Aging is the primary risk factor for Parkinson's disease (PD), and PD-related cognitive impairment remains a major unmet biomedical challenge. Klotho, a pleiotropic protein, extends lifespan and enhances cognition, but whether it confers resilience to cognitive impairments in PD is unclear. Here, we show that in humans, the KL-VS genetic variant of KLOTHO, linked to higher circulating klotho levels, associated with better executive cognition in individuals with PD across two independent cohorts. To test causality and explore mechanisms, we turned to mouse models. Transgenic elevation of klotho in a mouse model increased lifespan, improved synaptic and cognitive, but not motor, functions in mice, and decreased steady-state α-synuclein (α-syn) levels in the brains of male mice expressing wild-type human α-syn. Complementary in vitro studies showed that klotho rescued α-syn-induced deficits in NMDAR-dependent signaling through GluN2B and augmented α-syn microglial-related uptake, suggesting a potential mechanism by which klotho counters PD-related toxicity. Together, these findings indicate that klotho can counteract cognitive deficits related to PD, possibly by modulating α-syn levels, and these findings may be relevant to new therapeutic pathways for PD.

Antisense oligonucleotide (ASO) therapy for neurological disease has been successful in clinical settings and its potential has generated hope for Alzheimer’s disease (AD). We previously described that ablating SNCA encoding for α-synuclein (αSyn) in a mouse model of AD was beneficial. Here, we sought to demonstrate whether transient reduction of αSyn expression using ASO SNCA could be therapeutic in a mouse model of AD. The efficacy of the ASO SNCA was measured via immunocytochemistry, RT-qPCR and western blotting. To assess spatial learning and memory, ASO SNCA or PBS-injected APP and non-transgenic (NTG) mice, and separate groups of SNCA -null mice, were tested on the Barnes circular maze. Hippocampal slice electrophysiology and transcriptomic profiling were used to explore synaptic function and differential gene expression between groups. Reduction of SNCA transcripts alleviated cognitive deficits in male transgenic animals, but surprisingly, not in females. To determine the functional cause of this differential effect, we assessed memory function in SNCA -null mice. Learning and memory were intact in male mice but impaired in female animals, revealing that the role of αSyn on cognitive function is sex-specific. Transcriptional analyses identified a differentially expressed gene network centered around EGR1 , a central modulator of learning and memory, in the hippocampi of SNCA -null mice. Thus, these novel results demonstrate that the function of αSyn on memory differs between male and female brains.

Background: Assessing learning and memory has become critical to evaluate brain function in health, aging or neurological disease. The hippocampus is crucially involved in these processes as illustrated by H.M.’s remarkable case and by the well-established early symptoms of Alzheimer’s disease. Numerous studies have reported the impact of gut microbiota on hippocampal structure and function using pro-, pre- and antibiotics, diet manipulations, germ-free conditions or fecal transfer. However, most diet manipulations have relied on Western diet paradigms (high fat, high energy, high carbohydrates). Here, we compared the impact of two standard diets, 5K52 and 2918 (6% fat, 18% protein, 3.1kcal/g), and how they influenced hippocampal learning and memory in adult 6-month-old congenic C57BL/6J mice from two sources. Results: Using a hippocampal-dependent task, we found that 5K52-fed mice performed consistently better than 2918-fed animals in the Barnes circular maze. These behavioral differences were accompanied with marked changes in microbiota, which correlated with spatial memory retention performance. We next tested whether 2918-induced alterations in behavior and microbiome could be rescued by 5K52 diet for 3 months. Changing the 2918 diet to 5K52 diet mid-life improved spatial learning and memory in mice. Shotgun sequencing and principal component analyses revealed significant differences at both phylum and species levels. Multivariate analyses identified Akkermansia muciniphila or Bacteroidales bacterium M11 and Faecalibaculum rodentium as the strongest correlates to spatial memory retention in mice depending on the animal source. In both settings, the observed behavioral differences only affected hippocampal-dependent performance as mice fed with either diet did similarly well on the non-spatial variant of the Y-maze. Conclusions: In summary, these findings demonstrate the diverging effects of seemingly equivalent standard diets on hippocampal memory. Based on these results, we strongly recommend the mandatory inclusion of the diet and source of animals used in rodent behavioral studies.

