Platelet Interactions with Liver Sinusoidal Endothelial Cells and Hepatic Stellate Cells Lead to Hepatocyte Proliferation

Jeremy Meyer,Carmen Gonelle-Gispert,Léo Bühler,Simon C Robson,Philippe Morel,Karin Sadoul,Alexandre Balaphas,Pierre Fontana

doi:10.3390/cells9051243

Abstract

(1) Background: Platelets were postulated to constitute the trigger of liver regeneration. The aim of this study was to dissect the cellular interactions between the various liver cells involved in liver regeneration and to clarify the role of platelets. (2) Methods: Primary mouse liver sinusoidal endothelial cells (LSECs) were co-incubated with increasing numbers of resting platelets, activated platelets, or platelet releasates. Alterations in the secretion of growth factors were measured. The active fractions of platelet releasates were characterized and their effects on hepatocyte proliferation assessed. Finally, conditioned media of LSECs exposed to platelets were added to primary hepatic stellate cells (HSCs). Secretion of hepatocyte growth factor (HGF) and hepatocyte proliferation were measured. After partial hepatectomy in mice, platelet and liver sinusoidal endothelial cell (LSEC) interactions were analyzed in vivo by confocal microscopy, and interleukin-6 (IL-6) and HGF levels were determined. (3) Results: Co-incubation of increasing numbers of platelets with LSECs resulted in enhanced IL-6 secretion by LSECs. The effect was mediated by the platelet releasate, notably a thermolabile soluble factor with a molecular weight over 100 kDa. The conditioned medium of LSECs exposed to platelets did not increase proliferation of primary hepatocytes when compared to LSECs alone but stimulated hepatocyte growth factor (HGF) secretion by HSCs, which led to hepatocyte proliferation. Following partial hepatectomy, in vivo adhesion of platelets to LSECs was significantly increased when compared to sham-operated mice. Clopidogrel inhibited HGF secretion after partial hepatectomy. (4) Conclusion: Our findings indicate that platelets interact with LSECs after partial hepatectomy and activate them to release a large molecule of protein nature, which constitutes the initial trigger for liver regeneration.

Highlights

Acute liver failure is a medical emergency, which develops when liver function does not meet physiological requirements due to a critical loss of functional mass
Epidermal growth factor (EGF) was released by liver sinusoidal endothelial cells (LSECs), but this secretion was not modulated by platelets (Figure 1D,E)
Several factors, such as sphingosine-1-phosphate, angiopoietin-1, SDF-1α, vascular endothelial growth factor (VEGF), extracellular matrix protein-1, thrombospondin-1, and platelet-derived growth factor (PDGF) were assessed for their effects on IL-6 secretion from LSECs. These factors did not induce IL-6 secretion from LSECs. These results suggest that the active molecule released by platelets and able to induce IL-6 secretion by LSECs may be a protein with a molecular weight above 100 kDa or, alternatively, a smaller molecule associated with a co-factor of a molecular weight > 100 kDa

Summary

Introduction

Acute liver failure is a medical emergency, which develops when liver function does not meet physiological requirements due to a critical loss of functional mass This life-threatening syndrome occurs following drug toxicity, viral hepatitis, major liver resections, or small-for-size liver transplantation [1]. Techniques to prevent surgery-related liver failure in high-risk patients are mainly based on taking into account comorbid conditions, on limiting the extent of surgery, and on increasing the volume of the future remnant liver [2]. Despite these precautions, many patients, those with liver cirrhosis, cannot benefit from liver resection as a therapeutic procedure. It is of main interest to understand how liver regeneration is regulated and what molecular factors stimulate the regenerative process

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