Lysyl oxidases: a novel multifunctional amine oxidase family

Exosome-mediated secretion of LOXL4 promotes hepatocellular carcinoma cell invasion and metastasis

Background

Lysyl oxidase-like 4 (LOXL4) has been found to be dysregulated in several human malignancies, including hepatocellular carcinoma (HCC). However, the role of LOXL4 in HCC progression remains largely unclear. In this study, we investigated the clinical significance and biological involvement of LOXL4 in the progression of HCC.

Methods

LOXL4 expression was measured in HCC tissues and cell lines. Overexpression, shRNA-mediated knockdown, recombinant human LOXL4 (rhLOXL4), and deletion mutants were applied to study the function of LOXL4 in HCC. Exosomes derived from HCC cell lines were assessed for the ability to promote cancer progression in standard assays. The effects of LOXL4 on the FAK/Src pathway were examined by western blotting.

Results

LOXL4 was commonly upregulated in HCC tissues and predicted a poor prognosis. Elevated LOXL4 was associated with tumor differentiation, vascular invasion, and tumor-node-metastasis (TNM) stage. Overexpression of LOXL4 promoted, whereas knockdown of LOXL4 inhibited cell migration and invasion of HCC in vitro, and overexpressed LOXL4 promoted intrahepatic and pulmonary metastases of HCC in vivo. Most interestingly, we found that HCC-derived exosomes transferred LOXL4 between HCC cells, and intracellular but not extracellular LOXL4 promoted cell migration by activating the FAK/Src pathway dependent on its amine oxidase activity through a hydrogen peroxide-mediated mechanism. In addition, HCC-derived exosomes transferred LOXL4 to human umbilical vein endothelial cells (HUVECs) though a paracrine mechanism to promote angiogenesis.

Conclusions

Taken together, our data demonstrate a novel function of LOXL4 in tumor metastasis mediated by exosomes through regulation of the FAK/Src pathway and angiogenesis in HCC.

Electronic supplementary material

The online version of this article (10.1186/s12943-019-0948-8) contains supplementary material, which is available to authorized users.

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.

The importance of evaluating the chemical structures and strategies to avoid pitfalls in quantitative bioanalysis

Quantitative bioanalytical data are crucial in pharmaceutical research and development, allowing project teams to make informed scientific decisions on the progression of candidate molecules to medicines. Many challenges are often encountered during the bioanalysis of drugs in biological matrices which require resolution in a timely manner. In this publication, guidance is provided to bioanalytical scientists on how to identify potential problems before they become an obstacle for the drug development and to share our experiences dealing some of most common problems encountered in the bioanalytical laboratory. Relevant topics in bioanalysis such as stabilization approaches for glucuronides (Acyl and N-); prodrugs (phosphate and esters), amides, amines, N-oxides; bioanalysis of light sensitive molecules, halogenated drugs and lactones are discussed in this publication.

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

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

A serological marker of the N-terminal neoepitope generated during LOXL2 maturation is elevated in patients with cancer or idiopathic pulmonary fibrosis

Objectives

Lysyl oxidase like 2 (LOXL2) is associated with poor prognosis in idiopathic pulmonary disease (IPF) and cancer. We developed an Enzyme-linked immunosorbent assay (ELISA) targeting the LOXL2 neo-epitope generated through the release of the signal peptide during LOXL2 maturation.

Design and methods

An ELISA targeting the N-terminal site of the human LOXL2 was developed including technical optimization and validation steps. Serum LOXL2 was measured in patients with breast, colorectal, lung, ovarian, pancreatic and prostate cancer, melanoma, IPF and in healthy controls (n = 16).

Results

A technically robust and specific assay was developed. LOXL2 was detectable in serum from healthy controls and showed reactivity towards recombinant LOXL2. Compared to controls, LOXL2 levels were significantly (p < 0.001–0.05) elevated in serum from patients with breast, colerectal, lung, ovarian and pancreatic cancer (mean range: 49–84 ng/mL), but not in prostate cancer (mean: 36 ng/mL) and malignant melanoma patients (41 ng/mL). Serum LOXL2 was elevated in IPF patients compared to healthy controls (mean: 76.5 vs 46.8 ng/mL; p > 0.001)

Conclusions

A specific ELISA towards the N-terminal neo-epitope site in LOXL2 was developed which detected significantly elevated serum levels from patients with above-mentioned cancer types or IPF compared to healthy controls.

LOX/LOXL in pulmonary fibrosis: potential therapeutic targets

Lysyl oxidase (LOX) and lysyl oxidase-like proteins (LOXL), a family of extracellular matrix (ECM) crosslinking enzymes that have been recognised as playing an important role in fibrogenesis for more than 40 years, are logical targets for antifibrotic treatments. Pulmonary fibrosis, especially idiopathic pulmonary fibrosis (IPF), is a progressive and lethal disease characterised by excessive deposition of ECM in the lung parenchyma. In this review, we discuss the current clinical approaches for IPF and review members of LOX family-LOX, LOXL1, LOXL2, LOXL3 and LOXL4 in IPF patients and in animal models of bleomycin-induced pulmonary fibrosis. Although these findings are controversial and require further validation, LOX/LOXL1/LOXL2 as potential therapeutic targets for IPF deserve continued attention. So far to our knowledge, LOXL3 or LOXL4 has not clearly shown specific therapeutic potential.

