Lysyl oxidase-like-2 (LOXL2) is a major isoform in chondrocytes and is critically required for differentiation

Function and regulation of nuclear factor 1 X-type on chondrocyte proliferation and differentiation

Nuclear factor 1 X-type (Nfix) is a transcription factor related to mental and physical development. However, very few studies have reported the effects of Nfix on cartilage. This study aims to reveal the influence of Nfix on the proliferation and differentiation of chondrocytes, and to explore its potential action mechanism. We isolated primary chondrocytes from the costal cartilage of newborn C57BL/6 mice and with Nfix overexpression or silencing treatment. We used Alcian blue staining and found that Nfix overexpression significantly promoted ECM synthesis in chondrocytes while silencing inhibited ECM synthesis. Using RNA-seq technology to study the expression pattern of Nfix in primary chondrocytes. We found that Nfix overexpression significantly up-regulated genes that are related to chondrocyte proliferation and extracellular matrix (ECM) synthesis and significantly down-regulated genes related to chondrocyte differentiation and ECM degradation. Nfix silencing, however, significantly up-regulated genes associated with cartilage catabolism and significantly down-regulated genes associated with cartilage growth promotion. Furthermore, Nfix exerted a positive regulatory effect on Sox9, and we propose that Nfix may promote chondrocyte proliferation and inhibit differentiation by stimulating Sox9 and its downstream genes. Our findings suggest that Nfix may be a potential target for the regulation of chondrocyte proliferation and differentiation.

Mimicking Loading-Induced Cartilage Self-Heating in Vitro Promotes Matrix Formation in Chondrocyte-Laden Constructs with Different Mechanical Properties

Articular cartilage presents a mechanically sensitive tissue. Chondrocytes, the sole cell type residing in the tissue, perceive and react to physical cues as signals that significantly modulate their behavior. Hyaline cartilage is a connective tissue with high dissipative capabilities, able to increase its temperature during daily activities, thus providing a dynamic thermal milieu for the residing chondrocytes. This condition, self-heating, which is still chiefly ignored among the scientific community, adds a new thermal dimension in cartilage mechanobiology. Motivated by the lack of studies exploring this dynamic temperature increase as a potential stimulus in cartilage-engineered constructs, we aimed to elucidate whether loading-induced evolved temperature serves as an independent or complementary regulatory cue for chondrocyte function. In particular, we evaluated the chondrocytes' response to thermal and/or mechanical stimulation in two types of scaffolds exhibiting dissipation levels close to healthy and degenerated articular cartilage. It was found, in both scaffold groups, that the combination of dynamic thermal and mechanical stimuli induced superior effects in the expression of major chondrogenic genes, such as SOX9 and LOXL2, compared to either signal alone. Similar effects were also observed in proteoglycan accumulation over time, along with increased mRNA transcription and synthesis of TRPV4, and for the first time demonstrated in chondrocytes, TREK1 ion channels. Conversely, the chondrogenic response of cells to isolated thermal or mechanical cues was generally scaffold-type dependent. Nonetheless, the significance of thermal stimulus as a chondro-inductive signal was better supported in both studied groups. Our data indicates that the temperature evolution is necessary for chondrocytes to more effectively perceive and translate applied mechanical loading.

Regulators of collagen crosslinking in developing and adult tendons

Tendons are collagen-rich musculoskeletal tissues that possess the mechanical strength needed to transfer forces between muscles and bones. The mechanical development and function of tendons are impacted by collagen crosslinks. However, there is a limited understanding of how collagen crosslinking is regulated in tendon during development and aging. Therefore, the objective of the present review was to highlight potential regulators of enzymatic and non-enzymatic collagen crosslinking and how they impact tendon function. The main collagen crosslinking enzymes include lysyl oxidase (LOX) and the lysyl oxidase-like isoforms (LOXL), whereas non-enzymatic crosslinking is mainly mediated by the formation of advanced glycation end products (AGEs). Regulators of the LOX and LOXL enzymes may include mechanical stimuli, mechanotransducive cell signaling pathways, sex hormones, transforming growth factor (TGF)β family, hypoxia, and interactions with intracellular or extracellular proteins. AGE accumulation in tendon is due to diabetic conditions and aging, and can be mediated by diet and mechanical stimuli. The formation of these enzymatic and non-enzymatic collagen crosslinks plays a major role in tendon biomechanics and in the mechanisms of force transfer. A more complete understanding of how enzymatic and non-enzymatic collagen crosslinking is regulated in tendon will better inform tissue engineering and regenerative therapies aimed at restoring the mechanical function of damaged tendons.

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.

