The Biosynthesis of Elastin Cross-links

Migration of monocytes in the presence of elastolytic fragments of elastin and in synthetic derivates. Structure-activity relationships

YGVG and GLVPG, two new chemokinetic peptides, were identified in elastolytic digests of elastin, besides the known chemoattractant hexapeptide VGVAPG. In order to identify possible sequences responsible for the chemotactic and chemokinetic activities and to obtain structure-activity relationships we synthesized some analogues of these peptides: FGVG (an analogue of YGVG), GVAPG and VGAPG (derived from the hexapeptide by deletion of Val1 or Val3). FGVG has a higher chemotactic activity than YGVG (chemotactic indices of 0.62 and 0.49, respectively, at 10(-11) M) and is both chemotactic and chemokinetic. Checkerboard analysis demonstrated that both peptides derived from the hexapeptide present, in addition to the chemotactic activity, a chemokinetic activity. The chemotactic index of GVAPG is 0.66 at 10(-10) M, while for VGAPG it is 0.86 at 10(-9) M. These results indicate that the deletion of the N-terminal residue of the elastin chemotactic peptides, VGVAPG and GFGVG, gives rise to chemokinetic activity. CD and NMR studies showed that all peptides are largely unordered in aqueous solution.

In vitro and in vivo inhibition of lysyl oxidase by aminopropionitriles

Inhibition of lysyl oxidase (protein-lysine 6-oxidase, EC 1.4.3.13) decreases the rate of collagen and elastin cross-link formation and produces osteolathyrism in animals. Organic nitriles, including beta-aminopropionitrile (BAPN), have been shown to irreversibly inhibit lysyl oxidase in vitro. Both BAPN and 3,3'-iminodipropionitrile (IDPN) have been shown to produce osteolathyric changes when administered to animals. To date compounds that have been reported to inhibit this enzyme possess a primary amine functional group. In this study a series of primary and substituted aminopropionitriles was studied for their ability to inhibit lysyl oxidase activity both in vitro and in vivo. Our results show that of the compounds tested, BAPN was the most potent inhibitor of the enzyme. Reversible inhibition of lysyl oxidase in vitro was found with two secondary aminonitriles, IDPN and monomethylaminopropionitrile (MMAPN). There was no inhibition of enzyme activity associated with the tertiary compound 3,3'-dimethylaminopropionitrile (DMAPN) or propionitrile, a compound lacking an amine functional group. IDPN was found to produce a slight irreversible inhibition of the enzyme both in vitro and in vivo. Pretreatment of rats with pargyline, an inhibitor of monoamine oxidase, was found to increase the inhibitory potential of BAPN (p < or = .1). Pargyline pretreatment did not alter the inhibitory potential for any of the other aminonitriles tested. These results suggest that the presence of a primary amino functional group is not a strict requirement for inhibition of lysyl oxidase. In addition, reversible and irreversible mechanisms of inhibition may be involved in the production of osteolathyric changes associated with IDPN exposure.

Production of recombinant human tropoelastin: characterization and demonstration of immunologic and chemotactic activity

Tropoelastin cannot readily be prepared in quantity from natural sources and this has limited research in several important areas including structure/function relationships and fiber assembly. In order to eliminate this limitation, human tropoelastin has been expressed in a recombinant bacterial system and the protein has been highly purified. The size, amino acid composition, and sequence of the amino terminus of the recombinant tropoelastin (rTE) all agree with values predicted by the nucleotide sequence of the cDNA used in the expression vector. The rTE exhibits cross-reactivity with antibodies directed against a mixture of peptides derived from human elastin as well as antibody against a defined peptide located at the carboxy terminus of the protein. In addition, the rTE is chemotactic for fetal calf ligament fibroblasts. These results suggest that rTE could be a useful reagent for many types of studies.

Structure of the elastin gene and alternative splicing of elastin mRNA: implications for human disease

The protein elastin is largely responsible for the elastic properties of vertebrate lungs, large blood vessels, and skin. The structure of the human, bovine, and chick elastin gene and protein monomer, tropoelastin, has recently been elucidated by using techniques of molecular biology. Extensive homology of amino acid sequence exists among the mammalian species and there is in addition strong conservation of nucleotide sequences in the 3' untranslated region of the gene. The translated exons are small and embedded in large expanses of introns. Sequences coding for the hydrophobic regions, responsible for the elastic properties of the molecule, and the alanine-lysine rich regions, responsible for crosslink formation between molecules, reside in separate exons and alternate for the most part in the elastin gene. S1 analyses and sequence analysis of cDNA and genomic clones have indicated that there is substantial alternative splicing of the primary elastin transcript. Variations in the structure of mRNAs resulting from alternative splicing could explain the existence of the multiple forms of tropoelastin observed electrophoretically in several species. Different kinds of splicing patterns could occur in human populations and may contribute to aging and pathological situations in the cardiovascular and pulmonary systems.

