Proximal Tubular Cell Line HK-2 Research Articles

Hsa_circ_0010957 knockdown attenuates lipopolysaccharide-induced HK2 cell injury by regulating the miR-1224-5p/IRAK1 axis.

Circular RNAs (circRNAs) are involved in the progression of various diseases, including lupus nephritis. Hsa_circ_0010957 is reported to be dysregulated in lupus nephritis, but the exact function of this circRNA is unknown. This research aims to study the function and mechanism of circRNA hsa_circ_0010957 in a lipopolysaccharide (LPS)-induced cellular model of lupus nephritis. Human renal proximal tubular cell line HK2 cells were challenged by LPS. Hsa_circ_0010957, microRNA-1224-5p (miR-1224-5p), and interleukin-1 receptor-associated kinase 1 (IRAK1) abundances were examined by quantitative reverse transcription polymerase chain reaction or western blot. LPS-induced damage was evaluated via cell viability, apoptosis, inflammatory response and oxidative injury. The target interaction was analyzed by dual-luciferase reporter analysis and RNA immunoprecipitation. Hsa_circ_0010957 abundance was enhanced in LPS-challenged HK2 cells. Hsa_circ_0010957 knockdown alleviated LPS-induced apoptosis, the inflammatory response and oxidative injury in HK2 cells. MiR-1224-5p was targeted by hsa_circ_0010957, and miR-1224-5p knockdown reversed the influence of hsa_circ_0010957 silence on LPS-induced injury. IRAK1 was targeted via miR-1224-5p, and hsa_circ_0010957 could regulate IRAK1 by miR-1224-5p. MiR-1224-5p overexpression could mitigate LPS-induced apoptosis, the inflammatory response and oxidative injury, and this effect was abolished by IRAK1. Hsa_circ_0010957 silence weakened LPS-induced HK2 cell apoptosis, the inflammatory response and oxidative injury via regulating the miR-1224-5p/IRAK1 axis.

Dysregulated ion channels and transporters activate endoplasmic reticulum stress in rat kidney of fetal growth restriction

AimsThe mechanisms underlying the fetal origin of renal disease remains unknown. This study aimed to investigate the profiles of ion channel and transporter proteins in the fetal kidney in fetal growth restriction (FGR)rats, and to explore their association with the fetal origin of renal disease. Main methodsAn FGR rat model was developed by administration of a low-protein diet. Then 367 differentially expressed proteins (DEPs) from quantitative proteome analysis were subjected to Ingenuity Pathway Analysis. 22 DEPs associated with ion channels/transporters were evaluated in the fetal kidney. Na+/H+ exchanger1(NHE1) and its downstream unfolded protein response (UPR) pathway were investigated. Furthermore, overexpression of NHE1 were achieved via plasmid transfection to evaluate the potential influence on the UPR pathway and cell apoptosis in human proximal tubular epithelial cell line HK2 cells. Key findingsFindings were as follows: 1) In the FGR fetal kidney, aquaporin 2/4, solute carrier (SLC) 8a1, 33a1, etc. were downregulated, whereas other transporters including SLC 2a1, 4a1, 9a1, 29a3, etc. were upregulated. 2) NHE1 mRNA levels were markedly elevated in the FGR fetus. Further investigation revealed an increase in the UPR pathway regulators. 3) In vitro study showed that NHE1 overexpression in HK2 cells significantly induced expression of the endoplasmic reticulum stress (ERS) regulators and led to a decrease in the anti-apoptotic potential. SignificanceWe speculate that maternal protein malnutrition causes dysregulation of ion channels/transporters in the fetal kidney. Upregulated NHE1 may activate the UPR pathway and induce cell apoptosis thus leading to impairment of kidney function.

Fatty acids bound to albumin induce prostaglandin E2 production in human renal proximal tubular epithelial cell line HK-2

Fatty acids bound to albumin have been reported to be involved in various responses in renal proximal tubular cells following albumin overload, leading to progression of tubulointerstitial damage in the kidneys. In addition, it has been reported that prostaglandin E2 (PGE2) plays an important role in nephrotoxicity. The aim of this study was to examine whether albumin-bound fatty acids induce PGE2 production in human renal proximal tubular epithelial cell line HK-2. Fatty acid-bearing human serum albumin increased PGE2 release in the culture medium in concentration-dependent and time-dependent manners, but fatty acid-depleted albumin had no effect on PGE2 production. Next, we investigated the effect of arachidonic acid, a precursor of eicosanoids, on PGE2 production. Arachidonic acid with fatty acid-free albumin significantly enhanced the release of PGE2 into the medium in a concentration-dependent manner. Furthermore, we examined the effect of arachidonic acid on mRNA expression of hypoxia inducible factor-1α (HIF-1α). Arachidonic acid increased HIF-1α mRNA expression in a concentration-dependent manner. These findings suggest that fatty acids, at least in part arachidonic acid, bound to albumin increase PGE2 production and expression of HIF-1α mRNA and protein, possibly resulting in various cell responses induced by albumin overload.

