Endoglin modulation of TGF-beta1-induced collagen synthesis is dependent on ERK1/2 MAPK activation

Adhesive Hydrogel Patch-Mediated Combination Drug Therapy Induces Regenerative Wound Healing through Reconstruction of Regenerative Microenvironment

Regenerative wound healing involves the scarless wound healing as observed in fetal skin. Multiple features of regenerative wound healing have been well studied; however, the practical application of pro-regenerative materials to recapitulate the regenerative wound healing in adult skins has not yet been achieved. In this study, the authors identified that their novel pro-regenerative material, pyrogallol-functionalized hyaluronic acid (HA-PG) patches in combination with protein transduction domain-fused Dishevelled (Dvl)-binding motif (PTD-DBM), a peptide inhibiting the CXXC-type zinc finger protein 5 (CXXC5)-Dvl interaction, promoted regenerative wound healing in mice. The HA-PG patches loaded with this competitor peptide and valproic acid (VPA), a glycogen synthase kinase 3β (GSK3β) inhibitor, significantly inhibited scar formation during wound healing. The HA-PG patches with PTD-DBM and/or VPA inhibit the expression of differentiated cell markers such as α-smooth muscle actin (α-SMA) while inducing the expression of stem cell markers such as CD105 and Nestin. Moreover, Collagen III, an important factor for regenerative healing, is critically induced by the HA-PG patches with PTD-DBM and/or VPA, as also seen in VPA-treated Cxxc5-/- mouse fibroblasts. Overall, these findings suggest that the novel regeneration-promoting material can be utilized as a potential therapeutic agent to promote both wound healing and scar attenuation.

Endothelial Activin Receptor-Like Kinase 1 (ALK1) Regulates Myofibroblast Emergence and Peritubular Capillary Stability in the Early Stages of Kidney Fibrosis

Renal tubulo-interstitial fibrosis is characterized by the excessive accumulation of extracellular matrix (ECM) in the tubular interstitium during chronic kidney disease. The main source of ECM proteins are emerging and proliferating myofibroblasts. The sources of myofibroblasts in the renal tubular interstitium have been studied during decades, in which the epithelial contribution of the myofibroblast population through the epithelial-to-mesenchymal (EMT) process was assumed to be the major mechanism. However, it is now accepted that the EMT contribution is very limited and other mechanisms such as the proliferation of local resident fibroblasts or the transdifferentiation of endothelial cells seem to be more relevant. Activin receptor-like kinase 1 (ALK1) is a type I receptor which belongs to the transforming growth factor beta (TGF-β) superfamily, with a key role in tissue fibrosis and production of ECM by myofibroblast. Predominantly expressed in endothelial cells, ALK1 also plays an important role in angiogenesis and vessel maturation, but the relation of these processes with kidney fibrosis is not fully understood. We show that after 3 days of unilateral ureteral obstruction (UUO), ALK1 heterozygous mice (Alk1^+/−) display lower levels of kidney fibrosis associated to a lower number of myofibroblasts. Moreover, Alk1^+/− mice have a lower degree of vascular rarefaction, showing improved peritubular microvasculature after UUO. All these data suggest an important role of ALK1 in regulating vascular rarefaction and emergence of myofibroblasts.

The Role of Endoglin in Hepatocellular Carcinoma

Endoglin (CD105) is a type-1 integral transmembrane glycoprotein and coreceptor for transforming growth factor-β (TGF-β) ligands. The endoglin/TGF-β signaling pathway regulates hemostasis, cell proliferation/migration, extracellular matrix (ECM) synthesis and angiogenesis. Angiogenesis contributes to early progression, invasion, postoperative recurrence, and metastasis in hepatocellular carcinoma (HCC), one of the most widespread malignancies globally. Endoglin is overexpressed in newly formed HCC microvessels. It increases microvessel density in cirrhotic and regenerative HCC nodules. In addition, circulating endoglin is present in HCC patients, suggesting potential for use as a diagnostic or prognostic factor. HCC angiogenesis is dynamic and endoglin expression varies by stage. TRC105 (carotuximab) is an antibody against endoglin, and three of its clinical trials were related to liver diseases. A partial response was achieved when combining TRC105 with sorafenib. Although antiangiogenic therapy still carries some risks, combination therapy with endoglin inhibitors or other targeted therapies holds promise.

Endoglin in the Spotlight to Treat Cancer

A spotlight has been shone on endoglin in recent years due to that fact of its potential to serve as both a reliable disease biomarker and a therapeutic target. Indeed, endoglin has now been assigned many roles in both physiological and pathological processes. From a molecular point of view, endoglin mainly acts as a co-receptor in the canonical TGFβ pathway, but also it may be shed and released from the membrane, giving rise to the soluble form, which also plays important roles in cell signaling. In cancer, in particular, endoglin may contribute to either an oncogenic or a non-oncogenic phenotype depending on the cell context. The fact that endoglin is expressed by neoplastic and non-neoplastic cells within the tumor microenvironment suggests new possibilities for targeted therapies. Here, we aimed to review and discuss the many roles played by endoglin in different tumor types, as well as the strong evidence provided by pre-clinical and clinical studies that supports the therapeutic targeting of endoglin as a novel clinical strategy.

Transforming growth factor-β in tissue fibrosis

TGF-β is extensively implicated in the pathogenesis of fibrosis. In fibrotic lesions, spatially restricted generation of bioactive TGF-β from latent stores requires the cooperation of proteases, integrins, and specialized extracellular matrix molecules. Although fibroblasts are major targets of TGF-β, some fibrogenic actions may reflect activation of other cell types, including macrophages, epithelial cells, and vascular cells. TGF-β–driven fibrosis is mediated through Smad-dependent or non-Smad pathways and is modulated by coreceptors and by interacting networks. This review discusses the role of TGF-β in fibrosis, highlighting mechanisms of TGF-β activation and signaling, the cellular targets of TGF-β actions, and the challenges of therapeutic translation.

Endoglin: Beyond the Endothelium

Keywords: endoglin; CD105 TGF-β; BMP9; ALK-1; TRC105; tumor microenvironment.

Identification of an Endoglin Variant Associated With HCV-Related Liver Fibrosis Progression by Next-Generation Sequencing

Despite the astonishing progress in treating chronic hepatitis C virus (HCV) infection with direct-acting antiviral agents, liver fibrosis remains a major health concern in HCV infected patients, in particular due to the treatment cost and insufficient HCV screening in many countries. Only a fraction of patients with chronic HCV infection develop liver fibrosis. While there is evidence that host genetic factors are involved in the development of liver fibrosis, the common variants identified so far, in particular by genome-wide association studies, were found to have limited effects. Here, we conducted an exome association study in 88 highly selected HCV-infected patients with and without fibrosis. A strategy focusing on TGF-β pathway genes revealed an enrichment in rare variants of the endoglin gene (ENG) in fibrosis patients. Replication studies in additional cohorts (617 patients) identified one specific ENG variant, Thr5Met, with an overall odds ratio for fibrosis development in carriers of 3.04 (1.39-6.69). Our results suggest that endoglin, a key player in TGF-β signaling, is involved in HCV-related liver fibrogenesis.

