Progressive renal fibrosis in murine polycystic kidney disease: an immunohistochemical observation

The role of TGF-β and epithelial-to mesenchymal transition in diabetic nephropathy

Transforming Growth Factor-beta (TGF-β) is a pro-sclerotic cytokine widely associated with the development of fibrosis in diabetic nephropathy. Central to the underlying pathology of tubulointerstitial fibrosis is epithelial-to-mesenchymal transition (EMT), or the trans-differentiation of tubular epithelial cells into myofibroblasts. This process is accompanied by a number of key morphological and phenotypic changes culminating in detachment of cells from the tubular basement membrane and migration into the interstitium. Ultimately these cells reside as activated myofibroblasts and further exacerbate the state of fibrosis. A large body of evidence supports a role for TGF-β and downstream Smad signalling in the development and progression of renal fibrosis. Here we discuss a role for TGF-β as the principle effector in the development of renal fibrosis in diabetic nephropathy, focusing on the role of the TGF-β1 isoform and its downstream signalling intermediates, the Smad proteins. Specifically we review evidence for TGF-β1 induced EMT in both the proximal and distal regions of the nephron and describe potential therapeutic strategies that may target TGF-β1 activity.

Polycystic kidney disease: the complexity of planar cell polarity and signaling during tissue regeneration and cyst formation

Autosomal Dominant Polycystic Kidney Disease (ADPKD) is an inherited systemic disease with intrarenal cystogenesis as its primary characteristic. A variety of mouse models provided information on the requirement of loss of balanced polycystin levels for initiation of cyst formation, the role of proliferation in cystogenesis and the signaling pathways involved in cyst growth and expansion. Here we will review the involvement of different signaling pathways during renal development, renal epithelial regeneration and cyst formation in ADPKD, focusing on planar cell polarity (PCP) and oriented cell division (OCD). This will be discussed in context of the hypothesis that aberrant PCP signaling causes cyst formation. In addition, the role of the Hippo pathway, which was recently found to be involved in cyst growth and tissue regeneration, and well-known for regulating organ size control, will be reviewed. The fact that Hippo signaling is linked to PCP signaling makes the Hippo pathway a novel cascade in cystogenesis. The newly gained understanding of the complex signaling network involved in cystogenesis and disease progression, not only necessitates refining of the current hypothesis regarding initiation of cystogenesis, but also has implications for therapeutic intervention strategies. This article is part of a Special Issue entitled: Polycystic Kidney Disease.

Epithelial-mesenchymal transition in renal fibrosis - evidence for and against

Epithelial to mesenchymal transition (EMT) is a well established biological process in metazoan embryological development. Over the past 15 years, investigators have sought to establish whether EMT also occurs in renal epithelial cells, following kidney injury, and to show that the mesenchymal cells formed could give rise to myofibroblasts which populate the renal interstitium, causing fibrosis within it. There is no doubt that proximal tubular epithelial cells (PTECs) can undergo EMT in vitro in response to TGFβ-1 and other inflammatory stimuli. Moreover, the results of experiments with animal models of renal fibrosis and examination of biopsies from patients with chronic kidney disease have lent support to the hypothesis that EMT occurs in vivo. This review discusses some of the key evidence underlying that idea and summarises recent advances in understanding the molecular mechanism underlying the process. Early experiments using mice which were genetically engineered to mark PTECs with the LacZ gene to trace their fate following kidney injury provided evidence supporting the occurrence of EMT. Recently, however, cell lineage tracking experiments using the red fluorescent protein (RFP) as a high-resolution marker for cells of renal epithelial origin did not replicate this result; the interstitial space following kidney injury was devoid of RFP expressing cells, leading the investigators to reject the renal EMT hypothesis.

Epithelial-mesenchymal transition in renal fibrosis - evidence for and against

Epithelial to mesenchymal transition (EMT) is a well established biological process in metazoan embryological development. Over the past 15 years, investigators have sought to establish whether EMT also occurs in renal epithelial cells, following kidney injury, and to show that the mesenchymal cells formed could give rise to myofibroblasts which populate the renal interstitium, causing fibrosis within it. There is no doubt that proximal tubular epithelial cells (PTECs) can undergo EMT in vitro in response to TGFβ-1 and other inflammatory stimuli. Moreover, the results of experiments with animal models of renal fibrosis and examination of biopsies from patients with chronic kidney disease have lent support to the hypothesis that EMT occurs in vivo. This review discusses some of the key evidence underlying that idea and summarises recent advances in understanding the molecular mechanism underlying the process. Early experiments using mice which were genetically engineered to mark PTECs with the LacZ gene to trace their fate following kidney injury provided evidence supporting the occurrence of EMT. Recently, however, cell lineage tracking experiments using the red fluorescent protein (RFP) as a high-resolution marker for cells of renal epithelial origin did not replicate this result; the interstitial space following kidney injury was devoid of RFP expressing cells, leading the investigators to reject the renal EMT hypothesis.

Epithelial to mesenchymal transition as a biomarker in renal fibrosis: are we ready for the bedside?

Over the past two decades, the concept of the epithelial to mesenchymal transition (EMT) has been imported from embryology and oncology to fibrosis, particularly in the kidney. This interest in EMT in the context of renal fibrosis stems from observations of epithelial cells undergoing phenotypic changes reminiscent of fibroblasts. Whether EMT is actually a source of interstitial fibroblasts has been the subject of heated debate, and this controversy has caused physicians to neglect the value of EMT as a biomarker in renal fibrosis. In this review, we describe the evolution of the techniques used to detect EMT during fibrosing renal diseases, and what information they provide in the diagnosis of various renal diseases. Highlighting the great heterogeneity of these techniques and the need to standardize them, we warn against some misleading uses of EMT markers. We suggest using the association of vimentin and β-catenin for the diagnosis of EMT in renal pathology because it is both sensitive and prognostic, thus satisfying the properties required for a screening test. Finally, we discuss the potential interests to diagnose EMT for the comprehension of renal fibrosis and for clinical practice.

Two non-invasive GFR-estimation methods in rat models of polycystic kidney disease: 3.0 Tesla dynamic contrast-enhanced MRI and optical imaging

BACKGROUND

The aim of this study was the assessment of kidney morphology and glomerular filtration rate (GFR) in rat models of polycystic kidney disease and a healthy control group of Sprague-Dawley rats (SD rats). The performance of two non-invasive GFR estimation methods-3.0 Tesla magnetic resonance imaging (MRI) and optical imaging were investigated. Data of GFR assessment was compared to surrogate markers of kidney function and renal histology.

METHODS

Optical imaging of GFR was performed transcutaneously in a small animal imaging system with the fluorescent renal marker fluorescein-isothiocyanate-labelled-sinistrin. Morphologic and dynamic renal imaging was done on a clinical 3.0T MR scanner. Renal perfusion analysis was performed with a two-compartment filtration model.

RESULTS

The healthy SD rats showed physiological levels of creatinine and urea, indicating normal kidney function. These parameters were elevated in the small animal groups of polycystic kidney disease. For the calculation of perfusion and filtration parameters of kidney function in MRI, a 2D turbo FLASH sequence was performed and allowed to distinguish between normal GFR of healthy rats and reduced GFR of rats with polycystic kidney disease. Also, MRI GFR varied among two different rat strains of polycystic kidney disease, according to their status of renal function impairment. Optical imaging GFR confirmed higher GFR values in healthy rats compared to ill rats but did not show different results among the two rat strains of polycystic kidney disease. For this reason, MRI and optical imaging GFR estimation presented an intra-method bias.

CONCLUSIONS

Both non-invasive estimation methods of GFR, MRI and optical imaging, can differentiate between healthy rats and animals with limited kidney function. Furthermore, optical imaging, unlike MRI, seems to consider that disease progression with increase of renal polycystic deterioration does not correlate with decrease of GFR in the initial stage of compensatory hyperfiltration.

