AMPA receptor translocation and phosphorylation are induced by transcranial direct current stimulation in rats.

Over the last decade, the interest in transcranial direct current stimulation (tDCS) has continued to increase, along with consideration of how it affects neuroplasticity mechanisms in the brain. Both human and animal studies have demonstrated numerous benefits and, although its application has increased, the neurophysiological mechanisms underlying tDCS' beneficial effects remain largely unknown. Recent studies have shown that long-term potentiation (LTP) increases following tDCS. In this work, we utilized a rodent model of tDCS to directly assess changes in the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor, a critical protein for enhancing synaptic transmission. Animals were subjected to 250 µA of direct current (DC) stimulation for 30 min with immediate tissue collection. Translocation and phosphorylation of AMPA receptors were examined using protein immunoblot analysis following a subcellular fractionation method. Our findings show that a single application of in vivo tDCS can affect both the translocation and phosphorylation of AMPA receptors in the hippocampus while increasing AMPA receptor phosphorylation in the hypothalamus. In the hippocampus, tDCS increased AMPA translocation to the synapse and increased the phosphorylation of the S831 site on GluA1. In the hypothalamus, no statistically significant changes were observed in AMPA translocation while an increase in the phosphorylation of the S831 site was observed. No changes in the phosphorylation of GluA1 at the S845 site were detected in either brain region. In sum, our findings identify specific AMPA receptor changes induced by tDCS, thereby providing further details on the mechanisms by which tDCS could affect the establishment of LTP and modulate neuroplasticity.

Safety parameter considerations of anodal transcranial Direct Current Stimulation in rats.

A commonly referenced transcranial Direct Current Stimulation (tDCS) safety threshold derives from tDCS lesion studies in the rat and relies on electrode current density (and related electrode charge density) to support clinical guidelines. Concerns about the role of polarity (e.g. anodal tDCS), sub-lesion threshold injury (e.g. neuroinflammatory processes), and role of electrode montage across rodent and human studies support further investigation into animal models of tDCS safety. Thirty-two anesthetized rats received anodal tDCS between 0 and 5mA for 60min through one of three epicranial electrode montages. Tissue damage was evaluated using hemotoxylin and eosin (H&E) staining, Iba-1 immunohistochemistry, and computational brain current density modeling. Brain lesion occurred after anodal tDCS at and above 0.5mA using a 25.0mm2 electrode (electrode current density: 20.0A/m2). Lesion initially occurred using smaller 10.6mm2 or 5.3mm2 electrodes at 0.25mA (23.5A/m2) and 0.5mA (94.2A/m2), respectively. Histological damage was correlated with computational brain current density predictions. Changes in microglial phenotype occurred in higher stimulation groups. Lesions were observed using anodal tDCS at an electrode current density of 20.0A/m2, which is below the previously reported safety threshold of 142.9A/m2 using cathodal tDCS. The lesion area is not simply predicted by electrode current density (and so not by charge density as duration was fixed); rather computational modeling suggests average brain current density as a better predictor for anodal tDCS. Nonetheless, under the assumption that rodent epicranial stimulation is a hypersensitive model, an electrode current density of 20.0A/m2 represents a conservative threshold for clinical tDCS, which typically uses an electrode current density of 2A/m2 when electrodes are placed on the skin (resulting in a lower brain current density).

Calorie restriction does not restore brain mitochondrial function in P301L tau mice, but it does decrease mitochondrial F0F1-ATPase activity.

Calorie restriction (CR) has been shown to increase lifespan and delay aging phenotypes in many diverse eukaryotic species. In mouse models of Alzheimer's disease (AD), CR has been shown to decrease amyloid-beta and hyperphosphorylated tau levels and preserve cognitive function. Overexpression of human mutant tau protein has been shown to induce deficits in mitochondrial electron transport chain complex I activity. Therefore, experiments were performed to determine the effects of 4-month CR on brain mitochondrial function in Tg4510 mice, which express human P301L tau. Expression of mutant tau led to decreased ADP-stimulated respiratory rates, but not uncoupler-stimulated respiratory rates. The membrane potential was also slightly higher in mitochondria from the P301L tau mice. As shown previously, tau expression decreased mitochondrial complex I activity. The decreased complex I activity, decreased ADP-stimulated respiratory rate, and increased mitochondrial membrane potential occurring in mitochondria from Tg4510 mice were not restored by CR. However, the CR diet did result in a genotype independent decrease in mitochondrial F0F1-ATPase activity. This decrease in F0F1-ATPase activity was not due to lowered levels of the alpha or beta subunits of F0F1-ATPase. The possible mechanisms through which CR reduces the F0F1-ATPase activity in brain mitochondria are discussed.

