Interactions of fibroblasts with the extracellular matrix: implications for the understanding of fibrosis

Pyk2 regulates cell-edge protrusion dynamics by interacting with Crk

Focal adhesion kinase (FAK) is well established as a regulator of cell migration, but whether and how the closely related proline-rich tyrosine kinase 2 (Pyk2) regulates fibroblast motility is still under debate. Using mouse embryonic fibroblasts (MEFs) from Pyk2^-/- mice, we show here, for the first time, that lack of Pyk2 significantly impairs both random and directed fibroblast motility. Pyk2^-/- MEFs show reduced cell-edge protrusion dynamics, which is dependent on both the kinase and protein-protein binding activities of Pyk2. Using bioinformatics analysis of in vitro high- throughput screens followed by text mining, we identified CrkI/II as novel substrates and interactors of Pyk2. Knockdown of CrkI/II shows altered dynamics of cell-edge protrusions, which is similar to the phenotype observed in Pyk2^-/- MEFs. Moreover, epistasis experiments suggest that Pyk2 regulates the dynamics of cell-edge protrusions via direct and indirect interactions with Crk that enable both activation and down-regulation of Crk-mediated cytoskeletal signaling. This complex mechanism may enable fine-tuning of cell-edge protrusion dynamics and consequent cell migration on the one hand together with tight regulation of cell motility, a process that should be strictly limited to specific time and context in normal cells, on the other hand.

Role of CXCL16 in BLM-induced epithelial-mesenchymal transition in human A549 cells

Alveolar epithelial cells play an essential role in the initiation and progression of pulmonary fibrosis, and the occurrence of epithelial–mesenchymal transition (EMT) may be the early events of pulmonary fibrosis. Recent studies have shown chemokines are involved in the complex process of EMT, and CXC chemokine ligand 16 (CXCL16) is also associated with many fibrosis-related diseases. However, whether CXCL16 is dysregulated in alveolar epithelial cells and the role of CXCL16 in modulating EMT in pulmonary fibrosis has not been reported. In this study, we found that CXCL16 and its receptor C-X-C motif chemokine receptor 6 (CXCR6) were upregulated in bleomycin induced EMT in human alveolar type II-like epithelial A549 cells. Synergistic effect of CXCL16 and bleomycin in promoting EMT occurrence, extracellular matrix (ECM) excretion, as well as the pro-inflammatory and pro-fibrotic cytokines productions in A549 cells were observed, and those biological functions were impaired by CXCL16 siRNA. We further confirmed that CXCL16 regulated EMT in A549 cells via the TGF-β1/Smad3 pathways. These results indicated that CXCL16 could promote pulmonary fibrosis by promoting the process of EMT via the TGF-β1/Smad3 signaling pathway.

Nanofiber-expanded human umbilical cord blood-derived CD34(+) cell therapy accelerates cutaneous wound closure in NOD/SCID mice

Nanofiber-expanded human umbilical cord blood–derived CD34⁺ cell therapy has been shown to have potential applications for peripheral and myocardial ischaemic diseases. However, the efficacies of expanded CD34⁺ cell therapy for treating cutaneous wounds and its mechanisms of action have yet to be established. Using an excisional wound model in non-obese diabetic/severe combined immune deficient mice, we show herein that CD34⁺ cells accelerate the wound-healing process by enhancing collagen synthesis, and increasing fibroblast cell migration within the wound bed. Concomitantly, reduced levels of matrix metalloproteinase (MMPs) such as MMP1, MMP3, MMP9 and MMP13 were detected in the wound beds of animals treated with CD34⁺ cells compared with vehicle-treated controls. CD34⁺ cells were found to mediate enhanced migration and proliferation of dermal fibroblast cells in vitro. Moreover, CD34⁺ cells secrete collagen in a serum-deprived environment. In mechanistic studies, co-culture of CD34⁺ cells with primary skin fibroblasts increased the expression of collagen1A1, a component of type 1 collagen, and decreased the expression of MMP1 in fibroblast cells in the presence of a proteasome inhibitor. Finally, CD34⁺ cell–mediated functions were transcriptionally regulated by the c-Jun N-terminal kinases pathway. Collectively, these data provide evidence of therapeutic efficacy and a novel mechanism of nanofiber-expanded CD34⁺ cell–mediated accelerated wound healing.