Scar wars: mapping the fate of epithelial-mesenchymal-myofibroblast transition

The hypothesis that epithelial-mesenchymal transition (EMT) might be a contributor to the accumulation of fibroblasts and myofibroblasts (MFs) in the kidney during fibrogenesis was postulated 15 years ago. This paradigm offered an elegant explanation of how the loss of epithelial functions is coupled to the gain of deleterious mesenchymal functions; for example, excessive matrix deposition. Moreover, it interpreted chronic kidney disease in a developmental context: because the tubular epithelium originates from the metanephric mesenchyme, EMT can be viewed as a dedifferentiation process in response to injury, which might serve healing or--if dysregulated--might facilitate fibrosis. Several observations support the role of EMT in renal fibrosis: (1) Tubular cells can transform to fibroblasts and MFs in vitro. (2) Histological 'snapshots' reveal the coexistence of epithelial and mesenchymal markers in transitioning tubular cells in fibrosis models and human kidney diseases. (3) Early lineage-tracing experiments detected mesenchymal markers in the genetically tagged epithelium. However, the paradigm has been recently challenged; new fate-mapping studies found no evidence for the expression of (myo)fibroblast markers in the epithelium during fibrogenesis. This review summarizes the key findings and caveats, aiming at a balanced view, which neither overestimates the role of the epithelium in MF generation nor denies the importance of epithelial plasticity in fibrogenesis.

Myofibroblast differentiation during fibrosis: role of NAD(P)H oxidases

Progression of fibrosis involves interstitial hypercellularity, matrix accumulation, and atrophy of epithelial structures, resulting in loss of normal function and ultimately organ failure. There is common agreement that the fibroblast/myofibroblast is the cell type most responsible for interstitial matrix accumulation and consequent structural deformations associated with fibrosis. During wound healing and progressive fibrotic events, fibroblasts transform into myofibroblasts acquiring smooth muscle features, most notably the expression of alpha-smooth muscle actin and synthesis of mesenchymal cell-related matrix proteins. In renal disease, glomerular mesangial cells also acquire a myofibroblast phenotype and synthesize the same matrix proteins. The origin of interstitial myofibroblasts during fibrosis is a matter of debate, where the cells are proposed to derive from resident fibroblasts, pericytes, perivascular adventitial, epithelial, and/or endothelial sources. Regardless of the origin of the cells, transforming growth factor-beta1 (TGF-β1) is the principal growth factor responsible for myofibroblast differentiation to a profibrotic phenotype and exerts its effects via Smad signaling pathways involving mitogen-activated protein kinase and Akt/protein kinase B. Additionally, reactive oxygen species (ROS) have important roles in progression of fibrosis. ROS are derived from a variety of enzyme sources, of which the nicotinamide adenine dinucleotide phosphate (NAD(P)H) oxidase family has been identified as a major source of superoxide and hydrogen peroxide generation in the cardiovasculature and kidney during health and disease. Recent evidence indicates that the NAD(P)H oxidase homolog Nox4 is most accountable for ROS-induced fibroblast and mesangial cell activation, where it has an essential role in TGF-β1 signaling of fibroblast activation and differentiation into a profibrotic myofibroblast phenotype and matrix production. Information on the role of ROS in mesangial cell and fibroblast signaling is incomplete, and further research on myofibroblast differentiation during fibrosis is warranted.

Tissue-engineered three-dimensional in vitro models for normal and diseased kidney

Morphogenesis of epithelial cells involves processes by which kidney shape and function are regulated. The lack of in vitro models that are sustainable for longer time periods and emulating complex intercellular interactions of the kidney have limited understanding about epithelial tissue morphogenesis and its aberrations in diseases such as autosomal dominant polycystic kidney disease (ADPKD). A sustainable three-dimensional (3D) coculture system for normal and diseased kidney tissues is reported here. Tubule- and ADPKD cyst-derived cells were cultured in extracellular matrix molecules infused into 3D porous silk scaffolds, and these cultures were subsequently extended into a perfusion bioreactor. The results indicated collagen-matrigel-mediated morphogenesis for both (normal and disease) cell types and also supported coculturing with fibroblasts. The structural and functional features of the kidney-like tissue structures were validated based on the distribution of E-cadherin, N-cadherin, Na+ K+ ATPase pump, and cellular uptake of the organic anion (6-carboxy fluorescein). Further, the structures were sustained for longer time periods using a perfusion bioreactor to demonstrate the potential utility of this 3D in vitro coculture system for ADPKD research, other epithelial tissue systems, and for in vitro drug screening.

Abnormal fibrillin-1 expression and chronic oxidative stress mediate endothelial mesenchymal transition in a murine model of systemic sclerosis

Systemic sclerosis (SSc) is an autoimmune connective tissue disorder characterized by oxidative stress, impaired vascular function, and attenuated angiogenesis. The tight-skin (Tsk(-/+)) mouse is a model of SSc that displays many of the cellular features of the clinical disease. We tested the hypotheses that abnormal fibrillin-1 expression and chronic phospholipid oxidation occur in Tsk(-/+) mice and, furthermore, that these factors precipitate a prooxidant state, collagen-related protein expression, apoptosis, and mesenchymal transition in endothelial cells cultured on Tsk(-/+) extracellular matrix. Human umbilical vein endothelial cells were seeded on microfibrils isolated from skin of C57BL/6J (control) and Tsk(-/+) mice in the presence or absence of chronic pretreatment with the apolipoprotein Apo A-I mimetic D-4F (1 mg·kg(-1)·day(-1) ip for 6 to 8 wk). Nitric oxide-to-superoxide anion ratio was assessed 12 h after culture, and cell proliferation, apoptosis, and phenotype were studied 72 h after culture. Tsk(-/+) mice demonstrated abnormal "big fibrillin" expression (405 kDa) by Western blot analysis compared with control. Endothelial cells cultured on microfibrils prepared from Tsk(-/+) mice demonstrated reduced proliferation, a prooxidant state (reduced nitric oxide-to-superoxide anion ratio), increased apoptosis, and collagen-related protein expression associated with mesenchymal transition. Chronic D-4F pretreatment of Tsk(-/+) mice attenuated many of these adverse effects. The findings demonstrate that abnormal fibrillin-1 expression and chronic oxidative stress mediate endothelial mesenchymal transition in Tsk(-/+) mice. This mesenchymal transition may contribute to the reduction in angiogenesis that is known to occur in this model of SSc.

Epithelial-to-mesenchymal transition in cyst lining epithelial cells in an orthologous PCK rat model of autosomal-recessive polycystic kidney disease

In polycystic kidney disease (PKD), cyst lining cells show polarity abnormalities. Recent studies have demonstrated loss of cell contact in cyst cells, suggesting induction of epithelial-to-mesenchymal transition (EMT). Recently, EMT has been implicated in the pathogenesis of PKD. To explore further evidence of EMT in PKD, we examined age- and segment-specific expression of adhesion molecules and mesenchymal markers in PCK rats, an orthologous model of human autosomal-recessive PKD. Kidneys from 5 male PCK and 5 control rats each at 0 days, 1, 3, 10, and 14 wk, and 4 mo of age were serially sectioned and stained with segment-specific markers and antibodies against E-cadherin, Snail1, β-catenin, and N-cadherin. mRNAs for E-cadherin and Snail1 were quantified by real-time PCR. Vimentin, fibronectin, and α-smooth muscle actin (α-SMA) expressions were assessed as mesenchymal markers. E-cadherin expression pattern was correlated with the disease pathology in that tubule segments showing the highest expression in control had much severer cyst formation in PCK rats. In PCK rats, E-cadherin and β-catenin in cystic tubules was attenuated and localized to lateral areas of cell-cell contact, whereas nuclear expression of Snail1 increased in parallel with cyst enlargement. Some epithelial cells in large cysts derived from these segments, especially in adjacent fibrotic areas, showed positive immunoreactivity for vimentin and fibronectin. In conclusion, these findings suggest that epithelial cells in cysts acquire mesenchymal features in response to cyst enlargement and participate in progressive renal fibrosis. Our study clarified the nephron segment-specific cyst profile related to EMT in PCK rats. EMT may play a key role in polycystic kidney disease.

