Amyloid Pathology Impairs Experience-Dependent Inhibitory Synaptic Plasticity.

Alzheimer's disease patients and mouse models exhibit aberrant neuronal activity and altered excitatory-to-inhibitory synaptic ratio. Using multicolor two-photon microscopy, we test how amyloid pathology alters the structural dynamics of excitatory and inhibitory synapses and their adaptation to altered visual experience in vivo in the visual cortex. We show that the baseline dynamics of mature excitatory synapses and their adaptation to visual deprivation are not altered in amyloidosis. Likewise, the baseline dynamics of inhibitory synapses are not affected. In contrast, visual deprivation fails to induce inhibitory synapse loss in amyloidosis, a phenomenon observed in nonpathological conditions. Intriguingly, inhibitory synapse loss associated with visual deprivation in nonpathological mice is accompanied by subtle broadening of spontaneous but not visually evoked calcium transients. However, such broadening does not manifest in the context of amyloidosis. We also show that excitatory and inhibitory synapse loss is locally clustered under the nonpathological state. In contrast, a fraction of synapse loss is not locally clustered in amyloidosis, indicating an impairment in inhibitory synapse adaptation to changes in excitatory synaptic activity.

New cyclophilin D inhibitor rescues mitochondrial and cognitive function in Alzheimer's disease.

Mitochondrial dysfunction is an early pathological feature of Alzheimer disease and plays a crucial role in the development and progression of Alzheimer's disease. Strategies to rescue mitochondrial function and cognition remain to be explored. Cyclophilin D (CypD), the peptidylprolyl isomerase F (PPIase), is a key component in opening the mitochondrial membrane permeability transition pore, leading to mitochondrial dysfunction and cell death. Blocking membrane permeability transition pore opening by inhibiting CypD activity is a promising therapeutic approach for Alzheimer's disease. However, there is currently no effective CypD inhibitor for Alzheimer's disease, with previous candidates demonstrating high toxicity, poor ability to cross the blood-brain barrier, compromised biocompatibility and low selectivity. Here, we report a new class of non-toxic and biocompatible CypD inhibitor, ebselen, using a conventional PPIase assay to screen a library of ∼2000 FDA-approved drugs with crystallographic analysis of the CypD-ebselen crystal structure (PDB code: 8EJX). More importantly, we assessed the effects of genetic and pharmacological blockade of CypD on Alzheimer's disease mitochondrial and glycolytic bioenergetics in Alzheimer's disease-derived mitochondrial cybrid cells, an ex vivo human sporadic Alzheimer's disease mitochondrial model, and on synaptic function, inflammatory response and learning and memory in Alzheimer's disease mouse models. Inhibition of CypD by ebselen protects against sporadic Alzheimer's disease- and amyloid-ß-induced mitochondrial and glycolytic perturbation, synaptic and cognitive dysfunction, together with suppressing neuroinflammation in the brain of Alzheimer's disease mouse models, which is linked to CypD-related membrane permeability transition pore formation. Thus, CypD inhibitors have the potential to slow the progression of neurodegenerative diseases, including Alzheimer's disease, by boosting mitochondrial bioenergetics and improving synaptic and cognitive function.

Amyloid pathology impairs experience-dependent inhibitory synaptic plasticity.

Alzheimer's disease patients and mouse models exhibit aberrant neuronal activity and altered excitatory-to-inhibitory synaptic ratio. Using multicolor two-photon microscopy, we test how amyloid pathology alters the structural dynamics of excitatory and inhibitory synapses and their adaptation to altered visual experience in vivo in the visual cortex. We show that the baseline dynamics of mature excitatory synapses and their adaptation to visual deprivation are not altered in amyloidosis. Likewise, the baseline dynamics of inhibitory synapses are not affected. In contrast, visual deprivation fails to induce inhibitory synapse loss in amyloidosis, a phenomenon observed in nonpathological conditions. Intriguingly, inhibitory synapse loss associated with visual deprivation in nonpathological mice is accompanied by the broadening of spontaneous but not visually evoked calcium transients. However, such broadening does not manifest in the context of amyloidosis. We also show that excitatory and inhibitory synapse loss is locally clustered under the nonpathological state. In contrast, a fraction of synapse loss is not locally clustered in amyloidosis, indicating an impairment in inhibitory synapse adaptation to changes in excitatory synaptic activity.

Mitochondrial oxidative stress contributes to the pathological aggregation and accumulation of tau oligomers in 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.

Gain of PITRM1 peptidase in cortical neurons affords protection of mitochondrial and synaptic function in an advanced age mouse model of Alzheimer's disease.

