Chemical composition of the rabbit aorta during development

Morphometric Properties of the Thoracic Aorta of Warmblood and Friesian Horses with and without Aortic Rupture

Rupture of the aorta is much more common in Friesians compared with other breeds of horse. Rupture always occurs adjacent to the scar of the ligamentum arteriosum. Previous histological examination of ruptured aortic walls suggested the presence of an underlying connective tissue disorder. Therefore, the aim of the present study was to compare the structural characteristics of the tunica media of the mid-thoracic aorta, distant to the lesion, in warmblood and Friesian horses with and without thoracic aortic rupture. In unaffected Friesian horses, the thickness of the tunica media, as well as the percentage area comprised of collagen type I, were significantly higher compared with the warmblood horses, supporting the hypothesis of a primary collagen disorder in the Friesian horse breed. However, in the tunica media of the affected Friesian horses there was no significant wall thickening. Moreover, the percentage area comprised of elastin was significantly lower, while the percentage area comprised of smooth muscle was higher, compared with unaffected Friesian and warmblood horses. These lesions are suggestive of an additional mild elastin deficiency with compensatory smooth muscle cell hypertrophy in affected Friesians.

Transcriptional and posttranscriptional mechanisms contribute to the dysregulation of elastogenesis in Schimke immuno-osseous dysplasia

BACKGROUND

Schimke immuno-osseous dysplasia (SIOD) is an autosomal recessive disorder caused by mutations in SMARCAL1. A frequent complication is arteriosclerosis associated with reduced elastin expression; however, the mechanism underlying the reduced elastin expression remains unknown.

METHODS

Expression of transcriptional regulators of elastin (ELN) and microRNA (miRNA) regulators of ELN messenger RNA (mRNA), ELN promoter methylation, and ELN mRNA poly(A) tail length were assessed by quantitative RT-PCR, bisulfite Sanger sequencing, and the Poly(A) Tail Length Assay Kit, respectively, in unaffected developing human aortae and in an SIOD aorta.

RESULTS

Comparing unaffected fetal and adult aortae, ELN precursor mRNA (pre-mRNA) levels remained nearly constant, whereas mRNA levels declined by ~10(2)-fold. This corresponded with a reduction in poly(A) tail length but not with changes in the other parameters. In contrast, compared to the unaffected fetal aortae, the SIOD aorta had 18-fold less ELN pre-mRNA and 10(4)-fold less mRNA. This corresponded with increased expression of miRNA regulators and shorter ELN mRNA poly(A) tail lengths but not with altered expression of ELN transcriptional regulators or ELN promoter methylation.

CONCLUSION

Posttranscriptional mechanisms account for the reduction in ELN mRNA levels in unaffected aortae, whereas transcriptional and posttranscriptional mechanisms reduce elastin expression in SIOD aorta and predispose to arteriosclerosis.

In vivo and in vitro mechanical properties of the sheep thoracic aorta in the perinatal period and adulthood

The mammalian aorta undergoes rapid remodeling during the perinatal period and more gradual remodeling during subsequent development, but the implications of this remodeling for arterial mechanics are poorly understood. In this study in vivo and in vitro techniques were used to determine the static and viscoelastic properties of the thoracic aortas of 119-day-gestation fetal sheep (full term = 145 days), 21-day-old lambs, and adult sheep at control distending pressures and after 70% increases or 30% decreases in pressure. In the weeks surrounding birth, aortic wall tissue became substantially stiffer (static elastic modulus in vitro increased by 28%, and pressure wave velocity in vivo increased by 61%) but less viscous (pressure wave attenuation in vivo decreased by 46%, and viscoelastic phase angle in vitro decreased by 15%), whereas the wall thickness-to-radius ratio was unchanged. By contrast, modest changes in tissue viscoelasticity from neonatal to adult life were accompanied by a halving of the wall thickness-to-radius ratio from 0.19 +/- 0.01 to 0.10 +/- 0.01. The relative thinning of the vessel wall, combined with a doubling of blood pressure after birth, resulted in a 265% increase in aortic wall tensile stress over the period of study. We concluded that rapid remodeling in the perinatal period primarily alters the viscoelastic properties of aortic wall tissues, whereas more gradual postnatal remodeling largely affects vessel geometry.

Pattern of accumulation of elastin and the level of mRNA for elastin in aortic tissue of growing chickens

Synthesis and accumulation of elastin in many elastic tissues begins in the last third of fetal development, reaches a maximum shortly after birth, and then declines rapidly. For the aorta of the chick and the pig and the ligamentum nuchae and lung of the sheep, it has been shown that increased levels of elastin production with fetal development are correlated with increased levels of elastin mRNA in the tissue, measured both by cell-free translation and by hybridization to cDNA probes. In this study we examine the relationship between insoluble elastin accumulation and message levels for tropoelastin in aortic tissue of chickens during posthatching development and growth. Whether evaluated by cell-free translation or by dot blot hybridization, steady state levels of tropoelastin message increase to a maximum at 2 weeks after hatching, and then fall rapidly with further development and growth. This pattern correlates well with production of insoluble elastin by the aorta, determined either by direct measurements of synthesis or by rate of accumulation of insoluble elastin. The data indicate that the major site of regulation of elastin production is pretranslational throughout the entire period of development and growth of the chicken aorta.

