Muscle RING Finger 1 as a signalling hub for muscle atrophy, mitochondrial dysfunction, and insulin resistance in heart failure and diabetes

Loss of muscle strength, tiredness, and impaired glucose control are common side-effects in many illnesses such as cancer, diabetes, heart disease, but also in health due to ageing. These impairments are found in both the breathing and leg muscles, which lead to breathlessness and fatigue and a reduced ability to do activities of daily living such as housework and gardening. Muscle weakness, fatigue, and poor glucose control have been shown to contribute to a low quality of life and an earlier death. In particular, muscle damage is a very strong predictor of death in patients with heart failure - a disease in which the heart fails to adequately pump blood. An estimated 15 million Europeans have heart failure and rates are still increasing. Recently it has been found that many patients with heart failure and diabetes show greater symptoms and have a much worse survival. Most patients with heart failure and/or diabetes suffer from severe muscle damage. Unfortunately, no drugs are available to effectively treat this muscle damage, partly because we do not yet understand all of the changes or what makes this happens. Therefore, it is very important we identify what changes are occurring in the body (including inside the cells) that cause these adverse muscle adaptations, and also what sets these changes in motion. Until we understand in detail these processes, we cannot easily develop treatments that allow muscle strength and endurance to be maintained or improved.

Over the last years, we have found a protein in the muscle termed MuRF1, which seems to play a key role in muscle weakness, tiredness, and glucose dysregulation seen in heart failure and diabetes. We have found that heart failure and diabetes have increased levels of MuRF1 in the muscle. But when we reduce MuRF1 levels, for example by exercise training, muscle strength is improved. However, as many patients are often too weak to perform exercise interventions, we recently started an innovative drug discovery programme aimed at blocking MuRF1 using test tube experiments. We have identified one novel drug that could block MuRF1 and our preliminary findings in animals have shown can improve muscle strength, endurance, and glucose control. As such, elevated MuRF1 levels may represent a critical step that sets in motion muscle weakness, tiredness, and glucose dysregulation in patients with heart failure and diabetes. However, we now need to prove this exciting idea.

The main aim of this project is to provide conclusive evidence that our novel drug can inhibit the MuRF1 protein to benefit muscle strength, endurance, and glucose control in heart failure and diabetes. To answer this, in one approach we will collect muscle biopsies from patient volunteers (around a pea size amount from the leg), which we can take to our laboratory to measure mechanical properties such as muscle size, strength and endurance. We can also isolate muscle cells from these human samples and add our novel MuRF1 drug to see if this improves muscle growth. In another approach, we will use clinically-relevant mouse models of heart failure and diabetes. We can give mice heart failure in the same way as it happens in humans: by a heart attack. We can tie off the main coronary artery in the heart of mice to cause this heart attack (myocardial infarction), which leads to heart pumping weakness - also known as heart failure. We can give mice diabetes by simply feeding them a high fat diet, which is often a cause in humans. We will then treat mice with our new drug compound to block the effects of MuRF1. We can then assess if whole-body treatment of this drug can prevent muscle damage, improve muscle endurance, and improve glucose control. This second phase will allow us to confirm whether the drug might represent a new treatment option for patients with heart failure and diabetes. Our work therefore has the potential to benefit symptoms, quality of life and survival in patients.

