Overexpression of mitochondrial Hsp70/Hsp75 in rat brain protects mitochondria, reduces oxidative stress, and protects from focal ischemia

Effect of polyphenols on oxidative stress and mitochondrial dysfunction in neuronal death and brain edema in cerebral ischemia

Polyphenols are natural substances with variable phenolic structures and are elevated in vegetables, fruits, grains, bark, roots, tea, and wine. There are over 8000 polyphenolic structures identified in plants, but edible plants contain only several hundred polyphenolic structures. In addition to their well-known antioxidant effects, select polyphenols also have insulin-potentiating, anti-inflammatory, anti-carcinogenic, anti-viral, anti-ulcer, and anti-apoptotic properties. One important consequence of ischemia is neuronal death and oxidative stress plays a key role in neuronal viability. In addition, neuronal death may be initiated by the activation of mitochondria-associated cell death pathways. Another consequence of ischemia that is possibly mediated by oxidative stress and mitochondrial dysfunction is glial swelling, a component of cytotoxic brain edema. The purpose of this article is to review the current literature on the contribution of oxidative stress and mitochondrial dysfunction to neuronal death, cell swelling, and brain edema in ischemia. A review of currently known mechanisms underlying neuronal death and edema/cell swelling will be undertaken and the potential of dietary polyphenols to reduce such neural damage will be critically reviewed.

Mitochondrial compartmentalized protein folding and tumor cell survival

Molecular chaperones are master regulators of protein folding quality control, and it is widely accepted that these functions are aberrantly exploited in human tumors. What has also emerged in recent years is that chaperone control of protein folding does not occur randomly in cells, but is spatially compartmentalized in subcellular organelles and specialized microenvironments. Fresh experimental evidence has now uncovered a role for mitochondrial localized chaperones to oversee the protein folding environment within the organelle, selectively in tumor cells. Perturbation of this compartmentalized chaperone network triggers an array of compensatory responses that aims at restoring homeostasis, while also providing novel opportunities for rational cancer therapy.

miR-181 regulates GRP78 and influences outcome from cerebral ischemia in vitro and in vivo

MicroRNAs (miRNA) are short (~22nt) single stranded RNAs that downregulate gene expression. Although recent studies indicate extensive miRNA changes in response to ischemic brain injury, there is currently little information on the roles of specific miRNAs in this setting. Heat shock proteins (HSP) of the HSP70 family have been extensively studied for their multiple roles in cellular protection, but there is little information on their regulation by miRNAs. We used bioinformatics to identify miR-181 as a possible regulator of several HSP70 family members. We validated GRP78/BIP as a target by dual luciferase assay. In response to stroke in the mouse we find that miR-181 increases in the core, where cells die, but decreases in the penumbra, where cells survive. Increased levels of miR-181a are associated with decreased GRP78 protein levels, but increased levels of mRNA, implicating translational arrest. We manipulated levels of miR-181a using plasmid overexpression of pri-miR-181ab or mimic to increase, and antagomir or inhibitor to reduce levels. Increased miR-181a exacerbated injury both in vitro and in the mouse stroke model. Conversely, reduced levels were associated with reduced injury and increased GRP78 protein levels. Studies in C6 cells show that if GRP78 levels are maintained miR-181a no longer exerts a toxic effect. These data demonstrate that miR-181 levels change in response to stroke and inversely correlate with levels of GRP78. Importantly, reducing or blocking miR-181a protects the brain from stroke.

Inflammation, mitochondria, and the inhibition of adult neurogenesis

The process of neurogenesis continues throughout life, with thousands of new neurons generated every day in the mammalian brain. Impairment of hippocampal neurogenesis has been suggested to be involved in neurodegenerative conditions, including the cognitive decline associated with aging, Alzheimer's disease, Parkinson's disease, and ionizing radiation. These neurodegenerative conditions are all characterized by proinflammatory changes and increased numbers of activated microglia. Activated microglia produce a variety of proinflammatory factors, including interleukin-6, tumor necrosis factor-α, reactive oxygen species, and nitric oxide, all of which are antineurogenic. These same factors have also been shown to suppress mitochondrial function, but the role of mitochondria in neurogenesis remains barely investigated. This brief review summarizes the findings of several studies that support a role for mitochondrial impairment as part of the mechanism of the reduction of neurogenesis associated with inflammation.

