m6A Regulators in Human Adipose Tissue - Depot-Specificity and Correlation With Obesity.

Background: N6-methyladenosine (m6A) is one of the most abundant post-transcriptional modifications on mRNA influencing mRNA metabolism. There is emerging evidence for its implication in metabolic disease. No comprehensive analyses on gene expression of m6A regulators in human adipose tissue, especially in paired adipose tissue depots, and its correlation with clinical variables were reported so far. We hypothesized that inter-depot specific gene expression of m6A regulators may differentially correlate with clinical variables related to obesity and fat distribution. Methods: We extracted intra-individually paired gene expression data (omental visceral adipose tissue (OVAT) N=48; subcutaneous adipose tissue (SAT) N=56) of m6A regulators from an existing microarray dataset. We also measured gene expression in another sample set of paired OVAT and SAT (N=46) using RT-qPCR. Finally, we extracted existing gene expression data from peripheral mononuclear blood cells (PBMCs) and single nucleotide polymorphisms (SNPs) in METTL3 and YTHDF3 from genome wide data from the Sorbs population (N=1049). The data were analysed for differential gene expression between OVAT and SAT; and for association with obesity and clinical variables. We further tested for association of SNP markers with gene expression and clinical traits. Results: In adipose tissue we observed that several m6A regulators (WTAP, VIRMA, YTHDC1 and ALKBH5) correlate with obesity and clinical variables. Moreover, we found adipose tissue depot specific gene expression for METTL3, WTAP, VIRMA, FTO and YTHDC1. In PBMCs, we identified ALKBH5 and YTHDF3 correlated with obesity. Genetic markers in METTL3 associate with BMI whilst SNPs in YTHDF3 are associated with its gene expression. Conclusions: Our data show that expression of m6A regulators correlates with obesity, is adipose tissue depot-specific and related to clinical traits. Genetic variation in m6A regulators adds an additional layer of variability to the functional consequences.

Circulating MicroRNA-210 Concentrations in Patients with Acute Heart Failure: Data from the Akershus Cardiac Examination 2 Study.

BACKGROUND: MicroRNA (miR)-210 expression is induced by acute and chronic hypoxia and provides prognostic information in patients with aortic stenosis and acute coronary syndrome. We hypothesized that circulating miR-210 concentrations could provide diagnostic and prognostic information in patients with acute heart failure (HF). METHODS: We measured miR-210 concentrations in serum samples on admission from 314 patients hospitalized for acute dyspnea and 9 healthy control subjects. The diagnostic and prognostic properties of miR-210 were tested in patients after adjudication of all diagnoses and with median follow-up of 464 days. RESULTS: All patients and control subjects had miR-210 concentrations within the range of detection, and the analytical variation was low as the coefficient of variation of synthetic spike-in RNA was 4%. Circulating miR-210 concentrations were increased in patients with HF compared to healthy control subjects, but miR-210 concentrations did not separate patients with acute HF (n = 143) from patients with non-HF-related dyspnea (n = 171): the area under the curve was 0.50 (95% CI 0.43-0.57). Circulating miR-210 concentrations were associated with mortality (n = 114) after adjustment for clinical risk factors (hazard ratio 1.65 [95% CI 1.03-2.62] per unit miR-210 increase), but this association was attenuated and not significant after adjustment for established cardiac protein biomarkers. CONCLUSIONS: Circulating miR-210 concentrations are associated with mortality, but do not add to established protein biomarkers for diagnosis or prognosis in patients with acute dyspnea.

Glycosylated Chromogranin A in Heart Failure: Implications for Processing and Cardiomyocyte Calcium Homeostasis.

BACKGROUND: Chromogranin A (CgA) levels have previously been found to predict mortality in heart failure (HF), but currently no information is available regarding CgA processing in HF and whether the CgA fragment catestatin (CST) may directly influence cardiomyocyte function. METHODS AND RESULTS: CgA processing was characterized in postinfarction HF mice and in patients with acute HF, and the functional role of CST was explored in experimental models. Myocardial biopsies from HF, but not sham-operated mice, demonstrated high molecular weight CgA bands. Deglycosylation treatment attenuated high molecular weight bands, induced a mobility shift, and increased shorter CgA fragments. Adjusting for established risk indices and biomarkers, circulating CgA levels were found to be associated with mortality in patients with acute HF, but not in patients with acute exacerbation of chronic obstructive pulmonary disease. Low CgA-to-CST conversion was also associated with increased mortality in acute HF, thus, supporting functional relevance of impaired CgA processing in cardiovascular disease. CST was identified as a direct inhibitor of CaMKIIδ (Ca2+/calmodulin-dependent protein kinase IIδ) activity, and CST reduced CaMKIIδ-dependent phosphorylation of phospholamban and the ryanodine receptor 2. In line with CaMKIIδ inhibition, CST reduced Ca2+ spark and wave frequency, reduced Ca2+ spark dimensions, increased sarcoplasmic reticulum Ca2+ content, and augmented the magnitude and kinetics of cardiomyocyte Ca2+ transients and contractions. CONCLUSIONS: CgA-to-CST conversion in HF is impaired because of hyperglycosylation, which is associated with clinical outcomes in acute HF. The mechanism for increased mortality may be dysregulated cardiomyocyte Ca2+ handling because of reduced CaMKIIδ inhibition.

