DNase activation by hypoxia-acidosis parallels but is independent of programmed cell death

Pyroptosis inhibitors MCC950 and VX-765 mitigate myocardial injury by alleviating oxidative stress, inflammation, and apoptosis in acute myocardial hypoxia

Acute myocardial infarction (AMI) is a prevalent cardiovascular disease with high morbidity and mortality rates worldwide. Pyroptosis is an inflammatory form of programmed cell death that has been linked to various pathological conditions. However, its exact contribution to the onset and progression of heart injury in AMI has not yet fully elucidated. Herein, we established mouse AMI model by ligating the left anterior descending artery and performed transcriptome analysis during the early phase of AMI. Mouse HL-1 and human AC-16 cardiomyocytes were subjected to hypoxia to simulate ischemic injury in vitro. Our results revealed a significant activation of the inflammatory response at 3 h post-ligation, as confirmed by RNA sequencing. We identified the occurrence of NLRP3 inflammasome-mediated pyroptosis in the cardiac tissues of human cases with AMI, as well as in mouse models of AMI and hypoxia-induced cardiomyocytes, using immunohistochemistry staining and Western blotting assays. Concurrently, pharmacological inhibition of NLRP3 inflammasome-mediated pyroptosis with MCC950 and VX-765 effectively decreased hypoxia-induced cardiomyocytes injury, while mitigating myocardial oxidative stress, apoptosis and inflammation caused by hypoxia. Moreover, the circulating levels of gasdermin D (GSDMD), the pyroptosis executor, were remarkably elevated in the plasma of mice with early AMI and in the supernatant of hypoxia-exposed cardiomyocytes in a time-dependent manner using ELISA and Western blotting. Furthermore, the change in circulating GSDMD positively correlated with Creatine Kinase-MB (CK-MB) in the plasma of early-stage AMI mouse. In summary, these findings indicated a critical role for NLRP3 inflammasome-mediated pyroptosis in the progression of AMI, the administration of MCC950 and VX-765 may be attractive candidate therapeutic approaches for cardiac injury caused by acute hypoxia or even AMI. Additionally, the circulating GSDMD exhibits potential as a newly diagnostic biomarker for AMI.

Association of Acidemia With Short-Term Mortality of Acute Myocardial Infarction: A Retrospective Study Base on MIMIC-III Database

Acute myocardial infarction (AMI) is a leading cause of death and not a few of these patients are combined with acidemia. This study aimed to detect the association of acidemia with short-term mortality of AMI patients. A total of 972 AMI patients were selected from the Medical Information Mart for Intensive Care (MIMIC) III database for analysis. Propensity-score matching (PSM) was used to reduce the imbalance. Kaplan-Meier survival analysis was used to compare the mortality, and Cox-proportional hazards model was used to detect related factors associated with mortality. After PSM, a total of 345 non-acidemia patients and 345 matched acidemia patients were included. The non-acidemia patients had a significantly lower 30-day mortality (20.0% vs. 28.7%) and lower 90-day mortality (24.9% vs. 31.9%) than the acidemia patients (P < 0.001 for all). The severe-acidemia patients (PH < 7.25) had the highest 30-day mortality (52.6%) and 90-day mortality (53.9%) than non-acidemia patients and mild-acidemia (7.25 ≤ PH < 7.35) patients (P < 0.001). In Cox-proportional hazards model, acidemia was associated with improved 30-day mortality (HR = 1.518; 95%CI = 1.110-2.076, P = 0.009) and 90-day mortality (HR = 1.378; 95%CI = 1.034 -1.837, P = 0.029). These results suggest that severe acidemia is associated with improved 30-day mortality and 90-day mortality of AMI patients.

MiR-126-HMGB1-HIF-1 Axis Regulates Endothelial Cell Inflammation during Exposure to Hypoxia-Acidosis

