NF-kappaB inhibits expression of the alpha1(I) collagen gene

Fibrosis results from an increase in the synthesis and deposition of type I collagen. Fibrosis is frequently associated with inflammation, which is accompanied by increased levels of tumor necrosis factor-alpha (TNFalpha) and activation of the transcription factor NF-kappaB. However, several agents known to activate NF-kappaB, such as phorbol 12-myristate 13-acetate (PMA) and TNFalpha, result in decreased expression of type I collagen. Therefore, we directly examined the effects of NF-kappaB on alpha1(I) collagen gene expression in two collagen-producing cells, NIH 3T3 fibroblasts and hepatic stellate cells (HSCs). Transient transfections of NIH 3T3 cells or HSCs using NF-kappaB p50, p65, and c-Rel expression plasmids with collagen reporter gene plasmids demonstrated a strong inhibitory effect on transcription of the collagen gene promoter. Dose-response curves showed that p65 was a stronger inhibitor of collagen gene expression than was NF-kappaB p50 or c-Rel (maximum inhibition 90%). Transient transfections with reporter gene plasmids containing one or two Spl binding sites demonstrated similar inhibitory effects of NF-kappaB p65 on the activity of these reporter genes, suggesting that the inhibitory effects of NF-kappaB p65 are mediated through the critical Spl binding sites in the alpha1(I) collagen gene promoter. Cotransfection experiments using either a super-repressor I[ke]B or Spl partially blocked the inhibitory effects of p65 on collagen reporter gene activity. Coimmunoprecipitation experiments demonstrated that NF-kappaB and Spl do interact in vivo. Nuclear run-on assays showed that NF-kappaB p65 inhibited transcription of the endogenous alpha1(I) collagen gene. Together, these results demonstrate that NF-kappaB decreases transcription of the alpha1(I) collagen gene.

Curcumin blocks cytokine-mediated NF-kappa B activation and proinflammatory gene expression by inhibiting inhibitory factor I-kappa B kinase activity

NF-kappa B plays a critical role in the transcriptional regulation of proinflammatory gene expression in various cells. Cytokine-mediated activation of NF-kappa B requires activation of various kinases, which ultimately leads to the phosphorylation and degradation of I kappa B, the NF-kappa B cytoplasmic inhibitor. The food derivative curcumin has been shown to inhibit NF-kappa B activity in some cell types. In this report we investigate the mechanism of action of curcumin on cytokine-induced proinflammatory gene expression using intestinal epithelial cells (IEC). Curcumin inhibited IL-1 beta-mediated ICAM-1 and IL-8 gene expression in IEC-6, HT-29, and Caco-2 cells. Cytokine-induced NF-kappa B DNA binding activity, RelA nuclear translocation, I kappa B alpha degradation, I kappa B serine 32 phosphorylation, and I kappa B kinase (IKK) activity were blocked by curcumin treatment. Wound-induced p38 phosphorylation was not inhibited by curcumin treatment. In addition, mitogen-activated protein kinase/ERK kinase kinase-1-induced IL-8 gene expression and 12-O-tetraphorbol 12-myristate 13-acetate-responsive element-driven luciferase expression were inhibited by curcumin. However, I kappa B alpha degradation induced by ectopically expressed NF-kappa B-inducing kinase or IKK was not inhibited by curcumin treatment. Therefore, curcumin blocks a signal upstream of NF-kappa B-inducing kinase and IKK. We conclude that curcumin potently inhibits cytokine-mediated NF-kappa B activation by blocking a signal leading to IKK activity.

Estriol sensitizes rat Kupffer cells via gut-derived endotoxin

The relationship between gender and alcohol-induced liver disease is complex; however, endotoxin is most likely involved. Recently, it was reported that estriol activated Kupffer cells by upregulation of the endotoxin receptor CD14. Therefore, the purpose of this work was to study how estriol sensitizes Kupffer cells. Rats were given estriol (20 mg/kg ip), and Kupffer cells were isolated 24 h later. After addition of lipopolysaccharide (LPS), intracellular Ca2+ concentration was measured using a microspectrofluorometer with the fluorescent indicator fura 2, and tumor necrosis factor-alpha was measured by ELISA. CD14 was evaluated by Western analysis. One-half of the rats given estriol intraperitoneally 24 h before an injection of a sublethal dose of LPS (5 mg/kg) died within 24 h, whereas none of the control rats died. Mortality was prevented totally by sterilization of the gut with antibiotics. A similar pattern was obtained with liver histology and serum transaminases. Translocation of horseradish peroxidase was increased about threefold in gut segments by treatment with estriol. This increase was not altered by treatment with nonabsorbable antibiotics. On the other hand, endotoxin levels were increased to 60-70 pg/ml in plasma of rats treated with estriol. As expected, this increase was prevented (<20 pg/ml) by antibiotics. In isolated Kupffer cells, LPS-induced increases in intracellular Ca2+ concentration, tumor necrosis factor-alpha production, and CD14 were increased, as previously reported. All these phenomena were blocked by antibiotics. Therefore, it is concluded that estriol treatment in vivo sensitizes Kupffer cells to LPS via mechanisms dependent on increases in CD14. This is most likely due to elevated portal blood endotoxin caused by increased gut permeability.

