Angela Oranger

MYELOMA CELLS SUPPRESS OSTEOBLASTS THROUGH SCLEROSTIN SECRETION

Wingless-type (Wnt) signaling through the secretion of Wnt inhibitors Dickkopf1, soluble frizzled-related protein-2 and -3 has a key role in the decreased osteoblast (OB) activity associated with multiple myeloma (MM) bone disease. We provide evidence that another Wnt antagonist, sclerostin, an osteocyte-expressed negative regulator of bone formation, is expressed by myeloma cells, that is, human myeloma cell lines (HMCLs) and plasma cells (CD138+ cells) obtained from the bone marrow (BM) of a large number of MM patients with bone disease. We demonstrated that BM stromal cells (BMSCs), differentiated into OBs and co-cultured with HMCLs showed, compared with BMSCs alone, reduced expression of major osteoblastic-specific proteins, decreased mineralized nodule formation and attenuated the expression of members of the activator protein 1 transcription factor family (Fra-1, Fra-2 and Jun-D). Moreover, in the same co-culture system, the addition of neutralizing anti-sclerostin antibodies restored OB functions by inducing nuclear accumulation of β-catenin. We further demonstrated that the upregulation of receptor activator of nuclear factor κ-B ligand and the downregulation of osteoprotegerin in OBs were also sclerostin mediated. Our data indicated that sclerostin secretion by myeloma cells contribute to the suppression of bone formation in the osteolytic bone disease associated to MM.

Sclerostin is overexpressed by plasma cells from multiple myeloma patients

Sclerostin, an osteocyte‐expressed negative regulator of bone formation, is one of the inhibitors of Wnt signaling that is a critical pathway in the correct process of osteoblast differentiation. It has been demonstrated that Wnt signaling through the secretion of Wnt inhibitors, such as DKK1, sFRP‐2, and sFRP‐3, plays a key role in the decreased osteoblast activity associated with multiple myeloma (MM) bone disease. We provide evidence that sclerostin is expressed by myeloma cells that are human myeloma cell lines and plasma cells (CD138+ cells) obtained from the bone marrow (BM) of a large number of MM patients with bone disease. Moreover, we show that there are no differences in sclerostin serum levels between MM patients and controls. Thus, our data indicate that MM cells, as a sclerostin source in the BM, could create a microenvironment with high sclerostin concentration that could contribute toward inhibiting osteoblast differentiation.

Irisin enhances osteoblast differentiation in vitro.

It has been recently demonstrated that exercise activity increases the expression of the myokine Irisin in skeletal muscle, which is able to drive the transition of white to brown adipocytes, likely following a phenomenon of transdifferentiation. This new evidence supports the idea that muscle can be considered an endocrine organ, given its ability to target adipose tissue by promoting energy expenditure. In accordance with these new findings, we hypothesized that Irisin is directly involved in bone metabolism, demonstrating its ability to increase the differentiation of bone marrow stromal cells into mature osteoblasts. Firstly, we confirmed that myoblasts from mice subjected to 3 weeks of free wheel running increased Irisin expression compared to nonexercised state. The conditioned media (CM) collected from myoblasts of exercised mice induced osteoblast differentiation in vitro to a greater extent than those of mice housed in resting conditions. Furthermore, the differentiated osteoblasts increased alkaline phosphatase and collagen I expression by an Irisin-dependent mechanism. Our results show, for the first time, that Irisin directly targets osteoblasts, enhancing their differentiation. This finding advances notable perspectives in future studies which could satisfy the ongoing research of exercise-mimetic therapies with anabolic action on the skeleton.

Dental pulp stem cells: osteogenic differentiation and gene expression.

Dental pulp stem cells (DPSCs) are an adult stem cell population with high proliferative potential and the ability to differentiate in many cell types, and this has led scientists to consider these cells to be an alternative source of postnatal stem cells comparable to mesenchymal stem cells from bone marrow. In this work, we studied the osteoblastic phenotype developed by DPSCs cultured in osteogenic medium. In particular, we analyzed the expression of the typical osteoblast markers such as alkaline phosphatase, collagen type I, osteocalcin, osteopontin, as well as mineralized matrix production. Furthermore, the gene expression during DPSC differentiation into osteoblastic cells was studied by microarray technology. Using microarray and reverse transcriptase–polymerase chain reaction (RT‐PCR) analysis, we found that IGFBP‐5, JunB, and NURR1 genes are upregulated during the differentiation of DPSCs. These data indicate that opportunely differentiated DPSCs show a correct osteoblastic phenotype. Therefore, during the osteoblastic differentiation process, IGFBP‐5, JunB, and NURR1 gene expression is significantly increased.

