Showing papers on "Apoptosis published in 2014"

Self-consumption: the interplay of autophagy and apoptosis

Abstract: Autophagy and apoptosis control the turnover of organelles and proteins within cells, and of cells within organisms, respectively, and many stress pathways sequentially elicit autophagy, and apoptosis within the same cell. Generally autophagy blocks the induction of apoptosis, and apoptosis-associated caspase activation shuts off the autophagic process. However, in special cases, autophagy or autophagy-relevant proteins may help to induce apoptosis or necrosis, and autophagy has been shown to degrade the cytoplasm excessively, leading to 'autophagic cell death'. The dialogue between autophagy and cell death pathways influences the normal clearance of dying cells, as well as immune recognition of dead cell antigens. Therefore, the disruption of the relationship between autophagy and apoptosis has important pathophysiological consequences.

Cell death by pyroptosis drives CD4 T-cell depletion in HIV-1 infection

Abstract: The pathway causing CD4 T-cell death in HIV-infected hosts remains poorly understood although apoptosis has been proposed as a key mechanism. We now show that caspase-3-mediated apoptosis accounts for the death of only a small fraction of CD4 T cells corresponding to those that are both activated and productively infected. The remaining over 95% of quiescent lymphoid CD4 T cells die by caspase-1-mediated pyroptosis triggered by abortive viral infection. Pyroptosis corresponds to an intensely inflammatory form of programmed cell death in which cytoplasmic contents and pro-inflammatory cytokines, including IL-1β, are released. This death pathway thus links the two signature events in HIV infection-CD4 T-cell depletion and chronic inflammation-and creates a pathogenic vicious cycle in which dying CD4 T cells release inflammatory signals that attract more cells to die. This cycle can be broken by caspase 1 inhibitors shown to be safe in humans, raising the possibility of a new class of 'anti-AIDS' therapeutics targeting the host rather than the virus.

Apoptosis and Molecular Targeting Therapy in Cancer

Abstract: Apoptosis is the programmed cell death which maintains the healthy survival/death balance in metazoan cells. Defect in apoptosis can cause cancer or autoimmunity, while enhanced apoptosis may cause degenerative diseases. The apoptotic signals contribute into safeguarding the genomic integrity while defective apoptosis may promote carcinogenesis. The apoptotic signals are complicated and they are regulated at several levels. The signals of carcinogenesis modulate the central control points of the apoptotic pathways, including inhibitor of apoptosis (IAP) proteins and FLICE-inhibitory protein (c-FLIP). The tumor cells may use some of several molecular mechanisms to suppress apoptosis and acquire resistance to apoptotic agents, for example, by the expression of antiapoptotic proteins such as Bcl-2 or by the downregulation or mutation of proapoptotic proteins such as BAX. In this review, we provide the main regulatory molecules that govern the main basic mechanisms, extrinsic and intrinsic, of apoptosis in normal cells. We discuss how carcinogenesis could be developed via defective apoptotic pathways or their convergence. We listed some molecules which could be targeted to stimulate apoptosis in different cancers. Together, we briefly discuss the development of some promising cancer treatment strategies which target apoptotic inhibitors including Bcl-2 family proteins, IAPs, and c-FLIP for apoptosis induction.

