Exogenous collagen-enhanced recruitment of mesenchymal stem cells during rabbit articular cartilage repair

Abstract

Background Despite the well-known effect of type-I collagen in promoting cartilage repair, the mechanism still remains unknown. In this study we investigated this mechanism using a rabbit model of cartilage defects. Animals and methods 5-mm-diameter full-thickness defects were created on both patellar grooves of 53 Japanese white rabbits (approximately 13 weeks old). The left defect was filled with collagen gel and the right defect was left empty. The rabbits were killed and examined morphometrically until the twenty-fourth postoperative week, by (1) evaluation of matrix production, (2) enumeration of the total number of cells engaged in cartilage repair, (3) enumeration of the proliferating cells, (4) localization of mesenchymal stem cells, and (v) localization of apoptotic cells. Results We found that type-I collagen enhances cell recruitment, and thereby increases the number of proliferating cells. A considerable proportion of the proliferating cells were identified as bone marrow-derived mesenchymal stem cells. However, type-I collagen does not prevent the chondrocyte precursors from undergoing apoptotic disengagement from the chondrogenic lineage. Interpretation Type-I collagen promotes cartilage repair by enhancing recruitment of bone marrowderived mesenchymal stem cells. Additional use of agent(s) that sustain mesenchymal stem cells along the chondrogenic path of differentiation may constitute an appropriate environment for cartilage repair.