Experimental lathyrism in the chick embryo. The distribution of beta-aminopropionitrile

Lysyl Oxidase Activity Is Required for Ordered Collagen Fibrillogenesis by Tendon Cells

Lysyl oxidases (LOXs) are a family of copper-dependent oxido-deaminases that can modify the side chain of lysyl residues in collagen and elastin, thereby leading to the spontaneous formation of non-reducible aldehyde-derived interpolypeptide chain cross-links. The consequences of LOX inhibition in producing lathyrism are well documented, but the consequences on collagen fibril formation are less clear. Here we used β-aminoproprionitrile (BAPN) to inhibit LOX in tendon-like constructs (prepared from human tenocytes), which are an experimental model of cell-mediated collagen fibril formation. The improvement in structure and strength seen with time in control constructs was absent in constructs treated with BAPN. As expected, BAPN inhibited the formation of aldimine-derived cross-links in collagen, and the constructs were mechanically weak. However, an unexpected finding was that BAPN treatment led to structurally abnormal collagen fibrils with irregular profiles and widely dispersed diameters. Of special interest, the abnormal fibril profiles resembled those seen in some Ehlers-Danlos Syndrome phenotypes. Importantly, the total collagen content developed normally, and there was no difference in COL1A1 gene expression. Collagen type V, decorin, fibromodulin, and tenascin-X proteins were unaffected by the cross-link inhibition, suggesting that LOX regulates fibrillogenesis independently of these molecules. Collectively, the data show the importance of LOX for the mechanical development of early collagenous tissues and that LOX is essential for correct collagen fibril shape formation.

COLLAGEN METABOLISM IN THE NORMAL AND LATHYRITIC CHICK

1. Radioisotope incorporation studies of normal and lathyritic chick embryo bone collagen do not demonstrate any interference by lathyrism with collagen synthesis or fibril formation. 2. The results indicate that a portion of the extractable collagen from lathyritic chick embryo bone represents newly synthesized protein. Evidence from a double labeling experiment and from analysis of isotope flow between the extractable and non-extractable pools suggests the extractable lathyritic collagen is heterogeneous. We propose that the lathyritic process affects collagen in all states of aggregation, probably in varying degree. 3. Puromycin, administered intravenously, reduces the amount of extractable collagen in both normal and lathyritic chick embryo bone, and diminishes the incorporation of labeled proline into collagen. 4. Marked fluctuations in incorporation of labeled amino acids into chick embryo bone collagen suggests the occurrence of wide fluctuations in metabolism of this protein.

ORGANIZATION AND DISORGANIZATION OF COLLAGEN

The organization of the normal collagen molecule and fibrils is reviewed and the detection, assay, and isolation of a collagenolytic enzyme from amphibian tadpole tissue are described and its possible significance in metamorphosis is discussed

EXPERIMENTAL LATHYRISM. AN AUTORADIOGRAPHIC STUDY

In normal and lathyritic chick embryos bone collagen was synthesized primarily in the periosteum of the femurs, and was organized as radioactive spicules in these bones. Saline extraction of the lathyritic bones removed the radioactive spicules, although they eventually seemed to become non-extractable. Normal bone seemed to be unaffected by saline extraction. Marked variation in the degree of isotope incorporation was seen in collagenous and non-collagenous tissues. All the tissues of any one embryo, however, showed a similar degree of isotope incorporation. Tritiated β-aminopropionitrile was diffusely distributed throughout bone and was completely removed by saline extraction. This autoradiographic study supports the postulate that a portion of extractable lathyritic collagen is recently synthesized and is organized in fibrous structures in bone.

Mechanism of neurotoxic action of beta,beta'-iminodipropionitrile (IDPN): N-hydroxylation enhances neurotoxic potency

The molecular mechanism(s) whereby beta, beta'-iminodipropionitrile (IDPN) induces an excitatory behavioral syndrome and a distinct alteration of the axonal cytoskeleton in experimental animals is not known. We demonstrate here that upon intraperitoneal administration to rats, the N-hydroxy analog of IDPN (HOIDPN) induces a parallel spectrum of both neurotoxic effects of IDPN and is approximately 8 times more potent than IDPN in this regard. This is consistent with the involvement of a flavin monooxygenase-mediated N-oxygenation pathway in the toxic activation of IDPN.

Pathogenesis of experimental giant neurofilamentous axonopathies: a unified hypothesis based on chemical modification of neurofilaments

This review summarizes current evidence suggesting that the pathogenetic basis of giant axonal neuropathies induced by neurotoxic chemicals involves a direct chemical modification of neurofilaments (NF) and/or related cytoskeletal proteins. Chemical modification of NF is believed to disrupt the normal cytoskeletal organization, which results in an alteration in NF transport rate and accumulation of NF at prenodal sites along the axon. The exact location at which axonal enlargements occur appears to be a continuous function, dependent on both the structure and dosage schedule of the chemical toxin. A unified hypothesis for the neuropathologic effect of the diverse spectrum of toxic chemicals known to induce giant axonopathies is presented, based on recently published data on the structure of NF protein. Neurotoxic chemicals are believed to alter the charge balance of highly ionic domains of NF proteins which are thought to enter into intermolecular coulombic interactions in forming the supramolecular cytoskeletal framework.

