Data collection and processing
The NCBI Gene Expression Omnibus database was searched to obtain gene expression profiles of datasets for RSA, and inclusion criteria were applied to select relevant data sets. The selected data sets were generated through microarray or RNA-Seq techniques. They consisted of normal controls and RSA women of reproductive age without any evident endocrine disorders, karyotype abnormalities, uterine malformations, fallopian tube blockage, acute infections, or other issues, as verified by the 2022 update ESHRE guidelines (RPL, Bender Atik et al. 2023); Four GSE profiles were chosen and downloaded from the database (Table 1), including GSE179996, GSE178619, GSE201442, and GSE201469. The platforms used for the GSE profiles were GPL21827, GPL25134, GPL21576, and GPL21185, respectively. GPL21827 only included the probe name data (or sequence data) and not the gene symbol. Hence, for probes annotation of GPL21287 sequences according human genome (GRCH-37 release in GENCODE), the R package “Rsubread” was used. The regulatory pathways and genes involved in recurrent abortion were investigated by performing GO analysis on the mRNAs in the regulatory network of lncRNA-miRNA-mRNA constructed in this study (Harrow, Frankish et al. 2012, Liao, Smyth et al. 2019).
Identification of DEGs, DELs and DEmiRs
The study used the Limma package in R software (Ritchie, Phipson et al. 2015) to identify differentially expressed mRNAs, lncRNAs, and miRNAs, where statistical significance was determined based on a p-value <0.05 and |log2 fold-change|>2.0 threshold for DEGs, DELs, and DEmiRs. The results were presented using volcano plots using R packages "EnhancedVolcano" and "ggplot2 The overlapping miRNA and genes in each group were examined using the Venn diagram web tool. Moreover, the EnhancedVolcano package was used to generate a hierarchical cluster analysis of the volcano plots of DELs, DEmiRs, and DEGs for visualization.
Prediction of target miRNAs of DELs and miRNA-target interactions
This study used three databases, namely lncbasev3 (DIANA Tools), LncSEA, and LncTar, to predict lncRNA (Li, Ma et al. 2015, Karagkouni, Paraskevopoulou et al. 2020, Chen, Zhang et al. 2021). RNA interactions and miRNA target sites on non-coding RNAs for each DEL. Overlapped miRNAs of the between DEmiRs and miRNAs interacting with DELs were used as potential target miRNAs for future analysis. The predicted function of the overlapped miRNAs was assessed using DIANA-miRPath v3.0 (https://www.microrna.gr/miRPathv3), a web server database that evaluated miRNAs regulatory roles and estimated the associated regulation pathways. Finally, the overlapped miRNAs were selected for further target predictions.
The prediction of miRNA-mRNA interactions was performed using two Bioconductor packages in R software, namely "multiMiR" and "SpidermiR"(Ru, Kechris et al. 2014, Cava, Colaprico et al. 2017). "multiMiR" is an R package that predicts miRNA targets by combining data from 8 databases (Miranda, TargetScan, EIMMo, DIANA, MicroCosm, PicTar, PITA, and miRDB) and validated targets from miRTarBase, TarBase, and miRecords. As well as, "SpidermiR" provides miRNA-gene-gene interactions and analyzes miRNA gene regulatory networks to identify miRNA-gene relationships. Overlapping miRNA target genes from the analysis were selected and intersected with the DEGs to obtain candidate target genes.
Construction of the ceRNA network
According to previous research, lncRNAs can act as a sponge for miRNA and regulate mRNA expression by sequestering miRNA (Gupta 2014). This study established a regulatory network of lncRNA-mediated competing endogenous RNA (ceRNA) by constructing a miRNA-mRNA-lncRNA network. The network was created based on the binding of ceRNA to miRNA via miRNA response elements (MREs). The Cytoscape software version 3.9.1 was used to visualize the miRNA-mRNA-lncRNA network (Franz, Lopes et al. 2023). To construct the lncRNA-miRNA-mRNA network, overlapping miRNAs and lncRNAs or mRNAs with inverse relation in lncRNA-miRNA or miRNA-mRNA interactions were selected.
GO and KEGG enrichment analysis
To investigate the roles of differentially expressed genes (DEGs) in the ceRNA network, Fisher's test was used for GO and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses. Enrichr and clusterProfiler packages in R software were employed for the enrichment analysis. GO analysis was carried out for molecular function (MF), biological process (BP), and cell component (CC). KEGG enrichment analysis was conducted to identify the signaling pathways related to genes in the ceRNA regulatory network. A pvalue<0.05 was shown statistically significant.
protein–protein interaction (PPI) network construction
The mRNA molecules in the ceRNA network produced a protein-protein interaction (PPI) network, visualized using Cytoscape software version 3.9.1. A combined score > 0.4 was set as the cut-off value for the protein pairs in the PPI network (Kohl, Wiese et al. 2011). The molecular complex detection (MCODE) plugin was applied to detect essential modules in the PPI network, including hub genes and connective modules. The degree cut-off was established at 2, the node score was 0.2, and the maximum depth was set at 100. The STRING database (https://string-db.org/) was employed to construct the PPI network.