Emergent latent neurotoxic effects of manganese following nominal chronic exposures in human stem cell and Caenorhabditis elegans models.

Behavioral deficits can emerge after the removal of manganese (Mn) exposures in humans and other mammals. Although epidemiological studies provide substantial evidence supporting latency, challenges reproducing such effects in alternative models have slowed mechanistic understanding. Here, we report in 2 systems, human-induced pluripotent stem cell (hiPSC)-derived and Caenorhabditis elegans, that prior chronic exposure elicits clear latent neurotoxic effects in gene expression and functional outcomes. To identify these effects and investigate underlying mechanisms, single-cell RNA sequencing was employed in hiPSC-derived cortical culture to provide comparisons of transcriptomic changes immediately following versus after cessation of chronic Mn exposures. Transcriptomic alterations revealed latent effects after cessation of elevated Mn that were not detected immediately following 40-day exposures. To confirm the reproducibility of the observed latent magnification of chronic Mn-induced neurotoxicity, behavioral endpoints were evaluated in C. elegans. We detected a significant amplification of 2 motor phenotypes after a period of exposure cessation. These data demonstrate, in 2 genetic and mechanistically tractable systems, the detection of novel latent neurotoxic effects not detected until the cessation of a chronic exposure at a magnitude well beyond the effects of the chronic Mn exposure itself. Identified alterations support a linkage between the latent effects following chronic Mn exposure and a broad range of neurodegenerative etiologies and provide insight into the cellular pathways involved. Using both in vitro and in vivo experimental models provides complementary evidence that substantially strengthens the robustness and translational relevance of these novel findings.