Autocrine transforming growth factor β signaling regulates extracellular signal-regulated kinase 1/2 phosphorylation via modulation of protein phosphatase 2A expression in scleroderma fibroblasts

Biomarker analysis from the phase 2b randomized placebo-controlled trial of riociguat in early diffuse cutaneous systemic sclerosis

OBJECTIVE

To examine disease and target engagement biomarkers in the RISE-SSc trial of riociguat in early diffuse cutaneous systemic sclerosis and their potential to predict the response to treatment.

METHODS

Patients were randomized to riociguat (n = 60) or placebo (n = 61) for 52 weeks. Skin biopsies and plasma/serum samples were obtained at baseline and week 14. Plasma cyclic guanosine monophosphate (cGMP) was assessed using radio-immunoassay. α-Smooth muscle actin (αSMA) and skin thickness were determined by immunohistochemistry, mRNA markers of fibrosis by qRT-PCR in skin biopsies, and serum CXC motif chemokine ligand 4 (CXCL-4) and soluble platelet endothelial cell adhesion molecule-1 (sPECAM-1) by enzyme-linked immunosorbent assay.

RESULTS

By week 14, cGMP increased by 94 (78)% with riociguat and 10 (39)% with placebo (P < 0.001, riociguat vs placebo). Serum sPECAM-1 and CXCL-4 decreased with riociguat vs placebo (P = 0.004 and P = 0.008, respectively). There were no differences in skin collagen markers between the two groups. Higher baseline serum sPECAM-1 or the detection of αSMA-positive cells in baseline skin biopsies was associated with a larger reduction of modified Rodnan skin score from baseline at week 52 with riociguat vs placebo (interaction P-values 0.004 and 0.02, respectively).

CONCLUSION

Plasma cGMP increased with riociguat, suggesting engagement with the nitric oxide-soluble guanylate cyclase-cGMP pathway. Riociguat was associated with a significant reduction in sPECAM-1 (an angiogenic biomarker) vs placebo. Elevated sPECAM-1 and the presence of αSMA-positive skin cells may help to identify patients who could benefit from riociguat in terms of skin fibrosis.

TRIAL REGISTRATION

Clinicaltrials.gov, NCT02283762.

The involvement of the Wnt/β-catenin signaling cascade in fibrosis progression and its therapeutic targeting by relaxin

Organ scarring, referred to as fibrosis, results from a failed wound-healing response to chronic tissue injury and is characterised by the aberrant accumulation of various extracellular matrix (ECM) components. Once established, fibrosis is recognised as a hallmark of stiffened and dysfunctional tissues, hence, various fibrosis-related diseases collectively contribute to high morbidity and mortality in developed countries. Despite this, these diseases are ineffectively treated by currently-available medications. The pro-fibrotic cytokine, transforming growth factor (TGF)-β1, has emerged as the master regulator of fibrosis progression, owing to its ability to promote various factors and processes that facilitate rapid ECM synthesis and deposition, whilst negating ECM degradation. TGF-β1 signal transduction is tightly controlled by canonical (Smad-dependent) and non-canonical (MAP kinase- and Rho-associated protein kinase-dependent) intracellular protein activity, whereas its pro-fibrotic actions can also be facilitated by the Wnt/β-catenin pathway. This review outlines the pathological sequence of events and contributing roles of TGF-β1 in the progression of fibrosis, and how the Wnt/β-catenin pathway contributes to tissue repair in acute disease settings, but to fibrosis and related tissue dysfunction in synergy with TGF-β1 in chronic diseases. It also outlines the anti-fibrotic and related signal transduction mechanisms of the hormone, relaxin, that are mediated via its negative modulation of TGF-β1 and Wnt/β-catenin signaling, but through the promotion of Wnt/β-catenin activity in acute disease settings. Collectively, this highlights that the crosstalk between TGF-β1 signal transduction and the Wnt/β-catenin cascade may provide a therapeutic target that can be exploited to broadly treat and reverse established fibrosis.

