Human Liver Fibroblasts

Generation and Characterization of Human Liver Fibroblast Induced Pluripotent Stem Cells

The human liver fibroblasts (HLFs) were isolated from a Combined hepatocellular-cholangiocarcinoma (cHCC-CC) patient. They were reprogrammed into pluripotent stem cells (HLF iPSCs) using retroviral transduction of four factors include - OCT4, SOX2, KLF4, and c-MYC (OSKM) (Fig. 1A). Human skin fibroblasts (HSFs) were also reprogrammed into iPSCs as a normal control (Con iPSCs). Both HLF and Con iPSC colonies expanded well with typical hESC-like morphology (Fig. 1B). The HLF iPSCs were free of mycoplasma contamination (Fig. 1C). Both types retained undifferentiated characteristics with strong alkaline phosphatase activity (Fig. 1D). The short tandem repeats profile of HLF iPSCs matched the original fibroblasts (Fig. 1E).

Real-time PCR showed higher mRNA expressions of pluripotency markers (OCT4, SOX2, NANOG, REX1) in Con iPSCs and HLF iPSCs compared to fibroblasts (Fig. 2A). Immunostaining confirmed high expression of pluripotent markers such as OCT4, TRA-1-60, NANOG, and SSEA4 proteins in both iPSC types (Fig. 2B).

In vitro, embryoid bodies enabled spontaneous differentiation of iPSCs into the three germ layers, as shown by markers for ectoderm (TUJ1), mesoderm (α-SMA), and endoderm (FOXA2) (Fig. 3A). In vivo, iPSCs induced teratomas containing ectoderm (pigment epithelium with melanocytes or neural rosettes), mesoderm (cartilage), and endoderm (gut-like epithelium), confirmed by haematoxylin and eosin staining (Fig. 3B). These findings indicate that HLF iPSCs maintain pluripotency both in vitro and in vivo, similar to Con iPSCs.

Fig. 1. Generation of HLF iPSCs. (A) iPSC generation using HLFs and HSFs with OSKM. (B) Morphology of control iPSCs and HLF iPSCs. (C) Mycoplasma test for HLF iPSCs. (D) Alkaline phosphatase activity in iPSCs. (E) STR profiling for HLFs and iPSCs (bar = 200 μm) (Ahn, H., Ryu, J., et al., 2022).

Fig. 2. Pluripotency markers in cHCC-CC-derived HLF iPSCs. (A) mRNA levels of OCT4, SOX2, NANOG, REX-1 in control and cHCC-CC patient fibroblasts and iPSCs. (B) Immunostaining of control and cHCC-CC patient-derived iPSCs for pluripotency markers (Ahn, H., Ryu, J., et al., 2022)

Fig. 3. Differentiation of cHCC-CC-derived HLF iPSCs. (A) In vitro differentiation into three germ layers via EB formation. (B) In vivo differentiation by teratoma formation, showing all germ layers (Ahn, H., Ryu, J., et al., 2022).

Myostatin activated human primary liver fibroblasts

Serum myostatin levels were increased with liver fibrosis progression in hepatocellular carcinoma patients who underwent liver resection (Fig. 4A). To clarify the impact of myostatin on liver fibrosis, Yoshio's team cultured human hepatic stellate cells (LX-2) and primary human liver fibroblasts (NF1-3) with recombinant myostatin and transforming growth factor beta (TGF-ß) in vitro. Addition of myostatin increased the expression of ACTA2, COLIAI, and TIMPI in LX-2 cells and primary human liver fibroblasts in a dosedependent manner, as well as TGFB1 (Fig. 4B). All three primary human liver fibroblast lines (NF1-3) were activated by myostatin or TGF-ß (Fig. 4C). Recently, IL-11 was identified as a crucial factor for cardiovascular fibrosis, pulmonary fibrosis, liver fibrosis, and liver steatosis.

Fig. 4. Myostatin activates liver fibroblasts. (A) Myostatin levels in HCC patients' serum across fibrosis stages 0-4. (B) ACTA2, COLIA1, and TIMP1 expression level of LX-2 cells and NF1-3 after treated with myostatin or TGF-β. (C) Comparison of stimulated vs. non-stimulated LX-2 and primary fibroblasts. (Yoshio, S., Shimagaki, T., et al., 2021)

iPSCs derived from human mesenchymal stem cells and human liver fibroblasts display similar proliferative characteristics and DNA damage response as hESC

iMSC and iLC2 were generated by retroviral transduction of Human mesenchymal stem cells (MSC) and Primary human liver fibroblasts (LC2). Both iLC2 and iMSC demonstrate classical iPSC features. Using flow cytometry to measure ROS levels, Fan's team found no significant differences between human embryonic stem cells (hESC lines: H1 and H9) and iPSC lines (iMSC and iLC2), but both showed a significant increase in ROS compared to parental MSC and LC2 cells (Fig. 5A). H1 and H9 cells had a lower mean number of foci per cell compared to LC2 and MSC (Fig. 5B and C). Importantly, iPSCs derived from MSC also showed low γH2AX foci similar to hESCs, significantly different from their parental cells (iMSC vs MSC, p = 0.001; iLC2 vs LC2, p = 0.002) (Fig. 5B and C). Both hESCs and iPSCs displayed a high percentage of cells in the S phase (48-55%), while parental cells (MSC and LC2) had a lower percentage (30-37%) (Fig. 5E). Although there were no significant differences in S phase percentages between H1 or H9 and iLC2, iMSC had a small but significant increase in S phase cells compared to H1 and H9 (Fig. 5E). In the G0/G1 phase, hESCs and iPSCs were significantly different from parental cells (MSC and LC2) , but there were no significant differences between H9 and iLC2. However, iMSC cells showed a significant decrease in G0/G1 phase cells compared to H1 and H9 (Fig. 5E).

Fig. 5. ROS levels, γH2AX expression, and cell cycle analysis in hESC, iPSC, and control cells. (A) ROS measured using H2DCFDA staining and flow cytometry. (B) γH2AX visualized by immunofluorescence. (C) Cell cycle analyzed using propidium iodide staining. (D) Cell cycle profile. (E) Percentage of live cells. (Fan, J., Robert, C., et al., 2011)