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Biomedical subjects

David A Brenner

Publications and source records attributed to David A Brenner.

At least 55 records · Page 3Linked to original sources
PubMed2004

Differential requirement for c-Jun NH2-terminal kinase in TNFalpha- and Fas-mediated apoptosis in hepatocytes.

The c-Jun NH2-terminal kinase (JNK) is involved in the regulation of cell death, but its role in tumor necrosis factor (TNF)-alpha- and Fas-mediated apoptosis in primary cells is not well defined. In primary rat hepatocytes expressing an IkappaB superrepressor, the JNK inhibitor SP600125 strongly decreased TNF-alpha-induced cell death, caspase 3 activation, and DNA laddering. In contrast, SP600125 did not rescue mouse hepatocytes from Fas-induced apoptosis. Apoptosis in mouse hepatocytes, induced by human TNF-alpha, was blocked by SP600125, indicating that TNF-receptor (TNF-R) 1-mediated JNK activation is important for TNF-alpha-induced death. However, mouse TNF-alpha was more efficient than human TNF-alpha in activating JNK and killing mouse hepatocytes, suggesting that TNF-R1 and TNF-R2 cooperate in JNK activation and apoptosis. SP600125 rescued actinomycin D-pretreated hepatocytes and hepatocytes expressing a dominant negative c-Jun from TNF-alpha, indicating that JNK exerts its proapoptotic effect independently of transcription and c-Jun. SP600125 delayed the mitochondrial permeability transition, inhibited cytochrome c release and prevented bid degradation after TNF-alpha, suggesting that JNK-regulated proapoptotic factors act upstream of the mitochondria. Moreover, overexpression of JNK1 activated a mitochondrial death pathway in hepatocytes, albeit less efficiently than TNF-alpha. This study demonstrates that JNK augments TNF-alpha-induced apoptosis in hepatocytes through a signaling pathway that is distinct from the pathway by which it regulates proliferation.

Animals↗
PubMed2004

Antifibrotic effects of a tissue inhibitor of metalloproteinase-1 antibody on established liver fibrosis in rats.

Liver fibrosis is characterized by increased synthesis, and decreased degradation, of extracellular matrix (ECM) within the injured tissue. Decreased ECM degradation results, in part, from increased expression of tissue inhibitor of metalloproteinase-1 (TIMP-1), which blocks matrix metalloproteinase (MMP) activity. TIMP-1 is also involved in promoting survival of activated hepatic stellate cells (HSCs), a major source of ECM. This study examined the effects of blocking TIMP-1 activity in a clinically relevant model of established liver fibrosis. Rats were treated with carbon tetrachloride (CCl(4)), or olive oil control, for 6 weeks; 24 days into the treatment, the rats were administered a neutralizing anti-TIMP-1 antibody derived from a fully human combinatorial antibody library (HuCAL), PBS, or an isotype control antibody. Livers from CCl(4)-treated rats exhibited substantial damage, including bridging fibrosis, inflammation, and extensive expression of smooth muscle alpha-actin (alpha-SMA). Compared to controls, rats administered anti-TIMP-1 showed a reduction in collagen accumulation by histological examination and hydroxyproline content. Administration of anti-TIMP-1 resulted in a marked decrease in alpha-SMA staining. Zymography analysis showed antibody treatment decreased the activity of MMP-2. In conclusion, administration of a TIMP-1 antibody attenuated CCl(4)-induced liver fibrosis and decreased HSC activation and MMP-2 activity.

Actins↗
PubMed2004

A dual reporter gene transgenic mouse demonstrates heterogeneity in hepatic fibrogenic cell populations.

