Cerebral organoids with chromosome 21 trisomy secrete Alzheimer's disease-related soluble aggregates detectable by single-molecule-fluorescence and super-resolution microscopy.

Understanding the role of small, soluble aggregates of beta-amyloid (Aß) and tau in Alzheimer's disease (AD) is of great importance for the rational design of preventative therapies. Here we report a set of methods for the detection, quantification, and characterisation of soluble aggregates in conditioned media of cerebral organoids derived from human iPSCs with trisomy 21, thus containing an extra copy of the amyloid precursor protein (APP) gene. We detected soluble beta-amyloid (Aß) and tau aggregates secreted by cerebral organoids from both control and the isogenic trisomy 21 (T21) genotype. We developed a novel method to normalise measurements to the number of live neurons within organoid-conditioned media based on glucose consumption. Thus normalised, T21 organoids produced 2.5-fold more Aß aggregates with a higher proportion of larger (300-2000 nm2) and more fibrillary-shaped aggregates than controls, along with 1.3-fold more soluble phosphorylated tau (pTau) aggregates, increased inflammasome ASC-specks, and a higher level of oxidative stress inducing thioredoxin-interacting protein (TXNIP). Importantly, all this was detectable prior to the appearance of histological amyloid plaques or intraneuronal tau-pathology in organoid slices, demonstrating the feasibility to model the initial pathogenic mechanisms for AD in-vitro using cells from live genetically pre-disposed donors before the onset of clinical disease. Then, using different iPSC clones generated from the same donor at different times in two independent experiments, we tested the reproducibility of findings in organoids. While there were differences in rates of disease progression between the experiments, the disease mechanisms were conserved. Overall, our results show that it is possible to non-invasively follow the development of pathology in organoid models of AD over time, by monitoring changes in the aggregates and proteins in the conditioned media, and open possibilities to study the time-course of the key pathogenic processes taking place.

Patient-specific Alzheimer-like pathology in trisomy 21 cerebral organoids reveals BACE2 as a gene dose-sensitive AD suppressor in human brain.

A population of more than six million people worldwide at high risk of Alzheimer's disease (AD) are those with Down Syndrome (DS, caused by trisomy 21 (T21)), 70% of whom develop dementia during lifetime, caused by an extra copy of ß-amyloid-(Aß)-precursor-protein gene. We report AD-like pathology in cerebral organoids grown in vitro from non-invasively sampled strands of hair from 71% of DS donors. The pathology consisted of extracellular diffuse and fibrillar Aß deposits, hyperphosphorylated/pathologically conformed Tau, and premature neuronal loss. Presence/absence of AD-like pathology was donor-specific (reproducible between individual organoids/iPSC lines/experiments). Pathology could be triggered in pathology-negative T21 organoids by CRISPR/Cas9-mediated elimination of the third copy of chromosome 21 gene BACE2, but prevented by combined chemical ß and γ-secretase inhibition. We found that T21 organoids secrete increased proportions of Aß-preventing (Aß1-19) and Aß-degradation products (Aß1-20 and Aß1-34). We show these profiles mirror in cerebrospinal fluid of people with DS. We demonstrate that this protective mechanism is mediated by BACE2-trisomy and cross-inhibited by clinically trialled BACE1 inhibitors. Combined, our data prove the physiological role of BACE2 as a dose-sensitive AD-suppressor gene, potentially explaining the dementia delay in ~30% of people with DS. We also show that DS cerebral organoids could be explored as pre-morbid AD-risk population detector and a system for hypothesis-free drug screens as well as identification of natural suppressor genes for neurodegenerative diseases.

Differential Coassembly of α1-GABAARs Associated with Epileptic Encephalopathy.

