Hepatic Gene Expression Changes in Mouse Models with Liver-specific Deletion or Global Suppression of the NADPH-Cytochrome P450 Reductase Gene

Abstract

NADPH-cytochrome P450 reductase (CPR) is an essential component for the function of many enzymes, including microsomal cytochrome P450 (P450) monooxygenases and heme oxygenases. In liver-Cpr-null (with liver-specific Cpr deletion) and Cpr-low (with reduced CPR expression in all organs examined) mouse models, a reduced serum cholesterol level and an induction of hepatic P450s were observed, whereas hepatomegaly and fatty liver were only observed in the liver-Cpr-null model. Our goal was to identify hepatic gene expression changes related to these phenotypes. Cpr-lox mice (with a floxed Cpr gene and normal CPR expression) were used as the control. Through microarray analysis, we identified many genes that were differentially expressed among the three groups of mice. We also recognized the 12 gene ontology terms that contained the most significantly changed gene expression in at least one of the two mouse models. We further uncovered potential mechanisms, such as an increased activation of constitutive androstane receptor and a decreased activation of peroxisomal proliferatoractivated receptor-␣ by precursors of cholesterol biosynthesis, that underlie common changes (e.g. induction of multiple P450s and suppression of genes for fatty acid metabolism) in response to CPR loss in the two mouse models. Additionally, we observed model-specific gene expression changes, such as the induction of a fatty-acid translocase (Cd36 antigen) and the suppression of carnitine O-palmitoyltransferase 1 (Cpt1a) and acyl-CoA synthetase long chain family member 1 (Acsl1), that are potentially responsible for the severe hepatic lipidosis and an altered fatty acid profile observed in liver-Cprnull mice.

Suppression of Cytochrome P450 Reductase (POR) Expression in Hepatoma Cells Replicates the Hepatic Lipidosis Observed in Hepatic POR-Null Mice

“…Although the results obtained with bile acid supplementation suggest that triglyceride synthesis is up-regulated in POR-suppressed cells, studies with hepatic POR-null mice indicated that genes involved in fatty acid and triglyceride synthesis are not up-regulated in the livers of these mice (Wang et al, 2005;Weng et al, 2005). These studies instead suggested that the accumulating triglycerides are derived largely from the circulation.…”

“…To explore the role of microsomal P450s in drug metabolism and circumvent the embryonic lethality associated with genomic deletion of POR, the conditional, liver-specific deletion of P450 reductase was reported by two groups in 2003 (Gu et al, 2003;Henderson et al, 2003). Unexpectedly, these hepatic POR-null mice developed a severe hepatic lipidosis characterized by the accumulation of diglycerides, triglycerides, and monounsaturated fatty acids (Weng et al, 2005;Mutch et al, 2007), even while serum triglyceride and cholesterol levels were decreased. Since POR was not known to be involved in triglyceride synthesis or secretion the basis for the lipidosis was not readily apparent.…”

“…Because the liver serves as a depot for lipids from the peripheral tissues, it is unclear to what extent extrahepatic lipids contribute to the accumulation of triglycerides in hepatic POR-null mice. Weng et al (2005) found an increase in the expression of a gene responsible for fatty acid uptake (Cd36) and a decrease in the expression of genes involved in fatty acid oxidation (Cpt1a, Ascl1). Mutch et al (2007) made similar observations, concluding that although hepatic fatty acid synthesis was neither increased nor decreased in POR-null liver, lipid secretion was impaired and that this, coupled with continual uptake from the circulation, lead to the lipidosis.…”

Cytochrome P450 2A5 and bilirubin: Mechanisms of gene regulation and cytoprotection

“…The mechanism of the unique regulation of Cyp2a5 during these conditions is unclear and remains to be investigated. The one demonstrated mechanism that is common in these conditions is, in part, oxidative stress (Kirby et al, 1994b;Chomarat et al, 1997;Nebert et al, 2000;Cheung et al, 2003;Gilmore et al, 2003;Gilmore and Kirby, 2004;Su and Ding, 2004;Weng et al, 2005;Chen and Siddiqui, 2007;Fisher et al, 2009;De-Oliveira et al, 2010). Furthermore, these conditions appear to be associated with increased serum bilirubin levels (Bonacini, 2004;Malaguarnera et al, 2005;Richardson et al, 2006b;Hansen, 2010).…”

Low doses x-ray irradiation influence on liver detoxication system in rats with transplanted guerin's carcinoma

“…Поскольку местом взаимодействия субстратов І типа с гемопротеином является гидрофобный участок апофермента [18,19], то весьма вероятно, что в микросомальной мембране в формировании его принимают участие фосфолипиды. Свободнорадикальные состояния последних могут придавать апоферменту цитохрома Р450 определенные конформации и тем самым понижать N-деметилазную активность последнего, что приводит к компенсаторной активации n-гидроксилирования анилина [20,21]. В то же время, скорость перехода цитохрома Р450 в неактивною форму -цитохром Р420 повышается незначительно (рис.…”