FIGURE 2. Characterization of SC-390752 Ab in WT and FFAR4-KO mice.(A) Western blot of fractionated forebrain tissue lysates from WT and FFAR4-KO mice, stained with anti-FFAR4 (SC-390752) and anti-actin.Arrowheads indicate the location

Recent evidence has emphasized soluble species of amyloid-beta (A beta) and tau as pathogenic effectors in Alzheimer's disease (AD). Despite the fact that A beta, tau, and alpha-synuclein (alpha Syn) can promote each other's aggregation, the potential contribution of soluble alpha Syn to AD pathogenesis is unknown. Here, we found an approximate twofold increase over controls in soluble alpha Syn levels in AD brains in the absence of Lewy body cytopathology. Importantly, soluble alpha Syn levels were a quantitatively stronger correlate of cognitive impairment than soluble A beta and tau levels. To examine a putative role for alpha Syn in modulating cognitive function, we used the Barnes circular maze to assess spatial reference memory in transgenic mice overexpressing human wild-type alpha Syn. The results revealed that an approximate threefold elevation of alpha Syn in vivo induced memory deficits similar to those observed in AD mouse models. The neurobiological changes associated with this elevation of soluble alpha Syn included decreases in selected synaptic vesicle proteins and an alteration of the protein composition of synaptic vesicles. Finally, a synergism between A beta/APP and human tau seems to be responsible for the abnormal elevation of soluble alpha Syn in transgenic mice. Altogether, our data reveal an unexpected role for soluble, intraneuronal alpha Syn in AD pathophysiology.

Protein misfolding and aggregation is observed in many amyloidogenic diseases affecting either the central nervous system or a variety of peripheral tissues. Structural and dynamic characterization of all species along the pathways from monomers to fibrils is challenging by experimental and computational means because they involve intrinsically disordered proteins in most diseases. Yet understanding how amyloid species become toxic is the challenge in developing a treatment for these diseases. Here we review what computer, in vitro, in vivo, and pharmacological experiments tell us about the accumulation and deposition of the oligomers of the (Aβ, tau), α-synuclein, IAPP, and superoxide dismutase 1 proteins, which have been the mainstream concept underlying Alzheimer's disease (AD), Parkinson's disease (PD), type II diabetes (T2D), and amyotrophic lateral sclerosis (ALS) research, respectively, for many years.

A central question in aging and Alzheimer’s disease (AD) is when and how neural substrates underlying decision-making are altered. Here we show that while APP mice, a commonly used mouse model of AD, were able to learn Restaurant Row, a complex neuroeconomic decision-making task, they were significantly impaired in procedural, habit-forming, aspects of cognition and relied heavily on deliberation when making decisions. Surprisingly, these behavioral changes are associated with amyloid-beta (Aβ) pathology and network remodeling in the striatum, a key brain region involved in procedural cognition. Furthermore, APP mice and control mice relied on distinct sex-specific strategies in this neuroeconomic task. These findings provide foundational pillars to examine how aging and age-related neurodegenerative diseases impact decision-making across sexes. They also highlight the need for complex behavioral tasks that allow for the dissociation of competing neurally-distinct decision-making circuits to get an accurate picture of changes in neurodegenerative models of human disease.

Aging is the primary risk factor for Parkinson’s disease (PD) and cognitive impairment from PD is a major and unmet biomedical challenge. Klotho, a pleiotropic protein, extends lifespan and enhances cognition. Whether longevity factors such as klotho can counteract PD-related mortality and deficits in mice or associate with resistance to PD in humans is unknown. Here we show that transgenic elevation of klotho increased lifespan, improved synaptic and cognitive, but not motor, functions in mice, and decreased steady state α-synuclein levels in the brains of mice that express wildtype human α-synuclein. In humans, a genetic variant of KLOTHO that increases circulating klotho levels associated with better executive cognition and less CSF abnormalities of α-synuclein in individuals with PD. Thus, klotho can counteract cognitive deficits related to PD, possibly modulating α-synuclein levels – and these findings may be relevant to new therapeutic pathways for human PD.

