Regulation of alpha-smooth muscle actin expression in granulation tissue myofibroblasts is dependent on the intronic CArG element and the transforming growth factor-beta1 control element

JAK/STAT3 signaling in cardiac fibrosis: a promising therapeutic target

Cardiac fibrosis is a serious health problem because it is a common pathological change in almost all forms of cardiovascular diseases. Cardiac fibrosis is characterized by the transdifferentiation of cardiac fibroblasts (CFs) into cardiac myofibroblasts and the excessive deposition of extracellular matrix (ECM) components produced by activated myofibroblasts, which leads to fibrotic scar formation and subsequent cardiac dysfunction. However, there are currently few effective therapeutic strategies protecting against fibrogenesis. This lack is largely because the molecular mechanisms of cardiac fibrosis remain unclear despite extensive research. The Janus kinase/signal transducer and activator of transcription (JAK/STAT) signaling cascade is an extensively present intracellular signal transduction pathway and can regulate a wide range of biological processes, including cell proliferation, migration, differentiation, apoptosis, and immune response. Various upstream mediators such as cytokines, growth factors and hormones can initiate signal transmission via this pathway and play corresponding regulatory roles. STAT3 is a crucial player of the JAK/STAT pathway and its activation is related to inflammation, malignant tumors and autoimmune illnesses. Recently, the JAK/STAT3 signaling has been in the spotlight for its role in the occurrence and development of cardiac fibrosis and its activation can promote the proliferation and activation of CFs and the production of ECM proteins, thus leading to cardiac fibrosis. In this manuscript, we discuss the structure, transactivation and regulation of the JAK/STAT3 signaling pathway and review recent progress on the role of this pathway in cardiac fibrosis. Moreover, we summarize the current challenges and opportunities of targeting the JAK/STAT3 signaling for the treatment of fibrosis. In summary, the information presented in this article is critical for comprehending the role of the JAK/STAT3 pathway in cardiac fibrosis, and will also contribute to future research aimed at the development of effective anti-fibrotic therapeutic strategies targeting the JAK/STAT3 signaling.

Increased Chymase-Positive Mast Cells in High-Grade Mucoepidermoid Carcinoma of the Parotid Gland

It has long been known that high-grade mucoepidermoid carcinoma (MEC) has a poor prognosis, but the detailed molecular and biological mechanisms underlying this are not fully understood. In the present study, the pattern of chymase-positive mast cells, as well as chymase gene expression, in high-grade MEC was compared to that of low-grade and intermediate-grade MEC by using 44 resected tumor samples of MEC of the parotid gland. Chymase expression, as well as chymase-positive mast cells, was found to be markedly increased in high-grade MEC. Significant increases in PCNA-positive cells and VEGF gene expression, as well as lymphangiogenesis, were also confirmed in high-grade MEC. Chymase substrates, such as the latent transforming growth factor-beta (TGF-β) 1 and pro-matrix metalloproteinase (MMP)-9, were also detected immunohistologically in high-grade MEC. These findings suggested that the increased chymase activity may increase proliferative activity, as well as metastasis in the malignant condition, and the inhibition of chymase may be a strategy to improve the poor prognosis of high-grade MEC of the parotid gland.

A Rational Design of Metal-Organic Framework Nanozyme with High-Performance Copper Active Centers for Alleviating Chemical Corneal Burns

Metal-organic frameworks (MOFs) have attracted significant research interest in biomimetic catalysis. However, the modulation of the activity of MOFs by precisely tuning the coordination of metal nodes is still a significant challenge. Inspired by metalloenzymes with well-defined coordination structures, a series of MOFs containing halogen-coordinated copper nodes (Cu-X MOFs, X = Cl, Br, I) are employed to elucidate their structure-activity relationship. Intriguingly, experimental and theoretical results strongly support that precisely tuning the coordination of halogen atoms directly regulates the enzyme-like activities of Cu-X MOFs by influencing the spatial configuration and electronic structure of the Cu active center. The optimal Cu-Cl MOF exhibits excellent superoxide dismutase-like activity with a specific activity one order of magnitude higher than the reported Cu-based nanozymes. More importantly, by performing enzyme-mimicking catalysis, the Cu-Cl MOF nanozyme can significantly scavenge reactive oxygen species and alleviate oxidative stress, thus effectively relieving ocular chemical burns. Mechanistically, the antioxidant and antiapoptotic properties of Cu-Cl MOF are achieved by regulating the NRF2 and JNK or P38 MAPK pathways. Our work provides a novel way to refine MOF nanozymes by directly engineering the coordination microenvironment and, more significantly, demonstrating their potential therapeutic effect in ophthalmic disease.

Cysteine-Based Redox-Responsive Nanoparticles for Fibroblast-Targeted Drug Delivery in the Treatment of Myocardial Infarction

Upon myocardial infarction (MI), activated cardiac fibroblasts (CFs) begin to remodel the myocardium, leading to cardiac fibrosis and even heart failure. No therapeutic approaches are currently available to prevent the development of MI-induced pathological fibrosis. Most pharmacological trials fail from poor local drug activity and side effects caused by systemic toxicity, largely due to the lack of a heart-targeted drug delivery system that is selective for activated CFs. Here, we developed a reduced glutathione (GSH)-responsive nanoparticle platform capable of targeted delivering of drugs to activated CFs within the infarct area of a post-MI heart. Compared with systemic drug administration, CF-targeted delivery of PF543, a sphingosine kinase 1 inhibitor identified in a high-throughput antifibrotic drug screening, had higher therapeutic efficacy and lower systemic toxicity in a MI mouse model. Our results provide a CF-targeted strategy to deliver therapeutic agents for pharmacological intervention of cardiac fibrosis.

Transcriptional regulation of cardiac fibroblast phenotypic plasticity

Cardiac fibroblasts play critical roles in the maintenance of cardiac structure and the response to cardiac insult. Extracellular matrix deposition by activated resident cardiac fibroblasts, called myofibroblasts, is an essential wound healing response. However, persistent fibroblast activation contributes to pathological fibrosis and cardiac chamber stiffening, which can cause diastolic dysfunction, heart failure, and initiate lethal arrhythmias. The dynamic and phenotypically plastic nature of cardiac fibroblasts is governed in part by the transcriptional regulation of genes encoding extracellular matrix molecules. Understanding how fibroblasts integrate various biomechanical cues into a precise transcriptional response may uncover therapeutic strategies to prevent fibrosis. Here, we provide an overview of the recent literature on transcriptional control of cardiac fibroblast plasticity and fibrosis, with a focus on canonical and non-canonical TGF-β signaling, biomechanical regulation of Hippo/YAP and Rho/MRTF signaling, and metabolic and epigenetic control of fibroblast activation.

