The effect of myofibroblast on contracture of hypertrophic scar

Wound contraction in humans has both positive and negative effects. It is beneficial to wound healing by narrowing the wound margins, but the formation of undesirable scar contracture brings cosmetic and even functional problems. The entire mechanism of wound healing and scar contracture is not clear yet, but it is at least considered that both the fibroblasts and the myofibroblasts are responsible for contraction in healing wounds. The myofibroblast is a cell that possesses all the morphologic and biochemical characteristics of both a fibroblast and a smooth muscle cell. Normally, the myofibroblasts appear in the initial wound healing processes and generate contractile forces to pull both edges of an open wound until it disappears by apoptosis. But as an altered regulation of myofibroblast disappearance, they remain in the dermis and continuously contract the scar, eventually causing scar contracture. In this research, to compare and directly evaluate the influence on scar contracture of the myofibroblast versus the fibroblast, dermal tissues were taken from 10 patients who had highly contracted hypertrophic scars. The myofibroblasts were isolated and concentrated from the fibroblasts using the magnetic activating cell-sorting column to obtain the myofibroblast group, which contained about 28 to 41 percent of the myofibroblasts, and the fibroblast group, which contained less than 0.9 percent of the myofibroblasts. Each group was cultured in the fibroblast-populated collagen lattice for 13 days, and the contraction of the collagen gel was measured every other day. In addition, they were selectively treated with tranilast [N-(3',4'-dimethoxycinnamoyl) anthranilic acid] to evaluate the influence on the contraction of the collagen gel lattice. During the culture, the myofibroblast group, compared with the fibroblast group, showed statistically significant contraction of the collagen gel lattice day by day, except on the first day, and only the myofibroblast group was affected by tranilast treatment, showing significant inhibition of gel contraction. By utilizing an in vitro model, the authors have demonstrated that myofibroblasts play a more important role in the contracture of the hypertrophic scar.     

The stroma reaction myofibroblast: a key player in the control of tumor cell behavior

The cooperation between epithelial and mesenchymal cells is essential for embryonic development and probably plays an important role in pathological phenomena such as wound healing and tumor progression. It is well known that many epithelial tumors are characterized by the local accumulation of connective tissue cells and extracellular material; this phenomenon has been called the stroma reaction. One of the cellular components of the stroma reaction is the myofibroblast, a modulated fibroblast which has acquired the capacity to neoexpress alpha-smooth muscle actin, the actin isoform typical of vascular smooth muscle cells, and to synthesize important amounts of collagen and other extracellular matrix components. It is now well accepted that the myofibroblast is a key cell for the connective tissue remodeling which takes place during wound healing and fibrosis development. Myofibroblasts are capable of remodeling connective tissue but also interact with epithelial cells and other connective tissue cells and may thus control such phenomena as tumor invasion and angiogenesis. In this review we discuss the mechanisms of myofibroblast evolution during fibrotic and malignant conditions and the interaction of myofibroblasts with other cells in order to control tumor progression. On this basis we suggest that the myofibroblast may represent a new important target of antitumor therapy.     

Effect of nitric oxide on the differentiation of fibroblasts into myofibroblasts in the Peyronie’s fibrotic plaque and in its rat model

