Targeting apoptosis pathways in infections

Pasteurella multocida activates apoptosis via the FAK-AKT-FOXO1 axis to cause pulmonary integrity loss, bacteremia, and eventually a cytokine storm

Pasteurella multocida is an important zoonotic respiratory pathogen capable of infecting a diverse range of hosts, including humans, farm animals, and wild animals. However, the precise mechanisms by which P. multocida compromises the pulmonary integrity of mammals and subsequently induces systemic infection remain largely unexplored. In this study, based on mouse and rabbit models, we found that P. multocida causes not only lung damage but also bacteremia due to the loss of lung integrity. Furthermore, we demonstrated that bacteremia is an important aspect of P. multocida pathogenesis, as evidenced by the observed multiorgan damage and systemic inflammation, and ultimately found that this systemic infection leads to a cytokine storm that can be mitigated by IL-6-neutralizing antibodies. As a result, we divided the pathogenesis of P. multocida into two phases: the pulmonary infection phase and the systemic infection phase. Based on unbiased RNA-seq data, we discovered that P. multocida-induced apoptosis leads to the loss of pulmonary epithelial integrity. These findings have been validated in both TC-1 murine lung epithelial cells and the lungs of model mice. Conversely, the administration of Ac-DEVD-CHO, an apoptosis inhibitor, effectively restored pulmonary epithelial integrity, significantly mitigated lung damage, inhibited bacteremia, attenuated the cytokine storm, and reduced mortality in mouse models. At the molecular level, we demonstrated that the FAK-AKT-FOXO1 axis is involved in P. multocida-induced lung epithelial cell apoptosis in both cells and animals. Thus, our research provides crucial information with regard to the pathogenesis of P. multocida as well as potential treatment options for this and other respiratory bacterial diseases.

Expansion and diversity of caspases in Mytilus coruscus contribute to larval metamorphosis and environmental adaptation

BACKGROUND

Apoptosis is involved (directly and indirectly) in several physiological processes including tissue remodeling during the development, the turnover of immune cells, and a defense against harmful stimuli. The disordered apoptotic process participates in the pathogenesis of various diseases, such as neoplasms, and chronic inflammatory or systemic autoimmune diseases, which are associated with its inadequate regulation. Caspases are vital components of the apoptotic pathway that are involved in developmental and immune processes. However, genome-wide identification and functional analysis of caspase have not been conducted in Mytilus coruscus, which is an economically important bivalve.

RESULTS

Here, 47 caspase genes were identified from the genomes of M. coruscus, and the expansion of caspase-2/9 and caspase-3/6/7 genes were observed. Tandem duplication acts as an essential driver of gene expansion. The expanded caspase genes were highly diverse in terms of sequence, domain structure, and spatiotemporal expression profiles, suggesting their functional differentiation. The high expression of the expanded caspase genes at the pediveliger larvae stage and the result of apoptosis location in the velum suggest that the apoptosis mediated by them plays a critical role in the metamorphosis of M. coruscus larvae. In gill, caspase genes respond differently to the challenge of different strains, and most caspase-2/9 and caspase-3/6/7 genes were induced by copper stress, whereas caspase-8/10 genes were suppressed. Additionally, most caspase genes were upregulated in the mantle under ocean acidification which could weaken the biomineralization capacity of the mantle tissue.

CONCLUSIONS

These results provide a comprehensive overview of the evolution and function of the caspase family and enhanced the understanding of the biological function of caspases in M. coruscus larval development and response to biotic and abiotic challenges.

A1 is induced by pathogen ligands to limit myeloid cell death and NLRP3 inflammasome activation

Programmed cell death pathways play an important role in innate immune responses to infection. Activation of intrinsic apoptosis promotes infected cell clearance; however, comparatively little is known about how this mode of cell death is regulated during infections and whether it can induce inflammation. Here, we identify that the pro-survival BCL-2 family member, A1, controls activation of the essential intrinsic apoptotic effectors BAX/BAK in macrophages and monocytes following bacterial lipopolysaccharide (LPS) sensing. We show that, due to its tight transcriptional and post-translational regulation, A1 acts as a molecular rheostat to regulate BAX/BAK-dependent apoptosis and the subsequent NLRP3 inflammasome-dependent and inflammasome-independent maturation of the inflammatory cytokine IL-1β. Furthermore, induction of A1 expression in inflammatory monocytes limits cell death modalities and IL-1β activation triggered by Neisseria gonorrhoeae-derived outer membrane vesicles (NOMVs). Consequently, A1-deficient mice exhibit heightened IL-1β production in response to NOMV injection. These findings reveal that bacteria can induce A1 expression to delay myeloid cell death and inflammatory responses, which has implications for the development of host-directed antimicrobial therapeutics.

