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J C Lewis

Publications and source records attributed to J C Lewis.

At least 55 records · Page 3Linked to original sources
PubMed1993

Regulation of fibrinolysis by platelet-released plasminogen activator inhibitor 1: light scattering and ultrastructural examination of lysis of a model platelet-fibrin thrombus.

We have investigated the role of plasminogen activator inhibitor 1 (PAI-1) in the regulation of fibrinolysis using a model thrombus composed of thrombin-stimulated platelets, fibrin(ogen), plasminogen, and recombinant tissue-type plasminogen activator. Laser light scattering kinetic measurements showed that clot lysis was significantly delayed both by thrombin-stimulated platelets and their cell-free releasate. This delay in lysis was almost fully reversed by the addition of a PAI-1-specific monoclonal antibody that blocks the ability of PAI-1 to inhibit plasminogen activators. Lysis half-times exhibited a linear dependence on the concentration of PAI-1 antigen present, as determined by enzyme-linked immunosorbent assay (ELISA). Sodium dodecylsulfate-polyacrylamide gel electrophoresis (SDS-PAGE) followed by immunoblotting confirmed the presence of PAI-1 antigen in the platelet releasates. Scanning electron micrographs of the model thrombus components sampled late in lysis showed considerable unproteolyzed fibrin still attached to platelets. Immunogold cytochemistry detected large amounts of PAI-1 antigen in the partially lysed platelet-fibrin thrombi. This PAI-1 appeared to be bound to the fibrin network rather than to the platelet surface itself. We conclude that the residual clots observed late in lysis represent platelet-associated fibrin to which platelet-released PAI-1 has bound, rendering it less susceptible to degradation.

Adult↗
PubMed1993

acLDL binding and endocytosis by macrophages and macrophage foam cells in situ.

The direct binding and internalization of acLDL by monocyte-derived macrophages associated with atherosclerotic lesions in the White Carneau pigeon were observed. Using an organ culture labeling protocol, pigeon thoracic aortae containing atherosclerotic lesions were incubated with colloidal gold-acLDL conjugates. When analyzed by electron microscopy acLDL-gold was bound and internalized by monocyte-derived macrophages residing on the lumenal surface of the endothelium. Macrophage foam cells located within the intima and projecting from the lesion into the arterial lumen also bound and internalized acLDL. In contrast, acLDL was not observed in spherical (nonactivated) monocytes adherent to the lesion surface. Colabeling experiments with acLDL in combination with beta VLDL resulted in the preferential (> 90%) binding and internalization of acLDL by macrophages and macrophage foam cells. The results of this study indicated that macrophages located on the endothelial surface were able to bind and internalize lipoprotein, although this binding and internalization was enhanced in foam cells spanning the endothelium to the subendothelial intima. Acetyl-LDL binding and internalization was effectively inhibited through competition studies using an excess of unconjugated acLDL. Through the direct observation of lipoprotein binding by macrophages and foam cells, we have demonstrated the expression of a functional receptor for modified lipoprotein on monocyte-derived macrophages during different stages of association with foam cell lesions.

Animals↗
PubMed1993

Glycoprotein IIb/IIIa cross-reacting antigen in monocyte-derived macrophages from the pigeon.

The binding of fibrinogen to its receptor on mammalian platelets and avian thrombocytes has been extensively studied; and the receptors, composed of glycoproteins IIb and IIIa, have been characterized in both systems. Recently, monocytes have been implicated in the thrombotic complications of atherosclerosis, and in both the avian and human systems this appears to be through a procoagulant activity which leads to fibrinogen polymerization. Although fibrin polymerization by avian monocytes has been reported, the receptor for fibrinogen on these cells has not been reported previously. The present study describes the presence of glycoprotein IIb- and IIIa-like proteins in avian macrophages and correlates the localization of these glycoproteins with regions to which fibrinogen binds. Through the use of immunofluorescence light microscopy and immunogold electron microscopy in conjunction with monospecific, polyclonal antibodies, GPIIb and GPIIIa cross-reacting antigens were identified on membranes of monocyte/macrophages cultured from White Carneau pigeons. A specific concentration of the antigens was found on membrane ruffles and microvilli, sites to which FITC-labeled fibrinogen also bound. Interaction of the antibodies with pigeon macrophages was confirmed by enzyme-linked immunosorbent assays with cultured cells. Immunoblotting of membranes isolated from pigeon monocyte/macrophages identified a protein of 132,000 M(r) that was recognized by anti-GPIIb and a protein of 114,000 M(r) that was recognized by anti-GPIIIa. These pigeon monocyte glycoproteins comigrated with glycoproteins IIb and IIIa isolated from human platelets.

