Michael A Portman

Triiodothyronine increases myocardial function and pyruvate entry into the citric acid cycle after reperfusion in a model of infant cardiopulmonary bypass

Triiodothyronine (T3) supplementation improves clinical outcomes in infants after cardiac surgery using cardiopulmonary bypass by unknown mechanisms. We utilized a translational model of infant cardiopulmonary bypass to test the hypothesis that T3 modulates pyruvate entry into the citric acid cycle (CAC), thereby providing the energy support for improved cardiac function after ischemia-reperfusion (I/R). Neonatal piglets received intracoronary [2-(13)Carbon((13)C)]pyruvate for 40 min (8 mM) during control aerobic conditions (control) or immediately after reperfusion (I/R) from global hypothermic ischemia. A third group (I/R-Tr) received T3 (1.2 μg/kg) during reperfusion. We assessed absolute CAC intermediate levels and flux parameters into the CAC through oxidative pyruvate decarboxylation (PDC) and anaplerotic carboxylation (PC) using [2-(13)C]pyruvate and isotopomer analysis by gas and liquid chromatography-mass spectrometry and (13)C-nuclear magnetic resonance spectroscopy. When compared with I/R, T3 (group I/R-Tr) increased cardiac power and oxygen consumption after I/R while elevating flux of both PDC and PC (∼4-fold). Although neither I/R nor I/R-Tr modified absolute CAC levels, T3 inhibited I/R-induced reductions in their molar percent enrichment. Furthermore, (13)C-labeling of CAC intermediates suggests that T3 may decrease entry of unlabeled carbons at the level of oxaloacetate through anaplerosis or exchange reaction with asparate. T3 markedly enhances PC and PDC fluxes, thereby providing potential substrate for elevated cardiac function after reperfusion. This T3-induced increase in pyruvate fluxes occurs with preservation of the CAC intermediate pool. Our labeling data raise the possibility that T3 reduces reliance on amino acids for anaplerosis after reperfusion.

MuRF1 mono-ubiquitinates TRα to inhibit T3-induced cardiac hypertrophy in vivo

Thyroid hormone (TH) is recognized for its role in cellular metabolism and growth and participates in homeostasis of the heart. T3 activates pro-survival pathways including Akt and mTOR. Treatment with T3 after myocardial infarction is cardioprotective and promotes elements of physiological hypertrophic response after cardiac injury. Although T3 is known to benefit the heart, very little about its regulation at the molecular level has been described to date. The ubiquitin proteasome system (UPS) regulates nuclear hormone receptors such as estrogen, progesterone, androgen, and glucocorticoid receptors by both degradatory and non-degradatory mechanisms. However, how the UPS regulates T3-mediated activity is not well understood. In this study, we aim to determine the role of the muscle-specific ubiquitin ligase muscle ring finger-1 (MuRF1) in regulating T3-induced cardiomyocyte growth. An increase in MuRF1 expression inhibits T3-induced physiological cardiac hypertrophy, whereas a decrease in MuRF1 expression enhances T3s activity both in vitro and in cardiomyocytes in vivo MuRF1 interacts directly with TRα to inhibit its activity by posttranslational ubiquitination in a non-canonical manner. We then demonstrated that a nuclear localization apparatus that regulates/inhibits nuclear receptors by sequestering them within a subcompartment of the nucleus was necessary for MuRF1 to inhibit T3 activity. This work implicates a novel mechanism that enhances the beneficial T3 activity specifically within the heart, thereby offering a potential target to enhance cardiac T3 activity in an organ-specific manner.

Imputation of class I and II HLA loci using high-density SNPs from ImmunoChip and their associations with Kawasaki disease in family-based study.

