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I
nduced
pluripotent
stem
cells
reprogramming
: E
pigenetics
and
applications
in
the
regenerative
medicine
R
ev
A
ssoc
M
ed
B
ras
2017; 63(2):180-189
185
TABLE 3
Epigenetic changes using microRNAs.
Authors
Year miRNA Species Type of cell
Mechanism of action
Results
Judson et al.
54
2009 290-295 Mice
Fibroblast
Blocks p21, leading to
increased cell cycle proteins
Promotes the G1-S phase transition
(proliferation), indirectly activating
pluripotency factors
Li and He
50
2012 Let-7
Mice
Embryonic
stem cell
Reduced CyclinD/Cdk4
regulation
Blocks G1-S phase
Subramanyam et
al.; Lin et al.
55,56
2011 302-367
Mice
Fibroblast
Inhibits TGFII-
β
Promotes MET
Choi et al.
63
2011 34a and
34b/c
Mice
Fibroblast
Reduced regulation of p21
and p53
Indirectly blocks pluripotency factors
Li et al.
61
2014 135b
Mice
Fibroblast
Reduced expression of
TGF-
β
, Igfbp5, and Wisp1
Promotes MET
Zare et al.
49
2015 124-128 Humans Fibroblast
Regulate the development
of neurons
Promotes the migration, maturation
and differentiation of neurons,
maintaining adequate gene expression
and repressing unwanted genes
MET: mesenchymal-epithelial transition.
thology affects around 700,000 people in Japan, and is
the most common form of blindness in people aged over
60, causing progressive loss of the retinal pigment epi-
thelial monolayer. The transplant lasted around two hours
and, according to the researchers, the patient did not
suffer adverse effects, and there were an improvement in
the morphology of the macula and neovascularization.
66
This clinical trial was carried out by the group of Pro-
fessor Takahashi, co-author of the manuscripts that won
Professor Yamanaka the Nobel Prize in Medicine in 2012.
However, in March 2015, clinical testing intended to treat
six patients was suspended due to regulatory changes in
regenerative medicine in Japan.
67
Other clinical trials are currently underway to test
the effectiveness of cellular therapy with iPSC in the treat-
ment of AMD, Parkinson’s disease, spinal cord injury,
diabetes and myocardial infarction.
68
Preliminary results
have not yet been presented.
Maintenance of the epigenetic factors of the iPSC
after reprogramming has also been used to understand
the molecular pathways involved in the development of
diseases, development of new drugs and personalized
medicine.
69
The first study conducted of this kind used
a model of neuropathic disease. The authors repro-
grammed fibroblasts from patients with Riley-Day syn-
drome and monitored in vitro splicing of the IKBKAP
(mutation associated with the disorder). Furthermore,
the researchers also evaluated candidate drugs for rever-
sal of the splicing. The study of iPSC gains relevance in
this case, due to the inability of accessing the tissues
affected by Riley-Day syndrome.
70
Other studies have
been developed along this line,
69
and are promising in
the context of drug development. Figure 2 summarizes
the use of iPSC.
C
onclusion
Despite the improvement recently seen in iPSC reprogram-
ming by up to 100 times, when compared to Yamanaka
factors,
44
the yield remains relatively low and high costs.
Another problem is the long period for full iPSC repro-
gramming and the high cells proliferation rates associ-
ated with a greater chance of developing cancer.
71
Takahashi
and Yamanaka suggest considering using iPSC with al-
logeneic transplantation in regenerative medicine, which
would improve the effectiveness of the treatment of certain
diseases such as spinal cord injury, which requires quick
treatment without waiting for the time taken for repro-
gramming.
11
Furthermore, there is a need for better un-
derstanding of how the reprogramming interventions
influence the epigenetic memory of the reprogrammed
cells. Despite advances in iPSC reprogramming, certain
questions have emerged: 1) Is it possible to completely
erase the somatic epigenetic memory by associating the
different treatments mentioned?; 2) Could “forced” repro-
gramming cause long-term damage, such as the develop-
ment of cancer or other diseases?; 3) Is it possible to replace
embryonic stem cells with iPSC in regenerative medicine?
In spite of the extraordinary progress achieved recently in
the use of iPSC, the deepening of ongoing studies and
realization of new studies are necessary in order to elucidate