Platelet-Rich Plasma Induces Mixed Osteogenic/Osteoclastogenic Phenotype in Osteosarcoma SaOS-2 Cells: Role of TGF-Beta

Platelet-rich plasma (PRP) is widely used to promote tissue repair and accelerate osteogenesis, but there is no agreement about its mechanism of action. We characterized the modulatory effect of PRP on the in vitro osteoblast model SaOS-2, by using cell motility/chemoattraction and osteogenesis/mineralization assays, and a series of osteogenic/ osteoclastogenic genomic markers. Scratch wound assay showed that PRP stimulates cell motility, while transwell assay revealed a strong chemoattraction. Alkaline phosphatase (ALP) and alizarin red-S assays showed that PRP induces slight, but significant, stimulations of ALP activity and mineralization. The TGF-β inhibitor SB431542 reversed these effects, showing a main role for TGF-β1 released by PRP. Analyses of gene expression by qRT-PCR, showed the upregulation of osteocalcin, osteopontin, osteoprotegerin, receptor activator of NFαB (RANK), and runt-related transcription factor 2 (RUNX2) genes, with a total reversion by SB431542 for osteoprotegerin and RANK, and a partial reversion for ostecalcin, osteopontin, and RUNX2. The use of PCR array technique revealed the upregulation of the cathepsin K gene. These data show that PRP induces the development of mixed osteogenic/osteoclastogenic traits in the SaOS-2 model. Such a behavior may favour in vivo bone resorption and reconstitution at post-surgery or post-traumatic sites.