Wnt-signaling pathways in progressive renal fibrosis

Association of Urinary Dickkopf-3 Levels with Cardiovascular Events and Kidney Disease Progression in Systolic Blood Pressure Intervention Trial

Key Points

In unadjusted analyses, elevated urinary Dickkopf-3 levels were strongly associated with higher risks of cardiovascular disease, ESKD, AKI, and mortality. However, associations were substantially weakened after adjustment for eGFR and albuminuria, suggesting limited prognostic value.

Background

Urinary Dickkopf-3 (uDKK3) is a tubular epithelial-derived profibrotic protein secreted into the urine under tubular stress. It is associated with kidney disease progression in persons with CKD and diabetes and postoperative and contrast-associated AKI. We explored associations of uDKK3 with cardiovascular disease (CVD), kidney, and mortality outcomes within the subset of Systolic Blood Pressure Intervention Trial participants with nondiabetic CKD.

Methods

We included 2344 participants with eGFR <60 ml/min per 1.73 m2 at baseline. We used Cox proportional hazards models to evaluate associations of uDKK3 with CVD (acute decompensated heart failure, myocardial infarction, acute coronary syndrome, stroke, or CVD death), kidney outcomes (incident ESKD, incident AKI, and eGFR decline ≥30%), and all-cause mortality. We used linear mixed models to examine the association of uDKK3 with annual percentage change in eGFR. Models were adjusted for demographic and clinical characteristics, eGFR, and albuminuria.

Results

Over a median follow-up of 3.5 years, there were 292 CVD, 73 ESKD, 183 AKI, 471 eGFR decline, and 228 mortality events. In multivariable models without adjustment for eGFR and albuminuria, uDKK3 was strongly associated with CVD, ESKD, AKI, eGFR decline ≥30%, and mortality. However, after further adjustment for eGFR and albuminuria, uDKK3 was no longer associated with risks for composite CVD (hazard ratio, 1.07; 95% confidence interval, 0.92 to 1.23), ESKD (0.80; 0.62 to 1.02), AKI (1.01; 0.85 to 1.21), eGFR decline ≥30% (0.88; 0.79 to 0.99), or mortality (1.02; 0.87 to 1.20). For the linear eGFR change outcome, higher uDKK3 also had no association in the fully adjusted model (−0.03; −0.41 to 0.36).

Conclusions

Among individuals with hypertension and nondiabetic CKD, higher uDKK3 appeared to have associations with a greater risk of CVD events, incident ESKD, incident AKI, eGFR decline ≥30%, and mortality but these associations were not independent of eGFR and albuminuria.

Pharmacological functions of salidroside in renal diseases: facts and perspectives

Rhodiola rosea is a valuable functional medicinal plant widely utilized in China and other Asian countries for its anti-fatigue, anti-aging, and altitude sickness prevention properties. Salidroside, a most active constituent derived from Rhodiola rosea, exhibits potent antioxidative, hypoxia-resistant, anti-inflammatory, anticancer, and anti-aging effects that have garnered significant attention. The appreciation of the pharmacological role of salidroside has burgeoned over the last decade, making it a beneficial option for the prevention and treatment of multiple diseases, including atherosclerosis, Alzheimer's disease, Parkinson's disease, cardiovascular disease, and more. With its anti-aging and renoprotective effects, in parallel with the inhibition of oxidative stress and inflammation, salidroside holds promise as a potential therapeutic agent for kidney damage. This article provides an overview of the microinflammatory state in kidney disease and discuss the current therapeutic strategies, with a particular focus on highlighting the recent advancements in utilizing salidroside for renal disease. The potential mechanisms of action of salidroside are primarily associated with the regulation of gene and protein expression in glomerular endothelial cells, podocytes, renal tubule cells, renal mesangial cells and renal cell carcinoma cell, including TNF-α, TGF-β, IL-1β, IL-17A, IL-6, MCP-1, Bcl-2, VEGF, ECM protein, caspase-3, HIF-1α, BIM, as well as the modulation of AMPK/SIRT1, Nrf2/HO-1, Sirt1/PGC-1α, ROS/Src/Cav-1, Akt/GSK-3β, TXNIP-NLRP3, ERK1/2, TGF-β1/Smad2/3, PI3K/Akt, Wnt1/Wnt3a β-catenin, TLR4/NF-κB, MAPK, JAK2/STAT3, SIRT1/Nrf2 pathways. To the best of our knowledge, this review is the first to comprehensively cover the protective effects of salidroside on diverse renal diseases, and suggests that salidroside has great potential to be developed as a drug for the prevention and treatment of metabolic syndrome, cardiovascular and cerebrovascular diseases and renal complications.

Usefulness of urinary biomarkers to estimate the interstitial fibrosis surface in diabetic nephropathy with normal kidney function

BACKGROUND

Kidney biopsies of patients with diabetic nephropathy (DN) and normal kidney function may exhibit interstitial fibrosis (IF) without reduction of glomerular filtration rate because of hyperfiltration. The aim of our study was to analyze the performance of a set of biomarkers of tubular injury to estimate the extent of IF in patients with DN and normal kidney function.

PATIENTS AND METHODS

This cross-sectional study included 118 adults with DN diagnosed by kidney biopsy and GFR ≥ 90 mL/min/1.73 m2 and a control group of healthy subjects. We measured the urinary excretion of MCP-1, NGAL, KIM-1, L-FABP, β2-microglobulin and DKK-3 at the time of kidney biopsy. GFR was measured by Cr-EDTA (mGFR). IF was quantified using a quantitative morphometric procedure. Predictive multivariate models were developed to estimate the IF surface.

