Proline/arginine-rich end leucine-rich repeat protein N-terminus is a novel osteoclast antagonist that counteracts bone loss

Application of integrated omics in aseptic loosening of prostheses after hip replacement

Aseptic loosening (AL) of artificial hip joints is the most common complication following hip replacement surgery. A total of eight patients diagnosed with AL following total hip arthroplasty (THA) undergoing total hip replacement and eight control patients diagnosed with avascular necrosis of femoral head (ANFH) or femoral neck fracture undergoing THA were enrolled. The samples of the AL group were from synovial tissue surrounding the lining/head/neck of the prosthesis, and the samples of the control group were from the synovium in the joint cavity. The present study utilized second‑generation high‑throughput sequencing and mass spectrometry to detect differentially expressed genes, proteins and metabolites in the samples, as well as Gene Ontology and Kyoto Encyclopedia of Genes and Genomes analysis. Key genes cytokine receptor‑like factor‑1 (CRLF1) and glutathione‑S transferase µ1 (GSTM1) expression levels were verified by reverse transcription‑quantitative PCR and western blotting. The integrated transcriptomics, proteomics and untargeted metabolomics analyses revealed characteristic metabolite changes (biosynthesis of guanine, L‑glycine and adenosine) and decreased CRLF1 and GSTM1 in AL, which were primarily associated with amino acid metabolism and lipid metabolism. In summary, the present study may uncover the underlying mechanisms of AL pathology and provide stable and accurate biomarkers for early warning and diagnosis.

Primary Bone Tumors and Breast Cancer-Induced Bone Metastases: In Vivo Animal Models and New Alternative Approaches

Bone is the preferential site of metastasis for the most common tumors, including breast cancer. On the other hand, osteosarcoma is the primary bone cancer that most commonly occurs and causes bone cancer-related deaths in children. Several treatment strategies have been developed so far, with little or no efficacy for patient survival and with the development of side effects. Therefore, there is an urgent need to develop more effective therapies for bone primary tumors and bone metastatic disease. This almost necessarily requires the use of in vivo animal models that better mimic human pathology and at the same time follow the ethical principles for the humane use of animal testing. In this review we aim to illustrate the main and more suitable in vivo strategies employed to model bone metastases and osteosarcoma. We will also take a look at the recent technologies implemented for a partial replacement of animal testing.

Correlation of the tumor escape phenotype with loss of PRELP expression in melanoma

BACKGROUND

Despite immunotherapies having revolutionized the treatment of advanced cutaneous melanoma, effective and durable responses were only reported in a few patients. A better understanding of the interaction of melanoma cells with the microenvironment, including extracellular matrix (ECM) components, might provide novel therapeutic options. Although the ECM has been linked to several hallmarks of cancer, little information is available regarding the expression and function of the ECM protein purine-arginine-rich and leucine-rich protein (PRELP) in cancer, including melanoma.

METHODS

The structural integrity, expression and function of PRELP, its correlation with the expression of immune modulatory molecules, immune cell infiltration and clinical parameters were determined using standard methods and/or bioinformatics.

RESULTS

Bioinformatics analysis revealed a heterogeneous, but statistically significant reduced PRELP expression in available datasets of skin cutaneous melanoma when compared to adjacent normal tissues, which was associated with reduced patients' survival, low expression levels of components of the MHC class I antigen processing machinery (APM) and interferon (IFN)-γ signal transduction pathway, but increased expression of the transforming growth factor (TGF)-β isoform 1 (TFGB1) and TGF-β receptor 1 (TGFBR1). In addition, a high frequency of intra-tumoral T cells directly correlated with the expression of MHC class I and PRELP as well as the T cell attractant CCL5 in melanoma lesions. Marginal to low PRELP expression levels were found in the 47/49 human melanoma cell lines analysis. Transfection of PRELP into melanoma cell lines restored MHC class I surface expression due to transcriptional upregulation of major MHC class I APM and IFN-γ pathway components. In addition, PRELP overexpression is accompanied by high CCL5 secretion levels in cell supernatant, an impaired TGF-β signaling as well as a reduced cell proliferation, migration and invasion of melanoma cells.

