Solid platelet-rich fibrin (PRF), consisting of coagulated plasma from fractionated blood, has been proposed to be a suitable carrier for recombinant bone morphogenetic protein 2 (BMP2) to target mesenchymal cells during bone regeneration. However, whether solid PRF can increase the expression of BMPs in mesenchymal cells remains unknown. Proteomics analysis confirmed the presence of TGF-β1 but not BMP2 in PRF lysates. According to the existing knowledge of recombinant TGF-β1, we hypothesized that PRF can increase BMP2 expression in mesenchymal cells. To test this hypothesis, we blocked TGF-β receptor 1 kinase with SB431542 in gingival fibroblasts exposed to PRF lysates. RT-PCR and immunoassays confirmed that solid PRF lysates caused a robust SB431542-dependent increase in BMP2 expression in gingival fibroblasts. Additionally, fractions of liquid PRF, namely platelet-poor plasma (PPP) and the buffy coat (BC) layer, but not heat-denatured PPP (Alb-gel), greatly induced the expression of BMP2 in gingival fibroblasts. Even though PRF has no detectable BMPs, PRF lysates similar to recombinant TGF-β1 had the capacity to provoke canonical BMP signaling, as indicated by the nuclear translocation of Smad1/5 and the increase in its phosphorylation. Taken together, our data suggest that PRF can activate TGF-β receptor 1 kinase and consequently induce the production of BMP2 in cells of the mesenchymal lineage.
Keywords: BMP2; bone regeneration; buffy coat; platelet-poor plasma; platelet-rich fibrin; proteomics.