The Expression Pattern and Clinical Significance of Lysyl Oxidase Family in Gliomas

LOX (Lysyl oxidase) family participates in the catalysis of collagen and elastin to maintain ECM homeostasis. Glioma is the most common primary brain tumor and LOX family has not been systemic studied in glioma. In this study, we found LOX family members are upregulated expressed in gliomas samples. A protein-protein interaction network (PPIN) was construct to visualize and understand the differential expression pattern, as well as functional annotation, for LOX family and their interacting proteins, which involved in collagen fibril organization and MAPK signaling pathway. Through subcellular localization distribution, the LOX family members distribute both intracellular and extracellular. All five LOX members are consistently significantly correlate with dendritic cell both in immune infiltrate of GBM and LGG. Survival analysis showed that high expression of LOX family is associated with a poor prognosis of gliomas patients. These analyses provide important clues to identify the potential biological roles for LOX family in gliomas, which might serve as diagnosis markers.

The challenge of determining lysyl oxidase activity: Old methods and novel approaches

The lysyl oxidase (LOX) family of enzymes catalyze the oxidative deamination of lysine and hydroxylysine residues in collagen and elastin in the initiation step of the formation of covalent cross-linkages, an essential process for extracellular matrix (ECM) maturation. Elevated LOX expression levels leading to increased LOX activity is associated with diverse pathologies including fibrosis, cancer, and cardiovascular diseases. Different protocols have been so far established to detect and quantify LOX activity from tissue samples and cultured cells, all of them showing advantages and drawbacks. This review article presents a critical overview of the main features of currently available methods as well as introduces some recent technologies called to revolutionize our approach to LOX catalysis.

Lysyl oxidase and hypoxia-inducible factor 1α: biomarkers of gastric cancer

BACKGROUND

Gastric cancer (GC) is one of the main causes of cancer mortality worldwide. Recent studies on tumor microenvironments have shown that tumor metabolism exerts a vital role in cancer progression.

AIM

To investigate whether lysyl oxidase (LOX) and hypoxia-inducible factor 1α (HIF1α) are prognostic and predictive biomarkers in GC.

METHODS

A total of 80 tissue and blood samples were collected from 140 patients admitted to our hospital between August 2008 and March 2012. Immunohistochemical staining was performed to measure the expression of LOX and HIF1α in tumor and adjacent tissues collected from patients with GC. Real-time quantitative reverse transcription polymerase chain reaction (qRT-PCR) analysis was used to detect the mRNA expression levels of LOX and HIF1α in patients with GC. In addition, single-factor analysis was applied to analyze the relationship between LOX, HIF1α and prognosis of GC.

RESULTS

Immunohistochemical staining suggested that the expression levels of LOX and HIF1α increased in tumor tissues from patients with GC. QRT-PCR analysis indicated that mRNA expression of LOX and HIF1α was also upregulated in tumor tissues, which was in accordance with the above results. We also detected expression of these two genes in blood samples. The expression level of LOX and HIF1α was higher in patients with GC than in healthy controls. Additional analysis showed that the expression level of LOX and HIF1α was related to the clinicopathological characteristics of GC. Expression of LOX and HIF1α increased with the number of lymph node metastases, deeper infiltration depth and later tumor–node–metastasis stages. Single-factor analysis showed that high expression of LOX and HIF1α led to poor prognosis of patients with GC.

CONCLUSION

LOX and HIF1α can be used as prognostic and predictive biomarkers for GC.

Correlations of lysyl oxidase with MMP2/MMP9 expression and its prognostic value in non-small cell lung cancer

Lysyl oxidase (LOX) has been reported to regulate tumor metastasis and has been found to involve in modification of extracellular matrix (ECM) in the context of tumorigenesis. The aim of this study is to determine the prognostic significance of LOX in non-small cell lung cancer (NSCLC) patients and to examine the correlation between LOX expression and ECM remodeling-associated MMP2/MMP9 in NSCLC tissues. The mRNA expression of LOX, MMP2 and MMP9 was investigated by quantitative real-time reverse transcriptase-polymerase chain reaction (qRT-PCR) in 30 NSCLC patients. The protein expression of LOX was measured by immunohistochemistry (IHC) in 110 paraffin-embedded tissues with NSCLC and the protein expression of MMP2/MMP9 was measured by in 30 NSCLC patients. The correlation between LOX expression and clinical parameters and MMP2/MMP9 was analyzed by appropriate statistics. The Kaplan-Meier method, univariate and multivariate regression analysis was used to analyze the correlation between LOX expression and overall survival (OS). The relative mRNA expression or protein expression of LOX were significantly higher in NSCLC tumor tissues than in the corresponding noncancerous tissues (P < 0.05). High LOX expression was significantly associated with MMP2, MMP9, tumor size, lymph node metastasis, pathological stage and OS (P < 0.05). Univariate and multivariate analysis showed that LOX was an independent prognostic factor for OS. Our results indicate that LOX may play a role in the metastasis of NSCLC by promoting MMP2/MMP9 expression. LOX expression is an independent prognostic factor in OS in NSCLC.