The Role of Autophagy and Apoptosis in Affected Skin and Lungs in Patients with Systemic Sclerosis

Systemic sclerosis (SSc) is a complex autoimmune inflammatory disorder with multiple organ involvement. Skin changes present the hallmark of SSc and coincide with poor prognosis. Interstitial lung diseases (ILD) are the most widely reported complications in SSc patients and the primary cause of death. It has been proposed that the processes of autophagy and apoptosis could play a significant role in the pathogenesis and clinical course of different autoimmune diseases, and accordingly in SSc. In this manuscript, we review the current knowledge of autophagy and apoptosis processes in the skin and lungs of patients with SSc. Profiling of markers involved in these processes in skin cells can be useful to recognize the stage of fibrosis and can be used in the clinical stratification of patients. Furthermore, the knowledge of the molecular mechanisms underlying these processes enables the repurposing of already known drugs and the development of new biological therapeutics that aim to reverse fibrosis by promoting apoptosis and regulate autophagy in personalized treatment approach. In SSc-ILD patients, the molecular signature of the lung tissues of each patient could be a distinctive criterion in order to establish the correct lung pattern, which directly impacts the course and prognosis of the disease. In this case, resolving the role of tissue-specific markers, which could be detected in the circulation using sensitive molecular methods, would be an important step toward development of non-invasive diagnostic procedures that enable early and precise diagnosis and preventing the high mortality of this rare disease.

Tonic repression of Collagen I by the Bradykinin receptor 2 in skin fibroblasts

Imbalance of collagen I expression results in severe pathologies. Apart from activation by the TGFβ-receptor/Smad pathway, control of collagen I expression remains poorly understood. Here, we used human dermal fibroblasts expressing a mCherry fluorescent protein driven by endogenous COL1A1 promoter to functionally screen the kinome and phosphatome. We identify 8 negative regulators, revealing that collagen is under tonic repression. The cell surface receptor BDKRB2 represses collagen I and other pro-fibrotic genes. Interestingly, it also promotes other basal membrane ECM genes. This function is independent of the natural ligand, bradykinin, and of SMAD2/3 factors, instead requiring constant ERK1/2 repression. TGFβ stimulation induces rapid BDKRB2 transcriptional downregulation. Human fibrotic fibroblasts have reduced BDKRB2 levels and enhancing its expression in keloid fibroblasts represses COL1A1. We propose that tonic signalling by BDKRB2 prevents collagen overproduction in skin fibroblasts.

Swimming training modulates lung injury induced by ovariectomy in diabetic rats: involvement of inflammatory and fibrotic biomarkers

CONTEXT

Previous studies have noted that the incidence of inflammatory and fibrotic diseases is higher in diabetic menopausal women.

OBJECTIVE

In the present study, we evaluated effects of swimming training on inflammatory and fibrotic biomarkers in the lung of ovariectomized diabetic rats.

MATERIALS AND METHODS

Forty female rats were assigned into four groups: sham; rats underwent surgery without ovariectomies, OVX: rats that underwent ovariectomies, OVX.Dia: ovariectomized rats with high-fat diet, OVX.Dia. Exe: ovariectomized diabetic rats with 8 weeks of swimming training. At the end of experiment, protein expressions were assessed with western blot. Lung sections were subjected to immunohistochemical and haematoxylin eosin staining.

RESULTS

There was a significant difference in the protein expressions between exercise and ovariectomized diabetic groups (p < .05).

CONCLUSION

The present study showed strong potential of swimming training on oestrogen deficient diabetic lung. These data encourage further investigation into the inclusive effects of exercise in menopausal diabetic women.

Myofibroblasts: Function, Formation, and Scope of Molecular Therapies for Skin Fibrosis

Myofibroblasts are contractile, α-smooth muscle actin-positive cells with multiple roles in pathophysiological processes. Myofibroblasts mediate wound contractions, but their persistent presence in tissues is central to driving fibrosis, making them attractive cell targets for the development of therapeutic treatments. However, due to shared cellular markers with several other phenotypes, the specific targeting of myofibroblasts has long presented a scientific and clinical challenge. In recent years, myofibroblasts have drawn much attention among scientific research communities from multiple disciplines and specialisations. As further research uncovers the characterisations of myofibroblast formation, function, and regulation, the realisation of novel interventional routes for myofibroblasts within pathologies has emerged. The research community is approaching the means to finally target these cells, to prevent fibrosis, accelerate scarless wound healing, and attenuate associated disease-processes in clinical settings. This comprehensive review article describes the myofibroblast cell phenotype, their origins, and their diverse physiological and pathological functionality. Special attention has been given to mechanisms and molecular pathways governing myofibroblast differentiation, and updates in molecular interventions.

