Macrophage-mediated myelin recycling fuels brain cancer malignancy (RNA-Seq in vivo). Macrophage-mediated myelin recycling fuels brain cancer malignancy (RNA-Seq in vivo)

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，例如脑内胶质母细胞瘤（glioblastoma），尤其依赖与肿瘤微环境（tumor microenvironment, TME）的互作以满足其极高的能量需求。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，仍未得到充分探索。
我们通过对临床前胶质母细胞瘤小鼠模型及患者样本开展单细胞多组学分析，解析了胶质母细胞瘤TME的异质性，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。这些被命名为脂负荷巨噬细胞（lipid-laden macrophages, LLMs）的TAM亚群，因脂质代谢活性增强与胆固醇储存增加而得名，它们发生了表观遗传重编程，呈现免疫抑制特性，并在侵袭性间叶亚型胶质母细胞瘤中富集。
在肿瘤微环境来源的、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以LXR/Abca1依赖的方式直接将髓鞘来源的脂质转移至肿瘤细胞，从而满足间叶亚型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治疗响应。
本研究深入阐明了胶质母细胞瘤进展过程中，以亚型及微解剖微环境为依赖的免疫代谢互作机制，为发现胶质母细胞瘤可靶向的代谢脆弱性靶点提供了研究框架。
总体实验设计：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，我们在两种可重现人类胶质母细胞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层面解析了胶质母细胞瘤TME的动态构成。两种GEMMs均在巢蛋白（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, PDGF-b）：一种为Ink4a/Arf敲除背景（本研究命名为PDG-Ink4a），另一种为在肿瘤细胞中通过短发夹RNA介导敲低p53（本研究命名为PDG-p53）。作为正交验证，我们利用公开的胶质母细胞瘤患者转录组数据集，证实了小鼠模型的临床相关性。我们通过多组学方法及一系列离体、体外功能实验，探究了巨噬细胞亚群与其局部微环境间的动态异质性，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。