CONCLUSIONS

Our findings suggest that PRELP induces the expression of MHC class I and CCL5 in melanoma, which might be involved in an enhanced T cell recruitment and immunogenicity associated with an improved patients' outcome. Therefore, PRELP might serve as a marker for predicting disease progression and its recovery could revert the tumorigenic phenotype, which represents a novel therapeutic option for melanoma.

Obesity Modifies the Proteomic Profile of the Periodontal Ligament

This study aimed to assess the obesity effects on the proteomic profile of the periodontal ligament of rats submitted to obesity induction by a high-fat diet. Eight Holtzman rats were divided into control (n = 3) and obese (n = 5) groups. The maxillae were histologically processed for laser capture microdissection of the periodontal ligament of the first maxillary molars. Peptide mixtures were analyzed by LC-MS/MS. A total of 1379 proteins were identified in all groups. Among them, 335 (24.30%) were exclusively detected in the obese group, while 129 (9.35%) proteins were uniquely found in the control group. Out of the 110 (7.98%) differentially abundant proteins, 10 were more abundant and 100 had decreased abundance in the obese group. A gene ontology analysis showed some proteins related to obesity in the “extracellular exosome” term among differentially identified proteins in the gene ontology cellular component terms Prelp, Sec13, and Sod2. These three proteins were upregulated in the obese group (p < 0.05), as shown by proteomic and immunohistochemistry analyses. In summary, our study presents novel evidence that the proteomic profile of the periodontal ligament is altered in experimental obesity induction, providing a list of differentially abundant proteins associated with obesity, which indicates that the periodontal ligament is responsive to obesity.

Tumor Suppressive Role of the PRELP Gene in Ovarian Clear Cell Carcinoma

Ovarian clear cell carcinoma (OCCC) has a poor prognosis, and its therapeutic strategy has not been established. PRELP is a leucine-rich repeat protein in the extracellular matrix of connective tissues. Although PRELP anchors the basement membrane to the connective tissue and is absent in most epithelial cancers, much remains unknown regarding its function as a regulator of ligand-mediated signaling pathways. Here, we obtained sets of differentially expressed genes by PRELP expression using OCCC cell lines. We found that more than 1000 genes were significantly altered by PRELP expression, particularly affecting the expression of a group of genes involved in the PI3K-AKT signaling pathway. Furthermore, we revealed the loss of active histone marks on the loci of the PRELP gene in patients with OCCC and how its forced expression inhibited cell proliferation. These findings suggest that PRELP is not only a molecule anchored in connective tissues but is also a signaling molecule acting in a tumor-suppressive manner. It can serve as the basis for early detection and novel therapeutic approaches for OCCC toward precision medicine.

Ginsenoside Rb1 prevents osteoporosis via the AHR/PRELP/NF-κB signaling axis

BACKGROUND

Accumulating clinical and experimental evidence shows multiple biological effects of ginsenoside Rb1 (GRb1) in the treatment of aging related diseases such as osteoporosis (OP). Recently, GRb1 has attracted extensive attention as an anti-osteoporosis agent. Here, we sought to identify the mechanism by which GRb1 improves OP.

METHODS

A dexamethasone (DEX)-induced rat model of OP was constructed and the rats were treated with GRb1 to examine its role in OP. We screened the action targets of GRb1 online and validated by performing functional experiments. The correlation between aryl hydrocarbon receptor (AHR) and proline/arginine-rich end leucine-rich repeat protein (PRELP) was identified through luciferase and chromatin immunoprecipitation assays. In the isolated osteoblasts from DEX-induced OP rats, the expression of osteogenic differentiation-associated genes, and nuclear factor-kappa B (NF-κB) pathway-related genes, mineralization, and number of calcium nodules were assessed.

