The Pro-regions of lysyl oxidase and lysyl oxidase-like 1 are required for deposition onto elastic fibers

IGF-II Regulates Lysyl Oxidase Propeptide and Mediates its Effects in part via Basic Helix-Loop-Helix E40

Pulmonary fibrosis (PF) is a clinically severe and commonly fatal complication of Systemic Sclerosis (SSc). Our group has previously reported profibrotic roles for Insulin-like Growth Factor II (IGF-II) and Lysyl Oxidase (LOX) in SSc-PF. We sought to identify downstream regulatory mediators of IGF-II. In the present work, we show that SSc lung tissues have higher baseline levels of the total (N-glycosylated/unglycosylated) LOX-Propeptide (LOX-PP) than normal lung tissues. LOX-PP-mediated changes were consistent with the extracellular matrix (ECM) deregulation implicated in SSc-PF progression. Furthermore, Tolloid-like 1 (TLL1) and Bone Morphogenetic Protein 1 (BMP1), enzymes that can cleave ProLOX to release LOX-PP, were increased in SSc lung fibrosis and the bleomycin (BLM)-induced murine lung fibrosis model, respectively. In addition, IGF-II regulated the levels of ProLOX, active LOX, LOX-PP, BMP1, and isoforms of TLL1. The Class E Basic Helix-Loop-Helix protein 40 (BHLHE40) transcription factor localized to the nucleus in response to IGF-II. BHLHE40 silencing downregulated TLL1 isoforms and LOX-PP, and restored significant features of ECM deregulation triggered by IGF-II. Our findings indicate that IGF-II, BHLHE40, and LOX-PP may serve as targets of therapeutic intervention to halt SSc-PF progression.

Arteriolar degeneration and stiffness in cerebral amyloid angiopathy are linked to β-amyloid deposition and lysyl oxidase

Cerebral amyloid angiopathy (CAA) is a vasculopathy characterized by vascular β-amyloid (Aβ) deposition on cerebral blood vessels. CAA is closely linked to Alzheimer's disease (AD) and intracerebral hemorrhage. CAA is associated with the loss of autoregulation in the brain, vascular rupture, and cognitive decline. To assess morphological and molecular changes associated with the degeneration of penetrating arterioles in CAA, we analyzed post-mortem human brain tissue from 26 patients with mild, moderate, and severe CAA end neurological controls. The tissue was optically cleared for three-dimensional light sheet microscopy, and morphological features were quantified using surface volume rendering. We stained Aβ, vascular smooth muscle (VSM), lysyl oxidase (LOX), and vascular markers to visualize the relationship between degenerative morphological features, including vascular dilation, dolichoectasia (variability in lumenal diameter) and tortuosity, and the volumes of VSM, Aβ, and LOX in arterioles. Atomic force microscopy (AFM) was used to assess arteriolar wall stiffness, and we identified a pattern of morphological features associated with degenerating arterioles in the cortex. The volume of VSM associated with the arteriole was reduced by around 80% in arterioles with severe CAA and around 60% in cases with mild/moderate CAA. This loss of VSM correlated with increased arteriolar diameter and variability of diameter, suggesting VSM loss contributes to arteriolar laxity. These vascular morphological features correlated strongly with Aβ deposits. At sites of microhemorrhage, Aβ was consistently present, although the morphology of the deposits changed from the typical organized ring shape to sharply contoured shards with marked dilation of the vessel. AFM showed that arteriolar walls with CAA were more than 400% stiffer than those without CAA. Finally, we characterized the association of vascular degeneration with LOX, finding strong associations with VSM loss and vascular degeneration. These results show an association between vascular Aβ deposition, microvascular degeneration, and increased vascular stiffness, likely due to the combined effects of replacement of VSM by β-amyloid, cross-linking of extracellular matrices (ECM) by LOX, and possibly fibrosis. This advanced microscopic imaging study clarifies the association between Aβ deposition and vascular fragility. Restoration of physiologic ECM properties in penetrating arteries may yield a novel therapeutic strategy for CAA.

Lysine Deacetylation Is a Key Function of the Lysyl Oxidase Family of Proteins in Cancer

Mammalian members of the lysyl oxidase (LOX) family of proteins carry a copper-dependent monoamine oxidase domain exclusively within the C-terminal region, which catalyzes ε-amine oxidation of lysine residues of various proteins. However, recent studies have demonstrated that in LOX-like (LOXL) 2-4 the C-terminal canonical catalytic domain and N-terminal scavenger receptor cysteine-rich (SRCR) repeats domain exhibit lysine deacetylation and deacetylimination catalytic activities. Moreover, the N-terminal SRCR repeats domain is more catalytically active than the C-terminal oxidase domain. Thus, LOX is the third family of lysine deacetylases in addition to histone deacetylase and sirtuin families. In this review, we discuss how the LOX family targets different cellular proteins for deacetylation and deacetylimination to control the development and metastasis of cancer.

Exploring the Interplay between Polyphenols and Lysyl Oxidase Enzymes for Maintaining Extracellular Matrix Homeostasis

Collagen, the most abundant structural protein found in mammals, plays a vital role as a constituent of the extracellular matrix (ECM) that surrounds cells. Collagen fibrils are strengthened through the formation of covalent cross-links, which involve complex enzymatic and non-enzymatic reactions. Lysyl oxidase (LOX) is responsible for catalyzing the oxidative deamination of lysine and hydroxylysine residues, resulting in the production of aldehydes, allysine, and hydroxyallysine. These intermediates undergo spontaneous condensation reactions, leading to the formation of immature cross-links, which are the initial step in the development of mature covalent cross-links. Additionally, non-enzymatic glycation contributes to the formation of abnormal cross-linking in collagen fibrils. During glycation, specific lysine and arginine residues in collagen are modified by reducing sugars, leading to the creation of Advanced Glycation End-products (AGEs). These AGEs have been associated with changes in the mechanical properties of collagen fibers. Interestingly, various studies have reported that plant polyphenols possess amine oxidase-like activity and can act as potent inhibitors of protein glycation. This review article focuses on compiling the literature describing polyphenols with amine oxidase-like activity and antiglycation properties. Specifically, we explore the molecular mechanisms by which specific flavonoids impact or protect the normal collagen cross-linking process. Furthermore, we discuss how these dual activities can be harnessed to generate properly cross-linked collagen molecules, thereby promoting the stabilization of highly organized collagen fibrils.

Lysyl oxidase-like 2 processing by factor Xa modulates its activity and substrate preference

Lysyl oxidase-like 2 (LOXL2) has been identified as an essential mediator of extracellular matrix (ECM) remodeling in several disease processes including cardiovascular disease. Thus, there is growing interest in understanding the mechanisms by which LOXL2 is regulated in cells and tissue. While LOXL2 occurs both in full length and processed forms in cells and tissue, the precise identity of the proteases that process LOXL2 and the consequences of processing on LOXL2's function remain incompletely understood. Here we show that Factor Xa (FXa) is a protease that processes LOXL2 at Arg-338. Processing by FXa does not affect the enzymatic activity of soluble LOXL2. However, in situ in vascular smooth muscle cells, LOXL2 processing by FXa results in decreased cross-linking activity in the ECM and shifts substrate preference of LOXL2 from type IV collagen to type I collagen. Additionally, processing by FXa increases the interactions between LOXL2 and prototypical LOX, suggesting a potential compensatory mechanism to preserve total LOXs activity in the vascular ECM. FXa expression is prevalent in various organ systems and shares similar roles in fibrotic disease progression as LOXL2. Thus, LOXL2 processing by FXa could have significant implications in pathologies where LOXL2 is involved.

Analysis of genetically determined gene expression suggests role of inflammatory processes in exfoliation syndrome

BACKGROUND

Exfoliation syndrome (XFS) is an age-related systemic disorder characterized by excessive production and progressive accumulation of abnormal extracellular material, with pathognomonic ocular manifestations. It is the most common cause of secondary glaucoma, resulting in widespread global blindness. The largest global meta-analysis of XFS in 123,457 multi-ethnic individuals from 24 countries identified seven loci with the strongest association signal in chr15q22-25 region near LOXL1. Expression analysis have so far correlated coding and a few non-coding variants in the region with LOXL1 expression levels, but functional effects of these variants is unclear. We hypothesize that analysis of the contribution of the genetically determined component of gene expression to XFS risk can provide a powerful method to elucidate potential roles of additional genes and clarify biology that underlie XFS.

