Initiation of liver growth by tumor necrosis factor: deficient liver regeneration in mice lacking type I tumor necrosis factor receptor

Liver regeneration is not altered in patients with nonalcoholic steatohepatitis (NASH) when compared to chronic hepatitis C infection with similar grade of inflammation

Fatty infiltration is associated with an increased incidence of complications and mortality after liver resection and transplantation. The aim of this study was to document the regenerative response in patients with hepatic steatosis and mild inflammatory activity (NASH) and to identify potential levels of impaired regeneration. Ki-67 immunostaining was similar in patients with NASH (ages 44.6 +/- 15 years, labeling index, 0.4 +/- 0.3%) when compared to patients with chronic hepatitis C infection (ages 50.7 +/- 17 years, labeling index; 0.4 +/- 0.7%). The labeling index was not increased in patients with a higher level of inflammation, a higher level of fibrosis, and a higher level of fat in either study group. In conclusion, liver regeneration is not altered in patients with nonalcoholic steatohepatitis, suggesting that the delayed postoperative liver failure seen in these patients may be related to another mechanism.

Analysis of host response to hepatectomy by simultaneous measurement of cytokines in the portal vein, caval vein and radial artery

We analysed the host response to hepatectomy by simultaneous measurement of various cytokines and their antagonists in the portal vein, caval vein and radial artery in 10 patients with hepatocellular carcinoma. Concentrations of tumour necrosis factor-alpha (TNF), interleukin (IL) 1 beta, IL-2, IL-6, IL-10, soluble TNF receptor type I (sTNF-R), soluble IL-2 receptor (sIL-2R), IL-1 receptor antagonist (IL-1ra), soluble CD14 (sCD14) and endotoxin were determined just before and 1 h after hepatectomy. The values of IL-6, sTNF-R and IL-1ra were significantly increased after hepatectomy at each sampling site. In contrast, the levels of sIL-2R and sCD14 after hepatectomy were significantly decreased, and the levels of IL-1 beta, IL-2 and IL-10 were below the detection limits. Differences in cytokine concentrations between sampling sites revealed that the surgical stress of hepatectomy induced significant IL-1ra production in the liver and sTNF-R and IL-6 production in the lungs. These results suggest that hepatic resection is followed by the production of cytokine antagonists, such as IL-1ra, sTNF-R and IL-6, which could represent an important regulatory mechanism against surgical stress.

Hepatocyte-specific inhibition of NF-kappaB leads to apoptosis after TNF treatment, but not after partial hepatectomy

One of the earliest TNF-dependent events to occur during liver regeneration is the activation of the transcription factor NF-kappaB through TNF receptor type 1. NF-kappaB activation in the liver can have both antiapoptotic and proliferative effects, but it is unclear which liver cell types, hepatocytes or nonparenchymal cells (NPCs), contribute to these effects. To specifically evaluate the role of hepatocyte NF-kappaB, we created GLVP/DeltaN-IkappaB(alpha) transgenic mice, in which expression of a deletion mutant of IkappaB(alpha) (DeltaN-IkappaB(alpha)) was induced in hepatocytes after injection of mifepristone. In control mice, injection of 25 microg/kg TNF caused NF-kappaB nuclear translocation in virtually all hepatocytes by 30 minutes and no detectable apoptosis, while in mice expressing DeltaN-IkappaB(alpha), NF-kappaB nuclear translocation was blocked in 45% of hepatocytes, leading to apoptosis 4 hours after TNF injection. In contrast, expression of DeltaN-IkappaBalpha in hepatocytes during the first several hours after partial hepatectomy did not lead to apoptosis or decreased proliferation. As NF-kappaB activation was not inhibited in liver NPCs, it is likely that these cells are responsible for mediating the proliferative and antiapoptotic effects of NF-kappaB during liver regeneration.

STAT3 contributes to the mitogenic response of hepatocytes during liver regeneration

STAT3 is rapidly induced during liver regeneration in an interleukin 6 (IL-6)-dependent fashion, and IL-6 is required for normal liver regeneration. We wanted to know whether STAT3 was also required for liver regeneration but disruption of the STAT3 gene during embryonic stages causes lethality. Therefore, an albumin promoter-driven Cre-loxP recombination system was used to create a STAT3 deletion in the adult mouse liver to study the role of STAT3 in liver regeneration. After partial hepatectomy, there was virtually no STAT3 RNA or protein induction in Alb(+) STAT3(fl/fl) livers. STAT3 DNA binding activity was also absent in Alb(+) STAT3(fl/fl) livers. Unlike in control livers, STAT1 was activated in STAT3 conditional-mutant livers posthepatectomy. Hepatocyte DNA synthesis at 40 h posthepatectomy in Alb(+) STAT3(fl/fl) livers was reduced to approximately one-third of the control. Alb(+) STAT3(fl/fl) livers had abnormalities in immediate-early gene activation that largely correlated with but were not identical to those seen in IL-6-/- livers. G(1) phase cyclins including cyclins D1 and E had lower expression levels in Alb(+) STAT3(fl/fl) livers, indicating an abnormal G(1) to S phase transition. Therefore, STAT3 accounts for part of the DNA synthetic response of the hepatocytes during liver regeneration, which cannot be compensated for by induction of STAT1. Normal activation of the MAPK pathway in Alb(+) STAT3(fl/fl) livers reinforces the fact that at least part of the effect of IL-6 on hepatocyte proliferation is not mediated by STAT3. This study provides the first in vivo evidence that STAT3 promotes cell cycle progression and cell proliferation under physiological growth conditions.

Hepatobiliary organic anion transporters are differentially regulated in acute toxic liver injury induced by carbon tetrachloride

BACKGROUND/AIMS

Hepatobiliary transporters are down-regulated in cholestasis, but their expression in acute, non-cholestatic, cytokine-mediated liver injury is unknown. Thus we studied the molecular mechanisms, by which sodium taurocholate cotransporting polypeptide (Ntcp), organic anion transporting polypeptide 1 (Oatp1), Oatp2, Oatp4, multidrug-resistance protein 2 (Mrp2) and bile salt export pump (Bsep) are regulated in liver injury induced by carbon tetrachloride (CCl(4)).

METHODS

mRNA and protein levels were determined in rats 24 and 72h after CCl(4) injection. Transporter gene transcription and binding activities of Ntcp and Mrp2 transactivators were assessed by nuclear runoff and electrophoretic mobility shift assays.

RESULTS

mRNA levels significantly declined to 41+/-44% for Ntcp, 65+/-41% for Oatp1 and 64+/-28% for Oatp2, but remained unchanged for Oatp4, canalicular Mrp2 and Bsep. Protein levels declined only for Oatp4 (-50+/-17%) and Ntcp (-23+/-13%) at 24h. Reduced mRNA levels (Ntcp, Oatp1, Oatp2) were associated with decreased transcriptional activities. Binding activity of Ntcp transactivators (hepatocyte nuclear factor 1 alpha (HNF1alpha) and CAAT enhancer binding protein alpha (C/EBPalpha) were reduced by 24h, whereas retinoid X receptor alpha (RXRalpha):retinoid acid receptor alpha (RARalpha) as transactivator of both Ntcp and Mrp2 remained unaltered. Recovery of acute hepatitis and changes in gene expression occurred after 72h.

CONCLUSIONS

Acute liver injury results in down-regulation of basolateral organic anion transporters similar to liver regeneration after partial hepatectomy, but in contrast to endotoxin-induced cholestasis. Maintained binding activity of RXRalpha:RARalpha may explain differences in Mrp2 expression.