Kelch-like protein 42 is a profibrotic ubiquitin E3 ligase involved in systemic sclerosis

Systemic scleroderma (SSc) is an autoimmune disease that affects over 2.5 million people globally. SSc results in dysfunctional connective tissues with excessive profibrotic signaling, affecting skin, cardiovascular, and particularly lung tissue. Over three-quarters of individuals with SSc develop pulmonary fibrosis within 5 years, the main cause of SSc mortality. No approved medicines to manage lung SSc currently exist. Recent research suggests that profibrotic signaling by transforming growth factor β (TGF-β) is directly tied to SSc. Previous studies have also shown that ubiquitin E3 ligases potently control TGF-β signaling through targeted degradation of key regulatory proteins; however, the roles of these ligases in SSc-TGF-β signaling remain unclear. Here we utilized primary SSc patient lung cells for high-throughput screening of TGF-β signaling via high-content imaging of nuclear translocation of the profibrotic transcription factor SMAD family member 2/3 (SMAD2/3). We screened an RNAi library targeting ubiquitin E3 ligases and observed that knockdown of the E3 ligase Kelch-like protein 42 (KLHL42) impairs TGF-β-dependent profibrotic signaling. KLHL42 knockdown reduced fibrotic tissue production and decreased TGF-β-mediated SMAD activation. Using unbiased ubiquitin proteomics, we identified phosphatase 2 regulatory subunit B'ϵ (PPP2R5ϵ) as a KLHL42 substrate. Mechanistic experiments validated ubiquitin-mediated control of PPP2R5ϵ stability through KLHL42. PPP2R5ϵ knockdown exacerbated TGF-β-mediated profibrotic signaling, indicating a role of PPP2R5ϵ in SSc. Our findings indicate that the KLHL42-PPP2R5ϵ axis controls profibrotic signaling in SSc lung fibroblasts. We propose that future studies could investigate whether chemical inhibition of KLHL42 may ameliorate profibrotic signaling in SSc.

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.

Protein kinases G are essential downstream mediators of the antifibrotic effects of sGC stimulators

OBJECTIVES

Stimulators of soluble guanylate cyclase (sGC) are currently investigated in clinical trials for the treatment of fibrosis in systemic sclerosis (SSc). In this study, we aim to investigate the role of protein kinases G (PKG) as downstream mediators of sGC-cyclic guanosine monophosphate (cGMP) in SSc.

METHODS

Mice with combined knockout of PKG1 and 2 were challenged with bleomycin and treated with the sGC stimulator BAY 41-2272. Fibroblasts were treated with BAY 41-2272 and with the PKG inhibitor KT 5823.

RESULTS

PKG1 and 2 are upregulated in SSc in a transforming growth factor-β1 (TGFβ1)-dependent manner, as an attempt to compensate for the decreased signalling through the sGC-cGMP-PKG pathway. Inhibition or knockout of PKG1 and 2 abrogates the inhibitory effects of sGC stimulation on fibroblast activation in a SMAD-independent, but extracellular signal-regulated kinase (ERK)-dependent manner. In vivo, sGC stimulation fails to prevent bleomycin-induced fibrosis in PKG1 and 2 knockout mice.

CONCLUSIONS

Our data provide evidence that PKGs are essential mediators of the antifibrotic effects of sGC stimulators through interfering with non-canonical TGFβ signalling. TGFβ1 promotes its profibrotic effects through inhibition of sGC-cGMP-PKG signalling, sGC stimulation exerts its antifibrotic effects by inhibition of TGFβ1-induced ERK phosphorylation.

Scar management in burn injuries using drug delivery and molecular signaling: Current treatments and future directions

In recent decades, there have been tremendous improvements in burn care that have allowed patients to survive severe burn injuries that were once fatal. However, a major limitation of burn care currently is the development of hypertrophic scars in approximately 70% of patients. This significantly decreases the quality of life for patients due to the physical and psychosocial symptoms associated with scarring. Current approaches to manage scarring include surgical techniques and non-surgical methods such as laser therapy, steroid injections, and compression therapy. These treatments are limited in their effectiveness and regularly fail to manage symptoms. As a result, the development of novel treatments that aim to improve outcomes and quality of life is imperative. Drug delivery that targets the molecular cascades of wound healing to attenuate or prevent hypertrophic scarring is a promising approach that has therapeutic potential. In this review, we discuss current treatments for scar management after burn injury, and how drug delivery targeting molecular signaling can lead to new therapeutic strategies.

