A new mutation Rim3 resembling Re(den) is mapped close to retinoic acid receptor alpha (Rara) gene on mouse chromosome 11

Cell death as an architect of adult skin stem cell niches

Our skin provides a physical and immunological barrier against dehydration and environmental insults ranging from microbial attacks, toxins and UV irradiation to wounding. Proper functioning of the skin barrier largely depends on the interplay between keratinocytes- the epithelial cells of the skin- and immune cells. Two spatially distinct populations of keratinocyte stem cells (SCs) maintain the epidermal barrier function and the hair follicle. These SCs are inherently long-lived, but cell death can occur within their niches and impacts their functionality. The default cell death programme in skin is apoptosis, an orderly and non-inflammatory suicide programme. However, recent findings are shedding light on the significance of various modes of regulated necrotic cell death, which are lytic and can provoke inflammation within the local skin environment. While the presence of dying cells was generally regarded as a mere consequence of inflammation, findings in various human dermatological conditions and experimental mouse models of aberrant cell death control demonstrated that cell death programmes in keratinocytes (KCs) can drive skin inflammation and even tumour initiation. When cells die, they need to be removed by phagocytosis and KCs can function as non-professional phagocytes of apoptotic cells with important implications for their SC capacities. It is becoming apparent that in conditions of heightened SC activity, distinct cell death modalities differentially impact the different skin SC populations in their local niches. Here, we describe how regulated cell death modalities functionally affect epidermal SC niches along with their relevance to injury repair, inflammatory skin disorders and cancer.

The gasdermin family: emerging therapeutic targets in diseases

The gasdermin (GSDM) family has garnered significant attention for its pivotal role in immunity and disease as a key player in pyroptosis. This recently characterized class of pore-forming effector proteins is pivotal in orchestrating processes such as membrane permeabilization, pyroptosis, and the follow-up inflammatory response, which are crucial self-defense mechanisms against irritants and infections. GSDMs have been implicated in a range of diseases including, but not limited to, sepsis, viral infections, and cancer, either through involvement in pyroptosis or independently of this process. The regulation of GSDM-mediated pyroptosis is gaining recognition as a promising therapeutic strategy for the treatment of various diseases. Current strategies for inhibiting GSDMD primarily involve binding to GSDMD, blocking GSDMD cleavage or inhibiting GSDMD-N-terminal (NT) oligomerization, albeit with some off-target effects. In this review, we delve into the cutting-edge understanding of the interplay between GSDMs and pyroptosis, elucidate the activation mechanisms of GSDMs, explore their associations with a range of diseases, and discuss recent advancements and potential strategies for developing GSDMD inhibitors.

Harnessing Pyroptosis for Cancer Immunotherapy

Cancer immunotherapy is a novel pillar of cancer treatment that harnesses the immune system to fight tumors and generally results in robust antitumor immunity. Although immunotherapy has achieved remarkable clinical success for some patients, many patients do not respond, underscoring the need to develop new strategies to promote antitumor immunity. Pyroptosis is an immunostimulatory type of regulated cell death that activates the innate immune system. A hallmark of pyroptosis is the release of intracellular contents such as cytokines, alarmins, and chemokines that can stimulate adaptive immune activation. Recent studies suggest that pyroptosis promotes antitumor immunity. Here, we review the mechanisms by which pyroptosis can be induced and highlight new strategies to induce pyroptosis in cancer cells for antitumor defense. We discuss how pyroptosis modulates the tumor microenvironment to stimulate adaptive immunity and promote antitumor immunity. We also suggest research areas to focus on for continued development of pyroptosis as an anticancer treatment. Pyroptosis-based anticancer therapies offer a promising new avenue for treating immunologically 'cold' tumors.

Gasdermins and cancers

The identification of gasdermin as the executor of pyroptosis has opened new avenues for the study of this process. Although pyroptosis research has mainly focused on immune cells since it was discovered three decades ago, accumulating evidence suggests that pyroptosis plays crucial roles in many biological processes. One example is the discovery of gasdermin-mediated cancer cell pyroptosis (CCP) which has become an important and frontier field in oncology. Recent studies have shown that CCP induction can heat tumor microenvironment (TME) and thereby elicit the robust anti-tumor immunity to suppress tumor growth. As a newly discovered form of tumor cell death, CCP offers promising opportunities for improving tumor treatment and developing new drugs. Nevertheless, the research on CCP is still in its infancy, and the molecular mechanisms underlying the expression, regulation and activation of gasdermins are not yet fully understood. In this review, we summarize the recent progress of gasdermin research in cancer area, and propose that the anti-tumor effect of immune cell pyroptosis (ICP) and CCP depends on their duration, intensity, and the type of cells undergoing pyroptosis within TME.

The gasdermins: a pore-forming protein family expressed in the epidermis

Gasdermins comprise a family of pore-forming proteins, which play critical roles in (auto)inflammatory diseases and cancer. They are expressed as self-inhibited precursor proteins consisting of an aminoterminal cytotoxic effector domain (NT-GSDM) and a carboxyterminal inhibitor domain (GSDM-CT) separated by an unstructured linker region. Proteolytic processing in the linker region liberates NT-GSDM, which translocates to membranes, forms oligomers, and induces membrane permeabilization, which can disturb the cellular equilibrium that can lead to cell death. Gasdermin activation and pore formation are associated with inflammation, particularly when induced by the inflammatory protease caspase-1 upon inflammasome activation. These gasdermin pores allow the release of the pro-inflammatory cytokines interleukin(IL)-1β and IL-18 and induce a lytic type of cell death, termed pyroptosis that supports inflammation, immunity, and tissue repair. However, even at the cellular level, the consequences of gasdermin activation are diverse and range from induction of programmed cell death - pyroptosis or apoptosis - to poorly characterized protective mechanisms. The specific effects of gasdermin activation can vary between species, cell types, the membrane that is being permeabilized (plasma membrane, mitochondrial membrane, etc.), and the overall biological state of the local tissue/cells. In epithelia, gasdermins seem to play crucial roles. Keratinocytes represent the main cell type of the epidermis, which is the outermost skin layer with an essential barrier function. Compared to other tissues, keratinocytes express all members of the gasdermin family, in part in a differentiation-specific manner. That raises questions regarding the specific roles of individual GSDM family members in the skin, the mechanisms and consequences of their activation, and the potential crosstalk between them. In this review, we summarize the current knowledge about gasdermins with a focus on keratinocytes and the skin and discuss the possible roles of the different family members in immunity and disease.

