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PubMed1995

[Development of metabolic parameters in the early phases of liver regeneration].

Liver regeneration means the ability of the liver to restore the initial cellular mass after damage of various etiology. The primary mechanism of liver regeneration is not clearly defined yet. According to the recent knowledge the liver regeneration is directed by co-acting of many factors and events, among which the metabolic changes in regenerating liver tissue play important role. The aim of this study is to summarize the most important metabolic changes in the early steps of liver regeneration. The study presents the changes, which are taking place in the liver and in the other tissues and organs during liver regeneration, particularly after partial hepatectomy, but also in other types of liver damage. In the beginning the short overview of genetic changes, which enable the development of metabolic changes, is presented. After that the attention is drawn to the carbohydrate, lipid and protein metabolism. In the part, discussing the lipids, the results of experiments, in which the authors followed the influencing of liver regeneration in the rat after partial hepatectomy by means of parenteral and enteral application of various types of lipids and lipids combined with carnitine, is presented. In the next part the study discusses the metabolism of protein kinases and/or ions and trace elements. The energy metabolism as the necessary part of metabolic events is mentioned after that. In the last part the study draws attention to enzymatic retrodifferentiation in regenerating liver.

Animals↗
PubMed1993

Induction patterns of 70 genes during nine days after hepatectomy define the temporal course of liver regeneration.

Liver regeneration is an important process that allows for recovery from hepatic injuries caused by viruses, toxins, ischemia, surgery, and transplantation. Previously, we identified > 70 immediate-early genes induced in regenerating liver after hepatectomy, 41 of which were novel. While it is expected that the proteins encoded by these genes may have important roles in regulating progression through the G1 phase of the cell cycle during regeneration, we were surprised to note that many of these "early" genes are expressed for extended periods during the hepatic growth response. Here we define several patterns of expression of immediate-early, delayed-early, and liver-specific genes during the 9-d period after hepatectomy. One pattern of induction parallels the major growth period of the liver that ends at 60-72 h after hepatectomy. A second pattern has two peaks coincident with the first and second G1 phases of the two hepatic cell cycles. A third group, which includes liver-specific genes such as C/EBP alpha, shows maximal expression after the growth period. Although the peak in DNA synthesis in nonparenchymal cells occur 24 h later than in hepatocytes, most of the genes studied demonstrate similar induction in both cell types. This finding suggests that the G0/G1 transition occurs simultaneously in all cells in the liver, but that the G1 phase of nonparenchymal cells may be relatively prolonged. Finally, we examined the expression of > 70 genes in clinical settings that could induce liver regeneration, including after perfusion in a donor liver, hepatic ischemia, and fulminant hepatic failure. We found that a small number of early and liver-specific genes were selectively activated in human livers under these conditions, and we thereby provide a potential means of measuring the caliber of the regenerative response in clinical situations.

Adult↗
PubMed2005

Metalloproteinase inhibitor TIMP-1 affects hepatocyte cell cycle via HGF activation in murine liver regeneration.

Liver regeneration depends on timely restoration of cellular mass while orchestrating structural matrix remodeling. Matrix metalloproteinases (MMPs) and their endogenous inhibitors (TIMPs) are known to regulate the extracellular matrix (ECM) turnover and, more recently, the processing of growth factors and cytokines. We have previously demonstrated that TIMP-1 inhibits preneoplastic hepatocyte proliferation by attenuating growth factor bioavailability. In the present study, we examined the role of TIMP-1 in de novo hepatocyte cell division during liver regeneration. Comprehensive real-time reverse-transcriptase polymerase chain reaction analyses of regenerating livers revealed significant inductions in the messenger RNA of TIMP-1, TIMP-3, TIMP-4, MMP-2, MMP-9, MMP-13, MMP-14, and MMP-24, while MMP-15 expression was significantly reduced. Induction of TIMP-1 occurred during the peak of hepatocyte DNA synthesis. Studies using genetically altered mice revealed that TIMP-1 loss of function accelerated hepatocyte cell cycle progression. This finding was demonstrated by earlier expression of cyclin D1, proliferating cell nuclear antigen, and phosphorylated histone H3, which mark the G(1)-S, S, and M phase, respectively. Conversely, TIMP-1 gain of function delayed cell cycle progression. MMP activity was increased in the absence of Timp-1. Examination of hepatocyte growth factor (HGF), and its receptor Met, both of which provide a mitogenic signal for hepatocyte division, showed increased HGF activity in Timp-1(-/-)-regenerating livers. HGF is released from the ECM and is proteolytically processed to its active form. Active HGF was elevated in Timp-1(-/-) mice, leading to increased immunostaining of phosphorylated Met as well as activation of a downstream effector, p38. In conclusion, TIMP-1 is a novel negative regulator of HGF activity during liver regeneration.