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.

Factors affecting the production of insoluble elastin in aortic organ cultures

Aortic organ and cell culture systems have made important contributions to the understanding of the synthesis and accumulation of elastin in arterial tissues. However, methods used to quantitate production of elastin have been diverse, and evaluations of different culture conditions have not been made. In this study we describe a convenient and reproducible organ culture system for the assay of insoluble elastin synthesis. Under optimum incubation conditions, insoluble elastin is produced in organ culture at rates approximating in vivo accumulation rates. The assay is stable under a wide variety of incubation conditions, although elastin production is sensitively inhibited by acidification of the incubation medium. Alterations in intracellular calcium concentration had little effect on elastin production. In contrast, manipulations of sodium ion concentration, including treatment with ouabain or monensin, depressed elastin production. Except at high doses, pharmacological or humoral agents, including non-steroidal anti-inflammatory agents, alpha and beta adrenergic agonists, cyclic nucleotides, theophylline or aminophylline, and histamine, generally had only small effects on elastin production in this organ culture system.

Alterations of elastin and elastase-like activities in aortae of diabetic rats

The elastin content of the aortic muscle and the elastase-like activity of the extracts of aortic muscle were studied in spontaneously diabetic BB rats and in rats made diabetic by a single bolus i.v. injection of alloxan. In both modes of diabetes, the total alkaline-insoluble aortic elastin content was significantly reduced in diabetic rats compared to that in the corresponding control rats. This reduction in aortic elastin was also accompanied by a consistent increase in the elastase-like activities of the aortic extracts prepared from the same tissues. Such a reciprocal relationship between aortic elastin content and elastase-like activity has previously been reported in rats with malignant hypertension. Since the rats used in this study were not hypertensive, the altered elastin metabolism observed in this work is likely to be a manifestation of diabetic disease and may in part account for the vascular changes associated with diabetes mellitus.

Elastin and elastase-like enzyme change in aorta of rat with malignant hypertension

In order to study the role of elastin in arteries with respect to hypertension and hypertensive arterial disease, aortic elastin content and elastase-like enzyme activity were examined and compared in stroke-prone spontaneously hypertensive rats (SHRSP), which show malignant hypertension, and Wistar-Kyoto normotensive rats (WKY). The elastin content was lower, whereas the elastase-like activity was higher at 20 weeks of age in SHRSP than in WKY, so that the aortic elastin/enzyme ratio of SHRSP was lower than that in WKY. These differences were not found at 6 weeks of age (prehypertensive stage). For SHRSP anti-hypertensive treatment resulted in lowering the elastase-like activity and in increasing the elastin content in comparison to untreated animals. The subcellular distribution of the elastase-like activity closely correlated with that of 5'-nucleotidase activity, a plasma membrane marker enzyme. The results indicate involvement of a smooth muscle plasmalemmal elastase-like enzyme in vascular connective tissue metabolism in health and possibly also its participation in hypertensive arterial diseases.

Interstitial collagens and ageing in human aorta

Types I and III collagen were identified in four segments of human aorta using pepsin and cyanogen bromide digestion followed by sodium dodecyl sulphate polyacrylamide gel electrophoresis. Collagen is not uniformly distributed in the different segments of the arterial wall. Collagen type I is always the major collagen present. With ageing collagen type III decrease in quantity from the heart to the distal portion of the aorta. Histologically the elastic tissue is more altered in the lower abdominal section of aorta than in the arch. This study allowed a correlation between morphological observations and biochemical changes.

Synthesis of proteoglycans, collagen, and elastin by cultures of rabbit auricular chondrocytes--relation to age of the donor

Chondrocytes were isolated from the auricular cartilage of rabbits, aged 1 week to 30 months, and grown in short-term cell culture. The cells from the 1-week animals were small, polygonal, and mononucleated, while the chondrocytes from the older animals were larger, rounded, and frequently binucleated. The synthesis of proteoglycans, collagen, and elastin was determined by isotope incubation. Chemical characterization of the proteoglycans was also performed. The production of the matrix macromolecules showed a clear age dependence with peak synthesis occurring at different ages. Proteoglycans were actively synthesized by chondrocytes from all age groups with a broad maximum between 2 weeks and 5 months followed by a sharp decline to about 50% of the 1-week level at 12-30 months. Collagen synthesis peaked at 2 weeks, declining progressively thereafter to about 60% of the 1-week level at 30 months. Elastin synthesis was highest in the 1-week cultures and thereafter fell quickly to very low levels. In all age groups the chondrocytes synthesized predominantly cartilage-typic proteoglycans, i.e., large aggregate forming molecules containing chondroitin sulfate. Monomers and aggregates showed a size maximum at 2-8 weeks. The degree of sulfation of the chondroitin sulfate and the proportion of 6-sulfate increased with age. These findings support the concept of "age programs" for the biosynthesis and turnover of different matrix macromolecules.