Properties and Functions of Fibroblasts and Myofibroblasts in Myocardial Infarction

The adult mammalian heart contains abundant interstitial and perivascular fibroblasts that expand following injury and play a reparative role but also contribute to maladaptive fibrotic remodeling. Following myocardial infarction, cardiac fibroblasts undergo dynamic phenotypic transitions, contributing to the regulation of inflammatory, reparative, and angiogenic responses. This review manuscript discusses the mechanisms of regulation, roles and fate of fibroblasts in the infarcted heart. During the inflammatory phase of infarct healing, the release of alarmins by necrotic cells promotes a pro-inflammatory and matrix-degrading fibroblast phenotype that may contribute to leukocyte recruitment. The clearance of dead cells and matrix debris from the infarct stimulates anti-inflammatory pathways and activates transforming growth factor (TGF)-β cascades, resulting in the conversion of fibroblasts to α-smooth muscle actin (α-SMA)-expressing myofibroblasts. Activated myofibroblasts secrete large amounts of matrix proteins and form a collagen-based scar that protects the infarcted ventricle from catastrophic complications, such as cardiac rupture. Moreover, infarct fibroblasts may also contribute to cardiac repair by stimulating angiogenesis. During scar maturation, fibroblasts disassemble α-SMA+ stress fibers and convert to specialized cells that may serve in scar maintenance. The prolonged activation of fibroblasts and myofibroblasts in the infarct border zone and in the remote remodeling myocardium may contribute to adverse remodeling and to the pathogenesis of heart failure. In addition to their phenotypic plasticity, fibroblasts exhibit remarkable heterogeneity. Subsets with distinct phenotypic profiles may be responsible for the wide range of functions of fibroblast populations in infarcted and remodeling hearts.

Dermal αSMA+ myofibroblasts orchestrate skin wound repair via β1 integrin and independent of type I collagen production

Skin wound repair is essential for organismal survival and failure of which leads to non-healing wounds, a leading health issue worldwide. However, mechanistic understanding of chronic wounds remains a major challenge due to lack of appropriate genetic mouse models. αSMA⁺ myofibroblasts, a unique class of dermal fibroblasts, are associated with cutaneous wound healing but their precise function remains unknown. We demonstrate that genetic depletion of αSMA⁺ myofibroblasts leads to pleiotropic wound healing defects, including lack of reepithelialization and granulation, dampened angiogenesis, and heightened hypoxia, hallmarks of chronic non-healing wounds. Other wound-associated FAP⁺ and FSP1⁺ fibroblasts do not exhibit such dominant functions. While type I collagen (COL1) expressing cells play a role in the repair process, COL1 produced by αSMA⁺ myofibroblasts is surprisingly dispensable for wound repair. In contrast, we show that β1 integrin from αSMA⁺ myofibroblasts, but not TGFβRII, is essential for wound healing, facilitating contractility, reepithelization, and vascularization. Collectively, our study provides evidence for the functions of myofibroblasts in β1 integrin-mediated wound repair with potential implications for treating chronic non-healing wounds.

Activation of Mast-Cell-Derived Chymase in the Lacrimal Glands of Patients with IgG4-Related Ophthalmic Disease

The purpose of this present study was to investigate the distribution and expression of chymase in the lacrimal glands (LGs) of patients afflicted with IgG4-related ophthalmic disease (IgG4-ROD). LGs from patients with severe canalicular obstruction were considered the control group. Toluidine blue staining confirmed a significant increase in the number of mast cells in the LGs obtained from the IgG4-ROD patients. In addition, immunostaining of serial sections from the LGs showed a significant increase in the number of chymase-positive cells and tryptase-positive cells in the IgG4-ROD LGs compared to the normal control LGs. The mRNA expression of chymase, tryptase, TGF-β1, and collagen-I tended to increase in the IgG4-ROD LGs. Immunostaining of vimentin and α-smooth muscle actin (α-SMA) showed that myofibroblasts were the main cellular components in severely fibrotic regions of LGs in patients with IgG4-ROD. Linear regression analyses on the number of mast cells, chymase-positive cells, and tryptase-positive cells revealed significant positive correlations between those respective cells. Our findings suggest that chymase may play a role in the fibrotic disorder of IgG4-ROD LGs through the regulation of TGF-β1 activation and collagen-I deposition, and that it may be a therapeutic target for patients afflicted with IgG4-ROD.

The interplay of fibroblasts, the extracellular matrix, and inflammation in scar formation

Various forms of fibrosis, comprising tissue thickening and scarring, are involved in 40% of deaths across the world. Since the discovery of scarless functional healing in fetuses prior to a certain stage of development, scientists have attempted to replicate scarless wound healing in adults with little success. While the extracellular matrix (ECM), fibroblasts, and inflammatory mediators have been historically investigated as separate branches of biology, it has become increasingly necessary to consider them as parts of a complex and tightly regulated system that becomes dysregulated in fibrosis. With this new paradigm, revisiting fetal scarless wound healing provides a unique opportunity to better understand how this highly regulated system operates mechanistically. In the following review, we navigate the four stages of wound healing (hemostasis, inflammation, repair, and remodeling) against the backdrop of adult versus fetal wound healing, while also exploring the relationships between the ECM, effector cells, and signaling molecules. We conclude by singling out recent findings that offer promising leads to alter the dynamics between the ECM, fibroblasts, and inflammation to promote scarless healing. One factor that promises to be significant is fibroblast heterogeneity and how certain fibroblast subpopulations might be predisposed to scarless healing. Altogether, reconsidering fetal wound healing by examining the interplay of the various factors contributing to fibrosis provides new research directions that will hopefully help us better understand and address fibroproliferative diseases, such as idiopathic pulmonary fibrosis, liver cirrhosis, systemic sclerosis, progressive kidney disease, and cardiovascular fibrosis.

Increase in Chymase-Positive Mast Cells in Recurrent Pleomorphic Adenoma and Carcinoma Ex Pleomorphic Adenoma of the Parotid Gland

Incomplete excision of pleomorphic adenoma (PA) may result in recurrent pleomorphic adenoma (RPA). Furthermore, long-term neglected PA may become carcinoma ex pleomorphic adenoma (CXPA). In the present study, the relationships between mast cell-derived chymase and these tumors were examined. The tumor tissues of PA consisted of either or both glandular and fibrotic structures. Histological features of RPA were almost similar to those of PA, except that they showed multinodular structures. CXPA is composed of a mixture of PA and carcinoma. The main stromal cells in PA were myofibroblasts, whereas fibroblasts constituted the main cellular portion in the stromal tissue of RPA. Cancer-associated fibroblasts (CAFs) were present abundantly in CXPA. With increased VEGF expression, neovascularization tended to increase in RPA or CXPA. Compared with PA, chymase-positive mast cells, as well as chymase gene expression, were increased in the tumor tissues from patients with RPA or CXPA. SCF, TGFβ1, and PCNA-positive staining was widely observed in these tumor tissues. The above results suggest that mast cell-derived chymase through its direct or cooperative effects with other mediators may participate in the pathophysiology of RPA and CXPA.

