New Signature of Osseointegration: Does Vitamin-D Deficiency Change Expression Profiles?

Vitamin-D deficiency has been considered as systemic risk factor for reduced bone mineral density, osteoporosis, and impaired osseointegration. We have hypothesized that vitamin-D deficiency alters expression of genes that are critical for osseointegration. Objectives: Our aim was to compare gene expression profiles of bone healing around titanium implant in vitamin-D sufficient and deficient rats. Methods: Sixteen rats received T-shaped experimental implants or osteotomy in their femurs. RNA was isolated after 2 weeks of healing and Agilent-Microarray was used to screen 41,000 genes. Two-way ANOVA (Benjamini-Hochberg correction, adj-p_cuttoff.=0.01) was used to compare expression among the groups. We used KEGG pathway databases to investigate known biological pathways and functions. Results: We found 1,668 differently expressed genes distributed into two expression profiles, in which implant was the main inducer of over-expression (1080 genes) or under-expression (588 genes). From Partioning Around Medoids (PAM) clusterization, vitamin-D deficiency showed the clear tendency to attenuate the expression of these genes during osseointegration. From 16 KEGG pathways over-represented by our gene-list, we found 5 main processes occurring at 2-week osseointegration: [1] formation of extracellular matrix and cell-interaction; [2] angiogenesis; [3] resolution of inflammation and immune-system; [4] control of body energy/bone metabolism; and [5] cell proliferation. The ANOVA evaluations of Vitamin-D factor and Interaction between the presence of implant and vitamin-D deficiency identified significantly altered expression of the following genes: arachdonic-acid-epoxygenase CYP2b15, GILZ, Per2, NPAS-domain-2, IGF-binding-protein-3, FOS-like-antigen-1, RGD1564491, EPO, RIKEN, and CTTNBP2. Conclusion: Peri-implant healing revealed a different gene expression signature compared to bone healing, and vitamin-D deficiency attenuated their expression. These genes were found in 5 systems. The significantly affected genes may be involved in resolution process of inflammatory reactions and bone remodeling, and may play an essential role in the establishment of osseointegration. This study was supported in part by NIH C06RR14529, Biomet3i, and CAPES (#3876-07-1, Brazil).