Blockage of tubular epithelial to myofibroblast transition by hepatocyte growth factor prevents renal interstitial fibrosis

Synergistic Effects of Combining Anti-Midkine and Hepatocyte Growth Factor Therapies Against Diabetic Nephropathy in Rats

PURPOSE

This study aimed to assess whether synergism could be achieved when combining midkine (MK) antisense oligodeoxynucleotides (anti-MK ODN) and recombinant human hepatocyte growth factor (HGF) in diabetic nephropathy (DN) rat models.

METHODS

Rats were randomized into 6 groups: control, DN rats without treatment, DN rats treated with scrambled ODN, DN rats treated with anti-MK ODN, DN rats treated with HGF and DN rats treated with anti-MK ODN plus HGF. DN models were created by intraperitoneal injection of streptozotocin. Two weeks later, treatments commenced. ODN (1 mg/kg) was intravenously injected weekly for 4 weeks. HGF (500 μg/kg) was subcutaneously injected daily for 4 weeks. Eight weeks later, rats were euthanized. Serum and urine parameters, kidney histopathological injury scores, immunohistochemistry and protein expressions were measured.

RESULTS

Blood glucose, creatinine, blood urea nitrogen and urine albumin were significantly elevated in DN rats. Any single treatment markedly reduced their levels, yet combined treatment decreased them significantly further. Any monotherapy could decrease renal injury score and immunohistochemistry positive percentage, although the most prominent change was displayed in combinational therapy. Western blot showed the expression of MK was significantly elevated in DN rats. Anti-MK ODN suppressed MK significantly. The protein expressions and serum concentrations of transforming growth factor-β1 and connective tissue growth factor between monotherapy and the combined therapy were significant.

CONCLUSIONS

This study demonstrated that combining MK gene suppressing ODN and HGF protein synergistically attenuates renal injury in DN rats. This study may provide a novel avenue for designing future therapeutic regimens against DN.

Epigenetic repression of Krüppel-like factor 4 through Dnmt1 contributes to EMT in renal fibrosis

Krüppel-like factor 4 (KLF4) is a transcription factor which plays divergent roles in a number of physiological or pathological process. However, the expression and role of KLF4 in renal fibrosis remain undetermined. The aim of the present study was to determine the epigenetic alterations of KLF4 and its potential role and mechanisms of action in epithelial-to-mesenchymal transition (EMT) in renal fibrosis. The hypermethylation of the KLF4 promoter accompanied by a decrease in KLF4 expression were observed in mice subjected to unilateral ureteral obstruction (UUO) and in HK-2 cells stimulated with transforming growth factor (TGF)-β1. However, treatment with 5-aza-2'-deoxycytidine attenuated the TGF-β1-induced downregulation of KLF4 and E-cadherin and the upregulation of α-smooth muscle actin (α-SMA) in the HK-2 cells. DNA methyltransferase 1 (Dnmt1) participated in the TGF-β1-mediated hypermethylation of the KLF4 promoter in the HK-2 cells. In addition, functional analysis demonstrated that the overexpression of KLF4 led to an increase in the expression of E-cadherin and zonula occludens-l (ZO-1), and a decrease in the expression of α-SMA and fibroblast-specific protein 1 (FSP-1), thus reversing the effects of the suppression of KLF4. These data suggest that KLF4 inhibits the progression of EMT in renal epithelial cells. In conclusion, our findings demonstrate that KLF4 is downregulated during EMT in renal fibrosis in vivo and in vitro; thus, KLF4 functions as a suppressor of renal fibrogenesis. The hypermethylation of KLF4 directly mediated by Dnmt1 contributes to the progression of EMT in renal epithelial cells. KLF4 promoter methylation may thus be a promising diagnostic marker or therapeutic target in renal fibrosis.

[The epithelial-mesenchymal transition and fibrosis of the renal transplant]

Epithelial-mesenchymal transition (EMT) is a process by which differentiated epithelial cells undergo a phenotypic conversion and acquire a mesenchymal phenotype, including elongated morphology, enhanced migratory and invasion capacity, and greatly increased production of extracellular matrix (ECM) components. This phenomenon plays a pivotal role in embryonic development, wound healing and tissue regeneration. It has also been involved in organ fibrosis. Some studies suggest that following injury, renal tubular epithelial cells undergo reprograming in mesenchymal cells, and thus constitute an important source of de novo myofibroblasts invading the renal interstitium and contributing to fibrosis. However, an increasing number of studies raise doubts about the existence of this process in vivo. The role of EMT in the development of renal fibrosis remains a matter of intense debate and may depend on the model studied. In this review, we describe the role of EMT in the development of fibrosis of renal graft, and then we propose approaches for detecting and treating renal fibrogenesis by targeting TEM.

Diverse origins of the myofibroblast—implications for kidney fibrosis

Fibrosis is the common end point of chronic kidney disease. The persistent production of inflammatory cytokines and growth factors leads to an ongoing process of extracellular matrix production that eventually disrupts the normal functioning of the organ. During fibrosis, the myofibroblast is commonly regarded as the predominant effector cell. Accumulating evidence has demonstrated a diverse origin of myofibroblasts in kidney fibrosis. Proposed major contributors of myofibroblasts include bone marrow-derived fibroblasts, tubular epithelial cells, endothelial cells, pericytes and interstitial fibroblasts; the published data, however, have not yet clearly defined the relative contribution of these different cellular sources. Myofibroblasts have been reported to originate from various sources, irrespective of the nature of the initial damage responsible for the induction of kidney fibrosis. Here, we review the possible relevance of the diversity of myofibroblast progenitors in kidney fibrosis and the implications for the development of novel therapeutic approaches. Specifically, we discuss the current status of preclinical and clinical antifibrotic therapy and describe targeting strategies that might help support resident and circulating cells to maintain or regain their original functional differentiation state. Such strategies might help these cells resist their transition to a myofibroblast phenotype to prevent, or even reverse, the fibrotic state.

Hepatocyte growth factor: A regulator of inflammation and autoimmunity

Hepatocyte growth factor (HGF) is a pleiotropic cytokine that has been extensively studied over several decades, but was only recently recognized as a key player in mediating protection of many types of inflammatory and autoimmune diseases. HGF was reported to prevent and attenuate disease progression by influencing multiple pathophysiological processes involved in inflammatory and immune response, including cell migration, maturation, cytokine production, antigen presentation, and T cell effector function. In this review, we discuss the actions and mechanisms of HGF in inflammation and immunity and the therapeutic potential of this factor for the treatment of inflammatory and autoimmune diseases.

Glomerular endothelial cell injury and cross talk in diabetic kidney disease

Diabetic kidney disease (DKD) remains a leading cause of new-onset end-stage renal disease (ESRD), and yet, at present, the treatment is still very limited. A better understanding of the pathogenesis of DKD is therefore necessary to develop more effective therapies. Increasing evidence suggests that glomerular endothelial cell (GEC) injury plays a major role in the development and progression of DKD. Alteration of the glomerular endothelial cell surface layer, including its major component, glycocalyx, is a leading cause of microalbuminuria observed in early DKD. Many studies suggest a presence of cross talk between glomerular cells, such as between GEC and mesangial cells or GEC and podocytes. PDGFB/PDGFRβ is a major mediator for GEC and mesangial cell cross talk, while vascular endothelial growth factor (VEGF), angiopoietins, and endothelin-1 are the major mediators for GEC and podocyte communication. In DKD, GEC injury may lead to podocyte damage, while podocyte loss further exacerbates GEC injury, forming a vicious cycle. Therefore, GEC injury may predispose to albuminuria in diabetes either directly or indirectly by communication with neighboring podocytes and mesangial cells via secreted mediators. Identification of novel mediators of glomerular cell cross talk, such as microRNAs, will lead to a better understanding of the pathogenesis of DKD. Targeting these mediators may be a novel approach to develop more effective therapy for DKD.

