Genetic variation in a population has an influence on the manifestation of monogenic as well as multifactorial disorders, with the underlying genetic contribution dependent on several interacting variants. Common laboratory mouse strains used for modelling human disease lack the genetic variability of the human population. Therefore, outcomes of rodent studies show limited relevance to human disease. The functionality of brain vasculature is an important modifier of brain diseases. Importantly, the restrictive interface between blood and brain—the blood–brain barrier (BBB) serves as a major obstacle for the drug delivery into the central nervous system (CNS). Using genetically diverse mouse strains, we aimed to investigate the phenotypic and transcriptomic variation of the healthy BBB in different inbred mouse strains. We investigated the heterogeneity of brain vasculature in recently wild-derived mouse strains (CAST/EiJ, WSB/EiJ, PWK/PhJ) and long-inbred mouse strains (129S1/SvImJ, A/J, C57BL/6J, DBA/2J, NOD/ShiLtJ) using different phenotypic arms. We used immunohistochemistry and confocal laser microscopy followed by quantitative image analysis to determine vascular density and pericyte coverage in two brain regions—cortex and hippocampus. Using a low molecular weight fluorescence tracer, sodium fluorescein and spectrophotometry analysis, we assessed BBB permeability in young and aged mice of selected strains. For further phenotypic characterization of endothelial cells in inbred mouse strains, we performed bulk RNA sequencing of sorted endothelial cells isolated from cortex and hippocampus. Cortical vessel density and pericyte coverage did not differ among the investigated strains, except in the cortex, where PWK/PhJ showed lower vessel density compared to NOD/ShiLtJ, and a higher pericyte coverage than DBA/2J. The vascular density in the hippocampus differed among analyzed strains but not the pericyte coverage. The staining patterns of endothelial arteriovenous zonation markers were similar in different strains. BBB permeability to a small fluorescent tracer, sodium fluorescein, was also similar in different strains, except in the hippocampus where the CAST/EiJ showed higher permeability than NOD/ShiLtJ. Transcriptomic analysis of endothelial cells revealed that sex of the animal was a major determinant of gene expression differences. In addition, the expression level of several genes implicated in endothelial function and BBB biology differed between wild-derived and long-inbred mouse strains. In aged mice of three investigated strains (DBA/2J, A/J, C57BL/6J) vascular density and pericyte coverage did not change—expect for DBA/2J, whereas vascular permeability to sodium fluorescein increased in all three strains. Our analysis shows that although there were no major differences in parenchymal vascular morphology and paracellular BBB permeability for small molecular weight tracer between investigated mouse strains or sexes, transcriptomic differences of brain endothelial cells point to variation in gene expression of the intact BBB. These baseline variances might be confounding factors in pathological conditions that may lead to a differential functional outcome dependent on the sex or genetic polymorphism.

中文翻译：

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遗传多样的实验室小鼠品系中血脑屏障的表征

群体中的遗传变异对单基因和多因素疾病的表现有影响，其潜在的遗传贡献取决于几个相互作用的变异。用于模拟人类疾病的普通实验室小鼠品系缺乏人群的遗传变异性。因此，啮齿动物研究的结果显示与人类疾病的相关性有限。脑血管系统的功能是脑疾病的重要修饰因子。重要的是，血液和大脑之间的限制性界面——血脑屏障 (BBB) 是药物输送到中枢神经系统 (CNS) 的主要障碍。使用遗传多样化的小鼠品系，我们旨在研究不同近交小鼠品系中健康 BBB 的表型和转录组变异。我们研究了最近野生小鼠品系（CAST/EiJ、WSB/EiJ、PWK/PhJ）和长近交系小鼠品系（129S1/SvImJ、A/J、C57BL/6J、DBA/2J、 NOD/ShiLtJ) 使用不同的表型臂。我们使用免疫组织化学和共聚焦激光显微镜，然后进行定量图像分析，以确定两个大脑区域（皮质和海马）的血管密度和周细胞覆盖率。使用低分子量荧光示踪剂、荧光素钠和分光光度法分析，我们评估了选定品系的年轻和老年小鼠的 BBB 渗透性。对于近交系小鼠品系中内皮细胞的进一步表型表征，我们对从皮质和海马中分离的分选内皮细胞进行了批量 RNA 测序。皮质血管密度和周细胞覆盖率在所研究的菌株之间没有差异，除了在皮质中，与 NOD/ShiLtJ 相比，PWK/PhJ 的血管密度较低，而周细胞覆盖率高于 DBA/2J。海马中的血管密度在分析的菌株之间存在差异，但周细胞覆盖率却不同。内皮动静脉分区标记的染色模式在不同菌株中是相似的。BBB 对小型荧光示踪剂荧光素钠的渗透性在不同菌株中也相似，除了在海马中 CAST/EiJ 显示出比 NOD/ShiLtJ 更高的渗透性。内皮细胞的转录组学分析表明，动物的性别是基因表达差异的主要决定因素。此外，与内皮功能和 BBB 生物学有关的几个基因的表达水平在野生和长交系小鼠品系之间存在差异。在三种研究品系（DBA/2J、A/J、C57BL/6J）的老年小鼠中，血管密度和周细胞覆盖率没有改变——除了 DBA/2J，而在所有三种品系中，血管对荧光素钠的渗透性都增加了。我们的分析表明，尽管在所研究的小鼠品系或性别之间，小分子量示踪剂的实质血管形态和细胞旁 BBB 通透性没有重大差异，但脑内皮细胞的转录组差异表明完整 BBB 的基因表达存在差异。