Differential Role of TGF-β in Extracellular Matrix Regulation During Trypanosoma cruzi-Host Cell Interaction

Transforming growth factor beta (TGF-β) is a determinant for inflammation and fibrosis in cardiac and skeletal muscle in Chagas disease. To determine its regulatory mechanisms, we investigated the response of Trypanosoma cruzi-infected cardiomyocytes (CM), cardiac fibroblasts (CF), and L6E9 skeletal myoblasts to TGF-β. Cultures of CM, CF, and L6E9 were infected with T. cruzi (Y strain) and treated with TGF-β (1–10 ng/mL, 1 h or 48 h). Fibronectin (FN) distribution was analyzed by immunofluorescence and Western blot (WB). Phosphorylated SMAD2 (PS2), phospho-p38 (p-p38), and phospho-c-Jun (p-c-Jun) signaling were evaluated by WB. CF and L6E9 showed an increase in FN from 1 ng/mL of TGF-β, while CM displayed FN modulation only after 10 ng/mL treatment. CF and L6E9 showed higher PS2 levels than CM, while p38 was less stimulated in CF than CM and L6E9. T. cruzi infection resulted in localized FN disorganization in CF and L6E9. T. cruzi induced an increase in FN in CF cultures, mainly in uninfected cells. Infected CF cultures treated with TGF-β showed a reduction in PS2 and an increase in p-p38 and p-c-Jun levels. Our data suggest that p38 and c-Jun pathways may be participating in the fibrosis regulatory process mediated by TGF-β after T. cruzi infection.

Isolation and Characterization of a Human Fetal Mesenchymal Stem Cell Population: Exploring the Potential for Cell Banking in Wound Healing Therapies

Various cell-based therapies are in development to address chronic and acute skin wound healing, for example for burns and trauma patients. An off-the-shelf source of allogeneic dermal cells could be beneficial for innovative therapies accelerating the healing in extensive wounds where the availability of a patient’s own cells is limited. Human fetal-derived dermal fibroblasts (hFDFs) show high in vitro division rates, exhibit low immunological rejection properties, and present scarless wound healing in the fetus, and previous studies on human fetal tissue-derived cell therapies have shown promising results on tissue repair. However, little is known about cell lineage stability and cell differentiation during the cell expansion process, required for any potential therapeutic use. We describe an isolation method, characterize a population, and investigate its potential for cell banking and thus suitability as a potential product for cell grafting therapies. Our results show hFDFs and a bone marrow-derived mesenchymal stem cell (BM-MSC) line shared identification markers and in vitro multilineage differentiation potential into osteogenic, chondrogenic, and adipogenic lineages. The hFDF population exhibited similar cell characteristics as BM-MSCs while producing lower pro-inflammatory cytokine IL-6 levels and higher levels of the wound healing factor hepatocyte growth factor. We demonstrate in vitro differentiation of hFDFs, which may be a problem in maintaining long-term lineage stability, potentially limiting their use for cell banking and therapy development.

Role of Endoglin (CD105) in the Progression of Hepatocellular Carcinoma and Anti-Angiogenic Therapy

The liver is perfused by both arterial and venous blood, with a resulting abnormal microenvironment selecting for more-aggressive malignancies. Hepatocellular carcinoma (HCC) is the most frequent primary liver cancer, the sixth most common cancer globally, and the third leading cause of cancer-related mortality worldwide. HCC is characterized by its hypervascularization. Improving the efficiency of anti-angiogenic treatment and mitigation of anti-angiogenic drug resistance are the top priorities in the development of non-surgical HCC therapies. Endoglin (CD105), a transmembrane glycoprotein, is one of the transforming growth factor β (TGF-β) co-receptors. Involvement of that protein in angiogenesis of solid tumours is well documented. Endoglin is a marker of activated endothelial cells (ECs), and is preferentially expressed in the angiogenic endothelium of solid tumours, including HCC. HCC is associated with changes in CD105-positive ECs within and around the tumour. The large spectrum of endoglin effects in the liver is cell-type- and HCC- stage-specific. High expression of endoglin in non-tumour tissue suggests that this microenvironment might play an especially important role in the progression of HCC. Evaluation of tissue expression, as well as serum concentrations of this glycoprotein in HCC, tends to confirm its role as an important biomarker in HCC diagnosis and prognosis. The role of endoglin in liver fibrosis and HCC progression also makes it an attractive therapeutic target. Despite these facts, the exact molecular mechanisms of endoglin functioning in hepatocarcinogenesis are still poorly understood. This review summarizes the current data concerning the role and signalling pathways of endoglin in hepatocellular carcinoma development and progression, and provides an overview of the strategies available for a specific targeting of CD105 in anti-angiogenic therapy in HCC.

TGF-β1 Regulation of P-JNK and L-Type Calcium Channel Cav1.2 in Cortical Neurons

Central nervous system (CNS) diseases can cause a series of neuronal lesions, which may be improved by the anti-apoptotic neuroprotection of transforming growth factor-beta 1 (TGF-β1). In neurons, L-type Ca²⁺ channels (LTCC) are mainly composed of Cav1.2 subunits. Given the implication of TGF-β1 in numerous CNS diseases, we examined the neuroprotective effects of TGF-β1 on the Cav1.2 channel in the CNS. To simulate acute mechanical traumatic brain injury (TBI), we used a needle to create parallel scratches across plates, which were cultured for 9 h. Meanwhile, Fluo4-AM-loaded laser scanning confocal microscopy with a dual wavelength of 488 nm/530 nm was employed to determine intracellular calcium concentrations ([Ca²⁺]_i). We found that MAPK inhibitors impede TGF-β1-induced cell viability and that TGF-β1 recovered from the trauma-induced cell viability in neurons. Cav1.2 production was significantly decreased in the TGF-β1-treated (10 ng/mL) neurons. At this TGF-β1 concentration, Cav1.2 was significantly down-regulated in a time-dependent manner after 12 h. Moreover, TGF-β1 partially recovered the protein levels of Cav1.2 that were reduced by TBI. TGF-β1 significantly inhibited the fluorescence intensity of [Ca²⁺]_i increased by KCl and delayed the time of the peak [Ca²⁺]_i. The observed effects of TGF-β1 on Cav1.2 were regulated by MAPK inhibitors. The observed effects of TGF-β1 on P-JNK were also impeded by pre-incubation with the LTCC inhibitor (10 μM) nimodipine in trauma-injured neurons. Altogether, TGF-β1 regulated LTCCs through a mechanism dependent on MEK, JNK1/2 and p38 MAPK signal pathways in cortical neurons. Thus, we suggest the involvement of this mechanism in cell viability.

Screening for and validation of a hepatic fibrosis-related pathway induced by insulin-like growth factor-binding protein-related protein 1

OBJECTIVE

Our previous studies characterized insulin-like growth factor-binding protein-related protein 1 (IGFBPrP1) as a molecule that promotes hepatic fibrogenesis, but its mechanism has not been fully elucidated. Here, we have investigated the effect of IGFBPrP1 on gene expression in the hepatic fibrosis-related pathway.

