Endothelial cell subtypes co-opt a TGFb/miR-30c-driven fibrinolytic pathway that supports tumor growth

In tumors, extravascular fibrin forms provisional scaffolds for angiogenesis but is degraded by fibrinolysis and replaced with collagen in a process that resembles wound healing. We report that fibrin-mediated angiogenesis is inhibited and tumor growth is delayed following postnatal deletion of TGFβR2 in the endothelium (TGFβR2iECKO). TGFβR2iECKO endothelial cells (ECs) fail to up-regulate the fibrinolysis inhibitor Serpine1/PAI-1 due, in part, to uncoupled TGFβ-mediated suppression of miR-30c. Bypassing TGFβR signaling with vascular tropic nanoparticles that deliver miR-30c AntagomiRs is sufficient to promote PAI-1-dependent tumor growth and increase fibrin abundance whereas miR-30c Mimics inhibit tumor growth and promote vascular-directed fibrinolysis in vivo. Using single cell RNA sequencing, we also show that subtypes of ECs in tumors show a spectrum of Serpine1 and uPar (urokinase receptor) expression suggesting functional diversity in ECs at the level of individual cells; furthermore, fresh EC isolates from lung and mammary tumor models have differential abilities to degrade fibrin and launch new vessel sprouts which is linked to their inverse expression patterns of miR-30c and Serpine1 (i.e. miR-30chiSerpine1lo ECs are poorly angiogenic and miR-30cloSerpine1hi ECs are highly angiogenic). Thus, EC subtypes co-opt physiological processes such as wound healing by subverting a previously uncharacterized vascular-directed fibrinolytic pathway that supports tumor growth.

在肿瘤中，血管外纤维蛋白（extravascular fibrin）可作为血管生成的临时支架，但会经纤维蛋白溶解（fibrinolysis）降解，并被胶原蛋白取代，这一过程与伤口愈合（wound healing）相似。本研究报道，在内皮细胞中出生后特异性敲除转化生长因子β受体II（TGFβR2）（即构建TGFβR2iECKO模型）后，纤维蛋白介导的血管生成会受到抑制，且肿瘤生长出现延迟。TGFβR2iECKO内皮细胞（ECs）无法上调纤维蛋白溶解抑制剂Serpine1/PAI-1，这在一定程度上源于转化生长因子β（TGFβ）介导的微小RNA-30c（miR-30c）抑制通路解偶联。通过搭载miR-30c反义寡核苷酸（AntagomiRs）的血管趋向性纳米颗粒（vascular tropic nanoparticles）绕过TGFβR信号通路，足以促进依赖PAI-1的肿瘤生长并提升体内纤维蛋白丰度；而miR-30c模拟物（Mimics）则可抑制肿瘤生长并促进体内血管导向的纤维蛋白溶解。借助单细胞RNA测序（single cell RNA sequencing），本研究还发现肿瘤内的内皮细胞亚型存在Serpine1与尿激酶受体（urokinase receptor，uPar）的表达谱差异，这表明单个内皮细胞水平上存在功能多样性；此外，从肺癌与乳腺肿瘤模型中分离的新鲜内皮细胞，其降解纤维蛋白并启动新生血管芽的能力存在差异，这与其miR-30c与Serpine1的反向表达模式相关（即miR-30c高表达（miR-30chi）、Serpine1低表达（Serpine1lo）的内皮细胞血管生成能力较弱，而miR-30c低表达（miR-30clo）、Serpine1高表达（Serpine1hi）的内皮细胞血管生成能力较强）。综上，肿瘤内皮细胞亚型通过破坏此前尚未被阐明的、可支持肿瘤生长的血管导向纤维蛋白溶解途径，来利用伤口愈合等生理过程。