Bifunctional Molecular Probes for Activity-Based Visualization of Quinone-Dependent Amine Oxidases

The design, synthesis, and evaluation of two bifunctional molecular probes that can be used to visualize quinone-dependent amine oxidase enzymes in an activity-dependent manner are described. These probes use alkylhydrazines to irreversibly bind the target enzymes, which can then be visualized with either Western blotting or in-gel fluorescence. The results show that the Western blotting readout, which utilizes commercially available anti-nitrophenyl antibodies to detect a simple dinitrophenyl antigen, provides a stronger readout than the fluorescein-based fluorescence readout. This visualization strategy can be used to measure the potency of enzyme inhibitors by selectively visualizing the active enzyme that remains after treatment with an inhibitor. Looking forward, this probe molecule and visualization strategy will enable activity-based protein-profiling experiments, such as determining inhibitor selectivity values within full proteome mixtures, for this family of amine oxidase enzymes.

Lysyl oxidase-like protein secreted from an acidophilic red alga, Cyanidium caldarium

Cyanidium caldarium is a primitive acidophilic red alga which grown optimally at pH 1-3. When the alga was cultured at pH 6, which is the upper limit of acidity for its survival, most of the algal cells became large cells with four endospores which did not split into daughter cells. This suggests that the alga survives in the endospore state at pH 6 to protect against nutrient uptake deficiency due to low pH gradient across the cell membranes. The alga was also found to secrete an extracellular protein specifically at pH 6. The protein was identified to be lysyl oxidase-like protein, which had been reported to be widely distributed in the animal kingdom but not yet found in the plant kingdom. In the plant kingdom, only two primitive acidophilic algae, C. caldarium and Cyanidioschyzon merolae, possess a gene encoding this protein.

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.

Structural Remodeling of the Human Colonic Mesenchyme in Inflammatory Bowel Disease

Intestinal mesenchymal cells play essential roles in epithelial homeostasis, matrix remodeling, immunity, and inflammation. But the extent of heterogeneity within the colonic mesenchyme in these processes remains unknown. Using unbiased single-cell profiling of over 16,500 colonic mesenchymal cells, we reveal four subsets of fibroblasts expressing divergent transcriptional regulators and functional pathways, in addition to pericytes and myofibroblasts. We identified a niche population located in proximity to epithelial crypts expressing SOX6, F3 (CD142), and WNT genes essential for colonic epithelial stem cell function. In colitis, we observed dysregulation of this niche and emergence of an activated mesenchymal population. This subset expressed TNF superfamily member 14 (TNFSF14), fibroblastic reticular cell-associated genes, IL-33, and Lysyl oxidases. Further, it induced factors that impaired epithelial proliferation and maturation and contributed to oxidative stress and disease severity in vivo. Our work defines how the colonic mesenchyme remodels to fuel inflammation and barrier dysfunction in IBD.

•

Single-cell census of the colonic mesenchyme reveals unexpected heterogeneity

•

Identification of the colonic crypt niche mesenchymal cell expressing SOX6 and Wnts

•

Definition of fundamental aspects of mesenchymal remodeling in colitis

•

Analysis of colitis-associated mesenchymal cells reveals pathogenicity drivers

Multiscale mechanical effects of native collagen cross-linking in tendon

The hierarchical structure of tendon allows for attenuation of mechanical strain down decreasing length scales. While reorganization of collagen fibers accounts for microscale strain attenuation, cross-linking between collagen molecules contributes to deformation mechanisms at the fibrillar and molecular scales. Divalent and trivalent enzymatic cross-links form during the development of collagen fibrils through the enzymatic activity of lysyl oxidase (LOX). By establishing connections between telopeptidyl and triple-helical domains of adjacent molecules within collagen fibrils, these cross-links stiffen the fibrils by resisting intermolecular sliding. Ultimately, greater enzymatic cross-linking leads to less compliant and stronger tendon as a result of stiffer fibrils. In contrast, nonenzymatic cross-links such as glucosepane and pentosidine are not produced during development but slowly accumulate through glycation of collagen. Therefore, these cross-links are only expected to be present in significant quantities in advanced age, where there has been sufficient time for glycation to occur, and in diabetes, where the presence of more free sugar in the extracellular matrix increases the rate of glycation. Unlike enzymatic cross-links, current evidence suggests that nonenzymatic cross-links are at least partially isolated to the surface of collagen fibers. As a result, glycation has been proposed to primarily impact tendon mechanics by altering molecular interactions at the fiber interface, thereby diminishing sliding between fibers. Thus, increased nonenzymatic cross-linking decreases microscale strain attenuation and the viscous response of tendon. In conclusion, enzymatic and nonenzymatic collagen cross-links have demonstrable and distinct effects on the mechanical properties of tendon across different length scales.

Loxl2 is dispensable for dermal development, homeostasis and tumour stroma formation

Lysyl oxidase-like 2 (LOXL2) is a copper-dependent monoamine oxidase that contributes to the remodelling of the extracellular matrix (ECM) by cross linkage of collagen and elastin fibres and has emerged as a potential therapeutic target in cancer and fibrosis. In the skin, LOXL2 is essential for epidermal cell polarity and differentiation. However, its role in the dermis has not been evaluated. We found that Loxl2 is dispensable for mouse dermal development, maturation and homeostasis, yet affects dermal stiffness. Neither loss of Loxl2 nor increased Loxl2 expression affected dermal architecture following treatment with the phorbol ester TPA. Furthermore, Loxl2 expression did not alter the stroma of DMBA-TPA-induced tumours. We conclude that, although Loxl2 is expressed in both dermis and epidermis, its function appears largely confined to the epidermis.