Regulation of gasdermins in pyroptosis and cytokine release

Gasdermins are effectors of pyroptosis downstream of diverse signaling pathways. Emerging evidence suggests that a number of post-translational modifications regulate the function of gasdermins in pyroptosis, a highly inflammatory form of cell death, and lytic or non-lytic secretion of intracellular contents. These include processing by different caspases and other proteases that may activate or suppress pyroptosis, ubiquitination by a bacterial E3 ligase that suppresses pyroptosis as an immune evasion mechanism, modifications at Cys residues in mammalian or microbial gasdermins that promote or inhibit pyroptosis, and potential phosphorylation that represses pyroptosis. Such diverse regulatory mechanisms by host and microbial proteases, ubiquitin ligases, acyltransferases, kinases and phosphatases may underlie the divergent physiological and pathological functions of gasdermins, and furnish opportunities for therapeutic targeting of gasdermins in infectious diseases and inflammatory disorders.

Role of gasdermin family proteins in the occurrence and progression of hepatocellular carcinoma

Primary liver cancer is the sixth most common cancer and the third leading cause of cancer mortality worldwide, hepatocellular carcinoma (HCC) is the most common type of liver cancer, accounting for 75%–85% of cases. The occurrence and progression of HCC involve multiple events. Pyroptosis is a gasdermins mediated programmed cell death and is intricately associated with cancerogenesis, including HCC. This review mainly concerns the recent research advances of the gasdermin family members in HCC. The biological roles and specific expression patterns of the family members are discussed, especially those that are involved in the regulatory pathways in the occurrence and progression of HCC. We provide the latest progress into the distinct molecular mechanisms of gasdermin family members involved in the occurrence and development of HCC.

A new personalized vaccine strategy based on inducing the pyroptosis of tumor cells in vivo by transgenic expression of a truncated GSDMD N-terminus

The variability and heterogeneity of tumor antigens and the tumor-driven development of immunosuppressive mechanisms leading to tumor escape from established immunological surveillance. Here, the tumor cells were genetically modified to achieve an inducible overexpression of the N-terminal domain of gasdermin D (GSDMD-NT) and effectively cause pyroptosis under a strict control. Pyroptotic tumor cells release damage-associated molecular patterns (DAMPs) and inflammatory cytokines to promote the maturation and migration of bone marrow-derived dendritic cells (BMDCs). Furthermore, local tumor delivery, and preventive or therapeutic subcutaneous immunization of the modified cells, followed by the induction of GSDMD-NT expression, significantly stimulated both the systemic and local responses of antitumor immunity, and reprogrammed the tumor microenvironment, leading to the dramatic suppression of tumor growth in mice. This study has explored the application potency of inducing the pyroptosis of tumor cells in the field of tumor immunotherapy, especially for developing a new and promising personalized tumor vaccine.

Noncoding RNAs in pyroptosis and cancer progression: Effect, mechanism, and clinical application

Cell death is generally classified into two categories: regulated cell death (RCD) and accidental cell death (ACD). In particular, RCD is a kind of genetically controlled process, including programmed apoptotic death and programmed necrotic death. Pyroptosis, an inflammatory form of programmed necrotic death, causes inflammation in cells. The influence of pyroptosis on tumor is complicated. On the one hand, pyroptosis triggers antitumor response. On the other hand, pyroptosis may induce carcinogenesis. Pyroptosis is initiated by various factors, especially non-coding RNAs. In this review, we discuss the effects of ncRNAs on pyroptosis and the mechanisms by which ncRNAs initiate pyroptosis. Moreover, we introduce the influence of ncRNA on tumor resistance via pyroptosis. Additionally, we summarize how ncRNA-associated pyroptosis modulates the tumor microenvironment (TME) and thereafter triggers antitumor immune response. Finally, pyroptosis-related ncRNAs are promising diagnostic and immunotherapeutic biomarkers and therapeutic targets

Modulation of Autoimmune and Autoinflammatory Diseases by Gasdermins

Autoimmune diseases and autoinflammatory diseases are two types of the immune system disorders. Pyroptosis, a highly inflammatory cell death, plays an important role in diseases of immune system. The gasdermins belong to a pore-forming protein gene family which are mainly expressed in immune cells, gastrointestinal tract, and skin. Gasdermins are regarded as an executor of pyroptosis and have been shown to possess various cellular functions and pathological effects such as pro-inflammatory, immune activation, mediation of tumor, etc. Except for infectious diseases, the vital role of gasdermins in autoimmune diseases, autoinflammatory diseases, and immune-related neoplastic diseases has been proved recently. Therefore, gasdermins have been served as a potential therapeutic target for immune disordered diseases. The review summarizes the basic molecular structure and biological function of gasdermins, mainly discusses their role in autoimmune and autoinflammatory diseases, and highlights the recent research on gasdermin family inhibitors so as to provide potential therapeutic prospects.

Gasdermins in Innate Host Defense Against Entamoeba histolytica and Other Protozoan Parasites

Gasdermins (GSDMs) are a group of proteins that are cleaved by inflammatory caspases to induce pore formation in the plasma membrane to cause membrane permeabilization and lytic cell death or pyroptosis. All GSDMs share a conserved structure, containing a cytotoxic N-terminal (NT) pore-forming domain and a C-terminal (CT) repressor domain. Entamoeba histolytica (Eh) in contact with macrophages, triggers outside-in signaling to activate inflammatory caspase-4/1 via the noncanonical and canonical pathway to promote cleavage of gasdermin D (GSDMD). Cleavage of GSDMD removes the auto-inhibition that masks the active pore-forming NT domain in the full-length protein by interactions with GSDM-CT. The cleaved NT-GSDMD monomers then oligomerize to form pores in the plasma membrane to facilitate the release of IL-1β and IL-18 with a measured amount of pyroptosis. Pyroptosis is an effective way to counteract intracellular parasites, which exploit replicative niche to avoid killing. To date, most GSDMs have been verified to perform pore-forming activity and GSDMD-induced pyroptosis is rapidly emerging as a mechanism of anti-microbial host defence. Here, we review our comprehensive and current knowledge on the expression, activation, biological functions, and regulation of GSDMD cleavage with emphases on physiological scenario and related dysfunctions of each GSDM member as executioner of cell death, cytokine secretion and inflammation against Eh and other protozoan parasitic infections.

