Post Doctoral Grants

«Targeting Upstream Regulators of Ube3a in Angelman Syndrome»

Awarded to: Jason J. Yi, Ph.D., Department of Pharmacology, University of North Carolina School of Medicine, Co-mentors: Klaus M. Hahn, Ph.D. and Benjamin Philpot, Ph.D.

Dates: June 1st, 2011 – May 31st, 2014

Summary: As an E3 ubiquitin ligase, Ube3a catalyzes a reaction to label certain proteins in the cell so that they are targeted for degradation. Mutations that abolish this activity are sufficient to cause Angelman Syndrome (AS). Typically, ubiquitin ligases recognize several substrates, and numerous substrates of Ube3a have been proposed. Thus, Ube3a likely regulates an ensemble of proteins that contribute to AS pathogenesis, and therefore, targeting individual components of this group for AS therapies may not be sufficient to alleviate neurological deficits associated with AS. Increasing evidence suggests that abnormal variations in the quantity of Ube3a itself may be at the heart of neurodevelopmental diseases. UBE3A resides within chromosome 15q11-13, a heavily imprinted genomic region associated with a variety of neurodevelopmental disorders. In the brain, Ube3a is only expressed from the chromosome inherited from the mother. Children who inherit a maternal chromosome carrying a deletion in 15q11-13 develop AS, whereas the majority of children who inherit a maternal chromosome carrying duplications in 15q11-13 develop Autism spectrum disorder. Therefore, understanding the factors that control the cellular quantities of Ube3a may provide an effective strategy for the design of AS therapeutics. My preliminary work has found that Ube3a stability is subject to regulation by enzymes that act upstream of Ube3a. This identifies for the first time biological mechanisms within cell that function to maintain cellular Ube3a quantities. I have proposed a system of experiments that investigates how Ube3a misregulation leads to learning defects in individuals with AS. My approach will use recent advances in biosensor development as well as sophisticated microscopy techniques to visualize directly in the brain how loss of Ube3a function perturbs normal events that occur during learning and memory at synapses. Moreover, these experiments will simultaneously allow me to identify pharmacological targets for AS therapy, and test how manipulation of these targets affects the properties of neurons lacking Ube3a. I expect that these experiments will provide insight into previously unknown mechanisms of AS pathogenesis and provide novel targets for the development of therapeutic strategies in AS. The ultimate goals of these studies is to (1) identify the molecular casus of AS by understanding Ube3a regulation and (2) using this information, develop potential pharmacological strategies for AS treatment.

«Exploring FDA Approved Therapeutic Strategies for the Treatment of Angelman Syndrome»

Awarded to: Justin Todd Rogers, Ph.D. Department of Molecular Pharmacology, University of South Florida

Mentor: Edwin J. Weeber, Ph.D.

Dates: June 1st, 2011 – December 31^st, 2012

Summary: There is a growing consensus in the scientific community that believes that a treatment for Angelman syndrome (AS) is not just possible, but very probable. However, the lack of known therapeutic targets at the cellular level that underlies the mechanisms of AS has hampered the development of therapeutic strategies. Couple that with the laborious and timely task of obtaining FDA approval once a therapeutic strategy is found, it quickly becomes evident that a treatment for AS is years or maybe even decades away. With these roadblocks in mind, this proposal tries to circumvent both of these deficiencies in regard to successfully and responsibly developing a therapeutic strategy for the treatment of AS. In this regard, this proposal does not focus, necessarily, on understanding mechanisms of AS but rather treating AS. Two main concepts were taken into consideration when I developed this proposal: shortening the time to elucidate the underlying mechanisms of AS and shortening the amount of time to have a therapeutic strategy FDA approved. This was accomplished in two ways; 1) Use pharmacological agents that are known have correlates to counter the molecular or cognitive deficiencies involved with AS. 2) Use pharmacological agents that are already FDA approved for use in humans and have an established treatment regimen. The use of these two strategies will significantly reduce the amount of time from experimental testing, to preclinical evaluation to a working and publicly available treatment for AS. To test the validity of these compounds, the AS mouse model will be used and four compounds tested and treated AS mice compared to wild-type mice at the levels of 1) Degree of cognitive enhancement 2) Rectification a biological and genetic abnormalities 3) Increases in neuronal connectivity and neuronal efficiency. It is my hope that one of these compounds will have a positive effect on one or more of these aspects that underlie AS. Furthermore, any and all positive results will prompt a full preclinical evaluation of the compound(s) and could potentially lead to the development of an effective AS therapeutic strategy.

«Epigenetic Repression of the Paternal Ube3a allele in neurons»

Awarded to: Sarah G. (Black) Christian, Ph.D. Department of Veterinary Pathobiology, Texas A&M University

Mentor: Scott V. Dindot, Ph.D.

Dates: June 1st, 2012 – May 31^st, 2014

Summary: Angelman syndrome (AS) is a devastating disorder characterized by severe intellectual disability, absence of speech, abnormal gait, seizures, and inappropriate laughter. Loss of function or loss of expression of the maternal, but not paternal, UBE3A allele results in AS due to genomic imprinting of the gene in the brain. The mechanisms regulating genomic imprinting of UBE3A remain poorly understood. To address these important questions, our laboratory has initiated a number of molecular, epigenetic and genetic studies to identify factors regulating genomic imprinting of Ube3a in the brain. In our preliminary studies, we have found that Ube3a is expressed from both paternal and maternal alleles in neural stem cells (NSC) within the hippocampus of mice. Differentiation of these stem cells leads to repression of the paternal allele in neurons, but not in astrocytes. In specific aim 1, we will utilize RNA interference technology to identify epigenetic modifiers initiating and maintaining repression of the paternal Ube3a allele in neurons. Results from this study will provide valuable insight into the fundamental mechanisms regulating genomic imprinting of Ube3a in the brain and may provide the foundation for therapeutic strategies aimed at reactivating the paternal UBE3A allele in AS patients.