Crosstalk between molecular regulators miR-126, hypoxia-inducible factor 1-alpha (HIF-1-α), and high-mobility group box-1 (HMGB1) contributes to the regulation of inflammation and angiogenesis in multiple physiological and pathophysiological settings. Here, we present evidence of an overriding role for miR-126 in the regulation of HMGB1 and its downstream proinflammatory effectors in endothelial cells subjected to hypoxia with concurrent acidosis (H/A). Methods. Primary mouse endothelial cells (PMEC) were exposed to hypoxia or H/A to simulate short or chronic low-flow ischemia, respectively. RT-qPCR quantified mRNA transcripts, and proteins were measured by western blot. ROS were quantified by fluorogenic ELISA and luciferase reporter assays employed to confirm an active miR-126 target in the HMGB1 3'UTR. Results. Enhanced expression of miR-126 in PMECs cultured under neutral hypoxia was suppressed under H/A, whereas the HMGB1 expression increased sequentially under both conditions. Enhanced expression of HMGB1 and downstream inflammation markers was blocked by the premiR-126 overexpression and optimized by antagomiR. Compared with neutral hypoxia, H/A suppressed the HIF-1α expression independently of miR-126. The results show that HMGB1 and downstream effectors are optimally induced by H/A relative to neutral hypoxia via crosstalk between hypoxia signaling, miR-126, and HIF-1α, whereas B-cell lymphoma 2(Bcl2), a HIF-1α, and miR-126 regulated gene expressed optimally under neutral hypoxia. Conclusion. Inflammatory responses of ECs to H/A are dynamically regulated by the combined actions of hypoxia, miR-126, and HIF-1α on the master regulator HMGB1. The findings may be relevant to vascular diseases including atherosclerotic occlusion and interiors of plaque where coexisting hypoxia and acidosis promote inflammation as a defining etiology.

Neuronal Cell Death

Neuronal cell death occurs extensively during development and pathology, where it is especially important because of the limited capacity of adult neurons to proliferate or be replaced. The concept of cell death used to be simple as there were just two or three types, so we just had to work out which type was involved in our particular pathology and then block it. However, we now know that there are at least a dozen ways for neurons to die, that blocking a particular mechanism of cell death may not prevent the cell from dying, and that non-neuronal cells also contribute to neuronal death. We review here the mechanisms of neuronal death by intrinsic and extrinsic apoptosis, oncosis, necroptosis, parthanatos, ferroptosis, sarmoptosis, autophagic cell death, autosis, autolysis, paraptosis, pyroptosis, phagoptosis, and mitochondrial permeability transition. We next explore the mechanisms of neuronal death during development, and those induced by axotomy, aberrant cell-cycle reentry, glutamate (excitoxicity and oxytosis), loss of connected neurons, aggregated proteins and the unfolded protein response, oxidants, inflammation, and microglia. We then reassess which forms of cell death occur in stroke and Alzheimer's disease, two of the most important pathologies involving neuronal cell death. We also discuss why it has been so difficult to pinpoint the type of neuronal death involved, if and why the mechanism of neuronal death matters, the molecular overlap and interplay between death subroutines, and the therapeutic implications of these multiple overlapping forms of neuronal death.

BNIP3 promotes calcium and calpain-dependent cell death

AIMS

Loss of cardiac muscle by programmed cell death contributes to the progression of ischemic heart disease. Hypoxia, metabolite waste buildup and energy depletion are components of ischemia which may initiate caspase dependent and independent cell death pathways. Previous work from our laboratory has shown that combined hypoxia with acidosis, a hallmark of ischemia promotes cardiac myocyte injury with increasing severity as the pH declines. Hypoxia-acidosis was demonstrated to activate the pro-apoptotic Bcl-2 protein BNIP3 which initiated opening of the mitochondrial permeability transition pore and cell death in the absence of caspase activation. Because calpains are known to contribute to ischemic myocardial damage in some models, we hypothesized that they are intermediates in the BNIP3-mediated death caused by hypoxia-acidosis.

MAIN METHODS

Neonatal rat cardiac myocytes were subjected to hypoxia with and without acidosis and the contribution of calpains to hypoxia-acidosis cell death determined.

KEY FINDINGS

Here we report that the death pathway activated by hypoxia-acidosis is driven by a combination of calcium-activated calpains and pro-death factors (DNases) secreted by the mitochondria. Cytochrome c accumulated in the cytoplasm during hypoxia-acidosis but caspase activity was repressed through a calpain-dependent process that prevents the cleavage of procaspase 3. Calpain inhibitors provide vigorous protection against hypoxia-acidosis-induced programmed death. Knockdown of BNIP3 with siRNA prevented calpain activation confirming a central role of BNIP3 in this pathway.

SIGNIFICANCE

The results implicate BNIP3 and calpain as dependent components of cardiac myocyte death caused by hypoxia-acidosis.

