The role of inhibitory neurons in microcephaly and seizure caused by Asparagine synthetase (ASNS) deficiency

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Asparagine synthetase deficiency (ASNSD) is a recently identified autosomal recessive neurological disorder characterized by severe microcephaly, intellectual disability and intractable seizures. ASNSD is caused by mutations in the ASNS gene which encodes asparagine synthetase (ASNS). A known function of ASNS is to catalyze the conversion from aspartate and glutamine to asparagine (ASN). Thus, one tempting hypothesis is that ASNS deficiency results in low levels of ASN, which in turn impede neural progenitor cell proliferation during earlier stages of brain development, and subsequent neurological impairments such as microcephaly and seizures. In fact, a subset of ASNSD patients are found to have low plasma or CSF ASN levels. However, it was reported in one case study that an ASNSD patient showed only initial response to ASN intervention. Thus, it is critical to definitively determinate the function of ASNS and effects of ASNS deficiency in brain development, and establish the causal relationship between low ASN levels and ASNSD in a valid model system. To better understand ASNSD, I have generated a number of Asns knockout (KO) mouse models. Importantly, brain-specific KO of Asns results in severe microcephaly and spontaneous seizures, suggesting a specific and critical role for ASNS in brain development. Surprisingly, unlike known microcephaly models which caused by significant loss of cortical excitatory neurons, a drastic reduction in cortical interneurons in brain-specific Asns KO brain was observed. This data suggest a critical role of ASNS in interneuron development. In line with this observation, Asns KO in cortical excitatory neurons fails to induce microcephaly and seizure. Thus, I hypothesize that alterations in the development and function of selective inhibitory neurons underlie the pathophysiology of the microcephaly and seizure phenotypes in ASNSD. The objective of the study is to dissect the mechanistic link underlying the neurological impairments and evaluate the therapeutic intervention of ASN supplementation in various Asns mutant mice. Overall, this proposed study will provide mechanistic insight to the pathogenesis of ASNSD and the role of interneurons in early brain development. Additionally, this proposed research will test for a potential therapeutic strategy to ASNSD. Execution of the proposed training plan will not only expend my knowledge on neurobiology and neurodevelopmental disorder research, but also advance my training in mouse model generation and characterization, and allow me to master a number of neurophysiology techniques, cutting edge imaging and analytic technologies. These newly obtained knowledge and techniques will be critical supplements to my existing expertise in molecular and cell biology research. This broad spectrum of research expertise and diverse research experiences will be essential for my future career development into an independent investigator.