Activation of the developmental pathway neurogenin-3/microRNA-7a regulates cholangiocyte proliferation in response to injury

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Abstract
The activation of the biliary stem-cell signaling pathway hairy and enhancer of split 1/pancreatic duodenal homeobox-1 (Hes-1/PDX-1) in mature cholangiocytes determines cell proliferation. Neurogenin-3 (Ngn-3) is required for pancreas development and ductal cell neogenesis. PDX-1-dependent activation of Ngn-3 initiates the differentiation program by inducing microRNA (miR)−7 expression. Here we investigated the role Ngn-3 on cholangiocyte proliferation. Expression levels of Ngn-3 and miR-7 isoforms were tested in cholangiocytes from normal and cholestatic human livers. Ngn-3 was knocked-down in vitro in normal rat cholangiocytes by short interfering RNA (siRNA). In vivo, wild-type and Ngn-3-heterozygous (+/−) mice were subjected to 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) feeding (a model of sclerosing cholangitis) or bile duct ligation (BDL). In the liver, Ngn-3 is expressed specifically in cholangiocytes of primary sclerosing cholangitis (PSC) patients and in mice subjected to DDC or BDL, but not in normal human and mouse livers. Expression of miR-7a-1 and miR-7a-2 isoforms, but not miR-7b, was increased in DDC cholangiocytes compared to normal ones. In normal rat cholangiocytes, siRNA against Ngn-3 blocked the proliferation stimulated by exendin-4. In addition, Ngn-3 knockdown neutralized the overexpression of insulin growth factor-1 (IGF1; promitotic effector) observed after exposure to exendin-4, but not that of PDX-1 or VEGF-A/C. Oligonucleotides anti-miR-7 inhibited the exendin-4-induced proliferation in normal rat cholangiocytes, but did not affect Ngn-3 synthesis. Biliary hyperplasia and collagen deposition induced by DDC or BDL were significantly reduced in Ngn-3+/− mice compared to wild-type. Conclusion: Ngn-3-dependent activation of miR-7a is a determinant of cholangiocyte proliferation. These findings indicate that the reacquisition of a molecular profile typical of organ development is essential for the biological response to injury by mature cholangiocytes. (Hepatology 2014;60:1324–1335)
Funding Information
  • Ministero della Salute (GR-2010-2306996)

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