Differentiated Alzheimer's disease transmitochondrial cybrid cell lines exhibit reduced organelle movement

Increased expression of SLC25A18 is associated with Alzheimer's disease and is involved in Aβ42-induced mitochondrial dysfunction and apoptosis in neuronal cells

Alzheimer's disease (AD) is currently one of the most serious public health concerns in the world. However, the best approach to treat AD has yet to be discovered, implying that we must continue to work hard to find new AD target genes. In this study, we further analysed Gene Expression Omnibus (GEO) data and discovered that the expression of the Mitochondria glutamate carrier SLC25A18 is associated with AD by screening the differentially expressed genes in different regions of the brains of Alzheimer's disease patients. To verify the expression of SLC25A18 during Alzheimer's disease development, we analysed animal models (5×FAD transgenic AD animal model, chemically induced AD animal model, natural ageing animal model), and the results showed that the expression of SLC25A18 was increased in animal models of AD. Further investigation of the different regions found that SLC25A18 expression was elevated in the EC, TeA, and CA3, and expressed in neurons. Next, We found that Aβ42 treatment elevated SLC25A18 expression in Neuro 2A cells. Reducing SLC25A18 expression attenuated mitochondrial dysfunction and neuronal apoptosis caused by Aβ42. Overexpression of SLC25A18 increased ATP and intracellular superoxide anions but decreased mitochondrial membrane potential. The results indicate that SLC25A18 affects mitochondrial function and neuronal apoptosis, and is related to AD, which makes it a potential target for treating brain dysfunction.

Electroacupuncture pretreatment preserves telomerase reverse transcriptase function and alleviates postoperative cognitive dysfunction by suppressing oxidative stress and neuroinflammation in aged mice

BACKGROUND

Elderly patients often exhibit postoperative cognitive dysfunction (POCD), a postsurgical decline in memory and executive function. Oxidative stress and neuroinflammation, both pathological characteristics of the aged brain, contribute to this decline. This study posits that electroacupuncture (EA) stimulation, an effective antioxidant and anti-inflammatory modality, may enhance telomerase reverse transcriptase (TERT) function, the catalytic subunit of telomerase known for its protective properties against cellular senescence and oxidative damage, to alleviate POCD in aged mice.

METHODS

The animal POCD model was created by subjecting aged mice to abdominal surgery, followed by EA pretreatment at the Baihui acupoint (GV20). Postoperative cognitive function was gauged using the Morris water maze (MWM) test. Hippocampal TERT mRNA levels and telomerase activity were determined through qPCR and a Telomerase PCR ELISA kit, respectively. Oxidative stress was assessed through superoxide dismutase (SOD), reactive oxygen species (ROS), and malondialdehyde (MDA) levels. Iba-1 immunostaining determined the quantity of hippocampal microglia. Additionally, western blotting assessed TERT, autophagy markers, and proinflammatory cytokines at the protein level.

RESULTS

Abdominal surgery in aged mice significantly decreased telomerase activity and TERT mRNA and protein levels, but increased oxidative stress and neuroinflammation and decreased autophagy in the hippocampus. EA-pretreated mice demonstrated improved postoperative cognitive performance, enhanced telomerase activity, increased TERT protein expression, improved TERT mitochondrial localization, and reduced oxidative damage, autophagy dysfunction, and neuroinflammation. The neuroprotective benefits of EA pretreatment were diminished following TERT knockdown.

CONCLUSIONS

Our findings underscore the significance of TERT function preservation in alleviating surgery-induced oxidative stress and neuroinflammation in aged mice. A novel neuroprotective mechanism of EA stimulation is highlighted, whereby modulation of TERT and telomerase activity reduces oxidative damage and neuroinflammation. Consequently, maintaining TERT function via EA treatment could serve as an effective strategy for managing POCD in elderly patients.

Interaction of Tau with Kinesin-1: Effect of Kinesin-1 Heavy Chain Elimination on Autophagy-Mediated Mutant Tau Degradation

Natively unfolded tau has a low propensity to form aggregates, but in tauopathies, such as Alzheimer's disease (AD), tau aggregates into paired helical filaments (PHFs) and neurofibrillary tangles (NFTs). Multiple intracellular transport pathways utilize kinesin-1, a plus-end-directed microtubule-based motor. Kinesin-1 is crucial in various neurodegenerative diseases as it transports multiple cargoes along the microtubules (MT). Kinesin-1 proteins cannot progress along MTs due to an accumulation of tau on their surfaces. Although kinesin-1-mediated neuronal transport dysfunction is well-documented in other neurodegenerative diseases, its role in AD has received less attention. Very recently, we have shown that knocking down and knocking out of kinesin-1 heavy chain (KIF5B KO) expression significantly reduced the level and stability of tau in cells and tau transgenic mice, respectively. Here, we report that tau interacts with the motor domain of KIF5B in vivo and in vitro, possibly through its microtubule-binding repeat domain. This interaction leads to the inhibition of the ATPase activity of the motor domain. In addition, the KIF5B KO results in autophagy initiation, which subsequently assists in tau degradation. The mechanisms behind KIF5B KO-mediated tau degradation seem to involve its interaction with tau, promoting the trafficking of tau through retrograde transport into autophagosomes for subsequent lysosomal degradation of tau. Our results suggest how KIF5B removal facilitates the movement of autophagosomes toward lysosomes for efficient tau degradation. This mechanism can be enabled through the downregulation of kinesin-1 or the disruption of the association between kinesin-1 and tau, particularly in cases when neurons perceive disturbances in intercellular axonal transport.

The Alzheimer's Disease Mitochondrial Cascade Hypothesis: A Current Overview

Viable Alzheimer's disease (AD) hypotheses must account for its age-dependence; commonality; association with amyloid precursor protein, tau, and apolipoprotein E biology; connection with vascular, inflammation, and insulin signaling changes; and systemic features. Mitochondria and parameters influenced by mitochondria could link these diverse characteristics. Mitochondrial biology can initiate changes in pathways tied to AD and mediate the dysfunction that produces the clinical phenotype. For these reasons, conceptualizing a mitochondrial cascade hypothesis is a straightforward process and data accumulating over decades argue the validity of its principles. Alternative AD hypotheses may yet account for its mitochondria-related phenomena, but absent this happening a primary mitochondrial cascade hypothesis will continue to evolve and attract interest.