MATERIALS AND METHODS

Sprague-Dawley rats received injections of an adenovirus carrying IGFBPrP1 or EGFP cDNA into their tail veins. In hepatic preparations, hepatic stellate cell activation was determined by α-smooth muscle actin expression and hepatic fibrosis by Sirius red staining and hydroxyproline content analysis. IGFBPrP1-inducible genes of the hepatic fibrosis-related pathway were assessed by PCR array. Expression of IGFBPrP1 and transforming growth factor β1 (TGFβ1) and array results were evaluated by quantitative real-time PCR and western blotting.

RESULTS

IGFBPrP1-overexpressing rats showed an increase in α-smooth muscle actin expression and collagen and hydroxyproline content in the liver. The PCR array results indicated that some genes were upregulated and some were downregulated in Ad-IGFBPrP1-infected rats. Among these, Egr1, MAP2K2 (MEK2) and MAPK3 (ERK1) expression increased, whereas PTEN and Hhip mRNA expression decreased. Egr1 protein levels increased and peaked 2 weeks after infection and then decreased gradually. PTEN protein decreased gradually in Ad-IGFBPrP1-infected rats with a concurrent increase in the degree of hepatic fibrosis. TGFβ1 levels increased during hepatic fibrosis development in liver tissues.

CONCLUSION

Egr1, PTEN, Hhip, MAP2K2 (MEK2) and MAPK3 (ERK1) were identified as candidate genes of the IGFBPrP1-induced hepatic fibrosis-related pathway. IGFBPrP1 promoted hepatic fibrosis mainly by enhancing the TGFβ1 expression that it triggered.

Suppressive effect of epigallocatechin-3-O-gallate on endoglin molecular regulation in myocardial fibrosis in vitro and in vivo

Epigallocatechin-3-O-gallate (EGCG), derived from green tea, has been studied extensively because of its diverse physiological and pharmacological properties. This study evaluates the protective effect of EGCG on angiotensin II (Ang II)-induced endoglin expression in vitro and in vivo. Cardiac fibroblasts (CFs) from the thoracic aorta of adult Wistar rats were cultured and induced with Ang II. Western blotting, Northern blotting, real-time PCR and promoter activity assay were performed. Ang II increased endoglin expression significantly as compared with control cells. The specific extracellular signal-regulated kinase inhibitor SP600125 (JNK inhibitor), EGCG (100 μM) and c-Jun N-terminal kinase (JNK) siRNA attenuated endoglin proteins following Ang II induction. In addition, pre-treated Ang II-induced endoglin with EGCG diminished the binding activity of AP-1 by electrophoretic mobility shift assay. Moreover, the luciferase assay results revealed that EGCG suppressed the endoglin promoter activity in Ang II-induced CFs by AP-1 binding. Finally, EGCG and the JNK inhibitor (SP600125) were found to have attenuated endoglin expression significantly in Ang II-induced CFs, as determined through confocal microscopy. Following in vivo acute myocardial infarction (AMI)-related myocardial fibrosis study, as well as immunohistochemical and confocal analyses, after treatment with endoglin siRNA and EGCG (50 mg/kg), the area of myocardial fibrosis reduced by 53.4% and 64.5% and attenuated the left ventricular end-diastolic and systolic dimensions, and friction shortening in hemodynamic monitor. In conclusion, epigallocatechin-3-O-gallate (EGCG) attenuated the endoglin expression and myocardial fibrosis by anti-inflammatory effect in vitro and in vivo, the novel suppressive effect was mediated through JNK/AP-1 pathway.

Absence of K-Ras Reduces Proliferation and Migration But Increases Extracellular Matrix Synthesis in Fibroblasts

The involvement of Ras-GTPases in the development of renal fibrosis has been addressed in the last decade. We have previously shown that H- and N-Ras isoforms participate in the regulation of fibrosis. Herein, we assessed the role of K-Ras in cellular processes involved in the development of fibrosis: proliferation, migration, and extracellular matrix (ECM) proteins synthesis. K-Ras knockout (KO) mouse embryonic fibroblasts (K-ras(-/-) ) stimulated with transforming growth factor-β1 (TGF-β1) exhibited reduced proliferation and impaired mobility than wild-type fibroblasts. Moreover, an increase on ECM production was observed in K-Ras KO fibroblasts in basal conditions. The absence of K-Ras was accompanied by reduced Ras activation and ERK phosphorylation, and increased AKT phosphorylation, but no differences were observed in TGF-β1-induced Smad signaling. The MEK inhibitor U0126 decreased cell proliferation independently of the presence of K-ras but reduced migration and ECM proteins expression only in wild-type fibroblasts, while the PI3K-AKT inhibitor LY294002 decreased cell proliferation, migration, and ECM synthesis in both types of fibroblasts. Thus, our data unveil that K-Ras and its downstream effector pathways distinctively regulate key biological processes in the development of fibrosis. Moreover, we show that K-Ras may be a crucial mediator in TGF-β1-mediated effects in this cell type. J. Cell. Physiol. 231: 2224-2235, 2016. © 2016 Wiley Periodicals, Inc.

BMP9 Crosstalk with the Hippo Pathway Regulates Endothelial Cell Matricellular and Chemokine Responses

Endoglin is a type III TGFβ auxiliary receptor that is upregulated in endothelial cells during angiogenesis and, when mutated in humans, results in the vascular disease hereditary hemorrhagic telangiectasia (HHT). Though endoglin has been implicated in cell adhesion, the underlying molecular mechanisms are still poorly understood. Here we show endoglin expression in endothelial cells regulates subcellular localization of zyxin in focal adhesions in response to BMP9. RNA knockdown of endoglin resulted in mislocalization of zyxin and altered formation of focal adhesions. The mechanotransduction role of focal adhesions and their ability to transmit regulatory signals through binding of the extracellular matrix are altered by endoglin deficiency. BMP/TGFβ transcription factors, SMADs, and zyxin have recently been implicated in a newly emerging signaling cascade, the Hippo pathway. The Hippo transcription coactivator, YAP1 (yes-associated protein 1), has been suggested to play a crucial role in mechanotransduction and cell-cell contact. Identification of BMP9-dependent nuclear localization of YAP1 in response to endoglin expression suggests a mechanism of crosstalk between the two pathways. Suppression of endoglin and YAP1 alters BMP9-dependent expression of YAP1 target genes CCN1 (cysteine-rich 61, CYR61) and CCN2 (connective tissue growth factor, CTGF) as well as the chemokine CCL2 (monocyte chemotactic protein 1, MCP-1). These results suggest a coordinate effect of endoglin deficiency on cell matrix remodeling and local inflammatory responses. Identification of a direct link between the Hippo pathway and endoglin may reveal novel mechanisms in the etiology of HHT.

