Lysyl Oxidases: Functions and Disorders

Association between gene polymorphisms and glaucoma susceptibility among Africans: a systematic review and meta-analysis

PURPOSE

This study sought to analyze the effect of allele mutations and gene functions specific to glaucoma susceptibility among Africans.

METHODS

Potentially relevant studies were retrieved from major bibliographic databases (PubMed, Scopus, and Web of Science). Data were extracted and study-specific estimates were meta-analyzed using various models to obtain pooled results.

RESULTS

A total of 11 studies were included in the study. The studies included a total of 3,191 cases with glaucoma and 3,013 controls across all variants. There is no association between the E396E variants of the myocilin (MYOC) gene and an increased likelihood of susceptibility to POAG (OR: 0.91 [95% CI 0.42 to 1.97]). The R141L variant of the Lysyl Oxidase Like 1 (LOXL1) gene is associated with an approximately 3-fold increased likelihood of susceptibility to exfoliative syndrome/exfoliative glaucoma (XFS/XFG) (OR: 2.68 [95% CI 0.04 to 198.94]). There is no association between the G153D variant of the LOXL1 gene and an increased likelihood of susceptibility to XFS/XFG (OR: 0.42 [95% CI 0.02 to 7.65]). The rs59892895*C variant of the Amyloid Beta Precursor Protein Binding Family B Member 2 (APBB2) is associated with a 34% increased likelihood of susceptibility to POAG (OR: 1.34 [95% CI 1.13 to 1.58]).

CONCLUSION

Although progress has been made in understanding the genetic basis of the pathogenesis of glaucoma, several gene mutations related to glaucoma pathogenesis in Africans are yet to be discovered, especially those associated with the pathogenesis of POAG, the most prevalent glaucoma subtype in Africa.

TFC-1326 Compound Reduces Clinical Signs of Skin Aging. Evidence From In Vitro Human Adipose and Skin Models and Pilot Clinical Trial

BACKGROUND

Anti-freeze Glycoproteins (AFGPs) were described to preserve biological materials and protect them from different stresses.

AIMS

The effects of a synthetic anti-freeze glycoprotein-based compound, TFC-1326, on human skin quality and its biological actions were studied.

METHODS

The effects of various concentrations of TFC-1326 on the biology of human preadipocytes, differentiated in the proinflammatory microenvironment, and on human fibroblasts grown in coculture with human mature adipocytes or monocultured in stress conditions were investigated in, in vitro studies. Additionally, the efficacy of a 1% TFC-1326 topical cream was evaluated in a clinical investigation on the skin biology and appearance of 20 women aged between 40 and 65 years throughout 84 days of application.

RESULTS

The in vitro studies revealed that TFC-1326 mitigated the deleterious effects of a proinflammatory cytokine cocktail produced by human macrophages, by restoring preadipocyte adipogenic capacity and by reducing their fibroinflammatory state. TFC-1326 also stimulated the proliferative capacity of dermal fibroblasts co-cultured with mature adipocytes as well as their production of hyaluronic acid and procollagen type I, while decreasing IL6 secretion and increasing fibroblast viability. Furthermore, daily 1% TFC-1326 topical cream application, measurably improved skin radiance and laxity, as well as skin density. Finally, significant reductions of the volume and depth of the crow's feet wrinkles were also observed.

CONCLUSIONS

The compound TFC-1326 significantly improved the physiological appearance and cellular functions of aging skin.

The reactive stroma response regulates the immune landscape in prostate cancer

Prostate cancer remains the most commonly diagnosed and the second leading cause of cancer-related deaths in men in the United States. The neoplastic transformation of prostate epithelia, concomitant with modulations in the stromal compartment, known as reactive stromal response, is critical for the growth, development, and progression of prostate cancer. Reactive stroma typifies an emergent response to disrupted tissue homeostasis commonly observed in wound repair and pathological conditions such as cancer. Despite the significance of reactive stroma in prostate cancer pathobiology, our understanding of the ontogeny, phenotypic and functional heterogeneity, and reactive stromal regulation of the immune microenvironment in prostate cancer remains limited. Traditionally characterized to have an immunologically "cold" tumor microenvironment, prostate cancer presents significant challenges for advancing immunotherapy compared to other solid tumors. This review explores the detrimental role of reactive stroma in prostate cancer, particularly its immunomodulatory function. Understanding the molecular characteristics and dynamic transcriptional program of the reactive stromal populations in tandem with tumor progression could offer insights into enhancing immunotherapy efficacy against prostate cancer.

