Formation and function of the myofibroblast during tissue repair

Plasminogen activator inhibitor-1 regulates integrin alphavbeta3 expression and autocrine transforming growth factor beta signaling

Fibrosis is characterized by elevated transforming growth factor beta (TGFbeta) signaling, resulting in extracellular matrix accumulation and increased PAI-1 (plasminogen activator inhibitor) expression. PAI-1 induces the internalization of urokinase plasminogen activator/receptor and integrin alphavbeta3 from the cell surface. Since increased alphavbeta3 expression correlates with increased TGFbeta signaling, we hypothesized that aberrant PAI-1-mediated alphavbeta3 endocytosis could initiate an autocrine loop of TGFbeta activity. We found that in PAI-1 knock-out (KO) mouse embryonic fibroblasts), alphavbeta3 endocytosis was reduced by approximately 75%, leaving alphavbeta3 in enlarged focal adhesions, similar to wild type cells transfected with PAI-1 small interfering RNA. TGFbeta signaling was significantly enhanced in PAI-1 KO cells, as demonstrated by a 3-fold increase in SMAD2/3-containing nuclei and a 2.9-fold increase in TGFbeta activity that correlated with an increase in alphavbeta3 and TGFbeta receptor II expression. As expected, PAI-1 KO cells had unregulated plasmin activity, which was only partially responsible for TGFbeta activation, as evidenced by a mere 25% reduction in TGFbeta activity when plasmin was inhibited. Treatment of cells with an alphavbeta3-specific cyclic RGD peptide (GpenGRGD) led to a more profound (59%) TGFbeta inhibition; a nonspecific RGD peptide (GRGDNP) inhibited TGFbeta by only 23%. Human primary fibroblasts were used to confirm that PAI-1 inhibition and beta3 overexpression led to an increase in TGFbeta activity. Consistent with a fibrotic phenotype, PAI-1 KO cells were constitutively myofibroblasts that had a 1.6-fold increase in collagen deposition over wild type cells. These data suggest that PAI-1-mediated regulation of alphavbeta3 integrin is critical for the control of TGFbeta signaling and the prevention of fibrotic disease.

The extracellular matrix as a modulator of the inflammatory and reparative response following myocardial infarction

The dynamic alterations in the cardiac extracellular matrix following myocardial infarction not only determine the mechanical properties of the infarcted heart, but also directly modulate the inflammatory and reparative response. During the inflammatory phase of healing, rapid activation of Matrix Metalloproteinases (MMP) causes degradation of the cardiac extracellular matrix. Matrix fragments exert potent pro-inflammatory actions, while MMPs process cytokines and chemokines altering their biological activity. In addition, vascular hyperpermeability results in extravasation of fibronectin and fibrinogen leading to formation of a plasma-derived provisional matrix that serves as a scaffold for leukocyte infiltration. Clearance of the infarct from dead cells and matrix debris is essential for resolution of inflammation and marks the transition to the proliferative phase. The fibrin-based provisional matrix is lysed and cellular fibronectin is secreted. ED-A fibronectin, mechanical tension and Transforming Growth Factor (TGF)-beta are essential for modulation of fibroblasts into myofibroblasts, the main collagen-secreting cells in the wound. The matricellular proteins thrombospondin-1 and -2, osteopontin, tenascin-C, periostin, and secreted protein acidic and rich in cysteine (SPARC) are induced in the infarct regulating cellular interactions and promoting matrix organization. As the infarct matures, matrix cross-linking results in formation of a dense collagen-based scar. At this stage, shielding of fibroblasts from external mechanical tension by the mature matrix network may promote deactivation and cellular quiescence. The components of the extracellular matrix do not passively follow the pathologic alterations of the infarcted heart but critically modulate inflammatory and reparative pathways by transducing signals that affect cell survival, phenotype and gene expression.

Periostin differentially induces proliferation, contraction and apoptosis of primary Dupuytren's disease and adjacent palmar fascia cells

Dupuytren's disease, (DD), is a fibroproliferative condition of the palmar fascia in the hand, typically resulting in permanent contracture of one or more fingers. This fibromatosis is similar to scarring and other fibroses in displaying excess collagen secretion and contractile myofibroblast differentiation. In this report we expand on previous data demonstrating that POSTN mRNA, which encodes the extra-cellular matrix protein periostin, is up-regulated in Dupuytren's disease cord tissue relative to phenotypically normal palmar fascia. We demonstrate that the protein product of POSTN, periostin, is abundant in Dupuytren's disease cord tissue while little or no periostin immunoreactivity is evident in patient-matched control tissues. The relevance of periostin up-regulation in DD was assessed in primary cultures of cells derived from diseased and phenotypically unaffected palmar fascia from the same patients. These cells were grown in type-1 collagen-enriched culture conditions with or without periostin addition to more closely replicate the in vivo environment. Periostin was found to differentially regulate the apoptosis, proliferation, alpha smooth muscle actin expression and stressed Fibroblast Populated Collagen Lattice contraction of these cell types. We hypothesize that periostin, secreted by disease cord myofibroblasts into the extra-cellular matrix, promotes the transition of resident fibroblasts in the palmar fascia toward a myofibroblast phenotype, thereby promoting disease progression.

Characterization of DLK1+ cells emerging during skeletal muscle remodeling in response to myositis, myopathies, and acute injury

Delta like 1 (DLK1) has been proposed to act as a regulator of cell fate determination and is linked to the development of various tissues including skeletal muscle. Herein we further investigated DLK1 expression during skeletal muscle remodeling. Although practically absent in normal adult muscle, DLK1 was upregulated in all human myopathies analyzed, including Duchenne- and Becker muscular dystrophies. Substantial numbers of DLK1(+) satellite cells were observed in normal neonatal and Duchenne muscle, and furthermore, myogenic DLK1(+) cells were identified during muscle regeneration in animal models in which the peak expression of Dlk1 mRNA and protein coincided with that of myoblast differentiation and fusion. In addition to perivascular DLK1(+) cells, interstitial DLK1(+) cells were numerous in regenerating muscle, and in agreement with colocalization studies of DLK1 and CD90/DDR2, qPCR of fluorescence-activated cell sorting DLK1(+) and DLK1(-) cells revealed that the majority of DLK1(+) cells isolated at day 7 of regeneration had a fibroblast-like phenotype. The existence of different DLK1(+) populations was confirmed in cultures of primary derived myogenic cells, in which large flat nonmyogenic DLK1(+) cells and small spindle-shaped cells coexpressing DLK1 and muscle-specific markers were observed. Myogenic differentiation was achieved when sorted DLK1(+) cells were cocultured together with primary myoblasts revealing a myogenic potential that was 10% of the DLK1(-) population. Transplantation of DLK1(+) cells into lacerated muscle did, however, not give rise to DLK1(+) cell-derived myofibers. We suggest that the DLK1(+) subpopulations identified herein each may contribute at different levels/time points to the processes involved in muscle development and remodeling.

