Possible strategies for anti-fibrotic drug intervention in scleroderma

There are no approved drugs for treating the fibrosis in scleroderma (systemic sclerosis, SSc). Myfibroblasts within connective tissue express the highly contractile protein α-smooth muscle actin (α-SMA) and are responsible for the excessive synthesis and remodeling of extracellular matrix (ECM) characterizing SSc. Drugs targeting myofibroblast differentiation, recruitment and activity are currently under consideration as anti-fibrotic treatments in SSc but thus far have principally focused on the transforming growth factor β (TGFβ), endothelin-1 (ET-1), connective tissue growth factor (CCN2/CTGF) and platelet derived growth factor (PDGF) pathways, which display substantial signaling crosstalk. Moreover, peroxisome proliferator-activated receptor (PPAR)γ also appears to act by intervening in TGFβ signaling. This review discusses these potential candidates for antifibrotic therapy in SSc.     

Interstitial fluid flow and cyclic strain differentially regulate cardiac fibroblast activation via AT1R and TGF-β1

Cardiac fibroblasts are exposed to both cyclic strain and interstitial fluid flow in the myocardium. The balance of these stimuli is affected by fibrotic scarring, during which the fibroblasts transition to a myofibroblast phenotype. The present study investigates the mechanisms by which cardiac fibroblasts seeded in three-dimensional (3D) collagen gels differentiate between strain and fluid flow. Neonatal cardiac fibroblast-seeded 3D collagen gels were exposed to interstitial flow and/or cyclic strain and message levels of collagens type I and III, transforming growth factor β1 (TGF-β1), and α-smooth muscle actin (α-SMA) were assessed. Flow was found to significantly increase and strain to decrease expression of myofibroblast markers. Corresponding immunofluorescence indicated that flow and strain differentially regulated α-SMA protein expression. The effect of flow was inhibited by exposure to losartan, an angiotensin II type 1 receptor (AT1R) blocker, and by introduction of shRNA constructs limiting AT1R expression. Blocking of TGF-β also inhibited the myofibroblast transition, suggesting that flow-mediated cell signaling involved both AT1R and TGF-β1. Reduced smad2 phosphorylation in response to cyclic strain suggested that TGF-β is part of the mechanism by which cardiac fibroblasts differentiate between strain-induced and flow-induced mechanical stress. Our experiments show that fluid flow and mechanical deformation have distinct effects on cardiac fibroblast phenotype. Our data suggest a mechanism in which fluid flow directly acts on AT1R and causes increased TGF-β1 expression, whereas cyclic strain reduces activation of smad proteins. These results have relevance to the pathogenesis and treatment of heart failure.     

TGF-β1 induces EMT reprogramming of porcine bladder urothelial cells into collagen producing fibroblasts-like cells in a Smad2/Smad3-dependent manner

Activation of fibroblasts and their differentiation into myofibroblasts, excessive collagen production and fibrosis occurs in a number of bladder diseases. Similarly, conversion of epithelial cells into mesenchymal cells (EMT) has been shown to increase fibroblasts like cells. TGF-β1 can induce the EMT and the role of TGF-β1-induced EMT during bladder injury leading to fibrosis and possible organ failure is gaining increasing interest. Here we show that EMT and fibrosis in porcine bladder urothelial (UC) cells are Smad dependent. Fresh normal porcine bladder urothelial cells were grown in culture with or without TGF-β1 and EMT markers were assessed. TGF-β1 treatment induced changes in cellular morphology as depicted by a significant decrease in the expression of E-cadherin and corresponding increase in N-cadherin and α-SMA. We knocked down Smad2 and Smad3 by Smad specific siRNA. Downregulation of E-cadherin expression by TGF-β1 was Smad3-dependent, whereas N-cadherin and α-SMA were dependent on both Smad2 and Smad3. Connective tissue growth factor (CTGF/CCN2), matrix metalloproteinase-2 and -9 (MMP-2, MMP-9) has been shown to play important roles in the pathogenesis of fibrosis. Induction of these genes by TGF-β1 was found to be time dependent. Upregulation of CTGF/CCN2 by TGF-β1 was Smad3 dependent; whereas MMP-2 was Smad2 dependent. Smad2 and Smad3 both participated in MMP-9 expression. TGF-β1 reprogrammed mesenchymal fibroblast like cells robustly expressed collagen I and III and these was inhibited by SB-431542, a TGF-β receptor inhibitor. Our results indicate that EMT of porcine bladder UC cells is TGF-β1 dependent and is mediated through Smad2 and Smad3. TGF-β1 may be an important factor in the development of bladder fibrosis via an EMT mechanism. This identifies a potential amenable therapeutic target.     

