Down Syndrome Critical Region Research Articles

Abstract 12562: DYRK1A/PPARG/EGR1 Pathway Elicits Endothelial Dysfunctions and Predispose to Developing Pulmonary Hypertension in Down Syndrome

Introduction: Patients with Down syndrome (DS) have a higher prevalence of pulmonary arterial hypertension (PAH). Pulmonary vascular endothelial dysfunction has been recognized to be one of the predisposing factors to develop PAH, but pathophysiology of pulmonary endothelial cells in DS specific PAH is still unknown. Hypothesis: Endothelial dysfunctions contribute to developing PAH in DS. Methods: Induced pluripotent stem cell-derived vascular endothelial cells (iPSC-ECs) from DS patients were utilized for analyzing cellular and mitochondrial functions. A Cre-loxP mediated isogenic correction line of disomy 21 was established and used as a control. Results: DS-iPSC-ECs showed increased apoptosis, reduced angiogenesis, increased mitochondrial reactive oxygen species, and decreased ATP production, which were all consistent with features of endothelial dysfunctions previously reported in other types of PAH. RNA-seq revealed increased expression of EGR1 in DS-iPSC-ECs, and its inhibition restored cellular and mitochondrial dysfunctions, demonstrated by si EGR1 and pioglitazone treatment. Moreover, we revealed that increased expression of DYRK1a , one of the major pathogenic genes in DS critical region on chromosome 21, led to elevated EGR1 expression thorough PPARG suppression. These experimental results were reinforced by the observations that pulmonary ECs of a DS patient with severe PAH also exhibited increased EGR1. Conclusions: DYRK1A/PPARG/EGR1 pathway in DS is responsible for endothelial dysfunctions and might be a new therapeutic target for DS specific PAH.

Gain of chromosome 21 increases the propensity for P2RY8::CRLF2 acute lymphoblastic leukemia via increased HMGN1 expression.

Acute lymphoblastic leukemia (ALL) patients with a gain of chromosome 21, intrachromosomal amplification of chromosome 21 (iAMP21), or Down syndrome (DS), have increased expression of genes in the DS critical region (DSCR) of chromosome 21, including the high-mobility group nucleosome-binding protein 1, HMGN1. Children with DS are predisposed to develop hematologic malignancies, providing insight into the role of chromosome 21 in the development of leukemias. A 320-kb deletion in the pseudoautosomal region of the X/Y chromosome in leukemic cells, resulting in a gene fusion between the purinergic receptor and cytokine receptor-like factor-2 (P2Y Receptor Family Member 8 (P2RY8)::CRLF2), is a common feature in ~60% of DS-ALL and ~40% of iAMP21 patients, suggesting a link between chromosome 21 and P2RY8::CRLF2. In an Australian cohort of pediatric B-ALL patients with P2RY8::CRLF2 (n = 38), eight patients harbored gain of chromosome 21 (+21), and two patients had iAMP21, resulting in a significantly increased HMGN1 expression. An inducible CRISPR/Cas9 system was used to model P2RY8::CRLF2 and investigate its cooperation with HMGN1. This model was then used to validate HMGN1 as an influencing factor for P2RY8::CRLF2 development. Using Cas9 to cleave the DNA at the pseudoautosomal region without directed repair, cells expressing HMGN1 favored repair, resulting in P2RY8::CRLF2 generation, compared with cells without HMGN1. CRISPR/Cas9 P2RY8::CRLF2 cells expressing HMGN1 exhibit increased proliferation, thymic stromal lymphopoietin receptor (TSLPR) expression, and JAK/STAT signaling, consistent with cells from patients with P2RY8::CRLF2. Our patient expression data and unique CRISPR/Cas9 modeling, when taken together, suggest that HMGN1 increases the propensity for P2RY8::CRLF2 development. This has important implications for patients with DS, +21, or iAMP21.

