Sex-Linked Skeletal Phenotype of Lysyl Oxidase Like-1 Mutant Mice

LOXL2 in Cancer: A Two-Decade Perspective

Lysyl Oxidase Like 2 (LOXL2) belongs to the lysyl oxidase (LOX) family, which comprises five lysine tyrosylquinone (LTQ)-dependent copper amine oxidases in humans. In 2003, LOXL2 was first identified as a promoter of tumour progression and, over the course of two decades, numerous studies have firmly established its involvement in multiple cancers. Extensive research with large cohorts of human tumour samples has demonstrated that dysregulated LOXL2 expression is strongly associated with poor prognosis in patients. Moreover, investigations have revealed the association of LOXL2 with various targets affecting diverse aspects of tumour progression. Additionally, the discovery of a complex network of signalling factors acting at the transcriptional, post-transcriptional, and post-translational levels has provided insights into the mechanisms underlying the aberrant expression of LOXL2 in tumours. Furthermore, the development of genetically modified mouse models with silenced or overexpressed LOXL2 has enabled in-depth exploration of its in vivo role in various cancer models. Given the significant role of LOXL2 in numerous cancers, extensive efforts are underway to identify specific inhibitors that could potentially improve patient prognosis. In this review, we aim to provide a comprehensive overview of two decades of research on the role of LOXL2 in cancer.

LOXL4, but not LOXL2, is the critical determinant of pathological collagen cross-linking and fibrosis in the lung

Idiopathic pulmonary fibrosis is a progressive fibrotic disease characterized by excessive deposition of (myo)fibroblast produced collagen fibrils in alveolar areas of the lung. Lysyl oxidases (LOXs) have been proposed to be the central enzymes that catalyze the cross-linking of collagen fibers. Here, we report that, while its expression is increased in fibrotic lungs, genetic ablation of LOXL2 only leads to a modest reduction of pathological collagen cross-linking but not fibrosis in the lung. On the other hand, loss of another LOX family member, LOXL4, markedly disrupts pathological collagen cross-linking and fibrosis in the lung. Furthermore, knockout of both Loxl2 and Loxl4 does not offer any additive antifibrotic effects when compared to Loxl4 deletion only, as LOXL4 deficiency decreases the expression of other LOX family members including Loxl2. On the basis of these results, we propose that LOXL4 is the main LOX activity underlying pathological collagen cross-linking and lung fibrosis.

Lysyl oxidase family gene polymorphisms and risk of aneurysmal subarachnoid hemorrhage: a case-control study

Background

Aneurysmal subarachnoid hemorrhage (aSAH) is a devastating disease caused by intracranial aneurysm (IA) rupture. Lysyl oxidase (LOX) family genes (LOX-like [LOXL] 1-4) have roles in collagen cross-linking in the extracellular matrix (ECM) and may be associated with IA rupture. We aimed to explore the association between LOX polymorphisms and the risk of aSAH.

Methods

This case-control study included 2 cohorts: 133 single ruptured and 115 unruptured IA patients, and 65 multiple ruptured and 71 unruptured IA patients. Genotyping of 27 single nucleotide polymorphisms (SNPs) in LOX was performed. Logistic regression analysis was performed to calculate the odds ratios (ORs) and 95% confidence intervals (CIs) of the SNPs of LOX and the risk of aSAH.

Results

LOX rs1800449 and LOXL4 rs3793692 were positively associated with the risk of single IA rupture in the recessive model (OR =5.66, 2.06; 95% CI =1.22–26.24, 1.11–3.82, respectively) and LOX rs10519694 demonstrated a protective effect on single IA rupture (dominant model: OR =0.42, 95% CI =0.21–0.83; recessive model: OR =0.16, 95% CI =0.04–0.65; additive model: OR =0.46, 95% CI =0.28–0.78). LOXL1 rs2165241, LOXL2 rs1063582, and LOXL3 rs17010021 showed risk effects on multiple IAs rupture. LOXL3 rs17010022 showed a protective effect on multiple IAs ruptures (dominant model: OR =0.41, 95% CI =0.21–0.82; additive model: OR =0.51, 95% CI =0.30–0.85).

