Reduced serotonergic transmission alters sensitivity to cost and reward via 5-HT1A and 5-HT1B receptors in monkeys.

Serotonin (5-HT) deficiency is a core biological pathology underlying depression and other psychiatric disorders whose key symptoms include decreased motivation. However, the exact role of 5-HT in motivation remains controversial and elusive. Here, we pharmacologically manipulated the 5-HT system in macaque monkeys and quantified the effects on motivation for goal-directed actions in terms of incentives and costs. Reversible inhibition of 5-HT synthesis increased errors and reaction times on goal-directed tasks, indicating reduced motivation. Analysis found incentive-dependent and cost-dependent components of this reduction. To identify the receptor subtypes that mediate cost and incentive, we systemically administered antagonists specific to 4 major 5-HT receptor subtypes: 5-HT1A, 5-HT1B, 5-HT2A, and 5-HT4. Positron emission tomography (PET) visualized the unique distribution of each subtype in limbic brain regions and determined the systemic dosage for antagonists that would achieve approximately 30% occupancy. Only blockade of 5-HT1A decreased motivation through changes in both expected cost and incentive; sensitivity to future workload and time delay to reward increased (cost) and reward value decreased (incentive). Blocking the 5-HT1B receptor also reduced motivation through decreased incentive, although it did not affect expected cost. These results suggest that 5-HT deficiency disrupts 2 processes, the subjective valuation of costs and rewards, via 5-HT1A and 5-HT1B receptors, thus leading to reduced motivation.

Multimodal Imaging for Validation and Optimization of Ion Channel-Based Chemogenetics in Nonhuman Primates.

Chemogenetic tools provide an opportunity to manipulate neuronal activity and behavior selectively and repeatedly in nonhuman primates (NHPs) with minimal invasiveness. Designer Receptors Exclusively Activated by Designer Drugs (DREADDs) are one example that is based on mutated muscarinic acetylcholine receptors. Another channel-based chemogenetic system available for neuronal modulation in NHPs uses pharmacologically selective actuator modules (PSAMs), which are selectively activated by pharmacologically selective effector molecules (PSEMs). To facilitate the use of the PSAM/PSEM system, the selection and dosage of PSEMs should be validated and optimized for NHPs. To this end, we used a multimodal imaging approach. We virally expressed excitatory PSAM (PSAM4-5HT3) in the striatum and the primary motor cortex (M1) of two male macaque monkeys, and visualized its location through positron emission tomography (PET) with the reporter ligand [18F]ASEM. Chemogenetic excitability of neurons triggered by two PSEMs (uPSEM817 and uPSEM792) was evaluated using [18F]fluorodeoxyglucose-PET imaging, with uPSEM817 being more efficient than uPSEM792. Pharmacological magnetic resonance imaging (phMRI) showed that increased brain activity in the PSAM4-expressing region began ∼13 min after uPSEM817 administration and continued for at least 60 min. Our multimodal imaging data provide valuable information regarding the manipulation of neuronal activity using the PSAM/PSEM system in NHPs, facilitating future applications.SIGNIFICANCE STATEMENT Like other chemogenetic tools, the ion channel-based system called pharmacologically selective actuator module/pharmacologically selective effector molecule (PSAM/PSEM) allows remote manipulation of neuronal activity and behavior in living animals. Nevertheless, its application in nonhuman primates (NHPs) is still limited. Here, we used multitracer positron emission tomography (PET) imaging and pharmacological magnetic resonance imaging (phMRI) to visualize an excitatory chemogenetic ion channel (PSAM4-5HT3) and validate its chemometric function in macaque monkeys. Our results provide the optimal agonist, dose, and timing for chemogenetic neuronal manipulation, facilitating the use of the PSAM/PSEM system and expanding the flexibility and reliability of circuit manipulation in NHPs in a variety of situations.

Photo-oxygenation of histidine residue inhibits α-synuclein aggregation.

