Leukocytes induce epithelial to mesenchymal transition after unilateral ureteral obstruction in neonatal mice

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.

Dermatan sulfate reduces monocyte chemoattractant protein 1 and TGF-β production, as well as macrophage recruitment and myofibroblast accumulation in mice with unilateral ureteral obstruction

Selectins play an essential role in most inflammatory reactions, mediating the initial leukocyte-rolling event on activated endothelium. Heparin and dermatan sulfate (DS) bind and block P- and L-selectin function in vitro. Recently, we reported that subcutaneous administration of DS inhibits colon inflammation in rats by reducing macrophage and T-cell recruitment and macrophage activation. In the present study, we examined the effect of porcine intestinal mucosa DS on renal inflammation and fibrosis in mice after unilateral ureteral obstruction (UUO). Twenty-four adult male Swiss mice weighing 20-25 g were divided into 4 groups: group C (N = 6) was not subjected to any surgical manipulation; group SH (N = 6) was subjected to surgical manipulation but without ureter ligation; group UUO (N = 6) was subjected to unilateral ureteral obstruction and received no treatment; group UUO plus DS (N = 6) was subjected to UUO and received DS (4 mg/kg) subcutaneously daily for 14 days. An immunoblot study was also performed for TGF-β. Collagen (stained area ~3700 µm(2)), MCP-1 (stained area ~1700 µm(2)), TGF-β (stained area ~13% of total area), macrophage (number of cells ~40), and myofibroblast (stained area ~1900 µm(2)) levels were significantly (P < 0.05) higher in the UUO group compared to control. DS treatment significantly (P < 0.05) reduced the content of collagen (stained area ~700 µm(2)), MCP-1 (stained area ~160 µm(2)) and TGF-β (stained area ~5% of total area), in addition to myofibroblast (stained area ~190 µm(2)) and macrophage (number of cells ~32) accumulation in the obstructed kidney. Overall, these results indicate that DS attenuates kidney inflammation by reducing macrophage recruitment, myofibroblast population and fibrosis in mice submitted to UUO.

Congenital ureteropelvic junction obstruction: human disease and animal models

Ureteropelvic junction (UPJ) obstruction is the most frequently observed cause of obstructive nephropathy in children. Neonatal and foetal animal models have been developed that mimic closely what is observed in human disease. The purpose of this review is to discuss how obstructive nephropathy alters kidney histology and function and describe the molecular mechanisms involved in the progression of the lesions, including inflammation, proliferation/apoptosis, renin-angiotensin system activation and fibrosis, based on both human and animal data. Also we propose that during obstructive nephropathy, hydrodynamic modifications are early inducers of the tubular lesions, which are potentially at the origin of the pathology. Finally, an important observation in animal models is that relief of obstruction during kidney development has important effects on renal function later in adult life. A major short-coming is the absence of data on the impact of UPJ obstruction on long-term adult renal function to elucidate whether these animal data are also valid in humans.

Mechanistic connection between inflammation and fibrosis

Fibrosis of the kidney is caused by the prolonged injury and deregulation of normal wound healing and repair processes, and by an excess deposition of extracellular matrices. Despite intensive research, our current understanding of the precise mechanism of fibrosis is limited. There is a connection between fibrotic events involving inflammatory and non-inflammatory glomerulonephritis, inflammatory cell infiltration, and podocyte loss. The current review will discuss the inflammatory response after renal injury that leads to fibrosis in relation to non-inflammatory mechanisms.

Role of adipose tissue-derived stem cells in the progression of renal disease

OBJECTIVE

To analyze the role of adipose tissue-derived stem cells in reducing the progression of renal fibrosis.

