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

Mechanotransductive receptor Piezo1 as a promising target in the treatment of fibrosis diseases

Fibrosis could happen in every organ, leading to organic malfunction and even organ failure, which poses a serious threat to global health. Early treatment of fibrosis has been reported to be the turning point, therefore, exploring potential correlates in the pathogenesis of fibrosis and how to reverse fibrosis has become a pressing issue. As a mechanism-sensitive cationic calcium channel, Piezo1 turns on in response to changes in the lipid bilayer of the plasma membrane. Piezo1 exerts multiple biological roles, including inhibition of inflammation, cytoskeletal stabilization, epithelial-mesenchymal transition, stromal stiffness, and immune cell mechanotransduction, interestingly enough. These processes are closely associated with the development of fibrotic diseases. Recent studies have shown that deletion or knockdown of Piezo1 attenuates the onset of fibrosis. Therefore, in this paper we comprehensively describe the biology of this gene, focusing on its potential relevance in pulmonary fibrosis, renal fibrosis, pancreatic fibrosis, and cardiac fibrosis diseases, except for the role of drugs (agonists), increased intracellular calcium and mechanical stress using this gene in alleviating fibrosis.

FOSL2 participates in renal fibrosis via SGK1-mediated epithelial-mesenchymal transition of proximal tubular epithelial cells

Background

Fos-related antigen 2 (FOSL2) plays a facilitative role in fibrotic disease; however, its role in renal fibrosis remains unclear. This study aimed to clarify the role and underlying mechanisms of FOSL2 in renal fibrosis.

Methods

Upregulated genes in unilateral ureteral obstruction (UUO)-injured kidneys were screened in Gene Expression Omnibus (GEO) databases, and overlapping genes were identified using Venn diagram software. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses were performed for these genes. The UUO-induced mouse model and transforming growth factor-β1 (TGF-β1)-induced cell model were used for the in vivo and in vitro studies.

Results

A total of 43 commonly upregulated genes were identified. GO and KEGG pathway analyses indicated that FOSL2 may be involved in fibrosis. Furthermore, FOSL2 was confirmed to be upregulated in UUO-injured kidneys and TGF-β1-induced cells. Knockdown of FOSL2 ameliorated interstitial fibrosis, extracellular matrix deposition, and epithelial-mesenchymal transition via the downregulation of fibronectin, α-smooth muscle actin (α-SMA), collagen type I (Col1a1 and Col1a2), and Col5a1 and upregulation of E-cadherin. Bioinformatics analysis revealed that serum/glucocorticoid regulated kinase 1 (SGK1) may be regulated by FOSL2 and involved in renal fibrosis. Further experiments confirmed that TGF-β1 enhanced SGK1 expression and transcription, which were reversed by FOSL2 silencing. Moreover, FOSL2 was bound to the SGK1 promoter, and SGK1 overexpression reversed the effects of FOSL2 silencing in TGF-β1-induced cells.

Conclusion

FOSL2 plays an essential role in promoting renal fibrosis in an SGK1-dependent manner, and targeting the FOSL2/SGK1 signaling axis may offer a potential strategy for the treatment of renal fibrosis.

Arsenite Exposure to Human RPCs (HRTPT) Produces a Reversible Epithelial Mesenchymal Transition (EMT): In-Vitro and In-Silico Study

The human kidney is known to possess renal progenitor cells (RPCs) that can assist in the repair of acute tubular injury. The RPCs are sparsely located as single cells throughout the kidney. We recently generated an immortalized human renal progenitor cell line (HRTPT) that co-expresses PROM1/CD24 and expresses features expected on RPCs. This included the ability to form nephrospheres, differentiate on the surface of Matrigel, and undergo adipogenic, neurogenic, and osteogenic differentiation. These cells were used in the present study to determine how the cells would respond when exposed to nephrotoxin. Inorganic arsenite (iAs) was chosen as the nephrotoxin since the kidney is susceptible to this toxin and there is evidence of its involvement in renal disease. Gene expression profiles when the cells were exposed to iAs for 3, 8, and 10 passages (subcultured at 1:3 ratio) identified a shift from the control unexposed cells. The cells exposed to iAs for eight passages were then referred with growth media containing no iAs and within two passages the cells returned to an epithelial morphology with strong agreement in differential gene expression between control and cells recovered from iAs exposure. Results show within three serial passages of the cells exposed to iAs there was a shift in morphology from an epithelial to a mesenchymal phenotype. EMT was suggested based on an increase in known mesenchymal markers. We found RPCs can undergo EMT when exposed to a nephrotoxin and undergo MET when the agent is removed from the growth media.

Beclin-1 dependent autophagy improves renal outcomes following Unilateral Ureteral Obstruction (UUO) injury

Background

Interstitial Fibrosis and Tubular Atrophy (IFTA) is the most common cause of long-term graft failure following renal transplant. One of the hallmarks of IFTA is the development of interstitial fibrosis and loss of normal renal architecture. In this study, we evaluated the role of autophagy initiation factor Beclin-1 in protecting against post-renal injury fibrosis.

Methods

Adult male wild type (WT) C57BL/6 mice were subjected to Unilateral Ureteral Obstruction (UUO), and kidney tissue samples were harvested at 72-hour, 1- and 3-week post-injury. The UUO-injured and uninjured kidney samples were examined histologically for fibrosis, autophagy flux, inflammation as well activation of the Integrated Stress Response (ISR). We compared WT mice with mice carrying a forced expression of constitutively active mutant form of Beclin-1, Becn1F121A/F121A .

Results

In all experiments, UUO injury induces a progressive development of fibrosis and inflammation. These pathological signs were diminished in Becn1F121A/F121A mice. In WT animals, UUO caused a strong blockage of autophagy flux, indicated by continuously increases in LC3II accompanied by an over 3-fold accumulation of p62 1-week post injury. However, increases in LC3II and unaffected p62 level by UUO were observed in Becn1F121A/F121A mice, suggesting an alleviation of disrupted autophagy. Beclin-1 F121A mutation causes a significant decrease in phosphorylation of inflammatory STING signal and limited production of IL6 and IFNγ, but had little effect on TNF-α, in response to UUO. Furthermore, activation of ISR signal cascade was detected in UUO-injured in kidneys, namely the phosphorylation signals of elF2S1 and PERK in addition to the stimulated expression of ISR effector ATF4. However, Becn1F121A/F121A mice did not reveal signs of elF2S1 and PERK activation under the same condition and had a dramatically reduced ATF level at 3-week post injury.

