Collagens in atherosclerosis

Proteinases and restenosis in the human coronary artery: extracellular matrix production exceeds the expression of proteolytic activity

To understand the balance of proteinase antiproteinase activity and the production of extracellular matrix (ECM) at the site of arterial injury, we analyzed the composition of ECM and proteinase activity in normal internal mammary arteries, tissue samples obtained from atherosclerotic coronary lesions and restenotic lesions obtained during directional coronary atherectomy. Histologically and biochemically, collagen and proteoglycans increased, and elastin decreased in samples from restenotic lesions when compared to samples taken from patients undergoing their first revascularization (de novo). In contrast, cellularity was increased in samples obtained from de novo patients as compared to samples obtained from restenotic lesions. Intrinsic activity of matrix metalloproteinases (MMPs) was measured by using zymography and scanning all the lytic bands in zymographic gel. In these gels, identical amounts of total protein were loaded in each lane. MMP activity was determined as % of the total (latent and active) MMPs after trypsin activation (100%) in the normal artery. Intrinsic MMP activity was reduced to 6% +/- 1% in atherosclerotic lesions and 1% +/- 1% in restenotic lesions, when compared to activity found in normal (10% +/- 3%) arteries. Based on solubilization of fluorescein-conjugated elastin by the extracts, the MMP-mediated elastinolytic activity was 0.2 +/- 0.1, 8.8 +/- 1.5, and 24.0 +/- 3 nmol/min/mg in restenotic, native atherosclerotic and normal tissue, respectively. The results suggested that, in arterial tissue from patients with angiographic restenosis, there is an increased production of ECM collagen and a decrease in MMP activity compared to both normal artery and atherosclerotic samples from de novo patients undergoing an initial revascularization procedure of a significant coronary artery lesion.

Histomorphometric and biochemical correlates of arterial procollagen gene expression during vascular repair after experimental angioplasty

BACKGROUND

To determine the transcriptional, biochemical, and histomorphometric correlates of neointimal procollagen accumulation during arterial repair after balloon angioplasty of atherogenic vessels, rabbit iliac artery collagen content and the induction of alpha 1(I) and alpha 1(III) procollagen mRNA were assessed in normal vessels and at 2, 7, and 30 days after angioplasty.

METHODS AND RESULTS

Quantitative iliac artery histomorphometric neointimal collagen analysis was performed using a specific picrosirius red stain under polarized light. Arterial cross-sectional area reduction, total cellularity, and vascular smooth muscle cell density (per 10(4) mu2 of neointima) were quantified in routine and immunohistochemically stained sections (alpha-actin and RAM-11), from which biochemical concentrations of tissue protein, RNA, and DNA were also measured. Collagen comprised 0.23 +/- 0.1 mg/mg of total protein in the normal vessel wall and did not increase in vessels studied 2 and 7 days after angioplasty (0.26 +/- 0.06, 0.28 +/- 0.05 mg/mg of protein, P = NS). By 30 days after angioplasty, > 50% of the protein concentration was collagen (0.55 +/- 0.11 mg/mg of protein, P = .02). Collagen-positive histological staining also increased significantly from 17 +/- 2% of the neointima at day 2 to 32 +/- 5% by day 30 (P = .01). The transcript regulatory signal for alpha 1(I) procollagen mRNA was induced 2 days after angioplasty, peaking at 7 days for both alpha 1(I) and alpha 1(III), and returning to control levels 30 days after angioplasty. A significant luminal cross-sectional area reduction of the arterial wall was confirmed both by angiography and histomorphometry (P = .01). This was not associated with a significant change in alpha-actin (+) vascular smooth muscle cell density (38 +/- 7 nuclei per 10(4) mu2 at day 2 and at day 30) or tissue DNA concentration (P = NS).

CONCLUSIONS

We conclude that procollagen genes are transcriptionally activated early (2 to 7 days) after angioplasty vessel injury and that collagen subsequently constitutes a major biochemical and histological component of the proliferative neointima by 30 days after angioplasty. Alterations in pathways regulating procollagen metabolism may also contribute to the accumulation of extracellular matrix and growth of the neointima in the late repair phase after vessel wall injury.

Derivatized dextrans modulate collagen synthesis in aortic smooth muscle cells

The effect of specifically derivatized dextrans, with or without antiproliferative activity on smooth muscle cells (SMC), was investigated on type I and type III collagen biosynthesis and mRNA levels in post-confluent SMC cultures. Our results indicate that dextran derivatives decreased total protein and collagen synthesis independently of their antiproliferative activities. However, the most substituted dextran, the one exhibiting the strongest antiproliferative activity towards SMC, was the most active in modulating type III collagen expression. In addition, only the two dextran derivatives bearing benzylamide groups inhibited collagen excretion.

Comparative real-time effects on platelet adhesion and aggregation under flowing conditions of in vivo aspirin, heparin, and monoclonal antibody fragment against glycoprotein IIb-IIIa

BACKGROUND

A real-time in vitro system of human platelet thrombosis under arterylike flowing conditions similar to those produced in vivo by angioplasty would be useful for the evaluation of potential antiarterial thrombotic agents in association with in vivo trials. Aspirin, heparin, and the chimeric monoclonal antibody antigen-binding fragment 7E3 (c7E3 Fab) directed against platelet glycoprotein (GP) IIb-IIIa have been used in attempts to delay or prevent thrombotic reocclusion of coronary arteries after angioplasty. We compared the effects of these agents administered in vivo on GPIb-mediated platelet adhesion to von Willebrand factor (vWF)/collagen type I (as in atherosclerotic subendothelium) and on subsequent GPIIb-IIIa-fibrinogen/vWF-mediated platelet aggregation under flowing conditions analogous to those in constricted coronary arteries.

METHODS AND RESULTS

Citrated whole blood containing mepacrine-labeled platelets from patients and healthy donors was perfused for 1 minute at an abnormally elevated shear rate of 1500 seconds-1 (arterial wall shear stress of 50 to 60 dynes/cm2) at 37 degrees C over collagen I/vWF. The number of adherent fluorescent platelets was quantified every 15 seconds with a low-light-level video camera and epifluorescent microscopy. After 5 healthy donors had ingested 975 mg aspirin, platelet adhesion was unaffected in the aspirin-treated blood compared with the control blood in all experiments (10 of 10), and subsequent aggregation was unchanged in most runs (8 of 10). The blood of 3 aspirin-treated patients undergoing angioplasty was analyzed before and after a 12,000-U heparin injection and 2 minutes, 2 hours, and 24 hours after infusion of 0.25 mg/kg of c7E3 Fab. In these patients, the bolus of heparin did not inhibit either platelet adhesion to collagen I/vWF or subsequent aggregation. In contrast, there was > 50% inhibition of platelet aggregation 2 minutes after the infusion of c7E3 Fab in all 3 patients, and inhibition persisted in 2 of the 3 patients at 2 hours and 24 hours after c7E3 Fab.

CONCLUSIONS

In contrast to aspirin or heparin, the in vivo injection of c7E3 Fab considerably reduces platelet aggregate formation mediated by the binding of fibrinogen, vWF, or some other ligand to platelet GPIIb-IIIa under conditions of abnormally increased shear stress analogous to those in narrowed coronary arteries. Platelet adherence to collagen I/vWF is not affected. This study describes an in vitro model of arterial injury (similar to angioplasty) that uses human blood to compare directly, in real time, the precise relative effects of aspirin, heparin, and c7E3 Fab on platelet adhesion and subsequent aggregation.