Manganese-enhanced magnetic resonance imaging method detects age-related impairments in axonal transport in mice and attenuation of the impairments by a microtubule-stabilizing compound

In this study a manganese-enhanced magnetic resonance imaging (MEMRI) method was developed for mice for measuring axonal transport (AXT) rates in real time in olfactory receptor neurons, which project from the olfactory epithelium to the olfactory neuronal layer of the olfactory bulb. Using this MEMRI method, two major experiments were conducted: 1) an evaluation of the effects of age on AXT rates and 2) an evaluation of the brain-penetrant, microtubule-stabilizing agent, Epothilone D for effect on AXT rates in aged mice. In these studies, we improved upon previous MEMRI approaches to develop a method where real-time measurements (32 time points) of AXT rates in mice can be determined over a single (approximately 100 min) scanning session. In the age comparisons, AXT rates were significantly higher in young (mean age ∼4.0 months old) versus aged (mean age ∼24.5 months old) mice. Moreover, in aged mice, eight weeks of treatment with Epothilone D, (0.3 and 1.0 mg/kg) was associated with statistically significant increases in AXT rates compared to vehicle-treated subjects. These experiments conducted in a living mammalian model (i.e., wild type, C57BL/6 mice), using a new modified MEMRI method, thus provide further evidence that the process of aging leads to decreases in AXT rates in the brain and they further support the argument that microtubule-based therapeutic strategies designed to improve AXT rates have potential for age-related neurological disorders.

Mitochondrial defects: An emerging theranostic avenue towards Alzheimer's associated dysregulations

Mitochondria play a crucial role in expediting the energy homeostasis under varying environmental conditions. As mitochondria are controllers of both energy production and apoptotic pathways, they are also distinctively involved in controlling the neuronal cell survival and/or death. Numerous factors are responsible for mitochondria to get degraded with aging and huge functional failures in mitochondria are also found to be associated with the commencement of numerous neurodegenerative conditions, including Alzheimer's disease (AD). A large number of existing literatures promote the pivotal role of mitochondrial damage and oxidative impairment in the pathogenesis of AD. Numerous mitochondria associated processes such as mitochondrial biogenesis, fission, fusion, mitophagy, transportation and bioenergetics are crucial for proper functioning of mitochondria but are reported to be defective in AD patients. Though, the knowledge on the precise and in-depth mechanisms of these actions is still in infancy. Based upon the outcome of various significant studies, mitochondria are also being considered as therapeutic targets for AD. Here, we review the current status of mitochondrial defects in AD and also summarize the possible role of these defects in the pathogenesis of AD. The various approaches for developing the mitochondria-targeted therapies are also discussed here in detail. Consequently, it is suggested that improving mitochondrial activity via pharmacological and/or non-pharmacological interventions could postpone the onset and slow the development of AD. Further research and consequences of ongoing clinical trials should extend our understanding and help to validate conclusions regarding the causation of AD.

Synaptic plasticity in Alzheimer's disease and healthy aging

The strength and efficiency of synaptic connections are affected by the environment or the experience of the individual. This property, called synaptic plasticity, is directly related to memory and learning processes and has been modeled at the cellular level. These types of cellular memory and learning models include specific stimulation protocols that generate a long-term strengthening of the synapses, called long-term potentiation, or a weakening of the said long-term synapses, called long-term depression. Although, for decades, researchers have believed that the main cause of the cognitive deficit that characterizes Alzheimer's disease (AD) and aging was the loss of neurons, the hypothesis of an imbalance in the cellular and molecular mechanisms of synaptic plasticity underlying this deficit is currently widely accepted. An understanding of the molecular and cellular changes underlying the process of synaptic plasticity during the development of AD and aging will direct future studies to specific targets, resulting in the development of much more efficient and specific therapeutic strategies. In this review, we classify, discuss, and describe the main findings related to changes in the neurophysiological mechanisms of synaptic plasticity in excitatory synapses underlying AD and aging. In addition, we suggest possible mechanisms in which aging can become a high-risk factor for the development of AD and how its development could be prevented or slowed.

Brain Atrophy and White Matter Damage Linked to Peripheral Bioenergetic Deficits in the Neurodegenerative Disease FXTAS

Fragile X-associated tremor/ataxia syndrome (FXTAS) is a neurodegenerative disorder affecting subjects (premutation carriers) with a 55-200 CGG-trinucleotide expansion in the 5'UTR of the fragile X mental retardation 1 gene (FMR1) typically after age 50. As both the presence of white matter hyperintensities (WMHs) and atrophied gray matter on magnetic resonance imaging (MRI) are linked to age-dependent decline in cognition, here we tested whether MRI outcomes (WMH volume (WMHV) and brain volume) were correlated with mitochondrial bioenergetics from peripheral blood monocytic cells in 87 carriers with and without FXTAS. As a parameter assessing cumulative damage, WMHV was correlated to both FXTAS stages and age, and brain volume discriminated between carriers and non-carriers. Similarly, mitochondrial mass and ATP production showed an age-dependent decline across all participants, but in contrast to WMHV, only FADH2-linked ATP production was significantly reduced in carriers vs. non-carriers. In carriers, WMHV negatively correlated with ATP production sustained by glucose-glutamine and FADH2-linked substrates, whereas brain volume was positively associated with the latter and mitochondrial mass. The observed correlations between peripheral mitochondrial bioenergetics and MRI findings-and the lack of correlations with FXTAS diagnosis/stages-may stem from early brain bioenergetic deficits even before overt FXTAS symptoms and/or imaging findings.

Adaptation of mitochondrial network dynamics and velocity of mitochondrial movement to chronic stress present in fibroblasts derived from patients with sporadic form of Alzheimer's disease

Alzheimer's disease (AD) is one of the most common neurodegenerative diseases. Only 10% of all cases are familial form, the remaining 90% are sporadic form with unknown genetic background. The etiology of sporadic AD is still not fully understood. Pathogenesis and pathobiology of this disease are limited due to the limited number of experimental models. We used primary culture of fibroblasts derived from patients diagnosed with sporadic form of AD for investigation of dynamic properties of mitochondria, including fission-fusion process and localization of mitochondria within the cell. We observed differences in mitochondrial network organization with decreased mitochondrial transport velocity, and a drop in the frequency of fusion-fission events. These studies show how mitochondrial dynamics adapt to the conditions of long-term mitochondrial stress that prevails in cells of sporadic form 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.

