Targeting troubled translation : investigating novel therapeutic targets in mouse models of fragile X and 16p1 1.2 deletion syndrome

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Brain and Cognitive Sciences, February 2017.Cataloged from PDF version of thesis. "September 2016." Vita.Includes bibliographical references (pages 189-220).in 68 children born in the United States meets the diagnostic criteria for Autism Spectrum Disorder (ASD), a psychiatric illness that shares a high comorbidity with intellectual disability (ID). Despite the high prevalence of ASD, there are currently no mechanism-based treatments available due to a lack of understanding of the pathophysiological processes in the brain that disrupt behavior in affected individuals. Identifying convergent molecular pathways involved in known genetic causes of ASD and ID may broaden our understanding of these disorders and help advance potential targeted treatments for ASD. Synaptic protein synthesis is essential for modification of the brain through experience and is altered in several genetically-defined disorders, notably fragile X (FX), a heritable cause of ASD and ID. Neural activity directs local protein synthesis via activation of metabotropic glutamate receptor 5 (mGlu₅), yet the mechanism by which mGlu₅ couples to the intracellular signaling pathways that regulate synaptic mRNA translation is poorly understood. In this dissertation, we show that manipulation of two novel targets, [beta]-arrestin2 and glycogen synthase kinase 3[alpha] (GSK3[alpha]) are able to independently modulate translation downstream of mGlu₅ Avoiding dose-limiting consequences and unwanted side effects of globally targeting mGlu₅ signaling, pharmacological inhibition of these targets has the potential to provide significant advantages over first-generation mGlu₅ inhibitors for the treatment of FX. Finally, we show that a mouse model of 16p1 1.2 microdeletion disorder, a polygenic disorder known to confer risk for ASD and ID in humans, shares common features of synaptic dysfunction downstream of mGlu₅ with the Fmr KO mouse. Chronic administration of pharmaceutical agents previously shown to restore synaptic function in the Fmr KO mouse successfully corrected many biochemical, cognitive and behavioral impairments in 16p1 1 .2 df/+ mice supporting the hypothesis that troubled translation downstream of mGlu₅ may be a convergent point of dysfunction between these two genetically-defined disorders.by Laura J. Stoppel.Ph. D

Contribution of mGluR5 to hippocampal pathophysiology in a mouse model of human chromosome 16p11.2 microdeletion

Human chromosome 16p11.2 microdeletion is the most common gene copy number variation in autism, but the synaptic pathophysiology caused by this mutation is largely unknown. Here we show using a mouse with the same genetic deficiency that metabotropic glutamate receptor 5-(mGluR5-) dependent synaptic plasticity and protein synthesis is altered in the hippocampus, and that hippocampus-dependent memory is impaired. Remarkably, chronic treatment with a negative allosteric modulator of mGluR5 reverses the cognitive deficit

ß-Arrestin2 Couples Metabotropic Glutamate Receptor 5 to Neuronal Protein Synthesis and Is a Potential Target to Treat Fragile X

Synaptic protein synthesis is essential for modification of the brain by experience and is aberrant in several genetically defined disorders, notably fragile X (FX), a heritable cause of autism and intellectual disability. Neural activity directs local protein synthesis via activation of metabotropic glutamate receptor 5 (mGlu[subscript 5]), yet how mGlu[subscript 5] couples to the intracellular signaling pathways that regulate mRNA translation is poorly understood. Here, we provide evidence that β-arrestin2 mediates mGlu[subscript 5]-stimulated protein synthesis in the hippocampus and show that genetic reduction of β-arrestin2 corrects aberrant synaptic plasticity and cognition in the Fmr[superscript 1−/y] mouse model of FX. Importantly, reducing β-arrestin2 does not induce psychotomimetic activity associated with full mGlu[subscript 5] inhibitors and does not affect G[subscript q] signaling. Thus, in addition to identifying a key requirement for mGlu[subscript 5]-stimulated protein synthesis, these data suggest that β-arrestin2-biased negative modulators of mGlu[subscript 5] offer significant advantages over first-generation inhibitors for the treatment of FX and related disorders.National Institutes of Health (U.S.) (Grant R21NS087225)National Institutes of Health (U.S.) (Grant 2R01HD046943)National Institutes of Health (U.S.) (Grant R01MH106469)National Institutes of Health (U.S.) (Grant T32MH074249)FRAXA Research Foundation (Postdoctoral Fellowship