Animals↗
PubMed1992

Characterization of sodium-dependent amino acid transport activity during liver regeneration.

Liver regeneration occurs after removal of or damage to a portion of the liver; it leads to restoration of the original liver mass. The activities of three sodium-dependent amino acid transporters--system A, system N and system ASC--were determined during a 5-day period of liver regeneration in the rat. Seventy-percent hepatectomy or laparotomy was performed in pairs of rats; these rats' livers were removed at different time points after surgery. Transport activity was determined through measurement of the Na(+)-dependent uptake of tritiated amino acids by isolated hepatic plasma membrane vesicles. System A activity, as measured by the Na(+)-dependent uptake of 2-aminoisobutyric acid, is increased in the regenerating liver 2 to 24 hr after surgery compared with that of controls. Kinetic analysis of 2-(methylamino)isobutyric acid uptake showed a 100% increase in the maximum velocity of system A transport in the hepatectomized animals with no change in the Michaelis constant, suggesting an increase in the number of system A transport proteins in the plasma membrane of regenerating liver. During liver regeneration, no changes were noted in the transport activities of system N and system ASC as measured by the uptake of glutamine and cysteine, respectively, in the presence of 2-(methylamino)isobutyric acid. Our work suggests that system A performs a unique role in the secondary active transport of its substrate neutral amino acids to meet the metabolic demands of regenerating liver.

Amino Acid Transport Systems↗
PubMed1983

Characterization of nucleolar antigens of normal rat liver, regenerating rat liver, and Novikoff ascites hepatoma cells following in vitro translation of polyadenylic acid-containing messenger RNA.

Nucleolar antigens of normal rat liver, regenerating liver, and Novikoff ascites hepatoma cells were transplanted in vitro from polyadenylic acid-containing messenger RNAs isolated from the respective tissues and immunoprecipitated with specific antinucleolar antibodies and Protein A. By two-dimensional gel electrophoresis of the translation products, five antigens were detected in normal rat liver. The antigens detected in 18-hr regenerating rat liver were the same as those of normal rat liver when immunoprecipitated with the anti-liver nucleolar antibodies. In the Novikoff tumor, 11 antigens were detected with anti-Novikoff nucleolar antibodies. Of these, two were not found in either normal or regenerating liver. Four major antigens were detectable in both Novikoff hepatoma and regenerating liver messenger RNA translation products with anti-Novikoff nucleolar antibodies. Two antigens were found in normal and regenerating liver that were not found in Novikoff hepatoma. In agreement with previous results, these immunoprecipitation analyses provide further evidence that some nucleolar antigens are present in Novikoff hepatoma that are not found in either normal or regenerating rat liver.

Animals↗
PubMed2004

Role of growth hormone (GH) in liver regeneration.

Liver regeneration is a fundamental mechanism by which the liver responds to injury. This process is regulated by endogenous growth factors and cytokines, and it involves proliferation of all mature cells that exist within the intact organ. To understand the role of the GH/IGF-I axis in liver regeneration, we performed partial hepatectomies in three groups of mice: GH antagonist (GHa) transgenic mice, in which the action of GH is blocked; liver IGF-I-deficient mice that lack IGF-I specifically in the liver and also lack the acid-labile subunit (ALS; LID+ALSKO mice), in which IGF-I levels are very low and GH secretion is increased; and control mice. Interestingly, the survival rate of GHa transgenic mice was dramatically reduced after partial hepatectomy (57%) compared with the survival rate of controls (100%) or LID+ALSKO mice (88%). In control mice, the liver was completely regenerated after 4 d, whereas liver regeneration required 7 d in LID+ALSKO mice. In contrast, in GHa mice, liver regeneration reached only 70% of the original liver mass after 4 d and did not improve thereafter. Strikingly, 36 and 48 h after hepatectomy, the livers of control and LID+ALSKO mice, respectively, exhibited intense 5-bromo-2'-deoxyuridine (BrdU) staining, whereas BrdU staining was dramatically decreased in the livers of GHa-treated mice. These results suggest that GH plays a critical role in liver regeneration, although whether it acts directly or indirectly remains to be determined.

Animals↗
PubMed1996

Rapid activation of latent transcription factor complexes reflects initiating signals in liver regeneration.

