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Aging is a strong risk factor for brain dementia and cognitive decline. Age-related accumulation of metabolites such as advanced glycation end products (AGEs) could serve as danger signals to initiate and accelerate disease process and neurodegeneration. The underlying causes and consequences of cerebral AGEs accumulation remain largely unknown. Here, we comprehensively investigate age-related accumulation of AGEs and dicarbonyls, including methylglyoxal (MG), glyoxal (GO), and 3-deoxyglucosone (3-DG), and the effects of mitochondrial reactive oxygen species (ROS) on cerebral AGEs accumulation, mitochondrial function, and oxidative stress in the aging human and mouse brain. We demonstrate that AGEs, including arginine and lysine derived N(6)-carboxymethyl lysine (CML), Nε-(1-Carboxyethyl)-l-lysine (CEL), and methylglyoxal-derived hydro-imidazolone-1 (MG-H1), were significantly elevated in the cerebral cortex and hippocampus with advanced age in mice. Accordingly, aging mouse and human brains revealed decrease in activities of mitochondrial respiratory chain complexes I & IV and ATP levels, and increased ROS. Notably, administration of mitoTEMPO (2-(2,2,6,6-Tetramethylpiperidin-1-oxyl-4-ylamino)-2-oxoethyl)triphenylphosphonium chloride (mTEMPO), a scavenger of mitochondrial ROS, not only suppressed ROS production but also reduced aged-induced accumulation of AGEs and dicarbonyls. mTEMPO treatment improved mitochondrial respiratory function and restored ATP levels. Our findings provide evidence linking age-related accumulation of toxic metabolites (AGEs) to mitochondrial oxidative stress. This highlights a novel mechanism by which AGEs-dependent signaling promotes carbonyl stress and sustained mitochondrial dysfunction. Eliminating formation and accumulation of AGEs may represent a new therapeutic avenue for combating cognitive decline and mitochondrial degeneration relevant to aging and neurodegenerative diseases including Alzheimer’s disease.

Tau oligomers (oTau) are thought to precede neurofibrillary tangle formation and likely represent one of the toxic species in disease. This study addresses whether mitochondrial reactive oxygen species (ROS) contribute to tau oligomer accumulation. First, we determined whether elevated oxidative stress correlates with aggregation of tau oligomers in the brain and platelets of human Alzheimer’s disease (AD) patient, tauopathy mice, primary cortical neurons from tau mice and human trans-mitochondrial ‘cybrid’ (cytoplasmic hybrid) neuronal cells, whose mitochondria are derived from platelets of patients with sporadic AD- or mild cognitive impairment (MCI)-derived mitochondria. Increased formation of tau oligomers correlates with elevated ROS levels in the hippocampi of AD patients and tauopathy mice, AD- and MCI-derived mitochondria and AD and MCI cybrid cells. Furthermore, scavenging ROS by application of mito-TEMPO/2-(2,2,6,6-Tetramethylpiperidin-1-oxyl-4-ylamino)-2-oxoethyl)triphenylphosphonium chloride, a mitochondria-targeted antioxidant, not only inhibits the generation of mitochondrial ROS and rescues mitochondrial respiratory function but also robustly suppresses tau oligomer accumulation in MCI and AD cybrids as well as cortical neurons from tau mice. These studies provide substantial evidence that mitochondria-mediated oxidative stress contributes to tau oligomer formation and accumulation.

Mitochondrial dysfunction is one of the early pathological features of Alzheimer's disease (AD). Accumulation of cerebral and mitochondrial Aβ links to mitochondrial and synaptic toxicity. We have previously demonstrated the mechanism by which presequence peptidase (PITRM1)‐mediated clearance of mitochondrial Aβ contributes to mitochondrial and cerebral amyloid pathology and mitochondrial and synaptic stress in adult transgenic AD mice overexpressing Aβ up to 12 months old. Here, we investigate the effect of PITRM1 in an advanced age AD mouse model (up to 19–24 months) to address the fundamental unexplored question of whether restoration/gain of PITRM1 function protects against mitochondrial and synaptic dysfunction associated with Aβ accumulation and whether this protection is maintained even at later ages featuring profound amyloid pathology and synaptic failure. Using newly developed aged PITRM1/Aβ‐producing AD mice, we first uncovered reduction in PITRM1 expression in AD‐affected cortex of AD mice at 19–24 months of age. Increasing neuronal PITRM1 activity/expression re‐established mitochondrial respiration, suppressed reactive oxygen species, improved synaptic function, and reduced loss of synapses even at advanced ages (up to 19–24 months). Notably, loss of PITRM1 proteolytic activity resulted in Aβ accumulation and failure to rescue mitochondrial and synaptic function, suggesting that PITRM1 activity is required for the degradation and clearance of mitochondrial Aβ and Aβ deposition. These data indicate that augmenting PITRM1 function results in persistent life‐long protection against Aβ toxicity in an AD mouse model. Therefore, augmenting PITRM1 function may enhance Aβ clearance in mitochondria, thereby maintaining mitochondrial integrity and ultimately slowing the progression of AD., Restoration/gain of neuronal PITRM1 function by enhancing its proteolytic activity in the aged AD mouse model significantly promotes synaptic mitochondrial and cerebral Aβ degradation and clearance, and thereby improves mitochondrial and synaptic functions, and alleviates loss of synapses.

Background Advanced glycation end products (AGEs) are an important risk factor for the development of cognitive decline in aging and late-onset neurodegenerative diseases including Alzheimer's disease. However, whether and how dietary AGEs exacerbate cognitive impairment and brain mitochondrial dysfunction in the aging process remains largely unknown. Objective We investigated the direct effects of dietary AGEs on AGE adducts accumulation, mitochondrial function, and cognitive performance in mice. Methods Mice were fed the AGE+ diet or AGE- diet. We examined levels of AGE adducts in serum and cerebral cortexes by immunodetection and immunohistochemistry, determined levels of reactive oxygen species by biochemical analysis, detected enzyme activity associated with mitochondrial respiratory chain complexes I & IV and ATP levels, and assessed learning and memory ability by Morris Water Maze and nesting behavior. Results Levels of AGE adducts (MG-H1 and CEL) were robustly increased in the serum and brain of AGE+ diet fed mice compared to the AGE- group. Furthermore, greatly elevated levels of reactive oxygen species, decreased activities of mitochondrial respiratory chain complexes I & IV, reduced ATP levels, and impaired learning and memory were evident in AGE+ diet fed mice compared to the AGE- group. Conclusion These results indicate that dietary AGEs are important sources of AGE accumulation in vivo, resulting in mitochondrial dysfunction, impairment of energy metabolism, and subsequent cognitive impairment. Thus, reducing AGEs intake to lower accumulation of AGEs could hold therapeutic potential for the prevention and treatment of AGEs-induced mitochondrial dysfunction linked to cognitive decline.

Receptor for Advanced Glycation End products (RAGE) has been implicated in amyloid β-peptide (Aβ)-induced perturbation relevant to the pathogenesis of Alzheimer's disease (AD). However, whether and how RAGE regulates Aβ metabolism remains largely unknown. Aβ formation arises from aberrant cleavage of amyloid pre-cursor protein (APP) by β- and γ-secretase. To investigate whether RAGE modulates β- and γ-secretase activity potentiating Aβ formation, we generated mAPP mice with genetic deletion of RAGE (mAPP/RO). These mice displayed reduced cerebral amyloid pathology, inhibited aberrant APP-Aβ metabolism by reducing β- and γ-secretases activity, and attenuated impairment of learning and memory compared with mAPP mice. Similarly, RAGE signal transduction deficient mAPP mice (mAPP/DN-RAGE) exhibited the reduction in Aβ40 and Aβ42 production and decreased β-and γ-secretase activity compared with mAPP mice. Furthermore, RAGE-deficient mAPP brain revealed suppression of activation of p38 MAP kinase and glycogen synthase kinase 3β (GSK3β). Finally, RAGE siRNA-mediated gene silencing or DN-RAGE-mediated signaling deficiency in the enriched human APP neuronal cells demonstrated suppression of activation of GSK3β, accompanied with reduction in Aβ levels and decrease in β- and γ-secretases activity. Our findings highlight that RAGE-dependent signaling pathway regulates β- and γ-secretase cleavage of APP to generate Aβ, at least in part through activation of GSK3β and p38 MAP kinase. RAGE is a potential therapeutic target to limit aberrant APP-Aβ metabolism in halting progression of AD.

