Perinatal changes in myocardial metabolism in lambs

The characterization of protein lactylation in relation to cardiac metabolic reprogramming in neonatal mouse hearts

In mammals, the neonatal heart can regenerate upon injury within a short time after birth, while adults lose this ability. Metabolic reprogramming has been demonstrated to be critical for cardiomyocyte proliferation in the neonatal heart. Here, we reveal that cardiac metabolic reprogramming could be regulated by altering global protein lactylation. By performing 4D label-free proteomics and lysine lactylation (Kla) omics analyses in mouse hearts at postnatal days 1, 5, and 7, 2297 Kla sites from 980 proteins are identified, among which 1262 Kla sites from 409 proteins are quantified. Functional clustering analysis reveals that the proteins with altered Kla sites are mainly involved in metabolic processes. The expression and Kla levels of proteins in glycolysis show a positive correlation while a negative correlation in fatty acid oxidation. Furthermore, we verify the Kla levels of several differentially modified proteins, including ACAT1, ACADL, ACADVL, PFKM, PKM, and NPM1. Overall, our study reports a comprehensive Kla map in the neonatal mouse heart, which will help to understand the regulatory network of metabolic reprogramming and cardiac regeneration.

The role of metabolism in cardiac development

Metabolism is the fundamental process that sustains life. The heart, in particular, is an organ of high energy demand, and its energy substrates have been studied for more than a century. In recent years, there has been a growing interest in understanding the role of metabolism in the early differentiation of pluripotent stem cells and in cancer research. Studies have revealed that metabolic intermediates from glycolysis and the tricarboxylic acid cycle act as co-factors for intracellular signal transduction, playing crucial roles in regulating cell behaviors. Mitochondria, as the central hub of metabolism, are also under intensive investigation regarding the regulation of their dynamics. The metabolic environment of the fetus is intricately linked to the maternal metabolic status, and the impact of the mother's nutrition and metabolic health on fetal development is significant. For instance, it is well known that maternal diabetes increases the risk of cardiac and nervous system malformations in the fetus. Another notable example is the decrease in the risk of neural tube defects when pregnant women are supplemented with folic acid. These examples highlight the profound influence of the maternal metabolic environment on the fetal organ development program. Therefore, gaining insights into the metabolic environment within developing fetal organs is critical for deepening our understanding of normal organ development. This review aims to summarize recent findings that build upon the historical recognition of the environmental and metabolic factors involved in the developing embryo.

Physiological response to fetal intravenous lipid emulsion

In preterm neonates unable to obtain sufficient oral nutrition, intravenous lipid emulsion is life-saving. The contribution of post-conceptional level of maturation to pathology that some neonates experience is difficult to untangle from the global pathophysiology of premature birth. In the present study, we determined fetal physiological responses to intravenous lipid emulsion. Fetal sheep were given intravenous Intralipid 20® (n = 4 females, 7 males) or Lactated Ringer's Solution (n = 7 females, 4 males) between 125 ± 1 and 133 ± 1 d of gestation (term = 147 d). Manufacturer's recommendation for premature human infants was followed: 0.5-1 g/kg/d initial rate, increased by 0.5-1 to 3 g/kg/d. Hemodynamic parameters and arterial blood chemistry were measured, and organs were studied postmortem. Red blood cell lipidomics were analyzed by LC-MS. Intravenous Intralipid did not alter hemodynamic or most blood parameters. Compared with controls, Intralipid infusion increased final day plasma protein (P=0.004; 3.5 ± 0.3 vs. 3.9 ± 0.2 g/dL), albumin (P = 0.031; 2.2 ± 0.1 vs. 2.4 ± 0.2 g/dL), and bilirubin (P<0.001; conjugated: 0.2 ± 0.1 vs. 0.6 ± 0.2 mg/dL; unconjugated: 0.2 ± 0.1 vs. 1.1 ± 0.4 mg/dL). Circulating IGF-1 decreased following Intralipid infusion (P<0.001; 66 ± 24 vs. 46 ± 24 ng/mL). Compared with control Oil Red O liver stains (median score 0), Intralipid-infused fetuses scored 108 (P=0.0009). Lipidomic analysis revealed uptake and processing of infused lipids into red blood cells, increasing abundance of saturated fatty acids. The near-term fetal sheep tolerates intravenous lipid emulsion well, although lipid accumulates in the liver. Increased levels of unconjugated bilirubin may reflect increased red blood cell turnover or impaired placental clearance. Whether Intralipid is less well tolerated earlier in gestation remains to be determined.

Striated preferentially expressed gene deficiency leads to mitochondrial dysfunction in developing cardiomyocytes

A deficiency of striated preferentially expressed gene (Speg), a member of the myosin light chain kinase family, results in abnormal myofibril structure and function of immature cardiomyocytes (CMs), corresponding with a dilated cardiomyopathy, heart failure and perinatal death. Mitochondrial development plays a role in cardiomyocyte maturation. Therefore, this study investigated whether Speg deficiency ( - / - ) in CMs would result in mitochondrial abnormalities. Speg wild-type and Speg-/- C57BL/6 littermate mice were utilized for assessment of mitochondrial structure by transmission electron and confocal microscopies. Speg was expressed in the first and second heart fields at embryonic (E) day 7.5, prior to the expression of mitochondrial Na+/Ca2+/Li+ exchanger (NCLX) at E8.5. Decreases in NCLX expression (E11.5) and the mitochondrial-to-nuclear DNA ratio (E13.5) were observed in Speg-/- hearts. Imaging of E18.5 Speg-/- hearts revealed abnormal mitochondrial cristae, corresponding with decreased ATP production in cells fed glucose or palmitate, increased levels of mitochondrial superoxide and depolarization of mitochondrial membrane potential. Interestingly, phosphorylated (p) PGC-1α, a key mediator of mitochondrial development, was significantly reduced in Speg-/- hearts during screening for targeted genes. Besides Z-line expression, Speg partially co-localized with PGC-1α in the sarcomeric region and was found in the same complex by co-immunoprecipitation. Overexpression of a Speg internal serine/threonine kinase domain in Speg-/- CMs promoted translocation of pPGC-1α into the nucleus, and restored ATP production that was abolished by siRNA-mediated silencing of PGC-1α. Our results demonstrate a critical role of Speg in mitochondrial development and energy metabolism in CMs, mediated in part by phosphorylation of PGC-1α.

