Macrophage-mediated myelin recycling fuels brain cancer malignancy (VISIUM). Macrophage-mediated myelin recycling fuels brain cancer malignancy (VISIUM)

Tumors growing in metabolically-challenged environments, such as glioblastoma in the brain, are particularly reliant on cross-talk with their tumor microenvironment (TME) to satisfy their high energetic needs. However, the intricacies of this metabolic interplay and the consequences on immune cell subset diversity and function remain largely unexplored. We interrogated the heterogeneity of the glioblastoma TME using single cell multi-omics analyses in preclinical glioblastoma mouse models and patient samples, and identified metabolically-rewired tumor-associated macrophage (TAM) subpopulations that fuel glioblastoma malignancy. These TAM subsets, termed lipid-laden macrophages (LLMs) to reflect their increased lipid metabolism activity and cholesterol storage, are epigenetically rewired, display immunosuppressive features and are enriched in the aggressive mesenchymal glioblastoma subtype. In response to TME-derived cues triggering liver-X-receptor (LXR) expression, macrophages increase engulfment of cholesterol-rich myelin debris and acquire an LLM phenotype. Subsequently, LLMs directly transfer myelin-derived lipids to cancer cells in an LXR/Abca1-dependent manner, thereby fueling the heightened metabolic demands of mesenchymal glioblastoma. Furthermore, LLM content predicts clinical outcomes and immune checkpoint blockade response in glioblastoma patients and other cancer types. Our work provides an in-depth understanding of the immune-metabolic interplay during glioblastoma progression in a subtype- and microanatomical niche-dependent manner, thereby laying a framework for the discovery of targetable metabolic vulnerabilities in glioblastoma. Overall design: To reveal the reciprocal interactions between macrophages and tumor cells that fuel glioblastoma malignancy, we investigated the dynamic contexture of the glioblastoma TME at the single cell and spatial transcriptomic levels, in two genetically-engineered mouse models (GEMMs) that recapitulate key characteristics of human gliomagenesis and therapeutic response. Both GEMMs involve enforced expression of platelet-derived growth factor-b in Nestin-positive progenitor cells, either in an Ink4a/ArfKO background (herein termed PDG-Ink4a), or in combination with a short-hairpin-mediated knockdown of p53 in tumor cells (herein termed PDG-p53). Orthogonally, publicly available transcriptional datasets of glioblastoma patients enabled the validation of our murine models’ clinical relevance. We explored the dynamic heterogeneity of macrophage subsets in relation to their local microenvironment, employing multi-omics approaches and a wide range of functional ex vivo and in vitro assays to unveil novel pro-tumorigenic interactions underlying macrophage and tumor cell co-evolution in the glioblastoma TME.

在代谢应激微环境中生长的肿瘤，如脑部胶质母细胞瘤（glioblastoma），为满足其极高的能量需求，尤其依赖与肿瘤微环境（tumor microenvironment, TME）的交叉对话。然而，这种代谢互作的复杂机制，以及其对免疫细胞亚群多样性与功能的影响，在很大程度上仍未被阐明。本研究通过单细胞多组学（single cell multi-omics）分析，对临床前胶质母细胞瘤小鼠模型及患者样本中的胶质母细胞瘤TME异质性进行了探究，并鉴定出可促进胶质母细胞瘤恶性进展的代谢重编程肿瘤相关巨噬细胞（tumor-associated macrophage, TAM）亚群。这类TAM亚群被命名为脂质负载巨噬细胞（lipid-laden macrophages, LLMs），以体现其增强的脂质代谢活性与胆固醇储存能力；它们发生了表观遗传重编程，呈现免疫抑制特征，且在侵袭性间质性胶质母细胞瘤亚型中富集。在TME来源的、可触发肝X受体（liver-X-receptor, LXR）表达的信号刺激下，巨噬细胞会增强对富含胆固醇的髓鞘碎片的吞噬作用，并获得LLM表型。随后，LLMs会以LXR/Abca1依赖的方式，将髓鞘来源的脂质直接转运至肿瘤细胞，从而满足间质性胶质母细胞瘤激增的代谢需求。此外，LLM浸润水平可预测胶质母细胞瘤患者及其他癌症患者的临床结局与免疫检查点阻断（immune checkpoint blockade）治疗响应情况。本研究深入阐明了胶质母细胞瘤进展过程中，依赖于肿瘤亚型与微解剖龛的免疫代谢互作机制，从而为发现胶质母细胞瘤中可靶向的代谢脆弱位点提供了研究框架。

实验设计：为揭示促进胶质母细胞瘤恶性进展的巨噬细胞与肿瘤细胞间的双向互作机制，本研究在两种可重现人类神经胶质瘤发生与治疗响应关键特征的基因工程小鼠模型（genetically-engineered mouse models, GEMMs）中，从单细胞与空间转录组学（spatial transcriptomic）层面探究了胶质母细胞瘤TME的动态构成。两种GEMM均通过在Nestin阳性祖细胞中强制表达血小板衍生生长因子-b（platelet-derived growth factor-b）构建：一种置于Ink4a/Arf敲除背景下（本研究中命名为PDG-Ink4a），另一种则联合肿瘤细胞中短发夹RNA介导的p53敲低（本研究中命名为PDG-p53）。此外，本研究还利用公开的胶质母细胞瘤患者转录组数据集，验证了本研究所用小鼠模型的临床相关性。本研究采用多组学方法与一系列离体及体外功能实验，探究了巨噬细胞亚群与其局部微环境相关的动态异质性，以揭示胶质母细胞瘤TME中巨噬细胞与肿瘤细胞协同进化背后的新型促肿瘤互作机制。