Global brain ischemia and reperfusion: Golgi apparatus ultrastructure in neurons selectively vulnerable to death

UBIAD1 alleviates ferroptotic neuronal death by enhancing antioxidative capacity by cooperatively restoring impaired mitochondria and Golgi apparatus upon cerebral ischemic/reperfusion insult

Background

Neuronal death due to over-oxidative stress responses defines the pathology of cerebral ischemic/reperfusion (I/R) insult. Ferroptosis is a form of oxidative cell death that is induced by disruption of the balance between antioxidants and pro-oxidants in cells. However, the potential mechanisms responsible for cerebral I/R-induced ferroptotic neuronal death have not been conclusively determined. UBIAD1, is a newly identified antioxidant enzyme that catalyzes coenzyme Q10 (CoQ10) and vitamin K2 biosynthesis in the Golgi apparatus membrane and mitochondria, respectively. Even though UBIAD1 is a significant mediator of apoptosis in cerebral I/R challenge, its roles in ferroptotic neuronal death remain undefined. Therefore, we investigated whether ferroptotic neuronal death is involved in cerebral I/R injury. Further, we evaluated the functions and possible mechanisms of UBIAD1 in cerebral I/R-induced ferroptotic neuronal death, with a major focus on mitochondrial and Golgi apparatus dysfunctions.

Results

Ferroptosis occurred in cerebral I/R. Ferroptotic neuronal death promoted cerebral I/R-induced brain tissue injury and neuronal impairment. UBIAD1 was expressed in cerebral tissues and was localized in neurons, astrocytes, and microglia. Under cerebral I/R conditions overexpressed UBIAD1 significantly suppressed lipid peroxidation and ferroptosis. Moreover, upregulated UBIAD1 protected against brain tissue damage and neuronal death by alleviating I/R-mediated lipid peroxidation and ferroptosis. However, UBIAD1 knockdown reversed these changes. Enhanced UBIAD1-mediated ferroptosis elevated the antioxidative capacity by rescuing mitochondrial and Golgi apparatus dysfunction in cerebral I/R-mediated neuronal injury. They improved the morphology and biofunctions of the mitochondria and Golgi apparatus, thereby elevating the levels of SOD, T-AOC and production of CoQ10, endothelial nitric oxide synthase (eNOS)-regulated nitric oxide (NO) generation as well as suppressed MDA generation.

Conclusions

The neuroprotective agent, UBIAD1, modulates I/R-mediated ferroptosis by restoring mitochondrial and Golgi apparatus dysfunction in damaged brain tissues and neurons, thereby enhancing antioxidative capacities. Moreover, the rescue of impaired mitochondrial and Golgi apparatus as a possible mechanism of regulating ferroptotic neuronal death is a potential treatment strategy for ischemic stroke.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13578-022-00776-9.

The key roles of organelles and ferroptosis in Alzheimer's disease

Alzheimer's disease (AD), an age-related neurodegenerative disease, is a striking global health problem. Ferroptosis is a newly discovered form of cell death characterized by iron-dependent lipid peroxidation products and the accumulation of lethal reactive oxygen species. Strict regulation of iron metabolism is essential to ensure neuronal homeostasis. Excess and deficiency of iron are both associated with neurodegeneration. Studies have shown that oxidative stress caused by cerebral iron metabolism disorders in the body is involved in the process of AD, ferroptosis may play an important role in the pathogenesis of AD, and regulating ferroptosis is expected to be a new direction for the treatment of AD. Various organelles are closely related to ferroptosis: mitochondria, endoplasmic reticulum, Golgi apparatus, and lysosome are involved in the regulation of ferroptosis from the aspects of iron metabolism and redox imbalance. In this review, the relationship between AD and the dysfunction of organelles (including mitochondria, endoplasmic reticulum, lysosome, and Golgi apparatus) and the role of organelles in ferroptosis of AD were reviewed to provide insights for understanding the relationship between organelles and ferroptosis in AD and the treatment of AD.

How cytosolic compartments play safeguard functions against neuroinflammation and cell death in cerebral ischemia

Ischemic stroke is the second leading cause of mortality and disability globally. Neuronal damage following ischemic stroke is rapid and irreversible, and eventually results in neuronal death. In addition to activation of cell death signaling, neuroinflammation is also considered as another pathogenesis that can occur within hours after cerebral ischemia. Under physiological conditions, subcellular organelles play a substantial role in neuronal functionality and viability. However, their functions can be remarkably perturbed under neurological disorders, particularly cerebral ischemia. Therefore, their biochemical and structural response has a determining role in the sequel of neuronal cells and the progression of disease. However, their effects on cell death and neuroinflammation, as major underlying mechanisms of ischemic stroke, are still not understood. This review aims to provide a comprehensive overview of the contribution of each organelle on these pathological processes after ischemic stroke.

