根据既定的概念,血管生成的主要诱导因子之一,前基质金属蛋白酶-9(proMMP-9),由肿瘤相关巨噬细胞(TAMs)提供给肿瘤微环境。积累的证据,然而,表明肿瘤相关中性粒细胞(TAN)对于proMMP-9的递送也至关重要,尤其是在肿瘤发展的早期阶段。为了阐明TAM和TAN实际上贡献了多少血管生成proMMP-9,我们定量评估了不同肿瘤类型的TAM和TAN,包括在野生型和Mmp9敲除小鼠中生长的人异种移植物和同基因鼠肿瘤。而宿主MMP-9能力对于正常和肿瘤相关白细胞的完全血管生成潜力是必需的,嗜中性粒细胞与巨噬细胞和TAN与TAM的直接比较表明,巨噬细胞和TAM分泌的proMMP-9比相同数量的嗜中性粒细胞或TAN少40至50倍。相应地,中性粒细胞和TAN诱导的MMP-9介导的体内血管生成的水平大大超过了巨噬细胞和TAM诱导的水平。以≥11-μm大小的流明和部分覆盖稳定的周细胞为特征。重要的是,产生MMP-9的TAM表现出M2偏斜的表型,但不表达金属蛋白酶-1(TIMP-1)的组织抑制剂,一个新颖的特征,使他们能够分泌无TIMP-1,中性粒细胞样MMP-9酶原不受其天然抑制剂的阻碍。一起,我们的发现支持了TAN的概念,能够立即释放预先储存的货物,是高度血管生成的MMP-9的主要贡献者,而肿瘤侵袭性的巨噬细胞前体需要时间来分化,极化成M2偏斜的TAM,关闭他们的TIMP-1表达式,只有到那时,启动相对低水平的无TIMPMMP-9酶原生产。
According to established notion, one of the major angiogenesis-inducing factors, pro-matrix metalloproteinase-9 (proMMP-9), is supplied to the tumor microenvironment by tumor-associated macrophages (TAMs). Accumulated evidence, however, indicates that tumor-associated neutrophils (TANs) are also critically important for proMMP-9 delivery, especially at early stages of tumor development. To clarify how much angiogenic proMMP-9 is actually contributed by TAMs and TANs, we quantitatively evaluated TAMs and TANs from different tumor types, including human xenografts and syngeneic murine tumors grown in wild-type and Mmp9-knockout mice. Whereas host MMP-9 competence was required for full angiogenic potential of both normal and tumor-associated leukocytes, direct comparisons of neutrophils versus macrophages and TANs versus TAMs demonstrated that macrophages and TAMs secrete 40- to 50-fold less proMMP-9 than the same numbers of neutrophils or TANs. Correspondingly, the levels of MMP-9-mediated in vivo angiogenesis induced by neutrophils and TANs substantially exceeded those induced by macrophages and TAMs. MMP-9-delivering TANs were also required for development of metastasis-supporting intratumoral vasculature, characterized by ≥ 11-μm size lumens and partial coverage with stabilizing pericytes. Importantly, MMP-9-producing TAMs exhibit M2-skewed phenotype but do not express tissue inhibitor of metalloproteinases-1 (TIMP-1), a novel characteristic allowing them to secrete TIMP-1-free, neutrophil-like MMP-9 zymogen unencumbered by its natural inhibitor. Together, our findings support the notion whereby TANs, capable of immediate release of their pre-stored cargo, are the major contributors of highly angiogenic MMP-9, whereas tumor-influxing precursors of macrophages require time to differentiate, polarize into M2-skewed TAMs, shut down their TIMP-1 expression, and only then, initiate relatively low-level production of TIMP-free MMP-9 zymogen.