Aggregation of α-synuclein (α-syn) into amyloid is the pathological hallmark of several neurodegenerative disorders, including Parkinson disease, dementia with Lewy bodies, and multiple system atrophy. It is widely accepted that α-syn aggregation is associated with neurodegeneration, although the mechanisms are not yet fully understood. Therefore, the inhibition of α-syn aggregation is a potential therapeutic approach against these diseases. This study used the photocatalyst for α-syn photo-oxygenation, which selectively adds oxygen atoms to fibrils. Our findings demonstrate that photo-oxygenation using this photocatalyst successfully inhibits α-syn aggregation, particularly by reducing its seeding ability. Notably, we also discovered that photo-oxygenation of the histidine at the 50th residue in α-syn aggregates is responsible for the inhibitory effect. These findings indicate that photo-oxygenation of the histidine residue in α-syn is a potential therapeutic strategy for synucleinopathies.

D1- and D2-like receptors differentially mediate the effects of dopaminergic transmission on cost-benefit evaluation and motivation in monkeys.

It has been widely accepted that dopamine (DA) plays a major role in motivation, yet the specific contribution of DA signaling at D1-like receptor (D1R) and D2-like receptor (D2R) to cost-benefit trade-off remains unclear. Here, by combining pharmacological manipulation of DA receptors (DARs) and positron emission tomography (PET) imaging, we assessed the relationship between the degree of D1R/D2R blockade and changes in benefit- and cost-based motivation for goal-directed behavior of macaque monkeys. We found that the degree of blockade of either D1R or D2R was associated with a reduction of the positive impact of reward amount and increasing delay discounting. Workload discounting was selectively increased by D2R antagonism. In addition, blocking both D1R and D2R had a synergistic effect on delay discounting but an antagonist effect on workload discounting. These results provide fundamental insight into the distinct mechanisms of DA action in the regulation of the benefit- and cost-based motivation, which have important implications for motivational alterations in both neurological and psychiatric disorders.

Chronic Behavioral Manipulation via Orally Delivered Chemogenetic Actuator in Macaques.

The chemogenetic technology referred to as designer receptors exclusively activated by designer drugs (DREADDs) offers reversible means to control neuronal activity for investigating its functional correlation with behavioral action. Deschloroclozapine (DCZ), a recently developed highly potent and selective DREADD actuator, displays a capacity to expand the utility of DREADDs for chronic manipulation without side effects in nonhuman primates, which has not yet been validated. Here we investigated the pharmacokinetics and behavioral effects of orally administered DCZ in female and male macaque monkeys. Pharmacokinetic analysis and PET occupancy examination demonstrated that oral administration of DCZ yielded slower and prolonged kinetics, and that its bioavailability was 10%-20% of that in the case of systemic injection. Oral DCZ (300-1000 µg/kg) induced significant working memory impairments for at least 4 h in monkeys with hM4Di expressed in the dorsolateral prefrontal cortex (Brodmann's area 46). Repeated daily oral doses of DCZ consistently caused similar impairments over two weeks without discernible desensitization. Our results indicate that orally delivered DCZ affords a less invasive strategy for chronic but reversible chemogenetic manipulation of neuronal activity in nonhuman primates, and this has potential for clinical application.SIGNIFICANCE STATEMENT The use of designer receptors exclusively activated by designer drugs (DREADDs) for chronic manipulation of neuronal activity for days to weeks may be feasible for investigating brain functions and behavior on a long time-scale, and thereby for developing therapeutics for brain disorders, such as epilepsy. Here we performed pharmacokinetics and in vivo occupancy study of orally administered deschloroclozapine to determine a dose range suitable for DREADDs studies. In monkeys expressing hM4Di in the prefrontal cortex, single and repeated daily doses significantly induced working-memory impairments for hours and over two weeks, respectively, without discernible desensitization. These results indicate that orally delivered deschloroclozapine produces long-term stable chemogenetic effects, and holds great promise for the translational use of DREADDs technology.

Chemogenetic Disconnection between the Orbitofrontal Cortex and the Rostromedial Caudate Nucleus Disrupts Motivational Control of Goal-Directed Action.