Kawasaki disease (KD) is the leading cause of acquired heart disease in children in most developed countries including the United States. The etiology of KD is not known; however, epidemiological and immunological data suggest infectious or immune‐related factors in the manifestation of the disease. Further, KD has several hereditary features that strongly suggest a genetic component to disease pathogenesis. Human leucocyte antigen (HLA) loci have also been reported to be associated with KD, but results have been inconsistent, in part, because of small study samples and varying linkage disequilibrium (LD) patterns observed across different ethnic groups. To maximize the informativeness of single nucleotide polymorphism (SNP) genotypes in the major histocompatibility (MHC) region, we imputed classical HLA I (A, B, C) and HLA II (DRB1, DQA1, DQB1) alleles using SNP2HLA method from genotypes of 6700 SNPs within the extended MHC region contained in the ImmunoChip among 112 White patients with KD and their biological parents from North America and tested their association with KD susceptibility using the transmission disequilibrium test. Mendelian consistency in the trios suggested high accuracy and reliability of the imputed alleles (class I = 97.5%, class II = 96.6%). While several SNPs in the MHC region were individually associated with KD susceptibility, we report over‐transmission of HLA‐C*15 (z = +2.19, P = 0.03) and under‐transmission of HLA‐B*44 (z = −2.49, P = 0.01) alleles from parents to patients with KD. HLA‐B*44 has been associated with KD in other smaller studies, and both HLA‐C*15 and HLA‐B*44 have biological mechanisms that could potentially be involved in KD pathogenesis. Overall, inferring HLA loci within the same ethnic group, using family‐based information is a powerful approach. However, studies with larger sample sizes are warranted to evaluate the correlations of the strength and directions between the SNPs in MHC region and the imputed HLA alleles with KD.

DC-SIGN gene promoter variants and IVIG treatment response in Kawasaki disease

BackgroundGenetic variants in the inhibiting Fc γRIIB mediate anti-inflammatory responses and influence IVIG refractoriness (IVIG-R). However, these variants are rare in Asian and Hispanic populations so other genes in the pathway could be potentially involved. IVIG is ineffective in mice lacking SIGN-R1, a related molecule to human DC-SIGN. Further, DC-SIGN is a known receptor for sialylated Fc, the component responsible for the anti-inflammatory action of IVIG. Thus, we hypothesized that DC-SIGN would also be involved in the pathway of IVIG response in Kawasaki Disease (KD) patients.FindingsA case-control approach was performed to examine the differential distribution of five single nucleotide polymorphisms (SNPs) in DC-SIGN promoter with IVIG-R among White (158 vs. 62), Asian (64 vs. 12) and Hispanic (55 vs. 20) KD patients. Distinct differences in allele frequency distributions of several variants in the DC-SIGN promoter were observed in the three ethnic groups. Further, Asians with the major allele “A” in rs2287886 were more likely (OR = 1.76, p = 0.04) to be IVIG non-responder, but this allele is a minor allele in other two ethnic groups, where the association was not apparent.ConclusionsDC-SIGN can potentially complement the role of Fc γRIIB in the anti-inflammatory cascade involved in the IVIG response mechanism.

Coronary artery stenosis risk and time course in Kawasaki disease patients: experience at a US tertiary pediatric centre

Objective Despite treatment with intravenous immunoglobulin (IVIG), the natural progression to coronary artery stenosis in Kawasaki disease is not well defined and remains a potential cause of long-term morbidity. We present a novel study, at a US tertiary paediatric care centre, identifying risk factors for stenosis. Methods We reviewed charts of all children who underwent cardiac catheterisation for coronary artery abnormalities, from 1998 to January 2014, at a tertiary paediatric care centre. Demographic and diagnostic data included time intervals to echocardiographic changes and confirmed catheterisation cases of stenosis. Multivariate survival analysis was used to evaluate risk factors with stenosis formation as the main outcome measure. Results 53 children met the inclusion criteria and 18 (34.6%) developed stenosis. Only those with giant coronary aneurysms (GCA) developed stenosis, with the highest risk group overall being children under the age of 6 months (hazard ratio (HR) 2.82 3.79, p=0.004). In a subset of only cases of GCA (33), a majority went on to develop stenosis (18/33). Median time to diagnosis was 190 days. In this group, children under the age of 6 months were again at highest risk (HR 2.62, p=0.04). IVIG administration, sex and ethnicity were not statistically significant predictors. Conclusions This retrospective study demonstrates a relatively high incidence of stenosis in children with Kawasaki disease and coronary vascular abnormalities. Overall, a majority of cases with GCA progressed into stenosis, with children under the age of 6 months being at highest risk.

