Activation of human liver sinusoidal endothelial cell by human platelets induces hepatocyte proliferation

Background & Aims

We previously reported that platelets promote hepatocyte proliferation. In this study, we focused on the role of platelets in liver sinusoidal endothelial cells (LSECs) in addition to their role in hepatocyte in liver regeneration.

Methods

Immortalized human LSECs (TMNK-1) were used. The LSECs were co-cultured with human platelets, and the proliferation of LSECs and the excretion of growth factors and interleukin-6 (IL-6) were subsequently measured. The main factor from platelets which induced the excretion of IL-6 from LSECs was determined using inhibitors of each component contained in the platelets. The need for direct contact between platelets and LSECs was investigated using cell culture inserts. The proliferation of human primary hepatocytes was measured after the addition of the supernatant of LSECs cultured with or without platelets.

Results

The number of LSECs cocultured with platelets significantly increased. Excretion of IL-6 and vascular endothelial growth factor (VEGF) increased in LSECs with platelets. JTE-013, a specific antagonist for sphingosine 1-phosphate (S1P) 2 receptors, inhibited the excretion of IL-6 from LSECs after the addition of platelets. When the platelets and LSECs were separated by the cell culture insert, the excretion of IL-6 from LSECs was decreased. DNA synthesis was significantly increased in human primary hepatocytes cultured with the supernatant of LSECs with platelets.

Conclusions

Platelets promote LSEC proliferation and induce IL-6 and VEGF production. Direct contact between the platelets and LSECs and S1P, that are contained in platelets, were involved in the excretion of IL-6 from LSECs. IL-6 from LSECs induced proliferation of parenchymal hepatocytes.

Abbreviations: LSECs, liver sinusoidal endothelial cells, IL-6, interleukin-6, VEGF, vascular endothelial growth factor, S1P, sphingosine 1-phosphate, HGF, hepatocyte growth factor, EGF, epidermal growth factor, PDGF, platelet-derived growth factor, STAT3, signal transducer and activator of transcription 3, ERK1/2, extracellular signal-regulated protein kinase 1/2, NO, nitric oxide, IGF-1, insulin-like growth factor 1, I/R, ischemia/reperfusion, PRP, Platelet-rich plasma, ACD, acid citrate dextrose, HSA, human serum albumin, ANOVA, analysis of variance

Keywords: Liver regeneration, Liver non-parenchymal cell, Growth factor, Interleukin-6, Sphingosine 1-phosphate