Activation of hepatic stellate cells (HSCs) and other resident mesenchymal cells into myofibroblasts expressing alpha smooth muscle actin (alphaSMA) and collagen I is a key event in liver fibrogenesis. However, the temporal expression profiles of alphaSMA and collagen I genes in these cells is unknown. To address this question, we studied alphaSMA and collagen alpha1(I) transcriptional patterns in primary cultures of HSCs, and additionally, in an in vivo model of secondary biliary fibrosis using transgenic mice that express the Discomsoma sp. red fluorescent protein (RFP) and the enhanced green fluorescent protein (EGFP) reporter genes under direction of the mouse alphaSMA and collagen alpha1(I) promoter/enhancers, respectively. The alphaSMA-RFP mice were crossed with collagen-EGFP mice to generate double transgenic mice. Reporter gene expression in cultured HSCs demonstrated that both transgenes were induced at day 3 with continued expression through day 14. Interestingly, alphaSMA and collagen alpha1(I) transgenes were not coexpressed in all cells. Flow cytometry analysis showed three different patterns of gene expression: alphaSMA-RFP positive cells, collagen-EGFP positive cells, and cells expressing both transgenes. AlphaSMA-only and alphaSMA/collagen expressing cells showed higher expression levels of synaptophysin, reelin, MMP13, TIMP1, and ICAM-1 compared to collagen-only expressing cells, as assessed by real-time PCR. Following bile duct ligation, alphaSMA and collagen alpha1(I) transgenes were differentially expressed by peribiliary, parenchymal and vascular fibrogenic cells. Peribiliary cells preferentially expressed collagen alpha1(I), while parenchymal myofibroblasts expressed both alphaSMA and collagen alpha1(I). In conclusion, these data demonstrate heterogeneity of gene expression in myofibroblastic cells during active fibrogenesis. These reporter mice provide a useful tool to further characterize fibrogenic cell types and to evaluate antifibrotic drugs.

Actins↗
PubMed2004

Primary cirrhotic hepatocytes resist TGFbeta-induced apoptosis through a ROS-dependent mechanism.

BACKGROUND/AIMS: The cirrhotic liver manifests dysregulated hepatocyte growth by poor regenerative capacity, formation of regenerative nodules, and malignant transformation to hepatocellular carcinoma. The purpose of this study was to determine if dysregulated hepatocyte growth occurs through deficient apoptosis. METHODS: Hepatocytes were isolated from normal and CCl(4)-treated mice and treated with TGFbeta, TNFalpha, and UV-C, known apoptotic agents. RESULTS: Cirrhotic hepatocytes were less sensitive to TGFbeta- (45+/-5 vs. 15+/-3%; P<0.003), TNFalpha- (59+/-21 vs. 21+/-8%; P=0.02), and UV-C-induced (31+/-4 vs. 17+/-4%; P<0.03) apoptosis compared to normal hepatocytes. In normal hepatocytes, TGFbeta-induced apoptosis occurred through a ROS-, MPT-, and caspase-dependent pathway. Cirrhotic hepatocytes lacked caspase activation, had decreased procaspase-8 expression, failed to undergo the MPT, and had increased basal ROS activity compared to normal hepatocytes. After treatment with trolox, an antioxidant that reduced basal ROS activity, cirrhotic hepatocytes underwent apoptosis in response to TGFbeta treatment. CONCLUSIONS: These findings suggest that increased ROS activity in cirrhotic hepatocytes plays a critical role in mediating cirrhotic hepatocyte resistance to apoptosis. Cirrhotic hepatocyte resistance to TGFbeta-induced apoptosis is ROS-dependent and is a mechanism of dysregulated growth in the chronically inflamed liver.

Animals↗
PubMed2004

Akt activation protects rat liver from ischemia/reperfusion injury.