Nilotinib Improves Bioenergetic Profiling in Brain Astroglia in the 3xTg Mouse Model of Alzheimer's Disease

Current treatments targeting amyloid beta in Alzheimer's disease (AD) have minimal efficacy, which results in a huge unmet medical need worldwide. Accumulating data suggest that brain mitochondrial dysfunction play a critical role in AD pathogenesis. Targeting cellular mechanisms associated with mitochondrial dysfunction in AD create a novel approach for drug development. This study investigated the effects of nilotinib, as a selective tyrosine kinase inhibitor, in astroglia derived from 3xTg-AD mice versus their C57BL/6-controls. Parameters included oxygen consumption rates (OCR), ATP, cytochrome c oxidase (COX), citrate synthase (CS) activity, alterations in oxidative phosphorylation (OXPHOS), nuclear factor kappa B (NF-κB), key regulators of mitochondrial dynamics (mitofusin (Mfn1), dynamin-related protein 1 (Drp1)), and mitochondrial biogenesis (peroxisome proliferator-activated receptor gamma coactivator1-alpha (PGC-1α), calcium/calmodulin-dependent protein kinase II (CaMKII), and nuclear factor (erythroid-derived 2)-like 2 (Nrf2)). Nilotinib increased OCR, ATP, COX, Mfn1, and OXPHOS levels in 3xTg astroglia. No significant differences were detected in levels of Drp1 protein and CS activity. Nilotinib enhanced mitochondrial numbers, potentially through a CaMKII-PGC1α-Nrf2 pathway in 3xTg astroglia. Additionally, nilotinib-induced OCR increases were reduced in the presence of the NF-κB inhibitor, Bay11-7082. The data suggest that NF-κB signaling is intimately involved in nilotinib-induced changes in bioenergetics in 3xTg brain astroglia. Nilotinib increased translocation of the NF-κB p50 subunit into the nucleus of 3xTg astroglia that correlates with an increased expression and activation of NF-κB. The current findings support a role for nilotinib in improving mitochondrial function and suggest that astroglia may be a key therapeutic target in treating AD.

Mitochondrial Dysfunction in Alzheimer's Disease: A Biomarker of the Future?

Alzheimer's disease (AD) is the most common cause of dementia worldwide and is characterised pathologically by the accumulation of amyloid beta and tau protein aggregates. Currently, there are no approved disease modifying therapies for clearance of either of these proteins from the brain of people with AD. As well as abnormalities in protein aggregation, other pathological changes are seen in this condition. The function of mitochondria in both the nervous system and rest of the body is altered early in this disease, and both amyloid and tau have detrimental effects on mitochondrial function. In this review article, we describe how the function and structure of mitochondria change in AD. This review summarises current imaging techniques that use surrogate markers of mitochondrial function in both research and clinical practice, but also how mitochondrial functions such as ATP production, calcium homeostasis, mitophagy and reactive oxygen species production are affected in AD mitochondria. The evidence reviewed suggests that the measurement of mitochondrial function may be developed into a future biomarker for early AD. Further work with larger cohorts of patients is needed before mitochondrial functional biomarkers are ready for clinical use.

Intermittent Hypoxic Conditioning Rescues Cognition and Mitochondrial Bioenergetic Profile in the Triple Transgenic Mouse Model of Alzheimer's Disease

The lack of effective disease-modifying therapeutics to tackle Alzheimer’s disease (AD) is unsettling considering the actual prevalence of this devastating neurodegenerative disorder worldwide. Intermittent hypoxic conditioning (IHC) is a powerful non-pharmacological procedure known to enhance brain resilience. In this context, the aim of the present study was to investigate the potential long-term protective impact of IHC against AD-related phenotype, putting a special focus on cognition and mitochondrial bioenergetics and dynamics. For this purpose, six-month-old male triple transgenic AD mice (3×Tg-AD) were submitted to an IHC protocol for two weeks and the behavioral assessment was performed at 8.5 months of age, while the sacrifice of mice occurred at nine months of age and their brains were removed for the remaining analyses. Interestingly, IHC was able to prevent anxiety-like behavior and memory and learning deficits and significantly reduced brain cortical levels of amyloid-β (Aβ) in 3×Tg-AD mice. Concerning brain energy metabolism, IHC caused a significant increase in brain cortical levels of glucose and a robust improvement of the mitochondrial bioenergetic profile in 3×Tg-AD mice, as mirrored by the significant increase in mitochondrial membrane potential (ΔΨm) and respiratory control ratio (RCR). Notably, the improvement of mitochondrial bioenergetics seems to result from an adaptative coordination of the distinct but intertwined aspects of the mitochondrial quality control axis. Particularly, our results indicate that IHC favors mitochondrial fusion and promotes mitochondrial biogenesis and transport and mitophagy in the brain cortex of 3×Tg-AD mice. Lastly, IHC also induced a marked reduction in synaptosomal-associated protein 25 kDa (SNAP-25) levels and a significant increase in both glutamate and GABA levels in the brain cortex of 3×Tg-AD mice, suggesting a remodeling of the synaptic microenvironment. Overall, these results demonstrate the effectiveness of the IHC paradigm in forestalling the AD-related phenotype in the 3×Tg-AD mouse model, offering new insights to AD therapy and forcing a rethink concerning the potential value of non-pharmacological interventions in clinical practice.

Regulation of histone deacetylase activities and functions by phosphorylation and its physiological relevance

Histone deacetylases (HDACs) are conserved enzymes that regulate many cellular processes by catalyzing the removal of acetyl groups from lysine residues on histones and non-histone proteins. As appropriate for proteins that occupy such an essential biological role, HDAC activities and functions are in turn highly regulated. Overwhelming evidence suggests that the dysregulation of HDACs plays a major role in many human diseases. The regulation of HDACs is achieved by multiple different mechanisms, including posttranslational modifications. One of the most common posttranslational modifications on HDACs is reversible phosphorylation. Many HDAC phosphorylations are context-dependent, occurring in specific tissues or as a consequence of certain stimuli. Additionally, whereas phosphorylation can regulate some HDACs in a non-specific manner, many HDAC phosphorylations result in specific consequences. Although some of these modifications support normal HDAC function, aberrations can contribute to disease development. Here we review and critically evaluate how reversible phosphorylation activates or deactivates HDACs and, thereby, regulates their many functions under various cellular and physiological contexts.

Promising Molecular Targets for Pharmacological Therapy of Neurodegenerative Pathologies

Drug development for the treatment of neurodegenerative diseases has to confront numerous problems occurring, in particular, because of attempts to address only one of the causes of the pathogenesis of neurological disorders. Recent advances in multitarget therapy research are gaining momentum by utilizing pharmacophores that simultaneously affect different pathological pathways in the neurodegeneration process. The application of such a therapeutic strategy not only involves the treatment of symptoms, but also mainly addresses prevention of the fundamental pathological processes of neurodegenerative diseases and the reduction of cognitive abilities. Neuroinflammation and oxidative stress, mitochondrial dysfunction, dysregulation of the expression of histone deacetylases, and aggregation of pathogenic forms of proteins are among the most common and significant pathological features of neurodegenerative diseases. In this review, we focus on the molecular mechanisms and highlight the main aspects, including reactive oxygen species, the cell endogenous antioxidant system, neuroinflammation triggers, metalloproteinases, α-synuclein, tau proteins, neuromelanin, histone deacetylases, presenilins, etc. The processes and molecular targets discussed in this review could serve as a starting point for screening leader compounds that could help prevent or slow down the development of neurodegenerative diseases.