MO069HIF-1Α C-TERMINAL TRANSCRIPTIONAL ACTIVATION DOMAIN MEDIATED KLF5 SIGNALING DRIVES AKI TO CKD PROGRESSION

Abstract Background and Aims Acute kidney injury (AKI) is increasingly recognized as a major risk factor for progression to CKD. However, the mechanisms governing AKI to CKD progression are poorly understood. Hypoxia is a key player in the pathophysiology of the AKI to CKD transition. Thus, we aimed to investigate the exact mechanisms of AKI to CKD progression mediated by hypoxia. Method Mild ischemic injury and severe ischemic injury (AKI-to-CKD transition) were established by clamping renal pedicle for 30 and 40 minutes, respectively. Meanwhile, the mice model of AKI-to-CKD transition was treated with HIF-1α inhibitor, PX-478. In vitro, PHD inhibition and combined PHD with FIH inhibition mimic the HIF-1α activation caused by mild or severe hypoxia, respectively. Besides the human proximal tubular epithelial cell line HK-2, tubular cells were isolated from mice for primary culture. KLF5 knockdown, FIH and HIF-1α C-terminal transcriptional activation domain (C-TAD) overexpression in tubular cells were achieved by Lentiviral transfection. Immunocoprecipitation was used to explore the relationship between the HIF-1α and FIH-1. Luciferase reporter assay was used to investigate whether KLF5 was regulated transcriptionally by HIF-1α C-TAD. To explore the roles of FIH-1 and HIF-1α C-TAD in vivo, FIH-1 and HIF-1α C-TAD overexpression (Lentivirus-mediated) was given after severe ischemic injury or mild ischemic injury via tail vein injection, respectively. Results AKI to CKD progression was highly associated with the time-course expression of tubular HIF-1α in severe ischemia/reperfusion injury. Interestingly, ameliorated AKI-to-CKD transition was observed by treating PX-478, which destabilized HIF-1α. In vitro, fibrogenesis could be induced by combined PHD with FIH inhibitor treatment in TEC. More interestingly, alleviated fibrogenesis could be achieved by knockdown of KLF5 and overexpression of FIH, respectively, while HIF-1α C-TAD overexpression promoted fibrogenesis in tubular cells. Immunocoprecipitation results indicated that HIF-1α and FIH-1 are interactive. Furthermore, we demonstrated that KLF5 could be regulated transcriptionally by HIF-1α C-TAD by luciferase reporter assay. In vivo, AKI to CKD progression was ameliorated significantly when mice model of AKI-to-CKD transition intervened with FIH-1 overexpression (Lentivirus-mediated). However, treatment of HIF-1α C-TAD (Lentivirus-mediated) in mild ischemic injury model could promote progression of CKD significantly. Conclusion FIH-1 mediated HIF-1α C-TAD activation was the key mechanism of AKI to CKD transition by transcriptionally regulating the KLF5 pathway in tubules. Blockade of FIH-1 mediated HIF-1α C-TAD in tubules may serve as a novel therapeutic approach to ameliorate AKI to CKD progression.

Expression and pathophysiological significance of carbohydrate response element binding protein (ChREBP) in the renal tubules of diabetic kidney.

