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

Treatment of chronic kidney diseases with histone deacetylase inhibitors

Histone deacetylases (HDACs) induce deacetylation of both histone and non-histone proteins and play a critical role in the modulation of physiological and pathological gene expression. Pharmacological inhibition of HDAC has been reported to attenuate progression of renal fibrogenesis in obstructed kidney and reduce cyst formation in polycystic kidney disease. HDAC inhibitors (HDACis) are also able to ameliorate renal lesions in diabetes nephropathy, lupus nephritis, aristolochic acid nephropathy, and transplant nephropathy. The beneficial effects of HDACis are associated with their anti-fibrosis, anti-inflammation, and immunosuppressant effects. In this review, we summarize recent advances on the treatment of various chronic kidney diseases with HDACis in pre-clinical models.

Paclitaxel attenuates renal interstitial fibroblast activation and interstitial fibrosis by inhibiting STAT3 signaling

Recent studies have demonstrated that paclitaxel might inhibit renal fibrosis. However, the underlying molecular mechanism remains unclear. In this study, we hypothesized that low-dose paclitaxel may block the STAT3 (signal transducer and activator of transcription 3) signaling to attenuate fibrosis in a mouse model with unilateral ureteral obstruction. Both NRK-49F cells and mice with unilateral ureteral obstruction were treated with paclitaxel. The results showed that paclitaxel treatment resulted in a dose- and time-dependent decrease in tyrosine-phosphorylated STAT3, and inhibited the expression of fibronectin, alpha-smooth muscle actin (α-SMA), and collagen I in cultured NRK-49F cells. S3I-201, an STAT3 inhibitor, also suppressed the expression of fibronectin, α-SMA, and collagen I in cultured NRK-49F cells. Mechanistically, paclitaxel treatment blocked the STAT3 activity by disrupting the association of STAT3 with tubulin and inhibiting STAT3 nucleus translocation. Furthermore, paclitaxel also ameliorated renal fibrosis by down-regulating the expression of fibronectin, α-SMA, and collagen I, and suppressed the infiltration of macrophages and production of TNF-α, IL-1β, TGF-β, and ICAM-1 (intercellular adhesion molecule 1) by inhibition of STAT3 activity in obstructive nephropathy. These results suggest that paclitaxel may block the STAT3 activity by disrupting the association of STAT3 with tubulin and inhibiting STAT3 nucleus translocation, consequently leading to the suppression of renal interstitial fibroblast activation and the development of renal fibrosis, and inhibition of proinflammatory cytokine production.

The T-box transcription factor Brachyury promotes renal interstitial fibrosis by repressing E-cadherin expression

Background

Epithelial-to-mesenchymal transition (EMT) induced by TGF-β1 is one of well-recognized factors contributing to renal fibrosis. However, the underlying molecular mechanisms of EMT are not fully understood. Brachyury, an evolutionarily conserved transcription factor, was recently identified as an important factor promoting EMT in human carcinoma cell lines. There is no evidence that Brachyury is involved in renal tubular EMT.

Results

Our results demonstrated that Brachyury was prominently induced in TGF-β1-treated human proximal tubular epithelial (HK-2) cells and that this induction was accompanied by changes characteristic of EMT. Blockage of Brachyury expression by short interfering RNA (siRNA) in HK-2 cells effectively reversed the TGF-β1-induced EMT phenotype. Brachyury induction repressed E-cadherin transcription; the E-cadherin promoter contains a Brachyury binding site, and decreased expression of E-cadherin occurred in Brachyury-overexpressing cells when they were transfected with reporter constructs using the promoter. This effect was partially mediated by Slug and Snail, as knockdown of Snail and Slug by siRNA effectively reversed Brachyury-mediated EMT and partially restored E–cadherin expression. The expression of Brachyury also presented in a rat model of obstructive nephropathy and in tubulointerstitial fibrosis tissues of IgA nephropathy, suggesting that it may have a role in EMT and renal fibrosis in vivo.

Conclusion

Our results demonstrate for the first time that Brachyury plays an important role in regulating TGF-β1–mediated renal EMT and could be an attractive target for progression of renal disease therapies.

Acute interstitial nephritis - a reappraisal and update

Acute interstitial nephritis (AIN) is an under recognized and under diagnosed cause of acute kidney injury (AKI). It is estimated to account for 15 - 20% of cases of AKI; it is the reported diagnosis in 2.8% of all kidney biopsies, and 13.5% of biopsies done specifically for acute renal failure. Considerable evidence implicates antigen initiated cell-mediated injury in the pathogenesis of AIN. Drugs account for 70% of all cases, with over 150 different agents incriminated. The remaining cases are due to infections, autoimmune diseases, and rarely idiopathic. The central component of renal injury in AIN is altered tubular function, which usually precedes decrements in filtration rate. The key to early diagnosis is vigilance for the presence of tubular dysfunction in non-oliguric individuals, especially in patients with modest but gradual increments in creatinine level. The utility of urinary biomarkers to diagnose AIN in its early nascent and potentially reversible stage remains to be determined. Prompt recognition, elimination of the offending source of antigen, and use of a limited course of steroid therapy where indicated, will result in complete resolution in ~ 65% of cases, partial resolution in up to 20%, and irreversible damage in the rest.

Hibiscus sabdariffa polyphenols alleviate insulin resistance and renal epithelial to mesenchymal transition: a novel action mechanism mediated by type 4 dipeptidyl peptidase

The epithelial to mesenchymal transition (EMT) is important in renal fibrosis. Ser307 phosphorylation of insulin receptor substrate-1 (IRS-1 (S307)) is a hallmark of insulin resistance. We report that polyphenol extracts of Hibiscus sabdariffa (HPE) ameliorate diabetic nephropathy and EMT. Recently it has been observed that type 4 dipeptidyl peptidase (DPP-4) inhibitor linagliptin is effective for treating type 2 diabetes and albuminuria. We investigated if DPP-4 and insulin resistance are involved in renal EMT and explored the role of HPE. In high glucose-stimulated tubular cells, HPE, like linagliptin, inhibited DPP-4 activation, thereby regulating vimentin (EMT marker) and IRS-1 (S307). IRS-1 knockdown revealed its essential role in mediating downstream EMT. In type 2 diabetic rats, pIRS-1 (S307) abundantly surrounds the tubular region, with increased vimentin in kidney. Both the expressions were reduced by HPE. In conclusion, HPE exerts effects similar to those of linagliptin, which improves insulin resistance and EMT, and could be an adjuvant to prevent diabetic nephropathy.

Augmenter of liver regeneration inhibits TGF-β1-induced renal tubular epithelial-to-mesenchymal transition via suppressing TβR II expression in vitro

Tubular epithelial-to-mesenchymal transition (EMT) plays a crucial role in the progression of renal tubular interstitial fibrosis (TIF), which subsequently leads to chronic kidney disease (CKD) and eventually, end-stage renal disease (ESRD). We propose that augmenter of liver regeneration (ALR), a member of the newly discovered ALR/Erv1 protein family shown to ameliorate hepatic fibrosis, plays a similar protective role in renal tubular cells and has potential as a new treatment option for CKD. Here, we showed that recombinant human ALR (rhALR) inhibits EMT in renal tubular cells by antagonizing activation of the transforming growth factor-β1 (TGF-β1) signaling pathway. Further investigation revealed that rhALR suppresses the expression of TGF-β receptor type II (TβR II) and significantly alleviates TGF-β1-induced phosphorylation of Smad2 and nuclear factor-κB (NF-κB). No apparent adverse effects were observed upon the addition of rhALR alone to cells. These findings collectively suggest that ALR plays a role in inhibiting progression of renal tubular EMT, supporting its potential utility as an effective antifibrotic strategy to reverse TIF in CKD.

