Long noncoding RNA NEAT1 is involved in the protective effect of Klotho on renal tubular epithelial cells in diabetic kidney disease through the ERK1/2 signaling pathway.

Klotho, an antiaging protein, has been shown to play a protective role in renal tubular epithelial-mesenchymal transition (EMT) during the development of diabetic kidney disease (DKD). Long noncoding RNAs (lncRNAs) participate in the progression of EMT in many diseases. However, the effect of Klotho on lncRNAs during the development of DKD is still unknown. In this study, we found that Klotho overexpression in high-fat diet (HFD)- and streptozotocin (STZ)-induced DKD mice significantly inhibited the expression of lncRNA nuclear-enriched abundant transcript 1 (Neat1). We demonstrated that NEAT1 was significantly upregulated in both bovine serum albumin (BSA)-stimulated HK2 cells and mice with HFD- and STZ-induced diabetes. In addition, we observed that Klotho displays colocalization with NEAT1. Furthermore, overexpression of Klotho can inhibit the high expression of NEAT1 in BSA-stimulated HK2 cells, while silencing Klotho can further upregulate the expression of NEAT1. Silencing NEAT1 in HK2 cells resulted in inhibition of the EMT-related markers alpha smooth muscle actin (α-SMA) and vimentin (VIM) and the renal fibrosis-related markers transforming growth factor-ß1 (TGF-ß1) and connective tissue growth factor (CTGF). The effect of NEAT1 on DKD was partly mediated by regulation of the ERK1/2 signaling pathway. Finally, we found that silencing NEAT1 can reverse the activation of EMT and fibrosis caused by Klotho silencing in a manner dependent on the ERK1/2 signaling pathway. These findings reveal a new regulatory pathway by which Klotho regulates ERK1/2 signaling via NEAT1 to protect against EMT and renal fibrosis, suggesting that NEAT1 is a potential therapeutic target for DKD.

LncRNA GAS5 exacerbates renal tubular epithelial fibrosis by acting as a competing endogenous RNA of miR-96-5p.

Renal fibrosis is at the core of various renal diseases, including diabetic kidney disease (DKD). Long noncoding RNAs (lncRNAs) are known players in the regulation of renal fibrosis. However, their expression and function in DKD still need to be elucidated. The purpose of this study was to assess how lncRNA GAS5 regulates fibrosis and its mechanism in TGF-ß1-treated renal proximal tubular cell.In this study, the lncRNA GAS5 was upregulated in both TGF-ß1-treated HK-2 cells and the kidneys of HDF/STZ mice. Knockdown of GAS5 relieved renal tubular epithelial fibrosis. This effect was mediated by the downregulation and functional inactivation of miR-96-5p. Furthermore, miR-96-5p was downregulated in DKD mice, and this downregulation attenuated the repression of FN1(fibronectin, FN) and led to its upregulation. The decrease in miR-96-5p was partially attributed to the miRNA-sponge action of GAS5.Our research demonstrates that knockdown of lncRNA GAS5 leads to antifibrosis by competitively binding miR-96-5p, which inhibits the expression of FN1. These results indicate that targeting lncRNA GAS5 may be a promising therapeutic strategy for preventing DKD.

Early growth response protein-1 upregulates long noncoding RNA Arid2-IR to promote extracellular matrix production in diabetic kidney disease.

Diabetic kidney disease (DKD) has surpassed chronic glomerulonephritis as the leading cause of end-stage renal disease. Previously, we showed that early growth response protein-1 (Egr1) plays a key role in DKD by enhancing mesangial cell proliferation and extracellular matrix (ECM) production. The long noncoding RNA (lncRNA) AT-rich interactive domain 2-IR (Arid2-IR) has been identified as a mothers against decapentaplegic homolog 3 (Smad3)-associated lncRNA in unilateral ureteral obstructive kidney disease. However, the effect of Egr1 on Arid2-IR in the development of DKD is still unknown. In this study, we found that Arid2-IR was increased in mice with high-fat diet and streptozotocin-induced type 2 diabetes and in mouse mesangial cells cultured with high glucose to mimic diabetes. Knockdown of Arid2-IR in mouse mesangial cells reduced the high expression levels of collagen-α1(I) (Col1a1) and α-smooth muscle actin (α-SMA) induced by high glucose. Furthermore, Arid2-IR expression changed the increased expression of Col1a1 and α-SMA caused by overexpression of Egr1. Overall, these data suggest that increased Arid2-IR likely contributes to ECM production in DKD and that Egr1 promotes ECM production in DKD partly by upregulating Arid2-IR. Thus, Arid2-IR may be a new target in the treatment of DKD.

