Analysis of altered microRNA expression profiles in proximal renal tubular cells in response to calcium oxalate monohydrate crystal adhesion: implications for kidney stone disease

Non-Coding RNAs in Kidney Stones

Nephrolithiasis is a major public health concern associated with high morbidity and recurrence. Despite decades of research, the pathogenesis of nephrolithiasis remains incompletely understood, and effective prevention is lacking. An increasing body of evidence suggests that non-coding RNAs, especially microRNAs (miRNAs) and long non-coding RNAs (lncRNAs), play a role in stone formation and stone-related kidney injury. MiRNAs have been studied quite extensively in nephrolithiasis, and a plethora of specific miRNAs have been implicated in the pathogenesis of nephrolithiasis, involving remarkable changes in calcium metabolism, oxalate metabolism, oxidative stress, cell-crystal adhesion, cellular autophagy, apoptosis, and macrophage (Mp) polarization and metabolism. Emerging evidence suggests a potential for miRNAs as novel diagnostic biomarkers of nephrolithiasis. LncRNAs act as competing endogenous RNAs (ceRNAs) to bind miRNAs, thereby modulating mRNA expression to participate in the regulation of physiological mechanisms in kidney stones. Small interfering RNAs (siRNAs) may provide a novel approach to kidney stone prevention and treatment by treating related metabolic conditions that cause kidney stones. Further investigation into these non-coding RNAs will generate novel insights into the mechanisms of renal stone formation and stone-related renal injury and might lead to new strategies for diagnosing and treating this disease.

The Hidden Link between Polycystic Ovary Syndrome and Kidney Stones: Finding from the Tehran Lipid and Glucose Study (TLGS)

BACKGROUND

We aimed to investigate the association between kidney stones and polycystic ovarian syndrome (PCOS).

MATERIALS AND METHODS

In a cross-sectional study, data from the Tehran Lipid and Glucose Study (TLGS) were used to investigate the risk of kidney stones in women with Polycystic Ovary Syndrome (PCOS). Four distinct phenotypes of PCOS, as defined by the Rotterdam criteria, were examined in a sample of 520 women and compared to a control group of 1638 eumenorrheic non-hirsute healthy women. Univariate and multivariable logistic regression models were employed for analysis. The four PCOS phenotypes were classified as follows: Phenotype A, characterized by the presence of all three PCOS features (anovulation (OA), hyperandrogenism (HA), and polycystic ovarian morphology on ultrasound (PCOM)); Phenotype B, characterized by the presence of anovulation and hyperandrogenism; Phenotype C, characterized by the presence of hyperandrogenism and polycystic ovarian morphology on ultrasound; and Phenotype D, characterized by the presence of anovulation and polycystic ovarian morphology on ultrasound.

RESULTS

The prevalence of a history of kidney stones was found to be significantly higher in women with Polycystic Ovary Syndrome (PCOS) compared to healthy controls (12.5% vs. 7.7%, p = 0.001). This increased prevalence was observed across all PCOS phenotypes (p < 0.001). After adjusting for potential risk factors, including age, family history of kidney stones, waist-to-height ratio, total cholesterol, and low-density lipoprotein, the odds ratio for kidney stones in women with PCOS was found to be 1.59 [95% CI: 1.12-2.25, p = 0.01], indicating a 59% increase in risk compared to healthy women. Women with PCOS Phenotype A [OR: 1.97, 95% CI: 1.09-3.55, p = 0.02] and Phenotype D [OR: 3.03, 95% CI: 1.24-7.41, p = 0.01] were found to be at a higher risk for kidney stones.

CONCLUSION

Women with Polycystic Ovary Syndrome (PCOS), particularly those exhibiting menstrual irregularities and polycystic ovarian morphology on ultrasound (PCOM), have been found to be two to three times more likely to develop kidney stones. This increased prevalence should be taken into consideration when providing preventive care and counseling to these individuals.

Oxalate in Foods: Extraction Conditions, Analytical Methods, Occurrence, and Health Implications

Oxalate is an antinutrient present in a wide range of foods, with plant products, especially green leafy vegetables, being the main sources of dietary oxalates. This compound has been largely associated with hyperoxaluria, kidney stone formation, and, in more severe cases, systematic oxalosis. Due to its impact on human health, it is extremely important to control the amount of oxalate present in foods, particularly for patients with kidney stone issues. In this review, a summary and discussion of the current knowledge on oxalate analysis, its extraction conditions, specific features of analytical methods, reported occurrence in foods, and its health implications are presented. In addition, a brief conclusion and further perspectives on whether high-oxalate foods are truly problematic and can be seen as health threats are shown.

