Deficits in cerebral glucose metabolism demonstrated by positron emission tomography in individuals at risk of familial Alzheimer's disease

Imbalance in Glucose Metabolism Regulates the Transition of Microglia from Homeostasis to Disease-Associated Microglia Stage 1

Microglia undergo two-stage activation in neurodegenerative diseases, known as disease-associated microglia (DAM). TREM2 mediates the DAM2 stage transition, but what regulates the first DAM1 stage transition is unknown. We report that glucose dyshomeostasis inhibits DAM1 activation and PKM2 plays a role. As in tumors, PKM2 was aberrantly elevated in both male and female human AD brains, but unlike in tumors, it is expressed as active tetramers, as well as among TREM2+ microglia surrounding plaques in 5XFAD male and female mice. snRNAseq analyses of microglia without Pkm2 in 5XFAD mice revealed significant increases in DAM1 markers in a distinct metabolic cluster, which is enriched in genes for glucose metabolism, DAM1, and AD risk. 5XFAD mice incidentally exhibited a significant reduction in amyloid pathology without microglial Pkm2 Surprisingly, microglia in 5XFAD without Pkm2 exhibited increases in glycolysis and spare respiratory capacity, which correlated with restoration of mitochondrial cristae alterations. In addition, in situ spatial metabolomics of plaque-bearing microglia revealed an increase in respiratory activity. These results together suggest that it is not only glycolytic but also respiratory inputs that are critical to the development of DAM signatures in 5XFAD mice.

A strategic tool to improve the study of molecular determinants of Alzheimer's disease: The role of glyceraldehyde

Alzheimer's disease (AD) is the most prevalent form of dementia and is characterized by progressive neurodegeneration leading to severe cognitive, memory, and behavioral impairments. The onset of AD involves a complex interplay among various factors, including age, genetics, chronic inflammation, and impaired energy metabolism. Despite significant efforts, there are currently no effective therapies capable of modifying the course of AD, likely owing to an excessive focus on the amyloid hypothesis and a limited consideration of other intracellular pathways. In the present review, we emphasize the emerging concept of AD as a metabolic disease, where alterations in energy metabolism play a critical role in its development and progression. Notably, glucose metabolism impairment is associated with mitochondrial dysfunction, oxidative stress, Ca2+ dyshomeostasis, and protein misfolding, forming interconnected processes that perpetuate a detrimental self-feeding loop sustaining AD progression. Advanced glycation end products (AGEs), neurotoxic compounds that accumulate in AD, are considered an important consequence of glucose metabolism disruption, and glyceraldehyde (GA), a glycolytic intermediate, is a key contributor to AGEs formation in both neurons and astrocytes. Exploring the impact of GA-induced glucose metabolism impairment opens up exciting possibilities for creating an easy-to-handle in vitro model that recapitulates the early stage of the disease. This model holds great potential for advancing the development of novel therapeutics targeting various intracellular pathways implicated in AD pathogenesis. In conclusion, looking beyond the conventional amyloid hypothesis could lead researchers to discover promising targets for intervention, offering the possibility of addressing the existing medical gaps in AD treatment.

Hypometabolism, Alzheimer's Disease, and Possible Therapeutic Targets: An Overview

The brain is a highly dynamic organ that requires a constant energy source to function normally. This energy is mostly supplied by glucose, a simple sugar that serves as the brain's principal fuel source. Glucose transport across the blood-brain barrier (BBB) is primarily controlled via sodium-independent facilitated glucose transport, such as by glucose transporter 1 (GLUT1) and 3 (GLUT3). However, other glucose transporters, including GLUT4 and the sodium-dependent transporters SGLT1 and SGLT6, have been reported in vitro and in vivo. When the BBB endothelial layer is crossed, neurons and astrocytes can absorb the glucose using their GLUT1 and GLUT3 transporters. Glucose then enters the glycolytic pathway and is metabolized into adenosine triphosphate (ATP), which supplies the energy to support cellular functions. The transport and metabolism of glucose in the brain are impacted by several medical conditions, which can cause neurological and neuropsychiatric symptoms. Alzheimer's disease (AD), Parkinson's disease (PD), epilepsy, traumatic brain injury (TBI), schizophrenia, etc., are a few of the most prevalent disorders, characterized by a decline in brain metabolism or hypometabolism early in the course of the disease. Indeed, AD is considered a metabolic disorder related to decreased brain glucose metabolism, involving brain insulin resistance and age-dependent mitochondrial dysfunction. Although the conventional view is that reduced cerebral metabolism is an effect of neuronal loss and consequent brain atrophy, a growing body of evidence points to the opposite, where hypometabolism is prodromal or at least precedes the onset of brain atrophy and the manifestation of clinical symptoms. The underlying processes responsible for these glucose transport and metabolic abnormalities are complicated and remain poorly understood. This review article provides a comprehensive overview of the current understanding of hypometabolism in AD and potential therapeutic targets.

Identifying healthy individuals with Alzheimer's disease neuroimaging phenotypes in the UK Biobank

BACKGROUND

Identifying prediagnostic neurodegenerative disease is a critical issue in neurodegenerative disease research, and Alzheimer's disease (AD) in particular, to identify populations suitable for preventive and early disease-modifying trials. Evidence from genetic and other studies suggests the neurodegeneration of Alzheimer's disease measured by brain atrophy starts many years before diagnosis, but it is unclear whether these changes can be used to reliably detect prediagnostic sporadic disease.

METHODS

We trained a Bayesian machine learning neural network model to generate a neuroimaging phenotype and AD score representing the probability of AD using structural MRI data in the Alzheimer's Disease Neuroimaging Initiative (ADNI) Cohort (cut-off 0.5, AUC 0.92, PPV 0.90, NPV 0.93). We go on to validate the model in an independent real-world dataset of the National Alzheimer's Coordinating Centre (AUC 0.74, PPV 0.65, NPV 0.80) and demonstrate the correlation of the AD-score with cognitive scores in those with an AD-score above 0.5. We then apply the model to a healthy population in the UK Biobank study to identify a cohort at risk for Alzheimer's disease.

RESULTS

We show that the cohort with a neuroimaging Alzheimer's phenotype has a cognitive profile in keeping with Alzheimer's disease, with strong evidence for poorer fluid intelligence, and some evidence of poorer numeric memory, reaction time, working memory, and prospective memory. We found some evidence in the AD-score positive cohort for modifiable risk factors of hypertension and smoking.

CONCLUSIONS

This approach demonstrates the feasibility of using AI methods to identify a potentially prediagnostic population at high risk for developing sporadic Alzheimer's disease.

Detection and treatment of Alzheimer's disease in its preclinical stage

Longitudinal multimodal biomarker studies reveal that the continuum of Alzheimer's disease (AD) includes a long latent phase, referred to as preclinical AD, which precedes the onset of symptoms by decades. Treatment during the preclinical AD phase offers an optimal opportunity for slowing the progression of disease. However, trial design in this population is complex. In this Review, we discuss the recent advances in accurate plasma measurements, new recruitment approaches, sensitive cognitive instruments and self-reported outcomes that have facilitated the successful launch of multiple phase 3 trials for preclinical AD. The recent success of anti-amyloid immunotherapy trials in symptomatic AD has increased the enthusiasm for testing this strategy at the earliest feasible stage. We provide an outlook for standard screening of amyloid accumulation at the preclinical stage in clinically normal individuals, during which effective therapy to delay or prevent cognitive decline can be initiated.