The Antimicrobial Peptide Human β-Defensin-3 Accelerates Wound Healing by Promoting Angiogenesis, Cell Migration, and Proliferation Through the FGFR/JAK2/STAT3 Signaling Pathway

In addition to its antimicrobial activity, the skin-derived antimicrobial peptide human β-defensin-3 (hBD-3) promotes keratinocyte proliferation and migration to initiate the wound healing process; however, its effects on fibroblasts, which are the major cell type responsible for wound healing, remain unclear. We investigated the role of hBD-3 in cell migration, proliferation and production of angiogenic growth factors in human fibroblasts and evaluated the in vivo effect of hBD-3 on promoting wound healing and angiogenesis. Following hBD-3 treatment, the mouse wounds healed faster and showed accumulation of neutrophils and macrophages in the early phase of wound healing and reduction of these phagocytes 4 days later. hBD-3-treated wounds also displayed an increased number of fibroblasts and newly formed vessels compared to those of the control mice. Furthermore, the expression of various angiogenic growth factors was increased in the hBD-3-treated wounds. Additionally, in vitro studies demonstrated that hBD-3 enhanced the secretion of angiogenic growth factors such as fibroblast growth factor, platelet-derived growth factor and vascular endothelial growth factor and induced the migration and proliferation of human fibroblasts. The hBD-3-mediated activation of fibroblasts involves the fibroblast growth factor receptor 1 (FGFR1)/Janus kinase 2 (JAK2)/signal transducer and activator of transcription 3 (STAT3) pathways, as evidenced by the inhibitory effects of pathway-specific inhibitors. We indeed confirmed that hBD-3 enhanced the phosphorylation of FGFR1, JAK2 and STAT3. Collectively, the current study provides novel evidence that hBD-3 might be a potential candidate for the treatment of wounds through its ability to promote wound healing, angiogenesis and fibroblast activation.

Prevention of Fibrosis and Pathological Cardiac Remodeling by Salinomycin

[Figure: see text].

Hypoxia Mesenchymal Stem Cells Accelerate Wound Closure Improvement by Controlling α-smooth Muscle actin Expression in the Full-thickness Animal Model

BACKGROUND: The active myofibroblast producing extracellular matrix deposition regarding wound closure is characterized by alpha-smooth muscle actin (α-SMA) expression. However, the persistence of α-SMA expression due to prolonged inflammation may trigger scar formation. A new strategy to control α-SMA expression in line with wound closure improvement uses hypoxic mesenchymal stem cells (HMSCs) due to their ability to firmly control inflammation for early initiating cell proliferation, including the regulation of α-SMA expression associated with wound closure acceleration. AIM: This study aimed to explore the role of HMSCs in accelerating the optimum wound closure percentages through controlling the α-SMA expression. MATERIALS AND METHODS: Twenty-four full-thickness rats wound model were randomly divided into four groups: Sham (Sh), Control (C) by NaCl administration only, and two treatment groups by HMSCs at doses of 1.5×106 cells (T1) and HMSCs at doses of 3×106 cells (T2). HMSCs were incubated under hypoxic conditions. The α-SMA expression was analyzed under immunohistochemistry staining assay, and the wound closure percentage was analyzed by ImageJ software. RESULTS: This study showed a significant increase in wound closure percentage in all treatment groups that gradually initiated on days 6 and 9 (p < 0.05). In line with the increase of wound closure percentages on day 9, there was also a significant decrease in α-SMA expression in all treatment groups (p < 0.05), indicating the optimum wound healing has preceded. CONCLUSION: HMSCs have a robust ability to accelerated wound closure improvement to the optimum wound healing by controlling α-SMA expression depending on wound healing phases.

Fibroblast contributions to ischemic cardiac remodeling

The heart can respond to increased pathophysiological demand through alterations in tissue structure and function 1 . This process, called cardiac remodeling, is particularly evident following myocardial infarction (MI), where the blockage of a coronary artery leads to widespread death of cardiac muscle. Following MI, necrotic tissue is replaced with extracellular matrix (ECM), and the remaining viable cardiomyocytes (CMs) undergo hypertrophic growth. ECM deposition and cardiac hypertrophy are thought to represent an adaptive response to increase structural integrity and prevent cardiac rupture. However, sustained ECM deposition leads to the formation of a fibrotic scar that impedes cardiac compliance and can induce lethal arrhythmias. Resident cardiac fibroblasts (CFs) are considered the primary source of ECM molecules such as collagens and fibronectin, particularly after becoming activated by pathologic signals. CFs contribute to multiple phases of post-MI heart repair and remodeling, including the initial response to CM death, immune cell (IC) recruitment, and fibrotic scar formation. The goal of this review is to describe how resident fibroblasts contribute to the healing and remodeling that occurs after MI, with an emphasis on how fibroblasts communicate with other cell types in the healing infarct scar 1 –6 .

Kindlin-2 Mediates Mechanical Activation of Cardiac Myofibroblasts

We identify the focal adhesion protein kindlin-2 as player in a novel mechanotransduction pathway that controls profibrotic cardiac fibroblast to myofibroblast activation. Kindlin-2 is co-upregulated with the myofibroblast marker α-smooth muscle actin (α-SMA) in fibrotic rat hearts and in human cardiac fibroblasts exposed to fibrosis-stiff culture substrates and pro-fibrotic TGF-β1. Stressing fibroblasts using ferromagnetic microbeads, stretchable silicone membranes, and cell contraction agonists all result in kindlin-2 translocation to the nucleus. Overexpression of full-length kindlin-2 but not of kindlin-2 missing a putative nuclear localization sequence (∆NLS kindlin-2) results in increased α-SMA promoter activity. Downregulating kindlin-2 with siRNA leads to decreased myofibroblast contraction and reduced α-SMA expression, which is dependent on CC(A/T)-rich GG(CArG) box elements in the α-SMA promoter. Lost myofibroblast features under kindlin-2 knockdown are rescued with wild-type but not ∆NLS kindlin-2, indicating that myofibroblast control by kindlin-2 requires its nuclear translocation. Because kindlin-2 can act as a mechanotransducer regulating the transcription of α-SMA, it is a potential target to interfere with myofibroblast activation in tissue fibrosis.

Cardiac fibrosis

Myocardial fibrosis, the expansion of the cardiac interstitium through deposition of extracellular matrix proteins, is a common pathophysiologic companion of many different myocardial conditions. Fibrosis may reflect activation of reparative or maladaptive processes. Activated fibroblasts and myofibroblasts are the central cellular effectors in cardiac fibrosis, serving as the main source of matrix proteins. Immune cells, vascular cells and cardiomyocytes may also acquire a fibrogenic phenotype under conditions of stress, activating fibroblast populations. Fibrogenic growth factors (such as transforming growth factor-β and platelet-derived growth factors), cytokines [including tumour necrosis factor-α, interleukin (IL)-1, IL-6, IL-10, and IL-4], and neurohumoral pathways trigger fibrogenic signalling cascades through binding to surface receptors, and activation of downstream signalling cascades. In addition, matricellular macromolecules are deposited in the remodelling myocardium and regulate matrix assembly, while modulating signal transduction cascades and protease or growth factor activity. Cardiac fibroblasts can also sense mechanical stress through mechanosensitive receptors, ion channels and integrins, activating intracellular fibrogenic cascades that contribute to fibrosis in response to pressure overload. Although subpopulations of fibroblast-like cells may exert important protective actions in both reparative and interstitial/perivascular fibrosis, ultimately fibrotic changes perturb systolic and diastolic function, and may play an important role in the pathogenesis of arrhythmias. This review article discusses the molecular mechanisms involved in the pathogenesis of cardiac fibrosis in various myocardial diseases, including myocardial infarction, heart failure with reduced or preserved ejection fraction, genetic cardiomyopathies, and diabetic heart disease. Development of fibrosis-targeting therapies for patients with myocardial diseases will require not only understanding of the functional pluralism of cardiac fibroblasts and dissection of the molecular basis for fibrotic remodelling, but also appreciation of the pathophysiologic heterogeneity of fibrosis-associated myocardial disease.

