Graphical Abstract
This editorial refers to ‘Non-coding RNA yREX3 from human extracellular vesicles exerts macrophage-mediated cardioprotection via a novel gene-methylating mechanism’, by A. Ciullo et al., https://doi.org/10.1093/eurheartj/ehae357.
Despite decades of work, heart failure remains a global problem, claiming millions of lives each year. Procedural advancements and new medications have improved prognosis, but there is a critical gap in effective therapies for recovering damaged heart tissue post-injury. A recent study by Ciullo et al., published in this issue of the European Heart Journal, highlights a promising candidate: yREX3, a small Y RNA molecule (Graphical Abstract).1 Y RNA molecules belong to a family of small, non-coding RNAs that are highly conserved across species, particularly in humans, where they range from 83 to 112 nucleotides in length. These RNAs are transcribed by RNA polymerase III from individual genes and are known for their unique stem–loop structures. Discovered over three decades ago, the comprehensive roles of Y RNAs within the cell are still not fully understood. This research reveals a new mechanism by which yREX3, present in therapeutic extracellular vesicles (EVs), can significantly reduce heart damage following ischaemic injury. These findings not only expand our understanding of cell communication during heart repair but also open the door to the development of a new class of drugs targeting previously uncharted pathways.
Graphical Abstract.
Exploring the benefits and challenges of utilizing bio-inspired RNAs over parental extracellular vesicles in post-infarction repair.
EVs are microscopic membranous spheres released by cells that carry a diverse array of cargo molecules, including proteins, RNA (including various subtypes), and lipids.2 These packages act as intercellular messengers, shuttling information between cells and influencing various physiological processes. Emerging research suggests that EVs play a vital role in cell communication and hold immense therapeutic potential for a multitude of diseases, including cardiovascular ailments.
The current study focused on EVs derived from cardiosphere-derived cells (CDCs). CDCs are a population of stromal cells residing in the heart, recognized for their ability to regenerate damaged heart tissue.3 Recent studies have demonstrated that CDC-derived EVs (CDC-EVs) possess cardioprotective properties, promoting tissue repair and regeneration after ischaemic injury.4
The study employed a bio-inspired approach, leveraging principles and mechanisms found in natural biological systems, to identify the key players within these therapeutic CDC-EVs. They compared the RNA content of cardioprotective EVs from immortalized CDCs with those from primary CDCs. This analysis led to the identification of yREX3, a previously uncharacterized small Y RNA, as a potentially critical component in the therapeutic effects of immortalized CDCs.
Following myocardial infarction, the injured heart tissue undergoes a complex inflammatory response. Macrophages flood the infarcted area to clear tissue debris.5 Macrophage differentiation is a highly regulated process influenced by environmental cues. Initially, macrophages displaying enhanced phagocytic and microbicidal activities emerge in response to proinflammatory stimuli. In contrast, a different set of signals, such as those associated with anti-inflammatory conditions, guide the development of macrophages that favour tissue repair and immune regulation. This study revealed a role for yREX3, as it specifically targets macrophages and reprograms them to become more efficient at clearing debris and promoting tissue repair. Mechanistically, yREX3 acts by methylating Pick1, which silences its expression. This leads to the activation of Smad3, enhancing the ability of macrophages to engulf and clear dead cells, a process known as efferocytosis.6
The findings of the study are impressive. Administering yREX3 after coronary ligation in rats significantly reduced infarct size. This effect was comparable with treatment with the whole EVs secreted from immortalized CDCs (IMEX), highlighting the critical role of yREX3 in the cardioprotective properties of CDC-EVs. These results are particularly promising considering the limitations of current treatment options. While revascularization is the cornerstone of infarct treatment, it only addresses the blocked artery and does not directly impact the infarcted tissue itself. Drugs such as nitrates and beta-blockers, while improving blood flow and reducing workload on the heart, do not demonstrably affect scar size in the long term. In this context, yREX3 emerges as a potential therapeutic candidate with the ability to specifically target the injured tissue and promote repair.
