An interleukin-1 loop is induced in human skin fibroblasts upon stress relaxation in a three-dimensional collagen gel but is not involved in the up-regulation of matrix metalloproteinase 1

Matrix Metalloproteases from Adipose Tissue-Derived Stromal Cells Are Spatiotemporally Regulated by Hydrogel Mechanics in a 3D Microenvironment

Adipose tissue-derived stromal cells (ASCs) are of interest in tissue engineering and regenerative medicine (TERM) due to their easy acquisition, multipotency, and secretion of a host of factors that promote regeneration. Retention of ASCs in or around lesions is poor following direct administration. Therefore, for TERM applications, ASCs can be ‘immobilized’ via their incorporation into hydrogels such as gelatine methacryloyl (GelMA). Tweaking GelMA concentration is a common approach to approximate the mechanical properties found in organs or tissues that need repair. Distinct hydrogel mechanics influence the ability of a cell to spread, migrate, proliferate, and secrete trophic factors. Mesenchymal cells such as ASCs are potent remodellers of the extracellular matrix (ECM). Not only do ASCs deposit components, they also secrete matrix metalloproteases (MMPs) which degrade ECM. In this work, we investigated if GelMA polymer concentration influenced the expression of active MMPs by ASCs. In addition, MMPs’ presence was interrogated with regard to ASCs morphology and changes in hydrogel ultrastructure. For this, immortalised ASCs were embedded in 5%, 10%, and 15% (w/v) GelMA hydrogels, photopolymerised and cultured for 14 d. Zymography in situ indicated that MMPs had a variable, hydrogel concentration-dependent influence on ASCs-secreted MMPs. In 5% GelMA, ASCs showed a high and sustained expression of MMPs, while, in 10% and 15% GelMA, such expression was almost null. ASCs morphology based on F-actin staining showed that increasing GelMA concentrations inhibit their spreading. Scanning electron microscopy (SEM) showed that hydrogel ultrastructure in terms of pore density, pore size, and percentage porosity were not consistently influenced by cells. Interestingly, changes in ultrastructural parameters were detected also in cell-free materials, albeit without a clear trend. We conclude that hydrogel concentration and its underlying mechanics influenced MMP expression by ASCs. The exact MMPs that respond to these mechanical cues should be defined in follow-up experiments.

Cigarette smoke condensate inhibits collagen gel contraction and prostaglandin E2 production in human gingival fibroblasts

BACKGROUND

Granulation tissue remodeling and myofibroblastic differentiation are critically important events during wound healing. Tobacco smoking has a detrimental effect in gingival tissue repair. However, studies evaluating the effects of cigarette smoke on these events are lacking.

MATERIAL AND METHODS

We used gingival fibroblasts cultured within free-floating and restrained collagen gels to simulate the initial and final steps of the granulation tissue phase during tissue repair. Collagen gel contraction was stimulated with serum or transforming growth factor-β1. Cigarette smoke condensate (CSC) was used to evaluate the effects of tobacco smoke on gel contraction. Protein levels of alpha-smooth muscle actin, β1 integrin, matrix metalloproteinase-3 and connective tissue growth factor were evaluated through Western blot. Prostaglandin E(2) (PGE(2)) levels were determined through ELISA. Actin organization was evaluated through confocal microscopy.

RESULTS

CSC reduced collagen gel contraction induced by serum and transforming growth factor-β1 in restrained collagen gels. CSC also altered the development of actin stress fibers in fibroblasts cultured within restrained collagen gels. PGE(2) levels were strongly diminished by CSC in three-dimensional cell cultures. However, other proteins involved in granulation tissue remodeling and myofibroblastic differentiation such as alpha-smooth muscle actin, β1 integrin, matrix metalloproteinase-3 and connective tissue growth factor, were unmodified by CSC.

CONCLUSIONS

CSC may alter the capacity of gingival fibroblasts to remodel and contract a collagen matrix. Inhibition of PGE(2) production and alterations of actin stress fibers in these cells may impair proper tissue maturation during wound healing in smokers.

