Health Sciences Research Institute, University of California, Merced, CA, USA.
School of Medicine, University of Alabama at Birmingham, Birmingham, AL, USA.
Sci Rep. 2017 Oct 30;7(1):14346. doi: 10.1038/s41598-017-14574-8.
Chronic inflammation plays a key role in development of many liver diseases. Stimulation of Toll-like receptor 4 (TLR4) by bacterial lipopolysaccharide (LPS) initiates inflammation and promotes development of hepatocellular carcinoma and other liver diseases. NADPH oxidases contribute to LPS-induced reactive oxygen species (ROS) production and modulate TLR responses, but whether these enzymes function in TLR4 responses of hepatocytes is unknown. In the present work, we examined the role of NADPH oxidase 4 (Nox4) in LPS-induced TLR4 responses in human hepatoma cells and wildtype and Nox4-deficient mice. We found that LPS increased expression of Nox4, TNF-α, and proliferating cell nuclear antigen (PCNA). Nox4 silencing suppressed LPS-induced TNF-α and PCNA increases in human cells. The LPS-induced TNF-α increases were MyD88-dependent, and were attenuated in primary hepatocytes isolated from Nox4-deficient mice. We found that Nox4 mediated LPS-TLR4 signaling in hepatocytes via NF-ĸB and AP-1 pathways. Moreover, the effect of Nox4 depletion was time-dependent; following six weeks of repeated LPS stimulation in vivo, hepatic TNF-α and PCNA responses subsided in Nox4-deficient mice compared with wildtype mice. Therefore, our data suggest that Nox4 mediates LPS-TLR4 signaling in human hepatoma cells and murine hepatocytes and may contribute to the ability of LPS to stimulate liver pathology.
慢性炎症在许多肝脏疾病的发展中起着关键作用。细菌脂多糖（LPS）刺激 Toll 样受体 4（TLR4）引发炎症，并促进肝细胞癌和其他肝脏疾病的发展。NADPH 氧化酶有助于 LPS 诱导的活性氧（ROS）的产生，并调节 TLR 反应，但这些酶是否在肝细胞 TLR4 反应中起作用尚不清楚。在本工作中，我们研究了 NADPH 氧化酶 4（Nox4）在人肝癌细胞和野生型和 Nox4 缺陷型小鼠 LPS 诱导的 TLR4 反应中的作用。我们发现 LPS 增加了 Nox4、TNF-α 和增殖细胞核抗原（PCNA）的表达。Nox4 沉默抑制了人细胞中 LPS 诱导的 TNF-α 和 PCNA 增加。LPS 诱导的 TNF-α 增加是 MyD88 依赖性的，并且在从 Nox4 缺陷型小鼠分离的原代肝细胞中减弱。我们发现 Nox4 通过 NF-ĸB 和 AP-1 途径介导肝细胞中的 LPS-TLR4 信号转导。此外，Nox4 耗竭的作用具有时间依赖性；在体内重复 LPS 刺激六周后，与野生型小鼠相比，Nox4 缺陷型小鼠的肝 TNF-α 和 PCNA 反应减弱。因此，我们的数据表明 Nox4 介导人肝癌细胞和鼠肝细胞中的 LPS-TLR4 信号转导，并可能有助于 LPS 刺激肝病理学。
