Magnetic resonance elastography identifies fibrosis in adults with alpha-1 antitrypsin deficiency liver disease: a prospective study

BACKGROUND

Limited data exist on the clinical presentation and non-invasive detection of liver fibrosis in adults with homozygous Z genotype alpha-1 antitrypsin (AAT) deficiency.

AIMS

To compare demographic, biochemical, histological and imaging data of AAT deficient patients to normal-control and biopsy-proven non-alcoholic fatty liver disease (NAFLD) patients, and to assess the diagnostic accuracy of magnetic resonance elastography (MRE) in detecting fibrosis in AAT deficiency.

METHODS

Study includes 33 participants, 11 per group, who underwent clinical research evaluation, liver biopsy (AAT and NAFLD groups), and MRE. Histological fibrosis was quantified using a modified Ishak 6-point scale and liver stiffness by MRE. Diagnostic performance of MRE in detecting fibrosis was assessed by receiver operating characteristic (ROC) analysis.

RESULTS

Mean (±s.d.) of age and BMI of normal-control, AAT and NAFLD groups was 57 (±19), 57 (±18), and 57 (±13) years, and 22.7 (±2.5), 24.8 (±4.0) and 31.0 (±5.1) kg/m(2) respectively. Serum ALT [mean ± s.d.] was similar within normal-control [16.4 ± 4.0] and AAT groups [23.5 ± 10.8], but was significantly lower in AAT than NAFLD even after adjustment for stage of fibrosis (P < 0.05, P = 0.0172). For fibrosis detection, MRE-estimated stiffness had an area under the ROC curve of 0.90 (P < 0.0001); an MRE threshold of ≥3.0 kPa provided 88.9% accuracy, with 80% sensitivity and 100% specificity to detect presence of any fibrosis (stage ≥1).

CONCLUSIONS

This pilot prospective study suggests magnetic resonance elastography may be accurate for identifying fibrosis in patients with alpha-1 antitrypsin deficiency. Larger validation studies are warranted.

Novel association between serum pentraxin-2 levels and advanced fibrosis in well-characterised patients with non-alcoholic fatty liver disease

BACKGROUND

Pentraxin-2 (PTX-2), a serum protein, inhibits inflammation and fibrosis, and recombinant PTX-2 is being tested as an anti-fibrotic agent.

AIM

To evaluate the association between serum PTX-2 levels and fibrosis stage in patients with non-alcoholic fatty liver disease (NAFLD).

METHODS

Serum pentraxin-2 levels were compared between four groups of well-characterised patients including NAFLD with no fibrosis, NAFLD with mild-moderate fibrosis (stage 1-2), NAFLD with advanced fibrosis (stage 3-4), and age-sex matched non-NAFLD controls.

RESULTS

Sixty subjects were included in the study. The mean age was 58.9 years, 68% were male and 58% were Caucasian. In univariate analysis, serum PTX-2 levels significantly decreased from non-NAFLD controls to mild NAFLD with no fibrosis, to NAFLD with mild-moderate fibrosis and were lowest in patients with NAFLD and advanced fibrosis, in a dose-dependent manner (P < 0.0001). In multivariable-adjusted analyses controlling for age, sex, albumin, and CRP, the results remained consistent and statistically significant. Serum PTX-2 level had an AUROC of 0.84 (95% CI: 0.71-0.97) for the diagnosis of NAFLD, and an AUROC of 0.77 (95% CI: 0.65-0.90) for the diagnosis of advanced fibrosis in NAFLD. Serum PTX-2 levels also decreased with increasing liver stiffness as estimated by magnetic resonance elastography (r = -0.31, P = 0.02).

CONCLUSIONS

PTX-2 levels are significantly lower in patients with NAFLD compared to non-NAFLD controls, and decline further in patients with advanced fibrosis. PTX-2 may therefore be both a biomarker of disease and a potential target for anti-fibrotic therapy with the recombinant pentraxin-2.

Evidence for a common progenitor of epithelial and mesenchymal components of the liver

Tissues of the adult organism maintain the homeostasis and respond to injury by means of progenitor/stem cell compartments capable to give rise to appropriate progeny. In organs composed by histotypes of different embryological origins (e.g. the liver), the tissue turnover may in theory involve different stem/precursor cells able to respond coordinately to physiological or pathological stimuli. In the liver, a progenitor cell compartment, giving rise to hepatocytes and cholangiocytes, can be activated by chronic injury inhibiting hepatocyte proliferation. The precursor compartment guaranteeing turnover of hepatic stellate cells (HSCs) (perisinusoidal cells implicated with the origin of the liver fibrosis) in adult organ is yet unveiled. We show here that epithelial and mesenchymal liver cells (hepatocytes and HSCs) may arise from a common progenitor. Sca+ murine progenitor cells were found to coexpress markers of epithelial and mesenchymal lineages and to give rise, within few generations, to cells that segregate the lineage-specific markers into two distinct subpopulations. Notably, these progenitor cells, clonally derived, when transplanted in healthy livers, were found to generate epithelial and mesenchymal liver-specific derivatives (i.e. hepatocytes and HSCs) properly integrated in the liver architecture. These evidences suggest the existence of a 'bona fide' organ-specific meso-endodermal precursor cell, thus profoundly modifying current models of adult progenitor commitment believed, so far, to be lineage-restricted. Heterotopic transplantations, which confirm the dual differentiation potentiality of those cells, indicates as tissue local cues are necessary to drive a full hepatic differentiation. These data provide first evidences for an adult stem/precursor cell capable to differentiate in both parenchymal and non-parenchymal organ-specific components and candidate the liver as the instructive site for the reservoir compartment of HSC precursors as yet non-localized in the adult.

Association between novel MRI-estimated pancreatic fat and liver histology-determined steatosis and fibrosis in non-alcoholic fatty liver disease

BACKGROUND

Ectopic fat deposition in the pancreas and its association with hepatic steatosis have not previously been examined in patients with biopsy-proven non-alcoholic fatty liver disease (NAFLD).

AIM

To quantify pancreatic fat using a novel magnetic resonance imaging (MRI) technique and determine whether it is associated with hepatic steatosis and/or fibrosis in patients with NAFLD.

METHODS

This is a cross-sectional study including 43 adult patients with biopsy-proven NAFLD who underwent clinical evaluation, biochemical testing and MRI. The liver biopsy assessment was performed using the NASH-CRN histological scoring system, and liver and pancreas fat quantification was performed using a novel, validated MRI biomarker; the proton density fat fraction.

RESULTS

The average MRI-determined pancreatic fat in patients with NAFLD was 8.5% and did not vary significantly between head, body, and tail of the pancreas. MRI-determined pancreatic fat content increased significantly with increasing histology-determined hepatic steatosis grade; 4.6% in grade 1; 7.7% in grade 2; 13.0% in grade 3 (P = 0.004) respectively. Pancreatic fat content was lower in patients with histology-determined liver fibrosis than in those without fibrosis (11.2% in stage 0 fibrosis vs. 5.8% in stage 1-2 fibrosis, and 6.9% in stage 3-4 fibrosis, P = 0.013). Pancreatic fat did not correlate with age, body mass index or diabetes status.

CONCLUSIONS

In patients with NAFLD, increased pancreatic fat is associated with hepatic steatosis. However, liver fibrosis is inversely associated with pancreatic fat content. Further studies are needed to determine underlying mechanisms to understand if pancreatic steatosis affects progression of NAFLD.

Correlation between liver histology and novel magnetic resonance imaging in adult patients with non-alcoholic fatty liver disease - MRI accurately quantifies hepatic steatosis in NAFLD

BACKGROUND

Conventional magnetic resonance imaging (MRI) techniques that measure hepatic steatosis are limited by T1 bias, T(2)* decay and multi-frequency signal-interference effects of protons in fat. Newer MR techniques such as the proton density-fat fraction (PDFF) that correct for these factors have not been specifically compared to liver biopsy in adult patients with non-alcoholic fatty liver disease (NAFLD).

AIM

To examine the association between MRI-determined PDFF and histology-determined steatosis grade, and their association with fibrosis.

METHODS

A total of 51 adult patients with biopsy-confirmed NAFLD underwent metabolic-biochemical profiling, MRI-determined PDFF measurement of hepatic steatosis and liver biopsy assessment according to NASH-CRN histological scoring system.

RESULTS

The average MRI-determined PDFF increased significantly with increasing histology-determined steatosis grade: 8.9% at grade-1, 16.3% at grade-2, and 25.0% at grade-3 with P ≤ 0.0001 (correlation: r(2) = 0.56, P < 0.0001). Patients with stage-4 fibrosis, when compared with patients with stage 0-3 fibrosis, had significantly lower hepatic steatosis by both MRI-determined PDFF (7.6% vs. 17.8%, P < 0.005) and histology-determined steatosis grade (1.4 vs. 2.2, P < 0.05). NAFLD patients with grade 1 steatosis were more likely to have characteristics of advanced liver disease including higher average AST:ALT (0.87 vs. 0.60, P < 0.02), GGT (140 vs. 67, P < 0.01), and INR (1.06 vs. 0.99, P < 0.01), higher stage of fibrosis and hepatocellular ballooning.

CONCLUSIONS

MRI-determined proton density-fat fraction correlates with histology-determined steatosis grade in adults with NAFLD. Steatosis is non-linearly related to fibrosis progression. In patients with NAFLD, a low amount of hepatic steatosis on imaging does not necessarily indicate mild disease.