Mitochondria and Mitochondrial Cascades in Alzheimer's Disease

Decades of research indicate mitochondria from Alzheimer's disease (AD) patients differ from those of non-AD individuals. Initial studies revealed structural differences, and subsequent studies showed functional deficits. Observations of structure and function changes prompted investigators to consider the consequences, significance, and causes of AD-related mitochondrial dysfunction. Currently, extensive research argues mitochondria may mediate, drive, or contribute to a variety of AD pathologies. The perceived significance of these mitochondrial changes continues to grow, and many currently believe AD mitochondrial dysfunction represents a reasonable therapeutic target. Debate continues over the origin of AD mitochondrial changes. Some argue amyloid-β (Aβ) induces AD mitochondrial dysfunction, a view that does not challenge the amyloid cascade hypothesis and that may in fact help explain that hypothesis. Alternatively, data indicate mitochondrial dysfunction exists independent of Aβ, potentially lies upstream of Aβ deposition, and suggest a primary mitochondrial cascade hypothesis that assumes mitochondrial pathology hierarchically supersedes Aβ pathology. Mitochondria, therefore, appear at least to mediate or possibly even initiate pathologic molecular cascades in AD. This review considers studies and data that inform this area of AD research.

Emerging pathways to neurodegeneration: Dissecting the critical molecular mechanisms in Alzheimer's disease, Parkinson's disease

Neurodegenerative diseases are usually sporadic in nature and commonly influenced by a wide range of genetic, life style and environmental factors. A unifying feature of Alzheimer's disease (AD) and Parkinson's disease (PD) is the abnormal accumulation and processing of mutant or damaged intra and extracellular proteins; this leads to neuronal vulnerability and dysfunction in the brain. Through a detailed review of ubiquitin proteasome, mRNA splicing, mitochondrial dysfunction, and oxidative stress pathway interrelation on neurodegeneration can improve the understanding of the disease mechanism. The identified pathways common to AD and PD nominate promising new targets for further studies, and as well as biomarkers. These insights suggested would likely provide major stimuli for developing unified treatment approaches to combat neurodegeneration. More broadly, pathways can serve as vehicles for integrating findings from diverse studies of neurodegeneration. The evidence examined in this review provides a brief overview of the current literature on significant pathways in promoting in AD, PD. Additionally, these insights suggest that biomarkers and treatment strategies may require simultaneous targeting of multiple components.

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.

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.

Mitochondria in Alzheimer's Disease and Diabetes-Associated Neurodegeneration: License to Heal!

Alzheimer's disease (AD) is a difficult puzzle to solve, in part because the etiology of this devastating neurodegenerative disorder remains murky. However, diabetes has been pinpointed as a major risk factor for the sporadic forms of AD. Several overlapping neurodegenerative mechanisms have been identified between AD and diabetes, including mitochondrial malfunction. This is not surprising taking into account that neurons are cells with a complex morphology, long lifespan, and high energetic requirements which make them particularly reliant on a properly organized and dynamic mitochondrial network to sustain neuronal function and integrity. In this sense, this chapter provides an overview on the role of mitochondrial bioenergetics and dynamics to the neurodegenerative events that occur in AD and diabetes, and how these organelles may represent a mechanistic link between these two pathologies. From a therapeutic perspective, it will be discussed how mitochondria can be targeted in order to efficaciously counteract neurodegeneration associated with AD and diabetes.

Mitochondria, Cybrids, Aging, and Alzheimer's Disease

Mitochondrial and bioenergetic function change with advancing age and may drive aging phenotypes. Mitochondrial and bioenergetic changes are also documented in various age-related neurodegenerative diseases, including Alzheimer's disease (AD). In some instances AD mitochondrial and bioenergetic changes are reminiscent of those observed with advancing age but are greater in magnitude. Mitochondrial and bioenergetic dysfunction could, therefore, link neurodegeneration to brain aging. Interestingly, mitochondrial defects in AD patients are not brain-limited, and mitochondrial function can be linked to classic AD histologic changes including amyloid precursor protein processing to beta amyloid. Also, transferring mitochondria from AD subjects to cell lines depleted of endogenous mitochondrial DNA (mtDNA) creates cytoplasmic hybrid (cybrid) cell lines that recapitulate specific biochemical, molecular, and histologic AD features. Such findings have led to the formulation of a "mitochondrial cascade hypothesis" that places mitochondrial dysfunction at the apex of the AD pathology pyramid. Data pertinent to this premise are reviewed.

Alzheimer's Disease: From Mitochondrial Perturbations to Mitochondrial Medicine

Age-related neurodegenerative diseases such as Alzheimer's disease (AD) are distressing conditions causing countless levels of suffering for which treatment is often insufficient or inexistent. Considered to be the most common cause of dementia and an incurable, progressive neurodegenerative disorder, the intricate pathogenic mechanisms of AD continue to be revealed and, consequently, an effective treatment needs to be developed. Among the diverse hypothesis that have been proposed to explain AD pathogenesis, the one concerning mitochondrial dysfunction has raised as one of the most discussed with an actual acceptance in the field. It posits that manipulating mitochondrial function and understanding the deficits that result in mitochondrial injury may help to control and/or limit the development of AD. To achieve such goal, the concept of mitochondrial medicine places itself as a promising gathering of strategies to directly manage the major insidious disturbances of mitochondrial homeostasis as well as attempts to directly or indirectly manage its consequences in the context of AD. The aim of this review is to summarize the evolution that occurred from the establishment of mitochondrial homeostasis perturbation as masterpieces in AD pathogenesis up until the development of mitochondrial medicine. Following a brief glimpse in the past and current hypothesis regarding the triad of aging, mitochondria and AD, this manuscript will address the major mechanisms currently believed to participate in above mentioned events. Both pharmacological and lifestyle interventions will also be reviewed as AD-related mitochondrial therapeutics.

Mitochondrial homeostatic disruptions are sensitive indicators of stress in neurons with defective mitochondrial DNA transactions

Neurodegeneration and mitochondrial dysfunction are closely linked across many clinical conditions. In genetic diseases that result from defects in mitochondrial DNA (mtDNA) synthesis or maintenance, neurodegeneration is a frequent and major component of the disease pathology. In sporadic neurodegenerative diseases such as Alzheimer's and Parkinson's disease, mtDNA defects have been observed clinically. Mitochondrial stress related to mtDNA dysregulation can produce neuronal dysfunction and death via impaired electron transport chain activity, which results in deficient ATP production and related increases in mitochondrial reactive oxygen species (ROS) production. However, mtDNA dysregulation in post-mitotic neurons may also produce disturbances in mitochondrial homeostasis that are known to impair neuronal function as well. In this study, we used sub-toxic doses of ethidium bromide (EtBr) to induce mtDNA-associated mitochondrial stress in primary cortical neurons and measured several aspects of mitochondrial homeostasis, mitochondrial function and cell death. We found that low-dose EtBr severely depletes mtDNA synthesis and mitochondrial mRNA levels. Furthermore, homeostatic processes are especially disrupted in toxin treated neurons while mitochondrial function is relatively preserved. Mitochondria become fragmented and motility is abolished, while respiration and mitochondrial polarization are partially maintained. Moreover at these doses, cells do not exhibit increased ROS production, clear neurite retraction or loss of viability. These results indicate that mitochondrial homeostasis is a sensitive marker of mtDNA associated stress compared to mitochondria-functional outputs or endpoints related to cellular toxicity. These homeostatic disruptions are expected to contribute to neuronal dysfunction and potentially drive neurodegenerative disease pathology.

