Liver failure and defective hepatocyte regeneration in interleukin-6-deficient mice

Immobilization stress increases hepatic IL-6 expression in mice

When mice were subjected to restriction of movement in a small cylinder (immobilization stress), the serum interleukin (IL)-6 level rose in 1 h, following increased expression of IL-6 mRNA in both the liver and the spleen. The IL-6 mRNA induction was much greater in the liver than in the spleen when compared on a whole-organ basis. Intraperitoneal injection of bacterial lipopolysaccharide (LPS) also increased IL-6 mRNA expression in these organs, but more preferentially in the spleen. Immunohistochemical examinations of liver tissue using an antibody against murine IL-6 revealed that immobilization stress induced IL-6 mainly in hepatic parenchymal cells, whereas LPS injection did so only in sinusoidal mononuclear cells. These results indicate that immobilization stress induces IL-6 production in the liver, especially in hepatic parenchymal cells, probably by a different mechanism from that for IL-6 induction by LPS.

Leukemia inhibitory factor-dependent transcriptional activation in embryonic stem cells

STAT transcription factors are induced by a number of growth factors and cytokines. Within minutes of induction, the STAT proteins are phosphorylated on tyrosine and serine residues and translocated to the nucleus, where they bind to their DNA targets. The leukemia inhibitory factor (LIF) mediates pleiotropic and sometimes opposite effects both in vivo and in cultured cells. It is known, for example, to prevent differentiation of embryonic stem (ES) cells in vitro. To get insights into LIF-regulated signaling in ES cells, we have analyzed protein-binding and transcriptional properties of STAT recognition sites in ES cells cultivated in the presence and in the absence of LIF. We have detected a specific LIF-regulated DNA-binding activity implicating the STAT3 protein. We show that STAT3 phosphorylation is essential for this LIF-dependent DNA-binding activity. The possibility that ERK2 or a closely related protein kinase, whose activity is modulated in a LIF-dependent manner, contributes to this phosphorylation is discussed. Finally, we show that the multimerized STAT3-binding DNA element confers LIF responsiveness to a minimal thymidine kinase promoter. This, together with our observation that overexpression of STAT3 dominant-negative mutants abrogates this LIF responsiveness, clearly indicates that STAT3 is involved in LIF-regulated transcriptional events in ES cells. Finally, stable expression of such a dominant negative mutant of STAT3 induces morphological differentiation of ES cells despite continuous LIF supply. Our results suggest that STAT3 is a critical target of the LIF signaling pathway, which maintains pluripotent cell proliferation.

Nuclear factor kappaB is required for the transcriptional control of type II NO synthase in regenerating liver

A concerted activation of transcription factors involved in the transactivation of type II NO synthase (iNOS) gene occurred after partial hepatectomy (PH), resulting in the transient expression of iNOS. The corresponding mRNA and protein levels of iNOS reached a maximum at 4 h and 8 h post-PH respectively. This induction was preceded by an early and transient activation of nuclear factor kappaB (NF-kappaB). Analysis of the kappaB inhibitory (I) proteins showed an important role for IkappaBalpha in the process of NF-kappaB activation, whereas the contribution of IkappaBbeta was less evident. Interferon regulatory factor 1, which has been described as an important activator of iNOS expression, was up-regulated after PH but failed to bind to the corresponding DNA binding sequences of the iNOS promoter. The transcriptional control of iNOS after PH, was compared with the events associated with the hepatic expression of this enzyme in animals challenged with lipopolysaccharide, showing a differential pattern of transcription-factor activation and IkappaB degradation between both models. Transfection of hepatoma cell lines with iNOS promoter constructs, followed by stimulation with post-PH sera, revealed the requirement of NF-kappaB activation for iNOS expression. These data suggest that there is an important role for the restricted NF-kappaB activation in the temporal pattern of iNOS expression in regenerating liver.

Cloning, human chromosomal assignment, and adipose and hepatic expression of the CL-6/INSIG1 gene

Rat CL-6 is the most highly insulin-induced gene in a liver cell line and is expressed in proliferating liver during regeneration and development. CL-6 is now denoted INSIG1 (insulin-induced gene 1). Human INSIG1 was isolated and found to be 80% identical to the rat gene within the translated region. It was located on human chromosome 7 within band q36. The human INSIG1 promoter conferred a high level of expression in both liver and fibroblast cell lines. INSIG1 expression was upregulated at the transcriptional level in rat regenerating liver and induced in a model of murine adipocyte differentiation, suggesting that INSIG1 may play a role in growth and differentiation of tissues involved in metabolic control.

Differential regulation of the mitogen-activated protein and stress-activated protein kinase cascades by adrenergic agonists in quiescent and regenerating adult rat hepatocytes

