Neutrophil CD18-dependent arrest on intercellular adhesion molecule 1 (ICAM-1) in shear flow can be activated through L-selectin

Neutrophil emigration through endothelial cells under shear flow involves several adhesion processes including cell rolling, arrest, and transmigration. Rolling is mediated by selectins, while arrest and transmigration both require activated CD18 integrins. One mode of CD18 activation is via selectins expressed on neutrophils and endothelial cells. We have recently reported that cross-linking of L-selectin (CD62L) resulted in the rapid activation of CD18-dependent adhesion. In the current study, we examine whether binding of E-selectin (CD62E) and L-selectin can activate neutrophil CD18-dependent adhesion under shear flow. Human ICAM-1 (CD54) and E-selectin were co-transfected into L cells. Neutrophil capture, rolling, and arrest on these monolayers were quantitated in a parallel plate flow chamber at a wall shear stress of 2.0 dyne/cm2. Under these conditions, E-selectin supported cell capture and rolling on the monolayer, but did not trigger CD18-mediated cell arrest within 200 microm of rolling. However, when neutrophils were treated with anti-L-selectin mAb and cross-linked with a secondary mAb, approximately 50% of the cells arrested within 54 microm. Cell arrest was also observed in response to IL-8 stimulation. A subthreshold level of IL-8 in combination with L-selectin cross-linking potentiated the level of cell arrest due to either stimulus alone. The transition to cell arrest involved both LFA-1 (CD11a/CD18) and Mac-1 (CD11b/CD18). Blocking either subunit alone failed to reduce arrest, while blocking both molecules with mAbs reduced the number to baseline levels. These data support the conclusion that L-selectin, but not E-selectin, can signal the transition from neutrophil rolling to cell arrest under shear flow.

Developing an international nursing partnership with Nicaragua

With health conditions in the "least developed countries persisting at levels that are so limiting and destructive of human potential ... as to be unacceptable to the global community", WHO has put out a call for mandates to address these problems with "new approaches ... new partnerships." One answer to this call has come from the US' Duquesne University School of Nursing, which has founded an education and service partnership with Nicaragua that can serve as a "grass roots" model others can follow.

Functions of domain 1 and 4 of vascular cell adhesion molecule-1 in alpha4 integrin-dependent adhesion under static and flow conditions are differentially regulated

To assess the potential contributions of endothelial vascular cell adhesion molecule-1 (VCAM-1) to leukocyte adhesion under conditions of flow, we evaluated the effects of cytokine stimulation of HUVEC on primary capture, rolling, and stable adhesion of mono- and lymphoblastoid cells in a parallel-plate flow chamber. Stimulation of HUVEC with IL-1beta or IL-4 for 24 h induced surface expression of VCAM-1, consistent with published results. Using blocking mAbs to inhibit specific adhesion molecules, we found that a significant level of primary capture at wall shear stresses between 0.5 and 2.0 dynes/cm2 could be attributed to alpha4 integrin and VCAM-1. This primary adhesion under flow was most often characterized by abrupt stationary adhesion with little evidence of rolling. Studies with IL-1beta-stimulated HUVEC revealed that domain 1 of VCAM-1 was solely responsible for alpha4 integrin-dependent primary capture under flow, but both domains 1 and 4 were utilized in alpha4 integrin-dependent adhesion under static conditions. In contrast to results obtained with these cytokines alone, stimulation of HUVEC with a combination of IL-1beta and IL-4 markedly reduced alpha4/VCAM-1-dependent adhesion under flow, even though the surface levels of VCAM-1 were greater than with either cytokine alone, and alpha4/VCAM-1-dependent adhesion under static conditions was intact. These results demonstrate that distinct functional differences exist between the interactions of VCAM-1 and alpha4 integrin under static and flow conditions, and they reveal the potential for endothelial modulation of adhesion under flow without altering VCAM-1-dependent adhesion under static conditions.

Functions of domain 1 and 4 of vascular cell adhesion molecule-1 in alpha4 integrin-dependent adhesion under static and flow conditions are differentially regulated

