Molecular mechanisms of congenital heart disease in down syndrome

Methyltransferase METTL3 governs the modulation of SH3BGR expression through m6A methylation modification, imparting influence on apoptosis in the context of Down syndrome-associated cardiac development

Down syndrome (DS), caused by an additional chromosome 21, has a high risk of congenital heart defects (CHD), one of the primary causes of mortality in DS newborns. To elucidate the pathogenetic mechanisms underlying this condition, we explored the role of RNA m6A methylation, regulated by METTL3, in DS cardiac development and its impact on the expression of SH3BGR, a gene located at Down syndrome congenital heart disease (DS-CHD) minimal region. We analyzed DS fetal cardiac tissues to assess RNA m6A methylation levels and identify potential contributors. RNA sequencing was performed to detect differentially expressed genes in the same tissues. To further understand METTL3's function in heart development, we inactivated Mettl3 in the developing mouse heart to mimic the significantly reduced METTL3 observed in DS cardiac development. Additionally, human cardiomyocyte AC16 cells were used to investigate the molecular mechanism by which METTL3 regulates SH3BGR expression. Apoptosis was analyzed to evaluate METTL3's effect on heart development through SH3BGR regulation. Reduced m6A modification and decreased METTL3 expression were observed in human DS fetal hearts, along with a significant increase of SH3BGR expression. METTL3, through m6A modification, was found to regulate SH3BGR expression, by influencing mRNA stability. METTL3-deficient mouse embryos exhibited heart malformation with increased apoptosis, emphasizing its role in heart development. In DS hearts, METTL3 downregulation and SH3BGR upregulation, potentially orchestrated by abnormal m6A modification, contribute to gene dysregulation and apoptosis. This study reveals novel insights into DS cardiac pathology, highlighting the intricate role of METTL3 in DS congenital heart defects and presenting the m6A modification of SH3BGR as a potential therapeutic target.

RUN(X) out of blood: emerging RUNX1 functions beyond hematopoiesis and links to Down syndrome

BACKGROUND

RUNX1 is a transcription factor and a master regulator for the specification of the hematopoietic lineage during embryogenesis and postnatal megakaryopoiesis. Mutations and rearrangements on RUNX1 are key drivers of hematological malignancies. In humans, this gene is localized to the 'Down syndrome critical region' of chromosome 21, triplication of which is necessary and sufficient for most phenotypes that characterize Trisomy 21.

MAIN BODY

Individuals with Down syndrome show a higher predisposition to leukemias. Hence, RUNX1 overexpression was initially proposed as a critical player on Down syndrome-associated leukemogenesis. Less is known about the functions of RUNX1 in other tissues and organs, although growing reports show important implications in development or homeostasis of neural tissues, muscle, heart, bone, ovary, or the endothelium, among others. Even less is understood about the consequences on these tissues of RUNX1 gene dosage alterations in the context of Down syndrome. In this review, we summarize the current knowledge on RUNX1 activities outside blood/leukemia, while suggesting for the first time their potential relation to specific Trisomy 21 co-occurring conditions.

CONCLUSION

Our concise review on the emerging RUNX1 roles in different tissues outside the hematopoietic context provides a number of well-funded hypotheses that will open new research avenues toward a better understanding of RUNX1-mediated transcription in health and disease, contributing to novel potential diagnostic and therapeutic strategies for Down syndrome-associated conditions.

Triplication of the interferon receptor locus contributes to hallmarks of Down syndrome in a mouse model

Down syndrome (DS), the genetic condition caused by trisomy 21, is characterized by variable cognitive impairment, immune dysregulation, dysmorphogenesis and increased prevalence of diverse co-occurring conditions. The mechanisms by which trisomy 21 causes these effects remain largely unknown. We demonstrate that triplication of the interferon receptor (IFNR) gene cluster on chromosome 21 is necessary for multiple phenotypes in a mouse model of DS. Whole-blood transcriptome analysis demonstrated that IFNR overexpression associates with chronic interferon hyperactivity and inflammation in people with DS. To define the contribution of this locus to DS phenotypes, we used genome editing to correct its copy number in a mouse model of DS, which normalized antiviral responses, prevented heart malformations, ameliorated developmental delays, improved cognition and attenuated craniofacial anomalies. Triplication of the Ifnr locus modulates hallmarks of DS in mice, suggesting that trisomy 21 elicits an interferonopathy potentially amenable to therapeutic intervention.

