Towards the convergent therapeutic potential of G protein-coupled receptors in autism spectrum disorders.

Autism spectrum disorders (ASDs) are diagnosed in 1/100 children worldwide, based on two core symptoms: deficits in social interaction and communication, and stereotyped behaviours. G protein-coupled receptors (GPCRs) are the largest family of cell-surface receptors that transduce extracellular signals to convergent intracellular signalling and downstream cellular responses that are commonly dysregulated in ASD. Despite hundreds of GPCRs being expressed in the brain, only 23 are genetically associated with ASD according to the Simons Foundation Autism Research Initiative (SFARI) gene database: oxytocin OTR; vasopressin V1A and V1B ; metabotropic glutamate mGlu5 and mGlu7 ; GABAB2 ; dopamine D1 , D2 and D3 ; serotoninergic 5-HT1B ; ß2 -adrenoceptor; cholinergic M3 ; adenosine A2A and A3 ; angiotensin AT2 ; cannabinoid CB1 ; chemokine CX3 CR1; orphan GPR37 and GPR85; and olfactory OR1C1, OR2M4, OR2T10 and OR52M1. Here, we review the therapeutic potential of these 23 GPCRs, as well as 5-HT2A and 5-HT7 , for ASD. For each GPCR, we discuss its genetic association, genetic and pharmacological manipulation in animal models, pharmacopoeia for core symptoms of ASD and rank them based on these factors. Among these GPCRs, we highlight D2 , 5-HT2A , CB1 , OTR and V1A as the more promising targets for ASD. We discuss that the dysregulation of GPCRs and their signalling is a convergent pathological mechanism of ASD. Their therapeutic potential has only begun as multiple GPCRs could mitigate ASD.

Tonic inhibition of the chloride/proton antiporter ClC-7 by PI(3,5)P2 is crucial for lysosomal pH maintenance.

The acidic luminal pH of lysosomes, maintained within a narrow range, is essential for proper degrative function of the organelle and is generated by the action of a V-type H+ ATPase, but other pathways for ion movement are required to dissipate the voltage generated by this process. ClC-7, a Cl-/H+ antiporter responsible for lysosomal Cl- permeability, is a candidate to contribute to the acidification process as part of this 'counterion pathway' The signaling lipid PI(3,5)P2 modulates lysosomal dynamics, including by regulating lysosomal ion channels, raising the possibility that it could contribute to lysosomal pH regulation. Here, we demonstrate that depleting PI(3,5)P2 by inhibiting the kinase PIKfyve causes lysosomal hyperacidification, primarily via an effect on ClC-7. We further show that PI(3,5)P2 directly inhibits ClC-7 transport and that this inhibition is eliminated in a disease-causing gain-of-function ClC-7 mutation. Together, these observations suggest an intimate role for ClC-7 in lysosomal pH regulation.

Arginine-selective modulation of the lysosomal transporter PQLC2 through a gate-tuning mechanism.

Lysosomes degrade excess or damaged cellular components and recycle their building blocks through membrane transporters. They also act as nutrient-sensing signaling hubs to coordinate cell responses. The membrane protein PQ-loop repeat-containing protein 2 (PQLC2; "picklock two") is implicated in both functions, as it exports cationic amino acids from lysosomes and serves as a receptor and amino acid sensor to recruit the C9orf72/SMCR8/WDR41 complex to lysosomes upon nutrient starvation. Its transport activity is essential for drug treatment of the rare disease cystinosis. Here, we quantitatively studied PQLC2 transport activity using electrophysiological and biochemical methods. Charge/substrate ratio, intracellular pH, and reversal potential measurements showed that it operates in a uniporter mode. Thus, PQLC2 is uncoupled from the steep lysosomal proton gradient, unlike many lysosomal transporters, enabling bidirectional cationic amino acid transport across the organelle membrane. Surprisingly, the specific presence of arginine, but not other substrates (lysine, histidine), in the discharge ("trans") compartment impaired PQLC2 transport. Kinetic modeling of the uniport cycle recapitulated the paradoxical substrate-yet-inhibitor behavior of arginine, assuming that bound arginine facilitates closing of the transporter's cytosolic gate. Arginine binding may thus tune PQLC2 gating to control its conformation, suggesting a potential mechanism for nutrient signaling by PQLC2 to its interaction partners.