Mechanisms of tubulointerstitial fibrosis

The pathologic paradigm for renal progression is advancing tubulointerstitial fibrosis. Whereas mechanisms underlying fibrogenesis have grown in scope and understanding in recent decades, effective human treatment to directly halt or even reverse fibrosis remains elusive. Here, we examine key features mediating the molecular and cellular basis of tubulointerstitial fibrosis and highlight new insights that may lead to novel therapies. How to prevent chronic kidney disease from progressing to renal failure awaits even deeper biochemical understanding.

Fibroblast expression of an IκB dominant-negative transgene attenuates renal fibrosis

It is not clear whether interstitial fibroblasts or tubular epithelial cells are primarily responsible for the profibrotic effects of NF-κB activation during renal fibrogenesis. Here, we crossed mice carrying a conditional IκB dominant-negative transgene (IκBdN) with mice transgenic for cell-specific FSP1.Cre (FSP1(+) fibroblasts) or γGT.Cre (proximal tubular epithelia) and challenged all progeny with unilateral ureteral obstruction. We determined NF-κB activation by nuclear localization of phosphorylated p65 ((p)p65) in renal tissues after 7 days. We observed inhibition of NF-κB activation in interstitial cells and tubular epithelia in obstructed kidneys of FSP1.Cre;IκBdN and γGT.Cre;IκBdN mice, respectively, compared with IκBdN controls (P < 0.05). Deposition of extracellular matrix, however, was significantly lower in the obstructed kidneys of FSP1.Cre;IκBdN mice but not in γGT.Cre;IκBdN mice (P < 0.05). In addition, levels of mRNA encoding the profibrotic PAI-1, fibronectin-EIIIA, and type I (α1) procollagen were significantly lower in obstructed kidneys of FSP1.Cre;IκBdN mice compared with γGT.Cre;IκBdN mice (P < 0.05). Taken together, these data support a profibrotic role for fibroblasts, but not proximal tubular epithelial cells, in modulating NF-κB activation during renal fibrogenesis.

Elevated TGFbeta-Smad signalling in experimental Pkd1 models and human patients with polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is a common inherited renal disease characterized by many fluid-filled cysts and interstitial fibrosis in the kidneys, leading to chronic renal failure. During cystogenesis the renal tubules undergo extensive structural alterations that are accompanied by altered cellular signalling, directly and/or indirectly regulated by the PKD1 and PKD2 proteins. Since transforming growth factor (TGF)-beta signalling modulates cell proliferation, differentiation, apoptosis, adhesion and migration of various cell types, we studied the activation of this signalling pathway in Pkd1-mutant mouse models at different stages of the disease. Therefore, we analysed expression of the TGFbeta-Smad signalling pathway and its target genes in different Pkd1 mutant mouse models in various stages of polycystic disease. Nuclear accumulation of P-Smad2 in cyst lining epithelial cells was not observed in the initiation phase but was observed at mild and more advanced stages of PKD. This coincides with mild fibrosis and increased mRNA levels of TGFbeta target genes, such as fibronectin, collagen type I, plasminogen activator inhibitor 1 and matrix metalloproteinase-2. At this stage many interstitial fibroblasts were found around cysts, which also showed nuclear localization for P-Smad2. However, bone morphogenetic protein (BMP) signalling, which can antagonize TGFbeta signalling, is not affected, since nuclear expression of P-Smad1/5/8 and expression of the BMP target gene, inhibitor of DNA binding/differential-1 (ID-1) is not altered compared to wild-type controls. Also, human kidneys with progressive ADPKD showed increased nuclear localization of P-Smad2, while in general expression of P-Smad1/5/8 was weak. These results exclude TGFbeta signalling at the initiation of cystogenesis, but indicate an important role during cyst progression and in fibrogenesis of progressive ADPKD.

S100A4 expression is increased in stricture fibroblasts from patients with fibrostenosing Crohn's disease and promotes intestinal fibroblast migration

Fibroblasts represent the key cell type in fibrostenosing Crohn's disease (FCD) pathogenesis. S100A4 is an EF-hand calcium-binding protein family member, implicated in epithelial-mesenchymal transition and as a marker of activated T lymphocytes and fibroblasts in chronic tissue remodeling. The aim of this study was to examine the expression profile of S100A4 in the resected ileum of patients with FCD. Mucosa, seromuscular explants, and transmural biopsies were harvested from diseased and proximal, macroscopically normal margins of ileocecal resections from patients with FCD. Samples were processed for histochemistry, immunohistochemistry, real-time RT-PCR, Western blotting, and transmission electron microscopy. Primary explant cultures of seromuscular fibroblasts were exposed to transforming growth factor (TGF)-beta1 (1 ng/ml), and S100A4 expression and scratch wound-healing activity were assessed at 24 h. CCD-18Co fibroblasts were transfected with S100A4 small interfering RNA, treated with TGF-beta1 (1 ng/ml) for 30 min or 24 h, and then assessed for S100A4 and Smad3 expression and scratch wound-healing activity. S100A4 expression was increased in stricture mucosa, in the lamina propria, and in CD3-positive intraepithelial CD3-positive T lymphocytes. Fibroblastic S100A4 staining was observed in seromuscular scar tissue. Stricture fibroblast explant culture showed significant upregulation of S100A4 expression. TGF-beta1 increased S100A4 expression in cultured ileal fibroblasts. In CCD-18Co fibroblasts, S100A4 small interfering RNA inhibited scratch wound healing and modestly inhibited Smad3 activation. S100A4 expression is increased in fibroblasts, as well as immune cells, in Crohn's disease stricture and induced by TGF-beta1. Results from knockdown experiments indicate a potential role for S100A4 in mediating intestinal fibroblast migration.

Resolved: EMT produces fibroblasts in the kidney

Epithelial-mesenchymal transition (EMT) is a mechanism for generating primitive mesenchymal cells during gastrulation or mobile tumor cells during cancer metastasis. For 15 years, EMT has also been viewed as a principal source of fibroblasts in tissue fibrosis. Because several recent studies question its role in fibrogenesis, it seems like a good time for debate.

Evidence for epithelial-mesenchymal transition in adult human pancreatic exocrine cells

It has been shown that adult pancreatic ductal cells can dedifferentiate and act as pancreatic progenitors. Dedifferentiation of epithelial cells is often associated with the epithelial-mesenchymal transition (EMT). In this study, we investigated the occurrence of EMT in adult human exocrine pancreatic cells both in vitro and in vivo. Cells of exocrine fraction isolated from the pancreas of brain-dead donors were first cultured in suspension for eight days. This led to the formation of spheroids, composed of a principal population of cells with duct-like phenotype. When cultivated in tissue culture-treated flasks, spheroid cells exhibited a proliferative capacity and coexpressed epithelial (cytokeratin7 and cytokeratin19) and mesenchymal (vimentin and alpha-smooth muscle actin) markers as well as marker of progenitor pancreatic cells (pancreatic duodenal homeobox factor-1) and surface markers of mesenchymal stem cells. The switch from E-cadherin to N-cadherin associated with Snail1 expression suggested that these cells underwent EMT. In addition, we showed coexpression of epithelial and mesenchymal markers in ductal cells of one normal adult pancreas and three type 2 diabetic pancreases. Some of the vimentin-positive cells were found to coexpress glucagon or amylase. These results point to the occurrence of EMT, which may take place on dedifferentiation of ductal cells during the regeneration or renewal of human pancreatic tissues.

