Mechanisms of tubulointerstitial fibrosis

Osteopontin deficiency protects against aldosterone-induced inflammation, oxidative stress, and interstitial fibrosis in the kidney

Osteopontin (OPN) has been implicated in the pathology of several renal conditions. Recently, we demonstrated in vitro that aldosterone has important roles in collagen synthesis by inducing OPN (Irita J, Okura T, Kurata M, Miyoshi K, Fukuoka T, Higaki J. Hypertension 51: 507–513, 2008). The aim of the present study was to clarify the roles of OPN in aldosterone-mediated renal fibrosis by infusing aldosterone into either wild-type (WT) or OPN knockout mice (OPN−/−). We used uninephrectomized mice treated with aldosterone and high salt to exacerbate renal fibrosis. After 4 wk of treatment with aldosterone, we showed similar increases in systolic blood pressure in both strains of mice. Urine albumin excretion was greater in aldosterone-infused WT mice than in aldosterone-infused OPN−/− mice. Immunohistochemical analysis showed high levels of OPN expression in aldosterone-infused WT mice. Interstitial fibrosis and inflammatory infiltrations were increased in aldosterone-infused WT mice compared with either vehicle-infused WT or aldosterone-infused OPN−/− mice. These changes were ameliorated markedly by eplerenone treatment in aldosterone-infused WT mice. Aldosterone-infused WT mice also had increased expression of NADPH oxidase subunits compared with aldosterone-infused OPN−/− mice. We observed a marked increase in oxidative stress markers in aldosterone-infused WT mice compared with aldosterone-infused OPN−/− mice. These results indicate that OPN is a promoter of aldosterone-induced inflammation, oxidative stress, and interstitial fibrosis in the kidney and suggest that inhibition of OPN may be a potential therapeutic target for prevention of renal injury.

Silencing of hypoxia-inducible factor-1α gene attenuated angiotensin II-induced renal injury in Sprague-Dawley rats

Although it has been shown that upregulation of hypoxia-inducible factor (HIF)-1α is protective in acute ischemic renal injury, long-term overactivation of HIF-1α is implicated to be injurious in chronic kidney diseases. Angiotensin II (Ang II) is a well-known pathogenic factor producing chronic renal injury and has also been shown to increase HIF-1α. However, the contribution of HIF-1α to Ang II-induced renal injury has not been evidenced. The present study tested the hypothesis that HIF-1α mediates Ang II-induced renal injury in Sprague-Dawley rats. Chronic renal injury was induced by Ang II infusion (200 ng/kg per minute) for 2 weeks in uninephrectomized rats. Transfection of vectors expressing HIF-1α small hairpin RNA into the kidneys knocked down HIF-1α gene expression by 70%, blocked Ang II-induced HIF-1α activation, and significantly attenuated Ang II-induced albuminuria, which was accompanied by inhibition of Ang II-induced vascular endothelial growth factor, a known glomerular permeability factor, in glomeruli. HIF-1α small hairpin RNA also significantly improved the glomerular morphological damage induced by Ang II. Furthermore, HIF-1α small hairpin RNA blocked Ang II-induced upregulation of collagen and α-smooth muscle actin in tubulointerstitial region. There was no difference in creatinine clearance and Ang II-induced increase in blood pressure. HIF-1α small hairpin RNA had no effect on Ang II-induced reduction in renal blood flow and hypoxia in the kidneys. These data suggested that overactivation of HIF-1α-mediated gene regulation in the kidney is a pathogenic pathway mediating Ang II-induced chronic renal injuries, and normalization of overactivated HIF-1α may be used as a treatment strategy for chronic kidney damages associated with excessive Ang II.

Smad3-mediated upregulation of miR-21 promotes renal fibrosis

TGF-β/Smad signaling plays a role in fibrogenesis, but therapies targeting TGF-β are ineffective in treating renal fibrosis. Here, we explored the therapeutic potential of targeting TGF-β-induced microRNA in the progression of renal fibrosis. Microarray analysis and real-time PCR revealed upregulation of miR-21 in tubular epithelial cells (TECs) in response to TGF-β. Lack of Smad3, but not lack of Smad2, prevented cells from upregulating miR-21 in response to TGF-β. In addition, Smad3-deficient mice were protected from upregulation of miR-21 and fibrosis in the unilateral ureteral obstruction model. In contrast, conditional knockout of Smad2 enhanced miR-21 expression and renal fibrosis. Furthermore, ultrasound-microbubble-mediated gene transfer of a miR-21-knockdown plasmid halted the progression of renal fibrosis in established obstructive nephropathy. In conclusion, these data demonstrate that Smad3, but not Smad2, signaling increases expression of miR-21, which promotes renal fibrosis. Inhibition of miR-21 may be a therapeutic approach to suppress renal fibrosis.

Aldosterone-induced fibrosis in the kidney: questions and controversies

Over the years, aldosterone has been a favorite topic of renal physiologists given its role in the maintenance of body fluids. Investigators only recently are coming to appreciate a second proinflammatory and profibrotic role for this hormone. Mineralocorticoids such as aldosterone trigger a profibrotic process that in many respects mimics the early phase of wound healing. Depending on the type of cell involved, aldosterone may activate the profibrotic process through classic mineralocorticoid receptors, nonclassic membrane-associated mineralocorticoid receptors, and/or glucocorticoid receptors. In the kidney, the actions of aldosterone can be attenuated by 11-dehydro metabolites of endogenous glucocorticoids generated by isoforms of the enzyme 11β-hydroxysteroid dehydrogenase (11β-HSD-1 and 11β-HSD-2). Thus, the renal 11β-HSD isoforms may have 2 functions: to block the improper activation of mineralocorticoid receptors by binding endogenous glucocorticoids and to synthesize agents that limit the actions of aldosterone. Although sodium in the diet has been implicated in aggravating aldosterone-induced renal fibrotic processes, preliminary findings are consistent with the view that aldosterone alone can initiate matrix production in renal tissue even in the absence of active sodium transport. Thus, there is a growing body of laboratory and clinical evidence supporting the use of inhibitors of aldosterone action in patients with both glomerular and tubular diseases.

