HBV infection alters the transcriptional regulation of FXR-dependent microRNAs

The binding of HBV to the Na+-taurocholate cotransporting polypeptide (NTCP) was previously shown to limit its function, leading to reduced nuclear translocation of the bile acid sensor farnesoid X receptor (FXR) and alterations in the expression of key genes of hepatic cholesterol and bile acid metabolism in human hepatocytes in vivo (Oehler, Hepatology 2014). Furthermore, we showed that the capacity of FXR agonists to modulate bile acid homeostatic genes was strongly weakened by HBV infection (Bhadra, HBV international meeting, 2015). MicroRNAs play an important role in cellular processes and possibly in HBV infection. Moreover, growing evidence indicates that FXR is involved in transcriptional regulation of hepatic miRNAs.

Aim of this study was to investigate (I) the impact of FXR activation mediated by FXR-agonists on miRNAs expression in primary human hepatocytes in vivo and (II) to assess whether HBV can interfere with FXR-mediated miRNA induction.

Methods: Humanized uPA/SCID/beige mice with stable HBV infection treated with FXR-agonist PX20606 (0.2 mg/day, 3 week-oral feeding), while uninfected and vehicle fed infected mice served as controls. MicroRNA expression was determined by using a novel TaqMan™ Advanced miRNA Assay which includes miRNA amplification and reverse transcription after RNA phenol/chloroform purification. MicroRNA in situ hybridization was performed with the Affymetrix® viewRNA chemistry.

Results: Treatment with PX20606 caused a significant induction of miR-144 in the uninfected animals (2.42- fold change relative to untreated, uninfected controls; p = 0.01). Notably, no enhancement of miR144 was observed in HBV infected mice receiving the FXR-agonist. A similar behavior could be observed for miR-451, which is expressed in a cluster with miR-144. In contrast to previous reports based on HCC analyses, PX20606 administration did not induce miR-122 in uninfected animals, suggesting differential miRNA regulation in tumor and primary hepatocytes.

Flourescence in situ hybridization of miR-144 has approved these findings and also revealed dissimilar expression patterns in murine and human hepatocytes. Both miR-144 and miR-451 are highly abundant in the serum of chimeric mice.

Conclusion: Chronic HBV infection hinders FXR-dependent cellular pathways, thus altering the transcription not only of genes involved in bile acid and cholesterol metabolism, but also of FXR-targeted hepatic microRNAs.