Lgr5 + cell fate regulation by coordination of metabolic nuclear receptors during liver repair

Background: Leucine-rich repeat-containing G protein-coupled receptor 5 (Lgr5) is a target gene of Wnt/β-catenin which plays a vital role in hepatic development and regeneration. However, the regulation of Lgr5 gene and the fate of Lgr5 ⁺ cells in hepatic physiology and pathology are little known. This study aims to clarify the effect of metabolic nuclear receptors on Lgr5 ⁺ cell fate in liver. Methods: We performed cell experiments with primary hepatocytes, Hep 1-6, Hep G2, and Huh 7 cells, and animal studies with wild-type (WT), farnesoid X receptor (FXR) knockout mice, Peroxisome Proliferator-activated Receptor α (PPARα) knockout mice and Lgr5-Cre^ERT2; Rosa26-mTmG mice. GW4064 and CDCA were used to activate FXR. And GW7647 or Wy14643 was used for PPARα activation. Regulation of Lgr5 by FXR and PPARα was determined by QRT-PCR, western blot (WB) and RNAscope^® in situ hybridization (ISH) and immunofluorescence (IF), luciferase reporter assay, electrophoretic mobility shift assay (EMSA) and chromatin immunoprecipitation (ChIP). Diethyl 1,4-dihydro-2,4,6-trimethyl-3,5-pyridinedicarboxylate (DDC) diet was used to induce liver injury. Results: Pharmacologic activation of FXR induced Lgr5 expression, whereas activation of PPARα suppressed Lgr5 expression. Furthermore, FXR and PPARα competed for binding to shared site on Lgr5 promoter with opposite transcriptional outputs. DDC diet triggered the transition of Lgr5 ⁺ cells from resting state to proliferation. FXR activation enhanced Lgr5 ⁺ cell expansion mainly by symmetric cell division, but PPARα activation prevented Lgr5 ⁺ cell proliferation along with asymmetric cell division. Conclusion: Our findings unravel the opposite regulatory effects of FXR and PPARα on Lgr5 ⁺ cell fate in liver under physiological and pathological conditions, which will greatly assist novel therapeutic development targeting nuclear receptors.