The influence of corticosterone on antizyme gene expression in early regenerating rat liver

BACKGROUND AND STUDY AIMS

Antizyme 1, a specific inhibitor of Ornithine decarboxylase (ODC), plays a critical role in cell proliferation. Little is known about the impact of glucocorticoid on antizyme expression in the regenerating liver. In this paper, the effect of corticosterone on the gene expression of antizyme 1 in early regenerating rat liver induced by partial hepatectomy (PH) was investigated.

MATERIALS AND METHODS

Bilateral adrenalectomies (ADX) were performed 3 days before PH. Corticosterone in sesame oil or sesame oil was injected sub-cutaneously to ADX rats. Antizyme 1 mRNA and protein levels as well as polyamine contents in the regenerating liver were determined by RT-PCR, Western blotting and HPLC, respectively.

RESULTS

Antizyme 1 protein content in the oil-treated ADX group decreased significantly at 5, 7 and 9 h after PH compared to control. Following corticosterone administration the content rose dose-dependently during the whole experiment. At 5 h post-PH, the protein levels in 10 and 40 mg/kg corticosterone-treated ADX rats increased by 66% and 148%, respectively, when compared with the control group. However, no significant changes in antizyme 1 mRNA levels were observed in oil-treated ADX rats or corticosterone-treated groups compared to control. Polyamine contents in oil-treated ADX rats were the highest among all groups at 5 and 9 h. Corticosterone treatment resulted in a dramatic decrease of polyamine contents at most of the time points investigated when compared with those in control rats.

CONCLUSIONS

Corticosterone treatment induces antizyme 1 protein synthesis in early regenerating rat liver. However, it has little effect on antizyme 1 gene transcription. (Acta gastroenterol. belg., 2011, 74, 289-294).

Mir-34a is upregulated during liver regeneration in rats and is associated with the suppression of hepatocyte proliferation

Background

MicroRNAs are a class of small regulatory RNAs that modulate a variety of biological processes, including cellular differentiation, apoptosis, metabolism and proliferation. This study aims to explore the effect of miR-34a in hepatocyte proliferation and its potential role in liver regeneration termination.

Methodology/Principal Finding

MiR-34a was highly induced after partial hepatectomy. Overexpression of miR-34a in BRL-3A cells could significantly inhibit cell proliferation and down-regulate the expression of inhibin βB (INHBB) and Met. In BRL-3A cells, INHBB was identified as a direct target of miR-34a by luciferase reporter assay. More importantly, INHBB siRNA significantly repressed cell proliferation. A decrease of INHBB and Met was detected in regenerating liver.

Conclusion/Significance

MiR-34a expression was upregulated during the late phase of liver regeneration. MiR-34a-mediated regulation of INHBB and Met may collectively contribute to the suppression of hepatocyte proliferation.

Epiplakin1 is expressed in the cholangiocyte lineage cells in normal liver and adult progenitor cells in injured liver

We have previously identified Epiplakin1 (Eppk1) as a gene expressed in pancreatic progenitor cells. Here we studied the expression of Eppk1 in developing and regenerating livers in mice. Eppk1 is initially expressed in the early bipotential hepatoblasts and is later confined to the cholangiocytes. After birth, Eppk1 is expressed in the bile duct. In the livers of mice fed with a choline-deficient ethionine-supplemented (CDE) diet, Eppk1-positive cells dramatically increase in number. The Eppk1-positive cells express A6, thereby indicating that they are hepatic progenitor cells. Other cholangiocyte markers, such as Cytokeratins, E-cadherin, osteopontin and Sox9, are also co-expressed in the hepatic progenitor cells. Some of the Eppk1-positive cells express PCNA, a proliferation marker, thereby suggesting their identities as transient amplifying cells. In conclusion, we have shown that Eppk1 serves as a useful marker for detecting the hepatic progenitor population in the developing and adult liver. The use of Eppk1 as a marker will facilitate studies of mouse hepatic progenitor cells.

Analysis of gene expression profiles of liver stellate cells during liver regeneration in rats

This study performed a large-scale, high-throughput analysis of transcriptional profiling of liver stellate cells (LSCs) at the cellular level to investigate changes in the biological activity of LSCs during rat liver regeneration (LR) and the relation of these changes to LR. First, a rat liver regeneration model was established by partial hepatectomy (PH). Stellate cells were isolated in high purity and yield from the regenerating rat liver by Percoll density gradient centrifugation and immunomagnetic bead sorting. The changes in gene expression of LSCs after PH were examined using a rat genome 230 2.0 array composed of 24622 genes. The results indicated that 10241 of the 24622 genes investigated on the array were differentially expressed in LSCs. Of the 10241 genes, 1563 known genes were related to LR, which were grouped into three major gene expression clusters according to three-fold cut-off threshold: the upregulated gene cluster, the down-regulated gene cluster, and the cluster composed of genes showing complex changes in expression. Additionally, the genes were grouped into those involved in transcription regulation, signal transduction, transport, cellular metabolism, inflammation and immunity by functional analysis. When gene expression profiles were combined with the results of gene functional analysis, most of the genes involved in cytokine secretion and retinol metabolism in LSCs were significantly enriched in the cluster characterized by decreased expression, whereas genes involved in lipid metabolism were mostly enriched in the cluster showing increased expression. Based on further analysis of genes expressed in a phase-dependent manner during LR, it was suggested that lipid metabolism in LSCs was enhanced in the whole regeneration process, and that immune response and cytokine secretion were impaired during all three regenerative phases.

Segmental cholangitis impairs hepatic regeneration capacity after partial hepatectomy in rats

BACKGROUND

Patients with hilar cholangiocarcinoma or hepatolithiasis often develop segmental cholangitis (SC), but it is unclear whether hepatectomy for patients with SC can be performed safely.

METHODS

Rats were subjected to segmental bile duct ligation (SBDL) with LPS (SC group) or a saline (Sham group) infusion into the bile duct of the ligated lobes. The rats were sacrificed at 3, 24 and 48 h after the SBDL. For another experiment, the rats were subjected to partial hepatectomy (PHx) for the ligated lobes. Hepatic regeneration rates and the expression of regeneration-associated genes were evaluated.

RESULTS

In the SC group, severe parenchymal damage was observed in the acute phase (3 h). Altered gene expression in the liver in response to biliary infection occurred not only in the infected lobes but also in the non-infected lobes. In the rats of the SC group, both the hepatic regeneration rate and serum HGF levels were significantly lower than in the Sham group.

CONCLUSION

These results clearly demonstrate that SC impairs the regeneration capacity of the contralateral remnant liver. Therefore, hepatectomy should be avoided for patients with SC even if it occurs in the part of the liver to be resected.

Foxa2 (HNF-3beta) regulates expression of hepatotrophic factor ALR in liver cells

Liver regeneration is a multistep and well-orchestrated process which is initiated by injuries such as tissue loss, infectious or toxic insults. Augmenter of liver regeneration (ALR) is a hepatotrophic growth factor which has been shown to stimulate hepatic regeneration after partial hepatectomy and therefore seems to be regulated during the regenerative process in the liver. Our aim was to analyze how ALR is regulated in hepatic tissues and which transcription factors might regulate its tissue-specific expression. Promoter studies of ALR (-733/+527 bp) revealed potential regulatory elements for various transcription factors like Foxa2, IL-6 RE-BP and C/EBPbeta. Analysis of the promoter activity by performing luciferase assays revealed that co-transfection with Foxa2 significantly induced the activity of ALR promoter in HepG2 cells. EMSA and Supershift analysis using anti-Foxa2 antibody confirmed the specific binding of Foxa2 to ALR promoter and this binding was inducible when the cells were simultaneously stimulated with IL-6. The increased binding after activation with IL-6 and/or Foxa2 was confirmed by elevated ALR protein levels using Western blot technique. In addition, we could not detect any binding of C/EBPbeta and IL-6 RE-BP to the promoter of ALR. In conclusion, these results indicate that ALR is regulated by Foxa2, and this regulation may be amplified by IL-6.

