Artificial Scaffolds and Mesenchymal Stem Cells for Hard Tissues - Tissue Engineering: Cell-Surface Interactions for Tissue Culture - page 157

2 SCs for Bone Regeneration
2.1 SCs and Their Potential
SCs are the biological precursors of each unique cell type of all existing tissues
and organ within a body. They are generally defined by two major properties: they
can self-renew for extended time periods and they are to various degrees undif-
ferentiated, with the ability to differentiate into specialized cells under the
appropriate conditions [ 2 , 3 ]. SCs are classified according to their differentiation
potential and their source.
Totipotent (or omnipotent) SCs have the potential to differentiate into every cell
type needed to structure a complete, viable organism. For this purpose, they form the
embryonic and the extra-embryonic tissues. Pluripotent cells are capable of differ-
entiating into all cells of the three germ layers composing an organism, namely the
ectoderm, mesoderm and endoderm [ 3 , 4 ]. Multipotent SCs are lineage-restricted to
a number of closely related cell types, mainly from one of the germinal layers.
Oligopotent SCs have the potential to develop into a few cell types from a specific
family of cells and unipotent cells give rise to one cell type only and are therefore
also termed precursor cells. Pluripotent SCs are derived from the inner cell mass of
the blastocyst of an embryo. Depending on the tissue source, adult SCs have a
multipotent, oligopotent or unipotent differentiation potential.
SCs can be used in basic research as a key tool for the investigation of early
development of an organism or a specific cell type. For this, the identification of
regulatory genes and signaling pathways is crucial. Huge efforts have been
undertaken in recent years to define key marker genes for the individual steps of
commitment in the lineage-specific differentiation of SCs, and a broad set of more
or less specific markers is available for the various lineages. As well as basic
research, the abilities of self-renewal and differentiation of SCs can provide new
medical perspectives to re-establish cellular function for the regeneration of dam-
aged tissues or organs. The oldest and best-established SC therapy is hematopoietic
SC transplantation. Transplantation of bone marrow-derived or peripheral blood-
derived SCs is used to reconstitute the hematopoietic system after chemotherapy
treating blood cancers such as myeloma or leukemia [ 5 , 6 ]. Taken from a patient,
SCs can also be used as test material to better understand genetic diseases, which
can then be followed by specific drug development [ 7 , 8 ]. The treatment of patients
with injuries from accidents or degenerative diseases with SCs also holds great
promise for cell-based tissue reconstruction in the future, because mature, finally
differentiated cells are often not available in sufficient amounts or quality or can no
longer replicate in vitro. If the cells are obtained for the individual patient directly,
severe side effects such as tissue rejection can be eliminated. A new approach is the
creation of artificial SCs by reprogramming. These SCs are expected to combine the
positive characteristics of embryonal SCs, their pluripotency, with the positive
features of adult SCs, the prospect of an autologous source. As well as the regen-
eration of heart muscle [ 9 , 10 ] which is a major focus at the moment, SCs are