Integrin alpha 2 beta 1-independent activation of platelets by simple collagen-like peptides: collagen tertiary (triple-helical) and quaternary (polymeric) structures are sufficient alone for alpha 2 beta 1-independent platelet reactivity

The platelet reactivities of two simple collagen-like synthetic peptides, Gly-Lys-Hyp-(Gly-Pro-Hyp)10-Gly-Lys-Hyp-Gly and Gly-Cys-Hyp-(Gly-Pro-Hyp)10-Gly-Cys-Hyp-Gly, were investigated. Both peptides adopted a stable triple-helical conformation in solution. Following cross-linking, both peptides proved to be highly platelet-aggregatory, more active than collagen fibres, inducing aggregation at concentrations as low as 20 ng/ml. These peptides formed microaggregates in solution, and cross-linking was thought to stabilize these structures, allowing expression of their platelet reactivity at 37 degrees C. Like collagen fibres, the peptides caused platelet secretion and release of arachidonate from platelet membrane lipids as well as activation of integrin alpha IIb beta 3 culminating in aggregation. Monoclonal antibodies directed against the integrin alpha 2 beta 1 failed to prevent aggregation release of arachidonate or platelet adhesion to the peptides. Our results indicate that collagen can activate platelets by a mechanism that is independent of integrin alpha 2 beta 1 and for which collagen tertiary and quaternary structures are sufficient alone for activity without the involvement of highly specific cell-recognition sequences.

Identification of the characteristic vascular changes in a sural nerve biopsy of a case with cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL)

Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy' (CADASIL) has recently been identified as a hereditary disorder with characteristic fine structural changes of small intracerebral arteries and arterioles. Electron microscopically there are characteristic perivascular deposits of granular electron-dense material resembling immunoglobulin deposits. The present case from a family with four affected members in three successive generations shows that similar vascular changes as described in the central nervous system are present in blood vessels of the sural nerve, although less pronounced and, therefore, affording electron microscopy for their unequivocal detection. Nevertheless it has been shown for the first time that the diagnosis of CADASIL can be verified by a sural nerve biopsy. Occasional focal accumulation of pinocytotic vesicles opposite the granular deposits suggests exocytosis as one of the possible pathomechanisms for their production.

Quantitation of the crosslinks, pyridinoline, deoxypyridinoline and pentosidine, in human aorta with dystrophic calcification

Pyridinoline and, its minor analogue deoxypyridinoline, are trifunctional crosslinks of mature collagen in the connective tissues. Pentosidine, a new type of fluorescent crosslink, is possibly one of the senescent crosslinks but its function and metabolism are still unclear. In this study, we quantitated the crosslinks, pyridinoline, deoxypyridinoline and pentosidine, in human aorta which were obtained from 21 autopsy cases. In each case, the existence of dystrophic calcification in the aorta and complications (diabetes, chronic renal failure and hypertension) were examined. The determination of the content of the three crosslinks was carried out using high performance liquid chromatography (HPLC) analysis. In calcified lesions, the amount of deoxypyridinoline/collagen showed a decrease and the amount of deoxypyridinoline/pyridinoline showed a prominent decrease compared to those in non-calcified lesions (deoxypyridinoline/collagen, P < 0.005; deoxypyridinoline/pyridinoline, P < 0.0001). In non-calcified lesions without complications, the amount of pentosidine/pyridinoline and that of pentosidine/deoxypyridinoline significantly increased with age (pentosidine/pyridinoline, r = 0.704, P < 0.05; pentosidine/deoxypyridinoline, r = 0.624, P < 0.05). This result suggests a possible relationship between dystrophic calcification and crosslink formation of collagen in human aorta.

Interleukin-1 beta induces differential gene expression in aortic smooth muscle cells

PURPOSE

Abdominal aortic aneurysms are characterized by an accelerated turnover of extracellular matrix proteins and by an inflammatory infiltrate that releases the cytokines interleukin-1 beta and tumor necrosis factor-alpha. We examined the gene expression of human aneurysmal aortic smooth muscle cells and normal aortic smooth muscle cells after treatment with interleukin-1 beta and tumor necrosis factor-alpha by measuring the changes in smooth muscle cell collagen, elastin, collagenase, and tissue inhibitor of metalloproteinase messenger ribonucleic acid levels in response to these cytokines.

METHODS

Biopsy of aneurysmal aorta (n = 6) and donor normal aorta (n = 3) was obtained at operation. Medial smooth muscle cells were cultured, passaged (P2 to P4), and incubated with 0, 10, 100, or 1000 pg/ml interleukin-1 beta, tumor necrosis factor-alpha, or platelet-derived growth factor for 24 hours. Total ribonucleic acid was harvested. Percentage changes in messenger ribonucleic acid from control levels for type I and type III procollagen, elastin, collagenase, 72 kDa type IV collagenase, tissue inhibitor of metalloproteinase-1, and tissue inhibitor of metalloproteinase-2 were measured by Northern hybridization. Analyses were performed with analysis of variance (p < 0.05). All comparisons between aneurysmal aortic smooth muscle cells and normal aortic smooth muscle cells represent comparisons between one aneurysmal aorta and one normal aorta.

RESULTS

Added interleukin-1 beta resulted in significant, dose-dependent increases in the collagenase messenger ribonucleic acid level at all concentrations tested in both aneurysmal aorta and normal aorta. The increase in the collagenase messenger ribonucleic acid level ranged from a minimum increase of 123% for 10 pg/ml interleukin-1 beta in aneurysmal aortic smooth muscle cells to a maximum of 450% for 1000 pg/ml interleukin-1 beta in normal aortic smooth muscle cells. Interleukin-1 beta caused a significant decrease in the steady-state messenger ribonucleic acid levels for type 1 procollagen in both aneurysmal and normal aorta. The greatest reduction in type 1 procollagen messenger ribonucleic acid levels occurred at 100 pg/ml interleukin-1 beta in both aneurysmal aortic smooth muscle cells (-39%) and normal aortic smooth muscle cells (-48%). The only observed qualitative difference between aneurysmal aortic smooth muscle cells and normal aortic smooth muscle cells was the change in tissue inhibitor of metalloproteinase-1 messenger ribonucleic acid levels in response to added interleukin-1 beta. In aneurysmal aortic smooth muscle cells interleukin-1 beta at 1000 pg/ml significantly increased messenger ribonucleic acid levels by 82%, whereas levels of tissue inhibitor of metalloproteinase-1 messenger ribonucleic acid in normal aortic smooth muscle cells did not change in response to added interleukin-1 beta. Interleukin-1 beta did not alter messenger ribonucleic acid levels for type III procollagen, elastin, type IV collagenase, or tissue inhibitor of metalloproteinase-2 in aneurysmal aorta or normal aorta. When tumor necrosis factor-alpha or platelet-derived growth factor were added, this did not significantly change aneurysmal aortic smooth muscle cells messenger ribonucleic acid levels for collagenase, type IV collagenase, tissue inhibitor of metalloproteinase-1, tissue inhibitor of metalloproteinase-2, and type I and type III procollagen.

CONCLUSIONS

These findings suggest that interleukin-1 beta, through its effect on smooth muscle cell collagenase and collagen gene expression, mediates the increased matrix turnover observed in aneurysms. Macrophages may induce changes in aortic smooth muscle cell gene expression in a paracrine manner that could lead to aneurysm formation.