Fibroblast-myofibroblast transition is differentially regulated by bronchial epithelial cells from asthmatic children

Background

Airway remodeling is a proposed mechanism that underlies the persistent loss of lung function associated with childhood asthma. Previous studies have demonstrated that human lung fibroblasts (HLFs) co-cultured with primary human bronchial epithelial cells (BECs) from asthmatic children exhibit greater expression of extracellular matrix (ECM) components compared to co-culture with BECs derived from healthy children. Myofibroblasts represent a population of differentiated fibroblasts that have greater synthetic activity. We hypothesized co-culture with asthmatic BECs would lead to greater fibroblast to myofibroblast transition (FMT) compared to co-culture with healthy BECs.

Methods

BECs were obtained from well-characterized asthmatic and healthy children and were proliferated and differentiated at an air-liquid interface (ALI). BEC-ALI cultures were co-cultured with HLFs for 96 hours. RT-PCR was performed in HLFs for alpha smooth muscle actin (α-SMA) and flow cytometry was used to assay for α-SMA antibody labeling of HLFs. RT-PCR was also preformed for the expression of tropomyosin-I as an additional marker of myofibroblast phenotype. In separate experiments, we investigated the role of TGFβ₂ in BEC-HLF co-cultures using monoclonal antibody inhibition.

Results

Expression of α-SMA by HLFs alone was greater than by HLFs co-cultured with healthy BECs, but not different than α-SMA expression by HLFs co-cultured with asthmatic BECs. Flow cytometry also revealed significantly less α-SMA expression by healthy co-co-cultures compared to asthmatic co-cultures or HLF alone. Monoclonal antibody inhibition of TGFβ₂ led to similar expression of α-SMA between healthy and asthmatic BEC-HLF co-cultures. Expression of topomyosin-I was also significantly increased in HLF co-cultured with asthmatic BECs compared to healthy BEC-HLF co-cultures or HLF cultured alone.

Conclusion

These findings suggest dysregulation of FMT in HLF co-cultured with asthmatic as compared to healthy BECs. Our results suggest TGFβ₂ may be involved in the differential regulation of FMT by asthmatic BECs. These findings further illustrate the importance of BEC-HLF cross-talk in asthmatic airway remodeling.     

Lithium chloride inhibits TGF-β1-induced myofibroblast transdifferentiation via PI3K/Akt pathway in cultured fibroblasts from Tenon’s capsule of the human eye

Excess scarring of the conjunctiva after glaucoma filtration surgery is a major cause of failure. Transforming growth factor (TGF)-β is critically involved in post-operative scarring. Lithium inhibits TGF-β-induced gene protein expression in corneal fibroblasts and inhibits TGF-β-induced epithelial mesenchymal transition. Here, we investigated the effects of LiCl on TGF-β1-mediated signaling pathways and on myofibroblast transdifferentiation of human Tenon’s capsule fibroblasts (HTFs). LiCl treatment reduced expression of TGF-β1-induced α-SMA expression in HTFs. LiCl also decreased Akt phosphorylation induced by TGF-β1. TGF-β1-induced α-SMA expression was significantly decreased by LY294002 and Akt siRNA indicating that these changes are mediated by the PI3K/Akt pathway. Thus, LiCl induces the suppression of transdifferentiation stimulated by TGF-β1 by the regulation of PI3K/Akt signaling in HTFs.     

