Gsdma3(I359N) is a novel ENU-induced mutant mouse line for studying the function of Gasdermin A3 in the hair follicle and epidermis

Overview of pyroptosis mechanism and in-depth analysis of cardiomyocyte pyroptosis mediated by NF-κB pathway in heart failure

The pyroptosis of cardiomyocytes has become an essential topic in heart failure research. The abnormal accumulation of these biological factors, including angiotensin II, advanced glycation end products, and various growth factors (such as connective tissue growth factor, vascular endothelial growth factor, transforming growth factor beta, among others), activates the nuclear factor-κB (NF-κB) signaling pathway in cardiovascular diseases, ultimately leading to pyroptosis of cardiomyocytes. Therefore, exploring the underlying molecular biological mechanisms is essential for developing novel drugs and therapeutic strategies. However, our current understanding of the precise regulatory mechanism of this complex signaling pathway in cardiomyocyte pyroptosis is still limited. Given this, this study reviews the milestone discoveries in the field of pyroptosis research since 1986, analyzes in detail the similarities, differences, and interactions between pyroptosis and other cell death modes (such as apoptosis, necroptosis, autophagy, and ferroptosis), and explores the deep connection between pyroptosis and heart failure. At the same time, it depicts in detail the complete pathway of the activation, transmission, and eventual cardiomyocyte pyroptosis of the NF-κB signaling pathway in the process of heart failure. In addition, the study also systematically summarizes various therapeutic approaches that can inhibit NF-κB to reduce cardiomyocyte pyroptosis, including drugs, natural compounds, small molecule inhibitors, gene editing, and other cutting-edge technologies, aiming to provide solid scientific support and new research perspectives for the prevention and treatment of heart failure.

Insight into the structure, function and the tumor suppression effect of gasdermin E

Gasdermin E (GSDME), which is also known as DFNA5, was first identified as a deafness-related gene that is expressed in cochlear hair cells, and mutation of this gene causes autosomal dominant neurogenic hearing loss. Later studies revealed that GSDME is mostly expressed in the kidney, placenta, muscle and brain cells, but it is expressed at low levels in tumor cells. The GSDME gene encodes the GSDME protein, which is a member of the gasdermin (GSDM) family and has been shown to participate in the induction of apoptosis and pyroptosis. The current literature suggests that Caspase-3 and Granzyme B (Gzm B) can cleave GSDME to generate the active N-terminal fragment (GSDME-NT), which integrates with the cell membrane and forms pores in this membrane to induce pyroptosis. Furthermore, GSDME also forms pores in mitochondrial membranes to release apoptosis factors, such as cytochrome c (Cyt c) and high-temperature requirement protein A2 (HtrA2/Omi), and subsequently activates the intrinsic apoptosis pathway. In recent years, GSDME has been shown to exert tumor-suppressive effects, suggesting that it has potential therapeutic effects on tumors. In this review, we introduce the structure and function of GSDME and the mechanism by which it induces cell death, and we discuss its tumor suppressive effect.

Inflammasomes in epithelial innate immunity: front line warriors

Our epithelium represents a battle ground against a variety of insults including pathogens and danger signals. It encodes multiple sensors that detect and respond to such insults, playing an essential role in maintaining and defending tissue homeostasis. One key set of defense mechanisms is our inflammasomes which drive innate immune responses including, sensing and responding to pathogen attack, through the secretion of pro-inflammatory cytokines and cell death. Identification of physiologically relevant triggers for inflammasomes has greatly influenced our ability to decipher the mechanisms behind inflammasome activation. Furthermore, identification of patient mutations within inflammasome components implicates their involvement in a range of epithelial diseases. This review will focus on exploring the roles of inflammasomes in epithelial immunity and cover: the diversity and differential expression of inflammasome sensors amongst our epithelial barriers, their ability to sense local infection and damage and the contribution of the inflammasomes to epithelial homeostasis and disease.

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.