Hepatocyte-specific inhibition of NF-kappaB leads to apoptosis after TNF treatment, but not after partial hepatectomy

One of the earliest TNF-dependent events to occur during liver regeneration is the activation of the transcription factor NF-kappaB through TNF receptor type 1. NF-kappaB activation in the liver can have both antiapoptotic and proliferative effects, but it is unclear which liver cell types, hepatocytes or nonparenchymal cells (NPCs), contribute to these effects. To specifically evaluate the role of hepatocyte NF-kappaB, we created GLVP/DeltaN-IkappaB(alpha) transgenic mice, in which expression of a deletion mutant of IkappaB(alpha) (DeltaN-IkappaB(alpha)) was induced in hepatocytes after injection of mifepristone. In control mice, injection of 25 microg/kg TNF caused NF-kappaB nuclear translocation in virtually all hepatocytes by 30 minutes and no detectable apoptosis, while in mice expressing DeltaN-IkappaB(alpha), NF-kappaB nuclear translocation was blocked in 45% of hepatocytes, leading to apoptosis 4 hours after TNF injection. In contrast, expression of DeltaN-IkappaBalpha in hepatocytes during the first several hours after partial hepatectomy did not lead to apoptosis or decreased proliferation. As NF-kappaB activation was not inhibited in liver NPCs, it is likely that these cells are responsible for mediating the proliferative and antiapoptotic effects of NF-kappaB during liver regeneration.

Impaired liver regeneration in mice by lipopolysaccharide via TNF-alpha/kallikrein-mediated activation of latent TGF-beta

BACKGROUND & AIMS

Because impaired regeneration after surgical treatment of the liver is influenced by circulating endotoxin, the underlying molecular mechanism was investigated.

METHODS

Lipopolysaccharide (LPS) was injected intraperitoneally into mice, followed 24 hours later by 67% partial hepatectomy. We measured serum tumor necrosis factor (TNF) alpha levels as well as proliferating cell nuclear antigen labeling index, transforming growth factor (TGF) beta expression, and plasma kallikrein (PLK) activities in regenerating livers. We also examined the effect of LPS, TNF-alpha, and PLK on latent TGF-beta activation in homotypic and heterotypic cultures of rat or mouse hepatic stellate cells and Kupffer cells.

RESULTS

Serum TNF-alpha levels increased after LPS (500 ng/g body wt) injection and after partial hepatectomy, accompanying TGF-beta-mediated suppression of hepatic proliferating cell nuclear antigen labeling index. This suppression was mimicked by a combination of preadministration of 50 ng/g body wt LPS and postoperative administration of 5 ng/g body wt TNF-alpha. In vitro, LPS stimulated Kupffer cells to secrete TNF-alpha, which enhanced PLK activity on the hepatic stellate cell surface through increasing PLK binding, thereby inducing proteolytic activation of latent TGF-beta and its autoinduction. Blockade of TGF-beta, TNF-alpha, or PLK activity prevented LPS-induced impaired regeneration in vivo.

CONCLUSIONS

LPS provokes TNF-alpha/PLK-mediated proteolytic activation of latent TGF-beta in hepatic stellate cells, leading to impaired liver regeneration after partial hepatectomy.

Cocarcinogenic effects of alcohol in hepatocarcinogenesis

Alcohol is a major aetiological factor in hepatocarcinogenesis but our understanding of its importance as a modulating factor is just beginning to emerge. In the present review, a number of possible cofactors and mechanisms are discussed by which alcohol may enhance the development of hepatoma. These include dietary or environmental carcinogens ingested along with alcoholic beverages, alcoholic cirrhosis as a precancerous condition, and the effects of alcohol metabolism.

Macrophage migration inhibitory factor in drug-induced liver injury: a role in susceptibility and stress responsiveness

Idiosyncratic drug-induced hepatitis may depend upon many factors including a balance between pro- and anti-inflammatory mediator production levels. Using a guinea pig model of liver injury induced by bioactivation of the anesthetic drug, halothane, we found that toxicity was commensurate with an increase in serum macrophage migration inhibitory factor (MIF), a pro-inflammatory signal and counter-regulator of glucocorticoids, but only in susceptible animals. The pathogenic role of MIF was further investigated using a murine model in which liver injury was induced by the reactive metabolite of another drug, acetaminophen (APAP). MIF leakage from the liver into the sera preceded peak increases in toxicity following APAP administration. MIF null (-/-) mice were significantly less susceptible to this toxicity at 8 h. At 48 h following a 300 mg/kg dose, complete lethality was observed in wild-type mice, while 46% survival was noted in MIF-/- mice. The decreased hepatic injury in MIF-/- mice correlated with a reduction in mRNA levels of interferon-gamma and a significant increase in heat shock protein expression, but was unrelated to the APAP-protein adduct formation in the liver. These findings support MIF as a critical pro-toxicant signal in drug-induced liver injury with potentially important and novel effects on heat shock protein responsiveness.

RANK-L and RANK: T cells, bone loss, and mammalian evolution

TNF and TNFR family proteins play important roles in the control of cell death, proliferation, autoimmunity, the function of immune cells, or the organogenesis of lymphoid organs. Recently, novel members of this large family have been identified that have critical functions in immunity and that couple lymphoid cells with other organ systems such as bone morphogenesis and mammary gland formation in pregnancy. The TNF-family molecule RANK-L (RANK-L, TRANCE, ODF) and its receptor RANK are key regulators of bone remodeling, and they are essential for the development and activation of osteoclasts. Intriguingly, RANK-L/RANK interactions also regulate T cell/dendritic cell communications, dendritic cell survival, and lymph node formation; T cell-derived RANK-L can mediate bone loss in arthritis and periodontal disease. Moreover, RANK-L and RANK are expressed in mammary gland epithelial cells, and they control the development of a lactating mammary gland during pregnancy and the propagation of mammalian species. Modulation of these systems provides us with a unique opportunity to design novel therapeutics to inhibit bone loss in arthritis, periodontal disease, and osteoporosis.

Induction of macrophage-inflammatory protein-3alpha gene expression by TNF-dependent NF-kappaB activation

Macrophage-inflammatory protein-3alpha (MIP-3alpha), also designated as liver and activation-regulated chemokine (LARC), Exodus, or CCL20, is a recently identified CC chemokine that is expected to play a crucial role in the initiation of immune responses. In this study, we describe that MIP-3alpha expression is under the direct control of NF-kappaB, a key transcription factor of immune and inflammatory responses. Overexpression of the p65/RelA subunit of NF-kappaB significantly increased the MIP-3alpha mRNA level. MIP-3alpha transcription was stimulated by TNF, and this stimulation was inhibited by an NF-kappaB inhibitor, I-kappaBalpha superrepressor. Analysis of the human MIP-3alpha promoter demonstrated a functional NF-kappaB site responsible for its expression. We also show that MIP-3alpha expression is induced in LPS-treated mouse livers that were primed with Propionibacterium acnes, which developed massive liver injury with infiltration of inflammatory cells. This induction was fully dependent on the TNF signaling cascade, because it was not observed in the livers of TNFR1-deficient mice. Furthermore, pretreatment with gliotoxin, an inhibitor of NF-kappaB activity, abrogated the P. acnes/LPS-induced MIP-3alpha expression of wild-type mice. These results clearly demonstrate that MIP-3alpha gene expression is dependent on NF-kappaB activity in vitro, and indicate that the TNFR1-mediated TNF signaling cascade that leads to NF-kappaB activation plays an essential role in MIP-3alpha expression in the murine liver injury model.

Pro-inflammatory cytokines tumor necrosis factor alpha and interleukin-6 and survival factor epidermal growth factor positively regulate the murine GSTA4 enzyme in hepatocytes

We hypothesized that glutathione transferases could be induced and may participate to cellular defenses against the oxidative stress occurring during liver regeneration. Here, we evidenced that murine GSTA1 (mGSTA1), A4, Pi, and Mu are up-regulated during mouse liver regeneration, exhibiting a biphasic pattern of induction correlating early G(1) phase and G(1)/S transition of the cell cycle. Using confocal microscopy immunolocalization and subcellular fractionation, mGSTA4 was demonstrated in both mitochondria and cytosol and found preferentially increased in cytosol during liver regeneration. In addition, mGSTA4 was induced in vivo and in cultured hepatocytes by tumor necrosis factor alpha (TNFalpha), interleukin-6 (IL-6), and epidermal growth factor (EGF), factors that play crucial roles in hepatocyte survival and proliferation during liver regeneration. However, the mitogenic effect of EGF was not responsible for the induction of mGSTA4. In transient transfections, IL-6 and EGF, but not TNFalpha, transactivated the human GSTA4 (hGSTA4) promoter cloned upstream of the luciferase reporter gene suggesting that IL-6 and EGF up-regulated hGSTA4 at a transcriptional level, whereas TNFalpha could rather act at a post-transcriptional level. The inhibition of phosphoinositide 3-kinase, p38 MAPK, and MEK/ERK signaling pathways, using specific inhibitors, prevented EGF-dependent induction of mGSTA4 and transactivation of hGSTA4 promoter. Altogether, these data favor the conclusion that, in regenerating hepatocytes, several GST isoforms are induced and that cytokines TNFalpha and IL-6 and survival factor EGF positively regulate mGSTA4 via survival signaling pathways.

