Depletion of protein kinase Cepsilon in normal and scleroderma lung fibroblasts has opposite effects on tenascin expression

Potential of Curcumin in the Management of Skin Diseases

Curcumin is a polyphenolic molecule derived from the rhizoma of Curcuma longa L. This compound has been used for centuries due to its anti-inflammatory, antioxidant, and antimicrobial properties. These make it ideal for preventing and treating skin inflammation, premature skin ageing, psoriasis, and acne. Additionally, it exhibits antiviral, antimutagenic, and antifungal effects. Curcumin provides protection against skin damage caused by prolonged exposure to UVB radiation. It reduces wound healing times and improves collagen deposition. Moreover, it increases fibroblast and vascular density in wounds. This review summarizes the available information on the therapeutic effect of curcumin in treating skin diseases. The results suggest that curcumin may be an inexpensive, well-tolerated, and effective agent for treating skin diseases. However, larger clinical trials are needed to confirm these observations due to limitations in its in vivo use, such as low bioavailability after oral administration and metabolism.

Emerging Roles of Matricellular Proteins in Systemic Sclerosis

Systemic sclerosis is a rare chronic heterogenous disease that involves inflammation and vasculopathy, and converges in end-stage development of multisystem tissue fibrosis. The loss of tight spatial distribution and temporal expression of proteins in the extracellular matrix (ECM) leads to progressive organ stiffening, which is a hallmark of fibrotic disease. A group of nonstructural matrix proteins, known as matricellular proteins (MCPs) are implicated in dysregulated processes that drive fibrosis such as ECM remodeling and various cellular behaviors. Accordingly, MCPs have been described in the context of fibrosis in sclerosis (SSc) as predictive disease biomarkers and regulators of ECM synthesis, with promising therapeutic potential. In this present review, an informative summary of major MCPs is presented highlighting their clear correlations to SSc- fibrosis.

Recent advances in understanding the pathogenesis of scleroderma-interstitial lung disease

Systemic sclerosis (scleroderma, SSc) is a heterogeneous autoimmune connective tissue disease of unknown etiology. Interstitial lung disease (ILD) is a frequent complication, and a significant contributor to morbidity and mortality among SSc patients. SSc-ILD most commonly occurs within 10 years of diagnosis, and may be seen in patients with either the limited or diffuse cutaneous subset of SSc. SSc-ILD is a multifaceted disease process in which different factors and pathways are involved. Aberrant function of a variety of lung cells, cytokines, growth factors, peptides, and bioactive proteins, in combination with genetic and epigenetic regulators, have crucial functions in the pathogenesis of this disease. Here we present our view on recent advances regarding the pathogenesis of SSc-ILD.

Curcumin modulates the inflammatory response and inhibits subsequent fibrosis in a mouse model of viral-induced acute respiratory distress syndrome

Acute Respiratory Distress Syndrome (ARDS) is a clinical syndrome characterized by diffuse alveolar damage usually secondary to an intense host inflammatory response of the lung to a pulmonary or extrapulmonary infectious or non-infectious insult often leading to the development of intra-alveolar and interstitial fibrosis. Curcumin, the principal curcumoid of the popular Indian spice turmeric, has been demonstrated as an anti-oxidant and anti-inflammatory agent in a broad spectrum of diseases. Using our well-established model of reovirus 1/L-induced acute viral pneumonia, which displays many of the characteristics of the human ALI/ARDS, we evaluated the anti-inflammatory and anti-fibrotic effects of curcumin. Female CBA/J mice were treated with curcumin (50 mg/kg) 5 days prior to intranasal inoculation with 10(7)pfu reovirus 1/L and daily, thereafter. Mice were evaluated for key features associated with ALI/ARDS. Administration of curcumin significantly modulated inflammation and fibrosis, as revealed by histological and biochemical analysis. The expression of IL-6, IL-10, IFNγ, and MCP-1, key chemokines/cytokines implicated in the development of ALI/ARDS, from both the inflammatory infiltrate and whole lung tissue were modulated by curcumin potentially through a reduction in the phosphorylated form of NFκB p65. While the expression of TGFß1 was not modulated by curcumin, TGFß Receptor II, which is required for TGFß signaling, was significantly reduced. In addition, curcumin also significantly inhibited the expression of α-smooth muscle actin and Tenascin-C, key markers of myofibroblast activation. This data strongly supports a role for curcumin in modulating the pathogenesis of viral-induced ALI/ARDS in a pre-clinical model potentially manifested through the alteration of inflammation and myofibroblast differentiation.

Gene expression profiling in fetal rat lung during gestational perfluorooctane sulfonate exposure

Perfluorooctane sulfonate (PFOS) is a persistent environmental contaminant found in the tissues of humans and wildlife. It has been reported that gestational exposure to PFOS causes neonatal death of rats. However, the mechanism is still unclear. In this study, we investigated the effects of gestational PFOS exposure on the gene expression profiling of fetal rat lung at pseudoglandular stage. Adult Sprague Dawley dams were dosed orally from gestational day 12-18 with 0 (control), 5 mg/kg/day or 20 mg/kg/day PFOS. Animals were euthanized on day 18.5, fetal lung samples were collected for histochemical staining and RNA profiling analysis. PFOS did not cause apparent microscopic changes of fetal lungs. Gene expression profiling revealed that PFOS dose-dependently up-regulated the expression of 21 (5 mg/kg) and 43 (20 mg/kg) genes. These genes include five PPARα target genes (Acot1, Hmgcs2, Fabp4, Fabp1 and Myh7), and 4 of them are involved in lipid metabolism. The other genes were primarily included in the categories of cytoskeletal structure (Tpm1, Tnnt2, Actn3, Myoz2, Tmod1, and Mfap5), extracellular matrix (Ckm, Lum, Tnnc1, Art3, Dcn, Col17a1, Aspn, Ctsk, Itm2a, Spock2 and Orm1), transporting (Cox8h, Cox6a2 and Scnn1a) and secreted proteins (Scgb3a1, Nppb and Spp1). Our study demonstrates that in utero PFOS exposure resulted in the alteration of a set of genes which are involved in significant cytoskeletal, extracellular matrix remodeling, lipid metabolism and secreted proteins in the fetal rat lung.

