Download Signalling Adapter Expression Boosts Induced Neuron

Signalling Adapter Expression Boosts
Induced Neuron Functionality
Review of “Signaling Adaptor Protein SH2B1 Enhances Neurite Outgrowth and Accelerates
the Maturation of Human Induced Neurons” from Stem Cell Translational Medicine by Stuart
P. Atkinson.
Direct reprogramming strategies aim to produce therapeutically relevant patient-specific
cell types from somatic cells without first passing through the induced pluripotent stem
cell (iPSC) stage. Previous studies have demonstrated the direct conversion of human
cells to induced neurons (iNs) [1-5], although thus far each study has reported some level
of functional deficit. To address these problems, a team lead by Ing-Ming Chiu from the
National Health Research Institutes, Taiwan, have built on their work on the signaling
adaptor protein SH2B1 which can enhance fibroblast growth factor 1-induced neurite
outgrowth by modulation of the MEK-ERK1/2-STAT3-Egr1 pathway [6]. They now
report on their study into the role for SH2B1, alongside miR124, BRN2, and MYT1L (SIBM), in the enhancement of the conversion of human fibroblasts to functional neurons
[7].
The group first reprogrammed Doxinducible SH2B1-GFP human foetal fibroblasts (HFFs) towards iNs using IBM in the
presence or absence of SH2B1 expression (S-IBM or IBM) (see Figure). 14 days after
induction, S-IBM cells manifested typical neuronal morphology, with double the level of
neurite outgrowth, and significantly more neuronal processes and branches compared to
IBM-infected cells. This characteristic neural morphology was even more obvious at 28
days in the S-IBM cells, suggesting that SH2B1 may boost differentiation speed, or
enhance maturation.
Further characterisation of S-IBM iNs found that 61% expressed the neurotransmitter
GABA, 41% expressed Synapsin and they expressed significantly higher levels of
neuronal markers (TuJ1, NeuN, and TH) than IBM iNs cells. The researchers noted
spontaneous firing of action potentials in S-IBM iNs at day 14 with high peak amplitudes
(+5268 mV) compared to IBM iNs, where only one of 4 cultures fired action potentials
and at a lower amplitude (+10 mV). Analysis of stimulus-evoked action potentials found
repetitive firings in the S-IBM iN populations at day 14, but only a single evoked spike in
the IBM iNs, although the group did observed repetitive firings in both cultures by day
21, both spontaneously and stimulus-evoked. Resting membrane potential, measured by
whole-cell current-clamp mode, was significantly different between the two groups, with
a more negative resting membrane potential in S-IBM iNs (24569 mV) than in IBM iNs
(22264 mV) at day 14, although by day 21 and 28 both iNs had membrane potentials
close to that observed for regular neurons (~265 mV).
Overall, these authors have shown that expression of the signalling adapter protein
SH2B1 enhances the generation of iNs by boosting reprogramming, enhancing neurite
growth and shortening the neuronal maturation period. The authors posit that SH2B1 may
promote FGF- [6] and GDNF-induced neurite outgrowth [8], factors which are both
contained in the iN-defined culture media, although further work is required to fully
delineate any such mechanism. This finding should prove useful to efforts to reprogram
refractory somatic cell samples from patients with specific disease-related mutations,
allowing them to be used for personalized regenerative medicine, drug screening or in
vitro disease modeling.
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