Snail activation disrupts tissue homeostasis and induces fibrosis in the adult kidney

Epidermal growth factor promotes transforming growth factor-β1-induced epithelial-mesenchymal transition in HK-2 cells through a synergistic effect on Snail

Epithelial-mesenchymal transition (EMT) is a central mechanism for wound healing, tissue repair, organ fibrosis and carcinoma progression in adults. Evidence shows that both epidermal growth factor (EGF) and transforming growth factor-β1 (TGF-β1) are upregulated during renal interstitial fibrosis, and that co-stimulation of EGF and TGF-β1 could induce renal tubular epithelial cells to undergo EMT more effectively than EGF or TGF-β1 alone. This study was intended to explore the molecular mechanism underlying this effect. HK-2 cells underwent apparent EMT with increased cell motility after co-stimulation of EGF and TGF-β1 as compared with TGF-β1 or EGF alone. Co-stimulation of EGF and TGF-β1 resulted in rapid and robust ERK1/2 activation and induced persistent high expression of Snail protein. Treatment with the MEK inhibitor U0126 followed by co-stimulation with EGF and TGF-β1 prevented the upregulation of Snail protein, EMT and motility, without impairing Snail mRNA. TGF-β1 induced Snail at the transcriptional level, which was not influenced by EGF. Inhibition of Snail expression by siRNA interference also prevented EMT caused by co-stimulation of EGF and TGF-β1. These data suggest that EGF promotes TGF-β1-induced EMT through a synergistic effect on Snail at the post-transcriptional level in HK-2 cells.

All-transretinoic acid ameliorates bleomycin-induced lung fibrosis by downregulating the TGF-β1/Smad3 signaling pathway in rats

The transforming growth factor-β1 (TGF-β1)/Smad3 signaling pathway has a central role in pathogenesis of lung fibrosis. In the present study, we investigated if all-trans retinoic acid (ATRA) could attenuate fibrosis in bleomycin (BLM)-induced lung fibrosis in rats through regulating TGF-β1/Smad3 signaling. Beginning on day 14 after BLM administration, the ATRA I and II groups of rats received daily oral administration of ATRA for 14 days. All rats were killed on day 28. Lung tissue sections were prepared and subject to histological assessment, and expression levels of proteins involved in the TGF-β1 signaling cascade and epithelial-mesenchymal transition (EMT) were evaluated by transmission electron microscopy (TEM), quantitative real-time polymerase chain reaction (qRT-PCR), western blot procedure, and immunohistochemical or immunofluorescence staining. BLM significantly increased the alveolar septum infiltrates, inflammatory cell infiltrates, and collagen fibers. These BLM-induced changes were significantly ameliorated by ATRA treatment. In addition, BLM significantly increased levels of lung fibrosis markers α-SMA, hydroxyproline (Hyp), collagen I, Snail, and Twist, whereas significantly decreased E-cadherin expression. ATRA treatment largely reversed BLM-induced changes in these lung fibrosis markers. ATRA also blocked BLM-induced activation of the TGF-β1/Smad3 signaling pathway in lung tissues, including expression of TGF-β1, Smad3, p-Smad3, zinc-finger E-box-binding homeobox 1 and 2 (ZEB1 and ZEB2), and the high-mobility group AT-hook 2 (HMGA2). Our results suggest that ATRA may have potential therapeutic value for lung fibrosis treatment.

CD44v3-v10 reduces the profibrotic effects of TGF-β1 and attenuates tubular injury in the early stage of chronic obstructive nephropathy

CD44 family members are cell surface glycoproteins, which are expressed on tubular epithelial cells (TEC) solely upon kidney injury and are involved in renal fibrosis development. Renal interstitial fibrosis is the final manifestation of chronic kidney diseases and is regulated by a complex network of cytokines, including the profibrotic factor transforming growth factor-β1 (TGF-β1) and the two antifibrotic cytokines bone morphogenic protein-7 (BMP-7) and hepatocyte growth factor (HGF). The present study investigates the potential role of CD44 standard (CD44s) and CD44v3-v10 (CD44v3) isoforms as modulators of the balance between TGF-β1 and HGF/BMP-7. CD44s is the shortest and most common isoform. CD44v3-v10 (CD44v3) has heparan sulfate moieties, which enable the binding to HGF/BMP-7, and hence, might exert renoprotective effects. Using transgenic mice overexpressing either CD44s or CD44v3 specifically on proximal TEC, we found that in vitro the overexpression of CD44v3 on primary TEC renders cells less susceptible to TGF-β1 profibrotic actions and more sensitive to BMP-7 and HGF compared with TEC overexpressing CD44s. One day after unilateral ureteric obstruction, obstructed kidneys from CD44v3 transgenic mice showed less tubular damage and myofibroblasts accumulation, which was associated with decreased TGF-β1 signaling and increased BMP-7 synthesis and signaling compared with kidneys from wild-type and CD44s transgenic mice. These data suggest that CD44v3 plays a renoprotective role in early stage of chronic obstructive nephropathy.

Epithelial calreticulin up-regulation promotes profibrotic responses and tubulointerstitial fibrosis development

Renal fibrosis is the common anatomical feature underlying the progression of chronic kidney disease, a leading cause of morbidity and mortality worldwide. In a previous study, we demonstrated that during development of renal fibrosis in a rat model of unilateral ureteric obstruction, calreticulin (CRT) is up-regulated in tubular epithelial cells (TECs). In the present study, we used in vitro and in vivo approaches to examine the role of CRT in TECs and its contribution to the progression of fibrosis. In cultured renal TECs, CRT overexpression induced acquisition of an altered, profibrotic cellular phenotype. Consistently, the opposite effects were observed for CRT knockdown. Subsequently, we confirmed that critical changes observed in vitro were also apparent in tubular cells in vivo in the animal model of unilateral ureteric obstruction. In agreement with these results, we demonstrate that substantial (50%) reduction in the expression of CRT reduced the development of tubulointerstitial fibrosis at a comparable level through regulation of inflammation, transcriptional activation, transforming growth factor β1-associated effects, and apoptosis. In summary, our findings establish that CRT is critically involved in the molecular mechanisms that drive renal fibrosis progression and indicate that inhibition of CRT expression might be a therapeutic target for reduction of fibrosis and chronic kidney disease development.

Snail cooperates with KrasG12D to promote pancreatic fibrosis

Patients with pancreatic cancer, which is characterized by an extensive collagen-rich fibrotic reaction, often present with metastases. A critical step in cancer metastasis is epithelial-to-mesenchymal transition (EMT), which can be orchestrated by the Snail family of transcription factors. To understand the role of Snail (SNAI1) in pancreatic cancer development, we generated transgenic mice expressing Snail in the pancreas. Because chronic pancreatitis can contribute to pancreatic cancer development, Snail-expressing mice were treated with cerulein to induce pancreatitis. Although significant tissue injury was observed, a minimal difference in pancreatitis was seen between control and Snail-expressing mice. However, because Kras mutation is necessary for tumor development in mouse models of pancreatic cancer, we generated mice expressing both mutant Kras(G12D) and Snail (Kras(+)/Snail(+)). Compared with control mice (Kras(+)/Snai(-)), Kras(+)/Snail(+) mice developed acinar ectasia and more advanced acinar-to-ductal metaplasia. The Kras(+)/Snail(+) mice exhibited increased fibrosis, increased phosphorylated Smad2, increased TGF-β2 expression, and activation of pancreatic stellate cells. To further understand the mechanism by which Snail promoted fibrosis, we established an in vitro model to examine the effect of Snail expression in pancreatic cancer cells on stellate cell collagen production. Snail expression in pancreatic cancer cells increased TGF-β2 levels, and conditioned media from Snail-expressing pancreatic cancer cells increased collagen production by stellate cells. Additionally, inhibiting TGF-β signaling in stellate cells attenuated the conditioned media-induced collagen production by stellate cells. Together, these results suggest that Snail contributes to pancreatic tumor development by promoting fibrotic reaction through increased TGF-β signaling.