The myofibroblast shares phenotypic features of both fibroblasts and smooth muscle cells. It plays a critical role in collagen deposition and wound healing and disappears by apoptosis when the wound is closed. Its abnormal persistence leads to hypertrophic scar formation and other fibrotic conditions. Myofibroblasts are present in the fibrotic plaque of the tunica albuginea (TA) of the penis in men with Peyronie's disease (PD), a localized fibrosis that is accompanied by a spontaneous induction of the inducible nitric oxide synthase (iNOS), also observed in the TGFbeta1-elicited, PD-like lesion in the rat model. iNOS expression counteracts fibrosis, by producing nitric oxide (NO) that reduces collagen deposition in part by neutralization of profibrotic reactive oxygen species. In this study we investigated whether fibroblast differentiation into myofibroblasts is enhanced in the human and rat PD-like plaque and in cultures of human tissue fibroblasts. We also examined whether NO reduces this cell differentiation and collagen synthesis. The myofibroblast content in the fibroblast population was measured by quantitative immunohistochemistry as the ratio between alpha-smooth muscle actin (ASMA; myofibroblast marker) and vimentin (general fibroblast marker) levels. We found that myofibroblast content was considerably increased in the human and TGFbeta1-induced rat plaques as compared to control TA. Inhibition of iNOS activity by chronic administration of L-iminoethyl-L-lysine to rats with TGFbeta1-induced TA lesion increased myofibroblast abundance and collagen I synthesis measured in plaque and TA homogenates from animals injected with a collagen I promoter construct driving the expression of beta-galactosidase. Fibroblast differentiation into myofibroblasts occurred with passage in the cell cultures from the human PD plaque, but was minimal in cultures from the TA. Induction of iNOS in PD and TA cultures with a cytokine cocktail and a NO donor, S-nitroso-N-acetyl penicillamine (SNAP), was detected by immunohistochemistry. Both treatments reduced the total number of cells and the number of ASMA positive cells, whereas only SNAP decreased collagen I immunostaining. These results support the hypotheses that myofibroblasts play a role in the development of the PD plaque and that the antifibrotic effects of NO may be mediated at least in part by the reduction of myofibroblast abundance and lead to a reduction in collagen I synthesis.     

TGFβ signaling and the control of myofibroblast differentiation: Implications for chronic inflammatory disorders

The myofibroblast is a highly specialized cell type that plays a critical role during normal tissue wound healing, but also contributes pathologically to chronic inflammatory conditions such as fibrosis and cancer. As fibrotic conditions continue to be a major burden to the public health system, novel therapies that target the function of myofibroblasts may show promise in the clinic. The cytokine transforming growth factor β (TGFβ) is the most potent known inducer of myofibroblast differentiation and thus represents a powerful target to modify myofibroblast function during disease. This review focuses on our current understanding of the key signaling pathways activated by TGFβ during myofibroblast differentiation.     

Normal skin wound and hypertrophic scar myofibroblasts have differential responses to apoptotic inductors

During wound healing, myofibroblasts play a central role in matrix formation and wound contraction. At the end of healing, there is evidence that myofibroblasts disappear via apoptotic pathways. Hypertrophic scars are a fibroproliferative disorder that leads to considerable morbidity. It has been postulated that a defect in myofibroblast apoptosis could be responsible for the pathological scar formation, but no evidence exists. We have isolated and cultured human normal wound (Wmyo) and hypertrophic scar (Hmyo) myofibroblasts and compared their basal apoptotic rates and their sensitivity to serum starvation and Fas antibody-induced apoptosis to that obtained for dermal fibroblasts (Fb). A higher rate of apoptosis as evidenced by morphological criteria and a propidium iodide assay was observed for Wmyo in comparison to Fb and Hmyo. These results came along with a low level of the anti-apoptotic proteins Bcl-2 and Bclx(L) in Wmyo, whereas there was an increase in the level of the pro-apoptotic molecule Bax when compared to the results obtained for Fb and Hmyo. Hmyo showed a higher level of Bcl-2 compared to Fb but no difference in the Bax or Bclx(L) level. After serum starvation, Wmyo revealed an increased apoptotic rate, whereas Hmyo and Fb did not show any difference. Anti-Fas treatment did not modify the levels of apoptosis but strongly increased the cell growth of Hmyo as compared to Wmyo. This is the first study presenting a broad vision of the apoptotic sensitivity of normal and pathological myofibroblasts. These results confirmed the hypothesis of defects in apoptosis and growth during pathological scar formation impeding myofibroblast disappearance at the end of healing.     

Fibroblast Growth Factor 2 as an Antifibrotic: Antagonism of Myofibroblast Differentiation and Suppression of Pro-Fibrotic Gene Expression

