N6-adenomethylation of GsdmC is essential for Lgr5+ stem cell survival to maintain normal colonic epithelial morphogenesis

To die or not to die: Gasdermins in intestinal health and disease

Intestinal homeostasis is achieved by the balance among intestinal epithelium, immune cells, and gut microbiota. Gasdermins (GSDMs), a family of membrane pore forming proteins, can trigger rapid inflammatory cell death in the gut, mainly pyroptosis and NETosis. Importantly, there is increasing literature on the non-cell lytic roles of GSDMs in intestinal homeostasis and disease. While GSDMA is low and PJVK is not expressed in the gut, high GSDMB and GSDMC expression is found almost restrictively in intestinal epithelial cells. Conversely, GSDMD and GSDME show more ubiquitous expression among various cell types in the gut. The N-terminal region of GSDMs can be liberated for pore formation by an array of proteases in response to pathogen- and danger-associated signals, but it is not fully understood what cell type-specific mechanisms activate intestinal GSDMs. The host relies on GSDMs for pathogen defense, tissue tolerance, and cancerous cell death; however, pro-inflammatory milieu caused by pyroptosis and excessive cytokine release may favor the development and progression of inflammatory bowel disease and cancer. Therefore, a thorough understanding of spatiotemporal mechanisms that control gasdermin expression, activation, and function is essential for the development of future therapeutics for intestinal disorders.

Intestinal transit-amplifying cells require METTL3 for growth factor signaling and cell survival

Intestinal epithelial transit-amplifying cells are essential stem progenitors required for intestinal homeostasis, but their rapid proliferation renders them vulnerable to DNA damage from radiation and chemotherapy. Despite these cells' critical roles in intestinal homeostasis and disease, few studies have described genes that are essential to transit-amplifying cell function. We report that RNA methyltransferase-like 3 (METTL3) is required for survival of transit-amplifying cells in the murine small intestine. Transit-amplifying cell death after METTL3 deletion was associated with crypt and villus atrophy, loss of absorptive enterocytes, and uniform wasting and death in METTL3-depleted mice. Sequencing of polysome-bound and methylated RNAs in enteroids and in vivo demonstrated decreased translation of hundreds of methylated transcripts after METTL3 deletion, particularly transcripts involved in growth factor signal transduction such as Kras. Further investigation verified a relationship between METTL3 and Kras methylation and protein levels in vivo. Our study identifies METTL3 as an essential factor supporting the homeostasis of small intestinal tissue via direct maintenance of transit-amplifying cell survival. We highlight the crucial role of RNA modifications in regulating growth factor signaling in the intestine with important implications for both homeostatic tissue renewal and epithelial regeneration.

Gasdermins in sepsis

Sepsis is a hyper-heterogeneous syndrome in which the systemic inflammatory response persists throughout the course of the disease and the inflammatory and immune responses are dynamically altered at different pathogenic stages. Gasdermins (GSDMs) proteins are pore-forming executors in the membrane, subsequently mediating the release of pro-inflammatory mediators and inflammatory cell death. With the increasing research on GSDMs proteins and sepsis, it is believed that GSDMs protein are one of the most promising therapeutic targets in sepsis in the future. A more comprehensive and in-depth understanding of the functions of GSDMs proteins in sepsis is important to alleviate the multi-organ dysfunction and reduce sepsis-induced mortality. In this review, we focus on the function of GSDMs proteins, the molecular mechanism of GSDMs involved in sepsis, and the regulatory mechanism of GSDMs-mediated signaling pathways, aiming to provide novel ideas and therapeutic strategies for the diagnosis and treatment of sepsis.

The role of caspase-8 in inflammatory signalling and pyroptotic cell death

The programmed cell death machinery exhibits surprising flexibility, capable of crosstalk and non-apoptotic roles. Much of this complexity arises from the diverse functions of caspase-8, a cysteine-aspartic acid protease typically associated with activating caspase-3 and - 7 to induce apoptosis. However, recent research has revealed that caspase-8 also plays a role in regulating the lytic gasdermin cell death machinery, contributing to pyroptosis and immune responses in contexts such as infection, autoinflammation, and T-cell signalling. In mice, loss of caspase-8 results in embryonic lethality from unrestrained necroptotic killing, while in humans caspase-8 deficiency can lead to an autoimmune lymphoproliferative syndrome, immunodeficiency, inflammatory bowel disease or, when it can't cleave its substrate RIPK1, early onset periodic fevers. This review focuses on non-canonical caspase-8 signalling that drives immune responses, including its regulation of inflammatory gene transcription, activation within inflammasome complexes, and roles in pyroptotic cell death. Ultimately, a deeper understanding of caspase-8 function will aid in determining whether, and when, targeting caspase-8 pathways could be therapeutically beneficial in human diseases.

