Activation of IGF-2R stimulates cardiomyocyte hypertrophy in the late gestation sheep fetus

Cardiac growth and metabolism of the fetal sheep are not vulnerable to a 10 day increase in fetal glucose and insulin concentrations during late gestation

Aims

To evaluate the effects of fetal glucose infusion in late gestation on the mRNA expression and protein abundance of molecules involved in the regulation of cardiac growth and metabolism.

Main methods

Either saline or glucose was infused into fetal sheep from 130 to 140 days (d) gestation (term, 150 d). At 140 d gestation, left ventricle tissue samples were collected. Quantitative real-time RT-PCR and Western blot were used to determine the mRNA expression and protein abundance of key signalling molecules within the left ventricle of the fetal heart.

Key findings

Although intra-fetal glucose infusion increased fetal plasma glucose and insulin concentrations, there was no change in the expression of molecules within the signalling pathways that regulate proliferation, hypertrophy, apoptosis or fibrosis in the fetal heart. Cardiac Solute carrier family 2 member 1 (SLC2A1) mRNA expression was decreased by glucose infusion. Glucose infusion increased cardiac mRNA expression of both Peroxisome proliferator activated receptor alpha (PPARA) and peroxisome proliferator activated receptor gamma (PPARG). However, there was no change in the mRNA expression of PPAR cofactors or molecules with PPAR response elements. Furthermore, glucose infusion did not impact the protein abundance of the 5 oxidative phosphorylation complexes of the electron transport chain.

Significance

Despite a 10-day doubling of fetal plasma glucose and insulin concentrations, the present study suggests that within the fetal left ventricle, the mRNA and protein expression of the signalling molecules involved in cardiac growth, development and metabolism are relatively unaffected.

A change of heart: understanding the mechanisms regulating cardiac proliferation and metabolism before and after birth

Mammalian cardiomyocytes undergo major maturational changes in preparation for birth and postnatal life. Immature cardiomyocytes contribute to cardiac growth via proliferation and thus the heart has the capacity to regenerate. To prepare for postnatal life, structural and metabolic changes associated with increased cardiac output and function must occur. This includes exit from the cell cycle, hypertrophic growth, mitochondrial maturation and sarcomeric protein isoform switching. However, these changes come at a price: the loss of cardiac regenerative capacity such that damage to the heart in postnatal life is permanent. This is a significant barrier to the development of new treatments for cardiac repair and contributes to heart failure. The transitional period of cardiomyocyte growth is a complex and multifaceted event. In this review, we focus on studies that have investigated this critical transition period as well as novel factors that may regulate and drive this process. We also discuss the potential use of new biomarkers for the detection of myocardial infarction and, in the broader sense, cardiovascular disease.

Epigenome-Wide Changes in the Cell Layers of the Vein Wall When Exposing the Venous Endothelium to Oscillatory Shear Stress

Epigenomic changes in the venous cells exerted by oscillatory shear stress towards the endothelium may result in consolidation of gene expression alterations upon vein wall remodeling during varicose transformation. We aimed to reveal such epigenome-wide methylation changes. Primary culture cells were obtained from non-varicose vein segments left after surgery of 3 patients by growing the cells in selective media after magnetic immunosorting. Endothelial cells were either exposed to oscillatory shear stress or left at the static condition. Then, other cell types were treated with preconditioned media from the adjacent layer's cells. DNA isolated from the harvested cells was subjected to epigenome-wide study using Illumina microarrays followed by data analysis with GenomeStudio (Illumina), Excel (Microsoft), and Genome Enhancer (geneXplain) software packages. Differential (hypo-/hyper-) methylation was revealed for each cell layer's DNA. The most targetable master regulators controlling the activity of certain transcription factors regulating the genes near the differentially methylated sites appeared to be the following: (1) HGS, PDGFB, and AR for endothelial cells; (2) HGS, CDH2, SPRY2, SMAD2, ZFYVE9, and P2RY1 for smooth muscle cells; and (3) WWOX, F8, IGF2R, NFKB1, RELA, SOCS1, and FXN for fibroblasts. Some of the identified master regulators may serve as promising druggable targets for treating varicose veins in the future.

Developmental programming: adverse sexually dimorphic transcriptional programming of gestational testosterone excess in cardiac left ventricle of fetal sheep

Adverse in-utero insults during fetal life alters offspring's developmental trajectory, including that of the cardiovascular system. Gestational hyperandrogenism is once such adverse in-utero insult. Gestational testosterone (T)-treatment, an environment of gestational hyperandrogenism, manifests as hypertension and pathological left ventricular (LV) remodeling in adult ovine offspring. Furthermore, sexual dimorphism is noted in cardiomyocyte number and morphology in fetal life and at birth. This study investigated transcriptional changes and potential biomarkers of prenatal T excess-induced adverse cardiac programming. Genome-wide coding and non-coding (nc) RNA expression were compared between prenatal T-treated (T propionate 100 mg intramuscular twice weekly from days 30 to 90 of gestation; Term: 147 days) and control ovine LV at day 90 fetus in both sexes. Prenatal T induced differential expression of mRNAs in the LV of female (2 down, 5 up) and male (3 down, 1 up) (FDR < 0.05, absolute log2 fold change > 0.5); pathways analysis demonstrated 205 pathways unique to the female, 382 unique to the male and 23 common pathways. In the male, analysis of ncRNA showed differential regulation of 15 lncRNAs (14 down, 1 up) and 27 snoRNAs (26 down and 1 up). These findings suggest sexual dimorphic modulation of cardiac coding and ncRNA with gestational T excess.

Impact of maternal late gestation undernutrition on surfactant maturation, pulmonary blood flow and oxygen delivery measured by magnetic resonance imaging in the sheep fetus

