Dynamics of hepatic connective tissue matrix constituents during murine Schistosoma mansoni infection

Hepatic fibrosis is the major clinical sequela of infection with the helminth Schistosoma mansoni. However, little is known regarding its dynamics and regulation in schistosomiasis. The present study presents the dynamics of deposition and resorption of two major extracellular matrix components of fibrosis, glycosaminoglycans and collagens, during the course of experimental S. mansoni infection. Early in infection (6 weeks), glycosaminoglycan biosynthesis was markedly elevated, as was collagen biosynthesis. This led to significant accumulations of these two molecules at a glycosaminoglycan/collagen ratio similar to that observed in livers of uninfected mice (uronic acid/hydroxyproline ratio of 1.10 at 6 weeks compared to normal value of 1.25). During maximal hepatic fibrosis (12 to 18 weeks), both collagen and glycosaminoglycan biosynthesis continued to increase but the extracellular matrix shifted to a lower glycosaminoglycan/collagen ratio of 0.42, suggesting enhanced glycosaminoglycan breakdown. In addition, during this acute stage of infection, Type I collagen was the predominant isotype synthesized, whereas total collagenolytic activity degrading Type I collagen was maximal. During chronic infection, a decrease in the content of both hepatic glycosaminoglycans and collagens were noted, with a glycosaminoglycan/collagen ratio of 0.63. Decreased glycosaminoglycan content paralleled diminished biosynthetic rates. On the other hand, an over 50% reduction in collagen content (from 18 to 24 weeks) appeared not to result from diminished biosynthesis but from a switch in the predominant collagen isotype synthesized (from Type I to Type III), matched by an enhanced constitutive collagenolytic activity directed toward this type of collagen.(ABSTRACT TRUNCATED AT 250 WORDS)

Involvement of heparanase in tumor metastasis and angiogenesis

The capacity of various blood-borne cells, whether normal or malignant, to extravasate was found to correlate with heparanase-mediated degradation of HS in subendothelial ECM. This degradation was stimulated by proteases or plasminogen and inhibited by native heparin and by various modified nonanticoagulant species of heparin. These heparins also induced a marked reduction in tumor cell metastasis and autoimmune diseases in experimental animals. Heparanase-mediated degradation of HS in ECM also released EC growth factors that are stored in ECM, most likely by high affinity binding to HS. Such growth factors were extracted from subendothelial ECM synthesized in vitro and from basement membranes of the cornea in vivo, and are structurally and functionally related to bFGF;bFGF binds to ECM and is readily released by incubation with either HS, heparin or low MW heparin fragments as well as by various normal and malignant cells and by heparanase-mediated degradation of ECM HS. In contrast, there was little or no release of growth-promoting activity upon incubation of ECM with hyaluronic acid, chondroitin sulfate or chondroitinase ABC. A model is proposed suggesting that regulation of capillary growth and neovascular response may result from displacement of an angiogenic protein (bFGF) from its storage sites within basement membranes.

The extracellular matrix of the central and peripheral nervous systems: structure and function

The extracellular matrix (ECM) is the naturally occurring substrate upon which cells migrate, proliferate, and differentiate. The ECM functions as a biological adhesive that maintains the normal cytoarchitecture of different tissues and defines the key spatial relationships among dissimilar cell types. A loss of coordination and an alteration in the interactions between mesenchymal cells and epithelial cells separated by an ECM are thought to be fundamental steps in the development and progression of cancer. Although a substantial body of knowledge has been accumulated concerning the role of the ECM in most other tissues, much less is known of the structure and function of the ECM in the nervous system. Recent experiments in mammalian systems have shown that an increased knowledge of the ECM in the nervous system can lead to a better understanding of complex neurobiological processes under developmental, normal, and pathological conditions. This review focuses on the structure and function of the ECM in the peripheral and central nervous systems and on the importance of ECM macromolecules in axonal regeneration, cerebral edema, and cerebral neoplasia.

Role of platelet membrane in enhancement of tumor cell adhesion to endothelial cell extracellular matrix

Tumor cell adhesion to subendothelial matrix in the presence of platelets and plasma has been examined in vitro using an entirely homologous system of rat Walker 256 carcinosarcoma cells, matrix laid down by rat aortic endothelial cells and rat platelets and plasma. In the presence of platelets or platelets plus plasma, tumor cell adhesion was significantly enhanced when compared to adhesion in the absence of platelets. In the presence of plasma alone (0.1%), we observed no significant increase in tumor cell adhesion. In order to determine which platelet factors contribute to the enhancement of tumor cell adhesion by platelets, we subjected washed rat platelets to mechanical lysis or thrombin stimulation followed by centrifugation. The membrane fractions and supernatant fractions containing platelet attachment proteins were compared for their abilities to support tumor cell adhesion to subendothelial matrix. Platelet membranes were also recombined with platelet supernatant fractions to determine if platelet attachment proteins or platelet membranes required the presence of the other to enhance tumor cell adhesion. Platelet supernatant fractions which contained release reaction proteins (confirmed by polyacrylamide gel electrophoresis) did not enhance tumor cell adhesion. Purified thrombospondin, fibronectin, beta-thromboglobulin, platelet derived growth factor, and serotonin had no effect on tumor cell adhesion. Platelet membrane containing fractions affected tumor cell adhesion to subendothelial matrix as follows: (a) platelets formed an adhesive bridge between tumor cells and the subendothelial matrix as demonstrated by scanning electron microscopy; (b) intact platelets and thrombin stimulated platelets were the most effective at facilitating tumor cell adhesion; (c) preparations containing partially lysed platelet ghosts were more effective in supporting tumor cell adhesion to subendothelial matrix than were preparations containing completely lysed platelet membrane fragments; (d) recombination of platelet supernatant fractions with mechanically lysed platelets did not enhance their ability to support adhesion; (e) fixed platelets, either alone or in combination with platelet supernatant fractions, failed to enhance adhesion. These data indicate that platelet enhanced tumor cell adhesion appears to be dependent on platelet membrane factors including receptor mobility, rather than intraplatelet components.