The orbitofrontal cortex (OFC) and its major downstream target within the basal ganglia-the rostromedial caudate nucleus (rmCD)-are involved in reward-value processing and goal-directed behavior. However, a causal contribution of the pathway linking these two structures to goal-directed behavior has not been established. Using the chemogenetic technology of designer receptors exclusively activated by designer drugs with a crossed inactivation design, we functionally and reversibly disrupted interactions between the OFC and rmCD in two male macaque monkeys. We injected an adeno-associated virus vector expressing an inhibitory designer receptor, hM4Di, into the OFC and contralateral rmCD, the expression of which was visualized in vivo by positron emission tomography and confirmed by postmortem immunohistochemistry. Functional disconnection of the OFC and rmCD resulted in a significant and reproducible loss of sensitivity to the cued reward value for goal-directed action. This decreased sensitivity was most prominent when monkeys had accumulated a certain amount of reward. These results provide causal evidence that the interaction between the OFC and the rmCD is needed for motivational control of action on the basis of the relative reward value and internal drive. This finding extends the current understanding of the physiological basis of psychiatric disorders in which goal-directed behavior is affected, such as obsessive-compulsive disorder.SIGNIFICANCE STATEMENT In daily life, we routinely adjust the speed and accuracy of our actions on the basis of the value of expected reward. Abnormalities in these kinds of motivational adjustments might be related to behaviors seen in psychiatric disorders such as obsessive-compulsive disorder. In the current study, we show that the connection from the orbitofrontal cortex to the rostromedial caudate nucleus is essential for motivational control of action in monkeys. This finding expands our knowledge about how the primate brain controls motivation and behavior and provides a particular insight into disorders like obsessive-compulsive disorder in which altered connectivity between the orbitofrontal cortex and the striatum has been implicated.

GPR120 signaling controls amyloid-ß degrading activity of matrix metalloproteinases.

Alzheimer disease (AD) is characterized by the extensive deposition of amyloid-ß peptide (Aß) in the brain. Brain Aß level is regulated by a balance between Aß production and clearance. The clearance rate of Aß is decreased in the brains of sporadic AD patients, indicating that the dysregulation of Aß clearance mechanisms affects the pathological process of AD. Astrocytes are among the most abundant cells in the brain and are implicated in the clearance of brain Aß via their regulation of the blood-brain barrier, glymphatic system, and proteolytic degradation. The cellular morphology and activity of astrocytes are modulated by several molecules, including ω3 polyunsaturated fatty acids, such as docosahexaenoic acid, which is one of the most abundant lipids in the brain, via the G protein-coupled receptor GPR120/FFAR4. In this study, we analyzed the role of GPR120 signaling in the Aß-degrading activity of astrocytes. Treatment with the selective antagonist upregulated the matrix metalloproteinase (MMP) inhibitor-sensitive Aß-degrading activity in primary astrocytes. Moreover, the inhibition of GPR120 signaling increased the levels of Mmp2 and Mmp14 mRNAs, and decreased the expression levels of tissue inhibitor of metalloproteinases 3 (Timp3) and Timp4, suggesting that GPR120 negatively regulates the astrocyte-derived MMP network. Finally, the intracerebral injection of GPR120 specific antagonist substantially decreased the levels of Tris-buffered saline-soluble Aß in male AD model mice, and this effect was canceled by the coinjection of an MMP inhibitor. These data indicate that astrocytic GPR120 signaling negatively regulates the Aß degrading activity of MMPs.SIGNIFICANT STATEMENTThe level of amyloid ß (Aß) in the brain is a crucial determinant of the development of Alzheimer disease. Here we found that astrocytes, which are the most abundant cell type in the central nervous system, harbors degrading activity against amyloid ß, which is regulated by GPR120 signaling. GPR120 is involved in the inflammatory response and obesity in peripheral organs. However, the pathophysiological role of GPR120 in Alzheimer disease remains unknown. We found that selective inhibition of GPR120 signaling in astrocytes increased the Aß-degrading activity of matrix metalloproteases. Our results suggest that GPR120 in astrocytes is a novel therapeutic target for the development of anti-Aß therapeutics.

Photo-oxygenation by a biocompatible catalyst reduces amyloid-ß levels in Alzheimer's disease mice.