Molecular cytogenetic analysis using FISH and HD-oligo micro array identified an unusual novel Down syndrome caseMolecular cytogenetic analysis using FISH and HD-oligo micro array identified an unusual novel Down syndrome case

Background: Down syndrome, caused due to trisomy of chromosome 21. Methods: 131 suspected cases of DS from university hospital after obtaining written informed consent clinical history and photographs were also recorded. Diagnosis carried out by tacking peripheral blood from the children, setting up whole blood culture as well as DNA extraction from leukocytes for molecular analysis. G-banding by Saline-Trypsin-Giemsa (STG) method and Karyotyping. Results: They were into four categories using automated Karyotyper. Category 1, out of 131 96(73.28%) cases of these had trisomy 21 while Category 2, showed 3(2.29%) cases with translocation or isochromosome involving chromosome 21. Category 3, was 0 mosaics cases. Category 4, was 0, will be karyotypically 46,/XY but show partial duplications case. An unusual Down syndrome is Category 5, had remaining 32(24.42%) cases, though referred for DS were karyotypically 46,XX or 46,XY. Of these only one cases were judiciously selected and tested for partial duplication of Down syndrome critical region (DSCR) with the help of FISH by using LSI 21 chromosome 21 specific probe but as such no duplication was observed. One of the above two case was further investigated through oligo-based cytogenetic array for micro-duplication or deletion of region on chromosome 21 other than the DSCR and it revealed no duplication or deletion of any part of chromosome 21 or whole genome. Conclusion: This study suggested besides trisomy 21 and chromosomal rearrangements there might be genetic imbalances leading to perturbations of pathway/s could result unusual Down syndrome.

Inverse Comorbidity between Down Syndrome and Solid Tumors: Insights from In Silico Analyses of Down Syndrome Critical Region Genes.

An inverse comorbidity has been observed between Down syndrome (DS) and solid tumors such as breast and lung cancers, and it is posited that the overexpression of genes within the Down Syndrome Critical Region (DSCR) of human chromosome 21 may account for this phenomenon. By analyzing publicly available DS mouse model transcriptomics data, we aimed to identify DSCR genes that may protect against human breast and lung cancers. Gene expression analyses with GEPIA2 and UALCAN showed that DSCR genes ETS2 and RCAN1 are significantly downregulated in breast and lung cancers, and their expression levels are higher in triple-negative compared to luminal and HER2-positive breast cancers. KM Plotter showed that low levels of ETS2 and RCAN1 are associated with poor survival outcomes in breast and lung cancers. Correlation analyses using OncoDB revealed that both genes are positively correlated in breast and lung cancers, suggesting that they are co-expressed and perhaps have complementary functions. Functional enrichment analyses using LinkedOmics also demonstrated that ETS2 and RCAN1 expression correlates with T-cell receptor signaling, regulation of immunological synapses, TGF-β signaling, EGFR signaling, IFN-γ signaling, TNF signaling, angiogenesis, and the p53 pathway. Altogether, ETS2 and RCAN1 may be essential for the development of breast and lung cancers. Experimental validation of their biological functions may further unravel their roles in DS and breast and lung cancers.

DYRK1A (Dual Specificity Tyrosine Phosphorylation Regulated Kinase 1A), a Master Regulatory Protein Involved in Down Syndrome Clinical Neurological Abnormalities and Associated Mental Retardation and a Promising Potential Drug Target for Therapeutics and Treatments

Over-expression of chromosome 21 genes, particularly in Down Syndrome Critical Region (DSCR), is the main cause of Down syndrome (DS) neuropathological features including mental retardation, cognitive impairments and early onset of Alzheimer’s disease. One of DSCR genes, that we studied herein, DYRK1A (Dual-Specificity Tyrosine-Phosphorylation-Regulated Kinase 1A), is a master regulatory protein involved in DS neuropathological features and associated mental retardation. Interestingly, normalization of DYRK1A over-expression by DYRK1A inhibitor, epigalloctechin-3-gallate (EGCG), rescues brain defects, restores cognitive impairments in DS trisomic and DYRK1A transgenic mouse models and in DS patients. These results indicates DYRK1A inhibitor epigalloctechin-3-gallate (EGCG) as an effective treatment and DYRK1A as a key regulatory protein involved in DS clinical neuropathological features suggesting DYRK1A as a valuable potential drug target for therapeutics and Treatments of DS and mental retardation opening new directions for developing new medical preventive and therapeutic treatments.

