Surface microstructures of tricalcium phosphate regulate the autophagy of osteoclasts through the MAPK/ERK signaling pathway

Ceramics, including tricalcium phosphate (TCP), are widely used in bioengineering medicine due to their biocompatibility and bone conductivity. While calcium phosphate materials can induce bone formation without exogenous factors, the specific physical structures of these materials play a crucial role in their biological effects. Autophagy is involved in osteoclast proliferation, differentiation, and activation, with the MAPK signaling pathway being a key regulator of these processes. This study aimed to explore how the surface microstructures of TCP affect osteoclast function and illustrate the underlying mechanism related to autophagy. Three types of TCP disks with different surface microstructures (TCPc, TCPm, and TCPp) were prepared and characterized using scanning electron microscopy. Mouse mononuclear macrophage RAW264.7 cells were induced to differentiate into osteoclasts and cocultured with the TCP disks. Various experiments, including CCK-8 assays, MDC autophagy staining, quantitative real-time PCR, and Western blot analysis, were conducted to evaluate cell viability, autophagy activity, gene expression, and protein expression related to osteoclast function and the MAPK signaling pathway. The surface microstructures of the TCP disks significantly influenced osteoclast activity. TCPc promoted osteoclast proliferation and survival, while TCPm and TCPp inhibited osteoclast activity. The autophagosomes in the TCPm and TCPp groups were reduced, and the expression of autophagy-related proteins (Atg5, Atg7, LC3A, LC3B, Beclin-1) was lower compared to the TCPc and blank groups. The expression of osteoclast-related genes (TRAP, CTSK) was highest in the blank group, followed by the TCPc group, and lowest in the TCPm and TCPp groups. The phosphorylation levels of ERK, p38, and JNK in the TCP groups were lower than those in the blank group, indicating that TCP surface structures inhibit the MAPK signaling pathway. The study highlights the importance of material surface microstructures in bone tissue formation and suggests potential strategies for regulating bone metabolism through material design.