Regulation of type I collagen production by insulin and transforming growth factor-beta in human lung fibroblasts

Advancing the Adverse Outcome Pathway for PPARγ Inactivation Leading to Pulmonary Fibrosis Using Bradford-Hill Consideration and the Comparative Toxicogenomics Database

Pulmonary fibrosis is regulated by transforming growth factor-β (TGF-β) and peroxisome proliferator-activated receptor-gamma (PPARγ). An adverse outcome pathway (AOP) for PPARγ inactivation leading to pulmonary fibrosis has been previously developed. To advance the development of this AOP, the confidence of the overall AOP was assessed using the Bradford-Hill considerations as per the recommendations from the Organisation for Economic Co-operation and Development (OECD) Users' Handbook. Overall, the essentiality of key events (KEs) and the biological plausibility of key event relationships (KERs) were rated high. In contrast, the empirical support of KERs was found to be moderate. To experimentally evaluate the KERs from the molecular initiating event (MIE) and KE1, PPARγ (MIE) and TGF-β (KE1) inhibitors were used to examine the effects of downstream events following inhibition of their upstream events. PPARγ inhibition (MIE) led to TGF-β activation (KE1), upregulation in vimentin expression (KE3), and an increase in the fibronectin level (KE4). Similarly, activated TGF-β (KE1) led to an increase in vimentin (KE3) and fibronectin expression (KE4). In the database analysis using the Comparative Toxicogenomics Database, 31 genes related to each KE were found to be highly correlated with pulmonary fibrosis, and the top 21 potential stressors were suggested. The AOP for pulmonary fibrosis evaluated in this study will be the basis for the screening of inhaled toxic substances in the environment.

Changes in cardiac resident fibroblast physiology and phenotype in aging

The cardiac fibroblast plays a central role in tissue homeostasis and in repair after injury. With aging, dysregulated cardiac fibroblasts have a reduced capacity to activate a canonical transforming growth factor-β-Smad pathway and differentiate poorly into contractile myofibroblasts. That results in the formation of an insufficient scar after myocardial infarction. In contrast, in the uninjured aged heart, fibroblasts are activated and acquire a profibrotic phenotype that leads to interstitial fibrosis, ventricular stiffness, and diastolic dysfunction, all conditions that may lead to heart failure. There is an apparent paradox in aging, wherein reparative fibrosis is impaired but interstitial, adverse fibrosis is augmented. This could be explained by analyzing the effectiveness of signaling pathways in resident fibroblasts from young versus aged hearts. Whereas defective signaling by transforming growth factor-β leads to insufficient scar formation by myofibroblasts, enhanced activation of the ERK1/2 pathway may be responsible for interstitial fibrosis mediated by activated fibroblasts. Listen to this article's corresponding podcast at https://ajpheart.podbean.com/e/fibroblast-phenotypic-changes-in-the-aging-heart/ .

Nitric Oxide and Collagen Expression in Allergic Upper-Airway Disease

Background

The presence of nitric oxide (NO) in high concentrations has been described in the nasal mucosa of patients with untreated allergic rhinitis. We sought to examine the role of exogenous, as well as endogenous, NO in the production of collagen type I and type III by human nasal fibroblasts.

Methods

Primary cultured fibroblasts derived from eosinophilic nasal polyps were exposed to NO donors (500 μM of S-nitroso-N-acetyl-d,l-penicillamine (SNAP) 1000 μM of 3,3-bis(aminoethyl)-1-hydroxy-2-oxo-1-triazene (DETA-NONOate)) and various other compounds over a 24-hour incubation period. Collagen production was evaluated qualitatively by immunocytochemistry and quantitatively by Western blot analysis.

Results

Maximally stimulated fibroblasts established a 2.2-fold increase in the production of type III collagen relative type I, as compared with baseline. Oxyhemoglobin, an NO scavenger, abolished this effect. SNAP (500 μM) caused a 15.68 ± 0.68% increase in collagen type I synthesis as compared with unstimulated controls (p < 0.05). In contrast, incubation with SNAP caused an increase in collagen type III production by a factor of 34.68 ± 0.32% (p < 0.05).

Conclusion

NO stimulates collagen expression in human nasal polyp-derived fibroblasts. This stimulation appeared to favor the up-regulation of collagen type III, leading to a shift in the ratio of collagen type I to type III production.