Restriction of fetal substrate supply has an adverse effect on surfactant maturation in the lung and thus affects the transition from in utero placental oxygenation to pulmonary ventilation ex utero. The effects on surfactant maturation are mediated by alteration in mechanisms regulating surfactant protein and phospholipid synthesis. This study aimed to determine the effects of late gestation maternal undernutrition (LGUN) and LGUN plus fetal glucose infusion (LGUN+G) compared to Control on surfactant maturation and lung development, and the relationship with pulmonary blood flow and oxygen delivery ( D O 2 ) measured by magnetic resonance imaging (MRI) with molecules that regulate lung development. LGUN from 115 to 140 days' gestation significantly decreased fetal body weight, which was normalized by glucose infusion. LGUN and LGUN+G resulted in decreased fetal plasma glucose concentration, with no change in fetal arterial P O 2 compared to control. There was no effect of LGUN and LGUN+G on the mRNA expression of surfactant proteins (SFTP) and genes regulating surfactant maturation in the fetal lung. However, blood flow in the main pulmonary artery was significantly increased in LGUN, despite no change in blood flow in the left or right pulmonary artery and D O 2 to the fetal lung. There was a negative relationship between left pulmonary artery flow and D O 2 to the left lung with SFTP-B and GLUT1 mRNA expression, while their relationship with VEGFR2 was positive. These results suggest that increased pulmonary blood flow measured by MRI may have an adverse effect on surfactant maturation during fetal lung development. KEY POINTS: Maternal undernutrition during gestation alters fetal lung development by impacting surfactant maturation. However, the direction of change remains controversial. We examined the effects of maternal late gestation maternal undernutrition (LGUN) on maternal and fetal outcomes, signalling pathways involved in fetal lung development, pulmonary haemodynamics and oxygen delivery in sheep using a combination of molecular and magnetic resonance imaging (MRI) techniques. LGUN decreased fetal plasma glucose concentration without affecting arterial P O 2 . Surfactant maturation was not affected; however, main pulmonary artery blood flow was significantly increased in the LGUN fetuses. This is the first study to explore the relationship between in utero MRI measures of pulmonary haemodynamics and lung development. Across all treatment groups, left pulmonary artery blood flow and oxygen delivery were negatively correlated with surfactant protein B mRNA and protein expression in late gestation.

Placental insufficiency induces a sexually dimorphic response in the expression of cardiac growth and metabolic signalling molecules upon exposure to a postnatal western diet in guinea pigs

There is a strong relationship between low birth weight (LBW) and an increased risk of developing cardiovascular disease (CVD). In postnatal life, LBW offspring are becoming more commonly exposed to the additional independent CVD risk factors, such as an obesogenic diet. However, how an already detrimentally programmed LBW myocardium responds to a secondary insult, such as an obesogenic diet (western diet; WD), during postnatal life is ill defined. Herein, we aimed to determine in a pre-clinical guinea pig model of CVD, both the independent and interactive effects of LBW and a postnatal WD on the molecular pathways that regulate cardiac growth and metabolism. Uterine artery ablation was used to induce placental insufficiency (PI) in pregnant guinea pigs to generate LBW offspring. Normal birth weight (NBW) and LBW offspring were weaned onto either a Control diet or WD. At ˜145 days after birth (young adulthood), male and female offspring were humanely killed, the heart weighed and left ventricle tissue collected. The mRNA expression of signalling molecules involved in a pathological hypertrophic and fibrotic response was increased in the myocardium of LBW male, but not female offspring, fed a WD as was the mRNA expression of transcription factors involved in fatty acid oxidation. The mRNA expression of glucose transporters was downregulated by LBW and WD in male, but not female hearts. This study has highlighted a sexually dimorphic cardiac pathological hypertrophic and fibrotic response to the secondary insult of postnatal WD consumption in LBW offspring.

Gastrodin Exerts Cardioprotective Action via Inhibition of Insulin-Like Growth Factor Type 2/Insulin-Like Growth Factor Type 2 Receptor Expression in Cardiac Hypertrophy

Pathological cardiac hypertrophy is commonly associated with an upregulation of fetal genes, fibrosis, cardiac dysfunction, and heart failure. Previous studies have demonstrated that gastrodin (GAS) exerts cardioprotective action in the treatment of cardiac hypertrophy. However, the mechanism by which GAS protects against cardiac hypertrophy is yet to be elucidated. A mouse model of myocardial hypertrophy was established using an angiotensin II (Ang II) induction. GAS (5 or 50 mg/kg/d) was orally administered every day starting 7 days prior to the Ang II infusion combined with sham-operated controls. Heart samples from each group were collected for RNA sequencing. Using bioinformatics analysis, the key differentially expressed genes (DEGs) that are involved in reversing cardiac function were identified. Through bioinformatics analysis, the key DEGs that are involved in GAS's inhibition of Ang II-induced abnormal gene expression within the heart were identified. This was further validated using quantitative real-time PCR and Western blotting in neonatal rat cardiomyocytes (NRCMs). Oral administration of GAS significantly suppressed the Ang II-induced increase in heart size and heart weight to body weight. Furthermore, pretreatment of the NRCMs with GAS led to a dose-dependent inhibition of Ang II-induced increases in Nppb mRNA expression. We identified 620 upregulated and 87 downregulated Ang II-induced DEGs II, among which the expression patterns of 58 and 146 genes were inverted by low-dose and high-dose GAS, respectively. These inverted DEGs were found to be mainly enriched in the biological processes of regulation of Ras protein signal transduction, heart contraction, covalent chromatin modification, glucose metabolism, and positive regulation of cell cycle. Among them, the insulin-like growth factor type 2 (Igf2) gene, which was found to be highly reversed and downregulated by GAS, served as a core gene linking energy metabolism, immune regulation, and systemic development. Subsequent functional verification demonstrated that IGF2, and its receptor IGF2R, is one of the targets of GAS that helps protect against cardiac hypertrophy. Taken together, we have identified, for the first time, IGF2/IGF2R as a potential target influenced by GAS in the prevention of cardiac hypertrophy.

Role of Heme-Oxygenase-1 in Biology of Cardiomyocytes Derived from Human Induced Pluripotent Stem Cells

Heme oxygenase-1 (HO-1, encoded by HMOX1) is a cytoprotective enzyme degrading heme into CO, Fe²⁺, and biliverdin. HO-1 was demonstrated to affect cardiac differentiation of murine pluripotent stem cells (PSCs), regulate the metabolism of murine adult cardiomyocytes, and influence regeneration of infarcted myocardium in mice. However, the enzyme’s effect on human cardiogenesis and human cardiomyocytes’ electromechanical properties has not been described so far. Thus, this study aimed to investigate the role of HO-1 in the differentiation of human induced pluripotent stem cells (hiPSCs) into hiPSC-derived cardiomyocytes (hiPSC-CMs). hiPSCs were generated from human fibroblasts and peripheral blood mononuclear cells using Sendai vectors and subjected to CRISPR/Cas9-mediated HMOX1 knock-out. After confirming lack of HO-1 expression on the protein level, isogenic control and HO-1-deficient hiPSCs were differentiated into hiPSC-CMs. No differences in differentiation efficiency and hiPSC-CMs metabolism were observed in both cell types. The global transcriptomic analysis revealed, on the other hand, alterations in electrophysiological pathways in hiPSC-CMs devoid of HO-1, which also demonstrated increased size. Functional consequences in changes in expression of ion channels genes were then confirmed by patch-clamp analysis. To the best of our knowledge, this is the first report demonstrating the link between HO-1 and electrophysiology in human cardiomyocytes.