Mitochondrial abnormalities are well known to cause cognitive decline. However, the underlying molecular basis of mitochondria-associated neuronal and synaptic dysfunction in the diabetic brain remains unclear. Here, using a mitochondrial single-channel patch clamp and cyclophilin D (CypD)-deficient mice (Ppif −/−) with streptozotocin-induced diabetes, we observed an increase in the probability of Ca2+-induced mitochondrial permeability transition pore (mPTP) opening in brain mitochondria of diabetic mice, which was further confirmed by mitochondrial swelling and cytochrome c release induced by Ca2+ overload. Diabetes-induced elevation of CypD triggers enhancement of F1F0 ATP synthase–CypD interaction, which in turn leads to mPTP opening. Indeed, in patients with diabetes, brain cypD protein levels were increased. Notably, blockade of the F1F0 ATP synthase–CypD interaction by CypD ablation protected against diabetes-induced mPTP opening, ATP synthesis deficits, oxidative stress, and mitochondria dysfunction. Furthermore, the absence of CypD alleviated deficits in synaptic plasticity, learning, and memory in diabetic mice. Thus, blockade of ATP synthase interaction with CypD provides a promising new target for therapeutic intervention in diabetic encephalopathy.

Alzheimer's disease (AD) is a progressive neurodegenerative disease characterized clinically by cognitive decline and memory loss. The pathological features are amyloid-β peptide (Aβ) plaques and intracellular neurofibrillary tangles. Many studies have suggested that oxidative damage induced by reactive oxygen species (ROS) is an important mechanism for AD progression. Our recent study demonstrated that oxidative stress could further impair mitochondrial function. In the present study, we adopted a transgenic mouse model of AD (mAPP, overexpressing AβPP/Aβ in neurons) and performed redox measurements using in vivo electron paramagnetic resonance (EPR) imaging with methoxycarbamyl-proxyl (MCP) as a redox-sensitive probe for studying oxidative stress in an early stage of pathology in a transgenic AD mouse model. Through assessing oxidative stress, mitochondrial function and cognitive behaviors of mAPP mice at the age of 8-9 months, we found that oxidative stress and mitochondrial dysfunction appeared in the early onset of AD. Increased ROS levels were associated with defects of mitochondrial and cognitive dysfunction. Notably, the in vivo EPR method offers a unique way of assessing tissue oxidative stress in living animals under noninvasive conditions, and thus holds a potential for early diagnosis and monitoring the progression of AD.

The mitochondrial permeability transition pore (mPTP) has been considered a key contributor to cell death, inducing the process in several major neurodegenerative diseases. To date, the molecular nature of the mPTP remains confounding but its significance is universally acknowledged. Several targets have been screened and inhibition of mPTP has emerged as an attractive field for researchers. Nowadays, in silico-directed studies help to explore new small molecules targeting the mPTP to improve their drug-like properties and bioactivity. Here, we briefly summarize the role of mPTP in neurodegenerative diseases, including Alzheimer's disease (AD), Parkinson disease (PD), and Huntington's disease (HD), and discusses current and future potential therapeutic targets.

Mitochondrial and synaptic dysfunction is an early pathological feature of Alzheimer's disease (AD). Accumulation of amyloid beta-peptide (Aβ) in mitochondria, particularly in synaptic mitochondria, potentiates and amplifies synaptic injury and disruption of synaptic transmission, leading to synaptic dysfunction and ultimately to synaptic failure. Thus, determination of the presence and levels of Aβ in synaptic mitochondria associated with amyloid pathology is important for studying mitochondrial amyloid pathology. Here, we present a detailed methodology for the isolation of synaptic mitochondria from brain tissues and the determination of Aβ levels in the isolated mitochondria as well as ultrastructural localization of synaptic mitochondrial Aβ. These methods have been used successfully for the identification and characterization of Aβ accumulation in synaptic mitochondria from mouse brains derived from transgenic AD mouse model. Additionally, we comprehensively discuss the sample preparation, experimental details, our unique procedures, optimization of parameters, and troubleshooting.

Endophilin A1 (EP) is a protein enriched in synaptic terminals that has been linked to Alzheimer’s disease (AD). Previous in vitro studies have shown that EP can bind to a variety of proteins, which elicit changes in synaptic transmission of neurotransmitters and spine formation. Additionally, we previously showed that EP protein levels are elevated in AD patients and AD transgenic animal models. Here, we establish the in vivo consequences of upregulation of EP expression in amyloid-β peptide (Aβ)-rich environments, leading to changes in both long-term potentiation and learning and memory of transgenic animals. Specifically, increasing EP augmented cerebral Aβ accumulation. EP-mediated signal transduction via reactive oxygen species (ROS)/p38 mitogen-activated protein (MAP) kinase contributes to Aβ-induced mitochondrial dysfunction, synaptic injury, and cognitive decline, which could be rescued by blocking either ROS or p38 MAP kinase activity., Endophilin A1 protein is known to be elevated in Alzheimer’s disease (AD). Here the authors show that endophilin A1 overexpression exacerbates synaptic deficits in a mouse model of AD.

Accumulation of amyloid-β (Aβ) in synaptic mitochondria is associated with mitochondrial and synaptic injury. The underlying mechanisms and strategies to eliminate Aβ and rescue mitochondrial and synaptic defects remain elusive. Presequence protease (PreP), a mitochondrial peptidasome, is a novel mitochondrial Aβ degrading enzyme. Here, we demonstrate for the first time that increased expression of active human PreP in cortical neurons attenuates Alzheimer disease's (AD)-like mitochondrial amyloid pathology and synaptic mitochondrial dysfunction, and suppresses mitochondrial oxidative stress. Notably, PreP-overexpressed AD mice show significant reduction in the production of proinflammatory mediators. Accordingly, increased neuronal PreP expression improves learning and memory and synaptic function in vivo AD mice, and alleviates Aβ-mediated reduction of long-term potentiation (LTP). Our results provide in vivo evidence that PreP may play an important role in maintaining mitochondrial integrity and function by clearance and degradation of mitochondrial Aβ along with the improvement in synaptic and behavioral function in AD mouse model. Thus, enhancing PreP activity/expression may be a new therapeutic avenue for treatment of AD.

The receptor for advanced glycation end products (RAGE)-mediated signaling pathway is related to Aβ-induced pathogenic responses. Geniposide, a pharmacologically active component purified from gardenia fruit, could attenuate the oligomeric Aβ(1-42)-induced inflammatory response by blocking the ligation of Aβ to RAGE and suppressing the RAGE-mediated signaling in vitro. Here, we investigated whether geniposide can exert protective effects on the neuroinflammation and memory deficits in an Alzheimer's disease (AD) mouse model. The results indicate that geniposide treatment significantly suppresses RAGE-dependent signaling (activation of ERK and IκB/NF-κB), the production of tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) and cerebral Aβ accumulation in vivo. Furthermore, we demonstrate that geniposide augments synaptic plasticity by attenuating the Aβ-induced reduction of long-term potentiation and increasing the miniature excitatory postsynaptic current (mEPSC) amplitude and frequency in hippocampal neurons. In addition, the intragastric administration of geniposide improves learning and memory in APP/PS1 mice. Taken together, these studies indicate that geniposide has profound multifaceted neuroprotective effects in an AD mouse model. Geniposide demonstrates its neuroprotection by inhibiting inflammation, ameliorating amyloid pathology and improving cognition. Thus, geniposide may be a potential therapeutic agent for halting and preventing AD progression.