Thiosemicarbazide-induced osteolathyrism in metamorphosing Xenopus laevis

Exposure of Xenopus laevis tadpoles to thiosemicarbazide (TSC), at concentrations from 10 to 75 mg/liter, causes an inhibition of metamorphosis and produces the classic manifestations of the experimental disease, osteolathyrism. Concentration-dependent effects of TSC exposure are observed in growth rate and in the severity of the osteolathyrogenic effect. Concentrations allowing the most rapid growth produce the more extreme osteolathyrogenic defects. Osteolathyrism in these animals is identical in characteristics to the condition described in a wide variety of vertebrate species. In Xenopus, osteolathyrism is expressed morphologically as anomalies in bone development, skeletal conformation, and abnormal connective tissue organization in the aorta wall. The underlying defect responsible for these observations is apparently a perturbation of collagen fiber formation and maturation, as evidenced ultrastructurally by aberrant distribution and packing of collagen fibers. It is suspected that TSC produces this effect by altering the availability of copper ion, a cofactor to lysyl oxidase, an essential enzyme for intermolecular cross-linking of procollagen. This step in collagen metabolism has been consistently implicated as the site of action of several osteolathyrogenic agents. Xenopus tadpoles present a classic response to this known osteolathyrogen and demonstrate a high degree of uniformity of response within the experimental groups. In view of the developmentally significant events accessible with this system and inherent logistic and economical advantages, the metamorphosing tadpole of Xenopus holds considerable potential for the experimental analysis of teratogenic agents and events.

Changes in chemical composition of chick embryos treated with a beta-xyloside and a lathyrogen

Nine-day chick embryos were treated with 4-methylumbelliferyl beta-D-xyloside or beta-aminopropionitrile fumarate, and their gross chemical composition was examined one week later. Total DNA was 10--20% less in embryos treated with either drug than it was in control embryos. Xyloside-treated embryos showed marked increases in percent wet weight and in sodium/DNA and chloride/DNA ratios, and small decreases in protein/DNA, hydroxyproline/DNA and sulfate/DNA. None of these parameters was affected in embryos treated with beta-aminopropionitrile. Approximately 85% of the uronic acid of control embryos was present as chondroitin sulfate, with a degree of sulfation of 80% and charge density of 1.8; all of this chondroitin sulfate was covalently linked to peptide and had a number-average molecular weight of 29,300. In embryos treated with beta-xyloside, 90% of the uronic acid was present as chondroitin sulfate, with a degree of sulfation of 40% and charge density ranging from 1 to 2; 27% of this chondroitin sulfate, with an average molecular weight of 25,400, was peptide linked, while 73% was linked to 4-methylumbelliferone and had an average molecular weight of 22,900. The chemical differences between embryos treated with the xyloside and embryos treated with the lathyrogen reinforce the conclusion on morphological grounds that these are distinct syndromes involving different aspects of the extracellular matrix.

Studies in vivo on the biosynthesis of collagen and elastin in ascorbic acid-deficient guinea pigs

1. After the administration of labelled proline to guinea pigs deprived of ascorbic acid for 15 days, the dorsal skin was examined 5 days later in an attempt to detect the presence of hydroxyproline-deficient collagen (protocollagen). The extent of incorporation of proline into skin collagens indicated a severe impairment of collagen synthesis. 2. A comparison of proline and hydroxyproline specific radioactivities in diffusible peptides obtained by treatment with collagenase of either purified skin collagens or direct hot-trichloroacetic acid extracts of skin failed to indicate the presence of protocollagen. Possible reasons for this are discussed. 3. The incorporation results did not indicate an inability of normal collagen, i.e. collagen hydroxylated to the normal degree, to cross-link in scurvy. 4. Incorporation of labelled proline into aortic elastin isolated from the same animals did not indicate a decrease in elastin biosynthesis in ascorbic acid deficiency, beyond that attributable to the inanition accompanying the vitamin deficiency. The proline/hydroxyproline specific-radioactivity ratio in elastin from scorbutic guinea pigs was about 6:1 in contrast with the 1:1 ratio in control groups. It is concluded that the formation of elastin hydroxyproline was ascorbate-dependent and that a hydroxyproline-deficient elastin is formed and retained in scurvy. The formation of desmosines was unimpaired in scorbutic animals. 5. Studies with chick embryos confirmed the formation of elastin hydroxyproline from free proline. Incorporation of free hydroxyproline into elastin hydroxyproline was negligible. 6. Digestion of solubilized samples with collagenase indicated that the hydroxyproline in guinea-pig aortic elastin preparations was not derived from contamination by collagen. It is suggested that most if not all of the hydroxyproline in the guinea pig elastin preparations investigated can be considered an integral part of the elastin molecule.

Effect of beta-aminopropionit- rile on joint stiffness in rats

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