ABSTRACT
Hepatotoxicity is of major concern for humans exposed to industrial chemicals and drugs. Disruption of farnesoid X receptor (FXR), a master regulator of bile acid (BA) metabolism, enhanced the sensitivity to liver injury in mice after toxicant exposure, but the precise mechanism remains unclear. In this study, the interconnection between BA metabolism, FXR, and chemically induced hepatotoxicity was investigated using metabolomics, Fxr-null mice (Fxr-/-) and hepatocytes, and recombinant adenoviruses. A single low-dose intraperitoneal injection of carbon tetrachloride (CCl4), an inducer of acute hepatitis in mice, resulted in more severe hepatocyte damage and higher induction of pro-inflammatory mediators, such as chemokine (C-C motif) ligand 2 (Ccl2), in Fxr-/-. Serum metabolomics analysis revealed marked increases in circulating taurocholate (TCA) and tauro-ß-muricholate (T-ß-MCA) in these mice, and forced expression of bile salt export protein (BSEP) by recombinant adenovirus in Fxr-/- ameliorated CCl4-induced liver damage. Treatment of Fxr-null hepatocytes with TCA, but not T-ß-MCA, significantly increased c-Jun-N-terminal kinase (JNK) activation and Ccl2 mRNA levels, and up-regulation of Ccl2 mRNA was attenuated by co-treatment with a JNK inhibitor SP600125, indicating that TCA directly amplifies hepatocyte inflammatory signaling mainly mediated by JNK under FXR-deficiency. Additionally, pretreatment with SP600125 or restoration of FXR expression in liver by use of recombinant adenovirus, attenuated CCl4-induced liver injury. Collectively, these results suggest that the TCA-JNK axis is likely associated with increased susceptibility to CCl4-induced acute liver injury in Fxr-/-, and provide clues to the mechanism by which FXR and its downstream gene targets, such as BSEP, protects against chemically induced hepatotoxicity.
Subject(s)
Carbon Tetrachloride/toxicity , Chemical and Drug Induced Liver Injury/prevention & control , MAP Kinase Kinase 4/metabolism , Receptors, Cytoplasmic and Nuclear/physiology , Taurocholic Acid/metabolism , Animals , Carbon Tetrachloride/administration & dosage , Cells, Cultured , Dose-Response Relationship, Drug , Male , Mice , Mice, Inbred C57BLABSTRACT
Following the postnatal decline of cell proliferation in the mammalian central nervous system, the adult brain retains progenitor cells with stem cell-like properties in the subventricular zone (SVZ) and the subgranular zone (SGZ) of the hippocampus. Brain injury can stimulate proliferation and redirect the migration pattern of SVZ precursor cells to the injury site. Sublethal exposure to the neurotoxicant trimethyltin (TMT) causes dose-dependent necrosis and apoptosis in the hippocampus dentate gyrus and increases SGZ stem cell proliferation to generate new granule cells. To determine whether SVZ cells also contribute to the repopulation of the TMT-damaged dentate gyrus, 6-8 week old male C3H mice were injected with the carbocyanine dye spDiI and bromodeoxyuridine (80mg/kg; ip.) to label ventricular cells prior to TMT exposure. The presence of labeled cells in hippocampus was determined 7 and 28days after TMT exposure. No significant change in the number of BrdU(+) and spDiI(+) cells was observed in the dentate gyrus 7days after TMT treatment. However, 28days after TMT treatment there was a 3-4 fold increase in the number of spDiI-labeled cells in the hippocampal hilus and dentate gyrus. Few spDiI(+) cells stained positive for the mature phenotypic markers NeuN or GFAP, suggesting they may represent undifferentiated cells. A small percentage of migrating cells were BrdU(+)/spDiI(+), indicating some newly produced, SVZ- derived precursors migrated to the hippocampus. Taken together, these data suggest that TMT-induced injury of the hippocampus can stimulate the migration of ventricular zone-derived cells to injured dentate gyrus.