Maturation of lipid metabolism in the fetal and newborn sheep heart

At birth, the fetus experiences a dramatic change in environment that is accompanied by a shift in myocardial fuel preference from lactate and glucose in fetal life to fatty acid oxidation after birth. We hypothesized that fatty acid metabolic machinery would mature during fetal life in preparation for this extreme metabolic transformation at birth. We quantified the pre- (94-day and 135-day gestation, term ∼147 days) and postnatal (5 ± 4 days postnatal) gene expression and protein levels for fatty acid transporters and enzymes in hearts from a precocial species, the sheep. Gene expression of fatty acid translocase (CD36), acyl-CoA synthetase long-chain 1 (ACSL1), carnitine palmitoyltransferase 1 (CPT1), hydroxy-acyl dehydrogenase (HADH), acetyl-CoA acetyltransferase (ACAT1), isocitrate dehydrogenase (IDH), and glycerol phosphate acyltransferase (GPAT) progressively increased through the perinatal period, whereas several genes [fatty acid transport protein 6 (FATP6), acyl-CoA synthetase long chain 3 (ACSL3), long-chain acyl-CoA dehydrogenase (LCAD), very long-chain acyl-CoA dehydrogenase (VLCAD), pyruvate dehydrogenase kinase (PDK4), phosphatidic acid phosphatase (PAP), and diacylglycerol acyltransferase (DGAT)] were stable in fetal hearts and had high expression after birth. Protein expression of CD36 and ACSL1 progressively increased throughout the perinatal period, whereas protein expression of carnitine palmitoyltransferase 1a (fetal isoform) (CPT1a) decreased and carnitine palmitoyltransferase 1b (adult isoform) (CPT1b) remained constitutively expressed. Using fluorescent-tagged long-chain fatty acids (BODIPY-C12), we demonstrated that fetal (125 ± 1 days gestation) cardiomyocytes produce 59% larger lipid droplets (P < 0.05) compared with newborn (8 ± 1 day) cardiomyocytes. These results provide novel insights into the perinatal maturation of cardiac fatty acid metabolism in a precocial species.NEW & NOTEWORTHY This study characterized the previously unknown expression patterns of genes that regulate the metabolism of free fatty acids in the perinatal sheep myocardium. This study shows that the prenatal myocardium prepares for the dramatic switch from carbohydrate metabolism to near complete reliance on free fatty acids postnatally. Fetal and neonatal cardiomyocytes also demonstrate differing lipid storage mechanisms where fetal cardiomyocytes form larger lipid droplets compared with newborn cardiomyocytes.

Thyroid hormone increases fatty acid use in fetal ovine cardiac myocytes

Cardiac metabolic substrate preference shifts at parturition from carbohydrates to fatty acids. We hypothesized that thyroid hormone (T3 ) and palmitic acid (PA) stimulate fetal cardiomyocyte oxidative metabolism capacity. T3 was infused into fetal sheep to a target of 1.5 nM. Dispersed cardiomyocytes were assessed for lipid uptake and droplet formation with BODIPY-labeled fatty acids. Myocardial expression levels were assessed PCR. Cardiomyocytes from naïve fetuses were exposed to T3 and PA, and oxygen consumption was measured with the Seahorse Bioanalyzer. Cardiomyocytes (130-day gestational age) exposed to elevated T3 in utero accumulated 42% more long-chain fatty acid droplets than did cells from vehicle-infused fetuses. In utero T3 increased myocardial mRNA levels of CD36, CPT1A, CPT1B, LCAD, VLCAD, HADH, IDH, PDK4, and caspase 9. In vitro exposure to T3 increased maximal oxygen consumption rate in cultured cardiomyocytes in the absence of fatty acids, and when PA was provided as an acute (30 min) supply of cellular energy. Longer-term exposure (24 and 48 h) to PA abrogated increased oxygen consumption rates stimulated by elevated levels of T3 in cultured cardiomyocytes. T3 contributes to metabolic maturation of fetal cardiomyocytes. Prolonged exposure of fetal cardiomyocytes to PA, however, may impair oxidative capacity.

Adapting to a new environment: postnatal maturation of the human cardiomyocyte

The postnatal mammalian heart undergoes remarkable developmental changes, which are stimulated by the transition from the intrauterine to extrauterine environment. With birth, increased oxygen levels promote metabolic, structural and biophysical maturation of cardiomyocytes, resulting in mature muscle with increased efficiency, contractility and electrical conduction. In this Topical Review article, we highlight key studies that inform our current understanding of human cardiomyocyte maturation. Collectively, these studies suggest that human atrial and ventricular myocytes evolve quickly within the first year but might not reach a fully mature adult phenotype until nearly the first decade of life. However, it is important to note that fetal, neonatal and paediatric cardiac physiology studies are hindered by a number of limitations, including the scarcity of human tissue, small sample size and a heavy reliance on diseased tissue samples, often without age-matched healthy controls. Future developmental studies are warranted to expand our understanding of normal cardiac physiology/pathophysiology and inform age-appropriate treatment strategies for cardiac disease.

Coronary conductance in the normal development of sheep during the perinatal period

Birth is associated with substantial shifts in cardiovascular physiology. Little is known about coronary vascular adaptations during this period. We used fetal and neonatal lambs to measure coronary function at late gestation (92% of term) and shortly after birth (5-6 days postnatal age). In each animal we measured unanesthetized myocardial perfusion and oxygen delivery using a circumflex artery flow probe. We used inflatable occluders and adenosine to determine coronary conductance and flow reserve. In a subset of animals, we used myocardial contrast echocardiography (MCE, anesthetized) to assess its utility as a tool for studying changes in regional myocardial perfusion in normal development. Separate age-matched animals were instrumented with aortic and coronary sinus sampling catheters to determine myocardial oxygen extraction (unanesthetized). With an average of 17 days of developmental time separating our neonatal and fetal cohorts we found that heart-to-body weight ratio was significantly greater in neonates than fetuses. In resting animals, we found significant decreases in weight-normalized perfusion of, and oxygen delivery to, neonatal relative to fetal myocardium. Similar results were seen when measuring baseline MCE-derived perfusion. Pressure-flow relationship studies revealed lower baseline and maximal coronary conductance in neonates than fetuses, with similar coronary flow reserve between groups. There was greater oxygen extraction in neonates than fetuses. Combined analysis of oxygen extraction with coronary flow suggested greater oxygen consumption by the fetal than neonatal myocardium. We conclude that, during the immediate perinatal period, cardiac growth outpaces coronary microvascular growth resulting in lower capacity for microvascular perfusion in the early neonate.

Neonatal ketone body elevation regulates postnatal heart development by promoting cardiomyocyte mitochondrial maturation and metabolic reprogramming

Neonatal heart undergoes metabolic conversion and cell cycle arrest preparing for the increased workload during adulthood. Herein, we report that neonatal ketone body elevation is a critical regulatory factor for postnatal heart development. Through multiomics screening, we found that the expression of 3-hydroxy-3-methylglutaryl-CoA synthase 2 (HMGCS2), the rate-limiting enzyme of ketogenesis, was transiently induced by colostrum in the neonatal heart. Hmgcs2 knockout caused mitochondrial maturation defects. Meanwhile, postnatal heart development was compromised and cardiomyocytes reacquired proliferation capacity in Hmgcs2 knockout mice. Consequently, over 40% of newborn Hmgcs2 knockout mice died before weaning. The heart function of surviving Hmgcs2 knockout mice was also impaired, which could be rescued by ketone body supplementation during the suckling stage. Mechanistically, ketone body deficiency inhibited β-hydroxybutyrylation but enhanced acetylation of mitochondrial proteins, which might be responsible for the inhibition of the enzyme activity in mitochondria. These observations suggest that ketone body is critical for postnatal heart development through regulating mitochondrial maturation and metabolic reprogramming.

Evaluation of Fetal Cardiac Geometry and Contractility in Gestational Diabetes Mellitus by Two-Dimensional Speckle-Tracking Technology

Background: The most commonly known cardiac effect of gestational diabetes mellitus (GD) in the fetus is hypertrophic cardiomyopathy, but recent studies show that it is preceded by subclinical cardiac dysfunction. This study aimed to assess the effect of GD on fetal cardiac geometry and contractility by two-dimensional speckle-tracking technology. Methods: We performed a prospective observational study that included 33 pregnant patients with GD and 30 healthy individuals. For all fetuses, a four-chamber 3 s cine-loop was recorded and analyzed with Fetal Heart Quantification (FetalHQ®), a novel proprietary speckle-tracking software. The following cardiac indices were calculated: global sphericity index (GSI), global longitudinal strain (GLS), fractional area change (FAC), and 24-segment end-diastolic diameter (EDD), fractional shortening (FS), and sphericity index (SI) for both ventricles. Demographic and cardiac differences between the two groups were analyzed, as well as intra-rater and inter-rater reliability. Results: There were significant changes in right ventricular FAC and FS for segments 4−24 in fetuses exposed to GD (−1 SD, p < 0.05). No significant differences were detected for GSI, GLS, EDD, or SI for either ventricle. Conclusions: Fetuses exposed to GD present impaired right ventricular contractility, especially in the mid and apical segments.