There is growing recognition in the field of neurodegenerative diseases that mixed proteinopathies are occurring at greater frequency than originally thought. This is particularly true for three amyloid proteins defining most of these neurological disorders, amyloid-beta (Aβ), tau, and alpha-synuclein (αSyn). The co-existence and often co-localization of aggregated forms of these proteins has led to the emergence of concepts positing molecular interactions and cross-seeding between Aβ, tau, and αSyn aggregates. Amongst this trio, αSyn has received particular attention in this context during recent years due to its ability to modulate Aβ and tau aggregation in vivo, to interact at a molecular level with Aβ and tau in vivo and to cross-seed tau in mice. Here we provide a comprehensive, critical, and accessible review about the expression, role and nature of endogenous soluble αSyn oligomers because of recent developments in the understanding of αSyn multimerization, misfolding, aggregation, cross-talk, spreading and cross-seeding in neurodegenerative disorders, including Parkinson's disease, dementia with Lewy bodies, multiple system atrophy, Alzheimer's disease, and Huntington's disease. We will also discuss our current understanding about the relative toxicity of endogenous αSyn oligomers in vivo and in vitro, and introduce potential opportunities to counter their deleterious effects.

Parkinson’s disease dementia (PDD) and dementia with Lewy bodies (DLB) are clinically and neuropathologically highly related α-synucleinopathies that collectively constitute the second leading cause of neurodegenerative dementias. Genetic and neuropathological studies directly implicate α-synuclein (αS) abnormalities in PDD and DLB pathogenesis. However, it is currently unknown how αS abnormalities contribute to memory loss, particularly since forebrain neuronal loss in PDD and DLB is less severe than in Alzheimer’s disease. Previously, we found that familial Parkinson’s disease-linked human mutant A53T αS causes aberrant localization of the microtubule-associated protein tau to postsynaptic spines in neurons, leading to postsynaptic deficits. Thus, we directly tested if the synaptic and memory deficits in a mouse model of α-synucleinopathy (TgA53T) are mediated by tau. TgA53T mice exhibit progressive memory deficits associated with postsynaptic deficits in the absence of obvious neuropathological and neurodegenerative changes in the hippocampus. Significantly, removal of endogenous mouse tau expression in TgA53T mice (TgA53T/mTau −/− ), achieved by mating TgA53T mice to mouse tau-knockout mice, completely ameliorates cognitive dysfunction and concurrent synaptic deficits without affecting αS expression or accumulation of selected toxic αS oligomers. Among the known tau-dependent effects, memory deficits in TgA53T mice were associated with hippocampal circuit remodeling linked to chronic network hyperexcitability. This remodeling was absent in TgA53T/mTau −/− mice, indicating that postsynaptic deficits, aberrant network hyperactivity, and memory deficits are mechanistically linked. Our results directly implicate tau as a mediator of specific human mutant A53T αS-mediated abnormalities related to deficits in hippocampal neurotransmission and suggest a mechanism for memory impairment that occurs as a consequence of synaptic dysfunction rather than synaptic or neuronal loss. We hypothesize that these initial synaptic deficits contribute to network hyperexcitability which, in turn, exacerbate cognitive dysfunction. Our results indicate that these synaptic changes present potential therapeutic targets for amelioration of memory deficits in α-synucleinopathies.

α-Synuclein (αSyn) histopathology defines several neurodegenerative disorders, including Parkinson's disease, Lewy body dementia, and Alzheimer's disease (AD). However, the functional link between soluble αSyn and disease etiology remains elusive, especially in AD. We, therefore, genetically targeted αSyn in APP transgenic mice modeling AD and mouse primary neurons. Our results demonstrate bidirectional modulation of behavioral deficits and pathophysiology by αSyn. Overexpression of human wild-type αSyn in APP animals markedly reduced amyloid deposition but, counter-intuitively, exacerbated deficits in spatial memory. It also increased extracellular amyloid-β oligomers (AβOs), αSyn oligomers, exacerbated tau conformational and phosphorylation variants associated with AD, and enhanced neuronal cell cycle re-entry (CCR), a frequent prelude to neuron death in AD. Conversely, ablation of the SNCA gene encoding for αSyn in APP mice improved memory retention in spite of increased plaque burden. Reminiscent of the effect of MAPT ablation in APP mice, SNCA deletion prevented premature mortality. Moreover, the absence of αSyn decreased extracellular AβOs, ameliorated CCR, and rescued postsynaptic marker deficits. In summary, this complementary, bidirectional genetic approach implicates αSyn as an essential mediator of key phenotypes in AD and offers new functional insight into αSyn pathophysiology.

