Promotion by fibronectin of collagen gel contraction mediated by human corneal fibroblasts

Urokinase-type plasminogen activator (uPA) negatively regulates α-smooth muscle actin expression via Endo180 and the uPA receptor in corneal fibroblasts

Corneal fibroblasts are embedded within an extracellular matrix composed largely of collagen type 1, proteoglycans, and other proteins in the corneal stroma, and their morphology and function are subject to continuous regulation by collagen. During wound healing and in various pathological conditions, corneal fibroblasts differentiate into myofibroblasts characterized by the expression of α-smooth muscle actin (α-SMA). Endo180, also known as urokinase-type plasminogen activator (uPA) receptor-associated protein (uPARAP), is a collagen receptor. Here we investigated whether targeting of Endo180 and the uPA receptor (uPAR) by uPA might play a role in the regulation of α-SMA expression by culturing corneal fibroblasts derived from uPA-deficient (uPA^-/-) or wild-type (uPA^+/+) mice in a collagen gel or on plastic. The expression of α-SMA was upregulated, the amounts of full-length Endo180 and uPAR were increased, and the levels of both transforming growth factor-b (TGF-β) expression and Smad3 phosphorylation were higher in uPA^-/- corneal fibroblasts compared with uPA^+/+ cells under the collagen gel culture condition. Antibodies to Endo180 inhibited these effects of uPA deficiency on a-SMA and TGF-b expression, whereas a TGF-b signaling inhibitor blocked the effects on Smad3 phosphorylation and a-SMA expression. Our results suggest that uPA deficiency might promote the interaction between collagen and Endo180 and thereby increase a-SMA expression in a manner dependent on TGF-β signaling. Expression of α-SMA is thus negatively regulated by uPA through targeting of Endo180 and uPAR.

Foamy macrophages potentially inhibit tuberculous wound healing by inhibiting the TLRs/NF-κB signalling pathway

To characterise the distribution, classification, and quantity of foamy macrophages (FMs) in tuberculous wound tissue and the relationship between FM and delayed healing of tuberculous wounds. Morphological studies were performed to explore the distribution of FM and Mycobacterium tuberculosis (Mtb) in tuberculous wounds, with acute and chronic wounds included for comparison. Phorbol-12-myristate-13-acetate stimulation-differentiated THP-1 cells were treated with Mtb to induce their differentiation into FM with oxidised low-density lipoprotein treatment serving as a control. Relative cytokine levels were determined by quantitative PCR and Western blotting. Varied co-culture combinations of Mtb, THP-1, FM, and fibroblasts were performed, and proliferation, migration, ability to contract collagen gel, and protein levels of the chemokines in the supernatants of the fibroblasts were assessed. The differentially expressed genes in human skin fibroblasts (HSFs) after co-culture with or without FM were identified using microarray. Many FM were found in the tissues of tuberculous wounds. The FM that did not engulf Mtb (NM-FM) were mainly distributed in tissues surrounding tuberculous wounds, whereas the FM that engulfed Mtb (M-FM) were dominantly located within granulomatous tissues. Co-culture experiments showed that, with the Mtb co-culture, the portions of NM-FM in the total FM grew over time. The migration, proliferation, chemokine secretion, and the ability of fibroblasts to contract collagen gel were inhibited when co-cultured with Mtb, FM, or a combination of the two. Further investigation showed that the TLRs/NF-κB signalling pathway is involved in fibroblast function under the stimulation of FM. TLRs and NF-κB agonists could reverse the phenotypic changes in HSFs after co-culture with FM. The tuberculous wound microenvironment composed of Mtb and FM may affect wound healing by inhibiting the functions of fibroblasts. FM potentially inhibit fibroblasts' function by inhibiting the TLRs/NF-κB signalling pathway in tuberculous wounds.