IkappaBalpha gene transfer is cytotoxic to squamous-cell lung cancer cells and sensitizes them to tumor necrosis factor-alpha-mediated cell death

Current paradigms in cancer therapy suggest that activation of nuclear factor-kappaB (NF-kappaB) by a variety of stimuli, including some cytoreductive agents, may inhibit apoptosis. Thus, inhibiting NF-kappaB activation may sensitize cells to anticancer therapy, thereby providing a more effective treatment for certain cancers. E-1-deleted adenoviral (Ad) vectors encoding a "superrepressor" form of the NF-kappaB inhibitor IkappaBalpha (AdIkappaBalphaSR) or beta-galactosidase (AdLacZ) were tested alone and in combination with tumor necrosis factor-alpha (TNF-alpha) in lung cancer cells for sensitization of the cells to death. Following transduction with AdIkappaBalphaSR, lung cancer cells expressed IkappaBalphaSR in a dose-dependent manner. Probing nuclear extracts of lung cancer cells with NF-kappaB-sequence-specific oligonucleotides indicated that there was a minimal amount of NF-kappaB in the nucleus at baseline and an expected and dramatic increase in nuclear NF-kappaB following exposure of cells to TNF-alpha. Control E-1-deleted AdLacZ did not promote NF-kappaB activation. Importantly, AdIkappaBalphaSR-mediated gene transfer resulted in the complete block of nuclear translocation of NF-kappaB by specific binding of its p65/relA component with transgenic IkappaBalphaSR. At the cellular level, transduction with AdIkappaBalphaSR resulted in increased cytotoxicity in lung cancer cells as opposed to transduction with equivalent doses of AdLacZ. In addition, whereas the parental cells were resistant to TNF-alpha-mediated cytotoxicity, IkappaBalphaSR-transduced cells could be sensitized to TNF-alpha. Consequently, AdIkappaBalphaSR transduction followed by exposure to TNF-alpha uniformly resulted in the death of non-small-cell lung cancer cells. These data suggest that novel approaches incorporating IkappaBalpha gene therapy may have a role in the treatment of lung cancer.

Differential expression of human lysyl hydroxylase genes, lysine hydroxylation, and cross-linking of type I collagen during osteoblastic differentiation in vitro

The pattern of lysyl hydroxylation in the nontriple helical domains of collagen is critical in determining the cross-linking pathways that are tissue specific. We hypothesized that the tissue specificity of type I collagen cross-linking is, in part, due to the differential expression of lysyl hydroxylase genes (Procollagen-lysine,2-oxyglutarate,5-dioxygenase 1, 2, and 3 [PLOD1, PLOD2, and PLOD3]). In this study, we have examined the expression patterns of these three genes during the course of in vitro differentiation of human osteoprogenitor cells (bone marrow stromal cells [BMSCs]) and normal skin fibroblasts (NSFs). In addition, using the medium and cell layer/matrix fractions in these cultures, lysine hydroxylation of type I collagen alpha chains and collagen cross-linking chemistries have been characterized. High levels of PLOD1 and PLOD3 genes were expressed in both BMSCs and NSFs, and the expression levels did not change in the course of differentiation. In contrast to the PLOD1 and PLOD3 genes, both cell types showed low PLOD2 gene expression in undifferentiated and early differentiated conditions. However, fully differentiated BMSCs, but not NSFs, exhibited a significantly elevated level (6-fold increase) of PLOD2 mRNA. This increase coincided with the onset of matrix mineralization and with the increase in lysyl hydroxylation in the nontriple helical domains of alpha chains of type I collagen molecule. Furthermore, the collagen cross-links that are derived from the nontriple helical hydroxylysine-aldehyde were found only in fully differentiated BMSC cultures. The data suggests that PLOD2 expression is associated with lysine hydroxylation in the nontriple helical domains of collagen and, thus, could be partially responsible for the tissue-specific collagen cross-linking pattern.

Mitochondrial dysfunction in the pathogenesis of necrotic and apoptotic cell death

Mitochondria are frequently the target of injury after stresses leading to necrotic and apoptotic cell death. Inhibition of oxidative phosphorylation progresses to uncoupling when opening of a high conductance permeability transition (PT) pore in the mitochondrial inner membrane abruptly increases the permeability of the mitochondrial inner membrane to solutes of molecular mass up to 1500 Da. Cyclosporin A (CsA) blocks this mitochondrial permeability transition (MPT) and prevents necrotic cell death from oxidative stress, Ca2+ ionophore toxicity, Reye-related drug toxicity, pH-dependent ischemia/reperfusion injury, and other models of cell injury. Confocal fluorescence microscopy directly visualizes onset of the MPT from the movement of green-fluorescing calcein into mitochondria and the simultaneous release from mitochondria of red-fluorescing tetramethylrhodamine methylester, a membrane potential-indicating fluorophore. In oxidative stress to hepatocytes induced by tert-butylhydroperoxide, NAD(P)H oxidation, increased mitochondrial Ca2+, and mitochondrial generation of reactive oxygen species precede and contribute to onset of the MPT. Confocal microscopy also shows directly that the MPT is a critical event in apoptosis of hepatocytes induced by tumor necrosis factor-alpha. Progression to necrotic and apoptotic cell killing depends, at least in part, on the effect the MPT has on cellular ATP levels. If ATP levels fall profoundly, necrotic killing ensues. If ATP levels are at least partially maintained, apoptosis follows the MPT. Cellular features of both apoptosis and necrosis frequently occur together after death signals and toxic stresses. A new term, necrapoptosis, describes such death processes that begin with a common stress or death signal, progress by shared pathways, but culminate in either cell lysis (necrosis) or programmed cellular resorption (apoptosis) depending on modifying factors such as ATP.

