A mouse model to study the link between hypoxia, long QT interval and sudden infant death syndrome

Relationship Between Vitamin D Level and Index of CardioElectrophysiological Balance in Children

BACKGROUND

Vitamin D deficiency has been found to be associated with various cardiovascular disorders, including hypertension, coronary artery disease, heart failure, peripheral vascular diseases, and sudden cardiac death. In the literature, it has been reported that many electrocardiographic parameters have been developed to predict ventricular arrhythmias. In recent studies, it is noteworthy that the index of cardio-electrophysiological balance (iCEB) and correct cardioelectrophysiological balance (iCEBc), which are electrocardiographic parameters, can be used as new, easy, cheap and non-invasive parameters to predict ventricular arrhythmias.

OBJECTIVE

This study aimed to investigate the relationship between vitamin D deficiency and iCEB and iCEBc values in children.

METHODS

A total of 186 patients were included in this study. Group 1 included 114 patients with vitamin D levels below 20 ng/ml; 50 patients with vitamin D levels of 21-29 ng/ml were included in Group 2; Group 3 consisted of 36 patients with a vitamin D level above 30 ng/ml. iCEB and iCEBc values were calculated by taking 12-lead ECG from all individuals and comparing them between groups.

RESULTS

A total of 186 children, 114 subjects in Group 1, 36 subjects in Group 2, and 36 subjects in Group 3, were included in the study. Demographic characteristics and height-weight values of the groups were similar. Significant differences were found between the groups in terms of QT, QTc, QT/QRS, and QTc/QRS levels (p: 0.003, 0.028, 0.001, and 0.001, respectively). In the correlation analysis, a negative correlation was found between QTc/QRS and vitamin D level (r=-0.320, p=<0.001) and between QT/QRS and vitamin D level (r=-0.268, p=<0.001). Moreover, vitamin D level (β=0.389, p<0.001) was determined as an independent predictor of QTc/QRS in multivariate logistic regression analysis.

CONCLUSION

iCEB and iCEBc parameters increase significantly in children with low vitamin D levels. These parameters are also evaluated during the follow-up of children with vitamin D deficiency in terms of the risk of ventricular arrhythmia. iCEBc can be used as an easy, inexpensive, non-invasive, and reproducible parameter.

Chronic maternal hypercortisolemia models stress-induced adverse birth outcome and altered cardiac function in newborn lambs

Maternal stress in pregnancy is thought to be a contributing factor in adverse pregnancy outcome, including stillbirth and prematurity. Previous studies in our laboratory have shown that chronic elevation in maternal cortisol concentration in ewes (by maternal infusion of 1 mg·kg^-1·day^-1) during the late gestion increased the incidence of stillbirth and altered fetal heart rate and blood pressure at birth. We designed the current study to test the effect of chronically elevated maternal cortisol on fetal cardiac adaption from in utero life to ex utero life. The combined risk of stillbirth or prematurity was significantly greater in the pregnancies with maternal hypercortisolemia: in this cohort, 40% of the lambs of cortisol-infused ewes died in utero or at birth compared to 25% of lambs of control ewes, and 24% of lambs of cortisol-infused ewes were born preterm, whereas no lamb was born preterm in the control group. Compared to control lambs, the lambs of cortisol-infused ewes born at full term exhibited a significant increase in mean aortic pressure just prior to birth, and a significant decrease in mean aortic pressure that was evident during the first 9 hours after birth. The QT interval was decreased prior to birth and increased immediately after birth in the newborns of cortisol-treated ewes compared to control lambs. These findings suggest that an excess in utero corticosteroid exposure adversely affects fetal cardiac adaptation to extrauterine life and that chronic maternal stress or hypersecretion of corticosteroids may contribute to adverse obstetric outcomes.

What risk factors for sudden infant death syndrome are preterm and term medically complex infants exposed to at home?

OBJECTIVES

Risk factors for sudden infant death syndrome include premature birth, maternal smoking, prone or side sleeping position, sleeping with blankets, sharing a sleeping surface with an adult, and sleeping without an adult in the room. In this study, we compare parents' responses on sleep patterns in premature and term infants with medical complexity.

