Oestrogen-deficiency induces bone loss by modulating CD14⁺ monocyte and CD4⁺ T cell DR3 expression and serum TL1A...

Oestrogen-deficiency induced by menopause is associated with reduced bone density and primary osteoporosis, resulting in an increased risk of fracture. While the exact etiology of menopause-induced primary osteoporotic bone loss is not fully known, members of the tumour necrosis factor super family (TNFSF) are known to play a role. Recent studies have revealed that the TNFSF members death receptor 3 (DR3) and one of its ligands, TNF-like protein 1A (TL1A) have a key role in secondary osteoporosis; enhancing CD14⁺ peripheral blood mononuclear cell (PBMC) osteoclast formation and bone resorption. Whether DR3 and TL1A contribute towards bone loss in menopause-induced primary osteoporosis however, remains unknown.

To investigate this we performed flow cytometry analysis of DR3 expression on CD14⁺ PBMCs isolated from pre- and early post-menopausal females and late post-menopausal osteoporotic patients. Serum levels of TL1A, CCL3 and total MMP-9 were measured by ELISA. In vitro osteoclast differentiation assays were performed to determine CD14⁺ monocyte osteoclastogenic potential. In addition, splenic CD4⁺ T cell DR3 expression was investigated 1 week and 8 weeks post-surgery, using the murine ovariectomy model.

In contrast to pre-menopausal females, CD14⁺ monocytes isolated from post-menopausal females were unable to induce DR3 expression. Serum TL1A levels were decreased approx. 2-fold in early post-menopausal females compared to pre-menopausal controls and post-menopausal osteoporotic females; no difference was observed between pre-menopausal and late post-menopausal osteoporotic females. Analysis of in vitro CD14⁺ monocyte osteoclastogenic potential revealed no significant difference between the post-menopausal and post-menopausal osteoporotic cohorts. Interestingly, in the murine ovariectomy model splenic CD4⁺ T cell DR3 expression was significantly increased at 1 week but not 8 weeks post-surgery when compared to the sham control.

Our results reveals for the first time that loss of oestrogen has a significant effect on DR3; decreasing expression on CD14⁺ monocytes and increasing expression on CD4⁺ T cells. These data suggest that while oestrogen-deficiency induced changes in DR3 expression do not affect late post-menopausal bone loss they could potentially have an indirect role in early menopausal bone loss through the modulation of T cell activity.