Smooth muscle actin expression by human articular chondrocytes and their contraction of a collagen-glycosaminoglycan matrix in vitro

Recent studies have demonstrated that human articular chondrocytes can expr ess the gene for a contractile muscle actin, ct-smooth muscle actin (SMA), in situ. One objective of this work was to evaluate the SMA-content of isol ated human articular chondrocytes using Western blot analysis and to correl ate the amount of SMA in the cells with passage number and the number of da ys in culture. A second objective was to determine if articular cartilage-d erived cells expressing the gene for SMA in vitro also continue to express type II collagen. A final aim of the current study was to determine if SMA- containing cartilage-derived cells were capable of contracting a collagen-g lycosaminoglycan analog of extracellular matrix in vitro. Articular chondro cytes were isolated from 13 patients undergoing total joint arthroplasty. C ells were serially passaged through passage 7. Samples were allocated for W estern blot analysis of SMA. Cells in monolayer culture were also stained i mmunohistochemically for SMA and type II collagen. Cells from passage 3 and 7 were seeded into a porous type 1 collagen-glycosaminoglycan matrix and t he diameter of the scaffolds measured every other day for 21 days. Immunohi stochemistry of the articular cartilage samples revealed SMA in the articul ar chondrocytes in situ with a greater percentage of cells staining positiv e in the superficial half (60 +/- 1.2%; mean +/- SEM) of the cartilage than in the basal half (28 +/- 1.3%). There was an increasing amount of SMA in the cells in monolayer culture with passage number and a meaningful correla tion of the SMA content with the days in culture (linear regression analysi s; R-2 = 0.72). Double staining for SMA and type II collagen showed that ty pe II collagen-expressing cells in monolayer could also express SMA. SMA-co ntaining cells were found to contract the collagen-glycosaminoglycan matrix , with the cells containing more SMA (passage 7 cells) displaying mon matri x contraction than those with a lesser amount of SMA (passage 3 cells). The results indicate that control of the expression of SMA may be important wh en employing articular chondrocytes, expanded in monolayer culture, for imp lantation alone or in a cell-seeded matrix for cartilage repair procedures. (C) 2001 Orthopaedic Research Society. Published by Elsevier Science Ltd. All rights reserved.