Biomimicry of glycosaminoglycans in the bone marrow microenvironment favour the expansion of highly potent human mesenchymal stem cells

2019 
Background & Aim Mesenchymal stem cell (MSC) therapy offers significant potential for musculoskeletal regeneration following trauma or disease. However, the low abundance of MSCs in human bone marrow aspirates necessitates further expansion in culture before their clinical application. Such ex vivo expansion can lead to a loss of stem cell characteristics, and thus unpredictable therapeutic outcomes. This has necessitated moves to develop strategies that lead to retention of MSC potency over serial passages. Studies of the MSC secretome have highlighted the importance of endogenous FGF2 for their survival and maintenance of stemness. In this study, we aimed to establish a glycosaminoglycan-rich culture microenvironment that would bind and activate endogenous FGF2 to increase the growth of multipotent MSCs suitable for therapeutic application. Methods, Results & Conclusion We show that MSC potency and therapeutic efficacy can be enhanced by sustaining endogenous FGF2 signalling through supplementation with an affinity-selected heparan sulfate co-factor (termed HS8) generated by peptide-based affinity chromatography. Also, HS8 improves the bioavailability of FGF2, so providing MSCs access to active FGF2. This results in a significant increase in the pool of MSCs and sustained growth of multipotent MSCs over extended passaging. Importantly, this increase in cell division does not accelerate telomere loss, or adversely affect colony-forming ability, cell surface marker expression or multipotentiality. When used to treat osteochondral injury to the femoral trochlear groove of NIH nude rats, improvements in ICRS II and O'Driscoll scores were observed, with > 70% of defects treated with MSCs supplemented with HS8 achieving high scores compared with ∼ 50% for control. In a follow-on micropig osteochondral defect study, treatment with MSCs supplemented with HS8 showed significant increases in ICRS II and O'Driscoll scores compared to control. Moreover, Magnetic Resonance Imaging (MRI) analysis demonstrated reduced osteochondral lesioning following treatment with MSCs supplemented with HS8, with Instron biomechanical testing highlighting an associated improvement in biomechanical properties over control. Collectively, these data show that modulation of endogenous FGF2 signals by select heparan glycosaminoglycans represents an effective strategy for the bioprocessing of human mesenchymal stem cells with sustained therapeutic potency.
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