Sex differences in cardiovascular disease and dysregulation in Down syndrome

This meta-analysis, which consisted of a scoping review and retrospective medical record review, is focused on potential sex differences in cardiovascular diseases in patients with Down syndrome. We limited our review to peer-reviewed, primary articles in the English language, in the PubMed and Web of Science databases from 1965 to 2021. Guidelines for scoping reviews were followed throughout the process. Four categorical domains were identified and searched using additional keywords: 1) congenital heart disease, 2) baseline physiology and risk factors, 3) heart disease and hypertension, and 4) stroke and cerebrovascular disease. Articles were included if they reported male and female distinct data, participants with Down syndrome, and one of our keywords. The retrospective medical record review was completed using 75 participating health care organizations to identify the incidence of congenital and cardiovascular diseases and to quantify cardiovascular risk factors in male and female patients. Female patients with Down syndrome are at higher risk of hypertension, ischemic heart disease, and cerebrovascular disease. The risk of congenital heart disease is higher in males with Down syndrome at all ages included in our analyses. Some of the male-to-female sex differences in cardiovascular disease risk in the general patient population are not present, or reversed in the Down syndrome population. This information should be considered for future investigations and ongoing patient care.NEW & NOTEWORTHY In patients with Down syndrome (DS), CHD is the leading cause of death <20 yr old and cardiovascular disease is a leading cause of death in individuals >20 yr old. Men with DS live longer than women. It is unknown if sex differences are present in cardiovascular disease and dysregulation in DS across the lifespan. We observed higher risk of hypertension, ischemic heart disease, and cerebrovascular disease in females and a higher risk of CHD in males with DS.

DNMT3B rs2424913 as a Risk Factor for Congenital Heart Defects in Down Syndrome

Impairments of the genes that encode enzymes that are involved in one-carbon metabolism because of the presence of gene polymorphisms can affect the methylation pattern. The altered methylation profiles of the genes involved in cardiogenesis may result in congenital heart defects (CHDs). The aim of this study was to investigate the association between the MTHFR rs1801133, MTHFR rs1801131, MTRR rs1801394, DNMT1 rs2228611, DNMT3A rs1550117, DNMT3B rs1569686, and DNMT3B rs2424913 gene polymorphisms and congenital heart defects in Down syndrome (DS) individuals. The study was conducted on 350 participants, including 134 DS individuals with CHDs (DSCHD+), 124 DS individuals without CHDs (DSCHD−), and 92 individuals with non-syndromic CHD. The genotyping was performed using the PCR–RFLP method. A statistically significant higher frequency of the DNMT3B rs2424913 TT in the DSCHD+ individuals was observed. The DNMT3B rs2424913 TT genotype, as well as the T allele, had significantly higher frequencies in the individuals with DS and atrial septal defects (ASDs) in comparison with the individuals with DS and other CHDs. Furthermore, our results indicate a statistically significant effect of the DNMT3B rs1569686 TT genotype in individuals with non-syndromic CHDs. The results of the study suggest that the DNMT3B rs2424913 TT genotypes may be a possible predisposing factor for CHDs in DS individuals, and especially those with ASDs.

Genetics and Molecular Basis of Congenital Heart Defects in Down Syndrome: Role of Extracellular Matrix Regulation

Down syndrome (DS), a complex disorder that is caused by the trisomy of chromosome 21 (Hsa21), is a major cause of congenital heart defects (CHD). Interestingly, only about 50% of individuals with Hsa21 trisomy manifest CHD. Here we review the genetic basis of CHD in DS, focusing on genes that regulate extracellular matrix (ECM) organization. The overexpression of Hsa21 genes likely underlies the molecular mechanisms that contribute to CHD, even though the genes responsible for CHD could only be located in a critical region of Hsa21. A role in causing CHD has been attributed not only to protein-coding Hsa21 genes, but also to genes on other chromosomes, as well as miRNAs and lncRNAs. It is likely that the contribution of more than one gene is required, and that the overexpression of Hsa21 genes acts in combination with other genetic events, such as specific mutations or polymorphisms, amplifying their effect. Moreover, a key function in determining alterations in cardiac morphogenesis might be played by ECM. A large number of genes encoding ECM proteins are overexpressed in trisomic human fetal hearts, and many of them appear to be under the control of a Hsa21 gene, the RUNX1 transcription factor.

Cardiovascular Physiology and Pathophysiology in Down Syndrome

Down Syndrome (Ds) is the most common chromosomal cause of intellectual disability that results from triplication of chromosome 21 genes. Individuals with Ds demonstrate cognitive deficits in addition to comorbidities including cardiac defects, pulmonary arterial hypertension (PAH), low blood pressure (BP), and differences in autonomic regulation. Many individuals with Ds are born with heart malformations and some can be surgically corrected. Lower BP at rest and in response to exercise and other stressors are a prevalent feature in Ds. These reduced cardiovascular responses may be due to underlying autonomic dysfunction and have been implicated in lower exercise/work capacity in Ds, which is an important correlate of morbidity, mortality and quality of life. Exercise therapy can be beneficial to normalize autonomic function and may help prevent the development of co-morbidities in Ds. We will review cardiovascular physiology and pathophysiology in individuals with Ds, along with exercise therapy and special considerations for these individuals.

The Use of Virtual and Computational Technologies in the Psychomotor and Cognitive Development of Children with Down Syndrome: A Systematic Literature Review

Individuals with Down syndrome (DS) have numerous comorbidities due to trisomy 21. However, virtual reality-based therapy (VRT) has been used nowadays as a learning and visual motor tool in order to facilitate the development and learning process of this group. The aim of this article was to carry out an integrative review of the literature on the use of virtual and computational technologies in the stimulation of children with DS. A search was carried out according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) through single key words or their combinations using AND or OR operators: "Down syndrome" AND ("development" OR "cognition" OR "visomotor" OR "digital game" OR "virtual reality"). Eventually, 18 articles were included in our review. The games used in the research were able to stimulate, through the visual field, global motor skills, balance, body scheme and spatial organization, in addition to the learning of mathematical concepts, in order to directly influence the autonomous life activities, language skills, social skills and educational aspects of people with DS. Electronic games contribute to the teaching-learning relationship and stimulate neuropsychomotor and cognitive functions and development in children with DS.