GABAA receptors (GABAARs) are profoundly important for controlling neuronal excitability. Spontaneous and familial mutations to these receptors feature prominently in excitability disorders and neurodevelopmental deficits following disruption to GABA-mediated inhibition. Recent genotyping of an individual with severe epilepsy and Williams-Beuren syndrome identified a frameshifting de novo variant in a major GABAAR gene, GABRA1 This truncated the α1 subunit between the third and fourth transmembrane domains and introduced 24 new residues forming the mature protein, α1Lys374Serfs*25 Cell surface expression of mutant murine GABAARs is severely impaired compared with WT, due to retention in the endoplasmic reticulum. Mutant receptors were differentially coexpressed with ß3, but not with ß2, subunits in mammalian cells. Reduced surface expression was reflected by smaller IPSCs, which may underlie the induction of seizures. The mutant does not have a dominant-negative effect on native neuronal GABAAR expression since GABA current density was unaffected in hippocampal neurons, although mutant receptors exhibited limited GABA sensitivity. To date, the underlying mechanism is unique for epileptogenic variants and involves differential ß subunit expression of GABAAR populations, which profoundly affected receptor function and synaptic inhibition.SIGNIFICANCE STATEMENT GABAARs are critical for controlling neural network excitability. They are ubiquitously distributed throughout the brain, and their dysfunction underlies many neurologic disorders, especially epilepsy. Here we report the characterization of an α1-GABAAR variant that results in severe epilepsy. The underlying mechanism is structurally unusual, with the loss of part of the α1 subunit transmembrane domain and part-replacement with nonsense residues. This led to compromised and differential α1 subunit cell surface expression with ß subunits resulting in severely reduced synaptic inhibition. Our study reveals that disease-inducing variants can affect GABAAR structure, and consequently subunit assembly and cell surface expression, critically impacting on the efficacy of synaptic inhibition, a property that will orchestrate the extent and duration of neuronal excitability.

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

Down syndrome, which arises in individuals carrying an extra copy of chromosome 21, is associated with a greatly increased risk of early-onset Alzheimer disease. It is thought that this risk is conferred by the presence of three copies of the gene encoding amyloid precursor protein (APP)--an Alzheimer disease risk factor--although the possession of extra copies of other chromosome 21 genes may also play a part. Further study of the mechanisms underlying the development of Alzheimer disease in people with Down syndrome could provide insights into the mechanisms that cause dementia in the general population.

Brief report: isogenic induced pluripotent stem cell lines from an adult with mosaic down syndrome model accelerated neuronal ageing and neurodegeneration.

Trisomy 21 (T21), Down Syndrome (DS) is the most common genetic cause of dementia and intellectual disability. Modeling DS is beginning to yield pharmaceutical therapeutic interventions for amelioration of intellectual disability, which are currently being tested in clinical trials. DS is also a unique genetic system for investigation of pathological and protective mechanisms for accelerated ageing, neurodegeneration, dementia, cancer, and other important common diseases. New drugs could be identified and disease mechanisms better understood by establishment of well-controlled cell model systems. We have developed a first nonintegration-reprogrammed isogenic human induced pluripotent stem cell (iPSC) model of DS by reprogramming the skin fibroblasts from an adult individual with constitutional mosaicism for DS and separately cloning multiple isogenic T21 and euploid (D21) iPSC lines. Our model shows a very low number of reprogramming rearrangements as assessed by a high-resolution whole genome CGH-array hybridization, and it reproduces several cellular pathologies seen in primary human DS cells, as assessed by automated high-content microscopic analysis. Early differentiation shows an imbalance of the lineage-specific stem/progenitor cell compartments: T21 causes slower proliferation of neural and faster expansion of hematopoietic lineage. T21 iPSC-derived neurons show increased production of amyloid peptide-containing material, a decrease in mitochondrial membrane potential, and an increased number and abnormal appearance of mitochondria. Finally, T21-derived neurons show significantly higher number of DNA double-strand breaks than isogenic D21 controls. Our fully isogenic system therefore opens possibilities for modeling mechanisms of developmental, accelerated ageing, and neurodegenerative pathologies caused by T21.

Tumour angiogenesis is reduced in the Tc1 mouse model of Down's syndrome.