Pyroptosis: Role and Mechanisms in Cardiovascular Disease

Cardiovascular disease (CVD) is a common disease that poses a huge threat to human health. Irreversible cardiac damage due to cardiomyocyte death and lack of regenerative capacity under stressful conditions, ultimately leading to impaired cardiac function, is the leading cause of death worldwide. The regulation of cardiomyocyte death plays a crucial role in CVD. Previous studies have shown that the modes of cardiomyocyte death include apoptosis and necrosis. However, another new form of death, pyroptosis, plays an important role in CVD pathogenesis. Pyroptosis induces the amplification of inflammatory response, increases myocardial infarct size, and accelerates the occurrence of cardiovascular disease, and the control of cardiomyocyte pyroptosis holds great promise for the treatment of cardiovascular disease. In this paper, we summarized the characteristics, occurrence and regulation mechanism of pyroptosis are reviewed, and also discussed its role and mechanisms in CVD, such as atherosclerosis (AS), myocardial infarction (MI), arrhythmia and cardiac hypertrophy.

Inflammasome and gasdermin signalling in neutrophils

Inflammasomes and gasdermins mount potent host defence pathways against invading microbial pathogens, however, dysregulation in these pathways can drive a variety of inflammatory disorders. Neutrophils, historically regarded as effector phagocytes that drive host defence via microbial killing, are now emerging as critical drivers of immunity in vivo. Here, we summarise the latest advancement in inflammasome, gasdermin and cell death signalling in neutrophils. We discuss the mechanisms by which neutrophils resist caspase-1-dependent pyroptosis, thsse lytic function of gasdermin D and E during NETosis and Yersinia infection, and the contribution of neutrophil inflammasomes to inflammatory disorders.

Gasdermin Pore Forming Activities that Promote Inflammation from Living and Dead Cells

Gasdermins are proteins that can self-assemble into membrane channels (also known as pores). These pores can serve as conduits for the secretion of cytosolic molecules, with the most commonly studied being members of the interleukin-1 family of cytokines. However, gasdermin pore forming activities must be tightly regulated, as the channels that they form can lead to a lytic form of cell death known as pyroptosis. Recent studies have revealed multiple mechanisms that control gasdermin activities within cells and identified gasdermin proteins in organisms as diverse as bacteria, humans and yeast. In this Review, we discuss the molecular and cellular mechanisms that regulate gasdermin pore formation. These mechanisms of gasdermin regulation likely explain the flexibility of these proteins to display cell type specific (and potentially organism specific) functions.

Gasdermin D pores are dynamically regulated by local phosphoinositide circuitry

Gasdermin D forms large, ~21 nm diameter pores in the plasma membrane to drive the cell death program pyroptosis. These pores are thought to be permanently open, and the resultant osmotic imbalance is thought to be highly damaging. Yet some cells mitigate and survive pore formation, suggesting an undiscovered layer of regulation over the function of these pores. However, no methods exist to directly reveal these mechanistic details. Here, we combine optogenetic tools, live cell fluorescence biosensing, and electrophysiology to demonstrate that gasdermin pores display phosphoinositide-dependent dynamics. We quantify repeated and fast opening-closing of these pores on the tens of seconds timescale, visualize the dynamic pore geometry, and identify the signaling that controls dynamic pore activity. The identification of this circuit allows pharmacological tuning of pyroptosis and control of inflammatory cytokine release by living cells.

High Expression of GSDMC Is Associated with Poor Survival in Kidney Clear Cell Cancer

This study is aimed at exploring the potential role of GSDMC in kidney renal clear cell carcinoma (KIRC). We analyzed the expression of GSDMC in 33 types of cancers in TCGA database. The results showed that the expression of GSDMC was upregulated in most cancers. We found a significant association between high expression of GSDMC and shortened patient overall survival, progression-free survival, and disease-specific survival. In vitro experiments have shown that the expression of GSDMC was significantly elevated in KIRC cell lines. Moreover, decreased expression of GSDMC was significantly associated with decreased cell proliferation. In summary, we believe that this study provides valuable data supporting future clinical treatment.

Molecular mechanisms and therapeutic relevance of gasdermin E in human diseases

Gasdermin E (GSDME) is one of the main members of the GSDM family and is originally involved in hereditary hearing loss. Recent studies have reported that GSDME expression is epigenetically silenced by methylation in several common tumours, thereby enhancing tumour proliferation and metastasis. GSDME is also downregulated in cancer tissues compared with normal tissues, which suggests that GSDME can be considered a tumour suppressor. Furthermore, GSDME is the effector protein of caspase-3 and granzyme B in pyroptosis, and it plays a significant role in innate immunity, tissue damage, cancer, and hearing loss, thus revealing potential novel therapeutic avenues. A great deal of evidence reveals that GSDME can be implemented as a biomarker in cancer diagnosis and monitoring, chemotherapy, immunotherapy, and chemoresistance. Based on the current knowledge of GSDME, this review is focussed on its mechanism of action and the most recent advances in its role in cancer and normal physiology.