RESULTS

Transcriptomic Wide Association Studies (TWAS) using PrediXcan models trained in 48 GTEx tissues leveraging on results from the multi-ethnic and European ancestry GWAS were performed. To eliminate the possibility of false-positive results due to Linkage Disequilibrium (LD) contamination, we i) performed PrediXcan analysis in reduced models removing variants in LD with LOXL1 missense variants associated with XFS, and variants in LOXL1 models in both multiethnic and European ancestry individuals, ii) conducted conditional analysis of the significant signals in European ancestry individuals, and iii) filtered signals based on correlated gene expression, LD and shared eQTLs, iv) conducted expression validation analysis in human iris tissues. We observed twenty-eight genes in chr15q22-25 region that showed statistically significant associations, which were whittled down to ten genes after statistical validations. In experimental analysis, mRNA transcript levels for ARID3B, CD276, LOXL1, NEO1, SCAMP2, and UBL7 were significantly decreased in iris tissues from XFS patients compared to control samples. TWAS genes for XFS were significantly enriched for genes associated with inflammatory conditions. We also observed a higher incidence of XFS comorbidity with inflammatory and connective tissue diseases.

CONCLUSION

Our results implicate a role for connective tissues and inflammation pathways in the etiology of XFS. Targeting the inflammatory pathway may be a potential therapeutic option to reduce progression in XFS.

Lysyl oxidase-like 1 deficiency alters ultrastructural and biomechanical properties of the peripapillary sclera in mice

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Lysyl oxidate-like 1 knockout (Loxl1^-/-) mice have decreased vision without elevated intraocular pressure.

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Loxl1^-/- mice exhibit biometric changes of the anterior segment of the eye.

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Loxl1^-/- mice have altered elastin and collagen structure in peripapillary sclera.

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Structural alternations of peripapillary sclera correlate with its increased stiffness in Loxl1^-/- mice.

Lysyl oxidase-like 1 encoded by the LOXL1 gene is a member of the lysyl oxidase family of enzymes that are important in the maintenance of extracellular matrix (ECM)-rich tissue. LOXL1 is important for proper elastic fiber formation and mice lacking LOXL1 (Loxl1^−/−) exhibit systemic elastic fiber disorders, such as pelvic organ prolapse, a phenotype associated with exfoliation syndrome (XFS) in humans. Patients with XFS have a significant risk of developing exfoliation glaucoma (XFG), a severe form of glaucoma, which is a neurodegenerative condition leading to irreversible blindness if not detected and treated in a timely fashion. Although Loxl1^−/− mice have been used extensively to investigate mechanisms of pelvic organ prolapse, studies of eyes in those mice are limited and some showed inconsistent ocular phenotypes. In this study we demonstrate that Loxl1^−/− mice have significant anterior segment biometric abnormalities which recapitulate some human XFS features. We then focused on the peripapillary sclera (PPS), a critical structure for maintaining optic nerve health. We discovered quantitative and qualitive changes in ultrastructure of PPS, such as reduced elastic fibers, enlarged collagen fibrils, and transformed collagen lamella organization detected by transmission electron microscopy (TEM). Importantly, these changes corelate with altered tissue biomechanics detected by Atomic Force Microscopy (AFM) of PPS in mice. Together, our results support a crucial role for LOXL1 in ocular tissue structure and biomechanics, and Loxl1^−/− mice could be a valuable resource for understanding the role of scleral tissue biomechanics in ocular disease.

Copper-Binding Domain Variation in a Novel Murine Lysyl Oxidase Model Produces Structurally Inferior Aortic Elastic Fibers Whose Failure Is Modified by Age, Sex, and Blood Pressure

Lysyl oxidase (LOX) is a copper-binding enzyme that cross-links elastin and collagen. The dominant LOX variation contributes to familial thoracic aortic aneurysm. Previously reported murine Lox mutants had a mild phenotype and did not dilate without drug-induced provocation. Here, we present a new, more severe mutant, Loxb2b370.2Clo (c.G854T; p.Cys285Phe), whose mutation falls just N-terminal to the copper-binding domain. Unlike the other mutants, the C285F Lox protein was stably produced/secreted, and male C57Bl/6J Lox+/C285F mice exhibit increased systolic blood pressure (BP; p < 0.05) and reduced caliber aortas (p < 0.01 at 100mmHg) at 3 months that independently dilate by 6 months (p < 0.0001). Multimodal imaging reveals markedly irregular elastic sheets in the mutant (p = 2.8 × 10−8 for breaks by histology) that become increasingly disrupted with age (p < 0.05) and breeding into a high BP background (p = 6.8 × 10−4). Aortic dilation was amplified in males vs. females (p < 0.0001 at 100mmHg) and ameliorated by castration. The transcriptome of young Lox mutants showed alteration in dexamethasone (p = 9.83 × 10−30) and TGFβ-responsive genes (p = 7.42 × 10−29), and aortas from older C57Bl/6J Lox+/C285F mice showed both enhanced susceptibility to elastase (p < 0.01 by ANOVA) and increased deposition of aggrecan (p < 0.05). These findings suggest that the secreted Lox+/C285F mutants produce dysfunctional elastic fibers that show increased susceptibility to proteolytic damage. Over time, the progressive weakening of the connective tissue, modified by sex and blood pressure, leads to worsening aortic disease.

Cleavage of LOXL1 by BMP1 and ADAMTS14 Proteases Suggests a Role for Proteolytic Processing in the Regulation of LOXL1 Function

Members of the lysyl oxidase (LOX) family catalyze the oxidative deamination of lysine and hydroxylysine residues in collagen and elastin in the initiation step of the formation of covalent cross-links, an essential process for connective tissue maturation. Proteolysis has emerged as an important level of regulation of LOX enzymes with the cleavage of the LOX isoform by metalloproteinases of the BMP1 (bone morphogenetic protein 1) and ADAMTS (a disintegrin and metalloproteinase with thrombospondin motifs) families as a model example. Lysyl oxidase-like 1 (LOXL1), an isoform associated with pelvic organ prolapse and pseudoexfoliation (PEX) glaucoma, has also been reported to be proteolytically processed by these proteases. However, precise molecular information on these proteolytic events is not available. In this study, using genetic cellular models, along with proteomic analyses, we describe that LOXL1 is processed by BMP1 and ADAMTS14 and identify the processing sites in the LOXL1 protein sequence. Our data show that BMP1 cleaves LOXL1 in a unique location within the pro-peptide region, whereas ADAMTS14 processes LOXL1 in at least three different sites located within the pro-peptide and in the first residues of the catalytic domain. Taken together, these results suggest a complex regulation of LOXL1 function by BMP1- and ADAMTS14-mediated proteolysis where LOXL1 enzymes retaining variable fragments of N-terminal region may display different capabilities.

FBN2 Silencing Recapitulates Hypoxic Conditions and Induces Elastic Fiber Impairment in Human Dermal Fibroblasts

Most chronic wounds are characterized by varying degrees of hypoxia and low partial pressures of O2 that may favor the development of the wound and/or delay healing. However, most studies regarding extracellular matrix remodeling in wound healing are conducted under normoxic conditions. Here, we investigated the consequences of hypoxia on elastic network formation, both in a mouse model of pressure-induced hypoxic ulcer and in human primary fibroblasts cultured under hypoxic conditions. In vitro, hypoxia inhibited elastic fiber synthesis with a reduction in fibrillin-2 expression at the mRNA and protein levels. Lysyl oxidase maturation was reduced, concomitant with lower enzymatic activity. Fibrillin-2 and lysyl oxidase could interact directly, whereas the downregulation of fibrillin-2 was associated with deficient lysyl oxidase maturation. Elastic fibers were not synthesized in the hypoxic inflammatory tissues resulting from in vivo pressure-induced ulcer. Tropoelastin and fibrillin-2 were expressed sparsely in hypoxic tissues stained with carbonic anhydrase IX. Different hypoxic conditions in culture resulted in the arrest of elastic fiber synthesis. The present study demonstrated the involvement of FBN2 in regulating elastin deposition in adult skin models and described the specific impact of hypoxia on the elastin network without consequences on collagen and fibronectin networks.

