Introduction

Tumor metastasis to the brain occurs in approximately 20% of all cancer cases and often occurs due to tumor cells crossing the blood-brain barrier (BBB). The brain microenvironment is comprised of a soft hyaluronic acid (HA)-rich extracellular matrix with an elastic modulus of 0.1–1 kPa, whose crosslinking is often altered in disease states.

Methods

To explore the effects of HA crosslinking on breast tumor cell migration, we developed a biomimetic model of the human brain endothelium, consisting of brain microvascular endothelial cell (HBMEC) monolayers on HA and gelatin (HA/gelatin) films with different degrees of crosslinking, as established by varying the concentration of the crosslinker Extralink.

Results and Discussion

Metastatic breast tumor cell migration speed, diffusion coefficient, spreading area, and aspect ratio increased with decreasing HA crosslinking, a mechanosensing trend that correlated with tumor cell actin organization but not CD44 expression. Meanwhile, breast tumor cell incorporation into endothelial monolayers was independent of HA crosslinking density, suggesting that alterations in HA crosslinking density affect tumor cells only after they exit the vasculature. Tumor cells appeared to exploit both the paracellular and transcellular routes of trans-endothelial migration. Quantitative phenotyping of HBMEC junctions via a novel Python software revealed a VEGF-dependent decrease in punctate VE-cadherin junctions and an increase in continuous and perpendicular junctions when HBMECs were treated with tumor cell-secreted factors.

Conclusions

Overall, our quantitative results suggest that a combination of biochemical and physical factors promote tumor cell migration through the BBB.

中文翻译：

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肿瘤细胞在纳入脑微血管内皮期间的机械传感。

介绍

大约 20% 的癌症病例会发生脑部肿瘤转移，并且通常是由于肿瘤细胞穿过血脑屏障 (BBB) 而发生的。脑微环境由富含透明质酸 (HA) 的软细胞外基质组成，其弹性模量为 0.1-1 kPa，其交联通常在疾病状态下发生改变。

方法

为了探索 HA 交联对乳腺肿瘤细胞迁移的影响，我们开发了人脑内皮的仿生模型，由 HA 上的脑微血管内皮细胞 (HBMEC) 单层和具有不同交联程度的明胶 (HA/明胶) 薄膜组成，通过改变交联剂 Extralink 的浓度确定。

结果与讨论

转移性乳腺肿瘤细胞迁移速度、扩散系数、扩散面积和纵横比随着 HA 交联的减少而增加，这是一种与肿瘤细胞肌动蛋白组织相关但与 CD44 表达无关的机械传感趋势。同时，乳腺肿瘤细胞掺入内皮单层与 HA 交联密度无关，这表明 HA 交联密度的改变仅在肿瘤细胞离开脉管系统后才会影响它们。肿瘤细胞似乎利用跨内皮迁移的细胞旁和跨细胞途径。通过HBMEC 连接的定量表型一种新的 Python 软件显示，当 HBMEC 用肿瘤细胞分泌因子处理时，点状 VE-钙粘蛋白连接的 VEGF 依赖性减少以及连续和垂直连接的增加。

结论

总体而言，我们的定量结果表明，生化和物理因素的结合促进了肿瘤细胞通过 BBB 的迁移。