All‑trans‑retinoic acid modulates TGF‑β‑induced apoptosis, proliferation, migration and extracellular matrix synthesis of conjunctival fibroblasts by inhibiting PI3K/AKT signaling

Conjunctival fiber generation is implicated in a wide spectrum of ocular diseases. Conjunctival wound healing is characterized by inflammation followed by re‑epithelialization, synthesis of new extracellular matrix (ECM), wound contraction and subconjunctival scar formation. The primary cause for the failure of glaucoma filtration surgery results from the excessive scarring of the filtering bleb. All‑trans‑retinoic acid (ATRA), a derivative of vitamin A, is a potent regulator of ECM synthesis, growth and differentiation. Following a previous study, which revealed that ATRA could inhibit transforming growth factor‑β‑induced human conjunctival fibroblast (HConF)‑mediated collagen gel contraction, the present study aimed to investigate the effects of ATRA on HConF migration, apoptosis, proliferation and ECM synthesis. To achieve this, the present study used Transwell migration, wound healing and Cell Counting Kit‑8 assays, flow cytometry and western blot analysis. In addition, the present study aimed to elucidate the mechanism of ATRA in mediating resistance to conjunctival scar formation. ATRA treatment resulted in an increased level of HConF apoptosis, reduced proliferation and migration, decreased collagen I and fibronectin expression, and decreased phosphorylation of PI3K and AKT. Thus, the present study showed a role for ATRA in inhibiting HConF migration, proliferation and ECM synthesis, and in promoting HConF apoptosis through the inhibition of the PI3K/AKT signaling pathway.

Impaired Contracture of 3D Collagen Constructs by Fibronectin-Deficient Murine Fibroblasts

Fibronectin (FN) is an extracellular matrix glycoprotein that is abundantly expressed by fibroblasts in contracting wounds, where it mediates cell adhesion, migration and proliferation. FN also efficiently binds to collagen. Therefore, we and others hypothesized that FN and its cellular receptor integrin α₅β₁ might be involved in collagen matrix contracture by acting as linkers. However, there are conflicting reports on this issue. Moreover, several publications suggest an important role of collagen-binding integrin receptors α₂β₁ and α₁₁β₁ in collagen matrix contracture. Therefore, the aim of the present study was to determine the contributions of FN-integrin α₅β₁ interactions relative to those of collagen receptors α₂β₁ and α₁₁β₁ in this process. To assess the role of cellular FN directly, we employed FN-deficient mouse fibroblasts, subjected them to a collagen gel contracture assay in vitro, and compared them to their wildtype counterparts. Exogenous FN was removed from serum-containing medium. For dissecting the role of major collagen receptors, we used two FN-deficient mouse fibroblast lines that both possess integrin α₅β₁ but differ in their collagen-binding integrins. Embryo-derived FN-null fibroblasts, which express α₁₁- but no α₂-integrin, barely spread and tended to cluster on collagen gels. Moreover, FN-null fibroblasts required exogenously added FN to assemble α₅β₁-integrin in fibrillar adhesion contacts, and to contract collagen matrices. In contrast, postnatal kidney fibroblasts were found to express α₂- but barely α₁₁-integrin. When FN expression was suppressed in these cells by shRNA transfection, they were able to spread on and partially contract collagen gels in the absence of exogenous FN. Also in this case, however, collagen contracture was stimulated by adding FN to the medium. Antibody to integrin α₅β₁ or RGD peptide completely abolished collagen contracture by FN-deficient fibroblasts stimulated by FN addition. We conclude that although collagen-binding integrins (especially α₂β₁) can mediate contracture of fibrillar collagen gels by murine fibroblasts to some extent, full activity is causally linked to the presence of pericellular FN and its receptor integrin α₅β₁.

Tranilast inhibits TGF-β-induced collagen gel contraction mediated by human corneal fibroblasts

AIM

To determine if tranilast affects human corneal fibroblast (HCFs) contraction.

METHODS

HCFs cultured in a three-dimensional type I collagen gel were treated with or without transforming growth factor beta (TGF-β) or tranilast. Gel diameter was measured as an indicator for collagen contraction. Immunoblot was performed to evaluate myosin light chain (MLC) and paxillin phosphorylation. Confocal microscopy was employed to examine the focal adhesions and actin stress fiber formation. Immunoblot analysis and gelatin zymography were performed to detect tissue inhibitors of metalloproteinases and matrix metalloproteinases (MMPs) in supernatant.

RESULTS

The inhibitory effect of tranilast on HCFs-mediated collagen gel contraction induced by TGF-β was dose-dependent. The significant effect of tranilast was started from 100 µmol/L and maximized at 300 µmol/L. The peak effect of 300 µmol/L tranilast also relied on the duration of treatment, which showed statistical significance from day 2. TGF-β-induced paxillin and MLC phosphorylation, stress fiber formation, focal adhesions, and MMP-1, MMP-2, and MMP-3 secretion in HCFs were also inhibited by tranilast.

