The role and mechanism of action of p110delta PI3K signalling in gastrointestinal immunity and inflammation.

This proposal seeks to investigate the roles and mechanism of function of a group of enzymes, known as phosphoinositide 3-kinases (PI3Ks), in mammalian gut immunity and inflammation. PI3K enzymes generate second messengers that transmit signals inside cells, controlling a large number of important biological functions including cell division, proliferation, and motility but also stress response and host defence against danger signals of either microbial or environmental origin. There are three subgroups of the PI3K family, class I, II and III, which the class I PI3Ks are the best characterized family members. Some of the class I PI3Ks are mutated in certain human disease and inhibitors of these enzymes are currently being tested in clinical trials in cancer, airway inflammation and overgrowth syndromes. A full appreciation of the biochemistry of cell communication systems is therefore important to understand central physiological and patho-physiological processes associated in human diseases such as inflammatory bowel disease (IBD).

Host innate defences are generated by a set of pathogen recognition molecules (PRMs), which tailor protective immune responses by detecting and alerting the microbial activity and pathogenicity in the intestinal environment. The innate defences in this anatomical location consist of professional phagocytes and epithelial cells that are equipped with, NOD1 and/or NOD2, an important family of PRMs detecting microbial products and maintaining tolerance to the commensals microorganisms. In general, host commensal microorganisms in the gut do not lead to IBD in healthy individuals, indicating that host tolerance to microorganisms is achieved by healthy host-microbe interplay. Mutations causing inactivation of the gene encoding the NOD2 results in Crohn's disease, a type of IBD in humans.

PI3K pathway has been implicated in host defence and inflammation, but their role in gut health and chronic IBD remains not well understood. We therefore propose to investigate the roles of PI3K enzymes in animal models of intestinal inflammation with the potential to unravel the basic biological processes driving IBD pathology involving commensal microorganisms. A key and unique tool in our studies is a panel of unique mouse strains in which specific PI3K genes have been genetically inactivated. Using these mice, we have evidence that a single member of the PI3K family positively controls host defence to gut microbiota and hence protects against IBD. Pharmaceutical drugs that inhibit one or several of these enzymes are in clinical trials or have been approved for treatment of diseases including cancer and airway inflammation, but were reported to cause colitis as side effects, similar to the pathology observed in PI3K-targeted mice.

This is a fundamental and multi-disciplinary study that can contribute to greater understanding of key immunological and medical phenomena. The longer term impacts of this work may contribute to the greater understanding of major socio-economically relevant diseases, including inflammatory bowel disease and arthritis, reported to be linked to deregulated immune response to commensal microorganisms. Our preliminary findings suggest PI3Ks are important players in intestinal homeostasis and thus are good targets for therapeutic modulation. This project has the potential to benefit pharmaceutical industry, as it can reveal aetiologies underlying colitis susceptibility to PI3K inhibitors in humans and in the longer term might identify specific PI3K isoforms as new targets to develop therapeutics angles.

The central hypothesis of our proposal is that gut health is maintained by the interplay between the gut tissue (host genetics) and its luminal contents (microbiota and pathogens). A better understanding of these complex interactions holds the key for unravelling molecular and cellular events responsible for a variety of gastrointestinal inflammatory conditions. Phosphoinositide 3-kinases (PI3Ks) are a conserved family of lipid kinases which generate lipid second messengers. Mammals have 8 isoforms of PI3K, subdivided into three classes, most of which are expressed by innate immune cell populations, particularly phagocytes. Some PI3K isoforms have been implicated in host defence, inflammation and colitis but the underlying molecular mechanisms remain unexplored. Herein, we propose to investigate why mice targeted in the gene encoding class I p110delta isoform, highly expressed in leukocytes, develop spontaneous colitis mediated by microbiota. We have so far established that in myeloid, dendritic cell population, p110delta PI3K positively couples and controls signalling downstream of nucleotide oligomerisation domain (NOD)1/NOD2 receptors that regulate mucosal host defence and tolerance to commensal microorganisms. We now propose to explore this new mouse model of colitis through a molecular framework of studies involving biased and unbiased approaches involving cell biological, proteomic and microbiome sequencing studies along with in vivo infection models to unravel key biological phenomena driving gastrointestinal pathology.

The proposed project seeks to investigate the roles of phosphoinositide lipid kinase enzymes, called PI3Ks, in an established area of nucleotide oligomerisation domain (NOD)-like-receptor biology, involved in host immune defence and gut barrier functions. The PI3K pathway has been implicated in human diseases including cancer and inflammation, but its role in inflammatory bowel disease (IBD) has yet to be explored. We aim to decipher the molecular and cellular mechanisms of why single PI3K isoform mutant mice exhibit commensal microbiota-mediated spontaneous colitis.
Academics - This research is likely to provide insight into new and previously unexplored etiopathologies of chronic gastrointestinal inflammation, since the PI3K isoform under exploration is located in one of the IBD susceptibility loci. Consequently, it will be of interest to academics in this area of research. This project builds on our previous work at the forefront of innate immunity and inflammation research aimed at deciphering the roles of PI3K enzymes, which have now become drug targets for various cancers, with the first human clinical trials already established. Indeed, the UK is a world-leader in phosphoinositide signalling research, and our work has so far contributed significantly to this international position and competitiveness, making UK the hub of choice for an internationally competitive research base in this field and capital investment. We believe that our work will continue to reinforce science of strategic medical and industrial relevance, and that our research will contribute to the better understanding of the pathobiology of chronic inflammatory diseases and discovery of novel drug targets.
Industry - Pharmaceutical industry will most likely benefit from this research in the longer-term. This work will help provide insight into the underlying biology in gut health and inflammation and is expected to reveal new therapeutic targets/strategies that bring the prospect for new IBD therapies. The data from this research might identify protein phosphorylation biomarkers and other previously unknown interacting partners of the NOD2-PI3K pathway, the first susceptibility gene identified for Crohn's disease. In the longer term, the new mouse under study might be adapted or developed to provide useful drug screening tools for industry and/or tools to understand IBD pathology. Our past research has promoted UK competitiveness and benefitted clinical studies now targeting PI3Ks in inflammation and cancer, which will improve the quality of life of patients suffering from these conditions.
Patients and clinicians - This research will ultimately help improve the quality of life of IBD patients through a better understanding of IBD processes and microbial links and through the development of new therapies. This project may broaden genetic screening tests in patients with inflammatory bowel conditions for potential new mutations in the gene encoding the PI3K isoform. Consequently, clinicians may be better able to treat patients according to their particular genetic IBD susceptibility (selecting the right therapy or managing the disease in a certain way due to insights from our research in the long term). Furthermore, PI3K might be an important biomarker involved in autoinflammatory rare diseases such as Blau syndrome and early onset sarcoidosis. This complementary research may help improve the management of these conditions in the future.