Biomedical subjects

Mark A Bird

Publications and source records attributed to Mark A Bird.

7 recordsLinked to original sources

PubMed2004

Cirrhotic hepatocytes exhibit decreased TGFbeta growth inhibition associated with downregulated Smad protein expression.

TGFbeta controls hepatocyte growth through cell cycle arrest and apoptosis, and resistance to TGFbeta is a mechanism of malignant transformation. The aim of this study was to assess differences in TGFbeta-mediated growth inhibition in normal and cirrhotic hepatocytes. Cirrhosis was induced in mice and normal and cirrhotic hepatocytes were isolated by collagenase perfusion and treated with or without TGFbeta (5 ng/ml). DNA synthesis, Smad protein expression, and DNA binding activity were determined. TGFbeta reduced DNA synthesis to a greater degree in normal hepatocytes than in cirrhotic hepatocytes (87% vs. 68%; p<0.05). Smad protein expression was decreased in cirrhotic hepatocytes and Smad 2/3/4 complex formation was suppressed. Furthermore, cirrhotic hepatocytes had decreased DNA binding activity at 120 min following TGFbeta treatment. In conclusion, decreased Smad protein expression may impair TGFbeta-mediated growth inhibition in cirrhotic hepatocytes.

Active Transport, Cell Nucleus↗

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

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↗

PubMed2003

NFkappaB inhibition decreases hepatocyte proliferation but does not alter apoptosis in obstructive jaundice.

INTRODUCTION: Cholestasis activates nuclear factor kappa B (NFkappaB), which is involved in both hepatocyte proliferation and apoptosis, depending on the cellular microenvironment. We hypothesized that NFkappaB inhibition would decrease hepatocyte proliferation and potentiate hepatocyte apoptosis in a rat model of extrahepatic biliary obstruction. AIM: To determine if NFkappaB inhibition concomitantly decreases hepatocyte proliferation and increases apoptosis in obstructive jaundice. MATERIALS AND METHODS: Male Sprague-Dawley rats underwent either sham operation or bile-duct ligation (BDL) combined with portal vein injection of vehicle or 6 x 10(9) particles of an adenovirus carrying either the control luciferase or the IkappaB super-repressor (AdIkappaBSR) transgenes. Liver was harvested 3, 5, and 7 days after sham operation or BDL, and immunohistochemistry for proliferating cell nuclear antigen and terminal dUTP nick end-labeling was performed for detection of DNA synthesis and apoptosis, respectively. RESULTS: Increased serum total bilirubin and hematoxylin and eosin-stained liver sections confirmed cholestasis in BDL animals. Western blot analysis demonstrated IkappaBSR protein expression in AdIkappaBSR-infected animals only. At day 7, NFkappaB inhibition decreased hepatocyte DNA synthesis in BDL rats compared to both adenovirus carrying the control luciferase and vehicle-treated controls. Apoptosis was increased in BDL vehicle-treated animals compared to sham-operation animals, but NFkappaB inhibition did not alter hepatocyte apoptosis in the BDL group. CONCLUSION: In obstructive cholestasis, NFkappaB is required for hepatocyte proliferation, but does not augment apoptosis.

Adenoviridae↗

PubMed2002

Cholestasis induces murine hepatocyte apoptosis and DNA synthesis with preservation of the immediate-early gene response.