The Ayurvedic Medicine Salacia oblonga Attenuates Diabetic Renal Fibrosis in Rats: Suppression of Angiotensin II/AT1 Signaling

In human diabetic nephropathy, the extent of tubulointerstitial fibrosis is the leading cause of end-stage renal disease; fibrosis is closely correlated with renal dysfunction. Although a wide array of medicinal plants play a role in the prevention and treatment of diabetes, there are few reports of the application of herbal medicines in amelioration of renal fibrosis, or the underlying mechanisms by which such benefits are mediated. The efficacy of the Ayurvedic antidiabetic medicine Salacia oblonga (SO) root on rat renal fibrosis was investigated. An aqueous extract from SO (100 mg/kg, p.o., 6 weeks) diminished renal glomerulosclerosis and interstitial fibrosis in Zucker diabetic fatty (ZDF) rats, as revealed by van Giesen-staining. SO also reduced renal salt-soluble, acid-soluble and salt-insoluble collagen contents. These changes were accompanied by normalization of hypoalbuminemia and BUN. Gene profiling revealed that the increase in transcripts encoding the glomerulosclerotic mediators collagen I, collagen IV, fibronectin, angiotensin II type 1 receptor (AT1), transforming growth factor (TGF)-β1, plasminogen activator inhibitor (PAI)-1 observed in ZDF rat kidney was suppressed by SO. In rat-derived mesangial cells, similar to the effect of the AT1 antagonist telmisartan, SO and its major component mangiferin suppressed the stimulatory effect of angiotensin II on proliferation and increased mRNA expression and/or activities of collagen I, collagen IV, fibronectin, AT1, TGF-β1 and PAI-1. Considered together the present findings demonstrate that SO attenuates diabetic renal fibrosis, at least in part by suppressing anigiotensin II/AT1 signaling. Further, it now emerges that mangiferin is an effective antifibrogenic agent.

Adenovirus-mediated HIF-1α gene transfer promotes repair of mouse airway allograft microvasculature and attenuates chronic rejection

Chronic rejection, manifested as small airway fibrosis (obliterative bronchiolitis [OB]), is the main obstacle to long-term survival in lung transplantation. Recent studies demonstrate that the airways involved in a lung transplant are relatively hypoxic at baseline and that OB pathogenesis may be linked to ischemia induced by a transient loss of airway microvasculature. Here, we show that HIF-1α mediates airway microvascular repair in a model of orthotopic tracheal transplantation. Grafts with a conditional knockout of Hif1a demonstrated diminished recruitment of recipient-derived Tie2⁺ angiogenic cells to the allograft, impaired repair of damaged microvasculature, accelerated loss of microvascular perfusion, and hastened denudation of epithelial cells. In contrast, graft HIF-1α overexpression induced via an adenoviral vector prolonged airway microvascular perfusion, preserved epithelial integrity, extended the time window for the graft to be rescued from chronic rejection, and attenuated airway fibrotic remodeling. HIF-1α overexpression induced the expression of proangiogenic factors such as Sdf1, Plgf, and Vegf, and promoted the recruitment of vasoreparative Tie2⁺ cells. This study demonstrates that a therapy that enhances vascular integrity during acute rejection may promote graft health and prevent chronic rejection.

The Impact of Overnutrition on Insulin Metabolic Signaling in the Heart and the Kidney

Overnutrition characterized by overconsumption of food rich in fat and carbohydrates is a significant contributor to hypertension, type 2 diabetes, and the cardiorenal syndrome. Overnutrition activates the renin-angiotensin-aldosterone system (RAAS) and causes chronic exposure of cardiovascular and renal tissue to increased circulating nutrients, insulin (INS), and angiotensin II (ANG II). Emerging evidence suggests that overnutrition, aldosterone, and ANG II promote INS resistance, a chronic condition that underlies these co-morbidities, through activation of the mammalian target of the rapamycin (mTOR)/S6 kinase 1 (S6K1) signaling pathway in cardiovascular tissue and the kidney. However, a novel ANG II type 2 receptor (AT2R)-mediated cross talk between the RAAS and mTOR pathways ameliorates overnutrition-induced activation of mTOR/S6K1 signaling in cardiovascular tissue of rats, mice, and humans and confers cardioprotection.

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

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

Blocking core fucosylation of TGF-β1 receptors downregulates their functions and attenuates the epithelial-mesenchymal transition of renal tubular cells

Posttranslational modification of proteins could regulate their multiple biological functions. Transforming growth factor-β receptor I and II (ALK5 and TGF-βRII), which are glycoproteins, play important roles in the renal tubular epithelial-mesenchymal transition (EMT). In the present study, we examined the role of core fucosylation of TGF-βRII and ALK5, which is regulated by α-1,6 fucosyltransferase (Fut8), in the process of EMT of cultured human renal proximal tubular epithelial (HK-2) cells. The typical cell model of EMT induced by TGF-β1 was constructed to address the role of core fucosylation in EMT. Core fucosylation was found to be essential for both TGF-βRII and ALK5 to fulfill their functions, and blocking it with Fut8 small interfering RNA greatly reduced the phosphorylation of Smad2/3 protein, caused the inactivation of TGF-β/Smad2/3 signaling, and resulted in remission of EMT. More importantly, even with high levels of expressions of TGF-β1, TGF-βRII, and ALK5, blocking core fucosylation also could attenuate the EMT of HK-2 cells. Thus blocking core fucosylation of TGF-βRII and ALK5 may attenuate EMT independently of the expression of these proteins. This study may provide new insight into the role of glycosylation in renal interstitial fibrosis. Furthermore, core fucosylation may be a novel potential therapeutic target for treatment of renal tubular EMT.

Lentiviral-mediated RNA interference against TGF-beta receptor type II in renal epithelial and fibroblast cell populations in vitro demonstrates regulated renal fibrogenesis that is more efficient than a nonlentiviral vector

Background. Lentiviral constructs reportedly can integrate into the genome of non-dividing, terminally differentiated cells and dividing cells, for long-term gene expression. This investigation tested whether a third generation lentiviral-mediated small interfering RNA (siRNA) delivered into renal epithelial and fibroblast cells against type II transforming growth factor-beta receptor (siRNA-TBRII) could better attenuate renal fibrogenesis in comparison with a non-lentiviral construct. Methods. HIV-derived lentiviral and non-lentiviral constructs were used to transfect cells with siRNA-TBRII or siRNA-EGFP control. Human embryonic kidney (HEK-293T), renal epithelial cells (NRK-52E) and renal fibroblasts (NRK-49F) were transfected and gene silencing quantified (fluorescence microscopy, Western blotting, fluorescence-activated cell sorting). Renal fibrogenesis was assessed using extracellular matrix protein synthesis (fibronectin and collagen-III; Western immunoblot), and α-smooth muscle actin (α-SMA) was analysed as a marker of fibroblast activation and epithelial-to-mesenchymal transdifferentiation (EMT). Results. Lentiviral-mediated siRNA-TBRII significantly suppressed TBRII expression in all cell lines, and also significantly suppressed renal fibrogenesis. In comparison with the non-lentiviral construct, lentiviral-mediated siRNA-TBRII produced stronger and more persistent inhibition of collagen-III in NRK-49F cells, fibronectin in all renal cell lines, and α-SMA in renal epithelial cells. Conclusions. Lentiviral vector systems against TBRII can be delivered into renal cells to efficiently limit renal fibrogenesis by sequence-specific gene silencing.