Klotho suppresses renal tubulo-interstitial fibrosis by controlling basic fibroblast growth factor-2 signalling

Increased basic fibroblast growth factor-2 (FGF2) and reduced Klotho have both been reported to be closely associated with renal fibrosis. However, the relationship between Klotho and FGF2 remains unclear. We demonstrate that FGF2 induced tubulo-epithelial plasticity in cultured HK-2 cells, accompanied by a reduction in Klotho expression, whereas recombinant Klotho protein could inhibit the action of FGF2. The FGF2 effects required extracellular signal-regulated protein kinase 1/2 activation, which was suppressed by Klotho. Moreover, Klotho also restrained FGF2-induced fibroblast proliferation and activation. The inhibitory effect of Klotho on the activity of FGF2 was likely due to its potent ability to compete with FGF2 binding to FGF receptor 1. Unilateral ureteral obstruction (UUO)-induced renal fibrosis was associated with an increase in FGF2 and a reduction in Klotho expression in wild-type mice, whereas FGF2(-/-) mice largely preserved Klotho expression and developed only mild renal fibrosis after obstructive injury. Furthermore, administration of Klotho protein in UUO mice significantly reduced renal fibrosis, concomitant with a marked suppression of FGF2 production and signalling. These studies demonstrate a feedback loop between Klotho depletion and FGF2 activation in renal fibrosis. Our results also suggest that Klotho treatment reduces renal fibrosis, at least in part, by inhibiting FGF2 signalling.

The AMPK agonist AICAR inhibits TGF-β1 induced activation of kidney myofibroblasts

Activation of interstitial myofibroblasts and excessive production of extracellular matrix proteins are common pathways that contribute to chronic kidney disease. In a number of tissues, AMP-activated kinase (AMPK) activation has been shown to inhibit fibrosis. Here, we examined the inhibitory effect of the AMPK activator, 5-aminoimidazole-4-carboxyamide ribonucleoside (AICAR), on renal fibrosis invivo and TGF-β1-induced renal fibroblasts activation invitro. A unilateral ureteral obstruction (UUO) model was induced in male BALB/c mice. Mice with UUO were administered AICAR (500 mg/Kg/day) or saline intraperitoneally 1 day before UUO surgery and daily thereafter. Both kidneys were harvested 7 days after surgery for further analysis. For the in vitro studies, NRK-49F rat fibroblasts were pre-incubated with AICAR before TGF-β1 stimulation. The inhibitory effects of AICAR on signaling pathways down-stream of TGF-β1 were analyzed. In UUO model mice, administration of AICAR attenuated extracellular matrix protein deposition and the expression of α-smooth muscle actin (α-SMA), type I collagen and fibronectin. Pre-incubation of NRK-49F cells with AICAR inhibited TGF-β1-induced myofibroblast activation. Silencing of AMPKα1 by siRNA or by blocking AMPK activation with Compound C diminished the inhibitory effect of AICAR. Moreover, the inhibitory effects of AICAR on TGF-β1-mediated myofibroblast activation were associated with down-regulation of ERK 1/2 and STAT3. Our results suggest that AICAR reduces tubulointerstitial fibrosis in UUO mice and inhibits TGF-β1-induced kidney myofibroblast activation. AMPK activation by AICAR may have therapeutic potential for the treatment of renal tubulointerstitial fibrosis.

Stathmin destabilizing microtubule dynamics promotes malignant potential in cancer cells by epithelial-mesenchymal transition

BACKGROUND

Stathmin is a ubiquitous cytosolic regulatory phosphoprotein and is overexpressed in different human malignancies. The main physiological function of stathmin is to interfere with microtubule dynamics by promoting depolymerization of microtubules or by preventing polymerization of tubulin heterodimers. Stathmin plays important roles in regulating many cellular functions as a result of its microtubule-destabilizing activity. Currently, the critical roles of stathmin in cancer cells, as well as in lymphocytes have been valued. This review discusses stathmin and microtubule dynamics in cancer development, and hypothesizes their possible relationship with epithelial-mesenchymal transition (EMT).

DATA SOURCES

A PubMed search using such terms as "stathmin", "microtubule dynamics", "epithelial-mesenchymal transition", "EMT", "malignant potential" and "cancer" was performed to identify relevant studies published in English. More than 100 related articles were reviewed.

RESULTS

The literature clearly documented the relationship between stathmin and its microtubule-destabilizing activity of cancer development. However, the particular mechanism is poorly understood. Microtubule disruption is essential for EMT, which is a crucial process during cancer development. As a microtubule-destabilizing protein, stathmin may promote malignant potential in cancer cells by initiating EMT.

CONCLUSIONS

We propose that there is a stathmin-microtubule dynamics-EMT (S-M-E) axis during cancer development. By this axis, stathmin together with its microtubule-destabilizing activity contributes to EMT, which stimulates the malignant potential in cancer cells.

Antifibrotic effects of KS370G, a caffeamide derivative, in renal ischemia-reperfusion injured mice and renal tubular epithelial cells

Accumulating evidence suggests that renal tubulointerstitial fibrosis is a main cause of end-stage renal disease. Clinically, there are no beneficial treatments that can effectively reverse the progressive loss of renal functions. Caffeic acid phenethyl ester is a natural phenolic antifibrotic agent, but rapid decomposition by an esterase leads to its low bioavailability. In this study, we evaluated the effects of KS370G, a caffeic acid phenylethyl amide, on murine renal fibrosis induced by unilateral renal ischemia-reperfusion injury (IRI) and in TGF-β₁ stimulated renal tubular epithelial cells (NRK52E and HK-2). In the animal model, renal fibrosis was evaluated at 14 days post-operation. Immediately following the operation, KS370G (10 mg/kg) was administered by oral gavage once a day. Our results show that KS370G markedly attenuates collagen deposition and inhibits an IRI-induced increase of fibronectin, vimentin, α-SMA and TGF-β₁ expression and plasma TGF-β₁ levels in the mouse kidney. Furthermore, KS370G reverses TGF-β₁-induced downregulation of E-cadherin and upregulation of α-SMA and also decreases the expression of fibronectin, collagen I and PAI-1 and inhibits TGF-β₁-induced phosphorylation of Smad2/3. These findings show the beneficial effects of KS370G on renal fibrosis in vivo and in vitro with the possible mechanism being the inhibition of the Smad2/3 signaling pathway.

