Extracellular signal-regulated kinase and phosphoinositol-3 kinase mediate IGF-1 induced proliferation of fetal sheep cardiomyocytes

Molecular Basis of Cardiomyopathies in Type 2 Diabetes

Diabetic cardiomyopathy (DbCM) is a common complication in individuals with type 2 diabetes mellitus (T2DM), and its exact pathogenesis is still debated. It was hypothesized that chronic hyperglycemia and insulin resistance activate critical cellular pathways that are responsible for numerous functional and anatomical perturbations in the heart. Interstitial inflammation, oxidative stress, myocardial apoptosis, mitochondria dysfunction, defective cardiac metabolism, cardiac remodeling, hypertrophy and fibrosis with consequent impaired contractility are the most common mechanisms implicated. Epigenetic changes also have an emerging role in the regulation of these crucial pathways. The aim of this review was to highlight the increasing knowledge on the molecular mechanisms of DbCM and the new therapies targeting specific pathways.

Fetal cardiac troponin I levels decline toward birth in sheep

Elevated cardiac troponin I (cTnI), a myocardial damage biomarker, has been reported in cord blood of neonates delivered vaginally or by cesarean section. Although the neonatal peak likely reflects the physiological adjustment to extrauterine life, a better understanding of serial prepartum changes is required to determine physiological causes of fetal cTnI release. We longitudinally sampled eight healthy lambs (20 days before spontaneous birth to 5 days postnatal), and from three fetuses receiving intravenous IGF-1. Samples were collected into heparin, and the plasma was stored at -80°C for later determination of high-sensitivity (hs) cTnI levels (BeckmanCoulter UniCel DxI Access IA; log transformed detection limit = 0.30, quantification limit = 0.78, 99th percentile = 1.78). Positive and negative control samples were drawn from an adult ewe during a terminal experiment (myocardial ischemia) and similarly assessed. hs-cTnI data were log transformed from ng/L. Log(hs-cTnI) was 1.47 ± 0.30 (means ± SD) at 20 days before birth and declined to 1.02 ± 0.65 in fetuses 12 ± 4 h before birth (P < 0.0001, R2 = 0.7869). Birth stimulated a delayed, transient peak in hs-cTnI (P = 0.0058). Newborn (43 ± 19 min postnatal) levels were 1.39 ± 0.40 (P = 0.0650 vs. fetus on day of birth) and 2.14 ± 0.63 the day after birth (P = 0.0331 vs. newborn). The second day after birth, levels declined to 1.65 ± 0.48 (P = 0.0238 vs. day 1). IGF-1 infusion increased hs-cTnI levels 25-50% over baseline (P = 0.0252, R2 = 0.9938). Baseline adult ewe log(hs-cTnI) was below the limit of detection; 3 h following coronary artery ligation, levels were 3.21. In conclusion, we newly report that fetal hs-cTnI levels decline concomitantly with reduced proliferation of cardiomyocytes toward term.NEW & NOTEWORTHY Serial blood samples were collected from catheterized, normally developing fetal and newborn lambs and high-sensitivity cardiac troponin I (hs-cTnI) levels were assessed, providing unprecedented insight into the physiological processes leading to high levels in the perinatal period. Moderately high levels of hs-cTnI found in the normally developing fetus declined toward term. An elevation to high levels peaked the day after birth, after which hs-cTnI declined again. Stimulation of fetal cardiomyocyte proliferation with IGF-1 also elevated hs-cTnI.

Synergistic effects of hormones on structural and functional maturation of cardiomyocytes and implications for heart regeneration

The limited endogenous regenerative capacity of the human heart renders cardiovascular diseases a major health threat, thus motivating intense research on in vitro heart cell generation and cell replacement therapies. However, so far, in vitro-generated cardiomyocytes share a rather fetal phenotype, limiting their utility for drug testing and cell-based heart repair. Various strategies to foster cellular maturation provide some success, but fully matured cardiomyocytes are still to be achieved. Today, several hormones are recognized for their effects on cardiomyocyte proliferation, differentiation, and function. Here, we will discuss how the endocrine system impacts cardiomyocyte maturation. After detailing which features characterize a mature phenotype, we will contemplate hormones most promising to induce such a phenotype, the routes of their action, and experimental evidence for their significance in this process. Due to their pleiotropic effects, hormones might be not only valuable to improve in vitro heart cell generation but also beneficial for in vivo heart regeneration. Accordingly, we will also contemplate how the presented hormones might be exploited for hormone-based regenerative therapies.

Attenuated glucose-stimulated insulin secretion during an acute IGF-1 LR3 infusion into fetal sheep does not persist in isolated islets

Insulin-like growth factor-1 (IGF-1) is a critical fetal growth hormone that has been proposed as a therapy for intrauterine growth restriction. We previously demonstrated that a 1-week IGF-1 LR3 infusion into fetal sheep reduces in vivo and in vitro insulin secretion suggesting an intrinsic islet defect. Our objective herein was to determine whether this intrinsic islet defect was related to chronicity of exposure. We therefore tested the effects of a 90-min IGF-1 LR3 infusion on fetal glucose-stimulated insulin secretion (GSIS) and insulin secretion from isolated fetal islets. We first infused late gestation fetal sheep (n = 10) with either IGF-1 LR3 (IGF-1) or vehicle control (CON) and measured basal insulin secretion and in vivo GSIS utilizing a hyperglycemic clamp. We then isolated fetal islets immediately following a 90-min IGF-1 or CON in vivo infusion and exposed them to glucose or potassium chloride to measure in vitro insulin secretion (IGF-1, n = 6; CON, n = 6). Fetal plasma insulin concentrations decreased with IGF-1 LR3 infusion (P < 0.05), and insulin concentrations during the hyperglycemic clamp were 66% lower with IGF-1 LR3 infusion compared to CON (P < 0.0001). Insulin secretion in isolated fetal islets was not different based on infusion at the time of islet collection. Therefore, we speculate that while acute IGF-1 LR3 infusion may directly suppress insulin secretion, the fetal β-cell in vitro retains the ability to recover GSIS. This may have important implications when considering the long-term effects of treatment modalities for fetal growth restriction.

Sodium-glucose Cotransporter 2 Inhibitors and Pathological Myocardial Hypertrophy

Sodium-glucose cotransporter 2 (SGLT2) inhibitors are a new type of oral hypoglycemic drugs that exert a hypoglycemic effect by blocking the reabsorption of glucose in the proximal renal tubules, thus promoting the excretion of glucose from urine. Their hypoglycemic effect is not dependent on insulin. Increasing data shows that SGLT2 inhibitors improve cardiovascular outcomes in patients with type 2 diabetes. Previous studies have demonstrated that SGLT2 inhibitors can reduce pathological myocardial hypertrophy with or without diabetes, but the exact mechanism remains to be elucidated. To clarify the relationship between SGLT2 inhibitors and pathological myocardial hypertrophy, with a view to providing a reference for the future treatment thereof, this study reviewed the possible mechanisms of SGLT2 inhibitors in attenuating pathological myocardial hypertrophy. We focused specifically on the mechanisms in terms of inflammation, oxidative stress, myocardial fibrosis, mitochondrial function, epicardial lipids, endothelial function, insulin resistance, cardiac hydrogen and sodium exchange, and autophagy.

Sheep recombinant IGF-1 promotes organ-specific growth in fetal sheep

IGF-1 is a critical fetal growth-promoting hormone. Experimental infusion of an IGF-1 analog, human recombinant LR3 IGF-1, into late gestation fetal sheep increased fetal organ growth and skeletal muscle myoblast proliferation. However, LR3 IGF-1 has a low affinity for IGF binding proteins (IGFBP), thus reducing physiologic regulation of IGF-1 bioavailability. The peptide sequences for LR3 IGF-1 and sheep IGF-1 also differ. To overcome these limitations with LR3 IGF-1, we developed an ovine (sheep) specific recombinant IGF-1 (oIGF-1) and tested its effect on growth in fetal sheep. First, we measured in vitro myoblast proliferation in response to oIGF-1. Second, we examined anabolic signaling pathways from serial skeletal muscle biopsies in fetal sheep that received oIGF-1 or saline infusion for 2 hours. Finally, we measured the effect of fetal oIGF-1 infusion versus saline infusion (SAL) for 1 week on fetal body and organ growth, in vivo myoblast proliferation, skeletal muscle fractional protein synthetic rate, IGFBP expression in skeletal muscle and liver, and IGF-1 signaling pathways in skeletal muscle. Using this approach, we showed that oIGF-1 stimulated myoblast proliferation in vitro. When infused for 1 week, oIGF-1 increased organ growth of the heart, kidney, spleen, and adrenal glands and stimulated skeletal myoblast proliferation compared to SAL without increasing muscle fractional synthetic rate or hindlimb muscle mass. Hepatic and muscular gene expression of IGFBPs one to three was similar between oIGF-1 and SAL. We conclude that oIGF-1 promotes tissue and organ-specific growth in the normal sheep fetus.