LOXL2 attenuates osteoarthritis through inactivating Integrin/FAK signaling

Temporomandibular joint OA (TMJOA) is a common degenerative joint disease, leads to structural damage and ultimately loss of function. Matrix degradation is one of the first pathogenesis during the progression of OA, it was effective to inhibit matrix degradation to block the development of OA. In this study, an in vivo model (compressive mechanical force) and an in vitro model (IL-1β) were used to induce OA-like changes in TMJ cartilage and chondrocytes. We revealed lysyl oxidase like-2 (LOXL2) play a critical role in TMJOA. LOXL2 expression decreased in mechanical stress/IL-β induced TMJOA-like lesions in both in vivo models and in vitro models. Furthermore, recombinant LOXL2 (rhLOXL2) treatment ameliorated the degenerative changes induced by mechanical stress in vivo, including the thinning cartilage, down-expression of collagen II and proteoglycan, and over-expression of TNF-a, while LOXL2 antibody (anti-LOXL2) treatment exacerbated these changes. Mechanistically, the protection of LOXL2 in chondrocytes was induced partly through activation of the Integrin/FAK pathway. The inhibition of the Integrin/FAK pathway could neutralized the effects caused by rhLOXL2. Collectively, our study suggests that the LOXL2 plays a protective role in mechanical stress induced TMJOA-like changes, and the Integrin/FAK pathway may be a key downstream pathway in this process.

Significance of nuclear LOXL2 inhibition in fibroblasts and myofibroblasts in the fibrotic process of acute respiratory distress syndrome

Fibrotic scarring is an important prognostic factor of acute respiratory distress syndrome (ARDS). There are currently no antifibrotic drugs or other therapeutic agents for ARDS. Lysyl oxidase-like 2 (LOXL2), an amine oxidase, contributes to fibrotic scarring by facilitating collagen cross-linking. Recent clinical trials revealed that a monoclonal inhibitory antibody against LOXL2 failed to show benefit over placebo in patients with fibrotic disorders involving the lungs. These clinical results raise the possibility that targeting the extracellular enzymic activity of LOXL2 is not in itself sufficient to prevent fibrotic scarring. We investigated the role of LOXL2 in the pathogenesis of ARDS in vivo, in vitro, and in samples from patients with ARDS. After lung injury, LOXL2 was unevenly expressed in the nuclei of lung fibroblasts and myofibroblasts in the fibrotic phase. Nuclear LOXL2 expression was upregulated in lung fibroblasts after transforming growth factor-beta1 (TGF-β1)-treatment. LOXL2 silencing abrogated the TGF-β1-induced expression of a myofibrogenic-progenitor marker, the appearance of proto-myofibroblasts, and the evolution of differentiated myofibroblasts in lung fibroblasts. Nuclear upregulation of Snail was evident in myofibroblasts during the fibrotic phase after lung injury. We detected high levels of LOXL2 protein in the lungs of ARDS patients, specifically during the proliferative and fibrotic phases. Our results highlight nuclear LOXL2 in fibroblasts as a primary causative driver of cell-fate decision toward myofibroblasts and of the progression of fibrotic scarring. A nuclear-LOXL2-targeted agent could be a promising therapeutic strategy against fibrotic disorders including ARDS.

LOXL2 promotes aggrecan and gender-specific anabolic differences to TMJ cartilage

In the United States, 5–12% of adults have at least one symptom of temporomandibular joint (TMJ) disorders, including TMJ osteoarthritis (TMJ-OA). However, there is no chondroprotective agent that is approved for clinical application. We showed that LOXL2 is elevated in the regenerative response during fracture healing in mice and has a critical role in chondrogenic differentiation. Indeed, LOXL2 is an anabolic effector that attenuates pro-inflammatory signaling in OA cartilage of the TMJ and knee joint, induces chondroprotective and regenerative responses, and attenuates NF-kB signaling. The specific goal of the study was to evaluate if adenoviral delivery of LOXL2 is anabolic to human and mouse TMJ condylar cartilage in vivo and evaluate the protective and anabolic effect on cartilage-specific factors. We employed two different models to assess TMJ-OA. In one model, clinical TMJ-OA cartilage from 5 different samples in TMJ-OA cartilage plugs were implanted subcutaneously in nude mice. Adenovirus LOXL2 -treated implants showed higher mRNA levels of LOXL2, ACAN, and other anabolic genes compared to the adenovirus-Empty-treated implants. Further characterization by RNA-seq analysis showed LOXL2 promotes proteoglycan networks and extracellular matrix in human TMJ-OA cartilage implants in vivo. In order to evaluate if LOXL2-induced functional and sex-linked differences, both male and female four-month-old chondrodysplasia (Cho/+) mice, which develop progressive TMJ-OA due to a point mutation in the Col11a1 gene, were subjected to intraperitoneal injection with Adv-RFP-LOXL2 every 2 weeks for 12 weeks. The data showed that adenovirus delivery of LOXL2 upregulated LOXL2 and aggrecan (Acan), whereas MMP13 expression was slightly downregulated. The fold change expression of Acan and Runx2 induced by Adv-RFP-LOXL2 was higher in females compared to males. Interestingly, Adv-RFP-LOXL2 injection significantly increased Rankl expression in male but there was no change in females, whereas VegfB gene expression was increased in females, but not in males, as compared to those injected with Adv-RFP-Empty in respective groups. Our findings indicate that LOXL2 can induce specifically the expression of Acan and other anabolic genes in two preclinical models in vivo. Further, LOXL2 has beneficial functions in human TMJ-OA cartilage implants and promotes gender-specific anabolic responses in Cho/+ mice with progressive TMJ-OA, suggesting its merit for further study as an anabolic therapy for TMJ-OA.