The use of an IL-1 receptor antagonist peptide to control inflammation in the treatment of corneal limbal epithelial stem cell deficiency

Corneal limbal stem cell deficiency (LSCD) may be treated using ex vivo limbal epithelial stem cells (LESCs) derived from cadaveric donor tissue. However, continuing challenges exist around tissue availability, inflammation, and transplant rejection. Lipopolysaccharide (LPS) or recombinant human IL-1β stimulated primary human keratocyte and LESC models were used to investigate the anti-inflammatory properties of a short chain, IL-1 receptor antagonist peptide for use in LESC sheet growth to control inflammation. The peptide was characterized using mass spectroscopy and high performance liquid chromatography. Peptide cytotoxicity, patterns of cell cytokine expression in response to LPS or IL-1β stimulation, and peptide suppression of this response were investigated by MTS/LDH assays, ELISA, and q-PCR. Cell differences in LPS stimulated toll-like receptor 4 expression were investigated using immunocytochemistry. A significant reduction in rIL-1β stimulated inflammatory cytokine production occurred following LESC and keratocyte incubation with anti-inflammatory peptide and in LPS stimulated IL-6 and IL-8 production following keratocyte incubation with peptide (1 mg/mL) (P < 0.05). LESCs produced no cytokine response to LPS stimulation and showed no TLR4 expression. The peptide supported LESC growth when adhered to a silicone hydrogel contact lens indicating potential use in improved LESC grafting through suppression of inflammation.

Stimulatory effect of fibroblast-derived prostaglandin E₂ on keratinocyte stratification in the skin equivalent

Epidermal-dermal interaction plays important roles in physiological events such as wound healing. In this study, we examined a double paracrine mechanism between keratinocytes and fibroblasts through interleukin-1 (IL-1) and an IL-1-induced inflammatory mediator prostaglandin E₂ (PGE₂) using the skin equivalent. The epidermal layer of the skin equivalent expressed high levels of IL-1α mRNA (IL1A mRNA) and relatively low levels of IL-1β mRNA (IL1B mRNA). IL1A mRNA was not detected in fibroblasts. Fibroblasts also expressed low but not negligible levels of IL1B mRNA only in the presence of keratinocytes. Expression of prostaglandin-endoperoxide synthase 2 mRNA (PTGS2 mRNA) and production of PGE₂ in three-dimensionally cultured fibroblasts were noticeably stimulated by co-culture with keratinocytes, whereas PTGS2 mRNA expression in the epidermal layer was very low. In addition, hydroxyprostaglandin dehydrogenase 15-(NAD) mRNA was highly expressed in keratinocytes but not in fibroblasts, and exogenous IL-1β stimulated PTGS2 mRNA expression in the dermal equivalent. The thickness of the epidermal layer and the number of MKI67-positive keratinocytes in the skin equivalent were decreased by treatment with indomethacin, and the decrease recovered when exogenous PGE₂ was added. These results indicate that keratinocytes stimulate their own proliferation through a double paracrine mechanism mediated by IL-1 and PGE₂.

MyD88 protects from lethal encephalitis during infection with vesicular stomatitis virus

MyD88 is a key adaptor molecule in innate resistance, engaged in most Toll-like receptor, as well as IL-1 and IL-18, signalling. Here, we analyzed the role of MyD88 in innate resistance during infection with vesicular stomatitis virus (VSV) using myd88(-/-) mice. We found an increased susceptibility to VSV in myd88(-/-) mice, which was not explained by reduced type I IFN or neutralizing antibody responses. Susceptibility of myd88(-/-) mice correlated with impaired recruitment of immune cells to the site of infection. In the absence of MyD88 signalling, VSV rapidly spread to the spinal cord and brain causing lethal encephalitis.

Radiation-induced alterations in cytokine production by skin cells

Ionizing radiation exposure of skin results in a cutaneous radiation reaction comprising all pathophysiological reactions and clinical symptoms in irradiated skin. Biological responses of skin occur in a characteristic temporal pattern and mainly depend on radiation quality, dose rate, total dose, and cellular conditions. Immediately after irradiation, production of cytokines by skin cells is initiated and continues as a cascade during all stages of the cutaneous radiation syndrome leading to progressive late symptoms, the predominant of which is fibrosis. Cytokines are important signaling molecules mediating communicative interactions both locally between different cell types within dermal tissues and distantly between organs. Although during recent years much progress has been made in dissecting the complex cytokine network, the role of cytokines in the pathophysiology of the cutaneous radiation reaction is only beginning to be elucidated. Previous studies indicate that the major cytokines in the response of skin cells to ionizing radiation include IL (interleukin)-1, IL-6, tumor necrosis factor (TNF)-alpha, transforming growth factor (TGF)-beta, and the chemokines IL-8 and eotaxin. In this paper, existing data on the radiation-induced modulation of cytokine expression by skin cells are reviewed.

