RNA sequencing analysis shows that titanium dioxide nanoparticles induce endoplasmic reticulum stress, which has a central role in mediating plasma glucose in mice

Titanium dioxide nanoparticles (TiO₂ NPs) constitute the top five NPs in use today. In this study, oral administration of 50, 100, and 200 mg/kg body weight (b.w.) TiO₂ NPs increases plasma glucose in mice, whereas 10 and 20 mg/kg b.w. TiO₂ NPs did not. RNA sequencing (RNA-seq) technology was used to investigate genome-wide effects of TiO₂ NPs. Clustering analysis of the RNA-seq data showed the most significantly enriched gene ontology terms and KEGG pathways related to the endoplasmic reticulum (ER) and ER stress. Molecular biology verification showed that 50 mg/kg b.w. and higher doses TiO₂ NPs activated a xenobiotic biodegradation response and increased expression of cytochrome <i>P450</i> family genes in mouse livers, thus inducing ER stress in mice. ER stress-activated MAPK and NF-κB pathways and induced an inflammation response, resulting in phosphorylation of the insulin receptor substrate 1 and, consequently, insulin resistance. This was the main mechanism by which TiO₂ NPs increased plasma glucose in mice. Meanwhile, ER stress disturbed the monooxygenase system, and thus generated reactive oxygen species (ROS). Relief of ER stress with 4-phenylbutyric acid inhibited all the above effects of TiO₂ NPs, including the generation of ROS. Therefore, TiO₂ NP-induced ER stress was a decisive factor with a central role in plasma glucose disturbance in mice.

二氧化钛纳米颗粒（TiO₂ NPs）是当前全球应用量排名前五的纳米颗粒之一。本研究以小鼠为实验对象，经口给予50、100及200 mg/kg体重（b.w.）的TiO₂ NPs后，小鼠血浆葡萄糖水平显著升高；而10、20 mg/kg体重（b.w.）的TiO₂ NPs未引发此类变化。研究采用RNA测序（RNA-seq）技术，探究TiO₂ NPs对小鼠基因组的全局转录调控效应。对RNA-seq数据进行聚类分析后发现，富集程度最高的基因本体论（GO）术语与京都基因与基因组百科全书（KEGG）通路均与内质网（ER）及内质网应激密切相关。分子生物学验证实验证实，50 mg/kg体重及更高剂量的TiO₂ NPs可激活小鼠肝脏的外源性物质生物降解应答通路，并上调细胞色素P450家族基因的表达，进而诱导小鼠产生内质网应激。内质网应激可激活丝裂原活化蛋白激酶（Mitogen-Activated Protein Kinase，MAPK）与核因子κB（Nuclear Factor-κB，NF-κB）信号通路，诱发炎症反应，导致胰岛素受体底物1发生磷酸化，最终引发胰岛素抵抗。这正是TiO₂ NPs升高小鼠血浆葡萄糖水平的核心作用机制。与此同时，内质网应激会干扰单加氧酶系统，进而产生活性氧（ROS）。通过4-苯基丁酸缓解内质网应激后，TiO₂ NPs的上述所有效应（包括活性氧的生成）均受到显著抑制。综上，TiO₂ NPs诱导的内质网应激是导致小鼠血浆葡萄糖代谢紊乱的决定性因素，在该过程中发挥核心调控作用。