In vitro and in vivo inhibition of lysyl oxidase by aminopropionitriles

Enhanced Optic Nerve Expansion and Altered Ultrastructure of Elastic Fibers Induced by Lysyl Oxidase Inhibition in a Mouse Model of Marfan Syndrome

Two major constituents of exfoliation material, fibrillin-1 and lysyl oxidase-like 1 (encoded by FBN1 and LOXL1), are implicated in exfoliation glaucoma, yet their individual contributions to ocular phenotype are minor. To test the hypothesis that a combination of FBN1 mutation and LOXL1 deficiency exacerbates ocular phenotypes, the pan-LOX inhibitor β-aminopropionitrile (BAPN) was used to treat adult wild-type (WT) and Fbn1C1041G/+ mice for 8 weeks and their eyes were examined. Although intraocular pressure did not change and exfoliation material was not detected in the eyes, BAPN treatment worsened optic nerve and axon expansion in Fbn1C1041G/+ mice, an early sign of axonal damage in rodent models of glaucoma. Disruption of elastic fibers was detected only in Fbn1C1041G/+ mice, which increased with BAPN treatment, as shown by histologic and immunohistochemical staining of the optic nerve pia mater. Transmission electron microscopy showed that Fbn1C1041G/+ mice had fewer microfibrils, smaller elastin cores, and a lower density of elastic fibers compared with WT mice in control groups. BAPN treatment led to elastin core expansion in both WT and Fbn1C1041G/+ mice, but an increase in the density of elastic fiber was confined to Fbn1C1041G/+ mice. LOX inhibition had a stronger effect on optic nerve and elastic fiber parameters in the context of Fbn1 mutation, indicating the Marfan mouse model with LOX inhibition warrants further investigation for exfoliation glaucoma pathogenesis.

Building a Scaffold for Arteriovenous Fistula Maturation: Unravelling the Role of the Extracellular Matrix

Vascular access is the lifeline for patients receiving haemodialysis as kidney replacement therapy. As a surgically created arteriovenous fistula (AVF) provides a high-flow conduit suitable for cannulation, it remains the vascular access of choice. In order to use an AVF successfully, the luminal diameter and the vessel wall of the venous outflow tract have to increase. This process is referred to as AVF maturation. AVF non-maturation is an important limitation of AVFs that contributes to their poor primary patency rates. To date, there is no clear overview of the overall role of the extracellular matrix (ECM) in AVF maturation. The ECM is essential for vascular functioning, as it provides structural and mechanical strength and communicates with vascular cells to regulate their differentiation and proliferation. Thus, the ECM is involved in multiple processes that regulate AVF maturation, and it is essential to study its anatomy and vascular response to AVF surgery to define therapeutic targets to improve AVF maturation. In this review, we discuss the composition of both the arterial and venous ECM and its incorporation in the three vessel layers: the tunica intima, media, and adventitia. Furthermore, we examine the effect of chronic kidney failure on the vasculature, the timing of ECM remodelling post-AVF surgery, and current ECM interventions to improve AVF maturation. Lastly, the suitability of ECM interventions as a therapeutic target for AVF maturation will be discussed.

The Genetic Architecture of Non-Syndromic Rhegmatogenous Retinal Detachment

Rhegmatogenous retinal detachment (RRD) is the most common form of retinal detachment (RD), affecting 1 in 10,000 patients per year. The condition has significant ocular morbidity, with a sizeable proportion of patients obtaining poor visual outcomes. Despite this, the genetics underpinning Idiopathic Retinal Detachment (IRD) remain poorly understood; this is likely due to small sample sizes in relevant studies. The majority of research pertains to the well-characterised Mende lian syndromes, such as Sticklers and Wagners, associated with RRD. Nevertheless, in recent years, there has been an increasing body of literature identifying the common genetic mutations and mechanisms associated with IRD. Several recent Genomic Wide Association Studies (GWAS) studies have identified a number of genetic loci related to the development of IRD. Our review aims to provide an up-to-date summary of the significant genetic mechanisms and associations of Idiopathic RRD.

Protein Nanoparticles: Uniting the Power of Proteins with Engineering Design Approaches

Protein nanoparticles, PNPs, have played a long-standing role in food and industrial applications. More recently, their potential in nanomedicine has been more widely pursued. This review summarizes recent trends related to the preparation, application, and chemical construction of nanoparticles that use proteins as major building blocks. A particular focus has been given to emerging trends related to applications in nanomedicine, an area of research where PNPs are poised for major breakthroughs as drug delivery carriers, particle-based therapeutics or for non-viral gene therapy.

Adapting the Scar-in-a-Jar to Skin Fibrosis and Screening Traditional and Contemporary Anti-Fibrotic Therapies

Skin fibrosis still constitutes an unmet clinical need. Although pharmacological strategies are at the forefront of scientific and technological research and innovation, their clinical translation is hindered by the poor predictive capacity of the currently available in vitro fibrosis models. Indeed, customarily utilised in vitro scarring models are conducted in a low extracellular matrix milieu, which constitutes an oxymoron for the in-hand pathophysiology. Herein, we coupled macromolecular crowding (enhances and accelerates extracellular matrix deposition) with transforming growth factor β1 (TGFβ1; induces trans-differentiation of fibroblasts to myofibroblasts) in human dermal fibroblast cultures to develop a skin fibrosis in vitro model and to screen a range of anti-fibrotic families (corticosteroids, inhibitors of histone deacetylases, inhibitors of collagen crosslinking, inhibitors of TGFβ1 and pleiotropic inhibitors of fibrotic activation). Data obtained demonstrated that macromolecular crowding combined with TGFβ1 significantly enhanced collagen deposition and myofibroblast transformation. Among the anti-fibrotic compounds assessed, trichostatin A (inhibitors of histone deacetylases); serelaxin and pirfenidone (pleiotropic inhibitors of fibrotic activation); and soluble TGFβ receptor trap (inhibitor of TGFβ signalling) resulted in the highest decrease of collagen type I deposition (even higher than triamcinolone acetonide, the gold standard in clinical practice). This study further advocates the potential of macromolecular crowding in the development of in vitro pathophysiology models.