RESULTS

patients with DN showed significantly higher levels of DKK-3, MCP-1 and L-FABP and significantly lower levels of EGF than healthy controls. There were no significant between-group differences in the levels of β2-microglobulin, KIM-1 or NGAL. IF was negatively associated with EGF and a positively with age, proteinuria, MCP-1, DKK-3 and L-FABP but no with β2-microglobulin, KIM-1, NGAL or GFR. The best model to predict IF surface accounted for 59% of its variability and included age, proteinuria, EGF, DKK-3 and MCP-1.

CONCLUSIONS

our study provides a model to estimate the IF in DN that can be useful to assess the progression of IF in patients with normal kidney function.

Relaxin inhibits renal fibrosis and the epithelial-to-mesenchymal transition via the Wnt/β-catenin signaling pathway

Renal fibrosis is a common characteristic and the final pathological mechanism of chronic kidney disease (CKD). Although CKD remains incurable, inhibition of renal fibrosis is beneficial to inhibit the CKD process. Relaxin alleviates renal fibrosis in some experimental models, but its mechanism remains unclear. In the following, we studied the regulatory effect of relaxin on epithelial-mesenchymal transition (EMT) after unilateral ureteral obstruction (UUO). Our results demonstrate that relaxin could downregulate Wnt/β-catenin signaling and decrease EMT, thus protecting against loss of transporters in tubular epithelial cells (TECs) and abrogate renal interstitial fibrosis following UUO. We confirmed that relaxin can downregulate Wnt/β-catenin signaling and decrease EMT in NRK52E, thus abrogating G2 cell cycle arrest in vitro experiments. Therefore, a novel mechanism by which relaxin is antifibrotic is that relaxin regulates the EMT program of TECs via Wnt/β-catenin signaling pathway. The inhibition of EMT contributes to protecting the functional capabilities of TECs and promoting the regeneration of TECs.

Potential therapeutic efficacy of pachymic acid in chronic kidney disease induced in rats: role of Wnt/β-catenin/renin-angiotensin axis

OBJECTIVES

Chronic kidney disease (CKD) is a major public health problem associated with high mortality. The therapeutic effects of pachymic in CKD management and its underlying mechanisms have not been studied. Therefore, we aimed to investigate the possible inhibitory effect of PA on renal Wnt/β-catenin signalling in CKD.

METHODS

CKD was induced in rats by doxorubicin (DOX; 3.5 mg/kg i.p., twice weekly for 3 weeks). Rats were treated orally with PA (10 mg/kg/day), LOS (10 mg/kg/day) or their combination (PA + LOS) for 4 weeks starting after the last dose of DOX.

KEY FINDINGS

DOX-induced renal injury was characterized by high serum cystatin-C, and urine albumin/creatinine ratio, renal content of podocin and klotho were decreased. Tumour necrosis factor-α, interleukin-6, interleukin-1β, Wnt1, active β-catenin/total β-catenin ratio and fibronectin along with mRNA expression of RENIN, ACE and AT1 were increased in renal tissues. Treatment with either PA or LOS ameliorated all DOX-induced changes. The combined treatment was more effective in improving all changes than monotherapy.

CONCLUSIONS

These results suggest a new therapeutic benefit of PA in ameliorating CKD in rats through its up-regulatory effect on renal klotho thereby preventing Wnt/β-catenin reactivation and RAS gene expression. PA/LOS combination provided an additional inhibition of Wnt/β-catenin signalling and its downstream targets.

Urinary Dickkopf-3 and Contrast-Associated Kidney Damage

BACKGROUND

Administration of iodinated contrast medium (CM) during invasive cardiovascular procedures may be associated with impairment of kidney function.

OBJECTIVES

Urinary dickkopf-3 (DKK3), a stress-induced renal tubular epithelium-derived glycoprotein, has been identified as a biomarker predicting both acute kidney injury (AKI) and persistent kidney dysfunction.

METHODS

Urinary DKK3/creatinine ratio (uDKK3/uCr), urine and serum neutrophil gelatinase-associated lipocalin (uNGAL, sNGAL) and serum cystatin C (sCyC) were assessed in 458 patients with chronic kidney disease scheduled for invasive cardiovascular procedures requiring CM administration with universal adoption of nephroprotective interventions. Contrast-associated AKI (CA-AKI) was defined as serum creatinine increase ≥0.3 mg/dl at 48 h after CM administration. Persistent kidney dysfunction was defined as persistent estimated glomerular filtration rate reduction ≥25% at 1 month compared with baseline.

RESULTS

CA-AKI occurred in 64 or the 458 patients (14%), and baseline uDKK3/uCr ≥491 pg/mg was the best threshold for its prediction. Net reclassification improvement (NRI) was significantly increased by adding baseline uDKK3/uCr to the Mehran, Gurm, and National Cardiovascular Data Registry (NCDR) scores (all p < 0.05), and the same applied to integrated discrimination improvement (IDI) when adding uDKK3/uCr to the Gurm and NCDR scores (p < 0.001). Persistent kidney dysfunction occurred in 57 of the 458 patients (12%) and baseline uDKK3/uCr ≥322 pg/mg appeared as the best threshold for its prediction. Adding baseline uDKK3/uCr to the Mehran, Gurm, and NCDR scores significantly increased IDI and NRI (all p < 0.001).

CONCLUSIONS

Baseline uDKK3/uCr seems to be a reliable marker for improving the identification of patients with chronic kidney disease undergoing invasive coronary and peripheral procedures at risk for AKI and persistent kidney dysfunction.