Hepatocyte Growth Factor Isoforms in Tissue Repair, Cancer, and Fibrotic Remodeling

Hepatocyte growth factor (HGF), also known as scatter factor (SF), is a pleotropic factor required for normal organ development during embryogenesis. In the adult, basal expression of HGF maintains tissue homeostasis and is up-regulated in response to tissue injury. HGF expression is necessary for the proliferation, migration, and survival of epithelial and endothelial cells involved in tissue repair in a variety of organs, including heart, lung, kidney, liver, brain, and skin. The administration of full length HGF, either as a protein or using exogenous expression methodologies, increases tissue repair in animal models of tissue injury and increases angiogenesis. Full length HGF is comprised of an N-terminal hairpin turn, four kringle domains, and a serine protease-like domain. Several naturally occurring alternatively spliced isoforms of HGF were also identified. The NK1 variant contains the N-terminal hairpin and the first kringle domain, and the NK2 variant extends through the second kringle domain. These alternatively spliced forms of HGF activate the same receptor, MET, but they differ from the full length protein in their cellular activities and their biological functions. Here, we review the species-specific expression of the HGF isoforms, their regulation, the signal transduction pathways they activate, and their biological activities.

Renal dysfunction and intragraft proMMP9 activity in renal transplant recipients with interstitial fibrosis and tubular atrophy

Chronic renal allograft injury is reflected by interstitial fibrosis and tubular atrophy (IF/TA) and by the accumulation of extracellular matrix (ECM). Metalloproteinases (MMPs) are renal physiologic regulators of ECM degradation. Changes in MMPs expression or activity may disturb ECM turnover leading to glomerular scarring and worsening renal function. Our goal was to investigate intragraft MMP2 and MMP9 activities and their correlation with renal dysfunction. Plasma MMP2 and MMP9 activities were analyzed as noninvasive markers of renal allograft deterioration. Transplanted patients were biopsied and histopathologically characterized as IF/TA+ or IF/TA-. Renal function was evaluated by serum creatinine, glomerular filtration rate (GFR) estimated by Modification of Diet in Renal Disease equation and urinary protein/creatinine ratio. Kidney and plasma MMP2 and MMP9 activities were analyzed by zymography. A significant renal dysfunction was observed in IF/TA+ patients. Intragraft proMMP9 showed a significant higher activity in IF/TA+ than in IF/TA- samples and was inversely correlated with the GFR. Intragraft proMMP2 activity tended to increase in IF/TA+ samples, although no statistic significance was reached. Circulating proMMP2 and proMMP9 activities did not show significant differences between groups. Our data provide evidence that correlates intragraft proMMP9 activity with the fibrotic changes and renal dysfunction observed in IF/TA.

The network of epithelial-mesenchymal transition: potential new targets for tumor resistance

PURPOSE

In multiple cell metazoans, the ability of polarized epithelial cells to convert to motile mesenchymal cells in order to relocate to another location is governed by a unique process termed epithelial-mesenchymal transition (EMT). While being an essential process of cellular plasticity for normal tissue and organ developments, EMT is found to be involved in an array of malignant phenotypes of tumor cells including proliferation and invasion, angiogenesis, stemness of cancer cells and resistance to chemo-radiotherapy. Although EMT is being extensively studied and demonstrated to play a key role in tumor metastasis and in sustaining tumor hallmarks, there is a lack of clear picture of the overall EMT signaling network, wavering the potential clinical trials targeting EMT.

METHODS

In this review, we highlight the potential key therapeutic targets of EMT linked with tumor aggressiveness, hypoxia, angiogenesis and cancer stem cells, emphasizing on an emerging EMT-associated NF-κB/HER2/STAT3 pathway in radioresistance of breast cancer stem cells.

RESULTS

Further definition of cancer stem cell repopulation due to EMT-controlled tumor microenvironment will help to understand how tumors exploit the EMT mechanisms for their survival and expansion advantages.

CONCLUSIONS

The knowledge of EMT will offer more effective targets in clinical trials to treat therapy-resistant metastatic lesions.

Signal transduction in podocytes--spotlight on receptor tyrosine kinases

The mammalian kidney filtration barrier is a complex multicellular, multicomponent structure that maintains homeostasis by regulating electrolytes, acid-base balance, and blood pressure (via maintenance of salt and water balance). To perform these multiple functions, podocytes--an important component of the filtration apparatus--must process a series of intercellular signals. Integrating these signals with diverse cellular responses enables a coordinated response to various conditions. Although mature podocytes are terminally differentiated and cannot proliferate, they are able to respond to growth factors. It is possible that the initial response of podocytes to growth factors is beneficial and protective, and might include the induction of hypertrophic cell growth. However, extended and/or uncontrolled growth factor signalling might be maladaptive and could result in the induction of apoptosis and podocyte loss. Growth factors signal via the activation of receptor tyrosine kinases (RTKs) on their target cells and around a quarter of the 58 RTK family members that are encoded in the human genome have been identified in podocytes. Pharmacological inhibitors of many RTKs exist and are currently used in experimental and clinical cancer therapy. The identification of pathological RTK-mediated signal transduction pathways in podocytes could provide a starting point for the development of novel therapies for glomerular disorders.

Autophagy inhibition induces podocyte apoptosis by activating the pro-apoptotic pathway of endoplasmic reticulum stress

Podocyte apoptosis is a major factor inducing podocyte depletion that predicts the progressive course of glomerulosclerosis. However, the molecular mechanisms underlying podocyte apoptosis are still not well understood. Autophagy is a lysosomal degradation system involving the degradation and recycling of obsolete, damaged, or harmful cytoplasmic materials and organelles. Recent advances in the understanding of the molecular processes contributing to autophagy have provided insight into the relationship between autophagy and apoptosis. However, their cross-talk remains largely obscure until now. Here, we found that podocytes both in vivo and in vitro always exhibited high basal levels of autophagy, whereas autophagy inhibition could induce podocyte apoptosis, suggesting the pro-survival role of autophagy in podocytes. Besides, we found that autophagy inhibition by 3-methyladenine (3-MA) could induce the activation of endoplasmic reticulum stress even without any external stimulations, whereas knockdown of CHOP could effectively improve podocyte apoptosis and down-regulated expression of slit-diaphragm proteins induced by autophagy inhibition. Collectively, this study demonstrated that autophagy might act as a crucial regulatory mechanism of apoptotic cell death by modulating the balance between the pro-survival pathway and the pro-apoptotic pathway of endoplasmic reticulum stress, which might provide a novel mechanistic insight into the interface between autophagy and apoptosis in the progression of podocyte injury.

