Human skin chymotrypsin-like proteinase chymase. Subcellular localization to mast cell granules and interaction with heparin and other glycosaminoglycans

The subcellular localization of human skin chymase to mast cell granules was established by immunoelectron microscopy, and binding of chymase to the area of the dermo-epidermal junction, a basement membrane, was demonstrated immunocytochemically in cryosections incubated with purified proteinase prior to immunolabeling. Because heparin and heparan sulfate proteoglycans are major constituents of mast cell granules and basement membranes, respectively, the ability of chymase to bind to glycosaminoglycans (GAG) was investigated. Among a variety of GAGs, only binding of chymase to heparin and heparan sulfate appears physiologically significant. Binding was ionic strength-dependent, involved amino groups on the proteinase, and correlated with increasing GAG sulfate content, indicating a predominantly electrostatic association. Interaction with heparin was observed in solutions containing up to 0.5 M NaCl, and interaction with heparan sulfate was observed in solutions containing up to 0.3 M NaCl. Binding of heparin did not detectably affect catalysis of peptide substrates, but may reduce accessibility of proteinase to protein substrates. Measurements among a series of serine class proteinases indicated that heparin binding was a more common property of mast cell proteinases than proteinases stored in other secretory granules. Binding of chymase to heparin is likely to have a storage as well as a structural role within the mast cell granule, whereas binding of chymase to heparan sulfate may have physiological significance after degranulation.     

Cell surface heparan sulfate proteoglycan and the neoplastic phenotype

Cell surface proteoglycans are strategically positioned to regulate interactions between cells and their surrounding environment. Such interactions play key roles in several biological processes, such as cell recognition, adhesion, migration, and growth. These biological functions are in turn necessary for the maintenance of differentiated phenotype and for normal and neoplastic development. There is ample evidence that a special type of proteoglycan bearing heparan sulfate side chains is localized at the cell surface in a variety of epithelial and mesenchymal cells. This molecule exhibits selective patterns of reactivity with various constituents of the extracellular matrix and plasma membrane, and can act as growth modulator or as a receptor. Certainly, during cell division, membrane constituents undergo profound rearrangement, and proteoglycans may be intimately involved in such processes. The present work will focus on recent advances in our understanding of these complex macromolecules and will attempt to elucidate the biosynthesis, the structural diversity, the modes of cell surface association, and the turnover of heparan sulfate proteoglycans in various cell systems. It will then review the multiple proposed roles of this molecule, with particular emphasis on the binding properties and the interactions with various intracellular and extracellular elements. Finally, it will focus on the alterations associated with the neoplastic phenotype and will discuss the possible consequences that heparan sulfate may have on the growth of normal and transformed cells.     

Mapping of the versican proteoglycan gene (CSPG2) to the long arm of human chromosome 5 (5q12-5q14).

Versican is a major chondroitin sulfate proteoglycan of vascularized connective tissues whose eponym reflects its functional versatility in macromolecular affinity and interactions. In this report we have localized the versican gene (CSPG2) to the long arm of human chromosome 5 by utilizing a combination of somatic cell hybrids, Southern blotting, polymerase chain reaction, and chromosomal in situ hybridization. The proteoglycan gene segregated concordantly with hybrid cell lines containing the long arm of chromosome 5, comprising the 5q12-q14 band regions. To refine this locus further, we screened a chromosome 5-specific library and isolated several genomic clones encoding a portion of the 5' end of versican. One of these genomic clones was used as a probe for in situ hybridization of human chromosome metaphases. The results corroborated the data obtained using somatic cell hybrids and further refined the assignment of the versican gene to the narrow band region of 5q12-5q14, with the primary site likely to be 5q13.2. The availability of novel genomic clones and the mapping data presented here will make possible the identification of any defect genetically linked to this proteoglycan gene.     

