Role of protein kinase C-delta in the regulation of collagen gene expression in scleroderma fibroblasts

Topical Administration of an Apoptosis Inducer Mitigates Bleomycin-Induced Skin Fibrosis

Pathological fibrosis is distinguished from physiological wound healing by persistent myofibroblast activation, suggesting that therapies that induce myofibroblast apoptosis selectively could prevent progression and potentially reverse the established fibrosis, such as for scleroderma (a heterogeneous autoimmune disease characterized by multiorgan fibrosis). Navitoclax (NAVI) is a BCL-2/BCL-xL inhibitor with antifibrotic properties and has been investigated as a potential therapeutic for fibrosis. NAVI makes myofibroblasts particularly vulnerable to apoptosis. However, despite NAVI's significant potency, clinical translation of BCL-2 inhibitors, NAVI in this case, is hindered due to the risk of thrombocytopenia. Therefore, in this work, we utilized a newly developed ionic liquid formulation of NAVI for direct topical application to the skin, thereby avoiding systemic circulation and off-target-mediated side effects. The ionic liquid composed of choline and octanoic acid (COA) at a 1:2 molar ionic ratio increases skin diffusion and transportation of NAVI and maintains their retention within the dermis for a prolonged duration. Topical administration of NAVI-mediated BCL-xL and BCL-2 inhibition results in the transition of myofibroblast to fibroblast and ameliorates pre-existing fibrosis, as demonstrated in a scleroderma mouse model. We have observed a significant reduction of α-SMA and collagen, which are known as fibrosis marker proteins, as a result of the inhibition of anti-apoptotic proteins BCL-2/BCL-xL. Overall, our findings show that COA-assisted topical delivery of NAVI upregulates apoptosis specific to myofibroblasts, with minimal presence of the drug in the systemic circulation, resulting in an accelerated therapeutic effect with no discernible drug-associated toxicity.

PTH/PTHrP Receptor Signaling Restricts Arterial Fibrosis in Diabetic LDLR-/- Mice by Inhibiting Myocardin-Related Transcription Factor Relays

RATIONALE

The PTH1R (PTH [parathyroid hormone]/PTHrP [PTH-related protein] receptor) is expressed in vascular smooth muscle (VSM) and increased VSM PTH1R signaling mitigates diet-induced arteriosclerosis in LDLR-/- mice.

OBJECTIVE

To study the impact of VSM PTH1R deficiency, we generated mice SM22-Cre:PTH1R(fl/fl);LDLR-/- mice (PTH1R-VKO) and Cre-negative controls.

METHODS AND RESULTS

Immunofluorescence and Western blot confirmed PTH1R expression in arterial VSM that was reduced by Cre-mediated knockout. PTH1R-VKO cohorts exhibited increased aortic collagen accumulation in vivo, and VSM cultures from PTH1R-VKO mice elaborated more collagen (2.5-fold; P=0.01) with elevated Col3a1 and Col1a1 expression. To better understand these profibrotic responses, we performed mass spectrometry on nuclear proteins extracted from Cre-negative controls and PTH1R-VKO VSM. PTH1R deficiency reduced Gata6 but upregulated the MADS (MCM1, Agamous, Deficiens, and Srf DNA-binding domain)-box transcriptional co-regulator, Mkl-1 (megakaryoblastic leukemia [translocation] 1). Co-transfection assays (Col3a1 promoter-luciferase reporter) confirmed PTH1R-mediated inhibition and Mkl-1-mediated activation of Col3a1 transcription. Regulation mapped to a conserved hybrid CT(A/T)6GG MADS-box cognate in the Col3a1 promoter. Mutations of C/G in this motif markedly reduced Col3a1 transcriptional regulation by PTH1R and Mkl-1. Upregulation of Col3a1 and Col1a1 in PTH1R-VKO VSM was inhibited by small interfering RNA targeting Mkl1 and by treatment with the Mkl-1 antagonist CCG1423 or the Rock (Rho-associated coiled-coil containing protein kinase)-2 inhibitor KD025. Chromatin precipitation demonstrated that VSM PTH1R deficiency increased Mkl-1 binding to Col3a1 and Col1a1, but not TNF, promoters. Proteomic studies of plasma extracellular vesicles and VSM from PTH1R-VKO mice identified C1r (complement component 1, r) and C1s (complement component 1, s), complement proteins involved in vascular collagen metabolism, as potential biomarkers. VSM C1r protein and C1r message were increased with PTH1R deficiency, mediated by Mkl-1-dependent transcription and inhibited by CCG1423 or KD025.

CONCLUSIONS

PTH1R signaling restricts collagen production in the VSM lineage, in part, via Mkl-1 regulatory circuits that control collagen gene transcription. Strategies that maintain homeostatic VSM PTH1R signaling, as reflected in extracellular vesicle biomarkers of VSM PTH1R/Mkl-1 action, may help mitigate arteriosclerosis and vascular fibrosis.

