During inflammation, the inflammatory caspase‑1 (CASP1) can be activated downstream of canonical inflammasome activation in response to sensing of pathogen‑derived particles or host‑derived danger signals (reviewed in Kelley N et al. 2019; Zheng D et al. 2020). The non‑canonical inflammasome assembly is mediated by CASP4, CASP5 in humans and CASP11 in mice upon sensing intracellular bacterial lipopolysaccharide (LPS) (Vigano E et al. 2015; Kayagaki N et al. 2015). Activated inflammatory caspases induce a proinflammatory cell death known as pyroptosis via the proteolytic processing of gasdermin D (GSDMD) (Shi J et al. 2015; Kayagaki N et al. 2015; He W et al. 2015; Ding J et al. 2016; Liu X et al. 2016; Sborgi L et al. EMBO J 2016). Intact GSDMD cannot form pores due to the inhibitory function of its C-terminal domain. Caspase‑mediated cleavage of GSDMD releases the C‑terminal fragment of GSDMD (276‑484) (Shi J et al. 2015), enabling the N‑terminal fragment of GSDMD (1‑275) to form pores in cellular membranes leading to cytokine release and pyroptosis (Ding J et al. 2016; Liu X et al. 2016; Sborgi L et al. 2016; Mulvihill E et al. 2018). Dimethyl fumarate (DMF, trade name:Tecfidera®) was found to modify Сys191 of GSDMD to form S-(2-succinyl)-cysteine, a process known as succination of proteins (Humphries F et al. 2020). Cys191 in human GSDMD (corresponding to Cys192 in mouse) is thought to be critical for the GSDMD oligomerization and pore formation (reviewed in Pandeya A et al. 2019). DMF inhibited cell death and lactate dehydrogenase (LDH) release in LPS-primed mouse macrophages and human monocyte-like THP-1 cell in response to nigericin. Similarly, two fumarate analogs, diroximel fumarate (trade name: Vumerity®) and tepilamide fumarate, also blocked LPS-nigericin-induced pyroptosis and formation of GSDMD (1‑275) (Humphries F et al. 2020). Treatment with DMF is thought to inhibit the interaction of GSDMD with CASP1, cleavage by CASP1 and oligomerization of GSDMD (Humphries F et al. 2020). Moreover, GSDMD‑mediated pyroptosis when overactivated can lead to sepsis. Elevated levels of GSDMD were noted in microparticles isolated from plasma of septic patients (Homsy E et al. 2019). In the murine sepsis model, Gsdmd‑deficient mice showed significantly improved survival compared to the wild type mice (Kambara H et al. 2018). Treatment with fumarate protected mice from LPS‑induced septic shock (Humphries F et al. 2020). In addition, Gsdmd-/- mice are protected from disease in mouse models of familial Mediterranean fever and multiple sclerosis (MS) (Kanneganti A et al. 2018; Li S et al. 2019). Administration of DMF reduced GSDMD-driven responses in these mouse models (Humphries F et al. 2020). Further, DMF reduced levels of both interleukin (IL)-1β and GSDMD (1‑275) in peripheral blood mononuclear cells (PBMCs) from patients with MS. The data suggest that DMF blocks GSDMD pore formation and pyroptosis by modifying Cys191 of GSDMD (Humphries F et al. 2020). Endogenous fumarate may also inactivate GSDMD by succinating Cys191 (Humphries F et al. 2020).

This Reactome event shows the covalent modification of GSDMD, namely S-(2-succinyl)-Cys191-GSDMD, formed by a Michael addition reaction between DMF and the reactive thiol group on Cys191 of GSDMD.