Program/Grant Name: Developmental Regulation of Drug Processing Genes
Funding Agency: NIH/NIEHS (R01 ES019487)
Despite recent rapid progress in understanding the expression patterns and regulatory mechanisms of drug processing genes, namely drug metabolizing enzymes and transporters in adults, little is known about these in the pediatric period. The long-term goal is to understand mechanisms of ontogenic regulation of drug processing genes, so that efficacious and safe drug treatments can be achieved in children. Several factors are known to be essential for normal development, including hepatocyte nuclear factor 4 alpha (HNF4a), farnesoid X receptor (FXR), growth hormone (GH) signaling, and epigenetic influences. HNF4a, a master regulator of early liver development, regulates hepatic expression of a large battery of drug processing genes. Initiation of bile-acid signaling pathways, mediated largely via the FXR, is a hallmark of perinatal liver development. GH is essential for postnatal hepatic gene expression and maturation. The accessibility of transcription factors to the target genes is largely determined by the methylation/acetylation status of histones and DNA sequences. Preliminary studies illustrate that in developing mouse livers, drug processing genes and transcription factors are expressed in distinct dynamic patterns and correlate with epigenetic signatures. The objective of this proposal is to elucidate the regulatory mechanisms of ontogenic expression of drug processing genes in mice. The rationale of this proposal is that its successful completion will generate basic knowledge that will serve as the foundation for further understanding pediatric pharmacology in humans. The central hypothesis is: developmental regulation of drug processing genes is a sequential event regulated by hormones, which activate transcription factors to modify epigenetic signatures and regulate gene expression. This hypothesis will be tested in 2 aims. Aim 1 will determine the ontogenic expression patterns of drug processing genes and the correlation with transcription factors and epigenetic signatures. The relative mRNA expression of major phase I/II enzymes and drug transporters in male mouse livers versus intestine and kidney will be examined, and correlated with expression of transcription factors and chromosome modifications (genome-wide DNA methylation and histone modifications). Aim 2 will elucidate roles of transcription factors and GH in determining ontogenic hepatic expression of drug processing genes in HNF4a-null, FXR-null, and GH deficiency (lit/lit) mice using the same working strategy. This study is novel, because it will use a genome-wide approach to elucidate how alterations of hormones and transcription factors modulate epigenetic signatures and hepatic ontogenic expression of drug processing genes. This study is significant, because little is known about the regulation of hepatic drug processing genes in pediatric stages. Results from this study will: 1) provide basic knowledge on the ontogenic expression patterns of drug processing genes and nuclear receptors in liver, kidney, and intestine; and 2) help to understand how perinatal alterations in hormones and nuclear receptors, via modulating epigenetic signatures, affect stage-specific and long-term expression of drug processing genes.
Program/Grant Name: Developmental Regulation of Drug Metabolism by Targeting the Gut Microbiome
Funding Agency: NIH/NIGMS (R01 GM111381)
Very little is known about the developmental regulation of drug-metabolizing enzymes and transporters (together called "drug-processing genes" [DPGs]) in liver, placing newborns and children at a much higher risk of adverse drug reactions (ADRs). Using RNA-Seq, we have shown that drug metabolism is the top most differentially regulated pathway in the entire liver transcriptome of germ-free (GF) mice, suggesting that there is a novel interaction between gut microbiome and hepatic DPGs. One of the key functions of gut microbiome is to produce secondary bile acids (BAs), which can activate two most critical xenobiotic-sensing nuclear receptors in liver, namely the pregnane X receptor (PXR) and constitutive androstane receptor (CAR). During development, profound changes occur in the intestinal bacteria and the secondary BA profiles, suggesting that gut microbiome may at least in part contribute to the developmental regulation of DPGs in liver. No systematic studies have been performed to characterize the regulation of all DPGs by gut microbiome during development, and little is known regarding how targeting the gut microbiome by antibiotics or probiotics reprograms the ontogeny of DPGs in liver. Therefore the goal of this research is to utilize multidisciplinary approaches, including GF and genetically-engineered mice, BA metabolomics, Next-Generation Sequencing, and human fecal samples, to unveil the role of gut microbiota in modulating PXR and CAR signaling and the subsequent ontogenic re-programming of DPGs in liver. The proposed work will unveil a novel link between the ontogeny of gut microbiome and the developmental changes of drug processing capacities during development, and will lead to a paradigm shift in pediatric pharmacology, by establishing a new concept in considering ADRs in children, which is the "bug-drug" interactions, in addition to the known "drug-drug" and "food-drug" interactions.
Program/Grant Name: EPIGENETIC REGULATION OF DRUG METABOLISM BY DEVELOPMENTAL EXPOSURE TO PBDES
Funding Agency: NIH/NIEHS/(R01ES025708)
Developmental exposure to the flame-retardant polybrominated diphenyl ethers (PBDEs) has attracted growing concerns recently, because these highly persistent environmental toxicants are accumulated much more in infants through breast milk, and produce multiple detrimental effects. Although a growing body of research has been done regarding the toxicities of PBDEs themselves, little is known about the potential involvement of PBDEs in modulating the pharmacokinetics of drugs in newborns and children, who are at a much higher risk of adverse drug reactions. More importantly, there is no information regarding whether developmental exposure to PBDEs produces long lasting modifications of drug metabolism beyond childhood. We and others have identified that PBDEs are novel activators of the major xenobiotic-sensing nuclear receptors pregnane X receptor (PXR) and constitutive and rostane receptor (CAR). Neonatal activation of CAR results in epigenetic memory on histone methylation signatures and permanent change of drug metabolism in mouse liver, whereas PXR also regulates distinct epigenetic modifiers. Thus the objective of this research is to utilize multidisciplinary approaches to strategically investigate he epigenetic mechanisms of PBDEs in modulating the transcriptional activities of PXR and CAR and drug-processing capacities during and beyond the neonatal period on a genome-wide scale. Our central hypothesis is: neonatal exposure to PBDEs activates CAR and/or PXR, which in turn reprograms the ontogeny of critical chromatin epigenetic modifiers (such as DNA and histone methylation as well as histone acetylation), leading to epigenetic memory and altered ontogeny of drug-processing genes (DPGs), and long-term alterations in the pharmacokinetics and toxicokinetics beyond childhood. We will test this hypothesis in 3 specific aims: Aim 1 will use xeno-sensor null mice and second- generation sequencing to determine the roles of PXR and CAR in modulating the chromatin epigenetic signatures and expression of DPGs following neonatal exposure to PBDEs; Aim 2 will determine the effect of silencing key chromatin epigenetic modifiers on the expression of PXR- and CAR-target genes in PBDE- treated primary hepatocytes; Aim 3 will determine the role of neon