BACKGROUND: Major hepatic resection in patients with unrelieved obstructive jaundice carries an increased risk of postoperative liver failure. We hypothesized that cholestasis induces hepatocyte apoptosis and impairs hepatic regeneration by inhibiting up-regulation of the known immediate-early response genes, nuclear factor kappa B (NF-kappaB) and activating protein-1 (AP-1). The aim of this study was to determine whether the immediate-early gene response in hepatic regeneration remains intact in extrahepatic cholestasis. METHODS: Eight-week-old BALB/c mice underwent either sham operation (SO) or common bile duct ligation (BDL). Two-thirds partial hepatectomy (PH) was performed at 4 and 7 days, with remnant liver harvested 0, 15, 30, or 60 minutes after PH. Serum analysis for markers of cholestasis and histopathology was obtained. Proliferating cell nuclear antigen and terminal deoxyuridine triphosphate nick end labeling (TUNEL) immunohistochemistry for detection of DNA synthesis and apoptosis, respectively, was performed 4, 7, or 10 days after SO or BDL. Liver samples from 0, 15, 30, or 60 minutes after PH were analyzed for NF-kappaB and AP-1 DNA binding activity by using electrophoretic mobility shift assays. RESULTS: Increased serum bilirubin level and hematoxylin-eosin-stained liver sections confirmed cholestasis in BDL mice. BDL induced marked DNA synthesis and hepatocyte apoptosis in prehepatectomy liver at both 4 and 7 days. Substantially higher basal levels of both NF-kappaB and AP-1 binding activity were present in BDL compared with SO mice. Fold induction of NF-kappaB and AP-1, however, was similar between BDL and SO mice. Cholestasis induced hepatocyte DNA synthesis and apoptosis. Basal NF-kappaB and AP-1 DNA binding activity was increased in BDL mice, but fold induction of these immediate-early genes did not differ from controls. CONCLUSIONS: Although basal NF-kappaB and AP-1 DNA binding is increased in cholestasis, the immediate-early gene response to PH remains intact in BDL mice.

Animals↗

PubMed2002

Transforming growth factor-beta1 induces hepatocyte apoptosis by a c-Jun independent mechanism.

BACKGROUND: During hepatic regeneration, transforming growth factor (TGF)-beta1 messenger RNA increases after the initial cycle of DNA synthesis, and it may control hepatocyte growth by inducing apoptosis. TGF-beta1 also induces c-Jun, a potential proapoptotic transcription factor. We hypothesized that autocrine expression of activated TGF-beta1 (Ad5aTGF-beta1) would increase c-jun expression in rat liver and limit hepatic regeneration by inducing apoptosis. METHODS: Male rats (175 to 200 g) received portal venous injections with adenoviruses expressing either luciferase (Ad5Luc), as a control, or Ad5aTGF-beta1 at a dose of 6 x 10(9) plaque-forming units. Livers were harvested 24 or 48 hours after injection and nuclear extracts and total RNA isolated. TGF-beta1 expression was confirmed by Northern blot analysis in all TGF-beta1-injected rats. RESULTS: A 2.5-fold increase in c-jun mRNA expression was detected in Ad5aTGF-beta1-infected rats compared with control rats. Transcriptional activity was assessed with an AP-1-responsive-reporter gene that increased 3-fold in rat primary hepatocytes infected with Ad5aTGF-beta1. C-Jun N-terminal kinase activity also increased 6- to 7-fold in Ad5aTGF-beta1-treated rats 24 and 48 hours after injection. Ad5aTGF-beta1-injected rats demonstrated increased AP-1 binding activity compared with Ad5Luc rats. Hepatocytes infected in vitro with Ad5aTGF-beta1 demonstrated increased apoptosis compared with Ad5Luc-infected hepatocytes (47% vs 27%) 36 hours after infection. Dual adenoviral infection with Ad5aTGF-beta1 and a dominant-negative c-Jun (Ad5TAM67) decreased AP-1-induced Ad5Luc activity but not hepatocyte apoptosis (46% with dominant-negative c-Jun and 47% without). CONCLUSIONS: These data demonstrate that TGF-beta1 induces c-Jun, but c-Jun is not proapoptotic in hepatocytes.

Adenoviridae↗

PubMed2002

Primary splenic lymphoma complicated by hematemesis and gastric erosion.

Gastrosplenic fistula resulting from erosion of a primary splenic lymphoma is a rare cause of massive upper gastrointestinal hemorrhage associated with benign peptic ulcer disease, gastric Crohn's disease, gastric adenocarcinoma, and primary gastric and splenic lymphomas. Upper intestinal hemorrhage can be successfully treated with splenic artery embolization, followed by splenectory and gastric resection.

Adult↗