Overexpression of c-Met and CD44v6 receptors contributes to autocrine TGF-β1 signaling in interstitial lung disease

The hepatocyte growth factor (HGF) and the HGF receptor Met pathway are important in the pathogenesis of interstitial lung disease (ILD). Alternatively spliced isoforms of CD44 containing variable exon 6 (CD44v6) and its ligand hyaluronan (HA) alter cellular function in response to interaction between CD44v6 and HGF. TGF-β1 is the crucial cytokine that induces fibrotic action in ILD fibroblasts (ILDFbs). We have identified an autocrine TGF-β1 signaling that up-regulates both Met and CD44v6 mRNA and protein expression. Western blot analysis, flow cytometry, and immunostaining revealed that CD44v6 and Met colocalize in fibroblasts and in tissue sections from ILD patients and in lungs of bleomycin-treated mice. Interestingly, cell proliferation induced by TGF-β1 is mediated through Met and CD44v6. Further, cell proliferation mediated by TGF-β1/CD44v6 is ERK-dependent. In contrast, action of Met on ILDFb proliferation does not require ERK but does require p38(MAPK). ILDFbs were sorted into CD44v6(+)/Met(+) and CD44v6(-)/Met(+) subpopulations. HGF inhibited TGF-β1-stimulated collagen-1 and α-smooth muscle cell actin expression in both of these subpopulations by interfering with TGF-β1 signaling. HGF alone markedly stimulated CD44v6 expression, which in turn regulated collagen-1 synthesis. Our data with primary lung fibroblast cultures with respect to collagen-1, CD44v6, and Met expressions were supported by immunostaining of lung sections from bleomycin-treated mice and from ILD patients. These results define the relationships between CD44v6, Met, and autocrine TGF-β1 signaling and the potential modulating influence of HGF on TGF-β1-induced CD44v6-dependent fibroblast function in ILD fibrosis.

Involvement of endoplasmic reticulum stress in albuminuria induced inflammasome activation in renal proximal tubular cells

Albuminuria contributes to the progression of tubulointerstitial fibrosis. Although it has been demonstrated that ongoing albuminuria leads to tubular injury manifested by the overexpression of numerous proinflammatory cytokines, the mechanism remains largely unknown. In this study, we found that the inflammasome activation which has been recognized as one of the cornerstones of intracellular surveillance system was associated with the severity of albuminuria in the renal biopsies specimens. In vitro, bovine serum albumin (BSA) could also induce the activation of NLRP3 inflammasome in the cultured kidney epithelial cells (NRK-52E). Since there was a significant overlap of NLRP3 with the ER marker calreticulin, the ER stress provoked by BSA seemed to play a crucial role in the activation of inflammasome. Here, we demonstrated that the chemical chaperone taurine-conjugated ursodeoxycholic acid (TUDCA) which was proved to be an enhancer for the adaptive capacity of ER could attenuate the inflammasome activation induced by albuminuria not only in vitro but also in diabetic nephropathy. Taken together, these data suggested that ER stress seemed to play an important role in albuminuria-induced inflammasome activation, elimination of ER stress via TUDCA might hold promise as a novel avenue for preventing inflammasome activation ameliorating kidney epithelial cells injury induced by albuminuria.

Human Wharton's jelly-derived mesenchymal stromal cells reduce renal fibrosis through induction of native and foreign hepatocyte growth factor synthesis in injured tubular epithelial cells

Introduction

Based on some well-documented reports, we attempted to clarify the antifibrotic mechanisms of human Wharton’s-jelly-derived mesenchymal stromal cells (WJ-MSCs) from the perspective of induction of hepatocyte growth factor (HGF) expression in tubular epithelial cells (TECs).

Methods

A rat model of acute kidney injury (AKI) was established through unilateral renal ischemia for 1 hour. Two days later, a single intravenous cell or vehicle injection, or contralateral nephrectomy, was performed. Rats were sacrificed at 1 day, 1 week, 4 weeks, or 6 weeks after the intervention. Renal fibrosis was evaluated by Masson trichrome staining and Sircol collagen assay. The upregulation of α-smooth muscle actin (α-SMA) versus E-cadherin expression was adopted as an indicator of tubular epithelial-mesenchymal transition (EMT). Gene and protein expression of HGF or transforming growth factor-beta1 (TGF-β1) was determined by real-time polymerase chain reaction (RT-PCR) and Western blot, respectively. HGF expression in TECs was detected with immunostaining. In vitro, rat TECs subjected to hypoxia injury were incubated with or without conditioned medium (CM) from WJ-MSCs for 1, 3, 24, or 48 hours. Rat or human HGF synthesis in TECs was assessed with immunostaining, RT-PCR, or ELISA.

Results

Cell delivery or nephrectomy led to abrogation of renal scarring. At the incipient period of AKI, through induction of HGF expression, either of them remarkably promoted the upregulation of HGF versus TGF-β1 expression in damaged kidney. Rat TECs were not only the principal cells expressing HGF but also exhibited human HGF expression after cell infusion. During fibrogenesis, the downregulation of HGF versus TGF-β1 expression was greatly prevented by WJ-MSCs or kidney removal, thereby resulting in tubular EMT delay. In vitro, after 24 or 48 hours of incubation, CM not only robustly induced the upregulation of rat HGF gene expression in TECs but substantially amplified the release of rat HGF. Under the induction of CM, human HGF mRNA and protein were detected in rat TECs.

Conclusions

WJ-MSCs contribute to tubular EMT delay and the alleviation of renal fibrosis. Induction of native and foreign HGF synthesis in damaged TECs at the initial stage of AKI leads to recovery of the disturbed balance of HGF/TGF-β1 during scar formation, being one of the vital mechanisms.

Hepatocyte growth factor inhibits TGF-β1-induced myofibroblast differentiation in tendon fibroblasts: role of AMPK signaling pathway

The transforming growth factor-β1 (TGF-β1)-induced myofibroblastic differentiation in tendon fibroblasts was thought to be one of the most important features of scar fibrosis formation, which is associated with occurrence of re-rupture. Previously, we reported that hepatocyte growth factor (HGF) inhibited TGF-β1-induced myofibroblast differentiation and extracellular matrix deposition in the Achilles tendon of rats. Here, we investigated the potential molecular mechanisms underlying the inhibitory effect of HGF on TGF-β1-induced myofibroblast differentiation. We found that treatment with HGF (10, 20, and 40 ng/ml) increased phosphorylation of adenosine monophosphate kinase (AMPK) and acetyl-CoA carboxylase (ACC) in tendon fibroblasts. Pharmacological inhibition of the AMPK signaling pathway using compound C, a specific blocker of AMPK signaling, remarkably attenuated the inhibitory effect of HGF on TGF-β1-induced myofibroblastic differentiation in tendon fibroblasts. Moreover, small interfering RNA (siRNA)-mediated knockdown of AMPKα1 subunit decreased the inhibitory effect of HGF on TGF-β1-induced myofibroblastic differentiation in tendon fibroblasts. Finally, overexpression of constitutively active AMPKα1, which led to constitutive activation of the AMPK signaling pathway in tendon fibroblasts, mimicked the inhibitory effect of HGF on the TGF-β1-induced myofibroblastic differentiation. Our study therefore suggests that HGF inhibits TGF-β1-induced myofibroblastic differentiation via an AMPK signaling pathway-dependent manner in tendon fibroblasts.

EMT-MET in renal disease: should we curb our enthusiasm?

Renal epithelial cells arise during embryogenesis by mesenchymal to epithelial transition (MET). In the context of renal diseases, these cells can switch back to a mesenchymal phenotype, in a process thus reminiscent of an epithelial-to-mesenchymal transition (EMT) in which we referred to as "Epithelial Phenotypic Changes" (EPC). The pathophysiological consequence of EPC is controversial: in particular, to what extent EPC contribute to the pool of disease-associated renal fibroblasts is very uncertain. However, there is strong evidence that EPC correlate with a poor renal outcome. EPC indeed reflect an exposure to a profibrotic environment, at an early and potentially reversible stage. Detecting EPC has potential therapeutic implications for patients prone to renal fibrosis, both as a marker of efficacy or more directly as a target. In opposition to the EMT occurring during embryogenesis, EMT in fibrosis as well as in cancer is an anarchic cellular process actually developing at the expense of the whole organ(ism).