Protein Kinase C δ (PKCδ) Attenuates Bleomycin Induced Pulmonary Fibrosis via Inhibiting NF-κB Signaling Pathway

Idiopathic pulmonary fibrosis (IPF) is a chronic, progressive and lethal interstitial lung disease characterized by consistent pulmonary inflammation. Although protein kinase C delta (PKCδ) is involved in broad scope cellular response, the role of PKCδ in IPF is complicated and has not been fully defined yet. Here, we reported that PKCδ deficiency (PKCδ^-/-) aggravated bleomycin (BLM)-induced pulmonary fibrosis and inflammation. Upon challenge with BLM, the pulmonary capillary permeability, immune cell infiltration, inflammatory cytokine production, and collagen deposition were enhanced in PKCδ^-/- mice compared to that in PKCδ^+/+ mice. In response to poly(I:C) stimulation, PKCδ deficient macrophages displayed an increased production of IL-1β, IL-6, TNF-α, and IL-33, which were associated with an enhanced NF-κB activation. Furthermore, we found that PKCδ could directly bind to and phosphorylate A20, an inhibitory protein of NF-κB signal. These results suggested that PKCδ may inhibit the NF-κB signaling pathway via enhancing the stability and activity of A20, which in turn attenuates pulmonary fibrosis, suggesting that PKCδ is a promising target for treating pulmonary fibrosis.

Intrinsic Deregulation of Vascular Smooth Muscle and Myofibroblast Differentiation in Mesenchymal Stromal Cells from Patients with Systemic Sclerosis

Introduction

Obliterative vasculopathy and fibrosis are hallmarks of systemic sclerosis (SSc), a severe systemic autoimmune disease. Bone marrow-derived mesenchymal stromal cells (MSCs) from SSc patients may harbor disease-specific abnormalities. We hypothesized disturbed vascular smooth muscle cell (VSMC) differentiation with increased propensity towards myofibroblast differentiation in response to SSc-microenvironment defining growth factors and determined responsible mechanisms.

Methods

We studied responses of multipotent MSCs from SSc-patients (SSc-MSCs) and healthy controls (H-MSCs) to long-term exposure to CTGF, b-FGF, PDGF-BB or TGF-β1. Differentiation towards VSMC and myofibroblast lineages was analyzed on phenotypic, biochemical, and functional levels. Intracellular signaling studies included analysis of TGF-β receptor regulation, SMAD, AKT, ERK1/2 and autocrine loops.

Results

VSMC differentiation towards both, contractile and synthetic VSMC phenotypes in response to CTGF and b-FGF was disturbed in SSc-MSCs. H-MSCs and SSc-MSCs responded equally to PDGF-BB with prototypic fibroblastic differentiation. TGF-β1 initiated myofibroblast differentiation in both cell types, yet with striking phenotypic and functional differences: In relation to H-MSC-derived myofibroblasts induced by TGF-β1, those obtained from SSc-MSCs expressed more contractile proteins, migrated towards TGF-β1, had low proliferative capacity, and secreted higher amounts of collagen paralleled by reduced MMP expression. Higher levels of TGF-β receptor 1 and enhanced canonical and noncanonical TGF-β signaling in SSc-MSCs accompanied aberrant differentiation response of SSc-MSCs in comparison to H-MSCs.

Conclusions

Deregulated VSMC differentiation with a shift towards myofibroblast differentiation expands the concept of disturbed endogenous regenerative capacity of MSCs from SSc patients. Disease related intrinsic hyperresponsiveness to TGF-β1 with increased collagen production may represent one responsible mechanism. Better understanding of repair barriers and harnessing beneficial differentiation processes in MSCs could widen options of autologous MSC application in SSc patients.

Increased expression of NAPDH oxidase 4 in systemic sclerosis dermal fibroblasts: regulation by transforming growth factor β

OBJECTIVE

Systemic sclerosis (SSc) is characterized by severe and often progressive fibrosis of the skin and multiple internal organs. The mechanisms responsible for these alterations remain obscure, although excessive reactive oxygen species (ROS)-mediated oxidative stress has been implicated. NOX-4 is 1 of 7 isoforms of NADPH oxidase responsible for the generation of ROS. The purpose of this study was to examine NOX-4 expression in skin and cultured dermal fibroblasts from SSc patients and to examine its regulation by transforming growth factor β1 (TGFβ1).

METHODS

NOX-4 was assessed in normal and SSc skin by immunohistologic analysis and in normal and SSc cultured dermal fibroblasts by quantitative polymerase chain reaction analysis, fluorescence microscopy, and Western blotting. ROS levels were assessed by fluorescence measurement of H2 O2 production. Specific kinase inhibitors were used to study the TGFβ1 signaling involved in NOX-4 stimulation. NOX-4 inhibition/down-regulation was induced with a selective NOX-4 small-molecule inhibitor and NOX-4 small interfering RNA (siRNA).