Proteomics characterization of cell model with renal fibrosis phenotype: osmotic stress as fibrosis triggering factor

Renal fibroblasts are thought to play a major role in the development of renal fibrosis (RF). The mechanisms leading to this renal alteration remain poorly understood. We performed differential proteomic analyses with two established fibroblast cell lines with RF phenotype to identify new molecular pathways associated with RF. Differential 2-DE combined with mass spectrometry analysis revealed the alteration of more than 30 proteins in fibrotic kidney fibroblasts (TK188) compared to normal kidney fibroblast (TK173). Among these proteins, markers of the endoplasmic reticulum (ER) stress- and the unfolded protein response (UPR) pathway (GRP78, GRP94, ERP57, ERP72, and CALR) and the oxidative stress pathway proteins (PRDX1, PRDX2, PRDX6, HSP70, HYOU1) were highly up-regulated in fibrotic cells. Activation of these stress pathways through long time exposition of TK173, to high NaCl or glucose concentrations resulted in TK188 like phenotype. Parallel to an increase in reactive oxygen species, the stressed cells showed significant alteration of fibrosis markers, ER-stress and oxidative stress proteins. Similar effects of osmotic stress could be also observed on renal proximal tubule cells. Our data suggest an important role of the ER-stress proteins in fibrosis and highlights the pro-fibrotic effect of osmotic stress through activation of oxidative stress and ER-stress pathways.

Intragraft tubular vimentin and CD44 expression correlate with long-term renal allograft function and interstitial fibrosis and tubular atrophy

BACKGROUND

Development of interstitial fibrosis and tubular atrophy (IF/TA) is the main histologic feature involved in renal allograft deterioration. The aim of this study was to validate whether de novo tubular expression of CD44 (transmembrane glycoprotein) and vimentin (mesenchymal cell marker), both involved in renal fibrosis, can operate as surrogate markers for late IF/TA and renal function. Furthermore, we wanted to establish the interrater reproducibility for the scoring system, which can be a problem in histologic assessments.

METHODS

Six-month protocol renal allograft biopsies (n=30 for matching 12 months estimated glomerular filtration rate (eGFR) from which 20 matched the 12-month protocol biopsy) were immunostained for CD44 and vimentin, semiquantitatively scored by three observers of two centers, and correlated with IF/TA and eGFR at 12 months.

RESULTS

The interobserver agreement was excellent for CD44 (Kendall's W-coefficient: 0.69; P<0.001) and vimentin (Kendall's W-coefficient: 0.79; P<0.001). CD44 and vimentin expression at 6 months were significantly correlated with IF/TA (rho=0.481 for CD44 and rho=0.619 for vimentin) and eGFR (rho=-0.569 for CD44 and rho=-0.376 for vimentin) at 12 months.

CONCLUSIONS

Summarizing, de novo tubular expression of CD44 and vimentin can function as surrogate marker for IF/TA and eGFR at 12 months. Further area under receiver operator characteristic curve analysis has to establish the predictive value for both biomarkers.

Hypoxia-inducible factor-1α contributes to the profibrotic action of angiotensin II in renal medullary interstitial cells

To examine whether hypoxia-inducible factor (HIF)-1α mediates the profibrotic effects of angiotensin II, we treated cultured renal medullary interstitial cells with angiotensin II and found that it increased HIF-1α levels. This was accompanied by a significant upregulation of collagen I/III, the tissue inhibitor of metalloproteinase-1, elevation of the proliferation marker proliferating cell nuclear antigen, and a transdifferentiation marker vimentin. All these effects of angiotensin II were completely blocked by siRNA for HIF-1α but not HIF-2α. Overexpression of a prolyl-hydroxylase domain-containing protein 2 (PHD2) transgene, the predominant renal HIF prolyl-hydroxylase, attenuated the effects of angiotensin II and its gene silencing enhanced the effects of angiotensin II. Removal of hydrogen peroxide eliminated angiotensin II-induced profibrotic effects. A 2-week infusion of rats with angiotensin II increased the expression of HIF-1α and α-smooth muscle actin, another marker of transdifferentiation, in renal medullary interstitial cells in vivo. Thus, our study suggests that HIF-1α mediates angiotensin II-induced profibrotic effects through activation of cell transdifferentiation. We propose that redox regulation of prolyl-PHD2 plays a critical role in angiotensin II-induced activation of HIF-1α in renal cells.

Origin of new cells in the adult kidney: results from genetic labeling techniques

For nearly 100 years, developmental biologists have utilized fate mapping to understand the contributions of progenitor populations to organogenesis. More recently, Cre-Lox technology has allowed genetic fate mapping in adult mice, clarifying cell hierarchies in adult kidney disease models. In ischemia-reperfusion injury, genetic labeling of epithelial cells has demonstrated that intrinsic epithelial cells are responsible for nephron repair and not an interstitial or other non-epithelial cell type. In fibrotic kidney injury, fate mapping techniques have strongly challenged the theory that epithelial cells traverse the basement membrane to become myofibroblasts in a process of epithelial-to-mesenchymal transition and also indicate that interstitial pericytes/perivascular fibroblasts are the authentic myofibroblast progenitor pool. This mini review will summarize the fate mapping approach in mice, convey recent developments in kidney disease models, and outline future opportunities to apply this technology to better understand the cellular mechanisms of adult kidney homeostasis and disease.