Autophagy and apoptosis in tubular cells following unilateral ureteral obstruction are associated with mitochondrial oxidative stress

Tubular epithelial loss has been shown to be responsible for the formation of atubular glomeruli leading to nephron decomposition and interstitial fibrosis in obstructive uropathy. Cells undergoing apoptosis and autophagic cell death play an important role in this process, yet the mechanisms are not fully understood. In this study, we aimed to investigate whether autophagy cooperating with apoptosis is associated with mitochondrial damage and whether oxidative stress plays an important role in the loss of tubular epithelium following unilateral ureteral obstruction. In this model, we demonstrated that there is coexistence of autophagy and apoptosis with tubular atrophy in obstructed proximal tubules. After unilateral ureteral obstruction (UUO), autophagy in proximal tubular cells was enhanced steadily up to 7 days in the obstructed kidney and declined thereafter, while apoptosis was induced in a time-dependent manner from 3 to 14 days. Mitochondrial structure and number also changed during UUO. Lipid peroxidation products, NOX4, and NADPH oxidase activity were also increased in the obstructed renal cortex, and peaked at 7 days. In vitro, we showed that H2O2 induced mitochondrial injury leading to autophagy and apoptosis through the Beclin 1 pathway and interference with Bcl-2 expression. Thus, our data demonstrate that oxidative stress leading to mitochondrial damage and driven autophagy-dependent cell death and apoptosis are important mechanisms of tubular decomposition in obstructive nephropathy.

Diabetic nephropathy: the role of inflammation in fibroblast activation and kidney fibrosis

Kidney disease associated with diabetes mellitus is a major health problem worldwide. Although established therapeutic strategies, such as appropriate blood glucose control, blood pressure control with renin-angiotensin system blockade, and lipid lowering with statins, are used to treat diabetes, the contribution of diabetic end-stage kidney disease to the total number of cases requiring hemodialysis has increased tremendously in the past two decades. Once renal function starts declining, it can result in a higher frequency of renal and extra-renal events, including cardiovascular events. Therefore, slowing renal function decline is one of the main areas of focus in diabetic nephropathy research, and novel strategies are urgently needed to prevent diabetic kidney disease progression. Regardless of the type of injury and etiology, kidney fibrosis is the commonly the final outcome of progressive kidney diseases, and it results in significant destruction of normal kidney structure and accompanying functional deterioration. Kidney fibrosis is caused by prolonged injury and dysregulation of the normal wound-healing process in association with excess extracellular matrix deposition. Kidney fibroblasts play an important role in the fibrotic process, but the origin of the fibroblasts remains elusive. In addition to the activation of residential fibroblasts, other important sources of fibroblasts have been proposed, such as pericytes, fibrocytes, and fibroblasts originating from epithelial-to-mesenchymal and endothelial-to-mesenchymal transition. Inflammatory cells and cytokines play a vital role In the process of fibroblast activation. In this review, we will analyze the contribution of inflammation to the process of tissue fibrosis, the type of fibroblast activation and the therapeutic strategies targeting the inflammatory pathways in an effort to slow the progression of diabetic kidney disease.

20-Hydroxyecdysone attenuates TGF-β1-induced renal cellular fibrosis in proximal tubule cells

Renal fibrosis progresses to end stage of diabetes kidney disease, which causes irreversible progressive proximal tubular injury. In a previous study, 20-hydroxyecdysterone (20-HE), a phytoecdysteroid, attenuated renal injury in diabetes models. However, the fibrosis regulatory role remains to be investigated.

METHODS

The proximal tubular epithelial cells (designated as HK-2) were treated for 48 h with TGF-β1 (5 ng/ml) in different concentrations of 20-HE (0 to 500 nM/ml) in the last 24 h of culture. The extracellular fibronectin was measured by ELISA assay. Western blot and immunofluorescence were used to evaluate the expression of TGF-β1/Smads transducer (including Smad2/3, 4, and 7), epithelial and mesenchymal markers (e.g. E-cadherin and α-smooth muscle actin) and Snail (transcriptional regulators for EMT).

RESULTS

20-HE reverses TGF-β1-induced increase in fibronectin (both intracellular and extracellular fibronectin). Simultaneously, 20-HE reverses TGF-β1-induced down-regulation of Smad7. In addition, 20-HE significantly attenuates TGF-β1-induced upregulation of Smad2/3 and pSmad2/3, and downregulation of E-Cadherin. Moreover, 20-HE dramatically suppresses TGF-β1-induced increases in the expression of Snail.

CONCLUSION

We propose that 20-HE is a potential fibrosis antagonist for renal proximal tubule cells. 20-HE might act through suppressing post-receptor signaling of TGF-β1 and restoring tubule epithelial character by blocking the expression of Snail.

Discovery and validation of a molecular signature for the noninvasive diagnosis of human renal allograft fibrosis

BACKGROUND

Tubulointerstitial fibrosis (fibrosis), a histologic feature associated with a failing kidney allograft, is diagnosed using the invasive allograft biopsy. A noninvasive diagnostic test for fibrosis may help improve allograft outcome.

METHODS

We obtained 114 urine specimens from 114 renal allograft recipients: 48 from 48 recipients with fibrosis in their biopsy results and 66 from 66 recipients with normal biopsy results. Levels of messenger RNAs (mRNAs) in urinary cells were measured using kinetic, quantitative polymerase chain reaction assays, and the levels were related to allograft diagnosis. A discovery set of 76 recipients (32 with allograft fibrosis and 44 with normal biopsy results) was used to develop a diagnostic signature, and an independent validation set of 38 recipients (16 with allograft fibrosis and 22 with normal biopsy results) was used to validate the signature.

RESULTS

In the discovery set, urinary cell levels of the following mRNAs were significantly associated with the presence of allograft fibrosis: vimentin (P<0.0001, logistic regression model), hepatocyte growth factor (P<0.0001), α-smooth muscle actin (P<0.0001), fibronectin 1 (P<0.0001), perforin (P=0.0002), plasminogen activator inhibitor 1 (P=0.0002), transforming growth factor β1 (P=0.0004), tissue inhibitor of metalloproteinase 1 (P=0.0009), granzyme B (P=0.0009), fibroblast-specific protein 1 (P=0.006), CD103 (P=0.02), and collagen 1A1 (P=0.04). A four-gene model composed of the levels of mRNA for vimentin, NKCC2, and E-cadherin and of 18S ribosomal RNA provided the most accurate, parsimonious diagnostic model of allograft fibrosis with a sensitivity of 93.8% and a specificity of 84.1% (P<0.0001). In the independent validation set, this same model predicted the presence of allograft fibrosis with a sensitivity of 77.3% and a specificity of 87.5% (P<0.0001).

CONCLUSIONS

Measurement of mRNAs in urinary cells may offer a noninvasive means of diagnosing fibrosis in human renal allografts.