Accelerated carcinogenesis following liver regeneration is associated with chronic inflammation-induced double-strand DNA breaks

Hepatocellular carcinoma (HCC) is the third leading cause of cancer mortality worldwide and is considered to be the outcome of chronic liver inflammation. Currently, the main treatment for HCC is surgical resection. However, survival rates are suboptimal partially because of tumor recurrence in the remaining liver. Our aim was to understand the molecular mechanisms linking liver regeneration under chronic inflammation to hepatic tumorigenesis. Mdr2-KO mice, a model of inflammation-associated cancer, underwent partial hepatectomy (PHx), which led to enhanced hepatocarcinogenesis. Moreover, liver regeneration in these mice was severely attenuated. We demonstrate the activation of the DNA damage-response machinery and increased genomic instability during early liver inflammatory stages resulting in hepatocyte apoptosis, cell-cycle arrest, and senescence and suggest their involvement in tumor growth acceleration subsequent to PHx. We propose that under the regenerative proliferative stress induced by liver resection, the genomic unstable hepatocytes generated during chronic inflammation escape senescence and apoptosis and reenter the cell cycle, triggering the enhanced tumorigenesis. Thus, we clarify the immediate and long-term contributions of the DNA damage response to HCC development and recurrence.

Quantitative evaluation and selection of reference genes in a rat model of extended liver resection

Partial hepatectomy (PHx) is a frequently used experimental model for the study of liver regeneration. Real-time quantitative PCR (qPCR) has become the one of the methods of choice for expression profiling of selected genes in order to elucidate the regulation of liver function and regeneration. The expression of five commonly used housekeeping genes (HKGs; Alb, UBC, Hprt, Ywhaz, and GAPDH) were evaluated by qPCR in 70% and 90% rat PHx model at 1, 2, and 7 d after PHx. We set up a closely controlled qPCR procedure validating each critical step and the gene expression stability was statistically evaluated by linear regression and analysis of variance. Our results showed the HKG best suited for the evaluation of gene expression in the extended 90% PHx model is Hprt. The amplification of an HKG can be omitted when the same amount of cDNA from all samples is introduced into the amplification reaction. Determination of cDNA concentration employing the bioanalyzer proved to be an easy and reproducible approach. Using this technique the potential regulation of the transcription level of the HKG in response to the experimental condition tested or the stability of a housekeeping gene becomes irrelevant.

Variations in interferon gamma receptor gene expression during liver regeneration after partial hepatectomy in rats

Cell-mediated immunity, which includes interferon gamma (IFN-gamma) expression, is activated during the process of liver regeneration; however, the genetic pathway of this activation is still unclear. The present study evaluated variations in the interferon gamma receptor (IFN-gamma R) gene and its mRNA expression during liver regeneration after partial hepatectomy (PH). Male Wistar rats weighing approximately 200 g were subjected to PH (70 or 40%). IFN-gamma R gene expression in the remnant liver was measured by cDNA microarray, and mRNA expression was verified by real-time quantitative reverse transcription-polymerase chain reaction (Q-PCR) preoperatively and at 2, 4, 6, 12, 24, and 72 hours and 7 days postoperatively. The ratio of remnant liver weight to body weight increased markedly after 70 per cent PH and more gradually after 40 per cent PH. It reached near 90 per cent of the preoperative level at 72 hours after PH in both groups. The scanned spots of the genomic survey on the cDNA microarray chips were uneven and increased irregularly in number and density after PH. IFN-gamma R gene expression increased markedly in a single peak pattern, up to more than double the preoperative level, at 6 hours after 70 per cent PH. The curve in the 40 per cent PH group was flat and peaked at only 1.6 times the preoperative level. The variations in IFN-gamma R-related mRNA expression were verified by Q-PCR. Elevations in IFN-gamma R gene and mRNA expression were shown during the early stage of liver regeneration after PH. The genetic pathway of IFN-gamma/IFN-gamma R expression is activated during liver regeneration.

Proliferation of human HCC cells and chemically induced mouse liver cancers requires JNK1-dependent p21 downregulation

JNK proteins have been shown to be involved in liver carcinogenesis in mice, but the extent of their involvement in the development of human liver cancers is unknown. Here, we show that activation of JNK1 but not JNK2 was increased in human primary hepatocellular carcinomas (HCCs). Further, JNK1 was required for human HCC cell proliferation in vitro and tumorigenesis after xenotransplantation. Importantly, mice lacking JNK1 displayed decreased tumor cell proliferation in a mouse model of liver carcinogenesis and decreased hepatocyte proliferation in a mouse model of liver regeneration. In both cases, impaired proliferation was caused by increased expression of p21, a cell-cycle inhibitor, and reduced expression of c-Myc, a negative regulator of p21. Genetic inactivation of p21 in JNK1-/- mice restored hepatocyte proliferation in models of both liver carcinogenesis and liver regeneration, and overexpression of c-Myc increased proliferation of JNK1-/- liver cells. Similarly, JNK1 was found to control the proliferation of human HCC cells by affecting p21 and c-Myc expression. Pharmacologic inhibition of JNK reduced the growth of both xenografted human HCC cells and chemically induced mouse liver cancers. These findings provide a mechanistic link between JNK activity and liver cell proliferation via p21 and c-Myc and suggest JNK targeting can be considered as a new therapeutic approach for HCC treatment.

Reference gene selection for real-time RT-PCR in regenerating mouse livers

The liver has an intrinsic ability to undergo active proliferation and recover functional liver mass in response to an injury response. This regenerative process involves a complex yet well orchestrated change in the gene expression profile. To produce accurate and reliable gene expression of target genes during various stages of liver regeneration, the determination of internal control housekeeping genes (HKGs) those are uniformly expressed is required. In the present study, the gene expression of 8 commonly used HKGs, including GAPDH, ACTB, HPRT1, GUSB, PPIA, TBP, TFRC, and RPL4, were studied using mouse livers that were quiescent and actively regenerating induced by partial hepatectomy. The amplification of the HKGs was statistically analyzed by two different mathematical algorithms, geNorm and NormFinder. Using this method, PPIA and TBP gene expression found to be relatively stable regardless of the stages of liver regeneration and would be ideal for normalization to target gene expression.

Hepatocyte-specific inhibitor-of-kappaB-kinase deletion triggers the innate immune response and promotes earlier cell proliferation during liver regeneration

Nuclear factor kappaB (NF-kappaB) is one of the main transcription factors involved in liver regeneration after partial hepatectomy (PH). It is activated upon IkappaB phosphorylation by the IkappaB kinase (IKK) complex comprising inhibitor of kappaB kinase 1 (IKK1), inhibitor of kappaB kinase 2 (IKK2), and nuclear factor-B essential modifier (NEMO). We studied the impact of hepatocyte-specific IKK2 deletion during liver regeneration. A 70% PH was performed on IKK2(f/f) (wild-type) and IKK2DeltaLPCmice (hepatocyte-specific IKK2 knockout mice). PH in IKK2DeltaLPC compared with IKK2(f/f) mice resulted in weaker and delayed NF-kappaB activation in hepatocytes, while nonparenchymal liver cells showed earlier NF-kappaB activation and higher tumor necrosis factor expression. Additionally, these animals showed increased and earlier serum amyloid A and chemotactic cytokine L-1 levels followed by enhanced polymorphonuclear cell recruitment to the liver. These results correlated with earlier Jun kinase activity, c-myc expression, and matrix metalloproteinase-9 activity, suggesting earlier priming in IKK2DeltaLPC mice after PH. These data preceded a more rapid cell cycle progression and earlier hepatocyte proliferation as evidenced through cyclin and 5-bromo-2-deoxyuridine analysis. Interestingly, despite faster G(1)/S progression, IKK2DeltaLPC mice exhibited an enduring mitosis phase, because mitotic bodies were still observed at later stages after PH.

CONCLUSION

We demonstrate that PH in IKK2DeltaLPC mice triggers a more rapid and pronounced inflammatory response in nonparenchymal liver cells, which triggers earlier hepatocyte proliferation.

Messenger RNA expression of translationally controlled tumor protein (TCTP) in liver regeneration and cancer

OBJECTIVE

Translationally controlled tumor protein (TCTP) was recently reported to be involved in tumor reversion. In order to understand TCTP mRNA transcript in proliferative tissue and malignant lesions, the mRNA expression of TCTP was determined in a rat model of liver regeneration and human liver cancer tissues. In addition, the potential role of TCTP on suppression of liver cancer was investigated.

MATERIALS AND METHODS

Liver regeneration model was established by a two-thirds partial hepatectomy (PH) in adult, male Sprague-Dawley rat. TCTP mRNA expression was determined by semiquantitative RT-PCR analysis. Antisense mRNA of TCTP was transfected into the SMMC-7721 liver cancer cell line. Biological assay of proliferation and cell cycle were analysed by MTT and flow cytometry, respectively.