Animals↗
PubMed1993

Social cognitions as organizers of autonomic and affective responses to social challenge.

Autonomic and affective responses to children were assessed as a function of adult perceptions of interpersonal control. Women (N = 160) interacted with and provided feedback to computer-simulated children who "behaved" responsively or unresponsively on a computer game. Women were categorized as low in perceived control (PC) if they attributed high control to children but low control to self over negative events on the Parent Attribution Test. As predicted, low-PC women were maximally reactive to child characteristics, manifesting peak levels of defensive arousal (increased level of heart rate and electrodermal activity) and negative affect with unresponsive children and minimal levels of arousal and negative affect with responsive children. Intermediate response levels were shown by high-PC Ss. We interpreted results as suggesting mediating factors that may operate in dysfunctional interaction patterns previously found for low-PC caregivers.

Adult↗
PubMed1993

Beta very low density lipoprotein and clathrin-coated vesicles co-localize to microvilli in pigeon monocyte-derived macrophages.

Macrophages derived from blood monocytes are key in the development of atherosclerosis, as monocyte migration into the intima and accumulation of cholesterol leads to foam cell formation. To investigate the relationship between lipoprotein binding and the distribution of clathrin-coated endocytic vesicles, monocyte-derived macrophages were exposed in vitro to beta very low density lipoprotein (beta VLDL), conjugated to colloidal gold, and later were processed for immuno-electron microscopy to localize clathrin-coated vesicles. The immunolocalization was done in conjunction with either cryosectioning or whole mount intermediate voltage electron microscopy. Preferential binding of beta VLDL on small membrane ruffles and microvilli was quantitatively verified. Clathrin-coated vesicles were distributed throughout the cell; however, clusters of microvilli were associated with both a high concentration of coated vesicles and lipoprotein. Small membrane ruffles were not associated with clathrin-coated vesicles. These data support our hypothesis that endocytosis of beta VLDL near microvilli involves coated vesicles, whereas endocytosis of beta VLDL near ruffles is not mediated by coated endocytic vesicles. Furthermore, the association of coated vesicles with microvilli but not membrane ruffles may be important in understanding ligand trafficking within the cell. Given the distribution of coated vesicles within the cell, it is possible that the site of lipoprotein binding may determine the mechanism of entry into the cell and the metabolic effects of the internalized ligand.

Animals↗
PubMed1992

Ultrastructural localization of peroxidase in atherosclerotic lesions of pigeons.

Atherosclerotic lesions are known to have metabolic alterations which are associated with progressive lipid accumulation. Among the changes, lysosomal enzyme activity has been extensively characterized and at the ultrastructural level has been correlated with the amount of foam cell lipid. In a fashion paralleling lysosomal change, artery wall peroxidase activity is also altered during disease progression. The present study focuses upon the ultrastructural localization of peroxidase activity in atherosclerotic lesions of the aorta and coronary arteries from White Carneau pigeons fed a cholesterol-supplemented (0.3%) diet for 3 years. This resulted in fibrous lesions, rich in smooth muscle cells. The birds were necropsied by perfusion fixation, and peroxidase cytochemistry was carried out using the diaminobenzidine reaction. Peroxidase activity was found within endothelial cells and smooth muscle cells in both the media and intima, but cytochemically demonstrable activity was not found in macrophage foam cells. Peroxidase was localized within the nuclear envelope and endoplasmic reticulum, especially within cells that had lipid inclusions. The degree of peroxidase positivity varied within and among the arteries. In nonlesion regions of the aorta 20% of medial smooth muscle cells was peroxidase positive; the value for coronary artery smooth muscle cells was less. The peroxidase activity within aortic lesions was increased with 44% of intimal smooth muscle cells being positive. Notably, 85-90% of the lipid-containing intimal smooth muscle cells were positive. In contrast, intimal smooth muscle cells in the coronary artery lacked peroxidase reaction product, even in cells containing lipid. We conclude from these studies that aortic lesions contain a cytochemically differentiated subset of lipid-containing, peroxidase-positive smooth muscle cells; but coronary lesions lack a comparable subset of smooth muscle cells.

