Decreased bone formation and osteopenia in mice lacking alpha-calcitonin gene-related peptide.
We recently described an unexpected high bone mass phenotype in mice lacking the Calca gene that encodes CT and alphaCGRP. Here we show that mice specifically lacking alphaCGRP expression display an osteopenia caused by a decreased bone formation. These results show that alphaCGRP is a physiological activator of bone formation and that the high bone mass phenotype of the Calca-deficient mice is caused by the absence of CT.


BACKGROUND
Calcitonin (CT) and alpha-calcitonin gene-related peptide (alphaCGRP) are two polypeptides without completely defined physiologic functions that are both derived from the Calca gene by alternative splicing. We have recently described an unexpected high bone mass phenotype in mice carrying a targeted deletion of the Calca gene. To uncover whether this phenotype is caused by the absence of CT or by the absence of alphaCGRP, we analyzed a mouse model, where the production of alphaCGRP is selectively abolished.


METHODS
Bones from Calca(-/-) mice, alphaCGRP(-/-) mice, and their corresponding wildtype controls were analyzed using radiography, muCT imaging, and undecalcified histology. Cellular activities were assessed using dynamic histomorphometry and by measuring the urinary collagen degradation products. CT expression was determined using radioimmunoassay and RT-PCR. Immunohistochemistry was performed using an anti-CGRP antibody on decalcified bone sections.


RESULTS
Unlike the Calca-deficient mice, the alphaCGRP-deficient mice do not display a high bone mass phenotype. In contrast, they develop an osteopenia that is caused by a reduced bone formation rate. Serum levels and thyroid expression of CT are not elevated in alphaCGRP-deficient mice. While CGRP expression is detectable in neuronal cell close to trabecular bone structures, the components of the CGRP receptor are expressed in differentiated osteoblast cultures.


CONCLUSIONS
The discrepancy between the bone phenotypes of Calca(-/-) mice and alphaCGRP(-/-) mice show that the high bone mass phenotype of the Calca(-/-) mice is caused by the absence of CT. The osteopenia observed in the alphaCGRP(-/-) mice that have normal levels of CT further show that alphaCGRP is a physiologic activator of bone formation.
Schinke
Thorsten
T
Department of Trauma, Hand, and Reconstructive Surgery, Hamburg University School of Medicine, Martinistrasse 52, Hamburg 20246, Germany.
Liese
Sarah
S
Priemel
Matthias
M
Haberland
Michael
M
Schilling
Arndt F
AF
Catala-Lehnen
Philip
P
Blicharski
Dagmar
D
Rueger
Johannes M
JM
Gagel
Robert F
RF
Emeson
Ronald B
RB
Amling
Michael
M
D017398:Alternative Splicing; D000818:Animals; D001851:Bone Diseases, Metabolic / Q000473:pathology*; D001842:Bone and Bones / Q000473:pathology; D002116:Calcitonin / Q000737:chemistry / Q000235:genetics*; D015740:Calcitonin Gene-Related Peptide / Q000235:genetics* / Q000378:metabolism*; D017353:Gene Deletion; D007150:Immunohistochemistry; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D010006:Osteoblasts / Q000378:metabolism; D010012:Osteogenesis; D010455:Peptides / Q000737:chemistry; D010641:Phenotype; D011863:Radioimmunoassay; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014057:Tomography, X-Ray Computed
D010455:Peptides; D002116:Calcitonin; D015740:Calcitonin Gene-Related Peptide