Hypoxia promotes chondrogenesis in rat mesenchymal stem cells: A role for AKT and hypoxia‐inducible factor (HIF)‐1α

Abstract

Mesenchymal stem cells (MSCs) are multipotent cells capable of developing along the chondrogenic, osteogenic and adipogenic lineages. As such, they have received interest as a potential cell source for tissue engineering strategies. Cartilage is an avascular tissue and thus resides in a microenvironment with reduced oxygen tension. The aim of this study was to examine the effect of a low oxygen environment on MSC differentiation along the chondrogenic route. In MSCs exposed to chondrogenic growth factors, transforming growth factor-beta and dexamethasone, in a hypoxic environment (2% oxygen), the induction of collagen II expression and proteoglygan deposition was significantly greater than that observed when cells were exposed to the chondrogenic growth factors under normoxic (20% oxygen) conditions. The transcription factor, hypoxia-inducible factor-1alpha (HIF-1alpha), is a crucial mediator of the cellular response to hypoxia. Following exposure of MSCs to hypoxia (2% oxygen), HIF-1alpha translocated from the cytosol to the nucleus and bound to its target DNA consensus sequence. Similarly, hypoxia evoked an increase in phosphorylation of both AKT and p38 mitogen activated protein kinase, upstream of HIF-1alpha activation. Furthermore, the PI3 kinase/AKT inhibitor, LY294002, and p38 inhibitor, SB 203580, prevented the hypoxia-mediated stabilisation of HIF-1alpha. To assess the role of HIF-1alpha in the hypoxia-induced increase in chondrogenesis, we employed an siRNA knockdown approach. In cells exposed to HIF-1alpha siRNA, the hypoxia-induced enhancement of chondrogenesis, as evidenced by upregulation of collagen II, sox-9 and proteoglycan deposition, was absent. This provides evidence for HIF-1alpha being a key mediator of the beneficial effect of a low oxygen environment on chondrogenesis.

HIF-1α is critical for hypoxia-mediated maintenance of glioblastoma stem cells by activating Notch signaling pathway

“…HIF-2a is stabilized at a wider range of oxygen tensions, ranging from severe hypoxia (o2% oxygen) to more physiologically relevant tension for tumors (2-5% oxygen), whereas HIF-1a is only stabilized at severe hypoxia condition(o2% oxygen). 17,26,33 In this study, we show that HIF-1a may have an important role in hypoxia-mediated maintenance of GSC partly for its interaction with NICD. Besides, we also found that DLL1, a Notch Delta ligand, highly expresses in U251SC both at mRNA and protein level.…”

Metabolic programming of mesenchymal stromal cells by oxygen tension directs chondrogenic cell fate

“…In particular, chondrogenic differentiation under hypoxic conditions results in enhanced cartilage formation and suppresses hypertrophic differentiation (15). In contrast, chondrogenic differentiation under normoxic conditions yields less cartilage, which has a clear hypertrophic signature (11,18,19). Here, we demonstrate that oxygen tension can, in fact, metabolically program the chondrogenic fate of MSCs into different subtypes of hyaline cartilage.…”

A computational model to explore the role of angiogenic impairment on endochondral ossification during fracture healing

“…We have previously used such computational models to provide support for the hypothesis that stem cell fate during fracture healing is governed by the local oxygen concentration and stiffness of the surrounding substrate (Burke and Kelly, 2012;Burke et al, 2013Burke et al, , 2014. This algorithm was developed based on in-vitro observations which demonstrate the fundamental role played by substrate stiffness in regulating MSC lineage commitment (Engler et al, 2006;Huebsch et al, 2010;Young et al, 2013;Park et al, 2011), and by experiments demonstrating that hypoxia inhibits osteogenesis and adipogenesis while promoting chondrogenesis (Kanichai et al, 2008;Cao, 2007;Hankenson et al, 2011;Peiffer et al, 2011;Hirao et al, 2006;Street et al, 2002;Gomillion and Burg, 2006;Hausman and Richardson, 2004). This computational model did not however propose a specific hypothesis for how environmental factors regulate the initiation and progression of chondrocyte hypertrophy and endochondral ossification, which is central to successful secondary fracture healing.…”