MicroRNA-208a Increases Myocardial Endoglin Expression and Myocardial Fibrosis in Acute Myocardial Infarction

BACKGROUND

MicroRNAs (miRs) play a role in cardiac remodelling, and acute myocardial infarction (AMI) can regulate miR expression. MiR-208a is essential for the expression of the genes involved in cardiac hypertrophy and fibrosis. MiR-208a activates endoglin expression and may result in cardiac fibrosis. The role of miR-208a and endoglin in AMI is not known. We sought to investigate the regulation of miR-208a and endoglin in AMI.

METHODS

Ligation of the proximal left anterior descending artery was performed in adult Sprague-Dawley rats to induce AMI. Echocardiography was used to measure heart size and left ventricular function. The TaqMan miR real-time quantitative assay was used to quantitate miR-208a. Myocardial fibrosis was detected by Masson trichrome staining.

RESULTS

AMI and overexpression of miR-208a in the sham group without infarction significantly increased myocardial miR-208a, endoglin, and β-myosin heavy chain (β-MHC) expression. Overexpression of antagomir-208a significantly inhibited the increase of myocardial endoglin and β-MHC protein expression induced by infarction. Overexpression of mutant miR-208a in the sham group did not induce myocardial endoglin and β-MHC expression. Pretreatment with atorvastatin and the angiotensin-receptor antagonist valsartan significantly attenuated the increase of endoglin and β-MHC induced by infarction. AMI and overexpression of miR-208a in the sham group significantly increased the area of myocardial fibrosis compared with the sham group. Overexpression of antagomir-208a and pretreatment with atorvastatin and valsartan in the AMI group significantly decreased the area of myocardial fibrosis induced by infarction.

CONCLUSIONS

MiR-208a increases endoglin expression to induce myocardial fibrosis in rats with AMI. Treatment with atorvastatin and valsartan can decrease myocardial fibrosis induced by AMI through attenuating miR-208a and endoglin expression.

The role of endoglin in kidney fibrosis

Tubulointerstitial fibrosis and glomerulosclerosis, are a major feature of end stage chronic kidney disease (CKD), characterised by an excessive accumulation of extracellular matrix (ECM) proteins. Transforming growth factor beta-1 (TGF-β1) is a cytokine with an important role in many steps of renal fibrosis such as myofibroblast activation and proliferation, ECM protein synthesis and inflammatory cell infiltration. Endoglin is a TGF-β co-receptor that modulates TGF-β responses in different cell types. In numerous cells types, such as mesangial cells or myoblasts, endoglin regulates negatively TGF-β-induced ECM protein expression. However, recently it has been demonstrated that 'in vivo' endoglin promotes fibrotic responses. Furthermore, several studies have demonstrated an increase of endoglin expression in experimental models of renal fibrosis in the kidney and other tissues. Nevertheless, the role of endoglin in renal fibrosis development is unclear and a question arises: Does endoglin protect against renal fibrosis or promotes its development? The purpose of this review is to critically analyse the recent knowledge relating to endoglin and renal fibrosis. Knowledge of endoglin role in this pathology is necessary to consider endoglin as a possible therapeutic target against renal fibrosis.

L-Endoglin overexpression increases renal fibrosis after unilateral ureteral obstruction

Transforming growth factor-β (TGF-β) plays a pivotal role in renal fibrosis. Endoglin, a 180 KDa membrane glycoprotein, is a TGF-β co-receptor overexpressed in several models of chronic kidney disease, but its function in renal fibrosis remains uncertain. Two membrane isoforms generated by alternative splicing have been described, L-Endoglin (long) and S-Endoglin (short) that differ from each other in their cytoplasmic tails, being L-Endoglin the most abundant isoform. The aim of this study was to assess the effect of L-Endoglin overexpression in renal tubulo-interstitial fibrosis. For this purpose, a transgenic mouse which ubiquitously overexpresses human L-Endoglin (L-ENG+) was generated and unilateral ureteral obstruction (UUO) was performed in L-ENG+ mice and their wild type (WT) littermates. Obstructed kidneys from L-ENG+ mice showed higher amounts of type I collagen and fibronectin but similar levels of α-smooth muscle actin (α-SMA) than obstructed kidneys from WT mice. Smad1 and Smad3 phosphorylation were significantly higher in obstructed kidneys from L-ENG+ than in WT mice. Our results suggest that the higher increase of renal fibrosis observed in L-ENG+ mice is not due to a major abundance of myofibroblasts, as similar levels of α-SMA were observed in both L-ENG+ and WT mice, but to the higher collagen and fibronectin synthesis by these fibroblasts. Furthermore, in vivo L-Endoglin overexpression potentiates Smad1 and Smad3 pathways and this effect is associated with higher renal fibrosis development.

Association of increased levels of TGF-β1 and p14ARF in prostate carcinoma cell lines overexpressing Egr-1

The present study examined the effect of the overexpression of early growth response gene (Egr-1) on transforming growth factor β-1 (TGF-β1) and p14ARF levels, in PC-3 and LNCaP prostate carcinoma cell lines. Amplification of EGR-1, TGF-β1 and p14ARF were observed in the two cell lines treated with different stimuli and resulted in a corresponding mRNA and protein expression. The downregulation of TGF-β1 and the attenuation of p14ARF expression by siRNA against Egr-1 predominantly suggested that TGF-β1 and p14ARF may be regulated by the transcription factor EGR-1. A marginal attenuation of cell growth in PC-3 and LNCaP prostate carcinoma cell lines overexpressing p14ARF was observed. Cells transfected with Egr-1 wild-type were able to grow and avoid cell cycle arrest and apoptosis in the presence or absence of p14ARF. In addition, EGR-1 stimulated the expression of TGF β-l as well as the accumulation of the p14ARF proteins. The results suggested that TGF-β1 and p14ARF activities in the presence of EGR-1 overexpression can exist independently of the presence of cells carrying a mutant p53 (PC-3 cells) or cells carrying a wild‑type p53 (LNCaP cells). Thus, the effect of EGR-1 on the growth of prostate carcinoma cells may occur through multiple mechanisms, but be independent of p53 expression control.

Endoglin in liver fibrogenesis: Bridging basic science and clinical practice

Endoglin, also known as cluster of differentiation CD105, was originally identified 25 years ago as a novel marker of endothelial cells. Later it was shown that endoglin is also expressed in pro-fibrogenic cells including mesangial cells, cardiac and scleroderma fibroblasts, and hepatic stellate cells. It is an integral membrane-bound disulfide-linked 180 kDa homodimeric receptor that acts as a transforming growth factor-β (TGF-β) auxiliary co-receptor. In humans, several hundreds of mutations of the endoglin gene are known that give rise to an autosomal dominant bleeding disorder that is characterized by localized angiodysplasia and arteriovenous malformation. This disease is termed hereditary hemorrhagic telangiectasia type I and induces various vascular lesions, mainly on the face, lips, hands and gastrointestinal mucosa. Two variants of endoglin (i.e., S- and L-endoglin) are formed by alternative splicing that distinguishes from each other in the length of their cytoplasmic tails. Moreover, a soluble form of endoglin, i.e., sol-Eng, is shedded by the matrix metalloprotease-14 that cleaves within the extracellular juxtamembrane region. Endoglin interacts with the TGF-β signaling receptors and influences Smad-dependent and -independent effects. Recent work has demonstrated that endoglin is a crucial mediator during liver fibrogenesis that critically controls the activity of the different Smad branches. In the present review, we summarize the present knowledge of endoglin expression and function, its involvement in fibrogenic Smad signaling, current models to investigate endoglin function, and the diagnostic value of endoglin in liver disease.