RESULTS

After PH of rats, the level of TCTP mRNA transcript was upregulated slightly in liver tissue at 1 hour followed by a high expression from 3 to 12 hours, which then decreased dramatically at 24 hours before returning to original level during liver tissue proliferation. TCTP mRNA transcript increased significantly in liver cancer tissues when compared to non-cancerous adjacent tissues as control. The transfection with antisense oligodeoxynucleotides of TCTP led to decreased proliferation of SMMC-7721 cells resulting in cell cycle arrest and pro-apoptosis.

CONCLUSION

The results suggested that TCTP mRNA expression might be stage-specific in the proliferation of liver tissue but alter abnormally in cancer lesions. TCTP could be used as a potential target for suppression of liver tumorigenicity.

Expression profiles of the genes associated with the myocyte differentiation during rat liver regeneration

Myocytes are important parts of tissues and organs. To study the effects of myocyte differentiation-related genes on rat liver regeneration (LR) at transcriptional level, we obtained these genes through collecting the database data and retrieving the pertinent thesis, and detected the expression profiles of above-mentioned genes during LR using the Rat Genome 230 2.0 array. LR-associated genes were identified by comparing the discrepancy in gene expression changes between partial hepatectomy (PH) group and sham-operation (SO) group, by which 52 LR-associated genes were confirmed. They were classified into 5 groups based on time relevance, including 0.5-1h; 2-12h; 16h, 30h, 42h, 96h; 18-24h, 36h, 48-60h; 66-72h,120-168h, in which the numbers of up-regulation and down-regulation genes were 8 and 10, 24 and 8, 21 and 24, 53 and 64, 28 and 36, respectively. Among these genes, the total 143 times of up-regulation and 136 times of down-regulation, as well as their 8 expression patterns displayed diversity and complexity of the genes associated with the myocyte differentiation. It was inferred that the differentiation of myoblasts and smooth muscle cells were enhanced during LR and the genes associated with the differentiation of skeletal muscle cells and cardiac muscle cells participated in the cellular physiological and biochemical activities of LR.

Impact of hepatic vein deprivation on liver regeneration and function after major hepatectomy

BACKGROUND AND AIMS

In extended liver resections, the preservation of vascular and biliary structures of the entire remnant liver is of paramount importance. The impact of venous outflow impairment and its consequences for liver regeneration and function are still a matter of debate.

MATERIALS AND METHODS

Rats (n = 75) were subjected to a 90% partial hepatectomy (PH), to a 70% liver resection with narrowing of the hepatic outflow of an additional 20% parenchyma (70%+ PH) or to an anatomic 70% PH. Postoperatively hepatocyte proliferation (Ki-67), liver function and survival were assessed. Gene expression analysis for markers of regeneration was determined by in-house complementary (DNA) arrays and quantitative real-time polymerase chain reaction (RT-PCR).

RESULTS

Ninety percent PH led to a greater regenerative response as shown Ki-67 compared to animals with a 70%+PH (p < 0.05). However, liver function was equally impaired in both groups. Rats with 70% PH showed a greater proliferation index with less hepatic injury and better liver function. While mortality was 0% in the group of 70% PH, rats with 90% PH and 70+PH had a reduced survival of 75% (p < 0.05)

CONCLUSION

Venous outflow obstruction leads to an impairment of liver regeneration and liver function. In cases with critically small liver remnants, restoration of an adequate venous outflow may be mandatory.

Dispensability and dynamics of caveolin-1 during liver regeneration and in isolated hepatic cells

Caveolae participate in several cellular processes such as vesicular transport, cholesterol homeostasis, regulation of signal transduction, integrin signaling, and cell growth. The expression and functional role of caveolin (Cav), the most abundant protein of caveolae, has been reported in liver and in different hepatocyte cell lines, in human cirrhotic liver, and in hepatocellular carcinomas. The role of Cav-1 in liver regeneration after partial hepatectomy (PH) has been investigated as a model of liver proliferation in vivo. Our results show that Cav-1 increases in liver after PH with a redistribution of the protein from the caveola-enriched domain to the noncaveolar fraction. Moreover, the Cav-1 located in the noncaveolar fraction is phosphorylated in tyrosine 14, even though the Cav-1 gene is dispensable for liver regeneration after PH, as deduced from data obtained with commercially available animals lacking this gene. In addition to this, the proinflammatory stimulation of hepatocytes induces Cav-1 translocation to a noncaveolar fraction and tyrosine 14 phosphorylation mainly through the activation of tyrosine kinases such as Src.

CONCLUSION

These results support a dynamic role for Cav-1 in liver proliferation both in vivo after PH and in vitro in cultured hepatic cell lines, but with minimal implications for the liver regeneration process.

Expression profiles of the genes associated with metabolism and transport of amino acids and their derivatives in rat liver regeneration

Amino acids (AA) are components of protein and precursors of many important biological molecules. To address effects of the genes associated with metabolism and transport of AA and their derivatives during rat liver regeneration (LR), we firstly obtained the above genes by collecting databases data and retrieving related thesis, and then analyzed their expression profiles during LR using Rat Genome 230 2.0 array. The LR-associated genes were identified by comparing the gene expression difference between partial hepatectomy (PH) and sham-operation (SO) rat livers. It was approved that 134 genes associated with metabolism of AA and their derivatives and 26 genes involved in transport of them were LR-associated. The initially and totally expressing number of these genes occurring in initial phase of LR (0.5-4 h after PH), G0/G1 (4-6 h after PH), cell proliferation (6-66 h after PH), cell differentiation and structure-function reconstruction of liver tissue (72-168 h after PH) were respectively 76, 17, 79, 5 and 162, 89, 564, 195, illustrating that these LR-associated genes were initially expressed mainly in initial stage, and functioned in different phases. Frequencies of up-regulation and down-regulation of them being separately 564 and 357 demonstrated that genes up-regulated outnumbered those down-regulated. Categorization of their expression patterns into 22 types implied the diversity of cell physiological and biochemical activities. According to expression changes and patterns of the above-mentioned genes in LR, it was presumed that histidine biosynthesis in the metaphase and anaphase, valine metabolism in the anaphase, and metabolism of glutamate, glutamine, asparate, asparagine, methionine, alanine, leucine and aromatic amino acid almost were enhanced in the whole LR; as for amino acid derivatives, transport of neutral amino acids, urea, gamma-aminobutyric acid, betaine and taurine, metabolism of dopamine, heme, S-adenosylmethionine, thyroxine, and biosynthesis of hydroxyproline, nitric oxide, orinithine, polyamine, carnitine, selenocysteine were augmented during the entire liver restoration. Above results showed that metabolism and transport of AA and their derivates were necessary in liver regeneration.

Serial analysis of gene expression (SAGE) in rat liver regeneration

We have applied serial analysis of gene expression for studying the molecular mechanism of the rat liver regeneration in the model of 70% partial hepatectomy. We generated three SAGE libraries from a normal control liver (NL library: 52,343 tags), from a sham control operated liver (Sham library: 51,028 tags), and from a regenerating liver (PH library: 53,061 tags). By SAGE bioinformatics analysis we identified 40 induced genes and 20 repressed genes during the liver regeneration. We verified temporal expression of such genes by real time PCR during the regeneration process and we characterized 13 induced genes and 3 repressed genes. We found connective tissue growth factor transcript and protein induced very early at 4h after PH operation before hepatocytes proliferation is triggered. Our study suggests CTGF as a growth factor signaling mediator that could be involved directly in the mechanism of liver regeneration induction.

Hepatocyte differentiation of mesenchymal stem cells from rat peritoneal adipose tissue in vitro and in vivo

Mesenchymal tissues harbour stromal cells capable of multilineage differentiation. Here, we demonstrate the isolation of mesenchymal stem cells (MSC) from rat peritoneal adipose tissue capable of osteogenic and adipogenic differentiation. Under in vitro conditions favouring hepatocyte differentiation, these MSC gained characteristic functions of hepatocytes such as the capacity to synthesize urea or store glycogen. Hepatocyte-specific transcripts of dipeptidylpeptidase type IV (CD26), albumin, cytochrome P450 type 1A1 (CYP1A1) and connexin CX32 (CX32) were detected only in differentiated but not undifferentiated cells. Transient transgenic expression of luciferase could be stimulated by cAMP when driven by the hepatocyte-specific promoter of the cytosolic phosphoenolpyruvate carboxykinase (PCK1) gene. Finally, stem cell-derived hepatocytes from wild type (CD26+/+) rats were transplanted into the livers of CD26-deficient animals after lentiviral transduction with the GFP gene under the control of the ubiquitin promoter. GFP-positive cells engrafted in the host liver predominantly in the periportal region of the liver lobule. They continued to express CD26, a prominent feature of differentiated hepatocytes, indicating their topologically and functionally proper integration into the host liver parenchyma. Thus, MSCs from rat peritoneal adipose tissue exhibit the potential to differentiate into hepatocyte-like cells in vitro and in vivo.

