TREM2 Overexpression has No Improvement on Neuropathology and Cognitive Impairment in Aging APPswe/PS1dE9 Mice

Previously, we showed that overexpression of triggering receptor expressed on myeloid cells 2 (TREM2), a microglia-specific immune receptor, in the brain of a middle-aged (7 months old) APPswe/PS1dE9 mice could ameliorate Alzheimer’s disease (AD)-related neuropathology by enhancement of microglial amyloid-β (Aβ) phagocytosis. Since AD is an age-related neurodegenerative disorder, it is critical to assess the efficacy of TREM2 overexpression in aging animals with an advanced disease stage. In vivo, we employed a lentiviral strategy to overexpress TREM2 in the brain of aging (18 months old) APPswe/PS1dE9 mice, and observed its efficacy on AD-related neuropathology and cognitive functions. Afterwards, we directly isolated microglia from middle-aged and aging APPswe/PS1dE9 mice and determined effects of TREM2 overexpression on microglial Aβ phagocytosis and Aβ-binding receptors expression in vitro. In aging APPswe/PS1dE9 mice, TREM2 overexpression has no beneficial effect on AD-related neuropathology and spatial cognitive functions. Of note, in vitro experiments showed a significant reduction of Aβ phagocytosis in microglia from aging APPswe/PS1dE9 mice, possibly attributing to the declined expression of Aβ-binding receptors. Meanwhile, this phagocytic deficit in microglia from aging APPswe/PS1dE9 mice cannot be rescued by TREM2 overexpression. Taken together, our study shows that TREM2 overexpression fails to provide neuroprotection in aging APPswe/PS1dE9 mice, possibly attributing to deficits in microglial Aβ phagocytosis at the late-stage of disease progression. These findings indicate that TREM2-mediated protection in AD is at least partially dependent on the reservation of microglial phagocytic functions, emphasizing the importance of early therapeutic interventions for this devastating disease.     

Rodent A beta modulates the solubility and distribution of amyloid deposits in transgenic mice

The amino acid sequence of amyloid precursor protein (APP) is highly conserved, and age-related A beta aggregates have been described in a variety of vertebrate animals, with the notable exception of mice and rats. Three amino acid substitutions distinguish mouse and human A beta that might contribute to their differing properties in vivo. To examine the amyloidogenic potential of mouse A beta, we studied several lines of transgenic mice overexpressing wild-type mouse amyloid precursor protein (moAPP) either alone or in conjunction with mutant PS1 (PS1dE9). Neither overexpression of moAPP alone nor co-expression with PS1dE9 caused mice to develop Alzheimer-type amyloid pathology by 24 months of age. We further tested whether mouse A beta could accelerate the deposition of human A beta by crossing the moAPP transgenic mice to a bigenic line expressing human APPswe with PS1dE9. The triple transgenic animals (moAPP x APPswe/PS1dE9) produced 20% more A beta but formed amyloid deposits no faster and to no greater extent than APPswe/PS1dE9 siblings. Instead, the additional mouse A beta increased the detergent solubility of accumulated amyloid and exacerbated amyloid deposition in the vasculature. These findings suggest that, although mouse A beta does not influence the rate of amyloid formation, the incorporation of A beta peptides with differing sequences alters the solubility and localization of the resulting aggregates.     

The Proteasome Function Reporter GFPu Accumulates in Young Brains of the APPswe/PS1dE9 Alzheimer’s Disease Mouse Model

Alzheimer’s disease (AD), the most common cause of dementia, is neuropathologically characterized by accumulation of insoluble fibrous inclusions in the brain in the form of intracellular neurofibrillary tangles and extracellular senile plaques. Perturbation of the ubiquitin-proteasome system (UPS) has long been considered an attractive hypothesis to explain the pathogenesis of AD. However, studies on UPS functionality with various methods and AD models have achieved non-conclusive results. To get further insight into UPS functionality in AD, we have crossed a well-documented APPswe/PS1dE9 AD mouse model with a UPS functionality reporter, GFPu, mouse expressing green fluorescence protein (GFP) fused to a constitutive degradation signal (CL-1) that facilitates its rapid turnover in conditions of a normal UPS. Our western blot results indicate that GFPu reporter protein was accumulated in the cortex and hippocampus, but not striatum in the APPswe/PS1dE9 AD mouse model at 4 weeks of age, which is confirmed by fluorescence microscopy and elevated levels of p53, an endogenous UPS substrate. In accordance with this, the levels of ubiquitinated proteins were elevated in the AD mouse model. These results suggest that UPS is either impaired or functionally insufficient in specific brain regions in the APPswe/PS1dE9 AD mouse model at a very young age, long before senile plaque formation and the onset of memory loss. These observations may shed new light on the pathogenesis of AD.     

