Increased expression of NAPDH oxidase 4 in systemic sclerosis dermal fibroblasts: regulation by transforming growth factor β

Research landscape and pharmacological mechanisms of traditional Chinese medicines in treating and preventing urolithiasis: Unearthing an anti-urolithic treasure trove

ETHNOPHARMACOLOGICAL RELEVANCE

Urolithiasis represents a predominant concern within urology due to its high recurrence rate and consequential surgical complications. Traditional Chinese Medicine (TCM), with a history spanning over 2000 years in treating kidney diseases, not only offers a less invasive and cost-effective option for treating and preventing urolithiasis, but also serves as a pharmacological treasure trove for the development of anti-urolithic drugs.

AIM OF THE STUDY

With the continuous deepening of research on the anti-urolithic effects of Chinese medicines, the pharmacological mechanisms of TCMs against urolithiasis are continuously evolving. Therefore, it is essential to summarize the current research status, clinical effectiveness, and mechanisms of TCM in treating and preventing urolithiasis, to ascertain its potential in anti-urolithic treatments, and to provide a reference for future anti-urolithiasis drug research.

METHODS

The electronic databases such as PubMed, Web of Science, and China National Knowledge Infrastructure (CNKI) have been utilized to retrieve relevant literature spanning from 2000 to September 2023, using keywords "Traditional Chinese Medicine" and "Urolithiasis". Then we conducted a visual analysis of the current status of related research, as well as a systematic organization of the therapeutic effects and underlying mechanisms of anti-urolithic TCMs.

RESULTS

Through the organization of research models, therapeutic effects, and active ingredients of 31 potential anti-urolithic TCMs, we have systematically summarized the underlying mechanisms of TCMs in management of urolithiasis. Mechanistically, Chinese herbs facilitate stone expulsion by enhancing diuresis, instigating anti-spasmodic effects, and promoting ureteral peristalsis when addressing calculi. They also harbor the potential to dissolve pre-existing stones. In terms of stone recurrence prevention, TCM compounds obstruct stone formation through targeting the sequence of crystal adhesion, nucleation, growth, and aggregation to inhibit stone formation. Additionally, TCM's significant roles include stifling oxidative stress, augmenting urinary stone inhibitors, and harmonizing oxalate metabolism, all of which are critical actions in stone prevention.

CONCLUSION

The anti-urolithic mechanism of TCM is multifaceted. Investigating the anti-urolithiasis mechanisms of TCM not only illuminates the potential of Chinese medicine in treating and preventing urolithiasis, but also uncovers active molecules and targets for drug treatment against calculus formation.

Phosphodiesterase 4 is overexpressed in keloid epidermal scars and its inhibition reduces keratinocyte fibrotic alterations

BACKGROUND

Epidermal remodeling and hypertrophy are hallmarks of skin fibrotic disorders, and keratinocyte to mesenchymal (EMT)-like transformations drive epidermis alteration in skin fibrosis such as keloids and hypertrophic scars (HTS). While phosphodiesterase 4 (PDE4) inhibitors have shown effectiveness in various fibrotic disorders, their role in skin fibrosis is not fully understood. This study aimed to explore the specific role of PDE4B in epidermal remodeling and hypertrophy seen in skin fibrosis.

METHODS

In vitro experiments examined the effects of inhibiting PDE4A-D (with Roflumilast) or PDE4B (with siRNA) on TGFβ1-induced EMT differentiation and dedifferentiation in human 3D epidermis. In vivo studies investigated the impact of PDE4 inhibition on HOCl-induced skin fibrosis and epidermal hypertrophy in mice, employing both preventive and therapeutic approaches.

RESULTS

The study found increased levels of PDE4B (mRNA, protein) in keloids > HTS compared to healthy epidermis, as well as in TGFβ-stimulated 3D epidermis. Keloids and HTS epidermis exhibited elevated levels of collagen Iα1, fibronectin, αSMA, N-cadherin, and NOX4 mRNA, along with decreased levels of E-cadherin and ZO-1, confirming an EMT process. Inhibition of both PDE4A-D and PDE4B prevented TGFβ1-induced Smad3 and ERK1/2 phosphorylation and mesenchymal differentiation in vitro. PDE4A-D inhibition also promoted mesenchymal dedifferentiation and reduced TGFβ1-induced ROS and keratinocyte senescence by rescuing PPM1A, a Smad3 phosphatase. In vivo, PDE4 inhibition mitigated HOCl-induced epidermal hypertrophy in mice in both preventive and therapeutic settings.

CONCLUSIONS

Overall, the study supports the potential of PDE4 inhibitors, particularly PDE4B, in treating skin fibrosis, including keloids and HTS, shedding light on their functional role in this condition.

miR-146a Decreases Inflammation and ROS Production in Aged Dermal Fibroblasts

Aging is associated with a decline in the functionality of various cell types, including dermal fibroblasts, which play a crucial role in maintaining skin homeostasis and wound healing. Chronic inflammation and increased reactive oxygen species (ROS) production are hallmark features of aging, contributing to impaired wound healing. MicroRNA-146a (miR-146a) has been implicated as a critical regulator of inflammation and oxidative stress in different cell types, yet its role in aged dermal fibroblasts and its potential relevance to wound healing remains poorly understood. We hypothesize that miR-146a is differentially expressed in aged dermal fibroblasts and that overexpression of miR-146a will decrease aging-induced inflammatory responses and ROS production. Primary dermal fibroblasts were isolated from the skin of 17-week-old (young) and 88-week-old (aged) mice. Overexpression of miR-146a was achieved through miR-146a mimic transfection. ROS were detected using a reliable fluorogenic marker, 2,7-dichlorofluorescin diacetate. Real-time PCR was used to quantify relative gene expression. Our investigation revealed a significant reduction in miR-146a expression in aged dermal fibroblasts compared to their younger counterparts. Moreover, aged dermal fibroblasts exhibited heightened levels of inflammatory responses and increased ROS production. Importantly, the overexpression of miR-146a through miR-146a mimic transfection led to a substantial reduction in inflammatory responses through modulation of the NF-kB pathway in aged dermal fibroblasts. Additionally, the overexpression of miR-146a led to a substantial decrease in ROS production, achieved through the downregulation of NOX4 expression in aged dermal fibroblasts. These findings underscore the pivotal role of miR-146a in mitigating both inflammatory responses and ROS production in aged dermal fibroblasts, highlighting its potential as a therapeutic target for addressing age-related skin wound healing.

[An artificial neural network diagnostic model for scleroderma and immune cell infiltration analysis based on mitochondria-associated genes]

OBJECTIVE

To establish a diagnostic model for scleroderma by combining machine learning and artificial neural network based on mitochondria-related genes.

METHODS

The GSE95065 and GSE59785 datasets of scleroderma from GEO database were used for analyzing expressions of mitochondria-related genes, and the differential genes were identified by Random forest, LASSO regression and SVM algorithms. Based on these differential genes, an artificial neural network model was constructed, and its diagnostic accuracy was evaluated by 10-fold crossover verification and ROC curve analysis using the verification dataset GSE76807. The mRNA expressions of the key genes were verified by RT-qPCR in a mouse model of scleroderma. The CIBERSORT algorithm was used to estimate the bioinformatic association between scleroderma and the screened biomarkers.

RESULTS

A total of 24 differential genes were obtained, including 11 up-regulated and 13 down-regulated genes. Seven most relevant mitochondria-related genes (POLB, GSR, KRAS, NT5DC2, NOX4, IGF1, and TGM2) were screened using 3 machine learning algorithms, and the artificial neural network diagnostic model was constructed. The model showed an area under the ROC curves of 0.984 for scleroderma diagnosis (0.740 for the verification dataset and 0.980 for cross-over validation). RT-qPCR detected significant up-regulation of POLB, GSR, KRAS, NOX4, IGF1 and TGM2 mRNAs and significant down-regulation of NT5DC2 in the mouse models of scleroderma. Immune cell infiltration analysis showed that the differential genes in scleroderma were associated with follicular helper T cells, immature B cells, resting dendritic cells, memory activated CD4+T cells, M0 macrophages, monocytes, resting memory CD4+T cells and mast cell activation.