The death receptor DR5 is involved in TRAIL-mediated human osteoclast apoptosis

The number and activity of osteoclasts (OCs) are critical for maintaining normal bone turnover. The number is determined by the rates of cell differentiation and death. TNF-related apoptosis-inducing ligand (TRAIL), a member of the TNF superfamily, induces apoptosis by interacting with its death receptors, (DR4, DR5). However, its activity can be modulated by two decoy receptors, (DcR1 and DcR2). In this paper we show that TRAIL treatment causes reduced OC viability as well as an increased apoptotic OC number. Loss of nuclei integrity and derangement of the actin microfilament were also induced by TRAIL in OCs. Moreover, we demonstrated the expression of all TRAIL receptors in both precursors and differentiated OCs, and the upregulation of DR5 during OC differentiation. Interestingly, DcR2 was upregulated in the early stage of osteoclastogenesis and downregulated at the end of the differentiation process. We showed that DR5, upregulated by TRAIL, could be the mediator of TRAIL-induced OC apoptosis, since the addition of anti-DR5 neutralizing antibodies restores the OC viability previously reduced by TRAIL. Furthermore, the intracellular pathway induced by TRAIL in OCs involves caspase-8 and Bid activation. In conclusion, our data highlight an important role for the TRAIL/TRAIL receptor system in the regulation of OC apoptosis.

Aortic valvular interstitial cells apoptosis and calcification are mediated by TNF-related apoptosis-inducing ligand

BACKGROUND/OBJECTIVES Calcific aortic valvular disease (CAVD) is an actively regulated process characterized by the activation of specific osteogenic signaling pathways and apoptosis. We evaluated the involvement in CAVD of the TNF-related apoptosis-inducing ligand (TRAIL), an apoptotic molecule which induces apoptosis by interacting with the death receptor (DR)-4 and DR5, and whose activity is modulated by the decoy receptor (DcR)-1 and DcR2. METHODS Sections of calcific and normal aortic valves, obtained at surgery time, were subjected to immunohistochemistry and confocal microscopy for TRAIL immunostaining. Valvular interstitial cells (VICs) isolated from calcific (C-VICs) and normal (N-VICs) aortic valves were investigated for the gene and protein expression of TRAIL receptors. Cell viability was assayed by MTT. Von Kossa staining was performed to verify C-VIC ability to produce mineralized nodules. TRAIL serum levels were detected by ELISA. RESULTS Higher levels of TRAIL were detected in calcific aortic valves and in sera from the same patients respect to controls. C-VICs express significantly higher mRNA and protein levels of DR4, DR5, DcR1, DcR2 and Runx2 compared to N-VICs. C-VICs and N-VICs, cultured in osteogenic medium, express significantly higher mRNA levels of DR4, Runx2 and Osteocalcin compared to baseline. C-VICs and N-VICs were sensitive to TRAIL-apoptotic effect at baseline and after osteogenic differentiation, as demonstrated by MTT assay and caspase-3 activation. TRAIL enhanced mineralized matrix nodule synthesis by C-VICs cultured in osteogenic medium. CONCLUSIONS TRAIL is characteristically present within calcific aortic valves, and mediates the calcification of aortic valve interstitial cells in culture through mechanism involving apoptosis.

Cellular Mechanisms of Multiple Myeloma Bone Disease

Multiple myeloma (MM) is a hematologic malignancy of differentiated plasma cells that accumulates and proliferates in the bone marrow. MM patients often develop bone disease that results in severe bone pain, osteolytic lesions, and pathologic fractures. These skeletal complications have not only a negative impact on quality of life but also a possible effect in overall survival. MM osteolytic bone lesions arise from the altered bone remodeling due to both increased osteoclast activation and decreased osteoblast differentiation. A dysregulated production of numerous cytokines that can contribute to the uncoupling of bone cell activity is well documented in the bone marrow microenvironment of MM patients. These molecules are produced not only by malignant plasma cells, that directly contribute to MM bone disease, but also by bone, immune, and stromal cells interacting with each other in the bone microenvironment. This review focuses on the current knowledge of MM bone disease biology, with particular regard on the role of bone and immune cells in producing cytokines critical for malignant plasma cell proliferation as well as in osteolysis development. Therefore, the understanding of MM pathogenesis could be useful to the discovery of novel agents that will be able to both restore bone remodelling and reduce tumor burden.