To assess the potential contributions of endothelial vascular cell adhesion molecule-1 (VCAM-1) to leukocyte adhesion under conditions of flow, we evaluated the effects of cytokine stimulation of HUVEC on primary capture, rolling, and stable adhesion of mono- and lymphoblastoid cells in a parallel-plate flow chamber. Stimulation of HUVEC with IL-1beta or IL-4 for 24 h induced surface expression of VCAM-1, consistent with published results. Using blocking mAbs to inhibit specific adhesion molecules, we found that a significant level of primary capture at wall shear stresses between 0.5 and 2.0 dynes/cm2 could be attributed to alpha4 integrin and VCAM-1. This primary adhesion under flow was most often characterized by abrupt stationary adhesion with little evidence of rolling. Studies with IL-1beta-stimulated HUVEC revealed that domain 1 of VCAM-1 was solely responsible for alpha4 integrin-dependent primary capture under flow, but both domains 1 and 4 were utilized in alpha4 integrin-dependent adhesion under static conditions. In contrast to results obtained with these cytokines alone, stimulation of HUVEC with a combination of IL-1beta and IL-4 markedly reduced alpha4/VCAM-1-dependent adhesion under flow, even though the surface levels of VCAM-1 were greater than with either cytokine alone, and alpha4/VCAM-1-dependent adhesion under static conditions was intact. These results demonstrate that distinct functional differences exist between the interactions of VCAM-1 and alpha4 integrin under static and flow conditions, and they reveal the potential for endothelial modulation of adhesion under flow without altering VCAM-1-dependent adhesion under static conditions.

Molecular dynamics of the transition from L-selectin- to beta 2-integrin-dependent neutrophil adhesion under defined hydrodynamic shear

Homotypic adhesion o2 neutrophils stimulated with chemoattractant is analogous to capture on vascular endothelium in that both processes depend on L-selectin and beta 2-integrin adhesion receptors. Under hydrodynamic shear, cell adhesion requires that receptors bind sufficient ligand over the duration of intercellular contact to withstand hydrodynamic stresses. Using cone-plate viscometry to apply a uniform linear shear field to suspensions of neutrophils, we conducted a detailed examination of the effect of shear rate and shear stress on the kinetics of cell aggregation. A collisional analysis based on Smoluchowski's flocculation theory was employed to fit the kinetics of aggregation with an adhesion efficiency. Adhesion efficiency increased with shear rate from approximately 20% at 100 s-1 to approximately 80% at 400 s-1. The increase in adhesion efficiency. Adhesion efficiency increased with shear rate from approximately 20% at 100 s-1 to approximately 80% at 400 s-1. The increase in adhesion efficiency with shear was dependent on L-selectin, and peak efficiency was maintained over a relatively narrow range of shear rates (400-800 s-1) and shear stresses (4-7 dyn/cm2). When L-selectin was blocked with antibody, beta 2-integrin (CD11a, b) supported adhesion at low shear rates (< 400 s-1). The binding kinetics of selectin and integrin appear to be optimized to function within discrete ranges of shear rate and stress, providing an intrinsic mechanism for the transition from neutrophil tethering to stable adhesion.

Smooth muscle alternative splicing induced in fibroblasts by heterologous expression of a regulatory gene

Alternative splicing is a common mechanism for regulating gene expression in different cell types. In order to understand this important process, the trans-acting factors that enforce the choice of particular splicing pathways in different environments must be identified. We have used the rat alpha-tropomyosin gene as a model system of tissue-specific alternative splicing. Exon 3 of alpha-tropomyosin is specifically inhibited in smooth muscle cells allowing the alternative inclusion of exon 2. We have used a novel gene transfer and selection strategy to detect a gene whose expression in fibroblasts is sufficient to switch them to smooth muscle-specific splicing of alpha-tropomyosin and also alpha-actinin. Extracts from the regulating fibroblasts contain an apparently novel 55 kDa protein which binds to RNA elements required for regulation of tropomyosin splicing. This protein is not detected in extracts of non-regulating cells and is therefore a strong candidate cell-specific splicing regulator. These experiments advance our understanding of smooth muscle splicing regulation as well as establishing a means for direct cloning of tissue-specific splicing regulators which have so far been refractory to biochemical analysis.

Sequestration of neutrophils in the hepatic vasculature during endotoxemia is independent of beta 2 integrins and intercellular adhesion molecule-1

Antibodies against cellular adhesion molecules protect against neutrophil-induced hepatic injury during ischemia-reperfusion and endotoxemia. To test if beta 2 integrins on neutrophils and intercellular adhesion molecule-1 (ICAM-1) on endothelial cells are involved in neutrophil sequestration in the hepatic vasculature, neutrophil accumulation in the liver was characterized during the early phase of endotoxemia. Intravenous injection of Salmonella enteritidis endotoxin induced a dose-dependent activation of complement, tumor necrosis factor-alpha (TNF-alpha) formation, and an increase of hepatic neutrophils with maximal numbers at 5 mg/kg (90 min: 339 +/- 14 cells/50 high power fields; controls: 18 +/- 2). Administration of 15 micrograms/kg TNF-alpha and intravascular complement activation with cobra venom factor (75 micrograms/kg) had additive effects on hepatic neutrophil accumulation compared with each mediator alone. Monoclonal antibodies (2 mg/kg) to ICAM-1 and the alpha-chain (CD11a, CD11b) or the beta-chain (CD18) of beta 2 integrins had no significant effect on hepatic neutrophil count after endotoxin. In contrast, these antibodies inhibited peritoneal neutrophil infiltration in response to glycogen administration by 28% (CD11b), 60% (CD11a, ICAM-1), and 92% (CD18). Our data suggest that TNF-alpha and complement factors contribute to hepatic neutrophil sequestration during the early phase of endotoxemia. Despite the fact that these inflammatory mediators can up-regulate integrins and ICAM-1, these adhesion molecules are not necessary for neutrophil accumulation in hepatic sinusoids. The protective effect of these antibodies against neutrophil-induced liver injury appears to be due to inhibition of transendothelial migration and adherence to parenchymal cells.