Lysyl oxidase-like-2 mutations and reduced mRNA and protein expression in mid-dermal elastolysis

BACKGROUND

Mid-dermal elastolysis (MDE) is a rare skin condition, characterized by selective loss of elastic fibres in the mid dermis. The pathogenesis of MDE is still unclear.

AIM

To investigate expression of lysyl oxidase-like 2 (LOXL2) in a reasonable sample of patients with MDE and to search for mutations in LOXL2.

METHODS

We investigated archived lesional tissue of 13 patients with MDE and skin tissue samples of 10 sex- and age-matched healthy controls (HCs). Gene and protein expression of LOXL2 was investigated using real-time reverse-transcription PCR and immunohistochemistry. Mutation analysis was performed using the Sanger method.

RESULTS

We observed decreased LOXL2 mRNA expression in lesional skin of patients with MDE (0.48 ± 0.16) compared with healthy skin of the same patients (1.5 ± 0.51) and normal skin of HCs (1.9 ± 0.13). Compared with healthy patient skin (epidermis 2.38 ± 1.6, dermis 1.2 ± 1), LOXL2 protein expression in lesional patient skin (epidermis 1.1 ± 0.7, dermis 0.3 ± 0.45) was significantly decreased (P < 0.04 and P = 0.02, respectively). Mutation analysis of the entire LOXL2 gene could be performed for five patients, all of whom were found to have at least one mutation in the LOXL2 gene. Three of these had a mutation in the promoter region (c.967 G>C, c.1022 C>T, and c.1025 G>A, respectively), and one of them also had a mutation in the splice region of intron 11/exon 12 (IVS11-1 G>A). Of the remaining two patients, one had a mutation in exon 3 (T1391), and the other had a mutation in exon 11 (C663Y).

CONCLUSIONS

Our present data suggest that decreased elastin renewal due to LOXL2 mutations and consecutive reduced LOXL2 expression contribute to the pathogenesis of MDE.

Interactions between lysyl oxidases and ADAMTS proteins suggest a novel crosstalk between two extracellular matrix families

The extracellular matrix (ECM) regulates numerous cellular events in addition to providing structural integrity. Among several protein and enzyme families implicated in functions of the ECM, the lysyl oxidases and ADAMTS proteins are known to participate in microfibril and elastic fiber formation as well as ECM-associated signaling. A yeast two-hybrid screen to identify lysyl oxidase (LOX) binding proteins identified ADAMTSL4 as a potential interactor. We demonstrate here that several members of the LOX and ADAMTS families interact with one another. Upon investigating the interaction between LOX and ADAMTSL2 we found that the absence or inhibition of Lox affected ADAMTSL2 molecular forms and reduced its tissue levels. Thus, ADAMTSL2 stability and inter-molecular complexes may depend on the activity of lysyl oxidases.

The apparent competitive action of ECM proteases and cross-linking enzymes during fibrosis: Applications to drug discovery

Progressive loss of organ function in most organs is associated with fibrosis, a tissue state associated with abnormal matrix buildup. If highly progressive, the fibrotic process eventually leads to organ failure and death. Fibrosis is a basic connective tissue lesion defined by the increase in the amount of fibrillar extracellular matrix (ECM) components in a tissue or organ. In addition, intrinsic changes in important structural cells can induce the fibrotic response by regulating the differentiation, recruitment, proliferation and activation of extracellular matrix-producing myofibroblasts. ECM enzymes belonging to the family of matrix metalloproteinases (MMPs) and lysyl oxidases (LOXs) play a crucial role in ECM remodeling and regeneration. MMPs have a catalytic role in degradation of ECM, whereas LOX/LOXLs mediate ECM, especially collagen, cross-linking and stiffening. Importantly, enzymes from both families are elevated during the fibrotic response to tissue injury and its resolution. Yet, the apparent molecular competition or antagonistic activities of these enzyme families during the various stages of fibrosis is often overlooked. In this review, we discuss the diverse roles of MMPs and LOX/LOXL2 in chronic organ fibrosis. Finally, we review contemporary therapeutic strategies for fibrosis treatment, based on neutralization of MMP and LOX activity, as well as the development of novel drug delivery approaches.

LncRNAs in genetic basis of glaucoma

Glaucoma is an umbrella term used to designate a heterogeneous group of ocular disorders characterised by progressive excavation of the optic disc, optic atrophy and gradual loss of the visual field caused by the slow death of retinal ganglion cells and their axons. Glaucoma can potentially lead to blindness if left untreated. It usually starts from the periphery and progresses gradually toward the centre of the visual field. Vision loss caused by glaucoma is irreversible and causes a heavy burden on affected families and society, therefore the importance of early diagnosis and prevention should be emphasised. Genetic factors appear to play a role in glaucoma pathogenesis; it has been shown that individuals with a positive family history are at a greater risk because they are more likely predisposed be affected. Notable advances have been recorded in the past decade concerning the genetic and environmental factors likely to contribute or cause glaucoma with the discovery of multiple glaucoma-associated genes and genetic loci. Thorough investigations by a handful of studies on the function of long non-coding RNAs discovered that, although lacking protein-coding potential, lncRNAs can still participate in the regulation of gene expression at various levels, thus their possible implication in different disease aetiologies. In this review, we focus on the lncRNAs characteristics and its regulation, and summarise these results from separate, independent, glaucoma-related studies in addition to discussing possible pathways by which lncRNAs might contribute to glaucoma.

