a lot of hope and opened new avenues for stem cell applications in treatment for
different degenerative diseases. The field is developing at a rapid pace; we hope to
see a lot of cell-based treatment modalities for degenerative diseases in near future,
which is altogether set to change our current perception about a disease scenario.
12.2 Micro-environment of Stem Cell: The Niche
The word “niche” has different meaning in different contexts, it refers to a habitat
where an organism can reside and reproduce in ecology (Scadden 2006).
Schofield for the first time in 1978 used the term “stem cell niche” describing the
whole picture of stem cells survival and their interaction with the neighboring cells
(Wang et al. 2016; Wang and Kingshott 2016). Stem cells produce their own matrix
and milieu with the specialized micro-environment. The microenvironment of the
stem cells is very complex and dynamic structure which is very much required for
the self-renewal and differentiation of these cells. Due to complex structural organization of the stem cell niche it has not been characterized completely. In Drosophila
and Caenorhabditis elegans the first germline stem cell (GSC) niche has been
defined (De Cuevas and Matunis 2011). Several stem cell niches have been
identified in different tissues including the hematopoietic stem cells (HSCs), the
germline stem cells (GSCs) in ovaries and testes and MSCs in bone marrow, stem
cells in the epithelia muscle satellite cells in the skeletal muscle, neural stem cells in
the brain, dental pulp stem cells in the teeth, and even some cancer stem cell niches
(Lane et al. 2014; Xie and Li 2007). Bone marrow is considerably the most
nourishing niche for hematopoietic (HSCs) and mesenchymal stem cells (MSCs),
but human HSCs can be alternatively isolated from the peripheral blood, umbilical
cord, and umbilical cord blood. HSCs differentiate to form all the cells of the
myeloid and lymphoid lineage (Zhang et al. 2003), whereas MSCs can differentiate
into plethora of cell types including osteocytes, chondrocytes, stromal cells, cells of
myotube, and connective tissue. In vitro, MSCs can be differentiated outside their
lineage, which means stem cells of mesodermal origin can give rise to the cells of the
endodermal or ectodermal origin, this is called trans-differentiation or stem cell
plasticity (Lv et al. 2014).
One of the most important limiting steps in stem cells culture in vitro is to mimic
the stem cell micro-environment in vivo. Absence of proper culture systems and
protocols, normal growth of stem cells in in vitro is difficult and their differentiation
potential is compromised which leads to altered state or even apoptosis (De Cuevas
and Matunis 2011).
There are several structural features common between the stem cell niches of
different tissues and species, however, there are difference in the functional aspects
of these niches (Lane et al. 2014). Structurally the stem cell niche is highly dynamic,
with multiple cell types involving complex biochemical and biophysical interactions
(Ema 2012). There are niches which consist of one or few cell types which locally
regulate the stem cells, whereas there are niches which consist of multiple cell types
12 Environmental Interaction and Impact on the Life Span of Stem Cells
253
different degenerative diseases. The field is developing at a rapid pace; we hope to
see a lot of cell-based treatment modalities for degenerative diseases in near future,
which is altogether set to change our current perception about a disease scenario.
12.2 Micro-environment of Stem Cell: The Niche
The word “niche” has different meaning in different contexts, it refers to a habitat
where an organism can reside and reproduce in ecology (Scadden 2006).
Schofield for the first time in 1978 used the term “stem cell niche” describing the
whole picture of stem cells survival and their interaction with the neighboring cells
(Wang et al. 2016; Wang and Kingshott 2016). Stem cells produce their own matrix
and milieu with the specialized micro-environment. The microenvironment of the
stem cells is very complex and dynamic structure which is very much required for
the self-renewal and differentiation of these cells. Due to complex structural organization of the stem cell niche it has not been characterized completely. In Drosophila
and Caenorhabditis elegans the first germline stem cell (GSC) niche has been
defined (De Cuevas and Matunis 2011). Several stem cell niches have been
identified in different tissues including the hematopoietic stem cells (HSCs), the
germline stem cells (GSCs) in ovaries and testes and MSCs in bone marrow, stem
cells in the epithelia muscle satellite cells in the skeletal muscle, neural stem cells in
the brain, dental pulp stem cells in the teeth, and even some cancer stem cell niches
(Lane et al. 2014; Xie and Li 2007). Bone marrow is considerably the most
nourishing niche for hematopoietic (HSCs) and mesenchymal stem cells (MSCs),
but human HSCs can be alternatively isolated from the peripheral blood, umbilical
cord, and umbilical cord blood. HSCs differentiate to form all the cells of the
myeloid and lymphoid lineage (Zhang et al. 2003), whereas MSCs can differentiate
into plethora of cell types including osteocytes, chondrocytes, stromal cells, cells of
myotube, and connective tissue. In vitro, MSCs can be differentiated outside their
lineage, which means stem cells of mesodermal origin can give rise to the cells of the
endodermal or ectodermal origin, this is called trans-differentiation or stem cell
plasticity (Lv et al. 2014).
One of the most important limiting steps in stem cells culture in vitro is to mimic
the stem cell micro-environment in vivo. Absence of proper culture systems and
protocols, normal growth of stem cells in in vitro is difficult and their differentiation
potential is compromised which leads to altered state or even apoptosis (De Cuevas
and Matunis 2011).
There are several structural features common between the stem cell niches of
different tissues and species, however, there are difference in the functional aspects
of these niches (Lane et al. 2014). Structurally the stem cell niche is highly dynamic,
with multiple cell types involving complex biochemical and biophysical interactions
(Ema 2012). There are niches which consist of one or few cell types which locally
regulate the stem cells, whereas there are niches which consist of multiple cell types
12 Environmental Interaction and Impact on the Life Span of Stem Cells
253