Bax调控小神经胶质细胞发育的分子机制研究

Microglia are a special subtype of macrophages residing in the central nervous system, such as the brain. They play important roles in the neuron development and synapse sculpting and are indispensably required for the clearance of pathogens and dead cells to maintain the homeostasis of brain environment. However, the types and distribution of microglia in zebrafish, especially the mechanisms accounting for their development, still required further investigation. In the present study, we found that at least two types, the coro1a+apoeb- and coro1a+apoeb+, of microglia existed in 3 dpf zebrafish larval brain. The subsequent investigation of the V10 mutant with microglia defect phenotypes indicated that the coro1a+apoeb+, but not coro1a+apoeb- microglia, were compromised in the homozygous mutant. The positional cloning and rescue results indicated that the mutant gene in V10 was baxa. The enriched expression of baxa in the huc+ neurons suggested that baxa probably regulated the neurons which in turn played critical roles in the microglia development. Therefore, it is a very useful mutant that helps to elucidate the molecular crosstalk mechanisms between the brain cells and myeloid cells for the microglia formation. Taking advantage of the live imaging in various report lines in zebrafish, our followed studies will pay attention to: 1) The subtypes and spatial-temporal distribution of microglia and the cellular configuration of their locations. 2) The crosstalk behaviors between the brain cells and microglia. 3) The phenotypic studies of the brain cells and microglia in baxa-/-. 4) The molecular networks between brain cells and microglia and the mechanism regulated by baxa in the microglia development.

小神经胶质细胞(microglia)对维持脑环境稳态至关重要。本研究发现斑马鱼幼鱼脑中存在coro1a+apoeb-和coro1a+apoeb+2种microglia。通过分析ENU诱变筛选获得的microglia缺陷突变体V10，结果表明该突变体特异地影响coro1a+apoeb+ microglia的形成。定位克隆和拯救实验确认V10的突变基因为富集表达在神经元中的baxa。这是目前未报到的以非细胞自主性方式调控microglia发育的突变体，对于回答脑微环境调控microglia形成的分子机理意义重大。随后将关注：1)microglia种类和分布及其所处微环境的细胞构成。2)microglia发育过程中与关键微环境细胞相互作用的行为学。3)baxa-/-突变体中脑细胞的变化及对microglia的影响方式。4)baxa介导的脑微环境细胞调控microglia发育的分子信号网络。

小胶质细胞对于清除凋亡和异常的神经细胞至关重要。小胶质细胞还能分泌炎症及营养因子、修剪突触等以促进神经系统的发育、稳态和功能。因而，小胶质细胞在神经退行性等疾病的发生发展过程中举足轻重。小胶质细胞定植脑后如何被驯化而成熟和获得特性仍不清楚。本研究通过关注小胶质细胞成熟异常的斑马鱼突变体baxa-/-，发现baxa富集表达在神经元中。其经典的促神经元凋亡功能仅对小胶质细胞早期定植于脑中尤为关键，但对其成熟作用有限。进一步的深入分析提示baxa主要通过一类特殊的神经元活性而调控p-CaMKII-p-CREB通路以启动dlb的表达。神经元dlb激活定植在脑中的小胶质前体细胞的Notch信号以促进其分化和成熟。Bax-Notch通路调控早期小胶质细胞成熟的分子机理在小鼠等高等哺乳类动物中是保守的。我们的研究揭示了以往没有没报道的脑微环境驯化小胶质前体细胞分化与成熟的分子机制，为利用Notch通路有效体外培养和维持小胶质细胞的特性用于治疗神经退行性疾病提供了新的突破点。目前文章在《Nature communication》以及《SCIENCE CHINA Life Sciences》进行revision。此外，通过LPS诱导的急性感染模型，揭示了巨噬细胞作为吹哨人通过il1b作用于髓系前体中的NF-KB和Cebpb等因子，确保髓系急性应急造血的顺利完成(Journal of Immunology, 2020)。回答了ikzf1通过irf4和ccr9调控早期淋系细胞发育的分子机理(Journal of Biological Chemistry, 2019)。筛选并发现了以维生素类为代表数个小分子药物能够有效促使造血干细胞扩增（Cells, 2021）。我们的研究拓展了学界对小胶质细胞发育和功能的分子机制认知，为髓系应急造血发生提供参考信息，有助于候选有效扩增造血干细胞的小分子药物。