Long-Term Consequences of Adaptive Fetal Programming in Ruminant Livestock

Environmental perturbations during gestation can alter fetal development and postnatal animal performance. In humans, intrauterine growth restriction (IUGR) resulting from adaptive fetal programming is known as a leading cause of perinatal morbidity and mortality and predisposes offspring to metabolic disease, however, the prevalence and impact in livestock is not characterized as well. Multiple animal models have been developed as a proxy to determine mechanistic changes that underlie the postnatal phenotype resulting from these programming events in humans but have not been utilized as robustly in livestock. While the overall consequences are similar between models, the severity of the conditions appear to be dependent on type, timing, and duration of insult, indicating that some environmental insults are of more relevance to livestock production than others. Thus far, maternofetal stress during gestation has been shown to cause increased death loss, low birth weight, inefficient growth, and aberrant metabolism. A breadth of this data comes from the fetal ruminant collected near term or shortly thereafter, with fewer studies following these animals past weaning. Consequently, even less is known about how adaptive fetal programming impacts subsequent progeny. In this review, we summarize the current knowledge of the postnatal phenotype of livestock resulting from different models of fetal programming, with a focus on growth, metabolism, and reproductive efficiency. We further describe what is currently known about generational impacts of fetal programming in production systems, along with gaps and future directions to consider.

Moderate heart rate reduction promotes cardiac regeneration through stimulation of the metabolic pattern switch

As a biological pump, the heart needs to consume a substantial amount of energy to maintain sustained beating. Myocardial energy metabolism was recently reported to be related to the loss of proliferative capacity in cardiomyocytes (CMs). However, the intrinsic relationship between beating rate and proliferation in CMs and whether energy metabolism can regulate this relationship remains unclear. In this study, we find that moderate heart rate reduction (HRR) induces CM proliferation under physiological conditions and promotes cardiac regenerative repair after myocardial injury. Mechanistically, moderate HRR induces G1/S transition and increases the expression of glycolytic enzymes in CMs. Furthermore, moderate HRR induces a metabolic pattern switch, activating glucose metabolism and increasing the relative proportion of ATP production by the glycolytic pathway for biosynthesis of substrates needed for proliferative CMs. These results highlight the potential therapeutic role of HRR in not only acute myocardial protection but also long-term CM restoration.

Intrauterine growth restriction elevates circulating acylcarnitines and suppresses fatty acid metabolism genes in the fetal sheep heart

At birth, the mammalian myocardium switches from using carbohydrates as the primary energy substrate to free fatty acids as the primary fuel. Thus, a compromised switch could jeopardize normal heart function in the neonate. Placental embolization in sheep is a reliable model of intrauterine growth restriction (IUGR). It leads to suppression of both proliferation and terminal differentiation of cardiomyocytes. We hypothesized that the expression of genes regulating cardiac fatty acid metabolism would be similarly suppressed in IUGR, leading to compromised processing of lipids. Following 10 days of umbilicoplacental embolization in fetal sheep, IUGR fetuses had elevated circulating long-chain fatty acylcarnitines compared with controls (C14: CTRL 0.012 ± 0.005 nmol/ml vs. IUGR 0.018 ± 0.005 nmol/ml, P < 0.05; C18: CTRL 0.027 ± 0.009 nmol/mol vs. IUGR 0.043 ± 0.024 nmol/mol, P < 0.05, n = 12 control, n = 12 IUGR) indicative of impaired fatty acid metabolism. Uptake studies using fluorescently tagged BODIPY-C12-saturated free fatty acid in live, isolated cardiomyocytes showed lipid droplet area and number were not different between control and IUGR cells. mRNA levels of sarcolemmal fatty acid transporters (CD36, FATP6), acylation enzymes (ACSL1, ACSL3), mitochondrial transporter (CPT1), β-oxidation enzymes (LCAD, HADH, ACAT1), tricarboxylic acid cycle enzyme (IDH), esterification enzymes (PAP, DGAT) and regulator of the lipid droplet formation (BSCL2) gene were all suppressed in IUGR myocardium (P < 0.05). However, protein levels for these regulatory genes were not different between groups. This discordance between mRNA and protein levels in the stressed myocardium suggests an adaptive protection of key myocardial enzymes under conditions of placental insufficiency. KEY POINTS: The fetal heart relies on carbohydrates in utero and must be prepared to metabolize fatty acids after birth but the effects of compromised fetal growth on the maturation of this metabolic system are unknown. Plasma fatty acylcarnitines are elevated in intrauterine growth-restricted (IUGR) fetuses compared with control fetuses, indicative of impaired fatty acid metabolism in fetal organs. Fatty acid uptake and storage are not different in IUGR cardiomyocytes compared with controls. mRNA levels of genes regulating fatty acid transporter and metabolic enzymes are suppressed in the IUGR myocardium compared with controls, while protein levels remain unchanged. Mismatches in gene and protein expression, and increased circulating fatty acylcarnitines may have long-term implications for offspring heart metabolism and adult health in IUGR individuals. This requires further investigation.

PPAR control of metabolism and cardiovascular functions

Peroxisome proliferator-activated receptor-α (PPARα), PPARδ and PPARγ are transcription factors that regulate gene expression following ligand activation. PPARα increases cellular fatty acid uptake, esterification and trafficking, and regulates lipoprotein metabolism genes. PPARδ stimulates lipid and glucose utilization by increasing mitochondrial function and fatty acid desaturation pathways. By contrast, PPARγ promotes fatty acid uptake, triglyceride formation and storage in lipid droplets, thereby increasing insulin sensitivity and glucose metabolism. PPARs also exert antiatherogenic and anti-inflammatory effects on the vascular wall and immune cells. Clinically, PPARγ activation by glitazones and PPARα activation by fibrates reduce insulin resistance and dyslipidaemia, respectively. PPARs are also physiological master switches in the heart, steering cardiac energy metabolism in cardiomyocytes, thereby affecting pathological heart failure and diabetic cardiomyopathy. Novel PPAR agonists in clinical development are providing new opportunities in the management of metabolic and cardiovascular diseases.

Mitochondrial Biogenesis, Mitochondrial Dynamics, and Mitophagy in the Maturation of Cardiomyocytes

Pluripotent stem cells (PSCs) can undergo unlimited self-renewal and can differentiate into all the cell types present in our body, including cardiomyocytes. Therefore, PSCs can be an excellent source of cardiomyocytes for future regenerative medicine and medical research studies. However, cardiomyocytes obtained from PSC differentiation culture are regarded as immature structurally, electrophysiologically, metabolically, and functionally. Mitochondria are organelles responsible for various cellular functions such as energy metabolism, different catabolic and anabolic processes, calcium fluxes, and various signaling pathways. Cells can respond to cellular needs to increase the mitochondrial mass by mitochondrial biogenesis. On the other hand, cells can also degrade mitochondria through mitophagy. Mitochondria are also dynamic organelles that undergo continuous fusion and fission events. In this review, we aim to summarize previous findings on the changes of mitochondrial biogenesis, mitophagy, and mitochondrial dynamics during the maturation of cardiomyocytes. In addition, we intend to summarize whether changes in these processes would affect the maturation of cardiomyocytes. Lastly, we aim to discuss unanswered questions in the field and to provide insights for the possible strategies of enhancing the maturation of PSC-derived cardiomyocytes.

