Treatment of inflammation via activation of the mRNA-destabilising protein tristetraprolin

Inflammation is a healthy response to infection or physical damage, which helps to eliminate harmful microbes. However, many of the factors released during an inflammatory response cannot discriminate between self and microbe, and therefore risk causing collateral damage to the inflamed tissue. For this reason, inflammation is usually very tightly regulated. A healthy inflammatory response has a rapid onset and an orderly resolution phase, in which activated immune cells exit the inflamed tissue or return to their resting state. This allows normal function of the affected tissue to be restored with minimal damage. An inflammatory trigger can be thought of as an accelerator pedal, and resolution as the brake: safe driving requires judicious use of both.

Inadequately controlled, damaging inflammation is the defining characteristic of chronic diseases like rheumatoid arthritis, chronic obstructive pulmonary disease, inflammatory bowel disease and many others. Uncontrolled inflammation also strongly contributes to cardiovascular disease, neurodegenerative conditions like Alzheimer's disease, and many forms of cancer. For decades the main focus of researchers on these diseases has been to identify triggers of inflammation and try to block their effects. This approach has met with only moderate success, and the overall economic, societal and personal burdens of chronic inflammatory disease continue to grow in the developed world. The focus on triggers of inflammation risks overlooking the equally important process of resolution. Evidence both from genetic studies of human disease and from animal experiments clearly shows that inflammatory disease can be caused or made worse by defects in the "braking" mechanisms that underlie resolution. More and more researchers are now trying to understand the biological processes involved in the resolution of inflammation. It is thought that reinforcement of resolution mechanisms may be an effective way to treat inflammatory diseases.

Our research on a protein called tristetraprolin (TTP) develops the concept of reinforcing resolution. Mice that cannot produce TTP develop severe, spontaneous inflammatory disease, therefore we know that TTP is an important brake to inflammation. We have also learned that the function of TTP is controlled by a molecular switch that converts it between active and inactive states. We can detect a lot of TTP protein in chronically inflamed joints of patients with rheumatoid arthritis, but it seems to be in the inactive state. We suspect that the persistent inactivation of TTP prevents resolution of inflammation, much like a faulty brake. We believe it will be possible to reduce inflammation by restoring the function of TTP, effectively repairing the damaged brake. To do this, we plan to use two different drugs that we predict will switch TTP from inactive to active state. One of these drugs is already used to treat multiple sclerosis, whilst the other is being investigated as a potential treatment for cancer. If this work is successful it may lead to new clinical trials, and ultimately to an entirely new type of treatment for inflammatory diseases, one that is based on promoting resolution rather than blocking inflammatory triggers.

The mRNA-destabilising protein tristetraprolin (TTP) is a powerful negative regulator of many pro-inflammatory genes. This project tests the concept that the broad anti-inflammatory effects of TTP can be harnessed to achieve therapeutic effects in inflammatory diseases.

Both the expression and activity of TTP are controlled by reversible phosphorylation. The inflammation-responsive kinase MK2 mediates phosphorylation and inactivation of TTP, increasing expression of inflammatory mediators. The phosphatase PP2A mediates dephosphorylation and activation of TTP, decreasing the expression of inflammatory mediators. We made a genetically modified mouse strain in which endogenous TTP protein cannot be phosphorylated and inactivated by MK2. These mice were strongly protected against pathological consequences of inflammation in several infectious and non-infectious disease models. We also described evidence that TTP accumulates in a phosphorylated and inactive form at sites of inflammation. These pieces of evidence suggest that anti-inflammatory effects could be exerted by increasing PP2A activity and driving the dephosphorylation and activation of TTP.

Loss of PP2A activity is a common causative event in several types of cancer. PP2A-activating drugs (PADs) are considered very promising anti-tumour agents, and are generally well tolerated in vivo. We will investigate whether two such compounds exert anti-inflammatory effects via the dephosphorylation and activation of TTP. We propose a multidisciplinary approach using biochemical, molecular biological, bioinformatic and imaging methods to characterise effects of PADs upon macrophages, which are key mediators of inflammatory pathology. TTP mutant mice and cells derived from them will be used to rigorously test mechanisms of action of the drugs. As a further step towards translational development, we will also test anti-inflammatory effects of PADs in inflamed human synovial tissue ex vivo.

This ambitious and transformative programme of work aims to investigate the role of tristetraprolin (TTP) in chronic inflammatory diseases with an ultimate view to identify novel therapeutic targets and, in the long term, effective treatment pathways that will improve patient quality of life and reduce the economic burden on the UK healthcare system.

The multidisciplinary nature of this project will ensure significant impact on a range of scientific and clinical fields that are underpinned by inflammation and immune cell biology. For basic and clinician scientists, our work will enhance the depth of understanding of chronic inflammatory disease pathogenesis as well as further the knowledge in immune and inflammatory signalling pathways, cancer biology and animal experimentation.

If PP2A activating drugs (PADs) demonstrate promising anti-inflammatory activities in preclinical models of rheumatoid arthritis this could provide an exciting avenue for translation; the possibility of exploitation will be discussed with the University and our collaborators in the health and industrial sectors. This feeds into the strategic goals of our translational consortia in rheumatology and inflammation more widely (BRC and A-TAP) and will significantly contribute to better experimental approaches to finding effective treatment strategies.

Our unique set up through co-location with NIHR Clinical Research Facility's inflammation arm, the Inflammation Research Facility (IRF), is excellently placed to personalise our research to the clinical objective and nurture patient-researcher relationships. The Rheumatology Research Group (RRG) has established its own patient research partner (PRP) group R2P2 (https://www.birmingham.ac.uk/research/activity/mds/projects/ii/R2P2/index.aspx) that enables patients in the region to have their say on the research that we do. Our engagement with R2P2 will foster the patient-focussed element of the research and ensure we understand what relevance our research can have to benefit patients. Engagement with patients and the general public is critical to our success, and we have plans to exploit several opportunities through seminars, workshops and training events.

Additionally, this project will provide training and educational opportunities to the next generation of young scientists across a range of disciplines. The two appointed post-doctoral research fellows on this project will benefit from working within a multi-disciplinary team, and have strong opportunities for development of transferrable research skills. They will also be encouraged to engage with patient partners in order to strengthen their non-scientific communication skills.