Hypoxia triggers physiological and pathological cellular processes, including proliferation, differentiation, and death, in several cell types. Mesenchymal stem cells (MSCs) derived from various tissues have self-renewal activity and can differentiate towards multiple lineages. Recently, it has been reported that hypoxic conditions tip the balance between survival and death by hypoxia-induced autophagy, although the underlying mechanism is not clear. The objectives of this study are to compare the effect of hypoxia on the self-renewal of bone marrow-derived mesenchymal stem cells (BM-MSCs) and placental chorionic plate-derived mesenchymal stem cells (CP-MSCs) and to investigate the regulatory mechanisms of self-renewal in each MSC type during hypoxia. The expression of self-renewal markers (e.g., Oct4, Nanog, Sox2) was assessed in both cell lines. PI3K and stem cell factor (SCF) expression gradually increased in CP-MSCs but were markedly downregulated in BM-MSCs by hypoxia. The phosphorylation of ERK and mTOR was augmented by hypoxia in CP-MSCs compared to control. Also, the expression of LC3 II, a component of the autophagosome and the hoof-shaped autophagosome was detected more rapidly in CP-MSCs than in BM-MSCs under hypoxia. Hypoxia induced the expression of SCF in CP-MSCs and increased SCF/c-kit pathway promotes the self-renewal activities of CP-MSCs via an autocrine/paracrine mechanism that balances cell survival and cell death events by autophagy. These activities occur to a greater extent in CP-MSCs than in BM-MSCs through regulating the phosphorylation of mTOR. These findings will provide useful guidelines for better understanding the function of SCF/c-kit in the self-renewal and autophagy-regulated mechanisms that promote of MSC survival.
Copyright © 2012 Wiley Periodicals, Inc.