Tumor-associated myeloid cells aid GBM infiltration by organizing invasion tracks via guidance receptor Plexin-B2. Tumor-associated myeloid cells aid GBM infiltration by organizing invasion tracks via guidance receptor Plexin-B2

Glioblastoma (GBM) is highly invasive primary brain tumor. Here, we retraced early steps of GBM invasion and interactions with tumor-associated myeloid cells (TAM) in a highly infiltrative murine GBM model in immunocompetent background. We reveal early mobilization of microglia in a wide onco-field ahead of GBM invasion, forming glial nets encircling tumor micro-infiltrates that are enmeshed with a dense network of extracellular matrix (ECM). Physical contacts with GBM cells initiate an astounding morphological, spatial, and functional transformation of microglia and monocyte-derived macrophages to form collectively organized migration streams with intertwined GBM cells, paralleled by major ECM restructuring along invasion tracks. Mechanistically, this requires upregulation of guidance receptor Plexin-B2 in TAM, which functions to resolve collisions with GBM cells by providing cell contact guidance for cell alignment and ECM restructuring. Together, our results on stage- and niche-specific mobilization of microglia/macrophages, on governing factors, and the molecular insights into pro-invasion signaling open new therapeutic opportunities to curb GBM invasion. Overall design: Single cell RNA sequencing of mice brain bearing intracranial KR158 GBM transplants. Tamoxifen was injected every other day (i.p., 100 mg kg−1) from 3 days before KR158 transplantation until 8 weeks after. Cells from KR158 GBM bearing brains from Control or Plexin-B2 cKO hosts (C57BL/6 background) were prepared and ran with 10x genomics pipeline.

胶质母细胞瘤（Glioblastoma, GBM）是一类高度侵袭性的原发性脑肿瘤。本研究在免疫健全背景下的高浸润性小鼠胶质母细胞瘤模型中，追溯了胶质母细胞瘤侵袭的早期进程，以及其与肿瘤相关髓系细胞（tumor-associated myeloid cells, TAM）的相互作用。我们发现，在胶质母细胞瘤侵袭前的广阔癌场中，小胶质细胞已发生早期动员，形成包裹肿瘤微浸润灶的神经胶质网，该网络与致密的细胞外基质（extracellular matrix, ECM）交织缠绕。与胶质母细胞瘤细胞的物理接触可触发小胶质细胞和单核细胞衍生巨噬细胞发生显著的形态、空间及功能重塑，共同形成与胶质母细胞瘤细胞相互缠绕的集体迁移流；与此同时，侵袭通路沿线的细胞外基质也发生了大规模重构。从机制上看，这一过程需要肿瘤相关髓系细胞中导向受体Plexin-B2的上调表达，该受体通过为细胞排列提供接触导向、并介导细胞外基质重构，从而化解与胶质母细胞瘤细胞的碰撞冲突。综上，本研究关于小胶质细胞/巨噬细胞的阶段特异性和微环境特异性动员、其调控因子，以及促侵袭信号通路的分子机制解析，为抑制胶质母细胞瘤侵袭提供了全新的治疗思路与潜在靶点。

实验设计：对携带颅内KR158胶质母细胞瘤移植瘤的小鼠脑组织进行单细胞RNA测序。在KR158移植前3天至移植后8周期间，每隔一日腹腔注射（i.p.）他莫昔芬（100 mg·kg⁻¹）。分别从对照组或Plexin-B2条件性敲除（conditional knockout, cKO）宿主（C57BL/6背景）的KR158胶质母细胞瘤移植瘤小鼠脑组织中制备细胞，采用10x Genomics测序流程进行上机检测。