A Mechanism of Hypoxia-Mediated Escape from Adaptive Immunity in Cancer Cells

Abstract: Immune escape is a fundamental trait of cancer in which mechanistic knowledge is incomplete. Here, we describe a novel mechanism by which hypoxia contributes to tumoral immune escape from cytotoxic T lymphocytes (CTL). Exposure of human or murine cancer cells to hypoxia for 24 hours led to upregulation of the immune inhibitory molecule programmed cell death ligand-1 (PD-L1; also known as B7-H1), in a manner dependent on the transcription factor hypoxia-inducible factor-1α (HIF-1α). In vivo studies also demonstrated cellular colocalization of HIF-1α and PD-L1 in tumors. Hypoxia-induced expression of PD-L1 in cancer cells increased their resistance to CTL-mediated lysis. Using glyceryl trinitrate (GTN), an agonist of nitric oxide (NO) signaling known to block HIF-1α accumulation in hypoxic cells, we prevented hypoxia-induced PD-L1 expression and diminished resistance to CTL-mediated lysis. Moreover, transdermal administration of GTN attenuated tumor growth in mice. We found that higher expression of PD-L1 induced in tumor cells by exposure to hypoxia led to increased apoptosis of cocultured CTLs and Jurkat leukemia T cells. This increase in apoptosis was prevented by blocking the interaction of PD-L1 with PD-1, the PD-L1 receptor on T cells, or by addition of GTN. Our findings point to a role for hypoxia/HIF-1 in driving immune escape from CTL, and they suggest a novel cancer immunotherapy to block PD-L1 expression in hypoxic-tumor cells by administering NO mimetics.

Autophagy and apoptosis: where do they meet?

Abstract: Autophagy and apoptosis are two important cellular processes with complex and intersecting protein networks; as such, they have been the subjects of intense investigation. Recent advances have elucidated the key players and their molecular circuitry. For instance, the discovery of Beclin-1’s interacting partners has resulted in the identification of Bcl-2 as a central regulator of autophagy and apoptosis, which functions by interacting with both Beclin-1 and Bax/Bak respectively. When localized to the endoplasmic reticulum and mitochondria, Bcl-2 inhibits autophagy. Cellular stress causes the displacement of Bcl-2 from Beclin-1 and Bax, thereby triggering autophagy and apoptosis, respectively. The induction of autophagy or apoptosis results in disruption of complexes by BH3-only proteins and through post-translational modification. The mechanisms linking autophagy and apoptosis are not fully defined; however, recent discoveries have revealed that several apoptotic proteins (e.g., PUMA, Noxa, Nix, Bax, XIAP, and Bim) modulate autophagy. Moreover, autophagic proteins that control nucleation and elongation regulate intrinsic apoptosis through calpain- and caspase-mediated cleavage of autophagy-related proteins, which switches the cellular program from autophagy to apoptosis. Similarly, several autophagic proteins are implicated in extrinsic apoptosis. This highlights a dual cellular role for autophagy. On one hand, autophagy degrades damaged mitochondria and caspases, and on the other hand, it provides a membrane-based intracellular platform for caspase processing in the regulation of apoptosis. In this review, we highlight the crucial factors governing the crosstalk between autophagy and apoptosis and describe the mechanisms controlling cell survival and cell death.

Regulated Cell Death in AKI

Abstract: AKI is pathologically characterized by sublethal and lethal damage of renal tubules. Under these conditions, renal tubular cell death may occur by regulated necrosis (RN) or apoptosis. In the last two decades, tubular apoptosis has been shown in preclinical models and some clinical samples from patients with AKI. Mechanistically, apoptotic cell death in AKI may result from well described extrinsic and intrinsic pathways as well as ER stress. Central converging nodes of these pathways are mitochondria, which become fragmented and sensitized to membrane permeabilization in response to cellular stress, resulting in the release of cell death-inducing factors. Whereas apoptosis is known to be regulated, tubular necrosis was thought to occur by accident until recent work unveiled several RN subroutines, most prominently receptor-interacting protein kinase-dependent necroptosis and RN induced by mitochondrial permeability transition. Additionally, other cell death pathways, like pyroptosis and ferroptosis, may also be of pathophysiologic relevance in AKI. Combination therapy targeting multiple cell-death pathways may, therefore, provide maximal therapeutic benefits.

