Different populations and sources of human mesenchymal stem cells (MSC): A comparison of adult and neonatal tissue-derived MSC

Abstract

The mesenchymal stroma harbors an important population of cells that possess stem cell-like characteristics including self renewal and differentiation capacities and can be derived from a variety of different sources. These multipotent mesenchymal stem cells (MSC) can be found in nearly all tissues and are mostly located in perivascular niches. MSC have migratory abilities and can secrete protective factors and act as a primary matrix for tissue regeneration during inflammation, tissue injuries and certain cancers.These functions underlie the important physiological roles of MSC and underscore a significant potential for the clinical use of distinct populations from the various tissues. MSC derived from different adult (adipose tissue, peripheral blood, bone marrow) and neonatal tissues (particular parts of the placenta and umbilical cord) are therefore compared in this mini-review with respect to their cell biological properties, surface marker expression and proliferative capacities. In addition, several MSC functions including in vitro and in vivo differentiation capacities within a variety of lineages and immune-modulatory properties are highlighted. Differences in the extracellular milieu such as the presence of interacting neighbouring cell populations, exposure to proteases or a hypoxic microenvironment contribute to functional developments within MSC populations originating from different tissues, and intracellular conditions such as the expression levels of certain micro RNAs can additionally balance MSC function and fate.

Figure 1

Major sources of human mesenchymal stem cells (MSC) . The sources can be distinguished between adult tissues, preferably bone marrow (BM), peripheral blood (PB) and adipose tissue (AT) and neonatal birth-associated tissues including placenta (PL), umbilical cord (UC) and cord blood (CB). Besides cord blood-derived mesenchymal stem cells (CB-MSC) other stem/progenitor cell populations from cord blood also include hematopoietic stem cells CB-HSC and two endothelial populations such as endothelial progenitor cells (EPC) and endothelial colony-forming cells (ECFC).

Figure 2

Senescence-associated β-galactosidase (SA-β-gal)-positive cells in the UC-derived mesenchymal stem cell culture under low (2%) serum concentration . Nuclei of senescent cells are surrounded by cyan dye. Moreover, serum deprivation is accompanied by a decrease of the proliferative potential in the cells and a significant increase in cell size.

Figure 3

MSC mediate immunosuppression of T and NK cells via different mechanisms . Soluble factors secreted by MSC such as iNOS, IDO, PGE2, sHLA-G5 can suppress T- and NK cell functions, whereas galectin-1 inhibits T cells but not NK cells. In addition, MSC can indirectly mediate immunosuppression by inhibiting dendritic cells and inducing the expansion of regulatory T cells (Tregs). Furthermore, MSC can directly interact with T and NK cells via cell to cell contact. However, receptors and ligands involved in the cell contact-dependent interaction mechanisms are still largely unknown.

Figure 4

Major characteristics of MSC and their functions in vitro and in vivo . MSC are involved in important pathways of cell renewal by mediating the regeneration of damaged or aging cells, supporting tissue repair at wound sites and modulating immune functions. Due to the migratory capabilities, MSC can interact with and support damaged normal tissue cells in the local vicinity by providing an appropriate microenvironment.