What is Stem Cell: [StemCells] Improving hES differentiation efficiency

Thursday, April 10, 2008

[StemCells] Improving hES differentiation efficiency

Method To Deliver Molecules Within Embryonic Stem Cells Improves
Differentiation
Article Date: 10 Apr 2008 - 3:00 PDT

Embryonic stem cell therapies have been proposed for regenerative
medicine and tissue replacement after injury or disease. However, the
inability of stem cells to efficiently develop into the desired
specific cell type - such as muscle, skin, blood vessels, bone or
neurons - now limits the potential clinical utility of this therapy.

New research shows that delivering molecules within aggregates of
embryonic stem cells via biodegradable microspheres enhances the
efficiency and purity of differentiation, which is the process the
cells undergo to become more specialized. Details of the microsphere-
mediated delivery method, which is funded by the National Science
Foundation, were presented at the 235th American Chemical Society
national meeting.

"Directing embryonic stem cells to efficiently differentiate into a
specific cell type has been challenging to this point," said Todd
McDevitt, an assistant professor in the Wallace H. Coulter Department
of Biomedical Engineering at Georgia Tech and Emory University. "In
my lab, we're trying to better define and then control the
environmental cues that regulate the fate and function of the stem
cells."

Because physical interactions between stem cells is critical during
normal embryonic development, most laboratory growth methods allow
the cells to aggregate in three-dimensional clumps called "embryoid
bodies" in order to differentiate. After individual cells aggregate
together, hollow internal structures begin to develop and the
aggregate becomes larger and more complex over time.

"Many researchers add soluble factors to the culture dish medium to
direct differentiation, but this does not accurately mimic the time
and location of signaling events present in normal development, and
may contribute to heterogeneous differentiation," said McDevitt. "Our
method focuses on incorporating the differentiation factors directly
into the cell aggregates in order to have a more controlled mechanism
of presentation."

The research team - which also includes graduate students Richard
Carpenedo and Andrés Bratt-Leal and undergraduate students Ross
Marklein and Scott Seaman - fabricated biodegradable polymer
microspheres that could contain growth factors, proteins or other
small molecules.

McDevitt's team tested the impact of the poly(lactic-co-glycolic
acid) (PLGA) microspheres on embryonic stem cell differentiation
under different conditions by varying the microsphere-to-cell ratio
and speed at which the aggregate cells were mixed with the
microspheres. They also included a fluorescent dye in the
microspheres so the degree of incorporation of the microspheres
within the embryoid bodies could be assessed using fluorescent
microscopy and spectroscopy.

The results revealed that the microspheres were incorporated into
embryoid bodies under a variety of mixing conditions, but that slower
rotary speeds and higher microsphere-to-cell ratios resulted in a
greater degree of incorporation.

Next, the researchers compared differentiation of untreated cells,
cells mixed with empty microspheres, cells mixed with retinoic acid-
loaded microspheres, and cells treated with soluble retinoic acid.
Retinoic acid was chosen initially because it is a potent inducer of
embryonic stem cell differentiation.

After ten days, approximately 90 percent of the embryoid bodies mixed
with retinoic acid-loaded microspheres began to display the hollow
structure signifying differentiation, compared to 6 percent of the
untreated bodies, 10 percent of the bodies coated with soluble
retinoic acid, and 30 percent of the bodies mixed with empty
microspheres. In addition, thirty percent of the embryoid bodies
mixed with retinoic acid-loaded microspheres were completely hollow
in the center, compared to nearly zero percent for the other groups.

"These results suggest that if you can control the signaling by
presenting molecules locally on the inside of the embryoid body from
biodegradable microspheres, you can effectively change the course and
synchrony of differentiation," said McDevitt.

To examine the cells in more detail, McDevitt teamed with Georgia
Tech School of Biology chair John McDonald and research scientist
Nathan Bowen to conduct microarray gene expression studies to
determine cell phenotype.

The results revealed enhanced expression of fibroblast growth factor
5 (FGF-5) - a marker for primitive ectoderm - in the embryoid bodies
mixed with retinoic acid-loaded microspheres compared to the other
treatment groups after 10 days. The researchers also confirmed
increased or inhibited expression of many additional markers.

"The importance of these findings is that we've shown that
biomaterial-based approaches to regulate stem cell microenvironments
can significantly improve differentiation methods," said
McDevitt. "Our ultimate goal is to improve the efficiency of this
differentiation process into specific cell types for cell replacement
therapies."

----------------------------
Article adapted by Medical News Today from original press release.
----------------------------

Source: Abby Vogel
Georgia Institute of Technology Research News
http://www.medicalnewstoday.com/articles/103464.php

__._,_.___

Messages in this topic (1) Reply (via web post) | Start a new topic

Messages

____________________________________________
«¤»¥«¤»§«¤»¥«¤»§«¤»¥«¤»«¤»¥«¤»§«¤»¥«¤»§«¤»¥«
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
StemCells subscribers may also be interested in these sites:

Children's Neurobiological Solutions
http://www.CNSfoundation.org/

Cord Blood Registry
http://www.CordBlood.com/at.cgi?a=150123

The CNS Healing Group
http://groups.yahoo.com/group/CNS_Healing
____________________________________________
«¤»¥«¤»§«¤»¥«¤»§«¤»¥«¤»«¤»¥«¤»§«¤»¥«¤»§«¤»¥«
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