNA27a-3p-3p and the matrix-degrading enzyme MMP-1 was suppressed. Serum sFRP-1 is reduced in diffuse SSc patients and is regulated by microRNA27a-3p and this is a direct regulation. Modulation of microRNA27a-3p levels could mediate fibrosis regression.

The Pathogenesis of Systemic Sclerosis: An Understanding Based on a Common Pathologic Cascade across Multiple Organs and Additional Organ-Specific Pathologies

Systemic sclerosis (SSc) is a multisystem autoimmune and vascular disease resulting in fibrosis of various organs with unknown etiology. Accumulating evidence suggests that a common pathologic cascade across multiple organs and additional organ-specific pathologies underpin SSc development. The common pathologic cascade starts with vascular injury due to autoimmune attacks and unknown environmental factors. After that, dysregulated angiogenesis and defective vasculogenesis promote vascular structural abnormalities, such as capillary loss and arteriolar stenosis, while aberrantly activated endothelial cells facilitate the infiltration of circulating immune cells into perivascular areas of various organs. Arteriolar stenosis directly causes pulmonary arterial hypertension, scleroderma renal crisis and digital ulcers. Chronic inflammation persistently activates interstitial fibroblasts, leading to the irreversible fibrosis of multiple organs. The common pathologic cascade interacts with a variety of modifying factors in each organ, such as keratinocytes and adipocytes in the skin, esophageal stratified squamous epithelia and myenteric nerve system in gastrointestinal tract, vasospasm of arterioles in the heart and kidney, and microaspiration of gastric content in the lung. To better understand SSc pathogenesis and develop new disease-modifying therapies, it is quite important to understand the complex pathogenesis of SSc from the two distinct perspectives, namely the common pathologic cascade and additional organ-specific pathologies.

Damage-associated molecular patterns in trauma

In 1994, the "danger model" argued that adaptive immune responses are driven rather by molecules released upon tissue damage than by the recognition of "strange" molecules. Thus, an alternative to the "self versus non-self recognition model" has been provided. The model, which suggests that the immune system discriminates dangerous from safe molecules, has established the basis for the future designation of damage-associated molecular patterns (DAMPs), a term that was coined by Walter G. Land, Seong, and Matzinger. The pathological importance of DAMPs is barely somewhere else evident as in the posttraumatic or post-surgical inflammation and regeneration. Since DAMPs have been identified to trigger specific immune responses and inflammation, which is not necessarily detrimental but also regenerative, it still remains difficult to describe their "friend or foe" role in the posttraumatic immunogenicity and healing process. DAMPs can be used as biomarkers to indicate and/or to monitor a disease or injury severity, but they also may serve as clinically applicable parameters for optimized indication of the timing for, i.e., secondary surgeries. While experimental studies allow the detection of these biomarkers on different levels including cellular, tissue, and circulatory milieu, this is not always easily transferable to the human situation. Thus, in this review, we focus on the recent literature dealing with the pathophysiological importance of DAMPs after traumatic injury. Since dysregulated inflammation in traumatized patients always implies disturbed resolution of inflammation, so-called model of suppressing/inhibiting inducible DAMPs (SAMPs) will be very briefly introduced. Thus, an update on this topic in the field of trauma will be provided.

Interplay Between Keratinocytes and Fibroblasts: A Systematic Review Providing a New Angle for Understanding Skin Fibrotic Disorders

Background/Objective: Skin fibrosis is the result of aberrant processes leading to abnormal deposition of extracellular matrix (ECM) in the dermis. In healthy skin, keratinocytes participate to maintain skin homeostasis by actively crosstalking with fibroblasts. Within the wide spectrum of fibrotic skin disorders, relatively little attention has been devoted to the role of keratinocytes for their capacity to participate to skin fibrosis. This systematic review aims at summarizing the available knowledge on the reciprocal interplay of keratinocytes with fibroblasts and their soluble mediators in physiological states, mostly wound healing, and conditions associated with skin fibrosis.

Methods: We performed a systematic literature search on PubMed to identify in vitro and ex vivo human studies investigating the keratinocyte characteristics and their interplay with fibroblasts in physiological conditions and within fibrotic skin disorders including hypertrophic scars, keloids, and systemic sclerosis. Studies were selected according to pre-specified eligibility criteria. Data on study methods, models, stimuli and outcomes were retrieved and summarized according to pre-specified criteria.