Response gene to complement 32 is essential for fibroblast activation in renal fibrosis

Response gene to complement 32 (RGC-32) is a downstream target of transforming growth factor-β (TGF-β). TGF-β is known to play a pathogenic role in renal fibrosis. In this study, we investigated RGC-32 function in renal fibrosis following unilateral ureteral obstruction (UUO) in mice, a model of progressive tubulointerstitial fibrosis. RGC-32 is normally expressed only in blood vessels of mouse kidney. However, UUO induces RGC-32 expression in renal interstitial cells at the early stage of kidney injury, suggesting that RGC-32 is involved in interstitial fibroblast activation. Indeed, expression of smooth muscle α-actin (α-SMA), an indicator of fibroblast activation, is limited to the interstitial cells at the early stage, and became apparent later in both interstitial and tubular cells. RGC-32 knockdown by shRNA significantly inhibits UUO-induced renal structural damage, α-SMA expression and collagen deposition, suggesting that RGC-32 is essential for the onset of renal interstitial fibrosis. In vitro studies indicate that RGC-32 mediates TGF-β-induced fibroblast activation. Mechanistically, RGC-32 interacts with Smad3 and enhances Smad3 binding to the Smad binding element in α-SMA promoter as demonstrated by DNA affinity assay. In the chromatin setting, Smad3, but not Smad2, binds to α-SMA promoter in fibroblasts. RGC-32 appears to be essential for Smad3 interaction with the promoters of fibroblast activation-related genes in vivo. Functionally, RGC-32 is crucial for Smad3-mediated α-SMA promoter activity. Taken together, we identify RGC-32 as a novel fibrogenic factor contributing to the pathogenesis of renal fibrosis through fibroblast activation.     

MicroRNA-155 targets SMAD2 and modulates the response of macrophages to transforming growth factor-{beta}

Transforming growth factor-beta (TGF-β) is a pleiotropic cytokine with important effects on processes such as fibrosis, angiogenesis, and immunosupression. Using bioinformatics, we identified SMAD2, one of the mediators of TGF-β signaling, as a predicted target for a microRNA, microRNA-155 (miR-155). MicroRNAs are a class of small non-coding RNAs that have emerged as an important class of gene expression regulators. miR-155 has been found to be involved in the regulation of the immune response in myeloid cells. Here, we provide direct evidence of binding of miR-155 to a predicted binding site and the ability of miR-155 to repress SMAD2 protein expression. We employed a lentivirally transduced monocyte cell line (THP1-155) containing an inducible miR-155 transgene to show that endogenous levels of SMAD2 protein were decreased after sustained overexpression of miR-155. This decrease in SMAD2 led to a reduction in both TGF-β-induced SMAD-2 phosphorylation and SMAD-2-dependent activation of the expression of the CAGA(12)LUC reporter plasmid. Overexpression of miR-155 altered the cellular responses to TGF-β by changing the expression of a set of genes that is involved in inflammation, fibrosis, and angiogenesis. Our study provides firm evidence of a role for miR-155 in directly repressing SMAD2 expression, and our results demonstrate the relevance of one of the two predicted target sites in SMAD2 3'-UTR. Altogether, our data uncover an important role for miR-155 in modulating the cellular response to TGF-β with possible implications in several human diseases where homeostasis of TGF-β might be altered.     

Is cytochrome P450 3A4 regulated by menstrual cycle hormones in control endometrium and endometriosis?