Distinct role of Hsp70 in Drosophila hemocytes during severe hypoxia

Severe hypoxia can lead to injury and mortality in vertebrate or invertebrate organisms. Our research is focused on understanding the molecular mechanisms that lead to injury or adaptation to hypoxic stress using Drosophila as a model system. In this study, we employed the UAS-Gal4 system to dissect the protective role of Hsp70 in specific tissues in vivo under severe hypoxia. In contrast to overexpression in tissues such as muscles, heart, and brain, we found that overexpression of Hsp70 in hemocytes of flies provides a remarkable survival benefit to flies exposed to severe hypoxia for days. Furthermore, these flies were tolerant not only to severe hypoxia but also to other stresses such as oxidant stress (e.g., paraquat feeding or hyperoxia). Interestingly we observed that the better survival with Hsp70 overexpression in hemocytes under hypoxia or oxidant stress is causally linked to reactive oxygen species (ROS) reduction in whole flies. We also show that hemocytes are a major source of ROS generation, leading to injury during hypoxia, and their elimination results in a better survival under hypoxia. Hence, our study identified a protective role for Hsp70 in Drosophila hemocytes, which is linked to ROS reduction in the whole flies and thus helps in their remarkable survival during oxidant or hypoxic stress.

HSP75 protects against cardiac hypertrophy and fibrosis

Cardiac hypertrophy, a major determinant of heart failure, is associated with heat shock proteins (HSPs). HSP75 has been reported to protect against environmental stresses; however, its roles in cardiac hypertrophy remain unclear. Here, we generated cardiac-specific inducible HSP75 transgenic mice (TG) and cardiac hypertrophy was developed at 4 weeks after aortic banding in TG mice and wild-type littermates. The results revealed that overexpression of HSP75 prevented cardiac hypertrophy and fibrosis as assessed by heart weight/body weight ratio, heart weight/tibia length ratio, echocardiographic and hemodynamic parameters, cardiomyocyte width, left ventricular collagen volume, and gene expression of hypertrophic markers. Further studies showed that overexpression of HSP75 inhibited the activation of TAK/P38, JNK, and AKT signaling pathways. Thus, HSP75 likely reduces the hypertrophy and fibrosis induced by pressure overload through blocking TAK/P38, JNK, and AKT signaling pathways.

Increased brain injury and worsened neurological outcome in interleukin-4 knockout mice after transient focal cerebral ischemia

BACKGROUND AND PURPOSE

Stroke causes brain injury with activation of an inflammatory response that can contribute to injury. We tested the hypothesis that the anti-inflammatory cytokine interleukin-4 (IL-4) reduces injury after stroke using IL-4 knockout (KO) adult male mice.

METHODS

IL-4 KO and wild-type mice were subjected to transient middle cerebral artery occlusion. Outcome was assessed by triphenyltetrazolium chloride staining for infarct volume, neuroscore and spontaneous activity for behavioral outcome, and immunostaining and stereological counting for cellular response.

RESULTS

Infarction volume at 24 hours was significantly larger in IL-4 KO mice, neurological score was significantly worse, and spontaneous activity was reduced compared with wild-type mice. Increased macrophage/microglial infiltration, increased numbers of myeloperoxidase-positive cells, and increased Th1/Th2 ratio were observed in the infarct core in IL-4 KO mice. Reduced astrocyte activation was observed in the cortical penumbra in IL-4 KO mice. Recombinant IL-4 administered intracerebroventricularly before middle cerebral artery occlusion significantly reduced infarct volume, improved neurological score, reduced macrophages/microglia, and lowered the Th1/Th2 ratio in IL-4 KO mice, but not in wild-type.

CONCLUSIONS

Loss of IL-4 signaling in KO mice was associated with worse outcome, and this was reversed by giving exogenous IL-4. Worsened outcome was associated with increased inflammation in the core, which was reversed in IL-4 KO but not significantly changed in wild-type mice by exogenous IL-4. This is consistent with IL-4 signaling leading to reduced inflammation in the core and a possible beneficial role for activated astrocytes in the penumbra.