CONCLUSION

The artificial neural network diagnostic model for scleroderma established in this study provides a new perspective for exploring the pathogenesis of scleroderma.

Development and validation of a new diagnostic prediction model of ENHO and NOX4 for early diagnosis of systemic sclerosis

Objective

Systemic sclerosis (SSc) is a chronic autoimmune disease characterized by fibrosis. The challenge of early diagnosis, along with the lack of effective treatments for fibrosis, contribute to poor therapeutic outcomes and high mortality of SSc. Therefore, there is an urgent need to identify suitable biomarkers for early diagnosis of SSc.

Methods

Three skin gene expression datasets of SSc patients and healthy controls were downloaded from Gene Expression Omnibus (GEO) database (GSE130955, GSE58095, and GSE181549). GSE130955 (48 early diffuse cutaneous SSc and 33 controls) were utilized to screen differentially expressed genes (DEGs) between SSc and normal skin samples. Least absolute shrinkage and selection operator (LASSO) regression and support vector machine recursive feature elimination (SVM-RFE) were performed to identify diagnostic genes and construct a diagnostic prediction model. The results were further validated in GSE58095 (61 SSc and 36 controls) and GSE181549 (113 SSc and 44 controls) datasets. Receiver operating characteristic (ROC) curves were applied for assessing the level of diagnostic ability. Reverse transcription-quantitative polymerase chain reaction (RT-qPCR) was used to verify the diagnostic genes in skin tissues of out cohort (10 SSc and 5 controls). Immune infiltration analysis were performed using CIBERSORT algorithm.

Results

A total of 200 DEGs were identified between SSc and normal skin samples. Functional enrichment analysis revealed that these DEGs may be involved in the pathogenesis of SSc, such as extracellular matrix remodeling, cell-cell interactions, and metabolism. Subsequently, two critical genes (ENHO and NOX4) were identified by LASSO and SVM-RFE. ENHO was found down-regulated while NOX4 was up-regulated in skin of SSc patients and their expression levels were validated by above three datasets and our cohort. Notably, these differential expressions were more pronounced in patients with diffuse cutaneous SSc than in those with limited cutaneous SSc. Next, we developed a novel diagnostic model for SSc using ENHO and NOX4, which demonstrated strong predictive power in above three cohorts and in our own cohort. Furthermore, immune infiltration analysis revealed dysregulated levels of various immune cell subtypes within early SSc skin specimens, and a negative correlation was observed between the levels of ENHO and Macrophages M1 and M2, while a positive correlation was observed between the levels of NOX4 and Macrophages M1 and M2.

Conclusion

This study identified ENHO and NOX4 as novel biomarkers that can be serve as a diagnostic prediction model for early detection of SSc and play a potential role in the pathogenesis of the disease.

Preparation of Oxidized and Reduced PTP4A1 for Structural and Functional Studies

The formation of a reversible disulfide bond between the catalytic cysteine and a spatially neighboring cysteine (backdoor) in protein tyrosine phosphatases (PTPs) serves as a critical regulatory mechanism for maintaining the activity of protein tyrosine phosphatases. The failure of such protection results in the formation of irreversibly oxidized cysteines into sulfonic acid in a highly oxidative cellular environment in the presence of free radicals. Hence, it is important to develop methods to interconvert PTPs into reduced and oxidized forms to understand their catalytic function in vitro. Protein tyrosine phosphatase 4A type 1 (PTP4A1), a dual-specificity phosphatase, is catalytically active in the reduced form. Unexpectedly, also its oxidized form performs a key biological function in systemic sclerosis (SSc) by forming a kinase-phosphatase complex with Src kinases. Thus, we developed simple and efficient protocols for producing oxidized and reduced PTP4A1 to elucidate their biological function, which can be extended to study other protein tyrosine phosphatases and other recombinantly produced proteins.

Higher gamma-glutamyl transferase levels are associated with an increased risk of incident systemic sclerosis: a nationwide population-based study

Gamma-glutamyl transferase (GGT) is known to promote oxidative stress. As oxidative stress is a key component in the pathogenesis of systemic sclerosis (SSc), we investigated whether GGT levels are associated with the risk of incident SSc. A cohort of individuals without SSc who underwent national health examination in 2009 were extracted from the Korean National Health Insurance Service database. The incidence rate of SSc during the observation period, between 2009 and 2019, was estimated. GGT levels measured in 2009 were categorized into quartiles (Q1 [lowest], Q2, Q3, and Q4 [highest]). Multivariable Cox proportional hazard models were used to estimate the risk of incident SSc according to the quartiles of GGT, using Q1 as the reference. A total of 6,091,788 individuals were included. Incidence rate of SSc was 1.16 per 100,000 person-years over a mean observation period of 9.2 years. After adjusting for age, sex, body mass index, economic income, smoking status, alcohol consumption, physical activity, hypertension, type 2 diabetes, dyslipidemia, and chronic kidney disease, higher quartiles of GGT levels were significantly associated with a higher risk of incident SSc (Q4: adjusted hazard ratio [aHR] 1.807, 95% confidence interval CI 1.446-2.259; Q3: aHR 1.221, 95% CI 0.971-1.536; and Q2: aHR 1.034, 95% CI 0.807-1.324; p for trend < 0.001). Higher GGT levels were associated with a higher risk of incident SSc. These findings could lead to a closer monitoring for high risk individuals and an earlier diagnosis and treatment.

Oxidative Stress and Epigenetics: miRNA Involvement in Rare Autoimmune Diseases

Autoimmune diseases (ADs) such as Sjögren’s syndrome, Kawasaki disease, and systemic sclerosis are characterized by chronic inflammation, oxidative stress, and autoantibodies, which cause joint tissue damage, vascular injury, fibrosis, and debilitation. Epigenetics participate in immune cell proliferation and differentiation, which regulates the development and function of the immune system, and ultimately interacts with other tissues. Indeed, overlapping of certain clinical features between ADs indicate that numerous immunologic-related mechanisms may directly participate in the onset and progression of these diseases. Despite the increasing number of studies that have attempted to elucidate the relationship between miRNAs and oxidative stress, autoimmune disorders and oxidative stress, and inflammation and miRNAs, an overall picture of the complex regulation of these three actors in the pathogenesis of ADs has yet to be formed. This review aims to shed light from a critical perspective on the key AD-related mechanisms by explaining the intricate regulatory ROS/miRNA/inflammation axis and the phenotypic features of these rare autoimmune diseases. The inflamma-miRs miR-155 and miR-146, and the redox-sensitive miR miR-223 have relevant roles in the inflammatory response and antioxidant system regulation of these diseases. ADs are characterized by clinical heterogeneity, which impedes early diagnosis and effective personalized treatment. Redox-sensitive miRNAs and inflamma-miRs can help improve personalized medicine in these complex and heterogeneous diseases.

