Biomedical Engineering Reference
In-Depth Information
possess a limited ability to differentiate along a specific lineage. In contrast to ESCs,
differentiation of adult bone marrow stem cells into functional cardiomyocytes has
been more difficult to demonstrate. Transdifferentiation is a term used to define a
committed stem cell crossing lineage boundaries and differentiating into cells
belonging to another lineage. An HSC giving rise to cardiomyocytes is an example
of transdifferentiation. Fusion refers to the phenomenon in which stem cells fuse
with somatic cells; the resultant hybrid cells usually assume the more
undifferentiated phenotype but possess some characteristics of both cell types.
For example, bone marrow cells, when grown in culture with ESCs, could fuse
with ESCs and adopt the recipient phenotype. Stem cells can regulate tissue
regeneration and repair. Apart from angiogenesis and wound healing, stem cells
could exert a host of other paracrine effects on myocardial protection, cardiac
contractility, myogenic differentiation of resident cardiac progenitors, and scar
formation.
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12.3.5 Advantages of Adult Stem Cells
Although the implantation of skeletal myoblasts and adult BMC transplantation
appears promising, adult stem cell transplantation might be more effective than adult
BMC transplantation because cardiac stem cells may be better programmed. The
further identification, purification, and characterization of the adult stem cells as well
as a detailed knowledge of their interactions with the cardiac milieu or niche are
essential if we are to achieve the major goal of regenerating or transplanting the
tissue to treat myocardial infarction.
12.3.6 Limitations of Adult Stem Cells
Until recently, data on the presence of adult stem cells have been scarce. This subset
of stem cells appears to be extremely limited in number and difficult to identify and
expand in culture, thereby limiting their characterization and utilization and likely
contributing to difficulties in reproducing experiments concerning their isolation and
transplantation. In addition, there is presently no consensus regarding the definition
of selective markers specific for adult stem cell type.
12.3.7 Culturing Embryonic Stem Cells in the Laboratory
Human ESCs are isolated by transferring the inner cell mass to a plastic laboratory
culture dish that contains a nutrient broth known as culture medium. The cells divide
and spread over the surface of the dish. The inner surface of the culture dish is
typically coated with mouse embryonic skin cells that have been treated so they will
not divide. This coating layer of cells is called a feeder layer. This layer provides a
sticky surface for the inner cell mass to which they can attach. Also, the feeder cells
release nutrients into the culture medium. Culture media without the feeder cell layer
is also available, so there are no chances of transmission of viral disease. ESCs that
have proliferated in cell culture for 6 or more months without differentiating, are
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