Mortalin inhibition in experimental Parkinson's disease

Among heat shock proteins, mortalin has been linked to the pathogenesis of Parkinson's disease. In the present work a rat model of Parkinson's disease was used to analyze the expression of striatal proteins and, more specifically, mortalin expression. The possible involvement of mortalin in Parkinson's disease pathogenesis was further investigated by utilizing an electrophysiological approach and pharmacological inhibition of mortalin in both the physiological and the parkinsonian states. Proteomic analysis was used to investigate changes in striatal protein expression in the 6-hydroxydopamine rat model of Parkinson's disease. The electrophysiological effects of MKT-077, a rhodamine-123 analogue acting as an inhibitor of mortalin, were measured by field potential recordings from corticostriatal brain slices obtained from control, sham-operated, and 6-hydroxydopamine-denervated animals. Slices in the presence of rotenone, an inhibitor of mitochondrial complex I, were also analyzed. Proteomic analysis revealed downregulation of mortalin in the striata of 6-hydroxydopamine-treated rats in comparison with sham-operated animals. MKT-077 reduced corticostriatal field potential amplitude in physiological conditions, inducing membrane depolarization and inward current in striatal medium spiny neurons. In addition, we observed that concentrations of MKT-077 not inducing any electrophysiological effect in physiological conditions caused significant changes in striatal slices from parkinsonian animals as well as in slices treated with a submaximal concentration of rotenone. These findings suggest a critical link between mortalin function and mitochondrial activity in both physiological and pathological conditions mimicking Parkinson's disease.

The group II chaperonin Mm-Cpn binds and refolds human γD crystallin

Chaperonins assist in the folding of nascent and misfolded proteins, though the mechanism of folding within the lumen of the chaperonin remains poorly understood. The archeal chaperonin from Methanococcus marapaludis, Mm-Cpn, shares the eightfold double barrel structure with other group II chaperonins, including the eukaryotic TRiC/CCT, required for actin and tubulin folding. However, Mm-Cpn is composed of a single species subunit, similar to group I chaperonin GroEL, rather than the eight subunit species needed for TRiC/CCT. Features of the β-sheet fold have been identified as sites of recognition by group II chaperonins. The crystallins, the major components of the vertebrate eye lens, are β-sheet proteins with two homologous Greek key domains. During refolding in vitro a partially folded intermediate is populated, and partitions between productive folding and off-pathway aggregation. We report here that in the presence of physiological concentrations of ATP, Mm-Cpn suppressed the aggregation of HγD-Crys by binding the partially folded intermediate. The complex was sufficiently stable to permit recovery by size exclusion chromatography. In the presence of ATP, Mm-Cpn promoted the refolding of the HγD-Crys intermediates to the native state. The ability of Mm-Cpn to bind and refold a human β-sheet protein suggests that Mm-Cpn may be useful as a simplified model for the substrate recognition mechanism of TRiC/CCT.

Impairment of oxidative stress-induced heme oxygenase-1 expression by the defect of Parkinson-related gene of PINK1

Parkinson's disease (PD) is one of the most common neurodegenerative diseases. Mutation in the phosphatase and tensin homolog (PTEN)-induced putative kinase 1 (PINK1) gene causes an autosomal recessive form of PD. However, the etiology related to PINK1 is still not clear. Here, we examined the effect of PINK1 on heme oxygenase (HO)-1 induction in SH-SY5Y neuronal cells following H(2)O(2) or 1-methyl-4-phenylpyridinium (MPP(+)) treatment. The HO-1 induction in response to H(2)O(2) and MPP(+) treatment was impaired by the expression of recombinant PINK1 G309D mutant. PINK1 G309D mutation increased the apoptosis of SH-SY5Y cells following H(2)O(2) treatment and cell survival was rescued by the over-expression of HO-1 using adenovirus (Ad) infection. In addition, knockdown of tumor necrosis factor receptor-associated protein-1 (TRAP1), which is the substrate of PINK1 kinase, in SH-SY5Y cells also inhibited the expression of HO-1 in response to oxidative stress. The up-regulation of TRAP1 expression following H(2)O(2) treatment was inhibited by the expression of recombinant PINK1 G309D mutant. The H(2)O(2)-induced HO-1 induction was Akt- and ERK-dependent. The phosphorylation of ERK and Akt but not p38 was inhibited in cells expressing the PINK1 G309D mutant and knockdown of TRAP1. These results indicate a novel pathway by which the defect of PINK1 inhibits the oxidative stress-induced HO-1 production. Impairment of HO-1 production following oxidative stress may accelerate the dopaminergic neurodegeneration in Parkinson patients with PINK1 defect.