Conclusions

The results suggest that UUO causes a insufficient, maladaptive renal autophagy, which triggered downstream activation of inflammatory STING pathway, production of cytokines, and pathological activation of ISR, eventually leading to the development of fibrosis. Enhancing autophagy via Beclin-1 improved renal outcomes with diminished fibrosis, via underlying mechanisms of differential regulation of inflammatory mediators and control of maladaptive ISR.

Current view of liver cancer cell-of-origin and proposed mechanisms precluding its proper determination

Hepatocellular carcinoma and intrahepatic cholangiocarcinoma are devastating primary liver cancers with increasing prevalence in many parts of the world. Despite intense investigation, many aspects of their biology are still largely obscure. For example, numerous studies have tackled the question of the cell-of-origin of primary liver cancers using different experimental approaches; they have not, however, provided a clear and undisputed answer. Here, we will review the evidence from animal models supporting the role of all major types of liver epithelial cells: hepatocytes, cholangiocytes, and their common progenitor as liver cancer cell-of-origin. Moreover, we will also propose mechanisms that promote liver cancer cell plasticity (dedifferentiation, transdifferentiation, and epithelial-to-mesenchymal transition) which may contribute to misinterpretation of the results and which make the issue of liver cancer cell-of-origin particularly complex.

MYPT1 inhibits the metastasis of renal clear cell carcinoma via the MAPK8/N-cadherin pathway

Myosin phosphatase target subunit 1 (MYPT1) is a subunit of myosin phosphatase that is capable of regulating smooth muscle contraction. MYPT1 has been reported to be involved in a wide variety of tumours, but its expression and biological functions in renal clear cell carcinoma (ccRCC) remain obscure. Herein, we analysed the relationship between patient clinicopathological characteristics and MYPT1 expression levels in ccRCC patients using a tissue microarray (TMA) and data retrieved from the TCGA-KIRC dataset. MYPT1 was overexpressed or depleted using siRNA in ccRCC cells to assess the effects on migration and invasion in vitro and in vivo. Additionally, RNA-sequencing and bioinformatics analysis were performed to investigate the precise mechanism. MYPT1 expression in ccRCC tissues was observed to be lower than that in nonmalignant tissues (P < 0.05). In addition, MYPT1 downregulation was closely linked to advanced pathological stage (P < 0.05), and poor OS (overall survival; P < 0.05). Functionally, increased expression of MYPT1 suppressed ccRCC migration and invasion in vitro, and inhibited tumour metastasis in vivo. In addition, MYPT1 overexpression exerted its suppressive effects via the MAPK8/N-cadherin pathway in ccRCC.

ShenKang Injection Attenuates Renal Fibrosis by Inhibiting EMT and Regulating the Wnt/β-Catenin Pathway

Shenkang Injection (SKI) is a traditional Chinese medicine injection commonly used in the clinical treatment of chronic kidney disease. Although it has been confirmed that SKI has anti-kidney fibrosis effects, the underlying mechanism remains unclear. To investigate the effects of SKI on epithelial-mesenchymal transition (EMT) and Wnt/β-catenin pathway and explore its potential anti-fibrosis mechanism. A unilateral ureteral obstruction (UUO) model was induced by ligating the left ureter of male SD rats. A total of 24 rats were randomly divided into the following four groups: sham group, model group, SKI group, and benazepril group. The rats in each group were treated for 28 days, and renal function was evaluated by blood urea nitrogen (BUN) and serum creatinine (Scr). The degree of renal fibrosis was assessed by hematoxylin and eosin (HE) and Masson staining. Extracellular matrix (ECM) deposition was evaluated by immunohistochemistry. Real-time fluorescent quantitative PCR (RT-qPCR) and western blotting were used to detect the expression of genes and proteins in the Wnt/β-catenin signaling pathway. Further studies were performed in vitro using HK-2 cells treated with TGF-β1. At 28 days postoperation, the levels of BUN and Scr expression were significantly increased in the UUO group. SKI and benazepril reduced the levels of BUN and Scr, which displayed protective renal effects. Pathological staining showed that compared with the sham operation group, the renal parenchymal structure was severely damaged, the number of glomeruli was reduced, and a large amount of collagen was deposited in the kidney tissue of the UUO group. SKI treatment reduced morphological changes. Immunohistochemistry showed that compared with the sham operation group, the content of collagen I and FN in the kidney tissue of the UUO group were significantly increased, whereas the SKI content was decreased. In addition, compared with the UUO group, the levels of Wnt1, active β-catenin, Snail1, and PAI-1 expression were reduced in the SKI group, suggesting that SKI may reduce renal fibrosis by mediating the Wnt/β-catenin pathway. Further in vitro studies showed that collagen I, FN, and α-SMA levels in HK-2 cells were significantly increased following stimulation with TGF-β1. SKI could significantly reduce the expression of collagen I, FN, and α-SMA. A scratch test showed that SKI could reduce HK-2 migration. In addition, by stimulating TGF-β1, the levels of Wnt1, active β-catenin, snail1, and PAI-1 were significantly upregulated. SKI treatment could inhibit the activity of the Wnt/β-catenin signaling pathway in HK-2 cells. SKI improves kidney function by inhibiting renal fibrosis. The anti-fibrotic effects may be mediated by regulation of the Wnt/β-catenin pathway and EMT inhibition.

CXC Chemokine Receptor 2 Accelerates Tubular Cell Senescence and Renal Fibrosis via β-Catenin-Induced Mitochondrial Dysfunction

Renal fibrosis is a common feature of various chronic kidney diseases (CKD). However, its underlying mechanism has not been totally clarified. C-X-C motif chemokine receptor (CXCR) family plays a role in renal fibrosis, however, detailed mechanisms have not been elucidated. Here, we report that CXCR2 has a potential role in tubular cell senescence and renal fibrosis, and is associated with β-catenin-activated mitochondrial dysfunction. CXCR2 is one of most increased members among CXCR family in unilateral ureteral obstruction (UUO) mice. CXCR2 was expressed primarily in tubules and co-localized with p16^INK4A, a cellular senescence marker, and β-catenin. Administration of SB225002, a selective CXCR2 antagonist, significantly inhibited the activation of β-catenin signaling, restored mitochondrial function, protected against tubular cell senescence and renal fibrosis in unilateral ureteral obstruction (UUO) mice. In unilateral ischemia-reperfusion injury (UIRI) mice, treatment with interlukin-8 (IL-8), the ligand of CXCR2, further aggravated β-catenin activation, mitochondrial dysfunction, tubular cell senescence and renal fibrosis, whereas knockdown of p16^INK4A inhibited IL-8-induced these effects. In vitro, SB225002 inhibited mitochondrial dysfunction and tubular cell senescence. Furthermore, ICG-001, a β-catenin signaling blocker, significantly retarded CXCR2-induced cellular senescence and fibrotic changes. These results suggest that CXCR2 promotes tubular cell senescence and renal fibrosis through inducing β-catenin-activated mitochondrial dysfunction.

