Regional loss of the mitochondrial membrane potential in the hepatocyte is rapidly followed by externalization of phosphatidylserines at that specific site during apoptosis

Antiproliferative Mechanisms of a Polyphenolic Combination of Kaempferol and Fisetin in Triple-Negative Breast Cancer Cells

Herein, we investigate the combinatorial therapeutic effects of naturally occurring flavonoids kaempferol (K) and fisetin (F) on triple-negative breast cancer (TNBC: MDA-MB-231 cell line). Dose-dependent MTT assay results show that K and F exhibited cytotoxicity in MDA-MB-231 cells at 62 and 75 μM (IC50), respectively, after 24 h. However, combined K + F led to 40% and more than 50% TNBC cell death observed at 10 and 20 μM, respectively, which revealed the synergistic association of both. The combination of K and F was determined to be more effective in inhibiting cell viability than either of the agents alone. The morphological changes associated with significant apoptotic cell death were observed under a fluorescent microscope, strongly supporting the synergistic association between K and F. We also proposed that combining the effects of both polyphenols, as opposed to their individual effects, would increase their in vitro efficacy. Furthermore, we assessed the cell death pathway by the combinational treatment via reactive oxygen species-induced DNA damage and the mitochondrially mediated apoptotic pathway. This study reveals the prominent synergistic role of phytochemicals, which helps in elevating the therapeutic efficacy of dietary nutrients and that anticancer effects may be a result of nutrients that act in concert.

Molecular mechanisms of hepatic apoptosis regulated by nuclear factors

Apoptosis is a prominent characteristic in the pathogenesis of liver disease. The mechanism of hepatic apoptosis is not well understood. Hepatic apoptosis alters relative levels of nuclear factors such as Foxa2, NF-κB, C/EBPβ, and p53. Regulation of nuclear factors modulates the degree of hepatic apoptosis and the progression of liver disease. Nuclear factors have distinctive mechanisms to mediate hepatic apoptosis. The modification of nuclear factors is a novel therapeutic strategy for liver disease as demonstrated by pre-clinical models and clinical trials.

Angiotensin II induces mitochondrial dysfunction and promotes apoptosis via JNK signalling pathway in primary mouse calvaria osteoblast

OBJECTIVES

This present study was designed to investigate the effects of Angiotensin II on mitochondrial functions, ROS generation and c-jun N-terminal kinases (JNK) signalling pathway-mediated cell apoptosis in mouse calvaria osteoblasts.

METHODS

Calvaria osteoblast were isolated and cultured. The cells were separated into two groups-control and treated groups-where the latter was stimulated with angiotensin II (Ang II). Mitochondrial reactive oxygen species (ROS) and superoxide production were measured. Intracellular ATP levels were also detected. The cell proliferation rate was determined for the two groups. Protein production such as Anti-Bax, Bcl-2, COX IV and activation of c-jun N-terminal kinases signal (JNK) pathway was measured by enzyme-linked immunosorbent assay (ELISA) methods and Western blotting in this study.

RESULTS

Ang II treated cells showed significantly higher levels of superoxide production compared to the control group (p<0.05). Conversely, Ang II induced inhibitory effects on mitochondrial respiratory enzyme complexes, cause membrane potential dissipation, ATP loss and promote ROS generation, cell apoptosis in cultured osteoblasts. In addition, JNK phosphorylations were involved in activating the mitochondria-dependent apoptotic pathway following Ang II stimulation, as pre-treatment of JNK-specific inhibitor SP600125 could rescue osteoblast cells from apoptosis by enhancing the anti-apoptotic protein Bcl-2 expressions, suppressing the translocation of Bax from cytosol into mitochondria, blocking cytochrome C release and caspase-3 activation.

CONCLUSIONS

Ang II stimulates osteoblast apoptosis via suppression of the mitochondrial respiratory enzymes, membrane potential and cellular ATP productions. Clinical application with Ang II-stimulated osteoblast could be used for modelling or bone resorption in the oral region.

Mitochondrial function is altered in articular chondrocytes of an endemic osteoarthritis, Kashin-Beck disease

OBJECTIVE

Kashin-Beck disease (KBD) is an endemic degenerative osteoarthritis (OA) associated with extracellular matrix degradation and chondrocyte necrosis in the articular and growth plate cartilage. The role of mitochondria in degenerative diseases is widely recognized but its function in KBD is unknown. The aim of this investigation was to evaluate mitochondrial function to understand the mitochondria-mediated caspase activation and apoptosis in adult KBD chondrocytes.

