The cellular and signalling alterations conducted by TGF-β contributing to renal fibrosis

Fibrosis in Chronic Kidney Disease: Pathophysiology and Therapeutic Targets

Chronic kidney disease (CKD) is a slowly progressive condition characterized by decreased kidney function, tubular injury, oxidative stress, and inflammation. CKD is a leading global health burden that is asymptomatic in early stages but can ultimately cause kidney failure. Its etiology is complex and involves dysregulated signaling pathways that lead to fibrosis. Transforming growth factor (TGF)-β is a central mediator in promoting transdifferentiation of polarized renal tubular epithelial cells into mesenchymal cells, resulting in irreversible kidney injury. While current therapies are limited, the search for more effective diagnostic and treatment modalities is intensive. Although biopsy with histology is the most accurate method of diagnosis and staging, imaging techniques such as diffusion-weighted magnetic resonance imaging and shear wave elastography ultrasound are less invasive ways to stage fibrosis. Current therapies such as renin-angiotensin blockers, mineralocorticoid receptor antagonists, and sodium/glucose cotransporter 2 inhibitors aim to delay progression. Newer antifibrotic agents that suppress the downstream inflammatory mediators involved in the fibrotic process are in clinical trials, and potential therapeutic targets that interfere with TGF-β signaling are being explored. Small interfering RNAs and stem cell-based therapeutics are also being evaluated. Further research and clinical studies are necessary in order to avoid dialysis and kidney transplantation.

Altenusin, a fungal metabolite, alleviates TGF-β1-induced EMT in renal proximal tubular cells and renal fibrosis in unilateral ureteral obstruction

Renal fibrosis is a pathological feature of chronic kidney disease (CKD), progressing toward end-stage kidney disease (ESKD). The aim of this study is to investigate the therapeutic potential of altenusin, a farnesoid X receptor (FXR) agonist derived from fungi, on renal fibrosis. The effect of altenusin was determined (i) in vitro using the transforming growth factor β1 (TGF-β1)-induced epithelial to mesenchymal transition (EMT) of human renal proximal tubular cells and (ii) in vivo using mouse unilateral ureteral obstruction (UUO). The findings revealed that incubation of 10 ng/ml TGF-β1 promotes morphological change in RPTEC/TERT1 cells, a human renal proximal tubular cell line, from epithelial to fibroblast-like cells. TGF-β1 markedly increased EMT markers namely α-smooth muscle actin (α-SMA), fibronectin, and matrix metalloproteinase 9 (MMP-9), while decreased the epithelial marker E-cadherin. Co-incubation TGF-β1 with altenusin preserved the epithelial characteristics of the renal epithelial cells by antagonizing TGF-β/Smad signaling pathway, specifically a decreased phosphorylation of Smad2/3 with an increased level of Smad7. Interestingly, the antagonizing effect of altenusin does not require FXR activation. Moreover, altenusin could reverse TGF-β1-induced fibroblast-like cells to epithelial-like cells. Treatment on UUO mice with 30 mg/kg altenusin significantly reduced the expression of α-SMA, fibronectin, and collagen type 1A1 (COL1A1). The reduction in the renal fibrosis markers is correlated with the decreased phosphorylation of Smad2/3 levels but does not improve E-cadherin protein expression. Collectively, altenusin reduces EMT in human renal proximal tubular cells and renal fibrosis by antagonizing the TGF-β/Smad signaling pathway.

Noscapine alleviates unilateral ureteral obstruction-induced inflammation and fibrosis by regulating the TGFβ1/Smads signaling pathways

Renal fibrosis is a common pathway leading to progressive renal function loss in various forms of chronic kidney disease. Many fibrogenic factors regulate renal fibrosis; two key players are post-injury inflammation and transforming growth factor-β1 (TGF-β1)-induced myofibroblast differentiation. Myofibroblast differentiation is tightly regulated by the microtubule polymerization. Noscapine, an antitussive plant alkaloid, is a potent microtubule-interfering agent previously identified as a potential anticancer compound. Here, we examined how noscapine affects renal fibrogenesis in an in vitro renal fibroblast model and an in vivo unilateral ureteral obstruction (UUO) model. UUO mice were intraperitoneally treated with noscapine at 1 day before UUO surgery and daily thereafter. At 7 days post-surgery, kidneys were collected for further analysis. To analyze whether noscapine inhibits downstream TGF-β1-related signaling, we pre-incubated NRK-49F fibroblasts with noscapine and then performed TGF-β1 stimulation. In UUO mice, noscapine attenuated extracellular matrix protein deposition and the expression levels of type I collagen, type IV collagen, α-smooth muscle actin, and fibronectin. In addition, noscapine decreased tubulointerstitial inflammation in UUO kidneys by reducing TLR2 expression, modulating NLRP3 inflammasome activation, reducing macrophage infiltration, and antagonizing the M2 macrophage phenotype. Furthermore, noscapine pre-incubation suppressed the TGF-β1-induced fibroblast-myofibroblast transformation by downregulating the TGF-β/Smads signaling pathways in NRK-49F cells. These results suggest that noscapine reduces tubulointerstitial inflammation and fibrosis in the kidneys of UUO mice and inhibits the fibroblast-myofibroblast transformation induced by TGF-β1. Noscapine is an over-the-counter antitussive that has been used safely for several decades. Therefore, noscapine is an attractive therapeutic agent for inhibiting renal tubulointerstitial fibrosis.

LIM and Cysteine-Rich Domains 1 Promotes Transforming Growth Factor β1–Induced Epithelial–Mesenchymal Transition in Human Kidney 2 Cells

Renal fibrosis is the major pathologic manifestation of chronic kidney disease (CKD). LIM and cysteine-rich domains 1 (LMCD1) is upregulated in the kidney tissue from patients with CKD and the transforming growth factor β1 (TGF-β1)-treated human renal tubular epithelial cell line human kidney 2 (HK-2) (Gene Expression Omnibus: GSE66494 and GSE23338). Previously, we have demonstrated that the knockdown of LMCD1 ameliorated renal fibrosis in mice by blocking the activation of the extracellular signal-regulated kinase pathway. In this study, we sought to further investigate whether LMCD1 affects TGF-β1-induced epithelial-mesenchymal transition (EMT) of kidney tubular epithelial cells and its potential role in the TGF-β1/Smad signaling pathway. First, we confirmed that LMCD1 expression was increased in the fibrotic kidneys of patients with CKD compared with that in normal kidneys and that LMCD1 was predominantly localized in the renal tubules. LMCD1 and mesenchymal markers were upregulated in obstructed kidney tissues of mice at 21 days after unilateral ureteral obstruction surgery compared with the tissues in sham mice. Next, we demonstrated that TGF-β1 significantly increased LMCD1 expression through Smad-mediated transcription in HK-2 cells in vitro. In turn, LMCD1 acted as a transcriptional coactivator of E2F transcription factor 1 to promote the transcription of TGF-β1. Moreover, TGF-β1 increased the interaction between LMCD1 and Smad ubiquitination regulatory factor 2 (Smurf2) and accelerated Smurf2-mediated LMCD1 degradation via the ubiquitination system. The knockdown of LMCD1 inhibited TGF-β1-induced EMT in both HK-2 cells and unilateral ureteral obstruction mice. Our results indicate a positive feedback loop between TGF-β1 and LMCD1 for EMT induction in HK-2 cells and that Smurf2 acts as a negative regulator in this process by accelerating LMCD1 degradation.

Oncoprotein DJ-1 interacts with mTOR complexes to effect transcription factor Hif1α-dependent expression of collagen I (α2) during renal fibrosis

Proximal tubular epithelial cells respond to transforming growth factor β (TGFβ) to synthesize collagen I (α2) during renal fibrosis. The oncoprotein DJ-1 has previously been shown to promote tumorigenesis and prevent apoptosis of dopaminergic neurons; however, its role in fibrosis signaling is unclear. Here, we show TGFβ-stimulation increased expression of DJ-1, which promoted noncanonical mTORC1 and mTORC2 activities. We show DJ-1 augmented the phosphorylation/activation of PKCβII, a direct substrate of mTORC2. In addition, coimmunoprecipitation experiments revealed association of DJ-1 with Raptor and Rictor, exclusive subunits of mTORC1 and mTORC2, respectively, as well as with mTOR kinase. Interestingly, siRNAs against DJ-1 blocked TGFβ-stimulated expression of collagen I (α2), while expression of DJ-1 increased expression of this protein. In addition, expression of dominant negative PKCβII and siRNAs against PKCβII significantly inhibited TGFβ-induced collagen I (α2) expression. In fact, constitutively active PKCβII abrogated the effect of siRNAs against DJ-1, suggesting a role of PKCβII downstream of this oncoprotein. Moreover, we demonstrate expression of collagen I (α2) stimulated by DJ-1 and its target PKCβII is dependent on the transcription factor hypoxia-inducible factor 1α (Hif1α). Finally, we show in the renal cortex of diabetic rats that increased TGFβ was associated with enhanced expression of DJ-1 and activation of mTOR and PKCβII, concomitant with increased Hif1α and collagen I (α2). Overall, we identified that DJ-1 affects TGFβ-induced expression of collagen I (α2) via an mTOR-, PKCβII-, and Hif1α-dependent mechanism to regulate renal fibrosis.