Amyloid oligomers exacerbate tau pathology in a mouse model of tauopathy.

BACKGROUND: We aimed to investigate the influence of oligomeric forms of ß-amyloid (Aß) and the influence of the duration of exposure on the development of tau phosphorylation. METHODS: Aß oligomers were injected intracranially either acutely into 5-month-old rTg4510 mice and tissue was collected 3 days later, or chronically into 3-month-old mice and tissue was collected 2 months later. Several forms of phosphorylated tau (p-tau), GSK3 (glycogen synthase kinase-3) and microglial and astrocyte activation were measured. RESULTS: Acute injections of Aß oligomers had no effect on p-tau epitopes but did result in elevation of phosphorylated/activated GSK3 (pGSK3). Chronic infusion of Aß oligomers into the right hippocampus resulted in 3- to 4-fold elevations in several p-tau isoforms with no changes in total tau levels. A significant elevation in pGSK3 accompanied these changes. Microglial staining with CD68 paralleled the increase in tau phosphorylation, however, CD45 staining was unaffected by Aß. Control experiments revealed that the infusion of Aß from the minipumps was largely complete by 10 days after implantation. Thus, the elevation in p-tau 2 months after implantation implies that the changes are quite persistent. CONCLUSION: Soluble Aß(1-42) oligomers have long-lasting effects on tau phosphorylation in the rTg4510 model, possibly due to elevations in GSK3. These data suggest that even brief elevations in Aß production, may have enduring impact on the risk for tauopathy.

Fasting and diurnal blood ketonemia and glycemia responses to a six-week, energy-controlled ketogenic diet, supplemented with racemic R/S-BHB salts.

BACKGROUND: Single doses of exogenous ketone salts (KS) transiently increase circulating beta-hydroxybutyrate (BHB) (∼1 mM; 1-2 h) regardless of starting levels of ketosis; however, no studies have explored how sustained use of KS influences measures of ketonemia and glycemia. OBJECTIVES: To determine the response to a hypocaloric, well-formulated ketogenic diet (KD), with and without the inclusion of two daily racemic KS doses (6 g R-BHB + 6 g S-BHB per serving) on 1) daily fasting capillary R-BHB and glucose (R-BHB/GLUfast), 2) bi-weekly 13 h diurnal BHB and glucose (R-BHB/GLUdiur), 3) three-hours post-KS ingestion kinetics (R-BHBKS), and 4) bi-weekly fasting plasma enantiomer-specific BHB (R/S-BHBplasma). METHODS: Non-diabetic adults with overweight and obesity were randomized to receive a precisely measured hypocaloric KD (∼75 %en of maintenance) for six weeks, supplemented twice-daily with KS or placebo (PL). A non-randomized comparison group was provided an isonitrogenous/isoenergetic low-fat diet (LFD). All meals were provided to subjects. Capillary blood was collected daily to measure R-BHB/GLUfast and hourly for R-BHB/GLUdiur. Plasma was collected to measure R/S-BHBplasma, insulin, fasting glucose, and insulin resistance (HOMA-IR). Total AUC was calculated using the trapezoidal method. RESULTS: Mean R-BHBfast increased significantly during KD + PL (1.0 mM BHB), an effect enhanced 26% during KD + KS. GLUfast AUC was -6% lower during KD + KS versus LFD. Mean R-BHBdiur increased 40% in KD + KS versus KD + PL, whereas GLUdiur decreased 13% during both KDs versus LFD. R-BHBKS peaked (Δ: ∼1 mM) 1 h after the morning KS dose, but not following the afternoon dose. Both R/S-BHBplasma increased during KD independent of KS inclusion. R-BHBplasma was 50-times greater compared to S-BHBplasma, and the KS augmented S-BHBplasma 50% more than PL. Fasting insulin and HOMA-IR decreased after 14 days independent of diet. CONCLUSIONS: A hypocaloric KD was effective at reducing diurnal glucose compared to a LFD independent of weight loss, but twice-daily racemic KS ingestion during KD augmented ketonemia, both as R- and S-BHB, and decreased mean fasting glucose beyond a KD alone. The hypoglycemic effects of KD in combination with exogenous ketones merit further investigation.