Mechanosensitive Piezo1 channels mediate renal fibrosis

Kidney fibrosis is the final common pathway of progressive kidney diseases, the underlying mechanisms of which is not fully understood. The purpose of the current study is to investigate a role of Piezo1, a mechanosensitive nonselective cation channel, in kidney fibrosis. In human fibrotic kidneys, Piezo1 protein expression was markedly upregulated. The abundance of Piezo1 protein in kidneys of mice with UUO or with folic-acid treatment was significantly increased. Inhibition of Piezo1 with GsMTx4 markedly ameliorated UUO or folic acid-induced kidney fibrosis. Mechanical stretch, compression or stiffness induced Piezo1 activation and pro-fibrotic responses in human HK2 cells and primary cultured mouse proximal tubular cells (mPTCs), which were greatly prevented by inhibition or silence of Piezo1. TGFβ-1 induced increased Piezo1 expression and pro-fibrotic phenotypic alterations in HK2 cells and mPTCs, which was again markedly prevented by inhibition of Piezo1. Activation of Piezo1 by Yoda1, a Piezo1 agonist, caused calcium influx and profibrotic responses in HK2 cells and induced calpain2 activation, followed by talin1 cleavage and upregulation of integrinβ1. Also, Yoda1 promoted the link between ECM and integrinβ1. In conclusion, Piezo1 is involved in the progression of kidney fibrosis and pro-fibrotic alterations in renal proximal tubular cells, likely through activating calcium-calpain2-integrinβ1 pathway.

Dual inhibition of TGFβR and ROCK reverses the epithelial to mesenchymal transition in collectively migrating zebrafish keratocytes

There is a growing controversy about the role of the epithelial to mesenchymal transition (EMT) in the fibrosis associated with chronic disease. Recent studies suggest that it is not the EMT transcriptional program but differentiation of progenitor cells, response to chronic inflammation, or some combination of both which cause the appearance of fibroblasts and the production of the extracellular matrix. To address this issue, we study the EMT process in the zebrafish keratocytes which migrate from primary explants of epithelial tissue as these cells are both terminally differentiated and able to divide. To firmly place this EMT process in the context of other systems, we first demonstrate that the zebrafish keratocyte EMT process involves nuclear accumulation of twist and snail/slug transcription factors as part of a TGFβR‐mediated EMT process. As assessed by the expression and localization of EMT transcription factors, the zebrafish keratocyte EMT process is reversed by the addition of Rho‐activated kinase (ROCK) in combination with TGFβR inhibitors. The complete cycle of EMT to MET observed in this system links these in vitro results more closely to the process of wound healing in vivo. However, the absence of observable activation of EMT transcription factors when keratocytes are cultured on compliant substrata in a TGFβ1‐containing medium suggests that ROCK signaling, initiated by tension within the sheet, is an essential contributor to the EMT process. Most importantly, the requirement for ROCK activation by culturing on noncompliant substrata suggests that EMT in these terminally differentiated cells would not occur in vivo.

Micro-vesicles from mesenchymal stem cells over-expressing miR-34a inhibit transforming growth factor-β1-induced epithelial-mesenchymal transition in renal tubular epithelial cells in vitro

BACKGROUND

The use of microRNAs in the therapy of kidney disease is hampered by the difficulties in their effective delivery. Micro-vesicles (MVs) are known as natural carriers of small RNAs. Our prior research has demonstrated that MVs isolated from mesenchymal stem cells (MSCs) are capable of attenuating kidney injuries induced by unilateral ureteral obstruction and 5/6 sub-total nephrectomy in mice. The present study aimed to evaluate the effects of miR-34a-5p (miR-34a)-modified MSC-MVs on transforming growth factor (TGF)-β1-induced fibrosis and apoptosis in vitro.

METHODS

Bone marrow MSCs were modified by lentiviruses over-expressing miR-34a, from which MVs were collected for the treatment of human Kidney-2 (HK-2) renal tubular cells exposed to TGF-β1 (6 ng/mL). The survival of HK-2 cells was determined using 3-(4,5-dimethylthiazol-2-yl)-2, 5-diphenyl tetrazolium bromide (MTT) and Annexin V-Light 650/propidium iodide (PI) assays. The expression levels of epithelial markers (tight junction protein 1 [TJP1] and E-cadherin) and mesenchymal markers (smooth muscle actin alpha (α-SMA) and fibronectin) in HK-2 cells were measured using Western blot analysis and an immunofluorescence assay. In addition, changes in Notch-1/Jagged-1 signaling were analyzed using Western blotting. Data were analyzed using a Student's t test or one-way analysis of variance.

RESULTS

MiR-34a expression increased three-fold in MVs generated by miR-34a-modified MSCs compared with that expressed in control MVs (P < 0.01, t = 16.55). In HK-2 cells, TJP1 and E-cadherin levels decreased to 31% and 37% after treatment with TGF-β1, respectively, and were restored to 62% and 70% by miR-34a-enriched MSC-MVs, respectively. The expression of α-SMA and fibronectin increased by 3.9- and 5.0-fold following TGF-β1 treatment, and decreased to 2.0- and 1.7-fold after treatment of HK-2 cells with miR-34a-enriched MSC-MVs. The effects of miR-34a-enriched MSC-MVs on epithelial-mesenchymal transition (EMT) markers were stronger than control MSC-MVs. The effects of miR-34a-enriched MSC-MVs on these EMT markers were stronger than control MSC-MVs. Notch-1 receptor and Jagged-1 ligand, two major molecules of Notch signaling pathway, are predicted targets of miR-34a. It was further observed that elevation of Notch-1 and Jagged-1 induced by TGF-β1 was inhibited by miR-34a-enriched MSC-MVs. In addition, TGF-β1 exposure also induced apoptosis in HK-2 cells. Although miR-34a-mofidied MSC-MVs were able to inhibit TGF-β1-triggered apoptosis in HK-2 cells, the effects were less significant than control MSC-MVs (control:TGF-β1: miR-nc-MV:miR-34a-MV = 1.3:0.6:1.1:0.9 for MTT assay, 1.8%:23.3%:9.4%:17.4% for apoptosis assay). This phenomenon may be the result of the pro-apoptotic effects of miR-34a.