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

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

The fibrotic tumor stroma

Intratumoral fibrosis results from the deposition of a cross-linked collagen matrix by cancer-associated fibroblasts (CAFs). This type of fibrosis has been shown to exert mechanical forces and create a biochemical milieu that, together, shape intratumoral immunity and influence tumor cell metastatic behavior. In this Review, we present recent evidence that CAFs and tumor cells are regulated by provisional matrix molecules, that metastasis results from a change in the type of stromal collagen cross-link, and that fibrosis and inflammation perpetuate each other through proteolytic and chemotactic mediators released into the tumor stroma. We also discuss aspects of the emerging biology that have potential therapeutic value.

Association between lysyl oxidase and fibrotic focus in relation with inflammation in breast cancer

We hypothesized that lysyl oxidase (LOX) contributes to the formation of fibrotic focus (FF) in association with inflammation and serves a significant role in breast carcinogenesis. In the present study, the association between the expression of LOX family members and FF with regards to with inflammation was analyzed, and the prognostic significance of LOX and FF in breast cancer was investigated. Immunohistochemical staining for LOX, LOX-like protein (LOXL) 1, LOXL2 and LOXL3 was performed in primary breast cancer tissues. The status of FF within the tumor was assessed, including size and grade. Levels of inflammatory markers, intratumoral and peritumoral lymphocyte infiltration were also evaluated. The clinicopathological characteristics were evaluated from the medical records of patients. In the present study, the expression of LOX family members was not associated with the presence of FF. FF was identified to be associated with intratumoral and peritumoral inflammation, tumor stage, larger tumor size, lymph node metastasis, high histologic grade, and p53 expression. LOX and LOXL3 were associated with intratumoral, and peritumoral inflammation. Furthermore, LOXL1 was associated with intratumoral inflammation and interleukin-4. In addition, LOX was associated with cluster of differentiation 8⁺ T cells. LOXL3 was associated with expression of ER and PR, and molecular subtype. In the survival analysis, overall survival time was statistically significantly longer in the FF-negative compared with that in the FF-positive group. In conclusion, it was demonstrated that FF and the expression of LOX family members were associated with inflammation in breast cancer. FF was associated with poor prognostic markers of breast cancer. Further studies are required to clarify the mechanisms underlying the association between the LOX family, FF and inflammation in breast cancer.

Lysyl oxidase-like 3 is required for melanoma cell survival by maintaining genomic stability

Lysyl oxidase-like 3 (LOXL3) is a member of the lysyl oxidase family comprising multifunctional enzymes with depicted roles in extracellular matrix maturation, tumorigenesis, and metastasis. In silico expression analyses followed by experimental validation in a comprehensive cohort of human cell lines revealed a significant upregulation of LOXL3 in human melanoma. We show that LOXL3 silencing impairs cell proliferation and triggers apoptosis in various melanoma cell lines. Further supporting a pro-oncogenic role in melanoma, LOXL3 favors tumor growth in vivo and cooperates with oncogenic BRAF in melanocyte transformation. Upon LOXL3 depletion, melanoma cells display a faulty DNA damage response (DDR), characterized by ATM checkpoint activation and inefficient ATR activation leading to the accumulation of double-strand breaks (DSBs) and aberrant mitosis. Consistent with these findings, LOXL3 binds to proteins involved in the maintenance of genome integrity, in particular BRCA2 and MSH2, whose levels dramatically decrease upon LOXL3 depletion. Moreover, LOXL3 is required for efficient DSB repair in melanoma cells. Our results reveal an unexpected role for LOXL3 in the control of genome stability and melanoma progression, exposing its potential as a novel therapeutic target in malignant melanoma, a very aggressive condition yet in need for more effective treatment options.

Lysyl oxidases expression and histopathological changes of the diabetic rat nephron

Diabetic nephropathy (DN) is a major complication of diabetes, the accumulation of extracellular matrix (ECM) is considered an indication of nephropathological changes. Lysyl oxidases (LOXs) are also associated with ECM. However, the majority of studies on LOXs have focused on their potential role in renal fibrogenesis and there has no examination of LOXs expression or the correlation with histopathological changes of DN, including glomerular basement membrane (GBM) thickening and glomerulosclerosis. In this study, the association between histological changes and LOXs was explored using a type 2 diabetes model of male Zucker diabetic fatty rats. The expression of LOX and lysyl oxidase-like 1 to 3 (LOXL1 to 3) levels were evaluated by immunohistochemical staining. The expression levels of LOX and LOXL2 in the kidney tissue in the diabetic group were significantly higher compared with those of the control group, but LOXL1 and LOXL3 expression levels were not significantly different between the two groups. These results indicated that LOXL2 and LOX may be critical factors involved in the progression of DN.

Crosslinking Enzyme Lysyl Oxidase Modulates Scleral Remodeling in Form-Deprivation Myopia

PURPOSE

Scleral remodeling causes the excessive ocular elongation that underlies myopia. Lysyl oxidase (LOX), a copper-containing amine oxidase, can catalyze collagen and elastin crosslinking. The purpose of this study was to investigate the role of LOX in scleral remodeling in form-deprivation myopia (FDM).

METHODS

Seventy-five guinea pigs were randomly divided into five groups as follows: a normal control group, an FDM group, an FDM plus β-aminopropionitrile (BAPN) group, an FDM plus TGF-β1 (TGF-β1) group, and an FDM plus vehicle group. A translucent diffuser was used to induce FDM, and intravitreal injection was used to administer BAPN, TGF-β1 or vehicle. The scleral LOX and collagen gene and protein levels and the posterior scleral ultrastructure and biomechanics were measured.