Biosynthesis of heparan sulfate proteoglycan by human colon carcinoma cells and its localization at the cell surface

After 24 h of continuous labeling with radioactive precursors, a high molecular weight heparan sulfate proteoglycan (HS-PG) was isolated from both the medium and cell layer of human colon carcinoma cells (WiDr) in culture. The medium HS-PG eluted from a diethylaminoethyl anion exchange column with 0.45-0.50 M NaCl, had an average density of 1.46-1.49 g/ml on dissociative CsCl density-gradient ultracentrifugation, and eluted from Sepharose CL-2B with a Kav = 0.57. This proteoglycan had an estimated Mr of congruent to 8.5 X 10(5), with glycosaminoglycan chains of Mr = 3 X 10(4) which were all susceptible to HNO2 deaminative cleavage. Deglycosylation of the HS-PG with polyhydrogen fluoride resulted in a 3H-core protein with Mr congruent to 2.4 X 10(5). The cell layer contained a population of HS-PG with characteristics almost identical to that released into the medium but with a larger Mr = 9.5 X 10(5). Furthermore, an intracellular pool contained smaller heparan sulfate chains (Mr congruent to 1 X 10(4)) which were mostly devoid of protein core. In pulse chase experiments, only the large cell-associated HS-PG was released (approximately 58%) into the medium as intact proteoglycan and/or internalized and degraded (approximately 42%), with a t1/2 = 6 h. However, the small intracellular component was never released into the medium and was degraded at a much slower rate. When the cells were subjected to mild proteolytic treatment, only the large cell-associated HS-PG, but none of the small component, was displaced. Addition of exogenous heparin did not displace any HS-PG into the medium. Both light and electron microscopic immunocytochemistry revealed that the cell surface reacted with antibody against an HS-PG isolated from a basement membrane-producing tumor. Electron microscopic histochemistry using ruthenium red and/or cuprolinic blue revealed numerous 10-50-nm diam granules and 70-220-nm-long electron-dense filaments, respectively, on the surface of the tumor cells. The results indicate that colon carcinoma cells synthesize HS-PGs with distinct structural and metabolic characteristics: a large secretory pool with high turnover, which appears to be synthesized as an integral membrane component and localized primarily at the cell surface, and a small nonsecretory pool with low turnover localized predominantly within the cell interior. This culture system offers an opportunity to investigate in detail the mechanisms involved in the regulation of proteoglycan metabolism, and in the establishment of the neoplastic phenotype.     

Strain-rate sensitive mechanical properties of tendon fascicles from mice with genetically engineered alterations in collagen and decorin

Tendons have complex mechanical behaviors that are nonlinear and time dependent. It is widely held that these behaviors are provided by the tissue composition and structure. It is generally thought that type I collagen provides the primary elastic strength to tendon while proteoglycans, such as decorin, play a role in failure and viscoelastic properties. This study sought to quantify such structure-function relationships by comparing tendon mechanical properties between normal mice and mice genetically engineered for altered type I collagen content and absence of decorin. Uniaxial tensile ramp to failure experiments were performed on tail tendon fascicles at two strain rates, 0.5%/s and 50%/s. Mutations in type I collagen led to reduced failure load and stiffness with no changes in failure stress, modulus or strain rate sensitivity. Fascicles without decorin had similar elastic properties to normal fascicles, but reduced strain rate sensitivity. Fascicles from immature mice, with increased decorin content compared to adult fascicles, had inferior elastic properties but higher strain rate sensitivity. These results showed that tendon viscoelasticity is affected by decorin content but not by collagen alterations. This study provides quantitative evidence for structure-function relationships in tendon, including the role of proteoglycan in viscoelasticity.     

Angiogenesis in collagen I requires alpha2beta1 ligation of a GFP*GER sequence and possibly p38 MAPK activation and focal adhesion disassembly

Angiogenesis depends on proper collagen biosynthesis and cross-linking, and type I collagen is an ideal angiogenic scaffold, although its mechanism is unknown. We examined angiogenesis using an assay wherein confluent monolayers of human umbilical vein endothelial cells were overlain with collagen in a serum-free defined medium. Small spaces formed in the cell layer by 2 h, and cells formed net-like arrays by 6-8 h and capillary-like lumens by 24 h. Blocking of alpha2beta1, but not alpha1 or alpha(v)beta3 integrin function halted morphogenesis. We found that a triple-helical, homotrimeric peptide mimetic of a putative alpha2beta1 binding site: alpha1(I)496-507 GARGERGFP*GER (where single-letter amino acid nomenclature is used, P* = hydroxyproline) inhibited tube formation, whereas a peptide carrying another putative site: alpha1(I)127-138 GLP*GERGRP*GAP* or control peptides did not. A chemical inhibitor of p38 mitogen-activated protein kinase (p38 MAPK), SB202190, blocked tube formation, and p38 MAPK activity was increased in collagen-treated cultures, whereas targeting MAPK kinase (MEK), focal adhesion kinase (FAK), or phosphatidylinositol 3-kinase (PI3K) had little effect. Collagen-treated cells had fewer focal adhesions and 3- to 5-fold less activated FAK. Thus capillary morphogenesis requires endothelial alpha2beta1 integrin engagement of a single type I collagen integrin-binding site, possibly signaling via p38 MAPK and focal adhesion disassembly/FAK inactivation.     