The perivascular connective matrix

The functional properties of the perivascular matrix facilitate the movement, protection and the nutrition of the blood vessels. At the same time the matrix deliniates the vessels to the organs. Different vascular diseases of the vascular system implicate the perivascular matrix consisting of a network of structural and cellular connective tissue components. Impairment of its structural integrity predominantly occurs either from primary or secondary affections. Monospecific antibodies directed against different structural proteins enable detailed histomorphological examinations of the inflammatory tissue reaction in the perivascular space. Since myofibroblasts, fibrocytes, endothelial cells, and macrophages participate in tissue repair mechanisms, in vitro studies on the collagen synthesis may contribute to the understanding of the perivascular tissue reaction according to injury. The present report summarizes perivascular diseases and the in vitro synthesis of procollagen, collagen, and fibronectin of endothelial cells, fibroblasts, smooth muscle cells, and macrophages.

Abdominal aortic aneurysms are associated with altered matrix proteins of the nonaneurysmal aortic segments

PURPOSE

Abdominal aortic aneurysms (AAA) are associated with diffuse arteriomegaly and peripheral aneurysms, suggesting a generalized process. Elastin and collagen are the key structural proteins of the aorta, and their relative content is markedly altered in tissue from AAA. Our purpose was to investigate elastin and collagen content in the proximal, nonaneurysmal segments of aortas with infrarenal AAA.

METHODS

After extraction of lipid, calcium, and soluble proteins, hydroxyproline (collagen) and desmosine-isodesmosine (elastin) contents were determined by high-performance liquid chromatography in the ascending and descending thoracic, supraceliac, and suprarenal aorta. By repeated measures of analysis of covariance, collagen was found to be increased throughout the aorta in AAA as compared with normal aorta or aorta with atherosclerotic occlusive disease. This difference remained significant when adjustments were made for group differences in age and degree of atherosclerosis. This increase in collagen content results in a dilutional decrease in elastin concentration. These data demonstrate that the same matrix protein alterations found in AAA tissue occur throughout the aorta, differing only in magnitude in the aneurysmal and nonaneurysmal segments. These data suggest that aneurysm formation may related to alterations in the regulation of elastin and collagen.

Serum levels of type III procollagen peptide and peripheral vascular disease in diabetic patients

The aim of this study was to assess the possible relationship between serum levels of Type III procollagen peptide (PIIINP) and peripheral vascular disease (PVD) in diabetic patients. Ninety Type 2 diabetic patients being treated with sulfonylureas, and 37 non-diabetic subjects were studied using Doppler ultrasound. After an overnight fast, blood was taken for PIIINP, glucose, glucosylated hemoglobin (HbA1), C-peptide, and lipids. Data were analysed according to the non-paired Student's t-test and the correlation coefficient, after log transformation. PIIINP levels were significantly elevated in diabetics with PVD (n = 44), 4.3 micrograms/l (2.4-7.6, 95% confidence limits) compared with controls 3.1 micrograms/l (1.9-4.9), P < 0.001, and with diabetics without PVD (n = 46), 3.1 micrograms/l (1.9-5.0), P < 0.001. No correlation was found between PIIINP and HbA1, glucose, C-peptide, age or duration of diabetes. We conclude that PIIINP levels are elevated in Type 2 diabetics with PVD. It may reflect an increase in collagen deposition in the large arteries that accompanies the development of macroangiopathy.

The microvascular changes in cases of hereditary multi-infarct disease of the brain

A report on a cerebro-vascular disease with autosomal dominant inheritance, characterised by stroke-like episodes beginning in early adulthood and progressive dementia, afflicting one family living in Sweden was presented in 1977. Another afflicted member showing gait and coordination disturbances and impaired cognitive functions is now introduced. Magnetic resonance imaging revealed multiple brain lesions indicating ischaemic injuries. Previous autopsy studies of other cases revealed white matter atrophy, multiple infarcts and lacunes. In one patient who had died from a cerebral haemorrhage, obliteration of intracerebral arteries, occasionally with organised thrombi was present. Autopsy material has now been reinvestigated with special attention to changes of intracerebral arterioles. Cases with long duration of the disease presented pronounced fibrous thickening of the wall of numerous intracerebral arterioles, degeneration of smooth muscle cells of the media and obliteration of the lumen. Immunohistochemistry showed marked expression of fibrillary collagen types I, III and V and of the basal lamina components collagen type IV and laminin. These depositions are probably induced by some primary dysfunction of smooth muscle cells or endothelial cells. Perivascular reactive astrocytes with endothelin-1-like immunoreactivity were present in some brain regions. Endothelin-1 is the most powerful vasoconstrictor peptide known to date. Structural remodelling of intracerebral arterial vessels, actions of different vasoactive factors and rheological disturbances may all interfere with local blood flow in this disease and cause the parenchymal changes of the brain.

A disorder of collagen biosynthesis in patients with cerebral artery aneurysm

12 patients with subarachnoid hemorrhage due to rupture of a cerebral aneurysm were examined clinically for symptoms and signs of a connective tissue disorder and biochemically for details of the biosynthesis of collagen. No uniform clinical pattern of any connective tissue disorder was seen in these patients, although selected signs were observed. Skin fibroblast cultures were then established. The rate of procollagen production in two cell lines was reduced by 40% and 50%, respectively, and the intracellular accumulation of hydroxy[14C]proline (as a percentage of total hydroxy[14C]proline) was increased by 70% in each relative to eight control cell lines. No difference was found in the degree of intracellular degradation of procollagen. After pulse-labelling, however, the radioactive procollagen was secreted into the medium in 1 h in the control cells, but required at least 3 h in the two aneurysm patient cell lines. The results, thus, suggest that delayed secretion of procollagen rather than increased intracellular degradation led to the reduction in the rate of procollagen synthesis in these two fibroblast lines from patients with cerebral artery aneurysm.

Aortic smooth muscle cells in a three-dimensional collagen lattice culture. Evidence for posttranslational regulation of collagen synthesis

Aortic smooth muscle cells were cultivated as monolayers on plastic or within collagen lattices with low- and high-serum supplementation, and the expression of mRNAs specific for pro alpha 1 (I) and pro alpha 1 (III) collagen were studied by slot blot hybridization. The steady-state levels of pro alpha 1 (I) and pro alpha 1 (III) collagen mRNA of cells within collagen lattices were found to be higher than those grown on plastic, although the production of collagen was lower. The degradation of pro alpha 1 (I) and pro alpha 1 (III) collagen mRNAs as revealed in the presence of actinomycin D was not affected by culturing the cells within a collagen lattice. In vitro translation assays of mRNAs of monolayer- and lattice-cultured cells showed no differences in translatability. These data suggest the involvement of posttranslational control of collagen production in collagen lattice-cultured smooth muscle cells.

Responsiveness of aortic smooth muscle cells to soluble growth mediators is influenced by cell-matrix contact

Excessive proliferation and overexpression of collagens by smooth muscle cells (SMCs) are important features of atherogenesis. To understand the role of the extracellular matrix in the regulation of these processes, we examined proliferation and protein/collagen synthesis of SMCs in contact with a collagen matrix. Adult pig SMCs were isolated from the aortic media by collagenase digestion, subcultured as monolayers, and then embedded into a three-dimensional network of type I collagen, ie, a collagen lattice. Cells were subsequently exposed to growth-promoting media, and their behavior was observed in comparison with monolayer cultures on plastic. Treatment of monolayers with increasing concentrations of fetal calf serum resulted in activation of the cell cycle, onset of cell proliferation, and increased protein/collagen synthesis. In contrast, similar treatment of collagen lattice-cultured SMCs failed to influence cell proliferation and protein/collagen synthesis. However, stimulation of proliferation of lattice-cultured SMCs by platelet-derived growth factor-A/B was feasible; nevertheless, the rate of proliferation was modest compared with monolayers. In addition, the onset of proliferation was accompanied by a decrease in collagen synthesis of the cells. Thus, a collagenous matrix appears to suppress the responsiveness of SMCs to soluble growth mediators. It is speculated that interactions between SMCs and the extracellular matrix may modify proliferation and protein/collagen synthesis of cells not only in vitro but also in vivo during atherogenesis by making and breaking binding sites between extracellular collagen and matrix receptors.