Possible Roles of Periostin in the Formation of Hemodialysis Vascular Access Stenosis after Polytetrafluoroethylene Graft Implantation in Dogs

Periostin, a recently found matricellular protein, has been implicated in neointima formation after balloon injury. However, the relationship between periostin and hyperplastic intima formation after PTFE graft implantation is unclear. Under mixed anesthesia, PTFE grafts were implanted between the canine carotid artery and jugular vein, and PTFE graft samples were harvested 1, 2, and 4 months after implantation. Intima formation started on the luminal surface of PTFE grafts at the venous anastomotic region 1 month after implantation. Thereafter, the increase in intimal volume was not only observed in the venous and arterial anastomotic regions, but also in the middle region of the PTFE grafts. In accordance with the increased intimal formation, time-dependent increases in mRNA expressions of periostin and transforming growth factor beta 1 (TGF-β1), as well as a strong positive correlation between periostin and TGF-β1, were observed. These findings suggest that periostin may play a very important role in the pathogenesis of hemodialysis vascular access stenosis through the acceleration of intimal formation. Thus, periostin may be a very important therapeutic target for the treatment of vascular access graft dysfunction in hemodialysis patients.

Role of cancer-associated fibroblasts in tumor structure, composition and the microenvironment in ovarian cancer

Ovarian cancer (OVAC) remains the most lethal gynecological malignancy; it is ranked fifth among the most common types of cancer that affect women worldwide. Several aspects of the disease, including molecular pathogenesis, epidemiology, histological subtypes, poor prognosis at early stages due to the absence of specific signs and symptoms, and curative treatments in the advanced stages are all responsible for the poor survival rate, which is evaluated to be at 5 years once the cancer is diagnosed and treatment begins. A better understanding of the pathogenesis of ovarian cancer is therefore crucial, even though unexplored pathways, in order to improve the prognosis of patients with OVAC and to develop novel therapeutic approaches. Accordingly, the tumor microenvironment, defined as the combination of proteins produced by all tumor cells and by non-cancerous cells or the stroma, and composed of several cells, including those from the immune, inflammatory and adipose systems, as well as the mesenchymal stem, endothelial and fibroblasts cells, has recently attracted attention. Of particular interest are fibroblasts, which can be activated into cancer-associated fibroblast (CAFs) to become a potent supporter of carcinogenesis, promoting the initiation of epithelial tumor formation, tumor growth, angiogenesis and metastasis, as well as therapeutic resistance and immunosuppression. Thus, the targeting of CAFs for early diagnosis and effective therapy warrants our attention. In this review, we discuss the mechanisms through which CAFs may affect the structure, composition and microenvironment of the ovarian tumor. We also aim to highlight important aspects of OVAC pathobiology involving CAFs, in an attempt to provide insight into novel diagnostic windows and provide new therapeutic perspectives.

Fibroblasts in the Infarcted, Remodeling, and Failing Heart

Expansion and activation of fibroblasts following cardiac injury is important for repair but may also contribute to fibrosis, remodeling, and dysfunction. The authors discuss the dynamic alterations of fibroblasts in failing and remodeling myocardium. Emerging concepts suggest that fibroblasts are not unidimensional cells that act exclusively by secreting extracellular matrix proteins, thus promoting fibrosis and diastolic dysfunction. In addition to their involvement in extracellular matrix expansion, activated fibroblasts may also exert protective actions, preserving the cardiac extracellular matrix, transducing survival signals to cardiomyocytes, and regulating inflammation and angiogenesis. The functional diversity of cardiac fibroblasts may reflect their phenotypic heterogeneity.

Decrease in number of mast cells in resected nasal polyps as an indicator for postoperative recurrence of chronic rhinosinusitis

Background

In the clinical setting, chronic rhinosinusitis with nasal polyps (CRSwNP) is usually divided into eosinophilic‐CRS (ECRS) and non‐ECRS (NECRS) in Japan. Patients with the former are believed to be at risk for postoperative recurrence of CRS. However, some patients have been missed according to these phenotypic classifications due to the low number of infiltrating eosinophils in polyp tissues.

Objective

In the present study, we attempted to identify cellular or molecular candidate markers to predict nasal polyp recurrence.

Methods

Nasal polyps were collected from 32 patients with CRSwNP who had undergone an endoscopic sinus surgery. These patients were divided into ECRS and NECRS groups in accordance with the Japanese Epidemiological Survey of Refractory Eosinophilic Chronic Rhinosinusitis (JESREC) scoring system and the number of eosinophils in polyp tissues. Unclassifiable patients were referred to as the unknown group.

Results

Eosinophil infiltration in resected nasal polyps was most evident in the ECRS group. However, the number of mast cells and tryptase‐positive cells in nasal polyps were significantly lower in ECRS and unknown groups compared with the NECRS group. A significant positive correlation was detected between the JESREC score and number of eosinophils. The numbers of mast cells and tryptase‐positive cells were negatively correlated with the JESREC score in all included samples. Significant positive correlations were detected between the number of transforming growth factor β1‐positive cells and the number of mast cells, tryptase‐positive cells, and chymase‐positive cells mast cells.

Conclusions and clinical relevance

These findings indicated that the enumeration of mast cells in resected polyps may be another approach to predict postoperative polyp recurrence in CRSwNP patients.

Cardiac fibrosis: Cell biological mechanisms, molecular pathways and therapeutic opportunities

Cardiac fibrosis is a common pathophysiologic companion of most myocardial diseases, and is associated with systolic and diastolic dysfunction, arrhythmogenesis, and adverse outcome. Because the adult mammalian heart has negligible regenerative capacity, death of a large number of cardiomyocytes results in reparative fibrosis, a process that is critical for preservation of the structural integrity of the infarcted ventricle. On the other hand, pathophysiologic stimuli, such as pressure overload, volume overload, metabolic dysfunction, and aging may cause interstitial and perivascular fibrosis in the absence of infarction. Activated myofibroblasts are the main effector cells in cardiac fibrosis; their expansion following myocardial injury is primarily driven through activation of resident interstitial cell populations. Several other cell types, including cardiomyocytes, endothelial cells, pericytes, macrophages, lymphocytes and mast cells may contribute to the fibrotic process, by producing proteases that participate in matrix metabolism, by secreting fibrogenic mediators and matricellular proteins, or by exerting contact-dependent actions on fibroblast phenotype. The mechanisms of induction of fibrogenic signals are dependent on the type of primary myocardial injury. Activation of neurohumoral pathways stimulates fibroblasts both directly, and through effects on immune cell populations. Cytokines and growth factors, such as Tumor Necrosis Factor-α, Interleukin (IL)-1, IL-10, chemokines, members of the Transforming Growth Factor-β family, IL-11, and Platelet-Derived Growth Factors are secreted in the cardiac interstitium and play distinct roles in activating specific aspects of the fibrotic response. Secreted fibrogenic mediators and matricellular proteins bind to cell surface receptors in fibroblasts, such as cytokine receptors, integrins, syndecans and CD44, and transduce intracellular signaling cascades that regulate genes involved in synthesis, processing and metabolism of the extracellular matrix. Endogenous pathways involved in negative regulation of fibrosis are critical for cardiac repair and may protect the myocardium from excessive fibrogenic responses. Due to the reparative nature of many forms of cardiac fibrosis, targeting fibrotic remodeling following myocardial injury poses major challenges. Development of effective therapies will require careful dissection of the cell biological mechanisms, study of the functional consequences of fibrotic changes on the myocardium, and identification of heart failure patient subsets with overactive fibrotic responses.