Results: Among the 6,271 abstracts retrieved, 73 articles were included, of which 14 were specifically dealing with fibrotic skin pathologies. Fifty-six studies investigated how keratinocyte may affect fibroblast responses in terms of ECM-related genes or protein production, phenotype modification, and cytokine production. Most studies in both physiological conditions and fibrosis demonstrated that keratinocytes stimulate fibroblasts through the production of interleukin 1, inducing keratinocyte growth factor (KGF) and metalloproteinases in the fibroblasts. When the potential of keratinocytes to modulate collagen synthesis by healthy fibroblasts was explored, the results were controversial. Nevertheless, studies investigating keratinocytes from fibrotic skin, including keloids, hypertrophic scar, and scleroderma, suggested their potential involvement in enhancing ECM deposition. Twenty-three papers investigated keratinocyte proliferation differentiation and production of soluble mediators in response to interactions with fibroblasts. Most studies showed that fibroblasts modulate keratinocyte viability, proliferation, and differentiation. The production of KGF by fibroblast was identified as key for these functions.

Conclusions: This review condenses evidence for the active interaction between keratinocytes and fibroblasts in maintaining skin homeostasis and the altered homeostatic interplay between keratinocytes and dermal fibroblasts in scleroderma and scleroderma-like disorders.

Elucidation of molecular pathways responsible for the accelerated wound healing induced by a novel fibrous chitin dressing

Fibrous chitin dressing (FCD) prepared from a NaOH-urea aqueous solution of chitin via a physical process was used to study its effect on wound healing using a full-thickness cutaneous wound model in rats and mice. It was demonstrated that wounds in rats covered with the FCD showed faster collagen (especially type I collagen) growth and speedier healing than those with Gauze (12 days versus 16 days). The ability of FCD to promote wound healing was also observed on wild-type (WT) mice. For MyD88-knockout mice, however, FCD displayed no beneficial but an adverse effect on wound healing: the healing time for wounds treated with FCD was even longer than those treated with gauze. Importantly, in vivo studies indicated that FCD-treated mice, compared to gauze-treated ones, exhibited markedly higher expressions of MyD88, IKBα, TGF-β, P-TβR II, TβR II and P-Smad2/3 in wild-type mice. For MyD88 knockout mice, however, the expressions of those molecules were inhibited and lowered in FCD-treated ones than those treated with gauze. In vitro studies confirmed that chitin increased the expression of TGF-β, P-TβRII and P-Smad2/3 while the expressions of those molecules were significantly inhibited with CD14 antibody (p < 0.05). These results indicated that FCD accelerated wound healing through a MyD88-dependent pathway, followed by a TGF-β/Smad pathway. This work not only demonstrated the superior wound healing effect of chitin-derived dressing, but also provided for the first time the underlying molecular mechanism, further establishing chitin as an important biomedical material for potential clinical applications.

Increased expression of the TNF superfamily member LIGHT/TNFSF14 and its receptors (HVEM and LTßR) in patients with systemic sclerosis

OBJECTIVES

This study aimed to assess the potential role of the TNF superfamily member lymphocyte T-related inducible ligand that competes for glycoprotein D binding to herpesvirus entry mediator on T cells (LIGHT) in SSc through evaluation of: skin expression of LIGHT and its receptors, herpesvirus entry mediator and lymphotoxin ß-related receptor, and serum concentration of LIGHT in SSc patients.

METHODS

Expression of LIGHT and its receptors was investigated by immunohistochemistry and evaluated semi-quantitatively in skin biopsies from 19 SSc patients and 9 healthy controls. Serum levels of LIGHT were measured using ELISA in 329 patients with SSc and 50 control subjects.

RESULTS

Expression of LIGHT and both receptors was higher in SSc patients compared with controls (P < 0.05 for all comparisons). Patients with early SSc (⩽ 3 years from the first non-Raynaud's phenomenon symptom) showed higher expression of LIGHT and herpesvirus entry mediator compared with patients with longer disease duration (P < 0.05 for both comparisons). The mean serum concentration of LIGHT was significantly higher in SSc patients compared with the controls (P < 0.05). High serum concentration of LIGHT was associated with male sex, presence of digital ulcers, muscle involvement (defined by elevated serum creatine kinase levels), steroid treatment and lack of ACA. However, in multivariate regression analysis only presence of digital ulcers and creatine kinase elevation were independently associated with serum concentration of LIGHT.

CONCLUSION

These data provide the first evidence of overexpression of LIGHT and its receptors in SSc and suggest that the LIGHT axis might contribute to the pathogenesis of SSc. Increased serum concentrations of LIGHT seem to reflect vascular injury in SSc.