Antiinflammatory and antifibrotic effects of the oral direct thrombin inhibitor dabigatran etexilate in a murine model of interstitial lung disease

OBJECTIVE

Activation of the coagulation cascade leading to generation of thrombin has been documented extensively in various forms of lung injury, including that associated with systemic sclerosis. We previously demonstrated that the direct thrombin inhibitor dabigatran inhibits thrombin-induced profibrotic signaling in lung fibroblasts. This study was undertaken to test whether dabigatran etexilate attenuates lung injury in a murine model of interstitial lung disease.

METHODS

Lung injury was induced in female C57BL/6 mice by a single intratracheal instillation of bleomycin. Dabigatran etexilate was given as supplemented chow beginning on day 1 of bleomycin instillation (early treatment, study of antiinflammatory effect) or on day 8 following bleomycin instillation (late treatment, study of antifibrotic effect). Mice were killed 2 weeks or 3 weeks after bleomycin instillation, and lung tissue, bronchoalveolar lavage (BAL) fluid, and plasma were investigated.

RESULTS

Both early treatment and late treatment with dabigatran etexilate attenuated the development of bleomycin-induced pulmonary fibrosis. Dabigatran etexilate significantly reduced thrombin activity and levels of transforming growth factor β1 in BAL fluid, while simultaneously reducing the number of inflammatory cells and protein concentrations. Histologically evident lung inflammation and fibrosis were significantly decreased in dabigatran etexilate-treated mice. Additionally, dabigatran etexilate reduced collagen, connective tissue growth factor, and α-smooth muscle actin expression in mice with bleomycin-induced lung fibrosis, whereas it had no effect on basal levels of these proteins.

CONCLUSION

Inhibition of thrombin using the oral direct thrombin inhibitor dabigatran etexilate has marked antiinflammatory and antifibrotic effects in a bleomycin model of pulmonary fibrosis. Our data provide preclinical information about the feasibility and efficacy of dabigatran etexilate as a new therapeutic approach for the treatment of interstitial lung disease.

Expression of matrix metalloproteinase-13 is controlled by IL-13 via PI3K/Akt3 and PKC-δ in normal human dermal fibroblasts

IL-13, a T helper type 2 cytokine, is reported to be increased in the tissue of patients with atopic dermatitis (AD). In addition, chronic lichenified plaques in AD show thickened epidermis and dermis. We hypothesized that IL-13 is involved in tissue remodeling by altering the expression of matrix metalloproteinases (MMPs). In this study, we examined the MMP-related genes targeted by IL-13 in human dermal fibroblasts using a complementary DNA microarray. We focused on the MMP-13 gene, which was identified as one of the MMPs suppressed by IL-13. IL-13 downregulated both MMP-13 protein and mRNA expression. IL-13 suppressed MMP-13 expression more effectively in the presence of protein kinase C (PKC)-δ inhibitor, whereas IL-13 upregulated MMP-13 in the presence of inhibitors of phosphoinositide 3-kinase (PI3K)/Akt pathway or Akt3-specific small interfering RNA. Our results suggest that MMP-13 expression is negatively controlled by PI3K/Akt3 and positively regulated by PKC-δ in the presence of IL-13. Taken together, these findings indicate that IL-13 may induce the formation of thickened dermis in AD by decreasing collagen degradation. Blockade of IL-13 signaling cascades in AD patients may be a new therapeutic approach.

Dabigatran, a direct thrombin inhibitor, demonstrates antifibrotic effects on lung fibroblasts

OBJECTIVE

Myofibroblasts are the principal mesenchymal cells responsible for tissue remodeling, collagen deposition, and the restrictive nature of lung parenchyma associated with pulmonary fibrosis. We previously reported that thrombin activates protease-activated receptor 1 (PAR-1) and induces a myofibroblast phenotype in normal lung fibroblasts resembling the phenotype of scleroderma lung myofibroblasts. We undertook this study to investigate whether a selective direct thrombin inhibitor, dabigatran, interferes with signal transduction in human lung fibroblasts induced by thrombin and mediated via PAR-1.

METHODS

Lung fibroblast proliferation was analyzed using the Quick Cell Proliferation Assay. Expression and organization of alpha-smooth muscle actin (alpha-SMA) was studied by immunofluorescence staining and immunoblotting. Contractile activity of lung fibroblasts was measured by a collagen gel contraction assay. Connective tissue growth factor (CTGF) and type I collagen expression was analyzed on Western blots.

RESULTS

Dabigatran, at concentrations of 50-1,000 ng/ml, inhibited thrombin-induced cell proliferation, alpha-SMA expression and organization, and the production of collagen and CTGF in normal lung fibroblasts. Moreover, when treated with dabigatran (1 microg/ml), scleroderma lung myofibroblasts produced 6-fold less alpha-SMA, 3-fold less CTGF, and 2-fold less type I collagen compared with untreated cells.

