eric-elliott@uiowa.edu
Mentor: Fayyaz Sutterwala, M.D./Ph.D.
Lab Room: D115 MTF
Lab Phone: 319-335-4323

Cardiolipin drives NLRP3 and caspase-1 to mitochondria to promote inflammasome assembly

The NLRP3 inflammasome promotes innate immunity through caspase-1 activation and IL-1β and IL-18 maturation. Two-step NLRP3 activation requires an initial NFκB-activating priming stimulus and secondary agonist which induces cation flux and mitochondrial disruption. A number of mitochondrial molecules and proteins are implicated in NLRP3 activation, and NLRP3 associates with mitochondria under activating conditions. However, the precise dynamics of inflammasome assembly on mitochondria and extent of mitochondrial disruption required for NLRP3 activation remain uncertain. NLRP3 interacts with mitochondrial cardiolipin, and we hypothesized cardiolipin could activate NLRP3 in vitro. Indeed, cardiolipin specifically induced caspase-1 oligomerization and activation. NLRP3 was dispensable for caspase-1 autocatalysis using liposomes with high mol% cardiolipin, but NLRP3 is required at physiologic mol%. Cardiolipin specifically induces a molecular weight shift in caspase-1, caspase-1 specifically binds to cardiolipin over other membrane lipids, and purified caspase-1 binds to cardiolipin more effectively than other caspases. Finding that caspase-1 directly binds to cardiolipin, we examined whether caspase-1 associates with mitochondria endogenously. Surprisingly, NLRP3 and caspase-1 localize to the mitochondrial outer membrane upon priming with lipopolysaccharide, Pam3CSK4, and poly(I:C). Increased association of caspase-1 and NLRP3 with mitochondria occurs after even 30 minutes of stimulation, prior to NLRP3 upregulation. The mitochondrial association of caspase-1 is NLRP3- and ASC- independent, but relies on mitochondrial reactive oxygen species and is accompanied by increased outer membrane cardiolipin. In contrast, ASC associates following secondary stimulus (e.g. nigericin) in a NLRP3- and calcium-dependent manner. An emerging concept in innate immune signaling highlights how innate immune receptors signal through assembly of macromolecular platforms of ligands, receptors, and adaptors which lead to proximity-induced activation. Our finding that caspase-1 and NLRP3 bind to cardiolipin on stressed mitochondria provide another example of the critical role of mitochondria in nucleation of supramolecular organizing centres for innate immune signaling.

Elliott EI, Sutterwala FS. Monocytes Take Their Own Path to IL-1β. Immunity. 2016 Apr 19;44(4):713-5. doi: 10.1016/j.immuni.2016.03.015. PubMed PMID:27096310.

Elliott EI, Sutterwala FS. Initiation and perpetuation of NLRP3 inflammasome activation and assembly. Immunol Rev. 2015 May;265(1):35-52. doi:10.1111/imr.12286. Review. PubMed PMID: 25879282; PubMed Central PMCID:PMC4400874.

Ulland TK, Jain N, Hornick EE, Elliott EI, Clay GM, Sadler JJ, Mills KAM, Janowski AM, Volk APD, Wang K, Legge KL, Gakhar L, Bourdi M, Ferguson PJ, Wilson ME, Cassel SL, and Sutterwala FS. Nlrp12 mutation causes C57BL/6J strain-specific defect in neutrophil recruitment. Nat Comm, in press

Iyer SS, He Q, Janczy JR, Elliott EI, Zhong Z, Olivier AK, Sadler JJ, Knepper-Adrian V, Han R, Qiao L, Eisenbarth SC, Nauseef WM, Cassel SL, Sutterwala FS. Mitochondrial cardiolipin is required for nlrp3 inflammasome activation. Immunity. 2013 Aug 22;39(2):311-23. doi: 10.1016/j.immuni.2013.08.001. Epub 2013 Aug 15. PubMed PMID: 23954133.

Lu P, Hankel IL, Knisz J, Marquardt A, Chiang MY, Grosse J, Constien R, Meyer T, Schroeder A, Zeitlmann L, Al-Alem U, Friedman AD, Elliott EI, Meyerholz DK, Waldschmidt TJ, Rothman PB, Colgan JD. The Justy mutation identifies Gon4-like as a gene that is essential for B lymphopoiesis. J Exp Med. 2010 Jul 5;207(7):1359-67. doi: 10.1084/jem.20100147. Epub 2010 Jun 7. PubMed PMID:20530203; PubMed Central PMCID: PMC2901076.