Pathogenesis of tubulointerstitial fibrosis in chronic allograft dysfunction

The term chronic allograft nephropathy (CAN) was originally coined in 1991 to replace chronic rejection which was used too generalized. However, the revised Banff classification, published in 2007, eliminated the term CAN again because it was felt that the term was used too broadly and prevented the search for the underlying cause. Interstitial fibrosis and tubular atrophy are integral parts of chronic allograft dysfunction and represent in the new classification a separate entity with or without the identification of a specific etiology. Myofibroblasts are the key, albeit not exclusive, effector cells in renal fibrogenesis resulting in upregulated extracellular matrix synthesis and eventually in interstitial fibrosis. These cells are formed mainly by stimulation of resident interstitial fibroblasts but also by differentiation processes of periadventitial cells, bone marrow derived cells and by a process entitled epithelial mesenchymal transition (EMT) of tubular epithelial cells. EMT has been described by many groups to be of high prevalence in renal allograft dysfunction contributing to matrix accumulation and renal function deterioration. This is of particular interest because immunosuppressive therapy has differential effects on EMT with calcineurin inhibitors in particular inducing the process. Moreover, specific therapies inhibiting EMT have been applied in experimental studies although the effects of their application in chronic allograft dysfunction remain to be studied. At the same time, immunosuppression may interfere with physiologic clearance of myofibroblasts by apoptosis, explaining in part the high prevalence of interstitial fibrosis in allograft biopsies. The Fas system has been identified to be mainly responsible for this physiologic apoptosis in non-renal scarring models; however, its relevance for renal fibrosis and particular fibrosis in renal allograft dysfunction remains to be determined. These findings point to a cautious and individualized use of immunosuppressive therapy in patients with allografts and particular those with chronic allograft dysfunction not because of rejection processes. Protocols using CNI-free immunosuppression are interesting options to prevent fibrosis in chronic allograft dysfunction.

Rapamycin ameliorates PKD resulting from conditional inactivation of Pkd1

Aberrant activation of the mammalian target of rapamycin (mTOR) pathway occurs in polycystic kidney disease (PKD). mTOR inhibitors, such as rapamycin, are highly effective in several rodent models of PKD, but these models result from mutations in genes other than Pkd1 and Pkd2, which are the primary genes responsible for human autosomal dominant PKD. To address this limitation, we tested the efficacy of rapamycin in a mouse model that results from conditional inactivation of Pkd1. Mosaic deletion of Pkd1 resulted in PKD and replicated characteristic features of human PKD including aberrant mTOR activation, epithelial proliferation and apoptosis, and progressive fibrosis. Treatment with rapamycin was highly effective: It reduced cyst growth, preserved renal function, inhibited epithelial cell proliferation, increased apoptosis of cyst-lining cells, and inhibited fibrosis. These data provide in vivo evidence that rapamycin is effective in a human-orthologous mouse model of PKD.

Role of CX3C-chemokine CX3C-L/fractalkine expression in a model of slowly progressive renal failure

BACKGROUND

The chemokine/chemokine receptor pair CX(3)C-L/CX(3)C-R is suspected to play a role in renal fibrogenesis. The aim of this study was to investigate their function in an animal model of slowly progressive chronic renal failure.

METHODS

Functional data were analysed in folic acid nephropathy (FAN) at different time points (up to day 142 after induction). Immunostaining for CX(3)C-L, CD3, S100A4, collagen type I, fibronectin, alpha-smooth muscle actin, Tamm-horsfall protein, aquaporin 1 and 2 as well as quantitative real-time PCR (qRT-PCR) for CX(3)C-L, CX(3)C-R and fibroblast-specific protein 1 (FSP-1) were performed. Additionally, regulatory mechanisms and functional activity of CX(3)C-L in murine proximal and distal tubular epithelial cells as well as in fibroblasts were investigated.

RESULTS

CX(3)C-L/GAPDH ratio was upregulated in FAN 3.4-fold at day 7 further increasing up to 7.1-fold at day 106. The expression of mRNA CX(3)C-L correlated well with CX(3)C-R (R(2) = 0.96), the number of infiltrating CD3+ cells (R(2) = 0.60) and the degree of tubulointerstitial fibrosis (R(2) = 0.56) and moderately with FSP-1 (R(2) = 0.33). Interleukin-1beta, tumour necrosis factor-alpha, transforming growth factor-beta as well as the reactive oxygen species (ROS) H(2)O(2) were identified by qRT-PCR as inductors of CX(3)C-L/fractalkine (FKN) in tubular epithelial cells. Functionally, CX(3)C-L/FKN chemoattracts peripheral blood mononuclear cells, activates several aspects of fibrogenesis and induces the mitogen-activated protein kinases in renal fibroblasts.

CONCLUSIONS

In FAN, there is a good correlation between the expression of CX(3)C-L with markers of interstitial inflammation and fibrosis which may result from upregulation by pro-inflammatory and pro-fibrotic cytokines as well as by ROS in tubular epithelial cells. The FKN system may promote renal inflammation and renal fibrogenesis.

Epithelial-mesenchymal transition as a potential explanation for podocyte depletion in diabetic nephropathy

BACKGROUND

Depletion of glomerular podocytes is an important feature of progressive diabetic nephropathy. Although the most plausible explanation for this podocyte depletion is detachment from the glomerular basement membrane after cellular apoptosis, the mechanism is unclear. Fibroblast-specific protein 1 (FSP1; encoded by the S100A4 gene) is a member of the S100 family of calcium-binding proteins and is constitutively expressed in the cytoplasm of tissue fibroblasts or epithelial cells converted into fibroblasts by means of epithelial-mesenchymal transition.

STUDY DESIGN

Retrospective cross-sectional analysis.

SETTINGS & PARTICIPANTS

109 patients with type 2 diabetes mellitus, of whom 43 (39%) underwent kidney biopsy.

PREDICTOR

Clinical stage (4 categories) and histological grade (5 categories) of diabetic nephropathy.

OUTCOME

FSP1 expression in podocytes in urine and glomeruli in kidney biopsy specimens.

MEASUREMENTS

Immunohistochemistry, real-time polymerase chain reaction, and in situ hybridization.

RESULTS

38 of 109 patients (35%) were normoalbuminuric, 16 (15%) had microalbuminuria, 8 (7%) had macroalbuminuria, and 47 (43%) had decreased kidney function. Approximately 95% of podocytes in urine sediment were not apoptotic, and 86% expressed FSP1. The number of FSP1-positive podocytes in urine sediment was significantly larger in patients with macroalbuminuria than in those with normoalbuminuria (P = 0.03). Intraglomerular expression of FSP1 occurred almost exclusively in podocytes from patients with diabetes, and the number of FSP1-positive podocytes was larger in glomeruli showing diffuse mesangiopathy than in those showing focal mesangiopathy (P = 0.01). The number also was larger in glomeruli with nodular lesions than in those without nodular lesions (P < 0.001). FSP1-positive podocytes selectively expressed Snail1 and integrin-linked kinase, a known trigger for epithelial-mesenchymal transition.

LIMITATIONS

Nonrepresentative study population.

CONCLUSIONS

These results suggest that the appearance of FSP1 in podocytes of patients with diabetes is associated with more severe clinical and pathological findings of diabetic nephropathy, perhaps because of induction of podocyte detachment through epithelial-mesenchymal transition-like phenomena.

Biomarkers for epithelial-mesenchymal transitions

Somatic cells that change from one mature phenotype to another exhibit the property of plasticity. It is increasingly clear that epithelial and endothelial cells enjoy some of this plasticity, which is easily demonstrated by studying the process of epithelial-mesenchymal transition (EMT). Published reports from the literature typically rely on ad hoc criteria for determining EMT events; consequently, there is some uncertainty as to whether the same process occurs under different experimental conditions. As we discuss in this Personal Perspective, we believe that context and various changes in plasticity biomarkers can help identify at least three types of EMT and that using a collection of criteria for EMT increases the likelihood that everyone is studying the same phenomenon - namely, the transition of epithelial and endothelial cells to a motile phenotype.

TGF-beta mediated epithelial-mesenchymal transition in autosomal dominant polycystic kidney disease

PURPOSE

Recent studies have showed that epithelial-mesenchymal transition (EMT) is a key process of glomerular and tubulointerstitial pathology in many chronic kidney diseases. However, there are no data of EMT in humane autosomal dominant polycystic kidney disease (ADPKD).

