Contractile behavior of smooth muscle actin-containing osteoblasts in collagen-GAG matrices in vitro: implant-related cell contractions

The contraction of connective tissue cells may facilitate their production and maintenance of extracellular matrix architecture and can benefit healin g through wound closure. However, aberrant cell contraction can result in p athological contracture. Implants may stimulate this process leading to con tracture of the surrounding fibrous capsule. In the case of compliant porou s matrices used for tissue engineering the cell contraction may cause the c onstriction of pores and the distortion of the implant. The objective of th is study was to determine if osteoblasts expressed a specific muscle actin, a-smooth muscle actin (SMA), that could provide for their contraction. Imm unohistochemistry revealed the presence of SMA in some cells in all of thre e human and three canine trabecular bone specimens. The majority of the cel ls of an osteoblastic cell line, MC3T3-E1, also expressed this actin isofor m in two-dimensional culture and when seeded into a collagen-glycosaminogly can (GAG) matrix. These SMA-containing cells were found to cause contractio n of the collagen-GAG analog of extracellular matrix. These findings demons trate that osteoblasts can display contractile behavior that might help to explain the mechanism by which they impart architecture to bone matrix, inc luding that at implant interfaces. An understanding of this process could a lso guide the development of matrices for bone tissue engineering. (C) 2000 Elsevier Science Ltd. All rights reserved.