Molecular mechanisms of ATP secretion during immunogenic cell death

Abstract: The immunogenic demise of cancer cells can be induced by various chemotherapeutics, such as anthracyclines and oxaliplatin, and provokes an immune response against tumor-associated antigens. Thus, immunogenic cell death (ICD)-inducing antineoplastic agents stimulate a tumor-specific immune response that determines the long-term success of therapy. The release of ATP from dying cells constitutes one of the three major hallmarks of ICD and occurs independently of the two others, namely, the pre-apoptotic exposure of calreticulin on the cell surface and the postmortem release of high-mobility group box 1 (HMBG1) into the extracellular space. Pre-mortem autophagy is known to be required for the ICD-associated secretion of ATP, implying that autophagy-deficient cancer cells fail to elicit therapy-relevant immune responses in vivo. However, the precise molecular mechanisms whereby ATP is actively secreted in the course of ICD remain elusive. Using a combination of pharmacological screens, silencing experiments and techniques to monitor the subcellular localization of ATP, we show here that, in response to ICD inducers, ATP redistributes from lysosomes to autolysosomes and is secreted by a mechanism that requires the lysosomal protein LAMP1, which translocates to the plasma membrane in a strictly caspase-dependent manner. The secretion of ATP additionally involves the caspase-dependent activation of Rho-associated, coiled-coil containing protein kinase 1 (ROCK1)-mediated, myosin II-dependent cellular blebbing, as well as the opening of pannexin 1 (PANX1) channels, which is also triggered by caspases. Of note, although autophagy and LAMP1 fail to influence PANX1 channel opening, PANX1 is required for the ICD-associated translocation of LAMP1 to the plasma membrane. Altogether, these findings suggest that caspase- and PANX1-dependent lysosomal exocytosis has an essential role in ATP release as triggered by immunogenic chemotherapy.

Die another way – non-apoptotic mechanisms of cell death

Abstract: Regulated, programmed cell death is crucial for all multicellular organisms. Cell death is essential in many processes, including tissue sculpting during embryogenesis, development of the immune system and destruction of damaged cells. The best-studied form of programmed cell death is apoptosis, a process that requires activation of caspase proteases. Recently it has been appreciated that various non-apoptotic forms of cell death also exist, such as necroptosis and pyroptosis. These non-apoptotic cell death modalities can be either triggered independently of apoptosis or are engaged should apoptosis fail to execute. In this Commentary, we discuss several regulated non-apoptotic forms of cell death including necroptosis, autophagic cell death, pyroptosis and caspase-independent cell death. We outline what we know about their mechanism, potential roles in vivo and define outstanding questions. Finally, we review data arguing that the means by which a cell dies actually matters, focusing our discussion on inflammatory aspects of cell death.

Free Radicals in Cross Talk Between Autophagy and Apoptosis

Abstract: Significance: Oxidative (reactive oxygen species [ROS]) and nitrosative (reactive nitrogen species [RNS]) stress affects many physiological processes, including survival and death. Although high levels of ROS/RNS mainly causes cell death, low levels of free radicals directly modulate the activities of transcriptional factors, nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), p53, and nuclear factor (erythroid-derived) 2-like (Nrf2), and regulate numerous protein kinase cascades that participate in the regulation of the cross talk between autophagy and apoptosis. Recent Advances: Low levels of ROS modify Atg4 and high mobility group box 1 (HMGB1) proteins, activate AMP-activated protein kinase (AMPK) and apoptosis signal-regulating kinase/c-Jun N-terminal kinase (JNK) pathways, or transactivate various proteins that could upregulate autophagy, leading to reductions in apoptosis. Transactivation of antioxidant genes blocks apoptosis and serves as a feedback loop to reduce auto...

Mitochondria-mediated apoptosis in mammals

Abstract: The mitochondria-mediated caspase activation pathway is a major apoptotic pathway characterized by mitochondrial outer membrane permeabilization (MOMP) and subsequent release of cytochrome c into the cytoplasm to activate caspases. MOMP is regulated by the Bcl-2 family of proteins. This pathway plays important roles not only in normal development, maintenance of tissue homeostasis and the regulation of immune system, but also in human diseases such as immune disorders, neurodegeneration and cancer. In the past decades the molecular basis of this pathway and the regulatory mechanism have been comprehensively studied, yet a great deal of new evidence indicates that cytochrome c release from mitochondria does not always lead to irreversible cell death, and that caspase activation can also have non-death functions. Thus, many unsolved questions and new challenges are still remaining. Furthermore, the dysfunction of this pathway involved in cancer development is obvious, and targeting the pathway as a therapeutic strategy has been extensively explored, but the efficacy of the targeted therapies is still under development. In this review we will discuss the mitochondria-mediated apoptosis pathway and its physiological roles and therapeutic implications.

