Ketone bodies mediate alterations in brain energy metabolism and biomarkers of Alzheimer's disease.

Alzheimer's disease (AD) is the most common form of dementia. AD is a progressive neurodegenerative disorder characterized by cognitive dysfunction, including learning and memory deficits, and behavioral changes. Neuropathology hallmarks of AD such as amyloid beta (Aß) plaques and neurofibrillary tangles containing the neuron-specific protein tau is associated with changes in fluid biomarkers including Aß, phosphorylated tau (p-tau)-181, p-tau 231, p-tau 217, glial fibrillary acidic protein (GFAP), and neurofilament light (NFL). Another pathological feature of AD is neural damage and hyperactivation of astrocytes, that can cause increased pro-inflammatory mediators and oxidative stress. In addition, reduced brain glucose metabolism and mitochondrial dysfunction appears up to 15 years before the onset of clinical AD symptoms. As glucose utilization is compromised in the brain of patients with AD, ketone bodies (KBs) may serve as an alternative source of energy. KBs are generated from the ß-oxidation of fatty acids, which are enhanced following consumption of ketogenic diets with high fat, moderate protein, and low carbohydrate. KBs have been shown to cross the blood brain barrier to improve brain energy metabolism. This review comprehensively summarizes the current literature on how increasing KBs support brain energy metabolism. In addition, for the first time, this review discusses the effects of ketogenic diet on the putative AD biomarkers such as Aß, tau (mainly p-tau 181), GFAP, and NFL, and discusses the role of KBs on neuroinflammation, oxidative stress, and mitochondrial metabolism.

Tau target identification reveals NSF-dependent effects on AMPA receptor trafficking and memory formation.

Microtubule-associated protein tau is a central factor in Alzheimer's disease and other tauopathies. However, the physiological functions of tau are unclear. Here, we used proximity-labelling proteomics to chart tau interactomes in primary neurons and mouse brains in vivo. Tau interactors map onto pathways of cytoskeletal, synaptic vesicle and postsynaptic receptor regulation and show significant enrichment for Parkinson's, Alzheimer's and prion disease. We find that tau interacts with and dose-dependently reduces the activity of N-ethylmaleimide sensitive fusion protein (NSF), a vesicular ATPase essential for AMPA-type glutamate receptor (AMPAR) trafficking. Tau-deficient (tau-/- ) neurons showed mislocalised expression of NSF and enhanced synaptic AMPAR surface levels, reversible through the expression of human tau or inhibition of NSF. Consequently, enhanced AMPAR-mediated associative and object recognition memory in tau-/- mice is suppressed by both hippocampal tau and infusion with an NSF-inhibiting peptide. Pathologic mutant tau from mouse models or Alzheimer's disease significantly enhances NSF inhibition. Our results map neuronal tau interactomes and delineate a functional link of tau with NSF in plasticity-associated AMPAR-trafficking and memory.

Alzheimer's disease: Ablating single master site abolishes tau hyperphosphorylation.

Hyperphosphorylation of the neuronal tau protein is a hallmark of neurodegenerative tauopathies such as Alzheimer's disease. A central unanswered question is why tau becomes progressively hyperphosphorylated. Here, we show that tau phosphorylation is governed by interdependence- a mechanistic link between initial site-specific and subsequent multi-site phosphorylation. Systematic assessment of site interdependence identified distinct residues (threonine-50, threonine-69, and threonine-181) as master sites that determine propagation of phosphorylation at multiple epitopes. CRISPR point mutation and expression of human tau in Alzheimer's mice showed that site interdependence governs physiologic and amyloid-associated multi-site phosphorylation and cognitive deficits, respectively. Combined targeting of master sites and p38α, the most central tau kinase linked to interdependence, synergistically ablated hyperphosphorylation. In summary, our work delineates how complex tau phosphorylation arises to inform therapeutic and biomarker design for tauopathies.

Differential mitochondrial protein interaction profile between human translocator protein and its A147T polymorphism variant.