Exploring the multifaceted role of TGF-β signaling in diabetic complications

Diabetes is one of the most comprehensive metabolic disorders and is spread across the globe. The data from IDF Diabetes Atlas and National Diabetes Statistics mentions that the number of patients with diabetes is increasing at an exponential rate which is challenging the current therapeutics used for the management of diabetes. However, current therapies used for the treatment may provide symptomatic relief but lack in preventing the progression of the disease and thereby limiting the treatment of diabetes-associated complications. A thorough review and analysis were conducted using various databases including EMBASE, MEDLINE, and Google Scholar to extract the available information on challenges faced by current therapies which have triggered the development of novel molecules or drugs. From the analysis, it was analyzed that transforming growth factor βs (TGF-βs) have been shown to exhibit pleiotropic activity and are responsible for maintaining homeostasis and its overexpression is convoluted in the pathogenesis of various disorders. Therefore, developing drugs that block TGF-β signaling may provide therapeutic benefits. This extensive review concluded that drugs targeting TGF-β signaling pathway and its subsequent blockade have shown promising results and hold the potential to become drugs of choice in the management of diabetes and associated complications.

Losartan ameliorates renal interstitial fibrosis through metabolic pathway and Smurfs-TGF-β/Smad

The genesis and development of renal fibrosis involve a variety of pathways closely related to inflammation, cytokines, oxidative stress and metabolic abnormalities. Renal fibrosis is the result of a complex combination of a variety of lesions. Epithelial-mesenchymal transdifferentiation (EMT) of renal tubular epithelial cells is considered the key to renal fibrosis. Losartan is a typical Angiotensin II (ANG II) receptor antagonist and relaxes blood vessels. In this study, we investigated the effects of losartan on Unilateral Ureteral Obstruction (UUO) model mice by studying the changes in the TGF-β/Smad and metabolomics. Male C57BL/6 J mice were intervened with the UUO model and given losartan (10, 20, 30 mg/kg/d) for 28 consecutive days. The results showed that losartan could reduce UUO-induced abnormal serum metabolic spectrum and renal function. It could also improve renal tubular-interstitial injury and fibrosis by reducing tubulointerstitial dilation and collagen deposition. In addition, losartan promoted the expression of Smurf2 and Smurf1, i.e., Smad7 and E3 ubiquitin-linked enzymes, in the nucleus to degrade the type I receptor of TGF-β1 (TβR-I) and P-Smad2/3 to inhibit renal tubular epithelial cells EMT. In summary, these findings indicated that losartan could regulate the TGF-β/Smad and metabolic pathway in UUO model mice through ubiquitination to reduce renal fibrosis.

Rosmarinic acid ameliorates renal interstitial fibrosis by inhibiting the phosphorylated-AKT mediated epithelial-mesenchymal transition in vitro and in vivo

Indoxyl sulfate (IS), a uremic toxin, causes chronic kidney disease (CKD) progression via renal fibrosis. Epithelial-mesenchymal transition (EMT) is a crucial feature of renal fibrosis. Rosmarinic acid (RA) is an ester of caffeic acid and 3,4-dihydroxyphenylacetic acid with a wide range of desirable biological activities. In this study, we investigated whether RA exerted anti-renal fibrosis effects and its related mechanisms in a unilateral ureteral obstruction (UUO) mouse model. C57BL/6 mice were orally administered RA (10 and 20 mg kg-1 d-1) for 7 consecutive days before and after UUO surgery. The mice were then sacrificed to collect the blood and kidneys. Hematoxylin and eosin (H&E) and Masson's trichrome staining were used to evaluate the renal injury and function. Immunohistochemical analysis, reverse transcription-polymerase chain reaction (RT-PCR), and western blotting were used to detect the expression levels of EMT markers. In vitro studies were performed using the IS-stimulated NRK-52E cell line. Here, the pathological changes, collagen deposition, and mRNA and protein expression levels of profibrotic factors and fibrotic markers were found to be significantly elevated in the kidneys of UUO mice. We found that RA administration significantly ameliorated UUO-induced kidney damage by reversing abnormal serum creatinine and blood urea nitrogen levels. It was found that RA treatment decreased the expression levels of alpha-smooth muscle actin (α-SMA), collagen I, fibronectin, transforming growth factor (TGF)-β1, vimentin and phosphorylated AKT (p-AKT) while increasing the E-cadherin expression in both UUO kidneys and IS-treated NRK-52E cells. Our results demonstrate that RA may be a promising therapeutic agent for renal interstitial fibrosis.

Inhibitory Potential of Shen-Shuai-Ling Formulation on Renal Interstitial Fibrosis via Upregulation of PLZF

Background

Renal interstitial fibrosis (RIF) is an important cause of kidney disease, which seriously affects people's health. As a traditional Chinese medicine, Shen-Shuai-Ling Formulation (SSLF) has obvious kidney function. However, the therapeutic effect of SSLF on RIF and its molecular mechanism are still unclear.

Methods

First, the potential targets and pathways of SSLF for RIF were predicted by network pharmacology, and then, the binding of luteolin and target protein to SSLF was verified by molecular docking and Co-IP experiments. Finally, the effects of SSLF and luteolin on PLZF and (Pro) renin receptor (PRR) were verified by western blot and qPCR experiments. Angiotensin (Ang)-1, Ang-2, and transforming growth factor-β (TGF-β) were the indexes of renal interstitial fibrosis.

Results

Through the drug-active component-target network diagram, we found that luteolin has the most connections, and promyelocytic leukemia zinc finger (PLZF) is the target protein. GO analysis and KEGG pathway analysis of targets were performed using Cytoscape ClueGO. Molecular docking experiments and Co-IP are used to prove that luteolin and PLZF can be combined. Western blot and qPCR results showed that both SSLF and luteolin significantly upregulated the expression of PLZF and decreased the levels of PRR, Ang-1, Ang-2, and TGF-β. The overexpression of PLZF decreased the expression of PRR, the knockdown of PLZF increased the expression of PRR, and the overexpression of PRR decreased the expression of Ang-1, Ang-2, and TGF-β.

Conclusions

SSLF inhibits PRR and renal interstitial fibers by the upregulation of PLZF levels.

Renoprotective effects of tropisetron through regulation of the TGF-β1, p53 and matrix metalloproteinases in streptozotocin-induced diabetic rats

Renal fibrosis is a major cause of renal failure in diabetic nephropathy. Tropisetron is an antagonist of the 5HT3 receptor that exhibits anti-fibrosis effects. The present research aimed to investigate the protected role of tropisetron against renal fibrosis of diabetic nephropathy and its molecular mechanisms. For this purpose, male Wistar rats were allocated into 5 groups of control, tropisetron, diabetes, tropisetron + diabetes, and glibenclamide + diabetes (n = 7). After induction of type 1 diabetes with a single injection of STZ, tropisetron (3 mg/kg) and glibenclamide (1 mg/kg) were given to the rats daily by intraperitoneal injection for 2 weeks. The obtained data revealed that the treatment of diabetic rats with tropisetron led to a significant decrease in the elevated blood glucose, serum cystatin c, and urinary total protein (UTP) level, indicating the improvement of the impaired kidney function. Moreover, the results of Masson's trichrome staining showed that fibrosis attenuated in the kidney of diabetic rats after tropisetron treatment. RT-PCR and Western blotting revealed that TGF-β1, the apoptotic mediator, and p53 were considerably declined in the kidney of diabetic rats in response to tropisetron treatment. Meanwhile, the expressions of matrix metalloproteinase-9 (MMP-9) and matrix metalloproteinase-2 (MMP-2) were increased. These notable effects were equipotent with glibenclamide, as a standard drug, suggesting that tropisetron can alleviate renal fibrosis in diabetic nephropathy. Our data indicate that tropisetron could improve kidney function and attenuate renal fibrosis through regulation of TGF-β1, p53, and expression of extracellular matrix metalloproteinases.

L-carnitine suppresses cisplatin-induced renal injury in rats: impact on cytoskeleton proteins expression

We designed this work to examine the curative role of L-carnitine (LCAR) in a rat model of cisplatin (CDDP)-induced kidney injury. We induced kidney injury in rats by a single intraperitoneal injection of 5 mg/kg of CDDP. Fifteen days post injection, rats were orally supplemented with 354 mg/kg of LCAR for another 15 days. Kidney tissues were subjected to histo-biochemical analysis along with mRNA gene expression quantification for cytoskeleton proteins encoding genes (vimentin, nestin, and connexin 43) by real-time reverse transcription polymerase chain reaction. LCAR reversed CDDP-induced renal structural and functional impairments. LCAR significantly declined serum urea and creatinine concentrations, restored oxidant/antioxidant balance, reversed inflammation, and antagonized caspase 3-mediated apoptotic cell death in renal tissues. Moreover, LCAR effectively down-regulated cytoskeleton proteins mRNA levels, reflecting amelioration of CDDP-provoked podocyte injury. We concluded that LCAR has a favorable therapeutic utility against CDDP-induced kidney injury.