METHODS

Parents of children enrolled in the Canadian Respiratory Syncytial Virus Evaluation Study of Palivizumab were phoned monthly regarding their child's health status until the end of each respiratory syncytial virus season. Baseline data were obtained on patient demographics, medical history, and neonatal course. Responses on adherence to safe sleep recommendations were recorded as part of the assessment.

RESULTS

A total of 2,526 preterms and 670 term infants with medical complexity were enrolled. Statistically significant differences were found in maternal smoking rates between the two groups: 13.3% (preterm); 9.3% (term) infants (χ 2=8.1, df=1, P=0.004) and with respect to toys in the crib: 12.3% (term) versus 5.8% preterms (χ 2=24.5, df=1, P<0.0005). Preterm infants were also significantly more likely to be placed prone to sleep (8.8%), compared with term infants (3.3%), (χ 2=18.1, df=1, P<0.0005).

CONCLUSION

All the infants in this study had frequent medical contacts. There is a greater prevalence of some risk factors for sudden infant death syndrome in preterm infants compared to term infants with medical complexity. Specific educational interventions for vulnerable infants may be necessary.

Genetic Factors Underlying Sudden Infant Death Syndrome

Sudden Infant Death syndrome (SIDS) is a diagnosis of exclusion. Decades of research have made steady gains in understanding plausible mechanisms of terminal events. Current evidence suggests SIDS includes heterogeneous biological conditions, such as metabolic, cardiac, neurologic, respiratory, and infectious conditions. Here we review genetic studies that address each of these areas in SIDS cases and cohorts, providing a broad view of the genetic underpinnings of this devastating phenomenon. The current literature has established a role for monogenic genetic causes of SIDS mortality in a subset of cases. To expand upon our current knowledge of disease-causing genetic variants in SIDS cohorts and their mechanisms, future genetic studies may employ functional assessments of implicated variants, broader genetic tests, and the inclusion of parental genetic data and family history information.

Telmisartan cardioprotects from the ischaemic/hypoxic damage through a miR-1-dependent pathway

The aim of this study was to investigate whether telmisartan protects the heart from the ischaemia/reperfusion damage through a local microRNA‐1 modulation. Studies on the myocardial ischaemia/reperfusion injury in vivo and on the cardiomyocyte hypoxia/reoxygenation damage in vitro were done. In vivo, male Sprague‐Dawley rats administered for 3 weeks with telmisartan 12 mg/kg/d by gastric gavage underwent ischaemia/reperfusion of the left descending coronary artery. In these rats, infarct size measurement, ELISA, immunohistochemistry (IHC) and reverse transcriptase real‐time polymerase chain reaction showed that expressions of connexin 43, potassium voltage‐gated channel subfamily Q member 1 and the protein Bcl‐2 were significantly increased by telmisartan in the reperfused myocardium, paralleled by microRNA‐1 down‐regulation. In vitro, the transfection of cardiomyocytes with microRNA‐1 reduced the expressions of connexin 43, potassium voltage‐gated channel subfamily Q member 1 and Bcl‐2 in the cells. Telmisartan (50 µmol/L) 60 minutes before hypoxia/reoxygenation, while not affecting the levels of miR‐1 in transfected cells in normoxic condition, almost abolished the increment of miR‐1 induced by the hypoxia/reoxygenation to transfected cells. All together, telmisartan cardioprotected against the myocardial damage through the microRNA‐1 modulation, and consequent modifications of its downstream target connexin 43, potassium voltage‐gated channel subfamily Q member 1 and Bcl‐2.

Respiratory rhythm generation, hypoxia, and oxidative stress-Implications for development

Encountered in a number of clinical conditions, repeated hypoxia/reoxygenation during the neonatal period can pose both a threat to immediate survival as well as a diminished quality of living later in life. This review focuses on our current understanding of central respiratory rhythm generation and the role that hypoxia and reoxygenation play in influencing rhythmogenesis. Here, we examine the stereotypical response of the inspiratory rhythm from the preBötzinger complex (preBötC), basic neuronal mechanisms that support rhythm generation during the peri-hypoxic interval, and the physiological consequences of inspiratory network responsivity to hypoxia and reoxygenation, acute and chronic intermittent hypoxia, and oxidative stress. These topics are examined in the context of Sudden Infant Death Syndrome, apneas of prematurity, and neonatal abstinence syndrome.

