Intrahepatic cholestasis is often associated with impairment of biliary bile acid secretion, a process mediated by the sister of P-glycoprotein (Spgp or Abcb11) also known as the bile salt export pump (Bsep). In humans, mutations in the Spgp gene are associated with a fatal childhood disease, type 2 progressive familial intrahepatic cholestasis (PFIC2). However in mice, the "knockout" of Spgp only results in mild cholestasis. In this study, we fed spgp(-/-) knockout mice with a cholic acid (CA)-supplemented diet to determine whether a more pronounced PFIC2-like phenotype could be induced. Such mice developed severe cholestasis characterized by jaundice, weight loss, elevated plasma bile acid, elevated transaminase, cholangiopathy (proliferation of bile ductules and cholangitis), liver necrosis, high mortality, and wide-ranging changes in the mRNA expression of major liver genes (16/36 examined). A surprising observation was that the bile acid output and bile flow in CA-fed mutant mice was significantly higher than anticipated. This suggests that the spgp(-/-) mice are able to utilize an alternative bile salt transport system. However, unlike Spgp, this system is insufficient to protect the knockout mice from cholestasis despite its high capacity. In conclusion, the spgp(-/-) mice provide a unique model to investigate molecular pathways associated with cholestasis and related diseases.
"Because the human and murine ATP-binding cassette sub-family G member 5 (ABCG5) and ATP-binding cassette sub-family G member 8 (ABCG8) genes are not direct targets of miR-33 and no repression was observed after overexpressing miR-33 in mouse primary hepatocytes and human hepatocytes, the authors argue that this could be the result of off-target effects using the adenoviral approach. Indeed, mice deficient in ABCB11 showed reduced hepatic levels of ABCG5 and ABCG8 fed a lithogenic diet (Wang et al, 2003). However, the underlying mechanism involved in this reduced expression of Abcg5/8 needs to be elucidated. "
"Hence, the decreased expression of Abcg5 and Abcg8 noted in Fig 3F could be the result of off-target effects due to the supra-physiological levels of miR-33 achieved using adenovirus, thus potentially limiting the interpretation of the results. Intriguingly, mice deficient in ABCB11 show decreased hepatic levels of Abcg5 and Abcg8 when fed a lithogenic diet (Wang et al, 2003); the molecular mechanism of this cross-talk remains unknown, but authors speculate that it is independent on the levels/activity of LXR (Wang et al, 2003). Whether the drop in Abcg5/8 levels in the livers in Fig 3F are due to extreme levels of miR-33, or the result of a yet-unknown signalling pathway that links the expression of different bile transporters will require further investigation. "
[Show abstract][Hide abstract] ABSTRACT: Bile secretion is essential for whole body sterol homeostasis. Loss-of-function mutations in specific canalicular transporters in the hepatocyte disrupt bile flow and result in cholestasis. We show that two of these transporters, ABCB11 and ATP8B1, are functional targets of miR-33, a micro-RNA that is expressed from within an intron of SREBP-2. Consequently, manipulation of miR-33 levels in vivo with adenovirus or with antisense oligonucleotides results in changes in bile secretion and bile recovery from the gallbladder. Using radiolabelled cholesterol, we show that systemic silencing of miR-33 leads to increased sterols in bile and enhanced reverse cholesterol transport in vivo. Finally, we report that simvastatin causes, in a dose-dependent manner, profound hepatotoxicity and lethality in mice fed a lithogenic diet. These latter results are reminiscent of the recurrent cholestasis found in some patients prescribed statins. Importantly, pretreatment of mice with anti-miR-33 oligonucleotides rescues the hepatotoxic phenotype. Therefore, we conclude that miR-33 mediates some of the undesired, hepatotoxic effects of statins.
→See accompanying article http://dx.doi.org/10.1002/emmm.201201565
EMBO Molecular Medicine 09/2012; 4(9):882-95. DOI:10.1002/emmm.201201228 · 8.67 Impact Factor
"For example, the heme transporter Bcrp (Desuzinges-Mandon et al., 2010) is enriched in prenatal liver, suggesting a need to eliminate heme from the dead red blood cells during the transition of liver functions from a hematopoietic organ to an organ for drug metabolism and disposition. Bsep/Abcb11 is the major transporter for bile acids across the canalicular membrane into bile (Wang et al., 2003). The postnatal increase of Bsep favors the biliary excretion of bile acids in liver after birth to promote nutrient absorption (Fig. 4A). "
[Show abstract][Hide abstract] ABSTRACT: During development, the maturation of liver transporters is essential for chemical elimination in newborns and children. One cannot compare the real abundance of transcripts by conventional messenger RNA (mRNA) profiling methods; in comparison, RNA-Seq provides a "true quantification" of transcript counts and an unbiased detection of novel transcripts. The purpose of this study was to compare the mRNA abundance of liver transporters and seek their novel transcripts during liver development. Livers from male C57BL/6J mice were collected at 12 ages from prenatal to adulthood. The transcriptome was determined by RNA-Seq, with transcript abundance estimated by Cufflinks. Among 498 known transporters, the ontogeny of 62 known critical xenobiotic transporters was examined in detail. The cumulative mRNAs of the uptake transporters increased more than the efflux transporters in livers after birth. A heatmap revealed three ontogenic patterns of these transporters, namely perinatal (reaching maximal expression before birth), adolescent (about 20 days), and adult enriched (about 60 days of age). Before birth, equilibrative nucleoside transporter 1 was the transporter with highest expression in liver (29%), followed by breast cancer resistance protein (Bcrp) (26%). Within 1 day after birth, the mRNAs of these two transporters decreased markedly, and Ntcp became the transporter with highest expression (52%). In adult liver, the transporters with highest expression were organic cation transporter 1 and Ntcp (23% and 22%, respectively). Three isoforms of Bcrp with alternate leading exons were identified (E1a, E1b, and E1c), with E1b being the major isoform. In conclusion, this study reveals the mRNA abundance of transporters in liver and demonstrates that the expression of liver transporters is both age and isoform specific.
Data provided are for informational purposes only. Although carefully collected, accuracy cannot be guaranteed. The impact factor represents a rough estimation of the journal's impact factor and does not reflect the actual current impact factor. Publisher conditions are provided by RoMEO. Differing provisions from the publisher's actual policy or licence agreement may be applicable.