The Novel Role of Mitochondrial Citrate Synthase and Citrate in the Pathophysiology of Alzheimer's Disease

Citrate synthase is a key mitochondrial enzyme that utilizes acetyl-CoA and oxaloacetate to form citrate in the mitochondrial membrane, which participates in energy production in the TCA cycle and linked to the electron transport chain. Citrate transports through a citrate malate pump and synthesizes acetyl-CoA and acetylcholine (ACh) in neuronal cytoplasm. In a mature brain, acetyl-CoA is mainly utilized for ACh synthesis and is responsible for memory and cognition. Studies have shown low citrate synthase in different regions of brain in Alzheimer's disease (AD) patients, which reduces mitochondrial citrate, cellular bioenergetics, neurocytoplasmic citrate, acetyl-CoA, and ACh synthesis. Reduced citrate mediated low energy favors amyloid-β (Aβ) aggregation. Citrate inhibits Aβ25-35 and Aβ1-40 aggregation in vitro. Hence, citrate can be a better therapeutic option for AD by improving cellular energy and ACh synthesis, and inhibiting Aβ aggregation, which prevents tau hyperphosphorylation and glycogen synthase kinase-3 beta. Therefore, we need clinical studies if citrate reverses Aβ deposition by balancing mitochondrial energy pathway and neurocytoplasmic ACh production. Furthermore, in AD's silent phase pathophysiology, when neuronal cells are highly active, they shift ATP utilization from oxidative phosphorylation to glycolysis and prevent excessive generation of hydrogen peroxide and reactive oxygen species (oxidative stress) as neuroprotective action, which upregulates glucose transporter-3 (GLUT3) and pyruvate dehydrogenase kinase-3 (PDK3). PDK3 inhibits pyruvate dehydrogenase, which decreases mitochondrial-acetyl-CoA, citrate, and cellular bioenergetics, and decreases neurocytoplasmic citrate, acetyl-CoA, and ACh formation, thus initiating AD pathophysiology. Therefore, GLUT3 and PDK3 can be biomarkers for silent phase of AD.

Mitochondria - Nucleus communication in neurodegenerative disease. Who talks first, who talks louder?

Mitochondria - nuclear coadaptation has been central to eukaryotic evolution. The dynamic dialogue between the two compartments within the context of multiorganellar interactions is critical for maintaining cellular homeostasis and directing the balance survival-death in case of cellular stress. The conceptualisation of mitochondria - nucleus communication has so far been focused on the communication from the mitochondria under stress to the nucleus and the consequent signalling responses, as well as from the nucleus to mitochondria in the context of DNA damage and repair. During ageing processes this dialogue may be better viewed as an integrated bidirectional 'talk' with feedback loops that expand beyond these two organelles depending on physiological cues. Here we explore the current views on mitochondria - nucleus dialogue and its role in maintaining cellular health with a focus on brain cells and neurodegenerative disease. Thus, we detail the transcriptional responses initiated by mitochondrial dysfunction in order to protect itself and the general cellular homeostasis. Additionally, we are reviewing the knowledge of the stress pathways initiated by DNA damage which affect mitochondria homeostasis and we add the information provided by the study of combined mitochondrial and genotoxic damage. Finally, we reflect on how each organelle may take the lead in this dialogue in an ageing context where both compartments undergo accumulation of stress and damage and where, perhaps, even the communications' mechanisms may suffer interruptions.

Primitive detection of Alzheimer’s disease using neuroimaging: A progression model for Alzheimer’s disease: Their applications, benefits, and drawbacks

Alzheimer’s disease (A.D.) is the most widespread type of Dementia, and it is not a curable neurodegenerative disease that affects millions of older people. Researchers were able to use their understanding of Alzheimer’s disease risk variables to develop enrichment processes for longitudinal imaging studies. Using this method, they reduced their sample size and study time. This paper describes the primitive detective of Alzheimer’s diseases using Neuroimaging techniques. Several preprocessing methods were used to ensure that the dataset was ready for subsequent feature extraction and categorization. The noise was reduced by converting and averaging many scan frames from real to DCT space. Both sides of the averaged image were filtered and combined into a single shot after being converted to real space. InceptionV3 and DenseNet201 are two pre-trained models used in the suggested model. The PCA approach was used to select the traits, and the resulting explained variance ratio was 0.99The Simons Foundation Autism Research Initiative (SFARI)—Simon’s Simplex Collection (SSC)—and UCI machine learning datasets showed that our method is faster and more successful at identifying complete long-risk patterns when compared to existing methods.

Cerebrovascular alterations in NAFLD: Is it increasing our risk of Alzheimer's disease?

Non-alcoholic fatty liver disease (NAFLD) is a multisystem disease, which has been classified as an emerging epidemic not only confined to liver-related morbidity and mortality. It is also becoming apparent that NAFLD is associated with moderate cerebral dysfunction and cognitive decline. A possible link between NAFLD and Alzheimer's disease (AD) has only recently been proposed due to the multiple shared genes and pathological mechanisms contributing to the development of these conditions. Although AD is a progressive neurodegenerative disease, the exact pathophysiological mechanism remains ambiguous and similarly to NAFLD, currently available pharmacological therapies have mostly failed in clinical trials. In addition to the usual suspects (inflammation, oxidative stress, blood-brain barrier alterations and ageing) that could contribute to the NAFLD-induced development and progression of AD, changes in the vasculature, cerebral perfusion and waste clearance could be the missing link between these two diseases. Here, we review the most recent literature linking NAFLD and AD, focusing on cerebrovascular alterations and the brain's clearance system as risk factors involved in the development and progression of AD, with the aim of promoting further research using neuroimaging techniques and new mechanism-based therapeutic interventions.

Defective mitophagy and synaptic degeneration in Alzheimer's disease: Focus on aging, mitochondria and synapse

Alzheimer's disease (AD) is a progressive neurodegenerative disease characterized by memory loss and multiple cognitive impairments. AD is marked by multiple cellular changes, including deregulation of microRNAs, activation of glia and astrocytes, hormonal imbalance, defective mitophagy, synaptic degeneration, in addition to extracellular neuritic amyloid-beta (Aβ) plaques, phosphorylated tau (P-tau), and intracellular neurofibrillary tangles (NFTs). Recent research in AD revealed that defective synaptic mitophagy leads to synaptic degeneration and cognitive dysfunction in AD neurons. Our critical analyses of mitochondria and Aβ and P-tau revealed that increased levels of Aβ and P-Tau, and abnormal interactions between Aβ and Drp1, P-Tau and Drp1 induced increased mitochondrial fragmentation and proliferation of dysfunctional mitochondria in AD neurons and depleted Parkin and PINK1 levels. These events ultimately lead to impaired clearance of dead and/or dying mitochondria in AD neurons. The purpose of our article is to highlight the recent research on mitochondria and synapses in relation to Aβ and P-tau, focusing on recent developments.

Supplemental thiamine as a practical, potential way to prevent Alzheimer's disease from commencing

It is better to attempt stopping Alzheimer's disease (AD) before it starts than trying to cure it after it has developed. A cerebral scan showing deposition of either amyloid or tau identifies those elderly persons whose cognition is currently normal but who are at risk of subsequent cognitive loss that may develop into AD. Synaptic hypometabolism is usually present in such at-risk persons. Although inadequate adenosine triphosphate (ATP) may cause synaptic hypometabolism, that may not be the entire cause because, in fact, measurements in some of the at-risk persons have shown normal ATP levels. Thiamine deficiency is often seen in elderly, ambulatory persons in whom thiamine levels correlate with Mini-Mental State Examination scores. Thiamine deficiency has many consequences including hypometabolism, mitochondrial depression, oxidative stress, lactic acidosis and cerebral acidosis, amyloid deposition, tau deposition, synaptic dysfunction and abnormal neuro-transmission, astrocyte function, and blood brain barrier integrity, all of which are features of AD. Although the clinical benefits of administering supplementary thiamine to patients with AD or mild cognitive impairment have been mixed, it is more likely to succeed at preventing the onset of cognitive loss if administered at an earlier time, when the number of aberrant biochemical pathways is far fewer. Providing a thiamine supplement to elderly persons who still have normal cognition but who have deposition of either amyloid or tau, may prevent subsequent cognitive loss and eventual dementia. A clinical trial is needed to validate that possibility.