Glycosylation Modulates the Structure and Functions of Collagen: A Review

Collagens are fundamental constituents of the extracellular matrix and are the most abundant proteins in mammals. Collagens belong to the family of fibrous or fiber-forming proteins that self-assemble into fibrils that define their mechanical properties and biological functions. Up to now, 28 members of the collagen superfamily have been recognized. Collagen biosynthesis occurs in the endoplasmic reticulum, where specific post-translational modification-glycosylation-is also carried out. The glycosylation of collagens is very specific and adds β-d-galactopyranose and β-d-Glcp-(1→2)-d-Galp disaccharide through β-O-linkage to hydroxylysine. Several glycosyltransferases, namely COLGALT1, COLGALT2, LH3, and PGGHG glucosidase, were associated the with glycosylation of collagens, and recently, the crystal structure of LH3 has been solved. Although not fully understood, it is clear that the glycosylation of collagens influences collagen secretion and the alignment of collagen fibrils. A growing body of evidence also associates the glycosylation of collagen with its functions and various human diseases. Recent progress in understanding collagen glycosylation allows for the exploitation of its therapeutic potential and the discovery of new agents. This review will discuss the relevant contributions to understanding the glycosylation of collagens. Then, glycosyltransferases involved in collagen glycosylation, their structure, and catalytic mechanism will be surveyed. Furthermore, the involvement of glycosylation in collagen functions and collagen glycosylation-related diseases will be discussed.

Optimization of an Allysine-Targeted PET Probe for Quantifying Fibrogenesis in a Mouse Model of Pulmonary Fibrosis

PURPOSE

Idiopathic pulmonary fibrosis (IPF) is a destructive lung disease with a poor prognosis, an unpredictable clinical course, and inadequate therapies. There are currently no measures of disease activity to guide clinicians making treatment decisions. The aim of this study was to develop a PET probe to identify lung fibrogenesis using a pre-clinical model of pulmonary fibrosis, with potential for translation into clinical use to predict disease progression and inform treatment decisions.

METHODS

Eight novel allysine-targeting chelators, PIF-1, PIF-2, …, PIF-8, with different aldehyde-reactive moieties were designed, synthesized, and radiolabeled with gallium-68 or copper-64. PET probe performance was assessed in C57BL/6J male mice 2 weeks after intratracheal bleomycin challenge and in naïve mice by dynamic PET/MR imaging and with biodistribution at 90 min post injection. Lung hydroxyproline and allysine were quantified ex vivo and histological staining for fibrosis and aldehyde was performed.

RESULTS

In vivo screening of probes identified 68GaPIF-3 and 68GaPIF-7 as probes with high uptake in injured lung, high uptake in injured lung versus normal lung, and high uptake in injured lung versus adjacent liver and heart tissue. A crossover, intra-animal PET/MR imaging study of 68GaPIF-3 and 68GaPIF-7 confirmed 68GaPIF-7 as the superior probe. Specificity for fibrogenesis was confirmed in a crossover, intra-animal PET/MR imaging study with 68GaPIF-7 and a non-binding control compound, 68GaPIF-Ctrl. Substituting copper-64 for gallium-68 did not affect lung uptake or specificity indicating that either isotope could be used.

CONCLUSION

A series of allysine-reactive PET probes with variations in the aldehyde-reactive moiety were evaluated in a pre-clinical model of lung fibrosis. The hydrazine-bearing probe, 68GaPIF-7, exhibited the highest uptake in fibrogenic lung, low uptake in surrounding liver or heart tissue, and low lung uptake in healthy mice and should be considered for further clinical translation.