Lipopolysaccharide Activates Toll-Like Receptor 4 and Prevents Cardiac Fibroblast-to-Myofibroblast Differentiation

Bacterial lipopolysaccharide (LPS) is a known ligand of Toll-like receptor 4 (TLR4) which is expressed in cardiac fibroblasts (CF). Differentiation of CF to cardiac myofibroblasts (CMF) is induced by transforming growth factor-β1 (TGF-β1), increasing alpha-smooth muscle actin (α-SMA) expression. In endothelial cells, an antagonist effect between LPS-induced signaling and canonical TGF-β1 signaling was described; however, it has not been studied whether in CF and CMF the expression of α-SMA induced by TGF-β1 is antagonized by LPS and the mechanism involved. In adult rat CF and CMF, α-SMA, ERK1/2, Akt, NF-κβ, Smad3, and Smad7 protein levels were determined by western blot, TGF-β isoforms by ELISA, and α-SMA stress fibers by immunocytochemistry. CF and CMF secrete the three TGF-β isoforms, and the secretion levels of TGF-β2 was affected by LPS treatment. In CF, LPS treatment decreased the protein levels of α-SMA, and this effect was prevented by TAK-242 (TLR4 inhibitor) and LY294002 (Akt inhibitor), but not by BAY 11-7082 (NF-κβ inhibitor) and PD98059 (ERK1/2 inhibitor). TGF-β1 increased α-SMA protein levels in CF, and LPS prevented partially this effect. In addition, in CMF α-SMA protein levels were decreased by LPS treatment, which was abolished by TAK-242. Finally, in CF LPS decreased the p-Smad3 phosphorylation and increased the Smad7 protein levels. LPS treatment prevents the CF-to-CMF differentiation and reverses the CMF phenotype induced by TGF-β1, through decreasing p-Smad3 and increasing Smad7 protein levels.

Bone marrow-derived mesenchymal stem cells laden novel thermo-sensitive hydrogel for the management of severe skin wound healing

Bone marrow-derived mesenchymal stem cells (BMSCs) are easy to collect and culture, and it is identified that it has multi-directional differentiation potential, moreover it has low immunogenicity, hence it can be used as an allogeneic cell source for skin wound healing. Hydrogel has been widely used in skin wound healing own to it is able to mimic the 3D microenvironment of cells, which supports cell proliferation, migration and secretion. In this study, we created a novel biocompatible thermo-sensitive hydrogel to carry BMSCs for full-thickness skin wound healing. The thermo-sensitive hydrogel loaded with BMSCs can fast achieve sol-gel transition after implanting to the wound. Histological results confirmed that hydrogel-BMSCs combination group showed significant promotion of wound closure, epithelial cells' proliferation and re-epithelialization, and reduced inflammatory responses in the wounds and in the tissues surrounding the wounds. The combination therapy also can promote collagen deposition, TGF-β1 and bFGF secretion and tissue remodeling. The present study provides a promising strategy for the clinical treatment of skin wounds.

The deubiquitylase USP10 regulates integrin β1 and β5 and fibrotic wound healing

Scarring and fibrotic disease result from the persistence of myofibroblasts characterized by high surface expression of αv integrins and subsequent activation of the transforming growth factor β (TGFβ) proteins; however, the mechanism controlling their surface abundance is unknown. Genetic screening revealed that human primary stromal corneal myofibroblasts overexpress a subset of deubiquitylating enzymes (DUBs), which remove ubiquitin from proteins, preventing degradation. Silencing of the DUB USP10 induces a buildup of ubiquitin on integrins β1 and β5 in cell lysates, whereas recombinant USP10 removes ubiquitin from these integrin subunits. Correspondingly, the loss and gain of USP10 decreases and increases, respectively, αv/β1/β5 protein levels, without altering gene expression. Consequently, endogenous TGFβ is activated and the fibrotic markers alpha-smooth muscle actin (α-SMA) and cellular fibronectin (FN-EDA) are induced. Blocking either TGFβ signaling or cell-surface αv integrins after USP10 overexpression prevents or reduces fibrotic marker expression. Finally, silencing of USP10 in an ex vivo cornea organ culture model prevents the induction of fibrotic markers and promotes regenerative healing. This novel mechanism puts DUB expression at the head of a cascade regulating integrin abundance and suggests USP10 as a novel antifibrotic target.

Transcriptional control of cardiac fibroblast plasticity

Cardiac fibroblasts help maintain the normal architecture of the healthy heart and are responsible for scar formation and the healing response to pathological insults. Various genetic, biomechanical, or humoral factors stimulate fibroblasts to become contractile smooth muscle-like cells called myofibroblasts that secrete large amounts of extracellular matrix. Unfortunately, unchecked myofibroblast activation in heart disease leads to pathological fibrosis, which is a major risk factor for the development of cardiac arrhythmias and heart failure. A better understanding of the molecular mechanisms that control fibroblast plasticity and myofibroblast activation is essential to develop novel strategies to specifically target pathological cardiac fibrosis without disrupting the adaptive healing response. This review highlights the major transcriptional mediators of fibroblast origin and function in development and disease. The contribution of the fetal epicardial gene program will be discussed in the context of fibroblast origin in development and following injury, primarily focusing on Tcf21 and C/EBP. We will also highlight the major transcriptional regulatory axes that control fibroblast plasticity in the adult heart, including transforming growth factor β (TGFβ)/Smad signaling, the Rho/myocardin-related transcription factor (MRTF)/serum response factor (SRF) axis, and Calcineurin/transient receptor potential channel (TRP)/nuclear factor of activated T-Cell (NFAT) signaling. Finally, we will discuss recent strategies to divert the fibroblast transcriptional program in an effort to promote cardiomyocyte regeneration. This article is a part of a Special Issue entitled "Fibrosis and Myocardial Remodeling".

Reduced granulation tissue and wound strength in the absence of α11β1 integrin

Previous wound healing studies have failed to define a role for either α1β1 or α2β1 integrin in fibroblast-mediated wound contraction, suggesting the involvement of another collagen receptor in this process. Our previous work demonstrated that the integrin subunit α11 is highly induced during wound healing both at the mRNA and protein level, prompting us to investigate and dissect the role of the integrin α11β1 during this process. Therefore, we used mice with a global ablation of either α2 or α11 or both integrin subunits and investigated the repair of excisional wounds. Analyses of wounds demonstrated that α11β1 deficiency results in reduced granulation tissue formation and impaired wound contraction, independently of the presence of α2β1. Our combined in vivo and in vitro data further demonstrate that dermal fibroblasts lacking α11β1 are unable to efficiently convert to myofibroblasts, resulting in scar tissue with compromised tensile strength. Moreover, we suggest that the reduced stability of the scar is a consequence of poor collagen remodeling in α11^−/− wounds associated with defective transforming growth factor-β–dependent JNK signaling.