Plin5, a New Target in Diabetic Cardiomyopathy

Abnormal lipid accumulation is commonly observed in diabetic cardiomyopathy (DC), which can create a lipotoxic microenvironment and damage cardiomyocytes. Lipid toxicity is an important pathogenic factor due to abnormal lipid accumulation in DC. As a lipid droplet (LD) decomposition barrier, Plin5 can protect LDs from lipase decomposition and regulate lipid metabolism, which is involved in the occurrence and development of cardiovascular diseases. In recent years, studies have shown that Plin5 expression is involved in the pathogenesis of DC lipid toxicity, such as oxidative stress, mitochondrial dysfunction, endoplasmic reticulum (ER) stress, and insulin resistance (IR) and has become a key target of DC research. Therefore, understanding the relationship between Plin5 and DC progression as well as the mechanism of this process is crucial for developing new therapeutic approaches and exploring new therapeutic targets. This review is aimed at exploring the latest findings and roles of Plin5 in lipid metabolism and DC-related pathogenesis, to explore possible clinical intervention approaches.

Sexual dimorphism in testosterone programming of cardiomyocyte development in sheep

Perturbed in utero hormone milieu leads to intrauterine growth retardation (IUGR), a known risk factor for left ventricular (LV) dysfunction later in life. Gestational testosterone (T) excess predisposes offspring to IUGR and leads to LV myocardial disarray and hypertension in adult females. However, the early impact of T excess on LV programming and if it is female specific is unknown. LV tissues were obtained at day 90 gestation from days 30-90 T-treated or control fetuses (n = 6/group/sex) and morphometric and molecular analyses were conducted. Gestational T treatment increased cardiomyocyte number only in female fetuses. T excess upregulated receptor expression of insulin and insulin-like growth factor. Furthermore, in a sex-specific manner, T increased expression of phosphatidylinositol 3-kinase (PI3K) while downregulating phosphorylated mammalian target of rapamycin (pmTOR)-to-mTOR ratio suggestive of compensatory response. T excess 1) upregulated atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP), markers of stress and cardiac hypertrophy and 2) upregulated estrogen receptors1 (ESR1) and 2 (ESR2), but not in androgen receptor (AR). Thus, gestational T excess upregulated markers of cardiac stress and hypertrophy in both sexes while inducing cardiomyocyte hyperplasia only in females, likely mediated via insulin and estrogenic programming.NEW & NOTEWORTHY The present study demonstrates sex-specific effects of gestational T excess between days 30 and 90 of gestation on the cardiac phenotype. Furthermore, the sex-specific programming is likely secondary to perturbation in both estrogen and insulin signaling pathways collectively. These findings are supportive of the role of androgen excess to serve as early biomarkers of CVD and could be critical in identifying therapeutic targets for LV hypertrophy and predict long-term CVD.

Mechanisms of cardiac dysfunction in diabetic cardiomyopathy: molecular abnormalities and phenotypical variants

Diabetic cardiomyopathy (DCM) is a diabetes mellitus-induced pathophysiological condition characterized by cardiac structural, functional, and metabolic changes that can result in heart failure (HF), in the absence of coronary artery disease, hypertension, and valvular heart disease. Metabolic alterations such as hyperglycemia, insulin resistance, hyperinsulinemia, and increased metabolism of free fatty acids result in oxidative stress, inflammation, advanced glycation end products formation, abnormalities in calcium homeostasis, and apoptosis that are responsible for structural remodeling. Cardiac stiffness, hypertrophy, and fibrosis eventually lead to dysfunction and HF with preserved ejection fraction and/or HF with reduced ejection fraction. In this review, we analyzed in detail the cellular and molecular mechanisms and the metabolic pathways involved in the pathophysiology of DCM. Different phenotypes are observed in DCM, and it is not clear yet if the restrictive and the dilated phenotypes are distinct or represent an evolution of the same disease. Phenotypic differences can be observed between T1DM and T2DM DCM, possibly explained by the different myocardial insulin action. Further studies are needed in order to better understand the underlying mechanisms of DCM and to identify appropriate therapeutic targets and novel strategies to prevent and reverse the progression toward heart failure in diabetic patients.

Molecular Mechanisms and Epigenetic Regulation in Diabetic Cardiomyopathy

Diabetes mellitus (DM) is an important lifestyle disease. Type 2 diabetes is one of the prime contributors to cardiovascular diseases (CVD) and diabetic cardiomyopathy (DbCM) and leads to increased morbidity and mortality in patients with DM. DbCM is a typical cardiac disease, characterized by cardiac remodeling in the presence of DM and in the absence of other comorbidities such as hypertension, valvular diseases, and coronary artery disease. DbCM is associated with defective cardiac metabolism, altered mitochondrial structure and function, and other physiological and pathophysiological signaling mechanisms such as oxidative stress, inflammation, myocardial apoptosis, and autophagy. Epigenetic modifiers are crucial players in the pathogenesis of DbCM. Thus, it is important to explore the role of epigenetic modifiers or modifications in regulating molecular pathways associated with DbCM. In this review, we have discussed the role of various epigenetic mechanisms such as histone modifications (acetylation and methylation), DNA methylation and non-coding RNAs in modulating molecular pathways involved in the pathophysiology of the DbCM.

The Mystery of Diabetic Cardiomyopathy: From Early Concepts and Underlying Mechanisms to Novel Therapeutic Possibilities

Diabetic patients are predisposed to diabetic cardiomyopathy, a specific form of cardiomyopathy which is characterized by the development of myocardial fibrosis, cardiomyocyte hypertrophy, and apoptosis that develops independently of concomitant macrovascular and microvascular diabetic complications. Its pathophysiology is multifactorial and poorly understood and no specific therapeutic guideline has yet been established. Diabetic cardiomyopathy is a challenging diagnosis, made after excluding other potential entities, treated with different pharmacotherapeutic agents targeting various pathophysiological pathways that need yet to be unraveled. It has great clinical importance as diabetes is a disease with pandemic proportions. This review focuses on the potential mechanisms contributing to this entity, diagnostic options, as well as on potential therapeutic interventions taking in consideration their clinical feasibility and limitations in everyday practice. Besides conventional therapies, we discuss novel therapeutic possibilities that have not yet been translated into clinical practice.

Reduced glucose-stimulated insulin secretion following a 1-wk IGF-1 infusion in late gestation fetal sheep is due to an intrinsic islet defect

Insulin and insulin-like growth factor-1 (IGF-1) are fetal hormones critical to establishing normal fetal growth. Experimentally elevated IGF-1 concentrations during late gestation increase fetal weight but lower fetal plasma insulin concentrations. We therefore hypothesized that infusion of an IGF-1 analog for 1 wk into late gestation fetal sheep would attenuate fetal glucose-stimulated insulin secretion (GSIS) and insulin secretion in islets isolated from these fetuses. Late gestation fetal sheep received infusions with IGF-1 LR3 (IGF-1, n = 8), an analog of IGF-1 with low affinity for the IGF binding proteins and high affinity for the IGF-1 receptor, or vehicle control (CON, n = 9). Fetal GSIS was measured with a hyperglycemic clamp (IGF-1, n = 8; CON, n = 7). Fetal islets were isolated, and insulin secretion was assayed in static incubations (IGF-1, n = 8; CON, n = 7). Plasma insulin and glucose concentrations in IGF-1 fetuses were lower compared with CON (P = 0.0135 and P = 0.0012, respectively). During the GSIS study, IGF-1 fetuses had lower insulin secretion compared with CON (P = 0.0453). In vitro, glucose-stimulated insulin secretion remained lower in islets isolated from IGF-1 fetuses (P = 0.0447). In summary, IGF-1 LR3 infusion for 1 wk into fetal sheep lowers insulin concentrations and reduces fetal GSIS. Impaired insulin secretion persists in isolated fetal islets indicating an intrinsic islet defect in insulin release when exposed to IGF-1 LR3 infusion for 1 wk. We speculate this alteration in the insulin/IGF-1 axis contributes to the long-term reduction in β-cell function in neonates born with elevated IGF-1 concentrations following pregnancies complicated by diabetes or other conditions associated with fetal overgrowth.NEW & NOTEWORTHY After a 1-wk infusion of IGF-1 LR3, late gestation fetal sheep had lower plasma insulin and glucose concentrations, reduced fetal glucose-stimulated insulin secretion, and decreased fractional insulin secretion from isolated fetal islets without differences in pancreatic insulin content.

