Polyethylene particle-induced bone resorption in alpha-calcitonin gene-related peptide-deficient mice.
This study investigates the impact of alpha-CGRP on bone metabolism after implantation of polyethylene particles. alpha-CGRP knockout mice showed less osteolysis compared with wildtype mice. The local neurogenic microenvironment might be a crucial factor in particle-induced osteolysis.


BACKGROUND
Periprosthetic osteolysis is the major reason for aseptic loosening in joint arthroplasty. This study aimed to investigate the potential impact of alpha-calcitonin gene-related peptide (alpha-CGRP) deficiency on bone metabolism under conditions of polyethylene particle-induced osteolysis.


METHODS
We used the murine calvarial osteolysis model based on polyethylene particles in 14 C57BL 6 mice and 14 alpha-CGRP-deficient mice divided into four groups of 7 mice each. Groups 1 (C57BL/J 6) and 3 (alpha-CGRP knockout) received sham surgery, and groups 2 (C57BL/J 6) and 4 (alpha-CGRP knockout) were treated with polyethylene particles. Qualitative and quantitative 3D analyses were performed using microCT. 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 alpha-CGRP-deficient mice compared with their corresponding wildtype C57BL 6 mice as confirmed by histomorphometric data (p < 0.001) and microCT (p < 0.01). Osteoclast numbers were significantly reduced in group 3 and the particle subgroup compared with group 1 (p < 0.001). We observed a >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, alpha-CGRP knockout mice did not show the expected extended osteolysis compared with wildtype mice expressing alpha-CGRP. One of the most reasonable explanations for the observed decrease in osteolysis could be linked to the osteoprotegerin (OPG)/RANK/RANKL system in alpha-CGRP-deficient animals. As a consequence, the fine tuning of osteoclasts mediating resorption in alpha-CGRP-null mice may be deregulated.
Wedemeyer
Christian
C
Department of Orthopaedics, University of Duisburg-Essen, Essen, Germany.
Neuerburg
Carl
C
Pfeiffer
Anne
A
Heckelei
Anja
A
Bylski
David
D
von Knoch
Fabian
F
Schinke
Thorsten
T
Hilken
Gero
G
Gosheger
Georg
G
von Knoch
Marius
M
Löer
Franz
F
Saxler
Guido
G
D000135:Acid Phosphatase / Q000378:metabolism; D000818:Animals; D001862:Bone Resorption / Q000139:chemically induced / Q000473:pathology*; D015740:Calcitonin Gene-Related Peptide / Q000172:deficiency*; D002452:Cell Count; D007150:Immunohistochemistry; D020007:Implants, Experimental; D007527:Isoenzymes / Q000378:metabolism; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D010010:Osteoclasts / Q000166:cytology / Q000187:drug effects; D020959:Polyethylene / Q000494:pharmacology*; D053245:RANK Ligand / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012886:Skull / Q000187:drug effects / Q000473:pathology; D000071681:Tartrate-Resistant Acid Phosphatase; D014057:Tomography, X-Ray Computed
D007527:Isoenzymes; D053245:RANK Ligand; D020959:Polyethylene; D000135:Acid Phosphatase; D000071681:Tartrate-Resistant Acid Phosphatase; D015740:Calcitonin Gene-Related Peptide