Congestion enriches intra-hepatic macrophages through reverse zonation of CXCL9 in liver sinusoidal endothelial cells
Background & Aims Congestion alters the microenvironment of the liver sinusoid along the portal-central axis.  We studied spatial changes in immune cells in the sinusoid which contribute to congestive fibrosis and portal hypertension (PHTN). Methods To visualize the distribution of immune cells in congestive hepatopathy (CH), we performed imaging mass cytometry (IMC) on liver tissue from patients with CH, Fontan-associated liver disease (FALD), and controls. We performed partial ligation of the inferior vena cava (pIVCL) to simulate CH in mice and isolated primary liver cells for single cell RNA-sequencing (scRNA-seq) to study zonation of liver sinusoidal endothelial cells (LSECs).  After pIVCL, mice were treated with intraperitoneal injections of AMG487, an inhibitor of the CXCL9 receptor. Results Peri-central macrophages are enriched in CH and FALD.  Given the role of CXCL9 in macrophage patterning in the liver, we performed RNA in situ hybridization (RNAish) in CH and determined that CXCL9 was highly expressed in LSECs in FALD, suggesting that LSECs recruit macrophages in CH. After pIVCL, treatment with AMG487 attenuated portal pressures, fibrosis, and intra-hepatic macrophages. To study changes in LSECs which promote macrophage chemotaxis, we performed scRNA-seq after pIVCL and sham procedures. Analysis revealed 3 LSEC subpopulations according to sinusoidal location. RNANish identified peri-central LSECs as the predominant source of CXCL9 in FALD. In vitro analyses revealed that ?-catenin and hypoxia inducible factor-1a regulate CXCL9 transcription in peri-central LSECs. Conclusions CXCL9 derived from peri-central LSECs enriches intra-hepatic macrophages in CH and FALD, contributing to congestive fibrosis and PHTN.  Strategies to target LSEC-derived CXCL9 may prevent the progression of CH and FALD. Overall design: Isolated primary cells from mice livers that underwent 6 weeks of partial Inferior Vena Cava ligation to induce portal hypertension and were subjected to Single Cell RNA sequencing.