Zebrafish gasdermin E cleavage-engaged pyroptosis by inflammatory and apoptotic caspases

As the executor of pyroptosis known to date, gasdermins (GSDMs), consists of GSDMA, GSDMB, GSDMC, GSDMD, GSDME and pejvakin, might play critical roles in anti-bacterial infection as well as inflammatory diseases. However, zebrafish only harbors a pair of Gsdme (Gsdmea/b), and their activation mechanisms remain largely unknown. Herein, we investigate the activation mechanism of Gsdmea/b cleaved by inflammatory and apoptotic caspases in zebrafish，and found that Gsdmea/b are equally cleaved by Caspase 19b, a sister of Caspy2, but not Caspy. Moreover, the zebrafish apoptotic effector caspases, including Caspase 3a/b and Caspase 7, also can cleave Gsdmea/b at the same sites as inflammatory caspases recognized. Importantly, our results reveal that Caspase 8a/b can cleave Gsdmeb, but only Caspase 8a can cleave Gsdmea. Taken together, these findings suggest that zebrafish Gsdmea/b can concurrently function as GSDMD and GSDME in mammals, which will contribute to better understanding the mechanism of pyroptosis activation in teleost, as well as provide a clue for drug screening model against inflammatory diseases.

Regulation of Lytic and Non-Lytic Functions of Gasdermin Pores

Pyroptosis is a necrotic form of cell death that was initially found to be induced upon activation of inflammatory caspases by inflammasome complexes. Mechanistically, pyroptosis induction requires cleavage of the caspase substrate gasdermin D (GSDMD), and the release of the GSDMD N-terminal fragment, which targets the plasma membrane to form large β-barrel pores. GSDMD shares this pore-forming ability with other gasdermin family members, which induce pyroptosis during infection or upon treatment with chemotherapy drugs. While induction of cell death has been assumed to be the main function of the gasdermin pores, increasing evidence suggests that these pores have non-lytic functions, such as in releasing cytokines or alarmins and in regulating intracellular signaling via ionic fluxes. Here we discuss how gasdermin pore formation is regulated to induce membrane permeabilization or lysis, how gasdermin pores achieve specificity for cargo-release and how cells repair gasdermin-induced damage to the plasma membrane.

Comprehensive transcriptome and methylome analysis delineates the biological basis of hair follicle development and wool-related traits in Merino sheep

Background

Characterization of the molecular mechanisms underlying hair follicle development is of paramount importance in the genetic improvement of wool-related traits in sheep and skin-related traits in humans. The Merino is the most important breed of fine-wooled sheep in the world. In this study, we systematically investigated the complexity of sheep hair follicle development by integrating transcriptome and methylome datasets from Merino sheep skin.

Results

We analysed 72 sequence datasets, including DNA methylome and the whole transcriptome of four gene types, i.e. protein-coding genes (PCGs), lncRNAs, circRNAs, and miRNAs, across four embryonic days (E65, E85, E105, and E135) and two postnatal days (P7 and P30) from the skin tissue of 18 Merino sheep. We revealed distinct expression profiles of these four gene types across six hair follicle developmental stages, and demonstrated their complex interactions with DNA methylation. PCGs with stage-specific expression or regulated by stage-specific lncRNAs, circRNAs, and miRNAs were significantly enriched in epithelial differentiation and hair follicle morphogenesis. Regulatory network and gene co-expression analyses identified key transcripts controlling hair follicle development. We further predicted transcriptional factors (e.g. KLF4, LEF1, HOXC13, RBPJ, VDR, RARA, and STAT3) with stage-specific involvement in hair follicle morphogenesis. Through integrating these stage-specific genomic features with results from genome-wide association studies (GWAS) of five wool-related traits in 7135 Merino sheep, we detected developmental stages and genes that were relevant with wool-related traits in sheep. For instance, genes that were specifically upregulated at E105 were significantly associated with most of wool-related traits. A phenome-wide association study (PheWAS) demonstrated that candidate genes of wool-related traits (e.g. SPHK1, GHR, PPP1R27, CSRP2, EEF1A2, and PTPN1) in sheep were also significantly associated with dermatological, metabolic, and immune traits in humans.

Conclusions

Our study provides novel insights into the molecular basis of hair follicle morphogenesis and will serve as a foundation to improve breeding for wool traits in sheep. It also indicates the importance of studying gene expression in the normal development of organs in understanding the genetic architecture of economically important traits in livestock. The datasets generated here are useful resources for functionally annotating the sheep genome, and for elucidating early skin development in mammals, including humans.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12915-021-01127-9.

Channelling inflammation: gasdermins in physiology and disease

Gasdermins were recently identified as the mediators of pyroptosis — inflammatory cell death triggered by cytosolic sensing of invasive infection and danger signals. Upon activation, gasdermins form cell membrane pores, which release pro-inflammatory cytokines and alarmins and damage the integrity of the cell membrane. Roles for gasdermins in autoimmune and inflammatory diseases, infectious diseases, deafness and cancer are emerging, revealing potential novel therapeutic avenues. Here, we review current knowledge of the family of gasdermins, focusing on their mechanisms of action and roles in normal physiology and disease. Efforts to develop drugs to modulate gasdermin activity to reduce inflammation or activate more potent immune responses are highlighted.

Gasdermins (GSDMs) are a recently characterized protein family that mediate a programmed inflammatory cell death termed pyroptosis. Here, Lieberman and colleagues review current understanding of the expression, activation and regulation of GSDMs, highlighting their roles in cell death, cytokine secretion and inflammation. Emerging opportunities to develop GSDM-targeted drugs and the associated challenges are highlighted.

Gasdermins: pore-forming activities and beyond

Gasdermins (GSDMs) belong to a protein superfamily that is found only in vertebrates and consists of GSDMA, GSDMB, GSDMC, GSDMD, DFNA5 (a.k.a. GSDME) and DFNB59 (a.k.a. Pejvakin (PJVK)) in humans. Except for DFNB59, all members of the GSDM superfamily contain a conserved two-domain structure (N-terminal and C-terminal domains) and share an autoinhibitory mechanism. When the N-terminal domain of these GSDMs is released, it possesses pore-forming activity that causes inflammatory death associated with the loss of cell membrane integrity and release of inflammatory mediators. It has also been found that spontaneous mutations occurring in the genes of GSDMs have been associated with the development of certain autoimmune disorders, as well as cancers. Here, we review the current knowledge of the expression profile and regulation of GSDMs and the important roles of this protein family in inflammatory cell death, tumorigenesis and other related diseases.

