Biomedical Engineering Reference
In-Depth Information
layer. For example, many experiments on plasticity involve stem cells derived from bone
marrow, which is considered to be of mesodermal origin. The bone-marrow stem cells may
differentiate into another mesodermally derived tissue, such as skeletal muscle or cardiac
muscle [20, 32-34].
Classification of Adult Stem Cells
Adult stem cell niches are distributed throughout several regions of the body, including
bone marrow, brain, fat, skeletal muscle, retina, liver, and skin. Some of these adult stem-
cell types are discussed in detail below. Many tissues that have specific ASC phenotypes
have been identified so far. Some examples are mammary stem cells, intestinal stem cells,
endothelial stem cells, olfactory stem cells [35], liver-derived stem cells, testicular stem cells,
and dental pulp stem cells [8].
Bone Marrow-Derived Stem Cells
Today, bone marrow is one of the most popular sources of stem cells. Bone marrow-derived
stem cells (BMSCs) have a self-renewal potential and they are readily available through bone
marrow biopsy. The BMSCs contain at least three different types: HSCs, MSCs and EPCs [8].
The HSCs and the MSCs are presented in more detail later, since they are considered to have
the highest potential in therapeutic approaches.
Hematopoetic stem cells (HSCs) are involved in the production of blood cells. This process
is called hematopoiesis. They give rise to the entirety of the blood cells in the human body.
Therefore, HSCs are a potential tool for curing blood diseases, for example leukemia or lym-
phoma, as well as blood disorders, for example anemia or immunodeficiencies.
Mesenchymal stem cells (MSCs) are derived from bone marrow stromal progenitor cells
and can form “mesenchyme,” a loose connective tissue. The MSCs can be isolated from HSCs
by their capability to adhere to tissue culture plastic. They are able to form mesodermal and
non-mesodermal tissues, such as bone, cartilage, tendon, adipose tissue, and muscle [36].
Endothelial progenitor cells (EPCs) include a unique population of peripheral-blood mono-
nuclear cells derived from bone marrow that are involved in postnatal neovascularization dur-
ing wound healing, limb ischemia, post-myocardial infarction syndrome, arteriosclerosis, and
tumor development. Both HSCs and EPCs are derived from common a precursor called
hemangioblast [37].
Adipose Tissue-Derived Stem Cells or Adipocyte-Derived Mesenchymal Stem Cells
White adipose tissue is one of two types of adipose tissue found in mammals. The tasks of
this tissue consist in saving energy and in acting as a thermal insulator. Adipose tissues orig-
inate from the mesodermal layer of embryos and can develop pre- as well as postnatally.
Three different types of cells are present in adipose tissues: adipocytes, pre-adipocytes, and
a heterogeneous population called stromal vesicular fraction. Adipose tissue-derived stem
cells (ADSCs) are multipotent cells that are able to differentiate into other types of mesen-
chymal tissues, such as adipocytes, chondrocytes, myocytes, and osteoblasts [38]. Furthermore,
they grow faster and are easier to culture
in vitro
over a long period of time. In the past
decade, abundant evidence has been presented for the fact that the secretion of vascular
endothelial growth factor by ADSCs leads to the healing of damaged tissue. Several studies
have been presented indicating that adipocyte-derived mesenchymal stem cells (AD-MSCs)
have the ability to differentiate to hepatocyte-like cells under specific conditions [39-41].