RESULTS

In the FDM group, both the scleral LOX and collagen gene and protein levels were significantly lower than those in the control eyes. The collagen fibril diameters were significantly decreased in the FDM group compared with the diameters in the control group. A significant decrease in LOX gene and protein expression was observed after BAPN injection, and an increase was observed after TGF-β1 treatment compared with the levels in the FDM group. Additionally, the scleral collagen fibrils were significantly decreased in the BAPN-treated eyes but increased in the TGF-β1-treated eyes compared with the FDM eyes. The ultimate stress and Young's modulus of the sclera were lowest in the BAPN group, followed by the FDM group and the TGF-β1 group. The ultimate strain (%) of the sclera was lowest in the TGF-β1 group, followed by the FDM group and the BAPN group.

CONCLUSION

LOX expression was significantly lowered in myopic sclera. Modulating LOX expression induced a change in both the scleral collagen fibril diameter and the scleral biomechanics. Therefore, LOX may play a key role in the myopia scleral remodeling procedure.

Building collagen IV smart scaffolds on the outside of cells

Collagen IV scaffolds assemble through an intricate pathway that begins intracellularly and is completed extracellularly. Multiple intracellular enzymes act in concert to assemble collagen IV protomers, the building blocks of collagen IV scaffolds. After being secreted from cells, protomers are activated to initiate oligomerization, forming insoluble networks that are structurally reinforced with covalent crosslinks. Within these networks, embedded binding sites along the length of the protomer lead to the "decoration" of collagen IV triple helix with numerous functional molecules. We refer to these networks as "smart" scaffolds, which as a component of the basement membrane enable the development and function of multicellular tissues in all animal phyla. In this review, we present key molecular mechanisms that drive the assembly of collagen IV smart scaffolds.

Revealing Accessibility of Cryptic Protein Binding Sites within the Functional Collagen Fibril

Fibrillar collagens are the most abundant proteins in the extracellular matrix. Not only do they provide structural integrity to all of the connective tissues in the human body, but also their interactions with multiple cell receptors and other matrix molecules are essential to cell functions, such as growth, repair, and cell adhesion. Although specific binding sequences of several receptors have been determined along the collagen monomer, processes by which collagen binding partners recognize their binding sites in the collagen fibril, and the critical driving interactions, are poorly understood. The complex molecular assembly of bundled triple helices within the collagen fibril makes essential ligand binding sites cryptic or hidden from the molecular surface. Yet, critical biological processes that require collagen ligands to have access to interaction sites still occur. In this contribution, we will discuss the molecular packing of the collagen I fibril from the perspective of how collagen ligands access their known binding regions within the fibril, and we will present our analysis of binding site accessibility from the fibril surface. Understanding the basis of these interactions at the atomic level sets the stage for developing drug targets against debilitating collagen diseases and using collagen as drug delivery systems and new biomaterials.

Review article: next-generation transformative advances in the pathogenesis and management of autoimmune hepatitis

BACKGROUND

Advances in autoimmune hepatitis that transform current concepts of pathogenesis and management can be anticipated as products of ongoing investigations driven by unmet clinical needs and an evolving biotechnology.

AIM

To describe the advances that are likely to become transformative in autoimmune hepatitis, based on the direction of current investigations.

METHODS

Pertinent abstracts were identified in PubMed by multiple search terms. Full-length articles were selected for review, and a secondary bibliography was developed. The discovery process was repeated, and a tertiary bibliography was identified. The number of abstracts reviewed was 2830, and the number of full-length articles reviewed exceeded 150.

RESULTS

Risk-laden allelic variants outside the major histocompatibility complex (rs3184504, r36000782) are being identified by genome-wide association studies, and their gene products are potential therapeutic targets. Epigenetic changes associated with environmental cues can enhance the transcriptional activity of genes, and chromatin re-structuring and antagonists of noncoding molecules of ribonucleic acid are feasible interventions. The intestinal microbiome is a discovery field for microbial products and activated immune cells that may translocate to the periphery and respond to manipulation. Epidemiological studies and controlled interview-based surveys may implicate environmental and xenobiotic factors that warrant evidence-based changes in lifestyle, and site-directed molecular and cellular interventions promise to change the paradigm of treatment from one of blanket immunosuppression.

CONCLUSIONS

Advances in genetics, epigenetics, pathophysiology, epidemiology, and site-directed molecular and cellular interventions constitute the next generation of transformative advances in autoimmune hepatitis.

Proteolytic processing of lysyl oxidase-like-2 in the extracellular matrix is required for crosslinking of basement membrane collagen IV

Lysyl oxidase-like-2 (LOXL2) is an enzyme secreted into the extracellular matrix that crosslinks collagens by mediating oxidative deamination of lysine residues. Our previous work demonstrated that this enzyme crosslinks the 7S domain, a structural domain that stabilizes collagen IV scaffolds in the basement membrane. Despite its relevant role in extracellular matrix biosynthesis, little is known about the structural requirements of LOXL2 that enable collagen IV crosslinking. In this study, we demonstrate that LOXL2 is processed extracellularly by serine proteases, generating a 65-kDa form lacking the first two scavenger receptor cysteine-rich domains. Site-specific mutagenesis to prevent proteolytic processing generated a full-length enzyme that is active in vitro toward a soluble substrate, but fails to crosslink insoluble collagen IV within the extracellular matrix. In contrast, the processed form of LOXL2 binds to collagen IV and crosslinks the 7S domain. Together, our data demonstrate that proteolytic processing is an important event that allows LOXL2-mediated crosslinking of basement membrane collagen IV.