CONCLUSION

Dabigatran restrains important profibrotic events in lung fibroblasts and warrants study as a potential antifibrotic drug for the treatment of fibrosing lung diseases such as scleroderma lung disease and idiopathic pulmonary fibrosis.

Thrombin-stimulated growth factor and cytokine expression in osteoblasts is mediated by protease-activated receptor-1 and prostanoids

Thrombin exerts multiple effects upon osteoblasts including stimulating proliferation, and inhibiting osteoblast differentiation and apoptosis. Some of these effects are believed to be mediated by the synthesis and secretion of autocrine factors such as growth factors and cytokines. Many but not all cellular responses to thrombin are mediated by members of the protease-activated receptor (PAR) family of G protein-coupled receptors. The current study was undertaken to investigate the nature of thrombin's induction of autocrine factors by analysing the expression of twelve candidate genes in thrombin-stimulated primary mouse osteoblasts. Analysis by quantitative reverse transcription polymerase chain reaction (qRT-PCR) demonstrated that thrombin induced transforming growth factor beta, cyclooxygenase-2, tenascin C, fibroblast growth factor-1 and -2, connective tissue growth factor and interleukin-6 expression in wild type osteoblasts, but not PAR-1 null mouse osteoblasts. Induction of all the thrombin-responsive genes was blocked by the presence of the non-selective cyclooxygenase inhibitor indomethacin. Further studies were conducted on interleukin-6, which was the gene that showed the greatest increase in expression following stimulation of osteoblast-like cells with thrombin. A PAR-1-specific activating peptide, but neither a PAR-4-activating peptide nor catalytically inactive thrombin induced release of interleukin-6 by osteoblasts. Furthermore, in the presence of the selective cyclooxygenase-1 and -2 inhibitors SC-560 and NS-398 thrombin-induced interleukin-6 release was prevented. Levels of both prostaglandin E(2) and interleukin-6 in medium conditioned by thrombin-stimulated osteoblast-like cells were found to be significantly increased compared to medium conditioned by non-stimulated cells, however release of prostaglandin E(2) was found to precede release of interleukin-6. Treatment of isolated osteoblast-like cells with a number of synthetic prostanoids stimulated secretion of interleukin-6 with differing potencies. These studies suggest that activation of PAR-1 on osteoblasts by thrombin induces cyclooxygenase activity, which in turn results in the increased expression of multiple secreted factors. The induction of these secreted factors may act in an autocrine fashion to alter osteoblast function, allowing these cells to participate in the earliest stages of bone healing by both autocrine and paracrine mechanisms.

Synergistic effects of cyclic strain and Th1-like cytokines on tenascin-C production by rheumatic aortic valve interstitial cells

Tenascin-C (TN-C) is a key component of extracellular matrix (ECM) and its expression process is poorly understood during rheumatic heart valvular disease (RHVD). In this study, we found that interferon (IFN)-gamma, tumour necrosis factor (TNF)-alpha and TN-C concentrations in patients with RHVD were significantly higher than in normal controls. More IFN-gamma receptors and TNF receptors were found being expressed on rheumatic aortic valves interstitial cells than on non-rheumatic ones and their expression was patients' sera dependent. Antibodies neutralizing IFN-gamma or TNF-alpha could attenuate patients' sera-induced TN-C transcription by isolated rheumatic aortic valves interstitial cells. By application with different protein kinase inhibitors, we found that combined with cyclic strain, TNF-alpha and IFN-gamma induced TN-C transcription through the RhoA/ROCK signalling pathway. At the same time, p38 mitogen-activated protein kinase was involved in TNF-alpha and IFN-gamma induced TN-C transcription. TNF-alpha also increased TN-C mRNA level by additional PKC and ERK 1/2 activation. Our finding revealed a new insight into ECM remodelling during RHVD pathogenesis and new mechanisms involved in the clinical anti-IFN-gamma and anti-TNF-alpha therapy.

Antifibrotic properties of caveolin-1 scaffolding domain in vitro and in vivo

Lung fibrosis involves the overexpression of ECM proteins, primarily collagen, by α-smooth muscle actin (ASMA)-positive cells. Caveolin-1 is a master regulator of collagen expression by cultured lung fibroblasts and of lung fibrosis in vivo. A peptide equivalent to the caveolin-1 scaffolding domain (CSD peptide) inhibits collagen and tenascin-C expression by normal lung fibroblasts (NLF) and fibroblasts from the fibrotic lungs of scleroderma patients (SLF). CSD peptide inhibits ASMA expression in SLF but not NLF. Similar inhibition of collagen, tenascin-C, and ASMA expression was also observed when caveolin-1 expression was upregulated using adenovirus. These observations suggest that the low caveolin-1 levels in SLF cause their overexpression of collagen, tenascin-C, and ASMA. In mechanistic studies, MEK, ERK, JNK, and Akt were hyperactivated in SLF, and CSD peptide inhibited their activation and altered their subcellular localization. These studies and experiments using kinase inhibitors suggest many differences between NLF and SLF in signaling cascades. To validate these data, we determined that the alterations in signaling molecule activation observed in SLF also occur in fibrotic lung tissue from scleroderma patients and in mice with bleomycin-induced lung fibrosis. Finally, we demonstrated that systemic administration of CSD peptide to bleomycin-treated mice blocks epithelial cell apoptosis, inflammatory cell infiltration, and changes in tissue morphology as well as signaling molecule activation and collagen, tenascin-C, and ASMA expression associated with lung fibrosis. CSD peptide may be a prototype for novel treatments for human lung fibrosis that act, in part, by inhibiting the expression of ASMA and ECM proteins.