METHODS

Mitochondrial function was evaluated by analyzing the activities of respiratory chain enzyme complexes and citrate synthase (CS), intracellular adenosine triphosphate (ATP) contents, as well as changes in mitochondrial membrane potential (DeltaPsim). Apoptotic cell death was evaluated by analyzing the cytochrome c release from mitochondria to the cytosol, caspase-9 and 3 activities, and the apoptosis rate of KBD articular chondrocytes.

RESULTS

Activities of complexes II, III, IV and V were reduced in KBD articular chondrocytes compared with cells from normal controls. However, the mitochondrial mass was increased in KBD samples. Cultured KBD chondrocytes had a reduction of cellular ATP levels and contained a higher proportion of cells with de-energized mitochondria. Mitochondrial cytochrome c release and activation of caspase-9 and 3 were also observed. The percentages of positive apoptotic chondrocytes from the KBD patient group stained by Hoechst nuclear stain and Annexin V/PI for flow cytometry exhibited higher levels than that of the healthy controls.

CONCLUSION

These findings suggest the involvement of mitochondrial function and apoptotic cell death in the pathophysiology of KBD. The dysfunction of the mitochondria may play an important role in KBD articular chondrocytes apoptosis.

Early safety assessment using cellular systems biology yields insights into mechanisms of action

The integration of high-content screening (HCS) readers with organ-specific cell models, panels of functional biomarkers, and advanced informatics is a powerful approach to identifying the toxic liabilities of compounds early in the development process and forms the basis of "early safety assessment." This cellular systems biology (CSB) approach (CellCiphr profile) has been used to integrate rodent and human cellular hepatic models with panels of functional biomarkers measured at multiple time points to profile both the potency and specificity of the cellular toxicological response. These profiles also provide initial insights on the mechanism of the toxic response. The authors describe here mechanistic assay profiles designed to further dissect the toxic mechanisms of action and elucidate subtle effects apparent in subpopulations of cells. They measured 8 key mechanisms of toxicity with multiple biomarker feature measurements made simultaneously in populations of living primary hepatocytes and HepG2 cells. Mining the cell population response from these mechanistic profiles revealed the concentration dependence and nature of the heterogeneity of the response, as well as relationships between the functional responses. These more detailed mechanistic profiles define differences in compound activities that are not apparent in the average population response. Because cells and tissues encounter wide ranges of drug doses in space and time, these mechanistic profiles build on the CellCiphr profile and better reflect the complexity of the response in vivo.

The ins and outs of phospholipid asymmetry in the plasma membrane: roles in health and disease

A common feature of all eukaryotic membranes is the non-random distribution of different lipid species in the lipid bilayer (lipid asymmetry). Lipid asymmetry provides the two sides of the plasma membrane with different biophysical properties and influences numerous cellular functions. Alteration of lipid asymmetry plays a prominent role during cell fusion, activation of the coagulation cascade, and recognition and removal of apoptotic cell corpses by macrophages (programmed cell clearance). Here we discuss the origin and maintenance of phospholipid asymmetry, based on recent studies in mammalian systems as well as in Caenhorhabditis elegans and other model organisms, along with emerging evidence for a conserved role of mitochondria in the loss of lipid asymmetry during apoptosis. The functional significance of lipid asymmetry and its disruption during health and disease is also discussed.

Apoptotic insults to human HepG2 cells induced by S-(+)-ketamine occurs through activation of a Bax-mitochondria-caspase protease pathway

BACKGROUND

Ketamine is widely used as an i.v. anaesthetic agent and as a drug of abuse. Hepatocytes contribute to the metabolism of endogenous and exogenous substances. This study evaluated the toxic effects of S-(+)-ketamine and possible mechanisms using human hepatoma HepG2 cells as the experimental model.

METHODS

HepG2 cells were exposed to S-(+)-ketamine. Cell viability and the release of lactate dehydrogenase (LDH) and gamma-glutamyl transpeptidase (GPT) were measured to determine the toxicity of S-(+)-ketamine to HepG2 cells. Cell morphology, DNA fragmentation, and apoptotic cells were analysed to evaluate the mechanism of S-(+)-ketamine-induced cell death. Amounts of Bax, an apoptotic protein, and cytochrome c in the cytoplasm or mitochondria were quantified by immunoblotting. Cellular adenosine triphosphate levels were analysed using a bioluminescence assay. Caspases-3, -9, and -6 were measured fluorometrically.

