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Biomedical subjects

M J Barnes

Publications and source records attributed to M J Barnes.

At least 73 records · Page 4Linked to original sources
PubMed1988

Interaction of embryonic chick calvarial bone cells with collagen substrata; attachment characteristics and growth behaviour.

Freshly isolated bone cells from embryonic chick calvariae were found to attach to films of native monomeric type I or II collagen, to gels of native type I collagen and, to a lesser extent, to air-dried films of these collagens, in a fibronectin-independent manner, and with no requirement for collagen synthesis. Adhesion to type III collagen was relatively poor. Films of native monomeric type I or II collagen were preferred to the corresponding air-dried films as substrata for proliferation. Cis-hydroxyproline inhibited growth upon both plastic and type I and type II collagenous substrata, but this effect could largely be overcome by providing bone cell-conditioned medium, suggesting the possibility of a requirement in the growth process for synthesis of a collagen other than type I, the major form in bone matrix.

Animals↗
PubMed1987

Platelet-reactive sites in collagen. Collagens I and III possess different aggregatory sites.

Collagen type III possesses a highly reactive platelet-aggregatory site at a locus which in type I is essentially inactive whilst the latter collagen possesses reactive sites absent in type III. It is proposed that platelet aggregation by collagen involves the sequence GK[or R]PG(EY)GPK[or R]G(EY) or, less favourably, GPK[or R]G(EY)G(XY)GK[or R]PG(EY), one basic residue acting in combination with the second in an adjacent alpha-chain.

Arginine↗
PubMed1986

The platelet reactivity of collagen type I: evidence for multiple platelet-reactive sites in the type I collagen molecule.

In this study, the ability of peptides, obtained by fragmentation of the collagen type I molecule, to induce platelet aggregation has been examined. In order to satisfy requirements for tertiary and quaternary structure, peptides were first renatured (where necessary) to restore triple-helical configuration and then polymerised. Fragmentation with mammalian collagenase indicated the presence of platelet-reactive sites in both the N-terminal three-quarter and C-terminal one quarter fragment of the collagen molecule. Cleavage with cyanogen bromide indicated the presence in the constituent alpha 1(I)-chain of at least four platelet-reactive sites. Our results suggest a relatively wide distribution of platelet-binding sites situated throughout the length of the collagen (type I) molecule, each probably of relatively low affinity and low structural specificity, at least in terms of amino acid sequence, and probably of a similar nature to those that might be expected to exist in any collagen-like species.

Animals↗
PubMed1986

Delayed reconstruction of the calcaneal tendon.

Thirteen patients with ruptures of the calcaneal tendon diagnosed more than four weeks after injury were reviewed. Eleven patients had operative reconstruction with tendon shortening and the postoperative follow-up ranged from one to seven years. Isometric and isokinetic measurements, as well as the strength of the triceps surae, all compared favourably with the normal contralateral leg. Only one tendon re-ruptured. Eight of the eleven patients were satisfied with the results and the two patients who had refused reconstruction had worse functional results. Late reconstruction of a ruptured calcaneal tendon is thus a worthwhile procedure.

Adult↗
PubMed1985

Failure of highly purified lysyl hydroxylase to hydroxylate lysyl residues in the non-helical regions of collagen.

The activity of highly purified lysyl hydroxylase towards lysyl residues within both the helical and the N-terminal non-helical telopeptide regions of chick type I collagen has been examined. The peptides alpha 1(I)-CB1 and alpha 2(I)-CB1, isolated from protocollagen following CNBr digestion and containing the N-terminal telopeptidyl lysyl residues, failed themselves to act as substrates. With protocollagen as substrate, analysis of products obtained following bacterial collagenase digestion of the reaction mixture showed that overall 37% hydroxylation of lysyl residues within the helical region of collagen had been obtained, which may be maximal. No hydroxylation, however, of the single lysyl residue in either alpha 1(I)-CB1 or alpha 2(I)-CB1, isolated following CNBr digestion of the reaction mixture, was observed, despite the known susceptibility of these residues to hydroxylation. These findings provide strong circumstantial evidence for the suggestion that a lysyl hydroxylase specific for the telopeptidyl residues and distinct from that active towards lysyl residues in the helical portion of the molecule may exist [Barnes, Constable, Morton & Royce (1974) Biochem. J. 139, 461-468].