IMPLICATIONS

Expression of the EMT regulator Snail in the context of mutant Kras provides new insight into pancreatic cancer progression.

Transforming growth factor-Beta and urokinase-type plasminogen activator: dangerous partners in tumorigenesis-implications in skin cancer

Transforming growth factor-beta (TGF-β) is a pleiotropic factor, with several different roles in health and disease. TGF-β has been postulated as a dual factor in tumor progression, since it represses epithelial tumor development in early stages, whereas it stimulates tumor progression in advanced stages. During tumorigenesis, cancer cells acquire the capacity to migrate and invade surrounding tissues and to metastasize different organs. The urokinase-type plasminogen activator (uPA) system, comprising uPA, the uPA cell surface receptor, and plasminogen-plasmin, is involved in the proteolytic degradation of the extracellular matrix and regulates key cellular events by activating intracellular signal pathways, which together allow cancer cells to survive, thus, enhancing cell malignance during tumor progression. Due to their importance, uPA and its receptor are tightly transcriptionally regulated in normal development, but are deregulated in cancer, when their activity and expression are related to further development of cancer. TGF-β regulates uPA expression in cancer cells, while uPA, by plasminogen activation, may activate the secreted latent TGF-β, thus, producing a pernicious cycle which contributes to the enhancement of tumor progression. Here we review the specific roles and the interplay between TGF-β and uPA system in cancer cells and their implication in skin cancer.

Norcantharidin inhibits renal interstitial fibrosis by blocking the tubular epithelial-mesenchymal transition

Epithelial–mesenchymal transition (EMT) is thought to contribute to the progression of renal tubulointerstitial fibrosis. Norcantharidin (NCTD) is a promising agent for inhibiting renal interstitial fibrosis. However, the molecular mechanisms of NCTD are unclear. In this study, a unilateral ureteral obstruction (UUO) rat model was established and treated with intraperitoneal NCTD (0.1 mg/kg/day). The UUO rats treated with NCTD showed a reduction in obstruction-induced upregulation of α-SMA and downregulation of E-cadherin in the rat kidney (P<0.05). Human renal proximal tubule cell lines (HK-2) stimulated with TGF-β₁ were treated with different concentrations of NCTD. HK-2 cells stimulated by TGF-β₁ in vitro led to downregulation of E-cadherin and increased de novo expression of α-SMA; co-treatment with NCTD attenuated all of these changes (P<0.05). NCTD reduced TGF-β₁-induced expression and phosphorylation of Smad2/3 and downregulated the expression of Snail1 (P<0.05). These results suggest that NCTD antagonizes tubular EMT by inhibiting the Smad pathway. NCTD may play a critical role in preserving the normal epithelial phenotype and modulating tubular EMT.

Snail as a potential target molecule in cardiac fibrosis: paracrine action of endothelial cells on fibroblasts through snail and CTGF axis

Ischemia/reperfusion (I/R) injury to myocardium induces death of cardiomyocytes and destroys the vasculature, leading to cardiac fibrosis that is mainly mediated by the transdifferentiation of fibroblasts to myofibroblasts and the collagen deposition. Snail involvement in fibrosis is well known; however, the contribution of Snail to cardiac fibrosis during I/R injury and its underlying mechanisms have not been defined. We showed that I/R injury to mouse hearts significantly increases the expression of Snail. An in vitro hypoxia/reoxygenation (Hy/Reoxy) experiment showed that the cell source of Snail induction is endothelial cells rather than cardiac fibroblasts (cFibroblasts) or cardiomyoblasts. When Snail was overexpressed in endothelial cells, they underwent endothelial-to-mesenchymal transition (EndMT) but showed very poor capacity for collagen synthesis. Instead, reoxygenation- or Snail overexpression-mediated EndMT-like cells noticeably stimulated transdifferentiation of fibroblasts to myofibroblasts via secretion of connective tissue growth factor (CTGF). The injection of a peroxisome proliferator-activated receptor-γ (PPAR-γ) agonist, a selective Snail inhibitor, remarkably suppressed collagen deposition and cardiac fibrosis in mouse I/R injury, and significantly improved cardiac function and reduced Snail and CTGF expression in vivo. Our findings suggested a new mechanism of cell-to-cell communication between EndMT-like cells and fibroblasts for fibrosis induction and implicated Snail as a potential target molecule in cardiac fibrosis after I/R injury.

VEGF induces TGF-β1 expression and myofibroblast transformation after glaucoma surgery

Subconjunctival fibrosis at the surgical site determines the outcome of glaucoma surgery. Myofibroblast transformation has a significant role in fibrosis, and vascular endothelial growth factor (VEGF) is reported to trigger myofibroblast transformation by inducing transforming growth factor (TGF)-β1. In the present study, we used IHC, Western blot analysis, enzyme-linked immunosorbent assay, and electron microscopy to determine the contribution of VEGF to myofibroblast transformation in subconjunctival fibrosis after glaucoma surgery. A rabbit trabeculectomy model was generated, and VEGF stimulation or VEGF inhibition was performed during surgery. VEGF stimulation induced TGF-β1 expression in a dose-dependent manner. Down-regulation of epithelial markers (E-cadherin and β-catenin) and up-regulation of mesenchymal marker (α-smooth muscle actin) were observed in the subconjunctival layers after trabeculectomy with VEGF stimulation. Up-regulations of Smad and Snail, which play a central role in myofibroblast transformation, were observed in the conjunctival and subconjunctival layers at the site of trabeculectomy. Electron microscopy revealed changes of the conjunctival epithelial cells, especially the presence of myofilaments and increased rough endoplasmic reticulum in the cytoplasm. Myofibroblast transformation was activated by VEGF stimulation and decreased by VEGF inhibition. These findings suggest that VEGF potentially affected the TGF-β1/Smad/Snail pathway, thereby triggering myofibroblast transformation. Therapeutic approaches modulating VEGF may control myofibroblast transformation and reduce subconjunctival fibrosis after glaucoma surgery.