Suppression of NADPH oxidase 4 inhibits PM2.5-induced cardiac fibrosis through ROS-P38 MAPK pathway

Fine particulate matter (PM_2.5) has been consistently linked to cardiovascular diseases, and cardiac fibrosis plays a crucial role in the occurrence and development of heart diseases. It is reported that NOX4-dependent redox signaling are responsible for TGFβ-mediated profibrotic responses. The current study was designed to explore the possible mechanisms of cardiac fibrosis by PM_2.5 both in vitro and in vivo. Female C57BL/6 mice received PM_2.5 (3 mg/kg b.w.) exposure with/without NOX4 inhibitor (apocynin, 25 mg/kg b.w.) or ROS scavenger (NALC, 50 mg/kg b.w.), every other day, for 4 weeks. H9C2 cells were incubated with PM_2.5 (3 μg/mL) with/without 5 mM NALC, TGFβ inhibitor (SB431542, 10 μM), or siRNA-NOX4 for 24 h. The results demonstrated that PM_2.5 induced evident collagen deposition and elevated expression of fibrosis biomarkers (Col1a1 & Col3a1). Significant systemic inflammatory response and cardiac oxidative stress were triggered by PM_2.5. PM_2.5 increased the protein expression of TGFβ1, NOX4, and P38 MAPK. Notably, the increased effects of PM_2.5 could be suppressed by SB431542, siRNA-NOX4 in vitro or apocynin in vivo, and NALC. The reverse verification experiments further supported the involvement of the TGFβ/NOX4/ROS/P38 MAPK signaling pathway in the myocardial fibrosis induced by PM_2.5. In summary, the current study provided evidence that PM_2.5 challenge led to cardiac fibrosis through oxidative stress, systemic inflammation, and subsequent TGFβ/NOX4/ROS/P38 MAPK pathway and may offer new therapeutic targets in cardiac fibrosis.

Pyrrosia petiolosa Extract Ameliorates Ethylene Glycol-Induced Urolithiasis in Rats by Inhibiting Oxidative Stress and Inflammatory Response

Objective

To study the therapeutic effect and mechanism of Pyrrosia petiolosa (P. petiolosa) extract on ethylene glycol- (EG-) induced urolithiasis in rats.

Methods

Thirty SD male rats were randomly divided into five groups (n = 6): control group, EG group, and P. petiolosa group (25 mg/kg, 50 mg/kg group, and 100 mg/kg). Biochemical testing was adopted for measuring the blood and urine parameters, as well as the level of superoxide dismutase (SOD), glutathione (GSH), and malondialdehyde acid (MDA) in kidney tissues. HE staining and ELISA were utilized to observe the histopathological changes and detect the level of IL-1β, IL-6, MCP-1, and TNF-α in the kidney tissue, respectively. And western blot was performed for checking NOX2, NOX4, TGF-β1, p-Smad3, Smad3, p-Smad2, and Smad2 protein expression level in kidney tissues.

Results

EG could significantly increase the level of blood urea nitrogen, creatinine, and Na in serum and 24-hour urinary protein, oxalate, uric acid, creatinine, calcium, and phosphorus in urine and decreased the urine volume in rats. Whereas P. petiolosa extract was able to greatly decrease the level of related parameters in serum and urine in a dose-dependent manner, but did not affect the urine pH. In addition, P. petiolosa extract notably ameliorated EG-induced renal tissue injury. Compared with the EG group, P. petiolosa extract markedly raised the level of SOD and GSH and decreased the MDA level and the expression of NOX2 and NOX4 in the kidney tissue. Moreover, P. petiolosa extract also lowered the level of IL-1β, IL-6, MCP-1, and TNF-α in EG-stimulated kidney tissue and inhibited the protein level of EG-induced TGF-β1, p-Smad3, and p-Smad2 in a concentration-dependent manner.

Conclusion

P. petiolosa extract can improve EG-induced urolithiasis in rats by inhibiting oxidative stress, inflammatory response, and the activation of TGF-β pathway.

Oxidative stress promotes fibrosis in systemic sclerosis through stabilization of a kinase-phosphatase complex

Systemic sclerosis (SSc) is a fibrotic autoimmune disease characterized by pathogenic activation of fibroblasts enhanced by local oxidative stress. The tyrosine phosphatase PTP4A1 was identified as a critical promoter of TGF-β signaling in SSc. Oxidative stress is known to functionally inactivate tyrosine phosphatases. Here, we assessed whether oxidation of PTP4A1 modulates its profibrotic action and found that PTP4A1 forms a complex with the kinase SRC in scleroderma fibroblasts, but surprisingly, oxidative stress enhanced rather than reduced PTP4A1’s association with SRC and its profibrotic action. Through structural assessment of the oxo-PTP4A1-SRC complex, we unraveled an unexpected mechanism whereby oxidation of a tyrosine phosphatase promotes its function through modification of its protein complex. Considering the importance of oxidative stress in the pathogenesis of SSc and fibrosis, our findings suggest routes for leveraging PTP4A1 oxidation as a potential strategy for developing antifibrotic agents.

Protective effects of alpha-lipoic acid on bleomycin-induced skin fibrosis through the repression of NADPH Oxidase 4 and TGF-β1/Smad3 signaling pathways

The aim of this study was to determine the protective effects of alpha-lipoic acid (ALA), which is known as a powerful antioxidant, and the possible related molecular mechanisms that mediate its favorable action on skin fibrosis in the bleomycin (BLM)-induced scleroderma (SSc) model in mice. The experimental design was established with four groups of eight mice: Control, ALA (100 mg/kg), BLM (5 μg/kg), and BLM + ALA group. BLM was administered via subcutaneous (sc) once a day while ALA was injected intraperitoneally (ip) twice a week for 21 days. Histopathological and biochemical analyses showed that ALA significantly reduced BLM-induced dermal thickness, inflammation score, and mRNA expression of tumor necrosis factor-alpha (TNF-α) in the skin. Besides, the mRNA expressions of the subunits of NADPH oxidase, which are Nox4 and p22phox, were found to be significantly induced in the BLM group. However, ALA significantly reduced their mRNA expression, which were in parallel to its decreasing effect on serum total oxidant status (TOS) level. Moreover, it was found that ALA downregulated the mRNA expressions of alpha-smooth muscle actin (α-SMA), collagen type I and fibronectin in the skin tissue of the BLM group. Additionally, it was shown that ALA reduced significantly the TGF-β1 and p-Smad3 protein expressions in the BLM + ALA group. On the other hand, ALA did not exhibit any significant effect on the p38 mitogen-activated kinase (MAPK) activation induced by BLM. All these findings point out that ALA may be a promising treatment for the attenuation of skin fibrosis in SSc patients.

Molecular Basis of Accelerated Aging with Immune Dysfunction-Mediated Inflammation (Inflamm-Aging) in Patients with Systemic Sclerosis

Systemic sclerosis (SSc) is a chronic connective tissue disorder characterized by immune dysregulation, chronic inflammation, vascular endothelial cell dysfunction, and progressive tissue fibrosis of the skin and internal organs. Moreover, increased cancer incidence and accelerated aging are also found. The increased cancer incidence is believed to be a result of chromosome instability. Accelerated cellular senescence has been confirmed by the shortening of telomere length due to increased DNA breakage, abnormal DNA repair response, and telomerase deficiency mediated by enhanced oxidative/nitrative stresses. The immune dysfunctions of SSc patients are manifested by excessive production of proinflammatory cytokines IL-1, IL-6, IL-17, IFN-α, and TNF-α, which can elicit potent tissue inflammation followed by tissue fibrosis. Furthermore, a number of autoantibodies including anti-topoisomerase 1 (anti-TOPO-1), anti-centromere (ACA or anti-CENP-B), anti-RNA polymerase enzyme (anti-RNAP III), anti-ribonuclear proteins (anti-U1, U2, and U11/U12 RNP), anti-nucleolar antigens (anti-Th/T0, anti-NOR90, anti-Ku, anti-RuvBL1/2, and anti-PM/Scl), and anti-telomere-associated proteins were also found. Based on these data, inflamm-aging caused by immune dysfunction-mediated inflammation exists in patients with SSc. Hence, increased cellular senescence is elicited by the interactions among excessive oxidative stress, pro-inflammatory cytokines, and autoantibodies. In the present review, we will discuss in detail the molecular basis of chromosome instability, increased oxidative stress, and functional adaptation by deranged immunome, which are related to inflamm-aging in patients with SSc.