Collagen synthesis of human arterial smooth muscle cells: effects of platelet-derived growth factor, transforming growth factor-beta 1 and interleukin-1

The effects of platelet-derived growth factor (PDGF), transforming growth factor-beta 1 (TGF-beta 1) and interleukin-1 (IL-1) on collagen synthesis of cultured human arterial smooth muscle cells in a confluent state were investigated. Synthetic activity of collagenous protein was determined with [3H]-proline uptake, and subsequent analysis of collagen types by sodium dodecylsulfate-polyacrylamide gel electrophoresis (SDS-PAGE) followed by fluorography. Although PDGF (0.5 U/mL and 5.0 U/mL) enhanced total collagen synthesis per dish, it suppressed total collagen synthesis per DNA (DNA content in a dish). TGF-beta 1 (10 pmol/L and 100 pmol/L) enhanced total collagen synthesis both per dish and per DNA. IL-1 (0.1 U/mL and 1.0 U/mL) suppressed total collagen synthesis both per dish and per DNA. A fluorogram revealed that human arterial smooth muscle cells synthesize types I, III, IV and V collagen. Densitometric analysis showed PDGF suppressed the proportion of type IV collagen and increased that of type V collagen. TGF-beta 1 increased the proportions of types IV and V collagen. IL-1 elicited un- remarkable change in the proportion of collagen types. These results suggest that, in the event of human atherosclerosis, TGS-beta 1 is most effective in enhancing collagen synthesis, and PDGF modulates collagen metabolism by stimulating a cell division of smooth muscle cells with a resultant increase of collagenous protein, especially of type V collagen.

Type III collagen content in the skin of postmenopausal women receiving oestradiol and testosterone implants

OBJECTIVE

To investigate the effect of subcutaneous oestradiol and testosterone on the proportion of type III collagen in the skin of postmenopausal women.

DESIGN

A cross sectional comparison.

SETTING

Dulwich Hospital menopause clinic.

SUBJECTS

Fourteen untreated women and 11 women who had received subcutaneous oestradiol and testosterone for a median 8.0 years (range 3-14). Ten of the untreated women received subcutaneous hormone implants and the effect on skin collagen was studied prospectively.

MEASUREMENTS

The proportion of type III collagen in skin biopsies taken from the lateral aspect of the thigh.

RESULTS

The median type III collagen content in the skin of the women who had received hormone replacement therapy (25.4%, range 21.4-30.2) was significantly higher (P < 0.01) than in the untreated women (19.6%, range 18.2-28.8). The proportion of type III collagen in the skin of 10 untreated women increased significantly (P < 0.01) from a median of 19.9% (range 18.2-23.9) to 22.4% (range 20.5-31.5) following 6 months of treatment with hormone implants.

CONCLUSION

This study indicates an increase in the proportion of type III collagen in women receiving hormone replacement therapy.

Type IV collagen synthesis and accumulation in neonatal rat aortic smooth muscle cell cultures

The production of type IV collagen by cultured neonatal rat aortic smooth muscle cells was monitored over a three-week period to further characterize the extracellular matrix of this unique culture system. Type IV collagen was quantified using a dot immunobinding assay and was found to represent 1% or less of the total collagen produced by these cells in culture. Total collagen represented up to 33% of the total protein. The pattern of type IV collagen production in the media and the cell layer suggests that although these cells synthesize and secrete type IV collagen from the onset of culture, type IV collagen deposition only occurs after the cells have reached confluence. In the presence of ascorbate the amount of type IV collagen peaked in the media in preconfluent cultures. In the absence of ascorbate, little type IV collagen was detected in the media. On the other hand, the presence or absence of ascorbate made little difference in the amount of the total collagen detected in the media, although hydroxylation was affected. Remarkably, in the absence of ascorbate type IV collagen accumulation in the cell layer was similar by the end of the culture period to that in cultures treated with ascorbate. Laminin was not affected by the presence or absence of ascorbate. When these cells were exposed to ascorbate for 24 hours, a peak of soluble elastin was detected in the media. However, soluble elastin was not detected in the media in the absence of ascorbate or in cultures which were maintained in the presence of ascorbate. Modulation of the extracellular matrix with ascorbic acid indicated that type IV collagen deposition did not depend on the presence of ascorbic acid and that there was no discernable interaction between type IV collagen, laminin, and elastin.

Effect of insulin on serum amino-terminal propeptide of type III procollagen in non-insulin-dependent diabetes mellitus

The effect of insulin on the serum levels of the amino-terminal propeptide of type III procollagen (PIIINP) was investigated in patients with non-insulin-dependent diabetes mellitus, whose disease was unsatisfactorily controlled by oral drugs. Before insulin therapy the PIIINP values of the patients (3.2 +/- 1.3 micrograms/l, n = 38) varied within the range of healthy subjects (3.1 +/- 0.6 micrograms/l, n = 50, NS). Insulin therapy (6-20 IU at bedtime plus the oral drugs) improved the glycemic control and increased the serum PIIINP during a 4 week (3.1 +/- 0.9 to 3.8 +/- 1.1 micrograms/l, P less than 0.01, n = 8) and an 8 week period (3.2 +/- 1.3 to 3.8 +/- 1.6 micrograms/l, P less than 0.001, n = 22). The values were still elevated after 6 months on insulin (3.5 +/- 1.5 to 4.0 +/- 1.7 micrograms/l, P less than 0.01, n = 12). Placebo-insulin did not alter the concentration of PIIINP (3.1 +/- 0.6 to 2.8 +/- 0.6 micrograms/l, NS, n = 8) whereas the glycemic control improved and body weight decreased. The PIIINP values correlated with fasting insulin before (r = 0.403, P less than 0.05, n = 30) and after the therapy (r = 0.452, P less than 0.001, n = 60). Insulin therapy, while correcting the hormone deficiency and restoring glucose and protein metabolism, seems to activate the synthesis of type III procollagen in patients with NIDDM. This may promote the atherosclerotic process.

Collagen types I and III, collagen content, GAGs and mechanical strength of human atherosclerotic plaque caps: span-wise variations

Measurements of total collagen, of the ratio of collagen types III/(I+III) and of sulphated glycosaminoglycans (GAGs) were compared with mechanical strength for individual ulcerated and non-ulcerated human aortic plaque caps and with intima adjacent to the plaques. The distributions of the collagen type ratio were similar for both ulcerated and non-ulcerated plaque caps but different from that of the adjacent intima. The proportions of different collagen types were not related to fracture stress and are thus unlikely to affect the potential to ulcerate. The distributions of the sulphated GAGs showed lower amounts for the plaque caps compared with the nearby intima, with the centres of ulcerated plaque caps having the lowest values. Total collagen had higher values in the peripheries of plaque caps compared with the nearby intima, but was distinctly lower in the centres of ulcerated plaque caps. Plaque caps appeared to require a higher collagen content than adjacent intima to support a given level of mechanical strength, suggesting that while collagen production had occurred in the plaque caps it was not as efficiently organized to resist fracture as a similar amount of collagen in the adjacent intima. Ulcerated plaque caps are notable for much larger transverse (centre vs. periphery) gradients of connective tissue constituents than for non-ulcerated plaque caps. The development of these transverse gradients may be a critical aspect in determining the propensity of a plaque to ulcerate.