Peptidic inhibitors of insulin-degrading enzyme with potential for dermatological applications discovered via phage display

Insulin-degrading enzyme (IDE) is an atypical zinc-metalloendopeptidase that hydrolyzes insulin and other intermediate-sized peptide hormones, many of which are implicated in skin health and wound healing. Pharmacological inhibitors of IDE administered internally have been shown to slow the breakdown of insulin and thereby potentiate insulin action. Given the importance of insulin and other IDE substrates for a variety of dermatological processes, pharmacological inhibitors of IDE suitable for topical applications would be expected to hold significant therapeutic and cosmetic potential. Existing IDE inhibitors, however, are prohibitively expensive, difficult to synthesize and of undetermined toxicity. Here we used phage display to discover novel peptidic inhibitors of IDE, which were subsequently characterized in vitro and in cell culture assays. Among several peptide sequences tested, a cyclic dodecapeptide dubbed P12-3A was found to potently inhibit the degradation of insulin (K_i = 2.5 ± 0.31 μM) and other substrates by IDE, while also being resistant to degradation, stable in biological milieu, and highly selective for IDE. In cell culture, P12-3A was shown to potentiate several insulin-induced processes, including the transcription, translation and secretion of alpha-1 type I collagen in primary murine skin fibroblasts, and the migration of keratinocytes in a scratch wound migration assay. By virtue of its potency, stability, specificity for IDE, low cost of synthesis, and demonstrated ability to potentiate insulin-induced processes involved in wound healing and skin health, P12-3A holds significant therapeutic and cosmetic potential for topical applications.

STAT6-Dependent Collagen Synthesis in Human Fibroblasts Is Induced by Bovine Milk

Since the domestication of the urus, 10.000 years ago, mankind utilizes bovine milk for different purposes. Besides usage as a nutrient also the external application of milk on skin has a long tradition going back to at least the ancient Aegypt with Cleopatra VII as a great exponent. In order to test whether milk has impact on skin physiology, cultures of human skin fibroblasts were exposed to commercial bovine milk. Our data show significant induction of proliferation by milk (max. 2,3-fold, EC50: 2,5% milk) without toxic effects. Surprisingly, bovine milk was identified as strong inducer of collagen 1A1 synthesis at both, the protein (4-fold, EC50: 0,09% milk) and promoter level. Regarding the underlying molecular pathways, we show functional activation of STAT6 in a p44/42 and p38-dependent manner. More upstream, we identified IGF-1 and insulin as key factors responsible for milk-induced collagen synthesis. These findings show that bovine milk contains bioactive molecules that act on human skin cells. Therefore, it is tempting to test the herein introduced concept in treatment of atrophic skin conditions induced e.g. by UV light or corticosteroids.

Leukotriene C4 aggravates bleomycin-induced pulmonary fibrosis in mice

BACKGROUND AND OBJECTIVE

Synthesis of cysteinyl leukotrienes (cys-LT) is thought to cause inflammatory disorders such as bronchial asthma and allergic rhinitis. Recent reports have suggested that leukotriene C4 (LTC4 ) is an important regulator of pulmonary fibrosis. This study examined the effect of LTC4 in LTC4 synthase-overexpressed transgenic mice with bleomycin-induced pulmonary fibrosis. The function of lung-derived fibroblasts from transgenic mice was also investigated.

METHODS

Bleomycin was administrated to transgenic mice and wild-type (WT) mice by intratracheal instillation. Concentrations of interleukin (IL)-4 and -13, interferon-γ, and transforming growth factor (TGF)-β1 in bronchoalveolar lavage fluid were measured 1, 3, 7 and 14 days after the administration of bleomycin. Lung tissue was examined histopathologically on day 14. In addition, lung-derived fibroblasts from transgenic and WT mice were cultured for 7 days. Expression of TGF-β1 mRNA was measured by real-time polymerase chain reaction.

RESULTS

Both the pathological scores for pulmonary fibrosis (3.8 ± 0.4 vs 2.0 ± 0.1, P < 0.05) and the levels of IL-4 (12.1 ± 2.3 vs <7.8 pg/mL, P < 0.05), IL-13 (26.5 ± 5.2 vs <7.8 pg/mL, P < 0.01) and TGF-β1 (211.1 ± 30.2 vs 21.3 ± 1.2 pg/mL, P < 0.01) on day 14 were significantly greater in transgenic than in WT mice. Furthermore, the reduction of LTC4 by pranlukast hydrate, a cys-LT1 receptor antagonist, in fibroblasts from transgenic significantly (P < 0.05) decreased the expression of TGF-β1 mRNA (by ∼50%) compared with those from WT mice.

