HNF4α and FOXA2 form a hierarchical regulatory network to guarantee Albumin synthesis in response to pathophysiological challenge

Background and Aims Albumin is indispensable for homeostasis. In healthy humans, only hepatocytes synthesize albumin. To date, it is largely unknown how the liver produces albumin in physiological and diseased microenvironments. In this study, we scrutinize a hierarchical transcriptional regulatory network that controls albumin expression in response to different physiological and pathophysiological challenges.

Methods Albumin levels in liver tissues and serum were examined in 157 patients with end-stage liver diseases, including 84 hepatocellular carcinoma, 38 decompensated cirrhosis and 35 acute on chronic liver failure (ACLF). Candidate regulatory transcription factors HNF4aand FOXA2 were measured by IHC in these patients. The mechanism how HNF4a and FOXA2 regulated albumin transcription and expression was investigated in human and mouse primary hepatocytes and liver progenitor cell (LPC) lines HepaRG and BMOL.

Results Most patients with end stage liver disease maintain serum albumin concentrations in the normal range. In collected liver tissues, immunohistochemistry shows albumin expression in hepatocytes. However, in a subcohort of patients with massive hepatocyte loss, albumin is expressed in activated LPC. In vitro, ChIP assays reveal that HNF4a and FOXA2 are capable of binding to the albumin promoter. Knockdown of either of them by RNAi reduces albumin expression in both cell types. Immunohistochemistry analyses further show that in normal and non-cirrhotic livers, HNF4a, a constitutively expressed lineage transcription factor, but not FOXA2, is robustly expressed in hepatocytes. However, in a large portion of cirrhotic livers, HNF4a expression is undetectable by immunohistochemistry. In these patients, FOXA2 is remarkably expressed in hepatocytes. Further, FOXA2 positive staining is closely associated with Sonic hedgehog (SHH) induced Gli2 expression. In vitro, disruption of Sonic hedgehog signaling influences FOXA2 expression in hepatocytes. In patients with massive hepatocyte loss, active LPCs not only express albumin, but also display HNF4a or FOXA2, indicating that the two transcription factors are required for Albumin expression in LPCs.

Conclusions HNF4a and FOXA2 form a hierarchical regulatory network to guarantee essential albumin expression in response to different physiological and pathophysiological challenges.

Publication History

Article published online:
04 January 2021