Long QT molecular autopsy in sudden unexplained death in the young (1-40 years old): Lessons learnt from an eight year experience in New Zealand

BACKGROUND

To review long QT syndrome molecular autopsy results in sudden unexplained death in young (SUDY) between 2006 and 2013 in New Zealand.

METHODS

Audit of the LQTS molecular autopsy results, cardiac investigations and family screening data from gene-positive families.

RESULTS

During the study period, 365 SUDY cases were referred for molecular autopsy. 128 cases (35%) underwent LQTS genetic testing. 31 likely pathogenic variants were identified in 27 cases (21%); SCN5A (14/31, 45%), KCNH2 (7/31, 22%), KCNQ1 (4/31, 13%), KCNE2 (3/31, 10%), KCNE1 (2/31, 7%), KCNJ2 (1/31, 3%). Thirteen variants (13/128, 10%) were ultimately classified as pathogenic. Most deaths (63%) occurred during sleep. Gene variant carriage was more likely with a positive medical history (mostly seizures, 63% vs 36%, p = 0.01), amongst females (36% vs 12%, p = 0.001) and whites more than Maori (31% vs 0, p = 0.0009). Children 1-12 years were more likely to be gene-positive (33% vs 14%, p = 0.02). Family screening identified 42 gene-positive relatives, 18 with definitive phenotypic expression of LQTS/Brugada. 76% of the variants were maternally inherited (p = 0.007). Further family investigations and research now support pathogenicity of the variant in 13/27 (48%) of gene-positive cases.

CONCLUSION

In New Zealand, variants in SCN5A and KCNH2, with maternal inheritance, predominate. A rare variant in LQTS genes is more likely in whites rather than Maori, females, children 1-12 years and those with a positive personal and family history of seizures, syncope or SUDY. Family screening supported the diagnosis in a third of the cases. The changing classification of variants creates a significant challenge.

Use of radiotelemetry to assess perinatal cardiac function in the ovine fetus and newborn

The late gestation fetal ECG (fECG) has traditionally been difficult to characterize due to the low fECG signal relative to high maternal noise. Although new technologies have improved the feasibility of its acquisition and separation, little is known about its development in late gestation, a period in which the fetal heart undergoes extensive maturational changes. Here, we describe a method for the chronic implantation of radiotelemetry devices into late gestation ovine fetuses to characterize parameters of the fECG following surgery, throughout late gestation, and in the perinatal period. We found no significant changes in mean aortic pressure (MAP), heart rate (HR), or ECG in the 5 days following implantation; however, HR decreased in the first 24 h following the end of surgery, with associated increases in RR, PR, and QRS intervals. Over the last 14 days of fetal life, fetal MAP significantly increased, and HR significantly decreased, as expected. MAP and HR increased as labor progressed. Although there were no significant changes over time in the ECG during late gestation, the duration of the PR interval initially decreased and then increased as birth approached. These results indicate that although critical maturational changes occur in the late gestation fetal myocardium, the mechanisms that control the cardiac conduction are relatively mature in late gestation. The study demonstrates that radiotelemetry can be successfully used to assess fetal cardiac function, in particular conduction, through the process of labor and delivery, and may therefore be a useful tool for study of peripartum cardiac events.

Endothelial cells by inactivation of VHL gene direct angiogenesis, not vasculogenesis via Twist1 accumulation associated with hemangioblastoma neovascularization

Inactivation of the VHL tumour suppressor gene is a highly frequent genetic event in the carcinogenesis of central nervous system-(CNS) hemangioblastomas (HBs). The patterning of the similar embryonic vasculogenesis is an increasing concern in HB-neovascularization, and the classic vascular endothelial growth factor (VEGF)-mediated angiogenesis driven by VHL loss-of-function from human endothelium have been questioned. With this regard, we identify a distinct, VHL silencing-driven mechanism in which human vascular endothelial cells by means of increasing cell proliferation and decreasing cell apoptosis, is concomitant with facilitating accumulation of Twist1 protein in vascular endothelial cells in vitro. Importantly, this molecular mechanism is also pinpointed in CNS-HBs, and associated with the process of HB-neovascularization. In contrast with recent studies of HB-neovascularization, these modified cells did not endow with the typical features of vasculogenesis, indicating that this is a common angiogenesis implementing the formation of the vascular network. Taken together, these findings suggest that vasculogenesis and angiogenesis may constitute complementary mechanisms for HB-neovascularization, and could provide a rational recognition of single anti-angiogenic intervention including targeting to the Twist1 signalling for HBs.

