Identification of an inhibitor of caspase activation from heart extracts; ATP blocks apoptosome formation

Effects of caspase activity of yak meat and internal environment changing during aging

The objective of this study was to investigate the protease family caspases in skeletal muscle and their potential contribution to postmortem proteolysis and meat tenderization. Nine yaks were slaughtered, and samples of Longissimus dorsal were injected with AC-DEVD-CHO at a ratio of 1:1 (w/v) and then stored at 4 °C for 2, 6, 12, 24, 72, and 120 h. Results indicate that the morphological changes of the muscle fibers are significantly obstructed, which is not conducive to the subsequent degradation of proteins. After inhibiting the activity of Caspase- 3, the activity of Caspase-8 and 9 and the energy metabolism was affected. In the case of without inhibition of caspase, the pH value decreased and then increased. The meat color and the water retention are better, the muscle fiber skeleton protein degradation is remarkable, the tenderness is improved. Furthermore, yak meat tenderness was improved by apoptotic pathway during aging.

Mitochondrial Quality Control in Cardiac-Conditioning Strategies against Ischemia-Reperfusion Injury

Mitochondria are the central target of ischemic preconditioning and postconditioning cardioprotective strategies, which consist of either the application of brief intermittent ischemia/reperfusion (I/R) cycles or the administration of pharmacological agents. Such strategies reduce cardiac I/R injury by activating protective signaling pathways that prevent the exacerbated production of reactive oxygen/nitrogen species, inhibit opening of mitochondrial permeability transition pore and reduce apoptosis, maintaining normal mitochondrial function. Cardioprotection also involves the activation of mitochondrial quality control (MQC) processes, which replace defective mitochondria or eliminate mitochondrial debris, preserving the structure and function of the network of these organelles, and consequently ensuring homeostasis and survival of cardiomyocytes. Such processes include mitochondrial biogenesis, fission, fusion, mitophagy and mitochondrial-controlled cell death. This review updates recent advances in MQC mechanisms that are activated in the protection conferred by different cardiac conditioning interventions. Furthermore, the role of extracellular vesicles in mitochondrial protection and turnover of these organelles will be discussed. It is concluded that modulation of MQC mechanisms and recognition of mitochondrial targets could provide a potential and selective therapeutic approach for I/R-induced mitochondrial dysfunction.

Apoptosome-dependent myotube formation involves activation of caspase-3 in differentiating myoblasts

Caspase-2, -9, and -3 are reported to control myoblast differentiation into myotubes. This had been previously explained by phosphatidylserine exposure on apoptotic myoblasts inducing differentiation in neighboring cells. Here we show for the first time that caspase-3 is activated in the myoblasts undergoing differentiation. Using RNAi, we also demonstrate that differentiation requires both cytochrome c and Apaf-1, and by using a new pharmacological approach, we show that apoptosome formation is required. We also show that Bid, whose cleavage links caspase-2 to the mitochondrial death pathway, was required for differentiation, and that the caspase cleavage product, tBid, was generated during differentiation. Taken together, these data suggest that myoblast differentiation requires caspase-2 activation of the mitochondrial death pathway, and that this occurs in the cells that differentiate. Our data also reveal a hierarchy of caspases in differentiation with caspase-2 upstream of apoptosome activation, and exerting a more profound control of differentiation, while caspases downstream of the apoptosome primarily control cell fusion.

A new split-luciferase complementation assay identifies pentachlorophenol as an inhibitor of apoptosome formation

The expense and time required for in vivo reproductive and developmental toxicity studies have driven the development of in vitro alternatives. Here, we used a new in vitro split luciferase‐based assay to screen a library of 177 toxicants for inhibitors of apoptosome formation. The apoptosome contains seven Apoptotic Protease‐Activating Factor‐1 (Apaf‐1) molecules and induces cell death by activating caspase‐9. Apaf‐1‐dependent caspase activation also plays an important role in CNS development and spermatogenesis. In the in vitro assay, Apaf‐1 fused to an N‐terminal fragment of luciferase binds to Apaf‐1 fused to a C‐terminal fragment of luciferase and reconstitutes luciferase activity. Our assay indicated that pentachlorophenol (PCP) inhibits apoptosome formation, and further investigation revealed that PCP binds to cytochrome c. PCP is a wood preservative that reduces male fertility by ill‐defined mechanisms. Although the data show that PCP inhibited apoptosome formation, the concentration required suggests that other mechanisms may be more important for PCP's effects on spermatogenesis. Nonetheless, the data demonstrate the utility of the new assay in identifying apoptosome inhibitors, and we suggest that the assay may be useful in screening for reproductive and developmental toxicants.

