At this moment, we know that other miRNAs predicted to potentially target human AE2 mRNA, such as miR-149-3p and miR-765, were down-regulated in cultured PBC cholangiocytes versus normal cholangiocytes (Supporting

Fig. 2), and that expression of a third candidate (miR-944) was undetectable in both PBC and normal cholangiocytes. Thus, the particular role of miR-506 for the decreased AE2 in PBC livers appears to be further enlightened. Though PBMCs were also reported to have decreased AE2 mRNA expression in PBC,34 this decreased transcriptional expression is, however, unrelated to miR-506, because we found no up-regulation of miR-506 in the peripheral blood cells collected from patients with PBC (data not shown). PBC is currently click here regarded as a multifactorial liver disease that may ensue from highly complex interactions of genetic- and environmental-related factors, a view that is being stressed by recent results of genome-wide association studies36-39 and more conventional genetic and epidemiological studies.40-43 Exposure of susceptible individuals to environmental agents, such as chemical/xenobiotics,

tobacco, alcohol, and a variety of microorganisms, may result in epigenetic alterations, which might include not only DNA methylation and histone modification, but also dys-regulated expression of miRNAs.23 Indeed, miRNAs are recently being considered as authentic effectors of environmental influences on gene expression and disease.23 The mechanisms leading to miR-506 up-regulation in PBC cholangiocytes remain to be elucidated, and involvement Selleck Small molecule library of environmental agents may be postulated. Although in vivo animal experiments find more sound attractive to further explore this issue, unfortunately, rat and mouse animal models are not suitable, because the AE2 target sequence is present in the human AE2 mRNA,28 but not in the orthologous

sequences in rats and mice. On the other hand, the consequences of miR-506 up-regulation in the biliary epithelium might be more extensive than primarily inferred from its effects on AE2, and this possibility will certainly deserve further investigation in the future. Thus, miR-506 was also predicted by bioinformatic approaches to potentially target the 3′UTR region of human CK19 mRNA, with base complementarities to the sequence UGUCCUUUGGAGGGUGUCUUC. Interestingly, our western blotting data indicate that overexpression of miR-506 in H69 cholangiocytes result in down-regulation of CK19 protein expression (Supporting Materials and Supporting Fig. 3). In summary, our results identify a molecular mechanism (i.e., miRNA suppression of protein translation), which can account for the down-regulation of AE2 protein and activity in cholangiocytes of patients with PBC and provide direct evidence that a specific miRNA (i.e., miR-506) is important in the process. Our data therefore introduce the concept that miRNA dysfunction may be central to the pathogenesis of PBC.