Autism is a neurodevelopmental disorder that affects approximately 1% of the U.S. population. The causes of autism spectrum disorders are under intense investigation, with strong evidence for genetic substrates. Lifetime costs of caring for autistic individuals are high, both in terms of a) quality of life for the affected individuals and their families;b) financial expenses to the families, educational systems, and health care agencies. Discovery of multiple gene mutations, copy number variants, and epigenetic factors in people with autism has spurred the development of mouse models with homologous mutations. Genetic manipulations in mice offer an optimized experimental strategy to understand the consequences of candidate gene mutations. Effective treatments for the core symptoms of autism are currently limited to early behavioral interventions. Discovery of effective pharmacological treatments requires a greater understanding of the risk genes, biological mechanisms, and environmental factors that contribute to the etiology of autism. Animal models with robust phenotypes relevant to the diagnostic symptoms of autism offer an optimized experimental strategy to test the efficacy and safety of proposed treatments. Our Laboratory of Behavioral Neuroscience (LBN) is an international leader in behavioral assays for transgenic and knockout mice with mutations in genes expressed in brain pathways involved in neuropsychiatric disorders. We collaborate with a large number of molecular genetics laboratories that contribute mutant lines of mice with mutations in risk genes for autism to our research program. In FY2011 we tested Shank1 knockout mice generated by Morgan Sheng at the Massachusetts Institute of Technology, Shank3 knockout mice gnerated by Joseph Buxbaum at Mt. Sinai School of Medicine in New York, and Engrailed2 mice from Manny DiCicco-Bloom and Jim Millonig at RW Johnson Medical School in New Jersey. Shanks are a family of synaptic scaffolding proteins that regulate postsynaptic density formation in brain synapses. De novo mutations in SHANK3 have been detected in a small number of autistic individuals. Additionally, SHANK3 is the critical gene in chromosome 22q11-13 deletions underlying Phelan-McDermid syndrome, a neurodevelopmental disorder characterized by intellectual and motor impairments and features of autism. During FY2011, Shank3 mutant mice generated by Joseph Buxbaum at Mt. Sinai School of Medicine were evaluated on social, communication, and repetitive behavioral assays, as well as tasks relevant to associated symtoms including anxiety, seizures, cognition, and motor dysfunctions, and control measures of general health. These experiments were conducted by Research Fellow Dr. Mu Yang, Senior Research Associate Dr. Jill Silverman, Postbaccalaureates Adam Katz, Danielle Abrams, and James Zhang, and and HHMI student interns Leuk Woldeyohannes and Harry Simon. Results to date indicate normal adult sociability but reductions in specific juvenile social interactions and cognitive abilities in Shank3 mutant mice, relevant to the first diagnostic symptom of autism and components of Phelan-McDermid syndrome. In contrast, Shank1 mutant mice displayed minimal abnormalities, consistent with the current absence of mutations in SHANK1 in autism. We discovered multiple autism-relevant phenotypes in a little-known inbred strain of mice, BTBR T+tf/J (BTBR). Lack of sociability was confirmed in multiple independently bred cohorts, on multiple social tasks, by our lab and three other labs. Autism-relevant features in BTBR include low social approach, low reciprocal social interactions in juveniles and adults, and social transmission of food preference, relevant to the first diagnostic symptom of autism, abnormal social interactions. Reduced interest in social olfactory pheromones and reduced ultrasonic vocalizations in social settings by BTBR adults is relevant to the second diagnostic symptom of autism, impaired communication. High levels of repetitive self-grooming are routinely detected in cohorts of BTBR, relevant to the third diagnostic symptom of autism, repetitive behaviors. During FY2011, Dr. Silverman and postbaccalaureates discovered that BTBR responded normally on stress-related and anxiety-like tasks, confirming the relevance of their high self-grooming to the repetitive domain of autism rather than a non-selective stress response. Genetic mechanisms responsible for the autism-like phenotypes in BTBR were pursued in FY2010 and FY2011. In collaboration with Dr. Elliott Sherr, University of California San Francisco, Dr. Yang and Postbaccalaureate Adam Katz completed the behavioral phenotyping for a quantitative trait loci linkage analysis (QTL) of the BTBR x B6 cross, designed to discover genes in the BTBR background that correlate with their autism-like phenotypes. 400 F2 mice were scored for social and repetitive behaviors. Tailsnips of the 400 behaviorally tested F2 mice were genotyped in Dr. Sherr's laboratory. Linkages at several chromosomal loci were detected that correlated to F2 deficits in reciprocal social interactions. Genes within these sequences are currently being sequenced by the Sherr lab. Postdoctoral fellow Brooke Babineau is pursuing behavioral interventions that improve sociability in BTBR. Brooke is conducting structural imaging studies of BTBR brain regions, in collaboration with Jacob Ellegood at the University of Toronto, and immunological studies of BTBR, in collaboration with Paul Ashwood at the University of California Davis. Postdoctoral fellow Jennifer Brielmaier discovered severe social deficits and cognitive impairments in Engrailed2 knockout mice. ENGRAILED2 mutations were reported as a risk factor for autism in three large human association studies. A major translational component of our Project MH-002179 is the preclinical search for potential treatments. Robust and highly replicated social deficits and repetitive self-grooming in BTBR provide a good model system for testing the ability of drugs and behavioral treatments to reverse and prevent autism-like symptoms. During FY2009 and FY2010, Dr. Silverman and Postbaccalaureates Sarah Turner and Michael Karras discovered that MPEP, an mGluR5 antagonist reported to reverse phenotypes in Fragile X mice, blocked repetitive self-grooming in BTBR at doses that were not sedative. During FY2011, Mike and Sarah extended this finding to the more selective mGluR5 antagonist, MTEP, and a selective compound obtained from Pfizer. Postbaccalaureate Sarah Turner tested CX546, a prototypic AMPA receptor modulator, and detected significant improvement in sociability in BTBR in the first study. Postbaccalaureate Mike Karras replicated the CX546 experiments with a different vehicle and a different route of administration, and extended this finding to a more potent Ampakine obtained from Cortex Pharmaceuticals. These pharmacology studies provide evidence for the translational value of our assays in optimized mouse models of autism. Our preclinical discoveries are likely to lead to clinical trials of novel therapeutics for the diagnostic symptoms of autism spectrum disorders.
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