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.

Beyond apoptosis: evidence of other regulated cell death pathways in the ovary throughout development and life

BACKGROUND

Regulated cell death is a fundamental component of numerous physiological processes; spanning from organogenesis in utero, to normal cell turnover during adulthood, as well as the elimination of infected or damaged cells throughout life. Quality control through regulation of cell death pathways is particularly important in the germline, which is responsible for the generation of offspring. Women are born with their entire supply of germ cells, housed in functional units known as follicles. Follicles contain an oocyte, as well as specialized somatic granulosa cells essential for oocyte survival. Follicle loss-via regulated cell death-occurs throughout follicle development and life, and can be accelerated following exposure to various environmental and lifestyle factors. It is thought that the elimination of damaged follicles is necessary to ensure that only the best quality oocytes are available for reproduction.

OBJECTIVE AND RATIONALE

Understanding the precise factors involved in triggering and executing follicle death is crucial to uncovering how follicle endowment is initially determined, as well as how follicle number is maintained throughout puberty, reproductive life, and ovarian ageing in women. Apoptosis is established as essential for ovarian homeostasis at all stages of development and life. However, involvement of other cell death pathways in the ovary is less established. This review aims to summarize the most recent literature on cell death regulators in the ovary, with a particular focus on non-apoptotic pathways and their functions throughout the discrete stages of ovarian development and reproductive life.

SEARCH METHODS

Comprehensive literature searches were carried out using PubMed and Google Scholar for human, animal, and cellular studies published until August 2022 using the following search terms: oogenesis, follicle formation, follicle atresia, oocyte loss, oocyte apoptosis, regulated cell death in the ovary, non-apoptotic cell death in the ovary, premature ovarian insufficiency, primordial follicles, oocyte quality control, granulosa cell death, autophagy in the ovary, autophagy in oocytes, necroptosis in the ovary, necroptosis in oocytes, pyroptosis in the ovary, pyroptosis in oocytes, parthanatos in the ovary, and parthanatos in oocytes.

OUTCOMES

Numerous regulated cell death pathways operate in mammalian cells, including apoptosis, autophagic cell death, necroptosis, and pyroptosis. However, our understanding of the distinct cell death mediators in each ovarian cell type and follicle class across the different stages of life remains the source of ongoing investigation. Here, we highlight recent evidence for the contribution of non-apoptotic pathways to ovarian development and function. In particular, we discuss the involvement of autophagy during follicle formation and the role of autophagic cell death, necroptosis, pyroptosis, and parthanatos during follicle atresia, particularly in response to physiological stressors (e.g. oxidative stress).

WIDER IMPLICATIONS

Improved knowledge of the roles of each regulated cell death pathway in the ovary is vital for understanding ovarian development, as well as maintenance of ovarian function throughout the lifespan. This information is pertinent not only to our understanding of endocrine health, reproductive health, and fertility in women but also to enable identification of novel fertility preservation targets.

Septins promote caspase activity and coordinate mitochondrial apoptosis

Apoptosis is a form of regulated cell death essential for tissue homeostasis and embryonic development. Apoptosis also plays a key role during bacterial infection, yet some intracellular bacterial pathogens (such as Shigella flexneri, whose lipopolysaccharide can block apoptosis) can manipulate cell death programs as an important survival strategy. Septins are a component of the cytoskeleton essential for mitochondrial dynamics and host defense, however, the role of septins in regulated cell death is mostly unknown. Here, we discover that septins promote mitochondrial (i.e., intrinsic) apoptosis in response to treatment with staurosporine (a pan-kinase inhibitor) or etoposide (a DNA topoisomerase inhibitor). Consistent with a role for septins in mitochondrial dynamics, septins promote the release of mitochondrial protein cytochrome c in apoptotic cells and are required for the proteolytic activation of caspase-3, caspase-7, and caspase-9 (core components of the apoptotic machinery). Apoptosis of HeLa cells induced in response to infection by S. flexneri ΔgalU (a lipopolysaccharide mutant unable to block apoptosis) is also septin-dependent. In vivo, zebrafish larvae are significantly more susceptible to infection with S. flexneri ΔgalU (as compared to infection with wildtype S. flexneri), yet septin deficient larvae are equally susceptible to infection with S. flexneri ΔgalU and wildtype S. flexneri. These data provide a new molecular framework to understand the complexity of mitochondrial apoptosis and its ability to combat bacterial infection.