The effects of a 6-week controlled, hypocaloric ketogenic diet, with and without exogenous ketone salts, on cognitive performance and mood states in overweight and obese adults.

Background: Ketogenic diets are a commonly used weight loss method, but little is known how variations in sodium content and ketones influence cognition and mood during the early keto-adaptation period. Objectives: To investigate the effects of an exogenous ketone salt (KS) as part of a hypocaloric KD on mood and cognitive outcomes in overweight and obese adults. A secondary objective was to evaluate changes in biochemical markers associated with inflammatory and cognitive responses. Materials and methods: Adults who were overweight or obese participated in a 6-week controlled-feeding intervention comparing hypocaloric diets (∼75% of energy expenditure). KD groups received twice daily ketone salt (KD + KS; n = 12) or a flavor-matched placebo, free of minerals (KD + PL; n = 13). A separate group of age and BMI matched adults were later assigned to an isoenergetic low-fat diet (LFD; n = 12) as comparison to KD. Mood was assessed by shortened Profile of Mood States and Visual Analog Mood Scale surveys. Cognitive function was determined by the Automated Neuropsychological Assessment Metrics mental test battery. Results: Both KD groups achieved nutritional ketosis. Fasting serum glucose decreased in both KD groups, whereas glucose was unaffected in the LFD. Insulin decreased at week 2 and remained lower in all groups. At week 2, depression scores in the KD + PL group were higher compared to KD + KS. Performance in the math processing and go/no-go cognitive tests were lower for KD + PL and LFD participants, respectively, compared to KD + KS. Serum leptin levels decreased for all groups throughout the study but were higher for KD + KS group at week 6. Serum TNF-α steadily increased for LFD participants, reaching significance at week 6. Conclusion: During a short-term hypocaloric diet, no indication of a consistent decline in mood or cognitive function were seen in participants following either KD, despite KD + PL being relatively low in sodium. WK2 scores of "anger" and "depression" were higher in the LFD and KD + PL groups, suggesting that KS may attenuate negative mood parameters during the early intervention stages.

Accumulation of C-terminal cleaved tau is distinctly associated with cognitive deficits, synaptic plasticity impairment, and neurodegeneration in aged mice.

C-terminal cleaved tau at D421 (∆D421-tau) accumulates in the brains of Alzheimer's disease (AD) patients. However, it is unclear how tau truncation, an understudied tau post-translational modification, contributes to AD pathology and progression. Utilizing an adeno-associated virus (AAV) gene delivery-based approach, we overexpressed full-length tau (FL-tau) and ∆D421-tau in 4- and 12-month-old mice for 4 months to study the neuropathological impact of accumulation in young adult (8-month) and middle-aged (16-month) mice. Overall, we show that independent of the tau species, age was an important factor facilitating tau phosphorylation, oligomer formation, and deposition into silver-positive tangles. However, mice overexpressing ∆D421-tau exhibited a distinct phosphorylation profile to those overexpressing FL-tau and increased tau oligomerization in the middle-age group. Importantly, overexpression of ∆D421-tau, but not FL-tau in middle-aged mice, resulted in pronounced cognitive impairments and hippocampal long-term potentiation deficits. While both FL-tau and ∆D421-tau induced neuronal loss in mice with age, ∆D421-tau led to significant neuronal loss in the CA3 area of the hippocampus and medial entorhinal cortex compared to FL-tau. Based on our data, we conclude that age increases the susceptibility to neuronal degeneration associated with ΔD421-tau accumulation. Our findings suggest that ΔD421-tau accumulation contributes to synaptic plasticity and cognitive deficits, thus representing a potential target for tau-associated pathologies.

Arcuate nucleus of the hypothalamus contributes to the hypophagic effect and plasma metabolic changes induced by vasoactive intestinal peptide and pituitary adenylate cyclase-activating polypeptide.