Breast stiffness, a risk factor for cancer and the role of radiology for diagnosis

Over the last five decades, breast density has been associated with increased risk of developing breast cancer. Mammographically dense breasts are considered those belonging to the heterogeneously dense breasts, and extremely dense breasts subgroups according to the American College of Radiology's Breast Imaging Reporting and Data System (BI-RADS). There is a statistically significant correlation between the increased mammographic density and the presence of more glandular tissue alone. However, the strength of this correlation is weak. Although the mechanisms driving breast density-related tumor initiation and progression are still unknown, there is evidence suggesting that certain molecular pathways participating in epithelial-stromal interactions may play a pivotal role in the deposition of fibrillar collagen, increased matrix stiffness, and cell migration that favor breast density and carcinogenesis. This article describes these molecular mechanisms as potential "landscapers" for breast density-related cancer. We also introduce the term "Breast Compactness" to reflect collagen density of breast tissue on chest CT scan and the use of breast stiffness measurements as imaging biomarkers for breast cancer screening and risk stratification.

CD11b Deficiency Favors Cartilage Calcification via Increased Matrix Vesicles, Apoptosis, and Lysyl Oxidase Activity

Pathological cartilage calcification is a hallmark feature of osteoarthritis, a common degenerative joint disease, characterized by cartilage damage, progressively causing pain and loss of movement. The integrin subunit CD11b was shown to play a protective role against cartilage calcification in a mouse model of surgery-induced OA. Here, we investigated the possible mechanism by which CD11b deficiency could favor cartilage calcification by using naïve mice. First, we found by transmission electron microscopy (TEM) that CD11b KO cartilage from young mice presented early calcification spots compared with WT. CD11b KO cartilage from old mice showed progression of calcification areas. Mechanistically, we found more calcification-competent matrix vesicles and more apoptosis in both cartilage and chondrocytes isolated from CD11b-deficient mice. Additionally, the extracellular matrix from cartilage lacking the integrin was dysregulated with increased collagen fibrils with smaller diameters. Moreover, we revealed by TEM that CD11b KO cartilage had increased expression of lysyl oxidase (LOX), the enzyme that catalyzes matrix crosslinks. We confirmed this in murine primary CD11b KO chondrocytes, where Lox gene expression and crosslinking activity were increased. Overall, our results suggest that CD11b integrin regulates cartilage calcification through reduced MV release, apoptosis, LOX activity, and matrix crosslinking. As such, CD11b activation might be a key pathway for maintaining cartilage integrity.

The kidney matrisome in health, aging, and disease

Dysregulated extracellular matrix is the hallmark of fibrosis, and it has a profound impact on kidney function in disease. Furthermore, perturbation of matrix homeostasis is a feature of aging and is associated with declining kidney function. Understanding these dynamic processes, in the hope of developing therapies to combat matrix dysregulation, requires the integration of data acquired by both well-established and novel technologies. Owing to its complexity, the extracellular proteome, or matrisome, still holds many secrets and has great potential for the identification of clinical biomarkers and drug targets. The molecular resolution of matrix composition during aging and disease has been illuminated by cutting-edge mass spectrometry-based proteomics in recent years, but there remain key questions about the mechanisms that drive altered matrix composition. Basement membrane components are particularly important in the context of kidney function; and data from proteomic studies suggest that switches between basement membrane and interstitial matrix proteins are likely to contribute to organ dysfunction during aging and disease. Understanding the impact of such changes on physical properties of the matrix, and the subsequent cellular response to altered stiffness and viscoelasticity, is of critical importance. Likewise, the comparison of proteomic data sets from multiple organs is required to identify common matrix biomarkers and shared pathways for therapeutic intervention. Coupled with single-cell transcriptomics, there is the potential to identify the cellular origin of matrix changes, which could enable cell-targeted therapy. This review provides a contemporary perspective of the complex kidney matrisome and draws comparison to altered matrix in heart and liver disease.