Animals↗
PubMed1992

Cloned endothelium derived from autoimmune vascular disease retain structural and functional characteristics of normal endothelial cells.

MRL/1pr mice demonstrate anatomic specificity in their development of vasculitis including the small- and medium-sized muscular arteries of the mesentery. To define the functional role of endothelium in vasculitis, we have cloned endothelial cells derived from inflamed small- and medium-sized arteries. Primary cells were derived by enzymatic dispersement and endothelial cells were selected by utilizing a combination of specific culture conditions. Cloned endothelium were developed utilizing limiting dilution cultures supplemented by endothelial cell growth factor. The cloned endothelial cells express many structural features of mature endothelial cells including Factor VIII-RA, non-muscle-specific actin, and Weibel-Palade bodies. Functionally, the clones express functional receptors for the scavenger pathway for LDL metabolism. The cells do not express Class I MHC antigens; however, IFN-beta and IFN-gamma stimulate Class I MHC expression after 24 h, which induces lysis of virus-infected cloned endothelium by Class I-restricted virus-primed T cells. In direct contrast to site-identical vascular smooth muscle cells (VSMCs), endothelial cells do not spontaneously express Class II MHC antigens, nor do they secrete biologically relevant levels of IL-1 unless triggered by lipopolysaccharide. The availability of site-specific cloned endothelium along with cloned VSMCs from autoimmune mice should resolve major experimental controversies involving the pathophysiology of inflammatory vascular disease.

Actins↗
PubMed1992

Platelet morphologic changes and fibrinogen receptor localization. Initial responses in ADP-activated human platelets.

Platelet exposure to agonists results in rapid morphologic changes paralleled by fibrinogen binding and platelet aggregation. The current study used standardized stereology in conjunction with immunogold electron microscopy to correlate the initial morphologic changes with fibrinogen receptor localization on the surfaces of ADP-activated human platelets. A 45% increase in platelet circumference was observed after 3 seconds of activation (P = 0.001). Virtually all of this increase was due to a 13-fold increase in projection membrane, and the projections observed by stereo microscopy at this time were mostly blunt. Both blunt and long projections also accounted for the increase in platelet-platelet contacts at 10 seconds of activation. Immunogold electron microscopy using the monoclonal antibodies P2 and AP-2 against the fibrinogen receptor, glycoprotein IIb/IIIa (GP IIb/IIIa), showed relatively equivalent immunogold densities on projections compared with cell body during 30 seconds of activation. The activation-dependent anti-GP IIb/IIIa monoclonal antibody, 7E3, showed an immunogold density 37% greater on projections compared with cell body (P = 0.0001). Colocalization studies using 7E3 with a polyclonal antifibrinogen antibody showed bound fibrinogen in close proximity to the GP IIb/IIIa localized by 7E3 on projections. These studies support an important role for platelet projections during the earliest stages of fibrinogen binding and ADP-induced aggregation.

Adenosine Diphosphate↗
PubMed1991

Beta VLDL uptake by pigeon monocyte-derived macrophages: correlation of binding dynamics with three-dimensional ultrastructure.