Mitochondrial dysfunction is one of the early pathological features of Alzheimer's disease (AD). Accumulation of cerebral and mitochondrial Aß links to mitochondrial and synaptic toxicity. We have previously demonstrated the mechanism by which presequence peptidase (PITRM1)-mediated clearance of mitochondrial Aß contributes to mitochondrial and cerebral amyloid pathology and mitochondrial and synaptic stress in adult transgenic AD mice overexpressing Aß 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 Aß accumulation and whether this protection is maintained even at later ages featuring profound amyloid pathology and synaptic failure. Using newly developed aged PITRM1/Aß-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 Aß accumulation and failure to rescue mitochondrial and synaptic function, suggesting that PITRM1 activity is required for the degradation and clearance of mitochondrial Aß and Aß deposition. These data indicate that augmenting PITRM1 function results in persistent life-long protection against Aß toxicity in an AD mouse model. Therefore, augmenting PITRM1 function may enhance Aß clearance in mitochondria, thereby maintaining mitochondrial integrity and ultimately slowing the progression of AD.

PINK1 Activation Attenuates Impaired Neuronal-Like Differentiation and Synaptogenesis and Mitochondrial Dysfunction in Alzheimer's Disease Trans-Mitochondrial Cybrid Cells.

BACKGROUND: Mitochondrial dysfunction, bioenergetic deficit, and extensive oxidative stress underlie neuronal perturbation during the early stage of Alzheimer's disease (AD). Previously, we demonstrated that decreased PTEN-induced putative kinase 1 (PINK1) expression is associated with AD pathology in AD-affected human brains and AD mice. OBJECTIVE: In the present study, we highlight the essential role of PINK1 in AD-relevant mitochondrial perturbation and neuronal malfunction. METHODS: Using trans-mitochondrial "cybrid" (cytoplasmic hybrid) neuronal cells, whose mitochondria are transferred from platelets of patients with sporadic AD, we observed the effect of PINK1 in neuronal-like differentiation and synaptogenesis and mitochondrial functions. RESULTS: In AD cybrid cells, the downregulation of PINK1 is correlated to the alterations in mitochondrial morphology and function and deficit in neuronal-like differentiation. Restoring/increasing PINK1 by lentivirus transduction of PINK1 robustly attenuates mitochondrial defects and rescues neurite-like outgrowth. Importantly, defective PINK1 kinase activity fails to reverse these detrimental effects. Mechanistically, AD cybrid cells reveal a significant decrease in PINK1-dependent phosphorylated mitofusin (Mfn) 2, a key mitochondrial membrane protein that participates in mitochondrial fusion, and an insufficient autophagic activity for the clearance of dysfunctional mitochondria. Overexpression of PINK1, but not mutant PINK1 elevates phosphorylation of Mfn2 and autophagy signaling LC3-II. Accordingly, PINK1-overexpressed AD cybrids exhibit increases in mitochondrial length and density and suppressed reactive oxygen species. These results imply that activation of PINK1 protects against AD-affected mitochondrial dysfunction and impairment in neuronal maturation and differentiation. CONCLUSION: PINK1-mediated mitophagy is important for maintaining mitochondrial health by clearance of dysfunctional mitochondria and therefore, improves energy homeostasis in AD.

Age-dependent accumulation of dicarbonyls and advanced glycation endproducts (AGEs) associates with mitochondrial stress.

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 hydroimidazolone-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.

High Dietary Advanced Glycation End Products Impair Mitochondrial and Cognitive Function.

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.

Anxiety and task performance changes in an aging mouse model.

Due to the increasing focus on aging as an important risk factor for many serious diseases and an emphasis on animal models that have translational value, an increasing number of animal models are being aged. Animal behavior tests can be used to assess effects of aging in mouse models. Female mice begin exhibiting anxiety-like behaviors at 12 months of age which become more serious at 24 months, while males exhibit no age-induced anxiety-like behaviors. Males and females equally demonstrate a failure of daily task performance at 24 months. Despite these cognitive changes, the mice do not show changes in gross motor function. These results suggest cognitive impairment in non-genetically modified aging mice.

Overexpression of endophilin A1 exacerbates synaptic alterations in a mouse model of Alzheimer's disease.

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-ß peptide (Aß)-rich environments, leading to changes in both long-term potentiation and learning and memory of transgenic animals. Specifically, increasing EP augmented cerebral Aß accumulation. EP-mediated signal transduction via reactive oxygen species (ROS)/p38 mitogen-activated protein (MAP) kinase contributes to Aß-induced mitochondrial dysfunction, synaptic injury, and cognitive decline, which could be rescued by blocking either ROS or p38 MAP kinase activity.