Inflammatory stimuli promote growth and invasion of pancreatic cancer cells through NF-κB pathway dependent repression of PP2Ac

Previous studies have indicated that inflammatory stimulation represses protein phosphatase 2A (PP2A), a well-known tumor suppressor. However, whether PP2A repression participates in pancreatic cancer progression has not been verified. We used lipopolysaccharide (LPS) and macrophage-conditioned medium (MCM) to establish in vitro inflammation models, and investigated whether inflammatory stimuli affect pancreatic cancer cell growth and invasion PP2A catalytic subunit (PP2Ac)-dependently. Via nude mouse models of orthotopic tumor xenografts and dibutyltin dichloride (DBTC)-induced chronic pancreatitis, we evaluated the effect of an inflammatory microenvironment on PP2Ac expression in vivo. We cloned the PP2Acα and PP2Acβ isoform promoters to investigate the PP2Ac transcriptional regulation mechanisms. MCM accelerated pancreatic cancer cell growth; MCM and LPS promoted cell invasion. DBTC promoted xenograft growth and metastasis, induced tumor-associated macrophage infiltration, promoted angiogenesis, activated the nuclear factor-κB (NF-κB) pathway, and repressed PP2Ac expression. In vitro, LPS and MCM downregulated PP2Ac mRNA and protein. PP2Acα overexpression attenuated JNK, ERK, PKC, and IKK phosphorylation, and impaired LPS/MCM-stimulated cell invasion and MCM-promoted cell growth. LPS and MCM activated the NF-κB pathway in vitro. LPS and MCM induced IKK and IκB phosphorylation, leading to p65/RelA nuclear translocation and transcriptional activation. Overexpression of the dominant negative forms of IKKα attenuated LPS and MCM downregulation of PP2Ac, suggesting inflammatory stimuli repress PP2Ac expression NF-κB pathway-dependently. Luciferase reporter gene assay verified that LPS and MCM downregulated PP2Ac transcription through an NF-κB-dependent pathway. Our study presents a new mechanism in inflammation-driven cancer progression through NF-κB pathway-dependent PP2Ac repression.

Blocking protein phosphatase 2A signaling prevents endothelial-to-mesenchymal transition and renal fibrosis: a peptide-based drug therapy

Endothelial-to-mesenchymal transition (EndMT) contributes to the emergence of fibroblasts and plays a significant role in renal interstitial fibrosis. Protein phosphatase 2A (PP2A) is a major serine/threonine protein phosphatase in eukaryotic cells and regulates many signaling pathways. However, the significance of PP2A in EndMT is poorly understood. In present study, the role of PP2A in EndMT was evaluated. We demonstrated that PP2A activated in endothelial cells (EC) during their EndMT phenotype acquisition and in the mouse model of obstructive nephropathy (i.e., UUO). Inhibition of PP2A activity by its specific inhibitor prevented EC undergoing EndMT. Importantly, PP2A activation was dependent on tyrosine nitration at 127 in the catalytic subunit of PP2A (PP2Ac). Our renal-protective strategy was to block tyrosine127 nitration to inhibit PP2A activation by using a mimic peptide derived from PP2Ac conjugating a cell penetrating peptide (CPP: TAT), termed TAT-Y127WT. Pretreatment withTAT-Y127WT was able to prevent TGF-β1-induced EndMT. Administration of the peptide to UUO mice significantly ameliorated renal EndMT level, with preserved density of peritubular capillaries and reduction in extracellular matrix deposition. Taken together, these results suggest that inhibiting PP2Ac nitration using a mimic peptide is a potential preventive strategy for EndMT in renal fibrosis.

Depletion of folate receptor β-expressing macrophages alleviates bleomycin-induced experimental skin fibrosis

OBJECTIVES

Folate receptor β (FRβ)-expressing macrophages have been identified as activated macrophages. Here, we investigated the infiltration of FRβ-expressing macrophages in a murine model of bleomycin (BLM)-induced skin fibrosis and assessed the antifibrotic effects of depletion of FRβ-expressing macrophages in this model using a recombinant immunotoxin to FRβ.

METHODS

A recombinant immunotoxin (anti-FRβ-PE38) was prepared by conjugating the Fv portion of the anti-mouse FRβ heavy chain with truncated Pseudomonas exotoxin A (VH-PE38) and the Fv portion of the anti-mouse FRβ light chain. BLM-induced skin fibrosis mice were intravenously treated with either anti-FRβ-PE38 or VH-PE38 as a control protein. Skin fibrosis was evaluated by the change of skin thickness and hydroxyproline content on Day 29. The TGFβ1 mRNA levels in the treated skin were assessed by quantitative real-time RT-PCR on Day 9.

