Regulation Of Collagen Synthesis Research Articles

IL-18 Downregulates Collagen Production in Human Dermal Fibroblasts via the ERK Pathway

Excessive accumulation of collagen contributes to the fibrotic process. Several experimental studies have shown that IFN-gamma is effective in preventing fibrogenesis. IL-18, originally identified as an IFN-gamma-inducing factor, is a key mediator of inflammation and host defense responses. In this study, we investigated the regulatory effect of IL-18 on the expression of type I and III collagen genes in dermal fibroblasts. The exposure of human dermal fibroblasts (HDFs) to IL-18 resulted in a reduction of collagen gene expression and production. Also, IL-18 inhibited the fibrogenic cytokine transforming growth factor (TGF)-beta-induced collagen gene expression. Next, to determine the molecular mechanism involved in this regulation, we showed that IL-18-regulated collagen expression was blocked by small interfering RNA (siRNA)-mediated Ets-1 knockdown. Furthermore, we showed that IL-18 induced phosphorylation of extracellular signal-regulated kinase (ERK) within 10 minutes and that the ERK inhibitor PD98059 blocked the inhibitory effect of IL-18. IL-18 also inhibited the production of collagen in systemic sclerosis (SSc) dermal fibroblasts. Our data indicate that IL-18 downregulates collagen production in HDF directly via Ets-1 and the ERK pathway, suggesting that IL-18 may exert antifibrotic activities in dermal fibroblasts.

Differential control of collagen synthesis by the sympathetic and renin–angiotensin systems in the rat left ventricle

In the present study, we tested the hypothesis of the indirect (via the sympathetic nervous system (SNS)) and direct (via AT1 receptors) contributions of Angiotensin II (Ang II) on the synthesis of collagen types I and III in the left ventricle (LV) in vivo. Sympathectomy and blockade of the Ang II receptor AT1 were performed alone or in combination in normotensive rats. The mRNA and protein synthesis of collagen types I and III were examined by Q-RT-PCR and immunoblotting in the LV. Collagen types I and III mRNA were decreased respectively by 53% and 22% after sympathectomy and only collagen type I mRNA was increased by 52% after AT1 receptor blockade. mRNA was not changed for collagen type I but was decreased by 25% for collagen type III after double treatment. Only collagen protein type III was decreased after sympathectomy by 12%, but collagen proteins were increased respectively for types I and III by 145% and 52% after AT1 receptor blockade and by 45% and 60% after double treatment. Deducted interpretations from our experimental approach suggest that Ang II stimulates indirectly (via SNS) and inhibits directly (via AT1 receptors) the collagen type I at transcriptional and protein levels. For collagen type III, it stimulates indirectly the transcription and inhibited directly the protein level. Therefore, the Ang II regulates collagen synthesis differently through indirect and direct pathways.

Involvement of a Forkhead Transcription Factor, FOXO1a, in UV-Induced Changes of Collagen Metabolism

Transcription factors belonging to the forkhead box gene, group O (FOXOs) family have been found to be crucial in downstream suppression of life-shortening effects of the insulin/insulin-like growth factor-1 (IGF-1) signaling pathway, which accelerates aging by suppressing FOXOs. Thus, FOXOs could hold the key for counteracting aging. Although FOXOs may play a critical role in aging, the effects of FOXOs on UV-induced changes of collagen metabolism by dermal fibroblasts are unknown. In this study, UV-induced changes in FOXO1a expression and the roles of FOXO1a in the regulation of collagen synthesis and matrix metalloproteinase (MMPs) expression in human dermal fibroblasts were investigated. In UVA- or UVB-irradiated fibroblasts, the expression of FOXO1A mRNA decreased significantly. The expression of type I collagen (COLIAI) also decreased. On the other hand, MMP-1 and MMP-2 mRNA levels increased. FOXO1A-small interfering RNA transfection induced the downregulation of FOXO1A expression, it also induced a decrease in COLIAI expression, and it increased MMP-1 and MMP-2 expression. These changes are similar to those observed in UV-irradiated fibroblasts. Furthermore, FOXO1a-peptide induced opposite changes in COLIAI, MMP-1, and MMP-2 expression. Therefore, FOXO1a is involved in the UV-induced changes of type I collagen and MMPs expression.Journal of Investigative Dermatology Symposium Proceedings (2009) 14, 60-62; doi:10.1038/jidsymp.2009.2.

