The goal of this article is to provide a standardized approach to induce human hepatic progenitor differentiation from pluripotent stem cells. The development of this procedure with ready-to-use media formulations offer the user a facile system to generate human liver cells for biomedical research and translation.
Liver disease is an escalating global health issue. While liver transplantation is an effective mode of therapy, patient mortality has increased due to shortages in donor organ availability. Organ scarcity also affects the routine supply of human hepatocytes for basic research and the clinic. Therefore, the development of renewable sources of human liver progenitor cells is desirable and is the goal of this study. To be able to effectively generate and deploy human liver progenitors on a large scale, a reproducible hepatic progenitor differentiation system was developed. This protocol aids experimental reproducibility between users in a range of cell cultureware formats and permits differentiations using both, human embryonic and induced pluripotent stem cell lines. These are important advantages over current differentiation systems that will enhance the basic research and may pave the way towards clinical product development.
Liver disease represents a global health challenge, causing approximately 2 million deaths per year worldwide1. Although a number of model systems exist to study hepatic diseases and intervene clinically, the routine use of cell-based systems is limited by significant drawbacks (for a review see Szkolnicka et al.2). Advanced human pluripotent stem cell (hPSC) culture and somatic cell differentiation methods represent promising technologies to develop tools for basic biomedical research and renewable sources of differentiated cells for the clinic3,4.
To date, multiple protocols for hepatocyte-like cell (HLC) differentiation have been developed5,6,7,8. These protocols attempt to recreate aspects of human liver development by using a combination of small molecules and growth factors9,10. Most protocols consist of a stepwise differentiation process, where hPSCs are primed to definitive endoderm, followed by hepatic progenitor specification11,12,13, and ending with HLC specification. HLCs produced by these protocols display a mixture of fetal and adult phenotypes. This includes the expression of alpha fetoprotein (AFP), such as hepatocyte markers such as HNF4α and albumin (ALB), as well as drug metabolizing capacity14,15,16. Between laboratories, HLC differentiation can vary; therefore, the development of standardized protocols is necessary. This will enable researchers to effectively generate and apply stem cell-derived HLCs on a large scale for basic and clinical research.
A hepatic progenitor differentiation system was developed that can be applied to both human embryonic and induced pluripotent stem cell lines using easy-to-follow guidelines. This procedure yields homogenous populations of hepatic progenitors in varying cultureware formats, ranging from cell culture flasks to 96 well plates. Provided below is the protocol to produce stem cell-derived hepatic progenitors in 24 and 96 well formats.
Cell density used in the protocol presented below is specified for one well of a 24 and 96 well plate respectively (see Table 1). Optimization of the starting cell number is required for the different cell culture plate formats and cell lines. Suggested starting cell density for protocol optimization is 2 x 105 cells/cm2. For density optimization, several cell densities can be tested by adding ± 50,000 cells/cm2 at a time.
1. Human pluripotent stem cell (hPSC) maintenance on laminin-521
2. Laminin-521 multiwell preparation and hPSC seeding for differentiation
NOTE: For hPSCs not maintained on LN-521 (e.g., matrigel or fibronectin), split hPSCs onto LN-521 and culture for 1 week prior to passaging and eliciting differentiation to improve the efficiency of the process15,17,18.
3. Differentiating hPSCs to hepatic progenitors on laminin-521
4. Characterization of the hepatic progenitor differentiation cultures generated from hPSCs on laminin-521
5. Immunocytochemistry and image acquisition
Hepatic progenitor differentiation from both hESC (H9) and hiPSC (P106) lines was performed following the stepwise protocol described in Figure 2. Here, pluripotent stem cells were seeded as single cells into LN-521-coated plates prior to the start of the differentiation. Cell confluency is the key for a robust and reproducible differentiation. Once the right confluency was achieved (Figure 2), differentiation was initiated. At day 5, definitive endoderm specification was assessed via Sox17 expression. In both cell lines, Sox17 was highly expressed with 80% ± 0.5% and 87.8% ± 0.5% SEM of Sox17-positive cells for H9 and P106, respectively (Figure 3). At day 10, hepatic progenitors displayed a cobblestone-like morphology (Figure 2). In addition, hepatic progenitor specification was assessed for HNF4α, AFP, ALB, and cytokeratin-19 (CK19) expression as well as AFP and ALB protein secretion10,15,22 (Figure 4). Both H9 and P106 hepatic progenitor cultures expressed fetal hepatic markers such as HNF4α (91% ± 0.5% and 90% ± 0.2%), AFP (89.7% ± 1.8% and 86% ± 1.2%), and CK19 (78.5% ± 3.2% and 83.6 ± 1.8%) (Figure 4). AFP secretion was detected at day 10 in both cell lines (32.4 ± 1.6 and 47.8 ± 5.9 ng/mL/mg/24 h) (Figure 5). Albumin synthesis was observed at lower levels (30.7% ± 1.8% and 27.2% ± 1.1%) (Figure 4) and was not detected via ELISA (Figure 5).