Animals↗
PubMed1985

The platelet reactivity of the alpha 2(I)-chain of type I collagen: platelet aggregation induced by polymers of the molecule [alpha 2(I)]3.

Polymers of the collagenous species alpha 2(I) trimer, a molecule of which contains three alpha 2(I) chains derived from type I collagen, have been shown to induce the aggregation of platelets when tested at a temperature low enough to avoid loss of the tertiary structure of the molecule. Under these conditions, the alpha 2(I) chain appears to possess greater platelet reactivity than the corresponding type I collagen-derived alpha 1(I) chain. In contrast to previous reports of its lack of reactivity, our results indicate that the alpha 2(I) chain must contribute importantly to the overall platelet reactivity of collagen type I in vivo. Our findings furthermore support the concept that any collagen-like structure may be expected to interact with platelets provided due regard is given to tertiary and quaternary structural requirements.

Animals↗
PubMed1985

The platelet reactivity of collagen type VI.

Collagen type VI in native (undenatured or triple-helical) form has been shown, like collagen types I-V, alpha 1(I) trimer and alpha 2(I) trimer, to possess platelet reactivity provided that essential quaternary structural needs are first satisfied. Thus platelet aggregation was induced by the collagenous domain of collagen type VI, isolated free of the non-collagenous elements, when this entity was presented to platelets in fibrillar form. This implies that platelet recognition sites in collagen type VI are located in the collagenous sequence of the molecule. Aggregation of platelets was also induced, although a higher concentration was required, by the intact, "parent" collagen following its polymerisation by random association of molecules with the aid of a cross-linking agent (glutaraldehyde) to yield an amorphous polymer. This permits the suggestion that the more ordered molecular assembly of collagen type VI thought to occur in vivo, to yield a microfibrillar form, is likely to be associated with significant platelet reactivity. Our results support the notion that any collagenous species may be reactive towards platelets provided that essential tertiary and quaternary structural requirements are met and in this sense, therefore, they favour more the idea of multiple platelet-reactive sites in collagen of relatively low structural specificity and low affinity.

Animals↗
PubMed1984

Comparison of the collagenous products synthesized in culture by pig aortic endothelial and smooth-muscle cells. Variability in endothelial-cell cultures.

In contrast with smooth-muscle cells from the same tissue, endothelial cells from pig aorta were found to exhibit in culture considerable variability in the pattern of collagen synthesis between one isolation of cells and the next. Synthesis varied from largely collagen type I to virtually all type III in the absence of type I but with small amounts still of collagens types IV and V, to, in one instance, synthesis basically of only type V. Synthesis usually by these cells of collagen predominantly of the interstitial type (I and III) rather than, as might be expected, that from basement membrane (type IV) was not attributable to the influence of subculture. All four collagen types were deposited in the cell layer to an increased extent in primary compared with secondary cultures of either smooth muscle or endothelial origin. Endothelial cells appeared sometimes to synthesize a large-Mr collagenous entity that might conceivably be related to 'short-chain' collagen. In addition, small-Mr hydroxyproline-containing peptides were detected that might reflect rapid collagen(s) turnover in endothelial cultures.

Animals↗
PubMed1983

The interaction between collagens and factor VIII/von Willebrand factor: investigation of the structural requirements for interaction.

The blood protein Factor VIII/von Willebrand factor (FVIII/VWF) has been shown to bind to a variety of collagen polymers including (i), the native-type fibres (of collagens types I and III), (ii), segment-long-spacing (SLS) aggregates (of collagens types I, III, IV and V), (iii), the insoluble polymer obtained by random cross-linking of the type I monomer and (iv), the non-striated fibril (of type I) produced by alcohol precipitation. Relatively little binding of FVIII/VWF to the amorphous, non-fibrillar form of collagen (type I) produced by salt precipitation from acid solution was observed. No significant binding either to elastin or to the insoluble polymer derived by random cross-linking of bovine serum albumin was noted. The absorption of FVIII/VWF to collagens was affected by ionic concentration and FVIII/VWF was only totally bound at relatively low ionic strength. Binding of radiolabelled FVIII/VWF could be largely inhibited by an excess of the unlabelled protein. The interaction of FVIII/VWF with collagen fibres was inhibited in a concentration-dependent manner by monomeric collagen when present at relatively high concentrations. Gelatin did not appear to inhibit binding significantly. The structural requirements of collagen for binding to occur appear to resemble those required for collagen-induced platelet aggregation in which collagen quaternary structure rather than collagen type per se is the important factor. Loss of secondary or higher orders of structure of FVIII/VWF as a result of heat denaturation or reduction of disulphide bonds decreased or prevented binding. In accord with the association of biological activity with FVIII/VWF aggregates, optimal binding appeared to require the presence of aggregated FVIII/VWF.

