GPR52 is a key regulator of corticostriatal signalling and function

GPR52 is an orphan G protein-coupled receptor (GPCR) expressed in brain regions subject to dopaminergic and glutamatergic dysregulation in schizophrenia. GPR52 is highly expressed in the striatum, exclusively on dopamine D2 receptor-expressing medium spiny neurons (MSNs), and also on dopamine D1 receptor-expressing cortical pyramidal neurons. To examine the neurophysiological role of GPR52, we measured cAMP, ERK1/2 phosphorylation and β-arrestin recruitment in cells transfected with human GPR52 and/or mouse primary cultured embryonic striatal or cortical neurons treated with the selective synthetic agonist 3-[2-(3-chloro- 5- uorobenzyl)-1-benzothiophen-7-yl]-N-(2-methoxyethyl)benzamide (3-BTBZ). We also investigated 3-BTBZ-regulated phosphorylation of the striatal signal integrator, DARPP-32, at Thr34 and Thr75 in D1- and D2 receptor-expressing MSNs, by quantitative immunohistochemistry in acute mouse brain slices (Figure 1). In vivo activity of 3-BTBZ (3 - 30 mg/kg, i.p.) was assessed against amphetamine or phencyclidine (both 3 mg/kg, i.p.) induced hyperactivity in mice and also for effects on spontaneous motor activity. 3-BTBZ stimulated cAMP accumulation in CHO-hGPR52 cells (pEC50 = 7.5 ± 0.2) and in striatal neurons (pEC50 = 8.3 ± 0.2). Surprisingly, 3-BTBZ significantly increased Thr75 phosphorylation in D1-, but not D2-expressing MSNs, with no effect on Thr34 phosphorylation (Figure 1). The modulatory effect on Thr75 phosphorylation was lost in slices lacking cortical projection neurons, indicative of extra-striatal GPR52 signalling. Accordingly, we showed that 3-BTBZ stimulated both cAMP (pEC50 = 7.2 ± 0.3) and ERK1/2 phosphorylation (pEC50 = 8.2 ± 0.2) in cortical neurons, the latter (but not the former) response fully sensitive to knockdown of β-arrestin-2. Systemic administration of 3-BTBZ (i.p.) significantly reduced amphetamine-induced hyperactivity at only 30 mg/kg, which also significantly reduced spontaneous motor activity. However 3-BTBZ significantly inhibited phencyclidine-induced hyperactivity (MED = 3 mg/kg). These data show that GPR52 activation, likely via cAMP and ERK1/2 signalling, modulates DARPP-32 phosphorylation and PCP-stimulated behaviours in a mouse model of psychosis.