Regulation of Macrophage Motility by the Water Channel Aquaporin-1: Crucial Role of M0/M2 Phenotype Switch

The water channel aquaporin-1 (AQP1) promotes migration of many cell types. Although AQP1 is expressed in macrophages, its potential role in macrophage motility, particularly in relation with phenotype polarization, remains unknown. We here addressed these issues in peritoneal macrophages isolated from AQP1-deficient mice, either undifferentiated (M0) or stimulated with LPS to orientate towards pro-inflammatory phenotype (classical macrophage activation; M1). In non-stimulated macrophages, ablation of AQP1 (like inhibition by HgCl2) increased by 2–3 fold spontaneous migration in a Src/PI3K/Rac-dependent manner. This correlated with cell elongation and formation of lamellipodia/ruffles, resulting in membrane lipid and F4/80 recruitment to the leading edge. This indicated that AQP1 normally suppresses migration of resting macrophages, as opposed to other cell types. Resting Aqp1-/- macrophages exhibited CD206 redistribution into ruffles and increased arginase activity like IL4/IL13 (alternative macrophage activation; M2), indicating a M0-M2 shift. In contrast, upon M1 orientation by LPS in vitro or peritoneal inflammation in vivo, migration of Aqp1-/- macrophages was reduced. Taken together, these data indicate that AQP1 oppositely regulates macrophage migration, depending on stimulation or not by LPS, and that macrophage phenotypic and migratory changes may be regulated independently of external cues.

水通道蛋白1（AQP1）可促进多种细胞类型的迁移。尽管巨噬细胞中表达AQP1，但其在巨噬细胞运动中的潜在作用，尤其是与表型极化相关的机制仍未明确。本研究针对从AQP1基因敲除小鼠中分离的腹膜巨噬细胞展开相关探究，实验对象涵盖未分化状态（M0型）的巨噬细胞，以及经脂多糖（LPS）诱导向促炎表型极化的细胞（经典巨噬细胞活化，即M1型）。在未受刺激的巨噬细胞中，敲除AQP1（效果等同于氯化汞（HgCl₂）对AQP1的功能抑制）可使细胞自发迁移能力提升2~3倍，该调控过程依赖于Src/PI3K/Rac信号通路。这一现象与细胞伸长、片状伪足/膜褶皱形成密切相关，最终导致膜脂质及F4/80向细胞前沿募集。上述结果表明，与其他细胞类型不同，AQP1通常会抑制静息状态巨噬细胞的迁移。静息状态的Aqp1⁻/⁻巨噬细胞表现出CD206向膜褶皱的重新分布，同时精氨酸酶活性升高，这与白介素4/白介素13（IL4/IL13）诱导的替代性巨噬细胞活化（M2型）特征相符，提示巨噬细胞发生了M0向M2的表型转换。与之相反，当巨噬细胞在体外经LPS诱导为M1型，或体内发生腹膜炎症时，Aqp1⁻/⁻巨噬细胞的迁移能力会出现下降。综上，本研究数据表明，AQP1可双向调控巨噬细胞的迁移能力，这取决于是否存在LPS刺激；同时巨噬细胞的表型与迁移变化或许可独立于外部信号进行调控。