The identification of a key set of transcription factors has enabled scientists to generate functional mouse hepatocytes directly from fibroblasts. The resulting cells showed typical epithelial morphology, expressed hepatic genes, and acquired hepatocyte function. When transplanted into mouse models of liver injury the cells repopulated the damaged organs, restored liver function, and prevented death in nearly half the animals.
The research, led by a team at the Shanghai Institutes for Biological Sciences, Chinese Academy for Sciences in Shanghai, is published in Nature. The paper is titled “Induction of functional hepatocyte-like cells from mouse fibroblasts by defined factors.”
Rather than take the iPSC route to generating hepatocytes from adult cells, the Shanghai Institutes work focused on identifying the key factors required for converting fibroblasts into hepatocyes. By testing combinations of factors, they were able to directly induce the development of functional hepatocyte-like cells from mouse fibroblasts by the transduction of Gata4, Hnf1α, and Foxa3 as well as the inactivation of p19Arf.
Analysis of the resulting cell colonies confirmed that they showed similar expression patterns of hepatic genes and fibrotic genes. Importantly, the researchers note, cytochrome P450 (CYP) enzymes specific to mature hepatocytes were detectable in iHep cells, “suggesting that hepatic conversion undertakes a process without reversion to progenitors.”
The authors then tested the cells as transplants in mouse models of liver injury. While all untreated animals showed weight loss and died within seven weeks, five of twelve animals transplanted with the induced hepatocytes were still alive after eight weeks and showed increased body weight. In contrast with the control mice, the treated animals‘ livers looked normal, and the transplanted hepatocytes had replicated and comprised 5% to 80% of the liver hepatocytes in the surviving animals.
Comparing the livers of animals treated with either the induced hepatocytes or with primary hepatocytes, the researchers found that both types of cell expressed albumin and other hepatic genes at comparable levels. Encouragingly, their induced cells showed no propensity to generate tumors.
The researchers suggest that Gata4 and Foxa3 likely act as ‘pioneer factors’ to trigger a global chromatin modification during hepatic conversion, whereas Hnf1α probably stabilizes hepatic gene expression. Generating proliferative hepatic cells also required the inactivation of p19Arf, which is a key component of the cellular senescence pathway that inhibits induced pluripotent stem cell reprograming. It would be of interest to determine whether inactivating other components of this pathway could also be used to facilitate hepatic conversion, the team notes.
The authors conclude that their achievement supports the general principal that cell lineages can be converted by regulating the transcriptional network. “To our knowledge, this is the first time that adult fibroblasts have been directly converted to functional induced hepatocyte cells,” they add. “Thus, induced hepatocyte cells represent an alternative source of hepatocytes for disease modeling, transplantation, and tissue engineering.
"To apply this approach for the purpose of regenerative medicine, future studies will need to address whether human fibroblasts and other cell types could be successfully converted to functional induced hepatocyte cells.”