Mitochondrial dynamics, cell death and the pathogenesis of Parkinson's disease

The structure and function of the mitochondrial network is regulated by mitochondrial biogenesis, fission, fusion, transport and degradation. A well-maintained balance of these processes (mitochondrial dynamics) is essential for neuronal signaling, plasticity and transmitter release. Core proteins of the mitochondrial dynamics machinery play important roles in the regulation of apoptosis, and mutations or abnormal expression of these factors are associated with inherited and age-dependent neurodegenerative disorders. In Parkinson's disease (PD), oxidative stress and mitochondrial dysfunction underlie the development of neuropathology. The recessive Parkinsonism-linked genes PTEN-induced kinase 1 (PINK1) and Parkin maintain mitochondrial integrity by regulating diverse aspects of mitochondrial function, including membrane potential, calcium homeostasis, cristae structure, respiratory activity, and mtDNA integrity. In addition, Parkin is crucial for autophagy-dependent clearance of dysfunctional mitochondria. In the absence of PINK1 or Parkin, cells often develop fragmented mitochondria. Whereas excessive fission may cause apoptosis, coordinated induction of fission and autophagy is believed to facilitate the removal of damaged mitochondria through mitophagy, and has been observed in some types of cells. Compensatory mechanisms may also occur in mice lacking PINK1 that, in contrast to cells and Drosophila, have only mild mitochondrial dysfunction and lack dopaminergic neuron loss. A better understanding of the relationship between the specific changes in mitochondrial dynamics/turnover and cell death will be instrumental to identify potentially neuroprotective pathways steering PINK1-deficient cells towards survival. Such pathways may be manipulated in the future by specific drugs to treat PD and perhaps other neurodegenerative disorders characterized by abnormal mitochondrial function and dynamics.

Knockdown of mortalin within the medial prefrontal cortex impairs normal sensorimotor gating

The 70-kDa mitochondrial heat shock protein, mortalin, is a ubiquitously expressed, multifunctional protein that is capable of binding the neurotransmitter, dopamine, within the brain. Dopamine dysregulation has been implicated in many of the abnormal neurological behaviors. Although studies have indicated that mortalin is differentially regulated in response to dopaminergic modulation, research has yet to elucidate the role of mortalin in the regulation of dopaminergic activity. This study seeks to investigate the role of mortalin in the regulation of dopamine-dependent behavior, specifically as it pertains to schizophrenia (SCZ). Mortalin expression was knocked down through the infusion of antisense oligodeoxynucleotide molecules into the medial prefrontal cortex (mPFC). Rats infused with mortalin antisense oligodeoxynucleotide molecules exhibited significant prepulse inhibition deficits, suggestive of defects in normal sensorimotor gating. Furthermore, mortalin misexpression within the mPFC was coupled to a significant increase in mortalin protein expression within the nucleus accumbens at the molecular level. These findings demonstrate that mortalin plays an essential role in the regulation of dopamine-dependent behavior and plays an even greater role in the pathogenesis of SCZ.

Overexpressing GRP78 influences Ca2+ handling and function of mitochondria in astrocytes after ischemia-like stress

Ca(2+) transfer from endoplasmic reticulum (ER) to mitochondria at contact sites between the organelles can induce mitochondrial dysfunction and programmed cell death after stress. The ER-localized chaperone glucose-regulated protein 78kDa (GRP78/BiP) protects neurons against excitotoxicity and apoptosis. Here we show that overexpressing GRP78 protects astrocytes against ischemic injury, reduces net flux of Ca(2+) from ER to mitochondria, increases Ca(2+) uptake capacity in isolated mitochondria, reduces free radical production, and preserves respiratory activity and mitochondrial membrane potential after stress. We conclude that GRP78 influences ER-mitochondrial Ca(2+) crosstalk to maintain mitochondrial function and protect astrocytes from ischemic injury.