Decreased collagen production in chronologically aged skin: roles of age-dependent alteration in fibroblast function and defective mechanical stimulation

Reduced synthesis of collagen types I and III is characteristic of chronologically aged skin. The present report provides evidence that both cellular fibroblast aging and defective mechanical stimulation in the aged tissue contribute to reduced collagen synthesis. The reduction in collagen synthesis due to fibroblast aging was demonstrated by a lower in vitro production of type I procollagen by dermal fibroblasts isolated from skin of young (18 to 29 years) versus old (80+ years) individuals (82 +/- 16 versus 56 +/- 8 ng/ml; P < 0.05). A reduction in mechanical stimulation in chronologically aged skin was inferred from morphological, ultrastructural, and fluorescence microscopic studies. These studies, comparing dermal sections from young and old individuals, demonstrated a greater percentage of the cell surface attached to collagen fibers (78 +/- 6 versus 58 +/- 8%; P < 0.01) and more extensive cell spreading (1.0 +/- 0.3 vs. 0.5 +/- 0.3; P < 0.05) in young skin compared with old skin. These features are consistent with a lower level of mechanical stimulation on the cells in old versus young skin. Based on the findings presented here, we conclude that reduced collagen synthesis in chronologically aged skin reflects at least two different underlying mechanisms: cellular fibroblast aging and a lower level of mechanical stimulation.

Interleukin 1beta (IL1B) signaling is a critical component of radiation-induced skin fibrosis

Interleukin 1 beta (IL1B), a potent pro-inflammatory cytokine, is directly up-regulated by radiation and is known to regulate other inflammation-related molecules, such as the matrix metalloproteinases (MMPs) and their endogenous inhibitors (TIMPs). However, the nature of the interaction of IL1B with MMPs and TIMPs in radiation-induced skin fibrosis is unknown. We examined the response of primary dermal keratinocytes, fibroblasts and endothelial cells to single-fraction radiation (10 Gy) and compared the results to a temporal sequence of histology from irradiated C57BL/6 and IL1R1 knockout mice. These studies showed that keratinocytes are the major IL1-producing cells in vitro and that radiation induces an immediate and chronic elevation in the expression of IL1B mRNA in the skin of C57BL/6 mice. This elevation was principally early and was less pronounced in the IL1R1 knockout strain, which also demonstrated reduced late radiation fibrosis. Radiation also increased expression of MMP mRNA in C57BL/6 mice. Finally, exogenous IL1B protein induced robust endogenous IL1B mRNA expression, along with a brisk increase in MMPs and collagen III, but only in the C57BL/6 mice. In conclusion, these data suggest that IL1B plays a critical role in radiation-induced fibrosis and that the increased MMPs fail to block the IL1-related collagen accumulation.

RGDS and DGEA-induced [Ca2+]i signalling in human dermal fibroblasts

A pulse of short peptides, RGDS and DGEA in the millimolar range, immediately elicits in normal human fibroblasts a transient increase of intracellular Ca2+ ([Ca2+]i). In the present study, we show that this [Ca2+]i occurs in an increasing number of cells as a function of peptides concentration. It is specific of each peptide and inhibited at saturating concentration of the peptide in the culture medium. The [Ca2+]i transient depends on signalling pathways slightly different for DGEA and RGDS involving tyrosine kinase(s) and phosphatase(s), phospholipase C, production of inositol-trisphosphate and release of Ca2+ from the cellular stores. GFOGER, the classical collagen binding peptide of alpha1- alpha2- and alpha11-beta1 integrins, in triple helical or denatured form, does not produce any Ca2+ signal. The [Ca2+]i signalling induced by RGDS and DGEA is inhibited by antibodies against beta1 integrin subunit while that mediated by RGDS is also inhibited by antibodies against the alpha3 integrin. Delay in the acquisition of responsiveness is observed during cell adhesion and spreading on a coat of fibronectin for RGDS or collagen for DGEA or on a coat of the specific integrin-inhibiting antibodies but not by seeding cells on GFOGER or laminin-5. This delay is suppressed specifically by collagenase acting on the collagen coat or trypsin on the fibronectin coat. Our results suggest that free integrins and associated focal complexes generate a Ca2+ signal upon recognition of DGEA and RGDS by different cellular pathways.

