Hypoxia Promotes Differentiation of Pure Cartilage from Human iPS Cells

BackgroundWhile cartilage can be formed from induced pluripotent stem cells (iPSCs), challenges such as long culture periods and compromised tissue purity remain. We aimed to determine whether cartilaginous tissue can be produced from iPSCs under hypoxia and to evaluate the effects on the cellular metabolism and purity of the tissue.MethodsHuman iPSCs (hiPSCs) were cultured for cartilage differentiation in monolayers under normoxia or hypoxia (5% O2). We evaluated chondrocyte differentiation by real-time reverse transcription-polymerase chain reaction and fluorescence-activated cell sorting. Then, hiPSCs were cultured for cartilage differentiation in 3D culture under normoxia or hypoxia (5% O2). We evaluated cartilage-like tissues on days 28 and 56 through histological analyses.ResultsHypoxia suppressed the expression of immature mesodermal markers T (Brachyury) and Forkhead box protein F1 (FOXF1) and promoted the expression of the chondrogenic markers aggrecan and CD44. Sex determining region Y- box (SOX) 9-positive cells were increased by culture under hypoxia. Percentages of safranin O-positive and type 2 collagen-positive tissues were increased under hypoxia. Moreover, upon hypoxia-inducible factor (HIF)-1α staining, the nuclear dyeability in tissues cultured under hypoxia was greater than that under normoxia.ConclusionsHypoxia not only led to enhanced cartilage matrix production but also improved cell purity by promoting the expression of HIF-1α. By applying this method, highly pure cartilaginous-like tissues may be produced more rapidly and conveniently.