Examining perfluorohexane sulfonate (PFHxS) impacts on sensorimotor and circadian rhythm development

Perfluorohexane sulfonate (PFHxS) is a ubiquitous perfluoroalkyl substance known for its environmental persistence and potential toxicity. This study investigated PFHxS's impact on zebrafish embryos, focusing on sensorimotor behavior, circadian rhythm disruption, and underlying molecular mechanisms. Under 24 hr dark incubations, PFHxS exposure induced concentration-dependent hyperactivity within larval photomotor response, characterized by the distinctive "O-bend" response, strong light-phase hyperactive movement and seizure-like movements. It appears that PFHxS-treated embryos cannot sense light cues in a normal manner. Similar hyperactivity was seen for acoustic startle response assay, suggesting that the response is not merely visual, but sensorimotor. LC-MS studies confirmed detectable uptake of PFHxS into embryos. We then conducted mRNA-sequencing across multiple time points (48 and 120 hpf) and concentrations (0.00025, 0.0025 and 25 µM). Data at the 25 µM (2-120 hpf) exposure showed disrupted pathways associated with DNA and cell cycle. Interestingly, data at 0.00025 µM - an environmentally relevant concentration- at 48 hpf showed disruption of MAPK and other signaling pathways. Immunohistochemistry of eyes showed reduced retinal stem cell proliferation, consistent with observed DNA replication pathway disruptions. To assess if these impacts were driven by circadian rhythm development, we manipulated light/dark cycles during PFHxS incubation; this manipulation altered behavioral patterns, implicating circadian rhythm modulation as a target of PFHxS. Since circadian rhythm is modulated by the pineal gland, we ablated the gland using metronidazole; this ablation partially rescued hyperactivity, indicating the gland's role in driving the phenotype. Collectively, these findings underscore proclivity of PFHxS to cause neurodevelopmental toxicity, necessitating further mechanistic exploration and environmental health assessments.