Fuzheng Huayu recipe, a traditional Chinese compound herbal medicine, attenuates renal interstitial fibrosis via targeting the miR-21/PTEN/AKT axis

OBJECTIVE

MicroRNAs (miRNAs) may be viable targets for treating renal interstitial fibrosis (RIF). Fuzheng Huayu recipe (FZHY), a traditional Chinese compound herbal medicine, is often used in China to treat fibrosis. This study sought to assess the mechanisms through which FZHY influences miRNAs to treat RIF.

METHODS

RIF was induced in rats by mercury chloride and treated with FZHY. Hydroxyproline content, Masson's staining and type I collagen expression were used to evaluate renal collagen deposition. Renal miRNA profiles were evaluated using a miRNA microarray. Those miRNAs that were differentially expressed following FZHY treatment were identified and subjected to bioinformatic analyses. The miR-21 target gene phosphatase and tensin homolog (PTEN) expression and AKT phosphorylation in kidney tissues were assessed via Western blotting. In addition, HK-2 human proximal tubule epithelial cells were treated using angiotensin II (Ang-II) to induce epithelial-to-mesenchymal transition (EMT), followed by FZHY exposure. miR-21 and PTEN expressions were evaluated via quantitative reverse transcription-polymerase chain reaction (qRT-PCR), while E-cadherin and α-smooth muscle actin (α-SMA) expressions were assessed by immunofluorescent staining and qRT-PCR. Western blotting was used to assess PTEN and AKT phosphorylation.

RESULTS

FZHY significantly decreased kidney collagen deposition, hydroxyproline content and type I collagen level. The miRNA microarray identified 20 miRNAs that were differentially expressed in response to FZHY treatment. Subsequent bioinformatic analyses found that miR-21 was the key fibrosis-related miRNA regulated by FZHY. FZHY also decreased PTEN expression and AKT phosphorylation in fibrotic kidneys. Results from in vitro tests also suggested that FZHY promoted E-cadherin upregulation and inhibited α-SMA expression in Ang-II-treated HK-2 cells, effectively reversing Ang-II-mediated EMT. We also determined that FZHY reduced miR-21 expression, increased PTEN expression and decreased AKT phosphorylation in these cells.

CONCLUSION

miR-21 is the key fibrosis-related miRNA regulated by FZHY. The ability of FZHY to modulate miR-21/PTEN/AKT signaling may be a viable approach for treating RIF.

The Many Faces of Matrix Metalloproteinase-7 in Kidney Diseases

Matrix metalloproteinase-7 (MMP-7) is a secreted zinc-dependent endopeptidase that is implicated in regulating kidney homeostasis and diseases. MMP-7 is produced as an inactive zymogen, and proteolytic cleavage is required for its activation. MMP-7 is barely expressed in normal adult kidney but upregulated in acute kidney injury (AKI) and chronic kidney disease (CKD). The expression of MMP-7 is transcriptionally regulated by Wnt/β-catenin and other cues. As a secreted protein, MMP-7 is present and increased in the urine of patients, and its levels serve as a noninvasive biomarker for predicting AKI prognosis and monitoring CKD progression. Apart from degrading components of the extracellular matrix, MMP-7 also cleaves a wide range of substrates, such as E-cadherin, Fas ligand, and nephrin. As such, it plays an essential role in regulating many cellular processes, such as cell proliferation, apoptosis, epithelial-mesenchymal transition, and podocyte injury. The function of MMP-7 in kidney diseases is complex and context-dependent. It protects against AKI by priming tubular cells for survival and regeneration but promotes kidney fibrosis and CKD progression. MMP-7 also impairs podocyte integrity and induces proteinuria. In this review, we summarized recent advances in our understanding of the regulation, role, and mechanisms of MMP-7 in the pathogenesis of kidney diseases. We also discussed the potential of MMP-7 as a biomarker and therapeutic target in a clinical setting.

lncRNA MALAT1 mediated high glucose-induced HK-2 cell epithelial-to-mesenchymal transition and injury

Epithelial-to-mesenchymal transition (EMT) and injury of tubular cells play critical roles in the pathogenesis of diabetic nephropathy (DN). lncRNA metastasis-associated lung adenocarcinoma transcript 1 (MALAT1) has been shown to be involved in DN progression. However, whether MALAT1 induces EMT and injury in tubular cells is unclear. Here, we investigated the effects of MALAT1 on human proximal tubular cells (HK-2 cells) and the underlying mechanism. We performed qPCR to detect MALAT1, E-cadherin, α-smooth muscle actin (α-SMA), kidney injury molecule 1 (KIM-1), and neutrophil gelatinase-associated lipocalin (NGAL). Additionally, we conducted Western blot analyses to measure E-cadherin, α-SMA, cyclin D1, c-Myc, and β-catenin in HK-2 cells cultured with normal glucose and high glucose (HG) and in transfected cells or cells treated with LiCl and DKK-1. The β-catenin localization was observed using immunofluorescence, and the protein levels of NGAL and KIM-1 were evaluated by ELISA. We found that HG-upregulated MALAT1 decreased E-cadherin and increased α-SMA, KIM-1, NGAL, cyclin D1, c-Myc, and β-catenin in HK-2 cells. LiCl exposure increased the expression of α-SMA but decreased that of E-cadherin on the base of knocking down MALAT1, and decreased NGAL and KIM-1 expression. DKK-1 showed the opposite effects. Our results suggested that upregulated MALAT1 induced EMT in HG-treated HK-2 cells through activating the Wnt/β-catenin pathway. However, MALAT1-mediated injury in HK-2 cells was not mediated by activation of the Wnt/β-catenin pathway. Our results indicate that MALAT1 might serve as a novel therapeutic target for suppressing the progression of DN.