Celecoxib induces hepatic stellate cell apoptosis through inhibition of Akt activation and suppresses hepatic fibrosis in rats

BACKGROUND AND AIMS

Activated hepatic stellate cells (HSCs) but not quiescent HSCs express cyclo-oxygenase-2 (COX-2), suggesting that the COX-2/prostanoid pathway has an active role in hepatic fibrogenesis. However, the role of COX-2 inhibitors in hepatic fibrogenesis remains controversial. The aim of this study was to investigate the antifibrotic effects of celecoxib, a selective COX-2 inhibitor.

METHODS

The effects of various COX inhibitors-that is, ibuprofen, celecoxib, NS-398 and DFU, were investigated in activated human HSCs. Then, the antifibrotic effect of celecoxib was evaluated in hepatic fibrosis developed by bile duct ligation (BDL) or peritoneal thioacetamide (TAA) injection in rats.

RESULTS

Celecoxib, NS-398 and DFU inhibited platelet-derived growth facor (PDGF)-induced HSC proliferation; however, only celecoxib (> or =50 microM) induced HSC apoptosis. All COX inhibitors completely inhibited prostaglandin E(2) (PGE(2)) and PGI(2) production in HSCs. Separately, PGE(2) and PGI(2) induced cell proliferation and extracellular signal-regulated kinase (ERK) activation in HSCs. All COX inhibitors attenuated ERK activation, but only celecoxib significantly inhibited Akt activation in HSCs. Celecoxib-induced apoptosis was significantly attenuated in HSCs infected with adenovirus containing a constitutive active form of Akt (Ad5myrAkt). Celecoxib had no significant effect on PPARgamma (peroxisome proliferator-activated receptor gamma) expression in HSCs. Celecoxib inhibited type I collagen mRNA and protein production in HSCs. Oral administration of celecoxib (20 mg/kg/day) significantly decreased hepatic collagen deposition and alpha-SMA (alpha-smooth muscle actin) expression in BDL- and TAA-treated rats. Celecoxib treatment significantly decreased mRNA expression of COX-2, alpha-SMA, transforming growth factor beta1 (TGFbeta1) and collagen alpha1(I) in both models.

CONCLUSIONS

Celecoxib shows a proapoptotic effect on HSCs through Akt inactivation and shows antifibrogenic effects in BDL- and TAA-treated rats, suggesting celecoxib as a novel antifibrotic agent of hepatic fibrosis.

Expression of insulin-like growth factor I by activated hepatic stellate cells reduces fibrogenesis and enhances regeneration after liver injury

BACKGROUND/AIM

Hepatic stellate cells (HSCs) express alpha-smooth muscle actin (alphaSMA) and acquire a profibrogenic phenotype upon activation by noxious stimuli. Insulin-like growth I (IGF-I) has been shown to stimulate HSCs proliferation in vitro, but it has been reported to reduce liver damage and fibrogenesis when given to cirrhotic rats.

METHODS

The authors used transgenic mice (SMP8-IGF-I) expressing IGF-I under control of alphaSMA promoter to study the influence of IGF-I synthesised by activated HSCs on the recovery from liver injury.

RESULTS

The transgene was expressed by HSCs from SMP8-IGF-I mice upon activation in culture and in the livers of these animals after CCl4 challenge. Twenty four hours after administration of CCl4 both transgenic and wild type mice showed similar extensive necrosis and increased levels of serum transaminases. However at 72 hours SMP8-IGF-I mice exhibited lower serum transaminases, reduced hepatic expression of alphaSMA, and improved liver morphology compared with wild type littermates. Remarkably, at this time all eight CCl4 treated wild type mice manifested histological signs of liver necrosis that was severe in six of them, while six out of eight transgenic animals had virtually no necrosis. In SMP8-IGF-I mice robust DNA synthesis occurred earlier than in wild type animals and this was associated with enhanced production of HGF and lower TGFbeta1 mRNA expression in the SMP8-IGF-I group. Moreover, Colalpha1(I) mRNA abundance at 72 hours was reduced in SMP8-IGF-I mice compared with wild type controls.

CONCLUSIONS

Targeted overexpression of IGF-I by activated HSCs restricts their activation, attenuates fibrogenesis, and accelerates liver regeneration. These effects appear to be mediated in part by upregulation of HGF and downregulation of TGFbeta1. The data indicate that IGF-I can modulate the cytokine response to liver injury facilitating regeneration and reducing fibrosis.

Akt protects mouse hepatocytes from TNF-alpha- and Fas-mediated apoptosis through NK-kappa B activation

To determine the role of phosphatidylinositol 3-kinase (PI3K)/Akt and nuclear factor-kappa B (NF-kappa B) in protecting hepatocytes from tumor necrosis factor-alpha (TNF-alpha)- and Fas-mediated apoptosis, we pretreated primary cultures of mouse hepatocytes with pharmacological and adenovirus-mediated inhibitors of the PI3K/Akt and NF-kappa B pathways followed by treatment with TNF-alpha or Jo2, an anti-Fas antibody. Jo2 and, to a lesser extent, TNF-alpha phosphorylate Akt. The PI3K inhibitor LY-294002 blocks TNF-alpha- and Fas-mediated Akt phosphorylation. LY-294002 pretreatment reduces NF-kappa B binding activity and transcriptional activity and NF-kappa B-responsive gene expression by TNF-alpha or Jo2. LY-294002 promotes apoptosis after TNF-alpha or Jo2. The expression of dominant-negative Akt blocks NF-kappa B activation and sensitizes hepatocytes to TNF-alpha- and Fas-mediated apoptosis. The expression of constitutively active Akt rescues LY-294002-pretreated cells from TNF-alpha- and Fas-mediated apoptosis. Active Akt induces NF-kappa B transcriptional activity but not NF-kappa B binding activity or I kappa B degradation. Furthermore, LY-294002 pretreatment blocks TNF-alpha- and Jo2-induced Bcl-xL levels in hepatocytes, with no effect on the phosphorylation levels of Bad. Bcl-xL overexpression protects hepatocytes from Fas- but not TNF-alpha-induced apoptosis after sensitization by actinomycin D or the I kappa B superrepressor. Together, the PI3K/Akt pathway has a protective role in Fas-mediated apoptosis, which requires NF-kappa B activation, partially through the subsequent induction of Bcl-xL.

Decreasing fibrogenesis: an immunohistochemical study of paired liver biopsies following lamivudine therapy for chronic hepatitis B

BACKGROUND

Activation of hepatic stellate cells is the earliest step in fibrogenesis. Alpha-smooth muscle actin (alpha-SMA), expressed by activated hepatic stellate cells, and C-terminal procollagen alpha1(III) propeptide (PIIICP) are early markers of fibrogenesis and should precede fibrosis.

AIM

Determine if suppression of hepatitis B virus replication with lamivudine would decrease fibrogenesis as measured by immunohistochemical markers.

METHODS

Paired liver biopsies from patients with hepatitis B before and after therapy with lamivudine (n=47) or placebo (n=33) were studied. alpha-SMA and PIIICP were detected in paraffin-embedded tissue by immunohistochemistry and quantified in a blinded manner by video imaging analysis.

RESULTS

Liver biopsies from patients treated with lamivudine showed a significant decrease in alpha-SMA expression (1.06+/-0.23 vs. 0.58+/-0.11, pre vs. post, P<0.05). Placebo recipients had increased levels of alpha-SMA (0.82+/-0.14 vs. 1.32+/-0.21, P<0.05). PIIICP was similarly decreased after lamivudine. Among subjects whose Histologic Activity Index fibrosis score was unchanged or worsened, the mean change in alpha-SMA expression was significantly decreased in the lamivudine group compared with placebo.

CONCLUSIONS

Lamivudine decreased markers of hepatic stellate cell activation and collagen synthesis. Immunohistochemical techniques are sensitive for assessing fibrogenesis and will be useful in trials of antiviral and antifibrotic agents.

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.

TAK1/JNK and p38 have opposite effects on rat hepatic stellate cells

After liver injury, hepatic stellate cells (HSCs) undergo a process of activation with expression of smooth muscle alpha-actin (alpha-SMA), an increased proliferation rate, and a dramatic increase in synthesis of type I collagen. The intracellular signaling mechanisms of activation and perpetuation of the activated phenotype in HSCs are largely unknown. In this study the role of the stress-activated protein kinases, c-Jun N-terminal kinase (JNK) and p38, were evaluated in primary cultures of rat HSCs. The effect of JNK was assessed by using an adenovirus expressing a dominant negative form of transforming growth factor beta (TGF-beta)-activated kinase 1 (TAK1) (Ad5dnTAK1) and a new selective pharmacologic inhibitor SP600125. The effect of p38 was assessed with the selective pharmacologic inhibitor SB203580. These kinases were inhibited starting either in quiescent HSCs (culture day 1) or in activated HSCs (culture day 5). Although blocking TAK1/JNK and p38 decreased the expression of alpha-SMA protein in early stages of HSC activation, no effect was observed when TAK1/JNK or p38 were inhibited in activated HSCs. JNK inhibition increased and p38 inhibition decreased collagen alpha1(I) mRNA level as measured by RNase protection assays, with maximal effects observed in early stages of HSC activation. Furthermore, TAK1/JNK inhibition decreased HSC proliferation, whereas p38 inhibition led to an increased proliferation rate of HSCs, independently of its activation status. These results show novel roles for the TAK1/JNK pathway and p38 during HSC activation in culture. Despite similar activators of TAK1/JNK and p38, their functions in HSCs are distinct and opposed.