Carbohydrate response element binding protein (ChREBP), a glucose responsive transcription factor, mainly regulates expression of genes involved in glucose metabolism and lipogenesis. Recently, ChREBP is speculated to be involved in the onset and progression of diabetic nephropathy (DN). However, there exists no report regarding the localization and function of ChREBP in the kidney. Therefore, we analyzed the localization of Chrebp mRNA expression in the wild type (WT) mice kidney using laser microdissection method, and observed its dominant expression in the proximal tubules. In diabetic mice, mRNA expression of Chrebp target genes in the proximal tubules, including Chrebpβ and thioredoxin-interacting protein (Txnip), significantly increased comparing with that of WT mice. Co-overexpression of ChREBP and its partner Mlx, in the absence of glucose, also increased TXNIP mRNA expression as well as high glucose in human proximal tubular epithelial cell line HK-2. Since TXNIP is well known to be involved in the production of reactive oxygen species (ROS), we next examined the effect of ChREBP/Mlx co-overexpression, in the absence of glucose, on ROS production in HK-2 cells. Interestingly, ChREBP/Mlx co-overexpression also induced ROS production significantly as well as high glucose. Moreover, both high glucose-induced increase of TXNIP mRNA expression and ROS production were abrogated by ChREBP small interfering RNA transfection. Taken together, high glucose-activated ChREBP in the renal proximal tubules induce the expression of TXNIP mRNA, resulting in the production of ROS which may cause renal tubular damage. It is therefore speculated that ChREBP is involved in the onset and progression of DN.

Micro RNA-30b (inhibitor) nanoparticles suppressed the lipopolysaccharide (LPS)-induced acute kidney injury.

The main aim of present study is to evaluate the effect of miR-30b on the function of human proximal tubular epithelial cell line HK-2 cells. For this purpose, miRNA was loaded in an ionically cross-linked polysaccharide nanoparticle. The authors have demonstrated the influence of miR-30b mimic and inhibitor in HK-2 cell killing effect. Lipopolysaccharide (LPS) significantly increased the level of inflammatory cytokines of TNF-α, IL-1β and level was further increased with the treatment of PAg-miR mimic consistent with the cell viability assay. Interestingly, PAg-miR inhibitor significantly downregulated the expression of inflammatory cytokines and thereby reduced the inflammation in the body. Western blot analysis showed that LPS induced severe apoptosis of HK-2 cells and the apoptosis was further promoted by the PAg-miR (mimic). In contrast, PAg-miR (inhibitor) alleviated the apoptosis of HK-2 cells as indicated in the significantly reduced levels of Bax and c-Caspase-3 proteins. Overall, miR-30b promoted LPS-induced HK-2 cell inflammatory injury by inducing the apoptosis and by releasing inflammatory cytokines, as well as by impairing autophagy process.

Empagliflozin Protects HK-2 Cells from High Glucose-Mediated Injuries via a Mitochondrial Mechanism.

Empagliflozin is known to retard the progression of kidney disease in diabetic patients. However, the underlying mechanism is incompletely understood. High glucose induces oxidative stress in renal tubules, eventually leading to mitochondrial damage. Here, we investigated whether empagliflozin exhibits protective functions in renal tubules via a mitochondrial mechanism. We used human proximal tubular cell (PTC) line HK-2 and employed western blotting, terminal deoxynucleotidyl transferase dUTP nick end labelling assay, fluorescence staining, flow cytometry, and enzyme-linked immunosorbent assay to investigate the impact of high glucose and empagliflozin on cellular apoptosis, mitochondrial morphology, and functions including mitochondrial membrane potential (MMP), reactive oxygen species (ROS) production, and adenosine triphosphate (ATP) generation. We found that PTCs were susceptible to high glucose-induced mitochondrial fragmentation, and empagliflozin ameliorated this effect via the regulation of mitochondrial fission (FIS1 and DRP1) and fusion (MFN1 and MFN2) proteins. Empagliflozin reduced the high glucose-induced cellular apoptosis and improved mitochondrial functions by restoring mitochondrial ROS production, MMP, and ATP generation. Our results suggest that empagliflozin may protect renal PTCs from high glucose-mediated injuries through a mitochondrial mechanism. This could be one of the novel mechanisms explaining the benefits demonstrated in EMPA-REG OUTCOME trial.

Optimal Regimen of N-Acetylcysteine on Chromium-Induced Renal Cell Damage.