The arcuate nucleus of hypothalamus (ARC) integrates circulating factors that signal energy status. The vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) are widely distributed in the periphery and central nervous systems (CNS) and play important roles on energy balance. The present study aimed to investigate the responses of microinjection of VIP and PACAP in the ARC on metabolic changes and food intake. In addition, the activity of neurons in the ARC following intracerebroventricular (ICV) microinjection of these peptides was also evaluated. Microinjection of VIP or PACAP in the ARC decreased fasting-induced hyperphagia and food intake, decreased total lipids, and increased free fatty acids plasma concentrations. VIP microinjection in the ARC induced hyperglycemia and decreased total cholesterol level; and PACAP reduced triglycerides concentration. ICV microinjection of VIP and PACAP enhanced neuronal activation in the ARC, associated with lower fasting-induced hyperphagia and plasma metabolic changes (only VIP). These results suggest that VIP and PACAP play important roles in ARC, inducing hypophagia and peripheral metabolic changes, as hyperglycemia, increased free fatty acids and decreased total lipids plasma levels.

Vasoactive intestinal peptide promotes hypophagia and metabolic changes: Role of paraventricular hypothalamic nucleus and nitric oxide.

Vasoactive intestinal peptide (VIP), a neuromodulator present in the hypothalamus, plays an important role in the regulation of food intake. Paraventricular nucleus of the hypothalamus (PVN) is involved in ingestive responses and regulates the nitric oxide (NO) pathway. The main objectives of this study were to investigate metabolic changes established after different doses and times of VIP microinjection on the PVN, and the effect of VIP microinjection on the PVN on food intake and the role of NO in this control. In anesthetized rats, increased blood plasma glucose and insulin levels were observed following the doses of 40 and 80 ng/g of body weight. At the dose of 40 ng/g, VIP promoted hyperglycemia and hyperinsulinemia 5, 10, and 30 min after microinjection, and increased free fatty acids and total lipids plasma levels after 5 min, and triglycerides after 10 min. In awake animals, once again, VIP administration increased plasmatic levels of glucose, free fatty acids, corticosterone, and insulin 10 min after the microinjection. Moreover, VIP promoted hypophagia in the morning and night periods, and L-arginine (L-Arg) and monosodium glutamate (MSG) or a combination of both attenuated VIP-induced reduction on food intake. In addition, nitrate concentration in the PVN was decreased after VIP microinjection. Our data show that the PVN participates in the anorexigenic and metabolic effects of VIP, and that VIP-induced hypophagia is likely mediated by reduction of NO.

The Effects of a 6-Week Controlled, Hypocaloric Ketogenic Diet, With and Without Exogenous Ketone Salts, on Body Composition Responses.

Background: Ketogenic diets (KDs) that elevate beta-hydroxybutyrate (BHB) promote weight and fat loss. Exogenous ketones, such as ketone salts (KS), also elevate BHB concentrations with the potential to protect against muscle loss during caloric restriction. Whether augmenting ketosis with KS impacts body composition responses to a well-formulated KD remains unknown. Purpose: To explore the effects of energy-matched, hypocaloric KD feeding (<50 g carbohydrates/day; 1.5 g/kg/day protein), with and without the inclusion of KS, on weight loss and body composition responses. Methods: Overweight and obese adults were provided a precisely defined hypocaloric KD (~75% of energy expenditure) for 6 weeks. In a double-blind manner, subjects were randomly assigned to receive ~24 g/day of a racemic BHB-salt (KD + KS; n = 12) or placebo (KD + PL; n = 13). A matched comparison group (n = 12) was separately assigned to an isoenergetic/isonitrogenous low-fat diet (LFD). Body composition parameters were assessed by dual x-ray absorptiometry and magnetic resonance imaging. Results: The KD induced nutritional ketosis (>1.0 mM capillary BHB) throughout the study (p < 0.001), with higher fasting concentrations observed in KD + KS than KD + PL for the first 2 weeks (p < 0.05). There were decreases in body mass, whole body fat and lean mass, mid-thigh muscle cross-sectional area, and both visceral and subcutaneous adipose tissues (p < 0.001), but no group differences between the two KDs or with the LFD. Urine nitrogen excretion was significantly higher in KD + PL than LFD (p < 0.01) and trended higher in KD + PL compared to KD + KS (p = 0.076), whereas the nitrogen excretion during KD + KS was similar to LFD (p > 0.05). Conclusion: Energy-matched hypocaloric ketogenic diets favorably affected body composition but were not further impacted by administration of an exogenous BHB-salt that augmented ketosis. The trend for less nitrogen loss with the BHB-salt, if manifested over a longer period of time, may contribute to preserved lean mass.

