Transcriptomics changes in neural differentiated mouse embryonic stem cells (mESCs) under exposure to sodium valproate

Studying chemical disturbances during neural differentiation of mES cells has been established as an alternative in vitro testing approach for the identification of developmental toxicants. miRNAs represent a class of small regulatory RNA molecules, which bind to target mRNAs thereby repressing their translation. Many studies have shown an essential role of miRNAs in regulation of gene expression during development and ESC differentiation. Thus, neural differentiation of ESC in vitro allows investigating the role of miRNAs in chemical-mediated developmental toxicity. We analyzed the expression of miRNAs and transcriptomics changes during neural differentiation of mESC exposed to the developmental neurotoxicant sodium valproate (VPA). A total of 110 miRNAs and 377 mRNAs were identified differently expressed in neural differentiating mES cells under VPA treatment (300M) compared to solvent control on day 16 of differentiation. Analysis of miRNA expression revealed that valproate switches the lineage specification from neural to myogenic differentiation (upregulation of muscle-enriched miRNAs mir-206, mir-133a and mir-10a and downregulation of neuro-specific miRNAs mir-124a, mir-128 and mir-137). The findings on the miRNA level could be confirmed on mRNA level (induction of expression of myogenic regulatory factors (MRFs) as well as muscle specific genes (Actc1, calponin, myosin light chain, asporin, decorin) and repression of genes involved in neurogenesis (Otx1 and 2, Zic3, 4, 5)) as well as morphologically by immunocytochemistry. The observed results were VPA specific and most probably due to inhibition of histone deacetylase (HDAC) activity of VPA for two reasons: (i) we did not observe any induction of muscle specific miRNAs in neural differentiating ES cells exposed to the unrelated developmental neurotoxicant sodium arsenite; (ii) expression of muscle specific mir-206 and muscle enriched mir-10a was similarly increased in cells exposed to a structurally different HDAC inhibitor, trichostatin A (TSA). Furthermore, using our in vitro cell system we could confirm an aberrant expression of known VPA target genes and genes involved in neural tube closure. We conclude that miRNA expression profiling is a suitable molecular endpoint for developmental neurotoxicity. Observed lineage shift into myogenesis, where miRNAs play a significant role, could be a major developmental neurotoxical mechanism of VPA.

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