Activation of nuclear factor-kappaB during orthotopic liver transplantation in rats is protective and does not require Kupffer cells

Reperfusion after liver transplantation results in the induction of tumor necrosis factor-alpha (TNFalpha) as well as activation of the stress-associated signaling proteins, c-Jun N-terminal kinase (JNK), activating protein-1 (AP-1), and nuclear factor-kappaB (NF-kappaB). To test the hypothesis that Kupffer cells are involved in the activation of signal transduction cascades during rat liver transplantation, Kupffer cells were depleted from donor liver using gadolinium chloride (GdCl3), and then the activation of JNK, AP-1, and NF-kappaB were assessed after transplantation. The results showed that GdCl3 treatment did not inhibit the activation of these stress signals, although transplanted livers were depleted of Kupffer cells and partially protected from reperfusion injury. Interleukin-6 (IL-6) and IL-10 messenger RNAs (mRNAs) were induced by transplantation, and the induction was suppressed by Kupffer cell depletion. The induction of TNFalpha mRNA and serum protein during liver transplantation was unaffected by GdCl3. These results show that Kupffer cells are not a major source of TNFalpha production after liver transplantation and that stress-signaling protein activation occurs independently of Kupffer cells. Transplantation strongly activates the transcription factor NF-kappaB, which blocks TNFalpha-mediated apoptosis in hepatocytes in vitro. To assess the role of NF-kappaB activation during liver transplantation, the IkappaBalpha superrepressor was expressed in donor livers using adenoviral-mediated gene transfer. Inhibition of NF-kappaB resulted in increased serum alanine aminotransferase levels after 3 hours of transplantation. In addition, the blockade of NF-kappaB resulted in increased histological tissue injury and increased hepatic terminal deoxyribonucleotide transferase-mediated deoxyuridine triphosphate nick end labeling (TUNEL) staining, indicating apoptosis. These results show that NF-kappaB activation has a protective role in the transplanted liver.

Development of a new, simple rat model of early alcohol-induced liver injury based on sensitization of Kupffer cells

The continuous intragastric in vivo enteral feeding model in the rat developed by Tsukamoto and French has been very useful; however, it requires surgical expertise. Recently, we found that Kupffer cells isolated from rats treated only once with ethanol were sensitized to endotoxin 24 hours later. Accordingly, these experiments were designed to determine if a new, simple animal model of ethanol hepatotoxicity could be developed based on Kupffer cell sensitization. Female Wistar rats were given ethanol (5 g/kg body weight) once every 24 hours intragastrically. Livers were stained with hematoxylin-eosin to assess steatosis, inflammation, and necrosis, and tissue triglycerides, serum transaminases, and plasma endotoxin were measured. Kupffer cells were isolated 0 to 24 hours after one intragastric dose of ethanol daily, and intracellular Ca2+ ([Ca2+]i) was measured using fura-2, while tumor necrosis factor alpha (TNF-alpha) was measured by enzyme-linked immunosorbent assay. CD14 was evaluated by Western and Northern analysis. Ethanol caused steatosis, necrosis, and inflammation in only a few weeks, and after 8 weeks, serum aspartate transaminase (AST) levels were doubled. Values were similar to levels achieved in the enteral feeding model. Triglycerides were also increased significantly by ethanol as expected, and endotoxin levels were increased to 70 to 80 pg/mL. This latter increase was prevented (<20 pg/mL) by antibiotics implicating endotoxin. In isolated Kupffer cells from untreated control rats, [Ca2+]i increased to 82 +/- 7 nmol/L after addition of lipopolysaccharide (LPS) (100 ng/mL), and levels were elevated about twofold by ethanol given 24 hours earlier (174 +/- 15 nmol/L). In addition, TNF-alpha production by Kupffer cells was increased fourfold in cells isolated from rats treated with ethanol 24 hours earlier. Sterilization of the gut with antibiotics blocked all effects of ethanol on [Ca2+]i and TNF-alpha release completely. Moreover, 4 weeks after ethanol, CD14 in Kupffer cells was elevated about twofold. A new, simple chronic model of ethanol hepatotoxicity has been developed here based on sensitization of Kupffer cells to endotoxin.

Regulatory role of the conserved stem-loop structure at the 5' end of collagen alpha1(I) mRNA

Three fibrillar collagen mRNAs, alpha1(I), alpha2(I), and alpha1(III), are coordinately upregulated in the activated hepatic stellate cell (hsc) in liver fibrosis. These three mRNAs contain sequences surrounding the start codon that can be folded into a stem-loop structure. We investigated the role of this stem-loop structure in expression of collagen alpha1(I) reporter mRNAs in hsc's and fibroblasts. The stem-loop dramatically decreases accumulation of mRNAs in quiescent hsc's and to a lesser extent in activated hsc's and fibroblasts. The stem-loop decreases mRNA stability in fibroblasts. In activated hsc's and fibroblasts, a protein complex binds to the stem-loop, and this binding requires the presence of a 7mG cap on the RNA. Placing the 3' untranslated region (UTR) of collagen alpha1(I) mRNA in a reporter mRNA containing this stem-loop further increases the steady-state level in activated hsc's. This 3' UTR binds alphaCP, a protein implicated in increasing stability of collagen alpha1(I) mRNA in activated hsc's (B. Stefanovic, C. Hellerbrand, M. Holcik, M. Briendl, S. A. Liebhaber, and D. A. Brenner, Mol. Cell. Biol. 17:5201-5209, 1997). A set of protein complexes assembles on the 7mG capped stem-loop RNA, and a 120-kDa protein is specifically cross-linked to this structure. Thus, collagen alpha1(I) mRNA is regulated by a complex interaction between the 5' stem-loop and the 3' UTR, which may optimize collagen production in activated hsc's.