RESULTS

In contrast with normal skin fibroblasts, those from SSc skin showed intense NOX-4 staining. Cultured SSc fibroblasts displayed increased NOX-4 expression. TGFβ1 caused potent NOX-4 protein and messenger RNA stimulation in normal and SSc fibroblasts, which was mediated by the protein kinase Cδ (PKCδ) and Smad2/3 pathways. NOX-4 knockdown in SSc fibroblasts reduced the production of ROS and lowered the expression of type I collagen.

CONCLUSION

NOX-4 expression and production were found to be constitutively elevated in SSc skin and cultured SSc dermal fibroblasts. TGFβ1 stimulated NOX-4 expression in normal and SSc fibroblasts through PKCδ and Smad2/3 signaling pathways. A small-molecule NOX-4 inhibitor decreased collagen and fibronectin production by normal and SSc fibroblasts, and NOX-4 siRNA knockdown reduced ROS and collagen production by SSc fibroblasts. These results demonstrate the involvement of NOX-4 in SSc-associated fibrosis and indicate NOX-4 inhibitors as novel therapeutic approaches for SSc.

Prostaglandin Transporter (PGT/SLCO2A1) Protects the Lung from Bleomycin-Induced Fibrosis

Prostaglandin (PG) E₂ exhibits an anti-fibrotic effect in the lung in response to inflammatory reactions and is a high-affinity substrate of PG transporter (SLCO2A1). The present study aimed to evaluate the pathophysiological relevance of SLCO2A1 to bleomycin (BLM)-induced pulmonary fibrosis in mice. Immunohistochemical analysis indicated that Slco2a1 protein was expressed in airway and alveolar type I (ATI) and II (ATII) epithelial cells, and electron-microscopic immunohistochemistry further demonstrated cell surface expression of Slco2a1 in ATI cells in wild type (WT) C57BL/6 mice. PGE₂ uptake activity was abrogated in ATI-like cells from Slco2a1-deficient (Slco2a1^-/-) mice, which was clearly observed in the cells from WT mice. Furthermore, the PGE₂ concentrations in lung tissues were lower in Slco2a1^-/- than in WT mice. The pathological relevance of SLCO2A1 was further studied in mouse BLM-induced pulmonary fibrosis models. BLM (1 mg/kg) or vehicle (phosphate buffered saline) was intratracheally injected into WT and Slco2a1^-/- mice, and BLM-induced fibrosis was evaluated on day 14. BLM induced more severe fibrosis in Slco2a1^-/- than in WT mice, as indicated by thickened interstitial connective tissue and enhanced collagen deposition. PGE₂ levels were higher in bronchoalveolar lavage fluid, but lower in lung tissues of Slco2a1^-/- mice. Transcriptional upregulation of TGF-β1 was associated with enhanced gene transcriptions of downstream targets including plasminogen activator inhitor-1. Furthermore, Western blot analysis demonstrated a significant activation of protein kinase C (PKC) δ along with a modest activation of Smad3 in lung from Slco2a1^-/- mice, suggesting a role of PKCδ associated with TGF-β signaling in aggravated fibrosis in BLM-treated Slco2a1^-/- mice. In conclusion, pulmonary PGE₂ disposition is largely regulated by SLCO2A1, demonstrating that SLCO2A1 plays a critical role in protecting the lung from BLM-induced fibrosis.

PKC δ and βII regulate angiotensin II-mediated fibrosis through p38: a mechanism of RV fibrosis in pulmonary hypertension

Pulmonary hypertension (PH) eventually leads to right ventricular (RV) fibrosis and dysfunction that is associated with increased morbidity and mortality. Although angiotensin II plays an important role in RV remodeling associated with hypoxic PH, the molecular mechanisms underlying RV fibrosis in PH largely remain unresolved. We hypothesized that PKC-p38 signaling is involved in RV collagen accumulation in PH and in response to angiotensin II stimulation. Adult male Sprague-Dawley rats were exposed to 3 wk of normoxia or hypoxia (10% FiO2 ) as a model of PH. Hypoxic rats developed RV hypertrophy and fibrosis associated with an increase in PKC βII and δ protein expression and p38 dephosphorylation in freshly isolated RV cardiac fibroblasts. Further mechanistic studies were performed in cultured primary cardiac fibroblasts stimulated with angiotensin II, a key activator of ventricular fibrosis in PH. Angiotensin II induced a reduction in p38 phosphorylation that was attenuated following chemical inhibition of PKC βII and δ. Molecular and chemical inhibition of PKC βII and δ abrogated angiotensin II-induced cardiac fibroblast proliferation and collagen deposition in vitro. The effects of PKC inhibition on proliferation and fibrosis were reversed by chemical inhibition of p38. Conversely, constitutive activation of p38 attenuated angiotensin II-induced increase of cardiac fibroblast proliferation and collagen accumulation. PKC βII- and δ-dependent inactivation of p38 regulates cardiac fibroblast proliferation and collagen deposition in response to angiotensin II, which suggests that the PKC-p38 signaling in cardiac fibroblasts may be involved and important in the pathophysiology of RV fibrosis in PH.