PATIENTS AND METHODS

ADPKD kidneys (N = 5) with end stage renal disease (ESRD) and control kidneys (N = 4) were analyzed immnunohistochemically. We evaluated alpha-SMA, E-cadherin, vimentin, TGF-beta1 and Smad 2/3 expression in ADPKD and compared them with those in control kidney. These immunohistochemical findings were quantitatively analyzed by computer-assisted image analyzer and positive tubules (%).

RESULTS

There were severe interstitial fibrosis and proliferation of alpha-SMA+ myofibroblasts in ADPKD. Cystic tubular epithelial cells in ADPKD lost epithelial marker (E-cadherin) and expressed mesenchymal markers (alpha-SMA, vimentin). There were significant increases of alpha-SMA (34.3 +/- 11.7% vs 0.9 +/- 1.5%), vimentin (19.9 +/- 3.9% vs 3.3 +/- 1.4%), TGF-beta1 (5.42 +/- 2.83% vs 0%) and Smad 2/3 (3.4 +/- 1.7% vs 0.7 +/- 0.6%) in ADPKD kidneys compared with control kidneys evidenced by computer-assisted image analyzer. When we analyze the positive tubules (%), the results were the same as computer-assisted image analyzer.

CONCLUSION

Our results showed that the end stage of ADPKD is associated with TGF-beta, Smad 2/3 and markers of EMT. It suggests that TGF-beta mediated EMT has a role in progression of ADPKD.

Deletion of the alpha8 integrin gene does not protect mice from myocardial fibrosis in DOCA hypertension

BACKGROUND

In the heart, the alpha8 integrin chain is expressed in fibroblasts and vascular smooth-muscle cells but its functional role in the myocardium is unknown. Integrins can contribute to tissue fibrosis in several organs. We tested the hypothesis that alpha8 integrin-mediated cell-matrix interactions add to cardiac fibrotic alterations during hypertension.

METHODS

Desoxycorticosterone-acetate (DOCA)-salt hypertension was induced in mice homozygous for a deletion of the alpha8 integrin chain and wild-type mice. Histological and immunohistochemical evaluations were performed in heart tissue.

RESULTS

Blood pressure was slightly higher in DOCA-treated alpha8 integrin-deficient mice compared to DOCA-treated wild types. Expression of alpha8 integrin and its ligands fibronectin and osteopontin was increased in the hearts of DOCA-treated wild types compared to salt-loaded controls. However, relative left ventricular weights did not differ between DOCA-treated wild types and alpha8 integrin-deficient mice. Moreover, expansion of collagen I immunoreactivity and cell proliferation was similar in both groups. The number of osteopontin-positive cells was not different in DOCA-treated alpha8 integrin-deficient and DOCA-treated wild-type mice. Despite of a comparable degree of fibrosis in both groups, alpha-smooth-muscle actin and discoidin domain receptor 2 (DDR2)-positive myofibroblasts were only detected in wild-type DOCA-treated mice, not in DOCA-treated alpha8 integrin-deficient mice.

CONCLUSIONS

The results show that lack of alpha8 integrin does not reduce fibrotic changes in the hearts of DOCA-salt hypertensive mice. Our findings do not argue for a profibrotic effect of an increased alpha8 integrin expression in the myocardium in hypertension.

MKL1 mediates TGF-β1-induced α-smooth muscle actin expression in human renal epithelial cells

Transforming growth factor-β1 (TGF-β1) is known to induce epithelial-mesenchymal transition in the kidney, a process involved in tubulointerstitial fibrosis. We hypothesized that a coactivator of the serum response factor (SRF), megakaryoblastic leukemia factor-1 (MKL1), stimulates α-smooth muscle actin (α-SMA) transcription in primary cultures of renal tubular epithelial cells (RTC), which convert into myofibroblasts on treatment with TGF-β1. Herein, we study the effect of MKL1 expression on α-SMA in these cells. We demonstrate that TGF-β1 stimulation of α-SMA transcription is mediated through CC(A/T)6-rich GG elements known to bind to SRF. These elements also mediate the MKL1 effect that dramatically activates α-SMA transcription in serum-free media. MKL1 fused to green fluorescent protein localizes to the nucleus and induces α-SMA expression regardless of treatment with TGF-β1. Using proteasome inhibitors, we also demonstrate that the proteolytic ubiquitin pathway regulates MKL1 expression. These data indicate that MKL1 overexpression is sufficient to induce α-SMA expression. Inhibition of endogenous expression of MKL1 by small interfering RNA abolishes TGF-β1 stimulation of α-SMA expression. Therefore, MKL1 is also absolutely required for TGF-β1 stimulation of α-SMA expression. Western blot and immunofluorescence analysis show that overexpressed and endogenous MKL1 are located in the nucleus in non-stimulated RTC. Chromatin immunoprecipitation assay demonstrates that TGF-β1 induces binding of endogenous SRF and MKL1 to the α-SMA promoter in chromatin. Since MKL1 constitutes a potent factor regulating α-SMA expression, modulation of endogenous MKL1 expression or activity may have a profound effect on myofibroblast formation and function in the kidney.

Origin of renal myofibroblasts in the model of unilateral ureter obstruction in the rat

Tubulo-interstitial fibrosis is a constant feature of chronic renal failure and it is suspected to contribute importantly to the deterioration of renal function. In the fibrotic kidney there exists, besides normal fibroblasts, a large population of myofibroblasts, which are supposedly responsible for the increased production of intercellular matrix. It has been proposed that myofibroblasts in chronic renal failure originate from the transformation of tubular cells via epithelial–mesenchymal transition (EMT) or from infiltration by bone marrow-derived precursors. Little attention has been paid to the possibility of a transformation of resident fibroblasts into myofibroblasts in renal fibrosis. Therefore we examined the fate of resident fibroblasts in the initial phase of renal fibrosis in the classical model of unilateral ureter obstruction (UUO) in the rat. Rats were perfusion-fixed on days 1, 2, 3 and 4 after ligature of the right ureter. Starting from 1 day of UUO an increasing expression of alpha-smooth muscle actin (αSMA) in resident fibroblasts was revealed by immunofluorescence and confirmed by the observation of bundles of microfilaments and webs of intermediate filaments in the electron microscope. Inversely, there was a decreased expression of 5′-nucleotidase (5′NT), a marker of renal cortical fibroblasts. The RER became more voluminous, suggesting an increased synthesis of matrix. Intercellular junctions, a characteristic feature of myofibroblasts, became more frequent. The mitotic activity in fibroblasts was strongly increased. Renal tubules underwent severe regressive changes but the cells retained their epithelial characteristics and there was no sign of EMT. In conclusion, after ureter ligature, resident peritubular fibroblasts proliferated and they showed progressive alterations, suggesting a transformation in myofibroblasts. Thus the resident fibroblasts likely play a central role in fibrosis in that model.

S100A4: a common mediator of epithelial-mesenchymal transition, fibrosis and regeneration in diseases?

Multiple reports have focused on S100A4's role in cancer progression, specifically its ability to enhance metastasis. However, recent studies have linked S100A4 to several diseases besides cancer, including kidney fibrosis, cirrhosis, pulmonary disease, cardiac hypertrophy and fibrosis, arthritis and neuronal injuries. Common to all these diseases is the involvement of fibrotic and inflammatory processes, i.e. processes greatly dependent on tissue remodelling, cell motility and epithelial-mesenchymal transition. Therefore, the basic biological mechanisms behind S100A4's effects are emerging. S100A4 belongs to the S100 family of proteins that contain two Ca2+-binding sites including a canonical EF-hand motif. S100A4 is involved in the regulation of a wide range of biological effects including cell motility, survival, differentiation and contractility. S100A4 has both intracellular and extracellular effects. Hence, S100A4 interacts with cytoskeletal proteins and enhances metastasis of several types of cancer cells. In addition, S100A4 is secreted by unknown mechanisms, thus, paracrinely stimulating a variety of cellular responses, including angiogenesis and neuronal growth. Although many cellular effects of S100A4 are well described, the molecular mechanisms whereby S100A4 elicits these responses remain largely unknown. However, it is likely that the intracellular and the extracellular effects involve distinct mechanisms. In this review, we explore the possible roles of S100A4 in non-cancer diseases and employ this knowledge to describe underlying biological mechanisms including a change in cellular phenotype towards less tightly adherent cells and activation of fibrotic processes that may explain this protein's involvement in multiple pathologies.