Divergence in Morris Water Maze-Based Cognitive Performance under Chronic Stress Is Associated with the Hippocampal Whole Transcriptomic Modification in Mice.

Individual susceptibility determines the magnitude of stress effects on cognitive function. The hippocampus, a brain region of memory consolidation, is vulnerable to stressful environments, and the impact of stress on hippocampus may determine individual variability in cognitive performance. Therefore, the purpose of this study was to define the relationship between the divergence in spatial memory performance under chronically unpredictable stress and an associated transcriptomic alternation in hippocampus, the brain region of spatial memory consolidation. Multiple strains of BXD (B6 × D2) recombinant inbred mice went through a 4-week chronic variable stress (CVS) paradigm, and the Morris water maze (MWM) test was conducted during the last week of CVS to assess hippocampal-dependent spatial memory performance and grouped animals into low and high performing groups based on the cognitive performance. Using hippocampal whole transcriptome RNA-sequencing data, differential expression, PANTHER analysis, WGCNA, Ingenuity's upstream regulator analysis in the Ingenuity Pathway Analysis® and phenotype association analysis were conducted. Our data identified multiple genes and pathways that were significantly associated with chronic stress-associated cognitive modification and the divergence in hippocampal dependent memory performance under chronic stress. Biological pathways associated with memory performance following chronic stress included metabolism, neurotransmitter and receptor regulation, immune response and cellular process. The Ingenuity's upstream regulator analysis identified 247 upstream transcriptional regulators from 16 different molecule types. Transcripts predictive of cognitive performance under high stress included genes that are associated with a high occurrence of Alzheimer's and cognitive impairments (e.g., Ncl, Eno1, Scn9a, Slc19a3, Ncstn, Fos, Eif4h, Copa, etc.). Our results show that the variable effects of chronic stress on the hippocampal transcriptome are related to the ability to complete the MWM task and that the modulations of specific pathways are indicative of hippocampal dependent memory performance. Thus, the divergence in spatial memory performance following chronic stress is related to the unique pattern of gene expression within the hippocampus.

Nutritional Ketosis Affects Metabolism and Behavior in Sprague-Dawley Rats in Both Control and Chronic Stress Environments.

Nutritional ketosis may enhance cerebral energy metabolism and has received increased interest as a way to improve or preserve performance and resilience. Most studies to date have focused on metabolic or neurological disorders while anecdotal evidence suggests that ketosis may enhance performance in the absence of underlying dysfunction. Moreover, decreased availability of glucose in the brain following stressful events is associated with impaired cognition, suggesting the need for more efficient energy sources. We tested the hypotheses that ketosis induced by endogenous or exogenous ketones could: (a) augment cognitive outcomes in healthy subjects; and (b) prevent stress-induced detriments in cognitive parameters. Adult, male, Sprague Dawley rats were used to investigate metabolic and behavioral outcomes in 3 dietary conditions: ketogenic (KD), ketone supplemented (KS), or NIH-31 control diet in both control or chronic stress conditions. Acute administration of exogenous ketones resulted in reduction in blood glucose and sustained ketosis. Chronic experiments showed that in control conditions, only KD resulted in pronounced metabolic alterations and improved performance in the novel object recognition test. The hypothalamic-pituitary-adrenal (HPA) axis response revealed that KD-fed rats maintained peripheral ketosis despite increases in glucose whereas no diet effects were observed in ACTH or CORT levels. Both KD and KS-fed rats decreased escape latencies on the third day of water maze, whereas only KD prevented stress-induced deficits on the last testing day and improved probe test performance. Stress-induced decrease in hippocampal levels of ß-hydroxybutyrate was attenuated in KD group while both KD and KS prevented stress effects on BDNF levels. Mitochondrial enzymes associated with ketogenesis were increased in both KD and KS hippocampal samples and both endothelial and neuronal glucose transporters were affected by stress but only in the control diet group. Our results highlight the complex relationship between peripheral metabolism, behavioral performance and biochemical changes in the hippocampus. Endogenous ketosis improved behavioral and metabolic parameters associated with energy metabolism and cognition while ketone supplementation replicated the biochemical effects within the hippocampus but only showed modest effects on behavioral improvements.

