Bone Abstracts

Strontium ranelate (SrRan) is an efficient treatment for osteoporosis, because SrRan both inhibits osteoclasts and stimulates osteoblastic bone formation. We have previously shown that SrRan also affects mouse osteocyte signaling towards osteoclast precursors and mature osteoblasts. This study assessed the effect of SrRan on paracrine signaling from mechanically-stimulated human osteocytes towards mesenchymal stem cells.

Human primary bone cells, used as a model for osteocytes, were cultured for 24 h in the presence of SrRan (0–3 mM), and treated with/without pulsating fluid flow (PFF) for 60 min. Treatment effects were assessed by quantification of nitric oxide (NO; Griess assay) in the culture medium, and by quantification of mRNA expression of Wnt5a, Wnt10b, BMP2, IGF1, PTN, and VEGFA (Taqman PCR). Conditioned medium (CM) from SrRan and/or PFF-treated osteocytes was added to human adipose tissue-derived mesenchymal stem cells (ASCs) for 4 days. Proliferation of ASCs was determined at day 4 (Ki67 expression), and osteogenic differentiation at days 7 and 10 (Alizarin Red Staining).

SrRan alone, in the absence of PFF, enhanced gene expression of BMP2 and Wnt5a and reduced Wnt10b and IGF1 expression by human primary bone cells. PFF enhanced NO production as well as gene expression of Wnt5a, BMP2, PTN, and VEGFA. SrRan did not alter this response to PFF. SrRan (3 mM ) alone enhanced ki67 expression and bone nodule formation by AT-MSCs. CM from primary bone cells cultured in absence of mechanical stimulation did not affect bone nodule formation by ASCs. CM from PFF-treated primary bone cells enhanced bone nodule formation by ASCs, regardless whether the primary bone cells were cultured in the presence or absence of SrRan.

In summary, both SrRan and CM from mechanically-stimulated osteocytes enhanced osteogenic differentiation of ASCs, but not in a synergistic manner. Thus, SrRan did not appear to affect paracrine signaling from mechanically-stimulated human osteocytes towards cultured ASCs.