CONCLUSIONS

The present study demonstrated that miR-34a-over-expressing MSC-MVs inhibit EMT induced by pro-fibrotic TGF-β1 in renal tubular epithelial cells, possibly through inhibition of the Jagged-1/Notch-1 pathway. Genetic modification of MSC-MVs with an anti-fibrotic molecule may represent a novel strategy for the treatment of renal injuries.

Lefty-1 inhibits renal epithelial-mesenchymal transition by antagonizing the TGF-β/Smad signaling pathway

Epithelial-mesenchymal transition (EMT) is a biological process in which tubular epithelial cells lose their phenotypes, and new mesenchymal feature are obtained. In particular, type II EMT possibly contributes to renal tissue fibrogenesis. Recent studies indicate that Lefty-1, a novel member of the TGF-β superfamily with pleiotropical and biological regulation characteristics on TGF-β and other signaling pathways, is considered to have potential fibrotic effects. However, its role in EMT, which is often a long-term consequence of renal tubulointerstitial fibrosis, remains unknown. In this study, we found that Lefty-1 alleviates EMT induction through antagonizing TGF-β/Smad pathway in vivo and in vitro. In unilateral ureteral obstruction (UUO) model mice, administration of adenovirus-mediated overexpression of Lefty-1 (Ad-Lefty-1) significantly reduced TGF-β1/Smad expression and alleviated the phenotypic transition of epithelial cells to mesenchymal cells and extracellular matrix (ECM) accumulation. In high glucose-induced rat renal tubular duct epithelial cell line (NRK-52E), EMT and ECM synthesis were alleviated with Lefty-1 treatment, which significantly inhibited TGF-β1/Smad pathway activation in UUO mice and high glucose-treated NRK-52E cells. Thus, Lefty-1 can alleviate EMT and renal interstitial fibrosis in vivo and in vitro through antagonizing the TGF-β/Smad pathway, and Lefty-1 might have a potential novel therapeutic effect on fibrotic kidney diseases.

Origin and functional heterogeneity of fibroblasts

The inherent plasticity and resiliency of fibroblasts make this cell type a conventional tool for basic research. But where do they come from, are all fibroblasts the same, and how do they function in disease? The first fibroblast lineages in mammalian development emerge from the ooze of primary mesenchyme during gastrulation. They are cells that efficiently create and negotiate the extracellular matrix of the mesoderm in order to migrate and meet their developmental fate. Mature fibroblasts in epithelial tissues live in the interstitial spaces between basement membranes that spatially delimit complex organ structures. While the function of resident fibroblasts in healthy tissues is largely conjecture, the accumulation of fibroblasts in pathologic lesions offers insight into biologic mechanisms that control their function; fibroblasts are poised to coordinate fibrogenesis in tissue injury, neoplasia, and aging. Here, we examine the developmental origin and plasticity of fibroblasts, their molecular and functional definitions, the epigenetic control underlying their identity and activation, and the evolution of their immune regulatory functions. These topics are reviewed through the lens of fate mapping using genetically engineered mouse models and from the perspective of single-cell RNA sequencing. Recent observations suggest dynamic and heterogeneous functions for fibroblasts that underscore their complex molecular signatures and utility in injured tissues.

Activation of the prostaglandin E2 EP2 receptor attenuates renal fibrosis in unilateral ureteral obstructed mice and human kidney slices

Aim

Renal fibrosis plays a pivotal role in the development and progression of chronic kidney disease, which affects 10% of the adult population. Previously, it has been demonstrated that the cyclooxygenase‐2 (COX‐2)/prostaglandin (PG) system influences the progression of renal injury. Here, we evaluated the impact of butaprost, a selective EP₂ receptor agonist, on renal fibrosis in several models of kidney injury, including human tissue slices.

Methods

We studied the anti‐fibrotic efficacy of butaprost using Madin‐Darby Canine Kidney (MDCK) cells, mice that underwent unilateral ureteral obstruction and human precision‐cut kidney slices. Fibrogenesis was evaluated on a gene and protein level by qPCR and Western blotting.

Results

Butaprost (50 μM) reduced TGF‐β‐induced fibronectin (FN) expression, Smad2 phosphorylation and epithelial‐mesenchymal transition in MDCK cells. In addition, treatment with 4 mg/kg/day butaprost attenuated the development of fibrosis in mice that underwent unilateral ureteral obstruction surgery, as illustrated by a reduction in the gene and protein expression of α‐smooth muscle actin, FN and collagen 1A1. More importantly, a similar anti‐fibrotic effect of butaprost was observed in human precision‐cut kidney slices exposed to TGF‐β. The mechanism of action of butaprost appeared to be a direct effect on TGF‐β/Smad signalling, which was independent of the cAMP/PKA pathway.

Conclusion

In conclusion, this study demonstrates that stimulation of the EP₂ receptor effectively mitigates renal fibrogenesis in various fibrosis models. These findings warrant further research into the clinical application of butaprost, or other EP₂ agonists, for the inhibition of renal fibrosis.

The Key Role of Epithelial to Mesenchymal Transition (EMT) in Hypertensive Kidney Disease

Accumulating evidence indicates that epithelial-to-mesenchymal transition (EMT), originally described as a key process for organ development and metastasis budding in cancer, plays a key role in the development of renal fibrosis in several diseases, including hypertensive nephroangiosclerosis. We herein reviewed the concept of EMT and its role in renal diseases, with particular focus on hypertensive kidney disease, the second leading cause of end-stage renal disease after diabetes mellitus. After discussing the pathophysiology of hypertensive nephropathy, the 'classic' view of hypertensive nephrosclerosis entailing hyalinization, and sclerosis of interlobular and afferent arterioles, we examined the changes occurring in the glomerulus and tubulo-interstitium and the studies that investigated the role of EMT and its molecular mechanisms in hypertensive kidney disease. Finally, we examined the reasons why some studies failed to provide solid evidence for renal EMT in hypertension.

NDNF inhibits the migration and invasion of human renal cancer cells through epithelial-mesenchymal transition

Neuron-derived neurotrophic factor (NDNF) is a glycosylated, disulfide-bonded secretory protein that contains a fibronectin type III domain. NDNF has been identified as a neurotrophic factor; however, its role in carcinogenesis has not yet been identified. To investigate the expression and role of NDNF in carcinogenesis, the expression of NDNF in human Renal cell carcinoma (RCC) cell lines and tissues was detected by reverse transcription-quantitative polymerase chain reaction (RT-qPCR) and western blot analysis. Cell proliferation was investigated using CCK-8 and colony formation assays, and the cell invasion and immigration capacity was evaluated using the transwell assay. The results demonstrated that NDNF expression was downregulated in RCC cell lines and RCC tissues. Restoring NDNF expression significantly inhibited the proliferation, migration and invasion of RCC cells. The study also demonstrated that the inhibitory effect of NDNF on invasive ability was mediated by suppressing the epithelial-mesenchymal transition (EMT) in RCC cells. NDNF may therefore be considered an important regulator of EMT in RCC progression and may represent a novel promising target for antimetastatic therapy.