Reduction of chronic rejection of renal allografts by anti-transforming growth factor-β antibody therapy in a rat model

There is no effective treatment for chronic rejection (CR) that largely limits long-term survival of kidney transplants. Transforming growth factor (TGF)-β is a fibrogenic factor for tissue fibrosis. This study was to test the efficacy of an anti-TGF-β antibody in preventing the CR of renal allografts in a preclinical model. Male Lewis rats (RT1¹) were orthotopically transplanted with donor kidneys from male Fischer 344 (RT11v1) rats and were treated with either anti-TGF-β or a control antibody. The CR of renal allografts was assessed by semiquantitative histological analyses, and intragraft cytokines and fibrosis-related genes ware examined by PCR arrays. Compared with the control antibody, anti-TGF-β antibody treatment significantly reduced recipients' proteinuria (P = 0.0002), and CR in renal transplants, which was indicated by the fewer injured renal tubules, glomeruli, and interlobular arterioles or arteries, and by less mononuclear cell infiltration and interstitial fibrosis in the anti-TGF-β antibody-treated group (P < 0.05), but not significantly attenuate the ratios of different infiltrating leukocytes. These pathological changes were associated with downregulation of TGF-β1, TGF-β2, and proinflammatory cytokines, or with upregulation of anti-fibrotic HGF, BMP5, and BMP7. The therapeutic effect of the anti-TGF-β antibody was further confirmed by its prevention of graft dysfunction, indicated by lower levels of serum creatinine and blood urea nitrogen or higher creatinine clearance in anti-TGF-β antibody-treated recipients compared with those in control recipients (P < 0.05). In conclusion, the anti-TGF-β antibody (1D11) treatment significantly reduces CR of renal allografts in rats, suggesting the therapeutic potential of this antibody therapy for treating CR of kidney transplants in patients.

Loss of Klotho contributes to kidney injury by derepression of Wnt/β-catenin signaling

Aging is an independent risk factor for CKD, but the molecular mechanisms that link aging and CKD are not well understood. The antiaging protein Klotho may be an endogenous antagonist of Wnt/β-catenin signaling, which promotes fibrogenesis, suggesting that loss of Klotho may contribute to CKD through increased Wnt/β-catenin activity. Here, normal adult kidneys highly expressed Klotho in the tubular epithelium, but various models of nephropathy exhibited markedly less expression of Klotho. Loss of Klotho was closely associated with increased β-catenin in the diseased kidneys, suggesting an inverse correlation between Klotho and canonical Wnt signaling. In vitro, both full-length and secreted Klotho bound to multiple Wnts, including Wnt1, Wnt4, and Wnt7a. Klotho repressed gene transcription induced by Wnt but not by active β-catenin. Furthermore, Klotho blocked Wnt-triggered activation and nuclear translocation of β-catenin, as well as the expression of its target genes in tubular epithelial cells. Investigating potential mediators of Klotho loss in CKD, we found that TGF-β1 suppressed Klotho expression and concomitantly activated β-catenin; conversely, overexpression of Klotho abolished fibrogenic effects of TGF-β1. In two mouse models of CKD induced by unilateral ureteral obstruction or adriamycin, in vivo expression of secreted Klotho inhibited the activation of renal β-catenin and expression of its target genes. Secreted Klotho also suppressed myofibroblast activation, reduced matrix expression, and ameliorated renal fibrosis. Taken together, these results suggest that Klotho is an antagonist of endogenous Wnt/β-catenin activity; therefore, loss of Klotho may contribute to kidney injury by releasing the repression of pathogenic Wnt/β-catenin signaling.

Cellular mechanisms of tissue fibrosis. 1. Common and organ-specific mechanisms associated with tissue fibrosis

Fibrosis is a pathological scarring process that leads to destruction of organ architecture and impairment of organ function. Chronic loss of organ function in most organs, including bone marrow, heart, intestine, kidney, liver, lung, and skin, is associated with fibrosis, contributing to an estimated one third of natural deaths worldwide. Effective therapies to prevent or to even reverse existing fibrotic lesions are not yet available in any organ. There is hope that an understanding of common fibrosis pathways will lead to development of antifibrotic therapies that are effective in all of these tissues in the future. Here we review common and organ-specific pathways of tissue fibrosis.

Regulatory networks defining EMT during cancer initiation and progression

Epithelial to mesenchymal transition (EMT) is essential for driving plasticity during development, but is an unintentional behaviour of cells during cancer progression. The EMT-associated reprogramming of cells not only suggests that fundamental changes may occur to several regulatory networks but also that an intimate interplay exists between them. Disturbance of a controlled epithelial balance is triggered by altering several layers of regulation, including the transcriptional and translational machinery, expression of non-coding RNAs, alternative splicing and protein stability.

Inhibition of HSP27 blocks fibrosis development and EMT features by promoting Snail degradation

Idiopathic pulmonary fibrosis (IPF) is a devastating disease characterized by myofibroblast proliferation. Transition of epithelial/mesothelial cells into myofibroblasts [epithelial-to-mesenchymal transition (EMT)] occurs under the influence of transforming growth factor (TGF)-β1, with Snail being a major transcription factor. We study here the role of the heat-shock protein HSP27 in fibrogenesis and EMT. In vitro, we have up- and down-modulated HSP27 expression in mesothelial and epithelial cell lines and studied the expression of different EMT markers induced by TGF-β1. In vivo, we inhibited HSP27 with the antisense oligonucleotide OGX-427 (in phase II clinical trials as anticancer agent) in our rat subpleural/pulmonary fibrosis models. We demonstrate that HSP27 is strongly expressed during the fibrotic process in patients with IPF and in different in vivo models. We showed that HSP27 binds to and stabilizes Snail and consequently induces EMT. Conversely, HSP27 knockdown leads to Snail proteasomal degradation, thus inhibiting TGF-β1-induced EMT. Inhibition of HSP27 with OGX-427 efficiently blocks EMT and fibrosis development. Controls in vivo were an empty adenovirus that did not induce fibrosis and a control antisense oligonucleotide. The present work opens the possibility of a new therapeutic use for HSP27 inhibitors against IPF, for which there is no conclusively effective treatment.

New insights into the regulation of epithelial-mesenchymal transition and tissue fibrosis

Tissue fibrosis often presents as the final outcome of chronic disease and is a significant cause of morbidity and mortality worldwide. Fibrosis is driven by continuous expansion of fibroblasts and myofibroblasts. Epithelial-mesenchymal transition (EMT) is a form of cell plasticity in which epithelia acquire mesenchymal phenotypes and is increasingly recognized as an integral aspect of tissue fibrogenesis. In this review, we describe recent insight into the molecular and cellular factors that regulate EMT and its underlying signaling pathways. We also consider how mechanical cues from the microenvironment affect the regulation of EMT. Finally, we discuss the role of EMT in fibrotic diseases and propose approaches for detecting and treating fibrogenesis by targeting EMT.

Snail, a transcriptional regulator, represses adiponectin expression by directly binding to an E-box motif in the promoter

OBJECTIVE

Adiponectin is a hormone that modulates many metabolic processes and is exclusively expressed in adipose tissue. However, complete understanding of the factors that regulate adiponectin expression is lacking. The following were investigated: (1) functional analysis of the human adiponectin promoter, (2) putative adiponectin repressor sequence activity in 3T3-L1 adipocytes using promoter mutagenesis, (3) whether Snail, an E-box binding transcription factor, binds this repressor sequence, (4) if Snail regulates adiponectin expression in 3T3-L1 pre-adipocytes.

MATERIALS/METHODS

To further understand how adiponectin expression is regulated, we isolated the human adiponectin promoter and analyzed its activity after serial deletions.

