This is a competitive renewal of 5RO1NS070301-02, entitled "Dynamic Regulation of Shank3 and Autism Spectrum Disorders", which was awarded as an ARRA grant beginning 09/30/2009. Shank3 is linked in human genetic studies to both autism spectrum disorders (ASD) and schizophrenia, and our broad goals are to define the molecular basis for behavioral diseases linked to mutations of Shank3, and to identify unifying concepts that are applicable to other genetic causes of ASD. We created a mouse model that mimics human subjects with mutations that delete the C-terminus of Shank3 [Shank3(+/ ?exon21)], and have published findings that support a novel molecular model for ASD(1). We discovered that Shank3 (+/ ?exon21) mice express Shank3 mutant protein lacking the C-terminus (Shank3?C), and this acts in a "gain-of-function" manner to selectively increase the ubiquitination of WT Shank3 and the NR1 subunit of the NMDA receptor, and reduce their expression at synapses. Shank3(+/?exon 21) mice show reduced NMDA receptor-dependent synaptic plasticity, as well as enhanced mGluR-dependent long-term depression. Shank3(+/?exon21) mice have normal memory function but display prominent behavioral deficits in reciprocal social interaction, together with phenotypes classically associated with schizophrenia. These findings provide important validation that molecular mechanisms consequent to mutation of Shank3 can underlie behavioral dysfunction relevant to ASD in a mouse model.
Aims of this competitive continuation are;
Aim 1 will test our hypothesis that increased ubiquitination of Shank3 and NR1, and associated behavioral deficits, are dependent (inversely) on the degree of Shank3 cross-linking by Homer(1). We will use mouse genetic models that delete Homer2 (to reduce Homer crosslinking), or selectively delete the immediate early gene form Homer1a (to increase crosslinking), and determine how this modifies phenotypes in Shank3 (+/ ?exon21) mice. Since Homer1a is dynamically regulated by behavioral experience, these studies will test a molecular mechanism linking behavioral experience and severity of phenotypes.
Aim 2 will examine a candidate ubiquitin ligase for Shank3 and determine its contribution to phenotypes in Shank3 (+/ ?exon21) mice.
Aim 3 will evaluate the observation that mTORC1 (mammalian target of rapamycin complex 1) signaling is altered in Shank3 (+/?exon21) mice, and examine a hypothesized general mechanism that links protein turnover with mTORC1 activity.
Aim 4 will examine the link between Shank3?C expression and enhanced mGluR5 signaling, and test if inhibition of mGluR5 can reduce the severity of phenotypes.
Aim 5 will utilize the conditional property of the Shank3 mouse to examine the developmental, and cellular bases of phenotypes produced by Shank3 ?C. These studies address important goals set by the NIH to establish animal models of behavioral disease, and to provide a scientific basis for development of rational therapies.
With a goal to discover molecular mechanisms that contribute to autism spectrum disorders (ASD), we have created a novel mouse model that mimics human mutations of Shank3 linked to ASD and have reported behavioral deficits that mimic aspects of human ASD and schizophrenia. Most importantly, we have discovered a molecular mechanism can rationalize cellular and behavioral phenotypes. In this renewal proposal, we will gain a deeper understanding of molecular mechanisms and evaluate convergent mechanisms that could underlie multiple genetic causes of ASD, and rationalize new directions for therapy.
|Bangash, M Ali; Park, Joo Min; Melnikova, Tatiana et al. (2011) Enhanced polyubiquitination of Shank3 and NMDA receptor in a mouse model of autism. Cell 145:758-72|