Maria Chahrour, Ph.D. - US grants

Project Summary Autism spectrum disorder (ASD) is a highly heterogeneous constellation of neurodevelopmental conditions characterized by impaired language and communication skills, social behavior abnormalities, and stereotypic patterns of behavior. ASD affects more than 1% of the population with a societal and economic burden exceeding $150 billion a year. Advances in genomics are unraveling the complex genetic architecture of ASD, however our understanding of the molecular mechanisms underlying the disorder is lagging behind. Pathogenic mutations in the gene encoding an E3 ubiquitin ligase, UBE3B, have been recently identified in individuals with either ASD or ID, yet the mechanism(s) of how these mutations disrupt normal brain development and function are completely unknown. Our preliminary data identified a role for UBE3B in regulating the highly conserved branched-chain amino acid (BCAA) metabolism pathway. UBE3B could provide an entryway into studying disease mechanism underlying ASD, specifically in patients with defects in the BCAA metabolism pathway. This proposal aims to dissect the role of the BCAA metabolism pathway in ASD, through the study of UBE3B function in vivo. We will determine the role of UBE3B in BCAA metabolism by deleting Ube3b specifically in the brain (Ube3b cKOBrain) or the liver (Ube3b cKOLiver), and analyzing these conditional knockout mice in a series of biochemical and behavioral experiments. Results from our studies will enable us to determine whether the neurological phenotype in patients with UBE3B mutations is primarily due to a metabolic defect in the brain or the liver. Our work will lay the groundwork for targeted therapies for ASD, specifically in patients who carry pathogenic mutations in UBE3B, BCKDK, DBT, or genes encoding other components of the BCAA metabolism pathway. It will provide mechanistic understanding in a very complex, debilitating, and intractable disorder.

Project Summary Neurodevelopmental disorders (NDDs) affecting cognitive and social abilities are a phenotypically and genetically heterogeneous group of conditions. Understanding the molecular mechanisms underlying these disorders is crucial for the development of targeted therapies. Loss-of-function mutations in the gene BCKDK, encoding the branched-chain a-ketoacid dehydrogenase kinase, result in autism spectrum disorder (ASD) and epilepsy. Conversely, duplications of chromosome 16p11.2 spanning the BCKDK locus have been identified in patients with a spectrum of neurodevelopmental phenotypes, including developmental delay, speech and language abnormalities, intellectual disability, ASD, and microcephaly. However, it is not known whether the neurodevelopmental phenotypes arise due to an increased copy of BCKDK or how BCKDK overexpression mediates these phenotypes. The goal of this proposal is to generate a transgenic mouse model overexpressing BCKDK, and to characterize the resulting neurobehavioral phenotypes. Our proposal will develop the first mouse model of BCKDK overexpression and test, for the first time, the link between BCKDK overexpression and NDDs. Results from our studies will ?illuminate? an understudied protein kinase, BCKDK, by providing animal model- based evidence for disease relevance and generating reagents and data for the scientific community.

Project Summary The molecular pathways underlying cognition and vocal communication remain largely unknown. The genes and mechanisms governing these processes are disrupted in many neurodevelopmental disorders, including intellectual disability and autism spectrum disorder. The long-term goal of our laboratory is to study the normal function of genes disrupted in disorders with deficits in cognition, communication, and social behavior, to gain mechanistic understanding that can be leveraged for treatment opportunities. Mutations in the gene encoding the ubiquitin ligase UBE3B have been identified in patients with intellectual disability and lack of speech. The specific mechanism(s) that give rise to the neurodevelopmental phenotypes and the UBE3B substrates that mediate these mechanisms are completely unknown. Our preliminary studies suggest a role for UBE3B in brain development and vocalization. In addition, we identified the branched-chain a-ketoacid dehydrogenase kinase (BCKDK) as a substrate for UBE3B. We propose to dissect the molecular networks regulated by UBE3B and its role in mediating vocalization, through the following three specific aims: 1) Determine the role of UBE3B in vocalization; 2) Identify the neuronal substrates of UBE3B through quantitative proteomics and biochemical validation experiments; 3) Rescue the neurodevelopmental phenotypes associated with UBE3B loss of function by targeting its substrate BCKDK. Together, these aims will identify the molecular networks regulated by UBE3B that may underlie the lack of speech and other neurodevelopmental phenotypes observed in patients with UBE3B disruption. Successful completion of the proposed aims will provide new insights into pathways regulating vocalization, increase our knowledge of the specific pathogenic mechanism underlying neurodevelopmental disorders with communication deficits, and examine new therapeutic approaches.