Notch信号通过乳酸转运体调控TAMs极化和功能及在肿瘤进展中的作用机制研究

Macrophages are important component of innate immune system, which possess different polarization status responding to different inflammatory stimuli. The polarizations and function switch of tumor-associated macrophages (TAMs) participate into each stage of tumor development. Many factors in tumor microenvironment regulate TAMs polarization and function remodeling. The Warburg effect of tumor cells leads to lactate accumulation in microenvironment, which facilitates M2 polarization of TAMs to further promote angiogenesis and tumor progression. Our previous studies have found that forced activation of Notch signal could re-educate TAMs to M1 polarization with anti-tumor phenotype and improve immune microenvironment to inhibit tumor growth. Using next generation sequencing for further exploring the mechanism of Notch signaling regulation macrophage polarization, we found that expressions of several members of lactate transporters family showed significant difference between Notch activated macrophages and control group. Based on the above data, this study will clarify the regulation effect of Notch signal on TAMs polarization and function through lactate transporters, and explore the roles and mechanisms of lactate on modulating TAMs function and tumor progression. This project should replenish the network of Notch signal modulating TAMs polarization and function from the perspective of lactate metabolism, and provide new targets for tumor therapy, which has important theoretical significance and potential application value.

巨噬细胞是固有免疫的重要组成部分。在不同炎性刺激下，表现出不同的极化和功能状态。在肿瘤发生发展的各个阶段，肿瘤相关巨噬细胞（TAM）的极化和功能转变都会参与其中。肿瘤微环境中多种因素可以影响TAM的极化和功能重塑，其中肿瘤细胞的Warburg效应会导致微环境中乳酸堆积，高浓度乳酸可促进TAM向促肿瘤的的M2型极化转变，促进血管新生和肿瘤进展。申请人前期研究发现，Notch信号可教育TAM形成抗肿瘤的M1样极化，改善微环境，抑制肿瘤生长。对Notch信号激活和对照小鼠的巨噬细胞表达谱进行检测，发现乳酸转运体家族多个成员表达发生改变。据此，本研究拟进一步阐明Notch信号通过乳酸转运体参与TAM极化和功能的调控作用；探究乳酸对TAM功能的影响及在肿瘤进展中作用和机制。本研究有望从乳酸代谢角度完善Notch信号调控TAM极化和功能的分子网络，为肿瘤治疗提供新靶点，具有重要理论意义和潜在应用价值。

肿瘤相关髓系细胞在肿瘤进展中发挥关键作用，主要包括了髓源抑制性细胞（myeloid-derived suppressor cells, MDSC）和肿瘤相关巨噬细胞（tumor-associated macrophages, TAM）。在这其中，MDSC和TAM又分为不同的功能亚群。MDSCs由单核样MDSCs（monocytic MDSCs, M-MDSCs）和粒细胞样MDSCs（granulocyte MDSCs, G-MDSCs）组成。通常来说，M-MDSCs可以向下游继续分化，形成成熟的巨噬细胞和树突状细胞。最近的研究表明，在肿瘤微环境（tumor microenvironment, TME）中，M-MDSCs更倾向于分化为G-MDSCs，而不是TAM，然而，其潜在机制尚不清楚。在该项课题的资助下，我们利用小鼠肺腺癌模型和临床肺癌样本，发现肿瘤来源的乳酸可通过单羧酸转运体2（monocarboxylate transporter 2, MCT2）进入肿瘤相关髓系细胞中，并随后调节其发育和功能。外源性乳酸重新定义了M-MDSCs的选择性分化，使其更倾向分为成为G-MDSCs而非M1样成熟巨噬细胞。当我们使用AR-C155858（MCT2抑制剂）阻断MCT2功能后，可通过减少G-MDSC的生成和促进巨噬细胞成熟显著抑制肿瘤生长。分子机制的研究中，我们鉴定并验证了c-Jun是髓系细胞中乳酸的新型细胞内传感器。在髓系细胞中，乳酸与c-Jun的相互作用保护c-Jun免受E3泛素连接酶FBW7介导的降解，并随后促进了COX-2的转录表达。最重要的是，在临床肺癌样本中也可以观察到MCT2/乳酸-c-Jun-COX2轴的表达和激活，与髓系细胞发育和肿瘤进展密切相关。额外添加的乳酸促进肺腺癌患者外周血中分选的M-MDSCs分化为G-MDSCs，通过阻断MCT2或c-Jun信号完全恢复。综上所述，我们的研究首次证明，MCT2介导的乳酸转运通过与细胞内传感器c-Jun结合重新定义了M-MDSC的分化，从而加速了TME中的肿瘤生长。在髓样细胞中靶向乳酸代谢或c-Jun信号可能是临床上治疗肺癌的潜在选择。