Role of pyroptosis in the pathogenesis and treatment of diseases

Programmed cell death (PCD) is regarded as a pathological form of cell death with an intracellular program mediated, which plays a pivotal role in maintaining homeostasis and embryonic development. Pyroptosis is a new paradigm of PCD, which has received increasing attention due to its close association with immunity and disease. Pyroptosis is a form of inflammatory cell death mediated by gasdermin that promotes the release of proinflammatory cytokines and contents induced by inflammasome activation. Recently, increasing evidence in studies shows that pyroptosis has a crucial role in inflammatory conditions like cardiovascular diseases (CVDs), cancer, neurological diseases (NDs), and metabolic diseases (MDs), suggesting that targeting cell death is a potential intervention for the treatment of these inflammatory diseases. Based on this, the review aims to identify the molecular mechanisms and signaling pathways related to pyroptosis activation and summarizes the current insights into the complicated relationship between pyroptosis and multiple human inflammatory diseases (CVDs, cancer, NDs, and MDs). We also discuss a promising novel strategy and method for treating these inflammatory diseases by targeting pyroptosis and focus on the pyroptosis pathway application in clinics.

Protein engineering reveals that gasdermin A preferentially targets mitochondrial membranes over the plasma membrane during pyroptosis

When activated, gasdermin family members are thought to be pore-forming proteins that cause lytic cell death. Despite this, numerous studies have suggested that the threshold for lytic cell death is dependent on which gasdermin family member is activated. Determination of the propensity of various gasdermin family members to cause pyroptosis has been handicapped by the fact that for many of them, the mechanisms and timing of their activation are uncertain. In this article, we exploit the recently discovered exosite-mediated recognition of gasdermin D (GSDMD) by the inflammatory caspases to develop a system that activates gasdermin family members in an efficient and equivalent manner. We leverage this system to show that upon activation, GSDMD and gasdermin A (GSDMA) exhibit differential subcellular localization, differential plasma membrane permeabilization, and differential lytic cell death. While GSDMD localizes rapidly to both the plasma membrane and organelle membranes, GSDMA preferentially localizes to the mitochondria with delayed and diminished accumulation at the plasma membrane. As a consequence of this differential kinetics of subcellular localization, N-terminal GSDMA results in early mitochondrial dysfunction relative to plasma membrane permeabilization. This study thus challenges the assumption that gasdermin family members effect cell death through identical mechanisms and establishes that their activation in their respective tissues of expression likely results in different immunological outcomes.

Identification of a Novel Pyroptosis-Related Gene Signature Indicative of Disease Prognosis and Treatment Response in Skin Cutaneous Melanoma

Purpose

Pyroptosis plays an important role in the occurrence and progression of many tumors; however, the specific mechanisms involved remain unknown. Here, we construct a pyroptosis-related gene signature that can be used to predict survival prognosis of skin cutaneous melanoma (SKCM) and provide guidance for clinical treatment.

Methods

By integrating data from the two databases from the GTEx and TCGA, differentially expressed genes (DEGs) from normal tissues and skin cutaneous tumor tissues were identified. The main signaling pathways and function enrichment of these differential genes were determined. Univariate and multivariate COX regression analysis, and risk score analysis were used to construct a signature to assess its predictive value for overall survival. The mRNA expression of these five genes in melanoma cells was determined by quantitative polymerase chain reaction (qPCR). The pRRophetic algorithm was used to estimate the half-maximal inhibitory concentration (IC50) of chemotherapy drugs in SKCM patients. The expression of multiple immune checkpoint genes also was evaluated.

Results

Sixteen DEGs associated with pyroptosis in SKCM and normal skin tissues were identified. Of these, 12 pyroptosis-related DEGs were associated with the prognosis of SKCM. A five-gene signature (GSDMA, GSDMC, IL-18, NLRP6, and AIM2) model was constructed. Patients were divided into high-risk and low-risk groups using the risk scores. Of these, the high-risk group had a worse survival prognosis. There are significant differences in the predicted sensitivity of the high-risk and low-risk groups to chemotherapeutic drugs. In addition, compared with the high-risk group, the low-risk group showed higher expression of PD-1, PDL-1, CTLA-4, LAG-3, and VSIR.

