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PubMed1992

Growth-dependent inhibition of CCAAT enhancer-binding protein (C/EBP alpha) gene expression during hepatocyte proliferation in the regenerating liver and in culture.

As an approach to understanding physiological mechanisms that control the proliferation of highly differentiated cells, we are addressing whether certain hepatic transcription factors participate in mechanisms that control the growth of hepatocytes. We have focused on CCAAT enhancer-binding protein (C/EBP alpha), a transcription factor which is highly abundant in normal liver and is considered to regulate expression of many genes, including some involved in energy metabolism (S. L. McKnight, M. D. Lane, and S. Gluecksohn-Walsh. Genes Dev. 3:2021-2024, 1989). Using Northern (RNA) blot analysis, we have examined the expression of C/EBP alpha mRNA during liver regeneration and in primary cultures of hepatocytes. C/EBP alpha mRNA levels decrease 60 to 80% within 1 to 3 h after partial hepatectomy as the cells move from G0 to G1 and decrease further when cells progress into S phase. Run-on transcription analysis is in agreement with the Northern blot data, thus suggesting that C/EBP alpha is transcriptionally regulated in regenerating liver. C/EBP alpha mRNA expression also decreases dramatically during the growth of freshly isolated normal hepatocytes cultured under conventional conditions (on dried rat tail collagen; stimulated to proliferate by epidermal growth factor [EGF] and insulin). Cultures of hepatocytes on rat tail collagen in the presence or absence of EGF clearly show that within 3 h, EGF depresses C/EBP alpha mRNA expression and that this effect is substantially greater by 4 h. Inhibition of protein synthesis in the liver by cycloheximide or in cultured hepatocytes by puromycin or cycloheximide effectively blocks the down-regulation of C/EBP alpha gene expression, apparently by stabilizing the normal rapid turnover of the C/EBP alpha mRNA (half-life of <2 h). This drop in C/EBP alpha gene expression in response to activation of hepatocyte growth is consistent with the proposal that C/EBP alpha has an antiproliferative role to play in highly differentiated cells (R. M. Umek, A. D. Friedman, and S. L. McKnight, Science 251: 288-292, 1991).

Animals↗
PubMed2005

[Granulocyte colony-stimulating factor-mobilized autologous bone marrow stem cells promote the liver regeneration of partial liver transplant: an experiment with rats].

OBJECTIVE: To investigate the effects of granulocyte colony-stimulating factor (G-CSF)-mobilized autologous bone marrow stem cells on the liver regeneration of partial liver transplant. METHODS: A 50% partial liver transplantation model as established by transplanting parts of the liver of female rats to the male rats with the equal weights that had had parts of their livers resected. Then the transplanted male rats were randomly divided into 3 equal groups: G-CSF + PLTx group that was injected hypodermically with recombinant human G-CSF (rhG-CSF) daily for 5 days and then underwent liver resection and 50% partial liver transplantation (PLTx); PLTx + G-CSF group that underwent PLTx and 3 hours after the transplantation received injection of rhG-CSF daily for 5 days, and PLTx control group that underwent PLTx and 3 hours later received injection of normal saline daily for 5 days. One, 3, 5, 7, and 14 days after the PLTx blood samples and livers were collected from 6 rats from each group, and one hour before the liver was taken bromodeoxyuridine (BrdU) was injected intraperitoneally to be integrated into the synthesis of DNA in the liver cells. Immunohistochemistry was used to detect the CD34 and BrdU-positive cells. In situ hybridization was used to detect the sry (sex-determining region) gene so as to determine the origin of the proliferating cells in the transplanted liver. RESULTS: The 14-day survival rate of the G-CSF + PLTx group was 90%, significantly higher than those of the G-CSF + PLTx (60%) and PLTx group (50%) (both P < 0.05) with a significant difference between the latter 2 groups too (P < 0.05). The mitosis index of liver cells 3 days after the transplantation of the PLTx + G-CSF group was 30% +/- 5%, significantly higher than those of the G-CSF + PLTx group (24% +/- 7%) and PLTx group (24% +/- 6%) (both P < 0.05) without a significant difference between the latter 2 groups. The rate of BrdU-positive cells of the PLTx + G-CSF group was 42% +/- 6%, significantly higher than those of the G-CSF + PLTx group (38% +/- 4%) and PLTx group (34% +/- 8%) (both P < 0.05). The transplantation the mitosis index and rate of BrdU-positive cells decreased since the 7th days after transplantation in all 3 groups, however, with the same relationship among them. The numbers of CD34(+) cell around the portal area of the 2 G-CSF groups increased since the 3rd day after transplantation in comparison with the PLTx group, was the highest on the 3rd day for the G-CSF + PLTx group, and continued to increase in the PLTx + G-CSF group. Since the 3rd day after transplantation, sry-positive cells were seen in the hepatic sinusoid and portal area in the 2 G-CSF groups, and were rarely seen in the PLTx group. CONCLUSION: G-CSF treatment after 50% PLTx significantly promotes liver regeneration and ameliorates the liver damage, thus raising the survival rate.

