Role of dopaminergic RE1-silencing transcription factor (REST) in manganese-induced behavioral deficits and dysregulating dopaminergic and serotonergic neurotransmission in mice.

Chronic exposure to elevated levels of manganese (Mn) induces manganism, a neurological disorder, exhibiting symptoms resembling Parkinson's disease (PD). Mn is well known to dysregulate dopaminergic (DAergic) function, while the repressor element-1 silencing transcription factor (REST) induces protection against Mn-induced toxicity and several neurodegenerative diseases, including PD and Alzheimer's disease. In the present study, we investigated if DAergic REST plays a role in Mn-induced neurotoxicity by assessing behavioral deficits and alteration of neurotransmitter levels using high-performance liquid chromatography with electrochemical detector (HPLC-ECD), and microdialysis between DAergic-specific REST-deleted (REST cKO) mice and REST loxP mice as wild-type (WT) controls. Mice were exposed to Mn (330 μg, daily intranasal instillation for 3 weeks), followed by assessment of locomotor activity and novel object recognition, and subsequent brain dissection. Neurotransmitters, including DA, serotonin (5-HT), norepinephrine (NE), and glutamate, were analyzed in different brain regions, such as the striatum, midbrain, cortex, hippocampus, and cerebellum. After Mn exposure, extracellular DA levels in the striatum were measured by HPLC-microdialysis. The results showed that DAergic REST deletion exacerbated Mn-induced behavioral deficits and decreased DA levels in the nigrostriatal regions of WT mice. REST cKO increased DA turnover rates (DOPAC/DA and HVA/DA) by 10-fold in the nigrostriatal regions, showing lesser effects in other brain regions. Mn decreased extracellular DA levels, as measured by microdialysis, in the striatum in both genotypes. Mn decreased cortical NE levels in both genotypes and further exacerbated in REST cKO, while Mn decreased nigrostriatal NE levels only in REST cKO mice. REST cKO reduced 5-HT levels in all brain regions tested compared to WT mice. Mn increased glutamate and GABA levels in the striatum and midbrain, while these Mn effects were not altered by REST cKO. Taken together, our findings demonstrate that DAergic REST deficiency exacerbates Mn-induced motor and cognitive deficits along with dysregulation of neurotransmitters, mainly DA, 5-HT, and NE, suggesting that DAergic REST is important in Mn-induced dysregulation of monoaminergic neurotransmission.