To determine whether differentiated chondrocytes are motile.
Calf articular chondrocytes isolated from six animals were cultured in spinner flasks and removed on days 3 and 7. Boyden chamber assays and time-lapse videomicroscopy were performed to monitor and quantify cell migration. A novel method for selectively harvesting and metabolically labeling the migrated cells was developed, based on cell movement to the underside of the Boyden chamber membranes. The 3H-collagen synthesized by these cells was purified and analyzed by SDS-PAGE and autoradiography either before or after cyanogen bromide cleavage.
In Boyden chambers, locomotion of day 3 chondrocytes on fibronectin-coated membranes was approximately 3-fold higher than on bovine serum albumin-coated controls (39+/-15 vs 12+/-8 cells/mm(2), respectively (P=0.005)). Insulin-like growth factor-I (IGF-I, 10 ng/ml) was chemotactic, increasing motility to 87+/-16 cells/mm(-) (difference from fibronectin alone: P=0.0003). A similar response was observed for day 7 cells, but IGF-I activation was not as pronounced (P=0.055). The collagen patterns produced by the migrated cells closely resembled those of standard collagen type II, without any evidence of collagen I production. In videotracking experiments, motile cells attached on fibronectin exhibited typical lamellipodia and filopodia, and approximately 30% of attached cells were motile (speed >1 micro m/h and directional persistence >1h). Typical cell path lengths were 30-50 micro m, substantially greater than a full cell length displacement.
A population of well-differentiated chondrocytes capable of matrix (COL II) synthesis are motile in vitro. This original finding opens new avenues to study the potential of motile cells for cartilage repair.