Multimodal immunogenic cancer cell death as a consequence of anticancer cytotoxic treatments.

Abstract: Apoptotic cell death generally characterized by a morphologically homogenous entity has been considered to be essentially non-immunogenic. However, apoptotic cancer cell death, also known as type 1 programmed cell death (PCD), was recently found to be immunogenic after treatment with several chemotherapeutic agents and oncolytic viruses through the emission of various danger-associated molecular patterns (DAMPs). Extensive studies have revealed that two different types of immunogenic cell death (ICD) inducers, recently classified by their distinct actions in endoplasmic reticulum (ER) stress, can reinitiate immune responses suppressed by the tumor microenvironment. Indeed, recent clinical studies have shown that several immunotherapeutic modalities including therapeutic cancer vaccines and oncolytic viruses, but not conventional chemotherapies, culminate in beneficial outcomes, probably because of their different mechanisms of ICD induction. Furthermore, interests in PCD of cancer cells have shifted from its classical form to novel forms involving autophagic cell death (ACD), programmed necrotic cell death (necroptosis), and pyroptosis, some of which entail immunogenicity after anticancer treatments. In this review, we provide a brief outline of the well-characterized DAMPs such as calreticulin (CRT) exposure, high-mobility group protein B1 (HMGB1), and adenosine triphosphate (ATP) release, which are induced by the morphologically distinct types of cell death. In the latter part, our review focuses on how emerging oncolytic viruses induce different forms of cell death and the combinations of oncolytic virotherapies with further immunomodulation by cyclophosphamide and other immunotherapeutic modalities foster dendritic cell (DC)-mediated induction of antitumor immunity. Accordingly, it is increasingly important to fully understand how and which ICD inducers cause multimodal ICD, which should aid the design of reasonably multifaceted anticancer modalities to maximize ICD-triggered antitumor immunity and eliminate residual or metastasized tumors while sparing autoimmune diseases.

RIPK1 ensures intestinal homeostasis by protecting the epithelium against apoptosis

Abstract: Receptor interacting protein kinase 1 (RIPK1) has an essential role in the signalling triggered by death receptors and pattern recognition receptors. RIPK1 is believed to function as a node driving NF-κB-mediated cell survival and inflammation as well as caspase-8 (CASP8)-dependent apoptotic or RIPK3/MLKL-dependent necroptotic cell death. The physiological relevance of this dual function has remained elusive because of the perinatal death of RIPK1 full knockout mice. To circumvent this problem, we generated RIPK1 conditional knockout mice, and show that mice lacking RIPK1 in intestinal epithelial cells (IECs) spontaneously develop severe intestinal inflammation associated with IEC apoptosis leading to early death. This early lethality was rescued by antibiotic treatment, MYD88 deficiency or tumour-necrosis factor (TNF) receptor 1 deficiency, demonstrating the importance of commensal bacteria and TNF in the IEC Ripk1 knockout phenotype. CASP8 deficiency, but not RIPK3 deficiency, rescued the inflammatory phenotype completely, indicating the indispensable role of RIPK1 in suppressing CASP8-dependent apoptosis but not RIPK3-dependent necroptosis in the intestine. RIPK1 kinase-dead knock-in mice did not exhibit any sign of inflammation, suggesting that RIPK1-mediated protection resides in its kinase-independent platform function. Depletion of RIPK1 in intestinal organoid cultures sensitized them to TNF-induced apoptosis, confirming the in vivo observations. Unexpectedly, TNF-mediated NF-κB activation remained intact in these organoids. Our results demonstrate that RIPK1 is essential for survival of IECs, ensuring epithelial homeostasis by protecting the epithelium from CASP8-mediated IEC apoptosis independently of its kinase activity and NF-κB activation.

Molecular mechanisms of hepatic apoptosis.