Action Mechanisms and Therapeutic Targets of Renal Fibrosis

Renal fibrosis was a chronic and progressive process affecting kidneys in chronic kidney disease (CKD), regardless of cause. Although no effective targeted therapy yet existed to retard renal fibrosis, a number of important recent advances have highlighted the cellular and molecular mechanisms underlying the renal fibrosis. The advances including TGF-β/Smad pathway, oxidative stress and inflammation, hypoxia and gut microbiota-derived from uremic solutes were highlighted that could provide therapeutic targets. New therapeutic targets and strategies that are particularly promising for development of new treatments for patients with CKD were also highlighted.

Targeting histone methyltransferase enhancer of zeste homolog-2 inhibits renal epithelial-mesenchymal transition and attenuates renal fibrosis

Enhancer of zeste homolog-2 (EZH2) is a methyltransferase that induces histone H3 lysine 27 trimethylation (H3K27me3) and functions as an oncogenic factor in many cancer types. Its role in renal epithelial-mesenchymal transition (EMT) remains unknown. In this study, we found that EZH2 and H3K27me3 were highly expressed in mouse kidney with unilateral ureteral obstruction and cultured mouse kidney proximal tubular (TKPT) cells undergoing EMT. Inhibition of EZH2 with 3-deazaneplanocin A (3-DZNeP) attenuated renal fibrosis, which was associated with preserving E-cadherin expression and inhibiting Vimentin up-regulation in the obstructed kidney. Treatment with 3-DZNeP or transfection of EZH2 siRNA also inhibited TGF-β1-induced EMT of TKPT cells. Injury to the kidney or cultured TKPT cells resulted in up-regulation of Snail-l family transcriptional repressor (Snail)-1 and Twist family basic helix-loop-helix (BHLH) transcription factor (Twist)-1, which are 2 transcription factors, and down-regulation of phosphatase and tensin homolog, a protein tyrosine phosphatase associated with inhibition of PI3K-protein kinase B (AKT) signaling; EZH2 inhibition or silencing reversed all those responses. 3-DZNeP was also effective in suppressing epithelial arrest at the G2/M phase and dephosphorylating AKT and β-catenin in vivo and in vitro. These data indicate that EZH2 activation contributes to renal EMT and fibrosis through activation of multiple signaling pathways and suggest that EZH2 has potential as a therapeutic target for treatment of renal fibrosis.-Zhou, X., Xiong, C., Tolbert, E., Zhao, T. C., Bayliss, G., Zhuang, S. Targeting histone methyltransferase enhancer of zeste homolog-2 inhibits renal epithelial-mesenchymal transition and attenuates renal fibrosis.

Snail and kidney fibrosis

Snail family zinc finger 1 (SNAI1) is a transcription factor expressed during renal embryogenesis, and re-expressed in various settings of acute kidney injury (AKI). Subjected to tight regulation, SNAI1 controls major biological processes responsible for renal fibrogenesis, including mesenchymal reprogramming of tubular epithelial cells, shutdown of fatty acid metabolism, cell cycle arrest and inflammation of the microenvironment surrounding tubular epithelial cells. The present review describes in detail the interactions of SNAI1 with AKI-associated signalling pathways. We also discuss how this central factor has been iteratively (and promisingly) targeted in a number of animal models in order to prevent or slow down renal fibrogenesis.

Antifibrotic Effects of Hepatocyte Growth Factor on Endothelial-to-Mesenchymal Transition via Transforming Growth Factor-Beta1 (TGF-β1)/Smad and Akt/mTOR/P70S6K Signaling Pathways

Background

The related mechanisms involved in allograft interstitial fibrosis and chronic allograft dysfunction (CAD), following renal transplant, remain largely unknown. Here, we explored the role of hepatocyte growth factor (HGF) treatment on the endothelial-to-mesenchymal transition (EndMT) as a new way to target and prevent kidney fibrosis and improve outcomes for renal transplant recipients.

Method/Material

We extracted proteins and mRNAs from human umbilical vein endothelial cells (HUVECs) and human renal glomerular endothelial cells (HRGECs) treated with transforming growth factor-beta1 (TGF-β1) and/or varying doses of HGF, and assessed the effect of HGF on the EndMT using western blotting, qRT-PCR, and ELISA assays. We utilized cell motility and migration assays to evaluate cell movement, and applied western blotting to assess the mechanism by which TGF-β1 induced the EndMT.

Results

HGF significantly attenuated the development of TGF-β1-induced EndMT in a concentration-dependent way, and weakened the abilities of motility and migration of both HUVECs and HRGECs. Moreover, our results reveal that the antifibrotic effect of HGF on the EndMT was associated with the TGF-β/Smad and Akt/mTOR/p70S6K signaling pathways.

Conclusions

Our study suggests that HGF treatment significantly attenuates the development of EndMT induced by TGF-β1 via the TGFβ/Smad and Akt/mTOR/P70S6K signaling, which provides novel insights into the prevention and treatment of interstitial fibrosis and CAD following renal transplant.

Induction of Mesenchymal-Epithelial Transitions in Sarcoma Cells

Phenotypic plasticity refers to a phenomenon in which cells transiently gain traits of another lineage. During carcinoma progression, phenotypic plasticity drives invasion, dissemination and metastasis. Indeed, while most of the studies of phenotypic plasticity have been in the context of epithelial-derived carcinomas, it turns out sarcomas, which are mesenchymal in origin, also exhibit phenotypic plasticity, with a subset of sarcomas undergoing a phenomenon that resembles a mesenchymal-epithelial transition (MET). Here, we developed a method comprising the miR-200 family and grainyhead-like 2 (GRHL2) to mimic this MET-like phenomenon observed in sarcoma patient samples.We sequentially express GRHL2 and the miR-200 family using cell transduction and transfection, respectively, to better understand the molecular underpinnings of these phenotypic transitions in sarcoma cells. Sarcoma cells expressing miR-200s and GRHL2 demonstrated enhanced epithelial characteristics in cell morphology and alteration of epithelial and mesenchymal biomarkers. Future studies using these methods can be used to better understand the phenotypic consequences of MET-like processes on sarcoma cells, such as migration, invasion, metastatic propensity, and therapy resistance.