METHODS

adipose tissue-derived stem cells were isolated from C57Bl/6 mice and characterized by cytometry and differentiation. Renal fibrosis was established after unilateral clamping of the renal pedicle for 1 hour. Four hours after reperfusion, 2.105 adipose tissue-derived stem cells were administered intraperitoneally and the animals were followed for 24 hours during 6 weeks. In another experimental group, 2.105adipose tissue-derived stem cells were administered only after 6 weeks of reperfusion, and they were euthanized and studied 4 weeks later. Twenty-four hours after reperfusion, the animals treated with adipose tissue-derived stem cells displayed reduced renal and tubular dysfunction and an increase of the regenerative process. Renal expression of IL-6 and TNF mRNA were decreased in the animals treated with adipose tissue-derived stem cells, while the levels of IL-4, IL-10, and HO-1 were increased, despite the fact that adipose tissue-derived stem cells were not observed in the kidneys via SRY analysis.

RESULTS

In 6 weeks, the kidneys of non-treated animals decreased in size, and the kidneys of the animals treated with adipose tissue-derived stem cells remained at normal size and display less deposition of type 1 collagen and FSP-1. The renal protection observed in animals treated with adipose tissue-derived stem cells was followed by a drop in serum levels of TNF-α, KC, RANTES, and IL-1a. Treatment with adipose tissue-derived stem cells after 6 weeks, when the animals already displayed established fibrosis, demonstrated an improvement in functional parameters and less fibrosis analyzed by Picrosirius stain, as well as a reduction of the expression of type 1 collagen and vimentin mRNA.

CONCLUSION

Treatment with adipose tissue-derived stem cells may deter the progression of renal fibrosis by modulation of the early inflammatory response, likely via reduction of the epithelial-mesenchymal transition.

Macrophages and renal fibrosis

Renal fibrosis is a key determinant of the progression of renal disease irrespective of the original cause and thus can be regarded as a final common pathway that dictates eventual outcome. The development of renal fibrosis involves many cellular and molecular mediators including leukocytes, myofibroblasts, cytokines, and growth factors, as well as metalloproteinases and their endogenous inhibitors. Study of experimental and human renal disease has shown the involvement of macrophages in renal fibrosis resulting from diverse disease processes. Recent work exploring the nature of both circulating monocytes and tissue macrophages has highlighted their multifaceted phenotype and this impacts their role in renal fibrosis in vivo. In this review we outline the key players in the fibrotic response of the injured kidney and discuss the role of monocytes and macrophages in renal scarring.

The NLRP3 inflammasome promotes renal inflammation and contributes to CKD

Inflammation significantly contributes to the progression of chronic kidney disease (CKD). Inflammasome-dependent cytokines, such as IL-1β and IL-18, play a role in CKD, but their regulation during renal injury is unknown. Here, we analyzed the processing of caspase-1, IL-1β, and IL-18 after unilateral ureteral obstruction (UUO) in mice, which suggested activation of the Nlrp3 inflammasome during renal injury. Compared with wild-type mice, Nlrp3(-/-) mice had less tubular injury, inflammation, and fibrosis after UUO, associated with a reduction in caspase-1 activation and maturation of IL-1β and IL-18; these data confirm that the Nlrp3 inflammasome upregulates these cytokines in the kidney during injury. Bone marrow chimeras revealed that Nlrp3 mediates the injurious/inflammatory processes in both hematopoietic and nonhematopoietic cellular compartments. In tissue from human renal biopsies, a wide variety of nondiabetic kidney diseases exhibited increased expression of NLRP3 mRNA, which correlated with renal function. Taken together, these results strongly support a role for NLRP3 in renal injury and identify the inflammasome as a possible therapeutic target in the treatment of patients with progressive CKD.

Immune promotion of epithelial-mesenchymal transition and generation of breast cancer stem cells

Elements of the immune system act as intimate regulators of cancer progression, inhibiting early stages of tumor growth, through immunosurveillance while facilitating later stages of tumor progression. Recent findings have revealed that activated CD8 T cells can stimulate mammary epithelial tumor cells to undergo epithelial-mesenchymal transition (EMT) and to acquire the greatly increased tumorigenic capability and chemotherapeutic resistance of breast cancer stem cells (BCSC). These studies provide a window to understanding how BCSC arise and are maintained within tumors, and how to best target these processes for therapeutic benefit.