Myocardial VHL-HIF Signaling Controls an Embryonic Metabolic Switch Essential for Cardiac Maturation

While gene regulatory networks involved in cardiogenesis have been characterized, the role of bioenergetics remains less studied. Here we show that until midgestation, myocardial metabolism is compartmentalized, with a glycolytic signature restricted to compact myocardium contrasting with increased mitochondrial oxidative activity in the trabeculae. HIF1α regulation mirrors this pattern, with expression predominating in compact myocardium and scarce in trabeculae. By midgestation, the compact myocardium downregulates HIF1α and switches toward oxidative metabolism. Deletion of the E3 ubiquitin ligase Vhl results in HIF1α hyperactivation, blocking the midgestational metabolic shift and impairing cardiac maturation and function. Moreover, the altered glycolytic signature induced by HIF1 trabecular activation precludes regulation of genes essential for establishment of the cardiac conduction system. Our findings reveal VHL-HIF-mediated metabolic compartmentalization in the developing heart and the connection between metabolism and myocardial differentiation. These results highlight the importance of bioenergetics in ventricular myocardium specialization and its potential relevance to congenital heart disease.

Filamin C: a novel component of the KCNE2 interactome during hypoxia

Aim

KCNE2 encodes for the potassium voltage-gated channel, KCNE2. Mutations in KCNE2 have been associated with long-QT syndrome (LQTS). While KCNE2 has been extensively studied, the functions of its C-terminal domain remain inadequately described. Here, we aimed to elucidate the functions of this domain by identifying its protein interactors using yeast two-hybrid analysis.

Methods

The C-terminal domain of KCNE2 was used as bait to screen a human cardiac cDNA library for putative interacting proteins. Co-localisation and co-immunoprecipitation analyses were used for verification.

Results

Filamin C (FLNC) was identified as a putative interactor with KCNE2. FLNC and KCNE2 co-localised within the cell, however, a physical interaction was only observed under hypoxic conditions.

Conclusion

The identification of FLNC as a novel KCNE2 ligand not only enhances current understanding of ion channel function and regulation, but also provides valuable information about possible pathways likely to be involved in LQTS pathogenesis.

Steroid Receptor Coactivator-3 (SRC-3/AIB1) as a Novel Therapeutic Target in Triple Negative Breast Cancer and Its Inhibition with a Phospho-Bufalin Prodrug

Triple negative breast cancer (TNBC) has the poorest prognosis of all types of breast cancer and currently lacks efficient targeted therapy. Chemotherapy is the traditional standard-of-care for TNBC, but is frequently accompanied by severe side effects. Despite the fact that high expression of steroid receptor coactivator 3 (SRC-3) is correlated with poor survival in estrogen receptor positive breast cancer patients, its role in TNBC has not been extensively investigated. Here, we show that high expression of SRC-3 correlates with both poor overall survival and post progression survival in TNBC patients, suggesting that SRC-3 can serve as a prognostic marker for TNBC. Furthermore, we demonstrated that bufalin, a SRC-3 small molecule inhibitor, when introduced even at nM concentrations, can significantly reduce TNBC cell viability and motility. However, because bufalin has minimal water solubility, its in vivo application is limited. Therefore, we developed a water soluble prodrug, 3-phospho-bufalin, to facilitate its in vivo administration. In addition, we demonstrated that 3-phospho-bufalin can effectively inhibit tumor growth in an orthotopic TNBC mouse model, suggesting its potential application as a targeted therapy for TNBC treatment.