Effect of Lactobacillus reuteri GMNL-263 treatment on renal fibrosis in diabetic rats

Hyperglycemia is the most important factor in the progression of renal fibrosis in diabetic kidney. Prevention and treatment of renal fibrosis may improve diabetic nephropathy. To explore whether probiotic Lactobacillus reuteri GMNL-263 treatment was linked to altered hyperglycemia-mediated renal fibrosis in diabetic kidney, the mechanisms of L. reuteri GMNL-263 treatment responsible for the inhibition of renal fibrosis in streptozotocin (STZ)-induced diabetic rats were examined. Diabetic rats were induced by intraperitoneal injection of STZ (50 mg/kg). Induction of diabetes was confirmed by measurement of the blood glucose using the glucose oxidase method, and hyperglycemic rats with levels >16 mmol/L were used. We found that L. reuteri GMNL-263 treatment caused reduction of glycated hemoglobin and blood glucose levels in STZ-induced diabetic rats for 28 days (all p<0.05). Treatment with L. reuteri GMNL-263 increased body weight but decreased kidney weight in diabetic rats as compared to diabetic control (p<0.05). In diabetic renal cortex, the Janus kinase 2/signal transducers and activators of transcription 1 (but not extracellular signal-regulated kinase/c-Jun N-terminal kinase/p38 mitogen-activated protein kinase) activation was markedly blocked by L. reuteri GMNL-263 treatment. The ability of L. reuteri GMNL-263 treatment to inhibit renal fibrosis was verified by the observation that it significantly decreased protein levels of plasminogen activator inhibitor-1, p21(Waf1/Cip1), α-smooth muscle actin, and fibronectin in diabetic renal cortex. The results obtained in this study indicate that L. reuteri GMNL-263 treatment may protect STZ-induced diabetic rats from hyperglycemia-enhanced renal fibrosis.

Involvement of epimorphin in the repair of experimental renal fibrosis in mice

Interaction between epithelial cells and mesenchymal cells is essential in normal organ morphogenesis and in tissue repair after injury. Epimorphin, a mesenchymal protein that regulates epithelial morphogenesis through epithelial-mesenchymal interactions, has recently attracted attention as an important modulator of tissue repair. In this study we analyzed the role of epimorphin in renal fibrosis. We first found a progressive increase in epimorphin expression corresponding to the progression of renal fibrosis in mice with unilateral ureteral obstruction (UUO). To determine whether this expression has a role in the repair or progression of renal fibrosis, we analyzed a model of renal fibrosis repair, the UUO-release (UUO-R) model. Epimorphin expression was increased at 3 and 7 days after the UUO-R rather than on the day of release, but was decreased at 21 days after the release. Inhibition of endogenous epimorphin with anti-epimorphin antibody (MC-1) significantly delayed the repair of fibrosis. When compared with normal-IgG-injected mice, MC-1-injected mice showed significantly decreased renal matrix metalloproteinase (MMP)-2 and MMP-9 expressions by western blotting and increased expression of TGF-beta and collagen-I mRNA by real-time RT-PCR. Recombinant epimorphin induced prominent increases in MMP-2 and MMP-9 activities in the culture media of renal interstitial fibroblasts in vitro. These findings indicate that epimorphin has a pivotal role in the repair of renal fibrosis by modulating both extracellular matrix (ECM) degradation and its production.

New pharmacological treatments for improving renal outcomes in diabetes

Diabetic nephropathy is the most common and most rapidly growing cause of end-stage renal failure in developed countries. Diabetic nephropathy results from complex interactions between genetic, metabolic and hemodynamic factors. Improvements in our understanding of the pathogenesis of fibrosis associated with diabetic kidney disease have led to the identification of several novel targets for the treatment of diabetic nephropathy. Albuminuria is a useful clinical marker of diabetic nephropathy, as it can be used to predict a decline in renal function. A reduction in albuminuria might not, however, be reflective of a protective effect of therapies focused on ameliorating renal fibrosis. Although new strategies for slowing down the progression of several types of renal disease have emerged, the challenge of arresting the relentless progression of diabetic nephropathy remains. In this Review, we discuss novel pharmacological approaches that aim to improve the renal outcomes of diabetic nephropathy, including the use of direct renin inhibitors and statins. We also discuss the promise of using antifibrotic agents to treat diabetic nephropathy. The need for novel biomarkers of diabetic nephropathy is also highlighted.

Vitamin D receptor attenuates renal fibrosis by suppressing the renin-angiotensin system

Analogs of vitamin D attenuate renal injury in several models of kidney disease, but the mechanism underlying this renoprotective effect is unknown. To address the role of the vitamin D receptor (VDR) in renal fibrogenesis, we subjected VDR-null mice to unilateral ureteral obstruction for 7 days. Compared with wild-type mice, VDR-null mice developed more severe renal damage in the obstructed kidney, with marked tubular atrophy and interstitial fibrosis. Significant induction of extracellular matrix proteins (fibronectin and collagen I), profibrogenic and proinflammatory factors (TGF-beta, connective tissue growth factor, and monocyte chemoattractant protein 1), and epithelial-to-mesenchymal transition accompanied this histologic damage. Because VDR ablation activates the renin-angiotensin system and leads to accumulation of angiotensin II (AngII) in the kidney, we assessed whether elevated AngII in the VDR-null kidney promotes injury. Treatment with the angiotensin type 1 antagonist losartan eliminated the difference in obstruction-induced interstitial fibrosis between wild-type and VDR-null mice, suggesting that AngII contributes to the enhanced renal fibrosis observed in obstructed VDR-null kidneys. Taken together, these results suggest that the VDR attenuates obstructive renal injury at least in part by suppressing the renin-angiotensin system.

Cinnamaldehyde impairs high glucose-induced hypertrophy in renal interstitial fibroblasts

Cinnamaldehyde is a major and a bioactive compound isolated from the leaves of Cinnamomum osmophloeum kaneh. To explore whether cinnamaldehyde was linked to altered high glucose (HG)-mediated renal tubulointerstitial fibrosis in diabetic nephropathy (DN), the molecular mechanisms of cinnamaldehyde responsible for inhibition of HG-induced hypertrophy in renal interstitial fibroblasts were examined. We found that cinnamaldehyde caused inhibition of HG-induced cellular mitogenesis rather than cell death by either necrosis or apoptosis. There were no changes in caspase 3 activity, cleaved poly(ADP-ribose) polymerase (PARP) protein expression, and mitochondrial cytochrome c release in HG or cinnamaldehyde treatments in these cells. HG-induced extracellular signal-regulated kinase (ERK)/c-Jun N-terminal kinase (JNK)/p38 mitogen-activated protein kinase (MAPK) (but not the Janus kinase 2/signal transducers and activators of transcription) activation was markedly blocked by cinnamaldehyde. The ability of cinnamaldehyde to inhibit HG-induced hypertrophy was verified by the observation that it significantly decreased cell size, cellular hypertrophy index, and protein levels of collagen IV, fibronectin, and alpha-smooth muscle actin (alpha-SMA). The results obtained in this study suggest that cinnamaldehyde treatment of renal interstitial fibroblasts that have been stimulated by HG reduces their ability to proliferate and hypertrophy through mechanisms that may be dependent on inactivation of the ERK/JNK/p38 MAPK pathway.