Influence of glycosylation on diagnostic and prognostic accuracy of N-terminal pro-B-type natriuretic peptide in acute dyspnea: data from the Akershus Cardiac Examination 2 Study.

BACKGROUND: The N-terminal part of pro-B-type natriuretic peptide (NT-proBNP) is glycosylated, but whether glycosylation influences the diagnostic and prognostic accuracy of NT-proBNP measurements is not known. METHODS: We measured NT-proBNP concentrations of 309 patients with acute dyspnea by use of standard EDTA tubes and EDTA tubes pretreated with deglycosylation enzymes. The primary cause of dyspnea was classified as heart failure (HF) or non-HF, and the diagnosis was adjudicated by 2 independent physicians. We collected information on all-cause mortality during follow-up. RESULTS: In all, 142 patients (46%) were diagnosed with HF. NT-proBNP concentrations in nondeglycosylated samples distinguished HF patients from patients with non-HF related dyspnea [median 3588 (quartiles 1-3 1578-8404) vs 360 (126-1139) ng/L, P < 0.001], but concentrations were markedly higher in samples pretreated with deglycosylation enzymes (total NT-proBNP) [7497 (3374-14 915) vs 798 (332-2296) ng/L, P < 0.001]. The AUC to separate HF patients from patients with non-HF related dyspnea was 0.871 (95% CI 0.829-0.907) for total NT-proBNP compared with 0.852 (0.807-0.890) for NT-proBNP measurements in standard EDTA plasma. During a median follow-up of 816 days, 112 patients (36%) died. Both NT-proBNP and total NT-proBNP concentrations were associated with mortality in separate multivariate models, but only total NT-proBNP concentrations provided added value to the basic risk model of our dataset as assessed by the net reclassification index: 0.24 (95% CI 0.003-0.384). There was a graded increase in risk across total NT-proBNP quartiles, in contrast with the results for NT-proBNP measurements. CONCLUSIONS: NT-proBNP concentrations were higher, and diagnostic and prognostic accuracy was improved, by pretreating tubes with deglycosylation enzymes.

Prognostic value of circulating microRNA-210 levels in patients with moderate to severe aortic stenosis.

BACKGROUND: Circulating micro-RNAs have been proposed as a novel class of cardiovascular (CV) biomarkers, but whether they meet analytical requirements and provide additional information to establish risk indices have not been established. miR-210 levels are increased in subjects with low VO2 max, which is a recognized risk factor in patients with aortic stenosis (AS), and we hypothesized that circulating miR-210 levels may be increased in patients with AS and associated with a poor prognosis. METHODS: We measured circulating miR-210 levels by real-time PCR in 57 patients with moderate to severe AS and in 10 age- and gender-matched healthy controls. The merit of miR-210 as a biomarker was assessed according to established criteria, including by comparing miR-210 levels with NT-proBNP and miR-22 levels, which is another miRNA biomarker candidate. RESULTS: All patients and control subjects had miR-210 levels within the range of detection (Cq<35) and the analytical variability was low. Circulating miR-210 levels were 2.0±0.2 [mean±SEM] fold increased in AS patients compared to controls (p = 0.002), whereas miR-22 levels were not differently expressed in the AS patients (0.12±0.06 fold increase, p = 0.45). The increase in miR-210 levels in AS patients was comparable to the increment in NT-proBNP levels: [AUC] 0.82 (95% CI 0.70-0.90) vs. 0.85 (0.75-0.93), respectively, p = 0.71. During a median follow-up of 1287 days, 15 patients (26%) died. There was a significant association between higher circulating levels of miR-210 and increased mortality during follow-up: hazard ratio [supra- vs. inframedian levels] 3.3 (95% CI 1.1-10.5), p = 0.039. Adjusting for other risk indices in multivariate analysis did not attenuate the prognostic merit of circulating miR-210 levels. CONCLUSION: Circulating miR-210 levels are increased in patients with AS and provide independent prognostic information to established risk indices. Analytical characteristics were also excellent supporting the potential of micro-RNAs as novel CV biomarkers.

Secretogranin II; a protein increased in the myocardium and circulation in heart failure with cardioprotective properties.