RESULTS

We found a negative cis-regulatory element located in the adiponectin proximal promoter sequence (-174 to -152 bp), which contained an E-box site (CAACTG). The DNA binding activity of this putative negative regulatory factor was found to be sequence-specific and the binding activity is decreased during adipocyte differentiation time-dependently. Affinity chromatography identified the zinc-finger transcription factor Snail (SNAI1) as the putative negative regulatory factor. Chromatin immunoprecipitation assay and electrophoretic mobility shift assay confirmed that Snail binds to this negative cis-regulatory element in pre-adipocytes, exclusively. Inhibition of Snail expression using small interfering RNA techniques increased adiponectin expression in 3T3-L1 adipocytes, while overexpression of Snail reduced adiponectin expression. Furthermore, we observed an inverse relation between the expression of Snail and the expression of CCAAT-enhancer-binding protein alpha and peroxisome proliferator-activated receptor gamma, which are transcription factors that regulate adipogenesis.

CONCLUSIONS

Snail is a novel regulator of adiponectin expression and probably has a role in regulating adipogenesis.

Fell-Muir lecture: Connective tissue growth factor (CCN2) -- a pernicious and pleiotropic player in the development of kidney fibrosis

Connective tissue growth factor (CTGF, CCN2) is a member of the CCN family of matricellular proteins. It interacts with many other proteins, including plasma membrane proteins, modulating cell function. It is expressed at low levels in normal adult kidney cells but is increased in kidney diseases, playing important roles in inflammation and in the development of glomerular and interstitial fibrosis in chronic disease. This review reports the evidence for its expression in human and animal models of chronic kidney disease and summarizes data showing that anti-CTGF therapy can successfully attenuate fibrotic changes in several such models, suggesting that therapies targeting CTGF and events downstream of it in renal cells may be useful for the treatment of human kidney fibrosis. Connective tissue growth factor stimulates the development of fibrosis in the kidney in many ways including activating cells to increase extracellular matrix synthesis, inducing cell cycle arrest and hypertrophy, and prolonging survival of activated cells. The relationship between CTGF and the pro-fibrotic factor TGFβ is examined and mechanisms by which CTGF promotes signalling by the latter are discussed. No specific cellular receptors for CTGF have been discovered but it interacts with and activates several plasma membrane proteins including low-density lipoprotein receptor-related protein (LRP)-1, LRP-6, tropomyosin-related kinase A, integrins and heparan sulphate proteoglycans. Intracellular signalling and downstream events triggered by such interactions are reviewed. Finally, the relationships between CTGF and several anti-fibrotic factors, such as bone morphogenetic factor-4 (BMP4), BMP7, hepatocyte growth factor, CCN3 and Oncostatin M, are discussed. These may determine whether injured tissue heals or progresses to fibrosis.

Cancer Stem Cells, EMT, and Developmental Pathway Activation in Pancreatic Tumors

Pancreatic cancer is a disease with remarkably poor patient survival rates. The frequent presence of metastases and profound chemoresistance pose a severe problem for the treatment of these tumors. Moreover, cross-talk between the tumor and the local micro-environment contributes to tumorigenicity, metastasis and chemoresistance. Compared to bulk tumor cells, cancer stem cells (CSC) have reduced sensitivity to chemotherapy. CSC are tumor cells with stem-like features that possess the ability to self-renew, but can also give rise to more differentiated progeny. CSC can be identified based on increased in vitro spheroid- or colony formation, enhanced in vivo tumor initiating potential, or expression of cell surface markers. Since CSC are thought to be required for the maintenance of a tumor cell population, these cells could possibly serve as a therapeutic target. There appears to be a causal relationship between CSC and epithelial-to-mesenchymal transition (EMT) in pancreatic tumors. The occurrence of EMT in pancreatic cancer cells is often accompanied by re-activation of developmental pathways, such as the Hedgehog, WNT, NOTCH, and Nodal/Activin pathways. Therapeutics based on CSC markers, EMT, developmental pathways, or tumor micro-environment could potentially be used to target pancreatic CSC. This may lead to a reduction of tumor growth, metastatic events, and chemoresistance in pancreatic cancer.

A novel long-range enhancer regulates postnatal expression of Zeb2: implications for Mowat-Wilson syndrome phenotypes

The zinc-finger, E-box-binding homeobox-2 (Zeb2) gene encodes a SMAD-interacting transcription factor that has diverse roles in development and disease. Mutations at the hZeb2 locus cause Mowat-Wilson syndrome (MWS), a genetic disorder that is associated with mental retardation and other, case- and sex-dependent clinical features. Recent studies have detailed microRNA-mediated control of Zeb2, but little is known about the genomic context of this gene or of enhancer sequences that may direct its diverse functions. Here, we describe a novel transgenic rodent model in which Zeb2 regulatory sequence has been disrupted, resulting in a postnatal developmental phenotype that is autosomal dominant. The phenotype exhibits a genotype-by-sex interaction and manifests primarily as an acute attenuation of postnatal kidney development in males. Other aspects of embryonic and neonatal development, including neuronal, are unaffected. The transgene insertion site is associated with a 12 kb deletion, 1.2 Mb upstream of Zeb2, within a 4.1 Mb gene desert. A conserved sequence, derived from the deleted region, enhanced Zeb2 promoter activity in transcription assays. Tissue and temporal restriction of this enhancer activity may involve postnatal changes in proteins that bind this sequence. A control human/mouse VISTA enhancer (62 kb upstream of Zeb2) also up-regulated the Zeb2 promoter, providing evidence of a string of conserved distal enhancers. The phenotype arising from deletion of one copy of the extreme long-range enhancer indicates a critical role for this enhancer at one developmental stage. Haploinsufficiency of Zeb2 in this developmental context reflects inheritance of MWS and may underlie some sex-dependent, non-neural characteristics of this human inherited disorder.

Hyperglycemia causes renal cell damage via CCN2-induced activation of the TrkA receptor: implications for diabetic nephropathy

CCN2, a secreted profibrotic protein, is highly expressed in diabetic nephropathy (DN) and implicated in its pathogenesis; however, the actions of CCN2 in DN remain elusive. We previously demonstrated that CCN2 triggers signaling via tropomyosin receptor kinase A (TrkA). Trace expression of TrkA is found in normal kidneys, but its expression is elevated in several nephropathies; yet its role in DN is unexplored. In this study we show de novo expression of TrkA in human and murine DN. We go on to study the molecular mechanisms leading to TrkA activation and show that it involves hypoxia, as demonstrated by ischemia-reperfusion injury and in vitro experiments mimicking hypoxia, implicating hypoxia as a common pathway leading to disease. We also expose renal cells to hyperglycemia, which led to TrkA phosphorylation in mesangial cells, tubular epithelial cells, and podocytes but not in glomerular endothelial cells and renal fibroblasts. In addition, we report that hyperglycemia caused an induction of phosphorylated extracellular signal-related kinase 1/2 and Snail1 that was abrogated by silencing of TrkA or CCN2 using small interfering RNA. In conclusion, we provide novel evidence that TrkA is activated in diabetic kidneys and suggest that anti-TrkA therapy may prove beneficial in DN.