Gasdermin family: a promising therapeutic target for cancers and inflammation-driven diseases

This review focuses on current advances in researches of gasdermin family. The distinctive expression patterns and biological roles of members in this family were discussed. Most of them exhibit pore-forming activity on cell membranes and are executors for programmed cell death with cytokines release, and play roles in cancers and inflammation-driven diseases. Therefore, they can be used as potential therapeutic targets to treat related diseases.

The gasdermins, a protein family executing cell death and inflammation

The gasdermins are a family of recently identified pore-forming effector proteins that cause membrane permeabilization and pyroptosis, a lytic pro-inflammatory type of cell death. Gasdermins contain a cytotoxic N-terminal domain and a C-terminal repressor domain connected by a flexible linker. Proteolytic cleavage between these two domains releases the intramolecular inhibition on the cytotoxic domain, allowing it to insert into cell membranes and form large oligomeric pores, which disrupts ion homeostasis and induces cell death. Gasdermin-induced pyroptosis plays a prominent role in many hereditary diseases and (auto)inflammatory disorders as well as in cancer. In this Review, we discuss recent developments in gasdermin research with a focus on mechanisms that control gasdermin activation, pore formation and functional consequences of gasdermin-induced membrane permeabilization.

Pyroptosis: Gasdermin-Mediated Programmed Necrotic Cell Death

Pyroptosis was long regarded as caspase-1-mediated monocyte death in response to certain bacterial insults. Caspase-1 is activated upon various infectious and immunological challenges through different inflammasomes. The discovery of caspase-11/4/5 function in sensing intracellular lipopolysaccharide expands the spectrum of pyroptosis mediators and also reveals that pyroptosis is not cell type specific. Recent studies identified the pyroptosis executioner, gasdermin D (GSDMD), a substrate of both caspase-1 and caspase-11/4/5. GSDMD represents a large gasdermin family bearing a novel membrane pore-forming activity. Thus, pyroptosis is redefined as gasdermin-mediated programmed necrosis. Gasdermins are associated with various genetic diseases, but their cellular function and mechanism of activation (except for GSDMD) are unknown. The gasdermin family suggests a new area of research on pyroptosis function in immunity, disease, and beyond.

Genetically modified laboratory mice with sebaceous glands abnormalities

Sebaceous glands (SG) are exocrine glands that release their product by holocrine secretion, meaning that the whole cell becomes a secretion following disruption of the membrane. SG may be found in association with a hair follicle, forming the pilosebaceous unit, or as modified SG at different body sites such as the eyelids (Meibomian glands) or the preputial glands. Depending on their location, SG fulfill a number of functions, including protection of the skin and fur, thermoregulation, formation of the tear lipid film, and pheromone-based communication. Accordingly, SG abnormalities are associated with several diseases such as acne, cicatricial alopecia, and dry eye disease. An increasing number of genetically modified laboratory mouse lines develop SG abnormalities, and their study may provide important clues regarding the molecular pathways regulating SG development, physiology, and pathology. Here, we summarize in tabulated form the available mouse lines with SG abnormalities and, focusing on selected examples, discuss the insights they provide into SG biology and pathology. We hope this survey will become a helpful information source for researchers with a primary interest in SG but also as for researchers from unrelated fields that are unexpectedly confronted with a SG phenotype in newly generated mouse lines.

Pore-forming activity and structural autoinhibition of the gasdermin family

Inflammatory caspases cleave the gasdermin D (GSDMD) protein to trigger pyroptosis, a lytic form of cell death that is crucial for immune defences and diseases. GSDMD contains a functionally important gasdermin-N domain that is shared in the gasdermin family. The functional mechanism of action of gasdermin proteins is unknown. Here we show that the gasdermin-N domains of the gasdermin proteins GSDMD, GSDMA3 and GSDMA can bind membrane lipids, phosphoinositides and cardiolipin, and exhibit membrane-disrupting cytotoxicity in mammalian cells and artificially transformed bacteria. Gasdermin-N moved to the plasma membrane during pyroptosis. Purified gasdermin-N efficiently lysed phosphoinositide/cardiolipin-containing liposomes and formed pores on membranes made of artificial or natural phospholipid mixtures. Most gasdermin pores had an inner diameter of 10–14 nm and contained 16 symmetric protomers. The crystal structure of GSDMA3 showed an autoinhibited two-domain architecture that is conserved in the gasdermin family. Structure-guided mutagenesis demonstrated that the liposome-leakage and pore-forming activities of the gasdermin-N domain are required for pyroptosis. These findings reveal the mechanism for pyroptosis and provide insights into the roles of the gasdermin family in necrosis, immunity and diseases.

GSDM family genes meet autophagy

In the previous issue of Biochemical Journal, Shi et al. [(2015) 468, 325-336] report that Gasdermin (Gsdm) family proteins regulate autophagy activity, which is counter-balanced by the opposite functions of well-conserved N- and C-terminal domains of the proteins. The Gsdm family was originally identified as the causative gene of dominant skin mutations exhibiting alopecia. Each member of the Gsdm gene family shows characteristic expression patterns in the epithelium, which is tissue and differentiation stage-specific. Previous phenotype analyses of mutant mice, biochemical analyses of proteins and genome-wide association studies showed that the Gsdm gene family might be involved in epithelial cell development, apoptosis, inflammation, carcinogenesis and immune-related diseases. To date, however, their molecular function(s) remain unclear. Shi et al. found that mutations in the C-terminal domain of Gsdma3, a member of the Gsdm family, induce autophagy. Further studies revealed that the wild-type N-terminal domain has pro-autophagic activity and that the C-terminal domain conversely inhibits this N-terminal function. These opposite functions of the two domains were also observed in other Gsdm family members. Thus, their study provides a new insight into the function of Gsdm genes in epithelial cell lineage, causality of cancers and immune-related diseases including childhood-onset asthma.

