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Received:17 February 2011 Accepted:9 August 2011 Published:9
August 2011  © 2011 Zeng et al; licensee BioMed Central Ltd.
Human mesenchymal stem cells (hMSCs) were first identified by
Friedenstein et al. [1] in 1974. As non-hematopoetic,
multipotent bone marrow stem cells, hMSCs are more primitive and
embryonic-like cells with the potential to differentiate into
lineage-committed progenitors and mature cells, such as
osteoblasts and fibroblasts [2]. However, bone marrow is not the
exclusive source of MSCs; they have been isolated from virtually
all post-natal and extra-embryonic tissues, including amniotic
membrane, placenta, umbilical cord, and umbilical cord blood
[3-5]. In recent years, hMSCs have been commonly used in tissue
engineering, cell replacement therapy, gene therapy, and body
organ/fluid transplantation.  Oxygen is a potent signaling
molecule, affecting the