Peroxisome proliferator-activated receptor α activates human multidrug resistance transporter 3/ATP-binding cassette protein subfamily B4 transcription and increases rat biliary phosphatidylcholine secretion

Abstract

Multidrug resistance transporter 3/ATP-binding cassette protein subfamily B4 (MDR3/ABCB4) is a critical determinant of biliary phosphatidylcholine (PC) secretion. Clinically, mutations and partial deficiencies in MDR3 result in cholestatic liver injury. Thus, MDR3 is a potential therapeutic target for cholestatic liver disease. Fenofibrate is a peroxisome proliferator-activated receptor (PPAR) α ligand that has antiinflammatory actions and regulates bile acid detoxification. Here we examined the mechanism by which fenofibrate regulates MDR3 gene expression. Fenofibrate significantly up-regulated MDR3 messenger RNA (mRNA) and protein expression in primary cultured human hepatocytes, and stimulated MDR3 promoter activity in HepG2 cells. In silico analysis of 5′-upstream region of human MDR3 gene revealed a number of PPARα response elements (PPRE). Electrophoretic mobility shift (EMSA) and chromatin immunoprecipitation (ChIP) assays demonstrated specific binding of PPARα to the human MDR3 promoter. Targeted mutagenesis of three novel PPREs reduced inducibility of the MDR3 promoter by fenofibrate. In collagen sandwich cultured rat hepatocytes, treatment with fenofibrate increased secretion of fluorescent PC into bile canaliculi. Conclusion Fenofibrate transactivates MDR3 gene transcription by way of the binding of PPARα to three novel and functionally critical PPREs in the MDR3 promoter. Fenofibrate treatment further stimulates biliary phosphatidylcholine secretion in rat hepatocytes, thereby providing a functional correlate. We have established a molecular mechanism that may contribute to the beneficial use of fenofibrate therapy in human cholestatic liver disease.

Therapy of Primary Sclerosing Cholangitis - Today and Tomorrow

“…Of interest for therapy of cholangiopathies, fibrates stimulated the transcription and canalicular insertion of the phospholipid export pump MDR3/ABCB4 [132,133] , thereby facilitating the formation of mixed micelles in bile via increase in phosphatidylcholine and renders bile less toxic [133,134] . This finding was supported by the studies showing PPARα binding to response elements in the MDR3 promoter [135] . Functional evidence for fibrateinduced MDR3 activation was provided by increase in biliary phospholipid excretion in patients undergoing a percutaneous trans-hepatic biliary drainage after bezafibrate treatment [136] .…”

GW4064, an Agonist of Farnesoid X Receptor, Represses CYP3A4 Expression in Human Hepatocytes by Inducing Small Heterodimer Partner Expression

“…However, potential involvement of PPARa and LXR in CYP3A4 repression by GW4064 appears unlikely. Our results from human hepatocytes indicate that GW4064 does not alter the mRNA expression of the representative target genes of these nuclear receptors, including MDR3 (Ghonem et al, 2014), FASN, and SREBF1 (Wagner et al, 2003) (data not shown). Inflammation is also known to alter CYP3A4 expression; CYP3A4 expression is downregulated in the state of inflammation (Aitken et al, 2006).…”

Nuclear Receptors in Acute and Chronic Cholestasis

“…The anticholestatic effect of fibrates is linked to a direct control of the multidrug resistance protein 3 (MDR3 or ABCB4) gene expression by PPARα [49,50]. Indeed, activation of PPARα leads to increased phosphatidylcholine excretion in vitro [50], suggesting a protective mechanism against bile toxicity in vivo. Furthermore, PPARα may limit bile acids deleterious effects by decreasing CYP7A1 expression, while increasing CYP3A4 expression [49].…”

“…Activation of PPARs with fibrates has anticholestatic activity in patients with PBC under UDCA therapy [49]. The anticholestatic effect of fibrates is linked to a direct control of the multidrug resistance protein 3 (MDR3 or ABCB4) gene expression by PPARα [49,50]. Indeed, activation of PPARα leads to increased phosphatidylcholine excretion in vitro [50], suggesting a protective mechanism against bile toxicity in vivo.…”