Nitric oxide in liver diseases: friend, foe, or just passerby?

Research on the free radical gas, nitric oxide (NO), during the past twenty years is one of the most rapid growing areas in biology. NO seems to play a part in almost every organ and tissue. However, there is considerable controversy and confusion in understanding its role. The liver is one organ that is clearly influenced by NO. Acute versus chronic exposure to NO has been associated with distinct patterns of liver disease. In this paper we review and discuss the involvement of NO in various liver diseases collated from observations by various researchers. Overall, the important factors in determining the beneficial versus harmful effects of NO are the amount, duration, and site of NO production. A low dose of NO serves to maximize blood perfusion, prevent platelet aggregation and thrombosis, and neutralize toxic oxygen radicals in the liver during acute sepsis and reperfusion events. NO also demonstrates antimicrobial and antiapoptosis properties during acute hepatitis infection and other inflammatory processes. However, in the setting of chronic liver inflammation, when a large sustained amount of NO is present, NO might become genotoxic and lead to the development of liver cancer. Additionally, during prolonged ischemia, high levels of NO may have cytotoxic effects leading to severe liver injury. In view of the various possible roles that NO plays, the pharmacologic modulation of NO synthesis is promising in the future treatment of liver diseases, especially with the emergence of selective NO synthase inhibitors and cell-specific NO donors.

Coupling cAMP signaling to transcription in the liver: pivotal role of CREB and CREM

Transcriptional factors binding to cAMP-responsive elements (CREs) in the promoters of various genes belong to the basic domain-leucine zipper superfamily and are composed of three genes in mammals, CREB, CREM, and ATF-1. A large number of CREB, CREM, and ATF-1 proteins are generated by posttranscriptional events, mostly alternative splicing, and regulate gene expression by acting as activators or repressors. Activation is classically brought about by signaling-dependent phosphorylation of a key acceptor site (Ser133 in CREB) by a number of possible kinases, including PKA, CamKIV, and Rsk-2. Phosphorylation is the prerequisite for the interaction of CBP (CREB-binding protein), a co-activator that has also histone acetyltransferase activity. Repression may involve dynamic dephosphorylation of the activators and thus decreased association with CBP. Another pathway of transcriptional repression on CRE sites implicates the inducible repressor ICER (inducible cAMP early repressor), a product of the CREM gene. Being an inducible repressor, ICER is involved in autoregulatory feedback loops of transcription that govern the down-regulation of early response genes, such as the proto-oncogene c-fos. The liver represents a remarkable physiological setting where cAMP-responsive signaling plays a major role. Indeed, a finely tuned program of gene expression is triggered by partial hepatectomy, so that through specific checkpoints a coordinated regeneration of the tissue is obtained. Temporal kinetics of transcriptional activation after hepatectomy reveals a pattern of early induction for several genes, some of them controlled by the CREB/CREM transcription factors. An important role of CREM in liver physiology was suggested by the robust induction of ICER after partial hepatectomy. The delay in tissue regeneration in CREM-deficient mice confirmed the important function of this factor in regulating hepatocyte proliferation. As gene induction is accompanied by critical changes in chromatin organization, the deciphering of the specific modification codes that histones display during liver regeneration and physiology will provide exciting new insights into the dynamics of chromatin architecture.

NO sensitizes rat hepatocytes to proliferation by modifying S-adenosylmethionine levels

BACKGROUND & AIMS

Liver regeneration is a fundamental response of this organ to injury. Hepatocyte proliferation is triggered by growth factors, such as hepatocyte growth factor. However, hepatocytes need to be primed to react to mitogenic signals. It is known that nitrous oxide (NO), generated after partial hepatectomy, plays an important role in hepatocyte growth. Nevertheless, the molecular mechanisms behind this priming event are not completely known. S-adenosylmethionine (AdoMet) synthesis by methionine adenosyltransferase is the first step in methionine metabolism, and NO regulates hepatocyte S-adenosylmethionine levels through specific inhibition of this enzyme. We have studied the modulation of hepatocyte growth factor-induced proliferation by NO through the regulation of S-adenosylmethionine levels.

METHODS

Studies were conducted in cultured rat hepatocytes isolated by collagenase perfusion, which triggers NO synthesis.

RESULTS

The mitogenic response to hepatocyte growth factor was blunted when inducible NO synthase was inhibited; this process was overcome by the addition of an NO donor. This effect was dependent on methionine concentration in culture medium and intracellular S-adenosylmethionine levels. Accordingly, we found that S-adenosylmethionine inhibits hepatocyte growth factor-induced cyclin D1 and D2 expression, activator protein 1 induction, and hepatocyte proliferation.

CONCLUSIONS

Together our findings indicate that NO may switch hepatocytes into a hepatocyte growth factor-responsive state through the down-regulation of S-adenosylmethionine levels.

Apoptosis and keratin intermediate filaments

Intermediate filament (IF) proteins utilize central alpha-helical domains to generate polymeric fibers intermediate in size between actin microfilaments and microtubules. The regions flanking the central structural domains have diverged greatly to permit IF proteins to adopt specialized functions. Keratins represent the largest two groups of IF proteins. Most keratins serve structural functions in hair or epidermis. Intracellular epidermal keratins also provide strength to epithelial sheets. The intracellular type I keratins and other IF proteins are cleaved by caspases during apoptosis to ensure the disposal of the relatively insoluble cellular components. However, recent studies have also revealed an unexpected protective role for keratin 8 during TNF and Fas mediated apoptosis. Evidence for possible functions of keratins both upstream and downstream of apoptotic signaling are considered.

Impaired postnatal hepatocyte proliferation and liver regeneration in mice lacking c-jun in the liver

Mice lacking the AP-1 transcription factor c-jun die at mid-gestation showing heart defects and impaired hepatogenesis. To inactivate c-jun in hepatocytes, mice carrying a floxed c-jun allele were generated. Perinatal liver-specific c-jun deletion caused reduced hepatocyte proliferation and decreased body size. After partial hepatectomy, half of the mutants died and liver regeneration was impaired. This phenotype was not present in mice lacking the N-terminal phosphorylation sites of c-Jun. The failure to regenerate was accompanied by increased cell death and lipid accumulation in hepatocytes. Moreover, cyclin-dependent kinases and several cell cycle regulators were affected, resulting in inefficient G(1)-S phase progression. These studies identify c-Jun as a critical regulator of hepatocyte proliferation and survival during liver development and regeneration.

Intracellular signal transduction of cells in response to carcinogenic metals

Epidemiological and animal studies suggest that several metals and metal-containing compounds are potent mutagens and carcinogens. These metals include chromium, arsenic, vanadium, nickel, and others. During the last two decades, chemical and cellular studies have contributed enormously to our understanding of the mechanisms of metal-induced pathophysiological processes. Although each of these metals is unique in its mechanism of action, some common signaling molecules, such as reactive oxygen species (ROS), may be shared by many of the carcinogenic metals. New techniques are now available to reveal the mechanisms of carcinogenesis in precise molecular terms. In this review, we focused our attentions on carcinogenic metal-induced signal transduction pathways leading to the activation of NF-kappaB, cell apoptosis and cell cycle progression, three crucial steps or events involved in the transformation and carcinogenesis. This review summarizes current knowledge and our recent studies concerning intracellular signal transduction pathways initiated by carcinogenic metals and the cross-talk that occurs among these pathways in cells in response to metals.