Insulin-Like Growth Factor 2 As a Possible Neuroprotective Agent and Memory Enhancer-Its Comparative Expression, Processing and Signaling in Mammalian CNS

A number of studies performed on rodents suggest that insulin-like growth factor 2 (IGF-2) or its analogs may possibly be used for treating some conditions like Alzheimer’s disease, Huntington’s disease, autistic spectrum disorders or aging-related cognitive impairment. Still, for translational research a comparative knowledge about the function of IGF-2 and related molecules in model organisms (rats and mice) and humans is necessary. There is a number of important differences in IGF-2 signaling between species. In the present review we emphasize species-specific patterns of IGF-2 expression in rodents, humans and some other mammals, using, among other sources, publicly available transcriptomic data. We provide a detailed description of Igf2 mRNA expression regulation and pre-pro-IGF-2 protein processing in different species. We also summarize the function of IGF-binding proteins. We describe three different receptors able to bind IGF-2 and discuss the role of IGF-2 signaling in learning and memory, as well as in neuroprotection. We hope that comprehensive understanding of similarities and differences in IGF-2 signaling between model organisms and humans will be useful for development of more effective medicines targeting IGF-2 receptors.

The role of insulin-like growth factors in modulating the activity of dental mesenchymal stem cells

Regenerative treatment protocols are an exciting prospect in the management of oral pathology, as they allow for tissues to be restored to their original form and function, as compared to the reparative healing mechanisms which currently govern the outcomes of the majority of dental treatment. Stem cell therapy presents with a great deal of untapped potential in this pursuit of tissue regeneration, and, in particular, mesenchymal stem cells (MSCs) derived from dental tissues are of specific relevance with regards to their applications in engineering craniofacial tissues. A number of mediatory factors are involved in modulating the actions of dental MSCs, and, of these, insulin like growth factors (IGFs) are known to have potent effects in governing the behavior of these cells. The IGF family comprises a number of primary ligands, receptors, and binding proteins which are known to modulate the key properties of dental MSCs, such as their proliferation rates, differentiation potential, and mineralisation. The aims of this review are three-fold: (i) to present an overview of dental MSCs and the role of growth factors in modulating their characteristics, (ii) to discuss in greater detail the specific role of IGFs and the benefits they may convey for tissue engineering, and (iii) to provide a summary of potential for in vivo clinical translation of the current in vitro body of evidence.

Danshen (Salvia miltiorhiza) inhibits Leu27 IGF-II-induced hypertrophy in H9c2 cells

In this study, we used ICI 182 780 (ICI), an estrogen receptor (ER) antagonist, to investigate the estrogenic activity of Danshen, and to further explored whether Danshen extract can block Leu27IGF-II-induced hypertrophy in H9c2 cardiomyoblast cells. We first used an IGF-II analog Leu27IGF-II, which specifically activates IGF2R signaling cascades and induces H9c2 cardiomyoblast cell hypertrophy. However, Danshen extract completely inhibited Leu27IGF-II-induced cell size increase, ANP and BNP hypertrophic marker expression, and IGF2R induction. We also observed that Danshen extract inhibited calcineurin protein expression and NFAT3 nuclear translocation, leading to suppression of Leu27IGF-II-induced cardiac hypertrophy. Moreover, the anti-Leu27IGF-II-IGF2R signaling effect of Danshen was totally reversed by ICI, which suggest the cardio protective effect of Danshen is mediated through estrogen receptors. Our study suggests that, Danshen exerts estrogenic activity, and thus, it could be used as a selective ER modulator in IGFIIR induced hypertrophy model.

Feasibility of ventricular volumetry by cardiovascular MRI to assess cardiac function in the fetal sheep

KEY POINTS

The application of fetal cardiovascular magnetic resonance imaging (CMR) to assess fetal cardiovascular physiology and cardiac function through the quantification of ventricular volumes has previously been investigated, but the approach has not yet been fully validated. Ventricular output measurements calculated from heart rate and stroke volumes (SV) of the right and left ventricles measured by ventricular volumetry (VV) exhibited a high level of agreement with phase-contrast (PC) blood flow measurements in the main pulmonary artery and ascending aorta, respectively. Ejection fraction of the right ventricle, which is lower than that of the left ventricle in postnatal subjects, was similar to the left ventricular ejection fraction in the fetus; probably due to the different loading conditions present in the fetal circulation. This study provides evidence to support the reliability of VV in the sheep fetus, providing evidence for its use in animal models of human diseases affecting the fetal circulation.

ABSTRACT

The application of ventricular volumetry (VV) by cardiovascular magnetic resonance imaging (CMR) in the fetus remains challenging due to the small size of the fetal heart and high heart rate. The reliability of this technique in utero has not yet been established. The aim of this study was to assess the feasibility and reliability of VV in a fetal sheep model of human pregnancy. Right and left ventricular outputs by stroke volume (SV) measured using VV were compared with 2D phase-contrast (PC) CMR measurements of blood flow in the main pulmonary artery (MPA) and ascending aorta (AAo). At 124-140 days (d) gestation, singleton bearing Merino ewes underwent CMR under general anaesthesia using fetal femoral artery catheters, implanted at 109-117d, to trigger cine steady state free precession acquisitions of ventricular short-axis stacks. The short-axis cine stacks were segmented at end-systole and end-diastole, yielding right and left ventricular SV, ejection fraction, and cardiac outputs (SV × heart rate). PC cine acquisitions of MPA and AAo were analysed to measure blood flow, which served as comparators for the right and left cardiac outputs by VV. There was good correlation and agreement between VV and PC measures of ventricular outputs with no significant bias (r²  = 0.926; P < 0.0001; Bias = -4.7 ± 10.5 ml min^-1  kg^-1 ; 95% limits of agreement: -15.9 to 25.2 ml min^-1  kg^-1 ). This study validates fetal VV by CMR in a large animal model of human pregnancy and provides preliminary reference values of fetal sheep right and left ventricles in late gestation.

Detecting metabolic differences in fetal and adult sheep adipose and skeletal muscle tissues

The primary metabolic pathway required to produce ATP differs as a result of tissue type, developmental stage and substrate availability. We utilized molecular and histological techniques to define the metabolic status in foetal and adult, adipose and skeletal muscle tissues. Redox ratios of these tissues were also determined optically by two-photon microscopy. Adult perirenal adipose tissue had a higher optical redox ratio than fetal perirenal adipose tissue, which aligned with glycolysis being used for ATP production; whereas adult skeletal muscle had a lower optical redox ratio than fetal skeletal muscle, which aligned with oxygen demanding oxidative phosphorylation activity being utilized for ATP production. We have compared traditional molecular and microscopy techniques of metabolic tissue characterization with optical redox ratios to provide a more comprehensive report on the dynamics of tissue metabolism.