The role of interleukin-1 in the pathogenesis of human intervertebral disc degeneration

In this study, we investigated the hypotheses that in human intervertebral disc (IVD) degeneration there is local production of the cytokine IL-1, and that this locally produced cytokine can induce the cellular and matrix changes of IVD degeneration. Immunohistochemistry was used to localize five members of the IL-1 family (IL-1α, IL-1β, IL-1Ra (IL-1 receptor antagonist), IL-1RI (IL-1 receptor, type I), and ICE (IL-1β-converting enzyme)) in non-degenerate and degenerate human IVDs. In addition, cells derived from non-degenerate and degenerate human IVDs were challenged with IL-1 agonists and the response was investigated using real-time PCR for a number of matrix-degrading enzymes, matrix proteins, and members of the IL-1 family.

This study has shown that native disc cells from non-degenerate and degenerate discs produced the IL-1 agonists, antagonist, the active receptor, and IL-1β-converting enzyme. In addition, immunopositivity for these proteins, with the exception of IL-1Ra, increased with severity of degeneration. We have also shown that IL-1 treatment of human IVD cells resulted in increased gene expression for the matrix-degrading enzymes (MMP 3 (matrix metalloproteinase 3), MMP 13 (matrix metalloproteinase 13), and ADAMTS-4 (a disintegrin and metalloproteinase with thrombospondin motifs)) and a decrease in the gene expression for matrix genes (aggrecan, collagen II, collagen I, and SOX6).

In conclusion we have shown that IL-1 is produced in the degenerate IVD. It is synthesized by native disc cells, and treatment of human disc cells with IL-1 induces an imbalance between catabolic and anabolic events, responses that represent the changes seen during disc degeneration. Therefore, inhibiting IL-1 could be an important therapeutic target for preventing and reversing disc degeneration.

Cdc42 downregulates MMP-1 expression by inhibiting the ERK1/2 pathway

The small GTPases of the Rho family are key intermediates in cellular signalling triggered by activated cell-adhesion receptors. In this study, we took advantage of RNA interference (RNAi) using small interfering RNAs (siRNAs) to define the roles of the best-characterized members of the RhoGTPase family, RhoA, Rac1 and Cdc42, in the control of MMP-1, MMP-2 and type-I-collagen expression in normal human skin fibroblasts (HSFs). A specific and long-lasting repression, up to 7 days after transfection, of the three GTPases was achieved by transient transfection of specific siRNA. The silencing of Cdc42, but not that of RhoA or Rac1, induced a 15-fold increase in MMP-1 secretion. This upregulation was confirmed at the mRNA level and observed with two different siRNAs targeting Cdc42. Such a regulation was also observed in various human cell lines and was rescued by re-expressing wild-type Cdc42 encoded by a construct bearing silent mutations impeding its recognition by the siRNA. By contrast, MMP-2 and type-I-collagen expression was not affected by the individual silencing of each Rho GTPase. Cytokine protein array, enzyme-linked immunosorbent assays and reverse-transcription PCR measurements revealed that ablation of Cdc42 induced an overexpression of interleukin 8 and MCP-1. Although these cytokines are known to induce the expression of MMP-1, we showed that they were not involved in the Cdc42-mediated upregulation of MMP-1. Silencing of Cdc42 also induced an increased phosphorylation of ERK1/2 and p38 MAP kinase. The use of chemical inhibitors on Cdc42-ablated cells revealed that the upregulation of MMP-1 is dependent on the ERK1/2 pathways, whereas the p38 MAP kinase pathway displayed an inhibitory role. Simultaneous knock-down of two or three Rho GTPases allowed us to demonstrate that the RhoA-ROCK pathway was not involved in this regulation but that the silencing of Rac1 reduced the effect of Cdc42 suppression. These data suggest that, in vivo, when cell/extracellular-matrix interactions via integrins induce cytoskeleton organization, MMP-1 expression is maintained at a low level by Cdc42 via a repression of the Rac1 and ERK1/2 pathways. Therefore, Cdc42 contributes to ECM homeostasis and connective tissue integrity.