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.

Expression of P311, a transforming growth factor beta latency-associated protein-binding protein, in human kidneys with IgA nephropathy

Background

In cultured NIH3T3 cells, P311 binds to the transforming growth factor-beta (TGF-β)-1 latency-associated protein (LAP) and induces the myofibroblast phenotype. In this study, we determined the levels of P311 and TGF-β1 proteins in tubulointerstitial tissue of patients with different severities of immunoglobulin-A nephropathy (IgAN), and analyzed the relationships between P311 protein expression and clinical data.

Methods

A total of 57 patients with IgAN and 5 controls (from partial nephrectomy) were included. P311 and TGF-β1 protein expression were measured by immunohistochemistry and clinical data (proteinuria, serum creatinine (Scr), eGFR and biopsy index) were recorded. The relationship between P311, TGF-β1, and clinical data was analyzed.

Results

P311 expression was significantly higher in the kidneys of IgAN patients than in controls and was higher in patients with advanced pathological grades of IgAN. P311 protein expression in tubulointerstitial tissue correlated with TGF-β1 and proteinuria. P311 expression was higher in patients with Scr > 133 μmol/L than in patients with Scr < 133 μmol/L.

Conclusion

P311 protein expression in the kidneys of IgAN patients correlates with TGF-β1 expression and with proteinuria. P311 might be a key cytokine in renal fibrosis and be involved in the progression of IgAN.

Potassium channels: the 'master switch' of renal fibrosis?

Progressive renal fibrosis resulting from proliferation of interstitial fibroblasts is a hallmark of chronic kidney failure, whatever the origin. The intermediate/small-conductance Ca(2+)-activated K(+) channel (K(Ca)3.1) promotes mitogenesis in several cell types by altering the membrane potential, thus enabling extracellular Ca(2+) entry. Grgic et al. evaluated the role of K(Ca)3.1 in renal fibroblast proliferation, testing whether deficiency or pharmacological blockade of K(Ca)3.1 suppressed development of renal fibrosis. Mitogens stimulated K(Ca)3.1 in murine renal fibroblasts via a MEK-dependent mechanism, while selective blockade of K(Ca)3.1 inhibited fibroblast proliferation by promoting G0/G1 arrest. In a classical model of renal fibrosis, mouse unilateral ureteral obstruction (UUO), robust up-regulation of K(Ca)3.1 was detectable in affected kidneys. K(Ca)3.1 KO mice showed reduced expression of fibrotic marker expression, less chronic tubulointerstitial damage, collagen deposition and alpha-smooth muscle+ cells after UUO, with better preservation of functional renal parenchyma. The selective K(Ca)3.1 blocker TRAM-34 similarly attenuated progression of UUO-induced renal fibrosis in wild-type mice and rats. Thus, Grgic et al. believe that K(Ca)3.1 is involved in renal fibroblast proliferation and fibrogenesis, suggesting that K(Ca)3.1 may serve as a therapeutic target for the prevention of fibrotic kidney disease.

De novo synthesis of {beta}-catenin via H-Ras and MEK regulates airway smooth muscle growth

beta-Catenin is a component of adherens junctions that also acts as a transcriptional coactivator when expressed in the nucleus. Growth factors are believed to regulate the nuclear expression of beta-catenin via inactivation of glycogen synthase kinase 3 (GSK-3) by phosphorylation, resulting in increased beta-catenin protein stability. Here, we report on a novel pathway that regulates the expression and nuclear presence of beta-catenin. In proliferating human airway smooth muscle cells, we observed increased expression of beta-catenin, which was required for proliferation. Interestingly, increased beta-catenin expression was accompanied by an increase in beta-catenin mRNA and was independent of beta-catenin liberation from the plasma membrane, suggesting a role for de novo synthesis. This was confirmed using actinomycin D and cycloheximide, which abrogated the induction and nuclear localization of beta-catenin protein. GSK-3 inhibition using SB216763 failed to regulate beta-catenin mRNA. However, expression of dominant negative H-Ras or pharmacological inhibition of MEK reduced serum and TGF-beta-induced beta-catenin mRNA and protein. Collectively, these data indicate that beta-catenin is an important signaling intermediate in airway smooth muscle growth and that its cellular accumulation and nuclear localization require de novo protein synthesis effected, in part, via H-Ras and MEK.-Gosens, R., Baarsma, H. A., Heijink, I. H., Oenema, T. A., Halayko, A. J., Meurs, H., Schmidt, M. De novo synthesis of beta-catenin via H-Ras and MEK regulates airway smooth muscle growth.

Toll-like receptor 4: a novel signaling pathway during renal fibrogenesis

BACKGROUND

The toll-like receptor (TLR) family serves an important regulatory role in the innate immune system, and recent evidence has implicated TLR signaling in the pro-inflammatory response of a variety of endogenous and exogenous stimuli within the kidney. The role of TLR signaling in fibrotic renal injury, however, remains unknown.

MATERIALS AND METHODS

C3H/HeJ TLR4 hyporesponsive mice (TLR4(Lps-d)) or WT controls (C3H/HeOu/J) underwent either sham operation or 1 wk of unilateral ureteral obstruction (UUO). The kidneys were harvested and tissues were analyzed for TLR4 expression (Western blot; RTPCR), E-cadherin and alpha smooth muscle actin (α-SMA) expression (Western blot), fibroblast accumulation (fibroblast specific protein (FSP-1+) staining), renal fibrosis (collagen I RTPCR, total collagen assay, Masson's trichrome staining), cytokine gene expression (tumor necrosis factor-alpha (TNF-α) and transforming growth factor-beta1 (TGF-β1) RTPCR), and pSMAD2 and integrin α1 expression (Western blot).

RESULTS

Mice with intact TLR4 signaling demonstrate a significant increase in TLR4 expression, α-SMA expression, fibroblast accumulation, collagen deposition, and interstitial fibrosis, and a significant decrease in E-cadherin expression in response to UUO. TLR4 deficient mice, however, exhibit a significant reduction in obstruction-induced α-SMA expression, fibroblast accumulation, and renal fibrosis, with preservation of E-cadherin expression. TLR4's influence on fibroblast accumulation and renal fibrosis occurred independent of any alterations in TNF-α, TGF-β1, or pSMAD2 expression, but did involve alterations integrin α1 expression.

