Increased stemness and migration of human mesenchymal stem cells in hypoxia is associated with altered integrin expression

Abstract

Human mesenchymal stem cells (hMSCs) are regularly cultured and characterised under normoxic (21% O2) conditions, although the physiological oxygen tension in the stem cell niche is known to be as low as 1–2%. Oxygen itself is an important signalling molecule, but the distinct impact on various stem cell characteristics is still unclear. Therefore, the aim of this study was to evaluate the influence of oxygen concentration on the hMSC subpopulation composition, cell morphology and migration on different surfaces (polystyrene, collagen I, fibronectin, laminin) as well as on the expression of integrin receptors. Bone marrow-derived hMSCs were cultured either in normoxic (21% O2) or hypoxic (2% O2) conditions. The hMSC subpopulations were assessed by aspect ratio and cell area. Hypoxia promoted a more homogeneous cell population with a significantly higher fraction of rapidly self-renewing cells which are believed to be the true stem cells. Under hypoxic conditions hMSC volume and height were significantly decreased on all surfaces as measured by white light confocal microscopy. Furthermore, low oxygen tension led to a significant increase in cell velocity and Euclidian distance on all matrixes, which was evaluated by time-lapse microscopy. With regard to cell-matrix contacts, expression of several integrin subunits was evaluated by semi-quantitative RT-PCR. Increased expression of the subunits α1, α3, α5, α6, α11, αv, β1 and β3 was observed in hypoxic conditions, while α2 was higher expressed in normoxic cultured hMSCs. Taken together, our results indicate that hypoxic conditions promote stemness and migration of hMSC along with altering their integrin expression.