Disassembly of F-actin filaments in human endothelial cells cultured on type V collagen

We examined the inhibitory activity of type V collagen on cell attachment and cell growth and the role of stress fibers and beta 1 integrin in cultured human endothelial cells. Human endothelial cells cultured on type V collagen attached temporarily to the substrate and formed stress fibers. However, the cells failed to proliferate and gradually detached from the substrate. After 24 h, the cells on type V collagen lacked discernible stress fibers (F-actin filaments) and exhibited dots in small aggregates of F-actin. In addition, the cells expressed little or no proteins as focal adhesions, including vinculin and beta 1 integrin. In contrast, the cells on fibronectin and type I collagen formed complete F-actin filaments, exhibited sufficient vinculin and beta 1 integrin, and grew logarithmically from 2 days. On the other hand, human smooth muscle cells formed complete F-actin filaments, revealed typical focal adhesions, and started to proliferate rapidly after 24 h on type V collagen as well as on fibronectin and type I collagen. Thus, the disassembly of F-actin filaments was observed as a specific phenomenon in human endothelial cells cultured on type V collagen. Moreover, the F-actin filaments disappeared from endothelial cells treated with cytochalasin D after 24 h and the cells detached from fibronectin and type I collagen with time, a result consistent with the observations on type V collagen. Accordingly, the disassembly of F-actin filaments in focal adhesions may result in the detachment of endothelial cells from type V collagen.

Cell density and proliferation modulate collagen synthesis and procollagen mRNA levels in arterial smooth muscle cells

Collagen synthesis and procollagen mRNA levels were determined and compared in (1) sparse, rapidly proliferating smooth muscle cells (SMC); (2) postconfluent, density-arrested SMC; and (3) sparse, nonproliferating (mitogen-deprived) rabbit arterial SMC. Collagen synthesis per SMC was decreased by 70% in postconfluent versus proliferating cells. However, relative collagen synthesis, expressed as the percentage of total protein synthesis, increased from 3.7% in sparse cultures to approximately 7% in postconfluent cultures. Slot blot analyses demonstrated that the relative steady state alpha 1(I) and alpha 1(III) procollagen mRNA levels were also increased in postconfluent cultures when compared to sparse cultures. As with collagen synthesis per cell, the mRNA levels per cell for types I and III procollagen in postconfluent cells, determined by densitometry of blots, were likewise approximately half that found in sparse, proliferating cells. In a separate study to determine if cell-cell contact was necessary for eliciting these changes in collagen synthesis, we determined collagen synthesis in mitogen-deprived and proliferating SMC cultures at low density. Mitogen-deprived cultures synthesized only 10% the amount of collagen produced (per cell) by proliferating cultures in 10% fetal bovine serum. Relative collagen synthesis in proliferating and nonproliferating cultures was 5.0 and 8.3%, respectively. These results demonstrate elevated collagen synthesis, per cell, by proliferating cultures compared with nonproliferating cultures, regardless of whether cells were rendered quiescent by density arrest or by mitogen deprivation. Results also suggest a pretranslational mechanism for the regulation of collagen synthesis in rabbit aortic smooth muscle cells.

In situ optical histochemistry of human artery using near infrared Fourier transform Raman spectroscopy

In this paper we demonstrate that near infrared Fourier transform Raman spectroscopy provides unprecedented biochemical information about the extent of atherosclerosis in human aorta. In particular, elastin, collagen, cholesterol, cholesterol esters, lipids, carotenoids, and calcium apatite deposits all can be discerned by using this technique, permitting study of each stage in the disease process. Additionally, these moieties can be detected over 1.5 mm below the irradiated surface of the tissue, possibly allowing extraction of three-dimensional information about the histology of atherosclerotic plaques. We propose that this technique may be utilized for in situ optical histochemical analysis of atherosclerosis in particular and human disease in general.

Collagens in human atherosclerosis. Immunohistochemical analysis using collagen type-specific antibodies

This study represents a systematic analysis of the distribution of collagen types in human atherosclerotic lesions. Formalin-fixed, paraffin-embedded aortic tissues of 40 lesions from 16 different individuals ranging in age from 1 month to 84 years were examined immunohistochemically using antibodies to type I, III, IV, V, and VI collagens. Preembedding immunoelectron microscopy was used to simultaneously localize type V and VI collagens within the lesions. Localization of type III collagen was very similar to that of type I, and type VI collagen appeared together with these two types of collagen in the thickened intimas of all stages of the lesion. Type V collagen was not detected in either fatty streaks or the mild intimal thickening of the aortas of children. With advancing age and lesion progression, the immunoreactivity with anti-type V collagen antibody became more intense. Type IV collagen was detected in the basement membrane region of intimal cells. In advanced lesions thick deposits of type IV collagen were found around the elongated smooth muscle cells. Using immunoelectron microscopy, type V collagen was found to be localized to cross-banded collagen fibers, and type VI collagen was found to be localized to beaded filaments present throughout the interstitium of the thickened intima. These findings suggest that collagens preserve the pathophysiological and functional integrity of the vascular wall by providing mechanical support as well as assuring the proper interaction of cells during the formation of atherosclerotic lesions.

Type V collagen represses the attachment, spread, and growth of porcine vascular smooth muscle cells in vitro

We attempted to clarify the effects of various purified extracellular components, including types I, III, IV, and V collagen and fibronectin on attachment, spread, growth, and DNA synthesis of porcine aortic smooth muscle cells (SMCs) in vitro. The number, area and shape index (SI = 4 pi S/L2) of cells attached to different substrates were determined at various intervals of incubation. The cell number and [3H]thymidine incorporation into DNA were measured on the 1st and 6th days of culture. SMCs showed the largest number of attached cells on fibronectin, but the smallest number of attached cells on type V collagen. There was no evidence of effects of the serum in media on the attachment of SMCs to the substrates. The areas of attached SMCs were the largest on fibronectin and the smallest on type V collagen. The shape index of SMCs on fibronectin decreased relative to those on other substrates. On the 6th day in culture, the number and population doubling of SMCs on type V collagen were significantly fewer than those on other substrates. Both the incorporation rate of [3H]thymidine into DNA and the percentage of nuclei labeled with [3H]thymidine were significantly less in the SMCs on type V collagen on the 1st day than those on other substrates. SMCs on types I, III, and IV collagen showed intermediate levels of cell attachment, spread, and growth. These results suggest that attachment, spread, and growth of SMCs are affected mainly by solid phase purified extracellular components and are most strongly suppressed by type V collagen. When DNA synthesis of growth-arrested SMCs was reinitiated by the addition of serum, type V collagen most intensively inhibited the rate and amount of [3H]thymidine incorporation. Flow cytometric analysis demonstrated an increased in the proportion of cells in G0/G1 phase on type V collagen in comparison with that on other substrates. Thus, the antiproliferative effect of type V collagen may relate to inhibition of transition of SMCs from the G0/G1 into the S phase.

