Dissecting the mechanisms of A20 and ABIN-1 mediated programmed cell death in intestinal epithelial cells - A crucial step towards understanding intestinal barrier dysfunction in inflammatory bowel diseases

• Applicant: Dr. Dorothea Stibor
• Subject Area: Gastroenterology
• Term: from 2019 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 433275755

Inflammatory bowel diseases (IBDs) are characterized by excessive intestinal epithelial cell (IEC) death, loss of intestinal barrier function and chronic inflammation that promote a circle of chronic disease. The underlying pathophysiology is thereby incompletely understood. The translation of genetic risk loci into causative molecular pathways has illuminated previously unexpected mechanisms in the genesis of IBDs. Mutations in the genes for the ubiquitin-modifying and ubiquitin-binding proteins A20 and ABIN-1 have been associated with IBDs and other autoimmune diseases. Mechanistically, both proteins play a central role in the negative feedback of pro-inflammatory NF-KB activation and in the regulation of programmed cell death. A majority of the preceding studies in this topic has focused on immune cells. The hosting group has recently developed mice harboring IEC specific, tamoxifen-inducible A20 and/or ABIN-1 knock-out and has derived small intestinal organoids (called enteroids) from these mice. Interestingly, individual deletion of A20 or ABIN-1 only had minor effects whereas knock-out of both genes caused massive, spontaneous IEC death constituting a surprisingly powerful, epistatic synergy. These studies demonstrate a protective role of A20 and ABIN-1 in IEC homeostasis and establish a powerful, inducible model of IBD in mice. In this proposal, I will utilize this model to investigate unknown aspects in the geneses of IBDs: (1.) TNF-independent triggers that kill IECs in mice bearing A20 and ABIN-1 deficiency will be studied. The hosting group has shown that TNF is the main IEC-intrinsic death inducing agent, but that other, IEC-extrinsic triggers occur in-vivo. Given that many IBD patients do not respond to anti-TNF agents, the identification of TNF-independent mechanisms is a clinically important goal. I will now screen for potentially harmful ligands from immune cells or microbes and dissect candidate pathways in greater detail. (2.) Molecular mechanisms by which A20 and ABIN-1 synergize to protect IEC survival will also be determined. To this end, known biochemically active genetic motifs of A20 (OTU, ZF4, ZF7) and ABIN-1 (UBAN) will be challenged in terms of their contribution to the regulation of IEC survival. (3.) Lastly, the role of A20 and ABIN-1 in human cells will be investigated. Enteroids from IBD patients will be created and analyzed with regard to expression of A20, ABIN-1 and other biomarkers, in comparison to ex-vivo biopsies and in correlation with the clinical outcome. All aims will be evaluated using enteroid cultures as well as in complementing studies in gene-modified mice or human ex-vivo biopsies. An advantage is, that it will be possible to distinguish between IEC intrinsic or extrinsic mechanisms. Collectively, these investigations can not only expand the current understanding of the pathology behind IBDs but can also create exiting new therapeutic targets with a focus on the preservation of mucosal homeostasis.

• DFG Programme: Research Fellowships
• International Connection: USA
• Host: Professor Averil Ma, Ph.D.