Long-term alcohol exposure changes sensitivity of rat Kupffer cells to lipopolysaccharide

BACKGROUND

Chronic ethanol treatment enhances Kupffer cell sensitivity to lipopolysaccharide (LPS). In this model, CD14 in Kupffer cells was increased significantly 4 weeks after ethanol. Moreover, it was shown that prostaglandin E2 produced by activated Kupffer cells participated in the mechanism of ethanol-induced fatty liver. This study was designed to elucidate the temporal effect of chronic ethanol exposure on Kupffer cell sensitization to LPS.

METHODS

Rats were given ethanol every 24 hr intragastrically for up to 12 weeks, and Kupffer cells were isolated 24 hr after the final ethanol administration and cultured in RPMI 1640 with 10% fetal bovine serum. After addition of LPS to Kupffer cells, intracellular calcium ([Ca2+]i) was measured.

RESULTS

CD14 in Kupffer cells was increased approximately 2-fold, and then it decreased and returned to control levels. The LPS-induced increases in [Ca2+]i and tumor necrosis factor-alpha by Kupffer cells were also increased approximately 3-fold over control values, but they also returned to control levels. Triglyceride content increased with the duration of chronic ethanol treatment. At 8 weeks, prostaglandin E2 produced by Kupffer cells increased approximately 3-fold over control values and triglycerides by approximately 4-fold before gradually decreasing to basal levels. After 12 weeks of ethanol exposure, LPS-induced increases in [Ca2+]i and tumor necrosis factor-alpha production were only approximately 50% as high as peak levels at 4 weeks. Liver triglyceride content at 12 weeks was reduced significantly compared with values at 8 weeks.

CONCLUSIONS

Kupffer cells at the early stage of chronic ethanol exposure exhibited sensitization to LPS, but this sensitivity was blunted later. This correlated with triglyceride accumulation in the liver. These data indicate that long-term alcohol exposure changes the sensitivity of rat Kupffer cells to LPS but that the magnitude of the effect is time dependent.

Mice lacking inducible nitric oxide synthase have improved left ventricular contractile function and reduced apoptotic cell death late after myocardial infarction

Nitric oxide produced by inducible nitric oxide synthase (NOS2) has been implicated in the pathophysiology of chronic myocardial remodeling and failure. We tested the role of NOS2 in left ventricular (LV) remodeling early (1 month) and late (4 months) after myocardial infarction (MI) in mice lacking NOS2. MI size measured 7 days, 1 month, and 4 months after MI was the same in NOS2 knockout (KO) and wild-type (WT) mice. The LV end-diastolic pressure-volume relationship measured by the isovolumic Langendorff technique showed a progressive rightward shift from 1 to 4 months after MI in WT mice. LV developed pressure measured over a range of LV volumes was reduced at 1 and 4 months after MI in WT mice (P<0.05 and P<0.01 versus shams, respectively). In KO mice, the rightward shift was similar to that in WT mice at 1 and 4 months after MI, as was peak LV developed pressure at 1 month after MI. In contrast, at 4 months after MI, peak LV developed pressure in KO mice was higher than in WT mice (P<0.05 versus WT) and similar to that in sham-operated mice. At 1 month after MI, the frequency of terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL)-positive myocytes in the remote myocardium was increased to a similar extent in WT and KO mice. At 4 months after MI, the frequency of apoptotic myocytes was increased in WT mice but not in KO mice (P<0.05 versus WT). Improved contractile function and reduced apoptosis were associated with reduced mortality rate in KO mice at 4 months after MI. Thus, NOS2 does not play an important role in determining infarct size or early LV remodeling during the first month after MI. In contrast, during late (ie, 4 months after MI) remodeling, NOS2 in remote myocardium contributes to decreased contractile function, increased myocyte apoptosis in remote myocardium, and reduced survival.

CD40 activates NF-kappa B and c-Jun N-terminal kinase and enhances chemokine secretion on activated human hepatic stellate cells

Activated hepatic stellate cells (HSCs) are the main producers of extracellular matrix in the fibrotic liver and contribute to hepatic inflammation through the secretion of chemokines and the recruitment of leukocytes. This study assesses the function of CD40 on human HSCS: Activated human HSCs express CD40 in culture and in fibrotic liver, as determined by flow cytometry, RT-PCR, and immunohistochemistry. CD40 expression is strongly enhanced by IFN-gamma. Stimulation of CD40 with CD40 ligand (CD40L)-transfected baby hamster kidney cells induces NF-kappaB, as demonstrated by the activation of I-kappaB kinase (IKK), increased NF-kappaB DNA binding, and p65 nuclear translocation. CD40-activated IKK also phosphorylates a GST-p65 substrate at serine 536 in the transactivation domain 1. Concomitant with the activation of IKK, CD40L-transfected baby hamster kidney cell treatment strongly activates c-Jun N-terminal kinase. CD40 activation increases the secretion of IL-8 and monocyte chemoattractant protein-1 by HSCs 10- and 2-fold, respectively. Adenovirally delivered dominant negative (dn) IKK2 and TNFR-associated factor 2dn inhibit IKK-mediated GST-I-kappaB and GST-p65 phosphorylation, NF-kappaB binding, and IL-8 secretion, whereas IKK1dn and NF-kappaB-inducing kinase dominant negative do not have inhibitory effects. We conclude that the CD40-CD40L receptor-ligand pair is involved in a cross-talk between HSCs and immune effector cells that contributes to the perpetuation of HSC activation in liver fibrosis through TNFR-associated factor 2- and IKK2-dependent pathways.

Hepatic stellate cells as a target for the treatment of liver fibrosis

Following chronic liver injury of any etiology, there is progressive fibrosis. To date, removing the causative agent is the only effective therapy to stop or even reverse liver fibrosis. Therefore, the development of effective antifibrotic therapies represents a challenge for modern hepatology. In the past decade, dramatic advances have been made in the understanding of the cellular and molecular mechanisms underlying liver fibrogenesis. The identification of activated hepatic stellate cells (HSCs) as the major fibrogenic cell type in the injured liver, as well as the recognition of key cytokines involved in this process, have facilitated the design of promising new antifibrotic therapies. These therapies are aimed at inhibiting the accumulation of activated HSCs at the sites of liver injury and preventing the deposition of extracellular matrix. Although many of these approaches are effective in experimental models of liver fibrosis, their efficacy and safety in humans are still unknown. This review describes the current therapeutic approaches for liver fibrosis and discusses different features of activated HSCs as a target to design new treatments to inhibit scar formation in chronic liver diseases.

Exercise training attenuates age-associated diastolic dysfunction in rats

BACKGROUND

In contrast to systolic function, which is relatively well preserved with advancing age, diastolic function declines steadily after age 30. Our goal was to determine whether changes in diastolic function that occur with aging could be reversed with exercise training. Methods and Results-- Adult (6-month-old) and old (24-month-old) Fischer 344/BNF1 rats were studied after either 12 weeks of treadmill training or normal sedentary cage life. Three aspects of diastolic function were studied: (1) left ventricular (LV) filling in vivo via Doppler echocardiograph, (2) LV passive compliance, and (3) the degree of ischemia-induced LV stiffening. Maximal exercise capacity was lower in the old rats (18+/-1 minutes to exhaustion on a standard treadmill) than in the adult rats (25+/-1 minutes). Training increased exercise capacity by 43% in the old rats and 46% in the adults (to 26+/-1 and 37+/-1 minutes, respectively). Echocardiographic indices of LV relaxation were significantly lower in the old rats, but with training, they increased back to the levels seen in the adults. LV stiffness measured in the isolated, perfused hearts was not affected by age or training. Also in the isolated hearts, the LV stiffened more rapidly during low-flow ischemia in the old hearts than in the adults, but training eliminated this age-associated difference in the response to ischemia.

CONCLUSIONS

Our findings indicate that in rats, some age-associated changes in diastolic function are reversible and thus may not be intrinsic to aging but instead secondary to other processes, such as deconditioning.

The role of Smad3 in mediating mouse hepatic stellate cell activation

Transforming growth factor beta (TGF-beta) is the most potent profibrogenic mediator in liver fibrosis. Although Smad proteins have been identified as intracellular mediators in the TGF-beta signaling pathway, the function of individual Smad proteins remains poorly understood. The aim of this study was to explore the contribution of Smad3 in mediating TGF-beta responses in a model of acute liver injury in vivo and in culture-activated hepatic stellate cells (HSCs). Wild-type, Smad3 heterozygous or Smad3 homozygous knockout mice were treated with a single intragastric administration of CCl(4). After 72 hours, the induction of hepatic collagen alpha1(I) and alpha2(I) messenger RNA (mRNA) levels in Smad3 knockout mice was only 42% and 64%, respectively, of the levels induced in wild-type mice. However, smooth muscle alpha-actin (alpha-SMA) was expressed at a slightly higher level in livers from knockout mice compared with wild-type mice. In culture-activated HSCs from Smad3 knockout mice, collagen alpha1(I) mRNA was 73% of wild-type HSCs, but alpha-SMA expression was the same. HSCs from knockout mice showed a higher proliferation rate than wild-type HSCs. Smad3-deficient HSCs did not form TGF-beta1-induced Smad-containing DNA-binding complexes. In conclusion, (1) maximal expression of collagen type I in activated HSCs requires Smad3 in vivo and in culture; (2) Smad3 is not necessary for HSC activation as assessed by alpha-SMA expression; (3) Smad3 is necessary for inhibition of proliferation of HSCs, which might be TGF-beta-dependent; and (4) Smad3 is required for TGF-beta1-mediated Smad-containing DNA-binding complex formation in cultured HSCs.