Endocrine Influence on Cardiac Metabolism in Development and Regeneration

Mammalian cardiomyocytes mostly utilize oxidation of fatty acids to generate ATP. The fetal heart, in stark contrast, mostly uses anaerobic glycolysis. During perinatal development, thyroid hormone drives extensive metabolic remodeling in the heart for adaptation to extrauterine life. These changes coincide with critical functional maturation and exit of the cell cycle, making the heart a post-mitotic organ. Here, we review the current understanding on the perinatal shift in metabolism, hormonal status, and proliferative potential in cardiomyocytes. Thyroid hormone and glucocorticoids have roles in adult cardiac metabolism, and both pathways have been implicated as regulators of myocardial regeneration. We discuss the evidence that suggests these processes could be interrelated and how this can help explain variation in cardiac regeneration across ontogeny and phylogeny, and we note what breakthroughs are still to be made.

Fine particles in surgical smoke affect embryonic cardiomyocyte differentiation through oxidative stress and mitophagy

Surgical smoke is widespread in operating rooms, and fine particles are the main toxic components. However, the effect of fine particles in surgical smoke on embryonic development has not yet been studied. This study evaluated the effect of fine particles in surgical smoke on embryonic development and compared it with that of atmospheric fine particles. Afterwards, differentiated cardiomyocytes were purified, and the effect of exposure to fine particles in surgical smoke on cardiomyocyte differentiation was evaluated. Fine particles in surgical smoke exhibited weak embryotoxicity toward an embryonic stem cell test model, and their inhibitory effect on cardiomyocyte differentiation was slightly stronger than that of atmospheric fine particles. Fine particles in surgical smoke specifically inhibited the differentiation of the mesoderm lineage and promoted the differentiation of the ectoderm lineage. Furthermore, fine particles in surgical smoke reduced the beating rate of purified cardiomyocytes, promoted mitophagy, reduced ATP production and increased the reactive oxygen species (ROS) content. Antioxidants attenuated the inhibition of cardiomyocyte differentiation and the reduction in the cardiomyocyte beating rate caused by fine particles in surgical smoke and simultaneously restored mitophagy and other processes to the control levels. However, mitophagy inhibitors treatment blocked only the inhibition of cardiomyocyte differentiation caused by fine particles in surgical smoke; it had little effect on other changes caused by fine particles. Based on the results described above, we propose that fine particles in surgical smoke and atmospheric fine particles exhibit similar levels of toxicity toward embryonic development. Fine particles in surgical smoke potentially affect the beating of cardiomyocytes by damaging mitochondria and increasing oxidative stress.

Thyroid Hormone Signalling Alteration in Diabetic Nephropathy and Cardiomyopathy: a "Switch" to the Foetal Gene Programme

PURPOSE OF THE REVIEW

In this study, we will analyse how diabetes induces the reactivation of organs' developmental programmes and growth, discuss how thyroid hormone (TH) signalling orchestrates these processes, and suggest novel strategies for exploiting TH-mediated reparative and regenerative properties.

RECENT FINDINGS

Diabetes is a global pandemic that poses an enormous threat to human health. The kidney and the heart are among the organs that are the most severely damaged by diabetes over time. They undergo profound metabolic, structural, and functional changes that may be due (at least partially) to a recapitulation of their early developmental programmes. There is growing evidence to suggest that this foetal reprogramming is controlled by the TH/TH receptor alpha 1 (TRα1) axis. We introduce the hypothesis that in diabetes-and probably in other diseases-TH signalling acts in an antagonistic manner: it recapitulates a foetal profile that is necessary to coordinate metabolic and structural adaptations to sustain energy preservation and growth, but in the long term the persistent changes in these pathways are detrimental.

Right ventricular phenotype, function, and failure: a journey from evolution to clinics

The right ventricle has long been perceived as the "low pressure bystander" of the left ventricle. Although the structure consists of, at first glance, the same cardiomyocytes as the left ventricle, it is in fact derived from a different set of precursor cells and has a complex three-dimensional anatomy and a very distinct contraction pattern. Mechanisms of right ventricular failure, its detection and follow-up, and more specific different responses to pressure versus volume overload are still incompletely understood. In order to fully comprehend right ventricular form and function, evolutionary biological entities that have led to the specifics of right ventricular physiology and morphology need to be addressed. Processes responsible for cardiac formation are based on very ancient cardiac lineages and within the first few weeks of fetal life, the human heart seems to repeat cardiac evolution. Furthermore, it appears that most cardiogenic signal pathways (if not all) act in combination with tissue-specific transcriptional cofactors to exert inductive responses reflecting an important expansion of ancestral regulatory genes throughout evolution and eventually cardiac complexity. Such molecular entities result in specific biomechanics of the RV that differs from that of the left ventricle. It is clear that sole descriptions of right ventricular contraction patterns (and LV contraction patterns for that matter) are futile and need to be addressed into a bigger multilayer three-dimensional picture. Therefore, we aim to present a complete picture from evolution, formation, and clinical presentation of right ventricular (mal)adaptation and failure on a molecular, cellular, biomechanical, and (patho)anatomical basis.

Role of Parkin-mediated mitophagy in glucocorticoid-induced cardiomyocyte maturation

Glucocorticoids can promote cardiomyocyte maturation. However, the mechanism underlying glucocorticoid-mediated cardiomyocyte maturation is still unclear. Mitophagy plays a key role in cardiomyocyte maturation. Based on current knowledge, our study evaluated the effects of the glucocorticoid dexamethasone (100 nM) on the maturation of mouse embryonic stem cell-derived cardiomyocytes and the role of mitophagy in this maturation. The results showed that dexamethasone can promote embryonic stem cell-derived cardiomyocyte maturation, inhibit cardiomyocyte proliferation, and promote myocardial fiber arrangement. However, dexamethasone did not affect mitochondrial morphology in cardiomyocytes. Glucocorticoid receptor inhibitors (RU486, 1 nM) can inhibit dexamethasone-mediated cardiomyocyte maturation. Additionally, dexamethasone can promote mitophagy in embryonic stem cell-derived cardiomyocytes and induce LC3 and lysosomal aggregation in mitochondria. The inhibition of mitophagy can inhibit the cardiomyocyte maturation effect of dexamethasone. Furthermore, our research found that dexamethasone may mediate the occurrence of mitophagy in cardiomyocytes through Parkin. The siRNA-mediated inhibition of Parkin expression can inhibit mitochondrial autophagy caused by dexamethasone, thus inhibiting cardiomyocyte maturation. Overall, our study found that dexamethasone can promote embryonic stem cell-derived cardiomyocyte maturation through Parkin-mediated mitophagy.

Mitochondrial Adaptations in the Growing Heart

The heart pumps blood throughout the whole life of an organism, without rest periods during which to replenish energy or detoxify. Hence, cardiomyocytes, the working units of the heart, have mechanisms to ensure constitutive production of energy and detoxification to preserve fitness and function for decades. Even more challenging, the heart must adapt to the varying conditions of the organism from fetal life to adulthood, old age, and pathological stress. Mitochondria are at the nexus of these processes by producing not only energy but also metabolites and oxidative byproducts that can activate alarm signals and be toxic to the cell. We review basic concepts about cardiac mitochondria with a focus on their remarkable adaptations, including elimination, throughout the mammalian lifetime.

