Abstract:

Objective To explore whether protein kinase R-like ER kinase(PERK)-eukaryotic translation initator factor 2(eIF2α)-activating transcription factor 4(ATF4) signalling pathway is involved in periprosthetic osteolysis induced by tricalcium phosphate（TCP）wear particles in mice. Methods Thirty male ICR mice were randomly divided into sham group (n=10), TCP group (n=10) and salurinal (SAL) group (n=10). A murine calvarial model of osteolysis was established by 30 mg of TCP wear particles implantation onto the surface of bilateral parietal bones following removal of the periosteum. From the second postoperative day, SAL (1 mg/kg) was locally injected to the calvarium under the periosteum three times a week. After 2 weeks, the calvaria and serum were obtained. Western blotting was used to examine the expression of ER stress marker glucoseregulated protein 78（GRP78）and C/EBP homologous protein (CHOP), together with activation of PERK-eIF2α-ATF4 signalling pathway. Tartrate resistant acid phosphatase（TRAP）staining, HE staining and Real-time PCR were performed to observe the effects of SAL on TCP wear particles-induced osteolysis, osteoclastogenesis and mRNA levels of osteoclastogenic genes including TRAP, cathepsin K and c-Fos in the calvaria, respectively. Enzyme-linked immumsorbent as ay (ELISA) was performed to determine the effect of SAL on serum level of tumor necrosis factor-α (TNF-α), prostaglandin E₂ (PGE₂) and interleukin-1 beta (IL-1β). Results TCP wear particles triggered remarkable ER stress responses in the mouse calvaria, which was confirmed by up-regulation of ER stress markers GRP78 and C/EBP homologous protein (CHOP), and activation of protein kinase RNA-like ER kinase-eIF2α-activating transcription factor 4 pathway (including phosphorylation of both protein kinase RNA-like ER kinase and eIF2α and elevated level of activating transcription factor 4) (P<0.05). Block of the ER stress response with the eIF2α specific inhibitor salubrinal markedly prevented TCP wear particles-induced osteoclastogenesis and osteolysis, and suppressed the increase in mRNA level of osteoclastogenic genes such as TRAP, MMP-9 and c-fos in the mouse calvaria (P<0.05). In addition, SAL significantly inhibited TCP wear particles-induced release of TNF-α, PGE2 and IL-1β (P<0.05). Conclusion PERK-eIF2α-ATF4 pathway is involved in the calvarial osteolysis induced by TCP wear particle in mice, and inhibition of this signalling pathway reduces periprosthetic osteolysis and prostheses caused by TCP wear debris.

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