Quantitative and network pharmacology: A case study of rhein alleviating pathological progress of renal interstitial fibrosis

ETHNOPHARMACOLOGICAL RELEVANCE

The current network pharmacology model focuses mainly on static and qualitative characterisation between drugs and targets or molecular pathway networks, but it does not reflect the multi-scale, dynamic and quantitative process of drug action.

AIM OF THE STUDY

In this study, we developed a new model known as quantitative and network pharmacology (QNP) to characterise the dynamic and quantitative interventions of drugs within a multi-scale biological network.

MATERIALS AND METHODS

Firstly, we used a systems biology method to construct a molecule-cell dynamic network model to simulate the pathological processes of diseases. Secondly, according to the principles of enzymatic kinetics, we generated a multi-scale drug intervention model to simulate the intervention of drugs in multi-scale networks at different concentrations and pathological stages. Finally, we took rhein treatment of renal interstitial fibrosis (RIF) as an example to illustrate the QNP model.

RESULTS

We successfully constructed the a QNP model that includes both a multi-scale dynamic network disease model and drug intervention model. The QNP model accurately simulated the pathological process of RIF, and the simulation results were validated by a series of cell and animal experiments. Meanwhile, the QNP model demonstrated that rhein can delay the pathological process at the studied concentrations of 5 nM, 10 nM, and 20 nM, and can also exert a better therapeutic effect on fibrosis before the proliferation stage of RIF. Furthermore, through uncertainty and sensitivity analysis, we identified that FAK and Smad3 may be potential targets for RIF.

CONCLUSION

Our QNP model provides a molecular-cellular understanding of the pathological mechanisms of RIF, serving as a new approach and strategy for the construction of dynamic multi-scale network model of diseases and drug intervention.

STX-0119, a novel STAT3 dimerization inhibitor, prevents fibrotic gene expression in a mouse model of kidney fibrosis by regulating Cxcr4 and Ccr1 expression

Kidney fibrosis is a histological hallmark of chronic kidney disease (CKD) and is believed to be involved in the progression of CKD. Therefore, inhibition of kidney fibrosis is a potential strategy for slowing CKD progression. Signal transducer and activator of transcription 3 (STAT3) is a transcription factor that is activated by interleukin-6 and is reported to be involved in fibrosis. Previously, S3I-201, an inhibitor of STAT3 phosphorylation, was shown to inhibit renal fibrosis in a mouse model, but its mechanism was not clarified completely. In this study, we investigated whether STX-0119, a new inhibitor of STAT3 dimerization, suppressed kidney fibrotic gene expression using a mouse model of kidney fibrosis and examined the underlying mechanisms. Kidney fibrosis was induced by unilateral ureteral obstruction (UUO), which was accompanied by upregulation of STAT3 target genes. STX-0119 administration suppressed the expression of fibrotic genes in UUO kidneys without affecting STAT3 phosphorylation. STX-0119 decreased Cxcr4 mRNA in cultured rat kidney fibroblasts and Ccr1 mRNA in blood cells from UUO mice, both of which are reported to be involved in the progression of kidney fibrosis. These results suggest that STX-0119 inhibits fibrotic gene expression in kidney by suppressing Cxcr4 and Ccr1 expression. This is the first report to indicate a part of the mechanism of the antifibrotic effects of a STAT3 inhibitor and suggests that STX-0119 may be a lead compound for the treatment of kidney fibrosis.

In vitro versus in vivo models of kidney fibrosis: Time-course experimental design is crucial to avoid misinterpretations of gene expression data

Background:

In vitro models are common tools in nephrology research. However, their validity has rarely been scrutinized.

Materials and Methods:

Considering the critical role of transforming growth factor (TGF)-β and hypoxia pathways in kidney fibrosis, kidney-derived cells were exposed to TGF-β and/or hypoxic conditions and the expression levels of some genes related to these two signaling pathways were quantified in a time-course manner. Furthermore, a unilateral ureteral obstruction mouse model was generated, and the expressions of the same genes were assessed.

Results:

In all in vitro experimental groups, the expression of the genes was noisy with no consistent pattern. However, in the animal model, TGF-β pathway-related genes demonstrated considerable overexpression in the ureteral obstruction group compared with the sham controls. Interestingly, hypoxia pathway genes had prominent fluctuations with very similar patterns in both animal groups, suggesting a periodical pattern not affected by the intervention.

Conclusion:

The findings of this study suggest that in vitro findings should be interpreted cautiously and if possible are substituted or supported by animal models that are more consistent and reliable. Furthermore, we underscore the importance of time-course evaluation of both case and control groups in gene expression studies to avoid misconceptions caused by gene expression noise or intrinsic rhythms.

Tripartite motif-containing 35 (TRIM35) is up-regulated in UUO-induced renal fibrosis animal model

Renal fibrosis has been recognized as a serious health threat in the world because of the high cost of treatment and poor prognosis. However, the molecular mechanism of renal fibrosis is still largely unknown. In this study, we aimed at illustrating the role of TRIM35 in the renal fibrosis process. A UUO mouse model and a TGF-β1-induced tubulointerstitial fibrosis model were constructed for the research of renal fibrosis at animal and cell level, respectively. Hematoxylin-eosin and Masson staining were used for visualizing the pathological change. qRT-PCR, Western blot analysis and immunohistochemical staining were used to detect the expression of fibrosis-associated proteins and TRIM35. The results showed that, after the modeling, the expressions of α-SMA, Collagen I, Collagen III, Fibronectin and Snail1 were up-regulated, while the expression of E-cadherin was down-regulated, indicating the successful construction of animal and cell models. More importantly, TRIM35 was proved to be up-regulated in both animal and cell models. Therefore, this study demonstrates the potential promotional effect of TRIM35 in the renal fibrosis process, which may prove to be a new biomarker for the diagnosis and development of new treatments of renal fibrosis.

Soluble (pro)renin receptor promotes the fibrotic response in renal proximal tubule epithelial cells in vitro via the Akt/β-catenin/Snail signaling pathway

Tubulointerstitial fibrosis has been regarded as a critical event in the pathogenesis of chronic kidney disease. The soluble form of (pro)renin receptor (sPRR), generated by site-1 protease (S1P) cleavage of full-length PRR, can be detected in biological fluid and elevated under certain pathological conditions. The present study was designed to evaluate the potential role of sPRR in the regulation of the fibrotic response in a cultured human renal proximal tubular cell line (HK-2 cells) in the setting of transforming growth factor (TGF)-β or sPRR-His treatment. The TGF-β-induced fibrotic response of HK-2 cells was indicated by upregulation of fibronectin (FN) expression; meanwhile, TGF-β could also induce the generation of sPRR, due to enhanced cleavage of full-length PRR. To explore the role of sPRR in the fibrotic response of HK-2 cells, we blocked the production of sPRR with a the S1P inhibitor PF429242 and found that PF429242 remarkably suppressed TGF-β-induced sPRR generation and FN expression in HK-2 cells. Administration of sPRR-His restored the PF429242-attenuated FN expression in HK-2 cells, indicating that sPRR could promote the TGF-β-induced fibrotic response. Furthermore, sPRR-His alone also increased the abundance of FN in HK-2 cells. These data suggested that sPRR was sufficient and necessary for the TGF-β-induced fibrotic response of HK-2 cells. Mechanistically, sPRR activated the AKT and β-catenin pathway in HK-2 cells, and blockade of the AKT or β-catenin pathway significantly abrogated sPRR-induced FN and Snail expression. Taking together, sPRR promoted the fibrotic response of HK-2 cells by activating Akt/β-catenin/Snail signaling, and it may serve as a potential therapeutic target in renal fibrosis.