The Role of the Stromal Extracellular Matrix in the Development of Pterygium Pathology: An Update

Pterygium is a benign fibrovascular lesion of the bulbar conjunctiva with frequent involvement of the corneal limbus. Its pathogenesis has been mainly attributed to sun exposure to ultraviolet-B radiation. Obtained evidence has shown that it is a complex and multifactorial process which involves multiple mechanisms such as oxidative stress, dysregulation of cell cycle checkpoints, induction of inflammatory mediators and growth factors, angiogenic stimulation, extracellular matrix (ECM) disorders, and, most likely, viruses and hereditary changes. In this review, we aim to collect all authors’ experiences and our own, with respect to the study of fibroelastic ECM of pterygium. Collagen and elastin are intrinsic indicators of physiological and pathological states. Here, we focus on an in-depth analysis of collagen (types I and III), as well as the main constituents of elastic fibers (tropoelastin (TE), fibrillins (FBNs), and fibulins (FBLNs)) and the enzymes (lysyl oxidases (LOXs)) that carry out their assembly or crosslinking. All the studies established that changes in the fibroelastic ECM occur in pterygium, based on the following facts: An increase in the synthesis and deposition of an immature form of collagen type III, which showed the process of tissue remodeling. An increase in protein levels in most of the constituents necessary for the development of elastic fibers, except FBLN4, whose biological roles are critical in the binding of the enzyme LOX, as well as FBN1 for the development of stable elastin. There was gene overexpression of TE, FBN1, FBLN5, and LOXL1, while the expression of LOX and FBLN2 and -4 remained stable. In conclusion, collagen and elastin, as well as several constituents involved in elastic fiber assembly are overexpressed in human pterygium, thus, supporting the hypothesis that there is dysregulation in the synthesis and crosslinking of the fibroelastic component, constituting an important pathogenetic mechanism for the development of the disease.

Compositional Analysis of Extracellular Aggregates in the Eyes of Patients With Exfoliation Syndrome and Exfoliation Glaucoma

Purpose

Exfoliation syndrome (XFS) is a condition characterized by the production of insoluble fibrillar aggregates (exfoliation material; XFM) in the eye and elsewhere. Many patients with XFS progress to exfoliation glaucoma (XFG), a significant cause of global blindness. We used quantitative mass spectrometry to analyze the composition of XFM in lens capsule specimens and in aqueous humor (AH) samples from patients with XFS, patients with XFG and unaffected individuals.

Methods

Pieces of lens capsule and samples of AH were obtained with consent from patients undergoing cataract surgery. Tryptic digests of capsule or AH were analyzed by high-performance liquid chromatography–mass spectrometry and relative differences between samples were quantified using the tandem mass tag technique. The distribution of XFM on the capsular surface was visualized by SEM and super-resolution light microscopy.

Results

A small set of proteins was consistently upregulated in capsule samples from patients with XFS and patients with XFG, including microfibril components fibrillin-1, latent transforming growth factor-β–binding protein-2 and latent transforming growth factor-β–binding protein-3. Lysyl oxidase-like 1, a cross-linking enzyme associated with XFS in genetic studies, was an abundant XFM constituent. Ligands of the transforming growth factor-β superfamily were prominent, including LEFTY2, a protein best known for its role in establishing the embryonic body axis. Elevated levels of LEFTY2 were also detected in AH from patients with XFG, a finding confirmed subsequently by ELISA.

Conclusions

This analysis verified the presence of suspected XFM proteins and identified novel components. Quantitative comparisons between patient samples revealed a consistent XFM proteome characterized by strong expression of fibrillin-1, lysyl oxidase-like-1, and LEFTY2. Elevated levels of LEFTY2 in the AH of patients with XFG may serve as a biomarker for the disease.

Serum lysyl oxidase concentration increases in long-standing systemic sclerosis: Can lysyl oxidase change over time?

Objectives

This study aims to investigate the association of serum lysyl oxidase (LOX) levels with systemic sclerosis (SSc), to examine the relationship between LOX and disease onset, and to evaluate the probable effects of hyperlipidemia on the circulating levels of LOX among patients with SSc.

Patients and methods

Between May 2017 and November 2018, a total of 39 patients with SSc (2 males, 37 females; mean age: 46.6±12.3 years; range, 18 to 65 years) and 35 healthy controls (4 males, 31 females; mean age: 43.1±14.1 years; range, 18 to 65 years) were included. Serum LOX concentration was measured using the enzyme-linked immunoassay in triplicate.

Results

We found higher levels of serum LOX in patients with SSc compared to healthy controls. There was a significant relationship between serum LOX levels and disease onset. Patients with long-standing disease demonstrated increased levels of LOX in the blood compared to the recent-onset group. Hyperlipidemia did not have a significant effect on circulating levels of LOX. There was a significant negative correlation between LOX levels and modified Rodnan Skin Score in the subgroup of patients with skin involvement only and in patients without gastrointestinal involvement.

Conclusion

Our study findings show an increased level of LOX protein level in the blood of patients diagnosed with SSc. Hyperlipidemia seems not to affect the concentrations of LOX in the peripheral blood of patients with SSc.

An increase in elastogenic components in the placental villi of women with chronic venous disease during pregnancy is associated with decreased EGFL7 expression level

Chronic venous disease (CVD) is the response to a series of hemodynamic changes in the venous system and the onset of this disease is often triggered by pregnancy. Placental tissue is particularly sensitive to the characteristic changes which occurs in venous hypertension. In this regard, changes in the extracellular matrix (ECM), that occur to adapt to this situation, are fundamental to controlling elastogenesis. Therefore, the aim of the present study was to analyze the changes that occur in the mRNA and protein expression level of proteins related to elastogenesis in the placental villi of women diagnosed with CVD, in the third trimester of pregnancy. An observational, analytical and prospective cohort study was conducted, in which the placenta from 62 women with CVD were compared with that in placenta from 52 women without a diagnosis of CVD. Gene and protein expression levels were analyzed using reverse transcription-quantitative PCR and immunohistochemistry, respectively. The results showed a significant decrease in the gene and protein expression level of EGFL7 in the placental villi of women with CVD. By contrast, significant increases in the gene and protein expression level of ECM-related proteins, such as tropoelastin, fibulin 4, fibrillin 1 and members of the lysyl oxidase family (LOX and LOXL-1) were also found in the placental villi of women with CVD. To the best of our knowledge, the results from the present study showed for the first time that CVD during pregnancy was associated with changes in the mRNA and protein expression level in essential components of the EGFL7-modulated elastogenesis process in placental villi.

Correlation of the intronic LOXL1 polymorphism rs11638944 with pseudoexfoliation syndrome and glaucoma in a Greek population

BACKGROUND

The purpose of this study is the development and validation of a novel and robust genotyping method for a new lysyl oxidase-like 1 (LOXL1) intronic polymorphism (rs11638944, C > G) and the investigation of its potential association with pseudoexfoliation syndrome (PXS) and pseudoexfoliation glaucoma (PXG) in a Greek population.

MATERIAL AND METHODS

242 DNA samples from 49 PXS, 64 PXG, 50 primary open-angle glaucoma (POAG) patients and 79 healthy age-matched controls were analyzed. Novel methodologies were developed and optimized, in order to genotype the intronic LOXL1 polymorphism: a) a real-time qPCR and melting curve analysis in the Light Cycler platform for rapid and cost-effective analysis and, b) a conventional PCR-RFLP method for analysis of a small number of samples. In selected samples, validity was checked with the reference DNA Sequencing method.

RESULTS

The real-time qPCR methodology was reliable, demonstrating good efficiency, reproducibility, accuracy in genotyping (100% concordance with the PCR-RFLP method and DNA Sequencing), with good allele discrimination (Tm = 53.26°C for C allele, Tm = 61.83°C for G allele, ΔTm = 8.57°C). The results were characterized by Hardy-Weinberg equilibrium in all groups. An increase from 18% in healthy controls to 61% in PXS patients was detected for the G/G homozygote thus, the C allele is protective for PXS with OR = 0.22 (95%CI: 0.11-0.42, p < .0001). Moreover, an increase from 18% in healthy controls to 70% in PXG patients was detected for the G/G homozygote thus, the C allele is protective for PXG with OR = 0.13 (95%CI: 0.06-0.25, p < .0001).

CONCLUSIONS

A statistically significant association was verified for the intronic LOXL1 polymorphism rs11638944 and PXS/PXG in a Greek population.

Lysyl oxidase like protein-2 (LOXL-2); a novel marker for prediction of intrahepatic cholestasis of pregnancy

OBJECTIVE

Lysyl oxidase like protein 2 (LOXL-2) is an enzyme that is involved in the development of hepatic fibrosis and bile duct epithelial injury in hepatic cholestasis. Our aim was to investigate maternal serum levels of LOXL-2 and their relationship with fasting total bile acid (FTBA) levels in patients with intrahepatic cholestasis of pregnancy (ICP).

MATERIALS AND METHODS

Thirty-five pregnant women with ICP and 35 healthy women with uncomplicated pregnancies as the control group, were included in this cross-sectional study. Maternal serum LOXL-2, FTBA and other liver function test levels were compared between the two groups. The predictive cutoff value for LOXL-2 level in ICP was specified.

RESULTS

Serum LOXL-2 levels were found to be higher in the ICP group compared to the control group (225.699 ± 142.453 vs. 127.731 ± 63.419 pg/mL, p = .001). There was a significant positive correlation between serum LOXL-2 levels and FTBA levels (r = 0.330, p = .003). The optimal cutoff point for LOXL-2 for identifying increased risk of ICP was found to be ≥102 pg/mL, for which the sensitivity and specificity were 96.87% and 48.57%, respectively (p < .001).