Reassessment of Pioglitazone for Alzheimer's Disease

Alzheimer's disease is a quintessential 'unmet medical need', accounting for ∼65% of progressive cognitive impairment among the elderly, and 700,000 deaths in the United States in 2020. In 2019, the cost of caring for Alzheimer's sufferers was $244B, not including the emotional and physical toll on caregivers. In spite of this dismal reality, no treatments are available that reduce the risk of developing AD or that offer prolonged mitiagation of its most devestating symptoms. This review summarizes key aspects of the biology and genetics of Alzheimer's disease, and we describe how pioglitazone improves many of the patholophysiological determinants of AD. We also summarize the results of pre-clinical experiments, longitudinal observational studies, and clinical trials. The results of animal testing suggest that pioglitazone can be corrective as well as protective, and that its efficacy is enhanced in a time- and dose-dependent manner, but the dose-effect relations are not monotonic or sigmoid. Longitudinal cohort studies suggests that it delays the onset of dementia in individuals with pre-existing type 2 diabetes mellitus, which small scale, unblinded pilot studies seem to confirm. However, the results of placebo-controlled, blinded clinical trials have not borne this out, and we discuss possible explanations for these discrepancies.

Does synaptic hypometabolism or synaptic dysfunction, originate cognitive loss? Analysis of the evidence

Elderly persons with currently normal cognition who have cerebral hypometabolism as shown by low uptake of 18fluorine-fluorodeoxyglucose (18F-FDG), are at risk of future loss of cognition and, thus, of future Alzheimer's dementia (AD). Reduction of either 18F-FDG or cognition is assumed to reflect synaptic dysfunction, since synapses account for the majority of glucose use by the brain and cognition depends upon accurate synaptic function. The chronology of the connection between reduced cerebral synaptic function and hypometabolism is, therefore, a critical question, because if synaptic dysfunction came first, then correcting the hypometabolism would likely not benefit synaptic function; but if hypometabolism came first, then correcting the hypometabolism probably would benefit synaptic function. That correction might prevent initiation of the cognitive loss that eventuates in AD and, thereby, would benefit the vast numbers of persons in their eighth to tenth decades of life who are at risk for AD. Among the many citations reviewed in this presentation, seven show hypometabolism that precedes synaptic dysfunction, and two show the reverse. Thus the preponderance of evidence, 78%, suggests that the initiating event is synaptic hypometabolism and that it is 3.5-fold less likely that synaptic dysfunction is the initiator. In addition, it is inherently unlikely that synaptic dysfunction causes hypometabolism. This conclusion could be tested by a clinical trial whose primary objective would be to assess the benefit to cognition of improving synaptic metabolism in patients who are at risk for cognitive loss.

Cerebral blood flow decrease as an early pathological mechanism in Alzheimer's disease

Therapies targeting late events in Alzheimer's disease (AD), including aggregation of amyloid beta (Aβ) and hyperphosphorylated tau, have largely failed, probably because they are given after significant neuronal damage has occurred. Biomarkers suggest that the earliest event in AD is a decrease of cerebral blood flow (CBF). This is caused by constriction of capillaries by contractile pericytes, probably evoked by oligomeric Aβ. CBF is also reduced by neutrophil trapping in capillaries and clot formation, perhaps secondary to the capillary constriction. The fall in CBF potentiates neurodegeneration by upregulating the BACE1 enzyme that makes Aβ and by promoting tau hyperphosphorylation. Surprisingly, therefore, CBF reduction may play a crucial role in driving cognitive decline by initiating the amyloid cascade itself, or being caused by and amplifying Aβ production. Here, we review developments in this area that are neglected in current approaches to AD, with the aim of promoting novel mechanism-based therapeutic approaches.

Interleukin-6 Treatment Results in GLUT4 Translocation and AMPK Phosphorylation in Neuronal SH-SY5Y Cells

Interleukin-6 (IL-6) is a pleiotropic cytokine that can be released from the brain during prolonged exercise. In peripheral tissues, exercise induced IL-6 can result in GLUT4 translocation and increased glucose uptake through AMPK activation. GLUT4 is expressed in the brain and can be recruited to axonal plasma membranes with neuronal activity through AMPK activation. The aim of this study is to examine if IL-6 treatment: (1) results in AMPK activation in neuronal cells, (2) increases the activation of proteins involved in GLUT4 translocation, and (3) increases neuronal glucose uptake. Retinoic acid was used to differentiate SH-SY5Y neuronal cells. Treatment with 100 nM of insulin increased the phosphorylation of Akt and AS160 (p < 0.05). Treatment with 20 ng/mL of IL-6 resulted in the phosphorylation of STAT3 at Tyr705 (p ≤ 0.05) as well as AS160 (p < 0.05). Fluorescent Glut4GFP imaging revealed treatment with 20ng/mL of IL-6 resulted in a significant mobilization towards the plasma membrane after 5 min until 30 min. There was no difference in GLUT4 mobilization between the insulin and IL-6 treated groups. Importantly, IL-6 treatment increased glucose uptake. Our findings demonstrate that IL-6 and insulin can phosphorylate AS160 via different signaling pathways (AMPK and PI3K/Akt, respectively) and promote GLUT4 translocation towards the neuronal plasma membrane, resulting in increased neuronal glucose uptake in SH-SY5Y cells.

Going the Extra (Synaptic) Mile: Excitotoxicity as the Road Toward Neurodegenerative Diseases

Excitotoxicity is a phenomenon that describes the toxic actions of excitatory neurotransmitters, primarily glutamate, where the exacerbated or prolonged activation of glutamate receptors starts a cascade of neurotoxicity that ultimately leads to the loss of neuronal function and cell death. In this process, the shift between normal physiological function and excitotoxicity is largely controlled by astrocytes since they can control the levels of glutamate on the synaptic cleft. This control is achieved through glutamate clearance from the synaptic cleft and its underlying recycling through the glutamate-glutamine cycle. The molecular mechanism that triggers excitotoxicity involves alterations in glutamate and calcium metabolism, dysfunction of glutamate transporters, and malfunction of glutamate receptors, particularly N-methyl-D-aspartic acid receptors (NMDAR). On the other hand, excitotoxicity can be regarded as a consequence of other cellular phenomena, such as mitochondrial dysfunction, physical neuronal damage, and oxidative stress. Regardless, it is known that the excessive activation of NMDAR results in the sustained influx of calcium into neurons and leads to several deleterious consequences, including mitochondrial dysfunction, reactive oxygen species (ROS) overproduction, impairment of calcium buffering, the release of pro-apoptotic factors, among others, that inevitably contribute to neuronal loss. A large body of evidence implicates NMDAR-mediated excitotoxicity as a central mechanism in the pathogenesis of many neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS), Alzheimer's disease (AD), and epilepsy. In this review article, we explore different causes and consequences of excitotoxicity, discuss the involvement of NMDAR-mediated excitotoxicity and its downstream effects on several neurodegenerative disorders, and identify possible strategies to study new aspects of these diseases that may lead to the discovery of new therapeutic approaches. With the understanding that excitotoxicity is a common denominator in neurodegenerative diseases and other disorders, a new perspective on therapy can be considered, where the targets are not specific symptoms, but the underlying cellular phenomena of the disease.