Urine miRNA in nephrotic syndrome

Nephrotic syndrome is a common problem in clinical nephrology. In general, nephrotic syndrome is pathognomonic of glomerular disease, but the underlying pathological etiology is highly variable. Although kidney biopsy is the standard method to classify the histology and determine the extent of renal scarring, it is an invasive procedure with potential complications, and is generally not suitable for serial monitoring. MicroRNAs (miRNAs) are short noncoding RNA molecules that regulate gene expression. Recent studies show that the urinary levels of several miRNAs are significantly changed in nephrotic syndrome; some appear to be disease specific, others being damage related. Specifically, urinary miR-192 level is lower in patients with diabetic nephropathy than other causes of nephrotic syndrome, while patients with minimal change nephropathy or focal glomerulosclerosis had higher urinary miR-200c level than those with other diagnosis. Elevated urinary miR-21, miR-216a, and miR-494 levels may predict a high risk of disease progression and renal function loss, irrespective of the histological diagnosis. Furthermore, a number of small scale studies suggest that the urinary levels of certain miRNA targets may assist in the diagnosis and assessment of disease activity in patients with lupus nephritis. Since miRNA in urinary sediment is relatively stable and easily quantified, it has the potential to be developed as biomarkers for disease diagnosis and monitoring. However, available published evidence is limited to small scale studies. Further research is urgently needed in many areas.

Wogonin suppresses human alveolar adenocarcinoma cell A549 migration in inflammatory microenvironment by modulating the IL-6/STAT3 signaling pathway

Increasing evidence from various clinical and experimental studies has demonstrated that the inflammatory microenvironment facilitates tumor metastasis. Clinically, it will be a promising choice to suppress tumor metastasis by targeting inflammatory microenvironment. Our previous studies have demonstrated that wogonin (a bioflavonoid isolated from the traditional Chinese medicine of Huang-Qin) possesses the anti-metastatic and anti-inflammatory activity, but we have little idea about its efficacy on inflammatory-induced tumor metastasis and the mechanism underlying it. In this study, we focused on epithelial mesenchymal transition (EMT), the first step of tumor metastasis, to evaluate the effects of wogonin on tumor metastasis in inflammatory microenvironment. We found that wogonin inhibited THP-1 conditioned-medium- (CM-) and IL-6-induced EMT by inactivating STAT3 signal. And in wogonin-treated A549 cells which pretreated with THP-1 CM or IL-6, the expression level of E-cadherin, an EMT negative biomarker, increased while that of N-cadherin, Vimentin, and EMT-related transcription factors including Snail and Twist decreased. Moreover, wogonin inhibited IL-6-induced phosphorylation of STAT3, prevented p-STAT3 dimer translocation into the nucleus, and suppressed the DNA-binding activity of p-STAT3. Interestingly, similar results were obtained in the tumor xenografts mice, including downregulation of p-STAT3, N-cadherin, and Vimentin while up-regulation of E-cadherin. Wogonin also inhibit the metastasis of A549 cells in vivo. Taken all data together, we concluded that wogonin suppresses tumor cells migration in inflammatory microenvironment by inactivating STAT3 signal.

Losartan attenuates renal interstitial fibrosis and tubular cell apoptosis in a rat model of obstructive nephropathy

Ureteral obstruction leads to renal injury and progresses to irreversible renal fibrosis, with tubular cell atrophy and apoptosis. There is conflicting evidence concerning whether losartan (an angiotensin II type I receptor antagonist) mitigates renal interstitial fibrosis and renal tubular epithelial cell apoptosis following unilateral ureteral obstruction (UUO) in animal models. The aim of this study was to investigate the effect and mechanism of losartan on renal tubular cell apoptosis and renal fibrosis in a rat model of UUO. The rats were subjected to UUO by ureteral ligation and were treated with dimethyl sulfoxide (control) or losartan. The controls underwent sham surgery. The renal tissues were collected 3, 5, 7 and 14 days after surgery for measurement of various indicators of renal fibrosis. UUO increased the expression levels of α‑smooth muscle actin and collagen I, and the extent of renal tubular fibrosis and apoptosis in a time‑dependent manner. Losartan treatment partially attenuated these responses. Progression of renal interstitial fibrosis was accompanied by phosphorylation of signal transducer and activator of transcription 3 (STAT3) and altered the expression levels of two apoptosis‑related proteins (Bax and Bcl2). Losartan treatment also partially attenuated these responses. The results indicated that losartan attenuated renal fibrosis and renal tubular cell apoptosis in a rat model of UUO. This effect appeared to be mediated by partial blockage of STAT3 phosphorylation.

CXCR6 plays a critical role in angiotensin II-induced renal injury and fibrosis

OBJECTIVE

Recent studies have shown that angiotensin II (Ang II) plays a critical role in the pathogenesis and progression of hypertensive kidney disease. However, the signaling mechanisms are poorly understood. In this study, we investigated the role of CXCR6 in Ang II-induced renal injury and fibrosis.

APPROACH AND RESULTS

Wild-type and CXCR6-green fluorescent protein (GFP) knockin mice were treated with Ang II via subcutaneous osmotic minipumps at 1500 ng/kg per minute after unilateral nephrectomy for ≤ 4 weeks. Wild-type and CXCR6-GFP knockin mice had virtually identical blood pressure at baseline. Ang II treatment led to an increase in blood pressure that was similar between wild-type and CXCR6-GFP knockin mice. CXCR6-GFP knockin mice were protected from Ang II-induced renal dysfunction, proteinuria, and fibrosis. CXCR6-GFP knockin mice accumulated fewer bone marrow-derived fibroblasts and myofibroblasts and produced less extracellular matrix protein in the kidneys after Ang II treatment. Furthermore, CXCR6-GFP knockin mice exhibited fewer F4/80(+) macrophages and CD3(+) T cells and expressed less proinflammatory cytokines in the kidneys after Ang II treatment. Finally, wild-type mice engrafted with CXCR6(-/-) bone marrow cells displayed fewer bone marrow-derived fibroblasts, macrophages, and T cells in the kidney after Ang II treatment when compared with wild-type mice engrafted with CXCR6(+/+) bone marrow cells.

CONCLUSIONS

Our results indicate that CXCR6 plays a pivotal role in the development of Ang II-induced renal injury and fibrosis through regulation of macrophage and T-cell infiltration and bone marrow-derived fibroblast accumulation.

Blocking sirtuin 1 and 2 inhibits renal interstitial fibroblast activation and attenuates renal interstitial fibrosis in obstructive nephropathy

Our recent studies revealed that blocking class I/II histone deacetylases (HDACs) inhibits renal interstitial fibroblast activation and proliferation and alleviates development of renal fibrosis. However, the effect of class III HDAC, particularly sirtuin 1 and 2 (SIRT1 and SIRT2), inhibition on renal fibrogenesis remains elusive. Here, we demonstrate that both SIRT1 and SIRT2 were expressed in cultured renal interstitial fibroblasts (NRK-49F). Exposure of NRK-49F to sirtinol, a selective inhibitor of SIRT1/2, or EX527 (6-chloro-2,3,4,9-tetrahydro-1H-carbazole-1-carboxamide), an inhibitor for SIRT1, resulted in reduced expression of fibroblast activation markers (α-smooth muscle actin, fibronectin, and collagen I) as well as proliferation markers (proliferating cell nuclear antigen, cyclin D1, cyclin E) in dose- and time-dependent manners. Treatment with a SIRT2 inhibitor, AGK2 (2-cyano-3-[5-(2,5-dichlorophenyl)-2-furanyl]-N-5-quinolinyl-2-propenamide), also dose- and time-dependently inhibited renal fibroblast activation and, to a lesser extent, cell proliferation. Furthermore, silencing of either SIRT1 or SIRT2 by small interfering RNA exhibited similar inhibitory effects. In a mouse model of obstructive nephropathy, administration of sirtinol attenuated deposition of collagen fibrils as well as reduced expression of α-smooth muscle actin, collagen I, and fibronectin in the injured kidney. SIRT1/2 inhibition-mediated antifibrotic effects are associated with dephosphorylation of epidermal growth factor receptor (EGFR), platelet-derived growth factor receptor-β (PDGFRβ), and signal transducer and activator of transcription 3. Thus, SIRT1/2 activity may contribute to renal fibroblast activation and proliferation as well as renal fibrogenesis through activation of at least EGFR and PDGFRβ signaling. Blocking SIRT1/2 activation may have therapeutic potential for the treatment of chronic kidney disease.