The aim of this study is to investigate the effect of evodiamine on fibroblast activation in cardiac fibroblasts and endothelial to mesenchymal transition (EndMT) in human umbilical vein endothelial cells (HUVECs). Neonatal rat cardiac fibroblasts were stimulated with transforming growth factor beta 1 (TGF-β1) to induce fibroblast activation. After co-cultured with evodiamine (5, 10 μM), the proliferation and pro-fibrotic proteins expression of cardiac fibroblasts were evaluated. HUVECs were also stimulated with TGF-β1 to induce EndMT and treated with evodiamine (5, 10 μM) at the same time. The EndMT response in the HUVECs was evaluated as well as the capacity of the transitioned endothelial cells migrating to surrounding tissue. As a result, Evodiamine-blunted TGF-β1 induced activation of cardiac fibroblast into myofibroblast as assessed by the decreased expressions of α-SMA. Furthermore, evodiamine reduced the increased protein expression of fibrosis markers in neonatal and adult rat cardiac fibroblasts induced by TGF-β1. HUVECs stimulated with TGF-β1 exhibited lower expression levels of CD31, CD34, and higher levels of α-SMA, vimentin than the control cells. This phenotype was eliminated in the HUVECs treated with both 5 and 10 μM evodiamine. Evodiamine significantly reduced the increase in migration ability that occurred in response to TGF-β1 in HUVECs. In addition, the activation of Smad2, Smad3, ERK1/2, and Akt, and the nuclear translocation of Smad4 in both cardiac fibroblasts and HUVEC were blocked by evodiamine treatment. Thus, evodiamine could prevent cardiac fibroblasts from activation into myofibroblast and protect HUVEC against EndMT. These effects may be mediated by inhibition of the TGFβ pathway in both cardiac fibroblasts and HUVECs.     

Integrin β1 is required for maintenance of vascular tone in postnatal mice

Connective tissue is required for maintaining the integrity of tissues. Integrins are the cell surface receptors responsible for cell attachment to extracellular matrix; however, their tissue-specific role in this process is poorly understood. Here, we test whether integrin β1 is required for blood vessel maintenance and integrity in adult mice. We show that adult mice containing a fibroblast/smooth muscle cell-specific deletion of integrin β1 exhibit impaired bleeding time and maintenance of vessel architecture, including progressively reduced levels of extracellular matrix (ECM). Vessels also possessed diminished levels of α-smooth muscle actin (α-SMA), and cells derived from vessels showed reduced production of mRNAs encoding ECM and α-SMA as well as reduced α-SMA protein and stress fibers and ECM contraction. Integrin β1 in adult fibroblasts/smooth muscle cells/pericytes is required for vasoconstriction and vascular maintenance.     

B-MYB positively regulates serine-threonine kinase receptor-associated protein (STRAP) activity through direct interaction

Serine-threonine kinase receptor-associated protein (STRAP) functions as a regulator of both TGF-β and p53 signaling. However, the regulatory mechanism of STRAP activity is not understood. In this study, we report that B-MYB is a new STRAP-interacting protein, and that an amino-terminal DNA-binding domain and an area (amino acids 373-468) between the acidic and conserved regions of B-MYB mediate the B-MYB·STRAP interaction. Functionally, B-MYB enhances STRAP-mediated inhibition of TGF-β signaling pathways, such as apoptosis and growth inhibition, by modulating complex formation between the TGF-β receptor and SMAD3 or SMAD7. Furthermore, coexpression of B-MYB results in a dose-dependent increase in STRAP-mediated stimulation of p53-induced apoptosis and cell cycle arrest via direct interaction. Confocal microscopy showed that B-MYB prevents the normal translocation of SMAD3 in response to TGF-β1 and stimulates p53 nuclear translocation. These results suggest that B-MYB acts as a positive regulator of STRAP.     