Chromium (Cr) is a well-known heavy metal that can cause renal damage. The production of reactive oxygen species (ROS) due to chromium-induced toxicity induces cell dysfunction, apoptosis, and death. N-acetylcysteine (NAC) is an antioxidant used as an antidote for chromium-induced toxicity. However, the optimal regimen and protective mechanisms of NAC are not fully understood in human renal cells. Our results showed that exposure to 10 μM K2Cr2O7, a toxic Cr(VI) compound, induced apoptosis and production of intracellular ROS in the human proximal tubular epithelial cell line HK-2. Supplements of 600 or 1000 µg/mL NAC inhibited intracellular ROS in HK-2 cells exposed to Cr(VI) and significantly increased cell viability within 2 h of Cr(VI)-induced cytotoxicity. Moreover, Cr(VI) induced the expression of apoptosis markers, including cleaved-caspase-3, cleaved-poly (ADP-ribose) polymerase, cleaved-caspase 8, and cleaved-caspase 9, and altered the expression ratio of Bax/Bcl-xL. Expression of apoptosis markers within 2 h of Cr(VI)-induced cytotoxicity in cells treated with 600 µg/mL NAC was significantly suppressed. However, delayed treatment with NAC at 4 h and 8 h after exposure to Cr did not suppress the activation of apoptotic pathways. In summary, our study reports the optimum timing and dose of NAC for the protection of human renal proximal tubular cells from Cr(VI)-induced cell death. The NAC treatment strategy described could be applied in clinical practice to suppress renal cell apoptosis, which in turn could rescue renal function.

Astragaloside IV ameliorates high glucose-induced HK-2 cell apoptosis and oxidative stress by regulating the Nrf2/ARE signaling pathway.

Diabetic nephropathy (DN) has become the major cause of end-stage renal disease increasing the mortality risk of diabetes. Research has demonstrated that the oxidative damage and apoptosis of renal tubular cells is present during DN. Astragaloside IV (AS-IV) has been widely used for the treatment of many diseases, however, the role and mechanism by which AS-IV may ameliorate high glucose-induced apoptosis and oxidative stress of the human proximal tubular cell line HK-2 remains largely unknown. The present study investigated the effect of AS-IV on high glucose-induced apoptosis and oxidative stress in HK-2 cells. Cell viability, apoptosis and protein expression were detected by Trypan blue staining, Cell Counting Kit-8 assay, terminal deoxynucleotidyl transferase 2′-deoxyuridine-5′-triphosphate nick-end labelling, flow cytometry and western blot analyses. In addition, enzymatic activities, including superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), catalase (CAT) and lipid peroxide (LPO), were measured with the corresponding detection kits. DCFH-DA assay and flow cytometry were performed to detect the production of reactive oxygen species (ROS). Western blot analysis and reverse transcription-quantitative polymerase chain reaction were conducted to evaluate protein and mRNA expressions of the nuclear factor erythroid 2 like 2 (Nrf2)/antioxidant response element (ARE) signaling pathway. The results demonstrated that AS-IV significantly enhanced HK-2 cell viability induced by high glucose in a dose-dependent manner. In addition, AS-IV notably inhibited HK-2 cell apoptosis stimulated by high glucose, which may be associated with inhibition of BCL2 associated X protein, Cleaved-caspase-3 and Cleaved-caspase-9, expression and the promotion of Bcl-2. AS-IV significantly increased the activities of antioxidant enzymes SOD, GSH-Px and CAT, and decreased the high-glucose-induced ROS production in HK-2 cells, in a dose-dependent manner. Finally, it was determined that AS-IV regulated the Nrf2/ARE signaling pathway and inhibited the expression of liver-type fatty acid binding protein. In conclusion, these findings may provide evidence that AS-IV has a potential role for the treatment of DN.

Hyperbilirubinemia Induces Pro-Apoptotic Effects and Aggravates Renal Ischemia Reperfusion Injury

Aims: Hyperbilirubinemia is associated with postoperative acute kidney injury in patients undergoing cardiac surgeries. A high concentration of bilirubin could induce oxidative stress and cell apoptosis. The aim of this study was to investigate whether hyperbilirubinemia aggravated the renal tubule cells injury and the pro-apoptotic potential of bilirubin on renal ischemia reperfusion injury (RIRI). Methods: The human proximal tubular epithelial cell line HK-2 cells were challenged with a gradient concentration of bilirubin for 24 h. Cell injury was assessed by flow cytometry and MTT assay. Bilirubin was injected intraperitoneally into male Sprague-Dawley rats once every 12 h (100 mg/kg), 3 times in total. The same solvent volume without bilirubin powder was used as vehicle in non-bilirubin injection groups. The RIRI surgical procedure was a bilateral renal pedicles clamping (45 min) followed by 30 h reperfusion. The rats were divided into 4 groups: negative control (NC), similar surgical procedures without clamping; Bil, bilirubin injection for 36 h, then rats were sacrificed; RIRI, RIRI surgical procedures; Bil + RIRI, RIRI applied 6 h later than the first bilirubin injection, rats were sacrificed after another 30 h. Results: In vitro, bilirubin induced cell apoptosis and significantly decreased the cell viability of HK-2 cells. Bilirubin induced the active caspase 3 and phosphorylation of p38 in HK-2 cells. In vivo, serum creatinine was higher in Bil + RIRI compared with RIRI (p < 0.01). The tubular injury scores of hematoxylin and eosin and tubular necrosis scores of periodic acid-Schiff were higher in Bil + RIRI than these in RIRI (All p < 0.05). The number of Tunel-positive nuclei was higher in Bil + RIRI compared to RIRI (p < 0.001). The active caspase 3 and phosphorylation of p38 were higher and the Bcl2 was lower in Bil + RIRI compared to RIRI. Moreover, the apoptosis level was higher in Bil compared to NC. Conclusions: Our results reveal that the hyperbilirubinemia induces pro-apoptotic effects and aggravates RIRI.

