Abstract
We developed a new repeated dosing protocol; 14-day repeated dosing to all mice followed by a Percellome Project protocol study that monitors gene expression at 2, 4, 8, and 24 hours. The effect of repeated dosing can be decomposed into two elements, Transient Response (TR) seen within 24 hours after the last exposure, and the Basal Response (BR) as a drift in the basal expression due to repeated dosing. To decipher the BR, DNA methylation and histone modification were comprehensively monitored by WGBS and ChIP-seq against H3K4me3, H3K27me3, H3K27Ac, and H3K9me3. In case of clofibrate (CFB), a known PPARa activator, the repeated dosing has affected the TR and BR of many genes. For example, the TR of pdk4 and cyp4a14 had decreased and analysis on their enhancer-promoter region suggested that it can be explained by a decrease in PPARa signaling.
Here, we performed a 4-day new repeated dosing study on perfluorooctanic acid (PFOA). Firstly, the 24-hour no-effect dose (used for dose setting of Percellome Project) of single dose of PFOA was 10mg/kg whereas that of 4-day dosing was 0.1mg/kg (CFB was 100mg/kg and 70mg/kg respectively). Pdk4 gene, known to be located downstream of PPARa, was gradually induced towards 24 hours after the last dosing, and cyp4a14 showed increase in both TR and BR, suggesting difference from CFB. Further analysis on the difference based on the network description will be presented with an attempt to look in to regulatory mechanisms by referring to the epigenetic information of CFB and other examples in our database. (Research Grant of MHLW)