Vascular Ehlers-Danlos Syndrome: Pathological Variants, Recent Discoveries, and Theoretical Approaches

Vascular Ehlers-Danlos syndrome (vEDS) is a rare autosomal dominant genetic disorder. It is the most fatal among all types of EDS. In addition to typical EDS characteristics, vEDS patients are at risk of blood vessel rupture due to possession of pathogenic variants of the COL3A1 gene, which encodes type III collagen. Type III collagen is a major component of humans' vascular walls. The management of this disease is possible; however, there is no cure as of present. Recently, discoveries with potential impact on the management of vEDS have been elucidated. Mice with vEDS traits treated with a beta-blocker celiprolol showed significant improvements in their thoracic aorta biomechanical strength. Moreover, it has been demonstrated that the specifically designed small interference RNAs (siRNA) can effectively silence the pathogenic variant allele. To enhance the normal allele expression, an intracellularly expressed lysyl oxidase is shown to regulate the transcription rate of the COL3A1 promoter. Similarly, an embryonic homeobox transcription factor Nanog upregulates the wild-type COL3A1 expression through activation of the transforming growth factor-beta pathway, which increases type III collagen synthesis. Despite numerous advancements, more studies are to be performed to incorporate these discoveries into clinical settings, and eventually, more personalized treatments can be created.

Loxl2 and Loxl3 Paralogues Play Redundant Roles during Mouse Development

Lysyl oxidase-like 2 (LOXL2) and 3 (LOXL3) are members of the lysyl oxidase family of enzymes involved in the maturation of the extracellular matrix. Both enzymes share a highly conserved catalytic domain, but it is unclear whether they perform redundant functions in vivo. In this study, we show that mice lacking Loxl3 exhibit perinatal lethality and abnormal skeletal development. Additionally, analysis of the genotype of embryos carrying double knockout of Loxl2 and Loxl3 genes suggests that both enzymes have overlapping functions during mouse development. Furthermore, we also show that ubiquitous expression of Loxl2 suppresses the lethality associated with Loxl3 knockout mice.

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.

Overexpression of miR-328-5p influences cell growth and migration to promote NSCLC progression by targeting LOXL4

Background

Lung cancer is the leading cause of cancer-associated mortality worldwide, and most lung cancers are classified as non-small cell lung cancer (NSCLC). MiR-328 influence the progression of multiple tumors, but the role of miR-328-5p in NSCLC has not been elucidated. The aim of this study was to illuminate the oncogenic role and potential molecular mechanisms of the miR-328-5p and lysyl oxidase like 4 (LOXL4) in NSCLC.

Methods

Expression of miR-328-5p was detected by real-time quantitative polymerase chain reaction (qRT-PCR) in tumor and non-tumor adjacent tissues. After Lentivirus-miR-328-5p was employed to intervene this miRNA in NSCLC cell lines, RT-qPCR was used to detect the expression levels of miR-328-5p. Cell Counting Kit-8 (CCK-8), cell colony formation, flow cytometry, wound healing, Transwell assays were used to determine the malignant phenotypes of NSCLC cells. Nude mice models of subcutaneous tumors were established to observe the effect of miR-328-5p on tumorigenesis. Targeting the 3'UTR of LOXL4 by miR-328-5p was verified by integrated analysis including transcriptome sequencing, dual-luciferase and western-blot assays.

Results

High miR-328-5p level was observed in NSCLC cells from The Cancer Genome Atlas (TCGA) database and tumor tissues collected from NSCLC patients. Overexpressed miR-328-5p promoted NSCLC cell proliferation, survival, and migration, and promoted tumor growth in vivo. Knockdown of miR-328-5p suppressed tumorigenic activities. Transcriptome sequencing analysis revealed that LOXL4 was downregulated by miR-328-5p, which was confirmed by dual-luciferase reporter and western-blot assays.

Conclusions

miR-328-5p showed targeted regulation of LOXL4 to promote cell proliferation and migration in NSCLC.

