Cylindromatosis lysine 63 deubiquitinase (CYLD) suppress TLR3-mediated CCL5 expression in human renal proximal tubular epithelial cells.

BACKGROUND: One of the causes of tubulointerstitial nephritis is viral infection, with innate immune responses affecting its pathogenesis. Toll-like receptor 3 (TLR3) recognizes viral infections and acts antivirally by activating signaling to produce inflammatory cytokines/chemokines, including C-C motif chemokine ligand 5 (CCL5) and interferon-ß (IFN-ß). Although cylindromatosis lysine 63 deubiquitinase (CYLD) is known to be associated with tubulointerstitial nephritis and renal function, its role in the antiviral innate immune response in tubular epithelial cells remains unknown. In this study, we investigated the association between CYLD and TLR3-mediated CCL5 production in cultured human renal proximal tubular epithelial cells (hRPTECs). METHODS AND RESULTS: Polyinosinic-polycytidylic acid (poly IC), a synthetic TLR3 ligand, was used to stimulate hRPTECs. mRNA expression was measured using reverse transcription-quantitative polymerase chain reaction. Protein expression was assayed using western blotting or an enzyme-linked immunosorbent assay. Knockdown of IFN-ß, nuclear factor-kappa B (NF-κB) p65, and CYLD was performed by transfecting cells with specific small interfering RNAs. The intracellular localization of CYLD in hRPTECs was analyzed using immunofluorescence. Poly IC induced CCL5 expression in a time- and concentration-dependent manner, and knockdown of either IFN-ß or p65 reduced poly IC-induced CCL5 expression. CYLD knockdown increased the poly IC-induced CCL5, phosphorylated IκB kinase α/ß (IKK complex), and phosphorylated p65 expression. The CYLD protein was localized in the cytoplasm, and poly IC did not alter its expression. CONCLUSION: CYLD may prevent excessive inflammation due to an antiviral innate immune response by suppressing IKK complex and NF-κB activation downstream of TLR3 in hRPTECs.

LncRNA GABPB1-IT1 Is Upregulated in Ischemia-Induced Acute Kidney Injury and Downregulates miR-204-5p to Promote Hypoxia-Induced Human Renal Proximal Tubular Epithelial Cell Apoptosis.

INTRODUCTION: The present study investigated the role of long non-coding RNA (lncRNA) GABPB1-IT1 in ischemia-induced acute kidney injury (AKI). METHODS: The expression of GABPB1-IT1 in the plasma of patients with ischemia-induced AKI and healthy controls was detected by RT-qPCR. GABPB1-IT1 and miR-204-5p were overexpressed in human renal proximal tubular epithelial cells (HRPTEpCs), followed by RT-qPCR to assess the overexpression effect and the regulatory relationship between GABPB1-IT1 and miR-204-5p. Methylation-specific PCR was performed to assess the promoter methylation status of miR-204-5p. Additionally, a cell apoptosis assay was carried out to evaluate the correlation between miR-204-5p and GABPB1-IT1 in the context of hypoxia-induced apoptosis of HRPTEpCs. RESULTS: GABPB1-IT1 was upregulated in the plasma of patients with ischemia-induced AKI. In HRPTEpCs, hypoxia upregulated the expression of GABPB1-IT1. MiR-204-5p was downregulated in ischemia-induced AKI, and the expression of miR-204-5p was inversely correlated with GABPB1-IT1. In HRPTEpCs, overexpression of GABPB1-IT1 decreased the expression levels of miR-204-5p and increased miR-204-5p gene methylation. In addition, overexpression of GABPB1-IT1 reduced the inhibitory effects of miR-204-5p on the apoptosis of HRPTEpC induced by hypoxia. Furthermore, overexpression of GABPB1-IT1 promoted kidney injury, renal tissue injury scores, and the level of serum creatinine. However, miR-204-5p had the opposite effect. CONCLUSION: GABPB1-IT1 was upregulated in ischemia-induced AKI and may induce hypoxia-induced apoptosis of HRPTEpC by methylation of miR-204-5p.

