APP Intracellular Domain Impairs Adult Neurogenesis in Transgenic Mice by Inducing Neuroinflammation

Background

A devastating aspect of Alzheimer''s disease (AD) is the progressive deterioration of memory due to neuronal loss. Amyloid precursor protein (APP) occupies a central position in AD and APP-derived amyloid-β (Aβ) peptides are thought to play a pivotal role in disease pathogenesis. Nonetheless, it is becoming clear that AD etiology is highly complex and that factors other than Aβ also contribute to AD pathogenesis. APP intracellular domain (AICD) is generated together with Aβ and we recently showed that AICD transgenic mice recapitulate pathological features of AD such as tau hyperphosphorylation, memory deficits and neurodegeneration without increasing the Aβ levels. Since impaired adult neurogenesis is shown to augment memory deficits in AD mouse models, here we examined the status of adult neurogenesis in AICD transgenic mice.

Methodology/Principal Finding

We previously generated transgenic mice co-expressing 59-residue long AICD fragment and its binding partner Fe65. Hippocampal progenitor cell proliferation was determined by BrdU incorporation at 1.5, 3 and 12 months of age. Only male transgenic and their respective wilt type littermate control mice were used. We find age-dependent decrease in BrdU incorporation and doublecortin-positive cells in the dentate gyrus of AICD transgenic mice suggesting impaired adult neurogenesis. This deficit resulted from decreased proliferation and survival, whereas neuronal differentiation remained unaffected. Importantly, this impairment was independent of Aβ since APP-KO mice expressing AICD also exhibit reduced neurogenesis. The defects in adult neurogenesis are prevented by long-term treatment with the non-steroidal anti-inflammatory agents ibuprofen or naproxen suggesting that neuroinflammation is critically involved in impaired adult neurogenesis in AICD transgenic mice.

Conclusion/Significance

Since adult neurogenesis is crucial for spatial memory, which is particularly vulnerable in AD, these findings suggest that AICD can exacerbate memory defects in AD by impairing adult neurogenesis. Our findings further establish that AICD, in addition to Aβ, contributes to AD pathology and that neuroinflammation plays a much broader role in AD pathogenesis than previously thought.     

Overexpression of Human Apolipoprotein A-I Preserves Cognitive Function and Attenuates Neuroinflammation and Cerebral Amyloid Angiopathy in a Mouse Model of Alzheimer Disease

To date there is no effective therapy for Alzheimer disease (AD). High levels of circulating high density lipoprotein (HDL) and its main protein, apolipoprotein A-I (apoA-I), reduce the risk of cardiovascular disease. Clinical studies show that plasma HDL cholesterol and apoA-I levels are low in patients with AD. To investigate if increasing plasma apoA-I/HDL levels ameliorates AD-like memory deficits and amyloid-β (Aβ) deposition, we generated a line of triple transgenic (Tg) mice overexpressing mutant forms of amyloid-β precursor protein (APP) and presenilin 1 (PS1) as well as human apoA-I (AI). Here we show that APP/PS1/AI triple Tg mice have a 2-fold increase of plasma HDL cholesterol levels. When tested in the Morris water maze for spatial orientation abilities, whereas APP/PS1 mice develop age-related learning and memory deficits, APP/PS1/AI mice continue to perform normally during aging. Interestingly, no significant differences were found in the total level and deposition of Aβ in the brains of APP/PS1 and APP/PS1/AI mice, but cerebral amyloid angiopathy was reduced in APP/PS1/AI mice. Also, consistent with the anti-inflammatory properties of apoA-I/HDL, glial activation was reduced in the brain of APP/PS1/AI mice. In addition, Aβ-induced production of proinflammatory chemokines/cytokines was decreased in mouse organotypic hippocampal slice cultures expressing human apoA-I. Therefore, we conclude that overexpression of human apoA-I in the circulation prevents learning and memory deficits in APP/PS1 mice, partly by attenuating neuroinflammation and cerebral amyloid angiopathy. These findings suggest that elevating plasma apoA-I/HDL levels may be an effective approach to preserve cognitive function in patients with AD.     