Down's syndrome (DS) is a genetic disorder caused by full or partial trisomy of human chromosome 21 and presents with many clinical phenotypes including a reduced incidence of solid tumours. Recent work with the Ts65Dn model of DS, which has orthologues of about 50% of the genes on chromosome 21 (Hsa21), has indicated that three copies of the ETS2 (ref. 3) or DS candidate region 1 (DSCR1) genes (a previously known suppressor of angiogenesis) is sufficient to inhibit tumour growth. Here we use the Tc1 transchromosomic mouse model of DS to dissect the contribution of extra copies of genes on Hsa21 to tumour angiogenesis. This mouse expresses roughly 81% of Hsa21 genes but not the human DSCR1 region. We transplanted B16F0 and Lewis lung carcinoma tumour cells into Tc1 mice and showed that growth of these tumours was substantially reduced compared with wild-type littermate controls. Furthermore, tumour angiogenesis was significantly repressed in Tc1 mice. In particular, in vitro and in vivo angiogenic responses to vascular endothelial growth factor (VEGF) were inhibited. Examination of the genes on the segment of Hsa21 in Tc1 mice identified putative anti-angiogenic genes (ADAMTS1and ERG) and novel endothelial cell-specific genes, never previously shown to be involved in angiogenesis (JAM-B and PTTG1IP), that, when overexpressed, are responsible for inhibiting angiogenic responses to VEGF. Three copies of these genes within the stromal compartment reduced tumour angiogenesis, explaining the reduced tumour growth in DS. Furthermore, we expect that, in addition to the candidate genes that we show to be involved in the repression of angiogenesis, the Tc1 mouse model of DS will permit the identification of other endothelium-specific anti-angiogenic targets relevant to a broad spectrum of cancer patients.

Exome sequencing identifies putative drivers of progression of transient myeloproliferative disorder to AMKL in infants with Down syndrome.

Some neonates with Down syndrome (DS) are diagnosed with self-regressing transient myeloproliferative disorder (TMD), and 20% to 30% of those progress to acute megakaryoblastic leukemia (AMKL). We performed exome sequencing in 7 TMD/AMKL cases and copy-number analysis in these and 10 additional cases. All TMD/AMKL samples contained GATA1 mutations. No exome-sequenced TMD/AMKL sample had other recurrently mutated genes. However, 2 of 5 TMD cases, and all AMKL cases, showed mutations/deletions other than GATA1, in genes proven as transformation drivers in non-DS leukemia (EZH2, APC, FLT3, JAK1, PARK2-PACRG, EXT1, DLEC1, and SMC3). One patient at the TMD stage revealed 2 clonal expansions with different GATA1 mutations, of which 1 clone had an additional driver mutation. Interestingly, it was the other clone that gave rise to AMKL after accumulating mutations in 7 other genes. Data suggest that GATA1 mutations alone are sufficient for clonal expansions, and additional driver mutations at the TMD stage do not necessarily predict AMKL progression. Later in infancy, leukemic progression requires "third-hit driver" mutations/somatic copy-number alterations found in non-DS leukemias. Putative driver mutations affecting WNT (wingless-related integration site), JAK-STAT (Janus kinase/signal transducer and activator of transcription), or MAPK/PI3K (mitogen-activated kinase/phosphatidylinositol-3 kinase) pathways were found in all cases, aberrant activation of which converges on overexpression of MYC.

BACE2: A Promising Neuroprotective Candidate for Alzheimer's Disease.

Alzheimer's disease (AD) is the most common cause of dementia that affects millions of predominantly elderly individuals worldwide. Despite intensive research over several decades, controversies still surround the etiology of AD and the disease remains incurable. Meanwhile, new molecular players of the central amyloid cascade hypothesis have emerged and among these is a protease known as ß-site APP cleavage enzyme 2 (BACE2). Unlike BACE1, BACE2 cleaves the amyloid-ß protein precursor within the Aß domain that accordingly prevents the generation of Aß42 peptides, the aggregation of which is commonly regarded as the toxic entity that drives neurodegeneration in AD. Given this non-amyloidogenic role of BACE2, it is attractive to position BACE2 as a therapeutic target for AD. Indeed, several groups including ours have demonstrated a neuroprotective role for BACE2 in AD. In this review, we discuss emerging evidence supporting the ability of BACE2 in mitigating AD-associated pathology in various experimental systems including human pluripotent stem cell-derived cerebral organoid disease models. Alongside this, we also provide an update on the identification of single nucleotide polymorphisms occurring in the BACE2 gene that are linked to increased risk and earlier disease onset in the general population. In particular, we highlight a recently identified point mutation on BACE2 that apparently leads to sporadic early-onset AD. We believe that a better understanding of the role of BACE2 in AD would provide new insights for the development of viable therapeutic strategies for individuals with dementia.

