Flt1 at the neuro-vascular interface

在胚胎发育、成年期和组织再生过程中，血管网络与神经元网络密切相关。血管和神经元网络的紧密联系允许涉及可扩散分子的相互串扰，这对这两个领域的生理功能都很重要。血管和神经元网络的形成显示出许多相似之处，包括共同的分子线索和定向指导的原则。在血管系统中，血管内皮生长因子-α是血管生成的主要调节因子，也是植物萌发的导向因子。在神经系统中，血管内皮生长因子-α可以直接作用于神经元，调节神经元存活和轴突引导等过程。血管内皮生长因子受体-1(Flt1)主要作为一种诱饵受体，从而限制了血管内皮生长因子-α的生物利用度，并通过血管内皮生长因子受体-2(KDR)传递信号。Flt1在血管和神经中均有表达，因此独特地被赋予影响血管和神经生长的双重能力。我们推测Flt1在神经-血管沟通中起中心作用。与这一假说相一致，我们发现斑马鱼的脊髓血管化来自于涉及神经元可溶性Flt1(SFlt1)和Vegfaa的两级调控的静脉，这种新的发芽方式被称为三次发芽。在这里，我们建议分析驱动三次发芽、发芽引导和选择性与动脉吻合形成的分子机制。试点数据表明，第三级芽采样它们的目标，并优先与在特定动脉区域表达内皮的Neuropilin-1(Nrp1)相吻合。从机制上讲，神经元PlGF在这一过程中起着积极的调节作用。在脊髓发育过程中，干细胞和前体细胞分化为成熟的神经元，这一过程伴随着糖酵解向更多有氧组织代谢的转变，同时也增加了血管的形成。在这里，我们建议分析脊髓血管形成的程度如何通过新陈代谢或血管分泌信号的变化来控制干细胞扩张到分化的开关。为了测试这一点，我们创造了一系列转基因和突变斑马鱼，这些斑马鱼基于神经-血管交界处sFlt1和Vegfaa水平的调节，具有高血管或低血管脊髓。使用单细胞测序和RNA TOMO-SEQ，我们将以时空的方式跟踪细胞命运规范的变化。初步数据显示，在高度血管化的情况下，祖细胞池减少，这与决定神经元分化的血管功能一致。

The vascular network closely associates with the neuronal network throughout embryonic development, in adulthood and during tissue regeneration. Close association of vessels and neuronal networks allows reciprocal cross-talk involving diffusible molecules, which is important for physiological functions in both domains. Disturbances herein associate with neurodegenerative diseases, neuropathy, and cardiovascular disorders.Formation of vascular and neuronal networks shows many similarities including common molecular cues and the principle of directed guidance. In the vascular system, Vegf-a acts as the major regulator of angiogenesis and sprout guidance. In the neuronal system, Vegf-a can have direct effects on neurons and modulate processes such as neuronal survival and axon guidance. Vegf receptor-1 (Flt1) mainly acts as a Vegf-a decoy receptor, thereby limiting Vegf-a bio-availability and signaling through Vegf receptor-2 (Kdr). Flt1 is expressed in both vessels and nerves and therefor uniquely endowed with the dual ability to affect growth of vessels and nerves. We hypothesize that Flt1 plays a central role in neuro-vascular communication. In line with this hypothesis we found that spinal cord vascularization in zebrafish proceeds from veins involving two-tiered regulation of neuronal soluble Flt1 (sFlt1) and Vegfaa via a novel sprouting mode termed tertiary sprouting. Here we propose to analyze the molecular mechanism driving tertiary sprout initiation, sprout guidance and the selective anastomosis formation with arteries. Pilot data suggest that tertiary sprouts sample their targets and preferentially anastomose with Neuropilin-1 (Nrp1) expressing endothelium in specific arterial domains. Mechanistically, neuronal Plgf acts as a positive regulator of this process. Plgf provokes displacement of Vegfaa from arterial Nrp1, thereby augmenting Vegfaa around arteries, promoting arterial Kdrl signaling and filopodia formation, an endothelial feature that critically determines the propensity to form an anastomosis.During spinal cord development, stem and progenitor cells differentiate into mature neurons, a process that is paralleled by a change from glycolytic toward more aerobic tissue metabolism, and increased vascularization. Here we propose to analyze how the extent of spinal cord vascularization controls the switch of stem cell expansion to differentiation either via changes in metabolism or angiocrine signals. To test this we created a series of transgenic and mutant zebrafish with either hyper vascularized or hypo vascularized spinal cords based on modulation of sFlt1 and Vegfaa levels at the neuro-vascular interface. Using single cell sequencing and RNA tomo-seq we will track changes in cell fate specification in a spatio-temporal manner. Preliminary data show reduced progenitor pools in the hyper vascularization scenarios, consistent with blood vessel function determining neuronal differentiation.