PubMed Health⌕ Search

Biomedical subjects

H Muir

Publications and source records attributed to H Muir.

At least 37 records · Page 2Linked to original sources
PubMed1987

Viscoelastic properties of proteoglycan solutions with varying proportions present as aggregates.

Monomer and aggregated proteoglycans were prepared from pig laryngeal cartilage. Vascoelastic flow properties, comprising linear complex dynamic shear modulus, nonlinear steady-state shear-rate dependent viscosity, and primary normal stress difference, were measured in proteoglycan solutions containing varying proportions of aggregate (0-80%) and at different concentrations (10-50 mg/ml). Results were analyzed using the simple Oldroyd four-parameter nonlinear rate-type rheological equation. All solution properties were strongly dependent on proteoglycan concentration and on the proportion of aggregates present. Aggregation was found to have a great effect on the zero shear-rate viscosity at 50 mg/ml, which increased fivefold from 0-100% aggregate. The results showed that network formation in proteoglycan solutions increased with concentration from 10-50 mg/ml and also increased with aggregation. All proteoglycan solutions showed shear thinning, which was most marked with aggregated proteoglycan at high concentration (50 mg/ml), where the viscosity decreased tenfold from the zero shear-rate limit to the infinite shear-rate limit. The intermolecular interactions in the network were therefore increasingly disrupted by increasing shear rate, but repeated measurements showed that these were reversible changes and that testing did not induce disaggregation or degradation of proteoglycan. These rheological properties show that aggregation is likely to immobilize proteoglycan at high concentration within cartilage and to contribute to the material properties of the porous solid matrix of articular cartilage that are important for its load-bearing function.

Animals↗
PubMed1987

Multiple transfer of lysosomal enzymes from normal lymphocytes to I-cell disease fibroblasts.

Cells from patients with inherited lysosomal deficiency diseases can acquire the missing lysosomal enzyme by direct cell-to-cell transfer from normal lymphocytes. Cells from I-Cell Disease (Mucolipidosis type II; ICD) patients are simultaneously deficient in many lysosomal enzymes due to an inborn error of glycoprotein processing. In this study we show that such cells acquire high levels of several of the missing lysosomal enzymes when they are cultured in contact with lymphocytes. Moreover, the present results also show that enzyme levels in the donor lymphocytes are not depleted but increase during cell contact with the fibroblasts.

Animals↗
PubMed1986

Electrophoresis of 35S-labeled proteoglycans on polyacrylamide-agarose composite gels and their visualization by fluorography.

We have developed techniques for the electrophoresis of 35S-labeled proteoglycans on polyacrylamide-agarose gel slabs and subsequent fixation, impregnation, and fluorography of such electrophoretograms. The procedure permits the examination of newly synthesized proteoglycan subspecies using a rapid technique, previously unavailable for these labeled molecules.

Adolescent↗
PubMed1986

Role of cell adhesion in contact-dependent transfer of a lysosomal enzyme from lymphocytes to fibroblasts.

Normal lymphocytes were found to adhere strongly to monolayer cultures of fibroblasts deficient in the lysosomal enzyme, beta-glucuronidase. During this co-culture, the fibroblasts acquired from the lymphocytes substantial amounts of this enzyme, which often accumulated at sites of contact between the two types of cell. Enzyme transfer was prevented by addition to the co-cultures either of purified lymphocyte plasma membranes or of antibody raised against such plasma membranes, but it was not inhibited by the addition of antibody raised against lymphocyte-derived beta-glucuronidase. An active role for the lymphocyte in this contact-dependent process was suggested by interference contrast, immunofluorescence and scanning electron-microscopic studies. These revealed extensive arrays of projections of the lymphocyte that ramified over the fibroblast cell surface. By transmission electron microscopy, conspicuous clusters of micropinocytotic vesicles were evident in the cytoplasm of the 'recipient' fibroblasts, subjacent to the surface in regions closely apposed to adherent lymphocytes. Such high frequencies of these vesicles were restricted to sites of lymphocyte-fibroblast contact, suggesting that they may play an important part in the transfer of enzyme between these two types of cell.

Animals↗
PubMed1986

Effects of mitogenic stimulation on lymphocyte alpha-D-mannosidases.

Three types of alpha-D-mannosidase are present in human and murine lymphocytes. Their levels increased substantially when the cells were activated by T-cell mitogens, concanavalin A (Con A) and phytohaemagglutinin (PHA), and in the murine cells also by lipopolysaccharide (LPS), a B-cell mitogen. The intracellular localization of the alpha-D-mannosidases in the non-stimulated and activated murine cells was investigated by fractionation of lymphocyte lysates on colloidal silica (Percoll) and discontinuous sucrose gradients. In both types of cell, an enzyme having optimal activity at neutral pH was obtained in the cytosolic fraction and another alpha-D-mannosidase most active at an intermediate pH was obtained partly in membrane-bound form. In contrast, an acidic alpha-D-mannosidase, which was particularly elevated in the activated murine spleen cells, had a distribution in these lymphoblasts which was markedly different from that in non-stimulated lymphocytes. In the latter, the major proportion of the activity was obtained in a cytosolic fraction and the remainder in a particulate fraction of light density, whereas the enzyme in activated lymphocytes was distributed between vesicles of light and heavy density comparable with lysosomal organelles. Moreover, the acidic alpha-D-mannosidase still remained membrane bound even when cell lysates were prepared under hypotonic conditions which disrupt lysosome integrity. These results suggest that lymphocyte activation involves either stabilization of fragile lysosomes present in resting cells or de novo synthesis of lysosome-like structures. The acidic alpha-D-mannosidase present within isolated, intact lysosomes was found to be in a form, A, whereas a different form, B, was most prominent in whole-cell extracts of both types of lymphocyte.(ABSTRACT TRUNCATED AT 250 WORDS)