RESULTS

GRb1 enhanced the differentiation of osteoblasts, the mechanism of which was related to upregulation of AHR. AHR could promote the transcription of PRELP by binding to the PRELP promoter region and consequently caused its upregulation. Meanwhile, PRELP inhibited the activation of the NF-κB pathway, which underlay the promoting impact of AHR in the osteogenic differentiation. Additionally, GRb1 could ameliorate OP in DEX-induced rats via the AHR/PRELP/NF-κB axis.

CONCLUSIONS

Our findings demonstrate that GRb1 might function as an effective candidate to prevent the progression of OP via regulation of the AHR/PRELP/NF-κB axis, revealing a new molecular mechanism underpinning the impact of GRb1 in the progression of OP and offering a theoretical contribution to the treatment of OP.

Proteomic identification and validation of novel interactions of the putative tumor suppressor PRELP with membrane proteins including IGFI-R and p75NTR

Proline and arginine-rich end leucine-rich repeat protein (PRELP) is a member of the small leucine-rich repeat proteoglycans (SLRPs) family. Levels of PRELP mRNA are downregulated in many types of cancer, and PRELP has been reported to have suppressive effects on tumor cell growth, although the molecular mechanism has yet to be fully elucidated. Given that other SLRPs regulate signaling pathways through interactions with various membrane proteins, we reasoned that PRELP likely interacts with membrane proteins to maintain cellular homeostasis. To identify membrane proteins that interact with PRELP, we carried out coimmunoprecipitation coupled with mass spectrometry (CoIP-MS). We prepared membrane fractions from Expi293 cells transfected to overexpress FLAG-tagged PRELP or control cells and analyzed samples precipitated with anti-FLAG antibody by mass spectrometry. Comparison of membrane proteins in each sample identified several that seem to interact with PRELP; among them, we noted two growth factor receptors, insulin-like growth factor I receptor (IGFI-R) and low-affinity nerve growth factor receptor (p75NTR), interactions with which might help to explain PRELP's links to cancer. We demonstrated that PRELP directly binds to extracellular domains of these two growth factor receptors with low micromolar affinities by surface plasmon resonance analysis using recombinant proteins. Furthermore, cell-based analysis using recombinant PRELP protein showed that PRELP suppressed cell growth and affected cell morphology of A549 lung carcinoma cells, also at micromolar concentration. These results suggest that PRELP regulates cellular functions through interactions with IGFI-R and p75NTR and provide a broader set of candidate partners for further exploration.

Pharmacological Inhibition of the Skeletal IKKβ Reduces Breast Cancer-Induced Osteolysis

IKKβ has previously been implicated in breast cancer bone metastasis and bone remodelling. However, the contribution of IKKβ expressed by bone cells of the tumour microenvironment to breast cancer-induced osteolysis has yet to be investigated. Here, we studied the effects of the verified selective IKKβ inhibitors IKKβ^III or IKKβ^V on osteoclast formation and osteoblast differentiation in vitro and in vivo, human and mouse breast cancer cells' support for osteoclast formation and signalling in vitro and osteolysis ex vivo and in immunocompetent mice after supracalvarial injection of human MDA-MB-231 conditioned medium or intra-cardiac injection of syngeneic 4T1 breast cancer cells. Pre-treatment with IKKβ^III or IKKβ^V prior to exposure to tumour-derived factors from human and mouse breast cancer cell lines protected against breast cancer-induced osteolysis in two independent immunocompetent mouse models of osteolysis and the ex vivo calvarial bone organ system. Detailed functional and mechanistic studies showed that direct inhibition of IKKβ kinase activity in osteoblasts and osteoclasts was associated with significant reduction of osteoclast formation, enhanced osteoclast apoptosis and reduced the ability of osteoblasts to support osteoclastogenesis in vitro. When combined with previous findings that suggest NFκB inhibition reduces breast cancer tumorigenesis and metastasis our present findings have an important clinical implication on raising the possibility that IKKβ inhibitors, as bone anabolics, osteoclast inhibitors as well as anti-metastatic agents, may have advantages over anti-osteoclasts agents in the treatment of both skeletal and non-skeletal complications associated with metastatic breast cancer.