Mitochondrial protection attenuates inflammation-induced impairment of neurogenesis in vitro and in vivo

The impairment of hippocampal neurogenesis has been linked to the pathogenesis of neurological disorders from chronic neurodegenerative disease to the progressive cognitive impairment of children who receive brain irradiation. Numerous studies provide evidence that inflammation downregulates neurogenesis, with multiple factors contributing to this impairment. Although mitochondria are one of the primary targets of inflammatory injury, the role of mitochondrial function in the modulation of neurogenesis remains relatively unstudied. In this study, we used neurosphere-derived cells to show that immature doublecortin (Dcx)-positive neurons are uniquely sensitive to mitochondrial inhibition, demonstrating rapid loss of mitochondrial potential and cell viability compared with glial cells and more mature neurons. Mitochondrial inhibition for 24 h produced no significant changes in astrocyte or oligodendrocyte viability, but reduced viability of mature neurons by 30%, and reduced survival of Dcx(+) cells by 60%. We demonstrate that protection of mitochondrial function with mitochondrial metabolites or the mitochondrial chaperone mtHsp75/mortalin partially reverses the inflammation-associated impairment of neurogenesis in vitro and in irradiated mice in vivo. Our findings highlight mitochondrial mechanisms involved in neurogenesis and indicate mitochondria as a potential target for protective strategies to prevent the impairment of neurogenesis by inflammation.

Measuring endogenous 5-HT release by emission tomography: promises and pitfalls

Molecular in vivo neuroimaging techniques can be used to measure regional changes in endogenous neurotransmitters, evoked by challenges that alter synaptic neurotransmitter concentration. This technique has most successfully been applied to the study of endogenous dopamine release using positron emission tomography, but has not yet been adequately extended to other neurotransmitter systems. This review focuses on how the technique has been applied to the study of the 5-hydroxytryptamine (5-HT) system. The principles behind visualising fluctuations in neurotransmitters are introduced, with reference to the dopaminergic system. Studies that aim to image acute, endogenous 5-HT release or depletion at 5-HT receptor targets are summarised, with particular attention to studies in humans. Radiotracers targeting the 5-HT(1A), 5-HT(2A), and 5-HT(4) receptors and the serotonin reuptake transporter have been explored for their sensitivity to 5-HT fluctuations, but with mixed outcomes; tracers for these targets cannot reliably image endogenous 5-HT in humans. Shortcomings in our basic knowledge of the mechanisms underlying changes in binding potential are addressed, and suggestions are made as to how the selection of targets, radiotracers, challenge paradigms, and experimental design might be optimised to improve our chances of successfully imaging endogenous neurotransmitters in the future.

Astrocyte targeted overexpression of Hsp72 or SOD2 reduces neuronal vulnerability to forebrain ischemia

Brief forebrain ischemia is a model of the delayed hippocampal neuronal loss seen in patients following cardiac arrest and resuscitation. Previous studies demonstrated that selective dysfunction of hippocampal CA1 subregion astrocytes occurs hours to days before delayed neuronal death. In this study we tested the strategy of directing protection to astrocytes to protect neighboring neurons from forebrain ischemia. Two well-studied protective proteins, heat shock protein 72 (Hsp72) or superoxide dismutase 2 (SOD2), were genetically targeted for expression in astrocytes using the astrocyte-specific human glial fibrillary acidic protein (GFAP) promoter. The expression constructs were injected stereotacticly immediately above the hippocampal CA1 region on one side of the rat brain two days prior to forebrain ischemia. Cell type specific expression was confirmed by double label immunohistochemistry. When the expression constructs were injected two days before transient forebrain ischemia, the loss of CA1 hippocampal neurons observed seven days later was significantly reduced on the injected side compared with controls. This neuroprotection was associated with significantly better preservation of astrocyte glutamate transporter-1 immunoreactivity at 5-h reperfusion and reduced oxidative stress. Improving the resistance of astrocytes to ischemic stress by targeting either the cytosolic or mitochondrial compartment was thus associated with preservation of CA1 neurons following forebrain ischemia. Targeting astrocytes is a promising strategy for neuronal preservation following cardiac arrest and resuscitation.

Intracellular or extracellular heat shock protein 70 differentially regulates cardiac remodelling in pressure overload mice

AIMS

Innate and adaptive immune responses are associated with the development of hypertension-induced myocardial hypertrophy and fibrosis. As a result, we investigated whether heat shock protein (HSP) 70, which is a molecule of damage-associated molecular patterns, could induce inflammation in the myocardium and promote the development of hypertension-induced cardiac hypertrophy and fibrosis.