The coexistence of neuronal mitochondrial pathology and synaptic dysfunction is an early pathological feature of Alzheimer's disease (AD). Cyclophilin D (CypD), an integral part of mitochondrial permeability transition pore (mPTP), is involved in amyloid beta (Aβ)-instigated mitochondrial dysfunction. Blockade of CypD prevents Aβ-induced mitochondrial malfunction and the consequent cognitive impairments. Here, we showed the elimination of reactive oxygen species (ROS) by antioxidants probucol or superoxide dismutase (SOD)/catalase blocks Aβ-mediated inactivation of protein kinase A (PKA)/cAMP regulatory-element-binding (CREB) signal transduction pathway and loss of synapse, suggesting the detrimental effects of oxidative stress on neuronal PKA/CREB activity. Notably, neurons lacking CypD significantly attenuate Aβ-induced ROS. Consequently, CypD-deficient neurons are resistant to Aβ-disrupted PKA/CREB signaling by increased PKA activity, phosphorylation of PKA catalytic subunit (PKA C), and CREB. In parallel, lack of CypD protects neurons from Aβ-induced loss of synapses and synaptic dysfunction. Furthermore, compared to the mAPP mice, CypD-deficient mAPP mice reveal less inactivation of PKA–CREB activity and increased synaptic density, attenuate abnormalities in dendritic spine maturation, and improve spontaneous synaptic activity. These findings provide new insights into a mechanism in the crosstalk between the CypD-dependent mitochondrial oxidative stress and signaling cascade, leading to synaptic injury, functioning through the PKA/CREB signal transduction pathway.

Diabetes is considered to be a risk factor in Alzheimer’s disease (AD) pathogenesis. Although recent evidence indicates that diabetes exaggerates pathologic features of AD, the underlying mechanisms are not well understood. To determine whether mitochondrial perturbation is associated with the contribution of diabetes to AD progression, we characterized mouse models of streptozotocin (STZ)-induced type 1 diabetes and transgenic AD mouse models with diabetes. Brains from mice with STZ-induced diabetes revealed a significant increase of cyclophilin D (CypD) expression, reduced respiratory function, and decreased hippocampal long-term potentiation (LTP); these animals had impaired spatial learning and memory. Hyperglycemia exacerbated the upregulation of CypD, mitochondrial defects, synaptic injury, and cognitive dysfunction in the brains of transgenic AD mice overexpressing amyloid-β as shown by decreased mitochondrial respiratory complex I and IV enzyme activity and greatly decreased mitochondrial respiratory rate. Concomitantly, hippocampal LTP reduction and spatial learning and memory decline, two early pathologic indicators of AD, were enhanced in the brains of diabetic AD mice. Our results suggest that the synergistic interaction between effects of diabetes and AD on mitochondria may be responsible for brain dysfunction that is in common in both diabetes and AD.

Diabetes has adverse effects on the brain, especially the hippocampus, which is particularly susceptible to synaptic injury and cognitive dysfunction. The underlying mechanisms and strategies to rescue such injury and dysfunction are not well understood. Using a mouse model of type 2 diabetes (db/db mice) and a human neuronal cell line treated with high concentration of glucose, we demonstrate aberrant mitochondrial morphology, reduced ATP production, and impaired activity of complex I. These mitochondrial abnormalities are induced by imbalanced mitochondrial fusion and fission via a glycogen synthase kinase 3β (GSK3β)/dynamin-related protein-1 (Drp1)-dependent mechanism. Modulation of the Drp1 pathway or inhibition of GSK3β activity restores hippocampal long-term potentiation that is impaired in db/db mice. Our results point to a novel role for mitochondria in diabetes-induced synaptic impairment. Exploration of the mechanisms behind diabetes-induced synaptic deficit may provide a novel treatment for mitochondrial and synaptic injury in patients with diabetes.

The Entorhinal cortex (EC) has been implicated in the early stages of Alzheimer’s disease (AD). In particular, spreading of neuronal dysfunction within the EC-Hippocampal network has been suggested. We have investigated the time course of EC dysfunction in the AD mouse model carrying human mutation of amyloid precursor protein (mhAPP) expressing human Aβ. We found that in mhAPP mice plasticity impairment is first observed in EC superficial layer and further affected with time. A selective impairment of LTP was observed in layer II horizontal connections of EC slices from 2 month old mhAPP mice, whereas at later stage of neurodegeneration (6 month) basal synaptic transmission and LTD were also affected. Accordingly, early synaptic deficit in the mhAPP mice were associated with a selective impairment in EC-dependent associative memory tasks. The introduction of the dominant-negative form of RAGE lacking RAGE signalling targeted to microglia (DNMSR) in mhAPP mice prevented synaptic and behavioural deficit, reducing the activation of stress related kinases (p38MAPK and JNK). Our results support the involvement of the EC in the development and progression of the synaptic and behavioural deficit during amyloid-dependent neurodegeneration and demonstrate that microglial RAGE activation in presence of Aβ-enriched environment contributes to the EC vulnerability.

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 recoveries90.0% (RSD10%). 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.

Amyloid beta (Aβ ) binding alcohol dehydrogenase (ABAD) is a cellular cofactor for promoting (Aβ )-mediated mitochondrial and neuronal dysfunction, and cognitive decline in transgenic Alzheimer’s disease (AD) mouse models. Targeting mitochondrial ABAD may represent a novel therapeutic strategy against AD. Here, we report the biological activity of small molecule ABAD inhibitors. Using in vitro surface plasmon resonance (SPR) studies, we synthesized compounds with strong binding affinities for ABAD. Further, these ABAD inhibitors (ABAD-4a and 4b) reduced ABAD enzyme activity and administration of phosphonate derivatives of ABAD inhibitors antagonized calcium-mediated mitochondrial swelling. Importantly, these compounds also abolished A β-induced mitochondrial dysfunction as shown by increased cytochrome c oxidase activity and adenosine-5'-triphosphate levels, suggesting protective mitochondrial function effects of these synthesized compounds. Thus, these compounds are potential candidates for further pharmacologic development to target ABAD to improve mitochondrial function.

Mitochondrial dysfunction and synaptic damage are early pathological features of the Alzheimer's disease-affected brain. Memory impairment in Alzheimer's disease is a manifestation of brain pathologies such as accumulation of amyloid-β peptide and mitochondrial damage. The underlying pathogenic mechanisms and effective disease-modifying therapies for Alzheimer's disease remain elusive. Here, we demonstrate for the first time that decreased PTEN-induced putative kinase 1 (PINK1) expression is associated with Alzheimer's disease pathology. Restoring neuronal PINK1 function strikingly reduces amyloid-β levels, amyloid-associated pathology, oxidative stress, as well as mitochondrial and synaptic dysfunction. In contrast, PINK1-deficient mAPP mice augmented cerebral amyloid-β accumulation, mitochondrial abnormalities, impairments in learning and memory, as well as synaptic plasticity at an earlier age than mAPP mice. Notably, gene therapy-mediated PINK1 overexpression promotes the clearance of damaged mitochondria by augmenting autophagy signalling via activation of autophagy receptors (OPTN and NDP52), thereby alleviating amyloid-β-induced loss of synapses and cognitive decline in Alzheimer's disease mice. Loss of PINK1 activity or blockade of PINK1-mediated signalling (OPTN or NDP52) fails to reverse amyloid-β-induced detrimental effects. Our findings highlight a novel mechanism by which PINK1-dependent signalling promotes the rescue of amyloid pathology and amyloid-β-mediated mitochondrial and synaptic dysfunctions in a manner requiring activation of autophagy receptor OPTN or NDP52. Thus, activation of PINK1 may represent a new therapeutic avenue for combating Alzheimer's disease.

