Mechanism(s) for age-related sex differences in diet-induced cardiomyopathy: role of RNA methylation

Background/Introduction

Age and sexual dimorphism contribute to the differential cardiometabolic dysfunctions associated with diet-induced obesity. However, the underlying mechanisms remain elusive. RNA modifications via RNA m6A methylation, is an emerging mediator of RNA stability, translation and localization responsible for regulation of multiple biological functions. RNA m6A modifications are regulated by “writers”, “erasers” and “readers”. The role of RNA methylation machinery genes in the heart is largely unexplored, and may provide insight into the influence of age and sex on cardiometabolic dysfunction.

Purpose

We aim to determine differential RNA methylation changes within the heart in a diet-induced cardiomyopathy mouse model, stratified according to age and sex.

Methods

Male and female C57BL/6 mice (6–8wk-old) were fed normal chow (NC) or high-fat/high-sucrose (HFHS) diet for 1 or 4 months. Echocardiographic measurements were performed at 1 and 4 months according to the American Society of Echocardiography and European Association of Cardiovascular Imaging guidelines. At study endpoint, glucose and insulin tolerance testing was conducted by injecting mice intraperitoneally with 2g/kg glucose or 0.6U/kg insulin, and monitoring blood glucose levels over a 2 hour period. RNA from heart tissue was subjected to quantitative PCR for RNA methylation machinery genes (FTO, ALKBH5, METTL3, METTL4, METTL14, YTHDF1 and YTHDF2). PPIA was used to normalise qPCR data.

Results

Both male and female mice showed evidence of age- and diet-induced metabolic dysfunction, however, males and females showed markedly different metabolic impairments. For example, glucose tolerance was exacerbated by 4 months of HFHS diet in males but not females; and only females showed impaired insulin tolerance. Echocardiography showed that males had systolic (stoke volume, cardiac output) and diastolic (E/A ratio) dysfunction after 4 months of HFHS diet, while females were unperturbed. We identified that METTL3 and METTL14, the “writers” of m6A methylation, were consistently increased in male mouse hearts at 1 vs 4 months of age but were unchanged or decreased in females, irrespective of diet. Conversely, YTHDF1, a “reader”, was unchanged in male mouse hearts at 1 vs. 4 months of age but was significantly increased in female hearts.

Conclusion

Our study confirms that markedly different cardiometabolic impairments occur in male versus female mice in response to long-term HFHS diet. Despite significant metabolic impairment in both sexes, cardiac dysfunction was only evident in males. RNA methylation machinery genes were differentially expressed in mouse hearts according to age and sex, suggesting that RNA methylation may be involved in age-related sexual dimorphism in cardiometabolic impairments.

Funding Acknowledgement

Type of funding sources: Foundation. Main funding source(s): Heart Foundation

Dielectric-Modulated Biosensing with Ultrahigh-Frequency-Operated Graphene Field-Effect Transistors

Owing to their excellent electrical properties and chemical stability, graphene field-effect transistors (Gr-FET) are extensively studied for biosensing applications. However, hinging on surface interactions of charged biomolecules, the sensitivity of Gr-FET is hampered by ionic screening under physiological conditions with high salt concentrations up to frequencies as high as MHz. Here, an electrolyte-gated Gr-FET in reflectometry mode at ultrahigh frequencies (UHF, around 2 GHz), where the ionic screening is fully cancelled and the dielectric sensitivity of the device allows the Gr-FET to directly function in high-salt solutions, is configured. Strikingly, by simultaneous characterization using electrolyte gating and UHF reflectometry, the developed graphene biosensors offer unprecedented capability for real-time monitoring of dielectric-specified biomolecular/cell interactions/activities, with superior limit of detection compared to that of previously reported nanoscale high-frequency sensors. These achievements highlight the unique potential of ultrahigh-frequency operation for unblocking the true potential of graphene biosensors for point-of-care diagnostic.

Adipose-targeted overexpression of mitochondrial-targeted catalase does not improve cardio-metabolic parameters in mice with diet-induced obesity

Background

Obesity is associated with significant cardio-metabolic complications. Adipokines, and cytokines released from adipose tissue (AT) stimulate excessive mitochondrial production of reactive oxygen species (ROS). ROS-mediated oxidative modifications is associated with development of insulin resistance and impaired cardiac function. We hypothesised that adipose-targeted overexpression of mitochondrial-targeted catalase (AT-mCAT) could lead to improvement in diet-induced cardio-metabolic dysfunction.

Methods/Results

mCAT (floxed) and AdipoQ-Cre mice were crossed to generate mice overexpressing catalase with a mitochondrial-targeting sequence predominantly in AT (AT-mCAT). Wild-type (WT) and AT-mCAT male mice were fed normal chow (NC) or high-fat/high-sucrose (HFHS) diet (36%fat/34%sucrose) for 4 months. At endpoint, echocardiography showed reduced cardiac output in all groups v WT NC (p<0.05); reduced IVSd in AT-mCAT NC and HFHS groups v WT NC (p<0.01); reduced left ventricular ejection fraction in AT-mCAT HFHS v WT NC (p<0.05) and no differences in fractional shortening or E/A ratio between groups. Glucose tolerance tests (2g/kg) showed impairment in WT HFHS and AT-mCAT HFHS v WT NC (p<0.01, p<0.05 respectively). Triglyceride levels were increased in WT HFHS and AT-mCAT HFHS v WT NC (p<0.05). Analysis of hypertrophic signalling in cardiac tissues by ELISA showed p-AKT/total Akt levels were decreased in AT-mCAT hearts regardless of diet (WT NC v AT-mCAT NC p<0.01; WT HFHS v AT-mCAT HFHS p<0.05).