Early memory deficits precede plaque deposition in APPswe/PS1dE9 mice: involvement of oxidative stress and cholinergic dysfunction

A large body of evidence has shown that cognitive deficits occur early, before amyloid plaque deposition, suggesting that soluble amyloid-β protein (Aβ) contributes to the development of early cognitive dysfunction in Alzheimer disease (AD). However, the underlying mechanism(s) through which soluble Aβ exerts its neurotoxicity responsible for cognitive dysfunction in the early stage of AD remains unclear so far. In this study, we used preplaque APPswe/PS1dE9 mice ages 2.5 and 3.5 months to examine alterations in cognitive function, oxidative stress, and cholinergic function. We found that only soluble Aβ, not insoluble Aβ, was detected in these preplaque APPswe/PS1dE9 mice. APPswe/PS1dE9 mice 2.5 months of age did not show any significant changes in the measures of cognitive function, oxidative stress, and cholinergic function, whereas 3.5-month-old APPswe/PS1dE9 mice exhibited spatial memory impairment in the Morris water maze, accompanied by significantly decreased acetylcholine (ACh), choline acetyltransferase (ChAT), superoxide dismutase (SOD), and glutathione peroxidase (GSH-px) as well as increased malondialdehyde (MDA) and protein carbonyls. In 3.5-month-old preplaque APPswe/PS1dE9 mice, correlational analyses revealed that the performance of impaired spatial memory was inversely correlated with soluble Aβ, MDA, and protein carbonyls, as well as being positively correlated with ACh, ChAT, SOD, and GSH-px; soluble Aβ level was inversely correlated with ACh, ChAT, SOD, and GSH-px, as well as being positively correlated with MDA and protein carbonyls; ACh level showed a significant positive correlation with ChAT, SOD, and GSH-px, as well as a significant inverse correlation with MDA and protein carbonyls. Collectively, this study provides direct evidence that increased oxidative damage and cholinergic dysfunction may be early pathological responses to soluble Aβ and involved in early memory deficits in the preplaque stage of AD. These findings suggest that early antioxidant therapy and improving cholinergic function may be a promising strategy to prevent or delay the onset and progression of AD.     

Mithramycin A Alleviates Cognitive Deficits and Reduces Neuropathology in a Transgenic Mouse Model of Alzheimer’s Disease

Increasing evidence has shown that specificity protein 1 (Sp1) is abnormally increased in the brains of subjects with Alzheimer’s disease (AD) and transgenic AD models. However, whether the Sp1 activation plays a critical role in the AD pathogenesis and selective inhibition of Sp1 activation may have a disease-modifying effect on the AD-like phenotypes remain elusive. In this study, we reported that Sp1 mRNA and protein expression were markedly increased in the brain of APPswe/PS1dE9 transgenic mice, whereas chronic administration of mithramycin A (MTM), a selective Sp1 inhibitor, potently inhibited Sp1 activation in the APPswe/PS1dE9 mice down to the levels of wild-type mice. Specifically, we found that MTM treatment resulted in a significant improvement of learning and memory deficits, a dramatic reduction in cerebral Aβ levels and plaque burden, a profound reduction in tau hyperphosphorylation, and a marked increase in synaptic marker in the APPswe/PS1dE9 mice. In addition, MTM treatment was powerfully effective in inhibiting amyloid precursor protein (APP) processing via suppressing APP, beta-site APP cleaving enzyme 1 (BACE1), and presenilin-1 (PS1) mRNA and protein expression to preclude Aβ production in the APPswe/PS1dE9 mice. Furthermore, MTM treatment strongly inhibited phosphorylated CDK5 and GSK3β signal pathways to reduce tau hyperphosphorylation in the APPswe/PS1dE9 mice. Collectively, our findings provide evidence that Sp1 activation may contribute to the AD pathogenesis and may serve as a novel therapeutic target in the treatment of AD. The present study highlights that selective Sp1 inhibitors may be considered as disease-modifying therapeutic agents for AD.     