Inhibitory role of microRNA-484 in kidney stone formation by repressing calcium oxalate crystallization via a VDR/FoxO1 regulator axis

Kidney stones are regarded as common malignant diseases in the developed world. As a result, significant research examining their formation is ongoing, with microRNAs (miRs) recently being linked with kidney stone formation. Here, we aim to define the potential role of miR-484 in regulating renal tubular epithelial cell (RTEC) viability and the attachment of calcium oxalate (CaOx) crystals to RTECs via vitamin D receptor (VDR)/forkhead box protein O1 (FoxO1) axis. The pathological condition of CaOx crystallization was induced and examined in Sprague-Dawley rats, while RTECs were isolated and cultured in vitro. Loss- and gain-function assays were performed to study the effects that miR-484, VDR, and FoxO1 on RTEC functions and CaOx crystallization in vitro and on kidney stone formation in vivo. The interaction between miR-484 and VDR was confirmed by dual-luciferase reporter gene assays. Downregulation of miR-484 and FoxO1 as well as overexpression of VDR were identified in kidney stone modelled rats. VDR was confirmed as a target gene of miR-484, while knockdown of VDR upregulated the FoxO1 expression. miR-484 overexpression or VDR suppression reduced RTEC cytotoxicity and crystal attachment to RTECs in vitro and reduced the CaOx crystallization in vivo. Taken together, these findings suggest that miR-484 overexpression may be a potential inhibitor of RTEC proliferation and CaOx crystallization through a VDR/FoxO1 regulatory axis, providing a novel therapeutic target for the treatment of kidney stone.

miR-103a-3p Silencing Ameliorates Calcium Oxalate Deposition in Rat Kidney by Activating the UMOD/TRPV5 Axis

Maintaining the balance of calcium (Ca2+) metabolism in the kidney is crucial in preventing the formation of kidney stones. Functionally, the microRNA (miRNA) participating in this process needs to be unveiled. We induced NRK-52E cell injury by oxalate treatment. The role of transient receptor potential cation channel subfamily V member 5 (TRPV5) in oxalate-induced cells was studied by TRPV5 overexpression transfection, qRT-PCR, Western blot, MTT, and crystal adhesion detection. After identifying uromodulin (UMOD) expression in injured cells, we confirmed the interaction between TRPV5 and UMOD by coimmunoprecipitation (CoIP) and cell-surface biotinylation assays. The validation of UMOD-regulating TRPV5 in viability, crystal adhesion, and Ca2+ concentration of oxalate-induced cells was performed. Bioinformatics analysis and luciferase assay were used to identify the miRNA-targeting UMOD. The role of the miR-103a-3p-regulating UMOD/TRPV5 axis was detected by rescue experiments. We constructed a rat model with treatment of ethylene glycol (EG) to investigate the miR-103a-3p/UMOD/TRPV5 axis in vivo by hematoxylin-eosin (H&E) staining, Western blot, and immunohistochemistry (IHC). Upregulation of TRPV5 protected NRK-52E cells from oxalate-induced injury by enhancing cell viability and inhibiting CaOx adhesion. UMOD was depleted in oxalate-induced cells and positively interacted with TRPV5. UMOD silencing reversed the effect of TRPV overexpression on oxalate-induced cells. miR-103a-3p targeted UMOD and was mediated in the regulation of the UMOD/TRPV5 axis in oxalate-induced cells. Downregulating miR-103a-3p mitigated EG-induced CaOx deposition in kidney tissues in vivo by activating the UMOD/TRPV5 axis. miR-103a-3p silencing ameliorated CaOx deposition in the rat kidney by activating the UMOD/TRPV5 axis.

MicroRNA-204 attenuates oxidative stress damage of renal tubular epithelial cells in calcium oxalate kidney-stone formation via MUC4-mediated ERK signaling pathway

Oxalate-induced oxidative stress causes damage to cells, accompanied with renal deposition of calcium oxalate crystals. Recent studies have highlighted the extensive functions of microRNAs (miRNAs) in various processes, including cellular responses to oxidative stress. Hence, this study was intended to analyze the role of miR-204 in the calcium oxalate kidney-stone formation and the underlying mechanism. In silico analysis was performed to determine the miRNA/mRNA interaction involved in calculus, while dual-luciferase reporter assay was conducted for validation. A calcium oxalate kidney-stone model was established by H₂O₂ induction in RTEC HK-2 cells, in which the expression of miR-204 was examined. Gain- and loss-of-function approaches were employed to alter the expression of miR-204/MUC4 so as to assess the detailed role of miR-204 in oxidative stress injury in renal tubular epithelial cells (RTECs) and calcium oxalate kidney-stone formation. MUC4, an up-regulated gene in H₂O₂-induced HK-2 cells, was a target of MUC4. miR-204 functionally targeted MUC4 and blocked the ERK pathway activation. Furthermore, up-regulated miR-204 contributed to promotion of RTEC proliferation and suppression of ROS levels, RTEC apoptosis as well as formation of calcium oxalate crystal. Taken together, miR-204 impairs MUC4-dependent activation of the ERK signaling pathway and consequently ameliorates oxidative stress damage to RTECs and prevents calcium oxalate kidney-stone formation.

A polymorphism in the 3'-untranslated region of the matrix metallopeptidase 9 gene is associated with susceptibility to idiopathic calcium nephrolithiasis in the Chinese population

Objective

To investigate whether single nucleotide polymorphisms (SNPs) in the 3′ untranslated region (UTR) of the matrix metallopeptidase 9 gene (MMP9) are associated with susceptibility to calcium oxalate stones.

Methods

A total of 428 patients with kidney stone disease (KSD) and 450 control individuals were enrolled. Three MMP9 SNPs (rs20544, rs9509, and rs1056628) were genotyped, and MMP9 mRNA and protein expression was determined in patients and controls. The dual luciferase reporter gene assay was conducted by transfecting HEK293 cells with miR-491-5p mimics and plasmids containing MMP9 with rs1056628 AA/CC genotypes.

