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PubMed1999

The structures of elastins and their function.

Elastin structures and their significance towards elastic recoil properties have been reviewed. Starting from the initial hypothesis that elastin conformation is conditioned by that of its monomer, the structure of tropoelastin was first described using theoretical and experimental methods and a beta class folding type was evidenced for the isolated unbound tropoelastin molecules. The structure of elastin in the solid state was consistent with that of its monomer and consequently, fibrous elastin appeared constituted of globular tropoelastin molecules. Finally, theoretical and experimental considerations have led us to the conclusion that the functional form of the elastomer, water swollen elastin, could be a triphasic system comprising the protein chains, hydration water and solvent water. Following this description, the dynamic structural equilibria occurring within elastin hydrophobic domains and the plasticizing effect of water could explain elastin elasticity, in keeping with a classical entropic mechanism.

Amino Acid Sequence↗
PubMed1989

Evidence for insulin-like growth factor-I regulation of chick aortic elastogenesis.

The potential role of insulin-like growth factor-I (IGF-I) as a modulator of chick aortic embryogenesis was examined. Studies were designed to investigate the in vivo relationships between embryonic IGF-I serum concentrations, liver and aortic IGF-I mRNA steady-state levels and the inception and perpetuation of aortic elastogenesis. In addition to aortic tissue, elastogenesis was measured in heart and lung tissues in order to compare the responses of functionally unique elastin-containing tissues to the developmental appearance of IGF-I in embryonic serum. Our results demonstrate that the induction of aortic tropoelastin mRNA steady-state levels coincides with a major increase in serum IGF-I concentration. This is not the case with either lung or heart elastogenic responses. All three tissues examined (aorta, lung, and heart) exhibited different developmental patterns of tropoelastin mRNA steady-state levels during the embryonic ages studied (8- through 10-day). Only aortic tropoelastin mRNA levels paralleled the rise and fall of IGF-I serum levels. Steady-state levels of liver IGF-I mRNA peaked one day (9-day) prior to detectable IGF-I serum levels but otherwise mirrored the gradual, but steady decrease in IGF-I serum levels through 16-day. Aortic tissue also expresses IGF-I mRNA beginning at 8-day and continuing throughout the embryonic ages examined (16-day). Although the relative levels of aortic IGF-I mRNA are very low in comparison to corresponding mRNA levels in liver, the fact that IGF-I mRNA is transcribed in the aorta points to the possibility that autocrine and/or paracrine mechanisms of IGF-I action may be operative in aortic elastogenesis.

Animals↗
PubMed2003

ECM gene expression correlates with in vitro tissue growth and development in fibrin gel remodeled by neonatal smooth muscle cells.

A tissue growth and development process occurred in neonatal SMC-fibrin gel constructs when cultured in DMEM supplemented with TGF-beta1 and insulin over a 5 week period. These constructs may thus serve as the basis for cardiovascular tissue replacements and future models of cardiovascular tissue growth, repair and regeneration. Following fibrin gel contraction during week 1, peak rates of SMC proliferation, collagen production and tropoelastin production occurred between weeks 1-4. Organized, cross-linked collagen and elastic fibers replaced the degrading fibrin over weeks 3-5 and were manifested as increased mechanical strength. The peak rate of SMC proliferation (weeks 1-2) preceded that for maximum collagen production (weeks 2-4), which was consistent with the 3 week time point of maximum expression of collagen type I and III from qRT-PCR. Insoluble elastin quantification revealed that the majority of elastic fibers were produced by week 4, which was also consistent with the qRT-PCR data showing a dramatic down-regulation of tropoelastin expression by week 4, indicating elastogenesis occurred during the early stages of tissue growth and development. There was a strong up-regulation of lysyl oxidase expression during weeks 1-3 with a peak in expression at week 3, correlating with the phases of collagen and tropoelastin production. An increase in MMP-2 expression over weeks 1-5 suggested an increase in ECM remodeling as the tissue developed. Mechanical strength doubled over weeks 4-5 when production of collagen and elastic fibers and expression of lysyl oxidase were subsiding. This may have been due in part to the more organized collagen fibrils evident from the histological sections in weeks 3-5.

Animals↗
PubMed2000

Distribution and synthesis of elastin in porcine gingiva and alveolar mucosa.