Heart Failure and Diabetes Mellitus: Biomarkers in Risk Stratification and Prognostication

Heart failure (HF) and type 2 diabetes mellitus (T2DM) have a synergistic effect on cardiovascular (CV) morbidity and mortality in patients with established CV disease (CVD). The aim of this review is to summarize the knowledge regarding the discriminative abilities of conventional and novel biomarkers in T2DM patients with established HF or at higher risk of developing HF. While conventional biomarkers, such as natriuretic peptides and high-sensitivity troponins demonstrate high predictive ability in HF with reduced ejection fraction (HFrEF), this is not the case for HF with preserved ejection fraction (HFpEF). HFpEF is a heterogeneous disease with a high variability of CVD and conventional risk factors including T2DM, hypertension, renal disease, older age, and female sex; therefore, the extrapolation of predictive abilities of traditional biomarkers on this population is constrained. New biomarker-based approaches are disputed to be sufficient for improving risk stratification and the prediction of poor clinical outcomes in patients with HFpEF. Novel biomarkers of biomechanical stress, fibrosis, inflammation, oxidative stress, and collagen turn-over have shown potential benefits in determining prognosis in T2DM patients with HF regardless of natriuretic peptides, but their role in point-to-care and in routine practice requires elucidation in large clinical trials.

IGF-1 infusion to fetal sheep increases organ growth but not by stimulating nutrient transfer to the fetus

Insulin-like growth factor-1 (IGF-1) is an important fetal growth factor. However, the role of fetal IGF-1 in increasing placental blood flow, nutrient transfer, and nutrient availability to support fetal growth and protein accretion is not well understood. Catheterized fetuses from late gestation pregnant sheep received an intravenous infusion of LR3 IGF-1 (LR3 IGF-1; n = 8) or saline (SAL; n = 8) for 1 wk. Sheep then underwent a metabolic study to measure uterine and umbilical blood flow, nutrient uptake rates, and fetal protein kinetic rates. By the end of the infusion, fetal weights were not statistically different between groups (SAL: 3.260 ± 0.211 kg, LR3 IGF-1: 3.682 ± 0.183; P = 0.15). Fetal heart, adrenal gland, and spleen weights were higher (P < 0.05), and insulin was lower in LR3 IGF-1 (P < 0.05). Uterine and umbilical blood flow and umbilical uptake rates of glucose, lactate, and oxygen were similar between groups. Umbilical amino acid uptake rates were lower in LR3 IGF-1 (P < 0.05) as were fetal concentrations of multiple amino acids. Fetal protein kinetic rates were similar. LR3 IGF-1 skeletal muscle had higher myoblast proliferation (P < 0.05). In summary, LR3 IGF-1 infusion for 1 wk into late gestation fetal sheep increased the weight of some fetal organs. However, because umbilical amino acid uptake rates and fetal plasma amino acid concentrations were lower in the LR3 IGF-1 group, we speculate that animals treated with LR3 IGF-1 can efficiently utilize available nutrients to support organ-specific growth in the fetus rather than by stimulating placental blood flow or nutrient transfer to the fetus.NEW & NOTEWORTHY After a 1-wk infusion of LR3 IGF-1, late gestation fetal sheep had lower umbilical uptake rates of amino acids, lower fetal arterial amino acid and insulin concentrations, and lower fetal oxygen content; however, LR-3 IGF-1-treated fetuses were still able to effectively utilize the available nutrients and oxygen to support organ growth and myoblast proliferation.

Nutritional and developmental programming effects of insulin

The discovery of insulin in 1921 was a major breakthrough in medicine and for therapy in patients with diabetes. The dramatic rise in the prevalence of overweight and obesity has been tightly linked to an increased prevalence of gestational diabetes mellitus (GDM), which poses major health concerns. Babies born to GDM mothers are more likely to develop obesity, type 2 diabetes and cardiovascular disease later in life. Evidence accumulated during the past two decades has revealed that high levels insulin, such as those observed during GDM, can have a widespread effect on the development and function of a variety of organs. This review summarises our current knowledge on the role of insulin in the placenta, cardiovascular system and brain during critical periods of development, as well as how it can contribute to lifelong metabolic regulation. We also discuss possible intervention strategies to ameliorate and hopefully reverse the developmental defects associated with obesity and GDM.

Metabolic effects of carvedilol through β-arrestin proteins: investigations in a streptozotocin-induced diabetes rat model and in C2C12 myoblasts

BACKGROUND AND PURPOSE

Carvedilol is a third-generation β-adrenoceptor antagonist, which also stimulates β-arrestins. β-arrestins initiate intracellular signalling and are involved in insulin release and sensitivity. Carvedilol is superior in effectiveness to other drugs that are used for similar indications and does not cause insulin resistance or diabetes, which can occur with other β-antagonists. We have shown that carvedilol increased glucose usage in C2C12 cells. We investigate the biased agonist efficacy of carvedilol on β-arrestins.

EXPERIMENTAL APPROACH

Streptozotocin (STZ)-induced diabetes rat model was used to induce metabolic and cardiac disorders. After 8 weeks of diabetes, animals were treated with carvedilol or vehicle for another 4 weeks. In vitro heart function was evaluated at baseline as well as with increasing concentrations of isoprenaline. Effects of diabetes and carvedilol treatment on β-arrestins, ERK, PPARα, CD36 proteins and pyruvate kinase activity were evaluated. β-arrestins were silenced in C2C12 cells by using siRNA. Acute effects of carvedilol on ERK, CD36, mitochondrial transcription factor A, cardiolipin proteins and citrate synthase activity were investigated.

KEY RESULTS

Carvedilol reversed the deterioration of cardiac function in diabetes and diabetes-induced decrease in β-arrestins in rats. Carvedilol decreased the expression of CD36 in diabetes and increased mitochondrial transcription factor A and cardiolipin proteins. Silencing of β-arrestins in cells prevented the effects of carvedilol on these proteins.

CONCLUSION AND IMPLICATIONS

The metabolic effects of carvedilol seem to be related to biased activation of β-arrestins. Patients with cardiovascular and metabolic disorders may benefit from new compounds that selectively act on β-arrestins.

Molecular pathogenesis of heart failure in diabetes mellitus – new direction for the therapeutic approach

As it has been proven, cardiovascular diseases are several times more common in diabetic patients than in the general population. Despite many studies and hypotheses, is still not explained why this happens. Considering the frequent coexistence of cardiovascular risk factors with diabetes, the identification of diabetic cardiomyopathy as an independent complication is controversial, and diagnosis in clinical practice is rare. Nevertheless, the presence of diabetes significantly worsens the course and prognosis of cardiovascular diseases, and a better understanding of the diabetic component in the development of heart failure seems essential in the search for an effective therapy. The pathogenetic factors of the development of heart failure in diabetes include: metabolic disorders related to hyperglycaemia, lipotoxicity, insulin resistance, oxidative stress, immune system dysfunction, genetic predisposition and epigenetic disorders. The clinical pictures of diabetic cardiomyopathy vary depending on the type of diabetes, and dysfunction includes not only the cells of the myocardium, as well as stromal cells, endothelial and nervous system cells. The long-term and asymptomatic course of this complication and its progressive nature shortening the lives of diabetic patients prompt the search for new diagnostic and therapeutic methods. A better understanding of the molecular basis of myocardial dysfunction in diabetes appears essential in the search. Stopping the “cascade” of pathways responsible for activation of inflammation, fibrosis or apoptosis in individual organs could effectively prevent the development of diabetic complications. The paper presents existing pathogenetic concepts and their therapeutic implications, which may be used in the prevention of cardiovascular complications in diabetes and allow individualization of therapy.

Coronary vascular growth matches IGF-1-stimulated cardiac growth in fetal sheep

As loss of contractile function in heart disease could often be mitigated by increased cardiomyocyte number, expansion of cardiomyocyte endowment paired with increased vascular supply is a desirable therapeutic goal. Insulin-like growth factor 1 (IGF-1) administration increases fetal cardiomyocyte proliferation and heart mass, but how fetal IGF-1 treatment affects coronary growth and function is unknown. Near-term fetal sheep underwent surgical instrumentation and were studied from 127 to 134 d gestation (term = 147 d), receiving either IGF-1 LR3 or vehicle. Coronary growth and function were interrogated using pressure-flow relationships, an episode of acute hypoxia with progressive blockade of adenosine receptors and nitric oxide synthase, and by modeling the determinants of coronary flow. The main findings were that coronary conductance was preserved on a per-gram basis following IGF-1 treatment, adenosine and nitric oxide contributed to hypoxia-mediated coronary vasodilation similarly in IGF-1-treated and Control fetuses, and the relationships between coronary flow and blood oxygen contents were similar between groups. We conclude that IGF-1-stimulated fetal myocardial growth is accompanied by appropriate expansion and function of the coronary vasculature. These findings support IGF-1 as a potential strategy to increase cardiac myocyte and coronary vascular endowment at birth.