Oridonin Attenuates Aβ1–42-Induced Neuroinflammation and Inhibits NF-κB Pathway

Neuroinflammation induced by beta-amyloid (Aβ) plays a critical role in the pathogenesis of Alzheimer’s disease (AD), and inhibiting Aβ-induced neuroinflammation serves as a potential strategy for the treatment of AD. Oridonin (Ori), a compound of Rabdosia rubescens, has been shown to exert anti-inflammatory effects. In this study, we demonstrated that Ori inhibited glial activation and decreased the release of inflammatory cytokines in the hippocampus of Aβ_1–42-induced AD mice. In addition, Ori inhibited the NF-κB pathway and Aβ_1–42-induced apoptosis. Furthermore, Ori could attenuate memory deficits in Aβ_1–42-induced AD mice. In conclusion, our study demonstrated that Ori inhibited the neuroinflammation and attenuated memory deficits induced by Aβ_1–42, suggesting that Ori might be a promising candidate for AD treatment.     

Oral Administration of a Fusion Protein between the Cholera Toxin B Subunit and the 42-Amino Acid Isoform of Amyloid-β Peptide Produced in Silkworm Pupae Protects against Alzheimer's Disease in Mice

A key molecule in the pathogenesis of Alzheimer''s disease (AD) is a 42-amino acid isoform of the amyloid-β peptide (Aβ42), which is the most toxic element of senile plaques. In this study, to develop an edible, safe, low-cost vaccine for AD, a cholera toxin B subunit (CTB)-Aβ42 fusion protein was successfully expressed in silkworm pupae. We tested the silkworm pupae-derived oral vaccination containing CTB-Aβ42 in a transgenic mouse model of AD. Anti-Aβ42 antibodies were induced in these mice, leading to a decreased Aβ deposition in the brain. We also found that the oral administration of the silk worm pupae vaccine improved the memory and cognition of mice, as assessed using a water maze test. These results suggest that the new edible CTB-Aβ42 silkworm pupae-derived vaccine has potential clinical application in the prevention of AD.     

Apolipoprotein E in Synaptic Plasticity and Alzheimer’s Disease: Potential Cellular and Molecular Mechanisms

Alzheimer’s disease (AD) is clinically characterized with progressive memory loss and cognitive decline. Synaptic dysfunction is an early pathological feature that occurs prior to neurodegeneration and memory dysfunction. Mounting evidence suggests that aggregation of amyloid-β (Aβ) and hyperphosphorylated tau leads to synaptic deficits and neurodegeneration, thereby to memory loss. Among the established genetic risk factors for AD, the ɛ4 allele of apolipoprotein E (APOE) is the strongest genetic risk factor. We and others previously demonstrated that apoE regulates Aβ aggregation and clearance in an isoform-dependent manner. While the effect of apoE on Aβ may explain how apoE isoforms differentially affect AD pathogenesis, there are also other underexplored pathogenic mechanisms. They include differential effects of apoE on cerebral energy metabolism, neuroinflammation, neurovascular function, neurogenesis, and synaptic plasticity. ApoE is a major carrier of cholesterols that are required for neuronal activity and injury repair in the brain. Although there are a few conflicting findings and the underlying mechanism is still unclear, several lines of studies demonstrated that apoE4 leads to synaptic deficits and impairment in long-term potentiation, memory and cognition. In this review, we summarize current understanding of apoE function in the brain, with a particular emphasis on its role in synaptic plasticity and the underlying cellular and molecular mechanisms, involving low-density lipoprotein receptor-related protein 1 (LRP1), syndecan, and LRP8/ApoER2.     

Prion-Protein-interacting Amyloid-β Oligomers of High Molecular Weight Are Tightly Correlated with Memory Impairment in Multiple Alzheimer Mouse Models

Alzheimer disease (AD) is characterized by amyloid-β accumulation, with soluble oligomers (Aβo) being the most synaptotoxic. However, the multivalent and unstable nature of Aβo limits molecular characterization and hinders research reproducibility. Here, we characterized multiple Aβo forms throughout the life span of various AD mice and in post-mortem human brain. Aβo exists in several populations, where prion protein (PrP^C)-interacting Aβo is a high molecular weight Aβ assembly present in multiple mice and humans with AD. Levels of PrP^C-interacting Aβo match closely with mouse memory and are equal or superior to other Aβ measures in predicting behavioral impairment. However, Aβo metrics vary considerably between mouse strains. Deleting PrP^C expression in mice with relatively low PrP^C-interacting Aβo (Tg2576) results in partial rescue of cognitive performance as opposed to complete recovery in animals with a high percentage of PrP^C-interacting Aβo (APP/PSEN1). These findings highlight the relative contributions and interplay of Aβo forms in AD.     