TNF receptor-associated factor-2 is involved in both IL-1 beta and TNF-alpha signaling cascades leading to NF-kappa B activation and IL-8 expression in human intestinal epithelial cells

Cytokine signaling involves the participation of many adaptor proteins, including the docking protein TNF receptor-associated factor-2 (TRAF-2), which is believed to transmit the TNF-alpha signal through both the I kappa B/NF-kappa B and c-Jun N-terminal kinase (JNK)/stress-related protein kinase (SAPK) pathways. The physiological role of TRAF proteins in cytokine signaling in intestinal epithelial cells (IEC) is unknown. We characterized the effect of a dominant-negative TRAF-2 delivered by an adenoviral vector (Ad5dnTRAF-2) on the cytokine signaling cascade in several IEC and also investigated whether inhibiting the TRAF-2-transmitting signal blocked TNF-alpha-induced NF-kappa B and IL-8 gene expression. A high efficacy and level of Ad5dnTRAF-2 gene transfer were obtained in IEC using a multiplicity of infection of 50. Ad5dnTRAF-2 expression prevented TNF-alpha-induced, but not IL-1 beta-induced, I kappa B alpha degradation and NF-kappa B activation in NIH-3T3 and IEC-6 cells. TNF-alpha-induced JNK activation was also inhibited in Ad5dnTRAF-2-infected HT-29 cells. Induction of IL-8 gene expression by TNF-alpha was partially inhibited in Ad5dnTRAF-2-transfected HT-29, but not in control Ad5LacZ-infected, cells. Surprisingly, IL-1 beta-mediated IL-8 gene expression was also inhibited in HT-29 cells as measured by Northern blot and ELISA. We concluded that TRAF-2 is partially involved in TNF-alpha-mediated signaling through I kappa B/NF-kappa B in IEC. In addition, our data suggest that TRAF-2 is involved in IL-1 beta signaling in HT-29 cells. Manipulation of cytokine signaling pathways represents a new approach for inhibiting proinflammatory gene expression in IEC.

Gene regulation in hepatic stellate cell

Hepatic stellate cells are now recognized as the major source of extracellular matrix in hepatic fibrosis. Following liver injury the hepatic stellate cell changes from a quiescent to an activated cell. The activation process includes an increased proliferation rate, a phenotypic change to a myofibroblast-like cell, loss of vitamin A stores, increased extra-cellular matrix protein synthesis and contractility. Furthermore, hepatic stellate cells have been implicated in hepatic inflammation through their ability to secrete cytokines and chemokines. Here, we review the literature on the molecular pathogenesis of hepatic stellate cells activation with emphasis on the most recent findings. The reviewed topics include transcriptional and post-transcriptional regulation of the genes encoding type I collagen in hepatic stellate cells; the role of the transcription factor nuclear factor Kappa B in the hepatic stellate cell activation; focal adhesion kinase and integrin-mediated signal transduction in hepatic stellate cell, and apoptosis in hepatic stellate cells. New insight into hepatic stellate cell activation and death may lead to the development of novel therapies for hepatic fibrosis.

Pronase destroys the lipopolysaccharide receptor CD14 on Kupffer cells

CD14 is a lipopolysaccharide (LPS) receptor distributed largely in macrophages, monocytes, and neutrophils; however, the role of CD14 in activation of Kupffer cells by LPS remains controversial. The purpose of this study was to determine if different methods used to isolate Kupffer cells affect CD14. Kupffer cells were isolated by collagenase (0.025%) or collagenase-Pronase (0.02%) perfusion and differential centrifugation using Percoll gradients and cultured for 24 h before experiments. CD14 mRNA was detected by RT-PCR from Kupffer cell total RNA as well as from peritoneal macrophages. Western blotting showed that Kupffer cells prepared with collagenase possess CD14; however, it was absent in cells obtained by collagenase-Pronase perfusion. Intracellular calcium in Kupffer cells prepared with collagenase was increased transiently to levels around 300 nM by addition of LPS with 5% rat serum, which contains LPS binding protein. This increase in intracellular calcium was totally serum dependent. Moreover, LPS-induced increases in intracellular calcium in Kupffer cells were blunted significantly (40% of controls) when cells were treated with phosphatidylinositol-specific phospholipase C, which cleaves CD14 from the plasma membrane. However, intracellular calcium did not increase when LPS was added to cells prepared by collagenase-Pronase perfusion even in the presence of serum. These cells were viable, however, because ATP increased intracellular calcium to the same levels as cells prepared with collagenase perfusion. Tumor necrosis factor-alpha (TNF-alpha) mRNA was increased in Kupffer cells prepared with collagenase perfusion 1 h after addition of LPS, an effect potentiated over twofold by serum; however, serum did not increase TNF-alpha mRNA in cells isolated via collagenase-Pronase perfusion. Moreover, treatment with Pronase rapidly decreased CD14 on mouse macrophages (RAW 264.7 cells) and Kupffer cells. These findings indicate that Pronase cleaves CD14 from Kupffer cells, whereas collagenase perfusion does not, providing an explanation for why Kupffer cells do not exhibit a CD14-mediated pathway when prepared with procedures using Pronase. It is concluded that Kupffer cells indeed contain a functional CD14 LPS receptor when prepared gently.

