Abstract
INTRODUCTION
The generation of cartilage from progenitor cells for the purpose of cartilage repair is often hampered by unwanted hypertrophic differentiation of the generated tissue due to endochondral ossification. Continuing on our earlier studies, our goal is to further improve the engineering of hyaline cartilage for the treatment of a cartilage defect in our in vivo model for subperiosteal generation of cartilage, by tuning the differentiation status of the generated cartilage and prevent hypertrophic differentiation. As a healthy cartilage matrix contains high amounts of aggrecan we hypothesise that aggrecan supplementation of the bio-gel used in the generation of the subperiosteal cartilage, mimics the composition of the extracellular matrix environment of cartilage with potential beneficial properties for the engineered cartilage.
METHODS
A 2% (m/v) low melting agarose was injected between the bone and periosteum at the upper medial side of the tibia of both legs of New Zealand white rabbits (DEC 2012–151). The agarose was left unloaded (n=7) or supplemented (n=7) with 2% (w/v) bovine aggrecan (Sigma-Aldrich). After 14 days, rabbits were euthanised. Generated subperiosteal cartilage tissue was analysed for weight, GAG and DNA content. In addition, RT-qPCR and (immuno)histochemistry was performed for key markers of different phases of endochondral ossification.
RESULTS
The nett weight of the generated subperiosteal cartilage tissue was not significantly different between groups, nor was the GAG content different. No significant differences in chondrogenic marker expression (COL2A1, SOX9, ACAN and PTHrP) were detected. Interestingly, gene expression levels of hypertrophic markers COL10A1 and ALPL were significantly decreased. COL1A1 expression was not significantly different between groups.
DISCUSSION
In summary, generation of subperiosteal cartilage was successful when an agarose bio-gel was injected beneath the periosteum. The addition of aggrecan to the bio-gel did not result in differences in weight or GAG content in cartilage samples between conditions. However, lower levels of hypertrophic markers were observed, while leaving chondrogenic marker expression unaltered. These data show the potential of aggrecan to favourably influence the subperiosteal microenvironment for the in vivo generation of hyaline cartilage for the optimisation of cartilage regenerative medicine approaches.