Periostin localizes to cells in normal skin, but is associated with the extracellular matrix during wound repair

Epidermal tissue repair represents a complex series of temporal and dynamic events resulting in wound closure. Matricellular proteins, not normally expressed in quiescent adult tissues, play a pivotal role in wound repair and associated extracellular matrix remodeling by modulating the adhesion, migration, intracellular signaling, and gene expression of inflammatory cells, pericytes, fibroblasts and keratinocytes. Several matricellular proteins show temporal expression during dermal wound repair, but the expression pattern of the recently identified matricellular protein, periostin, has not yet been characterized. The primary aim of this study was to assess whether periostin protein is present in healthy human skin or in pathological remodeling (Nevus). The second aim was to determine if periostin is expressed during dermal wound repair. Using immunohistochemistry, periostin reactivity was detected in the keratinocytes, basal lamina, and dermal fibroblasts in healthy human skin. In pathological nevus samples, periostin was present in the extracellular matrix. In excisional wounds in mice, periostin protein was first detected in the granulation tissue at day 3, with levels peaking at day 7. Periostin protein co-localized with α-smooth muscle actin-positive cells and keratinocytes, but not CD68 positive inflammatory cells. We conclude that periostin is normally expressed at the cellular level in human and murine skin, but additionally becomes extracellular during tissue remodeling. Periostin may represent a new therapeutic target for modulating the wound repair process.

Inflammation recapitulates the ontogeny of lymphoid stromal cells

Stromal cells in lymphoid tissues regulate lymphocyte recruitment and survival through the expression of specific chemokines and cytokines. During inflammation, the same signals recruit lymphocytes to the site of injury; however, the "lymphoid" stromal (LS) cells producing these signals remain poorly characterized. We find that mouse inflammatory lesions and tumors develop gp38(+) LS cells, in recapitulation of the development of LS cells early during the ontogeny of lymphoid organs and the intestine, and express a set of genes that promotes the development of lymphocyte-permissive tissues. These gp38(+) LS cells are induced by a robust pathway that requires myeloid cells but not known Toll- or NOD-like receptors, the inflammasome, or adaptive immunity. Parabiosis and inducible genetic cell fate mapping experiments indicate that local precursors, presumably resident fibroblasts rather that circulating precursors, massively proliferate and give rise to LS cells during inflammation. Our results show that LS cells are both programmed during ontogeny and reinduced during inflammation.

A transgenic mouse model of inducible macrophage depletion: effects of diphtheria toxin-driven lysozyme M-specific cell lineage ablation on wound inflammatory, angiogenic, and contractive processes

Whether the wound macrophage is a key regulatory inflammatory cell type in skin repair has been a matter of debate. A transgenic mouse model mediating inducible macrophage depletion during skin repair has not been used to date to address this question. Here, we specifically rendered the monocyte/macrophage leukocyte lineage sensitive to diphtheria toxin by expressing the lysozyme M promoter-driven, Cre-mediated excision of a transcriptional STOP cassette from the simian DT receptor gene in mice (lysM-Cre/DTR). Application of diphtheria toxin to lysM-Cre/DTR mice led to a rapid reduction in both skin tissue and wound macrophage numbers at sites of injury. Macrophage-depleted mice revealed a severely impaired wound morphology and delayed healing. In the absence of macrophages, wounds were re-populated by large numbers of neutrophils. Accordingly, macrophage-reduced wound tissues exhibited the increased and prolonged persistence of macrophage inflammatory protein-2, macrophage chemoattractant protein-1, interleukin-1beta, and cyclooxygenase-2, paralleled by unaltered levels of bioactive transforming growth factor-beta1. Altered expression patterns of vascular endothelial growth factor on macrophage reduction were associated with a disturbed neo-vascularization at the wound site. Impaired wounds revealed a loss of myofibroblast differentiation and wound contraction. Our data in the use of lysM-Cre/DTR mice emphasize the pivotal function of wound macrophages in the integration of inflammation and cellular movements at the wound site to enable efficient skin repair.

Emerging concepts in the pathogenesis of lung fibrosis

Fibrogenesis is an often-deadly process with increasing world-wide incidence and limited therapeutic options. Pulmonary fibrogenesis involves remodeling of the distal airspace and parenchyma of the lung, and is characterized by excessive extracellular matrix deposition and accumulation of apoptosis-resistant myofibroblasts. Recent studies have added significantly to our understanding of the complex mechanisms involved in lung fibrogenesis. Emerging concepts in this field include the critical role of the epithelium, particularly type II pneumocytes, in the initiation and perpetuation of fibrosis in response to either endogenous or exogenous stress; a growing awareness of alternative activation of macrophages in tissue remodeling; growing appreciation of the alternative origins and phenotypic plasticity of fibroblasts; the roles of epigenetic reprogramming and context-dependent signaling in profibrotic phenotype alterations; and recognition of the importance of cross talk and convergence of intracellular signaling pathways. In vitro, in vivo, and in silico approaches support a paradigm of "disordered re-development" of the lung. Designing effective antifibrotic interventions will require accurate understanding of the complex interactions among the genetic, environmental, epigenetic, biochemical, cellular, and contextual abnormalities that promote pulmonary fibrogenesis.

Biomarkers for epithelial-mesenchymal transitions

Somatic cells that change from one mature phenotype to another exhibit the property of plasticity. It is increasingly clear that epithelial and endothelial cells enjoy some of this plasticity, which is easily demonstrated by studying the process of epithelial-mesenchymal transition (EMT). Published reports from the literature typically rely on ad hoc criteria for determining EMT events; consequently, there is some uncertainty as to whether the same process occurs under different experimental conditions. As we discuss in this Personal Perspective, we believe that context and various changes in plasticity biomarkers can help identify at least three types of EMT and that using a collection of criteria for EMT increases the likelihood that everyone is studying the same phenomenon - namely, the transition of epithelial and endothelial cells to a motile phenotype.