Dual‐Specificity Tyrosine Phosphorylation‐Regulated Kinase‐1A (DYRK1A), A Master Regulatory Protein Involved in Down Syndrome Brain Alterations and Mental Disability, A Key Contributor to Neurodegenerative Disorders of Alzheimer's Disease and A Potential Therapeutic Target

Down syndrome (DS) is the most frequent genetic disease characterized by several neuropathological features including alteration in neurogenesis, mental disability, cognitive impairments, learning-memory deficits and early onset of Alzheimer's disease (AD). Over expression of chromosome 21 genes, localized in Down Syndrome Critical Region (DSCR), is the main cause of DS neuropathological features.

DSCR1 deficiency ameliorates the Aβ pathology of Alzheimer's disease by enhancing microglial activity.

Microglial phagocytosis and clearance are important for the removal of amyloid-β (Aβ) plaques in Alzheimer's disease (AD). Chronic exposure of microglia to Aβ plaques leads to microglial metabolic dysfunction, and dysregulation of microglia can accelerate the deposition of Aβ plaques and cause learning and memory impairment. Thus, regulating microglial Aβ clearance is crucial for the development of therapeutics for AD-related dementia. Here, Down syndrome critical region 1 (DSCR1) deficiency ameliorated Aβ plaque deposition in the 5xFAD mouse model of AD by altering microglial activity; however, the Aβ synthesis pathway was not affected. DSCR1 deficiency improved spatial learning and memory impairment in 5xFAD mice. Furthermore, DSCR1-deficient microglia exhibited accelerated lysosomal degradation of Aβ after phagocytosis, and BV2 cells with stable knockdown of DSCR1 demonstrated enhanced lysosomal activity. RNA-sequencing analysis showed that the transcriptional signatures associated with responses to IFN-γ were significantly up-regulated in DSCR1-knockdown BV2 cells treated with Aβ. Our data strongly suggest that DSCR1 is a critical mediator of microglial degradation of amyloid plaques and a new potential microglial therapeutic target in AD.

Characterization of functionally deficient SIM2 variants found in patients with neurological phenotypes.

Single-minded 2 (SIM2) is a neuron-enriched basic Helix–Loop–Helix/PER–ARNT–SIM (bHLH/PAS) transcription factor essential for mammalian survival. SIM2 is located within the Down syndrome critical region (DSCR) of chromosome 21, and manipulation in mouse models suggests Sim2 may play a role in brain development and function. During the screening of a clinical exome sequencing database, nine SIM2 non-synonymous mutations were found which were subsequently investigated for impaired function using cell-based reporter gene assays. Many of these human variants attenuated abilities to activate transcription and were further characterized to determine the mechanisms underpinning their deficiencies. These included impaired partner protein dimerization, reduced DNA binding, and reduced expression and nuclear localization. This study highlighted several SIM2 variants found in patients with disabilities and validated a candidate set as potentially contributing to pathology.

Modulation of calcineurin signaling during development.

Calcineurin signaling pathways are suppressed in Down syndrome (trisomy 21), by overexpression of genes that are located on chromosome 21. Two key genes are the regulator of calcineurin 1 (RCAN1), also called the Down syndrome critical region 1 (DSCR1), and the dual-specificity tyrosine-phosphorylation-regulated kinase 1A (DYRK1A). The suppressed calcineurin pathway may potentially be restored using small-molecule DYRK inhibitors, which have been proposed as therapeutics in Down syndrome. However, little is known about the benefits and risks of such treatments during various stages of embryonic development, fetal development, and childhood. We examined the modulation of calcineurin signaling during development, using zebrafish as a model system. To mimic suppressed calcineurin signaling in Down syndrome, zebrafish were exposed to the calcineurin inhibitors cyclosporine and tacrolimus during development. We found that suppression of calcineurin signaling changed specific larval behaviors, including activity and responses to acoustic and visual stimuli, depending on the period of exposure. Cotreatment with the DYRK inhibitor proINDY restored a few of these behaviors but also induced a range of adverse side effects including decreased activity and reduced optomotor responses to visual stimuli. Based on these results, we conclude that proINDY has limited benefits and substantial risks when used during development. We propose that zebrafish is an efficient model system for preliminary safety and efficacy tests of other DYRK inhibitors that aim to restore calcineurin signaling during neural development.

