Growth factor regulation of smooth muscle actin expression and contractionof human articular chondrocytes and meniscal cells in a collagen-GAG matrix

Recent work has demonstrated that human articular chondrocytes and meniscus cells can express the gene for a contractile actin isoform, a-smooth muscl e actin (SMA), in vivo. The objective of the present study was to evaluate the effects of two growth factors, transforming growth factor (TGF)-beta1 a nd platelet-derived growth factor (PDGF)-BB, on the SMA content of these ce lls and their contraction of a collagen-glycosaminoglycan (GAG) analog of e xtracellular matrix in vitro. TGF-beta1 was found to markedly increase SMA content of the cells and PDGF-BB decreased SMA expression, with both findin gs achieving statistical significance. A notable finding was the increased contraction of the collagen-GAG matrix induced by TGF-beta1 and the decreas e in contraction resulting from PDGF-BB treatment, indicating a causal rela tionship between expression of SMA and the contractility of the cells. A no vel cell force monitor, employed to estimate the force exerted per cell, de monstrated a higher force exerted by the TGF-beta1-treated cells. The findi ngs demonstrate that the expression of SMA by articular chondrocytes and me niscal cells and their associated contractile behavior can be regulated by selected growth factors. This work provides a foundation for the rational i nvestigation of the mechanisms underlying SMA-enabled contraction of these cell types and the control of this behavior in tissue engineering. (C) 2001 Academic Press.