Qingshen Buyang Formula Attenuates Renal Fibrosis in 5/6 Nephrectomized Rats via Inhibiting EMT and Wnt/β-Catenin Pathway

As renal fibrosis significantly contributes to various kinds of chronic kidney diseases, this study aimed to investigate the renal protective effects of Qingshen Buyang Formula against renal fibrosis on 5/6 nephrectomized rats, and its underlying mechanisms were explored. A total of 24 male Sprague-Dawley rats were randomly divided into sham operation group (Sham group), 5/6 nephrectomy group (5/6Nx group), and Qingshen Buyang Formula treatment group (QBF group). The intervention was intragastric administration for 12 weeks. In the end, the blood samples were collected to test renal functional parameters, urine proteins were measured, and the left kidneys were removed for histological studies, as well as mRNA and protein expression analysis. The results showed that Qingshen Buyang Formula significantly decreased BUN, Scr, and proteinuria in 5/6Nx rats. Meanwhile, it ameliorated the kidney injury and fibrosis, exemplified by the depressed expression of collagen I and fibronectin (FN), which are the main components of ECM. Furthermore, the process of EMT inhibited the Wnt/β-catenin signaling pathway related genes, such as Wnt4, TCF4, β-catenin, and p-GSK3β. Collectively, the Qingshen Buyang Formula can improve renal function and attenuate renal fibrosis, and its underlying mechanisms may be related with inhibiting EMT and Wnt/β-catenin signaling pathway.

DNA hypermethylation of sFRP5 contributes to indoxyl sulfate-induced renal fibrosis

Renal fibrosis is the most common outcome of chronic kidney disease (CKD), while the pathogenesis of renal fibrosis is not fully understood. In this study, we first showed that the progress of renal fibrosis was positively related to serum levels of indoxyl sulfate, a typical protein-bound toxin, and that there was a close correlation between serum indoxyl sulfate levels and β-catenin expression in the kidneys (r = 0.908, p < 0.001) of CKD patients. We then demonstrated that intraperitoneal injections of indoxyl sulfate (100 mg/kg/day) for 4 weeks in uninephrectomized mice explicitly induced renal fibrosis, which was accompanied by a significant activation of Wnt/β-catenin signaling. In vitro investigations in human renal tubular HK-2 cells revealed that indoxyl sulfate exhibited a potent ability to induce Wnt/β-catenin activation through the downregulation of sFRP5, a gene that codes for an extracellular antagonist of Wnt signaling, by increasing the DNA methylation level of its promoter CpG islands. The increased expression of DNA methyltransferases following the activation of ROS/ERK1/2 signaling was responsible for the DNA hypermethylation of sFRP5 induced by indoxyl sulfate. Conversely, treatment with 5-aza-2'-deoxycytidine, an inhibitor of DNA methyltransferases, significantly reduced indoxyl sulfate-induced sFRP5 downregulation and Wnt/β-catenin activation. In vivo, intraperitoneal injections of recombinant sFRP5 protein or 5-aza-2'-deoxycytidine substantially alleviated renal fibrosis in indoxyl sulfate-treated uninephrectomized mice. Our results suggest that indoxyl sulfate promotes renal fibrosis through the induction of DNA hypermethylation of sFRP5, and thereafter the activation of Wnt/β-catenin signaling. These findings provide new insights into the pathogenesis of renal fibrosis in CKD patients.

KEY MESSAGES

IS induces renal fibrosis by increasing ß-catenin expression in CKD mice. IS-induced Wnt signaling activation is due to sFRP5 hypermethylation in HK-2 cells. ROS/ERK1/2 signaling activation is involved in IS-induced sFRP5 hypermethylation. sFRP5 upregulation attenuates IS-induced renal fibrosis by inhibiting Wnt signaling.

Matrix Metalloproteinases-7 and Kidney Fibrosis

Matrix metalloproteinase-7 (MMP-7) is a secreted zinc- and calcium-dependent endopeptidase that degrades a broad range of extracellular matrix substrates and additional substrates. MMP-7 playsa crucial role in a diverse array of cellular processes and appears to be a key regulator of fibrosis in several diseases, including pulmonary fibrosis, liver fibrosis, and cystic fibrosis. In particular, the relationship between MMP-7 and kidney fibrosis has attracted significant attention in recent years. Growing evidence indicates that MMP-7 plays an important role in the pathogenesis of kidney fibrosis. Here, we summarize the recent progress in the understanding of the role of MMP-7 in kidney fibrosis. In particular, we discuss how MMP-7 contributes to kidney fibrotic lesions via the following three pathways: epithelial-mesenchymal transition (EMT), transforming growth factor-beta (TGF-β) signaling, and extracellular matrix (ECM) deposition. Further dissection of the crosstalk among and regulation of these pathways will help clinicians and researchers develop effective therapeutic approaches for treating chronic kidney disease.