Regulation of fibroblast migration by tenascin-C

Synthesis of new tissue by fibroblasts is required for tissue rebuilding in response to injury. Fibroblast migration from surrounding healthy tissue into the fibrin-fibronectin provisional matrix deposited upon injury is a key rate-limiting step of this stage of tissue repair. These events must be tightly regulated. Excessive deposition of scar tissue is the major hallmark of fibrotic disease. Tenascin-C is an extracellular matrix glycoprotein that is transiently expressed upon tissue injury, where it is specifically localized to the wound edge, and persistently up-regulated in fibrotic disease. We have shown that full-length tenascin-C promotes fibroblast migration within fibrin-fibronectin matrices and we have mapped the domains within the molecule critical for enhancing migration. We also demonstrated that specific fragments of tenascin-C inhibit fibroblast migration. These results suggest that transient expression of tenascin-C at the wound boundary is key to tissue repair: its induction recruits fibroblasts into the wound and fragments resulting from its breakdown prevent excessive fibroblast infiltration. Our results demonstrate how fibroblast migration in three-dimensional provisional matrices may be differentially regulated by proteolysis of matrix molecules and could explain how persistent expression of tenascin-C contributes to the progression of fibrotic disease.

Deletion of Protein Kinase C-ε Signaling Pathway Induces Glomerulosclerosis and Tubulointerstitial FibrosisIn Vivo

Protein kinase C (PKC), a family of 12 distinct serine-threonine kinases, is an important intracellular signaling pathway involved in various cellular functions, such as proliferation, hypertrophy, apoptosis, and adhesion. PKC-epsilon, a novel PKC isoform that is activated in the diabetic kidney, has been demonstrated to have a central role in the underlying signaling infrastructure of myocardial ischemia and hypertrophy. The renal phenotype of PKC-epsilon(-/-) mice was studied with regard to renal hypertrophy and fibrosis. PKC-epsilon(-/-) deficient knockout mice were generated and then killed after 6, 16, and 26 wk of life. Kidney/body weight ratio did not show any significant group difference compared with appropriate wild-type controls. Urinary albumin/creatinine ratio remained normal in wild-type mice, whereas PKC-epsilon(-/-) mice after 6 and 16 wk showed elevated albuminuria. Masson-Goldner staining revealed that tubulointerstitial fibrosis and mesangial expansion were significantly increased in PKC-epsilon(-/-) mice. However, this profibrotic phenotype was not observed in other organs, such as liver and lung. Immunohistochemistry of the kidneys from PKC-epsilon(-/-) mice showed increased renal fibronectin and collagen IV expression that was further aggravated in the streptozotocin-induced diabetic stress model. Furthermore, TGF-beta(1), phospho-Smad2, and phospho-p38 mitogen-activate protein kinase expression was increased in PKC-epsilon(-/-) mice, suggesting a regulatory role of PKC-epsilon in TGF-beta(1) and its signaling pathway in the kidney. These results indicate that deletion of PKC-epsilon mediates renal fibrosis and that TGF-beta1 and its signaling pathway might be involved. Furthermore, these data suggest that activation of PKC-epsilon in the diabetic state may rather represent a protective response to injury than be a mediator of renal injury.

Therapies for bleomycin induced lung fibrosis through regulation of TGF-β1 induced collagen gene expression

This review describes normal and abnormal wound healing, the latter characterized by excessive fibrosis and scarring, which for lung can result in morbidity and sometimes mortality. The cells, the extracellular matrix (ECM) proteins, and the growth factors regulating the synthesis, degradation, and deposition of the ECM proteins will be discussed. Therapeutics with particular emphasis given to gene therapies and their effects on specific signaling pathways are described. Bleomycin (BM), a potent antineoplastic antibiotic increases TGF-beta1 transcription, TGF-beta1 gene expression, and TGF-beta protein. Like TGF-beta1, BM acts through the same distal promoter cis-element of the COL1A1 gene causing increased COL1 synthesis and lung fibrosis. Lung fibroblasts exist as subpopulations with one subset predominantly responding to fibrogenic stimuli which could be a specific cell therapeutic target for the onset and development of pulmonary fibrosis.