Current and upcoming therapies to modulate skin scarring and fibrosis

Skin is the largest organ of the human body. Being the interface between the body and the outer environment, makes it susceptible to physical injury. To maintain life, nature has endowed skin with a fast healing response that invariably ends in the formation of scar at the wounded dermal area. In many cases, skin remodelling may be impaired, leading to local hypertrophic scars or keloids. One should also consider that the scarring process is part of the wound healing response, which always starts with inflammation. Thus, scarring can also be induced in the dermis, in the absence of an actual wound, during chronic inflammatory processes. Considering the significant portion of the population that is subject to abnormal scarring, this review critically discusses the state-of-the-art and upcoming therapies in skin scarring and fibrosis.

ATP7A delivers copper to the lysyl oxidase family of enzymes and promotes tumorigenesis and metastasis

Lysyl oxidase (LOX) and LOX-like (LOXL) proteins are copper-dependent metalloenzymes with well-documented roles in tumor metastasis and fibrotic diseases. The mechanism by which copper is delivered to these enzymes is poorly understood. In this study, we demonstrate that the copper transporter ATP7A is necessary for the activity of LOX and LOXL enzymes. Silencing of ATP7A inhibited LOX activity in the 4T1 mammary carcinoma cell line, resulting in a loss of LOX-dependent mechanisms of metastasis, including the phosphorylation of focal adhesion kinase and myeloid cell recruitment to the lungs, in an orthotopic mouse model of breast cancer. ATP7A silencing was also found to attenuate LOX activity and metastasis of Lewis lung carcinoma cells in mice. Meta-analysis of breast cancer patients found that high ATP7A expression was significantly correlated with reduced survival. Taken together, these results identify ATP7A as a therapeutic target for blocking LOX- and LOXL-dependent malignancies.

Damage-induced reactive oxygen species regulate vimentin and dynamic collagen-based projections to mediate wound repair

Tissue injury leads to early wound-associated reactive oxygen species (ROS) production that mediate tissue regeneration. To identify mechanisms that function downstream of redox signals that modulate regeneration, a vimentin reporter of mesenchymal cells was generated by driving GFP from the vimentin promoter in zebrafish. Early redox signaling mediated vimentin reporter activity at the wound margin. Moreover, both ROS and vimentin were necessary for collagen production and reorganization into projections at the leading edge of the wound. Second harmonic generation time-lapse imaging revealed that the collagen projections were associated with dynamic epithelial extensions at the wound edge during wound repair. Perturbing collagen organization by burn wound disrupted epithelial projections and subsequent wound healing. Taken together our findings suggest that ROS and vimentin integrate early wound signals to orchestrate the formation of collagen-based projections that guide regenerative growth during efficient wound repair.

Lysyl oxidase family activity promotes resistance of pancreatic ductal adenocarcinoma to chemotherapy by limiting the intratumoral anticancer drug distribution

Solid tumors often display chemotherapy resistance. Pancreatic ductal adenocarcinoma (PDAC) is the archetype of resistant tumors as current chemotherapies are inefficient. The tumor stroma and extracellular matrix (ECM) are key contributors to PDAC aggressiveness and to limiting the efficacy of chemotherapy. Lysyl oxidase (LOX) family members mediate collagen cross-linking and thus promote ECM stiffening. Our data demonstrate increased LOX, LOXL1, and LOXL2 expression in PDAC, and that the level of fibrillar collagen, which is directly dependent of LOX family activity, is an independent predictive biomarker of adjuvant “Gemcitabine-based chemotherapy” benefit. Experimentally in mice, increased LOX family activity through LOXL2 promotes chemoresistance. This effect of LOX family activity seems to be due to decreased gemcitabine intra-tumoral diffusion. This observation might be explained by increased fibrillar collagen and decreased vessel size observed in tumors with increased LOX family activity. In conclusion, our data support that LOX family activity is both a novel target to improve chemotherapy as well as a novel biomarker to predict gemcitabine benefit in PDAC. Beyond the PDAC, it is possible that targeting LOX family activity might improve efficacy of chemotherapies against different kinds of solid tumors.

Impact of lysyl oxidase (G473A) polymorphism on diabetic foot ulcers

Lysyl oxidase (LOX) is an extra-cellular matrix-modifying enzyme that has been linked to cell proliferation, metastasis, angiogenesis and wound healing. This study was designed to examine the association of LOX gene polymorphism G473A, G>A, (rs1800449) located in exon 1 of the LOX gene in diabetic subjects with and without diabetic foot ulcers (DFU) and its impact of expression on DFU. Genotypic analysis of 906 samples showed a significant increase in the presence of 'A' allele in type 2 diabetes mellitus (T2DM) and DFU when compared to that of control subjects. Allele wise analysis showed a higher frequency of 'A' allele in the T2DM (36.23%, OR 1.069, P value 0.29) and DFU (41.69%, OR 1.195, P value 0.003) when compared to that of control subjects (33.17%). Interestingly, real time RT-PCR results showed significant increased transcript level of the LOX gene on the AA genotype of DFU when compared to that of the AA genotype of T2DM and control subjects. Our finding predicts that there is an association of LOX gene polymorphism (G473A) on diabetes and DFU patients when compared to that of healthy controls. Thus, this study merits further evaluation on a mechanistic approach of this gene.

