Redifferentiated Human Osteoarthritic Chondrocytes for Articular Cartilage Tissue Engineering and Repair

When chondrocytes are passaged, they lose their phenotype and the ability to form hyaline articular cartilage (AC) in a process termed dedifferentiation, limiting their clinical applications. Transforming growth factor beta (TGFb) is known to differentiate human progenitor cells to chondrocytes by upregulating chondrogenic genes. Therefore, we tested if TGFb could redifferentiate passaged human chondrocytes and restore their ability to form AC. Here we show for the first time that when passaged chondrocytes are cultured in the presence of TGFb3, hyaline- like cartilaginous tissues self-assemble and develop a superficial zone. In addition, we demonstrate that chondrocytes isolated from AC with advanced osteoarthritis (OA) can form cartilaginous tissues of similar quality to that of chondrocytes derived from moderate OA. This is significant as literature suggests that chondrocytes from advanced OA may have an impaired capacity to form tissues. We further demonstrated that high levels of endoglin (a TGFb co-receptor known to enhance signaling) may be required for chondrogenesis by human chondrocytes. This is a novel finding and suggests that for clinical applications cells expressing high levels of endoglin may enhance cartilage repair. Finally, redifferentiated chondrocytes were tested for their capacity to form hyaline-like cartilage in vivo in a rabbit osteochondral defect model; however, the use of these cells resulted in collagen type 2-containing granulation tissue and did not enhance repair when compared to dedifferentiated chondrocytes. Implanting an osteochondral-like tissue construct which resemble native AC may be a better alternative. Studies are ongoing to elucidate methods to generate tissue constructs containing hyaline cartilage, mineralized cartilage, and bone.

Mechanical testing was performed with a Mach-1 micromechanical tester (Biomomentum, Laval, QC) equipped with a 1 kg load cell (0.05 g resolution, 2.5 kHz sample rate). Thicknesses of the constructs were determined through the needle probe method [26] and was measured twice at different locations near the center of the construct and averaged. Construct mechanical properties (bulk modulus, Young’s modulus, and Poisson’s ratio) were determined through Hayes’s double indentation method using two plane-ended indenters (2 and 4 mm), indenting the samples to 10% strain at a rate of 10%/s. Constructs were allowed to equilibrate approximately 20 minutes between indentations.