Increased vesicular monoamine transporter enhances dopamine release and opposes Parkinson disease-related neurodegeneration in vivo

Abstract

Significance Several therapeutic strategies have been used to enhance monoamine neurotransmitter signaling. However, many of these interventions have deleterious side effects or lose effectiveness due to off-target actions and system feedback. These undesirable consequences likely occur because of temporal dysregulation of neurotransmitter release and uptake. We demonstrate that increasing vesicular packaging enhances dopamine neurotransmission without this signaling disruption. Mice with elevated vesicular monoamine transporter display increased dopamine release, improved outcomes on anxiety and depressive behaviors, enhanced locomotion, and protection from a Parkinson disease-related neurotoxic insult. The malleable nature of the dopamine vesicle suggests that interventions aimed at enhancing vesicle filling may be of therapeutic benefit.

Changes in Neuronal Dopamine Homeostasis following 1-Methyl-4-phenylpyridinium (MPP+) Exposure

“…L-DOPA and exogenously added DA can be toxic to dopaminergic neurons in vitro (28, 40, 70 -75), and several reports confirm that a buildup of DA cyt is sufficient to induce progressive neurodegeneration in rodents (67,76,77). MPP ϩ has been suspected to increase DA cyt based on indirect evidence, such as HPLC measurements of cellular DA contents (11) and an increase in 5-cysteinyl-DA in animals treated with MPTP (78).…”

Comparison of Monoamine Oxidase Inhibitors in Decreasing Production of the Autotoxic Dopamine Metabolite 3,4-Dihydroxyphenylacetaldehyde in PC12 Cells

“…Possible beneficial effects of MAO inhibition include augmented vesicular storage and, consequently, increased constitutive release of DA. There is indirect evidence that MAO inhibitor treatment enhances vesicular uptake of cytoplasmic catecholamines (Raffel and Wieland, 1999;Lohr et al, 2014), and animals with increased efficiency of vesicular uptake have augmented constitutive dopamine release (Geller et al, 1993;Sun et al, 2004;Lohr et al, 2014). Cellular DA content is mainly within vesicles (Mosharov et al, 2006), and since norepinephrine (NE) is produced exclusively within vesicles by the action of DA-b-hydroxylase acting on DA taken up from the cytoplasm, enhanced vesicular uptake would be expected to increase cell contents of endogenous DA and NE.…”

Synaptic vesicle glycoprotein 2C (SV2C) modulates dopamine release and is disrupted in Parkinson’s disease

“…Western blotting: Western blots were performed as previously described (60). Primary antibodies were used at the following dilutions: SV2C (1:2,500), DAT (1:5,000), TH (1:1,000), synaptotagmin 1 (1:1,000), α-synuclein (1:1,000), and β-actin (1:5,000 (61).…”

“…Brains were sectioned to 40µm. Staining was conducted as described previously (60,63), except that all washes and dilutions were conducted in PBS with 0.2% Triton X-100. Immunoprecipitation of SV2C and α-synuclein: Coimmunoprecipitation experiments were performed using the Pierce Co-Immunoprecipitation Kit (Thermo Scientific) according to manufacturer's protocols.…”

“…Latency to fall, speed of rotation at the time of fall, and total distance traveled was recorded and averaged over three testing trials. Fast-scan cyclic voltammetry in striatal slices: Fast-scan cyclic voltammetry was performed as described previously (60) in 300µm striatal slices bathed in 30°C oxygenated aCSF. Stimulations were 700µA 400ms monopolar pulse, either single pulse (baseline release) or five at 100Hz (high-intensity stimulation in acute nicotine experiments).…”