Downregulation of renal tubular Wnt/β-catenin signaling by Dickkopf-3 induces tubular cell death in proteinuric nephropathy

Studies on the role of Wnt/β-catenin signaling in different forms of kidney disease have yielded discrepant results. Here, we report the biphasic change of renal β-catenin expression in mice with overload proteinuria in which β-catenin was upregulated at the early stage (4 weeks after disease induction) but abrogated at the late phase (8 weeks). Acute albuminuria was observed at 1 week after bovine serum albumin injection, followed by partial remission at 4 weeks that coincided with overexpression of renal tubular β-catenin. Interestingly, a rebound in albuminuria at 8 weeks was accompanied by downregulated tubular β-catenin expression and heightened tubular apoptosis. In addition, there was an inverse relationship between Dickkopf-3 (Dkk-3) and renal tubular β-catenin expression at these time points. In vitro, a similar trend in β-catenin expression was observed in human kidney-2 (HK-2) cells with acute (upregulation) and prolonged (downregulation) exposure to albumin. Induction of a proapoptotic phenotype by albumin was significantly enhanced by silencing β-catenin in HK-2 cells. Finally, Dkk-3 expression and secretion was increased after prolonged exposure to albumin, leading to the suppression of intracellular β-catenin signaling pathway. The effect of Dkk-3 on β-catenin signaling was confirmed by incubation with exogenous Dkk-3 in HK-2 cells. Taken together, these data suggest that downregulation of tubular β-catenin signaling induced by Dkk-3 has a detrimental role in chronic proteinuria, partially through the increase in apoptosis.

Tubular Dickkopf-3 promotes the development of renal atrophy and fibrosis

Renal tubular atrophy and interstitial fibrosis are common hallmarks of etiologically different progressive chronic kidney diseases (CKD) that eventually result in organ failure. Even though these pathological manifestations constitute a major public health problem, diagnostic tests, as well as therapeutic options, are currently limited. Members of the dickkopf (DKK) family, DKK1 and -2, have been associated with inhibition of Wnt signaling and organ fibrosis. Here, we identify DKK3 as a stress-induced, tubular epithelia-derived, secreted glycoprotein that mediates kidney fibrosis. Genetic as well as antibody-mediated abrogation of DKK3 led to reduced tubular atrophy and decreased interstitial matrix accumulation in two mouse models of renal fibrosis. This was facilitated by an amplified, antifibrogenic, inflammatory T cell response and diminished canonical Wnt/β-catenin signaling in stressed tubular epithelial cells. Moreover, in humans, urinary DKK3 levels specifically correlated with the extent of tubular atrophy and interstitial fibrosis in different glomerular and tubulointerstitial diseases. In summary, our data suggest that DKK3 constitutes an immunosuppressive and a profibrotic epithelial protein that might serve as a potential therapeutic target and diagnostic marker in renal fibrosis.

Prostaglandin E2 promotes human cholangiocarcinoma cell proliferation, migration and invasion through the upregulation of β-catenin expression via EP3-4 receptor

Prostaglandin E2 (PGE2) is involved in cholangiocarcinoma cell proliferation, migration and invasion through E prostanoid receptors, including EP1, EP2 and EP4. However, the functions and the mechanisms of those splice variants of EP3 receptors in promoting liver cancer cell growth and invasion remain to be elucidated. In our previous studies, four isoforms of EP3 receptors, EP3-4, EP3-5, EP3-6 and EP3-7 receptors, were detected in CCLP1 and HuCCT1 cells. However, the functions of these receptors in these cells have yet to be determined. It was reported that β-catenin is closely correlated with malignancy, including cholangiocarcinoma. The present study was designed to examine the effects of 4-7 isoforms of EP3 in promoting cholangiocarcinoma progression and the mechanisms by which PGE2 increases β-catenin protein via EP3 receptors. The results showed that PGE2 promotes cholangiocarcinoma progression via the upregulation of β-catenin protein, and the EP3-4 receptor pathway is mainly responsible for this regulation. These findings reveal that PGE2 upregulated the cholangiocarcinoma cell β-catenin protein through the EP3-4R/Src/EGFR/PI3K/AKT/GSK-3β pathway. The present study identified the functions of EP3 and the mechanisms by which PGE2 regulates β-catenin expression and promoted cholangiocarcinoma cell growth and invasion.

Protective effect of Huang Gan formula in 5/6 nephrectomized rats by depressing the Wnt/β-catenin signaling pathway

Huang Gan formula (HGF) is a new traditional Chinese herbal medicine created according to the basic theory of traditional Chinese medicine. The aim of this study is to evaluate the effects of HGF on chronic kidney disease and determine the mechanisms of action. The extract of HGF was prepared, and qualitative and quantitative determination of phytochemical was performed with quadrupole time-of-flight mass spectrometer and high-performance liquid chromatography. Sprague-Dawley rats (n=72) were submitted to 5/6 nephrectomy (Nx), and then respectively treated with uremic clearance granule, losartan, HGF low dose, HGF middle dose, and HGF high dose once per day for 12 weeks. The sham group of operated rats (n=22) was treated with normal saline or HGF middle dose as a background control group. Blood and urine biochemical parameters, renal tissue morphology, and mRNA and proteins of Wnt/β-catenin signaling pathways were investigated. The results showed that the quality of the extraction process could be controlled, and a total of eight major compounds were identified and quantified. HGF could decrease the level of serum creatinine, blood urea nitrogen, and urine protein and increase the renal index and creatinine clearance rate in a dose-dependent manner. HGF also remarkably reduced the glomerulosclerosis and tubulointerstitial fibrosis by blocking the Wnt/β-catenin signaling pathway through inhibiting the Wnt1, β-catenin, transcription factor 4, and fibronectin 1 expressions, simultaneously measured through mRNA and protein levels in the remnant kidney. These results suggest that extraction of HGF could improve remnant renal function and possibly ameliorate glomerulosclerosis and tubulointerstitial fibrosis by depressing the Wnt/β-catenin signaling pathway.