Closed reduction and type-II external fixation of comminuted fractures of the radius and tibia in dogs: 23 cases (1990-1994)

OBJECTIVE

To describe a technique for closed reduction of and application of a type-II external fixator to comminuted fractures of the radius and tibia in dogs and to evaluate outcome of the technique in a series of client-owned dogs.

DESIGN

Retrospective case series.

ANIMALS

23 dogs that underwent closed reduction of severely comminuted (> or = 5 fragments); mid-diaphyseal radial (n = 9); and tibial (n = 14) fractures and stabilization with a type-II external fixator.

PROCEDURE

Radiographs were made postoperatively and every 4 to 6 weeks until the fixator was removed. The effect of type of fracture (open vs closed), type of pins (threaded vs smooth), and number of fixation pins on surgery time, time between surgery and development of bridging callus, and time between surgery and removal of the fixator was evaluated using one-sided Student's t-tests.

RESULTS

21 fractures healed after a single surgery. Two dogs with radial fractures required a second procedure because of complications. All fractures healed with the original fixation device in place. Mean time between surgery and the development of bridging callus was 11.4 weeks (range, 4 to 22 weeks), and mean time between surgery and fixator removal was 14.7 weeks (range, 4 to 27 weeks). Type of fracture, type of pins, and number of fixation pins did not have a significant effect on surgery time, time to development of bridging callus, or time to fixator removal.

CLINICAL IMPLICATIONS

Closed reduction and application of a type-II external fixator was an effective method of treating severely comminuted radial and tibial fractures.

Preservation of spatial organization and antigenicity of leukocyte surface molecules by aldehyde fixation: flow cytometry and high-resolution FESEM studies of CD62L, CD11b, and Thy-1

We used transmission and scanning electron microscopy in conjunction with immunogold labeling to study cell surface molecules for evidence of distribution-function relationships. Ascription of functional significance to surface distribution therefore requires preservation of cell morphology and maintenance of molecular expression and distribution through the multiple steps of cell preparation. These requirements prompted us to compare two methods for preparing leukocytes for analysis of surface molecule distribution: one method involved using low temperature to "stabilize" cell morphology and surface molecular organization through immunolabeling; the other involved fixation of the cells with dilute glutaraldehyde before their isolation and labeling. Binding of primary antibodies to several surface molecules, measured by flow cytometry, was comparable for cells prepared by the two methods. Cell morphology and molecular distributions, assessed by high-resolution field emission SEM, were likewise comparable. These results support the conclusion that cell morphologies and CAM distributions previously reported were not affected by exposure of the cells to low temperature through isolation and immunolabeling. Our additional observation that Thy-1 is expressed on both non-projecting and projecting membrane domains of mouse lymph node lymphocytes and rat thymocytes represents a third and new pattern of surface molecule distribution.

Leukocyte activation with platelet adhesion after coronary angioplasty: a mechanism for recurrent disease?

OBJECTIVES

The purpose of this pilot study was to determine whether leukocyte activation occurs, whether leukocyte-platelet complexes develop and whether there is any association between these findings and clinical outcome after coronary angioplasty.

BACKGROUND

Increased expression of CD11b on monocytes and neutrophils promotes their adhesion to endothelial cells, extracellular matrix and smooth muscle cells. Thrombin-activated platelets adhere to monocytes and neutrophils through P-selectin. These cell complexes may affect the inflammatory process and, thus, the outcome of coronary angioplasty.

METHODS

During elective single-vessel coronary angioplasty in 11 men, samples were obtained for flow cytometric detection of CD11b, as well as the percent of leukocytes with adherent platelets and the intensity of bound platelet fluorescence (number of platelets/leukocyte).

RESULTS

After angioplasty, there was an increase in CD11b (monocytes: p = 0.001, neutrophils: p = 0.02) and leukocytes with adherent platelets (p = 0.02). During follow-up, five patients remained in stable condition and six had subsequent clinical events: restenosis and progression of disease requiring coronary artery bypass grafting (n = 3), myocardial infarction involving the dilated artery (n = 1) and unstable angina (n = 2). Values for leukocyte CD11b expression, the percent of leukocytes with adherent platelets and the intensity of bound platelet fluorescence were higher both before and after angioplasty in the six patients experiencing clinical events.

