Altered patterning of trisomy 21 interneuron progenitors

Abstract

Multiple developmental processes go awry in Down syndrome (DS, trisomy 21, Ts21), the most common genetic cause of intellectual disability and a complex multigene disorder. DS individuals have smaller brains with reduced volume of frontal and temporal lobes, including hippocampus. This smaller brain volume corresponds to fewer neurons in the DS cortex measured at pre-and post-natal stages, implicating impaired neurogenesis during development. We employ Ts21 human induced pluripotent stem cells (iPSCs) and isogenic controls to identify disrupted interneuron developmental processes in DS. Interneuron progenitor specification, proliferation and migration is largely controlled by integrating known morphogen gradients, sonic hedgehog (SHH) and Wingless (WNT), and we find that Ts21 progenitors have altered patterning and generate different progenitor populations. Specifically, we find expression of WNT signaling genes is reduced and expression of GLI genes that regulate WNT and SHH signaling in this population is increased in Ts21 interneuron progenitors, suggesting Ts21 progenitors are patterned more ventrally and less caudally. Altered patterning affects lineage decisions and, in fact, fewer caudal interneuron progenitors expressing the transcription factor COUP-TFII differentiate from Ts21 iPSCs. In mouse, COUP-TFII+ progenitors are found in more caudal regions of the neurogenic regions, thus linking the patterning changes to altered generation of interneuron subpopulations. These data identify affected progenitor subpopulations in Ts21 and suggest that abnormal patterning of human Ts21 interneuron progenitors alters the generation of interneurons in DS and contributes to the reduced neurogenesis in DS.

Transcriptional consequences of trisomy 21 on neural induction

“…These data are consistent with previous work by our lab and others showing a downregulation of canonical WNT signaling in T21 cells (Hibaoui et al, 2014;Granno et al, 2019;Giffin-Rao et al, 2022;Qiu et al, 2023). DYRK1A, a Hsa21 dosage sensitive gene, interacts with the canonical pathway through GSK3β to inhibit pathway activity (Hibaoui et al, 2014;Qiu et al, 2023).…”

“…Single cell analysis is required to assess the cell type differences in our culture. In fact, our previous single cell analysis of T21 interneuron progenitors did indicate an enriched population of a progenitor subtype in T21 (Giffin-Rao et al, 2022) and so it would be interesting to see if there is a similar divergence of cells in T21 in neural induction.…”

“…One pair of trisomy 21 and euploid control iPSCs were generated from fibroblasts from a 24-year-old female mosaic for trisomy 21 (Weick et al, 2016;Giffin-Rao et al, 2022). iPSCs undergo regular karyotyping and mycoplasma testing to ensure quality (WiCell Institute, Madison WI).…”

“….1341141 McCann et al, 2021. Several non-exclusive hypotheses have emerged to explain these deficits including that T21 results in fewer progenitors and/or reduced progenitor proliferation, decreased migration of progenitors, or increased progenitor death (Lu et al, 2012;Huo et al, 2018;Giffin-Rao et al, 2022). Our results shed some mechanistic light on the impact of T21 on the establishment of the nervous system, and demonstrate that T21 dysregulates genes involved in pathways relevant to the phenotypes of individuals with DS and cells from these individuals including oxidative stress, morphological abnormalities, immune disorders, divergent metabolic states, and premature aging (Coskun and Busciglio, 2012;Muchová et al, 2014).…”