RESULTS

Exposure of HepG2 cells to S-(+)-ketamine increased the release of LDH and GPT, but decreased cell viability (all P<0.01). S-(+)-Ketamine time-dependently caused shrinkage of HepG2 cells. Exposure to S-(+)-ketamine led to significant DNA fragmentation and cell apoptosis (P=0.003 and 0.002). S-(+)-Ketamine increased translocation of Bax from the cytoplasm to mitochondria, but decreased the mitochondrial membrane potential and cellular adenosine triphosphate levels (all P<0.01). Sequentially, cytosolic cytochrome c levels and activities of caspases-9, -3, and -6 were augmented after S-(+)-ketamine administration (all P<0.001). Z-VEID-FMK, an inhibitor of caspase-6, alleviated the S-(+)-ketamine-induced augmentation of caspase-6 activity, DNA fragmentation, and cell apoptosis (all P<0.001).

CONCLUSIONS

This study shows that S-(+)-ketamine can induce apoptotic insults to human HepG2 cells via a Bax-mitochondria-caspase protease pathway. Thus, we suggest that S-(+)-ketamine at a clinically relevant or an abused concentration may induce liver dysfunction possibly due to its toxicity to hepatocytes.

Apoptotic insults to human chondrocytes induced by sodium nitroprusside are involved in sequential events, including cytoskeletal remodeling, phosphorylation of mitogen-activated protein kinase kinase kinase-1/c-Jun N-terminal kinase, and Bax-mitochondria-mediated caspase activation

Nitric oxide (NO) can regulate chondrocyte activities. This study was aimed to evaluate the molecular mechanisms of NO donor sodium nitroprusside (SNP)-induced insults to human chondrocytes. Exposure of human chondrocytes to SNP increased cellular NO levels but decreased cell viability in concentration- and time-dependent manners. SNP time dependently induced DNA fragmentation and cell apoptosis. Treatment with 2-phenyl-4,4,5,5-tetramethyl-imidazoline-1-oxyl 3-oxide, an NO scavenger, significantly lowered SNP-induced cell injuries. Administration of SNP interrupted F-actin and microtubule cytoskeletons and stimulated phosphorylation of mitogen-activated protein kinase kinase kinase-1 (MEKK1) and c-Jun N-terminal kinase (JNK). Similar to SNP, cytochalasin D, an inhibitor of F-actin formation, disturbed F-actin polymerization and increased MEKK1 and JNK activations. Overexpression of a dominant negative mutant of MEKK1 (dnMEK1) in human chondrocytes significantly ameliorated SNP-induced cell apoptosis. Exposure to SNP promoted Bax translocation from the cytoplasm to mitochondria, but application of dnMEKK1 lowered the translocation. SNP time dependently decreased the mitochondrial membrane potential, complex I NADH dehydrogenase activity, and cellular ATP levels, but increased the release of cytochrome c from mitochondria to the cytoplasm. Activities of caspase-9, -3, and -6 were sequentially increased by SNP administration. This study shows that SNP can induce apoptosis of human chondrocytes through sequential events, including cytoskeletal remodeling, activation of MEKK1/JNK, Bax translocation, mitochondrial dysfunction, cytochrome c release, caspase activation, and DNA fragmentation.

Nitric oxide from both exogenous and endogenous sources activates mitochondria-dependent events and induces insults to human chondrocytes

During inflammation, overproduction of nitric oxide (NO) can damage chondrocytes. In this study, we separately evaluated the toxic effects of exogenous and endogenous NO on human chondrocytes and their possible mechanisms. Human chondrocytes were exposed to sodium nitroprusside (SNP), an NO donor, or a combination of lipopolysaccharide (LPS) and interferon-gamma (IFN-gamma) as the exogenous and endogenous sources of NO, respectively. Administration of SNP or a combination of LPS and IFN-gamma in human chondrocytes increased cellular NO levels but decreased cell viability. Exposure to exogenous or endogenous NO significantly induced apoptosis of human chondrocytes. When treated with exogenous or endogenous NO, the mitochondrial membrane potential time-dependently decreased. Exposure to exogenous or endogenous NO significantly enhanced cellular reactive oxygen species (ROS) and cytochrome c (Cyt c) levels. Administration of exogenous or endogenous NO increased caspase-3 activity and consequently induced DNA fragmentation. Suppression of caspase-3 activation by Z-DEVD-FMK decreased NO-induced DNA fragmentation and cell apoptosis. Similar to SNP, exposure of human chondrocytes to S-nitrosoglutathione (GSNO), another NO donor, caused significant increases in Cyt c levels, caspase-3 activity, and DNA fragmentation, and induced cell apoptosis. Pretreatment with N-monomethyl arginine (NMMA), an inhibitor of NO synthase, significantly decreased cellular NO levels, and lowered endogenous NO-induced alterations in cellular Cyt c amounts, caspase-3 activity, DNA fragmentation, and cell apoptosis. Results of this study show that NO from exogenous and endogenous sources can induce apoptotic insults to human chondrocytes via a mitochondria-dependent mechanism.

