The Innate Osteogenic Potential of the Canine Maxillary Sinus Membrane: An In Vitro and In Vivo Study

Objective: To investigate the osteogenic potential of canine maxillary sinus mucosa using both in vitro and in vivo assays. Material and methods: The histological morphology of beagle dog sinus mucosa was observed under microscopy. Osteoprogenitor cells were harvested from canine maxillary sinus mucosa and cultured. To determine cell phenotype, expression of mesenchymal markers CD44 and CD146, as well as the hematopoietic stem cell marker CD34, were measured by flow cytometry. After osteogenic induction, alkaline phosphatase activity was measured at 3, 7, and 12 days. Immunohistochemical labeling of BMP-2 was performed 16 days after induction, and Western blot was used to measure BMP-2 protein expression level 0, 7, and 16 days after induction. Alizarin red staining and Von Kossa staining were used to observe the formation of mineralized nodules 28 days after induction. After their second passage, induced cells were composited with Bio-Oss and implanted subcutaneously into the back of a nude mouse for observation of new bone formation. Results: The canine maxillary sinus mucosa was composed of an epithelial layer, lamina propria, submucosa, and periosteum. Flow cytometry showed osteoprogenitor cells were positive for CD44 and CD146, but negative for CD34. Alkaline phosphatase activity increased gradually between 3, 7, and 12 days after osteogenic induction. BMP-2 protein expression was enhanced in experimental groups compared with controls. Western blot showed that BMP-2 expression increased between 0, 7, and 16 days after induction. Obvious mineralized nodules were found. Bone formation was observed after subcutaneous implantation of the composite of cells and Bio-Oss in nude mice. Conclusions: Canine maxillary sinus mucosa contains osteoprogenitor cells that possess the ability to undergo osteogenesis.