Mitochondrial permeability transition pore is a potential drug target for neurodegeneration

Bivalent Compound 17MN Exerts Neuroprotection through Interaction at Multiple Sites in a Cellular Model of Alzheimer's Disease

Multiple pathogenic factors have been suggested to play a role in the development of Alzheimer's disease (AD). The multifactorial nature of AD also suggests the potential use of compounds with polypharmacology as effective disease-modifying agents. Recently, we have developed a bivalent strategy to include cell membrane anchorage into the molecular design. Our results demonstrated that the bivalent compounds exhibited multifunctional properties and potent neuroprotection in a cellular AD model. Herein, we report the mechanistic exploration of one of the representative bivalent compounds, 17MN, in MC65 cells. Our results established that MC65 cells die through a necroptotic mechanism upon the removal of tetracycline (TC). Furthermore, we have shown that mitochondrial membrane potential and cytosolic Ca2+ levels are increased upon removal of TC. Our bivalent compound 17MN can reverse such changes and protect MC65 cells from TC removal induced cytotoxicity. The results also suggest that 17MN may function between the Aβ species and RIPK1 in producing its neuroprotection. Colocalization studies employing a fluorescent analog of 17MN and confocal microscopy demonstrated the interactions of 17MN with both mitochondria and endoplasmic reticulum, thus suggesting that 17MN exerts its neuroprotection via a multiple-site mechanism in MC65 cells. Collectively, these results strongly support our original design rationale of bivalent compounds and encourage further optimization of this bivalent strategy to develop more potent analogs as novel disease-modifying agents for AD.

Shawn, the Drosophila Homolog of SLC25A39/40, Is a Mitochondrial Carrier That Promotes Neuronal Survival

Mitochondria play an important role in the regulation of neurotransmission, and mitochondrial impairment is a key event in neurodegeneration. Cells rely on mitochondrial carrier proteins of the SLC25 family to shuttle ions, cofactors, and metabolites necessary for enzymatic reactions. Mutations in these carriers often result in rare but severe pathologies in the brain, and some of the genes, including SLC25A39 and SLC25A40, reside in susceptibility loci of severe forms of epilepsy. However, the role of most of these carriers has not been investigated in neurons in vivo. We identified shawn, the Drosophila homolog of SLC25A39 and SLC25A40, in a genetic screen to identify genes involved in neuronal function. Shawn localizes to mitochondria, and missense mutations result in an accumulation of reactive oxygen species, mitochondrial dysfunction, and neurodegeneration. Shawn regulates metal homeostasis, and we found in shawn mutants increased levels of manganese, calcium, and mitochondrial free iron. Mitochondrial mutants often cannot maintain synaptic transmission under demanding conditions, but shawn mutants do, and they also do not display endocytic defects. In contrast, shawn mutants harbor a significant increase in neurotransmitter release. Our work provides the first functional annotation of these essential mitochondrial carriers in the nervous system, and the results suggest that metal imbalances and mitochondrial dysfunction may contribute to defects in synaptic transmission and neuronal survival.

SIGNIFICANCE STATEMENT

We describe for the first time the role of the mitochondrial carrier Shawn/SLC25A39/SLC25A40 in the nervous system. In humans, these genes reside in susceptibility loci for epilepsy, and, in flies, we observe neuronal defects related to mitochondrial dysfunction and metal homeostasis defects. Interestingly, shawn mutants also harbor increased neurotransmitter release and neurodegeneration. Our data suggest a connection between maintaining a correct metal balance and mitochondrial function to regulate neuronal survival and neurotransmitter release.

Protein undernutrition during development and oxidative impairment in the central nervous system (CNS): potential factors in the occurrence of metabolic syndrome and CNS disease

Mitochondria play a regulatory role in several essential cell processes including cell metabolism, calcium balance and cell viability. In recent years, it has been postulated that mitochondria participate in the pathogenesis of a number of chronic diseases, including central nervous system disorders. Thus, the concept of mitochondrial function now extends far beyond the common view of this organelle as the ‘powerhouse’ of the cell to a new appreciation of the mitochondrion as a transducer of early metabolic insult into chronic disease in later life. In this review, we have attempted to describe some of the associations between nutritional status and mitochondrial function (and dysfunction) during embryonic development with the occurrence of neural oxidative imbalance and neurogenic disease in adulthood.

