William C. Wetsel

Cortico-striatal synaptic defects and OCD-like behaviours in Sapap3-mutant mice.

Obsessive-compulsive disorder (OCD) is an anxiety-spectrum disorder characterized by persistent intrusive thoughts (obsessions) and repetitive actions (compulsions). Dysfunction of cortico-striato-thalamo-cortical circuitry is implicated in OCD, although the underlying pathogenic mechanisms are unknown. SAP90/PSD95-associated protein 3 (SAPAP3; also known as DLGAP3) is a postsynaptic scaffolding protein at excitatory synapses that is highly expressed in the striatum. Here we show that mice with genetic deletion of Sapap3 exhibit increased anxiety and compulsive grooming behaviour leading to facial hair loss and skin lesions; both behaviours are alleviated by a selective serotonin reuptake inhibitor. Electrophysiological, structural and biochemical studies of Sapap3-mutant mice reveal defects in cortico-striatal synapses. Furthermore, lentiviral-mediated selective expression of Sapap3 in the striatum rescues the synaptic and behavioural defects of Sapap3-mutant mice. These findings demonstrate a critical role for SAPAP3 at cortico-striatal synapses and emphasize the importance of cortico-striatal circuitry in OCD-like behaviours.

Mice lacking the norepinephrine transporter are supersensitive to psychostimulants

The action of norepinephrine (NE) is terminated, in part, by its uptake into presynaptic noradrenergic neurons by the plasma-membrane NE transporter (NET), which is a target for antidepressants and psychostimulants. Disruption of the NET gene in mice prolonged the clearance of NE and elevated extracellular levels of this catecholamine. In a classical test for antidepressant drugs, the NET-deficient (NET−/−) animals behaved like antidepressant-treated wild-type mice. Mutants were hyper-responsive to locomotor stimulation by cocaine or amphetamine. These responses were accompanied by dopamine D2/D3 receptor supersensitivity. Thus altering NET expression significantly modulates midbrain dopaminergic function, an effect that may be an important component of the actions of antidepressants and psychostimulants.

Automated design of ligands to polypharmacological profiles

The clinical efficacy and safety of a drug is determined by its activity profile across many proteins in the proteome. However, designing drugs with a specific multi-target profile is both complex and difficult. Therefore methods to design drugs rationally a priori against profiles of several proteins would have immense value in drug discovery. Here we describe a new approach for the automated design of ligands against profiles of multiple drug targets. The method is demonstrated by the evolution of an approved acetylcholinesterase inhibitor drug into brain-penetrable ligands with either specific polypharmacology or exquisite selectivity profiles for G-protein-coupled receptors. Overall, 800 ligand–target predictions of prospectively designed ligands were tested experimentally, of which 75% were confirmed to be correct. We also demonstrate target engagement in vivo. The approach can be a useful source of drug leads when multi-target profiles are required to achieve either selectivity over other drug targets or a desired polypharmacology.

ANOVULATION IN CYCLOOXYGENASE-2-DEFICIENT MICE IS RESTORED BY PROSTAGLANDIN E2 AND INTERLEUKIN-1BETA

Mice carrying a null mutation for either of the two cyclooxygenase (COX) isoenzymes, necessary for prostanoid production, exhibit several isotype-specific reproductive abnormalities. Mice deficient in COX-1 are fertile but have decreased pup viability, whereas mice deficient in COX-2 fail to ovulate and have abnormal implantation and decidualization responses. The present study identifies the specific contribution of each COX isoenzyme in hypothalamic, pituitary, and ovarian function and establishes the pathology and rescue of the anovulatory syndrome in the COX-2-deficient mouse. In both COX-1- and COX-2-deficient mice, pituitary gonadotropins were selectively increased, whereas hypothalamic LHRH and serum gonadotropin levels were similar to those in wild-type animals (+/+). No significant differences in serum estrogen or progesterone were noted among the three genotypes. Exogenous gonadotropin stimulation with PMSG and hCG produced a comparable 4-fold increase in ovarian PGE2 levels in wild-type and COX...

