Stem cells catalyze cartilage formation by neonatal articular chondrocytes in 3D biomimetic hydrogels

Abstract

Cartilage loss is a leading cause of disability among adults and effective therapy remains elusive. Neonatal chondrocytes (NChons) are an attractive allogeneic cell source for cartilage repair, but their clinical translation has been hindered by scarce donor availability. Here we examine the potential for catalyzing cartilage tissue formation using a minimal number of NChons by co-culturing them with adipose-derived stem cells (ADSCs) in 3D hydrogels. Using three different co-culture models, we demonstrated that the effects of co-culture on cartilage tissue formation are dependent on the intercellular distance and cell distribution in 3D. Unexpectedly, increasing ADSC ratio in mixed co-culture led to increased synergy between NChons and ADSCs, and resulted in the formation of large neocartilage nodules. This work raises the potential of utilizing stem cells to catalyze tissue formation by neonatal chondrocytes via paracrine signaling, and highlights the importance of controlling cell distribution in 3D matrices to achieve optimal synergy.C artilage loss is a leading cause of disability among adults and represents a huge socio-economical burden.Articular cartilage has limited self-repair potential and damage is often irreversible 1 . Conventional cellbased therapy utilizes autologous chondrocytes for cartilage repair, which is associated with several shortcomings including donor site morbidity and the need for in vitro expansion and multiple surgeries 2 . Furthermore, the ability of autologous chondrocytes to regenerate cartilage tissue declines rapidly with patient age and in vitro expansion 3,4 , making them a suboptimal cell source for cartilage repair. Unlike autologous adult chondrocytes, allogeneic neonatal chondrocytes (NChons) are highly proliferative, immune-privileged, and can readily produce abundant cartilage matrix 3,5,6 . However, donor availability for NChons is scarce, which greatly hinders their broad application.In addition to chondrocytes, adult mesenchymal stem cells (MSCs) are an alternative cell source for cartilage repair 7 . Adipose-derived stem cells (ADSCs), in particular, are an attractive candidate due to their ease of isolation, relative abundance, and chondrogenic potential 8,9 . While stem cells are widely known for their potential to promote tissue regeneration through lineage-specific differentiation, emerging evidence suggests that paracrine signals secreted by stem cells may also contribute to tissue repair 10,11 . Several studies have examined the interactions between articular chondrocytes and MSCs; however, the reported results have been contradictory. While some studies indicated that MSCs inhibit cartilage production by chondrocytes 12,13 , others showed that MSCs stimulate chondrocyte proliferation and cartilage matrix production [14][15][16][17][18] . The discrepant findings may be due to the differences in various parameters in these studies such as co-culture models, medium composition (i.e. serum or other growth factor supplementation), and donor age or disease phenoty...

Mechanical confinement regulates cartilage matrix formation by chondrocytes

“…Chondrocyte isolation from bovine cartilage was conducted according to a previously published method 52 . Briefly, hyaline articular cartilage was harvested from a patellofemoral groove of a bovine leg.…”

“…Biochemical analysis was conducted as described previously 52 . Briefly, the hydrogels containing chondrocytes were removed from their culture medium.…”

Effects of Hydrogel Stiffness and Extracellular Compositions on Modulating Cartilage Regeneration by Mixed Populations of Stem Cells and ChondrocytesIn Vivo

“…We have recently reported that ADSCs can catalyze cartilage formation by Nchons when they are mixed co-cultured in 3D biomimetic hydrogels. 13 The present study seeks to further evaluate the effects of hydrogel compositions and stiffness on modulating such synergistic interactions and neocartilage formation. Three ECM molecules were chosen (CS, HA, and HS) and chemically incorporated into 3D hydrogels at a physiologically relevant concentration (2.5% [w/v]).…”

“…12 In addition to directly differentiating stem cells into chondrocytes, stem cells may also contribute to cartilage repair indirectly via paracrine signaling to catalyze chondrocytes to produce more neocartilage during co-culture. [13][14][15] Using a 3D co-culture model in biomimetic hydrogels, we have recently reported that ADSCs can catalyze cartilage formation by neonatal chondrocytes (Nchons), which allows a dramatic reduction of the number of chondrocytes needed for robust articular cartilage formation. 13 These results highlight the promise of harnessing the synergistic interactions between stem cells and chondrocytes for cartilage repair.…”

“…[13][14][15] Using a 3D co-culture model in biomimetic hydrogels, we have recently reported that ADSCs can catalyze cartilage formation by neonatal chondrocytes (Nchons), which allows a dramatic reduction of the number of chondrocytes needed for robust articular cartilage formation. 13 These results highlight the promise of harnessing the synergistic interactions between stem cells and chondrocytes for cartilage repair. However, how matrix cues, such as biochemical composition and mechanical stiffness, modulate such catalyzed neocartilage formation in vivo remains unknown.…”