Cardiorespiratory consequences of intrauterine growth restriction: Influence of timing, severity and duration of hypoxaemia

At birth, weight of the neonate is used as a marker of the 9-month journey as a fetus. Those neonates born less than the 10th centile for their gestational age are at risk of being intrauterine growth restricted. However, this depends on their genetic potential for growth and the intrauterine environment in which they grew. Alterations in the supply of oxygen and nutrients to the fetus will decrease fetal growth, but these alterations occur due to a range of causes that are maternal, placental or fetal in nature. Consequently, IUGR neonates are a heterogeneous population. For this reason, it is likely that these neonates will respond differently to interventions compared not only to normally grown fetuses, but also to other neonates that are IUGR but have travelled a different path to get there. Thus, a range of models of IUGR should be studied to determine the effects of IUGR on the development and function of the heart and lung and subsequently the impact of interventions to improve development of these organs. Here we focus on a range of models of IUGR caused by manipulation of the maternal, placental or fetal environment on cardiorespiratory outcomes.

Role of Insulin-Like Growth Factor Receptor 2 across Muscle Homeostasis: Implications for Treating Muscular Dystrophy

The insulin-like growth factor 2 receptor (IGF2R) plays a major role in binding and regulating the circulating and tissue levels of the mitogenic peptide insulin-like growth factor 2 (IGF2). IGF2/IGF2R interaction influences cell growth, survival, and migration in normal tissue development, and the deregulation of IGF2R expression has been associated with growth-related disease and cancer. IGF2R overexpression has been implicated in heart and muscle disease progression. Recent research findings suggest novel approaches to target IGF2R action. This review highlights recent advances in the understanding of the IGF2R structure and pathways related to muscle homeostasis.

Subcutaneous maternal resveratrol treatment increases uterine artery blood flow in the pregnant ewe and increases fetal but not cardiac growth

KEY POINTS

Substrate restriction during critical developmental windows of gestation programmes offspring for a predisposition towards cardiovascular disease in adult life. This study aimed to determine the effect of maternal resveratrol (RSV) treatment in an animal model in which chronic fetal catheterisation is possible and the timing of organ maturation reflects that of the human. Maternal RSV treatment increased uterine artery blood flow, fetal oxygenation and fetal weight. RSV was not detectable in the fetal circulation, indicating that it may not cross the sheep placenta. This study highlights RSV as a possible intervention to restore fetal substrate supply in pregnancies affected by placental insufficiency.

ABSTRACT

Suboptimal in utero environments with reduced substrate supply during critical developmental windows of gestation predispose offspring to non-communicable diseases such as cardiovascular disease (CVD). Improving fetal substrate supply in these pregnancies may ameliorate the predisposition these offspring have toward adult-onset CVD. This study aimed to determine the effect of maternal resveratrol (RSV) supplementation on uterine artery blood flow and the direct effects of RSV on the fetal heart in a chronically catheterised sheep model of human pregnancy. Maternal RSV treatment significantly increased uterine artery blood flow as measured by phase contrast magnetic resonance imaging, mean gestational fetal P a O 2 and S a O 2 as well as fetal weight. RSV was not detectable in the fetal circulation, and mRNA and protein expression of the histone/protein deacetylase SIRT1 did not differ between treatment groups. No effect of maternal RSV supplementation on AKT/mTOR or CAMKII signalling in the fetal left ventricle was observed. Maternal RSV supplementation is capable of increasing fetal oxygenation and growth in an animal model in which cardiac development parallels that of the human.

Cardiac myocyte proliferation and maturation near term is inhibited by early gestation maternal testosterone exposure

Polycystic ovary syndrome is a complex and common disorder in women, and those affected experience an increased burden of cardiovascular disease. It is an intergenerational syndrome, as affected women with high androgen levels during pregnancy "program" fetal development, leading to a similar phenotype in their female offspring. The effect of excess maternal testosterone exposure on fetal cardiomyocyte growth and maturation is unknown. Pregnant ewes received biweekly injections of vehicle (control) or 100 mg testosterone propionate between 30 and 59 days of gestation (early T) or between 60 and 90 days of gestation (late T). Fetuses were delivered at ~135 days of gestation, and their hearts were enzymatically dissociated to measure cardiomyocyte growth (dimensional measurements), maturation (proportion binucleate), and proliferation (nuclear Ki-67 protein). Early T depressed serum insulin-like growth factor 1 and caused intrauterine growth restriction (IUGR; P < 0.0005). Hearts were smaller with early T ( P < 0.001) due to reduced cardiac myocyte maturation ( P < 0.0005) and proliferation ( P = 0.017). Maturation was also lower in male than female fetuses ( P = 0.004) independent of treatment. Late T did not affect cardiac growth. Early excess maternal testosterone exposure depresses circulating insulin-like growth factor 1 near term and causes IUGR in both female and male offspring. These fetuses have small, immature hearts with reduced proliferation, which may reduce cardiac myocyte endowment and predispose to adverse cardiac growth in postnatal life. While excess maternal testosterone exposure leads to polycystic ovary syndrome and cardiovascular disease in female offspring, it may also predispose to complications of IUGR and cardiovascular disease in male offspring. NEW & NOTEWORTHY Using measurements of cardiac myocyte growth and maturation in an ovine model of polycystic ovary syndrome, this study demonstrates that early gestation excess maternal testosterone exposure reduces near-term cardiomyocyte proliferation and maturation in intrauterine growth-restricted female and male fetuses. The effect of testosterone is restricted to exposure during a specific period early in pregnancy, and the effects appear mediated through reduced insulin-like growth factor 1 signaling. Furthermore, male fetuses, regardless of treatment, had fewer mature cardiomyocytes than female fetuses.

Cardiac Glucolipotoxicity and Cardiovascular Outcomes

Cardiac insulin signaling can be impaired due to the altered fatty acid metabolism to induce insulin resistance. In diabetes and insulin resistance, the metabolic, structural and ultimately functional alterations in the heart and vasculature culminate in diabetic cardiomyopathy, coronary artery disease, ischemia and eventually heart failure. Glucolipotoxicity describes the combined, often synergistic, adverse effects of elevated glucose and free fatty acid concentrations on heart structure, function, and survival. The quality of fatty acid shapes the cardiac structure and function, often influencing survival. A healthy fatty acid balance is therefore critical for maintaining cardiac integrity and function.

Maternal undernutrition in late gestation increases IGF2 signalling molecules and collagen deposition in the right ventricle of the fetal sheep heart

KEY POINTS

This study investigates the impact of decreased fetal plasma glucose concentrations on the developing heart in late gestation, by subjecting pregnant ewes to a 50% global nutrient restriction. Late gestation undernutrition (LGUN) decreased fetal plasma glucose concentrations whilst maintaining a normoxemic blood gas status. LGUN increased the mRNA expression of IGF2 and IGF2R. Fetal plasma glucose concentrations, but not fetal blood pressure, were significantly correlated with IGF2 expression and the activation of CAMKII in the fetal right ventricle. LGUN increased interstitial collagen deposition and altered the protein abundance of phospho-PLB and phospho-troponin I, regulators of cardiac contractility and relaxation. This study shows that a decrease in fetal plasma glucose concentrations may play a role in the development of detrimental changes in the right ventricle in early life, highlighting CAMKII as a potential target for the development of intervention strategies.