Paeoniflorin improves cardiac function and decreases adverse postinfarction left ventricular remodeling in a rat model of acute myocardial infarction

Background

Paeoniflorin (PF) is the active component of Paeonia lactiflora Pall. or Paeonia veitchii Lynch. This study was, therefore, aimed to evaluate the improvement and mechanism of the PF on ventricular remodeling in rats with acute myocardial infarction (AMI).

Materials and methods

In this study, AMI model was established by ligating the anterior descending coronary artery in Wistar rats. After 4 weeks gavage of PF, the apparent signs and the left ventricle weight index of Wistar rats were observed. The left ventricular ejection fraction (LVEF) was evaluated by Doppler ultrasonography. Changes in cardiac morphology were observed by pathologic examination, and apoptosis was observed by the terminal deoxynucleotidyl transferase dUTP nick end labeling assay. In addition, enzyme-linked immunosorbent assay was used to detect the expression of tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6) interleukin-10 (IL-10) and brain natriuretic peptide (BNP). Immunohistochemistry and Western blot method were applied to detect Caspase-3 and Caspase-9.

Results

Compared with the model control, the survival conditions of rats in all treatment groups were generally improved after PF treatment. LVEF was significantly increased, and both left ventricular end-diastolic inner diameter and left ventricular end-systolic inner diameter were significantly reduced. Moreover, pathologic examination showed that the myocardium degeneration of the rats treated with PF was decreased, including neater arrangement, more complete myofilament, more uniform gap and less interstitial collagen fibers. Furthermore, the mitochondrial structure of cardiomyocytes was significantly improved. The ultrastructure was clear, and the arrangement of myofilament was more regular. Also, the expression of Caspase-3 and Caspase-9 was inhibited, and apoptosis was obviously reduced in the PF treatment groups. BNP, TNF-α and IL-6 were also decreased and IL-10 was increased in the treated rats.

Conclusion

PF could significantly improve the LVEF of rats. It decreased adverse left ventricular remodeling after myocardial infarction in rat models. The potential mechanism could be that PF decreased and inhibited BNP, TNF-α and IL-6, increased IL-10 and further inhibited the expression of Caspase-3 and Caspase-9, thus promoting ventricular remodeling.

In vitro toxicity of serum protein-adsorbed citrate-reduced gold nanoparticles in human lung adenocarcinoma cells

We examined the cytotoxicity effect of the serum protein coated gold nanoparticles (AuNPs) in the A549 cells. Negatively charged AuNPs were prepared by chemical reduction using citrate. The dimension and surface charge of AuNPs were characterized using transmission electron microscopy (TEM), dynamic light scattering (DLS), and zeta potential measurements. The AuNPs modified by the citrate anion were presumed to adsorb the serum proteins as indicated from the visible absorption spectroscopy, DLS, and quartz crystal microbalance (QCM) data. The QCM results indicated that among the constituents, fetal bovine serum (FBS) should be the major adsorbate species on the AuNPs incubated in the RPMI medium. The internalization of AuNPs into the A549 cells was also monitored using TEM and dark-field microscopy (DFM). Both methylthiazol tetrazolium (MTT) and lactate dehydrogenase (LDH) assays revealed that AuNPs were toxic as determined by their half-maximal inhibitory concentration. A flow cytometric and real-time PCR analysis of apoptotic genes along with the ATP depletion measurements suggested that AuNPs induce cell damages through extrinsic and intrinsic apoptotic pathways.