Cell Compartmentation↗
PubMed1986

Isolation and characterization of high-buoyant-density proteoglycans from semilunar menisci.

Proteoglycans were extracted from adult canine menisci in high yield and were purified, and the major species were characterized biochemically. Most proteoglycans in menisci were isolated in the high-buoyant-density fraction. By agarose-acrylamide composite gel electrophoresis, two proteoglycans were seen in this fraction. Although they were smaller than those from porcine laryngeal hyaline cartilage and had shorter chondroitin sulphate and keratan sulphate chains and a lower carbohydrate-to-protein ratio, they were functionally similar to those in hyaline cartilage in their specific interaction with hyaluronate.

Animals↗
PubMed1985

Direct enzyme transfer from lymphocytes corrects a lysosomal storage disease.

Fibroblasts from patients with mannosidosis, the lysosomal storage disease resulting from an inherited deficiency of lysosomal alpha-D-mannosidase (EC 3.2.1.24), accumulate specific mannose-containing oligosaccharides which are characteristic of the disease (1,2). The present study shows that these substances were extensively degraded following transfer of the missing enzyme from normal lymphocytes to mannosidosis fibroblasts on direct contact in tissue culture. Moreover, prolonged correction of the metabolic abnormality of the recipient cells was sustained if contact with fresh donor lymphocytes was periodically renewed. These findings may be highly relevant to lymphocyte function in enzyme replacement therapy by transplantation procedures currently being attempted.

Animals↗
PubMed1985

Structure of newly synthesised (35S)-proteoglycans and (35S)-proteoglycan turnover products of cartilage explant cultures from dogs with experimental osteoarthritis.

The structure of newly synthesised proteoglycans from explant cultures of cartilage from joints subjected to transection of the anterior cruciate ligament (osteoarthritic) and from normal (non- or sham-operated) joints was examined. The structure of the products of proteoglycan turnover was also examined using explants of normal and osteoarthritic cartilage maintained in culture for a 48 h chase period. The findings were as follows: Newly synthesised (35S)-proteoglycans extracted from cartilage explants from osteoarthritic joints whether examined 3 weeks, 3 months, or 6 months after surgery were larger than those from corresponding normal cartilage. This can be explained by the synthesis in osteoarthritic cartilage of abnormally long chondroitin sulphate chains on newly synthesised proteoglycans. The extracts also contained a newly formed small proteoglycan species that was unable to interact with hyaluronic acid. The proportion of this species was higher in osteoarthritic cartilage compared with normal, examined 3 weeks after surgery, but was generally absent from cartilage obtained 3 and 6 months after surgery. Compared with controls, a smaller proportion of the (35S)-proteoglycans released into the maintenance medium of explant cultures of osteoarthritic cartilage during a 48 h chase period was able to interact with hyaluronic acid. However, although furnished with longer (35S)-glycosaminoglycan chains, these proteoglycans were smaller than those from control explants.

Animals↗
PubMed1984

In vivo and in vitro stimulation of chondrocyte biosynthetic activity in early experimental osteoarthritis.

The biosynthesis of proteoglycans in the menisci and articular cartilages of the knee (stifle) of mature beagles was studied in the early stages of experimental osteoarthritis. The rate of proteoglycan synthesis, determined by systemic labeling in vivo at 21, 42, and 84 days after sectioning of the anterior cruciate ligament, was generally found to be 1.5-2.5-fold higher than control in articular cartilages and 3-10-fold higher than control in menisci. The medial meniscus was more stimulated than the lateral meniscus, and the medial tibial plateau under the meniscus was more stimulated than the adjacent tibial area. This area-specific stimulation suggests the involvement of mechanical factors in the cellular response. The rate of proteoglycan synthesis determined in vitro at 7, 14, and 21 days after operation was also about 2-fold higher than control in articular cartilages and about 3-fold higher in menisci. This increase in biosynthetic activity in vitro was confirmed by 35S-autoradiography and appeared to be due to general stimulation of existing chondrocytes, particularly in the middle and deep zones of the articular cartilage and throughout the meniscal cartilage. The rate of proteoglycan synthesis determined in vitro in cartilages from 2-week and 3-week sham operated joints was also increased relative to controls, suggesting that humoral as well as mechanical factors are involved in stimulating chondrocyte activity.