Zebrafish as a Model to Study Vascular Elastic Fibers and Associated Pathologies

Many extensible tissues such as skin, lungs, and blood vessels require elasticity to function properly. The recoil of elastic energy stored during a stretching phase is provided by elastic fibers, which are mostly composed of elastin and fibrillin-rich microfibrils. In arteries, the lack of elastic fibers leads to a weakening of the vessel wall with an increased risk to develop cardiovascular defects such as stenosis, aneurysms, and dissections. The development of new therapeutic molecules involves preliminary tests in animal models that recapitulate the disease and whose response to drugs should be as close as possible to that of humans. Due to its superior in vivo imaging possibilities and the broad tool kit for forward and reverse genetics, the zebrafish has become an important model organism to study human pathologies. Moreover, it is particularly adapted to large scale studies, making it an attractive model in particular for the first steps of investigations. In this review, we discuss the relevance of the zebrafish model for the study of elastic fiber-related vascular pathologies. We evidence zebrafish as a compelling alternative to conventional mouse models.

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

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

The Extracellular Matrix in Skin Inflammation and Infection

The extracellular matrix (ECM) is an integral component of all organs and plays a pivotal role in tissue homeostasis and repair. While the ECM was long thought to mostly have passive functions by providing physical stability to tissues, detailed characterization of its physical structure and biochemical properties have uncovered an unprecedented broad spectrum of functions. It is now clear that the ECM not only comprises the essential building block of tissues but also actively supports and maintains the dynamic interplay between tissue compartments as well as embedded resident and recruited inflammatory cells in response to pathologic stimuli. On the other hand, certain pathogens such as bacteria and viruses have evolved strategies that exploit ECM structures for infection of cells and tissues, and mutations in ECM proteins can give rise to a variety of genetic conditions. Here, we review the composition, structure and function of the ECM in cutaneous homeostasis, inflammatory skin diseases such as psoriasis and atopic dermatitis as well as infections as a paradigm for understanding its wider role in human health.

ATP7A-Regulated Enzyme Metalation and Trafficking in the Menkes Disease Puzzle

Copper is vital for numerous cellular functions affecting all tissues and organ systems in the body. The copper pump, ATP7A is critical for whole-body, cellular, and subcellular copper homeostasis, and dysfunction due to genetic defects results in Menkes disease. ATP7A dysfunction leads to copper deficiency in nervous tissue, liver, and blood but accumulation in other tissues. Site-specific cellular deficiencies of copper lead to loss of function of copper-dependent enzymes in all tissues, and the range of Menkes disease pathologies observed can now be explained in full by lack of specific copper enzymes. New pathways involving copper activated lysosomal and steroid sulfatases link patient symptoms usually related to other inborn errors of metabolism to Menkes disease. Additionally, new roles for lysyl oxidase in activation of molecules necessary for the innate immune system, and novel adapter molecules that play roles in ERGIC trafficking of brain receptors and other proteins, are emerging. We here summarize the current knowledge of the roles of copper enzyme function in Menkes disease, with a focus on ATP7A-mediated enzyme metalation in the secretory pathway. By establishing mechanistic relationships between copper-dependent cellular processes and Menkes disease symptoms in patients will not only increase understanding of copper biology but will also allow for the identification of an expanding range of copper-dependent enzymes and pathways. This will raise awareness of rare patient symptoms, and thus aid in early diagnosis of Menkes disease patients.

Polymorphisms in Lysyl Oxidase Family Genes Are Associated With Intracranial Aneurysm Susceptibility in a Chinese Population

PURPOSE

Intracranial aneurysms (IA) comprise a multifactorial disease with unclear physiological mechanisms. The lysyl oxidase (LOX) family genes (LOX, LOX-like 1-4) plays important roles in extracellular matrix (ECM) reconstruction and has been investigated in terms of susceptibility to IA in a few populations. We aimed to determine whether polymorphisms in LOX family genes are associated with susceptibility to IA in a Chinese population.