Loss of conserved Gsdma3 self-regulation causes autophagy and cell death

Gasdermin A3 (Gsdma3) was originally identified in association with hair-loss phenotype in mouse mutants. Our previous study found that AE mutant mice, with a Y344H substitution at the C-terminal domain of Gsdma3, display inflammation-dependent alopecia and excoriation [Zhou et al. (2012) Am. J. Pathol. 180, 763-774]. Interestingly, we found that the newly-generated null mutant of Gsdma3 mice did not display the skin dysmorphology, indicating that Gsdma3 is not essential for differentiation of epidermal cells and maintenance of the hair cycle in normal physiological conditions. Consistently, human embryonic kidney (HEK)293 and HaCaT cells transfected with wild-type (WT) Gsdma3 did not show abnormal morphology. However, Gsdma3 Y344H mutation induced autophagy. Gsdma3 N-terminal domain, but not the C-terminal domain, also displayed the similar pro-autophagic activity. The Gsdma3 Y344H mutant protein and N-terminal domain-induced autophagy was associated with mitochondria and ROS generation. Co-expression of C-terminal domain reversed the cell autophagy induced by N-terminal domain. Moreover, C-terminal domain could be co-precipitated with N-terminal domain. These data indicated that the potential pro-autophagic activity of WT Gsdma3 protein is suppressed through an intramolecular inhibition mechanism. Studies on other members of the GSDM family suggested this mechanism is conserved in several sub-families.

Gasdermin-B promotes invasion and metastasis in breast cancer cells

Gasdermin B (GSDMB) belongs to the Gasdermin protein family that comprises four members (GSDMA-D). Gasdermin B expression has been detected in some tumor types such as hepatocarcinomas, gastric and cervix cancers; and its over-expression has been related to tumor progression. At least four splicing isoforms of GSDMB have been identified, which may play differential roles in cancer. However, the implication of GSDMB in carcinogenesis and tumor progression is not well understood. Here, we uncover for the first time the functional implication of GSDMB in breast cancer. Our data shows that high levels of GSDMB expression is correlated with reduced survival and increased metastasis in breast cancer patients included in an expression dataset (>1,000 cases). We demonstrate that GSDMB is upregulated in breast carcinomas compared to normal breast tissue, being the isoform 2 (GSDMB-2) the most differentially expressed. In order to evaluate the functional role of GSDMB in breast cancer two GSDMB isoforms were studied (GSDMB-1 and GSDMB-2). The overexpression of both isoforms in the MCF7 breast carcinoma cell line promotes cell motility and invasion, while its silencing in HCC1954 breast carcinoma cells decreases the migratory and invasive phenotype. Importantly, we demonstrate that both isoforms have a differential role on the activation of Rac-1 and Cdc-42 Rho-GTPases. Moreover, our data support that GSMDB-2 induces a pro-tumorigenic and pro-metastatic behavior in mouse xenograft models as compared to GSDMB-1. Finally, we observed that although both GSDMB isoforms interact in vitro with the chaperone Hsp90, only the GSDMB-2 isoform relies on this chaperone for its stability. Taken together, our results provide for the first time evidences that GSDMB-2 induces invasion, tumor progression and metastasis in MCF7 cells and that GSDMB can be considered as a new potential prognostic marker in breast cancer.

Gsdma3 mutation causes bulge stem cell depletion and alopecia mediated by skin inflammation

Primary cicatricial alopecias (PCAs) are a group of permanent hair loss disorders, of which the pathogenesis is still poorly understood. The alopecia and excoriation (AE) mouse strain is a dominant mutant generated from ethyl nitrosourea mutagenesis. AE mice exhibit a progressive alopecia phenotype similar to that seen in PCAs, resulting from a point mutation in the gasdermin A3 gene. Mutant mice begin to show alopecia on the head from postnatal day 22 and experience complete hair loss by the age of 6 months, along with hyperkeratosis and catagen delay. The results of a histological examination showed that bulge stem cells in AE skin are gradually depleted, as indicated by decreased keratin 15 and CD34 expression, and reduced bromodeoxyuridine label-retaining cells in the AE bulge. In addition, AE mice display an inflammatory condition in the skin from postnatal day 7, including elevated tumor necrosis factor-α and monocyte chemotactic protein-1 mRNA levels and significantly increased macrophages and dendritic cell number. Immune privilege in the bulge was also compromised in AE skin. Consistently, after treatment with the immunosuppressive agent, cyclosporine A, immune privilege collapse, stem cell destruction, and alopecia phenotype of AE mice were all rescued. Collectively, our data demonstrate that immune-mediated destruction of bulge stem cells plays a crucial role in the pathogenesis of alopecia in AE mice, and this strain might be an interesting model for PCAs, especially for lichen planopilaris.

Alu-derived cis-element regulates tumorigenesis-dependent gastric expression of GASDERMIN B (GSDMB)

GASDERMIN B (GSDMB) belongs to the novel gene family GASDERMIN (GSDM). All GSDM family members are located in amplicons, genomic regions often amplified during cancer development. Given that GSDMB is highly expressed in cancerous cells and the locus resides in an amplicon, GSDMB may be involved in cancer development and/or progression. However, only limited information is available on GSDMB expression in tissues, normal and cancerous, from cancer patients. Furthermore, the molecular mechanisms that regulate GSDMB expression in gastric tissues are poorly understood. We investigated the spatiotemporal expression patterns of GSDMB in gastric cancer patients and the 5' regulatory sequences upstream of GSDMB. GSDMB was not expressed in the majority of normal gastric-tissue samples, and the expression level was very low in the few normal samples with GSDMB expression. Most pre-cancer samples showed moderate GSDMB expression, and most cancerous samples showed augmented GSDMB expression. Analysis of genome sequences revealed that an Alu element resides in the 5' region upstream of GSDMB. Reporter assays using intact, deleted, and mutated Alu elements clearly showed that this Alu element positively regulates GSDMB expression and that a putative IKZF binding motif in this element is crucial to upregulate GSDMB expression.

