Platelets Strongly Induce Hepatocyte Proliferation with IGF-1 and HGF In Vitro.
BACKGROUND
It is well known that platelets have a thrombotic effect. However, platelets play an important role not only in hemostasis but also in wound healing and tissue regeneration. Platelets have been reported to accumulate in the liver and promote liver regeneration after an extended hepatectomy, but the mechanism is unclear. The present study was designed to clarify the mechanism by which platelets have a direct proliferative effect on hepatocytes in vitro.


METHODS
Hepatocytes obtained from male BALB/c mice by collagenase digestion and immortalized hepatocytes (TLR2) were used. To elucidate the mechanism of the proliferative effect of platelets, DNA synthesis of hepatocytes was measured under various conditions and the related cellular signals were analyzed. Chromatographic analysis was also performed to clarify which elements of platelets have mitogenic activity.


RESULTS
DNA synthesis significantly increased in the hepatocytes cultured with platelets (P < 0.001). However, when the platelets and hepatocytes were separated, the platelets did not have a proliferative effect. Whole disrupted platelets, the supernatant fraction, and fresh isolated platelets had a similar proliferative effect, while the membrane fraction did not. After the addition of platelets, both Akt and extracellular signal-regulated kinases ERK1/2 were activated, but extracellular signal-regulated kinase STAT3 was not activated. Some mitogenic fractions were obtained from the platelet extracts by gel exclusion chromatography; the fractions were rich in hepatocyte growth factor and IGF-1.


CONCLUSIONS
Direct contact between platelets and hepatocytes was necessary for the proliferative effect. The direct contact initiated signal transduction involved in growth factor activation. Hepatocyte growth factor, vascular endothelial growth factor, and insulin-like growth factor-1, rather than platelet-derived growth factor, mainly contributed to hepatocyte proliferation.
Matsuo
Ryota
R
Department of Surgery, Advanced Biomedical Applications, Graduate School of Comprehensive Human Sciences, University of Tsukuba, Tsukuba, Japan.
Ohkohchi
Nobuhiro
N
Murata
Soichiro
S
Ikeda
Osamu
O
Nakano
Yoritaka
Y
Watanabe
Motonobu
M
Hisakura
Katsuji
K
Myronovych
Andriy
A
Kubota
Tomomi
T
Narimatsu
Hisashi
H
Ozaki
Michitaka
M
D000818:Animals; D001792:Blood Platelets / Q000166:cytology* / Q000378:metabolism; D002450:Cell Communication / Q000502:physiology*; D002455:Cell Division / Q000502:physiology; D002478:Cells, Cultured; D002850:Chromatography, Gel; D018920:Coculture Techniques; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D017228:Hepatocyte Growth Factor / Q000378:metabolism*; D022781:Hepatocytes / Q000166:cytology* / Q000378:metabolism; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D020935:MAP Kinase Signaling System / Q000502:physiology; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D050796:STAT3 Transcription Factor / Q000378:metabolism
D050796:STAT3 Transcription Factor; C494087:Stat3 protein, mouse; D017228:Hepatocyte Growth Factor; D007334:Insulin-Like Growth Factor I; D051057:Proto-Oncogene Proteins c-akt; D048049:Extracellular Signal-Regulated MAP Kinases