What is bad in cancer is good in the embryo: importance of EMT in neural crest development

Although the epithelial to mesenchymal transition (EMT) is famous for its role in cancer metastasis, it also is a normal developmental event in which epithelial cells are converted into migratory mesenchymal cells. A prime example of EMT during development occurs when neural crest (NC) cells emigrate from the neural tube thus providing an excellent model to study the principles of EMT in a nonmalignant environment. NC cells start life as neuroepithelial cells intermixed with precursors of the central nervous system. After EMT, they delaminate and begin migrating, often to distant sites in the embryo. While proliferating and maintaining multipotency and cell survival the transitioning neural crest cells lose apicobasal polarity and the basement membrane is broken down. This review discusses how these events are coordinated and regulated, by series of events involving signaling factors, gene regulatory interactions, as well as epigenetic and post-transcriptional modifications. Even though the series of events involved in NC EMT are well known, the sequence in which these steps take place remains a subject of debate, raising the intriguing possibility that, rather than being a single event, neural crest EMT may involve multiple parallel mechanisms.

Cancer stem cells and epithelial-mesenchymal transition: concepts and molecular links

The epithelial-mesenchymal transition (EMT) confers mesenchymal properties on epithelial cells and has been closely associated with the acquisition of aggressive traits by carcinoma cells. EMT programs are orchestrated by a set of pleiotropically acting transcription factors (TFs). The actions of these EMT-TFs enable the early steps of metastasis: local invasion and subsequent dissemination of carcinoma cells to distant sites. However, in most malignancies, the subsequent outgrowth of micrometastatic deposits into macroscopic metastases has the greatest impact on clinical progression. Such metastatic "colonization" reflects the ability of disseminated tumor cells to adapt to a foreign tissue microenvironment. The outgrowth of a metastasis is also thought to be associated with self-renewal, the defining cellular trait of cancer stem cells (CSCs), also termed tumor-initiating cells. Importantly, molecular links between EMT-TFs and self-renewal have emerged, suggesting that EMT programs play critical roles both early and late in the metastatic cascade. The genetic and epigenetic mechanisms that regulate the activation of EMT-TFs and the traits they induce are areas under intensive investigation. Such studies may provide new opportunities for therapeutic intervention and help to overcome tumor heterogeneity and therapeutic resistance.

Epithelial-mesenchymal transition in adult liver cells: a new mechanism of hepatic fibrosis

The research of epithelial-mesenchymal transitions (EMT) has become a hot spot in the area of hepatic fibrosis research recently. EMT can be divided into three subtypes based on different biological context in which it occur: embryogenesis/development, wound healing/tissue regeneration/organ fibrosis, and neoplasia. In order to study EMT conveniently, several types of biomarkers have been identified, including cell surface proteins, cell skeleton proteins, extracellular proteins, transcription factors and microRNAs. Among signaling pathways associated with EMT, TGF-β and Wnt pathways are studied more sufficiently. Nowadays, the methods used to study EMT include immunohistological method and fate-mapping technology. This article emphasizes the proofs that support or argue against the occurrence of EMT in three main types of liver cells: hepatocytes, cholangiocytes and stellate cells. Although many in vitro studies support the occurrence of EMT under certain stimulators, few in vivo results obtained by fate-mapping methods draw opposite conclusions. Whether and to what extent EMT influences hepatic fibrosis are interesting questions needed to be explored further. The purpose of this article is to summarize evidence for and against the possibility that EMT is involved in fibrogenic repair in resident liver cells.

A systems approach identifies HIPK2 as a key regulator of kidney fibrosis

Kidney fibrosis is a common process that leads to the progression of various types of kidney disease. We used an integrated computational and experimental systems biology approach to identify protein kinases that regulate gene expression changes in the kidneys of human immunodeficiency virus (HIV) transgenic mice (Tg26 mice), which have both tubulointerstitial fibrosis and glomerulosclerosis. We identified homeo-domain interacting protein kinase 2 (HIPK2) as a key regulator of kidney fibrosis. HIPK2 was upregulated in the kidneys of Tg26 mice and in those of patients with various kidney diseases. HIV infection increased the protein concentrations of HIPK2 by promoting oxidative stress, which inhibited the seven in absentia homolog 1 (SIAH1)-mediated proteasomal degradation of HIPK2. HIPK2 induced apoptosis and the expression of epithelial-to-mesenchymal transition markers in kidney epithelial cells by activating the p53, transforming growth factor β (TGF-β)-SMAD family member 3 (Smad3) and Wnt-Notch pathways. Knockout of HIPK2 improved renal function and attenuated proteinuria and kidney fibrosis in Tg26 mice, as well as in other murine models of kidney fibrosis. We therefore conclude that HIPK2 is a potential target for anti-fibrosis therapy.

Biochemical role of the collagen-rich tumour microenvironment in pancreatic cancer progression

PDAC (pancreatic ductal adenocarcinoma) is among the most deadly of human malignances. A hallmark of the disease is a pronounced collagen-rich fibrotic extracellular matrix known as the desmoplastic reaction. Intriguingly, it is precisely these areas of fibrosis in which human PDAC tumours demonstrate increased expression of a key collagenase, MT1-MMP [membrane-type 1 MMP (matrix metalloproteinase); also known as MMP-14]. Furthermore, a cytokine known to mediate fibrosis in vivo, TGF-β1 (transforming growth factor-β1), is up-regulated in human PDAC tumours and can promote MT1-MMP expression. In the present review, we examine the regulation of PDAC progression through the interplay between type I collagen (the most common extracellular matrix present in human PDAC tumours), MT1-MMP and TGF-β1. Specifically, we examine the way in which signalling events through these pathways mediates invasion, regulates microRNAs and contributes to chemoresistance.

Canonical Wnt/β-catenin signaling mediates transforming growth factor-β1-driven podocyte injury and proteinuria

Transforming growth factor-β1 (TGF-β1) upregulation occurs in virtually all chronic kidney diseases and is associated with podocyte injury and proteinuria; however, the mechanisms contributing to this in vivo are ambiguous. In vitro, incubation of podocytes with TGF-β1 induced Wnt1 expression, β-catenin activation, and stimulated the expression of Wnt/β-catenin downstream target genes. Ectopic expression of Wnt1 or β-catenin mimicked TGF-β1, induced Snail1, and suppressed nephrin expression. The Wnt antagonist, Dickkopf-1, blocked TGF-β1-induced β-catenin activation, Snail1 induction, and nephrin suppression. In vivo, ectopic expression of TGF-β1 induced Wnt1 expression, activated β-catenin, and upregulated Wnt target genes such as Snail1, MMP-7, MMP-9, desmin, Fsp1, and PAI-1 in mouse glomeruli, leading to podocyte injury and albuminuria. Consistently, concomitant expression of Dickkopf-1 gene abolished β-catenin activation, inhibited TGF-β1-triggered Wnt target gene expression, and mitigated albuminuria. Thus, canonical Wnt/β-catenin signaling mediates TGF-β1-driven podocyte injury and proteinuria. These studies suggest that Wnt/β-catenin signaling may be exploited as a therapeutic target for the treatment of proteinuric kidney diseases.