The roles of TGF-β1 gene transfer on collagen formation during Achilles tendon healing

Collagen content and cross-linking are believed to be major determinants of tendon structural integrity and function. The current study aimed to investigate the effects of transforming growth factor (TGF)-β1 on the collagen content and cross-linking of Achilles tendons, and on the histological and biomechanical changes occurring during Achilles tendon healing in rabbits. Bone marrow-derived mesenchymal stem cells (BMSCs) transfected with the TGF-β1 gene were surgically implanted into experimentally injured Achilles tendons. Collagen proteins were identified by immunohistochemical staining and fiber bundle accumulation was revealed by Sirius red staining. Achilles tendons treated with TGF-β1-transfected BMSCs showed higher concentrations of collagen I protein, more rapid matrix remodeling, and larger fiber bundles. Thus TGF-β1 can promote mechanical strength in healing Achilles tendons by regulating collagen synthesis, cross-link formation, and matrix remodeling.

Medallion-like dermal dendrocyte hamartoma in a 36-year-old male

Medallion-like dermal dendrocyte hamartoma in a 36-year-old male

Mechanisms of Arterial Remodeling in Hypertension

Diverse data collected over the past 4 decades suggest the existence of a mechanical homeostasis across multiple length and time scales in the vasculature. For example,1 stress fibers within endothelial and vascular smooth muscle cells appear to disassemble and then reassemble in a mechanically preferred manner when perturbed from a normal value of mechanical stress or strain; focal adhesions in smooth muscle cells and fibroblasts tend to increase in area in response to local increases in mechanical loading so as to maintain the stress constant at a preferred value; fibroblasts tend to increase the tractions that they exert on the extracellular matrix when external loads are decreased from a preferred value, thus suggesting an attempt to enforce a “tensional homeostasis”; vascular smooth muscle cells tend to relengthen to their normal, preferred values when an arteriole is forced into a vasoconstricted state for an extended period; and arteries tend to decrease in caliber in response to sustained decreases in flow-induced wall shear stress, to increase in thickness in response to sustained increases in pressure-induced circumferential stress, and to lengthen in response to extension-induced increases in axial stress. Although changes in the cytoskeleton and integrins occur within minutes, changes at the cell-cell and cell-matrix levels occur over hours, and those at the vessel level occur over days to weeks or months. Hence, despite marked differences in length scales (dimensions from nanometers to centimeters) and time scales (durations from minutes to months), mechanobiological control mechanisms in the vasculature tend to restore values of stress or strain toward preferred (homeostatic) values in response to diverse perturbations from normal.2–5 Biomechanics and mechanobiology thus play key roles in vascular development, tissue maintenance in maturity, normal adaptations, aging, disease progression, and responses to injury or clinical interventions. A current challenge in hypertension research is to …

Expression of transforming growth factor β isoforms and their roles in tendon healing

Transforming growth factor beta (TGF-beta) plays active roles in tendon healing. However, the differential effects of TGF-beta isoforms on tendon healing have not been investigated. In cultured tendon fibroblasts, we tested the effects of TGF-beta1, beta2, and beta3 on the mRNA levels of COL1A1 and COL3A1 by quantitative real-time polymerase chain reaction. We also investigated the expression of TGF-beta isoforms, TGF-beta receptors, procollagen Type I and Type III in a rat model of tendon healing. We found that TGF-beta3 exhibited the highest potency in stimulating COL1A1 and COL3A1. TGF-beta1 exerted antagonistic effects to TGF-beta2 and beta3. All TGF-beta isoforms and procollagen Type I were confined to the edges of the healing tendon at day 28 postinjury. Our results indicated that interaction of TGF-beta isoforms exist in the regulation of collagen synthesis in tendon fibroblasts. Their effects may be further complicated by uneven spatial distribution of TGF-beta and TGF-beta receptors in healing tendons.