Endocytosis of pigeon beta migrating very-low-density lipoprotein (beta VLDL) by monocyte-derived macrophages (monocyte/macrophages), cultured from Random Bred White Carneau (RBWC) pigeons, occurs by both coated and non-coated regions of the plasma membrane (Henson et al.: Exp. Mol. Pathol. 51:243-263, 1989). Secondary to binding, the beta VLDL is translocated to lysosomes for degradation. Ultimately these events lead to foam cell formation in vitro. Utilizing video-enhanced contrast light microscopy in conjunction with whole mount intermediate-voltage transmission electron microscopy (IVEM) and high-resolution scanning EM, the dynamics of beta VLDL binding have been correlated with ultrastructure. Beta VLDL conjugated to gold colloids was visualized at the surface of living cells by using Allen video-enhanced contrast-differential interference contrast microscopy (AVEC-DIC). Subsequent to AVEC-DIC, direct observation of the identical cells by IVEM and SEM was facilitated through the use of gold finder grids, and these EM observations confirmed identification of the video-observed beta VLDL particles. Upon addition of beta VLDL, pigeon monocyte/macrophages underwent gross morphological changes. These changes were recorded by video as movements at the cytoplasmic periphery, and the movements involved extension of microvilli, expression of retraction fibers, and elaboration of membrane ruffles. When secondarily observed by stereo (3-D) IVEM and SEM, the identification of microvilli, retraction fibers, and membrane ruffles was confirmed and the lipoprotein-gold conjugates were associated with these ligand-induced membrane structures. Beta VLDL-gold conjugates were also associated with pit-like regions at the base of microvilli, while at the base of ruffles, beta VLDL-gold conjugates were located in membrane invaginations and cytoplasmic vesicles.

Animals↗
PubMed1991

Morphologic characteristics of naturally occurring atherosclerosis in the brachiocephalic artery of the pigeon.

Endothelial characteristics and the macrophage foam cell nature of early naturally occurring lesions in the aorta and coronaries of the pigeon have been well characterized. However, the characteristics of pigeon atherosclerosis at other vascular sites have not been extensively studied. The present study was designed to compare atherosclerosis in the brachiocephalic artery with that in the coronaries and aorta. Forty-six White Carneau (WC) pigeons (26 female, 20 male) ranging in age from 2.5 to 7 years were necropsied after fixation under deep anesthesia by perfusion at 160 mm Hg with buffered glutaraldehyde. Arteries stained with Sudan IV for gross evaluation were subsequently processed for SEM and TEM. The occurrence of sudanophilia in the proximal brachiocephalic artery was greater in females (22/26) than in male (2/20). The endothelium, as studied by SEM, was intact over all normal and sudanophilic areas. Cell morphology varied with location in the vessel and gradually changed from polygonally shaped cells with prominent margins and protruding nuclei in the proximal brachiocephalic artery to elongated, flattened cells in distal regions. These regional differences were consistently observed, and did not correlate with age, gender, or areas of lipid accumulation. Unlike lesions in the coronary arteries and at the celiac bifurcation of the aorta, a relative paucity of white blood cells over diffuse sudanophilic areas was observed. This lack of adherent monocytes correlated with lesion ultrastructure. Connective tissue in the intima of the sudanophilic brachiocephalic arteries was disorganized, reflecting both an increase in matrix components and the presence of massive pools of extracellular lipid. Intracellular lipid was minimal and when present was confined to random droplets in the cytoplasm of intimal smooth muscle cells. Monocyte-derived foam cells, characteristic to other vascular beds, were absent from the brachiocephalic artery lesions. These results document differential lesion composition in the WC pigeons and suggest a gender-related susceptibility for brachiocephalic artery atherosclerosis in pigeons.

Animals↗
PubMed1991

Lysosomal lipid accumulation in vascular smooth muscle cells.

Using an inverted culture technique, the accumulation of lipid within vascular smooth muscle cells incubated with lipid droplets was studied. Initially, lipid was found exclusively within cytoplasmic inclusions but, as accumulation continued, lysosomes became the predominant site of lipid storage. After 3 hr of incubation, 84% of lipid was within lysosomes. This lysosomal lipid accumulation produced a tripling of the average size of lysosomes and resulted in lysosomes with complex, multilobed shapes. In contrast, although the number of cytoplasmic inclusions increased with lipid loading, individual inclusions maintained a spherical shape and a consistent diameter of 1-1.3 microns. Concomitant with changes in cellular lipid storage, incubation with lipid droplets induced development of an anastomosing network of acid phosphatase-containing tubules which were spatially related to sites of lysosomal lipid accumulation. Thus lipid accumulation produced ultrastructural alterations in a number of metabolic compartments. Similar alterations in the intracellular compartmentalization of acquired lipid have been demonstrated in foam cells during atherogenesis and have been hypothesized to have profound effects on lipid metabolism and disease progression.