MicroRNA-208a increases myocardial fibrosis via endoglin in volume overloading heart

MicroRNA-208a (mir-208a) is essential for cardiac hypertrophy and fibrosis. Endoglin, a co-receptor of transforming growth factor-β is also essential for cardiac fibrosis. Endoglin has been shown to be a target of mir-208a in the in vitro mechanical stress model. Volume overload can lead to heart failure and cardiac fibrosis. The role of mir-208a and endoglin in volume overload heart failure is well known. We sought to investigate the mechanism of regulation of mir-208a and endoglin in volume overload-induced heart failure. Aorta-caval (AV) shunt was performed in adult Sprague-Dawley rats to induce volume overload. Heart weight and heart weight/body weight ratio significantly increased in AV shunt animals. AV shunt significantly increased left ventricular end-diastolic dimension as compared to sham group. Mir-208a was significantly induced by AV shunt from 3 to 14 days. Endoglin, myosin heavy chain-β and brain natriuretic peptide were significantly induced by AV shunt from 3 to 14 days. Overexpression of mir-208a in the sham group without AV shunt significantly increased endoglin expression similar to the AV shunt group. Antagomir-208a attenuated the endoglin expression induced by AV shunt. Pretreatment with atorvastatin also attenuated the endoglin expression induced by AV shunt. AV shunt significantly increased myocardial fibrosis as compared to sham group. Overexpression of mir-208a in the sham group significantly increased myocardial fibrosis. Antagomir-208a and atorvastatin significantly attenuated the myocardial fibrosis induced by AV shunt. In conclusion, mir-208a increased endoglin expression to induce myocardial fibrosis in volume overloaded heart failure. Treatment with atorvastatin can attenuate the myocardial fibrosis induced by volume overload through inhibition of endoglin expression.

Venous endothelial injury in central nervous system diseases

The role of the venous system in the pathogenesis of inflammatory neurological/neurodegenerative diseases remains largely unknown and underinvestigated. Aside from cerebral venous infarcts, thromboembolic events, and cerebrovascular bleeding, several inflammatory central nervous system (CNS) diseases, such as multiple sclerosis (MS), acute disseminated encephalomyelitis (ADEM), and optic neuritis, appear to be associated with venous vascular dysfunction, and the neuropathologic hallmark of these diseases is a perivenous, rather than arterial, lesion. Such findings raise fundamental questions about the nature of these diseases, such as the reasons why their pathognomonic lesions do not develop around the arteries and what exactly are the roles of cerebral venous inflammation in their pathogenesis. Apart from this inflammatory-based view, a new hypothesis with more focus on the hemodynamic features of the cerebral and extracerebral venous system suggests that MS pathophysiology might be associated with the venous system that drains the CNS. Such a hypothesis, if proven correct, opens new therapeutic windows in MS and other neuroinflammatory diseases. Here, we present a comprehensive review of the pathophysiology of MS, ADEM, pseudotumor cerebri, and optic neuritis, with an emphasis on the roles of venous vascular system programming and dysfunction in their pathogenesis. We consider the fundamental differences between arterial and venous endothelium, their dissimilar responses to inflammation, and the potential theoretical contributions of venous insufficiency in the pathogenesis of neurovascular diseases.

The ALK-1/Smad1 pathway in cardiovascular physiopathology. A new target for therapy?

Activin receptor-like kinase-1 or ALK-1 is a type I cell surface receptor for the transforming growth factor-β (TGF-β) family of proteins. The role of ALK-1 in endothelial cells biology and in angiogenesis has been thoroughly studied by many authors. However, it has been recently suggested a possible role of ALK-1 in cardiovascular homeostasis. ALK-1 is not only expressed in endothelial cells but also in smooth muscle cells, myofibroblast, hepatic stellate cells, chondrocytes, monocytes, myoblasts, macrophages or fibroblasts, but its role in these cells have not been deeply analyzed. Due to the function of ALK-1 in these cells, this receptor plays a role in several cardiovascular diseases. Animals with ALK-1 haploinsufficiency and patients with mutations in Acvrl1 (the gene that codifies for ALK-1) develop type-2 Hereditary Hemorrhagic Telangiectasia. Moreover, ALK-1 heterozygous mice develop pulmonary hypertension. Higher levels of ALK-1 have been observed in atherosclerotic plaques, suggesting a possible protector role of this receptor. ALK-1 deficiency is also related to the development of arteriovenous malformations (AVMs). Besides, due to the ability of ALK-1 to regulate cell proliferation and migration, and to modulate extracellular matrix (ECM) protein expression in several cell types, ALK-1 has been now demonstrated to play an important role in cardiovascular remodeling. In this review, we would like to offer a complete vision of the role of ALK-1 in many process related to cardiovascular homeostasis, and the involvement of this protein in the development of cardiovascular diseases, suggesting the possibility of using the ALK-1/smad-1 pathway as a powerful therapeutic target.

Overexpression of endoglin modulates TGF-β1-signalling pathways in a novel immortalized mouse hepatic stellate cell line

Hepatic stellate cells (HSCs) play a major role in the pathogenesis of liver fibrosis. Working on primary HSCs requires difficult isolation procedures; therefore we have generated and here characterize a mouse hepatic stellate cell line expressing GFP under control of the collagen 1(I) promoter/enhancer. These cells are responsive to pro-fibrogenic stimuIi, such as PDGF or TGF-β1, and are able to activate intracellular signalling pathways including Smads and MAP kinases. Nevertheless, due to the basal level of activation, TGF-β1 did not significantly induce GFP expression contrasting the TGF-β1 regulated endogenous collagen I expression. We could demonstrate that the accessory TGF-β-receptor endoglin, which is endogenously expressed at very low levels, has a differential effect on signalling of these cells when transiently overexpressed. In the presence of endoglin activation of Smad1/5/8 was drastically enhanced. Moreover, the phosphorylation of ERK1/2 was increased, and the expression of vimentin, α-smooth muscle actin and connective tissue growth factor was upregulated. Endoglin induced a slight increase in expression of the inhibitor of differentiation-2 while the amount of endogenous collagen type I was reduced. Therefore, this profibrogenic cell line with hepatic stellate cell origin is not only a promising novel experimental tool, which can be used in vivo for cell tracing experiments. Furthermore it allows investigating the impact of various regulatory proteins (e.g. endoglin) on profibrogenic signal transduction, differentiation and hepatic stellate cell biology.