Animals↗
PubMed1998

Changes in TGF-beta receptors of rat hepatocytes during primary culture and liver regeneration: increased expression of TGF-beta receptors associated with increased sensitivity to TGF-beta-mediated growth inhibition.

To clarify the role of transforming growth factor-beta (TGF-beta) and its receptors in hepatocyte growth, we studied the expression of TGF-beta1 and its receptors and the sensitivity to growth inhibition by TGF-beta1 protein in rat hepatocytes derived from resting and regenerating livers. In hepatocytes derived from resting livers, mRNAs for TGF-beta type II receptor (TbetaR-II), insulin-like growth factor-II/mannose 6-phosphate receptor (IGF-II/M-6-PR), and TGF-beta1 increased with time in primary culture. The cell surface TGF-beta receptor proteins (TbetaR-I, II, and III), examined by the receptor affinity-labeling assay using 125I-TGF-beta1, also increased, especially after 48 hr of culture. Hepatocytes were more sensitive to inhibition of DNA synthesis, when the TGF-beta1 protein was added at later times in culture, corresponding to the presence of increased TGF-beta receptors. In hepatocytes from regenerating livers after a partial hepatectomy (PH), an increase of TbetaR-I, TbetaR-II, TbetaR-III, IGF-II/M-6-PR, and TGF-beta1 mRNAs was found, compared with hepatocytes from resting livers. Similarly, using TGF-beta receptor affinity-labeling assay, hepatocytes from PH livers were found to have an increase in TbetaR-I, II, and III proteins, with a peak at 4 days post-PH, compared with hepatocytes from resting livers. When TGF-beta1 protein was added for a short period (6 or 24 hr) after cell attachment to hepatocyte cultures, it inhibited DNA synthesis more effectively in hepatocytes from regenerating compared with resting livers. Our results show that hepatocyte TGF-beta receptors and sensitivity to growth inhibition by TGF-beta1 protein change together and are modulated during liver regeneration, as well as during the conditions of primary culture.

Activin Receptors, Type I↗
PubMed1976

Role of changes in protein degradation in the growth of regenerating livers.

The significance of changes in rates of synthesis, export, and degradation of proteins during liver regeneration was assessed. (a) Proteins were pulse labeled by the intravenous injection of radioactive leucine and, 5 min later, pactamycin (an inhibitor of the initiation of protein synthesis). One-half of the protein radioactivity was lost from the normal liver within 3 hours. From the radioactivity of the plasma proteins at that time and a study of the disappearance of these proteins from the circulation, it was calculated that 28% of the newly synthesized proteins were exported. Serum albumin accounted for a third of the exported proteins. Thirty-six hours after partial hepatectomy the proportion of albumin to total protein synthesis remained constant, while that of the other plasma proteins increased by 50%. The fraction of the newly synthesized proteins retained by the liver after 3 hours decreased by 20%. (b) During the first 36 hours of liver regeneration the average rates of protein degradation slowed down to one-half the normal values. This was determined either by the loss of radioactivity from total protein (or the guanidino-C of protein-bound arginine) in livers labeled with [14C]bicarbonate, or calculated as the balance between protein synthesis and net protein gain. (c) From these results, and those of our previous study of the protein synthetic machinery of normal and regenerating livers (Scornik, O.A. (1974)J. Biol. Chem. 249, 3876-3883), we conclude that changes in the rate of protein degradation are the single most important factor determining the increase in protein content during liver compensatory growth.

Animals↗
PubMed2005

Blocking of G1/S transition and cell death in the regenerating liver of Hepatitis B virus X protein transgenic mice.