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.

Mitochondrial traffic jams in Alzheimer's disease - pinpointing the roadblocks

The vigorous axonal transport of mitochondria, which serves to distribute these organelles in a dynamic and non-uniform fashion, is crucial to fulfill neuronal energetic requirements allowing the maintenance of neurons structure and function. Particularly, axonal transport of mitochondria and their spatial distribution among the synapses are directly correlated with synaptic activity and integrity. Despite the basis of Alzheimer's disease (AD) remains enigmatic, axonal pathology and synaptic dysfunction occur prior the occurrence of amyloid-β (Aβ) deposition and tau aggregation, the two classical hallmarks of this devastating neurodegenerative disease. Importantly, the early stages of AD are marked by defects on axonal transport of mitochondria as denoted by the abnormal accumulation of mitochondria within large swellings along dystrophic and degenerating neuritis. Within this scenario, this review is devoted to identify the molecular "roadblocks" underlying the abnormal axonal transport of mitochondria and consequent synaptic "starvation" and neuronal degeneration in AD. Understanding the molecular nature of defective mitochondrial transport may provide a new avenue to counteract AD pathology.

Mitochondria as a target for neuroprotection: implications for Alzheimer´s disease

INTRODUCTION

Alzheimer's disease (AD), the most common form of dementia, is marked by progressive loss of memory and impairment of cognitive ability. Despite decades of intensive research and scientific advances, the intricate pathogenic mechanisms of AD are still not fully understood and, consequently, an effective treatment is yet to be developed. As widely accepted, the alterations of mitochondrial function are actively engaged in a plethora of neurodegenerative diseases, including AD. With growing interest in the mitochondria as a potential target for understanding AD, it has even been hypothesized that deficits in these organelles may be at the heart of the progression of AD itself. Areas covered: The purpose of this review is to summarize relevant studies that suggest a role for mitochondrial (dys)function in AD and to provide a survey on latest developments regarding AD-related mitochondrial therapeutics. Expert commentary: As outlined in a plethora of studies, there is no doubt that mitochondria play a major role in several stages of AD progression. Even though more in-depth studies are needed before pharmaceutical industry can apply such knowledge to human medicine, the continuous advances in AD research field will certainly facilitate and accelerate the development of more effective preventive or therapeutic strategies to fight this devastating disease.

Mitochondrial Dysfunction Contributes to the Pathogenesis of Alzheimer's Disease

Alzheimer's disease (AD) is a neurodegenerative disease that affects millions of people worldwide. Currently, there is no effective treatment for AD, which indicates the necessity to understand the pathogenic mechanism of this disorder. Extracellular aggregates of amyloid precursor protein (APP), called Aβ peptide and neurofibrillary tangles (NFTs), formed by tau protein in the hyperphosphorylated form are considered the hallmarks of AD. Accumulative evidence suggests that tau pathology and Aβ affect neuronal cells compromising energy supply, antioxidant response, and synaptic activity. In this context, it has been showed that mitochondrial function could be affected by the presence of tau pathology and Aβ in AD. Mitochondria are essential for brain cells function and the improvement of mitochondrial activity contributes to preventing neurodegeneration. Several reports have suggested that mitochondria could be affected in terms of morphology, bioenergetics, and transport in AD. These defects affect mitochondrial health, which later will contribute to the pathogenesis of AD. In this review, we will discuss evidence that supports the importance of mitochondrial injury in the pathogenesis of AD and how studying these mechanisms could lead us to suggest new targets for diagnostic and therapeutic intervention against neurodegeneration.

Apolipoprotein E: structure and function in lipid metabolism, neurobiology, and Alzheimer's diseases

Apolipoprotein (apo) E is a multifunctional protein with central roles in lipid metabolism, neurobiology, and neurodegenerative diseases. It has three major isoforms (apoE2, apoE3, and apoE4) with different effects on lipid and neuronal homeostasis. A major function of apoE is to mediate the binding of lipoproteins or lipid complexes in the plasma or interstitial fluids to specific cell-surface receptors. These receptors internalize apoE-containing lipoprotein particles; thus, apoE participates in the distribution/redistribution of lipids among various tissues and cells of the body. In addition, intracellular apoE may modulate various cellular processes physiologically or pathophysiologically, including cytoskeletal assembly and stability, mitochondrial integrity and function, and dendritic morphology and function. Elucidation of the functional domains within this protein and of the three-dimensional structure of the major isoforms of apoE has contributed significantly to our understanding of its physiological and pathophysiological roles at a molecular level. It is likely that apoE, with its multiple cellular origins and multiple structural and biophysical properties, is involved widely in processes of lipid metabolism and neurobiology, possibly encompassing a variety of disorders of neuronal repair, remodeling, and degeneration by interacting with different factors through various pathways.

Cytoplasmic hybrid (cybrid) cell lines as a practical model for mitochondriopathies

Cytoplasmic hybrid (cybrid) cell lines can incorporate human subject mitochondria and perpetuate its mitochondrial DNA (mtDNA)-encoded components. Since the nuclear background of different cybrid lines can be kept constant, this technique allows investigators to study the influence of mtDNA on cell function. Prior use of cybrids has elucidated the contribution of mtDNA to a variety of biochemical parameters, including electron transport chain activities, bioenergetic fluxes, and free radical production. While the interpretation of data generated from cybrid cell lines has technical limitations, cybrids have contributed valuable insight into the relationship between mtDNA and phenotype alterations. This review discusses the creation of the cybrid technique and subsequent data obtained from cybrid applications.

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The cytoplasmic hybrid (cybrid) model can be used to determine mitochondrial DNA (mtDNA) contributions to phenotypic alterations.

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Cybrids are used to study mitochondriopathies such as Parkinson’s disease and Alzheimer’s disease.

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mtDNA heteroplasmy threshold and nuclear DNA-mtDNA compatibility can be determined using cybrid models.

