88
4.3.2.1 iPSCs and Neural Regenerative Medicine
Among specifi c cell lineages, neural cells have been considered as the fi rst lineage
to be reliably attained from iPSCs (Tabar and Studer 2014 ). A previous report
showed that neural lineage differentiation of iPSCs is similar to ESCs (Skalova
et al. 2015 ). iPSCs can differentiate into neural stem cells and neural crest stem cells
and subsequently into specifi c neural lineages (Hirschi et al. 2014 ). Biochemical
factors, small mo lecules, and morphogen-based induction have been explored to
generate neural cells from iPSCs (Table 4.1 ).
Embryoid body (EB) formation , coculture on feeder layers, and direct neural
induction using growth factors have been introduced to derive neuronal subtypes
from iPSCs (Tabar and Studer 2014 ). As an early protocol, EB formation was based
on using selection medium for neural cell lineages. Because of similarities between
iPSCs and ESCs, analogous factors can induce neural differentiation of these cells;
however, iPSC generation is associated with signifi cantly reduced effi ciency and
increased variability (Hu et al. 2010 ). For instance, retinoic acid has been effective
with both ESCs and iPSCs (Yuan et al. 2013 ). One challenge to differentiate human
iPSCs cells to Purkinje cells has recently been solved by using FGF2 and insulin in
EB formation (Wang et al. 2015 ). Coculture on stroma-feeder has also been exten-
sively applied for production of neural cells, including dopamine neuron-like cells,
from iPSCs (Tabar and Studer 2014 ). Muratone and colleagues showed that cocul-
ture of iPSC-derived neurons with astrocytes increases neuronal maturity by day 40
(Muratore et al. 2014 ).
Direct induction protocols do not require EB formation and coculture induction;
however, inhibition of TGF-β receptors (reviewed by Hirschi et al. 2014 ) and the
SMAD signaling pathway (Chambers et al. 2009 ) is an important key in the differ-
entiation of iPSCs into neural cells. Previous studies showed that inhibitors of TGF
and BMP (dual SMAD inhibition) have extremely enhanced the effi ciency and the
Table 4.1 Chemicals and small molecules used for neural differentiation
Name/factor Mechanism
Retinoic acid Morphogen/agonist of the Sonic Hedgehog pathway
Epidermal growth factor (EGF) Mitogen
Fibroblast growth factor (FGF-2,
FGF-8, FGF-4)Regulation of neural stem cell proliferation and
self-renewal
Platelet-derived growth factor (PDGF) Neural induction factor
Sonic Hedgehog (SHH) Morphogen, induction factor
Noggin Bone morphogenetic protein (BMP) antagonist
SB431542 Inhibition of the TGF-β/activin/nodal pathway/
inhibition of SMAD
Dorsomorphin Inhibition of BMP pathway/inhibition of SMAD
LDN193189 Inhibition of BMP pathway
Purmorphamine Activation of the Hedgehog pathway
Source: Skalova et al. ( 2015 )
P.V. Pham et al.