CONCLUSIONS

Overexpression of LTC4 , amplifies bleomycin-induced pulmonary fibrosis in mice. Our findings suggest a role for LTC4 in lung fibrosis.

Aberrant differentiation of fibroblast progenitors contributes to fibrosis in the aged murine heart: role of elevated circulating insulin levels

With age, the collagen content of the heart increases, leading to interstitial fibrosis. We have shown that CD44(pos) fibroblasts derived from aged murine hearts display reduced responsiveness to TGF-β but, paradoxically, have increased collagen expression in vivo and in vitro. We postulated that this phenomenon was due to the defect in mesenchymal stem cell (MSC) differentiation in a setting of elevated circulating insulin levels and production that we observed in aging mice. We discovered that cultured fibroblasts derived from aged but not young cardiac MSCs of nonhematopoietic lineage displayed increased basal and insulin-induced (1 nM) collagen expression (2-fold), accompanied by increased farnesyltransferase (FTase) and Erk activities. In a quest for a possible mechanism, we found that a chronic pathophysiologic insulin concentration (1 nM) caused abnormal fibroblast differentiation of MSCs isolated from young hearts. Fibroblasts derived from these MSCs responded to insulin by elevating collagen expression as seen in untreated aged fibroblast cultures, suggesting a causal link between increased insulin levels and defective MSC responses. Here we report an insulin-dependent pathway that specifically targets collagen type I transcriptional activation leading to a unique mechanism of fibrosis that is TGF-β and inflammation-independent in the aged heart.

Hypoxic culture and insulin yield improvements to fibrin-based engineered tissue

We examined the effect of insulin supplementation and hypoxic culture (2% vs. 20% oxygen tension) on collagen deposition and mechanical properties of fibrin-based tubular tissue constructs seeded with neonatal human dermal fibroblasts. The results presented here demonstrate that constructs cultured under hypoxic conditions with insulin supplementation increased in collagen density by approximately five-fold and both the ultimate tensile strength (UTS) and modulus by more than three-fold compared with normoxic (20% oxygen tension), noninsulin supplemented controls. In addition, collagen deposited on a per-cell basis increased by approximately four-fold. Interaction was demonstrated for hypoxia and insulin in combination in terms of UTS and collagen production on a per-cell basis. This interaction resulted from two distinct processes involved in collagen fibril formation. Western blot analysis showed that insulin supplementation alone increased Akt phosphorylation and the combined treatment increased collagen prolyl-4-hydroxylase. These molecules are distinct regulators of collagen deposition, having an impact at both the transcriptional and posttranslational modification stages of collagen fibril formation that, in turn, increase collagen density in the tissue constructs. These findings highlight the potential of utilizing insulin supplementation and hypoxic culture in combination to increase the mechanical strength and stiffness of fibrin-based engineered tissues.

The PI3K/Akt pathway mediates the expression of type I collagen induced by TGF-β2 in human retinal pigment epithelial cells

Purpose

Transforming growth factor (TGF)-β is a key mediator of proliferative vitreoretinopathy, but the cellular mechanisms by which TGF-β induces extracellular matrix protein (ECM) synthesis are not fully understood. This study examined whether the PI3K/Akt pathway is involved in TGF-β2-induced collagen expression in human retinal pigment epithelial cells.

Methods

Human retinal pigment epithelial cells ARPE-19 were cultured and stimulated with TGF-β2. The role of the PI3K/Akt pathway was evaluated using the biochemical inhibitor, wortmannin. The effect of wortmannin on the expression of type I collagen mRNA (COL1A1, COL1A2) induced by TGF-β2 was evaluated by real-time RT-PCR. The effect of wortmannin on the synthesis of type I collagen induced by TGF-β2 was assessed by an immunocytochemical analysis with anti-type I collagen antibody. Luciferase reporter assays were performed to examine the effect of wortmannin on the transcriptional activities of COL1A2. A luciferase assay using a mutation construct of the Smad binding site in COL1A2 promoter (Smad-mut/Luc) was also performed to examine the crosstalk between the Smad pathway and the PI3K/Akt pathway. The effects of wortmannin on the transcriptional activity of Smad3 were also examined using CAGA12-Luc. Moreover, the effect of wortmannin on TGF-β2-induced Smad7 mRNA expression was evaluated.

Results

The biochemical blockade of PI3K/Akt activation inhibited TGF-β2-induced type I collagen mRNA expression and type I collagen synthesis. The blockade of PI3K/Akt pathway inhibited the increase in COL1A2 promoter activities when induced by TGF-β2 and reduced TGF-β2 induction of Smad-mut/Luc promoter activity and CAGA12-Luc activity. Moreover, wortmannin increased the TGF-β2-induced Smad7 mRNA expression levels.