In vivo axonal transport deficits in a mouse model of fronto-temporal dementia

Background

Axonal transport is vital for neurons and deficits in this process have been previously reported in a few mouse models of Alzheimer's disease prior to the appearance of plaques and tangles. However, it remains to be determined whether axonal transport is defective prior to the onset of neurodegeneration. The rTg4510 mouse, a fronto-temporal dementia and parkinsonism-17 (FTDP-17) tauopathy model, over-express tau-P301L mutation found in familial forms of FTDP-17, in the forebrain driven by the calcium–calmodulin kinase II promoter. This mouse model exhibits tau pathology, neurodegeneration in the forebrain, and associated behavioral deficits beginning at 4–5 months of age.

Animal model

rTg4510 transgenic mice were used in these studies. Mice were given 2 μL of MnCl₂ in each nostril 1 h prior to Magnetic Resonance Imaging (MRI). Following MnCl₂ nasal lavage, mice were imaged using Manganese enhanced Magnetic Resonance Imaging (MEMRI) Protocol with TE = 8.5 ms, TR = 504 ms, FOV = 3.0 cm, matrix size = 128 × 128 × 128, number of cycles = 15 with each cycle taking approximately 2 min, 9 s, and 24 ms using Paravision software (BrukerBioSpin, Billerica, MA). During imaging, body temperature was maintained at 37.0 °C using an animal heating system (SA Instruments, Stony Brook, NY).

Data analysis

Resulting images were analyzed using Paravision software. Regions of interest (ROI) within the olfactory neuronal layer (ONL) and the water phantom consisting of one pixel (ONL) and 9 pixels (water) were selected and copied across each of the 15 cycles. Signal intensities (SI) of ONL and water phantom ROIs were measured. SI values obtained for ONL were then normalized the water phantom SI values. The correlation between normalized signal intensity in the ONL and time were assessed using Prism (GraphPad Software, San Diego, CA).

Results

Using the MEMRI technique on 1.5, 3, 5, and 10-month old rTg4510 mice and littermate controls, we found significant axonal transport deficits present in the rTg4510 mice beginning at 3 months of age in an age-dependent manner. Using linear regression analysis, we measured rates of axonal transport at 1.5, 3, 5, and 10 months of age in rTg4510 and WT mice. Axonal transport rates were observed in rTg4510 mice at 48% of WT levels at 3 months, 40% of WT levels at 5 months, and 30% of WT levels at 10 months of age. In order to determine the point at which tau appears in the cortex, we probed for phosphorylated tau levels, and found that pSer262 is present at 3 months of age, not earlier at 1.5 months of age, but observed no pathological tau species until 6 months of age, months after the onset of the transport deficits. In addition, we saw localization of tau in the ONL at 6 months of age.

Discussion

In our study, we identified the presence of age-dependent axonal transport deficits beginning at 3 months of age in rTg4510 mice. We correlated these deficits at 3 months to the presence of hyperphosphorylated tau in the brain and the presence within the olfactory epithelium. We observed tau pathology not only in the soma of these neurons but also within the axons and processes of these neurons. Our characterization of axonal transport in this tauopathy model provides a functional time point that can be used for future therapeutic interventions.

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We used MEMRI to define axonal transport rate changes in the rTg4510 mouse.

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We observed significant hyperphosphorylated tau starting at 3 months of age.

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We found an age-dependent decline in axonal transport rates.

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Declines in axonal transport correlated with increases in hyperphosphorylated tau.

Mitochondrial diseases of the brain

Neurodegenerative disorders are debilitating diseases of the brain, characterized by behavioral, motor and cognitive impairments. Ample evidence underpins mitochondrial dysfunction as a central causal factor in the pathogenesis of neurodegenerative disorders including Parkinson's disease, Huntington's disease, Alzheimer's disease, Amyotrophic lateral sclerosis, Friedreich's ataxia and Charcot-Marie-Tooth disease. In this review, we discuss the role of mitochondrial dysfunction such as bioenergetics defects, mitochondrial DNA mutations, gene mutations, altered mitochondrial dynamics (mitochondrial fusion/fission, morphology, size, transport/trafficking, and movement), impaired transcription and the association of mutated proteins with mitochondria in these diseases. We highlight the therapeutic role of mitochondrial bioenergetic agents in toxin and in cellular and genetic animal models of neurodegenerative disorders. We also discuss clinical trials of bioenergetics agents in neurodegenerative disorders. Lastly, we shed light on PGC-1α, TORC-1, AMP kinase, Nrf2-ARE, and Sirtuins as novel therapeutic targets for neurodegenerative disorders.

Tissue-specific implications of mitochondrial alterations in aging

Aging is a multifactorial process during which physiological alterations occur in all tissues. A decline in mitochondrial function plays an important role in the process of aging and in aging-associated diseases. The mitochondrial genome encodes 13 essential subunits of protein complexes belonging to the oxidative phosphorylation system, while most of the mitochondria-related genes are encoded by the nuclear genome. Coordination between the nucleus and mitochondria is crucial for the regulation of mitochondrial biogenesis and function. In this review, we will discuss aging-related mitochondrial dysfunction in various tissues and its implication in aging-related diseases and the aging process.

Mitochondria and cell bioenergetics: increasingly recognized components and a possible etiologic cause of Alzheimer's disease

SIGNIFICANCE

Mitochondria and brain bioenergetics are increasingly thought to play an important role in Alzheimer's disease (AD).

RECENT ADVANCES

Data that support this view are discussed from the perspective of the amyloid cascade hypothesis, which assumes beta-amyloid perturbs mitochondrial function, and from an opposite perspective that assumes mitochondrial dysfunction promotes brain amyloidosis. A detailed review of cytoplasmic hybrid (cybrid) studies, which argue mitochondrial DNA (mtDNA) contributes to sporadic AD, is provided. Recent AD endophenotype data that further suggest an mtDNA contribution are also summarized.

CRITICAL ISSUES AND FUTURE DIRECTIONS

Biochemical, molecular, cybrid, biomarker, and clinical data pertinent to the mitochondria-bioenergetics-AD nexus are synthesized and the mitochondrial cascade hypothesis, which represents a mitochondria-centric attempt to conceptualize sporadic AD, is discussed.

A mitochondrial etiology of Alzheimer and Parkinson disease

BACKGROUND

The genetics and pathophysiology of Alzheimer Disease (AD) and Parkinson Disease (PD) appears complex. However, mitochondrial dysfunction is a common observation in these and other neurodegenerative diseases.

SCOPE OF REVIEW

We argue that the available data on AD and PD can be incorporated into a single integrated paradigm based on mitochondrial genetics and pathophysiology.