LOXL2 from human amniotic mesenchymal stem cells accelerates wound epithelialization by promoting differentiation and migration of keratinocytes

In this study, we identified wound healing-related proteins secreted by human amniotic epithelial cells (hAECs) and human amniotic mesenchymal stem cells (hAMSCs). We observed increased migration and reduced proliferation and differentiation when keratinocytes were co-cultured in media conditioned by hAECs (hAECs-CM) and hAMSCs (hAMSCs-CM). Label-free mass spectrometry and bioinformatic analyses of the hAECs-CM and hAMSCs-CM proteome revealed several proteins associated with wound healing, angiogenesis, cellular differentiation, immune response and cell motility. The levels of the proteins related to wound healing, including CTHRC1, LOXL2 and LGALS1, were significantly higher in hAMSCs-CM than hAECs-CM. LOXL2 significantly enhanced in vitro keratinocyte migration and differentiation compared to CTHRC1 and LGALS1. Moreover, LOXL2 enhanced keratinocyte migration and differentiation by activating the JNK signaling pathway. We observed significant reduction in the in vitro migration and differentiation of keratinocytes when co-cultured with medium conditioned by LOXL2-silenced hAMSCs and when treated with 10 μM SP600125, a specific JNK inhibitor. Treatment with hAMSCs-CM and LOXL2 significantly accelerated wound healing in the murine skin wound model. These findings show that LOXL2 promotes wound healing by inducing keratinocyte migration and differentiation via a JNK signaling pathway.

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.

Site-Dependent Lineage Preference of Adipose Stem Cells

Adult stem cells have unique properties in both proliferation and differentiation preference. In this study, we hypothesized that adipose stem cells have a depot-dependent lineage preference. Four rabbits were used to provide donor-matched adipose stem cells from either subcutaneous adipose tissue (ScAT) or infrapatellar fat pad (IPFP). Proliferation and multi-lineage differentiation were evaluated in adipose stem cells from donor-matched ScAT and IPFP. RNA sequencing (RNA-seq) and proteomics were conducted to uncover potential molecular discrepancy in adipose stem cells and their corresponding matrix microenvironments. We found that stem cells from ScAT exhibited significantly higher proliferation and adipogenic capacity compared to those from donor-matched IPFP while stem cells from IPFP displayed significantly higher chondrogenic potential compared to those from donor-matched ScAT. Our findings are strongly endorsed by supportive data from transcriptome and proteomics analyses, indicating a site-dependent lineage preference of adipose stem cells.

Warfarin-exposed zebrafish embryos resembles human warfarin embryopathy in a dose and developmental-time dependent manner - From molecular mechanisms to environmental concerns

Warfarin is the most worldwide used anticoagulant drug and rodenticide. Since it crosses placental barrier it can induce warfarin embryopathy (WE), a fetal mortality in neonates characterized by skeletal deformities in addition to brain hemorrhages. Although the effects of warfarin exposure in aquatic off target species were already described, the particular molecular toxicological mechanisms during early development are still unclear. Here, we used zebrafish (Danio rerio) to describe and compare the developmental effects of warfarin exposure (0, 15.13, 75.68 and 378.43 mM) on two distinct early developmental phases (embryos and eleuthero-embryos). Although exposure to both developmental phases induced fish mortality, only embryos exposed to the highest warfarin level exhibited features mimicking mammalian WE, e.g. high mortality, higher incidence of hemorrhages and altered skeletal development, among other effects. To gain insights into the toxic mechanisms underlying warfarin exposure, the transcriptome of embryos exposed to warfarin was explored through RNA-Seq and compared to that of control embryos. 766 differentially expressed (564 up- and 202 down-regulated) genes were identified. Gene Ontology analysis revealed particular cellular components (cytoplasm, extracellular matrix, lysosome and vacuole), biological processes (mainly amino acid and lipid metabolism and response to stimulus) and pathways (oxidative stress response and apoptosis signaling pathways) being significantly overrepresented in zebrafish embryos upon warfarin exposure. Protein-protein interaction further evidenced an altered redox system, blood coagulation and vasculogenesis, visual phototransduction and collagen formation upon warfarin exposure. The present study not only describes for the first time the WE in zebrafish, it provides new insights for a better risk assessment, and highlights the need for programming the rat eradication actions outside the fish spawning season to avoid an impact on off target fish community. The urge for the development of more species-specific anticoagulants for rodent pest control is also highlighted.