Early-gestation fetal scarless wounds have less lysyl oxidase expression

BACKGROUND

Lysyl oxidase cross-links collagen and elastin. Because cross-linking likely influences collagen architecture, the authors compared lysyl oxidase expression during scarless and scarring fetal dermal wound repair.

METHODS

Excisional dermal wounds were made on E17 (gestational day 16.5) and E19 (gestational day 18.5) mouse fetuses. Skin and wound RNA was collected at 8, 12, and 24 hours. Quantitative real-time polymerase chain reaction was performed for lysyl oxidase. The effect of transforming growth factor (TGF)-beta1 on lysyl oxidase expression in fetal fibroblasts was tested. Confluent primary fetal and postnatal fibroblast cultures were stimulated with TGF-beta1 for 24 hours, and lysyl oxidase expression was quantitated by performing real-time polymerase chain reaction. Lysyl oxidase expression was also quantitated in unwounded fetal skin to determine its expression profile during development.

RESULTS

E17 and E19 fetal skin had approximately 2-fold greater lysyl oxidase expression than postnatal skin (p < 0.01), and fetal fibroblasts had greater baseline lysyl oxidase expression than postnatal fibroblasts. After TGF-beta1 stimulation, fetal and postnatal fibroblasts responded with increases in lysyl oxidase expression. In E17 early-gestation scarless fetal wounds, lysyl oxidase had small increases (<1.5-fold) in expression from 1 to 12 hours. In late-gestation E19 scarring fetal wounds, lysyl oxidase increased 1.8-fold at 8 hours and 2-fold at 12 hours, which was significantly greater than the changes observed in E17 scarless wounds (p < 0.01 for each).

CONCLUSIONS

Lysyl oxidase has greater expression in E19 late-gestation wounds that heal with scar compared with E17 early-gestation scarless wounds. This suggests a role for lysyl oxidase in scar formation.

Biochemical and functional modulation of the cartilage collagen network by IGF1, TGFbeta2 and FGF2

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.

Carotid arterial stiffness, elastic fibre network and vasoreactivity in semicarbazide-sensitive amine-oxidase null mouse

OBJECTIVE

We examined the arterial phenotype of semicarbazide-sensitive amine-oxidase null mouse (SSAO -/-) using various techniques including high resolution echotracking.

METHODS AND RESULTS

SSAO -/- mice showed no change in arterial pressure under anesthesia. The in vivo arterial diameter, only measured in the carotid artery (CA), was higher in SSAO -/- than in SSAO +/+ animals. Elastic modulus-wall stress curves and CA rupture pressure were similar between SSAO -/- and +/+ mice, indicating no change in arterial wall stiffness or mechanical strength. There was no significant difference in insoluble elastin, total collagen content and elastic lamellar morphology between the two genotypes. No alteration in vascular reactivity was observed in aortic rings and mesenteric arteries from SSAO -/- mice. Aortic lysyl oxidase (LO) activity remained unaltered, indicating that SSAO invalidation is not accompanied by a compensatory increase in LO activity.

CONCLUSION

This is the first functional study of arteries lacking SSAO. Our results indicate that SSAO -/- mice present an increased arterial diameter associated with normal arterial mechanical properties, suggesting that SSAO deficiency might contribute to arterial wall remodeling. However, these results argue against the hypothesis that SSAO intervenes in elastic fibre organization, elastin cross-linking processes and vasoreactivity.

Lysyl oxidase: an oxidative enzyme and effector of cell function

Lysyl oxidase (LOX) oxidizes the side chain of peptidyl lysine converting specific lysine residues to residues of alpha-aminoadipic-delta-semialdehyde. This posttranslational chemical change permits the covalent crosslinking of the component chains of collagen and those of elastin, thus stabilizing the fibrous deposits of these proteins in the extracellular matrix. Four LOX-like (LOXL) proteins with varying degrees of similarity to LOX have been described, constituting a family of related proteins. LOX is synthesized as a preproprotein which emerges from the cell as proLOX and then is processed to the active enzyme by proteolysis. In addition to elastin and collagen, LOX can oxidize lysine within a variety of cationic proteins, suggesting that its functions extend beyond its role in the stabilization of the extracellular matrix. Indeed, recent findings reveal that LOX and LOXL proteins markedly influence cell behavior including chemotactic responses, proliferation, and shifts between the normal and malignant phenotypes.