Developing novel anti-fibrotic therapeutics to modulate post-surgical wound healing in glaucoma: big potential for small molecules

Ocular fibrosis leads to significant visual impairment and blindness in millions of people worldwide, and is one of the largest areas of unmet need in clinical ophthalmology. The antimetabolites, mitomycin C and 5-fluorouracil, are the current gold standards used primarily to prevent fibrosis after glaucoma surgery, but have potentially blinding complications like tissue damage, breakdown and infection. This review thus focuses on the development of new classes of small molecule therapeutics to prevent post-surgical fibrosis in the eye, especially in the context of glaucoma filtration surgery. We discuss recent advances and innovations in ophthalmic wound healing research, including antibodies, RNAi, gene therapy, nanoparticles, liposomes, dendrimers, proteoglycans and small molecule inhibitors. We also review the challenges involved in terms of drug delivery, duration of action and potential toxicity of new anti-fibrotic agents in the eye.

From tissue mechanics to transcription factors

Changes in tissue stiffness are frequently associated with diseases such as cancer, fibrosis, and atherosclerosis. Several recent studies suggest that, in addition to resulting from pathology, mechanical changes may play a role akin to soluble factors in causing the progression of disease, and similar mechanical control might be essential for normal tissue development and homeostasis. Many cell types alter their structure and function in response to exogenous forces or as a function of the mechanical properties of the materials to which they adhere. This review summarizes recent progress in identifying intracellular signaling pathways, and especially transcriptional programs, that are differentially activated when cells adhere to materials with different mechanical properties or when they are subject to tension arising from external forces. Several cytoplasmic or cytoskeletal signaling pathways involving small GTPases, focal adhesion kinase and transforming growth factor beta as well as the transcriptional regulators MRTF-A, NFκB, and Yap/Taz have emerged as important mediators of mechanical signaling.

Activation of MRTF-A-dependent gene expression with a small molecule promotes myofibroblast differentiation and wound healing

Myocardin-related transcription factors (MRTFs) regulate cellular contractility and motility by associating with serum response factor (SRF) and activating genes involved in cytoskeletal dynamics. We reported previously that MRTF-A contributes to pathological cardiac remodeling by promoting differentiation of fibroblasts to myofibroblasts following myocardial infarction. Here, we show that forced expression of MRTF-A in dermal fibroblasts stimulates contraction of a collagen matrix, whereas contractility of MRTF-A null fibroblasts is impaired under basal conditions and in response to TGF-β1 stimulation. We also identify an isoxazole ring-containing small molecule, previously shown to induce smooth muscle α-actin gene expression in cardiac progenitor cells, as an agonist of myofibroblast differentiation. Isoxazole stimulates myofibroblast differentiation via induction of MRTF-A-dependent gene expression. The MRTF-SRF signaling axis is activated in response to skin injury, and treatment of dermal wounds with isoxazole accelerates wound closure and suppresses the inflammatory response. These results reveal an important role for MRTF-SRF signaling in dermal myofibroblast differentiation and wound healing and suggest that targeting MRTFs pharmacologically may prove useful in treating diseases associated with inappropriate myofibroblast activity.

[Expression of endoglin in human non-small cell lung cancer and its clinical significance]

OBJECTIVE

To investigate the expression of endoglin (ENG) in human non small cell lung cancer (NSCLC) cell lines, cancer and adjacent non-cancer tissues, and its role in NSCLC development, progression, metastasis and recurrence.

METHODS

Five strains of NSCLC cells and one strain of normal human bronchial epithelial (HBE) cells were cultured in vitro. Human NSCLC tissues and their corresponding adjacent lung tissues were taken from 22 NSCLC cases to detect the mRNA and protein levels of ENG using real-time PCR and Western blotting, respectively. Chi-square test was performed to analyze the correlations between the ENG expression and clinical data.

RESULTS

The mRNA and protein levels of ENG were up-regulated in 3 NSCLC cell strains of high metastasis. However, the expression of ENG was missing in the other low-metastatic NSCLC cell strains and the HBE cell strain. Besides, the mRNA and protein levels of ENG were up-regulated in the 19 out of 22 lung cancer tissues (86.36%), which were significantly higher than those in the adjacent non-cancer tissues (P<0.01). The over-expression of ENG was significantly correlated positively with lymph node metastasis (P<0.01), but not with age, sex, tumor size, clinical stage, pathological grade or histopathological type.

CONCLUSION

The expression of ENG in NSCLC is significantly correlated positively with lymph node metastasis, and it might be a biomarker for the metastasis and prognosis of NSCLC.

Investigation on novel chitosan nanoparticle-aptamer complexes targeting TGF-β receptor II

In our previous study, a dominant sequence called aptamer S58 antagonized TGF-β-induced myofibroblast transdifferentiation in human Tenon's capsule fibroblasts (HTFs) through sealing the targeting site of TGF-β receptor II (TβR II). However, rapid degradation by ubiquitous nucleases limited the aptamer's efficacy. Chitosan-nanoparticles (CS-NP) are good drug carriers. Herein we synthesises novel chitosan nanoparticle-aptamer S58 complexes called CS(S58)-NP in order to preserve and prolong S58's efficacy. We synthesised CS(S58)-NP at various molar ratios of CS-NP to S58 using an ionic gelation method. Then, the properties of the CS(S58)-NP including particle size, zeta potential, protection capacity, slow-release effect and cytotoxicity were studied. The targeting effect of the CS(S58)-NP was also studied. CS(S58)-NP at molar ratios of 20 and 30 showed high aptamer encapsulation efficiency, powerful aptamer protection, stable sustained-release ability and low cytotoxicity. FITC-labelled CS(S58)-NP could successfully bind to TβR II. As a result, TGF-β-induced cell proliferation and α-SMA expression were both inhibited. Furthermore, the CS(S58)-NP could inhibit TGF-β-induced α-SMA expression for a longer time than naked S58, even in serum. This research applied CS-NP as the aptamer carrier. The research results demonstrate that CS-NP are potentially able to preserve and prolong aptamer S58's efficacy. This study reveals that the use of CS-NP is promising for aptamer delivery and CS(S58)-NP can be a potential anti-scarring therapeutic approach after glaucoma filtration surgery.

Gray platelet syndrome and defective thrombo-inflammation in Nbeal2-deficient mice

Platelets are anuclear organelle-rich cell fragments derived from bone marrow megakaryocytes (MKs) that safeguard vascular integrity. The major platelet organelles, α-granules, release proteins that participate in thrombus formation and hemostasis. Proteins stored in α-granules are also thought to play a role in inflammation and wound healing, but their functional significance in vivo is unknown. Mutations in NBEAL2 have been linked to gray platelet syndrome (GPS), a rare bleeding disorder characterized by macrothrombocytopenia, with platelets lacking α-granules. Here we show that Nbeal2-knockout mice display the characteristics of human GPS, with defective α-granule biogenesis in MKs and their absence from platelets. Nbeal2 deficiency did not affect MK differentiation and proplatelet formation in vitro or platelet life span in vivo. Nbeal2-deficient platelets displayed impaired adhesion, aggregation, and coagulant activity ex vivo that translated into defective arterial thrombus formation and protection from thrombo-inflammatory brain infarction following focal cerebral ischemia. In a model of excisional skin wound repair, Nbeal2-deficient mice exhibited impaired development of functional granulation tissue due to severely reduced differentiation of myofibroblasts in the absence of α-granule secretion. This study demonstrates that platelet α-granule constituents are critically required not only for hemostasis but also thrombosis, acute thrombo-inflammatory disease states, and tissue reconstitution after injury.