CONCLUSIONS

Maternal serum LOXL-2 levels were significantly higher in women with ICP. LOXL-2 may be both an initiating factor in the pathophysiology of ICP and a marker in the prediction. It may also be a target in terms of preventing strategies in ICP.

LOXL1 exerts oncogenesis and stimulates angiogenesis through the LOXL1-FBLN5/αvβ3 integrin/FAK-MAPK axis in ICC

Aberrant expression of lysyl oxidase-like 1 (LOXL1) reportedly leads to fibrous diseases. Recent studies have revealed its role in cancers. In this study, we observed an elevated level of LOXL1 in the tissues and sera of patients with intrahepatic cholangiocarcinoma (ICC) compared with levels in nontumor tissues and sera of unaffected individuals. Overexpression of LOXL1 in RBE and 9810 cell lines promoted cell proliferation, colony formation, and metastasis in vivo and in vitro and induced angiogenesis. In contrast, depletion of LOXL1 showed the opposite effects. We further showed that LOXL1 interacted with fibulin 5 (FBLN5), which regulates angiogenesis, through binding to the αvβ3 integrin in an arginine-glycine-aspartic (Arg-Gly-Asp) domain-dependent mechanism and enhanced the focal adhesion kinase (FAK)-mitogen-activated protein kinase (MAPK) signaling pathway inside vascular endothelial cells. Our findings shed light on the molecular mechanism underlying LOXL1 regulation of angiogenesis in ICC development and indicate that the LOXL1-FBLN5/αvβ3 integrin/FAK-MAPK axis might be the critical pathological link leading to angiogenesis in ICC.

The Interactome of Cancer-Related Lysyl Oxidase and Lysyl Oxidase-Like Proteins

The members of the lysyl oxidase (LOX) family are amine oxidases, which initiate the covalent cross-linking of the extracellular matrix (ECM), regulate ECM stiffness, and contribute to cancer progression. The aim of this study was to build the first draft of the interactome of the five members of the LOX family in order to determine its molecular functions, the biological and signaling pathways mediating these functions, the biological processes it is involved in, and if and how it is rewired in cancer. In vitro binding assays, based on surface plasmon resonance and bio-layer interferometry, combined with queries of interaction databases and interaction datasets, were used to retrieve interaction data. The interactome was then analyzed using computational tools. We identified 31 new interactions and 14 new partners of LOXL2, including the α5β1 integrin, and built an interactome comprising 320 proteins, 5 glycosaminoglycans, and 399 interactions. This network participates in ECM organization, degradation and cross-linking, cell-ECM interactions mediated by non-integrin and integrin receptors, protein folding and chaperone activity, organ and blood vessel development, cellular response to stress, and signal transduction. We showed that this network is rewired in colorectal carcinoma, leading to a switch from ECM organization to protein folding and chaperone activity.

Integral role for lysyl oxidase-like-1 in conventional outflow tissue function and behavior

Lysyl oxidase-like-1 (LOXL1), a vital crosslinking enzyme in elastin fiber maintenance, is essential for the stability and strength of elastic vessels and tissues. Variants in the LOXL1 locus associate with a dramatic increase in risk of exfoliation syndrome (XFS), a systemic fibrillopathy, which often presents with ocular hypertension and exfoliation glaucoma (XFG). We examined the role of LOXL1 in conventional outflow function, the prime regulator of intraocular pressure (IOP). Using Loxl1^-/- , Loxl1^+/- , and Loxl1^+/+ mice, we observed an inverse relationship between LOXL1 expression and IOP, which worsened with age. Elevated IOP in Loxl1^-/- mice was associated with a larger globe, decreased ocular compliance, increased outflow facility, extracellular matrix (ECM) abnormalities, and dilated intrascleral veins, yet, no dilation of arteries or capillaries. Interestingly, in living Loxl1^-/- mouse eyes, Schlemm's canal (SC) was less susceptible to collapse when challenged with acute elevations in IOP, suggesting elevated episcleral venous pressure (EVP). Thus, LOXL1 expression is required for normal IOP control, while ablation results in altered ECM repair/homeostasis and conventional outflow physiology. Dilation of SC and distal veins, but not arteries, is consistent with key structural and functional roles for elastin in low-pressure vessels subjected to cyclical mechanical stress.

Insights from the in silico structural, functional and phylogenetic characterization of canine lysyl oxidase protein

Background

Lysyl oxidase is an extracellular regulatory enzyme with an imperative role in interlinking of collagen and elastin by oxidizing lysine residues. Lysyl oxidase has been implicated in incidence of mammary tumors in bitches. Therefore, it becomes significant to study the structural and functional features of this enzyme for a better understanding of its molecular mechanisms.

Results

The detailed computational investigation of the canine lysyl oxidase protein was analyzed in silico with respect to its physicochemical properties, secondary and tertiary structure predictions and functional analysis using standard bioinformatic tools. Lysyl oxidase is a flexible protein with an average molecular weight of around 46 kDa, unstable, hydrophilic, and extracellular (secretory) in nature. Twelve cysteine residues and a disulfide bridge were also found. Secondary structure analysis shows that most of the protein has predominant coiled configuration. A putative copper-binding region signature was predicted. The phylogenetic relationship of canine lysyl oxidase with a vast range of mammalian species indicates that the protein was very well conserved throughout the course of evolution. Top 10 interacting proteins were identified using STRING v10.0 analysis, elastin being the closest interacting protein. Functional analysis by InterproScan predicted protein’s biological role in oxidation-reduction process.

Conclusion

Understanding the structural and functional properties of the protein will facilitate a better understanding of its mechanism of enzyme action. Further, the predicted 3D model will serve as a cornerstone for further understanding towards the tumorigenesis potential of the protein.

LOXL1 confers antiapoptosis and promotes gliomagenesis through stabilizing BAG2

The lysyl oxidase (LOX) family is closely related to the progression of glioma. To ensure the clinical significance of LOX family in glioma, The Cancer Genome Atlas (TCGA) database was mined and the analysis indicated that higher LOXL1 expression was correlated with more malignant glioma progression. The functions of LOXL1 in promoting glioma cell survival and inhibiting apoptosis were studied by gain- and loss-of-function experiments in cells and animals. LOXL1 was found to exhibit antiapoptotic activity by interacting with multiple antiapoptosis modulators, especially BAG family molecular chaperone regulator 2 (BAG2). LOXL1-D515 interacted with BAG2-K186 through a hydrogen bond, and its lysyl oxidase activity prevented BAG2 degradation by competing with K186 ubiquitylation. Then, we discovered that LOXL1 expression was specifically upregulated through the VEGFR-Src-CEBPA axis. Clinically, the patients with higher LOXL1 levels in their blood had much more abundant BAG2 protein levels in glioma tissues. Conclusively, LOXL1 functions as an important mediator that increases the antiapoptotic capacity of tumor cells, and approaches targeting LOXL1 represent a potential strategy for treating glioma. In addition, blood LOXL1 levels can be used as a biomarker to monitor glioma progression.

Molecular Insights Into Lysyl Oxidases in Cartilage Regeneration and Rejuvenation

Articular cartilage remains among the most difficult tissues to regenerate due to its poor self-repair capacity. The lysyl oxidase family (LOX; also termed as protein-lysine 6-oxidase), mainly consists of lysyl oxidase (LO) and lysyl oxidase-like 1-4 (LOXL1-LOXL4), has been traditionally defined as cuproenzymes that are essential for stabilization of extracellular matrix, particularly cross-linking of collagen and elastin. LOX is essential in the musculoskeletal system, particularly cartilage. LOXs-mediated collagen cross-links are essential for the functional integrity of articular cartilage. Appropriate modulation of the expression or activity of certain LOX members selectively may become potential promising strategy for cartilage repair. In the current review, we summarized the advances of LOX in cartilage homeostasis and functioning, as well as copper-mediated activation of LOX through hypoxia-responsive signaling axis during recent decades. Also, the molecular signaling network governing LOX expression has been summarized, indicating that appropriate modulation of hypoxia-responsive-signaling-directed LOX expression through manipulation of bioavailability of copper and oxygen is promising for further clinical implications of cartilage regeneration, which has emerged as a potential therapeutic approach for cartilage rejuvenation in tissue engineering and regenerative medicine. Therefore, targeted regulation of copper-mediated hypoxia-responsive signalling axis for selective modulation of LOX expression may become potential effective therapeutics for enhanced cartilage regeneration and rejuvenation in future clinical implications.