Expression of pro-inflammatory markers by human dermal fibroblasts in a three-dimensional culture model is mediated by an autocrine interleukin-1 loop

In vivo, fibroblasts reside in connective tissues, with which they communicate in a reciprocal way. Such cell--extracellular matrix interactions can be studied in vitro by seeding fibroblasts in collagen lattices. Depending upon the mechanical properties of the system, fibroblasts are activated to assume defined phenotypes. In the present study, we examined a transcriptional profile of primary human dermal fibroblasts cultured in a relaxed collagen environment and found relative induction (>2-fold) of 393 out of approx. 7100 transcripts when compared with the same system under mechanical tension. Despite down-regulated proliferation and matrix synthesis, cells did not become generally quiescent, since they induced transcription of numerous other genes including matrix metalloproteinases (MMPs) and growth factors/cytokines. Of particular interest was the induction of gene transcripts encoding pro-inflammatory mediators, e.g. cyclo-oxygenase-2 (COX-2), and interleukins (ILs)-1 and -6. These are apparently regulated in a hierarchical fashion, since the addition of IL-1 receptor antagonist prevented induction of COX-2, IL-1 and IL-6, but not that of MMP-1 or keratinocyte growth factor (KGF). Our results suggest strongly that skin fibroblasts are versatile cells, which adapt to their extracellular environment by displaying specific phenotypes. One such phenotype, induced by a mechanically relaxed collagen environment, is the 'pro-inflammatory' fibroblast. We propose that fibroblasts that are embedded in a matrix environment can actively participate in the regulation of inflammatory processes.

Role of extracellular matrix in adaptation of tendon and skeletal muscle to mechanical loading

The extracellular matrix (ECM), and especially the connective tissue with its collagen, links tissues of the body together and plays an important role in the force transmission and tissue structure maintenance especially in tendons, ligaments, bone, and muscle. The ECM turnover is influenced by physical activity, and both collagen synthesis and degrading metalloprotease enzymes increase with mechanical loading. Both transcription and posttranslational modifications, as well as local and systemic release of growth factors, are enhanced following exercise. For tendons, metabolic activity, circulatory responses, and collagen turnover are demonstrated to be more pronounced in humans than hitherto thought. Conversely, inactivity markedly decreases collagen turnover in both tendon and muscle. Chronic loading in the form of physical training leads both to increased collagen turnover as well as, dependent on the type of collagen in question, some degree of net collagen synthesis. These changes will modify the mechanical properties and the viscoelastic characteristics of the tissue, decrease its stress, and likely make it more load resistant. Cross-linking in connective tissue involves an intimate, enzymatical interplay between collagen synthesis and ECM proteoglycan components during growth and maturation and influences the collagen-derived functional properties of the tissue. With aging, glycation contributes to additional cross-linking which modifies tissue stiffness. Physiological signaling pathways from mechanical loading to changes in ECM most likely involve feedback signaling that results in rapid alterations in the mechanical properties of the ECM. In developing skeletal muscle, an important interplay between muscle cells and the ECM is present, and some evidence from adult human muscle suggests common signaling pathways to stimulate contractile and ECM components. Unaccostumed overloading responses suggest an important role of ECM in the adaptation of myofibrillar structures in adult muscle. Development of overuse injury in tendons involve morphological and biochemical changes including altered collagen typing and fibril size, hypervascularization zones, accumulation of nociceptive substances, and impaired collagen degradation activity. Counteracting these phenomena requires adjusted loading rather than absence of loading in the form of immobilization. Full understanding of these physiological processes will provide the physiological basis for understanding of tissue overloading and injury seen in both tendons and muscle with repetitive work and leisure time physical activity.

ERK activation by mechanical strain is regulated by the small G proteins rac-1 and rhoA

Physical forces play an important role in regulating cell functions. We applied mechanical strain to human fibroblasts by magnetic attraction of superparamagnetic arginine-glycine-aspartic acid (RGD)-coated beads. We confirmed that the MAP kinases Erk and p38 are activated by mechanical strain, and went further by demonstrating the activation of Elk-1 by mechanical strain, mainly through a MEK-Erk pathway. Transfection of a dominant negative form of the G protein rac-1 (rac T17N), and inhibition of PI3K, an effector of rac-1, efficiently prevented Elk-1 activation by mechanical forces. Transfection with C3 transferase, known to inhibit rhoA, and inhibition of rock (a downstream effector of rhoA), gave similar results. However, contrary to the active form of rhoA (rho G14V), transfection of the active form of rac-1 (rac G12V) induced Elk activation and mimicked the effects of mechanical strain. These results point out that the two small G proteins rhoA and rac-1 participate in cell sensitivity to mechanical strain and lead to the modulation of the Erk pathway.