RESULTS

Numbers of FRβ-expressing macrophages increased in BLM-injected skin. Anti-FRβ-PE38 treatment led to a dramatic reduction in the number of FRβ-expressing macrophages. Additionally, skin thickness and hydroxyproline content, were markedly reduced. TGFβ1 mRNA levels were also down-regulated after the treatment. TGFβ1 expression was enriched in FRβ-expressing macrophages compared with FRβ-negative macrophages.

CONCLUSION

These results indicated that anti-FRβ-PE38 treatment efficiently depleted FRβ-expressing macrophages and consequently alleviated BLM-induced skin fibrosis.

Mysteries of TGF-β Paradox in Benign and Malignant Cells

TGF-β regulates a wide range of biological functions including embryonic development, wound healing, organogenesis, immune modulation, and cancer progression. Interestingly, TGF-β is known to inhibit cell growth in benign cells but promote progression in cancer cells; this phenomenon is known as TGF-β paradox. To date, the mechanism of this paradox still remains a scientific mystery. In this review, we present our experience, along with the literature, in an attempt to answer this mystery. First, we observed that, on TGF-β engagement, there is a differential activation of Erk between benign and cancer cells. Since activated Erk is a major mediator in tumor progression and metastasis, a differentially activated Erk represents the answer to this mystery. Second, we identified a key player, PP2A-B56α, which is differentially recruited by the activated type I TGF-β receptor (TBRI) in benign and tumor cells, resulting in differential Erk activation. Finally, TGF-β stimulation leads to suppressed TBRs in tumor cells but not in benign cells. This differentially suppressed TBRs triggers differential recruitment of PP2A-B56α and, thus, differential activation of Erk. The above three events explain the mysteries of TGF-β paradox. Understanding the mechanism of TGF-β paradox will help us to predict indolent from aggressive cancers and develop novel anti-cancer strategies.

Acid sphingomyelinase deficiency contributes to resistance of scleroderma fibroblasts to Fas-mediated apoptosis

BACKGROUND

Scleroderma (SSc) is characterized by excess production and deposition of extracellular matrix (ECM) proteins. Activated fibroblasts play a key role in fibrosis in SSc and are resistant to Fas-mediated apoptosis. Acid sphingomyelinase (ASMase), a major sphingolipid enzyme, plays an important role in the Fas-mediated apoptosis.

OBJECTIVE

We investigated whether dysregulation of ASMase contributes to Fas-mediated apoptosis resistance in SSc fibroblasts.

METHODS

Fibroblasts were isolated from SSc patients and healthy controls. Western blot was performed to analyze protein levels and quantitative real time RT-PCR was used to determine mRNA expression. Cells were transiently transfected with siRNA oligos against ASMase or transduced with adenoviruses overexpressing ASMase. Apoptosis was induced using anti-Fas antibody (1 μg/mL) and analyzed using caspase-3 antibody or Cell Death Detection ELISA.

RESULTS

SSc fibroblasts showed increased resistance to Fas-mediated apoptosis. ASMase expression was decreased in SSc fibroblasts and Transforming Growth Factor beta (TGFβ), the major fibrogenic cytokine involved in the pathogenesis of SSc, downregulated ASMase in normal fibroblasts. Forced expression of ASMase in SSc fibroblasts restored sensitivity of these cells to Fas-mediated apoptosis while blockade of ASMase was sufficient to induce partial resistance to Fas-induced apoptosis in normal fibroblasts. In addition, ASMase blockade decreased activity of protein phosphatase 2A (PP2A) through phosphorylation on Tyr(307) and resulted in activation of extracellular regulated kinase 1/2 (Erk1/2) and protein kinase B (Akt/PKB).

CONCLUSION

In conclusion, this study suggests that ASMase deficiency promotes apoptosis resistance and contributes to activation of profibrotic signaling in SSc fibroblasts.

Chitinase 1 is a biomarker for and therapeutic target in scleroderma-associated interstitial lung disease that augments TGF-β1 signaling

