Prolonged duration induces divergent transcriptomic responses to manganese, distinct from concentration effects, in...

Understanding manganese (Mn) neurotoxicity requires experimental models that realistically reflect human exposure scenarios. A key limitation of current in vitro paradigms is the reliance on acute, high-concentration exposures, which may not accurately capture the molecular consequences of long-term Mn accumulation. To address this, this study compared transcriptomic responses to acute (6-hour) and chronic (40-day) Mn exposures in SH-SY5Y cells, using Mn concentrations spanning near-physiological to sub-cytotoxic ranges. The 6-hour exposure design replicates a widely applied acute duration in the literature, while the 40-day duration was selected to mimic prolonged, low-level Mn burden reported in epidemiological and occupational studies. Bulk RNA sequencing revealed that chronic Mn exposure induced distinct and more extensive transcriptional alterations compared to acute exposure, independent of concentration. Pathway enrichment analyses indicated that cellular functions selectively perturbed under chronic conditions are highly relevant to neurodegenerative risks and aligns with independent Parkinson's disease transcriptomic datasets. These pathways include axonal guidance signaling, amyloid fiber formation, extracellular matrix organization, and synaptic functioning. In contrast, acute exposures primarily disturbed intracellular ion homeostasis maintenance mechanisms. Protein kinase A signaling and metallothionein-mediated metal-binding pathway were the only two pathways that were shared between both applied durations exposed at Mn concentrations with reported adverse outcomes. Transcriptomic alterations in this study highlighted the contribution of mechanisms related to normal Mn-dependent cellular functions in the development of its neurotoxicity. Furthermore, these results emphasized that exposure duration is a critical determinant to be considered when evaluating long-term Mn overload-induced neurodegeneration via in vitro platforms.