Conclusions

LOX and LOXL4 may be susceptibility genes for single IA rupture, whereas LOXL1-3 may have a role in susceptibility to multiple IAs ruptures in the Chinese population, suggesting that LOX family genes may be associated with aSAH.

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.

β-Catenin mediates glucose-dependent insulinotropic polypeptide increases in lysyl oxidase expression in osteoblasts

Osteoblast lysyl oxidase (LOX) is a strongly up-regulated mRNA and protein by the glucose-dependent insulinotropic polypeptide (GIP). LOX is critically required for collagen maturation, and was shown to be dramatically down-regulated in a mouse model of type 1 diabetes, consistent with known low collagen cross-linking and poor bone quality in diabetic bone disease in humans and in mouse models. GIP is a gastric hormone released by the gut upon consumption of nutrients, which then stimulates insulin release from β-cells in the pancreas. GIP is directly anabolic to osteoblasts and to bone, while gut-derived dopamine attenuates effects of GIP on osteoblast anabolic pathways, including LOX expression. GIP-stimulation of LOX expression was shown to be dependent on increased cAMP levels and protein kinase A activity, consistent with the fact that GIP receptors are G protein coupled receptors. Downstream signaling events resulting in increased LOX expression remain, however, unexplored. Here we provide evidence for β-catenin mediation of signaling from GIP to increase LOX expression. Moreover, we have identified a TCF/LEF element in the Lox promoter that is required for GIP-upregulation of LOX. These findings will be of importance in designing potential therapeutic approaches to address deficient LOX production in diabetic bone disease by pointing to the importance of exploring strategies to stimulate β-catenin signaling in osteoblasts under diabetic conditions as potential therapeutic strategies.

Intraductal xenografts show lobular carcinoma cells rely on their own extracellular matrix and LOXL1

Invasive lobular carcinoma (ILC) is the most frequent special histological subtype of breast cancer, typically characterized by loss of E-cadherin. It has clinical features distinct from other estrogen receptor-positive (ER+ ) breast cancers but the molecular mechanisms underlying its characteristic biology are poorly understood because we lack experimental models to study them. Here, we recapitulate the human disease, including its metastatic pattern, by grafting ILC-derived breast cancer cell lines, SUM-44 PE and MDA-MB-134-VI cells, into the mouse milk ducts. Using patient-derived intraductal xenografts from lobular and non-lobular ER+ HER2- tumors to compare global gene expression, we identify extracellular matrix modulation as a lobular carcinoma cell-intrinsic trait. Analysis of TCGA patient datasets shows matrisome signature is enriched in lobular carcinomas with overexpression of elastin, collagens, and the collagen modifying enzyme LOXL1. Treatment with the pan LOX inhibitor BAPN and silencing of LOXL1 expression decrease tumor growth, invasion, and metastasis by disrupting ECM structure resulting in decreased ER signaling. We conclude that LOXL1 inhibition is a promising therapeutic strategy for ILC.

Differential Lysyl oxidase like 1 expression in pseudoexfoliation glaucoma is orchestrated via DNA methylation