SIRT3 inhibited the formation of calcium oxalate-induced kidney stones through regulating NRF2/HO-1 signaling pathway.

Oxidative stress is important for the calcium oxalate (CaOx)-induced kidney stone formation. Sirtuin 3 (SIRT3) plays an essential role in the amelioration of oxidative damages. This study aims to explore the effect of SIRT3 on the formation of CaOx-induced kidney stones and the underlying mechanism. SIRT3 expression in renal tissues was detected by immunohistochemistry. Apoptosis in renal tissues was examined by TUNEL staining. Crystal-cell adherence and cell apoptosis in HK-2 cells were assessed by analyzing Ca2+ concentration and by the flow cytometry analysis, respectively. Protein expression of SIRT3, nuclear factor erythroid 2-related factor (NRF2), heme oxygenase-1 (HO-1), and Bax in renal tissues or HK-2 cells was examined by Western blot analysis. Renal pathological changes and the adhesion of CaOx crystals in the kidneys were examined by hematoxylin-eosin and von Kossa staining, respectively. Human kidneys with stones showed enhanced renal apoptosis, downregulated SIRT3 expression, and upregulated NRF2/HO-1 expression, compared with the controls. Furthermore, SIRT3 overexpression inhibited the CaOx-induced promotion of crystal-cell adherence and cell apoptosis in human proximal tubular cell line HK-2 cells, which was reversed by the NRF2 knockdown. Moreover, our in vivo assay further confirmed that SIRT3 overexpression alleviated the glyoxylate administration-induced renal damage, renal apoptosis, and crystals deposition in the kidneys from the stone model mice, which was also associated with its activation of the NRF2/HO-1 pathway. Our findings support the notion that overexpression of SIRT3 may inhibit the formation of CaOx-induced kidney stones, at least in part, through regulating the NRF2/HO-1 signaling pathway.

Baicalein protects renal tubular epithelial cells againsthypoxia-reoxygenation injury

Background: To investigate the protective effects and mechanism of baicalein (BAI), a naturally occurring flavonoid, against hypoxia-reoxygenation (HR) injury in renal tubular epithelial cells (HK-2).Methods: Cultured human renal proximal tubular cell line HK-2 was exposed to 24 h of hypoxia (5% CO2, 1% O2, and 94% N2), followed by 12 h of reoxygenation (5% CO2, 21% O2, and 74% N2). HK-2 cells were divided into three groups: control, HR, and HR-BAI (0.3 µg/ml). Reactive oxygen species (ROS) were measured and cell apoptosis was analyzed by flow cytometry and morphology. ELISAs were performed to determine the levels of IL-1, intercellular adhesion molecule-1 (ICAM-1), and monocyte chemotactic protein-1 (MCP-1). IL-1β, ICAM-1, and MCP-1 mRNA levels were determined by real-time quantitative PCR.Results: HK-2 cells that underwent HR exhibited increases in IL-1β expression by 0.94%, ROS by 0.59%, ICAM-1 expression by 0.8%, and MCP-1 expression by 1.2%. Moreover, HK-2 cell apoptosis was increased after HR (p < .05). Compared with the HR group, BAI treatment reduced the elevation of oxidative stress (ROS) by 0.76%, as well as HR-mediated induction of IL-1β and apoptosis of HK2 cells. Protein and mRNA levels of ICAM-1 and MCP-1 were also reduced.Conclusions: BAI protects renal tubular epithelial cells from HR injury by reducing inflammatory cytokine expression and oxidative stress.

The cat as a naturally occurring model of renal interstitial fibrosis: Characterisation of primary feline proximal tubular epithelial cells and comparative pro-fibrotic effects of TGF-β1.