The Hepatitis B virus X (HBx) protein has been strongly implicated in the carcinogenesis of hepatocellular carcinoma (HCC). However, effects of the HBx protein on cell proliferation and cell death are controversial. This study investigates the effects of the HBx protein on liver regeneration in two independent lines of HBx transgenic mice, which developed HCC at around 14 to 16 months of age. High mortality, lower liver mass restoration, and impaired liver regeneration were found in the HBx transgenic mice post-hepatectomy. The levels of alanine aminotransferase and alpha-fetoprotein detected post-hepatectomy increased significantly in the HBx transgenic livers, indicating that they were more susceptible to damage during the regenerative process. Prolonged activation of the immediate-early genes in the HBx transgenic livers suggested that the HBx protein creates a strong effect by promoting the transition of the quiescent hepatocytes from G0 to G1 phase. However, impaired DNA synthesis and mitosis, as well as inhibited activation of G1, S, and G2/M markers, were detected. These results indicated that HBx protein exerted strong growth arrest on hepatocytes and imbalanced cell-cycle progression resulting in the abnormal cell death; this was accompanied by severe fat accumulation and impaired glycogen storage in the HBx transgenic livers. In conclusion, this study provides the first physiological evidence that HBx protein blocks G1/S transition of the hepatocyte cell-cycle progression and causes both a failure of liver functionality and cell death in the regenerating liver of the HBx transgenic mice.

Alanine Transaminase↗
PubMed2002

Activation of signal transducer and activator transcription 3 and expression of suppressor of cytokine signal 1 during liver regeneration in rats.

BACKGROUND/AIMS: Recent work has shown that the signal transducer and activator of transcription (STAT) 3 activation is important for the initiation of the proliferative response following partial hepatectomy (PH). However, the issue of where STAT3 is activated and how it is regulated is unclear. The aims of this study were to identify STAT3-activated cells and to clarify the expression of suppressor of cytokine signal (SOCS), a negative feedback molecule of STAT3, after PH. METHODS: STAT3-activated cells and SOCS1-positive cells were identified by immunohistochemistry after a two-thirds PH in rats. SOCS mRNA was examined by Northern analysis. RESULTS: STAT3 was activated in hepatocytes from those localized in the periportal zones of hepatic lobules after PH. STAT3 activation was also detected in Kupffer cells and sinusoidal endothelial cells prior to its detection in hepatocytes. After STAT3 activation, SOCS1 protein in response to PH was detected immunohistochemically in regenerating liver. SOCS1 and SOCS3 mRNA were induced in regenerating liver after PH. CONCLUSIONS: STAT3 signaling can occur in Kupffer cells and sinusoidal endothelial cells prior to in hepatocytes from those localized in the periportal zones. SOCS1 as well as SOCS3 may regulate STAT3 signaling negatively after PH.

Animals↗
PubMed1985

Hepatic fat accumulation during liver regeneration.

Fat accumulates in the regenerating liver after partial hepatectomy. The role of intracellular acyltransferases in the synthesis of triglycerides was studied in the liver. Two-thirds hepatectomy was performed in 14 rats. An additional 14 rats had laparotomy only (sham group). Animals were sacrificed at 18 or 24 hr after operation. After 18 hr, microsomal sn-glycerol 3-phosphate acyltransferase specific activity was increased from 708 to 956 pmole of glycerol 3-phosphate incorporated X min-1 X mg-1 protein and the triglyceride content was increased from 2.2 to 12.6 mg/g liver. At 24 hr the microsomal enzyme activity was again increased from 742 to 1203 pmole of glycerol 3-phosphate incorporated X min-1 X mg-1 protein and the triglyceride content rose from 1.9 to 13.9 mg/g liver. A correlation existed between the microsomal enzyme activity and the triglyceride level (r = 0.608, P less than 0.05). The mitochondrial enzyme activity was not increased. At 24 hr peroxisomal dihydroxyacetone acyltransferase activity was elevated from 375 to 523 pmole of dihydroxyacetone phosphate incorporated X min-1 X mg-1 protein but showed no correlation with the triglyceride content; the microsomal activity of the enzyme was not increased. Cytoplasmic NAD+-dependent alpha-glycerol 3-phosphate dehydrogenase decreased by 24 and 32% at 18 and 24 hr. These data indicate that the microsomal sn-glycerol 3-phosphate acyltransferase activity has a major role in promoting triglyceride synthesis during liver regeneration.

Acyltransferases↗
PubMed1999

Morphological and biochemical effects of a low ethanol dose on rat liver regeneration: role of route and timing of administration.

