Osteogenic differentiation of human ligament fibroblasts induced by conditioned medium of osteoclast-like cells.

Osteoclasts secrete factors that may promote mesenchymal stem cell mineralization in vitro. Fibroblasts are the most common cells in connective tissue and are involved in the process of exotic ossification in many diseases such as ankylosing spondylitis. The purpose of this study was to investigate whether osteoclast-like cells would induce the osteogenic differentiation of fibroblasts in vitro. In the present study, osteoclast-like cells (OLCs) were generated by CD14(+) cells from human peripheral blood. Fibroblasts were primarily cultured from spinal ligaments. After treatment with conditioned medium of OLCs, the level of alkaline phosphatase (ALP) and mineralization of fibroblasts increased significantly. cDNA microarray analysis identified a set of differentially expressed mRNA associated with signal transduction, cell differentiation, and bone formation, and microarray analysis of microRNA expression profiles revealed a group of microRNAs, including hsa-miR-20a, hsa-miR-300, hsa-miR-185, hsa-miR-30d, hsa-miR-320a, hsamiR- 130b, hsa-miR-33a, hsa-miR-155, and hsa-miR-222, that were significantly downregulated. These microRNAs were predicted to have an inhibitory effect on genes associated with osteogenic differentiation, such as BMP2, Osteocalcin, and Runx2. The current results suggest that osteoclasts might induce the osteogenic differentiation of fibroblasts in vitro and that miRNA may play an important role in regulation of the cell-cell interaction between osteoclasts and fibroblasts.