Maternal iron deficiency perturbs embryonic cardiovascular development in mice

Maternal hemoglobin and iron status in early pregnancy and childhood cardiac outcomes

BACKGROUND & AIMS

Dysregulation of iron homeostasis is associated with cardiac alterations in a sex-dependent manner in adults. It is unknown whether iron status during pregnancy has long-term impact on cardiovascular health, and if this association is influenced by sex. Therefore, this study aimed to evaluate sex-specific association between maternal iron status during early pregnancy and cardiac outcomes in children aged 10 years.

METHODS

In a population-based cohort study among 1972 mother-child pairs, hemoglobin and ferritin were measured in early pregnancy (<18 weeks) and categorized into anemia (hemoglobin<11 g/dL), elevated hemoglobin (hemoglobin≥13.2 g/dL), iron deficiency (ferritin<15 μg/L), and iron overload (ferritin>150 μg/L). At 10 years of age, cardiac MRI was performed to measure right and left cardiac outcomes of function (ventricular end-diastolic volume (RVEDV and LVEDV) and ejection fraction (RVEF and LVEF)), and structure (left ventricular mass (LVM), and left ventricular mass-to-volume ratio (LMVR)). Results are presented for boys and girls separately and models were adjusted for confounders and multiple testing.

RESULTS

In boys, one standard deviation score (SDS) increase in maternal hemoglobin was associated with lower RVEDV and LVEDV (difference (95%CI) -0.10 (-0.17, -0.03) SDS and -0.09 (-0.16, -0.03) SDS, respectively). In boys, maternal anemia, as compared to normal hemoglobin levels, was associated with higher LVEDV (difference 0.34 (0.10, 0.59) SDS). No associations were observed for other cardiac outcomes and for ferritin in boys. No associations were observed in girls.

CONCLUSION

In boys, dysregulated iron status during early pregnancy might permanently alter cardiovascular RVEDV and LVEDV function. Underlying mechanisms need further study.

Why cells need iron: a compendium of iron utilisation

Iron deficiency is globally prevalent, causing an array of developmental, haematological, immunological, neurological, and cardiometabolic impairments, and is associated with symptoms ranging from chronic fatigue to hair loss. Within cells, iron is utilised in a variety of ways by hundreds of different proteins. Here, we review links between molecular activities regulated by iron and the pathophysiological effects of iron deficiency. We identify specific enzyme groups, biochemical pathways, cellular functions, and cell lineages that are particularly iron dependent. We provide examples of how iron deprivation influences multiple key systems and tissues, including immunity, hormone synthesis, and cholesterol metabolism. We propose that greater mechanistic understanding of how cellular iron influences physiological processes may lead to new therapeutic opportunities across a range of diseases.

On the involvement of the second heart field in congenital heart defects

Congenital heart defects (CHD) affect 1 in 100 live births and result from defects in cardiac development. Growth of the early heart tube occurs by the progressive addition of second heart field (SHF) progenitor cells to the cardiac poles. The SHF gives rise to ventricular septal, right ventricular and outflow tract myocardium at the arterial pole, and atrial, including atrial septal myocardium, at the venous pole. SHF deployment creates the template for subsequent cardiac septation and has been implicated in cardiac looping and in orchestrating outflow tract development with neural crest cells. Genetic or environmental perturbation of SHF deployment thus underlies a spectrum of common forms of CHD affecting conotruncal and septal morphogenesis. Here we review the major properties of SHF cells as well as recent insights into the developmental programs that drive normal cardiac progenitor cell addition and the origins of CHD.

Dysregulation of miRNA-mRNA expression in fetal growth restriction in a caloric restricted mouse model

Fetal growth restriction (FGR) is associated with aberrant placentation and accounts for a significant proportion of perinatal deaths. microRNAs have been shown to be dysregulated in FGR. The purpose of this study was to determine microRNA-regulated molecular pathways altered using a caloric restricted mouse model of FGR. Pregnant mice were subjected to a 50% caloric restricted diet beginning at E9. At E18.5, RNA sequencing of placental tissue was performed to identify differences in gene expression between caloric restricted and control placentas. Significant differences in gene expression between caloric restricted and control placentas were observed in 228 of the 1546 (14.7%) microRNAs. Functional analysis of microRNA-mRNA interactions demonstrated enrichment of several biological pathways with oxidative stress, apoptosis, and autophagy pathways upregulated and angiogenesis and signal transduction pathways downregulated. Ingenuity pathway analysis also suggested that ID1 signaling, a pathway integral for trophoblast differentiation, is also dysregulated in caloric restricted placentas. Thus, a maternal caloric restriction mouse model of FGR results in aberrant microRNA-regulated molecular pathways associated with angiogenesis, oxidative stress, signal transduction, apoptosis, and cell differentiation. As several of these pathways are dysregulated in human FGR, our findings suggest that this model may provide an excellent means to study placental microRNA derangements seen in FGR.

