Hypoxia affects mesenchymal stromal cell osteogenic differentiation and angiogenic factor expression

Abstract

Mesenchymal stromal cells (MSCs) seeded onto biocompatible scaffolds have been proposed for repairing bone defects. When transplanted in vivo, MSCs (expanded in vitro in 21% O(2)) undergo temporary oxygen deprivation due to the lack of pre-existing blood vessels within these scaffolds. In the present study, the effects of temporary (48 h) exposure to hypoxia (<or=1% O(2)) on primary human MSC survival and osteogenic potential were investigated. Temporary exposure of MSCs to hypoxia had no effect on MSC survival, but resulted in (i) persistent (up to 14 days post exposure) down-regulation of cbfa-1/Runx2, osteocalcin and type I collagen and (ii) permanent (up to 28 days post exposure) up-regulation of osteopontin mRNA expressions. Since angiogenesis is known to contribute crucially to alleviating hypoxia, the effects of temporary hypoxia on angiogenic factor expression by MSCs were also assessed. Temporary hypoxia led to a 2-fold increase in VEGF expression at both the mRNA and protein levels. Other growth factors and cytokines secreted by MSCs under control conditions (namely bFGF, TGFbeta1 and IL-8) were not affected by temporary exposure to hypoxia. All in all, these results indicate that temporary exposure of MSCs to hypoxia leads to limited stimulation of angiogenic factor secretion but to persistent down-regulation of several osteoblastic markers, which suggests that exposure of MSCs transplanted in vivo to hypoxia may affect their bone forming potential. These findings prompt for the development of appropriate cell culture or in vivo transplantation conditions preserving the full osteogenic potential of MSCs.

Concise Review: Optimizing Expansion of Bone Marrow Mesenchymal Stem/Stromal Cells for Clinical Applications

“…Furthermore, perfusion culture of MSCs stimulates the synthesis of growth factors including bone morphogenetic protein-2 (BMP-2), FGF-2, TGF-b1, and vascular endothelial growth factor (VEGF) [100]. Hypoxia also enhances MSC expression and secretion of VEGF [101]. The Michaelis-Menten constitutive equations for oxygen consumption assume the rate constant is independent of time and material, and cell density primarily influences the oxygen profile [102].…”

Mesenchymal Stem Cells: Roles and Relationships in Vascularization

“…13,14 Even though MSCs are located very closely to vascular structures, they are often still found in a relatively low oxygen environment, which further supports the finding that a hypoxic surrounding may be necessary in order to maintain the cells' undifferentiated state. 7 Hypoxia leads to decreased adipogenic and osteogenic differentiation, 15,16 triggering the release of angiogenic factors as well as promoting the expression of vasculogenic characteristics and functions in MSCs. 17,18 With physiological conditions in mind, there are proliferation benefits for cells cultured in low oxygen environments.…”

Hypoxia Induces Osteogenesis-Related Activities and Expression of Core Binding Factor .ALPHA.1 in Mesenchymal Stem Cells

“…The expression of HIF-1α was decreased with the time of hypoxia, whereas the expression of core binding factor alpha 1 (Cbfα1), another key transcription regulator involved in the chondrocyte differentiation and ossification, was increased gradually (Rabie et al 2004;Augello and De Bari 2010). However, other report showed that temporary exposure to hypoxia would inhibit the expression of Cbfα-1/Runx2 in MSCs (Potier et al 2007).…”