Oxidized low-density lipoprotein induces apoptotic insults to mouse cerebral endothelial cells via a Bax-mitochondria-caspase protease pathway

Cerebral endothelial cells (CECs) are crucial components of the blood-brain barrier. Oxidized low-density lipoprotein (oxLDL) can induce cell injuries. In this study, we attempted to evaluate the effects of oxLDL on mouse CECs and its possible mechanisms. Mouse CECs were isolated from brain tissues and identified by immunocytochemical staining of vimentin and Factor VIII. oxLDL was prepared from LDL oxidation by copper sulfate. Exposure of mouse CECs to oxLDL decreased cell viability in concentration- and time-dependent manners. oxLDL time-dependently caused shrinkage of cell morphologies. Administration of oxLDL to CECs induced DNA fragmentation in concentration- and time-dependent manners. Analysis of the cell cycle revealed that oxLDL concentration- and time-dependently increased the proportion of CECs which underwent apoptosis. Analysis of confocal microscopy and immunoblot revealed that oxLDL significantly increased cellular and mitochondrial Bax levels as well as the translocation of this proapoptotic protein from the cytoplasm to mitochondria. In parallel with the increase in the levels and translocation of Bax, oxLDL time-dependently decreased the mitochondrial membrane potential. Exposure of mouse CECs to oxLDL decreased the amounts of mitochondrial cytochrome c, but enhanced cytosolic cytochrome c levels. The amounts of intracellular reactive oxygen species were significantly augmented after oxLDL administration. Sequentially, oxLDL increased activities of caspase-9, -3, and -6 in time-dependent manners. Pretreatment with Z-VEID-FMK, an inhibitor of caspase-6, significantly decreased caspase-6 activity and the oxLDL-induced DNA fragmentation and cell apoptosis. This study showed that oxLDL induces apoptotic insults to CECs via signal-transducing events, including enhancing Bax translocation, mitochondrial dysfunction, cytochrome c release, increases in intracellular reactive oxygen species, and cascade activation of caspase-9, -3, and -6. Therefore, oxLDL can damage the blood-brain barrier through induction of CEC apoptosis via a Bax-mitochondria-caspase protease pathway.

Nanoelectropulse-driven membrane perturbation and small molecule permeabilization

BACKGROUND

Nanosecond, megavolt-per-meter pulsed electric fields scramble membrane phospholipids, release intracellular calcium, and induce apoptosis. Flow cytometric and fluorescence microscopy evidence has associated phospholipid rearrangement directly with nanoelectropulse exposure and supports the hypothesis that the potential that develops across the lipid bilayer during an electric pulse drives phosphatidylserine (PS) externalization.

RESULTS

In this work we extend observations of cells exposed to electric pulses with 30 ns and 7 ns durations to still narrower pulse widths, and we find that even 3 ns pulses are sufficient to produce responses similar to those reported previously. We show here that in contrast to unipolar pulses, which perturb membrane phospholipid order, tracked with FM1-43 fluorescence, only at the anode side of the cell, bipolar pulses redistribute phospholipids at both the anode and cathode poles, consistent with migration of the anionic PS head group in the transmembrane field. In addition, we demonstrate that, as predicted by the membrane charging hypothesis, a train of shorter pulses requires higher fields to produce phospholipid scrambling comparable to that produced by a time-equivalent train of longer pulses (for a given applied field, 30, 4 ns pulses produce a weaker response than 4, 30 ns pulses). Finally, we show that influx of YO-PRO-1, a fluorescent dye used to detect early apoptosis and activation of the purinergic P2X7 receptor channels, is observed after exposure of Jurkat T lymphoblasts to sufficiently large numbers of pulses, suggesting that membrane poration occurs even with nanosecond pulses when the electric field is high enough. Propidium iodide entry, a traditional indicator of electroporation, occurs with even higher pulse counts.