Fibrosis is a pathological condition that is characterized by the replacement of dead or damaged tissue with a nonfunctional, mechanically aberrant scar, and fibrotic pathologies account for nearly half of all deaths worldwide. The causes of fibrosis differ somewhat from tissue to tissue and pathology to pathology, but in general some of the cellular and molecular mechanisms remain constant regardless of the specific pathology in question. One of the common mechanisms underlying fibroses is the paradigm of the activated fibroblast, termed the “myofibroblast,” a differentiated mesenchymal cell with demonstrated contractile activity and a high rate of collagen deposition. Fibroblast growth factor 2 (FGF2), one of the members of the mammalian fibroblast growth factor family, is a cytokine with demonstrated antifibrotic activity in non-human animal, human, and in vitro models. FGF2 is highly pleiotropic and its receptors are present on many different cell types throughout the body, lending a great deal of variety to the potential mechanisms of FGF2 effects on fibrosis. However, recent reports demonstrate that a substantial contribution to the antifibrotic effects of FGF2 comes from the inhibitory effects of FGF2 on connective tissue fibroblasts, activated myofibroblasts, and myofibroblast progenitors. FGF2 demonstrates effects antagonistic towards fibroblast activation and towards mesenchymal transition of potential myofibroblast-forming cells, as well as promotes a gene expression paradigm more reminiscent of regenerative healing, such as that which occurs in the fetal wound healing response, than fibrotic resolution. With a better understanding of the mechanisms by which FGF2 alters the wound healing cascade and results in a shift away from scar formation and towards functional tissue regeneration, we may be able to further address the critical need of therapy for varied fibrotic pathologies across myriad tissue types.     

Keratocyte phenotype mediates proteoglycan structure: a role for fibroblasts in corneal fibrosis

In pathological corneas, accumulation of fibrotic extracellular matrix is characterized by proteoglycans with altered glycosaminoglycans that contribute to the reduced transparency of scarred tissue. During wound healing, keratocytes in the corneal stroma transdifferentiate into fibroblasts and myofibroblasts. In this study, molecular markers were developed to identify keratocyte, fibroblast, and myofibroblast phenotypes in primary cultures of corneal stromal cells and the structure of glycosaminoglycans secreted by these cells was characterized. Quiescent primary keratocytes expressed abundant protein and mRNA for keratocan and aldehyde dehydrogenase class 3 and secreted proteoglycans containing macromolecular keratan sulfate. Expression of these marker compounds was reduced in fibroblasts and also in transforming growth factor-beta-induced myofibroblasts, which expressed high levels of alpha-smooth muscle actin, biglycan, and the extra domain A (EDA or EIIIA) form of cellular fibronectin. Collagen types I and III mRNAs were elevated in both fibroblasts and in myofibroblasts. Expression of these molecular markers clearly distinguishes the phenotypic states of stromal cells in vitro. Glycosaminoglycans secreted by fibroblasts and myofibroblasts were qualitatively similar to and differed from those of keratocytes. Chondroitin/dermatan sulfate abundance, chain length, and sulfation were increased as keratocytes became fibroblasts and myofibroblasts. Fluorophore-assisted carbohydrate electrophoresis analysis demonstrated increased N-acetylgalactosamine sulfation at both 4- and 6-carbons. Hyaluronan, absent in keratocytes, was secreted by fibroblasts and myofibroblasts. Keratan sulfate biosynthesis, chain length, and sulfation were significantly reduced in both fibroblasts and myofibroblasts. The qualitatively similar expression of glycosaminoglycans shared by fibroblasts and myofibroblasts suggests a role for fibroblasts in deposition of non-transparent fibrotic tissue in pathological corneas.     

Coordinate expression of NGF and α-smooth muscle actin mRNA and protein in cutaneous wound tissue of developing and adult rats

Nerve growth factor (NGF) is synthesized in cutaneous wound tissue, and its higher levels in the neonate may contribute to more efficient wound healing. We used in situ hybridization and immunohistochemistry to define NGF mRNA and protein expression in intact skin and following excision wounding in neonatal and adult rats. To determine whether NGF is associated with wound contractile fibroblasts (myofibroblasts), we also examined expression of !-smooth muscle actin (!-SMA) mRNA and protein, established markers for these cells. In intact skin, NGF mRNA and protein were present in vascular and arrector pili smooth muscle, hair follicle sheath cells, keratinocytes, and hypodermal fibroblasts. Neonatal adipocytes and Schwann cells also expressed NGF mRNA and protein, while adult adipocytes and Schwann cells displayed only NGF-ir. Following wounding, NGF mRNA expression was exuberant in these cell types, and increased similarly at both ages and appeared de novo in skeletal muscle cells. Additionally, both NGF mRNA and protein were present in macrophages and myofibroblasts, and expression in myofibroblasts was significantly greater in neonates. Wound myofibroblasts also expressed !-SMA. Surprisingly, after wounding !-SMA mRNA and protein were present in essentially all cells in which NGF mRNA was detected. We conclude that NGF expression is enhanced in many cell types after wounding, but greater NGF synthesis in neonates appears to be due to a more robust myofibroblast response. In addition, cell types which demonstrated NGF mRNA also expressed !-SMA, and staining for both markers increased following wounding, suggesting synthesis of both proteins is regulated in a coordinated fashion.     