Determinants of Cardiac Growth and Size

Within the realm of zoological study, the question of how an organism reaches a specific size has been largely unexplored. Recently, studies performed to understand the regulation of organ size have revealed that both cellular signals and external cues contribute toward the determination of total cell mass within each organ. The establishment of final organ size requires the precise coordination of cell growth, proliferation, and survival throughout development and postnatal life. In the mammalian heart, the regulation of size is biphasic. During development, cardiomyocyte proliferation predominantly determines cardiac growth, whereas in the adult heart, total cell mass is governed by signals that regulate cardiac hypertrophy. Here, we review the current state of knowledge regarding the extrinsic factors and intrinsic mechanisms that control heart size during development. We also discuss the metabolic switch that occurs in the heart after birth and precedes homeostatic control of postnatal heart size.

The physiology of intrapartum fetal compromise at term

Uterine contractions in labor result in a 60% reduction in uteroplacental perfusion, causing transient fetal and placental hypoxia. A healthy term fetus with a normally developed placenta is able to accommodate this transient hypoxia by activation of the peripheral chemoreflex, resulting in a reduction in oxygen consumption and a centralization of oxygenated blood to critical organs, namely the heart, brain, and adrenals. Providing there is adequate time for placental and fetal reperfusion between contractions, these fetuses will be able to withstand prolonged periods of intermittent hypoxia and avoid severe hypoxic injury. However, there exists a cohort of fetuses in whom abnormal placental development in the first half of pregnancy results in failure of endovascular invasion of the spiral arteries by the cytotrophoblastic cells and inadequate placental angiogenesis. This produces a high-resistance, low-flow circulation predisposing to hypoperfusion, hypoxia, reperfusion injury, and oxidative stress within the placenta. Furthermore, this renders the placenta susceptible to fluctuations and reduction in uteroplacental perfusion in response to external compression and stimuli (as occurs in labor), further reducing fetal capillary perfusion, placing the fetus at risk of inadequate gas/nutrient exchange. This placental dysfunction predisposes the fetus to intrapartum fetal compromise. In the absence of a rare catastrophic event, intrapartum fetal compromise occurs as a gradual process when there is an inability of the fetal heart to respond to the peripheral chemoreflex to maintain cardiac output. This may arise as a consequence of placental dysfunction reducing pre-labor myocardial glycogen stores necessary for anaerobic metabolism or due to an inadequate placental perfusion between contractions to restore fetal oxygen and nutrient exchange. If the hypoxic insult is severe enough and long enough, profound multiorgan injury and even death may occur. This review provides a detailed synopsis of the events that can result in placental dysfunction, how this may predispose to intrapartum fetal hypoxia, and what protective mechanisms are in place to avoid hypoxic injury.

Metabolic Remodeling in the Pressure-Loaded Right Ventricle: Shifts in Glucose and Fatty Acid Metabolism-A Systematic Review and Meta-Analysis

Background

Right ventricular (RV) failure because of chronic pressure load is an important determinant of outcome in pulmonary hypertension. Progression towards RV failure is characterized by diastolic dysfunction, fibrosis and metabolic dysregulation. Metabolic modulation has been suggested as therapeutic option, yet, metabolic dysregulation may have various faces in different experimental models and disease severity. In this systematic review and meta‐analysis, we aimed to identify metabolic changes in the pressure loaded RV and formulate recommendations required to optimize translation between animal models and human disease.

Methods and Results

Medline and EMBASE were searched to identify original studies describing cardiac metabolic variables in the pressure loaded RV. We identified mostly rat‐models, inducing pressure load by hypoxia, Sugen‐hypoxia, monocrotaline (MCT), pulmonary artery banding (PAB) or strain (fawn hooded rats, FHR), and human studies. Meta‐analysis revealed increased Hedges’ g (effect size) of the gene expression of GLUT1 and HK1 and glycolytic flux. The expression of MCAD was uniformly decreased. Mitochondrial respiratory capacity and fatty acid uptake varied considerably between studies, yet there was a model effect in carbohydrate respiratory capacity in MCT‐rats.

Conclusions

This systematic review and meta‐analysis on metabolic remodeling in the pressure‐loaded RV showed a consistent increase in glucose uptake and glycolysis, strongly suggest a downregulation of beta‐oxidation, and showed divergent and model‐specific changes regarding fatty acid uptake and oxidative metabolism. To translate metabolic results from animal models to human disease, more extensive characterization, including function, and uniformity in methodology and studied variables, will be required.

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.

Mechanisms of in utero cortisol effects on the newborn heart revealed by transcriptomic modeling

We have identified effects of elevated maternal cortisol (induced by maternal infusion 1 mg·kg-1·day-1) on fetal cardiac maturation and function using an ovine model. Whereas short-term exposure (115-130-day gestation) increased myocyte proliferation and Purkinje fiber apoptosis, infusions until birth caused bradycardia with increased incidence of arrhythmias at birth and increased perinatal death, despite normal fetal cortisol concentrations from 130 days to birth. Statistical modeling of the transcriptomic changes in hearts at 130 and 140 days suggested that maternal cortisol excess disrupts cardiac metabolism. In the current study, we modeled pathways in the left ventricle (LV) and interventricular septum (IVS) of newborn lambs after maternal cortisol infusion from 115 days to birth. In both LV and IVS the transcriptomic model indicated over-representation of cell cycle genes and suggested disruption of cell cycle progression. Pathways in the LV involved in cardiac architecture, including SMAD and bone morphogenetic protein ( BMP) were altered, and collagen deposition was increased. Pathways in IVS related to metabolism, calcium signaling, and the actin cytoskeleton were altered. Comparison of the effects of maternal cortisol excess to the effects of normal maturation from day 140 to birth revealed that only 20% of the genes changed in the LV were consistent with normal maturation, indicating that chronic elevation of maternal cortisol alters normal maturation of the fetal myocardium. These effects of maternal cortisol on the cardiac transcriptome, which may be secondary to metabolic effects, are consistent with cardiac remodeling and likely contribute to the adverse impact of maternal stress on perinatal cardiac function.

Multiomics approach reveals metabolic changes in the heart at birth

During late gestation, the fetal heart primarily relies on glucose and lactate to support rapid growth and development. Although numerous studies describe changes in heart metabolism to utilize fatty acids preferentially a few weeks after birth, little is known about metabolic changes of the heart within the first day following birth. Therefore, we used the ovine model of pregnancy to investigate metabolic differences between the near-term fetal and the newborn heart. Heart tissue was collected for metabolomic, lipidomic, and transcriptomic approaches from the left and right ventricles and intraventricular septum in 7 fetuses at gestational day 142 and 7 newborn lambs on the day of birth. Significant metabolites and lipids were identified using a Student's t-test, whereas differentially expressed genes were identified using a moderated t-test with empirical Bayes method [false discovery rate (FDR)-corrected P < 0.10]. Single-sample gene set enrichment analysis (ssGSEA) was used to identify pathways enriched on a transcriptomic level (FDR-corrected P < 0.05), whereas overrepresentation enrichment analysis was used to identify pathways enriched on a metabolomic level ( P < 0.05). We observed greater abundance of metabolites involved in butanoate and propanoate metabolism, and glycolysis in the term fetal heart and differential expression in these pathways were confirmed with ssGSEA. Immediately following birth, newborn hearts displayed enrichment in purine, fatty acid, and glycerophospholipid metabolic pathways as well as oxidative phosphorylation with significant alterations in both lipids and metabolites to support transcriptomic findings. A better understanding of metabolic alterations that occur in the heart following birth may improve treatment of neonates at risk for heart failure.