Ketamine-induced bladder fibrosis involves epithelial-to-mesenchymal transition mediated by transforming growth factor-β1

Bladder wall fibrosis is a major complication of ketamine-induced cystitis (KC), but the underlying pathogenesis is poorly understood. The aim of the present study was to elucidate the mechanism of ketamine-induced fibrosis in association with epithelial-to-mesenchymal transition (EMT) mediated by transforming growth factor-β1 (TGF-β1). Sprague-Dawley rats were randomly distributed into four groups, which received saline, ketamine, ketamine combined with a TGF-β receptor inhibitor (SB-505124) for 16 wk, or 12 wk of ketamine and 4 wk of abstinence. In addition, the profibrotic effect of ketamine was confirmed in SV-40 immortalized human uroepithelial (SV-HUC-1) cells. The ketamine-treated rats displayed voiding dysfunction and decreased bladder compliance. Bladder fibrosis was accompanied by the appearance of a certain number of cells expressing both epithelial and mesenchymal markers, indicating that epithelial cells might undergo EMT upon ketamine administration. Meanwhile, the expression level of TGF-β1 was significantly upregulated in the urothelium of bladders in ketamine-treated rats. Treatment of SV-HUC-1 cells with ketamine increased the expression of TGF-β1 and EMT-inducing transcription factors, resulting in the downregulation of E-cadherin and upregulation of fibronectin and α-smooth muscle actin. Administration of SB-505124 inhibited EMT and fibrosis both in vitro and vivo. In addition, withdrawal from ketamine did not lead to recovery of bladder urinary function or decreased fibrosis. Taken together, our study shows for the first time that EMT might contribute to bladder fibrosis in KC. TGF-β1 may have an important role in bladder fibrogenesis via an EMT mechanism.

Mesenchymal-Epithelial Transition in Sarcomas Is Controlled by the Combinatorial Expression of MicroRNA 200s and GRHL2

Phenotypic plasticity involves a process in which cells transiently acquire phenotypic traits of another lineage. Two commonly studied types of phenotypic plasticity are epithelial-mesenchymal transition (EMT) and mesenchymal-epithelial transition (MET). In carcinomas, EMT drives invasion and metastatic dissemination, while MET is proposed to play a role in metastatic colonization. Phenotypic plasticity in sarcomas is not well studied; however, there is evidence that a subset of sarcomas undergo an MET-like phenomenon. While the exact mechanisms by which these transitions occur remain largely unknown, it is likely that some of the same master regulators that drive EMT and MET in carcinomas also act in sarcomas. In this study, we combined mathematical models with bench experiments to identify a core regulatory circuit that controls MET in sarcomas. This circuit comprises the microRNA 200 (miR-200) family, ZEB1, and GRHL2. Interestingly, combined expression of miR-200s and GRHL2 further upregulates epithelial genes to induce MET. This effect is phenocopied by downregulation of either ZEB1 or the ZEB1 cofactor, BRG1. In addition, an MET gene expression signature is prognostic for improved overall survival in sarcoma patients. Together, our results suggest that a miR-200, ZEB1, GRHL2 gene regulatory network may drive sarcoma cells to a more epithelial-like state and that this likely has prognostic relevance.

Hepatocyte Nuclear Factor-1β Induces Redifferentiation of Dedifferentiated Tubular Epithelial Cells

Tubular epithelial cells (TECs) can be dedifferentiated by repetitive insults, which activate scar-producing cells generated from interstitial cells such as fibroblasts, leading to the accumulation and deposition of extracellular matrix molecules. The dedifferentiated TECs play a crucial role in the development of renal fibrosis. Therefore, renal fibrosis may be attenuated if dedifferentiated TECs are converted back to their normal state (re-epithelialization). However, the mechanism underlying the re-epithelialization remains to be elucidated. In the present study, TGF-β1, a profibrotic cytokine, induced dedifferentiation of cultured TECs, and the dedifferentiated TECs were re-epithelialized by the removal of TGF-β1 stimulation. In the re-epithelialization process, transcription factor hepatocyte nuclear factor 1, beta (HNF-1β) was identified as a candidate molecule involved in inducing re-epithelialization by means of DNA microarray and biological network analysis. In functional validation studies, the re-epithelialization by TGF-β1 removal was abolished by HNF-1β knockdown. Furthermore, the ectopic expression of HNF-1β in the dedifferentiated TECs induced the re-epithelialization without the inhibition of TGF-β/Smad signaling, even in the presence of TGF-β1 stimulation. In mouse renal fibrosis model, unilateral ureteral obstruction model, HNF-1β expression in the TECs of the kidney was suppressed with fibrosis progression. Furthermore, the HNF-1β downregulated TECs resulted in dedifferentiation, which was characterized by expression of nestin. In conclusion, HNF-1β suppression in TECs is a crucial event for the dedifferentiation of TECs, and the upregulation of HNF-1β in TECs has a potential to restore the dedifferentiated TECs into their normal state, leading to the attenuation of renal fibrosis.

Prevention of trauma-induced cochlear fibrosis using intracochlear application of anti-inflammatory and antiproliferative drugs

Cochlear fibrosis is a common finding following cochlear implantation. Evidence suggests that cochlear fibrosis could be triggered by inflammation and epithelial-to-mesenchymal cell transition (EMT). In this study, we investigate the mechanisms of cochlear fibrosis and the risk/benefit ratio of local administration of the anti-inflammatory drug dexamethasone (DEX) and antimitotic drug aracytine (Ara-C). Cochlear fibrosis was evaluated in cochlear fibrosis models of rat cochlear slices in vitro and in KLH-induced immune labyrinthitis and platinum wire cochlear implantation-induced fibrosis in vivo. Cochleae were invaded with tissue containing fibroblastic cells expressing α-SMA (alpha smooth muscle actin), which along with collagen I, fibronectin, and laminin in the extracellular matrix, suggests the involvement of a fibrotic process triggered by EMT in vitro and in vivo. After perilymphatic injection of an adenoviral vector expressing GFP in vivo, we demonstrated that the fibroblastic cells derived from the mesothelial cells of the scalae tympani and vestibuli. Activation of inflammatory and EMT pathways was further assessed by ELISA analysis of the expression of IL-1β and TGF-β1. Both markers were elevated in vitro and in vivo, and DEX and Ara-C were able to reduce IL-1β and TGF-β1 production. After 5days of culture in vitro, quantification of calcein-positive cells revealed that Ara-C was 30-fold more efficient in preventing fibrosis, and provoked less sensory hair cell loss, than DEX. In KLH-induced immune labyrinthitis and platinum wire-implanted models, Ara-C was more efficient in preventing proliferation of fibrosis with less side effects on hair cells and neurons than DEX. In conclusion, DEX and Ara-C both prevent fibrosis in the cochlea. Analysis of the risk/benefit ratio favors the use of Ara-C for preventing cochlear fibrosis.