Histologically, there are variations in the distribution of the types of elastic fibers within the tissues of the masticatory mucosa. For example, the alveolar mucosa has heavy deposits of elastin which decrease in quantity and size as it merges with the attached gingiva. These differences in elastin content may result from the tissues' different physiological workload modulating the expression of tropoelastin mRNA. Alternatively, these differences could be due to the presence of phenotypically different fibroblasts that have different basal levels of tropoelastin mRNA expression. The aim of this study was to determine whether the differences in the distribution of elastin between alveolar mucosa and attached gingiva could be due to phenotypic differences between fibroblasts derived from these tissues. Histochemical (Miller's elastin stain) and immunohistochemical staining were used to localize elastin within these tissues. Elastin production by cultured fibroblasts derived from alveolar mucosa and attached gingiva was assessed by Western blot analyses, and Northern blot analyses were used to detect levels of elastin mRNA by these cells. The results from this study have confirmed that elastin is richly expressed in oral mucosa and poorly expressed in attached gingiva. In vitro, the cells demonstrated a capacity to synthesize and secrete tropoelastin, however this was not found to differ between cells from the two different sources. These findings indicate that while some heterogeneity in fibroblast populations may exist within various tissues of the periodontium, other factors, such as functional requirements of the tissues in which they reside, may also play an important role in the phenotypic expression of these cells.

Analysis of Variance↗
PubMed2001

Structural immaturity of the heart in congenital diaphragmatic hernia in rats.

PURPOSE: The form and function of the heart are the final result of an integration of cells, tissues, and extracellular material. The extracellular matrix (ECM) is a complex array of different molecular components, and it plays an important role for the transfer of mechanical force in both contraction and relaxation phases in the cardiac cycle. ECM plays also a significant role in the development of the heart. The aim of this study was to evaluate the expression of important ECM components in the heart of rats with induced CDH to test the hypothesis that an alteration of ECM may contribute to the cardiac maldevelopment, which recently has been identified as a contributive factor for the high mortality rate in babies with congenital diaphragmatic hernia (CDH). METHODS: CDH model was induced in pregnant rats after administration of 100 mg of nitrofen on day 9.5 of gestation (term, 22 days). In control animals the same dose of olive oil was given without nitrofen. Cesarean section was performed on day 21 of gestation. The fetuses were divided into 2 groups: normal control (n = 10) and nitrofen-induced CDH (n = 10). Reverse transcription polymerase chain reaction (RT-PCR) was performed to evaluate the relative amount of tropoelastin and alpha1 (I) procollagen mRNA expression. Elastin protein content was measured using enzyme-linked immunosorbent assay (ELISA). RESULTS: There was a reduction in tropoelastin mRNA (P <.05) and procollagen mRNA (P <.05) in CDH compared with controls. The cardiac alpha-elastin content also was reduced in CDH (P <.01). CONCLUSIONS: The reduced cardiac tropoelastin and procollagen gene expression and the reduced alpha-elastin content indicate that the heart in CDH structurally is immature. The reduced production of cardiac ECM may contribute to a contractile dysfunction, which makes the heart unable to respond to the hemodynamic load accompanying persistent pulmonary hypertension (PPH).

Abnormalities, Multiple↗
PubMed1995

Bovine elastin and kappa-elastin secondary structure determination by optical spectroscopies.

Elastin is the macromolecular polymer of tropoelastin molecules responsible for the elastic properties of tissues. The understanding of its specific elasticity is uncertain because its structure is still unknown. Here, we report the first experimental quantitative determination of bovine elastin secondary structures as well as those of its corresponding soluble kappa-elastin. Using circular dichroism and Fourier transform infrared and near infrared Fourier transform Raman spectroscopic data, we estimated the secondary structure contents of elastin to be approximately 10% alpha-helices, approximately 45% beta-sheets, and approximately 45% undefined conformations. These values were very close to those we had previously determined for the free monomeric tropoelastin molecule, suggesting thus that elastin would be constituted of a closely packed assembly of globular beta structural class tropoelastin molecules cross-linked to form the elastic network (liquid drop model of elastin architecture). The presence of a strong hydration shell is demonstrated for elastin, and its possible contribution to elasticity is discussed.

Amino Acids↗
PubMed2004

B-Myb represses elastin gene expression in aortic smooth muscle cells.