Thrombin induces epithelial-mesenchymal transition via PAR-1, PKC, and ERK1/2 pathways in A549 cells

Thrombin activates protease-activated receptor (PAR)-1 and induces a myofibroblast phenotype in normal lung fibroblasts. The origins of myofibroblasts are resident fibroblasts, fibrocytes, and epithelial-mesenchymal transition (EMT). We investigated the effects of thrombin, an important mediator of interstitial lung fibrosis, on EMT in A549 human alveolar epithelial cells. We show that thrombin induced EMT and collagen I secretion through the activation of PAR-1, and PKC and ERK1/2 phosphorylation in A549 cells. These effects were largely prevented by a specific PAR-1 antagonist, short interfering RNA (siRNA) directed against PAR-1, or specific PKCα/β, δ, and ε inhibitors. These data indicated that interaction with thrombin and alveolar epithelial cells might directly contribute to the pathogenesis of pulmonary fibrosis through EMT. Targeting PAR-1 on the pulmonary epithelium or specific inhibitors to PKCα/β, δ, and ε might stop the fibrotic processes in human idiopathic pulmonary fibrosis by preventing thrombin-induced EMT.

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.

Novel Insights into the Molecular Mechanism of Action of DNA Hypomethylating Agents: Role of Protein Kinase C δ in Decitabine-Induced Degradation of DNA Methyltransferase 1

We have previously demonstrated proteasomal degradation of DNMT1 in mammalian cells following treatment with several DNA hypomethylating agents. Here, we demonstrate dose-dependent degradation of Dnmt1 in mouse embryonic stem (ES) cells expressing catalytic site mutant (cys-ser), confirming that the covalent bond formation between Dnmt1 and decitabine-incorporated DNA is not essential for this process. DNMT1o, the oocyte-specific isoform that lacks the N-terminal 118-amino acid domain, did not undergo decitabine-mediated degradation, which further proves the requirement of multiple domains including nuclear localization signal, KEN box, and BAH domains for this process. Analysis of glycerol density gradient fractions of micrococcal nuclease-digested nuclei showed that both nucleosomal and nucleoplasmic DNMT1 are degraded upon decitabine treatment. Among different inhibitors tested, the inhibitors of the proteasomal pathway and several protein kinases impeded decitabine-induced DNMT1 degradation. The maximal effect caused by inhibiting protein kinase C (PKC) persuaded us to investigate further its role in decitabine-mediated DNMT1 degradation. Blockage of the degradation process after treatment with rottlerin, an inhibitor of PKCδ, or after siRNA-mediated depletion of PKCδ, indicated that this protein kinase is involved in decitabine-mediated depletion of DNMT1. PKCδ interacted with and phosphorylated DNMT1 in vitro. Moreover, rottlerin inhibited both basal and decitabine-induced phosphorylation of DNMT1. These studies provide substantial evidence that decitabine-induced degradation of the maintenance methyltransferase DNMT1 does not require covalent bond formation with the substrate and also elucidate its underlying molecular mechanism.

Esculetin promotes type I procollagen expression in human dermal fibroblasts through MAPK and PI3K/Akt pathways

Type I collagen is the major constituent of the skin and the reduction of dermal type I collagen content is closely associated with the intrinsic skin aging. We here found that esculetin, 6,7-dihydroxycoumarin, strongly induces type I procollagen expression in human dermal fibroblasts. Esculetin not only increased protein levels of type I procollagen but also increased mRNA levels of COL1A1 but not COL1A2. Esculetin activated the MAPKs (ERK1/2, p38, JNK) and PI3K/Akt pathways, through which it promoted the type I procollagen expression. We also demonstrated that the binding motifs for transcription factor Sp1 occur with the highest frequency in the COL1A1 promoter and that esculetin increases the Sp1 expression through the MAPK and PI3K/Akt pathways. These results suggest that esculetin promotes type I procollagen expression through the MAPK and PI3K/Akt pathways and that Sp1 might be involved in the esculetin-induced type I procollagen expression via activation of the COL1A1 transcription.