Early Growth Response 1 (Egr1) Is a Transcriptional Activator of NOX4 in Oxidative Stress of Diabetic Kidney Disease.

BACKGROUND: NADPH oxidase 4 (NOX4) plays a major role in renal oxidative stress of diabetic kidney disease (DKD). NOX4 was significantly increased in Egr1-expressing fibroblasts, but the relationship between Egr1 and NOX4 in DKD is unclear. METHODS: For the evaluation of the potential relationship between Egr1 and NOX4, both were detected in HFD/STZ-induced mice and HK-2 cells treated with TGF-ß1. Then, changes in NOX4 expression were detected in HK-2 cells and mice with overexpression and knockdown of Egr1. The direct relationship between Egr1 and NOX4 was explored via chromatin immunoprecipitation (ChIP). RESULTS: We found increased levels of Egr1, NOX4, and α-SMA in the kidney cortices of diabetic mice and in TGF-ß1-treated HK-2 cells. Overexpression or silencing of Egr1 in HK-2 cells could upregulate or downregulate NOX4 and α-SMA. ChIP assays revealed that TGF-ß1 induced Egr1 to bind to the NOX4 promoter. Finally, Egr1 overexpression or knockdown in diabetic mice could upregulate or downregulate the expression of NOX4 and ROS, and α-SMA was also changed. CONCLUSION: Our study provides strong evidence that Egr1 is a transcriptional activator of NOX4 in oxidative stress of DKD. Egr1 contributes to DKD by enhancing EMT, in part by targeting NOX4.

Role of p53/miR-155-5p/sirt1 loop in renal tubular injury of diabetic kidney disease.

BACKGROUND: Diabetic kidney disease is a renal microvascular disease caused by diabetes, known as one of the most serious and lethal complications of diabetes. Early renal hypertrophy is the main pathological feature, which gradually leads to the deposition of glomerular extracellular matrix and tubulointerstitial fibrosis, eventually developing irreversible structural damage to the kidneys. Autophagy is a cell self-homeostatic mechanism that is activated under stress conditions and may serve as a protective response to the survival of renal fibrogenic cells. MicroRNA (miRNA) network may be involved in the regulation of fibrosis. The purpose of this study is to assess how miRNAs regulate diabetic kidney disease and autophagy and fibrosis in renal proximal tubular cells under high glucose conditions. METHODS: Human renal proximal tubular (HK-2) cells were exposed to high glucose in vitro. Bioinformatic analysis was used to select the candidate gene for potential target regulation of miR-155, Sirt1. ATG5, ATG7 is the key to autophagosome formation, regulated by Sirt1. p53 regulates miR-155 expression as a transcription factor. MiR-155 overexpression and inhibition were achieved by transfection of miR-155 mimic and inhibit to evaluate its effect on Sirt1 and autophagy and fibrosis markers. Dual luciferase reporter assays were used to confirm the direct interaction of Sirt1 with miR-155. Overexpression and inhibition of Sirt1 gene were achieved by transfection of Sirt1 plasmid and Sirt1 si to observe its effect on P53. Chip assay experiments confirmed the direct regulation of P53 on miR-155. RESULTS: Under high glucose conditions, miR-155 was detected in HK-2 cells in concentration gradient, increased expression of p53 and down-regulated expression of sirt1 and autophagy-associated proteins LC3II, ATG5 and ATG7. Dual luciferase reporter assays indicate that miR-155 can target its binding to the Sirt1 3'UTR region to reduce its expression. Under high glucose conditions, over expression of miR-155 decreased the expression of LC3-II and ATG5 in HK-2 cells, while inhibition of miR-155 reversed this effect. Using chip assay testing in HK-2 cells, we demonstrated that p53 binds directly to miR-155. CONCLUSIONS: The signaling axis of p53, miR-155-5p, and sirt1 in autophagic process might be a critical adapting mechanism for diabetic kidney injury.

