Study of pathogenetic molecular mechanisms and new therapeutic approaches for the treatment of Inflammatory Bowel Disease

Inflammatory bowel diseases (IBDs), resulting from the interaction between genetic and environmental factors which influence the immune responses, are mainly divided into ulcerative colitis (UC) and Crohn’s disease (CD). New studies have shown that IBD is the most common chronic inflammatory disease worldwide, affecting millions of people mainly in industrialized countries. The number of people with IBD is increasing rapidly, thus, researchers are trying to identify new mechanisms underlying its pathogenesis and find out new treatments to cure the disease as well as to improve the general health and the quality of life of patients. High-mobility group box 1 (HMGB1) protein, a nuclear non-histone DNA-binding protein, is released into the extracellular milieu and mediates inflammatory responses contributing to the pathogenesis of IBD. Treatments based on antagonists specifically targeting extracellular HMGB1 have generated encouraging results in a wide number of experimental models of infectious and sterile inflammation. Interestingly, since the current therapeutic approaches for the management of IBD include drugs (immunosuppressors, steroids) and biological treatments that are often associated with adverse health consequences, the use of natural products is gaining worldwide attention. Accordingly, the whole purpose of this study is to explore novel strategies for limiting the inflammatory potential of HMGB1. More specifically, we aimed at: 1) to assess the ability of the dipotassium glycyrrhizate (DPG), a salt of the glycoconjugated triterpene glycyrrhizin, that has been shown to inhibit the extracellular HMGB1, to reduce intestinal inflammation and improves the mucosal healing; 2) to investigate the interaction between HMGB1 and Poly (ADP-ribose) polymerase 1 (PARP1), a protein recently involved in the regulation of HMGB1 release, and explore the role of PARP1 as a novel molecular target to control gut inflammation. The results and conclusion of the first point will be presented attaching the published original paper to the thesis (Stronati L, Palone F, Negroni A, Colantoni E, Mancuso AB, Cucchiara S, Cesi V, Isoldi S, Vitali R. Dipotassium Glycyrrhizate Improves Intestinal Mucosal Healing by Modulating Extracellular Matrix Remodeling Genes and Restoring Epithelial Barrier Functions. Front Immunol. 2019 Apr 26;10:939). The results of the second point will be presented and discussed in this thesis. Briefly, to induce a severe colitis, dextran sodium sulphate (DSS) was used in C57BL/6 WT or PARP1−/− mice. Undifferentiated and differentiated colonoid cultures of intestinal stem cells harvested from biopsies of UC patients were treated with cytomix (TNF + IFN) to induce inflammation. Results show that PARP1−/− mice exhibit a less severe colitis compared to WT mice, as evidenced by the reduction of HMGB1 in the serum and stool samples. 3D colonoid cultures exposed to cytomix show increased levels of IL-1, IL-8, TNF and DUOXA2 as well as extracellular HMGB1. Interestingly, PARP1 specific inhibitor, PJ34, decreases the release of HMGB1 in undifferentiated as well as differentiated colonoids. In conclusion these data demonstrate that: 1) PARP1 and HMGB1 are closely related; 2) PARP1 contributes to improve inflammation by promoting the release of extracellular HMGB1; 3) inhibition of PARP1 could represent a promising therapeutic approach to control gut inflammation.