Expression of interleukin 6 and apoptosis-related genes in suckling and weaning rat models of hepatectomy and liver regeneration

BACKGROUND/PURPOSE

The most commonly used model to study the mechanisms of liver regeneration is the adult rat submitted to 70% to 80% hepatectomy. However, there are no studies using newborn or weaning rat models. The process of liver regeneration includes both the hypertrophy and hyperplasia of cells (processes regulated by growth factors and cytokines, mainly interleukin 6 [IL-6]) as well as apoptosis, or programmed cell death (a process regulated mainly by the Bcl-2 family of proteins). Proapoptotic proteins in this family include Bax and Bak. Conversely, Bcl-2 and Bcl-XL are antiapoptotic regulators. Therefore, to expand our understanding of liver regeneration, our study had 2 goals: first, to standardize 2 animal models of hepatectomy and liver regeneration using the newborn suckling and the weaning rat and second, to quantitate the expression levels of IL-6 and several members of the Bcl-2 gene family during the regeneration process.

METHODS

To create the experimental models, newborn suckling rats (age, 5-7 days; weight, 6-10 g) and weaning rats (age, 21-23 days; weight, 30-50 g) underwent 70% hepatectomy. The animals were subsequently sacrificed at days 1, 2, 3, 4, and 7 after hepatectomy, and the remnant liver lobes were harvested for routine histologic examination. Groups of healthy animals not operated on served as controls. For the experimental study, 6 newborn rats and 6 weaning rats underwent hepatectomy. The animals were killed 1 day after liver resection and the remnant livers were harvested to assess gene expression by quantitative reverse transcription-polymerase chain reaction. The hepatectomized groups were compared with control and sham groups.

RESULTS

During the creation of the experimental models, 70% of the suckling animals and all the weaning animals survived the hepatectomy. The decreased liver weight was completely restored to control levels by day 7 after hepatectomy. Histologically, the remnant livers of both hepatectomy groups exhibited steatosis, tumefaction of hepatocytes, and mitosis, which ceased at 7 days after the hepatectomy. The weaning rat model showed more robust gene expression responses. Specifically, expression levels of IL-6 gene were significantly increased after both surgical insult (sham group) and hepatectomy. However, this increase was significantly higher in the latter group. Furthermore, hepatectomy promoted a decrease in the expression levels of the proapoptotic genes and an increase in the expression levels of Bcl-2.

CONCLUSIONS

Our data indicate that regulation of both IL-6 and genes involved in apoptosis are strongly implicated in the mechanisms of liver regeneration and that the weaning rat model represents an attractive model system for future investigations in this area.

Delayed liver regeneration in mice lacking liver serum response factor

Various immediate early genes (IEGs) upregulated during the early process of liver regeneration are transcriptional targets of the serum response factor (SRF). We show here that the expression of SRF is rapidly induced in rodent liver after partial hepatectomy. Because the inactivation of the SRF gene in mice is embryonic lethal, the in vivo role of SRF in liver regeneration after partial hepatectomy was analyzed in mutant mice conditionally deleted for SRF in the liver. We demonstrate that SRF is not an essential factor for liver ontogenesis. However, adult mutant mice show impaired liver regeneration after partial hepatectomy, associated with a blunted upregulation of various SRF target IEGs. In conclusion, our work suggests that SRF is an early response transcription factor that may contribute to the initial phases of liver regeneration through its activation of IEGs.

The sphingosine 1-phosphate receptor S1P2 triggers hepatic wound healing

Sphingosine 1-phosphate (S1P) is a bioactive sphingolipid produced by sphingosine kinase (SphK1 and 2). We previously showed that S1P receptors (S1P1, S1P2, and S1P3) are expressed in hepatic myofibroblasts (hMF), a population of cells that triggers matrix remodeling during liver injury. Here we investigated the function of these receptors in the wound healing response to acute liver injury elicited by carbon tetrachloride, a process that associates hepatocyte proliferation and matrix remodeling. Acute liver injury was associated with the induction of S1P2, S1P3, SphK1, and SphK2 mRNAs and increased SphK activity, with no change in S1P1 expression. Necrosis, inflammation, and hepatocyte regeneration were similar in S1P2-/- and wild-type (WT) mice. However, compared with WT mice, S1P2-/- mice displayed reduced accumulation of hMF, as shown by lower induction of smooth muscle alpha-actin mRNA and lower induction of TIMP-1, TGF-beta1, and PDGF-BB mRNAs, overall reflecting reduced activation of remodeling in response to liver injury. The wound healing response was similar in S1P3-/- and WT mice. In vitro, S1P enhanced proliferation of cultured WT hMF, and PDGF-BB further enhanced the mitogenic effect of S1P. In keeping with these findings, PDGF-BB up-regulated S1P2 and SphK1 mRNAs, increased SphK activity, and S1P2 induced PDGF-BB mRNA. These effects were blunted in S1P2-/- cells, and S1P2-/- hMF exhibited reduced mitogenic and comitogenic responses to S1P. These results unravel a novel major role of S1P2 in the wound healing response to acute liver injury by a mechanism involving enhanced proliferation of hMF.

Mice Lackingbi-1Gene Show Accelerated Liver Regeneration

The liver has enormous regenerative capacity such that, after partial hepatectomy, hepatocytes rapidly replicate to restore liver mass, thus providing a context for studying in vivo mechanisms of cell growth regulation. Bax inhibitor-1 (BI-1) is an evolutionarily conserved endoplasmic reticulum (ER) protein that suppresses cell death. Interestingly, the BI-1 protein has been shown to regulate Ca(2+) handling by the ER similar to antiapoptotic Bcl-2 family proteins. Effects on cell cycle entry by Bcl-2 family proteins have been described, prompting us to explore whether bi-1-deficient mice display alterations in the in vivo regulation of cell cycle entry using a model of liver regeneration. Accordingly, we compared bi-1(+/+) and bi-1(-/-) mice subjected to partial hepatectomy with respect to the kinetics of liver regeneration and molecular events associated with hepatocyte proliferation. We found that bi-1 deficiency accelerates liver regeneration after partial hepatectomy. Regenerating hepatocytes in bi-1(-/-) mice enter cell cycle faster, as documented by more rapid incorporation of deoxynucleotides, associated with earlier increases in cyclin D1, cyclin D3, cyclin-dependent kinase (Cdk) 2, and Cdk4 protein levels, more rapid hyperphosphorylation of retinoblastoma protein, and faster degradation of p27(Kip1). Dephosphorylation and nuclear translocation of nuclear factor of activated T cells 1 (NFAT1), a substrate of the Ca(2+)-sensitive phosphatase calcineurin, were also accelerated following partial hepatectomy in BI-1-deficient hepatocytes. These findings therefore reveal additional similarities between BI-1 and Bcl-2 family proteins, showing a role for BI-1 in regulating cell proliferation in vivo, in addition to its previously described actions as a regulator of cell survival.

The involvement of heat shock proteins in murine liver regeneration

Partial hepatectomy (PHx) in mammals is a very common experimental model to investigate the process of liver regeneration. The surgery itself could give birth to a series of stresses, such as the temporary raise of body temperature and the ischaemia-reperfusion injury. Heat shock proteins (HSPs) were a family of stress-inducible proteins involved in maintaining cell homeostasis and regulating the immune system. In our study, we intended to investigate the expression and role of HSPs in liver regeneration. Using RT-PCR and Western blotting, we determined the expression in regenerating liver of HSP27, HSP60, HSP70 and HSP90 in mRNA level and protein level, respectively, with mice treated with sham operation as controls. We also used quercertin as an inhibitor of HSPs to explore their effects on liver regeneration. We found that hepatic expression of HSPs increased at the early phase of liver regeneration and declined to the constitutively low level later. Moreover, quercetin pretreatment delayed the progress of liver regeneration in mice via inhibition of HSPs. The results indicated that HSPs played an important role in liver regeneration.

Expression patterns and action analysis of genes associated with inflammatory responses during rat liver regeneration

AIM: To study the relationship between inflammatory response and liver regeneration (LR) at transcriptional level.

METHODS: After partial hepatectomy (PH) of rats, the genes associated with inflammatory response were obtained according to the databases, and the gene expression changes during LR were checked by the Rat Genome 230 2.0 array.