Acetylglucosaminidase↗
PubMed1991

Lysosomal hydrolysis of lipids in a cell culture model of smooth muscle foam cells.

Rabbit aortic smooth muscle cells take up lipid droplets when they are presented using an inverted culture technique. These droplets were localized in secondary lysosomes as demonstrated by staining for acid phosphatase. Initially, 69% of the cell volume was occupied by lipid, and 94% of the lipid was in lysosomes. After a 24-hr clearance period, the cell volume occupied by lipid decreased to 53%, although there was no change in the fraction of cell lipid that was in lysosomes. To confirm that hydrolysis of droplet lipid was occurring in lysosomes, cultures were exposed to medium containing Sandoz 58-035, an inhibitor of acyl CoA:cholesterol acyl transferase, for 24 hr in the presence and absence of chloroquine, ammonium chloride, or methylamine. Although the hydrolysis of cholesteryl oleate was sensitive to these lysosomotropic agents, the hydrolysis of triolein was not. Using reconstituted LDL containing cholesteryl oleate and triolein, we demonstrated that the hydrolyses of cholesteryl oleate and triolein were equally sensitive to the lysosomotropic agents when the cells were not loaded with droplet lipid. However, in cells loaded with lipid, hydrolysis of LDL cholesteryl ester was sensitive to the lysosomotropic agents but hydrolysis of triolein was not. We therefore conclude that both droplet lipids were hydrolyzed in lysosomes, and we attribute the failure of the lysosomotropic agents to inhibit fully the hydrolysis of droplet triolein to the presence of a large mass of free fatty acids in the lysosome that maintains a sufficiently low pH to sustain the triglyceridase activity, but not the cholesteryl esterase activity, of the lysosomal acid lipase.

Ammonium Chloride↗
PubMed1991

Pigeon monocyte/macrophage lysosomes during beta VLDL uptake. Induction of acid phosphatase activity. A model for complex arterial lysosomes.

Lysosomes have long been implicated as a factor contributing to the progression and complication of atherosclerosis. The authors' laboratory previously has shown that lysosomal ultrastructure in arterial macrophage foam cells is altered as primary lysosomes give rise to large pleiomorphic organelles on lipid accumulation during lesion progression. To further explore the subcellular alterations in lysosomes and associated organelles during foam cell formation, three-dimensional (3D) intermediate voltage electron microscopy was used to examine monocyte-derived macrophages (monocyte/macrophages) during early in vitro uptake of beta migrating very-low-density lipoproteins (beta VLDL). Lysosomes were identified using acid phosphatase cytochemistry, and in control cells these organelles constituted 3.5% of the total cytoplasmic volume. Both primary and secondary lysosomes were observed. Upon beta VLDL uptake, the total volume of acid-phosphatase-positive organelles increased threefold over 30 minutes, and the reaction product was found in three additional morphologically distinct structures: tubular lysosomes, membrane stacks, and endoplasmic reticulum with widened cisternae. The proportion of the cell occupied by each of the five acid-phosphatase-positive organelles was quantitated at 10 minutes, 30 minutes, 1 hour, and 4 hours of beta VLDL incubation, and their relative abundance was compared with controls that were processed either with no lipoprotein challenge or albumin incubation for 1 hour. Secondary lysosomes compartment volume peaked at 30 minutes; over the ensuing 3.5 hours, however, the reaction progressively shifted to three new membrane-limited locations. Our observations document the complex 3D organization and spacial relationships among the acid-phosphatase-positive structures induced by lipoprotein uptake. The 3D organization patterns for acid-phosphatase-positive lysosomes in lipoprotein-stimulated pigeon monocyte/macrophages were similar in several aspects to the complex lysosomes previously observed in the macrophages of pigeon arterial lesions.

Acid Phosphatase↗