Laminin alpha 3 LG4 module induces matrix metalloproteinase-1 through mitogen-activated protein kinase signaling

The LG4 module of the laminin alpha 3 chain (alpha 3 LG4), a component of epithelial-specific laminin-5, has cell attachment activity and binds syndecan (Utani, A., Nomizu, M., Matsuura, H., Kato, K., Kobayashi, T., Takeda, U., Aota, S., Nielsen, P. K., and Shinkai, H. (2001) J. Biol. Chem. 276, 28779-28788). Here, we show that recombinant alpha 3 LG4 and a 19-mer synthetic peptide (A3G756) within alpha 3 LG4 active for syndecan binding increased the expression of matrix metalloproteinase-1 (MMP-1) in keratinocytes and fibroblasts. This induction was inhibited by heparin and required de novo synthesis of proteins. In keratinocytes, A3G756 up-regulated interleukin (IL)-1 beta and MMP-1 expression and an IL-1 receptor antagonist thoroughly inhibited A3G756-mediated induction of MMP-1. A3G756 also activated p38 mitogen-activated protein kinase (p38 MAPK) and extracellular signal-related kinase (Erk). Studies with specific inhibitors of MAPKs showed that p38 MAPK activation was necessary for both IL-1 beta and MMP-1 induction, but Erk activation was required only for MMP-1 induction. In fibroblasts, IL-1 receptor antagonist did not block A3G756-mediated induction of MMP-1. These results indicated that induction of MMP-1 by alpha 3 LG4 is mediated through the IL-1 beta autocrine loop in keratinocytes but the mechanism of the induction in fibroblasts is different. Our study suggests that the laminin alpha 3 LG4 module may play an important role in tissue remodeling by inducing MMP-1 expression during wound healing.

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.

Mechanical stress is required for high-level expression of connective tissue growth factor

We used gene array technology to analyze differences in gene expression between mechanically stressed and relaxed fibroblasts. A number of stress-responsive genes that showed a two- to sixfold difference in their relative expression were identified. Connective tissue growth factor (CTGF) was among those genes that showed the most striking up-regulation by mechanical stress. Its regulation occurred at the transcriptional level and was reversible. A new steady state level of CTGF mRNA was reached within less than 6 h after stress relaxation. Mechanical stress was absolutely required for sustained high-level expression; TGF-beta, which is also known to stimulate CTGF synthesis, was not sufficient on its own. Experiments with specific inhibitors suggested that a protein kinase and a tyrosine phosphatase were involved in the transduction of the mechanical stimulus to gene expression. Since CTGF controls the synthesis of several extracellular matrix proteins, it is likely that this growth factor is responsible for the increased synthesis of collagen I and other matrix proteins in stressed fibroblasts.

Cloning and characterization of ADAMTS-14, a novel ADAMTS displaying high homology with ADAMTS-2 and ADAMTS-3

The processing of amino- and carboxyl-propeptides of fibrillar collagens is required to generate collagen monomers that correctly assemble into fibrils. Mutations in the ADAMTS2 gene, the aminopropeptidase of procollagen I and II, result in the accumulation of non-fully processed type I procollagen, causing human Ehlers-Danlos syndrome type VIIC and animal dermatosparaxis. In this study, we show that the aminopropeptide of type I procollagen can be cleaved in vivo in absence of ADAMTS-2 activity and that this processing is performed at the cleavage site for ADAMTS-2. In an attempt to identify the enzyme responsible for this alternative aminoprocollagen peptidase activity, we have cloned the cDNA and determined the primary structure of human and mouse ADAMTS-14, a novel ADAMTS displaying striking homologies with ADAMTS-2 and -3. The structure of the human gene, which maps to 10q21.3, and the mechanisms of generation of the various transcripts are described. The existence of two sites of initiation of transcription, in two different promoter contexts, suggests that transcripts resulting from these two sites can be differently regulated. The tissue distribution of ADAMTS-14, the regulation of the gene expression by various cytokines and the activity of the recombinant enzyme are evaluated. The potential function of ADAMTS-14 as a physiological aminoprocollagen peptidase in vivo is discussed.