ABSTRACT

Exposure of the fetus to a range of environmental stressors, including maternal undernutrition, is associated with an increased risk of death from cardiovascular disease in adult life. This study aimed to determine the effect of maternal nutrient restriction in late gestation on the molecular mechanisms that regulate cardiac growth and development of the fetal heart. Maternal undernutrition resulted in a decrease in fetal glucose concentrations across late gestation, whilst fetal arterial PO2 remained unchanged between the control and late gestation undernutrition (LGUN) groups. There was evidence of an up-regulation of IGF2/IGF2R signalling through the CAMKII pathway in the fetal right ventricle in the LGUN group, suggesting an increase in hypertrophic signalling. LGUN also resulted in an increased mRNA expression of COL1A, TIMP1 and TIMP3 in the right ventricle of the fetal heart. In addition, there was an inverse relationship between fetal glucose concentrations and COL1A expression. The presence of interstitial fibrosis in the heart of the LGUN group was confirmed through the quantification of picrosirius red-stained sections of the right ventricle. We have therefore shown that maternal undernutrition in late gestation may drive the onset of myocardial remodelling in the fetal right ventricle and thus has negative implications for right ventricle function and cardiac health in later life.

Label-free imaging of healthy and infarcted fetal sheep hearts by two-photon microscopy

Coronary heart disease is one of the largest causes of death worldwide, making this a significant health care issue. A critical problem for the adult human heart is that it does not undergo effective repair in response to damage, leaving patients with a poor prognosis. Unlike the adult, fetal hearts have the ability to repair after myocardial damage. Using two-photon microscopy, we have visualised the morphological and metabolic changes following myocardial infarction in sheep fetuses, to characterise response to cardiac injury in a mammalian model. Following myocardial infarction, fetal hearts showed no significant increase in collagen deposition in the region of the infarction, when compared to either the surrounding tissue or shams. In contrast, metabolic activity (i. e. NAD(P)H and FAD) was significantly reduced in the region of myocardial infarction, when compared to either the surrounding tissue or sham hearts. For comparison, we also imaged two hearts from preadolescent sheep (sham and myocardial infarction) and showed highly ordered collagen deposition with decreased metabolic activity within the infarcted area. Therefore, two-photon imaging had the capacity to image both morphological and metabolic changes in response to myocardial infarction and showed differences in the response with age. Picture: Two-photon imaging of myocardial infarction (b and d) enabled the visualisation of increased collagen (blue; Em=431 nm) and changes in other tissue autofluorescence (green; Em=489-606 nm) in fetal (a and b) and preadolescent (c and d) hearts, compared to shams (a and c). The excitation wavelength was 840 nm. Scale bars: 10 μm.

Feasibility of phase-contrast cine magnetic resonance imaging for measuring blood flow in the sheep fetus

Phase-contrast cine MRI (PC-MRI) is the gold-standard noninvasive technique for measuring vessel blood flow and has previously been applied in the human fetal circulation. We aimed to assess the feasibility of using PC-MRI to define the distribution of the fetal circulation in sheep. Fetuses were catheterized at 119-120 days of gestation (term, 150 days) and underwent MRI at ∼123 days of gestation under isoflurane anesthesia, ventilated at a FIO2 of 1.0. PC-MRI was performed using a fetal arterial blood pressure catheter signal for cardiac triggering. Blood flows were measured in the major fetal vessels, including the main pulmonary artery, ascending and descending aorta, superior vena cava, ductus arteriosus, left and right pulmonary arteries, umbilical vein, ductus venosus, and common carotid artery and were indexed to estimated fetal weight. The combined ventricular output, pulmonary blood flow, and flow across the foramen ovale were calculated from vessel flows. Intraobserver and interobserver agreement and reproducibility was assessed. Blood flow measurements were successfully obtained in 61 out of 74 vessels (82.4%) interrogated in 9 fetuses. There was good intraobserver [R = 0.998, P < 0.0001; intraclass correlation (ICC) = 0.997] and interobserver agreement (R = 0.996, P < 0.0001; ICC = 0.996). Repeated MRI measurements showed good reproducibility (R = 0.989, P = 0.0002; ICC = 0.990). We conclude that PC-MRI using fetal catheters for gating triggers is feasible in the major vessels of late gestation fetal sheep. This approach may provide a useful new tool for assessing the circulatory characteristics of fetal sheep models of human disease, including fetal growth restriction and congenital heart disease.

Normalisation of surfactant protein -A and -B expression in the lungs of low birth weight lambs by 21 days old

Intrauterine growth restriction (IUGR) induced by placental restriction (PR) in the sheep negatively impacts lung and pulmonary surfactant development during fetal life. Using a sheep model of low birth weight (LBW), we found that there was an increase in mRNA expression of surfactant protein (SP)-A, -B and -C in the lung of LBW lambs but no difference in the protein expression of SP-A or -B. LBW also resulted in increased lysosome-associated membrane glycoprotein (LAMP)-3 mRNA expression, which may indicate an increase in either the density of type II Alveolar epithelial cells (AEC) or maturity of type II AECs. Although there was an increase in glucocorticoid receptor (GR) and 11β-hydroxysteroid dehydrogenase (11βHSD)-1 mRNA expression in the lung of LBW lambs, we found no change in the protein expression of these factors, suggesting that the increase in SP mRNA expression is not mediated by increased GC signalling in the lung. The increase in SP mRNA expression may, in part, be mediated by persistent alterations in hypoxia signalling as there was an increase in lung HIF-2α mRNA expression in the LBW lamb. The changes in the hypoxia signalling pathway that persist within the lung after birth may be involved in maintaining SP production in the LBW lamb.

Feasibility of detecting myocardial infarction in the sheep fetus using late gadolinium enhancement CMR imaging

BACKGROUND

Late gadolinium enhancement (LGE) cardiovascular magnetic resonance (CMR) imaging has enabled the accurate assessment of myocardial infarction (MI). However, LGE CMR has not been performed successfully in the fetus, where it could be useful for animal studies of interventions to promote cardiac regeneration. We believe that LGE imaging could allow us to document the presence, extent and effect of MI in utero and would thereby expand our capacity for conducting fetal sheep MI research. We therefore aimed to investigate the feasibility of using LGE to detect MI in sheep fetuses.