An essential role for Pax8 in the transcriptional regulation of cadherin-16 in thyroid cells

Cadherin-16 was originally identified as a tissue-specific cadherin present exclusively in kidney. Only recently, Cadherin-16 has been detected also on the plasma membrane of mouse thyrocytes. This last finding prompted us to note that the expression profile of Cadherin-16 resembles that of the transcription factor Pax8, a member of the Pax (paired-box) gene family, predominantly expressed in the developing and adult kidney and thyroid. Pax8 has been extensively characterized in the thyroid and shown to be a master gene for thyroid development and differentiation. In this study, we determined the role of the transcription factor Pax8 in the regulation of Cadherin-16 expression. We demonstrate that the Cadherin-16 minimal promoter is transcriptionally active in thyroid cells as well as in kidney cells, that Pax8 is able to activate transcription from a Cadherin-16 promoter reporter construct, and more importantly, that indeed Pax8 is able to bind in vivo the Cadherin-16 promoter region. In addition, by means of Pax8 RNA interference in thyroid cells and by analyzing Pax8 null mice, we demonstrate that Pax8 regulates also in vivo the expression of Cadherin-16. Finally, we reveal that the expression of Cadherin-16 is TSH dependent in FRTL-5 thyroid cells and significantly reduced in mouse thyroid carcinomas. Therefore, we conclude that Cadherin-16 is a novel downstream target of the transcription factor Pax8, likely since the early steps of thyroid development, and that its expression is associated with the fully differentiated state of the thyroid cell.

Cellular and molecular mechanisms of renal fibrosis

Renal fibrosis, particularly tubulointerstitial fibrosis, is the common final outcome of almost all progressive chronic kidney diseases. Renal fibrosis is also a reliable predictor of prognosis and a major determinant of renal insufficiency. Irrespective of the initial causes, renal fibrogenesis is a dynamic and converging process that consists of four overlapping phases: priming, activation, execution and progression. Nonresolving inflammation after a sustained injury sets up the fibrogenic stage (priming) and triggers the activation and expansion of matrix-producing cells from multiple sources through diverse mechanisms, including activation of interstitial fibroblasts and pericytes, phenotypic conversion of tubular epithelial and endothelial cells and recruitment of circulating fibrocytes. Upon activation, matrix-producing cells assemble a multicomponent, integrin-associated protein complex that integrates input from various fibrogenic signals and orchestrates the production of matrix components and their extracellular assembly. Multiple cellular and molecular events, such as tubular atrophy, microvascular rarefaction and tissue hypoxia, promote scar formation and ensure a vicious progression to end-stage kidney failure. This Review outlines our current understanding of the cellular and molecular mechanisms of renal fibrosis, which could offer novel insights into the development of new therapeutic strategies.

Mospd1, a new player in mesenchymal versus epidermal cell differentiation

Mospd1 codes for a small protein with unknown physiological function, which is part of a family of genes, including Mospd2 and Mospd3, defined by the presence of the major sperm protein domain and two transmembrane domains. This work characterizes the Mospd1 gene, the intracellular location of the protein and its expression in different mouse tissues and mesenchymal cell lines during differentiation. The role of Mospd1 in mesenchymal cellular differentiation was studied by siRNA knockdown experiments in mouse osteoblastic MC3T3-E1 cells. Transfection experiments of the targeted cDNA show MOSPD1 located in the endoplasmatic reticulum and in the Golgi apparatus. Removal of the last exon of the gene resulted in localization of the protein in the nucleus, which was attributed to a nuclear export sequence in the N-terminal part. In mouse tissues the gene was generally strongly expressed while mesenchymal tissues showed the highest expression. In mesenchymal cell lines Mospd1 mRNA was higher expressed in cells with advanced differentiation status. In osteoblastic, myoblastic, and adipocytic cell lines Mospd1 was up-regulated during differentiation. Genome-wide gene expression analysis after knockdown of Mospd1 by siRNA in MC3T3-E1 cells revealed a shift in the gene expression pattern from mesenchymal to epithelial genes featuring up-regulation of the epithelial cadherin Cdh1 and down-regulation of its inhibitors Snail1 and 2 and the mesenchymal cadherin Cdh11, suggesting a mesenchymal to epithelial transition. From these data we conclude that Mospd1 plays a pivotal role in the developmental regulation at the switch between mesenchymal and epithelial cells.

Contribution of epithelial-to-mesenchymal transition and cancer stem cells to pancreatic cancer progression

Pancreatic adenocarcinoma remains among the most lethal of human malignancies. Overall 5-y survival is less than 5%, and only 20% of patients presenting with localized disease amenable to surgical resection. Even in patients who undergo resection, long-term survival remains extremely poor. A major contributor to the aggressiveness of multiple cancers, and pancreatic cancer in particular, is the process of epithelial-to-mesenchymal transition (EMT). This review highlights the growing evidence of EMT in pancreatic cancer progression, focusing on the contribution of EMT to the development of cancer stem cells and on interaction of EMT with other pathways central to cancer progression, such as Hedgehog signaling, the K-ras oncogene, and transforming growth factor-beta (TGF-β). We will also discuss EMT-targeting agents currently in development and in clinical trials that may help to reduce the morbidity and mortality associated with pancreatic cancer.

Transcriptional networks in epithelial-mesenchymal transition

Backround

Epithelial-mesenchymal transition (EMT) changes polarized epithelial cells into migratory phenotypes associated with loss of cell-cell adhesion molecules and cytoskeletal rearrangements. This form of plasticity is seen in mesodermal development, fibroblast formation, and cancer metastasis.

Methods and Findings

Here we identify prominent transcriptional networks active during three time points of this transitional process, as epithelial cells become fibroblasts. DNA microarray in cultured epithelia undergoing EMT, validated in vivo, were used to detect various patterns of gene expression. In particular, the promoter sequences of differentially expressed genes and their transcription factors were analyzed to identify potential binding sites and partners. The four most frequent cis-regulatory elements (CREs) in up-regulated genes were SRY, FTS-1, Evi-1, and GC-Box, and RNA inhibition of the four transcription factors, Atf2, Klf10, Sox11, and SP1, most frequently binding these CREs, establish their importance in the initiation and propagation of EMT. Oligonucleotides that block the most frequent CREs restrain EMT at early and intermediate stages through apoptosis of the cells.

Conclusions

Our results identify new transcriptional interactions with high frequency CREs that modulate the stability of cellular plasticity, and may serve as targets for modulating these transitional states in fibroblasts.

Targeted inhibition of β-catenin/CBP signaling ameliorates renal interstitial fibrosis

Because fibrotic kidneys exhibit aberrant activation of β-catenin signaling, this pathway may be a potential target for antifibrotic therapy. In this study, we examined the effects of β-catenin activation on tubular epithelial-mesenchymal transition (EMT) in vitro and evaluated the therapeutic efficacy of the peptidomimetic small molecule ICG-001, which specifically disrupts β-catenin-mediated gene transcription, in obstructive nephropathy. In vitro, ectopic expression of stabilized β-catenin in tubular epithelial (HKC-8) cells suppressed E-cadherin and induced Snail1, fibronectin, and plasminogen activator inhibitor-1 (PAI-1) expression. ICG-001 suppressed β-catenin-driven gene transcription in a dose-dependent manner and abolished TGF-β1-induced expression of Snail1, PAI-1, collagen I, fibronectin, and α-smooth muscle actin (α-SMA). This antifibrotic effect of ICG-001 did not involve disruption of Smad signaling. In the unilateral ureteral obstruction model, ICG-001 ameliorated renal interstitial fibrosis and suppressed renal expression of fibronectin, collagen I, collagen III, α-SMA, PAI-1, fibroblast-specific protein-1, Snail1, and Snail2. Late administration of ICG-001 also effectively attenuated fibrotic lesions in obstructive nephropathy. In conclusion, inhibiting β-catenin signaling may be an effective approach to the treatment of fibrotic kidney diseases.

