Plasma membrane rupture (PMR) is the final cataclysmic event in lytic cell death. PMR releases intracellular molecules termed damage-associated molecular patterns (DAMPs) that propagate the inflammatory response. The underlying mechanism for PMR, however, is unknown. Here we show that the ill-characterized nerve injury-induced protein 1 (NINJ1) -a cell surface protein with two transmembrane regions -plays an essential role in the induction of PMR. A forward-genetic screen of randomly mutagenized mice linked NINJ1 to PMR. Ninj1 -/macrophages exhibited impaired PMR in response to diverse inducers of pyroptotic, necrotic and apoptotic cell death, and failed to release numerous intracellular proteins including High Mobility Group Box 1 (HMGB1, a known DAMP) and Lactate Dehydrogenase (LDH, a standard measure of PMR). Ninj1 -/macrophages died, but with a distinctive and persistent ballooned morphology, attributable to defective disintegration of bubble-like herniations. Ninj1 -/mice were more susceptible than wildtype mice to Citrobacter rodentium, suggesting a role for PMR in anti-bacterial host defense.Mechanistically, NINJ1 utilized an evolutionarily conserved extracellular α-helical domain for oligomerization and subsequent PMR. The discovery of NINJ1 as a mediator of PMR overturns the long-held dogma that cell death-related PMR is a passive event.Pyroptosis is a potent inflammatory mode of lytic cell death triggered by diverse infectious and sterile insults 1-3 . It is driven by the pore-forming fragment of gasdermin D (GSDMD) 4-7 and releases two exemplar proteins: interleukin-1β (IL-1β), a pro-inflammatory cytokine, and LDH, a standard marker of PMR and lytic cell death. An early landmark study 8 predicted two sequential steps for pyroptosis: (1) initial formation of a small plasma membrane pore causing IL-1β release and non-selective ionic fluxes, and (2) subsequent PMR attributable to oncotic cell swelling. PMR releases LDH (140 kDa) and large DAMPs. While the predicted size of gasdermin pores (~18 nm inner diameter 9 ) is large enough to release IL-1β (17 kDa, ~4.5 nm diameter), the underlying mechanism for subsequent PMR has been considered a passive osmotic lysis event. An unbiased forward genetic screen identifies NINJ1To identify essential mediators of PMR, we performed a forward genetic screen using bone marrow-derived macrophages (BMDMs) from N-ethyl-N-nitrosourea (ENU)-mutagenized mice.

Summary Mitochondria are dynamic organelles, remodeling and exchanging contents during cyclic fusion and fission. Genetic mutations of mitofusin (Mfn) 2 interrupt mitochondrial fusion and cause the untreatable neurodegenerative condition, Charcot Marie Tooth disease type 2A (CMT2A). It has not been possible to directly modulate mitochondrial fusion, in part because the structural basis of mitofusin function is incompletely understood. Here we show that mitofusins adopt either a fusion-constrained or fusion-permissive molecular conformation directed by specific intramolecular binding interactions, and demonstrate that mitofusin-dependent mitochondrial fusion can be regulated by targeting these conformational transitions. Based on this model we engineered a cell-permeant minipeptide to destabilize fusion-constrained mitofusin and promote the fusion-permissive conformation, reversing mitochondrial abnormalities in cultured fibroblasts and neurons harboring CMT2A gene defects. The relationship between mitofusin conformational plasticity and mitochondrial dynamism uncovers a central mechanism regulating mitochondrial fusion whose manipulation can correct mitochondrial pathology triggered by defective or imbalanced mitochondrial dynamics.

Gasdermin-D (GSDMD) is cleaved by caspase-1, caspase-4, and caspase-11 in response to canonical and noncanonical inflammasome activation. Upon cleavage, GSDMD oligomerizes and forms plasma membrane pores, resulting in interleukin-1β (IL-1β) secretion, pyroptotic cell death, and inflammatory pathologies, including periodic fever syndromes and septic shock—a plague on modern medicine. Here, we showed that IRF2, a member of the interferon regulatory factor (IRF) family of transcription factors, was essential for the transcriptional activation of GSDMD. A forward genetic screen with N-ethyl-N-nitrosourea (ENU)–mutagenized mice linked IRF2 to inflammasome signaling. GSDMD expression was substantially attenuated in IRF2-deficient macrophages, endothelial cells, and multiple tissues, which corresponded with reduced IL-1β secretion and inhibited pyroptosis. Mechanistically, IRF2 bound to a previously uncharacterized but unique site within the GSDMD promoter to directly drive GSDMD transcription for the execution of pyroptosis. Disruption of this single IRF2-binding site abolished signaling by both the canonical and noncanonical inflammasomes. Together, our data illuminate a key transcriptional mechanism for expression of the gene encoding GSDMD, a critical mediator of inflammatory pathologies.