Interruption of Endolysosomal Trafficking After Focal Brain Ischemia

A typical neuron consists of a soma, a single axon with numerous nerve terminals, and multiple dendritic trunks with numerous branches. Each of the 100 billion neurons in the brain has on average 7,000 synaptic connections to other neurons. The neuronal endolysosomal compartments for the degradation of axonal and dendritic waste are located in the soma region. That means that all autophagosomal and endosomal cargos from 7,000 synaptic connections must be transported to the soma region for degradation. For that reason, neuronal endolysosomal degradation is an extraordinarily demanding and dynamic event, and thus is highly susceptible to many pathological conditions. Dysfunction in the endolysosomal trafficking pathways occurs in virtually all neurodegenerative diseases. Most lysosomal storage disorders (LSDs) with defects in the endolysosomal system preferentially affect the central nervous system (CNS). Recently, significant progress has been made in understanding the role that the endolysosomal trafficking pathways play after brain ischemia. Brain ischemia damages the membrane fusion machinery co-operated by N-ethylmaleimide sensitive factor (NSF), soluble NSF attachment protein (SNAP), and soluble NSF attachment protein receptors (SNAREs), thus interrupting the membrane-to-membrane fusion between the late endosome and terminal lysosome. This interruption obstructs all incoming traffic. Consequently, both the size and number of endolysosomal structures, autophagosomes, early endosomes, and intra-neuronal protein aggregates are increased extensively in post-ischemic neurons. This cascade of events eventually damages the endolysosomal structures to release hydrolases leading to ischemic brain injury. Gene knockout and selective inhibition of key endolysosomal cathepsins protects the brain from ischemic injury. This review aims to provide an update of the current knowledge, future research directions, and the clinical implications regarding the critical role of the neuronal endolysosomal trafficking pathways in ischemic brain injury.

Golgi stress mediates redox imbalance and ferroptosis in human cells

Cytotoxic activities of several Golgi-dispersing compounds including AMF-26/M-COPA, brefeldin A and golgicide A have previously been shown to induce autophagy or apoptosis. Here, we demonstrate that these Golgi disruptors also trigger ferroptosis, a non-apoptotic form of cell death characterized by iron-dependent oxidative degradation of lipids. Inhibitors of ferroptosis not only counteract cell death, but they also protect from Golgi dispersal and inhibition of protein secretion in response to several Golgi stress agents. Furthermore, the application of sublethal doses of ferroptosis-inducers such as erastin and sorafenib, low cystine growth conditions, or genetic knockdown of SLC7A11 and GPX4 all similarly protect cells from Golgi stress and lead to modulation of ACSL4, SLC7A5, SLC7A11 or GPX4 levels. Collectively, this study suggests a previously unrecognized function of the Golgi apparatus, which involves cellular redox control and prevents ferroptotic cell death.

Hamed Alborzinia et al. show that Golgi-dispersing compounds trigger iron-dependent oxidative degradation of lipids, inducing a non-apoptotic cell death called ferroptosis. This study provides insight into the role of Golgi apparatus for preventing ferroptotic cell death through its cellular redox control.

The role of GRASPs in morphological alterations of Golgi apparatus: mechanisms and effects

The Golgi apparatus (GA) is a pivotal organelle in cell metabolism, functioning not only in the processing and transportation of cargoes but also in ion homeostasis, cell apoptosis, and stress sensing. We are interested in the intricate role of GA and the recently present novel concept of 'GA stress'. GA shows various morphological alterations in many neurodegenerative diseases and cell apoptosis induced by biochemical reagents, mechanisms in which oxidative stress is strongly involved. In turn, the structural changes and morphological alterations of the GA could also transduce stress signals. Therefore, besides the biochemical changes, more attention should be paid to the morphological alterations of the GA itself during pathological processes and diseases. The Golgi reassembly and stacking proteins (GRASPs) have been identified as important components acting in the transformation of Golgi structure, and they may thus affect the Golgi functions and cell behavior. In this review, we will discuss the intricate role of the GRASPs in remodeling the GA morphology and focus on their mechanisms and effects in the processes of Golgi stacking, mitosis, cell apoptosis, and cargo secretion. We would also like to provide a further prospective of their potential biological values in neurodegenerative diseases.