Protection effect of piperine and piperlonguminine from Piper longum L. alkaloids against rotenone-induced neuronal injury

Currently available treatment approaches for Parkinson׳s disease (PD) are limited in terms of variety and efficacy. Piper longum L. (PLL; Piperaceae) is used in traditional medicine in Asia and the Pacific Islands, with demonstrated anti-inflammatory and antioxidant activities in preclinical studies, and alkaloid extracts of PLL have shown protective effects in PD models. The present study investigated the mechanistic basis for the observed protective effects of PLL. Rats treated with PLL-derived alkaloids showed improvement in rotenone-induced motor deficits, while reactive oxygen species (ROS) production was decreased, mitochondrial membrane potential was stabilized, and the opening of the mitochondrial permeability transition pore (mPTP)-which is involved in ROS production-was inhibited. In addition, rotenone-induced apoptosis was abrogated in the presence of these alkaloids, while a pretreatment stimulated autophagy, likely mitigating neuronal injury by the removal of damaged mitochondria. These findings provide novel insight into the neuroprotective function of PLL as well as evidence in favor of its use in PD treatment. This article is part of a Special Issue entitled SI: Neuroprotection.

Identification of a Small Molecule Cyclophilin D Inhibitor for Rescuing Aβ-Mediated Mitochondrial Dysfunction

Cyclophilin D (CypD), a peptidylprolyl isomerase F (PPIase), plays a central role in opening the mitochondrial membrane permeability transition pore leading to cell death. CypD resides in the mitochondrial matrix, associates with the inner mitochondrial membrane, interacts with amyloid beta to exacerbate mitochondrial and neuronal stress and has been linked to Alzheimer's disease (AD). We report the biological activity of a small-molecule CypD inhibitor (C-9), which binds strongly to CypD and attenuates mitochondrial and cellular perturbation insulted by Aβ and calcium stress. Binding affinities for C-9 were determined using in vitro surface plasmon resonance. This compound antagonized calcium-mediated mitochondrial swelling, abolished Aβ-induced mitochondrial dysfunction as shown by increased cytochrome c oxidase activity and adenosine-5'-triphosphate levels, and inhibited CypD PPIase enzymatic activity by real-time fluorescence capture assay using Hamamatsu FDSS 7000. Compound C-9 seems a good candidate for further investigation as an AD drug.

ROS and ROS-Mediated Cellular Signaling

It has long been recognized that an increase of reactive oxygen species (ROS) can modify the cell-signaling proteins and have functional consequences, which successively mediate pathological processes such as atherosclerosis, diabetes, unchecked growth, neurodegeneration, inflammation, and aging. While numerous articles have demonstrated the impacts of ROS on various signaling pathways and clarify the mechanism of action of cell-signaling proteins, their influence on the level of intracellular ROS, and their complex interactions among multiple ROS associated signaling pathways, the systemic summary is necessary. In this review paper, we particularly focus on the pattern of the generation and homeostasis of intracellular ROS, the mechanisms and targets of ROS impacting on cell-signaling proteins (NF-κB, MAPKs, Keap1-Nrf2-ARE, and PI3K-Akt), ion channels and transporters (Ca(2+) and mPTP), and modifying protein kinase and Ubiquitination/Proteasome System.

Exposure to a 50-Hz magnetic field induced mitochondrial permeability transition through the ROS/GSK-3β signaling pathway

PURPOSE

To investigate the biological effects of a 50-Hz magnetic field (MF) on mitochondrial permeability.

MATERIALS AND METHODS

Human amniotic epithelial cells were exposed to MF (50 Hz, 0.4 mT) for different durations. Mitochondrial permeability, mitochondrial membrane potential (ΔΨm), cytochrome c (Cyt-c) release and the related mechanisms were explored.

RESULTS

Exposure to the MF at 0.4 mT for 60 min transiently induced mitochondrial permeability transition (MPT) and Cyt-c release, although there was no significant effect on mitochondrial membrane potential (ΔΨm). Other than decreasing the total Bcl-2 associated X protein (Bax) level, MF exposure did not significantly affect the levels of Bax and B-cell lymphoma-2 (Bcl-2) in mitochondria. In addition, cells exposed to the MF showed increased intracellular reactive oxidative species (ROS) levels and glycogen synthase kinase-3β (GSK-3β) dephosphorylation at 9 serine residue (Ser(9)). Moreover, the MF-induced MPT was attenuated by ROS scavenger (N-acetyl-L-cysteine, NAC) or GSK-3β inhibitor, and NAC pretreatment prevented GSK-3β dephosphorylation (Ser(9)) caused by MF exposure.