Urinary mRNA in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a relapsing autoimmune disease with clinical manifestations that affect multiple organ systems. Lupus nephritis is recognized as one of the most severe organ involvements in SLE and affects half of the lupus patients. Notably, lupus nephritis is characterized by intrarenal lymphocyte activation and inflammation. Since most of the cytokines exert their effects in a paracrine fashion, measuring their expression at the site of pathology should be of biological relevance. Although kidney biopsy is widely used to determine the histology and severity of lupus nephritis, this invasive procedure has its own risk and is not practical for serial monitoring. In the past decade, extraction and quantification of messenger RNA (mRNA) from urinary sediment has emerged as a robust laboratory technique. Quantification of mRNA expression in urinary sediment has been tested as a noninvasive means to assess the disease activity of SLE patients. Available published evidence, however, is limited to small-scale studies. Based on the result of these studies, a number of cytokine and transcript factor genes have been found to have potential for the differentiation between active and inactive SLE, between proliferative and membranous types of lupus nephritis, assessment of the systemic lupus activity or histological activity of kidney biopsy specimen, monitoring of treatment response in active lupus nephritis, or detection of lupus disease flare in clinically quiescent patients. Being a simple and noninvasive method, urinary mRNA level deserves further studies to validate its role in risk stratification and monitoring of therapeutic response in patients with lupus nephritis.

Assessment of metabolomic and proteomic biomarkers in detection and prognosis of progression of renal function in chronic kidney disease

Chronic kidney disease (CKD) is part of a number of systemic and renal diseases and may reach epidemic proportions over the next decade. Efforts have been made to improve diagnosis and management of CKD. We hypothesised that combining metabolomic and proteomic approaches could generate a more systemic and complete view of the disease mechanisms. To test this approach, we examined samples from a cohort of 49 patients representing different stages of CKD. Urine samples were analysed for proteomic changes using capillary electrophoresis-mass spectrometry and urine and plasma samples for metabolomic changes using different mass spectrometry-based techniques. The training set included 20 CKD patients selected according to their estimated glomerular filtration rate (eGFR) at mild (59.9±16.5 mL/min/1.73 m2; n = 10) or advanced (8.9±4.5 mL/min/1.73 m2; n = 10) CKD and the remaining 29 patients left for the test set. We identified a panel of 76 statistically significant metabolites and peptides that correlated with CKD in the training set. We combined these biomarkers in different classifiers and then performed correlation analyses with eGFR at baseline and follow-up after 2.8±0.8 years in the test set. A solely plasma metabolite biomarker-based classifier significantly correlated with the loss of kidney function in the test set at baseline and follow-up (ρ = -0.8031; p<0.0001 and ρ = -0.6009; p = 0.0019, respectively). Similarly, a urinary metabolite biomarker-based classifier did reveal significant association to kidney function (ρ = -0.6557; p = 0.0001 and ρ = -0.6574; p = 0.0005). A classifier utilising 46 identified urinary peptide biomarkers performed statistically equivalent to the urinary and plasma metabolite classifier (ρ = -0.7752; p<0.0001 and ρ = -0.8400; p<0.0001). The combination of both urinary proteomic and urinary and plasma metabolic biomarkers did not improve the correlation with eGFR. In conclusion, we found excellent association of plasma and urinary metabolites and urinary peptides with kidney function, and disease progression, but no added value in combining the different biomarkers data.

Smad3 signaling activates bone marrow-derived fibroblasts in renal fibrosis

Recent studies have demonstrated that bone marrow-derived fibroblasts contribute significantly to the pathogenesis of renal fibrosis. However, the signaling mechanisms underlying the activation of bone marrow-derived fibroblasts in the kidney are incompletely understood. As TGF-β1/Smad3 signaling has been shown to have an important role in the pathogenesis of kidney fibrosis, we investigated the role of Smad3 in the activation of bone marrow-derived fibroblasts in the kidney following obstructive injury using Smad3-knockout mice and Smad3-null monocytes. Compared with wild-type mice, Smad3-knockout mice accumulated significantly fewer bone marrow-derived fibroblasts in the kidney after obstructive injury. Furthermore, Smad3-knockout mice exhibited less myofibroblast activation and expressed less α-SMA in the obstructed kidney. Consistent with these findings, genetic deletion of Smad3 reduced total collagen deposition and suppressed the expression of extracellular matrix proteins. Moreover, wild-type mice engrafted with Smad3(-/-) bone marrow cells displayed fewer bone marrow-derived fibroblasts in the kidney with obstructive injury and showed less severe renal fibrosis compared with wild-type mice engrafted with Smad3(+/+) bone marrow cells. In cultured monocytes, TGF-β1 induced phosphorylation of Smad3 and Smad3 deficiency abolished TGF-β1-induced expression of α-SMA and extracellular matrix proteins. Taken together, our results demonstrate that Smad3 signaling has an essential role in the activation of bone marrow-derived fibroblasts in the kidney during the pathogenesis of renal fibrosis.

MicroRNAs in IgA nephropathy

IgA nephropathy is globally the most common primary glomerulonephritis, but the pathogenesis of this condition is still only partially understood. MicroRNAs (miRNAs) are short, noncoding RNA molecules that regulate gene expression. Genome-wide analysis of renal miRNA expression has identified a number of novel miRNAs related to immunological and pathological changes. Specifically, overexpression of miR-148b might explain the aberrant glycosylation of IgA1, which has a central pathogenetic role in the early phase of IgA nephropathy. By contrast, miR-29c is an antifibrotic miRNA that is probably important in the late stages of disease progression. In addition, urinary levels of several miRNAs are significantly changed in patients with IgA nephropathy compared with healthy individuals; some alterations seem to be disease-specific, whereas others are apparently damage-related. As miRNAs in urinary sediment are relatively stable and easily quantified, they have the potential to be used as biomarkers for the diagnosis and monitoring of disease. However, to date, limited data are available on the role of miRNAs in the pathogenesis of IgA nephropathy and their potential application as biomarkers. Consequently, further studies are urgently needed to address this shortfall. Here, we review the available literature on miRNAs in relation to IgA nephropathy.

