Issue published February 1, 1999 Previous issue | Next issue
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Research Articles
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Abstract
A fatty liver is characterized by the hyperaccumulation of lipids within hepatocytes and is often caused by excessive alcohol intake. Rats fed ethanol-containing diets for 37 days showed remarkable increase in hepatic lipids and lipid droplet accumulation in the hepatocytes, indicating the onset of alcoholic fatty liver. Administration of hepatocyte growth factor (HGF) for the last seven days of ethanol treatment markedly decreased hepatic lipids to a level lower than that seen before HGF treatment. In contrast, serum levels of lipids and lipoproteins increased with HGF administration. Primary cultured hepatocytes prepared from the fatty liver retained lipid droplets during a 48-hour culture. However, when cultured in the presence of HGF, intracellular lipid concentrations decreased and lipid secretion was enhanced. Consistent with these events, HGF stimulated the rate of protein synthesis of apolipoprotein B (apoB) and enhanced subsequent mobilization of lipids into the medium. These results indicate that HGF administration induced recovery from the fatty liver, at least in part, by enhancing apoB synthesis and the subsequent mobilization of lipids from hepatocytes with fatty change. The possibility that HGF can be therapeutic for subjects with an alcohol-related fatty liver warrants further attention.
Authors
Minoru Tahara, Kunio Matsumoto, Toshihiro Nukiwa, Toshikazu Nakamura
×Abstract
Integrins are a large family of transmembrane receptors that, in addition to mediating cell adhesion, modulate cell proliferation. The β1C integrin is an alternatively spliced variant of the β1 subfamily that contains a unique 48–amino acid sequence in its cytoplasmic domain. We have shown previously that in vitro β1C inhibits cell proliferation and that in vivo β1C is expressed in nonproliferative, differentiated epithelium and is selectively downregulated in prostatic adenocarcinoma. Here we show, by immunohistochemistry and immunoblotting analysis, that β1C is coexpressed in human prostate epithelial cells with the cell-cycle inhibitor p27kip1, the loss of which correlates with poor prognosis in prostate cancer. In the 37 specimens analyzed, β1C and p27kip1 are concurrently expressed in 93% of benign and 84%–91% of tumor prostate cells. Forced expression of β1Cin vitro is accompanied by an increase in p27kip1 levels, by inhibition of cyclin A–dependent kinase activity, and by increased association of p27kip1 with cyclin A. β1C inhibitory effect on cell proliferation is completely prevented by p27kip1 antisense, but not mismatch oligonucleotides. β1C expression does not affect either cyclin A or E levels, or cyclin E–associated kinase activity, nor the mitogen-activated protein (MAP) kinase pathway. These findings show a unique mechanism of cell growth inhibition by integrins and point to β1C as an upstream regulator of p27kip1 expression and, therefore, a potential target for tumor suppression in prostate cancer.
Authors
Mara Fornaro, Giovanni Tallini, Duo-Qi Zheng, W. Michael Flanagan, Michela Manzotti, Lucia R. Languino
×Abstract
A diverse family of protein 4.1R isoforms is encoded by a complex gene on human chromosome 1. Although the prototypical 80-kDa 4.1R in mature erythrocytes is a key component of the erythroid membrane skeleton that regulates erythrocyte morphology and mechanical stability, little is known about 4.1R function in nucleated cells. Using gene knockout technology, we have generated mice with complete deficiency of all 4.1R protein isoforms. These 4.1R-null mice were viable, with moderate hemolytic anemia but no gross abnormalities. Erythrocytes from these mice exhibited abnormal morphology, lowered membrane stability, and reduced expression of other skeletal proteins including spectrin and ankyrin, suggesting that loss of 4.1R compromises membrane skeleton assembly in erythroid progenitors. Platelet morphology and function were essentially normal, indicating that 4.1R deficiency may have less impact on other hematopoietic lineages. Nonerythroid 4.1R expression patterns, viewed using histochemical staining for lacZ reporter activity incorporated into the targeted gene, revealed focal expression in specific neurons in the brain and in select cells of other major organs, challenging the view that 4.1R expression is widespread among nonerythroid cells. The 4.1R knockout mice represent a valuable animal model for exploring 4.1R function in nonerythroid cells and for determining pathophysiological sequelae to 4.1R deficiency.