Biomedical implications from a morphoelastic continuum model for the simulation of contracture formation in skin grafts that cover excised burns

A continuum hypothesis-based model is developed for the simulation of the (long term) contraction of skin grafts that cover excised burns in order to obtain suggestions regarding the ideal length of splinting therapy and when to start with this therapy such that the therapy is effective optimally. Tissue is modeled as an isotropic, heterogeneous, morphoelastic solid. With respect to the constituents of the tissue, we selected the following constituents as primary model components: fibroblasts, myofibroblasts, collagen molecules, and a generic signaling molecule. Good agreement is demonstrated with respect to the evolution over time of the surface area of unmeshed skin grafts that cover excised burns between outcomes of computer simulations obtained in this study and scar assessment data gathered previously in a clinical study. Based on the simulation results, we suggest that the optimal point in time to start with splinting therapy is directly after placement of the skin graft on its recipient bed. Furthermore, we suggest that it is desirable to continue with splinting therapy until the concentration of the signaling molecules in the grafted area has become negligible such that the formation of contractures can be prevented. We conclude this study with a presentation of some alternative ideas on how to diminish the degree of contracture formation that are not based on a mechanical intervention, and a discussion about how the presented model can be adjusted.

VEGF-ablation therapy reduces drug delivery and therapeutic response in ECM-dense tumors

The inadequate transport of drugs into the tumor tissue caused by its abnormal vasculature is a major obstacle to the treatment of cancer. Anti-vascular endothelial growth factor (anti-VEGF) drugs can cause phenotypic alteration and maturation of the tumor's vasculature. However, whether this consistently improves delivery and subsequent response to therapy is still controversial. Clinical results indicate that not all patients benefit from antiangiogenic treatment, necessitating the development of criteria to predict the effect of these agents in individual tumors. We demonstrate that, in anti-VEGF-refractory murine tumors, vascular changes after VEGF ablation result in reduced delivery leading to therapeutic failure. In these tumors, the impaired response after anti-VEGF treatment is directly linked to strong deposition of fibrillar extracellular matrix (ECM) components and high expression of lysyl oxidases. The resulting condensed, highly crosslinked ECM impeded drug permeation, protecting tumor cells from exposure to small-molecule drugs. The reduced vascular density after anti-VEGF treatment further decreased delivery in these tumors, an effect not compensated by the improved vessel quality. Pharmacological inhibition of lysyl oxidases improved drug delivery in various tumor models and reversed the negative effect of VEGF ablation on drug delivery and therapeutic response in anti-VEGF-resistant tumors. In conclusion, the vascular changes after anti-VEGF therapy can have a context-dependent negative impact on overall therapeutic efficacy. A determining factor is the tumor ECM, which strongly influences the effect of anti-VEGF therapy. Our results reveal the prospect to revert a possible negative effect and to potentiate responsiveness to antiangiogenic therapy by concomitantly targeting ECM-modifying enzymes.

Targeting lysyl oxidase for molecular imaging in breast cancer

INTRODUCTION

Lysyl oxidase (LOX; ExPASy ENZYME entry: EC 1.4.3.13) and members of the LOX-like family, LOXL1-LOXL4, are copper-dependent enzymes that can modify proteins of the extracellular matrix. Expression of LOX is elevated in many human cancers, including breast cancer. LOX expression correlates with the level of tissue hypoxia, and it is known to play a critical role in breast cancer metastasis. The goal of the present study was to target LOX with (1) molecular probe fluorescent labeling to visualize LOX in vitro and (2) a radiolabeled peptide to target LOX in vivo in three different preclinical models of breast cancer.

METHODS

Gene expression of all five members of the LOX family was analyzed at the transcript level via microarray analysis using tissue biopsy samples from 176 patients with breast cancer. An oligopeptide sequence (GGGDPKGGGGG) was selected as a substrate-based, LOX-targeting structure. The peptide was labeled with fluorescein isothiocyanate (FITC) for confocal microscopy experiments with the murine breast cancer cell line EMT-6. In vivo molecular imaging experiments were performed using a C-terminal amidated peptide, GGGDPKGGGGG, labeled with a short-lived positron emitter, fluorine-18 ((18)F), for positron emission tomography (PET) in three different breast cancer models: EMT6, MCF-7 and MDA-MB-231. The PET experiments were carried out in the presence or absence of β-aminopropionitrile (BAPN), an irreversible inhibitor of LOX.

RESULTS

Immunostaining experiments using a LOX-specific antibody on EMT-6 cells cultured under hypoxic conditions confirmed the elevation of LOX expression in these cells. An FITC-labeled oligopeptide, FITC-Ava-GGGDPKGGGGG-NH2, was found to be localized in different cellular compartments under these conditions. After injection of [(18)F]fluorobenzoate-GGGDPKGGGGG-NH2, radioactivity uptake was visible in all three breast cancer models in vivo. Tumor uptake was reduced by predosing the animals with 2 mg of BAPN 4 h or 24 h before injection of the radiotracer.

CONCLUSIONS

The present data support further investigation into the development of LOX-binding radiolabeled peptides as molecular probes for molecular imaging of LOX expression in cancer.