Molecular and cellular biology of the small intestine

The crypt-villus axis is composed of a dynamic cell population in perpetual change from a crypt proliferative and undifferentiated stage to a mature villus stage. The migration of crypt cells is accompanied by cellular differentiation that leads to morphological and functional changes. In addition to this intrinsic gene program, intestinal epithelial cells respond to extrinsic signals by producing various molecules. Using different experimental approaches, recent studies have further characterized intestinal epithelial-cell biology and provided evidence of their polyvalent and important role in gut homeostasis.

Targeted disruption of the mouse ferrochelatase gene producing an exon 10 deletion

Protoporphyria is a disease characterized by a deficiency in ferrochelatase, the terminal enzyme in the heme biosynthetic pathway, which catalyzes the chelation of iron and protoporphyrin to form heme. Clinical symptoms arise from an accumulation of protoporphyrin behind the partial enzyme block and include photosensitivity and sometimes hepatobiliary disease. Protoporphyria is described as an dominant disease, yet patients exhibit decreased ferrochelatase activities of 15-30% of normal, not 50% as might be expected. Missense, nonsense, and splicing mutations have been identified in ferrochelatase cDNA from protoporphyric patients. In this study we introduce an exon 10 deletion, an analogous mutation to that described in some protoporphyric patients, into the mouse embryonic stem (ES) cell genome via homologous recombination. Targeted ES cells were confirmed by Southern blot analysis. Expression of wild-type and exon 10-deleted mRNA was demonstrated by reverse transcriptase-polymerase chain reaction (RT-PCR) and cDNA sequencing. Ferrochelatase levels were analyzed by immunoblotting. Ferrochelatase activity was measured by the chelation of zinc and mesoporphyrin, and by the decrease in protoporphyrin accumulation after adding delta-aminolevulinic acid. In the exon 10 +/- ES cells there is expression of both wild-type and exon 10-deleted mRNA, a 50% decrease in cross-reactive material with an anti-ferrochelatase antibody, and an approximate 50% decrease in ferrochelatase activity compared to wild-type ES cells. Therefore, an exon 10 deletion alone is insufficient to decrease ferrochelatase activity to the levels in protoporphyric patients. This suggests that requirement of an additional mutation to decrease the expression of the wild-type allele.

The role of TGFbeta1 in initiating hepatic stellate cell activation in vivo

BACKGROUND/AIMS

The activation of hepatic stellate cells is a key initiating event in hepatic fibrogenesis. Although TGFbeta1 is a potent inducer of collagen alpha1(I) expression in vitro and elevated levels of TGFbeta1 are found in patients and experimental animals with hepatic fibrosis and cirrhosis, the role of increased TGFbeta1 in the initiation of hepatic stellate cell activation in vivo is unknown. We used two experimental approaches to study this relationship: 1) Induction of an acute liver injury with carbon tetrachloride (CCl4) in normal and TGFbeta1-knockout (ko) mice, and 2) overexpression of TGFbeta1 in the liver of wild-type mice using a recombinant replication-deficient adenovirus encoding human TGFbeta1 (Ad-TGFbeta1).

METHODS

TGFbeta1-ko mice (n=6) and normal mice (n=6) were injected once intraperitoneally (i.p.) with CCl4 (1 microl/g BW) or mineral oil. Wild-type mice (n=3) were injected intravenously with Ad-TGFbeta1 (10(10) pfu) or a control virus expressing beta-galactosidase (Ad-LacZ, 10(10) pfu). Animals were sacrificed after 3 days and total liver RNA was prepared. The expression of collagen alpha1(I) mRNA normalized to GAPDH mRNA was measured by RNase protection assay, asmooth muscle actin (alpha-sma) protein expression was analyzed by Western blotting. The expression of TGFbeta1, TGFbeta2, and TGFbeta3 mRNAs were determined semi-quantitatively with RT-PCR.

RESULTS

The collagen alpha1(I) mRNA was increased 10-fold in CCl4-treated wild-type mice compared to the controls. This increase was reduced about 80% in the TGFbeta1-ko mice. The TGFbeta1 mRNA levels in the wild-type mice were proportional to the collagen alpha1(I) mRNA levels. a-sma, a marker of hepatic stellate cell activation, was expressed earlier and at a higher level in wild-type mice than TGFbeta-ko mice after CCl4 treatment. The Ad-TGFbeta1 infected mice had 14-fold higher hepatic TGFbeta protein levels and 15-fold higher collagen alpha1(I) mRNA levels than the Ad-LacZ-infected control mice. Collagen alpha1(I) mRNA levels were proportional to the transgenic TGFbeta1 mRNA levels, while the endogenous TGFbeta1 was only slightly higher than in the controls. TGFbeta2 and TGFbeta3 mRNA levels were elevated in CCl4-treated wild-type and TGFbeta1-ko mice and in Ad-TGFbeta1-infected mice compared to the controls.

CONCLUSIONS

Absence of TGFbeta1 inhibits hepatic collagen alpha1(I) mRNA and alpha-sma protein expression by the toxic stimulus CCl4, and targeted TGFbeta1 overexpression increases collagen alpha1(I) mRNA and alpha-sma protein levels in the liver in vivo. Other TGFbeta family members do not compensate for the TGFbeta1 deficiency. This indicates that TGFbeta1 accelerates, but is not absolutely required, for the activation of hepatic stellate cells.