Authors
Zheng-Tao Shi, Veena Afzal, Barry Coller, Dipti Patel, Joel A. Chasis, Marilyn Parra, Gloria Lee, Chris Paszty, Mary Stevens, Loren Walensky, Luanne L. Peters, Narla Mohandas, Edward Rubin, John G. Conboy
×Abstract
Human hepatocellular carcinoma (HCC) is generally a highly vascular tumor, but the mechanisms of neovascularization that permit rapid growth have not been defined. Angiopoietins (Ang) recently have been identified as ligands for vascular endothelial-specific Tie2 receptor tyrosine kinase and may be important growth factors in the generation of new blood vessels. We investigated Ang expression in 23 samples of HCC and paired adjacent uninvolved liver samples to determine if these genes have a potential role in the growth and spread of this disease. The full coding sequence of a variant angiopoietin-2 (Ang2) cDNA was obtained from HCC specimens, and the biologic consequences of overexpression on tumor formation and hemorrhage were determined in an animal model system. Angiopoietin-1 (Ang1) was equally expressed in HCC and adjacent noncarcinomatous liver tissue. Surprisingly, Ang2 was found to be highly expressed only in tumor tissue. In addition, Ang2 was expressed in 10 of 12 hypervascular HCC, but only in 2 of 11 hypovascular HCC. Ectopic expression of Ang2 in nonexpressing HCC cells promotes the rapid development of human hepatomas and produces hemorrhage within tumors in nude mice. These results suggest a role for Ang2 in the neovascularization of HCC. This enhanced gene expression may contribute to the clinical hypervascular phenotype, as well as tumor formation and progression.
Authors
Shinji Tanaka, Masaki Mori, Yoshihiro Sakamoto, Masatoshi Makuuchi, Keizo Sugimachi, Jack R. Wands
×Abstract
Increased Ca2+ influx through activated N-methyl-D-aspartate (NMDA) receptors and voltage-dependent Ca2+ channels (VDCC) is a major determinant of cell injury following brain ischemia. The activity of these channels is modulated by dynamic changes in the actin cytoskeleton, which may occur, in part, through the actions of the actin filament–severing protein gelsolin. We show that gelsolin-null neurons have enhanced cell death and rapid, sustained elevation of Ca2+ levels following glucose/oxygen deprivation, as well as augmented cytosolic Ca2+ levels in nerve terminals following depolarization in vitro. Moreover, major increases in infarct size are seen in gelsolin-null mice after reversible middle cerebral artery occlusion, compared with controls. In addition, treatment with cytochalasin D, a fungal toxin that depolymerizes actin filaments, reduced the infarct size of both gelsolin-null and control mice to the same final volume. Hence, enhancement or mimicry of gelsolin activity may be neuroprotective during stroke.
Authors
Matthias Endres, Klaus Fink, Jinmin Zhu, Nancy E. Stagliano, Vimala Bondada, James W. Geddes, Toshifumi Azuma, Mark P. Mattson, David J. Kwiatkowski, Michael A. Moskowitz
×Abstract
Heterozygous mutations of the receptor CD95 (Fas/Apo-1) are associated with defective lymphocyte apoptosis and a clinical disease characterized by lymphadenopathy, splenomegaly, and systemic autoimmunity. From our cohort of 11 families, we studied eight patients to define the mechanisms responsible for defective CD95-mediated apoptosis. Mutations in and around the death domain of CD95 had a dominant–negative effect that was explained by interference with the recruitment of the signal adapter protein, FADD, to the death domain. The intracellular domain (ICD) mutations were associated with a highly penetrant Canale-Smith syndrome (CSS) phenotype and an autosomal dominant inheritance pattern. In contrast, mutations affecting the CD95 extracellular domain (ECD) resulted in failure of extracellular expression of the mutant protein or impaired binding to CD95 ligand. They did not have a dominant–negative effect. In each of the families with an ECD mutation, only a single individual was affected. These observations were consistent with differing mechanisms of action and modes of inheritance of ICD and ECD mutations, suggesting that individuals with an ECD mutation may require additional defect(s) for expression of CSS.
