We would like to present you the abstract of The Coins 2017 keynote speaker Aras N. Mattis3,5, who worked with Cristina Esteva Font3, Caroline Duwaerts2, Jacquelyn J. Maher2,5, and Holger Willenbring1,4,5 in University of California San Francisco on liver metabolism.
1Eli and Edythe Broad Center for Regeneration Medicine and Stem Cell Research
2Department of Medicine/Gastroenterology
3Department of Pathology
4Department of Surgery, Division of Transplantation
Patient iPSC-Derived Hepatocytes Recapitulate NAFLD in vitro
With the rising obesity epidemic, non-alcoholic fatty liver disease (NAFLD) is increasing in prevalence affecting nearly 30% of the US population. Ten to twenty percent of NAFLD patients go on to develop non-alcoholic steatohepatitis (NASH), which progresses from hepatic inflammation to fibrosis/cirrhosis and puts patients at risk for hepatocarcinogenesis. In accord with a genetic predisposition for NAFLD/NASH, families exist in which the incidence of the disease is significantly increased. Here we generated induced pluripotent stem cell-derived hepatocytes (iPSC-Heps) from several members of such a family to investigate hepatocyte-specific disease mechanisms. Specifically, we tested the hypothesis that hepatocytes from NAFLD/NASH patients are susceptible to fatty acid-induced toxicity. For this, we obtained fibroblasts by skin punch biopsy and generated 3 iPSC lines per patient using non-integrating episomal vectors expressing the Yamanaka factors.
We tested and found that these patients were negative for the patatin-like phospholipase domain containing 3 protein (PNPLA3) I148M variant that is known to predispose to NAFLD. After differentiating the iPSCs into iPSC-Heps, we challenged them with increasing concentrations of unsaturated and saturated fatty acids oleate and palmitate respectively. We found increased steatosis and cell death in palmitate-treated NAFLD/NASH iPSC-Heps as compared to controls matched in gender and ethnicity. As a potential explanation for the observed phenotype, RNA-Seq of unchallenged iHeps revealed increased expression of sterol regulatory element-binding protein 1c (SREBP-1c) in NAFLD/NASH iPSC-Heps, a master regulator driving de novo lipogenesis.
Further analysis revealed elevated levels of the activating sterol regulatory element-binding protein chaperone (SCAP) and decreased levels of the SREBP-1c repressor insulin induced gene 2 (INSIG2) in these cells. As both mouse models and human tissue samples have shown increased endoplasmic reticulum (ER) stress in NAFLD/NASH, we surveyed stress response pathways and found increased levels of phosphorylated c-Jun N-terminal kinase (JNK) and eukaryotic initiation factor 2α (eIF2α).
Collectively, our findings suggest that hepatocytes within this NAFLD family are primed for de novo lipogenesis with increased baseline JNK and eIF2 α. Increased steatosis and hyperactive stress response drives increased cell death as a potential mechanism of NASH initiation and progression to inflammation and fibrosis. Moreover, our findings highlight the potential of our patient-specific disease model for elucidating the complex molecular mechanisms that induce and promote NAFLD/NASH.