Molecular Pathways and Animal Models of Tetralogy of Fallot and Double Outlet Right Ventricle

Tetralogy of Fallot and double-outlet right ventricle are outflow tract (OFT) alignment defects situated on a continuous disease spectrum. A myriad of upstream causes can impact on ventriculoarterial alignment that can be summarized as defects in either i) OFT elongation during looping morphogenesis or ii) OFT remodeling during cardiac septation. Embryological processes underlying these two developmental steps include deployment of second heart field cardiac progenitor cells, establishment and transmission of embryonic left/right information driving OFT rotation and OFT cushion and valve morphogenesis. The formation and remodeling of pulmonary trunk infundibular myocardium is a critical component of both steps. Defects in myocardial, endocardial, or neural crest cell lineages can result in alignment defects, reflecting the complex intercellular signaling events that coordinate arterial pole development. Importantly, however, OFT alignment is mechanistically distinct from neural crest-driven OFT septation, although neural crest cells impact indirectly on alignment through their role in modulating signaling during SHF development. As yet poorly understood nongenetic causes of alignment defects that impact the above processes include hemodynamic changes, maternal exposure to environmental teratogens, and stochastic events. The heterogeneity of causes converging on alignment defects characterizes the OFT as a hotspot of congenital heart defects.

Molecular Pathways and Animal Models of Truncus Arteriosus

In normal cardiovascular development in birds and mammals, the outflow tract of the heart is divided into two distinct channels to separate the oxygenated systemic blood flow from the deoxygenated pulmonary circulation. When the process of outflow tract septation fails, a single common outflow vessel persists resulting in a serious clinical condition known as persistent truncus arteriosus or common arterial trunk. In this chapter, we will review molecular pathways and the cells that are known to play a role in the formation and development of the outflow tract and how genetic manipulation of these pathways in animal models can result in common arterial trunk.

Perinatal iron restriction is associated with changes in neonatal cardiac function and structure in a sex-dependent manner

Iron deficiency (ID) is common during gestation and in early infancy and can alter developmental trajectories with lasting consequences on cardiovascular health. While the effects of ID and anemia on the mature heart are well documented, comparatively little is known about their effects and mechanisms on offspring cardiac development and function in the neonatal period. Female Sprague-Dawley rats were fed an iron-restricted or iron-replete diet before and during pregnancy. Cardiac function was assessed in a cohort of offspring on postnatal days (PD) 4, 14, and 28 by echocardiography; a separate cohort was euthanized for tissue collection and hearts underwent quantitative shotgun proteomic analysis. ID reduced body weight and increased relative heart weights at all time points assessed, despite recovering from anemia by PD28. Echocardiographic studies revealed unique functional impairments in ID male and female offspring, characterized by greater systolic dysfunction in the former and greater diastolic dysfunction in the latter. Proteomic analysis revealed down-regulation of structural components by ID, as well as enriched cellular responses to stress; in general, these effects were more pronounced in males. ID causes functional changes in the neonatal heart, which may reflect an inadequate or maladaptive compensation to anemia. This identifies systolic and diastolic dysfunction as comorbidities to perinatal ID anemia which may have important implications for both the short- and long-term cardiac health of newborn babies. Furthermore, therapies which improve cardiac output may mitigate the effects of ID on organ development.

Exposure to essential and non-essential trace elements and risks of congenital heart defects: A narrative review

Congenital heart defects (CHDs) are congenital abnormalities involving the gross structures of the heart and large blood vessels. Environmental factors, genetic factors and their interactions may contribute to the pathogenesis of CHDs. Generally, trace elements can be classified into essential trace elements and non-essential trace elements. Essential trace elements such as copper (Cu), zinc (Zn), iron (Fe), selenium (Se), and manganese (Mn) play important roles in human biological functions such as metabolic function, oxidative stress regulation, and embryonic development. Non-essential trace elements such as cadmium (Cd), arsenic (As), lead (Pb), nickle (Ni), barium (Ba), chromium (Cr) and mercury (Hg) are harmful to health even at low concentrations. Recent studies have revealed the potential involvement of these trace elements in the pathogenesis of CHDs. In this review, we summarized current studies exploring exposure to essential and non-essential trace elements and risks of CHDs, in order to provide further insights for the pathogenesis and prevention of CHDs.