Protein misfolding, aggregation, and autophagy after brain ischemia

Ischemic brain injury is a common disorder linked to a variety of diseases. Significant progress has been made in our understanding of the underlying mechanisms. Previous studies show that protein misfolding, aggregation, and multiple organelle damage are major pathological events in postischemic neurons. The autophagy pathway is the chief route for bulk degradation of protein aggregates and damaged organelles. The latest studies suggest that impairment of autophagy contributes to abnormal protein aggregation and organelle damages after brain ischemia. This article reviews recent studies of protein misfolding, aggregation, and impairment of autophagy after brain ischemia.

Inhibition of sevoflurane postconditioning against cerebral ischemia reperfusion-induced oxidative injury in rats

The volatile anesthetic sevoflurane is capable of inducing preconditioning and postconditioning effects in the brain. In this study, we investigated the effects of sevoflurane postconditioning on antioxidant and immunity indexes in cerebral ischemia reperfusion (CIR) rats. Rats were randomly assigned to five separate experimental groups I–V. In the sham group (I), rats were subjected to the same surgery procedures except for occlusion of the middle cerebral artery and exposed to 1.0 MAC sevoflurane 90 min after surgery for 30 min. IR control rats (group II) were subjected to middle cerebral artery occlusion (MCAO) for 90 min and exposed to O₂ for 30 min at the beginning of reperfusion. Sevoflurane 0.5, 1.0 and 1.5 groups (III, IV, V) were all subjected to MCAO for 90 min, but at the beginning of reperfusion exposed to 0.5 MAC, 1.0 MAC or 1.5 MAC sevoflurane for 30 min, respectively. Results showed that sevoflurane postconditioning can decrease serum tumor necrosis factor-alpha (TNF-α), interleukin-1 beta (IL-1β), nitric oxide (NO), nitric oxide synthase (NOS) and increase serum interleukin-10 (IL-10) levels in cerebral ischemia reperfusion rats. In addition, sevoflurane postconditioning can still decrease blood lipid, malondialdehyde (MDA) levels, infarct volume and increase antioxidant enzymes activities, normal pyramidal neurons density in cerebral ischemia reperfusion rats. It can be concluded that sevoflurane postconditioning may decrease blood and brain oxidative injury and enhance immunity indexes in cerebral ischemia reperfusion rats.

The role of the Golgi apparatus in oxidative stress: is this organelle less significant than mitochondria?

Reactive oxygen species (ROS)/reactive nitrogen species (RNS) and ROS/RNS-mediated oxidative stress have well-established roles in many physiological and pathological processes and are associated with the pathogenesis of many diseases, such as hypertension, ischemia/reperfusion injury, diabetes mellitus, atherosclerosis, stroke, cancer, and neurodegenerative disorders. It is generally accepted that mitochondria play an essential role in oxidative stress because they are responsible for the primary generation of superoxide radicals. Little attention, however, has been paid to the importance of the Golgi apparatus (GA) in this process. The GA is a pivotal organelle in cell metabolism and participates in modifying, sorting, and packaging macromolecules for cell secretion or use within the cell. It is inevitably involved in the process of oxidative stress, which can cause modification and damage of lipids, proteins, DNA, and other structural constituents. Here we discuss the connections between the GA and oxidative stress and highlight the role of the GA in oxidative stress-related Ca(2+)/Mn(2+) homeostasis, cell apoptosis, sphingolipid metabolism, signal transduction, and antioxidation. We also provide a novel perspective on the subcellular significance of oxidative stress and its pathological implications and present "GA stress" as a new concept to explain the GA-specific stress response.