Mitochondrial permeability transition pore: a potential drug target for neurodegeneration.

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.

Identification and Characterization of Amyloid-ß Accumulation in Synaptic Mitochondria.

Mitochondrial and synaptic dysfunction is an early pathological feature of Alzheimer's disease (AD). Accumulation of amyloid beta-peptide (Aß) 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 Aß 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 Aß levels in the isolated mitochondria as well as ultrastructural localization of synaptic mitochondrial Aß. These methods have been used successfully for the identification and characterization of Aß 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.

Astrocytes Attenuate Mitochondrial Dysfunctions in Human Dopaminergic Neurons Derived from iPSC.

Astrocytes, the most populous glial cell type in the brain, are critical for regulating the brain microenvironment. In various neurodegenerative diseases, astrocytes determine the progression and outcome of the neuropathological process. We have recently revealed the direct involvement of mitochondrial function in human pluripotent stem cell (hiPSC)-derived dopaminergic (DA) neuronal differentiation. Using the astroglial-neuronal co-culture system, we show here that astrocytes effectively rescue defects in neurogenesis of DA neurons with mitochondrial respiratory chain disruption. Co-culture of astrocytes with defective DA neurons completely restored mitochondrial functions and dynamics insulted by mitochondrial toxins. These results suggest the significance of astroglia in maintaining mitochondrial development and bioenergetics during differentiation of hiPSC-derived DA neurons. Our study also provides an active astroglial-neuronal interaction model for future investigation of mitochondrial involvement in neurogenesis and neurodegenerative diseases.

RAGE mediates Aß accumulation in a mouse model of Alzheimer's disease via modulation of ß- and γ-secretase activity.

Receptor for Advanced Glycation End products (RAGE) has been implicated in amyloid ß-peptide (Aß)-induced perturbation relevant to the pathogenesis of Alzheimer's disease (AD). However, whether and how RAGE regulates Aß metabolism remains largely unknown. Aß formation arises from aberrant cleavage of amyloid pre-cursor protein (APP) by ß- and γ-secretase. To investigate whether RAGE modulates ß- and γ-secretase activity potentiating Aß formation, we generated mAPP mice with genetic deletion of RAGE (mAPP/RO). These mice displayed reduced cerebral amyloid pathology, inhibited aberrant APP-Aß metabolism by reducing ß- 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 Aß40 and Aß42 production and decreased ß-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 3ß (GSK3ß). Finally, RAGE siRNA-mediated gene silencing or DN-RAGE-mediated signaling deficiency in the enriched human APP neuronal cells demonstrated suppression of activation of GSK3ß, accompanied with reduction in Aß levels and decrease in ß- and γ-secretases activity. Our findings highlight that RAGE-dependent signaling pathway regulates ß- and γ-secretase cleavage of APP to generate Aß, at least in part through activation of GSK3ß and p38 MAP kinase. RAGE is a potential therapeutic target to limit aberrant APP-Aß metabolism in halting progression of AD.

PINK1 signalling rescues amyloid pathology and mitochondrial dysfunction in Alzheimer's disease.

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-ß 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-ß levels, amyloid-associated pathology, oxidative stress, as well as mitochondrial and synaptic dysfunction. In contrast, PINK1-deficient mAPP mice augmented cerebral amyloid-ß 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-ß-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-ß-induced detrimental effects. Our findings highlight a novel mechanism by which PINK1-dependent signalling promotes the rescue of amyloid pathology and amyloid-ß-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.

Mitochondrial Dysfunction Triggers Synaptic Deficits via Activation of p38 MAP Kinase Signaling in Differentiated Alzheimer's Disease Trans-Mitochondrial Cybrid Cells.

Loss of synapse and synaptic dysfunction contribute importantly to cognitive impairment in Alzheimer's disease (AD). Mitochondrial dysfunction and oxidative stress are early pathological features in AD-affected brain. However, the effect of AD mitochondria on synaptogenesis remains to be determined. Using human trans-mitochondrial "cybrid" (cytoplasmic hybrid) neuronal cells whose mitochondria were transferred from platelets of patients with sporadic AD or age-matched non-AD subjects with relatively normal cognition, we provide the first evidence of mitochondrial dysfunction compromises synaptic development and formation of synapse in AD cybrid cells in response to chemical-induced neuronal differentiation. Compared to non-AD control cybrids, AD cybrid cells showed synaptic loss which was evidenced by a significant reduction in expression of two synaptic marker proteins: synaptophysin (presynaptic marker) and postsynaptic density protein-95, and neuronal proteins (MAP-2 and NeuN) upon neuronal differentiation. In parallel, AD-mediated synaptic deficits correlate to mitochondrial dysfunction and oxidative stress as well as activation of p38 MAP kinase. Notably, inhibition of p38 MAP kinase by pharmacological specific p38 inhibitor significantly increased synaptic density, improved mitochondrial function, and reduced oxidative stress. These results suggest that activation of p38 MAP kinase signaling pathway contributes to AD-mediated impairment in neurogenesis, possibly by inhibiting the neuronal differentiation. Our results provide new insight into the crosstalk of dysfunctional AD mitochondria to synaptic formation and maturation via activation of p38 MAP kinase. Therefore, blockade of p38 MAP kinase signal transduction could be a potential therapeutic strategy for AD by alleviating loss of synapses.