CONCLUSION

TLR4 appears to be a significant mediator of fibrotic renal injury. While TLR4 signaling is recognized as a critical component of the innate immune response, this is the first study to demonstrate a novel role for TLR4 in renal fibroblast accumulation and tubulointerstitial fibrosis.

Renal fibrosis is attenuated by targeted disruption of KCa3.1 potassium channels

Proliferation of interstitial fibroblasts is a hallmark of progressive renal fibrosis commonly resulting in chronic kidney failure. The intermediate-conductance Ca(2+)-activated K(+) channel (K(Ca)3.1) has been proposed to promote mitogenesis in several cell types and contribute to disease states characterized by excessive proliferation. Here, we hypothesized that K(Ca)3.1 activity is pivotal for renal fibroblast proliferation and that deficiency or pharmacological blockade of K(Ca)3.1 suppresses development of renal fibrosis. We found that mitogenic stimulation up-regulated K(Ca)3.1 in murine renal fibroblasts via a MEK-dependent mechanism and that selective blockade of K(Ca)3.1 functions potently inhibited fibroblast proliferation by G(0)/G(1) arrest. Renal fibrosis induced by unilateral ureteral obstruction (UUO) in mice was paralleled by a robust up-regulation of K(Ca)3.1 in affected kidneys. Mice lacking K(Ca)3.1 (K(Ca)3.1(-/-)) showed a significant reduction in fibrotic marker expression, chronic tubulointerstitial damage, collagen deposition and alphaSMA(+) cells in kidneys after UUO, whereas functional renal parenchyma was better preserved. Pharmacological treatment with the selective K(Ca)3.1 blocker TRAM-34 similarly attenuated progression of UUO-induced renal fibrosis in wild-type mice and rats. In conclusion, our data demonstrate that K(Ca)3.1 is involved in renal fibroblast proliferation and fibrogenesis and suggest that K(Ca)3.1 may represent a therapeutic target for the treatment of fibrotic kidney disease.

Astragalus mongholicus ameliorates renal fibrosis by modulating HGF and TGF-beta in rats with unilateral ureteral obstruction

Astragalus mongholicus (AM) derived from the dry root of Astragalus membranaceus Bge. var. mongolicus (Bge.) Hsiao is a widely used traditional Chinese medicine. The present study investigated the potential role of AM on renal fibrosis on a rat model of unilateral ureteral obstruction (UUO). We divided 48 Sprague-Dawley rats randomly into 4 groups: sham-operated group (Sham), untreated UUO group, AM-treated (10 g/(kg x d)) UUO group, and losartan-treated (20 mg/(kg x d)) UUO group as positive control. Haematoxylin & eosin (HE) and Masson staining were used to study the dynamic histological changes of the kidneys 7 and 14 d after operation. The expressions of fibronectin (FN), type I collagen (colI), hepatocyte growth factor (HGF), transforming growth factor-beta1 (TGF-beta1), and alpha-smooth muscle actin (alpha-SMA) were analyzed by real-time polymerase chain reaction (PCR), immunohistochemistry staining, and Western blot. Results show that, similar to losartan, AM alleviated the renal damage and decreased the deposition of FN and colI from UUO by reducing the expressions of TGF-beta1 and alpha-SMA (P<0.05), whereas HGF increased greatly with AM treatment (P<0.05). Our findings reveal that AM could retard the progression of renal fibrosis. The renoprotective effect of AM might be related to inhibition of myofibroblast activation, inducing of HGF and reducing of TGF-beta1 expression.

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

BACKGROUND

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

STUDY DESIGN

Retrospective cross-sectional analysis.

SETTINGS & PARTICIPANTS

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

PREDICTOR

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

OUTCOME

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

MEASUREMENTS

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

RESULTS

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

LIMITATIONS

Nonrepresentative study population.

CONCLUSIONS

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

CSF-1 signals directly to renal tubular epithelial cells to mediate repair in mice

Tubular damage following ischemic renal injury is often reversible, and tubular epithelial cell (TEC) proliferation is a hallmark of tubular repair. Macrophages have been implicated in tissue repair, and CSF-1, the principal macrophage growth factor, is expressed by TECs. We therefore tested the hypothesis that CSF-1 is central to tubular repair using an acute renal injury and repair model, ischemia/reperfusion (I/R). Mice injected with CSF-1 following I/R exhibited hastened healing, as evidenced by decreased tubular pathology, reduced fibrosis, and improved renal function. Notably, CSF-1 treatment increased TEC proliferation and reduced TEC apoptosis. Moreover, administration of a CSF-1 receptor-specific (CSF-1R-specific) antibody after I/R increased tubular pathology and fibrosis, suppressed TEC proliferation, and heightened TEC apoptosis. To determine the contribution of macrophages to CSF-1-dependent renal repair, we assessed the effect of CSF-1 on I/R in mice in which CD11b+ cells were genetically ablated and determined that macrophages only partially accounted for CSF-1-dependent tubular repair. We found that TECs expressed the CSF-1R and that this receptor was upregulated and coexpressed with CSF-1 in TECs following renal injury in mice and humans. Furthermore, signaling via the CSF-1R stimulated proliferation and reduced apoptosis in human and mouse TECs. Taken together, these data suggest that CSF-1 mediates renal repair by both a macrophage-dependent mechanism and direct autocrine/paracrine action on TECs.

Autologous and allogeneic marrow stromal cells are safe and effective for the treatment of acute kidney injury

Acute kidney injury (AKI) is a major clinical problem associated with high morbidity and mortality. Likely due to its complex pathophysiology, therapies with a single pharmacological agent have generally failed to improve outcomes. In contrast, stem cell-based interventions utilize these cells' ability to simultaneously target multiple pathophysiological components of AKI and thus represent a promising new tool for the treatment of AKI. The aims of the this study were to investigate the long-term outcome and safety of treatment with autologous and allogeneic mesenchymal stem cells (MSCs) after AKI and the role of vascular endothelial growth factor (VEGF) as one of the principal paracrine mediators of renoprotection of MSCs. MSC administration after AKI was not associated with adverse events and proved to be renoprotective in animals with severe renal failure. Identical doses of autologous MSC were more effective than allogeneic. At 3 months, MSCs were not engrafted in any tissues except in the bone marrow in 50% of animals given the highest allogeneic cell dose. There was no long-term fibrotic response in the kidneys attributable to MSC therapy, and animals with severe AKI were protected from development of fibrotic lesions after AKI. Furthermore, this study establishes VEGF as a critical factor mediating renal recovery. VEGF knockdown by small-interfering RNA reduced effectiveness of MSCs significantly and decreased survival. In summary, our results show that both autologous and allogeneic MSC are safe and effective in AKI, and importantly, reduce late renal fibrosis and loss of renal function in surviving animals and that VEGF is a critical factor in renoprotection by MSCs. Together, we posit that these data provide further justification for the conduct of clinical trails in which AKI is treated with MSC.