The protocol allowed the standardized production of hepatic progenitors from 24 well to 96 well plates. A semi-automated pipeline was employed to produce 96 well plates of hepatic progenitors from H9 and P106 cell lines as previously described17. Cell number variability and hepatic progenitor differentiation efficiency was assessed via quantification of HNF4α expression. Cell segmentation was performed for protein quantification via immunofluorescence using a high content imaging instrument (Figure 1). At day 10, hepatic progenitors showed no significant variability across rows with >94% of HNF4α-positive cells per well for H9 and 97% HNF4α-positive cells for P106 (Figure 6).
Figure 1: Cell segmentation pipeline overview. (A) Using the original image, (B) nuclear staining was used for nuclei segmentation. (C) A nuclear segmentation quality control step based on shape and size was performed to only quantify clearly segmented nuclei. (D) Following this, positive HNF4α-stained nuclei were quantified. (E) Finally, an intensity-based threshold was employed to identify HNF4α-expressing cells. In C and E, green nuclei represent selected cells and magenta nuclei indicate discarded cells. Scale bar = 50 µm. Please click here to view a larger version of this figure.
Figure 2: Hepatic progenitor differentiation from hPSCs. (A) Schematic representation of the hepatic progenitor differentiation protocol. (B) Representative images highlighting the morphological changes during the differentiation. At day 0 (D0), hPSCs presented a packed monolayer of cells. Following this, hPSCs were primed into definitive endoderm on day 5 (D5). This was followed by hepatic progenitor differentiation on day 10 (D10). Hepatic progenitors displayed a cobblestone-like cell morphology. Scale bar = 75 µm. Please click here to view a larger version of this figure.
Figure 3: Characterization of definitive endoderm specification. At day 5, cells were stained for Sox17, a definitive endoderm marker. The percentage of Sox17-positive cells was 80 ± 0.5% for H9 and 87.8 ± 0.5% for P106. Percentage quantification was based on 10 separate wells with 6 fields of view per well. Data are shown as the average ± SEM. Scale bar = 50 µm. Please click here to view a larger version of this figure.
Figure 4: Hepatic progenitor characterization. At day 10, hepatic progenitors were stained for hepatic markers (A) HNF4α, (B) AFP, and (C) ALB. For H9, the percentage of positive cells were 91% ± 0.4%, 89.7% ± 1.8%, and 30.7% ± 1.8% for HNF4α, AFP, and ALB, respectively. For P106, the percentage of positive cells were 90% ± 0.2%, 86% +/- 1.2%, and 27.2% ± 1.1% for HNF4α, AFP, and ALB, respectively. (D) Cholangiocyte lineage potential was assessed via CK19 expression; H9-derived hepatic progenitors expressed 78.5% ± 3.2% CK19-positive cells, whereas 83.6% ± 1.8% of CK19-positive cells were observed for P106 hepatic progenitors. Immunoglobulin G (IgG) staining was used as a staining control. Percentage quantification was based on 10 separate wells with 6 fields of view per well. Data are shown as the average ± SEM. Scale bar = 50 µm. Please click here to view a larger version of this figure.
Figure 5: Hepatic progenitor protein secretion analysis. The secretion of alpha fetoprotein (AFP) and albumin (ALB) was analyzed in hepatic progenitor cultures at day 10 in H9 and P109. The data represent three biological replicates and the error bars represent the SD. Secreted proteins were quantified from 24 h culture medium as nanograms of secreted protein per mL per mg of protein, n = 3; ND = not detected. Please click here to view a larger version of this figure.
Figure 6: Assessment of well-to-well variability in 96 well plate. (A) Visualization of a 96 well plate view of H9-derived hepatic progenitors stained with HNF4α. (B) Quantification of the HNF4α-positive cells. Average of cell number per well in rows, from six fields of view per well quantified. The average cell number across the plate was 94.81% ± 0.22 SEM HNF4α-positive cells per well. No statistically significant differences were observed between wells. (C) Visualization of a 96 well plate view of P106-derived hepatic progenitors stained with HNF4α. (D) Quantification of HNF4α-positive cells. The average cell number per wells in rows, from six fields of view per well and quantified. The average cell number across the plate was 97.7% ± 0.57 SEM HNF4α-positive cells per well. No statistically significant differences were observed between rows. Well H12 was used as an Immunoglobulin G (IgG) staining control. Scale bar = 1 mm. One-way ANOVA with Tukey's post-hoc statistical tests were employed. Please click here to view a larger version of this figure.