Quantitative cardiac phosphoproteomics profiling during ischemia-reperfusion in an immature swine model

Ischemia-reperfusion (I/R) results in altered metabolic and molecular responses, and phosphorylation is one of the most noted regulatory mechanisms mediating signaling mechanisms during physiological stresses. To expand our knowledge of the potential phosphoproteomic changes in the myocardium during I/R, we used Isobaric Tags for Relative and Absolute Quantitation-based analyses in left ventricular samples obtained from porcine hearts under control or I/R conditions. The data are available via ProteomeXchange with identifier PXD006066. We identified 1,896 phosphopeptides within left ventricular control and I/R porcine samples. Significant differential phosphorylation between control and I/R groups was discovered in 111 phosphopeptides from 86 proteins. Analysis of the phosphopeptides using Motif-x identified five motifs: (..R..S..), (..SP..), (..S.S..), (..S…S..), and (..S.T..). Semiquantitative immunoblots confirmed site location and directional changes in phosphorylation for phospholamban and pyruvate dehydrogenase E1, two proteins known to be altered by I/R and identified by this study. Novel phosphorylation sites associated with I/R were also identified. Functional characterization of the phosphopeptides identified by our methodology could expand our understanding of the signaling mechanisms involved during I/R damage in the heart as well as identify new areas to target therapeutic strategies.NEW & NOTEWORTHY We used Isobaric Tags for Relative and Absolute Quantitation technology to investigate the phosphoproteomic changes that occur in cardiac tissue under ischemia-reperfusion conditions. The results of this study provide an extensive catalog of phosphoproteins, both predicted and novel, associated with ischemia-reperfusion, thereby identifying new pathways for investigation.

PPARα Augments Heart Function and Cardiac Fatty Acid Oxidation in Early Experimental Polymicrobial Sepsis

Children with sepsis and multisystem organ failure have downregulated leukocyte gene expression of peroxisome proliferator-activated receptor-α (PPARα), a nuclear hormone receptor transcription factor that regulates inflammation and lipid metabolism. Mouse models of sepsis have likewise demonstrated that the absence of PPARα is associated with decreased survival and organ injury, specifically of the heart. Using a clinically relevant mouse model of early sepsis, we found that heart function increases in wild-type (WT) mice over the first 24 h of sepsis, but that mice lacking PPARα (Ppara-/-) cannot sustain the elevated heart function necessary to compensate for sepsis pathophysiology. Left ventricular shortening fraction, measured 24 h after initiation of sepsis by echocardiography, was higher in WT mice than in Ppara-/- mice. Ex vivo working heart studies demonstrated greater developed pressure, contractility, and aortic outflow in WT compared with Ppara-/- mice. Furthermore, cardiac fatty acid oxidation was increased in WT but not in Ppara-/- mice. Regulatory pathways controlling pyruvate incorporation into the citric acid cycle were inhibited by sepsis in both genotypes, but the regulatory state of enzymes controlling fatty acid oxidation appeared to be permissive in WT mice only. Mitochondrial ultrastructure was not altered in either genotype indicating that severe mitochondrial dysfunction is unlikely at this stage of sepsis. These data suggest that PPARα expression supports the hyperdynamic cardiac response early in the course of sepsis and that increased fatty acid oxidation may prevent morbidity and mortality. NEW & NOTEWORTHY In contrast to previous studies in septic shock using experimental mouse models, we are the first to demonstrate that heart function increases early in sepsis with an associated augmentation of cardiac fatty acid oxidation. Absence of peroxisome proliferator-activated receptor-α (PPARα) results in reduced cardiac performance and fatty acid oxidation in sepsis.

