Transcriptome analysis of β-TCP implanted in dog mandible

Beta-tricalcium phosphate (β-TCP) is widely used in clinical orthopedic surgery due to its high biodegradability, osteoconductivity, easy manipulation and lack of histotoxicity. However, little is known about the molecular mechanisms responsible for the beneficial effects of β-TCP in bone formation. In this study, β-TCP was implanted in dog mandibles, after which the gene expression profiles and signaling pathways were monitored using microarray and Ingenuity Pathways Analysis (IPA). Following the extraction of premolars and subsequent bone healing, β-TCP was implanted into the artificial osseous defect. Histological evaluation (H-E staining) was carried out 4, 7 and 14 days after implantation. In addition, total RNA was isolated from bone tissues and gene expression profiles were examined using microarray analysis coupled with Ingenuity Pathways Analysis (IPA). Finally, real-time PCR was used to confirm mRNA levels. It was found that β-TCP implantation led to a two-fold change in 3409 genes on day 4, 3956 genes on day 7, and 6899 genes on day 14. Among them, the expression of collagen type I α1 (COL1A1), alkaline phosphatase (ALP) and transforming growth factor (TGF)-β2 was increased on day 4, the expression of receptor activator of NF-kappaB ligand (RANKL) and interferon-γ (IFN-γ) was decreased on day 7, and the expression of osteoprotegerin (OPG) was decreased on day 14, affecting the bone morphogenetic protein (BMP), Wnt/β-catenin and nuclear factor-kappaB (NF-κB) signaling pathways in osteoblasts and osteoclasts. Simultaneously, vascular cell adhension molecule (VCAM)-1 expression was increased on day 4 and stromal cell-derived factor (SDF)-1 expression was increased on days 4 and 14. Taken together, these findings shed light on some of the cellular events associated with bone formation, bioresorption, regeneration and healing of β-TCP following its implantation. The results suggest that β-TCP enhances bone healing processes and stimulates the coordinated actions of osteoblasts and osteoclasts, leading to bone regeneration.