Accumulation of oxidized proteins, and especially β-amyloid (Aβ), is thought to be one of the common causes of Alzheimer's disease (AD). The current studies determine the effect of an in vivo methionine sulfoxidation of Aβ through ablation of the methionine sulfoxide reductase A (MsrA) in a mouse model of AD, a mouse that overexpresses amyloid precursor protein (APP) and Aβ in neurons. Lack of MsrA fosters the formation of methionine sulfoxide in proteins, and thus its ablation in the AD-mouse model will increase the formation of methionine sulfoxide in Aβ. Indeed, the novel MsrA-deficient APP mice ( APP+/ MsrAKO) exhibited higher levels of soluble Aβ in brain compared with APP+ mice. Furthermore, mitochondrial respiration and the activity of cytochrome c oxidase were compromised in the APP+/ MsrAKO compared with control mice. These results suggest that lower MsrA activity modifies Aβ solubility properties and causes mitochondrial dysfunction, and augmenting its activity may be beneficial in delaying AD progression.

Although epidemiological data associate hypertension with a strong predisposition to develop Alzheimer disease, no mechanistic explanation exists so far. We developed a model of hypertension, obtained by transverse aortic constriction, leading to alterations typical of Alzheimer disease, such as amyloid plaques, neuroinflammation, blood-brain barrier dysfunction, and cognitive impairment, shown here for the first time. The aim of this work was to investigate the mechanisms involved in Alzheimer disease of hypertensive mice. We focused on receptor for advanced glycation end products (RAGE) that critically regulates Aβ transport at the blood-brain barrier and could be influenced by vascular factors. The hypertensive challenge had an early and sustained effect on RAGE upregulation in brain vessels of the cortex and hippocampus. Interestingly, RAGE inhibition protected from hypertension-induced Alzheimer pathology, as showed by rescue from cognitive impairment and parenchymal Aβ deposition. The increased RAGE expression in transverse aortic coarctation mice was induced by increased circulating advanced glycation end products and sustained by their later deposition in brain vessels. Interestingly, a daily treatment with an advanced glycation end product inhibitor or antioxidant prevented the development of Alzheimer traits. So far, Alzheimer pathology in experimental animal models has been recognized using only transgenic mice overexpressing amyloid precursor. This is the first study demonstrating that a chronic vascular insult can activate brain vascular RAGE, favoring parenchymal Aβ deposition and the onset of cognitive deterioration. Overall we demonstrate that RAGE activation in brain vessels is a crucial pathogenetic event in hypertension-induced Alzheimer disease, suggesting that inhibiting this target can limit the onset of vascular-related Alzheimer disease.

Significance: Synaptic degeneration, an early pathological feature in Alzheimer's disease (AD), is closely correlated to impaired cognitive function and memory loss. Recent studies suggest that involvement of amyloid-beta peptide (Aβ) in synaptic mitochondrial alteration underlies these synaptic lesions. Thus, to understand the Aβ-associated synaptic mitochondrial perturbations would fortify our understanding of synaptic stress in the pathogenesis of AD. Recent Advances: Increasing evidence suggests that synaptic mitochondrial dysfunction is strongly associated with synaptic failure in many neurodegenerative diseases including AD. Based on recent findings in human AD subjects, AD animal models, and AD cellular models, synaptic mitochondria undergo multiple malfunctions including Aβ accumulation, increased oxidative stress, decreased respiration, and compromised calcium handling capacity, all of which occur earlier than changes seen in nonsynaptic mitochondria before predominant AD pathology. Of note, the impact of Aβ on mitochondrial motility and dynamics exacerbates synaptic mitochondrial alterations. Critical Issues: Synaptic mitochondria demonstrate early deficits in AD; in combination with the role that synaptic mitochondria play in sustaining synaptic functions, deficits in synaptic mitochondria may be a key factor involved in an early synaptic pathology in AD. Future Directions: The importance of synaptic mitochondria in supporting synapses and the high vulnerability of synaptic mitochondria to Aβ make them a promising target of new therapeutic strategy for AD. Antioxid. Redox Signal. 16, 1467–1475.

Accumulation of amyloid-β peptide (Aβ), the neurotoxic peptide implicated in the pathogenesis of Alzheimer's disease (AD), has been shown in brain mitochondria of AD patients and of AD transgenic mouse models. The presence of Aβ in mitochondria leads to free radical generation and neuronal stress. Recently, we identified the presequence protease, PreP, localized in the mitochondrial matrix in mammalian mitochondria as the novel mitochondrial Aβ-degrading enzyme. In the present study, we examined PreP activity in the mitochondrial matrix of the human brain's temporal lobe, an area of the brain highly susceptible to Aβ accumulation and reactive oxygen species (ROS) production. We found significantly lower hPreP activity in AD brains compared with non-AD age-matched controls. By contrast, in the cerebellum, a brain region typically spared from Aβ accumulation, there was no significant difference in hPreP activity when comparing AD samples to non-AD controls. We also found significantly reduced PreP activity in the mitochondrial matrix of AD transgenic mouse brains (Tg mAβPP and Tg mAβPP/ABAD) when compared to non-transgenic aged-matched mice. Furthermore, mitochondrial fractions isolated from AD brains and Tg mAβPP mice had higher levels of 4-hydroxynonenal, an oxidative product, as compared with those from non-AD and nonTg mice. Accordingly, activity of cytochrome c oxidase was significantly reduced in the AD mitochondria. These findings suggest that decreased PreP proteolytic activity, possibly due to enhanced ROS production, contributes to Aβ accumulation in mitochondria leading to the mitochondrial toxicity and neuronal death that is exacerbated in AD. Clearance of mitochondrial Aβ by PreP may thus be of importance in the pathology of AD.

Amyloid- beta (A beta) peptide-binding alcohol dehydrogenase (ABAD), an enzyme present in neuronal mitochondria, exacerbates A beta-induced cell stress. The interaction of ABAD with A beta exacerbates A beta-induced mitochondrial and neuronal dysfunction. Here, we show that inhibition of the ABAD-A beta interaction, using a decoy peptide (DP) in vitro and in vivo, protects against aberrant mitochondrial and neuronal function and improves spatial learning/memory. Intraperitoneal administration of ABAD-DP [fused to the transduction of human immunodeficiency virus 1-transactivator (Tat) protein and linked to the mitochondrial targeting sequence (Mito) (TAT-mito-DP) to transgenic APP mice (Tg mAPP)] blocked formation of ABAD-A beta complex in mitochondria, increased oxygen consumption and enzyme activity associated with the mitochondrial respiratory chain, attenuated mitochondrial oxidative stress, and improved spatial memory. Similar protective effects were observed in Tg mAPP mice overexpressing neuronal ABAD decoy peptide (Tg mAPP/mito-ABAD). Notably, inhibition of the ABAD-A beta interaction significantly reduced mitochondrial A beta accumulation. In parallel, the activity of mitochondrial A beta-degrading enzyme PreP (presequence peptidase) was enhanced in Tg mAPP mitochondria expressing the ABAD decoy peptide. These data indicate that segregating ABAD from A beta protects mitochondria/neurons from A beta toxicity; thus, ABAD-A beta interaction is an important mechanism underlying A beta-mediated mitochondrial and neuronal perturbation. Inhibitors of ABAD-A beta interaction may hold promise as targets for the prevention and treatment of Alzheimer's disease. Publisher PDF

The immunity-related GTPase Irgm1, also called LRG-47, is known to regulate host resistance to intracellular pathogens through multiple mechanisms that include controlling the survival of T lymphocytes. Here, we address whether Irgm1 also plays a role in the pathogenesis of experimental autoimmune encephalitis (EAE). We find that Irgm1/LRG-47 is a significant factor in the progression of EAE and multiple sclerosis (MS). Expression of Irgm1 was robustly elevated in MS-affected lesions and in the central nervous system (CNS) of myelin basic protein (MBP)-induced EAE mice, especially in cells of lymphoid and mononuclear phagocyte origin. Homozygous Irgm1 null mice were resistant to MBP-induced EAE, and CD4+ T cells in spleen and CNS of these mice displayed decreased proliferative capacity, increased apoptosis, and up-regulated interferon (IFN)-γ induction. Therefore, Irgm1-induced survival of autoreactive CD4+ T cells contributes significantly to the pathogenesis of EAE. Blockade of Irgm1 may be a potential therapeutic strategy for halting multiple sclerosis.—Xu, H., Wu, Z.-Y., Fang, F., Guo, L., Chen, D., Chen, J. X., Stern, D., Taylor, G. A., Jiang, H., Yan, S. S. Genetic deficiency of Irgm1 (LRG-47) suppresses induction of experimental autoimmune encephalomyelitis by promoting apoptosis of activated CD4+ T cells.