Effect of protein kinase C delta (PKC-δ) inhibition on the transcriptome of normal and systemic sclerosis human dermal fibroblasts in vitro

Previous studies demonstrated that protein kinase C- δ (PKC-δ) inhibition with the selective inhibitor, rottlerin, resulted in potent downregulation of type I collagen expression and production in normal human dermal fibroblasts and abrogated the exaggerated type I collagen production and expression in fibroblasts cultured from affected skin from patients with the fibrosing disorder systemic sclerosis (SSc). To elucidate the mechanisms involved in the ability of PKC-δ to regulate collagen production in fibroblasts, we examined the effects of PKC-δ inhibition on the transcriptome of normal and SSc human dermal fibroblasts. Normal and SSc human dermal fibroblasts were incubated with rottlerin (5 µM), and their gene expression was analyzed by microarrays. Pathway analysis and gene ontology analysis of differentially expressed genes in each comparison were performed. Identification of significantly overrepresented transcriptional regulatory elements (TREs) was performed using the Promoter Analysis and Interaction Network Toolset (PAINT) program. PKC-δ activity was also inhibited using RNA interference (siRNA) and by treating fibroblasts with a specific PKC-δ inhibitory cell permeable peptide. Differential gene expression of 20 genes was confirmed using real time PCR. PKC-δ inhibition caused a profound change in the transcriptome of normal and SSc human dermal fibroblasts in vitro. Pathway and gene ontology analysis identified multiple cellular and organismal pathways affected by PKC-δ inhibition. Furthermore, both pathway and PAINT analyses indicated that the transcription factor NFκB played an important role in the transcriptome changes induced by PKC-δ inhibition. Multiple genes involved in the degradation of the extracellular matrix components were significantly reduced in SSc fibroblasts and their expression was increased by PKC-δ inhibition. These results indicate that isoform-specific inhibition of PKC-δ profibrotic effects may represent a novel therapeutic approach for SSc and other fibrotic diseases.

Protein kinase Cδ and c-Abl kinase are required for transforming growth factor β induction of endothelial-mesenchymal transition in vitro

OBJECTIVE

The origin of the mesenchymal cells responsible for the intimal fibrosis in systemic sclerosis (SSc) has not been fully identified. The present study was undertaken to investigate whether subendothelial mesenchymal cells may emerge through transdifferentiation of endothelial cells (ECs) into myofibroblasts via endothelial-mesenchymal transition (EndoMT) in vitro and to explore the signaling pathways involved in this process.

METHODS

Primary mouse pulmonary ECs isolated by immunomagnetic methods with sequential anti-CD34 and anti-CD102 antibody selection were cultured in monolayers. Cell morphology and diacetylated low-density lipoprotein uptake assays confirmed their EC characteristics. The induction of EndoMT was assessed by determination of α-smooth muscle actin (α-SMA), type I collagen, and VE-cadherin expression, and the expression of the transcriptional repressor Snail-1 was analyzed. The signaling pathways involved were examined using small-molecule kinase inhibitors and RNA interference.

RESULTS

Transforming growth factor β1 (TGFβ1) induced α-SMA and type I collagen expression and inhibited VE-cadherin. These effects were mediated by a marked increase in Snail-1 expression and were abolished by treatment with either the c-Abl tyrosine kinase inhibitor imatinib mesylate or the protein kinase Cδ (PKCδ) inhibitor rottlerin. The inhibitory effects of imatinib mesylate and rottlerin were mediated by inhibition of phosphorylation of glycogen synthase kinase 3β at residue Ser(9). These observations were confirmed in experiments using small interfering RNA specific for c-Abl and PKCδ.

CONCLUSION

These results indicate that c-Abl and PKCδ are crucial for TGFβ-induced EndoMT and that imatinib mesylate and rottlerin or similar kinase inhibitor molecules may be effective therapeutic agents for SSc and other fibroproliferative vasculopathies in which EndoMT plays a pathogenetic role.

The c-Abl tyrosine kinase controls protein kinase Cδ-induced Fli-1 phosphorylation in human dermal fibroblasts

OBJECTIVE

We have previously demonstrated that in response to transforming growth factor β (TGFβ), Fli-1 activity is repressed through a series of sequential posttranslational modifications, consisting of protein kinase Cδ (PKCδ)-induced Thr312 phosphorylation, acetylation by p300/CREB binding protein-associated factor, and detachment from the collagen promoter. The purpose of this study was to further investigate the upstream events that lead to Fli-1 phosphorylation in response to TGFβ.

METHODS

Dermal fibroblasts were isolated from systemic sclerosis (SSc) patients and healthy control subjects matched for age, sex, and ethnicity. Western blotting was used to analyze protein levels and real-time quantitative reverse transcription-polymerase chain reaction analysis was used to measure messenger RNA expression. Cells were transduced with constitutively active PKCδ adenovirus or were transiently transfected with a Bcr-Abl-overexpressing plasmid. Subcellular localization of PKCδ was examined by immunocytochemistry.

RESULTS

Western blot analysis of cell lysates demonstrated that the levels of phospho-Fli-1 (Thr312) were up-regulated in SSc fibroblasts, correlating with increased levels of type I collagen and c-Abl protein. Experiments using a constitutively activated form of c-Abl, small interfering RNA against c-Abl and the specific tyrosine kinase inhibitor imatinib, demonstrated the requirement of c-Abl for the TGFβ-induced phosphorylation of Fli-1. Additionally, we showed that c-Abl kinase activity was required for nuclear localization of PKCδ.