MAJOR CONCLUSIONS

Rare chromosomal cases of AD and PD can be interpreted as affecting mitochondrial function, quality control, and mitochondrial DNA (mtDNA) integrity. mtDNA lineages, haplogroups, such haplogroup H5a which harbors the mtDNA tRNA(Gln) A8336G variant, are important risk factors for AD and PD. Somatic mtDNA mutations are elevated in AD, PD, and Down Syndrome and Dementia (DSAD) both in brains and also systemically. AD, DS, and DSAD brains also have reduced mtDNA ND6 mRNA levels, altered mtDNA copy number, and perturbed Aβ metabolism. Classical AD genetic changes incorporated into the 3XTg-AD (APP, Tau, PS1) mouse result in reduced forebrain size, life-long reduced mitochondrial respiration in 3XTg-AD males, and initially elevated respiration and complex I and IV activities in 3XTg-AD females which markedly declines with age.

GENERAL SIGNIFICANCE

Therefore, mitochondrial dysfunction provides a unifying genetic and pathophysiology explanation for AD, PD, and other neurodegenerative diseases. This article is part of a Special Issue entitled Biochemistry of Mitochondria.

KLC3 is involved in sperm tail midpiece formation and sperm function

Kinesin light chain 3 (KLC3) is the only known kinesin light chain expressed in post-meiotic male germ cells. We have reported that in rat spermatids KLC3 associates with outer dense fibers and mitochondrial sheath. KLC3 is able to bind to mitochondria in vitro and in vivo employing the conserved tetratrico-peptide repeat kinesin light chain motif. The temporal expression and association of KLC3 with mitochondria coincides with the stage in spermatogenesis when mitochondria move from the spermatid cell periphery to the developing midpiece suggesting a role in midpiece formation. In fibroblasts, expression of KLC3 results in formation of large KLC3 aggregates close to the nucleus that contain mitochondria. However, the molecular basis of the aggregation of mitochondria by KLC3 and its role in sperm tail midpiece formation are not clear. Here we show that KLC3 expression from an inducible system causes mitochondrial aggregation within 6h in a microtubule dependent manner. We identified the mitochondrial outer membrane porin protein VDAC2 as a KLC3 binding partner. To analyze a role for KLC3 in spermatids we developed a transgenic mouse model in which a KLC3ΔHR mutant protein is specifically expressed in spermatids: this KLC3 mutant protein binds mitochondria and causes aggregate formation, but cannot bind outer dense fibers. Male transgenic mice display significantly reduced reproductive efficiency siring small sized litters. We observed defects in the mitochondrial sheath structure in a number of transgenic spermatids. Transgenic males have a significantly reduced sperm count and produce spermatozoa that exhibit abnormal motility parameters. Our results indicate that KLC3 plays a role during spermiogenesis in the development of the midpiece and in the normal function of spermatozoa.

Proadrenomedullin N-terminal 20 peptide increases kinesin's velocity both in vitro and in vivo

Intracellular cargo transport relies on microtubules and motor proteins such as kinesins and dyneins. Currently we have ample knowledge of the mechanisms by which motor proteins propel themselves along the microtubules, but little is known about intracellular factors that regulate motor speed. Here we show that proadrenomedullin N-terminal 20 peptide (PAMP) increases kinesin velocity and ATP consumption in a dose-dependent manner, using a variety of human kinesins. Structure-activity studies found that the terminal amide of PAMP is required for modulating kinesin activity and that the smallest peptide fragment retaining this role is PAMP₁₂₋₂₀. On the other hand, peptide fragments as small as PAMP₁₈₋₂₀ maintained the ability of delaying tubulin polymerization, another function previously described for PAMP, indicating that these two activities depend on different regions of the molecule. To demonstrate that these observations are also relevant in vivo, hippocampal neurons were isolated from mice lacking the gene coding for PAMP and from wild type littermates. Intravital stains followed by time-lapse microscopy analysis revealed that mitochondrial speed inside neurons lacking PAMP was significantly slower than in cells expressing the peptide. External addition of synthetic PAMP reversed this phenotype in PAMP-null neurons. Besides the obvious implications for better understanding cell biology, these results may be also relevant for the rapidly evolving discipline of nanotechnology because PAMP may be used as an accelerator of nanodevices based on microtubules and motor proteins.

Role of mitochondrial homeostasis and dynamics in Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disease that affects a staggering percentage of the aging population and causes memory loss and cognitive decline. Mitochondrial abnormalities can be observed systemically and in brains of patients suffering from AD, and may account for part of the disease phenotype. In this review, we summarize some of the key findings that indicate mitochondrial dysfunction is present in AD-affected subjects, including cytochrome oxidase deficiency, endophenotype data, and altered mitochondrial morphology. Special attention is given to recently described perturbations in mitochondrial autophagy, fission-fusion dynamics, and biogenesis. We also briefly discuss how mitochondrial dysfunction may influence amyloidosis in Alzheimer's disease, why mitochondria are a valid therapeutic target, and strategies for addressing AD-specific mitochondrial dysfunction.

Mitochondrial abnormalities in Alzheimer's disease: possible targets for therapeutic intervention

Mitochondria from persons with Alzheimer's disease (AD) differ from those of age-matched control subjects. Differences in mitochondrial morphology and function are well documented, and are not brain-limited. Some of these differences are present during all stages of AD, and are even seen in individuals who are without AD symptoms and signs but who have an increased risk of developing AD. This chapter considers the status of mitochondria in AD subjects, the potential basis for AD subject mitochondrial perturbations, and the implications of these perturbations. Data from multiple lines of investigation, including epidemiologic, biochemical, molecular, and cytoplasmic hybrid studies, are reviewed. The possibility that mitochondria could potentially constitute a reasonable AD therapeutic target is discussed, as are several potential mitochondrial medicine treatment strategies.

Roles of apolipoprotein E4 (ApoE4) in the pathogenesis of Alzheimer's disease: lessons from ApoE mouse models

ApoE4 (apolipoprotein E4) is the major known genetic risk factor for AD (Alzheimer's disease). In most clinical studies, apoE4 carriers account for 65–80% of all AD cases, highlighting the importance of apoE4 in AD pathogenesis. Emerging data suggest that apoE4, with its multiple cellular origins and multiple structural and biophysical properties, contributes to AD in multiple ways either independently or in combination with other factors, such as Aβ (amyloid β-peptide) and tau. Many apoE mouse models have been established to study the mechanisms underlying the pathogenic actions of apoE4. These include transgenic mice expressing different apoE isoforms in neurons or astrocytes, those expressing neurotoxic apoE4 fragments in neurons and human apoE isoform knock-in mice. Since apoE is expressed in different types of cells, including astrocytes and neurons, and in brains under diverse physiological and/or pathophysiological conditions, these apoE mouse models provide unique tools to study the cellular source-dependent roles of apoE isoforms in neurobiology and in the pathogenesis of AD. They also provide useful tools for discovery and development of drugs targeting apoE4's detrimental effects.