Polycystic kidney disease and renal injury repair: common pathways, fluid flow, and the function of polycystin-1

The root cause for most cases of autosomal-dominant polycystic kidney disease (ADPKD) is mutations in the polycystin-1 (PC1) gene. While PC1 has been implicated in a perplexing variety of protein interactions and signaling pathways, what its normal function is and why its disruption leads to the proliferation of renal epithelial cells are unknown. Recent results suggest that PC1 is involved in mechanotransduction by primary cilia measuring the degree of luminal fluid flow. PC1 has also recently been shown to regulate the mTOR and signal transducers and activators of transcription (STAT) 6 pathways. These two pathways are normally dormant in the healthy kidney but are activated in response to injury and appear to drive a proliferative repair response. This review develops the idea that a critical function of PC1 and primary cilia in the adult kidney may be to sense renal injury by detecting changes in luminal fluid flow and to trigger proliferation. Constitutive activation of these pathways in ADPKD would lead to the futile attempt to repair a nonexisting injury, resulting in cyst growth. The existence of many known cellular and molecular similarities between renal repair and ADPKD supports this model.

TGF-beta-induced EMT: mechanisms and implications for fibrotic lung disease

Epithelial-mesenchymal transition (EMT), a process whereby fully differentiated epithelial cells undergo transition to a mesenchymal phenotype giving rise to fibroblasts and myofibroblasts, is increasingly recognized as playing an important role in repair and scar formation following epithelial injury. The extent to which this process contributes to fibrosis following injury in the lung is a subject of active investigation. Recently, it was demonstrated that transforming growth factor (TGF)-beta induces EMT in alveolar epithelial cells (AEC) in vitro and in vivo, and epithelial and mesenchymal markers have been colocalized to hyperplastic type II (AT2) cells in lung tissue from patients with idiopathic pulmonary fibrosis (IPF), suggesting that AEC may exhibit extreme plasticity and serve as a source of fibroblasts and/or myofibroblasts in lung fibrosis. In this review, we describe the characteristic features of EMT and its mechanistic underpinnings. We further describe the contribution of EMT to fibrosis in adult tissues following injury, focusing especially on the critical role of TGF-beta and its downstream mediators in this process. Finally, we highlight recent descriptions of EMT in the lung and the potential implications of this process for the treatment of fibrotic lung disease. Treatment for fibrosis of the lung in diseases such as IPF has heretofore focused largely on amelioration of potential inciting processes such as inflammation. It is hoped that this review will stimulate further consideration of the cellular mechanisms of fibrogenesis in the lung and especially the role of the epithelium in this process, potentially leading to innovative avenues of investigation and treatment.

Loss of GLIS2 causes nephronophthisis in humans and mice by increased apoptosis and fibrosis

Nephronophthisis (NPHP), an autosomal recessive kidney disease, is the most frequent genetic cause of end-stage renal failure in the first three decades of life. Positional cloning of the six known NPHP genes has linked its pathogenesis to primary cilia function. Here we identify mutation of GLIS2 as causing an NPHP-like phenotype in humans and mice, using positional cloning and mouse transgenics, respectively. Kidneys of Glis2 mutant mice show severe renal atrophy and fibrosis starting at 8 weeks of age. Differential gene expression studies on Glis2 mutant kidneys demonstrate that genes promoting epithelial-to-mesenchymal transition and fibrosis are upregulated in the absence of Glis2. Thus, we identify Glis2 as a transcription factor mutated in NPHP and demonstrate its essential role for the maintenance of renal tissue architecture through prevention of apoptosis and fibrosis.

Mechanisms of disease: Fibroblasts--a new look at an old problem

Fibroblasts are one of the most important and episodically active cell types in the kidney. Under normal conditions, these cells provide a delicate collagenous matrix that partitions the interstitial spaces between nephrons, blood vessels and the renal capsule. Fibroblasts also remodel the interstitium as kidneys grow with age. This episodic activity of various fibroblast populations has a biological basis. Most fibroblasts are created locally through a process called epithelial-mesenchymal transition (EMT) and, once formed, they can proliferate in response to local mitogens. EMT is driven by an alteration in the balance of local cytokine concentrations that reverses the differentiation of selected epithelia along tubular nephrons. During persistent injury and inflammation, fibroblasts further increase their numbers and secrete excess interstitial collagens, and EMT is particularly aggressive in this setting. The mechanisms by which fibroblasts simultaneously destroy normal interstitial architecture and disable epithelial nephrons are more comprehensible today. Recent therapeutic clues for attenuating fibroblast formation during renal fibrogenesis also suggest an advantage in shifting local cytokine balance to favor mesenchymal-epithelial transition. This review examines these issues and identifies new targets for the treatment of one of the most difficult problems facing clinical nephrology.

Smooth muscle alpha-actin deficiency in myofibroblasts leads to enhanced renal tissue fibrosis

Myofibroblasts are a major source of proinflammatory cytokines and extracellular matrix in progressive tissue fibrosis leading to chronic organ failure. Myofibroblasts are characterized by de novo expression of smooth muscle alpha-actin (SMalphaA), which correlates with the extent of disease progression, although their exact role is unknown. In vitro cultured myofibroblasts from kidney of SMalphaA knock-out mice demonstrate significantly more prominent cell motility, proliferation, and type-I procollagen expression than those of wild-type myofibroblasts. These pro-fibrotic properties are suppressed by adenovirus-mediated SMalphaA re-expression, accompanied by down-regulation of focal adhesion proteins. In interstitial fibrosis model, tissue fibrosis area, proliferating interstitial cell number, and type-I procollagen expression are enhanced under SMalphaA deficiency. In mesangioproliferative glomerulonephritis model, cell proliferation in the mesangial area is also enhanced in SMalphaA knock-out mice. Adenoviral SMalphaA introduction into renal interstitium obviously ameliorates tissue fibrosis in interstitial fibrosis model. These results indicate that SMalphaA suppresses the pro-fibrotic properties of myofibroblasts, highlighting the significance of smooth muscle-related proteins in moderating chronic organ fibrosis under pathological conditions.

Cardiac fibroblasts: friend or foe?

Cardiac function is determined by the dynamic interaction of various cell types and the extracellular matrix that composes the heart. This interaction varies with the stage of development and the degree and duration of mechanical, chemical, and electrical signals between the various cell types and the ECM. Understanding how these complex signals interact at the molecular, cellular, and organ levels is critical to understanding the function of the heart under a variety of physiological and pathophysiological conditions. Quantitative approaches, both in vivo and in vitro, are essential to understand the dynamic interaction of mechanical, chemical, and electrical stimuli that govern cardiac function. The fibroblast can thus be a friend in normal function or a foe in pathophysiological conditions.

Recapitulation of Embryological Programmes in Renal Fibrosis – The Importance of Epithelial Cell Plasticity and Developmental Genes

Chronic fibrosis represents the final common pathway in progressive renal disease. Myofibroblasts deposit the constituents of renal scar, thus crippling renal function. It has recently emerged that an important source of these pivotal effector cells is the injured renal epithelium. This review concentrates on the process of epithelial-mesenchymal transition (EMT) and its regulation. The role of the developmental gene, gremlin, which is reactivated in adult renal disease, is the subject of particular focus. This member of the cysteine knot protein superfamily is critical to the process of nephrogenesis but quiescent in normal adult kidney. There is increasing evidence that gremlin expression reactivates in diabetic nephropathy, and in the diseased fibrotic kidney per se. Known to antagonize members of the bone morphogenic protein (BMP) family, gremlin may also act downstream of TGF-beta in induction of EMT. An increased understanding of the extracellular modulation of EMT and, in particular, of the gremlin-BMP axis may result in strategies that can halt or reverse the devastating progression of chronic renal fibrosis.