Intracellular LPS sensing by caspase-4/5/11 triggers proteolytic activation of pore-forming gasdermin D (GSDMD), leading to pyroptotic cell death in Gram-negative bacteria-infected cells. Involvement of caspase-4/5/11 and GSDMD in inflammatory responses, such as lethal sepsis, makes them highly desirable drug targets. Using knock-in (KI) mouse strains, we herein provide genetic evidence to show that caspase-11 auto-cleavage at the inter-subunit linker is essential for optimal catalytic activity and subsequent proteolytic cleavage of GSDMD. Macrophages from caspase-11-processing dead KI mice ( ) exhibit defective caspase-11 auto-processing and phenocopy and caspase-11 enzymatically dead KI ( ) macrophages in attenuating responses to cytoplasmic LPS or Gram-negative bacteria infection. KI macrophages also fail to cleave GSDMD and are hypo-responsive to inflammasome stimuli, confirming that the GSDMD Asp residue is a nonredundant and indispensable site for proteolytic activation of GSDMD. Our data highlight the role of caspase-11 self-cleavage as a critical regulatory step for GSDMD processing and response against Gram-negative bacteria.

Reactive oxygen species (ROS) have been implicated in a variety of age-related diseases including multiple cardiovascular disorders. However, translation of ROS scavengers (anti-oxidants) into the clinic has not been successful. These anti-oxidants grossly reduce total levels of cellular ROS including ROS that participate in physiological signaling. In this review, we challenge the traditional anti-oxidant therapeutic approach that targets ROS directly with novel approaches that improve mitochondrial functions to more effectively treat cardiovascular diseases.

Mitochondria form a dynamic network governed by a balance between opposing fission and fusion processes. Because excessive mitochondrial fission correlates with numerous pathologies, including neurodegeneration, the mechanism governing fission has become an attractive therapeutic strategy. However, targeting fission is a double-edged sword as physiological fission is necessary for mitochondrial function. Fission is trigged by Drp1 anchoring to adaptors tethered to the outer mitochondrial membrane. We designed peptide P259 that distinguishes physiological from pathological fission by specifically inhibiting Drp1′s interaction with the Mff adaptor. Treatment of cells with P259 elongated mitochondria and disrupted mitochondrial function and motility. Sustained in vivo treatment caused a decline in ATP levels and altered mitochondrial structure in the brain, resulting in behavioral deficits in wild-type mice and a shorter lifespan in a mouse model of Huntington’s disease. Therefore, the Mff-Drp1 interaction is critical for physiological mitochondrial fission, motility, and function in vitro and in vivo. Tools, such as P259, that differentiate physiological from pathological fission will enable the examination of context-dependent roles of Drp1 and the suitability of mitochondrial fission as a target for drug development.

Endoplasmic reticulum (ER) and mitochondrial function have both been shown to be critical events in neurodegenerative diseases. The ER mediates protein folding, maturation, sorting as well acts as calcium storage. The unfolded protein response (UPR) is a stress response of the ER that is activated by the accumulation of misfolded proteins within the ER lumen. Although the molecular mechanisms underlying ER stress-induced apoptosis are not completely understood, increasing evidence suggests that ER and mitochondria cooperate to signal cell death. Similarly, calcium-mediated mitochondrial function and dynamics not only contribute to ATP generation and calcium buffering but are also a linchpin in mediating cell fate. Mitochondria and ER form structural and functional networks (mitochondria-associated ER membranes [MAMs]) essential to maintaining cellular homeostasis and determining cell fate under various pathophysiological conditions. Regulated Ca2+ transfer from the ER to the mitochondria is important in maintaining control of pro-survival/pro-death pathways. In this review, we summarize the latest therapeutic strategies that target these essential organelles in the context of neurodegenerative diseases.

Plasma membrane rupture (PMR) is the final cataclysmic event in lytic cell death. PMR releases intracellular molecules termed damage-associated molecular patterns (DAMPs) that propagate the inflammatory response. The underlying mechanism for PMR, however, is unknown. Here we show that the ill-characterized nerve injury-induced protein 1 (NINJ1) — a cell surface protein with two transmembrane regions — plays an essential role in the induction of PMR. A forward-genetic screen of randomly mutagenized mice linked NINJ1 to PMR. Ninj1–/– macrophages exhibited impaired PMR in response to diverse inducers of pyroptotic, necrotic and apoptotic cell death, and failed to release numerous intracellular proteins including High Mobility Group Box 1 (HMGB1, a known DAMP) and Lactate Dehydrogenase (LDH, a standard measure of PMR). Ninj1–/– macrophages died, but with a distinctive and persistent ballooned morphology, attributable to defective disintegration of bubble-like herniations. Ninj1–/– mice were more susceptible than wild-type mice to Citrobacter rodentium, suggesting a role for PMR in anti-bacterial host defense. Mechanistically, NINJ1 utilized an evolutionarily conserved extracellular α-helical domain for oligomerization and subsequent PMR. The discovery of NINJ1 as a mediator of PMR overturns the long-held dogma that cell death-related PMR is a passive event. Pyroptosis is a potent inflammatory mode of lytic cell death triggered by diverse infectious and sterile insults1-3. It is driven by the pore-forming fragment of gasdermin D (GSDMD)4-7 and releases two exemplar proteins: interleukin-1β (IL-1β), a pro-inflammatory cytokine, and LDH, a standard marker of PMR and lytic cell death. An early landmark study8 predicted two sequential steps for pyroptosis: (1) initial formation of a small plasma membrane pore causing IL-1β release and non-selective ionic fluxes, and (2) subsequent PMR attributable to oncotic cell swelling. PMR releases LDH (140 kDa) and large DAMPs. While the predicted size of gasdermin pores (~18 nm inner diameter9) is large enough to release IL-1β (17 kDa, ~4.5 nm diameter), the underlying mechanism for subsequent PMR has been considered a passive osmotic lysis event.