2.1 Microarray dataset
Two miRNA datasets, GSE118340 and GSE42716, were downloaded from the GEO database (https://www.ncbi.nlm.nih.gov/geo/). GSE11840 was based on the GPL19057 (Illumina NextSeq 500), and GSE42716 was based on the GPL10384 [Agilent-021828 Unrestricted Mouse miRNA Microarray (V2)]. In total, four kidney samples of the UUO model (GSM3325596, GSM3325597, GSM3325598, GSM3325599) and three kidney samples of the sham control (GSM3325589, GSM3325590, GSM3325591) from GSE118340 were selected for analysis. Four kidney samples of the UUO model (GSM1048441, GSM1048442, GSM1048443, GSM1048444) and four kidney samples of the sham control (GSM1048437, GSM1048438, GSM1048439, GSM1048440) from GSE42716 were also selected. The mRNA dataset GSE96101 was also downloaded from the GEO dataset, which is based on the GPL4134 (Agilent-014868 Whole Mouse Genome Microarray 4x44K G4122F). Six kidney samples of the UUO model (GSM2533412, GSM2533413, GSM2533414, GSM2533415, GSM2533416, GSM2533417) and five kidney samples of the sham control (GSM2533473, GSM2533474, GSM2533475, GSM2533476, GSM2533477) were selected for analysis. The above kidney samples were all harvested from mice seven days after UUO surgery and then were subjected to microarray analysis of miRNAs and mRNAs. Contralateral kidneys without ureteral obstruction were used as controls. Subsequently, data quality from these datasets was assessed using R software.
2.2 Identification of differentially expressed miRNAs (DE-miRNAs) and mRNAs (DE-mRNAs)
The R software “DESeq2” package was used to identify DE-miRNAs in kidney tissues between UUO and sham control [19]. DE mRNAs were identified using the online tool GEO2R (http://www.ncbi.nlm.nih.gov/geo/geo2r), which allows users to compare two or more datasets in the GEO series to determine DEGs under experimental conditions [20]. Genes with more than one probe set were removed. In the present study, DE-miRNAs and DE-mRNAs were combined using the cut-off point of adj.P-value < 0.05, and |logFC| > 1.0. Then, the R heatmap and ggplot2 package were applied to paint the heatmap and Volcano. adj.P <0.05 means statistical significance.
2.3. GO annotation and KEGG pathway enrichment analysis
The selected DE-miRNAs were then uploaded to miRpath v3.0 (http://www.microrna.gr/miRPathv3/), an online website that integrates miRNA target gene databases, including TarBase, TargetScan, and microT-CDS [21]. It only needs to input the miRNA Id of interest and obtain the results of Gene Ontology (GO) and Kyoto Encyclopedia of Gene and Genome (KEGG) enrichment analysis. The selected DE-mRNAs were then uploaded to DAVID (https://david.ncifcrf.gov), a database that conducts functional annotation bioinformatics microarray analysis [22]. The top 10 GO annotations and KEGG pathways were visualized using GraphPad Prism.
2.4. miRWalk and Targetscan
miRWalk (http://mirwalk.umm.uni-heidelberg.de/) can predict the mRNAs targeted by specific miRNAs using a machine learning algorithm. Thus, this database was used to predict the targeted mRNAs of miR-342-5p. Targetscan 7.2 (http://www.targetscan.org/mmu_72/), an online database that is currently used to predict the location of miRNA binding sites with an accuracy of up to 90%, was applied to revalidate the binding sites of miRNA and mRNA.
2.5 Comparative Toxicogenomics Database (CTD)
CTD (http://ctdbase.org) is a powerful, publicly available database designed to advance understanding of how environmental exposures affect human health and to clarify the relationship among genes, drugs, and diseases. We used this database to evaluate the inference score of selected mRNAs in chronic kidney diseases (CKDs).
2.6 The iRegulon
The iRegulon, a Cytoscape App that consists of a transcription factor( TF) and its direct transcriptional targets, which contain common TF binding sites in their cis-regulatory control elements. It predicts TFs by calculating motif enrichment analysis. The motif enrichment analysis applies multiple position weight matrices (PWM), and finally sorts each motif. The preferred motif was used to predict the final TFs [23].
2.7 Cell culture and treatment
Mouse kidney epithelial cell line TCMK-1 was cultured in RPMI-1640 (HycloneCat.No.SH30809.01B) supplemented with 10% fetal bovine serum (Hyclone, Cat.No.SH30087.01) and 1% penicillin-streptomycin (Hyclone, Cat.No. SH30010) at 37°C under saturated humidity and 5% CO2 conditions. The cells were starved for 12 h; on reaching 70% confluence, TGF-β1 (eBioscience, 14-8342-82) was added to the medium at a final concentration of 10 ng/ ml for 0, 1, 2, 4, 8, 12, and 24 h, to choose suitable time points for the follow-up experiment.