CONCLUSION

Tranilast suppresses the HCFs-cultured collagen gel contraction induced by TGF-β. It attenuates actin stress fibers formation, focal adhesions, and the secretion of MMPs, with these actions likely contributing to the inhibitory effect on HCF contractility. By attenuating the contractility of corneal fibroblasts, tranilast treatment may inhibit corneal scarring.

Triptolide inhibits TGF-β-induced matrix contraction and fibronectin production mediated by human Tenon fibroblasts

AIM

To determine if triptolide influences the contractility and fibronectin production in human Tenon fibroblasts (HTFs).

METHODS

HTFs were cultured in type I collagen gels with or without transforming growth factor beta (TGF-β) and/or triptolide. The diameter of the collagen gel was used to measure contraction. Immunoblot analysis was used to quantify myosin light chain (MLC) phosphorylation and integrin expression. Laser confocal fluorescence microscopy was used to monitor the formation of actin stress fibers. Fibronectin production was measured with an enzyme immunoassay.

RESULTS

Triptolide inhibition of contraction in TGF-β-induced collagen gel mediated by HTFs was dose-dependent and statistically significant at 3 nmol/L (P<0.05) and maximal at 30 nmol/L and significantly time dependent at 2d (P<0.05). Triptolide reduced TGF-β-induced expression of integrins α5 and β1, phosphorylation of MLC, and formation of stress fibers in HTFs. Furthermore, the inhibition of triptolide on the attenuated TGF-β-induced production of fibronectin by HTFs was concentration-dependent and significant at 1 nmol/L (P<0.05) and maximal at 30 nmol/L.

CONCLUSION

Triptolide suppress the contractility of HTFs induced by TGF-β and the production of fibronectin by these cells. It is promising that triptolide treatment may possibly inhibit scar formation after glaucoma filtration surgery.

Fibronectin promotes elastin deposition, elasticity and mechanical strength in cellularised collagen-based scaffolds

One of the tightest bottlenecks in vascular tissue engineering (vTE) is the lack of strength and elasticity of engineered vascular wall models caused by limited elastic fiber deposition. In this study, flat and tubular collagen gel-based scaffolds were cellularised with vascular smooth muscle cells (SMCs) and supplemented with human plasma fibronectin (FN), a known master organizer of several extracellular matrix (ECM) fiber systems. The consequences of FN on construct maturation was investigated in terms of geometrical contraction, viscoelastic mechanical properties and deposition of core elastic fiber proteins. FN was retained in the constructs and promoted deposition of elastin by SMCs as well as of several proteins required for elastogenesis such as fibrillin-1, lysyl oxidase, fibulin-4 and latent TGF-β binding protein-4. Notably, gel contraction, tensile equilibrium elastic modulus and elasticity were strongly improved in tubular engineered tissues, approaching the behaviour of native arteries. In conclusion, this study demonstrates that FN exerts pivotal roles in directing SMC-mediated remodeling of scaffolds toward the production of a physiological-like, elastin-containing ECM with excellent mechanical properties. The developed FN-supplemented systems are promising for tissue engineering applications where the generation of mature elastic tissue is desired and represent valuable advanced in vitro models to investigate elastogenesis.

Role of macrophage migration inhibitory factor (MIF) in the effects of oxidative stress on human retinal pigment epithelial cells

Proliferative vitreoretinopathy (PVR) is the major cause of treatment failure in individuals who undergo surgery for retinal detachment. The epithelial-mesenchymal transition (EMT) in retinal pigment epithelium (RPE) cells contributes to the pathogenesis of PVR. Oxidative stress is thought to play a role in the progression of retinal diseases including PVR. We have now examined the effects of oxidative stress on the EMT and related processes in the human RPE cell line. We found that H₂ O₂ induced the contraction of RPE cells in a three-dimensional collagen gel. Analysis of a cytokine array revealed that H₂ O₂ specifically increased the release of macrophage migration inhibitory factor (MIF) from RPE cells. Reverse transcription-polymerase chain reaction and immunoblot analyses showed that H₂ O₂ increased the expression of MIF in RPE cells. Immunoblot and immunofluorescence analyses revealed that H₂ O₂ upregulated the expression of α-SMA and vimentin and downregulated that of ZO-1 and N-cadherin. Consistent with these observations, the transepithelial electrical resistance of cell was reduced by exposure to H₂ O₂ . The effects of oxidative stress on EMT-related and junctional protein expression as well as on transepithelial electrical resistance were inhibited by antibodies to MIF, but they were not mimicked by treatment with recombinant MIF. Finally, analysis with a profiling array for mitogen-activated protein kinase signalling revealed that H₂ O₂ specifically induced the phosphorylation of p38 mitogen-activated protein kinase. Our results thus suggest that MIF may play a role in induction of the EMT and related processes by oxidative stress in RPE cells and that it might thereby contribute to the pathogenesis of PVR. Proliferative vitreoretinopathy is a major complication of rhegmatogenous retinal detachment, and both oxidative stress and induction of the EMT in RPE cells are thought to contribute to the pathogenesis of this condition. We have now examined the effects of oxidative stress on the EMT and related processes in the human RPE cell line ARPE19. Our results thus implicate MIF in induction of the EMT and related processes by oxidative stress in RPE cells and the regulated expression of EMT markers. They further suggest that MIF may play an important role in the pathogenesis of PVR.