The mitochondrial permeability transition is required for tumor necrosis factor alpha-mediated apoptosis and cytochrome c release

This study assesses the controversial role of the mitochondrial permeability transition (MPT) in apoptosis. In primary rat hepatocytes expressing an IkappaB superrepressor, tumor necrosis factor alpha (TNFalpha) induced apoptosis as shown by nuclear morphology, DNA ladder formation, and caspase 3 activation. Confocal microscopy showed that TNFalpha induced onset of the MPT and mitochondrial depolarization beginning 9 h after TNFalpha treatment. Initially, depolarization and the MPT occurred in only a subset of mitochondria; however, by 12 h after TNFalpha treatment, virtually all mitochondria were affected. Cyclosporin A (CsA), an inhibitor of the MPT, blocked TNFalpha-mediated apoptosis and cytochrome c release. Caspase 3 activation, cytochrome c release, and apoptotic nuclear morphological changes were induced after onset of the MPT and were prevented by CsA. Depolarization and onset of the MPT were blocked in hepatocytes expressing DeltaFADD, a dominant negative mutant of Fas-associated protein with death domain (FADD), or crmA, a natural serpin inhibitor of caspases. In contrast, Asp-Glu-Val-Asp-cho, an inhibitor of caspase 3, did not block depolarization or onset of the MPT induced by TNFalpha, although it inhibited cell death completely. In conclusion, the MPT is an essential component in the signaling pathway for TNFalpha-induced apoptosis in hepatocytes which is required for both cytochrome c release and cell death and functions downstream of FADD and crmA but upstream of caspase 3.

NF-kappaB inactivation converts a hepatocyte cell line TNF-alpha response from proliferation to apoptosis

Toxins convert the hepatocellular response to tumor necrosis factor-alpha (TNF-alpha) stimulation from proliferation to cell death, suggesting that hepatotoxins somehow sensitize hepatocytes to TNF-alpha toxicity. Because nuclear factor-kappaB (NF-kappaB) activation confers resistance to TNF-alpha cytotoxicity in nonhepatic cells, the possibility that toxin-induced sensitization to TNF-alpha killing results from inhibition of NF-kappaB-dependent gene expression was examined in the RALA rat hepatocyte cell line sensitized to TNF-alpha cytotoxicity by actinomycin D (ActD). ActD did not affect TNF-alpha-induced hepatocyte NF-kappaB activation but decreased NF-kappaB-dependent gene expression. Expression of an IkappaB superrepressor rendered RALA hepatocytes sensitive to TNF-alpha-induced apoptosis in the absence of ActD. Apoptosis was blocked by caspase inhibitors, and TNF-alpha treatment led to activation of caspase-2, caspase-3, and caspase-8 only when NF-kappaB activation was blocked. Although apoptosis was blocked by the NF-kappaB-dependent factor nitric oxide (NO), inhibition of endogenous NO production did not sensitize cells to TNF-alpha-induced cytotoxicity. Thus NF-kappaB activation is the critical intracellular signal that determines whether TNF-alpha stimulates hepatocyte proliferation or apoptosis. Although exogenous NO blocks RALA hepatocyte TNF-alpha cytotoxicity, endogenous production of NO is not the mechanism by which NF-kappaB activation inhibits this death pathway.

Porphyrias

The porphyrias are a heterogeneous group of metabolic disorders caused by genetic defects of the enzymes involved in heme biosynthesis. The diseases are characterized by excessive accumulation and excretion of porphyrin or porphyrin precursors. The disorders have been classified as cutaneous, hepatic, or neuropsychiatric according to the organ system involved. This review describes the enzymes of the heme biosynthetic pathway along with the clinical features and management of the porphyrias.

Mechanisms of hepatic toxicity. I. TNF-induced liver injury

Tumor necrosis factor-alpha (TNF-alpha) functions as a two-edged sword in the liver. TNF-alpha is required for normal hepatocyte proliferation during liver regeneration. It functions both as a comitogen and to induce the transcription factor nuclear factor-kappaB, which has antiapoptotic effects. On the other hand, TNF-alpha is the mediator of hepatotoxicity in many animal models, including those involving the toxins concanavalin A and lipopolysaccharide. TNF-alpha has also been implicated as an important pathogenic mediator in patients with alcoholic liver disease and viral hepatitis.

Signal transduction during liver regeneration

Following partial hepatectomy (PH), there is a rapid and highly orchestrated series of biochemical events which occur prior to cellular proliferation. Some of these events are presumably intimately linked with the eventual regeneration of the liver, whereas others are likely to be stress related or required for the continued differentiated function of the liver while regeneration is occurring. The regulation of the AP-1 transcription factor c-Jun during hepatic regeneration has been studied here. There is a progressive increase in c-Jun-mRNA levels after sham operation, one-third PH, and two-thirds PH. A concomitant increase in activating protein 1 (AP-1) binding activity is also observed. The c-Jun protein is a major constituent of the AP-1 complex in quiescent and early regenerating liver. The activity of c-Jun amino-terminal kinase (JNK), which phosphorylates the activation domain of the c-Jun protein, is markedly stimulated after one-third and two-thirds PH. c-Jun amino-terminal kinase-1 is a constituent of this stimulated JNK activity after PH. When primary cultures of adult rat hepatocytes are incubated with epidermal growth factor or transforming growth factor-alpha, AP-1 transcriptional activity is increased and the activation domain of the c-Jun protein is further potentiated. Phosphopeptide mapping of the endogenous c-Jun protein in proliferating cultured hepatocytes demonstrates phosphorylation of the c-Jun activation domain. Pretreatment of animals prior to PH with a neutralizing antibody to tumour necrosis factor-alpha (TNFalpha), inhibits hepatocyte DNA synthesis and JNK activation. It is concluded that the stimulation of one-third or two-thirds PH activates JNK through a mechanism that requires TNFalpha, which phosphorylates the c-Jun activation domain in hepatocytes, resulting in enhanced transcription of AP-1-dependent genes. Although nuclear factor-kappa B (NFkappaB) binding activity is induced during liver regeneration following PH, the physiological consequence of this induction is unknown. The role of NFkappaB during liver regeneration has been assessed by delivering to the liver a super-repressor of NFkappaB activity using an adenoviral vector expressing a mutated form of IkappaB. This adenovirus (Ad5IkappaB) was almost exclusively expressed in the liver and inhibited NFkappaB DNA binding activity and transcriptional activity in cultured cells as well as in the liver in vivo. Following PH, Ad5IkappaB, but not a control adenovirus (Ad5betagal), resulted in the induction of apoptosis as demonstrated by histological staining and TUNEL analysis. In addition, infection with Ad5IkappaB but not Ad5betagal decreased the mitotic index following PH. These two phenomena, increased apoptosis and cell cycle arrest, were associated with liver failure in animals infected with the ad5IkappaB but not Ad5betagal as demonstrated by elevated serum bilirubin and ammonia levels. Thus, the induction of NFkappaB during liver regeneration following PH appears to be a required event to prevent apoptosis and to allow for normal cell cycle progression.

