Elevated formation of pyridinoline cross-links by profibrotic cytokines is associated with enhanced lysyl hydroxylase 2b levels.
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The hallmark of fibrosis is the excessive accumulation of collagen. The deposited collagen contains increased pyridinoline cross-link levels due to an overhydroxylation of lysine residues within the collagen telopeptides. Lysyl hydroxylase 2b (LH2b) is the only lysyl hydroxylase consistently up-regulated in several forms of fibrosis, suggesting that an enhanced LH2b level is responsible for the overhydroxylation of collagen telopeptides. The present paper reports the effect of profibrotic cytokines on the expression of collagen, lysyl hydroxylases and lysyl oxidase in normal human skin fibroblasts, as well as the effect on pyridinoline formation in the deposited matrix. All three isoforms of TGF-beta induce a substantial increase in LH2b mRNA levels, also when expressed relatively to the mRNA levels of collagen type I alpha2 (COL1A2). The TGF-beta isoforms also clearly influence the collagen cross-linking pathway, since higher levels of pyridinoline cross-links were measured. Similar stimulatory effects on LH2b/COL1A2 mRNA expression and pyridinoline formation were observed for IL-4, activin A, and TNF-alpha. An exception was BMP-2, which has no effect on LH2b/COL1A2 mRNA levels nor on pyridinoline formation. Our data show for the first time that two processes, i.e., up-regulation of LH2b mRNA levels and increased formation of pyridinoline cross-links, previously recognized to be inherent to fibrotic processes, are induced by various profibrotic cytokines. (+info)
Identification of differentially expressed genes in hepatic HepG2 cells treated with acetaminophen using suppression subtractive hybridization.
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Acetaminophen (APAP) is widely used for the treatment of pain and fever. Although it is safe at therapeutic doses, APAP is toxic at higher doses and can cause severe damage to the liver. To clarify the mechanism of APAP-related liver damage, we attempted the identification of the differential gene expression in response to APAP treatment in hepatic HepG2 cells. In the present study, we used the technique of suppression subtractive hybridization (SSH) for the identification of the differentially expressed genes between untreated and treated cells and identified 14 candidate genes showing increased expression in response to APAP treatment. RT-PCR and real-time RT-PCR analysis confirmed that the expression of two genes was increased within 24 h following APAP treatment. Among them, only lysyl hydroxylase 2 expression was increased in a time- and dose-dependent manner. Furthermore, the expression of lysyl hydroxylase 2 was shown to be increased in the livers of APAP-treated mice compared to untreated controls. The increased expression of lysyl hydroxylase 2 was also observed when the cells were exposed to other hepatotoxins, ethanol and isoniazid. Since lysyl hydroxylase 2 is known to be a key enzyme of liver fibrosis, the increased expression of lysyl hydroxylase 2 may be involved in hepatotoxins-related liver fibrosis. (+info)
Glycosylation catalyzed by lysyl hydroxylase 3 is essential for basement membranes.
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Lysyl hydroxylase 3 (LH3) is a multifunctional enzyme possessing lysyl hydroxylase (LH), hydroxylysyl galactosyltransferase (GT) and galactosylhydroxylysyl glucosyltransferase (GGT) activities in vitro. To investigate the in vivo importance of LH3-catalyzed lysine hydroxylation and hydroxylysine-linked glycosylations, three different LH3-manipulated mouse lines were generated. Mice with a mutation that blocked only the LH activity of LH3 developed normally, but showed defects in the structure of the basement membrane and in collagen fibril organization in newborn skin and lung. Analysis of a hypomorphic LH3 mouse line with the same mutation, however, demonstrated that the reduction of the GGT activity of LH3 disrupts the localization of type IV collagen, and thus the formation of basement membranes during mouse embryogenesis leading to lethality at embryonic day (E) 9.5-14.5. Strikingly, survival of hypomorphic embryos and the formation of the basement membrane were directly correlated with the level of GGT activity. In addition, an LH3-knockout mouse lacked GGT activity leading to lethality at E9.5. The results confirm that LH3 has LH and GGT activities in vivo, LH3 is the main molecule responsible for GGT activity and that the GGT activity, not the LH activity of LH3, is essential for the formation of the basement membrane. Together our results demonstrate for the first time the importance of hydroxylysine-linked glycosylation for collagens. (+info)
Biochemical and functional modulation of the cartilage collagen network by IGF1, TGFbeta2 and FGF2.
