Degradation of connective tissue matrices by macrophages. I. Proteolysis of elastin, glycoproteins, and collagen by proteinases isolated from macrophages

Stimulation of murine macrophage cathepsin B by serum from patients with rheumatoid arthritis: an indicator of disease activity

Cultures of non-elicited mouse peritoneal macrophages were used as a test system to study the effect of sera from patients with rheumatoid arthritis (RA) on intra-cellular cathepsin B activity of macrophages. Sequential sera obtained during and after pregnancy from six RA patients, and sera from six actively ill, non-pregnant RA patients were compared to six healthy female controls and 3rd trimester healthy women. Sera from actively ill RA patients (both pregnant and non-pregnant) caused macrophage cathepsin B levels significantly above normal controls, while intra-cellular activities of beta-glucuronidase and N-acetyl-glucosaminidase did not differ from the controls. A significant correlation between activity of RA and intracellular cathepsin B was found in pregnant patients. It is suggested that a factor (or factors) present in serum from patients with active RA causes a rise of intracellular cathepsin B in macrophages.

Macrophage cell lines behave as activated macrophages in the production and regulation of plasminogen activator

Seven macrophagelike cell lines, WEHI-3, J774, RAW264, FC-1, P388D-1, PU5-R, and PU5-1.8, commonly used as in vitro models of macrophage function, were studied for their fibrinolytic activity in the presence and absence of purified plasminogen. All cell lines, as well as the freshly harvested peritoneal macrophages, produced plasminogen activator, as indicated by the levels of fibrinolytic activity in the presence of plasminogen. However, fibrinolytic proteolysis was most efficiently measured by direct attachment to 125I-fibrin plates, a method which measures both secreted and cell-membrane-associated plasminogen activator. Other non-plasminogen-dependent fibrinolytic activities were also produced by all cells studied and secreted by WEHI-3, FC-1, RAW-264, and thioglycollate-elicited macrophages. Activation of the thioglycollate-elicited macrophages with macrophage activation factor (MAF) induced threefold higher levels of plasminogen activator production but MAF treatment had no effect on the level of activity produced by macrophagelike cell lines. Indeed, the macrophagelike cell lines produced plasminogen activator at levels seen with MAF-activated thioglycollate-elicited macrophages. We conclude that these cell lines constitutively produce activators of plasminogen and, in their failure to respond to MAF, behave as activated macrophages.

Extracellular matrix destruction by invasive tumor cells

The invasion of normal tissues and penetration of basement membranes by malignant cells is likely to require the active participation of hydrolytic enzymes. The four major groups of connective tissue proteins, glycoproteins, proteoglycans, collagen and elastin, vary in their quantitative distributions between different tissues. With the exception of elastin, they also vary qualitatively within each class, so that there are no 'typical' connective tissue barriers to tumor cell penetration. The matrix constituents are stabilized and organized by a variety of covalent and noncovalent interactions between the connective tissue proteins. These interactions play important roles in matrix integrity and may alter the susceptibilities of the constituents to degradative enzymes. It is likely that the complete degradation of the matrix will require the action of more than one enzyme because of differing susceptibilities to tissue proteinases. Primary and transplantable tumors produce well-characterized enzymes which may participate in invasion. These enzymes may also be involved in connective tissue turnover in other normal and pathological situations. The use of long-term tumor cell cultures has verified that tumor cells themselves are capable of producing these enzymes. However, there are many potential modulating influences operative in vivo which are absent in culture so that details of actual mechanisms and control of digestion of complex substrates are not well understood. Recent work on the degradation by tumor cells of extracellular matrices previously produced by cultured cells is likely to shed more light on pathways of tissue destruction in vivo. Experiments with tumor cell variants of defined metastatic potentials will also be useful, but invasive and metastatic abilities are not necessarily correlated. It is unlikely that simple correlations can be drawn between the production of one particular degradative enzyme by all tumor cells and the complex biological mechanisms operative during tumor invasion.

In vitro differentiation of human monocytes. Differences in monocyte phenotypes induced by cultivation on glass or on collagen

We demonstrated that the in vitro differentiation of human peripheral blood monocytes to macrophages is dependent on the environment and conditions of monocyte culture. Cultivation of monocytes on glass or microexudate-coated glass gave rise to cells resembling foreign body granuloma macrophages. After an initial rise in Fc receptor- and C3 receptor-mediated phagocytosis, a progressive loss of Fc receptor expression and C3-mediated ingestion were observed. The monocyte surface antigens recognized by the anti-human monocyte monoclonal antibodies 1D5 and 63D3 were lost from the surface of the majority of cells cultured on glass and microexudates. A subpopulation of Fc receptor-positive cells that were 1D5 and 63D3 positive was retained in fully differentiated cell populations. In comparison, monocytes cultivated on collagen matrices gave rise to highly phagocytic cells resembling human resident tissue macrophages. Both Fc- and C3-mediated phagocytosis were enhanced and remained so during the entire length of culture. The surface antigens recognized by the 1D5 antibody, expressed on all freshly seeded monocytes, was maintained on the macrophages. The antigen recognized by the 63D3 antibody was not expressed on mature cells. The present evidence would indicate that variations in expression of phagocytic receptors and the surface antigens 1D5 and 63D3 can be ascribed to the stage of development of the macrophage or its stage of activation, rather than to independent subsets of mononuclear phagocytes.