Endoglin haploinsufficiency promotes fibroblast accumulation during wound healing through Akt activation

Accurate regulation of dermal fibroblast function plays a crucial role in wound healing. Many fibrotic diseases are characterized by a failure to conclude normal tissue repair and the persistence of fibroblasts inside lesions. In the present study we demonstrate that endoglin haploinsufficiency promotes fibroblast accumulation during wound healing. Moreover, scars from endoglin-heterozygous (Eng^+/−) mice show persisting fibroblasts 12 days after wounding, which could lead to a fibrotic scar. Endoglin haploinsufficiency results in increased proliferation and migration of primary cultured murine dermal fibroblasts (MDFs). Moreover, Eng^+/− MDF have diminished responses to apoptotic signals compared with control cells. Altogether, these modifications could explain the augmented presence of fibroblasts in Eng^+/− mice wounds. We demonstrate that endoglin expression regulates Akt phosphorylation and that PI3K inhibition abolishes the differences in proliferation between endoglin haploinsufficient and control cells. Finally, persistent fibroblasts in Eng^+/− mice wound co-localize with a greater degree of Akt phosphorylation. Thus, endoglin haploinsufficiency seems to promote fibroblast accumulation during wound healing through the activation of the PI3K/Akt pathway. These studies open new non-Smad signaling pathway for endoglin regulating fibroblast cell function during wound healing, as new therapeutic opportunities for the treatment of fibrotic wounds.

Endoglin (CD105) contributes to platinum resistance and is a target for tumor-specific therapy in epithelial ovarian cancer

PURPOSE

Endoglin (CD105) is a membranous protein overexpressed in tumor-associated endothelial cells, chemoresistant populations of ovarian cancer cells, and potentially stem cells. Our objective was to evaluate the effects and mechanisms of targeting endoglin in ovarian cancer.

EXPERIMENTAL DESIGN

Global and membranous endoglin expression was evaluated in multiple ovarian cancer lines. In vitro, the effects of siRNA-mediated endoglin knockdown with and without chemotherapy were evaluated by MTT assay, cell-cycle analysis, alkaline comet assay, γ-H2AX foci formation, and quantitative PCR. In an orthotopic mouse model, endoglin was targeted with chitosan-encapsulated siRNA with and without carboplatin.

RESULTS

Endoglin expression was surprisingly predominantly cytoplasmic, with a small population of surface-positive cells. Endoglin inhibition decreased cell viability, increased apoptosis, induced double-stranded DNA damage, and increased cisplatin sensitivity. Targeting endoglin downregulates expression of numerous DNA repair genes, including BARD1, H2AFX, NBN, NTHL1, and SIRT1. BARD1 was also associated with platinum resistance, and was induced by platinum exposure. In vivo, antiendoglin treatment decreased tumor weight in both ES2 and HeyA8MDR models when compared with control (35%-41% reduction, P < 0.05). Endoglin inhibition with carboplatin was associated with even greater inhibitory effect when compared with control (58%-62% reduction, P < 0.001).

CONCLUSIONS

Endoglin downregulation promotes apoptosis, induces significant DNA damage through modulation of numerous DNA repair genes, and improves platinum sensitivity both in vivo and in vitro. Antiendoglin therapy would allow dual treatment of both tumor angiogenesis and a subset of aggressive tumor cells expressing endoglin and is being actively pursued as therapy in ovarian cancer.

Mechanical stretch via transforming growth factor-β1 activates microRNA208a to regulate endoglin expression in cultured rat cardiac myoblasts

AIMS

MicroRNAs (miRNAs) play a role in cardiac remodelling. MiR208a is essential for the expression of the genes involved in cardiac hypertrophy and fibrosis. The mechanism of regulation of miR208a involved in cardiac hypertrophy by mechanical stress is still unclear. We sought to investigate the mechanism of regulation of miR208a and the target gene of miR208a in cardiac cells by mechanical stretch.

METHODS AND RESULTS

Rat H9c2 cells (cardiac myoblasts) grown on a flexible membrane base were stretched via vacuum to 20% of maximum elongation at 60 cycles/min. Mechanical stretch significantly enhanced miR208a expression after 4 h of stretch. Exogenous addition of transforming growth factor-β1 (TGF-β1) increased miR208a expression, and pre-treatment with TGF-β1 antibody attenuated the miR208a expression induced by stretch. Mechanical stretch significantly increased endoglin and collagen I expression for 6-24 h. Exogenous addition of TGF-β1 and overexpression of miR208a up-regulated endoglin and collagen I expression, while antagomir208a and Smad3/4 inhibitor attenuated endoglin and collagen I expression induced by stretch. Mechanical stretch and TGF-β1 increased Smad3/4-DNA binding activity and miR208a promoter activity, and TGF-β1 antibody and Smad3/4 inhibitor decreased the Smad3/4-DNA binding activity and miR208a promoter activity induced by stretch.

CONCLUSION

Cyclic mechanical stretch enhances miR208a expression in cultured rat cardiac myoblasts. The stretch-induced miR208a is mediated by TGF-β1. Mir208a activates endoglin expression and may result in cardiac fibrosis.

Reduced endoglin activity limits cardiac fibrosis and improves survival in heart failure

BACKGROUND

Heart failure is a major cause of morbidity and mortality worldwide. The ubiquitously expressed cytokine transforming growth factor-β1 (TGFβ1) promotes cardiac fibrosis, an important component of progressive heart failure. Membrane-associated endoglin is a coreceptor for TGFβ1 signaling and has been studied in vascular remodeling and preeclampsia. We hypothesized that reduced endoglin expression may limit cardiac fibrosis in heart failure.

METHODS AND RESULTS

We first report that endoglin expression is increased in the left ventricle of human subjects with heart failure and determined that endoglin is required for TGFβ1 signaling in human cardiac fibroblasts using neutralizing antibodies and an siRNA approach. We further identified that reduced endoglin expression attenuates cardiac fibrosis, preserves left ventricular function, and improves survival in a mouse model of pressure-overload-induced heart failure. Prior studies have shown that the extracellular domain of endoglin can be cleaved and released into the circulation as soluble endoglin, which disrupts TGFβ1 signaling in endothelium. We now demonstrate that soluble endoglin limits TGFβ1 signaling and type I collagen synthesis in cardiac fibroblasts and further show that soluble endoglin treatment attenuates cardiac fibrosis in an in vivo model of heart failure.

CONCLUSION

Our results identify endoglin as a critical component of TGFβ1 signaling in the cardiac fibroblast and show that targeting endoglin attenuates cardiac fibrosis, thereby providing a potentially novel therapeutic approach for individuals with heart failure.

Role of endoglin in fibrosis and scleroderma

Fibrosis plays a role in many pathological conditions, among which is the autoimmune disease systemic sclerosis (SSc). SSc is characterized by fibrosis in the skin and internal organs, but the etiology remains to be elucidated. Transforming growth factor-β (TGF-β) is a key player in the fibrotic process, also in SSc. TGF-β induces the production of several components of the extracellular matrix and induces differentiation of fibroblasts to myofibroblasts, which further worsens fibrosis. Although TGF-β has been extensively investigated in fibrosis, the roles of several components of its signaling pathway are still unknown. Endoglin is a coreceptor for TGF-β and is known to modulate TGF-β signaling. Therefore, endoglin could enhance the effects of TGF-β in fibrosis or act as an inhibitor. Multiple studies have been conducted that support either hypothesis. Elucidating the exact role of endoglin in TGF-β signaling during fibrosis is important in understanding the process of fibrosis and could lead to the development of better treatments.

