Manganese exposure and genetic diversity in risk mechanisms for neurodevelopmental disorders

ABSTRACT The broad, long-term objectives of the grant are to increase our understanding of the mechanisms underlying the gene x environment interactions that link developmental manganese (Mn) exposure, dopamine (DA) dysregulation and increased frequency of ADHD diagnoses. Through the use of both sexes and varied genetic

backgrounds in our testing models (mice and human iPSC lines) we use a rigorous approach to deepen our understanding of the role of genetics on the strength of the mechanisms under investigation. Strong epidemiological and correlation evidence points to a relationship between overexposure to metals, including

Mn, and development of childhood and adolescent neuropsychological disorders. We will use oral exposures to mimic exposure to Mn through poorly filtered water such as that obtained from wells, at levels relevant to known human exposures in N. America. We will support our behavioral studies with comprehensive analyses

of dopaminergic (DAergic) function including post-mortem analyses of brain tissues, electrophysiology approaches in live brain slices and in vitro study of human induced pluripotent stem cell (hiPSC)-derived DA neurons. Our first Specific Aim is to Determine the role of sex and genetic background on Mn exposure-

induced behavioral change and DAergic transport deficits. Three background strains have been selected for their baseline differences in DAergic function, Mn metabolism and locomotor activity. Mice will be exposed to control, moderate or high Mn through water from weaning to assess the impact of sub-toxic (i.e. no expected

cell death) Mn levels in brain during development. We will use a range of behavioral outcomes that are representative of changes observed in ADHD as well as variation observed in the general public. We will study DA metabolism and release/reuptake kinetics through neurochemistry, post translational protein modifications,

RNA and electrophysiology approaches. In Specific Aim 2 we will Test whether Mn modifies pharmacological modulation of DA transport in vivo. We will use genetic approaches to generate mild disturbances in the DAergic system from birth that cause only modestly altered phenotypes (behavioral and cellular). We will then

test whether Mn exposure is sufficient to drive these mild presentations towards full expression of abnormal phenotypes mimicking a classic gene x environmental exposure model of development of Intellectual and Developmental Disabilities. We will further test the potential for Mn to impact efficacy of common treatments for

ADHD. Finally, in Specific Aim 3 we will determine whether Mn has an ADHD-related differential impact on DA functional characteristics of human induced pluripotent stem cell (hiPSC)-derived DAergic neurons. We will use cell lines derived from males and females under baseline conditions, and following genetic mutation of the DA

transporter, or exposure to chemical ADHD risk factors. We will assess changes in neurochemistry and post- translational modifications to test the potential translational relevance of Aims 1 and 2. We will use single-cell genetic pathway analysis to test hypotheses about which pathways are disrupted by Mn.