CONCLUSION

Megavolt-per-meter electric pulses as short as 3 ns alter the structure of the plasma membrane and permeabilize the cell to small molecules. The dose responses of cells to unipolar and bipolar pulses ranging from 3 ns to 30 ns duration support the hypothesis that a field-driven charging of the membrane dielectric causes the formation of pores on a nanosecond time scale, and that the anionic phospholipid PS migrates electrophoretically along the wall of these pores to the external face of the membrane.

Nitric oxide protects osteoblasts from oxidative stress-induced apoptotic insults via a mitochondria-dependent mechanism

Nitric oxide (NO) contributes to the regulation of osteoblast activities. In this study, we evaluated the protective effects of NO pretreatment on oxidative stress-induced osteoblast apoptosis and its possible mechanism using neonatal rat calvarial osteoblasts as the experimental model. Exposure of osteoblasts to sodium nitroprusside (SNP) at a low concentration of 0.3 mM significantly increased cellular NO levels without affecting cell viability. However, when the concentration reached a high concentration of 2 mM, SNP increased the levels of intracellular reactive oxygen species and induced osteoblast injuries. Thus, administration of 0.3 and 2 mM SNP in osteoblasts were respectively used as sources of NO and oxidative stress. Pretreatment with NO for 24 h significantly ameliorated the oxidative stress-caused morphological alterations and decreases in alkaline phosphatase activity, and reduced cell death. Oxidative stress induced osteoblast death via an apoptotic mechanism, but NO pretreatment protected osteoblasts against the toxic effects. The mitochondrial membrane potential was significantly reduced following exposure to the oxidative stress. However, pretreatment with NO significantly lowered the suppressive effects. Oxidative stress increased cellular Bax protein production and cytochrome c release from mitochondria. Pretreatment with NO significantly decreased oxidative stress-caused augmentation of Bax and cytochrome c protein levels. In parallel with cytochrome c release, oxidative stress induced caspase-3 activation and DNA fragmentation. Pretreatment with NO significantly reduced the oxidative stress-enhanced caspase-3 activation and DNA damage. Results of this study show that NO pretreatment can protect osteoblasts from oxidative stress-induced apoptotic insults. The protective action involves a mitochondria-dependent mechanism.

Death of stoma guard cells in leaf epidermis under disturbance of energy provision

Cyanide is an apoptosis inducer in stoma guard cells from pea leaf epidermis. Unlike CN-, the uncoupler of oxidative and photosynthetic phosphorylation carbonyl cyanide m-chlorophenylhydrazone (CCCP), the combination of CCCP, 3-(3 ,4 -dichlorophenyl)-1,1-dimethylurea (DCMU), benzylhydroxamate (BH), myxothiazol, antimycin A, and a glycolysis inhibitor 2-deoxyglucose (DG) did not induce destruction of guard cell nuclei for 20 h of incubation of epidermal peels in the light. DCMU prevented the effect of CN- as a programmed cell death (PCD) inducer. CCCP, the combination of DCMU and CCCP, or the combination of DCMU, CCCP, BH, myxothiazol, antimycin A, and DG supplemented by CN- caused destruction of cell nuclei; the number of the cells lacking nuclei in this case was higher than with CN- alone. DG and CCCP caused cell destruction after longer incubation of the isolated epidermis - after 2 days and to a greater degree after 4 days. The effect of DG and CCCP was reduced by illumination. Cell destruction during long-term incubation was prevented by the combination of DG and CCCP. From data of electron microscopy, DCMU and dinitrophenyl ester of iodonitrothymol (DNP-INT) prevented apoptotic changes of the nuclear ultrastructure induced by CN-. The suppression of the destruction of the guard cell nuclei under combined action of DG and CCCP was apparently caused by switching of cell death from PCD to necrosis. Thus, the type of cell death - via apoptosis or necrosis - is controlled by the level of energy provision.