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OBJECTIVE: Examine effects of insulin-like growth factor 1 (IGF1), transforming growth factor beta2 (TGFbeta2) and fibroblast growth factor 2 (FGF2) on proteoglycan and collagen network and biomechanical properties of the newly formed cartilage matrix. METHODS: Bovine articular chondrocytes were cultured in alginate beads for 3 weeks with or without FGF2, TGFbeta2 or IGF1 in the presence of 10% FCS. Proteoglycan content, collagen content, hydroxylysylpyridinoline cross-links and overall matrix metalloproteinase (MMP) activity in the culture medium were measured. Alginate disks cultured for 5 weeks were used to evaluate the effect of growth factors on mechanical properties of the construct by determining the equilibrium aggregate modulus and secant modulus. RESULTS: IGF1 increased collagen and proteoglycan deposition. FGF2 mainly decreased collagen deposition and TGFbeta2 proteoglycan deposition. A decrease in cross-links was observed in matrix produced by chondrocytes cultured in the presence of TGFbeta2. IGF1 and FGF2 had no influence on the number of cross-links per collagen molecule. Overall MMP activity was significantly higher in culture medium of cells cultured with FGF2. TGFbeta2 and IGF1 had no effect on MMP activity. After 35 days of culture, the matrix produced under influence of IGF1 had a lower permeability and a trend to increase stiffness. FGF2 showed a trend to lower both properties. TGFbeta2 had no effect on these parameters. CONCLUSION: IGF1, TGFbeta2 and FGF2 had differential effects on collagen network formation. Of the three growth factors tested, IGF1 seems to be best in promoting the formation of a functional collagen network since it increased proteoglycan and collagen deposition and improved the mechanical properties. (+info)
The myotomal diwanka (lh3) glycosyltransferase and type XVIII collagen are critical for motor growth cone migration.
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The initial migration of motor growth cones from the spinal cord into the periphery requires extrinsic cues, yet their identities are largely unknown. In zebrafish diwanka mutants, motor growth cones are motile but fail to pioneer into the periphery. Here, we report on the positional cloning of diwanka and show that it encodes LH3, a myotomally expressed multifunctional enzyme with lysyl hydroxylase and glycosyltransferase domains. Cloning, expression analysis, and ubiquitous overexpression of other LH family members reveals that only diwanka (lh3) possesses a critical role in growth cone migration. We show that this unique role depends critically on the LH3 glycosyltransferase domain, and provide compelling evidence that diwanka (lh3) acts through myotomal type XVIII collagen, a ligand for neural-receptor protein tyrosine phosphatases that guide motor axons. Together, our results provide the first genetic evidence that glycosyltransferase modifications of the ECM play a critical role during vertebrate motor axon migration. (+info)
Molecular cloning of chick lysyl hydroxylase. Little homology in primary structure to the two types of subunit of prolyl 4-hydroxylase.