Lysyl Oxidase Like 1: Biological roles and regulation

Lysyl Oxidase Like 1 (LOXL1) is a gene that encodes for the LOXL1 enzyme. This enzyme is required for elastin biogenesis and collagen cross-linking, polymerising tropoelastin monomers into elastin polymers. Its main role is in elastin homeostasis and matrix remodelling during injury, fibrosis and cancer development. Because of its vast range of biological functions, abnormalities in LOXL1 underlie many disease processes. Decreased LOXL1 expression is observed in disorders of elastin such as Cutis Laxa and increased expression is reported in fibrotic disease such as Idiopathic Pulmonary Fibrosis. LOXL1 is also downregulated in the lamina cribrosa in pseudoexfoliation glaucoma and genetic variants in the LOXL1 gene have been linked with an increased risk of developing pseudoexfoliation glaucoma and pseudoexfoliation syndrome. However the two major risk alleles are reversed in certain ethnic groups and are present in a large proportion of the normal population, implying complex genetic and environmental regulation is involved in disease pathogenesis. It also appears that the non-coding variants in intron 1 of LOXL1 may be involved in the regulation of LOXL1 expression. Gene alteration may occur via a number of epigenetic and post translational mechanisms such as DNA methylation, long non-coding RNAs and microRNAs. These may represent future therapeutic targets for disease. Environmental factors such as hypoxia, oxidative stress and ultraviolet radiation exposure alter LOXL1 expression, and it is likely a combination of these genetic and environmental factors that influence disease development and progression. In this review, we discuss LOXL1 properties, biological roles and regulation in detail with a focus on pseudoexfoliation syndrome and glaucoma.

The role of lysyl oxidase-like 1 (LOXL1) in exfoliation syndrome and glaucoma

Exfoliation syndrome (XFS) is an age-related systemic disease that affects the extracellular matrix. It increases the risk of glaucoma (exfoliation glaucoma, XFG) and susceptibility to diseases of elastin-rich connective tissues. LOXL1 (lysyl oxidase-like 1) is still recognized as the major genetic effect locus in XFS and XFG in all populations worldwide, although its genetic architecture is incompletely understood. LOXL1 is a key cross-linking enzyme in elastic fiber formation and remodeling, which is compatible with the pathogenetic concept of XFS as a specific type of elastosis. This review provides an overview on the current knowledge about the role of LOXL1 in the etiology and pathophysiology of XFS and XFG. It covers the known genetic associations at the LOXL1 locus, potential mechanisms of gene regulation, implications of LOXL1 in XFS-associated fibrosis and connective tissue homeostasis, its role in the development of glaucoma and associated systemic diseases, and the currently available LOXL1-based in vivo and in vitro models. Finally, it also identifies gaps in knowledge and suggests potential areas for future research.

Recent updates on the molecular network of elastic fiber formation

Elastic fibers confer elasticity and recoiling to tissues and organs and play an essential role in induction of biochemical responses in a cell against mechanical forces derived from the microenvironment. The core component of elastic fibers is elastin (ELN), which is secreted as the monomer tropoelastin from elastogenic cells, and undergoes self-aggregation, cross-linking and deposition on to microfibrils, and assemble into insoluble ELN polymers. For elastic fibers to form, a microfibril scaffold (primarily formed by fibrillin-1 (FBN1)) is required. Numerous elastic fiber-associated proteins are involved in each step of elastogenesis and they instruct and/or facilitate the elastogenesis processes. In this review, we designated five proteins as key molecules in elastic fiber formation, including ELN, FBN1, fibulin-4 (FBLN4), fibulin-5 (FBLN5), and latent TGFβ-binding protein-4 (LTBP4). ELN and FBN1 serve as building blocks for elastic fibers. FBLN5, FBLN4 and LTBP4 have been demonstrated to play crucial roles in elastogenesis through knockout studies in mice. Using these molecules as a platform and expanding the elastic fiber network through the generation of an interactome map, we provide a concise review of elastogenesis with a recent update as well as discuss various biological functions of elastic fiber-associated proteins beyond elastogenesis in vivo.

Lysyl oxidases: from enzyme activity to extracellular matrix cross-links

The lysyl oxidase family comprises five members in mammals, lysyl oxidase (LOX) and four lysyl oxidase like proteins (LOXL1-4). They are copper amine oxidases with a highly conserved catalytic domain, a lysine tyrosylquinone cofactor, and a conserved copper-binding site. They catalyze the first step of the covalent cross-linking of the extracellular matrix (ECM) proteins collagens and elastin, which contribute to ECM stiffness and mechanical properties. The role of LOX and LOXL2 in fibrosis, tumorigenesis, and metastasis, including changes in their expression level and their regulation of cell signaling pathways, have been extensively reviewed, and both enzymes have been identified as therapeutic targets. We review here the molecular features and three-dimensional structure/models of LOX and LOXLs, their role in ECM cross-linking, and the regulation of their cross-linking activity by ECM proteins, proteoglycans, and by inhibitors. We also make an overview of the major ECM cross-links, because they are the ultimate molecular readouts of LOX/LOXL activity in tissues. The recent 3D model of LOX, which recapitulates its known structural and biochemical features, will be useful to decipher the molecular mechanisms of LOX interaction with its various substrates, and to design substrate-specific inhibitors, which are potential antifibrotic and antitumor drugs.

De novo variants in an extracellular matrix protein coding gene, fibulin-5 (FBLN5) are associated with pseudoexfoliation

Fibulin-5 (FBLN5), an extracellular scaffold protein, plays a crucial role in the activation of Lysyl oxidase like-1 (LOXL1), a tropoelastin crosslinking enzyme, and subsequent deposition of elastin in the extracellular matrix. Following study identifies polymorphisms within FBLN5 gene as risk factors and its aberrant expression in the pathogenesis of an ocular disorder, pseudoexfoliation (PEX). Exons and exon-intron boundaries within FBLN5 gene were scanned through fluorescence-based capillary electrophoresis for polymorphisms as risk factors for PEX pathogenesis in recruited study subjects with Indian ethnicity. mRNA and protein expression of FBLN5 was checked in lens capsule of study subjects through qRT-PCR and western blotting, respectively. In vitro functional analysis of risk variants was done through luciferase reporter assays. Thirty study subjects from control and PEX affected groups were scanned for potential risk variants. Putative polymorphisms identified by scanning were further evaluated for genetic association in a larger sample size comprising of 338 control and 375 PEX affected subjects. Two noncoding polymorphisms, hg38 chr14:g.91947643G>A (rs7149187:G>A) and hg38 chr14:g.91870431T>C (rs929608:T>C) within FBLN5 gene are found to be significantly associated with PEX as risk factors with a p-value of 0.005 and 0.004, respectively. Molecular assays showed a decreased expression of FBLN5 at both mRNA and protein level in lens capsule of pseudoexfoliation syndrome (PEXS) affected subjects than control. This study unravels two novel risk variants within FBLN5 gene in the pathogenesis of PEX. Further, a decreased expression of FBLN5 in PEXS affected lens capsules implicates a pathogenic link between extracellular matrix maintenance and onset of PEX.

CLU Polymorphisms in Patients with Pseudoexfoliation Syndrome in Polish Population

Purpose

To evaluate CLU polymorphisms in patients with pseudoexfoliation syndrome.

Materials and Methods

We studied 81 patients (23 males and 58 females, the median age 76 years) and 91 control subjects (27 males and 64 females, the median age 75 years). Genotypes of the CLU polymorphisms (SNPs), rs3087554 and rs2279590, were determined using a commercially available validated genotyping assays. The χ ² test was performed to compare patient and control groups for possible associations between SNP genotype/allele frequency and disease state.

Results

There were no significant differences for both allele and genotype frequencies between PEX patients and controls for rs3087554 and rs2279590 polymorphisms. The haplotypes distribution shows statistically significant difference between groups (p=0.03). The haplotype (CT) more often was found in controls than in PEX patients, conferring an 18-fold decreased risk to the disease.

Conclusion

Our results indicate that CLU variants may contribute to the risk of PEX in the Polish population.

