9 The SafeChrom project - integrative analyses of circulating microRNAs in hexavalent chromium exposed workers

Objective Exposure to hexavalent chromium (Cr(VI)) occurs during several occupational activities and leads to lung cancer. Growing evidence suggests that microRNA (miRNA) plays an important part in carcinogenesis. This study was to explore circulating miRNAs of Cr(VI) exposed workers and to identify the potential biological function of differentially expressed miRNA (DEM).Material and Methods This study included 89 Cr(VI) exposed workers and 47 controls (male and non- smokers) recruited in the SafeChrom project. MiRNA was extracted from plasma followed by DNAse treatment, library preparations, miRNA sequencing, and DEM analysis. Messenger RNA (mRNA) analysis was performed via qPCR. Target genes of DEM were predicted, and enrichment and protein interaction network analyses were performed to understand their potential biological function.Results A total of 1937 miRNAs were detected and 59 DEMs were identified in the exposed workers (21up-regulated and 38 down-regulated miRNAs). 169 genes were identified to be associated with the up-regulated DEMs and 609 genes were associated with the down-regulated DEMs. Target genes for both up- and down-regulated DEMs were significantly enriched in three KEGG terms: miRNAs in cancer, small cell lung cancer and non-small cell lung cancer. Network analysis revealed hsa-miR-184 as a central interactor in the up-regulated DEMs, and hsa-miR-200c-3p, hsa-miR-429, hsa-miR-106a-5p and hsa-miR-210-3p were central interactors in down-regulated DEMs. Protein-protein interaction showed a high number of interactions and confirmed the results obtained by enrichment analysis, in which AKT1, CCND1, CDK4 and E2F3 were recognized as hub genes. Blood mRNA expression levels of hub genes are ongoing.Conclusions Our study suggests that Cr(VI) exposure results in differential expression of miRNAs in occupational workers. The identified DEMs in exposed workers combined with bioinformatics analyses suggest possible roles for specific miRNAs, of which some may be associated with Cr(VI)-induced toxicity and carcinogenicity. Further studies are needed to validate the mechanism of those DEMs and their target genes.Acknowledgments This study has received funding from Forskningsrr adet för hälsa, arbetsliv och välfärd (Forte) (2020-00208) and Afa Försäkring (200279).