Dose-dependent cell-based assays in V-shaped microfluidic channels

The capability of lab-on-a-chip technologies in controlling cell transportation, generating concentration gradients, and monitoring cellular responses offers an opportunity to integrate dose-dependent cell-based bioassays on a chip. In this study, we have developed microfluidic modules featured with channel components and sandbag structures for positioning biological cells within the microchip. We have demonstrated that by geometric modulation of the microchannel architectures, it is possible to immobilize individual cells at desired locations with controllable numbers, to generate defined concentration gradients at various channel lengths, and to improve the efficiency and reproducibility in data acquisition. The microfluidic module was used to exercise a series of cell-based assays, including the measurement of kinetics and dynamics of intracellular enzymatic activities, the analysis of cellular response under the stimulation of two chemicals with defined concentration profiles, and the study of laser irradiation effect on cellular uptake of photosensitizers. The results demonstrated the capabilities of the microfluidic module for simultaneously conducting multiple sets of dose-dependent, cell-based bioassays, and for quantitatively comparing responses of individual cells under various stimulations.

Nitric Oxide Induces Osteoblast Apoptosis through a Mitochondria-Dependent Pathway

Osteoblasts contribute to bone remodeling. Nitric oxide can regulate osteoblast activities. In this study, we attempted to evaluate the pathophysiological effects of nitric oxide on osteoblasts and its possible mechanism using neonatal rat calvarial osteoblasts as the experimental model. Exposure of osteoblasts to sodium nitroprusside, a nitric oxide donor, decreased alkaline phosphatase activities and cell viability in a concentration- and time-dependent manner. Apoptotic analysis revealed that sodium nitroprusside time-dependently increased the percentages of osteoblasts undergoing apoptosis. Administration of sodium nitroprusside reduced the mitochondrial membrane potential of osteoblasts. In parallel with the mitochondrial dysfunction, levels of intracellular reactive oxygen species and cytochrome c were significantly elevated following sodium nitroprusside administration. Exposure of osteoblasts to sodium nitroprusside significantly increased caspase-3 activity. Results of this study show that nitric oxide, decomposed from sodium nitroprusside, can induce osteoblast apoptosis through a mitochondrion-dependent cascade that causes mitochondrial dysfunction, release of intracellular reactive oxygen species and cytochrome c from mitochondria to cytoplasm, and activation of caspase-3.

Apoptosis: a basic biological phenomenon with wide-ranging implications in human disease

Apoptosis is a highly regulated process of cell deletion and plays a fundamental role in the maintenance of tissue homeostasis in the adult organism. Numerous studies in recent years have revealed that apoptosis is a constitutive suicide programme expressed in most, if not all cells, and can be triggered by a variety of extrinsic and intrinsic signals. Many human diseases can be attributed directly or indirectly to a derangement of apoptosis, resulting in either cell accumulation, in which cell eradication or cell turnover is impaired, or cell loss, in which the apoptotic programme is inadvertently triggered. In addition, defective macrophage engulfment and degradation of cell corpses may also contribute to a dysregulation of tissue homeostasis. An increased understanding of the signalling pathways that govern the execution of apoptosis and the subsequent clearance of dying cells may thus yield novel targets for therapeutic intervention in a wide range of human maladies.

MLN64 is involved in actin-mediated dynamics of late endocytic organelles

MLN64 is a late endosomal cholesterol-binding membrane protein of an unknown function. Here, we show that MLN64 depletion results in the dispersion of late endocytic organelles to the cell periphery similarly as upon pharmacological actin disruption. The dispersed organelles in MLN64 knockdown cells exhibited decreased association with actin and the Arp2/3 complex subunit p34-Arc. MLN64 depletion was accompanied by impaired fusion of late endocytic organelles and delayed cargo degradation. MLN64 overexpression increased the number of actin and p34-Arc-positive patches on late endosomes, enhanced the fusion of late endocytic organelles in an actin-dependent manner, and stimulated the deposition of sterol in late endosomes harboring the protein. Overexpression of wild-type MLN64 was capable of rescuing the endosome dispersion in MLN64-depleted cells, whereas mutants of MLN64 defective in cholesterol binding were not, suggesting a functional connection between MLN64-mediated sterol transfer and actin-dependent late endosome dynamics. We propose that local sterol enrichment by MLN64 in the late endosomal membranes facilitates their association with actin, thereby governing actin-dependent fusion and degradative activity of late endocytic organelles.