A novel 165-kDa Golgin protein induced by brain ischemia and phosphorylated by Akt protects against apoptosis

A cDNA encoding a novel protein was cloned from ischemic rat brain and found to be homologous to testis Mea-2 Golgi-associated protein (Golga3). The sequence predicted a 165-kDa protein, and in vitro translated protein exhibited a molecular mass of 165-170 kDa. Because brain ischemia induced the mRNA, and the protein localized to the Golgi apparatus, this protein was designated Ischemia-Inducible Golgin Protein 165 (IIGP165). In HeLa cells, serum and glucose deprivation-induced caspase-dependent cleavage of the IIGP165 protein, after which the IIGP165 fragments translocated to the nucleus. The C-terminus of IIGP165, which contains a LXXLL motif, appears to function as a transcriptional co-regulator. Akt co-localizes with IIGP165 protein in the Golgi in vivo, and phosphorylates IIGP165 on serine residues 345 and 134. Though transfection of IIGP165 cDNA alone does not protect HeLa cells from serum deprivation or Brefeldin-A-triggered cell death, co-transfection of both Akt and IIGP165 cDNA or combined IIGP165-transfection with PDGF treatment significantly protects HeLa cells better than either treatment alone. These data show that Akt phosphorylation of IIGP165 protects against apoptotic cell death, and add to evidence that the Golgi apparatus also plays a role in regulating apoptosis.

Insulin like growth factor-1 (IGF-1) decreases ischemia-reperfusion induced apoptosis and necrosis in diabetic rats

Previous evidence supports the view that insulin, as well as insulin like growth factor-1 (IGF-1) provides neurotropic support for neurons in the central nervous system (CNS) and peripheral nervous system (PNS). In the present study we evaluated the effects of the intravenous infusion of IGF-1 on both necrosis and apoptosis in the CNS of streptozotocin induced diabetic animals before and/or following middle cerebral artery occlusion (MCAO) with reperfusion. The lesion volume was used as an index of necrosis and the sensorimotor cortex (layers 5 and 6) as well as the CA1 and CA3 regions of the hippocampus were analyzed for apoptosis using TUNEL staining and Caspase-3 immunoreactivity. A large lesion volume was produced in diabetic animals after 2-h MCAO and 24-h reperfusion. Diabetic animals also had an elevated basal level of apoptotic cells that are bilaterally distributed. Apoptosis was further increased over basal after 2-h MCAO and 24-h reperfusion. The acute administration of IGF-1 30-min before or 2 h after MCAO followed by 24-h reperfusion decreased the lesion volume as well as the number of apoptotic cells in the cortical penumbra. Apoptosis as assessed by TUNEL and caspase-3 immunoreactivity was decreased in select sensorimotor cortex and hippocampal areas. We conclude that treatment with IGF-1 before or after ischemic insult significantly decreases both lesion volume and apoptosis in selected areas of the cortex and hippocampus.

Prolonged translation arrest in reperfused hippocampal cornu Ammonis 1 is mediated by stress granules

Global brain ischemia and reperfusion cause phosphorylation of the alpha subunit of eukaryotic initiation factor 2alpha, a reversible event associated with neuronal translation inhibition. However, the selective vulnerability of cornu Ammonis (CA) 1 pyramidal neurons correlates with irreversible translation inhibition. Phosphorylation of eukaryotic initiation factor 2alpha also leads to the formation of stress granules, cytoplasmic foci containing, in part, components of the 48S pre-initiation complex and the RNA binding protein T cell internal antigen-1 (TIA-1). Stress granules are sites of translationally inactive protein synthesis machinery. Here we evaluated stress granules in rat hippocampal formation neurons after 10 min global brain ischemia and 10 min, 90 min or 4 h of reperfusion by double-labeling immunofluorescence for two stress granule components: small ribosomal subunit protein 6 and TIA-1. Stress granules in CA3, hilus and dentate gyrus, but not CA1, increased at 10 min reperfusion and returned to control levels by 90 min reperfusion. Dynamic changes in the nuclear distribution of TIA-1 occurred in resistant neurons. At 4 h reperfusion, small ribosomal subunit protein 6 was solely localized within stress granules only in CA1 pyramidal neurons. Both TIA-1 and small ribosomal subunit protein 6 levels decreased approximately 50% in hippocampus homogenates. Electron microscopy showed stress granules to be composed of electron dense bodies 100-200 nm in diameter, that were not membrane bound, but were associated with endoplasmic reticulum. Alterations in stress granule behavior in CA1 pyramidal neurons provide a definitive mechanism for the continued inhibition of protein synthesis in reperfused CA1 pyramidal neurons following dephosphorylation of eukaryotic initiation factor 2alpha.