Sensitivity of myofibroblasts to H2O2-mediated apoptosis and their antioxidant cell network

During wound healing, the transition from granulation to scar tissue shows a decrease in myofibroblast cellularity. Previous results have correlated the disappearance of these cells with the induction of apoptotic cell death by some unknown stimuli. In contrast, hypertrophic scar appearance after wound healing is thought to be linked to a disorder of apoptotic function which induces myofibroblast persistence in granulation tissue. Oxidative stress being an important mediator of apoptosis, we have evaluated the apoptotic response of normal and pathological wound myofibroblasts (WMyo and HMyo respectively) in their interaction with two oxidative stress inducers: hydrogen peroxide, using a high concentration as a single dose, and sodium ascorbate which induced a continuous release of H2O2 at a low concentration. Our results showed that, according to the H2O2 treatment type, HMyo were more sensitive (after ascorbate treatment) or less sensitive (after H2O2 treatment) when compared to WMyo and Fb. We next assessed the presence of several molecules known to be involved in the antioxidant network protecting cells against H2O2 injury and found HMyo to have a higher level of activity of glutathione peroxidase and a lower level of activity of catalase than WMyo. These results can help explain the contradictory responses of myofibroblasts according to the oxidative stress treatment. This is the first study linking refractory oxidative stress mediated cell death to cellular phenotype in hypertrophic myofibroblasts, and indicates a pivotal role for the antioxidant enzyme system in this type of resistance.     

Transforming growth factor-beta 1 induces alpha-smooth muscle actin expression in granulation tissue myofibroblasts and in quiescent and growing cultured fibroblasts

Granulation tissue fibroblasts (myofibroblasts) develop several ultrastructural and biochemical features of smooth muscle (SM) cells, including the presence of microfilament bundles and the expression of alpha-SM actin, the actin isoform typical of vascular SM cells. Myofibroblasts have been proposed to play a role in wound contraction and in retractile phenomena observed during fibrotic diseases. We show here that the subcutaneous administration of transforming growth factor- beta 1 (TGF beta 1) to rats results in the formation of a granulation tissue in which alpha-SM actin expressing myofibroblasts are particularly abundant. Other cytokines and growth factors, such as platelet-derived growth factor and tumor necrosis factor-alpha, despite their profibrotic activity, do not induce alpha-SM actin in myofibroblasts. In situ hybridization with an alpha-SM actin probe shows a high level of alpha-SM actin mRNA expression in myofibroblasts of TGF beta 1-induced granulation tissue. Moreover, TGF beta 1 induces alpha-SM actin protein and mRNA expression in growing and quiescent cultured fibroblasts and preincubation of culture medium containing whole blood serum with neutralizing antibodies to TGF beta 1 results in a decrease of alpha-SM actin expression by fibroblasts in replicative and non-replicative conditions. These results suggest that TGF beta 1 plays an important role in myofibroblast differentiation during wound healing and fibrocontractive diseases by regulating the expression of alpha-SM actin in these cells.     

Reversible differentiation of myofibroblasts by MyoD

Myofibroblasts participate in tissue repair processes in diverse mammalian organ systems. The deactivation of myofibroblasts is critical for termination of the reparative response and restoration of tissue structure and function. The current paradigm on normal tissue repair is the apoptotic clearance of terminally differentiated myofibroblasts; while, the accumulation of activated myofibroblasts is associated with progressive human fibrotic disorders. The capacity of myofibroblasts to undergo de-differentiation as a potential mechanism for myofibroblast deactivation has not been examined. In this report, we have uncovered a role for MyoD in the induction of myofibroblast differentiation by transforming growth factor-β1 (TGF-β1). Myofibroblasts demonstrate the capacity for de-differentiation and proliferation by modulation of endogenous levels of MyoD. We propose a model of reciprocal signaling between TGF-β1/ALK5/MyoD and mitogen(s)/ERK-MAPK/CDKs that regulate myofibroblast differentiation and de-differentiation, respectively. Our studies provide the first evidence for MyoD in controlling myofibroblast activation and deactivation. Restricted capacity for de-differentiation of myofibroblasts may underlie the progressive nature of recalcitrant human fibrotic disorders.     