The chemokine receptor CXCR6 contributes to recruitment of bone marrow-derived fibroblast precursors in renal fibrosis

Bone marrow-derived fibroblasts in circulation are of hematopoietic origin, proliferate, differentiate into myofibroblasts, and express the chemokine receptor CXCR6. Since chemokines mediate the trafficking of circulating cells to sites of injury, we studied the role of CXCR6 in mouse models of renal injury. Significantly fewer bone marrow-derived fibroblasts accumulated in the kidney of CXCR6 knockout mice in response to injury, expressed less profibrotic chemokines and cytokines, displayed fewer myofibroblasts, and expressed less α-smooth muscle actin in the obstructed kidneys compared with wild-type mice. CXCR6 deficiency inhibited total collagen deposition and suppressed expression of collagen I and fibronectin in the obstructed kidneys. Furthermore, wild type mice engrafted with CXCR6^−/− bone marrow cells displayed fewer bone marrow-derived fibroblasts in the kidneys with obstructive injury and showed less severe renal fibrosis compared with wild-type mice engrafted with CXCR6^+/+ bone marrow cells. Transplant of wild type bone marrow into CXCR6^−/− recipients restored recruitment of myeloid fibroblasts and susceptibility to fibrosis. Hematopoietic fibroblasts migrate into injured kidney and proliferate and differentiate into myofibroblasts. Thus, CXCR6, together with other chemokines and their receptors, may play important roles in the recruitment of bone marrow-derived fibroblast precursors into the kidney and contribute to the pathogenesis of renal fibrosis.

The role of reactive oxygen species and metabolism on cancer cells and their microenvironment

Compelling evidence show that reactive oxygen species (ROS) levels are finely regulated in the cell and can act as "second messengers" in response to diverse stimuli. In tumor epithelial cells, ROS accumulate abnormally and induce signaling cascades that mediate the oncogenic phenotype. In addition to their impact on tumor epithelial cells, ROS also affect the surrounding cells that constitute the tumor microenvironment. Indeed, ROS production increases tumor angiogenesis, drives the onset of inflammation and promotes conversion of fibroblast into myofibroblasts. These cells, initially identified upon wound healing, exhibit similar properties to those observed in fibroblasts associated with aggressive adenocarcinomas. Indeed, analyses of tumors with distinct severity revealed the existence of multiple distinct co-existing subtypes of carcinoma-associated fibroblasts (CAFs), with specific marker protein profiling. Chronic oxidative stress deeply modifies the proportion of these different fibroblast subtypes, further supporting tumor growth and metastatic dissemination. At last, ROS have been implicated in the metabolic reprogramming of both cancer cells and CAFs, allowing an adaptation to oxidative stress that ultimately promotes tumorigenesis and chemoresistance. In this review, we discuss the role of ROS in cancer cells and CAFs and their impact on tumor initiation, progression, and metastasis.

Soft matrix is a natural stimulator for cellular invasiveness

ECM softness (low stiffness comparable to soft tissues) alone is sufficient to prevent cell-to-cell adherens junction formation, up-regulate MMP secretion, promote MMP activity, and induce invadosome-like protrusion formation. Such findings suggest that cell invasion in vivo is a spontaneous cell behavior in response to ECM stiffness.

Directional mesenchymal cell invasion in vivo is understood to be a stimulated event and to be regulated by cytokines, chemokines, and types of extracellular matrix (ECM). Instead, by focusing on the cellular response to ECM stiffness, we found that soft ECM (low stiffness) itself is sufficient to prevent stable cell-to-cell adherens junction formation, up-regulate matrix metalloproteinase (MMP) secretion, promote MMP activity, and induce invadosome-like protrusion (ILP) formation. Consistently, similar ILP formation was also detected in a three-dimensional directional invasion assay in soft matrix. Primary human fibroblasts spontaneously form ILPs in a very narrow range of ECM stiffness (0.1–0.4 kPa), and such ILP formation is Src family kinase dependent. In contrast, spontaneous ILP formation in malignant cancer cells and fibrosarcoma cells occurs across a much wider range of ECM stiffness, and these tumor cell ILPs are also more prominent at lower stiffness. These findings suggest that ECM softness is a natural stimulator for cellular invasiveness.

Induction of epithelial-to-mesenchymal transition in proximal tubular epithelial cells on microfluidic devices

In proteinuric nephropathy, epithelial-to-mesenchymal transition (EMT) is an important mechanism that causes renal interstitial fibrosis. The precise role of EMT in the pathogenesis of fibrosis remains controversial, partly due to the absence of suitable in vitro or in vivo models. We developed two microfluidic and compartmental chips that reproduced the fluidic and three-dimensional microenvironment of proximal tubular epithelial cells in vivo. Using one microfluidic device, we stimulated epithelial cells with a flow of healthy human serum, heat-inactivated serum and complement C3a, which mimicked the flow of urine within the proximal tubule. We observed that epithelial cells exposed to serum proteins became apoptotic or developed a mesenchymal phenotype. Incubating cells with C3a induced similar features. However, cells exposed to heat-inactivated serum did not adopt the mesenchymal phenotype. Furthermore, we successfully recorded the cellular morphological changes and the process of transmigration into basement membrane extract during EMT in real-time using another three-dimensional microdevice. In conclusion, we have established a cell-culture system that mimics the native microenvironment of the proximal tubule to a certain extent. Our data indicates that EMT did occur in epithelial cells that were exposed to serum proteins, and C3a plays an essential role in this pathological process.

CCR2 regulates the uptake of bone marrow-derived fibroblasts in renal fibrosis

Recent studies have shown that bone marrow-derived fibroblasts contribute significantly to the pathogenesis of renal fibrosis. However, the molecular mechanisms underlying the recruitment of bone marrow-derived fibroblasts into the kidney are incompletely understood. Bone marrow-derived fibroblasts express the chemokine receptor--CCR2. In this study, we tested the hypothesis that CCR2 participates in the recruitment of fibroblasts into the kidney during the development of renal fibrosis. Bone marrow-derived collagen-expressing GFP⁺ fibroblasts were detected in the obstructed kidneys of chimeric mice transplanted with donor bone marrow from collagen α1(I)-GFP reporter mice. These bone marrow-derived fibroblasts expressed PDGFR-β and CCR2. CCR2 knockout mice accumulated significantly fewer bone marrow-derived fibroblast precursors expressing the hematopoietic marker-CD45 and the mesenchymal markers-PDGFR-β or procollagen I in the obstructed kidneys compared with wild-type mice. Furthermore, CCR2 knockout mice displayed fewer bone marrow-derived myofibroblasts and expressed less α-SMA or FSP-1 in the obstructed kidneys compared with wild-type mice. Consistent with these findings, genetic deletion of CCR2 inhibited total collagen deposition and suppressed expression of collagen I and fibronectin. Moreover, genetic deletion of CCR2 inhibits MCP-1 and CXCL16 gene expression associated with a reduction of inflammatory cytokine expression and macrophage infiltration, suggesting a linear interaction between two chemokines/ligand receptors in tubular epithelial cells. Taken together, our results demonstrate that CCR2 signaling plays an important role in the pathogenesis of renal fibrosis through regulation of bone marrow-derived fibroblasts. These data suggest that inhibition of CCR2 signaling could constitute a novel therapeutic approach for fibrotic kidney disease.