Cellular compartmentalization of phosphorylated eIF2alpha and neuronal NOS in human temporal lobe epilepsy with hippocampal sclerosis

Hippocampal sclerosis (HS) is the most common neuropathologic finding in patients with medically refractory temporal lobe epilepsy (TLE). The mechanisms resulting in neuronal injury and cell loss in HS are incompletely understood, but inhibition of protein synthesis may play a pivotal role in these processes. This study examined the relationships between two molecules known to be involved in reduced protein synthesis in animals subjected to traumatic brain injury. Translational initiation of protein synthesis is inhibited when 2alpha (eIF2alpha) is phosphorylated. Recently, nitric oxide (NO) has been shown to reduce protein synthesis by inducing phosphorylation of eIF2alpha. We performed immunocytochemistry for eIF2alpha(P) and histochemistry (NADPH-D reaction) for nitric oxide synthase (NOS) to determine the distribution of these molecules in hippocampi removed from patients undergoing anterior temporal lobectomy (ATL) for medically intractable TLE due to HS. The greatest number of eIF2alpha(P) positive cells was in the CA1 sector of the hippocampus, followed by the hilus of the dentate gyrus. NADPH-D positive neurons were observed most often in the hilus. Labeling in both instances involved neuronal cell body cytoplasm and varicose processes. Combination of both staining procedures revealed close relationships between differentially labeled neurons within the hilus. The results suggest that NO participates in the phosphorylation of eIF2alpha since we demonstrated that nNOS processes are closely related to eIF2alpha(P) positive cells. This may occur through activation of kinases such as PERK, which was recently revealed. In human, TLE protein synthesis inhibition may occur at the translational level since the eIF2alpha (P) labeling is cytoplasmic. Protein synthesis inhibition may contribute to neuronal cell injury and death in HS.

Effects of neonatal hypoxia/ischemia on ganglioside expression in the rat hippocampus

Neonatal Hypoxia-Ischemia (HI) triggers a cascade of biochemical events that result in neuronal injury, but the mechanisms underlying these processes are not completely understood, and information regarding the effect of HI on the synthesis of brain glycoconjugates is lacking. The present work evaluates the effects of neonatal HI on hippocampal ganglioside synthesis. Seven-day-old rat pups were exposed to HI for 2.5 h according to the modified Levine model and samples from hyppocampus were obtained at 30 min as well as at 1, 2 and 4 days later. The activity for synthesis of gangliosides was evaluated by determining the incorporation of N-acetyl [3H]neuraminc acid ([3H]NeuAc) into the endogenous gangliosides of Golgi membranes and by determining the activity of Sial-T2 (GD3 synthase) and GalNAc-T (GM2 synthase), the two enzymes acting on sialyllactosylceramide (GM3) at the branching point of synthesis of a- and b-ganglioside pathway. Northern blot experiments were also conducted to determine transcription levels of the mRNAs specific for these transferases. Neonatal HI caused a relative increase of in vitro [3H]NeuAc incorporation into endogenous lactosylceramide, which was most noticeable at 30 min and I day post-event and disappeared by day 2 and 4. The transient accumulation of [3H]GM3 correlated with decreases in the activities of GD3- and GM2 synthase measured at 30 min and at 1 day after the HI insult. No significant variations in the expression of the genes for these enzymes were observed. Results suggest that transient accumulation of GM3 may be due to post-translational events negatively modulating both GD3- and GM2 synthase activities.

Protein aggregation after transient cerebral ischemia

Protein aggregates containing ubiquitinated proteins are commonly present in neurodegenerative disorders and have been considered to cause neuronal degeneration. Here, we report that transient cerebral ischemia caused severe protein aggregation in hippocampal CA1 neurons. By using ethanolic phosphotungstic acid electron microscopy (EM) and ubiquitin immunogold EM, we found that protein aggregates were accumulated in CA1 neurons destined to die 72 hr after 15 min of cerebral ischemia. Protein aggregates appeared as clumps of electron-dense materials that stained heavily for ubiquitin and were associated with various intracellular membranous structures. The protein aggregates appeared at 4 hr and progressively accumulated at 24 and 48 hr of reperfusion in CA1 dying neurons. However, they were rarely observed in dentate gyrus neurons that were resistant to ischemia. At 4 hr of reperfusion, protein aggregates were mainly associated with intracellular vesicles in the soma and dendrites, and the nuclear membrane. By 24 hr of reperfusion, the aggregates were also associated with mitochondria, the Golgi apparatus, and the dendritic plasmalemma. High-resolution confocal microscopy further demonstrated that protein aggregates containing ubiquitin were persistently and progressively accumulated in all CA1 dying neurons but not in neuronal populations that survive in this model. We conclude that proteins are severely aggregated in hippocampal neurons vulnerable to transient brain ischemia. We hypothesize that the accumulation of protein aggregates cause ischemic neuronal death.

