Triclosan (TCS) exposure has widely adverse biological effects such as influencing biological reproduction and endocrine disorders. While some studies have addressed TCS-induced expression changes of miRNAs and their related down-stream target genes, no data are available concerning how TCS impairs miRNA expression.

In a recent study, small RNA sequencing showed four miRNAs (miR-125b, miR-205, miR-142a and miR-203a) to have differential expression between TCS-exposure treatments and the control group; their functions mainly involved fatty acid synthesis and metabolism. TCS exposure led to the up-regulation of mature miR-125b that was concomitant with consistent changes in pri-mir-125b-1 and pri-mir-125b-3 among its 3 pri-mir-125bs. Up-regulation of miR-125b originated from direct shear processes involving the two up-regulated precursors, but not pri-mir-125b2. Increased expression of pri-mir-125b-1 and pri-mir-125b-3 resulted from nfe2l2- and c/ebpα-integration with positive control elements of promoters for the two precursors. The overexpression of transcriptional factors, nfe2l2 and c/ebpα, initiated the promoter activity for the miR-125b precursor. CpG islands and Nfe2l2 were involved in constitutive expression of mir-125b-1 and mir-125b-3. The activities of two promoter regions, −487 to −1 bp for pri-mir-125b1 and −1327 to +14 bp for pri-mir-125b-3 having binding sites for NFE2 and Nfe2l2/MAF:NFE2, were higher than other regions, further demonstrating that the transcriptional factor Nfe2l2 was involved in the regulation of pri-mir-125b1 and pri-mir-125b-3. TCS’s estrogen activity resulted from its effects on GPER, a novel membrane receptor, rather than the classical ERα and ERβ.

These results explain, to some extent, the up-stream mechanism for miR-125b up-regulation, and also provide a guidance to future mechanistic study on TCS-exposure.

LC Sciences

A, Venn diagram for the dysregulated miRNAs in comparisons of control vs. 62.5 μg/L treatment, control vs. 125 μg/L treatment and control vs. 250 μg/L treatment; B, clustering analyses of four conserved and differentially expressed miRNAs;  C, heat map and clustering patterns of the differentially expressed miRNAs and their target gene-related pathways; C, prediction using human miRNAs (p-value threshold<0.05 and MicroT threshold<0.08); and  D, prediction using zebrafish miRNAs (p-value threshold<0.05 and MicroT threshold<0.08).

 

Reference
J. Lin, C. Wang, J. Liu, R. A. Dahlgren, W. Ai, A. Zeng, X. Wang, H. Wang (2017) Up-stream mechanisms for up-regulation of miR-125b from triclosan exposure to zebrafish (Danio rerio) Aqua. Tox. doi: 10.1016/j.aquatox.2017.10.021 [abstract]

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