The translocator protein (TSPO) has been implicated in mitochondrial transmembrane cholesterol transport, brain inflammation, and other mitochondrial functions. It is upregulated in glial cells during neuroinflammation in Alzheimer's disease. High affinity TSPO imaging radioligands are utilized to visualize neuroinflammation. However, this is hampered by the common A147T polymorphism which compromises ligand binding. Furthermore, this polymorphism has been linked to increased risk of neuropsychiatric disorders, and possibly reduces TSPO protein stability. Here, we used immunoprecipitation coupled to mass-spectrometry (IP-MS) to establish a mitochondrial protein binding profile of wild-type (WT) TSPO and the A147T polymorphism variant. Using mitochondria from human glial cells expressing either WT or A147T TSPO, we identified 30 WT TSPO binding partners, yet only 23 for A147T TSPO. Confirming that A147T polymorphism of the TSPO might confer loss of function, we found that one of the identified interactors of WT TSPO, 14-3-3 theta (YWHAQ), a protein involved in regulating mitochondrial membrane proteins, interacts much less with A147T TSPO. Our data presents a network of mitochondrial interactions of TSPO and its A147T polymorphism variant in human glial cells and indicate functional relevance of A147T in mitochondrial protein networks.

High Level Forebrain Expression of Active Tau Kinase p38γ Exacerbates Cognitive Dysfunction in Aged APP-transgenic Alzheimer's Mice.

Persistent improvement of cognitive deficits in Alzheimer's disease (AD), a common form of dementia, is an unattained therapeutic objective. Gene therapy holds promise for treatment of familial and sporadic forms of AD. p38γ, a member of the p38 mitogen-activated protein (MAP) kinase family, inhibits amyloid-ß toxicity through regulation of tau phosphorylation. We recently showed that a gene delivery approach increasing p38γ resulted in markedly better learning and memory performance in mouse models of AD at advanced stages of amyloid-ß- and tau-mediated cognitive impairment. Notably, low-to-moderate expression of p38γ had beneficial outcomes on cognition. The impact of high levels of p38γ on neuronal function remain unclear. Therefore, we addressed the outcomes of high levels of active p38γ on brain function, by direct injection of p38γ-encoding adeno-associated virus (AAV) into the forebrain of aged mice of an APP transgenic AD mouse model. While motor function in p38γ-expressing APP transgenic mice 2 months post-injection was comparable to control treated APP mice, their activity was markedly reduced in the open field test and included frequent bouts of immobility. Moreover, their learning and memory function was markedly impaired compared to control-treated aged APP mice. These results suggest that high neuronal levels of active p38γ emphasize a stress kinase role of p38γ, perturbing circuit function in motivation, navigation, and spatial learning. Overall, this work shows excessive neuronal p38γ levels can aggravate circuit dysfunction and advises adjustable expression systems will be required for sustainable AD gene therapy based on p38γ activity.

Diagnostic and prognostic plasma biomarkers for preclinical Alzheimer's disease.

INTRODUCTION: This study involved a parallel comparison of the diagnostic and longitudinal monitoring potential of plasma glial fibrillary acidic protein (GFAP), total tau (t-tau), phosphorylated tau (p-tau181 and p-tau231), and neurofilament light (NFL) in preclinical Alzheimer's disease (AD). METHODS: Plasma proteins were measured using Simoa assays in cognitively unimpaired older adults (CU), with either absence (Aß-) or presence (Aß+) of brain amyloidosis. RESULTS: Plasma GFAP, t-tau, p-tau181, and p-tau231 concentrations were higher in Aß+ CU compared with Aß- CU cross-sectionally. GFAP had the highest effect size and area under the curve (AUC) in differentiating between Aß+ and Aß- CU; however, no statistically significant differences were observed between the AUCs of GFAP, p-tau181, and p-tau231, but all were significantly higher than the AUC of NFL, and the AUC of GFAP was higher than the AUC of t-tau. The combination of a base model (BM), comprising the AD risk factors, age, sex, and apolipoprotein E gene (APOE) ε4 status with GFAP was observed to have a higher AUC (>90%) compared with the combination of BM with any of the other proteins investigated in the current study. Longitudinal analyses showed increased GFAP and p-tau181 in Aß+ CU and increased NFL in Aß- CU, over a 12-month duration. GFAP, p-tau181, p-tau231, and NFL showed significant correlations with cognition, whereas no significant correlations were observed with hippocampal volume. DISCUSSION: These findings highlight the diagnostic and longitudinal monitoring potential of GFAP and p-tau for preclinical AD.