Despite increasing appreciation that oligomeric amyloid-beta (A beta) may contribute to cognitive decline of Alzheimer disease, defining the most critical forms has been thwarted by the changeable nature of these aggregates and the varying methods used for detection. Herein, using a broad approach, we quantified A beta oligomers during the evolution of cognitive deficits in an aggressive model of A beta amyloidosis. Amyloid precursor protein/tetracycline transactivator mice underwent behavioral testing at 3, 6, 9, and 12 months of age to evaluate spatial learning and memory, followed by histologic assessment of amyloid burden and biochemical characterization of oligomeric A beta species. Transgenic mice displayed progressive impairments in acquisition and immediate recall of the trained platform location. Biochemical analysis of cortical extracts from behaviorally tested mice revealed distinct age-dependent patterns of accumulation in multiple oligomeric species. Dot blot analysis demonstrated that non fibrillar All oligomers were highly soluble and extracted into a fraction enriched for extracellular proteins, whereas prefibrillar species required high-detergent conditions to retrieve, consistent with membrane localization. Low-detergent extracts tested by 82E1 enzyme-linked immunosorbent assay confirmed the presence of bona fide All oligomers, whereas immunoprecipitation-Western blotting using high-detergent extracts revealed a variety of SDS-stable low-n species. These findings show that different A beta oligomers vary in solubility, consistent with distinct localization, and identify nonfibrillar A beta oligomer-positive aggregates as tracking most closely with cognitive decline in this model.

Significance Alzheimer’s disease (AD) is the most common form of dementia affecting an estimated 5.3 million Americans based on the 2015 Report of the Alzheimer Association. Our current understanding of the pathogenesis of AD suggests that soluble, nonfibrillar forms of amyloid proteins [e.g. amyloid-β, tau, and α-synuclein (αSyn)] may be responsible for impairing cognition and have therefore been advanced to be the most bioactive species in this brain disorder. We sought to determine the potential contribution of αSyn oligomers to AD-associated cognitive decline. We found that selective αSyn oligomers are elevated in AD brains and that genetically elevating oligomeric αSyn in an AD mouse model led to a selective decrease in presynaptic proteins and cognitive performance.

Oligomeric forms of amyloid-forming proteins are believed to be the principal initiating bioactive species in many neurodegenerative disorders, including Alzheimer's disease (AD). Amyloid-β (Aβ) oligomers are implicated in AD-associated phosphorylation and aggregation of the microtubule-associated protein tau. To investigate the specific molecular pathways activated by different assemblies, we isolated various forms of Aβ from Tg2576 mice, which are a model for AD. We found that Aβ*56, a 56-kDa oligomer that is detected before patients develop overt signs of AD, induced specific changes in neuronal signaling. In primary cortical neurons, Aβ*56 interacted with N-methyl-d-aspartate receptors (NMDARs), increased NMDAR-dependent Ca2+ influx, and consequently increased intracellular calcium concentrations and the activation of Ca2+-dependent calmodulin kinase IIα (CaMKIIα). In cultured neurons and in the brains of Tg2576 mice, activated CaMKIIα was associated with increased site-specific phosphorylation and missorting of tau, both of which are associated with AD pathology. In contrast, exposure of cultured primary cortical neurons to other oligomeric Aβ forms (dimers and trimers) did not trigger these effects. Our results indicate that distinct Aβ assemblies activate neuronal signaling pathways in a selective manner and that dissecting the molecular events caused by each oligomer may inform more effective therapeutic strategies.

Alzheimer's disease (AD) is a progressive dementia disorder characterized by synaptic degeneration and amyloid-beta (A beta) accumulation in the brain. Through whole-genome sequencing of 1345 individuals from 410 families with late-onset AD (LOAD), we identified three highly penetrant variants in PRKCA, the gene that encodes protein kinase C alpha (PKC alpha), in five of the families. All three variants linked with LOAD displayed increased catalytic activity relative to wild-type PKC alpha as assessed in live-cell imaging experiments using a genetically encoded PKC activity reporter. Deleting PRKCA in mice or adding PKC antagonists to mouse hippocampal slices infected with a virus expressing the Ab precursor CT100 revealed that PKC alpha was required for the reduced synaptic activity caused by A beta. InPRKCA(-/-) neurons expressing CT100, introduction of PKC alpha, but not PKC alpha lacking a PDZ interaction moiety, rescued synaptic depression, suggesting that a scaffolding interaction bringing PKC alpha to the synapse is required for itsmediation of the effects of A beta. Thus, enhanced PKC alpha activity may contribute to AD, possibly bymediating the actions of A beta on synapses. In contrast, reduced PKC alpha activity is implicated in cancer. Hence, these findings reinforce the importance of maintaining a careful balance in the activity of this enzyme.