RESULTS: Two hundred and thirty-nine genes were associated with liver regeneration. The initial and total expressing gene numbers found in initiation phase (0.5-4 h after PH), G₀/G₁ transition (4-6 h after PH), cell proliferation (6-66 h after PH), cell differentiation and structure-function reconstruction (66-168 h after PH) of liver regeneration were 107, 34, 126, 6 and 107, 92, 233, 145 respectively, showing that the associated genes were mainly triggered at the beginning of liver regeneration, and worked at different phases. According to their expression similarity, these genes were classified into 5 groups: only up-regulated, predominantly up-, only down-, predominantly down-, up- and down-, involving 92, 25, 77, 14 and 31 genes, respectively. The total times of their up- and down-regulated expression were 975 and 494, respectively, demonstrating that the expressions of the majority of genes were increased, and that of a few genes were decreased. Their time relevance was classified into 13 groups, showing that the cellular physiological and biochemical activities were staggered during liver regeneration. According to gene expression patterns, they were classified into 33 types, suggesting that the activities were diverse and complex during liver regeneration.

CONCLUSION: Inflammatory response is closely associated with liver regeneration, in which 239 LR-associated genes play an important role.

Gene expression analysis identifies novel genes participating in early murine liver development and adult liver regeneration

Adult liver tissue regeneration may recapitulate molecular events of liver organogenesis. As gaps in our understanding of the fundamental processes that govern development and regeneration of the liver still exist, we studied gene expression in the developing liver at embryonic day 9.5 post coitum (E d9.5 p.c.). Microarray data from E d9.5 p.c. as well as previously published data from embryonic day 11.5 post coitum (E d11.5 p.c.) and embryonic day 13.5 post coitum (E d13.5 p.c.) were subjected to cluster analysis. This led to the identification of 130 genes which were characterized by continuous expression at all stages of liver development with peak expression of 44 genes at E d9.5 p.c. Five of these genes, previously not known to be associated with early liver development or with adult liver regeneration were selected for further analysis. The expression of the genes was studied by real-time polymerase chain reaction at 0, 2, 4, 6, 12, 24 and 48 hr after partial hepatectomy in the adult liver. Two of the genes, growth arrest protein 43 (GAP43) and paired-like homeodomain transcription factor 2 (Pitx2) were exclusively detected at 24 hr, whereas the genes Twist1, Midkine, and zinc finger protein of cerebellum 1 (Zic1) each showed a specific expression profile in the regenerating liver with peak expressions at 4, 24, and 6 hr, respectively. In summary, we were able to identify novel genes, that may act as regulators during liver formation as well as in the regeneration phase of adult liver. This information may contribute to the development of new targets for the treatment of liver diseases in the future.

Tri-iodothyronine as a stimulator of liver regeneration after partial and subtotal hepatectomy

BACKGROUND

Tri-iodothyronine (T3) has been shown to be a hepatic mitogen. We investigated whether exogenous application of T3 improves liver regeneration after 70% partial hepatectomy (PH) and confers a survival advantage after 90% subtotal hepatectomy (SH) in rats and whether this is associated with the stimulation of angiogenesis.

METHODS

Rats were subjected to PH or SH 10 days after injection of a single dose of T3. Liver body weight ratio (LBR), hepatic proliferation (Ki-67), biochemical markers as well as vascular endothelial growth factor (VEGF) expression were assessed by immunohistochemistry. Gene expression of pathogenic relevant genes was determined by customized cDNA arrays and quantitative RT-PCR.

RESULTS

T3-treated rats showed an increased LBR and Ki-67 index after PH and SH, which reached statistical significance compared to placebo-treated rats (p < 0.05). On the transcriptional level, T3-treated rats had an increased expression of VEGF as demonstrated by immunohistochemistry, which was associated with a higher expression of its receptor Flt-1.

CONCLUSIONS

Exogenous administration of T3 ameliorates liver regeneration after 70% PH and 90% SH, possibly due to stimulation of angiogenesis. Therefore, its clinical use might be of interest due to its excellent general practicability.

Hepatocytes with extensive telomere deprotection and fusion remain viable and regenerate liver mass through endoreduplication

We report that mouse liver cells are highly resistant to extensive telomere dysfunction. In proliferating cells, telomere dysfunction results in chromosome end fusions, a DNA damage signal, and apoptosis or senescence. To determine the consequences of telomere dysfunction in noncycling cells, we used conditional deletion of the telomeric protein TRF2 in hepatocytes. TRF2 loss resulted in telomeric accumulation of gamma-H2AX and frequent telomere fusions, indicating telomere deprotection. However, there was no induction of p53 or apoptosis, and liver function appeared unaffected. Furthermore, the loss of TRF2 did not compromise liver regeneration after partial hepatectomy. Remarkably, liver regeneration occurred without cell division involving endoreduplication and cell growth, thereby circumventing the chromosome segregation problems associated with telomere fusions. We conclude that nondividing hepatocytes can maintain and regenerate liver function despite substantial loss of telomere integrity.

Transcription of the MAT2A gene, coding for methionine adenosyltransferase, is up-regulated by E2F and Sp1 at a chromatin level during proliferation of liver cells

Methionine adenosyltransferase (MAT) is an essential enzyme because it catalyzes the formation of S-adenosylmethionine, the main methyl donor. Two MAT-encoding genes (MAT1A, MAT2A) are found in mammals. The latter is expressed in proliferating liver, dedifferentiation and cancer, whereas MAT1A is expressed in adult quiescent hepatocytes. Here, we report studies on the molecular mechanisms controlling the induction of MAT2A in regenerating rat liver and in proliferating hepatocytes. The MAT2A is up-regulated at two discrete moments during liver regeneration, as confirmed by RNApol-ChIP analysis. The first one coincides with hepatocyte priming (i.e. G0-G1 transition), while the second one takes place at the G1-S interface. Electrophoretic mobility shift assays showed that a putative E2F sequence present in MAT2A promoter binds this factor and ChIP assays confirmed that E2F1, E2F3 and E2F4, as well as the pocket protein p130, are bound to the promoter in quiescent liver. MAT2A activation is accompanied by changes in the binding of histone-modifying enzymes to the promoter. Interestingly, p130 is not displaced from MAT2A promoter during hepatocyte priming, but it is in the late expression of the gene at the G1-S transition. Finally, the transcription factor Sp1 seems to play a decisive role in MAT2A induction, as it binds the promoter when the gene is being actively transcribed. In summary, the present work shows that the molecular mechanism of MAT2A expression is different during G0-G1 or G1-S transition and this may be related to the distinct requirements of S-adenosylmethionine during liver regeneration.

Gene Expression Profiles in Living Donors Immediately After Partial Hepatectomy—The Initial Response of Liver Regeneration

BACKGROUND/PURPOSE

Gene expression profiles of liver regeneration are well explored in rat models. However, there are limited relative data in humans. This study aimed to show that mRNA expression profiles change immediately after right hepatectomy in living-related donors and correlate with mechanisms of liver regeneration reported in the literature.

METHODS

Prospective study was conducted from March 2003 to August 2004. Living-related donors who donated right lobe of liver were included. Liver biopsies were performed at the beginning and, 5 hours later, at the end of liver resection. RNAs were isolated to synthesize cRNA. Oligo DNA microarray experiments were conducted and paired signal intensity ratios (Cy3/Cy5) were normalized with rank-invariant global Lowess regression analysis by taking base two logarithms. Genes whose average residuals more than 2.5-fold increased or less than -2.5-fold decreased were selected to get the most pronounced expression changes during this period.

RESULTS

Five of 34 donors were included with qualified samples. The expression patterns of paired DNA microarray experiments were similar in five donors. A total of 28 upregulated and 14 downregulated genes were collected. Acute-phase proteins (serum amyloid A, complement-reactive protein, heme oxygenase-1) were upregulated. Genes related to growth signal transduction (G-protein coupled receptor-30) were downregulated.

CONCLUSION

Gene expression profiles immediately after partial hepatectomy were reported first in humans with the techniques of oligo DNA microarray, which were compatible with the initial gene expression patterns of liver regeneration in rats.

Expression patterns and action analysis of genes associated with physiological responses during rat liver regeneration: Innate immune response

AIM: To study the relationship between innate immune response and liver regeneration (LR) at transcriptional level.

METHODS: Genes associated with innate immunity response were obtained by collecting the data from databases and retrieving articles. Gene expression changes in rat regenerating liver were detected by rat genome 230 2.0 array.