Collagen synthesis in cultured aortic smooth muscle cells. Modulation by collagen lattice culture, transforming growth factor-beta 1, and epidermal growth factor

We investigated the effects of transforming growth factor-beta 1 (TGF-beta 1) and epidermal growth factor (EGF) on the protein synthesis and production of collagen in cultured smooth muscle cells (SMCs) from the aortic media of pigs. SMCs were cultured as monolayers on plastic as well as in three-dimensional collagen lattices to gain some information about the influence of a preexisting collagenous matrix on the growth factor-induced effects. A 48-hour exposure of SMCs to TGF-beta 1 at concentrations of 5 ng/ml in the presence of 1% serum caused a marked enhancement of the production of collagen and noncollagen proteins. The rate of net collagen production by SMCs exposed to TGF-beta 1 was approximately threefold higher than that of control cells. Moreover, TGF-beta 1 specifically stimulated collagen synthesis, resulting in a greater proportion of collagen in total proteins synthesized compared with controls. The preexisting matrix of collagen lattices affects the response of SMCs to TGF-beta 1 and EGF. In monolayer cultures the collagen proportion increased twofold under the influence of TGF-beta 1, whereas in collagen lattices the specific stimulation of collagen synthesis was lower. We found that EGF enhanced TGF-beta 1-induced protein production in collagen lattices but not in monolayer cultures. In addition, the protein production by SMCs was influenced differently by EGF in these culture systems. Taken together, these data show a mutual influence of growth factors and extracellular matrix components on collagen production in SMCs, thus indicating that TGF-beta 1 may be an important pathophysiological regulator of collagen metabolism in the vessel wall.

Salt-soluble collagen and elastin in the human aorta and pulmonary artery

Collagen and elastin, the major structural components of blood vessels, have a very low turnover. In disease, this rate may be increased and an elevation of the tissue concentration of the soluble degradation fragments might be anticipated. In this preliminary study the concentration of extractable collagen and elastin in the aorta and pulmonary artery of eight human subjects postmortem was determined. The proportion of pulmonary artery collagen and elastin that was soluble was generally either equal to or greater than that in the abdominal aorta. The fraction of collagen that was salt extractable was larger than the soluble elastin fraction.

d-alpha-tocopherol inhibits collagen alpha 1(I) gene expression in cultured human fibroblasts. Modulation of constitutive collagen gene expression by lipid peroxidation

Ascorbic acid stimulates collagen gene transcription in cultured fibroblasts, and this effect is mediated through the induction of lipid peroxidation by ascorbic acid. Quiescent cultured fibroblasts in the absence of ascorbic acid have a high constitutive level of collagen production, but the mechanisms of collagen gene regulation in this unstimulated state are not known. Because lipid peroxidation also occurs in normal cells, we wondered if lipid peroxidation plays a role in the regulation of basal collagen gene expression. Inhibition of lipid peroxidation in cultured human fibroblasts with d-alpha-tocopherol or methylene blue decreased the synthesis of collagen, the steady-state levels of procollagen alpha 1(I) mRNA and the transcription of the procollagen alpha 1(I) gene. This effect on collagen gene expression was selective and not associated with cellular toxicity. Thus, these experiments suggest a role for lipid peroxidation in the modulation of constitutive collagen gene expression.

Age-related changes in collagen synthesis and degradation in rat tissues. Importance of degradation of newly synthesized collagen in regulating collagen production

During developmental growth, collagens are believed to be continuously deposited into an extracellular matrix which is increasingly stabilized by the formation of covalent cross-links throughout life. However, the age-related changes in rates of synthetic and degradative processes are less well understood. In the present study we measured rates of collagen synthesis in vivo using a flooding dose of unlabelled proline given with [14C]proline and determining production of hydroxy[14C]proline. Degradation of newly synthesized collagen was estimated from the amount of free hydroxy [14C]proline in tissues 30 min after injection. Collagen fractional synthesis rates ranged from about 5%/day in skeletal muscle to 20%/day in hearts of rats aged 1 month. At 15 months of age, collagen fractional synthesis rates had decreased markedly in lung and skin, but in skeletal muscle and heart, rates were unchanged. At 24 months of age, synthesis rates had decreased by at least 10-fold in all tissues, compared with rates at 1 month. The proportion of newly synthesized collagen degraded ranged from 6.4 +/- 0.4% in skin to 61.6 +/- 5.0% in heart at 1 month of age. During aging the proportion degraded increased in all tissues to maximal values at 15 months, ranging from 56 +/- 7% in skin to 96 +/- 1% in heart. These data suggest that there are marked age-related changes in rates of collagen metabolism. They also indicate that synthesis is active even in old animals, where the bulk of collagens produced are destined to be degraded.

Medial collagen organization in human arteries of the heart and brain by polarized light microscopy

The mechanical properties of collagen as a biopolymer ensures that collagen has a significant influence on the mechanical behavior of the host tissue. Structural organization is a key to that influence. We have assessed this relationship quantitatively in the tunica media of arteries from the heart and brain, using the polarizing light microscope and Universal stage. Arteries from 22 autopsies were isolated, cannulated and fixed with 10% buffered formalin, at a distending pressure spanning normal values in vivo. We prepared the tissue for light microscopy, with paraffin embedding, sectioning at 7 microns, and staining with picrosirius red to enhance the natural birefringence of medial collagen. Individual measurements, 30 to 50 per arterial section, referenced against the central axis of the vessel segment, revealed a coherent organization, with an average orientation which was within 1 to 2 degrees of being perfectly concentric for all artery segments. Analysis was done with Lambert projections and circular statistics. We calculated the circular standard deviation, which was 5.2 degrees for 27 brain arteries (S.D. 1.9 degrees) and 5.6 degrees (S.D. 2.1 degrees), for 5 coronary arteries sectioned at less than 15 degrees. Our interpretation is that medial collagen can be strained even though highly aligned, revealing a mechanical property which contrasts that of type I collagen.

Joint occurrence of collagen mRNA containing cells and macrophages in human atherosclerotic vessels

Cells with enhanced levels of collagen type I and III mRNA were identified and localized in frozen tissue sections from samples of human atherosclerotic renal and common iliac arteries by in situ hybridization using complementary 35S-labeled RNA probes. Serial sections were immunohistochemically stained for smooth muscle cells, monocytes, and differentiated macrophages. In the fibromuscular intima and in the fibrous plaques, cells with enhanced transcriptional activity were located mainly in the vicinity of differentiated macrophages. In three patients, lack of enhanced transcriptional activity in a proliferated intima was connected with complete absence of macrophages, thus indicating a quiescent stage of atherosclerosis. Immunohistochemical staining of serial sections for smooth muscle cells (SMC) revealed the presence of this cell type throughout the proliferated intima in atherosclerotic arteries including those areas in which enhanced collagen mRNAs were detected. The present results support the idea that macrophages play an important role in the activation of collagen synthesis in SMC of atherosclerotic vessel walls.

Determinants of smooth muscle injury during balloon angioplasty

To study the determinants of smooth muscle injury during balloon angioplasty, we conducted a series of experiments to examine the effects of degree of arterial stretching, duration of balloon inflation, and arterial precontraction on smooth muscle injury after balloon angioplasty in isolated, perfused whole-vessel segments of rabbit aortas and dog carotid arteries. Freshly dissected rabbit thoracic aortas and dog carotid arteries were mounted in a muscle bath-perfusion chamber and perfused at 80 mm Hg. The proximal half of each aorta was dilated with a 5-mm (41 +/- 6% stretch), 6-mm (64 +/- 6% stretch), or 8-mm (97 +/- 9% stretch) balloon angioplasty catheter, and the uninjured half of each vessel served as the control. The vasoconstrictor behavior of the dilated segment was then assessed by dose-response testing; long-axis, ultrasonic imaging combined with computerized edge-detection image processing was used to measure changes in segmental internal vessel diameters that were induced by phenylephrine. A similar series of experiments was performed in dog carotid arteries with 5-mm balloon catheters (42 +/- 2% stretch) to compare the susceptibility to smooth muscle injury between elastic (aortic) and muscular (carotid) arteries. Additional experiments were performed to determine the roles of prolonged (30 minutes) balloon inflation and arterial precontraction on smooth muscle injury after balloon angioplasty. In rabbit aortas, the dilated arterial segments demonstrated normal reactivity to phenylephrine after dilatation with 5- and 6-mm balloons (p = NS versus control). Severe smooth muscle injury (histopathologically) with "arterial paralysis" was observed after severe stretch (8-mm balloon) and after 5-mm balloon dilatation (46 +/- 5% stretch) in precontracted vessels. Prolonged balloon inflations did not impair aortic vasoconstrictor behavior. Dog carotid (muscular) arteries demonstrated angioplasty-induced smooth muscle injury with less severe degrees of stretch (47-52% stretch). Geometric modeling suggests that medial stretching during balloon angioplasty of diseased vessels in vivo is in the range of 15-41%.(ABSTRACT TRUNCATED AT 400 WORDS)