Regulation of breast cancer induced bone disease by cancer-specific IKKβ

NFκB is implicated in breast cancer bone metastasis and skeletal remodelling. However, the role of IKKβ, a key component of the canonical NFκB pathway, in the regulation of breast cancer osteolytic metastasis has not been investigated. Here, we describe the cancer-specific contribution of IKKβ to bone metastasis, skeletal tumour growth and osteolysis associated with breast cancer. IKKβ is highly expressed in invasive breast tumours and its level of expression was higher in patients with bone metastasis. IKKβ overexpression in parental MDA-MD-231 breast cancer cells, promoted mammary tumour growth but failed to convey osteolytic potential to these cells in mice. In contrast, IKKβ overexpression in osteotropic sub-clones of MDA-MB-231 cells with differing osteolytic phenotypes increased incidence of bone metastasis, exacerbated osteolysis and enhanced skeletal tumour growth, whereas its knockdown was inhibitory. Functional and mechanistic studies revealed that IKKβ enhanced the ability of osteotropic MDA-MB-231 cells to migrate, increase osteoclastogenesis, and to inhibit osteoblast differentiation via a mechanism mediated, at least in part, by cytoplasmic sequestering of FoxO3a and VEGFA production. Thus, tumour-selective manipulation of IKKβ and its interaction with FoxO3a may represent a novel strategy to reduce the development of secondary breast cancer in the skeleton.

Osteoblast-Derived Extracellular Vesicles Are Biological Tools for the Delivery of Active Molecules to Bone

Extracellular vesicles (EVs) are newly appreciated regulators of tissue homeostasis and a means of intercellular communication. Reports have investigated the role of EVs and their cargoes in cellular regulation and have tried to fine-tune their biotechnological use, but to date very little is known on their function in bone biology. To investigate the relevance of EV-mediated communication between bone cells, we isolated EVs from primary mouse osteoblasts and assessed membrane integrity, size, and structure by transmission electron microscopy (TEM) and fluorescence-activated cell sorting (FACS). EVs actively shuttled loaded fluorochromes to osteoblasts, monocytes, and endothelial cells. Moreover, osteoblast EVs contained mRNAs shared with donor cells. Osteoblasts are known to regulate osteoclastogenesis, osteoclast survival, and osteoclast function by the pro-osteoclastic cytokine, receptor activator of nuclear factor κ-B ligand (Rankl). Osteoblast EVs were enriched in Rankl, which increased after PTH treatment. These EVs were biologically active, supporting osteoclast survival. EVs isolated from rankl^-/- osteoblasts lost this pro-osteoclastic function, indicating its Rankl-dependence. They integrated ex vivo into murine calvariae, and EV-shuttled fluorochromes were quickly taken up by the bone upon in vivo EV systemic administration. Rankl^-/- mice lack the osteoclast lineage and are negative for its specific marker tartrate-resistant acid phosphatase (TRAcP). Treatment of rankl^-/- mice with wild-type osteoblast EVs induced the appearance of TRAcP-positive cells in an EV density-dependent manner. Finally, osteoblast EVs internalized and shuttled anti-osteoclast drugs (zoledronate and dasatinib), inhibiting osteoclast activity in vitro and in vivo. We conclude that osteoblast EVs are involved in intercellular communication between bone cells, contribute to the Rankl pro-osteoclastic effect, and shuttle anti-osteoclast drugs, representing a potential means of targeted therapeutic delivery. © 2017 The Authors. Journal of Bone and Mineral Research Published by Wiley Periodicals Inc.