Macrophage-stimulated cardiac fibroblast production of IL-6 is essential for TGF β/Smad activation and cardiac fibrosis induced by angiotensin II

Interleukin-6 (IL-6) is an important cytokine participating in multiple biologic activities in immune regulation and inflammation. IL-6 has been associated with cardiovascular remodeling. However, the mechanism of IL-6 in hypertensive cardiac fibrosis is still unclear. Angiotensin II (Ang II) infusion in mice increased IL-6 expression in the heart. IL-6 knockout (IL-6-/-) reduced Ang II-induced cardiac fibrosis: 1) Masson trichrome staining showed that Ang II infusion significantly increased fibrotic areas of the wild-type mouse heart, which was greatly suppressed in IL-6-/- mice and 2) immunohistochemistry staining showed decreased expression of α-smooth muscle actin (α-SMA), transforming growth factor β1 (TGF-β1) and collagen I in IL-6-/- mouse heart. The baseline mRNA expression of IL-6 in cardiac fibroblasts was low and was absent in cardiomyocytes or macrophages; however, co-culture of cardiac fibroblasts with macrophages significantly increased IL-6 production and expression of α-SMA and collagen I in fibroblasts. Moreover, TGF-β1 expression and phosphorylation of TGF-β downstream signal Smad3 was stimulated by co-culture of macrophages with cardiac fibroblasts, while IL-6 neutralizing antibody decreased TGF-β1 expression and Smad3 phosphorylation in co-culture of macrophage and fibroblast. Taken together, our results indicate that macrophages stimulate cardiac fibroblasts to produce IL-6, which leads to TGF-β1 production and Smad3 phosphorylation in cardiac fibroblasts and thus stimulates cardiac fibrosis.     

Cdc42-interacting protein-4 promotes TGF-Β1-induced epithelial-mesenchymal transition and extracellular matrix deposition in renal proximal tubular epithelial cells

Cdc42-interacting protein-4 (CIP4) is an F-BAR (Fer/CIP4 and Bin, amphiphysin, Rvs) family member that regulates membrane deformation and endocytosis, playing a key role in extracellular matrix (ECM) deposition and invasion of cancer cells. These processes are analogous to those observed during the initial epithelial-mesenchymal transition (EMT) of renal tubular epithelial cells. The role of CIP4 in renal tubular EMT and renal tubulointerstitial fibrosis was investigated over the course of the current study, demonstrating that the expression of CIP4 increased in the tubular epithelia of 5/6-nephrectomized rats and TGF-β1 treated HK-2 cells. Endogenous CIP4 evidenced punctate localization throughout the cytosol, with elevated levels observed in the perinuclear region of HK-2 cells. Subsequent to TGF-β1 treatment, CIP4 expression increased, forming clusters at the cell periphery that gradually redistributed into the cytoplasm. Simultaneously, EMT induction in cells was confirmed by the prevalence of morphological changes, loss of E-cadherin, increase in α-SMA expression, and secretion of fibronectin. Overexpression of CIP4 promoted characteristics similar to those commonly observed in EMT, and small interfering RNA (siRNA) molecules capable of CIP4 knockdown were used to demonstrate reversed EMT. Cumulatively, results of the current study suggest that CIP4 promotes TGF-β1-induced EMT in tubular epithelial cells. Through this mechanism, CIP4 is capable of inducing ECM deposition and exacerbating progressive fibrosis in chronic renal failure.     

Loss of LRP1 promotes acquisition of contractile-myofibroblast phenotype and release of active TGF-β1 from ECM stores

In healing tissue, fibroblasts differentiate to α-smooth muscle actin (SMA)-expressing contractile-myofibroblasts, which pull the wound edges together ensuring proper tissue repair. Uncontrolled expansion of the myofibroblast population may, however, lead to excessive tissue scarring and finally to organ dysfunction. Here, we demonstrate that the loss of low-density lipoprotein receptor-related protein (LRP) 1 overactivates the JNK1/2-c-Jun-Fra-2 signaling pathway leading to the induction of α-SMA and periostin expression in human lung fibroblasts (hLF). These changes are accompanied by increased contractility of the cells and the integrin- and protease-dependent release of active transforming growth factor (TGF)-β1 from the extracellular matrix (ECM) stores. Liberation of active TGF-β1 from the ECM further enhances α-SMA and periostin expression thus accelerating the phenotypic switch of hLF. Global gene expression profiling of LRP1-depleted hLF revealed that the loss of LRP1 affects cytoskeleton reorganization, cell-ECM contacts, and ECM production. In line with these findings, fibrotic changes in the skin and lung of Fra-2 transgenic mice were associated with LRP1 depletion and c-Jun overexpression. Altogether, our results suggest that dysregulation of LRP1 expression in fibroblasts in healing tissue may lead to the unrestrained expansion of contractile myofibroblasts and thereby to fibrosis development. Further studies identifying molecules, which regulate LRP1 expression, may provide new therapeutic options for largely untreatable human fibrotic diseases.     

