Bax shuttling after rotenone treatment of neuronal primary cultures: Effects on cell death phenotypes

Rotenone-induced necrosis in insect cells via the cytoplasmic membrane damage and mitochondrial dysfunction

Rotenone, a selective inhibitor of mitochondrial complex I, has been extensively studied on kinds of neuron and neuroblast in Parkinson's disease. However, little is known about the potential mechanism of this promising botanical insecticide upon insect cells. In the article, cell proliferation of two Lepidoptera cell lines, Spodoptera litura SL-1 cells and Spodoptera frugiperda Sf9 cells, were all inhibited by rotenone in a time- and dose-dependent manner. Typical necrotic characteristics of cell morphology and ultrastructure, such as plasma membrane collapses and organelle lyses, were all observed by transmission electron microscope and scanning electron microscope. Moreover, irregular DNA degradation was also detected by DNA gel electrophoresis and Hoechst 33258 staining, while the typical apoptotic feature, DNA ladder, hadn't been observed. Flow cytometric analysis showed that rotenone-induced cell death of Sf9 and SL-1 cells accompanied with the plasma membrane potential depolarization and mitochondrial membrane potential reduction. Furthermore, the activity of Na⁺-K⁺-ATPase was detected in our study. In conclusion, rotenone could cause necrosis but not apoptosis in insect cells through a mitochondrial- and plasmic membrane-dependent pattern, which shed a light on the rotenone-induced cytotoxicity on insects.

Simulated microgravity induces nuclear translocation of Bax and BCL-2 in glial cultured C6 cells

Alterations in the control of apoptotic processes were observed in cells during space flight or under simulated microgravity, the latter obtained with the 3D-Random Positioning Machine (3D-RPM).

Usually the proteins Bax and Bcl-2, act as pro- or anti-apoptotic regulators. Here we investigated the effects of simulated microgravity obtained by the 3D-RPM on cell viability, localization and expression of Bax and Bcl-2 in cultures of glial cancerous cells. We observed for the first time a transient cytoplasmic/nuclear translocation of Bax and Bcl-2 triggered by changing gravity vector. Bax translocates into the nucleus after 1 h, is present simultaneously in the cytoplasm after 6 h and comes back to the cytoplasm after 24 h. Bcl-2 translocate into the nucleus only after 6 h and comes back to the cytoplasm after 24 h. Physiological meaning, on the regulation of apoptotic event and possible applicative outcomes of such finding are discussed.

Anti- and Pro-apoptotic Bcl2 Proteins Distribution and Metabolic Profile in Human Coronary Aorta Endothelial Cells Before and After HypPDT

Understanding apoptosis regulatory mechanisms in endothelial cells (ECs) has great importance for the development of novel therapy strategies for cancer and cardiovascular pathologies. An oxidative stress with the generation of reactive oxygen species (ROS) is a common mechanism causing ECs' dysfunction and apoptosis. The generation of ROS can be triggered by various stimuli including photodynamic therapy (PDT). In most PDT treatments, photosensitizer (PS) is administered systemically, and thus, possibility of high exposure to PS in the ECs remains high. PS accumulation in ECs may be clinically relevant even without PDT, if PS molecules affect the pro-apoptotic cascade without illumination. In the present work, we focused on Hypericin (Hyp) and HypPDT effects on the cell viability, oxidative stress, and the distribution of Bcl2 family members in human coronary artery endothelial (HCAEC) cells. Our findings show that the presence of Hyp itself has an effect on cell viability, oxidative stress, and the distribution of Bcl2 family members, without affecting the mitochondria function. In contrast, HypPDT resulted in mitochondria dysfunction, further increase of oxidative stress and effect on the distribution of Bcl2 family members, and in primarily necrotic type of death in HCAEC cells.

Endoplasmic reticulum pathology and stress response in neurons precede programmed necrosis after neonatal hypoxia-ischemia

The endoplasmic reticulum (ER) is tasked, among many other functions, with preventing excitotoxicity from killing neurons following neonatal hypoxia-ischemia (HI). With the search for delayed therapies to treat neonatal HI, the study of delayed ER responses becomes relevant. We hypothesized that ER stress is a prominent feature of delayed neuronal death via programmed necrosis after neonatal HI. Since necrostatin-1 (Nec-1), an inhibitor of programmed necrosis, provides delayed neuroprotection against neonatal HI in male mice, Nec-1 is an ideal tool to study delayed ER responses. C57B6 male mice were exposed to right carotid ligation followed by exposure to FiO2=0.08 for 45 min at p7. Mice were treated with vehicle or Nec-1 (0.1 μl of 8 μmol) intracerebroventricularly with age-matched littermates as controls. Biochemistry assays at 3 and 24h and electron microscopy (EM) and immunohistochemistry at 96 h after HI were performed. EM showed ER dilation and mitochondrial swelling as apparent early changes in neurons. With advanced neurodegeneration, large cytoplasmic fragments containing dilated ER "shed" into the surrounding neuropil and calreticulin immunoreactivity was lost concurrent with nuclear features suggestive of programmed necrosis. Nec-1 attenuated biochemical markers of ER stress after neonatal HI, including PERK and eIF2α phosphorylation, and unconventional XBP-1 splicing, consistent with the mitigation of later ER pathology. ER pathology may be an indicator of severity of neuronal injury and potential for recovery characterized by cytoplasmic shedding, distinct from apoptotic blebbing, that we term neuronal macrozeiosis. Therapies to attenuate ER stress applied at delayed stages may rescue stressed neurons after neonatal HI.