Plasma glial fibrillary acidic protein is elevated in cognitively normal older adults at risk of Alzheimer's disease.

Glial fibrillary acidic protein (GFAP), an astrocytic cytoskeletal protein, can be measured in blood samples, and has been associated with Alzheimer's disease (AD). However, plasma GFAP has not been investigated in cognitively normal older adults at risk of AD, based on brain amyloid-ß (Aß) load. Cross-sectional analyses were carried out for plasma GFAP and plasma Aß1-42/Aß1-40 ratio, a blood-based marker associated with brain Aß load, in participants (65-90 years) categorised into low (Aß-, n = 63) and high (Aß+, n = 33) brain Aß load groups via Aß positron emission tomography. Plasma GFAP, Aß1-42, and Aß1-40 were measured using the Single molecule array (Simoa) platform. Plasma GFAP levels were significantly higher (p < 0.00001), and plasma Aß1-42/Aß1-40 ratios were significantly lower (p < 0.005), in Aß+ participants compared to Aß- participants, adjusted for covariates age, sex, and apolipoprotein E-ε4 carriage. A receiver operating characteristic curve based on a logistic regression of the same covariates, the base model, distinguished Aß+ from Aß- (area under the curve, AUC = 0.78), but was outperformed when plasma GFAP was added to the base model (AUC = 0.91) and further improved with plasma Aß1-42/Aß1-40 ratio (AUC = 0.92). The current findings demonstrate that plasma GFAP levels are elevated in cognitively normal older adults at risk of AD. These observations suggest that astrocytic damage or activation begins from the pre-symptomatic stage of AD and is associated with brain Aß load. Observations from the present study highlight the potential of plasma GFAP to contribute to a diagnostic blood biomarker panel (along with plasma Aß1-42/Aß1-40 ratios) for cognitively normal older adults at risk of AD.

Plasma metabolites associated with biomarker evidence of neurodegeneration in cognitively normal older adults.

Alzheimer's disease (AD) is a progressive neurodegenerative disorder that currently has no cure. Identifying biochemical changes associated with neurodegeneration prior to symptom onset, will provide insight into the biological mechanisms associated with neurodegenerative processes, that may also aid in identifying potential drug targets. The current study therefore investigated associations between plasma neurofilament light chain (NF-L), a marker of neurodegeneration, with plasma metabolites that are products of various cellular processes. Plasma NF-L, measured by ultrasensitive Single molecule array (Simoa) technology (Quanterix) and plasma metabolites, measured by mass-spectrometry (AbsoluteIDQ® p400HR kit, BIOCRATES), were assessed in the Kerr Anglican Retirement Village Initiative in Ageing Health (KARVIAH) cohort comprising 100 cognitively normal older adults. Metabolites belonging to biogenic amine (creatinine, symmetric dimethylarginine, asymmetric dimethylarginine; ADMA, kynurenine, trans-4-hydroxyproline), amino acid (citrulline, proline, arginine, asparagine, phenylalanine, threonine) and acylcarnitine classes were observed to have positive correlations with plasma NF-L, suggesting a link between neurodegeneration and biological pathways associated with neurotransmitter regulation, nitric oxide homoeostasis, inflammation and mitochondrial function. Additionally, after stratifying participants based on low/high brain amyloid-ß load (Aß ±) assessed by positron emission tomography, while creatinine, SDMA and citrulline correlated with NF-L in both Aß- and Aß+ groups, ADMA, proline, arginine, asparagine, phenylalanine and acylcarnitine species correlated with NF-L only in the Aß+ group after adjusting for confounding variables, suggesting that the association of these metabolites with neurodegeneration may be relevant to AD-related neuropathology. Metabolites identified to be associated with plasma NF-L may have the potential to serve as prognostic markers for neurodegenerative diseases, however, further studies are required to validate the current findings in an independent cohort, both cross-sectionally and longitudinally.