Biphasic recruitment of microchimeric fetal mesenchymal cells in fibrosis following acute kidney injury

Fetal microchimeric cells (FMCs) enter the maternal circulation and persist in tissue for decades. They have capacity to home to injured maternal tissue and differentiate along that tissue's lineage. This raises the question of the origin(s) of cells transferred to the mother during pregnancy. FMCs with a mesenchymal phenotype have been documented in several studies, which makes mesenchymal stem cells an attractive explanation for their broad plasticity. Here we assessed the recruitment and mesenchymal lineage contribution of FMCs in response to acute kidney fibrosis induced by aristolochic acid injection. Serial in vivo bioluminescence imaging revealed a biphasic recruitment of active collagen-producing FMCs during the repair process of injured kidney in post-partum wild-type mothers that had delivered transgenic pups expressing luciferase under the collagen type I-promoter. The presence of FMCs long-term post injury (day 60) was associated with profibrotic molecules (TGF-β/CTGF), serum urea levels, and collagen deposition. Immunostaining confirmed FMCs at short term (day 15) using post-partum wild-type mothers that had delivered green fluorescent protein-positive pups and suggested a mainly hematopoietic phenotype. We conclude that there is biphasic recruitment to, and activity of, FMCs at the injury site. Moreover, we identified five types of FMC, implicating them all in the reparative process at different stages of induced renal interstitial fibrosis.

Effect of EGF and bFGF on fibroblast proliferation and angiogenic cytokine production from cultured dermal substitutes

Growth factors accelerate wound healing but the underlying mechanisms remain poorly understood. The aim of this study was to investigate the effect of epidermal growth factor (EGF) and basic fibroblast growth factor (bFGF) on fibroblast proliferation and production of angiogenic factors from cultured dermal substitutes (CDS). In the first experiment, fibroblasts were seeded into a flask at a density of 1 × 10(4) cells/cm(2).Cell proliferation was assessed after culturing in media containing EGF or bFGF at concentrations ranging from 2 to 50 μg. The number of fibroblasts increased significantly in the presence of EGF or bFGF, but fibroblasts detached from the flasks in the presence of 50 μg bFGF. In the second experiment, CDS were prepared by incorporating fibroblasts into collagen gels. To make a wound surface model, the CDS was elevated to the air-liquid interface, on which a spongy sheet of hyaluronic acid (HA) containing EGF or bFGF was placed. The amount of vascular endothelial growth factor (VEGF) and hepatocyte growth factor (HGF) released from the CDS after 1 week of cultivation was measured by ELISA. When the CDS was covered with a HA sponge containing EGF (Group 1), fibroblasts released 3.5-times more VEGF compared with a HA-alone sponge (control group). When covered with a HA sponge containing bFGF (Group 2), 8.7-times more VEGF was released compared with the control group. Fibroblasts in Groups 1 and 2 released 9.6- and 9.3-times more HGF, respectively, compared with the control group. Thus, EGF stimulates fibroblasts to produce VEGF and HGF, in addition to its ability to enhance epidermal cell proliferation.

Interstitial fibrosis is associated with increased COL1A2 transcription in AA-injured renal tubular epithelial cells in vivo

Accumulation of type I collagen is a key event in renal interstitial fibrosis. As there is no effective treatment, understanding the site where collagen is transcribed and the factors driving it in response to disease in vivo is critical for designing future therapies. The present research investigated the transcriptional activity of the COL1A2 gene in a mouse model of progressive fibrosis induced by aristolochic acid (aristolochic acid nephropathy, AAN). To achieve this we genetically modified mice to express a reporter gene (LacZ) and CCN2 (connective tissue growth factor) under the transcriptional control of the COL1A2 promoter /enhancer sequences. Using these mice we asked where is collagen actively transcribed and secondly, what is the role of CCN2 in AAN. Here, we report that de-novo transcription of the COL1A2 gene occurred predominantly in damaged tubular epithelial cells during progressive interstitial fibrosis in vivo. The activation of COL1A2 was studied by detection of the reporter gene LacZ and COL1A2 mRNA in interstitial, glomerular, vascular, and tubular epithelial tissue from laser capture microscopy. We also demonstrated that LacZ-positive cells co-express E-Cadherin a marker of epithelial origin which is consistent with an epithelial phenotype which is capable of collagen expression during injury. There was no evidence of detachment of these cells from tubules to become myofibroblasts. Moreover, we showed that the transgenic mice show a modest enhancement of CCN2 expression; however fibrosis induced by AA is the same in transgenics and controls suggesting that CCN2, at this level of expression, is not sufficient to enhance fibrogenesis. Overall our study provides a better understanding into the expression patterns and roles of two major extracellular matrix proteins: type I collagen and CCN2.