High glucose up-regulates microRNA-34a-5p to aggravate fibrosis by targeting SIRT1 in HK-2 cells.

Tubulointerstitial fibrosis (TIF) is crucial in the development of renal fibrosis in diabetic nephropathy(DN). Previous data shows that SIRT1 plays an important role on fibrosis, but the effect on TIF in DN and underlying mechanisms remains uncertain. In this study, we evaluated the vital role of SIRT1 and identified SIRT1 as a downstream target gene of microRNA-34a-5p (miR-34a-5p) in TIF of DN. The result revealed that expression of miR-34a-5p, fibronectin(FN),collagen type I (COL1) and transforming growth factor ß1 (TGF-ß1) were up-regulated accompanied by the corresponding down-regulation of SIRT1 in renal tissues of high fat diet and streptozotocin(HFD/STZ)induced diabetic mice with DN, and that the SIRT1 mRNA level was negatively correlated with miR-34a-5p expression in high glucose stimulated human proximal tubule cell line(HK-2) cells. We then demonstrated that overexpression of SIRT1 reduced, whereas small interfering RNA targeting SIRT1 enhanced the expressions of TGF-ß1 and fibrosis-related genes including FN and COL1 in HK-2 cells. Furthermore, we identified that miR-34a-5p directly suppressed SIRT1 to increase the profibrogenic effects of TGFß1 through targeting the 3'untranslated region of SIRT1. The functional correlation of miR-34a-5p induced SIRT1 decrease was supported by overexpression and inhibition of miR-34a-5p in HK-2 cells. All the results reveal that SIRT1 which is vital in the evolution of renal TIF in DN can be directly suppressed by miR-34a-5p, and suggest that miR-34a-5p is a new target for DN treatment.

Klotho down-regulates Egr-1 by inhibiting TGF-ß1/Smad3 signaling in high glucose treated human mesangial cells.

Diabetic kidney disease (DKD) has become the leading cause of end-stage renal disease worldwide and is associated with glomerular mesangial cell (MC) proliferation and excessive extracellular matrix (ECM) production. Klotho can attenuate renal fibrosis in part by inhibiting TGF-ß1/Smad3 signaling in DKD. Early growth response factor 1 (Egr-1) has been shown to play a key role in renal fibrosis in part by facilitating the formation of a positive feedback loop involving TGF-ß1. However, whether Klotho down-regulates Egr-1 by inhibiting TGF-ß1/Smad3 signaling in DKD is unclear. In the present study, we assessed human MCs that were incubated under high-glucose conditions to mimic diabetes. Then, we transfected the cells with Klotho plasmid or siRNA to overexpress or knock down Klotho gene and protein expression. Klotho, Egr-1, fibronectin (FN), collagen type I (Col I), Smad3 and phosphorylated Smad3 (p-Smad3) gene and protein expression levels were determined by RT-qPCR and western blotting respectively. High glucose time-dependently down-regulated Klotho mRNA and protein expression in cultured human MCs. pcDNA3.1-Klotho transfection-mediated Klotho overexpression down-regulated Egr-1, FN and Col I expression and the p-Smad3/Smad3 ratio in human MCs. Conversely, siRNA-mediated Klotho silencing up-regulated Egr-1, FN, and Col I expression and the p-Smad3/Smad3 ratio. Moreover, the effects of si-Klotho on Egr-1 expression were abolished by the TGF-ß1 inhibitor SB-431542. Klotho overexpression can prevent mesangial ECM production in high-glucose-treated human MCs, an effect that has been partially attributed to Egr-1 down-regulation facilitated by TGF-ß1/Smad3 signaling inhibition.

High glucose down-regulates microRNA-181a-5p to increase pro-fibrotic gene expression by targeting early growth response factor 1 in HK-2 cells.