METHODS AND RESULTS

We found that HSP70 serum levels, as well as the amount of HSP70 translocation to the cardiomyocyte membranes and the interstitial space, were elevated in the hypertensive mice caused by abdominal aortic constriction (AAC). Transcriptional inhibition of HSP70 expression by a specific heat shock transcript factor inhibitor, KNK437, reduced the serum level, and the re-distribution of HSP70. It promoted myocardial hypertrophy and cardiac dysfunctions although it protected animals from AAC-induced cardiac fibrosis. On the other hand, the functional antagonism of HSP70 by an anti-HSP70 antibody attenuated AAC-induced cardiac hypertrophy and fibrosis without adverse haemodynamic effects. The cardioprotective effect of the anti-HSP70 antibody was largely attributed to its ability to block AAC-activated immune response in the heart, as was indicated by suppressing the hypertension-enhanced conjugation of HSP70 with toll-like receptor 4, reducing heart-infiltrating macrophages, decreasing the expression of pro-inflammatory factor monocyte chemoattractant protein-1 and profibrotic factor transforming growth factor beta 1, and attenuating pro-hypertrophy signal MAPK P38 and ERK.

CONCLUSION

These results indicate that intracellular and extracellular HSP70 have different roles in the regulation of cardiac remodelling and function in response to hypertension. Extracellular HSP70 is a potential therapeutic target against cardiac hypertrophy and fibrosis.

Heat shock proteins: cellular and molecular mechanisms in the central nervous system

Emerging evidence indicates that heat shock proteins (HSPs) are critical regulators in normal neural physiological function as well as in cell stress responses. The functions of HSPs represent an enormous and diverse range of cellular activities, far beyond the originally identified roles in protein folding and chaperoning. HSPs are now understood to be involved in processes such as synaptic transmission, autophagy, ER stress response, protein kinase and cell death signaling. In addition, manipulation of HSPs has robust effects on the fate of cells in neurological injury and disease states. The ongoing exploration of multiple HSP superfamilies has underscored the pluripotent nature of HSPs in the cellular context, and has demanded the recent revamping of the nomenclature referring to these families to reflect a re-organization based on structure and function. In keeping with this re-organization, we first discuss the HSP superfamilies in terms of protein structure, regulation, expression and distribution in the brain. We then explore major cellular functions of HSPs that are relevant to neural physiological states, and from there we discuss known and proposed HSP impacts on major neurological disease states. This review article presents a three-part discussion on the array of HSP families relevant to neuronal tissue, their cellular functions, and the exploration of therapeutic targets of these proteins in the context of neurological diseases.

Changes in the expression of mitochondrial peroxiredoxin and thioredoxin in neurons and glia and their protective effects in experimental cerebral ischemic damage

We observed chronological changes in the mitochondrial-specific antioxidant enzymes peroxiredoxin 3 (Prx3) and thioredoxin 2 (Trx2) and their neuroprotective effects in the hippocampal CA1 region after 5 min of transient cerebral ischemia in gerbils. In the sham-operated group, weak Prx3 and Trx2 immunoreactivity was detected in the stratum pyramidale. Prx3 immunoreactivity was increased in pyramidal neurons and expressed in microglia 1 and 3 days, respectively, after ischemia/reperfusion (I/R). Trx2 immunoreactivity in pyramidal neurons increased 30 min and 1 day after I/R and decreased 6 h after I/R. Trx2 immunoreaction was expressed in astrocytes at 3 days postischemia. The intraventricular administration of Prx3 or Prx3/Trx2 (16 microg/20 microl, icv) using an osmotic pump significantly reduced ischemia-induced hyperactivity in a spontaneous motor test and protected CA1 pyramidal neurons from the ischemic damage. In addition, the activation of astrocytes and microglia was decreased in the ischemic CA1 region after Prx3/Trx2 treatment. In addition, treatment with Prx3 or Prx3/Trx2 significantly reduced lipid peroxidation and the release of cytochrome c from mitochondria and cytoplasm in the ischemic CA1 region. These results suggest that changes in the expression of Prx3 and Trx2 in the hippocampal CA1 region after I/R may be associated with the delayed neuronal death of CA1 pyramidal cells induced by transient cerebral ischemia, and that treatment with Prx3 or Prx3/Trx2 in ischemic brains shows a potent neuroprotective effect against ischemic damage by reducing lipid peroxidation and mitochondrial-mediated apoptosis by I/R.