Loss of vitamin D receptor in chronic kidney disease: a potential mechanism linking inflammation to epithelial-to-mesenchymal transition

Both peritubular inflammation and tubular epithelial-to-mesenchymal transition (EMT) are critical events during the pathogenesis of renal fibrosis. However, the relationship between these two processes is unclear. Here, we investigated the potential role of the vitamin D receptor (VDR) in coupling peritubular inflammation and EMT. In a mouse model of unilateral ureteral obstruction (UUO), loss of VDR was observed as early as 1 day after surgery. In cultured proximal tubular epithelial HK-2 cells, proinflammatory TNF-α inhibited the expression of VDR in a dose- and time-dependant manner. Treatment with TNF-α sensitized HK-2 cells to EMT stimulated by transforming growth factor (TGF)-β1. Ectopic expression of VDR counteracted the synergistic effect of TNF-α and TGF-β1 on EMT. Furthermore, knockdown of VDR using a small interfering RNA strategy mimicked the effect of TNF-α on facilitating EMT. Either TNF-α treatment or a loss of VDR induced β-catenin activation and its nuclear translocation. The VDR ligand calcitriol reversed the VDR loss and inhibited EMT in the mouse UUO model, and late administration of active vitamin D was effective in restoring VDR expression as well, and reduced collagen accumulation and deposition compared with the vehicle control. β-Catenin expression induced by UUO was also significantly inhibited after the late administration of vitamin D. These results indicate that the early loss of VDR in chronic kidney diseases was likely mediated by proinflammatory TNF-α, which renders tubular cells susceptible to EMT. Our data suggest that loss of VDR couples peritubular inflammation and EMT, two key events in renal fibrogenesis.

Overexpression of HGF transgene attenuates renal inflammatory mediators, Na(+)-ATPase activity and hypertension in spontaneously hypertensive rats

Renal inflammation and oxidative stress are constantly present in experimental hypertension. Since the spontaneously hypertensive rat (SHR) has reduced levels of hepatocyte growth factor (HGF), which suppresses the activation of the proinflammatory nuclear transcription factor kappa B (NF-κB), we speculated that HGF deficiency could play a key role in the pathogenesis of hypertension in the SHR. To test this hypothesis we increased HGF in the SHR by HGF gene delivery. We found that kidneys of 15-week-old SHR had an important reduction in HGF mRNA and protein expression. Adult SHRs were randomly assigned to receive weekly hydrodynamic injection (1mg/kg) of a naked plasmid containing human HGF (hHGF) gene associated with a cytomegalovirus promoter (pCMV-HGF) or empty vector (pcDNA3.1) during 6weeks. WKY rats treated with pcDNA3.1 and pCMV-HGF served as controls. The kidneys in the hypertensive SHR untreated and treated with the empty vector had increased NF-κB activation, elevated mRNA and protein expression of RANTES, MCP-1 and IL-6 and increased oxidative stress. Activity of Na(+)-ATPase was increased while activity of Na(+), K(+)-ATPase was normal. hHGF gene therapy normalized renal NF-κB activity, proinflammatory cytokines, antioxidant status (GSH, SOD and CAT), Na(+)-ATPase activity, reduced renal injury and ameliorated hypertension. Our results suggest that reduction in HGF production plays a major role in the pathogenesis of hypertension in the SHR and increasing HGF is a potential therapeutic target in the treatment of hypertension.

Schisandra chinensis fruit extract attenuates albuminuria and protects podocyte integrity in a mouse model of streptozotocin-induced diabetic nephropathy

ETHNOPHARMACOLOGICAL RELEVANCE

Schisandra chinensis fruit is widely used in Chinese medicine for the treatment of hepatic, renal, heart, cerebrovascular and infectious diseases.

AIM OF THE STUDY

To investigate the effects of Schisandra chinensis fruit extract (SE) on albuminuria and podocyte injury as well as the underlying mechanism in the mouse model of streptozotocin (STZ)-induced diabetic nephropathy and in cultured mouse podocyte cells.

MATERIALS AND METHODS

SE was orally administrated in STZ-induced diabetic nephropathy mice for 7 weeks, at a daily dose of 5g/kg body weight. The urinary albumin/creatinine ratio and urine albumin excretion rate were measured at the 6th and 9th week of the experiment. The extent of glomerulosclerosis and extracellular matrix deposition were determined by periodic acid-silver methenamine and Masson's trichrome staining. The amount of podocytes and the integrity of the slit diaphragm were detected by immunohistological staining of podocyte markers, Wilms' tumor 1 and nephrin. Alpha-smooth muscle actin, E-cadherin and plasminogen activator inhibitor-1 were measured by western blot and immunohistological staining to evaluate the level of epithelial-to-mesenchymal transition (EMT). Real-time reverse transcription PCR was used to detect the mRNA level of E-cadherin, alpha-SMA and snail in cultured podocyte cells.

RESULTS

Treatment with SE significantly decreased the urine albumin excretion rate and urinary albumin/creatinine ratio. In addition, SE attenuated glomerulosclerosis and protected against podocyte loss and integrity of the slit diaphragm. Furthermore, SE effectively prevented the EMT of podocytes caused by diabetic nephropathy.

CONCLUSIONS

Our studies suggest that SE might be beneficial for diabetic nephropathy. The effects of SE on attenuating albuminuria and glomerulosclerosis are possibly mediated by preserving podocyte integrity through suppressing EMT.

Mesenchymal stem cells overexpressing hepatocyte growth factor (HGF) inhibit collagen deposit and improve bladder function in rat model of bladder outlet obstruction

Bladder outlet obstruction (BOO) caused by collagen deposit is one of the most common problems in elderly male. This study was performed to examine the capability of human mesenchymal stem cells (MSCs) overexpressing hepatocyte growth factor (HGF) to inhibit collagen deposition in rat model of bladder outlet obstruction (BOO). HGF is known for its antifibrotic effect and the most promising agent for treating bladder fibrosis. BM3.B10 stable immortalized human MSC line (B10) was transduced to encode human HGF with a retroviral vector was prepared (B10.HGF). Two weeks after the onset of BOO, B10, and B10.HGF cells were injected into the rat's bladder wall. After 4 weeks, bladder tissues were harvested and Masson's trichrome staining was performed. Transgene expression in HGF-expressing B10 cells was demonstrated by reverse transcriptase polymerase chain reaction and immunohistochemical staining, and the high levels of HGF secreted by B10.HGF cells was confirmed by ELISA. The mean bladder weight in BOO rats was 5.8 times of the normal controls, while in animals grafted with B10.HGF cells, the weight was down to four times of the control [90.2 ± 1.6 (control), 89.9 ± 2.8 (sham), 527.9 ± 150.9 (BOO), 447.7 ± 41.0 (BOO + B10), and 362.7 ± 113.2 (BOO + B10.HGF)]. The mean percentage of collagen area increased in BOO rats, while in the animals transplanted with B10.HGF cells, the collagen area decreased to the normal control level [12.2 ± 1.3, (control), 12.8 ± 1.1 (sham), 26.6 ± 2.7 (BOO), 19.9 ± 6.0 (BOO + B10), and 13.3 ± 2.1 (BOO + B10.HGF)]. The expression of collagen and TGF-b protein increased after BOO, while the expression of HGF and c-met protein increased in the group with B10.HGF transplantation after BOO. Intercontraction interval decreased after BOO, but it recovered after B10.HGF transplantation. Maximal voiding pressure (MVP) increased after BOO, and it recovered to levels of the normal control after transplantation of B10.HGF cells. Residual urine volume (RU) increased after BOO, but the RU increase was not reversed by transplantation of B10.HGF cells. Human MSCs overexpressing HGF inhibited collagen deposition and improved cystometric parameters in bladder outlet obstruction of rats. The present study indicates that transplantation of MSCs modified to overexpress HGF could serve as a novel therapeutic strategy against bladder fibrosis in patients with bladder outlet obstruction.