Role of corneal collagen fibrils in corneal disorders and related pathological conditions

The cornea is a soft tissue located at the front of the eye with the principal function of transmitting and refracting light rays to precisely sense visual information. Corneal shape, refraction, and stromal stiffness are to a large part determined by corneal fibrils, the arrangements of which define the corneal cells and their functional behaviour. However, the modality and alignment of native corneal collagen lamellae are altered in various corneal pathological states such as infection, injury, keratoconus, corneal scar formation, and keratoprosthesis. Furthermore, corneal recuperation after corneal pathological change is dependent on the balance of corneal collagen degradation and contraction. A thorough understanding of the characteristics of corneal collagen is thus necessary to develop viable therapies using the outcome of strategies using engineered corneas. In this review, we discuss the composition and distribution of corneal collagens as well as their degradation and contraction, and address the current status of corneal tissue engineering and the progress of corneal cross-linking.

Inhibition by all-trans retinoic acid of collagen degradation mediated by corneal fibroblasts

BACKGROUND

We examined the effect of all-trans retinoic acid on collagen degradation mediated by corneal fibroblasts.

METHODS

Rabbit corneal fibroblasts were cultured with or without all-trans retinoic acid in a three-dimensional collagen gel, and the extent of collagen degradation was determined by measurement of hydroxyproline in acid hydrolysates of culture supernatants. Matrix metalloproteinase expression was examined by immunoblot analysis and gelatin zymography. The abundance and phosphorylation state of the endogenous nuclear factor-kappaB inhibitor IκB-α were examined by immunoblot analysis. Corneal ulceration was induced by injection of lipopolysaccharide into the central corneal stroma of rabbits and was assessed by observation with a slitlamp microscope.

RESULTS

All-trans retinoic acid inhibited interleukin-1β-induced collagen degradation by corneal fibroblasts in a concentration- and time-dependent manner. It also attenuated the release and activation of matrix metalloproteinases as well as the phosphorylation and degradation of IκB-α induced by interleukin-1β in these cells. Topical application of all-trans retinoic acid suppressed corneal ulceration induced by injection of lipopolysaccharide into the corneal stroma.

CONCLUSIONS

All-trans retinoic acid inhibited collagen degradation mediated by corneal fibroblasts exposed to interleukin-1β, with this effect being accompanied by suppression of nuclear factor-kappaB signalling as well as of matrix metalloproteinase release and activation in these cells. All-trans retinoic acid also attenuated lipopolysaccharide-induced corneal ulceration in vivo. Our results therefore suggest that all-trans retinoic acid might prove effective for the treatment of patients with corneal ulceration.