Epigenetic and transcriptional control of gasdermins

Cells undergo an inflammatory programmed lytic cell death called 'pyroptosis' (with the Greek roots 'fiery'), often featuring morphological hallmarks such as large ballooning protrusions and subsequent bursting. Originally described as a caspase-1-dependent cell death in response to bacterial infection, pyroptosis has since been re-defined in 2018 as a cell death dependent on plasma membrane pores by a gasdermin (GSDM) family member [1,2]. GSDMs form pores in the plasma membrane as well as organelle membranes, thereby initiating membrane destruction and the rapid and lytic demise of a cell. The gasdermin family plays a profound role in the execution of pyroptosis in the context of infection, inflammation, tumor pathogenesis, and anti-tumor therapy. More recently, cell-death-independent functions for some of the GSDMs have been proposed. Therefore, a comprehensive understanding of gasdermin gene regulation, including mechanisms in both homeostatic conditions and during inflammation, is essential. In this review, we will summarize the role of gasdermins in pyroptosis and focus our discussion on the transcriptional and epigenetic mechanisms controlling the expression of GSDMs.

Tuft cells utilize taste signaling molecules to respond to the pathobiont microbe Ruminococcus gnavus in the proximal colon

Tuft cells are a type of rare epithelial cells that have been recently found to utilize taste signal transduction pathways to detect and respond to various noxious stimuli and pathogens, including allergens, bacteria, protists and parasitic helminths. It is, however, not fully understood how many different types of pathogens they can sense or what exact molecular mechanisms they employ to initiate targeted responses. In this study, we found that an anaerobic pathobiont microbe, Ruminococcus gnavus (R. gnavus), can induce tuft cell proliferation in the proximal colon whereas the microbe's lysate can stimulate these proximal colonic tuft cells to release interleukin-25 (IL-25). Nullification of the Gng13 and Trpm5 genes that encode the G protein subunit Gγ13 and transient receptor potential ion channel Trpm5, respectively, or application of the Tas2r inhibitor allyl isothiocyanate (AITC), G protein Gβγ subunit inhibitor Gallein or the phospholipase Cβ2 (PLCβ2) inhibitor U73122 reduces R. gnavus-elicited tuft cell proliferation or IL-25 release or both. Furthermore, Gng13 conditional knockout or Trpm5 knockout diminishes the expression of gasdermins C2, C3 and C4, and concomitantly increases the activated forms of caspases 3, 8 and 9 as well as the number of TUNEL-positive apoptotic cells in the proximal colon. Together, our data suggest that taste signal transduction pathways are not only involved in the detection of R. gnavus infection, but also contribute to helping maintain gasdermin expression and prevent apoptotic cell death in the proximal colon, and these findings provide another strategy to combat R. gnavus infection and sheds light on new roles of taste signaling proteins along with gasdermins in protecting the integrity of the proximal colonic epithelium.

Phase separation of BuGZ regulates gut regeneration and aging through interaction with m6A regulators

Exploring the role of phase separation in intracellular compartment formation is an active area of research. However, the associations of phase separation with intestinal stem cell (ISC)-dependent regeneration and aging remain unclear. Here, we demonstrate that BuGZ, a coacervating mitotic effector, shows age- and injury-associated condensation in Drosophila ISC nuclei during interphase. BuGZ condensation promotes ISC proliferation, affecting Drosophila gut repair and longevity. Moreover, m6A reader YT521-B acts as the transcriptional and functional downstream of BuGZ. The binding of YT521-B promotor or m6A writer Ime4/ Mettl14 to BuGZ controls its coacervation, indicating that the promotor may accelerate the phase transition of its binding transcription factor. Hence, we propose that phase separation and m6A regulators may be critical for ameliorating ISC-dependent gut regeneration and aging and requires further study.