Beta-catenin and transforming growth factor beta have distinct roles regulating fibroblast cell motility and the induction of collagen lattice contraction

Background

β-catenin and transforming growth factor β signaling are activated in fibroblasts during wound healing. Both signaling pathways positively regulate fibroblast proliferation during this reparative process, and the effect of transforming growth factor β is partially mediated by β-catenin. Other cellular processes, such as cell motility and the induction of extracellular matrix contraction, also play important roles during wound repair. We examined the function of β-catenin and its interaction with transforming growth factor β in cell motility and the induction of collagen lattice contraction.

Results

Floating three dimensional collagen lattices seeded with cells expressing conditional null and stabilized β-catenin alleles, showed a modest negative relationship between β-catenin level and the degree of lattice contraction. Transforming growth factor β had a more dramatic effect, positively regulating lattice contraction. In contrast to the situation in the regulation of cell proliferation, this effect of transforming growth factor β was not mediated by β-catenin. Treating wild-type cells or primary human fibroblasts with dickkopf-1, which inhibits β-catenin, or lithium, which stimulates β-catenin produced similar results. Scratch wound assays and Boyden chamber motility studies using these same cells found that β-catenin positively regulated cell motility, while transforming growth factor β had little effect.

Conclusion

This data demonstrates the complexity of the interaction of various signaling pathways in the regulation of cell behavior during wound repair. Cell motility and the induction of collagen lattice contraction are not always coupled, and are likely regulated by different intracellular mechanisms. There is unlikely to be a single signaling pathway that acts as master regulator of fibroblast behavior in wound repair. β-catenin plays dominant role regulating cell motility, while transforming growth factor β plays a dominant role regulating the induction of collagen lattice contraction.

3D collagen cultures under well-defined dynamic strain: a novel strain device with a porous elastomeric support

The field of mechanobiology has grown tremendously in the past few decades, and it is now well accepted that dynamic stresses and strains can impact cell and tissue organization, cell-cell and cell-matrix communication, matrix remodeling, cell proliferation and apoptosis, cell migration, and many other cell behaviors in both physiological and pathophysiological situations. Natural reconstituted matrices like collagen and fibrin are often used for three-dimensional (3D) mechanobiology studies because they naturally form fibrous architectures and are rich in cell adhesion sites; however, they are physically weak and typically contain >99% water, making it difficult to apply dynamic stresses to them in a truly 3D context. Here we present a composite matrix and strain device that can support natural matrices within a macroporous elastic structure of polyurethane. We characterize this system both in terms of its mechanical behavior and its ability to support the growth and in vivo-like behaviors of primary human lung fibroblasts cultured in collagen. The porous polyurethane was created with highly interconnected pores in the hundreds of microm size scale, so that while it did not affect cell behavior in the collagen gel within the pores, it could control the overall elastic behavior of the entire tissue culture system. In this way, a well-defined dynamic strain could be imposed on the 3D collagen and cells within the collagen for several days (with elastic recoil driven by the polyurethane) without the typical matrix contraction by fibroblasts when cultured in 3D collagen gels. We show lung fibroblast-to-myofibroblast differentiation under 30%, 0.1 Hz dynamic strain to validate the model and demonstrate its usefulness for a wide range of tissue engineering applications.

Dextranomer/hyaluronic Acid copolymer implant for vesicoureteral reflux: role of myofibroblast differentiation

PURPOSE

Dextranomer/hyaluronic acid implantation is associated with a granulomatous inflammatory reaction, replaced by fibrosis. Appearance of myofibroblasts is considered a crucial event in fibrosis, and CD68 positive cells and other factors are implied in their activation. Mast cells are a source of these factors and tryptase can induce fibroblast to express alpha-smooth muscle actin, which is characteristic of myofibroblasts. We evaluated histological changes in refluxing ureters treated with dextranomer/hyaluronic acid and immunolocalized CD68 positive cells, tryptase mast cells and myofibroblasts.

MATERIALS AND METHODS

We performed histological, histochemical and immunohistochemical analyses in 22 refluxing ureters treated with dextranomer/hyaluronic acid in comparison with 17 refluxing ureters who underwent ureteral reimplantation but did not receive endoscopic bulking agent. We used CD68 antibody for monocytes/macrophages and epithelioid cells, mast cell tryptase mouse antibody for mast cells, and alpha-smooth muscle actin and vimentin antibodies for myofibroblasts. The area of the ureteral lumen in dextranomer/hyaluronic acid treated and untreated ureteral endings was measured.

RESULTS

Sirius red documented a major grade of histological lesions in dextranomer/hyaluronic acid treated refluxing ureters. CD68 and tryptase mast cell staining showed a significant enhancement of positive cells in dextranomer/hyaluronic acid treated refluxing ureters. Immunostaining for alpha-smooth muscle actin and vimentin displayed a myofibroblastic invasion in dextranomer/hyaluronic acid. Measurement of surface in treated refluxing ureters was significantly less than in untreated refluxing ureters.

CONCLUSIONS

Our data documented a recruitment of CD68 and tryptase positive cells, abnormal accumulation of collagenous stroma and successive extracellular matrix remodeling through differentiation of myofibroblasts. Myofibroblasts might provoke tissue contraction, decreasing the ureteral diameter and modifying the ureteral length-to-diameter ratio, preventing urine reflux.

Expression profiles in surgically-induced carotid stenosis: a combined transcriptomic and proteomic investigation

Vascular injury aimed at stenosis removal induces local reactions often leading to restenosis. The aim of this study was a concerted transcriptomic-proteomics analysis of molecular variations in a model of rat carotid arteriotomy, to dissect the molecular pathways triggered by vascular surgical injury and to identify new potential anti-restenosis targets. RNA and proteins extracted from inbred Wistar Kyoro (WKY) rat carotids harvested 4 hrs, 48 hrs and 7 days after arteriotomy were analysed by Affymetrix rat microarrays and by bidimensional electrophoresis followed by liquid chromatography and tandem mass spectrometry, using as reference the RNA and the proteins extracted from uninjured rat carotids. Results were classified according to their biological function, and the most significant Kyoro Encyclopedia of Genes and Genomes (KEGG) pathways were identified. A total of 1163 mRNAs were differentially regulated in arteriotomy-injured carotids 4 hrs, 48 hrs and 7 days after injury (P < 0.0001, fold-change > or =2), while 48 spots exhibited significant changes after carotid arteriotomy (P < 0.05, fold-change > or =2). Among them, 16 spots were successfully identified and resulted to correspond to a set of 19 proteins. mRNAs were mainly involved in signal transduction, oxidative stress/inflammation and remodelling, including many new potential targets for limitation of surgically induced (re)stenosis (e.g. Arginase I, Kruppel like factors). Proteome analysis confirmed and extended the microrarray data, revealing time-dependent post-translational modifications of Hsp27, haptoglobin and contrapsin-like protease inhibitor 6, and the differential expression of proteins mainly involved in contractility. Transcriptomic and proteomic methods revealed functional categories with different preferences, related to the experimental sensitivity and to mechanisms of regulation. The comparative analysis revealed correlation between transcriptional and translational expression for 47% of identified proteins. Exceptions from this correlation confirm the complementarities of these approaches.