Functions of p38 MAP Kinases in the Central Nervous System.

Mitogen-activated protein (MAP) kinases are a central component in signaling networks in a multitude of mammalian cell types. This review covers recent advances on specific functions of p38 MAP kinases in cells of the central nervous system. Unique and specific functions of the four mammalian p38 kinases are found in all major cell types in the brain. Mechanisms of p38 activation and downstream phosphorylation substrates in these different contexts are outlined and how they contribute to functions of p38 in physiological and under disease conditions. Results in different model organisms demonstrated that p38 kinases are involved in cognitive functions, including functions related to anxiety, addiction behavior, neurotoxicity, neurodegeneration, and decision making. Finally, the role of p38 kinases in psychiatric and neurological conditions and the current progress on therapeutic inhibitors targeting p38 kinases are covered and implicate p38 kinases in a multitude of CNS-related physiological and disease states.

Contribution of endogenous antibodies to learning deficits and astrocytosis in human P301S mutant tau transgenic mice.

Antibodies have been explored extensively as a potential therapeutic for Alzheimer's disease, where amyloid-ß (Aß) peptides and the tau protein deposit in patient brains. While the major focus of antibody-based therapy development was on Aß, arguably with limited success in clinical trials, targeting tau has become an emerging strategy, possibly extending therapies to dementias with isolated tau pathology. Interestingly, low titres of autoantibodies to pathological tau have been described in humans and transgenic mouse models, but their pathophysiological relevance remained elusive. Here, we used two independent approaches to deplete the B-cell lineage and hence antibody formation in human P301S mutant tau transgenic mice, TAU58/2. TAU58/2 mice were either crossed with the B-cell-deficient Ighm knockout line (muMT-/-) or treated with anti-CD20 antibodies that target B-cell precursors. In both models, B-cell depletion significantly reduced astrocytosis in TAU58/2 mice. Only when B-cells were absent throughout life, in TAU58/2.muMT-/- mice, were spatial learning deficits moderately aggravated while motor performance improved as compared to B-cell-competent TAU58/2 mice. This was associated with changes in brain region-specific tau solubility. No other relevant behavioural or neuropathological changes were observed in TAU58/2 mice in the absence of B-cells/antibodies. Taken together, our data suggests that the presence of antibodies throughout life contributes to astrocytosis in TAU58/2 mice and limits learning deficits, while other deficits and neuropathological changes appear to be independent of the presence of B-cells/antibodies.

Serum Hepcidin Levels in Cognitively Normal Older Adults with High Neocortical Amyloid-ß Load.

BACKGROUND/OBJECTIVE: Hepcidin, an iron-regulating hormone, suppresses the release of iron by binding to the iron exporter protein, ferroportin, resulting in intracellular iron accumulation. Given that iron dyshomeostasis has been observed in Alzheimer's disease (AD) together with elevated serum hepcidin levels, the current study examined whether elevated serum hepcidin levels are an early event in AD pathogenesis by measuring the hormone in cognitively normal older adults at risk of AD, based on high neocortical amyloid-ß load (NAL). METHODS: Serum hepcidin levels in cognitively normal participants (n = 100) aged between 65-90 years were measured using ELISA. To evaluate NAL, all participants underwent 18F-florbetaben positron emission tomography. A standard uptake value ratio (SUVR)<1.35 was classified as low NAL (n = 65) and ≥1.35 (n = 35) was classified as high NAL. RESULTS: Serum hepcidin was significantly higher in participants with high NAL compared to those with low NAL before and after adjusting for covariates: age, gender, and APOEɛ4 carriage (p < 0.05). A receiver operating characteristic curve based on a logistic regression of the same covariates, the base model, distinguished high from low NAL (area under the curve, AUC = 0.766), but was outperformed when serum hepcidin was added to the base model (AUC = 0.794) and further improved with plasma Aß42/40 ratio (AUC = 0.829). CONCLUSION: The present findings indicate that serum hepcidin is increased in individuals at risk for AD and contribute to the body of evidence supporting iron dyshomeostasis as an early event of AD. Further, hepcidin may add value to a panel of markers that contribute toward identifying individuals at risk of AD; however, further validation studies are required.