N-cadherin is overexpressed in Crohn's stricture fibroblasts and promotes intestinal fibroblast migration

BACKGROUND

Intestinal fibroblasts mediate stricture formation in Crohn's disease (CD). Transforming growth factor-β₁ (TGF-β₁) is important in fibroblast activation, while cell attachment and migration is regulated by the adhesion molecule N-cadherin. The aim of this study was to investigate the expression and function of N-cadherin in intestinal fibroblasts in patients with fibrostenosing CD.

METHODS

Intestinal fibroblasts were cultured from seromuscular biopsies from patients undergoing resection for terminal ileal fibrostenosing CD (n = 14) or controls patients (n = 8). N-cadherin expression was assessed using Western blot and quantitative reverse-transcription polymerase chain reaction (qRT-PCR). Fibroblasts were stimulated with TGF-β₁ and selective pathway inhibitors Y27632, PD98050, and LY294002 were used to examine the Rho/ROCK, ERK-1/2, and Akt signaling pathways, respectively. Cell migration was assessed using a scratch wound assay. N-cadherin was selectively overexpressed using a plasmid.

RESULTS

Fibroblasts from fibrostenosing CD express increased constitutive N-cadherin mRNA and protein and exhibit enhanced basal cell migration relative to those from directly adjacent normal bowel. Control fibroblasts treated with TGF-β₁ induced N-cadherin in a dose-dependent manner which was inhibited by Rho/ROCK and Akt pathway modulation. Control fibroblasts exhibited enhanced cell migration in response to treatment with TGF-β₁ or transfection with an N-cadherin plasmid.

CONCLUSIONS

Fibroblasts from strictures in CD express increased constitutive N-cadherin and exhibit enhanced basal cell migration. TGF-β₁ is a potent inducer of N-cadherin in intestinal fibroblasts resulting in enhanced cell migration. The TGF-β₁-mediated induction of N-cadherin may potentiate Crohn's stricture formation.

Expression of integrin β1 by fibroblasts is required for tissue repair in vivo

In tissue repair, fibroblasts migrate into the wound to produce and remodel extracellular matrix (ECM). Integrins are believed to be crucial for tissue repair, but their tissue-specific role in this process is poorly understood. Here, we show that mice containing a fibroblast-specific deletion of integrin β1 exhibit delayed cutaneous wound closure and less granulation tissue formation, including reduced production of new ECM and reduced expression of α-smooth muscle actin (α-SMA). Integrin-β1-deficient fibroblasts showed reduced expression of type I collagen and connective tissue growth factor, and failed to differentiate into myofibroblasts as a result of reduced α-SMA stress fiber formation. Loss of integrin β1 in adult fibroblasts reduced their ability to adhere to, to spread on and to contract ECM. Within stressed collagen matrices, integrin-β1-deficient fibroblasts showed reduced activation of latent TGFβ. Addition of active TGFβ alleviated the phenotype of integrin-β1-deficient mice. Thus integrin β1 is essential for normal wound healing, where it acts, at least in part, through a TGFβ-dependent mechanism in vivo.

Comparison between human fetal and adult skin

Healing of early-gestation fetal wounds results in scarless healing. Since the capacity for regeneration is probably inherent to the fetal skin itself, knowledge of the fetal skin composition may contribute to the understanding of fetal wound healing. The aim of this study was to analyze the expression profiles of different epidermal and dermal components in the human fetal and adult skin. In the human fetal skin (ranging from 13 to 22 weeks' gestation) and adult skin biopsies, the expression patterns of several epidermal proteins (K10, K14, K16, K17, SKALP, involucrin), basement membrane proteins, Ki-67, blood vessels and extracellular matrix proteins (fibronectin, chondroitin sulfate, elastin) were determined using immunohistochemistry. The expression profiles of K17, involucrin, dermal Ki-67, fibronectin and chondroitin sulfate were higher in the fetal skin than in adult skin. In the fetal skin, elastin was not present in the dermis, but it was found in the adult skin. The expression patterns of basement membrane proteins, blood vessels, K10, K14, K16 and epidermal Ki-67 were similar in human fetal skin and adult skin. In this systematic overview, most of the differences between fetal and adult skin were found at the level of dermal extracellular matrix molecules expression. This study suggests that, especially, dermal components are important in fetal scarless healing.

