Anand Rahul J, Gribar Steven C, Li Jun, Kohler Jeff W, Branca Maria F, Dubowski Theresa, Sodhi Chhinder P, Hackam David J
Division of Pediatric Surgery, Children's Hospital of Pittsburgh, Pittsburgh, PA 15213, USA.
J Leukoc Biol. 2007 Nov;82(5):1257-65. doi: 10.1189/jlb.0307195. Epub 2007 Aug 3.
Phagocytosis is the process by which microbial pathogens are engulfed by macrophages and neutrophils and represents the first line of defense against bacterial infection. The importance of phagocytosis for bacterial clearance is of particular relevance to systemic inflammatory diseases, which are associated with the development of hypoxia, yet the precise effects of hypoxia on phagocytosis remain largely unexplored. We now hypothesize that hypoxia inhibits phagocytosis in macrophages and sought to determine the mechanisms involved. Despite our initial prediction, hypoxia significantly increased the phagocytosis rate of particles in vitro by RAW264.7 and primary peritoneal macrophages and increased phagocytosis of labeled bacteria in vivo by hypoxic mice compared with normoxic controls. In understanding the mechanisms involved, hypoxia caused no changes in RhoA-GTPase signaling but increased the phosphorylation of p38-MAPK significantly. Inhibition of p38 reversed the effects of hypoxia on phagocytosis, suggesting a role for p38 in the hypoxic regulation of phagocytosis. Hypoxia also significantly increased the expression of hypoxia-inducible factor-1alpha (HIF-1alpha) in macrophages, which was reversed after p38 inhibition, suggesting a link between p38 activation and HIF-1alpha expression. It is striking that small interfering RNA knockdown of HIF-1alpha reversed the effects of hypoxia on phagocytosis, and overexpression of HIF-1alpha caused a surprising increase in phagocytosis compared with nontransfected controls, demonstrating a specific role for HIF-1alpha in the regulation of phagocytosis. These data indicate that hypoxia enhances phagocytosis in macrophages in a HIF-1alpha-dependent manner and shed light on an important role for HIF-1alpha in host defense.
吞噬作用是巨噬细胞和中性粒细胞吞噬微生物病原体的过程，是抵御细菌感染的第一道防线。吞噬作用对于细菌清除的重要性与全身性炎症性疾病尤为相关，这些疾病与缺氧的发生有关，但缺氧对吞噬作用的确切影响在很大程度上仍未得到探索。我们现在假设缺氧会抑制巨噬细胞的吞噬作用，并试图确定其中涉及的机制。尽管我们最初有这样的预测，但与常氧对照组相比，缺氧显著提高了RAW264.7细胞和原代腹腔巨噬细胞在体外对颗粒的吞噬率，以及缺氧小鼠体内对标记细菌的吞噬率。在了解其中涉及的机制时，缺氧并未改变RhoA - GTP酶信号传导，但显著增加了p38 - MAPK的磷酸化。抑制p38可逆转缺氧对吞噬作用的影响，表明p38在缺氧对吞噬作用的调节中发挥作用。缺氧还显著增加了巨噬细胞中缺氧诱导因子 - 1α（HIF - 1α）的表达，在抑制p38后这种表达得以逆转，这表明p38激活与HIF - 1α表达之间存在联系。令人惊讶的是，小干扰RNA敲低HIF - 1α可逆转缺氧对吞噬作用的影响，与未转染的对照组相比，HIF - 1α的过表达导致吞噬作用惊人地增加，这证明了HIF - 1α在吞噬作用调节中的特定作用。这些数据表明，缺氧以HIF - 1α依赖的方式增强巨噬细胞的吞噬作用，并揭示了HIF - 1α在宿主防御中的重要作用。
