A two-front nutrient supply environment fuels small intestinal physiology through differential regulation of nutrient absorption and host defense.

The small intestine contains a two-front nutrient supply environment created by luminal dietary and microbial metabolites (enteral side) and systemic metabolites from the host (serosal side). Yet, it is unknown how each side contributes differentially to the small intestinal physiology. Here, we generated a comprehensive, high-resolution map of the small intestinal two-front nutrient supply environment. Using in vivo tracing of macronutrients and spatial metabolomics, we visualized the spatiotemporal dynamics and cell-type tropism in nutrient absorption and the region-specific metabolic heterogeneity within the villi. Specifically, glutamine from the enteral side fuels goblet cells to support mucus production, and the serosal side loosens the epithelial barrier by calibrating fungal metabolites. Disorganized feeding patterns, akin to the human lifestyle of skipping breakfast, increase the risk of metabolic diseases by inducing epithelial memory of lipid absorption. This study improves our understanding of how the small intestine is spatiotemporally regulated by its unique nutritional environment.

Gasdermin D-mediated metabolic crosstalk promotes tissue repair.

The establishment of an early pro-regenerative niche is crucial for tissue regeneration1,2. Gasdermin D (GSDMD)-dependent pyroptosis accounts for the release of inflammatory cytokines upon various insults3-5. However, little is known about its role in tissue regeneration followed by homeostatic maintenance. Here we show that macrophage GSDMD deficiency delays tissue recovery but has little effect on the local inflammatory milieu or the lytic pyroptosis process. Profiling of the metabolite secretome of hyperactivated macrophages revealed a non-canonical metabolite-secreting function of GSDMD. We further identified 11,12-epoxyeicosatrienoic acid (11,12-EET) as a bioactive, pro-healing oxylipin that is secreted from hyperactive macrophages in a GSDMD-dependent manner. Accumulation of 11,12-EET by direct supplementation or deletion of Ephx2, which encodes a 11,12-EET-hydrolytic enzyme, accelerated muscle regeneration. We further demonstrated that EPHX2 accumulated within aged muscle, and that consecutive 11,12-EET treatment rejuvenated aged muscle. Mechanistically, 11,12-EET amplifies fibroblast growth factor signalling by modulating liquid-liquid phase separation of fibroblast growth factors, thereby boosting the activation and proliferation of muscle stem cells. These data depict a GSDMD-guided metabolite crosstalk between macrophages and muscle stem cells that governs the repair process, which offers insights with therapeutic implications for the regeneration of injured or aged tissues.

Discovery of a triphenylamine-benzofuran derivative as fluorescent probe for hydrogen polysulfide in tea samples.

In this work, a novel triphenylamine-benzofuran derived fluorescent probe, TBF-SS, was developed for detecting hydrogen polysulfide in tea samples and intracellular imaging. TBF-SS showed the practical advantages including high sensitivity (LOD = 0.01 µM), high selectivity, rapid response (within 15 min), and steadiness in various environmental conditions. The detecting system was steady within pH range of 6.0-11.0 and temperature range of 20-55 °C. The probe TBF-SS could guarantee the stable detection of H2Sn for 7 d in storage of either solid or solution. In particular, in the application of various tea samples with different brewing times and testing temperatures, the recovery percentages varied in the range of 95.22 % to 105.0 %. Therefore accurate monitoring of H2Sn could be achieved by using the probe TBF-SS. In addition, TBF-SS could monitor the exogenous level, the ß-lapachone-induced generation and the tea-sample-treated introduction of H2Sn in living MCF-7 cells. This work might inspire the improvement of the serviceability of fluorescent implements.

Gasdermin D maintains bone mass by rewiring the endo-lysosomal pathway of osteoclastic bone resorption.

Gasdermin D (GSDMD)-mediated pyroptosis induces immunogenic cell death and promotes inflammation. However, the functions of GSDMD in tissue homeostasis remain unclear. Here, we identify a physiological function of GSDMD in osteoclasts via a non-lytic p20-generated protein, which prevents bone loss to maintain bone homeostasis. In the late stage of RANKL-induced osteoclastogenesis, GSDMD underwent cleavage, which is dependent on RIPK1 and caspase-8/-3, to yield this p20 product. Gsdmd-deficient osteoclasts showed normal differentiation but enhanced bone resorption with excessive lysosomal activity. Mice with complete or myeloid-specific Gsdmd deletion exhibited increased trabecular bone loss and more severe aging/ovariectomy-induced osteoporosis. GSDMD p20 was preferentially localized to early endosomes and limited endo-lysosomal trafficking and maturation, relying on its oligomerization and control of phosphoinositide conversion by binding to phosphatidylinositol 3-phosphate (PI(3)P). We have thus identified an anti-osteoclastic function of GSDMD as a checkpoint for lysosomal maturation and secretion and linked this to bone homeostasis and endosome-lysosome biology.