Signal transduction during liver regeneration

Following partial hepatectomy (PH), there is a rapid and highly orchestrated series of biochemical events which occur prior to cellular proliferation. Some of these events are presumably intimately linked with the eventual regeneration of the liver, whereas others are likely to be stress related or required for the continued differentiated function of the liver while regeneration is occurring. The regulation of the AP-1 transcription factor c-Jun during hepatic regeneration has been studied here. There is a progressive increase in c-Jun-mRNA levels after sham operation, one-third PH, and two-thirds PH. A concomitant increase in activating protein 1 (AP-1) binding activity is also observed. The c-Jun protein is a major constituent of the AP-1 complex in quiescent and early regenerating liver. The activity of c-Jun amino-terminal kinase (JNK), which phosphorylates the activation domain of the c-Jun protein, is markedly stimulated after one-third and two-thirds PH. c-Jun amino-terminal kinase-1 is a constituent of this stimulated JNK activity after PH. When primary cultures of adult rat hepatocytes are incubated with epidermal growth factor or transforming growth factor-α, AP-1 transcriptional activity is increased and the activation domain of the c-Jun protein is further potentiated. Phosphopeptide mapping of the endogenous c-Jun protein in proliferating cultured hepatocytes demonstrates phosphorylation of the c-Jun activation domain. Pretreatment of animals prior to PH with a neutralizing antibody to tumour necrosis factor-α (TNFα), inhibits hepatocyte DNA synthesis and JNK activation. It is concluded that the stimulation of one-third or two-thirds PH activates JNK through a mechanism that requires TNFα, which phosphorylates the c-Jun activation domain in hepatocytes, resulting in enhanced transcription of AP-1-dependent genes. Although nuclear factor-kappa B (NFκB) binding activity is induced during liver regeneration following PH, the physiological consequence of this induction is unknown. The role of NFκB during liver regeneration has been assessed by delivering to the liver a super-repressor of NFκB activity using an adenoviral vector expressing a mutated form of IκB. This adenovirus (Ad5IκB) was almost exclusively expressed in the liver and inhibited NFκB DNA binding activity and transcriptional activity in cultured cells as well as in the liver in vivo. Following PH, Ad5IκB, but not a control adenovirus (Ad5βgal), resulted in the induction of apoptosis as demonstrated by histological staining and TUNEL analysis. In addition, infection with Ad5IκB but not Ad5βgal decreased the mitotic index following PH. These two phenomena, increased apoptosis and cell cycle arrest, were associated with liver failure in animals infected with the ad5IκB but not Ad5βgal as demonstrated by elevated serum bilirubin and ammonia levels. Thus, the induction of NFκB during liver regeneration following PH appears to be a required event to prevent apoptosis and to allow for normal cell cycle progression.

The mitochondrial permeability transition in cell death: a common mechanism in necrosis, apoptosis and autophagy

Using confocal microscopy, onset of the mitochondrial permeability transition (MPT) in individual mitochondria within living cells can be visualized by the redistribution of the cytosolic fluorophore, calcein, into mitochondria. Simultaneously, mitochondria release membrane potential-indicating fluorophores like tetramethylrhodamine methylester. The MPT occurs in several forms of necrotic cell death, including oxidative stress, pH-dependent ischemia/reperfusion injury and Ca2+ ionophore toxicity. Cyclosporin A (CsA) and trifluoperazine block the MPT in these models and prevent cell killing, showing that the MPT is a causative factor in necrotic cell death. During oxidative injury induced by t-butylhydroperoxide, onset of the MPT is preceded by pyridine nucleotide oxidation, mitochondrial generation of reactive oxygen species, and an increase of mitochondrial free Ca2+, all changes that promote the MPT. During tissue ischemia, acidosis develops. Because of acidotic pH, anoxic cell death is substantially delayed. However, when pH is restored to normal after reperfusion (reoxygenation at pH 7.4), cell death occurs rapidly (pH paradox). This killing is caused by pH-dependent onset of the MPT, which is blocked by reperfusion at acidotic pH or with CsA. In isolated mitochondria, toxicants causing Reye's syndrome, such as salicylate and valproate, induce the MPT. Similarly, salicylate induces a CsA-sensitive MPT and killing of cultured hepatocytes. These in vitro findings suggest that the MPT is the pathophysiological mechanism underlying Reye's syndrome in vivo. Kroemer and coworkers proposed that the MPT is a critical event in the progression of apoptotic cell death. Using confocal microscopy, the MPT can be directly documented during tumor necrosis factor-alpha induced apoptosis in hepatocytes. CsA blocks this MPT and prevents apoptosis. The MPT does not occur uniformly during apoptosis. Initially, a small proportion of mitochondria undergo the MPT, which increases to nearly 100% over 1-3 h. A technique based on fluorescence resonance energy transfer can selectively reveal mitochondrial depolarization. After nutrient deprivation, a small fraction of mitochondria spontaneously depolarize and enter an acidic lysosomal compartment, suggesting that the MPT precedes the normal process of mitochondrial autophagy. A model is proposed in which onset of the MPT to increasing numbers of mitochondria within a cell leads progressively to autophagy, apoptosis and necrotic cell death.