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Lysyl hydroxylase (EC 1.14.11.4), an alpha 2 dimer, catalyzes the formation of hydroxylysine in collagens by the hydroxylation of lysine residues in X-Lys-Gly sequences. We report here on the isolation of cDNA clones coding for the enzyme from a chick embryo lambda gt11 library. Several overlapping clones covering all the coding sequences of the 4-kilobase mRNA and virtually all the noncoding sequences were characterized. These clones encode a polypeptide of 710 amino acid residues and a signal peptide of 20 amino acids. The polypeptide has four potential attachment sites for asparagine-linked oligosaccharides and 9 cysteine residues, at least one of which is likely to be involved in the binding of the Fe2+ atom to a catalytic site. A surprising finding was that no significant homology was found between the primary structures of lysyl hydroxylase and prolyl 4-hydroxylase in spite of the marked similarities in kinetic properties between these two enzymes. A computer-assisted comparison indicated only an 18% identity between lysyl hydroxylase and the alpha-subunit of prolyl 4-hydroxylase and a 19% identity between lysyl hydroxylase and the beta-subunit of prolyl 4-hydroxylase. Visual inspection of the most homologous areas nevertheless indicated the presence of several regions of 20-40 amino acids in which the identity between lysyl hydroxylase and one of the prolyl 4-hydroxylase subunits exceeded 30% or similarity exceeded 40%. Southern blot analyses of chick genomic DNA indicated the presence of only one gene coding for lysyl hydroxylase. (+info)
Genomic structure and embryonic expression of zebrafish lysyl hydroxylase 1 and lysyl hydroxylase 2.
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Collagen biosynthesis in both invertebrates and vertebrates is critically dependent upon the activity of lysyl hydroxylase (LH) enzymes. In humans, mutations in the genes encoding LH1 and LH2 have been shown to cause two distinct connective tissue disorders, Ehlers-Danlos (Type VIA) and Bruck syndromes. While the biochemical properties of these enzymes have been intensively studied, their embryonic patterns of expression and developmental roles remain unknown. We now present the cloning and analyses of the genes encoding LH1 and LH2 in the zebrafish, Danio rerio. We find these genes to be similarly organized to other vertebrate lh (plod) genes, including the presence of an alternatively spliced exon in lh2. We also examine the mRNA expression patterns of lh1 and lh2 during embryogenesis and find them to exhibit unique and dynamic patterns of expression. These results strongly suggest that LH enzymes are not merely housekeeping enzymes, but play distinct developmental roles. The identification of these genes in the zebrafish, a genetic model organism whose development is well characterized, now provides the basis for the establishment of the first animal models for both Ehlers-Danlos (Type VIA) and Bruck syndromes. (+info)
Tissue-specific changes in the hydroxylysine content and cross-links of collagens and alterations in fibril morphology in lysyl hydroxylase 1 knock-out mice.
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We have generated mice with targeted inactivation of the Plod1 gene for lysyl hydroxylase 1 (LH1). Its human mutations cause Ehlers-Danlos syndrome VIA (EDS VIA) characterized by muscular hypotonia, joint laxity, and kyphoscoliosis. The Plod1(-/-) mice are flaccid and have gait abnormalities. About 15% of them died because of aortic rupture and smooth muscle cells in non-ruptured Plod1(-/-) aortas showed degenerative changes. Collagen fibrils in the Plod1(-/-) aorta and skin had an abnormal morphology. The LH activity level in the Plod1(-/-) skin and aorta samples was 35-45% of that in the wild type. The hydroxylysine content was decreased in all the Plod1(-/-) tissues, ranging from 22% of that in the wild type in the skin to 75 and 86% in the femur and lung. The hydroxylysylpyridinoline crosslinks likewise showed decreases in all the Plod1(-/-) tissues, ranging from 28 and 33% of that in the wild type in the aorta and cornea to 47 and 59% in femur and tendon, while lysylpyridinolines were increased. The hydroxylysines found in the Plod1(-/-) collagens and their cross-links were evidently synthesized by the other two LH isoenzymes. Few data are available on abnormalities in EDS VIA tissues other than the skin. Plod1(-/-) mice offer an in vivo model for systematic analysis of the tissue-specific consequences of the lack of LH1 activity and may also provide a tool for analyzing the roles of connective tissue in muscle function and the complex interactions occurring in the proper assembly of the extracellular matrix. (+info)