Vascularised human skin equivalents as a novel in vitro model of skin fibrosis and platform for testing of antifibrotic drugs

OBJECTIVES

Fibrosis is a complex pathophysiological process involving interplay between multiple cell types. Experimental modelling of fibrosis is essential for the understanding of its pathogenesis and for testing of putative antifibrotic drugs. However, most current models employ either phylogenetically distant species or rely on human cells cultured in an artificial environment. Here we evaluated the potential of vascularised in vitro human skin equivalents as a novel model of skin fibrosis and a platform for the evaluation of antifibrotic drugs.

METHODS

Skin equivalents were assembled on a three-dimensional extracellular matrix by sequential seeding of endothelial cells, fibroblasts and keratinocytes. Fibrotic transformation on exposure to transforming growth factor-β (TGFβ) and response to treatment with nintedanib as an established antifibrotic agent were evaluated by quantitative polymerase chain reaction (qPCR), capillary Western immunoassay, immunostaining and histology.

RESULTS

Skin equivalents perfused at a physiological pressure formed a mature, polarised epidermis, a stratified dermis and a functional vessel system. Exposure of these models to TGFβ recapitulated key features of SSc skin with activation of TGFβ pathways, fibroblast to myofibroblast transition, increased release of collagen and excessive deposition of extracellular matrix. Treatment with the antifibrotic agent nintedanib ameliorated this fibrotic transformation.

CONCLUSION

Our data provide evidence that vascularised skin equivalents can replicate key features of fibrotic skin and may serve as a platform for evaluation of antifibrotic drugs in a pathophysiologically relevant human setting.

Elevated serum levels of interleukin-1β and interleukin-33 in patients with systemic sclerosis in Chinese population

PURPOSE OF THE STUDY

Systemic sclerosis (SSc) is a multisystem autoimmune disease. Although the pathogenesis of the disease remains incompletely understood, some cytokines or growth factors which regulate SSc induction may be involved in the injury of endothelial cells and the modulation of leukocyte function. We aimed to perform this case-control study to determine serum levels of interleukin (IL)-1α, IL-1β, IL-18 and IL-33 and their associations with clinical manifestations in SSc patients.

MATERIALS AND METHODS

There were 56 patients with SSc and 56 healthy individuals who were recruited from local hospital between 2012 and 2014. Serum IL-1α, IL-1β, IL-18 and IL-33 levels were measured with specific enzyme-linked immunosorbent assay kits.

RESULTS

Univariate analysis revealed that serum IL-1β, IL-18 and IL-33 levels in SSc patients were significantly higher than that in healthy controls. After adjusting possible confounding factors (sex, age, smoking and drinking) by multivariable analyses, serum IL-1β levels (OR = 1.082; 95 % CI: 1.013-1.155) and serum IL-33 levels (OR = 1.100; 95 %CI: 1.022-1.185) were still related factors. There were interrelationships among the serum levels of IL-1α, IL-1β, IL-18 and IL-33 and these associations were not consistent in SSc patients and controls. No associations of serum IL-1α, IL-1β, IL-18 and IL-33 levels with clinical parameters were found.

CONCLUSION

IL-1β and IL-33 may contribute to the development of SSc. While there were no direct associations between these cytokines and disease manifestations, they still could be considered as serum markers of development of SSc. Further studies are required to validate this incipient data.

GI Manifestations With a Focus on the Esophagus: Recent Progress in Understanding Pathogenesis

PURPOSE OF REVIEW

Esophageal dysfunction is common in systemic sclerosis (SSc) patients. Limited treatment options are available for scleroderma esophageal disease. Here, we discuss recent updates on the diagnosis, treatment, and characterization that have been made in patients with scleroderma esophageal disease.

RECENT FINDINGS

In the past few years, novel diagnostic tools have provided insight into esophageal dysmotility in SSc patients. New drugs are being tested and might improve symptoms and quality of life in SSc patients with esophageal dysfunction. Molecular stratification methods have facilitated the identification of molecular signatures in the esophagus of SSc patients. The Friend leukemia integration 1 (Fli1) conditional knockout mouse is the first animal model to report an esophageal phenotype with SSc features. The clinical presentation in SSc patients with esophageal dysfunction is heterogeneous, complicating diagnosis and management. The improvement of diagnostic tools for esophageal symptoms and dysfunction and the use of molecular approaches in SSc mouse models and patient biopsies offer an opportunity to improve the characterization of SSc esophageal disease, which should help improve management and treatment decisions.

