How non-coding RNAs might revolutionize the treatment of cardiovascular diseases
At first glance, non-coding RNAs (ncRNAs) in the cell appear completely useless. After all, unlike messenger RNAs (mRNAs) they do not contain any genetic information that can be used to build proteins. It has been known since the 1990s that a cell produces thousands of different ncRNA molecules that fulfil numerous important functions. Stefanie Dimmeler is investigating how ncRNAs control physiological processes in the heart and how they can be used for therapeutic purposes, such as heart regeneration after infarction or for repairing aneurysms.
Cardiovascular diseases take about 18 million lives each year and are the most common cause of death worldwide. At present, they are mainly treated with drugs that inhibit or activate the body’s own proteins. Since many proteins, however, cannot be influenced in this way, there is an urgent need for new therapeutic approaches. This is where nucleic acids open up entirely new possibilities. Although researchers have been looking at their therapeutic potential for decades, it was not until the coronavirus pandemic and the millions of mRNA vaccines administered during it that therapeutic nucleic acids finally made the breakthrough.
Today, medical research is increasingly casting the spotlight on non-coding RNAs (ncRNAs). These are found in almost all organisms, including humans, and, like messenger RNAs, they transcribe genes but do not contain instructions for building proteins. Some of these ncRNAs are involved in protein production, for example. Most ncRNAs and the part of the genome responsible for encoding them were, however, long regarded as worthless “trash”. We meanwhile know better: Many ncRNA molecules have important regulatory functions. Moreover, and according to estimates, in humans they exceed the number of “classic” protein-coding genes by a factor of about ten.
Finetuning of gene networks
At the Institute of Cardiovascular Regeneration, Goethe University Frankfurt, Professor Stefanie Dimmeler is studying the role of ncRNAs in the pathogenesis of cardiovascular diseases – always with an eye to the development of new therapies. “I already discovered translational research for myself back when I was a biology student,” she says, “and I appreciate having the opportunity to combine basic and clinical research.” Dimmeler is interested in very different aspects of the cardiovascular system, such as how the heart ages or how it is regulated by various processes in the body. Her research centers on the cells that line blood vessels, the endothelial cells. These are responsible for important tasks in the cardiovascular system, explains Dimmeler: “If endothelial cells are damaged, this affects not only blood flow but also heart function.” And yet no drugs so far exist that specifically influence the function of endothelial cells.
This is where ncRNAs come into play. They can be divided into several groups, of which one has been known and the subject of extensive research for a very long time: transfer RNAs (tRNAs), which play an important role in the translation of messenger RNAs into proteins. MicroRNAs, by contrast, were first discovered in the 1990s in the nematode Caenorhabditis elegans but are presumably present throughout the whole animal and plant kingdom. They are very short, usually with no more than 25 nucleotide building blocks, and their task in the cell is to downregulate gene expression. To do this, they bind via complementary base pairing to a specific messenger RNA, which cellular enzymes then degrade. The protein encoded by the messenger RNAs can no longer be produced. MicroRNAs thus have a similar mechanism of action as another ncRNA group, small interfering RNAs (siRNAs), which also regulate genes in the cell. MicroRNAs are, however, less specific than siRNAs, which broadens their effect, as Dimmeler explains: “MicroRNAs often recognize hundreds of different messenger RNAs. This enables them to regulate a whole gene network.” There are also differences in the level of efficiency: While siRNAs usually turn off a gene completely, microRNAs only reduce gene expression by 30 to 40 percent. “This is in principle a kind of fine-tuning,” concludes Dimmeler.
microRNAs protect against atherosclerosis
The first therapeutic approaches based on microRNAs, for example on a group called miR-143/145, are meanwhile available. Dimmeler was able to show that this microRNA cluster protects blood vessels by preventing the formation of atherosclerotic plaques. That is why she is now exploring whether miR-143/145 can be introduced directly into endothelial cells. To do this, she encapsulates the microRNAs in microvesicles. “Microvesicles are small membrane vesicles in which we can entrap the microRNAs,” explains Dimmeler. “The vesicles fuse with the cell membrane and in this way enable the microRNAs to enter the cell.” An even more recent discovery promises another positive effect: miR-143/145 protects not only against atherosclerosis but also stabilizes the interaction of cardiac endothelial cells with nerve cells. When the amount of miR-143/145 in the heart decreases with age, this protective effect is also lost, and the endothelial cells repel the nerve cells more and more. “If we can manage to maintain the neural interactions in the heart with the help of miR-143/145, we could kill two birds with one stone with this active substance,” hopes Dimmeler.
Inhibitors for harmful microRNAs
If certain microRNAs cause damage rather than having a protective effect, their use in therapeutic approaches depends on blocking the molecules. One such blocking agent, which targets a microRNA called miR-92a, has already successfully completed an initial Phase 1 clinical trial. In such a trial, a drug’s safety and efficacy are studied in a small number of healthy test persons. The human body produces miR-92a in the endothelial cells in response to stress. This damages blood vessels. “That is why we have developed specific molecules, called antisense molecules, which bind to miR-92a and in this way prevent it from blocking its target genes. This has a powerful protective effect, for example in the case of infarctions and other diseases associated with inadequate blood flow,” says Dimmeler in summing up. “The human body tolerates anti-miR-92a very well, and even a low dose is effective.” After a heart attack, the drug can be administered directly into the infarct region via a catheter. Studies have shown that a single treatment is already sufficient to reduce miR-92a for up to four weeks. The patent for the active substance has meanwhile been licensed to a company that will market it for patient treatment.