Inhibition of Wnt/β-catenin signal is alleviated reactive gliosis in rats with hydrocephalus

BACKGROUND

Reactive gliosis has been implicated in the pathogenesis of communicating hydrocephalus. Because the activation of Wnt/β-catenin signaling pathway is considered as a significant factor to contribute to brain development, neurodegenerative process, and reactive gliosis, we target this pathway for intervention by using sFRP-l and investigated the expression of β-catenin, cyclin D-1, and glial fibrillary acidic protein (GFAP) in the brain of experimental hydrocephalic rats in terms of protein and gene expression.

METHODS

Therefore, 30 adult SD rats were randomly divided into the normal group (n = 5), the sham operation group (n = 5), the hydrocephalus group (n = 10), and the sFRP-l group (n = 10). Hydrocephalic rat models were induced by intraventricular injections of 3% kaolin while sFRP-l group was treated by sFRP-l with kaolin injections. The ventricular dilatation was examinated by MRI at 2-week post-operation. After that, β-catenin, cyclin D-1, and GFAP were qualified by Western blot and immunohistochemistry.

RESULTS

According to the result, the expression of β-catenin and cyclin D-1 increased (P < 0. 05) in the brain tissue of the hydrocephalus group compared with that of the sham group, while GFAP expression in the hydrocephalus group is more obvious (P < 0. 05). In the sFRP-l group, the expression of β-catenin and cyclin D-1 and GFAP expression is lower (P < 0. 05) compared with those of the hydrocephalus group. We demonstrated that the Wnt/β-catenin pathway is activated in the experimental hydrocephalic rat brain. sFRP-l inhibited the expression of β-catenin and cyclin D-1 and alleviated reactive gliosis in the hydrocephalic rat brain tissue, while the development of hydrocephalus was delayed.

CONCLUSION

These results suggest that regulating Wnt/β-catenin signaling pathway may provide new therapeutic methods for hydrocephalic patients.

Multiple genes of the renin-angiotensin system are novel targets of Wnt/β-catenin signaling

Activation of the renin-angiotensin system (RAS) plays an essential role in the pathogenesis of CKD and cardiovascular disease. However, current anti-RAS therapy only has limited efficacy, partly because of compensatory upregulation of renin expression. Therefore, a treatment strategy to simultaneously target multiple RAS genes is necessary to achieve greater efficacy. By bioinformatics analyses, we discovered that the promoter regions of all RAS genes contained putative T-cell factor (TCF)/lymphoid enhancer factor (LEF)-binding sites, and β-catenin induced the binding of LEF-1 to these sites in kidney tubular cells. Overexpression of either β-catenin or different Wnt ligands induced the expression of all RAS genes. Conversely, a small-molecule β-catenin inhibitor ICG-001 abolished RAS induction. In a mouse model of nephropathy induced by adriamycin, either transient therapy or late administration of ICG-001 abolished established proteinuria and kidney lesions. ICG-001 inhibited renal expression of multiple RAS genes in vivo and abolished the expression of other Wnt/β-catenin target genes. Moreover, ICG-001 therapy restored expression of nephrin, podocin, and Wilms' tumor 1, attenuated interstitial myofibroblast activation, repressed matrix expression, and inhibited renal inflammation and fibrosis. Collectively, these studies identify all RAS genes as novel downstream targets of Wnt/β-catenin. Our results indicate that blockade of Wnt/β-catenin signaling can simultaneously repress multiple RAS genes, thereby leading to the reversal of established proteinuria and kidney injury.

Kidney tubular β-catenin signaling controls interstitial fibroblast fate via epithelial-mesenchymal communication

Activation of β-catenin, the principal mediator of canonical Wnt signaling, is a common pathologic finding in a wide variety of chronic kidney diseases (CKD). While β-catenin is induced predominantly in renal tubular epithelium in CKD, surprisingly, depletion of tubular β-catenin had little effect on the severity of renal fibrosis. Interestingly, less apoptosis was detected in interstitial fibroblasts in knockout mice, which was accompanied by a decreased expression of Bax and Fas ligand (FasL). Tubule-specific knockout of β-catenin diminished renal induction of matrix metalloproteinase (MMP-7), which induced FasL expression in interstitial fibroblasts and potentiated fibroblast apoptosis in vitro. These results demonstrate that loss of tubular β-catenin resulted in enhanced interstitial fibroblast survival due to decreased MMP-7 expression. Our studies uncover a novel role of the tubular β-catenin/MMP-7 axis in controlling the fate of interstitial fibroblasts via epithelial-mesenchymal communication.

High glucose induces podocyte injury via enhanced (pro)renin receptor-Wnt-β-catenin-snail signaling pathway

(Pro)renin receptor (PRR) expression is upregulated in diabetes. We hypothesized that PRR contributes to podocyte injury via activation of Wnt-β-catenin-snail signaling pathway. Mouse podocytes were cultured in normal (5 mM) or high (25 mM) D-glucose for 3 days. Compared to normal glucose, high glucose significantly decreased mRNA and protein expressions of podocin and nephrin, and increased mRNA and protein expressions of PRR, Wnt3a, β-catenin, and snail, respectively. Confocal microscopy studies showed significant reduction in expression and reorganization of podocyte cytoskeleton protein, F-actin, in response to high glucose. Transwell functional permeability studies demonstrated significant increase in albumin flux through podocytes monolayer with high glucose. Cells treated with high glucose and PRR siRNA demonstrated significantly attenuated mRNA and protein expressions of PRR, Wnt3a, β-catenin, and snail; enhanced expressions of podocin mRNA and protein, improved expression and reorganization of F-actin, and reduced transwell albumin flux. We conclude that high glucose induces podocyte injury via PRR-Wnt-β-catenin-snail signaling pathway.

