PM2.5暴露诱发胰岛素抵抗的分子作用机制

Epidemiological evidences have demonstrated that fine particulate matter (PM2.5, aerodynamic diameter <2.5 μm), a component of urban air pollution, induce the adverse health effects in humans. Exposure to PM2.5 is associated with increased lung cancer, asthma, and pulmonary and cardiovascular diseases in predisposed individuals. After inhalation and deposition of PM2.5 in the lung, the majority of the absorbed pollutants are released into the pulmonary surfactant, and result in a series of cytotoxic effects, such as reactive oxygen species (ROS) generation and cytokines release, which are responsible for the inflammatory responses. Recent studies have demonstrated that exposure to PM2.5 is associated with diabetes mellitus. However, we are still far from elucidating the mechanism that induce the toxic effect exerted by PM2.5. Also, very little is known about the intracellular molecular targets of PM2.5-indcuced ROS in insulin-sensitive tissues. We hypothesized that PM2.5-induced oxidative stress and inflammation responses cause oxidative damage in insulin-sensitive tissues, such as liver, muscle and adipose, and result in/aggravate insulin resistance in high-fat diet condition. Therefore, the aim of this project is to investigate whether PM2.5-induced oxidative stress can lead to proinflammatory response and insulin resistance in high-fat diet-fed ICR and nrf2-/- ICR mice. Firslty, the physical and chemical characterizations of PM2.5 will be carried out using electron microscope, gaschromatography and others. Then, ICR mice, nrf2 knock-out (nrf2-/-) mice, high-fat diet-fed ICR and nrf2-/- mice are simultaneously and separately exposed to the mean concentration of 75 μg/m3 PM2.5 and the filtered air in the exposure chamber. After long-term exposure to PM2.5, PM2.5-induced oxidative stress and inflammation response in insulin-sensitive tissues of PM2.5-treated mice will be carried out using biochemical and molecular immunohistochemical analyses. Moreover, we will investigate that PM2.5 induces Nrf2-mediated defense mechanisms against oxidative stress and inflammation response in insulin-sensitive tissues by activating Nrf2/ARE signaling pathway. In summary, our results obtained from this study can characterize the components of the particulate matter which may present a risk factor for diabetic progression. Furthermore, through in vivo analysis, we will reveal the Nrf2/ARE signaling pathways through which PM2.5 exposure promotes insulin resistance associated impairment of glucose metabolism.

针对当今人们普遍关注的大气可吸入颗粒物PM2.5与健康的问题，本项目拟从PM2.5介导的氧化应激和炎症反应对胰岛素敏感组织氧化损伤的作用机制为研究切入点，探讨PM2.5暴露和高脂饮食条件下诱发和加剧糖尿病胰岛素抵抗的分子作用机制。本研究将在PM2.5理化性质表征分析的基础上，将正常饲料喂养的ICR小鼠、nrf2-/- ICR小鼠、高脂饲料喂养的ICR和nrf2-/- ICR小鼠分别暴露于过滤空气和75 μg/m3 PM2.5空气中2、6和12周，采用生物化学和分子免疫组织化学方法研究PM2.5对胰岛素敏感组织的氧化应激和炎症反应，阐明氧化损伤和炎症因子诱发小鼠胰岛素抵抗的生物效应；利用分子生物学方法进一步明确Nrf2/ARE信号通路在PM2.5诱导的氧化应激和胰岛素抵抗发生的分子作用机制，该研究为PM2.5诱导和/或加重高脂饮食条件下糖尿病胰岛素抵抗的分子毒性效应和致病机理研究提供新思路。

针对当今人们普遍关注的大气可吸入颗粒物PM2.5与健康的问题，本项目从PM2.5介导的氧化应激和炎症反应对胰岛素敏感组织氧化损伤的作用机制为研究切入点，探讨PM2.5暴露和高脂饮食条件下诱发和加剧糖尿病胰岛素抵抗的分子作用机制。本研究将在PM2.5理化性质表征分析的基础上，将正常饲料喂养的ICR小鼠、nrf2-/- ICR小鼠、高脂饲料喂养的ICR和nrf2-/- ICR小鼠分别暴露于过滤空气和75 μg/m3 PM2.5 12周。野生型和Nrf2-/-小鼠体重、肝重、饮水饮食没有明显变化。但是，生化分析结果显示，PM2.5暴露组小鼠的血清谷丙转氨酶（ALT）和谷草转氨酶（AST）水平显著升高。肝组织的分析发现，肝脏出现炎症细胞浸润，炎症因子IL-1β、IL-6 mRNA表达水平升高。此外，PM2.5暴露引起野生型小鼠肝脏Nrf2、超氧化物歧化酶（SOD）、过氧化氢酶（CAT）和血红素氧合酶（HO-1）的表达水平显著升高，而Nrf2-/-小鼠肝脏的谷胱甘肽（GSH）表达水平降低。而且，Nrf2-/-小鼠暴露PM2.5后，其口服葡萄糖耐量和肝糖原合成水平明显低于野生型小鼠，肝脏糖原合成的相关基因表达水平受到抑制。同时，Western blot结果还表明PM2.5暴露显著升高野生型和Nrf2-/-小鼠肝脏的c-Jun氨基末端激酶（JNK）、胰岛素受体底物-1（IRS-1）磷酸化水平，抑制AKT磷酸化水平。与野生型小鼠相比，Nrf2-/-小鼠的上述变化更加明显。综上所述，PM2.5暴露引起小鼠肝脏炎症和氧化应激，降低口服糖耐量水平，激活JNK信号通路，抑制胰岛素信号通路，诱导肝脏发生胰岛素抵抗，影响肝脏的脂代谢，其中Nrf2/JNK/IRS-1/AKT信号通路在PM2.5诱导小鼠肝脏胰岛素抵抗中发挥着重要作用。