Conclusion

In this study, we constructed a novel prognostic pyroptosis-related gene-signature for SKCM. These genes showed good predictive value for patient prognosis and could provide guidance for better treatment of SKCM patients.

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.

Chemical Modulation of Gasdermin-Mediated Pyroptosis and Therapeutic Potential

Pyroptosis, a lytic form of programmed cell death, both stimulates effective immune responses and causes tissue damage. Gasdermin (GSDM) proteins are a family of pore-forming executors of pyroptosis. While the most-studied member, GSDMD, exerts critical functions in inflammasome biology, emerging evidence demonstrates potential broad relevance for GSDM-mediated pyroptosis across diverse pathologies. In this review, we describe GSDM biology, outline conditions where inflammasomes and GSDM-mediated pyroptosis represent rational therapeutic targets, and delineate strategies to manipulate these central immunologic processes for the treatment of human disease.

The Versatile Gasdermin Family: Their Function and Roles in Diseases

The gasdermin (GSDM) family, a novel group of structure-related proteins, consists of GSDMA, GSDMB, GSDMC, GSDMD, GSDME/DNFA5, and PVJK/GSDMF. GSDMs possess a C-terminal repressor domain, cytotoxic N-terminal domain, and flexible linker domain (except for GSDMF). The GSDM-NT domain can be cleaved and released to form large oligomeric pores in the membrane that facilitate pyroptosis. The emerging roles of GSDMs include the regulation of various physiological and pathological processes, such as cell differentiation, coagulation, inflammation, and tumorigenesis. Here, we introduce the basic structure, activation, and expression patterns of GSDMs, summarize their biological and pathological functions, and explore their regulatory mechanisms in health and disease. This review provides a reference for the development of GSDM-targeted drugs to treat various inflammatory and tissue damage-related conditions.

Pyroptosis, metabolism, and tumor immune microenvironment

In response to a wide range of stimulations, host cells activate pyroptosis, a kind of inflammatory cell death which is provoked by the cytosolic sensing of danger signals and pathogen infection. In manipulating the cleavage of gasdermins (GSDMs), researchers have found that GSDM proteins serve as the real executors and the deterministic players in fate decisions of pyroptotic cells. Whether inflammatory characteristics induced by pyroptosis could cause damage the host or improve immune activity is largely dependent on the context, timing, and response degree. Here, we systematically review current points involved in regulatory mechanisms and the multidimensional roles of pyroptosis in several metabolic diseases and the tumor microenvironment. Targeting pyroptosis may reveal potential therapeutic avenues.

Pyroptosis in Cancer: Friend or Foe?

Simple Summary

Pyroptosis is a new form of programmed cell death that differs from apoptosis in terms of its release of inflammatory factors and its characteristic bubble-like morphology. Pyroptosis was first discovered in the process of immune defense against bacterial infection, but the field of research soon spread to other inflammatory diseases and cancer. As cancer constitutes a serious risk for public health, numerous studies investigating pyroptosis in cancer have been carried out during these years. Tumorigenesis and new therapeutic treatments have been the focus of much recent research. This review discusses the role of pyroptosis in tumorigenesis and its influence on tumor immunity.

Abstract

Pyroptosis is an inflammatory form of programmed cell death that is mediated by pore-forming proteins such as the gasdermin family (GSDMs), including GSDMA-E. Upon cleavage by activated caspases or granzyme proteases, the N-terminal of GSDMs oligomerizes in membranes to form pores, resulting in pyroptosis. Though all the gasdermin proteins have been studied in cancer, the role of pyroptosis in cancer remains mysterious, with conflicting findings. Numerous studies have shown that various stimuli, such as pathogen-associated molecular patterns (PAMPs), damage-associated molecular patterns (DAMPs), and chemotherapeutic drugs, could trigger pyroptosis when the cells express GSDMs. However, it is not clear whether pyroptosis in cancer induced by chemotherapeutic drugs or CAR T cell therapy is beneficial or harmful for anti-tumor immunity. This review discusses the discovery of pyroptosis as well as its role in inflammatory diseases and cancer, with an emphasis on tumor immunity.