Oxidative Stress Induced by Reactive Oxygen Species (ROS) and NADPH Oxidase 4 (NOX4) in the Pathogenesis of the Fibrotic Process in Systemic Sclerosis: A Promising Therapeutic Target

Numerous clinical and research investigations conducted during the last two decades have implicated excessive oxidative stress caused by high levels of reactive oxygen species (ROS) in the development of the severe and frequently progressive fibrotic process in Systemic Sclerosis (SSc). The role of excessive oxidative stress in SSc pathogenesis has been supported by the demonstration of increased levels of numerous biomarkers, indicative of cellular and molecular oxidative damage in serum, plasma, and other biological fluids from SSc patients, and by the demonstration of elevated production of ROS by various cell types involved in the SSc fibrotic process. However, the precise mechanisms mediating oxidative stress development in SSc and its pathogenetic effects have not been fully elucidated. The participation of the NADPH oxidase NOX4, has been suggested and experimentally supported by the demonstration that SSc dermal fibroblasts display constitutively increased NOX4 expression and that reduction or abrogation of NOX4 effects decreased ROS production and the expression of genes encoding fibrotic proteins. Furthermore, NOX4-stimulated ROS production may be involved in the development of certain endothelial and vascular abnormalities and may even participate in the generation of SSc-specific autoantibodies. Collectively, these observations suggest NOX4 as a novel therapeutic target for SSc.

Backstage players of fibrosis: NOX4, mTOR, HDAC, and S1P; companions of TGF-β

The fibrotic process could be easily defined as a pathological excess of extracellular matrix deposition, leading to disruption of tissue architecture and eventually loss of function; however, this process involves a complex network of several signal transduction pathways. Virtually almost all organs could be affected by fibrosis, the most affected are the liver, lung, skin, kidney, heart, and eyes; in all of them, the transforming growth factor-beta (TGF-β) has a central role. The canonical and non-canonical signal pathways of TGF-β impact the fibrotic process at the cellular and molecular levels, inducing the epithelial-mesenchymal transition (EMT) and the induction of profibrotic gene expression with the consequent increase in proteins such as alpha-smooth actin (α-SMA), fibronectin, collagen, and other extracellular matrix proteins. Recently, it has been reported that some molecules that have not been typically associated with the fibrotic process, such as nicotinamide adenine dinucleotide phosphate (NADPH) oxidase 4 (NOX4), mammalian target of rapamycin (mTOR), histone deacetylases (HDAC), and sphingosine-1 phosphate (S1P); are critical in its development. In this review, we describe and discuss the role of these new players of fibrosis and the convergence with TGF-β signaling pathways, unveiling new insights into the panorama of fibrosis that could be useful for future therapeutic targets.

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

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

IL11 is elevated in systemic sclerosis and IL11-dependent ERK signaling underlies TGFβ-mediated activation of dermal fibroblasts

Objectives

Interleukin 11 (IL11) is highly upregulated in skin and lung fibroblasts from patients with systemic sclerosis (SSc). Here we tested whether IL11 is mechanistically linked with activation of human dermal fibroblasts (HDFs) from patients with SSc or controls.

Methods

We measured serum IL11 levels in volunteers and patients with early diffuse SSc and manipulated IL11 signalling in HDFs using gain- and loss-of-function approaches that we combined with molecular and cellular phenotyping.

Results

In patients with SSc, serum IL11 levels are elevated as compared with healthy controls. All transforming growth factor beta (TGFβ) isoforms induced IL11 secretion from HDFs, which highly express IL11 receptor α-subunit and the glycoprotein 130 (gp130) co-receptor, suggestive of an autocrine loop of IL11 activity in HDFs. IL11 stimulated ERK activation in HDFs and resulted in HDF-to-myofibroblast transformation and extracellular matrix secretion. The pro-fibrotic action of IL11 in HDFs appeared unrelated to STAT3 activity, independent of TGFβ upregulation and was not associated with phosphorylation of SMAD2/3. Inhibition of IL11 signalling using either a neutralizing antibody against IL11 or siRNA against IL11RA reduced TGFβ-induced HDF proliferation, matrix production and cell migration, which was phenocopied by pharmacological inhibition of ERK.

Conclusions

These data reveal that autocrine IL11-dependent ERK activity alone or downstream of TGFβ stimulation promotes fibrosis phenotypes in dermal fibroblasts and suggest IL11 as a potential therapeutic target in SSc.

Reactive Oxygen Species and Oxidative Stress in the Pathogenesis and Progression of Genetic Diseases of the Connective Tissue

Connective tissue is known to provide structural and functional “glue” properties to other tissues. It contains cellular and molecular components that are arranged in several dynamic organizations. Connective tissue is the focus of numerous genetic and nongenetic diseases. Genetic diseases of the connective tissue are minority or rare, but no less important than the nongenetic diseases. Here we review the impact of reactive oxygen species (ROS) and oxidative stress on the onset and/or progression of diseases that directly affect connective tissue and have a genetic origin. It is important to consider that ROS and oxidative stress are not synonymous, although they are often closely linked. In a normal range, ROS have a relevant physiological role, whose levels result from a fine balance between ROS producers and ROS scavenge enzymatic systems. However, pathology arises or worsens when such balance is lost, like when ROS production is abnormally and constantly high and/or when ROS scavenge (enzymatic) systems are impaired. These concepts apply to numerous diseases, and connective tissue is no exception. We have organized this review around the two basic structural molecular components of connective tissue: The ground substance and fibers (collagen and elastic fibers).

Brd4-p300 inhibition downregulates Nox4 and accelerates lung fibrosis resolution in aged mice

Tissue regeneration capacity declines with aging in association with heightened oxidative stress. Expression of the oxidant-generating enzyme, NADPH oxidase 4 (Nox4), is elevated in aged mice with diminished capacity for fibrosis resolution. Bromodomain-containing protein 4 (Brd4) is a member of the bromodomain and extraterminal (BET) family of proteins that function as epigenetic "readers" of acetylated lysine groups on histones. In this study, we explored the role of Brd4 and its interaction with the p300 acetyltransferase in the regulation of Nox4 and the in vivo efficacy of a BET inhibitor to reverse established age-associated lung fibrosis. BET inhibition interferes with the association of Brd4, p300, and acetylated histone H4K16 with the Nox4 promoter in lung fibroblasts stimulated with the profibrotic cytokine, TGF-β1. A number of BET inhibitors, including I-BET-762, JQ1, and OTX015, downregulate Nox4 gene expression and activity. Aged mice with established and persistent lung fibrosis recover capacity for fibrosis resolution with OTX015 treatment. This study implicates epigenetic regulation of Nox4 by Brd4 and p300 and supports BET/Brd4 inhibition as an effective strategy for the treatment of age-related fibrotic lung disease.

Increased expression of the transforming growth factor β–inducible gene HIC-5 in systemic sclerosis skin and fibroblasts: a novel antifibrotic therapeutic target

Objective

SSc is a systemic fibrotic disease affecting skin, numerous internal organs and the microvasculature. The molecular pathogenesis of SSc tissue fibrosis has not been fully elucidated, although TGF-β1 plays a crucial role. The Hic-5 protein encoded by the TGF-β1-inducible HIC-5 gene participates in numerous TGF-β-mediated pathways, however, the role of Hic-5 in SSc fibrosis has not been investigated. The aim of this study was to examine HIC-5 involvement in SSc tissue fibrosis.

Methods

Affected skin from three patients with diffuse SSc and dermal fibroblasts cultured from affected and non-affected SSc skin were examined for HIC-5 and COL1A1 gene expression. Real-time PCR, IF microscopy, western blotting and small interfering RNA–mediated HIC-5 were performed.