Characterization of rat heart tropoelastin

Several overlapping rat tropoelastin cDNA clones were isolated from a lambda gt11 rat heart cDNA library and their nucleotide sequence was determined. The corresponding deduced amino acid sequence of rat tropoelastin revealed strong homology to bovine and human tropoelastins although possessing some unique features including greater size (18%) and composition of repetitive units. Comparison of the amino acid sequence of rat tropoelastin to four other tropoelastin species reveals that the hydrophobic peptide repeat regions in the middle of each molecule and the crosslinking areas containing three lysine residues are remarkably conserved. A possible function for the clustering of three lysine residues in providing a mechanism for the in vivo reduction of dehydrolysinonorleucine via a redox shuttle with dihydrodesmosine is proposed. In addition, the COOH-terminal sequence of the rat tropoelastin is virtually identical to tropoelastins of other species in possessing a cysteine/arginine/lysine containing segment. There are no obvious amino acid insertions or substitutions in the COOH-terminal half of the rat tropoelastin molecule which would signal unique cleavage or glycosylation sites. Examination of the steady-state levels of rat tropoelastin mRNA in 8- and 12-day neonatal lung, heart, and aortic tissues showed that the amount of tropoelastin mRNA was abundant and of similar size (3.9 kb) in all three tissues.

Treatment of experimental silicosis with antifibrotic agents

We tested the efficacy of 2 antifibrotic agents, the proline analogue cis-4-hydroxy-L-proline (cHyp) and the lathyrogen beta-aminopropionitrile (BAPN), on experimental silicosis in hamsters. Silica (75 mg) was instilled intratracheally, and 3 months later lung hydroxyproline content, the volume density of silicotic nodules in lung parenchyma, fluid-filled lung pressure-volume curves, body weight and survival were measured. Animals were injected with cHyp, 200 mg/kg body weight, or BAPN, 150 mg/kg body weight, twice daily for 3 months. Hydroxyproline contents (mg/lung) at 3 months were: control, 0.8 +/- 0.1; silica, 1.4 +/- 0.1 (P less than 0.05 compared to control); silica-cHyp, 1.2 +/- 0.2; silica-BAPN, 1.4 +/- 0.1 (both NS compared to silica). The volume density of granuloma (% of surface area) was: silica, 0.7 +/- 0.1; silica-cHyp, 5.9 +/- 1.0; silica-BAPN, 9.7 +/- 1.5 (both P less than 0.5 compared to silica). There was no difference among the groups as assessed by lung pressure-volume curves. No toxic effects were produced on the skeletal system as assessed by bone hydroxyproline content and skeletal roentgenograms. Final body weights (g) were: silica, 114 +/- 5; silica-BAPN, 108 +/- 6; silica-cHyp, 88 +/- 7 (the latter P less than 0.05 compared to silica). Survival (%) was: silica, 62%; silica-BAPN, 34%, silica-cHyp, 28% (both P less than 0.05 compared to silica). These data show that cHyp and BAPN treatment did not prevent silica-induced pulmonary fibrosis, led to more extensive silicotic nodules, and were toxic. Both cHyp and BAPN have some efficacy in other models of fibrosis, and the observations in the present study could be specific to silicosis in the hamster.

Structure of the 3' region of the human elastin gene: great abundance of Alu repetitive sequences and few coding sequences

Two overlapping clones encompassing 8.5 kb of the human elastin gene were isolated from two genomic libraries constructed by partial digestion with either HaeIII/AluI or Sau3A and contained in lambda Charon 4A or EMBL3, respectively. The 6 kb of DNA comprising the most 3' portion of the gene were sequenced demonstrating an extremely low coding ratio since only three exons containing a total of 134 translated nucleotides were identified. Two exons totaling 78 bp of translated sequences which were previously found in the bovine gene were absent in the human gene. The 3' most exon encoded the unusual amino acid sequence, GGACLGKACGRKRK. The human gene was terminated by 1.2 kb of untranslated sequence which contained two polyadenylation attachment signals. The remainder of the 6 kb was composed of intervening sequences which were abundantly rich in Alu family repetitive sequences found in both orientations. This first report of the characterization of the human elastin gene suggests that significant variation in the gene may exist between species and raises the possibility of consequential polymorphism, mediated by recombination between Alu sequences, in the human population.