Curcumin Decreases Amyloid-β Peptide Levels by Attenuating the Maturation of Amyloid-β Precursor Protein

Alzheimer disease (AD) is a devastating neurodegenerative disease with no cure. The pathogenesis of AD is believed to be driven primarily by amyloid-β (Aβ), the principal component of senile plaques. Aβ is an ∼4-kDa peptide generated via cleavage of the amyloid-β precursor protein (APP). Curcumin is a compound in the widely used culinary spice, turmeric, which possesses potent and broad biological activities, including anti-inflammatory and antioxidant activities, chemopreventative effects, and effects on protein trafficking. Recent in vivo studies indicate that curcumin is able to reduce Aβ-related pathology in transgenic AD mouse models via unknown molecular mechanisms. Here, we investigated the effects of curcumin on Aβ levels and APP processing in various cell lines and mouse primary cortical neurons. We show for the first time that curcumin potently lowers Aβ levels by attenuating the maturation of APP in the secretory pathway. These data provide a mechanism of action for the ability of curcumin to attenuate amyloid-β pathology.     

Anti-Diabetes Drug Pioglitazone Ameliorates Synaptic Defects in AD Transgenic Mice by Inhibiting Cyclin-Dependent Kinase5 Activity

Cyclin-dependent kinase 5 (Cdk5) is a serine/threonine kinase that is activated by the neuron specific activators p35/p39 and plays many important roles in neuronal development. However, aberrant activation of Cdk5 is believed to be associated with the pathogenesis of several neurodegenerative diseases, including Alzheimer’s disease (AD) and Parkinson’s disease (PD). Here in the present study, enhanced Cdk5 activity was observed in mouse models of AD; whereas soluble amyloid-β oligomers (Aβ), which contribute to synaptic failures during AD pathogenesis, induced Cdk5 hyperactivation in cultured hippocampal neurons. Inhibition of Cdk5 activity by pharmacological or genetic approaches reversed dendritic spine loss caused by soluble amyloid-β oligomers (Aβ) treatment. Interestingly, we found that the anti-diabetes drug pioglitazone could inhibit Cdk5 activity by decreasing p35 protein level. More importantly, pioglitazone treatment corrected long-term potentiation (LTP) deficit caused by Aβ exposure in cultured slices and pioglitazone administration rescued impaired LTP and spatial memory in AD mouse models. Taken together, our study describes an unanticipated role of pioglitazone in alleviating AD and reveals a potential therapeutic drug for AD curing.     

CCL2 Accelerates Microglia-Mediated Aβ Oligomer Formation and Progression of Neurocognitive Dysfunction

Background

The linkages between neuroinflammation and Alzheimer''s disease (AD) pathogenesis are well established. What is not, however, is how specific immune pathways and proteins affect the disease. To this end, we previously demonstrated that transgenic over-expression of CCL2 enhanced microgliosis and induced diffuse amyloid plaque deposition in Tg2576 mice. This rodent model of AD expresses a Swedish β-amyloid (Aβ) precursor protein mutant.

Methodology/Principal Findings

We now report that CCL2 transgene expression accelerates deficits in spatial and working memory and hippocampal synaptic transmission in β-amyloid precursor protein (APP) mice as early as 2–3 months of age. This is followed by increased numbers of microglia that are seen surrounding Aβ oligomers. CCL2 does not suppress Aβ degradation. Rather, CCL2 and tumor necrosis factor-α directly facilitated Aβ uptake, intracellular Aβ oligomerization, and protein secretion.

Conclusions/Significance

We posit that CCL2 facilitates Aβ oligomer formation in microglia and propose that such events accelerate memory dysfunction by affecting Aβ seeding in the brain.     

Cathepsin B Degrades Amyloid-β in Mice Expressing Wild-type Human Amyloid Precursor Protein