Glucocorticoid Maturation of Fetal Cardiovascular Function

The last decade has seen rapid advances in the understanding of the central role of glucocorticoids in preparing the fetus for life after birth. However, relative to other organ systems, maturation by glucocorticoids of the fetal cardiovascular system has been ignored. Here, we review the effects of glucocorticoids on fetal basal cardiovascular function and on the fetal cardiovascular defense responses to acute stress. This is important because glucocorticoid-driven maturational changes in fetal cardiovascular function under basal and stressful conditions are central to the successful transition from intra- to extrauterine life. The cost-benefit balance for the cardiovascular health of the preterm baby of antenatal glucocorticoid therapy administered to pregnant women threatened with preterm birth is also discussed.

Diabetic Cardiomyopathy: An Update of Mechanisms Contributing to This Clinical Entity

Heart failure and related morbidity and mortality are increasing at an alarming rate, in large part, because of increases in aging, obesity, and diabetes mellitus. The clinical outcomes associated with heart failure are considerably worse for patients with diabetes mellitus than for those without diabetes mellitus. In people with diabetes mellitus, the presence of myocardial dysfunction in the absence of overt clinical coronary artery disease, valvular disease, and other conventional cardiovascular risk factors, such as hypertension and dyslipidemia, has led to the descriptive terminology, diabetic cardiomyopathy. The prevalence of diabetic cardiomyopathy is increasing in parallel with the increase in diabetes mellitus. Diabetic cardiomyopathy is initially characterized by myocardial fibrosis, dysfunctional remodeling, and associated diastolic dysfunction, later by systolic dysfunction, and eventually by clinical heart failure. Impaired cardiac insulin metabolic signaling, mitochondrial dysfunction, increases in oxidative stress, reduced nitric oxide bioavailability, elevations in advanced glycation end products and collagen-based cardiomyocyte and extracellular matrix stiffness, impaired mitochondrial and cardiomyocyte calcium handling, inflammation, renin-angiotensin-aldosterone system activation, cardiac autonomic neuropathy, endoplasmic reticulum stress, microvascular dysfunction, and a myriad of cardiac metabolic abnormalities have all been implicated in the development and progression of diabetic cardiomyopathy. Molecular mechanisms linked to the underlying pathophysiological changes include abnormalities in AMP-activated protein kinase, peroxisome proliferator-activated receptors, O-linked N-acetylglucosamine, protein kinase C, microRNA, and exosome pathways. The aim of this review is to provide a contemporary view of these instigators of diabetic cardiomyopathy, as well as mechanistically based strategies for the prevention and treatment of diabetic cardiomyopathy.

A Transcriptomic Model of Postnatal Cardiac Effects of Prenatal Maternal Cortisol Excess in Sheep

In utero treatment with glucocorticoids have been suggested to reprogram postnatal cardiovascular function and stress responsiveness. However, little is known about the effects of prenatal exposure to the natural corticosteroid, cortisol, on postnatal cardiovascular system or metabolism. We have demonstrated an increased incidence of stillbirth in sheep pregnancies in which there is mild maternal hypercortisolemia caused by infusion of 1 mg/kg/d cortisol. In order to model corticosteroid effects in the neonate, we created a second model in which cortisol was infused for 12 h per day for a daily infusion of 0.5 mg/kg/d. In this model we had previously found that neonatal plasma glucose was increased and plasma insulin was decreased compared to those in the control group, and that neonatal ponderal index and kidney weight were reduced and left ventricular wall thickness was increased in the 2 week old lamb. In this study, we have used transcriptomic modeling to better understand the programming effect of this maternal hypercortisolemia in these hearts. This is a time when both terminal differentiation and a shift in the metabolism of the heart from carbohydrates to lipid oxidation are thought to be complete. The transcriptomic model indicates suppression of genes in pathways for fatty acid and ketone production and upregulation of genes in pathways for angiogenesis in the epicardial adipose fat (EAT). The transcriptomic model indicates that RNA related pathways are overrepresented by downregulated genes, but ubiquitin-mediated proteolysis and protein targeting to the mitochondria are overrepresented by upregulated genes in the intraventricular septum (IVS) and left ventricle (LV). In IVS the AMPK pathway and adipocytokine signaling pathways were also modeled based on overrepresentation by downregulated genes. Peroxisomal activity is modeled as increased in EAT, but decreased in LV and IVS. Our results suggest that pathways for lipids as well as cell proliferation and cardiac remodeling have altered activity postnatally after the in utero cortisol exposure. Together, this model is consistent with the observed increase in cardiac wall thickness at necropsy and altered glucose metabolism observed in vivo, and predicts that in utero exposure to excess maternal cortisol will cause postnatal cardiac hypertrophy and altered responses to oxidative stress.

Thyroid hormone signaling and consequences for cardiac development

The fetal heart undergoes its own growth and maturation stages all while supplying blood and nutrients to the growing fetus and its organs. Immature contractile cardiomyocytes proliferate to rapidly increase and establish cardiomyocyte endowment in the perinatal period. Maturational changes in cellular maturation, size and biochemical capabilities occur, and require, a changing hormonal environment as the fetus prepares itself for the transition to extrauterine life. Thyroid hormone has long been known to be important for neuronal development, but also for fetal size and survival. Fetal circulating 3,5,3'-triiodothyronine (T3) levels surge near term in mammals and are responsible for maturation of several organ systems, including the heart. Growth factors like insulin-like growth factor-1 stimulate proliferation of fetal cardiomyocytes, while thyroid hormone has been shown to inhibit proliferation and drive maturation of the cells. Several cell signaling pathways appear to be involved in this complicated and coordinated process. The aim of this review was to discuss the foundational studies of thyroid hormone physiology and the mechanisms responsible for its actions as we speculate on potential fetal programming effects for cardiovascular health.

Right Ventricular Involution: Big Changes in Small Hearts

BACKGROUND

Before birth, the fetal right ventricle (RV) is the pump for the systemic circulation and is about as thick as the left ventricle (LV). After birth, the RV becomes the pump for the lower pressure pulmonary circulation, and the RV chamber elongates without change in its wall thickness. We hypothesize that the fetal RV may be a model of compensated RV hypertrophy, and understanding this process may aid in discovering therapeutic strategies for RV failure.

METHODS

We performed a literature review and identified pertinent articles from 1980 to present.

RESULTS

The following topics were identified to be most pertinent in right ventricular involution: morphologic and histologic changes of the RV, cellular proliferation and terminal differentiation, the effect of stress on RV development, excitation contraction coupling and inotropic response change over time, and the amount of apoptosis through RV development.

CONCLUSIONS

The RV changes on multiple levels after its transition from systemic to pulmonary circulation. Although published literature has variable results due partly from differences between animal models, the literature shows a clear need for more research in the field.

Thyroid hormone receptor function in maturing ovine cardiomyocytes

KEY POINTS

Plasma thyroid hormone (tri-iodo-l-thyronine; T3 ) concentrations rise near the end of gestation and is known to inhibit proliferation and stimulate maturation of cardiomyocytes before birth. Thyroid hormone receptors are required for the action of thyroid hormone in fetal cardiomyocytes. Loss of thyroid hormone receptor (TR)α1 abolishes T3 signalling via extracellular signal-related kinase and Akt in fetal cardiomyocytes. The expression of TRα1 and TRβ1 in ovine fetal myocardium increases with age, although TRα1 levels always remain higher than those of TRβ1. Near term fetal cardiac myocytes are more sensitive than younger myocytes to thyroid receptor blockade by antagonist, NH3, and to the effects of TRα1/α2 short interfering RNA. Although T3 is known to abrogate ovine cardiomyocyte proliferation stimulated by insulin-like growth factor 1, this effect is mediated via the genomic action of thyroid hormone receptors, with little evidence for non-genomic mechanisms.