Nuclear translocation of myocardin-related transcription factor-A during transforming growth factor beta-induced epithelial to mesenchymal transition of lens epithelial cells

PURPOSE

Transforming growth factor beta (TGFβ) is a known inducer of epithelial to mesenchymal transition (EMT), and studies in other systems have shown that nuclear localization of the myocardin-related transcription factor (MRTF) is downstream of TGFβ. In the following study, we investigated whether nuclear translocation of MRTF-A or MRTF-B is involved in TGFβ-induced EMT of lens epithelial cells (LECs). We further investigated the relationship between matrix metalloproteinase-2 and -9 (MMP-2/9) and MRTF in the EMT of LECs.

METHODS

Rat lens explant cultures were used as the model system. Explants were treated with TGFβ, an MMP-2/9 inhibitor, or actin binding drugs and immunostained for alpha smooth muscle actin (αSMA), MRTF-A, and MRTF-B. Cytoplasmic and nuclear intensities of cells were measured using ImageJ. Production of αSMA was measured using western blot analysis and ImageJ.

RESULTS

Untreated explant cells exhibited little αSMA expression, and MRTF-A and B were found to reside primarily in the cytosol. However, when stimulated with TGFβ, a significantly greater number of cells exhibited nuclear expression of MRTF-A, accompanied by an increase in αSMA expression. However, MRTF-B remained in the cytoplasm following TGFβ treatment. Cotreatment with an MMP-2/9 inhibitor and TGFβ resulted in reduced MRTF-A nuclear localization and αSMA expression compared to cells treated with TGFβ alone.

CONCLUSIONS

Our results are the first to demonstrate the expression of MRTF-A in LECs and that its nuclear translocation can be stimulated by TGFβ. Our data further suggest that MMP-2 and -9 are involved in the translocation of MRTF-A in LECs during TGFβ-induced EMT.

Stabilization of integrin-linked kinase by the Hsp90-CHIP axis impacts cellular force generation, migration and the fibrotic response

Integrin-linked kinase (ILK) is an adaptor protein required to establish and maintain the connection between integrins and the actin cytoskeleton. This linkage is essential for generating force between the extracellular matrix (ECM) and the cell during migration and matrix remodelling. The mechanisms by which ILK stability and turnover are regulated are unknown. Here we report that the E3 ligase CHIP-heat shock protein 90 (Hsp90) axis regulates ILK turnover in fibroblasts. The chaperone Hsp90 stabilizes ILK and facilitates the interaction of ILK with α-parvin. When Hsp90 activity is blocked, ILK is ubiquitinated by CHIP and degraded by the proteasome, resulting in impaired fibroblast migration and a dramatic reduction in the fibrotic response to bleomycin in mice. Together, our results uncover how Hsp90 regulates ILK stability and identify a potential therapeutic strategy to alleviate fibrotic diseases.

Dynamic Interplay of Smooth Muscle α-Actin Gene-Regulatory Proteins Reflects the Biological Complexity of Myofibroblast Differentiation

Myofibroblasts (MFBs) are smooth muscle-like cells that provide contractile force required for tissue repair during wound healing. The leading agonist for MFB differentiation is transforming growth factor β1 (TGFβ1) that induces transcription of genes encoding smooth muscle α-actin (SMαA) and interstitial collagen that are markers for MFB differentiation. TGFβ1 augments activation of Smad transcription factors, pro-survival Akt kinase, and p38 MAP kinase as well as Wingless/int (Wnt) developmental signaling. These actions conspire to activate β-catenin needed for expression of cyclin D, laminin, fibronectin, and metalloproteinases that aid in repairing epithelial cells and their associated basement membranes. Importantly, β-catenin also provides a feed-forward stimulus that amplifies local TGFβ1 autocrine/paracrine signaling causing transition of mesenchymal stromal cells, pericytes, and epithelial cells into contractile MFBs. Complex, mutually interactive mechanisms have evolved that permit several mammalian cell types to activate the SMαA promoter and undergo MFB differentiation. These molecular controls will be reviewed with an emphasis on the dynamic interplay between serum response factor, TGFβ1-activated Smads, Wnt-activated β-catenin, p38/calcium-activated NFAT protein, and the RNA-binding proteins, Purα, Purβ, and YB-1, in governing transcriptional and translational control of the SMαA gene in injury-activated MFBs.

Wounds that will not heal: pervasive cellular reprogramming in cancer

There has been an explosion of articles on epithelial-mesenchymal transition and other modes of cellular reprogramming that influence the tumor microenvironment. Many controversies exist and remain to be resolved. The interest of the pathologists in the molecular and functional parallels between wound healing and the developing tumor stroma has its earliest origin in the writings of Rudolph Virchow in the 19(th) century. Since then, most of the focus has been primarily on the dynamics of the extracellular matrix; however, new interest has been redirected toward deciphering and understanding the enigmatic, yet elegant, plasticity of the cellular components of the proliferating epithelia and stroma and how they are reciprocally influenced. Citing several examples from breast cancer research, we will trace how these perspectives have unfolded in the pages of The American Journal of Pathology and other investigative journals during the past century, their impact, and where the field is headed.

Whole animal knockout of smooth muscle alpha-actin does not alter excisional wound healing or the fibroblast-to-myofibroblast transition

The contractile phenotype and function of myofibroblasts have been proposed to play a critical role in wound closure. It has been hypothesized that smooth muscle α-actin expressed in myofibroblasts is critical for its formation and function. We have used smooth muscle α-actin-null mice to test this hypothesis. Full-thickness excisional wounds closed at a similar rate in smooth muscle α-actin-null and wild-type mice. In addition, fibroblasts in smooth muscle α-actin-null granulation tissue when immunostained with a monoclonal antibody that recognizes all muscle actin isoforms exhibited a myofibroblast-like distribution and a stress fiber-like pattern, showing that these cells acquired the myofibroblast phenotype. Dermal fibroblasts from smooth muscle α-actin-null and wild-type mice formed stress fibers and supermature focal adhesions, and generated similar amounts of contractile force in response to transforming growth factor-β1. Smooth muscle γ-actin and skeletal muscle α-actin were expressed in smooth muscle α-actin-null myofibroblasts, as shown by immunostaining, real-time polymerase chain reaction, and mass spectrometry. These results show that smooth muscle α-actin is not necessary for myofibroblast formation and function and for wound closure, and that smooth muscle γ-actin and skeletal muscle α-actin may be able to functionally compensate for the lack of smooth muscle α-actin in myofibroblasts.