Distinct pathways in the over-expression of matrix metalloproteinases in human fibroblasts by relaxation of mechanical tension

The aim of the work was to analyze, on a comparative basis, the signaling pathways operating in the regulation of a panel of matrix metalloproteinases (MMP) expressed by human dermal fibroblasts submitted to mechanical stress relaxation by cytochalasin D (CD) and in a retracting collagen gel (RCG). The mRNA steady-state level of MMPs was measured by a quantitative RT-PCR procedure using a synthetic RNA as internal standard. In monolayer, most MMPs were barely detected, except MMP-2. Disruption of the actin stress fibers by CD induced a moderate increase of MMP-2 mRNA and a much larger stimulation of MMP-3, -9, -13 and -14 mRNAs. In RCG, a significant up-regulation of these MMPs was also observed although to a lower extent than in CD-treated monolayers. Among the investigated MMPs, the MMP-8 and -11 were not reproducibly detected. MMP-2 was processed to its active form both by CD and in RCG. The CD-induced up-regulation of gene expression was largely repressed by blocking protein synthesis by cycloheximide for all the MMPs, by inhibiting the tyrosine-kinases of the src family by herbimycin A for all MMPs, except MMP-2, and by inhibiting the TPA-inducible PKC isoforms by bisindoyl maleimide for all MMPs, except MMP-14. The up-regulation induced by stress relaxation in RCG was protein synthesis-dependent for MMP-2 and MMP-13, tyrosine kinases-dependent for MMP-3 and MMP-13, as previously described for MMP-1. Inhibiting TPA-inducible PKC did not affect any MMP in RCG except MMP-13, which was strongly induced. The processing of MMP-2 was tyrosine kinases-dependent but PKC-independent. Inhibitors of the ERK1,2 and p38 MAP kinases pathways diversely affected the MMPs expression. Inhibiting the Rho-kinase activity by Y-27632 was inactive. These results point to the potent regulation operated by the status of the cytoskeleton on the cell phenotype, and to distinct regulatory pathways involved in the control of different MMPs expression.

Intercellular mechanotransduction: cellular circuits that coordinate tissue responses to mechanical loading

Physical forces play an important role in modulating cell function and shaping tissue structure. Mechanotransduction, the process by which cells transduce physical force-induced signals into biochemical responses, is critical for mediating adaptations to mechanical loading in connective tissues. While much is known about mechanotransduction in cells involving forces delivered through extracellular matrix proteins and integrins, there is limited understanding of how mechanical signals are propagated through the interconnected cellular networks found in tissues and organs. We propose that intercellular mechanotransduction is a critical component for achieving coordinated remodeling responses to force application in connective tissues. We examine here recent evidence on different pathways of intercellular mechanotransduction and suggest a general model for how multicellular structures respond to mechanical loading as an integrated unit.

Coordinated regulation of procollagens I and III and their post-translational enzymes by dissipation of mechanical tension in human dermal fibroblasts

Mechanical tension governs fibroblast proliferation and survival and the homeostasis of the extracellular matrix to adapt its resistance to the mechanical requirements of the organs. To consolidate this view, we analysed the effect of tension release on the expression of molecules involved in the architecture and stabilisation of the collagen fibres, namely the procollagens type I and III, the amino- and carboxy-procollagen peptidases (N-pCP and C-pCP) and lysyl oxidase. Cells were cultured in conditions of high mechanical stress in monolayer on a collagen coat and under reduced tension by disruption of the cytoskeleton upon treatment with cytochalasin D in monolayer on a collagen coat or by integrin-mediated stress relaxation in a freely retracting collagen gel. The mRNAs were measured by quantitative RT-PCR monitored by simultaneous reverse-transcription and amplification of an original internal standard. Tension relaxation resulted in a decreased expression of the procollagens type I and III, of the two expressed forms of C-pCP, of the two forms of N-pCP and of lysyl oxidase. Type III collagen, known to control diameter of the fibres, was less down-regulated than type I collagen. Interestingly, the expression of the two alternatively spliced forms of the N-pCP was dissimilarly regulated. These data suggest that mechanical tension may modulate the stiffness of the extracellular matrix by controlling not only the level of expression of its fibrillar constituents but also that of the enzymes participating in their extracellular processing and mechanical stabilisation.