Obstructive renal injury: from fluid mechanics to molecular cell biology

Urinary tract obstruction is a frequent cause of renal impairment. The physiopathology of obstructive nephropathy has long been viewed as a mere mechanical problem. However, recent advances in cell and systems biology have disclosed a complex physiopathology involving a high number of molecular mediators of injury that lead to cellular processes of apoptotic cell death, cell injury leading to inflammation and resultant fibrosis. Functional studies in animal models of ureteral obstruction using a variety of techniques that include genetically modified animals have disclosed an important role for the renin-angiotensin system, transforming growth factor-β1 (TGF-β1) and other mediators of inflammation in this process. In addition, high throughput techniques such as proteomics and transcriptomics have identified potential biomarkers that may guide clinical decision-making.

Role of inflammation in túbulo-interstitial damage associated to obstructive nephropathy

Obstructive nephropathy is characterized by an inflammatory state in the kidney, that is promoted by cytokines and growth factors produced by damaged tubular cells, infiltrated macrophages and accumulated myofibroblasts. This inflammatory state contributes to tubular atrophy and interstitial fibrosis characteristic of obstructive nephropathy. Accumulation of leukocytes, especially macrophages and T lymphocytes, in the renal interstitium is strongly associated to the progression of renal injury. Proinflammatory cytokines, NF-κB activation, adhesion molecules, chemokines, growth factors, NO and oxidative stress contribute in different ways to progressive renal damage induced by obstructive nephropathy, as they induce leukocytes recruitment, tubular cell apoptosis and interstitial fibrosis. Increased angiotensin II production, increased oxidative stress and high levels of proinflammatory cytokines contribute to NF-κB activation which in turn induce the expression of adhesion molecules and chemokines responsible for leukocyte recruitment and iNOS and cytokines overexpression, which aggravates the inflammatory response in the damaged kidney. In this manuscript we revise the different events and regulatory mechanisms involved in inflammation associated to obstructive nephropathy.

Lefty A attenuates the TGF-beta1-induced epithelial to mesenchymal transition of human renal proximal epithelial tubular cells

The epithelial to mesenchymal transition (EMT) is a crucial event for renal fibrosis that can be elicited by TGF-beta1/Smads signaling and its downstream mediator connective tissue growth factor (CTGF). As a distinct member of the TGF-beta superfamily, Lefty A has been shown to be significantly downregulated in the kidneys of patients with severe ureteral obstruction, suggesting its role in renal fibrosis induced by obstructive nephropathy. In order to determine whether Lefty A prevents TGF-beta1-induced EMT, human proximal tubule epithelial cells (HK-2) were stably transfected with Lefty A or control vectors and stimulated with 10 ng/ml TGF-beta1 for 48 h. The results show that stimulation with TGF-beta1 led to EMT including cell morphology changes, Smad2/3 signaling pathway activation, increased alpha-SMA, collagen type I, and CTGF expression, and decreased E-cadherin expression in mock-transfected HK-2 cells. Overexpression of Lefty A efficiently blocked p-Smad2/3 activation and attenuated all these EMT changes induced by TGF-beta1. This finding suggests that Lefty A may serve as a potential new therapeutic target to inhibit or even reverse EMT during the process of renal fibrosis.

Macrophage matrix metalloproteinase-9 mediates epithelial-mesenchymal transition in vitro in murine renal tubular cells

