Following hype, some skepticism about microRNA therapy for cardiovascular diseases

Our expert however hopes that a micro RNA biomarker for a specific cardiac event will only be a "question of time"

Cardiovascular diseases are still the number one cause of death globally. Some labs and pharmaceutical companies are looking at microRNAs, short non-coding RNAs that regulate gene expressions, as one way to fight it. We spoke with Francisco J. Enguita, professor at the Institute for Molecular Medicine at the University of Lisbon about the current state of the research and its future.

ResearchGate: What do we know of microRNA’s role in cardiovascular diseases so far?

Francisco J. Enguita: The human heart is an amazing mechanical wonder. It needs tight synchronization at the chemical, electrical and mechanical levels to keep pumping blood at the incredible rate of more than 80,000 beats per day. We call this equilibrium of all parts homeostasis. Since the heart can’t regenerate in adults, this homeostasis is volatile.

Under physiological conditions, microRNAs (miRNAs), are essential players contributing to heart homeostasis and physiology. They have a mild regulatory effect over the cells’ genomic output and influence cardiac protein composition, acting as buffers. However, a tiny imbalance of miRNA levels can also be involved in many cardiac conditions and result in impaired cardiac function.

A decade ago, miR-1 was the first miRNA to be described as an essential factor in heart development, and many more followed. We are starting to look at them and their role in heart disease from the viewpoint of systems biology. Systems biology is an approach that involves computational and mathematical modelling of complex biological systems. Following this approach, we would be unlikely to find a single miRNA that causes a pathological condition on its own in higher eukaryotic organisms such as humans.  More likely, we would find a rather complex interplay between several miRNAs. As a result, we need to consider the synergic actions of many miRNAs at the same time.

ResearchGate: What role do you think will microRNA play in their treatment in the future?

Enguita: There was a big hype in the field about possible new and better treatments for several cardiac conditions after the discovery of cardiac-specific miRNAs (miR-208 and miR-499) in the last decade. Since then the scientific community has become more sceptical about the use of these molecules as targets for treatment of cardiovascular diseases. One of the main problems is delivery. What’s more, we’ve come to see that the nature of miRNA’s regulatory effect is often unpredictable and in consequence, side effects are possible. On the other hand, and on a more positive note, therapeutic intervention by modulation of miRNA levels ensures a broad effect over complete metabolic pathways that is difficult to achieve with conventional drugs.

I think that the future of the use of miRNA therapeutics in heart conditions, as in other diseases, will be focused on the selective depletion of “pathological” miRNAs using competitive antagonists (antagomirs) or molecular sponges.

ResearchGate: Do you know of any therapies in development? If so, which and how far along are they?  

Enguita: The field of miRNA therapeutics has been very active in the past five years, with many companies appearing and disappearing, and some multinational enterprises buying the more promising small biotech companies. Up until now, all therapeutic strategies they pursued are still in pre-clinical or phase 1 assays.

Among them there are two very promising companies, one in the USA and the other in Europe. In the USA, miRagen therapeutics develops competitive synthetic miRNA inhibitors for the treatment of several diseases. In fact, miRagen is currently developing competitive inhibitors for the treatment of pathological fibrosis (antagonist of miR-29), ischemic heart failure and other ischemic diseases (antagonist of miR-92a). In Europe, Cardior, a German company, is developing miRNA inhibitors for the treatment of myocardial infarction, targeting the potential regenerative abilities of the adult myocardium.

ResearchGate: What role could your findings of microRNAs as diagnostic and prognostic biomarkers play?

Enguita: We have been working on the potential use of circulating miRNAs as biomarkers for cardiovascular and rare diseases for several years now. We found that miRNAs are excellent biomarkers due to their stability in fluids. We also found some interesting miRNAs that could potentially be used for the prognosis of a specific myocardial infarction, the ST-Elevation Myocardial Infarction (STEMI). We proposed that the ratio between circulating levels of miR-122 and miR-133b is a powerful predictor of the STEMI disease outcome.

Currently, we are looking for more patients to analyse the applicability of these miRNAs in the clinical practice. To me, it’s only a question of time when medical doctors will start using these biomarkers because they are easy to implement within existing analytical pipelines in hospitals and clinical services. We just need to raise awareness among clinicians for the power of these tiny molecules first.

ResearchGate: What equipment do you turn to for your research? 

Enguita: We always try to use as many experimental approaches as possible to tackle specific problems in our lab. In the case of cardiac-related miRNAs, we employ quantitative techniques such as next-generation sequencing and qPCR, which go hand in hand with heavy in silico functional analysis. We are fortunate to live close to the central hospital in Lisbon, which is an excellent source for clinical problems and solutions.

ResearchGate: What should be improved about it?

Enguita: The techniques used for the functional characterization of miRNAs have reached their maturity. However, some technical issues remain that need to be tackled by the scientific community in general, including clinicians. Protocols for the collection of samples and quantification of miRNAs in biofluids need to be standardized, and solid protocols for next generation sequencing techniques need to be established.  Recently, we also faced problems related to computer software for data analysis. Here, the variety of algorithms also needs to be standardized for the use in clinics. I wish for a bigger involvement of clinicians in general.

ResearchGate: What are you working on currently?

Enguita: My lab is currently very interested in the role of extracellular non-coding RNAs (ncRNAs) in cell-to-cell communication, both in physiological and pathological conditions. This goes beyond the classical biomarker concept because we’re trying to make sense of the role of these molecules at the organism level. It’s a very exciting field, where many discoveries are made on a daily basis. Scientists today know about the existence of transport routes of extracellular ncRNAs that involve several kinds of particles or vesicles. Now we focus on understanding the delicate balance among extracellular compartments which could modify the availability of extracellular ncRNAs and their physiological roles.

Another interesting topic I would like to study soon is the ncRNA sorting and secretion mechanism, which is relatively unknown for miRNAs. It is still not clear why cells decide to secrete miRNAs, and how cells “pack” miRNA cargo into specific conveyors.

ResearchGate: What are the next steps?

Enguita: We are currently working on cells from patients with monogenic diseases that have an impairment in miRNA secretion. We’re hoping to understand and characterize the affected mechanisms that underlie the generation of extracellular ncRNAs. We wanted to investigate the impairment we knew from clinical data in the molecular model to better understand it. When we speak again soon, I’ll be able to give you more details, and hopefully positive results.