The mesenchymal stem cell marker CD248 (endosialin) is a negative regulator of bone formation in mice.
OBJECTIVE
CD248 (tumor endothelial marker 1/endosialin) is found on stromal cells and is highly expressed during malignancy and inflammation. Studies have shown a reduction in inflammatory arthritis in CD248-knockout (CD248(-/-) ) mice. The aim of the present study was to investigate the functional effect of genetic deletion of CD248 on bone mass.


METHODS
Western blotting, polymerase chain reaction, and immunofluorescence were used to investigate the expression of CD248 in humans and mice. Micro-computed tomography and the 3-point bending test were used to measure bone parameters and mechanical properties of the tibiae of 10-week-old wild-type (WT) or CD248(-/-)  mice. Human and mouse primary osteoblasts were cultured in medium containing 10 mM β-glycerophosphate and 50 μg/ml ascorbic acid to induce mineralization, and then treated with platelet-derived growth factor BB (PDGF-BB). The mineral apposition rate in vivo was calculated by identifying newly formed bone via calcein labeling.


RESULTS
Expression of CD248 was seen in human and mouse osteoblasts, but not osteoclasts. CD248(-/-)  mouse tibiae had higher bone mass and superior mechanical properties (increased load required to cause fracture) compared to WT mice. Primary osteoblasts from CD248(-/-)  mice induced increased mineralization in vitro and produced increased bone over 7 days in vivo. There was no decrease in bone mineralization and no increase in proliferation of osteoblasts in response to stimulation with PDGF-BB, which could be attributed to a defect in PDGF signal transduction in the CD248(-/-)  mice.


CONCLUSIONS
There is an unmet clinical need to address rheumatoid arthritis-associated bone loss. Genetic deletion of CD248 in mice results in high bone mass due to increased osteoblast-mediated bone formation, suggesting that targeting CD248 in rheumatoid arthritis may have the effect of increasing bone mass in addition to the previously reported effect of reducing inflammation.
University of Birmingham, Birmingham, UK.
Amy J
AJ
Naylor
Eman
E
Azzam
Stuart
S
Smith
Adam
A
Croft
Callum
C
Poyser
Jeremy S
JS
Duffield
David L
DL
Huso
Steffen
S
Gay
Caroline
C
Ospelt
Mark S
MS
Cooper
Clare
C
Isacke
Simon R
SR
Goodyear
Michael J
MJ
Rogers
Christopher D
CD
Buckley
D000818:Animals; D015703:Antigens, CD / Q000235:genetics / Q000378:metabolism*; D000077214:Becaplermin; D001842:Bone and Bones / Q000187:drug effects / Q000378:metabolism*; D002113:Calcification, Physiologic / Q000187:drug effects / Q000502:physiology; D049109:Cell Proliferation / Q000187:drug effects; D002478:Cells, Cultured; D006801:Humans; D059630:Mesenchymal Stem Cells / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D009363:Neoplasm Proteins / Q000235:genetics / Q000378:metabolism*; D010006:Osteoblasts / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D010012:Osteogenesis / Q000187:drug effects / Q000502:physiology*; D020574:Proto-Oncogene Proteins c-sis / Q000494:pharmacology
D015703:Antigens, CD; D009363:Neoplasm Proteins; D020574:Proto-Oncogene Proteins c-sis; C509258:tumor endothelial marker 1, mouse; D000077214:Becaplermin