Conclusion

Our results confirm previous findings that diet-induced obesity is a systemic condition. Targeting adipose tissue with mitochondrial catalase may not be adequate to prevent development of cardio-metabolic dysfunction. More systemic approaches may be required to combat obesity-induced cardio-metabolic impairment.

Funding Acknowledgement

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): National Heart Foundation of Australia

Colchicine and quality of life in patients with acute coronary syndromes: results from the COPS randomized trial

Background

Recent data suggest that colchicine may reduce cardiovascular events among patients presenting with acute coronary syndromes. This sub-study of the Australian COPS trial aimed to assess whether colchicine affects health status outcomes.

Methods

Health status was assessed at baseline and 12-months using the EuroQol-5 Dimension 5-level (EQ-5D-5L) score and the full 19-question Seattle Angina Questionnaire (SAQ). Data were available for 786 patients (388 randomized to colchicine, 398 to placebo).

Results

Baseline characteristics were well matched between groups; mean age was 60.1 (SD 14.8) years, and 20% were female. Baseline health status scores were impaired, and most parameters demonstrated significant improvement from baseline to 12-months (EQ-5D-5L Visual Analogue Score [VAS] 69.3 to 77.7; SAQ angina frequency score 83.0 to 95.3, both p<0.001). No significant differences in adjusted mean score change among any of the EQ-5D-5L or SAQ dimensions were observed between treatment groups in either intention-to-treat or per-protocol analysis. There were borderline interactions in EQ-5D-5L scores for those with previous MI vs not, and in SAQ scores for those with obesity vs not. In categorical analysis using observed data, patients treated with colchicine were more likely to have clinically significant improvement in physical limitation score over the period (36% improved vs. 28%, P<0.05). Baseline health status scores were not associated with the primary endpoint at 12 months.

Conclusions

Treatment with colchicine did not appear to affect change in measures of health status following acute coronary syndromes, but it did lead to a greater likelihood of improvement in physical limitation scores.

Funding Acknowledgement

Type of funding sources: Public hospital(s). Main funding source(s): Peninsula Health, Monash University

Global longitudinal strain and mechanical dispersion at rest in exercise stress echocardiography for detecting obstructive coronary artery disease: a pilot study

Funding Acknowledgements

Type of funding sources: None.

BACKGROUND

Exercise stress echocardiography (ESE) is a commonly used investigation for risk stratification in coronary artery disease (CAD). The added value of resting indices such as Global Longitudinal Strain (GLS) and Mechanical Dispersion (MD) to detect obstructive CAD is not well established and would be of significant clinical benefit.

PURPOSE

To evaluate the diagnostic value of GLS and MD at rest and post-exercise during ESE to detect obstructive CAD, defined by angiographic stenosis >70% in any major coronary artery.

METHODS

Retrospective cohort study of 80 consecutive patients who underwent ESE and had coronary angiography (invasive or CT) within 6 months. Retrospective speckle tracking strain analysis was performed on digitally archived video-loops, using vendor independent software. Data on demographics, medications, outcomes and ESE characteristics were collected and analysed.

RESULTS

In 49 (61.3%) patients with any CAD >70%, GLS at rest was lower (-13.9% ± 4.2 vs -16.1% ± 5.2, p-value = 0.04), and MD at rest was higher (81ms ± 43 vs 58ms ± 28, p-value = 0.008), when compared to patients without CAD >70%. GLS and MD measured post-exercise were not significantly different between groups. Ejection fraction (EF) and Wall Motion Score Index (WMSI) at rest and post-exercise were not significantly different between groups. A resting GLS cutpoint of -14% had a sensitivity and specificity of 57/68%, comparable to the development of new regional wall motion abnormalities (71/39%) and peak WMSI >1.2 (59/48%). Additionally, in 39 (48.8%) patients who had >70% stenosis in the left anterior descending (LAD) artery, LS in the LAD territory segments was lower (-16.2% ± 4.4 vs -18.3% ± 4.7, p-value = 0.04), when compared to patients without >70% stenosis in the LAD artery.

CONCLUSION

Resting GLS was lower and MD higher in patients undergoing ESE, who have any CAD >70% compared to patients who do not have any CAD >70%. Resting GLS and MD may increase diagnostic accuracy during ESE to predict obstructive CAD. Further prospective studies evaluating the utility of resting indices to predict functionally significant CAD are required.

Single-shot frequency-resolved optical gating for retrieving the pulse shape of high energy picosecond pulses

Accurate characterization of laser pulses used in experiments is a crucial step to the analysis of their results. In this paper, a novel single-shot frequency-resolved optical gating (FROG) device is described, one that incorporates a dispersive element which allows it to fully characterize pulses up to 25 ps in duration with a 65 fs per pixel temporal resolution. A newly developed phase retrieval routine based on memetic algorithms is implemented and shown to circumvent the stagnation problem that often occurs with traditional FROG analysis programs when they encounter a local minimum.