Myelin recovery in multiple sclerosis: the challenge of remyelination

Multiple sclerosis (MS) is the most common demyelinating and an autoimmune disease of the central nervous system characterized by immune-mediated myelin and axonal damage, and chronic axonal loss attributable to the absence of myelin sheaths. T cell subsets (Th1, Th2, Th17, CD8⁺, NKT, CD4⁺CD25⁺ T regulatory cells) and B cells are involved in this disorder, thus new MS therapies seek damage prevention by resetting multiple components of the immune system. The currently approved therapies are immunoregulatory and reduce the number and rate of lesion formation but are only partially effective. This review summarizes current understanding of the processes at issue: myelination, demyelination and remyelination—with emphasis upon myelin composition/architecture and oligodendrocyte maturation and differentiation. The translational options target oligodendrocyte protection and myelin repair in animal models and assess their relevance in human. Remyelination may be enhanced by signals that promote myelin formation and repair. The crucial question of why remyelination fails is approached is several ways by examining the role in remyelination of available MS medications and avenues being actively pursued to promote remyelination including: (i) cytokine-based immune-intervention (targeting calpain inhibition), (ii) antigen-based immunomodulation (targeting glycolipid-reactive iNKT cells and sphingoid mediated inflammation) and (iii) recombinant monoclonal antibodies-induced remyelination.

Transgenerational effects of neonatal hypoxia-ischemia in progeny

Neonatal hypoxia-ischemia (HI) affects 60% of low birth weight infants and up to 40% of preterm births. Cell death and brain injury after HI have been shown to cause long-lasting behavioral deficits. By using a battery of behavioral tests on second generation 3-week-old rodents, we found that neonatal HI is associated with behavioral outcomes in the progeny of HI-affected parents. Our results suggest an epigenetic transfer mechanism of some of the neurological symptoms associated with neonatal HI. Elucidating the transfer of brain injury to the next generation after HI calls attention to the risks associated with HI injury and the need for proper treatment to reverse these effects. Assessing the devastating extent of HI's reach serves as a cautionary tale to the risks associated with neonatal HI, and provides an incentive to create improved therapeutic measures to treat HI.

Annonacin in Asimina triloba fruit: implication for neurotoxicity

INTRODUCTION

The acetogenin, annonacin, from the tropical annonaceous plant Annona muricata, is a lipophilic, mitochondrial complex I inhibitor reported to be more toxic than rotenone to mesencephalic neurons. The temperate annonaceous plant Asimina triloba (pawpaw) is native to the Eastern United States and products are available online. This study determined whether annonacin is in the pawpaw fruit pulp and whether it or the crude ethyl acetate extract is toxic to cortical neurons.

METHODS

Pawpaw extract was prepared by pulp extraction with methanol and liquid-liquid partitioning with ethyl acetate (EtOAc). Annonacin was isolated from the crude EtOAc extract via column chromatography using a gradient solvent system of increasing polarity. Mass spectroscopy, nuclear magnetic resonance and infrared spectroscopy were used to compare isolated material with synthetic annonacin data and a natural annonacin sample. Toxicity of isolated annonacin and the total EtOAc extract was determined in primary rat cortical neurons using the MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay.

RESULTS

The average concentration of annonacin in the fruit pulp was 0.0701±0.0305mg/g. Purified annonacin (30.07μg/ml) and crude EtOAc extract (47.96μg/ml) induced 50% death of cortical neurons 48h post treatment. Annonacin toxicity was enhanced in the presence of crude extract.

DISCUSSION

Pawpaw fruit contains a high concentration of annonacin, which is toxic to cortical neurons. Crude fruit extract also induced neurotoxicity, highlighting the need for additional studies to determine the potential risks of neurodegeneration associated with chronic exposure to pawpaw products.

Oxygen resuscitation after hypoxia ischemia stimulates prostaglandin pathway in rat cortex

Exposure to hypoxia and hyperoxia in a rodent model of perinatal ischemia results in delayed cell death and inflammation. Hyperoxia increases oxidative stress that can trigger inflammatory cascades, neutrophil activation, and brain microvascular injury. Here we show that 100% oxygen resuscitation in our rodent model of perinatal ischemia increases cortical COX-2 protein levels, S-nitrosylated COX-2cys526, PGE2, iNOS and 5-LOX, all components of the prostaglandin and leukotriene inflammatory pathway.

