Plasminogen activator-plasmin system potentiates the proliferation of hepatocytes in primary culture.
OBJECTIVE
Liver regeneration after partial hepatectomy is thought to be regulated by various molecules including the components of the plasminogen activator (PA)-plasmin system. We have examined the role of fibrinolytic factors, i.e., tissue-type plasminogen activator (tPA) and urokinase-type plasminogen activator (uPA), and their substrate, plasminogen, in the proliferation of hepatocytes in primary culture.


METHODS
Hepatocyte and nonparenchymal liver cells were isolated from Wistar strain rat by a method perfusing the liver with collagenase. DNA synthesis was assessed by measuring the incorporation of [3H]-thymidine into cellular DNA fraction. tPA, uPA and type-1 plasminogen activator inhibitor (PAI-1) gene expressions were measured by Northern blotting. PA activity was measured by fibrin/agarose plate method.


RESULTS
Cellular density-dependent DNA synthesis was observed in the primary cultured hepatocytes; DNA synthesis was lower at high cell density (1.0 x 10(5) cells/cm(2)) than that at low cell density (0.2 x 10(5) cells/cm(2)). DNA synthesis in the hepatocytes cultured at a low cell density was increased by co-culture with nonparenchymal liver cells. Under these growth-stimulated culture conditions, tPA and uPA mRNAs were induced and up-regulated. On the contrary, the PAI-1 mRNA level was decreased under these conditions, and total PA activity was augmented accordingly. The synthetic plasmin inhibitor tranexamic acid, a competitive inhibitor for the plasmin molecule, and PASI-535, a plasmin active center-directed inhibitor, both suppressed hepatocyte proliferation in a dose-dependent fashion. Anti-plasmin antibody also suppressed hepatocyte proliferation.


CONCLUSIONS
The up-regulation of PA activity for ensuring plasmin activity should be an important mechanism in the proliferation of hepatocytes.
Akao
Makoto
M
Department of Nutrition and Physiology, Nihon University Graduate School of Applied Life Sciences, Kameino 1866, Fujisawa, Kanagawa 252-8510, Japan.
Hasebe
Yuichi
Y
Okumura
Nobuaki
N
Hagiwara
Hiromi
H
Seki
Taiichiro
T
Ariga
Toyohiko
T
D000818:Animals; D018929:Cell Culture Techniques; D002455:Cell Division; D004247:DNA / Q000096:biosynthesis; D005341:Fibrinolysin / Q000502:physiology*; D005786:Gene Expression Regulation; D022781:Hepatocytes / Q000166:cytology* / Q000187:drug effects; D008115:Liver Regeneration / Q000187:drug effects; D010958:Plasminogen / Q000502:physiology; D010960:Plasminogen Activators / Q000235:genetics / Q000502:physiology*; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D017208:Rats, Wistar; D010959:Tissue Plasminogen Activator / Q000235:genetics / Q000502:physiology; D014568:Urokinase-Type Plasminogen Activator / Q000235:genetics / Q000502:physiology
D012333:RNA, Messenger; D010958:Plasminogen; D004247:DNA; D010960:Plasminogen Activators; D010959:Tissue Plasminogen Activator; D005341:Fibrinolysin; D014568:Urokinase-Type Plasminogen Activator