Introduction: Recent bone tissue engineering strategies propose recapitulating the endochondral ossification process for an effective repair. To this end, primary human mesenchymal stromal cells (hMSCs) can be primed in vitro towards hypertrophic cartilage (HyC) formation. While holding promises, limits arise from the performance variability associated with the use of primary cells. Recently, we developed a customized hMSC line, the MSOD-B, over-expressing BMP-2 and capable of reproducible cartilage formation in vitro. Following devitalization, the tissue exhibited remarkable osteoinductive properties. Here, we aim to move one step closer to clinical translation by investigating the possibility of decellularizing our cartilage graft and assessing its in vivo regenerative capacity in a rat critical-sized femoral defect.
Method: Our graft consists of in vitro engineered cartilage tissue produced by the MSOD-B. Subsequently, the tissue is decellularized by a combination of hypertonic/hypotonic, detergent (SDS), and DNase washes. The osteoinductivity of decellularized constructs was assessed through subcutaneous implantation in immunodeficient (ID) mice. To evaluate their repair capacity, , decellularized constructs were implanted in a critical-sized femoral defect (5-mm) in Sprague Dawley rats. Repair was assessed 6- and 12-weeks post-implantation through histological, micro-computed tomography (µCT), and mechanical analyses.
Results: We demonstrated the reproducible engineering of decellularized cartilage by exploiting a mesenchymal line. Decellularization resulted in a drastic reduction of DNA (<100ng/construct) with a minimal impact on tissue structure and composition (collagen, GAGS, and embedded growth factors). Remarkably, the capacity to instruct bone formation by endochondral ossification of our decellularized cartilage was not affected. This was validated both at ectopic site and in a critical-sized femoral defect in an immunocompetent rat model, with full-bridge after six weeks and complete bone repair observed 12 weeks post-implantation.
Conclusion and discussion: Our study illustrates the capacity of exploiting customized human lines to produce osteoinductive decellularized extracellular matrices (dECM). The strategy offers both standardization of performance and unlimited tissue availability, opening new avenues for the manufacturing of dECM for bone repair.