Defective molecular timer in the absence of nucleotides leads to inefficient caspase activation

In the intrinsic death pathway, cytochrome C (CC) released from mitochondria to the cytosol triggers Apaf-1 apoptosome formation and subsequent caspase activation. This process can be recapitulated using recombinant Apaf-1 and CC in the presence of nucleotides ATP or dATP [(d)ATP] or using fresh cytosol and CC without the need of exogenous nucleotides. Surprisingly, we found that stored cytosols failed to support CC-initiated caspase activation. Storage of cytosols at different temperatures led to the loss of all (deoxy)nucleotides including (d)ATP. Addition of (d)ATP to such stored cytosols partially restored CC-initiated caspase activation. Nevertheless, CC could not induce complete caspase-9/3 activation in stored cytosols, even with the addition of (d)ATP, despite robust Apaf-1 oligomerization. The Apaf-1 apoptosome, which functions as a proteolytic-based molecular timer appeared to be defective as auto-processing of recruited procaspase-9 was inhibited. Far Western analysis revealed that procaspase-9 directly interacted with Apaf-1 and this interaction was reduced in the presence of physiological levels of ATP. Co-incubation of recombinant Apaf-1 and procaspase-9 prior to CC and ATP addition inhibited CC-induced caspase activity. These findings suggest that in the absence of nucleotide such as ATP, direct association of procaspase-9 with Apaf-1 leads to defective molecular timer, and thus, inhibits apoptosome-mediated caspase activation. Altogether, our results provide novel insight on nucleotide regulation of apoptosome.

ATP acts as a regulatory effector in modulating structural transitions of cytochrome c: implications for apoptotic activity

The binding of lipids (free fatty acids as well as acidic phospholipids) to cytochrome c (cyt c) induces conformational changes and partial unfolding of the protein, strongly influencing cyt c oxidase/peroxidase activity. ATP is unique among the nucleotides in being able to turn non-native states of cyt c back to the native conformation. The peroxidase activity acquired by lipid-bound cyt c turns out to be very critical in the early stages of apoptosis. Nucleotide specificity is observed for apoptosome formation and caspase activation, the cleavage occurring only in the presence of dATP or ATP. In this study, we demonstrate the connection between peroxidase activity and oleic acid-induced conformational transitions of cyt c and show how ATP is capable of modulating such interplay. By NMR measurement, we have demonstrated that ATP interacts with a site (S1) formed by K88, R91, and E62 and such interaction was weakened by mutation of E62, suggesting the selective role in the interaction played by the base moiety. Interestingly, the interactions of ATP and GTP with cyt c are significantly different at low nucleotide concentrations, with GTP being less effective in perturbing the S1 site and in eliciting apoptotic activity. To gain insights into the structural features of cyt c required for its pro-apoptotic activity and to demonstrate a regulatory role for ATP (compared to the effect of GTP), we have performed experiments on cell lysates by using cyt c proteins mutated on amino acid residues that, as suggested by NMR measurements, belong to S1. Thus, we provide evidence that ATP acts as an allosteric effector, regulating structural transitions among different conformations and different oxidation states of cyt c, which are endowed with apoptotic activity or not. On this basis, we suggest a previously unrecognized role for ATP binding to cyt c at low millimolar concentrations in the cytosol, beyond the known regulatory role during the oxidative phosphorylation in mitochondria.

Glutathione and apoptosis

Apoptosis or programmed cell death represents a physiologically conserved mechanism of cell death that is pivotal in normal development and tissue homeostasis in all organisms. As a key modulator of cell functions, the most abundant non-protein thiol, glutathione (GSH), has important roles in cellular defense against oxidant aggression, redox regulation of proteins thiols and maintaining redox homeostasis that is critical for proper function of cellular processes, including apoptosis. Thus, a shift in the cellular GSH-to-GSSG redox balance in favour of the oxidized species, GSSG, constitutes an important signal that could decide the fate of a cell. The current review will focus on three main areas: (1) general description of cellular apoptotic pathways, (2) cellular compartmentation of GSH and the contribution of mitochondrial GSH and redox proteins to apoptotic signalling and (3) role of redox mechanisms in the initiation and execution phases of apoptosis.

The apoptosome: emerging insights and new potential targets for drug design

Apoptosis plays a crucial role in tissue homeostasis, development and many diseases. The relevance of Apaf1, the molecular core of apoptosome, has been underlined in mitochondria-dependent apoptosis, which according to a growing body of evidence, is involved in various pathologies where the equilibrium of life-and-death is dysregulated, such as heart attack, stroke, liver failure, cancer and autoimmune diseases. Consequently, great interest has emerged in devising therapeutic strategies for regulating the key molecules involved in the life-and-death decision. Here we review recent progress in apoptosis-based pharmacological therapies and, in particular, we point out a possible role of the apoptosome as an emerging and promising pharmacological target.