Inflammatory caspases (caspase-1, -4, -5 and -11) are critical for innate defences. Caspase-1 is activated by ligands of various canonical inflammasomes, and caspase-4, -5 and -11 directly recognize bacterial lipopolysaccharide, both of which trigger pyroptosis. Despite the crucial role in immunity and endotoxic shock, the mechanism for pyroptosis induction by inflammatory caspases is unknown. Here we identify gasdermin D (Gsdmd) by genome-wide clustered regularly interspaced palindromic repeat (CRISPR)-Cas9 nuclease screens of caspase-11- and caspase-1-mediated pyroptosis in mouse bone marrow macrophages. GSDMD-deficient cells resisted the induction of pyroptosis by cytosolic lipopolysaccharide and known canonical inflammasome ligands. Interleukin-1β release was also diminished in Gsdmd(-/-) cells, despite intact processing by caspase-1. Caspase-1 and caspase-4/5/11 specifically cleaved the linker between the amino-terminal gasdermin-N and carboxy-terminal gasdermin-C domains in GSDMD, which was required and sufficient for pyroptosis. The cleavage released the intramolecular inhibition on the gasdermin-N domain that showed intrinsic pyroptosis-inducing activity. Other gasdermin family members were not cleaved by inflammatory caspases but shared the autoinhibition; gain-of-function mutations in Gsdma3 that cause alopecia and skin defects disrupted the autoinhibition, allowing its gasdermin-N domain to trigger pyroptosis. These findings offer insight into inflammasome-mediated immunity/diseases and also change our understanding of pyroptosis and programmed necrosis.

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Highlights d Impaired alveolar regeneration results in sustained elevated tension on alveoli d Elevated mechanical tension activates a TGF-b signaling loop in AT2 cells d The impacts of mechanical tension on alveoli are not uniformly distributed d Mechanical tension-activated TGF-b signaling is essential for fibrosis progression

Circadian regulation is critically important in maintaining metabolic and physiological homeostasis. However, little is known about the possible influence of the clock on physiological abnormalities occurring under pathological conditions. Here, we report the discovery that hypoxia, a condition that causes catastrophic bodily damage, is gated by the circadian clock in vivo. Hypoxia signals conversely regulate the clock by slowing the circadian cycle and dampening the amplitude of oscillations in a dose-dependent manner. ChIP-seq analyses of hypoxia-inducible factor HIF1A and the core clock component BMAL1 revealed crosstalk between hypoxia and the clock at the genome level. Further, severe consequences caused by acute hypoxia, such as those that occur with heart attacks, were correlated with defects in circadian rhythms. We propose that the clock plays functions in fine-tuning hypoxic responses under pathophysiological conditions. We argue that the clock can, and likely should, be exploited therapeutically to reduce the severity of fatal hypoxia-related diseases.

RNA-directed DNA methylation (RdDM) is required for transcriptional silencing of transposons and other DNA repeats in Arabidopsis thaliana. Although previous research has demonstrated that the SET domain-containing SU(VAR)3–9 homologs SUVH2 and SUVH9 are involved in the RdDM pathway, the underlying mechanism remains unknown. Our results indicated that SUVH2 and/or SUVH9 not only interact with the chromatin-remodeling complex termed DDR (DMS3, DRD1, and RDM1) but also with the newly characterized complex composed of two conserved Microrchidia (MORC) family proteins, MORC1 and MORC6. The effect of suvh2suvh9 on Pol IV-dependent siRNA accumulation and DNA methylation is comparable to that of the Pol V mutant nrpe1 and the DDR complex mutant dms3, suggesting that SUVH2 and SUVH9 are functionally associated with RdDM. Our CHIP assay demonstrated that SUVH2 and SUVH9 are required for the occupancy of Pol V at RdDM loci and facilitate the production of Pol V-dependent noncoding RNAs. Moreover, SUVH2 and SUVH9 are also involved in the occupancy of DMS3 at RdDM loci. The putative catalytic active site in the SET domain of SUVH2 is dispensable for the function of SUVH2 in RdDM and H3K9 dimethylation. We propose that SUVH2 and SUVH9 bind to methylated DNA and facilitate the recruitment of Pol V to RdDM loci by associating with the DDR complex and the MORC complex.