The role of Toll-like receptor 2 in inflammation and fibrosis during progressive renal injury

Tissue fibrosis and chronic inflammation are common causes of progressive organ damage, including progressive renal disease, leading to loss of physiological functions. Recently, it was shown that Toll-like receptor 2 (TLR2) is expressed in the kidney and activated by endogenous danger signals. The expression and function of TLR2 during renal fibrosis and chronic inflammation has however not yet been elucidated. Therefore, we studied TLR2 expression in human and murine progressive renal diseases and explored its role by inducing obstructive nephropathy in TLR2^−/− or TLR2^+/+ mice. We found that TLR2 is markedly upregulated on tubular and tubulointerstitial cells in patients with chronic renal injury. In mice with obstructive nephropathy, renal injury was associated with a marked upregulation and change in distribution of TLR2 and upregulation of murine TLR2 danger ligands Gp96, biglycan, and HMGB1. Notably, TLR2 enhanced inflammation as reflected by a significantly reduced influx of neutrophils and production of chemokines and TGF-β in kidneys of TLR2^−/− mice compared with TLR2^+/+ animals. Although, the obstructed kidneys of TLR2^−/− mice had less interstitial myofibroblasts in the later phase of obstructive nephropathy, tubular injury and renal matrix accumulation was similar in both mouse strains. Together, these data demonstrate that TLR2 can initiate renal inflammation during progressive renal injury and that the absence of TLR2 does not affect the development of chronic renal injury and fibrosis.

Low-dose carbon monoxide inhibits progressive chronic allograft nephropathy and restores renal allograft function

Chronic allograft nephropathy (CAN) represents progressive deterioration of renal allograft function with fibroinflammatory changes. CAN, recently reclassified as interstitial fibrosis (IF) and tubular atrophy (TA) with no known specific etiology, is a major cause of late renal allograft loss and remains a significant deleterious factor of successful renal transplantation. Carbon monoxide (CO), an effector byproduct of heme oxygenase pathway, is known to have potent anti-inflammatory and antifibrotic functions. We hypothesized that inhaled CO would inhibit fibroinflammatory process of CAN and restore renal allograft function, even when the treatment was initiated after CAN was established. Lewis rat kidney grafts were orthotopically transplanted into binephrectomized allogenic Brown Norway rats under brief tacrolimus (0.5 mg/kg im, days 0-6). At day 60, CO (20 ppm) inhalation was initiated to recipients and continued until day 150 or animal death. Development of CAN was confirmed at day 60 with decreased creatinine clearance (CCr), significant proteinuria, and histopathological findings of TA, IF, and intimal arteritis. Air-treated control recipients continued to deteriorate with further declines of CCr and increases of urinary protein excretion and died with a median survival of 82 days. In contrast, progression of CAN was decelerated when recipients received CO on days 60-150, showing markedly improved graft histopathology, restored renal function, and improved recipient survival to a median of >150 days. CO significantly reduced intragraft mRNA levels for IFN-gamma and TNF-alpha at day 90. Expression of profibrotic TGF-beta/Smad was significantly suppressed with CO, together with downregulation of ERK-MAPK pathways. Continuous CO (20 ppm) treatment for days 0-30, days 30-60, or days 0-90, or daily 1-h CO (250 ppm) treatment for days 0-90, also showed efficacy in inhibiting CAN. The study demonstrates that CO is able to inhibit progression of fibroinflammatory process of CAN, restore renal allograft function, and improve survival even when the treatment is started after CAN is diagnosed.

Hypoxia-inducible factor-1alpha induces Twist expression in tubular epithelial cells subjected to hypoxia, leading to epithelial-to-mesenchymal transition

Epithelial-to-mesenchymal transition (EMT) induced by chronic hypoxia is one of the critical causes of renal fibrosis. Twist, a basic helix-loop-helix transcription factor, is believed to be important in promoting EMT. We found that the expression of Twist was increased in human tubule cell lines (HK-2 and HKC) grown under hypoxic conditions. This was accompanied by reduced expression of the epithelial markers E-cadherin and ZO-1 and enhanced expression of the mesenchymal markers vimentin and alpha-smooth muscle actin. When Twist was overexpressed in these cells it induced a mesenchymal phenotype, whereas its knockdown by short interfering RNA (siRNA) effectively reversed hypoxia-induced EMT. We showed that transfection with siRNA to hypoxia-inducible factor-1alpha (HIF-1alpha), another basic helix-loop-helix transcription factor, reduced Twist expression. Twist promoters contain HIF1-alpha-binding sites and transfection of reporter constructs using the promoter showed increased transcription in cells subjected to hypoxia. Electrophoretic mobility shift and chromatin immunoprecipitation assays identified the presence of a functional HIF-1alpha-binding site within the proximal Twist gene promoter. In an in vivo assay using the rat remnant kidney we found that both Twist and HIF-1alpha were overexpressed in tubular epithelial cells showing EMT. These studies suggest that HIF-1alpha induces Twist expression in hypoxic tubular cells and that this plays a role in EMT during renal fibrogenesis.