Pseudoexfoliation syndrome (PXF) is the most common cause of secondary open angle glaucoma worldwide. Single nucleotide polymorphisms (SNPs) in the gene Lysyl oxidase like 1 (LOXL1) are strongly associated with the development of pseudoexfoliation glaucoma (PXFG). However, these SNPs are also present in 50-80% of the general population, suggestive of other factors being involved in the pathogenesis of PXFG. In this study, we aimed to investigate the influence of epigenetic regulation, specifically DNA methylation, on LOXL1 expression in PXFG using human tenons fibroblasts (HTFs), aqueous humour and serum samples from donors with and without PXFG. LOXL1 expression in HTFs was measured by qPCR and Western Blotting and LOXL1 concentration in aqueous humour was determined by ELISA. Global DNA methylation levels were quantified using an ELISA for 5-methylcytosine. MeDIP assays assessed the methylation status of the LOXL1 promoter region. Expression of methylation-associated enzymes (DNMT1, DNMT3a and MeCP2) were determined by qPCR and inhibited by 0.3 μM 5-azacytidine (5-aza). Results showed that LOXL1 expression was significantly decreased in PXFG HTFs compared with Control HTFs at gene (Fold change 0.37 ± 0.05, P < 0.01) level and showed a decrease, when measured at the protein level (Fold change 0.65 ± 0.42, P = 0.22), however this was not found to be significant. LOXL1 concentration was increased in the aqueous of PXFG patients compared with Controls (2.76 ± 0.78 vs. 1.79 ± 0.33 ng/ml, P < 0.01). Increased global methylation (56.07% ± 4.87% vs. 32.39% ± 4.29%, P < 0.01) was observed in PXFG HTFs compared with Control HTFs, as was expression of methylation-associated enzymes (DNMT1 1.58 ± 0.30, P < 0.05, DNMT3a 1.89 ± 0.24, P < 0.05, MeCP2 1.63 ± 0.30, P < 0.01). Methylation-associated enzymes were also increased when measured at protein level (DNMT1 5.70 ± 2.64, P = 0.04, DNMT3a 1.79 ± 1.55, P = 0.42, MeCP2 1.64 ± 1.33, P = 0.45). LOXL1 promoter methylation was increased in patients with PXFG compared to Control patients in both blood (3.98 ± 2.24, 2.10 ± 1.29, P < 0.05) and HTF cells (37.31 ± 22.0, 8.66 ± 10.40, P < 0.01). Treatment of PXFG HTFs with in 5-azacytidine increased LOXL1 expression when compared with untreated PXFG HTFs (Fold change 2.26 ± 0.67, P < 0.05). These data demonstrate that LOXL1 expression is altered in PXFG via DNA methylation and that reversal of these epigenetic changes may represent future potential therapeutic targets in the management of PXFG.

Sexual Dimorphism in Osteoclasts

Osteoclasts are the principal mediators of bone resorption. They form through the fusion of mononuclear precursor cells under the principal influence of the cytokines macrophage colony stimulating factor (M-CSF, aka CSF-1) and receptor activator of NF-κB ligand (RANKL, aka TNFSF11). Sexual dimorphism in the development of the skeleton and in the incidence of skeletal diseases is well described. In general, females, at any given age, have a lower bone mass than males. The reasons for the differences in the bone mass of the skeleton between women and men at various ages, and the incidence of certain metabolic bone diseases, are multitude, and include the actions of sex steroids, genetics, age, environment and behavior. All of these influence the rate that osteoclasts form, resorb and die, and frequently produce different effects in females and males. Hence, a variety of factors are responsible for the sexual dimorphism of the skeleton and the activity of osteoclasts in bone. This review will provide an overview of what is currently known about these factors and their effects on osteoclasts.

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.

Precocious chondrocyte differentiation disrupts skeletal growth in Kabuki syndrome mice

Kabuki syndrome 1 (KS1) is a Mendelian disorder of the epigenetic machinery caused by mutations in the gene encoding KMT2D, which methylates lysine 4 on histone H3 (H3K4). KS1 is characterized by intellectual disability, postnatal growth retardation, and distinct craniofacial dysmorphisms. A mouse model (Kmt2d+/βGeo) exhibits features of the human disorder and has provided insight into other phenotypes; however, the mechanistic basis of skeletal abnormalities and growth retardation remains elusive. Using high-resolution micro-CT, we show that Kmt2d+/βGeo mice have shortened long bones and ventral bowing of skulls. In vivo expansion of growth plates within skulls and long bones suggests disrupted endochondral ossification as a common disease mechanism. Stable chondrocyte cell lines harboring inactivating mutations in Kmt2d exhibit precocious differentiation, further supporting this mechanism. A known inducer of chondrogenesis, SOX9, and its targets show markedly increased expression in Kmt2d-/- chondrocytes. By transcriptome profiling, we identify Shox2 as a putative KMT2D target. We propose that decreased KMT2D-mediated H3K4me3 at Shox2 releases Sox9 inhibition and thereby leads to enhanced chondrogenesis, providing a potentially novel and plausible explanation for precocious chondrocyte differentiation. Our findings provide insight into the pathogenesis of growth retardation in KS1 and suggest therapeutic approaches for this and related disorders.