Dose imbalance of DYRK1A kinase causes systemic progeroid status in Down syndrome by increasing the un-repaired DNA damage and reducing LaminB1 levels.

BACKGROUND: People with Down syndrome (DS) show clinical signs of accelerated ageing. Causative mechanisms remain unknown and hypotheses range from the (essentially untreatable) amplified-chromosomal-instability explanation, to potential actions of individual supernumerary chromosome-21 genes. The latter explanation could open a route to therapeutic amelioration if the specific over-acting genes could be identified and their action toned-down. METHODS: Biological age was estimated through patterns of sugar molecules attached to plasma immunoglobulin-G (IgG-glycans, an established "biological-ageing-clock") in n = 246 individuals with DS from three European populations, clinically characterised for the presence of co-morbidities, and compared to n = 256 age-, sex- and demography-matched healthy controls. Isogenic human induced pluripotent stem cell (hiPSCs) models of full and partial trisomy-21 with CRISPR-Cas9 gene editing and two kinase inhibitors were studied prior and after differentiation to cerebral organoids. FINDINGS: Biological age in adults with DS is (on average) 18.4-19.1 years older than in chronological-age-matched controls independent of co-morbidities, and this shift remains constant throughout lifespan. Changes are detectable from early childhood, and do not require a supernumerary chromosome, but are seen in segmental duplication of only 31 genes, along with increased DNA damage and decreased levels of LaminB1 in nucleated blood cells. We demonstrate that these cell-autonomous phenotypes can be gene-dose-modelled and pharmacologically corrected in hiPSCs and derived cerebral organoids. Using isogenic hiPSC models we show that chromosome-21 gene DYRK1A overdose is sufficient and necessary to cause excess unrepaired DNA damage. INTERPRETATION: Explanation of hitherto observed accelerated ageing in DS as a developmental progeroid syndrome driven by DYRK1A overdose provides a target for early pharmacological preventative intervention strategies. FUNDING: Main funding came from the "Research Cooperability" Program of the Croatian Science Foundation funded by the European Union from the European Social Fund under the Operational Programme Efficient Human Resources 2014-2020, Project PZS-2019-02-4277, and the Wellcome Trust Grants 098330/Z/12/Z and 217199/Z/19/Z (UK). All other funding is described in details in the "Acknowledgements".

Amplified segment in the 'Down syndrome critical region' on HSA21 shared between Down syndrome and euploid AML-M0 excludes RUNX1, ERG and ETS2.

Children with Down syndrome have a 20- to 50-fold increased risk of acute lymphocytic or myeloid leukaemia. Whole or partial gains of chromosome 21 have been described in multiple childhood leukaemias, and have recently been reported as a likely primary event in B-precursor-acute lymphoblastic leukaemia. It is unclear which amplified gene(s) on chromosome 21 play a key role in leukaemia progression. We describe a minimal amplified segment within the so-called 'Down syndrome critical region' shared between two cases of AML-M0; a Down syndrome, and a constitutionally normal individual. Interestingly, the amplified region does not include the oncogenes RUNX1, ETS2 and ERG.

Perturbed hematopoiesis in the Tc1 mouse model of Down syndrome.