Elevated expression levels of lysyl oxidases protect against aortic aneurysm progression in Marfan syndrome

Patients with Marfan syndrome (MFS) are at high risk of life-threatening aortic dissections. The condition is caused by mutations in the gene encoding fibrillin-1, an essential component in the formation of elastic fibers. While experimental findings in animal models of the disease have shown the involvement of transforming growth factor-β (TGF-β)- and angiotensin II-dependent pathways, alterations in the vascular extracellular matrix (ECM) may also play a role in the onset and progression of the aortic disease. Lysyl oxidases (LOX) are extracellular enzymes, which initiates the formation of covalent cross-linking of collagens and elastin, thereby contributing to the maturation of the ECM. Here we have explored the role of LOX in the formation of aortic aneurysms in MFS. We show that aortic tissue from MFS patients and MFS mouse model (Fbn1(C1039G/+)) displayed enhanced expression of the members of the LOX family, LOX and LOX-like 1 (LOXL1), and this is associated with the formation of mature collagen fibers. Administration of a LOX inhibitor for 8weeks blocked collagen accumulation and aggravated elastic fiber impairment, and these effects correlated with the induction of a strong and rapidly progressing aortic dilatation, and with premature death in the more severe MFS mouse model, Fbn1(mgR/mgR), without any significant effect on wild type animals. This detrimental effect occurred preferentially in the ascending portion of the aorta, with little or no involvement of the aortic root, and was associated to an overactivation of both canonical and non-canonical TGF-β signaling pathways. The blockade of angiotensin II type I receptor with losartan restored TGF-β signaling activation, normalized elastic fiber impairment and prevented the aortic dilatation induced by LOX inhibition in Fbn1(C1039G/+) mice. Our data indicate that LOX enzymes and LOX-mediated collagen accumulation play a critical protective role in aneurysm formation in MFS.

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.

Lysyl oxidase activity regulates oncogenic stress response and tumorigenesis

Cellular senescence, a stable proliferation arrest, is induced in response to various stresses. Oncogenic stress-induced senescence (OIS) results in blocked proliferation and constitutes a fail-safe program counteracting tumorigenesis. The events that enable a tumor in a benign senescent state to escape from OIS and become malignant are largely unknown. We show that lysyl oxidase activity contributes to the decision to maintain senescence. Indeed, in human epithelial cell the constitutive expression of the LOX or LOXL2 protein favored OIS escape, whereas inhibition of lysyl oxidase activity was found to stabilize OIS. The relevance of these in vitro observations is supported by in vivo findings: in a transgenic mouse model of aggressive pancreatic ductal adenocarcinoma (PDAC), increasing lysyl oxidase activity accelerates senescence escape, whereas inhibition of lysyl oxidase activity was found to stabilize senescence, delay tumorigenesis, and increase survival. Mechanistically, we show that lysyl oxidase activity favors the escape of senescence by regulating the focal-adhesion kinase. Altogether, our results demonstrate that lysyl oxidase activity participates in primary tumor growth by directly impacting the senescence stability.

Lysyl oxidase secreted by tumour endothelial cells promotes angiogenesis and metastasis

Background:

Molecules that are highly expressed in tumour endothelial cells (TECs) may be candidates for specifically targeting TECs. Using DNA microarray analysis, we found that the lysyl oxidase (LOX) gene was upregulated in TECs compared with its expression in normal endothelial cells (NECs). LOX is an enzyme that enhances invasion and metastasis of tumour cells. However, there are no reports on the function of LOX in isolated TECs.

Methods:

TECs and NECs were isolated to investigate LOX function in TECs. LOX inhibition of in vivo tumour growth was also assessed using β-aminopropionitrile (BAPN).

Results:

LOX expression was higher in TECs than in NECs. LOX knockdown inhibited cell migration and tube formation by TECs, which was associated with decreased phosphorylation of focal adhesion kinase (Tyr 397). Immunostaining showed high LOX expression in human tumour vessels in vivo. Tumour angiogenesis and micrometastasis were inhibited by BAPN in an in vivo tumour model.

Conclusion:

LOX may be a TEC marker and a possible therapeutic target for novel antiangiogenic therapy.

Stromally derived lysyl oxidase promotes metastasis of transforming growth factor-β-deficient mouse mammary carcinomas

The tumor stromal environment can dictate many aspects of tumor progression. A complete understanding of factors driving stromal activation and their role in tumor metastasis is critical to furthering research with the goal of therapeutic intervention. Polyoma middle T-induced mammary carcinomas lacking the type II TGF-β receptor (PyMT(mgko)) are highly metastatic compared with control PyMT-induced carcinomas (PyMT(fl/fl)). We hypothesized that the PyMT(mgko)-activated stroma interacts with carcinoma cells to promote invasion and metastasis. We show that the extracellular matrix associated with PyMT(mgko) tumors is stiffer and has more fibrillar collagen and increased expression of the collagen crosslinking enzyme lysyl oxidase (LOX) compared with PyMT(fl/fl) mammary carcinomas. Inhibition of LOX activity in PyMT(mgko) mice had no effect on tumor latency and size, but significantly decreased tumor metastasis through inhibition of tumor cell intravasation. This phenotype was associated with a decrease in keratin 14-positive myoepithelial cells in PyMT(mgko) tumors following LOX inhibition as well as a decrease in focal adhesion formation. Interestingly, the primary source of LOX was found to be activated fibroblasts. LOX expression in these fibroblasts can be driven by myeloid cell-derived TGF-β, which is significantly linked to human breast cancer. Overall, stromal expansion in PyMT(mgko) tumors is likely caused through the modulation of immune cell infiltrates to promote fibroblast activation. This feeds back to the epithelium to promote metastasis by modulating phenotypic characteristics of basal cells. Our data indicate that epithelial induction of microenvironmental changes can play a significant role in tumorigenesis and attenuating these changes can inhibit metastasis. Cancer Res; 73(17); 5336-46. ©2013 AACR.