Wnt3a induces myofibroblast differentiation by upregulating TGF-β signaling through SMAD2 in a β-catenin-dependent manner

Growing evidence suggests the Wnt family of secreted glycoproteins and their associated signaling pathways, linked to development, are recapitulated during wound repair and regeneration events. However, the role of the Wnt pathway in such settings remains unclear. In the current study, we treated mouse fibroblasts with 250 ng/mL of recombinant Wnt3a for 72 hours and examined its affect on cell morphology and function. Wnt3a induced a spindle-like morphology in fibroblasts characterized by the increased formation of stress fibres. Wnt3a decreased the proliferation of fibroblasts, but significantly increased cell migration as well as fibroblast-mediated contraction of a collagen lattice. Wnt3a significantly increased the expression of TGF-β and its associated signaling through SMAD2. Consistent with this, we observed significantly increased smooth muscle α-actin expression and incorporation of this contractile protein into stress fibres following Wnt3a treatment. Knockdown of β-catenin using siRNA reversed the Wnt3a-induced smooth muscle α-actin expression, suggesting these changes were dependent on canonical Wnt signaling through β-catenin. Neutralization of TGF-β with a blocking antibody significantly inhibited the Wnt3a-induced smooth muscle α-actin expression, indicating these changes were dependent on the increased TGF-β signaling. Collectively, this data strongly suggests Wnt3a promotes the formation of a myofibroblast-like phenotype in cultured fibroblasts, in part, by upregulating TGF-β signaling through SMAD2 in a β-catenin-dependent mechanism. As myofibroblasts are critical regulators of wound healing responses, these findings may have important implications for our understanding of normal and aberrant injury and repair events.     

Transglutaminase 2: a novel therapeutic target for idiopathic pulmonary fibrosis using selective small molecule inhibitors

This study investigates the effects of a site-directed TG2-selective inhibitor on the lung myofibroblast phenotype and ECM deposition to elucidate TG2 as a novel therapeutic target in idiopathic pulmonary fibrosis (IPF)—an incurable progressive fibrotic disease. IPF fibroblasts showed increased expression of TG2, α smooth muscle actin (αSMA) and fibronectin (FN) with increased extracellular TG2 and transforming growth factor β1 (TGFβ1) compared to normal human lung fibroblasts (NHLFs) which do not express αSMA and express lower levels of FN. The myofibroblast phenotype shown by IPF fibroblasts could be reversed by selective TG2 inhibition with a reduction in matrix FN and TGFβ1 deposition. TG2 transduction or TGFβ1 treatment of NHLFs led to a comparable phenotype to that of IPF fibroblasts which was reversible following selective TG2 inhibition. Addition of exogenous TG2 to NHLFs also induced the myofibroblast phenotype by a mechanism involving TGFβ1 activation which could be ameliorated by selective TG2 inhibition. SMAD3-deleted IPF fibroblasts via CRISPR-cas9 genome editing, showed reduced TG2 protein levels following TGFβ1 stimulation. This study demonstrates a key role for TG2 in the induction of the myofibroblast phenotype and shows the potential for TG2-selective inhibitors as therapeutic agents for the treatment of fibrotic lung diseases like IPF.