Lysyl Oxidase-Like 2 Protects against Progressive and Aging Related Knee Joint Osteoarthritis in Mice

Background: The goal of this study was to determine if adenovirus-delivered LOXL2 protects against progressive knee osteoarthritis (OA), assess its specific mechanism of action; and determine if the overexpression of LOXL2 in transgenic mice can protect against the development of OA-related cartilage damage and joint disability. Methods: Four-month-old Cho/+ male and female mice were intraperitoneally injected with either Adv-RFP-LOXL2 or an empty vector twice a month for four months. The proteoglycan levels and the expression of anabolic and catabolic genes were examined by immunostaining and qRT-PCR. The effect of LOXL2 expression on signaling was tested via the pro-inflammatory cytokine IL1β in the cartilage cell line ATDC5. Finally; the OA by monosodium iodoacetate (MIA) injection was also induced in transgenic mice with systemic overexpression of LOXL2 and examined gene expression and joint function by treadmill tests and assessment of allodynia. Results: The adenovirus treatment upregulated LOXL2; Sox9; Acan and Runx2 expression in both males and females. The Adv-RFP-LOXL2 injection; but not the empty vector injection increased proteoglycan staining and aggrecan expression but reduced MMP13 expression. LOXL2 attenuated IL-1β-induced phospho-NF-κB/p65 and rescued chondrogenic lineage-related genes in ATDC5 cells; demonstrating one potential protective mechanism. LOXL2 attenuated phospho-NF-κB independent of its enzymatic activity. Finally; LOXL2-overexpressing transgenic mice were protected from MIA-induced OA-related functional changes; including the time and distance traveled on the treadmill and allodynia. Conclusion: Our study demonstrates that systemic LOXL2 adenovirus or LOXL2 genetic overexpression in mice can protect against OA. These findings demonstrate the potential for LOXL2 gene therapy for knee-OA clinical treatment in the future.

Pathogenesis of fibrostenosing Crohn's disease

Crohn's disease (CD) is a chronic inflammatory disease, which could affect any part of the gastrointestinal tract. A severe complication of CD is fibrosis-associated strictures, which can cause bowel obstruction. Unfortunately, there is no specific antifibrotic therapy available. More than 80% of the patients with CD will have to undergo at least 1 surgery in their life and recurrence of strictures after surgery is common. Investigations on the mechanism of fibrostenosing CD have revealed that fibrosis is mainly driven by expansion of mesenchymal cells including fibroblasts, myofibroblasts, and smooth muscle cells. Being exposed to a pro-fibrotic milieu, these cells increase the secretion of extracellular matrix, as well as crosslinking enzymes, which drive tissue stiffness and remodeling. Fibrogenesis can become independent of inflammation in later stages of disease, which offers unique therapeutic potential. Exciting new evidence suggests smooth muscle cell hyperplasia as a strong contributor to luminal narrowing in fibrostenotic CD. Approval of new drugs in other fibrotic diseases, such as idiopathic pulmonary fibrosis, as well as new targets associated with fibrosis found in CD, such as cadherins or specific integrins, shed light on the development of novel antifibrotic approaches in CD.

Exogenous Lysyl Oxidase-Like 2 and Perfusion Culture Induce Collagen Crosslink Formation in Osteogenic Grafts

Lysyl oxidase (LOX)-mediated collagen crosslinking can regulate osteoblastic phenotype and enhance mechanical properties of tissues, both areas of interest in bone tissue engineering. The objective of this study is to investigate the effect of lysyl oxidase-like 2 (LOXL2) on osteogenic differentiation of mesenchymal stem cells (MSCs) cultured in perfusion bioreactors, enzymatic collagen crosslink formation in the extracellular matrix (ECM), and mechanical properties of engineered bone grafts. Exogenous LOXL2 to MSCs seeded in composite scaffolds under perfusion culture for up to 28 days is administered. Constructs treated with LOXL2 appear brown in color and possess greater DNA content and osteogenic potential measured by a twofold increase in bone sialoprotein gene expression. Collagen expression of LOXL2-treated scaffolds is lower than untreated controls. Functional outputs such as calcium deposition, osteocalcin expression, and compressive modulus are unaffected by LOXL2 supplementation. Excitingly, LOXL2-treated constructs contain 1.8- and 1.4-times more pyridinoline (PYD) crosslinks per mole of collagen and per wet weight, respectively, than untreated constructs. Despite these increases, compressive moduli of LOXL2-treated constructs are similar to untreated constructs over the 28-day culture duration. This is the first report of LOXL2 application to engineered, three-dimensional bony constructs. The results suggest a potentially new strategy for engineering osteogenic grafts with a mature ECM by modulating crosslink formation.

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.

Multiple Functions of Lysyl Oxidase Like-2 in Oral Fibroproliferative Processes

Gingival overgrowth is a side effect of certain medications, including calcium channel blockers, cyclosporin A, and phenytoin. Phenytoin-induced gingival overgrowth is fibrotic. Lysyl oxidases are extracellular enzymes that are required for biosynthetic cross-linking of collagens, and members of this enzyme family are upregulated in fibrosis. Previous studies in humans and in a mouse model of phenytoin-induced gingival overgrowth have shown that LOXL2 is elevated in the epithelium and connective tissue in gingival overgrowth tissues and not in normal tissues. Here, using a novel LOXL2 isoform-selective inhibitor and knockdown studies in loss- and gain-of-function studies, we investigated roles for LOXL2 in promoting cultures of human gingival fibroblasts to proliferate and to accumulate collagen. Data indicate that LOXL2 stimulates gingival fibroblast proliferation, likely by a platelet-derived growth factor B receptor-mediated mechanism. Moreover, collagen accumulation was stimulated by LOXL2 enzyme and inhibited by LOXL2 inhibitor or gene knockdown. These studies suggest that LOXL2 could serve as a potential therapeutic target to address oral fibrotic conditions.