ABSTRACT

We have previously shown that the late-term rise in tri-iodo-l-thyronine (T3 ) in fetal sheep leads to the inhibition of proliferation and promotion of maturation in cardiomyocytes. The present study was designed to determine whether these T3 -induced changes are mediated via thyroid hormone receptors (TRs) or by non-genomic mechanisms. Fetal cardiomyocytes were isolated from 102 ± 3 and 135 ± 1 days of gestational age (dGA) sheep (n = 7 per age; term ∼145 dGA). Cells were treated with T3 (1.5 nm), insulin-like growth factor (IGF)-1 (1 μg mL-1 ) or a combination in the presence of TR antagonist NH3 (100 nm) or following short interfering RNA (siRNA) knockdown of TRα1/α2. Proliferation was quantified by 5-bromo-2'-deoxyuridine (BrdU) uptake (10 μm). Western blots measured protein levels of extracellular signal-related kinase (ERK), Akt, TRα1/β1 and p21. Age specific levels of TRα1/β1 were measured in normal hearts from fetuses [95 dGA (n = 8), 135 dGA (n = 7)], neonates (n = 8) and adult ewes (n = 7). TRα1 protein levels were consistently >50% more than TRβ1 at each gestational age (P < 0.05). T3 reduced IGF-1 stimulated proliferation by ∼50% in 100 dGA and by ∼75% in 135 dGA cardiomyocytes (P < 0.05). NH3 blocked the T3  + IGF-1 reduction of BrdU uptake without altering the phosphorylation of ERK or Akt at both ages. NH3 did not suppress T3 -induced p21 expression in 100 dGA cardiomyocytes in 135 dGA cardiomyocytes, NH3 alone reduced BrdU uptake (-28%, P < 0.05), as well as T3 -induced p21 (-75%, P < 0.05). In both ages, siRNA knockdown of TRα1/α2 blocked the T3  + IGF-1 reduction of BrdU uptake and dramatically reduced ERK and Akt signalling in 135 dGA cardiomyocytes. In conclusion, TRs are required for normal proliferation and T3 signalling in fetal ovine cardiomyocytes, with the sensitivity to TR blockade being age-dependent.

Right ventricular remodeling in response to volume overload in fetal sheep

The fetal myocardium is known to be sensitive to hemodynamic load, responding to systolic overload with cellular hypertrophy, proliferation, and accelerated maturation. However, the fetal cardiac growth response to primary volume overload is unknown. We hypothesized that increased venous return would stimulate fetal cardiomyocyte proliferation and terminal differentiation, particularly in the right ventricle (RV). Vascular catheters and pulmonary artery flow probes were implanted in 16 late-gestation fetal sheep: a right carotid artery-jugular vein (AV) fistula was surgically created in nine fetuses, and sham operations were performed on seven fetuses. Instrumented fetuses were studied for 1 wk before hearts were dissected for component analysis or cardiomyocyte dispersion for cellular measurements. Within 1 day of AV fistula creation, RV output was 20% higher in experimental than sham fetuses ( P < 0.0001). Circulating atrial natriuretic peptide levels were elevated fivefold in fetuses with an AV fistula ( P < 0.002). On the terminal day, RV-to-body weight ratios were 35% higher in the AV fistula group ( P < 0.05). Both left ventricular and RV cardiomyocytes grew longer in fetuses with an AV fistula ( P < 0.02). Cell cycle activity was depressed by >50% [significant in left ventricle ( P < 0.02), but not RV ( P < 0.054)]. Rates of terminal differentiation were unchanged. Based on these studies, we speculate that atrial natriuretic peptide suppressed fetal cardiomyocyte cell cycle activity. Unlike systolic overload, fetal diastolic load appears to drive myocyte enlargement, but not cardiomyocyte proliferation or maturation. These changes could predispose to RV dysfunction later in life. NEW & NOTEWORTHY Adaptation of the fetal heart to changes in cardiac load allows the fetus to maintain adequate blood flow to its systemic and placental circulations, which is necessary for the well-being of the fetus. Addition of arterial-venous fistula flow to existing venous return increased right ventricular stroke volume and output. The fetal heart compensated by cardiomyocyte elongation without accelerated cellular maturation, while cardiomyocyte proliferation decreased. Even transient volume overload in utero alters myocardial structure and cardiomyocyte endowment.

Mechanisms of Sex Disparities in Cardiovascular Function and Remodeling

Epidemiological studies demonstrate disparities between men and women in cardiovascular disease prevalence, clinical symptoms, treatments, and outcomes. Enrollment of women in clinical trials is lower than men, and experimental studies investigating molecular mechanisms and efficacy of certain therapeutics in cardiovascular disease have been primarily conducted in male animals. These practices bias data interpretation and limit the implication of research findings in female clinical populations. This review will focus on the biological origins of sex differences in cardiovascular physiology, health, and disease, with an emphasis on the sex hormones, estrogen and testosterone. First, we will briefly discuss epidemiological evidence of sex disparities in cardiovascular disease prevalence and clinical manifestation. Second, we will describe studies suggesting sexual dimorphism in normal cardiovascular function from fetal life to older age. Third, we will summarize and critically discuss the current literature regarding the molecular mechanisms underlying the effects of estrogens and androgens on cardiac and vascular physiology and the contribution of these hormones to sex differences in cardiovascular disease. Fourth, we will present cardiovascular disease risk factors that are positively associated with the female sex, and thus, contributing to increased cardiovascular risk in women. We conclude that inclusion of both men and women in the investigation of the role of estrogens and androgens in cardiovascular physiology will advance our understanding of the mechanisms underlying sex differences in cardiovascular disease. In addition, investigating the role of sex-specific factors in the development of cardiovascular disease will reduce sex and gender disparities in the treatment and diagnosis of cardiovascular disease. © 2019 American Physiological Society. Compr Physiol 9:375-411, 2019.

The role of miRNA regulation in fetal cardiomyocytes, cardiac maturation and the risk of heart disease in adults

Myocardial infarction is a primary contributor towards the global burden of cardiovascular disease. Rather than repairing the existing damage of myocardial infarction, current treatments only address the symptoms of the disease and reducing the risk of a secondary infarction. Cardiac regenerative capacity is dependent on cardiomyocyte proliferation, which concludes soon after birth in humans and precocial species such as sheep. Human fetal cardiac tissue has some ability to repair following tissue damage, whereas a fully matured human heart has minimal capacity for cellular regeneration. This is in contrast to neonatal mice and adult zebrafish hearts, which retain the ability to undergo cardiomyocyte proliferation and can regenerate cardiac tissue after birth. In mice and zebrafish models, microRNAs (miRNAs) have been implicated in the regulation of genes involved in cardiac cell cycle progression and regeneration. However, the significance of miRNA regulation in cardiomyocyte proliferation for humans and other large mammals, where the timing of heart development in relation to birth is similar, remains unclear. miRNAs may be valuable targets for therapies that promote cardiac repair after injury. Therefore, elucidating the role of specific miRNAs in large animals, where heart development closely resembles that of humans, remains vitally important for identifying therapeutic targets that may be translated into clinical practice focused on tissue repair.

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.

IUGR impairs cardiomyocyte growth and maturation in fetal sheep

Placental insufficiency causes intrauterine growth restriction (IUGR), a common complication of pregnancy. In skeletal muscle, IUGR reduces fetal myofibril size, reduces myoblast proliferation and reduces expression of genes in cell cycle regulation clusters. The myocardium is striated like skeletal muscle, and IUGR also reduces cell cycle activity and maturation in cardiomyocytes, despite cardiac output preferentially directed to the coronary circulation. We hypothesized that cardiomyocyte growth restriction would be accompanied by similar changes in cell cycle regulation genes and would reduce cardiomyocyte cell cycle activity, number, maturity and size. Pregnant ewes were housed in elevated ambient temperatures from ~40 to ~115 days of gestation (dGA) to produce placental insufficiency and IUGR; fetal hearts were studied at ~134 dGA. Hearts were biopsied for mRNA analysis and then dissociated into individual myocytes (Control n = 8; IUGR n = 15) or dissected (Control n = 9; IUGR n = 13). IUGR fetuses had low circulating insulin and insulin-like growth factor 1 (IGF1) and high circulating cortisol. Bodies and hearts of IUGR fetuses were lighter than those of Controls. Cardiomyocytes of IUGR fetuses were smaller, less mature, less active in the cell cycle and less numerous than in Controls. Further, there was a pattern of downregulation of cell cycle genes in IUGR ventricles. IUGR growth profiles in heart and skeletal muscle suggest similar regulation despite differences in blood and nutrient delivery prioritization. IGF1 signaling is suggested as a mechanism regulating altered growth in IUGR striated muscle and a potential therapeutic candidate.

