N‐Acetylaspartylglutamate Selectively Activates mGluR3 Receptors in Transfected Cells

Abstract

Abstract:In previous studies, we demonstrated that the neuropeptide, N-acetylaspartylglutamate (NAAG), meets the traditional criteria for a neurotransmitter and selectively activates metabotropic glutamate receptor mGluR2 or mGluR3 in cultured cerebellar granule cells and glia. Sequence homology and pharmacological data suggest that these two receptors are highly related structurally and functionally. To define more rigorously the receptor specificity of NAAG, cloned rat cDNAs for mGluRi-6 were transiently or stably transfected into Chinese hamster ovary cells and human embryonic kidney cells and assayed for their second messenger responses to the two endogenous neurotransmitters, glutamate and NAAG, as well as to metabotropic receptor agonists, trans-i -aminocyclopentane-1,3-dicarboxylate (trans-ACPD) and L-2-amino-4-phosphonobutyrate (L-AP4). Despite the high degree of relatedness of mGluR2 and mGluR3, NAAG selectively activated the mGluR3 receptor. NAAG activated neither mGluR2 nor mGluRi, mGluR4, mGluR5, or mGluR6. The mGluR agonist, trans-ACPD, activated each of the transfected receptors, whereas L-AP4 activated mGluR4 and mGluR6, consistent with the published selectivity of these agonists. Hybrid cDNA constructs of the extracellular domains of mGluR2 and mGluR3 were independently fused with the transmembrane and cytoplasmic domain of mGluRl a. This latter receptor domain is coupled to phosphoinositol turnover, and its activation increases intracellular calcium. The cells transfected with these chimeric receptors responded to activation by glutamate and trans-ACPD with increases in intracellular calcium. NAAG activated the chimeric receptor that contained the extracellular domain of mGluR3 and did not activate the mGluR2 chimera. Key Words: Metabotropic glutamate receptors-Glutamate-N-Acetylaspartylglutamate-Cyclic AMP-mGluR3 agonist-Neuropeptide-Chimeric receptors. J. Neurochem. 69, i74-181 (1997).A Series of structurally related metabotropic glutamate receptors (mGluRs) have been cloned, characterized, and classified within one of three groups based on sequence homology and pharmacology (Houamed et al., 1991;Masu et al., 1991;Abe et al., 1992;pin et al., 1992, 1996 Tanabe et al., 1992; Minakami et al., 1993; Nakajima eta!., 1993; Thomsen et al., 1993; Okamoto et al., 1994;Saugstad et al., 1994;Duvoisin et al., 1995;Pin and Duvoisin, 1995; Kubokawa Ct a!., 1996). Cloned group I receptors (mUluR I and mGluR5) are coupled via phosphoinositide (PT) turnover to phospholipase C and activated by quisqualate, ibotenate, and (S)-3,5-dihydroxyphenylglycine. Cloned group II receptors (mGluR2 and mGluR3) are activated most effectively by (2R,4R)-4-aminopyrrolidine-2,4-dicarboxylic acid (APDC), trans-i -aminocyclopentane-I ,3-dicarboxylate (trans-ACPD), and (2S,1 'R,2'R,3'R)-2-(2',3'-dicarboxycyclopropyl )glycine (DCG-IV), whereas L-2-amirlo-4-phosphonobutyrate (L-AP4) and O-phosphono-Lserine are selective agonists for group III receptors (mGluR4, mGluR6, mGluR7, and mGluR8). Group I! and III receptor activation ...

NAAG Reduces NMDA Receptor Current in CA1 Hippocampal Pyramidal Neurons of Acute Slices and Dissociated Neurons

“…The antagonistic effects of NAAG are not related to its action at the mGluR3 receptor, which can downregulate glutamate release (Wroblewska et al, 1997). A decrease of synaptic glutamate release is inconsistent with our observations that AMPAR-EPSCs are not affected by NAAG.…”

Modulation of Amphetamine-Induced Dopamine Release by Group II Metabotropic Glutamate Receptor Agonist LY354740 in Non-Human Primates Studied with Positron Emission Tomography

“…Interestingly, Tsai et al (1995) described increased levels of N-acetylaspartylglutamate (NAAG) in schizophrenic brains. This observation is particularly relevant to the present study, as NAAG is an agonist at mGlu3 receptors (Wroblewska et al, 1997(Wroblewska et al, , 1998. Hypothetically, increased NAAG may lead to stimulation of mGlu3 receptors, decreased glutamate levels, and, as suggested here, dysregulation of the DA system.…”

Morphine Tolerance and Reward but not Expression of Morphine Dependence are Inhibited by the Selective Glutamate Carboxypeptidase II (GCP II, NAALADase) Inhibitor, 2-PMPA

“…In addition, an increase in NAAG concentration may decrease glutamatergic tone mediated by presynaptic mGluRII receptors (mGluR3), because another line of evidence indicates that NAAG is an agonist at mGluRII receptors (Wroblewska et al, 1993;Wroblewska et al, 1997) with EC 50 B26 mM (Tortella et al, 2000). Lastly, the inhibition of metabolism of NAAG to glutamate could directly produce a reduction of extracellular concentration of glutamate, and via this action may then attenuate the stimulation of both ionotropic and metabotropic receptors for glutamate.…”