Update of cellular responses to the efferocytosis of necroptosis and pyroptosis

Cell death is a basic physiological process that occurs in all living organisms. A few key players in these mechanisms, as well as various forms of cell death programming, have been identified. Apoptotic cell phagocytosis, also known as apoptotic cell clearance, is a well-established process regulated by a number of molecular components, including 'find-me', 'eat-me' and engulfment signals. Efferocytosis, or the rapid phagocytic clearance of cell death, is a critical mechanism for tissue homeostasis. Despite having similar mechanism to phagocytic clearance of infections, efferocytosis differs from phagocytosis in that it induces a tissue-healing response and is immunologically inert. However, as field of cell death has rapid expanded, much attention has recently been drawn to the efferocytosis of additional necrotic-like cell types, such as necroptosis and pyroptosis. Unlike apoptosis, this method of cell suicide allows the release of immunogenic cellular material and causes inflammation. Regardless of the cause of cell death, the clearance of dead cells is a necessary function to avoid uncontrolled synthesis of pro-inflammatory molecules and inflammatory disorder. We compare and contrast apoptosis, necroptosis and pyroptosis, as well as the various molecular mechanisms of efferocytosis in each type of cell death, and investigate how these may have functional effects on different intracellular organelles and signalling networks. Understanding how efferocytic cells react to necroptotic and pyroptotic cell uptake can help us understand how to modulate these cell death processes for therapeutic purposes.

Pgp3 protein of Chlamydia trachomatis inhibits apoptosis via HO-1 upregulation mediated by PI3K/Akt activation

As an obligate intracellular pathogen, Chlamydia trachomatis assumes various strategies to inhibit host cells apoptosis, thereby providing a suitable intracellular environment to ensure completion of the development cycle. In the current study, we revealed that Pgp3 protein, one of eight plasmid proteins of C. trachomatis that has been illustrated as the key virulence factor, increased HO-1 expression to suppress apoptosis, and downregulation of HO-1 with siRNA-HO-1 failed to exert anti-apoptosis activity of Pgp3 protein. Moreover, treatment of PI3K/Akt pathway inhibitor and Nrf2 inhibitor evidently reduced HO-1 expression and Nrf2 nuclear translocation was blocked by PI3K/Akt pathway inhibitor. These findings highlight that induction of HO-1 expression by Pgp3 protein is probably due to regulation of Nrf2 nuclear translocation activated by PI3K/Akt pathway, which provide clues on how C. trachomatis adjusts apoptosis.

The hidden power of secondary metabolites in plant-fungi interactions and sustainable phytoremediation

The global environment is dominated by various small exotic substances, known as secondary metabolites, produced by plants and microorganisms. Plants and fungi are particularly plentiful sources of these molecules, whose physiological functions, in many cases, remain a mystery. Fungal secondary metabolites (SM) are a diverse group of substances that exhibit a wide range of chemical properties and generally fall into one of four main family groups: Terpenoids, polyketides, non-ribosomal peptides, or a combination of the latter two. They are incredibly varied in their functions and are often related to the increased fitness of the respective fungus in its environment, often competing with other microbes or interacting with plant species. Several of these metabolites have essential roles in the biological control of plant diseases by various beneficial microorganisms used for crop protection and biofertilization worldwide. Besides direct toxic effects against phytopathogens, natural metabolites can promote root and shoot development and/or disease resistance by activating host systemic defenses. The ability of these microorganisms to synthesize and store biologically active metabolites that are a potent source of novel natural compounds beneficial for agriculture is becoming a top priority for SM fungi research. In this review, we will discuss fungal-plant secondary metabolites with antifungal properties and the role of signaling molecules in induced and acquired systemic resistance activities. Additionally, fungal secondary metabolites mimic plant promotion molecules such as auxins, gibberellins, and abscisic acid, which modulate plant growth under biotic stress. Moreover, we will present a new trend regarding phytoremediation applications using fungal secondary metabolites to achieve sustainable food production and microbial diversity in an eco-friendly environment.