CONCLUSIONS

Despite standard aspirin and heparin therapy, leukocyte activation with platelet adherence occurs after coronary angioplasty. The magnitude of leukocyte activation and platelet adherence appears to be higher in patients experiencing late clinical events.

CD18 antibody treatment limits early myocardial reperfusion injury after initial leukocyte deposition

Following myocardial ischemia, initial reperfusion with whole blood impairs the recovery of ventricular function. The exact mechanisms underlying early myocardial reperfusion injury are not clear, but leukocytes play an important role. In this study, we tested if treating the initial blood reperfusate with a monoclonal antibody (CL26) against the leukocyte adhesion protein (CD18 would reduce the leukocyte contribution to early reperfusion injury. We reasoned that blocking CD18 would reduce the initial retention of leukocytes in the heart and thereby limit the inflammatory response. Rat hearts were isolated and perfused at constant flow with a red cell-rich solution (K2RBC). The perfusate was not recirculated. Baseline measures were made of coronary flow, perfusion pressure, and ventricular pump function. No-flow, normothermic ischemia was induced for 30 min, followed immediately by reperfusion, at the preischemic flowrate, with diluted whole blood (DWB, treated with either vehicle or CL26). Reperfusion was continued with K2RBC for 40 min more, during which postischemic measures were made. We found that the cardiac retention of leukocytes was not significantly different for the two groups, nor were the recoveries of ventricular function. Later in reperfusion (R35), the coronary blood flowrate and the coronary vascular resistances were not different; however, the recoveries of ventricular pump function were significantly different (+dP/dt @ R35 (%Pre-I): Vehicle: 27 +/- 9% (n = 8); CL26: 51 +/- 6% (n = 7); P < 0.05). Also, at R35, the voltage required to capture and pace the vehicle-treated hearts was significantly greater than the voltage required to pace the CL26 hearts (P < 0.05). Because the coronary flowrate and leukocyte retention were similar for both groups, the improved recovery observed in the CL26-treated group was not due to either improved flow or to reduced leukocyte retention. Rather, the findings suggest that the beneficial effect of antibody treatment was to attenuate step(s) in the acute inflammatory response that occurred after the initial deposition of leukocytes in the heart.

Host defenses against disseminated candidiasis are impaired in intercellular adhesion molecule 1-deficient mice

Genetically engineered mice, which lack normal expression of intercellular adhesion molecule 1 (ICAM-1), were used to study the role of ICAM-1 in the host defense against disseminated candidiasis. The responses of ICAM-1-deficient mice and normal wild type mice were compared following an intravenous challenge with Candida albicans. ICAM-1-deficient mice lost more weight (P < .001) and had a significantly higher mortality (P < .001). Quantitative cultures revealed a greater tissue fungal burden in ICAM-1-deficient mice compared with normal mice, in both the kidney (P < .001) and the brain (P = .007). Extensive inflammation, composed primarily of histiocytes admixed with lymphocytes and occasional neutrophils, was present in the renal tissue of ICAM-1-deficient mice; this contrasted with a more localized and predominantly neutrophilic infiltrate in normal mice. This work suggests that the loss of ICAM-1 significantly impairs host defense against C. albicans, by impairing either neutrophil migration or phagocyte activation or both.

Mechanisms of inflammatory liver injury: adhesion molecules and cytotoxicity of neutrophils

During recent years, increasing experimental evidence has suggested that hepatic nonparenchymal cells, in particular Kupffer cells and neutrophils, can contribute significantly to the pathogenesis of liver injury in various chemical toxicities. Neutrophils are central to the mechanism of injury after hepatic ischemia reperfusion and endotoxemia. In this symposium summary, an overview of critical aspects of neutrophil-dependent liver injury is presented. A general introduction to the involvement of adhesion molecules in neutrophil rolling and transendothelial migration is provided. Mediators and mechanisms of neutrophil sequestration in the liver vasculature, extravasation, and adherence-dependent cytotoxicity are discussed using the examples of endotoxin-induced hepatic failure and ischemia-reperfusion injury. These processes involve a complex network of inflammatory mediators including cytokines, chemokines, and lipid-derived compounds. The role of neutrophil-derived cytotoxic mediators, e.g., reactive oxygen and proteases, in the molecular mechanisms of parenchymal cell injury is discussed. Furthermore, interactions between neutrophils and contractile, perisinusoidal, stellate cells that influence microvascular blood flow in the liver are discussed. Results of these and other investigations are leading to increased understanding of the complex interactions between neutrophils and tissues that result in injury.