TNF-alpha-induced sphingosine 1-phosphate inhibits apoptosis through a phosphatidylinositol 3-kinase/Akt pathway in human hepatocytes

Human hepatocytes usually are resistant to TNF-alpha cytotoxicity. In mouse or rat hepatocytes, repression of NF-kappaB activation is sufficient to induce TNF-alpha-mediated apoptosis. However, in both Huh-7 human hepatoma cells and Hc human normal hepatocytes, when infected with an adenovirus expressing a mutated form of IkappaBalpha (Ad5IkappaB), which almost completely blocks NF-kappaB activation, >80% of the cells survived 24 h after TNF-alpha stimulation. Here, we report that TNF-alpha activates other antiapoptotic factors, such as sphingosine kinase (SphK), phosphatidylinositol 3-kinase (PI3K), and Akt kinase. Pretreatment of cells with N,N-dimethylsphingosine (DMS), an inhibitor of SphK, or LY 294002, an inhibitor of PI3K that acts upstream of Akt, increased the number of apoptotic cells induced by TNF-alpha in Ad5IkappaB-infected Huh-7 and Hc cells. TNF-alpha-induced activations of PI3K and Akt were inhibited by DMS. In contrast, exogenous sphingosine 1-phosphate, a product of SphK, was found to activate Akt and partially rescued the cells from TNF-alpha-induced apoptosis. Although Akt has been reported to activate NF-kappaB, DMS and LY 294002 failed to prevent TNF-alpha-induced NF-kappaB activation, suggesting that the antiapoptotic effects of SphK and Akt are independent of NF-kappaB. Furthermore, apoptosis mediated by Fas ligand (FasL) involving Akt activation also was potentiated by DMS pretreatment in Hc cells. Sphingosine 1-phosphate administration partially protected cells from FasL-mediated apoptosis. These results indicate that not only NF-kappaB but also SphK and PI3K/Akt are involved in the signaling pathway(s) for protection of human hepatocytes from the apoptotic action of TNF-alpha and probably FasL.

Development of an animal model of chronic alcohol-induced pancreatitis in the rat

This study was designed to develop an animal model of alcoholic pancreatitis and to test the hypothesis that the dose of ethanol and the type of dietary fat affect free radical formation and pancreatic pathology. Female Wistar rats were fed liquid diets rich in corn oil (unsaturated fat), with or without a standard or high dose of ethanol, and medium-chain triglycerides (saturated fat) with a high dose of ethanol for 8 wk enterally. The dose of ethanol was increased as tolerance developed, which allowed approximately twice as much alcohol to be delivered in the high-dose group. Serum pancreatic enzymes and histology were normal after 4 wk of diets rich in unsaturated fat, with or without the standard dose of ethanol. In contrast, enzyme levels were elevated significantly by the high ethanol dose. Increases were blunted significantly by dietary saturated fat. Fibrosis and collagen alpha1(I) expression in the pancreas were not detectable after 4 wk of enteral ethanol feeding; however, they were enhanced significantly by the high dose after 8 wk. Furthermore, radical adducts detected by electron spin resonance were minimal with the standard dose; however, the high dose increased carbon-centered radical adducts as well as 4-hydroxynonenal, an index of lipid peroxidation, significantly. Radical adducts were also blunted by approximately 70% by dietary saturated fat. The animal model presented here is the first to demonstrate chronic alcohol-induced pancreatitis in a reproducible manner. The key factors responsible for pathology are the amount of ethanol administered and the type of dietary fat.

Mechanisms of alcoholic liver disease: cytokines

This article represents the proceedings of a workshop at the 2000 ISBRA Meeting in Yokohama, Japan. The chair was Manuela G. Neuman. The presentations were (1) New aspects of hepatic fibrosis, by D. A. Brenner; (2) Cellular immune response in hepatitis C models, by B. Rehermann; (3) The role of interleukin-10 in acute alcoholic hepatitis, by J. Taieb, S. Chollet-Martin, M. Cohard, J. J. Garaud, and T. Poynard; (4) Cytokine-mediated apoptosis in vitro, by M. G. Neuman; (5) Signaling for apoptosis and repair in vitro, by G. G. Katz, R. G. Cameron, N. H. Shear, and M. G. Neuman; (6) Interferons activate the P42/44 mitogen-activated protein kinase and Janus Kinase signal transducers and activation of transcription (JAK-STAT) signaling pathways in hepatocytes: Differential regulation by acute ethanol via a protein kinase C-dependent mechanism, by B. Gao; (7) Genetic polymorphisms of interleukin-1 in association with the development of Japanese alcoholic liver disease, by M. Takamatsu, M. Yamauchi, M. Ohata, S. Saito, S. Maeyama, T. Uchikoshi, and G. Toda; and (8) Increased levels of macrophage migration inhibitory factor in sera from patients with alcoholic liver diseases, by T. Kumagi, S. M. F. Akbar, M. Abe, K. Michitaka, N. Horiike, and M. Onji.

Cell therapy attenuates deleterious ventricular remodeling and improves cardiac performance after myocardial infarction

BACKGROUND

Myocardial infarction (MI) promotes deleterious remodeling of the myocardium, resulting in ventricular dilation and pump dysfunction. We examined whether supplementing infarcted myocardium with skeletal myoblasts would (1) result in viable myoblast implants, (2) attenuate deleterious remodeling, and (3) enhance in vivo and ex vivo contractile performance.

METHODS AND RESULTS

Experimental MI was induced by 1-hour coronary ligation followed by reperfusion in adult male Lewis rats. One week after MI, 10(6) myoblasts were injected directly into the infarct region. Three groups of animals were studied at 3 and 6 weeks after cell therapy: noninfarcted control (control), MI plus sham injection (MI), and MI plus cell injection (MI+cell). In vivo cardiac function was assessed by maximum exercise capacity testing and ex vivo function was determined by pressure-volume curves obtained from isolated, red cell-perfused, balloon-in-left ventricle (LV) hearts. MI and MI+cell hearts had indistinguishable infarct sizes of approximately 30% of the LV. At 3 and 6 weeks after cell therapy, 92% (13 of 14) of MI+cell hearts showed evidence of myoblast graft survival. MI+cell hearts exhibited attenuation of global ventricular dilation and reduced septum-to-free wall diameter compared with MI hearts not receiving cell therapy. Furthermore, cell therapy improved both post-MI in vivo exercise capacity and ex vivo LV systolic pressures.

CONCLUSIONS

Implanted skeletal myoblasts form viable grafts in infarcted myocardium, resulting in enhanced post-MI exercise capacity and contractile function and attenuated ventricular dilation. These data illustrate that syngeneic myoblast implantation after MI improves both in vivo and ex vivo indexes of global ventricular dysfunction and deleterious remodeling and suggests that cellular implantation may be beneficial after MI.

NF-kappaB stimulates inducible nitric oxide synthase to protect mouse hepatocytes from TNF-alpha- and Fas-mediated apoptosis

BACKGROUND AND AIMS

Hepatocyte apoptosis is induced by tumor necrosis factor alpha (TNF-alpha) and Fas ligand. Although nuclear factor-kappaB (NF-kappaB) activation protects hepatocytes from TNF-alpha-mediated apoptosis, the NF-kappaB responsive genes that protect hepatocytes are unknown. Our aim was to study the role of NF-kappaB activation and inducible nitric oxide synthases (iNOSs) in TNF-alpha- and Fas-mediated apoptosis in hepatocytes.

METHODS

Primary cultures of hepatocytes from wild-type and iNOS knockout mice were treated with TNF-alpha, the Fas agonistic antibody Jo2, a nitric oxide (NO) donor (S-nitroso-N-acetylpenicillamine), an NO inhibitor (N(G)-methyl-L-arginine acetate), and/or adenovirus-expressing NF-kappaB inhibitors.

RESULTS

The IkappaB superrepressor and a dominant-negative form of IkappaB kinase beta (IKKbeta) inhibited NF-kappaB binding activity by TNF-alpha or Jo2 and sensitized hepatocytes to TNF-alpha- and Jo2-mediated apoptosis. TNF-alpha and Jo2 induced iNOS messenger RNA and protein levels through the induction of NF-kappaB. S-nitroso-N-acetylpenicillamine inhibited Bid cleavage, the mitochondrial permeability transition, cytochrome c release, and caspase-8 and -3 activity, and reduced TNF-alpha- and Fas-mediated death in hepatocytes expressing IkappaB superrepressor. N(G)-methyl-L-arginine acetate partially sensitized hepatocytes to TNF-alpha- and Fas-mediated cell killing. TNF-alpha alone or Jo2 alone induced moderate cell death in hepatocytes from iNOS(-)/(-) mice.

CONCLUSIONS

NO protects hepatocytes from TNF-alpha- and Fas-mediated apoptosis. Endogenous iNOS, which is activated by NF-kappaB via IKKbeta, provides partial protection from apoptosis.