We have demonstrated that in rats subjected to partial hepatectomy (PH), the regenerating liver had an enhanced metabolism of ethanol, which largely depended on the route and timing of ethanol administration. Therefore, the influence of the administration route and timing for ethanol-induced deleterious effects on the regenerating rat liver was evaluated in animals subjected to 70% PH. Remnant liver showed moderate fatty infiltration, extended distortion of hepatocellular structure, and high mitotic index. Intragastric ethanol administration (1.5 g/kg body weight) considerably reduced the PH-induced changes in liver structures. Ethanol treatment also decreased liver thymidine kinase activity, serum albumin, and glucose levels. Intraperitoneal administration of the same ethanol dose to PH rats promoted lesser alterations on liver regeneration. Independently of its administration route, ethanol abruptly shortened a PH-induced selective increase in serum enzyme activities. These data suggest that the inhibitory effect of a low dose of ethanol on PH-induced liver regeneration is dependent on the timing and route of administration.

Animals↗
PubMed1992

Ethanol-associated alterations in the kinetics of putrescine uptake and metabolism by the regenerating liver.

Biosynthesis of the polyamines, putrescine, spermidine, and spermine is required for DNA synthesis and liver regeneration after partial hepatectomy. We have previously reported that chronic ethanol consumption impairs polyamine synthesis and significantly retards liver regeneration after partial hepatectomy. In those studies, supplementation with putrescine restored hepatic DNA synthesis in ethanol-fed rats but exerted no effect in pair-fed controls. These differences in the response to putrescine treatment may have resulted from ethanol-associated differences in hepatic uptake, release, or metabolism of putrescine. To resolve these issues and define more completely how putrescine treatment affects DNA synthesis, we now assess the kinetics of putrescine uptake and metabolism after intraperitoneal or intravenous injection of radiolabeled putrescine (1.2 mmol/kg, specific activity 1 microCi/mmol) into rats fed 36% ethanol diets or isocaloric, nonethanol diets for 6 weeks prior to partial hepatectomy. After putrescine treatment, hepatic putrescine concentrations were greater in ethanol-fed rats than controls. Differences in post-treatment hepatic putrescine levels between ethanol and pair-fed groups could not be explained by differences in the rates of hepatic putrescine uptake or excretion into bile; residual de novo synthesis of putrescine from ornithine or metabolism of hepatic putrescine to its polyamine products, spermidine and spermine. Indeed, supplemental putrescine was not appreciably converted to spermidine or spermine in either ethanol or control rats. Hence, these latter polyamines are unlikely to be responsible for the treatment-associated improvement in DNA synthesis that has been noted in ethanol-fed rats. This suggests that putrescine itself acts to restore hepatic DNA synthesis in ethanol-fed rats.

Alcoholism↗
PubMed1998

Transcription factor CREM coordinates the timing of hepatocyte proliferation in the regenerating liver.

The liver regenerates upon partial hepatectomy (PH) as terminally differentiated hepatocytes undergo a tremendous proliferative process. CREM gene expression is powerfully induced during liver regeneration. We show that cell proliferation is significantly reduced upon PH in CREM-/- mice. There is a reduction in DNA synthesis, in the number of mitosis and of phosphorylated histone H3-positive cells. The post-PH proliferation peak is delayed by 10 hr, indicating an altered hepatocyte cell cycle. Expression of cyclins A, B, D1, E, and cdc2, of c-fos and tyrosine aminotransferase is deregulated. CREM mutation results in delayed S-phase entry, impairing the synchronization of proliferation.

Animals↗
PubMed1979

The regenerating liver: a site of erythropoiesis in the adult Long-Evans rat.

Erythropoiesis, which is primarily hepatic in the rat during fetal and early neonatal life, shifts almost entirely to the bone marrow in the neonatal-adolescent stage of development. In the adult, extramedullary erythropoiesis has been demonstrated in the liver and spleen under certain pathological conditions when bone marrow red cell production is insufficient. In the present study, erythropoietic foci have been found in young-adult rat liver regenerating 24-72 hr after subtotal hepatectomy. This erythropoiesis is both extravascular and sinusoidal, with some erythroblastic islands noted. The centrolobular hepatic area contains the highest concentration of erythroblasts. Peripheral blood reticulocytosis coincides with the appearance of these cells and this is considered as an indicator of effective erythropoiesis. Liver regenerating after partial hepatectomy produces significant quantities of erythropoietin (Ep) in response to hypoxia. Subtotal hepatectomy may confer upon the adult liver the ability to revert to a fetal-like condition both in its ability to produce Ep and to function as a hematopoietic inductive microenvironment for erythropoiesis.