Results

The rs1056628 CC genotype was significantly increased in KSD patients compared with controls (CC vs AA: odds ratio [OR] = 2.279, 95% confidence interval [CI] = 1.048–4.956). The rs1056628 C allele frequency was higher in KSD patients than controls. The increased KSD risks associated with rs1056628 were more evident in individuals aged <30 years (OR = 3.504, 95% CI = 1.102–11.139) and men (OR = 2.522, 95% CI = 1.004–6.334). mRNA and protein levels of MMP9 were significantly higher in KSD patients with the CC genotype than in those with the AA genotype.

Conclusion

This study demonstrates that MMP9 SNP rs1056628 is associated with a significant KSD risk in Chinese Han individuals.

Comprehensive study of altered proteomic landscape in proximal renal tubular epithelial cells in response to calcium oxalate monohydrate crystals

Background

Calcium oxalate monohydrate (COM), the major crystalline composition of most kidney stones, induces inflammatory infiltration and injures in renal tubular cells. However, the mechanism of COM-induced toxic effects in renal tubular cells remain ambiguous. The present study aimed to investigate the potential changes in proteomic landscape of proximal renal tubular cells in response to the stimulation of COM crystals.

Methods

Clinical kidney stone samples were collected and characterized by a stone component analyzer. Three COM-enriched samples were applied to treat human proximal tubular epithelial cells HK-2. The proteomic landscape of COM-crystal treated HK-2 cells was screened by TMT-labeled quantitative proteomics analysis. The differentially expressed proteins (DEPs) were identified by pair-wise analysis. Gene Ontology (GO) analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis of DEPs were performed. Protein interaction networks were identified by STRING database.

Results

The data of TMT-labeled quantitative proteomic analysis showed that a total of 1141 proteins were differentially expressed in HK-2 cells, of which 699 were up-regulated and 442 were down-regulated. Functional characterization by KEGG, along with GO enrichments, suggests that the DEPs are mainly involved in cellular components and cellular processes, including regulation of actin cytoskeleton, tight junction and focal adhesion. 3 high-degree hub nodes, CFL1, ACTN and MYH9 were identified by STRING analysis.

Conclusion

These results suggested that calcium oxalate crystal has a significant effect on protein expression profile in human proximal renal tubular epithelial cells.

MiR-21 promotes calcium oxalate-induced renal tubular cell injury by targeting PPARA

Kidney stone disease is a crystal concretion formed in the kidneys that has been associated with an increased risk of chronic kidney disease. MicroRNAs are functionally involved in kidney injury. Data mining using a microRNA array database suggested that miR-21 may be associated with calcium oxalate monohydrate (COM)-induced renal tubular cell injury. Here, we confirmed that COM exposure significantly upregulated miR-21 expression, inhibited proliferation, promoted apoptosis, and caused lipid accumulation in an immortalized renal tubular cell line (HK-2). Moreover, inhibition of miR-21 enhanced proliferation and decreased apoptosis and lipid accumulation in HK-2 cells upon COM exposure. In a glyoxylate-induced mouse model of renal calcium oxalate deposition, increased miR-21 expression, lipid accumulation, and kidney injury were also observed. In silico analysis and subsequent experimental validation confirmed the peroxisome proliferator-activated receptor (PPAR)-α gene (PPARA) a key gene in fatty acid oxidation, as a direct miR-21 target. Suppression of miR-21 by miRNA antagomiR or activation of PPAR-α by its selective agonist fenofibrate significantly reduced renal lipid accumulation and protected against renal injury in vivo. In addition, miR-21 was significantly increased in urine samples from patients with calcium oxalate renal stones compared with healthy volunteers. In situ hybridization of biopsy samples from patients with nephrocalcinosis revealed that miR-21 was also significantly upregulated compared with normal kidney tissues from patients with renal cell carcinoma who underwent radical nephrectomy. These results suggested that miR-21 promoted calcium oxalate-induced renal tubular cell injury by targeting PPARA, indicating that miR-21 could be a potential therapeutic target and biomarker for nephrolithiasis.

Circulating human microRNA biomarkers of oxalic acid-induced acute kidney injury

Oxalic acid-induced nephrotoxicity and acute kidney injury result from formation of calcium oxalate crystals. Oxalic acid-induced acute kidney injury is a significant problem in many parts of the world. Circulating biomarkers that can accurately and reproducibly detect acute kidney injury are highly desirable. We used a high sensitivity discovery platform to identify signature microRNAs to distinguish healthy individuals never exposed to oxalic acid (n = 4) from those who were exposed to oxalic acid but had no injury (NOAKI; n = 4), moderate injury (AKIN2; n = 4) or severe injury (AKIN3; n = 4). Longitudinal analyses identified 4-8 h post-ingestion as the best time to detect AKIN2/3. We validated a signature of 53 microRNAs identified in the discovery, in a second cohort of individuals exposed to oxalic acid (NOAKI = 11, AKIN2 = 8 and AKIN3 = 18) and healthy controls (n = 19). Thirteen microRNAs were significantly downregulated in acute kidney injury patients compared to NOAKI within 8-h post-ingestion. Five microRNAs (miR-20a, miR-92a, miR-93, miR-195, miR-451) had a highly significant correlation with normalized urinary albumin, serum creatinine at 24 h and creatinine clearance. Logistic regression of these microRNAs had AUC-ROC of 0.85 predicting AKIN2/3 and discriminated patients from healthy controls (AUC-ROC = 0.93). mRNA targets of these microRNAs identified oxidative stress pathways of nephrotoxicity in proximal tubule and glomeruli nephrotoxicity. In conclusion, the downregulation of multiple circulating microRNAs in patients correlated with the severity of oxalic acid-induced acute kidney injury. A set of microRNAs (miR-20a, miR-92a, miR-93, miR-195, miR-451) could be promising biomarkers for early detection of oxalic acid-induced acute kidney injury.