Exercise intolerance in rats with hypertensive heart disease is associated with impaired diastolic relaxation

A decrease in functional capacity is one of the most important clinical manifestations of hypertensive heart disease, but its cause is poorly understood. Our purpose was to evaluate potential causes of hypertension-induced exercise intolerance, focusing on identifying the type(s) of cardiac dysfunction associated with the first signs of exercise intolerance during the course of hypertensive heart disease. Exercise capacity was measured weekly in Dahl salt-sensitive rats as they developed hypertension as well as in Dahl salt-resistant control rats. Exercise capacity was unchanged from baseline during the first 8 weeks of hypertension, suggesting that hypertension itself did not cause exercise intolerance. After 9 to 12 weeks of hypertension, exercise capacity decreased in salt-sensitive rats but not in control rats. After 10 weeks of hypertension, indices of diastolic function (early truncation of the E wave), as assessed by echocardiography at rest, were decreased in the salt-sensitive rats. When exercise capacity had decreased by approximately 25% in a rat, the heart was isolated, and left ventricular (LV) compliance and systolic function were measured. At that time point, LV hypertrophy was modest (an approximately 20% increase in LV mass), and systolic function was normal or supernormal, indicating that exercise intolerance began during "compensated" LV hypertrophy. Passive LV compliance remained normal in salt-sensitive rats. Thus, in this model of hypertensive heart disease, exercise intolerance develops during the compensated stage of LV hypertrophy and appears to be due to changes in diastolic rather than systolic function. However, studies in which LV function is assessed during exercise are needed to conclusively define the roles of systolic and diastolic dysfunction in causing exercise intolerance.

Autocrine expression of activated transforming growth factor-beta(1) induces apoptosis in normal rat liver

The aim of this study was to determine the differential effects of latent and activated transforming growth factor (TGF)-beta(1) in growth control of normal and proliferating hepatocytes in vivo. Rats were injected with adenoviruses expressing control transgenes (Ctrl), latent TGF-beta(1) [TGF-beta(L)], or activated TGF-beta(1) [TGF-beta(A)]. Additional animals underwent two-thirds partial hepatectomy (PH) 24 h after injection. Increased hepatocyte apoptosis was observed in TGF-beta(A)-injected but not TGF-beta(L)-injected animals 24 h postinjection (10.5%) compared with Ctrl animals (0.37%). The percent of apoptotic cells increased to 32.1% in TGF-beta(A)-injected animals 48 h after injection. Furthermore, TGF-beta(A)-injected rats did not survive 24 h after PH. Four hours after PH, 0.25 and 14.1% apoptotic hepatocytes were seen in Ctrl- and TGF-beta(A)-injected rats, respectively. TGF-beta(A)-induced apoptosis in primary rat hepatocytes was blocked with a pancaspase inhibitor. Thus autocrine expression of TGF-beta(A) but not TGF-beta(L) induces hepatocyte apoptosis in the normal rat liver. Rats overexpressing TGF-beta(A) do not survive two-thirds PH due to hepatic apoptosis. Thus activation of TGF-beta(1) may be a critical step in the growth control of normal and proliferating rat hepatocytes.

Differential role of I kappa B kinase 1 and 2 in primary rat hepatocytes

Nuclear factor-kappa B (NF-kappa B) protects hepatocytes from undergoing apoptosis during embryonic development and during liver regeneration. Activation of NF-kappa B is mediated through phosphorylation of its inhibitor, I kappa B, by a kinase complex that contains 2 I kappa B kinases. We analyzed the differential role of I kappa B kinase 1 (IKK1) and I kappa B kinase 2 (IKK2) in tumor necrosis factor alpha (TNF-alpha)- and interleukin-1 beta (IL-1 beta)-mediated NF-kappa B activation in primary rat hepatocytes. Maximal induction of IKK activity was observed 5 minutes after TNF-alpha and 15 minutes after IL-1 beta treatment, and activated IKK was able to phosphorylate GST-I kappa B (1-54) and GST-p65 (354-551), but not a GST-p65 (354-551) substrate with a serine-to-alanine substitution at position 536. Infection with an adenovirus containing catalytically inactive IKK2K44M (Ad5IKK2dn) completely blocked both TNF-alpha- and IL-1 beta-induced GST-I kappa B and GST-p65 phosphorylation, I kappa B degradation, and NF-kappa B DNA binding. Adenovirally transduced, catalytically inactive IKK1K44M (Ad5IKK1dn) reduced IKK activity and NF-kappa B DNA binding only slightly. Accordingly, Ad5IKK2dn induced apoptosis in 75% (+/-6%) of hepatocytes after 12 hours of TNF-alpha, which was accompanied by activation of caspases 3 and 8, nuclear fragmentation, and DNA laddering. In contrast, Ad5IKK1dn led to 21% (+/-2%) apoptosis in TNF-alpha-treated hepatocytes after 12 hours and comparatively low activity of caspases 3 and 8. Furthermore, Ad5IKK2dn completely blocked the induction of inducible nitric oxide synthase (iNOS), whereas Ad5IKK1dn had no influence on the expression of iNOS. Thus, IKK2 is the main mediator for cytokine-induced NF-kappa B activation in primary hepatocytes and protects against TNF-alpha-induced apoptosis, whereas IKK1 kinase activity is not required for NF-kappa B activation.

Gene delivery of Cu/Zn-superoxide dismutase improves graft function after transplantation of fatty livers in the rat

Oxygen-derived free radicals play a central role in reperfusion injury after organ transplantation, and fatty livers are particularly susceptible. Endogenous radical scavengers such as superoxide dismutase (SOD) degrade these radicals; however, SOD is destroyed rapidly when given exogenously. Therefore, an adenoviral vector encoding the Cu/Zn-SOD gene (Ad.SOD1) was used here to test the hypothesis that organ injury would be reduced and survival increased in a rat model of transplantation of fatty livers. Donors received chow diet (untreated), high-fat diet, or ethanol-containing high-fat diet. Some of the ethanol-fed donors were infected either with the gene lacZ encoding bacterial beta-galactosidase (Ad.lacZ), or Ad.SOD1. After liver transplantation, SOD activity and protein expression in liver, survival, histopathology, release of transaminases, free radical adducts in bile, and activation of NF-kappaB, IkappaB kinase (IKK), Jun-N-terminal kinase (JNK), and TNFalpha were evaluated. Ad.SOD1 treatment increased survival dramatically, blunted transaminase release, and reduced necrosis and apoptosis significantly. Free radical adducts were increased two-fold in the ethanol group compared with untreated controls. Ad. SOD1 blunted this increase and reduced the activation of NF-kappaB. However, release of TNFalpha was not affected. Ad.SOD1 also blunted JNK activity after transplantation. This study shows that gene therapy with Ad.SOD1 protects marginal livers from failure after transplantation because of decreased oxygen radical production. Genetic modification of fatty livers using viral vectors represents a new approach to protect marginal grafts against primary nonfunction.

Tumor necrosis factor alpha prevents tumor necrosis factor receptor-mediated mouse hepatocyte apoptosis, but not fas-mediated apoptosis: role of nuclear factor-kappaB

Tumor necrosis factor alpha (TNF-alpha) binding to the TNF receptor (TNFR) initiates apoptosis and simultaneously activates the transcription factor, nuclear factor-kappaB (NF-kappaB), which suppresses apoptosis by an unknown mechanism. Pretreatment with TNF-alpha or interleukin-1beta (IL-1beta), which activated NF-kappaB in the liver, dramatically prevented TNF-alpha-induced liver-cell apoptosis in D-galactosamine (GalN)-sensitized mice, but not anti-Fas antibody-induced hepatotoxicity. This protective effect of TNF-alpha continued for 5 hours after TNF-alpha administration, a time course similar to that found in NF-kappaB activation after TNF-alpha administration. In mice treated with adenoviruses expressing a mutant form of IkappaB, the antiapoptotic effect of TNF-alpha was inhibited in part. Prior TNF-alpha administration was not found to block the activation of caspase-8, although caspase-3 was inhibited in mice treated with TNF-alpha plus GalN/TNF-alpha compared with mice treated with GalN/TNF-alpha. These results indicate that TNFR and Fas independently regulate murine apoptotic liver failure, and that a rapid defense mechanism induced by the activation of NF-kappaB blocks death-signaling at the initiation stage of hepatic apoptosis mediated by TNFR, probably downstream of caspase-8, but not by Fas.

Expression of small heat shock protein alphaB-crystallin is induced after hepatic stellate cell activation

Using the differential PCR display method to select cDNA fragments that are differentially expressed after hepatic stellate cell (HSC) activation, we have isolated from activated HSCs a cDNA that corresponds to rat alphaB-crystallin. Northern blots confirmed expression of alphaB-crystallin in culture-activated HSCs but not in quiescent HSCs. Western blot analysis and immunocytochemical staining confirmed expression of alphaB-crystallin protein in activated but not quiescent HSCs. alphaB-crystallin is induced as early as 6 h after plating HSCs on plastic and continues to be expressed for 14 days in culture. Expression of alphaB-crystallin was also induced in vivo in activated HSCs from experimental cholestatic liver fibrosis. Confocal microscopy demonstrated a cytoplasmic distribution of alphaB-crystallin in a cytoskeletal pattern. Heat shock treatment resulted in an immediate perinuclear redistribution that in time returned to a normal cytoskeletal distribution. The expression pattern of alphaB-crystallin was similar to that of HSP25, another small heat shock protein, but differed from the classic heat shock protein HSP70. Therefore, alphaB-crystallin represents an early marker for HSC activation.

