IL-22 supports long-term expansion of mouse and human hepatocytes

Although the liver exhibits remarkable regenerative capacity, expanding hepatocytes in large quantities in vitro without compromising their function remains challenging, presumably due to the absence of key environmental signals. Identifying factors that enable long-term in vitro expansion of hepatocytes is essential for advancing liver research.

Mouse models of hepatectomy and hepatocyte transplantation were used to identify cytokines involved in liver regeneration. Mouse and human hepatocytes were cultured and passaged in IL-22 medium to assess their expansion ability. Genetic lineage tracing was applied to track the origin of the expanding cells. The function of expanded hepatocytes was evaluated by transplantation into Fah^-/- mice. The mechanism of IL-22-mediated proliferation was investigated via transcriptomic analysis and lineage-specific gene deletion.

We discovered that IL-22 supports long-term expansion (>30 passages, with a theoretical expansion of ∼10³⁰ times within ∼150 days) of mouse hepatocytes in vitro by dedifferentiating hepatocytes into hepatocyte progenitor cells (HPCs), which retain the capacity to differentiate into mature hepatocytes. The Stat3 pathway is essential in this process. Two key transcription factors downstream of Stat3, Bhlha15 and Arntl2, govern IL-22-induced hepatic dedifferentiation. Expression of these two transcription factors directly initiates the dedifferentiation of hepatocytes into HPCs, which could subsequently be expanded long term without IL-22 supplementation. IL-22 also promoted the growth of human hepatocytes under simple culture conditions; within 30 days, human hepatocytes expanded more than 10,000-fold via dedifferentiation into HPCs that retained maturation capacity.

IL-22 enables large-scale expansion of both mouse and human hepatocytes in vitro by activating the Stat3-Bhlha15/Arntl2 axis. Our discoveries may support future utilization of IL-22 in liver/hepatocyte-related clinical applications.

Hepatocytes have wide applications in drug development, disease modeling, and cell therapy. However, expanding hepatocytes in large quantities in vitro without compromising their function remains a significant challenge. We demonstrate that IL-22, a unique cytokine primarily mediating localized epithelial repair and cytoprotection without inducing systemic immune activation, enables large-scale expansion of both mouse and human hepatocytes in vitro by activating the Stat3-Bhlha15/Arntl2 axis. Our findings not only bridge the gap between liver regeneration in vivo and hepatocyte growth in vitro, but also support the future utilization of IL-22 in liver/hepatocyte-related clinical applications.