Peripheral dopamine system on immune cells is dysregulated in Parkinson's Disease
Phillip Mackie1, Adithya Gopinath1, Leila Saadatpour1, Dominic Montas1, and Habibeh Khoshbouei1 1Department of Neuroscience, University of Florida College of Medicine, Gainesville FL, 32611
The role of peripheral monocytes in Parkinson's Disease (PD) has received increased attention. Peripheral monocytes/macrophages are sensitive to dopamine (DA) regulation and contain key dopaminergic proteins such as the dopamine transporter (DAT). Importantly DAT controls DA signaling and its dysregulation is associated with PD. We therefore hypothesized that the peripheral DA system on monocytes/macrophages is dysregulated in PD patients. Complementary biochemical and fluorescence microscopy approaches confirm DAT is present and functional on human macrophages. Unexpectedly, we found DAT on human macrophages is sensitive to a novel LPS-induced immune-regulatory mechanism. DAT normally transports substrate and inward current in uptake mode. Using live-cell fluorescence microscopy and whole cell voltage clamp electrophysiology, we found LPS-stimulation significantly reduced the DAT-dependent forward transport of the substrate (p<0.0001) and inward current (p<0.05). Live-cell fluorescence microscopy and simultaneous patch clamp and amperometry revealed that LPS-stimulation favors DAT reverse-transport mode evidenced by increased DAT-dependent DA efflux (p<0.05). This LPS-induced immune-regulation of DAT was due to CD14-dependent reorganization of membrane microdomains. Additionally, we show DAT activation increases macrophage phagocytosis, that is reversed by LPS stimulation (p<0.05) thereby bilaterally linking DAT activity and immune function. Collectively, these findings reveal a DAT-mediated DA signaling and immune function interact in steady state. We therefore hypothesized DAT may be a nexus for dysregulated dopamine signaling and immune dysfunction in PD, as both are hallmarks of the disease. Flow cytometry showed a higher percentage of peripheral monocytes express DAT in PD compared to healthy controls, suggesting system-wide dysregulation of DA transmission (p<0.05). Notably, we found LPS-induced DAT regulation is attenuated (p<0.0001) and DAT modulation of phagocytosis is altered in PD macrophages compared to healthy controls. The compromised DAT response to immune stimulation in PD patients may putatively link aberrant peripheral dopamine signaling and immune function in PD.
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