In our current study, we explored miRNA expression profiles of peripheral blood from healthy control and asthma patients. Significant differences were found in the expression of multiple miRNAs between the groups. In the asthma group, the expressions of miR-6785-5p, miR-4428, miR-6893-5p, miR-513c-5p, miR-513b-5p, miR-5691, miR-512-3p, miR-4516, miR-8078 were remarkably elevated, while the expressions of miR-374a-5p, miR-26b-5p, miR-374b-5p, miR-223-3p, miR-20a-5p, miR-20b-5p, miR-140-5p, miR-107, miR-17-5p, miR-195-5p, miR-15b-5p were significantly reduced by miRNA microarray. The expressions of miR-107 and miR-140-5p were validated by Real Time PCR assay. Moreover, miR-107 and miR-140-5p are likely involved in the pathophysiology in asthma through regulating LIGHT gene.
Based on our previous research[5], LIGHT has been found to play a vital role in regulating the interactions between airway inflammation and remodeling in asthma. Many studies showed that miRNA stargeting asthma-susceptibility genes reflect the corresponding effect on the pathophysiology in asthma[6–8]. Several studies have identified aberrant miRNA expression profiles associated with asthma severity[9], or therapy responses[10–12]. As a miRNA target gene, LIGHT may be regulated by miR-512-3p, miR-513b-5p, miR-5691, miR-107, miR-140-5p, and miR-17-5p screened by TargetScan. And then the normalized levels of these six miRNAs were revalidated through Real-Time PCR. It was demonstrated that the change trend in the miRNA expression patterns in asthma patients was similar to that in the miRNA microarray, and the same change patterns were obtained by increasing the sample size for verification.
To investigate the candidate regulatory mechanism of the top two miRNAs (miR-107 and miR-140-5p) targeting LIGHT in asthma, we conducted GO functional and KEGG pathway enrichment analysis to investigate the target gene-miRNA network. Our findings indicated that the target genes have potential roles in the physiological processes of asthma, such as stem cell regulation and cytophagocytosis, through downstream signaling pathways (eg. PI3K-Akt, AMPK). Recent studies revealed that miR-107 and miR-140-5p were characterized as tumor suppressors.[13–16], and reduced in a various type of cancer. Additionally, the level of miR-140-5p was downregulated in the respiratory epithelium of patients with cystic fibrosis.[17]However, there is still no study analyzing the potential roles of miR-107 and miR-140-5p in the pathogenesis of asthma. PI3K-Akt signaling pathway has been known to be involved in AMPK-dependent autophagic cell death, cell proliferation and differentiation. According to a study on asthma, AMPK/PI3K/Akt pathway played a crucial role in promoting airway inflammation and lung injury in asthma model.[18] Further studies are required to reveal the crosstalk between miRNAs and AMPK/PI3K/Akt signaling pathway in asthma.
Statistical tools were utilized to analyze the correlation between the expression level of miR-107 and miR-140-5p and various common clinical parameters. The results showed that the relative expressions of miR-107 and miR-140-5p were both positively correlated with the absolute peripheral eosinophil counts. Moreover, a significant correlation was also seen between miR-107 expression levels and the percentage of peripheral eosinophils. It was implied that the post-transcriptional regulators, miR-107 and miR-140-5p, may be involved in eosinophilic inflammation by negatively regulating LIGHT gene, and thus alleviate asthma symptoms. We also found that the relative expressions of miR-107 and miR-140-5p can be used as diagnostic biomarkers to distinguish patients with asthma from healthy control, whereas the diagnostic performance has not been established for asthma severity.
There are several limitations of this study that deserve mention. First, this is a single-center study with a small sample size, and a larger sample size will give us more accurate results. Second, there is lack of research on the serum levels of LIGHT, AMPK, PI3k and Akt, which could provide more information for the roles of the miRNAs in asthma progression. Third, further researches are needed to assess the clinical values of miR-107 and miR-140-5p in asthma, and to establish the validity and reliability of our findings.