Microtubule and kinesin/dynein-dependent, bi-directional transport of autolysosomes in neurites of PC12 cells

Autophagy, a major degradative pathway of the lysosomal system, has been implicated in various neurodegenerative diseases. During autophagic process, organelles and proteins are encapsulated in double-membrane vacuoles called autophagosomes, which finally fuse with lysosomes to form autolysosomes where incorporated materials are degraded. Despite extensive investigations in identifying the molecular components that participate in autophagy, little is known about routes and dynamics of autophagosomes/autolysosomes in the neurites of live cells. Hence, in the present study, we aim to investigate the biophysical characteristics of neuritic transport of autolysosomes in PC12 cells. Our study demonstrated that monomeric red fluorescence protein-light chain 3 (mRFP-LC3)-labeled autolysosomes were motile and moved along PC12 neurites in both anterograde and retrograde directions with a bias towards the nucleus during starvation. By using image processing, quantitative analysis was made to show the dynamic biophysical characteristics of these vesicles. The average velocity of anterograde and retrograde transport was 0.33±0.04μm/s and 0.39±0.05μm/s, respectively. Disruption of microtubules by nocodazole completely abolished their movements, suggesting the neuritic transport of autolysosomes depends on microtubules. The directional transport of autolysosomes was also affected by blockage of motor protein activity. Altogether, our study documents many aspects of the highly dynamic movement of autolysosome in PC12 neurites. Autolysosomes transported in a bi-directional manner along microtubules by dynein and kinesin motor proteins. These findings provide valuable insight into understanding the mechanism and control of autophagy in neurites under physiological and pathological conditions.

Systemic mitochondrial dysfunction and the etiology of Alzheimer's disease and down syndrome dementia

Increasing evidence is implicating mitochondrial dysfunction as a central factor in the etiology of Alzheimer's disease (AD). The most significant risk factor in AD is advanced age and an important neuropathological correlate of AD is the deposition of amyloid-beta peptide (Abeta40 and Abeta42) in the brain. An AD-like dementia is also common in older individuals with Down syndrome (DS), though with a much earlier onset. We have shown that somatic mitochondrial DNA (mtDNA) control region (CR) mutations accumulate with age in post-mitotic tissues including the brain and that the level of mtDNA mutations is markedly elevated in the brains of AD patients. The elevated mtDNA CR mutations in AD brains are associated with a reduction in the mtDNA copy number and in the mtDNA L-strand transcript levels. We now show that mtDNA CR mutations increase with age in control brains; that they are markedly elevated in the brains of AD and DS and dementia (DSAD) patients; and that the increased mtDNA CR mutation rate in DSAD brains is associated with reduced mtDNA copy number and L-strand transcripts. The increased mtDNA CR mutation rate is also seen in peripheral blood DNA and in lymphoblastoid cell DNAs of AD and DSAD patients, and distinctive somatic mtDNA mutations, often at high heteroplasmy levels, are seen in AD and DSAD brain and blood cells DNA. In aging, DS, and DSAD, the mtDNA mutation level is positively correlated with beta-secretase activity and mtDNA copy number is inversely correlated with insoluble Abeta40 and Abeta42 levels. Therefore, mtDNA alterations may be responsible for both age-related dementia and the associated neuropathological changes observed in AD and DSAD.

Mechanisms linking apolipoprotein E isoforms with cardiovascular and neurological diseases

PURPOSE OF REVIEW

The purpose of this review is to provide insights into recent advances in mechanisms linking apolipoprotein (apo) E isoforms to cardiovascular and neurological diseases.

RECENT FINDINGS

Human apoE has three common isoforms (apoE2, apoE3, and apoE4) with different structural and biophysical properties and different effects on lipid and neuronal homeostasis. ApoE is a protein constituent of different plasma lipoproteins and serves as a high-affinity ligand for several receptors. By interacting with its receptors, apoE mediates the clearance of different lipoproteins from the circulation. Absence or structural mutations of apoE cause significant disorders in lipid metabolism and cardiovascular disease. ApoE also has significant roles in neurobiology. ApoE4 is the major known genetic risk factor for Alzheimer's disease. It increases the occurrence and lowers the age of onset of Alzheimer's disease. ApoE4 carriers account for 65-80% of all Alzheimer's disease cases, highlighting the importance of apoE4 in Alzheimer's disease pathogenesis. ApoE4 has both amyloid beta-dependent and amyloid beta-independent roles in Alzheimer's disease pathogenesis.

SUMMARY

Emerging data suggest that apoE isoforms, with their multiple cellular origins and multiple structural and biophysical properties, contribute to cardiovascular and neurological diseases by interacting with different factors through various pathways.

HDAC6 regulates mitochondrial transport in hippocampal neurons

Background

Tubulin is a major substrate of the cytoplasmic class II histone deacetylase HDAC6. Inhibition of HDAC6 results in higher levels of acetylated tubulin and enhanced binding of the motor protein kinesin-1 to tubulin, which promotes transport of cargoes along microtubules. Microtubule-dependent intracellular trafficking may therefore be regulated by modulating the activity of HDAC6. We have shown previously that the neuromodulator serotonin increases mitochondrial movement in hippocampal neurons via the Akt-GSK3β signaling pathway. Here, we demonstrate a role for HDAC6 in this signaling pathway.

Methodology/Principal Findings

We found that the presence of tubacin, a specific HDAC6 inhibitor, dramatically enhanced mitochondrial movement in hippocampal neurons, whereas niltubacin, an inactive tubacin analog, had no effect. Compared to control cultures, higher levels of acetylated tubulin were found in neurons treated with tubacin, and more kinesin-1 was associated with mitochondria isolated from these neurons. Inhibition of GSK3β decreased cytoplasmic deacetylase activity and increased tubulin acetylation, whereas blockade of Akt, which phosphorylates and down-regulates GSK3β, increased cytoplasmic deacetylase activity and decreased tubulin acetylation. Concordantly, the administration of 5-HT, 8-OH-DPAT (a specific 5-HT1A receptor agonist), or fluoxetine (a 5-HT reuptake inhibitor) increased tubulin acetylation. GSK3β was found to co-localize with HDAC6 in hippocampal neurons, and inhibition of GSK3β resulted in decreased binding of antibody to phosphoserine-22, a potential GSK3β phosphorylation site in HDAC6. GSK3β may therefore regulate HDAC6 activity by phosphorylation.

Conclusions/Significance

This study demonstrates that HDAC6 plays an important role in the modulation of mitochondrial transport. The link between HDAC6 and GSK3β, established here, has important implications for our understanding of neurodegenerative disorders. In particular, abnormal mitochondrial transport, which has been observed in such disorders as Alzheimer's disease and Parkinson's disease, could result from the misregulation of HDAC6 by GSK3β. HDAC6 may therefore constitute an attractive target in the treatment of these disorders.