Long Term Durable Repaired Cartilage Induced By SOX9 in Situ with Bone Marrow-Derived Mesenchymal Stem Cells

Background: Microfracture is a common procedure for cartilage repair, but it often produces inferior fibrocartilage. We previously reported that a super positively charged SOX9 (scSOX9) promoted hyaline-like cartilage regeneration by inducing bone marrow derived mesenchymal stem cell differentiation into chondrocytes in vivo. Here we examined the long-term efficacy of cartilage repair induced by microfracture with scSOX9 by assessing the biomechanical property of the repaired cartilage.

Methods: A cartilage defect was created at the right femoral trochlear groove in New Zealand female rabbits and microfracture was performed. The scSOX9 protein was administered at the site of microfracture incorporated in a collagen membrane.

Results: At 12 and 24 weeks, scSOX9 treatment induced hyaline-like cartilage while collagen-membrane alone induced fibrocartilage and mutant scSOX9-A76E poorly induced cartilage repair. The cartilage matrix in scSOX9-treated group showed highly enriched proteoglycan content.

Consistent with the histological feature and the thickness of the repaired cartilage, the mechanical property of scSOX9-induced cartilage was also similar to that of normal cartilage.

Conclusion: This long-term in vivo study demonstrated that in combination with microfracture, scSOX9 was able to induce reparative tissue with features of hyaline cartilage which was durable in long-term. This technology has the potential to translate into clinical use for cartilage repair to prevent progression to osteoarthritis.

Biomechanics of repaired cartilage: The distal femur was examined by three-dimensional assessment for repaired cartilage and bone structure to gain global biomechanical features by using the Mach-1 V500c mechanical tester (Biomomentum). At each site, a rapid indentation of the cartilage was performed in 1 second to a depth of 50 um using a spherical indenter (diameter = 1.0 mm) attached under a single-axis load cell (100 N load range and resolution of 5 mN). The load versus displacement curve obtained in indentation fitted to an elastic model in indentation with corresponding cartilage thickness for determination of mechanical properties. To measure cartilage thickness, the spherical indenter was replaced with a needle probe and the mechanical tester moves the needle towards the sample. The cartilage thickness corresponds to the displacement between the first increase in the load (cartilage surface) and a steep increase in the load (subchondral bone).