CD44a functions as a regulator of p53 signaling, apoptosis and autophagy in the antibacterial immune response

The cell adhesion molecule CD44 has been implicated in diverse biological functions including the pathological responses to infections and inflammatory diseases. The variable forms of CD44 contribute to functional variations, which are not yet defined in teleost. Here, we show that zebrafish CD44a plays a protective role in the host defense against Edwardsiella piscicida infection. Zebrafish CD44a deficiency inhibits cell growth and proliferation, impairs cell growth and death pathways, and regulates the expression levels of many genes involved in p53 signaling, apoptosis and autophagy. In addition, CD44a gene disruption in zebrafish leads to inhibition of apoptosis and induction of autophagy, with the increased susceptibility to E. piscicida infection. Furthermore, we show that zebrafish CD44a variants including CD44a_tv1 and CD44a_tv2 promote the translocation of p53 from the nucleus to the cytoplasm and interact with p53 in the cytoplasm. Mechanistically, zebrafish CD44a_tv1 mediates the beneficial effect for larvae survival infected with E. piscicida is depending on the CASP8-mediated apoptosis. However, the antibacterial effect of zebrafish CD44a_tv2 depends on the cytoplasmic p53-mediated inhibition of autophagy. Collectively, our results identify that different mechanisms regulate CD44a variants-mediated antibacterial responses.

The adhesion molecule CD44 drives host defence in zebrafish by regulating apoptosis and autophagy.

Vegetative forms of Clostridium chauvoei trigger apoptotic and inflammatory responses on macrophages

BACKGROUND

Clostridium chauvoei is a gram-positive, spore-forming, strictly anaerobic bacterium that causes blackleg, a disease that affects cattle by inducing fulminant myonecrosis, thereby leading to high and constant losses of cattle. Macrophages (Mɸs) are depleted in tissues infected with the vegetative form of C. chauvoei, but the mechanism remains partially known. Consequently, Mɸs may be a critical target in the pathogenicity of C. chauvoei.

AIM

The objective of this work was to study the mechanism of death of mouse-primary Mɸs infected in vitro for 24 h with the vegetative form of C. chauvoei.

METHODS

Mouse peritoneal Mɸs were infected in vitro with different multiplicities of infection (MOIs) of C. chauvoei (i.e., 5:1, 20:1, and 100:1). After 24 h post-infection, cell viability (MTT reduction assay), apoptosis (apoptotic bodies, DNA ladder, and Annexin V assays), and inflammatory cell response (iNOS and TNF-α expression) were assessed.

RESULTS

All the MOIs investigated decreased cell viability. An MOI of 20:1 caused the highest production of apoptotic bodies and an electrophoretic DNA-ladder pattern typical of an apoptosis cell death process. These results were corroborated using the Annexin V-flow cytometry assay. Concurrently with apoptotic cell death, Mϕs expressed iNOS and TNF-α.

CONCLUSION

Inflammation-mediated apoptosis of Mϕs can be a potential mechanism of evasion of the immune response used by C. chauvoei in tissues for depleting phagocytic cells at the site of infection.

No longer married to inflammasome signaling: the diverse interacting pathways leading to pyroptotic cell death

For over 15 years the lytic cell death termed pyroptosis was defined by its dependency on the inflammatory caspase, caspase-1, which, upon pathogen sensing, is activated by innate immune cytoplasmic protein complexes known as inflammasomes. However, this definition of pyroptosis changed when the pore-forming protein gasdermin D (GSDMD) was identified as the caspase-1 (and caspase-11) substrate required to mediate pyroptotic cell death. Consequently, pyroptosis has been redefined as a gasdermin-dependent cell death. Studies now show that, upon liberation of the N-terminal domain, five gasdermin family members, GSDMA, GSDMB, GSDMC, GSDMD and GSDME can all form plasma membrane pores to induce pyroptosis. Here, we review recent research into the diverse stimuli and cell death signaling pathways involved in the activation of gasdermins; death and toll-like receptor triggered caspase-8 activation of GSDMD or GSMDC, apoptotic caspase-3 activation of GSDME, perforin-granzyme A activation of GSDMB, and bacterial protease activation of GSDMA. We highlight findings that have begun to unravel the physiological situations and disease states that result from gasdermin signaling downstream of inflammasome activation, death receptor and mitochondrial apoptosis, and necroptosis. This new era in cell death research therefore holds significant promise in identifying how distinct, yet often networked, pyroptotic cell death pathways might be manipulated for therapeutic benefit to treat a range of malignant conditions associated with inflammation, infection and cancer.