Results

HIC-5 and COL1A1 transcripts and Hic-5, type 1 collagen (COL1) and α-smooth muscle actin (α-SMA) protein levels were increased in clinically affected SSc skin compared with normal skin and in cultured dermal fibroblasts from affected SSc skin compared with non-affected skin fibroblasts from the same patients. HIC-5 knockdown caused a marked reduction of COL1 production in SSc dermal fibroblasts.

Conclusion

HIC-5 expression is increased in affected SSc skin compared with skin from normal individuals. Affected SSc skin fibroblasts display increased HIC-5 and COL1A1 expression compared with non-affected skin fibroblasts from the same patients. Hic-5 protein was significantly increased in cultured SSc dermal fibroblasts. HIC-5 mRNA knockdown in SSc fibroblasts caused &gt;50% reduction of COL1 production. Although these are preliminary results owing to the small number of skin samples studied, they indicate that Hic-5 plays a role in the profibrotic activation of SSc dermal fibroblasts and may represent a novel molecular target for antifibrotic therapy in SSc.

Activin A-Mediated Regulation of XT-I in Human Skin Fibroblasts

Fibrosis is a fundamental feature of systemic sclerosis (SSc) and is characterized by excessive accumulation of extracellular matrix components like proteoglycans (PG) or collagens in skin and internal organs. Serum analysis from SSc patients showed an increase in the enzyme activity of xylosyltransferase (XT), the initial enzyme in PG biosynthesis. There are two distinct XT isoforms-XT-I and XT-II-in humans, but until now only XT-I is associated with fibrotic remodelling for an unknown reason. The aim of this study was to identify new XT mediators and clarify the underlying mechanisms, in view of developing putative therapeutic anti-fibrotic interventions in the future. Therefore, we used different cytokines and growth factors, small molecule inhibitors as well as small interfering RNAs, and assessed the cellular XT activity and XYLT1 expression in primary human dermal fibroblasts by radiochemical activity assays and qRT-PCR. We identified a new function of activin A as a regulator of XYLT1 mRNA expression and XT activity. While the activin A-induced XT-I increase was found to be mediated by activin A receptor type 1B, MAPK and Smad pathways, the activin A treatment did not alter the XYLT2 expression. Furthermore, we observed a reciprocal regulation of XYLT1 and XYLT2 transcription after inhibition of the activin A pathway components. These results improve the understanding of the differential expression regulation of XYLT isoforms under pathological fibroproliferative conditions.

Emerging targets of disease-modifying therapy for systemic sclerosis

Systemic sclerosis (SSc) has the highest cause-specific mortality of all the connective tissue diseases, and the aetiology of this complex and heterogeneous condition remains an enigma. Current disease-modifying therapies for SSc predominantly target inflammatory and vascular pathways but have variable and unpredictable clinical efficacy, and none is curative. Moreover, many of these therapies possess undesirable safety profiles and have no appreciable effect on long-term mortality. This Review describes the most promising of the existing therapeutic targets for SSc and places them in the context of our evolving understanding of the pathophysiology of this disease. As well as taking an in-depth look at the immune, inflammatory, vascular and fibrotic pathways implicated in the pathogenesis of SSc, this Review discusses emerging treatment targets and therapeutic strategies. The article concludes with an overview of important unanswered questions in SSc research that might inform the design of future studies of treatments aimed at modifying the course of this disease.

Microparticles in systemic sclerosis, targets or tools to control fibrosis: This is the question!

Systemic sclerosis is the main systemic fibrotic disease with unknown etiology characterized by peripheral microvascular injury, activation of immune system, and wide-spread progressive fibrosis. Microparticles can be derived from any cell type during normal cellular differentiation, senescence, and apoptosis, and also upon cellular activation. Carrying along a broad range of surface cytoplasmic and nuclear molecules of originating cells, microparticles are closely implicated in inflammation, thrombosis, angiogenesis, and immunopathogenesis. Recently, microparticles have been proposed as biomarkers of endothelial injury, which is the primary event in the genesis of tissue fibrosis. Microparticles may have a role in fostering endothelial to mesenchymal transition, thus giving a significant contribution to the development of myofibroblasts, the most important final effectors responsible for tissue fibrosis and fibroproliferative vasculopathy. Thanks to potent profibrotic mediators, such as transforming growth factor beta, platelet-derived growth factor, high mobility group box 1 protein, nicotinamide adenine dinucleotide phosphate oxidase 4, and antifibrotic agents, such as matrix metalloproteinases, microparticles may play an opposite role in fibrosis.

TGF-β3 Induces Autophagic Activity by Increasing ROS Generation in a NOX4-Dependent Pathway

Higher concentrations of reactive oxygen species (ROS) have been associated with epithelial cell damage, cell shedding, and airway hyperresponsiveness. Previous studies have indicated that transforming growth factor-beta (TGF-β) mediates ROS production and NADPH oxidase (NOX) activity. In our previous study, we also observed that TGF-β3 increases mucus secretion in airway epithelial cells in an autophagy-dependent fashion. Although it is well known that the relationship between ROS and autophagy is cell context-dependent, the exact mechanism of action remains unclear. The following study examined whether ROS act as upstream of autophagy activation in response to TGF-β3 induction. Using an allergic inflammation mouse model induced by house dust mite (HDM), we observed elevated lung amounts of TGF-β3 accompanied by increased ROS levels. And we found that ROS levels were elevated and NOX4 expression was increased in TGF-β3-induced epithelial cells, while the lack of NOX4 in the epithelial cells could reduce ROS generation and autophagy-dependent MUC5AC expression treated with TGF-β3. Furthermore, our studies demonstrated that the Smad2/3 pathway was involved in TGF-β3-induced ROS generation by promoting NOX4 expression. The inhibition of ROS generation by N-Acetyl-L-cysteine (NAC) resulted in a decrease in mucus expression and autophagy activity in vivo as well as in vitro. Finally, TGF-β3-neutralizing antibody significantly reduced the ROS generation, mucus expression, and autophagy activity and also decreased the phosphorylation of Smad2 and Smad3. Taken together, the obtained results revealed that persistent TGF-β3 activation increased ROS levels in a NOX4-dependent pathway and subsequently induced autophagy as well as MUC5AC expression in the epithelial cells.

Rationally-based therapeutic disease modification in systemic sclerosis: Novel strategies

Systemic sclerosis (SSc) is a highly challenging chronic condition that is dominated by the pathogenetic triad of vascular damage, immune dysregulation/autoimmunity and fibrosis in multiple organs. A hallmark of SSc is the remarkable degree of molecular and phenotypic disease heterogeneity, which surpasses that of other complex rheumatic diseases. Disease trajectories in SSc are unpredictable and variable from patient to patient. Disease-modifying therapies for SSc are lacking, long-term morbidity is considerable and mortality remains unacceptably high. Currently-used empirical approaches to disease modification have modest and variable clinical efficacy and impact on survival, are expensive and frequently associated with unfavorable side effects, and none can be considered curative. However, research during the past several years is yielding significant advances with therapeutic potential. In particular, the application of unbiased omics-based discovery technologies to large and well-characterized SSc patient cohorts, coupled with hypothesis-testing experimental research using a variety of model systems is revealing new insights into SSc that allow formulation of a more nuanced appreciation of disease heterogeneity, and a deepening understanding of pathogenesis. Indeed, we are now presented with numerous novel and rationally-based strategies for targeted SSc therapy, several of which are currently, or expected to be shortly, undergoing clinical evaluation. In this review, we discuss promising novel therapeutic targets and rationally-based approaches to disease modification that have the potential to improve long-term outcomes in SSc.

Tanshinone IIA Activates Nuclear Factor-Erythroid 2-Related Factor 2 to Restrain Pulmonary Fibrosis via Regulation of Redox Homeostasis and Glutaminolysis

AIMS

Pulmonary fibrosis (PF) is characterized by myofibroblast activation through oxidative stress. However, the precise regulation of myofibroblast transdifferentiation remains largely uncharacterized.