RESULTS: A total of 85 genes were found to be associated with LR. The initially and totally expressed number of genes at the phases of initiation [0.5-4 h after partial hepatectomy (PH)], transition from G0 to G1 (4-6 h after PH), cell proliferation (6-66 h after PH), cell differentiation and structure-function reconstruction (66-168 h after PH) was 36, 9, 47, 4 and 36, 26, 78, 50, respectively, illustrating that the associated genes were mainly triggered at the initial phase of LR and worked at different phases. According to their expression similarity, these genes were classified into 5 types: 41 up-regulated, 4 predominantly up-regulated, 26 down-regulated, 6 predominantly down-regulated, and 8 approximately up/down-regulated genes, respectively. The expression of these genes was up-regulated 350 times and down-regulated 129 times respectively, demonstrating that the expression of most genes was enhanced while the expression of a small number of genes was decreased during LR. Their time relevance was classified into 14 groups, showing that the cellular physiological and biochemical activities during LR were staggered. According to the gene expression patterns, they were classified into 28 types, indicating that the cellular physiological and biochemical activities were diverse and complicated during LR.

CONCLUSION: Congenital cellular immunity is enhanced mainly in the forepart, prophase and anaphase of LR while congenital molecular immunity is increased dominantly in the forepart and anaphase of LR. A total of 85 genes associated with LR play an important role in innate immunity.

Expression patterns and action analysis of genes associated with hepatitis virus infection during rat liver regeneration

AIM: To study the action of hepatitis virus infection-associated genes at transcription level during liver regeneration (LR).

METHODS: Hepatitis virus infection-associated genes were obtained by collecting the data from databases and retrieving the correlated articles, and their expression changes in the regenerating rat liver were detected with the rat genome 230 2.0 array.

RESULTS: Eighty-eight genes were found to be associated with liver regeneration. The number of genes initially and totally expressed during initial LR [0.5-4 h after partial hepatectomy (PH)], transition from G0 to G1 (4-6 h after PH), cell proliferation (6-66 h after PH), cell differentiation and reorganization of structure-function (66-168 h after PH) was 37, 8, 48, 3 and 37, 26, 80, 57, respectively, indicating that the genes were mainly triggered at the early stage of LR (0.5-4 h after PH), and worked at different phases. These genes were classified into 5 types according to their expression similarity, namely 37 up-regulated, 9 predominantly up-regulated, 34 down-regulated, 6 predominantly down-regulated and 2 up/down-regulated genes. Their total up- and down-regulation frequencies were 359 and 149 during LR, indicating that the expression of most genes was enhanced, while the expression of a small number of genes was attenuated during LR. According to time relevance, they were classified into 12 groups (0.5 and 1 h, 2 and 4 h, 6 h, 8 and 12 h, 16 and 96 h, 18 and 24 h, 30 and 42 h, 36 and 48 h, 54 and 60 h, 66 and 72 h, 120 and 144 h, 168 h), demonstrating that the cellular physiological and biochemical activities during LR were fluctuated. According to expression changes of the genes, their expression patterns were classified into 23 types, suggesting that the cellular physiological and biochemical activities during LR were diverse and complicated.

CONCLUSION: The anti-virus infection capacity of regenerating liver can be enhanced and 88 genes play an important role in LR.

Expression patterns and action analysis of genes associated with physiological responses during rat liver regeneration: cellular immune response

AIM

To study the cellular immune response during rat liver regeneration (LR) at a transcriptional level.

METHODS

Genes associated with the cellular immune response were obtained by collecting the data from databases and retrieving articles. Gene expression changes during LR were detected by rat genome 230 2.0 array.

RESULTS

A total of 127 genes were found to be associated with LR. The number of initially and totally expressing genes in the initial phase of LR [0.5-4 h after partial hepatectomy (PH)], transition from G(0)-G(1) (4-6 h after PH), cell proliferation (6-66 h after PH), cell differentiation and structure-function reconstruction (66-168 h after PH) was 54, 11, 34, 3 and 54, 49, 70, 49 respectively, illustrating that the associated genes were mainly triggered at the initiation of LR, and worked at different phases. According to their expression similarity, these genes were classified into 41 up-regulated, 21 predominantly up-regulated, 41 down-regulated, 14 predominantly down-regulated, 10 similarly up-regulated and down-regulated genes, respectively. The total up- and down-regulated expression times were 419 and 274, respectively, demonstrating that the expression of most genes was increased while the expression of a small number of genes was decreased. Their time relevance was classified into 14 groups, showing that the cellular physiological and biochemical activities were staggered during LR. According to the gene expression patterns, they were classified into 21 types, showing the activities were diverse and complicated during LR.

CONCLUSION

Antigen processing and presentation are enhanced mainly in the forepart, prophase and anaphase of LR. T-cell activation and antigen elimination are enhanced mainly in the forepart and prophase of LR. A total of 127 genes associated with LR play an important role in cellular immunity.

Transient Expression of Bone Morphogenic Protein-2 in Acute Liver Injury by Carbon Tetrachloride

Acute liver injury induced by administration of carbon tetrachloride (CCl4) was shown to be a model of wound-repair in rat liver. Albumin gene expression was significantly reduced at 24 h post injection with CCl4, but recovered at 48 h. We also observed significant and transient expression of bone morphogenic protein-2 (BMP-2) at 6-24 h post treatment. This expression was also shown with depletion of Kupffer cell by GdCl3, and immunostaining with anti-BMP-2 antibody showed BMP-2-producing cells interspersed in intralobular spaces of injured liver. These observations suggest that BMP-2 secreted from oval-like cells plays important roles in the wound healing response of injured liver.

Expression pattern and action analysis of genes associated with the responses to chemical stimuli during rat liver regeneration

AIM: To study the genes associated with the responses to chemokines, nutrients, inorganic substances, organic substances and xenobiotics after rat partial hepatectomy (PH) at transcriptional level.

METHODS: The associated genes involved in the five kinds of responses were obtained from database and literature, and the gene expression changes during liver regeneration in rats were checked by the Rat Genome 230 2.0 array.

RESULTS: It was found that 60, 10, 9, 6, 26 genes respectively participating in the above five kinds of responses were associated with liver regeneration. The numbers of initially and totally expressed genes occurring in the initial phase of liver regeneration (0.5-4 h after PH), G₀/G₁ transition (4-6 h after PH), cell proliferation (6-66 h after PH), cell differentiation and structure-functional reconstruction (66-168 h after PH) were 51, 19, 52, 6 and 51, 43, 98, 68 respectively, illustrating that the associated genes were mainly triggered in the initiation and transition stages, and functioned at different phases. According to their expression similarity, these genes were classified into 5 groups: only up-regulated (47), predominantly up-regulated (18), only down-regulated (24), predominantly down-regulated (10), and up- and down-regulated (8). The total times of their up-regulated and down-regulated expression were 441 and 221, demonstrating that the number of up-regulated genes is more than that of the down-regulated genes. Their time relevance and gene expression patterns were classified into 14 and 26 groups, showing that the cell physiological and biochemical activities were staggered, diversified and complicated during liver regeneration in rats.

CONCLUSION: The chemotaxis was enhanced mainly in the forepart and metaphase of LR. The response of regenerating liver to nutrients and chemical substances was increased, whereas that to xenobiotics was not strong. One hundred and seven genes associated with LR play important roles in the responses to chemical substances.

Expression patterns and action analysis of genes associated with drug-induced liver diseases during rat liver regeneration

AIM: To study the action of the genes associated with drug-induced liver diseases at the gene transcriptional level during liver regeneration (LR) in rats.

METHODS: The genes associated with drug-induced liver diseases were obtained by collecting the data from databases and literature, and the gene expression changes in the regenerating liver were checked by the Rat Genome 230 2.0 array.

RESULTS: The initial and total expression numbers of genes occurring in phases of 0.5-4 h after partial hepatectomy (PH), 4-6 h after PH (G0/G1 transition), 6-66 h after PH (cell proliferation), 66-168 h after PH (cell differentiation and structure-function reconstruction) were 21, 3, 9, 2 and 21, 9, 19, 18, respectively. It is illustrated that the associated genes were mainly triggered at the initial stage of LR and worked at different phases. According to their expression similarity, these genes were classified into 5 types: only up-regulated (12 genes), predominantly up-regulated (4 genes), only down-regulated (11 genes), predominantly down-regulated (3 genes), and approximately up-/down-regulated (2 genes). The total times of their up- and down-expression were 130 and 79, respectively, demonstrating that expression of most of the genes was increased during LR, while a few decreased. The cell physiological and biochemical activities during LR were staggered according to the time relevance and were diverse and complicated in gene expression patterns.