Authors
Akshay K. Vaishnaw, Jason R. Orlinick, Jia-Li Chu, Peter H. Krammer, Moses V. Chao, Keith B. Elkon
×Abstract
We have quantitatively determined gluconeogenesis (GNG) from all precursors, using a novel method employing 2H20 to address the question of whether changes in plasma free fatty acids (FFA) affect GNG in healthy, nonobese subjects. In the first study (n = 6), plasma FFA were lowered at 16 to 20 hours with nicotinic acid (NA) and were then allowed to rise at 20 to 24 hours (FFA rebound after administration of NA). FFA decreased from 387 μM at 16 hours to 43 μM at 20 hours, and then rebounded to 1,823 μM at 24 hours. GNG decreased from 58.1% at 16 hours to 38.6% of endogenous glucose production at 20 hours (P < 0.005) and then rebounded to 78.9% at 24 hours (P < 0.05). Conversely, glycogenolysis (GL) increased from 41.9% at 16 hours to 61.4% at 20 hours (P < 0.05), and then decreased to 21.1% at 24 hours (P < 0.05). In the second study (controls; n = 6), volunteers were analyzed between 16 and 24 hours after the last meal. FFA rose from 423 to 681 μM (P < 0.05), and GNG from 50.3% to 61.7% (P < 0.02), whereas GL decreased from 49.7% to 38.3% (P < 0.05). Endogenous glucose production decreased at the same rate in both studies, from 10.7 to 8.6 μmol/kg/min (P < 0.05). In study 3 (n = 6), in which the NA-mediated decrease of plasma FFA was prevented by infusion of lipid and heparin, neither FFA nor GNG changed significantly. In summary, our data suggest that (a) acute changes in plasma FFA produce acute changes in GNG and reciprocal changes in GL; (b) the decrease in EGP between 16 and 24 hours of fasting is due to a fall in GL; and (c) NA has no direct effect on GNG.
Authors
Xinhua Chen, Nayyar Iqbal, Guenther Boden
×Abstract
Transcription of the mouse parathyroid hormone (PTH)/PTH-related peptide (PTHrP) receptor (PTHR) gene is controlled by promoters P1 and P2. We performed transcript-specific in situ hybridization and found that P2 is the predominant promoter controlling PTHR gene expression in bone and cartilage. Treatment with 1α,25-dihydroxyvitamin D3 (D3) in vivo specifically downregulated P2-specific transcripts in osteoblasts, but not in chondrocytes, under conditions where it enhanced bone resorption. Treatment of the osteoblastic cell line MC3T3-E1 with D3 in vitro reduced expression of both P2-specific transcripts and PTHR protein. This effect was not blocked by cycloheximide, indicating that D3 inhibits PTHR expression by downregulating transcription of the P2 promoter. A similar inhibitory effect of D3 was not observed in the chondrocytic cell line CFK2. Gene-transfer experiments showed that P2, but not P1, is active in both MC3T3-E1 and CFK2 cells, and that D3 specifically inhibited P2 promoter activity in MC3T3-E1, but not in CFK2 cells. Inhibition of P2 activity by D3 required promoter sequences lying more that 1.6 kb upstream of the P2 transcription start site. Thus, the P2 promoter controls PTHR gene expression in both osteoblasts and chondrocytes. D3 downregulates PTHR gene transcription in a cell-specific manner by inhibiting P2 promoter activity in osteoblasts, but not in chondrocytes.
Authors
Norio Amizuka, Mei Yee Kwan, David Goltzman, Hidehiro Ozawa, John H. White
×Abstract
Food intake and body weight are determined by a complex interaction of regulatory pathways. To elucidate the contribution of the endogenous peptide cholecystokinin, mice lacking functional cholecystokinin-A receptors were generated by targeted gene disruption. To explore the role of the cholecystokinin-A receptor in mediating satiety, food intake of cholecystokinin-A receptor–/– mice was compared with the corresponding intakes of wild-type animals and mice lacking the other known cholecystokinin receptor subtype, cholecystokinin-B/gastrin. Intraperitoneal administration of cholecystokinin failed to decrease food intake in mice lacking cholecystokinin-A receptors. In contrast, cholecystokinin diminished food intake by up to 90% in wild-type and cholecystokinin-B/gastrin receptor–/– mice. Together, these findings indicate that cholecystokinin-induced inhibition of food intake is mediated by the cholecystokinin-A receptor. To explore the long-term consequences of either cholecystokinin-A or cholecystokinin-B/gastrin receptor absence, body weight as a function of age was compared between freely fed wild-type and mutant animals. Both cholecystokinin-A and cholecystokinin-B/gastrin receptor–/– mice maintained normal body weight well into adult life. In addition, each of the two receptor–/– strains had normal pancreatic morphology and were normoglycemic. Our results suggest that although cholecystokinin plays a role in the short-term inhibition of food intake, this pathway is not essential for the long-term maintenance of body weight.
