Multiple mechanisms of ontogenic regulation of nuclear receptors during rat liver development

Abstract

clear receptors (NRs) play pivotal roles in the regulation of genes contributing to hepatobiliary cholesterol and bile acid homeostasis. We have previously shown that transporters involved in bile formation are developmentally regulated and are poorly developed during the fetal stage, but their expression reached gradual maturity during the postnatal period. To define the molecular mechanisms underlying this regulation and the role that class II NRs and associated members [liver receptor homolog-1 (LRH-1) and short heterodimer partner (SHP)] play, we have analyzed the ontogeny of NR expression during liver development. Real-time PCR analysis of hepatic NR expression from fetal day 17 through adult revealed that steady-state mRNA levels for all NRs were very low during the embryonic period. However, mRNA levels peaked close to that of adult rats (Ͼ6 wk-old rats) by 4 wk of age for farnesoid X receptor (FXR), pregnane X receptor (PXR), liver X receptor-␣ (LXR␣), peroxisome proliferatoractivated receptor-␣ (PPAR␣), retinoid acid receptor-␣ (RAR␣), LRH-1, and SHP, whereas RXR␣ mRNA lagged behind. FXR, PXR, LXR␣, RAR␣, and PPAR␣ functional activity in liver nuclear extracts assayed by gel EMSA demonstrated that the activity attained adult levels by 4 wk of age, exhibiting a strict correlation with mRNA levels. Surprisingly, PPAR␣ activity was delayed as seen by EMSA assay. Protein levels for NRs also corresponded to the mRNA and functional activity except for RXR␣. RXR␣ protein levels were higher than message levels, suggesting increased protein stability. We conclude that expression of NRs during rat liver development is primarily regulated by transcriptional mechanisms, which in turn, control the regulation of bile acid and cholesterol metabolic pathways. ontogeny; bile acids; cholesterol NUCLEAR HORMONE RECEPTORS (NRs) are a group of transcription factors that control transcription of various genes after stimulation by hormones or other small lipophilic and xenobiotic compounds (24). Class II NRs comprise transcription factors that heterodimerize with a common partner retinoid X receptor (RXR; NR2B1) and bind to cis elements in the DNA that contain a dyad of six base pairs in direct, inverted or everted configuration separated by 0 -8 bases (14). Recent investigations over the last 5 yr have revealed the important role that class II NRs and associated family members, such as liver receptor homolog-1 (LRH-1; also known as FTF and CPF) and short heterodimer partner (SHP), play in cholesterol and bile acid metabolism and transport (5). Among the class II NRs are

Ontogeny of Novel Cytochrome P450 Gene Isoforms during Postnatal Liver Maturation in Mice

“…Findings indicate that CAR also regulates the basal expression of Cyp2c29 and Cyp2b13 (Hernandez et al, 2009). Nuclear receptors may contribute to the age-and genderspecific gene expression of P450 isoforms during development, given that many nuclear receptors, which are well known to regulate P450 gene expression in adults, begin to be expressed in livers after birth in both rats and mice (Balasubramaniyan et al, 2005;Cui et al, 2010). Therefore, it is possible that the postnatal enrichment and femalepredominant expression of CAR contribute to the female-specific expression of other novel P450 isoforms in the Cyp2b and Cyp2c subfamilies, including Cyp2b9, Cyp2b13, Cyp2c39, Cyp2c40, Cyp2c67, Cyp2c68, and Cyp2c69 (Figs.…”

Ostα-Ostβ is required for bile acid and conjugated steroid disposition in the intestine, kidney, and liver

“…Indeed, expression of Mrp3 and of some other Mrps is known to be very low in neonatal mice and reaches adult levels only after weaning (18,24). Likewise, expression of the nuclear receptors that are involved in bile acid and sterol homeostasis, including Fxr, are expressed at low levels in neonatal animals (1). The low expression of these transcription factors and alternate sterol transporters in neonatal mice may account for the inability of Ost␣-deficient mice to compensate for the lack of bile acid absorption; however, additional studies are needed to test these possibilities.…”

“…[ 3 H(G)]Taurocholic acid (2 Ci/mmol), [1,2,6, H(N)] DHEAS (74 Ci/mmol), and [6, H(N)]estrone 3-sulfate (46 Ci/mmol) were purchased from PerkinElmer Life and Analytical Sciences (Boston, MA). All other chemicals and reagents were purchased from Ambion (Austin, TX), Amersham Biosciences (Piscataway, NJ), Bio-Rad (Hercules, CA), Fermentas (Burlington, ON, Canada), Integrated DNA Technologies (Coralville, IA), Invitrogen (Carlsbad, CA), Jackson Immunology Research Laboratory (Bar Harbor, ME), Mallinckrodt Baker (Phillipsburg, NJ), New England Biolab (Beverly, MA), Perkin-Elmer (Foster City, CA), Qiagen (Valencia, CA), Roche (Mannheim, Germany), Sigma-Aldrich (St. Louis, MO), or Stratagene (La Jolla, CA).…”

Identification of Functionally Relevant Lysine Residues That Modulate Human Farnesoid X Receptor Activation

“…HepG2 cells were treated with 1 mM sodium butyrate (NaB), 1 mM trichostatin A (TSA), or 10 mM nicotinamide (NAM) for 6 hours at 37°C. The mRNA of hBSEP and hSHP in HepG2 cells was quantified by quantitative realtime PCR as described previously (Balasubramaniyan et al, 2005). Fold change values were calculated as the relative expression level compared with that of the cells in the absence of histone deacetylase (HDAC) inhibitors.…”