Distinctive expression and function of four GSDM family genes (GSDMA-D) in normal and malignant upper gastrointestinal epithelium

Gasdermin (GSDM or GSDMA), expressed in the upper gastrointestinal tract but frequently silenced in gastric cancers (GCs), regulates apoptosis of the gastric epithelium. It has three human homologs, GSDMB, GSDMC, and GSDMD (GSDM family) and they are considered to be involved in the regulation of epithelial apoptosis but not yet known. We investigated the expression pattern of the family genes in the upper gastrointestinal epithelium and cancers. Reverse transcriptase-polymerase chain reaction revealed that, unlike GSDMA expressed in differentiated cells, GSDMB is expressed in proliferating cells and GSDMD in differentiating cells. GSDMC, meanwhile, is expressed in both differentiating and differentiated cells. Colony formation assay showed that GSDMB, closely related to GSDMA, has no cell-growth inhibition activity in gastric cancer cells, and that GSDMC and GSDMD, respectively, exhibit the activity with different strengths from that of GSDMA. Expression analyses of the four family genes in esophageal and GCs suggested that GSDMC and GSDMD as well as GSDMA are tumor suppressors and that GSDMB, which was amplified and overexpressed in some GCs, could be an oncogene. The results of the expression analysis and colony formation assay suggest that each family gene may have a distinct function in the upper gastrointestinal epithelium.

Gasdermin D (Gsdmd) is dispensable for mouse intestinal epithelium development

Members of the novel gene family Gasdermin (Gsdm) are exclusively expressed in a highly tissue-specific manner in the epithelium of skin and the gastrointestinal tract. Based on their expression patterns and the phenotype of the Gsdma3 spontaneous mutations, it is inferred that the Gsdm family genes are involved in epithelial cell growth and/or differentiations in different tissues. To investigate possible roles of the Gsdm gene family in the development of intestinal tracts, we generated a Gsdmd mutant mouse, which is a solitary member of the Gsdmd subfamily and which is predominantly expressed in the intestinal tract by means of targeted disruption. In the mutant homozygotes, we found no abnormality of intestinal tract morphology. Moreover, in mutant mice, there was normal differentiation of all constituent cell types of the intestinal epithelium. Thus, this study clearly shows that Gsdmd is not essential for development of mouse intestinal tract or epithelial cell differentiation.

A new Gsdma3 mutation affecting anagen phase of first hair cycle

Recombination-induced mutation 3 (Rim3) is a spontaneous mouse mutation that exhibits dominant phenotype of hyperkeratosis and hair loss. Fine linkage analysis of Rim3 and sequencing revealed a novel single point mutation, G1124A leading to Ala348Thr, in Gsdma3 in chromosome 11. Transgenesis with BAC DNA harboring the Rim3-type Gsdma3 recaptured the Rim3 phenotype, providing direct evidence that Gsdma3 is the causative gene of Rim3. We examined the spatial expression of Gsdma3 and characterized the Rim3 phenotype in detail. Gsdma3 is expressed in differentiated epidermal cells in the skin, but not in the proliferating epidermal cells. Histological analysis of Rim3 mutant showed hyperplasia of the epidermal cells in the upper hair follicles and abnormal anagen phase at the first hair cycle. Furthermore, immunohistochemical analysis revealed hyperproliferation and misdifferentiation of the upper follicular epidermis in Rim3 mutant. These results suggest that Gsdma3 is involved in the proliferation and differentiation of epidermal stem cells.

GASDERMIN, suppressed frequently in gastric cancer, is a target of LMO1 in TGF-β-dependent apoptotic signalling

Defining apoptosis-regulatory cascades of the epithelium is important for understanding carcinogenesis, since cancer cells are considered to arise as a result of the collapse of the cascades. We previously reported that a novel gene GASDERMIN (GSDM) is expressed in the stomach but suppressed in gastric cancer cell lines. Furthermore, in this study, we demonstrated that GSDM is expressed in the mucus-secreting pit cells of the gastric epithelium and frequently silenced in primary gastric cancers. We found that GSDM has a highly apoptotic activity and its expression is regulated by a transcription factor LIM domain only 1 (LMO1) through a sequence to which Runt-related transcription factor 3 (RUNX3) binds, in a GSDM promoter region. We observed coexpression of GSDM with LMO1, RUNX3 and type II transforming growth factor-beta receptor (TGF-betaRII) in the pit cells, and found that TGF-beta upregulates the LMO1- and GSDM-expression in the gastric epithelial cell line and induces apoptosis, which was confirmed by the finding that the apoptosis induction is inhibited by suppression of each LMO1-, RUNX3- and GSDM expression, respectively. The present data suggest that TGF-beta, LMO1, possibly RUNX3, and GSDM form a regulatory pathway for directing the pit cells to apoptosis.

Members of a novel gene family, Gsdm, are expressed exclusively in the epithelium of the skin and gastrointestinal tract in a highly tissue-specific manner

Gasdermin (Gsdm) was originally identified as a candidate causative gene for several mouse skin mutants. Several Gsdm-related genes sharing a protein domain with DFNA5, the causative gene of human nonsyndromic hearing loss, have been found in the mouse and human genomes, and this group is referred to as the DFNA5-Gasdermin domain family. However, our current comparative genomic analysis identified several novel motifs distinct from the previously reported domain in the Gsdm-related genes. We also identified three new Gsdm genes clustered on mouse chromosome 15. We named these genes collectively the Gsdm family. Extensive expression analysis revealed exclusive expression of Gsdm family genes in the epithelium of the skin and gastrointestinal tract in a highly tissue-specific manner. Further database searching revealed the presence of other related genes with a similar N-terminal motif. These results suggest that the Gsdm family and related genes have evolved divergent epithelial expression profiles.

Mutations in gasdermin 3 cause aberrant differentiation of the hair follicle and sebaceous gland

Defolliculated (Dfl) is a spontaneous mouse mutant with a hair-loss phenotype that includes altered sebaceous gland differentiation, short hair shafts, aberrant catagen stage of the hair cycle, and eventual loss of the hair follicle. Recently a similar mutant, finnegan (Fgn), with an identical phenotype was discovered during a phenotypic screen for mutations induced by chemical mutagenesis. The gene underlying the phenotype of both finnegan and defolliculated has been mapped to chromosome 11 and here we show that both mice harbor mutations in gasdermin 3 (Gsdm3), a gene of unknown function. Gsdm3(Dfl) is a B2 insertion near the 3' splice site of exon 7 and Gsdm3(Fgn) is a point mutation T278P. To investigate the role of the gasdermin gene family an antiserum was raised to a peptide highly homologous to all three mouse gasdermins and human gasdermin. Immunohistochemical analysis revealed that gasdermins are expressed specifically in cells at advanced stages of differentiation in the upper epidermis, the differentiating inner root sheath and hair shaft and in the most mature sebocytes of the sebaceous gland and preputial, meibomium, ceruminous gland, and anal glands. This expression pattern suggests a role for gasdermins in differentiation of the epidermis and its appendages.