Critical role for lysyl oxidase in mesenchymal stem cell-driven breast cancer malignancy

Mesenchymal stem cells (MSCs) are multipotent progenitor cells with the ability to differentiate into multiple mesoderm lineages in the course of normal tissue homeostasis or during injury. We have previously shown that MSCs migrate to sites of tumorigenesis, where they become activated by cancer cells to promote metastasis. However, the molecular and phenotypic attributes of the MSC-induced metastatic state of the cancer cells remained undetermined. Here, we show that bone marrow-derived human MSCs promote de novo production of lysyl oxidase (LOX) from human breast carcinoma cells, which is sufficient to enhance the metastasis of otherwise weakly metastatic cancer cells to the lungs and bones. We also show that LOX is an essential component of the CD44-Twist signaling axis, in which extracellular hyaluronan causes nuclear translocation of CD44 in the cancer cells, thus triggering LOX transcription by associating with its promoter. Processed and enzymatically active LOX, in turn, stimulates Twist transcription, which mediates the MSC-triggered epithelial-to-mesenchymal transition (EMT) of carcinoma cells. Surprisingly, although induction of EMT in breast cancer cells has been tightly associated with the generation of cancer stem cells, we find that LOX, despite being critical for EMT, does not contribute to the ability of MSCs to promote the formation of cancer stem cells in the carcinoma cell populations. Collectively, our studies highlight a critical role for LOX in cancer metastasis and indicate that the signaling pathways controlling stroma-induced EMT are distinct from pathways regulating the development of cancer stem cells.

Development of collagen fibres and lysyl oxidase expression in the presumptive dermis of chick limb bud

Lysyl oxidase (LOX) plays a critical role in the formation of cross-linkages in extracellular matrix molecules. Thus, it is essential for the biogenesis and homeostasis of the connective tissue matrix. During development, collagen fibres and elastic system fibres emerge and accumulate in a temporospatial manner in the presumptive dermis of chicks. In this study, we investigated LOX mRNA expression by laser capture microdissection and RT-qPCR and LOX protein localization by immunohistochemistry. The picrosirius polarization method was used to investigate a relation between collagen accumulation and LOX expression. PCR analysis showed that the expression of LOX mRNA in the presumptive dermis became apparent at embryonic day 13 and increased considerably by ED17. Immunohistochemical staining for LOX in the dermis was very low at all stages of development. Accumulation of collagen fibres was seen in the dermis on ED10, and higher wavelengths of birefringence became evident by ED13. Our findings suggest that the temporal pattern of LOX mRNA expression correlates with collagen fibre accumulation in the dermis of the developing chick limb bud, whereas LOX expression was relatively constant at the protein level.

Enzymatic cross-linking of a nanofibrous peptide hydrogel

The rheological properties of the environment in which a cell lives play a key role in how the cells will respond to that environment and may modify cell proliferation, morphology and differentiation. Effective means of modifying these properties are needed, particularly for peptide hydrogels which are generally relatively weak and soft. In this report we describe the enzymatic cross-linking of a nanofibrous multidomain peptide hydrogel. When this method was used, the storage modulus, G', could be increased to over 4000 Pa without changes in hydrogel concentration and without dramatic changes in nanostructural architecture. Enzymatic cross-linking represents a mild and simple method for increasing the mechanical strength of peptide hydrogels in applications for which the robustness of the gel is essential. This method should be suitable for a broad array of peptide hydrogels containing lysine such as those currently under study by many different groups.

High glucose increases lysyl oxidase expression and activity in retinal endothelial cells: mechanism for compromised extracellular matrix barrier function

OBJECTIVE

In diabetes, retinal vascular basement membrane (BM) undergoes significant thickening and compromises vessel function including increased vascular permeability, a prominent lesion of early diabetic retinopathy. In this study we determined whether altered expression and activity of lysyl oxidase (LOX), a cross-linking enzyme, may compromise vascular basement membrane functional integrity under high-glucose (HG) conditions.

RESEARCH DESIGN AND METHODS

Rat retinal endothelial cells (RRECs) grown in normal (5 mmol/l) or HG (30 mmol/l glucose) medium for 7 days were assessed for expression of LOX and proLOX by Western blot analysis and LOX enzyme activity. To determine whether HG alters cellular distribution patterns of LOX and proLOX, immunostaining with respective antibodies was performed. Similarly, cells grown in normal or HG medium were subjected to both LOX inhibition with β-aminopropionitrile (BAPN) and by small interfering RNA knockdown, and respectively examined for cell monolayer permeability. Additionally, retinas of streptozotocin (STZ)-induced diabetic rats were analyzed to determine if diabetes altered LOX expression.

RESULTS

Western blot analysis revealed significantly increased LOX and proLOX expression in cells grown in HG medium compared with those grown in normal medium. The increased LOX level was strikingly similar to LOX upegulation in the diabetic retinas. In cells grown in HG medium, LOX activity and cell monolayer permeability was significantly increased, as were LOX and proLOX immunostaining. Small interfering RNA- or BAPN-induced-specific blockage of LOX expression or activity, respectively, reduced cell monolayer permeability.

CONCLUSIONS

HG-induced increased LOX expression and activity compromises barrier functional integrity, a prominent lesion of diabetic retinopathy.

The Scar-in-a-Jar: studying potential antifibrotic compounds from the epigenetic to extracellular level in a single well

BACKGROUND AND PURPOSE

Fibrosis, a pathological accumulation of collagen in tissues, represents a major global disease burden. Effective characterization of potential antifibrotic drugs has been constrained by poor formation of the extracellular matrix in vitro, due to tardy procollagen processing by collagen C-proteinase/BMP-1, and difficulties in relating this matrix to cell numbers in experimental samples.

EXPERIMENTAL APPROACH

The Scar-in-a-Jar model provided, in vitro, the complete biosynthetic cascade of collagen matrix formation including complete conversion of procollagen by C-proteinase/BMP-1, its subsequent extracellular deposition and lysyl oxidase-mediated cross-linking, achieved by applying the biophysical principle of macromolecular 'crowding'. Collagen matrix deposition, velocity and morphology can be controlled using negatively charged 'crowders' in a rapid (2 days) mode or a mixture of neutral 'crowders' in an accelerated (6 days) mode. Combined with quantitative optical bioimaging, this novel system allows for in situ assessment of the area of deposited collagen(s) per cell.

