Induced pluripotent stem cell (iPSC) modelling for the identification of mechanisms behind neurodevelopmental disorders

Abstract: Human induced pluripotent stem cells (iPSCs) have opened new possibilities to recapitulate disease mechanisms and to model disorders in vitro. In the studies presented here, iPSCs were established to model neural differentiation in Down syndrome (DS), caused by trisomy for chromosome 21 (T21); Dravet syndrome (DRS), caused by variants in the SCN1A gene; and an ataxia syndrome, caused by a variant in the NFASC gene. The major aim has been to uncover molecular and cellular mechanisms behind perturbed neurogenesis in the three disorders.In Paper I, the analysis of transcriptomes and proteomes of the DS iPSC derived neural model revealed several perturbed gene clusters with strong temporal dynamics along neural differentiation, markedly down-regulated mitochondrial genes and a dysregulation of hub proteins. These results predict complex and genome-wide changes in T21 neural cells associated with prolonged cell cycle, reduced cell growth and a perturbed energy metabolism.In Paper II, it was demonstrated that the transcriptional profile of iPSC based neural model system for DS was enriched for differentially methylated genes and gene families when compared to a corresponding euploid model. The differentially methylated genes were enriched for transcriptional regulation and chromatin structure, suggesting novel mechanistic links between the genomic imbalance caused by T21 and the global transcriptional dysregulation in DS. In Paper III, it was shown that DRS patient iPSCs differentiated into GABAergic interneurons exhibit a dysregulated epilepsy gene network as well as an altered expression of genes involved in chromatin remodelling, accompanied by abnormal electrophysiological properties and increased stress sensitivity.In Paper IV, it was shown that neural iPSCs, established from a patient with an ataxia syndrome and a novel homozygous variant in the NFASC gene, lack a full-length neurofascin-186 important for cell adhesion. The patient derived neural iPSCs showed delayed neuronal differentiation, reduced sprouting, shorter neurites and altered electrophysiology.The Papers I-IV show that patient derived neural iPSCs enable to identify molecular and cellular mechanisms associated with neuropathogenesis. Besides specific dysregulated pathways and cellular defects in models of three developmental disorders, with shortlists of novel candidate disease biomarkers, the results are consistent with prior data and clinical presentation of patients. The knowledge gained is of paramount importance for translation into clinical settings and a step towards development of novel therapies with the ultimate goal to alleviate symptoms of affected individuals.