RESULTS

In this study, we found that tanshinone IIA (Tan-IIA), an active component in the root of Salvia miltiorrhiza Bunge, can suppress reactive oxygen species (ROS)-mediated activation of myofibroblast and reduce extracellular matrix deposition in bleomycin (BLM)-challenged mice through the regulation of nuclear factor-erythroid 2-related factor 2 (Nrf2). Additionally, Tan-IIA restored redox homeostasis by upregulating Nrf2 with NADPH oxidase 4 suppression and effectively prevented myofibroblast activation by blocking ROS-mediated protein kinase C delta (PKCδ)/Smad3 signaling. Nrf2 knockdown in the fibroblasts and the lungs of BLM-treated mice reduced the inhibitory effects of Tan-IIA, indicating the essential role of Nrf2 in the Tan-IIA activity. Tan-IIA impaired the binding of kelch-like ECH-associated protein 1 (Keap1) to Nrf2 by promoting the degradation of Keap1 and thereby increasing Nrf2 induction by protecting Nrf2 stability against ubiquitination and proteasomal degradation. Importantly, we also found that the glutamate anaplerotic pathway was involved in energy generation and biosynthesis in activated myofibroblasts and their proliferation. Tan-IIA shunted glutaminolysis into glutathione (GSH) production by activating Nrf2, resulting in the reduction of glutamate availability for tricarboxylic acid cycle. Ultimately, myofibroblast activation was prevented by impairing cell proliferation. Innovation and Conclusion: In addition to the regulation of redox homeostasis, our work showed that Tan-IIA activated Nrf2/GSH signaling pathway to limit glutaminolysis in myofibroblast proliferation, which provided further insight into the critical function of Nrf2 in PF.

Endothelial to Mesenchymal Transition: Role in Physiology and in the Pathogenesis of Human Diseases

Numerous studies have demonstrated that endothelial cells are capable of undergoing endothelial to mesenchymal transition (EndMT), a newly recognized type of cellular transdifferentiation. EndMT is a complex biological process in which endothelial cells adopt a mesenchymal phenotype displaying typical mesenchymal cell morphology and functions, including the acquisition of cellular motility and contractile properties. Endothelial cells undergoing EndMT lose the expression of endothelial cell-specific proteins such as CD31/platelet-endothelial cell adhesion molecule, von Willebrand factor, and vascular-endothelial cadherin and initiate the expression of mesenchymal cell-specific genes and the production of their encoded proteins including α-smooth muscle actin, extra domain A fibronectin, N-cadherin, vimentin, fibroblast specific protein-1, also known as S100A4 protein, and fibrillar type I and type III collagens. Transforming growth factor-β1 is considered the main EndMT inducer. However, EndMT involves numerous molecular and signaling pathways that are triggered and modulated by multiple and often redundant mechanisms depending on the specific cellular context and on the physiological or pathological status of the cells. EndMT participates in highly important embryonic development processes, as well as in the pathogenesis of numerous genetically determined and acquired human diseases including malignant, vascular, inflammatory, and fibrotic disorders. Despite intensive investigation, many aspects of EndMT remain to be elucidated. The identification of molecules and regulatory pathways involved in EndMT and the discovery of specific EndMT inhibitors should provide novel therapeutic approaches for various human disorders mediated by EndMT.

Abrogation of transforming growth factor-β-induced tissue fibrosis in mice with a global genetic deletion of Nox4

Excessive connective tissue deposition in skin and various internal organs is characteristic of systemic sclerosis (SSc). The profibrotic growth factor TGF-β plays a crucial role in SSc pathogenesis. The expression of NADPH oxidase 4 (NOX4), a critical mediator of oxidative stress, is potently stimulated by TGF-β. Here, we evaluated the effect of NOX4 on the development of TGF-β-induced tissue fibrosis. C57BL6/J control mice and Nox4 knockout mice were implanted subcutaneously with osmotic pumps containing either saline or 2.5 µg TGF-β1. After 28 days, skin and lung samples were isolated for histopathologic analysis, measurement of hydroxyproline content and gene expression analysis. Histopathology of skin and lungs from normal C57BL6/J mice treated with TGF-β1 showed profound dermal fibrosis and peribronchial and diffuse interstitial lung fibrosis. In contrast, TGF-β-treated Nox4 knockout mice showed normal skin and lung histology. Hydroxyproline levels in TGF-β-treated C57BL6/J mice skin and lungs demonstrated significant increases, however, hydroxyproline content of TGF-β-treated Nox4 knockout mice tissues was not changed. Expression of various profibrotic and fibrosis-associated genes was upregulated in skin and lungs of TGF-β1-treated C57BL6/J mice but was not significantly changed in TGF-β1-treated Nox4 knockout mice. The induction of skin and lung tissue fibrosis by TGF-β1 parenteral administration in mice was abrogated by the genetic deletion of Nox4 confirming that NOX4 is an essential mediator of the profibrotic effects of TGF-β. These results suggest Nox4 inhibition as a potential therapeutic target for SSc and other fibroproliferative disorders.

HLA class II antibodies induce necrotic cell death in human endothelial cells via a lysosomal membrane permeabilization-mediated pathway

Antibody-mediated rejection (AMR) is the major cause of allograft loss after solid organ transplantation. Circulating donor-specific antibodies against human leukocyte antigen (HLA), in particular HLA class II antibodies are critical for the pathogenesis of AMR via interactions with endothelial cells (ECs). To investigate the effects of HLA class II antibody ligation to the graft endothelium, a model of HLA-DR antibody-dependent stimulation was utilized in primary human ECs. Antibody ligation of HLA class II molecules in interferon-γ-treated ECs caused necrotic cell death without complement via a pathway that was independent of apoptosis and necroptosis. HLA-DR-mediated cell death was blocked by specific neutralization of antibody ligation with recombinant HLA class II protein and by lentiviral knockdown of HLA-DR in ECs. Importantly, HLA class II-mediated cytotoxicity was also induced by relevant native allele-specific antibodies from human allosera. Necrosis of ECs in response to HLA-DR ligation was mediated via hyperactivation of lysosomes, lysosomal membrane permeabilization (LMP), and release of cathepsins. Notably, LMP was caused by reorganization of the actin cytoskeleton. This was indicated by the finding that LMP and actin stress fiber formation by HLA-DR antibodies were both downregulated by the actin polymerization inhibitor cytochalasin D and inhibition of Rho GTPases, respectively. Finally, HLA-DR-dependent actin stress fiber formation and LMP led to mitochondrial stress, which was revealed by decreased mitochondrial membrane potential and generation of reactive oxygen species in ECs. Taken together, ligation of HLA class II antibodies to ECs induces necrotic cell death independent of apoptosis and necroptosis via a LMP-mediated pathway. These findings may enable novel therapeutic approaches for the treatment of AMR in solid organ transplantation.

Mammalian NADPH Oxidases

Reactive oxygen species (ROS) are highly reactive oxygen derivatives. Initially, they were considered as metabolic by-products (of mitochondria in particular), which consistently lead to aging and disease. Over the last decades, however, it became increasingly apparent that virtually all eukaryotic cells possess specifically ROS-producing enzymes, namely, NOX NADPH oxidases. In most mammals, there are seven NOX isoforms: three closely related isoforms, NOX1, 2, 3, which are activated by cytoplasmic subunits; NOX4, which appears to be constitutively active; and the EF-hand-containing Ca²⁺-activated isoforms NOX5 and DUOX1 and 2. Loss-of-function mutations in NOX genes can lead to serious human disease. NOX2 deficiency leads to primary immune deficiency, while DUOX2 deficiency presents as congenital hypothyroidism. Nox-deficient mice provide important tools to explore the physiological functions of various NADPH oxidases as a loss of function in Nox2, Nox3, and Duox2 leads to a spontaneous phenotype. The genetic absence of Nox1, Nox4, and Duox1 does not result in an obvious mouse phenotype (the NOX5 gene is absent in rodents and can therefore not be studied using knockout mice). Since the discovery of the NOX family at the turn of the millennium, much progress in understanding the biochemistry and the physiology of NOX has been made; however many questions remain unanswered to date. This chapter is an overview of our present knowledge on mammalian NOX/DUOX enzymes.