Enhanced focal adhesion assembly reflects increased mechanosensation and mechanotransduction at maternal–conceptus interface and uterine wall during ovine pregnancy

The integrity of the fetal–maternal interface is critical for proper fetal nourishment during pregnancy. Integrins are important adhesion molecules present at the interface during implantation; however,in vivoevidence for integrin activation and focal adhesion formation at the maternal–conceptus interface is limited. We hypothesized that focal adhesion assembly in uterine luminal epithelium (LE) and conceptus trophectoderm (Tr) results from integrin binding of extracellular matrix (ECM) at this interface to provide increased tensile forces and signaling to coordinate utero-placental development. An ovine model of unilateral pregnancy was used to evaluate mechanotransduction events leading to focal adhesion assembly at the maternal–conceptus interface and within the uterine wall. Animals were hysterectomized on days 40, 80, or 120 of pregnancy, and uteri immunostained for integrins (ITGAV, ITGA4, ITGA5, ITGB1, ITGB3, and ITGB5), ECM proteins (SPP1, LGALS15, fibronectin (FN), and vitronectin (VTN)), cytoskeletal molecules (ACTN and TLN1), and a signal generator (PTK2). Focal adhesion assembly in myometrium and stroma was also studied to provide a frame of reference for mechanical stretch of the uterine wall. Large focal adhesions containing aggregates of ITGAV, ITGA4, ITGA5, ITGB1, ITGB5, ACTN, and PTK2 were detected in interplacentomal uterine LE and Tr of gravid but not non-gravid uterine horns and increased during pregnancy. SPP1 and LGALS15, but not FN or VTN, were present along LE and Tr interfaces in both uterine horns. These data support the idea that focal adhesion assembly at the maternal–conceptus interface reflects adaptation to increasing forces caused by the growing fetus. Cooperative binding of multiple integrins to SPP1 deposited at the maternal–conceptus interface forms an adhesive mosaic to maintain a tight connection between uterine and placental surfaces along regions of epitheliochorial placentation in sheep.

Changes in surgical anatomy following thyroidectomy

Thyroid reoperation is known to carry a higher risk for complications because of the increased challenge of identifying tissue planes, presence of adherent strap muscles, and generalized scarring of the thyroid bed. Consideration of postsurgical changes in the anatomy of important landmarks, such as the recurrent and superior laryngeal nerves, brachiocephalic artery, and parathyroid glands, is crucial during preoperative planning for thyroid reoperations. This article provides a review of these key changes in surgical anatomy and the implications of the anatomic changes after thyroidectomy.

Distinct roles for mammalian target of rapamycin complexes in the fibroblast response to transforming growth factor-beta

Transforming growth factor-beta (TGF-beta) promotes a multitude of diverse biological processes, including growth arrest of epithelial cells and proliferation of fibroblasts. Although the TGF-beta signaling pathways that promote inhibition of epithelial cell growth are well characterized, less is known about the mechanisms mediating the positive response to this growth factor. Given that TGF-beta has been shown to promote fibrotic diseases and desmoplasia, identifying the fibroblast-specific TGF-beta signaling pathways is critical. Here, we investigate the role of mammalian target of rapamycin (mTOR), a known effector of phosphatidylinositol 3-kinase (PI3K) and promoter of cell growth, in the fibroblast response to TGF-beta. We show that TGF-beta activates mTOR complex 1 (mTORC1) in fibroblasts but not epithelial cells via a PI3K-Akt-TSC2-dependent pathway. Rapamycin, the pharmacologic inhibitor of mTOR, prevents TGF-beta-mediated anchorage-independent growth without affecting TGF-beta transcriptional responses or extracellular matrix protein induction. In addition to mTORC1, we also examined the role of mTORC2 in TGF-beta action. mTORC2 promotes TGF-beta-induced morphologic transformation and is required for TGF-beta-induced Akt S473 phosphorylation but not mTORC1 activation. Interestingly, both mTOR complexes are necessary for TGF-beta-mediated growth in soft agar. These results define distinct and overlapping roles for mTORC1 and mTORC2 in the fibroblast response to TGF-beta and suggest that inhibitors of mTOR signaling may be useful in treating fibrotic processes, such as desmoplasia.

Integrin alpha1beta1 is involved in the differentiation into myofibroblasts in adult reactive tissues in vivo

Connective tissue cell activation is of importance during reactive conditions such as solid tumour growth, wound healing and pannus formation in rheumatoid arthritis. Here, we have compared connective tissue cells of mesenchymal origin in human tissues from these conditions and their normal counterparts using a panel of cell-type-specific markers. In particular, we investigated variations of integrin expression among connective tissue cell phenotypes. Connective tissue cell populations were defined based on their association with the microvasculature and their expression of activation markers. The phenotype of these cells varied according to the type of pathological connective tissue examined. Our morphological data from human tissues suggested that the alpha(1)beta(1) integrin, a collagen/laminin receptor, is involved in the differentiation of precursor cells into myofibroblasts. To mechanistically investigate this hypothesis, we employed experimental models for carcinoma growth and wound healing utilizing alpha(1) integrin-deficient mice. The data confirmed that the alpha(1)beta(1) integrin is of importance not only for the differentiation of mesenchymal cells into myofibroblasts but also for the neovascularization and connective tissue organization and emphasize the importance of myofibroblasts in the pathophysiology of tissue repair, inflammation and tumour growth.

