Deficits in human trisomy 21 iPSCs and neurons

Abstract

Down syndrome (trisomy 21) is the most common genetic cause of intellectual disability, but the precise molecular mechanisms underlying impaired cognition remain unclear. Elucidation of these mechanisms has been hindered by the lack of a model system that contains full trisomy of chromosome 21 (Ts21) in a human genome that enables normal gene regulation. To overcome this limitation, we created Ts21-induced pluripotent stem cells (iPSCs) from two sets of Ts21 human fibroblasts. One of the fibroblast lines had low level mosaicism for Ts21 and yielded Ts21 iPSCs and an isogenic control that is disomic for human chromosome 21 (HSA21). Differentiation of all Ts21 iPSCs yielded similar numbers of neurons expressing markers characteristic of dorsal forebrain neurons that were functionally similar to controls. Expression profiling of Ts21 iPSCs and their neuronal derivatives revealed changes in HSA21 genes consistent with the presence of 50% more genetic material as well as changes in non-HSA21 genes that suggested compensatory responses to oxidative stress. Ts21 neurons displayed reduced synaptic activity, affecting excitatory and inhibitory synapses equally. Thus, Ts21 iPSCs and neurons display unique developmental defects that are consistent with cognitive deficits in individuals with Down syndrome and may enable discovery of the underlying causes of and treatments for this disorder.cerebral cortex | developmental disorders D own syndrome (DS) is the most frequent single cause of human birth defects and intellectual disability (ID) (1). DS is caused by trisomy of chromosome 21 (Ts21) (2), resulting in the triplication of over 400 genes (3-5), which makes elucidation of the precise mechanisms underlying ID in DS a significant challenge. Confounding this difficulty is the relative inaccessibility of human tissue and incomplete human Ts21 in the context of mouse models. Despite these shortcomings, studies using mouse models containing trisomy of parts of syntenic chromosome 21 (HSA21) have put forth several critical hypotheses on the cellular and molecular mechanisms underlying DS features. It is essential, however, to test these hypotheses in human cells with full triplication of HSA21 in a context that allows for normal gene regulation. Here, we used Ts21-induced pluripotent stem cells (iPSCs) to test hypotheses of the underlying causes of ID in DS, with specific regard to neuropathophysiology. ResultsIsogenic Human Ts21 iPSCs. Fibroblasts from two individuals diagnosed with DS were reprogrammed to iPSCs. FISH for HSA21 in one fibroblast line showed mosaicism, where ∼90% of cells carried Ts21, whereas ∼10% were euploid (Fig. 1A). Reprogramming of the mosaic fibroblasts by retrovirus (6) resulted in three viable iPSC clones, two clones that carried Ts21 and one euploid (Fig. 1B). Mosaicism in DS individuals is rare, occurring in ∼1-3% of DS cases (7), but it can also emerge in vitro (8), potentially because of nondisjunction events during cell division.

A genetic cause of Alzheimer disease: mechanistic insights from Down syndrome

“…Mitochondrial dysfunction and enhanced production of reactive oxygen species (ROS) occur in people with DS and in trisomy 21 models [151][152][153][154] , and may contribute to the accelerated ageing reported in people who have DS 155 . Mitochondrial impairment may directly affect energy-hungry synapses, contributing to cognitive deficits 156 .…”

“…169); and nonintegration-reprogrammed isogenic lines from an adult with mosaic DS (a condition in which only a percentage of an individual's cells carry an extra copy of chromosome 21) 121 . Neurons derived from iPSCs show cellular phenotypes underpinning AD pathology, such as increased Aβ production, abnormal subcellular distribution of phosphorylated tau, mitochondrial abnormalities and accelerated cellular ageing 121,122,154,212 . DS iPSC models can be used to dissect the effect of trisomy of individual chromosome 21 genes (for example, by genome editing using clustered regularly interspaced short palindromic repeat-CRISPR-associated protein 9 (CRISPRCas9) technology), to develop high-throughput screening assays for phenotype-correcting compounds and to investigate cellular phenotypes in iPSCs generated from individuals with DS with very early versus very late ages of onset of dementia.…”

“…Comparisons have been made between euploid and trisomy 21 iPSCs derived from multiple sources, including different individuals (nonisogenic) 122,209 ; isogenic lines generated in cell culture, spontaneously or by selection 154,210 ; lines in which one of the three copies of chromosome 21 has been silenced 211 ; monozygotic twins that were discordant for trisomy 21 (REF. 169); and nonintegration-reprogrammed isogenic lines from an adult with mosaic DS (a condition in which only a percentage of an individual's cells carry an extra copy of chromosome 21) 121 .…”

The potential of induced pluripotent stem cells in models of neurological disorders: implications on future therapy

“…By comparison, disease-specific iPSCs provide new prospects for disease-related R&D by enabling screening for genes and disease processes potentially modifiable by drugs identified through in vitro screening. Consequently, iPSCs have been successfully derived from patients with NDv disorders including schizophrenia [3][4][5][6][7][8][9][10][11], Down's syndrome [12][13][14][15][16][17][18][19][20][21], autism spectrum disorders (ASDs) including fragile X, Rett and Timothy syndromes [22][23][24][25][26][27][28][29][30][31][32][33][34][35], and epilepsy [36][37][38][39], as well as NDg disorders such as Alzheimer's disease [40][41][42][43][44][45][46][47][48], Parkinson's disease [49][50][51][52]…”

Perspectives for Induced Pluripotent Stem Cell Technology

“…27,28 Somatic mutations can give rise to a broad range of diseases, including cancer, and noncancerous mosaic diseases. 18 Recently, heterogeneous patient-specific iPS cell lines have been generated from the somatic cells of patients with various mosaic diseases, such as Down syndrome (DS), [29][30][31][32][33][34][35] Fragile X syndrome, 36 Rett syndrome, [37][38][39][40][41][42] Fanconi anemia, 43 and chronic infantile neurologic cutaneous and articular (CINCA) syndrome. 44 Even though there are some limitations associated with the kinds of diseases that can be modeled, using iPS cells derived from patients with somatic mosaicism has an advantage in that it allows analyses with isogenic controls.…”