Conclusions

The PI3K/Akt pathway plays a role in relaying the TGF-β2 signal to induce type I collagen synthesis in the retinal pigment epithelium through Smad-dependent and Smad-independent pathways.

Effects of Th2 pulmonary inflammation in mice with bleomycin-induced pulmonary fibrosis

BACKGROUND AND OBJECTIVE

Leucocytes, especially lymphocytes and neutrophils, as well as alveolar macrophages, that infiltrate into the lung are involved in the development of pulmonary fibrosis. However, the role of T helper (Th)2-type inflammation, mediated by Th2 cells and eosinophils, in fibrosis remains unknown. Transgenic mice deficient in the transcriptional repressor, Bcl6, display an attenuation of Th2 cytokine production. We studied the effects of Th2-type pulmonary inflammation on bleomycin-induced pulmonary fibrosis using Bcl6 transgenic mice.

METHODS

Bleomycin was administered to ovalbumin (OVA)-sensitized Bcl6 transgenic and wild-type mice by intratracheal instillation during sequential OVA antigen challenge. Concentrations of transforming growth factor-beta1 in the BAL fluid were measured 2 weeks after bleomycin administration. At the same time lung tissue was examined histopathologically, and homogenized to assess collagen levels and Th1/Th2 cytokine mRNA expression.

RESULTS

Although OVA-sensitized, bleomycin-treated Bcl6 transgenic mice had markedly lower numbers of eosinophils in both BAL and lung tissue compared with OVA-sensitized, bleomycin-treated wild-type mice, the development of pulmonary fibrosis in response to bleomycin was similar in Bcl6 transgenic mice and wild-type mice.

CONCLUSION

These results suggest that Th2-dominant inflammation in the lung is not essential for the development of bleomycin-induced pulmonary fibrosis.

Alpha-ketoglutarate stimulates procollagen production in cultured human dermal fibroblasts, and decreases UVB-induced wrinkle formation following topical application on the dorsal skin of hairless mice

Alpha-ketoglutarate is a key intermediate in the Krebs cycle, and a rate-limiting cofactor of prolyl-4-hydroxylase. It also has a potent effect on increasing the proline pool during collagen production, but the details underlying the boosting effect on collagen production by alpha-ketoglutarate remain as yet unreported. To investigate the effects of alpha-ketoglutarate on procollagen production and wrinkle formation, we conducted experiments in cultured human dermal fibroblasts and UVB-irradiated hairless mice. Based on ELISA measurements, alpha-ketoglutarate (10 microM) stimulated procollagen production in fibroblasts by 25.6+/-4.6% compared to vehicle (dH(2)O)-treated control cells. Also, we demonstrated that alpha-ketoglutarate increased activities of prolidase, which is known to play an important role in collagen metabolism, in fibroblasts and N-benzyloxycarbonyl-L-proline (Cbz-Pro), prolidase inhibitor, inhibited procollagen synthesis by alpha-ketoglutarate in fibroblasts. To determine the effect of topically applied alpha-ketoglutarate on wrinkle formation, alpha-ketoglutarate (1%) and vehicle (70% propylene glycol, 30% ethanol) were applied on the dorsal skin of UVB-induced hairless mice for twelve weeks. We found that alpha-ketoglutarate decreased wrinkle formation upon long-term topical application. These results suggest that alpha-ketoglutarate diminishes UVB-induced wrinkle formation by increasing collagen production, through a pathway that involves prolidase activation. Therefore, application of alpha-ketoglutarate may represent an effective anti-wrinkle agent for the cosmetic field.

A new dermal equivalent: The use of dermal fibroblast culture alone without exogenous materials

BACKGROUND

During the past decade, several kinds of skin equivalents have been developed. However, the dermal equivalents have all contained exogenous materials, which can be difficult to obtain and a source of infections.

OBJECTIVES

The aim of this study was to develop a new dermal equivalent by culturing dermal fibroblasts alone without exogenous materials and to evaluate its applicability in vitro and in vivo.

METHODS

The postconfulent cultures of dermal fibroblasts in serum containing medium, that was supplemented with epidermal growth factor, insulin, hydrocortisone, transferrin and triiodothyronine for 3 weeks, produced a fibrous sheet that was visible macroscopically. To construct a skin equivalent, epidermal keratinocytes were cultured on the top of the fibrous sheet at the air-liquid interface. To evaluate its fate in vivo, the fibrous sheet was grafted into a nude mouse.

