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Human, mammalian, brain development is a very complex process and starts shortly after gastrulation. Human in vitro models for brain development as well as pathological changes were published in last few years, eliminating the ethical concerns that accompany the study of aborted foetal material. One of the recent approaches is the development of induced pluripotent stem cell (iPSC) technology and different types of organoids, which can be applied to any species. In our previous work we developed iPSCs from an adult individual with constitutional mosaicism for Down Syndrome (DS) (1). From those iPSCs, cerebral organoids were grown and corticogenesis and Alzheimer-like pathology in vitro were studied (2). Mixed cerebral (2), as well as midbrain (unpublished) organoids were grown in vitro from the isogenic, trisomic and disomic iPSCs. Organoids were analysed histologically by IMARIS software. Foetal human brains were stained with the same combinations of antibodies and the data were compared. Anonymized post-mortem brain samples were obtained from the Brain Bank of the Croatian Institute for Brain Research (CIBR). Isogenic cerebral organoids expressed the markers of all six cortical layers (Reelin, FOXG1, SATB2, TBR1, Ctip2 and Brn2) after 100 days differentiation in vitro (DIV). At the early time point of DIV30 the majority of cells were Nestin, SOX2, PAX6 positive. At that time point neurogenesis had already started, so we observed TRBR2, DCX, MAP2 and TUBB3 positive cells in disomic and trisomic organoids. Following further neuronal differentiation of cerebral organoids we observed decreased number of neural stem cells and increased number of neuronal markers specific for all six layers. On the other hand, midbrain organoids expressed markers specific for midbrain. At the early time points midbrain organoids expressed neuronal stem cells markers, similar to cerebral organoids, but with organoid maturation we found midbrain specific cells such as NURR1 and OTX2 specific for the early stages, and later Dopamine β Hydroxylase, NET and TH. Finally, all those markers were compared with expression in foetal human brain from individuals with Down Syndrome as well as euploid controls age, sex and brain region matched. Our data showed that isogenic cerebral organoids grown from iPSCs are good tool for multidisciplinary studies. In our group we study corticogenesis, synaptogenesis, pathology and possible drug treatments.

Background: Specific cell types from people with Down syndrome (DS) show faster accumulation of DNA damage and epigenetic senescence marks. Causative mechanisms remain un-proven ranging from amplified chromosomal instability to actions of chromosome 21 genes. Plasma immunoglobulin G (IgG) glycosylation profiles are established as a reliable predictor of biological and chronological ageing. Methods: We performed IgG glycan profiling of n=246 individuals with DS (208 adults and 38 children) clinically characterised for co- morbidities, from three European countries, and compared these to age-, sex- and demography- matched general populations. Results: We uncovered very significantly increased IgG glycosylation ageing marks associated with DS, beginning in early childhood. Average levels of IgG glycans without galactose (G0) and those with two galactoses (G2) as a function of age in persons with DS corresponded to levels detected in 19 years older euploid individuals. Sub-cohorts of DS without any known co-morbidities from different countries showed a similar result, eliminating DS- linked autoimmune diseases, frequent infections, or Alzheimer’s dementia as indirect causes of accelerated biological ageing. Importantly, no difference in slope of the curve relating IgG- glycan-age to chronological age was observed for any of the 3 analysed populations, discouraging the amplified-chromosomal-instability explanation. Remarkably, IgG-glycan profiles of a child with DS caused by a short segmental duplication of only 31 genes on chromosome-21 (DS-critical-region) had values like age-matched whole-chromosome-trisomy- 21 children, pointing to a causative contribution of one or more of the 31 genes. Conclusion: This shifts the paradigm from an (essentially untreateable) “amplified instability” mechanism, to a specific gene-overdose-driven cause of a progeria-like syndrome, opening possibilities for therapeutic amelioration strategies. We generated an induced pluripotent stem cell (iPSC) model of this child with partial trisomy 21, and editing experiments using CRISPR-Cas9 are underway in order to dissect the causative overdosed genes and mechanisms responsible for the accelerated ageing in DS.

Objectives: To describe neuronal differentiation from the disomic (D21) and trisomic (T21) isogenic human induced pluripotent stem cells (iPSCs) and neural stem cells (NSCs) derived from persons with partial and full trisomy 21, and mosaic Down syndrome (DS). Methods: NSC were generated form the isogenic iPSCs following published protocol (1) and expanded in our laboratory. NSCs, between passage 5 and 10 were seeded on the commercially available mouse astrocytes and differentiated to the mature neurons 100 days in vitro (DIV) (2). Moreover, cerebral organoids were generated following published protocol (3) with our modification (4) and fixed at 30, 50, 70 and 100 DIV and analysed by immunohistochemistry. Results: In our previous work we published neuronal differentiation from EBs D3 and 47-1 (5). Here we find that Tubb3 positive cells show a specific neuronal phenotype. Disomic cells showed normal neuronal morphology, on the other hand trisomic cells showed a very specific cellular dysmorphology: neurons were smaller, shorter with thicker processes, and abnormal branching patterns. The same pattern we have observed in neurons derived form iPSCs in monolayer as well as in cerebral organoids. Both, neurons in monolayer, as well as in cerebral organoids expressed all neuronal markers: pan neuronal markers (Dcx, MAP2. Tubb3, SMI, 3R-Tau) and cortical layer specific markers (Reelen, Brn2, Ctip2, SATB2, TBR1 and TBR2). Conclusion: Trisomic cells could differentiate to mature, synaptic active neurons but morphology of trisomic cells shows a unique and specific dysmorphology pattern.