Attenuation of EMT in RPE cells and subretinal fibrosis by an RAR-γ agonist

Subretinal fibrosis contributes to the loss of vision associated with age-related macular degeneration (AMD). Retinal pigment epithelial (RPE) cells play a key role in the pathogenesis of AMD including the fibrotic reaction. We examined the role of retinoic acid receptor-γ (RAR-γ) in the epithelial-mesenchymal transition (EMT) and other fibrosis-related processes in mouse RPE cells cultured in a type I collagen gel. Transforming growth factor-β2 (TGF-β2)-induced collagen gel contraction mediated by the RPE cells was inhibited by the RAR-γ agonist R667 in a concentration- and time-dependent manner. Expression of the mesenchymal markers α-smooth muscle actin and fibronectin, the release of interleukin-6, and the phosphorylation of paxillin, mitogen-activated protein kinases (ERK, p38, and JNK), Smad2, and AKT induced by TGF-β2 were also suppressed by the RAR-γ agonist. Furthermore, gelatin zymography and immunoblot analysis revealed that the TGF-β2-induced release of matrix metalloproteinase (MMP)-2, MMP-3, MMP-8, and MMP-9 from RPE cells was inhibited by R667, and the MMP inhibitor GM6001 attenuated TGF-β2-induced RPE cell contraction. Finally, immunohistofluorescence analysis with antibodies to glial fibrillary acidic protein showed that R667 inhibited the development of subretinal fibrosis in a mouse model in vivo. Our results thus suggest that RAR-γ agonists may prove effective for the treatment of subretinal fibrosis associated with AMD.

KEY MESSAGE

RAR-γ agonist R667 suppressed collagen gel contraction mediated by RPE cells. Epithelial-mesenchymal transition (EMT) in RPE cells was inhibited by RAR-γ agonist R667. RAR-γ agonist R667 inhibited fibrosis-related processes in RPE cells. RAR-γ agonists may attenuate AMD-associated fibrosis.

Collagen matrix as a tool in studying fibroblastic cell behavior

Type I collagen is a fibrillar protein, a member of a large family of collagen proteins. It is present in most body tissues, usually in combination with other collagens and other components of extracellular matrix. Its synthesis is increased in various pathological situations, in healing wounds, in fibrotic tissues and in many tumors. After extraction from collagen-rich tissues it is widely used in studies of cell behavior, especially those of fibroblasts and myofibroblasts. Cells cultured in a classical way, on planar plastic dishes, lack the third dimension that is characteristic of body tissues. Collagen I forms gel at neutral pH and may become a basis of a 3D matrix that better mimics conditions in tissue than plastic dishes.

Expression of the α5 integrin gene in corneal epithelial cells cultured on tissue-engineered human extracellular matrices

The integrin α5β1 plays a major role in corneal wound healing by promoting epithelial cell adhesion and migration over the fibronectin matrix secreted as a cellular response to corneal damage. Expression of α5 is induced when rabbit corneal epithelial cells (RCECs) are grown in the presence of fibronectin. Here, we examined whether α5 expression is similarly altered when RCECs or human corneal epithelial cells (HCECs) are grown on a reconstructed stromal matrix used as an underlying biomaterial. Mass spectrometry and immunofluorescence analyses revealed that the biomaterial matrix produced by culturing human corneal fibroblasts with ascorbic acid (ECM/35d) contains several types of collagens, fibronectin, tenascin and proteoglycans. Results from transfection of CAT/α5-promoter plasmids, Western blot and EMSA analyses indicated that ECM/35d significantly increase expression of α5 in HCECs as a result of alteration in the expression and DNA binding of the transcription factors NFI, Sp1, AP-1 and PAX6. The biological significance of this biomaterial substitute on the expression of the α5 gene may therefore contribute to better understand the function played by the α5β1 integrin during corneal wound healing.

Force-induced fibronectin assembly and matrix remodeling in a 3D microtissue model of tissue morphogenesis

Encapsulations of cells in type-I collagen matrices are widely used three-dimensional (3D) in vitro models of wound healing and tissue morphogenesis and are common constructs for drug delivery and for in vivo implantation. As cells remodel the exogenous collagen scaffold, they also assemble a dense fibronectin (Fn) matrix that aids in tissue compaction; however, the spatio-temporal (re)organization of Fn and collagen in this setting has yet to be quantitatively investigated. Here, we utilized microfabricated tissue gauges (μTUGs) to guide the contraction of microscale encapsulations of fibroblasts within collagen gels. We combined this system with a Foerster Radius Energy Transfer (FRET) labeled biosensor of Fn conformation to probe the organization, conformation and remodeling of both the exogenous collagen and the cell-assembled Fn matrices. We show that within hours, compact Fn from culture media adsorbed to the collagen scaffold. Over the course of tissue remodeling, this Fn-coated collagen scaffold was compacted into a thin, sparsely populated core around which cells assembled a dense fibrillar Fn shell that was rich in both cell and plasma derived Fn. This resulted in two separate Fn populations with different conformations (compact/adsorbed and extended/fibrillar) in microtissues. Cell contractility and microtissue geometry cooperated to remodel these two populations, resulting in spatial gradients in Fn conformation. Together, these results highlight an important spatio-temporal interplay between two prominent extracellular matrix (ECM) molecules (Fn and collagen) and cellular traction forces, and will have implications for future studies of the force-mediated remodeling events that occur within collagen scaffolds either in 3D in vitro models or within surgical implants in vivo.