TRAF2 in osteotropic breast cancer cells enhances skeletal tumour growth and promotes osteolysis

NFκB plays an important role in inflammation and bone remodelling. Tumour necrosis factor receptor associated factor 2 (TRAF2), a key component of NFκB signalling, has been identified as an oncogene, but its role in the regulation of breast cancer osteolytic metastasis remains unknown. Here, we report that stable overexpression of TRAF2 in parental and osteotropic sub-clones of human MDA-MB-231 (MDA-231) breast cancer cells increased cell growth and motility in vitro, whereas TRAF2 knockdown was inhibitory. In vivo, TRAF2 overexpression in the parental MDA-231-P cells enhanced tumour growth after orthotopic injection into the mammary fat pad of mice but failed to promote the metastasis of these cells to bone. In contrast, overexpression of TRAF2 in osteotropic MDA-231-BT cells increased skeletal tumour growth, enhanced osteoclast formation and worsened osteolytic bone loss after intra-tibial injection in mice. Mechanistic and functional studies in osteotropic MDA-231-BT and osteoclasts revealed that upregulation of TRAF2 increased the ability of osteotropic MDA-231-BT cells to migrate and to enhance osteoclastogenesis by a mechanism dependent, at least in part, on NFκB activation. Thus, the TRAF2/NFκB axis is implicated in the regulation of skeletal tumour burden and osteolysis associated with advanced breast cancer.

Non-conventional role of haemoglobin beta in breast malignancy

Background:

Besides its role as oxygen transporter, recent findings suggest that haemoglobin beta (HBB) may have roles in other contexts.

Methods:

We evaluated the impact of HBB expression in primary human breast cancers, and in breast cancer cell lines overexpressing HBB by in vitro and in vivo studies. Publicly available microarray databases were used to perform multivariate survival analyses.

Results:

A significantly higher expression of HBB was observed in invasive carcinoma histotypes vs in situ counterparts, along with a positive correlation between HBB and the Ki67 proliferation marker. HBB-overexpressing breast cancer cells migrate and invade more, show HIF-1α upregulation and their conditioned media enhances angiogenesis. Blocking the oxygen-binding site of HBB reverts the increase of migration and HIF-1α upregulation observed in HBB-overexpressing breast cancer cells. Orthotopically implanted MDA-MB-231 overexpressing HBB (MDA-HBB) generated tumours with faster growth rate and increased neoangiogenesis. Moreover, local recurrence and visceral metastases were observed only in MDA-HBB-implanted mice. Similar results were observed with 4T1 mouse breast cancer cells. Finally, bioinformatics analyses of public data sets correlated high HBB expression with lower overall survival.

Conclusions:

HBB expression increases breast cancer cells aggressiveness and associates with poor prognosis, pointing to HBB as a novel biomarker for breast cancer progression.

Murine models of breast cancer bone metastasis

Bone metastases cause significant morbidity and mortality in late-stage breast cancer patients and are currently considered incurable. Investigators rely on translational models to better understand the pathogenesis of skeletal complications of malignancy in order to identify therapeutic targets that may ultimately prevent and treat solid tumor metastasis to bone. Many experimental models of breast cancer bone metastases are in use today, each with its own caveats. In this methods review, we characterize the bone phenotype of commonly utilized human- and murine-derived breast cell lines that elicit osteoblastic and/or osteolytic destruction of bone in mice and report methods for optimizing tumor-take in murine models of bone metastasis. We then provide protocols for four of the most common xenograft and syngeneic inoculation routes for modeling breast cancer metastasis to the skeleton in mice, including the intra-cardiac, intra-arterial, orthotopic and intra-tibial methods of tumor cell injection. Recommendations for in vivo and ex vivo assessment of tumor progression and bone destruction are provided, followed by discussion of the strengths and limitations of the available tools and translational models that aid investigators in the study of breast cancer metastasis to bone.

The leucine-rich repeat protein PRELP binds fibroblast cell-surface proteoglycans and enhances focal adhesion formation