Formin mDia1 contributes to migration and epithelial-mesenchymal transition of tubular epithelial cells exposed to TGF-β1

Renal tubular epithelial cells may undergo epithelial-mesenchymal transition (EMT) in response to stimuli, such as transforming growth factor (TGF)-β1, leading to myofibroblast activation and renal fibrosis. The formin mDia1 is required for nucleation and polymerization of actin and the microtubule cytoskeleton. The present study sought to explore the role of mDia1 in EMT of tubular epithelial cells. A rat model of unilateral ureteral obstruction (UUO) was established. The expression of TGF-β1, collagen I, collagen III, and mDia1 in the kidneys was examined at day 7 after surgery. The effect of mDia1 on EMT was explored in NRK-52E cells by exposing them to TGF-β1. Increased expression of TGF-β1, collagen I, collagen III, and mDia1 was found in obstructive kidneys of UUO model rats. Exposing rat tubular epithelial cells to TGF-β1 promoted collagen I and collagen III expression but had no effect on mDia1 expression. Silencing mDia1 expression impeded epithelial cell migration as well as reduced TGF-β1, collagen, and Profilin1 expression, whereas mDia1 overexpression exerted an opposite effect. Furthermore, mDia1 regulated the expression of vimentin, α-smooth muscle actin, and E-cadherin and focal adhesion-kinase (FAK)/Src activation through Profilin1. Inhibition of the mDia1 activator RhoA by fasudil reversed EMT, and FAK/Src activation induced by mDia1. In conclusion, mDia1 regulated tubular epithelial cell migration, collagen expression, and EMT in NRK-52E cells exposed to TGF-β1. Thus, suppression of mDia1 activation might be a strategy to counteract renal fibrosis.

TGFβ acts through PDGFRβ to activate mTORC1 via the Akt/PRAS40 axis and causes glomerular mesangial cell hypertrophy and matrix protein expression

Interaction of transforming growth factor-β (TGFβ)-induced canonical signaling with the noncanonical kinase cascades regulates glomerular hypertrophy and matrix protein deposition, which are early features of glomerulosclerosis. However, the specific target downstream of the TGFβ receptor involved in the noncanonical signaling is unknown. Here, we show that TGFβ increased the catalytic loop phosphorylation of platelet-derived growth factor receptor β (PDGFRβ), a receptor tyrosine kinase expressed abundantly in glomerular mesangial cells. TGFβ increased phosphorylation of the PI 3-kinase-interacting Tyr-751 residue of PDGFRβ, thus activating Akt. Inhibition of PDGFRβ using a pharmacological inhibitor and siRNAs blocked TGFβ-stimulated phosphorylation of proline-rich Akt substrate of 40 kDa (PRAS40), an intrinsic inhibitory component of mTORC1, and prevented activation of mTORC1 in the absence of any effect on Smad 2/3 phosphorylation. Expression of constitutively active myristoylated Akt reversed the siPDGFRβ-mediated inhibition of mTORC1 activity; however, co-expression of the phospho-deficient mutant of PRAS40 inhibited the effect of myristoylated Akt, suggesting a definitive role of PRAS40 phosphorylation in mTORC1 activation downstream of PDGFRβ in mesangial cells. Additionally, we demonstrate that PDGFRβ-initiated phosphorylation of PRAS40 is required for TGFβ-induced mesangial cell hypertrophy and fibronectin and collagen I (α2) production. Increased activating phosphorylation of PDGFRβ is also associated with enhanced TGFβ expression and mTORC1 activation in the kidney cortex and glomeruli of diabetic mice and rats, respectively. Thus, pursuing TGFβ noncanonical signaling, we identified how TGFβ receptor I achieves mTORC1 activation through PDGFRβ-mediated Akt/PRAS40 phosphorylation to spur mesangial cell hypertrophy and matrix protein accumulation. These findings provide support for targeting PDGFRβ in TGFβ-driven renal fibrosis.

FoxM1 inhibition ameliorates renal interstitial fibrosis by decreasing extracellular matrix and epithelial-mesenchymal transition

FoxM1 is a transcriptional regulator involved in tumor development, pulmonary fibrosis, and cardiac fibrosis. However, its role in renal interstitial fibrosis (RIF) has yet to be elucidated. We established a TGF-β1-stimulated human proximal tubular epithelial cell (HK-2) model in vitro and a unilateral ureteral obstruction (UUO)-induced rat RIF model in vivo. FoxM1 inhibition was achieved by siRNA interference in vitro and by injecting thiostrepton into UUO-induced RIF rats in vivo. The degree of renal damage and fibrosis were determined by histological assessment via hematoxylin and eosin (H&E) staining. Immunohistochemistry, western blots, and qPCR were used to determine the expression levels of FoxM1, Collagen I, E-cadherin, α-SMA, and Snail1. Our results showed that FoxM1 inhibition could ameliorate RIF and reduce the deposition of Collagen I. H&E staining revealed that renal structural damage, inflammatory cell infiltration, and ECM deposition were significantly attenuated by thiostrepton treatment in the UUO rats. Furthermore, FoxM1 downregulation significantly suppressed epithelial-to-mesenchymal transition, as evidenced by decreased protein and mRNA expression levels of α-SMA and Snail1 and a significant increase in protein and mRNA expression levels of E-cadherin. Collectively, these results suggested that FoxM1 inhibition could be a novel therapeutic strategy for the treatment of RIF.

Intraglomerular Monocyte/Macrophage Infiltration and Macrophage-Myofibroblast Transition during Diabetic Nephropathy Is Regulated by the A2B Adenosine Receptor

Diabetic nephropathy (DN) is considered the main cause of kidney disease in which myofibroblasts lead to renal fibrosis. Macrophages were recently identified as the major source of myofibroblasts in a process known as macrophage–myofibroblast transition (MMT). Adenosine levels increase during DN and in vivo administration of MRS1754, an antagonist of the A_2B adenosine receptor (A_2BAR), attenuated glomerular fibrosis (glomerulosclerosis). We aimed to investigate the association between A_2BAR and MMT in glomerulosclerosis during DN. Kidneys/glomeruli of non-diabetic, diabetic, and MRS1754-treated diabetic (DM+MRS1754) rats were processed for histopathologic, transcriptomic, flow cytometry, and cellular in vitro analyses. Macrophages were used for in vitro cell migration/transmigration assays and MMT studies. In vivo MRS1754 treatment attenuated the clinical and histopathological signs of glomerulosclerosis in DN rats. Transcriptomic analysis demonstrated a decrease in chemokine-chemoattractants/cell-adhesion genes of monocytes/macrophages in DM+MRS1754 glomeruli. The number of intraglomerular infiltrated macrophages and MMT cells increased in diabetic rats. This was reverted by MRS1754 treatment. In vitro cell migration/transmigration decreased in macrophages treated with MRS1754. Human macrophages cultured with adenosine and/or TGF-β induced MMT, a process which was reduced by MRS1754. We concluded that pharmacologic blockade of A_2BAR attenuated some clinical signs of renal dysfunction and glomerulosclerosis, and decreased intraglomerular macrophage infiltration and MMT in DN rats.

C1q/Tumor Necrosis Factor-Related Protein-9 Attenuates Diabetic Nephropathy and Kidney Fibrosis in db/db Mice

Diabetic nephropathy (DN) is characterized by excessive accumulation of extracellular matrix leading to early thickening of glomerular and tubular basement membrane. C1q/tumor necrosis factor (TNF)-related protein-9 (CTRP9) was recently identified as an adiponectin paralog of superior prominence. CTRP9 is an anti-inflammatory, antioxidant, vasodilation and atheroprotective adipose cytokine that share a similar metabolic regulatory function as adiponectin. Additionally, CTRP9 inhibits apoptosis of endothelial cells, decreases blood glucose level, and increases insulin sensitivity. However, the renoprotective effects of CTRP9 and the underlying molecular mechanisms in DN have not been explored. This study examined the effects of CTRP9 on DN in diabetic db/db mice through adenovirus-mediated overexpression. From the results, CTRP9 ameliorated renal dysfunction and injury at the structural and functional level in diabetic db/db mice. Additionally, CTRP9 inhibited glomerular and tubular glycogen accumulation, fibrosis, relieved hyperglycemia-mediated oxidative stress, and apoptosis. This is the first study to report on therapeutic effects of CTRP9 on DN, presenting a potentially effective clinical treatment method for DN patients.

The TGF-β profibrotic cascade targets ecto-5'-nucleotidase gene in proximal tubule epithelial cells and is a traceable marker of progressive diabetic kidney disease

Progressive diabetic nephropathy (DN) and loss of renal function correlate with kidney fibrosis. Crosstalk between TGF-β and adenosinergic signaling contributes to the phenotypic transition of cells and to renal fibrosis in DN models. We evaluated the role of TGF-β on NT5E gene expression coding for the ecto-5`-nucleotidase CD73, the limiting enzyme in extracellular adenosine production. We showed that high d-glucose may predispose HK-2 cells towards active transcription of the proximal promoter region of the NT5E gene while additional TGF-β results in full activation. The epigenetic landscape of the NT5E gene promoter was modified by concurrent TGF-β with occupancy by the p300 co-activator and the phosphorylated forms of the Smad2/3 complex and RNA Pol II. Transcriptional induction at NT5E in response to TGF-β was earlier compared to the classic responsiveness genes PAI-1 and Fn1. CD73 levels and AMPase activity were concomitantly increased by TGF-β in HK-2 cells. Interestingly, we found increased CD73 content in urinary extracellular vesicles only in diabetic patients with renal repercussions. Further, CD73-mediated AMPase activity was increased in the urinary sediment of DN patients. We conclude that the NT5E gene is a target of the profibrotic TGF-β cascade and is a traceable marker of progressive DN.