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.

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).

Anabolic role of lysyl oxidase like-2 in cartilage of knee and temporomandibular joints with osteoarthritis

Background

Lysyl oxidase like-2 (LOXL2) is a copper-dependent amine oxidase. Our previous studies showed that LOXL2 is elevated during mouse fracture healing. The goal of this study was to evaluate the potential of LOXL2 to act as an anabolic agent in cartilage affected by osteoarthritis (OA).

Methods

LOXL2 was visualized in tissues from human knee and hip joints and temporomandibular joints (TMJ) by immunofluorescence. The activity of LOXL2 in human articular and TMJ chondrocytes was assessed by cell-based assays, microarray analysis, and RT-qPCR, and LOXL2-mediated activation of NF-κB and extracellular signal-related kinase (ERK) signaling pathways was measured by western blotting. To examine LOXL2-induced effect in vivo, we implanted Matrigel-imbedded human chondrocytes into nude mice and exposed them to exogenous LOXL2 for 6 weeks. Finally, LOXL2-induced effects on collagen type 2 α1 (COL2A1) and phospho-SMAD2/3 were evaluated by immunofluorescence analysis.

Results

LOXL2 staining was detected in damaged regions of human TMJ, hip and knee joints affected by OA. Stimulation with transforming growth factor (TGF)-β1 upregulated LOXL2 expression, while pro-inflammatory cytokines IL-1β and TNF-α downregulated LOXL2, in human chondrocytes. Viral transduction of LOXL2 in OA chondrocytes increased the mRNA levels of chondroitin sulfate proteoglycan (CSPG4), aggrecan (ACAN), sex determining region Y-box containing gene 9 (SOX9), and COL2A1 but reduced the levels of extracellular matrix (ECM)-degrading enzymes matrix metalloproteinase (MMP)1, MMP3, and MMP13. Further, forced expression of LOXL2 promoted chondrogenic lineage-specific gene expression, increased the expression of COL2A1 in the presence of TNF-α, and inhibited chondrocyte apoptosis. LOXL2 expression also inhibited IL-1β-induced phospho-NF-κB/p65 and TGF-β1-induced ERK1/2 phosphorylation. Matrigel constructs of human chondrocytes from the knee joint and TMJ implanted in nude mice showed anabolic responses after LOXL2 transduction, including increased expression of SOX9, ACAN, and COL2A1. Finally, immunofluorescence staining revealed co-localization of LOXL2 with SOX9 in the nuclei of cells in the implants, decreased phospho-SMAD2/3, and increased COL2A1 staining.

Conclusion

Our results suggest that although LOXL2 is upregulated in cartilage affected by OA, this may be a protective response that promotes anabolism while inhibiting specific catabolic responses in the pathophysiology of OA.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-017-1388-8) contains supplementary material, which is available to authorized users.

Tension stimulation drives tissue formation in scaffold-free systems

Scaffold-free systems have emerged as viable approaches for engineering load-bearing tissues. However, the tensile properties of engineered tissues have remained far below the values for native tissue. Here, by using self-assembled articular cartilage as a model to examine the effects of intermittent and continuous tension stimulation on tissue formation, we show that the application of tension alone, or in combination with matrix remodelling and synthesis agents, leads to neocartilage with tensile properties approaching those of native tissue. Implantation of tension-stimulated tissues results in neotissues that are morphologically reminiscent of native cartilage. We also show that tension stimulation can be translated to a human cell source to generate anisotropic human neocartilage with enhanced tensile properties. Tension stimulation, which results in nearly sixfold improvements in tensile properties over unstimulated controls, may allow the engineering of mechanically robust biological replacements of native tissue.

The Role of the Lysyl Oxidases in Tissue Repair and Remodeling: A Concise Review

Tissue injury provokes a series of events containing inflammation, new tissue formation and tissue remodeling which are regulated by the spatially and temporally coordinated organization. It is an evolutionarily conserved, multi-cellular, multi-molecular process via complex signalling network. Tissue injury disorders present grievous clinical problems and are likely to increase since they are generally associated with the prevailing diseases such as diabetes, hypertension and obesity. Although these dynamic responses vary not only for the different types of trauma but also for the different organs, a balancing act between the tissue degradation and tissue synthesis is the same. In this process, the degradation of old extracellular matrix (ECM) elements and new ones' synthesis and deposition play an essential role, especially collagens. Lysyl oxidase (LOX) and four lysyl oxidase-like proteins are a group of enzymes capable of catalyzing cross-linking reaction of collagen and elastin, thus initiating the formation of covalent cross-links that insolubilize ECM proteins. In this way, LOX facilitates ECM stabilization through ECM formation, development, maturation and remodeling. This ability determines its potential role in tissue repair and regeneration. In this review, based on the current in vitro, animal and human in vivo studies which have shown the significant role of the LOXs in tissue repair, e.g., tendon regeneration, ligament healing, cutaneous wound healing, and cartilage remodeling, we focused on the role of the LOXs in inflammation phase, proliferation phase, and tissue remodeling phase of the repair process. By summarizing its healing role, we hope to shed light on the understanding of its potential in tissue repair and provide up to date therapeutic strategies towards related injuries.

