EREG-secreting THBS1(+) tissue monocytes are recruited by C5a to promote rapid liver regeneration in patients and mice during the ALPPS procedure.

BACKGROUND: Associating liver partition and portal vein ligation for staged hepatectomy (ALPPS) is an important surgical treatment for unresectable liver tumors, while with its mechanism remaining unclear. We aim to comprehensively examine the key immune cells that induce the rapid liver regeneration during the ALPPS procedure and unearth the relevant mechanism(s) in patients with hepatocellular carcinoma (HCC). METHODS: Matched ALPPS stage I and II liver tissues were collected from five HCC patients and subjected to cytometry by time-of-flight (CyTOF) and single-cell RNA sequencing (scRNA-seq) analysis. Peripheral blood samples were collected during subsequent routine clinical examinations to explore the dynamic changes in circulating immune cells and cytokines. The changes in the transcription profiles of liver tissues between ALPPS stage I and II were explored by bulk RNA-seq analysis. Tissue microarrays containing paired tissues from another 22 HCC patients who underwent ALPPS were constructed for validation. RESULTS: The CyTOF data revealed an increase in tissue monocytes during the ALPPS-induced liver regeneration (from 13.36% to 29.78%, P=0.04). There was also a shift from a macrophage-enriched to monocyte-enriched local immune environment in the remnant liver tissues induced by ALPPS. The scRNA-seq analysis identified that a cluster of THBS1(+) tissue monocytes was significantly enriched in the regenerated liver tissues in all three patients, with high expression of epiregulin (EREG). Further analysis indicated that THBS1(+) tissue monocytes promote hepatocyte proliferation via EREG-epidermal growth factor receptor (EGFR) interactions. The secretion of C5a by hepatocytes could recruit THBS1(+) tissue monocytes via the C5a/C5aR1 interaction. The functions of EREG and C5a have been verified in vitro and in vivo. CONCLUSIONS: The ALPPS procedure induced activation of the complement system in hepatocytes, specifically increasing the expression of C5a, which led to the recruitment of THBS1(+) tissue monocytes through the C5a/C5aR1 interaction. These monocytes then secrete EREG to promote hepatocyte proliferation in the residual liver.