Ly6C⁺ Inflammatory Monocytes Are Extrahepatic Precursors of Hepatic Stellate Cells in Liver Injury.

It has been known that hepatic stellate cells (HpSCs) play an important role in the development of liver fibrosis. We previously reported that the HpSCs are hematopoietic origin in carbon tetrachloride (CCl₄)-induced liver injury. However, the differentiation pathway from hematopoietic stem cells to HpSCs remains largely unknown. In this study, we tried to elucidate the ability of terminally differentiated cells to transdifferentiate into HpSCs.

Male enhanced green fluorescent protein (EGFP)-transgenic mice 10–12 weeks old were used as bone marrow and spleen donors. Bone marrow mononuclear cells were incubated with purified anti-CD45R/B220, anti-CD4, anti-CD8, anti-Ly6G, anti-TER119, anti-c-kit, anti-Sca-1, anti-Thy-1.2, anti-IL-7 receptor α chain, and immunomagnetic beads. The resulting lineage negative cells were stained with anti-Ly6C, anti-c-kit, and anti-CD45.2. CD45.2⁺Ly6C^lowc-kit⁺ cells (monocytic precursors), CD45.2⁺Ly6C^highc-kit⁻ cells (mature monocytes), FSC^lowSSC^high CD45.2⁺ cells (eosinophils) were enriched by FACSAria. Ly6G⁺ cells (neutrophils), CD45R/B220⁺ cells (B cells) and CD3ε⁺ cells (T cells) were isolated from bone marrow or spleen using magnetic cell sorter device. We transferred these isolated cells into CCl₄-injured mice twice a week for two weeks, and analyzed the presence of EGFP⁺ HpSCs in the injured liver using immunofluorescence and laser confocal scanning microscopy.

Total number of transfused monocytic precursors, mature monocytes, eosinophils, neutrophils, B cells, and T cells per mouse was 1.1 × 10⁶, 6.4 × 10⁶, 4.8 × 10⁶, 22.0 × 10⁶, 29.0 × 10⁶, and 12.5 × 10⁶, respectively. Intravenous infusion of each type of cell showed their ability to localize to the injured liver. In the liver of mice, which were given eosinophils, neutrophils, B cells, and T cells, EGFP⁺ cells were all positive for CD45. However, in the liver of mice, which received monocyte precursors and mature monocytes, 20% and 39% of EGFP⁺ cells were negative for CD45. Vimentin and ADAMTS13 are identified in HpSCs but not hematopoietic cells. About 18% of EGFP⁺ cells in the liver of mice, which received monocytic precursors, were positive for both antigens. In the liver of mice, which received mature monocytes, 35% and 27% of EGFP⁺ cells were positive for vimentin and ADAMTS13, respectively.

Both Ly6C^lowc-kit⁺ monocytic precursors and Ly6C^highc-kit⁻ mature monocytes can give rise to HpSCs in CCl₄-injured liver.

No relevant conflicts of interest to declare.