A recessive variant in SIM2 in a child with complex craniofacial anomalies and global developmental delay

Rare deletions and duplications on the long arm of Chromosome 21 have previously been reported in many patients with craniofacial and developmental phenotypes. However, this Down Syndrome Critical Region (DSCR) contains multiple genes, making identifying a single causative gene difficult. Here, we report a case of a boy with bicoronal craniosynostosis, facial dysmorphism, developmental delay, and intellectual impairment who was found by whole genome sequencing to have a homozygous missense mutation in the Single-Minded Homolog 2 (SIM2) gene (c.461 A > G, p.Tyr154Cys) within the DSCR. SIM2 encodes an essential bHLH and PAS domain transcription factor expressed during fetal brain development and acts as a master regulator of neurogenesis. This variant is globally very rare, segregates in the family, and is predicted to be highly deleterious by in silico analysis, 3D molecular modeling of protein structure, and functional analysis of zebrafish models. Zebrafish expressing the human SIM2p.Y154C variant displayed a progressed microcephaly-like phenotype and head shape abnormalities. When combined with careful phenotyping of the patient vis-à-vis previously reported cases harboring structural variants in this critical 21q22 region, the data support a pathogenic role of SIM2 in this complex syndrome and demonstrates the utility of next-generation sequencing in prioritizing genes in contiguous deletions/duplications syndromes and diagnosing microarray-negative patients in the craniofacial clinic.

HMGN1 plays a significant role in CRLF2 driven Down Syndrome leukemia and provides a potential therapeutic target in this high-risk cohort.

The genetic basis of the predisposition for Down Syndrome (DS) patients to develop cytokine receptor-like factor 2 rearranged (CRLF2r) acute lymphoblastic leukemia (ALL) is currently unknown. Genes located on chromosome 21 and expressed in hematopoietic cells are likely candidates for investigation of CRLF2r DS-ALL pathogenesis. We explored the high-mobility group nucleosome-binding protein 1 (HMGN1), located in the DS critical region, in an inducible CRISPR/Cas9 knockout (KO) xenograft model to assess the effect of HMGN1 loss of function on the leukemic burden. We demonstrated HMGN1 KO-mitigated leukemic phenotypes including hepatosplenomegaly, thrombocytopenia, and anemia, commonly observed in leukemia patients, and significantly increased survival in vivo. HMGN1 overexpression in murine stem cells and Ba/F3 cells in vitro, in combination with P2RY8-CRLF2, resulted in cytokine-independent transformation and upregulation of cell signaling pathways associated with leukemic development. Finally, in vitro screening demonstrated successful targeting of P2RY8-CRLF2 and HMGN1 co-expressing cell lines and patient samples with fedratinib (JAK2 inhibitor), and GSK-J4 (demethylase inhibitor) in combination. Together, these data provide critical insight into the development and persistence of CRLF2r DS-ALL and identify HMGN1 as a potential therapeutic target to improve outcomes and reduce toxicity in this high-risk cohort of young patients.

MAP kinase/ERK kinase 1 (MEK1) phosphorylates regulator of calcineurin 1 (RCAN1) to regulate neuronal differentiation.