Vascular Dysfunction in Alzheimer's Disease: A Prelude to the Pathological Process or a Consequence of It?

Alzheimer's disease (AD) is the most prevalent form of dementia. Despite decades of research following several theoretical and clinical lines, all existing treatments for the disorder are purely symptomatic. AD research has traditionally been focused on neuronal and glial dysfunction. Although there is a wealth of evidence pointing to a significant vascular component in the disease, this angle has been relatively poorly explored. In this review, we consider the various aspects of vascular dysfunction in AD, which has a significant impact on brain metabolism and homeostasis and the clearance of β-amyloid and other toxic metabolites. This may potentially precede the onset of the hallmark pathophysiological and cognitive symptoms of the disease. Pathological changes in vessel haemodynamics, angiogenesis, vascular cell function, vascular coverage, blood-brain barrier permeability and immune cell migration may be related to amyloid toxicity, oxidative stress and apolipoprotein E (APOE) genotype. These vascular deficits may in turn contribute to parenchymal amyloid deposition, neurotoxicity, glial activation and metabolic dysfunction in multiple cell types. A vicious feedback cycle ensues, with progressively worsening neuronal and vascular pathology through the course of the disease. Thus, a better appreciation for the importance of vascular dysfunction in AD may open new avenues for research and therapy.

Dementia spectrum disorders: lessons learnt from decades with PET research

The dementia spectrum encompasses a range of disorders with complex diagnosis, pathophysiology and limited treatment options. Positron emission tomography (PET) imaging provides insights into specific neurodegenerative processes underlying dementia disorders in vivo. Here we focus on some of the most common dementias: Alzheimer's disease, Parkinsonism dementias including Parkinson's disease with dementia, dementia with Lewy bodies, progressive supranuclear palsy and corticobasal syndrome, and frontotemporal lobe degeneration. PET tracers have been developed to target specific proteinopathies (amyloid, tau and α-synuclein), glucose metabolism, cholinergic system and neuroinflammation. Studies have shown distinct imaging abnormalities can be detected early, in some cases prior to symptom onset, allowing disease progression to be monitored and providing the potential to predict symptom onset. Furthermore, advances in PET imaging have identified potential therapeutic targets and novel methods to accurately discriminate between different types of dementias in vivo. There are promising imaging markers with a clinical application on the horizon, however, further studies are required before they can be implantation into clinical practice.

Neuroimaging in aging and neurologic diseases

Neuroimaging biomarkers for neurologic diseases are important tools, both for understanding pathology associated with cognitive and clinical symptoms and for differential diagnosis. This chapter explores neuroimaging measures, including structural and functional measures from magnetic resonance imaging (MRI) and molecular measures primarily from positron emission tomography (PET), in healthy aging adults and in a number of neurologic diseases. The spectrum covers neuroimaging measures from normal aging to a variety of dementias: late-onset Alzheimer's disease [AD; including mild cognitive impairment (MCI)], familial and nonfamilial early-onset AD, atypical AD syndromes, posterior cortical atrophy (PCA), logopenic aphasia (lvPPA), cerebral amyloid angiopathy (CAA), vascular dementia (VaD), sporadic and familial behavioral-variant frontotemporal dementia (bvFTD), semantic dementia (SD), progressive nonfluent aphasia (PNFA), frontotemporal dementia with motor neuron disease (FTD-MND), frontotemporal dementia with amyotrophic lateral sclerosis (FTD-ALS), corticobasal degeneration (CBD), progressive supranuclear palsy (PSP), dementia with Lewy bodies (DLB), Parkinson's disease (PD) with and without dementia, and multiple systems atrophy (MSA). We also include a discussion of the appropriate use criteria (AUC) for amyloid imaging and conclude with a discussion of differential diagnosis of neurologic dementia disorders in the context of neuroimaging.

Comparison of EEG microstates with resting state fMRI and FDG-PET measures in the default mode network via simultaneously recorded trimodal (PET/MR/EEG) data

Simultaneous trimodal positron emission tomography/magnetic resonance imaging/electroencephalography (PET/MRI/EEG) resting state (rs) brain data were acquired from 10 healthy male volunteers. The rs-functional MRI (fMRI) metrics, such as regional homogeneity (ReHo), degree centrality (DC) and fractional amplitude of low-frequency fluctuations (fALFFs), as well as 2-[18F]fluoro-2-desoxy-d-glucose (FDG)-PET standardised uptake value (SUV), were calculated and the measures were extracted from the default mode network (DMN) regions of the brain. Similarly, four microstates for each subject, showing the diverse functional states of the whole brain via topographical variations due to global field power (GFP), were estimated from artefact-corrected EEG signals. In this exploratory analysis, the GFP of microstates was nonparametrically compared to rs-fMRI metrics and FDG-PET SUV measured in the DMN of the brain. The rs-fMRI metrics (ReHO, fALFF) and FDG-PET SUV did not show any significant correlations with any of the microstates. The DC metric showed a significant positive correlation with microstate C (r_s  = 0.73, p = .01). FDG-PET SUVs indicate a trend for a negative correlation with microstates A, B and C. The positive correlation of microstate C with DC metrics suggests a functional relationship between cortical hubs in the frontal and occipital lobes. The results of this study suggest further exploration of this method in a larger sample and in patients with neuropsychiatric disorders. The aim of this exploratory pilot study is to lay the foundation for the development of such multimodal measures to be applied as biomarkers for diagnosis, disease staging, treatment response and monitoring of neuropsychiatric disorders.

Presenilin1/γ-secretase protects neurons from glucose deprivation-induced death by regulating miR-212 and PEA15

Reduced cerebral glucose utilization is found in aged individuals and often is an early sign of neurodegeneration. Here, we show that under glucose deprivation (GD) conditions, decreased expression of presenilin 1 (PS1) results in decreased neuronal survival, whereas increased PS1 increases neuronal survival. Inhibition of γ-secretase also decreases neuronal survival under GD conditions, which suggests the PS1/γ-secretase system protects neurons from GD-induced death. We also show that neuronal levels of the survival protein, phosphoprotein enriched in astrocytes at ∼15 kDa (PEA15), and its mRNA are regulated by PS1/γ-secretase. Furthermore, down-regulation of PEA15 decreases neuronal survival under reduced glucose conditions, whereas exogenous PEA15 increases neuronal survival even in the absence of PS1, which indicates that PEA15 promotes neuronal survival under GD conditions. The absence or reduction of PS1, as well as γ-secretase inhibitors, increases neuronal miR-212, which targets PEA15 mRNA. PS1/γ-secretase activates the transcription factor, cAMP response element-binding protein, regulating miR-212, which targets PEA15 mRNA. Taken together, our data show that under conditions of reduced glucose, the PS1/γ-secretase system decreases neuronal losses by suppressing miR-212 and increasing its target survival factor, PEA15. These observations have implications for mechanisms of neuronal death under conditions of reduced glucose and may provide targets for intervention in neurodegenerative disorders.-Huang, Q., Voloudakis, G., Ren, Y., Yoon, Y., Zhang, E., Kajiwara, Y., Shao, Z., Xuan, Z., Lebedev, D., Georgakopoulos, A., Robakis, N. K. Presenilin1/γ-secretase protects neurons from glucose deprivation-induced death by regulating miR-212 and PEA15.

