Quantitation of collagen fibril cross-section profiles in aging human veins

Vascular histopathology and connective tissue ultrastructure in spontaneous coronary artery dissection: pathophysiological and clinical implications

Aims 

Spontaneous coronary artery dissection (SCAD) is a cause of acute coronary syndromes and in rare cases sudden cardiac death (SCD). Connective tissue abnormalities, coronary inflammation, increased coronary vasa vasorum (VV) density, and coronary fibromuscular dysplasia have all been implicated in the pathophysiology of SCAD but have not previously been systematically assessed. We designed a study to investigate the coronary histological and dermal collagen ultrastructural findings in SCAD.

Methods and results

Thirty-six autopsy SCAD cases were compared with 359 SCAD survivors. Coronary and myocardial histology and immunohistochemistry were undertaken. Transmission electron microscopy (TEM) of dermal extracellular matrix (ECM) components of n = 31 SCAD survivors and n = 16 healthy volunteers were compared. Autopsy cases were more likely male (19% vs. 5%; P = 0.0004) with greater proximal left coronary involvement (56% vs. 18%; P < 0.0001) compared to SCAD survivors. N = 24 (66%) of cases showed no myocardial infarction on macro- or microscopic examination consistent with arrhythmogenic death. There was significantly (P < 0.001) higher inflammation in cases with delayed-onset death vs. sudden death and significantly more inflammation surrounding the dissected vs. non-dissected vessel segments. N = 17 (47%) cases showed limited intimal fibro-elastic thickening but no features of fibromuscular dysplasia and no endothelial or internal elastic lamina abnormalities. There were no differences in VV density between SCAD and control cases. TEM revealed no general ultrastructural differences in ECM components or markers of fibroblast metabolic activity.

Conclusions 

Assessment of SCD requires careful exclusion of SCAD, particularly in cases without myocardial necrosis. Peri-coronary inflammation in SCAD is distinct from vasculitides and likely a reaction to, rather than a cause for SCAD. Coronary fibromuscular dysplasia or increased VV density does not appear pathophysiologically important. Dermal connective tissue changes are not common in SCAD survivors.

PICROSIRIUS RED AND MASSON’S TRICHROME STAINING TECHNIQUES AS TOOLS FOR DETECTION OF COLLAGEN FIBERS IN THE SKIN OF DOGS WITH ENDOCRINE DERMATOPATHOLOGIES

Abstract Canine endocrinopathies, such as hypothyroidism and hyperadrenocortism,induce typical dermatological alterations. Collagen fibers are significant for the maintenance of structural integrity,as well as in the determination of tissue function. This study aimed at assessing the coloration caused by Picrosirius Red staining under circular polarization and Masson Trichrome staining, as tools to quantify the total collagen in the skin of dogs exhibiting endocrine dermatopathies. Skin samples taken from dogs with hypothyroidism and hyperadrenocorticism were stained using Hematoxylin and Eosin (HE), Masson’s Trichrome (MT) and Picrosirius Red (PSR). The animals with hyperadrenocorticism revealed a higher percentage of collagen area than did the animals with hypothyroidism PSRp (hypothyroidism = 43.76 ± 0.8255 and hyperadrenocorticism = 47.08 ± 0.8584). The percentage of the collagen area using MT between the groups is given in parenthesis (hypothyroidism = 52.06 ± 0.9371, hyperadrenocorticism = 61 ± 0.7529 and control = 56.88 ± 0.64) (p <0.05). It is therefore, evident that the special stains employed are useful in estimating the percentage of collagen area in the skin, as they revealed that dogs with hypothyroidism had lower collagen deposition whereas those animals with hyperadrenocorticism showed higher quantity of collagen in the dermis.

Homeostatic maintenance via degradation and repair of elastic fibers under tension

Cellular maintenance of the extracellular matrix requires an effective regulation that balances enzymatic degradation with the repair of collagen fibrils and fibers. Here, we investigate the long-term maintenance of elastic fibers under tension combined with diffusion of general degradative and regenerative particles associated with digestion and repair processes. Computational results show that homeostatic fiber stiffness can be achieved by assuming that cells periodically probe fiber stiffness to adjust the production and release of degradative and regenerative particles. However, this mechanism is unable to maintain a homogeneous fiber. To account for axial homogeneity, we introduce a robust control mechanism that is locally governed by how the binding affinity of particles is modulated by mechanical forces applied to the ends of the fiber. This model predicts diameter variations along the fiber that are in agreement with the axial distribution of collagen fibril diameters obtained from scanning electron microscopic images of normal rat thoracic aorta. The model predictions match the experiments only when the applied force on the fiber is in the range where the variance of local stiffness along the fiber takes a minimum value. Our model thus predicts that the biophysical properties of the fibers play an important role in the long-term regulatory maintenance of these fibers.