RESULTS

Histologically, the fibrous sheet showed dermis-like tissue that consisted of an extracellular matrix around dermal fibroblasts, and revealed collagen fibers by Masson-trichrome staining. The components of dermal matrix such as type I collagen, type III collagen, elastin, fibrillin-1 and fibronectin were diffusely expressed. Some collagen fibrils were found by electron microscopy. In the skin equivalent, a multilayered epidermis with a horny layer was formed. Some differentiation markers (keratin 1 and 10, and involucrin) and the components of basement membrane (beta4 integrin chain, type IV and VII collagens) were expressed in a similar fashion to those in normal skin in vivo. Ultrastructurally, basement membrane zone such as hemidesmosomes, lamina lucida and lamina densa was found, although it was still incomplete. When the fibrous sheet was grafted in vivo, it revealed blood vessels that were derived from the nude mouse, and persisted for 4 weeks.

CONCLUSION

These findings demonstrated that a new dermal equivalent, closely resembling a dermis in vivo, could be constructed by culturing dermal fibroblasts alone in a special culture medium. In addition, the dermal equivalent may be useful for experimental and clinical purposes, such as the reconstruction of a skin equivalent in vitro and grafting in vivo.

BMP-7 opposes TGF-beta1-mediated collagen induction in mouse pulmonary myofibroblasts through Id2

Mesenchymal cells, primarily fibroblasts and myofibroblasts, are the principal matrix-producing cells during pulmonary fibrogenesis. Transforming growth factor (TGF)-beta signaling plays an important role in stimulating the expression of type I collagen of these cells. Bone morphogenetic protein (BMP)-7, a member of the TGF-beta superfamily, has been reported to oppose the fibrogenic activity of TGF-beta1. Here, we have addressed the effects of BMP-7 on the fibrogenic activity of pulmonary myofibroblasts. We first established cell lines from the lungs of transgenic mice harboring the COL1A2 upstream sequence fused to luciferase. They displayed a spindle shape and expressed vimentin and alpha-smooth muscle actin, but not E-cadherin. COL1A2 promoter activity was dose dependently induced by TGF-beta1, which was further augmented by adenoviral overexpression of Smad3, but was downregulated by Smad7. Under the identical condition, adenoviral overexpression of BMP-7 attenuated the TGF-beta1-dependent COL1A2 promoter activity. By immunocytochemistry, the ectopic expression of BMP-7 led to the nuclear localization of phospho-Smad1/5/8 and suppressed that of Smad3. BMP-7 suppressed the expression of mRNAs for COL1A2 and tissue inhibitor of metalloproteinase-2 while increasing those of inhibitors of differentiation (Id) 2 and 3. Ectopic expression of Id2 and Id3 was found to decrease the COL1A2 promoter activity. Finally, BMP-7 and Id2 decreased TGF-beta1-dependent collagen protein secretion. In conclusion, these data demonstrate that BMP-7 antagonizes the TGF-beta1-dependent fibrogenic activity of mouse pulmonary myofibroblastic cells by inducing Id2 and Id3.

Active transforming growth factor-beta1 activates the procollagen I promoter in patients with acute lung injury

OBJECTIVE

Fibroproliferation markers like procollagen I predict mortality in patients with acute lung injury (ALI) and acute respiratory distress syndrome (ARDS). We sought to determine whether bronchoalveolar lavage fluid (BALF) from patients with lung injury contained mediators that would activate procollagen I promoter and if this activation predicted important clinical outcomes.

DESIGN

Prospective controlled study of ALI/ARDS.

SETTING

Intensive care units and laboratory of a university hospital.

PATIENTS AND PARTICIPANTS

Acute lung injury/ARDS, cardiogenic edema (negative controls) and pulmonary fibrosis (positive controls) patients.

INTERVENTIONS

Bronchoalveolar lavage fluid was collected within 48 h of intubation from ALI/ARDS patients. BALF was also collected from patients with pulmonary fibrosis and cardiogenic pulmonary edema. Human lung fibroblasts were transfected with a procollagen I promoter-luciferase construct and incubated with BALF; procollagen I promoter activity was then measured. BALF active TGF-beta1 levels were measured by ELISA.