Accumulation of amyloid-β (Aβ), believed to be a key trigger of Alzheimer disease (AD), could result from impaired clearance mechanisms. Previously, we showed that the cysteine protease cathepsin B (CatB) degrades Aβ, most likely by C-terminal truncation, in mice expressing human amyloid precursor protein with familial AD-linked mutations (hAPP_FAD). In addition, the Aβ-degrading activity of CatB is inhibited by its endogenous inhibitor, cystatin C (CysC). Reducing CysC expression markedly lowers Aβ levels by enhancing CatB-mediated Aβ degradation in hAPP_FAD mice. However, because a vast majority of AD patients do not carry familial mutations, we investigated how the CysC-CatB axis affects Aβ levels in mice expressing wild-type hAPP (hAPP_WT). Enhancing CatB activity by CysC deletion significantly lowered total Aβ and Aβ42 levels in hAPP_WT mice, whereas CatB deletion increased Aβ levels. To determine whether neuron-derived CatB degrades Aβ in vivo, we generated transgenic mice overexpressing CatB under the control of a neuron-specific enolase promoter. Enhancing neuronal CatB activity in hAPP_WT mice significantly lowered Aβ42 levels. The processing of hAPP_WT was unaffected by increasing or ablating CatB activity. Thus, the CysC-CatB axis affects degradation of Aβ42 derived from hAPP lacking familial mutations. These findings support the notion that enhancing CatB activity could lower Aβ, especially Aβ42, in AD patients with or without familial mutations.     

β-Arrestin1 regulates γ-secretase complex assembly and modulates amyloid-β pathology

Alzheimer''s disease (AD) is a progressive and complex neurodegenerative disease in which the γ-secretase-mediated amyloid-β (Aβ) pathology plays an important role. We found that a multifunctional protein, β-arrestin1, facilitated the formation of NCT/APH-1 (anterior pharynx-defective phenotype 1) precomplex and mature γ-secretase complex through its functional interaction with APH-1. Deficiency of β-arrestin1 or inhibition of binding of β-arrestin1 with APH-1 by small peptides reduced Aβ production without affecting Notch processing. Genetic ablation of β-arrestin1 diminished Aβ pathology and behavioral deficits in transgenic AD mice. Moreover, in brains of sporadic AD patients and transgenic AD mice, the expression of β-arrestin1 was upregulated and correlated well with neuropathological severity and senile Aβ plaques. Thus, our study identifies a regulatory mechanism underlying both γ-secretase assembly and AD pathogenesis, and indicates that specific reduction of Aβ pathology can be achieved by regulation of the γ-secretase assembly.     

The Proton-Pump Inhibitor Lansoprazole Enhances Amyloid Beta Production

A key event in the pathogenesis of Alzheimer’s disease (AD) is the accumulation of amyloid-β (Aβ) species in the brain, derived from the sequential cleavage of the amyloid precursor protein (APP) by β- and γ-secretases. Based on a systems biology study to repurpose drugs for AD, we explore the effect of lansoprazole, and other proton-pump inhibitors (PPIs), on Aβ production in AD cellular and animal models. We found that lansoprazole enhances Aβ37, Aβ40 and Aβ42 production and lowers Aβ38 levels on amyloid cell models. Interestingly, acute lansoprazole treatment in wild type and AD transgenic mice promoted higher Aβ40 levels in brain, indicating that lansoprazole may also exacerbate Aβ production in vivo. Overall, our data presents for the first time that PPIs can affect amyloid metabolism, both in vitro and in vivo.     

The Resveratrol Trimer Miyabenol C Inhibits β-Secretase Activity and β-Amyloid Generation

Accumulation and deposition of amyloid-β peptide (Aβ) in the brain is a primary cause of the pathogenesis of Alzheimer’s disease (AD). Aβ is generated from amyloid-β precursor protein (APP) through sequential cleavages first by β-secretase and then by γ-secretase. Inhibiting β-secretase activity is believed to be one of the most promising strategies for AD treatment. In the present study, we found that a resveratrol trimer, miyabenol C, isolated from stems and leaves of the small-leaf grape (Vitisthunbergii var. taiwaniana), can markedly reduce Aβ and sAPPβ levels in both cell cultures and the brain of AD model mice. Mechanistic studies revealed that miyabenol C affects neither protein levels of APP, the two major α-secretases ADAM10 and TACE, and the γ-secretase component Presenilin 1, nor γ-secretase-mediated Notch processing and TACE activity. In contrast, although miyabenol C has no effect on altering protein levels of the β-secretase BACE1, it can inhibit both in vitro and in vivo β-secretase activity. Together, our results indicate that miyabenol C is a prominent β-secretase inhibitor and lead compound for AD drug development.     

