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Background: Hepatocyte growth factor (HGF), a potent mitogen for hepatocytes, enhances hepatocyte function without stimulating proliferation, depending on the physiological conditions. p53, a transcription factor, suppresses the cell proliferation by expressing p21WAF1/CIP1 in various tissues. Aim: To investigate the mechanism through which the hepatocytes maintain mitotically quiescent even in the presence of HGF. Methods: We studied the relationship between p53 and p21 expression and the effect of p53-p21 axis on hepatocyte proliferation in primary cultured rat hepatocytes stimulated by HGF. Hepatic p21 levels are determined serially after partial hepatectomy or sham operation in rats. Results: DNA synthesis was markedly increased by HGF addition in rat hepatocytes cultured at low density but not at high density. Cellular p53 levels increased in the hepatocytes cultured at both the densities. p21 levels were increased and correlated with cellular p53 levels in hepatocytes cultured at high density but not at low density. When the activity of p53 was suppressed by a chemical inhibitor for p53, cellular p21 levels were reduced, and DNA synthesis was increased. Similarly, p21 antisense oligonucleotide increased the DNA synthesis. In rats after partial hepatectomy, transient elevation of hepatic p21 levels was observed. In contrast, in sham-operated rats, hepatic p21 levels were increased on sustained time scales. Conclusion: p53-related induction of p21 may suppress hepatocyte proliferation in the presence of HGF in the setting that mitogenic activity of HGF is not elicitable. [ABSTRACT FROM AUTHOR]

Liver regeneration is considered to be retarded or suppressed in patients with acute liver failure. However, the mechanisms for this suppression remain to be elucidated. In order to evaluate deficiencies in liver regeneration in patients with acute liver failure, we focused on the cross-communication of growth-associated factors in experimental models. In primary cultured rat hepatocytes, the levels of cellular p53 and transforming growth factor-alpha (TGF-alpha), as well as DNA synthesis increased by the addition of hepatocyte growth factor (HGF). When p53 activity was suppressed, TGF-alpha expression and DNA synthesis were reduced. DNA synthesis was also reduced when TGF-alpha activity was suppressed. In rats after partial hepatectomy, hepatic HGF and p53 protein levels increased, followed by an increase of hepatic TGF-alpha levels and hepatocyte proliferation. Circulating levels of HGF and TGF-alpha correlated with changes in the hepatic levels. The suppression of TGF-alpha activity reduced the proliferation of hepatocytes in these rats. In patients suffering from acute hepatitis, serum HGF levels increased followed by an increase of serum TGF-alpha levels. In contrast, in patients with acute liver failure, the increase of serum TGF-alpha levels was suppressed depending on the severity of hepatic failure, even though serum HGF levels markedly increased. The patients' hepatic levels were consistent with serum levels. Cross-communication of growth associated factors may be important in the progression of liver regeneration, and impaired regenerative capacity in patients with acute liver failure may be attributable, at least in part, to a disruption of communication of growth-associated factors. [ABSTRACT FROM AUTHOR]

Abstract: Branched chain amino acids modulate various cellular functions in addition to providing substrates for the production of proteins. We examined the mechanism underlying the stimulation by leucine of hepatocyte growth factor (HGF) production by hepatic stellate cells. Both p70 S6 kinase activity and phosphorylation of eukaryotic initiation factor 4E-binding protein 1 (4E-BP1) were up-regulated rapidly after leucine treatment of a rat hepatic stellate cell clone. No such activation was observed following treatment with valine or isoleucine. Rapamycin, an inhibitor of mammalian target of rapamycin (mTOR), suppressed leucine-induced activation of p70 S6 kinase and 4E-BP1 and negated the stimulatory effect of leucine on HGF production. An mTOR-dependent signaling pathway mediates the stimulatory effect of leucine on the production of HGF by hepatic stellate cells. [Copyright &y& Elsevier]

Abstract: Although the functions associated with differentiation are thought to be suppressed when cells proliferate, recent studies have shown that several mitogens can stimulate functions such as protein production under certain physiological conditions. Hepatocyte growth factor (HGF) is now considered to be a pluripotent factor and has been shown to stimulate the differentiated functions of hepatocytes, as well as their proliferation. The use of HGF for the treatment of liver disease, especially hepatic failure, has been suggested. Because patients with decompensated liver cirrhosis have decreased plasma concentrations of branched-chain amino acids (BCAAs), many investigations in laboratory animals and patients have been designed to demonstrate the benefits of supplementation of BCAAs on the hepatic metabolism of proteins. However, the mechanisms involved in the specific actions of BCAAs remain to be elucidated. Amino acids are molecules that modulate numerous cellular functions. BCAAs are known to influence gene expression, cellular metabolism, amino acid transport, and protein turnover. In this paper, we show the potential of BCAAs for stimulating HGF synthesis in the liver and discuss the possibility that BCAAs stimulate protein production by hepatocytes through the induction of HGF. [Copyright &y& Elsevier]

Brief periods of tissue ischemia produced tissue resistance to prolonged ischemia and reperfusion, a phenomenon called ischemic preconditioning. The mechanisms of ischemic preconditioning were examined in a rat warm ischemia–reperfusion model as well as the effect of ischemic preconditioning on liver regeneration. Ischemic preconditioning decreased liver injury after warm ischemia–reperfusion, which was reversed by Kupffer cell depletion. Ischemic preconditioning stimulated Kupffer cells to produce reactive oxygen species. Scavengers of reactive oxygen species reversed the effect of ischemic preconditioning, and pretreatment with sublethal dose of hydrogen peroxide mimicked ischemic preconditioning effect. Rat livers were preconditioned by ischemia and subjected to 70% partial hepatectomy. Liver regeneration was then evaluated serially. Ischemic preconditioning promoted liver regeneration, which was reversed by adenosine A2 receptor antagonism and mimicked by adenosine A2 receptor agonism. Promotion of liver regeneration by ischemic preconditioning and adenosine A2 receptor agonism were reversed by Kupffer cell depletion. In conclusion, ischemic preconditioning stimulates Kupffer cells to produce reactive oxygen species, leading to hepatocyte protection against warm ischemia–reperfusion injury; and ischemic preconditioning promoted liver regeneration via adenosine A2 receptor pathway in Kupffer cells. [ABSTRACT FROM AUTHOR]

Using a rat myofibroblast-like hepatic stellate cell line, we studied the actomyosin-based cytoskeletal actions mediated by Rho-kinase and/or myosin light chain kinase (MLCK). Calmodulin/MLCK inhibitors W-7 and ML-7 attenuated cell migration dose-relatedly at concentrations from 10−6 to 10−4 M and collagen gel-contraction by the cells at 10−4 M, respectively. Rho-kinase inhibitors Y-27632 and HA1077 attenuated the gel-contraction at concentrations from 10−6 to 10−4 M, respectively. These Rho-kinase inhibitors attenuated cell migration at 10−7 M but enhanced the migration at 10−4 M, respectively. They altered cell morphology showing prominent peripheral actin bundles and sparse central stress fibers, in comparison with the calmodulin/MLCK inhibitors. Both ML-7 and Y-27632 attenuated phosphorylation of myosin regulatory light chain and cell attachment to extracellular substrate. ML-7 attenuated the activation of GTP-binding protein Rac, while Y-27632 did not. These findings suggest that the actomyosin-based cytoskeletal actions can be functionally diverse depending on the Rho-kinase-mediated pathway and the MLCK-mediated pathway. [Copyright &y& Elsevier]