Silibinin enhances anti-renal fibrosis effect of MK-521 via downregulation of TGF-β signaling pathway

Renal fibrosis is a common characteristic of chronic kidney disease (CKD), and it can lead to end-stage renal disease. It has been reported that silibinin or lisinopril (MK-521) can inhibit the progression of renal fibrosis. However, the effect of combination of silibinin with MK-521 on renal fibrosis remains unclear. Therefore, this study aimed to explore the combination of silibinin with MK-521 on renal fibrosis in vitro and in vivo. The cell viability of HK-2 was detected by CCK-8. The gene and protein expression in HK-2 cells were detected by qRT-PCR and Western blot, respectively. Moreover, HFD-induced renal fibrosis mouse model was established to investigate the effect of silibinin in combination with MK-521 on renal fibrosis in vivo. The expressions of collagen I, α-SMA, Smad2 and Smad3 in TGF-β-treated HK-2 cells were notably decreased by MK-521, which was further inhibited in the presence of silibinin. In addition, we found that silibinin significantly enhanced anti-fibrotic effect of MK-521 on HFD-induced renal fibrosis mice. These findings demonstrated that silibinin could significantly increase anti-fibrotic effect of MK-521 in vitro and in vivo. Therefore, the combination of silibinin with MK-521 may serve as a potential strategy for the treatment of renal fibrosis.

Mouse Umbilical Cord Mesenchymal Stem Cell Paracrine Alleviates Renal Fibrosis in Diabetic Nephropathy by Reducing Myofibroblast Transdifferentiation and Cell Proliferation and Upregulating MMPs in Mesangial Cells

Transplantation of umbilical cord mesenchymal stem cells (UC-MSCs) is currently considered a novel therapeutic strategy for diabetic nephropathy (DN). However, the mechanisms by which UC-MSCs ameliorate renal fibrosis in DN are not well understood. Herein, we firstly investigated the therapeutic effects of mouse UC-MSC infusion on kidney structural and functional impairment in streptozotocin- (STZ-) induced diabetic mice. We found that the repeated injection with mUC-MSCs alleviates albuminuria, glomerulus injury, and fibrosis in DN mouse models. Next, mesangial cells were exposed to 5.6 mM glucose, 30 mM glucose, or mUC-MSC-conditioned medium, and then we performed western blotting, immunofluorescence, wound healing assay, and cell proliferation assay to measure extracellular matrix (ECM) proteins and matrix metalloproteinases (MMPs), myofibroblast transdifferentiation (MFT), and cell proliferation. We demonstrated that mUC-MSC paracrine decreased the deposition of fibronectin and collagen I by inhibiting TGF-β1-triggered MFT and cell proliferation mediated by PI3K/Akt and MAPK signaling pathways, and elevating the levels of MMP2 and MMP9. Importantly, we provided evidence that the antifibrosis role of mUC-MSC paracrine in DN might be determined by exosomes shed by MSCs. Together, these findings reveal the mechanisms underlying the therapeutic effects of UC-MSCs on renal fibrosis in DN and provide the evidence for DN cell-free therapy based on UC-MSCs in the future.

Protein arginine methyltransferase 1 mediates renal fibroblast activation and fibrogenesis through activation of Smad3 signaling

Protein arginine methyltransferase 1 (PRMT1), which primarily causes asymmetric arginine methylation of histone and nonhistone proteins, has been found to activate gene expression and mediate multiple pathological processes. Its role in renal fibrosis, however, remains unclear. In the present study, we observed that PRMT1 and its specific epigenetic marker, asymmetric di-methylated histone 4 arginine 3 (H4R3Me2a), were highly expressed in cultured renal interstitial fibroblasts. Treatment of PRMT1 with AMI-1, a selective inhibitor of PRMT1, or silencing PRMT1 with siRNA inhibited serum-induced and transforming growth factor (TGF)-β₁-induced expression of α-smooth muscle actin (α-SMA) and collagen type I, two hallmarks of renal fibroblast activation, in a dose-dependent and time-dependent manner. In a murine model of renal fibrosis induced by unilateral ureteral obstruction, PRMT1 expression and H4R3Me2a were also upregulated, which was coincident with increased expression of α-SMA, collagen type I, and fibronectin. Administration of AMI-1 reduced PRMT1 and H4R3Me2a expression, attenuated extracellular matrix protein deposition, and inhibited renal fibroblast activation and proliferation. Moreover, AMI-1 treatment inhibited Smad3 phosphorylation and TGF-β receptor I expression but prevented Smad7 downregulation both in the kidney after unilateral ureteral obstruction injury and in cultured renal interstitial fibroblasts exposed to TGF-β₁. Collectively, these results demonstrate that PRMT1 may mediate renal fibroblast activation and renal fibrosis development through activation of the TGF-β/Smad3 signaling pathway. They also suggest that PRMT1 inhibition may be a potential therapeutic approach for the treatment of fibrotic kidney disease.

Immunohistochemical study of renal fibropoiesis associated with dogs naturally and experimentally infected with two different strains of Leishmania (L.) infantum

The objectives of this work were to study some pathological aspects of kidneys obtained from dogs naturally infected with Leishmania infantum and from dogs experimentally infected with two different strains of L infantum with special emphasis on fibrotic process. Seventy eight specimens of paraffin-embedded kidney fragments were collected as follows: (a) CNI group composed by 62 kidney samples of adult mongrel dogs, naturally infected with L infantum; (b) BH401 group composed by five kidney samples of adult Beagles experimentally infected with L infantum strain MCAN BR/2002/BH401; (c) BH400 group composed by eleven kidney samples of adult Beagles experimentally infected with L infantum strain MCAN/BR/2000/BH400, at the same dose and same route of the previous group, denominated group BH400; Control group (CC) composed by four kidney samples of adult Beagles. All animals revealed glomerular and interstitial fibropoiesis associated with different types of glomerulonephritis and chronic interstitial nephritis. Fibrosis was markedly more intense in the BH401 group, followed by animals in the CNI group. Markers for myofibroblasts (mesenchymal markers) such as alpha-actin (α-SMA), vimentin and the cytokine transforming growth factor beta (TGF-β) were done by immunohistochemistry. BH401 group showed higher expression of all these markers than others. Intracellular amastigotes forms of Leishmania was mainly found in BH401. These results could be indicating that the MCAN/BR/2002/BH401 strain is a good choice for the study of renal LVC experimental model.

Blockade of the Adenosine A3 Receptor Attenuates Caspase 1 Activation in Renal Tubule Epithelial Cells and Decreases Interleukins IL-1β and IL-18 in Diabetic Rats

Diabetic nephropathy (DN) is the main cause of end-stage renal disease, which remains incurable. The progression of DN is associated with progressive and irreversible renal fibrosis and also high levels of adenosine. Our aim was to evaluate the effects of ADORA3 antagonism on renal injury in streptozotocin-induced diabetic rats. An ADORA3 antagonist that was administered in diabetic rats greatly inhibited the levels of inflammatory interleukins IL-1β and IL-18, meanwhile when adenosine deaminase was administered, there was a non-selective attenuation of the inflammatory mediators IL-1β, IL-18, IL-6, and induction of IL-10. The ADORA3 antagonist attenuated the high glucose-induced activation of caspase 1 in HK2 cells in vitro. Additionally, ADORA3 antagonisms blocked the increase in caspase 1 and the nuclear localization of NFκB in the renal tubular epithelium of diabetic rats, both events that are involved in regulating the production and activation of IL-1β and IL-18. The effects of the A3 receptor antagonist resulted in the attenuation of kidney injury, as evidenced by decreased levels of the pro-fibrotic marker α-SMA at histological levels and the restoration of proteinuria in diabetic rats. We conclude that ADORA3 antagonism represents a potential therapeutic target that mechanistically works through the selective blockade of the NLRP3 inflammasome.

The effect of dicarbonyl stress on the development of kidney dysfunction in metabolic syndrome - a transcriptomic and proteomic approach

Background and aims

Dicarbonyl stress plays an important role in the pathogenesis of microvascular complications that precede the formation of advanced glycation end products, and contributes to the development of renal dysfunction. In renal cells, toxic metabolites like methylglyoxal lead to mitochondrial dysfunction and protein structure modifications.

In our study, we investigated the effect of methylglyoxal on metabolic, transcriptomic, metabolomic and proteomic profiles in the context of the development of kidney impairment in the model of metabolic syndrome.

Materials and methods

Dicarbonyl stress was induced by intragastric administration of methylglyoxal (0.5 mg/kg bw for 4 weeks) in a strain of hereditary hypertriglyceridaemic rats with insulin resistance and fatty liver.

