The authors have no conflict of interest.
Reduced Expression of Platelet Endothelial Cell Adhesion Molecule-1 in Bone Marrow Cells in Mice After Skeletal Unloading†
Article first published online: 4 JAN 2005
Copyright © 2005 ASBMR
Journal of Bone and Mineral Research
Volume 20, Issue 6, pages 1002–1010, June 2005
How to Cite
Sakuma-Zenke, M., Sakai, A., Nakayamada, S., Kunugita, N., Tabata, T., Uchida, S., Tanaka, S., Mori, T., Nakai, K., Tanaka, Y. and Nakamura, T. (2005), Reduced Expression of Platelet Endothelial Cell Adhesion Molecule-1 in Bone Marrow Cells in Mice After Skeletal Unloading. J Bone Miner Res, 20: 1002–1010. doi: 10.1359/JBMR.050102
- Issue published online: 4 DEC 2009
- Article first published online: 4 JAN 2005
- Manuscript Accepted: 29 DEC 2004
- Manuscript Revised: 26 AUG 2004
- Manuscript Received: 6 JUN 2004
- endothelial cell;
- alkaline phosphatase activity;
- colony-forming unit-fibroblastic
One week of tail suspension significantly decreased the expression of PECAM-1 in mouse tibial bone marrow cells but not those of a number of other vascular factors. Anti-PECAM-1 antibody suppressed both ALP+ CFU-f formation and ALP production under co-culture of the osteoblastic cell line and the PECAM-1+ endothelial cell line. This study suggests that the reduced ALP activity after skeletal unloading is related to downregulation of PECAM-1 expression in bone marrow cells in mice.
Introduction: Vascular factors play a role in bone development and regeneration. We tested the hypothesis that skeletal unloading reduces osteogenic potential by inhibiting the molecules related to angiogenesis and/or vasculogenesis in bone marrow cells.
Materials and Methods: Eight-week-old male mice were assigned to three groups after acclimatization for 1 week: ground control (GC), tail suspension (TS), and reloading after 7-day TS (RL). Bilateral tibial and humeral samples were used for analyses. MC3T3-E1, a mouse osteoblastic cell line, and EOMA and ISOS-1, mouse endothelial cell lines, were also used.
Results: Flow cytometric analysis revealed that 7-day TS significantly decreased the expression of platelet endothelial cell adhesion molecule-1 (PECAM-1, CD31) in tibial bone marrow cells, but not those of angiopoietin-1, angiopoietin-2, Flk-1 (vascular endothelial growth factor receptor-2), and vascular endothelial cadherin. The expression of PECAM-1 in tibial marrow cells was reduced at day 3 of TS to 80% and still showed significantly low levels at day 7 of TS to 72% of that at the respective days of GC. This decreased expression of PECAM-1 after 7-day TS showed the GC level at 5-day reloading after 7-day TS. However, the expression of PECAM-1 in humeral marrow cells (internal bone marrow control) after TS and RL remained unchanged and equivalent to that of GC. The expression level of PECAM-1 mRNA was significantly lower at day 7 of TS to 62% of that in GC. Double labeling analyses revealed that PECAM-1+ cells mostly consisted of endothelial cells and partially of granulocytes. In bone marrow cell cultures, the formation of alkaline phosphatase (ALP)+ colony forming units-fibroblastic was significantly reduced in the presence of anti-PECAM-1 antibody in the medium compared with the presence of immunoglobulin G (0.025 times as much as ALP production with immunoglobulin G). ALP production by cultured MC3T3-E1 was enhanced in combination with PECAM-1+ EOMA (1.8 times as much as ALP production by MC3T3-E1 alone), but not in combination with PECAM-1− ISOS-1. Anti-PECAM-1 antibody inhibited the increase in ALP production under co-culture with EOMA.
Conclusions: Our data show that the reduced ALP activity after skeletal unloading is closely correlated with reduced expression of PECAM-1 in bone marrow cells. We speculate that the loss of osteogenic potential after skeletal unloading is caused by the suppression of PECAM-1 signaling on endothelial cellular surface.