The effect of estrogen on tendon and ligament metabolism and function

Tendons and ligaments are crucial structures inside the musculoskeletal system. Still many issues in the treatment of tendon diseases and injuries have yet not been resolved sufficiently. In particular, the role of estrogen-like compound (ELC) in tendon biology has received until now little attention in modern research, despite ELC being a well-studied and important factor in the physiology of other parts of the musculoskeletal system. In this review we attempt to summarize the available information on this topic and to determine many open questions in this field.

Antibody-mediated blockade of JMJD6 interaction with collagen I exerts antifibrotic and antimetastatic activities

JMJD6 is known to localize in the nucleus, exerting histone arginine demethylase and lysyl hydroxylase activities. A novel localization of JMJD6 in the extracellular matrix, resulting from its secretion as a soluble protein, was unveiled by a new anti-JMJD6 mAb called P4E11, which was developed to identify new targets in the stroma. Recombinant JMJD6 binds with collagen type I (Coll-I), and distinct JMJD6 peptides interfere with collagen fibrillogenesis, collagen-fibronectin interaction, and adhesion of human tumor cells to the collagen substrate. P4E11 and collagen binding to JMJD6 are mutually exclusive because the amino acid sequences of JMJD6 necessary for the interaction with Coll-I are part of the conformational epitope recognized by P4E11. In mice injected with mouse 4T1 breast carcinoma cells, treatment with P4E11 reduced fibrosis at the primary tumor and prevented lung metastases. Reduction of fibrosis has also been documented in human breast and ovarian tumors (MDA-MB-231 and IGROV1, respectively) xenotransplanted into immunodeficient mice treated with P4E11. In summary, this study uncovers a new localization and function for JMJD6 that is most likely independent from its canonical enzymatic activities, and demonstrates that JMJD6 can functionally interact with Coll-I. P4E11 mAb, inhibiting JMJD6/Coll-I interaction, represents a new opportunity to target fibrotic and tumor diseases.-Miotti, S., Gulino, A., Ferri, R., Parenza, M., Chronowska, A., Lecis, D., Sangaletti, S., Tagliabue, E., Tripodo, C., Colombo, M. P. Antibody-mediated blockade of JMJD6 interaction with collagen I exerts antifibrotic and antimetastatic activities.

Protein analysis and gene expression indicate differential vulnerability of Iberian fish species under a climate change scenario

Current knowledge on the biological responses of freshwater fish under projected scenarios of climate change remains limited. Here, we examine differences in the protein configuration of two endemic Iberian freshwater fish species, Squalius carolitertii and the critically endangered S. torgalensis that inhabit in the Atlantic-type northern and in the Mediterranean-type southwestern regions, respectively. We performed protein structure modeling of fourteen genes linked to protein folding, energy metabolism, circadian rhythms and immune responses. Structural differences in proteins between the two species were found for HSC70, FKBP52, HIF1α and GPB1. For S. torgalensis, besides structural differences, we found higher thermostability for two proteins (HSP90 and GBP1), which can be advantageous in a warmer environment. Additionally, we investigated how these species might respond to projected scenarios of 3° climate change warming, acidification (ΔpH = -0.4), and their combined effects. Significant changes in gene expression were observed in response to all treatments, particularly under the combined warming and acidification. While S. carolitertii presented changes in gene expression for multiple proteins related to folding (hsp90aa1, hsc70, fkbp4 and stip1), only one such gene was altered in S. torgalensis (stip1). However, S. torgalensis showed a greater capacity for energy production under both the acidification and combined scenarios by increasing cs gene expression and maintaining ldha gene expression in muscle. Overall, these findings suggest that S. torgalensis is better prepared to cope with projected climate change. Worryingly, under the simulated scenarios, disturbances to circadian rhythm and immune system genes (cry1aa, per1a and gbp1) raise concerns for the persistence of both species, highlighting the need to consider multi-stressor effects when evaluating climate change impacts upon fish. This work also highlights that assessments of the potential of endangered freshwater species to cope with environmental change are crucial to help decision-makers adopt future conservation strategies.

Secreted molecules inducing epithelial-to-mesenchymal transition in cancer development

The epithelial-mesenchymal transition (EMT) is a biologic process that allows a polarized epithelial cell to undergo multiple biochemical changes that enable it to assume a mesenchymal cell phenotype. EMT is involved in embryo development, wound healing, tissue regeneration, organ fibrosis and has also been proposed as the critical mechanism for the acquisition of malignant phenotypes by epithelial cancer cells. These cells have been shown to acquire a mesenchymal phenotype when localized at the invasive front of primary tumours increasing aggressiveness, invasiveness, metastatic potential and resistance to chemotherapy. There is now increasing evidence demonstrating that a crucial role in the development of this process is played by factors secreted by cells of the tumour microenvironment or by the tumour cells themselves. This review summarises the current knowledge of EMT induction in cancer by paracrine or autocrine mechanisms, by exosomes or free proteins and miRNAs.