Skeletal muscle wasting occurs in chronic heart failure (CHF) and diabetes mellitus (DM). Our preliminary data have identified a unique patient cohort with coexistent CHF and DM (i.e. D-HF) whom demonstrate severe muscle wasting, mitochondrial dysfunction, and insulin resistance. Muscle impairments contribute to pulmonary complications, disability, and abnormal metabolism to severely limit quality of life and survival. Therapies to inhibit muscle impairments, therefore, will have major benefits in CHF and DM where prevalence is increasing. Activation of the key muscle-specific E3 ligase, MuRF1, is evident in CHF and DM and linked to fibre atrophy, mitochondrial dysfunction and insulin resistance. We have recently developed, for the first time, an exclusive set of novel compounds capable of blocking MuRF1 activation in vivo, supported by our pilot data in mice where treatment normalized muscle impairments during acute wasting. The present project will combine bench-to-bedside experiments that employ state-of-the-art analytical approaches in order to confirm the contribution of MuRF1 to muscle wasting, mitochondrial dysfunction, and insulin resistance in the chronic diseases of CHF and DM, where 4 experimental groups will be assessed (control, DM, CHF, D-HF). In the first approach, muscle biopsies from patients will be extensively characterized for morphology and function, with human primary cell culture experiments used to assess the impact of MuRF1 blockade on in vitro myotube morphology and mitochondrial function. In the second approach, MuRF1 will be blocked in vivo in mice to determine if this can rescue muscle atrophy, mitochondrial dysfunction, and insulin resistance. Validation of muscle protein homeostasis for anabolic-catabolic signaling in human and mouse will be done to confirm clinical translation between species. Cutting-edge proteomics and metabolomics will also be performed to identify unknown signaling targets modulated via in vivo MuRF1 inhibition.

Muscle weakness, mitochondrial dysfunction, and insulin resistance occur in many clinical conditions, and play a critical role in pulmonary complications and disabilities observed in patients which lead to significant reductions in quality of life and survival. The work proposed in this application will, in the long term, primarily benefit patients with heart failure and diabetes but also other conditions (e.g., cancer, ageing), as we aim to identify key mechanisms contributing to muscle dysfunction and how this can be prevented through novel small-molecule therapeutics. Therapeutic interventions, developed as a result of the outputs from this research, will contribute to improved human health in the medium term and have potential to extend survival in patients over the long-term. These research outputs will ultimately provide socio-economic benefits due to improved health and wellbeing, which will likely be due to reductions in disability, illness-based unemployment, and hospitalizations associated with fractures and mechanical-ventilation weaning problems. Healthcare professionals and services will also potentially benefit in the long term, through availability of improved treatment options.

Also in the long term, Government and other policy-makers (for example UK Chief Medical Officers via the Department of Health, and the European Society of Cardiology, who publish treatment guidelines) may benefit from the project outputs as they will help guide potential effectiveness of inhibiting molecular targets to deter heart failure progression. Novel biomarkers may also be identified to help aid more effective patient diagnosis and treatment. Our work on identifying mechanisms underlying muscle dysfunction in heart failure and developing novel small-molecule therapeutics has potential benefits for the commercial private sector, for example the pharmaceutical industry, which can use the outputs from this project to assist in the development of novel drugs used for the treatment of heart failure and other conditions. This may help foster a more competitive UK market in relation to drug development for myopathies.

In the lifetime of this grant, the main non-academic beneficiaries will be the researchers on the grant, the scientific community (as described in the academic beneficiaries section) and the general public. The researchers will benefit through developing high level scientific skills and fostering oversees scientific and cultural exchange, thus developing their transferrable skills and equipping them for further careers in academic or industrial research to benefit the UK economy. Communication of these research outcomes of this project to a wider audience - through public lectures, schools outreach programmes and press releases - will provide benefit to the wider public by raising awareness of muscle weakness associated heart failure and diabetes, its causes, and potential lifestyle choices that may prevent its onset.

The information generated by this project will fulfil a number of MRC strategic aims: "Picking Research That Delivers". The project will deliver novel research tools, moving from cell to organism, to deliver improved health outcomes, including: 1) "Resilience, repair & replacement", through our novel work on identifying mechanisms and treatments of tissue disease to help improve mobility in many disease via regenerative medicine; 2) "Living a long and healthy life", as this project will contribute to preventing loss of functional mobility in disease and ageing. Further, this project also fulfils the MRC strategic aims "Research to People", through translation of research outputs to the clinical setting via our existing collaboration with clinicians and clinical scientists: and "Supporting Scientists" as this multi-disciplinary work will provide world-class research and training opportunities for the applicants, both in the UK and abroad.