Chronic kidney disease (CKD) is common in both geriatric cats and aging humans, and is pathologically characterised by chronic tubulointerstitial inflammation and fibrosis in both species. Cats with CKD may represent a spontaneously occurring, non-rodent animal model of human disease, however little is known of feline renal cell biology. In other species, TGF-β1 signalling in the proximal tubular epithelium is thought to play a key role in the initiation and progression of renal fibrosis. In this study, we first aimed to isolate and characterise feline proximal tubular epithelial cells (FPTEC), comparing them to human primary renal epithelial cells (HREC) and the human proximal tubular cell line HK-2. Secondly, we aimed to examine and compare the effect of human recombinant TGF-β1 on cell proliferation, pro-apoptotic signalling and genes associated with epithelial-to-mesenchymal transition (EMT) in feline and human renal epithelial cells. FPTEC were successfully isolated from cadaverous feline renal tissue, and demonstrated a marker protein expression profile identical to that of HREC and HK-2. Exposure to TGF-β1 (0–10 ng/ml) induced a concentration-dependent loss of epithelial morphology and alterations in gene expression consistent with the occurrence of partial EMT in all cell types. This was associated with transcription of downstream pro-fibrotic mediators, growth arrest in FPTEC and HREC (but not HK-2), and increased apoptotic signalling at high concentrations of TGF- β1. These effects were inhibited by the ALK5 (TGF-β1RI) antagonist SB431542 (5 μM), suggesting they are mediated via the ALK5/TGF-β1RII receptor complex. Taken together, these results suggest that TGF-β1 may be involved in epithelial cell dedifferentiation, growth arrest and apoptosis in feline CKD as in human disease, and that cats may be a useful, naturally occurring model of human CKD.

Pioglitazone induces hypoxia-inducible factor 1 activation in human renal proximal tubular epithelial cell line HK-2

We previously reported that fatty acid-bearing albumin but not fatty acid-depleted albumin induces hypoxia-inducible factor-1 (HIF-1) activation in human renal proximal tubular epithelial cell line HK-2. Then, an increase in mRNA expression of peroxisome proliferator-activated receptor gamma (PPARγ) was observed on treatment with fatty acid-bearing albumin but not fatty acid-depleted albumin. The aim of this study was to determine whether a PPARγ agonist, pioglitazone, induces HIF-1 activation or not. Treatment with pioglitazone induced HIF-1α mRNA as well as PPARγ mRNA expression in a concentration dependent manner. In addition, pioglitazone increased HIF-1 target genes such as the mRNAs of glucose transporter 1 (GLUT1) and breast cancer resistance protein (BCRP/ABCG2), in a concentration-dependent manner. Consistent with the increases in GLUT1 and ABCG2 mRNAs, protein expression of GLUT1 and BCRP was increased by pioglitazone. In addition, GLUT inhibitor phloretin-sensitive D-[3H]glucose uptake activity and BCRP inhibitor Ko143-sensitive accumulation of Hoecsht33342, a BCRP substrate, were significantly enhanced by treatment with pioglitazone. These findings suggest that PPARγ activation by pioglitazone leads to HIF-1 protein expression induction followed by changes in HIF-1 target gene expression and protein product activity.

Downregulation of the S1P Transporter Spinster Homology Protein 2 (Spns2) Exerts an Anti-Fibrotic and Anti-Inflammatory Effect in Human Renal Proximal Tubular Epithelial Cells.

Sphingosine kinase (SK) catalyses the formation of sphingosine 1-phosphate (S1P), which acts as a key regulator of inflammatory and fibrotic reactions, mainly via S1P receptor activation. Here, we show that in the human renal proximal tubular epithelial cell line HK2, the profibrotic mediator transforming growth factor β (TGFβ) induces SK-1 mRNA and protein expression, and in parallel, it also upregulates the expression of the fibrotic markers connective tissue growth factor (CTGF) and fibronectin. Stable downregulation of SK-1 by RNAi resulted in the increased expression of CTGF, suggesting a suppressive effect of SK-1-derived intracellular S1P in the fibrotic process, which is lost when SK-1 is downregulated. In a further approach, the S1P transporter Spns2, which is known to export S1P and thereby reduces intracellular S1P levels, was stably downregulated in HK2 cells by RNAi. This treatment decreased TGFβ-induced CTGF and fibronectin expression, and it abolished the strong induction of the monocyte chemotactic protein 1 (MCP-1) by the pro-inflammatory cytokines tumor necrosis factor (TNF)α and interleukin (IL)-1β. Moreover, it enhanced the expression of aquaporin 1, which is an important water channel that is expressed in the proximal tubules, and reverted aquaporin 1 downregulation induced by IL-1β/TNFα. On the other hand, overexpression of a Spns2-GFP construct increased S1P secretion and it resulted in enhanced TGFβ-induced CTGF expression. In summary, our data demonstrate that in human renal proximal tubular epithelial cells, SK-1 downregulation accelerates an inflammatory and fibrotic reaction, whereas Spns2 downregulation has an opposite effect. We conclude that Spns2 represents a promising new target for the treatment of tubulointerstitial inflammation and fibrosis.