Trisomy of human chromosome 21 (Hsa21) results in Down syndrome (DS), a disorder that affects many aspects of physiology, including hematopoiesis. DS children have greatly increased rates of acute lymphoblastic leukemia and acute megakaryoblastic leukemia (AMKL); DS newborns present with transient myeloproliferative disorder (TMD), a preleukemic form of AMKL. TMD and DS-AMKL almost always carry an acquired mutation in GATA1 resulting in exclusive synthesis of a truncated protein (GATA1s), suggesting that both trisomy 21 and GATA1 mutations are required for leukemogenesis. To gain further understanding of how Hsa21 contributes to hematopoietic abnormalities, we examined the Tc1 mouse model of DS, which carries an almost complete freely segregating copy of Hsa21, and is the most complete model of DS available. We show that although Tc1 mice do not develop leukemia, they have macrocytic anemia and increased extramedullary hematopoiesis. Introduction of GATA1s into Tc1 mice resulted in a synergistic increase in megakaryopoiesis, but did not result in leukemia or a TMD-like phenotype, demonstrating that GATA1s and trisomy of approximately 80% of Hsa21 perturb megakaryopoiesis but are insufficient to induce leukemia.

DYRK1A-dosage imbalance perturbs NRSF/REST levels, deregulating pluripotency and embryonic stem cell fate in Down syndrome.

Down syndrome (DS) is the most common cause of mental retardation. Many neural phenotypes are shared between DS individuals and DS mouse models; however, the common underlying molecular pathogenetic mechanisms remain unclear. Using a transchromosomic model of DS, we show that a 30%-60% reduced expression of Nrsf/Rest (a key regulator of pluripotency and neuronal differentiation) is an alteration that persists in trisomy 21 from undifferentiated embryonic stem (ES) cells to adult brain and is reproducible across several DS models. Using partially trisomic ES cells, we map this effect to a three-gene segment of HSA21, containing DYRK1A. We independently identify the same locus as the most significant eQTL controlling REST expression in the human genome. We show that specifically silencing the third copy of DYRK1A rescues Rest levels, and we demonstrate altered Rest expression in response to inhibition of DYRK1A expression or kinase activity, and in a transgenic Dyrk1A mouse. We reveal that undifferentiated trisomy 21 ES cells show DYRK1A-dose-sensitive reductions in levels of some pluripotency regulators, causing premature expression of transcription factors driving early endodermal and mesodermal differentiation, partially overlapping recently reported downstream effects of Rest +/-. They produce embryoid bodies with elevated levels of the primitive endoderm progenitor marker Gata4 and a strongly reduced neuroectodermal progenitor compartment. Our results suggest that DYRK1A-mediated deregulation of REST is a very early pathological consequence of trisomy 21 with potential to disturb the development of all embryonic lineages, warranting closer research into its contribution to DS pathology and new rationales for therapeutic approaches.

Quantitative proteomics characterization of a mouse embryonic stem cell model of Down syndrome.

Down syndrome, caused by the trisomy of chromosome 21, is a complex condition characterized by a number of phenotypic features, including reduced neuron number and synaptic plasticity, early Alzheimer disease-like neurodegeneration, craniofacial dysmorphia, heart development defects, increased incidence of childhood leukemia, and powerful suppression of the incidence of most solid tumors. Mouse models replicate a number of these phenotypes. The Tc1 Down syndrome model was constructed by introducing a single supernumerary human chromosome 21 into a mouse embryonic stem cell, and it reproduces a large number of Down syndrome phenotypes including heart development defects. However, little is still known about the developmental onset of the trisomy 21-induced mechanisms behind these phenotypes or the proteins that are responsible for them. This study determined the proteomic differences that are present in undifferentiated embryonic stem cells and are caused by an additional human chromosome 21. A total of 1661 proteins were identified using two-dimensional liquid chromatography followed by tandem mass spectrometry from whole embryonic stem cell lysates. Using isobaric tags for relative and absolute quantification, we found 52 proteins that differed in expression by greater than two standard deviations from the mean when an extra human chromosome 21 was present. Of these, at least 11 have a possible functional association with a Down syndrome phenotype or a human chromosome 21-encoded gene. This study also showed that quantitative protein expression differences in embryonic stem cells can persist to adult mouse as well as reproduce in human Down syndrome fetal tissue. This indicates that changes that are determined in embryonic stem cells of Down syndrome could potentially identify proteins that are involved in phenotypes of Down syndrome, and it shows that these cell lines can be used for the purpose of studying these pathomechanisms.

Mechanical Stress Induces a Transient Suppression of Cytokine Secretion in Astrocytes Assessed at the Single-Cell Level with a High-Throughput Microfluidic Chip.