Insights into the Role of a Cardiomyopathy-Causing Genetic Variant in ACTN2

Pathogenic variants in ACTN2, coding for alpha-actinin 2, are known to be rare causes of Hypertrophic Cardiomyopathy. However, little is known about the underlying disease mechanisms. Adult heterozygous mice carrying the Actn2 p.Met228Thr variant were phenotyped by echocardiography. For homozygous mice, viable E15.5 embryonic hearts were analysed by High Resolution Episcopic Microscopy and wholemount staining, complemented by unbiased proteomics, qPCR and Western blotting. Heterozygous Actn2 p.Met228Thr mice have no overt phenotype. Only mature males show molecular parameters indicative of cardiomyopathy. By contrast, the variant is embryonically lethal in the homozygous setting and E15.5 hearts show multiple morphological abnormalities. Molecular analyses, including unbiased proteomics, identified quantitative abnormalities in sarcomeric parameters, cell-cycle defects and mitochondrial dysfunction. The mutant alpha-actinin protein is found to be destabilised, associated with increased activity of the ubiquitin-proteasomal system. This missense variant in alpha-actinin renders the protein less stable. In response, the ubiquitin-proteasomal system is activated; a mechanism that has been implicated in cardiomyopathies previously. In parallel, a lack of functional alpha-actinin is thought to cause energetic defects through mitochondrial dysfunction. This seems, together with cell-cycle defects, the likely cause of the death of the embryos. The defects also have wide-ranging morphological consequences.

Perinatal iron deficiency causes sex-dependent alterations in renal retinoic acid signaling and nephrogenesis

Long-term alterations in kidney structure and function have been observed in offspring exposed to perinatal stressors such as iron deficiency (ID), albeit the mechanisms underlying these changes remain unclear. Here, we assessed how perinatal ID alters renal vitamin A metabolism, an important contributor to nephrogenesis, in the developing kidney. Pregnant Sprague Dawley rats were fed either an iron-restricted or -replete diet throughout gestation, and offspring were studied on postnatal day (PD)1 and 28. Maternal iron restriction results in reduced renal retinoid concentrations in male and female offspring on PD1 (P=.005). Nephron endowment was reduced by 21% in male perinatal ID offspring (P<.001), whereas it was unaffected in perinatal ID females. Perinatal ID resulted in sex-dependent changes in kidney retinoid synthesis and metabolism, whereby male offspring exhibited increased expression of Raldh2 and Rar/Rxr isoforms, while females exhibited unchanged or decreased expression (all interaction P<.05). Male perinatal ID offspring exhibit sex-specific enhancements of retinoic acid pathway signaling components on PD1, including Gdnf (P<.01) and Ctnnb1 (P<.01), albeit robust upregulation of RA transcriptional target Stra6 was observed in both sexes (P=.006). On PD28, perinatal ID resulted in elevated renal retinoid concentrations (P=.02) coinciding with enhanced expression of Raldh2 (P=.04), but not any Rar isoform or Rxr. Further, perinatal ID resulted in robust upregulation of Gdnf, Ret, Ctnnb1, associated with further increases in both Cxcr4 and Stra6 (all P<.01) at PD28. Together, these data suggest perinatal ID results in sustained sex-dependent perturbations in vitamin A metabolism, which likely underlie sex-specific reductions in nephron endowment.

Long-Term Impact of the Great Chinese Famine on the Risks of Specific Arrhythmias and Severe Hypertension in the Offspring at an Early Stage of Aging

Perinatal malnutrition affects postnatal cardiovascular functions. This study used the Great Chinese Famine (GCF) to determine the long-term impact of perinatal undernutrition on hypertension and arrhythmias in older offspring. Subjects (n = 10,065) were divided into an exposed group whose fetal life was in the GCF and an unexposed group. The exposed group showed higher systolic/diastolic pressure, heart rate, and total cholesterol. Perinatal exposure to the GCF was a significant risk to Grade 2 and Grade 3 hypertension (OR = 1.724, 95%CI: 1.441-2.064, p < 0.001; OR = 1.480, 95%CI: 1.050-2.086, p < 0.05) compared to the control. The GCF also increased risks for myocardial ischemia (OR = 1.301, 95%CI: 1.135-1.490, p < 0.001), bradycardia (OR = 1.383, 95%CI: 1.154-1.657, p < 0.001), atrial fibrillation (OR = 1.931, 95%CI: 1.033-3.610, p < 0.05), and atrioventricular block (OR = 1.333, 95%CI: 1.034-1.719, p < 0.05). Total cholesterol, diabetes, and metabolic syndrome were associated with Grade 2 or Grade 3 hypertension after exposure to the GCF; high cholesterol, high BMI, diabetes, metabolic syndrome, and elevated blood pressure were linked to certain types of arrhythmias in exposed offspring. The results first demonstrated perinatal undernutrition was a significant risk factor for the development of Grade 2-3 hypertension and certain arrhythmias in humans. Perinatal undernutrition still significantly impacted cardiovascular systems of the aged offspring even 50 years after the GCF. The results also provided information to a specific population with a history of prenatal undernutrition for early prevention against cardiovascular diseases before aging.

