Factors involved in cardiac physiological and pathological remodeling

Abstract

During life, the heart is exposed to different types of stresses. In response to changing demands or stimuli the heart can cope by growing in size. In this thesis, molecular changes underlying cardiac physiological and pathological adaptations are investigated. First, we validated physiological remodeling of the heart in a mouse exercise model. After two weeks of swim exercise the murine hearts presented induction of an adaptive hypertrophy with maintenance of cardiac function. Both gene and miRNA expression analysis of cardiac tissue from sedentary and exercised mice revealed changes underlying the protective effect induced by exercise. Next, we validated pathological remodeling of the heart in the transverse aortic banding (TAB) mouse model. Short term TAB was found to present compensatory remodeling, whereas longer TAB time points showed adverse remodeling and failing of the heart. Subsequently, we continued this comparison by looking at the functional cells of the heart, the cardiomyocytes (CMs), specifically. By using a genetic approach to label CM with a fluorescent protein in vivo, we were able to sort and perform RNA analysis on CMs. Next to known stress genes, this method revealed novel genes that were previously not linked with hypertrophy of failure. Future studies in human induced pluripotent stem cell (hiPSC)-CMs will be performed to reveal the exact regulation and function of the novel identified genes.We also investigated whether AC6, a gene involved in regulation of CM contractility, can be increased with use of antimiR therapeutics. Luciferase screening revealed two clustered miRNAs, miR-182 and miR-96, that potently regulate AC6. Both in vitro and in vivo regulation of these two miRNAs showed that the combination of the two is most potent in increasing Adcy6 mRNA levels. Unexpectedly, during TAB-induced heart failure antimiR-96/182 combination therapy did neither result in functional benefits, nor upregulation of AC6 and other targets. RNA sequencing analysis confirmed minimal effects of miR-96/182 on gene expression during TAB induced HF.Finally, we investigated antimiR efficacy by looking at target regulation under physiological or pathological conditions after using an antimiR specifically targeting the CM-restricted miRNA miR-208a. Here, we found that under stress more potential targets are regulated and that the level of target regulation is higher. As demonstrated in neonatal rat ventricular myocytes, a possible mechanism for this might be increased cellular uptake under stress conditions. This thesis describes several different approaches to use fundamental research to identify determinants important during hypertrophic and failing heart. Newly identified factors can be used for novel approaches in the development of cardiac therapy.