RESULTS

Twenty-nine ARDS patients, nine negative and six positive controls were enrolled. BALF from ARDS patients induced 41% greater procollagen I promoter activation than that from negative controls (p<0.05) and a TGF-beta1 blocking antibody significantly reduced this activation in ARDS patients. There was a trend toward higher TGF-beta1 levels in the ARDS group compared to negative controls (-1.056 log(10)+/-0.1415 vs -1.505 log(10)+/-0.1425) (p<0.09). Procollagen I promoter activation was not associated with mortality; however, lower TGF-beta1 levels were associated with more ventilator-free and ICU-free days.

CONCLUSIONS

Bronchoalveolar lavage fluid from ALI/ARDS patients activates procollagen I promoter, which is due partly to TGF-beta1. Activated TGF-beta1 may impact ARDS outcome independent of its effect on procollagen I activation.

Overexpression of TGF-beta by infiltrated granulocytes correlates with the expression of collagen mRNA in pancreatic cancer

Pancreatic cancer is often associated with an intense production of interstitial collagens, known as the desmoplastic reaction. To understand more about desmoplasia in pancreatic cancer, the expression of mRNA for type I and III collagens and potent desmoplastic inducing growth factors transforming growth factor-β (TGF-β), connective tissue growth factor (CTGF), acidic and basic fibroblast growth factor (FGF), platelet-derived growth factor (PDGF) A and C and epidermal growth factor (EGF) was analysed by quantitative RT–PCR. Expression of both collagens in 23 frozen primary pancreatic cancer nodules was significantly higher than that in 15 non-neoplastic pancreatic tissues. The expressions of mRNAs for TGF-β, acidic FGF, basic FGF and PDGF C were likewise higher in surgical cancer nodules, while that of CTGF, PDGF A and EGF were not. Among these growth factors, the expression of TGF-β mRNA showed the most significant correlation with that of collagens (P<0.0001). By immunohistochemistry, TGF-β showed faint cytoplasmic staining in cancer cells. In contrast, isolated cells, mainly located on the invasive front surrounding cancerous nests, were prominently and strongly stained. These TGF-β-positive cells contained a segmented nucleus, were negative for anti-macrophage (CD68) and positive for anti-granulocyte antibodies, indicating their granulocytic nature. In conclusion, TGF-β seemed to play a major role among the various growth factors in characteristic overproduction of collagens in pancreatic cancer. Moreover, the predominant cells that express TGF-β were likely to be infiltrated granulocytes (mostly are neutrophils) and not pancreatic cancer cells.

IL-4-induced macrophage-derived IGF-I protects myofibroblasts from apoptosis following growth factor withdrawal

The development of idiopathic pulmonary fibrosis (IPF) is associated with myofibroblast accumulation and collagen deposition in the lung parenchyma. Recent studies have suggested that the fibroproliferative response is associated with immune deviation toward a T helper cell type 2 (Th2) cytokine profile. In addition, myofibroblast accumulation may be the result of resistance to physiologic apoptosis. If and how these events are linked remain largely unknown. Insulin-like growth factor-I (IGF-I) is a fibroblast growth and survival factor that has long been implicated in the pathogenesis of IPF. We have previously shown that interstitial macrophage-derived IGF-I correlates with disease severity in IPF, and the Th2 cytokines interleukin (IL)-4 and IL-13 stimulate the expression and secretion of IGF-I by macrophages. In the present study, we tested the hypothesis that IL-4-induced, macrophage-derived IGF-I protects myofibroblasts from apoptosis. Using a growth factor withdrawal model of apoptosis in the myofibroblast cell line, CCL39, we demonstrate that conditioned media from IL-4-stimulated macrophages protect myofibroblasts from apoptosis. The survival effect is lost when IGF-I is immunodepleted from macrophage-conditioned media with IGF-I-specific antibodies. We also show that the protection of myofibroblasts by macrophage-derived IGF-I correlates with and is dependent on the activation of the prosurvival kinases Akt and extracellular signal-regulated kinase. These findings support the view that IL-4-stimulated, macrophage-derived IGF-I may contribute to the persistence of myofibroblasts in pulmonary fibrosis in the Th2-deviated environment of the fibrotic lung.

TRAIL in the airways

Tumor necrosis factor-related apoptosis inducing ligand (TRAIL) is an important immunomodulatory factor that may play a role in the structural changes observed in the asthmatic airways. In vitro as well as in vivo studies have evidenced a dual role for TRAIL: it can either function as a pro- or anti-inflammatory cytokine on inflammatory cells, participating in the initiation and resolution of inflammatory and immune responses. TRAIL is expressed in the airways by inflammatory cells infiltrated in the bronchial mucosa, as well as by structural cells of the airway wall including fibroblasts, epithelial, endothelial, and smooth muscle cells. By releasing TRAIL, these different cell types may then participate in the increased levels of TRAIL observed in bronchoalveolar lavage fluid from asthmatic patients. Taken together, this suggests that TRAIL may play a role in inflammation in asthma. However, concerning its role is dual in the modulation of inflammation, further studies are needed to elucidate the precise role of TRAIL in the airways.