Liver regeneration following partial hepatectomy represents a physiologic response to a growth stimulus occurring in the intact animal. Understanding what growth factors and cytokines trigger liver regeneration will provide insights into recovery from hepatic injury mediated by viruses and toxins, and promote an understanding of normal cellular growth control. The modification of pre-existing latent transcription factors in the remnant liver by extracellular signals immediately post-hepatectomy provides a mechanism for the transcriptional activation of primary or immediate early growth response genes, thereby establishing a transcriptional cascade. Two factors activated within minutes to hours post-hepatectomy in a protein synthesis-independent fashion include PHF/NF-kappaB and Stat3. Interestingly, these factors are commonly activated by cytokines such as TNFalpha, IL-1 and IL-6 suggesting that there may be a connection between cytokine release and the onset of liver regeneration. In addition to these known transcription factor complexes, we have used a reporter gene assay in transgenic mice to attempt to identify promoter sequences that are responsible for the transcriptional activation of the liver-restricted IGFBP-1 immediate early gene within minutes posthepatectomy. Studies so far indicate that an upstream region of 800 bp is able to confer both tissue-restricted expression and induction during liver regeneration. Identification of the transcriptional activators or liver regeneration factors responsible for this induction will result in further dissection of the initiating signals.

Journal Article↗
PubMed1995

Rapid activation of the Stat3 transcription complex in liver regeneration.

Liver regeneration in response to partial hepatectomy is a physiological growth response observed in the intact animal. Understanding the early signals that trigger liver regeneration is of vital importance to understand the liver's response to injury. It has been observed that several growth factors and cytokines, including epidermal growth factor (EGF) and interleukin-6 (IL-6), can activate members of the signal transducers and activators of transcription (Stat) family of transcription factors resulting in tyrosine phosphorylation of these factors, nuclear translocation, and an active DNA binding transcriptional complex. Because Stat3 participates in the regulation of primary growth response genes, we wondered if it is induced in the early phase of liver regeneration. We found that Stat3 DNA-binding activity is increased in the remnant liver within 30 minutes of partial hepatectomy and peaks at more than 30-fold at 3 hours. This induction is not observed after sham surgery. The induction of Stat3 appears to be part of the initial response of the remnant liver to partial hepatectomy, because it occurs in the presence of cycloheximide-mediated protein synthesis blockade. Activation of Stat3 is unusual, because it extends beyond the immediate-early time period and remains near peak level at 5 hours posthepatectomy. Although insulin-treated H35 cells activate many of the same immediate-early genes as regenerating liver, Stat3 is not induced in these cells. Because Stat factors are known to be inactivated by protein tyrosine phosphatases (PTPase), we showed that a PTPase is able to eliminate the DNA binding of hepatic Stat3.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1977

Adsorption of messenger RNA of Novikoff hepatoma, normal liver, and regenerating liver on complementary DNA-cellulose affinity matrices.

Complementary DNA (cDNA)-oligodeoxythmidylate-celluloses were prepared from cDNA copies of polysomal messenger RNA (mRNA) of Novikoff hepatoma, normal rat liver, and regenerating rat liver. cDNA synthesis with reverse transcriptase was approximately 46% with respect to input mRNA with oligodeoxythymidylate-cellulose primer. The cDNA's of normal liver, regenerating liver, and Novikoff hepatomas were used as affinity matrices for hybridization of different mRNA species. Under the conditions used, degradation of mRNA was not detected. After normalization for homologous hybridization efficiency, 53 and 65% of the Novikoff hepatoma mRNA bound to normal liver and regenerating liver cDNA's. Under these conditions an average of 82% of mRNA of normal liver bound to regenerating liver cDNA, and 92% of regenerating liver mRNA bound to normal liver cDNA. The bound and unbound mRNA's were analyzed by translation in the wheat germ system; 2-D gel analysis of the proteins synthesized in the wheat germ system indicated that the cDNA affinity columns selectively adsorbed some mRNA species.

Animals↗
PubMed2006

Involvement of alcohol and aldehyde dehydrogenase activities on hepatic retinoid metabolism and its possible participation in the progression of rat liver regeneration.