Tubulointerstitial fibrosis (TIF) plays an important role in the progression of renal fibrosis in diabetic nephropathy (DN). Accumulating evidence supports a crucial effect of early growth response factor 1 (Egr1) on renal fibrosis in DN, but the underlying mechanisms are not entirely clear. Here, we explored the aggravating role of Egr1 and identified microRNA-181a-5p (miR-181a-5p) as an upstream regulator of Egr1 in TIF of DN. We demonstrated that overexpression of Egr1 enhanced, whereas small interfering RNA targeting Egr1 decreased the expressions of transforming growth factor ß1 (TGF-ß1) and fibrosis-related genes including fibronectin and collagen I in human proximal tubule cell line (HK-2) cells. We then found that miR-181a-5p expression was down-regulated, accompanied by the corresponding up-regulation of Egr1, TGF-ß1, fibronectin and collagen I in renal tissues of type 2 diabetic Otsuka-Long-Evans-Tokushima-Fatty rats with DN, and that the expression of miR-181a-5p was negatively correlated with the level of Egr1 in HK-2 cells treated with high glucose. Furthermore, we identified that miR-181a-5p directly suppressed Egr1 to decrease the expressions of TGF-ß1, fibronectin and collagen I in HK-2 cells through targeting the 3' untranslated region of Egr1. The functional relevance of miR-181a-5p-induced Egr1 decrease was supported by inhibition and overexpression of miR-181a-5p in HK-2 cells. Thus, we concluded that aberrant Egr1 expression, which can be suppressed by miR-181a-5p directly, plays a crucial role in the progression of renal TIF in DN. This study indicates that targeting miR-181a-5p may be a novel therapeutic approach of DN.

Let-7d miRNA prevents TGF-ß1-induced EMT and renal fibrogenesis through regulation of HMGA2 expression.

TGF-ß1-induced epithelial to mesenchymal transition (EMT) process of tubular epithelial cells plays a leading role in the occurrence and progression of renal fibrosis as seen in diabetic nephropathy (DN). High mobility group AT-hook 2 (HMGA2) is considered to be involved in TGF-ß1-mediated EMT via multifactorial mechanisms. Specific microRNAs (miRNAs) are closely associated with EMT, and here we focused on let-7d miRNA as a regulator of HMGA2. This study aims to investigate the effects of HMGA2 on EMT process induced by TGF-ß1 using small interfering RNA (siRNA) technique in vitro, and further explore the potential role of let-7d miRNA during renal fibrosis in DN. We demonstrated that siRNA targeting HMGA2 was sufficient to inhibit TGF-ß1-induced EMT and fibrogenesis in rat kidney tubular epithelial cells (NRK52E). Furthermore, let-7d expression was significantly reduced by TGF-ß1 stimulation, we focused on let-7d and found that overexpression of let-7d down-regulated the expression of HMGA2 and in turn suppressed TGF-ß1-induced EMT and renal fibrogenesis. Inhibition of let-7d increased HMGA2 expression and enhanced the profibrogenic effects of TGF-ß1 on NRK-52E cells. Consistent with the above observations in vitro, let-7d expression was also decreased in the kidneys of unilateral ureter obstruction model, accompanied by the correspondingly increased expression of HMGA2 and fibrotic genes in this model. Collectively, HMGA2 and let-7d miRNA significantly impact on the progression of TGF-ß1-induced EMT and fibrogenesis both in vitro and in vivo, and they may represent novel targets for the prevention strategies of renal fibrosis in the context of DN.

[Effects of exendin-4 on extracellular matrix metabolism in human mesangial cells cultured in high glucose].

