Redox and epigenetic modulators regulate cardiac function and remodeling in health and disease

Oxidative species are a divergent group of cellular metabolites with a wide variety of functions. Together with reductants, they regulate almost all cellular functions, from mediating cellular communications to catalyzing a variety of biochemical reactions, and further to posttranslationally modifying proteins. The past decades’ focus on oxidative species as injurious byproducts associated with diseases have not yielded any clinical success. For example, attempts to improve heart function by antioxidative treatments have rather, in some cases, had adverse effects on heart failure. Therefore, there is unmet need for a change in the way we perceive redox biology, namely, to replace the traditional view on oxidants as unambiguous foes with more openminded perspective on the broad functions of the redox system and the novel mechanisms that regulate the endogenous antioxidative capacity. An urge for unbiased approaches is further supported by the recent technical advances in multi omics, which have enabled the exploration of complex mechanisms beyond traditional boundaries.

In our recent manuscript on BioRxiv (Elbeck et al., 2022), on which this thesis is largely based, we present evidence using multipronged omics that mitochondrial isocitrate dehydrogenase 2 (IDH2) governs an extensive redox-regulatory mechanism in cardiac mitochondria. We found that IDH2 together with nuclear factor erythroid 2-related factor 2 (NRF2) coordinates a novel antioxidative mechanism through a feedforward cycle involving 2-oxoglutarate (2OG) and L2hydroxyglutarate (L2HG). We further found that this redox cycle regulates gene expression through an unconventional mechanism involving intronic DNA hydroxymethylation. We explored the possible implications of these findings for the treatment of heart failure, taking into consideration the previously failed clinical trials. We obtained evidence for sexual dimorphism in mice in which females showed a more robust antioxidative defense reflecting on their heart failure phenotype: a less severe dilated cardiomyopathy (DCM) compared to males. We tested our hypothesis using a novel pharmacological compound AZ925, which activated the NRF2 pathway. Our conclusion is that enhancing the antioxidative capacity has a positive impact on cardiac function only when endogenous antioxidative capacity is limited, highlighting new possibilities for precision medicine.

In the literature review part of this thesis, I aimed to explore literature beyond the protective role of the redox system. Here, I dig deeply into the multifaceted essential—but overlooked— functions of this system. I also aimed to explain my reasoning behind the design and interpretation of some of the data presented in Elbeck et al., 2022. Moreover, I further explored if data from cases of patients with DCM were potentially supportive of my hypothesis (Project I).

In Project II, I have investigated the importance of miR-208b-3p, which is a highly induced micro-RNA (miR) in the myocardia of patients with DCM. I propose that miR208b-3p plays a role in the cardiac reverse remodeling observed in some patients with heart failure as a potential redoxmiR, which represents one of the arms of the redox system discussed in this monograph.

Project III does not deal directly with redox biology, but it is rather related to the concept of translatable genetic information beyond the canonical protein coding and translational reading frames via alternative splicing. We propose the existence of multiple isoforms of muscle lim protein (MLP) translated at extremely low levels from same Mlp pre-mRNA as the full length MPL protein, even in Mlp-/- animals that have a deletion in Mlp exon2. These isoforms retain some of the functional domains of their full-length protein, and therefore may mediate distinct functions.

The overall goal of my work has been to use recent technical advances to explore biological mechanisms beyond some of its preconceived boundaries, and thereby to unveil novel molecular mechanisms that could ultimately lead to improved personalized and precise treatments of several diseases, including redox therapies for heart failure.