Cells of the mononuclear phagocytic system resorb implanted bone matrix: a histologic and ultrastructural study

Implantation of mineral-containing bone fragments into calvarial defects in rats initiates a rapid and reproducible resorption of the bone matrix. After 7 days, a dense tissue develops with mononucleated as well as multinucleated cells surrounding and between the bone fragments. Electron microscopy revealed that these cells belong to the mononuclear phagocytic system: they were identified as macrophages, epithelioid cells, foreign body giant cells, and Langerhans cells. In addition to the common ultrastructural characteristics, these cells had electron-dense, focal specializations along their cell membrane with a coating on the exterior, corresponding to subplasmalemmal linear densities. Small, unidentified cells with electron-dense ground cytoplasm were often seen in close proximity to more differentiated cells. No halisteresis had occurred on the surfaces of the bone fragments. Indentations resembling Howship's lacunae were frequent; these contained mononucleated as well as multinucleated cells. Some surfaces were frayed and collagen fibers were exposed, but the cells apposed to these surfaces did not have ruffled borders as are seen in osteoclasts. Some bone fragments were broken up and cell processes had penetrated deep into the cracks, separating pieces of matrix. Small matrix particles were phagocytosed by macrophages, but not by epithelioid cells or giant cells. It appears that enzymes capable of degrading bone matrix components were secreted by the more differentiated cells of the mononuclear phagocytic system. They eroded the bone surface in a way reminiscent of osteoclastic bone resorption. They also entered the canaliculi to act from within the bone fragment, a process possible only in dead bone. We suggest a possible relationship of these cells with osteoclasts.

Pathogenesis of scleroderma (systemic sclerosis)

Increasing interest in the vascular features of scleroderma has led to the hypothesis that the blood vessel is the major target tissue and that the endothelial cell is the principal cell target. Useful observations stemming from the vascular hypothesis include the use of microvascular abnormalities in the early detection of the patient destined to develop classical scleroderma, the discovery of a serum protease selectively cytotoxic to endothelial cells, and the study of a serum mitogenic activity for fibroblasts in scleroderma patients. Immune events related to the vascular lesions are under active study but have not as yet provided a unique immunological lesion in scleroderma patients. The possibility that immunity to basement membrane (type IV) collagen may be selective for scleroderma patients deserves further study. Persistent immunity to endothelial basement membrane structures would provide a basis for continued endothelial injury. Techniques to quantify endothelial injury are useful to assess activity of the vascular lesions and to monitor therapies designed to block further vascular injury. The definition of pre-fibrotic vascular lesions may have future therapeutic and preventive implications for scleroderma.

Murine lymphoid procoagulant activity induced by bacterial lipopolysaccharide and immune complexes is a monocyte prothrombinase

Murine lymphoid cells respond rapidly to bacterial lipopolysaccharide or antigen-antibody complexes to initiate or accelerate the blood coagulation pathways. The monocyte or macrophage has been identified as the cellular source, although lymphocyte collaboration is required for the rapid induction of the procoagulant response. This procoagulant activity is identified in the present study as a direct prothrombin activator, i.e., a prothrombinase. Studies with plasmas deficient in single coagulation factors demonstrate that the induced murine procoagulant activity effector molecule does not require factors XII, VIII, VII, X, or V, but does require prothrombin to transform fibrinogen to fibrin. This enzyme(s) produces limited proteolysis of prothrombin to yield thrombin or thrombinlike products that are functionally capable of converting fibrinogen to fibrin. The prothrombinase is undetectable in freshly isolated Murine lymphoid cells respond rapidly to bacterial lipopolysaccharide or antigen-antibody complexes to initiate or accelerate the blood coagulation pathways. The monocyte or macrophage has been identified as the cellular source, although lymphocyte collaboration is required for the rapid induction of the procoagulant response. This procoagulant activity is identified in the present study as a direct prothrombin activator, i.e., a prothrombinase. Studies with plasmas deficient in single coagulation factors demonstrate that the induced murine procoagulant activity effector molecule does not require factors XII, VIII, VII, X, or V, but does require prothrombin to transform fibrinogen to fibrin. This enzyme(s) produces limited proteolysis of prothrombin to yield thrombin or thrombinlike products that are functionally capable of converting fibrinogen to fibrin. The prothrombinase is undetectable in freshly isolated

Elastase of U-937 monocytelike cells. Comparisons with elastases derived from human monocytes and neutrophils and murine macrophagelike cells