PKCalpha mediates CCL18-stimulated collagen production in pulmonary fibroblasts

A CC chemokine, CCL18, has been previously reported to stimulate collagen production in pulmonary fibroblasts. This study focused on the role of protein kinase C (PKC) in the profibrotic signaling activated by CCL18 in pulmonary fibroblasts. Of the three PKC isoforms that are predominantly expressed in fibroblasts (PKCalpha, PKCdelta, and PKCepsilon), two isoforms (PKCdelta and PKCepsilon) have been implicated in profibrotic intracellular signaling. The role of PKCalpha-mediated signaling in the regulation of collagen production remains unclear. In this study, PKCalpha was found mostly in the cytoplasm, whereas PKCdelta and PKCepsilon were found mostly in the nucleus of cultured primary pulmonary fibroblasts. In response to stimulation with CCL18, PKCalpha but not PKCdelta or PKCepsilon underwent rapid (within 5-10 min) transient phosphorylation and nuclear translocation. Inhibition with dominant-negative mutants of PKCalpha and ERK2, but not PKCdelta or PKCepsilon, abrogated CCL18-stimulated ERK2 phosphorylation and collagen production. The effect of CCL18 on collagen production and the activity of collagen promoter reporter constructs were also abrogated by a selective pharmacologic inhibitor of PKCalpha Gö6976. Stimulation of fibroblasts with CCL18 caused an increase in intracellular calcium concentration. Consistent with the known calcium dependence of PKCalpha signaling, blocking of the calcium signaling with the intracellular calcium-chelating agent BAPTA led to abrogation of PKCalpha nuclear translocation, ERK2 phosphorylation, and collagen production. These observations suggest that in primary pulmonary fibroblasts, PKCalpha but not PKCdelta or PKCepsilon mediate the profibrotic effect of CCL18. PKCalpha may therefore become a viable target for future antifibrotic therapies.

Upregulation of tenascin-C expression by IL-13 in human dermal fibroblasts via the phosphoinositide 3-kinase/Akt and the protein kinase C signaling pathways

In this study, we examined the genes targeted by IL-13 in human dermal fibroblasts using a cDNA microarray. We focused on the tenascin-C (TN-C) gene, which was identified as one of the genes induced by IL-13. IL-13 induced transcriptional activity of TN-C. IL-13-mediated TN-C expression was inhibited by treatment with wortmannin or LY294002, or Calphostin C. IL-13 induced the phosphorylation of the phosphoinositide 3-kinase (PI3K) regulatory subunit p85, induced tyrosine phosphorylation of Akt, upregulated Akt kinase activity, and activated protein kinase C (PKC)-delta and -epsilon. The IL-13-induced increase in TN-C protein expression was abrogated by the transfection of a dominant-negative mutant of Akt, PKC-delta, or PKC-epsilon. In conclusion, we showed that the PI3K/Akt and/or PKC signaling pathways are essential for the IL-13-mediated increase in TN-C. Both serum levels of IL-13 and the expression levels of TN-C in the dermis are increased in patients with systemic sclerosis. Our findings suggest that the expression of TN-C is upregulated in this disease due to IL-13 signaling, and that a blockade of the PI3K or PKC signaling pathway may also have therapeutic value by reducing the amount of TN-C produced during fibrosis.

Signaling pathways regulating intercellular adhesion molecule 1 expression by endothelin 1: Comparison with interleukin-1β in normal and scleroderma dermal fibroblasts

OBJECTIVE

Endothelin 1 (ET-1) has been implicated in the pathogenesis of fibrotic and inflammatory diseases, including scleroderma. In addition to modulating vascular tone and extracellular matrix turnover, ET-1 up-regulates cell surface adhesion molecules including intercellular adhesion molecule 1 (ICAM-1), which is key to cell-cell and cell-matrix adhesion and leukocyte infiltration. This study was undertaken to delineate the signal transduction pathways utilized by ET-1 and compare them with those adopted by proinflammatory cytokine interleukin-1beta (IL-1beta) in normal and scleroderma dermal fibroblasts.

METHODS

Protein expression induced by ET-1 and IL-1beta on normal dermal fibroblasts, with or without signaling inhibitors, was detected by enzyme-linked immunosorbent assay, while messenger RNA (mRNA) levels were analyzed by LightCycler polymerase chain reaction. Expression of protein kinase Cdelta (PKCdelta) and PKCepsilon protein in normal dermal fibroblasts and scleroderma dermal fibroblasts was determined by Western blotting, and PKCepsilon involvement in ET-1 signaling was confirmed through transfection of an ICAM-1 promoter construct into murine PKCepsilon-/- fibroblasts. NF-kappaB activation was confirmed via electrophoretic mobility supershift assay, and analysis of the ICAM-1 promoter region was achieved via transfection of deletion constructs into human dermal fibroblasts.

RESULTS

In normal dermal fibroblasts, ET-1 induced ICAM-1 mRNA and surface protein expression in a dose- and time-dependent manner via both receptor subtypes, ET(A) and ET(B); antagonism of both abolished the ET-1 response. MEK was involved in the signaling cascade, but phosphatidylinositol 3-kinase and p38 MAPK were not. Key to the cascade was activation of NF-kappaB, achieved by ligation of either receptor subtype. PKCepsilon activation led to downstream activation of MEK and, in part, NF-kappaB. IL-1beta signaling required NF-kappaB and MEK activation, along with activation of PKCdelta. ET-1 and IL-1beta each utilized the same ICAM-1 promoter region and the same NF-kappaB site at -157 bp. Responses to ET-1 and IL-1beta differed in scleroderma dermal fibroblasts, with ET-1 sensitivity decreasing and IL-1beta responses remaining intact. Expression of PKCepsilon and PKCdelta in scleroderma dermal fibroblasts was also altered.

CONCLUSION

The findings of this study indicate that differences in sensitivity to ET-1 and IL-1beta in scleroderma dermal fibroblasts may be explained by altered expression of the PKC isoforms and cytokine receptors.