Effects of tanshinone IIA on transforming growth factor beta1-Smads signal pathway in renal interstitial fibroblasts of rats

The effects of tanshinone IIA (TSN) on transforming growth factor beta1 (TGFbeta1) signal transduction in renal interstitial fibroblasts of rats were studied in order to investigate its mechanism in prevention of renal interstitial fibrosis. Rat renal fibroblasts of the line NRK/49F were cultured in vitro, stimulated with 5 ng/mL TGFbeta1 and pretreated with 10(-6), 10(-5), 10(-4) mol/L TSN respectively. The mRNA levels of fibronectin (FN) were examined by RT-PCR. The protein expression of FN and Smads was detected by Western blot. TGFbeta1 induced the expression of FN mRNA and Smads in a time-dependent manner in a certain range. Compared with pre-stimulation, the FN mRNA and protein levels were increased by 1.1 times and 1.5 times respectively (P<0.01, P<0.01), and the protein expression of phosphorylated Smad2/3 (p-Smad2/3) increased by 7 times at the end of TGFbeta1 stimulation (P<0.01). TSN pretreatment may down-regulate the FN and p-Smad2/3 expression in a dose-dependent manner. 10(-6) mol/L TSN pretreatment had no effect on the FN and p-Smad2/3 expression (both P>0.05). After pretreatment with 10(-5) and 10(-4) mol/L TSN, the FN mRNA levels were decreased by 28.1% and 43.8% respectively (P<0.05, P<0.01), the FN protein levels were decreased by 40% and 44% respectively (P<0.05, P<0.05), and the p-Smad2/3 protein expression were decreased by 40% and 65% respectively (P<0.05, P<0.01). The inhibitory effect of TSN on renal interstitial fibrosis may be related to its blocking effect on TGFbeta1-Smads signal pathway in renal interstitial fibroblasts.

Delayed blockade of the kinin B1 receptor reduces renal inflammation and fibrosis in obstructive nephropathy

Renal fibrosis is the common histological feature of advanced glomerular and tubulointerstitial disease leading to end-stage renal disease (ESRD). However, specific antifibrotic therapies to slow down the evolution to ESRD are still absent. Because persistent inflammation is a key event in the development of fibrosis, we hypothesized that the proinflammatory kinin B1 receptor (B1R) could be such a new target. Here we show that, in the unilateral ureteral obstruction model of renal fibrosis, the B1R is overexpressed and that delayed treatment with an orally active nonpeptide B1R antagonist blocks macrophage infiltration, leading to a reversal of the level of renal fibrosis. In vivo bone marrow transplantation studies as well as in vitro studies on renal cells show that part of this antifibrotic mechanism of B1R blockade involves a direct effect on resident renal cells by inhibiting chemokine CCL2 and CCL7 expression. These findings suggest that blocking the B1R is a promising antifibrotic therapy.

Stable expression of HIF-1alpha in tubular epithelial cells promotes interstitial fibrosis

Chronic hypoxia accelerates renal fibrosis. The chief mediator of the hypoxic response is hypoxia-inducible factor 1 (HIF-1) and its oxygen-sensitive component HIF-1alpha. HIF-1 regulates a wide variety of genes, some of which are closely associated with tissue fibrosis. To determine the specific role of HIF-1 in renal fibrosis, we generated a knockout mouse in which tubular epithelial expression of von Hippel-Lindau tumor suppressor (VHL), which acts as a ubiquitin ligase to promote proteolysis of HIF-1alpha, was targeted. We investigated the effect of VHL deletion (i.e., stable expression of HIF-1alpha) histologically and used the anti-HIF-1alpha agent [3-(5'-hydroxymethyl-2'-furyl)-1-benzyl indazole] (YC-1) to test whether inhibition of HIF-1alpha could represent a novel approach to treating renal fibrosis. The area of renal fibrosis was significantly increased in a 5/6 renal ablation model of VHL-/- mice and in all VHL-/- mice at least 60 wk of age. Injection of YC-1 inhibited the progression of renal fibrosis in unilateral ureteral obstruction model mice. In conclusion, HIF-1alpha appears to be a critical contributor to the progression of renal fibrosis and could be a useful target for its treatment.

The GSK-3/beta-catenin-signalling axis in smooth muscle and its relationship with remodelling

beta-Catenin is a plasma membrane-associated protein that plays a dual role in cellular signalling by stabilizing cadherin mediated cell-cell contact and by regulating TCF-/LEF-mediated gene transcription. Traditionally, the role of beta-catenin in health and disease has mainly been studied in the context of development and uncontrolled cell growth in diseases such as cancer. Recent findings indicate, however, that beta-catenin also plays a significant role in fibro-proliferative diseases of several organ systems and that beta-catenin regulates mitogenic responses of smooth muscle cells. As several diseases of the internal organs are characterized by structural and phenotypic abnormalities of smooth muscle, including increased fibro-proliferative responses, these findings implicate that beta-catenin could play a broad pathophysiological role. This article will review this potential novel role for beta-catenin and associated intracellular signalling in smooth muscle and discuss the hypothesis that it plays a central role in smooth muscle remodelling.

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

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

Early epithelial phenotypic changes predict graft fibrosis

Chronic allograft nephropathy accounts for the loss of approximately 40% of allografts at 10 yr. Currently, no biomarker is available to detect interstitial fibrosis and tubular atrophy in the renal graft at an early stage, when intervention may be beneficial. Because tubular epithelial cells have been shown to exhibit phenotypic changes suggestive of epithelial-to-mesenchymal transition, we studied whether these changes predict the progression of fibrosis in the allograft. Eighty-three kidney transplant recipients who had undergone a protocol graft biopsy at both 3 and 12 mo after transplantation were enrolled. De novo vimentin expression and translocation of beta-catenin into the cytoplasm of tubular cells were detected on the first biopsy by immunohistochemistry. Patients with expression of these markers in >or=10% of tubules at 3 mo had a higher interstitial fibrosis score at 1 yr and a greater progression of this score between 3 and 12 mo. The intensity of these phenotypic changes positively and significantly correlated with the progression of fibrosis, and multivariate analysis showed that their presence was an independent risk factor for this progression. In addition, the presence of early phenotypic changes was associated with poorer graft function 18 mo after transplantation. In conclusion, early phenotypic changes indicative of epithelial-to-mesenchymal transition predict the progression toward interstitial fibrosis in human renal allografts.

Lysophosphatidic acid and renal fibrosis

The development of fibrosis involves a multitude of events and molecules. Until now the majority of these molecules were found to be proteins or peptides. But recent data show significant involvement of the phospholipid lysophosphatidic acid (LPA) in the development of pulmonary, liver and renal fibrosis. The latest data on the role of LPA and the G-protein-coupled LPA1 receptor in the development of renal fibrosis will be discussed. LPA1-receptor activation was found to be associated with increased vascular leakage and increased fibroblast recruitment in pulmonary fibrosis. Furthermore, in renal fibrosis LPA1-receptor activation stimulates macrophage recruitment and connective tissue growth factor expression. The observations make this receptor an interesting alternative and new therapeutic target in fibrotic diseases.