Intracellular amyloid-beta peptide (Abeta) has been implicated in neuronal death associated with Alzheimer's disease. Although Abeta is predominantly secreted into the extracellular space, mechanisms of Abeta transport at the level of the neuronal cell membrane remain to be fully elucidated. We demonstrate that receptor for advanced glycation end products (RAGE) contributes to transport of Abeta from the cell surface to the intracellular space. Mouse cortical neurons exposed to extracellular human Abeta subsequently showed detectable peptide intracellularly in the cytosol and mitochondria by confocal microscope and immunogold electron microscopy. Pretreatment of cultured neurons from wild-type mice with neutralizing antibody to RAGE, and neurons from RAGE knockout mice displayed decreased uptake of Abeta and protection from Abeta-mediated mitochondrial dysfunction. Abeta activated p38 MAPK, but not SAPK/JNK, and then stimulated intracellular uptake of Abeta-RAGE complex. Similar intraneuronal co-localization of Abeta and RAGE was observed in the hippocampus of transgenic mice overexpressing mutant amyloid precursor protein. These findings indicate that RAGE contributes to mechanisms involved in the translocation of Abeta from the extracellular to the intracellular space, thereby enhancing Abeta cytotoxicity.

Genetic and biological studies provide strong support for the hypothesis that accumulation of beta amyloid peptide (Abeta) contributes to the etiology of Alzheimer's disease (AD). Growing evidence indicates that oligomeric soluble Abeta plays an important role in the development of synaptic dysfunction and the impairment of cognitive function in AD. The receptor for advanced glycation end products (RAGE), a multiligand receptor in the immunoglobulin superfamily, acts as a cell surface binding site for Abeta and mediates alternations in the phosphorylation state of mitogen-activated protein kinase (MAPKs). Recent results have shown that MAPKs are involved in neurodegenerative processes. In particular, changes in the phosphorylation state of various MAPKs by Abeta lead to synaptic dysfunction and cognitive decline, as well as development of inflammatory responses in AD. The present review summarizes the evidence justifying a novel therapeutic approach focused on inhibition of RAGE signaling in order to arrest or halt the development of neuronal dysfunction in AD.

Background 17β-hydroxysteroid dehydrogenase type 10 (HSD10) has been shown to play a protective role in cells undergoing stress. Upregulation of HSD10 under nutrient-limiting conditions leads to recovery of a homeostatic state. Across disease states, increased HSD10 levels can have a profound and varied impact, such as beneficial in Parkinson’s disease and harmful in Alzheimer’s disease. Recently, HSD10 overexpression has been observed in some prostate and bone cancers, consistently correlating with poor patient prognosis. As the role of HSD10 in cancer remains underexplored, we propose that cancer cells utilize this enzyme to promote cancer cell survival under cell death conditions. Methods The proliferative effect of HSD10 was examined in transfected pheochromocytoma cells by growth curve analysis and a xenograft model. Fluctuations in mitochondrial bioenergetics were evaluated by electron transport chain complex enzyme activity assays and energy production. Additionally, the effect of HSD10 on pheochromocytoma resistance to cell death was investigated using TUNEL staining, MTT, and complex IV enzyme activity assays. Results In this study, we examined the tumor-promoting effect of HSD10 in pheochromocytoma cells. Overexpression of HSD10 increased pheochromocytoma cell growth in both in vitro cell culture and an in vivo xenograft mouse model. The increases in respiratory enzymes and energy generation observed in HSD10-overexpressing cells likely supported the accelerated growth rate observed. Furthermore, cells overexpressing HSD10 were more resistant to oxidative stress-induced perturbation. Conclusions Our findings demonstrate that overexpression of HSD10 accelerates pheochromocytoma cell growth, enhances cell respiration, and increases cellular resistance to cell death induction. This suggests that blockade of HSD10 may halt and/or prevent cancer growth, thus providing a promising novel target for cancer patients as a screening or therapeutic option.

Mitochondrial and metabolic dysfunction have been linked to Alzheimer's disease for some time. Key questions regarding this association concern the nature and mechanisms of mitochondrial dysfunction, and whether such changes in metabolic properties are pathogenic or secondary, with respect to neuronal degeneration. In terms of mitochondria and Alzheimer's, altered function could reflect intrinsic properties of this organelle, potentially due to mutations in mitochondrial DNA, or extrinsic changes secondary to signal transduction mechanisms activated in the cytosol. This review presents data relevant to these questions, and considers the implication of recent findings demonstrating the presence of amyloid-beta peptide in mitochondria, as well as intra-mitochondrial molecular targets with which it can interact. Regardless of the underlying mechanism(s), it is likely that mitochondrial dysfunction contributes to oxidant stress which is commonly observed in brains of patients with Alzheimer's and transgenic models of Alzheimer's-like pathology.

Amyloid-beta peptide (Abeta) binding alcohol dehydrogenase (ABAD), an enzyme present in neuronal mitochondria, is a cofactor facilitating Abeta-induced cell stress. We hypothesized that ABAD provides a direct link between Abeta and cytotoxicity via mitochondrial oxidant stress. Neurons cultured from transgenic (Tg) mice with targeted overexpression of a mutant form of amyloid precursor protein and ABAD (Tg mAPP/ABAD) displayed spontaneous generation of hydrogen peroxide and superoxide anion, and decreased ATP, as well as subsequent release of cytochrome c from mitochondria and induction of caspase-3-like activity followed by DNA fragmentation and loss of cell viability. Generation of reactive oxygen species (ROS) was associated with dysfunction at the level of mitochondrial complex IV (cytochrome c oxidase, or COX). In neurons cultured from Tg mAPP/ABAD mice, COX activity was selectively decreased, and cyanide, an inhibitor of complex IV, exacerbated leakage of ROS, induction of caspase-3-like activity, and DNA fragmentation. In vivo, Tg mAPP/ABAD mice displayed reduced levels of brain ATP and COX activity, diminished glucose utilization, as well as electrophysiological abnormalities in hippocampal slices compared with Tg mAPP mice. In contrast, neither Tg ABAD mice nor nontransgenic (non-TG) littermates showed similar changes in ATP, COX activity, glucose utilization or electrophysiological properties. Each of the genotypes (Tg ABAD, Tg mAPP and Tg mAPP/ABAD mice, and non-TG littermates) displayed normal reproductive fitness, development and lifespan (1) These findings link ABAD-induced oxidant stress to critical aspects of Alzheimer's disease (AD)-associated cellular dysfunction, suggesting a pivotal role for this enzyme in the pathogenesis of AD.

Receptor for Advanced Glycation Endproducts (RAGE), a multiligand receptor in the immunoglobulin superfamily, functions as a signal-transducing cell surface acceptor for amyloid-beta peptide (Abeta). In view of increased neuronal expression of RAGE in Alzheimer's disease, a murine model was developed to assess the impact of RAGE in an Abeta-rich environment, employing transgenics (Tgs) with targeted neuronal overexpression of RAGE and mutant amyloid precursor protein (APP). Double Tgs (mutant APP (mAPP)/RAGE) displayed early abnormalities in spatial learning/memory, accompanied by altered activation of markers of synaptic plasticity and exaggerated neuropathologic findings, before such changes were found in mAPP mice. In contrast, Tg mice bearing a dominant-negative RAGE construct targeted to neurons crossed with mAPP animals displayed preservation of spatial learning/memory and diminished neuropathologic changes. These data indicate that RAGE is a cofactor for Abeta-induced neuronal perturbation in a model of Alzheimer's-type pathology, and suggest its potential as a therapeutic target to ameliorate cellular dysfunction.