Pyroptosis and Sarcopenia: Frontier Perspective of Disease Mechanism

With global ageing, sarcopenia, as an age-related disease, has brought a heavy burden to individuals and society. Increasing attention has been given to further exploring the morbidity mechanism and intervention measures for sarcopenia. Pyroptosis, also known as cellular inflammatory necrosis, is a kind of regulated cell death that plays a role in the ageing progress at the cellular level. It is closely related to age-related diseases such as cardiovascular diseases, Alzheimer’s disease, osteoarthritis, and sarcopenia. In the process of ageing, aggravated oxidative stress and poor skeletal muscle perfusion in ageing muscle tissues can activate the nod-like receptor (NLRP) family to trigger pyroptosis. Chronic inflammation is a representative characteristic of ageing. The levels of inflammatory factors such as TNF-α may activate the signaling pathways of pyroptosis by the NF-κB-GSDMD axis, which remains to be further studied. Autophagy is a protective mechanism in maintaining the integrity of intracellular organelles and the survival of cells in adverse conditions. The autophagy of skeletal muscle cells can inhibit the activation of the pyroptosis pathway to some extent. A profound understanding of the mechanism of pyroptosis in sarcopenia may help to identify new therapeutic targets in the future. This review article focuses on the role of pyroptosis in the development and progression of sarcopenia.

The Anti-Apoptotic Role of COX-2 during In Vitro Infection of Human Intestinal Cell Line by Giardia duodenalis and The Potential Regulators

The protozoan parasite Giardia duodenalis inhabits the upper small intestine of mammals including humans and causes a disease known as giardiasis, which can lead to diarrhea, abdominal cramps, and bloating. G. duodenalis was known as a causative factor of intestinal epithelial cell (IEC) apoptosis. Cyclooxygenase-2 (COX-2) has been identified as an influencing factor of pathogen infection by participating in immune response, while its role in host defense against Giardia infection is not clear. Here we initially observed the involvement of COX-2 in the regulation of Giardia-induced IEC apoptosis. Inhibition of COX-2 activity could promote Giardia-induced reduction of IEC viability, increase of reactive oxygen species (ROS) production, and decrease of nitric oxide (NO) release, which would exacerbate IEC apoptosis. In addition, during Giardia-IEC interactions, COX-2 inhibition was able to accelerate caspase-3 activation and PARP cleavage, and inhibit the expressions of some anti-apoptotic proteins like cIAP-2 and survivin. In contrast, COX-2 over-expression could reduce Giardia-induced IEC apoptosis. We further investigated the regulatory mechanisms affecting COX-2 expression in terms of anti-apoptosis. The results showed that p38/ERK/AKT/NF-κB signaling could regulate COX-2-mediated ROS/NO production and anti-IEC apoptosis during Giardia infection. We also found that COX-2-mediated anti-IEC apoptosis induced by Giardia was related to TLR4-dependent activation of p38-NF-κB signaling. Collectively, this study identified COX-2 as a promoter for apoptotic resistance during Giardia-IEC interactions and determined the potential regulators, furthering our knowledge of anti-Giardia host defense mechanism.

Dietary Glutamine Inclusion Regulates Immune and Antioxidant System, as Well as Programmed Cell Death in Fish to Protect against Flavobacterium columnare Infection

The susceptibility of animals to pathogenic infection is significantly affected by nutritional status. The present study took yellow catfish (Pelteobagrus fulvidraco) as a model to test the hypothesis that the protective roles of glutamine during bacterial infection are largely related to its regulation on the immune and antioxidant system, apoptosis and autophagy. Dietary glutamine supplementation significantly improved fish growth performance and feed utilization. After a challenge with Flavobacterium columnare, glutamine supplementation promoted il-8 and il-1β expression via NF-κB signaling in the head kidney and spleen, but inhibited the over-inflammation in the gut and gills. Additionally, dietary glutamine inclusion also enhanced the systematic antioxidant capacity. Histological analysis showed the protective role of glutamine in gill structures. Further study indicated that glutamine alleviated apoptosis during bacterial infection, along with the reduced protein levels of caspase-3 and the reduced expression of apoptosis-related genes. Moreover, glutamine also showed an inhibitory role in autophagy which was due to the increased activation of the mTOR signaling pathway. Thus, our study for the first time illustrated the regulatory roles of glutamine in the fish immune and antioxidant system, and reported its inhibitory effects on fish apoptosis and autophagy during bacterial infection.