CONCLUSION: Drug metabolic capacity in regenerating liver was enhanced. Thirty-two genes play important roles during liver regeneration in rats.

Expression patterns and action analysis of genes associated with blood coagulation responses during rat liver regeneration

AIM: To study the blood coagulation response after partial hepatectomy (PH) at transcriptional level.

METHODS: After PH of rats, the associated genes with blood coagulation were obtained through reference to the databases, and the gene expression changes in rat regenerating liver were analyzed by the Rat Genome 230 2.0 array.

RESULTS: It was found that 107 genes were associated with liver regeneration. The initially and totally expressing gene numbers occurring in initiation phase of liver regeneration (0.5-4 h after PH), G₀/G₁ transition (4-6 h after PH), cell proliferation (6-66 h after PH), cell differentiation and structure-function reconstruction (66-168 h after PH) were 44, 11, 58, 7 and 44, 33, 100, 71 respectively, showing that the associated genes were mainly triggered in the forepart and prophase, and worked at different phases. According to their expression similarity, these genes were classified into 5 groups: only up-, predominantly up-, only down-, predominantly down-, up- and down-regulation, involving 44, 8, 36, 13 and 6 genes, respectively, and the total times of their up- and down-regulation expression were 342 and 253, respectively, demonstrating that the number of the up-regulated genes was more than that of the down- regulated genes. Their time relevance was classified into 15 groups, showing that the cellular physiological and biochemical activities were staggered during liver regeneration. According to gene expression patterns, they were classified into 29 types, suggesting that their protein activities were diverse and complex during liver regeneration.

CONCLUSION: The blood coagulation response is enhanced mainly in the forepart, prophase and anaphase of liver regeneration, in which the response in the forepart, prophase of liver regeneration can prevent the bleeding caused by partial hepatectomy, whereas that in the anaphase contributes to the structure-function reorganization of regenerating liver. In the process, 107 genes associated with liver regeneration play an important role.

Disruption of Phospholipase Cδ4 Gene Modulates the Liver Regeneration in Cooperation with Nuclear Protein Kinase C

Phospholipase Cdelta4 (PLC delta4) gene has been cloned from the cDNA library of regenerating rat liver. Using PLC delta4 gene-disrupted mice (PLC delta4(-/-)), we studied a role of PLC delta4 during liver regeneration after partial hepatectomy (PH). In PLC delta4(-/-), liver regeneration occurred in an apparently normal way. However, BrdU-indices indicated that PLC delta4 gene disruption delayed the onset of DNA synthesis by 2 h. Noticeably, the BrdU-indices in PLC delta4(+/+) remained rather constant throughout S phase, 25-35%, whereas in PLC delta4(-/-), it fluctuated drastically from 25% at 34 h to 65% at late S, 42 h after PH. This fact showed that PLC delta4 gene disruption caused a higher synchronization of cell proliferation. The mRNA for PLC delta4 in PLC delta4(+/+) appeared at late G1, and the expression continued throughout S phase. PLC activity increased transiently in chromatin at the late G1 and S phases in only PLC delta4(+/+), but not in PLC delta4(-/-). The specific increases in PLC activity well correlated with the transient increases of protein kinase C (PKC) alpha in chromatin of PLC delta4(+/+). PKC epsilon also increased transiently in chromatin from PLC delta4(+/+) at late S. It is concluded that PLC delta4 regulates the liver regeneration in cooperation with nuclear PKC alpha and epsilon.

Increased DNA binding activity of NF-kB, STAT-3, SMAD3 and AP-1 in acutely damaged liver

AIM: To investigate the role of genes and kinetics of specific transcription factors in liver regeneration, and to analyze the gene expression and the activity of some molecules crucially involved in hepatic regeneration.

METHODS: USING gel-shift assay and RT-PCR, transcription factors, such as NF-κB, STAT-3, SMAD3 and AP-1, and gene expression of inducible nitric oxide synthase (iNOS), hepatocyte growth factor (HGF) and c-met were analyzed in an animal model of chemically induced hepatectomy.

RESULTS: Gene expression of HGF and its receptor c-met peaked at 3 h and 24 h after acute CCl₄ intoxi-cation. iNOS expression was only observed from 6 to 48 h. Transcriptional factor NF-κB had an early activation at 30 min after acute liver damage. STAT-3 peaked 3 h post-intoxication, while AP-1 displayed a peak of activation at 48 h. SMAD3 showed a high activity at all analyzed times.

CONCLUSION: TNF-α and IL-6 play a central role in hepatic regeneration. These two molecules are responsible for triggering the cascade of events and switch-on of genes involved in cell proliferation, such as growth factors, kinases and cyclins which are direct participants of cell proliferation.

Comprehensive analysis of differential gene expression profiles on d-galactosamine-induced acute mouse liver injury and regeneration

Microarray analysis of RNA from d-galactosamine (GalN)-administered mouse livers was performed to establish a global gene expression profile during injury and regeneration stages at two different doses. A single dose of GalN at 266 or 26.6 mg/kg body weight was given intraperitoneally, and the liver samples were obtained after 6, 24, and 72 h. Histopathologic studies enabled the classification of the D-galactosamine effect into injury (6, 24 h) and regeneration (72 h) stages. By using the Applied Biosystems mouse genome survey microarray, a total of 7267 out of 33,315 (21.8%) genes were found to be statistically reliable at p<0.05 by two-way ANOVA, and 1469 (4.4%) probes at false discovery rate <5% by significance analysis of microarray. Among the statistically reliable clones by both analytical methods, 389 genes were differentially expressed when compared with non-treated control, with more than a 1.625-fold difference (which equals 0.7 in log(2) scale) at one or more GalN treatment conditions and with less than 1.625-fold difference at all three vehicle-treated conditions. Three hundred thirty six genes and 13 genes were identified as injury- and regeneration-specific genes, respectively, showing that most of the transcriptomic changes were seen during the injury stage. Furthermore, multiple genes involved in protein synthesis and degradation, mRNA processing and binding, and cell cycle regulation showed variable transcript levels upon acute GalN administration.

c-Jun/AP-1 controls liver regeneration by repressing p53/p21 and p38 MAPK activity

The AP-1 transcription factor c-Jun is a key regulator of hepatocyte proliferation. Mice lacking c-Jun in the liver (c-jun (Deltali*)) display impaired liver regeneration after partial hepatectomy (PH). This phenotype correlates with increased protein levels of the cdk-inhibitor p21 in the liver. We performed PH experiments in several double-knockout mouse models to genetically identify the signaling events regulated by c-Jun. Inactivation of p53 in c-jun (Deltali*) mice abrogated both hepatocyte cell cycle block and increased p21 protein expression. Consistently, liver regeneration was rescued in c-jun (Deltali*) p21 (-/-) double-mutant mice. This indicated that c-Jun controls hepatocyte proliferation by a p53/p21-dependent mechanism. Analyses of p21 mRNA and protein expression in livers of c-jun (Deltali*) mice after PH revealed that the accumulation of p21 protein is due to a post-transcriptional/post-translational mechanism. We have investigated several candidate pathways implicated in the regulation of p21 expression, and observed increased activity of the stress kinase p38 in regenerating livers of c-jun (Deltali*) mice. Importantly, conditional deletion of p38alpha in livers of c-jun (Deltali*) mice fully restored hepatocyte proliferation and attenuated increased p21 protein levels after PH. These data demonstrate that c-Jun/AP-1 regulates liver regeneration through a novel molecular pathway that involves p53, p21, and the stress kinase p38alpha.

Comprehensive analysis of differential gene expression profiles on diclofenac-induced acute mouse liver injury and recovery

Microarray analysis of RNA from diclofenac-administered mouse livers was performed to establish a global gene expression profile during injury and recovery stages at two different doses. A single dose of diclofenac at 9.5 mg/kg or 0.95 mg/kg body weight was given orally, and the liver samples were obtained after 6, 24, and 72 h. Histopathologic studies enabled the classification of the diclofenac effect into injury (6, 24 h) and recovery (72 h) stages. By using the Applied Biosystems Mouse Genome Survey Microarray, a total of 7370 out of 33,315 (22.1%) genes were found to be statistically reliable at p<0.05 by two-way ANOVA, and 602 (1.8%) probes at false discovery rate <5% by Significance Analysis of Microarray. Among the statistically reliable clones by both analytical methods, 49 genes were differentially expressed with more than a 1.625-fold difference (which equals 0.7 in log(2) scale) at one or more treatment conditions. Forty genes and two genes were identified as injury- and recovery-specific genes, respectively, showing that most of the transcriptomic changes were seen during the injury stage. Furthermore, multiple genes involved in oxidative stress, eicosanoid synthesis, apoptosis, and ATP synthesis showed variable transcript levels upon acute diclofenac administration.

