Infectious bacteria and inflammatory insults can be so toxic to an organism that they require an immediate response. One such response, called pyroptosis, causes an inflammatory cell death that both alerts the immune system to the immediate threat and also ensures a continued inflammatory effort. In classical pyroptosis, Caspase-1 or Caspase-11 (Caspase-4/5 human) cleaves the pore forming protein, Gasdermin D (GSDMD). This cleaved GSDMD then oligomerizes to form a pore in cellular membranes. Gasdermin D pore formation allows the acute release of IL-1 from the cell, while also destroying membrane integrity such that mitochondrial damage and electrolyte imbalances quickly kill the cell. Implicit in this is that should pyroptosis be blocked, either genetically or pharmacologically, neutralization of the pathogen is so important to organismal survival that alternative mechanisms to initiate cytokine release and inflammatory cell death must have evolved. We are only now beginning to understand these compensatory responses and their role in shaping the immune response. Our preliminary data, with support from the preliminary data from the other three projects in this PPG application, will establish that mechanisms of compensation involve both Gasdermin redundancy and alternative protease cleavage events. We hypothesize that these compensatory mechanisms are cell-type specific. We further posit that they influence the timing and amplitude of cytokine release, the timing and inflammatory capacity of the resulting cell death and the in vivo immune response to inflammatory stimuli. The overall hypothesis of this application is that mechanisms to compensate for loss of pyroptosis alter the inflammatory and immunologic response to an inflammatory insult. We further hypothesize that this compensation helps establish myeloid cell homeostasis and that disruption of these compensatory mechanisms influences the pathologic development of Myelodysplasia and subsequent Leukemia progression. The long-term goal of this work is to better understand how pyroptotic compensatory mechanisms influence the inflammatory response and immunologic homeostasis in hopes of better understanding how to manipulate these pathways in disease.
Lay Summary Throughout human history, infectious diseases and inflammatory such as the flu or cold viruses or stomach bugs, have been drivers of human evolution. These threats are so dangerous that humans have evolved redundant mechanisms to neutralize them. The Gasdermin family of proteins helps drive inflammation in the face of these threats. Despite this, little is known about Gasdermin family redundancy, the mechanisms by which Gasdermin family members are regulated and Gasdermin family members role in normal blood cell development. This grant application aims to study these important problems in the context of inflammatory disease.