Expression of hepatic progenitor cell markers in acute cellular rejection of liver allografts-An immunohistochemical study

Extracellular microparticles derived from hepatic progenitor cells deliver a death signal to hepatoma-initiating cells

The malignant transformation of normal resident hepatic stem/progenitor cells has a critical role in hepatocarcinogenesis and the recurrence of hepatocellular carcinoma (HCC). We defined such hepatic progenitor cells as hepatoma-initiating cells. An efficient strategy is required to target and kill the hepatoma-initiating cells. We isolated extracellular microparticles (MPs) derived from apoptotic hepatic progenitor cells (HPCs) and tested their ability to inhibit hepatocarcinogenesis. Extracellular MPs were isolated from HPCs, hepatocytes and liver tumor cells. Their effects on tumor growth were investigated in rat primary HCC models, in which hepatocarcinogenesis is induced by diethylnitrosamine (DEN). The extracellular MPs derived from apoptotic HPCs, apoptotic hepatocytes and apoptotic liver tumor cells were similar in morphology, diameter and zeta potential. However, they had different antitumor effects. In DEN-exposed rats, only the MPs derived from apoptotic HPCs effectively inhibit hepatocarcinogenesis. In vitro and in vivo analyses confirmed that HPCs preferentially take up MPs derived from apoptotic HPCs compared to MPs from other liver cell types. Proteomic analysis of MPs from apoptotic HPCs showed enrichment of proteins involved in cell death pathways. Thus, HPC-derived MPs contain a death signal to induce the killing of hepatoma-initiating cells. Our findings provide evidence that a death signal encapsulated in HPC-derived extracellular microparticles can efficiently clear hepatoma-initiating cells and prevent hepatocarcinogenesis.

Graphical Abstract

Hepatic progenitor cell activation is induced by the depletion of the gut microbiome in mice

The homeostasis of the gut microbiome is crucial for human health and for liver function. However, it has not been established whether the gut microbiome influence hepatic progenitor cells (HPCs). HPCs are capable of self‐renewal and differentiate into hepatocytes and cholangiocytes; however, HPCs are normally quiescent and are rare in adults. After sustained liver damage, a ductular reaction occurs, and the number of HPCs is substantially increased. Here, we administered five broad‐spectrum antibiotics for 14 days to deplete the gut microbiomes of male C57BL/6 mice, and we measured the plasma aminotransferases and other biochemical indices. The expression levels of two HPC markers, SRY‐related high mobility group‐box gene 9 (Sox9) and cytokeratin (CK), were also measured. The plasma aminotransferase activities were not affected, but the triglyceride, lactate dehydrogenase, low‐density lipoprotein, and high‐density lipoprotein concentrations were significantly altered; this suggests that liver function is affected by the composition of the gut microbiome. The mRNA expression of Sox9 was significantly higher in the treated mice than it was in the control mice (p < 0.0001), and a substantial expression of Sox9 and CK was observed around the bile ducts. The mRNA expression levels of proinflammatory factors (interleukin [IL]‐1β, IL‐6, tumor necrosis factor [TNF]‐α, and TNF‐like weak inducer of apoptosis [Tweak]) were also significantly higher in the antibiotic‐treated mice than the levels in the control mice. These data imply that the depletion of the gut microbiome leads to liver damage, negatively impacts the hepatic metabolism and function, and activates HPCs. However, the underlying mechanisms remain to be determined.