Neutrophil adhesion to 24-hour IL-1-stimulated endothelial cells under flow conditions

In this study, we examine neutrophil adhesion under flow conditions to cultured HUVEC stimulated for 4 or 24 h with IL-1. Interactions are measured using videomicroscopy and a parallel-plate flow system which is capable of distinguishing primary adhesion and rolling from secondary (firm) adhesion. We find that after 24 h, E-selectin does not contribute to primary adhesion, in contrast to a significant contribution after 4 h. Endothelial cell P-selectin does not contribute at either time point. Blocking or removing L-selectin from the neutrophil surface decreases adhesion 50 to 70% at either time point, and neuraminidase treatment of neutrophils decreases adhesion by 85%. These results suggest that after a 24-h stimulation, primary adhesion depends on a distinct selectin-like interaction in which a HUVEC receptor binds carbohydrates on neutrophil glycoproteins, including L-selectin. We also find that secondary adhesion in this system can be inhibited 90% with Ab blockade of CD18/ICAM-1 interactions after a 24-h stimulation, and that a combination of IL-1 and IL-4 selectively down-regulates the pathway for primary adhesion at 24 h. These results demonstrate that neutrophils adhere using different receptor pathways following 4- and 24-h stimulations, and provide experimental data characterizing some properties of the receptors involved. One of the pathways that is evident at 24 h appears to be a novel selectin-like interaction.

A scintillation proximity assay for UDP-GalNAc:polypeptide, N-acetylgalactosaminyltransferase

A rapid and simple method for quantitating the reaction product of UDP-GalNAc:polypeptide, N-acetylgalactosaminyltransferase (GalNAc-transferase) by scintillation proximity assay (SPA) was developed. The assay quantitates the radioactivity incorporated from 3H-labeled UDP-GalNAc into a biotin-labeled acceptor peptide, as measured after adsorption of the acceptor peptide to avidin-coated SPA beads. The acceptor peptide, PPASTSAPG (Elhammer et al. (1993) J. Biol. Chem. 268, 10029-10038) was conjugated to biotin using a di-beta-alanine spacer arm. The conjugated peptide reacted readily with the enzyme and it had an apparent Km comparable to that of the parent peptide. Using a reaction mixture consisting of 4 mg of SPA beads, 17 microM acceptor, 0.5 microM nucleotide sugar, and 7.5 U/ml enzyme, the time dependence of product formation obeyed Michaelis-Menten-type kinetics throughout the full course of the reaction-until exhaustion of the donor substrate-and the beginning portion of the reaction was sufficiently linear for calculating accurate initial rates. Analysis of the time dependency yielded an apparent Km of 0.38 +/- 0.12 microM for UDP-GalNAc. The assay is conveniently carried out in 96-well microtiter plates; it is ideally suited for assaying large numbers of samples and for screening large collections of chemicals for competitive inhibitors.

Neutrophil adhesion to 24-hour IL-1-stimulated endothelial cells under flow conditions

In this study, we examine neutrophil adhesion under flow conditions to cultured HUVEC stimulated for 4 or 24 h with IL-1. Interactions are measured using videomicroscopy and a parallel-plate flow system which is capable of distinguishing primary adhesion and rolling from secondary (firm) adhesion. We find that after 24 h, E-selectin does not contribute to primary adhesion, in contrast to a significant contribution after 4 h. Endothelial cell P-selectin does not contribute at either time point. Blocking or removing L-selectin from the neutrophil surface decreases adhesion 50 to 70% at either time point, and neuraminidase treatment of neutrophils decreases adhesion by 85%. These results suggest that after a 24-h stimulation, primary adhesion depends on a distinct selectin-like interaction in which a HUVEC receptor binds carbohydrates on neutrophil glycoproteins, including L-selectin. We also find that secondary adhesion in this system can be inhibited 90% with Ab blockade of CD18/ICAM-1 interactions after a 24-h stimulation, and that a combination of IL-1 and IL-4 selectively down-regulates the pathway for primary adhesion at 24 h. These results demonstrate that neutrophils adhere using different receptor pathways following 4- and 24-h stimulations, and provide experimental data characterizing some properties of the receptors involved. One of the pathways that is evident at 24 h appears to be a novel selectin-like interaction.

