Rare Autism-Associated Variants Implicate Syntaxin 1 (STX1 R26Q) Phosphorylation and the Dopamine Transporter (hDAT R51W) in Dopamine Neurotransmission and Behaviors

Abstract

BackgroundSyntaxin 1 (STX1) is a presynaptic plasma membrane protein that coordinates synaptic vesicle fusion. STX1 also regulates the function of neurotransmitter transporters, including the dopamine (DA) transporter (DAT). The DAT is a membrane protein that controls DA homeostasis through the high-affinity re-uptake of synaptically released DA.MethodsWe adopt newly developed animal models and state-of-the-art biophysical techniques to determine the contribution of the identified gene variants to impairments in DA neurotransmission observed in autism spectrum disorder (ASD).OutcomesHere, we characterize two independent autism-associated variants in the genes that encode STX1 and the DAT. We demonstrate that each variant dramatically alters DAT function. We identify molecular mechanisms that converge to inhibit reverse transport of DA and DA-associated behaviors. These mechanisms involve decreased phosphorylation of STX1 at Ser14 mediated by casein kinase 2 as well as a reduction in STX1/DAT interaction. These findings point to STX1/DAT interactions and STX1 phosphorylation as key regulators of DA homeostasis.InterpretationWe determine the molecular identity and the impact of these variants with the intent of defining DA dysfunction and associated behaviors as possible complications of ASD.

The BTBR mouse model of idiopathic autism – Current view on mechanisms

“…Impairments in monoaminergic neurotransmission have been associated with the severity of symptoms in ASD patients (Cartier et al 2015, Gangi et al 2016, Muller et al 2016). BTBR mice were reported to have higher hippocampal 5HT 1A receptor density (Gould et al 2011, 2014) as well as lower [(3)H] cyanoimipramine and citalopram binding to the serotonin transporter (SERT, Gould et al 2011).…”

Kinase-dependent Regulation of Monoamine Neurotransmitter Transporters

“…Although the pathway through which this change in phosphorylation occurs has not been established and the effects of BoNT/C may be indirect, they suggest that a reciprocal relationship may exist between DAT phosphorylation states and DAT/syntaxin 1A interactions. Interestingly, a recent study from the Galli laboratory reveals coding mutations in the human syntaxin 1A and DAT genes, found in subjects with autism, that individually reduce Kinase Modulation of Biogenic Amine Transport DAT/syntaxin 1A associations and diminish AMPHevoked DA efflux (Cartier et al, 2015). Although studies are needed to associate synaptic changes with these effects, they remind us that basal interactions between DAT and syntaxin 1A are readily detectible in vivo and thus are likely to play key roles in the normal functional modulation of DAT.…”

Neuropsychiatric disease–associated genetic variants of the dopamine transporter display heterogeneous molecular phenotypes

“…A number of studies have found associations between common genetic variants of SLC6A3 and increased risk of psychiatric disease, but deduction of their biological implications is largely elusive (22)(23)(24). During recent years, a number of rare exonic DAT variants have been identified in patients suffering from diverse neuropsychiatric and/or neurodevelopmental disorders (25)(26)(27)(28)(29)(30)(31). The negative health consequences of genetic changes in DAT are strongly supported by the constrain metrics reported in the comprehensive EXaC database, where DAT is classified as 'loss of function intolerant' and reported to be missense constrained (32), indicating that mutations affecting aspects of DAT function are under considerable negative selection.…”