CONCLUSION

MPT induced by MF exposure was mediated through the ROS/GSK-3β signaling pathway.

Calcium signaling as a mediator of cell energy demand and a trigger to cell death

Calcium signaling is pivotal to a host of physiological pathways. A rise in calcium concentration almost invariably signals an increased cellular energy demand. Consistent with this, calcium signals mediate a number of pathways that together serve to balance energy supply and demand. In pathological states, calcium signals can precipitate mitochondrial injury and cell death, especially when coupled to energy depletion and oxidative or nitrosative stress. This review explores the mechanisms that couple cell signaling pathways to metabolic regulation or to cell death. The significance of these pathways is exemplified by pathological case studies, such as those showing loss of mitochondrial calcium uptake 1 in patients and ischemia/reperfusion injury.

Overexpression of mitochondrial Hsp75 protects neural stem cells against microglia-derived soluble factor-induced neurotoxicity by regulating mitochondrial permeability transition pore opening in vitro

Microglia (MG)-induced neurotoxicity, a major determinant of Alzheimer's disease, is closely related to the survival of neural stem cells (NSCs). Heat shock protein 75 (Hsp75) has been reported to exert protective effects against environmental stresses; however, whether or not it protects NSCs against MG-derived soluble factor-induced neurotoxicity remains unclear. In the present study, we constructed NSCs that overexpressed human Hsp75 protein and established a co-culture system in order to elucidate the role of Hsp75 in NSC-MG interactions. The results obtained indicated that Hsp75 expression increased after 12 h of soluble factor induction and continued to increase for up to 36 h of treatment. The overexpression of Hsp75 decreased NSC apoptosis and preserved mitochondrial membrane potential. Further experiments revealed that the overexpression of Hsp75 inhibited the formation of cyclophilin D (CypD)-dependent mitochondrial permeability transition pore (mPTP) involvement in neurotoxicity-mediated mitochondrial dysfunction and suppressed the activation of the mitochondrial apoptotic cascade, as demonstrated by the inhibition of the release of cytochrome c (Cytc) and the activation of caspase-3. The findings of this study demonstrate that Hsp75 overexpression prevents the impairment of NSCs induced by MG-derived soluble factors by regulating the opening of mPTP. Thus, Hsp75 warrants further investigation as a potential candidate for protection against neurotoxicity.

Oxidative stress, mitochondrial and proteostasis malfunction in adrenoleukodystrophy: A paradigm for axonal degeneration

Peroxisomal and mitochondrial malfunction, which are highly intertwined through redox regulation, in combination with defective proteostasis, are hallmarks of the most prevalent multifactorial neurodegenerative diseases-including Alzheimer's (AD) and Parkinson's disease (PD)-and of the aging process, and are also found in inherited conditions. Here we review the interplay between oxidative stress and axonal degeneration, taking as groundwork recent findings on pathomechanisms of the peroxisomal neurometabolic disease adrenoleukodystrophy (X-ALD). We explore the impact of chronic redox imbalance caused by the excess of very long-chain fatty acids (VLCFA) on mitochondrial respiration and biogenesis, and discuss how this impairs protein quality control mechanisms essential for neural cell survival, such as the proteasome and autophagy systems. As consequence, prime molecular targets in the pathogenetic cascade emerge, such as the SIRT1/PGC-1α axis of mitochondrial biogenesis, and the inhibitor of autophagy mTOR. Thus, we propose that mitochondria-targeted antioxidants; mitochondrial biogenesis boosters such as the antidiabetic pioglitazone and the SIRT1 ligand resveratrol; and the autophagy activator temsirolimus, a derivative of the mTOR inhibitor rapamycin, hold promise as disease-modifying therapies for X-ALD.

Deletion of Cyclophilin D Impairs β-Oxidation and Promotes Glucose Metabolism

Cyclophilin D (CypD) is a mitochondrial matrix protein implicated in cell death, but a potential role in bioenergetics is not understood. Here, we show that loss or depletion of CypD in cell lines and mice induces defects in mitochondrial bioenergetics due to impaired fatty acid β-oxidation. In turn, CypD loss triggers a global compensatory shift towards glycolysis, with transcriptional upregulation of effectors of glucose metabolism, increased glucose consumption and higher ATP production. In vivo, the glycolytic shift secondary to CypD deletion is associated with expansion of insulin-producing β-cells, mild hyperinsulinemia, improved glucose tolerance, and resistance to high fat diet-induced liver damage and weight gain. Therefore, CypD is a novel regulator of mitochondrial bioenergetics, and unexpectedly controls glucose homeostasis, in vivo.