Functional neuroimaging findings in healthy middle-aged adults at risk of Alzheimer's disease

It is well established that the neurodegenerative process of Alzheimer's disease (AD) begins many years before symptom onset. This preclinical phase provides a crucial time-window for therapeutic intervention, though this requires biomarkers that could evaluate the efficacy of future disease-modification treatments in asymptomatic individuals. The last decade has witnessed a proliferation of studies characterizing the temporal sequence of the earliest functional and structural brain imaging changes in AD. These efforts have focused on studying individuals who are highly vulnerable to develop AD, such as those with familial genetic mutations, susceptibility genes (i.e. apolipoprotein epsilon-4 allele), and/or a positive family history of AD. In this paper, we review the rapidly growing literature of functional imaging changes in cognitively intact individuals who are middle-aged: positron emission tomography (PET) studies of amyloid deposition, glucose metabolism, as well as arterial spin labeling (ASL), task-dependent, resting-state functional magnetic resonance imaging (fMRI) and magnetic resonance spectroscopy (MRS) studies. The prevailing evidence points to early brain functional changes in the relative absence of cognitive impairment and structural atrophy, although there is marked variability in the directionality of the changes, which could, in turn, be related to antagonistic pleiotropy early in life. A common theme across studies relates to the spatial extent of these changes, most of which overlap with brain regions that are implicated in established AD. Notwithstanding several methodological caveats, functional imaging techniques could be preferentially sensitive to the earliest events of AD pathology prior to macroscopic grey matter loss and clinical manifestations of AD. We conclude that while these techniques have great potential to serve as biomarkers to identify at-risk individuals, more longitudinal studies with greater sample size and robust correction for multiple comparisons are still warranted to establish their utility.

Mitochondria-Targeted Molecules as Potential Drugs to Treat Patients With Alzheimer's Disease

Alzheimer's disease (AD) is the most common multifactorial mental illness affecting the elderly population in the world. Its prevalence increases as person ages. There is no known drug or agent that can delay or prevent the AD and its progression. Extensive research has revealed that multiple cellular pathways involved, including amyloid beta production, mitochondrial structural and functional changes, hyperphosphorylation of Tau and NFT formation, inflammatory responses, and neuronal loss in AD pathogenesis. Amyloid beta-induced synaptic damage, mitochondrial abnormalities, and phosphorylated Tau are major areas of present research investigations. Synaptic pathology and mitochondrial oxidative damage are early events in disease process. In this chapter, a systematic literature survey has been conducted and presented a summary of antioxidants used in (1) AD mouse models, (2) elderly populations, and (3) randomized clinical trials in AD patients. This chapter highlights the recent progress in developing and testing mitochondria-targeted molecules using AD cell cultures and AD mouse models. This chapter also discusses recent research on AD pathogenesis and therapeutics, focusing on mitochondria-targeted molecules as potential therapeutic targets to delay or prevent AD progression.

Adenosine A1 receptor antagonist rolofylline alleviates axonopathy caused by human Tau ΔK280

Accumulation of Tau is a characteristic hallmark of several neurodegenerative diseases but the mode of toxic action of Tau is poorly understood. Here, we show that the Tau protein is toxic due to its aggregation propensity, whereas phosphorylation and/or missorting is not sufficient to cause neuronal dysfunction. Aggregate-prone Tau accumulates, when expressed in vitro at near-endogenous levels, in axons as spindle-shaped grains. These axonal grains contain Tau that is folded in a pathological (MC-1) conformation. Proaggregant Tau induces a reduction of neuronal ATP, concomitant with loss of dendritic spines. Counterintuitively, axonal grains of Tau are not targeted for degradation and do not induce a molecular stress response. Proaggregant Tau causes neuronal and astrocytic hypoactivity and presynaptic dysfunction instead. Here, we show that the adenosine A₁ receptor antagonist rolofylline (KW-3902) is alleviating the presynaptic dysfunction and restores neuronal activity as well as dendritic spine levels in vitro. Oral administration of rolofylline for 2-wk to 14-mo-old proaggregant Tau transgenic mice restores the spatial memory deficits and normalizes the basic synaptic transmission. These findings make rolofylline an interesting candidate to combat the hypometabolism and neuronal dysfunction associated with Tau-induced neurodegenerative diseases.

Amyloid imaging: Past, present and future perspectives

Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterised by the gradual onset of dementia. The pathological hallmarks of the disease are Aβ amyloid plaques, and tau neurofibrillary tangles, along dendritic and synaptic loss and reactive gliosis. Functional and molecular neuroimaging techniques such as positron emission tomography (PET) using functional and molecular tracers, in conjuction with other Aβ and tau biomarkers in CSF, are proving valuable in the differential diagnosis of AD, as well as in establishing disease prognosis. With the advent of new therapeutic strategies, there has been an increasing application of these techniques for the determination of Aβ burden in vivo in the patient selection, evaluation of target engagement and assessment of the efficacy of therapeutic approaches aimed at reducing Aβ in the brain.

Neuroimaging biomarkers in Alzheimer's disease and other dementias

In vivo imaging of β-amyloid (Aβ) has transformed the assessment of Aβ pathology and its changes over time, extending our insight into Aβ deposition in the brain by providing highly accurate, reliable, and reproducible quantitative statements of regional or global Aβ burden in the brain. This knowledge is essential for therapeutic trial recruitment and for the evaluation of anti-Aβ treatments. Although cross sectional evaluation of Aβ burden does not strongly correlate with cognitive impairment, it does correlate with cognitive (especially memory) decline and with a higher risk for conversion to AD in the aging population and MCI subjects. This suggests that Aβ deposition is a protracted pathological process starting well before the onset of symptoms. Longitudinal observations, coupled with different disease-specific biomarkers to assess potential downstream effects of Aβ are required to confirm this hypothesis and further elucidate the role of Aβ deposition in the course of Alzheimer's disease.

Biomarkers in Sporadic and Familial Alzheimer's Disease

Most forms of Alzheimer's disease (AD) are sporadic (sAD) or inherited in a non-Mendelian fashion, and less than 1% of cases are autosomal-dominant. Forms of sAD do not exhibit familial aggregation and are characterized by complex genetic and environmental interactions. Recently, the expansion of genomic methodologies, in association with substantially larger combined cohorts, has resulted in various genome-wide association studies that have identified several novel genetic associations of AD. Currently, the most effective methods for establishing the diagnosis of AD are defined by multi-modal pathways, starting with clinical and neuropsychological assessment, cerebrospinal fluid (CSF) analysis, and brain-imaging procedures, all of which have significant cost- and access-to-care barriers. Consequently, research efforts have focused on the development and validation of non-invasive and generalizable blood-based biomarkers. Among the modalities conceptualized by the systems biology paradigm and utilized in the "exploratory biomarker discovery arena", proteome analysis has received the most attention. However, metabolomics, lipidomics, transcriptomics, and epigenomics have recently become key modalities in the search for AD biomarkers. Interestingly, biomarker changes for familial AD (fAD), in many but not all cases, seem similar to those for sAD. The integration of neurogenetics with systems biology/physiology-based strategies and high-throughput technologies for molecular profiling is expected to help identify the causes, mechanisms, and biomarkers associated with the various forms of AD. Moreover, in order to hypothesize the dynamic trajectories of biomarkers through disease stages and elucidate the mechanisms of biomarker alterations, updated and more sophisticated theoretical models have been proposed for both sAD and fAD.