2.8 Cell transfection
TCMK-1 cells were passaged one day before transfection to obtain 30%-50% confluence. Transfection was performed using Lipofectamine ™ RNAiMAX (Invitrogen, Cat. 13778075), and the miRNA / siRNA working concentration was 50 nM using Opti-MEM (Invitrogen, Cat. No. 31985070). In LC3 plasmid cell transfection, TCMK-1 cells were passaged one day before transfection to obtain 70%-80% confluence. Transfection was performed using Lipofectamine 2000 ( Invitrogen , Cat. 11668019) , Premo™ Autophagy Sensor LC3B-RFP (BacMam 2.0 Invitrogen™, P36236), and Opti-MEM (Invitrogen, Cat. No. 31985070). Approximately four h after transfection, the transfection mixture was replaced with DMEM-10% FBS. The punctate distribution of GFP-LC3 was observed using fluorescence microscopy. The remaining cells were then harvested for RNA and protein preparation.
2.9 Quantitative real-time PCR
Total RNA of TCMK-1 cells was extracted with TRIzol® Reagent (Invitrogen,15596026) according to the manufacturer's protocol. DNA was removed by treating with DNase (Fermentas, EN0521) and the purity of the RNA was assessed by determining the absorbance ratio at OD260/OD280. Total RNA was reverse transcribed into cDNA using TaKaRa PrimeScript II 1st Strand cDNA Synthesis Kit (TaKaRa, D6210A), Oligo dT Primer, dNTP Mixture, total RNA, and RNase Free dH2O. Real-time PCR was performed using the TaKaRa SYBR® Premix Ex Taq™ II kit (Perfect Real Time), and ABI PRISM® 7500 Sequence Detection System Real-Time PCR System. Primer sequences for the TCMK-1 cell samples were as follows:
FoxO3-F: 5′ - AACCGGCTCCTTCAACAGTA
FoxO3-R: 5’ GAAGCAAGCAGGTCTTGGA
Ptch1-F: 5′ - TCTGCTTCGGTGACTGTTG
Ptch1-R: 5′ - CCACGTCCTGTAGCTCTATG
β-actin-F: 5′ GCTTCTAGGCGGACTGTTAC
β-actin-R: 5’ CCATGCCAATGTTGTCTCTT
miR-342-5p-F: 5’ ACACTCCAGCTGGGAGGGGTGCTATCTGTGAT
miR-342-5p-R: 5’ CTCAACTGGT GTCGTGGA
miR-342-5p-RT:5’ CTCAACTGGTGTCGTGGAGTCGGCAATTCAGTTGAGCTCAATCA
U6-F:5′ - CTCGCTTCGGCAGCACA
U6-R:5′ AACGCTTCACGAATTTGCGT
U6-RT: 5′ AACGCTTCAC GAATTTGCGT
Reactions to determine the levels of Ptch1 and FoxO3 were carried out in a total volume of 20 μL, including 10 μL SYBR® Premix Ex Taq TM(2×), 2 μL cDNA, 6.4 dH2O, and 0.8 μL of each specific primer (10 μM), while the reaction for miR-342-5p was carried out in a total volume of 8 μL, including 2 μL 10 mM dNTP (Promega), 0.5 μL RNase inhibitor (Promega), 0.5 μL miR-342-5 primer, 0.5 μL U6 primer, 4 μL 5x buffer, and 0.5 μL M-MLV (Promega). The cycling conditions were set at 94°C for 3-4 min; 30 cycles at 94°C for 30 s, 60°C for 30 s, and 72°C for 30 s; the last cycle (1x) was set at 72°C for 10 min and 16°C for ∞. β-actin was utilized for standardization of Ptch1 and FoxO3, and U6 was used as the endogenous control for miR-342-5p. The levels of mRNAs and miRNAs were calculated using the 2-ΔΔCt method with the ABI PRISM® 7500 Sequence Detection System SDSShell Software 1.6.
2.10 Western blot
Protein samples were extracted with RIPA buffer. The extracted total protein was separated by SDS-PAGE and transferred to PVDF membranes. Following incubation in blocking buffer for 1 h at room temperature, the membrane was incubated at 4°C overnight with Ptch1 antibody (Abcam, ab109096), Foxo3 antibody (Thermo, FA1-14171), SQSTM1 / p62 antibody (Abcam, ab56416), and LC3B (D11) XP antibody (Cell Signaling Technology, 3868S). The results were visualized using Beyo ECL Plus substrate and exposed to X-ray film. β-actin was used for normalization.
2.11 Fluorescence in situ hybridization
Fluorescence in situ hybridization (FISH) was performed to detect the location of miR-342-5p, FoxO3, and Ptch1. We used a miR-342-5p probe labeled with FAM (green) and FoxO3 and Ptch1 probes labeled with cy3 (red). The cells were then visualized using a scanning laser confocal microscope (Leica, TCS SP2 AOBS).
2.12. Statistical Analyses
All data are shown as the mean ± standard deviation (s.d) and visualized using GraphPad Prism 8. Statistical analysis was conducted using SPSS 24.0. P < 0.05 was considered significant. All experiments were performed at least three times.