Reorganized Collagen in the Tumor Microenvironment of Gastric Cancer and Its Association with Prognosis

Collagen components in the tumor microenvironment substantially influence cancer pathogenesis and progression. Nevertheless, in gastric cancer, collagen status and its prognostic role remain unclear. Using picrosirius red staining and immunohistochemistry, we found that collagen deposition was significantly increased in gastric cancer when compared with non-neoplastic tissues, and in cancer stroma, more immature collagen components were present, suggesting a qualitative change. Furthermore, the morphology of collagen fibers could be weakly, moderately or strongly changed in gastric cancer; when weakly or moderately changed, they appeared similar to normal collagen fibers, except for a higher linearization and density; when strongly changed, they were thicker and less eosinophilic, sharply differently from their normal counterparts. In addition, we found abundant myofibroblasts and elevated expression of lysyl oxidase-like 2 (the enzyme that mediates crosslinking of collagen molecules) in cancer stroma, which might contribute to the increased collagen deposition and crosslinking. Last, five collagen architectural parameters (alignment, density, width, length and straightness) were analyzed with second harmonic generation imaging, a highly specific technology for detection of collagen fibers, and our data indicated that all the parameters were significantly increased in the tumor microenvironment. Of the five parameters, collagen width was the most powerful parameter in predicting 5-year overall survival, and increased collagen width was associated with reduced survival. The prognostic value of collagen width was superior to traditional clinicopathological parameters, and this was validated in two unrelated gastric cancer cohorts that contained 225 and 151 patients. Collectively, the collagen status (content, maturity, morphology and architecture) was profoundly reorganized in the tumor microenvironment of gastric cancer, and collagen width could serve as a valuable prognostic indicator.

Inhibition of Lysyl Oxidases Impairs Migration and Angiogenic Properties of Tumor-Associated Pericytes

Pericytes are important cellular components of the tumor microenviroment with established roles in angiogenesis and metastasis. These two cancer hallmarks are modulated by enzymes of the LOX family, but thus far, information about LOX relevance in tumor-associated pericytes is lacking. Here, we performed a comparative characterization of normal and tumoral pericytes and report for the first time the modulatory effects of LOX enzymes on activated pericyte properties. Tumoral pericytes isolated from childhood ependymoma and neuroblastoma specimens displayed angiogenic properties in vitro and expressed typical markers, including CD146, NG2, and PDGFRβ. Expression of all LOX family members could be detected in both normal and tumor-associated pericytes. In most pericyte samples, LOXL3 was the family member displaying the highest transcript levels. Inhibition of LOX/LOXL activity with the inhibitor β-aminopropionitrile (βAPN) significantly reduced migration of pericytes, while proliferation rates were kept unaltered. Formation of tube-like structures in vitro by pericytes was also significantly impaired upon inhibition of LOX/LOXL activity with βAPN, which induced more prominent effects in tumor-associated pericytes. These findings reveal a novel involvement of the LOX family of enzymes in migration and angiogenic properties of pericytes, with implications in tumor development and in therapeutic targeting tumor microenvironment constituents.

Association of altered collagen content and lysyl oxidase expression in degenerative mitral valve disease

BACKGROUND

Collagen cross-linking is mediated by lysyl oxidase (LOX) enzyme in the extracellular matrix (ECM) of mitral valve leaflets. Alterations in collagen content and LOX protein expression in the ECM of degenerative mitral valve may enhance leaflet expansion and disease severity.

METHODS

Twenty posterior degenerative mitral valve leaflets from patients with severe mitral regurgitation were obtained at surgery. Five normal posterior mitral valve leaflets procured during autopsy served as controls. Valvular interstitial cells (VICs) density was quantified by immunohistochemistry, collagen Types I and III by picro-sirius red staining and immunohistochemistry, and proteoglycans by alcian blue staining. Protein expression of LOX and its mediator TGFβ1 were quantified by immunofluorescence and gene expression by PCR.

RESULTS

VIC density was increased, structural Type I collagen density was reduced, while reparative Type III collagen and proteoglycan densities were increased (P<.0001) with an increase in spongiosa layer thickness in myxomatous valves. These changes were associated with a reduction in LOX (P<.0001) and increase in TGFβ1 protein expression (P<.0001). However, no significant change was seen in gene expression. Linear regression analysis identified a correlation between Type I collagen density and LOX grade (R²=0.855; P<.0001).

CONCLUSIONS

Reduced Type I collagen density with a simultaneous increase in Type III collagen and proteoglycan densities possibly contributes to spongiosa layer expansion resulting in incompetent mitral valve leaflets. Observed changes in Type I and III collagen densities in Degenerative Mitral Valve Disease may be secondary to alterations in LOX protein expression, contributing to disorganization of ECM and disease severity.

Fibronectin: How Its Aberrant Expression in Tumors May Improve Therapeutic Targeting

Fibronectin is a matrix glycoprotein which has not only been found to be over-expressed in several cancers, but has been shown to participate in several steps of tumorigenesis. The purpose of this review is to illustrate how aberrant fibronectin expression influences tumor growth, invasion, metastasis and therapy resistance. In particular, this review will focus on the interactions between cell receptor ligands and fibronectin and how this interaction influences downstream signaling events that aid tumor progression. This review will further discuss the possible implications of therapeutic drugs directed against fibronectin and/or cellular interactions with fibronectin and will additionally discuss novel approaches by which to limit intra- and extra-tumoral fibronectin expression and the cellular events which lead to aberrant fibronectin expression. It is anticipated that these studies will set a basis for future research that will not only aid understanding of fibronectin and its prognostic significance, but will further elucidate novel targets for therapeutics.