As an approach to facilitating the understanding of proteinases associated with monocytes we have studied U-937 monocytelike cells. Elastase activity was identified in U-937 cell extracts and compared to monocyte elastase activity, neutrophil elastase, and the elastase activity from a continuous line of murine macrophagelike cells (P388D1). Serine proteinase activity which solubilized (14)C-labeled elastin accounted for >90% of the neutral proteinase activity of both U-937 cells and monocyte extracts. U-937 cell and monocyte elastase activities were similar catalytically, resembling neutrophil elastase. U-937 cells and monocytes showed other similarities: (a) both had activities reacting with [(3)H]diisopropylfluorophosphate that migrated in sodium dodecyl sulfate (SDS) polyacrylamide gels at approximately 30,000 and 60,000 daltons and (b) both contained material that cross-reacted with antiserum raised to neutrophil elastase. Preliminary characterization of U-937 cell elastase activity by affinity chromatography and ion-exchange chromatography suggested the presence of at least two distinct elastases. Minimal elastase activity was found in U-937 cell-conditioned medium, indicating that the activity is not spontaneously released by the cells. In contrast to the elastase activity associated with U-937 cells and monocytes, the elastase activity associated with P388D1 cells was a metalloproteinase and was found principally in the culture medium. These results indicate (a) U-937 cells will be useful for further investigation of proteinases associated with normal monocytes; (b) monocytes and U-937 cells contain material with catalytic and immunologic similarities to neutrophil elastase; (c) monocyte elastase activity differs from elastase activity secreted by murine macrophages and murine macrophagelike cells of the P388D1 line.

Improved medium for extraction of plasminogen activator from tissue

Quantitation of plasminogen activators present in tissue may depend to a large extent on the extraction procedure used to solubilize the enzymes. Potassium thiocyanate solution is known to be an efficient solubilizer, but it can inhibit assay systems other than fibrin plates. An equally effective acetate-detergent extractant is reported here which can be used with the highly sensitive azocaseinolytic assay procedure. The results indicate that a three-fold increase in activator activity can be extracted from selected tissues relative to that previously reported for a phosphate-detergent extractant. The extraction medium contains 75 mM K acetate, 0.3 M NaCl, 0.1 M L-arginine, 10 mM EDTA, 0.25% Triton X-100, final pH 4.2.

Degradation of connective tissue matrices by macrophages. III. Morphological and biochemical studies on extracellular, pericellular, and intracellular events in matrix proteolysis by macrophages in culture

We have shown that macrophages in culture degrade the glycoproteins and amorphous elastin of insoluble extracellular matrices. Ultrastructural observation of the macrophage-matrix interaction revealed that connective tissue macromolecules were solubilized from the matrix extracellularly. At least part of the matrix breakdown was localized to the immediate vicinity of the cells, as shown by morphological and biochemical studies, although the rate of degradation correlated closely with the secretion of proteinases by various inflammatory stimuli in vivo, by glucocorticoids, prostaglandin E2 or colchicine, or by phagocytosis of latex, zymosan, or cholesterol-albumin complexes in culture was reflected in altered rates of glycoprotein and elastin degradation by the macrophages. Alteration of endocytosis and lysosomal digestion by cytochalasin B, NH4Cl, and proteinase inhibitors did not decrease the overall rate of matrix solubilization, but reduced the processing of the matrix fragments to peptides. Therefore, extracellular, pericellular, and lysosomal events each contribute to degradation of extracellular matrix macromolecules by inflammatory macrophages.

Degradation of connective tissue matrices by macrophages. II. Influence of matrix composition on proteolysis of glycoproteins, elastin, and collagen by macrophages in culture

Thioglycollate-elicited mouse peritoneal macrophages were cultured in contact with the mixture of extracellular matrix proteins produced by rat smooth muscle cells in culture. Both live macrophages and their conditioned media hydrolyzed glycoproteins, elastin, and collagen. Live macrophages also degraded extracellular connective tissue proteins secreted by endothelial cells and fibroblasts. The glycoproteins in the matrix markedly inhibited the rate of digestion of the other macromolecules, particularly elastin. When plasminogen was added to the matrix, activation of plasminogen to plasmin resulted in the hydrolysis of the glycoprotein components, which then allowed the macrophage elastase easier access to its substrate, elastin. Thus, although plasmin has no direct elastinolytic activity, its presence accelerated the rate of hydrolysis of elastin and therefore the rate of matrix degradation. These findings may be important in an understanding of disease states, such as emphysema and atherosclerosis, that are characterized by the destruction of connective tissue.

Limited proteolysis by macrophage elastase inactivates human alpha 1-proteinase inhibitor

Inflammatory mouse peritoneal macrophages secrete a metalloproteinase that is not inhibited by alpha 1-proteinase inhibitor. This proteinase, macrophage elastase, recognizes alpha 1-proteinase inhibitor with macrophage elastase does not involve a stable proteinase-inhibitor complex and results in the proteolytic removal of a peptide of apparent molecular weight 4,000-5,000 from the inhibitor. After degradation by macrophage elastase, alpha 1-proteinase inhibitor is no longer able to inhibit human granulocyte elastase, a serine proteinase implicated in the pathogenesis of emphysema. Macrophage elastase apparently does not degrade human granulocyte elastase-alpha 1-proteinase inhibitor complexes or release active granulocyte elastase from these complexes. The ability of macrophage elastase to degrade alpha 1-proteinase inhibitor is inhibited by EDTA and alpha 2-macroglobulin.