初步探讨鸟嘌呤核苷、姜黄素对AD双转基因小鼠学习记忆的影响

目的通过Morris水迷宫检测学习记忆和记忆保持能力,判断鸟嘌呤核苷、姜黄素对4月龄APPswe/PS1dE9双转基因小鼠认知功能的影响。方法将3月龄APPswe/PS1dE9双转基因小鼠随机分为模型组、盐酸多奈哌齐组0.92 mg/(kg·d)、鸟嘌呤核苷组20 mg/(kg·d)、姜黄素组200 mg/(kg·d)、姜黄素200 mg/(kg·d)和鸟嘌呤核苷组20 mg/(kg·d),每组12只;并以同月龄野生型C57/BL6J小鼠作对照。每天给药1次,连续给药1个月。应用Morris水迷宫进行行为学检测。结果鸟嘌呤核苷、姜黄素对空间探索、定位航行障碍有改善作用,尤其以姜黄素组明显。结论鸟嘌呤核苷、姜黄素能改善APPswe/PS1dE9双转基因小鼠的早期出现的认知障碍。     

Long-term treadmill exercise improves spatial memory of male APPswe/PS1dE9 mice by regulation of BDNF expression and microglia activation

Increasing evidence suggests that physical activity could delay or attenuate the symptoms of Alzheimer''s disease (AD). But the underlying mechanisms are still not fully understood. To investigate the effect of long-term treadmill exercise on the spatial memory of AD mice and the possible role of β-amyloid, brain-derived neurotrophic factor (BDNF) and microglia in the effect, male APPswe/PS1dE9 AD mice aged 4 months were subjected to treadmill exercise for 5 months with 6 sessions per week and gradually increased load. A Morris water maze was used to evaluate the spatial memory. Expression levels of β-amyloid, BDNF and Iba-1 (a microglia marker) in brain tissue were detected by immunohistochemistry. Sedentary AD mice and wildtype C57BL/6J mice served as controls. The results showed that 5-month treadmill exercise significantly decreased the escape latencies (P < 0.01 on the 4th day) and improved the spatial memory of the AD mice in the water maze test. Meanwhile, treadmill exercise significantly increased the number of BDNF-positive cells and decreased the ratios of activated microglia in both the cerebral cortex and the hippocampus. However, treadmill exercise did not significantly alleviate the accumulation of β-amyloid in either the cerebral cortex or the hippocampus of the AD mice (P > 0.05). The study suggested that long-term treadmill exercise could improve the spatial memory of the male APPswe/PS1dE9 AD mice. The increase in BDNF-positive cells and decrease in activated microglia might underpin the beneficial effect.     

Effects of prenatal stress exposure on soluble Aβ and brain-derived neurotrophic factor signaling in male and female APPswe/PS1dE9 mice

Chronic stress and stress-related disorders, such as major depression (MD), have been shown to increase the risk for developing Alzheimer's disease (AD). Brain-derived neurotrophic factor (BDNF) has been postulated as a neurophysiological link between these illnesses. Our previous research has indicated that exposing the APPswe/PS1dE9 mouse model of AD to prenatal maternal stress (PS) induced a depressive-like phenotype, specifically in female mice. Considering the role of BDNF in depressive-like behavior and its interactions with amyloid-β (Aβ), our aim was to explore whether these mice would also exhibit alterations in soluble Aβ, mature BDNF (mBDNF), proBDNF, and the receptors TrkB and p75(NTR) in comparison to non-stressed animals. Our results demonstrate that female APPswe/PS1dE9 mice have higher levels of hippocampal proBDNF and soluble Aβ as compared to their male littermates. Additionally, a tendency was observed for PS to lower mBDNF protein levels in the hippocampus, but only in female mice, while receptor levels remained unaltered by sex or PS exposure. Given that female mice both have higher proBDNF and Aβ levels, these findings suggest an underlying role for BDNF signaling and Aβ production in the selective vulnerability of women for MD and AD development.     

