RESUMEN
RIPK3 and its substrate MLKL are essential for necroptosis, a lytic cell death proposed to cause inflammation via the release of intracellular molecules. Whether and how RIPK3 might drive inflammation in a manner independent of MLKL and cell lysis remains unclear. Here we show that following LPS treatment, or LPS-induced necroptosis, the TLR adaptor protein TRIF and inhibitor of apoptosis proteins (IAPs: X-linked IAP, cellular IAP1 and IAP2) regulate RIPK3 and MLKL ubiquitylation. Hence, when IAPs are absent, LPS triggers RIPK3 to activate caspase-8, promoting apoptosis and NLRP3-caspase-1 activation, independent of RIPK3 kinase activity and MLKL. In contrast, in the absence of both IAPs and caspase-8, RIPK3 kinase activity and MLKL are essential for TLR-induced NLRP3 activation. Consistent with in vitro experiments, interleukin-1 (IL-1)-dependent autoantibody-mediated arthritis is exacerbated in mice lacking IAPs, and is reduced by deletion of RIPK3, but not MLKL. Therefore RIPK3 can promote NLRP3 inflammasome and IL-1ß inflammatory responses independent of MLKL and necroptotic cell death.
Asunto(s)
Células de la Médula Ósea/citología , Proteínas Portadoras/metabolismo , Inflamasomas/metabolismo , Proteínas Quinasas/metabolismo , Proteína Serina-Treonina Quinasas de Interacción con Receptores/metabolismo , Animales , Apoptosis , Autoanticuerpos/química , Caspasa 8/metabolismo , Activación Enzimática , Femenino , Inflamación , Proteínas Inhibidoras de la Apoptosis/metabolismo , Interleucina-1beta/metabolismo , Lipopolisacáridos/química , Hígado/embriología , Masculino , Ratones , Ratones Endogámicos C57BL , Proteína con Dominio Pirina 3 de la Familia NLR , Necrosis , Factor de Necrosis Tumoral alfa/metabolismo , Proteína Inhibidora de la Apoptosis Ligada a X/metabolismoRESUMEN
A current paradigm proposes that mitochondrial damage is a critical determinant of NLRP3 inflammasome activation. Here, we genetically assess whether mitochondrial signalling represents a unified mechanism to explain how NLRP3 is activated by divergent stimuli. Neither co-deletion of the essential executioners of mitochondrial apoptosis BAK and BAX, nor removal of the mitochondrial permeability transition pore component cyclophilin D, nor loss of the mitophagy regulator Parkin, nor deficiency in MAVS affects NLRP3 inflammasome function. In contrast, caspase-8, a caspase essential for death-receptor-mediated apoptosis, is required for efficient Toll-like-receptor-induced inflammasome priming and cytokine production. Collectively, these results demonstrate that mitochondrial apoptosis is not required for NLRP3 activation, and highlight an important non-apoptotic role for caspase-8 in regulating inflammasome activation and pro-inflammatory cytokine levels.