KEY RESULTS

Optical evaluation of known and novel antifibrotic compounds effective at the epigenetic, post-transcriptional/translational/secretional level correlated excellently with corresponding biochemical analyses. Focusing on quantitation of deposited collagen, the Scar-in-a-Jar was most effective in assessing novel inhibitors that may have multiple targets, such as microRNA29c, found to be a promising antifibrotic agent.

CONCLUSIONS AND IMPLICATIONS

This novel screening system supersedes current in vitro fibroplasia models, as a fast, quantitative and non-destructive technique. This method distinguishes a reduction in collagen I deposition, excluding collagen cross-linking, and allows full evaluation of inhibitors of C-proteinase/BMP-1 and other matrix metalloproteinases.

Neuraminidase-1, a subunit of the cell surface elastin receptor, desialylates and functionally inactivates adjacent receptors interacting with the mitogenic growth factors PDGF-BB and IGF-2

We recently established that the elastin-binding protein, which is identical to the spliced variant of beta-galactosidase, forms a cell surface-targeted complex with two proteins considered "classic lysosomal enzymes": protective protein/cathepsin A and neuraminidase-1 (Neu1). We also found that cell surface-residing Neu1 can desialylate neighboring microfibrillar glycoproteins and facilitate the deposition of insoluble elastin, which contributes to the maintenance of cellular quiescence. Here we provide evidence that cell surface-residing Neu1 contributes to a novel mechanism that limits cellular proliferation by desialylating cell membrane-residing sialoglycoproteins that directly propagate mitogenic signals. We demonstrated that treatment of cultured human aortic smooth muscle cells (SMCs) with either a sialidase inhibitor or an antibody that blocks Neu1 activity induced significant up-regulation in SMC proliferation in response to fetal bovine serum. Conversely, treatment with Clostridium perfringens neuraminidase (which is highly homologous to Neu1) decreased SMC proliferation, even in cultures that did not deposit elastin. Further, we found that pretreatment of aortic SMCs with exogenous neuraminidase abolished their mitogenic responses to recombinant platelet-derived growth factor (PDGF)-BB and insulin-like growth factor (IGF)-2 and that sialidosis fibroblasts (which are exclusively deficient in Neu1) were more responsive to PDGF-BB and IGF-2 compared with normal fibroblasts. Furthermore, we provide direct evidence that neuraminidase caused the desialylation of both PDGF and IGF-1 receptors and diminished the intracellular signals induced by the mitogenic ligands PDGF-BB and IGF-2.

Mechanism for Covalent Binding of Rofecoxib to Elastin of Rat Aorta

We have previously reported that oral administration of [(14)C]rofecoxib to rats resulted in the long retention of radioactivity by the aorta as a consequence of covalent binding to elastin. Treatment of rats with alpha-phenyl-alpha-propylbenzeneacetic acid 2-[diethylamino]-ethyl ester hydrochloride (SKF-525A), a cytochrome P450 inhibitor, significantly decreased the systemic exposure of 5-hydroxyrofecoxib, one of the main metabolites of rofecoxib, whereas there was no statistically significant change in the retention of radioactivity from [(14)C]rofecoxib in the aorta. On the other hand, the aortic retention of radioactivity closely correlated to the systemic exposure of unchanged rofecoxib in the dose range between 2 and 10 mg/kg. A covalent binding study of [(14)C]rofecoxib in vitro using rat aorta homogenate in the presence of d-penicillamine, hydralazine, beta-aminopropionitrile, and sodium borohydride suggested that the aldehyde group of allysine in elastin was relevant to the covalent binding. In a model reaction using benzaldehyde, rofecoxib but not 5-hydroxyrofecoxib reacted with the aldehyde group of benzaldehyde in a manner of condensation reaction under a physiological pH condition. A histopathological examination using an electron microscope demonstrated that multiple oral administration of rofecoxib to rats caused marked degradation of the elastic fiber system of the aorta. These results suggested that rofecoxib as such is reactive in vivo, undergoing a condensation reaction with allysine, thereby preventing the formation of cross-linkages in elastin, i.e., desmosine and isodesmosine, and causing the degradation of the elastic fibers.

Single intratumoral injection of long-acting benzyl ester of D-penicillamine inhibits the growth of melanoma tumor in mice

Using a murine model of melanoma we tested the effect of D-penicillamine administered in repetitive, daily injections, or as a single large dose injected either in saline or in a biodegradable polymer. We also studied the effect of a single intratumoral injection of benzyl-ester-D-penicillamine on the growth of the tumor. Daily injections of the drug or its administration in a polymer or benzyl-ester of D-penicillamine were all significantly inhibitory. The inhibitory effect manifested 4-5 days after injection. The inhibition lasted 8-10 days. There was no evidence of local or systemic toxicity and no changes in body weight. Several possible mechanisms for the inhibitory effect are presented.

Effects of long-term dietary lipids on mature bone mineral content, collagen, crosslinks, and prostaglandin E2 production in Japanese quail

This study investigated the effects of long-term dietary lipids on mature bone mineral content, collagen concentration, crosslink levels, bone marrow and ex vivo prostaglandin E2 (PGE2) biosynthesis, as well as the relationship of PGE2 production to these bone formation parameters. One-month-old male Japanese quail were given a basal diet containing 1 of 4 lipid sources: soybean oil (SBO), hydrogenated soybean oil (HSBO), chicken fat (CF), or menhaden fish oil (FO) at 50 g/kg of the diet. At 8 mo of age, lipid treatments did not affect bone length, diameter, or weight in quail. Quail fed SBO or CF had significantly lower levels of mineral content in tibial bones compared with those given FO. Bone collagen level was significantly higher in quail consuming SBO than those given HSBO or CF. Collagen crosslink concentration was markedly increased in birds provided FO or HSBO compared with those fed SBO or CF. Prostaglandin E2 biosynthesis in bone organ culture and marrow were greatly increased in quail maintained on the SBO or CF diet compared with those given the FO or HSBO diet. Prostaglandin E2 production in the bone microenvironment was negatively correlated with tibial ash and collagen crosslinks but had a positive correlation with tibial collagen levels. These results support our previous findings that long-term exposure to diets high in SBO or CF impaired mature bone mechanical properties and histological characteristics. Further, the results suggest that long-term supplementation of SBO or CF in the diet had a significant adverse effect on mature bone metabolism, and that dietary lipids altered bone metabolism, perhaps partially by controlling the production of local regulatory factor in bone.