Regulator of calcineurin 1 (RCAN1) is located close to the Down syndrome critical region (DSCR) on human chromosome 21 and is related to the Down syndrome (DS) phenotype. To identify a novel binding partner of RCAN1, we performed yeast two-hybrid screening and identified mitogen-activated protein (MAP) kinase/extracellular signal-regulated kinase (ERK) kinase 1 (MEK1) as a partner. MEK1 was able to bind and phosphorylate RCAN1 in vitro and in vivo. MEK1-dependent RCAN1 phosphorylation caused an increase in RCAN1 expression by increasing the protein half-life. Nerve growth factor (NGF)-dependent activation of the MEK1 pathway consistently induced RCAN1 expression. Moreover, we found that RCAN1 overexpression inhibited NGF-induced neurite outgrowth and expression of neuronal marker genes, such as growth cone-associated protein 43 (GAP43) and synapsin I, via inhibition of MEK1-ERK1/2 pathways. Our findings provide evidence that MEK1-dependent RCAN1 phosphorylation acts as an important molecular mechanism in the control of neuronal differentiation.

DSCR1 upregulation enhances dural meningeal lymphatic drainage to attenuate amyloid pathology of Alzheimer's disease.

Highly developed meningeal lymphatics remove waste products from the brain. Disruption of meningeal lymphatic vessels in a mouse model of amyloid pathology (5XFAD) accelerates the accumulation of amyloid plaques in the meninges and brain, and causes learning and memory deficits, suggesting that clearance of toxic wastes by lymphatic vessels plays a key role in neurodegenerative diseases. Here, we discovered that DSCR1 (Down syndrome critical region 1, known also as RCAN1, regulator of calcineurin 1) facilitates the drainage of waste products by increasing the coverage of dorsal meningeal lymphatic vessels. Furthermore, upregulation of DSCR1 in 5XFAD mice diminishes Aβ pathology in the brain and improves memory defects. Surgical ligation of cervical lymphatic vessels afferent to dcLN blocks the beneficial effects of DSCR1 on Aβ accumulation and cognitive function. Interestingly, intracerebroventricular delivery of AAV1-DSCR1 to 5XFAD mice is sufficient to rebuild the meningeal lymphatic system and re-establish cognitive performance. Collectively, our data indicate that DSCR1 facilitates the growth of dorsal meningeal lymphatics to improve drainage efficiency and protect against Alzheimer's disease (AD) pathologies, further highlighting that improving meningeal lymphatic function is a feasible treatment strategy for AD. © 2021 The Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

NFAT indicates nucleocytoplasmic damped oscillation via its feedback modulator

Cell signaling and the following gene regulation are tightly regulated to keep homeostasis. NF-κB is a famous key transcription factor for inflammatory cell regulations that obtain a closed feedback loop with IκB. Similarly, we show here, NFAT is also tightly regulated via its downstream target, down syndrome critical region (DSCR)-1. In primary cultured endothelium, either shear stress or VEGF treatment revealed quick NFAT1 nuclear localization following the DSCR-1 transactivation, which in turn induced NFAT1 cytoplasm sequestration. Interestingly, both NFAT and DSCR-1 can be competitive substrates for calcineurin phosphatase and DSCR-1 is known to unstable protein, which caused NFAT1-nucleocytoplasmic damped oscillation via sustained shear stress or VEGF stimulation in endothelial cell (EC)s. To understand the molecular mechanism underlying the NFAT1 oscillation, we built a mathematical model of spatiotemporal regulation of NFAT1 combined with calcineurin and DSCR-1. Theoretically, manipulation of DSCR-1 expression in simulation predicted that DSCR-1 reduction would cause nuclear retention of dephosphorylated NFAT1 and disappearance of NFAT1 oscillation. To confirm this in ECs, DSCR-1 knockdown analysis was performed. DSCR-1 reduction indeed increased dephosphorylated NFAT1 in both the nucleus and cytoplasm, which eventually led to nuclear retention of NFAT1. Taken together, these studies suggest that DSCR-1 is a responsible critical factor for NFAT1 nucleocytoplasmic oscillation in shear stress or VEGF treated ECs. Our mathematical model successfully reproduced the experimental observations of NFAT1 dynamics. Combined mathematical and experimental approaches would provide a quantitative understanding way for the spatiotemporal NFAT1 feedback system.