Gene-environment interactions in birth defect etiology: Challenges and opportunities

Birth defects are relatively common congenital outcomes that significantly impact affected individuals, their families, and communities. Effective development and deployment of prevention and therapeutic strategies for these conditions requires sufficient understanding of etiology, including underlying genetic and environmental causes. Tremendous progress has been made in defining the genetic basis of familial and syndromic forms of birth defects. However, the majority of birth defect cases are considered nonsyndromic and thought to result from multifactorial gene-environment interactions. While substantial advances have been made in elucidating the genetic landscape of these etiologically complex conditions, significant biological and technical constraints have stymied progress toward a refined knowledge of environmental risk factors. Defining specific gene-environment interactions in birth defect etiology is even more challenging. However, progress has been made, including demonstration of critical proofs of concept and development of new conceptual and technical approaches for resolving complex gene-environment interactions. In this review, we discuss current views of multifactorial birth defect etiology, comparing them with other diseases that also involve gene-environment interactions, including primary immunodeficiency and cancer. We describe how various model systems have illuminated mechanisms of multifactorial etiology and these models' individual strengths and weaknesses. Finally, suggestions for areas of future emphasis are proposed.

Coupling Transition Metal Catalysts with Ir for Enhanced Electrochemical Water Splitting Activity

Developing advanced electrocatalysts is of great significance for boosting electrochemical water splitting to produce hydrogen. The electrocatalytic activity of a catalyst is associated with the surface/interface, geometric structure, and electronic properties. Coupling Ir with transition metal compounds is an effective strategy to improve their electrocatalytic performance. In this review, we summarize the recent progress of Ir coupled transition metal compound catalysts for the application in driving electrochemical water splitting. The significant role of Ir played in the promotion of electrocatalytic performance is firstly illustrated. Then, the applications of Ir-based catalysts in the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are comprehensively discussed, with an emphasis on correlating the structure-function relationships. Lastly, the challenges and future directions for the fabrication of more advanced Ir coupled electrocatalysts are also presented.

Maternal micronutrient deficiency and congenital heart disease risk: A systematic review of observational studies

BACKGROUND

Congenital anomalies affect over 2% of pregnancies, with congenital heart disease (CHD) the most common. Understanding of causal factors is limited. Micronutrients are essential trace elements with key roles in growth and development. We aimed to investigate whether maternal micronutrient deficiencies increase the risk of fetal CHD through systematic review of published literature.

METHOD

We performed a systematic review registered at PROSPERO as CRD42021276699. Ovid-MEDLINE, Ovid-EMBASE, and Cochrane Library were searched from their inception until September 7, 2021. Case control trials were included with a population of biological mothers of fetuses with and without CHD. The exposure was maternal micronutrient level measured in pregnancy or the postpartum period. Data extraction was performed by one author and checked by a second. Risk of bias assessment was performed according to the Scottish Intercollegiate Guidelines Network guidance. We performed a narrative synthesis for analysis.

RESULTS

726 articles were identified of which 8 met our inclusion criteria. Final analysis incorporated data from 2,427 pregnancies, 1,199 of which were complicated by fetal CHD assessing 8 maternal micronutrients: vitamin D, vitamin B12, folate, vitamin A, zinc, copper, selenium, and ferritin. Studies were heterogenous with limited sample sizes and differing methods and timing of maternal micronutrient sampling. Definitions of deficiency varied and differed from published literature. Published results were contradictory.

CONCLUSION

There is not enough evidence to confidently conclude if maternal micronutrient deficiencies increase the risk of fetal CHD. Further large-scale prospective study is required to answer this question.