BACKGROUND: Apoptosis as well as necrosis may play an important role in hepatic ischemia/reperfusion (I/R) injury. Akt, a serine-threonine protein kinase, is known to promote cell survival. We investigated whether gene transfer of constitutively active or dominant negative Akt could affect hepatic I/R injury. MATERIALS AND METHODS: Hepatic I/R injury was induced in rats by Pringle's maneuver for 20 min followed by reperfusion. Adenoviruses encoding a constitutively active form of Akt (myrAkt), a dominant negative form of Akt (dnAkt), or beta-galactosidase (LacZ) were injected through the tail vein 72 h before hepatic I/R. RESULTS: Terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick-end labeling (TUNEL) staining demonstrated a significant increase in the positive cells 240 min after reperfusion. Immunoblotting with phospho-Akt antibody showed phosphorylation of Akt from 90 to 180 min after reperfusion. The expression of myrAkt reduced the number of TUNEL-positive cells and hepatic necrosis around the central veins in the liver after reperfusion. This expression also significantly inhibited the increase in serum alanine aminotransferase (297 +/- 131 IU/L, P < 0.05) 120 min after I/R, compared with increases in uninfected (1761 +/- 671 IU/L), LacZ adenovirus (1528 +/- 671 IU/L)-, and dnAkt adenovirus (1342 +/- 485 IU/L)-infected rats. MyrAkt expression phosphorylated Bad and inhibited the release of cytochrome-c after reperfusion. No difference in nuclear translocation of nuclear factor (NF)-kappaB, p65 was seen among the three groups of rats, however. CONCLUSION: Adenoviral gene transfer of myrAkt could inhibit apoptotic cell death and subsequent hepatic I/R injury in the rat, through Bad, not NF-kappaB.

Adenoviridae↗
PubMed2004

TNF alpha-induced hepatocyte apoptosis is associated with alterations of the cell cycle and decreased stem loop binding protein.

BACKGROUND: Inhibition of nuclear factor kappa B (NF kappa B) during liver regeneration induces hepatocyte apoptosis associated with normal DNA synthesis but decreased mitosis, suggesting that inhibition of NF kappa B impairs progression from S-phase through the G(2)/M phase of the cell cycle. Our aim was to determine if inhibition of NF kappa B alters cell cycle characteristics in hepatocytes treated with tumor necrosis factor alpha (TNF alpha). METHODS: Primary hepatocytes from BALB/c mice were infected with adenoviruses expressing luciferase (control; AdLuc) or the I kappa B super-repressor (AdI kappa B) and treated with or without TNF alpha (30 ng/ml). Flow cytometry was performed (0 to 40 hours) to determine apoptosis and cell cycle progression. Reverse transcriptase-polymerase chain reaction and immunoblots assessed changes in cell cycle mediators and antiapoptotic factors. RESULTS: Primary hepatocytes treated with AdI kappa B and TNF alpha demonstrated significantly more S-phase cells (14% +/- 3% vs 6% +/- 2%, P<.05) at 14 hours compared with controls. Inhibition of NF kappa B with or without TNFalpha was associated with decreased expression of stem loop bind protein, a marker of cell cycle progression through S-phase. The NF kappa B-induced antiapoptotic proteins, iNOS and TRAF2, had decreased message at 9 and 12 hours, respectively, in TNF alpha- and AdI kappa B-treated cells. CONCLUSION: Inhibition of NF kappa B in TNF alpha-treated primary mouse hepatocytes is associated with increased S-phase cell cycle retention and decreased stem loop bind protein.

Animals↗
PubMed2004

Gastrointestinal basic science 2002-2003: the year in review.

The Board of Editors of Gastroenterology identified 6 topics in basic gastroenterology research in which exciting advancements have been made during the past year. These topics are (1) NOD2 variants in Crohn's disease, (2) Heliobacter pylori and CagA and VacA pathogenesis, (3) beta-catenin function in normal colonic epithelia and colon cancer, (4) DNA methylation in colonic cancer, (5) the HCV replicon, and (6) the use of small interfering RNA in somatic cell genetics. Basic research in gastroenterology has been characterized during the past year by the rapid translation from fundamental research into pathophysiological systems. New technological advances are being applied to difficult areas of gastrointestinal research. Well-defined patient populations are critical to extend the knowledge derived from the human genome to gastrointestinal diseases.