Arterial Smooth Muscle Mitochondria Amplify Hydrogen Peroxide Microdomains Functionally Coupled to L-Type Calcium Channels

RATIONALE

Mitochondria are key integrators of convergent intracellular signaling pathways. Two important second messengers modulated by mitochondria are calcium and reactive oxygen species. To date, coherent mechanisms describing mitochondrial integration of calcium and oxidative signaling in arterial smooth muscle are incomplete.

OBJECTIVE

To address and add clarity to this issue, we tested the hypothesis that mitochondria regulate subplasmalemmal calcium and hydrogen peroxide microdomain signaling in cerebral arterial smooth muscle.

METHODS AND RESULTS

Using an image-based approach, we investigated the impact of mitochondrial regulation of L-type calcium channels on subcellular calcium and reactive oxygen species signaling microdomains in isolated arterial smooth muscle cells. Our single-cell observations were then related experimentally to intact arterial segments and to living animals. We found that subplasmalemmal mitochondrial amplification of hydrogen peroxide microdomain signaling stimulates L-type calcium channels, and that this mechanism strongly impacts the functional capacity of the vasoconstrictor angiotensin II. Importantly, we also found that disrupting this mitochondrial amplification mechanism in vivo normalized arterial function and attenuated the hypertensive response to systemic endothelial dysfunction.

CONCLUSIONS

From these observations, we conclude that mitochondrial amplification of subplasmalemmal calcium and hydrogen peroxide microdomain signaling is a fundamental mechanism regulating arterial smooth muscle function. As the principle components involved are fairly ubiquitous and positioning of mitochondria near the plasma membrane is not restricted to arterial smooth muscle, this mechanism could occur in many cell types and contribute to pathological elevations of intracellular calcium and increased oxidative stress associated with many diseases.

Melatonin and Ischemic Stroke: Mechanistic Roles and Action

Stroke is one of the most devastating neurological disabilities and brain's vulnerability towards it proves to be fatal and socio-economic loss of millions of people worldwide. Ischemic stroke remains at the center stage of it, because of its prevalence amongst the several other types attacking the brain. The various cascades of events that have been associated with stroke involve oxidative stress, excitotoxicity, mitochondrial dysfunction, upregulation of Ca(2+) level, and so forth. Melatonin is a neurohormone secreted by pineal and extra pineal tissues responsible for various physiological processes like sleep and mood behaviour. Melatonin has been implicated in various neurological diseases because of its antioxidative, antiapoptotic, and anti-inflammatory properties. We have previously reviewed the neuroprotective effect of melatonin in various models of brain injury like traumatic brain injury and spinal cord injury. In this review, we have put together the various causes and consequence of stroke and protective role of melatonin in ischemic stroke.

Curcumin micelles improve mitochondrial function in neuronal PC12 cells and brains of NMRI mice - Impact on bioavailability

Curcumin, a polyphenolic compound abundant in the rhizome of Curcuma longa, has been reported to have various beneficial biological and pharmacological activities. Recent research revealed that curcumin might be valuable in the prevention and therapy of numerous disorders including neurodegenerative diseases like Alzheimer's disease. Due to its low absorption and quick elimination from the body, curcumin bioavailability is rather low which poses major problems for the use of curcumin as a therapeutic agent. There are several approaches to ameliorate curcumin bioavailability after oral administration, amongst them simultaneous administration with secondary plant compounds, micronization and micellation. We examined bioavailability in vivo in NMRI mice and the effects of native curcumin and a newly developed curcumin micelles formulation on mitochondrial function in vitro in PC12 cells and ex vivo in isolated mouse brain mitochondria. We found that curcumin micelles improved bioavailability of native curcumin around 10- to 40-fold in plasma and brain of mice. Incubation with native curcumin and curcumin micelles prevented isolated mouse brain mitochondria from swelling, indicating less mitochondrial permeability transition pore (mPTP) opening and prevention of injury. Curcumin micelles proved to be more efficient in preventing mitochondrial swelling in isolated mouse brain mitochondria and protecting PC12 cells from nitrosative stress than native curcumin. Due to their improved effectivity, curcumin micelles might be a suitable formulation for the prevention of mitochondrial dysfunction in brain aging and neurodegeneration.