Oxidative/nitrative stress in the pathogenesis of systemic sclerosis: are antioxidants beneficial?

Systemic sclerosis (SSc) is a multisystem autoimmune disease: characterised from the clinical side by progressive vasculopathy and fibrosis of the skin and different organs and from the biochemical side by fibroblast deregulation with excessive production of collagen and increased expression of nicotinamide adenine dinucleotide phosphate oxidase 4 (NOX4). The latter contributes to an overproduction of reactive oxygen species that through an autocrine loop maintains NOX4 in a state of activation. Reactive oxygen and nitrogen species are implicated in the origin and perpetuation of several clinical manifestations of SSc having vascular damage in common; attempts to dampen oxidative and nitrative stress through different agents with antioxidant properties have not translated into a sustained clinical benefit. Objective of this narrative review is to describe the origin and clinical implications of oxidative and nitrative stress in SSc, with particular focus on the central role of NOX4 and its interactions, to re-evaluate the antioxidant approaches so far used to limit disease progression, to appraise the complexity of antioxidant treatment and to touch on novel pathways elements of which may represent specific treatment targets in the not so distant future.

NADPH oxidase, oxidative stress and fibrosis in systemic sclerosis

Systemic sclerosis (SSc) is an autoimmune disease characterized by damage of small vessels, immune abnormalities and exaggerated production of extracellular matrix. The etiology of the disease is unknown and the pathogenesis ill defined. However, there is consistent evidence that oxidative stress contributes to the establishment and progression of the disease. This review examines the most relevant research regarding the involvement of free radicals and of nicotinamide adenine dinucleotide phosphate oxidases (NADPH oxidases; NOX) in the pathogenesis of systemic sclerosis.

NADPH Oxidases and Their Roles in Skin Homeostasis and Carcinogenesis

SIGNIFICANCE

Skin protects the body from dehydration, pathogens, and external mutagens. NADPH oxidases are central components for regulating the cellular redox balance. There is increasing evidence indicating that reactive oxygen species (ROS) generated by members of this enzyme family play important roles in the physiology and pathophysiology of the skin. Recent Advances: NADPH oxidases are active producers of ROS such as superoxide and hydrogen peroxide. Different isoforms are found in virtually all tissues. They play pivotal roles in normal cell homeostasis and in the cellular responses to various stressors. In particular, these enzymes are integral parts of redox-sensitive prosurvival and proapoptotic signaling pathways, in which they act both as effectors and as modulators. However, continuous (re)activation of NADPH oxidases can disturb the redox balance of cells, in the worst-case scenario in a permanent manner. Abnormal NADPH oxidase activity has been associated with a wide spectrum of diseases, as well as with aging and carcinogenesis.

CRITICAL ISSUES

Sunlight with its beneficial and deleterious effects induces the activation of NADPH oxidases in the skin. Evidence for the important roles of this enzyme family in skin cancer and skin aging, as well as in many chronic skin diseases, is now emerging.

FUTURE DIRECTIONS

Understanding the precise roles of NADPH oxidases in normal skin homeostasis, in the cellular responses to solar radiation, and during carcinogenesis will pave the way for their validation as therapeutic targets not only for the prevention and treatment of skin cancers but also for many other skin-related disorders. Antioxid. Redox Signal. 28, 1238-1261.

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.

Tread carefully: A functional variant in the human NADPH oxidase 4 (NOX4) is not disease causing

In this study, we report a paediatric patient with a lethal phenotype of respiratory distress, failure to thrive, pancreatic insufficiency, liver dysfunction, hypertrophic cardiomyopathy, bone marrow suppression, humoral and cellular immune deficiency. To identify the genetic basis of this unusual clinical phenotype and potentially make available the option of future prenatal testing, whole exome sequencing (WES) was used followed by functional studies in a bid to confirm pathogenicity. The WES we identified a homozygous novel variant, AK298328; c.9_10insGAG; p.[Glu3dup], in NOX4 in the proband, and parental heterozygosity for the variant (confirmed by Sanger sequencing). NADPH Oxidase 4 NOX4 (OMIM 605261) encodes an enzyme that functions as the catalytic subunit of the NADPH oxidase complex. NOX4 acts as an oxygen sensor, catalysing the reduction of molecular oxygen, mainly to hydrogen peroxide (H₂O₂). However, although, our functional data including 60% reduction in NOX4 protein levels and a 75% reduction in the production of H₂O₂ in patient fibroblast extracts compared to controls was initially considered to be the likely cause of the phenotype in our patient, the potential contribution of the NOX4 variant as the primary cause of the disease was clearly excluded based on following pieces of evidence. First, Sanger sequencing of other family members revealed that two of the grandparents were also homozygous for the NOX4 variant, one of who has fibromuscular dysplasia. Second, re-evaluation of more recent variant databases revealed a high allele frequency for this variant. Our case highlights the need to re-interrogate bioinformatics resources as they are constantly evolving, and is reminiscent of the short-chain acyl-CoA dehydrogenase deficiency (SCADD) story, where a functional defect in fatty acid oxidation has doubtful clinical ramifications.

Targeting of NADPH oxidase in vitro and in vivo suppresses fibroblast activation and experimental skin fibrosis

Although there is increasing evidence that oxidative stress is involved in collagen synthesis and myofibroblast activation, the NADPH oxidase (Nox) system is incompletely investigated in the context of human dermal fibroblasts (HDFs) and skin fibrosis. Using the pan-Nox inhibitor diphenyleneiodonium (DPI) as an initial tool, we show that gene expression of collagen type I, α-smooth muscle actin (α-SMA) and fibronectin 1 is suppressed in HDFs. Detailed expression analysis of all Nox isoforms and adaptors revealed expression of RNA and protein expression of Nox4, p22^phox and Poldip2 but neither Nox1 nor Nox2. Nox4 could be immunolocalized to the endoplasmic reticulum. Importantly, TGF-β₁ had a dose- and time-dependent upregulating effect on NADH activity and Nox4 gene expression in HDFs. Genetic silencing of Nox4 as demonstrated by siRNA in HDFs as well as in murine fibroblasts established from Nox4 knockout mice confirmed that TGF-β₁ -mediated collagen type I gene, α-SMA and fibronectin 1 gene expressions were Nox4-dependent. This TGF-β₁ effect was mediated by Smad3 as shown by in silico promoter analysis, pharmacological inhibition and gene silencing of Smad3. The relevance of these findings is highlighted in the bleomycin-induced scleroderma mouse model. DPI treatment attenuated skin fibrosis and myofibroblast activation. Moreover, Nox4 knockdown by siRNA reduced skin collagen synthesis, α-SMA and fibronectin 1 expression in vivo. Finally, analyses of HDFs from patients with systemic sclerosis confirmed the expression of Nox4 and its adaptors, whereas Nox1 and Nox2 were not detectable. Our findings indicate that Nox4 targeting is a promising future treatment for fibrotic skin diseases.