Liver alcohol dehydrogenase (ADH) activity is decreased towards exogenous substrates after partial hepatectomy (PH), probably due to putative endogenous substrates acting as ADH inhibitors. Hence, retinoids could be suitable candidates as such endogenous substrates. Therefore, cytosolic ADH kinetic analysis using several substrates, liver cytosolic and mitochondrial aldehyde dehydrogenase (ALDH) activities, retinal and retinol content, as well as expression of proteins for ADH and CRBPI (a retinol carrier protein) were determined in liver samples, at two stages of liver regeneration (one- or two-thirds PH). The effect of inhibiting in vivo liver ADH by 4-methylpyrazole (4-MP) was also evaluated after 70%-PH. With 70%-PH, in vitro ADH activity towards exogenous alcohols and aldehydes was diminished, but retinol oxidation was increased and retinal reduction was decreased. These activities that be due to the participation of an ADH type which did not correlate with the amount of immunoreactive ADH protein. Cytosolic and mitochondrial ALDH activities oxidized actively retinal, whereas retinol and CBRP-I expression were reduced in these animals. With 30%-PH, these changes were less evident and sometimes opposite to those found with 70%-PH. In addition, retinol readily inhibited ADH-mediated ethanol oxidation. Interestingly, in vivo 4-MP administration inhibited ADH activity in a dose-dependent manner correlating with a progressive inhibition of liver regeneration. In conclusion, PH-induced inhibition of ADH (mainly type I) seems to be related to ADH-mediated retinoid metabolism during liver proliferation. Thus, results suggest a role of ADH in retinoid metabolism, which is apparently required during rat liver regeneration.

Alcohol Dehydrogenase↗
PubMed2005

Possible involvement of 4-hydroxynonenal in splenocyte regulated liver regeneration.

Liver regeneration is a complex, systemic process regulated by humoral and cellular mechanisms. Inflammatory response to the extensive tissue damage, as in partial hepatectomy, plays important role during regeneration. Hence, it is assumed that the spleen might play a role in systemic inflammatory response involved in liver regeneration. On the other hand, liver damage and consequential regeneration are often associated with oxidative stress and lipid peroxidation. One of the end products of lipid peroxidation, 4-hydroxynonenal (HNE), is nowadays considered not only as a "second toxic messenger of free radicals" but also as a growth-regulating factor. We therefore studied in vitro interactions of the HNE-treated murine liver cells and autologous spleen cells. The spleen cells supported recovery of liver cells from the HNE cytotoxicity although spleen cells themselves exerted cytotoxic effects against the proliferating liver cells that were not treated with HNE. Our results imply that the cytokines secreted by activated immunocompetent cells may be responsible for the observed recovery of the HNE-damage liver cells, suggesting that HNE might be an important factor regulating cellular and cytokine mediated mechanisms of liver regeneration control.

Aldehydes↗
PubMed1988

Desensitization of adenylate cyclase and cyclic AMP flux during the early stages of liver regeneration.

Liver regeneration is controlled by a complex network of interactions between hormones, growth factors, and a variety of hepatotrophic factors. Transient increases in cAMP in the early stages of liver regeneration that are necessary for DNA synthesis and subsequent mitosis have been reported; however, studies on the mechanisms that control cellular cAMP levels during liver regeneration, namely adenylate cyclase activity, cAMP-dependent phosphodiesterase activity, and cAMP efflux from the cell, have been generally incomplete. In this study we have shown that although there are three peaks in intracellular cAMP levels in the first 24 hours after partial hepatectomy, the adenylate cyclase activity stimulated by glucagon, prostaglandin E2, adrenaline, and fluoride in vitro decreases with time. KD and BMAX of hepatocyte glucagon and beta receptors were similar to the sham controls. Our results are consistent with a mixed homologous/heterologous desensitization of the adenylate cyclase system. There was also a loss of cAMP-dependent phosphodiesterase activity after partial hepatectomy. We speculate that even though the hormone-stimulated adenylate cyclase system has been desensitized, the system retains the ability to respond to the transient pulses of the variety of hormones secreted after partial hepatectomy and thus raise the intracellular concentration of cAMP. The decrease in cAMP-dependent phosphodiesterase may be necessary to prevent rapid breakdown of cAMP.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed2005

Recent events in alcoholic liver disease V. effects of ethanol on liver regeneration.

Liver regeneration is necessary to recover from alcoholic liver injury. Herein, we review evidence that ethanol interferes with liver regeneration. Briefly, alcoholic fatty livers demonstrate increased rates of hepatocyte death. The latter provides a regenerative stimulus. However, unlike mature hepatocytes in healthy adult livers, most surviving mature hepatocytes in alcoholic fatty livers cannot replicate. Therefore, less mature cells (progenitors) must differentiate to replace dead hepatocytes. Little is known about the general mechanisms that modulate the differentiation of liver progenitors in adults. Delineation of these mechanisms and clarification of how ethanol influences them might suggest new therapies for alcoholic liver disease.

Alcohol Drinking↗
PubMed1995

Differential display and cloning of messenger RNAs from the late phase of rat liver regeneration.

