Generation of inducible pluripotent stem cells (iPS) offers
the possibility of creating patient-specific stem cells with embryonic stem cell
therapeutic potential from adult sources. Recently the main hurdle of iPS cell
generation, the need for introduction of oncogenes in the adult cells, has been
removed by use of chemical modulators as well as alternative non-cancer causing
genes. Another drawback of creating iPS cells is the need for mass screening of
many transfected target cells before identification and extraction of the
correct cell can be made. In the current paper the histone deacetylase
inhibitor butyrate was used to enhance potency of iPS generation in vitro.
Histone deacetylase inhibitors are a type of compounds that decrease the density
of DNA in chromosomes. By performing this function the DNA because more
amenable to reprogramming, in the sense that the cells can be coaxed to
de-differentiate with less effort. Another histone deacetylase inhibitor,
valproic acid, which is used clinically to treat convulsions, has been shown to
increase the ability of blood making stem cells to self-replicate with higher
efficiency, which is a characteristic of earlier de-differentiation.
In a recent paper it was demonstrated that temporary
treatment with butyrate increases efficacy of iPS generation by 15-51 fold using
two techniques that are commonly used for generation of these cells. It was
demonstrated that in the presence of butyrate stimulation a remarkable (>100-200
fold) increase on reprogramming in the absence of either KLF4 or MYC transgene.
This suggests that butyrate may be a useful agent to
incorporate in the iPS generation protocols that are currently under
development. Furthermore, butyrate treatment did not negatively affect
properties of iPS cell lines established. The generated iPS cell lines,
including those derived from an adult patient with sickle cell disease by two
methods show normal karyotypes and pluripotency.
To mechanistically identify molecular pathways of butyrate
enhancement of iPS generation, the investigators performed conducted genome-wide
gene expression and promoter DNA methylation microarrays and other epigenetic
analyses on established iPS cells and cells from intermediate stages of the
reprogramming process.
By day 6-12 after exposing cells to butyrate, enhanced
histone 3 acetylation, promoter DNA demethylation, and the expression of
endogenous pluripotency-associated genes including DPPA2, whose over-expression
partially substitutes for butyrate stimulation is known.
According to Dr. Mali " Thus, butyrate as a cell
permeable small molecule provides a simple tool to further investigate molecular
mechanisms of cellular reprogramming. Moreover, butyrate stimulation provides an
efficient method for reprogramming various human adult somatic cells, including
those from patients that are more refractory to reprogramming"
Methods of increasing efficacy of iPS generation have
included not only chemical manipulation but also starting from cell sources that
are generally considered more immature. For example a previous study
demonstrated that mesenchymal stem cells create a much higher per-cell number of
iPS cells as compared to skin fibroblasts.
One of the interesting points of this finding is that
butyrate may theoretically be useful at expanding potential of stem cells
already in an organism. Since butyrate is used clinically for treatment of urea
cycle disorders and is non-toxic at pharmacological doses, it may be a good
candidate for expanding stem cells in vivo. Manipulation of the stem cell
compartment by administration of therapeutic agents has already been performed
for mobilization, which has been published with the neutraceutical Stem-Kine
http://www.translational-medicine.com/content/pdf/1479-5876-7-106.pdf.