Characterization of the interaction between alphaCP(2) and the 3'-untranslated region of collagen alpha1(I) mRNA

Activated hepatic stellate cells produce increased type I collagen in hepatic fibrosis. The increase in type I collagen protein results from an increase in mRNA levels that is mainly mediated by increased mRNA stability. Protein-RNA interactions in the 3'-UTR of the collagen alpha1(I) mRNA correlate with stabilization of the mRNA during hepatic stellate cell activation. A component of the binding complex is alphaCP(2). Recombinant alphaCP(2) is sufficient for binding to the 3'-UTR of collagen alpha1(I). To characterize the binding affinity of and specificity for alphaCP(2), we performed electrophoretic mobility shift assays using the poly(C)-rich sequence in the 3'-UTR of collagen alpha1(I) as probe. The binding affinity of alphaCP(2) for the 3'-UTR sequence is approximately 2 nM in vitro and the wild-type 3' sequence binds with high specificity. Furthermore, we demonstrate a system for detecting protein-nucleotide interactions that is suitable for high throughput assays using molecular beacons. Molecular beacons, developed for DNA-DNA hybridization, are oligonucleotides with a fluorophore and quencher brought together by a hairpin sequence. Fluorescence increases when the hairpin is disrupted by binding to an antisense sequence or interaction with a protein. Molecular beacons displayed a similar high affinity for binding to recombinant alphaCP(2) to the wild-type 3' sequence, although the kinetics of binding were slower.

Confocal microscopy of the mitochondrial permeability transition in necrotic and apoptotic cell death

Opening of a high-conductance pore in the mitochondrial inner membrane induces onset of the mitochondrial permeability transition (mPT). Cyclosporin A and trifluoperazine inhibit this pore and block necrotic cell death in oxidative stress, Ca2+ ionophore toxicity, Reye-related drug toxicity, pH-dependent ischaemia/reperfusion injury and other models of cell injury. Confocal fluorescence microscopy directly visualizes the increased mitochondrial membrane permeability of the mPT from the movement of calcein from the cytosol into the matrix space. Pyridine nucleotide oxidation, increased mitochondrial Ca2+ and mitochondrial generation of reactive oxygen species (ROS) all contribute to the onset of the mPT in situ. Confocal microscopy also shows directly that the mPT is a critical link in apoptotic signalling by tumour necrosis factor-alpha at a point downstream of caspase 8 and upstream of caspase 3. Cyclosporin A blocks this mPT, preventing release of pro-apoptotic cytochrome c from mitochondria and subsequent apoptotic cell killing. Progression to necrosis or apoptosis after the mPT depends on the availability of ATP, which blocks necrosis but promotes the apoptotic programme. Given the pathophysiological importance of the mPT, development of agents to modulate the mPT represents an important new goal for pharmaceutical drug discovery.

The focal adhesion kinase suppresses transformation-associated, anchorage-independent apoptosis in human breast cancer cells. Involvement of death receptor-related signaling pathways

The focal adhesion kinase (FAK) is a mediator of cell-extracellular matrix signaling events and is overexpressed in tumor cells. In order to rapidly down-regulate FAK function in normal and transformed mammary cells, we have used adenoviral gene transduction of the carboxyl-terminal domain of FAK (FAK-CD). Transduction of adenovirus containing FAK-CD in breast cancer cells caused loss of adhesion, degradation of p125(FAK), and induced apoptosis. Furthermore, breast tumor cells that were viable without matrix attachment also underwent apoptosis upon interruption of FAK function, demonstrating that FAK is a survival signal in breast tumor cells even in the absence of matrix signaling. In addition, both anchorage-dependent and anchorage-independent apoptotic signaling required Fas-associated death domain and caspase-8, suggesting that a death receptor-mediated apoptotic pathway is involved. Finally, FAK-CD had no effect on adhesion or viability in normal mammary cells, despite the loss of tyrosine phosphorylation of p125(FAK). These results indicate that FAK-mediated signaling is required for both cell adhesion and anchorage-independent survival and the disruption of FAK function involves the Fas-associated death domain and caspase-8 apoptotic pathway.

Regulation of collagen alpha1(I) expression in hepatic stellate cells

The regulation of collagen alpha1(I) expression in hepatic stellate cells (HSCs) occurs in a complex fashion that is just beginning to be determined. The presence of regulatory sequences in both the 5' and 3' regions of the mRNA appear to be critical to its regulation in HSCs and are involved in the increased expression of collagen in activated HSCs. The 3' UTR contains a C-rich site that binds alphaCP, a known RNA-binding protein that is responsible for the increased stability of the mRNA in activated HSCs. Given that alphaCP is present in both activated and quiescent HSCs, there must be a mechanism for modifying alpha(CP to bind to the RNA in activated but not quiescent HSCs. The 5' region contains an evolutionary conserved stem-loop region that encompasses the translation initiation codon. This stem-loop can bind protein(s) in activated HSCs in an RNA cap-dependent manner. Such binding, together with the binding of alphaCP to the 3' UTR, can facilitate translation of collagen alpha1(I) mRNA, resulting in increased mRNA steady-state levels and collagen synthesis. A role of alphaCP in activating translation initiation has also been demonstrated. These two mechanisms work together to upregulate collagen alpha1(I) production in activated but not quiescent HSCs.

Kupffer cell-derived prostaglandin E(2) is involved in alcohol-induced fat accumulation in rat liver

Destruction of Kupffer cells with gadolinium chloride (GdCl(3)) and intestinal sterilization with antibiotics diminished ethanol-induced steatosis in the enteral ethanol feeding model. However, mechanisms of ethanol-induced fatty liver remain unclear. Accordingly, the role of Kupffer cells in ethanol-induced fat accumulation was studied. Rats were given ethanol (5 g/kg body wt) intragastrically, and tissue triglycerides were measured enzymatically. Kupffer cells were isolated 0-24 h after ethanol, and PGE(2) production was measured by ELISA, whereas inducible cyclooxygenase (COX-2) mRNA was detected by RT-PCR. As expected, ethanol increased liver triglycerides about threefold. This increase was blunted by antibiotics, GdCl(3), the dihydropyridine-type Ca(2+) channel blocker nimodipine, and the COX inhibitor indomethacin. Ethanol also increased PGE(2) production by Kupffer cells about threefold. This increase was also blunted significantly by antibiotics, nimodipine, and indomethacin. Furthermore, tissue triglycerides were increased about threefold by PGE(2) treatment in vivo as well as by a PGE(2) EP(2)/EP(4) receptor agonist, whereas an EP(1)/EP(3) agonist had no effect. Moreover, permeable cAMP analogs also increased triglyceride content in the liver significantly. We conclude that PGE(2) derived from Kupffer cells, which are activated by ethanol, interacts with prostanoid receptors on hepatocytes to increase cAMP, which causes triglyceride accumulation in the liver. This mechanism is one of many involved in fatty liver caused by ethanol.

Nuclear factor kappaB in proliferation, activation, and apoptosis in rat hepatic stellate cells

BACKGROUND/AIMS

Activation of the transcription factor NFkappaB has been demonstrated in activated hepatic stellate cells (HSCs). We investigated the role of NFkappaB in proliferation, in activation, and in TNFalpha-induced apoptosis of HSCs.

METHODS

NFkappaB activation was inhibited using an adenovirus expressing an IkappaB dominant negative protein (Ad5IkappaB) in both quiescent and activated HSCs. Quiescent HSCs were infected with Ad5IkappaB or an adenovirus expressing beta-galactosidase (Ad5LacZ). The cells were cultured for 7 days. HSCs activation was determined by cell morphology, smooth muscle alpha-actin (alpha-sma) expression, and steady-state mRNA levels of alpha1(I) collagen as assessed by Western blot and RNase protection assay, respectively. Proliferation was determined in culture-activated HSCs by 3H-thymidine incorporation and direct cell counting. Apoptosis was analyzed by infecting quiescent or activated HSCs with Ad5IkappaB or Ad5LacZ, and then treating with TNFalpha. Apoptosis was demonstrated by determining cell number, assessing nuclear morphology, TUNEL assay and caspase 3 activity.

RESULTS

After 7 days in culture no differences were noted between the Ad5IkappaB- and the Ad5LacZ-infected cells in the morphology, alpha-sma expression or in alpha1(I) collagen mRNA levels. Ad5IkappaB infection did not modify proliferation in activated HSCs. TNFalpha induced apoptosis only in Ad5IkappaB-infected activated, but not quiescent HSCs. Apoptosis was initially demonstrated 12 h after exposure to TNFalpha. Twenty-four h after the TNFalpha treatment, 60% of the activated HSCs were apoptotic.

CONCLUSION

NFkappaB activity is not required for proliferation or activation of HSCs; however, NFkappaB protects activated HSCs against TNFalpha-induced apoptosis.

Analysis of ferrochelatase expression during hematopoietic development of embryonic stem cells

Ferrochelatase, the last enzyme in the heme pathway, chelates protoporphyrin IX and iron to form heme and is mutated in protoporphyria. The ferrochelatase gene is expressed in all tissues at low levels to provide heme for essential heme-containing proteins and is up-regulated during erythropoiesis for the synthesis of hemoglobin. The human ferrochelatase promoter contains 2 Sp1 cis-elements and GATA and NF-E2 sites, all of which bind their cognate trans-acting factors in vitro. To investigate the role of these elements during erythropoiesis, we introduced expression of the green fluorescent protein (EGFP) transgenes driven by various ferrochelatase promoter fragments into a single locus in mouse embryonic stem cells. EGFP expression was monitored during hematopoietic differentiation in vitro using flow cytometry. We show that a promoter fragment containing the Sp1 sites, the NF-E2 and GATA elements, was sufficient to confer developmental-specific expression of the EGFP transgene, with an expression profile identical to that of the endogenous gene. In this system the -0.275 kb NF-E2 cis-element is required for erythroid-enhanced expression, the GATA cis-element functions as a stage-specific repressor and enhancer, and elements located between -0.375kb and -1.1kb are necessary for optimal levels of expression. Ferrochelatase mRNA increased before the primitive erythroid-cell stage without a concomitant increase in ferrochelatase protein, suggesting the presence of a translational control mechanism. Because of the sensitivity of this system, we were able to assess the effect of an A-to-G polymorphism identified in the promoters of patients with protoporphyria. There was no effect of the G haplotype on transcriptional activity of the -1.1 kb transgene.