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.

Knocking 'em Dead: Pore-Forming Proteins in Immune Defense

Immune cells use a variety of membrane-disrupting proteins [complement, perforin, perforin-2, granulysin, gasdermins, mixed lineage kinase domain-like pseudokinase (MLKL)] to induce different kinds of death of microbes and host cells, some of which cause inflammation. After activation by proteolytic cleavage or phosphorylation, these proteins oligomerize, bind to membrane lipids, and disrupt membrane integrity. These membrane disruptors play a critical role in both innate and adaptive immunity. Here we review our current knowledge of the functions, specificity, activation, and regulation of membrane-disrupting immune proteins and what is known about the mechanisms behind membrane damage, the structure of the pores they form, how the cells expressing these lethal proteins are protected, and how cells targeted for destruction can sometimes escape death by repairing membrane damage.

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.

Mechanisms of Gasdermin Family Members in Inflammasome Signaling and Cell Death

The Gasdermin (GSDM) family consists of Gasdermin A (GSDMA), Gasdermin B (GSDMB), Gasdermin C (GSDMC), Gasdermin D (GSDMD), Gasdermin E (GSDME) and Pejvakin (PJVK). GSDMD is activated by inflammasome-associated inflammatory caspases. Cleavage of GSDMD by human or mouse caspase-1, human caspase-4, human caspase-5, and mouse caspase-11 liberates the N-terminal effector domain from the C-terminal inhibitory domain. The N-terminal domain oligomerizes in the cell membrane and forms a pore of 10-16 nm in diameter, through which substrates of a smaller diameter, such as interleukin-1β and interleukin-18, are secreted. The increasing abundance of membrane pores ultimately leads to membrane rupture and pyroptosis, releasing the entire cellular content. Other than GSDMD, the N-terminal domain of all GSDMs, with the exception of PJVK, have the ability to form pores. There is evidence to suggest that GSDMB and GSDME are cleaved by apoptotic caspases. Here, we review the mechanistic functions of GSDM proteins with respect to their expression and signaling profile in the cell, with more focused discussions on inflammasome activation and cell death.

Gasdermins: Effectors of Pyroptosis

Pyroptosis is a form of lytic programmed cell death initiated by inflammasomes, which detect cytosolic contamination or perturbation. This drives activation of caspase-1 or caspase-11/4/5, which cleave gasdermin D, separating its N-terminal pore-forming domain (PFD) from the C-terminal repressor domain (RD). The PFD oligomerizes to form large pores in the membrane that drive swelling and membrane rupture. Gasdermin D is one of six (in humans) gasdermin family members; several other gasdermins have also been shown to form pores that cause pyroptosis after cleavage to activate their PFDs. One of these, gasdermin E, is activated by caspase-3 cleavage. We review our current understanding of pyroptosis as well as current knowledge of the gasdermin family.

A Mechanistic Understanding of Pyroptosis: The Fiery Death Triggered by Invasive Infection

Immune cells and skin and mucosal epithelial cells recognize invasive microbes and other signs of danger to sound alarms that recruit responder cells and initiate an immediate "innate" immune response. An especially powerful alarm is triggered by cytosolic sensors of invasive infection that assemble into multimolecular complexes, called inflammasomes, that activate the inflammatory caspases, leading to maturation and secretion of proinflammatory cytokines and pyroptosis, an inflammatory death of the infected cell. Work in the past year has defined the molecular basis of pyroptosis. Activated inflammatory caspases cleave Gasdermin D (GSDMD), a cytosolic protein in immune antigen-presenting cells and epithelia. Cleavage separates the autoinhibitory C-terminal fragment from the active N-terminal fragment, which moves to the cell membrane, binds to lipids on the inside of the cell membrane, and oligomerizes to form membrane pores that disrupt cell membrane integrity, causing death and leakage of small molecules, including the proinflammatory cytokines and GSDMD itself. GSDMD also binds to cardiolipin on bacterial membranes and kills the very bacteria that activate the inflammasome. GSDMD belongs to a family of poorly studied gasdermins, expressed in the skin and mucosa, which can also form membrane pores. Spontaneous mutations that disrupt the binding of the N- and C-terminal domains of other gasdermins are associated with alopecia and asthma. Here, we review recent studies that identified the roles of the inflammasome, inflammatory caspases, and GSDMD in pyroptosis and highlight some of the outstanding questions about their roles in innate immunity, control of infection, and sepsis.

