The second-most common neurodegenerative disease, Parkinson's Disease (PD) has three hallmarks: dysfunctional dopamine transmission due, at least in part, to dopamine neuron degeneration; intracellular inclusions of α-synuclein aggregates; and neuroinflammation. The origin and interplay of these features remains a puzzle, as does the underlying mechanism of PD pathogenesis and progression. When viewed in the context of neuroimmunology, dopamine also plays a role in regulating peripheral immune cells. Intriguingly, plasma dopamine levels are altered in PD, suggesting collateral dysregulation of peripheral dopamine transmission. The dopamine transporter (DAT), the main regulator of dopaminergic tone in the CNS, is known to exist in lymphocytes and monocytes/macrophages, but little is known about peripheral DAT biology or how DAT regulates the dopaminergic tone, much less how peripheral DAT alters immune function. Our review is guided by the hypothesis that dysfunctional peripheral dopamine signaling might be linked to the dysfunctional immune responses in PD and thereby suggests a potential bidirectional communication between central and peripheral dopamine systems. This review seeks to foster new perspectives concerning PD pathogenesis and progression.

Pathophysiological damages and loss of function of dopamine neurons precedes their demise and contributes to the early phases of Parkinson's disease. The presence of aberrant intercellular pathological inclusions of the protein α-synuclein within ventral midbrain dopaminergic neurons is one of the cardinal features of Parkinson's disease. We employed multiple complementary approaches in molecular biology, electrophysiology, and live-cell imaging to investigate how excessive α-synuclein levels alters multiple characteristics of dopaminergic neuronal dynamics and dopamine transmission prior to neuronal demise. These studies demonstrate that α-synuclein dysregulation of D2 receptor autoinhibition contributes to the vulnerability of dopaminergic neurons, and that modulation thereof can ameliorate the resulting pathophysiology. These novel findings provide mechanistic insights in the insidious loss of dopaminergic function and neurons that characterize Parkinson's disease progression with significant therapeutic implications.

Functional interactions between transmembrane proteins fine‐tune neuronal excitability in response to changing homeostatic demands. Dysregulation of neuronal excitability is thought to impose a significant energetic challenge on neurons, and it is implicated as a contributing factor in the demise of substantia nigra (SNc) dopamine neurons in Parkinson's Disease (PD). The objective of this study is to examine whether or not a novel interaction discovered by our lab between the dopamine transporter (DAT) and Kv2.1 has the potential to modulate the excitability (and thusly vulnerability) of SNc dopamine neurons. This is of particular interest because DAT can be targeted by numerous FDA‐approved compounds (bupropion, amphetamine, methylphenidate), eliminating a significant hurdle should the interaction reveal neuroprotective potential. DAT efficiently reuptakes dopamine along with co‐substrates Na+ and Cl− to recycle the released monoamine. This process triggers multiple concurrent events such as the induction of an inward depolarizing current as well as an increase in intracellular Ca2+, both of which impact neuronal activity. In this study, we have identified a novel functional interaction between DAT and the delayed‐rectifier K+ channel Kv2.1. Kv2.1 repolarizes dopamine neurons and excitotoxic stimuli elicit a negative shift in its activation potential such that neuronal excitability is decreased. This shift in activation voltage is coupled to a loss of channel phosphorylation as well as a dispersal of membrane‐bound Kv2.1 clusters. Examining DAT and Kv2.1 distribution in SNc and ventral tegmental area (VTA) dopamine neurons revealed increased colocalization of the two proteins in the axon hillock compared to the soma of SNc DA neurons, but there was no difference in sub‐cellular colocalization in the less vulnerable VTA dopamine neurons, suggesting a heightened modulatory potential of this interaction in the SNc. Functionally, we found that DAT activation induces a negative shift in Kv2.1's activation potential (VEH = 5.61 ± 2.8 mV; METH = 2.675 ± 2.6 mV; n=8, p=0.0292) as well as the canonical decrease in Kv2.1 cluster size (VEH = 0.2871 ± 0.05 μm3, n = 2541 clusters; AMPH = 0.1418 ± 0.03 μm3, n = 1486 clusters; Cyto‐D = 0.1123 ± 0.04 μm3, n = 419 clusters), suggesting that DAT can be targeted to modulate excitability through its downstream effects on Kv2.1. Additionally, we found DAT activation weakens the interaction between the two proteins measured via FRET microscopy (VEH = 12.48 ± 2.48 % n=10; AMPH = 6.55 ± 1.76% n=14; p=.0484), further suggesting that the axon hillock of SNc dopamine neurons represents a uniquely promising site to target this interaction. Ongoing experiments utilizing high‐speed in vitro imaging coupled with single neuron recordings and ex vivo two‐photon microscopy aim to identify the functional significance of the DAT/Kv2.1 interaction in the axon hillock of SNc dopamine neurons.Support or Funding InformationNINDS Interdisciplinary T32 in Movement Disorders & Neurorestoration (T32‐NS082168), R01DA026947‐08S1/NIDA (HK), 1S10OD020026‐01/NIH (HK)This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.