Role of GSK3β in behavioral abnormalities induced by serotonin deficiency

Dysregulation of brain serotonin (5-HT) neurotransmission is thought to underlie mental conditions as diverse as depression, anxiety disorders, bipolar disorder, autism, and schizophrenia. Despite treatment of these conditions with serotonergic drugs, the molecular mechanisms by which 5-HT is involved in the regulation of aberrant emotional behaviors are poorly understood. Here, we generated knockin mice expressing a mutant form of the brain 5-HT synthesis enzyme, tryptophan hydroxylase 2 (Tph2). This mutant is equivalent to a rare human variant (R441H) identified in few individuals with unipolar major depression. Expression of mutant Tph2 in mice results in markedly reduced (≈80%) brain 5-HT production and leads to behavioral abnormalities in tests assessing 5-HT-mediated emotional states. This reduction in brain 5-HT levels is accompanied by activation of glycogen synthase kinase 3β (GSK3β), a signaling molecule modulated by many psychiatric therapeutic agents. Importantly, inactivation of GSK3β in Tph2 knockin mice, using pharmacological or genetic approaches, alleviates the aberrant behaviors produced by 5-HT deficiency. These findings establish a critical role of Tph2 in the maintenance of brain serotonin homeostasis and identify GSK3β signaling as an important pathway through which brain 5-HT deficiency induces abnormal behaviors. Targeting GSK3β and related signaling events may afford therapeutic advantages for the management of certain 5-HT-related psychiatric conditions.

A β-arrestin 2 Signaling Complex Mediates Lithium Action on Behavior

Besides their role in desensitization, beta-arrestin 1 and 2 promote the formation of signaling complexes allowing G protein-coupled receptors (GPCR) to signal independently from G proteins. Here we show that lithium, a pharmacological agent used for the management of psychiatric disorders such as bipolar disorder, schizophrenia, and depression, regulates Akt/glycogen synthase kinase 3 (GSK3) signaling and related behaviors in mice by disrupting a signaling complex composed of Akt, beta-arrestin 2, and protein phosphatase 2A. When administered to beta-arrestin 2 knockout mice, lithium fails to affect Akt/GSK3 signaling and induce behavioral changes associated with GSK3 inhibition as it does in normal animals. These results point toward a pharmacological approach to modulating GPCR function that affects the formation of beta-arrestin-mediated signaling complexes.

Synaptic dysfunction and abnormal behaviors in mice lacking major isoforms of Shank3

SHANK3 is a synaptic scaffolding protein enriched in the postsynaptic density (PSD) of excitatory synapses. Small microdeletions and point mutations in SHANK3 have been identified in a small subgroup of individuals with autism spectrum disorder (ASD) and intellectual disability. SHANK3 also plays a key role in the chromosome 22q13.3 microdeletion syndrome (Phelan-McDermid syndrome), which includes ASD and cognitive dysfunction as major clinical features. To evaluate the role of Shank3 in vivo, we disrupted major isoforms of the gene in mice by deleting exons 4-9. Isoform-specific Shank3(e4-9) homozygous mutant mice display abnormal social behaviors, communication patterns, repetitive behaviors and learning and memory. Shank3(e4-9) male mice display more severe impairments than females in motor coordination. Shank3(e4-9) mice have reduced levels of Homer1b/c, GKAP and GluA1 at the PSD, and show attenuated activity-dependent redistribution of GluA1-containing AMPA receptors. Subtle morphological alterations in dendritic spines are also observed. Although synaptic transmission is normal in CA1 hippocampus, long-term potentiation is deficient in Shank3(e4-9) mice. We conclude that loss of major Shank3 species produces biochemical, cellular and morphological changes, leading to behavioral abnormalities in mice that bear similarities to human ASD patients with SHANK3 mutations.

Different presynaptic roles of synapsins at excitatory and inhibitory synapses.

The functions of synapsins were examined by characterizing the phenotype of mice in which all three synapsin genes were knocked out. Although these triple knock-out mice were viable and had normal brain anatomy, they exhibited a number of behavioral defects. Synaptic transmission was altered in cultured neurons from the hippocampus of knock-out mice. At excitatory synapses, loss of synapsins did not affect basal transmission evoked by single stimuli but caused a threefold increase in the rate of synaptic depression during trains of stimuli. This suggests that synapsins regulate the reserve pool of synaptic vesicles. This possibility was examined further by measuring synaptic vesicle density in living neurons transfected with green fluorescent protein-tagged synaptobrevin 2, a marker of synaptic vesicles. The relative amount of fluorescent synaptobrevin was substantially lower at synapses of knock-out neurons than of wild-type neurons. Electron microscopy also revealed a parallel reduction in the number of vesicles in the reserve pool of vesicles >150 nm away from the active zone at excitatory synapses. Thus, synapsins are required for maintaining vesicles in the reserve pool at excitatory synapses. In contrast, basal transmission at inhibitory synapses was reduced by loss of synapsins, but the kinetics of synaptic depression were unaffected. In these terminals, there was a mild reduction in the total number of synaptic vesicles, but this was not restricted to the reserve pool of vesicles. Thus, synapsins maintain the reserve pool of glutamatergic vesicles but regulate the size of the readily releasable pool of GABAergic vesicles.