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.

Cleavage of GSDMD by inflammatory caspases determines pyroptotic cell death

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.

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.

N-terminal functional domain of Gasdermin A3 regulates mitochondrial homeostasis via mitochondrial targeting

BACKGROUND

The epidermis forms a critical barrier that is maintained by orchestrated programs of proliferation, differentiation, and cell death. Gene mutations that disturb this turnover process may cause skin diseases. Human GASDERMIN A (GSDMA) is frequently silenced in gastric cancer cell lines and its overexpression has been reported to induce apoptosis. GSDMA has also been linked with airway hyperresponsiveness in genetic association studies. The function of GSDMA in the skin was deduced by dominant mutations in mouse gasdermin A3 (Gsdma3), which caused skin inflammation and hair loss. However, the mechanism for the autosomal dominance of Gsdma3 mutations and the mode of Gsdma3's action remain unanswered.

RESULTS

We demonstrated a novel function of Gsdma3 in modulating mitochondrial oxidative stress. We showed that Gsdma3 is regulated by intramolecular fold-back inhibition, which is disrupted by dominant mutations in the C-terminal domain. The unmasked N-terminal domain of Gsdma3 associates with Hsp90 and is delivered to mitochondrial via mitochondrial importer receptor Tom70, where it interacts with the mitochondrial chaperone Trap1 and causes increased production of mitochondrial reactive oxygen species (ROS), dissipation of mitochondrial membrane potential, and mitochondrial permeability transition (MPT). Overexpression of the C-terminal domain of Gsdma3 as well as pharmacological interventions of mitochondrial translocation, ROS production, and MPT pore opening alleviate the cell death induced by Gsdma3 mutants.

CONCLUSIONS

Our results indicate that the genetic mutations in the C-terminal domain of Gsdma3 are gain-of-function mutations which unmask the N-terminal functional domain of Gsdma3. Gsdma3 regulates mitochondrial oxidative stress through mitochondrial targeting. Since mitochondrial ROS has been shown to promote epidermal differentiation, we hypothesize that Gsdma3 regulates context-dependent response of keratinocytes to differentiation and cell death signals by impinging on mitochondria.

Roles of GasderminA3 in Catagen-Telogen Transition During Hair Cycling

Hair follicles undergo cyclic behavior through regression (catagen), rest (telogen) and regeneration (anagen) during postnatal life. The hair cycle transition is strictly regulated by the autonomous and extrinsic molecular environment. However, whether there is a switch controlling catagen-telogen transition remains largely unknown. Here we show that hair follicles cycle from catagen to the next anagen without transitioning through a morphologically typical telogen after Gsdma3 mutation. This leaves an ESLS (epithelial strand-like structure) during the time period corresponding to telogen phase in WT mice. Molecularly, Wnt10b is upregulated in Gsdma3 mutant mice. Restoration of Gsdma3 expression in AE (alopecia and excoriation) mouse skin rescues hair follicle telogen entry and significantly decreases the Wnt10b-mediated Wnt/β-catenin signaling pathway. Overexpression of Wnt10b inhibits telogen entry by increasing epithelial strand cell proliferation. Subsequently, hair follicles with a Gsdma3 mutation enter the second anagen simultaneously as WT mice. Hair follicles cannot enter the second anagen with ectopic WT Gsdma3 overexpression. A luciferase reporter assay proves Gsdma3 directly suppresses Wnt signaling. Our findings suggest Gsdma3 plays an important role in catagen-telogen transition by balancing the Wnt signaling pathway, and that morphologically typical telogen is not essential for the initiation of a new hair cycle.