Myosin heavy chain 15 is associated with bovine pulmonary arterial pressure

Bovine pulmonary hypertension, brisket disease, causes significant morbidity and mortality at elevations above 2,000 m. Mean pulmonary arterial pressure (mPAP) is moderately heritable, with inheritance estimated to lie within a few major genes. Invasive mPAP measurement is currently the only tool available to identify cattle at risk of hypoxia-induced pulmonary hypertension. A genetic test could allow selection of cattle suitable for high altitude without the need for invasive testing. In this study we evaluated three candidate genes (myosin heavy chain 15 [MYH15], NADH dehydrogenase flavoprotein 2, and FK binding protein 1A) for association with mPAP in 166 yearling Angus bulls grazing at 2,182 m. The T allele (rs29016420) of MYH15 was linked to lower mPAP in a dominant manner (CC 47.2 ± 1.6 mmHg [mean ± standard error of the mean]; CT/TT 42.8 ± 0.7 mmHg; P = 0.02). The proportions of cattle with MYH15 CC, CT, and TT genotypes were 55%, 41%, and 4%, respectively. Given the high frequency of the deleterious allele, it is likely that the relative contribution of MYH15 polymorphisms to pulmonary hypertension is small, supporting previous predictions that the disease is polygenic. We evaluated allelic frequency of MYH15 in the Himalayan yak (Bos grunniens), a closely related species adapted to high altitude, and found 100% prevalence of T allele homozygosity. In summary, we identified a polymorphism in MYH15 significantly associated with mPAP. This finding may aid selection of cattle suitable for high altitude and contribute to understanding human hypoxia-induced pulmonary hypertension.

ECG in neonate mice with spinal muscular atrophy allows assessment of drug efficacy

Molecular technologies have produced diverse arrays of animal models for studying genetic diseases and potential therapeutics. Many have neonatal phenotypes. Spinal muscular atrophy (SMA) is a neuromuscular disorder primarily affecting children, and is of great interest in translational medicine. The most widely used SMA mouse models require all phenotyping to be performed in neonates since they do not survive much past weaning. Pre-clinical studies in neonate mice can be hindered by toxicity and a lack of quality phenotyping assays, since many assays are invalid in pups or require subjective scoring with poor inter-rater variability. We find, however, that passive electrocardiography (ECG) recording in conscious 11-day old SMA mice provides sensitive outcome measures, detecting large differences in heart rate, cardiac conduction, and autonomic control resulting from disease. We find significant drug benefits upon treatment with G418, an aminoglycoside targeting the underlying protein deficiency, even in the absence of overt effects on growth and survival. These findings provide several quantitative physiological biomarkers for SMA preclinical studies, and will be of utility to diverse disease models featuring neonatal cardiac arrhythmias.

Heart-rate-corrected QT interval evolution in premature infants during the first week of life

Automated monitoring of the QT interval is increasingly common in a variety of clinical settings. A better understanding of how the heart-rate-corrected QT interval (QTc) evolves in early postnatal life is needed before its clinical utility in neonates can be determined. This study aimed to use real-time bedside monitoring as a tool to describe the QTc evolution of premature neonates during the first week of life. All neonates born at a gestation age (GA) of 31 weeks or later and admitted to the level 2 intensive care nursery of the authors' institution between December 2012 and March 2013 were included in this study. The authors prospectively collected QTc values at 15-min intervals during the first week of life, then used two-way analysis of variance (ANOVA) to compare these data among three GA cohorts: 31 to <34 weeks (cohort A), 34 to <37 weeks (cohort B), and ≥37 weeks (cohort C). All the cohorts demonstrated a statistically significant decline in the 24-h average QTc during the first 3-4 days of life before reaching a stable baseline. No diurnal variation in the QTc was identified in any of the study patients. Marked variability and a progressive decline in the QTc of premature neonates occur during the first 3-4 days of life. Understanding this phenomenon is imperative when screening programs for the early detection of QT prolongation are considered.

Hypoxia signaling controls postnatal changes in cardiac mitochondrial morphology and function

Fetal cardiomyocyte adaptation to low levels of oxygen in utero is incompletely understood, and is of interest as hypoxia tolerance is lost after birth, leading to vulnerability of adult cardiomyocytes. It is known that cardiac mitochondrial morphology, number and function change significantly following birth, although the underlying molecular mechanisms and physiological stimuli are undefined.

Here we show that the decrease in cardiomyocyte HIF-signaling in cardiomyocytes immediately after birth acts as a physiological switch driving mitochondrial fusion and increased postnatal mitochondrial biogenesis. We also investigated mechanisms of ATP generation in embryonic cardiac mitochondria. We found that embryonic cardiac cardiomyocytes rely on both glycolysis and the tricarboxylic acid cycle to generate ATP, and that the balance between these two metabolic pathways in the heart is controlled around birth by the reduction in HIF signaling. We therefore propose that the increase in ambient oxygen encountered by the neonate at birth acts as a key physiological stimulus to cardiac mitochondrial adaptation.