A CHAF1B-Dependent Molecular Switch in Hematopoiesis and Leukemic Pathogenesis

Children with Down syndrome (DS) are at substantial risk of developing acute leukemia, which suggests that there are leukemia promoting genes on chromosome 21. Chromatin Assembly Factor 1B (CHAF1B), which resides in the DS critical region, is a member of the heterotrimeric CAF1 chromatin assembly complex that is responsible for depositing H3/H4 heterodimers at the replication fork during S-phase. We previously demonstrated that CHAF1B is overexpressed in acute megakaryocytic leukemia cells with trisomy 21 and have now discovered that it is also elevated in AML cell lines and primary tumor samples. This elevated expression is correlated with poor prognosis but the mechanism by which CHAF1B may promote leukemogenesis is unknown. In this study, we demonstrate that CHAF1B acts as regulator of transcription, maintaining an undifferentiated state by competing with CEBPA, FLI1, and RUNX2 for occupancy at the promoters and enhancers of myeloid differentiation genes.To study CHAF1Bin the context of normal hematopoiesis, we generated Chaf1b floxed mice and found that homozygous deletion was associated with rapid pancytopenia and bone marrow failure due to a cell cycle arrest and cell death. These effects were associated with downregulation of cell adhesion and metabolic pathways, as well as upregulation of genes related to sensitivity to stress and inflammatory stimuli. On the other hand, consistent with a pro-leukemic function, overexpression of CHAF1B promoted serial replating in vitro and was associated with the upregulation of genes involved in metabolism and proliferation. However, CHAF1B overexpression alone was not sufficient to promote leukemia in vivo .Since CHAF1B expression is elevated in cell lines with MLL rearrangements and primary AML samples, we next studied its requirements in the murine MLL-AF9 AML model. First, we found that overexpression of CHAF1B enhanced the formation of MLL-AF9 leukemic cells (LCs) in vitro and significantly accelerated disease in vivo . In contrast to the cell death and cell cycle arrest observed in HSPCs following Chaf1b deletion, there were no changes in proliferation or survival of LCs at 48 hours following Chaf1b deletion. Instead, we found Chaf1b deletion led to terminal myeloid differentiation of LCs, suggesting that CHAF1B has a major role in maintaining leukemic stem cells. In fact, heterozygous deletion of Chaf1b or overexpression of a dominant negative allele was sufficient to substantially reduce colony formation, as well as completely prevent leukemia in vivo .Transcriptome analysis of Chaf1b- deficient LCs revealed an increase in expression of over 1500 genes, including many of those associated with differentiation of myeloid leukemia cells. In comparison, we only identified 255 significantly downregulated genes, suggesting that CHAF1B primarily functions as a transcriptional repressor. By ChIP-seq, we determined that CHAF1B, but not the DNA replication factor PCNA, co-occupied the promoter and enhancer regions of many of these upregulated genes. Surprisingly, by ATAC-seq we found a widespread decrease in accessibility at CHAF1B binding sites following its knockdown, suggesting that other mechanisms are likely the key contributors to the differentiation phenotype. Motif analysis of CHAF1B-bound peaks in MLL-AF9 cells revealed specific enrichment of differentiation-driving transcription factor binding sites, including CEBPA, FLI1, and RUNX2. Therefore, we hypothesized that CHAF1B competes with transcription factors for occupancy at promoters of differentiation genes, preventing their expression and maintaining a leukemia stem cell state. We tested our hypothesis by comparing the occupancy of CEBA, FLI1, and RUNX2 at CHAF1B bound sites by ChIP-seq in cells replete or deficient for CHAF1B. We found that occupancy of these factors was significantly enhanced at CHAF1B-bound regions in LCs following Chaf1b deletion, and that this was associated with concomitant increases in expression of the differentiation target genes. We conclude that CHAF1B maintains the leukemic stem cell state by preventing differentiation through direct competition for chromatin occupancy with transcription factors at regulatory regions of genes that promote terminal maturation. DisclosuresNo relevant conflicts of interest to declare.

