Abstract 318: Vitamin E Affects Pathological Cardiac Hypertrophy and MicroRNAs Expression in Mice

Aims: Vitamin E is a usual antioxidant, but little is known about its effects on cardiac hypertrophy and microRNAs (miRs) expression induced by transverse aortic constriction (TAC) in mice.

Methods and Results: Male Balb/c mice were randomly divided into four cohorts: SHAM ( n= 22), TAC ( n =34), SHAM supplemented with vitamin E (SHAM+VIT, n =22), and TAC supplemented with vitamin E (TAC+VIT, n =34). VIT groups received 200 mg/kg of α-tocopherol once a day, and the other groups received placebo, both by gavage. After 7 and 35 days of surgery analysis of cardiac hypertrophy, fibrosis, miRs and gene expression and carbonyl concentrations in cardiac tissue were performed. Left ventricle mass increased 23% and 35% in 7 and 35 days, respectively, in TAC group, similar data were observed in TAC+VIT group (all p <0.05 vs. SHAM groups). Cardiac fibrosis was increased by TAC surgery as early as 7 days and remained high after 35 days. Still, TAC mice exhibit higher levels of protein damage at 35 days. This pathological phenotype was not seen in animals of the TAC+VIT group. Vitamin E seemed to inhibit cardiac fibrosis and oxidative damage. Moreover, cardiac hypertrophy was followed by increased miR-21 and -499 expression in TAC group, mainly 35 days ( miR-21 : 2.9 ± 0.6 fold vs . SHAM: 1 ± 0.1 fold , miR 499 : 3 ± 0.4 fold vs. 1.1 ± 0.1 fold , p <0.05). However, TAC+VIT mice displayed a different miR expression profile, with decreased miR-21 and - 499 expression ( miR-21 : 0.5 ± 0.1 fold , miR-499 : 0.4 ± 0.1 fold ; TAC vs. p <0.05) and increased miR-210 expression (3.2 ± 0.5 fold vs. TAC: 1.9 ± 0.2 fold, p =0.034). Computational target prediction of these miRs demonstrated that they can be involved in the control of major pathways in the heart disease scenario such as MAPK, mTOR, PI3K-AKT, among others.

Conclusion: TAC model induced pathological cardiac hypertrophy, fibrosis and protein damage followed by changes in miRs expression. Vitamin E supplementation was associated with a different miR expression profile and mitigated the pathological phenotype.

Abstract 427: Micrornas Have Differential Degree of Expression in Pathological Cardiac Hypertrophy Compared to Physiological Cardiac Hypertrophy

Physiological and pathological left ventricular hypertrophies (LVH) are distinct processes that have differential pattern of gene expression. Based on initial stimuli, miRs expression levels can fluctuate and then cause a variance on their targets culminating in diverse cellular pathway activation. AIM: Here we compared miRs expression between pathological cardiac hypertrophy induced by transverse aortic constriction (TAC) and physiological cardiac hypertrophy induced by voluntary exercise in running wheels (EXE). METHODS: Adult male Balb/c mice (12-14 weeks old) mice were subjected to TAC or EXE protocol and data were evaluated at 7 (TAC-7D; EXE-7D) and 35 (TAC-35D; EXE-35D) days. Hypertrophy was measured by normalizing left ventricular weight to body weight (LVW/BW). We evaluated left ventricular expression levels of miRs: -26b, 27a, -143, -150, -195 and -499 by qRT-PCR in TAC and EXE groups. Comparisons between groups were performed by ANOVA with Bonferroni correction. Results are shown as mean±SEM. Results: Sedentary and Sham groups were similar among all variables tested. Animals subjected to TAC surgery demonstrated a greater hypertrophy than EXE animals at both time points (7D: 16% vs. 7%; 35D 26% vs 12%, p<0.05 for both). MiR-26b had increased levels in TAC group at both time points (7D: 1.14±0.1 vs 0.6±0.01; 35D: 4.8±1.4 vs 1.17±0.12; p<0.01 for both). We only detected an increase in miR-27a levels in TAC-7D compared to EXE-7D (2.7±1.0 vs 0.78±0.1, p <0.05). We identified an augmentation in miR-143 levels in TAC group at both time points (7D: 1.1±0.1 vs 0.75±0.1; 35D: 1.42±0.2 vs 0.9±0.1; p<0.05 for both). We detected an increase in miR-499 levels at both time points in TAC group (7D: 4.1±0.5 vs 0.67±0.2, p<0.001; 35D: 2.2±0.4 vs 0.9±0.2, p<0.01). We found an increase in miR-195 levels only in TAC-35D group compared to EXE-35D (2.6±0.3 vs 0.9±0.1, p<0.05). We did not notice any change in miR-150 levels neither at 7 days nor at 35 days. Conclusions: These preliminary data demonstrate a differential degree of miR expression between physiological and pathological hypertrophy. Further studies comparing physiological and pathological cardiac hypertrophy are necessary to find out the turning point that deviates heart from adaptive to maladaptive growth.

Abstract 317: Physiologic Cardiac Hypertrophy in Mice Reduces mRNA Levels of Myostatin and Autophagy Genes

Myostatin and autophagy are involved in muscle growth regulation. However, there are few studies exploring their role in physiologic cardiac hypertrophy. We evaluated myostatin and autophagy in mice subjected to a swimming protocol to induce physiologic cardiac hypertrophy. Methods: Adult (8 weeks-old) male BALB/c mice ( n =52) were divided in sedentary (S) and trained (T) groups, which were evaluated in 7 (S7 or T7, initial hypertrophy) and 28 (S28 or T28, stablished hypertrophy) days after the start of the protocol. Left ventricular/tibial length ratio (LV/TL) and cardiomyocyte diameter were used to assess cardiac hypertrophy. Gene expression was evaluated by RT-qPCR, while protein expression was analyzed by western blot. Bioinformatic analysis was performed by TargetScan to predict potential miRNAs’ targets and Genemania to create an interaction network between miRNAs and genes. All results were expressed as mean ± SEM and comparisons were performed using the Student T test. Results: Myocardial hypertrophy was confirmed in trained group both by the increase in LV/TL ratio in 28 days (13%, p=0.0001) and cardiomyocyte diameter in 7 days (20%, p=0.04) and 28 days (30%, p=0.002). There was a decrease in myostatin gene expression levels in T7 compared to S7 group (0.8 ± 0.1 vs 1.2 ± 0.1, p=0.01) without changes at day 28. However, there was no difference in mTOR phosphorylation at T7, although it was increased in T28 compared to S28 (397±95 vs 90±23 AU; p=0.02). Autophagic genes showed reduced expression levels in trained groups at both time points (reductions of 19% and 10% for Lc3, 22% and 11% for P62 , 19% and 10% for Beclin1 in T7 and T28, respectively; p<0.05 for all analyses compared to sedentary groups), but there was no difference at protein level. Bioinformatics analysis showed that miR-30a, - 221, -27a/b and 208a/b are possible regulators of autophagic and myostatin genes. Conclusions: Taken together, reduced myostatin during initial hypertrophy and increased mTOR phosphorylation in the established hypertrophic phenotype might favor muscular growth and reduce basal autophagy. Candidate miRNAs identified through bioinformatic analysis might regulate this process, and should be further validated in this scenario.