Deciphering the cell type-specific and zonal distribution of drug-metabolizing enzymes, transporters, and transcription factors in livers of mice using single-cell transcriptomics.

The liver contains multiple cell types, including resident cell types and immune cells. The liver is also categorized into 3 zones: periportal (zone 1), midzonal (zone 2), and centrilobular (zone 3). The goal of this study was to characterize the distribution of drug-processing genes (DPGs) in mouse liver using published single-cell and nuclei transcriptomic datasets, which were subjected to zonal deconvolution. Filtering, normalization, clustering, and differential expression analyses were performed using Seurat V5 in R. Hepatocytes were assigned to 3 zones based on known zonal markers and validated with published spatial transcriptomics data. Among the 195 DPGs profiled, most were expressed highest in hepatocytes (61.3%). Interestingly, certain DPGs were expressed most highly in nonparenchymal cells, such as in cholangiocytes (11.2%, eg, carboxylesterase [Ces] 2e, Ces2g), endothelial cells (7.2%, eg, aldo-keto reductase [Akr] 1c19, Akr1e1), Kupffer cells (5.3%, eg, Akr1a1, Akr1b10), stellate cells (5.1%, eg, retinoic acid receptor [Rar] α, Rarβ), myofibroblasts (2.9%, RAR-related orphan receptor [Rar] α), and a few were expressed in immune cell types. In hepatocytes, 72.4% of phase-I enzymes were enriched in zone 3. Phase-II conjugation enzymes such as UDP-glucuronosyltransferases (75%) were enriched in zone 3, whereas sulfotransferases (40%) were enriched in zone 1. Hepatic xenobiotic transporters were enriched in zone 3. The xenobiotic biotransformation-regulating transcription factors were enriched in zone 3 hepatocytes. The enrichment of DPGs in liver cell types, including non-parenchymal cells and zone 1 hepatocytes, may serve as an additional repertoire for xenobiotic biotransformation. SIGNIFICANCE STATEMENT: Our study is among the first to systematically characterize the baseline mRNA enrichment of important drug-processing genes in different cell types and zones in the liver. This finding will aid in further understanding the mechanisms of chemical-induced liver injury with improved resolution and precision.