Adrenal stress hormone regulation of hepatic homeostatic function after an acute ozone exposure

Ozone-induced lung injury/inflammation and pulmonary/hypothalamus gene expression are diminished in adrenalectomized (ADREX) rats. Acute ozone exposure induces metabolic alterations concomitant with increases in epinephrine and corticosterone. We hypothesized that adrenal hormones are responsible for observed hepatic ozone effects, and in ADREX rats, these changes would be diminished. Five-seven days after sham or ADREX surgeries, male Wistar-Kyoto rats were exposed to air or 0.8-ppm ozone for 4-hrs. Serum samples were analyzed for metabolites and liver for transcriptional changes immediately post-exposure. Ozone increased circulating triglycerides, cholesterol, free fatty acids, and leptin in sham but not ADREX rats. Ozone-induced inhibition of glucose-mediated insulin release was reversed in ADREX rats. Unlike diminution of hypothalamus and lung mRNA expression changes, ADREX in air-exposed rats (ADREX-air/sham-air) caused differential expression of ~1000 genes in liver. Likewise, ~1000 genes were differentially expressed in ozone-exposed ADREX rats (ADREX-ozone/ADREX-air). Ozone-induced hepatic changes in sham rats reflected enrichment for pathways involving metabolic processes, including acetyl-CoA biosynthesis, TCA cycle, and sirtuins. Upstream predictor analysis identified significant similarity to glucocorticoids and pathways involving CREBBP. These changes were absent in ADREX rats exposed to ozone. However, ozone caused unique changes in ADREX liver mRNA reflecting activation of synaptogenesis, neurovascular coupling, neuroinflammation, and insulin signaling with inhibition of senescence pathways. In these rats, upstream predictor analysis identified numerous microRNAs involved under glucocorticoid insufficiency. These data demonstrate the critical role of adrenal stress hormones in ozone-induced hepatic homeostasis and the need for further research elucidating their role in propagating environmentally driven diseases.肾上腺切除（adrenalectomized, ADREX）大鼠中，臭氧诱导的肺损伤/炎症以及肺部/下丘脑基因表达均得到缓解。急性臭氧暴露可诱导代谢改变，并伴随肾上腺素与皮质酮水平升高。本研究提出假说：肾上腺激素是臭氧诱导肝脏效应的介导因子，而在ADREX大鼠体内，这类肝脏改变将得到缓解。假手术或ADREX术后5至7天，将雄性Wistar-Kyoto大鼠暴露于空气或0.8ppm臭氧环境中4小时。暴露结束后立即采集血清样本以分析代谢物，并采集肝脏组织以检测转录组变化。在假手术组大鼠中，臭氧可升高循环中的甘油三酯、胆固醇、游离脂肪酸及瘦素水平，但该效应在ADREX大鼠中未出现。臭氧诱导的葡萄糖介导胰岛素释放抑制效应在ADREX大鼠中得到逆转。与下丘脑及肺部mRNA表达变化的缓解不同，空气暴露组的ADREX大鼠（ADREX-air/sham-air组）肝脏内出现约1000个基因的差异表达。同样，臭氧暴露的ADREX大鼠（ADREX-ozone/ADREX-air组）肝脏内也有约1000个基因呈现差异表达。假手术组大鼠的臭氧诱导肝脏改变，显著富集于包括乙酰辅酶A生物合成、三羧酸（TCA）循环以及沉默信息调节因子（sirtuins）在内的代谢通路。上游调控因子分析显示，该通路与糖皮质激素及含CREB结合蛋白（CREBBP）的通路高度相似。上述改变在臭氧暴露的ADREX大鼠中均未出现。但臭氧可在ADREX大鼠肝脏内诱导独特的mRNA表达改变，体现为突触发生、神经血管耦合、神经炎症及胰岛素信号通路的激活，同时伴随衰老通路的抑制。在该类大鼠中，上游调控因子分析发现了大量参与糖皮质激素功能不足状态的微小RNA（microRNA, miRNA）。本研究数据证实，肾上腺应激激素在臭氧诱导的肝脏稳态调控中发挥关键作用，同时也提示需开展进一步研究以阐明其在环境诱导疾病发生发展中的具体机制。