Ketamine Increases Permeability and Alters Epithelial Phenotype of Renal Distal Tubular Cells via a GSK-3β-Dependent Mechanism

Ketamine, a dissociative anesthetic, is misused and abused worldwide as an illegal recreational drug. In addition to its neuropathic toxicity, ketamine abuse has numerous effects, including renal failure; however, the underlying mechanism is poorly understood. The process called epithelial phenotypic changes (EPCs) causes the loss of cell-cell adhesion and cell polarity in renal diseases, as well as the acquisition of migratory and invasive properties. Madin-Darby canine kidney cells, an in vitro cell model, were subjected to experimental manipulation to investigate whether ketamine could promote EPCs. Our data showed that ketamine dramatically decreased transepithelial electrical resistance and increased paracellular permeability and junction disruption, which were coupled to decreased levels of apical junctional proteins (ZO-1, occludin, and E-cadherin). Consistent with the downregulation of epithelial markers, the mesenchymal markers N-cadherin, fibronectin, and vimentin were markedly upregulated following ketamine stimulation. Of the E-cadherin repressor complexes tested, the mRNA levels of Snail, Slug, Twist, and ZEB1 were elevated. Moreover, ketamine significantly enhanced migration and invasion. Ketamine-mediated changes were at least partly caused by the inhibition of GSK-3β activity through Ser-9 phosphorylation by the PI3K/Akt pathway. Inhibiting PI3K/Akt with LY294002 reactivated GSK-3β and suppressed ketamine-enhanced permeability, EPCs, and motility. These findings were recapitulated by the inactivation of GSK-3β using the inhibitor 3F8. Taken together, these results provide evidence that ketamine induces renal distal tubular EPCs through the downregulation of several junction proteins, the upregulation of mesenchymal markers, the activation of Akt, and the inactivation of GSK-3β.

A population of mitochondrion-rich cells in the pars recta of mouse kidney

Following perfusion of adult mouse kidney with a solution of nitroblue tetrazolium (NBT), certain epithelial cells in the pars recta (S3) segments of proximal tubules react to form cytoplasmic deposits of blue diformazan particles. Such cells are characterized by dark cytoplasm, small and often elliptical nuclei, elaborate, process-bearing profiles, and abundant mitochondria. The atypical epithelial cells display the additional characteristic of immunoreactivity for a wide spectrum of antigens, including mesenchymal proteins such as vimentin. Though present in kidneys of untreated or sham-operated animals, they are particularly evident under experimental conditions such as unilateral ureteral obstruction (UUO), appearing in both contralateral and obstructed kidneys over the course of a week's duration, but disappearing from the obstructed kidney as it undergoes the profound atrophy attributable to deterioration of the population of its proximal tubules. The cells do not appear in neonatal kidneys, even those undergoing UUO, but begin to be recognizable soon after weaning (28 days). It is possible that diformazan-positive cells in the mouse S3 tubular segment constitute a resident population of cells that can replenish or augment the tubule. Although somewhat similar cells, with dark cytoplasm and vimentin expression, have been described in human, rat, and transgenic mouse kidney (Smeets et al. in J Pathol 229: 645-659, 2013; Berger et al. in Proc Natl Acad Sci U S A 111: 1533-1538, 2014), those cells-known as "scattered tubule cells" or "proximal tubule rare cells"- differ from the S3-specific cells in that they are present throughout the entire proximal tubule, often lack a brush border, and have only a few mitochondria.

Chronic Kidney Disease and Fibrosis: The Role of Uremic Retention Solutes

Chronic kidney disease (CKD) is a major global health concern, and the uremic state is highly associated with fibrogenesis in several organs and tissues. Fibrosis is characterized by excessive production and deposition of extracellular matrix proteins with a detrimental impact on organ function. Another key feature of CKD is the retention and subsequent accumulation of solutes that are normally cleared by the healthy kidney. Several of these uremic retention solutes, including indoxyl sulfate and p-cresyl sulfate, have been suggested to be CKD-specific triggers for the development and perpetuation of fibrosis. The purpose of this brief review is to gather and discuss the current body of evidence linking uremic retention solutes to the fibrotic response during CKD, with a special emphasis on the pathophysiological mechanisms in the kidney.

Cdc42-Interacting Protein 4 Represses E-Cadherin Expression by Promoting β-Catenin Translocation to the Nucleus in Murine Renal Tubular Epithelial Cells

Renal fibrosis is an inevitable outcome of end-stage chronic kidney disease. During this process, epithelial cells lose E-cadherin expression. β-Catenin may act as a mediator by accumulation and translocation to the nucleus. Studies have suggested that CIP4, a Cdc42 effector protein, is associated with β-catenin. However, whether CIP4 contributes to E-cadherin loss in epithelial cells by regulating β-catenin translocation is unclear. In this study, we investigated the involvement of CIP4 in β-catenin translocation. Expression of CIP4 was upregulated in renal tissues of 5/6 nephrectomized rats and mainly distributed in renal tubular epithelia. In TGF-β1-treated NRK-52E cells, upregulation of CIP4 expression was accompanied by reduced expression of E-cadherin. CIP4 overexpression promoted the translocation of β-catenin to the nucleus, which was accompanied by reduced expression of E-cadherin even without TGF-β1 stimulation. In contrast, CIP4 depletion by using siRNA inhibited the translocation of β-catenin to the nucleus and reversed the decrease in expression of E-cadherin. The interaction between CIP4 and β-catenin was detected. We also show that β-catenin depletion could restore the expression of E-cadherin that was suppressed by CIP4 overexpression. In conclusion, these results suggest that CIP4 overexpression represses E-cadherin expression by promoting β-catenin translocation to the nucleus.

Alteration of Fatty Acid Oxidation in Tubular Epithelial Cells: From Acute Kidney Injury to Renal Fibrogenesis

Renal proximal tubular cells are the most energy-demanding cells in the body. The ATP that they use is mostly produced in their mitochondrial and peroxisomal compartments, by the oxidation of fatty acids. When those cells are placed under a biological stress, such as a transient hypoxia, fatty acid oxidation (FAO) is shut down for a period of time that outlasts injury, and carbohydrate oxidation does not take over. Facing those metabolic constraints, surviving tubular epithelial cells exhibit a phenotypic switch that includes cytoskeletal rearrangement and production of extracellular matrix proteins, most probably contributing to acute kidney injury-induced renal fibrogenesis, thence to the development of chronic kidney disease. Here, we review experimental evidence that dysregulation of FAO profoundly affects the fate of tubular epithelial cells, by promoting epithelial-to-mesenchymal transition, inflammation, and eventually interstitial fibrosis. Restoring physiological production of energy is undoubtedly a possible therapeutic approach to unlock the mesenchymal reprograming of tubular epithelial cells in the kidney. In this respect, the benefit of the use of fibrates is uncertain, but new drugs that could specifically target this metabolic pathway, and, hopefully, attenuate renal fibrosis merit future research.

