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

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.

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 Type-Specific Biomarkers of Systemic Sclerosis Disease Severity Capture Cell-Intrinsic and Cell-Extrinsic Circuits

OBJECTIVE

Systemic sclerosis (SSc) is a multifactorial autoimmune fibrotic disorder involving complex rewiring of cell-intrinsic and cell-extrinsic signaling coexpression networks involving a range of cell types. However, the rewired circuits as well as corresponding cell-cell interactions remain poorly understood. To address this, we used a predictive machine learning framework to analyze single-cell RNA-sequencing data from 24 SSc patients across the severity spectrum as quantified by the modified Rodnan skin score (MRSS).

METHODS

We used a least absolute shrinkage and selection operator (LASSO)-based predictive machine learning approach on the single-cell RNA-sequencing data set to identify predictive biomarkers of SSc severity, both across and within cell types. The use of L1 regularization helps prevent overfitting on high-dimensional data. Correlation network analyses were coupled to the LASSO model to identify cell-intrinsic and cell-extrinsic co-correlates of the identified biomarkers of SSc severity.

RESULTS

We found that the uncovered cell type-specific predictive biomarkers of MRSS included previously implicated genes in fibroblast and myeloid cell subsets (e.g., SFPR2+ fibroblasts and monocytes), as well as novel gene biomarkers of MRSS, especially in keratinocytes. Correlation network analyses revealed novel cross-talk between immune pathways and implicated keratinocytes in addition to fibroblast and myeloid cells as key cell types involved in SSc pathogenesis. We then validated the uncovered association of key gene expression and protein markers in keratinocytes, KRT6A and S100A8, with SSc skin disease severity.

CONCLUSION

Our global systems analyses reveal previously uncharacterized cell-intrinsic and cell-extrinsic signaling coexpression networks underlying SSc severity that involve keratinocytes, myeloid cells, and fibroblasts.

Evaluating the Effects of Cryopreservation on the Viability and Gene Expression of Porcine-Ear-Skin Fibroblasts

Owing to the inherent heterogeneity and plasticity of fibroblasts, they are considered as the conventional biological resources for basic and clinical medical research. Thus, it is essential to generate knowledge about the establishment of fibroblast cultures and the effects of cryopreservation processes on their biological characteristics. Since the pig (Sus scrofa) possesses numerous genetic, physiological, and anatomical similarities with humans, porcine fibroblasts are naturally regarded as useful analogues of human fibroblasts. Nonetheless, less attention has been given to the alterations in viability and gene expression of cryopreserved porcine fibroblasts. In this study, we aimed to obtain fibroblasts from porcine ear skin and evaluate the effects of cryopreservation on the cell survival, proliferation, and gene expression profiles of the fibroblasts by trypan-blue-staining assay, Cell Counting kit-8 (CCK-8) assay, and RNA-sequencing analysis, respectively. Our results suggested that morphologically stable fibroblast cultures can be constructed from pig-ear skin. The post-thaw survival rate of the cryopreserved fibroblasts at 0 h and 24 h was over 90%. The proliferative activity of the cryopreserved fibroblasts was similar to that of the non-cryopreserved fibroblasts after 7 days of in vitro culture, which suggested that cryopreservation did not influence the viability. The RNA-sequencing analysis indicated that this should be attributed to the 867 differentially expressed genes (DGEs) identified, which are involved in molecular process related to cell recovery and survival after cryo-stimulation. In addition, eight important DEGs BMP2, GDF15, EREG, AREG, HBEGF, LIF, IL-6, and HOX-7 could potentially be applied to improve the efficiency of fibroblast cryopreservation, but comprehensive and systematic studies on understanding the underlying mechanisms responsible for their modulatory roles are urgently needed.

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.

Fibroblast-Conditioned Media Enhance the Yield of Microglia Isolated from Mixed Glial Cultures

Microglia are the main immune cells of the central nervous system (CNS) and comprise various model systems used to investigate inflammatory mechanisms in CNS disorders. Currently, shaking and mild trypsinization are widely used microglial culture methods; however, the problems with culturing microglia include low yield and a time-consuming process. In this study, we replaced normal culture media (NM) with media containing 25% fibroblast-conditioned media (F-CM) to culture mixed glia and compared microglia obtained by these two methods. We found that F-CM significantly improved the yield and purity of microglia and reduced the total culture time of mixed glia. The microglia obtained from the F-CM group showed longer ramified morphology than those from the NM group, but no difference was observed in cell size. Microglia from the two groups had similar phagocytic function and baseline phenotype markers. Both methods yielded microglia were responsive to various stimuli such as lipopolysaccharide (LPS), interferon-γ (IFN-γ), and interleukin-4 (IL-4). The current results suggest that F-CM affect the growth of primary microglia in mixed glia culture. This method can produce a high yield of primary microglia within a short time and may be a convenient method for researchers to investigate inflammatory mechanisms and some CNS disorders.

