Mechanical loading is an important regulator of bone formation and bone loss. Decreased osteoblast number and function are important cellular mechanisms by which mechanical disuse leads to decreased bone formation. Decreased ostesed osteoblast number may be a result of decreased osteoprogenitor proliferation, differentiation, or both. However, the effects of cellular level physical signals on osteoprogenitors are not well understood. In this study, we examined the effects of loading induced oscillatory fluid flow (OFF), a potent regulator of osteoblastic cell function, on marrow stromal cells (MSCs). MSCs subjected to OFF exhibited increased intracellular Ca2+ mobilization. In addition, MSCs exhibited increased proliferation and increased mRNA levels for osteopontin and osteocalcin genes. Collagen I and core binding factor 1 mRNA levels did not change. MSCs subjected to OFF also exhibited decreased alkaline phosphatase activity. These results suggest that MSCs are mechanosensitive and that Ca2+ may play a role in the signaling pathway.
Mechanical loading; Stromal cells; Osteoprogenitors; Osteoblasts; Differentiation; Calcium imaging