SELENOT regulates endoplasmic reticulum calcium flux via SERCA2 and maintains dopaminergic DAT to protect against attention deficit hyperactivity disorder in mice

Attention deficit and hyperactivity disorder (ADHD) is a prevalent developmental disorder. SELENOT is an endoplasmic reticulum-resident selenocysteine-containing protein. We aimed to investigate the role of SELENOT in dopaminergic neurons. Results from Selenotfl/fl;Dat-cre mice showed that SELENOT deficiency in dopaminergic neurons resulted in ADHD-like behaviors including hyperlocomotion, recognition memory deficit, repetitive movement, and impulsivity. Dopamine metabolism, extrasynaptic dopamine, spontaneous excitatory postsynaptic currents in the striatum and electroencephalogram theta power were enhanced in Selenotfl/fl;Dat-cre mice, whereas dopaminergic neurons in the substantia nigra were slightly reduced but exhibited normal neuronal firing and little cellular stress. Among dopamine- associated proteins, dopamine transporter (DAT) level was remarkably reduced and monoamine oxidase A increased mildly in the striatum and/or midbrain of Selenotfl/fl;Dat-cre mice. The ADHD-like phenotype and DAT ablation were corroborated in Selenotfl/fl;Nestin- cre mice, but not in Selenotfl/fl;Gfap-cre mice. In vitro overexpression and knockdown analyses and RNA-sequencing data revealed that SELENOT causatively regulated DAT mRNA and protein expression through Ca2+ signaling and NURR1. SELENOT maintained cellular Ca2+ levels via interaction with endoplasmic reticulum SERCA2, but not IP3Rs and RYRs, as demonstrated by Ca2+ imaging, co-immunoprecipitation coupled with mass spectrometry, and colocalization analyses. Treatment with psychostimulants, amphetamine or methylphenidate, rescued the hyperactivity in Selenotfl/fl;Dat-cre mice. In conclusion, SELENOT in dopaminergic neurons is indispensable to maintain proper dopamine signaling in the midbrain against ADHD.