Authors
Alan S. Kopin, Wendy Foulds Mathes, Edward W. McBride, Minh Nguyen, Wisam Al-Haider, Frank Schmitz, Susan Bonner-Weir, Robin Kanarek, Martin Beinborn
×Abstract
Since thiols can undergo nitrosation and the cell membrane is rich in thiol-containing proteins, we considered the possibility that membrane surface thiols may regulate cellular entry of NO. Recently, protein disulfide isomerase (PDI), a protein that catalyzes thio–disulfide exchange reactions, has been found on the cell-surface membrane. We hypothesized that cell-surface PDI reacts with NO, catalyzes S-nitrosation reactions, and facilitates NO transfer from the extracellular to intracellular compartment. We observed that PDI catalyzes the S-nitrosothiol–dependent oxidation of the heme group of myoglobin (15-fold increase in the rate of oxidation compared with control), and that NO reduces the activity of PDI by 73.1 ± 21.8% (P < 0.005). To assess the role of PDI in the cellular action of NO, we inhibited human erythroleukemia (HEL) cell-surface PDI expression using an antisense phosphorothioate oligodeoxynucleotide directed against PDI mRNA. This oligodeoxynucleotide decreased cell-surface PDI content by 74.1 ± 9.3% and PDI folding activity by 46.6 ± 3.5% compared with untreated or “scrambled” phosphorothioate oligodeoxynucleotide–treated cells (P < 0.0001). This decrease in cell-surface PDI was associated with a significant decrease in cyclic guanosine monophosphate (cGMP) generation after S-nitrosothiol exposure (65.4 ± 26.7% reduction compared with control; P < 0.05), with no effect on cyclic adenosine monophosphate (cAMP) generation after prostaglandin E1 exposure. These data demonstrate that the cellular entry of NO involves a transnitrosation mechanism catalyzed by cell-surface PDI. These observations suggest a unique mechanism by which extracellular NO gains access to the intracellular environment.
Authors
Adrian Zai, M. Audrey Rudd, Anne Ward Scribner, Joseph Loscalzo
×Abstract
Estrogen is an important vasoprotective molecule that causes the rapid dilation of blood vessels by activating endothelial nitric oxide synthase (eNOS) through an unknown mechanism. In studies of intact ovine endothelial cells, 17β-estradiol (E2) caused acute (five-minute) activation of eNOS that was unaffected by actinomycin D but was fully inhibited by concomitant acute treatment with specific estrogen receptor (ER) antagonists. Overexpression of the known transcription factor ERα led to marked enhancement of the acute response to E2, and this was blocked by ER antagonists, was specific to E2, and required the ERα hormone-binding domain. In addition, the acute response of eNOS to E2 was reconstituted in COS-7 cells cotransfected with wild-type ERα and eNOS, but not by transfection with eNOS alone. Furthermore, the inhibition of tyrosine kinases or mitogen-activated protein (MAP) kinase kinase prevented the activation of eNOS by E2, and E2 caused rapid ER-dependent activation of MAP kinase. These findings demonstrate that the short-term effects of estrogen central to cardiovascular physiology are mediated by ERα functioning in a novel, nongenomic manner to activate eNOS via MAP kinase–dependent mechanisms.
Authors
Zhong Chen, Ivan S. Yuhanna, Zoya Galcheva-Gargova, Richard H. Karas, Michael E. Mendelsohn, Philip W. Shaul
×Abstract
Human granulocytic ehrlichiosis (HGE) is an emerging tickborne illness caused by an intracellular bacterium that infects neutrophils. Cells susceptible to HGE express sialylated Lewis x (CD15s), a ligand for cell selectins. We demonstrate that adhesion of HGE to both HL60 cells and normal bone marrow cells directly correlates with their CD15s expression. HGE infection of HL60 cells, bone marrow progenitors, granulocytes, and monocytes was blocked by monoclonal antibodies against CD15s. However, these antibodies did not inhibit HGE binding, and anti-CD15s was capable of inhibiting the growth of HGE after its entry into the target cell. In contrast, neuraminidase treatment of HL60 cells prevented both HGE binding and infection. A cloned cell line (HL60-A2), derived from HL60 cells and resistant to HGE, was deficient in the expression of α-(1,3)fucosyltransferase (Fuc-TVII), an enzyme known to be required for CD15s biosynthesis. Less than 1% of HL60-A2 cells expressed CD15s, and only these rare CD15s-expressing cells bound HGE and became infected. After transfection with Fuc-TVII, cells regained CD15s expression, as well as their ability to bind HGE and become infected. Thus, CD15s expression is highly correlated with susceptibility to HGE, and it, and/or a closely related sialylated and α-(1,3) fucosylated molecule, plays a key role in HGE infection, an observation that may help explain the organism's tropism for leukocytes.