Factors influencing myofibroblast differentiation during wound healing and fibrosis.

Granulation tissue fibroblasts (myofibroblasts) develop several ultrastructural and biochemical features of smooth muscle (SM) cells, including the presence of microfilaments bundles and the expression of α-SM actin, the actin isoform typical of contractile vascular SM cells. Myofibroblasts have been suggested to play a role in wound contraction and in retractile phenomena observed during fibrotic diseases. When granulation tissue evolves into a scar, myofibroblasts containing α-SM actin disappear, probably as a result of apoptosis. In contrast, myofibroblasts expressing α-SM actin persist in excessive scarring and in fibrotic conditions. The mechanisms leading to the development of myofibroblastic features remain to be investigated. Studies on the factors regulating the phenotype of myofibroblasts will be necessary for understanding their behavior in vivo, and possibly modifying this behavior during the different clinical settings.     

Urokinase receptor cleavage: a crucial step in fibroblast-to-myofibroblast differentiation

Fibroblasts migrate into and repopulate connective tissue wounds. At the wound edge, fibroblasts differentiate into myofibroblasts, and they promote wound closure. Regulated fibroblast-to-myofibroblast differentiation is critical for regenerative healing. Previous studies have focused on the role in fibroblasts of urokinase plasmingen activator/urokinase plasmingen activator receptor (uPA/uPAR), an extracellular protease system that promotes matrix remodeling, growth factor activation, and cell migration. Whereas fibroblasts have substantial uPA activity and uPAR expression, we discovered that cultured myofibroblasts eventually lost cell surface uPA/uPAR. This led us to investigate the relevance of uPA/uPAR activity to myofibroblast differentiation. We found that fibroblasts expressed increased amounts of full-length cell surface uPAR (D1D2D3) compared with myofibroblasts, which had reduced expression of D1D2D3 but increased expression of the truncated form of uPAR (D2D3) on their cell surface. Retaining full-length uPAR was found to be essential for regulating myofibroblast differentiation, because 1) protease inhibitors that prevented uPAR cleavage also prevented myofibroblast differentiation, and 2) overexpression of cDNA for a noncleavable form of uPAR inhibited myofibroblast differentiation. These data support a novel hypothesis that maintaining full-length uPAR on the cell surface regulates the fibroblast to myofibroblast transition and that down-regulation of uPAR is necessary for myofibroblast differentiation.     

Differential and combined effects of cardiotrophin-1 and TGF-beta1 on cardiac myofibroblast proliferation and contraction

Myofibroblasts respond to an array of signals from mitogens and cytokines during the course of wound healing following a myocardial infarction (MI), and these signals may coordinate ventricular myofibroblast proliferation. Furthermore, myofibroblasts are contractile and contribute to wound contraction by imparting mechanical tension on surrounding extracellular matrix. Although TGF-beta(1), CT-1, and PDGF-BB participate in various stages of post-MI wound healing, their combined net effect(s) on myofibroblast function is unknown. We investigated myofibroblast proliferation, expression of cell cycle proteins, and contractile function of cells treated with TGF-beta(1) and/or CT-1. We confirmed that TGF-beta(1) (10 ng/ml) suppresses proliferation of these cells, whereas CT-1 (10 ng/ml) and, for comparative purposes, PDGF-BB (1 ng/ml) treatments were associated with proliferation. Specific TGF-beta(1) treatment ablated CT-1-induced myofibroblast proliferation. TGF-beta(1) effects were specific, as they were suppressed by either TGF-beta-neutralizing antibody or viral Smad7 overexpression. TGF-beta(1) treatment also increased expression of p27 and decreased expression of cyclin E and Cdk2 in primary cells. CT-1 (10 ng/ml) treatment of myofibroblasts had no effect on collagen gel deformation versus controls, whereas TGF-beta(1) (10 ng/ml) and PDGF (10 ng/ml) treatments were associated with significant cell contraction; again, TGF-beta(1)-mediated contraction was unaffected by CT-1. Alone, CT-1 and TGF-beta(1) treatments exert opposing effects on myofibroblast function, whereas in combination TGF-beta(1)-mediated effects supersede those of CT-1 (and PDGF-BB). Thus TGF-beta(1) and CT-1 exert differential effects on myofibroblast proliferation and contraction in vitro, and we suggest that a balance of these effects may be important for the execution of normal cardiac wound healing.     