Apoptotic death of osteocytes was recognized over 15 years ago, but its significance for bone homeostasis has remained elusive. A new paradigm has emerged that invokes osteocyte apoptosis as a critical event in the recruitment of osteoclasts to a specific site in response to skeletal unloading, fatigue damage, estrogen deficiency and perhaps in other states where bone must be removed. This is accomplished by yet to be defined signals emanating from dying osteocytes, which stimulate neighboring viable osteocytes to produce osteoclastogenic cytokines. The osteocyte apoptosis caused by chronic glucocorticoid administration does not increase osteoclasts; however, it does negatively impact maintenance of bone hydration, vascularity, and strength.

The neuroinflammation induced by amyloid-β (Aβ) is one of the key events in Alzheimer's disease (AD) progress in which microglia are the main cells involved. Receptor for advanced glycation end products (RAGE) mediates and enhances Aβ-induced microglial activation and leads to induction of proinflammatory mediators, such as tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β). Geniposide, a pharmacologically active component purified from gardenia fruit, exhibits a broad spectrum anti-inflammatory effect as well as neurotrophic and neuroprotective properties. However, the effects of geniposide on Aβ-mediated microglial pathways have not been fully discovered. Here, we demonstrate that geniposide treatment significantly blocks Aβ-induced RAGE-dependent signaling (activation of ERK and NF-κB) along with the production of TNF-α and IL-1β in cultured BV2 microglia cells. Notably, based on the data from coimmunoprecipitation assay, we infer that geniposide exerts protective effects on Aβ-induced inflammatroy response through blocking Aβ binding to RAGE and suppressing the RAGE-mediated signaling pathway. Taken together, these findings indicate that geniposide is a potent suppressor of neuroflammation through inhibiting RAGE-dependent signaling pathway. Thus, geniposide may be a potential therapeutic agent for the treatment of neuroinflammation that is involved in neurological diseases such as AD.

Current strategies for the treatment of Alzheimer’s disease (AD) involve tackling the formation or clearance of the amyloid-beta peptide (Aβ) and/or hyper-phosphorylated tau, or the support and stabilization of the remaining neuronal networks. However, as we gain a clearer idea of the large number of molecular mechanisms at work in this disease, it is becoming clearer that the treatment of AD should take a combined approach of dealing with several aspects of the pathology. The concept that we also need to protect specific sensitive targets within the cell should also be considered. In particular the role of protecting the function of a specific mitochondrial protein, amyloid binding alcohol dehydrogenase (ABAD), will be the focus of this review. Mitochondrial dysfunction is a well-recognized fact in the progression of AD, though until recently the mechanisms involved could only be loosely labeled as changes in ‘metabolism’. The discovery that Aβ can be present within the mitochondria and specifically bind to ABAD, has opened up a new area of AD research. Here we review the evidence that the prevention of Aβ binding to ABAD is a drug target for the treatment of AD.

Acute neutrophil (PMN) recruitment to postischemic cardiac or pulmonary tissue has deleterious effects in the early reperfusion period, but the mechanisms and effects of neutrophil influx in the pathogenesis of evolving stroke remain controversial. To investigate whether PMNs contribute to adverse neurologic sequelae and mortality after stroke, and to study the potential role of the leukocyte adhesion molecule intercellular adhesion molecule-1 (ICAM-1) in the pathogenesis of stroke, we used a murine model of transient focal cerebral ischemia consisting of intraluminal middle cerebral artery occlusion for 45 min followed by 22 h of reperfusion. PMN accumulation, monitored by deposition of 111In-labeled PMNs in postischemic cerebral tissue, was increased 2.5-fold in the ipsilateral (infarcted) hemisphere compared with the contralateral (noninfarcted) hemisphere (P < 0.01). Mice immunodepleted of neutrophils before surgery demonstrated a 3.0-fold reduction in infarct volumes (P < 0.001), based on triphenyltetrazolium chloride staining of serial cerebral sections, improved ipsilateral cortical cerebral blood flow (measured by laser Doppler), and reduced neurological deficit compared with controls. In wild-type mice subjected to 45 min of ischemia followed by 22 h of reperfusion, ICAM-1 mRNA was increased in the ipsilateral hemisphere, with immunohistochemistry localizing increased ICAM-1 expression on cerebral microvascular endothelium. The role of ICAM-1 expression in stroke was investigated in homozygous null ICAM-1 mice (ICAM-1 -/-) in comparison with wild-type controls (ICAM-1 +/+). ICAM-1 -/- mice demonstrated a 3.7-fold reduction in infarct volume (P < 0.005), a 35% increase in survival (P < 0.05), and reduced neurologic deficit compared with ICAM-1 +/+ controls. Cerebral blood flow to the infarcted hemisphere was 3.1-fold greater in ICAM-1 -/- mice compared with ICAM-1 +/+ controls (P < 0.01), suggesting an important role for ICAM-1 in the genesis of postischemic cerebral no-reflow. Because PMN-depleted and ICAM-1-deficient mice are relatively resistant to cerebral ischemia-reperfusion injury, these studies suggest an important role for ICAM-1-mediated PMN adhesion in the pathophysiology of evolving stroke.

Vascular cell adhesion molecule-1 (VCAM-1), an inducible cell-cell recognition protein on the endothelial cell surface (EC), has been associated with early stages of atherosclerosis. In view of the accelerated vascular disease observed in patients with diabetes, and the enhanced expression of VCAM-1 in diabetic rabbits, we examined whether irreversible advanced glycation endproducts (AGEs), could mediate VCAM-1 expression by interacting with their endothelial cell receptor (receptor for AGE, RAGE). Exposure of cultured human ECs to AGEs induced expression of VCAM-1, increased adhesivity of the monolayer for Molt-4 cells, and was associated with increased levels of VCAM-1 transcripts. The inhibitory effect of anti-RAGE IgG, a truncated form of the receptor (soluble RAGE) or N-acetylcysteine on VCAM-1 expression indicated that AGE-RAGE-induced oxidant stress was central to VCAM-1 induction. Electrophoretic mobility shift assays on nuclear extracts from AGE-treated ECs showed induction of specific DNA binding activity for NF-kB in the VCAM-1 promoter, which was blocked by anti-RAGE IgG or N-acetylcysteine. Soluble VCAM-1 antigen was elevated in human diabetic plasma. These data are consistent with the hypothesis that AGE-RAGE interaction induces expression of VCAM-1 which can prime diabetic vasculature for enhanced interaction with circulating monocytes.

To elucidate mechanisms underlying neuroprotective properties of astrocytes in brain ischemia, production of neurotrophic mediators was studied in astrocytes exposed to hypoxia/reoxygenation (H/R). Rat astrocytes subjected to H/R released increased amounts of interleukin (IL) 6 in a time-dependent manner, whereas levels of tumor necrosis factor and IL-1 remained undetectable. IL-6 transcripts were induced in hypoxia and the early phase of reoxygenation, whereas synthesis and release of IL-6 antigen/activity occurred during reoxygenation. Elevated levels of IL-6 mRNA were due, at least in part, to increased transcription, as shown by nuclear runoff analysis. The mechanism stimulating synthesis and release of IL-6 antigen by astrocytes was probably production of reactive oxygen intermediates (ROIs), which occurred within 15-20 minutes after placing hypoxia cultures back into normoxia, as the inhibitor diphenyl iodonium inhibited the burst of ROIs and subsequent IL-6 generation (blockade of nitric oxide formation had no effect on ROI generation or IL-6 production). Enhanced IL-6 generation was also observed in human astrocytoma cultures exposed to H/R. Survival of differentiated PC12 cells exposed to H/R was potentiated by conditioned medium from H/R astrocytes, an effect blocked by neutralizing anti-IL-6 antibody. In a gerbil model of brain ischemia, IL-6 activity was lower in the hippocampus, an area sensitive to ischemia, compared with IL-6 activity in the cortex, an area more resistant to ischemia. IL-6 antigen, demonstrated immunohistochemically, was increased in astrocytes from ischemic regions of gerbil brain. These data suggest that H/R enhances transcription of IL-6, resulting in increased translation and release of IL-6 antigen after the burst of ROI generated early during reoxygenation. Release of IL-6 from astrocytes could exert a paracrine neurotrophic effect in brain ischemia.