The role of the tumor microenvironment in regulating angiogenesis

The tumor-associated stroma has been shown to play a significant role in cancer formation. Paracrine signaling interactions between epithelial tumor cells and stromal cells are a key component in the transformation and proliferation of tumors in several organs. Whereas the intracellular signaling pathways regulating the expression of several pro- and antiangiogenic proteins have been well characterized in human cancer cells, the intercellular signaling that takes place between tumor cells and the surrounding tumor-associated stroma has not been as extensively studied with regard to the regulation of angiogenesis. In this chapter we define the key players in the regulation of angiogenesis and examine how their expression is regulated in the tumor-associated stroma. The resulting analysis is often seemingly paradoxical, underscoring the complexity of intercellular signaling within tumors and the need to better understand the environmental context underlying these signaling mechanisms.

The actin-MRTF-SRF gene regulatory axis and myofibroblast differentiation

Cardiac fibroblasts are responsible for necrotic tissue replacement and scar formation after myocardial infarction (MI) and contribute to remodeling in response to pathological stimuli. This response to insult or injury is largely due to the phenotypic plasticity of fibroblasts. When fibroblasts encounter environmental disturbances, whether biomechanical or humoral, they often transform into smooth muscle-like, contractile cells called "myofibroblasts." The signals that control myofibroblast differentiation include the transforming growth factor (TGF)-β1-Smad pathway and Rho GTPase-dependent actin polymerization. Recent evidence implicates serum response factor (SRF) and the myocardin-related transcription factors (MRTFs) as key mediators of the contractile gene program in response to TGF-β1 or RhoA signaling. This review highlights the function of myofibroblasts in cardiac remodeling and the role of the actin-MRTF-SRF signaling axis in regulating this process.

CCR2 recruits an inflammatory macrophage subpopulation critical for angiogenesis in tissue repair

Monocytes/macrophages are critical in orchestrating the tissue-repair response. However, the mechanisms that govern macrophage regenerative activities during the sequential phases of repair are largely unknown. In the present study, we examined the dynamics and functions of diverse monocyte/macrophage phenotypes during the sequential stages of skin repair. By combining the analysis of a new CCR2-eGFP reporter mouse model with conditional mouse mutants defective in myeloid cell-restricted CCR2 signaling or VEGF-A synthesis, we show herein that among the large number of inflammatory CCR2(+)Ly6C(+) macrophages that dominate the early stage of repair, only a small fraction strongly expresses VEGF-A that has nonredundant functions for the induction of vascular sprouts. The switch of macrophage-derived VEGF-A during the early stage of tissue growth toward epidermal-derived VEGF-A during the late stage of tissue maturation was critical to achieving physiologic tissue vascularization and healing progression. The results of the present study provide new mechanistic insights into CCR2-mediated recruitment of blood monocyte subsets into damaged tissue, the dynamics and functional consequences of macrophage plasticity during the sequential repair phases, and the complementary role of macrophage-derived VEGF-A in coordinating effective tissue growth and vascularization in the context of tissue-resident wound cells. Our findings may be relevant for novel monocyte-based therapies to promote tissue vascularization.

β-catenin and Smad3 regulate the activity and stability of myocardin-related transcription factor during epithelial-myofibroblast transition

Two novel mechanisms are shown by which injury of intercellular junctions via β-catenin promotes epithelial–myofibroblast transition. β-Catenin interacts with Smad3, thereby preventing the inhibitory effect of the latter on myocardin-related transcription factor (MRTF), and maintains MRTF stability by inhibiting Smad3-mediated, GSK-3β–dependent degradation of MRTF.

Injury to the adherens junctions (AJs) synergizes with transforming growth factor-β1 (TGFβ) to activate a myogenic program (α-smooth muscle actin [SMA] expression) in the epithelium during epithelial–myofibroblast transition (EMyT). Although this synergy plays a key role in organ fibrosis, the underlying mechanisms have not been fully defined. Because we recently showed that Smad3 inhibits myocardin-related transcription factor (MRTF), the driver of the SMA promoter and many other CC(A/T)-rich GG element (CArG) box–dependent cytoskeletal genes, we asked whether AJ components might affect SMA expression through interfering with Smad3. We demonstrate that E-cadherin down-regulation potentiates, whereas β-catenin knockdown inhibits, SMA expression. Contact injury and TGFβ enhance the binding of β-catenin to Smad3, and this interaction facilitates MRTF signaling by two novel mechanisms. First, it inhibits the Smad3/MRTF association and thereby allows the binding of MRTF to its myogenic partner, serum response factor (SRF). Accordingly, β-catenin down-regulation disrupts the SRF/MRTF complex. Second, β-catenin maintains the stability of MRTF by suppressing the Smad3-mediated recruitment of glycogen synthase kinase-3β to MRTF, an event that otherwise leads to MRTF ubiquitination and degradation and the consequent loss of SRF/MRTF–dependent proteins. Thus β-catenin controls MRTF-dependent transcription and emerges as a critical regulator of an array of cytoskeletal genes, the “CArGome.”

Myocardin-related transcription factors A and B are key regulators of TGF-β1-induced fibroblast to myofibroblast differentiation

Myofibroblasts are contractile, smooth muscle-like cells that are characterized by the de novo expression of smooth muscle α-actin (SMαA) and normally function to assist in wound closure, but have been implicated in pathological contractures. Transforming growth factor β-1 (TGF-β1) helps facilitate the differentiation of fibroblasts into myofibroblasts, but the exact mechanism by which this differentiation occurs, in response to TGF-β1, remains unclear. Myocardin-related transcription factors A and B (MRTFs, MRTF-A/B) are transcriptional co-activators that regulate the expression of smooth muscle-specific cytoskeletal proteins, including SMαA, in smooth muscle cells and fibroblasts. In this study, we demonstrate that TGF-β1 mediates myofibroblast differentiation and the expression of a contractile gene program through the actions of the MRTFs. Transient transfection of a constitutively active MRTF-A induced an increase in the expression of SMαA and other smooth muscle-specific cytoskeletal proteins, and an increase in myofibroblast contractility, even in the absence of TGF-β1. MRTF-A/B knockdown, in TGF-β1-differentiated myofibroblasts, resulted in decreased smooth muscle-specific cytoskeletal protein expression levels and reduced contractile force generation, as well as a decrease in focal adhesion size and number. These results provide direct evidence that the MRTFs are mediators of myofibroblast differentiation in response to TGF-β1.

Regulation of Epithelial-Mesenchymal Transition by Transmission of Mechanical Stress through Epithelial Tissues

Epithelial-mesenchymal transition (EMT) is a phenotypic shift wherein epithelial cells lose or loosen attachments to their neighbors and assume a mesenchymal-like morphology. EMT drives a variety of developmental processes, but may also be adopted by tumor cells during neoplastic progression. EMT is regulated by both biochemical and physical signals from the microenvironment, including mechanical stress, which is increasingly recognized to play a major role in development and disease progression. Biological systems generate, transmit and concentrate mechanical stress into spatial patterns; these gradients in mechanical stress may serve to spatially pattern developmental and pathologic EMTs. Here we review how epithelial tissues generate and respond to mechanical stress gradients, and highlight the mechanisms by which mechanical stress regulates and patterns EMT.