Overexpression of miR‑30c‑5p reduces cellular cytotoxicity and inhibits the formation of kidney stones through ATG5

MicroRNAs (miRNAs or miRs) are critical regulators in various diseases. In the current study, the role of miR-30c-5p in the formation of sodium oxalate-induced kidney stones was investigated. For this purpose, human renal tubular epithelial cells (HK-2 cells) were incubated with sodium oxalate at the concentrations of 100, 250, 500, 750 and 1,000 µM. Cell viability and the miR-30c-5p expression level were respectively measured by CCK-8 assay and RT-qPCR. After separately transfecting miR-30c-5p mimic and inhibitor into the HK-2 cells, the cell apoptotic rate, the levels of mitochondrial membrane potential (MMP) and ROS were determined by flow cytometry. The levels of oxidative stress indicators [lactate dehydrogenase (LDH), malondialdehyde (MDA), superoxide dismutase (SOD) and catalase (CAT)] were determined using commercial kits. Crystal-cell adhesion assay was performed to evaluate the crystal adhesion capacity in vitro. miR-30c-5p binding at autophagy related 5 (ATG5) was predicted by TargetScan7.2 and further verified by dual-luciferase reporter assay. Rescue experiments were performed to confirm the molecular mechanisms underlying sodium oxalate-induced kidney formation in HK-2 cells. The results revealed that sodium oxalate decreased the viability of HK-2 cells in a concentration-dependent manner, and that miR-30c-5p expression was significantly downregulated by exposure to 750 µM sodium oxalate. In addition, the increase in cell apoptosis and crystal number, and the upregulated levels of LDH, MDA and ROS were reversed by the overexpression of miR-30c-5p. Moreover, the overexpression of miR-30c-5p upregulated the levels of SOD, CAT and MMP induced by sodium oxalate. ATG5 was directly regulated by miR-30c-5p, and the inhibition of cell cytotoxicity and crystal-cell adhesion induced by miR-30c-5p mimic was blocked by ATG5. These data indicated that the overexpression of miR-30c-5p alleviated cell cytotoxicity and crystal-cell adhesion induced by sodium oxalate through ATG5. Thus, the current study provides a better understanding of the role of miR-30c-5p in sodium oxalate-induced kidney stones.

miRNA-34a inhibits cell adhesion by targeting CD44 in human renal epithelial cells: implications for renal stone disease

Nephrolithiasis is a very common disease in which cell-crystal adhesion is an essential mechanism for kidney stone formation. This study has explored the anti-adhesion function of the microRNA, miR-34a, by targeting CD44, a cell surface receptor, in human renal epithelial (HK-2) cells. The expression of CD44 was monitored by qPCR and western blot. A luciferase assay validated the target of miR-34a in CD44 3' UTR. Immunofluorescence staining under confocal microscopy was used to detect the cell-crystal adhesion effects in vitro. Pizzolato staining was performed to examine the adhesion role of miR-34a in vivo. In HK-2 cells, miR-34a was down-regulated and CD44 was up-regulated when exposed to calcium oxalate monohydrate crystals. Moreover, miR-34a negatively regulated the expression of CD44. According to the luciferase report assay, miR-34a direct targeted a binding site in the CD44 3'UTR. In vitro experiments, miR-34a overexpression inhibited CD44 expression and cell-crystals adhesion; whereas CD44 overexpression showed reversed results. Furthermore, miR-34a suppressed cell-crystals adhesion and stone formation in vivo. These findings indicate that miR-34a targets CD44 in HK-2 cells and inhibits cell-crystal adhesion both in vitro and in vivo. Based on these results, miR-34a may be a potential therapeutic target for renal stone disease.

In vitro effects on calcium oxalate crystallization kinetics and crystal morphology of an aqueous extract from Ceterach officinarum: Analysis of a potential antilithiatic mechanism

Ceterach officinarum Willd is a plant widespread throughout Europe and used in southern Italy as a diuretic. Beliefs in the benefits of C. officinarum aqueous extract in the treatment of calcium oxalate kidney stones are widely held. Little is known, however, about the actual mechanism of its antilithiatic action. Our results in this in vitro study corroborate C. officinarum aqueous extract as a good source of antioxidants with a high antioxidant effects. Our results also demonstrate a major impact of C. officinarum aqueous extract on in vitro induced calcium oxalate crystallization kinetics and crystal morphology, showing its critical role in kidney stone formation and/or elimination. We show that progressively increasing doses of C. officinarum aqueous extract cause a sequence of effects. A powerful inhibitory action on calcium oxalate monohydrate (COM) growth and aggregation is first observed. C. officinarum aqueous extract also appears highly effective in stimulating nucleation increasing the number and reducing the size of COM crystals, which become progressively thinner, rounded and concave in a dose-dependent manner. These shape-modified COM crystals are known to be less adherent to renal tubular cells and more easily excreted through the urinary tract preventing kidney stone formation. Further, C. officinarum aqueous extract promotes the formation of calcium oxalate dihydrate (COD) rather than the monohydrate so that, at the highest concentrations used, only COD crystals are observed, in significant greater numbers with a clear reduction in their size, in a dose-dependent manner. Furthermore, AFM analyses allowed us to reveal the presence of C. officinarum component(s) on the surfaces of COD and modified COM crystals. The crystal surface adsorbed component(s) are shown to be similarly active as the total aqueous extract, suggesting a trigger factor which may direct crystal modification towards COD forms. In urolithiasis pathogenesis COD crystals are less dangerous than the COM forms due to their lower affinity for renal tubular cells. Our results are important in understanding the mechanisms which guide the modification induced by C. officinarum on the crystallization process. Based on these data, together with no adverse toxic effect being observed on the in vitro model of human intestinal enterocytes, C. officinarum aqueous extract could represent an attractive natural therapy for the treatment of urolithiasis.

