GPR37 associates with the dopamine transporter to modulate dopamine uptake and behavioral responses to dopaminergic drugs

Abstract

The orphan G protein-coupled receptor 37 (GPR37) is a substrate of parkin; its insoluble aggregates accumulate in brain samples of Parkinson's disease patients. We report here that GPR37 interacts with the dopamine transporter (DAT) and modulates DAT activity. GPR37 and DAT were found colocalized in mouse striatal presynaptic membranes and in transfected cells and their interaction was confirmed by coimmunoprecipitation assays. Gpr37-null mutant mice showed enhanced DAT-mediated dopamine uptake in striatal membrane samples, with a significant increase in the number of plasma membrane DAT molecules. The null mutant mice also exhibited a decrease in cocaine-induced locomotor activity and in catalepsy induced by dopamine receptor antagonists. These results reveal the specific role of GPR37, a putative peptidergic G proteincoupled receptor, in modulating the functional expression of DAT and the behavioral responses to dopaminergic drugs.G protein-coupled receptor ͉ Parkinson's disease ͉ dopamine transporter T he orphan G protein-coupled receptor 37 (GPR37) is homologous to endothelin (ET B -R) and bombesin (GRP-R, NMB-R) receptors (1) and it is highly expressed in mammalian brain oligodendrocytes, Purkinje cells, and neurons belonging to the CA3 hippocampal region and to the substantia nigra (SN) pars compacta (2). GPR37 is a substrate of the ubiquitin-protein ligase parkin, and it has been named parkin-associated endothelin-like receptor (PAEL-R) (3). An insoluble form of GPR37 is accumulated in brain samples of Parkinson's disease (PD) patients, and the overexpression of GPR37 in cell cultures, in the absence of parkin, can lead to unfolded protein-induced cell death (3, 4). Little is known about the physiological function of the receptor in the brain and in dopaminergic neurons in particular, although it has been speculated that the aggregation of GPR37 in insoluble complexes is responsible for the preferential loss of SN neurons through the endoplasmic reticulum-specific apoptotic pathway (5, 6). Recent data reported an interaction between GPR37, the head activator neuropeptide and its binding protein (sorting protein-related receptor; SorLA), supporting the hypothesis that GPR37 is involved in neuronal cell survival (7). To investigate the receptor's function, we generated homozygous Gpr37-null mutant mice, which exhibit a reduction in striatal dopamine (DA) content, specific locomotor deficits, and enhanced sensitivity to amphetamine (8).Several binding partners for the DA transporter (DAT) have been identified, suggesting that a regulated multiprotein complex controls its synthesis, targeting, and expression at specific cellular membrane domains (9). Presynaptic DAT expression is of crucial importance in modulating the synaptic availability of DA at nigrostriatal synapses, and its regulation is dynamically controlled for the maintenance of normal dopaminergic neurotransmission. The increase or decrease of DAT expression in the presynaptic membranes results in decreased or increased synaptic DA concentration, ...

The Parkinson's-disease-associated receptor GPR37 undergoes metalloproteinase-mediated N-terminal cleavage and ectodomain shedding

“…It also remains to be investigated whether the shed ectodomain has any functional role. Neither can we fully exclude the possibility that the N-terminal processing has a role in a functional interplay of GPR37 with other receptors, a phenomenon that has been suggested to occur between GPR37 and adenosine A2A and dopamine D2 receptors (Gandía et al, 2015;Lopes et al, 2015), as well as the dopamine transporter (Marazziti et al, 2007). In addition, GPR37 has been recently identified in at least two screens for novel interacting partners for GPCRs, one identifying partners for the β 2 adrenergic receptor (Kittanakom et al, 2014) and the other for the glucagon-like peptide 1 receptor (Huang et al, 2013).…”

“…It is abundantly expressed in glial and neuronal cells in several brain regions, including dopaminergic cells of the substantia nigra, and has been reported to have a role in dopaminergic signalling (Marazziti et al, 2004(Marazziti et al, , 2007Imai et al, 2007). Incidentally, GPR37 has been implicated in certain brain disorders (Imai et al, 2001;Fujita-Jimbo et al, 2012;Tomita et al, 2013), the most widely acknowledged of which is the autosomal recessive juvenile parkinsonism (AR-JP), an early onset familial Parkinson's disease.…”

International Union of Basic and Clinical Pharmacology. LXXXVIII. G Protein-Coupled Receptor List: Recommendations for New Pairings with Cognate Ligands

“…Overexpression of GPR37 led to aggregate formation, retention of the receptor in the cytoplasm, and low survival rates of transfected cells, leading to the suggestion that misfolded GPR37 contributes to the cell death that can be detected in conditions such as Parkinson's disease (Rezgaoui et al, 2006). GPR37 has been reported to associate with and regulate the dopamine transporter, while gene disruption results in altered striatal signaling (Marazziti et al, 2007(Marazziti et al, , 2011. Although the isolation of a peptide of identical amino acid sequence to Hydra head activator from human hypothalamus, bovine hypothalamus, and rat intestine has been reported (Bodenmuller and Schaller, 1981), its existence in mammals is unclear because there is currently no evidence for the presence of a precursor gene for this peptide in any sequenced genome.…”

GPR37 and GPR37L1 are receptors for the neuroprotective and glioprotective factors prosaptide and prosaposin

“…Although parkin has many substrates (11), GPR37 may be one of the key substrates related to pathology in patients with parkin mutations, which are associated with autosomal recessive juvenile Parkinson disease (9,12,13). The connection between GPR37 and parkin has led to a focus on the dopaminergic system in GPR37 knockout mice, which exhibit a reduced dopaminergic tone and various subtle perturbations in dopaminergic signaling in the brain (14)(15)(16). However, GPR37 and GPR37L1 are expressed in many different brain regions beyond just dopaminergic areas, so it seems probable that these receptors play a broader role in the regulation of neuronal and glial physiology beyond simply modulating dopaminergic neurotransmission.…”