A prenatal diagnosis case of partial duplication 21q21.1-q21.2 with normal phenotype maternally inherited

BackgroundDown syndrome is characterized by trisomy 21 or partial duplication of chromosome 21. Extensive studies have focused on the identification of the Down Syndrome Critical Region (DSCR). We aim to provide evidence that duplication of 21q21.1-q21.2 should not be included in the DSCR and it has no clinical consequences on the phenotype.Case presentationBecause serological screening was not performed at the appropriate gestational age, noninvasive prenatal testing (NIPT) analysis was performed for a pregnant woman with normal prenatal examinations at 22 weeks of gestation. The NIPT results revealed a 5.8 Mb maternally inherited duplication of 21q21.1-q21.2. To assess whether the fetus also carried this duplication, ultrasound-guided amniocentesis was conducted, and the result of chromosomal microarray analysis (CMA) with amniotic fluid showed a 6.7 Mb duplication of 21q21.1-q21.2 (ranging from position 18,981,715 to 25,707,009). This partial duplication of 21q21.1-q21.2 in the fetus was maternally inherited. After genetic counseling, the pregnant woman and her family decided to continue the pregnancy.ConclusionOur case clearly indicates that 21q21.1-q21.2 duplication is not included in the DSCR and most likely has no clinical consequences on phenotype.

Subtle Roles of Down Syndrome Cell Adhesion Molecules in Embryonic Forebrain Development and Neuronal Migration.

Down Syndrome (DS) Cell Adhesion Molecules (DSCAMs) are transmembrane proteins of the immunoglobulin superfamily. Human DSCAM is located within the DS critical region of chromosome 21 (duplicated in Down Syndrome patients), and mutations or copy-number variations of this gene have also been associated to Fragile X syndrome, intellectual disability, autism, and bipolar disorder. The DSCAM paralogue DSCAM-like 1 (DSCAML1) maps to chromosome 11q23, implicated in the development of Jacobsen and Tourette syndromes. Additionally, a spontaneous mouse DSCAM deletion leads to motor coordination defects and seizures. Previous research has revealed roles for DSCAMs in several neurodevelopmental processes, including synaptogenesis, dendritic self-avoidance, cell sorting, axon growth and branching. However, their functions in embryonic mammalian forebrain development have yet to be completely elucidated. In this study, we revealed highly dynamic spatiotemporal patterns of Dscam and Dscaml1 expression in definite cortical layers of the embryonic mouse brain, as well as in structures and ganglionic eminence-derived neural populations within the embryonic subpallium. However, an in-depth histological analysis of cortical development, ventral forebrain morphogenesis, cortical interneuron migration, and cortical-subcortical connectivity formation processes in Dscam and Dscaml1 knockout mice (Dscamdel17 and Dscaml1GT) at several embryonic stages indicated that constitutive loss of Dscam and Dscaml1 does not affect these developmental events in a significant manner. Given that several Dscam- and Dscaml1-linked neurodevelopmental disorders are associated to chromosomal region duplication events, we furthermore sought to examine the neurodevelopmental effects of Dscam and Dscaml1 gain of function (GOF). In vitro, ex vivo, and in vivo GOF negatively impacted neural migration processes important to cortical development, and affected the morphology of maturing neurons. Overall, these findings contribute to existing knowledge on the molecular etiology of human neurodevelopmental disorders by elucidating how dosage variations of genes encoding adhesive cues can disrupt cell-cell or cell-environment interactions crucial for neuronal migration.

Loss of Down syndrome critical region-1 leads to cholesterol metabolic dysfunction that exaggerates hypercholesterolemia in ApoE-null background