Amyloid formation and the deposition of the amyloid-ß peptide are hallmarks of Alzheimer's disease pathogenesis. Immunotherapies using anti-amyloid-ß antibodies have been highlighted as a promising approach for the prevention and treatment of Alzheimer's disease by enhancing microglial clearance of amyloid-ß peptide. However, the efficiency of antibody delivery into the brain is limited, and therefore an alternative strategy to facilitate the clearance of brain amyloid is needed. We previously developed an artificial photo-oxygenation system using a low molecular weight catalytic compound. The photocatalyst specifically attached oxygen atoms to amyloids upon irradiation with light, and successfully reduced the neurotoxicity of aggregated amyloid-ß via inhibition of amyloid formation. However, the therapeutic effect and mode of actions of the photo-oxygenation system in vivo remained unclear. In this study, we demonstrate that photo-oxygenation facilitates the clearance of aggregated amyloid-ß from the brains of living Alzheimer's disease model mice, and enhances the microglial degradation of amyloid-ß peptide. These results suggest that photo-oxygenation may represent a novel anti-amyloid-ß strategy in Alzheimer's disease, which is compatible with immunotherapy.

EphA4 regulates Aß production via BACE1 expression in neurons.

Several lines of evidence suggest that the aggregation and deposition of amyloid-ß peptide (Aß) initiate the pathology of Alzheimer's disease (AD). Recently, a genome-wide association study demonstrated that a single-nucleotide polymorphism proximal to the EPHA4 gene, which encodes a receptor tyrosine kinase, is associated with AD risk. However, the molecular mechanism of EphA4 in the pathogenesis of AD, particularly in Aß production, remains unknown. Here, we performed several pharmacological and biological experiments both in vitro and in vivo and demonstrated that EphA4 is responsible for the regulation of Aß production. Pharmacological inhibition of EphA4 signaling and knockdown of Epha4 led to increased Aß levels accompanied by increased expression of ß-site APP cleaving enzyme 1 (BACE1), which is an enzyme responsible for Aß production. Moreover, EPHA4 overexpression and activation of EphA4 signaling via ephrin ligands decreased Aß levels. In particular, the sterile-alpha motif domain of EphA4 was necessary for the regulation of Aß production. Finally, EPHA4 mRNA levels were significantly reduced in the brains of AD patients, and negatively correlated with BACE1 mRNA levels. Our results indicate a novel mechanism of Aß regulation by EphA4, which is involved in AD pathogenesis.

Identification of calcium and integrin-binding protein 1 as a novel regulator of production of amyloid ß peptide using CRISPR/Cas9-based screening system.

The aberrant metabolism of amyloid ß peptide (Aß) has been implicated in the etiology of Alzheimer disease (AD). Aß is produced via the sequential cleavage of amyloid precursor protein (APP) by ß- and γ-secretases. However, the precise regulatory mechanism of Aß generation still remains unclear. To gain a better understanding of the molecular mechanism of Aß production, we established a genetic screening method based on the CRISPR/Cas9 system to identify novel regulators of Aß production. We successfully identified calcium and integrin-binding protein 1 (CIB1) as a potential negative regulator of Aß production. The disruption of Cib1 significantly upregulated Aß levels. In addition, immunoprecipitation experiments demonstrated that CIB1 interacts with the γ-secretase complex. Moreover, the disruption of Cib1 specifically reduced the cell-surface localization of mature Nicastrin (Nct), which is a component of the γ-secretase complex, without changing the intrinsic activity of γ-secretase. Finally, we confirmed using the single-cell RNA-seq data in human that CIB1 mRNA level in neuron was decreased in the early stage of AD. Taken together, our results indicate that CIB1 regulates Aß production via controlling the subcellular localization of γ-secretase, suggesting CIB1 is involved in the development of AD.

Photo-Oxygenation: An Innovative New Therapeutic Approach Against Amyloidoses.

Many types of amyloidoses are pathologically characterized by the deposition of amyloid, which is comprised of fibrils formed by abnormally aggregated proteins, in various peripheral tissues and the central nervous system (CNS). Neurodegenerative disorders, such as Alzheimer disease (AD), Parkinson disease (PD), frontotemporal dementia (FTD), and amyotrophic lateral sclerosis (ALS), are well-known CNS amyloidoses that are characterized by amyloid deposition both inside and outside of cells. The amyloidogenic proteins of each disease have distinct primary sequences, and they normally function as soluble proteins. However, these proteins all aggregate and form amyloid with a common intermolecular tertiary structure, namely, a cross-ß-sheet structure, finally leading to the onset of each disease. Therefore, inhibition of the aggregation of amyloid proteins or efficient clearance of the already formed amyloids are thought to be promising therapeutic strategies against amyloidoses.

Signaling Incentive and Drive in the Primate Ventral Pallidum for Motivational Control of Goal-Directed Action.

