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

天冬酰胺合成酶缺乏症(ASNSD)是一种新发现的常染色体隐性遗传 以严重的小头畸形、智力残疾和顽固性为特征的神经性疾病 癫痫发作。ASNSD是由编码天冬氨酸合成酶的ASNS基因突变引起的 (ASNS)。ASNS的一个已知功能是催化天冬氨酸和谷氨酰胺转化为 天冬酰胺(ASN)。因此，一个诱人的假设是ASNS缺乏会导致低水平的ASN， 这反过来又会在大脑发育的早期阶段阻碍神经前体细胞的增殖，以及 随后的神经损伤，如小头畸形和癫痫发作。事实上，ASNSD的一个子集 患者的血浆或脑脊液ASN水平较低。然而，在一个案例研究中报告了这一点 ASNSD患者对ASN干预仅有初步反应。因此，至关重要的是要明确地 确定ASNS的功能及ASNS缺陷对脑发育的影响，并建立 在有效的模型系统中，低ASN水平与ASNSD之间的因果关系。为了更好地 了解ASNSD，我已经生成了一些ASNS基因敲除(KO)小鼠模型。重要的是 ASNS的脑特异性KO导致严重的小头畸形和自发性癫痫发作，提示 ASN在大脑发育中的特定和关键作用。令人惊讶的是，与已知的小头畸形症不同 模型造成大脑皮层兴奋性神经元显著丧失，大脑皮层急剧减少 观察脑特异性ASNS-KO脑内的中间神经元。这一数据表明ASN在 中间神经元发育。与此观察一致的是，皮质兴奋性神经元中的ASNS KO未能 导致小头畸形和癫痫。因此，我假设发育和功能的变化 选择性抑制神经元是小头畸形和癫痫的病理生理学基础 ASNSD的表型。这项研究的目的是剖析 神经功能损害与补充三七总皂苷治疗干预的评价 ASNS突变小鼠。总体而言，这项拟议的研究将提供机制洞察力的发病机制。 ASNSD和中间神经元在早期大脑发育中的作用。此外，这项拟议的研究 将测试ASNSD的潜在治疗策略。拟议培训计划的执行将不会 不仅扩展了我在神经生物学和神经发育障碍研究方面的知识，而且 提高我在老鼠模型生成和表征方面的培训，并让我掌握一个 多项神经生理学技术、前沿成像和分析技术。这些新的 所获得的知识和技术将是我在分子方面现有专业知识的重要补充 和细胞生物学研究。这种广泛的研究专业知识和多样化的研究经验 对我未来的职业发展成为一名独立调查员是必不可少的。

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.