Plasma neurofilament light chain and amyloid-ß are associated with the kynurenine pathway metabolites in preclinical Alzheimer's disease.

BACKGROUND: Blood markers indicative of neurodegeneration (neurofilament light chain; NFL), Alzheimer's disease amyloid pathology (amyloid-ß; Aß), and neuroinflammation (kynurenine pathway; KP metabolites) have been investigated independently in neurodegenerative diseases. However, the association of these markers of neurodegeneration and AD pathology with neuroinflammation has not been investigated previously. Therefore, the current study examined whether NFL and Aß correlate with KP metabolites in elderly individuals to provide insight on the association between blood indicators of neurodegeneration and neuroinflammation. METHODS: Correlations between KP metabolites, measured using liquid chromatography and gas chromatography coupled with mass spectrometry, and plasma NFL and Aß concentrations, measured using single molecule array (Simoa) assays, were investigated in elderly individuals aged 65-90 years, with normal global cognition (Mini-Mental State Examination Score ≥ 26) from the Kerr Anglican Retirement Village Initiative in Ageing Health cohort. RESULTS: A positive correlation between NFL and the kynurenine to tryptophan ratio (K/T) reflecting indoleamine 2,3-dioxygenase activity was observed (r = .451, p < .0001). Positive correlations were also observed between NFL and kynurenine (r = .364, p < .0005), kynurenic acid (r = .384, p < .0001), 3-hydroxykynurenine (r = .246, p = .014), anthranilic acid (r = .311, p = .002), and quinolinic acid (r = .296, p = .003). Further, significant associations were observed between plasma Aß40 and the K/T (r = .375, p < .0005), kynurenine (r = .374, p < .0005), kynurenic acid (r = .352, p < .0005), anthranilic acid (r = .381, p < .0005), and quinolinic acid (r = .352, p < .0005). Significant associations were also observed between plasma Aß42 and the K/T ratio (r = .215, p = .034), kynurenic acid (r = .214, p = .035), anthranilic acid (r = .278, p = .006), and quinolinic acid (r = .224, p = .027) in the cohort. On stratifying participants based on their neocortical Aß load (NAL) status, NFL correlated with KP metabolites irrespective of NAL status; however, associations between plasma Aß and KP metabolites were only pronounced in individuals with high NAL while associations in individuals with low NAL were nearly absent. CONCLUSIONS: The current study shows that KP metabolite changes are associated with biomarker evidence of neurodegeneration. Additionally, the association between KP metabolites and plasma Aß seems to be NAL status dependent. Finally, the current study suggests that an association between neurodegeneration and neuroinflammation manifests in the periphery, suggesting that preventing cytoskeleton cytotoxicity by KP metabolites may have therapeutic potential.

Ultrasensitive Detection of Plasma Amyloid-ß as a Biomarker for Cognitively Normal Elderly Individuals at Risk of Alzheimer's Disease.