Herpes simplex virus interference with immunity: Focus on dendritic cells

Herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2) are highly prevalent in the human population. These viruses cause lifelong infections by establishing latency in neurons and undergo sporadic reactivations that promote recurrent disease and new infections. The success of HSVs in persisting in infected individuals is likely due to their multiple molecular determinants involved in escaping the host antiviral and immune responses. Importantly, HSVs infect and negatively modulate the function of dendritic cells (DCs), key immune cells that are involved in establishing effective and balanced immunity against viruses. Here, we review and discuss several molecular and cellular processes modulated by HSVs in DCs, such as autophagy, apoptosis, and the unfolded protein response. Given the central role of DCs in establishing optimal antiviral immunity, particular emphasis should be given to the outcome of the interactions occurring between HSVs and DCs.

Chronic inflammation and long-lasting changes in the gastric mucosa after Helicobacter pylori infection involved in gastric cancer

OBJECTIVE

Helicobacter pylori (H. pylori) infects approximately half of the world's population, as one of the most common chronic infections. H. pylori infection has been widely recognized as a major risk factor for gastric cancer (GC).

METHODS

Eradication treatment is considered to abolish the inflammatory response and prevent progression to GC. However, only 1-3% of H. pylori-infected patients develop GC, whereas GC can occur even after eradicating H. pylori. In addition, the incidence of GC following H. pylori infection is significantly higher compared to the gross incidence induced by all causes, although eradicating H. pylori reduces the risk of developing GC.

RESULTS

Therefore, it is reasonable to hypothesize that H. pylori infection results in changes that persist even after its eradication. Several of these changes may not be reversible within a short time, including the status of inflammation, the dysfunction of immunity and apoptosis, mitochondrial changes, aging and gastric dysbacteriosis.

CONCLUSION

The present review article aimed to discuss these potential long-lasting changes induced by H. pylori infection that may follow the eradication of H. pylori and contribute to the development of GC.

Multiple Autonomous Cell Death Suppression Strategies Ensure Cytomegalovirus Fitness

Programmed cell death pathways eliminate infected cells and regulate infection-associated inflammation during pathogen invasion. Cytomegaloviruses encode several distinct suppressors that block intrinsic apoptosis, extrinsic apoptosis, and necroptosis, pathways that impact pathogenesis of this ubiquitous herpesvirus. Here, we expanded the understanding of three cell autonomous suppression mechanisms on which murine cytomegalovirus relies: (i) M38.5-encoded viral mitochondrial inhibitor of apoptosis (vMIA), a BAX suppressor that functions in concert with M41.1-encoded viral inhibitor of BAK oligomerization (vIBO), (ii) M36-encoded viral inhibitor of caspase-8 activation (vICA), and (iii) M45-encoded viral inhibitor of RIP/RHIM activation (vIRA). Following infection of bone marrow-derived macrophages, the virus initially deflected receptor-interacting protein kinase (RIPK)3-dependent necroptosis, the most potent of the three cell death pathways. This process remained independent of caspase-8, although suppression of this apoptotic protease enhances necroptosis in most cell types. Second, the virus deflected TNF-mediated extrinsic apoptosis, a pathway dependent on autocrine TNF production by macrophages that proceeds independently of mitochondrial death machinery or RIPK3. Third, cytomegalovirus deflected BCL-2 family protein-dependent mitochondrial cell death through combined TNF-dependent and -independent signaling even in the absence of RIPK1, RIPK3, and caspase-8. Furthermore, each of these cell death pathways dictated a distinct pattern of cytokine and chemokine activation. Therefore, cytomegalovirus employs sequential, non-redundant suppression strategies to specifically modulate the timing and execution of necroptosis, extrinsic apoptosis, and intrinsic apoptosis within infected cells to orchestrate virus control and infection-dependent inflammation. Virus-encoded death suppressors together hold control over an intricate network that upends host defense and supports pathogenesis in the intact mammalian host.