Results

Methylglyoxal administration aggravated glucose intolerance (AUC_0–120p < 0.05), and increased plasma glucose (p < 0.01) and insulin (p < 0.05). Compared to controls, methylglyoxal-treated rats exhibited microalbuminuria (p < 0.01). Targeted proteomic analysis revealed increases in urinary secretion of pro-inflammatory parameters (MCP-1, IL-6, IL-8), specific collagen IV fragments and extracellular matrix proteins. Urine metabolomic biomarkers in methylglyoxal-treated rats were mainly associated with impairment of membrane phospholipids (8-isoprostane, 4-hydroxynonenal).

Decreased levels of glutathione (p < 0.01) together with diminished activity of glutathione-dependent antioxidant enzymes contributed to oxidative and dicarbonyl stress. Methylglyoxal administration elevated glyoxalase 1 expression (p < 0.05), involved in methylglyoxal degradation. Based on comparative transcriptomic analysis of the kidney cortex, 96 genes were identified as differentially expressed (FDR < 0.05). Network analysis revealed an over-representation of genes related to oxidative stress and pro-inflammatory signalling pathways as well as an inhibition of angiogenesis suggesting its contribution to renal fibrosis.

Conclusion

Our results support the hypothesis that dicarbonyl stress plays a key role in renal microvascular complications. At the transcriptome level, methylglyoxal activated oxidative and pro-inflammatory pathways and inhibited angiogenesis. These effects were further supported by the results of urinary proteomic and metabolomic analyses.

Proteasome inhibitor MG132 inhibits the process of renal interstitial fibrosis

The proteasome inhibitor pathway serves a crucial role in cell cycle progression and apoptosis, and in the activation of transcription factors and cytokines in tumor cells. The aim of the current study was to investigate the effect of the proteasome inhibitor, MG132, on transforming growth factor (TGF)-β1-induced expression of extracellular matrix proteins in rat renal interstitial fibroblasts (NRK-49F cells) and to better elucidate the mechanism by which MG132 functions. The level of connective tissue growth factor (CTGF), α-smooth muscle actin (SMA), fibronectin (FN) and collagen type III (Col III) in the MG132-pretreated groups was significantly decreased compared with groups treated with TGF-β1 alone. MG132 significantly decreased mRNA and the protein levels of fibrosis-associated factors induced by TGF-β1 treatment. The MG132-pretreated groups exhibited lower phosphorylated-mothers against decapentaplegic homolog (p-Smad)2, p-Smad3 and FN protein expression compared with the groups treated with TGF-β1 alone. In conclusion, MG132 reduced mRNA and protein expression of fibrosis-associated factors. It can successfully inhibit the inflammatory reaction induced by TGF-β via the Smad signaling pathway. These results indicate that MG132 appears to have a potent effect in counteracting renal fibrosis. MG132 may be applied in the treatment of patients with chronic kidney disease.

Calcium-sensing receptor activation attenuates collagen expression in renal proximal tubular epithelial cells

316: F1006-F1015, 2019. First published March 6, 2019; doi: 10.1152/ajprenal.00413.2018 .-Experimental studies have shown that pharmacological activation of calcium-sensing receptor (CaSR) attenuates renal fibrosis in some animal models beyond modification of bone and mineral homeostasis; however, its underlying mechanisms remain largely unknown. Since excessive collagen deposition is the key feature of fibrosis, the present study aimed to examine whether CaSR was involved in the regulation of collagen expression in rats with adenine diet-induced renal fibrosis and in profibrotic transforming growth factor (TGF)-β₁-treated renal proximal tubular epithelial cells (PTECs). The results showed that the CaSR agonist cinacalcet significantly attenuated renal collagen accumulation and tubular injury in adenine diet-fed rats. Additionally, the in vitro experiment showed that profibrotic TGF-β₁ significantly increased the expression of collagen and decreased CaSR expression at the mRNA and protein levels in a concentration- and time-dependent manner. Furthermore, the CaSR CRISPR activation plasmid and cinacalcet partially abrogated the upregulation of collagen induced by TGF-β₁ treatment. Blockade of CaSR by the CRISPR/Cas9 KO plasmid or the pharmacological antagonist Calhex231 further enhanced TGF-β₁-induced collagen expression. Mechanistic experiments found that Smad2 phosphorylation and Snail expression were markedly increased in PTECs treated with TGF-β₁, whereas the CaSR CRISPR activation plasmid and cinacalcet substantially suppressed this induction. In summary, this study provides evidence for a direct renal tubular epithelial protective effect of CaSR activation in renal fibrosis, possibly through suppression of collagen expression in PTECs.

The TGFβ-ERK pathway contributes to Notch3 upregulation in the renal tubular epithelial cells of patients with obstructive nephropathy

Renal interstitial fibrosis is a common renal injury resulted from a variety of chronic kidney conditions and an array of factors. We report here that Notch3 is a potential contributor. In comparison to 6 healthy individuals, a robust elevation of Notch3 expression was observed in the renal tubular epithelial cells of 18 patients with obstructive nephropathy. In a rat unilateral ureteral obstruction (UUO) model which mimics the human disease, Notch3 upregulation closely followed the course of renal injury, renal fibrosis, TGFβ expression, and alpha-smooth muscle actin (α-SMA) expression, suggesting a role of Notch3 in promoting tubulointerstitial fibrosis. This possibility was supported by the observation that TGFβ, the major renal fibrogenic cytokine, stimulated Notch3 expression in human proximal tubule epithelial HK-2 cells. TGFβ enhanced the activation of ERK, p38, but not JNK MAP kinases in HK-2 cells. While inhibition of p38 activation using SB203580 did not affect TGFβ-induced Notch3 expression, inhibition of ERK activation with a MEK1 inhibitor PD98059 dramatically reduced the event. Furthermore, enforced ERK activation through overexpression of the constitutively active MEK1 mutant MEK1Q56P upregulated Notch3 expression in HK-2 cells, and PD98059 reduced ERK activation and Notch3 expression in HK-2 cells expressing MEK1Q56P. Collectively, we provide the first clinical evidence for Notch3 upregulation in patients with obstructive nephropathy; the upregulation is likely mediated through the TGFβ-ERK pathway. This study suggests that Notch3 upregulation contributes to renal injury caused by obstructive nephropathy, which could be prevented or delayed through ERK inhibition.

Receptor-independent modulation of TGF-β-induced pro-fibrotic pathways by relaxin-2 in human primary tubular epithelial cells

Renal tubular epithelial cells actively contribute to the development of renal fibrosis and may be targeted by anti-fibrotic drugs. Relaxin-2 (RLX2) applied as recombinant protein is suggested to be renoprotective. Therefore, we investigated whether human primary tubular epithelial cells (hPTEC) obtained from various donors were target cells for the anti-fibrotic actions of RLX2. Treatment of hPTEC with RLX2 reduced the TGF-β1-induced secretion of the pro-fibrotic factor CTGF (connective tissue growth factor) and inhibited fibronectin synthesis and secretion. Furthermore, metalloproteinase MMP2 secretion was increased, with no effect on MMP9. Considerable differences were observed between hPTEC obtained from different donors. Therefore, expression of the relaxin family peptide receptor RXFP1, the major mediator of renal RLX2 effects, was analyzed. A validated antibody detected a double band of 80-90 kDa in cellular homogenates by Western blotting. Expression of the detected protein was not altered by incubation with TGF-β1 and RLX2-induced modulation of CTGF expression did not correlate with the putative receptor expression. Therefore, relaxin family receptors RXFP1-4 were assessed by RNA-seq analysis. No evidence was found for mRNA expression of any of these receptors in several hPTEC preparations. Lack of RXFP1 mRNA was confirmed by qPCR using mRNA obtained from THP-1 cells as positive control. Our data thus provide evidence for primary renal human tubular epithelial cells as targets for the anti-fibrotic actions of RLX2. However, anti-fibrotic effects were observed at micromolar concentrations of RLX2 and shown to be independent of RXFP1 expression.

Quercetin is able to alleviate TGF-β-induced fibrosis in renal tubular epithelial cells by suppressing miR-21

Patients with chronic kidney disease (CKD) are characterized by a gradual loss of kidney function over time. A number of studies have indicated that tubule interstitial fibrosis (TIF) is associated with the occurrence and development of CKD. The aim of the present study was to investigate the effect of quercetin treatment on the fibrosis of renal tubular epithelial cells and to determine whether the anti-fibrotic effects of quercetin are achieved via microRNA (miR)-21. Human tubular epithelial HK-2 cells were cultured with transforming growth factor (TGF)-β to induce fibrosis and the expression of fibrotic markers collagen I, fibronectin, α-smooth muscle actin (SMA) and epithelial-cadherin were measured using reverse transcription-quantitative polymerase chain reaction (RT-qPCR) and western blotting. Cells were treated with 7.5, 15 or 30 mg/ml quercetin, following which fibrosis and miR-21 expression were evaluated. Quercetin-treated cells were transfected with miR-21 mimics and the expression of fibrotic markers was examined using RT-qPCR. Finally, the expression of fibrosis-associated miR-21 target genes, phosphatase and tensin homolog (PTEN) and TIMP Metallopeptidase Inhibitor 3 (TIMP3), was measured in cells treated with quercetin with or without miR-21 mimics using RT-qPCR, western blotting and immunocytochemistry. The results revealed that TGF-β treatment induced a significant increase in the expression of fibrotic markers in HK-2 cells, while quercetin treatment partially inhibited the fibrosis of HK-2 cells. Furthermore, quercetin treatment significantly inhibited TGF-β-induced miR-21 upregulation and transfection with miR-21 mimics reversed the anti-fibrotic effects of quercetin. Quercetin treatment markedly upregulated PTEN and TIMP3 expression, whereas transfection with miR-21 mimics reversed this effect. The results of the present study suggest that quercetin is able to alleviate TGF-β-induced fibrosis in HK-2 cells via suppressing the miR-21 and upregulating PTEN and TIMP3. Quercetin may have potential as an anti-fibrotic treatment for patients with renal fibrosis.

