Activation of autophagy in macrophages by pro-resolving lipid mediators

The resolution of inflammation is an active process driven by specialized pro-resolving lipid mediators, such as 15-epi-LXA4 and resolvin D1 (RvD1), that promote tissue regeneration. Macrophages regulate the innate immune response being key players during the resolution phase to avoid chronic inflammatory pathologies. Their half-life is tightly regulated to accomplish its phagocytic function, allowing the complete cleaning of the affected area. The balance between apoptosis and autophagy appears to be essential to control the survival of these immune cells within the inflammatory context. In the present work, we demonstrate that 15-epi-LXA4 and RvD1 at nanomolar concentrations promote autophagy in murine and human macrophages. Both compounds induced the MAP1LC3-I to MAP1LC3-II processing and the degradation of SQSTM1 as well as the formation of MAP1LC3+ autophagosomes, a typical signature of autophagy. Furthermore, 15-epi-LXA4 and RvD1 treatment favored the fusion of the autophagosomes with lysosomes, allowing the final processing of the autophagic vesicles. This autophagic response involves the activation of MAPK1 and NFE2L2 pathways, but by an MTOR-independent mechanism. Moreover, these pro-resolving lipids improved the phagocytic activity of macrophages via NFE2L2. Therefore, 15-epi-LXA4 and RvD1 improved both survival and functionality of macrophages, which likely supports the recovery of tissue homeostasis and avoiding chronic inflammatory diseases.

炎症消退是由特异性促消退脂质介质驱动的主动过程，这类介质包括15-表氧脂质A4（15-epi-LXA4）与消退素D1（resolvin D1, RvD1），可促进组织再生。巨噬细胞作为先天免疫应答的调控核心，在炎症消退阶段发挥关键作用，以避免慢性炎症性病理的发生。巨噬细胞的半衰期受到严格调控，以保障其吞噬功能正常执行，实现炎症受累区域的彻底清除。在炎症微环境中，细胞凋亡与自噬之间的动态平衡，对于调控这类免疫细胞的存活至关重要。本研究证实，纳摩尔浓度的15-表氧脂质A4与消退素D1，可分别在小鼠与人类巨噬细胞中诱导自噬过程。两类化合物均可促进MAP1LC3-I向MAP1LC3-II的脂化加工，并介导SQSTM1蛋白的降解，同时诱导MAP1LC3阳性自噬小体的形成——这是自噬激活的典型特征。进一步研究发现，15-表氧脂质A4与消退素D1可促进自噬小体与溶酶体的融合，完成自噬囊泡的最终成熟降解。该自噬应答依赖于丝裂原活化蛋白激酶1（mitogen-activated protein kinase 1, MAPK1）与核因子红细胞2相关因子2（nuclear factor erythroid 2-related factor 2, NFE2L2）信号通路的激活，且不依赖雷帕霉素靶蛋白（mechanistic target of rapamycin, MTOR）信号通路。此外，这类促消退脂质可通过NFE2L2通路增强巨噬细胞的吞噬活性。综上，15-表氧脂质A4与消退素D1可同时改善巨噬细胞的存活状态与功能，这可能有助于恢复组织稳态，并预防慢性炎症性疾病的发生。