Authors
Jesse L. Goodman, Curtis M. Nelson, Marina B. Klein, Stanley F. Hayes, Brent W. Weston
×Abstract
We investigated the possible involvement of the autonomic nervous system in the effect of a long-term elevation of plasma free fatty acid (FFA) concentration on glucose-induced insulin secretion (GIIS) in rats. Rats were infused with an emulsion of triglycerides (Intralipid) for 48 hours (IL rats). This resulted in a twofold increase in plasma FFA concentration. At the end of infusion, GIIS as reflected in the insulinogenic index (ΔI/ΔG) was 2.5-fold greater in IL rats compared with control saline-infused rats. The ratio of sympathetic to parasympathetic nervous activities was sharply decreased in IL rats relative to controls. GIIS was studied in the presence of increasing amounts of α- and β-adrenoreceptor agonists and antagonists. The lowest concentrations of the α2A-adrenoreceptor agonist oxymetazoline, which were ineffective in control rats, reduced GIIS in IL rats. At the dose of 0.3 pmol/kg, GIIS became similar in IL and control rats. The use of β-adrenoreceptor agonist (isoproterenol) or antagonist (propranolol) did not result in a significant alteration in GIIS in both groups. GIIS remained as high in IL vagotomized rats as in intact IL rats, indicating that changes in parasympathetic tone were of minor importance. Altogether, the data show that lipid infusion provokes β-cell hyperresponsiveness in vivo, at least in part through changes in α2-adrenergic innervation.
Authors
Christophe Magnan, Stephan Collins, Marie-France Berthault, Nadim Kassis, Mylène Vincent, Marc Gilbert, Luc Pénicaud, Alain Ktorza, Françoise Assimacopoulos-Jeannet
×Abstract
Evidence for increased oxidant stress has been reported in human atherosclerosis. However, no information is available about the importance of in situ oxidant stress in relation to plaque stability. This information is relevant because the morbidity and mortality of atherosclerosis are essentially the consequences of acute ischemic syndromes due to unstable plaques. We studied 30 carotid atherosclerotic plaques retrieved by endarterectomy from 18 asymptomatic (stable plaques) and 12 symptomatic patients (unstable plaques). Four normal arteries served as controls. After lipid extraction and ester hydrolysis, quantitation of different indices of oxidant stress were analyzed, including hydroxyeicosatetraenoic acids (HETEs), epoxyeicosatetraenoic acids (EETs), ketoeicosatetraenoic acids (oxo-ETEs), and F2-isoprostanes using online reverse-phase high-performance liquid chromatography tandem mass spectrometry (LC/MS/MS). All measurements were carried out in a strictly double-blind procedure. We found elevated levels of the different compounds in atherosclerotic plaques. Levels of HETEs were 24 times higher than EETs, oxo-ETEs, or F2-isoprostanes. Levels of HETEs, but not those of EETs, oxo-ETEs or F2-isoprostanes, were significantly elevated in plaques retrieved from symptomatic patients compared with those retrieved from asymptomatic patients (1,738 ± 274 vs. 1,002 ± 107 pmol/μmol lipid phosphorous, respectively; P < 0.01). One monooxygenated arachidonate species, 9-HETE, which cannot be derived from known enzymatic reactions, was the most abundant and significant compound observed in plaques, suggesting that nonenzymatic lipid peroxidation predominates in advanced atherosclerosis and may promote plaque instability.
Authors
Ziad Mallat, Tatsuji Nakamura, Jeanny Ohan, Guy Lesèche, Alain Tedgui, Jacques Maclouf, Robert C. Murphy
×Abstract
In the absence of exogenous glucocorticoids, decreasing media pH (from 7.4 to 6.8) for 24 hours increased the Na+/H+ exchanger 3 (NHE3) activity in opossum kidney (OKP) cells. 10–7 M and 10–8 M hydrocortisone increased NHE3 activity, and in their presence, acid incubation further increased NHE3 activity. Hydrocortisone (10–9 M) had no effect on NHE3 activity, but in its presence, the effect of acid incubation on NHE3 activity increased twofold. Aldosterone (10–8 M) had no effect. In the absence of hydrocortisone, acid incubation increased NHE3 protein abundance by 47%; in the presence of 10–9 M hydrocortisone, acid incubation increased NHE3 protein abundance by 132%. The increase in NHE3 protein abundance was dependent on protein synthesis. However, 10–9 M hydrocortisone did not modify the effect of acid incubation to cause a twofold increase in NHE3 mRNA abundance. In the absence of protein synthesis, 10–9 M hydrocortisone did potentiate an effect of acid on NHE3 activity, which was due to trafficking of NHE3 to the apical membrane. These results suggest that glucocorticoids and acid interact synergistically at the level of NHE3 translation and trafficking.
Authors
Patrice M. Ambühl, Xiaojing Yang, Yan Peng, Patricia A. Preisig, Orson W. Moe, Robert J. Alpern
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ISSN: 0021-9738 (print), 1558-8238 (online)