As a rich source of pro-fibrogenic growth factors and matrix metalloproteinases (MMPs), macrophages are well-placed to play an important role in renal fibrosis. However, the exact underlying mechanisms and the extent of macrophage involvement are unclear. Tubular cell epithelial-mesenchymal transition (EMT) is an important contributor to renal fibrosis and MMPs to induction of tubular cell EMT. The aim of this study was to investigate the contribution of macrophages and MMPs to induction of tubular cell EMT. The murine C1.1 tubular epithelial cell line and primary tubular epithelial cells were cultured in activated macrophage-conditioned medium (AMCM) derived from lipopolysaccharide-activated J774 macrophages. MMP-9, but not MMP-2 activity was detected in AMCM. AMCM-induced tubular cell EMT in C1.1 cells was inhibited by broad-spectrum MMP inhibitor (GM6001), MMP-2/9 inhibitor, and in AMCM after MMP-9 removal by monoclonal Ab against MMP-9. AMCM-induced EMT in primary tubular epithelial cells was inhibited by MMP-2/9 inhibitor. MMP-9 induced tubular cell EMT in both C1.1 cells and primary tubular epithelial cells. Furthermore, MMP-9 induced tubular cell EMT in C1.1 cells to an extent similar to transforming growth factor-beta. Transforming growth factor-beta-induced tubular cell EMT in C1.1 cells was inhibited by MMP-2/9 inhibitor. Our in vitro study provides evidence that MMPs, specifically MMP-9, secreted by effector macrophages can induce tubular cell EMT and thereby contribute to renal fibrosis.

Deletion of H-Ras decreases renal fibrosis and myofibroblast activation following ureteral obstruction in mice

Tubulointerstitial fibrosis is characterized by the presence of myofibroblasts that contribute to extracellular matrix accumulation. These cells may originate from resident fibroblasts, bone-marrow-derived cells, or renal epithelial cells converting to a mesenchymal phenotype. Ras GTPases are activated during renal fibrosis and play crucial roles in regulating both cell proliferation and TGF-beta-induced epithelial-mesenchymal transition. Here we set out to assess the contribution of Ras to experimental renal fibrosis using the well-established model of unilateral ureteral obstruction. Fifteen days after obstruction, both fibroblast proliferation and inducers of epithelial-mesenchymal transition were lower in obstructed kidneys of H-ras knockout mice and in fibroblast cell lines derived from these mice. Interestingly, fibronectin, collagen I accumulation, overall interstitial fibrosis, and the myofibroblast population were also lower in the knockout than in the wild-type mice. As expected, we found lower levels of activated Akt in the kidneys and cultured fibroblasts of the knockout. Whether Ras inhibition will turn out to prevent progression of renal fibrosis will require more direct studies.

New insights into epithelial-mesenchymal transition in kidney fibrosis

Epithelial-mesenchymal transition (EMT), a process by which differentiated epithelial cells undergo a phenotypic conversion that gives rise to the matrix-producing fibroblasts and myofibroblasts, is increasingly recognized as an integral part of tissue fibrogenesis after injury. However, the degree to which this process contributes to kidney fibrosis remains a matter of intense debate and is likely to be context-dependent. EMT is often preceded by and closely associated with chronic interstitial inflammation and could be an adaptive response of epithelial cells to a hostile or changing microenvironment. In addition to tubular epithelial cells, recent studies indicate that endothelial cells and glomerular podocytes may also undergo transition after injury. Phenotypic alteration of podocytes sets them in motion to functional impairment, resulting in proteinuria and glomerulosclerosis. Several intracellular signal transduction pathways such as TGFbeta/Smad, integrin-linked kinase (ILK) and Wnt/beta-catenin signaling are essential in controlling the process of EMT and presently are potential targets of antifibrotic therapy. This review highlights the current understanding of EMT and its underlying mechanisms to stimulate further discussion on its role, not only in the pathogenesis of renal interstitial fibrosis but also in the onset of podocyte dysfunction, proteinuria, and glomerulosclerosis.