Maternal obesity impairs fetal cardiomyocyte contractile function in sheep

Obesity is a major public health problem worldwide. In the United States, one-third of women of reproductive age are obese. Human studies show that maternal obesity (MO) predisposes offspring to cardiovascular disease. However, the underlying mechanisms remain unclear. Given the similarities between pregnancy in sheep and humans, we studied sheep to examine the impact of MO on fetal cardiomyocyte contractility at term. We observed that MO impaired cardiomyocyte contractility by reducing peak shortening and shortening/relengthening velocity, prolonging time to relengthening. MO disrupted Ca²⁺ homeostasis in fetal cardiomyocytes, increasing intracellular Ca²⁺ and inducing cellular Ca²⁺ insensitivity. The Ca²⁺-release channel was impaired, but Ca²⁺ uptake was unaffected by MO. The upstream kinases that phosphorylate the Ca²⁺-release channel-ryanodine receptor-2, PKA, and calmodulin-dependent protein kinase II-were activated in MO fetuses. Contractile dysfunction was associated with an increased ratio of myosin heavy chain (MHC)-β to MHC-α and upregulated cardiac troponin (cTn)-T and tropomyosin, as well as cTn-I phosphorylation. In summary, this is the first characterization of the effects of MO on fetal cardiomyocyte contractility. Our findings indicate that MO impairs fetal cardiomyocyte contractility through altered intracellular Ca²⁺ handling, overloading fetal cardiomyocyte intracellular Ca²⁺ and aberrant myofilament protein composition. These mechanisms may contribute to developmental programming by MO of offspring cardiac function and predisposition to later life cardiovascular disease in the offspring.-Wang, Q., Zhu, C., Sun, M., Maimaiti, R., Ford, S. P., Nathanielsz, P. W., Ren, J., Guo, W. Maternal obesity impairs fetal cardiomyocyte contractile function in sheep.

Systemic arterial hypertension but not IGF-I treatment stimulates cardiomyocyte enlargement in neonatal lambs

Although cardiomyocyte terminal differentiation is nearly complete at birth in sheep, as in humans, very limited postnatal expansion of myocyte number may occur. The capacity of newborn cardiomyocytes to respond to growth stimulation by proliferation is poorly understood. Our objective was to test this growth response in newborn lambs with two stimuli shown to be potent inducers of cardiomyocyte growth in fetuses and adults: increased systolic load (Load) and insulin-like growth factor I (IGF-I). Vascular catheters and an inflatable aortic occluder were implanted in lambs. Hearts were collected for analysis at 18 days of age after a 7-day experiment and compared with control hearts. Load hearts, but not IGF-I hearts, were heavier ( P = 0.001) because of increased mass of the left ventricle (LV), septum, and left atrium (40-50%, P = 0.004). Terminal differentiation and cell cycle activity were not different between groups. Myocyte length was 7% greater in Load lamb hearts ( P < 0.05), and binucleated myocytes, which comprise ~90% of LV cells, were 25% larger in volume ( P = 0.03). Myocyte number per gram of myocardium was decreased in all ventricles of Load lambs ( P = 0.01). Cells from the IGF-I group were not different by any comparison. These results suggest that the newborn sheep LV responds to systolic stress with cardiomyocyte hypertrophy, not proliferation. Furthermore, IGF-I is ineffective at stimulating cardiomyocyte proliferation at this age (despite effectiveness when administered before birth). Thus, to expand cardiomyocyte number in the newborn heart, therapies other than systolic pressure load and IGF-I treatment need to be developed.

A 1 week IGF-1 infusion decreases arterial insulin concentrations but increases pancreatic insulin content and islet vascularity in fetal sheep

Fetal insulin is critical for regulation of growth. Insulin concentrations are partly determined by the amount of β-cells present and their insulin content. Insulin-like growth factor-1 (IGF-1) is a fetal anabolic growth factor which also impacts β-cell mass in models of β-cell injury and diabetes. The extent to which circulating concentrations of IGF-1 impact fetal β-cell mass and pancreatic insulin content is unknown. We hypothesized that an infusion of an IGF-1 analog for 1 week into the late gestation fetal sheep circulation would increase β-cell mass, pancreatic islet size, and pancreatic insulin content. After the 1-week infusion, pancreatic insulin concentrations were 80% higher than control fetuses (P < 0.05), but there were no differences in β-cell area, β-cell mass, or pancreatic vascularity. However, pancreatic islet vascularity was 15% higher in IGF-1 fetuses and pancreatic VEGFA, HGF, IGF1, and IGF2 mRNA expressions were 70-90% higher in IGF-1 fetuses compared to control fetuses (P < 0.05). Plasma oxygen, glucose, and insulin concentrations were 25%, 22%, and 84% lower in IGF-1 fetuses, respectively (P < 0.05). The previously described role for IGF-1 as a β-cell growth factor may be more relevant for local paracrine signaling in the pancreas compared to circulating endocrine signaling.

Near to One's Heart: The Intimate Relationship Between the Placenta and Fetal Heart

The development of the fetal heart is exquisitely controlled by a multitude of factors, ranging from humoral to mechanical forces. The gatekeeper regulating many of these factors is the placenta, an external fetal organ. As such, resistance within the placental vascular bed has a direct influence on the fetal circulation and therefore, the developing heart. In addition, the placenta serves as the interface between the mother and fetus, controlling substrate exchange and release of hormones into both circulations. The intricate relationship between the placenta and fetal heart is appreciated in instances of clinical placental pathology. Abnormal umbilical cord insertion is associated with congenital heart defects. Likewise, twin-to-twin transfusion syndrome, where monochorionic twins have unequal sharing of their placenta due to inter-twin vascular anastomoses, can result in cardiac remodeling and dysfunction in both fetuses. Moreover, epidemiological studies have suggested a link between placental phenotypic traits and increased risk of cardiovascular disease in adult life. To date, the mechanistic basis of the relationships between the placenta, fetal heart development and later risk of cardiac dysfunction have not been fully elucidated. However, studies using environmental exposures and gene manipulations in experimental animals are providing insights into the pathways involved. Likewise, surgical instrumentation of the maternal and fetal circulations in large animal species has enabled the manipulation of specific humoral and mechanical factors to investigate their roles in fetal cardiac development. This review will focus on such studies and what is known to date about the link between the placenta and heart development.

In utero programming and early detection of cardiovascular disease in the offspring of mothers with obesity

The offspring of women with obesity during their pregnancy are exposed to an altered intra-uterine environment. A subsequent influence on the cardiovascular development during fetal life is assumed. In the present thematic review, we report on the current knowledge about this early development of cardiovascular disease from fetal life until adolescence. Based on animal studies, different contributing mechanisms have been hypothesized that still need confirmation in human subjects. Insulin resistance, increased levels of leptin, chronic inflammatory state, perturbation of sympathetic tone and epigenetic modifications contribute to a suboptimal nutrient environment and changed hemodynamics. The ensuing aberrant cardiomyocyte development, impaired endothelial cell relaxation and atherogenic lipid profile put these children at risk for the development of endothelial cell dysfunction. Increasing possibilities for early detection of this preliminary stage of atherosclerotic disease offer new insights into future prevention and treatment strategies. Future research should focus on further unraveling the effect of moderate intense, aerobic exercise. Since it is used to treat the condition in children and adolescents with good results, it might be a contributor to tackling endothelial cell dysfunction at its cradle when applied in early pregnancy.

Cardiac Outcomes After Perinatal Sertraline Exposure in Mice

Selective serotonin reuptake inhibitors are prescribed to 6%-10% of pregnant women in the United States. Using an intrauterine plus neonatal exposure model to represent exposure throughout human pregnancy, we hypothesized sertraline exposure would impact intracardiac serotonin signaling and lead to small left heart syndrome in the absence of maternal psychopathology. C57BL/6 adult female mice received sertraline (5 mg·kg·d IP) or saline throughout pregnancy to time of delivery. Pups maintained exposure on postnatal days 1-14 to encompass the developmental window analogous to human gestation. Sertraline-exposed mice had increased cardiac hydroxyproline content, decreased 5-HT2B receptor mRNA levels, and increased 5-HT2A receptor and serotonin transporter mRNA levels on postnatal day 21 (P < 0.05). These changes were associated with diminished exercise capacity at 6 weeks (P < 0.05) and decreased adult shortening fraction and stroke volume at 5 months. Isolated cardiomyocytes from neonatal sertraline-exposed mice had significantly decreased proliferation, cross-sectional area, and phosphorylation of Akt (P < 0.05 vs. neonatal control mice). Perinatal sertraline exposure alters neonatal cardiac development and produces long-standing changes in adult cardiac function and exercise capacity. Further studies are needed to assess whether similar findings are present in the growing population that has been exposed to selective serotonin reuptake inhibitors during development.