Comparison of the adhesion of calcium oxalate monohydrate to HK-2 cells before and after repair using tea polysaccharides

Background: Kidney stone formation is closely related to renal epithelial cell damage and the adhesion of calcium oxalate crystals to cells. Methods: In this research, the adhesion of human kidney proximal tubular epithelial cells (HK-2) to calcium oxalate monohydrate crystals with a size of approximately 100 nm was studied. In addition, the inhibition of crystal adhesion by four tea polysaccharides (TPS0, TPS1, TPS2, and TPS3) with the molecular weights of 10.88, 8.16, 4.82, and 2.31 kDa, respectively were compared. Results: When oxalic acid-damaged HK-2 cells were repaired, cell viability increased. By contrast, reactive oxygen species level, phosphatidylserine eversion, and osteopontin expression decreased, thus indicating that tea polysaccharides have a repairing effect on damaged HK-2 cells. Moreover, after repairing the damaged cells, the amount of adherent crystals was reduced. The repair effect of tea polysaccharides is closely related to molecular weight, and TPS2 with the moderate molecular weight displayed the best repair effect. Conclusion: These results suggest that tea polysaccharides, especially TPS2, may inhibit the formation and recurrence of calcium oxalate kidney stones.

Exosomes from Human Umbilical Cord Mesenchymal Stem Cells Reduce Damage from Oxidative Stress and the Epithelial-Mesenchymal Transition in Renal Epithelial Cells Exposed to Oxalate and Calcium Oxalate Monohydrate

Objective

To investigate whether exosomes from human umbilical cord mesenchymal stem cells (hUC-MSCs) can protect against the toxic effects of oxalate and calcium oxalate monohydrate (COM) crystals in human proximal tubular epithelial (HK-2) cells.

Methods

Exosomes were isolated from hUC-MSCs, purified by ultracentrifugation, and verified by examination of cell morphology using transmission electron microscopy and the presence of specific biomarkers. HK-2 cells received 1 of 4 treatments: control (cells alone), hUC-MSC exosomes, oxalate+COM, or oxalate+COM and hUC-MSC exosomes. Cell viability was determined using the MTT assay. Oxidative stress was determined by measuring LDH activity and the levels of H₂O₂, malondialdehyde (MDA), and reactive oxygen species (ROS). Expressions of N-cadherin, TGF-β, and ZO-1 were determined by immunofluorescence. Expressions of epithelial markers, mesenchymal markers, and related signaling pathway proteins were determined by western blotting.

Results

After 48 h, cells in the oxalate+COM group lost their adhesion, appeared long, spindle-shaped, and scattered, and the number of cells had significantly decreased. The oxalate+COM treatment also upregulated TGF-β and mesenchymal markers, downregulated epithelial markers, increased the levels of LDH, H₂O₂, MDA, and ROS, decreased cell viability, and increased cell migration. The isolated exosomes had double-layer membranes, had hollow, circular, or elliptical shapes, had diameters mostly between 30 and 100 nm, and expressed CD9, CD63, and Alix. Treatment of HK-2 cells with hUC-MSC exosomes reversed or partly reversed all the effects of oxalate+COM.

Conclusions

Exosomes from hUC-MSCs alleviate the oxidative injury and the epithelial-mesenchymal transformation of HK-2 cells that is induced by oxalate+COM.

Analyses of long non-coding RNA and mRNA profiling using RNA sequencing in calcium oxalate monohydrate-stimulated renal tubular epithelial cells

To study the expression profiles of lncRNA and mRNA in the calcium oxalate monohydrate-attached HK-2 cells, and investigate the association between critical lncRNA expression level and renal injury. The HK-2 cells were treated with crystal suspension of calcium oxalate. The effects of calcium oxalate crystals on the growth of HK-2 cells were determined by MTT assay. Total RNA was extracted and the lncRNA and mRNA expression profiles were analyzed by high-throughput transcriptase sequencing platform HiSeq 2500. The profile of identified lncRNAs and mRNAs were verified by real-time PCR and their potential function was analyzed by Gene Ontology database and KEGG signal pathway analysis. Calcium oxalate crystals adhered to the surface of HK-2 cells in few minutes and showed obvious cytotoxicity. RNA seq results showed that there were 25 differentially expressed lncRNAs in HK-2 cells treated with calcium oxalate crystals, of which 9 were up-regulated and 16 were down-regulated. The difference was verified by real-time PCR which showed statistically significant (P < 0.05). Calcium oxalate crystals have a significant effect on lncRNA and mRNA expression in human renal epithelial cells, which may play critical roles in kidney stone-mediated renal injury.