Animals↗
PubMed1984

Demonstration of increased proteoglycan turnover in cartilage explants from dogs with experimental osteoarthritis.

The turnover of proteoglycans (assessed by the release into the medium of newly synthesised [35S]-proteoglycan) in explant cultures of articular cartilage from various anatomical sites of the knee joints (stifle) of mature beagles with experimental osteoarthritis has been studied with the following findings: (a) The proportion of newly synthesised proteoglycans released from cartilage explants maintained in vitro was generally increased for cartilage from operated compared with nonoperated control joints. (b) At 3 weeks after surgery there was a significant increase in the release of [35S]-proteoglycans from explants of the lateral and medial tibial plateaux of operated joints compared with sham-operated joints but not from other sites. On the other hand, when this comparison was made at 3 to 6 months after surgery, significant increases in the release of [35S]-proteoglycans were observed from cartilage of all anatomical areas except the patellar groove. (c) The release of [35S]-proteoglycan from cartilage explant cultures was dependent on live chondrocytes, since freeze-thawing the tissue immediately after labelling markedly reduced the release from both normal and osteoarthritic cartilage.

Animals↗
PubMed1983

Proteoglycan aggregate formation by articular chondrocytes. Decrease in link-protein synthesis during culture.

The synthesis of link-stabilized proteoglycan aggregates by rabbit articular chondrocytes was investigated by [35S]sulphate labelling of primary monolayer cultures maintained for up to 21 days. (1) At all culture times the cells secreted a high-molecular-weight cartilage-type proteoglycan monomer of which 75%-80% formed aggregates with hyaluronic acid. (2) At 2 days of culture all of the aggregates were in link-stabilized form, but by 21 days only 5% were link-stabilized, as shown by displacement of monomers from the aggregate by hyaluronic acid oligosaccharides. (3) The addition of purified link protein to 21-day culture medium increased the proportion of link-stable aggregate from 5% to 70%. (4) Analysis of [3H]serine-labelled proteoglycan aggregates in the medium showed a marked decrease with culture time in the ratio of 3H-labelled link protein to 3H-labelled core protein present. The results suggest that the secretion of proteoglycan monomers and link protein by articular chondrocytes changes independently during prolonged monolayer culture.

Animals↗
PubMed1983

The glycosaminoglycans in menisci in experimental and natural osteoarthritis.

The glycosaminoglycans in the menisci of beagles 5--7 years old were analyzed at various times after osteoarthritis was induced by sectioning the anterior cruciate ligament of one knee; the unoperated knee served as control. In the first month after induction, there were signs of inflammation in the operated joint. After 1 week, the water content was elevated and the glycosaminoglycan content (per dry weight) was reduced. The content of keratan sulfate decreased more than that of chondroitin sulfate, but the hyaluronic acid content did not change consistently. The relative proportions of chondroitin-4-sulfate, chondroitin-6-sulfate, and dermatan sulfate remained unchanged. After 3--18 months, the glycosaminoglycan levels reverted to normal, and there was some evidence that after 15--18 months, they were elevated above normal. These results, together with results obtained from single examples of mild and severe osteoarthritis in working foxhounds, suggest that, in contrast to articular cartilage, the meniscus is capable of some regeneration in response to injury.

Animals↗
PubMed1983

Effects of mitogenic stimulation of lymphocytes on lysosomal enzyme activity.

Changes in the activities of several lysosomal enzymes were studied during transformation of mouse spleen cells in vitro. The activity of beta-glucuronidase increased during culture in the presence of T or B-cell mitogens, and lymphoblasts contained higher levels of activity than did small, non-transformed lymphocytes. Moreover, lymphoblasts in well-transformed cultures had higher activities than those in poorly-transformed cultures. The activities of other lysosomal enzymes (N-acetyl-beta-glucosaminidase, alpha-mannosidase, beta-glucosidase) also increased during mitogenic stimulation, but each at different rates, although aryl sulphatase was unaffected. Such differences may be of importance when lymphocytes are used for diagnosis of inherited lysosomal deficiency diseases.

Acetylglucosaminidase↗
PubMed1983

Ultrastructural changes in articular cartilage after experimental section of the anterior cruciate ligament of the dog knee.

Ultrastructural changes in articular cartilage were studied in joint laxity induced by severing the anterior cruciate ligament of the right knee in sixteen mature dogs. The left knees provided controls; sham operations on six other dogs consisted of stab incision only, leaving the ligament intact. Cartilage from the medial tibial condyles was examined at intervals from two days to eighteen months later. In the superficial zone of the cartilage, collagen fibrils became abnormally widely spaced at four days, and narrower fibrils appeared from seven days after operation. Chondrocytes, particularly in the middle zone, became more active, with hypertrophy of cytoplasmic organelles detectable from four days. Superficial cells were initially healthy and became more numerous while their lipid content increased. The articular surface was fissured from two months and cell degeneration was rarely seen until several months after operation. These findings correlate with previous biochemical studies and are similar to early changes noted in degeneration of human articular cartilage.

Animals↗