Effect of Titanium Nanoparticles on Differentially Activated Human Primary Macrophages

Long term use of titanium implants generates wearing particles off. Titanium nanoparticles (TiNP) favor a pro-inflammatory macrophage polarization (M1) and lower the tolerogenic activation (M2). Our previous Affymetrix data showed that TiNP upregulate GDF15 and downregulate STAB1 expression in macrophages. GDF15 is a cytokine that regulates energy expenditure and fibrosis, and is endocytosed by the scavenger receptor Stabilin-1. Our study aim was to investigate the effect of TiNP on GDF15 and STAB1 expression, on GDF15 secretion and on endocytosis efficiency in macrophages. We used the model system of primary human macrophages derived from CD14+ monocytes. After 6 days of incubation with TiNP, we quantified GDF15 and STAB1 expression, and GDF15 secretion in INF-γ stimulated (M1) and IL-4 stimulated (M2) macrophages using RT-PCR and ELISA, respectively. Flow cytometry assessed the effect of TiNP on endocytosis based on the uptake of fluorescently labelled acLDL, a known ligand of stabilin-1, and MS-1, an antibody directed against the extracellular portion of stabilin-1 in M1 and M2. Our results revealed a strong up-modulating effect of TiNP on GDF15 expression and secretion in all subtypes of macrophages. In contrast, stabilin-1 expression was significantly suppressed by TiNP. acLDL and MS-1 uptake by macrophages was also significantly suppressed under the treatment with TiNP. Our findings highlight a consistent ex vivo stimulatory effect of TiNP on GDF15 production and inhibitory effect on STAB1 expression and Stabilin-1-mediated endocytosis. Our results suggest an important implication of TiNP on macrophage healing functions. 60 samples are analyzed, no duplicates, control are considered the samples without titanium nanoparticles treatment