Osteogenic differentiation of dental follicle stem cells.

Background: Stem cells are defined as clonogenic cells capable of self-renewal and multi-lineage differentiation. A population of these cells has been identified in human Dental Follicle (DF). Dental Follicle Stem Cells (DFSCs) were found in pediatric unerupted wisdom teeth and have been shown to differentiate, under particular conditions, into various cell types of the mesenchymal tissues. Aim: The aim of this study was to investigate if cells isolated from DF show stem features, differentiate toward osteoblastic phenotype and express osteoblastic markers. Methods: We studied the immunophenotype of DFSCs by flow cytometric analysis, the osteoblastic markers of differentiated DFSCs were assayed by histochemical methods and real-time PCR. Results: We demonstrated that DFSCs expressed a heterogeneous assortment of makers associated with stemness. Moreover DFSCs differentiated into osteoblast-like cells, producing mineralized matrix nodules and expressed the typical osteoblastic markers, Alkaline Phosphatase (ALP) and Collagen I (Coll I). Conclusion: This study suggests that DFSCs may provide a cell source for tissue engineering of bone.

Soluble decoy receptor 3 modulates the survival and formation of osteoclasts from multiple myeloma bone disease patients

Decoy receptor 3 (DcR3), a member of the tumor necrosis factor (TNF) receptor superfamily, is known to be involved in cell survival and osteoclast (OC) formation. In this study, we show that malignant plasma cells and T lymphocytes from multiple myeloma (MM) bone disease patients, as well as Karpas 909, a human myeloma cell line, directly produce DcR3. By interacting with FasL, this molecule could inhibit OC apoptosis. In fact, the use of a neutralizing anti-DcR3 antibody induces a reduction of cell viability with a consequent increase of apoptotic cell number, the activation of caspase-8 and -3, and DNA fragmentation. Furthermore, we show that DcR3 supports OC formation in samples from MM patients through the upregulation of RANKL and TNFα by T lymphocytes and only TNFα by CD14+ cells. In conclusion, our data provide the first evidence of the expression of DcR3 in MM, and the involvement of this molecule in supporting the survival and formation of OCs from MM bone disease patients. The production of DcR3 by T lymphocytes confers these cells a role in the pathogenesis of bone disease associated with MM.

High dickkopf-1 levels in sera and leukocytes from children with 21-hydroxylase deficiency on chronic glucocorticoid treatment

Children with 21-hydroxylase deficiency (21-OHD) need chronic glucocorticoid (cGC) therapy to replace congenital deficit of cortisol synthesis, and this therapy is the most frequent and severe form of drug-induced osteoporosis. In this study, we enrolled 18 patients (9 females) and 18 sex- and age-matched controls. We found in 21-OHD patients high serum and leukocyte levels of dickkopf-1 (DKK1), a secreted antagonist of the Wnt/β-catenin signaling pathway known to be a key regulator of bone mass. In particular, we demonstrated by flow cytometry, confocal microscopy, and real-time PCR that monocytes, T lymphocytes, and neutrophils from patients expressed high levels of DKK1, which may be related to the cGC therapy. In fact, we showed that dexamethasone treatment markedly induced the expression of DKK1 in a dose- and time-dependent manner in leukocytes. The serum from patients containing elevated levels of DKK1 can directly inhibit in vitro osteoblast differentiation and receptor activator of NF-κB ligand (RANKL) expression. We also found a correlation between both DKK1 and RANKL or COOH-terminal telopeptides of type I collagen (CTX) serum levels in 21-OHD patients on cGC treatment. Our data indicated that DKK1, produced by leukocytes, may contribute to the alteration of bone remodeling in 21-OHD patients on cGC treatment.