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.

Lysyl oxidase-like 2 (LOXL2)-mediated cross-linking of tropoelastin

Lysyl oxidases (LOXs) play a central role in extracellular matrix remodeling during development and tumor growth and fibrosis through cross-linking of collagens and elastin. We have limited knowledge of the structure and substrate specificity of these secreted enzymes. LOXs share a conserved C-terminal catalytic domain but differ in their N-terminal region, which is composed of 4 repeats of scavenger receptor cysteine-rich (SRCR) domains in LOX-like (LOXL) 2. We investigated by X-ray scattering and electron microscopy the low-resolution structure of the full-length enzyme and the structure of a shorter form lacking the catalytic domain. Our data demonstrate that LOXL2 has a rod-like structure with a stalk composed of the SRCR domains and the catalytic domain at its tip. We detected direct interaction between LOXL2 and tropoelastin (TE) and also LOXL2-mediated deamination of TE. Using proteomics, we identified several allysines together with cross-linked TE peptides. The elastin-like material generated was resistant to trypsin proteolysis and displayed mechanical properties similar to mature elastin. Finally, we detected the codistribution of LOXL2 and elastin in the vascular wall. Altogether, these data suggest that LOXL2 could participate in elastogenesis in vivo and could be used as a means of cross-linking TE in vitro for biomimetic and cell-compatible tissue engineering purposes.-Schmelzer, C. E. H., Heinz, A., Troilo, H., Lockhart-Cairns, M.-P., Jowitt, T. A., Marchand, M. F., Bidault, L., Bignon, M., Hedtke, T., Barret, A., McConnell, J. C., Sherratt, M. J., Germain, S., Hulmes, D. J. S., Baldock, C., Muller, L. Lysyl oxidase-like 2 (LOXL2)-mediated cross-linking of tropoelastin.

Effects of parathyroid hormone (1-34) on the regulation of the lysyl oxidase family in ovariectomized mice

Osteoporosis (OP) is a highly prevalent chronic disease. The anabolic agent parathyroid hormone (PTH) is often prescribed for the treatment of OP to strengthen bone quality and decrease the risk of fracture, although the specific mechanisms are still unclear. Lysyl oxidase (LOX) can stabilize the organic matrix through catalyzing the cross-linking of collagen and elastin. In this study, we established osteoporotic models via ovariectomizing C57BL/6J mice and treating them with PTH. We further aimed to determine the expression changes of the LOX family, impacted by PTH, in ovariectomized mice. We observed that bone mass was reduced and bone microstructure was deteriorative in ovariectomized mice. And PTH attenuated the microstructural damage and accelerated bone remodeling, as confirmed via μCT and HE staining. Serum levels of copper and zinc indirectly proved the results. The expression levels of five members of the LOX family all declined in ovariectomized mice compared to in sham-operated control mice (p < 0.05), and the daily injection of PTH successfully reversed the low expression of LOXs in OP. The current study examined expression changes of LOXs in osteoporotic mice and PTH-treated osteoporotic mice for the first time, and provided an important piece of evidence that the aberrant expression of LOXs had intimate associations with the occurrence and development of OP. And LOXs may act as the downstream effectors of PTH, contributing to unbalanced bone metabolism and damaged bone microstructure. Consequently, LOXs may act as promising therapeutic targets for OP.

LOX family is a potential target in ovariectomized osteoporosis (OP).

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.

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.

Enzymatic and non-enzymatic functions of the lysyl oxidase family in bone

Advances in the understanding of the biological roles of the lysyl oxidase family of enzyme proteins in bone structure and function are reviewed. This family of proteins is well-known as catalyzing the final reaction required for cross-linking of collagens and elastin. Novel emerging roles for these proteins in the phenotypic development of progenitor cells and in angiogenesis are highlighted and which point to enzymatic and non-enzymatic roles for this family in bone development and homeostasis and in disease. The explosion of interest in the lysyl oxidase family in the cancer field highlights the need to have a better understanding of the functions of this protein family in normal and abnormal connective tissue homeostasis at fundamental molecular and cellular levels including in mineralized tissues.