The role of the tumor necrosis factor (TNF)-related weak inducer of apoptosis (TWEAK) in offspring exposed to prenatal hypoxia

Exposure to prenatal hypoxia in rats leads to intrauterine growth restriction (IUGR), decreases fetal cardiomyocyte proliferation and increases the risk to develop cardiovascular diseases (CVD) later in life. The tumor necrosis factor-related weak inducer of apoptosis (TWEAK) induces cardiomyocyte proliferation through activation of the fibroblast growth factor-inducible molecule 14 (Fn-14) receptor. The TWEAK/Fn-14 pathway becomes quiescent shortly after birth, however, it becomes upregulated with CVD; suggesting that it could be a link between the increased susceptibility to CVD in pregnancies complicated by hypoxia/IUGR. We hypothesized that offspring exposed to prenatal hypoxia will exhibit reduced cardiomyocyte proliferation due to reduced Fn-14 expression and that the TWEAK/Fn-14 pathway will be expressed in those adult offspring. We exposed pregnant Sprague Dawley rats to control (21% oxygen) or hypoxic (11% oxygen) conditions from gestational days 15 to 21. Ventricular cardiomyocytes were isolated from male and female, control and hypoxic offspring at postnatal day 1. Proliferation was assessed in the presence or absence of r-TWEAK (72 h, 100 ng/ml). Prenatal hypoxia was not associated with differences in Fn-14 protein expression in either male or female offspring. Cardiomyocytes from prenatal hypoxic male, but not female, offspring had decreased proliferation compared with controls. Addition of r-TWEAK increased cardiomyocyte proliferation in all offspring. In adult offspring of all groups, the TWEAK/Fn-14 pathway was not detectable. Cardiomyocyte proliferation was reduced in only male offspring exposed to prenatal hypoxia but this was not due to changes in the Fn-14 pathway. Studies addressing other pathways associated with CVD and prenatal hypoxia are needed.

Skeletal muscle protein accretion rates and hindlimb growth are reduced in late gestation intrauterine growth-restricted fetal sheep

KEY POINTS

Adults who were affected by intrauterine growth restriction (IUGR) suffer from reductions in muscle mass, which may contribute to insulin resistance and the development of diabetes. We demonstrate slower hindlimb linear growth and muscle protein synthesis rates that match the reduced hindlimb blood flow and oxygen consumption rates in IUGR fetal sheep. These adaptations resulted in hindlimb blood flow rates in IUGR that were similar to control fetuses on a weight-specific basis. Net hindlimb glucose uptake and lactate output rates were similar between groups, whereas amino acid uptake was significantly lower in IUGR fetal sheep. Among all fetuses, blood O₂ saturation and plasma glucose, insulin and insulin-like growth factor-1 were positively associated and norepinephrine was negatively associated with hindlimb weight. These results further our understanding of the metabolic and hormonal adaptations to reduced oxygen and nutrient supply with placental insufficiency that develop to slow hindlimb growth and muscle protein accretion.

ABSTRACT

Reduced skeletal muscle mass in the fetus with intrauterine growth restriction (IUGR) persists into adulthood and may contribute to increased metabolic disease risk. To determine how placental insufficiency with reduced oxygen and nutrient supply to the fetus affects hindlimb blood flow, substrate uptake and protein accretion rates in skeletal muscle, late gestation control (CON) (n = 8) and IUGR (n = 13) fetal sheep were catheterized with aortic and femoral catheters and a flow transducer around the external iliac artery. Muscle protein kinetic rates were measured using isotopic tracers. Hindlimb weight, linear growth rate, muscle protein accretion rate and fractional synthetic rate were lower in IUGR compared to CON (P < 0.05). Absolute hindlimb blood flow was reduced in IUGR (IUGR: 32.9 ± 5.6 ml min^-1 ; CON: 60.9 ± 6.5 ml min^-1 ; P < 0.005), although flow normalized to hindlimb weight was similar between groups. Hindlimb oxygen consumption rate was lower in IUGR (IUGR: 10.4 ± 1.4 μmol min^-1  100 g^-1 ; CON: 14.7 ± 1.3 μmol min^-1  100 g^-1 ; P < 0.05). Hindlimb glucose uptake and lactate output rates were similar between groups, whereas amino acid uptake was lower in IUGR (IUGR: 1.3 ± 0.5 μmol min^-1  100 g^-1 ; CON: 2.9 ± 0.2 μmol min^-1  100 g^-1 ; P < 0.05). Blood O₂ saturation (r²  = 0.80, P < 0.0001) and plasma glucose (r²  = 0.68, P < 0.0001), insulin (r²  = 0.40, P < 0.005) and insulin-like growth factor (IGF)-1 (r²  = 0.80, P < 0.0001) were positively associated and norepinephrine (r²  = 0.59, P < 0.0001) was negatively associated with hindlimb weight. Slower hindlimb linear growth and muscle protein synthesis rates match reduced hindlimb blood flow and oxygen consumption rates in the IUGR fetus. Metabolic adaptations to slow hindlimb growth are probably hormonally-mediated by mechanisms that include increased fetal norepinephrine and reduced IGF-1 and insulin.

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 Mitogen-Activated Protein Kinases and Akt Are Developmentally Regulated in the Chronically Anemic Fetal Sheep Heart

OBJECTIVE

Protein kinase B (Akt) and the mitogen-activated protein kinases (MAPKs) mediate hypertrophy in the adult heart, although their importance in the developing heart is poorly understood. The goal of the current study was to determine if volume loading the fetal heart resulting from chronic anemia affects regulation of Akt and the MAPKs and if this response is developmentally regulated.

METHODS

Anemia was created by 7 days of isovolumic hemorrhage beginning at 101 days (early GA) or 129 days (late GA) gestational age (GA) in fetal sheep (term = 145 days), following which protein levels of total and active Akt, extracellular signal-regulated kinase 1/2 (ERK1/2), c-Jun NH2-terminal kinase (JNK), and p38 were determined in the right and left ventricle (RV and LV). RV protein-to-DNA ratios were also assessed.

RESULTS

At both GAs, ventricular (RV + LV + septum) weight normalized to body weight was significantly increased in anemic fetuses. Anemia had no effect on expression of myocardial total or active Akt, JNK, or p38 at either GA. Levels of total ERK1/2 were also unchanged, although active ERK1/2 was significantly decreased in the late but not early GA anemic fetuses. Total JNK and total and active ERK1/2 and Akt were significantly greater in early versus late GA anemic fetuses. Protein-to-DNA ratios were unchanged in response to anemia at both GAs, but were greater in late GA compared to early GA anemic fetuses.

CONCLUSION

These results identify important developmental differences in the response of the MAPKs and Akt in the stressed fetal heart. Differences in protein-to-DNA ratios likely reflect the different populations of cardiomyocytes composing the fetal heart at these two GAs and their cell-dependent response to a hemodynamic load.

Endogenous Mechanisms of Cardiac Regeneration

Zebrafish possess a remarkable capacity for cardiac regeneration throughout their lifetime, providing a model for investigating endogenous cellular and molecular mechanisms regulating myocardial regeneration. By contrast, adult mammals have an extremely limited capacity for cardiac regeneration, contributing to mortality and morbidity from cardiac diseases such as myocardial infarction and heart failure. However, the viewpoint of the mammalian heart as a postmitotic organ was recently revised based on findings that the mammalian heart contains multiple undifferentiated cell types with cardiogenic potential as well as a robust regenerative capacity during a short period early in life. Although it occurs at an extremely low level, continuous cardiomyocyte turnover has been detected in adult mouse and human hearts, which could potentially be enhanced to restore lost myocardium in damaged human hearts. This review summarizes and discusses recent advances in the understanding of endogenous mechanisms of cardiac regeneration.

Endocrine and other physiologic modulators of perinatal cardiomyocyte endowment

Immature contractile cardiomyocytes proliferate to rapidly increase cell number, establishing cardiomyocyte endowment in the perinatal period. Developmental changes in cellular maturation, size and attrition further contribute to cardiac anatomy. These physiological processes occur concomitant with a changing hormonal environment as the fetus prepares itself for the transition to extrauterine life. There are complex interactions between endocrine, hemodynamic and nutritional regulators of cardiac development. Birth has been long assumed to be the trigger for major differences between the fetal and postnatal cardiomyocyte growth patterns, but investigations in normally growing sheep and rodents suggest this may not be entirely true; in sheep, these differences are initiated before birth, while in rodents they occur after birth. The aim of this review is to draw together our understanding of the temporal regulation of these signals and cardiomyocyte responses relative to birth. Further, we consider how these dynamics are altered in stressed and suboptimal intrauterine environments.

Regulation of microRNA during cardiomyocyte maturation in sheep

Background

There is a limited capacity to repair damage in the mammalian heart after birth, which is primarily due to the inability of cardiomyocytes to proliferate after birth. This is in contrast to zebrafish and salamander, in which cardiomyocytes retain the ability to proliferate throughout life and can regenerate their heart after significant damage. Recent studies in zebrafish and rodents implicate microRNA (miRNA) in the regulation of genes responsible for cardiac cell cycle progression and regeneration, in particular, miR-133a, the miR-15 family, miR-199a and miR-590. However, the significance of these miRNA and miRNA in general in the regulation of cardiomyocyte proliferation in large mammals, including humans, where the timing of heart development relative to birth is very different than in rodents, is unclear. To determine the involvement of miRNA in the down-regulation of cardiomyocyte proliferation occurring before birth in large mammals, we investigated miRNA and target gene expression in sheep hearts before and after birth. The experimental approach included targeted transcriptional profiling of miRNA and target mRNA previously identified in rodent studies as well as genome-wide miRNA profiling using microarrays.