Human female hair follicles are a direct, nonclassical target for thyroid-stimulating hormone

Pituitary thyroid-stimulating hormone (TSH) regulates thyroid hormone synthesis via receptors (TSH-R) expressed on thyroid epithelial cells. As the hair follicle (HF) is uniquely hormone-sensitive and, hypothyroidism with its associated, increased TSH serum levels clinically can lead to hair loss, we asked whether human HFs are a direct target for TSH. Here, we report that normal human scalp skin and microdissected human HFs express TSH-R mRNA. TSH-R-like immunoreactivity is limited to the mesenchymal skin compartments in situ. TSH may alter HF mesenchymal functions, as it upregulates alpha-smooth muscle actin expression in HF fibroblasts. TSH-R stimulation by its natural ligand in organ culture changes the expression of several genes of human scalp HFs (for example keratin K5), upregulates the transcription of classical TSH target genes and enhances cAMP production. Although the functional role of TSH in human HF biology awaits further dissection, these findings document that intracutaneous TSH-Rs are fully functional in situ and that HFs of female individuals are direct targets for nonclassical, extrathyroidal TSH bioregulation. This suggests that organ-cultured scalp HFs provide an instructive and physiologically relevant human model for exploring nonclassical functions of TSH, in and beyond the skin.

Deep dermal fibroblasts contribute to hypertrophic scarring

Hypertrophic scar (HTS) following thermal injury is a dermal fibroproliferative disorder that leads to considerable morbidity. The development of HTS involves numerous cell types and cytokines with dermal fibroblasts being a key cell. We have previously reported that the phenotype of fibroblasts isolated from HTS was altered compared to fibroblasts from normal skin. In this study, normal skin was horizontally sectioned into five layers using a dermatome from which fibroblasts were isolated and cultured. Cells from the deeper layers were observed to proliferate at a slow rate, but were morphologically larger. In ELISA and FACS assays, cells from the deeper layers produced more TGF-beta1 and TGF-beta1 producing cells were higher. In quantitative RT-PCR, the cells from the deeper layers had higher CTGF and HSP47 mRNA levels compared to those from superficial layers. In western blot, FACS and collagen gel assays, fibroblasts from the deeper layers produced more alpha-smooth muscle actin (alpha-SMA), had higher alpha-SMA positive cells and contracted collagen gels more. Fibroblasts from the deeper layers were also found to produce more collagen, but less collagenase by mass spectrometry and collagenase assay. Interestingly, cells from the deeper layers also produced more of the proteoglycan, versican, but less decorin. Taken together, these data strongly demonstrate that fibroblasts from the deeper layers of the dermis resemble HTS fibroblasts, suggesting that the deeper layer fibroblasts may be critical in the formation of HTS.

Differential gene expression in a coculture model of angiogenesis reveals modulation of select pathways and a role for Notch signaling

Communication between endothelial and mural cells (smooth muscle cells, pericytes, and fibroblasts) can dictate blood vessel size and shape during angiogenesis, and control the functional aspects of mature blood vessels, by determining things such as contractile properties. The ability of these different cell types to regulate each other's activities led us to ask how their interactions directly modulate gene expression. To address this, we utilized a three-dimensional model of angiogenesis and screened for genes whose expression was altered under coculture conditions. Using a BeadChip array, we identified 323 genes that were uniquely regulated when endothelial cells and mural cells (fibroblasts) were cultured together. Data mining tools revealed that differential expression of genes from the integrin, blood coagulation, and angiogenesis pathways were overrepresented in coculture conditions. Scans of the promoters of these differentially modulated genes identified a multitude of conserved C promoter binding factor (CBF)1/CSL elements, implicating Notch signaling in their regulation. Accordingly, inhibition of the Notch pathway with gamma-secretase inhibitor DAPT or NOTCH3-specific small interfering RNA blocked the coculture-induced regulation of several of these genes in fibroblasts. These data show that coculturing of endothelial cells and fibroblasts causes profound changes in gene expression and suggest that Notch signaling is a critical mediator of the resultant transcription.

The expression and potential regulatory function of microRNAs in the pathogenesis of leiomyoma

Leiomyomas are benign uterine tumors considered to arise from transformation of myometrial cells. What initiates the conversion of myometrial cells into leiomyoma is unknown, however cytogenetic analysis often shows occurrence of nonrandom chromosomal abnormalities that may account for their establishment. It is clear that ovarian steroids are essential for leiomyoma growth, and local expression of many autocrine/paracrine mediators serving as key regulators of cell-cycle progression, cellular hypertrophy, extracellular matrix accumulation, and apoptosis appear to play central roles in this capacity. However, the stability of the expression of these genes represents the hallmarks of leiomyoma establishment, growth, and regression. With the emergence of microRNA (miRNA) as a key regulator of gene expression stability, in this review we present evidence for the expression and potential regulatory functions on miRNAs in leiomyoma with particular emphasis on the expression of their selective target genes whose products influence various cellular activities critical to pathogenesis of leiomyomas.

Potential cellular and molecular causes of hypertrophic scar formation

A scar is an expected result of wound healing. However, in some individuals, and particularly in burn victims, the wound healing processes may lead to a fibrotic hypertrophic scar, which is raised, red, inflexible and responsible for serious functional and cosmetic problems. It seems that a wide array of subsequent processes are involved in hypertrophic scar formation, like an affected haemostasis, exaggerated inflammation, prolonged reepithelialization, overabundant extracellular matrix production, augmented neovascularization, atypical extracellular matrix remodeling and reduced apoptosis. Platelets, macrophages, T-lymphocytes, mast cells, Langerhans cells and keratinocytes are directly and indirectly involved in the activation of fibroblasts, which in turn produce excess extracellular matrix. Following the chronology of normal wound healing, we unravel, clarify and reorganize the complex molecular and cellular key processes that may be responsible for hypertrophic scars. It remains unclear whether these processes are a cause or a consequence of unusual scar tissue formation, but raising evidence exists that immunological responses early following wounding play an important role. Therefore, when developing preventive treatment modalities, one should aim to put the early affected wound healing processes back on track as quickly as possible.

Stromal myofibroblasts are drivers of invasive cancer growth

Tissue integrity is maintained by the stroma in physiology. In cancer, however, tissue invasion is driven by the stroma. Myofibroblasts and cancer-associated fibroblasts are important components of the tumor stroma. The origin of myofibroblasts remains controversial, although fibroblasts and bone marrow-derived precursors are considered to be the main progenitor cells. Myofibroblast reactions also occur in fibrosis. Therefore, we wonder whether nontumorous myofibroblasts have different characteristics and different origins as compared to tumor-associated myofibroblasts. The mutual interaction between cancer cells and myofibroblasts is dependent on multiple invasive growth-promoting factors, through direct cell-cell contacts and paracrine signals. Since fibrosis is a major side effect of radiotherapy, we address the question how the main methods of cancer management, including chemotherapy, hormonotherapy and surgery affect myofibroblasts and by inference the surrogate endpoints invasion and metastasis.