Binding, Competitive↗
PubMed1983

Investigation of the attachment of bovine corneal endothelial cells to collagens and other components of the subendothelium. Role of fibronectin.

Bovine corneal endothelial cells adhered equally well to a variety of collagens (types I, III, IV and V) consistent with a role for fibronectin in this process. They did not exhibit a preferential binding to collagen type IV--as might be anticipated if laminin were to play a significant role in their adhesion. Inhibition studies with anti-fibronectin antibodies demonstrated the importance of endogenous fibronectin in the mediation of attachment. Consistent with this, binding did not appear to require the presence of exogenous protein, since cells bound to collagens equally well in the presence or absence of added fibronectin and binding was not stimulated by pretreatment of collagens with this protein.

Animals↗
PubMed1983

Analysis of the collagenous products synthesised in vitro by chick blood vessels: alterations during development and effects of serum on the pattern of synthesis.

Chick blood vessels synthesise in vitro collagens types I and III and, in much smaller amount, type V. In the presence of beta APN during synthesis, type I collagen is easily extracted whilst, in contrast, types III and V are insoluble and require the use of pepsin for their release into solution. The ratio of collagen type I to type III decreases during the course of development from around 9:1 in the young (11-day) embryo to a value approaching unity in the young chick. Type V collagen increases relative to the interstitial collagens. The synthesis of 'short-chain' and 'endothelial' collagens was not detected with certainty. Evidence for the possible synthesis of type IV and of additional, collagenase-sensitive, non-reducible, low-molecular weight species is presented. The presence of serum increased the proportion of collagen type I relative to that of type III. This appeared to be due in part to a direct stimulation of type I synthesis by serum but also in part to the replacement by serum of tissue 'factors' (or inhibitors of degradation) removed from the tissue during its preincubation with unlabelled medium.

Age Factors↗
PubMed1982

Collagen polymorphism in the normal and diseased blood vessel wall. Investigation of collagens types I, III and V.

Estimation of collagens types I and III in pepsin digests and by analysis of specific cyanogen-bromide derived peptides by SDS-polyacrylamide gel electrophoresis, has indicated that both the undiseased human aortic media and the atherosclerotic plaque of the diseased intima contain more type I collagen than type III. There was only a relatively small shift in composition in favour of type I collagen in the diseased compared to the undiseased tissue. Diffusely thickened intima was similar in composition to the atherosclerotic plaque. These results suggest that both atherogenesis and diffuse intimal thickening may involve primarily smooth muscle cell hyperplasia with increased overall collagen production but little alteration in cell phenotype as regards the relative proportions of the individual collagens produced. They do not support the contention that atherosclerosis involves a 'transformation' of smooth muscle cells to fibroblast in type, whereby a major switch in synthesis occurs from largely type III collagen to mainly type I in disease. Type V collagen(s) containing both alpha A- and alpha B-chains has been detected throughout the vessel wall in diffusely thickened intima, media and adventitia, as well as in the plaque where, in the latter case, a marked enrichment relative to interstitial collagens was noted. This is presumed to reflect the relatively cellular nature of the atherosclerotic lesion. The alpha C-chain of type V collagen was detected in porcine but not human aorta.

Adult↗
PubMed1981

Metalloproteinases from rabbit bone culture medium degrade types IV and V collagens, laminin and fibronectin.

Gel-filtration chromatography of culture medium from rabbit bone explants separates three latent metalloproteinases with activities against collagen, proteoglycan and gelatin respectively. The fractions degrading proteoglycan also degrade laminin, fibronectin and the polymeric products of pepsin-solubilized type IV collagen and can also solubilize insoluble type IV collagen. The fractions degrading gelatin are capable of degrading solubilized type V and 1 alpha,2 alpha,3 alpha (cartilage) collagens, as well as the lower-molecular-weight products of pepsin-solubilized type IV collagen. All activities can be inhibited by 1,10-phenanthroline and occur in either partially or totally latent forms that can be activated by 4-aminophenylmercuric acetate.

Animals↗