Processing incentive and drive is essential for control of goal-directed behavior. The limbic part of the basal ganglia has been emphasized in these processes, yet the exact neuronal mechanism has remained elusive. In this study, we examined the neuronal activity of the ventral pallidum (VP) and its upstream area, the rostromedial caudate (rmCD), while two male macaque monkeys performed an instrumental lever release task in which a visual cue indicated the forthcoming reward size. We found that the activity of some neurons in VP and rmCD reflected the expected reward size transiently following the cue. Reward size coding appeared earlier and stronger in VP than in rmCD. We also found that the activity in these areas was modulated by the satiation level of monkeys, which also occurred more frequently in VP than in rmCD. The information regarding reward size and satiation level was independently signaled in the neuronal populations of these areas. The data thus highlighted the neuronal coding of key variables for goal-directed behavior in VP. Furthermore, pharmacological inactivation of VP induced more severe deficit of goal-directed behavior than inactivation of rmCD, which was indicated by abnormal error repetition and diminished satiation effect on the performance. These results suggest that VP encodes incentive value and internal drive and plays a pivotal role in the control of motivation to promote goal-directed behavior.SIGNIFICANCE STATEMENT The limbic part of the basal ganglia has been implicated in the motivational control of goal-directed action. Here, we investigated how the ventral pallidum (VP) and the rostromedial caudate (rmCD) encode incentive value and internal drive and control goal-directed behavior. Neuronal recording and subsequent pharmacological inactivation revealed that VP had stronger coding of reward size and satiation level than rmCD. Reward size and satiation level were independently encoded in the neuronal population of these areas. Furthermore, VP inactivation impaired goal-directed behavior more severely than rmCD inactivation. These results highlight the central role of VP in the motivational control of goal-directed action.

CD2-associated protein (CD2AP) overexpression accelerates amyloid precursor protein (APP) transfer from early endosomes to the lysosomal degradation pathway.

A hallmark of Alzheimer's disease (AD) pathology is the appearance of senile plaques, which are composed of ß-amyloid (Aß) peptides. Aß is produced by sequential cleavages of amyloid precursor protein (APP) by ß- and γ-secretases. These cleavages take place in endosomes during intracellular trafficking of APP through the endocytic and recycling pathways. Genome-wide association studies have identified several risk factors for late-onset AD, one of which is CD2-associated protein (CD2AP), an adaptor molecule that regulates membrane trafficking. Although CD2AP's involvement in APP trafficking has recently been reported, how APP trafficking is regulated remains unclear. We sought to address this question by investigating the effect of CD2AP overexpression or knockdown on the intracellular APP distribution and degradation of APP in cultured COS-7 and HEK293 cells. We found that overexpression of CD2AP increases the localization of APP to Rab7-positive late endosomes, and decreases its localization to Rab5-positive early endosomes. CD2AP overexpression accelerated the onset of APP degradation without affecting its degradation rate. Furthermore, nutrient starvation increased the localization of APP to Rab7-positive late endosomes, and CD2AP overexpression stimulated starvation-induced lysosomal APP degradation. Moreover, the effect of CD2AP on the degradation of APP was confirmed by CD2AP overexpression and knockdown in primary cortical neurons from mice. We conclude that CD2AP accelerates the transfer of APP from early to late endosomes. This transfer in localization stimulates APP degradation by reducing the amount of time before degradation initiation. Taken together, these results may explain why impaired CD2AP function is a risk factor for AD.

Retrograde transport of γ-secretase from endosomes to the trans-Golgi network regulates Aß42 production.

