Download Williams syndrome: findings from the dish

Thanathom ‘Earl’ Chailangkarn
Williams syndrome: findings from the dish
Induced pluripotent stem cell (iPSC) technology has become one of the major
approaches for disease modeling since its first report in 2006. The ability to reprogram cells
from somatic into embryonic stem cell-like state and to differentiate them into desired cell types
in the culture dish has allowed scientists to carry out the study of several diseases in cells such
as neurons which, in the past, could not be isolated from living subjects. Williams syndrome
(WS), a genetic neurodevelopmental disorder where 25-28 genes are hemizygously deleted, is
among those. Despite cardiovascular abnormalities, its unique neurological phenotypes i.e.
hypersociability is of our interest. For several decades, research on different neurological
aspects of WS has been conducted in a variety of models such as patient-derived cell lines
(lymphoblastoid cells and fibroblasts), post mortem tissue, and mouse models. However, the
lack of physiologically relevant cell types such as neural progenitor cells (NPCs) and neurons
has left a critical gap in our knowledge the disease’s cellular and molecular phenotypes.
To fill this gap, we took the advantage of the reprogramming technology to capture the
genomes of WS subjects in iPSCs, which could be then differentiated into NPCs and neurons,
enabling evaluation of whether the captured genome with hemizygous deletion of those genes
leads to relevant neuronal cellular phenotypes. Dental pulp cells-derived iPSCs of classical WS,
rare WS and typical developing (TD) subjects were neurally induced via dual-SMAD inhibition in
order to generate NPCs and neurons. We discovered that classical WS NPCs exhibited
increased apoptosis, and, therefore, doubling time, compared to TD neurons. This could
possibly contribute to the reduction in cortical surface area in classical WS individuals as
assessed by magnetic resonance imaging. Surprisingly, we found that rare WS NPCs behaved
similarly to TD NPCs rather than to classical WS NPCs in terms of apoptosis. We confirmed that
frizzled9, which is deleted in the classical WS but not in our rare WS genome, is responsible for
such phenotype via gain- and loss-of-function assays. Moreover, classical WS neurons in
general showed increased frequency of activity-dependent calcium transient compared to TD
neurons. Finally, classical WS neurons expressing CTIP2, a cortical layer V marker, exhibited
an increase in total dendritic length and number of dendritic spines compared to TD neurons,
which was in agreement with the results obtained from WS cortical layer V neurons in post
mortem brain. These findings in WS neurons offer new insights into the haploinsufficiency effect
in cortical layer V neurons whose role is implicated in social behavior, suggesting an increase in
neuronal activity that could possibly be linked to hypersociability observed in WS individuals.
We demonstrated that iPSC technology holds great potential for disease modeling by revealing
the missing pieces of cellular and molecular information needed for further drug screening and
discovery.