Abstract

Hepatic progenitor cells (HPCs) are small cells with a relative large oval nucleus and a scanty cytoplasm situated in the canals of Hering that express markers of (immature) hepatocytes and cholangiocytes. HPCs are present in large numbers in alcoholic steatohepatitis (ASH), one of the leading causes of chronic liver disease. To date, the mechanisms responsible for proliferation and differentiation of human HPCs are still poorly understood and the role of HPCs in ASH development is unknown. In this study, we aimed to characterise human HPCs and their interactions with other cells through comparison, on both protein and RNA level, of HPC-enriched cell populations from adult human liver tissue using different isolation methods. Fresh human liver tissue was collected from ASH explant livers and HPC-enriched cell populations were obtained via four different isolation methods: side population (SP), epithelial cell adhesion molecule (EpCAM) and trophoblast antigen 2 (TROP-2) membrane marker isolation and laser capture microdissection. Gene expression profiles of fluorescent-activated cell-sorted HPCs, whole liver extracts and laser microdissected HPC niches were determined by RNA-sequencing. Immunohistochemical evaluation of the isolated populations indicated the enrichment of HPCs in the SP, EpCAM+ and TROP-2+ cell populations. Pathway analysis of the transcription profiles of human HPCs showed an enrichment and activation of known HPC pathways like Wnt/β-catenin, TWEAK and HGF. Integration of the HPC niche profile suggests autocrine signalling by HPCs (TNFα, PDGFB and VEGFA) as well as paracrine signalling from the surrounding niche cells including MIF and IGF-1. In addition, we identified IL-17 A signalling as a potentially novel pathway in HPC biology. In conclusion, we provide the first RNA-seq-based, comparative transcriptome analysis of isolated human HPCs from ASH patients and revealed active signalling between HPCs and their surrounding niche cells in ASH livers and suggest that HPCs can actively contribute to liver inflammation.

Highlights

  • The adult human liver, as part of the gastrointestinal tract, has a high capacity to regenerate and to restore its liver mass after liver damage.[1]

  • Low expression of Trophoblast antigen 2 (TROP-2) was detected in cholangiocytes, while K19 was strongly expressed in these cells (Figure 1a)

  • The degree of ductular reaction, or the activation of hepatic progenitor cells (HPCs), in the different alcoholic steatohepatitis (ASH) samples, could be correlated with the percentage of TROP-2+ cells isolated by Fluorescent-activated cell sorting (FACS) (Figure 1e); the more activated HPCs, the higher the ductular reaction score, which resulted in higher amount of sorted TROP-2+ cells

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Summary

Introduction

The adult human liver, as part of the gastrointestinal tract, has a high capacity to regenerate and to restore its liver mass after liver damage.[1]. Trophoblast antigen 2 (TROP-2) is a relatively new epithelial marker and is expressed by activated progenitor cells in mouse models of liver disease.[11] TROP-2 is an epithelial membrane protein known as tumour-associated calcium signal transducer 2 (TACSTD2). It is the only other tacstd gene family member of TACSTD1, known as EpCAM.[12] During liver injury in murine models, HPCs (aka oval cells) start to express TROP-2 and can be used to isolate oval cells from animal models of liver disease.[11] TROP-2 expression in human HPCs has been described within our group.[13,14] To isolate human HPCs, TROP-2 expression and isolation potential has not been tested yet in alcoholic liver

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