. Inflammation is our primary response from the innate immune system to fight infection and self-protect from damage. However, dysfunctional regulation of inflammation results in disease, including certain types of cancer, autoimmune, cardiovascular and neurological disorders, rheumatoid arthritis, and even depression. The onset of inflammation depends on the assembly of a multiprotein complex known as the inflammasome. The main players in inflammasome assembly are; - sensor proteins that react upon danger signals derived from pathogens or damaged tissue; - procaspase-1 that activates inflammatory cytokines as a result of inflammasome assembly; - the adapter ASC that functions like a molecular glue by connecting sensor and procaspase-1 molecules. ASC exists in two inflammasome activating isoforms; canonical ASC and ASC_short (both subject of study of the parent R15), and has two more isoforms, one that inhibits inflammasome formation (ASCc) and one isoform with unknown function (ASCd). The presence of protein isoforms is a well- known, natural mechanism for the regulation of protein function. However, little is known on the factors controlling the formation of the inflammasome at the level of the adapter and its isoforms, or how these isoforms impact inflammation. In the parent R15 grant we proposed to study the regulation of the inflammasome via its two activating isoforms (canonical ASC and ASC_short). Both bimodular proteins have two Death Domains connected by a linker, and their amino acid sequences differ solely in the linker length. Our recent findings resulting from the parent R15 indicate that the two isoforms have significantly different kinetics of oligomerization, which in turn correlate with their different dynamic behavior. Our results provide the first explanation at the molecular level of why these isoforms activate the inflammasome to different extent based on their respective oligomerizing capabilities. This Diversity Supplement proposal aims at addressing a knowledge gap in the role of the other two ASC isoforms (ASCc and ASCd) on inflammasome formation and thus in the inflammatory response. The objective of this proposal is innovative because it will decipher the unknown molecular bases for inflammasome regulation mediated by ASCc and ASCd. Our hypotheses are that; 1) ASCc, with an intact Death Domain, inhibits inflammasome formation by competing with ASC self-association, which can account for the observed decreased in the inflammatory response, 2) Based on our preliminary studies, ASCd is an intrinsically disordered protein (IDP), thus we propose that ASCd can fold upon binding to ASC, a typical mechanism of IDPs, resulting in a more moderate inhibition. To test these hypotheses we propose to; 1) study at the atomic level the structural characteristic of ASCc and ASCd with NMR, and 2) quantitatively determine their potential interactions with ASC (identifying the interacting regions and measuring the affinity of the complexes) and 3) discern with Transmission Electron Microscopy the potentially different characteristics of the macrostructures formed by canonical ASC in the presence of ASCc and ASCd.
. The inflammasome is a multiprotein ensemble that triggers the inflammatory response, which is our first line of defense (innate immunity) against infection or tissue injury. Deciphering the factors that impact inflammasome regulation is critical to tackle the molecular bases of human diseases resulting from chronic inflammation (autoimmune and neurological disorders, cardiovascular diseases such as atherosclerosis, acute respiratory distress syndrome, rheumatoid arthritis and even depression). This project is relevant to NIH?s mission because it proposes to determine how different isoforms of the inflammasome adapter ASC regulate inflammation at the molecular level, providing information useful in the design and improvement of therapeutic targets.