Autocrine regulation of proliferation and extracellular matrix homeostasis in human fibroblasts

In the late stages of the tissue repair process, as well as during normal tissue turnover, tissue homeostasis may rely mostly on autocrine mechanisms. Accordingly, we have cultured normal human fibroblasts on plastic surfaces and within three-dimensional collagen gels in order to study, in this environment, the action of autologous medium conditioned by the same cells. We have observed that inside collagen gels the autologous medium strongly restrains cell proliferation, due to fibroblast-secreted growth factors, whose inhibitory effect can be annulled by suramin. Furthermore, concerning extracellular matrix formation, conditioned medium has no effect on novel collagen synthesis, while it up-regulates collagenase MMP-1 only in cultures on plastic. On the other hand, it strongly inhibits the secretion of the collagenase inhibitor TIMP-1, irrespective of the substratum. This effect is completely blocked by SB 203580, an inhibitor of the p38 MAP kinase. The above suggest the presence of an autoregulatory mechanism involved in tissue homeostasis.

Macrophage migration inhibitory factor up-regulates expression of matrix metalloproteinases in synovial fibroblasts of rheumatoid arthritis

Neutral matrix metalloproteinases (MMPs) are responsible for the pathological features of rheumatoid arthritis (RA) such as degradation of cartilage. We herein show the up-regulation of MMP-1 (interstitial collagenase) and MMP-3 (stromelysin) mRNAs of cultured synovial fibroblasts retrieved from rheumatoid arthritis (RA) patients in response to macrophage migration inhibitory factor (MIF). The elevation of MMP-1 and MMP-3 mRNA was dose-dependent and started at 6 h post-stimulation by MIF, reached the maximum level at 24 h, and was sustained at least up to 36 h. Interleukin (IL)-1beta mRNA was also up-regulated by MIF. These events were preceded by up-regulation of c-jun and c-fos mRNA. Tissue inhibitor of metalloproteinase (TIMP)-1, a common inhibitor of these proteases, was slightly up-regulated by MIF. Similarly, mRNA up-regulation of MMP-1 and MMP-3 was observed in the synovial fibroblasts of patients with osteoarthritis. However, their expression levels were much lower than those of RA synovial fibroblasts. The mRNA up-regulation by MIF was inhibited by the tyrosine kinase inhibitors genestein and herbimycin A, as well as the protein kinase C inhibitors staurosporine and H-7. On the other hand, the inhibition was not seen after the addition of the cyclic AMP-dependent kinase inhibitor, H-8. The mRNA up-regulation of MMPs was also inhibited by curcumin, an inhibitor of transcription factor AP-1, whereas interleukin-1 receptor antagonist, an IL-1 receptor antagonist, failed to inhibit the mRNA up-regulation. Considering these results, it is suggested that 1) MIF plays an important role in the tissue destruction of rheumatoid joints via induction of the proteinases, and 2) MIF up-regulates MMP-1 and MMP-3 via tyrosine kinase-, protein kinase C-, and AP-1- dependent pathways, bypassing IL-1beta signal transduction.

Proteolysis and cell migration: creating a path?

Both serine and metalloproteinases have been implicated in the complex integrated events underlying cell migration but no definitive single mechanism has emerged. Work over the past two years linking both membrane and soluble proteinases with integrins and other adhesion proteins and with intracellular signalling systems could herald the beginnings of a potential expansion of our understanding of the role and regulation of proteolysis in cell migration.

Discoidin domain receptors: structural relations and functional implications

Multicellular life relies on the presence of extracellular matrix to provide scaffolding for cells and tissue compartments. To provide communication between cells and tissues, a multitude of cell surface receptors are triggered by soluble ligands and components of the extracellular matrix. A large family of these receptors transmit signals through the use of an intrinsic tyrosine kinase function. The subgroup of discoidin domain receptors (DDRs) is distinguished from other members of the receptor tyrosine kinase family by a discoidin homology repeat in their extracellular domains that is also found in a variety of other transmembrane and secreted proteins. Sequence comparisons show that non-mammalian orthologs of DDRs exist: three closely related genes in Caenorhabditis and one in the sponge Geodia cydonium. Recently, various types of collagen have been identified as the ligands for the two mammalian discoidin domain receptor tyrosine kinases, DDR1 and DDR2. The binding of collagen to DDRs results in a delayed but sustained tyrosine kinase activation. Both receptors display several potential tyrosine phosphorylation sites that are able to relay the signal by interacting with cytoplasmic effector proteins. The potential cross-talk to other receptors for collagen and the clinical aspects of DDR function are discussed.