Alpha2(I) collagen gene regulation by protein kinase C signaling in human dermal fibroblasts

We investigated the mechanisms by which protein kinase C (PKC) regulates the expression of the α2(I) collagen gene in normal dermal fibroblasts. Reduction of PKC-α activity by treatment with Gö697-6 or by overexpression of a dominant negative (DN) mutant form decreased α2(I) collagen gene expression. This decrease required a sequence element in the collagen promoter that contains Sp1/Sp3 binding sites. Reduction of PKC-δ activity by rottlerin or overexpression of DN PKC-δ also decreased α2(I) collagen gene expression. This effect required a separate sequence element containing Sp1/Sp3-binding sites and an Ets-binding site. In both cases, point mutations within the response elements abrogated the response to PKC inhibition. Forced overexpression of Sp1 rescued the PKC inhibitor-mediated reduction in collagen protein expression. A DNA affinity precipitation assay revealed that inhibition of PKC-δ by rottlerin increased the binding activity of endogenous Fli1 and decreased that of Ets1. On the other hand, TGF-β1, which increased the expression of PKC-δ, had the opposite effect, increasing the binding activity of Ets1 and decreasing that of Fli1. Our results suggest that PKC-δ is involved in the regulation of the α2(I) collagen gene in the presence or absence of TGF-β. Alteration of the balance of Ets1 and Fli1 may be a novel mechanism regulating α2(I) collagen expression.

Opposing effects of protein kinase Calpha and protein kinase Cepsilon on collagen expression by human lung fibroblasts are mediated via MEK/ERK and caveolin-1 signaling

The roles of MEK, ERK, the epsilon and alpha isoforms of protein kinase C (PKC), and caveolin-1 in regulating collagen expression were studied in normal lung fibroblasts. Knocking down caveolin-1 gave particularly striking results. A 70% decrease caused a 5-fold increase in MEK/ERK activation and collagen expression. The combined data reveal a branched signaling pathway. In its central portion MEK activates ERK, leading to increased collagen expression. Two branches converge on MEK/ERK. In one, increased PKCepsilon leads to MEK/ERK activation. In another, increased PKCalpha induces caveolin-1 expression, which in turn inhibits MEK/ERK activation and collagen expression. Lung fibroblasts from scleroderma patients with pulmonary fibrosis showed altered signaling. Consistent with their overexpression of collagen, scleroderma lung fibroblasts contain more activated MEK/ERK and less caveolin-1 than normal lung fibroblasts. Because cutaneous fibrosis is the hallmark of scleroderma, we also studied dermal fibroblasts. As in lung, there was more activated MEK/ERK in cells from scleroderma patients than in control cells, and MEK inhibition decreased collagen expression. However, the distinctive levels of PKCepsilon, PKCalpha, and caveolin-1 in lung and dermal fibroblasts from scleroderma patients and control subjects indicate that the links between these signaling proteins and MEK/ERK must function differently in the four cell types. Finally, we confirmed the relevance of these signaling cascades in vivo. The combined results demonstrate that a branched signaling pathway involving MEK, ERK, PKCepsilon, PKCalpha, and caveolin-1 regulates collagen expression in normal lung tissue and is perturbed during fibrosis.

Recent advances in fibroblast signaling and biology in scleroderma

PURPOSE OF REVIEW

Systemic sclerosis is a complex disease manifesting itself by fibrosis of skin and other internal organs. Fibroblasts isolated from scleroderma lesions and cultured in vitro are characterized by increased synthesis of collagen and other extracellular matrix proteins, consistent with the disease phenotype. Cultured systemic sclerosis fibroblasts therefore serve as a principal experimental model for studying the molecular and cellular mechanisms involved in collagen overproduction in this disease. This review will discuss recent findings related to intracellular signal transduction pathways implicated in deregulated extracellular matrix deposition by systemic sclerosis fibroblasts.

RECENT FINDINGS

Recent findings suggest that constitutively elevated synthesis of extracellular matrix by cultured systemic sclerosis fibroblasts is, at least in part, due to the aberrant activation of the autocrine transforming growth factor-beta signaling. Enhanced constitutive transforming growth factor-beta signaling may result from the elevated levels of transforming growth factor-beta receptor type I and/or inappropriate activation of Smad3. These alterations of the transforming growth factor-beta signaling in systemic sclerosis fibroblasts may facilitate increased collagen production in vivo even under conditions of low ligand availability. However, there exist many inconsistencies among published reports regarding the detailed mechanisms of this pathway in systemic sclerosis fibroblasts, and additional studies in this area are needed. Other signaling molecules implicated in fibrotic phenotype include several members of the protein kinase C family, mammalian target of rapamycin, mitogen-activated protein kinase, necdin, reactive oxygen species, and sphingolipids. These signaling pathways may work in conjunction with transforming growth factor-beta signaling to regulate the behavior of systemic sclerosis fibroblasts.

SUMMARY

Alterations in multiple signaling pathways contribute to elevated extracellular matrix synthesis by systemic sclerosis fibroblasts. Improved understanding of the key signaling molecules may provide a novel avenue for therapeutic interventions.