B-Myb represses collagen gene transcription in vascular smooth muscle cells (SMCs) in vitro and in vivo. Here we sought to determine whether elastin is similarly repressed by B-Myb. Levels of tropoelastin mRNA and protein were lower in aortas and isolated SMCs of adult transgenic mice expressing the human B-myb gene, driven by the basal cytomegalovirus promoter, compared with age-matched wild type (WT) animals. However, the vessel wall architecture and levels of insoluble elastin revealed no differences. Since elastin deposition occurs early in development, microarray analysis was performed using nontransgenic mice. Aortic levels of tropoelastin mRNA were low during embryonal growth and increased substantially in neonates, whereas B-myb levels varied inversely. Tropoelastin mRNA expression in aortas of 6-day-old neonatal transgenic and WT animals was comparable. Recently, we demonstrated that cyclin A-Cdk2 prevents B-Myb-mediated repression of collagen promoter activity. Cyclin A2 levels were higher in neonatal versus adult WT or transgenic mouse aortas. Ectopic cyclin A expression reversed the ability of B-Myb to repress elastin gene promoter activity in adult SMCs. These results demonstrate for the first time that B-Myb represses SMC elastin gene expression and that cyclin A plays a role in the developmental regulation of elastin gene expression in the aorta. Furthermore, the findings provide additional insight into the mechanism of B-myb-mediated resistance to femoral artery injury.

Animals↗
PubMed2005

Lysosomal sialidase (neuraminidase-1) is targeted to the cell surface in a multiprotein complex that facilitates elastic fiber assembly.

We have established previously that the 67-kDa elastin-binding protein (EBP), identical to the spliced variant of beta-galactosidase, acts as a recyclable chaperone that facilitates secretion of tropoelastin. (Hinek, A., Keeley, F. W., and Callahan, J. W. (1995) Exp. Cell Res. 220, 312-324). We now demonstrate that EBP also forms a cell surface-targeted molecular complex with protective protein/cathepsin A and sialidase (neuraminidase-1), and provide evidence that this sialidase activity is a prerequisite for the subsequent release of tropoelastin. We found that treatment with sialidase inhibitors repressed assembly of elastic fibers in cultures of human skin fibroblasts, aortic smooth muscle cells, and ear cartilage chondrocytes and caused impaired elastogenesis in developing chick embryos. Fibroblasts derived from patients with congenital sialidosis (primary deficiency of neuraminidase-1) and galactosialidosis (secondary deficiency of neuraminidase-1) demonstrated impaired elastogenesis, which could be reversed after their transduction with neuraminidase-1 cDNA or after treatment with bacterial sialidase, which has a similar substrate specificity to human neuraminidase-1. We postulate that neuraminidase-1 catalyzes removal of the terminal sialic acids from carbohydrate chains of microfibrillar glycoproteins and other adjacent matrix glycoconjugates, unmasking their penultimate galactosugars. In turn, the exposed galactosugars interact with the galectin domain of EBP, thereby inducing the release of transported tropoelastin molecules and facilitating their subsequent assembly into elastic fibers.

Aorta↗
PubMed2000

Decreased elastin deposition and high proliferation of fibroblasts from Costello syndrome are related to functional deficiency in the 67-kD elastin-binding protein.

Costello syndrome is characterized by mental retardation, loose skin, coarse face, skeletal deformations, cardiomyopathy, and predisposition to numerous malignancies. The genetic origin of Costello syndrome has not yet been defined. Using immunohistochemistry and metabolic labeling with [3H]-valine, we have established that cultured skin fibroblasts obtained from patients with Costello syndrome did not assemble elastic fibers, despite an adequate synthesis of tropoelastin and normal deposition of the microfibrillar scaffold. We found that impaired production of elastic fibers by these fibroblasts is associated with a functional deficiency of the 67-kD elastin-binding protein (EBP), which is normally required to chaperone tropoelastin through the secretory pathways and to its extracellular assembly. Metabolic pulse labeling of the 67-kD EBP with radioactive serine and further chase of this tracer indicated that both normal fibroblasts and fibroblasts from patients with Costello syndrome initially synthesized comparable amounts of this protein; however, the fibroblasts from Costello syndrome patients quickly lost it into the conditioned media. Because the normal association between EBP and tropoelastin can be disrupted on contact with galactosugar-bearing moieties, and the fibroblasts from patients with Costello syndrome revealed an unusual accumulation of chondroitin sulfate-bearing proteoglycans (CD44 and biglycan), we postulate that a chondroitin sulfate may be responsible for shedding EBP from Costello cells and in turn for their impaired elastogenesis. This was further supported by the fact that exposure to chondroitinase ABC, an enzyme capable of chondroitin sulfate degradation, restored normal production of elastic fibers by fibroblasts from patients with Costello syndrome. We also present evidence that loss of EBP from fibroblasts of Costello syndrome patients is associated with an unusually high rate of cellular proliferation.