Lysyl oxidase is essential for normal development and function of the respiratory system and for the integrity of elastic and collagen fibers in various tissues

Lysyl oxidases, a family comprising LOX and four LOX-like enzymes, catalyze crosslinking of elastin and collagens. Mouse Lox was recently shown to be crucial for development of the cardiovascular system because null mice died perinatally of aortic aneurysms and cardiovascular dysfunction. We show here that Lox is also essential for development of the respiratory system and the integrity of elastic and collagen fibers in the lungs and skin. The lungs of E18.5 Lox(-/-) embryos showed impaired development of the distal and proximal airways. Elastic fibers in E18.5 Lox(-/-) lungs were markedly less intensely stained and more disperse than in the wild type, especially in the mesenchyme surrounding the distal airways, bronchioles, bronchi, and trachea, and were fragmented in pulmonary arterial walls. The organization of individual collagen fibers into tight bundles was likewise abnormal. Similar elastic and collagen fiber abnormalities were seen in the skin. Lysyl oxidase activity in cultured Lox(-/-) skin fibroblasts and aortic smooth muscle cells was reduced by approximately 80%, indicating that Lox is the main isoenzyme in these cells. LOX abnormalities may thus be critical for the pathogenesis of several common diseases, including pulmonary, skin, and cardiovascular disorders.

Inhibition of lysyl oxidase activity can delay phenotypic modulation of chondrocytes in two-dimensional culture

OBJECTIVE

Chondrocytes frequently de-differentiate in two-dimensional (2D) culture, especially in the presence of serum. To examine the role of lysyl oxidase (LOX) induced cross-linking in this phenomenon, the effect of the specific LOX inhibitor beta-aminopropionitrile (BAPN) was studied in 2D chondrocyte culture.

DESIGN

Chick embryo sternal chondrocytes (both proliferative and hypertrophic, from caudal and cranial zones, respectively) were cultured in the presence and absence of BAPN. The production and activities of LOX and LOX-like (LOXL) were assessed by enzyme assay and the use of specific antibodies. Seventeen batches of serum of different origin were compared. Chondrocyte phenotype was assessed both morphologically and biochemically, the latter by quantitative analysis of production of radiolabeled cartilage collagens II, IX, X and XI, and the de-differentiation marker collagen I, for up to 4 weeks in culture.

RESULTS

LOX and LOXL were identified, by Western blotting and immunofluorescence, and LO activity was measured in the medium, with both proliferative and hypertrophic chondrocytes. Inhibition of LO activity prevented or delayed chondrocyte de-differentiation, as characterized by changes in cell shape and synthesis of the five different collagen types, from the first days of culture for up to 4 weeks, depending on the origin of the serum added to the culture medium.

CONCLUSION

LO activity may be involved in the control of chondrocyte phenotype, in addition to serum factors. Inhibition of LO activity by BAPN may be useful for the maintenance of the chondrocyte phenotype in 2D culture. Specific variations in the relative proportions of collagens II, IX and XI could be involved in the mechanism underlying these observations.

Expression of FACIT collagens XII and XIV during bleomycin-induced pulmonary fibrosis in mice

Collagens XII and XIV are members of a subfamily of fibril-associated collagens with interrupted triple-helices (FACITs) that facilitate the interactions of adjacent collagen fibrils. Using immunohistochemistry and in situ hybridization, we analyzed the spatial and temporal expression pattern of collagens XII and XIV during bleomycin-induced pulmonary fibrosis. C57Bl mice were treated with bleomycin (1 U, i.p., every other day for 8 days) or saline (control), and lung tissue samples were analyzed 2-12 weeks later. Collagen I protein expression was increased in the lung 2 weeks post bleomycin treatment and persisted for at least 12 weeks. In contrast, collagen XII and XIV expression was low until 4 weeks after bleomycin treatment. Whereas collagen XII expression was greatest between 4 weeks and 8 weeks, expression of collagen XIV persisted from 4 to 12 weeks, which suggests that these two proteins may play distinct roles in the fibrotic process. The mRNA for lysyl oxidase (LOX), an enzyme for cross-linking of collagens, had a delayed increase in the lung after bleomycin administration. It reached a maximum after 8 weeks, and persisted throughout the 12 weeks of the study. These data support the hypothesis that fibrosis is a multistep process that involves both collagen accumulation and changes in the molecules that modulate the biomechanical properties of fibrils.

Lysyl oxidase-like and lysyl oxidase are present in the dermis and epidermis of a skin equivalent and in human skin and are associated to elastic fibers

Elastic fiber formation involves the secretion of tropoelastin which is converted to insoluble elastin by cross-linking, initiated by the oxidative deamination of lysine residues by lysyl oxidase. Five lysyl oxidase genes have been discovered. This study deals with the expression of two isoforms, LOX and LOX-like (LOXL), in human foreskin and in a human skin-equivalent (SE) model that allows the formation of elastic fibers. In this model, keratinocytes are added to a dermal equivalent made of fibroblasts grown on a chitosan-cross-linked collagen-GAG matrix. LOX and LOXL were detected by immunohistochemistry in the dermis and the epidermis of both normal skin and in a SE. This expression was confirmed by in situ hybridization on the SE. LOX and LOXL expression patterns were confirmed in human skin. The ultrastructural localization of LOXL was indicative of its association with elastin-positive materials within the SE and human skin, though interaction with collagen could not be discarded. LOX was found on collagen fibers and could be associated with elastin-positive materials in the SE and human skin. LOXL and LOX were detected in keratinocytes where LOX was mainly expressed by differentiating keratinocytes, in contrast to LOXL that can be found in both proliferating and differentiating fibroblasts. These data favor a role for LOXL in elastic fiber formation, together with LOX, and within the epidermis where both enzymes should play a role in post-translational modification of yet unknown substrates.

