The developing nervous system is highly susceptible to methylmercury (MeHg), a widespread environmental neurotoxic contaminant. A wide range of morphological and functional outcomes have been described; however, there are still open questions regarding the mechanisms behind the developmental neurotoxic effects induced by low-level exposure. In the present study, we have examined the effects of nanomolar concentrations of MeHg on primary fetal human progenitor cells (hNPCs) with special focus on the role played by developmental stage and sex on the neurotoxic outcome. We found that neurospheres derived from earlier gestational time points exhibit higher susceptibility to MeHg, as they undergo apoptosis at a much lower dose (25 nM) as compared to neurospheres established from older fetuses (100 nM). At subapoptotic concentrations (10 nM), MeHg inhibited neuronal differentiation and maturation of hNPCs, as shown by a reduced number of Tuj1-positive cells and a visible reduction in neurite extension and cell migration, associated with a misregulation of Notch1 and BDNF signaling pathways. Interestingly, cells derived from male fetuses showed more severe alterations of neuronal morphology as compared to cells from females, indicating that the MeHg-induced impairment of neurite extension and cell migration is sex-dependent. Accordingly, the expression of the CDKL5 gene, a major factor regulating neurite outgrowth, was significantly more downregulated in male-derived cells. Altogether, gestational age and sex appear to be critical factors influencing in vitro hNPC sensitivity to low levels of MeHg.
Keywords: Cell migration; Developmental neurotoxicity; Human neural progenitor cells; Methylmercury; Sex-related differences.