Loss of dioxin-receptor expression accelerates wound healing in vivo by a mechanism involving TGFbeta

Delayed wound healing caused by inefficient re-epithelialization underlines chronic skin lesions such as those found in diabetes. The dioxin receptor (AhR) modulates cell plasticity and migration and its activation by occupational polycyclic aromatic hydrocarbons (PAHs) results in severe skin lesions such as contact hypersensitivity, dermatitis and chloracne. Using wild-type (Ahr+/+) and AhR-null (Ahr-/-) mouse primary keratinocyte cultures and tissue explants, we show that lack of AhR increases keratinocyte migration and accelerates skin re-epithelialization without affecting cell proliferation or recruitment of inflammatory cells. Wounds in Ahr-/- animals had elevated numbers of fibroblasts and increased collagen content in their granulation tissue. Importantly, Ahr-/- dermal fibroblasts secreted higher levels of active TGFbeta that increased keratinocyte migration in culture and that could account for over-activation of the TGFbeta pathway and for faster wound healing in the AhR-null neo-epithelium. Consistently, a TGFbeta neutralizing antibody decreased keratinocyte migration in culture and halted re-epithelialization in Ahr-/- mice. Moreover, in vivo treatment with an antisense oligonucleotide for AhR increased TGFbeta signaling and improved re-epithelialization in wounds of wild-type mice. These data indicate that AhR is relevant for wound repair and suggest that AhR downmodulation might be a potential new tool for the treatment of chronic, surgical or accidental wounds.

Rac1 expression by fibroblasts is required for tissue repair in vivo

Tissue repair requires that fibroblasts migrate into the wound to produce and remodel extracellular matrix, a process that requires adhesion. Failure to suppress the tissue repair program results in fibrotic disorders that are characterized by excessive adhesive signaling. The role of specific components of adhesive signaling in fibrogenic responses is unclear, but may involve small GTPases such as Rac1. To address the functions of Rac1 in fibroblasts, we generated mice containing a fibroblast-specific deletion of Rac1. These mice show delayed cutaneous wound closure, including reduced collagen production and myofibroblast formation. In cultured Rac1-deficient fibroblasts, adhesion, spreading, and migration were significantly inhibited. Rac1-deficient fibroblasts possessed impaired myofibroblast formation and function as visualized by reduced alpha-smooth muscle actin expression as well as matrix contraction. Both in vivo and in vitro, Rac1- deficient fibroblasts showed a reduced generation of reactive oxygen species; in vitro, hydrogen peroxide alleviated the phenotype of Rac1-deficient fibroblasts. Thus, Rac1 is an essential signaling integrator that is required for normal wound healing and dermal homeostasis.

GSK-3beta in mouse fibroblasts controls wound healing and fibrosis through an endothelin-1-dependent mechanism

Glycogen synthase kinase-3 (GSK-3) is a widely expressed and highly conserved serine/threonine protein kinase encoded by 2 genes, GSK3A and GSK3B. GSK-3 is thought to be involved in tissue repair and fibrogenesis, but its role in these processes is currently unknown. To investigate the function of GSK-3beta in fibroblasts, we generated mice harboring a fibroblast-specific deletion of Gsk3b and evaluated their wound-healing and fibrogenic responses. We have shown that Gsk3b-conditional-KO mice (Gsk3b-CKO mice) exhibited accelerated wound closure, increased fibrogenesis, and excessive scarring compared with control mice. In addition, Gsk3b-CKO mice showed elevated collagen production, decreased cell apoptosis, elevated levels of profibrotic alpha-SMA, and increased myofibroblast formation during wound healing. In cultured Gsk3b-CKO fibroblasts, adhesion, spreading, migration, and contraction were enhanced. Both Gsk3b-CKO mice and fibroblasts showed elevated expression and production of endothelin-1 (ET-1) compared with control mice and cells. Antagonizing ET-1 reversed the phenotype of Gsk3b-CKO fibroblasts and mice. Thus, GSK-3beta appears to control the progression of wound healing and fibrosis by modulating ET-1 levels. These results suggest that targeting the GSK-3beta pathway or ET-1 may be of benefit in controlling tissue repair and fibrogenic responses in vivo.

