Discipline: Biological Sciences
Subcategory: Physiology and Health
Room: Exhibit Hall A
Alex Lish - Utah State University
Co-Author(s): Aya Zucca, Scripps Research Institute, Jupiter, Florida; Amy Clipperton-Allen, Scripps Research Institute, Jupiter, Florida; Damon Page, Scripps Research Institute, Jupiter, Florida
Dopaminergic neurons have been implicated in autism spectrum disorder based on dopamine’s role in processing natural and conditional rewards and social behavior. Many autism risk genes are associated with mTOR signaling, a critical effector of neuronal growth and connectivity. However, the role of dysregulated mTOR signaling in dopamine neurons and their projections is unknown. The medial prefrontal cortex (mPFC) has also been implicated in the regulation of social behavior and is thought to function as a central hub in the brain circuitry underlying core symptoms of ASD. These evidences led us to investigate how the mesocortical pathway could be modulating mPFC activity, specifically in germline heterozygous Pten mutant mice (Pten+/-), a model for autism/macrocephaly syndrome. PTEN, a negative regulator of the PI3K-Akt-mTOR pathway, is mutated in approximately 15% of individuals with autism spectrum disorder and macrocephaly. We hypothesized dopamine cells in the ventral tegmental area (VTA) and dopamine projections to the mPFC will be increased in Pten+/- mice due to dysregulated mTOR signaling. To test this hypothesis, we stained 40 m coronal sections of VTA and mPFC Pten+/- and wildtype tissue with anti-tyrosine hydroxylase and anti-phospho-S6, a marker for mTOR activity. Stainings were analyzed in ImageJ and measurements of soma size and axon fiber density were compared using a paired t-test. Our findings demonstrate that the somas of dopaminergic neurons residing in the VTA are enlarged in Pten+/- mice. Dopaminergic neurons in the VTA also display greater mTOR activity compared to non-dopaminergic cells in Pten+/- mice. Analysis of VTA to mPFC axonal projections reveals that the distribution of dopaminergic axons in the mPFC is altered in Pten+/- mice, with deeper layers receiving greater axon innervation compared to upper layers. Increased axon fiber density in deeper layers may drive increased activity in the mPFC in response to social stimuli, leading to social behavioral deficits. To test this hypothesis, we attempted a rescue by reducing VTA to mPFC neuronal activity using DREADDs technology. Upon reducing VTA to mPFC neuronal activity, social interaction increased in Pten+/- mice. Our findings suggest PTEN mutations drive aberrant dopaminergic projections to the mPFC and decrease social interactions due to dysregulated mTOR signaling, in relation to the pathophysiology of autism/macrocephaly syndrome. Future research involves the investigation of dopamine release and receptor binding mechanisms to further elucidate the molecular underpinnings of PTEN mutations. References: Brumback, A.C., et al. Identifying specific prefrontal neurons that contribute to autism-associated abnormalities in physiology and behavior. Mol. Psychiatry 23, 2078-2089 (2018).
Page, D.T. et al. Haploinsufficiency for Pten and Serotonin transporter cooperatively influences brain size and social behavior. Proc Natl Acad Sci, 106(6): 1989-94 (2009).
Funder Acknowledgement(s): I would like to thank the Scripps Research Institute and the National Science Foundation for providing funding for this project. Funding was also provided by a National Institutes of Health grant R01MH105610.
Faculty Advisor: Damon Page, Paged@scripps.edu
Role: The only part of this research that I did not complete independently were the mice perfusions and DREADDS injections. I sectioned all of the brains for analysis, performed all immunhistochemistry stainings, conducted the 3-chamber behavioral experiments, and completed all of the analysis (ImageJ quantification, behavioral analysis, and statistical analysis).