Elucidation of rutin's role in inducing caspase-dependent apoptosis via HPV-E6 and E7 down-regulation in cervical cancer HeLa cells

Over the recent few years rutin has gained wider attention in exhibiting inhibitory potential against several oncotargets for inducing apoptotic and antiproliferative activity in several human cancer cells. Several deregulated signaling pathways are implicated in cancer pathogenesis. Therefore we have inclined our research towards exploring the anticancerous efficacy of a very potent phytocompound for modulating the incontinent expression of these two crucial E6 and E7 oncogenes. Further, inhibitory efficacy of rutin against human papillomavirus (HPV)-E6 and E7 oncoproteins in cervical cancer has not been elucidated yet. This research addresses the growth inhibitory efficacy of rutin against E6 and E7 oncoproteins in HeLa cells, which is known to inactivate several tumor suppressor proteins such as p53 and pRB. Rutin treatment exhibited reduced cell viability with increased cell accumulation in G0/G1 phase of cell cycle in HeLa cell lines. Additionally, rutin treatment has also led to down-regulation of E6 and E7 expression associated with an increased expression of p53 and pRB levels. This has further resulted in enhanced Bax expression and decreased Bcl-2 expression releasing cytochrome c into cytosol followed by caspase cascade activation with cleavage of caspase-3, caspase-8 and caspase-9. Further, in silico studies have also supported our in vitro findings by exhibiting significant binding energy against selected target oncoproteins. Therefore, our research findings might recommend rutin as one of the potent drug candidate in cervical cancer management via targeting two crucial oncoproteins associated with viral progression.

Intrinsic drug potential of oxazolo[5,4-d]pyrimidines and oxazolo[4,5-d]pyrimidines

The oxazole and pyrimidine rings are widely displayed in natural products and synthetic molecules. They are known as the prime skeletons for drug discovery. On the account of structural and chemical diversity, oxazole and pyrimidine-based molecules, as central scaffolds, not only provide different types of interactions with various receptors and enzymes, showing broad biological activities, but also occupy a core position in medicinal chemistry, showing their importance for development and discovery of newer potential therapeutic agents (Curr Top Med Chem, 16, 2016, 3133; Int J Pharm Pharm Sci, 8, 2016, 8; BMC Chem, 13, 2019, 44). For a long time, relatively little attention has been paid to their fused rings that are oxazolopyrimidines, whose chemical structure is similar to that of natural purines because probably none of these compounds were found in natural products or their biological activities turned out to be unexpressed (Bull Chem Soc Jpn, 43, 1970, 187). Recently, however, a significant number of studies have been published on the biological properties of oxazolo[5,4-d]pyrimidines, showing their significant activity as agonists and antagonists of signaling pathways involved in the regulation of the cell life cycle, whereas oxazolo[4,5-d]pyrimidines, on the contrary, represent a poorly studied class of compounds. Limited access to this scaffold has resulted in a corresponding lack of biological research (Eur J Organ Chem, 18, 2018, 2148). Actually, oxazolo[5,4-d]pyrimidine is a versatile scaffold used for the design of bioactive ligands against enzymes and receptors. This review focuses on biological targets and associated pathogenetic mechanisms, as well as pathological disorders that can be modified by well-known oxazolopyrimidines that have been proven to date. Many molecular details of these processes are omitted here, which the interested reader will find in the cited literature. This work also does not cover the methods for the synthesis of the oxazolopyrimidines, which are exhaustively described by De Coen et al. (Eur J Organ Chem, 18, 2018, 2148). The review as well does not discuss the structure-activity relationship, which is described in detail in the original works and deliberately, whenever possible, cites not primary sources, but mostly relevant review articles, so that the reader who wants to delve into a particular problem will immediately receive more complete information. It is expected that the information presented in this review will help readers better understand the purpose of the development of oxazolopyrimidines and the possibility of their development as drugs for the treatment of a wide range of diseases.

Fungal-Induced Programmed Cell Death

Fungal infections are a cause of morbidity in humans, and despite the availability of a range of antifungal treatments, the mortality rate remains unacceptably high. Although our knowledge of the interactions between pathogenic fungi and the host continues to grow, further research is still required to fully understand the mechanism underpinning fungal pathogenicity, which may provide new insights for the treatment of fungal disease. There is great interest regarding how microbes induce programmed cell death and what this means in terms of the immune response and resolution of infection as well as microbe-specific mechanisms that influence cell death pathways to aid in their survival and continued infection. Here, we discuss how programmed cell death is induced by fungi that commonly cause opportunistic infections, including Candida albicans, Aspergillus fumigatus, and Cryptococcus neoformans, the role of programmed cell death in fungal immunity, and how fungi manipulate these pathways.