Results

The cardiac expression of miR-133a increased and its target gene IGF1R decreased with increasing age, reaching their respective maximum and minimum abundance when the majority of ovine cardiomyocytes were quiescent. The expression of the miR-15 family members was variable with age, however, four of their target genes decreased with age. These latter profiles are inconsistent with the direct involvement of this family of miRNA in cardiomyocyte quiescence in late gestation sheep. The expression patterns of ‘pro-proliferative’ miR-199a and miR-590 were also inconsistent with their involvement in cardiomyocyte quiescence. Consequently, miRNA microarray analysis was undertaken, which identified six discrete clusters of miRNA with characteristic developmental profiles. The functions of predicted target genes for the miRNA in four of the six clusters were enriched for aspects of cell division and regulation of cell proliferation suggesting a potential role of these miRNA in regulating cardiomyocyte proliferation.

Conclusion

The results of this study show that the expression of miR-133a and one of its target genes is consistent with it being involved in the suppression of cardiomyocyte proliferation, which occurs across the last third of gestation in sheep. The expression patterns of the miR-15 family, miR-199a and miR-590 were inconsistent with direct involvement in the regulation cardiomyocyte proliferation in sheep, despite studies in rodents demonstrating that their manipulation can influence the degree of cardiomyocyte proliferation. miRNA microarray analysis suggests a coordinated and potentially more complex role of multiple miRNA in the regulation of cardiomyocyte quiescence and highlights significant differences between species that may reflect their substantial differences in the timing of this developmental process.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1693-z) contains supplementary material, which is available to authorized users.

The programming of cardiovascular disease

In spite of improving life expectancy over the course of the previous century, the health of the U.S. population is now worsening. Recent increasing rates of type 2 diabetes, obesity and uncontrolled high blood pressure predict a growing incidence of cardiovascular disease and shortened average lifespan. The daily >$1billion current price tag for cardiovascular disease in the United States is expected to double within the next decade or two. Other countries are seeing similar trends. Current popular explanations for these trends are inadequate. Rather, increasingly poor diets in young people and in women during pregnancy are a likely cause of declining health in the U.S. population through a process known as programming. The fetal cardiovascular system is sensitive to poor maternal nutritional conditions during the periconceptional period, in the womb and in early postnatal life. Developmental plasticity accommodates changes in organ systems that lead to endothelial dysfunction, small coronary arteries, stiffer vascular tree, fewer nephrons, fewer cardiomyocytes, coagulopathies and atherogenic blood lipid profiles in fetuses born at the extremes of birthweight. Of equal importance are epigenetic modifications to genes driving important growth regulatory processes. Changes in microRNA, DNA methylation patterns and histone structure have all been implicated in the cardiovascular disease vulnerabilities that cross-generations. Recent experiments offer hope that detrimental epigenetic changes can be prevented or reversed. The large number of studies that provide the foundational concepts for the developmental origins of disease can be traced to the brilliant discoveries of David J.P. Barker.

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.

Impact of maternal obesity on fetal programming of cardiovascular disease

The in utero environment is a key determinant of long-term health outcomes; poor maternal metabolic state and placental insufficiency are strongly associated with these long-term health risks. Human epidemiological studies link maternal obesity and offspring cardiovascular disease in later life, but mechanistic studies in animal models are limited. Here, we review the literature pertaining to maternal consequences of obesity during pregnancy and the subsequent impact on fetal cardiovascular development.

Thyroid hormone does not induce maturation of embryonic chicken cardiomyocytes in vitro

Fetal cardiac growth in mammalian models occurs primarily by cell proliferation (hyperplasia). However, most cardiomyocytes lose the ability to proliferate close to term and heart growth continues by increasing cell size (hypertrophy). In mammals, the thyroid hormone triiodothyronine (T₃) is an important driver of this process. Chicken cardiomyocytes, however, keep their proliferating ability long after hatching but little information is available on the mechanisms controlling cell growth and myocyte maturation in the chicken heart. Our aim was to study the role of T₃ on proliferation and differentiation of embryonic chicken cardiomyocytes (ECCM), enzymatically isolated from 19‐day‐old embryos and to compare the effects to those of insulin‐like growth factor‐1 (IGF‐1) and phenylephrine (PE). Hyperplasia was measured using a proliferation assay (MTS) and hypertrophy/multinucleation was analyzed morphologically by phalloidin staining of F‐actin and nuclear staining with DAPI. We show that IGF‐1 induces a significant increase in ECCM proliferation (30%) which is absent with T₃ and PE. PE induced both hypertrophy (61%) and multinucleation (41%) but IGF‐1 or T₃ did not. In conclusion, we show that T₃ does not induce maturation or proliferation of cardiomyocytes, while IGF‐1 induces cardiomyocyte proliferation and PE induces maturation of cardiomyocytes.

Our main findings in the study show that T₃ does not affect proliferation or maturation of embryonic chicken cardiomyocytes (ECCMs). Furthermore, phenylephrine induces maturation of ECCMs and IGF‐1 act as a pro‐proliferative mediator.

Elevated neonatal insulin-like growth factor I is associated with fetal hypertrophic cardiomyopathy in diabetic women

OBJECTIVE

We sought to determine if fetal hypertrophic cardiomyopathy (HCM) or cardiac dysfunction is associated with elevated maternal or neonatal insulin-like growth factor (IGF)-I levels in women with diabetes.

STUDY DESIGN

In a prospective cohort study, fetal echocardiogram findings at 36 weeks' gestation in women with pregestational diabetes mellitus were compared to those in women without diabetes mellitus. HCM was defined as septal or free wall thickness ≥5 mm and cardiac dysfunction as a modified myocardial performance index ≥0.43. Cord serum IGF-I levels at delivery were measured with enzyme-linked immunosorbent assay. Neonates with abnormal fetal echocardiogram were followed up until resolution or 6 months of life.

RESULTS

In all, 75 participants completed fetal echocardiography (55 diabetics and 20 controls). In the diabetic group, 33 of 55 (60%) had abnormal fetal echocardiograms with cardiac dysfunction in 21 of 55 (38.2%) and HCM in 8 of 55 (14.5%) and both in 4 of 55 (7.3%). At 6 months of age, 1 of 12 (8%) had persistent HCM. None in the comparison group had abnormal findings. There were no significant clinical differences in those diabetic women with normal vs abnormal fetal echocardiograms. However, among diabetic women, mean neonatal IGF-I was significantly higher in fetuses with HCM (80 ± 16 ng/mL) as compared to those without HCM (61 ± 18 ng/mL), (P < .001).

CONCLUSION

Elevated neonatal IGF-I appears to be associated with fetal HCM in fetuses of diabetic women.

Unexpected maturation of PI3K and MAPK-ERK signaling in fetal ovine cardiomyocytes

In the first two-thirds of gestation, ovine fetal cardiomyocytes undergo mitosis to increase cardiac mass and accommodate fetal growth. Thereafter, some myocytes continue to proliferate while others mature and terminally differentiate into binucleated cells. At term (145 days gestational age; dGA) about 60% of cardiomyocytes become binucleated and exit the cell cycle under hormonal control. Rising thyroid hormone (T3) levels near term (135 dGA) inhibit proliferation and stimulate maturation. However, the degree to which intracellular signaling patterns change with age in response to T3 is unknown. We hypothesized that in vitro activation of ERK, Akt, and p70(S6K) by two regulators of cardiomyocyte cell cycle activity, T3 and insulin like growth factor-1 (IGF-1), would be similar in cardiomyocytes at gestational ages 100 and 135 dGA. IGF-1 and T3 each independently stimulated phosphorylation of ERK, Akt, and p70(S6K) in cells at both ages. In the younger mononucleated myocytes, the phosphorylation of ERK and Akt was reduced in the presence of IGF-1 and T3. However, the same hormone combination led to a dramatic twofold increase in the phosphorylation of these signaling proteins in the 135 dGA cardiomyocytes-even in cells that were not proliferating. In the older cells, both mono- and binucleated cells were affected. In conclusion, fetal ovine cardiomyocytes undergo profound maturation-related changes in signaling in response to T3 and IGF-1, but not to either factor alone. Differences in age-related response are likely to be related to milestones in fetal cardiac development as the myocardium prepares for ex utero 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.