Analysis of the 3' region of the sheep elastin gene

The nucleotide sequences of a 1279-bp sheep elastin cDNA clone, pcSEL1 [Yoon et al. (1984) Biochem. Biophys. Res. Commun. 118, 261-269], and a 1230-bp sheep elastin genomic subclone, pSS1 [Davidson et al. (1984) Biochem. J. 220, 643-652], corresponding to a portion of the cDNA clone, were determined. These analyses permitted determination of the 100 amino acids at the carboxy terminus of sheep tropoelastin. A portion of this sequence showed strong homology to known sequences of pig tropoelastin, but most of the sequence had not been previously determined through protein sequencing. Novel aspects of the tropoelastin molecule which have been revealed by the present analyses are (i) the presence of an unusual sequence, KPPKP, which may contribute to crosslink formation; and (ii) the finding of cysteine within a sequence, CLGKSCGRKRK, at the putative carboxy terminus of tropoelastin. Because of the presence of these sequences, it is speculated that the carboxy-terminal region may be of importance in crosslinking tropoelastin molecules to themselves or to other matrix macromolecules. The nucleotide analyses revealed that sheep elastin mRNA contains a 974-bp untranslated sequence at the 3' end, which appears to be strongly conserved among species.

Structure of the 3' portion of the bovine elastin gene

A bovine genomic library constructed by partial Sau3A digestion and contained in lambda Charon 30 was screened by in situ hybridization with a 1.3-kilobase (kb) sheep elastin cDNA clone [Yoon, K., May, M., Goldstein, N., Indik, Z., Oliver, L., Boyd, C., & Rosenbloom, J. (1984) Biochem. Biophys. Res. Commun. 118, 261-269]. Three clones encompassing 10 kb of the bovine elastin gene were identified and characterized by restriction mapping and DNA sequencing of the 6.2 kb of the most 3' region of the gene. These analyses have permitted localization of eight exons in the 6.2 kb in which the translated exons vary in size from 27 to 69 base pairs, and there is an approximately 1-kb untranslated region at the 3' end. In addition to identification of sequences homologous to those found in porcine tropoelastin, the analyses defined a 58 amino acid sequence that forms the carboxy-terminal region of tropoelastin, and this sequence, which contains two cysteine residues, was previously not observed in the protein sequence data. The analyses also suggest that functionally distinct cross-link and hydrophobic domains of the protein are encoded in separate exons.

Pseudoxanthoma elasticum-like skin changes induced by penicillamine

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The perforating disorders

This article reviews the diseases that may show epidermal perforation as a histologic feature. Many of these represent examples of transepithelial elimination (TEE), a mechanism by which the skin rids itself of abnormal substances. After a review of disorders in which perforation is an occasional finding, four diseases that have been considered essential perforating disorders are discussed: elastosis perforans serpiginosa (EPS), reactive perforating collagenosis (RPC), perforating folliculitis (PF), and Kyrle 's disease (KD). A review of the literature, including recent reports of perforating diseases associated with chronic renal failure, suggests that there may be considerable clinical and histologic overlap among PF, KD, and the adult form of "perforating collagenosis." A working classification for the perforating disorders is suggested.

Characterization of a sheep elastin cDNA clone containing translated sequences

mRNA, isolated from the ligamentum nuchae of fetal sheep by guanidine HCl extraction and oligo(dT) cellulose chromatography, was used to synthesize blunt-ended cDNA molecules by the successive application of AMV reverse transcriptase, DNA polymerase and S1 nuclease. The cDNA was centrifuged on a 15-30% sucrose gradient and molecules greater than 700 bp were tailed with dCTP and cloned into the PstI site of pBR322 which had been tailed with dGTP. Ampicillin-sensitive and tetracycline-resistant colonies were screened by in situ hybridization with elastin-enriched mRNA that had been terminally labeled with 32p. Recombinant plasmids prepared from strongly hybridizing colonies were characterized by restriction mapping and the plasmid with the largest insert (1300 bp) thought to contain elastin sequences was characterized in more detail. The nick-translated cDNA hybridized to a single 3.5 kb mRNA species upon blot hybridization, a size identical to that previously identified for chick elastin mRNA (Burnett et al. (1982) J. Biol. Chem. 259, 1569-1572). Nucleotide sequencing of the 5' end of the cDNA demonstrated a sequence which was extremely GC rich and which corresponded to an amino acid sequence partially homologous to that previously identified in porcine tropoelastin (Foster et al. (1973) J. Biol. Chem. 248, 2876-2879). This is the first report of the identification of a plasmid containing sequences complementary to a translated region of elastin mRNA.