Oxidative protein folding in the endoplasmic reticulum: tight links to the mitochondria-associated membrane (MAM)

The production of secretory proteins at the ER (endoplasmic reticulum) depends on a ready supply of energy and metabolites as well as the close monitoring of the chemical conditions that favor oxidative protein folding. ER oxidoreductases and chaperones fold nascent proteins into their export-competent three-dimensional structure. Interference with these protein folding enzymes leads to the accumulation of unfolded proteins within the ER lumen, causing an acute organellar stress that triggers the UPR (unfolded protein response). The UPR increases the transcription of ER chaperones commensurate with the load of newly synthesized proteins and can protect the cell from ER stress. Persistant stress, however, can force the UPR to commit cells to undergo apoptotic cell death, which requires the emptying of ER calcium stores. Conversely, a continuous ebb and flow of calcium occurs between the ER and mitochondria during resting conditions on a domain of the ER that forms close contacts with mitochondria, the MAM (mitochondria-associated membrane). On the MAM, ER folding chaperones such as calnexin and calreticulin and oxidoreductases such as ERp44, ERp57 and Ero1alpha regulate calcium flux from the ER through reversible, calcium and redox-dependent interactions with IP3Rs (inositol 1,4,5-trisphophate receptors) and with SERCAs (sarcoplasmic/endoplasmic reticulum calcium ATPases). During apoptosis progression and depending on the identity of the ER chaperone and oxidoreductase, these interactions increase or decrease, suggesting that the extent of MAM targeting of ER chaperones and oxidoreductases could shift the readout of ER-mitochondria calcium exchange from housekeeping to apoptotic. However, little is known about the cytosolic factors that mediate the on/off interactions between ER chaperones and oxidoreductases with ER calcium channels and pumps. One candidate regulator is the multi-functional molecule PACS-2 (phosphofurin acidic cluster sorting protein-2). Recent studies suggest that PACS-2 mediates localization of a mobile pool of calnexin to the MAM in addition to regulating homeostatic ER calcium signaling as well as MAM integrity. Together, these findings suggest that cytosolic, membrane and lumenal proteins combine to form a two-way switch that determines the rate of protein secretion by providing ions and metabolites and that appears to participate in the pro-apoptotic ER-mitochondria calcium transfer.

Mitochondrial chaperone tumour necrosis factor receptor-associated protein 1 protects cardiomyocytes from hypoxic injury by regulating mitochondrial permeability transition pore opening

Tumour necrosis factor receptor-associated protein 1 (TRAP1) is a mitochondrial chaperone that plays a role in maintaining mitochondrial function and regulating cell apoptosis. The opening of the mitochondrial permeability transition pore (MPTP) is a key step in cell death after hypoxia. However, it is still unclear whether TRAP1 protects cardiomyocytes from hypoxic damage by regulating the opening of the pore. In the present study, primary cultured cardiomyocytes from neonatal rats were used to investigate changes in TRAP1 expression after hypoxia treatment as well as the mechanism and effect of TRAP1 on hypoxic damage. The results obtained showed that TRAP1 expression increased after 1 h of hypoxia and continued to increase for up to 12 h of treatment. Hypoxia caused an increase in cell death and decreased cell viability and mitochondrial membrane potential; overexpressing TRAP1 prevented hypoxia-induced damage to cardiomyocytes. The silencing of TRAP1 induced an increase in cell death and decreased both cell viability and mitochondrial membrane potential in cardiomyocytes under normoxic and hypoxic conditions. Furthermore, cell damage induced by the silencing of TRAP1 was prevented by the mitochondrial permeability transition pore inhibitor, cyclosporin A. These data demonstrate that hypoxia induces an increase in TRAP1 expression in cardiomyocytes, and that TRAP1 plays a protective role by regulating the opening of the mitochondrial permeability transition pore.