Epithelial-Mesenchymal Transition in tumor microenvironment

The epithelial to mesenchymal transition (EMT) plays crucial roles in the formation of the body plan and also in the tumor invasion process. In addition, EMT also causes disruption of cell-cell adherence, loss of apico-basal polarity, matrix remodeling, increased motility and invasiveness in promoting tumor metastasis. The tumor microenvironment plays an important role in facilitating cancer metastasis and may induce the occurrence of EMT in tumor cells. A large number of inflammatory cells infiltrating the tumor site, as well as hypoxia existing in a large area of tumor, in addition many stem cells present in tumor microenvironment, such as cancer stem cells (CSCs), mesenchymal stem cells (MSCs), all of these may be the inducers of EMT in tumor cells. The signaling pathways involved in EMT are various, including TGF-β, NF-κB, Wnt, Notch, and others. In this review, we discuss the current knowledge about the role of the tumor microenvironment in EMT and the related signaling pathways as well as the interaction between them.

The role of EMT in renal fibrosis

It is clear that the well-described phenomenon of epithelial-mesenchymal transition (EMT) plays a pivotal role in embryonic development, wound healing, tissue regeneration, organ fibrosis and cancer progression. EMTs have been classified into three subtypes based on the functional consequences and biomarker context in which they are encountered. This review will highlight findings on type II EMT as a direct contributor to the kidney myofibroblast population in the development of renal fibrosis, specifically in diabetic nephropathy, the signalling molecules and the pathways involved in type II EMT and changes in the expression of specific miRNA with the EMT process. These findings have provided new insights into the activation and development of EMT during disease processes and may lead to possible therapeutic interventions to suppress EMTs and potentially reverse organ fibrosis.

Snail involves in the transforming growth factor β1-mediated epithelial-mesenchymal transition of retinal pigment epithelial cells

Background

The proliferation of retinal pigment epithelium (RPE) cells resulting from an epithelial-mesenchymal transition (EMT) plays a key role in proliferative vitreoretinopathy (PVR), which leads to complex retinal detachment and the loss of vision. Genes of Snail family encode the zinc finger transcription factors that have been reported to be essential in EMT during embryonic development and cancer metastasis. However, the function of Snail in RPE cells undergoing EMT is largely unknown.

Principal Findings

Transforming growth factor beta(TGF-β)-1 resulted in EMT in human RPE cells (ARPE-19), which was characterized by the expected decrease in E-cadherin and Zona occludin-1(ZO-1) expression, and the increase in fibronectin and α-smooth muscle actin (α-SMA) expression, as well as the associated increase of Snail expression at both mRNA and protein levels. Furthermore, TGF-β1 treatment caused a significant change in ARPE-19 cells morphology, with transition from a typical epithelial morphology to mesenchymal spindle-shaped. More interestingly, Snail silencing significantly attenuated TGF-β1-induced EMT in ARPE-19 cells by decreasing the mesenchymal markers fibronectin and a-SMA and increasing the epithelial marker E-cadherin and ZO-1. Snail knockdown could effectively suppress ARPE-19 cell migration. Finally, Snail was activated in epiretinal membranes from PVR patients. Taken together, Snail plays very important roles in TGF-β-1-induced EMT in human RPE cells and may contribute to the development of PVR.

Significance

Snail transcription factor plays a critical role in TGF-β1-induced EMT in human RPE cells, which provides deep insight into the pathogenesis of human PVR disease. The specific inhibition of Snail may provide a new approach to treat and prevent PVR.

Chromatin-based mechanisms of renal epithelial differentiation

Successful regenerative renal medicine depends on understanding the molecular mechanisms by which diverse phenotypes of epithelial cells differentiate from metanephric mesenchyme to populate nephrons. Whereas many genes are maintained in a poised state within the population of pluripotent progenitors, specialized epithelial functions reflect the selective expression of a subset of genes and the repression of all others. Here we highlight some common mechanisms of cell differentiation and epigenetic regulation to discuss their implications for renal epithelial development, repair, and disease.

Transcriptional factors associated with epithelial-mesenchymal transition in choroidal neovascularization

PURPOSE

To investigate the transcriptional factors associated with epithelial-mesenchymal transition (EMT) in choroidal neovascularization (CNV) secondary to age-related macular degeneration (AMD).

METHODS

Paraffin sections of CNV obtained from patients with AMD (n = 12) were stained for transcriptional factors related to EMT, i.e., Snail, Slug, SIP1, and Twist. As a control, postmortem sections of ocular normal tissue were used. Furthermore, using a human retinal pigment epithelial (RPE) cell line (ARPE-19), reverse transcription-polymerase chain reaction (RT-PCR) and immunofluorescence microscopy were performed to explore the cellular localization and expression levels of EMT-associated transcriptional factors upon cytokine stimulation.

RESULTS

Of 12 specimens, 11 CNV tissues (91.6%) showed staining for Snail localized in cellular nuclei, particularly in those of RPE cells. Snail was strongly co-localized with α-smooth muscle antigen (SMA) in RPE cells. In contrast, postmortem human retina showed no Snail staining in RPE cells. Other transcriptional factors, Slug, Twist and SIP1 were not detected in CNV or normal human retina. In ARPE-19 cells, RT-PCR and immunofluorescence microscopy showed that Snail mRNA was upregulated by transforming growth factor (TGF)-β and VEGF stimulation. Furthermore, TGF-β induced relocalization of Snail to the nucleus in RPE cells.

CONCLUSIONS

The current data indicate that Snail is a major transcriptional factor for EMT changes of RPE cells in human CNV.

Hepatocyte-derived Snail1 propagates liver fibrosis progression

Chronic exposure of the liver to hepatotoxic agents initiates an aberrant wound healing response marked by proinflammatory, as well as fibrotic, changes, leading to compromised organ structure and function. In a variety of pathological states, correlative links have been established between tissue fibrosis and the expression of transcription factors associated with the induction of epithelial-mesenchymal cell transition (EMT) programs similar to those engaged during development. However, the role played by endogenously derived, EMT-associated transcription factors in fibrotic states in vivo remains undefined. Using a mouse model of acute liver fibrosis, we demonstrate that hepatocytes upregulate the expression of the zinc finger transcriptional repressor, Snail1, during tissue remodeling. Hepatocyte-specific ablation of Snail1 demonstrates that this transcription factor plays a key role in liver fibrosis progression in vivo by triggering the proximal genetic programs that control multiple aspects of fibrogenesis, ranging from growth factor expression and extracellular matrix biosynthesis to the ensuing chronic inflammatory responses that characterize this class of pathological disorders.

Epithelial-mesenchymal transition (EMT) in kidney fibrosis: fact or fantasy?

Epithelial-mesenchymal transition (EMT) has become widely accepted as a mechanism by which injured renal tubular cells transform into mesenchymal cells that contribute to the development of fibrosis in chronic renal failure. However, an increasing number of studies raise doubts about the existence of this process in vivo. Herein, we review and summarize both sides of this debate, but it is our view that unequivocal evidence supporting EMT as an in vivo process in kidney fibrosis is lacking.