Role for Taurine in Development of Oxidative Metabolism After Birth

The heart undergoes a major metabolic transition after birth, a change largely caused by alterations in substrate availability, hormone levels and transcription factor content. However, another factor that could contribute to the resulting upregulation of oxidative metabolism is the increase in taurine levels. We proposed that by increasing UUG decoding and the biosynthesis of mitochondria encoded proteins, elevations in taurine content enhance electron transport flux and increase oxidative metabolism. To test our hypothesis, the effect of reduced taurine content on oxidative metabolism of myocardial mitochondria and neonatal cardiomyocytes was examined. Taurine deficient neonatal mitochondria exhibited impaired oxidation of complex I specific- but not complex II specific-substrates, indicating that taurine deficiency regulates complex I activity. Taurine deficiency also reduced respiration of neonatal cardiomyocytes oxidizing carbohydrate (glucose, lactate and pyruvate). However, cardiomyocytes from 2-3 day-old hearts respiring either β-hydroxybutyrate, an important substrate in the neonatal heart, or palmitate, which is poorly metabolized during the early neonatal period, were resistant to the metabolic defects of taurine deficiency, These data support the hypothesis that taurine contributes to development of respiratory chain function after birth, which is required for oxidative metabolism of multiple substrates.

Maturation of Cardiac Energy Metabolism During Perinatal Development

As one of the highest energy consumer organ in mammals, the heart has to be provided with a high amount of energy as soon as its first beats in utero. During the development of this organ, energy is produced within the cardiac muscle cell depending on substrate availability, oxygen pressure and cardiac workload that drastically change at birth. Thus, energy metabolism relying essentially on carbohydrates in fetal heart is very different from the adult one and birth is the trigger of a profound maturation which ensures the transition to a highly oxidative metabolism depending on lipid utilization. To face the substantial increase in cardiac workload resulting from the growth of the organism during the postnatal period, the heart not only develops its capacity for energy production but also undergoes a hypertrophic growth to adapt its contractile capacity to its new function. This leads to a profound cytoarchitectural remodeling of the cardiomyocyte which becomes a highly compartmentalized structure. As a consequence, within the mature cardiac muscle, energy transfer between energy producing and consuming compartments requires organized energy transfer systems that are established in the early postnatal life. This review aims at describing the major rearrangements of energy metabolism during the perinatal development.

The peripheral chemoreflex: indefatigable guardian of fetal physiological adaptation to labour

The fetus is consistently exposed to repeated periods of impaired oxygen (hypoxaemia) and nutrient supply in labour. This is balanced by the healthy fetus's remarkable anaerobic tolerance and impressive ability to mount protective adaptations to hypoxaemia. The most important mediator of fetal adaptations to brief repeated hypoxaemia is the peripheral chemoreflex, a rapid reflex response to acute falls in arterial oxygen tension. The overwhelming majority of fetuses are able to respond to repeated uterine contractions without developing hypotension or hypoxic-ischaemic injury. In contrast, fetuses who are either exposed to severe hypoxaemia, for example during uterine hyperstimulation, or enter labour with reduced anaerobic reserve (e.g. as shown by severe fetal growth restriction) are at increased risk of developing intermittent hypotension and cerebral hypoperfusion. It is remarkable to note that when fetuses develop hypotension during such repeated severe hypoxaemia, it is not mediated by impaired reflex adaptation, but by failure to maintain combined ventricular output, likely due to a combination of exhaustion of myocardial glycogen and evolving myocardial injury. The chemoreflex is suppressed by relatively long periods of severe hypoxaemia of 1.5-2 min, longer than the typical contraction. Even in this setting, the peripheral chemoreflex is consistently reactivated between contractions. These findings demonstrate that the peripheral chemoreflex is an indefatigable guardian of fetal adaptation to labour.

Chronic maternal hypercortisolemia in late gestation alters fetal cardiac function at birth

Studies in our laboratory have shown that modest chronic increases in maternal cortisol concentrations over the last 0.20 of gestation impair maternal glucose metabolism and increase the incidence of perinatal stillbirth. Previous studies had found that an increase in maternal cortisol concentrations from 115 to 130 days of gestation in sheep increased both proliferation in fetal cardiomyocytes and apoptosis in the fetal cardiac Purkinje fibers. We hypothesized that the adverse effects of excess cortisol may result in defects in cardiac conduction during labor and delivery. In the present study, we infused cortisol (1 mg·kg^-1·day^-1) into late gestation pregnant ewes and continuously monitored fetal aortic pressure and ECG through labor and delivery. We found that, although the fetuses of cortisol infused ewes had normal late gestation patterns of arterial pressure and heart rate, there was a significant decrease in fetal aortic pressure and heart rate on the day of birth, specifically in the final hour before delivery. Significant changes in the fetal ECG were also apparent on the day of birth, including prolongation of the P wave and P-R interval. We speculate that chronic exposure to glucocorticoids alters cardiac metabolism or ion homeostasis, contributing to cardiac dysfunction, precipitated by active labor and delivery.

Trimedazidine alleviates pulmonary artery banding-induced acute right heart dysfunction and activates PRAS40 in rats

The molecular mechanism underlying acute right heart failure (RHF) is poorly understood. We used pulmonary artery banding (PAB) to induce acute RHF characterized by a rapid rise of right ventricular pressure, and then a decrease in right ventricular pressure along with a decrease in blood pressure right after banding. We found higher brain natriuretic peptide (BNP) and beta-myosin heavy chain (βMHC) levels and lower alpha-myosin heavy chain (αMHC) levels in RHF rats than sham-operated rats. Hemodynamic indexes in rats with acute RHF were slightly improved by trimedazidine TMZ, a key inhibitor of fatty acid (FA) oxidation. TMZ also reversed downregulation of peroxisome proliferator-activated receptor gamma coactivator 1-beta (PGC-1β) and peroxisome proliferator-activated receptor alpha (PPARα) by PAB and up-regulates peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α), peroxisome proliferator-activated receptor delta (PPARδ) and pyruvate dehydrogenase kinase isoform 4 (PDK4). In addition, TMZ reversed upregulation of phosphorylated Akt by PAB and increased phosphorylated proline-rich Akt-substrate 40 (PRAS40). Autophagy and apoptosis were not modified by PAB or TMZ. An acute RHF model was established in rats through 70% constriction of the pulmonary artery. TMZ treatment alleviated PAB-induced acute RHF by activating PRAS40 and upregulatingPGC-1α, PGC-1β, PPARα, PPARδ, and PDK4.