NF-kappaB activation in non-parenchymal liver cells after partial hepatectomy in rats: possible involvement in expression of heparin-binding epidermal growth factor-like growth factor

BACKGROUND/AIMS

Nuclear factor (NF) B activation plays a critical role in the initiation of liver growth after partial hepatectomy (PH). However, the issue of where specifically NF-B is activated is unclear. We previously reported that heparin-binding epidermal growth factor-like growth factor (HB-EGF) is a hepatotrophic factor. The aims of this study were to identify NF-B-activated cells and to clarify their involvement in HB-EGF expression after PH.

METHODS

Using rats, a two-thirds PH was performed, after which NF-B-activated cells and HB-EGF-positive cells were identified by Southwestern histochemistry or immunohistochemistry. NF-B binding activity and HB-EGF gene expression were analyzed in rat hepatocytes and non-parenchymal cells (NPC) in primary culture.

RESULTS

NF-B was activated in Kupffer cells and sinusoidal endothelial cells prior to activation in hepatocytes. HB-EGF immunoreactivity was detected after NF-B activation in the sinusoidal cells from those localized in the periportal zones of hepatic lobules. HB-EGF gene expression by tumor necrosis factor was accompanied by an increase in NF-B binding activity in NPC but not in hepatocytes in primary culture, which was abolished by pyrrolidine dithiocarbamate, an inhibitor of NF-B activation. CONCLUSIONS; NF-B was activated in NPC prior to activation in hepatocytes. NF-B activation may be involved in HB-EGF expression in NPC after PH.

Role of hepatocyte direct hyperplasia in lentivirus-mediated liver transduction in vivo

Lentiviral vectors have been used for gene transfer into the liver, but the ability of these vectors to efficiently transduce quiescent hepatocytes remains controversial. Regardless, lentivirus-mediated gene transfer is greatly enhanced when delivered during hepatocellular cycling. For this reason, the present study was designed to determine the role of hepatocyte proliferation in the enhancement of lentiviral transduction by using three different modes of liver regeneration: (1) compensatory regeneration stimulated by two-thirds partial hepatectomy, (2) direct hyperplasia after intragastric administration of the primary mitogen 1,4-bis[2-(3,5-dichloropyridyloxy)] benzene (TCPOBOP), and (3) a combination of modes 1 and 2. Vesicular stomatitis virus glycoprotein (VSV-G)-pseudotyped lentiviral vector expressing beta-galactosidase was administered to mice via the peripheral circulation after a regeneration stimulus. Gene transfer as measured by 5-bromo-4-chloro-3-indolyl-beta-D-galactoside (X-Gal) staining showed 30-fold higher levels of liver transduction in groups 1 and 2 as compared with the non-liver-manipulated control group (p < 0.005). The combination of TCPOBOP and partial hepatectomy (group 3) resulted in an ~80-fold increase in transduction efficiency compared with the control animals. The enhanced transduction was consistent with higher levels of hepatocellular proliferation observed in animals that received both treatments compared with either single treatment alone. Importantly, the hepatocytes were the predominant cell type transduced, although transgene expression was observed in a low number of nonparenchymal cells regardless of which liver stimulus was received. Biodistribution studies confirmed that most of the gene transfer was limited to the liver and spleen. Taken together, this study suggests that disease-induced cellular proliferation in the liver will enhance the utility of this vector in treating diseases such as viral hepatitis, liver cirrhosis, and cancer.

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

BACKGROUND/AIMS

Recent work has shown that the signal transducer and activator of transcription (STAT) 3 activation is important for the initiation of the proliferative response following partial hepatectomy (PH). However, the issue of where STAT3 is activated and how it is regulated is unclear. The aims of this study were to identify STAT3-activated cells and to clarify the expression of suppressor of cytokine signal (SOCS), a negative feedback molecule of STAT3, after PH.

METHODS

STAT3-activated cells and SOCS1-positive cells were identified by immunohistochemistry after a two-thirds PH in rats. SOCS mRNA was examined by Northern analysis.

RESULTS

STAT3 was activated in hepatocytes from those localized in the periportal zones of hepatic lobules after PH. STAT3 activation was also detected in Kupffer cells and sinusoidal endothelial cells prior to its detection in hepatocytes. After STAT3 activation, SOCS1 protein in response to PH was detected immunohistochemically in regenerating liver. SOCS1 and SOCS3 mRNA were induced in regenerating liver after PH.

CONCLUSIONS

STAT3 signaling can occur in Kupffer cells and sinusoidal endothelial cells prior to in hepatocytes from those localized in the periportal zones. SOCS1 as well as SOCS3 may regulate STAT3 signaling negatively after PH.

Independent and overlapping transcriptional activation during liver development and regeneration in mice

Liver development and regeneration share the requirement for simultaneous proliferation and acquisition of highly specialized cellular functions. However, little is known about molecules with regulatory roles in both processes. We hypothesized that transcriptional reprogramming induced by regeneration recapitulates that of developing liver. To address this hypothesis, we determined global hepatic gene expression at embryonic day 14.5, postnatal day 14, and 6 to 24 hours following partial hepatectomy using microarrays containing 8,635 cDNAs. Analysis of genes overexpressed during these conditions revealed 3 unique expression patterns. The first was predominantly signature gene clusters specific for each growth phase. Major groups were hematopoiesis-related genes in embryonic livers, metabolic genes during postnatal liver development, and growth/inflammation and metabolic genes during regeneration. The second pattern consisted of dual overexpression during regeneration and at least one phase of development. Consistent with potential regulatory roles in liver growth, most of these transcripts control cell-cell contact, membrane trafficking, cell growth, metabolism, and inflammatory response. The third pattern, revealed by surveying their expression across 76 hepatic and extra-hepatic tissues, uncovered a restricted temporospatial pattern of liver overexpression for CD14, orosomucoid 1, hepcidin, Spi 2.1, Ith3, and Tim-44. In conclusion, these results provide a basis for the identification of gene and gene groups that play critical roles at different phases of liver development and regeneration, and underscore the importance of maintaining metabolic demands during organ growth.

A20 protects mice from D-galactosamine/lipopolysaccharide acute toxic lethal hepatitis

Apoptosis of hepatocytes is a seminal feature of fulminant hepatic failure. We show that the anti-apoptotic protein A20 is upregulated in hepatocytes by pro-inflammatory stimuli and functions to protect from apoptosis and limit inflammation by inhibiting NF-kappaB. Adenoviral mediated hepatic expression of A20 in BALB/c mice yields an 85% survival rate in the D-galactosamine (D-gal)/lipolysaccharide (LPS) model of acute toxic hepatitis compared with 15% to 20 % in control mice. Expression of A20 preserves normal liver function as assessed by prothrombin time. The protective effect of A20 is independent of tumor necrosis factor (TNF) inhibition. Maintaining high circulating TNF levels may be advantageous for liver regeneration. Our data supports this hypothesis as evidenced by increased proliferating cell nuclear antigen (PCNA) expression in the livers of mice expressing A20 compared with a dominant negative mutant of the TNF receptor (TNF-R), 6 hours following D-gal/LPS administration. In conclusion, these results qualify A20 as part of a physiologic, protective response of hepatocytes to injury and a promising gene therapy candidate for clinical applications aimed at preventing and treating viral and toxic fulminant hepatic failure.