Expression of the semicarbazide-sensitive amine oxidase in articular cartilage: its role in terminal differentiation of chondrocytes in rat and human

OBJECTIVE

Semicarbazide-sensitive amine oxidase (SSAO) catalyzes the oxidation of primary amines into ammonia and reactive species (hydrogen peroxide, aldehydes). It is highly expressed in mammalian tissues, especially in vascular smooth muscle cells and adipocytes, where it plays a role in cell differentiation and glucose transport. The study aims at characterizing the expression and the activity of SSAO in rat and human articular cartilage of the knee, and to investigate its potential role in chondrocyte terminal differentiation.

DESIGN

SSAO expression was examined by immunohistochemistry and western blot. Enzyme activity was measured using radiolabeled benzylamine as a substrate. Primary cell cultures of rat chondrocytes were treated for 21 days by a specific SSAO inhibitor, LJP 1586. Terminal chondrocyte differentiation markers were quantified by RT-qPCR. The basal and IL1β-stimulated glucose transport was monitored by the entrance of (3)[H]2-deoxyglucose in chondrocytes.

RESULTS

SSAO was expressed in chondrocytes of rat and human articular cartilage. SSAO expression was significantly enhanced during the hypertrophic differentiation of chondrocytes characterized by an increase in MMP13 and in alkaline phosphatase (ALP) expressions. SSAO inhibition delayed the late stage of chondrocyte differentiation without cell survival alteration and diminished the basal and IL1β-stimulated glucose transport. Interestingly, SSAO activity was strongly increased in human osteoarthritic cartilage.

CONCLUSIONS

SSAO was expressed as an active form in rat and human cartilage. The results suggest the involvement of SSAO in rat chondrocyte terminal differentiation via a modulation of the glucose transport. In man, the increased SSAO activity detected in osteoarthritic patients may trigger hypertrophy and cartilage degeneration.

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.

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

Lysyl oxidases are required for collagen and elastin cross-linking and extracellular matrix maturation including in bone. The lysyl oxidase family consists of lysyl oxidase (LOX) and 4 isoforms (LOXL1-4). Here we investigate whether deletion of LOXL1, which has been linked primarily to elastin maturation, leads to skeletal abnormalities. Left femurs (n = 8), L5 vertebrae (n = 8), and tibiae (n = 8) were analyzed by micro-computed tomography in 13-week-old wild-type (WT) and LOXL1-/- male and female mice. Right femurs (n = 8) were subjected to immunohistochemistry for LOXL1, and histochemical/histology analyses of osteoclasts and growth plates. Sera from all mice were analyzed for bone turnover markers. Results indicate strong expression of LOXL1 in wild-type growth plates in femurs. Significant deterioration of trabecular bone structure in long bones and vertebrae from female was observed but not from male, mutant mice compared with WT. Decreases in BV/TV, Conn.D, trabecular thickness, and number in the femoral distal metaphysis were observed in female, but not in male, mutant mice. Trabecular spacing was increased significantly in femurs of female mutant mice. Findings were similar in trabeculae of L5 vertebrae from female mutant mice. The number of TRAP positive osteoclasts at the trabecular bone surface was increased in female mutant mice compared with WT females, consistent with increased serum RANKL and decreased OPG levels. Analysis of bone turnover markers confirmed increased bone resorption as indicated by significantly elevated CTX-1 in the serum of female LOXL1-/- mice compared to their wild-type counterparts, as well as decreased bone formation as measured by decreased serum levels of PINP. Picrosirius red staining revealed a loss of heterogeneity in collagen organization in female LOXL1-/- mice only, with little to no yellow and orange birefringence. Organization was also impaired in chondrocyte columns in both female and male LOXL1-/- mice, but to a greater extent in females. Data indicate that LOXL1-/- mutant mice develop appendicular and axial skeletal phenotypes characterized by decreased bone volume fraction and compromised trabecular microstructure, predominantly in females.

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.