The translocator protein ligands as mitochondrial functional modulators for the potential anti-Alzheimer agents

Small molecule modulators of mitochondrial function have been attracted much attention in recent years due to their potential therapeutic applications for neurodegenerative diseases. The mitochondrial translocator protein (TSPO) is a promising target for such compounds, given its involvement in the formation of the mitochondrial permeability transition pore in response to mitochondrial stress. In this study, we performed a ligand-based pharmacophore design and virtual screening, and identified a potent hit compound, 7 (VH34) as a TSPO ligand. After validating its biological activity against amyloid-β (Aβ) induced mitochondrial dysfunction and in acute and transgenic Alzheimer’s disease (AD) model mice, we developed a library of analogs, and we found two most active compounds, 31 and 44, which restored the mitochondrial membrane potential, ATP production, and cell viability under Aβ-induced mitochondrial toxicity. These compounds recovered learning and memory function in acute AD model mice with improved pharmacokinetic properties.     

Amyloid-β oligomers induce tau-independent disruption of BDNF axonal transport via calcineurin activation in cultured hippocampal neurons

Disruption of fast axonal transport (FAT) is an early pathological event in Alzheimer''s disease (AD). Soluble amyloid-β oligomers (AβOs), increasingly recognized as proximal neurotoxins in AD, impair organelle transport in cultured neurons and transgenic mouse models. AβOs also stimulate hyperphosphorylation of the axonal microtubule-associated protein, tau. However, the role of tau in FAT disruption is controversial. Here we show that AβOs reduce vesicular transport of brain-derived neurotrophic factor (BDNF) in hippocampal neurons from both wild-type and tau-knockout mice, indicating that tau is not required for transport disruption. FAT inhibition is not accompanied by microtubule destabilization or neuronal death. Significantly, inhibition of calcineurin (CaN), a calcium-dependent phosphatase implicated in AD pathogenesis, rescues BDNF transport. Moreover, inhibition of protein phosphatase 1 and glycogen synthase kinase 3β, downstream targets of CaN, prevents BDNF transport defects induced by AβOs. We further show that AβOs induce CaN activation through nonexcitotoxic calcium signaling. Results implicate CaN in FAT regulation and demonstrate that tau is not required for AβO-induced BDNF transport disruption.     

Protection of TGF-β1 against Neuroinflammation and Neurodegeneration in Aβ1–42-Induced Alzheimer’s Disease Model Rats

Neuroinflammation has been reported to be associated with Alzheimer’s disease (AD) pathogenesis. Neuroinflammation is generally considered as an outcome of glial activation; however, we recently demonstrated that T helper (Th)17 cells, a subpopulation of proinflammatory CD4+ T cells, are also involved in AD pathogenesis. Transforming growth factor (TGF)-β1, a cytokine that can be expressed in the brain, can be immunosuppressive, but its effects on lymphocyte-mediated neuroinflammation in AD pathogenesis have not been well addressed. In the current study we administered TGF-β1 via intracerebroventricle (ICV) and intranasal (IN) routes in AD model rats to investigate its antiinflammatory and neuroprotective effects. The AD rat model was prepared by bilateral hippocampal injection of amyloid-β (Aβ)_1–42. TGF-β1 was administered via ICV one hour prior to Aβ_1–42 injection or via both nares seven days after Aβ_1–42 injection. ICV administration of TGF-β1 before Aβ_1–42 injection remarkably ameliorated Aβ_1–42-induced neurodegeneration and prevented Aβ_1–42-induced increases in glia-derived proinflammatory mediators (TNF-α, IL-1β and iNOS), as well as T cell-derived proinflammatory cytokines (IFN-γ, IL-2, IL-17 and IL-22), in the hypothalamus, serum or cerebrospinal fluid (CSF) in a concentration-dependent manner. TGF-β1 pretreatment also prevented Aβ_1–42-induced decreases in the neurotrophic factors, IGF-1, GDNF and BDNF, and in the antiinflammatory cytokine, IL-10. Similarly, IN administration of TGF-β1 after Aβ_1–42 injection reduced neurodegeneration, elevation of proinflammatory mediators and cytokines, and reduction of neurotrophic and antiinflammatory factors, in the hypothalamus, serum or CSF. These findings suggest that TGF-β1 suppresses glial and T cell-mediated neuroinflammation and thereby alleviates AD-related neurodegeneration. The effectiveness of IN administered TGF-β1 in reducing Aβ_1–42 neurotoxicity suggests a possible therapeutic approach in patients with AD.     