Factors influencing collagen biosynthesis

The importance of collagen, the major structural protein of animal kingdom, in maintaining the normal structure and function of the skin is well known. The same property is exploited widely in medical and industrial fields in finding agents, which could influence the synthesis of this protein. In this context in vitro production of collagen is of high significance. A literature survey has been made to analyze the various factors that influence collagen biosynthesis. There are various physical and biological factors that can either induce or inhibit collagen biosynthesis at various levels of gene expression. However reports concentrating on the effects of plants-derived compounds in stimulating collagen synthesis are scanty. Since extracts of many plants are known to be beneficial in the wound healing process, plants-derived compounds will have a definite role in the regulation of collagen synthesis. The present study emphasizes the need for unearthing the role of these plant derived factors on collagen synthesis which will be of immense application in the medical field.

Suppressor of cytokine signaling 1 inhibits pulmonary inflammation and fibrosis

Suppressor of cytokine signaling (SOCS) proteins are inhibitors of cytokine signaling. Our previous study suggested that SOCS1 regulates collagen synthesis by lung fibroblasts, suggesting a role of SOCS1 in the pathophysiology of pulmonary fibrosis. We sought to investigate the role of SOCS1 in pulmonary inflammation and fibrosis in vivo. SOCS1-haplodeficient mice treated with bleomycin (BLM) were evaluated for pulmonary inflammation and fibrosis compared with wild-type mice. The human study group was composed of 18 patients with interstitial lung disease. Lung specimens obtained by means of open lung biopsy were investigated to determine whether the severity of fibrosis was associated with decreased SOCS1 expression. Finally, we further analyzed the effect of exogenous SOCS1 on BLM-induced lung injury based on adenoviral SOCS1 gene transfer to the lung. SOCS1-haplodeficient mice treated with BLM showed markedly enhanced pulmonary inflammation and fibrosis compared with wild-type mice. Using human lung specimens, we found that SOCS1 mRNA levels inversely correlated with duration of the disease. SOCS1 expression was significantly less in lung tissue from patients with idiopathic pulmonary fibrosis (IPF) compared with that in non-IPF patients. Moreover, SOCS1 expression was significantly less in severe fibrotic lesions (lower lobe) than in less fibrotic lesions (upper lobe). Adenoviral SOCS1 gene transfer to murine lungs significantly decreased lymphocytic inflammation, pulmonary fibrosis, and mortality because of BLM-induced lung injury. Exogenous SOCS1 inhibited expression of various cytokines, including TNF-alpha, which might play a key role. These results suggest that SOCS1 might act as a suppressor for pulmonary fibrosis. SOCS1 might be a target of IPF treatment.

Extensive Downregulation of Matrix Scaffolding Genes and TGF‐beta in Isolated Mitral Regurgitation in the Dog

The volume overload of isolated mitral regurgitation (MR) in the dog is characterized by LV dilatation and loss of extracellular matrix. We hypothesize that the MR heart is not only marked by increased matrix metalloproteinase (MMP) expression but also by downregulation of collagen synthesis. Gene arrays were compared from biopsy specimens obtained in 4 dogs prior to MR and 4 months after MR induction. There was a 50% increase in LV end‐diastolic volume by magnetic resonance imaging. MMP‐1 and ‐9 increased 5‐ and 10‐fold, in the face of no change in collagen I, a 1.5‐fold increase in collagen III, but a 35% decrease in LV hydroxyproline levels. Genes associated with cell‐matrix scaffolding including decorin, fibulin, fibrillin, were significantly downregulated. Genes regulating collagen synthesis including thrombospondin, TGF‐beta binding protein, TGF‐beta receptor, connective tissue growth factor, and plasminogen activator inhibitor were also significantly downregulated. LV TGF‐beta activity decreased 30% in MR compared to normal LV. These results indicate that LV collagen loss in MR is chiefly due to post‐translational processing and degradation of collagen I and III. In addition, there is an extensive downregulation of cell‐matrix scaffolding genes controlled by TGF‐beta pathway which is also downregulated. Taken together, this could explain why RAS blockade does not improve LV remodeling in isolated MR.