The mitochondrial permeability transition augments Fas-induced apoptosis in mouse hepatocytes

Tumor necrosis factor-alpha receptor 1 and Fas recruit overlapping signaling pathways. To clarify the differences between tumor necrosis factor alpha (TNFalpha) and Fas pathways in hepatocyte apoptosis, primary mouse hepatocytes were treated with TNFalpha or an agonist anti-Fas antibody after infection with an adenovirus expressing an IkappaB superrepressor (Ad5IkappaB). Treatment with TNFalpha induced apoptosis in Ad5IkappaB-infected mouse hepatocytes, as we previously reported for rat hepatocytes. Ad5IkappaB plus anti-Fas antibody or actinomycin D plus anti-Fas antibody rapidly induced apoptosis, whereas anti-Fas antibody alone produced little cytotoxicity. The proteasome inhibitor (MG-132) and a dominant-negative mutant of nuclear factor-kappaB-inducing kinase also promoted TNFalpha- and Fas-mediated apoptosis. Expression of either crmA or a dominant-negative mutant of the Fas-associated death domain protein prevented TNFalpha- and Fas-mediated apoptosis. In addition, the caspase inhibitors, DEVD-cho and IETD-fmk, inhibited TNFalpha- and Fas-mediated apoptosis. In Ad5IkappaB-infected hepatocytes, caspases-3 and -8 were activated within 2 h after treatment with anti-Fas antibody or within 6 h after TNFalpha treatment. Confocal microscopy demonstrated onset of the mitochondrial permeability transition (MPT) and mitochondrial depolarization by 2-3 h after anti-Fas antibody treatment and 8-10 h after TNFalpha treatment, followed by cytochrome c release. The combination of the MPT inhibitors, cyclosporin A, and trifluoperazine, protected Ad5IkappaB-infected hepatocytes from TNFalpha-mediated apoptosis. After anti-Fas antibody, cyclosporin A and trifluoperazine decreased cytochrome c release but did not prevent caspase-3 activation and cell-death. In conclusion, nuclear factor-kappaB activation protects mouse hepatocytes against both TNFalpha- and Fas-mediated apoptosis. TNFalpha and Fas recruit similar but nonidentical, pathways signaling apoptosis. The MPT is obligatory for TNFalpha-induced apoptosis. In Fas-mediated apoptosis, the MPT accelerates the apoptogenic events but is not obligatory for them.

Cellular differentiation causes a selective down-regulation of interleukin (IL)-1beta-mediated NF-kappaB activation and IL-8 gene expression in intestinal epithelial cells

Interleukin (IL)-1beta signals through various adapter proteins and kinases that lead to activation of numerous downstream targets, including the transcription factors including NF-kappaB. In this study, we analyzed and characterized the effect of the differentiation of intestinal epithelial cells on IL-1beta-mediated NF-kappaB activation and IL-8 gene expression. We report that IL-8 mRNA accumulation and protein secretion were down-regulated in IL-1beta- and lipopolysaccharide-stimulated differentiated HT-29 cells (HT-29/MTX, where MTX is methotrexate) compared with undifferentiated cells (HT-29/p), whereas no differential effects were found following tumor necrosis factor (TNF)-alpha or phorbol myristate acetate stimulation. Cross-linking and affinity binding studies reveal that IL-1beta exclusively binds the type I receptor (IL-1RI) and not IL-1RII in both HT-29/p and HT-29/MTX cells. IL-1beta-mediated IkappaB kinase and c-Jun N-terminal kinase (JNK) activity were both diminished in differentiated HT-29 cells. DNA binding activity in differentiated HT-29 cells relative to HT-29/p cells was strongly reduced following IL-1beta exposure but not after TNF-alpha stimulation. The proximal IL-1 signaling molecule IL-1 receptor-associated kinase was not degraded in IL-1beta-stimulated HT-29 cells, in contrast to Caco-2 cells. kappaB-luciferase reporter gene activity was 16-fold higher following TNF receptor-associated factor-6 transfection after IL-1beta stimulation in HT-29/MTX cells. We conclude that cellular differentiation of HT-29 cells selectively impairs the IL-1beta signaling pathway inhibiting both NF-kappaB and JNK activity in response to IL-1beta. This relative unresponsiveness to IL-1beta may represent an important regulatory mechanism of differentiated intestinal epithelial cells.

New aspects of hepatic fibrosis

Hepatic stellate cells are the major source of extracellular matrix proteins in hepatic fibrosis, including Type I collagen. In response to liver injury, the hepatic stellate cells change from a quiescent to an activated phenotype. This activation process includes a phenotypic change to a myofibroblast-like cell, increased proliferation rate, loss of retinoid stores, increased production of extracellular matrix proteins, chemokines, and cytokines, and contractility. Ongoing studies are characterizing the genes that are differentially expressed in the quiescent and activated hepatic stellate cells. We have also investigated the regulation of Type I collagen expression, the cleavage of collagen propeptides, and the formation of collagen cross-links. Understanding these pathways may provide new insights into the molecular pathogenesis of hepatic fibrosis.

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.

Role of Kupffer cells and gut-derived endotoxins in alcoholic liver injury

The hepatotoxic effects of alcohol have been described in detail, but factors responsible for its hepatotoxicity have only partially been characterized. For example, it is known that chronic ethanol ingestion increases hepatotoxicity and produces fatty liver, hepatitis and cirrhosis. However, acute ethanol consumption reduces endotoxin hepatotoxicity. It now appears that Kupffer cells participate in several aspects of these phenomena. Previously, most studies on the effects of alcohol on liver function have focused chiefly on the hepatocyte. Recently, attention has been directed towards the effect of ethanol ingestion on Kupffer cell function, which is stimulated by gut-derived endotoxins (lipopolysaccharides) via mechanisms dependent on increased gut permeability and the possible relationship between Kupffer cells and alcohol-induced liver injury. Here we will review new evidence for the proposal that Kupffer cells and endotoxins play a pivotal role in hepatotoxicity following alcohol exposure, based on studies using the continuous intragastric enteral feeding model developed by Tsukamoto and French and an acute model developed by us.

Gene expression and cytokine and enzyme activation in the liver after a burn injury

The liver plays a critical role in the inflammatory response to injury; however, the mechanisms by which the liver is affected and how it influences the rest of the immune system are not well understood. Partial hepatectomy is a direct injury to the liver, whereas a burn is an indirect injury to liver, but both injuries appear to produce damage to the liver. In this study, we used a mouse model of 25% total body surface area and 40% total body surface area full-thickness burns to investigate the mechanism of liver damage and response to burn injury by measuring levels of c-Jun messenger (m)RNA, NFkappaB nuclear protein, interleukin-6, transaminases, and liver tissue histology over time. c-Jun and NFkappaB are 2 transcription factors that are induced by partial hepatectomy and related to hepatocyte injury and growth. In both groups of mice with burns, expression of c-Jun mRNA and NFkappaB nuclear protein was activated within 30 minutes after the burn injury, followed by increased levels of interleukin-6 and, finally, elevated enzyme levels. Liver injuries were similar in both groups despite the magnitude of the burns. We believe that these gene products are initiated in the hepatocyte injury after a burn and that they precede other inflammatory responses such as cytokine release, plasma transaminase levels, and histologic changes.

c-Jun does not mediate hepatocyte apoptosis following NFkappaB inhibition and partial hepatectomy

Inhibition of the transcription factor nuclear factor kappa B (NFkappaB) induces marked hepatocyte apoptosis and liver dysfunction after partial hepatectomy (PH) in rats. Hepatocyte apoptosis may be due to direct inhibition of NFkappaB-induced hepatocyte survival genes or due to indirect increased signaling through the stress-activated protein kinase pathway (SAPK), resulting in increased c-Jun. c-Jun, an AP-1 transcription factor, induces apoptosis in fibroblasts. Our aim was to determine if hepatocyte apoptosis following inhibition of NFkappaB and partial hepatectomy in rats is due to increased c-Jun. Adult male Sprague-Dawley rats (200 g) were injected intraportally with 6 x 10(9) PFU adenoviral vector containing luciferase (Ad5Luc) or superrepressor IkappaB (Ad5IkappaB) transgene that inhibits NFkappaB translocation into the nucleus. Two-thirds PH was performed 24 h after vector administration, and the remnant liver was harvested 30 min or 24 h after PH. Northern and Western blots were performed to examine the presence of IkappaB and c-Jun. A GST c-Jun kinase assay was used to examine Jun-N-terminal kinase (JNK) activity. AP-1 DNA binding activity was assessed by electrophoretic mobility shift assay. TUNEL assay was performed to assess apoptosis. All rats receiving adenoviral vectors expressed the luciferase or superrepressor IkappaB transgenes. c-Jun mRNA, protein levels, and DNA binding activity were not increased in rats treated with Ad5IkappaB at 30 min after PH compared to rats injected with Ad5Luc. Jun kinase activity increased following partial hepatectomy, but activity was similar in Ad5Luc- and Ad5IkappaB-treated animals. AP-1 DNA binding activity was not altered substantially in rats treated with Ad5IkappaB. The percentage of apoptotic hepatocytes was similar between Ad5Luc- and Ad5IkappaB-injected animals at 0 h, but livers from Ad5IkappaB-treated rats had increased apoptosis at 24 h compared to Ad5Luc rats (24% vs. 4%) after PH. Hepatocyte apoptosis after NFkappaB inhibition and PH is not mediated by increased JNK activity or c-Jun.