Neuronal death in newborn striatum after hypoxia-ischemia is necrosis and evolves with oxidative stress

The mechanisms for neurodegeneration after hypoxia-ischemia (HI) in newborns are not understood. We tested the hypothesis that striatal neuron death is necrosis and evolves with oxidative stress and selective organelle damage. Piglets ( approximately 1 week old) were used in a model of hypoxia-asphyxia and survived for 3, 6, 12, or 24 h. Neuronal death was progressive over 3-24 h recovery, with approximately 80% of putaminal neurons dead at 24 h. Striatal DNA was digested randomly at 6-12 h. Ultrastructurally, dying neurons were necrotic. Damage to the Golgi apparatus and rough endoplasmic reticulum occurred at 3-12 h, while most mitochondria appeared intact until 12 h. Mitochondria showed early suppression of activity, then a transient burst of activity at 6 h, followed by mitochondrial failure (determined by cytochrome c oxidase assay). Cytochrome c was depleted at 6 h after HI and thereafter. Damage to lysosomes occurred within 3-6 h. By 3 h recovery, glutathione levels were reduced, and peroxynitrite-mediated oxidative damage to membrane proteins, determined by immunoblots for nitrotyrosine, occurred at 3-12 h. The Golgi apparatus and cytoskeleton were early targets for extensive tyrosine nitration. Striatal neurons also sustained hydroxyl radical damage to DNA and RNA within 6 h after HI. We conclude that early glutathione depletion and oxidative stress between 3 and 6 h reperfusion promote damage to membrane and cytoskeletal proteins, DNA and RNA, as well as damage to most organelles, thereby causing neuronal necrosis in the striatum of newborns after HI.

Survival- and death-promoting events after transient cerebral ischemia: phosphorylation of Akt, release of cytochrome C and Activation of caspase-like proteases

Release of cytochrome c (cyt c) into cytoplasm initiates caspase-mediated apoptosis, whereas activation of Akt kinase by phosphorylation at serine-473 prevents apoptosis in several cell systems. To investigate cell death and cell survival pathways, the authors studied release of cyt c, activation of caspase, and changes in Akt phosphorylation in rat brains subjected to 15 minutes of ischemia followed by varying periods of reperfusion. The authors found by electron microscopic study that a portion of mitochondria was swollen and structurally altered, whereas the cell membrane and nuclei were intact in hippocampal CA1 neurons after 36 hours of reperfusion. In some neurons, the pattern of immunostaining for cyt c changed from a punctuate pattern, likely representing mitochondria, to a more diffuse cytoplasmic localization at 36 and 48 hours of reperfusion as examined by laser-scanning confocal microscopic study. Western blot analysis showed that cyt c was increased in the cytosolic fraction in the hippocampus after 36 and 48 hours of reperfusion. Consistently, caspase-3-like activity was increased in these hippocampal samples. As demonstrated by Western blot using phosphospecific Akt antibody, phosphorylation of Akt at serine-473 in the hippocampal region was highly increased during the first 24 hours but not at 48 hours of reperfusion. The authors conclude that transient cerebral ischemia activates both cell death and cell survival pathways after ischemia. The activation of Akt during the first 24 hours conceivably may be one of the factors responsible for the delay in neuronal death after global ischemia.

Cell death, calcium mobilization, and immunostaining for phosphorylated eukaryotic initiation factor 2-alpha (eIF2alpha) in neuronally differentiated NB-104 cells: arachidonate and radical-mediated injury mechanisms