Drug treatments in Alzheimer's disease

Despite the significant public health issue that it poses, only five medical treatments have been approved for Alzheimer's disease (AD) and these act to control symptoms rather than alter the course of the disease. Studies of potential disease-modifying therapy have generally been undertaken in patients with clinically detectable disease, yet evidence suggests that the pathological changes associated with AD begin several years before this. It is possible that pharmacological therapy may be beneficial in this pre-clinical stage before the neurodegenerative process is established. Techniques providing earlier diagnosis, such as cerebrospinal fluid biomarkers and amyloid positron emission tomography neuroimaging, are key to testing this theory in clinical trials. Recent results from trials of agents such as aducanumab are encouraging but must also be interpreted with caution. Such medicines could potentially delay the onset of dementia and would therefore markedly reduce its prevalence. However, we currently remain a good distance away from clinically available disease-modifying therapy.

Can ketones compensate for deteriorating brain glucose uptake during aging? Implications for the risk and treatment of Alzheimer's disease

Brain glucose uptake is impaired in Alzheimer's disease (AD). A key question is whether cognitive decline can be delayed if this brain energy defect is at least partly corrected or bypassed early in the disease. The principal ketones (also called ketone bodies), β-hydroxybutyrate and acetoacetate, are the brain's main physiological alternative fuel to glucose. Three studies in mild-to-moderate AD have shown that, unlike with glucose, brain ketone uptake is not different from that in healthy age-matched controls. Published clinical trials demonstrate that increasing ketone availability to the brain via moderate nutritional ketosis has a modest beneficial effect on cognitive outcomes in mild-to-moderate AD and in mild cognitive impairment. Nutritional ketosis can be safely achieved by a high-fat ketogenic diet, by supplements providing 20-70 g/day of medium-chain triglycerides containing the eight- and ten-carbon fatty acids octanoate and decanoate, or by ketone esters. Given the acute dependence of the brain on its energy supply, it seems reasonable that the development of therapeutic strategies aimed at AD mandates consideration of how the underlying problem of deteriorating brain fuel supply can be corrected or delayed.

Monitoring of Intracellular Tau Aggregation Regulated by OGA/OGT Inhibitors

Abnormal phosphorylation of tau has been considered as a key pathogenic mechanism inducing tau aggregation in multiple neurodegenerative disorders, collectively called tauopathies. Recent evidence showed that tau phosphorylation sites are protected with O-linked β-N-acetylglucosamine (O-GlcNAc) in normal brain. In pathological condition, tau is de-glycosylated and becomes a substrate for kinases. Despite the importance of O-GlcNAcylation in tau pathology, O-GlcNAc transferase (OGT), and an enzyme catalyzing O-GlcNAc to tau, has not been carefully investigated in the context of tau aggregation. Here, we investigated intracellular tau aggregation regulated by BZX2, an inhibitor of OGT. Upon the inhibition of OGT, tau phosphorylation increased 2.0-fold at Ser199 and 1.5-fold at Ser396, resulting in increased tau aggregation. Moreover, the BZX2 induced tau aggregation was efficiently reduced by the treatment of Thiamet G, an inhibitor of O-GlcNAcase (OGA). Our results demonstrated the protective role of OGT in tau aggregation and also suggest the counter-regulatory mechanism of OGA and OGT in tau pathology.

Glycolytic enzyme upregulation and numbness of mitochondrial activity characterize the early phase of apoptosis in cerebellar granule cells

Alzheimer's disease (AD) and cancer proceed via one or more common molecular mechanisms: a metabolic shift from oxidative phosphorylation to glycolysis-corresponding to the activation of the Warburg effect-occurs in both diseases. The findings reported in this paper demonstrate that, in the early phase of apoptosis, glucose metabolism is enhanced, i.e. key proteins which internalize and metabolize glucose-glucose transporter, hexokinase and phosphofructokinase-are up-regulated, in concomitance with a parallel decrease in oxygen consumption by mitochondria and increase of L-lactate accumulation. Reversal of the glycolytic phenotype occurs in the presence of dichloroacetate, inhibitor of the pyruvate dehydrogenase kinase enzyme, which speeds up apoptosis of cerebellar granule cells, reawakening mitochondria and then modulating glycolytic enzymes. Loss of the adaptive advantage afforded by aerobic glycolysis, which occurs in the late phase of apoptosis, exacerbates the pathological processes underlying neurodegeneration, leading inevitably the cell to death. In conclusion, the data propose that both aerobic, i.e. Warburg effect, essentially due to the protective numbness of mitochondria, and anaerobic glycolysis, rather due to the mitochondrial impairment, characterize the entire time frame of apoptosis, from the early to the late phase, which mimics the development of AD.

Neuron-astrocyte interactions in neurodegenerative diseases: Role of neuroinflammation

Selective neuron loss in discrete brain regions is a hallmark of various neurodegenerative disorders, although the mechanisms responsible for this regional vulnerability of neurons remain largely unknown. Earlier studies attributed neuron dysfunction and eventual loss during neurodegenerative diseases as exclusively cell autonomous. Although cell-intrinsic factors are one critical aspect in dictating neuron death, recent evidence also supports the involvement of other central nervous system cell types in propagating non-cell autonomous neuronal injury during neurodegenerative diseases. One such example is astrocytes, which support neuronal and synaptic function, but can also contribute to neuroinflammatory processes through robust chemokine secretion. Indeed, aberrations in astrocyte function have been shown to negatively impact neuronal integrity in several neurological diseases. The present review focuses on neuroinflammatory paradigms influenced by neuron-astrocyte cross-talk in the context of select neurodegenerative diseases.

Molecular imaging in genetics

Neuroimaging is a potentially valuable tool to link individual differences in the human genome to structure and functional variations, narrowing the gaps in the casual chain from a given genetic variation to a brain disorder. Because genes are not usually expressed at the level of mental behavior, but are mediated by their molecular and cellular effects, molecular imaging could play a key role. This article reviews the literature using molecular imaging as an intermediate phenotype and/or biomarker for illness related to certain genetic alterations, focusing on the most common neurodegenerative disorders, Alzheimer's disease (AD) and Parkinson disease.

Advancing research diagnostic criteria for Alzheimer's disease: the IWG-2 criteria

In the past 8 years, both the International Working Group (IWG) and the US National Institute on Aging-Alzheimer's Association have contributed criteria for the diagnosis of Alzheimer's disease (AD) that better define clinical phenotypes and integrate biomarkers into the diagnostic process, covering the full staging of the disease. This Position Paper considers the strengths and limitations of the IWG research diagnostic criteria and proposes advances to improve the diagnostic framework. On the basis of these refinements, the diagnosis of AD can be simplified, requiring the presence of an appropriate clinical AD phenotype (typical or atypical) and a pathophysiological biomarker consistent with the presence of Alzheimer's pathology. We propose that downstream topographical biomarkers of the disease, such as volumetric MRI and fluorodeoxyglucose PET, might better serve in the measurement and monitoring of the course of disease. This paper also elaborates on the specific diagnostic criteria for atypical forms of AD, for mixed AD, and for the preclinical states of AD.

Neuropsychological detection of the early stage of amnestic mild cognitive impairment without objective memory impairment

AIM

We investigate the assessment method to detect the early stage of amnestic mild cognitive impairment (aMCI) using Wechsler Memory Scale - Revised (WMS-R) and Wechsler Adult Intelligence Scale - Third Edition (WAIS-III).