MiR-193a-3p and miR-224 mediate renal cell carcinoma progression by targeting alpha-2,3-sialyltransferase IV and the phosphatidylinositol 3 kinase/Akt pathway.

Tumor metastasis is a major cause of cancer-related death in renal cell carcinoma (RCC). MicroRNAs (miRNAs) have been widely known to modulate proliferation invasion, metastasis, and apoptosis of cancer cells. In this study, we aimed to investigate the function and novel target of miR-193a-3p and miR-224 in RCC. The levels of miR-193a-3p and miR-224 were significantly increased in RCC tissues and RCC cell lines. Alpha-2,3-Sialyltransferase IV (ST3GalIV) was highly expressed in adjacent nontumor tissues and human normal proximal tubular cell line HK-2 compared to RCC tissues and cell lines. ST3GalIV expression was negatively correlated with miR-193a-3p and miR-224. Further analysis indicated that miR-193a-3p and miR-224 directly targeted ST3GalIV. MiR-193a-3p and miR-224 increased cell proliferation and migration by directly inhibiting ST3GalIV, and this effect was reversed by co-transfection with ST3GalIV in vitro. Overexpression of miR-193a-3p and miR-224 increased RCC cell proliferation in vivo. Furthermore, the phosphatidylinositol 3 kinase (PI3K)/Akt pathway was mediated by miR-193a-3p and miR-224 in RCC cell lines. Collectively, these results suggested that miR-193a-3p and miR-224 played an important role in regulation of RCC by targeting ST3GalIV via PI3K/Akt pathway.

Targeting Histone Deacetylase in Renal Tubular Epithelial Cells Inhibits Amplification of TH1 Cell-Mediated Inflammation

Background More studies are focusing on renal tubular epithelial cells (RTECs) as a new target to restore inflammatory environment as clarifying their immune regulatory function. Here, we investigated whether histone deacetylases (HDACs) are activated in RTECs during T cell-mediated inflammation and their blockade is able to reduce the inflammatory responses. Methods Human renal proximal tubular epithelial cell line HK-2 was cultured in the presence or absence of recombinant interferon gamma (IFN-g) 200 U/ml plus tumor necrosis factor alpha(TNF-a) 5 ng/ml. The HDAC activity was determined on the expression levels of acetylated H3 and a-tubulin by immune blot assay. To determine the functional activity of HDAC inhibitor SB939, we analyzed the immune stimulatory phenotype of HK-2 cells such as class II MHC molecule, CD80, CD86, and CD40 by flow cytometry. In addition, the culture supernatants were used for measuring cytokines and chemokines by ELISA assay. Results We found that HDAC activity was markedly increased in HK-2 cells by treatment of IFN-g/TNF-a within 12 hours. Treatment of pan-HDAC inhibitor SB939 in HK-2 cells completely prevented HDAC activity increased by IFN-g treatment. SB939 treatment predominantly inhibited up-regulating CD40 expression but not MHC class II, CD80, and CD86. In addition, MCP-1 was significantly inhibited more than IL-6 and TNF-a by SB939 treatment. We found that HDAC activity was markedly increased in HK-2 cells by treatment of IFN-g/TNF-a within 12 hours. Treatment of pan-HDAC inhibitor SB939 in HK-2 cells completely prevented HDAC activity increased by IFN-g treatment. SB939 treatment predominantly inhibited up-regulating CD40 expression but not MHC class II, CD80, and CD86. In addition, MCP-1 was significantly inhibited more than IL-6 and TNF-a by SB939 treatment. Conclusion Our results demonstrate that 1) HDAC activity is increased in RTECs in response to IFN-g, 2) which further facilitates T cell-mediated inflammatory responses through CD40 and MCP-1. Therefore, our study suggests that HDAC inhibitor has a therapeutic potential for the treatment of acute renal inflammatory diseases such as allograft rejection in transplantation.