Down syndrome critical region (DSCR)-1 functions as a feedback modulator for calcineurin-nuclear factor for activated T cell (NFAT) signals, which are crucial for cell proliferation and inflammation. Stable expression of DSCR-1 inhibits pathological angiogenesis and septic inflammation. DSCR-1 also plays a critical role in vascular wall remodeling associated with aneurysm development that occurs primarily in smooth muscle cells. Besides, Dscr-1 deficiency promotes the M1-to M2-like phenotypic switch in macrophages, which correlates to the reduction of denatured cholesterol uptakes. However, the distinct roles of DSCR-1 in cholesterol and lipid metabolism are not well understood. Here, we show that loss of apolipoprotein (Apo) E in mice with chronic hypercholesterolemia induced Dscr-1 expression in the liver and aortic atheroma. In Dscr-1-null mice fed a high-fat diet, oxidative- and endoplasmic reticulum (ER) stress was induced, and sterol regulatory element-binding protein (SREBP) 2 production in hepatocytes was stimulated. This exaggerated ApoE−/−-mediated nonalcoholic fatty liver disease (NAFLD) and subsequent hypercholesterolemia. Genome-wide screening revealed that loss of both ApoE and Dscr-1 resulted in the induction of immune- and leukocyte activation-related genes in the liver compared with ApoE deficiency alone. However, expressions of inflammation-activated markers and levels of monocyte adhesion were suspended upon induction of the Dscr-1 null background in the aortic endothelium. Collectively, our study shows that the combined loss of Dscr-1 and ApoE causes metabolic dysfunction in the liver but reduces atherosclerotic plaques, thereby leading to a dramatic increase in serum cholesterol and the formation of sporadic vasculopathy.

Down Syndrome Critical Region 1 Reduces Oxidative Stress-Induced Retinal Ganglion Cells Apoptosis via CREB-Bcl-2 Pathway.

PurposeIrreversible retina ganglion cell (RGC) loss is a key process during glaucoma progression. Down syndrome critical region 1 (DSCR1) has been shown to have protective effects against neuronal death. In this study, we aimed to investigate the neuroprotective mechanisms of DSCR1 on RGCs.MethodsDBA/2J mice and optic nerve crush (ONC) rat model were used for vivo assays. Oxidative stress model of primary RGCs was carried out with in vitro transduction. DSCR1 protein localization was assessed by immunofluorescence. Differential protein expression was validated by Western blot, and gene expression was detected by real-time PCR. TUNEL was used to identify cell apoptosis, and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide was used to analyze cell viability.ResultsSignificant upregulation of DSCR1 was observed in DBA/2J mice, ONC rat model, and RGCs treated with H2O2, reaching peaks at the age of 6 months in DBA/2J mice, 5 days after ONC in rats, and 24 hours after H2O2 treatment in RGCs, respectively. DSCR1 was shown to be expressed in the ganglion cell layer. In vitro, overexpressed DSCR1 significantly promoted phosphorylation of cyclic AMP response element binding protein (CREB), B-cell lymphoma 2 (Bcl-2) expression, and RGC survival rate while reducing cleaved caspase 3 expression in H2O2-treated RGCs. On the other hand, the opposite effects were shown after knockdown of DSCR1. In addition, silencing of CREB inhibited expression of DSCR1.ConclusionsOur results suggested that DSCR1 might protect the RGCs against oxidative stress via the CREB–Bcl-2 pathway, which may provide a theoretical basis for future treatments of glaucoma.

DYRK1A: a down syndrome-related dual protein kinase with a versatile role in tumorigenesis.

Dual-specificity tyrosine phosphorylation-regulated kinase 1A (DYRK1A) is a dual kinase that can phosphorylate its own activation loop on tyrosine residue and phosphorylate its substrates on threonine and serine residues. It is the most studied member of DYRK kinases, because its gene maps to human chromosome 21 within the Down syndrome critical region (DSCR). DYRK1A overexpression was found to be responsible for the phenotypic features observed in Down syndrome such as mental retardation, early onset neurodegenerative, and developmental heart defects. Besides its dual activity in phosphorylation, DYRK1A carries the characteristic of duality in tumorigenesis. Many studies indicate its possible role as a tumor suppressor gene; however, others prove its pro-oncogenic activity. In this review, we will focus on its multifaceted role in tumorigenesis by explaining its participation in some cancer hallmarks pathways such as proliferative signaling, transcription, stress, DNA damage repair, apoptosis, and angiogenesis, and finally, we will discuss targeting DYRK1A as a potential strategy for management of cancer and neurodegenerative disorders.