Microfluidic Screening Reveals Heparan Sulfate Enhances Human Mesenchymal Stem Cell Growth by Modulating Fibroblast Growth Factor‐2 Transport

Cost‐effective expansion of human mesenchymal stem/stromal cells (hMSCs) remains a key challenge for their widespread clinical deployment. Fibroblast growth factor‐2 (FGF‐2) is a key hMSC mitogen often supplemented to increase hMSC growth rates. However, hMSCs also produce endogenous FGF‐2, which critically interacts with cell surface heparan sulfate (HS). We assessed the interplay of FGF‐2 with a heparan sulfate variant (HS8) engineered to bind FGF‐2 and potentiate its activity. Bone marrow‐derived hMSCs were screened in perfused microbioreactor arrays (MBAs), showing that HS8 (50 μg/ml) increased hMSC proliferation and cell number after 3 days, with an effect equivalent to FGF‐2 (50 ng/ml). In combination, the effects of HS8 and FGF‐2 were additive. Differential cell responses, from upstream to downstream culture chambers under constant flow of media in the MBA, provided insights into modulation of FGF‐2 transport by HS8. HS8 treatment induced proliferation mainly in the downstream chambers, suggesting a requirement for endogenous FGF‐2 accumulation, whereas responses to FGF‐2 occurred primarily in the upstream chambers. Adding HS8 along with FGF‐2, however, maximized the range of FGF‐2 effectiveness. Measurements of FGF‐2 in static cultures then revealed that this was because HS8 caused increased endogenous FGF‐2 production and liberated FGF‐2 from the cell surface into the supernatant. HS8 also sustained levels of supplemented FGF‐2 available over 3 days. These results suggest HS8 enhances hMSC proliferation and expansion by leveraging endogenous FGF‐2 production and maximizing the effect of supplemented FGF‐2. This is an exciting strategy for cost‐effective expansion of hMSCs. S tem C ells T ranslational M edicine 2017;6:1178–1190