Abstract
Cell-based approaches of cartilage lesions use different culture systems to obtain optimal cell quality. Pellet cultures with high cellular density (HD) are the gold standard to keep chondrocytes in a differentiated stage. Bacterial cellulose (BC) hydrogel is discussed to prevent cellular aging and dedifferentiation. The hypothesis of this study was that HD culture on BC hydrogel (HD hydrogel) might reach the chondrogenic potential of pellet culture (pellet). Human articular osteoarthritic (OA) and non-osteoarthritic (non-OA) chondrocytes were cultured for seven days within pellets and compared to HD hydrogel and HD polystyrene. Gene expression analysis and histological assessment were performed. We observed no significant change of COL2A1 expression by the culture system (pellet, HD hydrogel and HD polystyrene) but a significant change of COL2A1/COL1A1-ratio, with the highest ratio in pellets. Chondrocytes on HD hydrogel showed an elevated expression of MMP13 and on polystyrene an increased expression of COL1A1 and MMP13. The patterns of gene expression changes observed in OA and non-OA chondrocytes in reaction to the different culture systems were similar in those two cell groups. Pellet cultures moreover formed a histomorphologically superior neocartilage. Concluding, human chondrocytes kept the potential to express COL2A1 in all HD culture systems. However, pellets excelled in a higher COL2A1/COL1A1-ratio, a higher extracellular matrix deposit and in not developing degeneration and dedifferentiation markers. This underlines the superiority of pellet culture in maintaining the chondrogenic potential of human chondrocytes in vitro.
Highlights
Most approaches of regenerative medicine in cartilage lesions depend on the implantation of highly differentiated chondrogenic cells
We observed no significant change of COL2A1 expression by the culture system but a significant change of COL2A1/COL1A1-ratio, with the highest ratio in pellets
The patterns of gene expression changes observed in OA and non-OA chondrocytes in reaction to the different culture systems were similar in those two cell groups
Summary
Most approaches of regenerative medicine in cartilage lesions depend on the implantation of highly differentiated chondrogenic cells. To gain enough cellular material before re-implantation in vitro, expansion of isolated cells is essential. The improvement of chondrocytes culture conditions is necessary in order to generate better tissue-engineered cartilage products. Beneficial effects on chondrogenesis have been shown for high density (HD) and three dimensional (3D) culture systems (providing intensive cell–cell contacts) [1,2,3], alternative culture surfaces such as hydrogels (addressing cell–surface contacts) [4], and various physical stimuli (e.g., electromagnetic fields of a certain spectrum [5], or hydrostatic pressure and perfusion [6]) as well as chemical stimuli [7]. When cultured within 3D systems, chondrocytes have been shown to be even able to redifferentiate [8]. Pellet culture conditions with relatively small pellet sizes and the difficulty of anchorage make it obvious to further search for other alternatives
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