Interleukin-6 from intrahepatic cells of bone marrow origin is required for normal murine liver regeneration

Interleukin-6 (IL-6) is required for normal liver regeneration, but the specific cellular source of this growth factor is unknown. We investigated whether this signal originates from the resident macrophage, the Kupffer cell. Using a murine model of bone marrow transplantation, we replaced recipient bone marrow-derived cells, including Kupffer cells, with cells of donor genetic phenotype. Recipients deficient in IL-6 (IL-6(-/-)) were lethally irradiated, then rescued with 10(7) donor bone marrow cells capable of expressing IL-6 (IL-6(+/+)). Conversely, IL-6(+/+) recipients received IL-6(-/-) marrow. Successful engraftment was measured by the presence of the Y chromosome SRY locus in the livers of female recipients receiving male marrow, in situ IL-6 expression by Kupffer cells, and up-regulation of IL-6 in splenocytes after activation with lipopolysaccharide (LPS). Kupffer cell isolation in IL-6(-/-) females receiving IL-6(+/+) male marrow clearly showed the presence of the SRY locus and IL-6 disrupted allele, whereas males receiving female marrow demonstrated no SRY or IL-6 signals, confirming the extent of replacement. Replacement of these cells in IL-6(-/-) mice with IL-6(+/+) bone marrow successfully restored the regenerative response after partial hepatectomy (PHx) as indicated by signal transduction and activator of transcription 3 (STAT3) activation and hepatocyte DNA replication. Alternatively, complete replacement of Kupffer cells in IL-6(+/+) mice by transplantation with IL-6(-/-) cells significantly inhibited liver regeneration and was partially restored by administration of IL-6. This investigation demonstrates a paracrine mechanism by which cells of bone marrow origin, most likely Kupffer cells, regulate the regenerative capacity of the hepatocyte through IL-6 expression.

Tumor necrosis factor alpha, but not Fas, mediates hepatocellular apoptosis in the murine ischemic liver

BACKGROUND & AIMS

Apoptosis of hepatocytes is a central feature of ischemic injury in the liver. The aim of this study was to identify extracellular inducers of apoptosis in the murine ischemic liver.

METHODS

Involvement of tumor necrosis factor (TNF)-alpha and Fas signaling was evaluated using various knockout mice (TNF-receptor 1 [TNF-R1]-/-, Fas[lpr]-/-, and Fas ligand[gld]-/-) and wild-type mice pretreated with pentoxifylline, an inhibitor of TNF-alpha synthesis.

RESULTS

Expression of TNF-alpha was increased after ischemia and reperfusion in wild-type mice and TNF-R1-deficient mice when compared with sham-operated animals. Pentoxifylline prevented up-regulation of TNF-alpha expression. Inhibition of TNF-alpha resulted in significant decrease of serum aspartate aminotransferase levels and prolonged animal survival. Markers of apoptosis (terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling staining, cytochrome C release, and caspase 3 activity) were consistently decreased, and animal survival was prolonged after blocking TNF-alpha. In contrast, inhibition of Fas signaling did not alter parameters of tissue injury or apoptosis, and animal survival remained unchanged.

CONCLUSIONS

We identify TNF-alpha as a crucial inducer of apoptotic cell death in the ischemic liver. A role for Fas could not be identified. These findings may lead to novel strategies to prevent ischemic injury of the liver.

Minimally invasive hepatectomy: modulation of systemic reactions to operation or laparoscopic approach?

BACKGROUND

A new concept of surgical stress has been proposed that consists of both aggressiveness of operation and systemic reactions to an operation.

METHODS AND RESULTS

We have investigated a possible modulation of such systemic reactions to operation and have demonstrated the following 3 points: (1) coagulation and fibrinolytic systems are independently activated during hepatectomy and such activation can be modulated by protease inhibitors such as nafamostat mesilate and antithrombin III; (2) elevated thromboxane A2 during hepatectomy is characterized in the prostanoid system, the elevation of thromboxane A2 is inhibited by thromboxane A2 synthetase inhibitor, and postoperative liver injury is reduced; (3) cytokine response induced by hepatectomy is modulated by preoperative administration of methylprednisolone, leading to possible prevention of bacterial translocation. Therefore, modulating systemic reactions to hepatectomy may be important for successful minimally invasive hepatectomy. Another important option for minimally invasive hepatectomy is the use of operative procedures such as laparoscope or thoracoscope. We have investigated the usefulness of a laparoscopic hepatectomy from the standpoints of early and long-term outcome after hepatectomy. Laparoscopic hepatectomy, which is a difficult and dangerous procedure, can be a feasible option and can result in better short-term outcome and a similar long-term outcome after hepatectomy when compared with conventional open hepatectomy. Therefore, the laparoscopic approach is also a viable option for minimally invasive hepatectomy.

CONCLUSIONS

Modulation of systemic reactions to the operation itself and laparoscopic hepatectomy may be new strategies for performing minimally invasive hepatectomy.

Smad7 is induced by norepinephrine and protects rat hepatocytes from activin A-induced growth inhibition

Activin A induces growth arrest of rat hepatocytes in vitro and in vivo. The alpha(1)-adrenergic agonist, norepinephrine (NE), enhances epidermal growth factor-stimulated DNA synthesis and inhibits activin A-induced growth inhibition, but the mechanisms of these actions are unclear. Smad proteins have recently been identified as intracellular signaling mediators of transforming growth factor-beta family members. In the present study, we explored how NE modulates the Smad signaling pathway in rat cultured hepatocytes. We demonstrate that NE inhibits activin A-induced nuclear accumulation of Smad2/3 and that NE rapidly induces inhibitory Smad7 mRNA expression. Infection of Smad7 adenovirus into rat hepatocytes inhibited activin A-induced nuclear accumulation of Smad2/3, enhanced epidermal growth factor-stimulated DNA synthesis, and abolished the growth inhibitory effect of activin A. We also demonstrated that the induction of Smad7 by NE is dependent on nuclear factor-kappa B (NF-kappa B). The amount of active NF-kappa B complex rapidly increased after NE treatment. Preincubation of the cells with an NF-kappa B pathway inhibitor N-tosyl-l-phenylalanine chloromethyl ketone or infection of the cells with an adenovirus expressing an I kappa B super-repressor (Ad5I kappa B) abolished the NE-induced Smad7 expression. These results indicate a mechanism of transmodulation between the Smad and trimeric G protein signaling pathways in rat hepatocytes.

The role of tumor necrosis factor-alpha in liver toxicity, inflammation, and fibrosis induced by carbon tetrachloride

Hepatic expression of the proinflammatory cytokine tumor necrosis factor-alpha (TNFalpha) occurs in many acute and chronic liver diseases, as well as following exposure to hepatotoxic chemicals, and is believed to help influence both the damage and repair processes that occur following these insults by regulating additional mediators. We examined the role of TNFalpha in transgenic mice deficient in TNF receptors (TNFR) utilizing carbon tetrachloride (CCl(4)) as a model hepatotoxic agent that allowed for the evaluation of necrosis, inflammation, and fibrosis. Hepatocyte damage, as evident by local areas of liver necrosis and elevated levels of serum transaminase, occurred to a similar degree in wild-type and TNFR-deficient knockout (KO) mice following acute exposure to CCl(4). In contrast, the inflammatory response, manifested as an inflammatory cell influx, as well as induction of chemokines and adhesion molecules that occurred in wild-type mice following treatment with CCl(4), was not as evident in TNFR-KO mice. This response was associated primarily with type-1 (TNFR1) rather than type-2 (TNFR2) receptor responses. Liver fibrosis resulting from chronic CCl(4) exposure was also markedly dependent upon TNFalpha as demonstrated by almost a complete histological absence of fibrosis in TNFR-deficient mice. This was further supported by marked reductions in procollagen and transforming growth factor beta synthesis in TNFR-deficient mice. Taken together, these results indicate that TNFalpha is responsible for regulating products that induce inflammation and fibrosis but not direct hepatocyte damage in CCl(4)-induced hepatotoxicity.

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.