Disruption of the Dapper3 gene aggravates ureteral obstruction-mediated renal fibrosis by amplifying Wnt/β-catenin signaling

Wnt/β-catenin signaling plays key roles in embryonic development and tissue homeostasis. Dapper3/Dact3, one of the three members of the Dapper gene family, is transcriptionally repressed in colorectal cancer and may function as a negative regulator of Wnt/β-catenin signaling. To investigate its physiological functions, we generated a mouse strain harboring conditional null alleles of Dapper3 (Dapper3(flox/flox)), and homozygous Dapper3-deficient (Dapper3(-/-)) mice were produced after crossing with EIIa-cre transgenic mice. We found that Dapper3 is not essential for mouse embryogenesis, postnatal survival, and reproduction. However, adult Dapper3(-/-) mice exhibited a mild reduction in body weight compared with their wild-type littermates, suggesting a functional role of Dapper3 in postnatal growth. To investigate the role of Dapper3 in renal fibrosis, we employed the unilateral ureteral obstruction model. Dapper3 mRNA expression was up-regulated in kidney after unilateral ureteral obstruction. Loss of the Dapper3 gene enhanced myofibroblast activation and extracellular matrix overproduction in the obstructed kidney. Moreover, this aggravated fibrotic phenotype was accompanied with accumulation of Dishevelled2 and β-catenin proteins and activation of Wnt-targeted fibrotic genes. In primary renal tubular cells, Dapper3 inhibits Wnt-induced epithelial-to-mesenchymal transition. Consistently, Dapper3 interacted with and down-regulated Dishevelled2 protein and attenuated the Wnt-responsive Topflash reporter expression. These findings together suggest that Dapper3 antagonizes the fibrotic actions of Wnt signaling in kidney.

Loss of Klotho contributes to kidney injury by derepression of Wnt/β-catenin signaling

Aging is an independent risk factor for CKD, but the molecular mechanisms that link aging and CKD are not well understood. The antiaging protein Klotho may be an endogenous antagonist of Wnt/β-catenin signaling, which promotes fibrogenesis, suggesting that loss of Klotho may contribute to CKD through increased Wnt/β-catenin activity. Here, normal adult kidneys highly expressed Klotho in the tubular epithelium, but various models of nephropathy exhibited markedly less expression of Klotho. Loss of Klotho was closely associated with increased β-catenin in the diseased kidneys, suggesting an inverse correlation between Klotho and canonical Wnt signaling. In vitro, both full-length and secreted Klotho bound to multiple Wnts, including Wnt1, Wnt4, and Wnt7a. Klotho repressed gene transcription induced by Wnt but not by active β-catenin. Furthermore, Klotho blocked Wnt-triggered activation and nuclear translocation of β-catenin, as well as the expression of its target genes in tubular epithelial cells. Investigating potential mediators of Klotho loss in CKD, we found that TGF-β1 suppressed Klotho expression and concomitantly activated β-catenin; conversely, overexpression of Klotho abolished fibrogenic effects of TGF-β1. In two mouse models of CKD induced by unilateral ureteral obstruction or adriamycin, in vivo expression of secreted Klotho inhibited the activation of renal β-catenin and expression of its target genes. Secreted Klotho also suppressed myofibroblast activation, reduced matrix expression, and ameliorated renal fibrosis. Taken together, these results suggest that Klotho is an antagonist of endogenous Wnt/β-catenin activity; therefore, loss of Klotho may contribute to kidney injury by releasing the repression of pathogenic Wnt/β-catenin signaling.

Klotho protects against mouse renal fibrosis by inhibiting Wnt signaling

Augmented Wnt signaling has been implicated in many fibrotic diseases including obstructive nephropathy. Soluble form Klotho has been reported to function as a secreted Wnt antagonist. In this study, we tested whether Klotho protein could reduce renal fibrosis by inhibition of Wnt signaling. Transgenic mice that overexpressed Klotho, wild-type mice, and Klotho hetero mutant mice underwent unilateral ureteral obstruction (UUO). In some Klotho hetero mutant mice, Klotho-encoding plasmid was transferred into the skeletal muscle by electroporation. UUO induced activation of Wnt signaling in wild-type but less in Klotho transgenic mice. Enhanced tubulointerstitial fibrosis in wild-type mice was also attenuated in Klotho transgenic mice. In contrast, Wnt signaling and concomitant tubulointerstitial fibrosis were further augmented in Klotho hetero mutant mice after UUO compared with wild-type mice. In Klotho-encoding plasmid-transfected Klotho hetero mutant mice, however, Wnt signaling was markedly reduced accompanied by a decrease in extracellular matrix deposition after UUO. In vitro studies showed that stimulation of Wnt3a induced prolonged cell cycle arrest at G(2)/M phase, with a resultant increase in production of fibrogenic cytokines. Cotreatment with Klotho bypassed the G(2)/M arrest and reduced fibrogenic cytokine production. In conclusion, Klotho is a critical negative regulator of Wnt signaling and a suppressor of renal fibrosis in the obstructed kidney model.