Acute inflammatory reaction after myocardial ischemic injury and reperfusion. Development and use of a neutrophil-specific antibody

Reperfusion of the infarcted canine myocardium after 1 hour of ischemia is associated with an acute inflammatory infiltrate at the border of the infarct. In this paper, we demonstrate that early margination and emigration of neutrophils originate in thin-walled (approximately 5 micrometers) venous cisterns that average 200 micrometers in length and vary from 10 to 70 micrometers in width and show strong constitutive expression of both ICAM-1 and P-selectin; this class of vessels (venous cisterns) appears to be a unique feature in heart. A monoclonal antibody (SG8H6) with specificity for canine neutrophils was developed that allowed much more sensitive immunohistochemical detection of neutrophils in tissue and allowed us to follow tissue infiltration with time. Samples from 1 hour of reperfusion revealed dense margination and substantial emigration of neutrophils associated with the venous cisterns and collecting venules. By 2 hours, there was intense local emigration to the extravascular space between cardiac myocytes. By 3 hours, the infiltrate extended deeper into the infarct, and there was a continuous border zone of neutrophil infiltration that overlapped a region where intact cardiac myocytes strongly expressed ICAM-1 mRNA and extended into the necrotic tissue. At later times, neutrophil migration into infarcted tissue continued to progress. Neutrophil transmigration into reperfused myocardium is more extensive than previously described, and its extravascular distribution during early reperfusion is primarily in the viable border zone of the myocardium where myocyte ICAM-1 mRNA is found. These data are compatible with the hypothesis that extravascular neutrophils may participate in reperfusion injury.

Detection of double-stranded RNA-protein interactions by methylene blue-mediated photo-crosslinking

Double-stranded(ds) RNA-binding proteins have diverse functions in the cell. An obstacle to investigating the interactions between these proteins and dsRNA is the relative inefficiency of traditional UV-crosslinking methods for extended regions of dsRNA. We have therefore developed an alternative procedure for RNA-protein photo-crosslinking that efficiently induces RNA-protein crosslinks in double-stranded regions of RNA. We show that dsRNA-protein crosslinks can be induced by visible light in the presence of the dye methylene blue, which most likely mediates crosslinking by intercalating in the dsRNA helix. A recombinant dsRNA binding domain from the Drosophila staufen protein and human protein kinase R were crosslinked by UV or methylene blue to a series of dsRNAs. In each case, the degree of crosslinking was greater with methylene blue, particularly with RNAs with few single-stranded loops. Methylene blue-mediated crosslinking therefore complements and extends the existing repertoire of crosslinking methods for detecting RNA-protein interactions.

Effects of dexamethasone and anabolic agents on proliferation and protein synthesis and degradation in C2C12 myogenic cells

The objective of this experiment was to determine the dose response of dexamethasone (DEX) on C2C12 myogenic cells and to examine the effects of the anabolic compounds estradiol (E), testosterone (T), and dihydrotestosterone (D) alone and in combination with DEX on proliferation and protein turnover in cultured C2C12 myogenic cells. In the first study, cells were treated with seven concentrations (0, 25, 50, 75, 100, 150, or 200 nM) of DEX in medium with or without 5% horse serum (HS) for the determination of protein synthesis and degradation, and six concentrations (0, 50, 100, 150, 200, or 250 nM) of DEX in medium with 5% fetal bovine serum for cell proliferation measurements. Proliferation of myoblasts decreased (P < .05) with DEX. As DEX concentration increased, protein degradation in myotubes increased (P < .05) up to 100 nM, then declined. Protein synthesis decreased linearly (P < .01) as DEX concentration increased. The presence of HS in the medium decreased (P < .01) protein degradation by 32% as compared with no HS and increased (P < .05) protein synthesis. In the second study, cells were treated with E, T, or D at four concentrations (0, 100, 500, or 1,000 nM) in medium containing 0 or 100 nM DEX. Cells were assayed for protein synthesis or protein degradation. Synthesis decreased (P < .01) and degradation increased (P < .01) with DEX. No differences (P > .05) were found between E, T, or D hormone treatments or concentrations. To measure proliferation, myoblasts were treated 1 d after plating with the same anabolic hormone treatments in medium containing 0 to 100 nM DEX. Cells were grown to confluence and assayed for proliferation. Proliferation decreased (P < .01) in the presence of DEX in each treatment compared with controls. Cells treated with E had significantly lower (P < .05) proliferation rates than cells treated with T and D. The presence of concentrations of DEX at 100 nM inhibited proliferation and protein synthesis and increased protein degradation. Anabolic agents at pharmacological doses do not inhibit the DEX effects on C2C12 myogenic cells, nor do they directly affect proliferation or protein turnover.