Interstitial lung disease (ILD) with pulmonary fibrosis is an important manifestation in systemic sclerosis (SSc, scleroderma) where it portends a poor prognosis. However, biomarkers that predict the development and or severity of SSc-ILD have not been validated, and the pathogenetic mechanisms that engender this pulmonary response are poorly understood. In this study, we demonstrate in two different patient cohorts that the levels of chitotriosidase (Chit1) bioactivity and protein are significantly increased in the circulation and lungs of SSc patients compared with demographically matched controls. We also demonstrate that, compared with patients without lung involvement, patients with ILD show high levels of circulating Chit1 activity that correlate with disease severity. Murine modeling shows that in comparison with wild-type mice, bleomycin-induced pulmonary fibrosis was significantly reduced in Chit1⁻/⁻ mice and significantly enhanced in lungs from Chit1 overexpressing transgenic animals. In vitro studies also demonstrated that Chit1 interacts with TGF-β1 to augment fibroblast TGF-β receptors 1 and 2 expression and TGF-β-induced Smad and MAPK/ERK activation. These studies indicate that Chit1 is potential biomarker for ILD in SSc and a therapeutic target in SSc-associated lung fibrosis and demonstrate that Chit1 augments TGF-β1 effects by increasing receptor expression and canonical and noncanonical TGF-β1 signaling.

The Role of TGF-β Receptors in Fibrosis

Recent advances in defining TGF-β signaling pathways have provided a new level of understanding of the role of this pleiotropic growth factor in the development of fibrosis. Here, we review selected topics related to the profibrotic role of TGF-β . We will discuss new insights into the mechanisms of ligand activation and the contribution of Erk1/2 MAPK, PI3K/FAK, and Endoglin/Smad1 signaling pathways to the process of fibrosis. There is growing evidence of the disease-specific alterations of the downstream components of the TGF-β signaling pathway that may be explored for the future therapeutic interventions.

Effect of oxidative stress on protein tyrosine phosphatase 1B in scleroderma dermal fibroblasts

OBJECTIVE

Platelet-derived growth factor (PDGF) and its receptor, PDGFR, promote fibrosis in systemic sclerosis (SSc; scleroderma) dermal fibroblasts, and such cells in scleroderma skin lesions produce excessive reactive oxygen species (ROS). PDGFR is phosphorylated upon PDGF stimulation, and is dephosphorylated by protein tyrosine phosphatases (PTPs), including PTP1B. This study was undertaken to determine whether the thiol-sensitive PTP1B is affected by ROS in SSc dermal fibroblasts, thereby enhancing the phosphorylation of PDGFR and synthesis of type I collagen. This study also sought to investigate the effect of a thiol antioxidant, N-acetylcysteine (NAC), in SSc.

METHODS

Fibroblasts were isolated from the skin of patients with diffuse SSc and normal healthy donors for cell culture experiments and immunofluorescence analyses. A phosphate release assay was used to determine the activity of PTP1B.

RESULTS

Levels of ROS and type I collagen were significantly higher and amounts of free thiol were significantly lower in SSc fibroblasts compared to normal fibroblasts. After stimulation with PDGF, not only were PDGFR and ERK-1/2 phosphorylated to a greater extent, but also the ability to produce PTP1B was hampered in SSc fibroblasts. The activity of PTP1B was significantly inactivated in SSc fibroblasts as a result of cysteine oxidation by the raised levels of ROS, which was confirmed by the oxidation of multiple PTPs, including PTP1B, in SSc fibroblasts. Decreased expression of PTP1B in normal fibroblasts led to increased expression of type I collagen. Treatment of the cells with NAC restored the activity of PTP1B, improved the profile of PDGFR phosphorylation, decreased the numbers of tyrosine-phosphorylated proteins and levels of type I collagen, and scavenged ROS in SSc fibroblasts.

CONCLUSION

This study describes a new mechanism by which ROS may promote a profibrotic phenotype in SSc fibroblasts through the oxidative inactivation of PTP1B, leading to pronounced activation of PDGFR. The study also presents a novel molecular mechanism by which NAC may act on ROS and PTP1B to provide therapeutic benefit in SSc.

MEK/ERK inhibitors: proof-of-concept studies in lung fibrosis

There is no therapy for chronic fibroproliferative diseases, in spite of the fact that current health statistics suggest that these (which include cardiovascular disease, pulmonary fibrosis, diabetic nephropathy, liver cirrhosis and systemic sclerosis) have been estimated to cause approximately 45% of the deaths in the developed world. Recently, many studies have shown that mitogen activated protein kinases (MAPKs) are activated in response to fibrogenic agents and contribute to the formation and function of the myofibroblast, the critical cell type responsible for excessive scarring. A recent report by Madala and colleagues (Am J Respir Cell Mol Biol, 2011) has provided a proof-of-concept study showing that the specific MEK inhibitor ARRY-142886 (ARRY) can both suppress the progression of fibrosis and reverse an animal model of lung fibrosis. Thus MEK inhibition could be a valuable method to treat lung fibrosis.