Deciphering the Function of the Blunt Circadian Rhythm of Melatonin in the Newborn Lamb: Impact on Adrenal and Heart

Neonatal lambs, as with human and other neonates, have low arrhythmic endogenous levels of melatonin for several weeks until they start their own pineal rhythm of melatonin production at approximately 2 weeks of life. During pregnancy, daily rhythmic transfer of maternal melatonin to the fetus has important physiological roles in sheep, nonhuman primates, and rats. This melatonin rhythm provides a circadian signal and also participates in adjusting the physiology of several organs in preparation for extrauterine life. We propose that the ensuing absence of a melatonin rhythm plays a role in neonatal adaptation. To test this hypothesis, we studied the effects of imposing a high-amplitude melatonin rhythm in the newborn lamb on (1) clock time-related changes in cortisol and plasma variables and (2) clock time-related changes of gene expression of clock genes and selected functional genes in the adrenal gland and heart. We treated newborn lambs with a daily oral dose of melatonin (0.25 mg/kg) from birth to 5 days of age, recreating a high-amplitude melatonin rhythm. This treatment suppressed clock time-related changes of plasma adrenocorticotropic hormone, cortisol, clock gene expression, and functional genes in the newborn adrenal gland. In the heart, it decreased heart/body weight ratio, increased expression of Anp and Bnp, and resulted in different heart gene expression from control newborns. The interference of this postnatal melatonin treatment with the normal postnatal pattern of adrenocortical function and heart development support a physiological role for the window of flat postnatal melatonin levels during the neonatal transition.

Right ventricular failure due to chronic pressure load: What have we learned in animal models since the NIH working group statement?

Right ventricular (RV) failure determines outcome in patients with pulmonary hypertension, congenital heart diseases and in left ventricular failure. In 2006, the Working Group on Cellular and Molecular Mechanisms of Right Heart Failure of the NIH advocated the development of preclinical models to study the pathophysiology and pathobiology of RV failure. In this review, we summarize the progress of research into the pathobiology of RV failure and potential therapeutic interventions. The picture emerging from this research is that RV adaptation to increased afterload is characterized by increased contractility, dilatation and hypertrophy. Clinical RV failure is associated with progressive diastolic deterioration and disturbed ventricular–arterial coupling in the presence of increased contractility. The pathobiology of the failing RV shows similarities with that of the LV and is marked by lack of adequate increase in capillary density leading to a hypoxic environment and oxidative stress and a metabolic switch from fatty acids to glucose utilization. However, RV failure also has characteristic features. So far, therapies aiming to specifically improve RV function have had limited success. The use of beta blockers and sildenafil may hold promise, but new therapies have to be developed. The use of recently developed animal models will aid in further understanding of the pathobiology of RV failure and development of new therapeutic strategies.

Increased fetal myocardial sensitivity to insulin-stimulated glucose metabolism during ovine fetal growth restriction

Unlike other visceral organs, myocardial weight is maintained in relation to fetal body weight in intrauterine growth restriction (IUGR) fetal sheep despite hypoinsulinemia and global nutrient restriction. We designed experiments in fetal sheep with placental insufficiency and restricted growth to determine basal and insulin-stimulated myocardial glucose and oxygen metabolism and test the hypothesis that myocardial insulin sensitivity would be increased in the IUGR heart. IUGR was induced by maternal hyperthermia during gestation. Control (C) and IUGR fetal myocardial metabolism were measured at baseline and under acute hyperinsulinemic/euglycemic clamp conditions at 128-132 days gestation using fluorescent microspheres to determine myocardial blood flow. Fetal body and heart weights were reduced by 33% (P = 0.008) and 30% (P = 0.027), respectively. Heart weight to body weight ratios were not different. Basal left ventricular (LV) myocardial blood flow per gram of LV tissue was maintained in IUGR fetuses compared to controls. Insulin increased LV myocardial blood flow by ∼38% (P < 0.01), but insulin-stimulated LV myocardial blood flow in IUGR fetuses was 73% greater than controls. Similar to previous reports testing acute hypoxia, LV blood flow was inversely related to arterial oxygen concentration (r(2 )= 0.71) in both control and IUGR animals. Basal LV myocardial glucose delivery and uptake rates were not different between IUGR and control fetuses. Insulin increased LV myocardial glucose delivery (by 40%) and uptake (by 78%) (P < 0.01), but to a greater extent in the IUGR fetuses compared to controls. During basal and hyperinsulinemic-euglycemic clamp conditions LV myocardial oxygen delivery, oxygen uptake, and oxygen extraction efficiency were not different between groups. These novel results demonstrate that the fetal heart exposed to nutrient and oxygen deprivation from placental insufficiency appears to maintain myocardial energy supply in the IUGR condition via increased glucose uptake and metabolic response to insulin, which support myocardial function and growth.

Assessing Cardiac Metabolism: A Scientific Statement From the American Heart Association

In a complex system of interrelated reactions, the heart converts chemical energy to mechanical energy. Energy transfer is achieved through coordinated activation of enzymes, ion channels, and contractile elements, as well as structural and membrane proteins. The heart's needs for energy are difficult to overestimate. At a time when the cardiovascular research community is discovering a plethora of new molecular methods to assess cardiac metabolism, the methods remain scattered in the literature. The present statement on "Assessing Cardiac Metabolism" seeks to provide a collective and curated resource on methods and models used to investigate established and emerging aspects of cardiac metabolism. Some of those methods are refinements of classic biochemical tools, whereas most others are recent additions from the powerful tools of molecular biology. The aim of this statement is to be useful to many and to do justice to a dynamic field of great complexity.

Central Parkin: The evolving role of Parkin in the heart

Parkin is familiar to many because of its link to Parkinson's disease, and to others because of its well-characterized role as a central factor mediating selective mitophagy of damaged mitochondria for mitochondrial quality control. The genetic connection between Parkin and Parkinson's disease derives from clinical gene-association studies, whereas our mechanistic understanding of Parkin functioning in mitophagy is based almost entirely on work performed in cultured cells. Surprisingly, experimental evidence linking the disease and the presumed mechanism derives almost entirely from fruit flies; germline Parkin deficient mice do not develop Parkinson's disease phenotypes. Moreover, genetic manipulation of Parkin signaling in mouse hearts does not support a central role for Parkin in homeostatic mitochondrial quality control in this mitochondria-rich and -dependent organ. Here, I provide an overview of data suggesting that (in mouse hearts at least) Parkin functions more as a stress-induced and developmentally-programmed facilitator of cardiomyocyte mitochondrial turnover. This article is part of a Special Issue entitled 'EBEC 2016: 19th European Bioenergetics Conference, Riva del Garda, Italy, July 2-6, 2016.

Development of endothermy and concomitant increases in cardiac and skeletal muscle mitochondrial respiration in the precocial Pekin duck (Anas platyrhynchos domestica)

Attaining endothermic homeothermy occurs at different times post-hatching in birds and is associated with maturation of metabolic and aerobic capacity. Simultaneous measurements at the organism, organ and cellular levels during the transition to endothermy reveal means by which this change in phenotype occurs. We examined development of endothermy in precocial Pekin ducks ( ITALIC! Anas platyrhynchos domestica) by measuring whole-animal O2consumption ( ITALIC! V̇O2 ) as animals cooled from 35 to 15°C. We measured heart ventricle mass, an indicator of O2delivery capacity, and mitochondrial respiration in permeabilized skeletal and cardiac muscle to elucidate associated changes in mitochondrial capacities at the cellular level. We examined animals on day 24 of incubation through 7 days post-hatching. ITALIC! V̇O2  of embryos decreased when cooling from 35 to 15°C; ITALIC! V̇O2  of hatchlings, beginning on day 0 post-hatching, increased during cooling with a lower critical temperature of 32°C. Yolk-free body mass did not change between internal pipping and hatching, but the heart and thigh skeletal muscle grew at faster rates than the rest of the body as the animals transitioned from an externally pipped paranate to a hatchling. Large changes in oxidative phosphorylation capacity occurred during ontogeny in both thigh muscles, the primary site of shivering, and cardiac ventricles. Thus, increased metabolic capacity necessary to attain endothermy was associated with augmented metabolic capacity of the tissue and augmented increasing O2delivery capacity, both of which were attained rapidly at hatching.