BACKGROUND: Aberrant amyloid-ß (Aß) deposition in the brain occurs two decades prior to the manifestation of Alzheimer's disease (AD) clinical symptoms and therefore brain Aß load measured using PET serves as a gold standard biomarker for the early diagnosis of AD. However, the uneconomical nature of PET makes blood markers, that reflect brain Aß deposition, attractive candidates for investigation as surrogate markers. OBJECTIVE: Investigation of plasma Aß as a surrogate marker for brain Aß deposition in cognitively normal elderly individuals. METHODS: Plasma Aß40 and Aß42 concentrations were measured using the ultrasensitive Single Molecule Array (Simoa) assay in 95 cognitively normal elderly individuals, who have all undergone PET to assess brain Aß deposition. Based on the standard uptake value ratios (SUVR) obtained from PET imaging, using the tracer 18F-Florbetaben, plasma Aß was compared between 32 participants assessed to have low brain Aß load (Aß-, SUVR <1.35) and 63 assessed to have high brain Aß load (Aß+, SUVR ≥1.35). RESULTS: Plasma Aß42/Aß40 ratios were lower in the Aß+ group compared to the Aß-group. Plasma Aß40 and Aß42 levels were not significantly different between Aß-and Aß+ groups, although a trend of higher plasma Aß40 was observed in the Aß+ group. Additionally, plasma Aß42/Aß40 ratios along with the known AD risk factors, age and APOEɛ4 status, resulted in Aß+ participants being distinguished from Aß-participants based on an area under the receiver operating characteristic curve shown to be 78%. CONCLUSION: Plasma Aß ratios in this study are a potential biomarker for brain Aß deposition and therefore, for preclinical AD. However, this method to measure plasma Aß needs further development to increase the accuracy of this promising AD blood biomarker.

Alterations in serum kynurenine pathway metabolites in individuals with high neocortical amyloid-ß load: A pilot study.

The kynurenine pathway (KP) is dysregulated in neuroinflammatory diseases including Alzheimer's disease (AD), however has not been investigated in preclinical AD characterized by high neocortical amyloid-ß load (NAL), prior to cognitive impairment. Serum KP metabolites were measured in the cognitively normal KARVIAH cohort. Participants, aged 65-90 y, were categorised into NAL+ (n = 35) and NAL- (n = 65) using a standard uptake value ratio cut-off = 1.35. Employing linear models adjusting for age and APOEε4, higher kynurenine and anthranilic acid (AA) in NAL+ versus NAL- participants were observed in females (kynurenine, p = 0.004; AA, p = 0.001) but not males (NALxGender, p = 0.001, 0.038, respectively). To evaluate the predictive potential of kynurenine or/and AA for NAL+ in females, logistic regressions with NAL+/- as outcome were carried out. After age and APOEε4 adjustment, kynurenine and AA were individually and jointly significant predictors (p = 0.007, 0.005, 0.0004, respectively). Areas under the receiver operating characteristic curves were 0.794 using age and APOEε4 as predictors, and 0.844, 0.866 and 0.871 when kynurenine, AA and both were added. Findings from the current study exhibit increased KP activation in NAL+ females and highlight the predictive potential of KP metabolites, AA and kynurenine, for NAL+. Additionally, the current study also provides insight into he influence of gender in AD pathogenesis.

Association of Plasma Neurofilament Light Chain with Neocortical Amyloid-ß Load and Cognitive Performance in Cognitively Normal Elderly Participants.

BACKGROUND: The disruption of neurofilament, an axonal cytoskeletal protein, in neurodegenerative conditions may result in neuronal damage and its release into the cerebrospinal fluid and blood. In Alzheimer's disease (AD), neurofilament light chain (NFL), a neurofilament subunit, is elevated in the cerebrospinal fluid and blood. OBJECTIVE: Investigate the association of plasma NFL with preclinical-AD features, such as high neocortical amyloid-ß load (NAL) and subjective memory complaints, and cognitive performance in cognitively normal older adults. METHODS: Plasma NFL concentrations were measured employing the single molecule array platform in participants from the Kerr Anglican Retirement Village Initiative in Ageing Health cohort, aged 65- 90 years. Participants underwent a battery of neuropsychological testing to evaluate cognitive performance and were categorized as low NAL (NAL-, n = 65) and high NAL (NAL+, n = 35) assessed via PET, and further stratified into subjective memory complainers (SMC; nNAL- = 51, nNAL+ = 25) and non-SMC (nNAL- = 14, nNAL+ = 10) based on the Memory Assessment Clinic- Questionnaire. RESULTS: Plasma NFL inversely correlated with cognitive performance. No significant difference in NFL was observed between NAL+ and NAL- participants; however, within APOEɛ4 non-carriers, higher NAL was observed in individuals with NFL concentrations within quartiles 3 and 4 (versus quartile 1). Additionally, within the NAL+ participants, SMC had a trend of higher NFL compared to non-SMC. CONCLUSION: Plasma NFL is inversely associated with cognitive performance in elderly individuals. While plasma NFL may not reflect NAL in individuals with normal global cognition, the current observations indicate that onset of axonal injury, reflected by increased plasma NFL, within the preclinical phase of AD may contribute to the pathogenesis of AD.