Brain cells are constantly subjected to mechanical signals. Astrocytes are the most abundant glial cells of the central nervous system (CNS), which display immunoreactivity and have been suggested as an emerging disease focus in the recent years. However, how mechanical signals regulate astrocyte immunoreactivity, and the cytokine release in particular, remains to be fully characterized. Here, human neural stem cells are used to induce astrocytes, from which the release of 15 types of cytokines are screened, and nine of them are detected using a protein microfluidic chip. When a gentle compressive force is applied, altered cell morphology and reinforced cytoskeleton are observed. The force induces a transient suppression of cytokine secretions including IL-6, MCP-1, and IL-8 in the early astrocytes. Further, using a multiplexed single-cell culture and protein detection microfluidic chip, the mechanical effects at a single-cell level are analyzed, which validates a concerted downregulation by force on IL-6 and MCP-1 secretions in the cells releasing both factors. This work demonstrates an original attempt of employing the protein detection microfluidic chips in the assessment of mechanical regulation on the brain cells at a single-cell resolution, offering novel approach and unique insights for the understanding of the CNS immune regulation.

RAS-protein activation but not mutation status is an outcome predictor and unifying therapeutic target for high-risk acute lymphoblastic leukemia.

Leukemias are routinely sub-typed for risk/outcome prediction and therapy choice using acquired mutations and chromosomal rearrangements. Down syndrome acute lymphoblastic leukemia (DS-ALL) is characterized by high frequency of CRLF2-rearrangements, JAK2-mutations, or RAS-pathway mutations. Intriguingly, JAK2 and RAS-mutations are mutually exclusive in leukemic sub-clones, causing dichotomy in therapeutic target choices. We prove in a cell model that elevated CRLF2 in combination with constitutionally active JAK2 is sufficient to activate wtRAS. On primary clinical DS-ALL samples, we show that wtRAS-activation is an obligatory consequence of mutated/hyperphosphorylated JAK2. We further prove that CRLF2-ligand TSLP boosts the direct binding of active PTPN11 to wtRAS, providing the molecular mechanism for the wtRAS activation. Pre-inhibition of RAS or PTPN11, but not of PI3K or JAK-signaling, prevented TSLP-induced RAS-GTP boost. Cytotoxicity assays on primary clinical DS-ALL samples demonstrated that, regardless of mutation status, high-risk leukemic cells could only be killed using RAS-inhibitor or PTPN11-inhibitor, but not PI3K/JAK-inhibitors, suggesting a unified treatment target for up to 80% of DS-ALL. Importantly, protein activities-based principal-component-analysis multivariate clusters analyzed for independent outcome prediction using Cox proportional-hazards model showed that protein-activity (but not mutation-status) was independently predictive of outcome, demanding a paradigm-shift in patient-stratification strategy for precision therapy in high-risk ALL.

Effects of miR-219/miR-338 on microglia and astrocyte behaviors and astrocyte-oligodendrocyte precursor cell interactions.

MiR-219 and miR-338 (miR-219/miR-338) are oligodendrocyte-specific microRNAs. The overexpression of these miRs in oligodendrocyte precursor cells promotes their differentiation and maturation into oligodendrocytes, which may enhance axonal remyelination after nerve injuries in the central nervous system (CNS). As such, the delivery of miR-219/miR-338 to the CNS to promote oligodendrocyte precursor cell differentiation, maturation and myelination could be a promising approach for nerve repair. However, nerve injuries in the CNS also involve other cell types, such as microglia and astrocytes. Herein, we investigated the effects of miR-219/miR-338 treatment on microglia and astrocytes in vitro and in vivo. We found that miR-219/miR-338 diminished microglial expression of pro-inflammatory cytokines and suppressed astrocyte activation. In addition, we showed that miR-219/miR-338 enhanced oligodendrocyte precursor cell differentiation and maturation in a scratch assay paradigm that re-created a nerve injury condition in vitro. Collectively, our results suggest miR-219/miR-338 as a promising treatment for axonal remyelination in the CNS following nerve injuries. All experimental procedures were approved by the Institutional Animal Care and Use Committee (IACUC), Nanyang Technological University (approval No. A0309 and A0333) on April 27, 2016 and October 8, 2016.