Critical role of CXCL16 in hypertensive kidney injury and fibrosis

Recent evidence indicates that inflammation plays a critical role in the initiation and progression of hypertensive kidney disease. However, the signaling mechanisms underlying the induction of inflammation are poorly understood. We found that chemokine (C-X-C motif) ligand 16 (CXCL16) was induced in renal tubular epithelial cells in response to angiotensin II in a nuclear factor-κB-dependent manner. To determine whether CXCL16 plays a role in angiotensin II-induced renal inflammation and fibrosis, wild-type and CXCL16 knockout mice were infused with angiotensin II at 1500 ng/kg per minute for up to 4 weeks. Wild-type and CXCL16 knockout mice had comparable blood pressure at baseline. Angiotensin II treatment led to an increase in blood pressure that was similar between wild-type and CXCL16 knockout mice. CXCL16 knockout mice were protected from angiotensin II-induced renal dysfunction, proteinuria, and fibrosis. CXCL16 deficiency suppressed bone marrow-derived fibroblast accumulation and myofibroblast formation in the kidneys of angiotensin II-treated mice, which was associated with less expression of extracellular matrix proteins. Furthermore, CXCL16 deficiency inhibited infiltration of F4/80(+) macrophages and CD3(+) T cells in the kidneys of angiotensin II-treated mice compared with wild-type mice. Finally, CXCL16 deficiency reduced angiotensin II-induced proinflammatory cytokine expressions in the kidneys. Taken together, our results indicate that CXCL16 plays a pivotal role in the pathogenesis of angiotensin II-induced renal injury and fibrosis through regulation of macrophage and T cell infiltration and bone marrow-derived fibroblast accumulation.

Polyphenols of Hibiscus sabdariffa improved diabetic nephropathy via attenuating renal epithelial mesenchymal transition

We previously reported that Hibiscus sabdariffa polyphenol extracts (HPE) are beneficial for diabetic nephropathy. Since an epithelial to mesenchymal transition (EMT) is critical in renal fibrosis, the present study aimed to investigate whether HPE could prevent EMT of tubular cells. Treatment of HPE reduced angiotensin II receptors (AT)-1 and transforming growth factor β1 (TGF-β1) evoked by high glucose and recovered the increased vimentin and decreased E-cadherin. HPE decreased fibronectin, thus avoiding EMT and accompanying fibrosis. AT-1 was upstream to TGF-β1, while there were recruitment signals between AT-1 and TGF-β1. Scan electron microscopy (SEM) and immunohistochemistry (IHC) revealed that the interacting filaments of tubular cells disappeared when treated with high glucose, and type IV collagen of tubulointerstitial decreased in diabetic kidneys. Treatment of HPE recovered morphological changes of cell junction and basement membrane. We suggest that HPE has the potential to be an adjuvant for diabetic nephropathy by regulating AT-1/TGF-β1 and EMT.

Adiponectin promotes monocyte-to-fibroblast transition in renal fibrosis

Bone marrow-derived fibroblasts may contribute substantially to the pathogenesis of renal fibrosis through the excessive production and deposition of extracellular matrix. However, the mechanisms underlying the accumulation and activation of these fibroblasts are not understood. Here, we used a mouse model of tubulointerstitial fibrosis to determine whether adiponectin, which is elevated in CKD and is associated with disease progression, regulates monocyte-to-fibroblast transition and fibroblast activation in injured kidneys. In wild-type mice, the expression of adiponectin and the number of bone marrow-derived fibroblasts in the kidney increased after renal obstruction. In contrast, the obstructed kidneys of adiponectin-knockout mice had fewer bone marrow-derived fibroblasts. Adiponectin deficiency also led to a reduction in the number of myofibroblasts, the expression of profibrotic chemokines and cytokines, and the number of procollagen-expressing M2 macrophages in injured kidneys. Consistent with these findings, adiponectin-deficiency reduced the expression of collagen I and fibronectin. Similar results were observed in wild-type and adiponectin-knockout mice after ischemia-reperfusion injury. In cultured bone marrow-derived monocytes, adiponectin stimulated the expression of α-smooth muscle actin (SMA) and extracellular matrix proteins and activated AMP-activated protein kinase (AMPK) in a time- and dose-dependent manner. Furthermore, specific activation of AMPK increased the expression of α-SMA and extracellular matrix proteins, while inhibition of AMPK attenuated these responses. Taken together, these findings identify adiponectin as a critical regulator of monocyte-to-fibroblast transition and renal fibrosis, suggesting that inhibition of adiponectin/AMPK signaling may represent a novel therapeutic target for fibrotic kidney disease.

Expression of Smad7 in cholangiocarcinoma: prognostic significance and implications for tumor metastasis

BACKGROUND

There are few molecular markers known to predict cholangiocarcinoma (CCA) prognosis. Smad7 has a certain relationship with epithelial-mesenchymal transition (EMT), but its relevance to CCA in unclear. Therefore expression and clinical significance of Smad7 in CCA was the focus of this study.

METHODS

Expression of Smad7, E-cadherin and vimentin was assessed in 41 patients with CCA by immunohistochemistry and analyzed for associations with clinical parameters.

RESULTS

Smad7 and vimentin expression in the CCA tissue was dramatically higher than that in adjacent tissues. In addition, Smad7, vimentin and E-cadherin expression was significantly associated with CCA lymph node metastasis and perineural invasion(P ≤ 0.05), but not other factors, such as gender, age, tumor location, tumor type and tumor differentiation degree (P>0.05). The overall survival and relapse-free survival rate was significantly higher in patients with negative Smad7 expression than those with positive Smad7 expression.

CONCLUSION

EMT phenomena may occur in the process of CCA invasion and metastasis. Smad7, which was highly expressed in CCA, may be considered to be one feedback regulator in late stages and could have potential as a prognostic indicator for clinical assessment.

CKD273, a new proteomics classifier assessing CKD and its prognosis

National Kidney Foundation CKD staging has allowed uniformity in studies on CKD. However, early diagnosis and predicting progression to end stage renal disease are yet to be improved. Seventy six patients with different levels of CKD, including outpatients and dialysed patients were studied for transcriptome, metabolome and proteome description. High resolution urinary proteome analysis was blindly performed in the 53 non-anuric out of the 76 CKD patients. In addition to routine clinical parameters, CKD273, a urinary proteomics-based classifier and its peptides were quantified. The baseline values were analyzed with regard to the clinical parameters and the occurrence of death or renal death during follow-up (3.6 years) as the main outcome measurements. None of the patients with CKD273<0.55 required dialysis or died while all fifteen patients that reached an endpoint had a CKD273 score >0.55. Unsupervised clustering analysis of the CKD273 peptides separated the patients into two main groups differing in CKD associated parameters. Among the 273 biomarkers, peptides derived from serum proteins were relatively increased in patients with lower glomerular filtration rate, while collagen-derived peptides were relatively decreased (p<0.05; Spearman). CKD273 was different in the groups with different renal function (p<0.003). The CKD273 classifier separated CKD patients according to their renal function and informed on the likelihood of experiencing adverse outcome. Recently defined in a large population, CKD273 is the first proteomic-based classifier successfully tested for prognosis of CKD progression in an independent cohort.

