GABBR2 is a genetic factor that determines RTT- or EE-like phenotype expression depending on the variant positions. GABBR2-mediated γ-aminobutyric acid signaling is a crucial factor in determining the severity and nature of neurodevelopmental phenotypes. Ann Neurol 2017;82:466-478.

The novel neuropeptide spexin (SPX) was discovered to activate galanin receptor 2 (GALR2) and 3 (GALR3) but not galanin receptor 1 (GALR1). Although GALR2 is known to display a function, particularly in anxiety, depression, and appetite regulation, the further determination of its function would benefit from a more stable and selective agonist that acts only at GALR2. In the present study, we developed a GALR2-specific agonist with increased stability in serum. As galanin (GAL) showed a low affinity to GALR3, the residues in SPX were replaced with those in GAL, revealing that particular mutations such as Gln5 → Asn, Met7 → Ala, Lys11 → Phe, and Ala13 → Pro significantly decreased potencies toward GALR3 but not toward GALR2. Quadruple (Qu) mutation of these residues still retained potency to GALR2 but totally abolished the potency to both GALR3 and GALR1. The first amino acid modifications or D-Asn1 substitution significantly increased the stability when they are incubated in 100% fetal bovine serum. Intracerebroventricular administration of the mutant peptide with D-Asn1 and quadruple substitution (dN1-Qu) exhibited an anxiolytic effect in mice. Taken together, the GALR2-specific agonist with increased stability can greatly help delineation of GALR2-mediated functions and be very useful for treatments of anxiety disorder.The novel neuropeptide spexin (SPX), which is encoded by the C12ORF39 gene, was originally discovered using bioinformatics tools 1,2 . The predicted mature SPX peptide sequence of 14 amino acids flanked by dibasic cleavage sites is evolutionarily conserved across vertebrate species [1][2][3][4][5] . SPX expression at the mRNA and/or protein level has been documented in brain regions and peripheral tissues of humans, mice, rats, and goldfish 1-8 , suggesting multiple physiological functions of SPX. Recently, SPX was implicated in regulation of feeding behaviors and related metabolic processes. SPX mRNA levels are markedly decreased in the fat of obese humans, and administration of SPX leads to weight loss in diet-induced obese rodents 9 . SPX also suppresses appetite in goldfish 5 . In addition, SPX is likely involved in reproduction, cardiovascular/renal function, and nociception 4,10 . The precise roles of SPX in these processes, however, are not well understood due to a lack of information on the SPX receptor. Recently, we demonstrated that SPX is an endogenous ligand that acts at GALR2 and GALR3 but not at GALR1, while GAL activates all three receptor subtypes with relatively low potency and affinity for GALR3 11 .The SPX and GAL genes likely emerged through a local duplication from a common ancestor gene, and as a result, their mature peptides share several conserved residues, including Trp2, Thr3, Tyr9, Leu10, and Gly12 11,12 . Like SPX, GAL is widely expressed in the central nervous system and peripheral tissues [13][14][15][16] . The actions of SPX and GAL in appetite behavior and reproduction, however, appear to oppose each other. For instance, levels of circulating GAL, along with neuro...

Despite the established comorbidity between mood disorders and abnormal eating behaviors, the underlying molecular mechanism and therapeutics remain to be resolved. Here, we show that a spexin-based galanin receptor type 2 agonist (SG2A) simultaneously normalized mood behaviors and body weight in corticosterone pellet-implanted (CORTI) mice, which are underweight and exhibit signs of anhedonia, increased anxiety, and depression. Administration of SG2A into the lateral ventricle produced antidepressive and anxiolytic effects in CORTI mice. Additionally, SG2A led to a recovery of body weight in CORTI mice while it induced significant weight loss in normal mice. In Pavlovian fear-conditioned mice, SG2A decreased contextual and auditory fear memory consolidation but accelerated the extinction of acquired fear memory without altering innate fear and recognition memory. The main action sites of SG2A in the brain may include serotonergic neurons in the dorsal raphe nucleus for mood control, and proopiomelanocortin/corticotropin-releasing hormone neurons in the hypothalamus for appetite and body weight control. Furthermore, intranasal administration of SG2A exerted the same anxiolytic and antidepressant-like effects and decreased food intake and body weight in a dose-dependent manner. Altogether, these results indicate that SG2A holds promise as a clinical treatment for patients with comorbid mood disorders and abnormal appetite/body weight.

Discovery of biased ligands and receptor mutants allows characterization of G-protein- and β-arrestin-mediated signaling mechanisms of G-protein-coupled receptors (GPCRs). However, the structural mechanisms underlying biased agonism remain unclear for many GPCRs. We show that while Galanin induces the activation of the galanin receptor 2 (Galr2) that leads to a robust stimulation toward Gαq-protein and β-arrestin1/2, an alternative ligand Spexin and its analog have biased agonism toward G-protein signaling relative to Galanin. We used intramolecular fluorescein arsenical hairpin bioluminescence resonance energy transfer-based biosensors of β-arrestin2 combined with NanoBit technology to measure β-arrestin2–Galr2 interactions in real-time living systems. We found that Spexin and Galanin induce specific active conformations of Galr2, which may lead to different internalization rates of the receptor as well as different signaling outputs. This work represents an additional pharmacological evidence of endogenous G-protein-biased agonism at a GPCR.

Background:Little is known about the interaction between GLP-1 and the heptahelical core domain of GLP1R. Results: GLP-1 Asp 9 and Gly 4 interact with the evolutionarily conserved residues in extracellular loop 3. Conclusion: Ligand binding pocket formed by evolutionarily conserved residues in the GLP1R core domain. Significance: This study highlights the mechanism underlying high affinity interaction between GLP-1 and the binding pocket of the receptor.