Plate format | Surface area (cm2) | Cells per cm2 | Total cells per well | Dispensing volume (mL) | Cell concentration (cells/ml) |
24-well plate | 1.9 | 210526 | 400000 | 0.5 | 800000 |
96-well plate | 0.32 | 187500 | 60000 | 0.05 | 1200000 |
Table 1: Recommended cell density for the different plate formats for the hPSC cell lines used in this protocol.
The generation of human hepatic progenitor cells from pluripotent stem cells on a large scale could represent a promising alternative to cadaver-derived material. Protocol standardization and reproducibility are key to ensure technology translation and impact for biomedical research. To address this, previous work has focused on developing a stepwise differentiation protocol from hESC and iPSCs using defined additives and matrices15,23,24,25,26,27,28. By doing this, hepatocyte phenotype and reproducibility have been improved, permitting the semi-automation of the differentiation process19. The system presented is strengthened by its combination with off-the-shelf cell culture media and a facile hepatocyte differentiation system.
Previously, pluripotent cell density prior to the start of the differentiation protocol was highlighted as a key variable to achieve a homogenous population of hepatic progenitor cells26. Using this more refined procedure, it is possible to generate large numbers of stem cell-derived hepatic progenitors in a stepwise manner using a range of starting cell densities (Table 1). At day 5, definitive endoderm induction was validated by Sox17 staining (Figure 3). Efficient and robust differentiation into definitive endoderm was achieved with both tested ESC and iPSC lines, with more than 80% expressing Sox17 (Figure 3). At day 10, hepatic progenitors displayed a uniform cobblestone-like morphology, and liver stem cell markers were highly enriched for both AFP and HNF4α (>86%, Figure 4). Using a combination of manual and semi-automated technologies it was possible to perform differentiation in multiple plate formats19.
In its current form, cell differentiation is suitable for in vitro based experimentation. However, cell enrichment would likely be required before clinical application to ensure that a homogenous population of hepatic progenitors are prepared for delivery.
In conclusion, the protocol described here provides the field with a standardized approach to produce hepatic progenitors on a large scale. Future work will focus on the production of a new medium for subsequent HLC differentiation, maturation, and maintenance.
The authors have nothing to disclose.
This study was supported with awards from the MRC Doctoral Training Partnership (MR/K501293/1), the UK Regenerative Medicine Platform (MRC MR/L022974/1 and MR/K026666/1), the Chief Scientist Office (TCS/16/37).
DPBS with Calcium and Magnesium | ThermoFisher | 14040133 | |
Gentle cell dissociation reagent | STEMCELL Technologies | 7174 | |
Hoechst 33342 Ready Flow Reagent | thermofisher | R37165 | |
Human Recombinant Laminin 521 | BioLamina | LN521-02 | |
Human Serum Albumin ELISA | Alpha Diagnostics | 1190 | |
Human Serum Alpha Fetoprotein ELISA | Alpha Diagnostics | 500 | |
mTeSR1 medium | STEMCELL Technologies | 5850 | |
Operetta High-Content Imaging System | PerkinElmer | HH12000000 | |
PBS, no calcium, no magnesium | ThermoFisher | 14190250 | |
Penicillin-Streptomycin (10,000 U/mL) | Life Technologies | 15140122 | |
Rho-associated kinase (ROCK)inhibitor Y27632 | Sigma-Aldrich | Y0503-1MG | |
STEMdiff Definitive Endoderm Supplement CJ | STEMCELL Technologies | ||
STEMdiff Definitive Endoderm Supplement MR | STEMCELL Technologies | ||
STEMdiff Endoderm Basal Medium | STEMCELL Technologies | ||
STEMdiff Hepatic Progenitor Medium | STEMCELL Technologies | ||
TWEEN 20 | Sigma-Aldrich | P9416 | |
Antibodies | |||
Albumin | Sigma-Aldrich | A6684 | 1:200 (mouse) |
Alpha-fetoprotein | Sigma-Aldrich | A8452 | 1:400 (mouse) |
HNF-4α | Santa Cruz | sc-8987 | 1:400 (rabbit) |
IgG | DAKO | 1:400 | |
Sox17 | R&D Systems, Inc. | AF1924 | 1:200 (Goat) |
Software | |||
Columbus Image Data Storage and Analysis system | PerkinElmer |