Histone deacetylase modulates the proinflammatory and -fibrotic changes in tubulointerstitial injury

Histone deacetylase (HDAC) regulates gene expression by modifying chromatin structure. Although changes in the expression and activities of HDAC may affect the course of kidney disease, the role of HDAC in tubulointerstitial injury has not been explored. We therefore investigated the alterations in HDAC expression and determined the effects of HDAC inhibition on the tubulointerstitial injury induced by unilateral ureteral obstruction. The induction of HDAC1 and HDAC2, accompanied by a decrease in histone acetylation was observed in kidneys injured by ureteral obstruction. Immunohistochemical analysis revealed that HDAC1 and HDAC2 were induced in renal tubular cells. Treatment with an HDAC inhibitor, trichostatin A (TSA), attenuated macrophage infiltration and fibrotic changes in tubulointerstitial injury induced by ureteral obstruction. The induction of colony-stimulating factor-1 (CSF-1), a chemokine known to be involved in macrophage infiltration in tubulointerstitial injury, was reduced in injured kidneys from mice treated with TSA. TSA, valproate, and the knockdown of HDAC1 or HDAC2 significantly reduced CSF-1 induced by TNF-alpha in renal tubular cells. These results suggest that tubular HDAC1 and HDAC2, induced in response to injury, may contribute to the induction of CSF-1 and the initiation of macrophage infiltration and profibrotic responses. These findings suggest a potential of HDAC inhibition therapy aimed at reducing inflammation and fibrosis in tubulointerstitial injury.

Inflammation and EMT: an alliance towards organ fibrosis and cancer progression

Recent advances in our understanding of the molecular pathways that govern the association of inflammation with organ fibrosis and cancer point to the epithelial to mesenchymal transition (EMT) as the common link in the progression of these devastating diseases. The EMT is a crucial process in the development of different tissues in the embryo and its reactivation in the adult may be regarded as a physiological attempt to control inflammatory responses and to 'heal' damaged tissue. However, in pathological contexts such as in tumours or during the development of organ fibrosis, this healing response adopts a sinister nature, steering these diseases towards metastasis and organ failure. Importantly, the chronic inflammatory microenvironment common to fibrotic and cancer cells emerges as a decisive factor in the induction of the pathological EMT.

Fibroblast activation and myofibroblast generation in obstructive nephropathy

Obstructive nephropathy is a major cause of renal failure, particularly in newborn babies and children. After urinary tract obstruction, and under the influence of mechanical forces and cytokines produced by tubular cells and cells that have infiltrated the interstitium, resident fibroblasts undergo activation and myofibroblasts are generated from bone-marrow-derived cells, pericytes and endothelial cells. In addition, selected tubular epithelial cells can become fibroblast-like cells via epithelial-mesenchymal transition. This transition is characterized by downregulation of epithelial marker proteins such as E-cadherin, zonula occludens 1 and cytokeratin; loss of cell-to-cell adhesion; upregulation of mesenchymal markers including vimentin, alpha-smooth muscle actin and fibroblast-specific protein 1; basement membrane degradation; and migration to the interstitial compartment. All the events of epithelial-mesenchymal transition are strictly regulated by complex signaling pathways. Myofibroblasts and activated fibroblasts proliferate and produce large amounts of extracellular matrix, which accumulates in the tubular interstitium; together with tubular atrophy, this accumulation leads to interstitial fibrosis. This Review examines the molecular mechanisms of fibroblast activation and epithelial-mesenchymal transition, processes that seem to be promising targets for the prevention, or even reversal, of interstitial fibrosis and renal dysfunction associated with obstructive nephropathy.

Age-dependent renal expression of acid-base transporters in neonatal ureter obstruction