Chrysin Inhibits Advanced Glycation End Products-Induced Kidney Fibrosis in Renal Mesangial Cells and Diabetic Kidneys

Advanced glycation end products (AGEs) play a causative role in the development of diabetic nephropathy via induction of matrix protein deposition in kidneys. This study investigated inhibitory effects of chrysin, present in bee propolis and herbs, on glomerulosclerosis in db/db mice and AGEs-exposed renal mesangial cells. The in vivo study explored the demoting effects of 10 mg/kg chrysin on glomerular fibrosis in a type 2 diabetic model. Oral supplementation of chrysin inhibited the collagen fiber accumulation and &alpha;-smooth muscle actin (&alpha;-SMA) induction in periodic acid schiff-positive renal tissues of db/db mice. Moreover, treating db/db mice with chrysin diminished the level of AGEs increased in diabetic glomeruli. The in vitro study employed human mesangial cells exposed to 100 &mu;g/mL AGE-BSA for 72 h in the presence of 1⁻20 &mu;M chrysin. Glucose increased mesangial AGE production via induction of receptor for AGEs. Chrysin suppressed the induction of collagens, &alpha;-SMA, fibroblast-specific protein-1 and matrix metalloproteinases enhanced by AGE-bovine serum albumin. Furthermore, chrysin blunted transforming growth factor-&beta;1 induction and Smad 2/3 activation in AGEs-exposed mesangial cells. These results demonstrate that chrysin attenuated accumulation of myofibroblast-like cells and matrix proteins in AGEs-laden diabetic glomeruli. Therefore, chrysin may be a potential renoprotective agent targeting glucose-mediated AGEs-associated glomerulosclerosis and fibrosis.

Upregulation of allograft inflammatory factor‑1 expression and secretion by macrophages stimulated with aldosterone promotes renal fibroblasts to a profibrotic phenotype

Macrophages have been identified as a key cell type in the pathogenesis of renal interstitial fibrosis (RIF). However, the mechanism through which macrophages drive fibrosis remains unclear. The current study focuses on the effects and possible underlying mechanism of allograft inflammatory factor-1 (AIF-1), an inflammation-responsive scaffold protein expressed and secreted by macrophages, in promoting fibroblasts to a profibrotic phenotype. In vivo experiments indicated that AIF-1, CD68 and α-smooth muscle actin (α-SMA) were upregulated in kidney tissues of mice subjected to unilateral ureteric obstruction, while their expressions were inhibited by an aldosterone receptor antagonist, spironolactone. Double immunofluorescence staining revealed that AIF-1 expression co-localized with CD68-positive macrophages in the renal interstitium, indicating that AIF-1 expression in macrophages was increased in the RIF animal model. Furthermore, to identify the role of AIF-1 in promoting fibrosis, its expression and secretion by the RAW264.7 macrophage cell line were detected in vitro. The expression levels of α-SMA, phosphorylated p38 (p-p38) and fibronectin (FN) in fibroblasts were examined subsequent to co-culture with macrophages. The increase in AIF-1 expression and secretion was confirmed in RAW264.7 cells in response to aldosterone. After 72 h of co-culture between fibroblasts and macrophages stimulated with aldosterone, the α-SMA expression was induced in fibroblasts, with significantly increased expression levels of FN and p-p38 observed. In addition, AIF-1 expression was reduced by stable transfection of RAW264.7 cells with AIF-1 small interfering RNA, resulting in significantly reduced expression levels of α-SMA, p-p38 and FN in fibroblasts co-cultured with macrophages as compared with normal macrophages. These findings indicate that the expression of AIF-1 in macrophages is critical for the activation of renal fibroblasts to a profibrotic phenotype. AIF-1 expression was upregulated in macrophages, and may be a novel mechanism linking macrophages to the promotion of RIF via the p38 signaling pathway.

microRNA-181a downregulates deptor for TGFβ-induced glomerular mesangial cell hypertrophy and matrix protein expression

TGFβ contributes to mesangial cell hypertrophy and matrix protein increase in various kidney diseases including diabetic nephropathy. Deptor is an mTOR-interacting protein and suppresses mTORC1 and mTORC2 activities. We have recently shown that TGFβ-induced inhibition of deptor increases the mTOR activity. The mechanism by which TGFβ regulates deptor expression is not known. Here we identify deptor as a target of the microRNA-181a. We show that in mesangial cells, TGFβ increases the expression of miR-181a to downregulate deptor. Decrease in deptor augments mTORC2 activity, resulting in phosphorylation/activation of Akt kinase. Akt promotes inactivating phosphorylation of PRAS40 and tuberin, leading to stimulation of mTORC1. miR-181a-mimic increased mTORC1 and C2 activities, while anti-miR-181a inhibited them. mTORC1 controls protein synthesis via phosphorylation of translation initiation and elongation suppressors 4EBP-1 and eEF2 kinase. TGFβ-stimulated miR-181a increased the phosphorylation of 4EBP-1 and eEF2 kinase, resulting in their inactivation. miR-181a-dependent inactivation of eEF2 kinase caused dephosphorylation of eEF2. Consequently, miR-181a-mimic increased protein synthesis and hypertrophy of mesangial cells similar to TGFβ. Anti-miR-181a blocked these events in a deptor-dependent manner. Finally, TGFβ-miR-181a-driven deptor downregulation increased the expression of fibronectin. Our results identify a novel mechanism involving miR-181a-driven deptor downregulation, which contributes to mesangial cell pathologies in renal complications.

Danger-Associated Molecular Patterns Derived From the Extracellular Matrix Provide Temporal Control of Innate Immunity

It is evident that components of the extracellular matrix (ECM) act as danger-associated molecular patterns (DAMPs) through direct interactions with pattern recognition receptors (PRRs) including Toll-like receptors (TLRs) and inflammasomes. Through these interactions, ECM-derived DAMPs autonomously trigger sterile inflammation or prolong pathogen-induced responses through the production of proinflammatory mediators and the recruitment of leukocytes to sites of injury and infection. Recent research, however, suggests that ECM-derived DAMPs are additionally involved in the resolution and fine-tuning of inflammation by orchestrating the production of anti-inflammatory mediators that are required for the resolution of tissue inflammation and the transition to acquired immunity. Thus, in this review, we discuss the current knowledge of the interplay between ECM-derived DAMPs and the innate immune signaling pathways that are activated to provide temporal control of innate immunity.

Renal fibrosis: Recent translational aspects

Renal fibrogenesis is the common final pathway to all renal injuries that consequently leads to Chronic Kidney Disease (CKD). Renal fibrogenesis corresponds to the replacement of renal functional tissue by extra-cellular matrix proteins, mainly collagens, that ultimately impairs kidney function. Blockade of the renin angiotensin system by Angiotensin Converting Enzyme inhibitors (ACEi) or Angiotensin Receptor Blockers (ARBs) was the first strategy that proved efficient to blunt the development of renal fibrogenesis independently of its systemic action on blood pressure. Although this strategy has been published 20years ago, there is to date no novel therapeutic targets that are both safe and efficient in hindering renal fibrogenesis and CKD in humans, nor there is any new biomarker to precisely quantify this process. In our review, we will focus on the most recent pathways leading to fibrogenesis which have a high therapeutic potential in humans and on the most promising biomarkers of renal fibrosis.

Telbivudine attenuates UUO-induced renal fibrosis via TGF-β/Smad and NF-κB signaling

Renal fibrosis yields decreased renal function and is a potent contributor to chronic kidney disease (CKD). Telbivudine (LdT) is an anti-hepatitis B virus (HBV) drug that has been found to steadily improve renal function, but the mechanism of drug action is unclear. One explanation is that LdT impacts inflammatory or fibrotic pathways. In this study, we investigated renal protection by LdT in a rat model of unilateral ureteral obstruction (UUO). UUO rats received oral gavage of LdT (1, 1.5, or 2g/kg/day) for 5weeks. Kidney tissues were examined histopathologically with hematoxylin and eosin and Masson's trichrome stain. To assess proliferation of myofibroblasts and matrix accumulation, α-smooth muscle actin (α-sma) and collagen type I and III were detected. Interleukin-1 (IL-1) and tumor necrosis factor (TNF)-α were evaluated as a measure of proinflammatory cytokines. Transforming growth factor (TGF)-β and nuclear factor-κB (NF-κB) were considered the canonical signaling components in our investigation of the underlying mechanism of LdT action. Histopathology results indicated that LdT ameliorates renal injury and matrix accumulation. Expression of α-sma and collagen I/III as well as key fibrotic signaling factors in the TGF-β/Smad pathway were downregulated. In addition, LdT suppressed the release of IL-1 and TNF-α and decreased the expression of NF-κB by inhibiting toll-like receptor 4. Taken together, these findings indicate that LdT can attenuate renal fibrosis and inflammation via TGF-β/Smad and NF-κB pathways in UUO.

