PINK1/Parkin-dependent mitophagy regulates macrophage polarization and osseointegration of titanium implant in inflammatory microenvironments

Abstract

A controlled inflammatory response, particularly the timely transition from pro-inflammatory (M1) to pro-regenerative (M2) macrophages, is crucial for successful osseointegration of titanium (Ti) implants. However, the intracellular mechanisms regulating this phenotypic switch remain unclear. Given the close interplay between inflammation and mitochondrial dysfunction, we investigated the role of PINK1/Parkin-dependent mitophagy in macrophage polarization at the Ti implants interface. Micro-/nanostructured Ti surfaces, including sandblasted/acid-etched (SLA) and anodized (AO) surfaces, were evaluated in comparison with polished (PT) controls. Both SLA and AO surfaces promoted M2 macrophage polarization in vitro and in vivo, accompanied by upregulation of the PINK1/Parkin mitophagy pathway. Silencing Pink1 using siRNA abolished surface-induced M2 polarization, demonstrating the essential role of PINK1/Parkin-dependent mitophagy in this process. Under lipopolysaccharide (LPS)– induced inflammatory conditions, AO surfaces partially restored M2 polarization and mitophagy activation compared to PT controls. However, this effect alone was insufficient to fully overcome inflammation-mediated suppression. Pharmacological activation of mitophagy using rapamycin (RAPA) further enhanced M2 polarization, promoted osteogenic differentiation and significantly improved osseointegration under inflammatory conditions. In vivo validation using a rat distal femur implantation model demonstrated that RAPA-enhanced bone integration was markedly attenuated by Pink1 knockdown, confirming the mechanistic dependence on PINK1/Parkin signaling. These findings identify PINK1/Parkin-dependent mitophagy as a critical intracellular regulator of macrophage polarization and peri-implant immune balance and highlight mitophagy activation as a promising therapeutic strategy to enhance Ti implant osseointegration in inflammatory microenvironments.