Penicillamine: review and cutaneous manifestations

D-Penicillamine, a heavy metal chelator used in the treatment of Wilson's disease and other conditions, may be associated with both noncutaneous and cutaneous side effects. Some of the cutaneous lesions are due to a toxic-metabolic effect on connective tissue; some may be explained on the basis of autoimmunity; some are acute sensitivity reactions, and some are secondary to unknown mechanisms. The types of cutaneous manifestations may, in some instances, be correlated with the disease being treated and the dosage and duration of penicillamine therapy.

Inhibition of beta-aminopropionitrile (beta APN)-induced skeletal teratogenesis by the flavonoid beta-hydroxyethylrutosides (HR) in hamster fetuses

Since biochemical studies have shown that flavonoids such as beta-hydroxyethylrutosides (HR) protect against the damage to collagen induced by lathyrogens in adult rats, this compound was given to pregnant hamsters in order to determine its effects on the teratogenicity induced by beta-aminopropionitrile (beta APN). A dose of 2,500 mg/kg of beta APN alone given by gavage on day 11 produced a high frequency (69.5%) of skeletal anomalies in the offspring of hamsters. Administration of HR immediately following beta APN to pregnant animals resulted in a significantly decreased teratogenic response (P less than 0.05). These data provide evidence to support the view that the primary mechanism for the beta APN-induced skeletal dysmorphogenesis is the inhibition of cross linking during the maturation of collagen fibers.

Control of elastin synthesis

mRNA was isolated from the thoracic aortas of 16-day chick embryos and used to synthesize blunt-ended heteroduplex molecules consisting of one strand of mRNA and one of cDNA using AMV reverse transcriptase and S1 nuclease. The duplexes were tailed with dCTP and hybridized to the plasmid pBR322 which had been restricted with Pst I and tailed with dGTP. Recombinant plasmids were used to transform E. coli C600 and colonies containing elastin cDNA were selected by in situ hybridization with 32P labeled elastin mRNA and by hybrid selected translation using the nuclease-treated reticulocyte lysate system. mRNA recovered from hybridization to DNA of one clone, pWB1, markedly stimulated incorporation of [3H]valine into a protein which was immunoprecipitable with elastin-specific antibody and had a molecular weight of 72,000, characteristic of tropoelastin. The 230 bp insert of pWB1 was sequenced by the technique of Maxam and Gilbert and found to be derived from a nontranslated region of the 3' end of the mRNA. Nick-translated pWB1 was used to identify and to estimate the relative amounts of elastin mRNA in the developing chick embryo aorta by blot hybridization. A single mRNA species of 3.5 kb hybridized to the pWB1 probe and this species increased greatly in amount between day 7 and day 14. This increase was paralleled by an increase in translatable elastin mRNA and by the rate of elastin synthesis of aortas from various age embryos incubated in vivo. The injection of 150 microgram of hydrocortisone 21-phosphate into 8-day eggs produced a significant increase in both the relative rate of tropoelastin synthesized by the isolated aortas and the relative amount of elastin mRNA. These results suggest that the observed changes in elastin synthesis during development and after hydrocortisone administration are governed by the elastin mRNA content of the aortas.

Characterization of a structural glycoprotein from bovine ligamentum nuchae exhibiting dual amine oxidase activity

A structural glycoprotein has been extracted from bovine ligamentum nuchae by using 5 M guanidine hydrochloride containing a disulfide bond reducing agent and purified by preparative gel electrophoresis. The isolated material appeared to be monodisperse, with a molecular weight of approximately 34000, as shown by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and by analytical ultracentrifugation. It contains 10% carbohydrate comprising mannose, N-acetylglucosamine, galactose, and sialic acid in a 6:5:3:3 molar ratio. The glycoprotein has been assayed for peptidyl-lysine oxidase activity by using [3H]lysine-aortic elastin, prepared from 15- to 17-day-old chick embryos, as a substrate. In the absence of free lysine, the specific activity of the preparation over a 2-h incubation was approximately 60 X 10(4) dpm/mg of purified protein. Addition of 10 mM lysine resulted in an approximately 50% decrease in the specific activity. Free lysine was shown to act as a substrate for the glycoprotein preparation as indicated by control experiments using [3H]lysine in place of the aortic substrate. These results demonstrate that the glycoprotein exhibits a dual amine oxidase activity. In the presence of 0.27 mM beta-aminopropionitrile fumarate, a concentration which completely inhibits peptidyl-lysine oxidase activity in other lysyl oxidases, the glycoprotein preparation was inhibited by approximately 14%. In the absence of 5 M guanidine hydrochloride and reducing agent, the glycoprotein undergoes aggregation which in the presences of copper ions results in the formation of cylindrical tactoids, the diameter of which (11 nm) corresponds closely to that of the fibrils which in the majority of connective tissue matrices constitute the microfibrillar component mainly associated with elastic fibers.