Analysis of Biomarkers for Congenital Heart Disease Based on Maternal Amniotic Fluid Metabolomics

Congenital heart disease (CHD) is the most common birth defect. The prenatal diagnosis of fetal CHD is completely dependent on ultrasound testing, but only ~40% of CHD can be detected. The purpose of this study is to find good biomarkers in amniotic fluid (AF) to detect CHD in the second trimester, so as to better manage this group of people and reduce the harm of CHD to the fetus. Metabolites analysis were performed in two separate sets. The discovery set consisted of 18 CHD fetal maternal AF samples and 35 control samples, and the validation set consisted of 53 CHD fetal maternal AF samples and 114 control samples. Untargeted metabolite profiles were analyzed by gas chromatography/time-of-flight-mass spectrometry (GC-TOF/MS). Orthogonal partial least square discrimination analysis (OPLS-DA) demonstrated that CHD and control samples had significantly different metabolic profiles. Two metabolites, uric acid and proline, were significantly elevated in CHD and verified in two data sets. Uric acid was associated with CHD [odds ratio (OR): 7.69 (95% CI: 1.18-50.13) in the discovery set and 3.24 (95% CI:1.62-6.48) in the validation set]. Additionally, uric acid showed moderate predictive power; the area under curve (AUC) was 0.890 in the discovery set and 0.741 in the validation set. The sensitivity and specificity of uric acid to detect CHD was, respectively, 94.4 and 74.3% in the discovery set and 67.9 and 71.9% in the validation set. The identification of uric acid as a biomarker for CHD has the potential to stimulate research on the pathological mechanism of CHD and the development of a diagnostic test for clinical applications.

Tnni1b-ECR183-d2, an 87 bp cardiac enhancer of zebrafish

Background

Several heart malformations are associated with mutations in the regulatory regions of cardiac genes. Troponin I type 1b (tnni1b) is important for the formation of the atrioventricular canal in zebrafish hearts; however, the regulation of tnni1b is poorly understand. We aimed to identify a small but functional enhancer that is distal to tnni1b.

Methods

Evolutionary Conserved Region (ECR) Browser was used to analyze the 219 kb zebrafish and human genomes covering the tnni1b gene as well as the 100 kb regions upstream and downstream of tnni1b. Putative transcription factor binding sites (TFBSs) were analyzed using JASPAR and PROMO, and the enhancer activity was identified using zebrafish embryos and the luciferase reporter assay. A correlation analysis between the enhancer and transcription factors (TFs) was performed via TF overexpression and TFBS mutation experiments and the electrophoretic mobility shift assay (EMSA). To analyze the conservation between zebrafish and human enhancers, human DNA fragments were functionally verified. Images were captured and analyzed by fluorescence microscopy or confocal microscopy.

Results

Combined with comparative analysis and functional validation, we identified a 183 bp ECR (termed tnni1b-ECR183) that was located approximately 84 kb upstream of tnni1b that had the heart-specific enhancer activity in zebrafish. TFBS analysis and the enhancer activity detection assay data showed that the 87 bp core region (termed tnni1b-ECR183-d2) was capable of driving specific GFP expression near the atrioventricular junction and increased luciferase expression in HEK293 and HL1 cell lines. The GFP pattern in zebrafish embryos was similar to the expression profiles of tnni1b. A correlation analysis showed that the enhancer activity of tnni1b-ECR183-d2 was increased when NKX2.5 (p = 0.0006) or JUN (p < 0.0001) was overexpressed and was decreased when the TFBSs of NKX2.5 (p < 0.0001) or JUN (p = 0.0018) were mutated. In addition, DNA-protein interactions were not observed between these TFs and tnni1b-ECR183-d2 in the EMSA experiment. The conservation analysis showed that tnni1b-ECR183-h179 (aligned from tnni1b-ECR183) drove GFP expression in the heart and skeletal muscles and increased the luciferase expression after NKX2.5 (p < 0.0001), JUN (p < 0.0001) or ETS1 (p < 0.0001) was overexpressed. Interestingly, the truncated fragment tnni1b-ECR183-h84 mainly drove GFP expression in the skeletal muscles of zebrafish and the enhancer activity decreased when NKX2.5 (p = 0.0028), ETS1 (p = 0.0001) or GATA4 (p < 0.0001) was overexpressed.

Conclusions

An 87 bp cardiac-specific enhancer located 84 kb upstream of tnni1b in zebrafish was positively correlated with NKX2.5 or JUN. The zebrafish and human enhancers in this study target different tissues. The GFP expression mediated by tnni1b-ECR183-d2 is a valuable tool for marking the domain around the atrioventricular junction.