CONCLUSION

Our results demonstrate that in SSc fibroblasts, c-Abl is an upstream regulator of the profibrotic PKCδ/phospho-Fli-1 pathway, via induction of PKCδ nuclear localization. Additionally, the finding that Fli-1 is phosphorylated at higher levels in SSc fibroblasts supports the notion that the c-Abl/PKCδ/phospho-Fli-1 pathway is constitutively activated in these cells. Thus, blocking the TGFβ/c-Abl/PKCδ/phospho-Fli-1 pathway could be an attractive alternative approach to therapy for scleroderma.

Fli1 is a negative regulator of estrogen receptor α in dermal fibroblasts

Estrogen is an important regulator of dermal fibroblast functions, including extracellular matrix (ECM) synthesis. Estrogen mediates its effects through estrogen receptors (ERs), ERα and ERβ; however, regulation of ERs in dermal fibroblasts remains poorly understood. Friend leukemia integration factor 1 (Fli1), a member of the Ets transcription factor family, has been shown to play a pivotal role in regulation of the ECM genes in dermal fibroblasts. The aim of this study was to examine a possible interaction between Fli1 and estrogen pathways, focusing on ERα. We show that treatment of human dermal fibroblasts with transforming growth factor-β (TGF-β) increases ERα protein and mRNA levels. Similarly, ERα expression was increased in response to small interfering RNA (siRNA)-mediated depletion of Fli1, suggesting that Fli1 is a mediator of the TGF-β effects on ERα expression. Accordingly, we showed that Fli1 binds to the most proximal region of the ERα promoter, and dissociates from the promoter upon TGF-β treatment. An inverse correlation between Fli1 and ERα expression levels was confirmed in cultured skin fibroblasts obtained from Fli1(+/-) mice and in the skin of Fli1(+/-) mice in vivo. This study supports a role of Fli1 as a negative regulator of the ERα gene in dermal fibroblasts.

The impact of Fli1 deficiency on the pathogenesis of systemic sclerosis

Systemic sclerosis (SSc) is an autoimmune inflammatory disease with unknown etiology characterized by microvascular injury and fibrosis of the skin and internal organs. A growing body of evidence suggests that deficiency of the transcription factor Fli1 (Friend leukemia integration-1) has a pivotal role in the pathogenesis of SSc. Fli1 is expressed in fibroblasts, endothelial cells, and immune cells, and has important roles in the activation, differentiation, development, and survival of these cells. Previous studies demonstrated that Fli1 is downregulated in SSc fibroblasts by an epigenetic mechanism and a series of experiments with Fli1-deficient animal models revealed that Fli1 deficiency in fibroblasts and endothelial cells reproduces the histopathologic features of fibrosis and vasculopathy in SSc, respectively. In this article, we review the impact of Fli1 deficiency on the pathogenesis of SSc and discuss a new therapeutic strategy for SSc by targeting the transcription factor Fli1.

Persistent activation of dermal fibroblasts from patients with gadolinium-associated nephrogenic systemic fibrosis

BACKGROUND

Nephrogenic systemic fibrosis (NSF) is a systemic fibrotic disorder occurring in some patients with renal insufficiency after exposure to gadolinium-based contrast agents (GdBCA).

OBJECTIVES

To examine cultured NSF dermal fibroblast production and expression of collagens I and III, fibronectin, hyaluronic acid and α-smooth muscle actin (α-SMA) during serial passages and the effects of two GdBCA on collagen gene expression and production by normal dermal fibroblasts.

METHODS

NSF fibroblasts were analysed for expression and production of types I and III collagen, fibronectin, hyaluronic acid and α-SMA. Collagen, type I, α1 (COL1A1) promoter transcription was examined in transient transfections. Nuclear extracts were assayed for binding activity of 108 transcription factors, and specific transcription factor binding was examined by electrophoretic gel mobility assays. Normal fibroblasts were cultured with GdBCA, and collagen expression assessed by real-time PCR and western blots.

RESULTS

NSF fibroblasts displayed a marked increase in collagens I and III, fibronectin and hyaluronic acid production, which was maintained for 9-11 subpassages in vitro. NSF fibroblasts also showed a marked increase in α-SMA expression, twofold higher transcriptional activity of the COL1A1 promoter and increased cREL binding in nuclear extracts compared with normal fibroblasts. GdBCA induced a dose-dependent stimulation of COL1A1 expression and production of type I collagen in normal fibroblasts.

CONCLUSIONS

Fibroblasts from patients with NSF displayed a markedly profibrotic phenotype, which was maintained for several passages in culture. Elevated COL1A1 expression was mediated by transcriptional activation of its promoter associated with increased cREL binding activity. GdBCA stimulated cultured normal fibroblasts to produce increased amounts of collagen.