Congenital obstructive nephropathy accounts for a major proportion of renal insufficiency in infancy and childhood. In an earlier investigation we demonstrated that bilateral complete ureteral obstruction (BUO) in rats is associated with inadequate urinary acidification [Am J Physiol Renal Physiol. 295(2):F497-506, 2008]. The aim of the study reported here was to determine whether this defect is also associated with unilateral ureteral obstruction (UUO), which is clinically more common than BUO. The time-course of the changes in protein expression levels of major renal acid-base transporters was examined at 7 and 14 weeks in rats with neonatally induced partial unilateral ureteral obstruction (PUUO), which was performed within the first 48 h of life. We observed that protein expression of the renal acid-base transporters NHE3, NBC1, NBCn1, pendrin and Na(+)-K(+)-ATPase was increased in both obstructed and non-obstructed kidneys 7 weeks after the induction of neonatal PUUO. This was confirmed by immunocytochemistry. In contrast, 14 weeks after the induction of PUUO, there was a significant downregulation of the renal acid-base transporters NBC1, NBCn1 and Na(+)-K(+)-ATPase in the obstructed kidneys. These time/age-dependent changes in protein expression were associated with parallel changes in renal function resulting in urine acidification in response to exogenous acid loading. In conclusion, these results show that downregulation of protein expression is a time/age-dependent response to PUUO, which could contribute to the decreased net acid excretion and development of metabolic acidosis in neonatal rats with PUUO.

Soluble HB-EGF induces epithelial-to-mesenchymal transition in inner medullary collecting duct cells by upregulating Snail-2

Animal models of acute renal injury suggest that the epidermal growth factor receptor (EGFR) axis may have a beneficial role in the recovery from acute renal injury, but recent reports describe detrimental effects of EGFR activation in chronic renal injury. Expression of the EGFR ligand heparin-binding EGF-like growth factor (HB-EGF) increases following renal injury, but the effects of this sustained upregulation have not been well studied. Here, stable overexpression of soluble HB-EGF (sHB-EGF) in mouse inner medullary collecting duct (IMCD) cells led to marked phenotypic changes: sHB-EGF-expressing cells demonstrated a fibroblast-like morphology, did not form epithelial sheets, exhibited cytoplasmic projections, decreased expression of epithelial markers, and increased expression of fibroblast-specific protein-1. They also demonstrated anchorage-independent growth and formed tumors when injected subcutaneously into nude mice. Quantitative RT-PCR and a luciferase reporter assay suggested that sHB-EGF repressed transcription of E-cadherin, and a concomitant TGF-beta-independent upregulation of the E-cadherin repressor Snail-2 was observed. Stable downregulation of Snail-2 in sHB-EGF-overexpressing cells restored epithelial characteristics (E-cadherin and cytokeratin expression) but did not alter their anchorage-independent growth. In summary, sustained exposure to sHB-EGF induces epithelial-to-mesenchymal transition of IMCD cells, in part by upregulating the E-cadherin transcriptional repressor Snail-2.

The cardiotonic steroid hormone marinobufagenin induces renal fibrosis: implication of epithelial-to-mesenchymal transition

We recently demonstrated that the cardiotonic steroid marinobufagenin (MBG) induced fibrosis in rat hearts through direct stimulation of collagen I secretion by cardiac fibroblasts. This stimulation was also responsible for the cardiac fibrosis seen in experimental renal failure. In this study, the effect of MBG on the development of renal fibrosis in rats was investigated. Four weeks of MBG infusion triggered mild periglomerular and peritubular fibrosis in the cortex and the appearance of fibrotic scars in the corticomedullary junction of the kidney. MBG also significantly increased the protein levels and nuclear localization of the transcription factor Snail in the tubular epithelia. It is known that activation of Snail is associated with epithelial-to-mesenchymal transition (EMT) during renal fibrosis. To examine whether MBG alone can trigger EMT, we used the porcine proximal tubular cell line LLC-PK1. MBG (100 nM) caused LLC-PK1 cells grown to confluence to acquire a fibroblast-like shape and have an invasive motility. The expressions of the mesenchymal proteins collagen I, fibronectin, and vimentin were increased twofold. However, the total level of E-cadherin remained unchanged. These alterations in LLC-PK1 cells in the presence of MBG were accompanied by elevated expression and nuclear translocation of Snail. During the time course of EMT, MBG did not have measurable inhibitory effects on the ion pumping activity of its natural ligand, Na(+)-K(+)-ATPase. Our data suggest that the MBG may be an important factor in inducing EMT and, through this mechanism, elevated levels of MBG in chronic renal failure may play a role in the progressive fibrosis.