METHODS

This case-control study included 384 patients with IA and 384 healthy individuals without IA (controls). We genotyped 27 single nucleotide polymorphisms (SNPs) of LOX family genes using the Sequenom MassARRAY^® platform. These SNPs were adjusted for known risk factors and then, odds ratios (OR) and 95% confidence intervals (CI) were evaluated using binary logistic regression analysis.

RESULTS

The result showed that LOX rs10519694 was associated with the risk of IA in recessive (OR, 3.88; 95% CI, 1.12-13.47) and additive (OR, 1.56; 95%CI, 1.05-2.34) models. Stratified analyses illustrated that LOX rs10519694 was associated with the risk of single IA in the recessive (OR, 3.95; 95%CI, 1.04-15.11) and additive (OR, 1.64; 95%CI, 1.04-2.56) models. The LOXL2 rs1010156 polymorphism was associated with multiple IA in the dominant model (OR, 1.92; 95%CI, 1.02-3.62). No associations were observed between SNPs of LOXL1, LOXL3, and LOXL4 and risk of IA.

CONCLUSION

LOX and LOXL2 polymorphisms were associated with risk of single IA and multiple IA in a Chinese population, suggesting potential roles of these genes in IA. The effects of these genes on IA require further investigation.

Lysyl oxidase suppresses the inflammatory response in anterior cruciate ligament fibroblasts and promotes tissue regeneration by targeting myotrophin via the nuclear factor-kappa B pathway

Anterior cruciate ligament (ACL) regeneration is severely affected by the injury-induced overexpression of matrix metalloproteinases (MMPs) and downregulation of lysyl oxidase (LOX). Previous studies have focused on how the expression of MMPs and downregulation of LOX are physiologically balanced at injured sites for regenerating the ACL tissue, but the role of LOX in regulating cellular functions has not been investigated yet. Herein, we conducted an in vitro cellular experiment and unexpectedly found that exogenous LOX inhibited the expression of MMPs and inflammatory factors and recovered the cell growth; thus, LOX strongly inhibited the tumor necrosis factor-alpha (TNF-α)-induced inflammatory responses. In an in vivo animal model, LOX supplementation suppressed the expression of TNF-α in injured ACLs and promoted the recovery of the damaged tissues. RNA-sequencing-identified differentially expressed genes (DEGs) were highly enriched in the nuclear factor-kappa B (NF-κB), chemokine, cytokine-cytokine receptor interaction, Toll-like receptor, and TNF signaling pathways. Immunofluorescence tracing was employed to localise the exogenous LOX in the cell nucleus; the exogenous LOX indirectly suggests that it has other biological roles apart from the cross-linking of the extracellular matrix. Protein-protein interaction network analysis revealed the anti-inflammatory effect of LOX was alleviated by silencing the myotrophin (MTPN) expression, suggesting that LOX might interact with MTPN and regulate inflammation. Finally, this study suggests that LOX can inhibit the inflammatory response of ACL fibroblasts (ACLfs) and promote the recovery of the damaged ACL tissue through the MTPN-mediated NF-κB signaling pathway.

Elevated intracellular copper contributes a unique role to kidney fibrosis by lysyl oxidase mediated matrix crosslinking

Copper ions play various roles in mammalian cells, presumably due to their involvement in different enzymatic reactions. Some studies indicated that serum copper correlates with fibrosis in organs, such as liver and lung. However, the mechanism is unknown. Here, we explored the role of copper in kidney fibrosis development and possible underlying mechanisms. We found that copper transporter 1 (CTR1) expression was increased in the kidney tissues in two fibrosis models and in patients with kidney fibrosis. Similar results were also found in renal tubular epithelial cells and fibroblast cells treated with transforming growth factor beta (TGF-β). Mechanistically, the upregulation of CTR1 required Smads-dependent TGF-β signaling pathway and Smad3 directly binded to the promoter of CTR1 in renal fibroblast cells using chromatin immunoprecipitation. Elevated CTR1 induced increase of copper intracellular influx. The elevated intracellular copper ions activated lysyl oxidase (LOX) to enhance the crosslinking of collagen and elastin, which then promoted kidney fibrosis. Reducing intracellular copper accumulation by knocking down CTR1 ameliorated kidney fibrosis in unilateral ureteral obstruction induced renal fibrosis model and renal fibroblast cells stimulated by TGF-β. Treatment with copper chelator tetrathiomolybdate (TM) also alleviated renal fibrosis in vivo and in vitro. In conclusion, intracellular copper accumulation plays a unique role to kidney fibrosis by activating LOX mediated collagen and elastin crosslinking. Inhibition of intracellular copper overload may be a potential portal to alleviate kidney fibrosis.