Age Factors↗
PubMed1999

The role of Kupffer cells in liver regeneration.

The liver has a remarkable proliferative capacity after a partial hepatectomy. Previous studies have indicated that Kupffer cells have the potential to exert both stimulatory and inhibitory influences on hepatocyte proliferation. To elucidate the role of Kupffer cells in liver regeneration, mice were selectively depleted of Kupffer cells by injection of liposome-encapsulated dichloromethylene diphosphonate (lipo-MDP) at day 3 after a two-thirds hepatectomy. Results showed that liver regeneration was delayed after Kupffer cell-depletion. In control mice, hepatocyte growth factor (HGF) mRNA expressions were enhanced during liver regeneration and expressions of HGF were localized in fat-storing cells (Ito cells). In Kupffer cell-depleted mice, the number of HGF-expressing cells decreased in the regenerating liver, and expressions of HGF and its receptor (c-met) as well as other growth factors/cytokines were less prominent than in control mice. In contrast, expressions of TNF-alpha, another potent cytokine involved in liver regeneration, did not differ between Kupffer cell-depleted and control mice during the regeneration. Administration of TNF-alpha antibody did not reduce the expression of HGF or liver regeneration. These findings imply that Kupffer cells play a stimulatory role in liver regeneration by enhancing HGF expression via TNF-alpha-non-mediated mechanisms.

Animals↗
PubMed1992

Effects of methotrexate on rat liver regeneration after partial hepatectomy.

1. Methotrexate was administered immediately after partial (70%) hepatectomy, resulting in complete inhibition of dihydrofolate reductase in 24 h-regenerating liver. 2. At 48 h and 72 h after partial hepatectomy, thymidylate synthase activity was increased, whereas thymidine kinase was inhibited, by the injection of methotrexate. The DNA and RNA contents and the liver weight were also reduced in methotrexate-treated rats. 3. The immunoblotting assay showed that methotrexate stimulated the synthesis of thymidylate synthase protein in 48 h-regenerating liver. At the same time, thymidylate synthase activity was directly inhibited by methotrexate. The mechanisms of inhibition of these enzymes by methotrexate appeared to be different.

Animals↗
PubMed1982

Effect of doxorubicin on liver regeneration and host survival after two-thirds hepatectomy in rats.

The effects of doxorubicin (Adriamycin) on regenerating liver were studied after two-thirds hepatectomy in rats. In Group I, standard two-thirds hepatectomy was performed. Doxorubicin in a dose of 2 mg/kg (Group II) and 6 mg/kg (Group III) was given intravenously immediately after the same hepatectomy. In Group IV, 6 mg/kg doxorubicin was given after sham operation. Animal survival, body weight restoration, wet weight and mitotic activity of remnant livers, and serum albumin concentrations were examined 1-14 days after operation. The survival rates were 95.5% in Group I, 76.8% in Group II, 10.3% in Group III, and 96.7% in Group IV. Although there were no differences in the residual liver weights among the hepatectomized groups, treatment with doxorubicin induced substantial, dose-dependent suppression and delay of liver cell division. Serum albumin levels dropped considerably in hepatectomized, doxorubicin-treated rats. Light microscopy showed degenerative changes with a single cell necrosis of hepatocytes in Group III. Death among rats hepatectomized and treated with doxorubicin was considered to be mainly due to the failure of residual livers since albumin synthesis was impaired and no marked changes were seen in vital organs other than the liver. For patients with hepatoma, the present results may indicate that the administration of adjuvant chemotherapy with doxorubicin, when necessary immediately after hepatectomy, should be performed with great care. In the absence of such necessity, doxorubicin should be withheld until life-sustaining liver regeneration has taken place.

Animals↗
PubMed1978

The effect of halothane anaesthesia on liver regeneration.

The effects of halothane and diethyl ether on the regenerating liver following 70 per cent hepatectomy were studied in Fisher/344 (F) rats. Our aim was to discover whether halothane administered repeatedly and over prolonged periods could influence the liver regenerative process or hepatocyte function. We also wished to know if the effects of halothane differed from those of diethyl ether. We found: 1. Prolonged halothane or diethyl ether anaesthesia did not inhibit liver mitotic activity, even if administered repeatedly. 2. The effects of halothane and diethyl ether on liver cell division were identical. 3. With reference to liver regeneration, halothane is as safe as diethyl ether when administered during extensive hepatectomy.

Animals↗