Comparing hydrazine-derived reactive groups as inhibitors of quinone-dependent amine oxidases

Lysyl oxidase has emerged as an important enzyme in cancer metastasis. Its activity has been reported to become upregulated in several types of cancer, and blocking its activity has been shown to limit the metastatic potential of various cancers. The small-molecules phenylhydrazine and β-aminopropionitrile are known to inhibit lysyl oxidase; however, issues of stability, toxicity, and poorly defined mechanisms limit their potential use in medical applications. The experiments presented herein evaluate three other families of hydrazine-derived compounds – hydrazides, alkyl hydrazines, and semicarbazides – as irreversible inhibitors of lysyl oxidase including determining the kinetic parameters and comparing the inhibition selectivities for lysyl oxidase against the topaquinone-containing diamine oxidase from lentil seedlings. The results suggest that the hydrazide group may be a useful core functionality that can be developed into potent and selective inhibitors of lysyl oxidase and eventually find application in cancer metastasis research.

Three distinct cell populations express extracellular matrix proteins and increase in number during skeletal muscle fibrosis

Tissue extracellular matrix (ECM) provides structural support and creates unique environments for resident cells (Bateman JF, Boot-Handford RP, Lamandé SR. Nat Rev Genet 10: 173-183, 2009; Kjaer M. Physiol Rev 84: 649-98, 2004). However, the identities of cells responsible for creating specific ECM components have not been determined. In striated muscle, the identity of these cells becomes important in disease when ECM changes result in fibrosis and subsequent increased tissue stiffness and dysfunction. Here we describe a novel approach to isolate and identify cells that maintain the ECM in both healthy and fibrotic muscle. Using a collagen I reporter mouse, we show that there are three distinct cell populations that express collagen I in both healthy and fibrotic skeletal muscle. Interestingly, the number of collagen I-expressing cells in all three cell populations increases proportionally in fibrotic muscle, indicating that all cell types participate in the fibrosis process. Furthermore, while some profibrotic ECM and ECM-associated genes are significantly upregulated in fibrotic muscle, the fibrillar collagen gene expression profile is not qualitatively altered. This suggests that muscle fibrosis in this model results from an increased number of collagen I-expressing cells and not the initiation of a specific fibrotic collagen gene expression program. Finally, in fibrotic muscle, we show that these collagen I-expressing cell populations differentially express distinct ECM proteins-fibroblasts express the fibrillar components of ECM, fibro/adipogenic progenitors cells differentially express basal laminar proteins, and skeletal muscle progenitor cells differentially express genes important for the satellite cell.

LOXL3-sv2, a novel variant of human lysyl oxidase-like 3 (LOXL3), functions as an amine oxidase

Human lysyl oxidase-like 3 (LOXL3) functions as a copper-dependent amine oxidase toward collagen and elastin. The LOXL3 protein contains four scavenger receptor cysteine-rich (SRCR) domains in the N-terminus in addition to the C-terminal characteristic domains of the lysyl oxidase (LOX) family, such as a copper-binding domain, a cytokine receptor‑like domain and residues for the lysyl-tyrosyl quinone cofactor. Using BLASTN searches, we identified a novel variant of LOXL3 (termed LOXL3-sv2), which lacked the sequences corresponding to exons 4 and 5 of LOXL3. The LOXL3-sv2 mRNA is at least 2,398 bp in length, encoding a 608 amino acid-long polypeptide with a calculated molecular mass of 67.4 kDa. The deletion of exons 4 and 5 do not change the open-reading frame of LOXL3 but results in deletion of the SRCR domain 2. The recombinant LOXL3-sv2 protein showed a β-aminopropionitrile-inhibitable amine oxidase activity toward collagen type I. In RT-PCR analysis, LOXL3-sv2 was detected in all human tissues tested, along with LOXL3 and LOXL3-sv1, a previously identified variant of LOXL3. These findings indicate that the human LOXL3 gene encodes at least three variants, LOXL3, LOXL3-sv1 and LOXL3-sv2, all of which function as amine oxidases.

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.

Axial and limb muscle development: dialogue with the neighbourhood

Skeletal muscles are part of the musculoskeletal system which also includes nerves, tendons, connective tissue, bones and blood vessels. Here we review the development of axial and limb muscles in amniotes within the context of their surrounding tissues in vivo. We highlight the reciprocal dialogue mediated by signalling factors between cells of these adjacent tissues and developing muscles and also demonstrate its importance from the onset of muscle cell differentiation well into foetal development. Early embryonic tissues secrete factors which are important regulators of myogenesis. However, later muscle development relies on other tissue collaborators, such as developing nerves and connective tissue, which are in turn influenced by the developing muscles themselves. We conclude that skeletal muscle development in vivo is a compelling example of the importance of reciprocal interactions between developing tissues for the complete and coordinated development of a functional system.

Molecular Cues Guiding Matrix Stiffness in Liver Fibrosis

Tissue and matrix stiffness affect cell properties during morphogenesis, cell growth, differentiation, and migration and are altered in the tissue remodeling following injury and the pathological progression. However, detailed molecular mechanisms underlying alterations of stiffness in vivo are still poorly understood. Recent engineering technologies have developed powerful techniques to characterize the mechanical properties of cell and matrix at nanoscale levels. Extracellular matrix (ECM) influences mechanical tension and activation of pathogenic signaling during the development of chronic fibrotic diseases. In this short review, we will focus on the present knowledge of the mechanisms of how ECM stiffness is regulated during the development of liver fibrosis and the molecules involved in ECM stiffness as a potential therapeutic target for liver fibrosis.