Determination of small molecule ABAD inhibitors crossing blood-brain barrier and pharmacokinetics

A major obstacle to the development of effective treatment of Alzheimer's disease (AD) is successfully delivery of drugs to the brain. We have previously identified a series of benzothiazole phosphonate compounds that block the interaction of amyloid-β peptide with amyloid-β binding alcohol dehydrogenase (ABAD). A selective and sensitive method for the presence of three new benzothiazole ABAD inhibitors in mouse plasma, brain, and artificial cerebrospinal fluid has been developed and validated based on high performance liquid chromatography tandem mass spectrometry. Mass spectra were generated using Micromass Quattro Ultima "triple" quadrupole mass spectrometer equipped with an Electrospray Ionization interface. Good linearity was obtained over a concentration range of 0.05-2.5 μg/ml. The lowest limit of quantification and detection was found to be 0.05 μg/ml. All inter-day accuracies and precisions were within ± 15% of the nominal value and ± 20%, respectively, at the lower limit of quantitation. The tested compounds were stable at various conditions with recoveries >90.0% (RSD <10%). The method used for pharmacokinetic studies of compounds in mouse cerebrospinal fluid, plasma, and brain is accurate, precise, and specific with no matrix effect. Pharmacokinetic data showed that these compounds penetrate the blood-brain barrier (BBB) yielding 4-50 ng/ml peak brain concentrations and 2 μg/ml peak plasma concentrations from a 10 mg/kg dose. These results indicate that our newly synthesized small molecule ABAD inhibitors have a good drug properties with the ability to cross the blood-brain barrier, which holds a great potential for AD therapy.

How the Wnt signaling pathway protects from neurodegeneration: the mitochondrial scenario

Alzheimer’s disease (AD) is the most common neurodegenerative disorder and is characterized by progressive memory loss and cognitive decline. One of the hallmarks of AD is the overproduction of amyloid-beta aggregates that range from the toxic soluble oligomer (Aβo) form to extracellular accumulations in the brain. Growing evidence indicates that mitochondrial dysfunction is a common feature of neurodegenerative diseases and is observed at an early stage in the pathogenesis of AD. Reports indicate that mitochondrial structure and function are affected by Aβo and can trigger neuronal cell death. Mitochondria are highly dynamic organelles, and the balance between their fusion and fission processes is essential for neuronal function. Interestingly, in AD, the process known as “mitochondrial dynamics” is also impaired by Aβo. On the other hand, the activation of the Wnt signaling pathway has an essential role in synaptic maintenance and neuronal functions, and its deregulation has also been implicated in AD. We have demonstrated that canonical Wnt signaling, through the Wnt3a ligand, prevents the permeabilization of mitochondrial membranes through the inhibition of the mitochondrial permeability transition pore (mPTP), induced by Aβo. In addition, we showed that non-canonical Wnt signaling, through the Wnt5a ligand, protects mitochondria from fission-fusion alterations in AD. These results suggest new approaches by which different Wnt signaling pathways protect neurons in AD, and support the idea that mitochondria have become potential therapeutic targets for the treatment of neurodegenerative disorders. Here we discuss the neuroprotective role of the canonical and non-canonical Wnt signaling pathways in AD and their differential modulation of mitochondrial processes, associated with mitochondrial dysfunction and neurodegeneration.

The Parkinson Disease Mitochondrial Hypothesis

Parkinson’s disease is a common, adult-onset neurodegenerative disorder whose pathogenesis is still under intense investigation. Substantial evidence from postmortem human brain tissue, genetic- and toxin-induced animal and cellular models indicates that mitochondrial dysfunction plays a central role in the pathophysiology of the disease. This review discusses our current understanding of Parkinson’s disease–related mitochondrial dysfunction, including bioenergetic defects, mitochondrial DNA alterations, altered mitochondrial dynamics, activation of mitochondrial-dependent programmed cell death, and perturbations in mitochondrial tethering to the endoplasmic reticulum. Whether a primary or secondary event, mitochondrial dysfunction holds promise as a potential therapeutic target to halt the progression of neurodegeneration in Parkinson’s disease.

