[Comparison study on the differential expression of miRNAs in rat pulmonary fibrosis induced by nanosized SiO(2) and microsized SiO(2)].

Objective: To explore the correlation between expression level of miRNAs and pulmonary fibrosis on the basis of comparison the differential expression of miRNAs in rat pulmonary fibrosis induced by nano SiO(2) and micron SiO(2). Methods: Thirty-six healthy male SD rats weighting 180-220 g were randomly divided into 3 groups. They were instilled intratracheally with 1 ml suspension of saline, 25 mg/ml nanosized SiO(2) and microsized SiO(2) particles and sacrificed at 60 d and 90 d postexposure from each group with six rats. The change of pathological morphology and ultrastructure of lung were observed by optical and transmission electron microscopy. The differentially expressed microRNAs in lung tissue of the rats after instilled intrachcally nanosized SiO(2) and microsized SiO(2) particles at 60 d and 90 d were determined by Illumina HiSeq 2 000 sequencing technique. Target prediction for miRNAs was conducted by databases of Target-scan. Function-significant enrichment analysis and signal pathway analysis for predicted target genes were respectively conducted by the GO and the KEGG, then target genes related to pulmonary fibrosis were screened out. Results: Light microscope examination showed that wide bronchi, vessels, interlobular septa and slight fibrous connective tissue proliferation at 60 d and 90 d postexposure in 25 mg/ml nanosized SiO(2) group. A few fused nodules at 30 d postexposure, a lot of fused nodules at 60 d postexposure, fibrous cell nodules and compensatory emphysema around alveolar at 90 d postexposure in 25 mg/mL microsized SiO(2) group were observed. Electron microscopy demonstrated swelling and vacuolar degeneration of osmiophilic lamellar bodies in type Ⅱ alveolar epithelial cells, collagen fiber and elastic fiber hyperplasia in pulmonary interstitial at 60 d, 90 d postexposure in 25 mg/ml nanosized SiO(2) group. Increased and vacuoloid changed osmiophilic lamellar bodies in type Ⅱ alveolar epithelial cells, collagen fiber and elastic fiber hyperplasia in the interstitial at 60 d, 90 d postexposure in 25 mg/ml microsized SiO(2) group were observed. Comparing to saline control group, the number of miRNA up-regulated expression was 50, 70, and down-regulated expression was 22 and 24 at 60 d, 90 d postexposure in 25 mg/ml nanosized SiO(2) group respectively. There were 91,70 miRNAs up-regulated expression and 34,78 miRNAs down-regulated expression at 60 d, 90 d postexposure in 25 mg/ml microscale SiO(2) group. The common miRNA of differential up-regulated expression are miRNA-18a and miRNA-702-3p, down-regulated expression are miRNA-541, miRNA-127 and miRNA-379 both in nanosized SiO(2) and microscale SiO(2) group. The target genes related to pulmonary fibrosis were CTGF, IGF, BMP7, FGF7, TGF-ß RIII, IGF1R and TGF-ß1 respectively. Their biologic functions are to regulate signal pathway of TGF-ß, MAPK and Wnt, and activation of fibroblast. Conclusion: These findings suggested that same dose of nanosized SiO(2) particles could cause mainly characterized by pulmonary interstitial fibrosis differing from silicotic nodule caused by microsized SiO(2). miRNA-18a, miRNA-702-3p, miRNA-541, miRNA-127 and miRNA-379 may play a role in the process of pulmonary fibrosis in nanosized SiO(2) and microscale SiO(2) by regulating its target genes.