A fluorometric assay for detection of lysyl oxidase enzyme activity in biological samples

Lysyl oxidase catalyzes the final known enzymatic step required for collagen and elastin cross-linking in the biosynthesis of normal mature functional insoluble extracellular matrices. In addition, lysyl oxidase has been identified as a possible tumor suppressor. Lysyl oxidase activity in biological samples is traditionally and most reliably assessed by tritium release end-point assays using radiolabeled collagen or elastin substrates involving laborious vacuum distillation of the released tritiated water. In addition, a less sensitive fluorometric method exists that employs nonpeptidyl amine lysyl oxidase substrates and measures hydrogen peroxide production with horseradish peroxidase coupled to homovanillate oxidation. The present study describes a more sensitive fluorescent assay for lysyl oxidase activity that utilizes 1,5-diaminopentane as substrate, and released hydrogen peroxide is detected using Amplex red in horseradish peroxidase-coupled reactions. This method allows the detection of 40 ng of enzyme per 2 ml assay at 37 degrees C and is 7.5 times more sensitive than the currently available fluorometric assay for enzyme activity. This method eliminates the interference that occurs in some biological samples and can be successfully used to detect lysyl oxidase activity in cell culture experiments.

Echinococcus multilocularis: relationship between susceptibility/resistance and liver fibrogenesis in experimental mice

To analyze collagen and other matrix protein deposits in experimental alveolar echinococcosis as well as the expression of lysyl oxidase, the enzyme that initiates the first steps in the pyridinoline cross-linking of collagen, and to establish a relationship between resistance/susceptibility to Echinococcus multilocularis larval growth and fibrogenesis, we compared AKR/J mice (susceptible to E. multilocularis infection) with NMRI mice (resistant hosts) in this study. Collagen deposits in the lesions were evaluated using a colorimetric method; the nature of matrix proteins involved in the periparasitic fibrosis and lysyl oxidase expression were assessed using immunostaining on tissue sections. The results obtained in this sequential study confirm that fibrogenesis is an important aspect of the host immune reaction against parasitic development and that both the extent and the course of matrix protein deposition differ in the liver of susceptible and resistant mice, respectively. The long-lasting expression of alpha-actin and lysyl oxidase by host cells in NMRI mice suggests that in this resistant strain, fibrosis was not only more developed but also more highly cross-linked and, thus, less sensitive to collagenases than in susceptible mice. A very strong expression of lysyl oxidase by parasitic cells was observed in both strains of mice; the observation that E. multilocularis itself has a role in lysyl oxidase cross-linking of host collagens can be hypothesized and would be a new example of parasite-host interplay.

Modulation of lysyl oxidase by dietary copper in rats

Lysyl oxidase levels were estimated in rat tissues using an enzyme-linked immunosorption assay (ELISA) and a functional assay standardized against known amounts of purified lysyl oxidase. High concentrations of lysyl oxidase (> or = 150 micrograms/g of tissue or packed cells) were detected in connective tissues, such as tendon and skin. Values for aorta, kidney, lung and liver ranged from 30 to 150 micrograms/g of tissue; values for skeletal muscle and diaphragm were < 30 micrograms/g tissue. Purified rat skin lysyl oxidase catalyzed the release of 50-100 Bq of tritium per micrograms enzyme in assays that used 3H-elastin-rich substrates. In dense connective tissues, good agreement was obtained for the values from ELISA and those derived from measurements of functional activity in aorta, lung, skin and tendon (r2 > 0.9). When egg white-based experimental diets containing 2 or 10 micrograms/g added copper were fed to weanling rats, values for skin lysyl oxidase functional activity in the group fed 2 micrograms/g added copper were one-third to one-half the values for skin lysyl oxidase functional activity in rats fed 10 micrograms/g copper. This reduction in lysyl oxidase activity, however, had minimal effect on indices of collagen maturation in rat skin, e.g., collagen solubility in neutral salt and dilute acid or the levels of acid stable cross-links. Moreover, copper deficiency did not influence the steady-state levels of lysyl oxidase specific mRNA in rat skin or the apparent amounts of lysyl oxidase in rat skin as determined by ELISA. These observations underscore that the concentration of lysyl oxidase is relatively high in dense corrective tissues, and although decreasing dietary copper influences functional activity, there is little apparent effect on the production of lysyl oxidase protein.