METHODS

Six sheep fetuses underwent a thoracotomy and ligation of a left anterior descending (LAD) coronary artery branch; while two fetuses underwent a sham surgery. LGE CMR was performed in a subset of fetuses immediately after the surgery and three days later. Early gadolinium enhancement (EGE) CMR was also performed in a subset of fetuses on both days. Cine imaging of the heart was performed to measure ventricular function.

RESULTS

The imaging performed immediately after LAD ligation revealed no evidence of infarct on LGE (n=3). Two of four infarcted fetuses (50%) showed hypoenhancement at the infarct site on the EGE images. Three days after the ligation, LGE images revealed a clear, hyper-enhanced infarct zone in four of the five infarcted fetuses (80%). No hyper-enhanced infarct zone was seen on the one sham fetus that underwent LGE CMR. No hypoenhancement could be seen in the EGE images in either the sham (n=1) or the infarcted fetus (n=1). No regional wall motion abnormalities were apparent in two of the five infarcted fetuses.

CONCLUSION

LGE CMR detected the MI three days after LAD ligation, but not immediately after. Using available methods, EGE imaging was less useful for detecting deficits in perfusion. Our study provides evidence for the ability of a non-invasive tool to monitor the progression of cardiac repair and damage in fetuses with MI. However, further investigation into the optimal timing of LGE and EGE scans and improvement of the sequences should be pursued with the aim of expanding our capacity to monitor cardiac regeneration after MI in fetal sheep.

Akt signaling as a mediator of cardiac adaptation to low birth weight

Intrauterine insults, such as poor nutrition and placental insufficiency, can alter cardiomyocyte development, and this can have significant long-term implications for heart health. Consequently, epidemiological studies have shown that low-birth-weight babies have an increased risk of death from cardiovascular disease in adult life. In addition, intrauterine growth restriction can result in increased left ventricular hypertrophy, which is the strongest predictor for poor health outcomes in cardiac patients. The mechanisms responsible for these associations are not clear, but a suboptimal intrauterine environment can program alternative expression of genes such as cardiac IGF-2/H19, IGF-2R and AT₁R through either an increase or decrease in DNA methylation or histone acetylation at specific loci. Furthermore, hypoxia and other intrauterine insults can also activate the IGF-1 receptor via IGF-1 and IGF-2, and the AT₁ receptor via angiotensin signaling pathways; both of which can result in the phosphorylation of Akt and the activation of a range of downstream pathways. In turn, Akt activation can increase cardiac angiogenesis and cardiomyocyte apoptosis and promote a reversion of metabolism in postnatal life to a fetal phenotype, which involves increased reliance on glucose. Cardiac Akt can also be indirectly regulated by microRNAs and conversely can target microRNAs that will eventually affect other specific cardiac genes and proteins. This review aims to discuss our understanding of this complex network of interactions, which may help explain the link between low birth weight and the increased risk of cardiovascular disease in adult life.

The Role of Insulin Receptor Isoforms in Diabetes and Its Metabolic and Vascular Complications

The insulin receptor (IR) presents by alternative splicing two isoforms: IRA and IRB. The differential physiological and pathological role of both isoforms is not completely known, and it is determinant the different binding affinity for insulin-like growth factor. IRB is more abundant in adult tissues and it exerts mainly the metabolic actions of insulin, whereas IRA is mainly expressed in fetal and prenatal period and exerts mitogenic actions. However, the change in the expression profile of both IR isoforms and its dysregulation are associated with the development of different pathologies, such as cancer, insulin resistance, diabetes, obesity, and atherosclerosis. In some of them, there is a significant increase of IRA/IRB ratio conferring a proliferative and migratory advantage to different cell types and favouring IGF-II actions with a sustained detriment in the metabolic effects of insulin. This review discussed specifically the role of IR isoforms as well as IGF-IR in diabetes and its associated complications as obesity and atherosclerosis. Future research with new IR modulators might be considered as possible targets to improve the treatment of diabetes and its associated complications.

Doxorubicin attenuates CHIP-guarded HSF1 nuclear translocation and protein stability to trigger IGF-IIR-dependent cardiomyocyte death

Doxorubicin (DOX) is one of the most effective antitumor drugs, but its cardiotoxicity has been a major concern for its use in cancer therapy for decades. Although DOX-induced cardiotoxicity has been investigated, the underlying mechanisms responsible for this cardiotoxicity have not been completely elucidated. Here, we found that the insulin-like growth factor receptor II (IGF-IIR) apoptotic signaling pathway was responsible for DOX-induced cardiotoxicity via proteasome-mediated heat shock transcription factor 1 (HSF1) degradation. The carboxyl-terminus of Hsp70 interacting protein (CHIP) mediated HSF1 stability and nuclear translocation through direct interactions via its tetratricopeptide repeat domain to suppress IGF-IIR expression and membrane translocation under physiological conditions. However, DOX attenuated the HSF1 inhibition of IGF-IIR expression by diminishing the CHIP–HSF1 interaction, removing active nuclear HSF1 and triggering HSF1 proteasomal degradation. Overexpression of CHIP redistributed HSF1 into the nucleus, inhibiting IGF-IIR expression and preventing DOX-induced cardiomyocyte apoptosis. Moreover, HSF1A, a small molecular drug that enhances HSF1 activity, stabilized HSF1 expression and minimized DOX-induced cardiac damage in vitro and in vivo. Our results suggest that the cardiotoxic effects of DOX result from the prevention of CHIP-mediated HSF1 nuclear translocation and activation, which leads to an upregulation of the IGF-IIR apoptotic signaling pathway. We believe that the administration of an HSF1 activator or agonist may further protect against the DOX-induced cell death of cardiomyocytes.

Patterns of gene expression in the sheep heart during the perinatal period revealed by transcriptomic modeling

Septa from sheep hearts at 130 days gestation, term, and 14-day-old lambs were used to model the changes in gene expression patterns during the perinatal period using Agilent 15k ovine microarrays. We used Bioconductor for R to model five major patterns of coexpressed genes. Gene ontology and transcription factor analyses using Webgestalt modeled the biological significances and transcription factors of the gene expression patterns. Modeling indicated a decreased expression of genes associated with anatomical development and differentiation during this period, whereas those associated with increased protein synthesis and growth associated with maturation of the endoplasmic reticulum rose to term but did not further increase from the near term expression. Expression of genes associated with cell responsiveness, for example, immune responses, decreased at term but expression returned by postnatal day 14. Changes in genes related to metabolism showed differential substrate-associated patterns: those related to carbohydrate metabolism rose to term and remained stable thereafter, whereas those associated with fatty acid oxidation facility rose throughout the period. The timing of many of these maturational processes was earlier in relation to birth than in the rodent. The importance of the transcription factors, estrogen-related receptors, and v-myc avian myelocytomatosis viral oncogene homolog was also highlighted in the pattern of gene expression during development of the perinatal sheep heart.