Therapeutic potential of NADPH oxidase 1/4 inhibitors

The NADPH oxidase (NOX) family of enzymes produces ROS as their sole function and is becoming recognized as key modulators of signal transduction pathways with a physiological role under acute stress and a pathological role after excessive activation under chronic stress. The seven isoforms differ in their regulation, tissue and subcellular localization and ROS products. The most studied are NOX1, 2 and 4. Genetic deletion of NOX1 and 4, in contrast to NOX2, has revealed no significant spontaneous pathologies and a pathogenic relevance of both NOX1 and 4 across multiple organs in a wide range of diseases and in particular inflammatory and fibrotic diseases. This has stimulated interest in NOX inhibitors for therapeutic application. GKT136901 and GKT137831 are two structurally related compounds demonstrating a preferential inhibition of NOX1 and 4 that have suitable properties for in vivo studies and have consequently been evaluated across a range of disease models and compared with gene deletion. In contrast to gene deletion, these inhibitors do not completely suppress ROS production, maintaining some basal level of ROS. Despite this and consistent with most gene deletion studies, these inhibitors are well tolerated and slow or prevent disease progression in a range of models of chronic inflammatory and fibrotic diseases by modulating common signal transduction pathways. Clinical trials in patients with GKT137831 have demonstrated excellent tolerability and reduction of various markers of chronic inflammation. NOX1/4 inhibition may provide a safe and effective therapeutic strategy for a range of inflammatory and fibrotic diseases.

LINKED ARTICLES

This article is part of a themed section on Redox Biology and Oxidative Stress in Health and Disease. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.12/issuetoc.

Human Fibrotic Diseases: Current Challenges in Fibrosis Research

Human fibrotic diseases constitute a major health problem worldwide owing to the large number of affected individuals, the incomplete knowledge of the fibrotic process pathogenesis, the marked heterogeneity in their etiology and clinical manifestations, the absence of appropriate and fully validated biomarkers, and, most importantly, the current void of effective disease-modifying therapeutic agents. The fibrotic disorders encompass a wide spectrum of clinical entities including systemic fibrotic diseases such as systemic sclerosis (SSc), sclerodermatous graft vs. host disease, and nephrogenic systemic fibrosis, as well as numerous organ-specific disorders including radiation-induced fibrosis and cardiac, pulmonary, liver, and kidney fibrosis. Although their causative mechanisms are quite diverse and in several instances have remained elusive, these diseases share the common feature of an uncontrolled and progressive accumulation of fibrotic tissue in affected organs causing their dysfunction and ultimate failure. Despite the remarkable heterogeneity in the etiologic mechanisms responsible for the development of fibrotic diseases and in their clinical manifestations, numerous studies have identified activated myofibroblasts as the common cellular element ultimately responsible for the replacement of normal tissues with nonfunctional fibrotic tissue. Critical signaling cascades, initiated primarily by transforming growth factor-β (TGF-β), but also involving numerous cytokines and signaling molecules which stimulate profibrotic reactions in myofibroblasts, offer potential therapeutic targets. Here, we briefly review the current knowledge of the molecular mechanisms involved in the development of tissue fibrosis and point out some of the most important challenges to research in the fibrotic diseases and to the development of effective therapeutic approaches for this often fatal group of disorders. Efforts to further clarify the complex pathogenetic mechanisms of the fibrotic process should be encouraged to attain the elusive goal of developing effective therapies for these serious, untreatable, and often fatal disorders.

Proteomic Investigation of Dermal Fibroblasts Isolated from Affected and Unaffected Skin Samples from Patients with Limited Cutaneous Systemic Sclerosis: 2 Distinct Entities?

Objective.

To identify using proteomic analysis the proteins of altered abundance in the affected and unaffected limited cutaneous systemic sclerosis (lcSSc) skin fibroblasts.

Methods.

Excision biopsies (3 mm) were obtained from the affected and unaffected skin of 5 patients with lcSSc. Dermal fibroblasts were isolated enzymatically. Two-dimensional gel electrophoresis was used to separate and define proteins in affected and unaffected fibroblast lysates. Proteins of altered abundance were identified by mass spectrometry. Differences among skin samples were confirmed also by immunohistochemistry (IHC) and by quantitative real-time PCR (qRT-PCR) for type I collagen (Col-1) and vimentin (VIM).

Results.

Proteomic analysis revealed different expressions of proteins involved in cytoskeleton organization (27%), extracellular matrix remodeling (11%), response to oxidative stress (22%), energy metabolism (19%), protein metabolism (5%), cellular homeostasis (5%), signal transduction (3%), and protein transcription, synthesis, and turnover (8%). IHC analysis showed that SSc-affected epidermis is thickened and the dermis is strongly reactive to Col-1 and VIM (typical markers of activated myofibroblasts) compared to SSc-unaffected skin, whose stainings are comparable to those of control healthy skin. Overexpression of Col-1 and VIM mRNA levels in affected lcSSc fibroblasts compared to unaffected lcSSc ones was confirmed by qRT-PCR.

Conclusion.

Consistent with previous studies, these findings are important for 2 reasons: first, because they reveal the opposite behavior of dermal fibroblasts in the unaffected and affected skin areas of the same patient with lcSSc; second, because they demonstrate the histological/histochemical similarities between unaffected skin from patients with lcSSc and healthy control skin.

Endothelial to Mesenchymal Transition (EndoMT) in the Pathogenesis of Human Fibrotic Diseases

Fibrotic diseases encompass a wide spectrum of clinical entities including systemic fibrotic diseases such as systemic sclerosis, sclerodermatous graft versus host disease, nephrogenic systemic fibrosis, and IgG₄-associated sclerosing disease, as well as numerous organ-specific disorders including radiation-induced fibrosis, and cardiac, pulmonary, liver, and kidney fibrosis. Although their causative mechanisms are quite diverse, these diseases share the common feature of an uncontrolled and progressive accumulation of fibrous tissue macromolecules in affected organs leading to their dysfunction and ultimate failure. The pathogenesis of fibrotic diseases is complex and despite extensive investigation has remained elusive. Numerous studies have identified myofibroblasts as the cells responsible for the establishment and progression of the fibrotic process. Tissue myofibroblasts in fibrotic diseases originate from several sources including quiescent tissue fibroblasts, circulating CD34+ fibrocytes, and the phenotypic conversion of various cell types including epithelial and endothelial cells into activated myofibroblasts. However, the role of the phenotypic transition of endothelial cells into mesenchymal cells (Endothelial to Mesenchymal Transition or EndoMT) in the pathogenesis of fibrotic disorders has not been fully elucidated. Here, we review the evidence supporting EndoMT's contribution to human fibrotic disease pathogenesis.

Treatment of Rapidly Progressive Systemic Sclerosis: Current and Futures Perspectives

INTRODUCTION

Systemic Sclerosis (SSc) is a systemic autoimmune disease characterized by severe and often progressive cutaneous, pulmonary, cardiac and gastrointestinal tract fibrosis, cellular and humoral immunologic alterations, and pronounced fibroproliferative vasculopathy. There is no effective SSc disease modifying therapy. Patients with rapidly progressive SSc have poor prognosis with frequent disability and very high mortality.

AREAS COVERED

This paper reviews currently available therapeutic approaches for rapidly progressive SSc and discuss novel drugs under study for SSc disease modification.

EXPERT OPINION

The extent, severity, and rate of progression of SSc skin and internal organ involvement determines the optimal therapeutic interventions for SSc. Cyclophosphamide for progressive SSc-associated interstitial lung disease and mycophenolate for rapidly progressive cutaneous involvement have shown effectiveness. Methotrexate has been used for less severe skin progression and for patients unable to tolerate mycophenolate. Rituximab was shown to induce improvement in SSc-cutaneous and lung involvement. Autologous bone marrow transplantation is reserved for selected cases in whom poor survival risk outweighs the high mortality rate of the procedure. Novel agents capable of modulating fibrotic and inflammatory pathways involved in SSc pathogenesis, including tocilizumab, pirfenidone, tyrosine kinase inhibitors, lipid lysophosphatidic acid 1, and NOX4 inhibitors are currently under development for the treatment of rapidly progressive SSc.