Transforming growth factor-beta and its role in asthma

Transforming growth factor-beta (TGF-beta) is an important fibrogenic and immunomodulatory factor that may play a role in the structural changes observed in the asthmatic airways. In vitro as well as in vivo studies have evidenced a dual role for TGF-beta: it can either function as a pro- or anti-inflammatory cytokine on inflammatory cells, participating into the initiation and resultion of inflammatory and immune responses in the airways. TGF-beta is also involved in the remodelling of the airway wall, and has in particular been related to the subepithelial fibrosis. TGF-beta is produced in the airways by inflammatory cells infiltrated in the bronchial mucosa, as well as by structural cells of the airway wall including fibroblasts, epithelial, endothelial and smooth muscle cells. By releasing TGF-beta, these different cell types may then participate into the increased levels of TGF-beta observed in bronchoalveolar lavage fluid from asthmatic patients. Taken together, these results suggest that TGF-beta may play a role in inflammation in asthma. However, as its role is dual in the modulation of inflammation, further studies are needed to elucidate the precise role of TGF-beta in the airways.

A fibrin-based arterial media equivalent

We report here, with respect to collagen production and the mechanical properties of a fibrin-based media equivalent (ME), on our efforts to optimize the culture conditions of neonatal SMCs entrapped in tubular fibrin gels. We examined several factors, including the concentration of fibrinolysis inhibitor, the cell source and initial number, the addition of TGF-beta and insulin to the culture medium, and the time in culture. We found that varying the concentration of epsilon-aminocaproic acid (ACA), an inhibitor of fibrinolysis, did not affect the collagen production, but that lower concentrations resulted in a compromised physical integrity of the ME. While use of neonatal SMCs yielded superior results over adult SMCs, a higher initial cell number did not improve results. The addition of 1 ng/mL of TGF-beta to the medium increased the collagen content fourfold and the ultimate tensile strength (UTS) and modulus approximately tenfold after 3 weeks, while the addition of both TGF-beta and insulin improved collagen content sixfold and UTS and modulus almost 20-fold. Additional TGF-beta (5 ng/mL) did not improve any of the properties measured, but additional time in culture did. Samples incubated for 6 weeks with TGF-beta and insulin contained about seven times the amount of collagen and had a three-times higher UTS and modulus than did samples incubated for only 3 weeks. When compared to collagen MEs, the fibrin MEs compacted to a greater extent and were both stronger and stiffer when cultured under the same conditions, having after 6 weeks a tensile modulus and ultimate tensile strength similar to those of rat abdominal aorta.

Type Ialpha collagen is an IGFBP-3 binding protein

Insulin-like growth factor (IGF) binding protein-3 (IGFBP-3) possesses both growth-inhibitory and -potentiating effects on cells, which are independent of IGF action and mediated through specific IGFBP-3 binding proteins/receptors located at the cell membrane, cytosol, or nuclear compartments as well as in the extracellular matrix. We here characterized type Ialpha collagen as one of these IGFBP-3 binding proteins. Human serum was fractionated over an IGFBP-3 affinity column, and bands at 70-100 kDa were eluted as IGFBP-3 ligands. The 100-kDa band was extracted, subjected to N-terminal amino acid sequencing, and identified through database searching as the N-terminal chain of type Ialpha collagen protein. In a separate screening approach, using a yeast two-hybrid system, we cloned the type Ialpha collagen cDNA from a human liver cDNA library as an IGFBP-3 protein partner. Anti-IGFBP-3 antibodies co-immunoprecipitated type Ialpha collagen and IGFBP-3 from the conditioned media of human fibroblasts and vice versa. We demonstrated through ligand dot blot analysis that type Ialpha collagen binds IGFBP-3. IGFBP-3 mutants, with altered sequence at the nuclear localization sequence, bound type Ialpha collagen poorly. Western immunoblot showed that type Ialpha collagen binds only IGFBP-3 but not IGF-I, suggesting an IGF-I-independent mechanism of this interaction. Physiological effects of IGFBP-3-collagen interactions may include modulation of cell adhesion and migration.