Transcriptome analysis of renal ischemia/reperfusion injury and its modulation by ischemic pre-conditioning or hemin treatment

Ischemia/reperfusion injury (IRI) is a leading cause of acute renal failure. The definition of the molecular mechanisms involved in renal IRI and counter protection promoted by ischemic pre-conditioning (IPC) or Hemin treatment is an important milestone that needs to be accomplished in this research area. We examined, through an oligonucleotide microarray protocol, the renal differential transcriptome profiles of mice submitted to IRI, IPC and Hemin treatment. After identifying the profiles of differentially expressed genes observed for each comparison, we carried out functional enrichment analysis to reveal transcripts putatively involved in potential relevant biological processes and signaling pathways. The most relevant processes found in these comparisons were stress, apoptosis, cell differentiation, angiogenesis, focal adhesion, ECM-receptor interaction, ion transport, angiogenesis, mitosis and cell cycle, inflammatory response, olfactory transduction and regulation of actin cytoskeleton. In addition, the most important overrepresented pathways were MAPK, ErbB, JAK/STAT, Toll and Nod like receptors, Angiotensin II, Arachidonic acid metabolism, Wnt and coagulation cascade. Also, new insights were gained about the underlying protection mechanisms against renal IRI promoted by IPC and Hemin treatment. Venn diagram analysis allowed us to uncover common and exclusively differentially expressed genes between these two protective maneuvers, underscoring potential common and exclusive biological functions regulated in each case. In summary, IPC exclusively regulated the expression of genes belonging to stress, protein modification and apoptosis, highlighting the role of IPC in controlling exacerbated stress response. Treatment with the Hmox1 inducer Hemin, in turn, exclusively regulated the expression of genes associated with cell differentiation, metabolic pathways, cell cycle, mitosis, development, regulation of actin cytoskeleton and arachidonic acid metabolism, suggesting a pleiotropic effect for Hemin. These findings improve the biological understanding of how the kidney behaves after IRI. They also illustrate some possible underlying molecular mechanisms involved in kidney protection observed with IPC or Hemin treatment maneuvers.

Fell-Muir lecture: Connective tissue growth factor (CCN2) -- a pernicious and pleiotropic player in the development of kidney fibrosis

Connective tissue growth factor (CTGF, CCN2) is a member of the CCN family of matricellular proteins. It interacts with many other proteins, including plasma membrane proteins, modulating cell function. It is expressed at low levels in normal adult kidney cells but is increased in kidney diseases, playing important roles in inflammation and in the development of glomerular and interstitial fibrosis in chronic disease. This review reports the evidence for its expression in human and animal models of chronic kidney disease and summarizes data showing that anti-CTGF therapy can successfully attenuate fibrotic changes in several such models, suggesting that therapies targeting CTGF and events downstream of it in renal cells may be useful for the treatment of human kidney fibrosis. Connective tissue growth factor stimulates the development of fibrosis in the kidney in many ways including activating cells to increase extracellular matrix synthesis, inducing cell cycle arrest and hypertrophy, and prolonging survival of activated cells. The relationship between CTGF and the pro-fibrotic factor TGFβ is examined and mechanisms by which CTGF promotes signalling by the latter are discussed. No specific cellular receptors for CTGF have been discovered but it interacts with and activates several plasma membrane proteins including low-density lipoprotein receptor-related protein (LRP)-1, LRP-6, tropomyosin-related kinase A, integrins and heparan sulphate proteoglycans. Intracellular signalling and downstream events triggered by such interactions are reviewed. Finally, the relationships between CTGF and several anti-fibrotic factors, such as bone morphogenetic factor-4 (BMP4), BMP7, hepatocyte growth factor, CCN3 and Oncostatin M, are discussed. These may determine whether injured tissue heals or progresses to fibrosis.

Tubule-specific ablation of endogenous β-catenin aggravates acute kidney injury in mice

β-Catenin is a unique intracellular protein functioning as an integral component of the cell-cell adherens complex and a principal signaling protein mediating canonical Wnt signaling. Little is known about its function in adult kidneys in the normal physiologic state or after acute kidney injury (AKI). To study this, we generated conditional knockout mice in which the β-catenin gene was specifically disrupted in renal tubules (Ksp-β-cat-/-). These mice were phenotypically normal with no appreciable defects in kidney morphology and function. In the absence of β-catenin, γ-catenin functionally substituted for it in E-cadherin binding, thereby sustaining the integrity of epithelial adherens junctions in the kidneys. In AKI induced by ischemia reperfusion or folic acid, the loss of tubular β-catenin substantially aggravated renal lesions. Compared with controls, Ksp-β-cat-/- mice displayed higher mortality, elevated serum creatinine, and more severe morphologic injury. Consistently, apoptosis was more prevalent in kidneys of the knockout mice, which was accompanied by increased expression of p53 and Bax, and decreased phosphorylated Akt and survivin. In vitro activation of β-catenin by Wnt1 or stabilization of β-catenin protected tubular epithelial cells from apoptosis, activated Akt, induced survivin, and repressed p53 and Bax expression. Hence, endogenous β-catenin is pivotal for renal tubular protection after AKI by promoting cell survival through multiple mechanisms.

Wnt signaling and cardiac differentiation

The Wnt family of secreted glycoproteins participates in a wide array of biological processes, including cellular differentiation, proliferation, survival, apoptosis, adhesion, angiogenesis, hypertrophy, and aging. The canonical Wnt signaling primarily utilizes β-catenin-mediated activation of transcription, while the noncanonical mechanisms involve a calcium-dependent protein kinase C-mediated Wnt/Ca(2+) pathway and a dishevelled-dependent c-Jun N-terminal kinase-mediated planar cell polarity pathway. Although both canonical and noncanonical Wnts have been implicated in cardiac specification, morphogenesis, and differentiation; the molecular events remain unclear and often depend on the cell type and biological context. In this regard, growing evidence indicates that Wnt11 is able to induce cardiogenesis not only during embryonic development but also in adult cells. The cardiogenic properties of Wnt11 may prove useful for preprogramming adult stem cells before myocardial transplantation. Further, elucidation of the molecular steps in Wnt11-induced cardiac differentiation will be necessary to enhance the outcomes of cardiac cell therapy.