Extracellular Processing of Lysyl Oxidase-like 2 and Its Effect on Amine Oxidase Activity

Overexpression of lysyl oxidase-like 2 (LOXL2) is associated with several hepatic and vascular fibrotic diseases and tumor progression in some aggressive cancers. Secreted LOXL2 promotes extracellular matrix cross-linking by catalyzing the oxidative deamination of peptidyl lysine. A great deal remains to be learned about the post-translational modifications of LOXL2, including whether such modifications modulate enzymatic and disease-promoting activities; such knowledge would inform the development of potential therapies. We discovered that upon secretion in cell culture, LOXL2 undergoes proteolytic processing of the first two of four scavenger receptor cysteine-rich domains at the N-terminus. A similar pattern of processing was also evident in tissue extracts from an invasive ductal carcinoma patient. Processing occurred at ³¹⁴Arg-³¹⁵Phe-³¹⁶Arg-³¹⁷Lys↓-³¹⁸Ala-, implicating proprotein convertases. siRNA-mediated knockdown of proprotein convertases (furin, PACE4, and PC5/6), as well as incubation with their recombinant forms, showed that PACE4 is the major protease that acts on extracellular LOXL2. Unlike LOX, which requires cleavage of its propeptide for catalytic activation, cleavage of LOXL2 was not essential for tropoelastin oxidation or for cross-linking of collagen type IV in vitro. However, in the latter case, processing enhanced the extent of collagen cross-linking ∼2-fold at ≤10 nM LOXL2. These results demonstrate an important difference in the regulatory mechanisms for LOX and LOXL2 catalytic activity. Moreover, they pave the way for further studies of potential differential functions of LOXL2 isoforms in fibrosis and tumor progression.

Association of LOXL1 gene common sequence variants in Jordanian patients with exfoliation syndrome and exfoliative glaucoma

AIM

To investigate the association between single nucleotide polymorphisms (SNPs) in the LOXL1 gene with exfoliation syndrome/glaucoma (XFS/XFG) among Jordanians.

METHODS

Sixty-one patients with XFS/XFG and 59 healthy control individuals were recruited in the study. Patients were diagnosed with XFS/XFG using standard clinical examination techniques. The exonic rs1048661 SNP and the intronic rs2165241 SNP in LOXL1 gene were genotyped using sequencing technique. Allele and genotype frequencies were compared between cases and controls using Chi-square analysis.

RESULTS

The G allele of the rs1048661 SNP and the T allele of the rs2165241 SNP were common in the sample with frequencies of 86.4% and 81.4%, respectively. In addition, there were no significant differences in the genotypic and allelic distributions between patients and controls for rs1048661 SNP (P=0.770, OR=1.21, 95%CI: 0.56-2.60) and for rs2165241 SNP (P=0.605, OR=1.12, 95%CI: 0.59-2.09). In addition, no significant associations were found between haplotypes of the examined SNPs and XFS/XFG in the sample (P>0.05).

CONCLUSION

Variations in LOXL1 gene may not be associated with XFS/XFG in the Jordanian population. More studies are required to confirm the current findings.

Insights into the structure and dynamics of lysyl oxidase propeptide, a flexible protein with numerous partners

Lysyl oxidase (LOX) catalyzes the oxidative deamination of lysine and hydroxylysine residues in collagens and elastin, which is the first step of the cross-linking of these extracellular matrix proteins. It is secreted as a proenzyme activated by bone morphogenetic protein-1, which releases the LOX catalytic domain and its bioactive N-terminal propeptide. We characterized the recombinant human propeptide by circular dichroism, dynamic light scattering, and small-angle X-ray scattering (SAXS), and showed that it is elongated, monomeric, disordered and flexible (D_max: 11.7 nm, R_g: 3.7 nm). We generated 3D models of the propeptide by coarse-grained molecular dynamics simulations restrained by SAXS data, which were used for docking experiments. Furthermore, we have identified 17 new binding partners of the propeptide by label-free assays. They include four glycosaminoglycans (hyaluronan, chondroitin, dermatan and heparan sulfate), collagen I, cross-linking and proteolytic enzymes (lysyl oxidase-like 2, transglutaminase-2, matrix metalloproteinase-2), a proteoglycan (fibromodulin), one growth factor (Epidermal Growth Factor, EGF), and one membrane protein (tumor endothelial marker-8). This suggests new roles for the propeptide in EGF signaling pathway.

Lysyl oxidase-like protein 2 (LOXL2) modulates barrier function in cholangiocytes in cholestasis

BACKGROUND & AIMS

The lysyl oxidase-like protein 2 (LOXL2) promotes stabilization of the extracellular matrix, chemotaxis, cell growth and cell mobility. We aimed to (i) identify stimuli of LOXL2 in cholangiopathies, (ii) characterize the effects of LOXL2 on biliary epithelial cells' (BECs) barrier function, (iii) compare LOXL2 expression in primary sclerosing cholangitis (PSC), primary biliary cholangitis, and disease controls, and (iv) to determine LOXL2 expression and its cellular sources in four mouse models of cholangiopathies.

METHODS

Cultured murine BECs were challenged with well-known triggers of cellular senescence, hypoxia, phospholipid-deficient Abcb4^-/- mouse bile and chenodeoxycholic acid and investigated for LOXL2, SNAIL1 and E-cadherin expression and transepithelial electrical resistance with and without LOX-inhibition. In vivo, LOXL2 expression was studied in PSC livers, and controls and mouse models. We compared LOXL2 serum levels in patients with PSC, secondary SC, primary biliary cholangitis, and controls.

RESULTS

Cellular senescence, hypoxia, Abcb4^-/- bile and chenodeoxycholic acid induced LOXL2 and SNAIL1 expression, repressed E-cadherin expression, and significantly reduced transepithelial electrical resistance in BECs. Notably, all of the pathological changes could be recovered via pharmacological LOX-inhibition. Mouse models showed induced LOXL2 expression in the portal region and in association with ductular reaction. LOXL2 serum levels were significantly elevated in patients with cholangiopathies. In PSC, LOXL2 expression was located to characteristic periductal onion skin-type fibrosis, ductular reaction, Kupffer cells, and fibrotic septa. Importantly, in PSC, LOXL2 overexpression was paralleled by E-cadherin loss in BECs from medium-sized bile ducts.

CONCLUSIONS

Reactive BECs produce LOXL2, resulting in increased tight junction permeability, which can be ameliorated by pharmacological LOX-inhibition in vitro. Reactive BECs, portal myofibroblasts, and Kupffer cells are the main sources of LOXL2 in cholangiopathies.

LAY SUMMARY

In this study, we investigate the role of lysyl oxidase-like protein 2 (LOXL2), an enzyme pivotal in the development of organ fibrosis, in the pathogenesis of cholangiopathies (diseases of bile ducts), such as primary sclerosing cholangitis. We found LOXL2 to be expressed in association with bile duct epithelial injury and uncovered mechanisms for its upregulation and the subsequent effects in vitro and in vivo. Our findings support testing of anti-LOXL2 treatment strategies for patients with primary sclerosing cholangitis.

Liver fibrosis: Direct antifibrotic agents and targeted therapies

Liver fibrosis and in particular cirrhosis are the major causes of morbidity and mortality of patients with chronic liver disease. Their prevention or reversal have become major endpoints in clinical trials with novel liver specific drugs. Remarkable progress has been made with therapies that efficiently address the cause of the underlying liver disease, as in chronic hepatitis B and C. Highly effective antiviral therapy can prevent progression or even induce reversal in the majority of patients, but such treatment remains elusive for the majority of liver patients with advanced alcoholic or nonalcoholic steatohepatitis, genetic or autoimmune liver diseases. Moreover, drugs that would speed up fibrosis reversal are needed for patients with cirrhosis, since even with effective causal therapy reversal is slow or the disease may further progress. Therefore, highly efficient and specific antifibrotic agents are needed that can address advanced fibrosis, i.e., the detrimental downstream result of all chronic liver diseases. This review discusses targeted antifibrotic therapies that address molecules and mechanisms that are central to fibrogenesis or fibrolysis, including strategies that allow targeting of activated hepatic stellate cells and myofibroblasts and other fibrogenic effector cells. Focus is on collagen synthesis, integrins and cells and mechanisms specific including specific downregulation of TGFbeta signaling, major extracellular matrix (ECM) components, ECM-crosslinking, and ECM-receptors such as integrins and discoidin domain receptors, ECM-crosslinking and methods for targeted delivery of small interfering RNA, antisense oligonucleotides and small molecules to increase potency and reduce side effects. With an increased understanding of the biology of the ECM and liver fibrosis and an improved preclinical validation, the translation of these approaches to the clinic is currently ongoing. Application to patients with liver fibrosis and a personalized treatment is tightly linked to the development of noninvasive biomarkers of fibrosis, fibrogenesis and fibrolysis.