The 5' stem-loop regulates expression of collagen alpha1(I) mRNA in mouse fibroblasts cultured in a three-dimensional matrix

The stability of collagen alpha1(I) mRNA is regulated by its 5' stem-loop, which binds a cytoplasmic protein in a cap-dependent manner, and its 3'-untranslated region (UTR), which binds alphaCP. When cultured in a three-dimensional gel composed of type I collagen, mouse fibroblasts had decreased collagen alpha1(I) mRNA steady-state levels, which resulted from a decreased mRNA half-life. In cells cultured in gel, hybrid mouse-human collagen alpha1(I) mRNA with a wild-type 5' stem-loop decayed faster than the same mRNA with a mutated stem-loop. When the 5' stem-loop was placed in a heterologous mRNA, the mRNA accumulated to a lower level in cells grown in gel than in cells grown on plastic. This suggests that the 5' stem-loop down-regulates collagen alpha1(I) mRNA. Protein binding to the 5' stem-loop was reduced in cells grown in gel, which was associated with destabilization of the collagen alpha1(I) mRNA. In addition to the binding of a cytoplasmic protein, there was also a nuclear binding activity directed to the collagen alpha1(I) 5' stem-loop. The nuclear binding was increased in cells grown in gel, suggesting that it may negatively regulate expression of collagen alpha1(I) mRNA. Binding of alphaCP, a protein involved in stabilization of collagen alpha1(I) mRNA, was unchanged by the culture conditions.

Glutamine metabolism stimulates intestinal cell MAPKs by a cAMP-inhibitable, Raf-independent mechanism

BACKGROUND & AIMS

Infectious diarrhea caused by viruses plus enterotoxigenic bacteria is often more severe than diarrhea induced by either pathogen alone. We postulated that the increased cell adenosine 3',5'-cyclic monophosphate (cAMP) concentration observed during infection by enterotoxigenic organisms retards the intestinal repair process by blocking activation of mitogen-activated protein kinases (MAPKs) in proliferating intestinal cells.

METHODS

We evaluated the effects of glutamine on MAPK activity, thymidine incorporation, and cell number in glutamine-starved and -sufficient rat intestinal crypt cells (IEC-6).

RESULTS

In glutamine-starved cells, 10 mmol/L glutamine in the absence of serum stimulated [(3)H]thymidine incorporation 8-fold. This effect was inhibited by 60% with 8-(4-chlorophenylthio) (8-CPT)-cAMP (100 micromol/L) + isobutyl methylxanthine (100 micromol/L). In cells not starved of glutamine, glutamine stimulated thymidine incorporation by 3-fold, and 8-CPT-cAMP completely blocked the mitogenic effect. Inhibition of proliferation by cAMP persisted for at least 68 hours after cAMP removal. In vitro kinase assays showed that glutamine signaling requires an intact ERK (extracellular signal-related kinase) pathway in unstarved cells. In starved cells, at least one other pathway (JNK) was activated by glutamine, and the mitogenic inhibition by 8-CPT-cAMP was incomplete. Other intestinal fuels (glucose and acetate) were not mitogenic.

CONCLUSIONS

Increased levels of intracellular cAMP inhibit ERKs but only partially reduce glutamine-stimulated proliferation in enterocytes adapted to low glutamine.

Impact of burn injury on hepatic TGF-beta1 expression and plasma TGF-beta1 levels

BACKGROUND

The liver plays a critical regulatory role in the acute inflammatory response to injury, although the mechanisms of this regulation are not well understood. transforming growth factor-beta1 (TGF-beta1) is induced after burn injury and may contribute to an inhibitory or fatal effect on hepatocytes. We investigated the association over time between plasma concentration of TGF-beta1, expression of TGF-beta1 m-RNA in liver tissue, and histologic analysis of liver apoptosis after burn injury.

METHODS

Male BALB/c mice were anesthetized and randomized to receive 0% (sham), moderate (approximately 25%) (M), or large (approximately 50%) (L) body surface area full-thickness contact burn, followed by resuscitation and analgesia. Animals were killed over a time course from 15 minutes to 24 hours after burn injury, and liver tissue and peripheral blood were collected. Plasma levels of TGF-beta1 (nanograms per milliliter) were measured by enzyme-linked immunosorbent assay. TGF-beta1 m-RNA was extracted from liver and measured by reverse transcription-polymerase chain reaction. Histology of liver apoptosis was examined after fixation and staining with TdT-mediated dUTP nick-end labeling (TUNEL) method.

RESULTS

The plasma concentration of TGF-beta in burn group L was significantly increased at 4 hours after burn when compared with sham and M burn groups. This rise in plasma TGF-beta1 was preceded by an increase in hepatic TGF-beta1 m-RNA expression at 30 minutes, 1, 2, and 4 hours after burn in the L group. Histologic analysis found greater hepatocyte death in the L group than in the M group at 8 hours after burn.

CONCLUSION

The levels of induced TGF-beta1 and TGF-beta1 m-RNA after L burn injury are higher and peak earlier than after M burn injury. Elevated TGF-beta1 may be associated with cell death in hepatocytes. The TGF-beta1 rise may be associated with hepatocyte injury and systemic response to massive burn.

Corn oil rapidly activates nuclear factor-kappaB in hepatic Kupffer cells by oxidant-dependent mechanisms

N-6 polyunsaturated fatty acids (N-6 PUFAs), major constituents of corn oil and natural ligands for peroxisome proliferator-activated receptors, increase the rate of growth of established tumors. It has been proposed that chemical peroxisome proliferators increase hepatocyte proliferation by mechanisms involving activation of nuclear factor-kappaB (NF-kappaB) and production of low levels of tumor necrosis factor alpha (TNFalpha) by Kupffer cells; however, how N-6 PUFAs are involved in increased cell proliferation in liver is not well understood. Here, the hypothesis that N-6 PUFAs increase production of mitogens by activation of Kupffer cell NF-kappaB was tested. A single dose of corn oil (2 ml/kg, i.g.), but not olive oil or medium-chain triglycerides (saturated fat), caused an approximately 3-fold increase in hepatocyte proliferation. Similarly, when activity of NF-kappaB in whole rat liver or isolated hepatocytes and Kupffer cells was measured at various time intervals for up to 36 h, only corn oil activated NF-kappaB. Corn oil increased NF-kappaB activity approximately 3-fold 1-2 h after treatment exclusively in the Kupffer cell fraction. In contrast, increases were small and only occurred after approximately 8 h in hepatocytes. The activation of NF-kappaB at 2 h and increases in cell proliferation at 24 h due to corn oil were prevented almost completely when rats were pretreated for 4 days with either dietary glycine (5% w/w), an agent that inactivates Kupffer cells, or the NADPH oxidase inhibitor, diphenyleneiodonium (s.c., 1 mg/kg/day). Furthermore, arachidonic acid (100 microM) activated superoxide production approximately 4-fold when added to isolated Kupffer cells in vitro. This phenomenon was not observed with oleic or linoleic acids. Interestingly, a single dose of corn oil increased TNFalpha mRNA nearly 2-fold 8 h after treatment. It is concluded that corn oil rapidly activates NF-kappaB in Kupffer cells via oxidant-dependent mechanisms. This triggers production of low levels of TNFalpha which is mitogenic in liver and promotes growth of hepatocytes.

Interleukin-6 increases rat metalloproteinase-13 gene expression through stimulation of activator protein 1 transcription factor in cultured fibroblasts

The role of IL-6 in collagen production and tissue remodeling is controversial. In Rat-1 fibroblasts, we measured the effect of IL-6 on matrix metalloproteinase-13 (MMP-13), c-jun, junB, and c-fos gene expression, binding of activator protein 1 (AP1) to DNA, amount of AP1 proteins, immunoreactive MMP-13 and TIMP-1 proteins, and Jun N-terminal kinase activity. We show that IL-6 increased MMP-13-mRNA and MMP-13 protein. These effects were exerted by acting on the AP1-binding site of the MMP-13 promoter, as shown by transfecting cells with reporter plasmids containing mutations in this element. Mobility shift assays demonstrated that IL-6 induced the DNA binding activity of AP1. This effect was accompanied by a marked increase in c-Jun, JunB, and c-Fos mRNA, as well as in c-Jun protein and its phosphorylated form. The latter is not due to increased Jun N-terminal kinase activity but to a decreased serine/threonine phosphatase activity. We conclude that IL-6 increases interstitial MMP-13 gene expression at the promoter level. This effect seems to be mediated by the induction of c-jun, junB, and c-fos gene expression, by the binding of AP1 to DNA, by increasing phosphorylated c-Jun, and by the inhibition of serine/threonine phosphatase activity. These effects of IL-6 might contribute to remodeling connective tissue.