Abnormalities, Multiple↗
PubMed1988

Increased elastin production by progeria skin fibroblasts is controlled by the steady-state levels of elastin mRNA.

Hutchinson-Gilford progeria is a unique, rare disease with markedly accelerated aging. The average lifespan of affected individuals is 12 years. Although the biochemical basis of the syndrome is unknown, its influence appears to be primarily upon mesodermal tissues. Characteristics such as the altered appearance of the skin and the extensive and fatal involvement of the cardiovascular system led us to study elastin production in cultured skin fibroblasts from three progeroid individuals. We found tropoelastin production by progeroid cells was elevated six- to nine-fold at the protein and mRNA levels, while relative collagen synthesis was similar to control strains. There was little difference between progeroid and normal cells in expression of total protein or in total cellular mRNA content. Western blot analysis of tropoelastin from progeroid fibroblasts confirmed increased production of elastin but revealed no gross changes in the molecular mass. The significant increase in tropoelastin expression lends support to the concept that progeria results from a mesenchymal dysplasia, and offers a possible biochemical marker for the phenotype.

Adolescent↗
PubMed1996

Synthesis of elastin by pleomorphic adenomas.

Previous morphologic and histochemical studies have documented extracellular elastin and elastic fibers within the matrix of pleomorphic adenomas of the salivary glands. By morphologic criteria, the elastin appeared to be synthesized by the tumor rather than being a consequence of stroma produced in response to the tumor cells. To examine this issue, nine pleomorphic adenomas were studied by immunohistochemistry and in situ hybridization with tropoelastin-specific antibodies and complementary DNAs. Corroborating the previous morphologic studies, immunohistochemistry demonstrated abundant extracellular elastin within the matrix of pleomorphic adenomas. Additionally, both immunohistochemistry and in situ hybridization demonstrated continued synthesis of tropoelastin by the neoplastic cells. Tropoelastin production was seen in neoplastic cells with all morphologies.

Adenoma, Pleomorphic↗
PubMed1998

Mechanical forces alter extracellular matrix synthesis by human periodontal ligament fibroblasts.

Periodontal ligament fibroblasts (PDLFs) are a heterogeneous population of cells that are involved in the normal maintenance, repair and regeneration of both the ligament and adjacent hard tissues. Additionally, the ability of these cells to respond to mechanical stimulation suggests that they have a central role in mediating the osseous remodeling that underlies physiological and orthodontic tooth movement. To characterize their role further in this process, the current study evaluated the effect of tensional stress on the biosynthesis of extracellular matrix (ECM) proteins by human PDLFs. Cell strains were established from extracted human premolars and third molars. Cells exposed to 5% biaxial deformation (strain) at a frequency of 30 times/min for 24 hr exhibited statistically significant increases in type I collagen and fibronectin synthesis, and a statistically significant decrease in tropoelastin production relative to unstretched controls. Cells exposed to 10% strain exhibited similar responses for fibronectin and tropoelastin while the amount of type I collagen synthesized by stretched cells did not differ from control levels. These results indicate that mechanical stimulation of PDLFs alters type I collagen, tropoelastin and fibronectin production and that these cells are differentially responsive to varying levels of mechanical stress. The ability of these cells to alter ECM protein synthesis in response to specific magnitudes of tensional stress may in part explain how PDLFs regulate ligament and hard tissue remodeling.

Cells, Cultured↗
PubMed1996

Elastic fiber-associated proteins of skin in development and photoaging.