Contribution of LFA-1 and Mac-1 to CD18-dependent neutrophil emigration in a neonatal rabbit model

Human neonatal polymorphonuclear leukocytes (PMNs) exhibit decreased mobility, adherence, and transendothelial migration in vitro compared with adult PMNs. These deficits, in part, are due to functional and quantitative defects in neonatal Mac-1 (CD11b/CD18), whereas LFA-1 (CD11a/CD18) function is similar to that found in adults (D.C.Anderson, O.Abbassi, T.K.Kishimoto, J.M.Koenig, L.V.McIntire, and C.W.Smith, J.Immunol. 146: 3372-3379, 1991; C. W. Smith, T. K. Kishimoto, O. Abbassi, B.J.Hughes, R.Rothlein, L.V.McIntire, E.Butcher, and D.C. Anderson, J. Clin. Invest. 87: 609-618, 1991). We tested the hypothesis that the primary mechanism for the neonatal PMN CD18-dependent emigration in vivo is due to LFA-1. Neutrophils from 1-day-old rabbit pups had 32 and 60% of adult rabbit levels of CD11a and CD11b, respectively. Rabbit pups or adult rabbits received the monoclonal antibody (MAb) R7.1 (anti-CD11a) or R15.7 (anti-CD18) or the vehicle phosphate-buffered saline (PBS) before the instillation of intraperitoneal thioglycollate. Six hours later peritoneal exudate was collected. The administration of MAbs R7.1 and R15.7 in adult animals resulted in 60 and 83% inhibition of leukocyte emigration, respectively, compared with PBS-treated animals (P < 0.01). In neonatal animals, R7.1 and R15.7 inhibited leukocyte peritoneal accumulation to the same extent (50 and 60%, respectively) compared with PBS-treated animals (P < 0.01). Adult animals were also treated with the anti-CD11b MAb 198. MAb 198 decreased emigration by 25%, although this was not significant compared with PBS-treated animals. We conclude that although neonatal animals have significantly less neutrophil CD11a, the diminished levels did not contribute to a reduced ability to emigrate to the peritoneum and, like adult animals, neonatal animals primarily utilize LFA-1 for accumulation in this model. The contribution of Mac-1 to neonatal leukocyte emigration remains uncertain.

Chemotactic factors stimulate CD18-dependent canine neutrophil adherence and motility on lung fibroblasts

The mechanisms by which neutrophils migrate through the alveolar interstitium during acute lung inflammation are unknown. We wished to determine whether platelet-activating factor (PAF) and IL-8, two important mediators in neutrophil transendothelial migration, stimulated neutrophil adherence and motility on lung fibroblasts. Canine fibroblasts grown from lung explants were characterized by light and electron microscopy, and flow cytometry. Unstimulated neutrophils adhered poorly (less than 2%) to cultured fibroblasts. However, neutrophils stimulated with PAF (20-200 nM) showed a dose-dependent increase in adherence that was largely (70%) mediated by the beta 2 (CD11/CD18) integrins; adherence was less dependent (50%) on fibroblast intercellular adhesion molecule-1. Conversely, neutrophils stimulated with canine rIL-8 did not increase their adherence to fibroblasts. PAF-stimulated neutrophils were nonmotile on the surface of the fibroblast, but subsequent addition of rIL-8 (10(-8) M) induced motility that was entirely CD1 8 dependent. Fibroblasts stimulated with human rTNF-alpha or Escherichia coli endotoxin (LPS) were a significant source of IL-8 mRNA. In response to rTNF-alpha (50 U/ml), IL-8 mRNA was detected at 2 h by northern blot analysis; it peaked at 6 h and returned to baseline by 24 h. Fibroblasts stimulated with rTNF-alpha secreted IL-8 protein into the culture medium; secreted IL-8 was chemotactic for neutrophils. These data suggest that fibroblasts can function not only as an adhesive substrate, but also as a source of stimulation for neutrophil migration through the inflamed alveolar interstitium.

Chemotactic factors stimulate CD18-dependent canine neutrophil adherence and motility on lung fibroblasts

The mechanisms by which neutrophils migrate through the alveolar interstitium during acute lung inflammation are unknown. We wished to determine whether platelet-activating factor (PAF) and IL-8, two important mediators in neutrophil transendothelial migration, stimulated neutrophil adherence and motility on lung fibroblasts. Canine fibroblasts grown from lung explants were characterized by light and electron microscopy, and flow cytometry. Unstimulated neutrophils adhered poorly (less than 2%) to cultured fibroblasts. However, neutrophils stimulated with PAF (20-200 nM) showed a dose-dependent increase in adherence that was largely (70%) mediated by the beta 2 (CD11/CD18) integrins; adherence was less dependent (50%) on fibroblast intercellular adhesion molecule-1. Conversely, neutrophils stimulated with canine rIL-8 did not increase their adherence to fibroblasts. PAF-stimulated neutrophils were nonmotile on the surface of the fibroblast, but subsequent addition of rIL-8 (10(-8) M) induced motility that was entirely CD1 8 dependent. Fibroblasts stimulated with human rTNF-alpha or Escherichia coli endotoxin (LPS) were a significant source of IL-8 mRNA. In response to rTNF-alpha (50 U/ml), IL-8 mRNA was detected at 2 h by northern blot analysis; it peaked at 6 h and returned to baseline by 24 h. Fibroblasts stimulated with rTNF-alpha secreted IL-8 protein into the culture medium; secreted IL-8 was chemotactic for neutrophils. These data suggest that fibroblasts can function not only as an adhesive substrate, but also as a source of stimulation for neutrophil migration through the inflamed alveolar interstitium.

