Comparison of ligamentization potential between anterior cruciate ligament- derived cells and adipose- derived mesenchymal stem cells reseeded to acellularized tendon allograft

Abstract

Aims To test the hypothesis that reseeded anterior cruciate ligament (ACL)-derived cells have a better ability to survive and integrate into tendon extracellular matrix (ECM) and accelerate the ligamentization process, compared to adipose-derived mesenchymal stem cells (ADM-SCs). Methods Acellularized tibialis allograft tendons were used. Tendons were randomly reseeded with ACL-derived cells or ADMSCs. ACL-derived cells were harvested and isolated from remnants of ruptured ACLs during reconstruction surgery and cultured at passage three. Cell suspen-sions (200 mu l) containing 2 x 106 ACL-derived cells or ADMSCs were prepared for the purpose of reseeding. At days 1, 3, and 7 post-reseeding, graft composites were assessed for repop-ulation with histological and immunohistochemical analysis. Matrix protein contents and gene expression levels were analyzed. Results In the graft reseeded with ACL-derived cells, a large number of elongated cells that inte-grated into the matrix were evident at day 3 and day 7. However, in the graft reseeded with ADMSCs, only a small number of elongated cells were found integrated into the matrix. Im-munofluorescence for Ki- 67 and type I collagen confirmed the pronounced production of type I collagen by Ki- 67-positive ACL-derived cells integrated into the ECM. A messenger RNA (mRNA) expression assay demonstrated significantly higher gene expression levels of types I (p = 0.013) and III (p = 0.050) collagen in the composites reseeded with ACL-derived cells than ADMSCs. Conclusion ACL-derived cells, when reseeded to acellularized tendon graft, demonstrated earlier better survival and integration in the tendon ECM and resulted in higher gene expression levels of collagen, which may be essential to the normal ligamentization process compared to ADM-SCs.