Immuno electron microscopic studies on cells synthesizing elastin

Embryonic chick and hamster aortas were examined in the electron microscope using ferritin-conjugated, elastin-specific antibodies after etching of the plastic, thin sections with a dilute solution of benzene, methanol and ethanol. Specific staining of intracellular vesicles was observed in both smooth muscle and endothelial cells in addition to extracellular elastin fibers. In the chick cells, these ferritin-stained vesicles had a lipid-laden appearance. In both species the vesicles appeared to fuse with the plasma membrane and discharge their contents into the extracellular space suggesting elastin is secreted via vesicular structures.

An analysis of the organ and species immunospecificity of elastin

The connective tissue protein elastin is largely responsible for maintaining the elasticity of major blood vessels and lung tissue. Comparatively few studies have been made of the immunologic properties of elastin because of its high degree of insolubility and because of its apparent limited capacity to elicit precipitating antibodies. Recent studies have focused on the possible role of elastolytic enzymes, particularly leukocyte elastase, in the pathogenesis of chronic obstructive lung disease, but there are no reports in the literature concerning the antigenic properties of peptides released by digestion of insoluble elastin with leukocyte elastase. In the present study, we have obtained antibodies in rabbits to peptides prepared by digestion of dog and human lung and aortic elastin with either oxalic acid or leukocyte elastase. By hemagglutination assays, we have shown generally that: (1) within a given species the peptides from aorta and lung cross-react strongly with one another, (2) there was rather poor cross-reactivity between peptides from different species (3) the peptides obtained by oxalic acid digestion cross-react poorly with those obtained by elastase digestion, (4) the antibodies to the peptides cross-reacted with the insoluble elastin from which the peptides were derived. These elastin-specific antibodies may be useful for ultrastructural localization of elastin and identification of fragments derived from elastin in the sera of humans and experimental animals.

Biosynthesis of tropoelastin by elastic cartilage

Elastic ear cartilage and aortae from nine-day-old hamsters were incubated in Krebs-Ringer medium containing ascorbate, beta-aminopropionitrile and either [14C]proline or [3H]valine. The [14C]proline-labeled proteins were separated by chromatography on Agarose A-5 m in sodium dodecyl sulfate and their [14C]-hydroxyproline content measured. A fraction having an approximate molecular weight of 70,000 measured by polyacrylamide gel electrophoresis had a [14C]hydroxyproline content of 9.1% in the cartilage and 11.8% in the aorta. This fraction was also relatively heavily labeled with [3H]valine. The 70,000 dalton, [3H]valine-labeled protein of both the aorta and ear cartilage was precipitated by elastin-specific antibody prepared against hamster insoluble aorta elastin, but no higher molecular weight protein was immunoprecipitated. Based on these results we identify the 70,000 dalton protein from the elastic cartilage as tropoelastin.

Arterial elastin synthesis in the young chick

In the growing chick a marked stimulation in soluble and mature arterial elastin synthesis occurs 2 and 5 weeks after hatching. Measurement of [3H]valine and [3H]proline incorporation into arterial soluble protein during this period indicated that most of the label is found in a 70 000 dalton protein subunit. The labeled soluble subunit had the characteristics of native soluble elastin or tropoelastin. During the period in which the greatest percentage increase in mature elastin occurs, the highest specific activities of soluble [3H]valine-labeled protein were observed. These changes were striking and suggest a developmental period for the growing chick in which factors related to elastin metabolism may be more easily studied.

The teratogenic effects of beta-aminopropionitrile in hamsters

The teratogenicity of beta-aminopropionitrile (beta APN) was evaluated in golden Syrian hamsters; single doses of 1250, 2500, and 3750 mg/kg given on days 7-13 produced fetal mortality, growth retardation and malformations. All time-dose combinations produced gross external abnormalities with the highest rate (92.5%) occurring following day-12 treatment. High frequencies of skeletal abnormalities including deformities of the ribs, fibula, and scapula occurred after days-10-12 treatment. Deformed ribs occurred in 100% of fetuses exposed on day 11 to any of the dosages. The types of abnormality generally resembled those produced by lathyrogens in other species except for exencephaly and encephalocele, which occurred after treatment on day 7. These results indicate that betaAPN is a typical teratogen, capable of producing abnormalities of the central nervous system early in gestation, and may reflect a broader mechanism for its activity than previously suggested.