Loss of protein kinase Cϵ results in impaired cutaneous wound closure and myofibroblast function

Cutaneous wound repair requires the de novo induction of a specialized form of fibroblast, the α-smooth muscle actin (α-SMA)-expressing myofibroblast, which migrates into the wound where it adheres to and contracts extracellular matrix (ECM), resulting in wound closure. Persistence of the myofibroblast results in scarring and fibrotic disease. In this report, we show that, compared with wild-type littermates, PKCϵ-/- mice display delayed impaired cutaneous wound closure and a reduction in myofibroblasts. Moreover, both in the presence and absence of TGFβ, dermal fibroblasts from PKCϵ-/- mice cultured on fibronectin show impaired abilities to form `supermature' focal adhesions and α-SMA stress fibers, and reduced pro-fibrotic gene expression. Smad3 phosphorylation in response to TGFβ1 was impaired in PKCϵ-/- fibroblasts. PKCϵ-/- fibroblasts show reduced FAK and Rac activation, and adhesive, contractile and migratory abilities. Overexpressing constitutively active Rac1 rescues the defective FAK phosphorylation, cell migration, adhesion and stress fiber formation of these PKCϵ-/- fibroblasts, indicating that Rac1 operates downstream of PKCϵ, yet upstream of FAK. These results suggest that loss of PKCϵ severely impairs myofibroblast formation and function, and that targeting PKCϵ may be beneficial in selectively modulating wound healing and fibrotic responses in vivo.

Hypoxia influences the cellular cross-talk of human dermal fibroblasts. A proteomic approach

The ability of cells to respond to changes in oxygen availability is critical for many physiological and pathological processes (i.e. development, aging, wound healing, hypertension, cancer). Changes in the protein profile of normal human dermal fibroblasts were investigated in vitro after 96 h in 5% CO(2) and 21% O(2) (pO(2) = 140 mm Hg) or 2% O(2) (pO(2) = 14 mm Hg), these parameters representing a mild chronic hypoxic exposure which fibroblasts may undergo in vivo. The proliferation rate and the protein content were not significantly modified by hypoxia, whereas proteome analysis demonstrated changes in the expression of 56 proteins. Protein identification was performed by mass spectrometry. Data demonstrate that human fibroblasts respond to mild hypoxia increasing the expression of hypoxia inducible factor (HIF1a) and of the 150-kDa oxygen-regulated protein. Other differentially expressed proteins appeared to be related to stress response, transcriptional control, metabolism, cytoskeleton, matrix remodelling and angiogenesis. Furthermore, some of them, like galectin 1, 40S ribosomal protein SA, N-myc-downstream regulated gene-1 protein, that have been described in the literature as possible cancer markers, significantly changed their expression also in normal hypoxic fibroblasts. Interestingly, a bovine fetuin was also identified that appeared significantly less internalised by hypoxic fibroblasts. In conclusion, results indicate that human dermal fibroblasts respond to an in vitro mild chronic hypoxic exposure by modifying a number of multifunctional proteins. Furthermore, data highlight the importance of stromal cells in modulating the intercellular cross-talk occurring in physiological and in pathologic conditions.

Extracellular matrix containing mutated fibrillin-1 (Fbn1) down regulates Col1a1, Col1a2, Col3a1, Col5a1, and Col5a2 mRNA levels in Tsk/+ and Tsk/Tsk embryonic fibroblasts

It is known that the extracellular matrix (ECM) is able to signal to cells and thereby direct or modulate the transcription of certain mRNAs. This signaling plays an important role in tumor invasion and metastasis, wound healing, remodeling of the ECM and cell differentiation. There are several mechanisms whereby the ECM signals cells to change their metabolism: (1) receptor molecules binding to specific domains in the ECM, (2) direct phagocytosis of the ECM molecules or domains into the cell, (3) structural changes of the ECM domains. We report the effect of an ECM containing either mutant or normal Fbn1 on the transcription levels of several collagen mRNAs. Tsk/Tsk, Tsk/+ and +/+ mouse embryonic fibroblast cell lines were used. Tsk/Tsk cells produce only mutated fibrillin-1 which arises from mRNA containing an in-frame duplication of exons 17-40. To test the effect of the ECM containing mutant Fbn1, cells of the Tsk/Tsk, Tsk/+ and the wild-type (+/+) genotype were each grown on an ECM produced by either Tsk/Tsk, Tsk/+ cells or by wild-type cells (+/+). The embryonic cells were genotyped by Northern analyses for Fbn1 and grown to confluence. The cultures were then harvested and the cells removed, leaving the matrix in the flasks. Matrices produced from Tsk/Tsk, Tsk/+ and from +/+ cells were reseeded with Tsk/Tsk cells, Tsk/+ cells or +/+ cells. The cells were plated at a confluent concentration and incubated on the matrices for 48 h, after which total RNA was harvested and cDNA generated. Real-time PCR using cDNA or Northern analyses using RNA were performed for Fbn1 and Types I, III and V collagens. The PCR and Northern results were normalized using beta-actin and GAPDH, respectively. The Northern analyses showed that the steady state levels of mRNA for Col1a1 were depressed in both Tsk/Tsk and +/+ cells when grown on the matrix produced by Tsk/Tsk cells. Real-time PCR was then performed with primers specific for Col1a2, Col3a1, Col5a1 and Col5a2. The results showed that cells with the Tsk/Tsk, Tsk/+, and +/+ genotype all had lower steady-state levels of the above 4 collagen mRNAs when grown on the matrix produced by homozygous Tsk/Tsk cells or the matrix produced by heterozygous Tsk/+ cells compared with those grown on a matrix produced by +/+ cells. We hypothesize that the mutated Fbn1 molecules with many additional EGF-calcium binding regions and TGF-beta binding domains may (1) change the homeostasis of the ECM by binding additional growth factors and/or (2) present a radically different ECM 3-dimensional architecture. Either or both of these changes could signal the cell to produce less collagen.