Accumulation of autophagosomes contributes to enhanced amyloidogenic APP processing under insulin-resistant conditions

Alzheimer disease (AD) is sometimes referred to as type III diabetes because of the shared risk factors for the two disorders. Insulin resistance, one of the major components of type II diabetes mellitus (T2DM), is a known risk factor for AD. Insulin resistance increases amyloid-β peptide (Aβ) generation, but the exact mechanism underlying the linkage of insulin resistance to increased Aβ generation in the brain is unknown. In this study, we investigated the effect of insulin resistance on amyloid β (A4) precursor protein (APP) processing in mice fed a high-fat diet (HFD), and diabetic db/db mice. We found that insulin resistance promotes Aβ generation in the brain via altered insulin signal transduction, increased BACE1/β-secretase and γ-secretase activities, and accumulation of autophagosomes. Using an in vitro model of insulin resistance, we found that defects in insulin signal transduction affect autophagic flux by inhibiting the mechanistic target of rapamycin (MTOR) pathway. The insulin resistance-induced autophagosome accumulation resulted in alteration of APP processing through enrichment of secretase proteins in autophagosomes. We speculate that the insulin resistance that underlies the pathogenesis of T2DM might alter APP processing through autophagy activation, which might be involved in the pathogenesis of AD. Therefore, we propose that insulin resistance-induced autophagosome accumulation becomes a potential linker between AD and T2DM.     

Calpain Activation Promotes BACE1 Expression,Amyloid Precursor Protein Processing,and Amyloid Plaque Formation in a Transgenic Mouse Model of Alzheimer Disease

Abnormal activation of calpain is implicated in synaptic dysfunction and participates in neuronal death in Alzheimer disease (AD) and other neurological disorders. Pharmacological inhibition of calpain has been shown to improve memory and synaptic transmission in the mouse model of AD. However, the role and mechanism of calpain in AD progression remain elusive. Here we demonstrate a role of calpain in the neuropathology in amyloid precursor protein (APP) and presenilin 1 (PS1) double-transgenic mice, an established mouse model of AD. We found that overexpression of endogenous calpain inhibitor calpastatin (CAST) under the control of the calcium/calmodulin-dependent protein kinase II promoter in APP/PS1 mice caused a remarkable decrease of amyloid plaque burdens and prevented Tau phosphorylation and the loss of synapses. Furthermore, CAST overexpression prevented the decrease in the phosphorylation of the memory-related molecules CREB and ERK in the brain of APP/PS1 mice and improved spatial learning and memory. Interestingly, treatment of cultured primary neurons with amyloid-β (Aβ) peptides caused an increase in the level of β-site APP-cleaving enzyme 1 (BACE1), the key enzyme responsible for APP processing and Aβ production. This effect was inhibited by CAST overexpression. Consistently, overexpression of calpain in heterologous APP expressing cells up-regulated the level of BACE1 and increased Aβ production. Finally, CAST transgene prevented the increase of BACE1 in APP/PS1 mice. Thus, calpain activation plays an important role in APP processing and plaque formation, probably by regulating the expression of BACE1.     

Triptolide Preserves Cognitive Function and Reduces Neuropathology in a Mouse Model of Alzheimer's Disease

Triptolide, a major bioactive ingredient of a widely used herbal medicine, has been shown to possess multiple pharmacological functions, including potential neuroprotective effects pertinent to Alzheimer''s disease (AD) in vitro. However, the therapeutic potential of triptolide for AD in vivo has not been thoroughly evaluated. In the present study, we investigated the impact of peripherally administered triptolide on AD-related behavior and neuropathology in APP_swe/PS1_ΔE9 (APP/PS1) mice, an established model of AD. Our results showed that two-month treatment with triptolide rescued cognitive function in APP/PS1 mice. Immunohistochemical analyses indicated that triptolide treatment led to a significant decrease in amyloid-β (Aβ) deposition and neuroinflammation in treated mice. In contrast to previous findings in vitro, biochemical analyses showed that triptolide treatment did not significantly affect the production pathway of Aβ in vivo. Intriguingly, further analyses revealed that triptolide treatment upregulated the level of insulin-degrading enzyme, a major Aβ-degrading enzyme in the brain, indicating that triptolide treatment reduced Aβ pathology by enhancing the proteolytic degradation of Aβ. Our findings demonstrate that triptolide treatment ameliorates key behavioral and neuropathological changes found in AD, suggesting that triptolide may serve as a potential therapeutic agent for AD.