METHODS

Three groups (normal group, aMCI group, and early aMCI group), controlled for age and years of education, underwent brain (18)F-fluorodeoxyglucose positron emission tomography ((18)F-FDG PET), WAIS-III, WMS-R, and other tests. The early aMCI group does not fulfill the clinical diagnostic criteria of aMCI because patients do not have objective memory impairment, but their clinical symptoms and results of (18)F-FDG PET indicate that they should be included in the category of aMCI.

RESULTS

The discrepancy of scores between Verbal IQ and General Memory had the highest accuracy in discriminating between normal and early aMCI groups.

CONCLUSION

The cutoff point determined in this study is useful to detect an early stage of aMCI, which may be distinguished from aMCI using the current criteria.

Cerebral hypoperfusion induces cortical watershed microinfarcts which may further aggravate cognitive decline in Alzheimer's disease

Increasing number of data, including the existence of common risk factors, indicate an association between cerebrovascular disease and Alzheimer's disease (AD). AD is known to be often associated with cerebral hypoperfusion. Recent histopathological evidence showed a significant association between watershed cortical microinfarcts and AD indicating that cerebral hypoperfusion induces not only white matter damage, known as leuko-araiosis, but cortical border zone infarcts as well, further aggravating the degenerative process and worsening dementia. In late stages of Alzheimer's disease--in cases with neuropathologically confirmed definite AD--the occurrence of watershed cortical microinfarcts was ten times higher than in aged matched control cases. Congophilic angiopathy and perturbed hemodynamic factors were found to be important factors in the genesis of watershed microinfarcts. To consider the vulnerability of the cerebral blood flow and the perturbed cortical vascular network in AD is important. Neuroleptic and sedative treatments frequently employed in AD may further accentuate cerebral hypoperfusion by decreasing blood pressure. Therefore, to treat and prevent arterial hypotension and maintain cerebral perfusion at an appropriate level in AD is essential.

Clinical applications of neuroimaging in patients with Alzheimer's disease: a review from the Fourth Canadian Consensus Conference on the Diagnosis and Treatment of Dementia 2012

In May 2012, the Fourth Canadian Consensus Conference on the Diagnosis and Treatment of Dementia brought together in Montreal experts from around Canada to update Canadian recommendations for the diagnosis and management of patients with neurodegenerative conditions associated with deterioration of cognition. Multiple topics were discussed. The present paper is a highly condensed version of those recommendations that were produced to support discussions in the field of neuroimaging for clinical diagnosis of those conditions.

Ushering in the study and treatment of preclinical Alzheimer disease

Researchers have begun to characterize the subtle biological and cognitive processes that precede the clinical onset of Alzheimer disease (AD), and to set the stage for accelerated evaluation of experimental treatments to delay the onset, reduce the risk of, or completely prevent clinical decline. In this Review, we provide an overview of the experimental strategies, and brain imaging and cerebrospinal fluid biomarker measures that are used in early detection and tracking of AD, highlighting at-risk individuals who could be suitable for preclinical monitoring. We discuss how advances in the field have contributed to reconceptualization of AD as a sequence of biological changes that occur during progression from preclinical AD, to mild cognitive impairment and finally dementia, and we review recently proposed research criteria for preclinical AD. Advances in the study of preclinical AD have driven the recognition that efficacy of at least some AD therapies may depend on initiation of treatment before clinical manifestation of disease, leading to a new era of AD prevention research.

Intelligence or years of education: which is better correlated with memory function in normal elderly Japanese subjects?

BACKGROUND

We compared differences in intelligence and memory function between normal elderly Japanese subjects with more years of education and those with fewer years of education. We also investigated clinical and neuropsychological factors that are strongly correlated with memory function.

METHODS

There were 118 normal elderly subjects who underwent the Mini-Mental State Examination, Wechsler Adult Intelligence Scale, 3rd edition (WAIS-III), and Wechsler Memory Scale Revised. Subjects with at least 13 years of education were categorized as the H group, and those with 12 years of education or less were categorized as the L group.

RESULTS

Age and Mini-Mental State Examination scores were not significantly different between the two groups. On the WAIS-III, there were significant differences between the two groups in Verbal IQ and Full Scale IQ. On the Wechsler Memory Scale Revised, there were significant differences between the two groups in Visual Memory, General Memory, and Delayed Recall. Correlation coefficients between memory function and the other factors demonstrated significant but weak correlations between years of education and General Memory (R = 0.22) and between years of education and Delayed Recall (R = 0.20). Strong correlations were found between Verbal IQ and Verbal Memory (R = 0.45), between Verbal IQ and General Memory (R = 0.49), between Full Scale IQ and General Memory (R = 0.50) and between Full Scale IQ and Delayed Recall (R = 0.48).

CONCLUSIONS

In normal elderly Japanese subjects, years of education weakly correlated with memory function while Verbal IQ, Full Scale IQ and Verbal Comprehension on WAIS-III had stronger correlations with memory function. Verbal IQ and Verbal Comprehension on WAIS-III were found to be insusceptible to the cognitive decline characteristic of Alzheimer's disease or amnestic mild cognitive impairment. Therefore, verbal intelligence, as measured by Verbal IQ and Verbal Comprehension, may be the most useful factor for inferring premorbid memory function in Alzheimer's disease or amnestic mild cognitive impairment patients.

CREB regulates the expression of neuronal glucose transporter 3: a possible mechanism related to impaired brain glucose uptake in Alzheimer's disease

Impaired brain glucose uptake and metabolism precede the appearance of clinical symptoms in Alzheimer disease (AD). Neuronal glucose transporter 3 (GLUT3) is decreased in AD brain and correlates with tau pathology. However, what leads to the decreased GLUT3 is yet unknown. In this study, we found that the promoter of human GLUT3 contains three potential cAMP response element (CRE)-like elements, CRE1, CRE2 and CRE3. Overexpression of CRE-binding protein (CREB) or activation of cAMP-dependent protein kinase significantly increased GLUT3 expression. CREB bound to the CREs and promoted luciferase expression driven by human GLUT3-promoter. Among the CREs, CRE2 and CRE3 were required for the promotion of GLUT3 expression. Full-length CREB was decreased and truncation of CREB was increased in AD brain. This truncation was correlated with calpain I activation in human brain. Further study demonstrated that calpain I proteolysed CREB at Gln₂₈–Ala₂₉ and generated a 41-kDa truncated CREB, which had less activity to promote GLUT3 expression. Importantly, human brain GLUT3 was correlated with full-length CREB positively and with activation of calpain I negatively. These findings suggest that overactivation of calpain I caused by calcium overload proteolyses CREB, resulting in a reduction of GLUT3 expression and consequently impairing glucose uptake and metabolism in AD brain.

Characterizing the preclinical stages of Alzheimer's disease and the prospect of presymptomatic intervention

Studies of asymptomatic carriers of genes that are known to predispose to Alzheimer's disease (AD) have facilitated the characterization of preclinical AD. The most prevalent genetic risk factor is the ε4 allele of apolipoprotein E (APOE). Neuropathological studies of young deceased ε4 carriers have shown modest but abnormal amounts of neocortical amyloid and medial temporal neurofibrillary tangles that is also reflected in cerebrospinal fluid (CSF) biomarkers, amyloid-β, and phospho-tau in particular. MRI studies have shown progressive hippocampal and gray matter atrophy with the advent of mild cognitive impairment (MCI), and fluorodeoxyglucose PET scans show reduced cerebral metabolism in posterior cingulate and related AD regions evident even in 30 year olds. Cerebral amyloidosis disclosed by more recent amyloid ligand PET studies in asymptomatic 60 year olds increases in parallel with ε4 gene dose. Longitudinal neuropsychological studies have revealed accelerated memory decline in ε4 carriers beginning around age 55-60 years whose severity again parallels ε4 gene dose. The clinico-pathological correlation of declining memory and AD-like neuropathological change defines preclinical AD and has set the stage for the accelerated evaluation of presymptomatic AD treatments. In this article, we briefly consider some of the earliest detectable changes associated with the predisposition to AD, and some of the prevention trial strategies that have been proposed to help find treatments to reduce the risk, postpone the onset of, or completely prevent AD symptoms as soon as possible.