Extracellular Matrix Composition and Remodeling: Current Perspectives on Secondary Palate Formation, Cleft Lip/Palate, and Palatal Reconstruction

Craniofacial development comprises a complex process in humans in which failures or disturbances frequently lead to congenital anomalies. Cleft lip with/without palate (CL/P) is a common congenital anomaly that occurs due to variations in craniofacial development genes, and may occur as part of a syndrome, or more commonly in isolated forms (non-syndromic). The etiology of CL/P is multifactorial with genes, environmental factors, and their potential interactions contributing to the condition. Rehabilitation of CL/P patients requires a multidisciplinary team to perform the multiple surgical, dental, and psychological interventions required throughout the patient's life. Despite progress, lip/palatal reconstruction is still a major treatment challenge. Genetic mutations and polymorphisms in several genes, including extracellular matrix (ECM) genes, soluble factors, and enzymes responsible for ECM remodeling (e.g., metalloproteinases), have been suggested to play a role in the etiology of CL/P; hence, these may be considered likely targets for the development of new preventive and/or therapeutic strategies. In this context, investigations are being conducted on new therapeutic approaches based on tissue bioengineering, associating stem cells with biomaterials, signaling molecules, and innovative technologies. In this review, we discuss the role of genes involved in ECM composition and remodeling during secondary palate formation and pathogenesis and genetic etiology of CL/P. We also discuss potential therapeutic approaches using bioactive molecules and principles of tissue bioengineering for state-of-the-art CL/P repair and palatal reconstruction.

A novel splice variant of LOXL2 promotes progression of human papillomavirus-negative head and neck squamous cell carcinoma

BACKGROUND

Head and neck squamous cell carcinoma (HNSCC) is one of the most frequently diagnosed cancers worldwide. LOXL2 demonstrates alternative splicing events in patients with human papillomavirus (HPV)-negative HNSCC. The current study explored the role of a dominant LOXL2 variant in HPV-negative HNSCC.

METHODS

Expression of the LOXL2 variant was analyzed using The Cancer Genome Atlas cohorts and validated using quantitative reverse transcriptase-polymerase chain reaction in a separate primary tumor set. The authors defined the effect of LOXL2 splice variants in assays for cell proliferation using a cell viability assay and colony formation assay. Cell migration and invasion were examined using a cell scratch assay and transwell cell migration and invasion assay in LOXL2 splice variant gain and loss of expression cells. Western blot analysis and gene set enrichment analysis were used to explore the potential mechanism of the LOXL2 splice variant in HPV-negative HNSCC.

RESULTS

Expression of a novel LOXL2 variant was found to be upregulated in The Cancer Genome Atlas HPV-negative HNSCC, and confirmed in the separate primary tumor validation set. Analyses of loss and gain of function demonstrated that this LOXL2 variant enhanced proliferation, migration, and invasion in HPV-negative HNSCC cells and activated the FAK/AKT pathway. A total of 837 upregulated and 820 downregulated genes and 526 upregulated and 124 downregulated pathways associated with LOXL2 variant expression were identified using gene set enrichment analysis, which helped in developing a better understanding of the networks activated by this LOXL2 variant in patients with HPV-negative HNSCC.

CONCLUSIONS

The novel LOXL2 variant can promote the progression of HPV-negative HNSCC, in part through FAK/AKT pathway activation, which may provide a new potential therapeutic target among patients with HPV-negative HNSCC.

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.