Increased lung prolyl hydroxylase and decreased glucocorticoid receptor are related to decreased surfactant protein in the growth-restricted sheep fetus

Experimental placental restriction (PR) by carunclectomy in fetal sheep results in intrauterine growth restriction (IUGR), chronic hypoxemia, increased plasma cortisol, and decreased lung surfactant protein (SP) expression. The mechanisms responsible for decreased SP expression are unknown but may involve decreased glucocorticoid (GC) action or changes in hypoxia signaling. Endometrial caruncles were removed from nonpregnant ewes to induce PR. Lungs were collected from control and PR fetuses at 130-135 (n = 19) and 139-145 (n = 28) days of gestation. qRT-PCR and Western blotting were used to quantify lung mRNA and protein expression, respectively, of molecular regulators and downstream targets of the GC and hypoxia-signaling pathways. We confirmed a decrease in SP-A, -B, and -C, but not SP-D, mRNA expression in PR fetuses at both ages. There was a net downregulation of GC signaling with a reduction in GC receptor (GR)-α and -β protein expression and a decrease in the cofactor, GATA-6. GC-responsive genes including transforming growth factor-β1, IL-1β, and β2-adrenergic receptor were not stimulated. Prolyl hydroxylase domain (PHD)2 mRNA and protein and PHD3 mRNA expression increased with a concomitant increase in hypoxia-inducible factor-1α (HIF-1α) and HIF-1β mRNA expression. There was an increase in mRNA expression of several, but not all, hypoxia-responsive genes. Hence, both GC and hypoxia signaling may contribute to reduced SP expression. Although acute hypoxia normally inactivates PHDs, chronic hypoxemia in the PR fetus increased PHD abundance, which normally prevents HIF signaling. This may represent a mechanism by which chronic hypoxemia contributes to the decrease in SP production in the IUGR fetal lung.

Low birth weight activates the renin-angiotensin system, but limits cardiac angiogenesis in early postnatal life

Low birth weight (LBW) is associated with increased risk of adult cardiovascular disease and this association may be partly a consequence of early programming of the renin-angiotensin system (RAS). We investigated the effects of LBW on expression of molecules in the RAS and cardiac tissue remodeling. Left ventricular samples were collected from the hearts of 21 days old lambs that were born average birth weight (ABW) and LBW. Cardiac mRNA expression was quantified using real-time RT-PCR and protein expression was quantified using Western blotting. DNA methylation and histone acetylation were assessed by combined bisulfite restriction analysis and chromatin immunoprecipitation, respectively. There were increased plasma renin activity, angiotensin I (ANGI), and ANGII concentrations in LBW compared to ABW lambs at day 20. In LBW lambs, there was increased expression of cardiac ACE2 mRNA, decreased ANGII receptor type 1 (AT1R) protein, and acetylation of histone H3K9 of the AT1R promoter but no changes in AT1R mRNA expression and AT1R promoter DNA methylation. There was no difference in the abundance of proteins involved in autophagy or fibrosis. BIRC5 and VEGF mRNA expression was increased; however, the total length of the capillaries was decreased in the hearts of LBW lambs. Activation of the circulating and local cardiac RAS in neonatal LBW lambs may be expected to increase cardiac fibrosis, autophagy, and capillary length. However, we observed only a decrease in total capillary length, suggesting a dysregulation of the RAS in the heart of LBW lambs and this may have significant implications for heart health in later life.

Impact of chronic hypoxemia on blood flow to the brain, heart, and adrenal gland in the late-gestation IUGR sheep fetus

In the fetus, there is a redistribution of cardiac output in response to acute hypoxemia, to maintain perfusion of key organs, including the brain, heart, and adrenal glands. There may be a similar redistribution of cardiac output in the chronically hypoxemic, intrauterine growth-restricted fetus. Surgical removal of uterine caruncles in nonpregnant ewe results in the restriction of placental growth (PR) and intrauterine growth. Vascular catheters were implanted in seven control and six PR fetal sheep, and blood flow to organs was determined using microspheres. Placental and fetal weight was significantly reduced in the PR group. Despite an increase in the relative brain weight in the PR group, there was no difference in blood flow to the brain between the groups, although PR fetuses had higher blood flow to the temporal lobe. Adrenal blood flow was significantly higher in PR fetuses, and there was a direct relationship between mean gestational PaO2 and blood flow to the adrenal gland. There was no change in blood flow, but a decrease in oxygen and glucose delivery to the heart in the PR fetuses. In another group, there was a decrease in femoral artery blood flow in the PR compared with the Control group, and this may support blood flow changes to the adrenal and temporal lobe. In contrast to the response to acute hypoxemia, these data show that there is a redistribution of blood flow to the adrenals and temporal lobe, but not the heart or whole brain, in chronically hypoxemic PR fetuses in late gestation.

IGF-2R-Gαq signaling and cardiac hypertrophy in the low-birth-weight lamb

The cardiac insulin-like growth factor 2 receptor (IGF-2R) can induce cardiomyocyte hypertrophy in a heterotrimeric G protein receptor-coupled manner involving αq (Gαq) or αs (Gαs). We have previously shown increased left ventricular weight and cardiac IGF-2 and IGF-2R gene expression in low-birth-weight (LBW) compared with average-birth-weight (ABW) lambs. Here, we have investigated the cardiac expression of IGF-2 gene variants, the degree of histone acetylation, and the abundance of proteins in the IGF-2R downstream signaling pathway in ABW and LBW lambs. Samples from the left ventricle of ABW and LBW lambs were collected at 21 days of age. There was increased phospho-CaMKII protein with decreased HDAC 4 abundance in the LBW compared with ABW lambs. There was increased GATA 4 and decreased phospho-troponin I abundance in LBW compared with ABW lambs, which are markers of pathological cardiac hypertrophy and impaired or reduced contractility, respectively. There was increased histone acetylation of H3K9 at IGF-2R promoter and IGF-2R intron 2 differentially methylated region in the LBW lamb. In conclusion, histone acetylation of IGF-2R may lead to increased IGF-2R mRNA expression and subsequently mediate Gαq signaling early in life via CaMKII, resulting in an increased risk of left ventricular hypertrophy and cardiovascular disease in adult life.