Hepatocellular proliferation in response to a peroxisome proliferator does not require TNFalpha signaling

Rodents exposed to peroxisome proliferator xenobiotics respond with marked increases in hepatocellular replication and growth that results in tumor formation. Recently, tumor necrosis factor-alpha (TNFalpha) was proposed as the central mediator of this maladaptive response. To define the role of TNFalpha signaling in hepatocellular growth induced by peroxisome proliferators we administered three daily gavage doses of the potent peroxisome proliferator, Wy-14 643, to mice nullizygous for TNF-receptor I (TNFR1), TNFR2, or both receptors. We demonstrate here that regardless of genotype the mice responded with almost identical increases in liver to body weight ratios and hepatocyte proliferation. Lacking evidence that TNFalpha signaling mediates these effects, we then examined the possible contribution of alternative cytokine pathways. Semi-quantitative, reverse transcriptase polymerase chain reaction analysis revealed that wild type mice acutely exposed to Wy-14 643 had increased hepatic expression of Il1beta, Il1r1, Hnf4, and Stat3 genes. Moreover, hepatic adenomas from mice chronically exposed to Wy-14 643 had increased expression of Il1beta, Il1r1, Il6, and Ppargamma1. Expression of Il1alpha, Tnfalpha, Tnfr1, Tnfr2, Pparalpha, or C/ebpalpha was not altered by acute Wy-14 643 exposure or in adenomas induced by Wy-14643. These data suggest that the hepatic mitogenesis and carcinogenesis associated with peroxisome proliferator exposure is not mediated via TNFalpha but instead may involve an alternative pathway requiring IL1beta and IL6.

Protection against Fas-mediated and tumor necrosis factor receptor 1-mediated liver injury by blockade of FADD without loss of nuclear factor-kappaB activation

OBJECTIVE

To investigate the role of FADD (Fas-associated protein with death domain) in Fas and tumor necrosis factor receptor 1 (TNFR1)-mediated hepatic injury and inflammatory response in vivo.

SUMMARY BACKGROUND DATA

Fas and TNFR1 are cell surface molecules that trigger apoptosis or inflammation on engagement by a specific ligand or antibody. FADD is recruited to the cytoplasmic domain of these receptors on their activation and works as a common mediator to induce apoptosis. It is known that a blockade of FADD can inhibit apoptosis mediated by Fas or TNFR1 in vitro. However, it is not known whether the blockade can prevent organ injury and whether the inflammatory cascade is affected in vivo.

METHODS

A FADD deletion mutant lacking the death effector domain was introduced into mice by transduction with an adenovirus vector, and the effect of this FADD dominant negative mutant was examined in several liver injury models.

RESULTS

Hepatic injury induced by anti-Fas monoclonal antibody or tumor necrosis factor (TNF)-alpha plus D-galactosamine was markedly ameliorated by the FADD dominant negative transduction, which abrogated the death rate. Further, the FADD dominant negative transduction efficiently blocked T cell- mediated concanavalin A-induced hepatitis while not affecting TNF-alpha production or TNF-alpha-induced nuclear factor-kappaB activation in the liver.

CONCLUSIONS

These results provide the basis for a novel therapeutic modality in which an unfavorable apoptotic process can be inhibited without affecting a favorable response for liver regeneration; this would be relevant to the clinical treatment of acute and chronic liver diseases as well as to some inflammatory disorders with hypercytokinemia, such as sepsis.

Dominant-negative TAK1 induces c-Myc and G(0) exit in liver

Transforming growth factor-beta (TGF-beta)-activated kinase 1 (TAK1), a serine/threonine kinase, is reported to function in the signaling pathways of TGF-beta, interleukin 1, and ceramide. However, the physiological role of TAK1 in vivo is largely unknown. To assess the function of TAK1 in vivo, dominant-negative TAK1 (dnTAK1) was expressed in the rat liver by adenoviral gene transfer. dnTAK1 expression abrogated c-Jun NH(2)-terminal kinase and c-Jun but not nuclear factor (NF)-kappaB or SMAD activation after partial hepatectomy (PH). Expression of dnTAK1 or TAM-67, a dominant-negative c-Jun, induced G(0) exit in quiescent liver and accelerated cell cycle progression after PH. Finally, dnTAK1 and TAM-67 induced c-myc expression in the liver before and after PH, suggesting that G(0) exit induced by dnTAK1 and TAM-67 is mediated by c-myc induction.

Intestinal expressions of eNOSmRNA and iNOSmRNA in rats with acute liver failure

AIM: To observe the gene expression change of eNOSmRNA and iNOSmRNA in the small and large intestines with acute liver failure (ALF), and to reveal the biological function of NO on the pathogenesis of ALF and multiple organs dysfunction at the molecular level.

METHODS: Sixty male Wistar rats were selected, weighing from 250 g to 350 g, and divided into 5 groups randomly: SO, ALF (6 h, 12 h), L-Arg, L-NAME, L-Arg and L-NAME, each group with 10 rats. The dose of L-Arg was 300 mg•kg¯¹, and L-NAME was 30 mg•kg¯¹, the reagents diluted by normal saline were injected through tail vein 30 minutes pre- and post-operation. The rats in the ALF group were respectively sacrificed postoperatively at 6 h, 12 h, and the rats in the other groups were sacrificed postoperatively at 6 h. The tissues of small and large intestines were harvested in 4% paraforaldehyde containing the reagent of DEPC and fixed at 6 h, embedded in paraffin, and 4 μm section was cut. The expression of eNOSmRNA and iNOSmRNA in these tissues was determined with in situ hybridization, and analyzed with the imaging analysis system of CMM-3 and SPSS statistical software.

RESULTS: The expression of eNOSmRNA in the large intestine and iNOSmRNA in the small and large intestines increased significantly at 6 h after ALF, but the expression of iNOSmRNA in the small and large intestines reduced notably at 12 h after ALF (P ＜ 0.05); the expression of eNOSmRNA in the large intestine and iNOSmRNA in the small and large intestines decreased significantly with the reagents of L-Arg at 6 h ALF, but the expression of eNOSmRNA and iNOSmRNA in the small and large intestines decreased totally with the reagents of L-NAME or association with L-Arg 6 h ALF.

CONCLUSION: The expression of eNOSmRNA in the large intestine increased notably at the early stage of ALF, NO induced by the enzyme of eNOS from the transplantation of eNOSmRNA can protect the function of the large intestine, the high expression of iNOSmRNA is involved in the damaged function of the small and large intestines. NO precursor can reduce the expression of iNOSmRNA in the small and large intestines and the damage to intestines; NOS inhibitor or association with NO precursor can totally lower the expression of eNOSmRNA and iNOSmRNA in the small and large intestines, it cannot notably influence the NOS inhibitor in the gene expression of eNOSmRNA and iNOSmRNA to supply the additional NO precursor.

Increased levels of forkhead box M1B transcription factor in transgenic mouse hepatocytes prevent age-related proliferation defects in regenerating liver

The forkhead box (Fox) family of transcription factors share homology in the winged helix/forkhead DNA-binding domain and play important roles in regulating cellular proliferation, differentiation, longevity, and cellular transformation. Forkhead box M1B (FoxM1B) is a ubiquitously expressed member of the Fox transcription factor family whose expression is restricted to proliferating cells and that mediates hepatocyte entry into DNA synthesis and mitosis during liver regeneration. Recent cDNA microarray studies indicated that age-related defects in cellular proliferation are associated with diminished expression of the FoxM1B transcription factor. Here, we show that increased levels of FoxM1B in regenerating liver of old transgenic mice restore the sharp peaks in hepatocyte DNA replication and mitosis that are the hallmarks of young regenerating mouse liver. Restoration of the young regenerating liver phenotype is associated with increased expression of numerous cell cycle regulatory genes that include cyclin D1, cyclin A2, cyclin F, cyclin B1, cyclin B2, Cdc25B, and p55cdc. Cotransfection assays in the human hepatoma HepG2 cell line demonstrated that FoxM1B protein stimulated expression of both the cyclin B1 and cyclin D1 promoters, suggesting that these cyclin genes are a direct FoxM1B transcriptional target. These results suggest that FoxM1B controls the transcriptional network of genes that are essential for cell division and exit from mitosis. Our results indicate that reduced expression of the FoxM1B transcription factor contributes to the decline in cellular proliferation observed in the aging process.