Integrative Analysis of miRNA and mRNA Expression Profiles in Calcium Oxalate Nephrolithiasis Rat Model

The microRNA (miRNA) expression profiles and their biological functions in calcium oxalate nephrolithiasis remain unclear. In this study, we investigate the miRNA and mRNA expression profiles of kidney tissues in calcium oxalate stone rats. 16 Sprague Dawley rats were divided into control group and stone-forming group. 24-hour urine samples and kidney tissues were collected for biochemical and histological determination after 4 weeks. MiRNA and mRNA microarray were applied to evaluate the miRNA and mRNA expression profiles. To validate the microarray results, the quantitative real-time PCR (qRT-PCR) was performed. A total of 38 miRNAs and 2728 mRNAs were significantly and differentially expressed in kidney tissues of stone-forming group versus control group. Gene Ontology (GO) analysis revealed that most of the target genes were enriched in terms of oxidation reduction, ion transport, inflammatory response, and response to wounding. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis of these targets highlights their critical role in cytokine-cytokine receptor interaction, gap junction, and chemokine signaling pathway. Furthermore, the reliability of the microarray-based results was confirmed by using qRT-PCR determination. The miRNA and mRNA expressions in calcium oxalate stone rat kidneys might provide a basis for further research on urolithiasis mechanism.

The effects of HAP and macrophage cells to the expression of inflammatory factors and apoptosis in HK-2 cells of vitro co-cultured system

This study developed an in vitro system by co-culturing HK-2 cells with different concentration of hydroxyapatite (HAP) and/or macrophage cells to simulate the internal environment of urolithiasis as far as possible, investigating the regulatory effects of macrophage cells on HAP-induced expression of relative inflammatory factors of HK-2 cells. The control group (H group) was only comprised of HK-2 cells. Experimental groups included co-culturing HK-2 cells and macrophage cells (H + M group), co-culturing HK-2 cells and HAP (H + A group), co-culturing macrophage cells and HAP (M + A group), and co-culturing HK-2 cells and macrophage cells with HAP (H + M + A group). In the H + A, M + A, and H + M + A group, we set the concentration of HAP as 5 μg/cm² (A1) and 10 μg/cm² (A2). After co-culturing for 2, 4, and 6 h, we detected the expression of CCL-2 in the liquid by ELISA. We tested the expression of LDH and ROS to evaluate the damage of HK-2 cells. We assessed the apoptosis of HK-2 cells using DAPI staining assay, flow cytometry, and the rate of BAX/BCL-2. Western Blotting detected OPN, Fetuin-A, BAX, and BCL-2 of HK-2 cells. The expression of CCL-2 in the medium of H + A1 and H + A2 group increased significantly compared with the control (P < 0.05); CCL-2 of M + A1 and M + A2 group was higher than the H + A1 and H + A2 group (P < 0.05). The expression of CCL-2 in H + M + A1 and H + M + A2 group was also higher than M + A1 and M + A2 group (P < 0.05). Compared with control, the expression of OPN, LDH release, the ratio of BAX/BCL-2, and the generation of ROS in HK-2 cells increased in a dose- and time-dependent manner. Compared with the control, the expression of Fetuin-A decreased in various degrees at different incubation periods. Especially when co-culturing for 6 h, Fetuin-A decreased most seriously in the H + M + A1 group. (1) The HAP can induce the HK-2 cells oxidative stress and inflammatory damage and apoptosis, when adding the macrophages to co-culture, macrophage cells can aggravate the damage and apoptosis of the HK-2 cells. (2) After the stimulation of HAP, the expression of OPN in HK-2 cells increased in a time- and dose-dependent manner; macrophage cells can aggravate the increase of OPN in HK-2 cells. (3) In the HAP and HK-2 cells co-cultured system, the low-level Fetuin-A of HK-2 cells may be related to the excessive consumption of Fetuin-A in the process of HAP-induced renal tubular epithelial cell excessive oxidative stress, inflammatory injury, and cell apoptosis. When adding macrophage cells to co-culture, Fetuin-A decreased even more seriously, it reminds us that macrophage cells can slightly regulate the expression of Fetuin-A in the HK-2 cells.

Protective Effects of Pistacia lentiscus L. fruit extract against calcium oxalate monohydrate induced proximal tubular injury

ETHNOPHARMACOLOGICAL RELEVANCE

The world prevalence of kidney stones is increasing and plants are frequently used to treat urolithiasis. Pistacia lentiscus L, a plant which freely grows around the Mediterranean basin areas, is widely used for various pathologies. P. lentiscus has an important impact as it has economical value on top of its pharmacological interest. Decoctions of its aerial parts and/or resin are used to treat kidney stones.

AIM OF THE STUDY

To in vitro assess the potential nephroprotective effect of Pistacia lentiscus ethanolic fruit extract (PLEF) on proximal tubular cells in response to the adhesion of calcium oxalate monohydrate (COM) crystals.

MATERIALS AND METHODS

Human Kidney [HK]-2 cells were incubated with and without COM in the presence or absence of PLEF. Cell viability was measured by the resazurin assay. The expression of E-cadherin was analyzed by PCR. The extracellular production of H₂O₂ was measured by Amplex® Red H₂O₂ Assay. The numbers of detached or non-adherent COM crystals in the presence of PLEF were microscopically captured and counted using ImageJ software. The interaction of PLEF with COM and the effect of PLEF on crystal size were analyzed by flow cytometry. The spectrophotometric measurement of turbidity was performed for assessing the COM concentration.

