Project description:Dopamine (DA) neurons modulate neural circuits and behaviors via dopamine release from expansive, long range axonal projections. The elaborate cytoarchitecture of DA neurons is embedded within complex brain tissues, making it difficult to access the DA neuronal proteome using conventional methods. Here, we demonstrate APEX2 proximity labeling within genetically targeted neurons in the mouse brain, enabling subcellular proteomics with cell type-specificity. By combining APEX2 biotinylation with mass spectrometry, we mapped the somatodendritic and axonal proteomes of DA neurons. Our dataset reveals the proteomic architecture underlying axonal transport, dopamine transmission, and axonal metabolism in DA neurons. We find a significant enrichment of proteins encoded by Parkinson’s disease-linked genes in dopaminergic axons, including proteins with previously undescribed axonal localization. Our proteomic datasets comprise a significant resource for axonal and DA neuronal cell biology, while the methodology developed here will enable future studies of other neural cell types.
Project description:The circadian regulation of gene expression underlies orchestrated daily rhythms in physiology, metabolism, and behavior. The central dopamine (DA) system arising from DA neurons in the ventral midbrain has been implicated in a wide range of brain functions. Growing evidence suggests that DA transmission follows daily oscillations at multiple regulatory steps, and its dysfunction is closely related to the onset of various neuropsychiatric diseases. We examined diurnal gene expression profiles across key brain areas constituting the central DA pathways in mice by use of microarray analyses to identify rhythmically expressed genes according to the time of day (TOD).
Project description:Loss-of-function mutations of the gene encoding the trafficking protein particle complex subunit 9 (trappc9) cause autosomal recessive intellectual disability and obesity by unknown mechanisms. Genome-wide analysis links trappc9 to non-alcoholic fatty liver disease (NAFLD). Trappc9-deficient mice have been shown to appear overweight shortly after weaning. Here, we analyzed serum biochemistry and histology of adipose and liver tissues to determine the incidence of obesity and NAFLD in trappc9-deficient mice and combined transcriptomic and proteomic analyses, pharmacological studies, and biochemical and histological examinations of postmortem mouse brains to unveil mechanisms involved. We found that trappc9-deficient mice presented with systemic glucose homeostatic disturbance, obesity and NAFLD, which were relieved upon chronic treatment combining dopamine receptor D2 (DRD2) agonist quinpirole and DRD1 antagonist SCH23390. Blood glucose homeostasis in trappc9-deficient mice was restored upon administrating quinpirole alone. RNA-sequencing analysis of DRD2- containing neurons and proteomic study of brain synaptosomes revealed signs of impaired neurotransmitter secretion in trappc9-deficient mice. Biochemical and histological studies of mouse brains showed that trappc9-deficient mice synthesized dopamine normally, but their dopamine-secreting neurons had a lower abundance of structures for releasing dopamine in the striatum. Our study suggests that trappc9 loss- of-function causes obesity and NAFLD by constraining dopamine synapse formation.
Project description:Patients with schizophrenia show increased striatal dopamine synthesis capacity in imaging studies. However, the mechanism underlying this is unclear but may be due to N-methyl-D-aspartate receptor (NMDAR) hypofunction and parvalbumin (PV) neuronal dysfunction leading to disinhibition of mesostriatal dopamine neurons. Here, we test this in a translational mouse imaging study using a ketamine model. Mice were treated with sub-chronic ketamine (30mg/kg) or saline followed by in-vivo positron emission tomography of striatal dopamine synthesis capacity, analogous to measures used in patients. Locomotor activity was measured using the open field test. In-vivo cell-type-specific chemogenetic approaches and pharmacological interventions were used to manipulate neuronal excitability. Immunohistochemistry and RNA sequencing were used to investigate molecular mechanisms. Sub-chronic ketamine increased striatal dopamine synthesis capacity (Cohen’s d=2.5) and locomotor activity. These effects were countered by inhibition of midbrain dopamine neurons, and by activation of cortical and ventral subiculum PV interneurons. Sub-chronic ketamine reduced PV expression in these neurons. Pharmacological intervention with SEP-363856, a novel psychotropic agent with agonism at trace amine receptor 1 (TAAR1), significantly reduced the ketamine-induced increase in dopamine synthesis capacity. These results show that sub-chronic ketamine treatment in mice mimics the dopaminergic alterations in patients with psychosis, and suggest an underlying neurocircuit involving PV interneuron hypofunction in frontal cortex and hippocampus as well as activation of midbrain dopamine neurons. A novel TAAR1 agonist reversed the dopaminergic alterations suggesting a therapeutic mechanism for targeting presynaptic dopamine dysfunction in patients.
Project description:The dopamine transporter facilitates dopamine reuptake from the extracellular space to terminate neurotransmission. The transporter belongs to the neurotransmitter:sodium symporter family, which includes transporters for serotonin, norepinephrine, and GABA that utilize the Na+ gradient to drive the uptake of substrate. Decades ago, it was shown that the serotonin transporter also antiports K+, but investigations of K+-coupled transport in other neurotransmitter:sodium symporters have been inconclusive. Here, we show that ligand binding to the drosophila- and human dopamine transporters are inhibited by K+, and the conformational dynamics of the drosophila dopamine transporter in K+ are divergent from the apo- and Na+-states. Furthermore, we found that K+ increased dopamine uptake by the drosophila dopamine transporter in liposomes, and visualized Na+ and K+ fluxes in single proteoliposomes using fluorescent ion indicators. Our results expand on the fundamentals of dopamine transport and prompt a reevaluation of the impact of K+ on other transporters in this pharmacologically important family.
Project description:Dopaminylation, the covalent attachment of dopamine to the side chain of glutamine (Gln, Q) in proteins, has been identified as a class of posttranslational modification. Due to the limited number of substrates, the functions and underlying molecular mechanisms of dopaminylation are not fully characterized. Utilizing an alkyne-functionalized dopamine probe, we have developed a method to selectively enrich dopaminylated proteins in the whole-cell context. We identified 4133 proteins potentially modified with dopamine and validated the modification of histone H4 glutamine 27 by dopamine (H4Q27dop). H4Q27dop can inhibit cell proliferation through downregulating cyclin D1 gene CCND1 transcription, a classical well-known proliferation promoter. Our study provides a valuable resource of putative substrate proteins modified with dopamine and reveals a novel mechanism of dopamine regulating cell growth in a neuroblastoma cancer model.
Project description:The dopamine transporter is a member of the neurotransmitter:sodium symporters (NSSs), which are responsible for termination of neurotransmission through Na+-driven reuptake of neurotransmitter from the extracellular space. Experimental evidence elucidating the coordinated conformational rearrangements related to the transport mechanism has so far been limited. Here we probe the global Na+- and dopamine-induced conformational dynamics of the wild-type Drosophila melanogaster dopamine transporter using hydrogen-deuterium exchange mass spectrometry. We identify Na+- and dopamine-induced changes in specific regions of the transporter, suggesting their involvement in protein conformational transitions. Furthermore, we detect ligand-dependent slow cooperative fluctuations of helical stretches in several domains of the transporter, which could be a molecular mechanism that assists in the transporter function. Our results provide a framework for understanding the molecular mechanism underlying the function of NSSs by revealing detailed insight into the state-dependent conformational changes associated with the alternating access model of the dopamine transporter.