Amygdalin inhibits renal fibrosis in chronic kidney disease

Renal interstitial fibrosis is a common outcome of chronic renal diseases. Amygdalin is one of a number of nitrilosides, the natural cyanide‑containing substances abundant in the seeds of plants of the prunasin family that are used to treat cancer and relieve pain. However, whether amygdalin inhibits the progression of renal fibrosis or not remains unknown. The present study aimed to assess the therapeutic potential of amygdalin by investigating its effect and potential mechanism on the activation of renal interstitial fibroblast cells and renal fibrosis in rat unilateral ureteral obstruction (UUO). Treatment of the cultured renal interstitial fibroblasts with amygdalin inhibited their proliferation and the production of transforming growth factor (TGF)‑β1. In the rat model of obstructive nephropathy, following ureteral obstruction, the administration of amygdalin immediately eliminated the extracellular matrix accumulation and alleviated the renal injury on the 21st day. Collectively, amygdalin attenuated kidney fibroblast (KFB) activation and rat renal interstitial fibrosis. These results indicate that amygdalin is a potent antifibrotic agent that may have therapeutic potential for patients with fibrotic kidney diseases.

Effect of interleukin 6 deficiency on renal interstitial fibrosis

Our recent studies have shown that bone marrow-derived fibroblast precursors contribute significantly to the pathogenesis of renal fibrosis. However, the molecular mechanisms underlying the recruitment and activation of bone marrow-derived fibroblast precursors are incompletely understood. We found that interleukin 6 was induced in the kidney in a murine model of renal fibrosis induced by unilateral ureteral obstruction. Therefore, we investigated if interleukin 6 play a role in the recruitment and maturation of bone marrow-derived fibroblast precursors in the kidney during the development of renal fibrosis. Wild-type and interleukin 6 knockout mice were subjected to unilateral obstructive injury for up to two weeks. Interleukin 6 knockout mice accumulated similar number of bone marrow-derived fibroblast precursors and myofibroblasts in the kidney in response to obstructive injury compared to wild-type mice. Furthermore, IL-6 knockout mice expressed comparable α-SMA in the obstructed kidney compared to wild-type mice. Moreover, targeted disruption of Interleukin 6 did not affect gene expression of profibrotic chemokine and cytokines in the obstructed kidney. Finally, there were no significant differences in renal interstitial fibrosis or expression of extracellular matrix proteins between wild-type and interleukin 6 knockout mice following obstructive injury. Our results indicate that interleukin 6 does not play a significant role in the recruitment of bone marrow-derived fibroblast precursors and the development of renal fibrosis.

3-Hydroxy-3-methylglutaryl-coenzyme A reductase inhibitor simvastatin ameliorates renal fibrosis through HOXA13-USAG-1 pathway

Epidemiological data have suggested that 3-hydroxy-3-methylglutaryl-coenzyme A reductase inhibitors (statins) prevent the progression of chronic kidney diseases (CKDs), whereas the precise mechanism explaining in vitro to in vivo is missing. This study is aimed at exploring a new mechanism of action by statins on renal fibrosis, a hallmark of CKD, using mouse renal fibrosis model in vivo and Madin-Darby canine kidney (MDCK) cells expressing USAG-1 in vitro. C57/BL6 mice fed a 0.2% adenine-containing diet for 4 weeks developed renal dysfunction accompanied with severe tubulointerstitial fibrosis. Subsequent simvastatin (SIM) treatment (50 mg/kg per day) for 2 weeks significantly suppressed fibrosis progression. We found that SIM enhanced bone morphogenetic protein-7 (BMP-7)-mediated anti-fibrotic signaling with the reduced expression of uterine sensitization-associated gene-1 (USAG-1), a BMP-7 antagonist produced by renal distal tubular epithelial cells. Therefore, MDCK cells were incubated with transforming growth factor-β1 and showed increased expression of USAG-1 and α-smooth muscle actin; SIM significantly reduced them. SIM significantly increased E-cadherin expression. Gene knockdown experiments using MDCK suggested that homeobox protein Hox-A13 (HOXA13) played a suppressive role in the USAG-1 gene and thus SIM reduced USAG-1 by increasing HOXA13 expression. The data from our study demonstrate that SIM, one of statins, contributes to prevent the progression of renal fibrosis by upregulating BMP-7-mediated anti-fibrotic signaling and that one aspect of crucial efficacies is achieved by regulating HOXA13 and USAG-1. HOXA13-USAG-1 pathway is a newly identified mechanism in renal fibrosis and will be a new therapeutic target for preventing renal fibrosis progression in CKDs.

Molecular mechanisms of endothelial to mesenchymal cell transition (EndoMT) in experimentally induced fibrotic diseases

Several recent studies have demonstrated that endothelial to mesenchymal transition (EndoMT), a newly recognized type of cellular transdifferentiation may be an important source of myofibroblasts during the development of experimentally induced pulmonary, cardiac and kidney fibrosis. EndoMT is a complex biological process induced by members of the transforming growth factor (TGF-β) family of regulatory polypeptides in which endothelial cells adopt a mesenchymal or myofibroblastic phenotype acquiring motile and contractile properties and initiating expression of mesenchymal cell products such as α smooth muscle actin (α-SMA) and type I collagen. Although these experimental studies provide compelling evidence for the participation of EndoMT in the development of experimentally-induced fibrotic processes the precise role of EndoMT in the pathogenesis of human fibrotic disorders requires confirmation and validation from studies of human clinical pathologic conditions. Such confirmation should lead to a change in the paradigm of the origin of profibrogenic myofibroblasts involved in human fibrotic diseases. Further understanding of the molecular mechanisms and the regulatory pathways involved in EndoMT may lead to the development of novel therapeutic approaches for the incurable and often devastating fibrotic disorders.

Angiotensin-(1-7) attenuates high glucose-induced proximal tubular epithelial-to-mesenchymal transition via inhibiting ERK1/2 and p38 phosphorylation

AIMS

The kidney is an important target for both Angiotensin II and angiotensin-(1-7) [Ang-(1-7)] in the renin-angiotensin system. However, the renal function of Ang-(1-7) remains unclear. This study is aimed at investigating the effect of Ang-(1-7) on high glucose-induced epithelial to mesenchymal transition (EMT) in cultured renal epithelial cells.

MAIN METHODS

Cultured renal epithelial (NRK-52E) cell line was used in the experiment. Fluorescence immunocytochemistry was performed to observe α-smooth muscle actin (α-SMA). Real-time PCR and Western blot were used to determine mRNA and protein levels. Enzyme-linked immunosorbent assay was used to measure the concentration of transforming growth factor-β1 (TGF-β1) in the culture media.

KEY FINDINGS

High glucose-induced decreased in both angiotensin-converting enzyme-related carboxypeptidase (ACE2) and Mas mRNA levels. Meanwhile, high glucose induced increases in α-SMA and vimentin, decreases in E-cadherin, elevations in TGF-β1 and fibronectin secretions. Ang-(1-7) partially reversed high glucose-induced changes in α-SMA, vimentin, E-cadherin, TGF-β1 and fibronectin. High glucose stimulated ERK, p38 and JNK phosphorylation and Ang-(1-7) reversed the changes in ERK and p38 but not JNK phosphorylation.

SIGNIFICANCE

Inhibition and insufficiency in ACE2-Ang-(1-7)-Mas axis under high glucose condition participate EMT. Supplementation of Ang-(1-7) attenuates high glucose-induced EMT. ERK and p38 intracellular signaling pathways, not JNK, mediate the effect of Ang-(1-7) on EMT.