Role of protein kinase C-delta in angiotensin II induced cardiac fibrosis

Previous studies have demonstrated a role for angiotensin II (AngII) and myofibroblasts (myoFb) in cardiac fibrosis. However, the role of PKC-delta in AngII mediated cardiac fibrosis is unclear. Therefore, the present study was designed to investigate the role of PKC-delta in AngII induced cardiac collagen expression and fibrosis. AngII treatment significantly (p<0.05) increased myoFb collagen expression, whereas PKC-delta siRNA treatment or rottlerin, a PKC-delta inhibitor abrogated (p<0.05) AngII induced collagen expression. MyoFb transfected with PKC-delta over expression vector showed significant increase (p<0.05) in the collagen expression as compared to control. Two weeks of chronic AngII infused rats showed significant (p<0.05) increase in collagen expression compared to sham operated rats. This increase in cardiac collagen expression was abrogated by rottlerin treatment. In conclusion, both in vitro and in vivo data strongly suggest a role for PKC-delta in AngII induced cardiac fibrosis.

Phosphorylation of Fli1 at threonine 312 by protein kinase C delta promotes its interaction with p300/CREB-binding protein-associated factor and subsequent acetylation in response to transforming growth factor beta

Previous studies have shown that transforming growth factor beta (TGF-beta)-induced collagen gene expression involves acetylation-dependent dissociation from the human alpha2(I) collagen (COL1A2) promoter of the transcriptional repressor Fli1. The goal of this study was to elucidate the regulatory steps preceding the acetylation of Fli1. We first showed that TGF-beta induces Fli1 phosphorylation on a threonine residue(s). The major phosphorylation site was localized to threonine 312 located in the DNA binding domain of Fli1. Using several independent approaches, we demonstrated that Fli1 is directly phosphorylated by protein kinase C delta (PKC delta). Additional experiments showed that in response to TGF-beta, PKC delta is recruited to the collagen promoter to phosphorylate Fli1 and that this step is a prerequisite for the subsequent interaction of Fli1 with p300/CREB-binding protein-associated factor (PCAF) and an acetylation event. The phosphorylation of endogenous Fli1 preceded its acetylation in response to TGF-beta stimulation, and the blockade of PKC delta abrogated both the phosphorylation and acetylation of Fli1 in dermal fibroblasts. Promoter studies showed that a phosphorylation-deficient mutant of Fli1 exhibited an increased inhibitory effect on the COL1A2 gene, which could not be reversed by the forced expression of PCAF or PKC delta. These data strongly suggest that the phosphorylation-acetylation cascade triggered by PKC delta represents the primary mechanism whereby TGF-beta regulates the transcriptional activity of Fli1 in the context of the collagen promoter.

Prostaglandin E2 inhibits specific lung fibroblast functions via selective actions of PKA and Epac-1

Via their capacities for proliferation and synthesis of matrix proteins such as collagen, fibroblasts are key effectors in the pathogenesis of fibrotic disorders such as idiopathic pulmonary fibrosis. Prostaglandin E(2) (PGE(2)) potently inhibits these functions in lung fibroblasts through receptor ligation and production of the second messenger cAMP, but the downstream pathways mediating such actions have not been fully characterized. We sought to investigate the roles of the cAMP effectors protein kinase A (PKA) and exchange protein activated by cAMP-1 (Epac-1) in modulating these two functions in primary human fetal lung IMR-90 fibroblasts. The specific roles of these two effector pathways were examined by treating cells with PKA-specific (6-bnz-cAMP) and Epac-specific (8-pCPT-2'-O-Me-cAMP) agonists, inhibiting PKA with the inhibitor KT 5720, overexpressing the PKA catalytic subunit, and silencing Epac-1 using short hairpin RNA. PGE(2) inhibition of collagen I expression was mediated exclusively by activation of PKA, while inhibition of fibroblast proliferation was mediated exclusively by activation of Epac-1. PGE(2) and Epac-1 inhibited cell proliferation through activation of the small GTPase Rap1, since decreasing Rap1 activity by transfection with Rap1GAP or the dominant-negative Rap1N17 prevented, and transfection with the constitutively active Rap1V12 mimicked, the anti-proliferative effects of PGE(2). On the other hand, PKA inhibition of collagen was dependent on inhibition of protein kinase C-delta. The selective use of PKA and Epac-1 pathways to inhibit distinct aspects of fibroblast activation illustrate the pleiotropic ability of PGE(2) to inhibit diverse fibroblast functions.