Proteasome blockade exerts an antifibrotic activity by coordinately down-regulating type I collagen and tissue inhibitor of metalloproteinase-1 and up-regulating metalloproteinase-1 production in human dermal fibroblasts

Tissue fibrosis results when dysregulation of extracellular matrix (ECM) turnover favors deposition of collagen and other ECM proteins over degradation. Fibrosis may then lead to organ dysfunction and pathology as observed in systemic sclerosis (SSc). In the present study, we investigated the antifibrotic properties of proteasome blockade. A dose- and time-dependent reduction in type-I collagen and tissue inhibitor of metalloproteinase-1 (TIMP-1) production was observed in normal fibroblasts exposed to proteasome inhibitors (PI). In the same culture conditions, metalloproteinase-1 (MMP-1) protein and the collagenolytic activity on type I collagen was increased. The steady-state mRNA levels of COL1A1, TIMP-1, and MMP-1 paralleled protein levels. These effects were dominant over the profibrotic properties of TGF-beta and were observed with fibroblasts generated from normal and SSc skin. PI decreased type I collagen mRNA levels with kinetics similar to those observed with DRB, a specific RNA polymerase II inhibitor, thus indicating transcriptional inhibition. Of interest, PI induced c-Jun phosphorylation and c-Jun nuclear accumulation. The specific N-terminal Jun-kinase inhibitor SP-600125 selectively abrogated c-Jun phosphorylation and, in a dose-dependent fashion, the up-regulated synthesis of MMP-1 induced by PI. Finally, PI did not affect fibroblast viability. Thus, the coordinated down-regulation of collagen and TIMP-1 and up-regulation of MMP-1 renders proteasome blockade an attractive strategy for treating conditions as SSc, characterized by excessive fibrosis.

Interstitial fluid flow induces myofibroblast differentiation and collagen alignment in vitro

The differentiation of fibroblasts to contractile myofibroblasts, which is characterized by de novo expression of alpha-smooth muscle actin (alpha-SMA), is crucial for wound healing and a hallmark of tissue scarring and fibrosis. These processes often follow inflammatory events, particularly in soft tissues such as skin, lung and liver. Although inflammatory cells and damaged epithelium can release transforming growth factor beta1 (TGF-beta1), which largely mediates myofibroblast differentiation, the biophysical environment of inflammation and tissue regeneration, namely increased interstitial flow owing to vessel hyperpermeability and/or angiogenesis, may also play a role. We demonstrate that low levels of interstitial (3D) flow induce fibroblast-to-myofibroblast differentiation as well as collagen alignment and fibroblast proliferation, all in the absence of exogenous mediators. These effects were associated with TGF-beta1 induction, and could be eliminated with TGF-beta1 blocking antibodies. Furthermore, alpha1beta1 integrin was seen to play an important role in the specific response to flow, as its inhibition prevented fibroblast differentiation and subsequent collagen alignment but did not block their ability to contract the gel in a separate floating gel assay. This study suggests that the biophysical environment that often precedes fibrosis, such as swelling, increased microvascular permeability and increased lymphatic drainage--all which involve interstitial fluid flow--may itself play an important role in fibrogenesis.