Cyclophilin D-mediated apoptosis attributes to sorafenib-induced cytotoxicity in clear cell-renal cell carcinoma

Cyclophilin D (CypD) is an essential regulatory component of the mitochondrial permeability transition pore (MPTP) and mediates cell necrosis. The aim of this study was to assess the effects of the multi-target drug, sorafenib, on clear cell-renal cell carcinoma (ccRCC) necrosis by regulating CypD expression and to explore whether this effect was related to the phosphorylation of extracellular signal-regulated kinases (ERKs). We used immunohistochemical analysis to compare CypD and p-ERK expression in human ccRCC tissues (n=53) and adjacent non-cancerous tissues (ANCT, n=34). CypD expression was localized to the cytoplasm of renal tubular epithelial cells and was lower in ccRCC samples while p-ERK expression was higher in ccRCC samples. In the in vitro assay, CypD was downregulated in ccRCC cell lines 786-O and A498 as compared with HK-2 which is a normal human renal tubular epithelial cell line. Overexpression of CypD induced the apoptosis of 786-O and A498 cells. Sorafenib induced the apoptosis of 786-O cells, which was coupled with the upregulation of CypD. Cyclosporin A (CsA, the inhibitor of CypD) and CypD siRNA inhibited the effect of sorafenib on apoptosis-induced 786-O and mitochondrial membrane potential depolarization. Epidermal growth factor (EGF, the activator of ERK) and ERK overexpression inhibited the effect of sorafenib on CypD expression, apoptosis-induced 786-O and mitochondrial membrane potential depolarization. In conclusion, our results suggested that CypD may represent a new therapeutic target for the treatment of ccRCC. Sorafenib induced apoptosis in ccRCC through CypD upregulation and this effect was related to the inhibition of p-ERK.

Monitoring mitochondrial membranes permeability in live neurons and mitochondrial swelling through electron microscopy analysis

Maintenance of mitochondrial membrane integrity is essential for mitochondrial function and neuronal viability. Apoptotic stimulus or calcium overload leads to mitochondrial permeability transition pore (mPTP ) opening and induces mitochondrial swelling, a common feature of mitochondrial membrane permeabilization. The first phenomenon can be evaluated in cells loaded with the dye calcein -AM quenched by cobalt, and mitochondrial swelling can be detected by electron microscopy through the analysis of mitochondrial membrane integrity. Here, we describe a live cell imaging assay to detect mitochondrial permeability transition and the development of a detailed analysis of morphological and ultrastructural changes that mitochondria undergo during this process.

Mitochondrial targets for pharmacological intervention in human disease

Over the past several years, mitochondrial dysfunction has been linked to an increasing number of human illnesses, making mitochondrial proteins (MPs) an ever more appealing target for therapeutic intervention. With 20% of the mitochondrial proteome (312 of an estimated 1500 MPs) having known interactions with small molecules, MPs appear to be highly targetable. Yet, despite these targeted proteins functioning in a range of biological processes (including induction of apoptosis, calcium homeostasis, and metabolism), very few of the compounds targeting MPs find clinical use. Recent work has greatly expanded the number of proteins known to localize to the mitochondria and has generated a considerable increase in MP 3D structures available in public databases, allowing experimental screening and in silico prediction of mitochondrial drug targets on an unprecedented scale. Here, we summarize the current literature on clinically active drugs that target MPs, with a focus on how existing drug targets are distributed across biochemical pathways and organelle substructures. Also, we examine current strategies for mitochondrial drug discovery, focusing on genetic, proteomic, and chemogenomic assays, and relevant model systems. As cell models and screening techniques improve, MPs appear poised to emerge as relevant targets for a wide range of complex human diseases, an eventuality that can be expedited through systematic analysis of MP function.

Toxicity of brominated flame retardants, BDE-47 and BDE-99 stems from impaired mitochondrial bioenergetics

Polybrominated diphenyl ethers (PBDEs) are used as flame retardants, and they have been detected in human blood, adipose tissue and breast milk, a consequence of their physicochemical and bioaccumulative properties, as well as their high environmental persistence. Many studies report liver toxicity related to exposure to PBDEs. In the present study, we investigated the toxicity of BDE-47 and BDE-99 at concentrations ranging from 0.1 to 50 µM in isolated rat liver mitochondria. We evaluated how incubation of a mitochondrial suspension with the PBDEs affected the mitochondrial inner membrane, membrane potential, oxygen consumption, calcium release, mitochondrial swelling, and ATP levels to find out whether the tested compound interfered with the bioenergetics of this organelle. Both PBDEs were toxic to mitochondria: BDE-47 and BDE-99 concentrations equal to or higher than 25 and 50 µM, respectively, modified all the parameters used to assess mitochondrial bioenergetics, which culminated in ATP depletion. These effects stemmed from the ability of both PBDEs to cause Membrane Permeability Transition (MPT) in mitochondria, which impaired mitochondrial bioenergetics. In particular, BDE-47, which has fewer bromine atoms in the molecule, can easily overcome biological membranes what would be responsible for the major negative effects exerted by this congener when compared with BDE-99.