Effects of the isothiocyanate sulforaphane on TGF-β1-induced rat cardiac fibroblast activation and extracellular matrix interactions

An important step in many pathological conditions, particularly tissue and organ fibrosis, is the conversion of relatively quiescent cells into active myofibroblasts. These are highly specialized cells that participate in normal wound healing but also contribute to pathogenesis. These cells possess characteristics of smooth muscle cells and fibroblasts, have enhanced synthetic activity secreting abundant extracellular matrix components, cytokines, and growth factors, and are capable of generating contractile force. As such, these cells have become potential therapeutic targets in a number of disease settings. Transforming growth factor β (TGF-β) is a potent stimulus of fibrosis and myofibroblast formation and likewise is an important therapeutic target in several disease conditions. The plant-derived isothiocyanate sulforaphane has been shown to have protective effects in several pathological models including diabetic cardiomyopathy, carcinogenesis, and fibrosis. These studies suggest that sulforaphane may be an attractive preventive agent against disease progression, particularly in conditions involving alterations of the extracellular matrix and activation of myofibroblasts. However, few studies have evaluated the effects of sulforaphane on cardiac fibroblast activation and their interactions with the extracellular matrix. The present studies were carried out to determine the potential effects of sulforaphane on the conversion of quiescent cardiac fibroblasts to an activated myofibroblast phenotype and associated alterations in signaling, expression of extracellular matrix receptors, and cellular physiology following stimulation with TGF-β1. These studies demonstrate that sulforaphane attenuates TGF-β1-induced myofibroblast formation and contractile activity. Sulforaphane also reduces expression of collagen-binding integrins and inhibits canonical and noncanonical TGF-β signaling pathways.     

P311-induced myofibroblasts exhibit ameboid-like migration through RalA activation

We previously showed that P311, an intracellular protein involved in cell migration, is found in human wound myofibroblast precursors (proto-myofibroblasts) and myofibroblasts. Furthermore, by binding to the TGF-beta1 latency associated protein (LAP), P311 induced NIH 3T3 cells to transform into non-fibrogenic myofibroblasts characterized by lack of TGF-beta1 production. Here we demonstrate that P311-induced myofibroblasts migrate in an ameboid rather than a mesenchymal pattern. Ameboid migration is characterized by lack of focal adhesions and stress fibers, absence of integrins and MMPs clustering/activation and changes in small GTPases activity, all leading to increased cell motility. P311-induced ameboid migration depended on activation of the GTPase RalA and was reverted to mesenchymal-type migration by RalA RNA interference. Ameboid migration was conserved in cells plated on fibrin, the initial wound matrix, but was switched back to mesenchymal-type migration by collagen I, the main ECM component in late stages of wound healing. TGF-beta1, the major stimulus of collagen production during wound repair, also reversed the ameboid phenotype to mesenchymal. Our studies therefore suggest that, by inducing RalA activity, P311 promotes a motile proto-myofibroblast and myofibroblast phenotype specifically adapted to rapidly populate the initial wound matrix.     