Mettl14-mediated m6 A modification regulates the abnormal differentiation of small intestinal epithelial stem cells in diabetic state

Diabetes mellitus (DM) and its related complications are a global epidemic characterized by high morbidity and mortality. However, little is known about diabetic enteropathy (DE) and its the potential underlying mechanism. Intestinal epithelial stem cells (IESCs) were harvested from experimental mice, and the levels of dominant N6-methyladenosine (m6 A)-related enzyme were detected by RT-PCR, Western blotting, immunohistochemistry. The role of Mettl14 in the abnormal differentiation of intestinal epithelial cells (IECs) during DM was confirmed by knockdown experiments. RT-PCR, MeRIP, and bioinformatics analysis were carried out to confirm the downstream target of Mettl14. Through bioinformatics analysis, RT-PCR, and Western blotting, we further analyzed the differentiation-related gene in the IECs from mice with DM. In this study, the levels of Mettl14 and m6 A were higher in db/db mice than that in control mice. And abnormal differentiation of IECs in DM was associated with Mettl14 overexpression. Additionally, Mettl14 is a major determinant of IESCs identity and organoid-forming upon DM state. Mechanistically, we revealed that the candidate binding target of Mettl14 was Fzd2 mRNA and affected Fzd2 stability. Moreover, Mettl14 downregulation was observed to attenuate the abnormal differentiation of IECs through modulating Fzd2 m6A modification in DM state. Together, our results provide definitive evidence for the essential role of Mettl14 in differentiation of IESCs in DM state.

METTL14-upregulated miR-6858 triggers cell apoptosis in keratinocytes of oral lichen planus through decreasing GSDMC

Oral lichen planus (OLP), a chronic inflammatory disorder, is characterized by the massive cell apoptosis in the keratinocytes of oral mucosa. However, the mechanism responsible for triggering oral keratinocyte apoptosis is not fully explained. Here, we identify that Gasdermin C (GSDMC) downregulation contributes to apoptosis in human oral keratinocytes. Mechanistically, we describe that activated nuclear factor kappa B (NF-κB) pathway induces overexpression of methyltransferase-like 14 (METTL14), which increases N6-adenosine methylation (m6A) levels in the epithelial layer of OLP. m6A modification is capable of regulating primary miR-6858 processing and alternative splicing, leading to miR-6858 increases. miR-6858 can bind and promote GSDMC mRNA degradation. Forced expression of GSDMC is able to rescue cell apoptosis in human oral keratinocyte models resembling OLP. Collectively, our data unveil that m6A modification regulates miR-6858 production to decrease GSDMC expression and to trigger keratinocyte apoptosis in the context of OLP.

Modulation of stem cell fate in intestinal homeostasis, injury and repair

The mammalian intestinal epithelium constitutes the largest barrier against the external environment and makes flexible responses to various types of stimuli. Epithelial cells are fast-renewed to counteract constant damage and disrupted barrier function to maintain their integrity. The homeostatic repair and regeneration of the intestinal epithelium are governed by the Lgr5⁺ intestinal stem cells (ISCs) located at the base of crypts, which fuel rapid renewal and give rise to the different epithelial cell types. Protracted biological and physicochemical stress may challenge epithelial integrity and the function of ISCs. The field of ISCs is thus of interest for complete mucosal healing, given its relevance to diseases of intestinal injury and inflammation such as inflammatory bowel diseases. Here, we review the current understanding of the signals and mechanisms that control homeostasis and regeneration of the intestinal epithelium. We focus on recent insights into the intrinsic and extrinsic elements involved in the process of intestinal homeostasis, injury, and repair, which fine-tune the balance between self-renewal and cell fate specification in ISCs. Deciphering the regulatory machinery that modulates stem cell fate would aid in the development of novel therapeutics that facilitate mucosal healing and restore epithelial barrier function.

Intestinal transit amplifying cells require METTL3 for growth factor signaling, KRAS expression, and cell survival

Intestinal epithelial transit amplifying cells are essential stem progenitors required for intestinal homeostasis, but their rapid proliferation renders them vulnerable to DNA damage from radiation and chemotherapy. Despite their critical roles in intestinal homeostasis and disease, few studies have described genes that are essential to transit amplifying cell function. We report that the RNA methyltransferase, METTL3, is required for survival of transit amplifying cells in the murine small intestine. Transit amplifying cell death after METTL3 deletion was associated with crypt and villus atrophy, loss of absorptive enterocytes, and uniform wasting and death in METTL3-depleted mice. Ribosome profiling and sequencing of methylated RNAs in enteroids and in vivo demonstrated decreased translation of hundreds of unique methylated transcripts after METTL3 deletion, particularly transcripts involved in growth factor signal transduction such as Kras. Further investigation confirmed a novel relationship between METTL3 and Kras methylation and protein levels in vivo. Our study identifies METTL3 as an essential factor supporting the homeostasis of small intestinal tissue via direct maintenance of transit amplifying cell survival. We highlight the crucial role of RNA modifications in regulating growth factor signaling in the intestine, with important implications for both homeostatic tissue renewal and epithelial regeneration.