Expression of presumed specific early and late factors associated with liver regeneration in different rat surgical models

Experiments performed on the portal branch ligation (PBL) model indicate that early changes observed after surgery are not related to the regenerative process because they also occur in atrophying lobes. To further confirm the lack of specificity of the early events and to exclude the influence of circulatory factors released by proliferating lobes on their occurrence, we investigated this response after sham operation (SO) and portacaval shunt (PCS), a model characterized by liver atrophy. We also attempted to determine expression of later events associated specifically with regeneration, ie, expression of p53 or c-Ha-ras, or inhibition of proliferation, ie, interleukin-1beta (IL-1beta) and transforming growth factor-beta1 (TGF-beta1) after partial (PH) and temporary partial (TPH) hepatectomy, SO and PCS. Nuclear factor-kappaB (NF-kappaB) and signal transducer and activator of transcription 3 (STAT3) DNA binding were assessed by electrophoretic mobility shift assay (EMSA), interleukin-6 (IL-6) mRNA by reverse transcription-polymerase chain reaction (RT-PCR), c-myc and c-jun mRNAs by Northern blot analysis at 0.5 and 2 hours, p53 and c-Ha-ras mRNAs by Northern blot analysis at 8 and 24 hours, and IL-1beta and TGF-beta1 by RT-PCR at 24 hours. The early response including an increase of NF-kappaB, STAT3, IL-6, and immediate-early genes expression was present after PH, PCS, and SO. In SO, slight differences were observed in comparison with PH: no NF-kappaB p65/p50 DNA binding was observed, only three of six SO rats were positive for IL-6, and immediate-early genes induction showed differences in the intensity of the response. At later times, p53 mRNA increased at 8 hours after PH and TPH, c-Ha-ras mRNA at 24 hours after PH, and IL-1beta mRNA at 24 hours after PCS. Early events are not specifically associated with the reduction of liver mass or with the regenerative process, are not predictive of future cell fate, and are most likely related to surgical stress. p53 and c-Ha-ras induction is closely associated with cell cycle progression whereas IL-1beta, but not TGF-beta1, appears to be one of the negative growth regulators that might play an important role in atrophy.

HMG box transcriptional repressor HBP1 maintains a proliferation barrier in differentiated liver tissue

We previously isolated HBP1 as a target of the retinoblastoma (RB) and p130 family members and as the first of the HMG box transcriptional repressors. Our subsequent work demonstrated that HBP1 coordinates differentiation in cell culture models. In the present study, we show that HBP1 regulates proliferation in a differentiated tissue of an animal. Using transgenic mice in which HBP1 expression was specifically increased in hepatocytes under control of the transthyretin promoter, we determined the impact of HBP1 on synchronous cell cycle reentry following partial hepatectomy. Modest overexpression of HBP1 yielded a detectable cell cycle phenotype. Following a mitogenic stimulus induced by two-thirds partial hepatectomy, mice expressing the HBP1 transgene showed a 10- to 12-h delay in progression through G(1) to the peak of S phase. There was a concomitant delay in mid-G(1) events, such as the induction of cyclin E. While the delay in G(1) and S phases correlated with the slight overexpression of transgenic HBP1, the level of the endogenous HBP1 protein itself declined in S phase. In contrast, the onset of the immediate-early response following partial hepatectomy was unchanged in HBP1 transgenic mice. This observation indicated that the observed delay in S phase did not result from changes in signaling pathways leading into the G(0)-to-G(1) transition. Finally, transgenic mice expressing a mutant HBP1 lacking the N-terminal RB interacting domain showed a stronger S-phase response following partial hepatectomy. These results provide the first evidence that HBP1 can regulate cell cycle progression in differentiated tissues.

Ras adenoviruses modulate cyclin E protein expression and DNA synthesis after partial hepatectomy

Ras-genes encode for proteins important for transmitting extracellular signals from the cytoplasm to the nucleus. In this study we investigated the impact of Ras on cell cycle progression after hepatectomy by using adenoviral vectors (adv) expressing beta-galactosidase (beta-gal), a dominant-negative (Ras N17) or a dominant-active (Ras 61L) form of H-Ras. Partial hepatectomy was performed in mice treated with the different adenoviruses and cell cycle progression was studied by analysing factors involved in cell cycle control during liver regeneration. After hepatectomy, adv Ras 61L increases DNA synthesis significantly in comparison to the other treatment groups. Higher Ras activity results in an early increase of transcriptional active E2F-3, which is associated with higher cyclin E, but almost unchanged cyclin D protein expression. However, Northern blot analysis and cyclin E promoter experiments indicate that, besides transcriptional mechanisms also post-transcriptional mechanisms are involved in regulating cyclin E protein expression after partial hepatectomy in mice treated with adv Ras 61L. Cyclin E phosphorylation studies demonstrate that adv Ras 61L results in hypophosphorylation of cyclin E compared to the control group at early time points after hepatectomy, when cyclin E protein expression strongly increases and there is only a minor effect on cyclin E mRNA levels. Our experiments indicate adv Ras 61L in vivo increases Cyclin E expression by higher transcription via E2F and a post-transcriptional mechanism. These mechanisms result in an earlier activation of an active CDK2/Cyclin E complex which, in turn, triggers DNA synthesis.

Genetic deletion of the tumor necrosis factor receptor p60 or p80 abrogates ligand-mediated activation of nuclear factor-kappa B and of mitogen-activated protein kinases in macrophages

Tumor necrosis factor (TNF) is a pleiotropic cytokine known to regulate cell growth, viral replication, inflammation, immune system functioning, angiogenesis, and tumorigenesis. These effects are mediated through two different receptors, TNFR1 and TNFR2 (also called p60 and p80, respectively), with p60 receptor being expressed on all cell types and p80 receptor only on cells of the immune system and on endothelial cells. Although the role of p60 receptor in TNF signaling is well established, the role of p80 is less clear. In this report, by using macrophages derived from wild-type mice (having both receptors) and mice in which the gene for either p60 (p60(-/-)), or p80 (p80(-/-)), or both (p60(-/-) p80(-/-)) receptor have been deleted, we have redefined the role of these receptors in TNF-induced activation of nuclear factor (NF)-kappa B and of mitogen-activated protein kinases. TNF activated NF-kappa B in a dose- and time-dependent manner in wild-type macrophages but not in p60(-/-), p80(-/-), or p60(-/-) p80(-/-) macrophages. These results correlated with the I kappa B alpha degradation needed for NF-kappa B activation. We also found that TNF activated c-Jun N-terminal protein kinase in a dose- and time-dependent manner in wild-type macrophages but not in p60(-/-), p80(-/-), or p60(-/-) p80(-/-) macrophages. TNF activated p38 MAPK and p44/p42 MAPK in wild-type but not in p60(-/-), p80(-/-), or p60(-/-) p80(-/-) macrophages. TNF induced the proliferation of wild-type macrophages, but for p60(-/-) and p80(-/-) macrophages proliferation was lower, and in p60(-/-) p80(-/-) it was absent. Overall, our studies suggest that both types of TNF receptors are needed in macrophages for optimum TNF cell signaling.

Functional cooperation between JunD and NF-kappaB in rat hepatocytes

AP-1 and NF-kappaB are rapidly activated during liver regeneration. Whether these parallel inductions have potential functional implications is not known. Isolated rat hepatocytes were stimulated with two mitogens, epidermal growth factor or hepatocyte growth factor and with tumor necrosis factor alpha, a cytokine involved in the liver regenerative response in vivo and a strong inducer of NF-kappaB. All three cytokines increased AP-1 and NF-kappaB binding to their cognate cis-element and induced a 2.5-fold activation of NF-kappaB-dependent transcription. Inactivation of AP-1 by TAM67, a dominant negative mutant of AP-1 drastically inhibited basal and cytokine-induced NF-kappaB transactivation. Overexpression of Jun D, but not of the other Jun or Fos proteins increased by threefold NF-kappaB transactivation. Functional cooperation between JunD and p65 was demonstrated in a simple Gal-hybrid system. Finally, a twofold decrease in NF-kappaB transactivation was found in hepatocytes isolated from JunD(-/-) mice compared with hepatocytes from JunD(+/+) mice. Altogether these data demonstrate a functional cooperation of p65 with JunD, a major constituent of AP-1 in normal hepatocytes.