Distinct PKC isoforms mediate cell survival and DNA synthesis in thrombin-induced myofibroblasts

Thrombin activates protease-activated receptor (PAR)-1 and induces a myofibroblast phenotype in normal lung fibroblasts that resembles the phenotype of scleroderma lung fibroblasts. We now demonstrate that PAR-1 expression is dramatically increased in lung tissue from scleroderma patients, where it is associated with inflammatory and fibroproliferative foci. We also observe that thrombin induces resistance to apoptosis in normal lung fibroblasts, and this process is regulated by protein kinase C (PKC)-epsilon but not by PKC-alpha. Overexpression of a constitutively active (c-a) form of PAR-1 or PKC-epsilon significantly inhibits Fas ligand-induced apoptosis in lung fibroblasts, whereas scleroderma lung fibroblasts are resistant to apoptosis de novo. Thrombin translocates p21Cip1/WAF1, a signaling molecule downstream of PKC, from the nucleus to cytoplasm in normal lung fibroblasts mimicking the localization of p21Cip1/WAF1 in scleroderma lung fibroblasts. Overexpression of c-a PKC-alpha or PKC-epsilon results in accumulation of p21Cip1/WAF1 in the cytoplasm. Depletion of PKC-alpha or inhibition of mitogen-activated protein kinase (MAPK) blocks thrombin-induced DNA synthesis in lung fibroblasts. Inhibition of PKC by calphostin or PKC-alpha, but not PKC-epsilon, by antisense oligonucleotides prevents thrombin-induced MAPK phosphorylation and accumulation of G(1) phase regulatory protein cyclin D1, suggesting that PKC-alpha, MAPK, and cyclin D1 mediate lung fibroblast proliferation. These data demonstrate that two distinct PKC isoforms mediate thrombin-induced resistance to apoptosis and proliferation and suggest that p21Cip1/WAF1 promotes both phenomena.

Cytokine regulation of pulmonary fibrosis in scleroderma

Pulmonary fibrosis occurs in up to 70% of scleroderma patients and progresses to cause severe restrictive lung disease in about 15% of patients. The mechanisms that cause pulmonary fibrosis in scleroderma remain incompletely understood. Increased amounts of mRNA or protein for multiple profibrotic cytokines and chemokines have been identified in lung tissue or broncholveolar lavage samples from scleroderma patients, when compared to healthy controls. These cytokines include transforming growth factor (TGF)-beta, connective tissue growth factor (CTGF), platelet-derived growth factor (PDGF), oncostatin M (OSM), monocyte chemotactic factor-1 and pulmonary and activation-regulated chemokine (PARC). Potential cellular sources of these profibrotic cytokines and chemokines in scleroderma lung disease include alternatively activated macrophages, activated CD8+ T cells, eosinophils, mast cells, epithelial cells and fibroblasts themselves. This review summarizes the literature on involvement of cytokines and chemokines in the development of pulmonary fibrosis in scleroderma.

Curcumin-induced apoptosis in scleroderma lung fibroblasts: role of protein kinase cepsilon

Scleroderma, a disease involving excessive collagen deposition, can be studied using fibroblasts cultured from affected tissues. We find that curcumin, the active component of the spice turmeric, causes apoptosis in scleroderma lung fibroblasts (SLF), but not in normal lung fibroblasts (NLF). This effect is likely to be linked to the fact that although curcumin induces the expression of the phase 2 detoxification enzymes heme oxygenase 1 and glutathione S-transferase P1 (GST P1) in NLF, SLF are deficient in these enzymes, particularly after curcumin treatment. The sensitivity of cells to curcumin-induced apoptosis and the expression of GST P1 (but not heme oxygenase 1) are regulated by the epsilon isoform of protein kinase C (PKCepsilon). SLF, which contain less PKCepsilon and less GST P1 than NLF, become less sensitive to curcumin-induced apoptosis and express higher levels of GST P1 when transfected with wild-type PKCepsilon, but not with dominant-negative PKCepsilon. Conversely, NLF become sensitive to curcumin-induced apoptosis and express lower levels of GST P1 when PKCepsilon expression or function is inhibited. The subcellular distribution of PKCepsilon also differs in NLF and SLF. PKCepsilon is predominantly nuclear or perinuclear in NLF but is associated with stress fibers in SLF. Just as PKCepsilon levels are lower in SLF than in NLF in vitro, PKCepsilon expression is decreased in fibrotic lung tissue in vivo. In summary, our results suggest that a signaling pathway involving PKCepsilon and phase 2 detoxification enzymes provides protection against curcumin-induced apoptosis in NLF and is defective in SLF. These observations suggest that curcumin may have therapeutic value in treating scleroderma, just as it has already been shown to protect rats from lung fibrosis induced by a variety of agents.

Contractile activity and smooth muscle alpha-actin organization in thrombin-induced human lung myofibroblasts

Activated fibroblasts, or myofibroblasts, are crucial players in tissue remodeling, wound healing, and various fibrotic disorders, including interstitial lung fibrosis associated with scleroderma. Here we characterize the signaling pathways in normal lung fibroblasts exposed to thrombin as they acquire two of the main features of myofibroblasts: smooth muscle (SM) alpha-actin organization and collagen gel contraction. Our results show that the small G protein Rho is involved in lung myofibroblast differentiation. Thrombin induces Rho-35S-labeled guanosine 5'-O-(3-thiotriphosphate) binding in a dose-dependent manner. It potently stimulates Rho activity in vivo and initiates protein kinase C (PKC)-epsilon-Rho complex formation. Toxin B, which inactivates Rho by ADP ribosylation, inhibits thrombin-induced SM alpha-actin organization, collagen gel contraction, and PKC-epsilon-SM alpha-actin and PKC-epsilon-RhoA coimmunoprecipitation. However, it has no effect on PKC-epsilon activation or translocation of PKC-epsilon to the membrane. Overexpression of constitutively active PKC-epsilon and constitutively active RhoA induces collagen gel contraction or SM alpha-actin organization, whereas, individually, they do not perform these functions. We therefore conclude that the contractile activity of myofibroblasts induced by thrombin is mediated via PKC-epsilon- and RhoA-dependent pathways and that activation of both of these molecules is required. We postulate that PKC-epsilon-RhoA complex formation is an early event in thrombin activation of lung fibroblasts, followed by PKC-epsilon-SM alpha-actin coimmunoprecipitation, which leads to the PKC-epsilon-RhoA-SM alpha-actin ternary complex formation.