Mitochondrial dysfunction is one of the major pathological changes seen in Alzheimer's disease (AD). Amyloid beta-peptide (Aβ), a neurotoxic peptide, accumulates in the brain of AD subjects and mediates mitochondrial and neuronal stress. Therefore, protecting mitochondrion from Aβ-induced toxicity holds potential benefits for halting and treating and perhaps preventing AD. Here, we report that administration of ginsenoside Rg1, a known neuroprotective drug, to primary cultured cortical neurons, rescues Aβ-mediated mitochondrial dysfunction as shown by increases in mitochondrial membrane potential, ATP levels, activity of cytochrome c oxidase (a key enzyme associated with mitochondrial respiratory function), and decreases in cytochrome c release. The protective effects of Rg1 on mitochondrial dysfunction correlate to neuronal injury in the presence of Aβ. This finding suggests that ginsenoside Rg1 may attenuate Aβ-induced neuronal death through the suppression of intracellular mitochondrial oxidative stress and may rescue neurons in AD.

Synaptic dysfunction and the loss of synapses are early pathological features of Alzheimer's disease (AD). Synapses are sites of high energy demand and extensive calcium fluctuations; accordingly, synaptic transmission requires high levels of ATP and constant calcium fluctuation. Thus, synaptic mitochondria are vital for maintenance of synaptic function and transmission through normal mitochondrial energy metabolism, distribution and trafficking, and through synaptic calcium modulation. To date, there has been no extensive analysis of alterations in synaptic mitochondria associated with amyloid pathology in an amyloid β (Aβ)-rich milieu. Here, we identified differences in mitochondrial properties and function of synaptic vs. nonsynaptic mitochondrial populations in the transgenic mouse brain, which overexpresses the human mutant form of amyloid precursor protein and Aβ. Compared with nonsynaptic mitochondria, synaptic mitochondria showed a greater degree of age-dependent accumulation of Aβ and mitochondrial alterations. The synaptic mitochondrial pool of Aβ was detected at an age as young as 4 mo, well before the onset of nonsynaptic mitochondrial and extensive extracellular Aβ accumulation. Aβ-insulted synaptic mitochondria revealed early deficits in mitochondrial function, as shown by increased mitochondrial permeability transition, decline in both respiratory function and activity of cytochrome c oxidase, and increased mitochondrial oxidative stress. Furthermore, a low concentration of Aβ (200 nM) significantly interfered with mitochondrial distribution and trafficking in axons. These results demonstrate that synaptic mitochondria, especially Aβ-rich synaptic mitochondria, are more susceptible to Aβ-induced damage, highlighting the central importance of synaptic mitochondrial dysfunction relevant to the development of synaptic degeneration in AD.

Overproduction of beta-amyloid (Abeta) is a pathologic feature of Alzheimer's disease, leading to cognitive impairment. Here, we investigated the impact of cell-specific receptor for advanced glycation end products (RAGE) on Abeta-induced entorhinal cortex (EC) synaptic dysfunction. We found both a transient depression of basal synaptic transmission and inhibition of long-term depression (LTD) after the application of Abeta in EC slices. Synaptic depression and LTD impairment induced by Abeta were rescued by functional suppression of RAGE. Remarkably, the rescue was only observed in slices from mice expressing a defective form of RAGE targeted to microglia, but not in slices from mice expressing defective RAGE targeted to neurons. Moreover, we found that the inflammatory cytokine IL-1beta (interleukin-1beta) and stress-activated kinases [p38 MAPK (p38 mitogen-activated protein kinase) and JNK (c-Jun N-terminal kinase)] were significantly altered and involved in RAGE signaling pathways depending on RAGE expression in neuron or microglia. These findings suggest a prominent role of microglial RAGE signaling in Abeta-induced EC synaptic dysfunction.

Mitochondrial dysfunction is an early feature of Alzheimer's disease (AD). Abnormalities in mitochondrial properties include impaired energy metabolism, defects in key respiratory enzyme activity/function, accumulation/generation of mitochondrial reactive oxygen species, and formation of membrane permeability transition pore. While the mechanisms underlying mitochondrial dysfunction remain incompletely understood, recent studies provide substantial evidence for the progressive accumulation of mitochondrial Abeta, which directly links to mitochondria-mediated toxicity. In this review, we describe recent studies addressing the following key questions: 1) Does Abeta accumulate in mitochondria of AD brain and AD mouse models? 2) How does Abeta gain access to the mitochondria? 3) If mitochondria are loaded with Abeta, do they develop similar evidence of dysfunction? 4) What are the mechanisms underlying mitochondrial Abeta-induced neuronal toxicity? and 5) What is the impact of interaction of mitochondrial Abeta with its binding partners (cyclophilin D and ABAD) on mitochondrial and neuronal properties/function in an Abeta milieu? The answers to these questions provide new insights into mechanisms of mitochondrial stress related to the pathogenesis of AD and information necessary for developing therapeutic strategy for AD.

Microglia are critical for amyloid-beta peptide (Abeta)-mediated neuronal perturbation relevant to Alzheimer's disease (AD) pathogenesis. We demonstrate that overexpression of receptor for advanced glycation end products (RAGE) in imbroglio exaggerates neuroinflammation, as evidenced by increased proinflammatory mediator production, Abeta accumulation, impaired learning/memory, and neurotoxicity in an Abeta-rich environment. Transgenic (Tg) mice expressing human mutant APP (mAPP) in neurons and RAGE in microglia displayed enhanced IL-1beta and TNF-alpha production, increased infiltration of microglia and astrocytes, accumulation of Abeta, reduced acetylcholine esterase (AChE) activity, and accelerated deterioration of spatial learning/memory. Notably, introduction of a signal transduction-defective mutant RAGE (DN-RAGE) to microglia attenuates deterioration induced by Abeta. These findings indicate that RAGE signaling in microglia contributes to the pathogenesis of an inflammatory response that ultimately impairs neuronal function and directly affects amyloid accumulation. We conclude that blockade of microglial RAGE may have a beneficial effect on Abeta-mediated neuronal perturbation relevant to AD pathogenesis.-Fang, F., Lue, L.-F., Yan, S., Xu, H., Luddy, J. S., Chen, D., Walker, D. G., Stern, D. M., Yan, S., Schmidt, A. M., Chen, J. X., Yan, S. S. RAGE-dependent signaling in microglia contributes to neuroinflammation, Abeta accumulation, and impaired learning/memory in a mouse model of Alzheimer's disease.

Mitochondrial dysfunction has been reported in a wide array of neurological disorders ranging from neuromuscular to neurodegenerative diseases. Recent studies on neurodegenerative diseases have revealed that mitochondrial pathology is generally found in inherited or sporadic neurodegenerative diseases and is believed to be involved in the pathophysiological process of these diseases. Commonly seen types of mitochondrial dysfunction in neurodegenerative diseases include excessive free radical generation, lowered ATP production, mitochondrial permeability transition, mitochondrial DNA lesions, perturbed mitochondrial dynamics and apoptosis. Mitochondrial medicine as an emerging therapeutic strategy targeted to mitochondrial dysfunction in neurodegenerative diseases has been proven to be of value, though this area of research is still at in its early stage. In this article, we report on recent progress in the development of several mitochondrial therapies including antioxidants, blockade of mitochondrial permeability transition, and mitochondrial gene therapy as evidence that mitochondrial medicine has promise in the treatment of neurodegenerative diseases.