A Phase I–II, Open-Label, Multicenter Trial to Determine the Dosimetry and Safety of 99mTc-Sestamibi in Pediatric Subjects

Myocardial perfusion imaging has long been used off label by practitioners attending for children with cardiac aliments. To provide clinicians with evidence-based dosage recommendation, a phase I–II, open-label, nonrandomized, multicenter trial was therefore designed using 99mTc-sestamibi in pediatric subjects (registered under www.clinicaltrials.gov identifier no. NCT00162045). Methods: Safety and pharmacokinetic data were collected from 78 subjects using either a 1-d imaging protocol (3.7–7.4 MBq/kg, followed by 11.1 MBq/kg) or a 2-d protocol (7.4 MBq/kg for both rest and stress). Anterior and posterior planar images were collected at 15 min, 1.5 h, 4 h, and 8 h. Blood and urine samples were collected at predetermined times. Results: Subjects included 39 children (mean age ± SD, 8.5 ± 2.04 y) and 39 adolescents (mean age ± SD, 13.6 ± 1.39 y). Mean estimated organ-absorbed doses to the upper large intestine, small intestine, gallbladder wall, and lower large intestines were 0.082, 0.043, 0.042, and 0.035 mSv/MBq, respectively. All patients tolerated the radiotracer without serious adverse effects. Significant differences were observed in the liver, upper large intestine contents, and small intestine contents between rest and stress imaging. The effective dose equivalent and effective dose averages were lower in adolescents than younger children (0.011 and 0.019 mSv/MBq, respectively; P < 0.0001). Percentage injected doses (%IDs) corrected for radioactive decay in all dosimetry-evaluable subjects at 15 min and 4 h were 1.9% and 1.2% in the myocardium. Similarly in the lungs, the %ID for all dosimetry-evaluable subjects was 4.9% at 15 min after injection. At rest, the %ID in the liver decreased from a maximum of about 26% at 15 min to less than 9% at 90 min. With stress, values decreased from 15% to 7%, respectively. Conclusion: The estimates of radiation dosimetry, pharmacokinetic parameters, and safety profile in this study population are similar to published studies based on body-mass extrapolations from studies in adults. As such, applying current 99mTc-sestamibi dosing regimens for 1- and 2-d protocols based on those extrapolations will result in the expected radiation dose in children and adolescents.

Nuclear Receptors and the Adaptive Response of the Heart

The nuclear receptor (NR) superfamily is involved in a wide range of physiological processes, including homeostasis, development, and metabolism. Since NRs can directly or indirectly interact with DNA, they often play key regulatory roles in health and disease. More recently NRs have been identified in the myocardium, making them interesting pharmacological targets for disease. This chapter explores the different classes and structure of myocardial NRs, their transcription factor-like regulatory mechanisms, the response elements they target, and the processes that regulate them through ligand binding and posttranslational modifications.

Targeting Transcriptional Control of Fatty Acid Oxidation to Treat Heart Disease

The role of fatty acid oxidation in influencing clinical outcome in congestive heart failure still requires determination. However, the impact of fatty acid oxidation on contractile function likely depends on the specific form and on the etiology of the heart disease. Modifications in transcription of genes regulating fatty acid metabolism represent strategies for clarifying this impact, and may provide treatment options. The nuclear receptors, which regulate pathways controlling substrate metabolism, provide targets for transcriptional regulation. To date there have been few if any clinical trials examining the role of these receptors in modifying transcriptional regulation of fatty acid oxidation in heart failure. We will review the perturbations of these receptors as they occur with heart failure and their potential as therapeutic targets.