Increased transcriptional activities of transforming growth factor beta receptors in scleroderma fibroblasts

OBJECTIVE

To investigate the molecular mechanism of the overexpression of transforming growth factor beta receptors (TGF(beta)Rs) in dermal fibroblasts from patients with systemic sclerosis (SSc).

METHODS

Dermal fibroblasts from 7 patients with diffuse SSc of recent onset and from 7 healthy individuals were studied. The expression of TGF(beta)R type I (TGF(beta)RI), TGF(beta)RII, and type I collagen proteins in dermal fibroblasts was determined by immunoblotting. TGF(beta)RI, TGF(beta)RII, and alpha2(I) collagen messenger RNA (mRNA) were evaluated by Northern blot analysis. The transcriptional activities of the TGF(beta)RI and TGF(beta)RII genes were examined by luciferase assay.

RESULTS

SSc fibroblasts expressed increased levels of TGF(beta)RI and TGF(beta)RII protein and mRNA, as well as increased levels of type I collagen protein and alpha2(I) collagen mRNA. Moreover, the half-lives of TGF(beta)RI and TGF(beta)RII mRNA in SSc fibroblasts did not change compared with those in control dermal fibroblasts. The promoter activities of the TGF(beta)RI and TGF(beta)RII genes were both significantly increased in SSc fibroblasts compared with those in control fibroblasts. Calphostin C, a specific inhibitor of protein kinase C (PKC), inhibited TGF(beta)RI promoter activity in SSc fibroblasts, and LY294002, an inhibitor of phosphoinositide 3-kinase (PI 3-kinase), inhibited TGF(beta)RII promoter activity in SSc fibroblasts. Moreover, calphostin C and LY294002 inhibited the up-regulation of TGF(beta)RI and TGF(beta)RII mRNA, respectively, in SSc fibroblasts.

CONCLUSION

These results suggest that increased levels of TGF(beta)Rs in SSc fibroblasts play a role in excessive collagen production, and that up-regulation of TGF(beta)R expression might occur at the transcriptional levels. PKC and/or PI 3-kinase might contribute to the up-regulation of TGF(beta)R expression in SSc fibroblasts.

Evaluation and management of pulmonary fibrosis in scleroderma

Pulmonary fibrosis causes significant morbidity and mortality in patients with scleroderma. Lung inflammation identifies patients at greater risk for decline in forced vital capacity and diffusing capacity for carbon monoxide. Factors that are increased in patients with scleroderma with lung fibrosis include connective tissue growth factor, KL-6, pulmonary surfactant-D, tissue inhibitor of metalloproteinase 2, monocyte chemotactic protein-1, macrophage inhibitory protein-1 alpha, soluble interleukin-6 receptors, anti-endothelial cell antibodies, and anti-DNA topoisomerase I antibodies. Potential mechanisms of lung damage in scleroderma include increased production of profibrotic type 2 cytokines and abnormal signaling by thrombin of tenascin-C production by lung fibroblasts, with protein kinase C epsilon as an intermediate in the signaling pathway. Treatment of scleroderma lung disease with cyclophosphamide may have a beneficial effect on pulmonary function and survival. Lung transplantation provides a therapeutic option for patients with scleroderma with end-stage lung disease.

Thrombin differentiates normal lung fibroblasts to a myofibroblast phenotype via the proteolytically activated receptor-1 and a protein kinase C-dependent pathway

Myofibroblasts are ultrastructurally and metabolically distinctive fibroblasts that express smooth muscle (SM)-alpha actin and are associated with various fibrotic lesions. The present study was undertaken to investigate the myofibroblast phenotype that appears after activation of normal lung fibroblasts by thrombin. We demonstrate that thrombin induces smooth muscle-alpha actin expression and rapid collagen gel contraction by normal lung fibroblasts via the proteolytically activated receptor-1 and independent of transforming growth factor-beta pathway. Using antisense oligonucleotides we demonstrate that a decreased level of PKCepsilon abolishes SM-alpha actin expression and collagen gel contraction induced by thrombin in normal lung fibroblasts. Inhibition of PKCepsilon translocation also abolishes thrombin-induced collagen gel contraction, SM-alpha actin increase, and its organization by normal lung fibroblasts, suggesting that activation of PKCepsilon is required for these effects. In normal lung fibroblasts PKCepsilon binds to SM-alpha actin after thrombin treatment, but in activated fibroblasts derived from scleroderma lung they associate even in untreated cells. This suggests that SM-alpha actin may serve as a substrate for PKCepsilon in lung fibroblasts when activated by thrombin. We propose that thrombin differentiates normal lung fibroblasts to a myofibroblast phenotype via a PKC-dependent pathway. Thrombin-induced differentiation of normal lung fibroblasts to a myofibroblast phenotype resembles the phenotype observed in scleroderma lung fibroblasts. Therefore, we conclude that chronic exposure to thrombin after microvascular injury leads to activation of normal lung fibroblasts and to the appearance of a myofibroblast phenotype in vivo. Our study provides novel, compelling evidence that thrombin is an important mediator of the interstitial lung fibrosis associated with scleroderma.