Burn healing is dependent on burn site: a quantitative analysis from a porcine burn model

This retrospective review examines healing in different sites on a porcine burn model; 24 pairs of burns on 18 pigs from other animal trials were selected for analysis. Each pair of burns was located on the either the cranial or the caudal part of the thoracic ribs region, on the same side of the animal. The burns were 40-50 cm(2) in size and of uniform deep-dermal partial thickness. Caudal burns healed significantly better than cranial burns, demonstrated by earlier closure of wounds, less scar formation and better cosmesis. To our knowledge, this is the first detailed study reporting that burn healing is affected by location on a porcine burn model. We recommend that similar symmetrical burns should be used for future comparative assessments of burn healing.

Nemosis of fibroblasts is inhibited by benign HaCaT keratinocytes but promoted by malignant HaCaT cells

Cell-cell clustering of fibroblasts, called nemosis, leads to a massive growth factor, proteolytic and proinflammatory response. Culturing fibroblasts in conditioned medium collected from HaCaT keratinocyte cell panel representing different stages of skin carcinogenesis had a differential effect on fibroblast nemosis. Non-malignant keratinocytes had a nemosis-inhibiting effect on fibroblasts as seen by inhibition of COX-2 protein expression. Conditioned medium from malignant cells promoted fibroblast nemosis by inducing higher levels of COX-2, HGF/SF and VEGF. Even a small amount of malignant medium converted the inhibitory effect of benign medium, whereas non-malignant medium neutralized the nemosis-promoting effect of malignant medium. In collagen co-cultures benign keratinocytes caused a nemosis-inhibiting effect on fibroblast spheroids by inhibiting COX-2 induction, while with malignant keratinocytes myofibroblastic differentiation of fibroblasts was seen.

Myofibroblast communication is controlled by intercellular mechanical coupling

Neoformation of intercellular adherens junctions accompanies the differentiation of fibroblasts into contractile myofibroblasts, a key event during development of fibrosis and in wound healing. We have previously shown that intercellular mechanical coupling of stress fibres via adherens junctions improves contraction of collagen gels by myofibroblasts. By assessing spontaneous intracellular Ca2+ oscillations, we here test whether adherens junctions mechanically coordinate myofibroblast activities. Periodic Ca2+ oscillations are synchronised between physically contacting myofibroblasts and become desynchronised upon dissociation of adherens junctions with function-blocking peptides. Similar uncoupling is obtained by inhibiting myofibroblast contraction using myosin inhibitors and by blocking mechanosensitive ion channels using Gd3+ and GSMTx4. By contrast, gap junction uncouplers do not affect myofibroblast coordination. We propose the following model of mechanical coupling for myofibroblasts: individual cell contraction is transmitted via adherens junctions and leads to the opening of mechanosensitive ion channels in adjacent cells. The resulting Ca2+ influx induces a contraction that can feed back on the first cell and/or stimulate other contacting cells. This mechanism could improve the remodelling of cell-dense tissue by coordinating the activity of myofibroblasts.

Carcinogenesis induced by foreign bodies

This review deals with the contemporary investigations of carcinogenesis induced by foreign bodies. The main attention is given to the interactions of macrophages with an implanted foreign body and their possible role in tumorigenesis.

Hepatic fibrogenesis in response to chronic liver injury: novel insights on the role of cell-to-cell interaction and transition

Hepatic fibrosis represents the wound-healing response process of the liver to chronic injury, independently from aetiology. Advanced liver fibrosis results in cirrhosis that can lead to liver failure, portal hypertension and hepatocellular carcinoma. Currently, no effective therapies are available for hepatic fibrosis. After the definition of hepatic stellate cells (HSCs) as the main liver extracellular matrix-producing cells in the 1980s, the subsequent decade was dedicated to determine the role of specific cytokines and growth factors. Fibrotic progression of chronic liver diseases can be nowadays considered as a dynamic and highly integrated process of cellular response to chronic liver injury. The present review is dedicated to the novel mechanisms of cellular response to chronic liver injury leading to hepatic myofibroblasts' activation. The understanding of the cellular and molecular pathways regulating their function is crucial to counteract therapeutically the organ dysfunction caused by myofibroblasts' activation.

TLR9 is expressed in idiopathic interstitial pneumonia and its activation promotes in vitro myofibroblast differentiation

Infectious diseases can be cofactors in idiopathic interstitial pneumonias (IIP) pathogenesis; recent data suggests that toll-like receptors 9 (TLR9) ligands contribute to experimental chronic tissue remodeling. Real-time TAQMAN and immunohistochemical analysis of IIP normal surgical lung biopsies (SLBs), primary fibroblast lines grown from both IIP and normal SLBs indicate that TLR9 is prominently and differentially expressed in a disease-specific manner. TLR9 expression was increased in biopsies from patients with IIP compared with normal lung biopsies and its expression is localized to areas of marked interstitial fibrosis. TLR9 in fibroblasts appeared to be increased by profibrotic Th2 cytokines (IL-4 and IL-13) and this was true in fibroblasts cultured from the most severe form of IIP, idiopathic pulmonary fibrosis (IPF) SLBs, in non-specific interstitial pneumonia fibroblast lines, and in normal fibroblasts. Finally, confocal microscopy studies have shown that TLR9 activation by its synthetic agonist CpG-ODN significantly increased the expression of alpha smooth muscle actin, the main marker of myofibroblast differentiation. These data indicate that TLR9 expression may drive the abnormal tissue healing response in severe forms of IIP and its activation can have a key role in myofibroblast differentiation promoting the progression of disease during the terminal phase of IPF.