Neuronal Nicotinic Receptors Are Crucial for Tuning of E/I Balance in Prelimbic Cortex and for Decision-Making Processes.

RATIONALE: Decision-making is an essential component of our everyday life commonly disabled in a myriad of psychiatric conditions, such as bipolar and impulsive control disorders, addiction and pathological gambling, or schizophrenia. A large cerebral network encompassing the prefrontal cortex, the amygdala, and the nucleus accumbens is activated for efficient decision-making. METHODS: We developed a mouse gambling task well suited to investigate the influence of uncertainty and risk in decision-making and the role of neurobiological circuits and their monoaminergic inputs. Neuronal nicotinic acetylcholine receptors (nAChRs) of the PFC are important for decision-making processes but their presumed roles in risk-taking and uncertainty management, as well as in cellular balance of excitation and inhibition (E/I) need to be investigated. RESULTS: Using mice lacking nAChRs - ß2-/- mice, we evidence for the first time the crucial role of nAChRs in the fine tuning of prefrontal E/I balance together with the PFC, insular, and hippocampal alterations in gambling behavior likely due to sensitivity to penalties and flexibility alterations. Risky behaviors and perseveration in extinction task were largely increased in ß2-/- mice as compared to control mice, suggesting the important role of nAChRs in the ability to make appropriate choices adapted to the outcome.

Quinuclidine compounds differently act as agonists of Kenyon cell nicotinic acetylcholine receptors and induced distinct effect on insect ganglionic depolarizations.

We have recently demonstrated that a new quinuclidine benzamide compound named LMA10203 acted as an agonist of insect nicotinic acetylcholine receptors. Its specific pharmacological profile on cockroach dorsal unpaired median neurons (DUM) helped to identify alpha-bungarotoxin-insensitive nAChR2 receptors. In the present study, we tested its effect on cockroach Kenyon cells. We found that it induced an inward current demonstrating that it bounds to nicotinic acetylcholine receptors expressed on Kenyon cells. Interestingly, LMA10203-induced currents were completely blocked by the nicotinic antagonist α-bungarotoxin. We suggested that LMA10203 effect occurred through the activation of α-bungarotoxin-sensitive receptors and did not involve α-bungarotoxin-insensitive nAChR2, previously identified in DUM neurons. In addition, we have synthesized two new compounds, LMA10210 and LMA10211, and compared their effects on Kenyon cells. These compounds were members of the 3-quinuclidinyl benzamide or benzoate families. Interestingly, 1 mM LMA10210 was not able to induce an inward current on Kenyon cells compared to LMA10211. Similarly, we did not find any significant effect of LMA10210 on cockroach ganglionic depolarization, whereas these three compounds were able to induce an effect on the central nervous system of the third instar M. domestica larvae. Our data suggested that these three compounds could bind to distinct cockroach nicotinic acetylcholine receptors.

Pretreatment of the cockroach cercal afferent/giant interneuron synapses with nicotinoids and neonicotinoids differently affects acetylcholine and nicotine-induced ganglionic depolarizations.

We have recently demonstrated that neonicotinoid insecticides were able to act as agonists of postsynaptic nicotinic acetylcholine receptors (nAChRs) expressed at the synapse between the cercal nerve XI and the giant interneurons, in the sixth abdominal ganglion. In this work, we demonstrated that nicotinoids such as nornicotine acted as an agonist of nicotinic acetylcholine receptors expressed at cercal afferent/giant interneurons while cotinine was a poor agonist. Indeed, nornicotine induced a ganglionic depolarization which was blocked by the nicotinic antagonist mecamylamine. In addition, we found that pretreatment of the sixth abdominal ganglion with 1 and 10 µM nornicotine and cotinine had no significant effect on acetylcholine and nicotine-induced depolarization. But pretreatment with 1 and 10 µM acetamiprid and imidacloprid had a strong effect. 1 and 10 µM acetamiprid completely blocked acetylcholine-induced depolarization, whereas imidacloprid had a partial effect. The present work therefore suggests, in agreement with previous studies, that nornicotine and cotinine bind to distinct cockroach postsynaptic nAChRs, whereas acetamiprid and imidacloprid have competitive effects with acetylcholine and nicotine on ganglionic depolarization.