Polyethylene Particle–Induced Bone Resorption in α‐Calcitonin Gene–Related Peptide–Deficient Mice

This study investigates the impact of α-CGRP on bone metabolism after implantation of polyethylene particles. α-CGRP knockout mice showed less osteolysis compared with wildtype mice. The local neurogenic microenvironment might be a crucial factor in particle-induced osteolysis. Introduction: Periprosthetic osteolysis is the major reason for aseptic loosening in joint arthroplasty. This study aimed to investigate the potential impact of α-calcitonin gene–related peptide (α-CGRP) deficiency on bone metabolism under conditions of polyethylene particle–induced osteolysis. Materials and Methods: We used the murine calvarial osteolysis model based on polyethylene particles in 14 C57BL 6 mice and 14 α-CGRP–deficient mice divided into four groups of 7 mice each. Groups 1 (C57BL/J 6) and 3 (α-CGRP knockout) received sham surgery, and groups 2 (C57BL/J 6) and 4 (α-CGRP knockout) were treated with polyethylene particles. Qualitative and quantitative 3D analyses were performed using μCT. In addition, bone resorption was measured within the midline suture by histological examination. The number of osteoclasts was determined by counting the TRACP+ cells. Calvarial bone was tested for RANKL expression by RT-PCR and immunocytochemistry. Results: Bone resorption was significantly reduced in α-CGRP–deficient mice compared with their corresponding wildtype C57BL 6 mice as confirmed by histomorphometric data (p 3-fold increase of basal RANKL mRNA levels within group 1 compared with group 3. Additional low RANKL immunochemistry staining was noted in groups 3 and 4. Conclusions: In conclusion, α-CGRP knockout mice did not show the expected extended osteolysis compared with wildtype mice expressing α-CGRP. One of the most reasonable explanations for the observed decrease in osteolysis could be linked to the osteoprotegerin (OPG)/RANK/RANKL system in α-CGRP–deficient animals. As a consequence, the fine tuning of osteoclasts mediating resorption in α-CGRP–null mice may be deregulated.