Animals↗
PubMed2004

Hepatitis C virus core and nonstructural proteins induce fibrogenic effects in hepatic stellate cells.

BACKGROUND & AIMS: The mechanisms by which hepatitis C virus (HCV) induces liver fibrosis are unknown. Hepatocytes secrete HCV proteins, which may interact with hepatic stellate cells (HSCs). Our aims were to investigate whether HCV proteins induce fibrogenic effects on HSCs. METHODS & RESULTS: Human-activated HSCs expressed messenger RNA (mRNA) for the putative HCV receptors CD81, LDL receptor, and C1q receptor as assessed by RT-PCR. Incubation of activated but not quiescent human HSCs with recombinant core and NS3 protein increased intracellular calcium concentration and reactive oxygen species production, as well as stimulated intracellular signaling pathways. Adenoviruses encoding core and nonstructural proteins (NS3-NS5) were used to express HCV proteins in HSCs. Expression of core protein increased cell proliferation in a Ras/ERK and PI3K/AKT dependent manner. In contrast, NS3-NS5 protein expression preferentially induced proinflammatory actions, such as increased chemokine secretion and expression of intercellular cell adhesion molecule type 1 (ICAM-1) through the NF-kappa B and c-Jun N-terminal kinase pathways. These effects were attenuated by antioxidants. Infection of freshly isolated rat HSCs with adenovirus-encoding core protein resulted in accelerated cell activation, as assessed by alpha-smooth muscle actin expression. Moreover, adenovirus-encoding core and NS3-NS5 proteins increased the secretion of bioactive TGF beta 1 and the expression of procollagen alpha1(I) in early cultured rat HSCs, as assessed by ELISA and RNase protection assay, respectively. CONCLUSIONS: HCV core and nonstructural proteins regulate distinct biologic functions in HSCs. A direct interaction between HCV proteins and HSCs may contribute to HCV-induced liver fibrosis.

Animals↗
PubMed2004

TRAM2 protein interacts with endoplasmic reticulum Ca2+ pump Serca2b and is necessary for collagen type I synthesis.

Cotranslational insertion of type I collagen chains into the lumen of the endoplasmic reticulum (ER) and their subsequent folding into a heterotrimeric helix is a complex process which requires coordinated action of the translation machinery, components of translocons, molecular chaperones, and modifying enzymes. Here we describe a role for the protein TRAM2 in collagen type I expression in hepatic stellate cells (HSCs) and fibroblasts. Activated HSCs are collagen-producing cells in the fibrotic liver. Quiescent HSCs produce trace amounts of type I collagen, while upon activation collagen synthesis increases 50- to 70-fold. Likewise, expression of TRAM2 dramatically increases in activated HSCs. TRAM2 shares 53% amino acid identity with the protein TRAM, which is a component of the translocon. However, TRAM2 has a C terminus with only a 15% identity. The C-terminal part of TRAM2 interacts with the Ca(2+) pump of the ER, SERCA2b, as demonstrated in a Saccharomyces cerevisiae two-hybrid screen and by immunoprecipitations in human cells. TRAM2 also coprecipitates with anticollagen antibody, suggesting that these two proteins interact. Deletion of the C-terminal part of TRAM2 inhibits type I collagen synthesis during activation of HSCs. The pharmacological inhibitor of SERCA2b, thapsigargin, has a similar effect. Depletion of ER Ca(2+) with thapsigargin results in inhibition of triple helical collagen folding and increased intracellular degradation. We propose that TRAM2, as a part of the translocon, is required for the biosynthesis of type I collagen by coupling the activity of SERCA2b with the activity of the translocon. This coupling may increase the local Ca(2+) concentration at the site of collagen synthesis, and a high Ca(2+) concentration may be necessary for the function of molecular chaperones involved in collagen folding.

