Abstract
Epicardial adipose tissue (EAT) is a layer of fat surrounding the heart. EAT has gained interest due to its unique physiology and direct interface with the heart. EAT thickness strongly correlates with obesity and cardiovascular disease, which are associated with increased myocardial fibrosis and apoptosis. Specific markers for myocardial fibrosis and cellular ageing are miR-15a and miR-15b, and miR-34a, respectively. However, microRNAs 15a, 15b, and 34a have not been characterised in the neighbouring EAT. Therefore, I aimed to determine miR-15a, miR-15b, and miR-34a expression in EAT of lean, overweight, and obese patients. I hypothesised that increased body mass index (BMI) is associated with lower miR-15a/b and greater miR-34a expression in EAT.
After informed consent, EAT biopsies of the atrioventricular groove and medical records of cardiac surgery patients of Dunedin Hospital were collected. 42 patients were categorised into lean (BMI ≥20<25 kg/m2), overweight (BMI ≥25<30 kg/m2), and obese (BMI ≥30 kg/m2) groups. After excluding low purity RNA samples, there were 9 lean patients, 8 overweight patients, and 15 obese patients. Standard RT-qPCR techniques were used to quantify miR-15a/b and miR-34a expression. Housekeeping miRNAs (miR-16 and miR-24) and a calibrator sample were implemented to calculate fold change. Differences between BMI groups were analysed using one-way ANOVA, followed by Tukey’s multiple comparisons test. Linear regression was also used to test for relationships between microRNA expression and BMI. If BMI groups had unequal variance, Kruskal-Wallis test followed by Dunn’s multiple comparisons test was implemented.
Out of the 32 samples, 6 samples expressed miR-15a, 26 samples expressed miR-15b, and 14 samples expressed miR-34a. Linear regression, one-way ANOVA, and the Kruskal-Wallis test showed no relationship between miR-15a/b expression and BMI. For miR-34a, only one-way ANOVA (normalised with miR-16) and linear regression (normalised with miR-24) showed significant differences in miR-34a expression. The linear regression showed a significant negative association with BMI, whilst the one-way ANOVA showed that the overweight group had significantly greater miR-34a expression than the obese group.
The results suggest that EAT miR-15a/b expression is unaffected by obesity whilst EAT miR-34a expression might decrease in obesity. This relationship is potentially explained by an increase in EAT size via hyperplasia.