Although yREX3 presents a promising avenue for developing new cardioprotective therapies, there is still work to be done before it can be translated into clinical practice. The current study focused on short-term outcomes, evaluating the effects of yREX3 in the immediate aftermath of a cardiac injury. Long-term studies are necessary to assess the sustained benefits and safety of yREX3. Potential long-term effects, such as unintended consequences of macrophage reprogramming or unforeseen off-target methylation events, need to be investigated. Another crucial step towards clinical translation is validating the efficacy of yREX3 in larger animal models that more closely resemble the human heart. Studies in pigs or non-human primates would provide valuable insights into the potential effectiveness, safety, and scalability of yREX3 in humans before initiating clinical trials.
This research underscores the potential of uncharacterized molecules within EVs for therapeutic purposes. For example, the inhibition of miR-92a using antagomirs has been shown to significantly enhance angiogenesis7 and reduce infarct size.8 These insights have led to the development of an inhibitor of miR-92a, MRG-110, which is currently being tested in early Phase I clinical trials (NCT03603431). Studies in pigs have shown that MRG-110 increases blood flow and blood vessel growth around wounds.9 Similarly, overexpression of miR-199a, a transcript abundantly present in EVs from many clinical-grade producer cell lines,10 in pig hearts post-myocardial infarction has been shown to improve cardiac contractility and muscle mass while reducing scar size.11 These findings are not restricted to classical micro-RNAs (i.e. non-coding RNA with a length of ∼22 bases), as recent studies have begun to ascribe salutary benefits to other non-coding RNAs.12–14 For example, a study by Cambier et al. revealed that a Y-fragment RNA in CDC-EVs confers cardioprotection after myocardial infarction via modulation of interleukin (IL)-10 production by resident macrophages.12 These findings suggest that a deeper understanding of the complex interplay between different EV-derived small RNAs could lead to the development of targeted therapies tailored to specific aspects of cardiovascular diseases.
Despite the potential advantages of targeting specific disease pathways and ease of production, challenges remain regarding RNA stability, immunogenicity, dosing issues, and off-target effects.15 On the other hand, EVs offer a natural delivery system with inherent targeting capabilities and a diverse cargo of bioactive molecules that might provide a more holistic therapeutic effect. However, challenges related to heterogeneity and scalability with allogeneic EVs necessitate further research for the optimal standardization and production protocols. Ultimately, the ideal therapeutic strategy for ischaemic cardiomyopathy might involve a synergistic approach, combining the targeted nature of RNA therapeutics with the comprehensive cargo delivery by EVs.
yREX3, with its ability to modulate macrophages and promote tissue repair, embodies the principles of a bio-inspired innovation, holding promise for the future of cardiovascular medicine. The potential therapeutic avenues explored in this study, including direct yREX3 administration and yREX3-pre-conditioned macrophage therapy, warrant further investigation. Crucially, the research emphasizes the critical role of deciphering the intricate communication networks within EVs and their contents of small RNAs. Unravelling these mechanisms could pave the way for novel therapeutic targets applicable to a broad spectrum of diseases, extending well beyond those affecting the ischaemic heart.
Contributor Information
Noreen Ahmed, Division of Cardiology, Department of Medicine, University of Ottawa Heart Institute, University of Ottawa, H3214, 40 Ruskin Street, Ottawa K1Y 4W7, Canada; Department of Cellular and Molecular Medicine, University of Ottawa, Ottawa K1H 8M5, Canada.
Darryl R Davis, Division of Cardiology, Department of Medicine, University of Ottawa Heart Institute, University of Ottawa, H3214, 40 Ruskin Street, Ottawa K1Y 4W7, Canada; Department of Cellular and Molecular Medicine, University of Ottawa, Ottawa K1H 8M5, Canada.
Declarations
Disclosure of Interest
D.R.D. is a co-inventor for a patent application submitted regarding extracellular vesicle treatment of atrial fibrillation (US patent filing number 63/278,518); he holds a patent regarding serum-free and xenogen-free human cardiac explant-derived stem cells (US patent 11083756) and a patent regarding the engineered cardiac-derived stem cells and extracellular vesicles secreted by such cells (US patent 62758160). N.A. has no conflicts to declare.
Funding
This work was supported by the Canadian Institutes of Health Research (Project Grant 410103) and the Natural Sciences and Engineering Research Council of Canada (CHRPJ 549626-20 and I2IPJ 571244-22).
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