Platelet-reactive sites in human collagens I and III: evidence for cell-recognition sites in collagen unrelated to RGD and like sequences

Following fragmentation of the collagen molecule with cyanogen bromide (CB), two major platelet-aggregatory sites were detected with human platelets in the alpha 1(I)-chain of human collagen I corresponding to those detected previously in bovine alpha 1(I)-chains. Two main sites were also detected in the human alpha 1(III)-chain, at locations different from those in the alpha 1(I)-chain. Only one of these had been previously recognised. The new site was found in the peptide alpha 1(III)CB3, the amino acid sequence of which does not contain the cell-recognition site RGD nor comparable sequences that might be supposed to serve this function such as KGD, RGE or KGE. The peptide does, however, contain the sequence GRPGRPGER which reflects a spacing of basic residues (at positions 2 and 9) we have previously postulated to be essential for collagen to cause platelet aggregation. None of the CB-derived peptides was able to cause an aggregation of rabbit platelets. Human platelet secretion, as aggregation, was only induced by CB-derived fragments in triple-helical, polymeric form. One fragment, peptide alpha 1(III)CB8, was able to induce secretion although lacking aggregatory activity. Platelet adhesion occurred to all of the fragments, including those lacking aggregatory activity. Adhesion also occurred to the collagen-like polypeptide (PGP) n. However, inhibition studies suggested that the GPP sequence which occurs frequently along the length of the collagen molecule is not responsible for platelet adhesion to collagen.

Platelet adhesion to collagen. Factors affecting Mg2(+)-dependent and bivalent-cation-independent adhesion

Platelet adhesion to collagens immobilized on plastic has been measured, with the following results. (1) Human, but not rabbit, platelets adhered readily to pepsin-extracted monomeric collagens in an Mg2(+)-dependent manner. (2) Rabbit platelets adhered to a monomeric collagen extracted without pepsin by a process that was cation-independent; human platelet adhesion to this collagen exhibited a cation-independent element. (3) Human platelet adhesion to polymeric collagens, including intact native fibres and those reconstituted from pepsin-extracted monomeric collagens, exhibited appreciable cation-independence; adhesion of rabbit platelets to these collagens occurred only by a cation-independent process; pepsin treatment of the intact fibres caused a reduction in cation-independent binding. Two mechanisms of adhesion can therefore be distinguished, one Mg2(+)-dependent, expressed by human, but not rabbit, platelets, the other cation-independent and exhibited by platelets of both species. Mg2(+)-dependent and cation-independent adhesion sites are located within the triple helix of collagen, but the latter sites are only expressed in collagen in polymeric form. In neither case is the helical conformation of the sites essential for their binding activity. Cation-independent adhesion sites are also located in the pepsin-sensitive non-helical telopeptides of collagen and can be expressed in both monomeric and polymeric collagens. Chemical modification of collagen lysine residues indicates that specific lysine residues may be involved in Mg2(+)-dependent adhesion. Adhesion using human citrated platelet-rich plasma is Mg2(+)-independent. Plasma contains factors, conceivably the adhesive proteins fibronectin and von Willebrand factor, that promote the Mg2(+)-independent mechanism.

Collagen type III induced ex vivo thrombogenesis in humans. Role of platelets and leukocytes in deposition of fibrin

Exposure of type III collagen coats on plastic cover slips in parallel-plate perfusion chambers to flowing nonanticoagulated human blood resulted in deposition of platelets and fibrin. Blood was drawn directly from an antecubital vein by an occlusive roller pump over the collagen coats in chambers having flow slits of different dimensions, so that wall shear rates of 100, 650, and 2600 s-1 were obtained at 10 ml/min. Coagulation was minimally activated during the passage of blood from the vein to the chamber as shown by fibrinopeptide A levels of 3.7 ng/ml after 5-minute perfusions. The surface coverage with platelets increased from 18% at 100 s-1 to 59% at 2600 s-1, and the corresponding thrombus volumes increased from 2 to 22 microns 3/microns 2, respectively. This contrasted with the coverage with fibrin on collagen, which decreased from 28% at 100 s-1 to 9% at 2600 s-1. Fibrin deposits on the thrombi covered 6% of the surface irrespective of the shear rate, indicating that some of the deposited platelets accelerated the deposition of fibrin. The type III collagen preparation did not activate factor XII and did not possess tissue factor activity, indicating that the surface itself was not procoagulant. However, a correlation between deposited leukocytes and surface coverage with fibrin was observed (r = 0.78, p less than 0.01), suggesting a role for these cells in the deposition of fibrin. The data demonstrate that thrombogenesis is triggered by pure type III collagen, although the deposition of fibrin is not initiated by the collagen itself but presumably by deposited leukocytes.(ABSTRACT TRUNCATED AT 250 WORDS)

Collagen synthesis by cultured arterial smooth muscle cells during spontaneous phenotypic modulation

Quantitative and qualitative changes in collagen synthetic activity by rabbit arterial smooth muscle cells were monitored during spontaneous phenotypic modulation from days 2-15 of culture. The cultured smooth muscle cells transformed into a synthetic phenotype, reaching a maximum of 94.6% on day 4, and then gradually returned to a contractile phenotype accounting for 59.3% on day 15 of culture. The maximum collagen synthesis was found on day 7 when the cells were in early quiescent phase and showed a 91.7% synthetic phenotype. With an increasing proportion of cells in a contractile state, total collagen synthesis per cell decreased in parallel with the reduction in total protein synthesis. Synthesis of type I collagen was predominant, and the proportion of type I + III collagen was over 85% during the entire period of culture. Synthetic activity of type IV collagen, however, was relatively increased, and reached 3.8 +/- 0.4% at day 15 in comparison with 0.8 +/- 0.1% in the late logarithmic growth phase on day 4. This significant increment of type IV collagen in vitro seems to be correlated with the phenotypic modulation of cultured smooth muscle cells into a contractile phenotype.

Collagen synthesis by cultured rabbit aortic smooth-muscle cells. Alteration with phenotype

Enzymically isolated rabbit aortic smooth-muscle cells (SMC) in the first few days of primary culture express a 'contractile phenotype', but with time these cells modulate to a 'synthetic phenotype'. Synthetic-state SMC are able to proliferate, and, provided that they undergo fewer than 5 cumulative population doublings, return to the contractile phenotype after reaching confluency [Campbell, Kocher, Skalli, Gabbiani & Campbell (1989) Arteriosclerosis 9, 633-643]. The present study has determined the synthesis of collagen, at the protein and mRNA levels, by cultured SMC as they undergo a change in phenotypic state. The results show that, upon modulating to the synthetic phenotype, SMC synthesized 25-30 times more collagen than did contractile cells. At the same time, non-collagen-protein synthesis increased only 5-6-fold, indicating a specific stimulation of collagen synthesis. Steady-state mRNA levels are also elevated, with alpha 2(I) and alpha 1(III) mRNA levels 30 times and 20 times higher respectively, probably reflecting increased transcriptional activity. Phenotypic modulation was also associated with an alteration in the relative proportions of type I and III collagens synthesized, contractile SMC synthesizing 78.1 +/- 3.6% (mean +/- S.D.) type I collagen and 17.5 +/- 4.7% type III collagen, and synthetic cells synthesizing 90.3 +/- 2.0% type I collagen and 5.8% +/- 1.8% type III collagen. Enrichment of type I collagen was similarly noted at the mRNA level. On return to the contractile state, at confluency, collagen production and the percentage of type I collagen decreased. This further illustrates the close association between the phenotypic state of SMC and their collagen-biosynthetic phenotype.