Interleukin-15 increases hepatic regenerative activity

BACKGROUND/AIMS

Interleukin-15 (IL-15) is expressed in many organs. It generally inhibits apoptosis and increases cellular proliferation and differentiation. However, IL-15's roles in liver are unknown. We aimed to determine if IL-15 influences hepatic integrity and regenerative activity.

METHODS

Expression of IL-15 and its receptors was evaluated in several liver injury models, primary hepatocytes, and two liver cell lines. Effects of IL-15 on viability, proliferation, and apoptosis were assessed in cultured liver cells, and also in the livers of healthy mice.

RESULTS

IL-15 and its receptors are expressed constitutively in healthy livers, and ligand expression is induced in injured livers. Cultured primary hepatocytes and liver cell lines express IL-15 and its receptors. Administration of IL-15 has minimal effects on cultured liver cells, but significantly up-regulates oval cell accumulation, cyclin mRNA expression, and mature hepatocyte replication in healthy mice. These effects are associated with focal hepatic inflammation and increased expression of TNF-alpha and IFN-gamma, but not with increased cell death or aminotransferase release.

CONCLUSIONS

IL-15 expression increases during liver injury and IL-15 treatment induces a wound healing-type response in healthy adult mice. These findings suggest that IL-15 may contribute to regenerative activity in damaged liver.

Lipid spectrum in fractions of liver cell chromatin from mice after partial hepatectomy

The qualitative and quantitative differences in lipids composition were found in chromatin fractions differing by attachment to the nuclear matrix and transcriptional activity. During liver regeneration after partial hepatectomy Changes in the lipid spectrum of chromatin fractions in G1- and S-phases are associated with transcriptional activity and their primary involvement in replication.

Hematopoietic stem cell mobilization after rat partial orthotopic liver transplantation

BACKGROUND

On the basis of the recently recognized potential of hematopoietic stem cells (HSC) to give rise to hepatocytes, we investigated the possibility that HSC could be mobilized and home to the injured liver promoting tissue repair after 50% partial orthotopic liver transplantation (PLTx) in the rat.

METHODS

Using sex-mismatched (female to male) syngeneic SD rats, we performed 50% PLTx or whole orthotopic liver transplantation (WLTx) versus 50% partial hepatectomy (PHx) and sham operation (O). Elements with stem cell markers were detected in peripheral blood (PB) and in the liver. Liver injury and regeneration were estimated. The sex-determining region for Y chromosome gene (SRY) was used to define cell origin by in situ hybridization in liver sections.

RESULTS

Comparison of WLTx and PHx groups showed a lower survival rate (50%), in the PLTx group were (P<.05). Further, the liver injury was more serious and the levels of serum biochemical parameters were higher. Compared with PHx groups, on days 3 and 5 postoperatively, the mitosis index and the expression of PCNA were lower among the PLTx groups. Compared with WLTx and sham operation groups, beta2m-/Thy-1.1+, CD34+ cells in PB in PLTx groups and PHx were increased on day 1 postoperatively and decreased on the following days. Compared with PHx groups, beta2m-/Thy-1.1+, CD34+ cells were higher in PLTx. The CD34-, c-kit-, and Thy-1.1-positive cells detected in portal tract areas peaked during 3 to 5 days postoperatively in PLTx. Few SRY+ cells were detected in PLTx liver grafts.

CONCLUSIONS

beta2m-/Thy-1.1+ and CD34+ stem cells mobilized after PLTx and PHx may be related to the reduced-size liver. Few HSC are involved in liver regeneration in PLTx.

Concerted functions of Gab1 and Shp2 in liver regeneration and hepatoprotection

Liver regeneration is a rapid and concerted response to injury, in which growth factor-generated intracellular signals result in activation of transcription factors, DNA synthesis, and hepatocyte proliferation. However, the link between cytoplasmic signals resulting in proliferative response to liver injury remains to be elucidated. We show here that association of Gab1 adaptor protein and Shp2 tyrosine phosphatase is a critical event at the early phase of liver regeneration. Partial hepatectomy (PH) rapidly and transiently induced assembly of a complex comprising Shp2 and tyrosine-phosphorylated Gab1 in wild-type hepatocytes. Consistently, liver-specific Shp2 knockout (LSKO) and liver-specific Gab1 knockout (LGKO) mice displayed very similar phenotypes of defective liver regeneration triggered by PH, including blunted extracellular signal-regulated kinase 1/2 (Erk1/2) activation, decreased expression of immediate-early genes, and reduced levels of cyclins A, E, and B1, as well as suppression of hepatocyte proliferation. In contrast, the Akt and interleukin-6/Stat3 pathways were up-regulated posthepatectomy in LSKO and LGKO mice, accompanied by improved hepatoprotection. Collectively, this study establishes the physiological significance of the Gab1/Shp2 link in promoting mitogenic signaling through the Erk pathway in mammalian liver regeneration.

A liver specific gene that is expressed in growth hormone transgenic mice and in normal female mice as a function of age

Growth hormone (GH) acts on various organs to exert its growth and metabolic effects. GH induces transcription of a number of genes in different organs including liver. By performing subtractive hybridization analysis on liver cDNAs of GH transgenic and non-transgenic mice, differentially expressed cDNAs were obtained. This paper describes the isolation and characterization of a liver cDNA, termed cDNA #5, that contains 1897 bp and is predicted to encode a protein (P5) of 512 aa residues. P5 has five immunoglobulin related domains thus allowing it to be classified as a member of the immunoglobulin super family (IGSF). Also, P5 shows significant similarity to both rat and human alpha-1-B glycoprotein which is an acidic serum protein of unknown function. mRNA #5 was detected in the liver hepatocytes of male and female GH transgenic mice and in the liver of female, but not of male, non-transgenic mice. mRNA #5 was not present in dwarf mice including the Ames dwarf, those that express a GH antagonist and those with the GH receptor and binding protein gene disrupted. These findings suggest that induction of mRNA #5 in the liver requires a continuous pattern of GH secretion and an intact GH-GH receptor-signaling complex. mRNA #5 levels in female non-transgenic mice were observed to vary with age implying that gender-specific age-dependent factor(s) may be involved in the induction of mRNA #5. The appearance of mRNA #5 in post-hepatectomized liver that coincides with the proliferative phase of liver regeneration suggests that it may be involved in hepatocyte proliferation. Together these data suggest that expression of cDNA #5 is liver-specific, sexually dimorphic, age-dependent, and may be involved in hepatocyte hyperplasia and liver enlargement.

In vivo hepatic HB-EGF gene transduction inhibits Fas-induced liver injury and induces liver regeneration in mice: a comparative study to HGF

BACKGROUND/AIMS

It is unknown whether heparin-binding EGF-like growth factor (HB-EGF) can be a therapeutic agent, although previous studies suggested that HB-EGF might be a hepatotrophic factor. This study explores the potential of hepatic HB-EGF gene therapy in comparison with HGF.

METHODS

Mice received an intraperitoneal injection of the agonistic anti-Fas antibody 72 h after an intravenous injection of either adenoviral vector (1x10(11) particles) expressing human HB-EGF (Ad.HB-EGF), human HGF (Ad.HGF) or no gene (Ad.dE1.3), and were sacrificed 24 or 36 h later to assess liver injury and regeneration.

RESULTS

Exogenous HB-EGF was predominantly localized on the membrane, suggesting the initial synthesis of proHB-EGF in hepatocytes. The control Ad.dE1.3-treated mice represented remarkable increases in serum ALT and AST levels and histopathologically severe liver injuries with numerous apoptosis, but a limited number of mitogenic hepatocytes. In contrast, the liver injuries and apoptotic changes were significantly inhibited, but the mitogenic hepatocytes remarkably increased, in both the Ad.HB-EGF- and Ad.HGF-treated mice. More mitogenic hepatocytes and milder injuries were observed in the Ad.HB-EGF-treated mice.

CONCLUSIONS

HB-EGF has more potent protective and mitogenic effects for hepatocytes than HGF, at least for the present conditions. In vivo hepatic HB-EGF gene transduction is therapeutic for Fas-induced liver injury.