Molecular Characterization of Postoperative Adhesions: The Adhesion Phenotype

Postoperative adhesion development remains a very frequent occurrence, which is often unrecognized by surgeons because of limited ability to conduct early second-look laparoscopies. The consequences include infertility, pelvic pain, bowel obstruction, and difficult reoperative procedures. To date, approaches to limit adhesions primarily have involved barriers to separate tissue during reepithelization. Future progress in regulating adhesion development and tissue fibrosis likely will require an improved understanding of the molecular processes involved in normal peritoneal repair and its aberrations leading to adhesion development. We hypothesize that tissue hypoxia (in part resulting from tissue incision, fulguration, suture ligation, etc.) is the major inciting event, which leads to a coordinated series of molecular events that promote an inflammatory response leading to enhanced tissue fibrosis. These events are reduced plasminogen activator activity, extracellular matrix deposition, increased cytokine production, increased angiogenesis, and reduced apoptosis (programmed cell death). Improved understanding of these events and their regulation will provide the opportunity to regulate better postoperative adhesion development and tissue fibrosis, thereby reducing the morbidity and mortality they cause.

Progesterone and gravidity differentially regulate expression of extracellular matrix components in the pregnant rat myometrium

Myometrial growth and remodeling during pregnancy depends on increased synthesis of interstitial matrix proteins. We hypothesize that the presence of mechanical tension in a specific hormonal environment regulates the expression of extracellular matrix (ECM) components in the uterus. Myometrial tissue was collected from pregnant rats on Gestational Days 0, 12, 15, 17, 19, 21, 22, 23 (labor), and 1 day postpartum and ECM expression was analyzed by Northern blotting. Expression of fibronectin, laminin beta2, and collagen IV mRNA was low during early gestation but increased dramatically on Day 23 during labor. Expression of fibrillar collagens (type I and III) peaked Day 19 and decreased near term. In contrast, elastin mRNA remained elevated from midgestation onward. Injection of progesterone (P4) on Days 20-23 (to maintain elevated plasma P4 levels) delayed the onset of labor, caused dramatic reductions in the levels of fibronectin and laminin mRNA, and prevented the fall of collagen III mRNA levels on Day 23. Treatment of pregnant rats with the progesterone receptor antagonist RU486 on Day 19 induced preterm labor on Day 20 and a premature increase in mRNA levels of collagen IV, fibronectin, and laminin. Analysis of the uterine tissue from unilaterally pregnant rats revealed that most of the changes in ECM gene expression occurred specifically in the gravid horn. Our results show a decrease in expression of fibrillar collagens and a coordinated temporal increase in expression of components of the basement membrane near term associated with decreased P4 and increased mechanical tension. These ECM changes contribute to myometrial growth and remodeling during late pregnancy and the preparation for the synchronized contractions of labor.

The role of autocrine FGF-2 in the distinctive bone marrow fibrosis of hairy-cell leukemia (HCL)

Bone marrow (BM) fibrosis is a central diagnostic and pathogenetic feature of hairy-cell leukemia (HCL). It is known that fibronectin (FN) produced and assembled by the malignant hairy cells (HCs) themselves is a major component of this fibrosis. It is also known that FN production is greatly enhanced by adhesion of HCs to hyaluronan (HA) via CD44. The aim of the present study was to establish the roles of fibrogenic autocrine cytokines (fibroblast growth factor-2 [FGF-2] and transforming growth factor beta [TGFbeta]) and of different isoforms of CD44 in this FN production. We show that HC adhesion to HA stimulates FGF-2, but not TGFbeta, production and that HCs possess FGF-2 receptor. In a range of experiments, FN production was greatly reduced by blocking FGF-2 but not TGFbeta. Moreover FN, but not FGF-2, secretion was blocked by down-regulation of the v3 isoform of CD44 and by addition of heparitinase. These results show that autocrine FGF-2 secreted by HCs is the principal cytokine responsible for FN production by these cells when cultured on HA. The central role of FGF-2 in the pathogenesis of the BM fibrosis of HCL was supported by our immunohistochemical demonstration of large amounts of this cytokine in fibrotic BM but not in HCL spleen where there is no fibrosis. As regards CD44 isoforms, the present work demonstrates that CD44v3 is essential for providing the heparan sulfate necessary for HC stimulation by FGF-2, whereas the signal for production of the cytokine was provided by HA binding to CD44H, the standard hematopoietic form of the molecule.

Altered proliferative responses of dermal fibroblasts to TGF-beta1 may contribute to chronic venous stasis ulcer

PURPOSE

Venous ulcer fibroblasts demonstrate decreased proliferative responses to growth factor stimulation, suggesting cellular senescence. However, the role of chronic venous insufficiency (CVI) disease progression and extracellular matrix (ECM) proteins in agonist-induced cellular proliferation is ill-defined. We hypothesize that CVI-induced fibroblast proliferative resistance to growth factors worsens with disease progression and is regulated by the composition of ECM.

