Medical Biology - Theses
Permanent URI for this collection
Search Results
1 - 1 of 1
-
ItemA genetics-based investigation into the regulation of RIPK1 and caspase-8 during cell death and disease( 2022)Cell death is a fundamental process needed for healthy development, immunity and life. The tight control and regulation of cell death signalling is important for cellular homeostasis, and the de-regulation of cell death is a hallmark of many diseases ranging from infection to cancer. Several regulated cell death (RCD) pathways have been described, with genetically encoded cell death signalling molecules and effectors dictating cellular fate. Some of these, such as necroptosis and pyroptosis, are highly inflammatory and immunomodulatory, while others, such as apoptosis, are generally considered non-inflammatory and tolerogenic. Caspase-8 is a critical cell death protein that also has a pleiotropic role in inflammation. Receptor interacting protein kinase (RIPK)1 liaises with external signals to control the death and inflammatory functions of caspase-8, but major gaps remain in our understanding of how RIPK1 regulates the death and non-death functions of caspase-8. Identifying and characterising the mechanisms that control caspase-8 activity is crucial to understanding how we might best therapeutically target cell death signalling to overcome relevant diseases. This PhD thesis explores the regulation of caspase-8 activity and identifies key upstream checkpoints to therapeutically intersect and modulate caspase-8 activity. Firstly, this thesis genetically delineates a unique caspase-8-dependent cell death triggered by combined signalling of host-derived interferon (IFN)-gamma and pathogen ligands that engage Toll-like receptors (TLRs). Experiments show that caspase-8 cell death signalling is licensed by nitric oxide (NO), which is produced by the inducible nitric oxide synthase (iNOS) protein. Physiologically, both caspase-8 and iNOS contributed to disease severity in a model of severe acute respiratory syndrome-associated coronavirus-2 (SARS-CoV-2) infection, suggesting iNOS might licence damaging cell death and inflammation during coronavirus disease of 2019 (COVID-19). Secondly, the physiological role of Mind Bomb-2 (MIB2), a recently described pro-survival protein that prevents caspase-8 activation by RIPK1 in cancer cells, is examined using novel MIB2 gene targeted mice. This thesis reveals the physiological function of MIB2 in vivo and examines the function of MIB2 in both inflammation and cancer disease models to determine whether therapeutics designed to inhibit MIB2 could be used to safely activate caspase-8. These studies find that deficiency or inactivation of MIB2 is well-tolerated in mice and does not impact important biological processes including development, haematopoiesis, viability or fertility. Interestingly, challenging MIB2 knockout mice to drive excessive caspase-8 activity leads to enhanced cell death-induced dermatitis, while inactivation of MIB2 limits tumourigenesis in a model of inflammation-driven colorectal cancer. This thesis provides critical insight into the regulation of caspase-8 and uncovers distinct modes of regulation detailing how elevated NO or, inhibition of MIB2 contribute to excessive cell death and disease. This work aids the design of next generation treatments to overcome cell death resistance and transforms our understanding of how caspase-8 is regulated in inflammation and disease.