Fetal nuchal edema and developmental anomalies caused by gene mutations in mice

Fetal nuchal edema, a subcutaneous accumulation of extracellular fluid in the fetal neck, is detected as increased nuchal translucency (NT) by ultrasonography in the first trimester of pregnancy. It has been demonstrated that increased NT is associated with chromosomal anomalies and genetic syndromes accompanied with fetal malformations such as defective lymphatic vascular development, cardiac anomalies, anemia, and a wide range of other fetal anomalies. However, in many clinical cases of increased NT, causative genes, pathogenesis and prognosis have not been elucidated in humans. On the other hand, a large number of gene mutations have been reported to induce fetal nuchal edema in mouse models. Here, we review the relationship between the gene mutants causing fetal nuchal edema with defective lymphatic vascular development, cardiac anomalies, anemia and blood vascular endothelial barrier anomalies in mice. Moreover, we discuss how studies using gene mutant mouse models will be useful in developing diagnostic method and predicting prognosis.

Molecular Mechanisms of Iron and Heme Metabolism

An abundant metal in the human body, iron is essential for key biological pathways including oxygen transport, DNA metabolism, and mitochondrial function. Most iron is bound to heme but it can also be incorporated into iron-sulfur clusters or bind directly to proteins. Iron's capacity to cycle between Fe²⁺ and Fe³⁺ contributes to its biological utility but also renders it toxic in excess. Heme is an iron-containing tetrapyrrole essential for diverse biological functions including gas transport and sensing, oxidative metabolism, and xenobiotic detoxification. Like iron, heme is essential yet toxic in excess. As such, both iron and heme homeostasis are tightly regulated. Here we discuss molecular and physiologic aspects of iron and heme metabolism. We focus on dietary absorption; cellular import; utilization; and export, recycling, and elimination, emphasizing studies published in recent years. We end with a discussion on current challenges and needs in the field of iron and heme biology.

Characterization of Lymphatic Vasculature Using Whole-Mount Immunostaining of Mouse Embryonic Dorsal Skin

Understanding the development of the lymphatic vasculature is essential to the understanding of how these vessels function in health and disease. High-resolution imaging of histological techniques such as immunostaining of sectioned tissue provides a snapshot into lymphatic vessel morphogenesis, patterning, and organization. Whole-mount staining of embryonic dermal vasculature allows for a deeper analysis and characterization of the developing lymphatic vascular network.

Analysis of Placental Arteriovenous Formation Reveals New Insights Into Embryos With Congenital Heart Defects

The placental vasculature provides the developing embryo with a circulation to deliver nutrients and dispose of waste products. However, in the mouse, the vascular components of the chorio-allantoic placenta have been largely unexplored due to a lack of well-validated molecular markers. This is required to study how these blood vessels form in development and how they are impacted by embryonic or maternal defects. Here, we employed marker analysis to characterize the arterial/arteriole and venous/venule endothelial cells (ECs) during normal mouse placental development. We reveal that placental ECs are potentially unique compared with their embryonic counterparts. We assessed embryonic markers of arterial ECs, venous ECs, and their capillary counterparts-arteriole and venule ECs. Major findings were that the arterial tree exclusively expressed Dll4, and venous vascular tree could be distinguished from the arterial tree by Endomucin (EMCN) expression levels. The relationship between the placenta and developing heart is particularly interesting. These two organs form at the same stages of embryogenesis and are well known to affect each other's growth trajectories. However, although there are many mouse models of heart defects, these are not routinely assessed for placental defects. Using these new placental vascular markers, we reveal that mouse embryos from one model of heart defects, caused by maternal iron deficiency, also have defects in the formation of the placental arterial, but not the venous, vascular tree. Defects to the embryonic cardiovascular system can therefore have a significant impact on blood flow delivery and expansion of the placental arterial tree.

Micronutrient imbalance and common phenotypes in neural tube defects

Neural tube defects (NTDs) are among the most common birth defects, with a prevalence of close to 19 per 10,000 births worldwide. The etiology of NTDs is complex involving the interplay of genetic and environmental factors. Since nutrient deficiency is a risk factor and dietary changes are the major preventative measure to reduce the risk of NTDs, a more detailed understanding of how common micronutrient imbalances contribute to NTDs is crucial. While folic acid has been the most discussed environmental factor due to the success that population-wide fortification has had on prevention of NTDs, folic acid supplementation does not prevent all NTDs. The imbalance of several other micronutrients has been implicated as risks for NTDs by epidemiological studies and in vivo studies in animal models. In this review, we highlight recent literature deciphering the multifactorial mechanisms underlying NTDs with an emphasis on mouse and human data. Specifically, we focus on advances in our understanding of how too much or too little retinoic acid, zinc, and iron alter gene expression and cellular processes contributing to the pathobiology of NTDs. Synthesis of the discussed literature reveals common cellular phenotypes found in embryos with NTDs resulting from several micronutrient imbalances. The goal is to combine knowledge of these common cellular phenotypes with mechanisms underlying micronutrient imbalances to provide insights into possible new targets for preventative measures against NTDs.