The aberrant metabolism of amyloid-ß protein (Aß) in the human brain has been implicated in the etiology of Alzheimer disease (AD). γ-Secretase is the enzyme that generates various forms of Aß, such as Aß40 and Aß42, the latter being an aggregation-prone toxic peptide that is involved in the pathogenesis of AD. Recently, we found that clathrin-mediated endocytosis of γ-secretase affects the production and deposition of Aß42 in vivo, suggesting that the membrane trafficking of γ-secretase affects its enzymatic activity. However, the detailed intracellular trafficking pathway of γ-secretase and its contribution to Aß42 generation remain unclear. Here, we show that Retro-2, which inhibits the retrograde transport, elevated the Aß42-generating activity both in cultured cells and mice brain. However, the result of in vitro γ-secretase assay using a recombinant substrate suggested that Retro-2 did not elevate the intrinsic Aß42-production activity of γ-secretase. Immunocytochemistry and cell-surface biotinylation experiments revealed that γ-secretase is recycled via the endosome-to-trans-Golgi network transport. In addition, γ-secretase is retrogradely transported by syntaxin 5/6, known as targets of Retro-2, independent pathway. Conversely, TPT-260, which enhances the trafficking function of retromers, lowered Aß42 levels and the Aß42/(Aß40 + Aß42) ratio in secreted Aß from cultured cells. Our results strongly suggest that the endosome-to-trans-Golgi network trafficking of γ-secretase regulates its Aß42 production activity. Modulation of this trafficking pathway might be a potential target for the development of Aß42-lowering AD therapeutics. OPEN PRACTICES: Open Science: This manuscript was awarded with the Open Materials Badge. For more information see: https://cos.io/our-services/open-science-badges/.

Partial loss of CALM function reduces Aß42 production and amyloid deposition in vivo.

Aberrant production, clearance and deposition of amyloid-ß protein (Aß) in the human brain have been implicated in the aetiology of Alzheimer disease (AD). γ-Secretase is the enzyme responsible for generating various Aß species, such as Aß40 and toxic Aß42. Recently, genome-wide association studies in late-onset AD patients have identified the endocytosis-related phosphatidylinositol-binding clathrin assembly protein (PICALM) gene as a genetic risk factor for AD. We previously found that the loss of expression of CALM protein encoded by PICALM affects the ratio of production of Aß42, through the regulation of the clathrin-mediated endocytosis of γ-secretase. Here, we show that the binding capacity of the assembly protein 180 N-terminal homology (ANTH) domain of CALM to phosphatidylinositol-4,5-biphosphate, as well as to nicastrin, is critical to the modulation of the internalization of γ-secretase and to the Aß42 production ratio. Moreover, reduction of CALM decreases Aß deposition as well as brain levels of insoluble Aß42 in vivo These results suggest that CALM expression modifies AD risk by regulating Aß pathology.

BIN1 regulates BACE1 intracellular trafficking and amyloid-ß production.

BIN1 is a genetic risk factor of late-onset Alzheimer disease (AD), which was identified in multiple genome-wide association studies. BIN1 is a member of the amphiphysin family of proteins, and contains N-terminal Bin-Amphiphysin-Rvs and C-terminal Src homology 3 domains. BIN1 is widely expressed in the mouse and human brains, and has been reported to function in the endocytosis and the endosomal sorting of membrane proteins. BACE1 is a type 1 transmembrane aspartyl protease expressed predominantly in neurons of the brain and responsible for the production of amyloid-ß peptide (Aß). Here we report that the depletion of BIN1 increases cellular BACE1 levels through impaired endosomal trafficking and reduces BACE1 lysosomal degradation, resulting in increased Aß production. Our findings provide a mechanistic role of BIN1 in the pathogenesis of AD as a novel genetic regulator of BACE1 levels and Aß production.

Roles of centromedian parafascicular nuclei of thalamus and cholinergic interneurons in the dorsal striatum in associative learning of environmental events.

The thalamus provides a massive input to the striatum, but despite accumulating evidence, the functions of this system remain unclear. It is known, however, that the centromedian (CM) and parafascicular (Pf) nuclei of the thalamus can strongly influence particular striatal neuron subtypes, notably including the cholinergic interneurons of the striatum (CINs), key regulators of striatal function. Here, we highlight the thalamostriatal system through the CM-Pf to striatal CINs. We consider how, by virtue of the direct synaptic connections of the CM and PF, their neural activity contributes to the activity of CINs and striatal projection neurons (SPNs). CM-Pf neurons are strongly activated at sudden changes in behavioral context, such as switches in action-outcome contingency or sequence of behavioral requirements, suggesting that their activity may represent change of context operationalized as associability. Striatal CINs, on the other hand, acquire and loose responses to external events associated with particular contexts. In light of this physiological evidence, we propose a hypothesis of the CM-Pf-CINs system, suggesting that it augments associative learning by generating an associability signal and promotes reinforcement learning guided by reward prediction error signals from dopamine-containing neurons. We discuss neuronal circuit and synaptic organizations based on in vivo/in vitro studies that we suppose to underlie our hypothesis. Possible implications of CM-Pf-CINs dysfunction (or degeneration) in brain diseases are also discussed by focusing on Parkinson's disease.