RGC-32 mediates transforming growth factor-beta-induced epithelial-mesenchymal transition in human renal proximal tubular cells

Epithelial-mesenchymal transition (EMT) occurs in several disease states, including renal fibrosis and carcinogenesis. Myofibroblasts produced from EMT of renal tubular cells are responsible for the deposition of extracellular matrix components in a large portion of renal interstitial fibrosis. Transforming growth factor-beta (TGF-beta) plays an essential role in the EMT of renal tubular cells, but the molecular mechanism governing this process remains largely unknown. In this study, we found that RGC-32 (response gene to complement 32) is critical for TGF-beta-induced EMT of human renal proximal tubular cells (HPTCs). RGC-32 is not normally expressed in the HPTCs. However, TGF-beta stimulation markedly activates RGC-32 while inducing an EMT, as shown by the induction of smooth muscle alpha-actin (alpha-SMA) and extracellular matrix proteins collagen I and fibronectin, as well as the reduction of epithelial marker E-cadherin. TGF-beta function is mediated by several signaling pathways, but RGC-32 expression in HPTCs appears to be mainly regulated by Smad. Functionally, RGC-32 appears to mediate TGF-beta-induced EMT of HPTCs. Blockage of RGC-32 using short hairpin interfering RNA significantly inhibits TGF-beta induction of myofibroblast marker gene alpha-SMA while repressing the expression of E-cadherin. In contrast, overexpression of RGC-32 induces alpha-SMA expression while restoring E-cadherin. RGC-32 also inhibits the expression of another adherens junction protein, N-cadherin, suggesting that RGC-32 alone induces the phenotypic conversion of renal epithelial cells to myofibroblasts. Additional studies show that RGC-32 stimulates the production of extracellular matrix components fibronectin and collagen I. Mechanistically, RGC-32 induces EMT via the activation of other transcription factors such as Snail and Slug. RGC-32 knockdown inhibits the expression of Snail and Slug during TGF-beta-induced EMT. Taken together, our data demonstrate for the first time that RGC-32 plays a critical role in TGF-beta-induced EMT of renal tubular cells.

EMT and proteinuria as progression factors

Tubulointerstitial fibrosis is an integral part of the structural changes of the kidney in chronic progressive renal failure. The accumulation of the extracellular matrix in the tubulointerstitial space is mediated mainly by myofibroblasts. These are derived from resident interstitial fibroblasts, tubular epithelial cells, periadventitial cells, and possibly also mesenchymal stem cells and endothelial cells. Fibrosis is usually preceded by tubulointerstitial infiltration of mononuclear inflammatory cells. Proteinuria is one of several mechanisms of primary glomerular or vascular disease to transmit the disease process to the interstitial space. Increased protein filtration may have direct toxic effects on tubular epithelial cells, induce chemokine and cytokine secretion and result in increased expression of adhesion molecules, all contributing to the influx of mononuclear cells. Inflammatory cells in return secrete cytokines, which stimulate resident fibroblasts and tubular epithelial cells to differentiate into matrix-producing cells. The phenotypic conversion of primary epithelial cells into mesenchymal cells, termed epithelial-mesenchymal transition (EMT), has been studied in great detail in recent years. Several signal transduction pathways of this process have been clarified and may eventually result in novel therapeutic approaches. The severity of proteinuria and the extent of EMT have both been associated with the decline in renal function in clinical studies. Limiting proteinuria results in a slower decline of renal function deterioration, whereas reducing EMT has had beneficial effects in a number of animal studies, including those indicating reversal of fibrotic lesions. However, the association between proteinuria and EMT and vice versa is far from clear and has not been carefully studied.

Idiopathic pulmonary fibrosis: aberrant recapitulation of developmental programs?

The authors discuss evidence suggesting that embryonic signaling pathways involved in epithelium/mesenchymal communication and epithelial cell plasticity may be aberrantly switched on in idiopathic pulmonary fibrosis.