Department of Molecular and Cell Biology, University of Connecticut, Storrs, Connecticut, United States of America.
PLoS One. 2011 Feb 2;6(2):e14647. doi: 10.1371/journal.pone.0014647.
Inhalation of crystalline silica is known to cause an inflammatory reaction and chronic exposure leads to lung fibrosis and can progress into the disease, silicosis. Cultured macrophages bind crystalline silica particles, phagocytose them, and rapidly undergo apoptotic and necrotic death. The mechanism by which particles are bound and internalized and the reason particles are toxic is unclear. Amorphous silica has been considered to be a less toxic form, but this view is controversial. We compared the uptake and toxicity of amorphous silica to crystalline silica.
METHODOLOGY/PRINCIPAL FINDINGS: Amorphous silica particles are phagocytosed by macrophage cells and a single internalized particle is capable of killing a cell. Fluorescent dextran is released from endo-lysosomes within two hours after silica treatment and Caspase-3 activation occurs within 4 hours. Interestingly, toxicity is specific to macrophage cell lines. Other cell types are resistant to silica particle toxicity even though they internalize the particles. The large and uniform size of the spherical, amorphous silica particles allowed us to monitor them during the uptake process. In mCherry-actin transfected macrophages, actin rings began to form 1-3 minutes after silica binding and the actin coat disassembled rapidly following particle internalization. Pre-loading cells with fluorescent dextran allowed us to visualize the fusion of phagosomes with endosomes during internalization. These markers provided two new ways to visualize and quantify particle internalization. At 37 °C the rate of amorphous silica internalization was very rapid regardless of particle coating. However, at room temperature, opsonized silica is internalized much faster than non-opsonized silica.
CONCLUSIONS/SIGNIFICANCE: Our results indicate that amorphous and crystalline silica are both phagocytosed and both toxic to mouse alveolar macrophage (MH-S) cells. The pathway leading to apoptosis appears to be similar in both cases. However, the result suggests a mechanistic difference between FcγRIIA receptor-mediated and non-opsonized silica particle phagocytosis.
已知吸入结晶二氧化硅会引起炎症反应，长期暴露会导致肺纤维化，并可发展为矽肺。培养的巨噬细胞会结合结晶二氧化硅颗粒，吞噬它们，并迅速发生凋亡和坏死。颗粒结合和内化的机制以及颗粒毒性的原因尚不清楚。无定形二氧化硅被认为是一种毒性较低的形式，但这种观点存在争议。我们比较了无定形二氧化硅和结晶二氧化硅的摄取和毒性。
方法/主要发现：无定形二氧化硅颗粒被巨噬细胞吞噬，单个内化颗粒就能杀死一个细胞。在硅处理后两小时内，荧光葡聚糖从内溶酶体中释放出来，Caspase-3 在 4 小时内激活。有趣的是，毒性是特异性的巨噬细胞细胞系。其他细胞类型对硅颗粒毒性有抗性，即使它们能内化颗粒。球形、无定形二氧化硅颗粒的大小和均匀性允许我们在摄取过程中监测它们。在 mCherry-actin 转染的巨噬细胞中，在硅结合后 1-3 分钟内开始形成肌动蛋白环，并且在颗粒内化后肌动蛋白涂层迅速解体。预先用荧光葡聚糖加载细胞，使我们能够在内化过程中观察吞噬体与内体的融合。这些标记物提供了两种新的可视化和量化颗粒内化的方法。在 37°C 下，无论颗粒涂层如何，无定形二氧化硅的内化速度都非常快。然而，在室温下，调理后的二氧化硅比非调理的二氧化硅内化得更快。
结论/意义：我们的结果表明，无定形和结晶二氧化硅都被吞噬，并且对小鼠肺泡巨噬细胞（MH-S）细胞都有毒性。导致细胞凋亡的途径在两种情况下似乎相似。然而，结果表明 FcγRIIA 受体介导的和非调理的二氧化硅颗粒吞噬的机制存在差异。
