Wear particles-induced inflammatory
osteolysis, a major factor of aseptic loosening affects the long-term survival of orthopedic
prostheses. Increasing observations have demonstrated that osteocytes, making up over 95% of all the bone cells, is involved in wear particle-induced periprosthetic
osteolysis, but its mechanism remains unclear. In the present study, we embedded micro-sized
tricalcium phosphate (TCP) particles (30 mg) under the periosteum around the middle
suture of the mouse calvaria to establish a calvarial
osteolysis model and investigated the
biological effects of the particles on calvaria osteocytes in vivo. Results showed that TCP particles induced pyroptosis and activated the NLRP3
inflammasome in calvaria osteocytes, which was confirmed by obvious increases in empty lacunae,
protein expressions of speck-like
protein containing CARD (ASC),
NOD-like receptor protein 3 (NLRP3), cleaved caspase-1 (Casp-1 p20) and cleaved gasdermin D (GSDMD-N), and resulted in elevated ratios of Casp-1 p20/Casp-1 and
interleukin (IL)-1β/pro-IL-1β. Simultaneously, TCP particles enhanced serum levels of
lactate dehydrogenase (LDH) and IL-1β. Furthermore, the pyroptotic effect was reversed by the Casp-1 inhibitor
VX765 or the NLRP3 inhibitor
MCC950. In addition, TCP particles increased the levels of intracellular
reactive oxygen species (ROS) and
malonaldehyde (MDA), whereas decreased the
antioxidant enzyme nuclear factor E2-related factor 2 (Nrf2) level, leading to oxidative stress in calvaria osteocytes; the ROS scavenger
N-acetylcysteine (NAC) attenuated these effects of pyroptotic death and the NLPR3 activation triggered by TCP particles. Collectively, our data suggested that TCP particles promote pyroptotic death of calvaria osteocytes through the ROS/NLRP3/
Caspase-1 signaling axis, contributing to osteoclastogenesis and periprosthetic
osteolysis.