Abstract: Apoptosis is a prominent feature of liver diseases. Causative factors such as alcohol, viruses, toxic bile acids, fatty acids, drugs, and immune response, can induce apoptotic cell death via membrane receptors and intracellular stress. Apoptotic signaling network, including membrane death receptor-mediated cascade, reactive oxygen species (ROS) generation, endoplasmic reticulum (ER) stress, lysosomal permeabilization, and mitochondrial dysfunction, is intermixed each other, but one mechanism may dominate at a particular stage. Mechanisms of hepatic apoptosis are complicated by multiple signaling pathways. The progression of liver disease is affected by the balance between apoptotic and antiapoptotic capabilities. Therapeutic options of liver injury are impacted by the clear understanding toward mechanisms of hepatic apoptosis.

CRM1 inhibition induces tumor cell cytotoxicity and impairs osteoclastogenesis in multiple myeloma: molecular mechanisms and therapeutic implications.

Abstract: The key nuclear export protein CRM1/XPO1 may represent a promising novel therapeutic target in human multiple myeloma (MM). Here we showed that chromosome region maintenance 1 (CRM1) is highly expressed in patients with MM, plasma cell leukemia cells and increased in patient cells resistant to bortezomib treatment. CRM1 expression also correlates with increased lytic bone and shorter survival. Importantly, CRM1 knockdown inhibits MM cell viability. Novel, oral, irreversible selective inhibitors of nuclear export (SINEs) targeting CRM1 (KPT-185, KPT-330) induce cytotoxicity against MM cells (ED50<200 nM), alone and cocultured with bone marrow stromal cells (BMSCs) or osteoclasts (OC). SINEs trigger nuclear accumulation of multiple CRM1 cargo tumor suppressor proteins followed by growth arrest and apoptosis in MM cells. They further block c-myc, Mcl-1, and nuclear factor κB (NF-κB) activity. SINEs induce proteasome-dependent CRM1 protein degradation; concurrently, they upregulate CRM1, p53-targeted, apoptosis-related, anti-inflammatory and stress-related gene transcripts in MM cells. In SCID mice with diffuse human MM bone lesions, SINEs show strong anti-MM activity, inhibit MM-induced bone lysis and prolong survival. Moreover, SINEs directly impair osteoclastogenesis and bone resorption via blockade of RANKL-induced NF-κB and NFATc1, with minimal impact on osteoblasts and BMSCs. These results support clinical development of SINE CRM1 antagonists to improve patient outcome in MM.

Rescue of Hippo coactivator YAP1 triggers DNA damage-induced apoptosis in hematological cancers

Abstract: Oncogene-induced DNA damage elicits genomic instability in epithelial cancer cells, but apoptosis is blocked through inactivation of the tumor suppressor p53. In hematological cancers, the relevance of ongoing DNA damage and the mechanisms by which apoptosis is suppressed are largely unknown. We found pervasive DNA damage in hematologic malignancies, including multiple myeloma, lymphoma and leukemia, which leads to activation of a p53-independent, proapoptotic network centered on nuclear relocalization of ABL1 kinase. Although nuclear ABL1 triggers cell death through its interaction with the Hippo pathway coactivator YAP1 in normal cells, we show that low YAP1 levels prevent nuclear ABL1-induced apoptosis in these hematologic malignancies. YAP1 is under the control of a serine-threonine kinase, STK4. Notably, genetic inactivation of STK4 restores YAP1 levels, triggering cell death in vitro and in vivo. Our data therefore identify a new synthetic-lethal strategy to selectively target cancer cells presenting with endogenous DNA damage and low YAP1 levels.

