Optimizing 3D Co-culture Models to Enhance Synergy Between Adipose-Derived Stem Cells and Chondrocytes for Cartilage Tissue Regeneration

Abstract

Donor cell scarcity is a key barrier for clinical translation of chondrocytes for regenerating cartilage. To overcome this challenge, recent studies have utilized mixed populations of chondrocytes and adult stem cells to show synergistic interactions during 3D co-culture using hydrogels or pellets. Yet, how different co-culture models impact the synergy and resulting cartilage formation remains unknown. To determine the optimal delivery method of a mixed population of stem cells and chondrocytes for cartilage regeneration, here we compared hydrogel and pellet co-culture on the interactions between adipose-derived stem cells (ADSCs) and neonatal chondrocytes (NChons). While both co-culture models supported synergy, hydrogel co-culture led to over a 5-fold increase in synergistic index in cell proliferation, and over 11 and 15-fold increases in synergistic indices for production of cartilage matrix (collagen and sGAG respectively). Interaction index analyses of gene expressions showed hydrogel co-culture significantly reduced hypertrophic phenotype of both ADSCs and NChons. In hydrogel co-culture, NChons contributed to the neocartilage deposition while ADSCs resided outside the newly formed cartilage nodule, serving as supporting cells through paracrine signaling. In contrast, during pellet co-culture, both NChons and ADSCs contributed to the newly formed cartilage. Using the same number of cells, hydrogel co-culture supported higher synergy and produced neocartilage tissues approximately 5 times the size of pellet co-culture. In contrast, pellet co-culture resulted in denser cartilage matrix suitable only for small defects. The outcomes of this study suggest hydrogel delivery as a more advantageous co-culture method for regenerating cartilage using mixed cell populations. Donor cell scarcity is a key barrier for clinical translation of cell-based therapies for cartilage regeneration. To overcome this challenge, here we harnessed abundantly available fat-derived stem cells and mixed them with juvenile chondrocytes, a cell type from native cartilage that can produce robust cartilage. We compared two different co-culture methods, hydrogel versus cell pellet, to grow the mixed cell populations for cartilage regeneration. We demonstrate that 3D hydrogels induced higher synergy using mixed cell populations, allowing cartilage repair with a reduced number of chondrocytes and defect filling of larger volumes than pellets. Future work will validate the potential of using hydrogels to deliver mixed population of fat-derived stem cells and juvenile chondrocytes for cartilage regeneration in vivo using relevant animal models.