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The effect of surface topography on gene expression of macrophages Wong, Angela Ting Ting


Osseointegration, the direct attachment of living bone to an implant surface, is necessary for the success of dental implant therapy. The surface topography of an implant influences cellular behaviour and osseointegration. In-vivo studies have shown that rough surface topographies are associated with accumulation of macrophages and subsequent bone formation (Chehroudi et al., 2009). Macrophages can exhibit classic inflammatory (M1) or alternative (M2) phenotypes that secrete different patterns of cytokines, chemokines and growth factors that affect wound healing. These experiments aim to characterize the phenotypes of unstimulated RAW264.7 macrophages grown on polished and SLA (sandblasted and acid-etched) surfaces using gene expression microarray technology. Whole genome microarray analysis showed differential expression of 199 genes on day 1 and 4943 genes on day 5 on SLA compared to polished surfaces. These genes were assigned to network categories related to cellular movement, immune cell trafficking, inflammation, cell-to-cell signalling and tissue development. Gene profiles were also compared to M1 and M2 macrophages obtained by stimulation with LPS and IL-4 respectively. Stimulated macrophages exhibited gene expression profiles consistent with their predicted phenotypes. Confirmation of upregulated expression of CCL4 and CCL7, macrophage chemoattractants associated with early inflammatory responses, was performed with quantitative real time polymerase chain reaction (qPCR). CCL4 was significantly upregulated on SLA surfaces by a factor of 2.18 after 1 day, and CCL7 was significantly upregulated on SLA surfaces by a factor of 4.01 after 5 days. Both CCL4 and CCL7 were also significantly upregulated after 1 day by M1 and M2 stimulated macrophages on the microarray. These experiments show that unstimulated macrophages grown on SLA surfaces increase gene expression of macrophage chemoattractants, and exhibit an intermediate phenotype with a mixture of M1 and M2 characteristics.

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