HNF4A is essential for specification of hepatic progenitors from human pluripotent stem cells

Abstract

The availability of pluripotent stem cells offers the possibility of using such cells to model hepatic disease and development. With this in mind, we previously established a protocol that facilitates the differentiation of both human embryonic stem cells and induced pluripotent stem cells into cells that share many characteristics with hepatocytes. The use of highly defined culture conditions and the avoidance of feeder cells or embryoid bodies allowed synchronous and reproducible differentiation to occur. The differentiation towards a hepatocyte-like fate appeared to recapitulate many of the developmental stages normally associated with the formation of hepatocytes in vivo. In the current study, we addressed the feasibility of using human pluripotent stem cells to probe the molecular mechanisms underlying human hepatocyte differentiation. We demonstrate (1) that human embryonic stem cells express a number of mRNAs that characterize each stage in the differentiation process, (2) that gene expression can be efficiently depleted throughout the differentiation time course using shRNAs expressed from lentiviruses and (3) that the nuclear hormone receptor HNF4A is essential for specification of human hepatic progenitor cells by establishing the expression of the network of transcription factors that controls the onset of hepatocyte cell fate.

Fig. 1.

Identification of mRNA profiles that are characteristic of the differentiation of hepatocyte-like cells from human ES cells. (A) The differentiation procedure. (B) Heat map summarizing relative changes in mRNA levels at each stage of differentiation (red, high; blue, low). (C,D) The total number of genes whose expression is predicted to (C) increase at least fourfold (P≤0.05, Affymetrix signal of at least 200) on a specific day of differentiation or (D) whose expression initiates on a specific day (fourfold, P≤0.05, Affymetrix signal of at least 200, compared with the previous stage) and is maintained throughout differentiation.

Fig. 2.

Quantitative RT-PCR analyses of differentiation stage-specific mRNAs. (A-D) Changes in mRNA levels with characteristic expression profiles at (A) day 0, (B) day 5, (C) day 10 and (D) day 20 of differentiation. Graphs represent the relative mean expression value and s.d. normalized to GAPDH from two independent differentiations.

Fig. 3.

Quantitative RT-PCR analyses of mRNAs with maintained expression. (A-C) Changes in mRNA levels that are induced at a specific stage of differentiation and are maintained throughout the differentiation process: (A) day 5 to 20, (B) day 10 to 20 and (C) day 15 to 20. Graphs represent the mean expression value and s.d. normalized to GAPDH levels from two independent differentiations.

Fig. 4.

HNF4A is essential for differentiation of hepatocyte-like cells from human ES cells. (A) Immunoblot analyses comparing HNF4A protein levels during differentiation of H9 ES cells (day 0) to definitive endoderm (day 5) and hepatic progenitor cells (day 10). (B) Real-time qRT-PCR comparing HNF4A mRNA levels during differentiation of HNF4i3 cells (black bars) and control H9 ES cells (white bars). Data are mean±s.d. (C) Immunocytochemistry identified the presence of HNF4A (red) in control cells (Vector, HNF4i2), but not in HNF4i3 cells, following differentiation. Scale bar: 100 μm. (D) Semi-quantitative RT-PCR revealed that, in contrast to hepatocyte-like cells derived from control cells (H9, HNF4i2), expression of characteristic hepatocyte mRNAs was severely disrupted in HNF4i3 cells. CYCG was used as a loading control. (E) Heat map summarizing oligonucleotide array analyses (red, high expression; blue, low expression) that confirmed the loss of expression of hepatocyte-specific mRNAs in differentiated HNF4i3 cells in contrast to control cells (H9).

Fig. 5.

HNF4A is required for hepatic specification of human ES cells. Real-time qRT-PCR identified the levels of mRNAs defined as being characteristic of (A) mature hepatocyte, (B) immature hepatocyte, (C) hepatic specification and (D) definitive endoderm throughout the differentiation of control (H9) or HNF4i3 cells. Results plotted are the mean. Error bars represent s.d. generated from two independent differentiations.

Fig. 6.

HNF4A is essential for expression of transcription factors with roles in controlling the formation of hepatic progenitor cells. The level of mRNAs encoding transcription factors that have been associated with differentiation of mouse hepatocytes was measured by real-time qRT-PCR in either control H9 (black bars) or HNF4i3 (gray bars) cells throughout differentiation. Data are mean±s.d.

Fig. 7.

Schematic of the role of HNF4A during the differentiation of human ES cells into hepatocyte-like cells. Definitive endoderm generated from human ES cells expresses key hepatic transcription factors, including FOXA2, FOXA3, GATA4, GATA6 and HHEX that, based on studies in the mouse, probably regulate the ability of the endoderm to adopt a hepatic fate. In response to inductive cues, including FGFs and BMPs, the receptive endoderm expresses HNF4A within the nascent hepatic progenitor cells where it is responsible for the initiation and maintenance of expression of several hepatic transcription factors, including HNF1B, that control formation of hepatoblasts and their differentiation towards functional hepatocytes.