Size-dependent effects of gold nanoparticles on osteogenic differentiation of human periodontal ligament progenitor cells

Gold nanoparticles (AuNPs) have been reported to promote osteogenic differentiation of mesenchymal stem cells and osteoblasts, but little is known about their effects on human periodontal ligament progenitor cells (PDLPs). In this study, we evaluated the effects of AuNPs with various diameters (5, 13 and 45 nm) on the osteogenic differentiation of PDLPs and explored the underlying mechanisms. 5 nm AuNPs reduced the alkaline phosphatase activity, mineralized nodule formation and expression of osteogenic genes, while 13 and 45 nm AuNPs increased these osteogenic markers. Compared with 13 nm, 45 nm AuNPs showed more effective in promoting osteogenic differentiation. Meanwhile, autophagy was up-regulated by 13 and 45 nm AuNPs but blocked by 5 nm AuNPs, which corresponded with their effects on osteogenic differentiation and indicated that autophagy might be involved in this process. Furthermore, the osteogenesis induced by 45 nm AuNPs could be reversed by autophagy inhibitors (3-methyladenine and chloroquine). These findings revealed that AuNPs affected the osteogenic differentiation of PDLPs in a size-dependent manner with autophagy as a potential explanation, which suggested AuNPs with defined size could be a promising material for periodontal bone regeneration.