RESULTS

PLEF incubated with COM was able to increase the cell viability. The decrease of E-cadherin expression after incubation with COM was counteracted by PLEF. Overproduction of H₂O₂ induced by COM was also inhibited by PLEF. Observations using flow cytometry showed that interactions between PLEF and the COM crystals occurred. PLEF was also effective in reducing the particles size and in lowering COM concentration.

CONCLUSION

Our data show that COM tubulotoxicity can be significantly reversed by PLEF -at least in part- via an inhibition of COM crystals adhesion onto the apical membrane. This early beneficial effect of PLEF needs to be further investigated as a useful strategy in nephrolithiasis prevention.

Analysis of altered microRNA expression profiles in the kidney tissues of ethylene glycol-induced hyperoxaluric rats

Calcium oxalate stones account for >80% of urinary stones, however the mechanisms underlying their formation remains to be elucidated. Hyperoxaluria serves an important role in the pathophysiological process of stone formation. In the present study, differences in the miRNA expression profiles between experimental hyperoxaluric rats and normal rats were analyzed, in order to identify target genes and signaling pathways involved in the pathogenesis of hyperoxaluria. Ethylene glycol and ammonium chloride was fed to male hyperoxaluric rats (EXP) and normal age-matched male rats (CON). The oxalate concentration in the urine of each experimental rat was collected every 24 h and measured on day 14. Three rats exhibiting the highest concentrations were selected for microarray analysis. Microarray analysis was performed to evaluate differences in the expression of microRNA (miRNA) in the kidney tissues from EXP and CON groups, and miRNAs that exhibited a >2-fold or a <0.5-fold alteration in expression between these groups were screened for differential expression patterns according to the threshold P-values. Reverse transcription-quantitative polymerase chain reaction analysis was employed to confirm the microarray results. In order to predict the potential role of miRNAs in pathophysiological processes, gene ontology (GO), pathway and target prediction analyses were conducted. A total of 28 miRNAs were observed to be differentially expressed (>2-fold change) between EXP and CON groups. Among these miRNAs, 20 were upregulated and 8 were downregulated. GO and pathway analyses revealed that the insulin resistance and phosphatidylinositol-bisphosphonate 3-kinase/AKT serine threonine kinase signaling pathways were potentially associated with miRNA regulation in this setting. In conclusion, the results of the present study identified differentially expressed miRNAs in hyperoxaluric rats, and provided a novel perspective for the role of miRNAs in the formation of calcium oxalate stones.

Differential activation of CD95-mediated apoptosis related proteins in proximal and distal tubules during rat renal development

The CD95-mediated apoptotic pathway is the best characterized of the death receptor-mediated apoptotic pathways. The present study characterized localization and expression of proteins involved in CD95-mediated apoptosis during rat renal development. Kidneys were obtained from embryonic (E) 18 and 20-day-old fetuses and postnatal (P) 1-, 3-, 5-, 7-, 14-, and 21-day-old pups. Immunohistochemical characterization revealed that CD95, FasL and cleaved caspase-3 were strongly expressed in proximal tubules and weakly expressed in distal tubules, but that expression of caspase-8 in distal tubules was stronger than that in proximal tubules. Results from terminal deoxynucleotidyl transferase dUTP nick end labeling assays showed that levels of apoptosis in proximal tubules slowly increased after E18, while those of distal tubules slowly decreased after P5. Western blotting demonstrated that expression of CD95, FasL and FADD was very weak during embryonic development, but rapidly increased at P14. Expression of cleaved caspase-3 was maintained at high levels after P1, while caspase-8 expression gradually reached a peak at P7. Results from this study reveal that the CD95-mediated apoptotic pathway is a key driver of apoptosis in proximal tubules during late postnatal kidney development in rats and suggest that apoptosis in distal tubules is mediated by a different apoptotic pathway.

Reinjury risk of nano-calcium oxalate monohydrate and calcium oxalate dihydrate crystals on injured renal epithelial cells: aggravation of crystal adhesion and aggregation

BACKGROUND

Renal epithelial cell injury facilitates crystal adhesion to cell surface and serves as a key step in renal stone formation. However, the effects of cell injury on the adhesion of nano-calcium oxalate crystals and the nano-crystal-induced reinjury risk of injured cells remain unclear.

METHODS

African green monkey renal epithelial (Vero) cells were injured with H2O2 to establish a cell injury model. Cell viability, superoxide dismutase (SOD) activity, malonaldehyde (MDA) content, propidium iodide staining, hematoxylin-eosin staining, reactive oxygen species production, and mitochondrial membrane potential (Δψm) were determined to examine cell injury during adhesion. Changes in the surface structure of H2O2-injured cells were assessed through atomic force microscopy. The altered expression of hyaluronan during adhesion was examined through laser scanning confocal microscopy. The adhesion of nano-calcium oxalate monohydrate (COM) and calcium oxalate dihydrate (COD) crystals to Vero cells was observed through scanning electron microscopy. Nano-COM and COD binding was quantitatively determined through inductively coupled plasma emission spectrometry.

RESULTS

The expression of hyaluronan on the cell surface was increased during wound healing because of Vero cell injury. The structure and function of the cell membrane were also altered by cell injury; thus, nano-crystal adhesion occurred. The ability of nano-COM to adhere to the injured Vero cells was higher than that of nano-COD crystals. The cell viability, SOD activity, and Δψm decreased when nano-crystals attached to the cell surface. By contrast, the MDA content, reactive oxygen species production, and cell death rate increased.

