Chondrocyte-Derived Decellularized Matrices Support the Expansion and Redifferentiation of Superficial Zone Chondrocytes

• Lilly Smull, Biological Sciences, University of Delaware

• Justin Parreno, Biological Sciences, University of Delaware

Articular cartilage is crucial forproper joint function, providing a surface for frictionless movement and load distribution. However, cartilage has a limited ability to self-repair and any damage initiates degeneration, leading to Osteoarthritis (OA). The superficial zone, the surface layer of cartilage, contains chondrocytes that produce the lubricating molecule proteoglycan 4 (PRG4), which helps create a frictionless environment. This zone deteriorates first in OA. 

Bioengineered cartilage holds promise in repairing small cartilage defects and preventing OA progression. Monolayer-expanded (passaged) chondrocytes, harvested from full-thickness cartilage, are an FDA-approved cell source for cartilage repair. However, our previous work has shown that the redifferentiation of passaged full-thickness chondrocytes does not produce a robust superficial zone due to the limited number of superficial zone chondrocytes (SZC) obtained following monolayer expansion. Compared to deep zone cells, SZC attach poorly and proliferate slowly on polystyrene dishes. Additionally, during cell number expansion, the actin cytoskeleton reorganizes cortical actin into stress fibers and increases the proportion of filamentous (F-)actin to monomeric, globular (G-)actin. The increase in F/G-actin causes an increase in fibroblastic and contractile molecule expression, which coincides with a loss of chondrogenic expression during dedifferentiation. 

Culturing full-thickness chondrocytes on decellularized chondrocyte-derived extracellular matrix (CD-ECM) has been shown to enhance proliferation and reduce dedifferentiation. We hypothesized that expanding SZC on CD-ECM would increase attachment and proliferation rates while reducing SZC dedifferentiation.  In this study, we found that CD-ECM  improves SZC expansion through better attachment, increased proliferation rate, and limiting chondrocyte dedifferentiation. Additionally, tissues formed from SZC passaged in CD-ECM have a higher expression of PRG4 than SZC passaged on polystyrene. Ultimately, using a CD-ECM enhances the expansion and redifferentiation of SZC. Therefore, optimizing expansion methods is necessary to obtain adequate SZC to improve the formation of a robust superficial zone for bioengineering.