The renal cortical interstitium: morphological and functional aspects

The renal interstitial compartment, situated between basement membranes of epithelia and vessels, contains two contiguous cellular networks. One network is formed by interstitial fibroblasts, the second one by dendritic cells. Both are in intimate contact with each other. Fibroblasts are interconnected by junctions and connected to basement membranes of vessels and tubules by focal adhesions. Fibroblasts constitute the “skeleton” of the kidney. In the renal cortex, fibroblasts produce erythropoietin and are distinguished from other interstitial cells by their prominent F-actin cytoskeleton, abundance of rough endoplasmic reticulum, and by ecto-5′-nucleotidase expression in their plasma membrane. The resident dendritic cells belong to the mononuclear phagocyte system and fulfil a sentinel function. They are characterized by their expression of MHC class II and CD11c. The central situation of fibroblasts suggests that signals from tubules, vessels, and inflammatory cells converge in fibroblasts and elicit an integrated response. Following tubular damage and inflammatory signals fibroblasts proliferate, change to the myofibroblast phenotype and increase their collagen production, potentially resulting in renal fibrosis. The acquisition of a profibrotic phenotype by fibroblasts in renal diseases is generally considered a main causal event in the progression of chronic renal failure. However, it might also be seen as a repair process.

The synthetic peroxisome proliferator-activated receptor-gamma agonist ciglitazone attenuates neuroinflammation and accelerates encapsulation in bacterial brain abscesses

Brain abscesses result from a pyogenic parenchymal infection commonly initiated by Gram-positive bacteria such as Staphylococcus aureus. Although the host immune response elicited following infection is essential for effective bacterial containment, this response also contributes to the significant loss of brain parenchyma by necrosis that may be reduced by modulating the inflammatory response. Ciglitazone, a PPAR-gamma agonist with anti-inflammatory properties, was evaluated for its ability to influence the course of brain abscess development when treatment was initiated 3 days following infection. Interestingly, abscess-associated bacterial burdens were significantly lower following ciglitazone administration, which could be explained, in part, by the finding that ciglitazone enhanced S. aureus phagocytosis by microglia. In addition, ciglitazone attenuated the expression of select inflammatory mediators during brain abscess development including inducible NO synthase, TNF-alpha, IL-1beta, CXCL2, and CCL3. Unexpectedly, ciglitazone also accelerated brain abscess encapsulation, which was typified by the heightened expression of fibronectin and alpha-smooth muscle actin-positive myofibroblasts. Collectively, through its ability to attenuate excessive inflammation and accelerate abscess encapsulation, ciglitazone may effectively sequester brain abscesses and limit bacterial dissemination.

Myofibroblasts work best under stress

Myofibroblasts are reparative connective tissue cells that contribute to the reconstruction of injured tissue by secreting new extracellular matrix and by exerting high contractile force. Deregulation of these activities results in tissue contracture and development of fibrosis which makes the myofibroblast an important target for anti-fibrotic therapies. Two principle factors drive the development of myofibroblasts from different precursor cells and guarantee maintenance of the contractile phenotype: mechanical stress and transforming growth factor beta (TGFbeta1). In this mini-review, we recapitulate the current understanding (1) of how myofibroblasts feel stress using specialized matrix adhesions, (2) of the level of stress that is required to induce their development and (3) of how myofibroblast mechanical activity can have a direct influence on the level of TGFbeta1 activation. From these findings it emerges that the specific matrix adhesion structures of myofibroblasts are promising targets to modulate myofibroblast differentiation and activity.

Pharmacological blockade of A2A receptors prevents dermal fibrosis in a model of elevated tissue adenosine

Adenosine is a potent modulator of inflammation and tissue repair. We have recently reported that activation of adenosine A(2A) receptors promotes collagen synthesis by human dermal fibroblasts and that blockade or deletion of this receptor in mice protects against bleomycin-induced dermal fibrosis, a murine model of scleroderma. Adenosine deaminase (ADA) is the principal catabolic enzyme for adenosine in vivo, and its deficiency leads to the spontaneous development of pulmonary fibrosis in mice. The aim of this study was to characterize further the contributions of endogenous adenosine and adenosine A(2A) receptors to skin fibrosis. Taking advantage of genetically modified ADA-deficient mice, we herein report a direct fibrogenic effect of adenosine on the skin, in which increased collagen deposition is accompanied by increased levels of key mediators of fibrosis, including transforming growth factor beta1, connective tissue growth factor, and interleukin-13. Pharmacological treatment of ADA-deficient mice with the A(2A) receptor antagonist ZM-241385 prevented the development of dermal fibrosis in this model of elevated tissue adenosine, by reducing dermal collagen content and expression of profibrotic cytokines and growth factors. These data confirm a fibrogenic role for adenosine in the skin and reveal A(2A) receptor antagonists as novel therapeutic agents for the modulation of dermal fibrotic disorders.

Gadodiamide contrast agent 'activates' fibroblasts: a possible cause of nephrogenic systemic fibrosis

Nephrogenic systemic fibrosis (NSF) is a fibrotic disease generating intense interest due to its recent discovery, and unknown cause. It appears confined to patients with renal disease and presents as grossly thickened, indurated, tight skin that is woody to palpation. Histologically, the dermis contains thickened collagen bundles, numerous plump fibroblast-like cells, and elevated hyaluronan expression. Recent data suggest a link between the use of gadolinium chelate as an MRI contrast agent and the onset of the disease. Fibroblasts from the lesions of six NSF patients, all of whom were exposed to gadodiamide, were compared with control fibroblasts for hyaluronan and collagen synthesis. Serum from NSF patients was assessed for fibroblast hyaluronan-stimulating activity, collagen synthesis, and gadodiamide for its effect on fibroblast proliferation and matrix synthesis. NSF fibroblasts synthesized excess levels of hyaluronan and collagen compared with control fibroblasts, with up to 2.8-fold and 3.3-fold increases, respectively. NSF patient serum stimulated control fibroblast hyaluronan synthesis by up to 7-fold, and collagen synthesis by up to 2.4-fold. 1 mM gadodiamide added to culture medium stimulated fibroblast growth in a dose-dependent manner, decreasing their doubling time from 28 h to 22 h, and increasing the maximum cell density. Even a short exposure to gadodiamide stimulated cell growth, suggesting that the cells were activated by the gadodiamide. The growth of fibroblasts within contracted collagen lattices was also significantly stimulated by gadodiamide, while fibroblasts exposed to gadodiamide synthesized increased levels of hyaluronan. Control fibroblasts exposed to gadodiamide, and NSF fibroblasts exhibited an extensive pericellular coat of hyaluronan, and expressed alpha-smooth muscle actin. Gadolinium chloride did not affect fibroblast growth. This report demonstrates that NSF fibroblasts synthesize excess levels of hyaluronan and collagen, and that gadodiamide stimulates control fibroblast growth, matrix synthesis, and differentiation into myofibroblasts, suggesting a possible role for gadodiamide in the pathophysiology of NSF.