These experiments examine the effects of arachidonate with respect to cell death, radical-mediated injury, Ca2+ mobilization, and formation of ser-51-phosphorylated eukaryotic initiation factor 2alpha [eIF2alpha(P)]. It is known that during brain ischemia the concentration of free arachidonate can reach 180 microM, and during reperfusion oxidative metabolism of arachidonate leads to generation of superoxide that can reduce stored ferric iron and promote lipid peroxidation. During early brain reperfusion, we have shown an approximately 20-fold increase in eIF2alpha(P) which maps to vulnerable neurons that display inhibition of protein synthesis. Here in neuronally differentiated NB-104 cells, equivalent cell death (assessed by LDH release) was induced by 40 microM arachidonate and 20 microM cumene hydroperoxide (CumOOH, a known alkoxyl radical generator). In these injury models (1) radical inhibitors (BHA, BHT, and the lipophilic iron chelator EMHP) block CumOOH-induced cell death but do not block arachidonate-induced death; (2) 40 microM arachidonate (but not up to 40 microM CumOOH) rapidly induces Ca2+ release from intracellular stores; (3) both 40 microM arachidonate and 20 microM CumOOH induce intense immunostaining for eIF2alpha(P); and (4) the elF2alpha(P) immunostaining induced by CumOOH but not that induced by arachidonate is completely blocked by anti-radical intervention with EMHP. Arachidonate-induced formation of eIF2alpha(P) and cell death do not require iron-mediated radical mechanisms and are associated with Ca2+ release from intracellular stores; however, radical-mediated injury also induces both eIF2alpha(P) and cell death without release of intracellular Ca2+. Our data link eIF2alpha(P) formation during brain reperfusion to two established injury mechanisms that may operate concurrently.

Modification of postsynaptic densities after transient cerebral ischemia: a quantitative and three-dimensional ultrastructural study

Abnormal synaptic transmission has been hypothesized to be a cause of neuronal death resulting from transient ischemia, although the mechanisms are not fully understood. Here, we present evidence that synapses are markedly modified in the hippocampus after transient cerebral ischemia. Using both conventional and high-voltage electron microscopy, we performed two- and three-dimensional analyses of synapses selectively stained with ethanolic phosphotungstic acid in the hippocampus of rats subjected to 15 min of ischemia followed by various periods of reperfusion. Postsynaptic densities (PSDs) from both area CA1 and the dentate gyrus were thicker and fluffier in postischemic hippocampus than in controls. Three-dimensional reconstructions of selectively stained PSDs created using electron tomography indicated that postsynaptic densities became more irregular and loosely configured in postischemic brains compared with those in controls. A quantitative study based on thin sections of the time course of PSD modification indicated that the increase in thickness was both greater and more long-lived in area CA1 than in dentate gyrus. Whereas the magnitude of morphological change in dentate gyrus peaked at 4 hr of reperfusion (140% of control values) and declined thereafter, changes in area CA1 persisted and increased at 24 hr of reperfusion (191% of control values). We hypothesize that the degenerative ultrastructural alteration of PSDs may produce a toxic signal such as a greater calcium influx, which is integrated from the thousands of excitatory synapses onto dendrites, and is propagated to the neuronal somata where it causes or contributes to neuronal damage during the postischemic phase.

Usual and unusual methods for detection of lipid peroxides as indicators of tissue injury in cerebral ischemia: what is appropriate and useful?

1. Free radical-dependent lipid peroxidation processes have long been thought to contribute to brain damage following stroke or cerebral ischemia/reperfusion. 2. The preponderance of evidence for this belief has been derived indirectly, through diminution of tissue injury indices (e.g., brain infarct volume) facilitated by application of free radical scavenger substances. 3. Direct, unequivocal evidence for lipid peroxidation in terms of classical assays (detection of conjugated diene absorbance or thiobarbituric acid-reactive substances) is considerably less common, and its validity can be questioned. 4. Correlations of treatment-induced diminishment of brain injury indices with reductions in lipid peroxidation level are rarer still. 5. Reasons underlying the disparity between the belief that lipid peroxidation contributes to ischemic brain injury and direct evidence for this contribution (at least acutely) are proposed, along with evidence that new methods are being developed which should provide the basis for obtaining a definitive answer.

Assembly of proteins to postsynaptic densities after transient cerebral ischemia

Transient ischemia leads to changes in synaptic efficacy and results in selective neuronal damage during the postischemic phase, although the mechanisms are not fully understood. The protein composition and ultrastructure of postsynaptic densities (PSDs) were studied by using a rat transient ischemic model. We found that a brief ischemic episode induced a marked accumulation in PSDs of the protein assembly ATPases, N-ethylmaleimide-sensitive fusion protein, and heat-shock cognate protein-70 as well as the BDNF receptor (trkB) and protein kinases, as determined by protein microsequencing. The changes in PSD composition were accompanied by a 2.5-fold increase in the yield of PSD protein relative to controls. Biochemical modification of PSDs correlated well with an increase in PSD thickness observed in vivo by electron microscopy. We conclude that a brief ischemic episode modifies the molecular composition and ultrastructure of synapses by assembly of proteins to the postsynaptic density, which may underlie observed changes in synaptic function and selective neuronal damage.