Adhesion, phenotypic expression, and biosynthetic capacity of corneal keratocytes on surfaces coated with hyaluronic acid of different molecular weights

In ophthalmology, hyaluronic acid (HA) is an important extracellular matrix (ECM) component and is appropriate for use in generating a microenvironment for cell cultivation. The aim of this work was to evaluate the rabbit corneal keratocyte (RCK) growth in response to HA coatings under serum-free conditions. After modification with HA of varying molecular weights (MWs: 35-1500kDa), the surfaces were characterized by atomic force microscopy and contact angle measurements, and were used for cell culture studies. Our data indicated that the substrates coated with higher negatively charged HA become rougher and are more hydrophilic, resulting in the decrease of cell adhesion and cell-matrix interaction. This early cellular event was likely responsible for the determination of keratocyte configuration. Additionally, for the growth of RCKs on dry HA coatings with surface roughness of 1.1-1.7 nm, a strong cell-cell interaction was observed, which may facilitate the formation of multicellular spheroid aggregates and maintenance of mitotically quiescent state. At each culture time point from 1 to 5 days, a better biosynthetic capacity associated with a higher prevalence of elevated ECM production was found for the cells in a spherical configuration. Irrespective of polysaccharide MW of surface coatings, the RCKs presented good viability without hypoxia-induced death. As compared with a monolayer of adherent keratocytes on tissue culture polystyrene plates and low MW HA-modified samples, the cell spheroids (76-110 μm in diameter) showed significantly higher expressions of keratocan and lumican and lower expressions of biglycan, similar to those of keratocytes in vivo. Moreover, the expression levels of corneal crystallin aldehyde dehydrogenase (7-9-fold increase) and nestin (10-16-fold increase) were greater in larger-sized spheroids, indicating higher ability to maintain cellular transparency and self-renewal potential. It is concluded that the cultured RCKs on surfaces coated with HA of different MWs can sense ECM cues, and the multicellular spheroids may potentially be used for corneal stromal tissue engineering applications.

Cell-matrix adhesions in 3D

Cells in a three-dimensional (3D) extracellular matrix environment often display different properties and behavior compared to cells cultured on a two-dimensional (2D) substrate. Recent studies characterizing the cell-matrix adhesions formed by cells within a 3D matrix have arrived at contradictory conclusions regarding the presence and composition of adhesions. Here we review this literature, and provide a comparative compilation of information found in published studies from the 3D cell-matrix adhesion field in order to identify shared and divergent conclusions and conceptually important areas that require further research. Although there is a general consensus that discrete cell-matrix adhesions exist in various 3D matrix environments, there are specific exceptions, particularly in cells undergoing amoeboid migration. There are also technical issues to consider when imaging adhesions in 3D matrix; for example, over-expression of a cytoskeletal cell adhesion component can potentially cloud the visualization of adhesions and even alter the mode of cell migration. Properties such as stiffness and local matrix topography may also affect the composition of cell-matrix adhesions. For example, even though cells contain integrin-based 3D adhesions, there can be substantial variability within these adhesions in the presence of force-dependent cytoskeletal components such as vinculin. These new findings and ideas provide promising new leads for understanding the regulation and function of cell-matrix adhesions in 3D matrix.

A chemical biology screen reveals a role for Rab21-mediated control of actomyosin contractility in fibroblast-driven cancer invasion

Background:

Carcinoma-associated fibroblasts (CAFs) can promote the progression of tumours in many ways. They can remodel the extracellular matrix to generate an environment that enables the invasion of cancer cells. We hypothesised that compounds that prevent matrix remodelling by CAFs would block their ability to promote carcinoma cell invasion.

Methods:

We designed a screen for compounds that interfere with CAF-promoted matrix remodelling. Hits from this screen were investigated in organotypic invasion models of squamous cell carcinoma (SCC).

Results:

We find that lovastatin and simvastatin reduce matrix remodelling by fibroblasts and thereby reduce SCC invasion. This class of compounds exert their effects partly through disrupting the function of Rab proteins, and we show a new role for Rab21 in promoting cancer cell invasion promoted by CAFs.