Alcohol causes both tolerance and sensitization of rat Kupffer cells via mechanisms dependent on endotoxin

BACKGROUND & AIMS

Ethanol causes both tolerance and sensitization of Kupffer cells. This study was designed to evaluate temporal effects of ethanol in an attempt to understand this paradox.

METHODS

Rats were given ethanol (4 g/kg body wt) intragastrically, and Kupffer cells were isolated 0-48 hours later. After addition of lipopolysaccharide (LPS), intracellular calcium concentration ([Ca2+]i) was measured using a microspectrofluorometer with the fluorescent indicator fura-2, and tumor necrosis factor alpha (TNF-alpha) was measured by enzyme-linked immunosorbent assay. CD14 was evaluated by Western and Northern analysis.

RESULTS

Two hours after ethanol administration, the LPS-induced increase in [Ca2+]i and TNF-alpha release by Kupffer cells was diminished by 50%, and these parameters were reciprocally enhanced twofold at 24 hours. Sterilization of the gut with antibiotics blocked all effects of ethanol on [Ca2+]i and TNF-alpha release completely. Twenty-four hours after ethanol, CD14 in Kupffer cells was elevated about fivefold.

CONCLUSIONS

Kupffer cells isolated from rats early after ethanol exhibited tolerance to LPS, whereas sensitization was observed later. It is likely that both of these phenomena are caused by gut-derived endotoxin and that sensitization in Kupffer cells is caused by increases in CD14.

Cytokines induce NF-kappaB in activated but not in quiescent rat hepatic stellate cells

The hepatic stellate cell (HSC), after a fibrogenic stimulus, is transformed from a quiescent to an activated phenotype, including the induction of responsiveness to a variety of agonists. We investigated the activation of nuclear factor-kappaB (NF-kappaB) and the expression of the NF-kappaB-responsive genes intercellular adhesion molecule 1 (ICAM-1) and macrophage inflammatory protein-2 (MIP-2) in freshly isolated and culture-activated HSC by tumor necrosis factor-alpha (TNF-alpha) or interleukin-1beta. Inhibitor-kappaB was rapidly (<15 min) degraded, and NF-kappaB activity was induced in culture-activated but not in freshly isolated HSC after cytokine stimulation. After 30 min of stimulation, immunofluorescence revealed that the NF-kappaB p65 subunit was predominantly found in the nuclei of activated HSC compared with the cytoplasmic localization in unstimulated cells. No nuclear translocation appeared in freshly isolated HSC after stimulation, despite the presence of functional TNF-alpha receptors. NF-kappaB nuclear translocation appeared first partially after 4-5 days and completely after 9 days in culture. Consistent with this time course TNF-alpha induced the mRNA of the NF-kappaB-dependent genes ICAM-1 and MIP-2 in activated but not in quiescent HSC. Therefore, cytokines induce NF-kappaB activity and ICAM-1 and MIP-2 mRNAs in activated but not in quiescent HSC, through a postreceptor mechanism of regulation.

Analysis of the human ferrochelatase promoter in transgenic mice

Ferrochelatase catalyzes the chelation of ferrous iron and protoporphyrin to form heme. It is expressed as a housekeeping gene in all cells, but is upregulated during erythropoiesis. Ferrochelatase activity is deficient in the inherited disease protoporphyria as a result of heterogeneous mutations. Although human ferrochelatase is transcribed from a single promoter in both nonerythroid and erythroid cells, previous studies using transient transfection assays failed to demonstrate erythroid-specific increased expression from 4.0 kb of the human ferrochelatase promoter containing the erythroid cis-elements, GATA and NF-E2. The present study analyzes the in vivo regulation of the ferrochelatase gene to provide insights into the mechanism of its erythroid-specific enhancement. Transgenic (TG) mouse lines were generated in which the luciferase reporter gene was driven by either a 150-bp ferrochelatase minimal promoter (-0.15 TG) or by a 4.0 kb extended 5' upstream region (-4.0 TG). Expression of the -4.0 TG transgene was generally consistent with the endogenous gene during embryonic development and in nonerythroid and erythroid tissues as demonstrated by Northern blotting and mRNA in situ hybridization. The -4.0 TG was expressed at a higher level than the -0.15 TG in nonerythroid and erythroid tissues, including during extramedullary erythropoiesis induced by n-acetylphenylhydrazine injection. The enhanced erythroid expression of the -4.0 TG correlates with the appearance of a DNase I hypersensitive site in the 5' flanking region of the transgene. Therefore, in the context of chromosomal integration, the 5' flanking region of the ferrochelatase gene is necessary and sufficient to confer high levels of transgene expression in erythroid tissue.