Localized delivery of CRISPR/dCas9 via layer-by-layer self-assembling peptide coating on nanofibers for neural tissue engineering.

The clustered regularly interspaced short palindromic repeat (CRISPR) systems have a wide variety of applications besides precise genome editing. In particular, the CRISPR/dCas9 system can be used to control specific gene expression by CRISPR activation (CRISPRa) or interference (CRISPRi). However, the safety concerns associated with viral vectors and the possible off-target issues of systemic administration remain huge concerns to be safe delivery methods for CRISPR/Cas9 systems. In this study, a layer-by-layer (LbL) self-assembling peptide (SAP) coating on nanofibers is developed to mediate localized delivery of CRISPR/dCas9 systems. Specifically, an amphiphilic negatively charged SAP- is first coated onto PCL nanofibers through strong hydrophobic interactions, and the pDNA complexes and positively charged SAP+-RGD are then absorbed via electrostatic interactions. The SAPcoated scaffolds facilitate efficient loading and sustained release of the pDNA complexes, while enhancing cell adhesion and proliferation. As a proof of concept, the scaffolds are used to activate GDNF expression in mammalian cells, and the secreted GDNF subsequently promotes neurite outgrowth of rat neurons. These promising results suggest that the LbL self-assembling peptide coated nanofibers can be a new route to establish a bioactive interface, which provides a simple and efficient platform for the delivery of CRISPR/dCas9 systems for regenerative medicine.

Modeling Down syndrome in cells: From stem cells to organoids.

Down Syndrome (DS) is a complex chromosomal disorder, with neurological issues, featuring among the symptoms. Primary neuronal cells and tissues are extremely useful, but limited both in supply and experimental manipulability. To better understand the cellular, molecular and pathological mechanisms involved in DS neurodevelopment and neurodegeneration, a range of different cellular models have been developed over the years including human: mouse hybrid cells, transchromosomic mouse embryonic stem cells (ESCs) and human ESC and induced pluripotent stem cells derived from different sources. All of these model systems have provided useful information in the study of DS. Furthermore, different technologies to genetically modify or correct trisomy of either single genes or the whole chromosome have been developed using these cellular models. New techniques and protocols to allow better modeling of cellular mechanisms and disease processes are being developed and the use of cerebral organoids offers great promise for future research into the neural phenotypes seen in DS.

Ultrastructural and dynamic studies of the endosomal compartment in Down syndrome.

Enlarged early endosomes have been visualized in Alzheimer's disease (AD) and Down syndrome (DS) using conventional confocal microscopy at a resolution corresponding to endosomal size (hundreds of nm). In order to overtake the diffraction limit, we used super-resolution structured illumination microscopy (SR-SIM) and transmission electron microscopies (TEM) to analyze the early endosomal compartment in DS.By immunofluorescence and confocal microscopy, we confirmed that the volume of Early Endosome Antigen 1 (EEA1)-positive puncta was 13-19% larger in fibroblasts and iPSC-derived neurons from individuals with DS, and in basal forebrain cholinergic neurons (BFCN) of the Ts65Dn mice modelling DS. However, EEA1-positive structures imaged by TEM or SR-SIM after chemical fixation had a normal size but appeared clustered. In order to disentangle these discrepancies, we imaged optimally preserved High Pressure Freezing (HPF)-vitrified DS fibroblasts by TEM and found that early endosomes were 75% denser but remained normal-sized.RNA sequencing of DS and euploid fibroblasts revealed a subgroup of differentially-expressed genes related to cargo sorting at multivesicular bodies (MVBs). We thus studied the dynamics of endocytosis, recycling and MVB-dependent degradation in DS fibroblasts. We found no change in endocytosis, increased recycling and delayed degradation, suggesting a "traffic jam" in the endosomal compartment.Finally, we show that the phosphoinositide PI (3) P, involved in early endosome fusion, is decreased in DS fibroblasts, unveiling a new mechanism for endosomal dysfunctions in DS and a target for pharmacotherapy.