Carbon dots prepared from ginger exhibiting efficient inhibition of human hepatocellular carcinoma cells

Abstract: Fluorescent carbon nanodots (C-dots; 4.3 ± 0.8 nm) from fresh tender ginger juice provide high suppression of the growth of human hepatocellular carcinoma cells (HepG2), with low toxicity to normal mammary epithelial cells (MCF-10A) and normal liver cells (FL83B). The inhibition is selective to HepG2 over other tested cancer cells, including human lung cancer cell line (A549), human breast cancer cell line (MDA-MB-231), and human cervical cancer cell line (HeLa). Western blot results reveal that the C-dots up-regulate the expression of p53 protein only in the HepG2 cell line. The 50% inhibiting concentration (IC50) value of the C-dots on HepG2 cells is 0.35 mg mL−1. Image cytometry results show significant uptake of C-dots by HepG2 cells that induce intracellular production of reactive oxygen species (ROS, 18.2-fold increased), while other cells remain almost the same in ROS levels after treatment with C-dots (1.11 mg mL−1). The C-dots trigger the pro-apoptotic factor to promote HepG2 cell apoptosis. The C-dots effectively inhibit the growth of tumors in nude mice (104 ± 14 vs. 3.7 ± 0.2 mg with and without treatment within 14 days).

Metformin promotes autophagy and apoptosis in esophageal squamous cell carcinoma by downregulating Stat3 signaling.

Abstract: The antidiabetic drug metformin exerts chemopreventive and antineoplastic effects in many types of malignancies. However, the mechanisms responsible for metformin actions appear diverse and may differ in different types of cancer. Understanding the molecular and cellular mechanisms specific for different cancers is important to optimize strategy for metformin treatment in different cancer types. Here, we investigate the in vitro and in vivo effects of metformin on esophageal squamous cell carcinoma (ESCC) cells. Metformin selectively inhibited cell growth in ESCC tumor cells but not immortalized noncancerous esophageal epithelial cells. In addition to apoptosis, metformin triggered autophagy. Pharmacological or genetic inhibition of autophagy sensitized ESCC cells to metformin-induced apoptotic cell death. Mechanistically, signal transducer and activator of transcription 3 (Stat3) and its downstream target Bcl-2 was inactivated by metformin treatment. Accordingly, small interfering RNA (siRNA)-mediated Stat3 knockdown enhanced metformin-induced autophagy and apoptosis, and concomitantly enhanced the inhibitory effect of metformin on cell viability. Similarly, the Bcl-2 proto-oncogene, an inhibitor of both apoptosis and autophagy, was repressed by metformin. Ectopic expression of Bcl-2 protected cells from metformin-mediated autophagy and apoptosis. In vivo, metformin downregulated Stat3 activity and Bcl-2 expression, induced apoptosis and autophagy, and inhibited tumor growth. Together, inactivation of Stat3-Bcl-2 pathway contributes to metformin-induced growth inhibition of ESCC by facilitating crosstalk between apoptosis and autophagy.

Metformin induces apoptosis and cell cycle arrest mediated by oxidative stress, AMPK and FOXO3a in MCF-7 breast cancer cells.

Abstract: Recent studies have demonstrated that the anti-diabetic drug, metformin, can exhibit direct antitumoral effects, or can indirectly decrease tumor proliferation by improving insulin sensitivity. Despite these recent advances, the underlying molecular mechanisms involved in decreasing tumor formation are not well understood. In this study, we examined the antiproliferative role and mechanism of action of metformin in MCF-7 cancer cells treated with 10 mM of metformin for 24, 48, and 72 hours. Using BrdU and the MTT assay, it was found that metformin demonstrated an antiproliferative effect in MCF-7 cells that occurred in a time- and concentration- dependent manner. Flow cytometry was used to analyze markers of cell cycle, apoptosis, necrosis and oxidative stress. Exposure to metformin induced cell cycle arrest in G0-G1 phase and increased cell apoptosis and necrosis, which were associated with increased oxidative stress. Gene and protein expression were determined in MCF-7 cells by real time RT-PCR and western blotting, respectively. In MCF-7 cells metformin decreased the activation of IRβ, Akt and ERK1/2, increased p-AMPK, FOXO3a, p27, Bax and cleaved caspase-3, and decreased phosphorylation of p70S6K and Bcl-2 protein expression. Co-treatment with metformin and H2O2 increased oxidative stress which was associated with reduced cell number. In the presence of metformin, treating with SOD and catalase improved cell viability. Treatment with metformin resulted in an increase in p-p38 MAPK, catalase, MnSOD and Cu/Zn SOD protein expression. These results show that metformin has an antiproliferative effect associated with cell cycle arrest and apoptosis, which is mediated by oxidative stress, as well as AMPK and FOXO3a activation. Our study further reinforces the potential benefit of metformin in cancer treatment and provides novel mechanistic insight into its antiproliferative role.