The role of tumor necrosis factor-alpha (TNF-alpha) in skeletal muscle regeneration. Studies in TNF-alpha(-/-) and TNF-alpha(-/-)/LT-alpha(-/-) mice

The role of tumor necrosis factor-alpha (TNF-alpha), an important mediator of the inflammatory response after injury, was investigated in regenerating skeletal muscle. The pattern of expression of TNF-alpha during muscle regeneration was examined by immunohistochemistry in tissue sections of crush-injured or transplanted muscle autografts and in primary cultures of adult skeletal muscle. TNF-alpha was highly expressed in injured myofibers, inflammatory cells, endothelial cells, fibroblasts, and mast cells. Myoblasts and myotubes also expressed TNF-alpha in primary muscle cultures and tissue sections. The essential role of TNF-alpha and its homologue lymphotoxin-alpha (LT-alpha) during muscle regeneration was assessed by basic histology in TNF-alpha(-/-) and TNF-alpha(-/-)/LT-alpha(-/-) mice. No difference was apparent in the onset or pattern of muscle regeneration (i.e., inflammatory response, activation and fusion of myoblasts) between the two strains of null mice or between nulls and normal control mice. However, both strains of null mice appeared more prone to bystander damage of host muscle and regeneration distant from the site of injury/transplantation. Although expression of TNF-alpha may play an important role in muscle regeneration, the studies in the null mice show that redundancy within the cytokine system (or some other response) can effectively compensate for the absence of TNF-alpha in vivo.

Regenerating soleus and extensor digitorum longus muscles of the rat show elevated levels of TNF-alpha and its receptors, TNFR-60 and TNFR-80

We measured the mRNA and protein levels of tumor necrosis factor-alpha (TNF-alpha) and the transcript levels of its receptors (TNFR-60 and TNFR-80) in the rat soleus (slow twitch) and extensor digitorum longus (EDL; fast twitch) muscles regenerating from notexin-induced necrosis. On the first day after administration of the toxin, when most fibers were necrotic and invaded by inflammatory cells/macrophages, dramatic increases of transcript and protein levels of TNF-alpha and of the mRNA levels of its receptors were observed. The transcript levels of TNF-alpha and TNFR-60, but not of TNFR-80, showed a second but smaller increase at the time when newly formed muscle fibers became reinnervated. In situ hybridization showed that on day 1, during the phase of extensive necrosis, the transcript of TNF-alpha was abundantly present and on day 4 of regeneration it was most often seen in areas devoid of desmin. The mRNA level of TNF-alpha was not detectable in BC(3)H1- and C2C12-cultured myoblasts and it was low in freeze-injured muscle, corresponding to the relatively mild degree of inflammation elicited by freezing. Therefore, our results are most consistent with the view that inflammatory cells/macrophages are the main source of TNF-alpha.

New insights into the role of nuclear factor-kappaB in cell growth regulation

The nuclear factor (NF)-kappaB family of eukaryotic transcription factors plays an important role in the regulation of immune response, embryo and cell lineage development, cell apoptosis, cell-cycle progression, inflammation, and oncogenesis. A wide range of stimuli, including cytokines, mitogens, environmental particles, toxic metals, and viral or bacterial products, activate NF-kappaB, mostly through IkappaB kinase (IKK)-dependent phosphorylation and subsequent degradation of its inhibitor, the IkappaB family of proteins. Activated NF-kappaB translocates into the nucleus where it modulates the expression of a variety of genes, including those encoding cytokines, growth factors, acute phase response proteins, cell adhesion molecules, other transcription factors, and several cell apoptosis regulators. During the past few years, tremendous progress has been achieved in our understanding on how intracellular signaling pathways are transmitted in either a linear or a network manner leading to the activation of NF-kappaB and subsequent cell growth control. However, a detailed molecular mechanism of NF-kappaB regulating cell growth has yet to be determined. Elucidation of the relationships between NF-kappaB activation and cell growth will be important in developing new strategies for the treatment of various human diseases, such as chronic autoimmune disorder and cancer.

Prolonged Jun N-terminal kinase (JNK) activation and the upregulation of p53 and p21(WAF1/CIP1) preceded apoptosis in hepatocytes after partial hepatectomy and cisplatin

Cisplatin induced apoptosis in regenerating liver after partial hepatectomy (PH). Apoptosis was determined by in situ end-labeling and gel electrophoresis of DNA fragmentation. Characteristic DNA fragmentation was obvious at 4 h and peaked at 8 h after PH. The activity of Jun N-terminal kinase (JNK) transiently increased at 1 h after PH. However, in cisplatin-injected rats, the JNK activity increased at 30 min and the increased level was maintained up to 4 h after PH. The in vivo activation of JNK was confirmed by the increased level of the phosphorylated c-Jun protein. Western blot analysis showed that the phosphorylated c-Jun level increased at 1 h and reached more than 30-fold the control level at 2 h after PH with cisplatin. The c-jun mRNA levels also markedly increased at 1 h after PH with cisplatin. The protein level of p53 increased after 1 h on cisplatin injection, but no significant change in the mRNA level was observed. The rise in the p53 protein level was followed by the upregulation of p21(WAF1/CIP1) mRNA and protein levels. These results suggested that the enhanced and sustained JNK activation and the upregulation of p53 and p21(WAF1/CIP1) were involved in hepatocyte apoptosis induced by PH with cisplatin.

Prostaglandins are required for CREB activation and cellular proliferation during liver regeneration

The liver responds to multiple types of injury with an extraordinarily well orchestrated and tightly regulated form of regeneration. The response to partial hepatectomy has been used as a model system to elucidate the molecular basis of this regenerative response. In this study, we used cyclooxygenase (COX)-selective antagonists and -null mice to determine the role of prostaglandin signaling in the response of liver to partial hepatectomy. The results show that liver regeneration is markedly impaired when both COX-1 and COX-2 are inhibited by indocin or by a combination of the COX-1 selective antagonist, SC-560, and the COX-2 selective antagonist, SC-236. Inhibition of COX-2 alone partially inhibits regeneration whereas inhibition of COX-1 alone tends to delay regeneration. Neither the rise in IL-6 nor the activation of signal transducer and activator of transcription-3 (STAT3) that is seen during liver regeneration is inhibited by indocin or the selective COX antagonists. In contrast, indocin treatment prevents the activation of CREB by phosphorylation that occurs during hepatic regeneration. These data indicate that prostaglandin signaling is required during liver regeneration, that COX-2 plays a particularly important role but COX-1 is also involved, and implicate the activation of CREB rather than STAT3 as the mediator of prostaglandin signaling during liver regeneration.

Expression of Bcl-2 family reduces apoptotic hepatocytes after excessive hepatectomy

Excessive hepatectomy often causes fatal hepatic failure, but the mechanism is unknown. We used a novel protocol of partial 90 and 95% hepatectomy (PHx) to investigate this mechanism in 2 groups of rats. The 90% PHx rats survived, but the 95% PHx animals died of hepatic failure. In the latter, cytokine (interleukin-6, tumor necrosis factor-alpha) levels and the apoptotic hepatocyte count increased, and there were few mitotic cells. By contrast, in the 90% PHx rats, the mitotic cell count increased, and more anti-apoptotic Bcl-xL protein was expressed. These results demonstrate that expression of Bcl-xL protein as an anti-apoptotic factor or regeneration factor contributes to survival after 90% PHx. Using an adenovirus vector, the human bcl-2 gene (hbcl-2) was therefore transfected to DA rat livers where it was efficiently expressed, and then 95% PHx was performed. Liver damage was decreased and the apoptotic cell count decreased too, but the rats died. We concluded that transfection of the hbcl-2 gene partly prevents cytotoxicity (apoptosis), but cannot ensure survival. Thus, some other factor is required (e.g., a regeneration stimulator) to maintain life in these models.