CONCLUSION

Cell injury contributes to crystal adhesion to Vero cell surface. The attached nano-COM and COD crystals can aggravate Vero cell injury. As a consequence, crystal adhesion and aggregation are enhanced. These findings provide further insights into kidney stone formation.

MicroRNA Expression Profile in Penile Cancer Revealed by Next-Generation Small RNA Sequencing

Penile cancer (PeCa) is a relatively rare tumor entity but possesses higher morbidity and mortality rates especially in developing countries. To date, the concrete pathogenic signaling pathways and core machineries involved in tumorigenesis and progression of PeCa remain to be elucidated. Several studies suggested miRNAs, which modulate gene expression at posttranscriptional level, were frequently mis-regulated and aberrantly expressed in human cancers. However, the miRNA profile in human PeCa has not been reported before. In this present study, the miRNA profile was obtained from 10 fresh penile cancerous tissues and matched adjacent non-cancerous tissues via next-generation sequencing. As a result, a total of 751 and 806 annotated miRNAs were identified in normal and cancerous penile tissues, respectively. Among which, 56 miRNAs with significantly different expression levels between paired tissues were identified. Subsequently, several annotated miRNAs were selected randomly and validated using quantitative real-time PCR. Compared with the previous publications regarding to the altered miRNAs expression in various cancers and especially genitourinary (prostate, bladder, kidney, testis) cancers, the most majority of deregulated miRNAs showed the similar expression pattern in penile cancer. Moreover, the bioinformatics analyses suggested that the putative target genes of differentially expressed miRNAs between cancerous and matched normal penile tissues were tightly associated with cell junction, proliferation, growth as well as genomic instability and so on, by modulating Wnt, MAPK, p53, PI3K-Akt, Notch and TGF-β signaling pathways, which were all well-established to participate in cancer initiation and progression. Our work presents a global view of the differentially expressed miRNAs and potentially regulatory networks of their target genes for clarifying the pathogenic transformation of normal penis to PeCa, which research resource also provides new insights into future investigations aimed to explore the in-depth mechanisms of miRNAs and other small RNAs including piRNAs in penile carcinogenesis regulation and effective target-specific theragnosis.

Size-dependent toxicity and interactions of calcium oxalate dihydrate crystals on Vero renal epithelial cells

Urinary crystals in normal and kidney stone patients often have varying sizes; the interaction between renal epithelial cells and COD crystals generated in the tubular fluid could play an initiating role in the pathophysiology of calcium oxalate nephrolithiasis. This study aims to compare the cytotoxicity of micro/nano-calcium oxalate dihydrate (COD) crystals (50 nm, 100 nm, 600 nm, 3 μm, and 10 μm) toward African green monkey renal epithelial (Vero) cells to reveal the mechanism of kidney stone formation at the molecular and cellular levels.

METHODS

Vero cells were exposed to COD crystals of varying sizes at a concentration of 200 μg mL^-1 for 6 h. The effects of COD crystals on Vero cell viability, apoptosis rate, and cellular biochemical parameters [lactate dehydrogenase (LDH), superoxide dismutase (SOD), reactive oxygen species (ROS), hyaluronic acid (HA), osteopontin (OPN), and mitochondrial membrane potential (Δψ_m)] were determined using biochemical and morphological analyses.

RESULTS

Vero cell viability and apoptotic rate were closely associated with the size of COD crystals; lower cell viability and higher apoptosis rate were observed in cells exposed to smaller COD crystal size. The expression of SOD, ROS, HA and OPN also changed in a size-dependent manner after exposure to the five different sizes of COD crystals. The area ratio of the (100) face with a high density of Ca²⁺ ions to the total surface area was also found to influence the severity of cell injury. Cell injury induced by COD crystals was mainly caused by excessive expression of intracellular ROS and reduction of free-radical scavenger SOD. Moreover, binding of large crystals on the cell membrane surface takes more time to cause cell injury than internalized small-sized crystals. The cell death rate was found to be positively correlated with the amount of internalized COD crystals.

CONCLUSIONS

although the COD toxicity is often disregarded, the size-dependent cytotoxicity of COD crystals toward Vero cells is demonstrated in this study.

Inhibition of urinary macromolecule heparin on aggregation of nano-COM and nano-COD crystals

Purpose: This research aims to study the influences of heparin (HP) on the aggregation of nano calcium oxalate monohydrate (COM) and nano calcium oxalate dihydrate (COD) with mean diameter of about 50 nm. Method: The influences of different concentrations of HP on the mean diameter and Zeta potential of nano COM and nano COD were investigated using a nanoparticle size Zeta potential analyzer. Results: HP could be adsorbed on the surface of nano COM and nano COD crystals, leading to an increase in the absolute value of Zeta potential on the crystals and an increase in the electrostatic repulsion force between crystals. Consequently, the aggregation of the crystals is reduced and the stability of the system is improved. The strong adsorption ability of HP was closely related to the -OSO₃⁻ and -COO⁻ groups contained in the HP molecules. X-ray photoelectron spectroscopy confirmed the coordination of HP with Ca²⁺ ions of COM and COD crystals. Conclusion: HP could inhibit the aggregation of nano COM and nano COD crystals and increase their stability in aqueous solution, which is conducive in inhibiting the formation of calcium oxalate stones.