Maternal undernutrition around the time of conception and embryo number each impact on the abundance of key regulators of cardiac growth and metabolism in the fetal sheep heart

Poor maternal nutrition before and during pregnancy is associated with an increased risk of cardiovascular disease in later life. To determine the impact of maternal undernutrition during the periconceptional (PCUN: -45 days to 6 days) and preimplantation (PIUN: 0-6 days) periods on cardiac growth and metabolism, we have quantified the mRNA and protein abundance of key regulators of cardiac growth and metabolism in the left ventricle of the sheep fetus in late gestation. The cardiac protein abundance of AMP-activated protein kinase (AMPK), phospho-acetyl CoA carboxykinase (ACC) and pyruvate dehydrogenase kinase-4 (PDK-4) were decreased, whereas ACC was increased in singletons in the PCUN and PIUN groups. In twins, however, cardiac ACC was decreased in the PCUN and PIUN groups, and carnitine palmitoyltransferase-1 (CPT-1) was increased in the PIUN group. In singletons, the cardiac abundance of insulin receptor β (IRβ) was decreased in the PCUN group, and phosphoinositide-dependent protein kinase-1 (PDPK-1) was decreased in the PCUN and PIUN groups. In twins, however, the cardiac abundance of IRβ and phospho-Akt substrate 160kDa (pAS160) were increased in the PIUN group. The cardiac abundance of insulin-like growth factor-2 receptor (IGF-2R), protein kinase C alpha (PKCα) and mammalian target of rapamycin (mTOR) were decreased in PCUN and PIUN singletons and extracellular-signal-regulated kinase (ERK) was also decreased in the PIUN singletons. In contrast, in twins, cardiac abundance of IGF-2R and PKCα were increased in the PCUN and PIUN groups, phospho-ribosomal protein S6 (pRPS6) was increased in the PCUN group, and ERK and eukaryotic initiation factor 4E (eIF4E) were also increased in the PIUN fetuses. In conclusion, maternal undernutrition limited to around the time of conception is sufficient to alter the abundance of key factors regulating cardiac growth and metabolism and this may increase the propensity for cardiovascular diseases in later life.

Exposure to rosiglitazone, a PPAR-γ agonist, in late gestation reduces the abundance of factors regulating cardiac metabolism and cardiomyocyte size in the sheep fetus

It is unknown whether cardiomyocyte hypertrophy and the transition to fatty acid oxidation as the main source of energy after birth is dependent on the maturation of the cardiomyocytes' metabolic system, or on the limitation of substrate availability before birth. This study aimed to investigate whether intrafetal administration of a peroxisome proliferator-activated receptor-γ (PPAR-γ) agonist, rosiglitazone, during late gestation can stimulate the expression of factors regulating cardiac growth and metabolism in preparation for birth, and the consequences of cardiac contractility in the fetal sheep at ∼140 days gestation. The mRNA expression and protein abundance of key factors regulating growth and metabolism were quantified using quantitative RT-PCR and Western blot analysis, respectively. Cardiac contractility was determined by measuring the Ca(2+) sensitivity and maximum Ca(2+)-activated force of skinned cardiomyocyte bundles. Rosiglitazone-treated fetuses had a lower cardiac abundance of insulin-signaling molecules, including insulin receptor-β, insulin receptor substrate-1 (IRS-1), phospho-IRS-1 (Tyr-895), phosphatidylinositol 3-kinase (PI3K) regulatory subunit p85, PI3K catalytic subunit p110α, phospho-3-phosphoinositide-dependent protein kinase 1 (Ser-241), protein kinase B (Akt-1), phospho-Akt (Ser-273), PKCζ, phospho-PKCζ(Thr-410), Akt substrate 160 kDa (AS160), phospho-AS160 (Thr-642), and glucose transporter type-4. Additionally, cardiac abundance of regulators of fatty acid β-oxidation, including adiponectin receptor 1, AMPKα, phospho-AMPKα (Thr-172), phospho-acetyl CoA carboxylase (Ser-79), carnitine palmitoyltransferase-1, and PGC-1α was lower in the rosiglitazone-treated group. Rosiglitazone administration also resulted in a decrease in cardiomyocyte size. Rosiglitazone administration in the late-gestation sheep fetus resulted in a decreased abundance of factors regulating cardiac glucose uptake, fatty acid β-oxidation, and cardiomyocyte size. These findings suggest that activation of PPAR-γ using rosiglitazone does not promote the maturation of cardiomyocytes; rather, it may decrease cardiac metabolism and compromise cardiac health later in life.

Alteration of cardiac glucose metabolism in association to low birth weight: experimental evidence in lambs with left ventricular hypertrophy

OBJECTIVE

Intrauterine growth restriction that results in low birth weight (LBW) has been linked to the onset of pathological cardiac hypertrophy. An altered transition from a fetal to an adult energy metabolism phenotype, with increased reliance on glucose rather than fatty acids for energy production, could help explain this connection. We have therefore investigated cardiac metabolism in relation to left ventricular hypertrophy in LBW lambs, at 21days after birth.

MATERIALS/METHODS

The expression of regulatory molecules involved in cardiac glucose and fatty acid metabolism was measured using real-time PCR and Western blotting. A section of the left ventricle was fixed for Periodic Acid Schiff staining to determine tissue glycogen content.

RESULTS

There was increased abundance of insulin signalling pathway proteins (phospho-insulin receptor, insulin receptor and phospho-Akt) and the glucose transporter (GLUT)-1, but no change in GLUT-4 or glycogen content in the heart of LBW compared to ABW lambs. There was, however, increased abundance of cardiac pyruvate dehydrogenase kinase 4 (PDK-4) in LBW compared to ABW lambs. There were no significant changes in the mRNA expression of components of the peroxisome proliferator activated receptor regulatory complex or proteins involved in fatty acid metabolism.

CONCLUSION

We concluded that LBW induced left ventricular hypertrophy was associated with increased GLUT-1 and PDK-4, suggesting increased glucose uptake, but decreased efficacy for the conversion of glucose to ATP. A reduced capacity for energy conversion could have significant implications for vulnerability to cardiovascular disease in adults who are born LBW.

Hormonal and nutritional drivers of intrauterine growth

PURPOSE OF REVIEW

Size at birth is critical in determining life expectancy with both small and large neonates at risk of shortened life spans. This review examines the hormonal and nutritional drivers of intrauterine growth with emphasis on the role of foetal hormones as nutritional signals in utero.

RECENT FINDINGS

Nutrients drive intrauterine growth by providing substrate for tissue accretion, whereas hormones regulate nutrient distribution between foetal oxidative metabolism and mass accumulation. The main hormonal drivers of intrauterine growth are insulin, insulin-like growth factors and thyroid hormones. Together with leptin and cortisol, these hormones control cellular nutrient uptake and the balance between accretion and differentiation in regulating tissue growth. They also act indirectly via the placenta to alter the materno-foetal supply of nutrients and oxygen. By responding to nutrient and oxygen availability, foetal hormones optimize the survival and growth of the foetus with respect to its genetic potential, particularly during adverse conditions. However, changes in the intrauterine growth of individual tissues may alter their function permanently.

SUMMARY

In both normal and compromised pregnancies, intrauterine growth is determined by multiple hormonal and nutritional drivers which interact to produce a specific pattern of intrauterine development with potential lifelong consequences for health.