Pentagalloyl glucose increases elastin deposition, decreases reactive oxygen species and matrix metalloproteinase activity in pulmonary fibroblasts under inflammatory conditions

Emphysema is characterized by degradation of lung alveoli that leads to poor airflow in lungs. Irreversible elastic fiber degradation by matrix metalloproteinases (MMPs) and reactive oxygen species (ROS) activity leads to loss of elasticity and drives the progression of this disease. We investigated if a polyphenol, pentagalloyl glucose (PGG) can increase elastin production in pulmonary fibroblasts. We also studied the effect of PGG treatment in reducing MMP activity and ROS levels in cells. We exposed rat pulmonary fibroblasts to two different types of inflammatory environments i.e., tumor necrosis factor-α (TNF-α) and cigarette smoke extract (CSE) to mimic the disease. Parameters like lysyl oxidase (LOX) and elastin gene expression, MMP-9 activity in the medium, lysyl oxidase (LOX) activity and ROS levels were studied to assess the effect of PGG on pulmonary fibroblasts. CSE inhibited lysyl oxidase (LOX) enzyme activity that resulted in a decreased elastin formation. Similarly, TNF-α treated cells showed less elastin in the cell layers. Both these agents caused increase in MMP activity and ROS levels in cells. However, when supplemented with PGG treatment along with these two inflammatory agents, we saw a significant increase in elastin deposition, reduction in both MMP activity and ROS levels. Thus PGG, which has anti-inflammatory, anti-oxidant properties coupled with its ability to aid in elastic fiber formation, can be a multifunctional drug to potentially arrest the progression of emphysema.

Dynamic changes in copper homeostasis and post-transcriptional regulation of Atp7a during myogenic differentiation

Copper (Cu) is an essential metal required for activity of a number of redox active enzymes that participate in critical cellular pathways such as metabolism and cell signaling. Because it is also a toxic metal, Cu must be tightly controlled by a series of transporters and chaperone proteins that regulate Cu homeostasis. The critical nature of Cu is highlighted by the fact that mutations in Cu homeostasis genes cause pathologic conditions such as Menkes and Wilson diseases. While Cu homeostasis in highly affected tissues like the liver and brain is well understood, no study has probed the role of Cu in development of skeletal muscle, another tissue that often shows pathology in these conditions. Here, we found an increase in whole cell Cu content during differentiation of cultured immortalized or primary myoblasts derived from mouse satellite cells. We demonstrate that Cu is required for both proliferation and differentiation of primary myoblasts. We also show that a key Cu homeostasis gene, Atp7a, undergoes dynamic changes in expression during myogenic differentiation. Alternative polyadenylation and stability of Atp7a mRNA fluctuates with differentiation stage of the myoblasts, indicating post-transcriptional regulation of Atp7a that depends on the differentiation state. This is the first report of a requirement for Cu during myogenic differentiation and provides the basis for understanding the network of Cu transport associated with myogenesis.

The copper dependent-lysyl oxidases contribute to the pathogenesis of pulmonary emphysema in chronic obstructive pulmonary disease patients

Abnormalities in the elastic fiber biology are seen in pulmonary emphysema (PE). The copper-dependent lysyl oxidases regulate the production and accumulation of elastic fibers in the connective tissue. This study focused on the relationship between lysyl oxidase (LOX), LOX-like protein 1 (LOXL1), and LOXL2 and PE pathogenesis. Lung samples with or without PE from patients with chronic obstructive lung disease (n=35) were used. Protein levels of elastin, LOX, LOXL1, LOXL2, hypoxia inducible factor 1-alpha (HIF-1α), copper metabolism domain containing-1 (COMMD1), and phosphatase and tensin homolog (PTEN) were assayed using microscopic and biochemical methods The emphysematous areas were characterized by enlargement of the alveoli, destruction of the alveolar structure, accumulation of macrophages in the alveolar lumens, and showed increased HIF-1α immunoreactivity. Additionally, the emphysematous areas had significantly lower elastin, LOX, LOXL1, LOXL2, HIF-1α, COMMD1, and PTEN protein levels than the non-emphysematous areas. We suppose that the reductions in the HIF-1α levels led to decreases in the protein levels of active LOX, LOXL1, and LOXL2. These decreases might cause abnormalities in the elastic fiber biology. HIF-1α activation induced by decreased COMMD1 and protease activation induced by decreased PTEN might contribute to the development of PE. Finally, methods aimed at increasing the protein levels of LOXs, COMMD1 and PTEN might be effective for treating PE.

Functional importance of lysyl oxidase family propeptide regions

The lysyl oxidase family of proteins is primarily known for its critical role in catalyzing extracellular oxidative deamination of hydroxylysine and lysine residues in collagens, and lysine residues in elastin required for connective tissue structure and function. Lysyl oxidases have additional important biological functions in health and disease. While the enzyme domains are highly conserved, the propeptide regions are less uniform, and have biological activity, some of which are independent of their respective enzymes. This review summarizes what has been published regarding the functions of the propeptide regions of this family of proteins in the context of extracellular matrix biosynthesis, fibrosis and cancer biology. Although much has been learned, there is a need for greater attention to structure/function relationships and mechanisms to more fully understand these multifunctional proteins.

Collagen cross-linking: insights on the evolution of metazoan extracellular matrix

Collagens constitute a large family of extracellular matrix (ECM) proteins that play a fundamental role in supporting the structure of various tissues in multicellular animals. The mechanical strength of fibrillar collagens is highly dependent on the formation of covalent cross-links between individual fibrils, a process initiated by the enzymatic action of members of the lysyl oxidase (LOX) family. Fibrillar collagens are present in a wide variety of animals, therefore often being associated with metazoan evolution, where the emergence of an ancestral collagen chain has been proposed to lead to the formation of different clades. While LOX-generated collagen cross-linking metabolites have been detected in different metazoan families, there is limited information about when and how collagen acquired this particular modification. By analyzing telopeptide and helical sequences, we identified highly conserved, potential cross-linking sites throughout the metazoan tree of life. Based on this analysis, we propose that they have importantly contributed to the formation and further expansion of fibrillar collagens.

Major review: Exfoliation syndrome; advances in disease genetics, molecular biology, and epidemiology

Exfoliation syndrome (XFS) is a common age-related disorder that leads to deposition of extracellular fibrillar material throughout the body. The most recognized disease manifestation is exfoliation glaucoma (XFG), which is a common cause of blindness worldwide. Recent developments in XFS genetics, cell biology and epidemiology have greatly improved our understanding of the etiology of this complex inherited disease. This review summarizes current knowledge of XFS pathogenesis, identifies gaps in knowledge, and discusses areas for future research.

Methylation of LOXL1 Promoter by DNMT3A in Aged Human Skin Fibroblasts

Lysyl oxidase-like 1 (LOXL1) is an amino-oxidase involved in maturation of elastic fibers. Its downregulation has been associated with elastic fibers repair loss in aging aorta, lung, ligament, and skin. Several evidences of LOXL1 epigenetic silencing by promoter methylation were reported in cancer and cutis laxa syndrome. We hypothesized that this mechanism could be implicated in skin aging process, as far as elastic fibers are also concerned. Anti-DNMT3A chromatin immunoprecipitation was conducted with nuclear extracts from skin fibroblasts isolated from young and elderly individuals, and showed a higher level of DNMT3A protein binding to the LOXL1 promoter in older cells concomitantly to the decrease of LOXL1 mRNA expression and the increase of LOXL1 promoter methylation. Using luciferase reporter assay driven by LOXL1 promoter in HEK293 cells, we demonstrated that LOXL1 transcriptional activity was dramatically reduced when a recombinant DNMT3A was concomitantly overexpressed. LOXL1 promoter transcriptional activity was restored in the presence of a broad-spectrum inhibitor of DNMT activity, 5-aza-2'-deoxycytidine. Finally, to assess whether the interplay between DNMT3A and LOXL1 promoter could be targeted to increase LOXL1 mRNA expression level, an Origanum majorana extract was selected among 43 plant extracts as a new inhibitor of human DNMT3A activity to restore LOXL1 secretion without cytotoxicity in aged skin fibroblasts.

Loss of function mutation in LOX causes thoracic aortic aneurysm and dissection in humans

Thoracic aortic aneurysms and dissections (TAAD) represent a substantial cause of morbidity and mortality worldwide. Many individuals presenting with an inherited form of TAAD do not have causal mutations in the set of genes known to underlie disease. Using whole-genome sequencing in two first cousins with TAAD, we identified a missense mutation in the lysyl oxidase (LOX) gene (c.893T > G encoding p.Met298Arg) that cosegregated with disease in the family. Using clustered regularly interspaced short palindromic repeats (CRISPR)/clustered regularly interspaced short palindromic repeats-associated protein-9 nuclease (Cas9) genome engineering tools, we introduced the human mutation into the homologous position in the mouse genome, creating mice that were heterozygous and homozygous for the human allele. Mutant mice that were heterozygous for the human allele displayed disorganized ultrastructural properties of the aortic wall characterized by fragmented elastic lamellae, whereas mice homozygous for the human allele died shortly after parturition from ascending aortic aneurysm and spontaneous hemorrhage. These data suggest that a missense mutation in LOX is associated with aortic disease in humans, likely through insufficient cross-linking of elastin and collagen in the aortic wall. Mutation carriers may be predisposed to vascular diseases because of weakened vessel walls under stress conditions. LOX sequencing for clinical TAAD may identify additional mutation carriers in the future. Additional studies using our mouse model of LOX-associated TAAD have the potential to clarify the mechanism of disease and identify novel therapeutics specific to this genetic cause.