Three-dimensional spheroid culture induces apical-basal polarity and the original characteristics of immortalized human renal proximal tubule epithelial cells.

The proximal tubules, which are part of the kidney, maintain blood homeostasis by absorbing amino acids, glucose, water, and ions such as sodium (Na), potassium, and bicarbonate. Proximal tubule dysfunction is associated with the pathogenesis of many kidney diseases. Renal proximal tubular epithelial cells (RPTECs) are responsible for the main functions of the proximal tubules. Therefore, in vitro experiments using RPTECs would greatly enhance our understanding of nephron physiology and pathobiology. It is preferable to use immortalized cell lines, such as human kidney-2 (HK-2) cells, because they are derived from humans and maintain growth indefinitely. However, tissue-specific RPTEC phenotypes, including apical-basal polarization, are frequently lost in conventional two-dimensional culture methods in part due to microenvironmental deficiencies. To overcome this limitation, we developed a three-dimensional (3D) spheroid culture method for HK-2 cells using an extracellular matrix. HK-2 spheroids in 3D culture formed a tubule-like architecture with cellular polarity and showed markedly restored Na transport function. 3D culture of HK-2 cells also increased expression of kidney development-related genes, including WNT9B. Models of human renal tubules using HK-2 spheroids will greatly improve our understanding of the physiology and pathobiology of the kidney.

Effect of Replicative Senescence on the Expression and Function of Transporters in Human Proximal Renal Tubular Epithelial Cells.

In the field of cosmetic research, there is a growing interest in alternatives to animal experiments, such as in vitro models using cultured cells. The trend is spreading to the field of food and drugs. Although various types of cells are used as in vitro models, the effect of cellular senescence on the expression and function of transporters in these models is unclear. In the present study, we examined the effect of replicative senescence (by passage culture) on the expression and function of transporters in renal proximal tubular epithelial cells (RPTECs). The increase in senescence-associated-ß-galactosidase (SA-ß-gal)-positive cells, cell cycle arrest markers, and senescence-associated secretory phenotype (SASP) markers was associated with an increase in passage numbers of RPTECs. Gene expression of various transporters in RPTEC was also altered. The mRNA level of organic cation transporter 2 decreased most rapidly with passage numbers among the transporters. The uptake of fluorescent cationic substrates in SA-ß-gal-positive RPTECs was less than that in SA-ß-gal-negative RPTECs. However, these changes in the expression of transporters seem to be significantly different from those observed in rodents and human kidneys in many aspects. As cellular senescence is observed in various situations, especially in RPTECs, it may be necessary to exclude it from toxicological and pharmacokinetic evaluations using in vitro models as much as possible. Additionally, when discussing cellular senescence, it is important to note the differences between aging in cells and aging and senescence in individuals.

Bisphenol A impairs renal function by reducing Na+/K+-ATPase and F-actin expression, kidney tubule formation in vitro and in vivo.

The kidney proximal tubule is responsible for reabsorbing water and NaCl to maintain the homeostasis of the body fluids, electrolytes, and nutrients. Thus, abnormal functioning of the renal proximal tubule can lead to life-threatening imbalances. Bisphenol A (BPA) has been used for decades as a representative chemical in household plastic products, but studies on its effects on the kidney proximal tubule are insufficient. In this study, immunocytochemical and cytotoxicity tests were performed using two- and three-dimensional human renal proximal tubular epithelial cell (hRPTEC) cultures to investigate the impact of low-dose BPA (1-10 µM) exposure. BPA was found to interfere with straight tubule formation as observed by low filamentous actin formation and reduced Na+/K+-ATPase expression in the tubules of hRPTEC 3D cultures. Similar results were observed in rat pup kidneys following oral administration of 250 mg/kg BPA. Moreover, the expression of HO-1 and 8-OHdG, key markers for oxidative stress, was increased in vitro and in vivo following BPA administration, whereas that of OAT1 and OAT, important transporters of the renal proximal tubules, was not altered. Overall, no-observed-adverse-effect-level (NOAEL)-dose BPA exposure can decrease renal function by promoting abnormal tubular formation both in vitro and in vivo. Therefore, we propose that although it does not exhibit life-threatening toxicity, exposure to low levels of BPA can negatively affect homeostasis in the body by means of long-term deterioration of renal proximal tubular function in humans.