Bnip3 Binds and Activates p300: Possible Role in Cardiac Transcription and Myocyte Morphology

Bnip3 is a hypoxia-regulated member of the Bcl-2 family of proteins that is implicated in apoptosis, programmed necrosis, autophagy and mitophagy. Mitochondria are thought to be the primary targets of Bnip3 although its activities may extend to the ER, cytoplasm, and nucleus. Bnip3 is induced in the heart by ischemia and pressure-overload, and may contribute to cardiomyopathy and heart failure. Only mitochondrial-dependent programmed death actions have been described for Bnip3 in the heart. Here we describe a novel activity of Bnip3 in cultured cardiac myocytes and transgenic mice overexpressing Bnip3 in the heart (Bnip3-TG). In cultured myocytes Bnip3 bound and activated the acetyltransferase p300, increased acetylation of histones and the transcription factor GATA4, and conferred p300 and GATA4-sensitive cellular morphological changes. In intact Bnip3-TG hearts Bnip3 also bound p300 and GATA4 and conferred enhanced GATA4 acetylation. Bnip3-TG mice underwent age-dependent ventricular dilation and heart failure that was partially prevented by p300 inhibition with curcumin. The results suggest that Bnip3 regulates cardiac gene expression and perhaps myocyte morphology by activating nuclear p300 acetyltransferase activity and hyperacetylating histones and p300-selective transcription factors.

Inhibition of the vacuolar ATPase induces Bnip3-dependent death of cancer cells and a reduction in tumor burden and metastasis

The pro-apoptotic protein Bnip3 is induced by hypoxia and is present in the core regions of most solid tumors. Bnip3 induces programmed necrosis by an intrinsic caspase independent mitochondrial pathway. Many tumor cells have evolved pathways to evade Bnip3-mediated death attesting to the physiological relevance of the survival threat imposed by Bnip3. We have reported that acidosis can trigger the Bnip3 death pathway in hypoxic cells therefore we hypothesized that manipulation of intracellular pH by pharmacological inhibition of the vacuolar (v)ATPase proton pump, a significant pH control pathway, may activate Bnip3 and promote death of hypoxic cells within the tumor. Here we confirm that bafilomycin A1 (BafA1), a selective vATPase inhibitor, significantly increased death of breast cancer cells in a hypoxia and Bnip3-dependent manner and significantly reduced tumor growth in MCF7 and MDA-MB-231 mouse xenografts. Combined treatment of cells with BafA1 and the ERK1/2 inhibitor U0126 further augmented cell death. Combined treatment of mice containing MDA-MB-231 xenografts with BafA1 and the ERK1/2 inhibitor sorafenib was superior to either treatment alone and supported tumor regression. BafA1 and sorafenib treatments alone reduced MDA-MB-231 cell metastasis and again the combination was significantly more effective than either treatment alone and was without apparent side effects. These results present a novel mechanism to destroy hypoxic tumor cells that may help reverse the resistance of hypoxic tumors to radiation and chemotherapy and perhaps target tumor stem cells.

Poly(ADP-ribose) polymerase-1 causes mitochondrial damage and neuron death mediated by Bnip3

Excessive pathophysiological activity of the nuclear enzyme poly(ADP-ribose) polymerase-1 (PARP1) causes neuron death in brain hypoxia/ischemia by inducing mitochondrial permeability transition and nuclear translocation of apoptosis-inducing factor (AIF). Bcl-2/adenovirus E1B 19 kDa-interacting protein (Bnip3) is a prodeath BH3-only Bcl-2 protein family member that is induced in hypoxia, and has effects on mitochondrial permeability and neuronal survival similar to those caused by PARP1 activation. We hypothesized that Bnip3 is a critical mediator of PARP1-induced mitochondrial dysfunction and neuron death. Hypoxic death of mouse cortical neuron cultures was mitigated by deletion of either PARP1 or Bnip3, indicating that both factors are involved. Direct normoxic PARP1 activation by a DNA alkylating agent enhanced Bnip3 expression, and caused Bnip3-dependent mitochondrial membrane permeability, AIF translocation, and neuron death. Hypoxia produced PARP1-dependent depletion of nicotinamide adenine dinucleotide (NAD(+)) and inhibition of the NAD(+)-dependent class III histone deactelyase (HDAC) sirtuin-1 (SIRT1). This, in turn, led to hyperacetylation and nuclear localization of the forkhead box (Fox) protein FoxO3a, followed by enhanced association of FoxO3a with the Bnip3 upstream promoter region, increased levels of Bnip3 transcript, and elevated mitochondrial Bnip3 immunoreactivity. Finally, FoxO3a silencing using a lentiviral short hairpin RNA approach significantly reduced hypoxic Bnip3 expression, mitochondrial damage, and neuron death. Together, these data illustrate a direct PARP1-mediated hypoxic signaling pathway involving NAD(+) depletion, SIRT1 inhibition, FoxO3a-driven Bnip3 generation, and mitochondrial AIF release.