[MicroRNAs in kidney fibrosis]

Renal fibrosis represents the final stage of most chronic kidney diseases and contributes to the progressive and irreversible decline in kidney function with accumulation of extracellular matrix components in the renal parenchyma. The molecular mechanisms governing the renal fibrosis process are complex and remain poorly understood. Recently, the profibrotic role of several microRNAs (miRNAs) has been described in kidney fibrosis. MiRNAs are a new class of, small non-coding RNAs of about 20 nucleotides that act as gene expression negative regulators at the post-transcriptional level. Seminal studies have highlighted the potential importance of miRNA as new therapeutic targets and innovative diagnostic and/or prognostic biomarkers. This review summarizes recent scientific advances on the role played by miRNAs in kidney fibrogenesis and discusses potential clinical applications as well as future research directions.

Cellular and Molecular Mechanisms of Chronic Kidney Disease with Diabetes Mellitus and Cardiovascular Diseases as Its Comorbidities

Chronic kidney disease (CKD), diabetes mellitus (DM), and cardiovascular diseases (CVD) are complex disorders of partly unknown genesis and mostly known progression factors. CVD and DM are the risk factors of CKD and are strongly intertwined since DM can lead to both CKD and/or CVD, and CVD can lead to kidney disease. In recent years, our knowledge of CKD, DM, and CVD has been expanded and several important experimental, clinical, and epidemiological associations have been reported. The tight cellular and molecular interactions between the renal, diabetic, and cardiovascular systems in acute or chronic disease settings are becoming increasingly evident. However, the (patho-) physiological basis of the interactions of CKD, DM, and CVD with involvement of multiple endogenous and environmental factors is highly complex and our knowledge is still at its infancy. Not only single pathways and mediators of progression of these diseases have to be considered in these processes but also the mutual interactions of these factors are essential. The recent advances in proteomics and integrative analysis technologies have allowed rapid progress in analyzing complex disorders and clearly show the opportunity for new efficient and specific therapies. More than a dozen pathways have been identified so far, including hyperactivity of the renin–angiotensin (RAS)–aldosterone system, osmotic sodium retention, endothelial dysfunction, dyslipidemia, RAS/RAF/extracellular-signal-regulated kinase pathway, modification of the purinergic system, phosphatidylinositol 3-kinase (PI 3-kinase)-dependent signaling pathways, and inflammation, all leading to histomorphological alterations of the kidney and vessels of diabetic and non-diabetic patients. Since a better understanding of the common cellular and molecular mechanisms of these diseases may be a key to successful identification of new therapeutic targets, we review in this paper the current literature about cellular and molecular mechanisms of CKD.

Hepatocyte fate upon TGF-β challenge is determined by the matrix environment

Primary hepatocytes are a versatile tool to investigate all aspects of liver function, and frequently used in drug development and testing. Upon TGF-β challenge, hepatocytes either undergo an epithelial to mesenchymal transition (EMT) or apoptosis: culture on stiff collagen (monolayer) results in EMT whereas hepatocytes in a soft collagen matrix (sandwich) undergo programmed cell death. In this study, we analyzed the transcriptional programs triggered by TGF-β under different culture conditions. Our results indicate that TGF-β initiates an identical transcription profile in hepatocytes irrespective of the cellular environment. The fact that we nevertheless observe two vastly different phenotypes indicates that the matrix environment rather than the TGF-β induced expression signature is the major determinant of the hepatocellular response. To confirm the impact of the surrounding matrix environment on the hepatocytes׳ phenotype in response to TGF-β signaling, we studied the effect of Snail overexpression and knockout in both culture conditions. Neither genetic manipulation showed an impact on hepatocytes' fate upon TGF-β treatment, confirming the crucial role of the surrounding matrix. Our findings provide novel insights into the hepatocellular basis of the fate decision between EMT and apoptotic cell death, and might explain why liver cells can react in very different manners to identical stimuli when tissue remodeling has changed the matrix environment, as occurs in a fibrotic liver.

Diverse origins of the myofibroblast—implications for kidney fibrosis

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

Egr-1 mediates chronic hypoxia-induced renal interstitial fibrosis via the PKC/ERK pathway

BACKGROUND

Chronic hypoxia-induced epithelial-to-mesenchymal transition (EMT) is a crucial process in renal fibrogenesis. Egr-1, as a transcription factor, has been proven to be important in promoting EMT. However, whether it functions in hypoxia-induced renal tubular EMT has not been fully elucidated.

METHODS

Egr-1 were detected at mRNA and protein levels by qPCR and Western blot analysis respectively after renal epithelial cells were subjected to hypoxia treatment. Meanwhile, EMT phenotype was also observed through identification of relevant EMT-specific markers. siRNA was used to knock down Egr-1 expression and subsequent changes were observed. Specific PKC and MAPK/ERK inhibitors were employed to determine the molecular signaling pathway involved in Egr-1-mediated EMT phenotype. In vivo assays using rat remnant kidney model were used to validate the in vitro results. Furthermore, Egr-1 expression was examined in the samples of CKD patients with the clinical relevance revealed.

RESULTS

Hypoxia treatment enhanced the mRNA and protein levels of Egr-1 in HK-2 cells, which was accompanied by a reduced expression of the epithelial marker E-cadherin and an enhanced expression of the mesenchymal marker Fsp-1. Downregulation of Egr-1 with siRNA reversed hypoxia-induced EMT. Using the specific inhibitors to protein kinase C (calphostin C) or MAPK/ERK (PD98059), we identified that hypoxia induced Egr-1 expression through the PKC/ERK pathway. In addition, the upregulation of Egr-1 raised endogenous Snail levels, and the downregulation of Snail inhibited Egr-1-mediated EMT in HK-2 cells. Through in vivo assays using rat remnant kidney and CKD patients' kidney tissues, we found that Egr-1 and Snail were overexpressed in tubular epithelial cells with EMT.

CONCLUSION

Egr-1 may be an important regulator of the development of renal tubular EMT induced by hypoxia through the PKC/ERK pathway and the activation of Snail. Targeting Egr-1 expression or activity might be a novel therapeutic strategy to control renal fibrosis.