Maturing human pluripotent stem cell-derived cardiomyocytes in human engineered cardiac tissues

Engineering functional human cardiac tissue that mimics the native adult morphological and functional phenotype has been a long held objective. In the last 5 years, the field of cardiac tissue engineering has transitioned from cardiac tissues derived from various animal species to the production of the first generation of human engineered cardiac tissues (hECTs), due to recent advances in human stem cell biology. Despite this progress, the hECTs generated to date remain immature relative to the native adult myocardium. In this review, we focus on the maturation challenge in the context of hECTs, the present state of the art, and future perspectives in terms of regenerative medicine, drug discovery, preclinical safety testing and pathophysiological studies.

Parkin-mediated mitophagy directs perinatal cardiac metabolic maturation in mice

In developing hearts, changes in the cardiac metabolic milieu during the perinatal period redirect mitochondrial substrate preference from carbohydrates to fatty acids. Mechanisms responsible for this mitochondrial plasticity are unknown. Here, we found that PINK1-Mfn2-Parkin-mediated mitophagy directs this metabolic transformation in mouse hearts. A mitofusin (Mfn) 2 mutant lacking PINK1 phosphorylation sites necessary for Parkin binding (Mfn2 AA) inhibited mitochondrial Parkin translocation, suppressing mitophagy without impairing mitochondrial fusion. Cardiac Parkin deletion or expression of Mfn2 AA from birth, but not after weaning, prevented postnatal mitochondrial maturation essential to survival. Five-week-old Mfn2 AA hearts retained a fetal mitochondrial transcriptional signature without normal increases in fatty acid metabolism and mitochondrial biogenesis genes. Myocardial fatty acylcarnitine levels and cardiomyocyte respiration induced by palmitoylcarnitine were concordantly depressed. Thus, instead of transcriptional reprogramming, fetal cardiomyocyte mitochondria undergo perinatal Parkin-mediated mitophagy and replacement by mature adult mitochondria. Mitophagic mitochondrial removal underlies developmental cardiomyocyte mitochondrial plasticity and metabolic transitioning of perinatal hearts.

Parkin-dependent mitophagy in the heart

Mitochondria can undergo autophagic elimination for differing reasons, e.g. as part of a cell-wide macroautophagic response, as part of mitochondrial turnover during metabolic remodeling, or in the case of selective mitophagic destruction of dysfunctional mitochondria, during mitochondrial quality control. Multiple mechanistically distinct pathways converge upon, and activate, mitochondrial autophagy. Here, the evidence supporting a role for the prototypical mitochondrial quality control pathway, PINK1-Parkin mediated mitophagy, in cardiac homeostasis and heart disease is reviewed. Contrary to popular wisdom based on findings from non-cardiac systems, current data do not support a major role for Parkin-mediated mitophagy as a mechanism for constitutive mitochondrial housekeeping, and instead suggest that this pathway primarily functions in adult hearts as an inducible cardiac stress-response mechanism. Recent findings have also uncovered an unsuspected role for Parkin-mediated mitochondrial turnover in the normal perinatal transformation of myocardial metabolism.

Recurrent Ventricular Tachycardia in Medium-Chain Acyl-Coenzyme A Dehydrogenase Deficiency

We report a baby with medium-chain acyl-coenzyme A dehydrogenase (MCAD) deficiency who presented on day 2 with poor feeding and lethargy. She was floppy with hypoglycaemia (1.8 mmol/l) and hyperammonaemia (182 μmol/l). Despite correction of these and a continuous intravenous infusion of glucose at 4.5-6.2 mg/kg/min, she developed generalised tonic clonic seizures on day 3. She also suffered two episodes of pulseless ventricular tachycardia, from which she was resuscitated successfully. Unfortunately, she died on day 5, following a third episode of pulseless ventricular tachycardia. Arrhythmias are generally thought to be rarer in MCAD deficiency than in disorders of long-chain fatty acid oxidation. This is, however, the sixth report of ventricular tachyarrhythmias in MCAD deficiency. Five of these involved neonates and it may be that patients with MCAD deficiency are particularly prone to ventricular arrhythmias in the newborn period. Three of the patients (including ours) had normal blood glucose concentrations at the time of the arrhythmias and had been receiving intravenous glucose for many hours. These cases suggest that arrhythmias can be induced by medium-chain acylcarnitines or other metabolites accumulating in MCAD deficiency. Ventricular tachyarrhythmias can occur in MCAD deficiency, especially in neonates.

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.

A novel ETFB mutation in a patient with glutaric aciduria type II

Glutaric aciduria type II (GAII) is a rare inborn error of metabolism clinically classified into a neonatal-onset form with congenital anomalies, a neonatal-onset form without congenital anomalies and a mild and/or late-onset form (MIM #231680). Here, we report on a GAII patient carrying a homozygous novel c.143_145delAGG (p.Glu48del) mutation in the ETFB gene, who presented with a neonatal-onset form with congenital anomalies and rapidly developed cardiomegaly after birth.

Favorable outcome after physiologic dose of sodium-D,L-3-hydroxybutyrate in severe MADD

Multiple acyl coenzyme A dehydrogenase deficiency (MADD) is a severe inborn error of metabolism. Experiences with sodium-D,L-3-hydroxybutyrate (3-HB) treatment are limited although positive; however, the general view on outcome of severely affected patients with MADD is relatively pessimistic. Here we present an infant with MADD in whom the previously reported dose of 3-HB did not prevent the acute, severe, metabolic decompensation or progressive cardiomyopathy in the subsequent months. Only after a physiologic dose of 2600 mg/kg of 3-HB per day were ketone bodies detected in blood associated with improvement of the clinical course, N-terminal prohormone of brain natriuretic peptide and echocardiographic parameters. Long-term studies are warranted on 3-HB treatment in patients with MADD.

Mechanisms for the adverse effects of late gestational increases in maternal cortisol on the heart revealed by transcriptomic analyses of the fetal septum

We have previously shown in sheep that 10 days of modest chronic increase in maternal cortisol resulting from maternal infusion of cortisol (1 mg/kg/day) caused fetal heart enlargement and Purkinje cell apoptosis. In subsequent studies we extended the cortisol infusion to term, finding a dramatic incidence of stillbirth in the pregnancies with chronically increased cortisol. To investigate effects of maternal cortisol on the heart, we performed transcriptomic analyses on the septa using ovine microarrays and Webgestalt and Cytoscape programs for pathway inference. Analyses of the transcriptomic effects of maternal cortisol infusion for 10 days (130 day cortisol vs 130 day control), or ∼25 days (140 day cortisol vs 140 day control) and of normal maturation (140 day control vs 130 day control) were performed. Gene ontology terms related to immune function and cytokine actions were significantly overrepresented as genes altered by both cortisol and maturation in the septa. After 10 days of cortisol, growth factor and muscle cell apoptosis pathways were significantly overrepresented, consistent with our previous histologic findings. In the term fetuses (∼25 days of cortisol) nutrient pathways were significantly overrepresented, consistent with altered metabolism and reduced mitochondria. Analysis of mitochondrial number by mitochondrial DNA expression confirmed a significant decrease in mitochondria. The metabolic pathways modeled as altered by cortisol treatment to term were different from those modeled during maturation of the heart to term, and thus changes in gene expression in these metabolic pathways may be indicative of the fetal heart pathophysiologies seen in pregnancies complicated by stillbirth, including gestational diabetes, Cushing's disease and chronic stress.