Resveratrol rescues cutaneous radiation-induced DNA damage via a novel AMPK/SIRT7/HMGB1 regulatory axis

Cutaneous radiation injury (CRI) interrupts the scheduled process of radiotherapy and even compromises the life quality of patients. However, the current clinical options for alleviating CRI are relatively limited. Resveratrol (RSV) has been shown to be a promising protective agent against CRI; yet the mechanisms of RSV enhancing radioresistance were not fully elucidated and limited its clinical application. In this study, we demonstrate RSV promotes cutaneous radioresistance mainly through SIRT7. During ionizing radiation (IR) treatment, RSV indirectly phosphorylates and activates SIRT7 through AMPK, which is critical for maintaining the genome stability of keratinocytes. Immunoprecipitation and mass spectrometry identified HMGB1 to be the key interacting partner of SIRT7 to mediate the radioprotective function of RSV. Mechanistic study elucidated that SIRT7 interacts with and deacetylates HMGB1 to redistribute it into nucleus and "switch on" its function for DNA damage repair. Our findings establish a novel AMPK/SIRT7/HMGB1 regulatory axis that mediates the radioprotective function of RSV to alleviate IR-induced cutaneous DNA injury, providing an efficiently-curative option for patients with CRI during radiotherapy.

Extracellular matrix stiffness-The central cue for skin fibrosis

Skin fibrosis is a physiopathological process featuring the excessive deposition of extracellular matrix (ECM), which is the main architecture that provides structural support and constitutes the microenvironment for various cellular behaviors. Recently, increasing interest has been drawn to the relationship between the mechanical properties of the ECM and the initiation and modulation of skin fibrosis, with the engagement of a complex network of signaling pathways, the activation of mechanosensitive proteins, and changes in immunoregulation and metabolism. Simultaneous with the progression of skin fibrosis, the stiffness of ECM increases, which in turn perturbs mechanical and humoral homeostasis to drive cell fate toward an outcome that maintains and enhances the fibrosis process, thus forming a pro-fibrotic "positive feedback loop". In this review, we highlighted the central role of the ECM and its dynamic changes at both the molecular and cellular levels in skin fibrosis. We paid special attention to signaling pathways regulated by mechanical cues in ECM remodeling. We also systematically summarized antifibrotic interventions targeting the ECM, hopefully enlightening new strategies for fibrotic 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.

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.

Porous Se@SiO2 Nanoparticles Enhance Wound Healing by ROS-PI3K/Akt Pathway in Dermal Fibroblasts and Reduce Scar Formation

Hypertrophic scarring, which is characterized by excessive extracellular matrix deposition and abnormal fibroblast homeostasis, is an undesirable outcome of dermal wound healing. Once formed, the scar will replace the normal function of local skin, and there are few noninvasive clinical treatments that can cure it. Se@SiO₂ nanoparticles were synthesized to suppress oxidative stress, which induced the presence and activation of myofibroblasts during wound recovery. The characterization, antioxidant capacity and biological safety of Se@SiO₂ NPs were evaluated. A full-thickness excisional wound model was established, and the wounds were divided into three groups. The re-epithelization and distribution of collagen fibers were assessed using hematoxylin and eosin staining and Masson’s trichome staining after specific treatments. Our results revealed that the Se@SiO₂ NPs accelerated dermal wound healing and suppressed the formation of hypertrophic scars, accompanied by oxidative stress inhibition. Moreover, we found that Se@SiO₂ NPs worked by activating the PI3K/Akt pathway and upregulating the phosphorylation of Akt. The findings of our study provide a new method to promote dermal scar-free wound healing by suppressing excessive oxidative stress and through PI3K/Akt pathway activation.

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.

Cellular and Molecular Diversity in Scleroderma

With the increasing armamentarium of high-throughput tools available at manageable cost, it is attractive and informative to determine the molecular underpinnings of patient heterogeneity in systemic sclerosis (SSc). Given the highly variable clinical outcomes of patients labelled with the same diagnosis, unravelling the cellular and molecular basis of disease heterogeneity will be crucial to predicting disease risk, stratifying management and ultimately informing a patient-centered precision medicine approach. Herein, we summarise the findings of the past several years in the fields of genomics, transcriptomics, and proteomics that contribute to unraveling the cellular and molecular heterogeneity of SSc. Expansion of these findings and their routine integration with quantitative analysis of histopathology and imaging studies into clinical care promise to inform a scientifically driven patient-centred personalized medicine approach to SSc in the near future.

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.