Biological effect of LOXL1 coding variants associated with pseudoexfoliation syndrome

Pseudoexfoliation (PEX) syndrome is a systemic disease involving the extracellular matrix. It increases the risk of glaucoma, an irreversible cause of blindness, and susceptibility to heart disease, stroke and hearing loss. Single nucleotide polymorphisms (SNPs) in the LOXL1 (Lysyl oxidase-like 1) gene are the major known genetic risk factor for PEX syndrome. Two coding SNPs, rs1048861 (G > T; Arg141Leu) and rs3825942 (G > A; Gly153Asp), in the LOXL1 gene are strongly associated with the disease risk in multiple populations worldwide. In the present study, we investigated functional effects of these SNPs on the LOXL1 protein. We show through molecular modelling that positions 141 and 153 are likely surface residues and hence possible recognition sites for protein-protein interactions; the Arg141Leu and Gly153Asp substitutions cause charge changes that would lead to local differences in protein electrostatic potential and in turn the potential to modify protein-protein interactions. In RFL-6 rat fetal lung fibroblast cells ectopically expressing the LOXL1 protein variants related to PEX (Arg141_Gly153, Arg141_Asp153 or Leu141_Gly153), immunoprecipitation of the secreted variants showed differences in their processing by endogenous proteins, possibly Bone morphogenetic protein-1 (BMP-1) that cleaves and leads to enzymatic activation of LOXL1. Immunofluorescence labelling of the ectopically expressed protein variants in RFL-6 cells showed no significant difference in their extracellular accumulation tendency. In conclusion, this is the first report of a biological effect of the coding SNPs in the LOXL1 gene associated with PEX syndrome, on the LOXL1 protein. The findings indicate that the disease associated coding variants themselves may be involved in the manifestation of PEX syndrome.

Lysyl Oxidase Isoforms and Potential Therapeutic Opportunities for Fibrosis and Cancer

INTRODUCTION

The lysyl oxidase family of enzymes is classically known as being required for connective tissue maturation by oxidizing lysine residues in elastin and lysine and hydroxylysine residues in collagen precursors. The resulting aldehydes then participate in cross-link formation, which is required for normal connective tissue integrity. These enzymes have biological functions that extend beyond this fundamental biosynthetic role, with contributions to angiogenesis, cell proliferation, and cell differentiation. Dysregulation of lysyl oxidases occurs in multiple pathologies including fibrosis, primary and metastatic cancers, and complications of diabetes in a variety of tissues.

AREAS COVERED

This review summarizes the major findings of novel roles for lysyl oxidases in pathologies, and highlights some of the potential therapeutic approaches that are in development and which stem from these new findings.

EXPERT OPINION

Fundamental questions remain regarding the mechanisms of novel biological functions of this family of proteins, and regarding functions that are independent of their catalytic enzyme activity. However, progress is underway in the development of isoform-specific pharmacologic inhibitors, potential therapeutic antibodies and gaining an increased understanding of both tumor suppressor and metastasis promotion activities. Ultimately, this is likely to lead to novel therapeutic agents.

Lysyl oxidase-like 1 polymorphisms in a southwestern Greek cataract population with pseudoexfoliation syndrome

Purpose

The aim of this study was to determine the possible association of rs1048661 and rs3825942 single nucleotide polymorphisms (SNPs) in the lysyl oxidase-like 1 (LOXL1) gene of cataract patients from southwestern Greece with pseudoexfoliation (PEX) syndrome.

Patients and methods

Ninety-three patients with PEX syndrome and 74 without PEX syndrome were recruited with the principal diagnosis being cataract. LOXL1 SNPs, rs1048661 and rs3825942, were genotyped by using polymerase chain reaction.

Results

The G allele of rs1048661 was found in 96.7% in the PEX group as compared to 80.5% of non-PEX alleles (P=19×10⁻⁴; Odds ratio [OR] =5.37; 95% confidence interval [CI] =1.68–17.12). Similarly, the G allele of rs3825942 was found in 72.1% of the PEX group as compared to 41.8% of non-PEX alleles (P=4×10⁻⁵; OR =3.78; 95% CI =1.98–7.23). The T and A allele frequencies of rs1048661 and rs3825942, respectively, were underrepresented in the PEX group patients as compared to non-PEX group.

Conclusion

Our data confirm previously reported association between LOXL1 polymorphisms and PEX syndrome in a southwestern Greek population. A significant association was found for the G allele of rs1048661 and rs3825942 demonstrating that the GG haplotype is a high-risk factor for the development of PEX syndrome.

LOX Mutations Predispose to Thoracic Aortic Aneurysms and Dissections

RATIONALE

Mutations in several genes have been identified that are responsible for 25% of families with familial thoracic aortic aneurysms and dissections. However, the causative gene remains unknown in 75% of families.

OBJECTIVES

To identify the causative mutation in families with autosomal dominant inheritance of thoracic aortic aneurysms and dissections.

METHODS AND RESULTS

Exome sequencing was used to identify the mutation responsible for a large family with thoracic aortic aneurysms and dissections. A heterozygous rare variant, c.839G>T (p.Ser280Arg), was identified in LOX, encoding a lysyl oxidase, that segregated with disease in the family. Sanger and exome sequencing was used to investigate mutations in LOX in an additional 410 probands from unrelated families. Additional LOX rare variants that segregated with disease in families were identified, including c.125G>A (p.Trp42*), c.604G>T (p.Gly202*), c.743C>T (p.Thr248Ile), c.800A>C (p.Gln267Pro), and c.1044T>A (p.Ser348Arg). The altered amino acids cause haploinsufficiency for LOX or are located at a highly conserved LOX catalytic domain, which is relatively invariant in the population. Expression of the LOX variants p.Ser280Arg and p.Ser348Arg resulted in significantly lower lysyl oxidase activity when compared with the wild-type protein. Individuals with LOX variants had fusiform enlargement of the root and ascending thoracic aorta, leading to ascending aortic dissections.

CONCLUSIONS

These data, along with previous studies showing that the deficiency of LOX in mice or inhibition of lysyl oxidases in turkeys and rats causes aortic dissections, support the conclusion that rare genetic variants in LOX predispose to thoracic aortic disease.

4.1N suppresses hypoxia-induced epithelial-mesenchymal transition in epithelial ovarian cancer cells

Protein 4.1N (4.1N) is a member of the protein 4.1 family and is essential for the regulation of cell adhesion, motility and signaling. Previous studies have suggested that 4.1N may serve a tumor suppressor role. However, the molecular mechanisms remain unclear. In the current study, the role of 4.1N in the downregulation of hypoxia‑induced factor 1α (HIF‑1α) under hypoxic conditions and therefore the suppression of hypoxia induced epithelial‑mesenchymal transition (EMT) was investigated. The data were obtained from overexpressed and knockdown 4.1N epithelial ovarian cancer (EOC) cell lines. It was identified that 4.1N was capable of regulating the sub‑cellular localization and expression levels of HIF‑1α, by which 4.1N served a dominant role in the suppression of hypoxia‑induced EMT and associated genes. Collectively, the data of the current study identified 4.1N as an inhibitor of hypoxia‑induced tumor progression in EOC cells and highlighted its potential role in EOC therapy.

Characterization of Microfibrillar-associated Protein 4 (MFAP4) as a Tropoelastin- and Fibrillin-binding Protein Involved in Elastic Fiber Formation

MFAP4 (microfibrillar-associated protein 4) is an extracellular glycoprotein found in elastic fibers without a clearly defined role in elastic fiber assembly. In the present study, we characterized molecular interactions between MFAP4 and elastic fiber components. We established that MFAP4 primarily assembles into trimeric and hexameric structures of homodimers. Binding analysis revealed that MFAP4 specifically binds tropoelastin and fibrillin-1 and -2, as well as the elastin cross-linking amino acid desmosine, and that it co-localizes with fibrillin-1-positive fibers in vivo. Site-directed mutagenesis disclosed residues Phe(241) and Ser(203) in MFAP4 as being crucial for type I collagen, elastin, and tropoelastin binding. Furthermore, we found that MFAP4 actively promotes tropoelastin self-assembly. In conclusion, our data identify MFAP4 as a new ligand of microfibrils and tropoelastin involved in proper elastic fiber organization.