BACKGROUND: Several beneficial effects have been demonstrated for secretogranin II (SgII) in non-cardiac tissue. As cardiac production of chromogranin A and B, two related proteins, is increased in heart failure (HF), we hypothesized that SgII could play a role in cardiovascular pathophysiology. METHODOLOGY/PRINCIPAL FINDINGS: SgII production was characterized in a post-myocardial infarction heart failure (HF) mouse model, functional properties explored in experimental models, and circulating levels measured in mice and patients with stable HF of moderate severity. SgII mRNA levels were 10.5 fold upregulated in the left ventricle (LV) of animals with myocardial infarction and HF (p<0.001 vs. sham-operated animals). SgII protein levels were also increased in the LV, but not in other organs investigated. SgII was produced in several cell types in the myocardium and cardiomyocyte synthesis of SgII was potently induced by transforming growth factor-ß and norepinephrine stimulation in vitro. Processing of SgII to shorter peptides was enhanced in the failing myocardium due to increased levels of the proteases PC1/3 and PC2 and circulating SgII levels were increased in mice with HF. Examining a pathophysiological role of SgII in the initial phase of post-infarction HF, the SgII fragment secretoneurin reduced myocardial ischemia-reperfusion injury and cardiomyocyte apoptosis by 30% and rapidly increased cardiomyocyte Erk1/2 and Stat3 phosphorylation. SgII levels were also higher in patients with stable, chronic HF compared to age- and gender-matched control subjects: median 0.16 (Q1-3 0.14-0.18) vs. 0.12 (0.10-0.14) nmol/L, p<0.001. CONCLUSIONS: We demonstrate increased myocardial SgII production and processing in the LV in animals with myocardial infarction and HF, which could be beneficial as the SgII fragment secretoneurin protects from ischemia-reperfusion injury and cardiomyocyte apoptosis. Circulating SgII levels are also increased in patients with chronic, stable HF and may represent a new cardiac biomarker.

Chromogranin B in heart failure: a putative cardiac biomarker expressed in the failing myocardium.

BACKGROUND: Chromogranin B (CgB) is a member of the granin protein family. Because CgB is often colocalized with chromogranin A (CgA), a recently discovered cardiac biomarker, we hypothesized that CgB is regulated during heart failure (HF) development. METHODS AND RESULTS: CgB regulation was investigated in patients with chronic HF and in a post-myocardial infarction HF mouse model. Animals were phenotypically characterized by echocardiography and euthanized 1 week after myocardial infarction. CgB mRNA levels were 5.2-fold increased in the noninfarcted part of the left ventricle of HF animals compared with sham-operated animals (P<0.001). CgB mRNA level in HF animals correlated closely with animal lung weight (r=0.74, P=0.04) but not with CgA mRNA levels (r=0.20, P=0.61). CgB protein levels were markedly increased in both the noninfarcted (110%) and the infarcted part of the left ventricle (70%) but unaltered in other tissues investigated. Myocardial CgB immunoreactivity was confined to cardiomyocytes. Norepinephrine, angiotensin II, and transforming growth factor-beta increased CgB gene expression in cardiomyocytes. Circulating CgB levels were increased in HF animals (median levels in HF animals versus sham, 1.23 [interquartile range, 1.03 to 1.93] versus 0.98 [0.90 to 1.04] nmol/L; P=0.003) and in HF patients (HF patients versus control, 1.66 [1.48 to 1.85] versus 1.47 [1.39 to 1.58] nmol/L; P=0.007), with levels increasing in proportion to New York Heart Association functional class (P=0.03 for trend). Circulating CgB levels were only modestly correlated with CgA (r=0.31, P=0.009) and B-type natriuretic peptide levels (r=0.27, P=0.014). CONCLUSIONS: CgB production is increased and regulated in proportion to disease severity in the left ventricle and circulation during HF development.

Differential regulation of AMP-activated kinase and AKT kinase in response to oxygen availability in crucian carp (Carassius carassius).

We investigated whether two kinases critical for survival during periods of energy deficiency in anoxia-intolerant mammalian species, AMP-activated kinase (AMPK), and protein kinase B (AKT), are equally important for hypoxic/anoxic survival in the extremely anoxia-tolerant crucian carp (Carassius carassius). We report that phosphorylation of AMPK and AKT in heart and brain showed small changes after 10 days of severe hypoxia (0.3 mg O2/l at 9 degrees C). In contrast, anoxia exposure (0.01 mg O2/l at 8 degrees C) substantially increased AMPK phosphorylation but decreased AKT phosphorylation in carp heart and brain, indicating activation of AMPK and deactivation of AKT. In agreement, blocking the activity of AMPK in anoxic fish in vivo with 20 mg/kg Compound C resulted in an elevated metabolic rate (as indicated by increased ethanol production) and tended to reduce energy charge. This is the first in vivo experiment with Compound C in a nonmammalian vertebrate, and it appears that AMPK plays a role in mediating anoxic metabolic depression in crucian carp. Real-time RT-PCR analysis of the investigated AMPK subunit revealed that the most likely composition of subunits in the carp heart is alpha2, beta1B, gamma2a, whereas a more even expression of subunits was found in the brain. In the heart, expression of the regulatory gamma2-subunit increased in the heart during anoxia. In the brain, expression of the alpha1-, alpha2-, and gamma1-subunits decreased with anoxia exposure, but expression of the gamma2-subunit remained constant. Combined, our findings suggest that AMPK and AKT may play important, but opposing roles for hypoxic/anoxic survival in the anoxia-tolerant crucian carp.