Role of microRNAs in kidney homeostasis and disease

MicroRNAs (miRNAs) are endogenous short (20-22 nucleotides) non-coding RNA molecules that mediate gene expression. This is an important regulatory mechanism to modulate fundamental cellular processes such as differentiation, proliferation, death, metabolism, and pathophysiology of many diseases. The miRNA expression profile of the kidney differs greatly from that of other organs, as well as between the different regions in the kidney. In kidneys, miRNAs are indispensable for development and homeostasis. In this review, we explore the involvement of miRNAs in the regulation of blood pressure, hormone, water, and ion balance pertaining to kidney homeostasis. We also highlight their importance in renal pathophysiology, such as in polycystic disease, diabetic nephropathy, nephrogenic diabetes insipidus, hypertension, renal cancer, and kidney fibrosis (epithelial-mesenchymal transition). In addition, we highlight the need for further investigations on miRNA-based studies in the development of diagnostic, prognostic, and therapeutic tools for renal diseases.

Cell signals influencing hepatic fibrosis

Liver fibrosis is the result of the entire organism responding to a chronic injury. Every cell type in the liver contributes to the fibrosis. This paper first discusses key intracellular signaling pathways that are induced during liver fibrosis. The paper then examines the effects of these signaling pathways on the major cell types in the liver. This will provide insights into the molecular pathophysiology of liver fibrosis and should identify therapeutic targets.

Alternative origins of stroma in normal organs and disease

Stromal fibroblasts are a new prospective drug target. Mesenchymal stromal cells (MSCs) and monocyte-derived stromal cells, also known as fibrocytes, are distinct fibroblastic populations derived from separate lineages. Mesenchymal and myeloid fibroblast progenitors are multipotent, serve as progenitor cells in animal models, and are implicated in several diseases. In addition, epithelial-mesenchymal transition (EMT) has been established as a mechanism for generation of stromal cells. Organ sources, relative contributions, and functions of these populations in normal development and pathology are not well understood. Innovative approaches are needed to identify markers that can distinguish these stromal populations.

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.

Transcriptional networks in epithelial-mesenchymal transition

Backround

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

Methods and Findings

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

Conclusions

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

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.

CXCL16 recruits bone marrow-derived fibroblast precursors in renal fibrosis

Although fibroblasts are responsible for the production and deposition of extracellular matrix in renal fibrosis, their origin is controversial. Circulating fibroblast precursors may contribute to the pathogenesis of renal fibrosis, but the signaling mechanisms underlying the recruitment of bone marrow-derived fibroblast precursors into the kidney in response to injury are incompletely understood. Here, in the unilateral ureteral obstruction model of renal fibrosis, tubular epithelial cells upregulated the chemokine CXCL16 in obstructed kidneys, and circulating fibroblast precursors expressed the CXCL16 receptor, CXCR6. Compared with wild-type mice, CXCL16-knockout mice accumulated significantly fewer bone marrow-derived fibroblast precursors in obstructed kidneys. CXCL16-knockout mice also exhibited significantly fewer CD45-, collagen I-, and CXCR6-triple-positive fibroblast precursors in injured kidneys. Furthermore, targeted deletion of CXCL16 inhibited myofibroblast activation, reduced collagen deposition, and suppressed expression of collagen I and fibronectin. In conclusion, CXCL16 contributes to the pathogenesis of renal fibrosis by recruiting bone marrow-derived fibroblast precursors.

Role of endothelial-mesenchymal transition (EndoMT) in the pathogenesis of fibrotic disorders

The accumulation of a large number of myofibroblasts is responsible for exaggerated and uncontrolled production of extracellular matrix during the development and progression of pathological fibrosis. Myofibroblasts in fibrotic tissues are derived from at least three sources: expansion and activation of resident tissue fibroblasts, transition of epithelial cells into mesenchymal cells (epithelial-mesenchymal transition, EMT), and tissue migration of bone marrow-derived circulating fibrocytes. Recently, endothelial to mesenchymal transition (EndoMT), a newly recognized type of cellular transdifferentiation, has emerged as another possible source of tissue myofibroblasts. EndoMT is a complex biological process in which endothelial cells lose their specific markers and acquire a mesenchymal or myofibroblastic phenotype and express mesenchymal cell products such as α smooth muscle actin (α-SMA) and type I collagen. Similar to EMT, EndoMT can be induced by transforming growth factor (TGF-β). Recent studies using cell-lineage analysis have demonstrated that EndoMT may be an important mechanism in the pathogenesis of pulmonary, cardiac, and kidney fibrosis, and may represent a novel therapeutic target for fibrotic disorders.

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.

Delayed administration of suramin attenuates the progression of renal fibrosis in obstructive nephropathy

We recently showed that suramin treatment prevents the onset of renal fibrosis in a model of obstructive nephropathy induced by unilateral ureteral obstruction (UUO). In this study, we further assessed the effect of delayed administration of suramin on the progression of tubulointerstitial fibrosis. Mice were given a single dose of suramin at 20 mg/kg starting at day 3 of obstruction, and kidneys were harvested after an additional 7 or 14 days of obstruction. Suramin completely blocked further increase in expression of type I collagen and fibronectin and largely suppressed expression of α-smooth muscle actin (α-SMA) in both treatment groups. UUO injury induced phosphorylation of Smad-3, a key mediator of transforming growth factor-β (TGF-β) signaling, epidermal growth factor receptor, and platelet-derived growth factor receptor after 3 days and further increased at 10 days after UUO injury. When suramin was administered at 3 days after obstruction, phosphorylation of these molecules was not further increased in the obstructed kidney. Suramin treatment also inhibited activation of signal transducer and activator of transcription 3 and extracellular signal-regulated kinase 1 and 2, two signaling pathways associated with renal fibrogenesis. Furthermore, delayed application of suramin suppressed TGF-β1-induced expression of α-SMA and fibronectin in cultured renal interstitial fibroblasts. These results indicate that administration of suramin is effective in attenuating the progression of renal fibrosis after injury and suggest the potential clinical application of suramin as an antifibrotic treatment in patients with chronic kidney disease.

Suramin inhibits renal fibrosis in chronic kidney disease

The activation of cytokine and growth factor receptors associates with the development and progression of renal fibrosis. Suramin is a compound that inhibits the interaction of several cytokines and growth factors with their receptors, but whether suramin inhibits the progression of renal fibrosis is unknown. Here, treatment of cultured renal interstitial fibroblasts with suramin inhibited their activation induced by TGF-β1 and serum. In a mouse model of obstructive nephropathy, administration of a single dose of suramin immediately after ureteral obstruction abolished the expression of fibronectin, largely suppressed expression of α-SMA and type I collagen, and reduced the deposition of extracellular matrix proteins. Suramin also decreased the expression of multiple cytokines including TGF-β1 and reduced the interstitial infiltration of leukocytes. Moreover, suramin decreased expression of the type II TGF-β receptor, blocked phosphorylation of the EGF and PDGF receptors, and inactivated several signaling pathways associated with the progression of renal fibrosis. In a rat model of CKD, suramin abrogated proteinuria, limited the decline of renal function, and prevented glomerular and tubulointerstitial damage. Collectively, these findings indicate that suramin is a potent antifibrotic agent that may have therapeutic potential for patients with fibrotic kidney diseases.