Tumor-associated macrophages are shaped by intratumoral high potassium via Kir2.1.

The tumor microenvironment (TME) is a unique niche governed by constant crosstalk within and across all intratumoral cellular compartments. In particular, intratumoral high potassium (K+) has shown immune-suppressive potency on T cells. However, as a pan-cancer characteristic associated with local necrosis, the impact of this ionic disturbance on innate immunity is unknown. Here, we reveal that intratumoral high K+ suppresses the anti-tumor capacity of tumor-associated macrophages (TAMs). We identify the inwardly rectifying K+ channel Kir2.1 as a central modulator of TAM functional polarization in high K+ TME, and its conditional depletion repolarizes TAMs toward an anti-tumor state, sequentially boosting local anti-tumor immunity. Kir2.1 deficiency disturbs the electrochemically dependent glutamine uptake, engendering TAM metabolic reprogramming from oxidative phosphorylation toward glycolysis. Kir2.1 blockade attenuates both murine tumor- and patient-derived xenograft growth. Collectively, our findings reveal Kir2.1 as a determinant and potential therapeutic target for regaining the anti-tumor capacity of TAMs within ionic-imbalanced TME.

Ubiquitination of NLRP3 by gp78/Insig-1 restrains NLRP3 inflammasome activation.

The NLRP3 (NOD-, LRR- and pyrin domain-containing protein 3) inflammasome plays a pivotal role in defending the host against infection as well as sterile inflammation. Activation of the NLRP3 inflammasome is critically regulated by a de-ubiquitination mechanism, but little is known about how ubiquitination restrains NLRP3 activity. Here, we showed that the membrane-bound E3 ubiquitin ligase gp78 mediated mixed ubiquitination of NLRP3, which inhibited NLRP3 inflammasome activation by suppressing the oligomerization and subcellular translocation of NLRP3. In addition, the endoplasmic reticulum membrane protein insulin-induced gene 1 (Insig-1) was required for this gp78-NLRP3 interaction and gp78-mediated NLRP3 ubiquitination. gp78 or Insig-1 deficiency in myeloid cells led to exacerbated NLRP3 inflammasome-dependent inflammation in vivo, including lipopolysaccharide-induced systemic inflammation and alum-induced peritonitis. Taken together, our study identifies gp78-mediated NLRP3 ubiquitination as a regulatory mechanism that restrains inflammasome activation and highlights NLRP3 ubiquitination as a potential therapeutic target for inflammatory diseases.

Epithelial Gasdermin D shapes the host-microbial interface by driving mucus layer formation.

Goblet cells and their main secretory product, mucus, play crucial roles in orchestrating the colonic host-microbe interactions that help maintain gut homeostasis. However, the precise intracellular machinery underlying this goblet cell-induced mucus secretion remains poorly understood. Gasdermin D (GSDMD) is a recently identified pore-forming effector protein that causes pyroptosis, a lytic proinflammatory type of cell death occurring during various pathophysiological conditions. Here, we reveal an unexpected function of GSDMD in goblet cell mucin secretion and mucus layer formation. Specific deletion of Gsdmd in intestinal epithelial cells (ΔIEC) led to abrogated mucus secretion with a concomitant loss of the mucus layer. This impaired colonic mucus layer in GsdmdΔIEC mice featured a disturbed host-microbial interface and inefficient clearance of enteric pathogens from the mucosal surface. Mechanistically, stimulation of goblet cells activates caspases to process GSDMD via reactive oxygen species production; in turn, this activated GSDMD drives mucin secretion through calcium ion-dependent scinderin-mediated cortical F-actin disassembly, which is a key step in granule exocytosis. This study links epithelial GSDMD to the secretory granule exocytotic pathway and highlights its physiological nonpyroptotic role in shaping mucosal homeostasis in the gut.

AKT controls NLRP3 inflammasome activation by inducing DDX3X phosphorylation.

The NLRP3 inflammasome, a critical component of the innate immune system, induces caspase-1 activation and interleukin-1ß maturation and drives cell fate toward pyroptosis. However, the mechanism of NLRP3 inflammasome activation still remains elusive. Here we provide evidence that AKT regulates NLRP3 inflammasome activation. Upon NLRP3 activation, AKT activity is inhibited by second stimulus-induced reactive oxygen species. In contrast, AKT activation leads to NLRP3 inhibition and improved mitochondrial fitness. Mechanistically, AKT induces the phosphorylation of the DDX3X (DEAD-box helicase 3, X-linked), a recently identified NLRP3 inflammasome component, and impairs the interaction between DDX3X and NLRP3. Furthermore, an AKT agonist reduces NLRP3-dependent inflammation in two in vivo models of LPS-induced sepsis and Alum-induced peritonitis. Altogether, our study highlights an important role of AKT in controlling NLRP3 inflammasome activation.