Increased lysyl oxidase activity in fibroblasts cultured from oral submucous fibrosis associated with betel nut chewing in Taiwan

Growth characteristics and lysyl oxidase activity of fibroblasts derived from human normal mucosa (NM) and oral submucous fibrosis (OSF) associated with betel nut chewing were compared in cell cultures. The growth rates of cultured cells were identified by plating 5 x 10(5) cells/35 mm culture dish (Day 0) and every 24 hours cell proliferation was determined by quantifying the cell number (using a hemocytometer). The third to seventh passages were used. A medium without serum but supplemented with 5 mg/ml bovine serum albumin was substituted for the original medium at the subconfluent period and cultured for an additional 24 h. The medium was collected and used for assays of protein content and lysyl oxidase activity. Lysyl oxidase activity was assayed with [4,5-3H]--lysine labelled purified chick--embryo aorta elastin substrate. After incubation for 10 h at 37 degrees C, the enzyme activity was measured from 3HHO (tritiated water) separated by ultrafiltration using Amicon C-10 micro-concentrators. The results showed the mean doubling time of OSF fibroblasts was 3.2 days and of NM fibroblasts was 3.6 days. NM fibroblasts became confluent at day 6 as determined by cell number, while OSF fibroblasts were confluent by Day 5. Furthermore, the immunoenzymatic assay for BrdUrd incorporation revealed that OSF fibroblasts proliferate significantly faster than NM fibroblasts under standard culture conditions. Both total protein content (10.84 +/- 1.15 mg/ml) and lysyl oxidase activity (3558.6 +/- 345.5 cpm/10(6) cell) in OSF fibroblasts were greater than in NM fibroblasts (6.35 +/- 0.96 mg/ml and 2436.0 +/- 352.6 cpm/10(6) cell). The results of this study provide evidence that fibroblasts derived from oral submucous fibrosis (OSF) tissue and normal mucosa (NM), although similar in many respects, exhibit specific differences in proliferation rates and lysyl oxidase activity. Moreover, collagen deposition in OSF tissue may, at least in part, be ascribed to increased lysyl oxidase activity.

Identification of lysyl oxidase and other platelet-derived growth factor-inducible genes in vascular smooth muscle cells by differential screening

BACKGROUND

Atherosclerosis and arterial injury are characterized by vascular smooth muscle cell (VSMC) migration and growth and an increase in synthesis of extracellular matrix. Platelet-derived growth factor (PDGF) has been implicated in these processes. This study was designed to identify additional PDGF-regulated genes in VSMC.

EXPERIMENTAL DESIGN

A cDNA library prepared from PDGF-stimulated rat aortic VSMC was screened by differential hybridization to identify clones representing PDGF-inducible genes. The time course of growth factor-induced changes in gene expression was examined by RNA blot hybridization. Assays of protein activity were also performed for selected gene products.

RESULTS

Four PDGF-regulated cDNA clones were identified by DNA sequencing. These encoded the extracellular matrix proteins lysyl oxidase (LO), thrombospondin, and osteopontin and the intracellular enzyme lactate dehydrogenase (LDH). Levels of mRNA corresponding to all four genes were low in quiescent VSMC and were markedly induced by PDGF, angiotensin II, and 10% calf serum. The regulation of LO and LDH mRNA by these agonists in VSMC has not been previously reported. LO enzymatic activity in the culture media was increased by approximately equals to 700% after exposure to PDGF. In contrast, LDH activity was not increased by PDGF treatment.

CONCLUSIONS

The induction of LO mRNA and its secretion by VSMC is an early event accompanying growth factor stimulation and may contribute to organization of the extracellular matrix.

Gender, dietary copper and carbohydrate source influence cardiac collagen and lysyl oxidase in weanling rats

The present investigation was conducted to determine the effects of consumption of diets containing fructose or cornstarch on cardiac collagen metabolism in weanling male and female rats fed copper-deficient or copper-adequate diets for 5 wk. Although both male and female rats that consumed the copper-deficient diet containing fructose were similarly copper deficient, only the males showed severe cardiac pathologies and two died prematurely due to heart-related abnormalities. These pathologies were accompanied by a significant reduction of cardiac lysyl oxidase activity and elevated soluble and total cardiac collagen concentrations compared with rats fed copper-adequate diets. These abnormalities were less severe in copper-deficient rats fed cornstarch. The data show that the activity of the copper-containing enzyme lysyl oxidase is affected by both dietary carbohydrate and gender. The pathologies of heart tissue could be the result of abnormal crosslinking of collagen induced by the combination of copper deficiency, fructose feeding and the sex of the rats.

Transient expression of lysyl oxidase by liver myofibroblasts in murine schistosomiasis

BACKGROUND

Murine schistosomiasis provides an experimental model of reversible fibrosis. The lysyl oxidase catalyzes the first step of collagen and elastin enzymatic cross-linking and appears to be a crucial factor in stabilizing the neosynthesized extracellular matrix in the liver.

EXPERIMENTAL DESIGN

A cDNA probe encoding a portion of the murine lysyl oxidase was cloned, and antibodies were raised against the corresponding recombinant peptide expressed as a fusion protein. Both tools were used to examine the expression of the lysyl oxidase mRNAs and peptides, all within granulomas and cells extracted from infected liver.