14-3-3theta protects against neurotoxicity in a cellular Parkinson's disease model through inhibition of the apoptotic factor Bax

Disruption of 14-3-3 function by alpha-synuclein has been implicated in Parkinson's disease. As 14-3-3s are important regulators of cell death pathways, disruption of 14-3-3s could result in the release of pro-apoptotic factors, such as Bax. We have previously shown that overexpression of 14-3-3θ reduces cell loss in response to rotenone and MPP⁺ in dopaminergic cell culture and reduces cell loss in transgenic C. elegans that overexpress alpha-synuclein. In this study, we investigate the mechanism for 14-3-3θ's neuroprotection against rotenone toxicity. While 14-3-3s can inhibit many pro-apoptotic factors, we demonstrate that inhibition of one factor in particular, Bax, is important to 14-3-3s' protection against rotenone toxicity in dopaminergic cells. We found that 14-3-3θ overexpression reduced Bax activation and downstream signaling events, including cytochrome C release and caspase 3 activation. Pharmacological inhibition or shRNA knockdown of Bax provided protection against rotenone, comparable to 14-3-3θ's neuroprotective effects. A 14-3-3θ mutant incapable of binding Bax failed to protect against rotenone. These data suggest that 14-3-3θ's neuroprotective effects against rotenone are at least partially mediated by Bax inhibition and point to a potential therapeutic role of 14-3-3s in Parkinson's disease.

Role of cAMP-responsive element-binding protein (CREB)-regulated transcription coactivator 3 (CRTC3) in the initiation of mitochondrial biogenesis and stress response in liver cells

Peroxisome proliferator-activated receptor α, coactivator 1α (PGC-1α) is the master regulator of mitochondrial biogenesis. PGC-1α expression is under the control of the transcription factor, cAMP-responsive element-binding protein (CREB). In searching for candidate transcription factors that mediate mitochondrial stress-initiated mitochondria-to-nucleus signaling in the regulation of mitochondrial biogenesis, we assessed the effect of silencing CREB-regulated transcription co-activators (CRTC). CRTC isoforms are co-activators of CREB-regulated transcription by a CREB phosphorylation-independent pathway. Using cultured HepG2 cells and primary mouse hepatocytes, we determined that mitochondrial stress imposed by the complex I inhibitor rotenone elicited mitochondrial biogenesis, which was dependent on an induction of PGC-1α, which was inhibited by silencing PGC-1α. PGC-1α induction in response to rotenone was inhibited by silencing the expression of CRTC3, which blocked downstream mitochondria biogenesis. In contrast, silencing CRTC2 did not affect the induction of this pathway in response to rotenone. Thus, CRTC3 plays a selective role in mitochondrial biogenesis in response to rotenone.

Association with endoplasmic reticulum promotes proteasomal degradation of GADD34 protein

Stress-induced endogenous and ectopically expressed GADD34 proteins were present both in the cytoplasm and in membranes, with their membrane association showing similar biochemical properties. Deletion of N-terminal sequences in GADD34-GFP proteins highlighted an amphipathic helix, whose hydrophobic surface, specifically valine 25 and leucine 29, mediated endoplasmic reticulum (ER) localization. Substitution of leucines for three arginines on the polar surface indicated that the same helix also mediated the association of GADD34 with mitochondria. Fluorescence protease protection and chemical modification of cysteines substituted in the membrane-binding domain pointed to a monotopic insertion of GADD34 into the outer layer of the ER membrane. Fluorescence recovery after photobleaching showed that ER association retards the mobility of GADD34 in living cells. Both WT GADD34 and the mutant, V25R, effectively scaffolded the α-isoform of protein phosphatase-1 (PP1α) and enabled eIF2α dephosphorylation. However, the largely cytosolic V25R protein displayed a reduced rate of proteasomal degradation, and unlike WT GADD34, whose ectopic expression resulted in a dilated or distended ER, V25R did not modify ER morphology. These studies suggested that the association of with ER modulates intracellular trafficking and proteasomal degradation of GADD34, and in turn, its ability to modify ER morphology.

Regulation of Th1/Th17 cytokines and IDO gene expression by inhibition of calpain in PBMCs from MS patients

Multiple sclerosis (MS) pathology is marked by the massive infiltration of myelin-specific T cells into the central nervous system (CNS). During active disease, pro-inflammatory Th1/Th17 cells predominate over immunoregulatory Th2/Treg cells. Here, we show that calpain inhibition downregulates Th1/Th17 inflammatory cytokines and mRNA in MS patient peripheral blood mononuclear cells (PBMCs) activated with anti-CD3/28 or MBP. Interestingly, calpain inhibition elevated IDO gene expression in MS PBMCs, which was markedly decreased in calpain expressing cells. Functional assay showed that incubation of MS patient PBMCs with calpain inhibitor or recombinant IDO attenuates T cell proliferation. These results suggest that calpain inhibition may attenuate MS pathology and augment the efficacy of standard immunomodulatory agents used to treat this disease.