Nicotinamide forestalls pathology and cognitive decline in Alzheimer mice: evidence for improved neuronal bioenergetics and autophagy procession

Impaired brain energy metabolism and oxidative stress are implicated in cognitive decline and the pathologic accumulations of amyloid β-peptide (Aβ) and hyperphosphorylated tau in Alzheimer's disease (AD). To determine whether improving brain energy metabolism will forestall disease progress in AD, the impact of the β-nicotinamide adenine dinucleotide precursor nicotinamide on brain cell mitochondrial function and macroautophagy, bioenergetics-related signaling, and cognitive performance were studied in cultured neurons and in a mouse model of AD. Oxidative stress resulted in decreased mitochondrial mass, mitochondrial degeneration, and autophagosome accumulation in neurons. Nicotinamide preserved mitochondrial integrity and autophagy function, and reduced neuronal vulnerability to oxidative/metabolic insults and Aβ toxicity. β-Nicotinamide adenine dinucleotide biosynthesis, autophagy, and phosphatidylinositol-3-kinase signaling were required for the neuroprotective action of nicotinamide. Treatment of 3xTgAD mice with nicotinamide for 8 months resulted in improved cognitive performance, and reduced Aβ and hyperphosphorylated tau pathologies in hippocampus and cerebral cortex. Nicotinamide treatment preserved mitochondrial integrity, and improved autophagy-lysosome procession by enhancing lysosome/autolysosome acidification to reduce autophagosome accumulation. Treatment of 3xTgAD mice with nicotinamide resulted in elevated levels of activated neuroplasticity-related kinases (protein kinase B [Akt] and extracellular signal-regulated kinases) and the transcription factor cyclic adenosine monophosphate (AMP) response element-binding protein in the hippocampus and cerebral cortex. Thus, nicotinamide suppresses AD pathology and cognitive decline in a mouse model of AD by a mechanism involving improved brain bioenergetics with preserved functionality of mitochondria and the autophagy system.

FTIR imaging of brain tissue reveals crystalline creatine deposits are an ex vivo marker of localized ischemia during murine cerebral malaria: general implications for disease neurochemistry

Phosphocreatine is a major cellular source of high energy phosphates, which is crucial to maintain cell viability under conditions of impaired metabolic states, such as decreased oxygen and energy availability (i.e., ischemia). Many methods exist for the bulk analysis of phosphocreatine and its dephosphorylated product creatine; however, no method exists to image the distribution of creatine or phosphocreatine at the cellular level. In this study, Fourier transform infrared (FTIR) spectroscopic imaging has revealed the ex vivo development of creatine microdeposits in situ in the brain region most affected by the disease, the cerebellum of cerebral malaria (CM) diseased mice; however, such deposits were also observed at significantly lower levels in the brains of control mice and mice with severe malaria. In addition, the number of deposits was observed to increase in a time-dependent manner during dehydration post tissue cutting. This challenges the hypotheses in recent reports of FTIR spectroscopic imaging where creatine microdeposits found in situ within thin sections from epileptic, Alzheimer's (AD), and amlyoid lateral sclerosis (ALS) diseased brains were proposed to be disease specific markers and/or postulated to contribute to the brain pathogenesis. As such, a detailed investigation was undertaken, which has established that the creatine microdeposits exist as the highly soluble HCl salt or zwitterion and are an ex-vivo tissue processing artifact and, hence, have no effect on disease pathogenesis. They occur as a result of creatine crystallization during dehydration (i.e., air-drying) of thin sections of brain tissue. As ischemia and decreased aerobic (oxidative metabolism) are common to many brain disorders, regions of elevated creatine-to-phosphocreatine ratio are likely to promote crystal formation during tissue dehydration (due to the lower water solubility of creatine relative to phosphocreatine). The results of this study have demonstrated that although the deposits do not occur in vivo, and do not directly play any role in disease pathogenesis, increased levels of creatine deposits within air-dried tissue sections serve as a highly valuable marker for the identification of tissue regions with an altered metabolic status. In this study, the location of crystalline creatine deposits were used to identify whether an altered metabolic state exists within the molecular and granular layers of the cerebellum during CM, which complements the recent discovery of decreased oxygen availability in the brain during this disease.

Complexity and synchronicity of resting state blood oxygenation level-dependent (BOLD) functional MRI in normal aging and cognitive decline

PURPOSE

To explore the use of approximate entropy (ApEn) as an index of the complexity and the synchronicity of resting state blood oxygenation level-dependent (BOLD) functional magnetic resonance imaging (fMRI) in normal aging and cognitive decline associated with familial Alzheimer's disease (fAD).

MATERIALS AND METHODS

Resting state BOLD fMRI data were acquired at 3T from two independent cohorts of subjects consisting of healthy young (age 23 ± 2 years, n = 8) and aged volunteers (age 66 ± 3 years, n = 8), as well as 22 fAD associated subjects (14 mutation carriers, age 41.2 ± 15.8 years; and eight nonmutation carrying family members, age 28.8 ± 5.9 years). Mean ApEn values were compared between the two age groups and correlated with cognitive performance in the fAD group. Cross-ApEn (C-ApEn) was further calculated to assess the asynchrony between precuneus and the rest of the brain.

RESULTS

Complexity of brain activity measured by mean ApEn in gray and white matter decreased with normal aging. In the fAD group, cognitive impairment was associated with decreased mean ApEn in gray matter as well as decreased regional ApEn in right precuneus, right lateral parietal regions, left precentral gyrus, and right paracentral gyrus. A pattern of asynchrony between BOLD fMRI series emerged from C-ApEn analysis, with significant regional anti-correlation with cross-correlation coefficient of functional connectivity analysis.

CONCLUSION

ApEn and C-ApEn may be useful for assessing the complexity and synchronicity of brain activity in normal aging and cognitive decline associated with neurodegenerative diseases.

Preclinical Alzheimer disease: identification of cases at risk among cognitively intact older individuals

Since the first description of the case of Auguste Deter, presented in Tübingen in 1906 by Alois Alzheimer, there has been an exponential increase in our knowledge of the neuropathological, cellular, and molecular foundation of Alzheimer's disease (AD). The concept of AD pathogenesis has evolved from a static, binary view discriminating cognitive normality from dementia, towards a dynamic view that considers AD pathology as a long-lasting morbid process that takes place progressively over years, or even decades, before the first symptoms become apparent, and thus operating in a continuum between the two aforementioned extreme states. Several biomarkers have been proposed to predict AD-related cognitive decline, initially in cases with mild cognitive impairment, and more recently in cognitively intact individuals. These early markers define at-risk individuals thought to be in the preclinical phase of AD. However, the clinical relevance of this preclinical phase remains controversial. The fate of such individuals, who are cognitively intact, but positive for some early AD biomarkers, is currently uncertain at best. In this report, we advocate the point of view that although most of these preclinical cases will evolve to clinically overt AD, some appear to have efficient compensatory mechanisms and virtually never develop dementia. We critically review the currently available early AD markers, discuss their clinical relevance, and propose a novel classification of preclinical AD, designating these non-progressing cases as 'stable asymptomatic cerebral amyloidosis'.