Indoxyl sulfate-induced epithelial-to-mesenchymal transition and apoptosis of renal tubular cells as novel mechanisms of progression of renal disease

Indoxyl sulfate (IS), one of the uremic toxins, is regarded to have a substantial role in the progression of chronic kidney disease (CKD). Epithelial-to-mesenchymal transition (EMT) and apoptosis of renal tubular cells are known to be the critical mechanisms of the development and aggravation of CKD. We investigated the effect of IS on EMT and apoptosis in renal proximal tubular cells, NRK-52E cells. IS significantly inhibited cell proliferation and induced cell migration with a morphological transition from cuboidal epithelial cells to spindle-shaped scattered fibroblast-like cells. IS downregulated the expressions of zonula occluden-1 and E-cadherin, whereas upregulated α-SMA expression at 48 h, which was blocked by a pretreatment of the organic anion transporter, probenecid. IS also induced apoptosis of NRK cells from a concentration of 25 μg/ml with an activation of ERK1/2 and p38 MAP kinase (MAPK). Pretreatment of ERK1/2 or p38 MAPK inhibitors, PD98059 or SB203580, resulted in no significant effect on IS-induced EMT, whereas it ameliorated IS-induced apoptosis of NRK cells. These findings suggested phenotypic transition and apoptosis as potential mechanisms of IS-induced renal damage and the differential role of MAPK activation in IS-induced EMT and apoptosis of renal tubular cells.

Sustained-release prostacyclin analog ONO-1301 ameliorates tubulointerstitial alterations in a mouse obstructive nephropathy model

Tubulointerstitial injuries are crucial histological alterations that predict the deterioration of renal function in chronic kidney disease. ONO-1301, a novel sustained-release prostacyclin analog, accompanied by thromboxane synthase activity, exerts therapeutic effects on experimental pulmonary hypertension, lung fibrosis, cardiomyopathy, and myocardial ischemia, partly associated with the induction of hepatocyte growth factor (HGF). In the present study, we examined the therapeutic efficacies of ONO-1301 on tubulointerstitial alterations induced by unilateral ureteral obstruction (UUO). After inducing unilateral ureteral obstruction in C57/BL6J mice, a single injection of sustained-release ONO-1301 polymerized with poly (D,L-lactic-co-glycolic acid) sustained-release ONO-1301 (SR-ONO) significantly suppressed interstitial fibrosis, accumulation of types I and III collagen, increase in the number of interstitial fibroblast-specific protein-1 (FSP-1)(+) cells, and interstitial infiltration of monocytes/macrophages (F4/80(+)) in the obstructed kidneys (OBK; day 7). Treatment with SR-ONO significantly suppressed the increase of the renal levels of profibrotic factor TGF-β and phosphorylation of Smad2/3, and elevated the renal levels of HGF in the OBK. In cultured mouse proximal tubular epithelial cells (mProx24), ONO-1301 significantly ameliorated the expression of fibroblast-specific protein-1 and α-smooth muscle actin as well as phosphorylation of Smad3 and increased the expression of zonula occludens-1 and E-cadherin in the presence of TGF-β1 as detected by immunoblot and immunocytochemistry, partly dependent on PGI(2) receptor-mediated signaling. Administration of rabbit anti-HGF antibodies, but not the control IgG, partly reversed the suppressive effects of SR-ONO on tubulointerstitial injuries in the OBK. Taken together, our findings suggest the potential therapeutic efficacies of ONO-1301 in suppressing tubulointerstitial alterations partly mediated via inducing HGF, an antifibrotic factor counteracting TGF-β.

Preventive effects and mechanisms of rhein on renal interstitial fibrosis in obstructive nephropathy

Renal interstitial fibrosis is a common outcome of a variety of chronic renal diseases. Here we evaluated the therapeutic efficacy of rhein on renal interstitial fibrosis induced by unilateral ureteral obstruction (UUO) and investigated the potential mechanisms. Mice underwent UUO, followed by orally administrated rhein (150 mg/kg/d) or control vehicle. Renal interstitial injury and the degree of fibrosis were evaluated by pathological staining and Western blot. The possible mechanisms were studied by Western blot, indirect immune-fluorescence and enzyme-linked immunosorbent assay. Our results showed that rhein therapy markedly ameliorated renal interstitial fibrotic lesions, reduced α-smooth muscle actin (α-SMA) expression, attenuated deposition of fibronectin (FN). Rhein also suppressed transforming growth factor-β1 (TGF-β1) and its type I receptor expression in obstructed kidneys. In vitro, rhein abolished the α-SMA and fibronectin expression of rat kidney interstitial fibroblasts cells (NRK-49F) induced by TGF-β1. These observations strongly suggest that rhein is a potent inhibitor of renal interstitial fibrosis, and its therapeutic mechanism is, at least in part, blocking interstitial fibroblasts cells activation.

Telmisartan exerts renoprotective actions via peroxisome proliferator-activated receptor-γ/hepatocyte growth factor pathway independent of angiotensin II type 1 receptor blockade

Angiotensin (Ang) II type 1 receptor blockers have demonstrated beneficial effects beyond blood pressure control in the treatment of chronic kidney disease. There is clinical evidence that telmisartan is more effective than losartan in reducing proteinuria in hypertensive patients with diabetic nephropathy, because it is a partial agonist of peroxisome-proliferator activated receptor-γ (PPARγ), as well as an Ang II type 1 receptor blocker (AMADEO Study [A comparison of telMisartan versus losArtan in hypertensive type 2 DiabEtic patients with Overt nephropathy]). In this study, we examined the role of PPARγ activation in the renal protective actions of telmisartan using Ang II type 1 receptor-deficient mice. Renal injury was induced in Ang II type 1 receptor-deficient mice by producing unilateral ureteral obstruction, which exhibited severe renal interstitial fibrosis and inflammation. In these mice, telmisartan prevented hydronephrosis induced by unilateral ureteral obstruction more strongly than did losartan. Importantly, the prevention of renal atrophy and fibrosis by telmisartan was significantly attenuated by GW9662, a PPARγ antagonist. Interestingly, the downstream effector of PPARγ activation by telmisartan is hepatocyte growth factor (HGF), a well-known antifibrotic factor, because renal HGF expression was significantly increased by telmisartan, and a neutralizing antibody against HGF diminished the renal protective action of telmisartan. These beneficial changes by telmisartan were associated with a decrease in the expression of transforming growth factor-β1 and other proinflammatory and profibrotic cytokine genes through PPARγ/HGF activation. Our findings provide evidence of organ protective actions of telmisartan through the PPARγ/HGF pathway, independent of Ang II type 1 receptor blockade. Further development of the next generation of Ang II type 1 receptor blockers with added organ protective actions, such as PPARγ activation, might provide new beneficial drugs to treat renal and cardiovascular diseases.

VEGF ameliorates tubulointerstitial fibrosis in unilateral ureteral obstruction mice via inhibition of epithelial-mesenchymal transition

AIM

Vascular endothelial growth factor (VEGF) has been shown to be a survival factor for renal tubular epithelial cells. In the present study, we investigated whether administration of VEGF ameliorates tubulointerstitial fibrosis in a mouse model of unilateral ureteral obstruction (UUO).