We sought to use antibodies against structural (tropoelastin fibrillin) and nonstructural (decay-accelerating factor [DAF], serum amyloid P -SAP- components of elastic fibers to characterize fiber structure in neonatal skin, normal adult skin and adult skin with solar elastosis from advanced photoaging. We found by immunohistochemistry and by western blotting that DAF, unlike SAP, is present on cutaneous elastic fibers in neonates and young children, suggesting that DAF may play an early, integral role in protecting elastic fibers from destruction by complement. The most superficial portion of oxytalan fibers stained with antibodies against fibrillin and DAF, while anti-tropoelastin stained only the deeper portion of oxytalan fibers. This suggests that deep oxytalan fibers are composed of both elastin and microfibrils, while the most superficial component is composed solely of microfibrillar proteins. Solar elastosis showed increased fibrillin, DAF, tropoelastin and SAP. Thus, solar elastosis is composed of both microfibrillar and elastin proteins.

Adult↗
PubMed2003

Abnormalities of serum antielastin antibodies in connective tissue diseases.

BACKGROUND: Antibodies (Abs) to alpha-elastin (elastin breakdown product) and tropoelastin (elastin precursor) are found in the serum of all human subjects and correlate with their respective serum peptide levels; however, peptide levels vary with age and some disease states. This study was undertaken to determine if serum elastin Abs, peptides, and elastin metabolism were altered in autoimmune diseases by detecting a changing ratio of serum anti-alpha:tropoelastin Ab levels. METHODS: Serum from patients with a variety of connective tissue diseases, including 28 with systemic lupus erythematosus (SLE), 24 with scleroderma, 18 with rheumatoid arthritis (RA), 10 with polymyositis, and 39 with vasculitis, was compared with serum from 19 age-matched healthy subjects for levels of antitropoelastin and anti-alpha-elastin Abs. RESULTS: We found an increase in IgG anti-alpha-elastin and a decrease in antitropoelastin Abs in the sera of patients with scleroderma (p < .02 and .00005) and SLE (p < .006 and .011). There was also a marked increase in anti-alpha-elastin Abs in patients with polyarteritis nodosa (p < .0005) and decreases in antitropoelastin Abs in patients with RA (p < .05), polymyositis (p < .01), and a variety of other vasculidities (p < .0003). CONCLUSIONS: Abnormal variations in elastin metabolism may be detected in several connective tissue diseases by measuring ratios of alpha- and tropoelastin IgG Abs as markers of elastin degradation and synthesis.

Adolescent↗
PubMed2003

Elastogenesis in human arterial disease: a role for macrophages in disordered elastin synthesis.

OBJECTIVE: Elastin, an extracellular matrix protein, constitutes about 30% of the dry weight of the arteries. Elastolysis induced by inflammatory processes is active in chronic arterial diseases. However, elastogenesis in arterial diseases has received little attention. In this work we hypothesized that disordered elastogenesis is active in matrix remodeling in atheroma and abdominal aortic aneurysm (AAA). METHODS AND RESULTS: Human AAA and atheroma have 4- to 6-fold more tropoelastin protein than nondiseased arteries. The smooth muscle cell-containing media and fibrous cap of atherosclerotic arteries contain ordered mature elastin, whereas macrophage (MPhi)-rich regions often have disorganized elastic fibers. Surprisingly, in addition to smooth muscle cells, MPhis in diseased arteries also produce the elastin precursor tropoelastin, as shown by double immunostaining, in situ hybridization, and reverse transcription-polymerase chain reaction for tropoelastin mRNA. Cultured monocyte-derived MPhis can express the elastin gene. AAA have 9-fold but atheroma only 1.6-fold lower levels of desmosine, a marker for mature cross-linked elastin, than normal arteries. CONCLUSIONS: This study demonstrates ongoing but often ineffective elastogenesis in arterial disease and establishes human macrophages as a novel source for this important matrix protein. These results have considerable import for understanding mechanisms of extracellular matrix remodeling in arterial diseases.

Aorta↗
PubMed1996

Site-specific responses to monocrotaline-induced vascular injury: evidence for two distinct mechanisms of remodeling.