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The reduction in HIF signaling encountered by the heart following birth acts as a physiological switch.

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Reduced postnatal cardiac HIF signaling affects mitochondrial number, structure and function.

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Experimental study of mitochondria is prone to artifacts due to the effect of oxygen.

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Cardiomyocytes employ multiple strategies to function in low oxygen in utero.

Hypoxia at the heart of sudden infant death syndrome?

Sudden infant death syndrome (SIDS) is a significant clinical problem without an accepted pathological mechanism, but with multiple conflicting models. Mutations in a growing number of genes have been found postmortem in SIDS cases, notably genes encoding ion channels. This can only account for a minority of cases, however. Our recent work on a novel mouse model of SIDS suggests a potentially more widespread role for cardiac arrhythmia in SIDS without needing to invoke the inheritance of abnormal ion-channel genes. We propose a model for SIDS pathogenesis whereby postnatal hypoxia leads to delayed maturation of the cardiac conduction system and an increased risk of cardiac arrhythmia. Our model may integrate several epidemiological findings related to risks factors for SIDS, and agrees with previous work suggesting a common final pathological pathway in SIDS.

Hypoxic regulation of hand1 controls the fetal-neonatal switch in cardiac metabolism

This study reveals a novel pathway that responds to hypoxia and modulates energy metabolism by cardiomyocytes in the mouse heart, thereby determining oxygen consumption.

Cardiomyocytes are vulnerable to hypoxia in the adult, but adapted to hypoxia in utero. Current understanding of endogenous cardiac oxygen sensing pathways is limited. Myocardial oxygen consumption is determined by regulation of energy metabolism, which shifts from glycolysis to lipid oxidation soon after birth, and is reversed in failing adult hearts, accompanying re-expression of several “fetal” genes whose role in disease phenotypes remains unknown. Here we show that hypoxia-controlled expression of the transcription factor Hand1 determines oxygen consumption by inhibition of lipid metabolism in the fetal and adult cardiomyocyte, leading to downregulation of mitochondrial energy generation. Hand1 is under direct transcriptional control by HIF1α. Transgenic mice prolonging cardiac Hand1 expression die immediately following birth, failing to activate the neonatal lipid metabolising gene expression programme. Deletion of Hand1 in embryonic cardiomyocytes results in premature expression of these genes. Using metabolic flux analysis, we show that Hand1 expression controls cardiomyocyte oxygen consumption by direct transcriptional repression of lipid metabolising genes. This leads, in turn, to increased production of lactate from glucose, decreased lipid oxidation, reduced inner mitochondrial membrane potential, and mitochondrial ATP generation. We found that this pathway is active in adult cardiomyocytes. Up-regulation of Hand1 is protective in a mouse model of myocardial ischaemia. We propose that Hand1 is part of a novel regulatory pathway linking cardiac oxygen levels with oxygen consumption. Understanding hypoxia adaptation in the fetal heart may allow development of strategies to protect cardiomyocytes vulnerable to ischaemia, for example during cardiac ischaemia or surgery.

Regulation of oxygen usage in cardiomyocytes is of great medical interest, because adult cardiac tissue is extremely vulnerable to hypoxia during myocardial infarction and cardiac surgery. While some progress has been made toward protecting cardiomyocytes from hypoxia in these circumstances, it has been limited by a lack of understanding of endogenous oxygen-sensing pathways. In contrast to adult cardiac tissue, embryonic cardiomyocytes are highly resistant to hypoxia, although the mechanisms underlying this have hitherto been unclear. Using mice we show that the transcription factor Hand1 is expressed at high levels in the fetal heart, under direct control of HIF1α signaling, a pathway well known to respond to hypoxia. We show that Hand1 expression decreases at birth as the neonate is exposed to higher levels of oxygen. By experimentally increasing Hand1 expression in the neonatal heart, we see lower oxygen consumption in cardiomyocytes and this is caused by Hand1 repressing key regulatory genes involved in cardiomyocyte lipid metabolism. This has the effect of decreasing mitochondrial ATP generation via the tricarboxylic acid cycle. Furthermore, we show that increasing Hand1 expression in adult transgenic hearts is protective against myocardial infarction, suggesting that a hypoxia–Hand1 pathway may also be of importance in the adult heart.