Asbestos-induced peribronchiolar cell proliferation and cytokine production are attenuated in lungs of protein kinase C-delta knockout mice

The signaling pathways leading to the development of asbestos-associated diseases are poorly understood. Here we used normal and protein kinase C (PKC)-delta knockout (PKCdelta-/-) mice to demonstrate multiple roles of PKC-delta in the development of cell proliferation and inflammation after inhalation of chrysotile asbestos. At 3 days, asbestos-induced peribronchiolar cell proliferation in wild-type mice was attenuated in PKCdelta-/- mice. Cytokine profiles in bronchoalveolar lavage fluids showed increases in interleukin (IL)-1beta, IL-4, IL-6, and IL-13 that were decreased in PKCdelta-/- mice. At 9 days, microarray and quantitative reverse transcriptase-polymerase chain reaction analysis of lung tissues revealed increased mRNA levels of the profibrotic cytokine, IL-4, in asbestos-exposed wild-type mice but not PKCdelta-/- mice. PKCdelta-/- mice also exhibited decreased lung infiltration of polymorphonuclear cells, natural killer cells, and macrophages in bronchoalveolar lavage fluid and lung, as well as increased numbers of B lymphocytes and plasma cells. These changes were accompanied by elevated mRNA levels of immunoglobulin chains. These data show that modulation of PKC-delta has multiple effects on peribronchiolar cell proliferation, proinflammatory and profibrotic cytokine expression, and immune cell profiles in lung. These results also implicate targeted interruption of PKC-delta as a potential therapeutic option in asbestos-induced lung diseases.

TEF-1 and C/EBPbeta are major p38alpha MAPK-regulated transcription factors in proliferating cardiomyocytes

p38 MAPKs (mitogen-activated protein kinases) play important roles in the regulation of cellular responses to environmental stress. Recently, this signalling pathway has also been implicated in the regulation of processes unrelated to stress, for example, in T lymphocytes and cardiomyocytes. In order to identify molecular targets responsible for the housekeeping functions of p38 MAPKs, we have analysed the differences in the transcriptomes of normally proliferating wild-type and p38alpha knockout immortalized embryonic cardiomyocytes. Interestingly, many potential components of the myocardium extracellular matrix were found to be upregulated in the absence of p38alpha. Further analysis of the microarray data identified TEF-1 (transcriptional enhancer factor-1), a known regulator of heart-specific gene expression, and C/EBPbeta (CCAAT/enhancer-binding protein beta), as the two transcription factors the binding sites of which were most enriched in the promoters of p38alpha-regulated genes. We have focused on the study of the extracellular matrix component COL1A1 (alpha1 chain of type I collagen) and found evidence for the involvement of both TEF-1 and C/EBPbeta in the p38alpha-dependent inhibition of COL1A1 transcription. Our data therefore show that p38 MAPKs regulate TEF-1 and C/EBPbeta transcriptional activity in the absence of environmental stress and suggests a role for p38alpha in the expression of extracellular matrix components that maintain organ architecture.

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.

Scleroderma, fibroblasts, signaling, and excessive extracellular matrix

Excessive extracellular matrix (ECM) deposition in the skin, lung, and other organs is a hallmark of systemic sclerosis (SSc). The pathogenesis of SSc is still poorly understood, but increasing evidence suggests that various cytokines such as transforming growth factor (TGF)-beta and their signaling pathways are key mediators of tissue fibrosis as a consequence of ECM accumulation in the pathogenesis of fibrosis such as SSc. TGF-beta regulates diverse biologic activities including cell growth, cell death or apoptosis, cell differentiation, and ECM synthesis. TGF-beta is known to induce the expression of ECM proteins in mesenchymal cells, and to stimulate the production of protease inhibitors that prevent enzymatic breakdown of the ECM. This paper focuses on the possible role of ECM, various cytokines, especially TGF-beta signal transduction pathways in the pathogenesis of fibrosis in SSc.

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.

Extracellular ATP stimulates the early growth response protein 1 (Egr-1) via a protein kinase C-dependent pathway in the human osteoblastic HOBIT cell line

Extracellular nucleotides exert an important role in controlling cell physiology by activating intracellular signalling cascades. Osteoblast HOBIT cells express P2Y(1) and P2Y(2) G-protein-coupled receptors, and respond to extracellular ATP by increasing cytosolic calcium concentrations. Early growth response protein 1 (Egr-1) is a C(2)H(2)-zinc-finger-containing transcriptional regulator responsible for the activation of several genes involved in the control of cell proliferation and apoptosis, and is thought to have a central role in osteoblast biology. We show that ATP treatment of HOBIT cells increases Egr-1 protein levels and binding activity via a mechanism involving a Ca(2+)-independent protein kinase C isoform. Moreover, hypotonic stress and increased medium turbulence, by inducing ATP release, result in a similar effect on Egr-1. Increased levels of Egr-1 protein expression and activity are achieved at very early times after stimulation (5 min), possibly accounting for a rapid way for changing the osteoblast gene-expression profile. A target gene for Egr-1 that is fundamental in osteoblast physiology, COL1A2, is up-regulated by ATP stimulation of HOBIT cells in a timescale that is compatible with that of Egr-1 activation.