Suppression of Renal Tubulointerstitial Fibrosis by Small Interfering RNA Targeting Heat Shock Protein 47

Background/Aim: Unilateral ureteral obstruction (UUO) is a well-established model for tubulointerstitial fibrosis. During the progression of tubulointerstitial fibrosis, upregulation of collagen synthesis and subsequent accumulation of collagen were observed in the tubulointerstitial area. Heat shock protein 47 (HSP47) is a collagen-specific molecular chaperone and plays an essential role in regulating collagen synthesis. We designed small interfering RNA (siRNA) sequences for HSP47 mRNA to examine whether HSP47 is involved in the progression of renal tubulointerstitial fibrosis in a mouse UUO model. Methods: The HSP47 siRNA was injected once via the ureter at the time of UUO preparation. We also applied a new gene delivery system for siRNA using cationized gelatin microspheres. The kidneys were harvested 7 and 14 days after UUO. The HSP47 and type I, III, and IV collagen expression levels were analyzed by immunohistochemistry and Western blotting. Results: Seven days after UUO, the expression levels of HSP47 and type I, III, and IV collagens were markedly upregulated in obstructed kidneys or green fluorescent protein siRNA treated obstructed kidneys. HSP47 siRNA injection significantly reduced the protein expression levels and significantly diminished the accompanying interstitial fibrosis. Moreover, cationized gelatin microspheres as a delivery system enhanced and lengthened the antifibrotic effect of HSP47 siRNA. Conclusions: Our results indicate that HSP47 is a candidate target for the prevention of tubulointerstitial fibrosis and that selective blockade of the HSP47 expression by using siRNA could be a potentially useful therapeutic approach for patients with renal disease.

All-trans retinoic acid regulates collagen synthesis in human uterine leiomyomas

All-trans retinoic acid regulates collagen synthesis in human uterine leiomyomas

TGF‐β–induced fibrosis and SMAD signaling: oligo decoys as natural therapeutics for inhibition of tissue fibrosis and scarring

Transforming-growth factor-beta (TGF-beta) is a pleiotrophic growth factor that is synthesized by many cells in the body. This growth factor is chemotactic for fibroblasts, stimulates fibroblast proliferation, and increases the synthesis of a number of extracellular matrix proteins including collagens. The TGF-beta activator protein is a transacting factor, which binds to the TGF-beta element in the distal promoter of the COL1A1 collagen gene and induces transcription of this gene. Although transient TGF-beta 1 activity participates in repair and regeneration of tissues, persistent TGF-beta 1 function affects excessive fibrosis and ultimately scarring of both skin and internal organs. Scarring of internal organ (e.g., liver and lung) results in a loss of function and ultimately death may occur. The central issue of this review is that phosphorothioate double-stranded decoys or other decoys decrease procollagen gene expression, procollagen synthesis, and collagen during fibrogenesis. The rationale is that the decoys containing the TGF-beta element or other gene transcription regulatory CIS-elements bind the transacting proteins preventing the latter from binding to the CIS-element in the 5'-flanking region of the natural gene resulting in transcription inhibition. We will, in part, focus on aspects involved in TGF-beta 1-induced fibrosis that occur during fibrogenesis and the use of the dsTGF-beta element containing oligodeoxynucleotide decoys to control excessive collagen synthesis, and deposition resulting from persistent TGF-beta. In our model of regulation of collagen synthesis, these double-stranded oligo decoys act as promoter competitors, binding to the activator protein either in the cytoplasm or in the nucleus. The significance of the proposed studies is that these novel natural antifibrotics will mimic the effect of glucocorticoids on collagen synthesis during fibrogenesis without the unwanted side effects of these steroids. Based on our previous studies on the molecular mechanisms by which glucocorticoids selectively decrease collagen synthesis, designed phosphorothioate oligodeoxynucleotides resistant to nuclease action will mimic the effects of glucocorticoids at the molecular, cellular, and in vivo levels of collagen synthesis. However, the glucocorticoids significantly inhibit noncollagen protein synthesis. Both the single-stranded and double-stranded oligodeoxynucleotide specifically decrease collagen synthesis without an inhibitory effect on noncollagen protein synthesis. In this review, we will specifically ask if TGF-beta-induced collagen synthesis is inhibited in cell culture and in vivo by using the double-stranded oligodeoxynucleotide decoys, will this inhibit fibrogenesis and ultimately scarring?