Receptor for Advanced Glycation Endproducts (RAGE) is a multiligand member of the immunoglobulin superfamily of cell surface molecules which serves as a receptor for amyloid-beta peptide (Abeta) on neurons, microglia, astrocytes, and cells of vessel wall. Increased expression of RAGE is observed in regions of the brain affected by Alzheimer's disease (AD), and Abeta-RAGE interaction in vitro leads to cell stress with the generation of reactive oxygen species and activation of downstream signaling mechanisms including the MAP kinase pathway. RAGE-mediated activation of p38 MAP kinase in neurons causes Abeta-induced inhibition of long-term potentiation in slices of entorhinal cortex. Increased expression of RAGE in an Abeta-rich environment, using transgenic mouse models, accelerates and accentuates pathologic, biochemical, and behavioral abnormalities compared with mice overexpressing only mutant amyloid-beta protein precursor. Interception of Abeta interaction with RAGE, by infusion of soluble RAGE, decreases Abeta content and amyloid load, as well as improving learning/memory and synaptic function, in a murine transgenic model of Abeta accumulation. These data suggest that RAGE may be a therapeutic target for AD.

Oligomeric amyloid-beta (Abeta) interferes with long-term potentiation (LTP) and cognitive processes, suggesting that Abeta peptides may play a role in the neuronal dysfunction which characterizes the early stages of Alzheimer's disease (AD). Multiple lines of evidence have highlighted RAGE (receptor for advanced glycation end-products) as a receptor involved in Abeta-induced neuronal and synaptic dysfunction. In the present study, we investigated the effect of oligomeric soluble Abeta1-42 on LTP elicited by the stimulation of different intracortical pathways in the mouse visual cortex. A variety of nanomolar concentrations (20-200 nM) of Abeta1-42 were able to inhibit LTP in cortical layer II-III induced by either white matter (WM-Layer II/III) or the layer II/III (horizontal pathway) stimulation, whereas the inhibition of LTP was more susceptible to Abeta1-42, which occurred at 20 nM of Abeta, when stimulating layer II-III horizontal pathway. Remarkably, cortical slices were resistant to nanomolar Abeta1-42 in the absence of RAGE (genetic deletion of RAGE) or blocking RAGE by RAGE antibody. These results indicate that nanomolar Abeta inhibits LTP expression in different neocortical circuits. Crucially, it is demonstrated that Abeta-induced reduction of LTP in different cortical pathways is mediated by RAGE.

The products of nonenzymatic glycation and oxidation of proteins and lipids, the advanced glycation end products (AGEs), accumulate in a wide variety of environments. AGEs may be generated rapidly or over long times stimulated by a range of distinct triggering mechanisms, thereby accounting for their roles in multiple settings and disease states. A critical property of AGEs is their ability to activate receptor for advanced glycation end products (RAGE), a signal transduction receptor of the immunoglobulin superfamily. It is our hypothesis that due to such interaction, AGEs impart a potent impact in tissues, stimulating processes linked to inflammation and its consequences. We hypothesize that AGEs cause perturbation in a diverse group of diseases, such as diabetes, inflammation, neurodegeneration, and aging. Thus, we propose that targeting this pathway may represent a logical step in the prevention/treatment of the sequelae of these disorders.

Ligation of the receptor for advanced glycation end products (RAGE) occurs during inflammation. Engagement of RAGE results in enhanced expression of addressins and it is therefore, not surprising that previous studies have shown a role of RAGE/ligand interactions in immune responses including cell/cell contact but the role of RAGE in spontaneous autoimmunity has not been clearly defined. To study the role of RAGE/ligand interactions in autoimmune diabetes, we tested the ability of soluble RAGE, a scavenger of RAGE ligands, in late stages of diabetes development in the NOD mouse-disease transferred with diabetogenic T cells and recurrent disease in NOD/scid recipients of syngeneic islet transplants. RAGE expression was detected on CD4+, CD8+, and B cells from diabetic mice and transferred to NOD/scid recipients. RAGE and its ligand, S100B, were found in the islets of NOD/scid mice that developed diabetes. Treatment of recipient NOD/scid mice with soluble RAGE prevented transfer of diabetes and delayed recurrent disease in syngeneic islet transplants. RAGE blockade was associated with increased expression of IL-10 and TGF-β in the islets from protected mice. RAGE blockade reduced the transfer of disease with enriched T cells, but had no effect when diabetes was transferred with the activated CD4+ T cell clone, BDC2.5. We conclude that RAGE/ligand interactions are involved in the differentiation of T cells to a mature pathogenic phenotype during the late stages of the development of diabetes.

Mitochondrial dysfunction is a hallmark of beta-amyloid (Abeta)-induced neuronal toxicity in Alzheimer's disease (AD). Here, we demonstrate that Abeta-binding alcohol dehydrogenase (ABAD) is a direct molecular link from Abeta to mitochondrial toxicity. Abeta interacts with ABAD in the mitochondria of AD patients and transgenic mice. The crystal structure of Abeta-bound ABAD shows substantial deformation of the active site that prevents nicotinamide adenine dinucleotide (NAD) binding. An ABAD peptide specifically inhibits ABAD-Abeta interaction and suppresses Abeta-induced apoptosis and free-radical generation in neurons. Transgenic mice overexpressing ABAD in an Abeta-rich environment manifest exaggerated neuronal oxidative stress and impaired memory. These data suggest that the ABAD-Abeta interaction may be a therapeutic target in AD.

Multiple sclerosis (MS) is a devastating neuroinflammatory disorder of the central nervous system (CNS) in which T cells that are reactive with major components of myelin sheaths have a central role. The receptor for advanced glycation end products (RAGE) is present on T cells, mononuclear phagocytes and endothelium. Its pro-inflammatory ligands, S100-calgranulins, are upregulated in MS and in the related rodent model, experimental autoimmune encephalomyelitis (EAE). Blockade of RAGE suppressed EAE when disease was induced by myelin basic protein (MBP) peptide or encephalitogenic T cells, or when EAE occurred spontaneously in T-cell receptor (TCR)-transgenic mice devoid of endogenous TCR-alpha and TCR-beta chains. Inhibition of RAGE markedly decreased infiltration of the CNS by immune and inflammatory cells. Transgenic mice with targeted overexpression of dominant-negative RAGE in CD4+ T cells were resistant to MBP-induced EAE. These data reinforce the importance of RAGE-ligand interactions in modulating properties of CD4+ T cells that infiltrate the CNS.

Synaptic dysfunction and degeneration is an early pathological feature of aging and age-related diseases, including Alzheimer's disease (AD). Aging is associated with increased generation and deposition of advanced glycation endproducts (AGEs), resulting from nonenzymatic glycation (or oxidation) proteins and lipids. AGE formation is accelerated in diabetes and AD-affected brain, contributing to cellular perturbation. The extent of AGEs' involvement, if at all, in alterations in synaptic structure and function is currently unknown. Here we analyze the contribution of neuronal receptor of AGEs (RAGE) signaling to AGE-mediated synaptic injury using novel transgenic neuronal RAGE knockout mice specifically targeted to the forebrain and transgenic mice expressing neuronal dominant-negative RAGE (DN-RAGE). Addition of AGEs to brain slices impaired hippocampal long-term potentiation (LTP). Similarly, treatment of hippocampal neurons with AGEs significantly decreases synaptic density. Such detrimental effects are largely reversed by genetic RAGE depletion. Notably, brain slices from mice with neuronal RAGE deficiency or DN-RAGE are resistant to AGE-induced LTP deficit. Further, RAGE deficiency or DN-RAGE blocks AGE-induced activation of p38 signaling. Taken together, these data show that neuronal RAGE functions as a signal transducer for AGE-induced synaptic dysfunction, thereby providing new insights into a mechanism by which the AGEs-RAGE-dependent signaling cascade contributes to synaptic injury via the p38 MAP kinase signal transduction pathway. Thus, RAGE blockade may be a target for development of interventions aimed at preventing the progression of cognitive decline in aging and age-related neurodegenerative diseases.