Background: Intracellular GPR37 accumulation is neurotoxic and associated with parkinsonism, whereas plasma membrane association is protective. Results: The endogenous GPR37 ligand prosaposin promotes GPR37 surface density and association with GM1-enriched lipid rafts. Conclusion: GPR37, prosaposin, and GM1 constitute a pathway that improves cell viability through GPR37 trafficking to the plasma membrane. Significance: Targeting this pathway could reduce toxic intracellular GPR37 accumulation observed in parkinsonism.

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Background Alteration in glycosphingolipids (GSLs) in Parkinson's disease (PD) still needs to be determined. Objectives We evaluated if PD subjects show abnormal GSLs levels compared to healthy controls (HC) and if GSLs correlate with clinical features. Methods We analyzed GSLs and glucosylceramide (GlcCer) in plasma using two normal‐phase high‐performance liquid chromatography assays; clinico‐demographic data were extracted. Results Eighty PD subjects and 25 HCs were analyzed. Levels of GlcCer, GD1b, Gb4, GalNAcGA1, and b‐series were higher in PD patients than in HCs; total GSLs, GT1b, GM1a, GM3, GM2, and a‐series levels were lower in PD patients than in HCs. Changes in GSLs were present in PD subjects, with GlcCer levels similar to those in HCs. The results were similar after excluding certain GBA1 mutation carriers. Movement Disorder Society Unified Parkinson's Disease Rating Scale, Part III, correlated with Gb4 and Montreal Cognitive Assessment with GD1b levels. Conclusions Multiple GSL abnormalities in plasma were detected in patients with and without GlcCer changes, indicating a broader shift in lipid homeostasis. © 2022 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson Movement Disorder Society.

Receptor-receptor interactions are essential to fine tune receptor responses and new techniques enable closer characterization of the interactions between involved proteins directly in the plasma membrane. Fluorescence cross-correlation spectroscopy (FCCS), which analyses concurrent movement of bound molecules with single-molecule detection limit, was here used to, in live N2a cells, study interactions between the Parkinson's disease (PD) associated orphan receptor GPR37, its homologue GPR37L1, and the two splice variants of the dopamine 2 receptor (D2R). An interaction between GPR37 and both splice forms of D2R was detected. 4-phenylbutyrate (4-PBA), a neuroprotective chemical chaperone known to increase GPR37 expression at the cell surface, increased the fraction of interacting molecules. The interaction was also increased by pramipexole, a D2R agonist commonly used in the treatment of PD, indicating a possible clinically relevance. Cross-correlation, indicating interaction between GPR37L1 and the short isoform of D2R, was also detected. However, this interaction was not changed with 4-PBA or pramipexole treatment. Overall, these data provide further evidence that heteromeric GPR37-D2R exist and can be pharmacologically modulated, which is relevant for the treatment of PD. This article is part of the Special Issue entitled ‘Receptor heteromers and their allosteric receptor-receptor interactions’.