Obesity and Hepatic Steatosis Are Associated with Elevated Serum Amyloid Beta in Metabolically Stressed APPswe/PS1dE9 Mice

Diabesity-associated metabolic stresses modulate the development of Alzheimer’s disease (AD). For further insights into the underlying mechanisms, we examine whether the genetic background of APPswe/PS1dE9 at the prodromal stage of AD affects peripheral metabolism in the context of diabesity. We characterized APPswe/PS1dE9 transgenic mice treated with a combination of high-fat diet with streptozotocin (HFSTZ) in the early stage of AD. HFSTZ-treated APPswe/PS1dE9 transgenic mice exhibited worse metabolic stresses related to diabesity, while serum β-amyloid levels were elevated and hepatic steatosis became apparent. Importantly, two-way analysis of variance shows a significant interaction between HFSTZ and genetic background of AD, indicating that APPswe/PS1dE9 transgenic mice are more vulnerable to HFSTZ treatment. In addition, body weight gain, high hepatic triglyceride, and hyperglycemia were positively associated with serum β-amyloid, as validated by Pearson’s correlation analysis. Our data suggests that the interplay between genetic background of AD and HFSTZ-induced metabolic stresses contributes to the development of obesity and hepatic steatosis. Alleviating metabolic stresses including dysglycemia, obesity, and hepatic steatosis could be critical to prevent peripheral β-amyloid accumulation at the early stage of AD.     

HDAC3 negatively regulates spatial memory in a mouse model of Alzheimer's disease

The accumulation and deposition of beta‐amyloid (Aβ) is a key neuropathological hallmark of Alzheimer's disease (AD). Histone deacetylases (HDACs) are promising therapeutic targets for the treatment of AD, while the specific HDAC isoforms associated with cognitive improvement are poorly understood. In this study, we investigate the role of HDAC3 in the pathogenesis of AD. Nuclear HDAC3 is significantly increased in the hippocampus of 6‐ and 9‐month‐old APPswe/PS1dE9 (APP/PS1) mice compared with that in age‐matched wild‐type C57BL/6 (B6) mice. Lentivirus ‐mediated inhibition or overexpression of HDAC3 was used in the hippocampus of APP/PS1 mice to investigate the role of HDAC3 in spatial memory, amyloid burden, dendritic spine density, glial activation and tau phosphorylation. Inhibition of HDAC3 in the hippocampus attenuates spatial memory deficits, as indicated in the Morris water maze test, and decreases amyloid plaque load and Aβ levels in the brains of APP/PS1 mice. Dendritic spine density is increased, while microglial activation is alleviated after HDAC3 inhibition in the hippocampus of 9‐month‐old APP/PS1 mice. Furthermore, HDAC3 overexpression in the hippocampus increases Aβ levels, activates microglia, and decreases dendritic spine density in 6‐month‐old APP/PS1 mice. In conclusion, our results indicate that HDAC3 negatively regulates spatial memory in APP/PS1 mice and HDAC3 inhibition might represent a potential therapy for the treatment of AD.     

Receptor-Associated Protein (RAP) Plays a Central Role in Modulating Aβ Deposition in APP/PS1 Transgenic Mice

Background

Receptor associated protein (RAP) functions in the endoplasmic reticulum (ER) to assist in the maturation of several membrane receptor proteins, including low density lipoprotein receptor-related protein (LRP) and lipoprotein receptor 11 (SorLA/LR11). Previous studies in cell and mouse model systems have demonstrated that these proteins play roles in the metabolism of the amyloid precursor protein (APP), including processes involved in the generation, catabolism and deposition of β-amyloid (Aβ) peptides.

Methodology/Principal Findings

Mice transgenic for mutant APPswe and mutant presenilin 1 (PS1dE9) were mated to mice with homozygous deletion of RAP. Unexpectedly, mice that were homozygous null for RAP and transgenic for APPswe/PS1dE9 showed high post-natal mortality, necessitating a shift in focus to examine the levels of amyloid deposition in APPswe/PS1dE9 that were hemizygous null for RAP. Immunoblot analysis confirmed 50% reductions in the levels of RAP with modest reductions in the levels of proteins dependent upon RAP for maturation [LRP trend towards a 20% reduction ; SorLA/LR11 statistically significant 15% reduction (p<0.05)]. Changes in the levels of these proteins in the brains of [APPswe/PS1dE9](+/−)/RAP(+/−) mice correlated with 30–40% increases in amyloid deposition by 9 months of age.

Conclusions/Significance

Partial reductions in the ER chaperone RAP enhance amyloid deposition in the APPswe/PS1dE9 model of Alzheimer amyloidosis. Partial reductions in RAP also affect the maturation of LRP and SorLA/LR11, which are each involved in several different aspects of APP processing and Aβ catabolism. Together, these findings suggest a central role for RAP in Alzheimer amyloidogenesis.     