ß-Endosulfan-mediated induction of pro-fibrotic markers in renal (HK-2) cells in vitro: A new insight in the pathogenesis of chronic kidney disease of unknown etiology.

Chronic kidney disease of unknown etiology (CKDu), manifested clinically as tubulo interstitial fibrosis, has emerged as the second major cause of chronic kidney disease (CKD) in the Indian subcontinent and various agrochemicals have been implicated in its occurance. Among the agrochemicals organochlorine pesticides particularly endosulfan is well known for its toxicity and recent residue analysis have shown its presence in the blood samples of general population. In this present study, we have investigated the consequences of endosulfan exposure at a concentration (0.01 µM) equivalent to their highest reported presence in human blood sample of some CKDu patients, to human renal proximal tubular epithelial (HK-2) cell line with regard to ROS generation and expression of profibrotic and epithelial to mesenchymal (EMT) markers in order to find out endosulfan's ability to induce profibrotic changes in renal cell. We demonstrated a significant increase in intracellular ROS generation and increased expression of TGF-ß1 when cells were incubated with ß-endosulfan (0.01 µM) indicating occurrence of oxidative stress and fibrotic process. Again, decreased expression of epithelial marker E-cadherin and increase in the expression of mesenchymal marker α-smooth muscle actin (α-SMA) suggest possible onset of EMT process. Pre-treatment with 5 mM concentration of anti-oxidant N-acetyl cysteine partially attenuated the above process. In conclusion, these findings suggest possible involvement of ß-endosulfan in the development of CKDu through oxidative stress and profibrotic signaling.

Interferon-stimulated gene 56 positively regulates Toll-like receptor 3-mediated CXCL10 expression in human renal proximal tubular epithelial cells.

Viral infections in tubular epithelial cells lead to the production of inflammatory cytokines by innate immunity, causing tubulointerstitial nephritis. TLR3 recognizes viral infections and acts via the activation of interferon (IFN)/IFN-stimulated genes (ISGs). This study investigates the role of ISG56, a representative ISG, in TLR3 signaling in cultured human renal proximal tubular epithelial cells (hRPTECs). To this end, hRPTECs were stimulated by a synthetic TLR3 ligand, polyinosinic-polycytidylic acid (poly IC), recombinant human interferon-ß [r(h)IFN-ß] or Japanese encephalitis virus (JEV) infection and assayed for inflammatory cytokine mRNA expression by RT-qPCR, and protein expression via western blotting or ELISA. ISG56 was expressed by poly IC or r(h)IFN-ß and IFN-ß knockdown reduced poly IC-induced expression of ISG56 and CXCL10. Moreover, ISG56 knockdown reduced poly IC- or r(h)IFN-ß-induced expression of CXCL10 at the same time as increasing JEV growth and reducing CXCL10 expression induced by JEV infection. Overall, TLR3 signaling induced IFN-ß-dependent expression of ISG56 and CXCL10. We show that ISG56 possibly plays a critical role in antiviral immunity of hRPTECs by positive regulation of IFN-ß-mediated CXCL10 expression downstream of TLR3.

Renal Hypoxic Reperfusion Injury-on-Chip Model for Studying Combinational Vitamin Therapy.

