| Summary: | Gold nanoparticles (GNPs) have attracted considerable attention in promoting osteogenic differentiation. However, little is known about their osteogenic effects on cells from various origins, and further in vivo investigation as a promising osteogenic agent upon hydrogel-conjugation is required. Herein, the effects of PEGylated GNPs with the sizes of 4, 18 and 45 nm on osteogenic differentiation in the pre-osteoblastic MC3T3-E1 cell line, human bone marrow-derived mesenchymal stem cells (hBMSCs) and rat bone marrow-derived mesenchymal stem cells (rBMSCs) were comprehensively evaluated. The results showed that GNPs with all of three different sizes had excellent biocompatibility, and their effects on induction of osteogenic differentiation of various cell types were dependent on size. Specifically, 45-nm GNPs showed more pronounced alkaline phosphatase (ALP) activity, mineralized nodule formation and expression of osteogenic marker genes compared with the 18-nm group, while 4-nm GNPs reduced the above osteogenic effects. Meanwhile, β-catenin and p-GSK-3β were upregulated by GNPs-45 nm and GNPs-18 nm, but suppressed by GNPs-4 nm, indicating that Wnt/β-catenin signaling pathway mighy play an important role in GNPs-induce osteogenic differentiation. In addition, specific blocking of Wnt/β-catenin signals by KYA1797K inhibited 45 nm GNPs-induced osteogenic differentiation of MC3T3-E1 cells. Furthermore, 45-nm GNPs conjugated with PEG-hydrogel were chosen for in vivo bone regeneration testing in rabbits with 4-mm femur defects. The results demonstrated that the GNPs stimulated bone regeneration rapidly and effectively. Such comprehensive evaluation of GNPs' effects on in vitro osteogenic differentiation and in vivo bone regeneration could promote their applications in clinical translation.
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