Collagen accumulation in the major structures of the rabbit lung during postnatal development

In order to study the accumulation of collagen during postnatal development in the major structures of the lung, trachea, bronchi, pulmonary vasculature, and parenchyma were isolated from the lungs of 1-week, 2-month, and 6-month-old rabbits. The concentrations of DNA, protein, and collagen in parenchyma were similar to those for whole lung. DNA per day weight for all structures declined with age. The DNA concentration of trachea at 6 months was only one-tenth that of parenchyma. Protein per dry weight was constant in parenchyma but dropped by half in trachea and nearly that in bronchi. Collagen per dry weight increased significantly between 1 week and 6 months in all structures. The collagen concentrations in vessels, bronchi, and trachea are similar to each other and three to five times that of parenchyma. The total amount of collagen in bronchi, trachea and parenchyma increased approximately 12-, 50-, and 90-fold, respectively, between 1 week and 6 months of age.

Changes in aortic lysyl oxidase activity in diet-induced atherosclerosis in the rabbit

This study assessed the responses of lysyl oxidase, the enzyme that initiates covalent crosslinking in elastic and collagen, by studying the aortic tissue of rabbits after arteriosclerosis had been induced by diet. Rabbits in the experimental group were fed an atherogenic diet of rabbit chow supplemented with 8% peanut oil and 2% cholesterol for varying periods of time, while the control group was fed only rabbit chow. Lysyl oxidase activity was found to be distributed throughout the length of the thoracic and abdominal aortas of the normal rabbits, However, rabbits fed the atherogenic diet showed marked increases in enzyme in the aortic arch, a change that was initially evident after 30 days and became greatest (2.5 times that of the controls) after 90 days. Enzyme activity in the study rabbits increased only minimally in the abdominal aortic wall. Aortic prolyl hydroxylase activity measured after 60 days of feeding changed in degree and manner similar to lysyl oxidase activity. These region-specific changes in enzyme activities correlated with the distribution and severity of aortic lesions in this model of the disease. Lysyl oxidase activity increased dramatically in this model of atherosclerosis, suggesting that this extracellular enzyme activity may prove to be a vulnerable and accessible point of control of the fibrotic response in atherosclerosis.

Aortic collagen, elastin and non-fibrous protein synthesis in rabbits red cholesterol and peanut oil

Alteration of the fatty acid composition of atherogenic test diets has been a widely recognized method for influencing the character and severity of atherosclerotic lesions. The addition of peanut oil or coconut oil to cholesterol-supplemented diets has been shown to produce lesions of a fibrous nature in several species. In the present study, addition of 8% peanut oil to a 2% cholesterol diet accelerated the formation of atherosclerotic lesions which were more fibrous after only 90 days than those previously seen in rabbits even after 6 months on a diet supplemented with cholesterol alone. Collagen, elastin and non-fibrous protein synthesis were all increased over control values, as previously seen in aortas from rabbits given cholesterol supplementation alone. However, the addition of peanut oil to the 2% cholesterol diet produced a preferential increase in the rate of aortic collagen synthesis per unit dry, defatted weight compared with the increases seen in elastin, non-fibrous protein or total protein synthesis. Collagen deposition in proliferative intimal plaques was evident by histological examination. These focal accumulations, however, did not result in significant increases in either total collagen content of the whole descending thoracic aorta or in collagen concentration expressed per unit of dry, defatted weight. These data suggest that, while a portion of the increased synthetic rates may be a direct result of aortic hyperplasia, the proportionally greater increase in collagen synthesis in these lesions is attributable to the addition of peanut oil to the atherogenic diet. Although the lesions produced in this experiment lacked the overt fibrosis seen in man and in some forms of experimentally induced atherosclerosis, the relative synthetic rates of collagen, elastin and nonfibrous protein described here suggest that even a small preferential increase in collagen synthesis compared with non-collagen protein synthesis may gradually lead to a more fibrous lesion.

[Some mechanical properties of the pig aorta (author's transl)]

In a machine for tensile tests the ultimate strength, stress and strain of the aorta ascendens of 47 female pigs (German landrace) at three different regions of the vessel wall were determined. The animals were fattened under identical conditions in a progeny testing station and slaughtered at the same living weight (102 +/- 2 kg). Weak regressions of body weight and age on parameters measured were nevertheless accounted for. The average elastin content of the aorta ascendens diminished with advancing age but was not significantly correlated to biomechanical properties of the three single samples. Maximum load, stress and modulus of vessel wall segment I (stamped out nearer to the heart) was greater than in sample II. These circumferential segments however exhibited highly stronger biomechanical resistance than sample III, which was stamped longitudinally. In samples I and II there was a negative correlation between thickness of the wall and ultimate tensile stress (N/mm2). Freezing of the material prior to test at -18degrees C for one week resulted in a significant rise in ultimate tensile strength and stress. The meaning of these findings for comparative angiology is discussed.