Abstract
Osteogenic protein‐1 (OP‐1, also called BMP‐7), a member of the BMP family and the TGF‐β superfamily, induces formation of new bone and cartilage, but also regulates a wide array of processes. In the present study, the expression of several characteristic biochemical markers of ligaments, such as Six1, Scleraxis, aggrecan, and type I collagen in primary cultures of adult rat medial collateral ligament (MCL) cells was determined. The effects of OP‐1 on cell proliferation and on gene expression were subsequently examined. OP‐1 stimulated cell proliferation, alkaline phosphatase (AP) activity, and the steady‐state mRNA levels of the transcription factor Runx2/Cbfa1 in a dose‐ and time‐dependent manner. The mRNA levels of type I collagen only increased slightly, but the activity of the cloned collagen promoter increased by 2‐fold in transiently transfected MCL cells. OP‐1 also stimulated aggrecan mRNA expression. The mRNA levels of Six1 and Scleraxis were not detectably altered by OP‐1. In control cultures, the steady‐state mRNA levels of ActR‐I, BMPR‐IA, BMPR‐IB, and BMPR‐II increased as a function of time in culture. The mRNA levels of BMP‐1 and ‐4 increased significantly after 12 days, but those of BMP‐2 and ‐6 did not change. The GDF‐1, ‐3, ‐5, ‐6, and ‐8 mRNA levels in the control cultures also increased as a function of time. OP‐1 treatment stimulated mRNA expression of BMPR‐IA and BMPR‐II, but had little effect on ActR‐I and BMPR‐IB mRNA expression. OP‐1 lowered the BMP‐1, ‐2, and ‐6 mRNA levels without changing the BMP‐4 mRNA level. OP‐1 treatment also reduced the mRNA levels of GDFs detected. In summary, the present study demonstrated that OP‐1 stimulated cell proliferation and mRNA expression of several biochemical markers in this ligament cell culture model and established the spatial and temporal appearance of several members of the TGF‐β superfamily. © 2003 Wiley‐Liss, Inc.