Chemical and biomechanical characterization of hyperhomocysteinemic bone disease in an animal model

BACKGROUND

Classical homocystinuria is an autosomal recessive disorder caused by cystathionine beta-synthase (CBS) deficiency and characterized by distinctive alterations of bone growth and skeletal development. Skeletal changes include a reduction in bone density, making it a potentially attractive model for the study of idiopathic osteoporosis.

METHODS

To investigate this aspect of hyperhomocysteinemia, we supplemented developing chicks (n = 8) with 0.6% dl-homocysteine (hCySH) for the first 8 weeks of life in comparison to controls (n = 10), and studied biochemical, biomechanical and morphologic effects of this nutritional intervention.

RESULTS

hCySH-fed animals grew faster and had longer tibiae at the end of the study. Plasma levels of hCySH, methionine, cystathionine, and inorganic sulfate were higher, but calcium, phosphate, and other indices of osteoblast metabolism were not different. Radiographs of the lower limbs showed generalized osteopenia and accelerated epiphyseal ossification with distinct metaphyseal and suprametaphyseal lucencies similar to those found in human homocystinurics. Although biomechanical testing of the tibiae, including maximal load to failure and bone stiffness, indicated stronger bone, strength was proportional to the increased length and cortical thickness in the hCySH-supplemented group. Bone ash weights and IR-spectroscopy of cortical bone showed no difference in mineral content, but there were higher Ca2+/PO4(3-) and lower Ca2+/CO3(2-) molar ratios than in controls. Mineral crystallization was unchanged.

CONCLUSION

In this chick model, hyperhomocysteinemia causes greater radial and longitudinal bone growth, despite normal indices of bone formation. Although there is also evidence for an abnormal matrix and altered bone composition, our finding of normal biomechanical bone strength, once corrected for altered morphometry, suggests that any increase in the risk of long bone fracture in human hyperhomocysteinemic disease is small. We also conclude that the hCySH-supplemented chick is a promising model for study of the connective tissue abnormalities associated with homocystinuria and an important alternative model to the CBS knock-out mouse.

Integrative cartilage repair: inhibition by beta-aminopropionitrile

The effects of beta-aminopropionitrile, a known inhibitor of lysyl oxidase, on the extractability of newly synthesized collagen and integrative cartilage repair were determined in explant cultures of adult bovine articular cartilage. Dose-escalation studies indicated that treatment of cartilage explants for 6 days with beta-aminopropionitrile caused a dose-dependent inhibition of proteoglycan synthesis ([35S]sulfate incorporation) with a 50% inhibition at 2.2 mM. However, 0.25 mM beta-aminopropionitrile had no detectable effect on proteoglycan synthesis and was thus used for subsequent experiments. Treatment of cartilage with beta-aminopropionitrile for 14 days increased the extractability of newly synthesized collagen with 4 M guanidine-HCl while having little effect on proteoglycan synthesis, proteoglycan deposition, collagen synthesis (formation of [3H]hydroxyproline after labeling with [3H]proline), collagen deposition, or cartilage cellularity (DNA content). In untreated cultures, the percentage of radiolabeled collagen ([3H]hydroxyproline) that was extractable after 1 day of radiolabeling, 6 days of radiolabeling, or 6 days of label and 6 days of chase decreased from 81 to 25 and 9%, respectively. In beta-aminopropionitrile-treated cultures, the extractability was relatively higher (96, 62, and 47%, respectively). Treatment with beta-aminopropionitrile after radiolabeling with [14C]lysine also significantly inhibited the formation of the reducible crosslink [14C]dihydroxylysinonorleucine without affecting the overall deposition in cartilage of [14C]lysine and [14C]hydroxylysine. In functional repair studies, treatment with beta-aminopropionitrile caused an almost complete inhibition of integration between pairs of cartilage explants maintained in apposition for 2 weeks. These results indicate that beta-aminopropionitrile blocks the formation of collagen crosslinks in cartilage explants and suggest that such crosslinks are critical to integrative cartilage repair.