OBJECTIVE: To explore effects of exendin-4 on the metabolism of extracellular matrix (ECM) in human mesangial cells (HMC) cultured in the presence of high glucose and explore the possible mechanism. METHODS: Human mesangial cells (HMC) were treated with exendin-4 under high glucose conditions. The cell proliferation was observed using CCK8 assay, and the expressions of collagen type I, fibronectin, transforming growth factor-ß1 (TGFß1) expression and extracellular signal- regulated kinase (ERK) signaling pathway activity were assessed using Western blotting. RESULTS: Exendin-4 inhibited cell proliferation and the expressions of collagen type I, fibronectin and TGFß1 and reversed ERK phosphorylation in high glucose-induced HMC. CONCLUSION: Exendin-4 can regulate ECM metabolism in HMC cultured in high glucose by inhibiting TGFß1/ERK pathway, suggesting the beneficial effects of exendin-4 in preventing and treating diabetic nephropathy.

Transcription Factor Egr1 is Involved in High Glucose-Induced Proliferation and Fibrosis in Rat Glomerular Mesangial Cells.

UNLABELLED: Backgroud: Diabetic nephropathy is one of the most frequent causes of end-stage renal disease and is associated with proliferation of glomerular mesangial cells (MCs) and excessive production of the extracellular matrix (ECM). Several studies have shown that early growth response factor 1 (Egr1) plays a key role in renal fibrosis by regulating the expression of genes encoding ECM components. However, whether Egr1 also contributes to diabetic nephropathy is unclear. METHODS: In the present study, we compared the expression of Egr1 in kidneys from OLETF rats with spontaneous type 2 diabetes and healthy LETO rats. We also examined whether high glucose and TGF-ß1 signaling up-regulated Egr1 expression in cultured MCs, and whether Egr1 expression influenced MC proliferation and expression of ECM genes. RESULTS: We found that higher expression of Egr1 and TGF-ß1, at both the mRNA and protein levels, the kidneys from OLETF rats vs. LETO rats. High glucose or TGF-ß1 signaling rapidly up-regulated expression of Egr1 mRNA and protein in cultured MCs. Overexpressing Egr1 in MCs by transfection with M61-Egr1 plasmid or treatment with high glucose up-regulated expression of fibronectin, type IV collagen and TGF-ß1, and promoted MC proliferation. Conversely, siRNA-mediated silencing of Egr1 expression down-regulated these genes and inhibited MC proliferation. Chromatin immunoprecipitation (ChIP) assays revealed that Egr1 bound to the TGF-ß1 promoter. CONCLUSION: Our results provide strong evidence that Egr1 contributes to diabetic nephropathy by enhancing MC proliferation and ECM production, in part by interacting with TGF-ß1.

Exendin-4 alleviates high glucose-induced rat mesangial cell dysfunction through the AMPK pathway.

BACKGROUND/AIMS: Glucagon-like peptide-1 (GLP-1), which counteracts insulin resistance in humans with type 2 diabetes, has been shown to ameliorate diabetic nephropathy in experimental models. However, the mechanisms through which GLP-1 modulates renal function remained illdefined. The present study investigated the putative mechanisms underlying effects of exendin-4, a GLP-1 analog, on mesangial cell proliferation and fibronectin. METHODS: Rat mesangial cells (MCs) were treated with exendin-4 under high glucose conditions. AMP-activated protein kinase (AMPK) inhibitors (compound C) and agonists (AICAR) were used to analyze the role of this kinase. Cell proliferation was measured using a MTT assay. Fibronectin expression and AMPK-signaling pathway activity were assessed using ELISA and Western blotting, respectively. The production of matrix metalloproteinase (MMP)-2 and tissue inhibitors of metalloproteinases (TIMP)-2 was evaluated using quantitative real-time RT-PCR. RESULTS: Exendin-4 inhibited cell proliferation and fibronectin secretion in high glucose-induced MCs. It also caused phosphorylation of AMPK and subsequently increased the ratio of MMP-2 to TIMP-2, which resulted in the degradation of fibronectin. Exendin-4 reversed extracellular signal-regulated kinase (ERK) phosphorylation and enhanced expression of mammalian target of rapamycin (mTOR) in MCs. Moreover, the activation of the AMPK pathway by exendin-4 was induced by AICAR, which was inhibited by compound C. CONCLUSION: Exendin-4 exerts an inhibitory effect on cell proliferation and fibronectin secretion in rat MCs, partly through AMPK activation. These results may explain some of the beneficial effects of exendin-4 on the kidney.