Monocrotaline (MCT)-induced pulmonary vascular injury was used to begin studying the mechanism(s) of vascular remodeling in Fischer 344 rats, using extracellular matrix (ECM) gene expression to define areas of remodeling. By day 28 after injection, pulmonary artery pressures were increased and right ventricular hypertrophy had developed compared with normal controls. Tropoelastin, fibronectin, and alpha 1(I) procollagen mRNA levels increased at least 2-fold by day 28. In situ hybridization demonstrated tropoelastin gene expression by cells adjacent to the lumen and procollagen gene expression at the medial-adventitial border in both small muscular and large elastic pulmonary arteries. This pattern of gene expression was observed as early as 1 wk after MCT injury. These observations indicated two distinct areas of remodeling, one along the vascular lumen at the site of monocrotaline-induced injury and the other at a second distinct site. To determine whether other differences may be involved at these two sites, the presence of transforming growth factor-beta (TGF-beta) was studied. Total TGF-beta protein was 4-fold higher in remodeling lungs compared with normal lungs. Gene expression for all three isoforms of TGF-beta colocalized with tropoelastin gene expression along the vascular lumen but not with alpha 1(I) procollagen gene expression. These results suggest a complex site-specific response to injury mediated by two distinct pathways in this model of pulmonary vascular remodeling.

Animals↗
PubMed1997

Exogenous and endogenous transforming growth factors-beta influence elastin gene expression in cultured lung fibroblasts.

Elastin, an important structural protein of the extracellular matrix, confers elastic properties on the pulmonary alveolar interstitium. In the alveolar wall, elastin is primarily produced postnatally by fibroblasts. The mechanisms that regulate lung fibroblast (LF) elastin gene expression have not been completely defined, although both transcriptional and posttranscriptional mechanisms appear to be involved. Transforming growth factors-beta (TGF-beta s) have been shown to increase elastin production by cultured neonatal rat LF. Analyses of elastin gene transcription and mRNA stability indicate that exogenous TGF-beta 1 increases the half-life of tropoelastin mRNA by 1.5-fold and does not alter elastin gene transcription. Interference with the functions of endogenous TGF-beta 1 in cultured LF, through the addition of neutralizing antibodies or antisense oligodeoxynucleotides, decreases tropoelastin and tropoelastin mRNA production by these cells. The content of total (latent plus active) TGF-beta s was approximately 4.5-fold greater in lungs obtained from rats on postnatal day 8 than in lungs obtained from adults. These findings indicate that endogenous TGF-beta s, in cultured LF, regulate elastin gene expression, most likely by a posttranscriptional mechanism. Since others have shown that elastin mRNA appears to have a longer half-life in neonatal than in adult rat lungs, we hypothesize that the higher content of TGF-beta s could contribute to the greater elastin mRNA stability in neonatal lungs.

Animals↗
PubMed2006

Quantitative and comparative studies of the vocal fold extracellular matrix. I: Elastic fibers and hyaluronic acid.

OBJECTIVES: This study examines the elastic fiber and hyaluronic acid (HA) content of the midmembranous vocal fold laminae propriae (LPs) of humans, dogs, pigs, and ferrets. METHODS: Lamina propria elastin was quantified by measuring the amino acid desmosine, and HA was measured by an enzyme-linked immunosorbent assay-based technique. Quantitative histology was used to evaluate elastin and HA levels in specific LP regions. The distributions of fibrillin-1, a primary microfibrillar component of elastic fibers, and of tropoelastin, an indicator of elastin synthesis, were immunohistochemically analyzed. RESULTS: Elastin and HA constituted 8.5% +/- 2.1% and 0.82% +/- 0.11% of human LP, respectively, relative to tissue total protein. Although the mean LP desmosine levels were similar across species, the mean HA levels in canine (p < 3.1 x 10(-5)), porcine (p < 1.5 x 10(-5)), and ferret (p < 6.6 x 10(-4)) LPs were 3 to 4 times higher than that in humans. Marked interspecies differences in elastin, fibrillin-1, tropoelastin, and HA distributions were observed histologically. CONCLUSIONS: The elastin content of the human LP is roughly twice that of the dermis, whereas the HA content of the human LP is similar to that of the dermis. Although all species had similar levels of desmosine, histologic evaluation indicates that the porcine elastin distribution is most similar to that of the human LP. Fibrillin-1 staining suggests that stress in the human LP may be particularly high in the superior superficial layer, and tropoelastin staining indicates that the rate of LP elastin turnover may vary spatially.

Animals↗