RESULTS

Transient up-regulation of two dominant 4.5 kb and 5.5 kb transcripts was observed among four mRNAs hybridizing with the lysyl oxidase cDNA probe during the development of granulomas. An identical time course was obtained for alpha 1(I) procollagen messenger expression. The lysyl oxidase expression was observed in type I collagen producing cells mainly localized at the periphery of fibroinflammatory granulomas and it disappeared in late granulomas. The lysyl oxidase and type I collagen expressing cells, located within granulomas, exhibited the characteristics of myofibroblasts, as judged by their expression of alpha-smooth muscle actin and desmin and by their ultrastructural morphology. Four antigenically related peptides were immunopurified from an enriched preparation of myofibroblast-like cells extracted from infected mouse liver. Two of these peptides had the molecular weight of prolysyl oxidase (50,000) and activated lysyl oxidase (32,000). The two others (28,000 and 66,000) might correspond to cleavage product or dimeric form respectively.

CONCLUSIONS

This study demonstrates that the lysyl oxidase was transiently up-regulated at the transcriptional level parallely to alpha(1)I procollagen within developing granulomas. Myofibroblasts are involved in the expression of the lysyl oxidase which may be secreted as a proenzyme and an activated enzyme.

Central nervous system involvement and generalized muscular atrophy in occipital horn syndrome: Ehlers-Danlos type IX. A first Japanese case

Occipital horn syndrome (OHS, Ehlers-Danlos syndrome type IX) belongs to the category of the copper metabolism disorders and is at present being investigated biochemically as is Menkes' disease. Unlike Menkes' disease, most patients with OHS have mild submentality. We report a case of OHS with severe central nervous system involvement and muscular atrophy in a 34-year-old male. He had psychomotor retardation and seizures since early childhood and now presented severe mental retardation and generalized muscular atrophy in addition to characteristic facial appearance, hyperelasticity of the skin and joint subluxation. Laboratory investigations revealed a low serum copper and ceruloplasmin level as well as intestinal non-absorption of copper. Radiographic imaging showed occipital exostoses, bladder diverticula, tortuosity of the peripheral vein and osteoporosis of the skeletal bones. The activity of lysyl oxidase, a copper-enzyme involved in cross-link formation in collagen, was found to be decreased in a skin-biopsy specimen. Electron-microscopic investigation of a muscle biopsy showed irregularity of the myofibrillar network and accumulation of concentric laminated bodies in the subsarcolemmal regions.

Role of the extracellular matrix in age-related modifications of the rat aorta. Ultrastructural, morphometric, and enzymatic evaluations

Connective tissues such as blood vessels are known to be greatly affected by age because of impaired functional properties and increased susceptibility to diseases. With the aim of providing further information on the role of the extracellular matrix in age-related modifications, we investigated the aorta in the rat model from birth to senescence by means of morphological and morphometric observations and by evaluation of lysyl oxidase activity. Results focused on the dramatic vascular rearrangements due to progressive fibrosis of the extracellular matrix and on prominent elastin modifications. The presence of lysyl oxidase activity, even in the oldest animals, might be at least partly responsible for the increased stiffness of the aging extracellular matrix. The striking age-related remodeling of the aortic architecture and the alterations of the interactions between cellular and extracellular compartments might greatly influence the functional properties of the arterial wall in senescence, at least contributing to the consequences of some apparently age-related vascular disorders.

Induction of lung lysyl oxidase activity and lysyl oxidase protein by exposure of rats to cadmium chloride: properties of the induced enzyme

Inspiration of CdCl2 results in a focally fibrotic response in rat lungs and markedly increases the activity of lung lysyl oxidase. Western blot analyses of urea-extractable rat lung proteins revealed that the levels of an immunoreactive, 32,000-Da protein were markedly increased in the cadmium-exposed rat lung tissue, consistent with the induction of lysyl oxidase protein. Anion exchange chromatography revealed low levels of multiple peaks of catalytically functional lysyl oxidase in control rat lung extracts, while the profile of cadmium-exposed rat lung extracts displayed markedly elevated levels of multiple peaks of enzyme activity indicating that the charge heterogeneity is expressed in the activated enzyme. The cadmium-induced enzyme was purified as a species of 32 kDa, without resolving individual ionic variants. The catalytic and physical properties of the isolated enzyme were very similar to those of previously well characterized basal enzyme of bovine aorta, including the presence of a pyrroloquinoline quinone-like carbonyl cofactor. The copper and cadmium content of the cadmium-induced enzyme indicated little if any replacement of tightly-bound copper by cadmium in the exposed lung.

Correlations between age and rat dermis modifications. Ultrastructural-morphometric evaluations and lysyl oxidase activity

The extracellular matrix is a complex, integrated macromolecular system which plays a crucial role in the economy of each organ. In this study we focused our attention on the correlations between age and rat skin dermis. The latter was chosen as a model of the connective tissue, and was analyzed by means of electron microscopy and by measurement of the activity of lysyl oxidase, the enzyme involved in collagen and elastin crosslink formation. Ultrastructural and morphometric evaluations associated to body weight growth, showed a progressive increase in the amounts of extracellular components and a progressive reduction in the cell density. Skin from adult animals appeared characterized by a well organized matrix; by contrast, in old rats, we observed several degenerative features such as the disorganization of collagen bundles, the vacuolization of elastic fibers, and the atrophy of the mesenchimal cells. Morphometric evaluations in old animals showed a slight but significant reduction in the percentage of the total collagen measured, a fair stability in the area occupied by the elastin fibers, and an increase of the apparently non-structured matrix. The fact that lysyl oxidase activity was diminished in old rats does not corroborate the observation by several authors that increased collagen insolubility is a consequence of higher intra- and intermolecular crosslinking. This would suggest that other chemical modifications, such as crosslink oxidation or non enzymatic glycosylation, might be involved during the aging of connective tissue. The qualitative and quantitative modifications observed at all ages illustrate the correlation between connective tissue modifications and structural and/or functional properties of the skin.