Liver regeneration allows for recovery from hepatic injuries and regeneration after partial hepatectomy has been extensively used as a model system to study mitogenesis. Many genes have been identified that are induced in the early growing phase of liver regeneration but only a few genes have been identified that are induced in the later stages of regeneration before growth arrest. We used the newly discovered differential display method to identify several genes that were found to be induced at this later stage. Two of them were analyzed further. DNA sequencing of one of them revealed perfect homology to ribosomal protein S24. The sequence of the other gene did not have extensive homology to any sequence in the databases. These results may suggest a role of these two genes in the growth arrest phase of liver regeneration.

Aniline Compounds↗
PubMed1995

Rapid DNA binding by nuclear factor kappa B in hepatocytes at the start of liver regeneration.

Liver regeneration after two-thirds partial hepatectomy (PH) is a process in which quiescent, fully differentiated hepatocytes rapidly reenter the cell cycle and eventually divide until the original liver mass is restored. Although the exact nature of the growth-initiating signals is unknown, enhanced expression of growth-related genes has been detected during the first hour after operation. This suggests that activation of transcriptional and posttranscriptional regulatory factors is likely to be a very early event in liver regeneration. Here we report the rapid, transient induction of DNA binding by nuclear factor (NF)-kappa B (p50/p65 heterodimer) and p50 homodimers within 30 min after PH. We also detected binding of post-hepatectomy factor. NF-kappa B binding peaks at 1 h after PH before declining and is not induced by sham operation. Liver cell separation studies indicated that the binding activation occurs in hepatocytes, a conclusion further supported by cell culture studies using the hepatocyte cell line AML-12. Furthermore, studies with the liver epithelial cell line LE-6 indicated that these DNA-binding activities are mitogen inducible. One-third hepatectomy, a procedure which primes hepatocytes to respond to growth factors, also induced NF-kappa B binding. We also found that tumor necrosis factor alpha, which may be involved in the control of liver regeneration, rapidly induced NF-kappa B DNA-binding activities in intact animals, similar to those induced by PH. These results suggest that NF-kappa B binding may play a role in making hepatocytes competent to proliferate.

Animals↗
PubMed2005

The role of STAT3 in liver regeneration.

Liver regeneration is a process in which the liver recovers its mass and function after injury due to various causes such as hepatectomy, virus infection and intoxication. This regeneration invokes a series of complex processes which may involve the actions of various cytokines, cell proliferation and cell growth. In response to cytokine stimuli, receptor-mediated signaling systems are activated, and many proteins are transcriptionally up-regulated to increase liver mass and improve liver function. In this review, we focus on the roles of signal transducer and activator of transcription-3 (STAT3) and its functions in mitogenic and other responses during liver regeneration following hepatectomy. We also describe newly discovered target genes of STAT3 and discuss their potential roles in liver regeneration after injury due to various causes.

Animals↗
PubMed2006

Caveolin-1 is essential for liver regeneration.

Liver regeneration is an orchestrated cellular response that coordinates cell activation, lipid metabolism, and cell division. We found that caveolin-1 gene-disrupted mice (cav1-/- mice) exhibited impaired liver regeneration and low survival after a partial hepatectomy. Hepatocytes showed dramatically reduced lipid droplet accumulation and did not advance through the cell division cycle. Treatment of cav1-/- mice with glucose (which is a predominant energy substrate when compared to lipids) drastically increased survival and reestablished progression of the cell cycle. Thus, caveolin-1 plays a crucial role in the mechanisms that coordinate lipid metabolism with the proliferative response occurring in the liver after cellular injury.

Animals↗
PubMed2001

Apolipoprotein A-V: a novel apolipoprotein associated with an early phase of liver regeneration.

Liver regeneration in response to various forms of liver injury is a complex process, which ultimately results in restoration of the original liver mass and function. Because the underlying mechanisms that initiate this response are still incompletely defined, this study was aimed to identify novel factors. Liver genes that were up-regulated 6 h after 70% hepatectomy (PHx) in the rat were selected by cDNA subtractive hybridization. Besides known genes associated with cell proliferation, several novel genes were isolated. The novel gene that was most up-regulated was further studied. Its mRNA showed a liver-specific expression and encoded a protein comprising 367 amino acids. The mouse and human cDNA analogues were also isolated and appeared to be highly homologous. The human gene analogue was located at an apolipoprotein gene cluster on chromosome 11q23. The protein encoded by this gene had appreciable homology with apolipoproteins A-I and A-IV. Maximal expression of the gene in the rat liver and its gene product in rat plasma was observed 6 h after PHx. The protein was present in plasma fractions containing high density lipoprotein particles. Therefore, we have identified a novel apolipoprotein, designated apolipoprotein A-V, that is associated with an early phase of liver regeneration.

Amino Acid Sequence↗