Detection of apoptosis of bone cells in vitro

Osteoclast profile of medication-related osteonecrosis of the jaw secondary to bisphosphonate therapy: a comparison with osteoradionecrosis and osteomyelitis

Background

The medication-related osteonecrosis of the jaw secondary to bisphosphonate therapy [MRONJ (BP)] is characterized by non-healing exposed bone in the maxillofacial region. The pathogenesis of MRONJ (BP) is not fully understood. Giant, hypernucleated, inactive osteoclasts were found in MRONJ (BP) tissues, which indicated that accelerated cell–cell fusion might play a role. Dendritic cell-specific transmembrane protein (DC-STAMP) is associated with the cell–cell fusion of osteoclasts and precursor cells. Tartrate-resistant acid phosphatase (TRAP) is essential for osteoclastic bone resorption. The cell–cell fusion, as part of the osteoclastogenesis, and the resorptive activity can determine the morphology of osteoclasts. This study analyzed jaw bone from patients with MRONJ (BP), osteomyelitis (OM) and osteoradionecrosis (ORN) because a comparison with the osteoclast profiles of OM and ORN is essential for characterizing the osteoclast profile of MRONJ (BP).

Methods

Formalin-fixed routine jaw bone specimens from 70 patients [MRONJ (BP) n = 30; OM: n = 15, ORN: n = 15, control: n = 10] were analyzed retrospectively for osteoclast quantity, morphology and the expression of TRAP and DC-STAMP. The specimens were processed for hematoxylin and eosin staining (H&E), histochemistry (TRAP) and immunohistochemistry (anti-DC-STAMP) and were analyzed via virtual microscopy.

Results

The quantity, diameter and nuclearity of osteoclasts were significantly higher in MRONJ (BP) specimens than in OM, ORN and control specimens. Giant, hypernucleated osteoclasts were detected in MRONJ (BP) specimens only. Osteoclastic TRAP expression was lower in MRONJ (BP) and ORN specimens than in OM and control specimens. The DC-STAMP expression of osteoclasts and mononuclear cells was significantly higher in MRONJ (BP) and ORN specimens than in OM and control specimens.

Conclusions

This study indicates that the osteoclast profile of MRONJ (BP) is characterized by osteoclast inactivation and a high cell–cell fusion rate; however, the presence of giant, hypernucleated osteoclasts cannot be attributed to increased DC-STAMP-triggered cell–cell fusion alone. The incidental characterization of the osteoclast profiles of OM and ORN revealed differences that might facilitate the histopathological differentiation of these diseases from MRONJ (BP), which is essential because their therapies are somewhat different.

Bidirectional Notch Signaling and Osteocyte-Derived Factors in the Bone Marrow Microenvironment Promote Tumor Cell Proliferation and Bone Destruction in Multiple Myeloma

In multiple myeloma, an overabundance of monoclonal plasma cells in the bone marrow induces localized osteolytic lesions that rarely heal due to increased bone resorption and suppressed bone formation. Matrix-embedded osteocytes comprise more than 95% of bone cells and are major regulators of osteoclast and osteoblast activity, but their contribution to multiple myeloma growth and bone disease is unknown. Here, we report that osteocytes in a mouse model of human MM physically interact with multiple myeloma cells in vivo, undergo caspase-3-dependent apoptosis, and express higher RANKL (TNFSF11) and sclerostin levels than osteocytes in control mice. Mechanistic studies revealed that osteocyte apoptosis was initiated by multiple myeloma cell-mediated activation of Notch signaling and was further amplified by multiple myeloma cell-secreted TNF. The induction of apoptosis increased osteocytic Rankl expression, the osteocytic Rankl/Opg (TNFRSF11B) ratio, and the ability of osteocytes to attract osteoclast precursors to induce local bone resorption. Furthermore, osteocytes in contact with multiple myeloma cells expressed high levels of Sost/sclerostin, leading to a reduction in Wnt signaling and subsequent inhibition of osteoblast differentiation. Importantly, direct contact between osteocytes and multiple myeloma cells reciprocally activated Notch signaling and increased Notch receptor expression, particularly Notch3 and 4, stimulating multiple myeloma cell growth. These studies reveal a previously unknown role for bidirectional Notch signaling that enhances MM growth and bone disease, suggesting that targeting osteocyte-multiple myeloma cell interactions through specific Notch receptor blockade may represent a promising treatment strategy in multiple myeloma.

Alcoholic and isocaloric diet, but not ovariectomy, influence the apoptosis of bone cells within the alveolar bone crest of rats

OBJECTIVE

Studies suggest that chronic alcoholism as well as oestrogen deficiencies may affect bones in general, including alveolar bone and, by doing so, increase individuals' susceptibility to develop progressive periodontal disease. This paper aims to verify the influence of chronic alcoholism and/or oestrogen deficiencies in the apoptosis of bone cells of the alveolar bone crest region in rats.

DESIGN

Initially, 54 rats were divided into ovariectomized (Ovx) and Sham operated (Sham) groups. Thirty days after surgery, these two groups were equally sub-divided, and received, for 56 days, the following dietary intervention: alcoholic diet (with 20% alcohol solution,), isocaloric diet and ad libitum diet (free diet). Analysis was undertaken by immunohistochemistry, using an antibody to detect apoptosis (anti PARP p-85).

RESULTS

When comparing the six experimental groups, no significant differences were observed in the apoptosis of bone cells. Also, there was no significant difference in the quantity of cells undergoing apoptosis when the animals from Ovx groups were compared with those from Sham groups. However, when comparing only different dietary groups, differences were observed between the groups ad libitum and isocaloric, to osteoblasts (p=0.045); and ad libitum and alcohol, to osteocytes (p=0.007).

CONCLUSION

It is concluded that ovariectomy was not able to influence the rate of apoptosis of bone cells of the alveolar bone crest region in rats and that a possible influence of diet on apoptosis of osteoblasts and osteocytes cannot be ruled out.

Thiazolidinediones induce osteocyte apoptosis and increase sclerostin expression

AIMS

Thiazolidinediones (TZDs) are associated with a higher risk of bone fracture in women compared with men. The aim of the present study was to investigate whether TZDs could influence osteocyte behaviour and contribute to the skeletal phenotype observed in TZD-treated patients.

METHODS

The murine MLO-Y4 cell line was used as a source of osteocytes. These cells were cultured for 24 h with 0, 10(-8) m, 10(-7) m, 10(-6) m, 10(-5) m or 10(-4) m of pioglitazone, rosiglitazone or troglitazone in the presence or absence of 17beta-oestradiol. The extent of osteocyte apoptosis was assessed, as was the expression of the bone formation inhibitor sclerostin and receptor activator for nuclear factor kappaB ligand (RANKL) also.

RESULTS

In the absence of 17beta-oestradiol, pioglitazone, rosiglitazone and troglitazone induced osteocyte apoptosis dose-dependently even at the lowest concentration of 10(-8) m. Furthermore, the expression of sclerostin but not RANKL was significantly increased in TZD-treated cultures compared with untreated cultures. The presence of 17beta-oestradiol significantly reduced TZD-induced osteocyte apoptosis and also sclerostin up-regulation.

CONCLUSIONS

These findings therefore raise the potential concern of using TZDs in post-menopausal women where the lack of oestrogen would not prevent osteocyte apoptosis and sclerostin up-regulation and may aggravate the reduction in bone mass in these patients.