Presented in part in preliminary form as a short communication in Trans Orthop Res Soc 2001, p. 620.
Article first published online: 1 MAR 2002
Copyright © 2002 ASBMR
Journal of Bone and Mineral Research
Volume 17, Issue 3, pages 415–425, March 2002
How to Cite
Hankenson, K. D. and Bornstein, P. (2002), The Secreted Protein Thrombospondin 2 Is an Autocrine Inhibitor of Marrow Stromal Cell Proliferation. J Bone Miner Res, 17: 415–425. doi: 10.1359/jbmr.2002.17.3.415
The authors have no conflict of interest.
- Issue published online: 2 DEC 2009
- Article first published online: 1 MAR 2002
- Manuscript Accepted: 29 OCT 2001
- Manuscript Revised: 17 SEP 2001
- Manuscript Received: 23 MAY 2001
- marrow stromal cell;
- thrombospondin 2;
Marrow stromal cells (MSCs) are obtained in increased number from mice in which the thrombospondin 2 (TSP2) gene is disrupted, and these cells show increased DNA synthesis in vitro. To examine more closely the role of TSP2 in the physiology and osteogenic differentiation of MSCs, an in-depth characterization of TSP2-null MSCs was conducted. Determination of TSP2 protein content by Western analysis and RNA levels by reverse-transcription polymerase chain reaction (RT-PCR) indicated that MSCs are the primary source of TSP2 in the marrow and secrete abundant TSP2 into culture medium. Morphologically, the TSP2-null and wild-type (WT) cell populations were similar and by flow cytometry contained equivalent numbers of CD44+, Mac1+, intercellular adhesion molecule-1 (ICAM-1+), and ScaI+ cells. TSP2-null cells showed delayed mineralization associated with an increased rate of proliferation. Consistent with this finding, there was a decrease in expression of collagen and osteocalcin RNA by TSP2-null MSCs on day 7 and increased osteopontin expression on day 7 and day 14. In add-back experiments, recombinant TSP2 produced a dose-dependent decrease in proliferation. This reduction was associated with an accumulation of TSP2-treated cells in the G1 phase of the cell cycle and did not result from an increase in apoptosis. When TSP2 treatment was terminated, the cell population reentered the S phase. We conclude that the increased endosteal bone formation observed in TSP2-null mice results primarily from the failure of TSP2 to regulate locally MSC cell cycle progression.