To study the mechanisms by which catecholamines regulate hepatocyte proliferation after partial hepatectomy (PHX), hepatocytes were isolated from adult male rats 24 h after sham operation or two-thirds PHX and treated with catecholamines and other agonists. In freshly isolated sham cells, p42 mitogen-activated protein (MAP) kinase activity was stimulated by the alpha1-adrenergic agonist phenylephrine (PHE). Activation of p42 MAP kinase by growth factors was blunted by pretreatment of sham hepatocytes with glucagon but not by that with the beta2-adrenergic agonist isoproterenol (ISO). In PHX cells, the ability of PHE to activate p42 MAP kinase was dramatically reduced, whereas ISO became competent to inhibit p42 MAP kinase activation. PHE treatment of sham but not PHX and ISO treatment of PHX but not sham hepatocytes also activated the stress-activated protein (SAP) kinases p46/54 SAP kinase and p38 SAP kinase. These data demonstrate that an alpha1- to beta2-adrenergic receptor switch occurs upon PHX and results in an increase in SAP kinase versus MAP kinase signaling by catecholamines. In primary cultures of hepatocytes, ISO treatment of PHX but not sham cells inhibited [3H]thymidine incorporation. In contrast, PHE treatment of sham but not PHX cells stimulated [3H]thymidine incorporation, which was reduced by approximately 25 and approximately 95% with specific inhibitors of p42 MAP kinase and p38 SAP kinase function, respectively. Inhibition of the p38 SAP kinase also dramatically reduced basal [3H]thymidine incorporation. These data suggest that p38 SAP kinase plays a permissive role in liver regeneration. Alterations in the abilities of catecholamines to modulate the activities of protein kinase A and the MAP and SAP kinase pathways may represent one physiological mechanism by which these agonists can regulate hepatocyte proliferation after PHX.

IFN-gamma potentiates atherosclerosis in ApoE knock-out mice

The early colocalization of T cells and the potent immunostimulatory cytokine IFN-gamma to atherosclerotic lesions suggest that the immune system contributes to atherogenesis. Since mice with a targeted disruption of the apoE gene (apoE 0 mice) develop profound atherosclerosis, we examined the role of IFN-gamma in this process. First, the presence of CD4(+) and CD8(+) cells, which secrete lesional IFN-gamma, was documented in apoE 0 atheromata. Then, the apoE 0 mice were crossed with IFN-gamma receptor (IFNgammaR) 0 mice to generate apoE 0/IFNgammaR 0 mice. Compared to the apoE 0 mice, the compound knock-out mice exhibited a substantial reduction in atherosclerotic lesion size, a 60% reduction in lesion lipid accumulation, a decrease in lesion cellularity, but a marked increase in lesion collagen content. Evaluation of the plasma lipoproteins showed that the compound knockout mice had a marked increase in potentially atheroprotective phospholipid/apoA-IV rich particles as well. This correlated with an induction of hepatic apoA-IV transcripts. These observations suggest that IFN-gamma promotes and modifies atherosclerosis through both local effects in the arterial wall as well as a systemic effect on plasma lipoproteins. Therefore, therapeutic inhibition of IFN-gamma signaling may lead to the formation of more lipid-poor and stable atheromata.

Liver regeneration

Liver regeneration after the loss of hepatic tissue is a fundamental parameter of liver response to injury. Recognized as a phenomenon from mythological times, it is now defined as an orchestrated response induced by specific external stimuli and involving sequential changes in gene expression, growth factor production, and morphologic structure. Many growth factors and cytokines, most notably hepatocyte growth factor, epidermal growth factor, transforming growth factor-alpha, interleukin-6, tumor necrosis factor-alpha, insulin, and norepinephrine, appear to play important roles in this process. This review attempts to integrate the findings of the last three decades and looks toward clues as to the nature of the causes that trigger this fascinating organ and cellular response.

Liver regeneration: prospects for therapy based on new technologies

The liver is an amazing organ because it can regenerate. The differentiated parenchymal cells, which do not normally divide, can undergo multiple rounds of cellular division. This brings into question the exact role of the liver stem-cell, which has not been fully characterized. The knowledge gained from the dissection of the basic molecular and cellular events that occur during hepatic regeneration will be useful for advancing therapeutic interventions for individuals with liver disease or genetic deficiencies. This article reviews the basic principles of liver regeneration, experimental manipulations in animal models, and human clinical applications including cellular transplantation, gene therapy and artificial livers.

Inhibition of tumor necrosis factor-alpha production retards liver regeneration after partial hepatectomy in rats

We studied the effects of a tumor necrosis factor-alpha (TNF-alpha) production inhibitor E3330, [(2E)-3-[5-(2,3-dimethoxy-6-methyl-1,4-benzoquinolyl)]-2-nonyl-2-+ ++propenoic acid] on liver regeneration in rats subjected to 70% partial hepatectomy. The BrdU labeling index was 53.5 +/- 3.8% 24 h after partial hepatectomy alone and was significantly inhibited by E3330 (25 and 50 mg/ kg) in a dose-dependent manner (43.3 +/- 2.1% and 19.0 +/- 10.3%, respectively; p < 0.05, p < 0.01). In these 3 groups, TNF-alpha protein levels in liver tissue were 187 +/- 18, 123 +/- 47, and 89 +/- 33 pg/mg total protein, respectively, with a significant decrease by E3330 administration (p < 0.01). TNF-alpha mRNA expression in liver tissue was also reduced by E3330. These results suggest that TNF-alpha promotes liver regeneration after partial hepatectomy.

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

The mechanisms that initiate liver regeneration after resection of liver tissue are not known. To determine whether cytokines are involved in the initiation of liver growth, we studied the regeneration of the liver after partial hepatectomy (PH) in mice lacking type I tumor necrosis factor receptor (TNFR-I). DNA synthesis after PH was severely impaired in these animals, and the expected increases in the binding of the NF-kappaB and STAT3 transcription factors shortly after PH failed to occur. Binding of AP-1 after PH was decreased in TNFR-I knockout mice compared with animals with the intact receptor whereas C/EBP binding was not modified. Injection of interleukin 6 in TNFR-I-deficient animals 30 min before PH corrected the defect in DNA synthesis and restored STAT3 and AP-1 binding to normal levels but had no effect on NF-kappaB binding in the regenerating liver. The results indicate that TNF, signaling through the TNFR-I, can initiate liver regeneration and acts by activating an interleukin 6-dependent pathway that involves the STAT3 transcription factor.