Wnt‐induced activation of glucose metabolism mediates the in vivo neuroprotective roles of Wnt signaling in Alzheimer disease

Dysregulated Wnt signaling is linked to major neurodegenerative diseases, including Alzheimer disease (AD). In mouse models of AD, activation of the canonical Wnt signaling pathway improves learning/memory, but the mechanism for this remains unclear. The decline in brain function in AD patients correlates with reduced glucose utilization by neurons. Here, we test whether improvements in glucose metabolism mediate the neuroprotective effects of Wnt in AD mouse model. APPswe/PS1dE9 transgenic mice were used to model AD, Andrographolide or Lithium was used to activate Wnt signaling, and cytochalasin B was used to block glucose uptake. Cognitive function was assessed by novel object recognition and memory flexibility tests. Glucose uptake and the glycolytic rate were determined using radiotracer glucose. The activities of key enzymes of glycolysis such as hexokinase and phosphofructokinase, Adenosine triphosphate (ATP)/Adenosine diphosphate (ADP) levels and the pentose phosphate pathway and activity of glucose‐6 phosphate dehydrogenase were measured. Wnt activators significantly improved brain glucose utilization and cognitive performance in transgenic mice. Wnt signaling enhanced glucose metabolism by increasing the expression and/or activity of hexokinase, phosphofructokinase and AMP‐activated protein kinase. Inhibiting glucose uptake partially abolished the beneficial effects of Wnt signaling on learning/memory. Wnt activation also enhanced glucose metabolism in cortical and hippocampal neurons, as well as brain slices derived from APPswe/PS1E9 transgenic mice. Combined, these data provide evidence that the neuroprotective effects of Wnt signaling in AD mouse models result, at least in part, from Wnt‐mediated improvements in neuronal glucose metabolism.     

APPswe／PS1dE9／TAU三转基因阿尔兹海默病大鼠模型的建立

目的大鼠的大脑比小鼠更大,是研究神经系统的重要模型。建立APPswe／PS1dE9／TAU三转基因大鼠,发展能更全面表现人类阿尔兹海默病表型的动物模型。方法构建人PrP—hAPP695K595N／M596L、PrP-hPS1dE9和PDGF-TAU转基因表达载体,显微注射法制备转基因大鼠。PCR法鉴定转基因首建鼠及其子代基因型。Western blot检测转基因大鼠脑组织中人APP、PS1和TAU蛋白的表达。Morris水迷宫检测6月龄三转基因大鼠学习记忆能力改变。APP、PHF—TAU免疫组织化学染色观察三转基因大鼠脑组织APP及TAU的表达。结果得到1个同时高表达人APP、PS1和TAU三个基因的转基因大鼠品系。转基因大鼠6月龄已经出现显著的行为学改变：学习记忆能力下降,病理学改变表现为过度磷酸化TAU增多和神经元胞浆内AB表达异常增加。结论成功建立了APPswe／PS1dE9／TAU三转AD大鼠,可做为新一代工具动物模型用于基础医学和AD转化医学研究。     

Abnormal dendritic calcium activity and synaptic depotentiation occur early in a mouse model of Alzheimer’s disease

Background

Alzheimer’s disease (AD) is characterized by amyloid deposition, tangle formation as well as synapse loss. Synaptic abnormalities occur early in the pathogenesis of AD. Identifying early synaptic abnormalities and their underlying mechanisms is likely important for the prevention and treatment of AD.

Methods

We performed in vivo two-photon calcium imaging to examine the activities of somas, dendrites and dendritic spines of layer 2/3 pyramidal neurons in the primary motor cortex in the APPswe/PS1dE9 mouse model of AD and age-matched wild type control mice. We also performed calcium imaging to determine the effect of Aβ oligomers on dendritic calcium activity. In addition, structural and functional two-photon imaging were used to examine the link between abnormal dendritic calcium activity and changes in dendritic spine size in the AD mouse model.