TGF-β signaling is required for maintenance of retinal ganglion cell differentiation and survival

PURPOSE

To determine the role of TGF-β1 in the maintenance of retinal ganglion cell line (RGC-5) differentiation and integrity.

METHODS

RGC-5 cells were differentiated in media conditioned by human non-pigmented ciliary epithelial cells (HNPE) for 4 days before treatment with TGF-β1 for 24 h. Cells were examined for morphological changes and harvested for western blot and real-time PCR analysis. For study of apoptosis, differentiated RGC-5 cells were grown in serum-free medium for 24 h in the presence or absence of TGF-β1 and collected for Annexin V/Propidium iodide FACs analysis. The role of MAPK pathways in TGF-β1-dependent signaling was determined by treatment with specific inhibitors of ERK, JNK and p38.

RESULTS

Differentiation of RGC-5 cells in HNPE-conditioned media (CM) increased the neural cell markers, Brn-3c, NF-160, Thy1.2, Tau and PGP9.5. Treatment with TGF-β1 significantly increased the length of neurites extended by differentiated RGC-5s, concomitant with increased expression of NF-160 and PGP9.5, but not Brn-3c, Thy1.2 or Tau. TGF-β1 also decreased RGC-5 cell apoptosis in serum-free medium. p38 phosphorylation, but not smad2/3, JNK or ERK phosphorylation, was increased in TGF-β1 treated cells. Specific inhibition of p38 signaling reversed TGF-β1 induced neurite growth.

CONCLUSIONS

These findings demonstrate the induction of RGC-5 cell differentiation by HNPE-derived CM and illustrate a role for TGF-β1 in maintaining RGC-5 cell survival and promoting neurite outgrowth through p38 MAPK.

Expression and functional analysis of endoglin in isolated liver cells and its involvement in fibrogenic Smad signalling

Endoglin is an accessory component of the TGF-β-binding receptor complex that differentially modulates TGF-β and BMP responses. The existence of two splice variants L- and S-endoglin which differ in their cytoplasmic domain has already been shown in human and mice. Endoglin is located on the cell surfaces of cultured hepatic stellate cells and transdifferentiated myofibroblasts suggesting that this receptor might be associated with the profibrogenic attributes of these liver cell subpopulations. We now show that endoglin expression is increased in transdifferentiating hepatic stellate cells and in two models of liver fibrosis (i.e. bile duct ligation and carbon tetrachloride model) and further detectable in cultured portal fibroblasts representing another important fibrogenic cell type but not in hepatocytes. In respect to TGF-β1-signalling, we demonstrate that endoglin interacts with and is phosphorylated by TβRII. In hepatic stellate cells, TGF-β1 upregulates endoglin expression most likely via the ALK5 pathway and requires the SP1 transcription factor. We further identified a novel rat splice variant that is structurally and functionally different from that identified in human and mouse. Transient overexpression of endoglin resulted in a strong increase of TGF-β1-driven Smad1/5 phosphorylation and α-smooth muscle actin expression in a hepatic stellate cell line. In supernatants of respective cultures, we could detect the ectodomain of endoglin suggesting that shedding is a further key process involved in the regulation of this surface receptor.

The TGF-beta co-receptor endoglin modulates the expression and transforming potential of H-Ras

Endoglin is a coreceptor for transforming growth factor-β (TGF-β) that acts as a suppressor of malignancy during mouse skin carcinogenesis. Because in this model system H-Ras activation drives tumor initiation and progression, we have assessed the effects of endoglin on the expression of H-Ras in transformed keratinocytes. We found that TGF-β1 increases the expression of H-Ras at both messenger RNA and protein levels. The TGF-β1-induced H-Ras promoter transactivation was Smad4 independent but mediated by the activation of the TGF-β type I receptor ALK5 and the Ras-mitogen-activated protein kinase (MAPK) pathway. Endoglin attenuated stimulation by TGF-β1 of both MAPK signaling activity and H-Ras gene expression. Moreover, endoglin inhibited the Ras/MAPK pathway in transformed epidermal cells containing an H-Ras oncogene, as evidenced by the levels of Ras-guanosine triphosphate, phospho-MAPK kinase (MEK) and phospho-extracellular signal-regulated kinase (ERK) as well as the expression of c-fos, a MAPK downstream target gene. Interestingly, in spindle carcinoma cells, that have a hyperactivated Ras/MAPK pathway, endoglin inhibited ERK phosphorylation without affecting MEK or Ras activity. The mechanism for this effect is unknown but strongly depends on the endoglin extracellular domain. Because the MAPK pathway is a downstream mediator of the transforming potential of Ras, the effect of endoglin on the oncogenic function of H-Ras was assessed. Endoglin inhibited the transforming capacity of H-Ras(Q61K) and H-Ras(G12V) oncogenes in a NIH3T3 focus formation assay. The ability to interfere with the expression and oncogenic potential of H-Ras provides a new face of the suppressor role exhibited by endoglin in H-Ras-driven carcinogenesis.

Neuropilin-1 mediates divergent R-Smad signaling and the myofibroblast phenotype

The transforming growth factor-beta (TGF-β) superfamily is one of the most diversified cell signaling pathways and regulates many physiological and pathological processes. Recently, neuropilin-1 (NRP-1) was reported to bind and activate the latent form of TGF-β1 (LAP-TGF-β1). We investigated the role of NRP-1 on Smad signaling in stromal fibroblasts upon TGF-β stimulation. Elimination of NRP-1 in stromal fibroblast cell lines increases Smad1/5 phosphorylation and downstream responses as evidenced by up-regulation of inhibitor of differentiation (Id-1). Conversely, NRP-1 loss decreases Smad2/3 phosphorylation and its responses as shown by down-regulation of α-smooth muscle actin (α-SMA) and also cells exhibit more quiescent phenotypes and growth arrest. Moreover, we also observed that NRP-1 expression is increased during the culture activation of hepatic stellate cells (HSCs), a liver resident fibroblast. Taken together, our data suggest that NRP-1 functions as a key determinant of the diverse responses downstream of TGF-β1 that are mediated by distinct Smad proteins and promotes myofibroblast phenotype.

