Dopamine D2 Long Receptors Are Critical for Caveolae-Mediated α-Synuclein Uptake in Cultured Dopaminergic Neurons

Abstract

α-synuclein accumulation into dopaminergic neurons is a pathological hallmark of Parkinson’s disease. We previously demonstrated that fatty acid-binding protein 3 (FABP3) is critical for α-synuclein uptake and propagation to accumulate in dopaminergic neurons. FABP3 is abundant in dopaminergic neurons and interacts with dopamine D2 receptors, specifically the long type (D2L). Here, we investigated the importance of dopamine D2L receptors in the uptake of α-synuclein monomers and their fibrils. We employed mesencephalic neurons derived from dopamine D2L−/−, dopamine D2 receptor null (D2 null), FABP3−/−, and wild type C57BL6 mice, and analyzed the uptake ability of fluorescence-conjugated α-synuclein monomers and fibrils. We found that D2L receptors are co-localized with FABP3. Immunocytochemistry revealed that TH+ D2L−/− or D2 null neurons do not take up α-synuclein monomers. The deletion of α-synuclein C-terminus completely abolished the uptake to dopamine neurons. Likewise, dynasore, a dynamin inhibitor, and caveolin-1 knockdown also abolished the uptake. D2L and FABP3 were also critical for α-synuclein fibrils uptake. D2L and accumulated α-synuclein fibrils were well co-localized. These data indicate that dopamine D2L with a caveola structure coupled with FABP3 is critical for α-synuclein uptake by dopaminergic neurons, suggesting a novel pathogenic mechanism of synucleinopathies, including Parkinson’s disease.

Fatty Acid Binding Protein 3 (FABP3) and Apolipoprotein E4 (ApoE4) as Lipid Metabolism-Related Biomarkers of Alzheimer’s Disease

“…We suggest that FABP3 play a pivotal role in the development of cognitive decline. FABP3 may also regulate dopamine D2R function in the striatum and anterior cingulate cortex (ACC), a crucial brain region of GABAergic interneurons responsible for coordinating cognitive processes [ 28 , 42 , 44 ]. FABP3 regulates GABA synthesis by transcriptional regulation of Gad67, which affects abnormal cognitive function and emotional behavior [ 42 ].…”

An α-synuclein decoy peptide prevents cytotoxic α-synuclein aggregation caused by fatty acid binding protein 3

“…These intriguing aspects regarding the in vivo aspects and consequences of FABP3–αSyn binding are being actively probed ( 35 ). Recent studies toward this objective have revealed that FABP3 is indeed relevant to αSyn import into mammalian cells and also that the interaction between the C-terminal region of αSyn and FABP3 is critical to this import ( 55 , 56 ).…”

Impact of Fatty Acid-Binding Proteins in α-Synuclein-Induced Mitochondrial Injury in Synucleinopathy

“…In contrast, FABP3 also plays critical roles in extracellular α-synuclein monomer uptake and is critical for MPTP-induced neuronal retraction, mitochondrial function, and oxidative stress [ 14 ]. To elucidate the mechanism through which FABP3 mediates α-synuclein uptake, mesencephalic neurons derived from dopamine D2L knockout mice, FABP3 knockout mice, and wild-type C57BL6 mice were employed and the ability of fluorescence-conjugated α-synuclein monomers and fibrils uptake was measured in a previous study [ 119 ]. The physiological significance of D2L in α-synuclein uptake in dopaminergic neurons in D2L knockout mice and wild-type C57BL6 mice was investigated and the uptake ability of ATTO-55O-labeled α-synuclein monomers in D2L knockout neurons was observed.…”

“…As with α-synuclein monomers, the uptake of α-synuclein fibrils by FABP3 knockout mice and D2L knockout mice was also identified, and both FABP3 and D2L receptors were found to be vital for the uptake of α-synuclein fibrils. The results indicated that dopamine D2L with a caveola structure, coupled with FABP3, plays an essential role in both α-synuclein monomer and fibril uptake by dopaminergic neurons, suggesting a novel pathogenic mechanism of synucleinopathies, including PD [ 119 ].…”