Laser induced fluorescence spectroscopy of normal and atherosclerotic human aorta using 306-310 nm excitation

Ultraviolet excited laser induced fluorescence (LIF) was studied in normal and atherosclerotic human arterial wall in vitro. Using excitation wavelengths from 306 to 310 nm, two distinct emission bands were observed in the LIF of both normal and pathologic aorta: a short wavelength band, peaking at 340 nm emission, which was attributed to tryptophan; and a long wavelength band, peaking at 380 nm emission, which was assigned to a combination of collagen and elastin. The intensity of the short wavelength band was quite sensitive to the choice of excitation wavelength, while the long wavelength band was not, so that the relative contributions of the bands could be controlled by the precise choice of excitation wavelength. A valley in the spectra at 418 nm was attributed to fluorescence reabsorption by oxy-hemoglobin. By using 308 nm excitation to observe emission simultaneously from both the short and long wavelength bands, normal and atherosclerotic aorta were spectrally distinct. Two LIF emission intensity ratios were defined to characterize both the relative tryptophan fluorescence content as well as the ratio of elastin to collagen fluorescence in each spectrum. The differences in these two emission ratios among the various histologic tissue types correlated qualitatively with the histologic and biochemical compositions of these tissues. By combining these parameters in a binary classification scheme, normal and atherosclerotic aorta were correctly distinguished in 56 of 60 total cases. Furthermore, atherosclerotic plaques, atheromatous plaques, and exposed calcifications could be classified individually with sensitivities/predictive values of 90%/90%, 100%/75%, and 82%/82%, respectively.

Changes in vascular extracellular matrix accumulation reflect phenotypic differences between the arterial wall of pigeons resistant and susceptible to the development of spontaneous atherosclerosis

White Carneau pigeons have previously been shown to be genetically susceptible to the development of spontaneous atherogenesis. The severity of development of atheromatous lesions is considerably greater than a more resistant breed of Show Racer pigeons. Analysis of levels of total hydroxyproline and isodesmosine in the thoracic aorta and celiac bifurcation of prelesion, six-week-old White Carneau and Show Racer pigeons, revealed an increased accumulation of total collagen and cross-linked elastin in the White Carneau arterial tissue. Using dot blot hybridization, measurements of steady state levels of several mRNAs in total RNA extracted from pigeon aortic tissue were also determined. While the increased deposition of extracellular matrix proteins was paralleled by a significantly greater recovery of mRNAs coding for pro alpha 1(1) collagen and elastin, in RNA extracted from White Carneau aortal tissue, increased recovery of mRNAs coding for an intracellular protein, gamma-actin were also observed in White Carneau aortal tissue. No differences in steady state levels of mRNAs coding for pro alpha 1(1) collagen and elastin were observed in RNA extracted from pigeon liver, suggesting a tissue specific increase in the mRNAs coding for these connective tissue proteins in aorta. A markedly reduced cell population however, was responsible for this overall increase in biosynthetic activity in White Carneau pigeon aortic tissue. This was demonstrated by a reduced cell count and by the recovery of reduced levels of total DNA in the thoracic aorta and celiac bifurcation of the White Carneau pigeon. The cell population in White Carneau aortic tissue exhibits therefore a markedly different phenotype with respect to a capacity for the biosynthesis of extracellular and intracellular proteins.

Biosyntheses of interstitial collagens and fibronectin by porcine aorta smooth muscle cells. Modulation by low-molecular-weight heparin fragments

The effect of low-molecular-weight heparin fragments (CY222) on the biosynthetic phenotype of porcine aortic smooth muscle cells (SMC) was investigated in vitro on overconfluent cell cultures. Addition of increasing concentrations of CY222 to the culture medium of early passage SMC resulted in a dose-dependent decrease of type III to type I collagen ratio without change in total collagen biosynthesis. In the same range of concentrations CY222 did not affect the biosynthesis of fibronectin. However, heparin fragments decreased the proportion of the freshly synthesized pericellular form of fibronectin with a concomitant increase of neosynthesized intracellular fibronectin, indicating an inhibitory effect of CY222 on fibronectin secretion. Our results demonstrate that the biosynthetic phenotype of SMC in vitro can be modulated by low-molecular-weight heparin fragments and confirm also that interactions between cells and extracellular matrix molecules can modify the biosynthetic pattern of mesenchymal cells.

Interaction of type I collagen fibrils with phospholipid vesicles

Type I collagen fibrils interact with phosphatidylcholine and phosphatidylglycerol vesicles. Fluorescence polarization of (1,6-diphenyl-1,3,5-hexatriene) DPH-labeled vesicles, circular dichroism and differential scanning calorimetry studies have been performed. The protein-lipid interaction produces a decrease of the enthalpy of the phospholipid phase transition. Positive charges of lysine residues of the protein are involved in the interaction as experiments with succinylated collagen show. The kinetic parameters and the extent of the fibrillogenesis of collagen are modified by the phospholipid vesicles.

Mechanisms of arterial thrombosis in nonparallel streamlines: platelet thrombi grow on the apex of stenotic severely injured vessel wall. Experimental study in the pig model

The role of thrombosis in various acute coronary syndromes has been established. However, the basic mechanism by which plaque rupture leads to a growing thrombus in the vicinity of stenotic lesions is not well understood. Using a characterized flow chamber in a rheologically controlled system, we have mimicked stenotic vessels and studied for the first time cell-vessel wall interaction in nonparallel streamlines. Stenoses ranging from 0 to 80% were produced with stripped tunica media to mimic severe vessel wall damage, and perfused with heparinized flowing blood. This perfusion device was placed within an extracorporeal system in swine, and blood was perfused for selected times from 1 to 30 min. Platelet deposition on the surface was evaluated by 111Indium-labeled platelets. As percent stenosis increased, platelet deposition significantly increased (P less than 0.001), indicating a shear-induced cell activation. Analysis of the axial distribution of platelet deposition indicated that the apex, and not the flow recirculation zone distal to the apex, was the segment of greater platelet accumulation within 30 min of blood perfusion (P less than 0.001). These results also indicate that the severity of the acute platelet response to plaque rupture probably depends on the location of the rupture with relation to the apex of the plaque.

Etiology of intracranial berry aneurysms

The congenital theory of the etiology of intracranial berry aneurysms has been widely accepted for many years. Review of the supporting evidence indicates that it is not based on sound scientific data but on unscientific and unsubstantiated allegations. There is no evidence of a congenital, developmental, or inherited weakness of the vessel wall. The most plausible explanation is that the aneurysms are acquired degenerative lesions--the effect of hemodynamic stress. The mural atrophy leading to aneurysmal dilatation is an acquired lesion which can be produced experimentally by hemodynamics alone. Hypertension and connective tissue disorders associated with acquired loss of tensile strength of the connective tissues are not essential: they appear to be aggravating rather than causal factors. Occlusion of one or more feeding vessels may enhance the possibility of aneurysm formation at large arterial forks subjected to the augmented hemodynamic stress associated with collateral flow.