Amino Acid Sequence↗
PubMed2003

Effects of three superoxide dismutase genes delivered with an adenovirus on graft function after transplantation of fatty livers in the rat.

BACKGROUND: Oxygen-derived free radicals play a central role in ischemia/reperfusion injury after organ transplantation and are degraded by endogenous radical scavengers such as superoxide dismutase (SOD). Overexpression of SOD by delivery of the cytosolic SOD gene with an adenovirus (Ad.SOD1) decreases organ injury and increases survival in a rat model of liver transplantation. However, it is unclear which of the three isoforms of SOD provides the most protective effect. The purpose of this study was to identify the isoform with the highest effectiveness against ischemia/reperfusion injury after transplantation of fatty livers, which are particularly susceptible. METHODS: Donor rats were given ethanol by gavage before harvest to induce steatotic livers. Some of the donors were infected with adenoviruses expressing either the gene lacZ encoding bacterial beta-galactosidase (Ad.lacZ), Ad.SOD1, Ad.SOD2 (mitochondrial isoform), or Ad.SOD3 (extracellular isoform). After transplantation, SOD activity in liver, survival, histopathology, transaminases, and activation of nuclear factor (NF)-kappaB, IkappaB kinase, Jun-N-terminal kinase (JNK), and tumor necrosis factor (TNF)-alpha were evaluated. RESULTS: Ad.SOD1 treatment increased survival, blunted transaminase release, and reduced necrosis, whereas Ad.SOD3 had no protective effect. Ad.SOD2 was not as protective as Ad.SOD1. Ad.SOD1 reduced the activation of NF-kappaB, blunted JNK activity, and reduced TNF-alpha activity. Ad.SOD2 treatment resulted in lower kinase, TNF-alpha, and NF-kappaB activities but was not as effective as Ad.SOD1. IkappaB kinase activity was not affected. CONCLUSION: This study demonstrates that cytosolic SOD represents the most effective isoform of SOD to protect transplanted livers from failure; this may be related to lowered NF-kappaB and JNK activities because of reduced oxygen-derived radical production.

Adenoviridae↗
PubMed2003

Human hepatic stellate cells express CCR5 and RANTES to induce proliferation and migration.

Activated hepatic stellate cells (HSCs) are the main producers of extracellular matrix in the fibrotic liver and are involved in the regulation of hepatic inflammation. The aim of this study was to characterize the role of regulated on activation, normal T-cell expressed, and presumably secreted (RANTES) in activated HSCs. RANTES mRNA and protein secretion were strongly induced after stimulating HSCs with TNF-alpha, IL-1beta, or CD40L. RANTES production was NF-kappaB dependent, because inhibitor-kappaB (IkappaB) superrepressor and dominant-negative IkappaB kinase-2 almost completely blocked RANTES expression. NF-kappaB activation was sufficient to drive RANTES expression as demonstrated by the strong induction of RANTES in HSCs expressing NF-kappaB-inducing kinase. The JNK/activator protein-1 pathway also contributed to RANTES expression as demonstrated by the blocking effects of the JNK inhibitor SP600125. HSCs responded to stimulation with recombinant human (rh)RANTES with an increase in intracellular calcium concentration and a rapid increase in free radical formation. Furthermore, rhRANTES induced ERK phosphorylation, ERK-dependent [3H]thymidine incorporation, and HSC proliferation. Additionally, rhRANTES induced focal adhesion kinase phosphorylation and a substantial increase in HSC migration. HSCs functionally expressed chemokine receptor-5 (CCR5), as shown by flow-cytometric analysis and RT-PCR, and the inhibitory effects of a blocking CCR5 antibody on rhRANTES-induced ERK activation, proliferation, and migration. Diphenylene iodonium and N-acetylcysteine inhibited rhRANTES-induced ERK activation and HSC proliferation, indicating that NADPH oxidase-dependent production of reactive oxygen species was required. In conclusion, RANTES and CCR5 represent potential mediators of 1) HSC migration and proliferation and 2) a cross-talk between HSCs and leukocytes during fibrogenesis.

