Genes Involved in DNA Repair and Mitophagy Protect Embryoid Bodies from the Toxic Effect of Methylmercury Chloride under Physioxia Conditions

The formation of embryoid bodies (EBs) from human pluripotent stem cells resembles the early stages of human embryo development, mimicking the organization of three germ layers. In our study, EBs were tested for their vulnerability to chronic exposure to low doses of MeHgCl (1 nM) under atmospheric (21%O-2) and physioxia (5%O-2) conditions. Significant differences were observed in the relative expression of genes associated with DNA repair and mitophagy between the tested oxygen conditions in nontreated EBs. When compared to physioxia conditions, the significant differences recorded in EBs cultured at 21% O-2 included: (1) lower expression of genes associated with DNA repair (ATM, OGG1, PARP1, POLG1) and mitophagy (PARK2); (2) higher level of mtDNA copy number; and (3) higher expression of the neuroectodermal gene (NES). Chronic exposure to a low dose of MeHgCl (1 nM) disrupted the development of EBs under both oxygen conditions. However, only EBs exposed to MeHgCl at 21% O-2 revealed downregulation of mtDNA copy number, increased oxidative DNA damage and DNA fragmentation, as well as disturbances in SOX17 (endoderm) and TBXT (mesoderm) genes expression. Our data revealed that physioxia conditions protected EBs genome integrity and their further differentiation.

Automated summary

In this study, the vulnerability of human pluripotent stem cell derived embryoid bodies (EBs) to chronic exposure to low doses of MeHgCl was investigated under atmospheric (21% O-2) and physioxia (5% O-2) conditions. Significant differences in gene expression related to DNA repair and mitophagy were observed between the two oxygen conditions in untreated EBs. Chronic exposure to MeHgCl disrupted the development of EBs under both oxygen conditions, but only the EBs exposed to MeHgCl at 21% O-2 showed downregulation of mtDNA copy number, increased oxidative DNA damage, and disturbances in certain gene expressions. Physioxia conditions protected EBs genome integrity and their further differentiation.