Role of Apolipoprotein E in ß-Amyloidogenesis: ISOFORM-SPECIFIC EFFECTS ON PROTOFIBRIL TO FIBRIL CONVERSION OF Aß IN VITRO AND BRAIN Aß DEPOSITION IN VIVO.

Human APOE ϵ4 allele is a strong genetic risk factor of Alzheimer disease. Neuropathological and genetic studies suggested that apolipoprotein E4 (apoE4) protein facilitates deposition of amyloid ß peptide (Aß) in the brain, although the mechanism whereby apoE4 increases amyloid aggregates remains elusive. Here we show that injection of Aß protofibrils induced Aß deposition in the brain of APP transgenic mice, suggesting that Aß protofibrils acted as a seed for aggregation and deposition of Aß in vivo. Injection of Aß protofibrils together with apoE3 significantly attenuated Aß deposition, whereas apoE4 did not have this effect. In vitro assays revealed that the conversion of Aß protofibrils to fibrils progressed more slowly upon coincubation with apoE2 or apoE3 compared with that with apoE4. Aß protofibrils complexed with apoE4 were less stable than those with apoE2 or apoE3. These data suggest that the suppression effect of apoE2 or apoE3 on the structural conversion of Aß protofibrils to fibrils is stronger than those of apoE4, thereby impeding ß-amyloid deposition.

A Food and Drug Administration-approved asthma therapeutic agent impacts amyloid ß in the brain in a transgenic model of Alzheimer disease.

Interfering with the assembly of Amyloid ß (Aß) peptides from monomer to oligomeric species and fibrils or promoting their clearance from the brain are targets of anti-Aß-directed therapies in Alzheimer disease. Here we demonstrate that cromolyn sodium (disodium cromoglycate), a Food and Drug Administration-approved drug already in use for the treatment of asthma, efficiently inhibits the aggregation of Aß monomers into higher-order oligomers and fibrils in vitro without affecting Aß production. In vivo, the levels of soluble Aß are decreased by over 50% after only 1 week of daily intraperitoneally administered cromolyn sodium. Additional in vivo microdialysis studies also show that this compound decreases the half-life of soluble Aß in the brain. These data suggest a clear effect of a peripherally administered, Food and Drug Administration-approved medication on Aß economy, supporting further investigation of the potential long-term efficacy of cromolyn sodium in Alzheimer disease.

Anti-ApoE antibody given after plaque onset decreases Aß accumulation and improves brain function in a mouse model of Aß amyloidosis.

Apolipoprotein E (apoE) is the strongest known genetic risk factor for late onset Alzheimer's disease (AD). It influences amyloid-ß (Aß) clearance and aggregation, which likely contributes in large part to its role in AD pathogenesis. We recently found that HJ6.3, a monoclonal antibody against apoE, significantly reduced Aß plaque load when given to APPswe/PS1ΔE9 (APP/PS1) mice starting before the onset of plaque deposition. To determine whether the anti-apoE antibody HJ6.3 affects Aß plaques, neuronal network function, and behavior in APP/PS1 mice after plaque onset, we administered HJ6.3 (10 mg/kg/week) or PBS intraperitoneally to 7-month-old APP/PS1 mice for 21 weeks. HJ6.3 mildly improved spatial learning performance in the water maze, restored resting-state functional connectivity, and modestly reduced brain Aß plaque load. There was no effect of HJ6.3 on total plasma cholesterol or cerebral amyloid angiopathy. To investigate the underlying mechanisms of anti-apoE immunotherapy, HJ6.3 was applied to the brain cortical surface and amyloid deposition was followed over 2 weeks using in vivo imaging. Acute exposure to HJ6.3 affected the course of amyloid deposition in that it prevented the formation of new amyloid deposits, limited their growth, and was associated with occasional clearance of plaques, a process likely associated with direct binding to amyloid aggregates. Topical application of HJ6.3 for only 14 d also decreased the density of amyloid plaques assessed postmortem. Collectively, these studies suggest that anti-apoE antibodies have therapeutic potential when given before or after the onset of Aß pathology.