Efferocytosis induces a novel SLC program to promote glucose uptake and lactate release

On a daily basis, we turnover billions of apoptotic cells that are removed by professional and non-professional phagocytes1-10. While characterizing the transcriptional program of phagocytes, we discovered a novel solute carrier family (SLC) gene signature (33 SLC members) that is specifically modified during engulfment of apoptotic cells (efferocytosis) but not during antibody-mediated phagocytosis. When we assessed the functional relevance of these SLCs, we noted robust induction of an aerobic glycolysis program in engulfing phagocytes, initiated by SLC2A1-mediated glucose uptake, and suppression of oxidative phosphorylation program. Interestingly, the different steps of phagocytosis10,11, i.e. smell (‘find-me’ signals / sensing factors released by apoptotic cells), taste (phagocyte- apoptotic cell contact), and ingestion (corpse internalization), activated different molecules to promote this glycolytic process. Further, lactate, a natural by-product of aerobic glycolysis12,13, was released from engulfing phagocytes via SLC16A1, an SLC member activated after corpse uptake. While glycolysis within phagocytes contributed to actin polymerization and the continued uptake of corpses, the lactate released via SLC16A1 influenced the establishment of an anti-inflammatory environment. Collectively, these data reveal a novel SLC program activated during efferocytosis, identify a previously unknown reliance on aerobic glycolysis during apoptotic cell uptake, and that glycolytic byproducts of efferocytosis can also influence other cells in the microenvironment. The experiment consisted of two conditions: Phagocytes (LR73 cells) alone or co-cultured with apoptotic Jurkat lymphoma cells. Each condition consisted of four biological replicates.

我们每日会产生数十亿个凋亡细胞（apoptotic cells），此类细胞由专职吞噬细胞（professional phagocytes）与非专职吞噬细胞（non-professional phagocytes）完成清除1-10。在对吞噬细胞的转录程序（transcriptional program）进行表征分析时，我们发现了一类全新的溶质载体家族（solute carrier family, SLC）基因特征，包含33个SLC家族成员，该特征仅在凋亡细胞吞噬过程（胞葬作用，efferocytosis）中发生特异性修饰，而在抗体介导的吞噬作用（antibody-mediated phagocytosis）中无此类变化。在评估这些SLC家族基因的功能相关性时，我们观察到正在吞噬凋亡细胞的吞噬细胞中，有氧糖酵解（aerobic glycolysis）通路被显著激活——该通路由SLC2A1介导的葡萄糖摄取启动，同时氧化磷酸化（oxidative phosphorylation）通路受到抑制。有趣的是，吞噬作用的不同阶段10,11，即“嗅探”（凋亡细胞释放的“find-me”信号/感知因子）、“接触”（吞噬细胞与凋亡细胞的结合）与“摄取”（细胞尸体内化），分别通过不同的分子通路促进这一糖酵解过程。此外，作为有氧糖酵解的天然代谢副产物12,13，乳酸通过SLC16A1（一种在吞噬细胞摄取凋亡细胞尸体后被激活的SLC家族成员）从正在吞噬的吞噬细胞中释放。吞噬细胞内的糖酵解过程可促进肌动蛋白聚合（actin polymerization）以及凋亡细胞尸体的持续摄取，而通过SLC16A1释放的乳酸则有助于构建抗炎微环境。综上，本研究数据揭示了一条在胞葬作用中被激活的全新SLC调控程序，明确了凋亡细胞吞噬过程中此前未被发现的有氧糖酵解依赖机制，同时证实胞葬作用产生的糖酵解副产物亦可对微环境中的其他细胞产生调控作用。本实验设置两组对照条件：单独培养的吞噬细胞（LR73细胞），以及与凋亡性Jurkat淋巴瘤细胞共培养的吞噬细胞。每组条件均设置4次生物学重复（biological replicates）。