Reactive oxygen species (ROS) mediate the effects of leucine on translation regulation and type I collagen production in hepatic stellate cells

The amino acid leucine causes an increase of collagen α1(I) synthesis in hepatic stellate cells through the activation of translational regulatory mechanisms and PI3K/Akt/mTOR and ERK signaling pathways. The aim of the present study was to evaluate the role played by reactive oxygen species on these effects. Intracellular reactive oxygen species levels were increased in hepatic stellate cells incubated with leucine 5 mM at early time points, and this effect was abolished by pretreatment with the antioxidant glutathione. Preincubation with glutathione also prevented 4E-BP1, eIF4E and Mnk-1 phosphorylation induced by leucine, as well as enhancement of procollagen α1(I) protein levels. Inhibitors for MEK-1 (PD98059), PI3K (wortmannin) or mTOR (rapamycin) did not affect leucine-induced reactive oxygen species production. However, preincubation with glutathione prevented ERK, Akt and mTOR phosphorylation caused by treatment with leucine. The mitochondrial electron chain inhibitor rotenone and the NADPH oxidase inhibitor apocynin prevented reactive oxygen species production caused by leucine. Leucine also induced an increased phosphorylation of IR/IGF-R that was abolished by pretreatment with either rotenone or apocynin. Therefore, leucine exerts on hepatic stellate cells a prooxidant action through NADPH oxidase and mitochondrial Reactive oxygen species production and these effects mediate the activation of IR/IGF-IR and signaling pathways, finally leading to changes in translational regulation of collagen synthesis.

Distinct effects of gonadectomy in male and female mice on collagen fibrillogenesis in the skin

Collagen biosynthesis and deposition is a complex, multistep process, which is tightly regulated to maintain proper tissue homeostasis. Sex steroid hormones have been implicated in regulating collagen synthesis; however the specific mechanisms regulating the process remain largely unknown. To investigate the role of estrogens and androgens in the regulation of genes involved in collagen synthesis and fibrillogenesis using gonadectomized C57/B6 mice. Collagen content was assessed by hydroxyproline measurement and acetic acid extraction of collagen with or without the addition of pepsin. The mRNA levels of fibrillar collagens and enzymes involved in fibrillogenesis were determined by QPCR analysis. The protein expression of decorin, lumican and fibromodulin was confirmed by immunostaining. We have shown that castration resulted in a markedly decreased skin thickness and collagen content without affecting collagen solubility. Furthermore, the mRNA levels of fibrillar collagen genes including types I, III, and V were decreased, suggesting that androgens positively regulate the rate of collagen gene transcription. Conversely, ovariectomy mainly affected collagen solubility. The absence of estrogens resulted in decreased expression levels of several of the small leucine-rich repeat proteins and proteoglycans (SLRPs) including decorin, fibromodulin and lumican. Estrogens may not be directly involved in the regulation of collagen synthesis; however, they may play a critical role in regulating organization and stability of collagen fibrils. Androgens play a positive role in the regulation of collagen biosynthesis. In summary, our data demonstrate that androgens and estrogens regulate distinct aspects of collagen fibrillogenesis in mouse skin.