Cellular basis of diabetic nephropathy: V. Endoglin expression levels and diabetic nephropathy risk in patients with Type 1 diabetes

Endoglin is an accessory receptor molecule that, in association with transforming growth factor beta (TGF-beta) family receptors Types I and II, binds TGF-beta1, TGF-beta3, activin A, bone morphogenetic protein (BMP)-2 and BMP-7, regulating TGF-beta dependent cellular responses. Relevant to diabetic nephropathy, endoglin, expressed in vascular endothelial and smooth muscle cells, fibroblasts, and mesangial cells, negatively regulates extracellular matrix (ECM). The aim of this study was to evaluate endoglin expression in cultured skin fibroblasts from patients with Type 1 diabetes with and without diabetic nephropathy. Kidney and skin biopsies were performed in 125 Type 1 diabetic patients. The 20 with the fastest rate of mesangial expansion (estimated by electron microscopy) and proteinuria ("fast-track") and the 20 with the slowest rate and normoalbuminuria ("slow-track"), along with 20 controls were studied. Endoglin mRNA expression was assessed by microarray and quantitative real-time polymerase chain reaction (QRT-PCR) and protein expression by Western blot. Age and sex distribution were similar among groups. Diabetes duration was similar (20+/-8 vs. 24+/-7 years), hemoglobin A1c lower (8.4+/-1.2% vs. 9.4+/-1.5%), and glomerular filtration rate higher (115+/-13 vs. 72+/-20 ml/min per 1.73 m2) in slow-track vs. fast-track patients. Microarray endoglin mRNA expression levels were higher in slow-track (1516.0+/-349.9) than fast-track (1211.0+/-274.9; P=.008) patients or controls (1223.1+/-422.9; P=.018). This was confirmed by QRT-PCR. Endoglin protein expression levels correlated with microarray (r=0.59; P=.044) and QRTPCR (r=0.61; P=.034) endoglin mRNA expression. These studies are compatible with the hypothesis that slow-track Type 1 diabetic patients, strongly protected from diabetic nephropathy, have distinct cellular behaviors that may be associated with reduced ECM production.

Endoglin is involved in BMP-2-induced osteogenic differentiation of periodontal ligament cells through a pathway independent of Smad-1/5/8 phosphorylation

The periodontal ligament (PDL), a connective tissue located between the cementum of teeth and the alveolar bone of mandibula, plays a crucial role in the maintenance and regeneration of periodontal tissues. The PDL contains fibroblastic cells of a heterogeneous cell population, from which we have established several cell lines previously. To analyze characteristics unique for PDL at a molecular level, we performed cDNA microarray analysis of the PDL cells versus MC3T3-E1 osteoblastic cells. The analysis followed by validation by reverse transcription-polymerase chain reaction and immunochemical staining revealed that endoglin, which had been shown to associate with transforming growth factor (TGF)-beta and bone morphogenetic proteins (BMPs) as signaling modulators, was abundantly expressed in PDL cells but absent in osteoblastic cells. The knockdown of endoglin greatly suppressed the BMP-2-induced osteoblastic differentiation of PDL cells and subsequent mineralization. Interestingly, the endoglin knockdown did not alter the level of Smad-1/5/8 phosphorylation induced by BMP-2, while it suppressed the BMP-2-induced expression of Id1, a representative BMP-responsive gene. Therefore, it is conceivable that endoglin regulates the expression of BMP-2-responsive genes in PDL cells at some site downstream of Smad-1/5/8 phosphorylation. Alternatively, we found that Smad-2 as well as Smad-1/5/8 was phosphorylated by BMP-2 in the PDL cells, and that the BMP-2-induced Smad-2 phosphorylation was suppressed by the endoglin knockdown. These results, taken together, raise a possibility that PDL cells respond to BMP-2 via a unique signaling pathway dependent on endoglin, which is involved in the osteoblastic differentiation and mineralization of the cells.

alpha2-antiplasmin is associated with the progression of fibrosis

Systemic sclerosis results in tissue fibrosis due to the activation of fibroblasts and the ensuing overproduction of the extracellular matrix. We previously reported that the absence of alpha2-antiplasmin (alpha2AP) attenuated the process of dermal fibrosis; however, the detailed mechanism of how alpha2AP affects the progression of fibrosis remained unclear. The goal of the present study was to examine the role of alpha2AP in fibrotic change. We observed significantly higher levels of alpha2AP expression in the skin of bleomycin-injected systemic sclerosis model mice in comparison with the levels seen in control mice. We also demonstrated that alpha2AP induced myofibroblast differentiation, and the absence of alpha2AP attenuated the induction of myofibroblast differentiation. Moreover, we found that connective tissue growth factor induced the expression of alpha2AP through both the extracellular signal-regulated kinase 1/2 (ERK1/2) and c-Jun N-terminal kinase (JNK) pathways in fibroblasts. Interestingly, alpha2AP also induced transforming growth factor-beta expression through the same pathways, and the inhibition of ERK1/2 and JNK slowed the progression of bleomycin-induced fibrosis. Our findings suggest that alpha2AP is associated with the progression of fibrosis, and regulation of alpha2AP expression by the ERK1/2 and JNK pathways may be an effective antifibrotic therapy for the treatment of systemic sclerosis.

Endogenous nerve growth factor regulates collagen expression and bladder hypertrophy through Akt and MAPK pathways during cystitis

Type I collagen forms the main constituent of the extracellular matrix in visceral organs. We reported here that cyclophosphamide (CYP)-induced cystitis significantly increased the production of type I collagen in the inflamed bladder leading to increases in the bladder weight and the thickness of the bladder wall. The endogenous nerve growth factor (NGF) in the urinary bladder regulated type I collagen expression because the neutralizing NGF antibody attenuated cystitis-induced type I collagen up-regulation in the inflamed bladder. Neutralizing NGF antibody also subsequently reversed cystitis-induced increases in bladder weight. Further studies on the intermediate signaling pathways mediating NGF-induced type I collagen expression in the inflamed bladder during cystitis revealed that Akt, JNK, and ERK1/2 activities were increased in the inflamed bladder, whereas p38 MAPK remained unchanged. Suppression of endogenous NGF level with neutralizing NGF antibody significantly blocked the increased activity of Akt, JNK, and ERK1/2 in the inflamed bladder during cystitis. These results indicate that endogenous NGF plays an important role in the activation of Akt and MAPK in the urinary bladder and in bladder hypertrophy during cystitis.

The emerging role of TGF-beta superfamily coreceptors in cancer

The transforming growth factor beta (TGF-beta) signaling pathway plays a key role in different physiological processes such as development, cellular proliferation, extracellular matrix synthesis, angiogenesis or immune responses and its deregulation may result in tumor development. The TGF-beta coreceptors endoglin and betaglycan are emerging as modulators of the TGF-beta response with important roles in cancer. Endoglin is highly expressed in the tumor-associated vascular endothelium with prognostic significance in selected neoplasias and with potential to be a prime vascular target for antiangiogenic cancer therapy. On the other hand, the expression of endoglin and betaglycan in tumor cells themselves appears to play an important role in the progression of cancer, influencing cell proliferation, motility, invasiveness and tumorigenicity. In addition, experiments in vitro and in vivo in which endoglin or betaglycan expression is modulated have provided evidence that they act as tumor suppressors. The purpose of this review was to highlight the potential of membrane and soluble forms of the endoglin and betaglycan proteins as molecular targets in cancer diagnosis and therapy.