In collaboration with partners at the German Center for Cardiovascular Research (DZHK), Dimmeler’s team is currently developing a second therapy, which is based on the inhibition of another microRNA, miR-29. miR-29 is a contributing factor in aneurysm formation. These life-threatening bulges form when a blood vessel weakens. Responsible for this is the increased formation of miR-29, which causes the stabilizing collagen in the affected vessels to degrade. “Together with Professor Lars Mägdefessel from the center’s partner site in Munich, we coat catheter balloons with anti-miR-29 and insert them directly into the bulge with a catheter,” says Dimmeler, explaining the therapeutic principle. “This blocks miR-29, allowing the cells to form collagen again and stabilize the blood vessel.” The effectiveness of this approach has already been corroborated in tests with pigs. If the result is confirmed in humans, balloons coated with anti-miR-29 could already counteract aneurysms at an early stage and perhaps even repair them – this would constitute a major advance compared to current surgical procedures, which are often risky.
(Still) speculative lncRNA research
In comparison to microRNAs, far less research has been conducted into the highly heterogeneous group of long ncRNAs (lncRNA). All ncRNAs comprising over 200 nucleotides fall under this group. They have many different functions, which makes it difficult, alongside their unwieldiness, to use them for therapeutic purposes. Moreover, lncRNA genes have altered much more than microRNA genes over the course of evolution so that it is more difficult to transfer results from animal studies to humans. Nevertheless, research on lncRNAs is illuminating and important, says Dimmeler: “We have already found a large number of them that are regulated in different ways in vascular lesions and contribute to disease development. If we can understand what role the lncRNAs play and which biomolecules they interact with, we can try to systematically inhibit these interactions.” This could then lead in the future to a completely new form of therapeutic agent.
In Dimmeler’s opinion, it is essential, especially for such complex lncRNA research, to work with other partners. Her collaboration with the researchers at the German Center for Cardiovascular Research (DZHK) in Munich is funded by Collaborative Research Center Transregio 267 “Non-Coding RNA in the Cardiovascular System” of the German Research Foundation (DFG), among others. Particularly important for this pioneering work on ncRNAs is also the Cluster of Excellence “Cardio-Pulmonary Institute” (CPI), likewise funded by the German Research Foundation, in which Justus Liebig University Giessen (JLU) and the Max Planck Institute for Heart and Lung Research in Bad Nauheim are participating alongside Goethe University Frankfurt. The cluster focuses on the interface between cardiovascular and lung research, as well as supporting early, high-risk and innovative projects to gain first evidence, which then paves the way for applying for subsequent third party funding. “The start-up funding provided by the CPI for our still very speculative ncRNA research is one of the main reasons why we are able to penetrate a variety of new areas so successfully and had an opportunity to develop such innovative therapeutic approaches in the first place,” Dimmeler is convinced.
Cardio-Pulmonary Institute / The aim of the Cluster of Excellence “Cardio-Pulmonary Institute (CPI)” is to understand the molecular biology processes underlying the function of the heart and lungs and their malfunction in cardio-pulmonary diseases. To this end, the CPI researchers are developing cross-university modeling systems ranging from cell cultures to animal models and combining the results with patient data to find new therapeutic approaches. The cluster was first funded from 2006 to 2018 as the “Excellence Cluster Cardio-Pulmonary System (ECCPS)” and was successful again in 2019 as the Cluster of Excellence “Cardio-Pulmonary Institute”. The project partners are Goethe University Frankfurt, Justus Liebig University Giessen (JLU), the Max Planck Institute for Heart and Lung Research in Bad Nauheim and the University Medical Center Göttingen (UMG).
About / Stefanie Dimmeleris Professor for Molecular Cardiology and Director of the Institute of Cardiovascular Regeneration at Goethe University Frankfurt. Having studied biology and earned her doctoral degree at the University of Konstanz, Dimmeler completed her postdoctoral degree (Habilitation) in experimental medicine in Frankfurt. She is the spokesperson for the Cluster of Excellence “Cardio-Pulmonary Institute (CPI)” funded by the German Research Foundation (DFG), co-spokesperson for Collaborative Research Center TRR 267 “Non-Coding RNA in the Cardiovascular System” and founding spokesperson of the Profile Area “Molecular and Translational Medicine” at Goethe University Frankfurt. She is also the spokesperson for the Executive Board of the German Center for Cardiovascular Research (DZHK). In addition to various visiting professorships abroad and countless distinctions, in 2005 Dimmeler received the Gottfried Wilhelm Leibniz Prize, Germany’s most prestigious research award.
dimmeler@em.uni-frankfurt.de
The author / Larissa Tetsch studied biology and earned her doctoral degree in microbiology. She then worked in basic research and later in medical training. She has been working as a freelance science and medical journalist since 2015 and is also the managing editor of the science magazine “Biologie in unserer Zeit”. www.larissa-tetsch.de
