Alteration of activity and survival of osteoblasts obtained from human periodontitis patients: role of TRAIL

Periodontal disease (Pd) is characterized by extensive alveolar bone loss, that occurs as a consequence of the impairment of the normal bone remodelling. Bone remodelling is regulated by the correct balance between osteoclast and osteoblast formation and activity. Alveolar bone loss could be due to an increased bone resorption by osteoclasts or a decreased bone formation by osteoblasts (OBs) or both. Although the role played by osteoclasts in increasing bone resorption in Pd is already known, the behaviour of OBs in this disease is poorly understood. In the present study we hypothesized that activity and survival of OBs, locally present in alveolar bone of Pd patients, are altered. Thus, we studied the activity and survival of OBs obtained from alveolar bone fragments of Pd patients. The results, obtained in OBs from the patients were compared with those from OBs obtained from healthy donors. We demonstrated that OBs from Pd patients weakly express OB phenotype in respect to the control cells. In particular, the alkaline phosphatase activity and the collagen type I production, as well as the formation of mineralized nodules, typical markers of differentiated OBs, were significantly lower in Pd patients. Interestingly, we also demonstrated that OBs from the patients were more sensitive to the apoptotic effect induced by TNF-related apoptosis-inducing ligand (TRAIL). 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. Thus, the sensitiveness of TRAIL induced apoptosis is determined by the ratio of death and decoy receptor. We demonstrated that OBs from Pd patients showed an imbalanced ratio between death and decoy TRAIL receptors due to the down-regulation of DcR2 expression. Furthermore, the levels of TRAIL in the serum of the same patients were significantly higher than those detected in the controls. In conclusion, we show for the first time that the alveolar bone loss in Pd patients could be due to the increased TRAIL-mediated apoptosis of OBs.

T cells support osteoclastogenesis in an in vitro model derived from human periodontitis patients

BACKGROUND

Periodontitis is characterized by alveolar bone destruction; however, the mechanisms responsible for bone damage are poorly understood. It has been reported that T cells are implicated in the pathogenesis of periodontitis. It has been also demonstrated that activated T lymphocytes secrete receptor activator of nuclear factor-kappa B ligand (RANKL) and can support the differentiation of monocytes into resorbing osteoclasts (OCs). Therefore, the purpose of this study was to examine the OC formation in periodontitis patients (PP) and the role of T cells in osteoclastogenesis.

METHODS

To study OC formation, we used an in vitro model consisting of unstimulated and unfractionated peripheral blood mononuclear cells (PBMCs) from PP and controls. In parallel, T-cell-depleted PBMCs from the same patients were also established. The expression of RANKL and tumor necrosis factor-alpha (TNF-alpha) was analyzed by reverse transcription-polymerase chain reaction (RT-PCR) and Western blot in fresh T cells isolated from PP and controls. Functional antibodies, anti-RANKL and anti-TNF-alpha, were utilized to study osteoclastogenesis in PBMC cultures from PP.

RESULTS

We showed that, in unfractionated PBMCs from PP, the OCs spontaneously developed in a T-cell-dependent way. The addition of macrophage colony stimulating factor (MCSF) and RANKL was necessary to promote the osteoclastogenesis in T-cell-depleted PBMC cultures from PP and in unfractionated PBMCs from periodontally healthy controls. Moreover, freshly isolated T cells from PBMCs of PP overexpressed RANKL and TNF-alpha. Finally, functional anti-RANKL and anti-TNF-alpha antibodies significantly inhibited osteoclastogenesis.

CONCLUSION

Our data suggest that T cells support spontaneous osteoclastogenesis in PP via RANKL and TNF-alpha overexpression.

Interleukin-7 production by B lymphocytes affects the T cell-dependent osteoclast formation in an in vitro model derived from human periodontitis patients

Periodontitis is characterized by irreversible destruction of alveolar bone and connective tissue attachment in the periodontium. We recently reported that T cells support the osteoclastogenesis by the overproduction of nuclear factor-kappa-B-ligand (RANKL) and Tumor Necrosis Factor-alpha (TNF-alpha) in an in vitro osteoclastogenesis model from periodontitis patients (Pp). It is known that IL-7 stimulates the production of osteoclastogenic factors by T cells and IL-6 potentiates IL-7 expression. Thus, we studied the involvement of IL-6 and IL-7 in the T cell regulation of osteoclast (OC) formation, in an in vitro osteoclastogenesis model from Pp. We demonstrated high levels of IL-7 in both the media collected from PBMC cultures of Pp and the sera of the same patients. We also demonstrated that freshly isolated B cells from PBMCs of Pp were the source of IL-7 in our model. B cells, in fact, overexpressed IL-7 at mRNA and protein levels, and this production was up-regulated by IL-6. Moreover, the OC formation decreased in the presence of anti-IL-6 and IL-7 functional antibodies in PBMC cultures from Pp. These data suggest that B cells could be responsible for the T cell-dependent osteoclastogenesis in periodontitis through the involvement of IL-6 and IL-7.