Cortical astrocytic neogenin, a key protein switching HIF1/2?-VEGFa-induced angiogenesis to MEGF10-driven phagocytosis

Astrocytes play key roles in multi-cellular processes in the brain, including maintaining homeostasis of blood vessels (BVs) and clearance of damaged cell debris. The detailed underlying mechanisms remain elusive. Here, we provide evidence that cortical astrocytic neogenin (NEO1) coordinates MEGF10-mediated phagocytosis with HIF1/2? driven VEGFa-induced angiogenesis. Knocking-out (KO) NEO1 in astrocytes increases in HIF1/2?, VEGFa, and immature BVs, but decreases in MEGF10 and MEGF10-regulated phagocytosis, in mouse cortex, but not hippocampus. Further studies suggest that the NEO1-KO impairs prolyl hydroxylase domain protein (PHD) mediated HIF1/2? hydroxylation by inducing iron deficiency, thus increasing HIF1/2?-HIF1b-P300 protein complex driven VEGFa expression at the expense of HIF1ß-P300 binding to the MEGF10 promoter; consequently, reducing MEGF10 expression. Thus, these results suggest that cortical astrocytic NEO1 promotes MEGF10 mediated phagocytosis, likely by suppressing HIF1/2?-HIF1ß-P300 induced VEGFa. Overall design: RNA-seq profiling of cultured cortical astrocytes from GFAP-Cre::NEOf/f and its littermate control pups

星形胶质细胞（Astrocytes）在大脑多细胞生理过程中发挥关键作用，包括维持血管（blood vessels, BVs）稳态以及清除受损细胞碎片，但其背后的详细潜在机制仍未明确。本研究提供证据表明，大脑皮层星形胶质细胞的神经胶质素1（neogenin, NEO1）可协同调控MEGF10介导的吞噬作用与HIF1/2α驱动的VEGFA诱导的血管生成。在小鼠大脑皮层中，星形胶质细胞的NEO1基因敲除（KO）会升高HIF1/2α、VEGFA以及未成熟血管的水平，但会降低MEGF10的表达及其调控的吞噬作用，该现象并未在海马体中出现。
进一步研究显示，NEO1敲除会通过诱导铁缺乏，损害脯氨酰羟化酶结构域蛋白（prolyl hydroxylase domain protein, PHD）介导的HIF1/2α羟化修饰，进而以削弱HIF1β-P300结合MEGF10启动子为代价，上调HIF1/2α-HIF1β-P300蛋白复合物驱动的VEGFA表达，最终降低MEGF10的表达水平。
综上，本研究结果提示，大脑皮层星形胶质细胞的NEO1可通过抑制HIF1/2α-HIF1β-P300复合物诱导的VEGFA表达，促进MEGF10介导的吞噬作用。
整体实验设计：对来自GFAP-Cre::NEOf/f及其同窝对照幼鼠的原代培养大脑皮层星形胶质细胞进行RNA测序（RNA-seq）转录组分析。