Despite the demonstration that amyloid-beta (A beta) can trigger increased tau phosphorylation and neurofibrillary tangle (NFT) formation in vivo, the molecular link associating A beta and tau pathologies remains ill defined. Here, we observed that exposure of cultured primary neurons to A beta trimers isolated from brain tissue of subjects with Alzheimer's disease led to a specific conformational change of tau detected by the antibody Alz50. A similar association was supported by postmortem human brain analyses. To study the role of A beta trimers in vivo, we created a novel bigenic Tg-A beta + Tau mouse line by crossing Tg2576 (Tg-A beta) and rTg4510 (Tg-Tau) mice. Before neurodegeneration and amyloidosis, apparent A beta trimers were increased by similar to 2-fold in 3-month-old Tg-A beta and Tg-A beta +Tau mice compared with younger mice, whereas soluble monomeric A beta levels were unchanged. Under these conditions, the expression of soluble Alz50-tau conformers rose by similar to 2.2-fold in the forebrains of Tg-A beta +Tau mice compared with nontransgenic littermates. In parallel, APP accumulated intracellularly, suggestive of a putative dysfunction of anterograde axonal transport. We found that the protein abundance of the kinesin-1 light chain (KLC1) was reduced selectively in vivo and in vitro when soluble A beta trimers/Alz50-tau were present. Importantly, the reduction in KLC1 was prevented by the intraneuronal delivery of Alz50 antibodies. Collectively, our findings reveal that specific soluble conformers of A beta and tau cooperatively disrupt axonal transport independently from plaques and tangles. Finally, these results suggest that not all endogenous A beta oligomers trigger the same deleterious changes and that the role of each assembly should be considered separately.

PKCα variants in some patients with Alzheimer’s disease may mediate the pathological effects of amyloid-β.

Increasing evidence indicates that plaque-associated amyloid-β (Aβ) oligomers might be responsible for neuronal architecture changes occurring in the vicinity of amyloid deposits in Alzheimer's disease. However, the underlying mechanism regulating these changes remains unclear. Cellular prion protein (PrPC) has recently been proposed to act as a receptor for Aβ oligomers that mediates amyloid toxicity. We here investigate whether PrPCmediates oligomeric Aβ-induced cytopathology associated with amyloid plaques. To understand whether PrPC mediates plaque-associated neuronal architectural abnormalities, we stained dense-core Aβ plaques using thioflavin S and axonal structure using SMI-312, a monoclonal anti-neurofilament antibody, in brain sections of 12-month-old hAPP-J20 and hAPP-J20/PrP-null mice. Neuronal morphology analyses were performed to assess axonal curvature ratios and the numbers of dystrophic neurites per plaque. Using conformation-sensitive antibodies OC and A11, which recognize distinct structural epitopes of amyloid proteins, we performed co-immunoprecipitation assays on water-soluble brain extracts of hAPP-J20 mice to identify what class of brain-derived Aβ oligomers might bind to PrPC. Finally, unbiased stereology and non-denaturing immunoblotting were used to evaluate the consequence of Prnpgene ablation on amyloid burden and oligomeric Aβ levels in hAPP-J20 and hAPP-J20/PrP-null mice. Genetic ablation of PrPC ameliorated neuronal architecture abnormalities in the vicinity of plaques in hAPP-J20 mice. PrPC immunoprecipitated with Aβ oligomers immunoreactive to OC antibodies, known to recognize the in-register, parallel β-sheet structure of amyloid fibrils. In contrast, PrPC was not pulled down with A11-immunoreactive oligomers. Stereological analyses revealed that Prnp ablation reduced dense-core and 6E10-immunoreactive plaque loads by 28% and 37%, respectively. Genetic ablation of PrPCalso affected levels of Aβ oligomers but did not alter levels of amyloid precursor protein (APP) or APP processing. We found that PrPC interacts with OC-immunoreactive Aβ oligomers, but not with A11-positive oligomers, and mediates plaque-associated cytopathology. Overall, these results suggest that PrPC-mediated neurotoxicity is specific for a given class of Aβ oligomers.