Molecular mechanism of nitric oxide-induced osteoblast apoptosis

Nitric oxide (NO) can regulate osteoblast activities. Our previous study showed that NO induced osteoblast apoptosis. This study was further aimed to evaluate the mechanism of NO-induced osteoblast apoptosis from the viewpoints of mitochondrial functions, intracellular oxidative stress, and the anti-apoptotic Bcl-2 protein using neonatal rat calvarial osteoblasts as the experimental model. Exposure of osteoblasts to sodium nitroprusside (SNP), an NO donor, significantly increased amounts of lactate dehydrogenase in the culture medium, and decreased cell viability in concentration- and time-dependent manners. Administration of SNP in osteoblasts time-dependently led to DNA fragmentation. The mitochondrial membrane potential was significantly reduced following SNP administration. SNP decreased complex I NADH dehydrogenase activity in a time-dependent manner. Levels of cellular adenosine triphosphate (ATP) were suppressed by SNP. In parallel with the mitochondrial dysfunction, SNP time-dependently increased levels of intracellular reactive oxygen species. Immunoblotting analysis revealed that SNP reduced Bcl-2 protein levels. Exposure to lipopolysaccharide (LPS) and IFN-gamma significant increased endogenous nitrite production. In parallel with the increase in endogenous NO, administration of LPS and IFN-gamma suppressed cell viability, mitochondrial membrane potential, and ATP synthesis. Results of this study show that NO released from SNP can induce osteoblast insults and apoptosis, and the mechanism may involve the modulation of mitochondrial functions, intracellular reactive oxygen species, and Bcl-2 protein.

Nanoelectropulse-induced phosphatidylserine translocation

Nanosecond, megavolt-per-meter, pulsed electric fields induce phosphatidylserine (PS) externalization, intracellular calcium redistribution, and apoptosis in Jurkat T-lymphoblasts, without causing immediately apparent physical damage to the cells. Intracellular calcium mobilization occurs within milliseconds of pulse exposure, and membrane phospholipid translocation is observed within minutes. Pulsed cells maintain cytoplasmic membrane integrity, blocking propidium iodide and Trypan blue. Indicators of apoptosis-caspase activation and loss of mitochondrial membrane potential-appear in nanoelectropulsed cells at later times. Although a theoretical framework has been established, specific mechanisms through which external nanosecond pulsed electric fields trigger intracellular responses in actively growing cells have not yet been experimentally characterized. This report focuses on the membrane phospholipid rearrangement that appears after ultrashort pulse exposure. We present evidence that the minimum field strength required for PS externalization in actively metabolizing Jurkat cells with 7-ns pulses produces transmembrane potentials associated with increased membrane conductance when pulse widths are microseconds rather than nanoseconds. We also show that nanoelectropulse trains delivered at repetition rates from 2 to 2000 Hz have similar effects, that nanoelectropulse-induced PS externalization does not require calcium in the external medium, and that the pulse regimens used in these experiments do not cause significant intra- or extracellular Joule heating.

Mutant prenyltransferase-like mitochondrial protein (PLMP) and mitochondrial abnormalities in kd/kd mice

BACKGROUND

Mice that are homozygous for the kidney disease (kd) mutation are apparently healthy for the first 8 weeks of life, but spontaneously develop a severe form of interstitial nephritis that progresses to end-stage renal disease (ESRD) by 4 to 8 months of age. By testing for linkage to microsatellite markers, we previously localized the kd gene to a YAC/BAC contig.

METHODS

The sequence of the entire critical region was examined, and candidate genes were identified. These candidate genes were sequenced in both mutant (kd/kd) mice and normal controls. The phenotype was further characterized by immunohistochemistry and electron microscopy. Transgenic mice were constructed that carried the wild-type allele of the prime candidate gene, and this transgene was transferred to a kd/kd background by breeding.

RESULTS

We have obtained evidence that kd is a mutant allele of a novel gene for a prenyltransferase-like mitochondrial protein (PLMP). This gene is alternatively spliced, with the larger gene product having one domain that resembles transprenyltransferase and another that is similar to geranylgeranyl pyrophosphate synthase. The smaller gene product includes only the first domain. An antiserum to PLMP localizes to mitochondria, and ultrastructural defects are present in the mitochondria of renal tubular epithelial cells, and to a lesser extent, hepatocytes and heart cells from kd/kd mice. In a line of kd/kd mice that carried the wild-type PLMP allele as a transgene, only 1 out of 13 animals expressed the disease by 120 days of age.

CONCLUSION

The kd allele codes for a novel protein that localizes to the mitochondria, and the kd/kd mouse has dysmorphic mitochondria in the renal tubular epithelial cells. This mouse is therefore a unique animal model for studying mechanisms that lead to tubulointerstitial nephritis.