The transcriptional coactivator and acetyltransferase p300 in fibroblast biology and fibrosis

The transcriptional coactivator p300 is a ubiquitous nuclear phosphoprotein and transcriptional cofactor with intrinsic acetyltransferase activity. p300 controls the expression of numerous genes in cell-type and signal-specific manner, and plays a pivotal role in cellular proliferation, apoptosis, and embryogenesis. By catalyzing acetylation of histones and transcription factors, p300 plays a significant role in epigenetic regulation. Recent evidence suggests that abnormal p300 function is associated with deregulated target gene expression, and is implicated in inflammation, cancer, cardiac hypertrophy, and genetic disorders such as the Rubinstein-Taybi syndrome. The activity of p300 is regulated at multiple levels, including developmental stage-specific expression, post-translational modifications, subcellular localization, and cell-type and gene-specific interactions with transcription factors. Although p300 has been investigated extensively in epithelial and hematopoietic cells, its role in fibroblast biology and tissue repair has received little attention to date. Recent studies implicate p300 in the regulation of collagen synthesis by transforming growth factor-beta (TGF-beta). Both the acetyltransferase activity of p300 and its inducible interaction with Smad3 are essential for mediating TGF-beta-induced stimulation of collagen synthesis. As a signal integrator whose availability for intracellular interactions with transcription factors is strictly limiting, p300 mediates the antagonistic regulation of TGF-beta-induced collagen synthesis by IFN-gamma and TNF-alpha via intracellular competition for limiting amount of p300. Significantly, p300 is itself a direct transcriptional target of TGF-beta in normal fibroblasts, and its levels are significantly elevated in fibrotic lesions as well as in experimental models of fibrosis. The emerging appreciation of the importance of p300 in extracellular matrix (ECM) remodeling and fibrosis and novel insights concerning the regulation, mechanism of action, and significance of p300 in fibroblast biology are discussed in this minireview.

Regulation of collagen synthesis by inhibitory Smad7 in cardiac myofibroblasts

Transforming growth factor-beta(1) (TGF-beta(1)) signal and downstream Smads play an important role in tissue fibrosis and matrix remodeling in various etiologies of heart failure. Inhibitory Smad7 (I-Smad7) is an inducible regulatory Smad protein that antagonizes TGF-beta(1) signal mediated via direct abrogation of R-Smad phosphorylation. The effect of ectopic I-Smad7 on net collagen production was investigated using hydroxyproline assay. Adenovirus-mediated I-Smad7 gene (at 100 multiplicity of infection) transfer was associated with significant decrease of collagen synthesis in the presence and absence of TGF-beta(1) in primary rat cardiac myofibroblasts. In I-Smad7-infected cells, we also observed the ablation of TGF-beta(1)-induced R-Smad2 phosphorylation vs. LacZ controls. Overdriven I-Smad7 was associated with significantly increased expression of immunoreactive 65-kDa matrix metalloproteinase-2 (MMP-2) protein in culture medium of myofibroblast compared with LacZ-infected cells. Expression of the 72-kDa MMP-2 variant, e.g., the inactive form, was not altered by exogenous I-Smad7 transfection/overexpression. Furthermore, I-Smad7 overexpression was associated with a significant increase and decrease in expression of p27 and phospho-Rb protein, respectively, as well as reduced [(3)H]thymidine incorporation vs. Ad-LacZ-infected controls. We suggest that negative modulation of R-Smad phosphorylation by ectopic I-Smad7 may contribute to the downregulation of collagen in cardiac myofibroblasts and may suppress the proliferation of these cells. Thus treatments targeting the collagen deposition by overexpression of I-Smad7 may provide a new therapeutic strategy for cardiac fibrosis.

Integrin α1β1 Controls Reactive Oxygen Species Synthesis by Negatively Regulating Epidermal Growth Factor Receptor-Mediated Rac Activation

Integrins control many cell functions, including generation of reactive oxygen species (ROS) and regulation of collagen synthesis. Mesangial cells, found in the glomerulus of the kidney, are able to produce large amounts of ROS via the NADPH oxidase. We previously demonstrated that integrin alpha1-null mice develop worse fibrosis than wild-type mice following glomerular injury and this is due, in part, to excessive ROS production by alpha1-null mesangial cells. In the present studies, we describe the mechanism whereby integrin alpha1-null mesangial cells produce excessive ROS. Integrin alpha1-null mesangial cells have constitutively increased basal levels of activated Rac1, which result in its increased translocation to the cell membrane, excessive ROS production, and consequent collagen IV deposition. Basal Rac1 activation is a direct consequence of ligand-independent increased epidermal growth factor receptor (EGFR) phosphorylation in alpha1-null mesangial cells. Thus, our study demonstrates that integrin alpha1beta1-EGFR cross talk is a key step in negatively regulating Rac1 activation, ROS production, and excessive collagen synthesis, which is a hallmark of diseases characterized by irreversible fibrosis.

