Based on the six eligible microarray datasets, we compared the expression levels of circulating miR-21，miR-155，miR-210，miR-126，miR-486，miR-182, and miR-17 between LUAD patients and healthy controls, and found that miR-210 was the only statistically significant circulating miRNA with excellent diagnostic performance for LUAD (AUC value was 0.83). Then we elucidated the oncogenic role of miR-210 in LUAD through bioinformatics analysis. We identified 38 statistically significant GO items and 21 KEGG pathways. Consistent with previous researches, we again proved that hypoxia was an important feature in LUAD and miR-210 was regarded as the most important hypoxemir associated with the tumorigenesis of LUAD. We also constructed PPI network of the target genes and identified nine hub genes involved. Therefore, this study provided evidences for circulating miR-210 as a promising noninvasive biomarker for early LUAD detection, and provided a foundation for further researches on circulating miR-210 in the pathogenetic of LUAD.
MiR-210 is one of the most widely studied miRNAs and has captured great attention since it has been shown to be associated with various biological processes and the development of different human diseases thus far . The increasing literatures exploring the role of circulating miR-210 in LUAD have been proved miR-210 to be a noninvasive biomarker for LUAD detection [45-47]. In Tamiya H’s research, it revealed the AUC value of exosomes miR-210 in the diagnosis of LUAD combined with pleural effusion was 0.81 . In Y. HE’s study, circulating miR-210 combined with other miRNAs (miR-199a-3p, miR-148a-3p, miR-378d, miR-138-5p) had a diagnostic specificity of 90.2% in LUAD presenting with pulmonary nodules . Also, Shen et al used plasma miRNAs panel (miR-210, miR-21, miR-486-5p, and miR-126) for the detection of LUAD which yield 92% sensitivity and 97% specificity . Not long ago, one research demonstrated that serum miR-210 displayed considerable accuracy in discriminating LUAD patients from healthy controls, the AUC value was 0.84 . With the consistent of previous results, this study showed the combined AUC value of circulating miR-210 for LUAD were 0.83. Theoretically, circulating miR-210 test was a promising method to diagnosis LUAD in this study. It provides a novel approach for improving management of LUAD, which is a major subtype of NSCLC, and finding efficacy noninvasive detection markers to classify NSCLC subtypes. Thus, future validation on circulating miR-210 as a noninvasive specific biomarker for LUAD should preferably be done in the context of large scale prospective studies.
Overall，we demonstrated that the diagnostic performance of circulating miR-210 for LUAD appeared to be rather promising. However, there was severe heterogeneity among studies reported circulating miR-210 as biomarkers for LUAD in this meta-analysis (Figure 2). One of the heterogeneity is that the variation of sample types and population characteristics among studies. The miRNA profiles are differences, which were abtained form different sample types and different sample preparation [34, 51]. Although plasma, serum and whole blood are all origin of blood-based samples, reports described the variations circulating miRNA profile by sample handling and preparation [52, 53], and in which the major factor of concern is the blood fractionation protocol [51, 54, 55]. Population characteristics, such as age, smoking status, and ethnicity, have been demonstrated as the other potential source of miRNA level variability in LC patients [37, 56, 57]. Another important source of heterogeneity was the small size sample in eligible datasets. Three of six datasets have small size sample (GSE93300, GSE94536, GSE111803). Sample size is one of the critical elements affecting the statistical power, and large population researches can help to reduce analytical bias and to improve diagnostic performance. In this study, one dataset (GSE103149) only uploaded the averaged normalized values without the original expression levels of circulating miRNAs and in which SD values were estimated by estimation formula. It may be one more factor of the heterogeneity. Considering the limitations mentioned above, developing new constantly technologies and bioinformatics tools to reduce the analysis bias are necessary.
The roles of miRNAs in the initiation and progression of LUAD is with complicated gene expression and signaling pathways, researchers worldwide have been focus on the theme recent years [27, 31, 58, 59]. In this study, we predicted the target genes of miR-210 in LUAD as well, and then used bioinformatics analysis to explore the potential biological processes and molecular pathogenesis of the target genes involved. And the results showed that nine central genes were identified (FBXO, FBXL, MGRN1, ATG7, CUL3, RAB, ADAMTS, SEMA, THBS2). In GO annotation and KEGG pathway analysis, the results revealed that responsing to hypoxia was the mainly involved biological process, the major site of biological process was extracellular matrix, protein complex binding was the dominating molecular function, and pathways in cancer was the significant pathway aggregating most genes. In solid tumors, oxygen concentration is reduced variously in which hypoxia is the most common neoplastic microenvironment. A current overview shows miR-210 has been identified as a major miRNA induced under hypoxia, and plays numerous crucial roles in the cellular response to hypoxia, such as in apoptosis , angiogenesis , cell cycle regulation , and mitochondrial metabolism . Furthermore, several studies have suggested a direct connection between miR-210 and hypoxia, specially carrying the HIF-1a-binding site in its promoter [64-66]. While miR-210 has garnered interest as a prospective biomarker for LUAD detection, further work is require to confirm its detailed role in biological processes and molecular mechanisms.