Biomedical Engineering Reference
In-Depth Information
alternative explanation of the plasticity of bone marrow-derived cells, by providing
the evidence that bone marrow, in addition to HSC, contains an admixture of very
rare tissue-committed stem/progenitor cells (TCSC)—for liver, pancreas, neural tis-
sue, skeletal muscles, or heart—which in some experimental models gave a “false”
impression that HSC changed their tissue commitment [
47-
54
]. It is an important
observation which questions the concept of stem cell plasticity [
54-
57
] and points
out that we should consider other sources of stem cells for tissue repair and regen-
eration (e.g., embryonic stem cells, amniotic fluid stem cells, and maybe the adult
stem cells found in other already differentiated tissues such as adipose tissue, liver,
olfactory tissue stem cells, etc.) [
58-
63
]. This requires additional research since the
pluripotent stem cells from these sources might be not as efficient in homing and
repairing damaged tissue as they are coming from different environment.
This group has also confirmed, at both: the mRNA and protein level that BM
contains, in addition to HSCs, a population of heterogeneous TCSC. Some of these
cells possess internal markers characteristic of pluripotent stem cells and that they,
similarly to HSC, could be mobilized from the BM into peripheral blood in situa-
tions of stress and, via the blood stream, may reach distinct organ locations to con-
tribute to tissue repair/regeneration. So, the circulation of these TCSCs under
steady-state condition plays an important physiological role in maintaining the pool
of stem cells in distant part of the body. They might compete for SDF-1—positive
niches and this explains why is it possible to isolate HSCs from muscle or neural
tissue and conversely muscle or neural progenitors from BM [
53
] .
Finally, Kucia/Ratajczak et al. [
52
], described a new strategy to identify and iso-
late adult non-HSC from BM. They found that these cells, similarly to HSC, express
CXCR4 and respond to an SDF-1 gradient; however, in contrast to HSC; these cells
are CD45 negative, which is a fundamental difference between two categories. In
summary, these very small embryonic like stem cells (VSELSCs) found for the first
time in the bone marrow of mice, have very little cytoplasm with few mitochondria
and internal markers of all three embryonic cell lineages, e.g., pluripotency (Oct4,
Nanog, Rex-1 transcription factors). The morphology and phenotype of these mouse
cells were similar to that found in the human MIAMI cells discovered by D' Ipolito,
MAP (multipotent adult progenitor) cells (named also MAPSC) determined by
Catherine Verfaillie and hBMSC detected by Youn Soop Yun in a latest, very con-
densed period of time, suggesting that it might be the same cell except that many
investigators were not capable of reproducing them [
64-
66
] (Figs.
15.2
and
15.3
).
This is important in so much, since subpopulations of human mesenchymal stem
cells (MSCs, hMSCs) exhibiting features of primitive adult pluripotent or multipo-
tent stem cells have been described even earlier by different investigators. Cells with
features of adult pluripotent stem cells have also been isolated from umbilical cord
blood, peripheral blood, adipose tissue, but so far nobody gave such convincing
data in distinguishing them from mesodermal stem cell, hematopoietic and pluripo-
tent non-hematopoietic cell, neither they gave an undoubted reproducibility for
pluripotent non-hematopoietic stem cell as it did Ratajczak's group, recently.
The reason for that was the most probably due to the fact that the superficial
markers were sometimes at such a low concentration that the PCR amplification
