Direct contact between iPSC-derived macrophages and hepatocytes drives reciprocal acquisition of Kupffer cell identity and hepatocyte maturation
As the resident tissue macrophage of the liver, Kupffer Cells (KC) play an important role in homeostasis and tissue support. However, current in-vitro liver models often ignore the contribution of these KCs toward the proper response and function of the tissue. This is especially relevant when we consider the implications of immune-mediated drug injuries. To address this issue, we developed an isogenic co-culture system utilizing iPSC-derived macrophages (iMacs) and hepatocytes (iHeps). Directly co-culturing iHeps with iMacs improved the differentiation and maturation of the iHeps, with significant downregulation of fetal hepatocyte markers as well as upregulation of cytochrome genes. Furthermore, the co-culture also imparted stronger KC identity to the iMacs in a contact-dependent manner, with iMacs cultured in iHep conditioned media alone showing weaker expression of key KC markers. Finally, challenging the iHep-iMac co-culture system with 7 paradigm hepatotoxic compounds showed dose-dependent cytokine response in the 5 compounds associated with immune-mediated liver injuries, while no significant changes were observed in the 2 compounds with no reported immune-dependent complications. This effect was also not recapitulated when the co-culture was instead performed with human peripheral blood monocyte-derived macrophages, suggesting that iMacs are essential for liver toxicity response. Taken together, our study shows not only the importance of macrophages in tissue systems, but also that the source of macrophages is critical to the development of accurate in-vitro human models. Overall design: IMR90-iPSCs were differentiated into iPSC-hepatocytes and iPSC-macrophages. 2 x 10^5 iMacs or monocyte-derived macrophages were added to 5 x 10^5 iHeps during a full media change (4ml) per well of a 6 well plate on Day 0. 50ng/ml of CSF-1 was added to each well. The cells were cultured for 7 days, with a half-media change (2ml) on Day 4. The cells were collected by digesting with Accutase.