PRELP (proline/arginine-rich end leucine-rich repeat protein) is a member of the leucine-rich repeat (LRR) family of extracellular matrix proteins in connective tissue. In contrast with other members of the family, the N-terminal domain of PRELP has a high content of proline and positively charged amino acids. This domain has previously been shown to bind chondrocytes and to inhibit osteoclast differentiation. In the present study, we show that PRELP mediates cell adhesion by binding to cell-surface glycosaminoglycans (GAGs). Thus, rat skin fibroblasts (RSFs) bound to full-length PRELP and to the N-terminal part of PRELP alone, but not to truncated PRELP lacking the positively charged N-terminal region. Cell attachment to PRELP was inhibited by addition of soluble heparin or heparan sulfate (HS), by blocking sulfation of the fibroblasts or by treating the cells with a combination of chondroitinase and heparinase. Using affinity chromatography, we identified syndecan-1, syndecan-4 and glypican-1 as cell-surface proteoglycans (PGs) binding to the N-terminal part of PRELP. Finally, we show that the N-terminal domain of PRELP in combination with the integrin-binding domain of fibronectin, but neither of the fragments alone, induced fibroblast focal adhesion formation. These findings provide support for a role of the N-terminal region of PRELP as an important regulator of cell adhesion and behaviour, which may be of importance in pathological conditions.

The "love-hate" relationship between osteoclasts and bone matrix

Osteoclasts are unique cells that destroy the mineralized matrix of the skeleton. There is a "love-hate" relationship between the osteoclasts and the bone matrix, whereby the osteoclast is stimulated by the contact with the matrix but, at the same time, it disrupts the matrix, which, in turn, counteracts this disruption by some of its components. The balance between these concerted events brings about bone resorption to be controlled and to contribute to bone tissue integrity and skeletal health. The matrix components released by osteoclasts are also involved in the local regulation of other bone cells and in the systemic control of organismal homeostasis. Disruption of this regulatory loop causes bone diseases, which may end up with either reduced or increased bone mass, often associated with poor bone quality. Expanding the knowledge on osteoclast-to-matrix interaction could help to counteract these diseases and improve the human bone health. In this article, we will present evidence of the physical, molecular and regulatory relationships between the osteoclasts and the mineralized matrix, discussing the underlying mechanisms as well as their pathologic alterations and potential targeting.

The small leucine-rich repeat proteoglycans in tissue repair and atherosclerosis

Proteoglycans consist of a protein core with one or more covalently attached glycosaminoglycan (GAG) side chains and have multiple roles in the initiation and progression of atherosclerosis. Here we discuss the potential and known functions of a group of small leucine-rich repeat proteoglycans (SLRPs) in atherosclerosis. We focus on five SLRPs, decorin, biglycan, lumican, fibromodulin and PRELP, because these have been detected in atherosclerotic plaques or demonstrated to have a role in animal models of atherosclerosis. Decorin and biglycan are modified post-translationally by substitution with chondroitin/dermatan sulphate GAGs, whereas lumican, fibromodulin and PRELP have keratan sulphate side chains, and the core proteins have leucine-rich repeat (LRR) motifs that are characteristic of the LRR superfamily. The chondroitin/dermatan sulphate GAG side chains have been implicated in lipid retention in atherosclerosis. The core proteins are discussed here in the context of (i) interactions with collagens and their implications in tissue integrity, fibrosis and wound repair and (ii) interactions with growth factors, cytokines, pathogen-associated molecular patterns and cell surface receptors that impact normal physiology and disease processes such as inflammation, innate immune responses and wound healing (i.e. processes that are all important in plaque development and progression). Thus, studies of these SLRPs in the context of wound healing are providing clues about their functions in early stages of atherosclerosis to plaque vulnerability and cardiovascular disease at later stages. Understanding of signal transduction pathways regulated by the core protein interactions is leading to novel roles and therapeutic potential for these proteins in wound repair and atherosclerosis.

Proteoglycan form and function: A comprehensive nomenclature of proteoglycans

We provide a comprehensive classification of the proteoglycan gene families and respective protein cores. This updated nomenclature is based on three criteria: Cellular and subcellular location, overall gene/protein homology, and the utilization of specific protein modules within their respective protein cores. These three signatures were utilized to design four major classes of proteoglycans with distinct forms and functions: the intracellular, cell-surface, pericellular and extracellular proteoglycans. The proposed nomenclature encompasses forty-three distinct proteoglycan-encoding genes and many alternatively-spliced variants. The biological functions of these four proteoglycan families are critically assessed in development, cancer and angiogenesis, and in various acquired and genetic diseases where their expression is aberrant.