Regulation of connective tissue growth factor expression by prostaglandin E(2)

Transforming growth factor-beta (TGF-beta) stimulates alpha(1)(I) collagen mRNA synthesis in human lung fibroblasts through a mechanism that is partially sensitive to cycloheximide and that may involve synthesis of connective tissue growth factor (CTGF). Northern blot analyses indicate that TGF-beta stimulates time- and dose-dependent increases in CTGF mRNA. In TGF-beta-stimulated fibroblasts, maximal levels of CTGF mRNA (3.7-fold above baseline) occur at 6 h. The TGF-beta-stimulated increase in CTGF mRNA was not blocked by cycloheximide. Nuclear run-on analysis indicates that TGF-beta increases the CTGF transcription rate. The TGF-beta-stimulated increases in CTGF transcription and steady-state levels of CTGF mRNA are attenuated in prostaglandin E(2) (PGE(2))-treated fibroblasts. PGE(2) fails to attenuate luciferase activity induced by TGF-beta in fibroblasts transfected with the TGF-beta-responsive luciferase reporter construct p3TP-LUX. In amino acid-deprived fibroblasts, PGE(2) and insulin regulate alpha(1)(I) collagen mRNA levels without affecting CTGF mRNA levels. The data suggest that the regulation of alpha(1)(I) collagen mRNA levels by TGF-beta and PGE(2) may function through both CTGF-dependent and CTGF-independent mechanisms.

Extracellular matrix deposition by primary human lung fibroblasts in response to TGF-beta1 and TGF-beta3

Increased collagen and extracellular matrix (ECM) deposition within the lung is a characteristic feature of lung fibrosis. Transforming growth factor (TGF)-beta isoforms play a pivotal role in the production of collagen and ECM. In this study, we investigated the effects of TGF-beta1 and TGF-beta3 on the main processes controlling ECM deposition using primary human lung fibroblasts. We analyzed 1) collagen metabolism by [3H]proline incorporation, 2) matrix metalloproteinase (MMP) expression by substrate gel zymography, and 3) tissue inhibitor of metalloproteinases (TIMP) expression by Western blot analysis. TGF-beta1 and TGF-beta3 increased the percentage of secreted collagens in supernatants of primary fibroblasts from 8.0 +/- 1.2 (control) to 23.6 +/- 4.6 and 22.3 +/- 1.3%, respectively. The collagen percentage in deposited ECM was increased from 5.8 +/- 0.3 (control) to 9.0 +/- 0.5 and 8.8 +/- 0.5% by TGF-beta1 and TGF-beta3, respectively. Secretion of MMP-1 (interstitial collagenase) by fibroblasts was reduced by both TGF-beta isoforms, whereas secretion of MMP-2 (gelatinase A) was unaffected by either of the two isoforms. Both TGF-beta isoforms increased TIMP-1 protein expression, whereas TIMP-2 protein was decreased. We thus conclude that TGF-beta1 and TGF-beta3 are equally potent in increasing ECM deposition. Their fibrotic effect in lung fibroblasts results from 1) an increase in the secretion and deposition of total ECM and collagens, 2) a decrease in MMP-1 secretion, and 3) an increase of TIMP-1 expression.

Collagen and elastin synthesis by desmoid tumor in vitro

In order to characterize human desmoid tumors in vitro, the production of collagen and elastin and the expression of collagen types alpha1(I), alpha1(III) and transforming growth factor (TGF)-beta1 mRNA were investigated in six desmoid tumors; five derived from familial adenomatous polyposis patients and one from a sporadic case. The proportion of collagen production to total protein production was determined by 3H-imino acid incorporation, an indicator of collagen synthesis, using high-performance liquid chromatography (HPLC). The proportion of collagen production to total protein production was much higher in all six desmoid tumors compared with human skin fibroblasts (HSF). Quantitatively, the rate of elastin synthesis in desmoid tumor cells monitored by valine-proline peptide was also significantly higher than in HSF. Pro-alpha1(I) collagen mRNA was highly expressed in both desmoid tumors and HSF at approximately the same level, whereas pro-alpha1(III) collagen mRNA was more abundant in some of the desmoid tumors than the normal skin fibroblastic cell lines. Tumor growth factor-beta1 mRNA, which is believed to stimulate collagen synthesis, was expressed in both desmoid tumors and HSF to the same extent. These results demonstrate the increased formation of collagen and elastin in desmoid tumors in vitro and suggest that the increased synthesis of elastin rather than of collagen and TGF-beta1 may be involved in increased fibrogenesis by desmoid tumors.