Alzheimer's Disease: A Journey from Amyloid Peptides and Oxidative Stress, to Biomarker Technologies and Disease Prevention Strategies-Gains from AIBL and DIAN Cohort Studies.

Worldwide there are over 46 million people living with dementia, and this number is expected to double every 20 years reaching about 131 million by 2050. The cost to the community and government health systems, as well as the stress on families and carers is incalculable. Over three decades of research into this disease have been undertaken by several research groups in Australia, including work by our original research group in Western Australia which was involved in the discovery and sequencing of the amyloid-ß peptide (also known as Aß or A4 peptide) extracted from cerebral amyloid plaques. This review discusses the journey from the discovery of the Aß peptide in Alzheimer's disease (AD) brain to the establishment of pre-clinical AD using PET amyloid tracers, a method now serving as the gold standard for developing peripheral diagnostic approaches in the blood and the eye. The latter developments for early diagnosis have been largely achieved through the establishment of the Australian Imaging Biomarker and Lifestyle research group that has followed 1,100 Australians for 11 years. AIBL has also been instrumental in providing insight into the role of the major genetic risk factor apolipoprotein E ɛ4, as well as better understanding the role of lifestyle factors particularly diet, physical activity and sleep to cognitive decline and the accumulation of cerebral Aß.

Selective Spatiotemporal Vulnerability of Central Nervous System Neurons to Pathologic TAR DNA-Binding Protein 43 in Aged Transgenic Mice.

Amyotrophic lateral sclerosis (ALS) is a rapidly progressing and fatal disease characterized by muscular atrophy because of loss of upper and lower motor neurons. Histopathologically, most patients with ALS have abnormal cytoplasmic accumulation and aggregation of the nuclear RNA-regulating protein TAR DNA-binding protein 43 (TDP-43). Pathogenic mutations in the TARDBP gene that encode TDP-43 have been identified in familial ALS. We have previously reported transgenic mice with neuronal expression of human TDP-43 carrying the pathogenic A315T mutation (iTDP-43A315T mice), presenting with early-onset motor deficits in adolescent animals. Here, we analyzed aged iTDP-43A315T mice, focusing on the spatiotemporal profile and progression of neurodegeneration in upper and lower motor neurons. Magnetic resonance imaging and histologic analysis revealed a differential loss of upper motor neurons in a hierarchical order as iTDP-43A315T mice aged. Furthermore, we report progressive gait problems, profound motor deficits, and muscle atrophy in aged iTDP-43A315T mice. Despite these deficits and TDP-43 pathologic disorders in lower motor neurons, stereological analysis did not show cell loss in spinal cords. Taken together, neuronal populations in aging iTDP-43A315T mice show differential susceptibility to the expression of human TDP-43A315T.

Multiple Mechanisms Linking Type 2 Diabetes and Alzheimer's Disease: Testosterone as a Modifier.