Entorhinal Cortex dysfunction can be rescued by inhibition of microglial RAGE in an Alzheimer's disease mouse model.

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 Aß. 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 Aß-enriched environment contributes to the EC vulnerability.

Development and Dynamic Regulation of Mitochondrial Network in Human Midbrain Dopaminergic Neurons Differentiated from iPSCs.

Mitochondria are critical to neurogenesis, but the mechanisms of mitochondria in neurogenesis have not been well explored. We fully characterized mitochondrial alterations and function in relation to the development of human induced pluripotent stem cell (hiPSC)-derived dopaminergic (DA) neurons. Following directed differentiation of hiPSCs to DA neurons, mitochondria in these neurons exhibit pronounced changes during differentiation, including mature neurophysiology characterization and functional synaptic network formation. Inhibition of mitochondrial respiratory chains via application of complex IV inhibitor KCN (potassium cyanide) or complex I inhibitor rotenone restricted neurogenesis of DA neurons. These results demonstrated the direct importance of mitochondrial development and bioenergetics in DA neuronal differentiation. Our study also provides a neurophysiologic model of mitochondrial involvement in neurogenesis, which will enhance our understanding of the role of mitochondrial dysfunctions in neurodegenerative diseases.

Antioxidants Rescue Mitochondrial Transport in Differentiated Alzheimer's Disease Trans-Mitochondrial Cybrid Cells.

Mitochondrial dysfunction and axonal degeneration are early pathological features of Alzheimer's disease (AD)-affected brains. The underlying mechanisms and strategies to rescue it have not been well elucidated. Here, we evaluated axonal mitochondrial transport and function in AD subject-derived mitochondria. We analyzed mitochondrial transport and kinetics in human trans-mitochondrial "cybrid" (cytoplasmic hybrid) neuronal cells whose mitochondria were derived from platelets of patients with sporadic AD and compared these AD cybrid cell lines with cybrid cell lines whose mitochondria were derived from age-matched, cognitively normal subjects. Human AD cybrid cell lines, when induced to differentiate, developed stunted projections. Mitochondrial transport and function within neuronal processes/axons was altered in AD-derived mitochondria. Antioxidants reversed deficits in axonal mitochondrial transport and function. These findings suggest that antioxidants may be able to mitigate the consequences of AD-associated mitochondrial dysfunction. The present study provides evidence of the cause/effect of AD specific mitochondrial defects, which significantly enhances our understanding of the AD pathogenesis and exploring the effective therapeutic strategy for AD.

Mfn2 is Required for Mitochondrial Development and Synapse Formation in Human Induced Pluripotent Stem Cells/hiPSC Derived Cortical Neurons.

Mitochondria are essential dynamic organelles for energy production. Mitochondria dynamically change their shapes tightly coupled to fission and fusion. Imbalance of fission and fusion can cause deficits in mitochondrial respiration, morphology and motility. Mfn2 (mitofusin 2), a mitochondrial membrane protein that participates in mitochondrial fusion in mammalian cells, contributes to the maintenance and operation of the mitochondrial network. Due to lack of applicable model systems, the mechanisms and involvement of mitochondria in neurogenesis in human brain cells have not been well explored. Here, by employing the human induced pluripotent stem cells (hiPSCs) differentiation system, we fully characterized mitochondrial development, neurogenesis and synapse formation in hiPSCs-derived cortical neurons. Differentiation of hiPSCs to cortical neurons with extended period demonstrates mature neurophysiology characterization and functional synaptic network formation. Mitochondrial respiration, morphology and motility in the differentiated neurons also exhibit pronounced development during differentiation. Mfn2 knock-down results in deficits in mitochondrial metabolism and network, neurogenesis and synapse formation, while Mfn2 overexpression enhances mitochondrial bioenergetics and functions, and promotes the differentiation and maturation of neurons. Together, our data indicate that Mfn2 is essential for human mitochondrial development in neuronal maturation and differentiation, which will enhance our understanding of the role of Mfn2 in neurogenesis.