Use of transgenic mice in UDP-glucuronosyltransferase (UGT) studies

Abstract

Transgenic mouse models are useful to understand the function and regulation of drug-metabolizing enzymes in vivo. This article is intended to describe the general strategies and to discuss specific examples on how to use transgenic, gene knockout, and humanized mice to study the function as well as genetic and pharmacological regulation of UDP-glucuronosyltransferases (UGTs). The physiological and pharmacological implications of transcription factor-mediated UGT regulation will also be discussed. The UGT-regulating transcription factors to be discussed in this article include nuclear hormone receptors (NRs), aryl hydrocarbon receptor (AhR), and nuclear factor erythroid 2-related factor 2 (Nrf2).

Fig. 1

Strategies to create the loss-of-function knockout, gain-of-function transgenic, and the combined “humanized” function models. Adopted from Gong et al. (2005), with the permission of the publisher.

Fig. 2

Creation of PXR knockout mice. (A) Restriction map of the PXR gene and strategy to generate PXR mutant allele. The PXR probes used for Southern blot and expected fragment sizes after EcoR I digestion are indicated. E, exon; Neo, neomycin resistance gene; TK, thymidine kinase promoter. (B) Southern blot of EcoR I-digested genomic DNA. WT, wild type; MT, Mutant. (C) Loss of PXR mRNA expression in the liver and small intestine of PXR knockout (PXR^-/-) mice. Adapted from Xie et al., 2000, with the permission of the publisher.

Fig. 3

Creation of PXR transgenic mice. (A) Schematic representation of the albumin (Alb)-hPXR transgene construct. (B) Northern blot analysis of mouse and human PXR gene expression in the liver of wild type (-) and transgenic (+) mice. Adapted from Xie et al., 2000, with the permission of the publisher.

Fig. 4

Drug response profile in the humanized mice. Mice with indicated genotypes were treated with a single dose of RIF (5 mg/kg) or PCN (40 mg/kg) 24 hrs prior to liver harvesting. Liver RNA was isolated and subjected to Northern blot analysis with indicated probes. Adopted from Xie et al., 2000, with the permission of the publisher.

Fig. 5

Creation of transgenic mice that harbor conditional expression of the activated CAR (VP-CAR) in the liver. (A) Outline of the TRE-VP-CAR/Lap-tTA Tet-Off transgenic system. (B) Conditional expression of VP-CAR as revealed by Northern blot analysis. Adopted from Saini et al., 2005, with the permission of the publisher.