Giulio Gabbiani and the discovery of myofibroblasts

Myofibroblasts, specialized fibroblasts expressing the protein alpha-smooth muscle actin, are instrumental in wound contraction during normal wound healing. Tissue shortening is then stabilized by the synthesis of extracellular matrix, collagen in particular. Alpha-smooth muscle actin within myofibroblasts becomes organized in filamentous bundles, called stress fibers, that allow the retractile movement producing wound contraction. During hypertrophic scarring, skin deformations depend on the inappropriate action of these stress fibers that for unknown reasons persist even after the epithelialization of the wound. This historical review article is dedicated to the reconstruction of the discovery of this cell by the Italian scientist Giulio Gabbiani.

Targeting TLRs and the inflammasome in systemic sclerosis

Systemic sclerosis (SSc) is an idiopathic autoimmune disease characterised by inflammation, vascular problems, cytokine dysregulation and ultimately fibrosis, which accounts for poor prognosis and eventual mortality. At present no curative treatments exist, hence there is an urgent need to better understand the aetiology and develop improved therapies accordingly. Although still widely debated, significant evidence points to upregulation of the innate immune response via the activity of Toll-like receptors (TLRs) and the NLRP3 inflammasome as the start points in a cascade of signaling events which drives excessive extracellular matrix protein production, causing fibrosis. Herein the recent breakthroughs which have implicated TLR signaling and the NLRP3 inflammasome in SSc and the novel therapeutic possibilities this introduces to the field will be discussed.

Danger signals in trauma

This review summarizes a short list of currently discussed trauma-induced danger-associated molecular patterns (DAMP). Due to the bivalent character and often pleiotropic effects of a DAMP, it is difficult to describe its "friend or foe" role in post-traumatic inflammation and regeneration, both systemically as well locally in tissues. DAMP can be used as biomarkers to indicate or monitor disease or injury severity, but also may serve as clinically applicable parameters for better indication and timing of surgery. Due to the inflammatory processes at the local tissue level or the systemic level, the precise role of DAMP is not always clear to define. While in vitro and experimental studies allow for the detection of these biomarkers at the different levels of an organism-cellular, tissue, circulation-this is not always easily transferable to the human setting. Increased knowledge exploring the dual role of DAMP after trauma, and concentrating on their nuclear functions, transcriptional targets, release mechanisms, cellular sources, multiple functions, their interactions and potential therapeutic targeting is warranted.

Selective deletion of PPARβ/δ in fibroblasts causes dermal fibrosis by attenuated LRG1 expression

Connective tissue diseases of the skin are characterized by excessive collagen deposition in the skin and internal organs. Fibroblasts play a pivotal role in the clinical presentation of these conditions. Nuclear receptor peroxisome-proliferator activated receptors (PPARs) are therapeutic targets for dermal fibrosis, but the contribution of the different PPAR subtypes are poorly understood. Particularly, the role of fibroblast PPARβ/δ in dermal fibrosis has not been elucidated. Thus, we generated a mouse strain with selective deletion of PPARβ/δ in the fibroblast (FSPCre-Pparb/d-/-) and interrogated its epidermal and dermal transcriptome profiles. We uncovered a downregulated gene, leucine-rich alpha-2-glycoprotein-1 (Lrg1), of previously unknown function in skin development and architecture. Our findings suggest that the regulation of Lrg1 by PPARβ/δ in fibroblasts is an important signaling conduit integrating PPARβ/δ and TGFβ1-signaling networks in skin health and disease. Thus, the FSPCre-Pparb/d-/- mouse model could serve as a novel tool in the current gunnery of animal models to better understand dermal fibrosis.

What can we learn from Fli1-deficient mice, new animal models of systemic sclerosis?

Systemic sclerosis is a complex multifactorial disease characterized by autoimmunity, vasculopathy, and selective organ fibrosis. A series of genetic and epidemiological studies have demonstrated that environmental influences play a central role in the onset of systemic sclerosis, while genetic factors determine the susceptibility to and the severity of this disease. Therefore, the identification of predisposing factors related to environmental influences would provide us with an informative clue to better understand the pathological process of this disease. Based on this concept, the deficiency of transcription factor Friend leukemia virus integration 1, which is epigenetically suppressed in systemic sclerosis, seems to be a potential candidate acting as the predisposing factor of this disease. Indeed, Fli1-mutated mice serve as a set of useful disease models to disclose the complex pathology of systemic sclerosis. This article overviews the recent advancement in systemic sclerosis animal models associated with Friend leukemia virus integration 1 deficiency.