Fibroblast-specific protein 1 is a specific prognostic marker for renal survival in patients with IgAN

BACKGROUND

There is little direct evidence that fibroblasts are involved in the progression of the renal interstitial fibrosis in human glomerulonephritis. With the availability of a new specific marker for fibroblasts, we determined the presence of fibroblasts in kidneys with IgA nephropathy (IgAN) and correlated their numbers with various clinical parameters. In particular, we also prospectively asked if the number of fibroblasts in the renal interstitium correlates with prognosis.

METHODS

Cells positive for fibroblast-specific protein 1 (FSP1) were localized in renal biopsy specimens using immunohistochemistry with anti-FSP1 antibody. Clinical features were analyzed by one-way analysis of variance (ANOVA) with the Bonferroni correction. To assess the prognostic impact of the number of FSP1+ fibroblasts on renal survival in 142 patients with normal serum creatinine, the relationship between covariates to renal survival were evaluated univariately using the log-rank test and multivariately using Cox proportional hazards.

RESULTS

Fibroblasts identified by their expression of FSP1 accumulate in areas showing severe interstitial fibrosis. Some tubular epithelial cells undergoing epithelial-mesenchymal transition (EMT) in fibrotic areas also express FSP1. Numbers of FSP1+ fibroblasts directly correlate with serum creatinine (r = 0.74, P < 0.0001) and inversely correlate with estimated creatinine clearance (r = -0.54, P < 0.0001), and by multivariate analysis, the clinical factors influencing renal survival are urinary protein excretion [> or = 1.0 g/day, relative risk (RR) = 4.20, P= 0.032], hypertension (RR 5.85, P = 0.0027), and > or = 20 FSP1+ fibroblasts per high power field (HPF) (RR 7.39, P = 0.0015). Staining for FSP1+ fibroblasts is largely nonoverlapping with alpha-smooth muscle actin+ (alpha-SMA) cells in the interstitium.

CONCLUSION

The target protein FSP1 identifies human fibroblasts and tubular epithelium undergoing EMT, and distinguishes them from the diaspora of alpha-SMA+ vascular smooth muscle cells. FSP1+ fibroblasts are critically related to the progression of IgAN; consequently, staining FSP1 in renal biopsy specimens provides a valuable histologic index of progression.

Histogenesis of human renal cell carcinoma by using electron microscopy and immunohistochemical techniques

Electron microscopy and immunohistochemical techniques are powerful tools for the determination of tissue origin. Both techniques have been used in the current experiment for histogenesis of renal cell carcinoma. Fifty kidney tumors were subjected to immunohistochemical detection for intermediate filaments cytokeratin and vimentin, which are normally expressed in epithelial tissue and mesenchymal tissues, respectively. Twenty cases of the above were examined by electron microscopy for detection of ultrastructure features. From each kidney, two specimens were taken, one from the diseased area and another far from it to serve as a control. Immunohistochemical study revealed in cases of renal cell carcinoma, cytokeratin and vimentin were expressed alone in 44% of cases, and 40% of cases, respectively. Twelve percent of cases were coexpressed with both cytokeratin and vimentin. Electron microscopic study of diseased specimens revealed the expression of desmosomes which was observed in almost all tumor specimens. The expression of the vimentin in some cases either alone or with cytokeratin was interpreted as a change in the characters of some tumor cells which indicates the need for additional techniques in such cases to get the proper interpretation. The prevalence of the expression of cytokeratin and the persistence existence of desmosomes indicate the epithelial origin of the tumor. This data is very beneficial for determination of line of therapy and follow up of the patients. The results confirm the power of combined use of both immunohistochemistry and electron microscopy in the field of histogenesis.

Antibodies against macrophages that overlap in specificity with fibroblasts

BACKGROUND

Fibroblasts can be misidentified as macrophages because both cell types share antigens that are associated with popular antibodies targeting the monocyte/macrophage lineage. With the recent description of fibroblast-specific protein 1 (FSP1), we revisited the specificity of antibodies directed against macrophages to determine systematically which antibodies best distinguish both cell types in fibrotic tissues.

METHODS

Tissue fibrosis was produced in mice carrying the GFP transgene encoding green fluorescent protein under the control of the FSP1 promoter. Single cell suspensions from these marked tissues were submitted for flow cytometry using antibodies against Mac-1, Mac-2, Mac-3, F4/80, CD68, major histocompatibility complex (MHC) class II, and CD45, and cDNA amplification of mRNA encoding the above target antigens was performed using specific primer sets in sorted pools of cells. Fibrotic tissues were also stained by immunohistochemistry with the same antibodies and examined under confocal microscopy.

RESULTS

Comparison overlap between FSP1(+) fibroblasts with each of the macrophage markers demonstrated that all antimacrophage antibodies (Mac-1, Mac-2, Mac-3, CD68, MHC class II, and CD45) except one (F4/80) recognize both cell types.

CONCLUSION

Antibodies directed against F4/80 clearly distinguish macrophages from FSP1(+) fibroblasts in fibrotic tissues and is the preferred antibody in mice.

The cardiac fibroblast: therapeutic target in myocardial remodeling and failure

Cardiac fibroblasts play a central role in the maintenance of extracellular matrix in the normal heart and as mediators of inflammatory and fibrotic myocardial remodeling in the injured and failing heart. In this review, we evaluate the cardiac fibroblast as a therapeutic target in heart disease. Unique features of cardiac fibroblast cell biology are discussed in relation to normal and pathophysiological cardiac function. The contribution of cardiac fibrosis as an independent risk factor in the outcome of heart failure is considered. Candidate drug therapies that derive benefit from actions on cardiac fibroblasts are summarized, including inhibitors of angiotensin-aldosterone systems, endothelin receptor antagonists, statins, anticytokine therapies, matrix metalloproteinase inhibitors, and novel antifibrotic/anti-inflammatory agents. These findings point the way to future challenges in cardiac fibroblast biology and pharmacotherapy.

Characterization of renal interstitial fibroblast-specific protein 1/S100A4-positive cells in healthy and inflamed rodent kidneys

Fibrosis is considered as a central factor in the loss of renal function in chronic kidney diseases. The origin of fibroblasts and myofibroblasts that accumulate in the interstitium of the diseased kidney is still a matter of debate. It has been shown that accumulation of myofibroblasts in inflamed and fibrotic kidneys is associated with upregulation of fibroblast-specific protein 1 (FSP1, S100A4), not only in the renal interstitium but also in the injured renal epithelia. The tubular expression of FSP1 has been taken as evidence of myofibroblast formation by epithelial-mesenchymal transition (EMT). The identity of FSP1/S100A4 cells has not been defined in detail. We originally intended to use FSP1/S100A4 as a marker of putative EMT in a model of distal tubular injury. However, since the immunoreactivity of FSP1 did not seem to fit with the distribution and shape of fibroblasts or myofibroblasts, we undertook the characterization of FSP1/S100A4-expressing cells in the interstitium of rodent kidneys. We performed immunolabeling for FSP1/S100A4 on thin cryostat sections of perfusion-fixed rat and mouse kidneys with peritubular inflammation, induced by thiazides and glomerulonephritis, respectively, in combination with ecto-5'-nucleotidase (5'NT), recognizing local cortical peritubular fibroblasts, with CD45, MHC class II, CD3, CD4 and Thy 1, recognizing mononuclear cells, with alpha smooth muscle actin (alphaSMA), as marker for myofibroblasts, and vimentin for intracellular intermediate filaments in cells of mesenchymal origin. In the healthy interstitium of rodents the rare FSP1/S100A4+ cells consistently co-expressed CD45 or lymphocyte surface molecules. Around the injured distal tubules of rats treated for 3-4 days with thiazides, FSP1+/S100A4+, 5'NT+, alphaSMA+, CD45+ and MHC class II+ cells accumulated. FSP1+/S100A4+ cells consistently co-expressed CD45. In the inflamed regions, alphaSMA was co-expressed by 5'NT+ cells. In glomerulonephritic mice, FSP1+/S100A4+ cells co-expressed Thy 1, CD4 or CD3. Thus, in the inflamed interstitium around distal tubules of rats and of glomerulonephritic mice, the majority of FSP1+ cells express markers of mononuclear cells. Consequently, the usefulness of FSP1/S100A4 as a tool for detection of (myo)fibroblasts in inflamed kidneys and of EMT in vivo is put into question. In the given rat model the consistent co-expression of alphaSMA and 5'NT suggests that myofibroblasts originate from resident peritubular fibroblasts.