Diminished soluble and total cellular L-selectin in cord blood is associated with its impaired shedding from activated neutrophils

We have previously shown that surface levels of the adhesive glycoprotein, L-selectin, are diminished on cord blood neutrophils (polymorphonuclear leukocytes, PMN) and associated with impaired adherence to endothelium under flow conditions. To test the hypothesis that diminished surface levels reflect a total cellular deficiency, we measured L-selectin in PMN lysates and plasma from cord and adult blood. L-selectin content was decreased in cord blood PMN lysates compared with those of adults by both Western blot analyses and ELISA (cord blood, 1195 +/- 160 pg/mL; adult, 1870 +/- 260 pg/mL; X +/- SEM; p < 0.05). Soluble L-selectin levels were also decreased in cord blood plasma (324 +/- 24 ng/mL versus 537 +/- 28 ng/mLiter in adult plasma, p < 0.01). To evaluate L-selectin function, we next compared the dose dependent effect of several chemoattractants on shedding of L-selectin from cord blood and adult PMN. Adult PMN showed greater overall shedding of L-selectin as compared with cord blood PMN after stimulation with fMet-Leu-Phe (p < 0.03) and granulocyte-macrophage colony-stimulating factor (p < 0.02). In contrast, shedding of L-selectin was similar between groups after IL-8 tested stimulation. We conclude that cord blood PMN have a decreased cellular content of L-selectin in addition to an impaired ability to shed surface L-selectin in response to specific inflammatory mediators.

Release of soluble intercellular adhesion molecule 1 into bile and serum in murine endotoxin shock

Neutrophil-induced liver injury during endotoxemia is dependent on the adhesion molecules Mac-1 (CD11b/CD18) on neutrophils and its counterreceptor on endothelial cells and hepatocytes, intercellular adhesion molecule 1 (ICAM-1). To investigate a potential release of a soluble form of ICAM-1 (sICAM-1), animals received 100 micrograms/kg Salmonella abortus equi endotoxin alone or in combination with 700 mg/kg galactosamine. In endotoxin-sensitive mice (C3Heb/FeJ), injection of endotoxin did not cause liver injury but induced a time-dependent increase of sICAM-1 in serum (300%) and in bile (615%) without affecting bile flow. In galactosamine/endotoxin-treated animals, which developed liver injury, the increase in both compartments was only 97% and 104%, respectively. In either case, the increase in sICAM-1 concentrations paralleled the enhanced ICAM-1 expression in the liver. The endotoxin-resistant strain (C3H/HeJ) did not show elevated sICAM-1 levels in serum or bile after endotoxin administration. In contrast, the intravenous injection of murine tumor necrosis factor alpha (TNF-alpha), interleukin-1 alpha (IL-1 alpha) or IL-1 beta (13-23 micrograms/kg) into endotoxin-resistant mice induced a 225% to 364% increase in serum sICAM-1 and a 370% elevation of the biliary efflux of sICAM-1, again independent of changes in bile flow. These data indicate that cytokines are major inducers of sICAM-1 formation during endotoxemia in vivo. The described experimental model can be used to investigate the role of sICAM-1 in the pathophysiology of inflammatory liver disease.

Chemoattractant-induced changes in surface expression and redistribution of a functional ligand for P-selectin on neutrophils

Adhesion between platelets and neutrophils is mediated through the interaction of P-selectin on activated platelets with a carbohydrate-containing structure on neutrophils, and occurs under both static and shear conditions. Recent studies using flow chambers have shown that neutrophils become activated after binding to surface-adherent platelets expressing P-selectin. The objective of the present study was to investigate the effect of such activation on the interactions of platelet P-selectin with its ligand on neutrophils. Flow cytometric analyses using P-selectin chimeras revealed that activation induced a rapid and marked reduction in chimera binding, with levels of binding decreased by 71% after 15 minutes of stimulation with the chemotactic agent, FMLP. Using a visual assay of platelet-neutrophil rosetting, we showed that the P-selectin ligand was translocated and clustered at the uropod of neutrophils following the shape changes and polarization induced by chemotactic stimulation. Activated neutrophils bound to surface-adherent platelets also displayed the clustering of P-selectin ligand at the uropod, and these neutrophils detached from the platelets when a shear stress (2 dynes/cm2) was applied through the adhesion chamber. These results indicate that chemotactic stimulation of neutrophils induces changes in the surface expression and distribution of a biologically relevant ligand for P-selectin, and that these changes might influence the adhesive interactions occurring between neutrophils and activated platelets.