R-Baclofen Reverses Cognitive Deficits and Improves Social Interactions in Two Lines of 16p11.2 Deletion Mice

Human chromosome 16p11.2 microdeletion is among the most common gene copy number variations (CNVs) known to confer risk for intellectual disability (ID) and autism spectrum disorder (ASD) and affects an estimated 3 in 10 000 people. Caused by a single copy deletion of ∼27 genes, 16p11.2 microdeletion syndrome is characterized by ID, impaired language, communication and socialization skills, and ASD. Studies in animal models where a single copy of the syntenic 16p11.2 region has been deleted have revealed morphological, behavioral, and electrophysiological abnormalities. Previous studies suggested the possibility of some overlap in the mechanisms of pathophysiology in 16p11.2 microdeletion syndrome and fragile X syndrome. Improvements in fragile X phenotypes have been observed following chronic treatment with R-baclofen, a selective agonist of GABA B receptors. We were therefore motivated to investigate the effects of chronic oral R-baclofen administration in two independently generated mouse models of 16p11.2 microdeletion syndrome. In studies performed across two independent laboratories, we found that chronic activation of GABA B receptors improved performance on a series of cognitive and social tasks known to be impaired in two different 16p11.2 deletion mouse models. Our findings suggest that R-baclofen may have clinical utility for some of the core symptoms of human 16p11.2 microdeletion syndrome.National Institutes of Health (Grants R01NS085709, U54HD079125

Selective inhibition of glycogen synthase kinase 3α corrects pathophysiology in a mouse model of fragile X syndrome

Copyright © 2020 The Authors, some rights reserved. Fragile X syndrome is caused by FMR1 gene silencing and loss of the encoded fragile X mental retardation protein (FMRP), which binds to mRNA and regulates translation. Studies in the Fmr1-/y mouse model of fragile X syndrome indicate that aberrant cerebral protein synthesis downstream of metabotropic glutamate receptor 5 (mGluR5) signaling contributes to disease pathogenesis, but clinical trials using mGluR5 inhibitors were not successful. Animal studies suggested that treatment with lithium might be an alternative approach. Targets of lithium include paralogs of glycogen synthase kinase 3 (GSK3), and nonselective small-molecule inhibitors of these enzymes improved disease phenotypes in a fragile X syndrome mouse model. However, the potential therapeutic use of GSK3 inhibitors has been hampered by toxicity arising from inhibition of both α and β paralogs. Recently, we developed GSK3 inhibitors with sufficient paralog selectivity to avoid a known toxic consequence of dual inhibition, that is, increased β-catenin stabilization. We show here that inhibition of GSK3α, but not GSK3β, corrected aberrant protein synthesis, audiogenic seizures, and sensory cortex hyperexcitability in Fmr1-/y mice. Although inhibiting either paralog prevented induction of NMDA receptor–dependent long-term depression (LTD) in the hippocampus, only inhibition of GSK3α impaired mGluR5-dependent and protein synthesis–dependent LTD. Inhibition of GSK3α additionally corrected deficits in learning and memory in Fmr1-/y mice; unlike mGluR5 inhibitors, there was no evidence of tachyphylaxis or enhanced psychotomimetic-induced hyperlocomotion. GSK3α selective inhibitors may have potential as a therapeutic approach for treating fragile X syndrome

Contribution of mGluR5 to pathophysiology in a mouse model of human chromosome 16p11.2 microdeletion

Human chromosome 16p11.2 microdeletion is the most common gene copy number variation in autism, but the synaptic pathophysiology caused by this mutation is largely unknown. Using a mouse with the same genetic deficiency, we found that metabotropic glutamate receptor 5 (mGluR5)-dependent synaptic plasticity and protein synthesis was altered in the hippocampus and that hippocampus-dependent memory was impaired. Notably, chronic treatment with a negative allosteric modulator of mGluR5 reversed the cognitive deficit