Portal fibroblasts regulate the proliferation of bile duct epithelia via expression of NTPDase2

Bile duct epithelia are the target of a number of "cholangiopathies" characterized by disordered bile ductular proliferation. Although mechanisms for bile ductular proliferation are unknown, recent evidence suggests that extracellular nucleotides regulate cell proliferation via activation of P2Y receptors. Portal fibroblasts may regulate bile duct epithelial P2Y receptors via expression of the ecto-nucleotidase NTPDase2. Thus, we tested the hypothesis that portal fibroblasts regulate bile duct epithelial proliferation via expression of NTPDase2. We generated a novel co-culture model of Mz-ChA-1 human cholangiocarcinoma cells and primary portal fibroblasts. Cell proliferation was measured by bromodeoxyuridine uptake. NTPDase2 expression was assessed by immunofluorescence and quantitative real-time reverse transcription PCR. NTPDase2 expression in portal fibroblasts was blocked using short interfering RNA. NTPDase2 overexpression in portal myofibroblasts isolated from bile duct-ligated rats was achieved by cDNA transfection. Co-culture of Mz-ChA-1 cells with portal fibroblasts decreased their proliferation to 26% of control. Similar decreases in Mz-ChA-1 proliferation were induced by the soluble ecto-nucleotidase apyrase and the P2 receptor inhibitor suramin. The proliferation of Mz-ChA-1 cells returned to baseline when NTPDase2 expression in portal fibroblasts was inhibited using NTPDase2-specific short interfering RNA. Untransfected portal myofibroblasts lacking NTPDase2 had no effect on Mz-ChA-1 proliferation, yet portal myofibroblasts transfected with NTPDase2 cDNA inhibited Mz-ChA-1 proliferation. We conclude that portal fibroblasts inhibit bile ductular proliferation via expression of NTPDase2 and blockade of P2Y activation. Loss of NTPDase2 may mediate the bile ductular proliferation typical of obstructive cholestasis. This novel cross-talk signaling pathway may mediate pathologic alterations in bile ductular proliferation in other cholangiopathic conditions.

Characterization of fibroblast-specific protein 1 in pulmonary fibrosis

Because fibroblasts produce collagen and other extracellular matrix components that are deposited during tissue fibrosis, defining the behavior of these cells is critical to understanding the pathogenesis of fibrotic diseases. We investigated the utility of fibroblast-specific protein 1 (FSP1), a member of the calmodulin S100 troponin C superfamily, for identifying lung fibroblasts in a murine model of pulmonary fibrosis induced by intratracheal administration of bleomycin. Protein and mRNA expression of FSP1 was minimal in untreated lungs, but increased by 1 week after bleomycin administration and remained increased at 2 and 3 weeks after treatment. By immunohistochemistry, the number of FSP1(+) cells increased in a dose-dependent manner in the lungs after bleomycin treatment. Colocalization of alpha1 procollagen and FSP1 in interstitial cells demonstrated that FSP1(+) fibroblasts contribute to the deposition of collagen after bleomycin administration. In primary lung cell cultures, lung fibroblasts, but not macrophages or type II alveolar epithelial cells, expressed FSP1. FSP1 also identified fibroblasts in lung biopsy specimens from patients with documented usual interstitial pneumonitis. Therefore, FSP1 is an improved marker for lung fibroblasts that could be useful for investigating the pathogenesis of pulmonary fibrosis.

Mechanisms of tubulointerstitial fibrosis

PURPOSE OF REVIEW

Tubulointerstitial fibrosis is the final common pathway to end-stage renal disease. Understanding the mechanisms of tubulointerstitial fibrosis is essential in establishing novel therapeutic strategies for the prevention or arrest of progressive kidney diseases. The present review focuses on a newly proposed mechanism of tubulointerstitial fibrosis, one that emphasizes the roles of epithelial-mesenchymal transition and cellular activation.

RECENT FINDINGS

Among the cells that accumulate in the renal interstitium, fibroblasts are the principal effectors mediating tubulointerstitial fibrosis. By contrast, the phagocytosis of extracellular matrix and apoptotic cells by macrophages may actually exert a beneficial effect. Interstitial fibroblasts are more heterogeneous than expected, and during renal fibrosis new fibroblasts are derived mainly through epithelial-mesenchymal transition. The intracellular signaling pathways leading to initiation of epithelial-mesenchymal transition remain largely unknown, though recent studies have identified beta-catenin and Smad3 activation of lymphoid enhancer factor, integrin-linked kinase, and small GTPases and mitogen-activated protein kinases as key components. Transforming growth factor-beta is believed to be a critical fibrogenic factor, but recent studies have also focused on transforming growth factor-beta independent pathways as mechanisms of tubulointerstitial fibrosis. As the mechanisms underlying tubulointerstitial fibrosis leading to epithelial-mesenchymal transition have been identified, so have cytokines that efficiently antagonize renal fibrosis, particularly bone morphogenic protein-7 and hepatocyte growth factor.

SUMMARY

In combination with traditional angiotensin converting enzyme inhibitors, newly identified cytokines may eventually form the basis for new therapeutic strategies aimed at inhibiting the progression of renal disease.

Transdifferentiation of cultured tubular cells induced by hypoxia

BACKGROUND

Tubulointerstitial fibrosis leads to progressive kidney disease and, ultimately, may result in end-stage renal disease (ESRD). Myofibroblasts, which express alpha-smooth muscle actin (alpha-SMA) in their cytoplasm, regulate renal fibrogenesis. Recent studies suggest that certain interstitial myofibroblasts derive from renal tubular cells that have undergone epithelial-mesenchymal transformation (EMT) (transdifferentiation). However, the role(s) of hypoxia, which is involved in progressive kidney disease, on tubular EMT remains unclear.

METHODS

Immortalized rat proximal tubular cells (IRPTC) were cultured in normobaric hypoxia (1% O2) for 3, 6, or 15 days, with match control in normoxic conditions. alpha-SMA, vimentin, and desmin chosen as markers of EMT were measured by immunocytochemistry and immunoblots collagen I production and cell motility were chosen as functional assays. Various concentrations of cobaltous chloride (CoCl2) were used as hypoxic mimickers. In vivo studies were carried out in a chronic ischemic kidney model.

RESULTS

Immunohistochemical studies revealed increased expression of alpha-SMA. Striking morphologic changes were detected after 6 days of hypoxia for alpha-SMA-positive fibroblast-like cells (SMA + fib) and after 15 days for alpha-SMA-positive myofibroblast-like cells (SMA + myo). Immunoblots confirmed these findings. Collagen I production increased in a time-dependent manner parallel to alpha-SMA expression. Cell motility assays demonstrated that transformed cells had higher migratory capacity than normal tubular cells. Cobaltous salt also induced alpha-SMA and collagen I synthesis. Chronic ischemic kidney revealed in vivo tubular EMT at day 7.

CONCLUSION

Hypoxia can induce tubular EMT. This process may play an important role in progression of kidney disease.