[Determination of L-amino acid oxidase activity]

Activity of L-amino acid oxidases was studied using several procedures. Optimal concentrations of L-lysine-alpha-oxidase, suitable for each procedure, were established involving highly purified preparations of the enzyme from Trichoderma sp. Estimation of the enzymatic activity carried out by means of calculation of the reduced cofactor accumulated led to two-fold exceeding of the results. The most sensitive procedure was based on evaluation of ammonium content in the reaction catalyzed by glutamate dehydrogenase and the procedure where peroxidase and o-dianizidine were used.

Ultrastructural immunolocalization of lysyl oxidase in vascular connective tissue

The localization of lysyl oxidase was examined in calf and rat aortic connective tissue at the ultrastructural level using polyclonal chicken anti-lysyl oxidase and gold conjugated rabbit anti-chicken immunoglobulin G to identify immunoreactive sites. Electron microscopy of calf aortic specimens revealed discrete gold deposits at the interface between extracellular bundles of amorphous elastin and the microfibrils circumferentially surrounding these bundles. The antibody did not react with microfibrils which were distant from the interface with elastin. There was negligible deposition of gold within the bundles of amorphous elastin and those few deposits seen at these sites appeared to be associated with strands of microfibrils. Lysyl oxidase was similarly localized in newborn rat aorta at the interface between microfibrils and nascent elastin fibers. Gold deposits were not seen in association with extracellular collagen fibers even after collagen-associated proteoglycans had been degraded by chondroitinase ABC. However, the antibody did recognize collagen-bound lysyl oxidase in collagen fibers prepared from purified collagen to which the enzyme had been added in vitro. No reaction product was seen if the anti-lysyl oxidase was preadsorbed with purified lysyl oxidase illustrating the specificity of the antibody probe. The present results are consistent with a model of elastogenesis predicting the radial growth of the elastin fiber by the deposition and crosslinking of tropoelastin units at the fiber-microfibril interface.

Biochemical defect in chick lung resulting from copper deficiency

Lung tissue from groups of chicks raised 23 d on diets deficient in copper had a higher proportion of 0.15 M NaCl-extractable collagen but lower aldehyde-reacting compounds and elastin than controls the same age. Although the lungs from deficient chicks weighed less, the ratio of lung to body weight for the two groups stayed relatively constant throughout the 23-d period. Lysyl oxidase activity in lungs of deficient chicks was strongly suppressed. Feeding the deficient chicks the diet with copper supplements restored lysyl oxidase activity in lung. This showed the close and specific control of lung lysyl oxidase by copper. The impairment in cross-linking through lysyl oxidase failure is implied from these studies. Clearly, copper is needed for the normal development of lung.

Depressor effect of diabetes in spontaneously hypertensive rat: role of vascular reactivity and prolyl hydroxylase and lysyl oxidase activities

Streptozotocin (STZ)-induced diabetes (8 weeks) produced a marked depressor effect in the spontaneously hypertensive rat (SHR), confirming earlier studies, but had no effect on arterial pressure of normotensive controls (WKY). We investigated the phenomenon further by examining the effects of diabetes on the activities of aortic prolyl hydroxylase (PH) and lysyl oxidase (LO), marker enzymes for collagen biosynthesis, and on the reactivity of isolated mesenteric arteries to vasoactive agents. PH and LO activities of nondiabetic SHR were greater than those of the WKY controls. Diabetes markedly reduced PH and LO activities of SHR aortae, but had no significant effect on PH and LO activities of the WKY strain. The effects of diabetes on vascular collagen biosynthetic enzymes of SHR were not associated with reductions in mesenteric arterial responsiveness or sensitivity to norepinephrine, methoxamine, serotonin or KC1. These results suggest that the depressor effect of diabetes in SHR is associated with a reduction in vascular collagen biosynthesis but not a reduction in vascular reactivity.