Results

We found that somatic calcium activities of layer 2/3 neurons were significantly lower in the primary motor cortex of 3-month-old APPswe/PS1dE9 mice than in wild type mice during quiet resting, but not during running on a treadmill. Notably, a significantly larger fraction of apical dendrites of layer 2/3 pyramidal neurons showed calcium transients with abnormally long duration and high peak amplitudes during treadmill running in AD mice. Administration of Aβ oligomers into the brain of wild type mice also induced abnormal dendritic calcium transients during running. Furthermore, we found that the activity and size of dendritic spines were significantly reduced on dendritic branches with abnormally prolonged dendritic calcium transients in AD mice.

Conclusion

Our findings show that abnormal dendritic calcium transients and synaptic depotentiation occur before amyloid plaque formation in the motor cortex of the APPswe/PS1dE9 mouse model of AD. Dendritic calcium transients with abnormally long durations and high amplitudes could be induced by soluble Aβ oligomers and contribute to synaptic deficits in the early pathogenesis of AD.

     

Impairments of long‐term depression induction and motor coordination precede Aβ accumulation in the cerebellum of APPswe/PS1dE9 double transgenic mice

Alzheimer's disease (AD) is a neurodegenerative disorder that represents the most common type of dementia among elderly people. Amyloid beta (Aβ) peptides in extracellular Aβ plaques, produced from the amyloid precursor protein (APP) via sequential processing by β‐ and γ‐secretases, impair hippocampal synaptic plasticity, and cause cognitive dysfunction in AD patients. Here, we report that Aβ peptides also impair another form of synaptic plasticity; cerebellar long‐term depression (LTD). In the cerebellum of commonly used AD mouse model, APPswe/PS1dE9 mice, Aβ plaques were detected from 8 months and profound accumulation of Aβ plaques was observed at 18 months of age. Biochemical analysis revealed relatively high levels of APP protein and Aβ in the cerebellum of APPswe/PS1dE9 mice. At pre‐Aβ accumulation stage, LTD induction, and motor coordination are disturbed. These results indicate that soluble Aβ oligomers disturb LTD induction and cerebellar function in AD mouse model.

     

Loss of ferroportin induces memory impairment by promoting ferroptosis in Alzheimer’s disease

Iron homeostasis disturbance has been implicated in Alzheimer’s disease (AD), and excess iron exacerbates oxidative damage and cognitive defects. Ferroptosis is a nonapoptotic form of cell death dependent upon intracellular iron. However, the involvement of ferroptosis in the pathogenesis of AD remains elusive. Here, we report that ferroportin1 (Fpn), the only identified mammalian nonheme iron exporter, was downregulated in the brains of APPswe/PS1dE9 mice as an Alzheimer’s mouse model and Alzheimer’s patients. Genetic deletion of Fpn in principal neurons of the neocortex and hippocampus by breeding Fpn^fl/fl mice with NEX-Cre mice led to AD-like hippocampal atrophy and memory deficits. Interestingly, the canonical morphological and molecular characteristics of ferroptosis were observed in both Fpn^fl/fl/NEXcre and AD mice. Gene set enrichment analysis (GSEA) of ferroptosis-related RNA-seq data showed that the differentially expressed genes were highly enriched in gene sets associated with AD. Furthermore, administration of specific inhibitors of ferroptosis effectively reduced the neuronal death and memory impairments induced by Aβ aggregation in vitro and in vivo. In addition, restoring Fpn ameliorated ferroptosis and memory impairment in APPswe/PS1dE9 mice. Our study demonstrates the critical role of Fpn and ferroptosis in the progression of AD, thus provides promising therapeutic approaches for this disease.Subject terms: Neural ageing, Ageing     

Dietary energy substrates reverse early neuronal hyperactivity in a mouse model of Alzheimer's disease