METHODS

Thirty-six male CD-1 mice were randomly divided into three groups: sham-operation, UUO and UUO+VEGF group. VEGF (50 μg/kg) was subcutaneously injected twice daily from d 1 to d 14. Mice in each group were killed at d 3, 7, or 14 after the operation, and the tubulointerstitial fibrosis was histopathologically evaluated. Human proximal tubular epithelial cells (HK-2) were used for in vitro study. The expression levels of α-SMA, E-cadherin, TGF-β1, CTGF, and BMP-7 in the kidney were determined using Western blot and RT-PCR.

RESULTS

In the UUO mice, the degree of interstitial fibrosis was dramatically increased in a time-dependent manner. At d 3, 7, and 14, both the mRNA and protein expression levels for α-SMA, TGF-β1, and CTGF were significantly upregulated, whereas those for E-cadherin and BMP-7 were significantly downregulated. At d 3 and 7, VEGF treatment significantly reduced interstitial fibrosis and the expression levels for α-SMA, TGF-β1, and CTGF, while significantly increased the expression of E-cadherin and BMP-7, as compared with the UUO mice. At d 14 after operation, no significant differences were observed in the expression of the examined markers between VEGF-treated mice and UUO mice, with the exception of CTGF. In HK-2 cells, VEGF blocked TGF-β1-induced α-SMA and vimentin expression and restored E-cadherin expression in a dose-dependent manner.

CONCLUSION

VEGF may ameliorate renal tubulointerstitial fibrosis at the early stage in UUO mice. This effect may be related to inhibition of VEGF on renal tubular epithelial-mesenchymal transition (EMT).

Cellular and molecular mechanisms of renal fibrosis

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

Effects of ligustrazine on ureteral obstruction-induced renal tubulointerstitial fibrosis

Ligustrazine (LIG) is a purified and chemically identified component of the Chinese herb Ligusticum wallichii Franchat. It is a potent blocker of vasoconstriction and has strong scavenger of oxygen free radicals. We investigated the effect of LIG on renal tubulointerstitial fibrosis using a rat model of unilateral ureteral obstruction. Ligustrazine treatment significantly reduced the scores of interstitial collagen deposition, amounts of hydroxyproline, the density of myofibroblasts and macrophages, and amounts of transforming growth factor-β1 (TGF-β1) and connective tissue growth factor (CTGF) compared with their level in a saline-treated control group. Using quantitative polymerase chain reaction we found that LIG treatment significantly reduced the mRNA expression of TGF-β1, CTGF, monocyte chemoattractant protein-1 and osteopontin. Moreover, the mRNA expression of hepatocyte growth factor and bone morphogenetic protein-7 were significantly increased by LIG. In vitro, LIG inhibited the TGF-β1-induced loss of cytokeratin-18 expression and de novo increase of the expression of α-smooth muscle actin of HK-2 cells in a dose-dependent manner, which suggested that LIG could restrain the process of epithelial-myofibroblast transition of tubular epithelial cells. This study indicates that LIG can attenuate renal tubulointerstitial fibrosis. It might be useful as a potential candidate in the treatment of chronic renal diseases.

Diminished met signaling in podocytes contributes to the development of podocytopenia in transplant glomerulopathy

Transplant glomerulopathy (TxG) can show secondary focal and segmental glomerulosclerosis (FSGS). FSGS in native kidneys is caused by podocytopenia. This study examines podocytopenia and the role of decreased paracrine Met activation on podocytes by decreased glomerular hepatocyte growth factor (HGF) levels in the development of podocytopenia in TxG. Podocytes were counted in 10 zero-hour biopsies and 10 specimens each with and without TxG. HGF/Met was examined with immunostains and quantitative RT-PCR in a set of three consecutive biopsies from 10 patients with TxG, including the diagnostic biopsy (DiagnBx) and the two previous biopsies (1stPrevBx and 2ndPrevBx). Antiapoptotic effects of HGF on podocytes were examined in vitro. Mean podocyte numbers per glomerulus were lower and glomerular volume higher in TxG. Fewer of the two preceding biopsies of the patients than of the controls contained phospho-Met(Tyr1349)-positive podocytes (2 of 8 versus 7 of 7, P = 0.0070; 4 of 9 versus 9 of 9, P = 0.0294). Glomerular HGF mRNA levels were lower in the 1stPrevBx of the patients (0.049 ± 0.083 versus 0.284 ± 0.331; P = 0.0155). In vitro, HGF stimulation of podocytes resulted in antiapoptotic phosphorylation of AKT and extracellular signal-regulated kinase (ERK) and induction of X-linked inhibitor of apoptosis protein (XIAP). Decreased antiapoptotic Met signaling in podocytes, probably due to decreased HGF secretion by glomerular epithelial cells, could contribute to podocyte loss and FSGS in TxG.

The role of EMT in renal fibrosis

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

Systemic administration of naked plasmid encoding HGF attenuates puromycin aminonucleoside-induced damage of murine glomerular podocytes

Podocyte injury is considered to play important roles in the pathogenesis of human glomerular disease. There is accumulating evidence suggesting that hepatocyte growth factor (HGF) elicits preventive activity for glomerular cells in animal models of chronic renal diseases. In this study, we demonstrated that delivery of a naked plasmid vector encoding the human HGF gene into mice by a hydrodynamic-based in vivo gene transfection approach markedly reduced proteinuria and attenuated podocyte injury in a mouse model induced by puromycin aminonucleoside (PAN) injection. Systemic administration by rapid injection via the tail vein of a naked plasmid containing HGF cDNA driven under a cytomegalovirus promoter (pCMV-HGF) produced a remarkable level of human HGF protein in the circulation. Tissue distribution studies suggested that the kidney expressed a high level of the HGF transgene. Meanwhile, compared with tubules and interstitium, a higher level of exogenous HGF protein was detected in the glomeruli. Administration of pCMV-HGF dramatically abated the urine albumin excretion and podocyte injury in PAN nephropathy in mice. Exogenous expression of HGF produced evidently beneficial effects, leading to restoration of Wilms' tumor-1 (WT1) and α-actinin-4 expression and attenuation of ultrastructural damage of the podocytes. In vitro, HGF not only restored WT1 and α-actinin-4 expression but also inhibited albumin leakage of podocytes incubated with PAN in a Transwell culture chamber. These results suggest that HGF might provide a novel strategy for amelioration of podocyte injury.

Angiotensin II as a morphogenic cytokine stimulating renal fibrogenesis

Inhibitors of the renin-angiotensin-aldosterone system attenuate glomerulosclerosis and interstitial fibrosis. Although the mechanisms underlying their antifibrotic effects are complex, angiotensin II (Ang II) emerges as a major profibrogenic cytokine. Ang II modulates renal cell growth, extracellular matrix synthesis, and degradation by multiple fibrotic pathways. One of the main targets of Ang II in renal fibrosis is TGFβ. Many, but not all, of the stimulatory effects of Ang II on fibrogenesis depend on the induction of TGFβ and its downstream mediators of matrix accumulation, inflammation, and apoptosis. However because of the difficulty in targeting TGFβ, connective tissue growth factor β (CTGF), a downstream mediator of TGFβ, has become a more promising antifibrotic target. Ang II can directly induce expression of renal CTGF and mediate epithelial-mesenchymal transition. Other profibrotic factors stimulated by Ang II include endothelin-1, plasminogen activator inhibitor-1, matrix metalloproteinase (MMP)-2, and a tissue inhibitor of metalloproteinase-2. Finally, connections among Ang II, hypoxia, and the induction of hypoxia-inducible factor-1α contribute to fibrogenesis. A better understanding of the multiple morphogenic effects of Ang II may be necessary to develop better strategies to halt the progression of renal disease.