Regulation of human neutrophil apoptosis and lifespan in health and disease.

Abstract: Neutrophils (also called polymorphonuclear leukocytes, PMNs) are the most abundant white blood cells in humans and play a central role in innate host defense. Another distinguishing feature of PMNs is their short lifespan. Specifically, these cells survive for less than 24 hours in the bloodstream and are inherently pre-programed to die by constitutive apoptosis. Recent data indicate that this process is regulated by intracellular signaling and changes in gene expression that define an “apoptosis differentiation program.” Infection typically accelerates neutrophil turnover, and as such, phagocytosis-induced cell death (PICD) and subsequent clearance of the corpses by macrophages are essential for control of infection and resolution of the inflammatory response. Herein we reprise recent advances in our understanding of the molecular mechanisms of neutrophil apoptosis with a focus on regulatory factors and pathway intermediates that are specific to this cell type. In addition, we summarize mechanisms whereby perturbation of PMN death contributes directly to the pathogenesis of many infectious and inflammatory disease states.

Targeting the programmed cell death 1: programmed cell death ligand 1 pathway reverses T cell exhaustion in patients with sepsis

Abstract: A major pathophysiologic mechanism in sepsis is impaired host immunity which results in failure to eradicate invading pathogens and increased susceptibility to secondary infections. Although many immunosuppressive mechanisms exist, increased expression of the inhibitory receptor programmed cell death 1 (PD-1) and its ligand (PD-L1) are thought to play key roles. The newly recognized phenomenon of T cell exhaustion is mediated in part by PD-1 effects on T cells. This study tested the ability of anti-PD-1 and anti-PD-L1 antibodies to prevent apoptosis and improve lymphocyte function in septic patients. Blood was obtained from 43 septic and 15 non-septic critically-ill patients. Effects of anti-PD-1, anti-PD-L1, or isotype-control antibody on lymphocyte apoptosis and interferon gamma (IFN-γ) and interleukin-2 (IL-2) production were quantitated by flow cytometry. Lymphocytes from septic patients produced decreased IFN-γ and IL-2 and had increased CD8 T cell expression of PD-1 and decreased PD-L1 expression compared to non-septic patients (P<0.05). Monocytes from septic patients had increased PD-L1 and decreased HLA-DR expression compared to non-septic patients (P<0.01). CD8 T cell expression of PD-1 increased over time in ICU as PD-L1, IFN-γ, and IL2 decreased. In addition, donors with the highest CD8 PD-1 expression together with the lowest CD8 PD-L1 expression also had lower levels of HLA-DR expression in monocytes, and an increased rate of secondary infections, suggestive of a more immune exhausted phenotype. Treatment of cells from septic patients with anti-PD-1 or anti-PD-L1 antibody decreased apoptosis and increased IFN-γ and IL-2 production in septic patients; (P<0.01). The percentage of CD4 T cells that were PD-1 positive correlated with the degree of cellular apoptosis (P<0.01). In vitro blockade of the PD-1:PD-L1 pathway decreases apoptosis and improves immune cell function in septic patients. The current results together with multiple positive studies of anti-PD-1 and anti-PD-L1 in animal models of bacterial and fungal infections and the relative safety profile of anti-PD-1/anti-PD-L1 in human oncology trials to date strongly support the initiation of clinical trials testing these antibodies in sepsis, a disorder with a high mortality.

Caspases: a molecular switch node in the crosstalk between autophagy and apoptosis.