The dominant alopecia phenotypes Bareskin, Rex-denuded, and Reduced Coat 2 are caused by mutations in gasdermin 3

Reduced Coat 2 (Rco2) is an ENU-induced mutation affecting hair follicle morphogenesis by an abnormal and protracted catagen. We describe chromosomal mapping and molecular identification of the autosomal dominant Rco2 mutation. The Rco2 critical region on mouse chromosome 11 encompasses the alopecia loci, Bareskin (Bsk), Rex-denuded (Re(den)), Recombination induced mutation 3 (Rim3), and Defolliculated (Dfl). Recently, the gasdermin (Gsdm) gene was described as predominantly expressed in skin and gastric tissues. We provide evidence for a murine-specific gene cluster consisting of Gsdm and two closely related genes which we designate as Gsdm2 and Gsdm3. We show that Gsdm3 reflects a mutation hotspot and that Gsdm3 mutations cause alopecia in Rco2, Re(den), and Bsk mice. We infer a role of Gsdm3 during the catagen to telogen transition at the end of hair follicle morphogenesis and the formation of hair follicle-associated sebaceous glands.

A Small Deletion Hotspot in the Type II Keratin Gene mK6irs1/Krt2-6g on Mouse Chromosome 15, a Candidate for Causing the Wavy Hair of the Caracul (Ca) Mutation

A new mutation has arisen in a colony of mice transgenic for human α-galactosidase. The mutation is independent of the transgenic insertion, autosomal dominant, and morphologically very similar to the classical wavy coat mutation, caracul (Ca), on chromosome 15. Therefore, we designated this locus the caracul Rinshoken (CaRin). Applying a positional cloning approach, we identified the mK6irs1/Krt2-6g gene as a strong candidate for CaRin because among five Ca alleles examined mutations always occurred in the highly conserved positions of the α-helical rod domain (1A and 2B subdomain) of this putative gene product. The most striking finding is that four independently discovered alleles, the three preexistent alleles CaJ, Ca9J, Ca10J, and our allele CaRin, all share one identical amino acid deletion (N 140 del) and the fifth, CamedJ, has an amino acid substitution (A 431 D). These findings indicate that a mutation hotspot exists in the Ca locus. Additionally, we describe a Ca mutant allele induced by ENU mutagenesis, which also possesses an amino acid substitution (L 424 W) in the mK6irs1/Krt2-6g gene. The identification of the Ca candidate gene enables us to further define the nature of the genetic pathway required for hair formation and provides an important new candidate that may be implicated in human hair and skin diseases.

Structure and regulation of the envoplakin gene

Envoplakin, a member of the plakin family of proteins, is a component of desmosomes and the epidermal cornified envelope. To understand how envoplakin expression is regulated, we have analyzed the structure of the mouse envoplakin gene and characterized the promoters of both the human and mouse genes. The mouse gene consists of 22 exons and maps to chromosome 11E1, syntenic to the location of the human gene on 17q25. The exon-intron structure of the mouse envoplakin gene is common to all members of the plakin family: the N-terminal protein domain is encoded by 21 small exons, and the central rod domain and the C-terminal globular domain are coded by a single large exon. The C terminus shows the highest sequence conservation between mouse and human envoplakins and between envoplakin and the other family members. The N terminus is also conserved, with sequence homology extending to Drosophila Kakapo. A region between nucleotides -101 and 288 was necessary for promoter activity in transiently transfected primary keratinocytes. This region is highly conserved between the human and mouse genes and contains at least two different positively acting elements identified by site-directed mutagenesis and electrophoretic mobility shift assays. Mutation of a GC box binding Sp1 and Sp3 proteins or a combined E box and Krüppel-like element interacting with unidentified nuclear proteins virtually abolished promoter activity. 600 base pairs of the mouse upstream sequence was sufficient to drive expression of a beta-galactosidase reporter gene in the suprabasal layers of epidermis, esophagus, and forestomach of transgenic mice. Thus, we have identified a regulatory region in the envoplakin gene that can account for the expression pattern of the endogenous protein in stratified squamous epithelia.

The genomic organization of type I keratin genes in mice

We isolated two new keratin cDNAs by screening a cDNA library constructed from poly(A)+ RNA of the dorsal and abdominal skin of C57BL/10J mice with a probe of human KRT14. Due to its high sequence homology to human keratin 17 cDNA, one full-length cDNA is most likely to be mouse keratin 17 (Krt1-17) cDNA. The other is the putative full-length cDNA of a novel type I keratin gene, designated Krt1-c29. These two keratin genes were mapped to the distal portion of Chromosome 11, where the mouse keratin gene complex-1 (Krt1) is localized. To elucidate the genomic organization of Krt1 in mice, we carried out genetic and physical analyses of Krt1. A large-scale linkage analysis using intersubspecific backcrosses suggested that there are two major clusters in Krt1, one containing Krt1-c29, Krt1-10, and Krt1-12 and the other containing Krt1-14, -15, -17, and -19. Truncation experiments with two yeast artificial chromosome clones containing the two clusters above have revealed that the gene order of Krt1 is centromere-Krt1-c29-Krt1-10-Krt1-12-Krt1-13-K rt1-15-Krt1-19-Krt1-14-K rt1-17-telomere. Finally, we analyzed sequence divergence between the genes belonging to the Krt1 complex. The results clearly indicated that genes are classified into two major groups with respect to phylogenetic relationship. Each group consists of the respective gene cluster demonstrated by genetic and physical analyses in this study, suggesting that the physical organization of the Krt1 complex reflects the evolutionary process of gene duplication of this complex.