Deficient energy metabolism and network hyperactivity are the early symptoms of Alzheimer's disease (AD). In this study, we show that administration of exogenous oxidative energy substrates (OES) corrects neuronal energy supply deficiency that reduces the amyloid‐beta‐induced abnormal neuronal activity in vitro and the epileptic phenotype in AD model in vivo. In vitro, acute application of protofibrillar amyloid‐β_1–42 (Aβ_1–42) induced aberrant network activity in wild‐type hippocampal slices that was underlain by depolarization of both the neuronal resting membrane potential and GABA‐mediated current reversal potential. Aβ_1–42 also impaired synaptic function and long‐term potentiation. These changes were paralleled by clear indications of impaired energy metabolism, as indicated by abnormal NAD(P)H signaling induced by network activity. However, when glucose was supplemented with OES pyruvate and 3‐beta‐hydroxybutyrate, Aβ_1–42 failed to induce detrimental changes in any of the above parameters. We administered the same OES as chronic supplementation to a standard diet to APPswe/PS1dE9 transgenic mice displaying AD‐related epilepsy phenotype. In the ex‐vivo slices, we found neuronal subpopulations with significantly depolarized resting and GABA‐mediated current reversal potentials, mirroring abnormalities we observed under acute Aβ_1‐42 application. Ex‐vivo cortex of transgenic mice fed with standard diet displayed signs of impaired energy metabolism, such as abnormal NAD(P)H signaling and strongly reduced tolerance to hypoglycemia. Transgenic mice also possessed brain glycogen levels twofold lower than those of wild‐type mice. However, none of the above neuronal and metabolic dysfunctions were observed in transgenic mice fed with the OES‐enriched diet. In vivo, dietary OES supplementation abated neuronal hyperexcitability, as the frequency of both epileptiform discharges and spikes was strongly decreased in the APPswe/PS1dE9 mice placed on the diet. Altogether, our results suggest that early AD‐related neuronal malfunctions underlying hyperexcitability and energy metabolism deficiency can be prevented by dietary supplementation with native energy substrates.     

Specific Serotonergic Denervation Affects tau Pathology and Cognition without Altering Senile Plaques Deposition in APP/PS1 Mice

Senile plaques and neurofibrillary tangles are major neuropathological features of Alzheimer''s Disease (AD), however neuronal loss is the alteration that best correlates with cognitive impairment in AD patients. Underlying neurotoxic mechanisms are not completely understood although specific neurotransmission deficiencies have been observed in AD patients and, in animal models, cholinergic and noradrenergic denervation may increase amyloid-beta deposition and tau phosphorylation in denervated areas. On the other hand brainstem neurodegeneration has been suggested as an initial event in AD, and serotonergic dysfunction, as well as reductions in raphe neurones density, have been reported in AD patients. In this study we addressed whether specific serotonergic denervation, by administering 5,7-dihydroxitriptamine (5,7-DHT) in the raphe nuclei, could also worsen central pathology in APPswe/PS1dE9 mice or interfere with learning and memory activities. In our hands specific serotonergic denervation increased tau phosphorylation in denervated cortex, without affecting amyloid-beta (Aβ) pathology. We also observed that APPswe/PS1dE9 mice lesioned with 5,7-DHT were impaired in the Morris water maze test, supporting a synergistic effect of the serotonergic denervation and the presence of APP/PS1 transgenes on learning and memory impairment. Altogether our data suggest that serotonergic denervation may interfere with some pathological aspects observed in AD, including tau phosphorylation or cognitive impairment, without affecting Aβ pathology, supporting a differential role of specific neurotransmitter systems in AD.     

Increased Aβ production prompts the onset of glucose intolerance and insulin resistance

Type 2 diabetes (T2D) mellitus and Alzheimer's disease (AD) are two prevalent diseases with comparable pathophysiological features and genetic predisposition. Patients with AD are more susceptible to develop T2D. However, the molecular mechanism linking AD and T2D remains elusive. In this study, we have generated a new mouse model to test the hypothesis that AD would prompt the onset of T2D in mice. To test our hypothesis, we crossed Alzheimer APPswe/PS1dE9 (APP/PS1) transgenic mice with mice partially deficient in leptin signaling (db/+). Body weight, plasma glucose, and insulin levels were monitored. Phenotypic characterization of glucose metabolism was performed using glucose and insulin tolerance tests. β-Cell mass, islet volume, and islet number were analyzed by histomorphometry. APP/PS1 coexpression in mice with intact leptin receptor signaling did not show any metabolic perturbations in glucose metabolism or insulin sensitivity. In contrast, APP/PS1 coexpression in db/+ mice resulted in nonfasting hyperglycemia, hyperinsulinemia, and hypercholesterolemia without changes in body weight. Conversely, fasting blood glucose and cholesterol levels remained unchanged. Coinciding with altered glucose metabolism, APP/PS1 coexpression in db/+ mice resulted in glucose intolerance, insulin resistance, and impaired insulin signaling. In addition, histomorphometric analysis of pancreata revealed augmented β-cell mass. Taken together, these findings provide experimental evidence to support the notion that aberrant Aβ production might be a mechanistic link underlying the pathology of insulin resistance and T2D in AD.