Renal ischemic-reperfusion injury decreases the chances of long-term kidney graft survival and may lead to the loss of a transplanted kidney. During organ excision, the cycle of warm ischemia from the donor and cold ischemia is due to storage in a cold medium after revascularization following organ transplantation. The reperfusion of the kidney graft activates several pathways that generate reactive oxygen species, forming a hypoxic-reperfusion injury. Animal models are generally used to model and investigate renal hypoxic-reperfusion injury. However, these models face ethical concerns and present a lack of robustness and intraspecies genetic variations, among other limitations. We introduce a microfluidics-based renal hypoxic-reperfusion (RHR) injury-on-chip model to overcome current limitations. Primary human renal proximal tubular epithelial cells and primary human endothelial cells were cultured on the apical and basal sides of a porous membrane. Hypoxic and normoxic cell culture media were used to create the RHR injury-on-chip model. The disease model was validated by estimating various specific hypoxic biomarkers of RHR. Furthermore, retinol, ascorbic acid, and combinational doses were tested to devise a therapeutic solution for RHR. We found that combinational vitamin therapy can decrease the chances of RHR injury. The proposed RHR injury-on-chip model can serve as an alternative to animal testing for injury investigation and the identification of new therapies.

Stx2 Induces Differential Gene Expression and Disturbs Circadian Rhythm Genes in the Proximal Tubule.

Shiga toxin-producing Escherichia coli (STEC) causes proximal tubular defects in the kidney. However, factors altered by Shiga toxin (Stx) within the proximal tubules are yet to be shown. We determined Stx receptor Gb3 in murine and human kidneys and confirmed the receptor expression in the proximal tubules. Stx2-injected mouse kidney tissues and Stx2-treated human primary renal proximal tubular epithelial cell (RPTEC) were collected and microarray analysis was performed. We compared murine kidney and RPTEC arrays and selected common 58 genes that are differentially expressed vs. control (0 h, no toxin-treated). We found that the most highly expressed gene was GDF15, which may be involved in Stx2-induced weight loss. Genes associated with previously reported Stx2 activities such as src kinase Yes phosphorylation pathway activation, unfolded protein response (UPR) and ribotoxic stress response (RSR) showed differential expressions. Moreover, circadian clock genes were differentially expressed, suggesting Stx2-induced renal circadian rhythm disturbance. Circadian rhythm-regulated proximal tubular Na+-glucose transporter SGLT1 (SLC5A1) was down-regulated, indicating proximal tubular functional deterioration, and mice developed glucosuria confirming proximal tubular dysfunction. Stx2 alters gene expression in murine and human proximal tubules through known activities and newly investigated circadian rhythm disturbance, which may result in proximal tubular dysfunctions.

Inhibition of Nrf2 alters cell stress induced by chronic iron exposure in human proximal tubular epithelial cells.

Iron can catalyze reactive oxygen species (ROS) formation, causing cellular injury. In systemic iron overload, renal tubular epithelial cells are luminally exposed to high iron levels due to glomerular filtration of increased circulating iron. Reports of tubular dysfunction and iron deposition in ß-thalassemia major support an association between increased chronic iron exposure and renal tubular injury. In acute iron exposure, Nuclear factor-erythroid 2-related factor 2 (Nrf2) may protect from iron-induced injury, whereas chronic renal stress may lead to Nrf2 exhaustion. We studied the cytotoxic mechanisms of chronic iron exposure using human conditionally immortalized proximal tubular epithelial cells (ciPTECs). Long-term iron exposure resulted in iron accumulation, cytosolic ROS formation and increased heme oxygenase 1 (HMOX-1) mRNA expression (all p < 0.001). This was accompanied by nuclear translocation of Nrf2 and induction of its target protein NQO1, which both could be blocked by the Nrf2 inhibitor trigonelline. Interestingly, iron and trigonelline incubation reduced ROS production, but did not affect HMOX-1 mRNA levels. Moreover, ferritin protein and CHOP mRNA expression were induced in combined iron and trigonelline incubated cells (p < 0.05). Together, these findings suggest that chronic iron exposure induces oxidative stress and that exhaustion of the antioxidant Nrf2 pathway may lead to renal injury.