TGF-β1/p53 signaling in renal fibrogenesis

Fibrotic disorders of the renal, pulmonary, cardiac, and hepatic systems are associated with significant morbidity and mortality. Effective therapies to prevent or curtail the advancement to organ failure, however, remain a major clinical challenge. Chronic kidney disease, in particular, constitutes an increasing medical burden affecting >15% of the US population. Regardless of etiology (diabetes, hypertension, ischemia, acute injury, urologic obstruction), persistently elevated TGF-β1 levels are causatively linked to the activation of profibrotic signaling networks and disease progression. TGF-β1 is the principal driver of renal fibrogenesis, a dynamic pathophysiologic process that involves tubular cell injury/apoptosis, infiltration of inflammatory cells, interstitial fibroblast activation and excess extracellular matrix synthesis/deposition leading to impaired kidney function and, eventually, to chronic and end-stage disease. TGF-β1 activates the ALK5 type I receptor (which phosphorylates SMAD2/3) as well as non-canonical (e.g., src kinase, EGFR, JAK/STAT, p53) pathways that collectively drive the fibrotic genomic program. Such multiplexed signal integration has pathophysiological consequences. Indeed, TGF-β1 stimulates the activation and assembly of p53-SMAD3 complexes required for transcription of the renal fibrotic genes plasminogen activator inhibitor-1, connective tissue growth factor and TGF-β1. Tubular-specific ablation of p53 in mice or pifithrin-α-mediated inactivation of p53 prevents epithelial G₂/M arrest, reduces the secretion of fibrotic effectors and attenuates the transition from acute to chronic renal injury, further supporting the involvement of p53 in disease progression. This review focuses on the pathophysiology of TGF-β1-initiated renal fibrogenesis and the role of p53 as a regulator of profibrotic gene expression.

Does Mineralocorticoid Receptor Antagonism Prevent Calcineurin Inhibitor-Induced Nephrotoxicity?

Calcineurin inhibitors have markedly reduced acute rejection rates in renal transplantation, thus significantly improved short-term outcome. The beneficial effects are, however, tampered by acute and chronic nephrotoxicity leading to interstitial fibrosis and tubular atrophy, which impairs long-term allograft survival. The mineralocorticoid hormone aldosterone induces fibrosis in numerous organs, including the kidney. Evidence from animal models suggests a beneficial effect of aldosterone antagonism in reducing calcineurin inhibitor-induced nephrotoxicity. This review summarizes current evidence of mineralocorticoid receptor antagonism in animal models of calcineurin inhibitor-induced nephrotoxicity and the results from studies of mineralocorticoid antagonism in renal transplant patients.

Monitoring and manipulating cellular crosstalk during kidney fibrosis inside a 3D in vitro co-culture

In pharmacological research the development of promising lead compounds requires a detailed understanding of the dynamics of disease progression. However, for many diseases, such as kidney fibrosis, gaining such understanding requires complex real-time, multi-dimensional analysis of diseased and healthy tissue. To allow for such studies with increased throughput we established a dextran hydrogel-based in vitro 3D co-culture as a disease model for kidney fibrosis aimed at the discovery of compounds modulating the epithelial/mesenchymal crosstalk. This platform mimics a simplified pathological renal microenvironment at the interface between tubular epithelial cells and surrounding quiescent fibroblasts. We combined this 3D technology with epithelial reporter cell lines expressing fluorescent biomarkers in order to visualize pathophysiological cell state changes resulting from toxin-mediated chemical injury. Epithelial cell damage onset was robustly detected by image-based monitoring, and injured epithelial spheroids induced myofibroblast differentiation of co-cultured quiescent human fibroblasts. The presented 3D co-culture system therefore provides a unique model system for screening of novel therapeutic molecules capable to interfere and modulate the dialogue between epithelial and mesenchymal cells.

The Role of Transforming Growth Factor Beta-1 in the Progression of HIV/AIDS and Development of Non-AIDS-Defining Fibrotic Disorders

Even after attainment of sustained viral suppression following implementation of highly active antiretroviral therapy, HIV-infected persons continue to experience persistent, low-grade, systemic inflammation. Among other mechanisms, this appears to result from ongoing microbial translocation from a damaged gastrointestinal tract. This HIV-related chronic inflammatory response is paralleled by counteracting, but only partially effective, biological anti-inflammatory processes. Paradoxically, however, this anti-inflammatory response not only exacerbates immunosuppression but also predisposes for development of non-AIDS-related, non-communicable disorders. With respect to the pathogenesis of both sustained immunosuppression and the increased frequency of non-AIDS-related disorders, the anti-inflammatory/profibrotic cytokine, transforming growth factor-β1 (TGF-β1), which remains persistently elevated in both untreated and virally suppressed HIV-infected persons, may provide a common link. In this context, the current review is focused on two different, albeit related, harmful activities of TGF-β1 in HIV infection. First, on the spectrum of anti-inflammatory/immunosuppressive activities of TGF-β1 and the involvement of this cytokine, derived predominantly from T regulatory cells, in driving disease progression in HIV-infected persons via both non-fibrotic and profibrotic mechanisms. Second, the possible involvement of sustained elevations in circulating and tissue TGF-β1 in the pathogenesis of non-AIDS-defining cardiovascular, hepatic, pulmonary and renal disorders, together with a brief comment on potential TGF-β1-targeted therapeutic strategies.

Mechanisms and consequences of carbamoylation

Protein carbamoylation is a non-enzymatic post-translational modification that binds isocyanic acid, which can be derived from the dissociation of urea or from the myeloperoxidase-mediated catabolism of thiocyanate, to the free amino groups of a multitude of proteins. Although the term 'carbamoylation' is usually replaced by the term "carbamylation" in the literature, carbamylation refers to a different chemical reaction (the reversible interaction of CO₂ with α and ε-amino groups of proteins). Depending on the altered molecule (for example, collagen, erythropoietin, haemoglobin, low-density lipoprotein or high-density lipoprotein), carbamoylation can have different pathophysiological effects. Carbamoylated proteins have been linked to atherosclerosis, lipid metabolism, immune system dysfunction (such as inhibition of the classical complement pathway, inhibition of complement-dependent rituximab cytotoxicity, reduced oxidative neutrophil burst, and the formation of anti-carbamoylated protein antibodies) and renal fibrosis. In this Review, we discuss the carbamoylation process and evaluate the available biomarkers of carbamoylation (for example, homocitrulline, the percentage of carbamoylated albumin, carbamoylated haemoglobin, and carbamoylated low-density lipoprotein). We also discuss the relationship between carbamoylation and the occurrence of cardiovascular events and mortality in patients with chronic kidney disease and assess the effects of strategies to lower the carbamoylation load.

The production of fibroblast growth factor 23 is controlled by TGF-β2

Transforming growth factor-β (TGF-β) is a cytokine produced by many cell types and implicated in cell growth, differentiation, apoptosis, and inflammation. It stimulates store-operated calcium entry (SOCE) through the calcium release-activated calcium (CRAC) channel Orai1/Stim1 in endometrial Ishikawa cells. Bone cells generate fibroblast growth factor (FGF) 23, which inhibits renal phosphate reabsorption and 1,25(OH)2D3 formation in concert with its co-receptor Klotho. Moreover, Klotho and FGF23 counteract aging and age-related clinical conditions. FGF23 production is dependent on Orai1-mediated SOCE and inflammation. Here, we explored a putative role of TGF-β2 in FGF23 synthesis. To this end, UMR106 osteoblast-like cells were cultured, Fgf23 transcript levels determined by qRT-PCR, FGF23 protein measured by ELISA, and SOCE analyzed by fluorescence optics. UMR106 cells expressed TGF-β receptors 1 and 2. TGF-β2 enhanced SOCE and potently stimulated the production of FGF23, an effect significantly attenuated by SB431542, an inhibitor of the transforming growth factor-β (TGF-β) type I receptor activin receptor-like kinases ALK5, ALK4, and ALK7. Furthermore, the TGF-β2 effect on FGF23 production was blunted by SOCE inhibitor 2-APB. We conclude that TGF-β2 induces FGF23 production, an effect involving up-regulation of SOCE.