Ovarian normal and tumor-associated fibroblasts retain in vivo stromal characteristics in a 3-D matrix-dependent manner

OBJECTIVE

Due to a lack of experimental systems, little is known about ovarian stroma. Here, we introduce an in vivo-like 3-D system of mesenchymal stromal progression during ovarian tumorigenesis to support the study of stroma permissiveness in human ovarian neoplasias.

METHODS

To sort 3-D cultures into 'normal,' 'primed' and 'activated' stromagenic stages, 29 fibroblastic cell lines from 5 ovarian tumor samples (tumor ovarian fibroblasts, TOFs) and 14 cell lines from normal prophylactic oophorectomy samples (normal ovarian fibroblasts, NOFs) were harvested and characterized for their morphological, biochemical and 3-D culture features.

RESULTS

Under 2-D conditions, cells displayed three distinct morphologies: spread, spindle, and intermediate. We found that spread and spindle cells have similar levels of alpha-SMA, a desmoplastic marker, and consistent ratios of pFAKY(397)/totalFAK. In 3-D intermediate cultures, alpha-SMA levels were virtually undetectable while pFAKY(397)/totalFAK ratios were low. In addition, we used confocal microscopy to assess in vivo-like extracellular matrix topography, nuclei morphology and alpha-SMA features in the 3-D cultures. We found that all NOFs presented 'normal' characteristics, while TOFs presented both 'primed' and 'activated' features. Moreover, immunohistochemistry analyses confirmed that the 3-D matrix-dependent characteristics are reminiscent of those observed in in vivo stromal counterparts.

CONCLUSIONS

We conclude that primary human ovarian fibroblasts maintain in vivo-like (staged) stromal characteristics in a 3-D matrix-dependent manner. Therefore, our stromal 3-D system offers a tool that can enhance the understanding of both stromal progression and stroma-induced ovarian tumorigenesis. In the future, this system could also be used to develop ovarian stroma-targeted therapies.

A hypomorphic mouse model of dystrophic epidermolysis bullosa reveals mechanisms of disease and response to fibroblast therapy

Dystrophic epidermolysis bullosa (DEB) is a severe skin fragility disorder associated with trauma-induced blistering, progressive soft tissue scarring, and increased risk of skin cancer. DEB is caused by mutations in type VII collagen. In this study, we describe the generation of a collagen VII hypomorphic mouse that serves as an immunocompetent animal model for DEB. These mice expressed collagen VII at about 10% of normal levels, and their phenotype closely resembled characteristics of severe human DEB, including mucocutaneous blistering, nail dystrophy, and mitten deformities of the extremities. The oral blistering experienced by these mice resulted in growth retardation, and repeated blistering led to excessive induction of tissue repair, causing TGF-beta1-mediated contractile fibrosis generated by myofibroblasts and pseudosyndactyly in the extremities. Intradermal injection of WT fibroblasts resulted in neodeposition of collagen VII and functional restoration of the dermal-epidermal junction. Treated areas were also resistant to induced frictional stress. In contrast, untreated areas of the same mouse showed dermal-epidermal separation following induced stress. These data demonstrate that fibroblast-based treatment can be used to treat DEB in a mouse model and suggest that this approach may be effective in the development of clinical therapeutic regimens for patients with DEB.

A Case of Two Different Tumors in the Heart of a Dog

A 9-year-old, spayed, female Maremmano shepherd had a bilateral mastectomy for multiple mammary adenocarcinomas 2 years previous and was referred to the Cardiology Service of the School of Veterinary Medicine of Milan after an acute episode of cardiogenic collapse. Because of severe cardiovascular symptoms and poor prognosis, the dog was euthanized. Necropsy examination revealed the presence of multiple firm grayish neoplastic nodules in the myocardium of the left ventricle and scattered in the pulmonary parenchyma. Neoplastic nodules were also detected in the spleen, pancreas, liver, kidneys, and omentum. Histological examination revealed the coexistence of tubular adenocarcinoma and an undifferentiated sarcoma in the myocardium. Immunohistochemical staining of the sarcoma cells was negative for cytokeratin, desmin, and smooth muscle myosin, thus excluding their epithelial or myoepithelial origin, as well as an origin from smooth muscles cells. These findings, together with the coexpression of vimentin and α-smooth muscle actin, suggested that the sarcoma was derived from myofibroblasts. To the authors' knowledge, this is the first report describing cardiac sarcoma of presumptive myofibroblastic origin in a dog with simultaneous occurrence of cardiac metastasis of mammary gland adenocarcinoma.

Origin of renal myofibroblasts in the model of unilateral ureter obstruction in the rat

Tubulo-interstitial fibrosis is a constant feature of chronic renal failure and it is suspected to contribute importantly to the deterioration of renal function. In the fibrotic kidney there exists, besides normal fibroblasts, a large population of myofibroblasts, which are supposedly responsible for the increased production of intercellular matrix. It has been proposed that myofibroblasts in chronic renal failure originate from the transformation of tubular cells via epithelial–mesenchymal transition (EMT) or from infiltration by bone marrow-derived precursors. Little attention has been paid to the possibility of a transformation of resident fibroblasts into myofibroblasts in renal fibrosis. Therefore we examined the fate of resident fibroblasts in the initial phase of renal fibrosis in the classical model of unilateral ureter obstruction (UUO) in the rat. Rats were perfusion-fixed on days 1, 2, 3 and 4 after ligature of the right ureter. Starting from 1 day of UUO an increasing expression of alpha-smooth muscle actin (αSMA) in resident fibroblasts was revealed by immunofluorescence and confirmed by the observation of bundles of microfilaments and webs of intermediate filaments in the electron microscope. Inversely, there was a decreased expression of 5′-nucleotidase (5′NT), a marker of renal cortical fibroblasts. The RER became more voluminous, suggesting an increased synthesis of matrix. Intercellular junctions, a characteristic feature of myofibroblasts, became more frequent. The mitotic activity in fibroblasts was strongly increased. Renal tubules underwent severe regressive changes but the cells retained their epithelial characteristics and there was no sign of EMT. In conclusion, after ureter ligature, resident peritubular fibroblasts proliferated and they showed progressive alterations, suggesting a transformation in myofibroblasts. Thus the resident fibroblasts likely play a central role in fibrosis in that model.