Klotho inhibits transforming growth factor-beta1 (TGF-beta1) signaling and suppresses renal fibrosis and cancer metastasis in mice

Fibrosis is a pathological process characterized by infiltration and proliferation of mesenchymal cells in interstitial space. A substantial portion of these cells is derived from residing non-epithelial and/or epithelial cells that have acquired the ability to migrate and proliferate. The mesenchymal transition is also observed in cancer cells to confer the ability to metastasize. Here, we show that renal fibrosis induced by unilateral ureteral obstruction and metastasis of human cancer xenografts are suppressed by administration of secreted Klotho protein to mice. Klotho is a single-pass transmembrane protein expressed in renal tubular epithelial cells. The extracellular domain of Klotho is secreted by ectodomain shedding. Secreted Klotho protein directly binds to the type-II TGF-β receptor and inhibits TGF-β1 binding to cell surface receptors, thereby inhibiting TGF-β1 signaling. Klotho suppresses TGF-β1-induced epithelial-to-mesenchymal transition (EMT) responses in cultured cells, including decreased epithelial marker expression, increased mesenchymal marker expression, and/or increased cell migration. In addition to TGF-β1 signaling, secreted Klotho has been shown to inhibit Wnt and IGF-1 signaling that can promote EMT. These results have raised the possibility that secreted Klotho may function as an endogenous anti-EMT factor by inhibiting multiple growth factor signaling pathways simultaneously.

Identification of anchor genes during kidney development defines ontological relationships, molecular subcompartments and regulatory pathways

The development of the mammalian kidney is well conserved from mouse to man. Despite considerable temporal and spatial data on gene expression in mammalian kidney development, primarily in rodent species, there is a paucity of genes whose expression is absolutely specific to a given anatomical compartment and/or developmental stage, defined here as ‘anchor’ genes. We previously generated an atlas of gene expression in the developing mouse kidney using microarray analysis of anatomical compartments collected via laser capture microdissection. Here, this data is further analysed to identify anchor genes via stringent bioinformatic filtering followed by high resolution section in situ hybridisation performed on 200 transcripts selected as specific to one of 11 anatomical compartments within the midgestation mouse kidney. A total of 37 anchor genes were identified across 6 compartments with the early proximal tubule being the compartment richest in anchor genes. Analysis of minimal and evolutionarily conserved promoter regions of this set of 25 anchor genes identified enrichment of transcription factor binding sites for Hnf4a and Hnf1b, RbpJ (Notch signalling), PPARγ:RxRA and COUP-TF family transcription factors. This was reinforced by GO analyses which also identified these anchor genes as targets in processes including epithelial proliferation and proximal tubular function. As well as defining anchor genes, this large scale validation of gene expression identified a further 92 compartment-enriched genes able to subcompartmentalise key processes during murine renal organogenesis spatially or ontologically. This included a cohort of 13 ureteric epithelial genes revealing previously unappreciated compartmentalisation of the collecting duct system and a series of early tubule genes suggesting that segmentation into proximal tubule, loop of Henle and distal tubule does not occur until the onset of glomerular vascularisation. Overall, this study serves to illuminate previously ill-defined stages of patterning and will enable further refinement of the lineage relationships within mammalian kidney development.

Tubular nuclear accumulation of Snail and epithelial phenotypic changes in human myeloma cast nephropathy

The transcription factor Snail is an important repressor of E-cadherin gene expression. It plays a key role in the induction of epithelial-mesenchymal transition, an essential process important not only in embryonic development and tumor progression but also in organ fibrogenesis. We studied the expression of Snail by immunohistochemistry, along with several epithelial phenotypic changes suggestive of epithelial-mesenchymal transition, in 14 patients with multiple myeloma cast nephropathy. This nephropathy is characterized by a rapid progression toward fibrosis. As controls, we used normal kidneys and kidneys from patients displaying an idiopathic nephrotic syndrome, a syndrome unassociated with renal fibrosis. We discovered that, in all patients with multiple myeloma nephropathy, a drastic accumulation of Snail is seen in the nuclei from tubular epithelial cells showing epithelial phenotypic changes. In contrast, normal and idiopathic nephrotic syndrome kidneys did not exhibit either of these markers. Snail, a major player in the process of epithelial-to-mesenchymal transition, is highly expressed by tubular epithelial cells during multiple myeloma nephropathy. It is, therefore, a potential target to prevent multiple myeloma kidneys from fibrosing. Intranuclear accumulation of Snail is a characteristic in phenotypically altered tubular cells from multiple myeloma kidneys. The epithelial-mesenchymal transition pathway could, therefore, be involved in the rapid renal fibrogenesis observed in this setting.

Snail1 transcription factor is a critical mediator of hepatic stellate cell activation following hepatic injury

Following liver injury, the wound-healing process is characterized by hepatic stellate cell (HSC) activation from the quiescent fat-storing phenotype to a highly proliferative myofibroblast-like phenotype. Snail1 is a transcription factor best known for its ability to trigger epithelial-mesenchymal transition, to influence mesoderm formation during embryonic development, and to favor cell survival. In this study, we evaluated the expression of Snail1 in experimental and human liver fibrosis and analyzed its role in the HSC transdifferentiation process. Liver samples from patients with liver fibrosis and from mice treated by either carbon tetrachloride (CCl(4)) or thioacetamide (TAA) were evaluated for mRNA expression of Snail1. The transcription factor expression was investigated by immunostaining and real-time quantitative RT-PCR (qRT-PCR) on in vitro and in vivo activated murine HSC. Snail1 knockdown studies on cultured HSC and on CCl(4)-treated mice were performed by adenoviral delivery of short-hairpin RNA; activation-related genes were quantitated by real-time qRT-PCR and Western blotting. Snail1 mRNA expression resulted upregulated in murine experimental models of liver injury and in human hepatic fibrosis. In vitro studies showed that Snail1 is expressed by HSC and that its transcription is augmented in in vitro and in vivo activated HSC compared with quiescent HSC. At the protein level, we could observe the nuclear translocation of Snail1 in activated HSC. Snail1 knockdown resulted in the downregulation of activation-related genes both in vitro and in vivo. Our data support a role for Snail1 transcription factor in the hepatic wound-healing response and its involvement in the HSC transdifferentiation process.

Snail1 suppresses TGF-beta-induced apoptosis and is sufficient to trigger EMT in hepatocytes

Although TGF-β suppresses early stages of tumour development, it later contributes to tumour progression when cells become resistant to its suppressive effects. In addition to circumventing TGF-β-induced growth arrest and apoptosis, malignant tumour cells become capable of undergoing epithelial-to-mesenchymal transition (EMT), favouring invasion and metastasis. Therefore, defining the mechanisms that allow cancer cells to escape from the suppressive effects of TGF-β is fundamental to understand tumour progression and to design specific therapies. Here, we have examined the role of Snail1 as a suppressor of TGF-β-induced apoptosis in murine non-transformed hepatocytes, rat and human hepatocarcinoma cell lines and transgenic mice. We show that Snail1 confers resistance to TGF-β-induced cell death and that it is sufficient to induce EMT in adult hepatocytes, cells otherwise refractory to this transition upon exposure to TGF-β. Furthermore, we show that Snail1 silencing prevents EMT and restores the cell death response induced by TGF-β. As Snail1 is a known target of TGF-β signalling, our data indicate that Snail1 might transduce the tumour-promoting effects of TGF-β, namely the EMT concomitant with the resistance to cell death.