Caspase-1 inhibition prevents glial inflammasome activation and pyroptosis in models of multiple sclerosis

Abstract

Multiple sclerosis (MS) is a progressive inflammatory demyelinating disease of the CNS of unknown cause that remains incurable. Inflammasome-associated caspases mediate the maturation and release of the proinflammatory cytokines IL-1β and IL-18 and activate the pore-forming protein gasdermin D (GSDMD). Inflammatory programmed cell death, pyroptosis, was recently shown to be mediated by GSDMD. Here, we report molecular evidence for GSDMD-mediated inflammasome activation and pyroptosis in both myeloid cells (macrophages/microglia) and, unexpectedly, in myelin-forming oligodendrocytes (ODCs) in the CNS of patients with MS and in the MS animal model, experimental autoimmune encephalomyelitis (EAE). We observed inflammasome activation and pyroptosis in human microglia and ODCs in vitro after exposure to inflammatory stimuli and demonstrate caspase-1 inhibition by the small-molecule inhibitor VX-765 in both cell types. GSDMD inhibition by siRNA transduction suppressed pyroptosis in human microglia. VX-765 treatment of EAE animals reduced the expression of inflammasome- and pyroptosis-associated proteins in the CNS, prevented axonal injury, and improved neurobehavioral performance. Thus, GSDMD-mediated pyroptosis in select glia cells is a previously unrecognized mechanism of inflammatory demyelination and represents a unique therapeutic opportunity for mitigating the disease process in MS and other CNS inflammatory diseases.

Inflammasomes in neuroinflammatory and neurodegenerative diseases

“…The anti‐inflammatory protein A20 has been shown to negatively regulate NLRP3 inflammasome activation (Vande Walle et al , ), and deletion of A20 in microglia and CNS macrophages exacerbated EAE in mice due to NLRP3 hyperactivation that resulted in increased IL‐1β secretion and CNS inflammation (Voet et al , ). CNS‐intrinsic inflammasome activation was further reported in another study that showed caspase‐1‐ and GSDMD‐mediated pyroptosis in microglia, as well as in myelin‐forming oligodendrocytes in the CNS of MS patients and EAE mice (Mckenzie et al , ).…”

“…Although inflammasome signaling in the CNS is mainly attributed to microglia, the key innate immune cells of the brain, expression of inflammasome components has also been reported in other cell types of the CNS, including neurons (Kaushal et al , ), astrocytes (Freeman et al , ), perivascular CNS macrophages (Kawana et al , ), oligodendrocytes (Mckenzie et al , ), and endothelial cells (Gong et al , ) (Fig ). However, current understanding of inflammasome activation in microglia and its role in CNS inflammation and disease is still fragmentary and primarily based on in vitro studies with primary microglia and microglial cell lines, and in vivo studies with transgenic knockout mice that lack expression of specific inflammasome components throughout the body.…”

“…Moreover, the pharmacological NLRP3 inflammasome inhibitor MCC950/CRID3 was shown to suppress IL‐1β production and attenuate EAE severity in wild‐type mice (Coll et al , ). Similarly, pharmacological blockade of caspase protease activity with Z‐Val‐Ala‐DL‐Asp‐fluoromethylketone or the inflammatory caspase prodrug VX‐765 reduced EAE symptoms in mice (Furlan et al , ; Mckenzie et al , ). Interestingly, IFNβ, the first line treatment for MS, is only effective in an NLRP3 inflammasome‐dependent EAE subtype, whereas NLRP3‐independent EAE could not be reversed by IFN‐β therapy (Inoue et al , , ).…”

Species differences in immune‐mediated CNS tissue injury and repair: A (neuro)inflammatory topic

“…Regarding the basis of OL injury in animal models of CNS demyelination, apoptosis of OLs is described in the EAE model, being linked to effects of TNF; it is also observed in the cuprizone toxicity model (Valentin‐Torres, Savarin, Barnett, & Bergmann, ). Additional forms of active cell death (pyroptosis) have been recognized in OLs in both MS and in EAE (McKenzie et al, ). In our electron microscopical analyses of the acute lesions (using much of the same material as reported in Lucchinetti et al ()), we observed multiple surviving OLs with evidence of withdrawal of terminal processes in all cases, suggestive of an initial sublethal stage of injury in the human brain (Cui et al, ; Rone et al, ).…”

Update of inflammasome activation in microglia/macrophage in aging and aging‐related disease

“…Inflammasome activation was first discovered in myeloid cells, including macrophage/microglia, neutrophil, and dendritic cell . Recently, it was demonstrated that other cell types, including, oligodendrocyte, astrocyte, neurons, and epithelial cell, could also trigger inflammasome activation . Among inflammasome‐forming cells, it is microglia/macrophage that has the most potent inflammasome activation, thus is most widely studied …”