Extracellular matrix of the human aortic media: an ultrastructural histochemical and immunohistochemical study of the adult aortic media

Aortic distensability is the key to normal aortic function and relates to the lamellar unit in the media. However, the organization of the extracellular matrix components in these lamellar units, which are largely responsible for the distensability, is insufficiently known, especially in the human. We therefore performed a detailed ultrastructural analysis of these components. Thoracic aortas of 56 individuals (age 45-74 years), none of whom suffered from aortic disease, were studied by immunoelectron microscopy of elastin, collagen types I, III, IV, V, and VI, fibronectin, and fibrillin-1, and by ultrastructural histochemistry of proteoglycans, which were further characterized by enzymatic digestion. The elastic lamellae were closely associated with thick collagen fibers containing types I, III, and V collagen. Between these collagen fibers, numerous complex, circumferentially oriented streaks of elastin protruded from the lamellae. In contrast to what is usually reported in the aortas of experimental animals, the smooth muscle cells preferentially adhered to these ill-defined streaks rather than directly to the solid lamellae. Fibrillin-1- and type VI collagen-containing bundles of microfibrils (oxytalan fibers) were also involved in the smooth muscle cell-elastin contact. The smooth muscle cells were invested by basal lamina-like layers connecting them to each other as well as to the oxytalan fibers. Unexpectedly, these layers were abundantly labeled by anti-fibronectin, whereas type IV collagen, a specific basement membrane component, was mainly found in larger, flocculent deposits. The proteoglycans present were collagen-associated dermatan sulfate proteoglycan, cell-associated heparan sulfate proteoglycan, and interstitial chondroitin sulfate proteoglycan. Our observations demonstrate that the extracellular matrix in the human aorta is extremely complex and therefore differs from most descriptions based on experimental animals. They serve as reference for future studies on aortic diseases, such as aneurysmas and dissections.

Abnormalities of collagen fibrils in a rabbit with a connective tissue defect similar to Ehlers-Danlos syndrome

A morphometric ultrastructural study was performed to confirm the presence of an abnormality of the collagen fibrils in a rabbit with a connective tissue defect similar to Ehlers-Danlos syndrome. Median fibril diameter and perimeter were not altered but their ranges were significantly increased. As indicated by the median fibril 'form factor', fibrils were significantly more irregular in shape; the range of irregularity in shape was also increased. Fibril periodicity was unchanged. The results are discussed in relation to collagen fibril structure and fibril abnormalities in similar diseases in man and other animals.

Ultrastructural morphometry of matrical changes induced by exercise and food restriction in the rat calcaneal tendon

The ultrastructural morphometry of collagen fibril populations in 24 calcaneal tendons obtained from 12 Fischer 344 rats were studied to elucidate matrical changes induced by food restriction and/or endurance exercise. Rats were randomly assigned to four equal groups: ad libitum control (AC), ad libitum exercise (AE), restricted diet control (RC) and restricted diet exercise (RE) groups. Beginning from 6 weeks of age, animals in the two food restriction groups were fed 60% of the mean food consumption of ad libitum fed rats. Then, starting from 6-7 months of age, the rats in the two exercise groups performed 40-50 min of treadmill running at 1.2-1.6 miles h-1 every day for a total of 10 weeks. Endurance training did not significantly alter body weight, but food restriction with or without exercise resulted in a significant loss of body weight. In ad libitum fed controls, food restriction alone did not significantly alter the mean collagen fibril CSA, but predisposed a preponderance of small-sized collagen fibrils. Endurance training per se induced a significant (32%) increase in mean fibril CSA (P less than 0.05), but this adaptive response to exercise was prevented by food restriction, as indicated by a 33% decline in fibril CSA (P less than 0.05). These findings demonstrate that dietary restriction modifies the adaptation of tendon collagen morphometry in response to endurance training, and that weight loss is better achieved with food restriction than endurance exercise.

Glycation alters collagen fibril organization

Incubation of rat tail tendon in 0.2M ribose results in accelerated non-enzymatic glycosylation of collagen, with the formation of fluorescent cross-links between molecules and decreased solubility. Electron micrographs of tendon cross-sections show an increased fibril packing density with increasing degrees of glycation. After a one-week incubation in ribose, every fibril appears in close contact with all of its neighbors, and the packing density has increased to 76%, from a value of 62% in controls. Irregular diameters and fusion of fibrils also are seen. All of the fibrils in a bundle appear to become cross-linked together, creating a larger stress bearing unit. This model is consistent with stress-strain curves showing a large increase in tensile stress and stiffness after a one-week incubation period in ribose. The diameters of the collagen fibrils increase in size in glycated tendon. We hypothesize larger diameters result from an increased resistance to shrinkage during the specimen preparation process, as a result of the rigid sugar derived cross-links. Closer fibril packing, increased fibril diameters, and irregular diameters have been reported in diabetic tissues, and may result from decades of glycation induced cross-link accumulation.