Calcium↗
PubMed2003

Prolonged infusion of angiotensin II into normal rats induces stellate cell activation and proinflammatory events in liver.

Recent evidence indicates that angiotensin II (ANG II) plays an important role in liver fibrogenesis. However, the underlying mechanisms are largely unknown. In advanced chronic liver diseases, circulating levels of ANG II are frequently elevated. We investigated the hepatic effects of prolonged systemic infusion of ANG II in normal rats. Saline or ANG II at subpressor and pressor doses (15 and 50 ng.kg-1.min-1, respectively) were infused to normal rats for 4 wk through a subcutaneous osmotic pump. Infusion of ANG II resulted in liver injury, as assessed by elevated serum liver enzymes. Livers from ANG II-perfused rats showed activation of JNK and ERK as well as increased NF-kappaB and activating protein-1 DNA-binding activity. Moreover, ANG II perfusion induced oxidative stress, increased concentration of proinflammatory cytokines, and upregulated the inflammatory proteins inducible nitric oxide synthase and cyclooxygenase-2. Histological examination of the livers from ANG II-infused rats showed mild portal inflammation as well as thickening and thrombosis of small hepatic vessels. ANG II-treated livers showed accumulation of CD43-positive inflammatory cells and activated hepatic stellate cells (HSCs) at the pericentral areas. A slight increase in collagen synthesis was observed, as assessed by Sirius red staining and hepatic hydroxyproline. All of these effects were observed when ANG II was perfused at subpressor and pressor doses. ANG II also accelerated the activation of primary cultured rat HSCs. In conclusion, increased systemic ANG II can induce liver injury by promoting proinflammatory events and vascular damage. ANG II-induced hepatic effects are not dependent on increase in arterial pressure.

Angiotensin II↗
PubMed2003

Salicylate enhances necrosis and apoptosis mediated by the mitochondrial permeability transition.

Onset of the mitochondrial permeability transition (MPT) causes both necrotic and apoptotic cell death in cultured hepatocytes. Salicylate lowers the threshold for onset of the MPT. In this study, our aim was to determine whether nontoxic concentrations of salicylate potentiate MPT-mediated cell killing. In necrotic killing models to rat hepatocytes, salicylate (1 mM) enhanced calcium ionophore (Br-A23187)- and tert-butylhydroperoxide (t-BuOOH)-induced cell death, which was blocked or delayed by cyclosporin A (CsA, 2 microM), a specific inhibitor of the MPT. In hepatocyte apoptosis induced by tumor necrosis factor-alpha (TNF-alpha), salicylate accelerated cell killing after low-dose TNF-alpha (1 ng/ml), which by itself induced little apoptosis. Salicylate enhancement of apoptosis was associated with onset of the MPT and accelerated caspase 3 activation. Salicylate also augmented killing of MCF-7 human breast tumor cells by etoposide and PLC/PRF/5 human hepatoma cells by tumor necrosis factor-related apoptosis-inducing ligand (TRAIL). In conclusion, salicylate potentiates both necrotic and apoptotic cell killing by promoting onset of the MPT. Enhancement by salicylate of MPT-dependent apoptosis may play a role in protection by aspirin and other nonsteroidal anti-inflammatory drugs against colon, lung, and breast cancer.

Animals↗
PubMed2003

Expression of the NF-kappa B target gene X-ray-inducible immediate early response factor-1 short enhances TNF-alpha-induced hepatocyte apoptosis by inhibiting Akt activation.