Evidence in support of links between type-2 diabetes mellitus (T2DM) and Alzheimer's disease (AD) has increased considerably in recent years. AD pathological hallmarks include the accumulation of extracellular amyloid-ß (Aß) and intracellular hyperphosphorylated tau in the brain, which are hypothesized to promote inflammation, oxidative stress, and neuronal loss. T2DM exhibits many AD pathological features, including reduced brain insulin uptake, lipid dysregulation, inflammation, oxidative stress, and depression; T2DM has also been shown to increase AD risk, and with increasing age, the prevalence of both conditions increases. In addition, amylin deposition in the pancreas is more common in AD than in normal aging, and although there is no significant increase in cerebral Aß deposition in T2DM, the extent of Aß accumulation in AD correlates with T2DM duration. Given these similarities and correlations, there may be common underlying mechanism(s) that predispose to both T2DM and AD. In other studies, an age-related gradual loss of testosterone and an increase in testosterone resistance has been shown in men; low testosterone levels can also occur in women. In this review, we focus on the evidence for low testosterone levels contributing to an increased risk of T2DM and AD, and the potential of testosterone treatment in reducing this risk in both men and women. However, such testosterone treatment may need to be long-term, and would need regular monitoring to maintain testosterone at physiological levels. It is possible that a combination of testosterone therapy together with a healthy lifestyle approach, including improved diet and exercise, may significantly reduce AD risk.

Alterations in erythrocyte fatty acid composition in preclinical Alzheimer's disease.

Brain and blood fatty acids (FA) are altered in Alzheimer's disease and cognitively impaired individuals, however, FA alterations in the preclinical phase, prior to cognitive impairment have not been investigated previously. The current study therefore evaluated erythrocyte FA in cognitively normal elderly participants aged 65-90 years via trans-methylation followed by gas chromatography. The neocortical beta-amyloid load (NAL) measured via positron emission tomography (PET) using ligand 18F-Florbetaben, was employed to categorise participants as low NAL (standard uptake value ratio; SUVR < 1.35, N = 65) and high NAL or preclinical AD (SUVR ≥ 1.35, N = 35) wherein, linear models were employed to compare FA compositions between the two groups. Increased arachidonic acid (AA, p < 0.05) and decreased docosapentaenoic acid (DPA, p < 0.05) were observed in high NAL. To differentiate low from high NAL, the area under the curve (AUC) generated from a 'base model' comprising age, gender, APOEε4 and education (AUC = 0.794) was outperformed by base model + AA:DPA (AUC = 0.836). Our findings suggest that specific alterations in erythrocyte FA composition occur very early in the disease pathogenic trajectory, prior to cognitive impairment. As erythrocyte FA levels are reflective of tissue FA, these alterations may provide insight into the pathogenic mechanism(s) of the disease and may highlight potential early diagnostic markers and therapeutic targets.

The Effects of Testosterone Supplementation on Cognitive Functioning in Older Men.

Reduction in testosterone levels in men during aging is associated with cognitive decline and risk of dementia. Animal studies have shown benefits for testosterone supplementation in improving cognition and reducing Alzheimer's disease pathology. In a randomized, placebo-controlled, crossover study of men with subjective memory complaint and low testosterone levels, we investigated whether testosterone treatment significantly improved performance on various measures of cognitive functioning. Forty-four men were administered a battery of neuropsychological tests to establish the baseline prior to being randomly divided into two groups. The first group (Group A) received 24 weeks of testosterone treatment (T treatment) followed by 4 weeks washout, and then 24 weeks of placebo (P); the second group (Group B) received the same treatments, in reverse order (Placebo, washout, and then T treatment). In group A (TèP), compared to baseline, there was a modest (1 point) but significant improvement in general cognitive functioning as measured by the Mini Mental State Examination (MMSE) following testosterone treatment. This improvement from baseline was sustained following the washout period and crossover to placebo treatment. Similar Mini Mental State Examination (MMSE) scores were observed when comparing testosterone treatment with placebo. In group B (PèT) a significant increase was observed from baseline following testosterone treatment and a trend towards an increase when compared to placebo treatment. Improvements in baseline depression scores (assessed by Geriatric Depression Scale) were observed following testosterone/placebo treatment in both groups, and no difference was observed when comparing testosterone with placebo treatment. Our findings indicate a modest improvement on global cognition with testosterone treatment. Larger clinical trials with a longer follow- up and with the inclusion of blood and brain imaging markers are now needed to conclusively determine the significance of testosterone treatment.