A salmon DNA scaffold promotes osteogenesis through activation of sodium-dependent phosphate cotransporters

Abstract

We previously reported the promotion of bone regeneration in calvarial defects of both normal and ovariectomy-induced osteoporotic rats, with the use of biodegradable DNA/protamine scaffold. However, the method by which this DNA-containing scaffold promotes bone formation is still not understood. We hypothesize that the salmon DNA, from which this scaffold is derived, has an osteoinductive effect on pre-osteoblasts and osteoblasts. We examined the effects of salmon DNA on osteoblastic differentiation and calcification in MC3T3-E1 cells, mouse osteoblasts, in vitro and bone regeneration in a calvarial defect model of aged mouse in vivo. The salmon DNA fragments (300 bps) upregulated the expression of the osteogenic markers, such as alkaline phosphatase, Runx2, and osterix (Osx) in MC3T3E1 cells compared with incubation with osteogenic induction medium alone. Measurement of phosphate ion concentrations in cultures showed that the DNA scaffold degraded phosphate ions were released to the cell cultures. Interestingly, we found that the inclusion of DNA in osteoblastic cell cultures upregulated the expression of sodium-dependent phosphate (NaPi) cotransporters, SLC20A1 and SLC34A2, in MC3T3-E1 cells in a time dependent manner. Furthermore, the inclusion of DNA in cell cultures increased the transcellular permeability of phosphate. Conversely, the incubation of phosphonoformic acid, an inhibitor of NaPi cotransporters, attenuated the DNA-induced expression and activation of SLC20A1 and SLC34A2 in MC3T3-E1 cells, resulting in suppression of the osteogenic markers. The implantation of a salmon DNA scaffold disk promoted bone regeneration using calvarial defect models in 30-week-old mice. Our results indicate that the phosphate released from salmon DNA upregulated the expression and activation of NaPi cotransporters, resulting in the promotion of bone regeneration.