Metabolic changes over the course of aging in a mouse model of tau deposition.

Weight loss and food intake disturbances that often precede cognitive decline and diagnosis have been extensively reported in Alzheimer's disease patients. Previously, we observed that transgenic mice overexpressing tau seemed to eat more food yet weigh less than nontransgenic littermates. Thus, the present longitudinal study measured the time course of changes in metabolic state over the lifespan of the tau depositing Tg4510 mouse model of tau deposition. Although body weight was comparable to nontransgenic littermates at 2 months of age, Tg4510 mice weighed less at older ages. This was accompanied by the accumulation of tau pathology and by dramatically increased activity in all phases of the 24-hour cycle. Resting metabolic rate was also increased at 7 months of age. At 12 months near the end of the Tg4510 lifespan, there was a wasting phase, with a considerable decrease of resting metabolic rate, although hyperactivity was maintained. These diverse changes in metabolism in a mouse model of tau deposition are discussed in the context of known changes in energy metabolism in Alzheimer's disease.

Partial rescue of memory deficits induced by calorie restriction in a mouse model of tau deposition.

Calorie restriction (CR) was shown previously to improve cognition and decrease pathology in transgenic mouse models with Alzheimer-like amyloid deposition. In the present study, we investigated the effects of CR on the Tg4510 model of tau deposition. Mice in the calorie restriction group had food intake gradually decreased until they reached an average of 35% body weight reduction. Body weight and food intake were monitored throughout the study. After being on their respective diets for 3 months, all animals were submitted to behavioral testing. Tg4510 mice fed ad libitum showed lower body weight than nontransgenic littermates despite their increased food intake. Additionally, Tg4510 showed increased locomotor activity in the open field regardless of diet. Calorie restricted Tg4510 mice performed significantly better than ad libitum fed mice in the novel object recognition test, suggesting improved short-term memory. CR Tg4510 mice also performed significantly better in contextual fear conditioning than mice fed ad libitum. However, in a modified version of the novelty test that allows for interaction with other mice instead of inanimate objects, CR was not able to rescue the deficit found in Tg4510 mice in this ethologically more salient version of the task. No treatment differences in motor performance or spatial memory were observed in the rotarod or radial arm water maze tests, respectively. Histopathological and biochemical assessments showed no diet-induced changes in total or phospho-tau levels. Moreover, increased activation of both astrocytes and microglia in Tg4510 mice was not rescued by calorie restriction. Taken together, our data suggests that, despite an apparent rescue of associative memory, CR had no consistent effects on pathological outcomes of a mouse model of tau deposition.

Intraventricular human immunoglobulin distributes extensively but fails to modify amyloid in a mouse model of amyloid deposition.

Intravenous immunoglobulin infusions into Alzheimer patients have been found to provide cognitive benefit over a period of 6 mo in open label studies. One suggestion has been that these preparations contain small amounts of antibodies directed against monomeric and oligomeric Aß which underlie their effectiveness in patients. To test this hypothesis, we infused Gammagard, a version of intravenous immunoglobulin (IVIG), into the lateral ventricle of amyloid precursor protein (APP) transgenic mice with pre-existing amyloid deposits. Mice were infused over 4 weeks, and tested behaviorally for the last 2 weeks of treatment. Brains were analyzed for histopathology. We found widespread distribution of human-immunoglobulin G (h-IgG) staining in the mouse forebrain, including cerebral cortices and hippocampus. Some cortical neurons appeared to concentrate the h-IgG, but we did not detect evidence of amyloid plaque labeling by h-IgG. The IVIG-treated mice had no change in phenotype compared to saline-infused animals with respect to activity, learning and memory, or amyloid deposition. APP mice infused with an anti-Aß monoclonal antibody did show some reduction in amyloid deposits. These data do not support the argument that anti-Aß antibodies in IVIG preparations are responsible for cognitive benefits seen with these preparations.