Atgl gene deletion predisposes to proximal tubule damage by impairing the fatty acid metabolism

Fibrosis is the final common pathway of chronic kidney disease (CKD). Normal lipid metabolism is integral to renal physiology, and disturbances of renal lipid metabolism are increasingly being linked with CKD, including the fibrosis.Adipose triglyceride lipase (ATGL) is the rate-limiting enzyme of lipolysis. In the present study, we used Atgl−/− mice to investigate whether ATGL played a role in the regulation of proximal convoluted tubule (PCT) lipid metabolism and renal fibrosis development. ATGL deficiency led to lipid vacuolation of PCT and tubulointerstitial fibrosis, accompanied by massive albuminuria and decreased creatinine clearance rate (Ccr). In vitro experiments indicated that inhibition of ATGL in proximal tubular cell line HK-2 promoted intracellular lipid deposition, reactive oxygen species (ROS) accumulation and cell apoptosis. Both in vitro and in vivo experiments showed that ATGL inhibition decreased the renal peroxisome proliferator-activated receptorα(PPARα) expression, which implied the suppressed lipid metabolism. The antioxidant N-acetylcysteine (NAC) could partially reverse the effect of ROS accumulation and cell apoptosis, but could not restore the PPARαdecrease.These data raise the possibility that ATGL deficiency could impair the renal fatty acid metabolism though inhibiting PPARαexpression, which may lead to lipid deposition and cell apoptosis of PCT, and finally contribute to the renal fibrosis and dysfunction.

Cobalt Chloride Induces Expression and Function of Breast Cancer Resistance Protein (BCRP/ABCG2) in Human Renal Proximal Tubular Epithelial Cell Line HK-2.

The human breast cancer resistance protein (BCRP/ABCG2), a member of the ATP-binding cassette transporter family, is a drug transporter restricting absorption and enhancing excretion of many compounds including anticancer drugs. The cis-regulatory elements in the BCRP promoter include a hypoxia response element, i.e., the DNA binding site for hypoxia-inducible factor-1 (HIF-1). In this study, we investigated the effect of cobalt chloride, a chemical inducer of HIF-1α, on the expression and function of BCRP in human renal proximal tubular cell line HK-2. Cobalt chloride treatment significantly increased the mRNA expression of not only glucose transporter 1 (GLUT1), a typical HIF-1 target gene mRNA, but also ABCG2 mRNA in HK-2 cells. The BCRP inhibitor Ko143-sensitive accumulation of BCRP substrates such as Hoechst33342 and mitoxantrone was significantly enhanced by cobalt chloride treatment. In addition, treatment with cobalt chloride significantly increased the Ko143-sensitive accumulation of fluorescein isothiocyanate-labeled methotrexate in HK-2 cells. Furthermore, cobalt chloride treatment attenuated the cytotoxicity induced by mitoxantrone and methotrexate, which might be, at least in part, due to the increase in BCRP-mediated transport activity via HIF-1 activation. These findings indicate that HIF-1 activation protects renal proximal tubular cells against BCRP substrate-induced cytotoxicity by enhancing the expression and function of BCRP in renal proximal tubular cells.

Erythropoietin Inhibits Hypoxia–Induced Epithelial-To-Mesenchymal Transition via Upregulation of miR-200b in HK-2 Cells

Background/Aims: Renal tubular epithelial-mesenchymal transition (EMT) is regarded as an important factor leading to renal interstitial fibrosis. Erythropoietin (EPO) has been reported to attenuate renal fibrosis. The mechanism underlying this protective effect of EPO remains unclear. In this study, we aim to identify possible mechanisms of the EPO renoprotective effect. Methods: Hypoxia was induced in vitro by incubating human proximal tubular epithelial cell line HK-2 cells in 1% O₂ and 5% CO₂. Western blotting and reverse transcription polymerase chain reaction analyses were used to evaluate the expression of epithelial and mesenchymal markers in the cell samples. The expression of miR-200b in the HK-2 cells under hypoxia or treatment with EPO was examined. Results: EPO represses hypoxia-induced EMT by upregulating miR-200b in HK-2 cells. Overexpression of miR-200b represses the effect of ETS proto-oncogene 1 (Ets-1)-induced EMT in HK-2 cells. Conclusion: miR-200 mediates the protective effects of EPO on EMT in hypoxic HK-2 cells. EPO attenuated hypoxia-induced EMT by increasing miR-200 expression via the repression of Ets-1.