Effect of High-Fidelity Simulation on Medical Students’ Knowledge about Advanced Life Support: A Randomized Study

High-fidelity simulation (HFS) is a learning method which has proven effective in medical education for technical and non-technical skills. However, its effectiveness for knowledge acquisition is less validated. We performed a randomized study with the primary aim of investigating whether HFS, in association with frontal lessons, would improve knowledge about advanced life support (ALS), in comparison to frontal lessons only among medical students. The secondary aims were to evaluate the effect of HFS on knowledge acquisition of different sections of ALS and personal knowledge perception. Participants answered a pre-test questionnaire consisting of a subjective (evaluating personal perception of knowledge) and an objective section (measuring level of knowledge) containing 100 questions about algorithms, technical skills, team working/early warning scores/communication strategies according to ALS guidelines. All students participated in 3 frontal lessons before being randomized in group S, undergoing a HFS session, and group C, receiving no further interventions. After 10 days from the end of each intervention, both groups answered a questionnaire (post-test) with the same subjective section but a different objective one. The overall number of correct answers of the post-test was significantly higher in group S (mean 74.1, SD 11.2) than in group C (mean 65.5, SD 14.3), p = 0.0017, 95% C.I. 3.34 – 13.9. A significantly higher number of correct answers was reported in group S than in group C for questions investigating knowledge of algorithms (p = 0.0001; 95% C.I 2.22–5.99) and team working/early warning scores/communication strategies (p = 0.0060; 95% C.I 1.13–6.53). Students in group S showed a significantly higher score in the post-test subjective section (p = 0.0074). A lower proportion of students in group S confirmed their perception of knowledge compared to group C (p = 0.0079). HFS showed a beneficial effect on knowledge of ALS among medical students, especially for notions of algorithms and team working/early warning scores/communication.     

Early behavioral changes and quantitative analysis of neuropathological features in murine prion disease: Stereological analysis in the albino Swiss mice model

Behavioral and neuropathological changes have been widely investigated in murine prion disease but stereological based unbiased estimates of key neuropathological features have not been carried out. After injections of ME7 infected (ME7) or normal brain homogenates (NBH) into dorsal CA1 of albino Swiss mice and C57BL6, we assessed behavioral changes on hippocampal-dependent tasks. We also estimated by optical fractionator at 15 and 18 weeks post-injections (w.p.i.) the total number of neurons, reactive astrocytes, activated microglia and perineuronal nets (PN) in the polymorphic layer of dentate gyrus (PolDG), CA1 and septum in albino Swiss mice. On average, early behavioral changes in albino Swiss mice start four weeks later than in C57BL6. Cluster and discriminant analysis of behavioral data in albino Swiss mice revealed that four of nine subjects start to change their behavior at 12 w.p.i. and reach terminal stage at 22 w.p.i and the remaining subjects start at 22 w.p.i. and reach terminal stage at 26 w.p.i. Biotinylated dextran-amine BDA-tracer experiments in mossy fiber pathway confirmed axonal degeneration and stereological data showed that early astrocytosis, microgliosis and reduction in the perineuronal nets are independent of a change in the number of neuronal cell bodies. Statistical analysis revealed that the septal region had greater levels of neuroinflammation and extracellular matrix damage than CA1. This stereological and multivariate analysis at early stages of disease in an outbred model of prion disease provided new insights connecting behavioral changes and neuroinflammation and seems to be important to understand the mechanisms of prion disease progression.Key words: prion disease, optical fractionator, neuropathology, behavioral changes, albino Swiss mice