Motile chondrocytes from newborn calf: migration properties and synthesis of collagen II.

OBJECTIVE

To determine whether differentiated chondrocytes are motile.

DESIGN

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.

RESULTS

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.

CONCLUSION

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.