Noninvasive assessment of the brain redox status after transient middle cerebral artery occlusion using Overhauser-enhanced magnetic resonance imaging

Oxidative stress has been implicated in the cell death that occurs after ischemia-reperfusion of the brain, which causes the production of reactive oxygen species and a decrease in antioxidants, leading to mitochondrial dysfunction. However, the invasive methods used to collect much of this evidence are themselves stress inducing, which could skew the results. In this study, we aimed at demonstrating brain redox alterations after ischemia-reperfusion noninvasively, using Overhauser-enhanced magnetic resonance imaging. The reduction rate of 3-methoxycarbonyl-2,2,5,5-tetramethylpyrrolidine-L-oxyl (methoxycarbonyl-PROXYL), a redox-sensitive contrast agent, was used as an index of the redox status in vivo. No changes were observed in the antioxidant concentration, the mitochondrial complex activity, or in the redox status image intensity after 3 h of reperfusion, following transient middle cerebral artery occlusion; however, after 24 h of reperfusion, the methoxycarbonyl-PROXYL reduction rate, calculated from continuous images, had decreased significantly. Concordantly, biochemical assays showed that the concentration of ascorbic acid in the ischemic hemisphere and the activity of mitochondrial complex II had also decreased. Thus, the noninvasive imaging of the brain redox alterations faithfully reflected changes in antioxidant levels and in mitochondrial complex II activity after ischemia-reperfusion.

Heat-shock pretreatment inhibits sorbitol-induced apoptosis in K562, U937 and HeLa cells

The aim of this study was to determine whether heat-shock pretreatment exerted a protective effect against sorbitol-induced apoptotic cell death in K562, U937 and HeLa cell lines and whether such protection was associated with a decreased cytochrome c release from mithocondria and a decreased activation of caspase-9 and -3. Following heat-shock pretreatment (42 +/- 0.3 degrees C for 1 hr), these cell lines were exposed to sorbitol for 1 hr. Apoptosis was evaluated by DNA fragmentation, whereas caspase-9,-3 activation, cytochrome c release and heat-shock protein70 (HSP70) were assayed by Western Blot. Sorbitol exposure-induced apoptosis in these different cell lines with a marked activation of caspase-9 and caspase-3, whereas heat-shock pretreatment before sorbitol exposure, induced expression of HSP70 and inhibited sorbitol-mediated cytochrome c release and subsequent activation of caspase-9 and caspase-3. Similarly, overexpression of HSP70 in the three cell lines studied prevented caspase-9 cleavage and activation as well as cell death. Furthermore, we showed that the mRNA expression of iNOS decreased during both the heat-shock treatment and heat-shock pretreatment before sorbitol exposure. By contrast, the expression of Cu-Zn superoxide dismutase (SOD) and Mn-SOD proteins increased during heat-shock pretreatment before sorbitol exposure. We conclude that, heat-shock pretreatment protects different cell lines against sorbitol-induced apoptosis through a mechanism that is likely to involve SOD family members.

Phyllaemblicin B inhibits Coxsackie virus B3 induced apoptosis and myocarditis

Coxsackie virus B3 (CVB3) is believed to be a major contributor to viral myocarditis since virus-associated apoptosis plays a role in the pathogenesis of experimental myocarditis. In this study, we investigated the in vitro and in vivo antiviral activities of Phyllaemblicin B, the main ellagitannin compound isolated from Phyllanthus emblica, a Chinese herb medicine, against CVB3. Herein we report that Phyllaemblicin B inhibited CVB3-mediated cytopathic effects on HeLa cells with an IC(50) value of 7.75+/-0.15microg/mL. In an in vivo assay, treatment with 12mgkg(-1)d(-1) Phyllaemblicin B reduced cardiac CVB3 titers, decreased the activities of LDH and CK in murine serum, and alleviated pathological damages of cardiac muscle in myocarditic mice. Moreover, Phyllaemblicin B clearly inhibited CVB3-associated apoptosis effects both in vitro and in vivo. These results show that Phyllaemblicin B exerts significant antiviral activities against CVB3. Therefore, Phyllaemblicin B may represent a potential therapeutic agent for viral myocarditis.

Compartmentalized cancer drug discovery targeting mitochondrial Hsp90 chaperones

There is a plethora of attractive drug targets in cancer, but their therapeutic exploitation proved more difficult than expected, and only rarely truly successful. One possibility not often considered in drug discovery is that cancer signaling pathways are not randomly arranged in cells, but orchestrated in specialized subcellular compartments. The identification of heat shock protein-90 (Hsp90) chaperones in mitochondria of tumors, but not most normal tissues, provides an example of a compartmentalized network of cell survival, opening fresh prospects for novel, subcellularly targeted cancer drug discovery.