The Phylogenetically Conserved Molluscan Chitinase-like Protein 1 (Cg-Clp1), Homologue of Human HC-gp39, Stimulates Proliferation and Regulates Synthesis of Extracellular Matrix Components of Mammalian Chondrocytes

Members of chitinase-like proteins (CLPs) have attracted much attention because of their ability to promote cell proliferation in insects (imaginal disc growth factors) and mammals (YKL-40). To gain insights into the molecular processes underlying the physiological control of growth and development in Lophotrochozoa, we report here the cloning and biochemical characterization of the first Lophotrochozoan CLP from the oyster Crassostrea gigas (Cg-Clp1). Gene expression profiles monitored by real time quantitative reverse transcription-PCR in different adult tissues and during development support the involvement of this protein in the control of growth and development in C. gigas. Recombinant Cg-Clp1 demonstrates a strong affinity for chitin but no chitinolytic activity, as was described for the HC-gp39 mammalian homolog. Furthermore, transient expression of Cg-Clp1 in primary cultures of rabbit articular chondrocytes as well as the use of both purified recombinant protein and conditioned medium from Cg-Clp1-expressing rabbit articular chondrocytes established that Cg-Clp1 stimulates cell proliferation and regulates extracellular matrix component synthesis, showing for the first time a possible involvement of a CLP on type II collagen synthesis regulation. These observations together with the fact that Cg-Clp1 gene organization strongly resembles that of its mammalian homologues argue for an early evolutionary origin and a high conservation of this class of proteins at both the structural and functional levels.

The Early-Immediate Gene EGR-1 Is Induced by Transforming Growth Factor-β and Mediates Stimulation of Collagen Gene Expression

Transforming growth factor-beta (TGF-beta) stimulates collagen synthesis and accumulation, and aberrant TGF-beta signaling is implicated in pathological organ fibrosis. Regulation of type I procollagen gene (COL1A2) transcription by TGF-beta involves the canonical Smad signaling pathway as well as additional protein and lipid kinases, coactivators, and DNA-binding transcription factors that constitute alternate non-Smad pathways. By using Affymetrix microarrays to detect cellular genes whose expression is regulated by Smad3, we identified early growth response factor-1 (EGR-1) as a novel Smad3-inducible gene. Previous studies implicated Egr-1 in cell growth, differentiation, and survival. We found that TGF-beta induced rapid and transient accumulation of Egr-1 protein and mRNA in human skin fibroblasts. In transient transfection assays, TGF-beta stimulated the activity of the Egr-1 gene promoter, as well as that of a minimal Egr-1-responsive reporter construct. Furthermore, TGF-beta enhanced endogenous Egr-1 interaction with a consensus Egr-1-binding site element and with GC-rich DNA sequences of the human COL1A2 promoter in vitro and in vivo. Forced expression of Egr-1 by itself caused dose-dependent up-regulation of COL1A2 promoter activity and further enhanced the stimulation induced by TGF-beta. In contrast, the TGF-beta response was abrogated when the Egr-1-binding sites of the COL1A2 promoter were mutated or deleted. Furthermore, Egr-1-deficient embryonic mouse fibroblasts showed attenuated TGF-beta responses despite intact Smad activation, and forced expression of ectopic EGR-1 in these cells could restore COL1A2 stimulation in a dose-dependent manner. Taken together, these findings identify Egr-1 as a novel intracellular TGF-beta target that is necessary for maximal stimulation of collagen gene expression in fibroblasts. The results therefore implicate Egr-1 in the profibrotic responses elicited by TGF-beta and suggest that Egr-1 may play a new and important role in the pathogenesis of fibrosis.