Lysophosphatidic acid accelerates lung fibrosis by inducing differentiation of mesenchymal stem cells into myofibroblasts

Lung fibrosis is characterized by vascular leakage and myofibroblast recruitment, and both phenomena are mediated by lysophosphatidic acid (LPA) via its type‐1 receptor (LPA1). Following lung damage, the accumulated myofibroblasts activate and secrete excessive extracellular matrix (ECM), and form fibrotic foci. Studies have shown that bone marrow‐derived cells are an important source of myofibroblasts in the fibrotic organ. However, the type of cells in the bone marrow contributing predominantly to the myofibroblasts and the involvement of LPA‐LPA1 signalling in this is yet unclear. Using a bleomycin‐induced mouse lung‐fibrosis model with an enhanced green fluorescent protein (EGFP) transgenic mouse bone marrow replacement, we first demonstrated that bone marrow derived‐mesenchymal stem cells (BMSCs) migrated markedly to the bleomycin‐injured lung. The migrated BMSC contributed significantly to α‐smooth muscle actin (α‐SMA)‐positive myofibroblasts. By transplantation of GFP‐labelled human BMSC (hBMSC) or EGFP transgenic mouse BMSC (mBMSC), we further showed that BMSC might be involved in lung fibrosis in severe combined immune deficiency (SCID)/Beige mice induced by bleomycin. In addition, using quantitative‐RT‐PCR, western blot, Sircol collagen assay and migration assay, we determined the underlying mechanism was LPA‐induced BMSC differentiation into myofibroblast and the secretion of ECM via LPA1. By employing a novel LPA1 antagonist, Antalpa1, we then showed that Antalpa1 could attenuate lung fibrosis by inhibiting both BMSC differentiation into myofibroblast and the secretion of ECM. Collectively, the above findings not only further validate LPA1 as a drug target in the treatment of pulmonary fibrosis but also elucidate a novel pathway in which BMSCs contribute to the pathologic process.     

LEP and LEPR are possibly a double-edged sword for wound healing

Wound healing is a complex and error-prone process. Wound healing in adults often leads to the formation of scars, a type of fibrotic tissue that lacks skin appendages. Hypertrophic scars and keloids can also form when the wound-healing process goes wrong. Leptin (Lep) and leptin receptors (LepRs) have recently been shown to affect multiple stages of wound healing. This effect, however, is paradoxical for scarless wound healing. On the one hand, Lep exerts pro-inflammatory and profibrotic effects; on the other hand, Lep can regulate hair follicle growth. This paper summarises the role of Lep and LepRs on cells in different stages of wound healing, briefly introduces the process of wound healing and Lep and LepRs, and examines the possibility of promoting scarless wound healing through spatiotemporal, systemic, and local regulation of Lep levels and the binding of Lep and LepRs.     

Hyaluronan in intestinal homeostasis and inflammation: implications for fibrosis

The causes of fibrosis, or the inappropriate wound healing, that follows chronic intestinal inflammation are not well defined and likely involve the contributions of multiple cellular mechanisms. As other articles in this series confirm, inflammatory cytokines clearly play a role in driving cell differentiation to the myofibroblast phenotype, promoting proliferation and extracellular matrix deposition that are characteristic of fibrotic tissue. However, controlling the balance of cytokines produced and process of myofibroblast differentiation appears to be more complex. This review considers ways in which hyaluronan, an extracellular matrix component that is remodeled during the progression of colitis, may provide indirect as well as direct cues that influence the balancing act of intestinal wound healing.     

LIM-domain proteins in transforming growth factor β-induced epithelial-to-mesenchymal transition and myofibroblast differentiation

Epithelial to mesenchymal transition (EMT) is a process during which junctions of the cell-cell contacts are dissolved, actin cytoskeleton is deformed, apical-basolateral cell polarity is lost and cell motility is increased. EMT is needed during normal embryonal development and wound healing, but may also lead to pathogenic transformation and formation of myofibroblasts. Transforming growth factor β (TGFβ) is a multifunctional cytokine promoting EMT and myofibroblast differentiation, and its dysregulation is involved in pathological disorders like cancer and fibrosis. Lin11, Isl-1 and Mec-3 (LIM) domain proteins are associated with actin cytoskeleton and linked to regulation of cell growth, damage signaling, cell fate determination and signal transduction. LIM-domain proteins generally do not bind DNA, but are more likely to function via protein-protein interactions. Despite being a disparate group of proteins, similarities in their functions are observed. In this review we will discuss the role of LIM-domain proteins in TGFβ-signaling pathway and in EMT-driven processes. LIM-domain proteins regulate TGFβ-induced actin cytoskeleton reorganization, motility and adhesion, but also dissolution of cell-cell junctions during EMT. Finally, the role of LIM-domain proteins in myofibroblasts found in fibrotic foci and tumor stroma will be discussed.