Dihydroartemisinin is a Hypoxia-Active Anti-Cancer Drug in Colorectal Carcinoma Cells

Tumor hypoxia is one main biological factor that drives resistance to chemotherapy and radiotherapy. To develop a novel strategy for overcoming hypoxia-induced therapy resistance, we examined the anti-neoplastic activity of the reactive oxygen donor dihydroartemisinin (DHA) in human colon cancer cell lines in normoxia and severe hypoxia. In addition, we analyzed the involvement of the intrinsic apoptosis pathway for DHA-mediated cytotoxicity in HCT116 cells in short-term and long-term in vitro assays. When applied at lower concentrations (≤25 μM), DHA induced apoptosis in Colo205, HCT15, and HCT116 cells, whereas necrotic cell death was increased when cells were treated with higher DHA concentrations (50 μM). However, no preference for DHA-induced apoptosis or necrosis could be detected between the treatment under normoxic or hypoxic conditions. Moreover, DHA potently reduced clonogenic survival of HCT116 cells in normoxia and hypoxia. Treatment of HCT116 cells with 25 μM DHA resulted in activation of Bax under normoxic and hypoxic conditions. Interestingly, cytochrome c release from the mitochondria and caspase-activation were observed only under normoxic conditions, whereas, under hypoxic conditions DHA induced a caspase-independent apoptosis-like cell death. However, under both conditions, generation of reactive oxygen species was an important mediator of DHA-induced toxicity. Further molecular analysis suggests that DHA-mediated cell death involves different sets of pro-apoptotic Bcl-2 family members. The pronounced cytotoxic activity of DHA in severe hypoxia as well as normoxia offers new perspectives for targeting the hypoxic tumor cell fraction to improve treatment outcome for cancer patients.

E1B and E4 oncoproteins of adenovirus antagonize the effect of apoptosis inducing factor

Adenovirus inundates the productively infected cell with linear, double-stranded DNA and an abundance of single-stranded DNA. The cellular response to this stimulus is antagonized by the adenoviral E1B and E4 early genes. A mutant group C adenovirus that fails to express the E1B-55K and E4orf3 genes is unable to suppress the DNA-damage response. Cells infected with this double-mutant virus display significant morphological heterogeneity at late times of infection and frequently contain fragmented nuclei. Nuclear fragmentation was due to the translocation of apoptosis inducing factor (AIF) from the mitochondria into the nucleus. The release of AIF was dependent on active poly(ADP-ribose) polymerase-1 (PARP-1), which appeared to be activated by viral DNA replication. Nuclear fragmentation did not occur in AIF-deficient cells or in cells treated with a PARP-1 inhibitor. The E1B-55K or E4orf3 proteins independently prevented nuclear fragmentation subsequent to PARP-1 activation, possibly by altering the intracellular distribution of PAR-modified proteins.

Mitochondrial membrane permeabilization and cell death during myocardial infarction: roles of calcium and reactive oxygen species

Excess generation of reactive oxygen species (ROS) and cytosolic calcium accumulation play major roles in the initiation of programmed cell death during acute myocardial infarction. Cell death may include necrosis, apoptosis and autophagy, and combinations thereof. During ischemia, calcium handling between the sarcoplasmic reticulum and myofilament is disrupted and calcium is diverted to the mitochondria causing swelling. Reperfusion, while essential for survival, reactivates energy transduction and contractility and causes the release of ROS and additional ionic imbalance. During acute ischemia-reperfusion, the principal death pathways are programmed necrosis and apoptosis through the intrinsic pathway, initiated by the opening of the mitochondrial permeability transition pore and outer mitochondrial membrane permeabilization, respectively. Despite intense investigation, the mechanisms of action and modes of regulation of mitochondrial membrane permeabilization are incompletely understood. Extrinsic apoptosis, necroptosis and autophagy may also contribute to ischemia-reperfusion injury. In this review, the roles of dysregulated calcium and ROS and the contributions of Bcl-2 proteins, as well as mitochondrial morphology in promoting mitochondrial membrane permeability change and the ensuing cell death during myocardial infarction are discussed.