Using a cDNA microarray analysis, we identified x-ray-inducible immediate early response factor-1 (IEX-1) as a proapoptotic gene which was induced by TNF-alpha and also depend on NF-kappaB activation in Hc human hepatocytes. In these cells only the original form of IEX-1, termed IEX-1S, but not its longer transcript IEX-1L, was expressed. Overexpression of IEX-1S resulted in promotion of TNF-alpha-induced apoptosis in Hc cells expressing a mutant form of IkappaB. This proapoptotic action can be explained by its inhibitory findings on survival signals; inhibition of TNF-alpha-induced activation and expression of phosphatidylinositol 3-kinase (PI3K)/Akt, and also blockage of expression of Mcl-1, an antiapoptotic Bcl-2 family member which is located downstream of Akt, was inhibited by IEX-1S. LY 294002, an inhibitor of PI3K, increased IEX-1S expression induced by TNF-alpha and accelerated TNF-alpha-induced apoptosis in IkappaB-treated Hc cells. Overexpression of the dominant-negative Akt enhanced, but the constitutively active Akt suppressed, TNF-alpha-induced IEX-1S expression, suggesting that PI3K/Akt negatively regulated IEX-1S expression. These results demonstrate that NF-kappaB-dependent recruitment of IEX-1S may play a proapoptotic role in TNF-alpha-stimulated hepatocytes through blockage of the PI3K/Akt pathway. Moreover, the reciprocal cross-talk between IEX-1S and PI3K/Akt may closely be involved in the regulation of TNF-alpha-induced hepatocyte apoptosis.

Adjuvants, Immunologic↗
PubMed2003

Liver fibrosis: signals leading to the amplification of the fibrogenic hepatic stellate cell.

Liver fibrosis represents a major medical problem with significant morbidity and mortality. Worldwide hepatitis viral infections represent the major cause liver fibrosis; however, within the United States chronic ethanol consumption is the leading cause of hepatic fibrosis. Other known stimuli for liver fibrosis include helminthic infection, iron or copper overload and biliary obstruction. Fibrosis can be classified as a wound healing response to a variety of chronic stimuli that is characterized by an excessive deposition of extracellular matrix proteins of which type I collagen predominates. This excess deposition of extracellular matrix proteins disrupts the normal architecture of the liver resulting in pathophysiological damage to the organ. If left untreated fibrosis can progress to liver cirrhosis ultimately leading to organ failure and death if left untreated. This review will discuss the molecular events leading to liver fibrosis. The discussion will include collagen gene regulation and proliferative signals that contribute to the amplification of the hepatic stellate cell, the primary fibrogenic cell type that resides in the liver.

Animals↗
PubMed2003

Increased expression of collagenase in the liver induces hepatocyte proliferation with cytoplasmic accumulation of beta-catenin in the rat.

BACKGROUND/AIMS: Since the hepatic extracellular matrix is remodeled in liver regeneration, we investigated whether increased collagenase activity in the liver can induce hepatocyte proliferation in vivo. METHODS: To increase hepatic collagenase activity, human matrix metalloproteinase-1 was delivered to the rat liver by the recombinant adenoviral vector Ad5MMP-1. RESULTS: Hepatic delivery of Ad5MMP-1 increased the 5-bromo-2-deoxyuridine labeling index and mitotic index in hepatocytes, causing an increase in the dry liver weight; control adenovirus, Ad5LacZ, had minimal effect. Hepatocyte proliferation started approximately 48 h after infection with Ad5MMP-1 and ended after about 2 weeks. The increase in the dry liver weight also returned to baseline after 2 weeks. Transient liver injury by Ad5MMP-1, reflected by increased aspartate and alanine aminotransferase levels, peaked around 1 week, and was associated with hepatocyte apoptosis. Collagenase-induced hepatocyte proliferation was accompanied by cytoplasmic accumulation of beta-catenin and a transient decrease in E-cadherin expression. CONCLUSIONS: Modification of the hepatic extracellular matrix by collagenase induces transient hepatocyte proliferation in vivo, suggesting that the condition of the hepatic extracellular matrix per se plays a pivotal role in regulating hepatocyte proliferation.

Adenoviridae↗