Pyridoxine deficiency affects biomechanical properties of chick tibial bone

The mechanical integrity of bone is dependent on the bone matrix, which is believed to account for the plastic deformation of the tissue, and the mineral, which is believed to account for the elastic deformation. The validity of this model is shown in this study based on analysis of the bones of vitamin B6-deficient and vitamin B6-replete chick bones. In this model, when B6-deficient and control animals are compared, vitamin B6 deficiency has no effect on the mineral content or composition of cortical bone as measured by ash weight (63 +/- 6 vs. 58 +/- 3); mineral to matrix ratio of the FTIR spectra (4.2 +/- 0.6 vs. 4.5 +/- 0.2), line-broadening analyses of the X-ray diffraction 002 peak (beta 002 = 0.50 +/- 0.1 vs. 0.49 +/- 0.01), or other features of the infrared spectra. In contrast, collagen was significantly more extractable from vitamin B6-deficient chick bones (20 +/- 2% of total hydroxyproline extracted vs. 10 +/- 3% p < or = 0.001). The B6-deficient bones also contained an increased amount of the reducible cross-links DHLNL, dehydro-dihydroxylysinonorleucine, (1.03 +/- 0.07 vs. 0.84 +/- 0.13 p < or = 0.001); and a nonsignificant increase in HLNL, dehydro-hydroxylysinonorleucine, (0.51 +/- 0.03 vs. 0.43 +/- 0.03, p < or = 0.10). There were no significant changes in bone length, bone diameter, or area moment of inertia. In four-point bending, no significant changes in elastic modulus, stiffness, offset yield deflection, or fracture deflection were detected. However, fracture load in the B6-deficient animals was decreased from 203 +/- 35 MPa to 151 +/- 23 MPa, p < or = 0.01, and offset yield load was decreased from 165 +/- 9 MPa to 125 +/- 14 MPa, p < or = 0.05. Since earlier histomorphometric studies had demonstrated that the B6-deficient bones were osteopenic, these data suggest that although proper cortical bone mineralization occurred, the alterations of the collagen resulted in changes to bone mechanical performance.

Characterization of the effects of N-hydroxy-IDPN on the auditory, vestibular, and olfactory systems in rats

The mechanism of neurotoxicity of 3,3'-iminodipropionitrile (IDPN) has been widely debated, with either the parent compound or putative metabolites implicated in various studies. The N-hydroxylated form of IDPN (HO-IDPN) has been reported to cause the excitation with choreiform and circling (ECC) syndrome in rats at doses approximately one-eighth of that required to cause comparable signs in rats treated with IDPN. Because of the similarity of symptoms induced by HO-IDPN and IDPN, we investigated the effect of HO-IDPN on other aspects of the nervous system affected by IDPN, specifically the auditory, vestibular, and olfactory systems. In addition, ECC symptoms were quantified to replicate the previous findings. HO-IDPN was administered ip in saline for 3 consecutive days to two different cohorts of young adult male Sprague-Dawley rats. The first cohort (60, 80, 100, and 120 mg/kg; n = 2/group, except for the 120 mg/kg group, where n = 1) was used in a dose range-finding study. After making the neurobehavioral assessments, animals were sacrificed for olfactory mucosal histopathology. Based on the outcome of the first study, the second cohort (n = 10/group) received saline or HO-IDPN at 100 mg/kg/day for 3 consecutive days. Two animals from each of these groups were sacrificed for olfactory mucosal histopathology; the remaining animals were tested for neurobehavioral effects 3 weeks after the last dose. Animals in the second cohort lost approximately 8% of their pretreatment body weight. All rats receiving the 100 mg/kg/day dose of HO-IDPN (and the rat receiving 120 mg/kg/day) developed the ECC syndrome and signs of vestibular dysfunction within 4 days after the last dose. HO-IDPN caused a large decrease in the acoustic startle response and markedly elevated auditory thresholds at all frequencies tested. The threshold for the ECC syndrome and olfactory mucosal damage was 100 mg/kg. These studies extend previous findings on the neurotoxicity of HO-IDPN and point to the need for determining whether HO-IDPN is an in vivo metabolite of IDPN.

Mitigating the effects of halofuginone on skin strength by feeding L-proline to broiler chickens

Two experiments were conducted to determine whether supplemental levels of L-proline in the diets of broiler chickens would mitigate the skin weakening effect caused by continuous feeding of the anticoccidial halofuginone. In Experiment 1, tensile strength and collagen levels in thigh apteria skin were determined at 21 and 42 d of age in male broilers fed 0, .5, and 1% L-proline with either halofuginone (3 mg/kg) or salinomycin (61 mg/kg). In Experiment 2, the same measurements were made on female broilers receiving diets containing halofuginone and supplemented with 0, .5, or 1% L-proline, 1% L-proline through 21 d of age, or 1% L-glutamic acid through 21 d of age, or a diet containing high L-proline feedstuffs (corn gluten meal and ring dried blood meal). In Experiment 1, dermis thickness of thigh apteria was measured in the males at Day 21. Skin strength was increased in male and female broilers fed halofuginone with addition of .5 and 1% L-proline, respectively, at 21 and 42 d of age. Continuous incorporation of synthetic L-proline into diets was shown to improve skin strength in females, whereas diets formulated to contain high levels of L-proline from feedstuffs, 21-d feeding of L-proline, or L-glutamic acid did not increase skin strength.

Cell-extracellular matrix interactions under in vivo conditions during interstitial cell migration in Hydra vulgaris

Interstitial cell (I-cell) migration in hydra is essential for establishment of the regional cell differentiation pattern in the organism. All previous in vivo studies have indicated that cell migration in hydra is a result of cell-cell interactions and chemotaxic gradients. Recently, in vitro cell adhesion studies indicated that isolated nematocytes could bind to substrata coated with isolated hydra mesoglea, fibronectin and type IV collagen. Under these conditions, nematocytes could be observed to migrate on some of these extracellular matrix components. By modifying previously described hydra grafting techniques, two procedures were developed to test specifically the role of extracellular matrix components during in vivo I-cell migration in hydra. In one approach, the extracellular matrix structure of the apical half of the hydra graft was perturbed using beta-aminopropionitrile and beta-xyloside. In the second approach, grafts were treated with fibronectin, RGDS synthetic peptide and antibody to fibronectin after grafting was performed. In both cases, I-cell migration from the basal half to the apical half of the grafts was quantitatively analyzed. Statistical analysis indicated that beta-aminopropionitrile, fibronectin, RGDS synthetic peptide and antibody to fibronectin all were inhibitory to I-cell migration as compared to their respective controls. beta-xyloside treatment had no effect on interstitial cell migration. These results indicate the potential importance of cell-extracellular matrix interactions during in vivo I-cell migration in hydra.