Prevention of phenytoin-induced gingival overgrowth by lovastatin in mice

Drug-induced gingival overgrowth is caused by the antiseizure medication phenytoin, calcium channel blockers, and ciclosporin. Characteristics of these drug-induced gingival overgrowth lesions differ. We evaluate the ability of a mouse model to mimic human phenytoin-induced gingival overgrowth and assess the ability of a drug to prevent its development. Lovastatin was chosen based on previous analyses of tissue-specific regulation of CCN2 production in human gingival fibroblasts and the known roles of CCN2 in promoting fibrosis and epithelial to mesenchymal transition. Data indicate that anterior gingival tissue overgrowth occurred in phenytoin-treated mice based on gross tissue observations and histomorphometry of tissue sections. Molecular markers of epithelial plasticity and fibrosis were regulated by phenytoin in gingival epithelial tissues and in connective tissues similar to that seen in humans. Lovastatin attenuated epithelial gingival tissue growth in phenytoin-treated mice and altered the expressions of markers for epithelial to mesenchymal transition. Data indicate that phenytoin-induced gingival overgrowth in mice mimics molecular aspects of human gingival overgrowth and that lovastatin normalizes the tissue morphology and the expression of the molecular markers studied. Data are consistent with characterization of phenytoin-induced human gingival overgrowth in vivo and in vitro characteristics of cultured human gingival epithelial and connective tissue cells. Findings suggest that statins may serve to prevent or attenuate phenytoin-induced human gingival overgrowth, although specific human studies are required.

The potential for targeting extracellular LOX proteins in human malignancy

The extracellular matrix (ECM) is the physical scaffold where cells are organized into tissues and organs. The ECM may be modified during cancer to allow and promote proliferation, invasion, and metastasis. The family of lysyl oxidase (LOX) enzymes cross-links collagens and elastin and, therefore, is a central player in ECM deposition and maturation. Extensive research has revealed how the LOX proteins participate in every stage of cancer progression, and two family members, LOX and LOX-like 2, have been linked to metastasis, the final stage of cancer responsible for over 90% of cancer patient deaths. However, LOX biosynthesis results in by-product with antiproliferative properties in certain cancers, and LOX enzymes may have different effects depending on the molecular network in which they are active. Therefore, the design of therapies targeting the LOX family needs to be guided by the molecular makeup of the individual disease and will probably require other agents to act on both the LOX enzymes and their associated network.

Different circadian expression of major matrix-related genes in various types of cartilage: modulation by light-dark conditions

We screened circadian-regulated genes in rat cartilage by using a DNA microarray analysis. In rib growth-plate cartilage, numerous genes showed statistically significant circadian mRNA expression under both 12:12 h light-dark and constant darkness conditions. Type II collagen and aggrecan genes--along with several genes essential for post-translational modifications of collagen and aggrecan, including prolyl 4-hydroxylase 1, lysyl oxidase, lysyl oxidase-like 2 and 3'-phosphoadenosine 5'-phosphosulphate synthase 2--showed the same circadian phase. In addition, the mRNA level of SOX9, a master transcription factor for the synthesis of type II collagen and aggrecan, has a similar phase of circadian rhythms. The circadian expression of the matrix-related genes may be critical in the development and the growth of various cartilages, because similar circadian expression of the matrix-related genes was observed in hip joint cartilage. However, the circadian phase of the major matrix-related genes in the rib permanent cartilage was almost the converse of that in the rib growth-plate cartilage under light-dark conditions. We also found that half of the oscillating genes had conserved clock-regulatory elements, indicating contribution of the elements to the clock outputs. These findings suggest that the synthesis of the cartilage matrix macromolecules is controlled by cell-autonomous clocks depending upon the in vivo location of cartilage.

Localization of the gene for hyperostosis cranialis interna to chromosome 8p21 with analysis of three candidate genes

Hyperostosis cranialis interna (HCI) is a rare autosomal dominant disorder characterized by intracranial hyperostosis and osteosclerosis, which is confined to the skull, especially the calvarium and the skull base. The rest of the skeleton is not affected. Progressive bone overgrowth causes nerve entrapment that leads to recurrent facial nerve palsy, disturbance of the sense of smell, hearing and vision impairments, impairment of facial sensibility, and disturbance of balance due to vestibular areflexia. The treatment is symptomatic. Histomorphological investigations showed increased bone formation with a normal tissue structure. Biochemical parameters were normal. Until today the disease has been described in only three related Dutch families with common progenitors and which consist of 32 individuals over five generations. HCI was observed in 12 family members over four generations. Patients are mildly to severely affected. Besides HCI, several bone dysplasias with hyperostosis and sclerosis of the craniofacial bones are known. Examples are Van Buchem disease, sclerosteosis, craniometaphyseal dysplasia, and Camurati-Engelmann disease. However, in these cases the long bones are affected as well. Linkage analysis in a family with HCI resulted in the localization of the disease-causing gene to a region on chromosome 8p21 delineated by markers D8S282 and D8S382. Interesting candidate genes in this region are BMP1, LOXL2, and ADAM28. Sequence analysis of these genes did not reveal any putative mutations. This suggests that a gene not previously involved in a sclerosing bone dysplasia is responsible for the abnormal growth in the skull of these patients.