The mitochondrial complex V-associated large-conductance inner membrane current is regulated by cyclosporine and dexpramipexole

Inefficiency of oxidative phosphorylation can result from futile leak conductance through the inner mitochondrial membrane. Stress or injury may exacerbate this leak conductance, putting cells, and particularly neurons, at risk of dysfunction and even death when energy demand exceeds cellular energy production. Using a novel method, we have recently described an ion conductance consistent with mitochondrial permeability transition pore (mPTP) within the c-subunit of the ATP synthase. Excitotoxicity, reactive oxygen species-producing stimuli, or elevated mitochondrial matrix calcium opens the channel, which is inhibited by cyclosporine A and ATP/ADP. Here we show that ATP and the neuroprotective drug dexpramipexole (DEX) inhibited an ion conductance consistent with this c-subunit channel (mPTP) in brain-derived submitochondrial vesicles (SMVs) enriched for F1FO ATP synthase (complex V). Treatment of SMVs with urea denatured extramembrane components of complex V, eliminated DEX- but not ATP-mediated current inhibition, and reduced binding of [(14)C]DEX. Direct effects of DEX on the synthesis and hydrolysis of ATP by complex V suggest that interaction of the compound with its target results in functional conformational changes in the enzyme complex. [(14)C]DEX bound specifically to purified recombinant b and oligomycin sensitivity-conferring protein subunits of the mitochondrial F1FO ATP synthase. Previous data indicate that DEX increased the efficiency of energy production in cells, including neurons. Taken together, these studies suggest that modulation of a complex V-associated inner mitochondrial membrane current is metabolically important and may represent an avenue for the development of new therapeutics for neurodegenerative disorders.

Aldose reductase inhibition alleviates hyperglycemic effects on human retinal pigment epithelial cells

Chronic hyperglycemia is an important risk factor involved in the onset and progression of diabetic retinopathy (DR). Among other effectors, aldose reductase (AR) has been linked to the pathogenesis of this degenerative disease. The purpose of this study was to investigate whether the novel AR inhibitor, beta-glucogallin (BGG), can offer protection against various hyperglycemia-induced abnormalities in human adult retinal pigment epithelial (ARPE-19) cells. AR is an enzyme that contributes to cellular stress by production of reactive oxygen species (ROS) under high glucose conditions. A marked decrease in cell viability (from 100% to 78%) following long-term exposure (4 days) of RPE cells to high glucose (HG) was largely prevented by siRNA-mediated knockdown of AR gene expression (from 79% to 97%) or inhibition using sorbinil (from 66% to 86%). In HG, BGG decreased sorbitol accumulation (44%), ROS production (27%) as well as ER stress (22%). Additionally, we demonstrated that BGG prevented loss of mitochondrial membrane potential (MMP) under HG exposure. We also showed that AR inhibitor pretreatment reduced retinal microglia-induced apoptosis in APRE-19 cells. These results suggest that BGG may be useful as a therapeutic agent against retinal degeneration in the diabetic eye by preventing RPE cell death.

Mitochondrial dysfunction: different routes to Alzheimer's disease therapy

Mitochondria are dynamic ATP-generating organelle which contribute to many cellular functions including bioenergetics processes, intracellular calcium regulation, alteration of reduction-oxidation potential of cells, free radical scavenging, and activation of caspase mediated cell death. Mitochondrial functions can be negatively affected by amyloid β peptide (Aβ), an important component in Alzheimer's disease (AD) pathogenesis, and Aβ can interact with mitochondria and cause mitochondrial dysfunction. One of the most accepted hypotheses for AD onset implicates that mitochondrial dysfunction and oxidative stress are one of the primary events in the insurgence of the pathology. Here, we examine structural and functional mitochondrial changes in presence of Aβ. In particular we review data concerning Aβ import into mitochondrion and its involvement in mitochondrial oxidative stress, bioenergetics, biogenesis, trafficking, mitochondrial permeability transition pore (mPTP) formation, and mitochondrial protein interaction. Moreover, the development of AD therapy targeting mitochondria is also discussed.