METHODS

Fibroblast explants were isolated from biopsy specimens from two patients without CVI and 16 patients with CVI of the lower calf (LC) and lower thigh (LT) and stratified according to CEAP disease severity: non-CVI (NC; n = 2), class 2-3 (n = 5), class 4 (n = 5), class 5 (n = 3), and class 6 (n = 3). Proliferation experiments were standardized with a neonatal foreskin fibroblast cell line (HS68). A 10-day course and dose response experiment with 0, 0.5, 1.0, 2.5, 5, 10, and 20 ng/mL of transforming growth factor-beta(1) (TGF-beta(1)) demonstrated maximal cell proliferation at 5 ng/mL of TGF-beta(1) on day 4. Under these conditions, CVI dermal fibroblasts were challenged with and without TGF-beta(1) and evaluated for proliferative responses on plates coated with polystyrene, collagen, and fibronectin.

RESULTS

No differences in unstimulated proliferation were observed in LT and LC fibroblasts from patients with class 2-3 disease and LT fibroblasts from patients with class 4 and 5 disease, compared with NC and HS68 cells. LC fibroblasts from patients with class 4 disease (P <.05) and class 5 disease (P <.001), and LC (P <.001), and LT fibroblasts from patients with class 6 disease (P <.001) proliferated to a lesser degree than did NC and HS68 cells. The diminished proliferation observed in class 4 LC cells was reversible with TGF-beta(1) stimulation (P <.004); however, class 5 and class 6 LC and LT fibroblasts did not respond to stimulation with TGF-beta(1). Collagen increased proliferation of HS68 cells with (P <.05) and without (P <.01) TGF-beta(1), compared with cells grown on polystyrene, but did not increase proliferative responses in NC or CVI fibroblasts with and without TGF-beta(1). Similarly, fibronectin increased proliferation of HS68 cells (P <.05) compared with cells grown on polystyrene, but did not alter proliferation in CVI fibroblasts. Fibronectin did seem to inhibit TGF-beta(1)-induced proliferation observed in class 4 LC cells.

CONCLUSION

These data indicate that clinical disease progression correlates with cellular dysfunction. Fibroblasts from patients with class 2-3 disease retain their unstimulated and agonist- induced proliferative capacity, compared with NC and HS68 cells. The onset of inflammatory skin changes (class 4 and class 5 disease) diminishes agonist-induced proliferation, and ulcer formation (class 6 disease) severely inhibits it. In addition, the composition of ECM does not affect TGF-beta(1)-induced proliferation of fibroblasts in CVI.

Fibroblast biology in three-dimensional collagen matrices

Research on fibroblast biology in three-dimensional collagen matrices offers new opportunities to understand the reciprocal and adaptive interactions that occur between cells and surrounding matrix in a tissue-like environment. Such interactions are integral to the regulation of connective tissue morphogenesis and dynamics that characterizes tissue homeostasis and wound repair. During fibroblast-collagen matrix remodeling, mechanical signals from the remodeled matrix feed back to modulate cell behavior in an iterative process. As mechanical loading (tension) within the matrix increases, the mechanisms used by cells to remodel the matrix change. Fibroblasts in matrices that are under tension or relaxed respond differently to growth factor stimulation, and switching between mechanically loaded and unloaded conditions influences whether cells acquire proliferative/biosynthetic active or quiescent/resting phenotypes.

Factor XIII a-positive dermal dendrocytes and shear wave propagation in human skin

BACKGROUND

The in vivo interdependence between the phenotypic characteristics of dermal cells and the strain imposed on the tissue has not been studied thoroughly in humans. In particular the mechanical force modulation of Factor XIII a expression in dermal dendrocytes (DD) remains unknown.

MATERIALS AND METHODS

The present study compares the numerical density of Factor XIII a-positive DD and the in vivo shear wave velocity in the skin. The investigation was performed in 20 men of normal weight and 20 obese men before and after entering a slimming process.

RESULTS

Excess cutaneous fat places the skin under increased intrinsic tension. The resonance running time measurement (RRTM) and the DD density were significantly reduced in overweight individuals. After a short-term but intense slimming process, the same individuals showed a trend to normalization of these two parameters without, however, reaching significance. Pooling all data yielded a significant logarithmic correlation between RRTM values and densities in Factor XIII a-positive DD.

CONCLUSION

Factor XIII a expression in human DD may be partially regulated by the intrinsic resting tensions in the skin.