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.

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.

Etiopathology of chronic tubular, glomerular and renovascular nephropathies: clinical implications

Chronic kidney disease (CKD) comprises a group of pathologies in which the renal excretory function is chronically compromised. Most, but not all, forms of CKD are progressive and irreversible, pathological syndromes that start silently (i.e. no functional alterations are evident), continue through renal dysfunction and ends up in renal failure. At this point, kidney transplant or dialysis (renal replacement therapy, RRT) becomes necessary to prevent death derived from the inability of the kidneys to cleanse the blood and achieve hydroelectrolytic balance. Worldwide, nearly 1.5 million people need RRT, and the incidence of CKD has increased significantly over the last decades. Diabetes and hypertension are among the leading causes of end stage renal disease, although autoimmunity, renal atherosclerosis, certain infections, drugs and toxins, obstruction of the urinary tract, genetic alterations, and other insults may initiate the disease by damaging the glomerular, tubular, vascular or interstitial compartments of the kidneys. In all cases, CKD eventually compromises all these structures and gives rise to a similar phenotype regardless of etiology. This review describes with an integrative approach the pathophysiological process of tubulointerstitial, glomerular and renovascular diseases, and makes emphasis on the key cellular and molecular events involved. It further analyses the key mechanisms leading to a merging phenotype and pathophysiological scenario as etiologically distinct diseases progress. Finally clinical implications and future experimental and therapeutic perspectives are discussed.

Tranilast modulates fibrosis, epithelial-mesenchymal transition and peritubular capillary injury in unilateral ureteral obstruction rats

AIM

Tranilast is an anti-allergic compound suppressing transforming growth factor-beta 1 (TGF-β1) induced fibrosis. This study evaluated the efficacy of tranilast to attenuate renal fibrosis induced by unilateral ureteral obstruction (UUO) in rats in relation to epithelial-mesenchymal transition (EMT) and peritubular capillary injury.

METHODS

Rats were divided into four groups: UUO with vehicle or tranilast and sham operation with vehicle or tranilast. Tranilast (400 mg/kg/day) was administrated to rats for 7 and 14 days after UUO.

RESULTS

Fibrosis and tubular injuries were attenuated in UUO kidneys with tranilast (Tr-UUO kidneys) compared with UUO kidneys with vehicle (V-UUO kidneys). Decreased E-cadherin and increased vimentin expression in the tubular epithelium and Snail expression in V-UUO kidneys were also attenuated in Tr-UUO kidneys in which heparan sulfate proteoglycan in the tubular basement membrane was preserved and matrix metalloproteinase-2 expression was attenuated. Increased TGF-β1 and phospho-Smad2 expression and increased numbers of myofibroblasts and macrophages in V-UUO kidneys were attenuated by tranilast. Decreased VE-cadherin expression and cytoplasmic swelling of the endothelium of peritubular capillaries that occurred in V-UUO kidneys was prevented by tranilast.

CONCLUSIONS

Tranilast modulates fibrogenesis by reducing EMT, preventing disintegration of the tubular basement membrane, and reducing peritubular capillary injury in UUO kidneys.

Mesenchymal stem cells in renal function recovery after acute kidney injury: use of a differentiating agent in a rat model

Acute kidney injury (AKI) is a major health care condition with limited current treatment options. Within this context, stem cells may provide a clinical approach for AKI. Moreover, a synthetic compound previously developed, hyaluronan monoesters with butyric acid (HB), able to induce metanephric differentiation, formation of capillary-like structures, and secretion of angiogenic cytokines, was tested in vitro. Thereafter, we investigated the effects of human mesenchymal stem cells from fetal membranes (FMhMSCs), both treated and untreated with HB, after induction of ischemic AKI in a rat model. At reperfusion following 45-min clamping of renal pedicles, each rat was randomly assigned to one of four groups: CTR, PBS, MSC, and MSC-HB. Renal function at 1, 3, 5, and 7 days was assessed. Histological samples were analyzed by light and electron microscopy and renal injury was graded. Cytokine analysis on serum samples was performed. FMhMSCs induced an accelerated renal functional recovery, demonstrated by biochemical parameters and confirmed by histology showing that histopathological alterations associated with ischemic injury were less severe in cell-treated kidneys. HB-treated rats showed a minor degree of inflammation, both at cytokine and TEM analyses. Better functional and morphological recovery were not associated to stem cells' regenerative processes, but possibly suggest paracrine effects on microenvironment that induce retrieval of renal damaged tissues. These results suggest that FMhMSCs could be useful in the treatment of AKI and the utilization of synthetic compounds could enhance the recovery induction ability of cells.

Mice lacking the matrix metalloproteinase-9 gene reduce renal interstitial fibrosis in obstructive nephropathy

Matrix metalloproteinase-9 (MMP-9) is one of the major components of the matrix proteolytic network, and its role in the pathogenesis of renal interstitial fibrosis remains largely unknown. Here, we demonstrate that ablation of MMP-9 attenuated renal interstitial fibrotic lesions in obstructive nephropathy. Mice lacking MMP-9 were less likely to develop morphological injury, which was characterized by a reduced disruption of tubular basement membrane (TBM) and expression of fibronectin as well as deposition of total tissue collagen in the kidneys after sustained ureteral obstruction compared with their wild-type counterparts. Deficiency of MMP-9 blocked tubular epithelial-to-myofibroblast transition (EMT) but did not alter the induction of transforming growth factor (TGF)-β1 axis expression in the obstructed kidneys. In vitro, TBM, which was digested by MMP-9 instead of MMP-9 itself, induces EMT and enhances migration of transformed cells. Thus increased MMP-9 is detrimental in renal interstitial fibrogenesis through a cascade of events that leads to TBM destruction and in turn to promotion of EMT. Our findings establish a crucial and definite importance of MMP-9 in the pathogenesis of renal interstitial fibrosis at the whole-animal level.

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.

Asiatic acid preserves beta cell mass and mitigates hyperglycemia in streptozocin-induced diabetic rats

BACKGROUND

Type 1 diabetes is a chronic condition in which the pancreas produces little or no insulin due to the loss or dysfunction of pancreatic beta cells. This study investigated the beneficial effects of asiatic acid-a triterpenoid compound-preserved beta mass and mitigated hyperglycemia in streptozocin-induced diabetic rats.

METHODS

Diabetes mellitus was induced in adult male Wistar rats by a single intraperitoneal injection of streptozocin (60 mg/kg body weight). The diabetic rats were divided into untreated and asiatic acid (25 mg/kg) groups. Controls were intraperitoneal injection with citrate buffer. Blood glucose level, plasma insulin, and pancreas immunohistochemistry analysis were examined after a 2-week experimental period. AKT and Bcl-xL expression in the pancreatic islets of rats were evaluated by Western blot methods.

RESULTS

Blood glucose levels were significantly reduced in rats receiving asiatic acid after streptozocin administration. Asiatic acid concomitantly increased serum insulin levels in diabetic rats. Immunohistochemical staining revealed a marked preservation by asiatic acid of insulin-producing beta cells in the pancreatic islets of the diabetic rats. Furthermore, asiatic acid in vivo induced pro-survival Akt kinase activation and Bcl-xL expression in the pancreatic islets of diabetic rats.

CONCLUSIONS

These results suggest that asiatic acid exerts its glucose-lowering effects, in part through influences on beta-cell mass. Asiatic acid administration resulted in preservation and restoration of beta-cell mass and function in diabetic rodent models.