High-resolution crystal structures of two crystal forms of human cyclophilin D in complex with PEG 400 molecules

Cyclophilin D (CypD) is a key mitochondrial target for amyloid-β-induced mitochondrial and synaptic dysfunction and is considered a potential drug target for Alzheimer's disease. The high-resolution crystal structures of primitive orthorhombic (CypD-o) and primitive tetragonal (CypD-t) forms have been determined to 1.45 and 0.85 Å resolution, respectively, and are nearly identical structurally. Although an isomorphous structure of CypD-t has previously been reported, the structure reported here was determined at atomic resolution, while CypD-o represents a new crystal form for this protein. In addition, each crystal form contains a PEG 400 molecule bound to the same region along with a second PEG 400 site in CypD-t which occupies the cyclosporine A inhibitor binding site of CypD. Highly precise structural information for CypD should be extremely useful for discerning the detailed interaction of small molecules, particularly drugs and/or inhibitors, bound to CypD. The 0.85 Å resolution structure of CypD-t is the highest to date for any CypD structure.

Inhibition of cyclophilin D by cyclosporin A promotes retinal ganglion cell survival by preventing mitochondrial alteration in ischemic injury

Cyclosporin A (CsA) inhibits the opening of the mitochondrial permeability transition pore (MPTP) by interacting with cyclophilin D (CypD) and ameliorates neuronal cell death in the central nervous system against ischemic injury. However, the molecular mechanisms underlying CypD/MPTP opening-mediated cell death in ischemic retinal injury induced by acute intraocular pressure (IOP) elevation remain unknown. We observed the first direct evidence that acute IOP elevation significantly upregulated CypD protein expression in ischemic retina at 12 h. However, CsA prevented the upregulation of CypD protein expression and promoted retinal ganglion cell (RGC) survival against ischemic injury. Moreover, CsA blocked apoptotic cell death by decreasing cleaved caspase-3 protein expression in ischemic retina. Of interest, although the expression level of Bcl-xL protein did not show a significant change in ischemic retina treated with vehicle or CsA at 12 h, ischemic damage induced the reduction of Bcl-xL immunoreactivity in RGCs. More importantly, CsA preserved Bcl-xL immunoreactivity in RGCs of ischemic retina. In parallel, acute IOP elevation significantly increased phosphorylated Bad (pBad) at Ser112 protein expression in ischemic retina at 12 h. However, CsA significantly preserved pBad protein expression in ischemic retina. Finally, acute IOP elevation significantly increased mitochondrial transcription factor A (Tfam) protein expression in ischemic retina at 12 h. However, CsA significantly preserved Tfam protein expression in ischemic retina. Studies on mitochondrial DNA (mtDNA) content in ischemic retina showed that there were no statistically significant differences in mtDNA content among control and ischemic groups treated with vehicle or CsA. Therefore, these results provide evidence that the activation of CypD-mediated MPTP opening is associated with the apoptotic pathway and the mitochondrial alteration in RGC death of ischemic retinal injury. On the basis of these observations, our findings suggest that CsA-mediated CypD inhibition may provide a promising therapeutic potential for protecting RGCs against ischemic injury-mediated mitochondrial dysfunction.

Identification of human presequence protease (hPreP) agonists for the treatment of Alzheimer's disease

Amyloid-β (Aβ), a neurotoxic peptide, is linked to the onset of Alzheimer's disease (AD). Increased Aβ content within neuronal cell mitochondria is a pathological feature in both human and mouse models with AD. This accumulation of Aβ within the mitochondrial landscape perpetuates increased free radical production and activation of the apoptotic pathway. Human Presequence Protease (hPreP) is responsible for the degradation of mitochondrial amyloid-β peptide in human neuronal cells, and is thus an attractive target to increase the proteolysis of Aβ. Therefore, it offers a potential target for Alzheimer's drug design, by identifying potential activators of hPreP. We applied structure-based drug design, combined with experimental methodologies to investigate the ability of various compounds to enhance hPreP proteolytic activity. Compounds 3c &4c enhanced hPreP-mediated proteolysis of Aβ (1-42), pF₁β (2-54) and fluorogenic-substrate V. These results suggest that activation of hPreP by small benzimidazole derivatives provide a promising avenue for AD treatment.