Knockdown of RNF2 enhances the radiosensitivity of squamous cell carcinoma in lung

A previous study has reported that knockdown of RING finger protein 2 (RNF2) increases the radiosensitivity of esophageal cancer cells both in vitro and in vivo. However, the effect of RNF2 knockdown on radiosensitivity in squamous cell carcinoma (SqCC) remains unknown. For this, NCI-H226 and SK-MES-1 cells were exposed to X-ray irradiation and then RNF2 levels were determined. RNF2 was knocked-down and stable transfectants were selected. Radiosensitivity, cell proliferation, apoptosis, cell cycle, and γ-H2AX foci formation were evaluated. Interaction among ataxia telangiectasia mutated protein (ATM), mediator of DNA damage checkpoint 1 (MDC1), and H2AX were examined. Xenograft models were used to explore the effect of RNF2 knockdown on radiosensitivity in vivo. The results showed that RNF2 expression was significantly increased by X-ray irradiation. RNF2 knockdown combined with X-ray irradiation markedly inhibited cell proliferation, caused cell cycle arrest at the G1 phase, and induced cell apoptosis. In addition, RNF2 knockdown enhanced the radiosensitivity of SqCC cells, inhibited irradiation-induced γ-H2AX foci formation, and impaired the interactions among ATM, MDC1, and H2AX. Furthermore, combination of RNF2 knockdown and X-ray irradiation suppressed tumor growth and promoted tumor cell apoptosis in vivo. RNF2 may be a new therapeutic target to enhance the radiosensitivity of SqCC cells in lung.

Organization of the Skin Immune System and Compartmentalized Immune Responses in Infectious Diseases

The skin is an organ harboring several types of immune cells that participate in innate and adaptive immune responses. The immune system of the skin comprises both skin cells and professional immune cells that together constitute what is designated skin-associated lymphoid tissue (SALT). In this review, I extensively discuss the organization of SALT and the mechanisms involved in its responses to infectious diseases of the skin and mucosa. The nature of these SALT responses, and the cellular mediators involved, often determines the clinical course of such infections. I list and describe the components of innate immunity, such as the roles of the keratinocyte barrier and of inflammatory and natural killer cells. I also examine the mechanisms involved in adaptive immune responses, with emphasis on new cytokine profiles, and the role of cell death phenomena in host-pathogen interactions and control of the immune responses to infectious agents. Finally, I highlight the importance of studying SALT in order to better understand host-pathogen relationships involving the skin and detail future directions in the immunological investigation of this organ, especially in light of recent findings regarding the skin immune system.

The role of cell surface expression of influenza virus neuraminidase in induction of human lymphocyte apoptosis

The immunopathological mechanisms as well as the role played by influenza A virus infection of human leukocytes and induction of apoptosis have not been fully elucidated. We confirm here that the percentage of cells that are infected is less than the percent of apoptotic cells. Depletion of monocytes/macrophages and depletion of cells expressing influenza neuraminidase from the cultures after exposure to virus decreased lymphocyte apoptosis. Treatment of virus-exposed leukocyte cultures with anti-neuraminidase antibodies but not with anti-hemagglutinin antibodies, reduced lymphocyte production of active caspase-3 and induction of apoptosis. Different strains of virus induced different levels of apoptosis. Variations in induction of apoptosis correlated with production and expression of viral neuraminidase by infected leukocytes. The data suggest that cell surface expression of neuraminidase plays an important role in the induction of apoptosis in human lymphocytes. The benefit, or cost, to the host of lymphocyte apoptosis warrants continued investigation.

Pyroptosis versus necroptosis: similarities, differences, and crosstalk

Pyroptosis and necroptosis represent two pathways of genetically encoded necrotic cell death. Although these cell death programmes can protect the host against microbial pathogens, their dysregulation has been implicated in a variety of autoimmune and auto-inflammatory conditions. The disease-promoting potential of necroptosis and pyroptosis is likely a consequence of their ability to induce a lytic cell death. This cell suicide mechanism, distinct from apoptosis, allows the release of immunogenic cellular content, including damage-associated molecular patterns (DAMPs), and inflammatory cytokines such as interleukin-1β (IL-1β), to trigger inflammation. In this Review, we discuss recent discoveries that have advanced our understanding on the primary functions of pyroptosis and necroptosis, including evidence for the specific cytokines and DAMPs responsible for driving inflammation. We compare the similar and unique aspects of pyroptotic- and necroptotic-induced membrane damage, and explore how these may functionally impact distinct intracellular organelles and signalling pathways. We also examine studies highlighting the crosstalk that can occur between necroptosis and pyroptosis signalling, and evidence supporting the physiological significance of this convergence. Ultimately, a better understanding of the similarities, unique aspects and crosstalk of pyroptosis and necroptosis will inform as to how these cell death pathways might be manipulated for therapeutic benefit.