Abstract: Autophagy and apoptosis are two important catabolic processes contributing to the maintenance of cellular and tissue homeostasis. Autophagy controls the turnover of protein aggregates and damaged organelles within cells, while apoptosis is the principal mechanism by which unwanted cells are dismantled and eliminated from organisms. Despite marked differences between these two pathways, they are highly interconnected in determining the fate of cells. Intriguingly, caspases, the primary drivers of apoptotic cell death, play a critical role in mediating the complex crosstalk between autophagy and apoptosis. Pro-apoptotic signals can converge to activate caspases to execute apoptotic cell death. In addition, activated caspases can degrade autophagy proteins (i.e., Beclin-1, Atg5, and Atg7) to shut down the autophagic response. Moreover, caspases can convert pro-autophagic proteins into pro-apoptotic proteints to trigger apoptotic cell death instead. It is clear that caspases are important in both apoptosis and autophagy, thus a detailed deciphering of the role of caspases in these two processes is still required to clarify the functional relationship between them. In this article, we provide a current overview of caspases in its interplay between autophagy and apoptosis. We emphasized that defining the role of caspases in autophagy-apoptosis crosstalk will provide a framework for more precise manipulation of these two processes during cell death.

Regulated Cell Death: Signaling and Mechanisms

Abstract: Cell turnover is a fundamental feature in metazoans. Cells can die passively, as a consequence of severe damage to their structural integrity, or actively, owing to a more confined biological disruption such as DNA damage. Passive cell death is uncontrolled and often harmful to the organism. In contrast, active cell death is tightly regulated and serves to support the organism's life. Apoptosis—the primary form of regulated cell death—is relatively well defined. Necroptosis—an alternative, distinct kind of regulated cell death discovered more recently—is less well understood. Apoptosis and necroptosis can be triggered either from within the cell or by extracellular stimuli. Certain signaling components, including several death ligands and receptors, can regulate both processes. Whereas apoptosis is triggered and executed via intracellular proteases called caspases, necroptosis is suppressed by caspase activity. Here we highlight current understanding of the key signaling mechanisms that control regulated ...

Role of mitochondria ROS generation in ethanol-induced NLRP3 inflammasome activation and cell death in astroglial cells

Abstract: Toll-like receptors (TLRs) and Nod-like receptors (NLRs) are innate immunity sensors that provide an early/effective response to pathogenic or injury conditions. We have reported that ethanol-induced TLR4 activation triggers signaling inflammatory responses in glial cells, causing neuroinflammation and brain damage. However, it is uncertain if ethanol is able to activate NLRs /inflammasome in astroglial cells, which is the mechanism of activation, and whether there is crosstalk between both immune sensors in glial cells. Here we show that chronic ethanol treatment increases the co-localization of caspase-1 with GFAP+ cells, and up-regulates IL-1β and IL-18 in the frontal medial cortex in WT, but not in TLR4 knock-out mice. We further show that cultured cortical astrocytes expressed several inflammasomes (NLRP3, AIM2, NLRP1 and IPAF), although NLRP3 mRNA is the predominant form. Ethanol, as ATP and LPS treatments, up-regulates NLRP3 expression, and causes caspase-1 cleavage and the release of IL-1β and IL-18 in astrocytes supernatant. Ethanol-induced NLRP3/caspase-1 activation is mediated by mitochondrial (m) ROS generation because when using a specific mitochondria ROS scavenger, the mito-TEMPO (500 M) or NLRP3 blocking peptide (4g/ml) or a specific caspase-1 inhibitor, Z-YVAD-FMK (10 M), abrogates mROS release and reduces the up-regulation of IL-1β and IL-18 induced by ethanol or LPS or ATP. Confocal microscopy studies further confirm that ethanol, ATP or LPS promotes NLRP3/caspase-1 complex recruitment within the mitochondria to promote cell death by caspase-1-mediated pyroptosis, which accounts for ≈ 73 % of total cell death (≈22%) and the remaining (≈25%) die by caspase-3-dependent apoptosis. Suppression of the TLR4 function abrogates most ethanol effects on NLRP3 activation and reduces cell death. These findings suggest that NLRP3 participates, in ethanol-induced neuroinflammation and highlight the NLRP3/TLR4 crosstalk in ethanol-induced brain injury.