Alteration of the connective tissue network of striated muscle in copper deficient rats

The connective tissue network in striated muscle, consisting principally of collagen is arranged in a three dimensional network and is intimately associated with muscle function. Previous studies have shown that animals maintained on a copper-deficient diet undergo myocardial hypertrophy and exhibit cardiovascular lesions such as ventricular aneurysms that eventually rupture. A deficiency of copper in the diet is known to inhibit lysyl oxidase, a metalloenzyme requiring copper as a cofactor and which is also responsible for collagen and elastin crosslinking. Examination by scanning and transmission electron microscopy of skeletal and cardiac muscle from rats maintained on copper-deficient diets showed both gross and microscopic lesions to the connective tissue network. Immunohistochemical staining by light microscopy with antibodies against lysyl oxidase showed that the enzyme was equally present in both control and experimental animals. Fluorescent staining for antibodies against collagen types I and III showed similar results. From these studies we concluded that the collagen secreted during hypertrophy was not crosslinked by lysyl oxidase due to the absence of the copper cofactor. This resulted in the failure of the connective tissue network to transmit and distribute the increased force associated with myocardial hypertrophy and resulted in myocardial aneurysms.

Modulation of lysyl oxidase substrate specificity by the oleate anion

Extracts of bovine ligamentum nuchae have been assayed for lysyl oxidase activity using as substrates soluble elastin and soluble collagen labeled with tritiated lysine. The assays were performed in the presence and absence of sodium oleate. At 0.8 mM, oleate decreased activity with elastin more than 50% and enhanced activity with collagen to approximately 200% that of controls without oleate. The results show that this hydrophobic anion modulates lysyl oxidase specificity in crude extracts and suggests a mechanism for modifying activity in tissues.

Dupuytren's contracture: morphological and biochemical changes in palmar aponeurosis

The palmar aponeurosis removed from ten patients with Dupuytren's contracture was studied using morphological and biochemical approaches. The histological characteristic of Dupuytren's contracture is the presence of numerous nodules among the lamellar structures of the collagen fibres. In the nodules, there are many active fibroblasts which are surrounded by immature fibres and metachromatic substances demonstrated by toluidine blue staining. Ultrastructurally, the active fibroblasts have the characteristics of myofibroblasts, as previously reported by Dr. Gabbiani. We found that some fibroblasts have intracellular collagen fibrils in the cytoplasm. When assayed by Siegel and Martin's method, lysyl oxidase activity of the palmar aponeurosis was significantly higher in Dupuytren's contracture than in normal hands. Biochemical studies such as electrophoretic analysis of mucopolysaccharides, determination of uronic acid and collagen contents were undertaken to compare the aponeurosis of Dupuytren's contracture with normal cases. The uronic acid contents were higher in Dupuytren's contracture than in the controls. However, no difference between the two groups was found in the collagen contents and in the composition of the mucopolysaccharides. These characteristic features; existence of myofibroblasts and intracellular collagen fibrils and increase in the activity of lysyl oxidase probably play a significant role in the establishment of flexion contracture of the fingers in Dupuytren's contracture.

Measurement of medium lysyl oxidase activity in aorta smooth muscle cells. Effects of multiple medium changes and inhibition of protein synthesis

Cultures of rabbit aortic smooth muscle (RSM) cells are a valuable model system for studying production and metabolism of connective tissue components. This report describes various assay procedures for lysyl oxidase, the enzyme responsible for deaminating lysine residues to give aldehyde cross-link precursors, in culture medium from these cells. Studies of the medium enzyme from second-passage RSM cells indicate that approximately 40% of the total enzyme activity in the flask of cells is in the medium. The medium enzyme levels are replenished quite rapidly following refeeding, and enzyme levels in the medium appear to be feedback controlled. The mechanism for this control is unknown at present. Multiple refeeding experiments in which the medium was changed every 2-4 h for up to 40 h indicate that these cells are cap]able of producing large amounts of enzyme and are capable of altering enzyme production and secretion quite rapidly in response to changes in their environment. Protein synthesis inhibitor studies with cycloheximide suggest that the major portion of the enzyme released into the medium following refeeding is newly synthesized although a pool of latent enzyme is also present. As in intact tissue, extraction of the enzyme from the cell layer requires strong denaturing reagents such as 4 M urea. These results suggest that the production of lysyl oxidase is closely regulated and is very responsive to changes in the external environment of the cells. This cell culture system appears to be an excellent one to study the production of lysyl oxidase and its role in connective tissue fibrillogenesis.

Increased lysyl oxidase activity in blood vessels of hypertensive rats and effect of beta-aminopropionitrile on arteriosclerosis

The activity of lysyl oxidase which catalyzes the initial step of cross-linking of collagen and elastin polypeptides was measured in blood vessels of the hypertensive rat. The enzyme activity was increased in the aorta and mesenteric artery when hypertension was induced in 8-week-old rats with administration of deoxycorticosterone acetate (DOCA) and 1% saline. Reserpine diminished this increase in vascular lysyl oxidase activity concomitant with reduction in blood pressure. When beta-aminopropionitrile, a specific inhibitor of lysyl oxidase, was administered before the onset of DOCA-salt hypertension, the aortic collagen content was reduced markedly. Concomitant with reduction in the aortic collagen content, the development of hypertension and arteriosclerotic changes in the kidney was partially prevented. These results would indicate that hypertension increases the amount and the degree of cross-linking of vascular collagen and that the deposition of excess collagen in the vascular wall contributes to the development of hypertension and arteriosclerosis.