During chronic liver injury, inflammation leads to liver fibrosis— particularly due to the activation of hepatic stellate cells (HSCs). However, the involvement of inflammatory cytokines in HSC activation and the relationship among different liver cells is unclear. To examine their interactions, many in vitro liver models are performed in organoid or spheroid culture with random 3D structure, complicating analysis. Herein, we demonstrated the hierarchical coculture of primary rat hepatocytes with non-parenchymal cells such as the human-derived HSC line (LX-2) and liver sinusoidal endothelial cell line (TMNK-1). The cocultured tissue had high usability with simple operation of separating solid and liquid phases with improved liver functions such as albumin production and hepatic cytochrome P450 3A4 activity. We also studied the effects of stimulation by both oxygen tension and the key pro-fibrogenic cytokine, transforming growth factor beta (TGF-β), on HSC activation. Gene expression analysis revealed that lower oxygen tension and TGF-β1 stimulation enhanced collagen type I and alpha-smooth muscle actin expression from LX-2 cells in the hierarchical coculture. Therefore, this hierarchical in vitro cocultured liver tissue could provide an improved platform as a disease model for elucidating the interactions of various liver cell types and biochemical signals in future liver fibrogenesis studies.

Background: Idiopathic pulmonary fibrosis (IPF) is a fatal lung disease of unknown origin, with a median survival time of ~3 years after diagnosis without anti-fibrotic therapy. It is characterized by progressive fibrosis indicated by increased collagen deposition and high numbers of fibroblasts in the lung. It was demonstrated that CCL18 induces collagen and αSMA synthesis in fibroblasts. We aimed to identify the CCL18 receptor responsible for its pro-fibrotic activities. Methods: We used a random phage display library to screen for potential CCL18-binding peptides, demonstrated its expression in human lungs and fibroblast lines by PCR and immunostaining and verified its function in cell lines. Results: We identified CCR6 (CD196) as a CCL18 receptor and found its expression in fibrotic lung tissue and on lung fibroblast lines derived from fibrotic lungs but it is almost absent in control lines and tissue. CCL18 induces receptor-internalization in a CCR6-overexpressing cell line. CCR6 blockade in primary human lung fibroblasts reduces CCL18-induced FGF2 release as well as collagen-1 and αSMA expression. Knock-down of CCR6 in a mouse fibroblast cell line abolishes the induction of collagen and -smooth muscle actin expression. Conclusion: Our data indicate that CCL18 triggers pro-fibrotic processes via CCR6, highlighting its role in fibrogenesis.