Nanosecond pulsed electric fields perturb membrane phospholipids in T lymphoblasts

Nanosecond, megavolt-per-meter pulsed electric fields scramble the asymmetric arrangement of phospholipids in cell membranes without the permeabilization associated with longer, lower-field pulses. A single 30 ns, 2.5 MV/m pulse produces perturbations consistent with phosphatidylserine (PS) externalization in Jurkat T lymphoblasts within milliseconds, polarized in the direction of the applied field, indicating an immediate interaction between membrane components and the electric field. This disturbance occurs only at the anode pole of the cell, supporting the hypothesis that the pulsed field drives the negatively charged PS head group toward the positive electrode, directly providing the energy for crossing the membrane dielectric barrier.

Involvement of sodium in early phosphatidylserine exposure and phospholipid scrambling induced by P2X7 purinoceptor activation in thymocytes

Extracellular ATP (ATP(ec)), a possible effector in thymocyte selection, induces thymocyte death via purinoceptor activation. We show that ATP(ec) induced cell death by apoptosis, rather than lysis, and early phosphatidylserine (PS) exposure and phospholipid scrambling in a limited thymocyte population (35-40%). PS externalization resulted from the activation of the cationic channel P2X7 (formerly P2Z) receptor and was triggered in all thymocyte subsets although to different proportions in each one. Phospholipid movement was dependent on ATP(ec)-induced Ca(2+) and/or Na(+) influx. At physiological external Na(+) concentration, without external Ca(2+), PS was exposed in all ATP(ec)-responsive cells. In contrast, without external Na(+), physiological external Ca(2+) concentration promoted a submaximal response. Altogether these data show that Na(+) influx plays a major role in the rapid PS exposure induced by P2X7 receptor activation in thymocytes.

Transfection of prion protein gene suppresses coxsackievirus B3 replication in prion protein gene-deficient cells

The susceptibility of prion protein gene (Prnp)-null cells to coxsackievirus B3 (CVB3) was investigated. Primary cultures of murine Prnp(-/-) brain cells were more sensitive to CVBs than corresponding cells from wild-type mice. The viral susceptibility of a Prnp-null cell line (HpL3-4) derived from the murine hippocampus was compared with that of two established cell lines (HeLa and HEp-2) that are widely employed for CVB3 studies. After infection with CVB3, HpL3-4 cells showed a very rapid and complete cytopathic effect (CPE). CPE developed earlier and viruses replicated at higher titres in HpL3-4 cells compared with HeLa and HEp-2 cells. Under a semi-solid medium, plaques developed rapidly in CVB3-infected HpL3-4 cells. To confirm the effect of Prnp on virus infection, a Prnp(-/-) cell line and a Prnp-transfected neuronal cell line were analysed. The replication and release of infectious particles of CVB3 in Prnp(-/-) cells were significantly more effective than those of the Prnp-transfected cell line. Levels of type I interferon (IFN) after CVB3 infection were higher in the Prnp-transfected cell line than in Prnp(-/-) cells, whereas apoptotic cells were more obvious in the Prnp(-/-) cells than in those of the Prnp-transfected cell line. These findings suggest that the absence of Prnp retards the induction of CVB3-induced IFNs, resulting in an enhanced CVB3 production and apoptotic cell death. Furthermore, our data indicate that the HpL3-4 cell line may provide a novel and sensitive system for isolation of CVB3 from clinical specimens.

Calcium bursts induced by nanosecond electric pulses

We report here real-time imaging of calcium bursts in human lymphocytes exposed to nanosecond, megavolt-per-meter pulsed electric fields. Ultra-short (less than 30 ns), high-field (greater than 1 MV/m), electric pulses induce increases in cytosolic calcium concentration and translocation of phosphatidylserine (PS) to the outer layer of the plasma membrane in Jurkat T lymphoblasts. Pulse-induced calcium bursts occur within milliseconds and PS externalization within minutes. Caspase activation and other indicators of apoptosis follow these initial symptoms of nanosecond pulse exposure. Pulse-induced PS translocation is observed even in the presence of caspase inhibitors. Ultra-short, high-field, electroperturbative pulse effects differ substantially from those associated with electroporation, where pulses of a few tens of kilovolts-per-meter lasting a few tens of microseconds open pores in the cytoplasmic membrane. Nanosecond pulsed electric fields, because their duration is less than the plasma membrane charging time, develop voltages across intracellular structures without porating the cell.