N-Desalkylquetiapine, a potent norepinephrine reuptake inhibitor and partial 5-HT1A agonist, as a putative mediator of quetiapine's antidepressant activity

Quetiapine is an atypical antipsychotic drug that is also US FDA approved for treating bipolar depression, albeit by an unknown mechanism. To discover the potential mechanism for this apparently unique action, we screened quetiapine, its metabolite N-Desalkylquetiapine, and dibenzo[b,f][1,4]thiazepine-11(10-H)-one (DBTO) against a large panel of G-protein–coupled receptors, ion channels, and neurotransmitter transporters. DBTO was inactive at all tested molecular targets. N-Desalkylquetiapine had a high affinity (3.4 nM) for the histamine H1 receptor and moderate affinities (10–100 nM) for the norepinephrine reuptake transporter (NET), the serotonin 5-HT1A, 5-HT1E, 5-HT2A, 5-HT2B, 5-HT7 receptors, the α1B-adrenergic receptor, and the M1, M3, and M5 muscarinic receptors. The compound had low affinities (100–1000 nM) for the 5-HT1D, 5-HT2C, 5-HT3, 5-HT5, 5-HT6, α1A, α2A, α2B, α2C, H2, M2, M4, and dopamine D1, D2, D3, and D4 receptors. N-Desalkylquetiapine potently inhibited human NE transporter with a Ki of 12 nM, about 100-fold more potent than quetiapine itself. N-Desalkylquetiapine was also 10-fold more potent and more efficacious than quetiapine at the 5-HT1A receptor. N-Desalkylquetiapine was an antagonist at 5-HT2A, 5-HT2B, 5-HT2C, α1A, α1D, α2A, α2C, H1, M1, M3, and M5 receptors. In the mouse tail suspension test, N-Desalkylquetiapine displayed potent antidepressant-like activity in VMAT2 heterozygous mice at doses as low as 0.1 mg/kg. These data strongly suggest that the antidepressant activity of quetiapine is mediated, at least in part, by its metabolite N-Desalkylquetiapine through NET inhibition and partial 5-HT1A agonism. Possible contributions of this metabolite to the side effects of quetiapine are discussed.

Discovery of β-Arrestin–Biased Dopamine D2 Ligands for Probing Signal Transduction Pathways Essential for Antipsychotic Efficacy

Elucidating the key signal transduction pathways essential for both antipsychotic efficacy and side-effect profiles is essential for developing safer and more effective therapies. Recent work has highlighted noncanonical modes of dopamine D2 receptor (D2R) signaling via β-arrestins as being important for the therapeutic actions of both antipsychotic and antimanic agents. We thus sought to create unique D2R agonists that display signaling bias via β-arrestin–ergic signaling. Through a robust diversity-oriented modification of the scaffold represented by aripiprazole (1), we discovered UNC9975 (2), UNC0006 (3), and UNC9994 (4) as unprecedented β-arrestin–biased D2R ligands. These compounds also represent unprecedented β-arrestin–biased ligands for a Gi-coupled G protein–coupled receptor (GPCR). Significantly, UNC9975, UNC0006, and UNC9994 are simultaneously antagonists of Gi-regulated cAMP production and partial agonists for D2R/β-arrestin-2 interactions. Importantly, UNC9975 displayed potent antipsychotic-like activity without inducing motoric side effects in inbred C57BL/6 mice in vivo. Genetic deletion of β-arrestin-2 simultaneously attenuated the antipsychotic actions of UNC9975 and transformed it into a typical antipsychotic drug with a high propensity to induce catalepsy. Similarly, the antipsychotic-like activity displayed by UNC9994, an extremely β-arrestin–biased D2R agonist, in wild-type mice was completely abolished in β-arrestin-2 knockout mice. Taken together, our results suggest that β-arrestin signaling and recruitment can be simultaneously a significant contributor to antipsychotic efficacy and protective against motoric side effects. These functionally selective, β-arrestin–biased D2R ligands represent valuable chemical probes for further investigations of D2R signaling in health and disease.