Conclusions:

Rab21 is required for CAFs to promote the invasion of cancer cells. It enables the accumulation of integrin α5 at the plasma membrane and subsequent force-mediated matrix remodelling.

Biomineralization of a self-assembled extracellular matrix for bone tissue engineering

Understanding how biomineralization occurs in the extracellular matrix (ECM) of bone cells is crucial to the understanding of bone formation and the development of a successfully engineered bone tissue scaffold. It is still unclear how ECM mechanical properties affect protein-mineral interactions in early stages of bone mineralization. We investigated the longitudinal mineralization properties of MC3T3-E1 cells and the elastic modulus of their ECM using shear modulation force microscopy, synchrotron grazing incidence X-ray diffraction (GIXD), scanning electron microscopy, energy dispersive X-ray spectroscopy, and confocal laser scanning microscopy (CLSM). The elastic modulus of the ECM fibers underwent significant changes for the mineralizing cells, which were not observed in the nonmineralizing cells. On substrates conducive to ECM network production, the elastic modulus of mineralizing cells increased at time points corresponding to mineral production, whereas that of the nonmineralizing cells did not vary over time. The presence of hydroxyapatite in mineralizing cells and the absence thereof in the nonmineralizing ones were confirmed by GIXD, and CLSM showed that a restructuring of actin occurred only for mineral-producing cells. These results show that the correct and complete development of the ECM network is required for osteoblasts to mineralize. This in turn requires a suitably prepared synthetic substrate for bone development to succeed in vitro.

Epidermal growth factor synergism with TGF-beta1 via PI-3 kinase activity in corneal keratocyte differentiation

PURPOSE

To investigate the action of epidermal growth factor (EGF) on corneal keratocyte differentiation and its effects in conjunction with transforming growth factor (TGF)-beta1.

METHODS

Rabbit corneal keratocytes (RCKs) were treated with EGF, TGF-beta1, or EGF plus TGF-beta1 in the presence or absence of inhibitors of EGF-receptor (EGF-R), neutralizing concentrations of EGF antibody and of signaling kinases for 2 days to 1 week. RCK differentiation to myofibroblasts was identified with anti-aldehyde dehydrogenase (ALDH)-1 and alpha-smooth muscle actin (alpha-SMA) antibodies. Cell proliferation was evaluated with anti-Ki-67 antibody. Extracellular matrix (ECM) components were assayed by immunochemistry and Western blot. Cell migration images were captured with a camera attached to the microscope, and the area of the wound was calculated using imaging software.

RESULTS

RCKs cultured in serum-free DMEM/F12 without frequent changes of medium maintained the phenotype for more than 1 month. EGF stimulated differentiation into a proto-myofibroblast phenotype with the loss of dendritic shape and the expression of alpha-SMA. Treatment with TGF-beta1 stimulated 12% of the cells to differentiate to defined myofibroblasts, but in the presence of EGF, TGF-beta1 induced 90% of RCKs to transform into myofibroblasts. Inhibition of EGF-R activation and of the phosphatidylinositol-3 kinase (PI-3K)/Akt-1 pathway prevented the action of EGF on TGF-beta1 cell differentiation. TGF-beta1 in the presence of EGF also increased cell migration, which is inhibited by blocking EGF-R activation.

CONCLUSIONS

These data show that EGF contributes to the differentiation and migration of myofibroblasts induced by TGF-beta1 through EGF-R activation and that it is an important modulator of wound healing and scar tissue formation.

Cell-matrix adhesion

The complex interactions of cells with extracellular matrix (ECM) play crucial roles in mediating and regulating many processes, including cell adhesion, migration, and signaling during morphogenesis, tissue homeostasis, wound healing, and tumorigenesis. Many of these interactions involve transmembrane integrin receptors. Integrins cluster in specific cell-matrix adhesions to provide dynamic links between extracellular and intracellular environments by bi-directional signaling and by organizing the ECM and intracellular cytoskeletal and signaling molecules. This mini review discusses these interconnections, including the roles of matrix properties such as composition, three-dimensionality, and porosity, the bi-directional functions of cellular contractility and matrix rigidity, and cell signaling. The review concludes by speculating on the application of this knowledge of cell-matrix interactions in the formation of cell adhesions, assembly of matrix, migration, and tumorigenesis to potential future therapeutic approaches.