Human umbilical cord-derived mesenchymal stem cells affect urea synthesis and the cell apoptosis of human induced hepatocytes by secreting IL-6 in a serum-free co-culture system.

Background: Bioartificial livers (BALs) are emerging as a potential supportive therapy for liver diseases. However, the maintenance of hepatocyte function and viability in vitro is a major challenge. Mesenchymal stem cells (MSCs) have attracted extensive attention for providing trophic support to hepatocytes, but only few studies have explored the interaction between human MSCs and human hepatocytes, and very little is known about the underlying molecular mechanisms whereby MSCs affect hepatocyte function, especially in serum-free medium (SFM).

Method And Results: This study aims to explore the effects of human umbilical cord-derived MSCs (hUMSCs) on human-induced hepatocytes (hiHeps) function and viability, and know about the underlying molecular mechanism of interaction in SFM. The liver-specific function of hiHeps was evaluated by analysis of albumin secretion, urea synthesis, and metabolic enzyme activity. hiHeps apoptosis was mainly characterized by live/dead staining assay, JC-1 mitochondrial membrane potential assay, reactive oxygen species (ROS) generation, and cell apoptosis detection. The expression of related genes and proteins were measured by qRT-PCR and western blotting. The results indicate that co-culture with hUMSCs improved hiHep urea synthesis and reduced cell apoptosis compared to monoculture in SFM, and this effect was found to be mediated by secreted interleukin-6 (IL-6). Further, studies revealed that IL-6 reduced hiHep apoptosis via the activation of the JAK-Stat3-Ref-1 and JAK-Stat3-Bcl-2/Bax-Caspase3 pathways by binding to the IL-6 receptor. IL-6 also enhanced hiHep urea synthesis through the JAK-Akt-P53-ARG1 pathway. Finally, hiHep-specific functions were further prolonged and increased when co-cultured with hUMSCs on 3D polyethylene terephthalate (PET) fibrous scaffolds.

Conclusion: The SFM co-culture strategy showed major advantages in maintaining hiHep function and viability in vitro, which is of great significance for the clinical application of hiHeps in BALs.