Differential cleavage of lysyl oxidase by the metalloproteinases BMP1 and ADAMTS2/14 regulates collagen binding through a tyrosine sulfate domain

Collagens are the main structural component of the extracellular matrix and provide biomechanical properties to connective tissues. A critical step in collagen fibril formation is the proteolytic removal of N- and C-terminal propeptides from procollagens by metalloproteinases of the ADAMTS (a disintegrin and metalloproteinase with thrombospondin motifs) and BMP1 (bone morphogenetic protein 1)/Tolloid-like families, respectively. BMP1 also cleaves and activates the lysyl oxidase (LOX) precursor, the enzyme catalyzing the initial step in the formation of covalent collagen cross-links, an essential process for fibril stabilization. In this study, using murine skin fibroblasts and HEK293 cells, along with immunoprecipitation, LOX enzymatic activity, solid-phase binding assays, and proteomics analyses, we report that the LOX precursor is proteolytically processed by the procollagen N-proteinases ADAMTS2 and ADAMTS14 between Asp-218 and Tyr-219, 50 amino acids downstream of the BMP1 cleavage site. We noted that the LOX sequence between the BMP1- and ADAMTS-processing sites contains several conserved tyrosine residues, of which some are post-translationally modified by tyrosine O-sulfation and contribute to binding to collagen. Taken together, these findings unravel an additional level of regulation in the formation of collagen fibrils. They point to a mechanism that controls the binding of LOX to collagen and is based on differential BMP1- and ADAMTS2/14-mediated cleavage of a tyrosine-sulfated domain.

Extracellular Matrix Interactions with Gram-Positive Pathogens

The main strategies used by pathogenic bacteria to infect eukaryotic tissue include their adherence to cells and the extracellular matrix (ECM), the subsequent colonization and invasion as well as the evasion of immune defences. A variety of structurally and functionally characterized adhesins and binding proteins of gram-positive bacteria facilitate these processes by specifically recognizing and interacting with various components of the host ECM, including different collagens, fibronectin and other macromolecules. The ECM affects the cellular physiology of our body and is critical for adhesion, migration, proliferation, and differentiation of many host cell types, but also provides the support for infiltrating pathogens, particularly under conditions of injury and trauma. Moreover, microbial binding to a variety of adhesive components in host tissue fluids leads to structural and/or functional alterations of host proteins and to the activation of cellular mechanisms that influence tissue and cell invasion of pathogens. Since the diverse interactions of gram-positive bacteria with the ECM represent important pathogenicity mechanisms, their characterization not only allows a better understanding of microbial invasion but also provides clues for the design of novel therapeutic strategies to manage infectious diseases.

Lysyl oxidase (LOX) limits VSMC proliferation and neointimal thickening through its extracellular enzymatic activity

Lysyl oxidase (LOX) plays a critical role in extracellular matrix maturation and limits VSMC proliferation and vascular remodeling. We have investigated whether this anti-proliferative effect relies on the extracellular catalytically active LOX or on its biologically active propeptide (LOX-PP). High expression levels of both LOX and LOX-PP were detected in the vascular wall from transgenic mice over-expressing the full-length human LOX cDNA under the control of SM22α promoter (TgLOX), which targets the transgene to VSMC without affecting the expression of mouse LOX isoenzymes. TgLOX VSMC also secrete high amounts of both mature LOX and LOX-PP. Wild-type (WT) mouse VSMC exposed to VSMC supernatants from transgenic animals showed reduced proliferative rates (low [³H]-thymidine uptake and expression of PCNA) than those incubated with conditioned media from WT cells, effect that was abrogated by β-aminopropionitrile (BAPN), an inhibitor of LOX activity. Lentiviral over-expression of LOX, but not LOX-PP, decreased human VSMC proliferation, effect that was also prevented by BAPN. LOX transgenesis neither impacted local nor systemic inflammatory response induced by carotid artery ligation. Interestingly, in this model, BAPN normalized the reduced neointimal thickening observed in TgLOX mice. Therefore, extracellular enzymatically active LOX is required to limit both VSMC proliferation and vascular remodeling.