Lysyl oxidase like-2 reinforces unsatisfactory ossification induced by bone morphogenetic protein-2: relating nanomechanical properties and molecular changes

Bone morphogenetic protein-2 (BMP2) is among the most popular anabolic agents and substantially increase bone volume related to enhanced osteoblast differentiation. Here we demonstrate a remarkable deterioration in the nanomechanical properties of mineralized tissue induced from osteoblasts solely by the function of BMP2. Mineralized tissue of primary osteoblasts cultured with BMP2 shows molecular features of both bone and cartilage, but depletion of lysyl oxidase family members leads to poor nanomechanical properties of the mineralized tissue. Lysyl oxidase like-2 supplementation reinforces the inferior mineralized tissue induced from osteoblasts by BMP2 through intermolecular cross-linking of type II or type X collagen-rich extracellular matrix. This may also mimic a consolidation of bone fracture gaps, despite the fact that the distribution of the bone properties in such microenvironments has been poorly elucidated. These findings confirm the importance of testing newly induced bone down to the microscale and nanoscale in bone tissue engineering.

FROM THE CLINICAL EDITOR

Bone morphogenetic protein-2 is known to substantially increase bone volume related to enhanced osteoblast differentiation; however, this team of investigators report a remarkable deterioration in the nanomechanical properties of mineralized tissue induced from osteoblasts solely by the function of BMP2.

The expression and role of Lysyl oxidase (LOX) in dentinogenesis

AIM

To establish whether eliminating Lysyl oxidase (LOX) gene would affect dentine formation.

METHODOLOGY

Newborn wild-type (wt) and homo- and heterozygous LOX knock-out (Lox(-/-) and Lox(+/-) , respectively) mice were used to study developing tooth morphology and dentine formation. Collagen aggregation in the developing dentine was examined histochemically with picrosirius red (PSR) staining followed by polarized microscopy. Because Lox(-/-) die at birth, adult wt and Lox(+/-) mouse tooth morphologies were examined with FESEM. Human odontoblasts and pulp tissue were used to study the expression of LOX and its isoenzymes with Affymetrix cDNA microarray.

RESULTS

No differences between Lox(-/-) , Lox(+/-) and wt mice developing tooth morphology were seen by light microscopy. Histochemically, however, teeth in wt mice demonstrated yellow-orange and orange-red polarization colours with PSR staining, indicating thick and more densely packed collagen fibres, whilst in Lox(-/-) and Lox(+/-) mice, most of the polarization colours were green to green-yellow, indicating thinner, less aggregated collagen fibres. Fully developed teeth did not show any differences between Lox(+/-) and wt mice with FESEM. Human odontoblasts expressed LOX and three of four of its isoenzymes.

CONCLUSIONS

The data indicate that LOX is not essential in dentinogenesis, even though LOX deletion may affect dentine matrix collagen thickness and packing. The absence of functional LOX may be compensated by LOX isoenzymes.

LOXL2 in epithelial cell plasticity and tumor progression

Several members of the lysyl oxidase family have recently emerged as important regulators of tumor progression. Among them, LOXL2 has been shown to be involved in tumor progression and metastasis of several tumor types, including breast carcinomas. Secreted LOXL2 participates in the remodeling of the extracellular matrix of the tumor microenvironment, in a similar fashion to prototypical lysyl oxidase. In addition, new intracellular functions of LOXL2 have been described, such as its involvement in the regulation of the epithelial-to-mesenchymal transition, epithelial cell polarity and differentiation mediated by transcriptional repression mechanisms. Importantly, intracellular (perinuclear) expression of LOXL2 is associated with poor prognosis and distant metastasis of specific tumor types, such as larynx squamous cell carcinoma and basal breast carcinomas. These recent findings open new avenues for the therapeutic utility of LOXL2.

Common polymorphisms in human lysyl oxidase genes are not associated with the adolescent idiopathic scoliosis phenotype

Background

Although adolescent idiopathic scoliosis affects approximately 3% of adolescents, the genetic contributions have proven difficult to identify. Work in model organisms, including zebrafish, chickens, and mice, has implicated the lysyl oxidase family of enzymes in the development of scoliosis. We hypothesized that common polymorphisms in the five human lysyl oxidase genes (LOX, LOXL1, LOXL2, LOXL3, and LOXL4) may be associated with the phenotype of adolescent idiopathic scoliosis.

Methods

This was a case-control genetic association study. A total of 112 coding and tag SNPs in LOX, LOXL1, LOXL2, LOXL3, and LOXL4 were genotyped in a discovery cohort of 138 cases and 411 controls. Genotypes were tested for association with adolescent idiopathic scoliosis by logistic regression with a two degree of freedom genotypic model and gender as a covariate. Fourteen SNPs with p < 0.1 in the discovery phase were genotyped in an independent replication cohort of 400 cases and 506 controls.

Results

No evidence for significant association was found between coding or tag SNPs in LOX, LOXL1, LOXL2, LOXL3, and LOXL4 and the phenotype of adolescent idiopathic scoliosis.

Conclusions

Despite suggestive evidence in model organisms, common variants and known coding SNPs in the five human lysyl oxidase genes do not confer increased genotypic risk for adolescent idiopathic scoliosis. The above methodology does not address rare variants or individually private mutations in these genes, and future research may focus on this area.