Ketogenic diet improves motor performance but not cognition in two mouse models of Alzheimer's pathology.

Dietary manipulations are increasingly viewed as possible approaches to treating neurodegenerative diseases. Previous studies suggest that Alzheimer's disease (AD) patients present an energy imbalance with brain hypometabolism and mitochondrial deficits. Ketogenic diets (KDs), widely investigated in the treatment and prevention of seizures, have been suggested to bypass metabolic deficits present in AD brain by providing ketone bodies as an alternative fuel to neurons. We investigated the effects of a ketogenic diet in two transgenic mouse lines. Five months old APP/PS1 (a model of amyloid deposition) and Tg4510 (a model of tau deposition) mice were offered either a ketogenic or a control (NIH-31) diet for 3 months. Body weight and food intake were monitored throughout the experiment, and blood was collected at 4 weeks and 4 months for ketone and glucose assessments. Both lines of transgenic mice weighed less than nontransgenic mice, yet, surprisingly, had elevated food intake. The ketogenic diet did not affect these differences in body weight or food consumption. Behavioral testing during the last two weeks of treatment found that mice offered KD performed significantly better on the rotarod compared to mice on the control diet independent of genotype. In the open field test, both transgenic mouse lines presented increased locomotor activity compared to nontransgenic, age-matched controls, and this effect was not influenced by KD. The radial arm water maze identified learning deficits in both transgenic lines with no significant differences between diets. Tissue measures of amyloid, tau, astroglial and microglial markers in transgenic lines showed no differences between animals fed the control or the ketogenic diet. These data suggest that ketogenic diets may play an important role in enhancing motor performance in mice, but have minimal impact on the phenotype of murine models of amyloid or tau deposition.

Intracranial injection of AAV expressing NEP but not IDE reduces amyloid pathology in APP+PS1 transgenic mice.

The accumulation of ß-amyloid peptides in the brain has been recognized as an essential factor in Alzheimer's disease pathology. Several proteases, including Neprilysin (NEP), endothelin converting enzyme (ECE), and insulin degrading enzyme (IDE), have been shown to cleave ß-amyloid peptides (Aß). We have previously reported reductions in amyloid in APP+PS1 mice with increased expression of ECE. In this study we compared the vector-induced increased expression of NEP and IDE. We used recombinant adeno-associated viral vectors expressing either native forms of NEP (NEP-n) or IDE (IDE-n), or engineered secreted forms of NEP (NEP-s) or IDE (IDE-s). In a six-week study, immunohistochemistry staining for total Aß was significantly decreased in animals receiving the NEP-n and NEP-s but not for IDE-n or IDE-s in either the hippocampus or cortex. Congo red staining followed a similar trend revealing significant decreases in the hippocampus and the cortex for NEP-n and NEP-s treatment groups. Our results indicate that while rAAV-IDE does not have the same therapeutic potential as rAAV-NEP, rAAV-NEP-s and NEP-n are effective at reducing amyloid loads, and both of these vectors continue to have significant effects nine months post-injection. As such, they may be considered reasonable candidates for gene therapy trials in AD.

Fractalkine overexpression suppresses tau pathology in a mouse model of tauopathy.

Alzheimer's disease is characterized by amyloid plaques, neurofibrillary tangles, glial activation, and neurodegeneration. In mouse models, inflammatory activation of microglia accelerates tau pathology. The chemokine fractalkine serves as an endogenous neuronal modulator to quell microglial activation. Experiments with fractalkine receptor null mice suggest that fractalkine signaling diminishes tau pathology, but exacerbates amyloid pathology. Consistent with this outcome, we report here that soluble fractalkine overexpression using adeno-associated viral vectors significantly reduced tau pathology in the rTg4510 mouse model of tau deposition. Furthermore, this treatment reduced microglial activation and appeared to prevent neurodegeneration normally found in this model. However, in contrast to studies with fractalkine receptor null mice, parallel studies in an APP/PS1 model found no effect of increased fractalkine signaling on amyloid deposition. These data argue that agonism at fractalkine receptors might be an excellent target for therapeutic intervention in tauopathies, including those associated with amyloid deposition.