Longevity and stress resilience require precise coordination of gene expression programs across tissues. Here, we demonstrate that overexpression of the chromatin reader bet-1 specifically in neurons of Caenorhabditis elegans promotes organismal longevity and stress resistance via cell-nonautonomous signaling. Neuronal bet-1 elicits a neurotransmitter-dependent signal that activates the conserved stress-responsive transcription factor HSF-1 in the intestine, enhancing proteostasis, oxidative stress resistance, metabolic remodeling, and immune defense. Life span extension by neuronal bet-1 requires both hsf-1 and daf-16 in neurons but only requires hsf-1 in peripheral tissues. Using bulk RNA sequencing, we reveal distinct prolongevity pathways that include enhanced heat-shock response, proteostasis, increased actin stability, and resistance to pathogens, which likely together coordinate the prolongevity effects of neuronal bet-1 . Our findings establish BET-1 as a potent nonautonomous regulator of aging and stress response, highlighting chromatin readers as upstream modulators of intertissue signaling and systemic resilience.

Introduction:Air pollution (AirPoll) is a major environmental risk factor for age-related cognitive decline and dementia, yet we poorly understood the cellular and molecular mechanisms underlying its effects and their potential attenuation. Methods:We combined single cell RNA sequencing with immunohistochemistry to determine transcriptional responses in microglia, astrocytes, neurons and neural stem cells in the hippocampus of mice following exposure to chronic diesel exhaust particle (DEP). Differential gene expression profiles were compared between filtered-air and DEP exposed animals. The gamma secretase modulator GSM-15606 (BPN) was used to probe selective rescue of inflammatory signatures across distinct cell populations. Results:DEP exposure triggered robust inflammatory programs in microglia and astrocytes, including upregulation of cytokine signaling components, innate immune receptors, stress-responsive transcription factors, and markers of reactive glial phenotypes. In neural stem cells, DEP induced activation of gliosis-associated pathways, including Il6st, Stat3, and Txnip, consistent with a pro-inflammatory state that may bias lineage decisions. Immunostaining confirmed a significant reduction in immature neurons in the neurogenic niche after AirPoll exposure. GSM-15606 attenuated many DEP-induced transcriptional alterations in microglia and astrocytes, reducing expression of inflammatory mediators and reactive gliosis markers, but did not modulate the inflammatory profile of neural stem cells. Conclusions:AirPoll activates divergent inflammatory pathways across hippocampal cell populations and suppresses neurogenesis. Targeting inflammation with GSM-15606 selectively reverses glial but not neural stem cell responses, highlighting cell-type-specific mechanisms and potential therapeutic pathways to mitigate pollution-related cognitive vulnerability. These results support GSM-15606 as a protective agent against AirPoll-induced hippocampal dysfunction and amyloidogenic stress.

Air pollution (AirP) exposure is associated with increased Alzheimer's disease (AD) risk, yet AirP is chemically heterogeneous, complicating identification of shared pathogenic drivers. We examined acute cortical responses to two metal-rich AirP sources, diesel exhaust particles (DEP) and World Trade Center (WTC) dust, and compared them to woodsmoke (WS), a particulate exposure with low metal content. DEP and WTC elicited highly convergent transcriptional responses, sharing over 1200 differentially expressed genes linked to inflammation, ferroptosis, neuronal remodeling, and amyloid processing. These changes were accompanied by impaired antioxidant activity and increased lipid peroxidation within lipid rafts, a membrane microdomain critical for amyloid processing, resulting in increased Aβ generation. In contrast, WS produced a distinct transcriptional signature and failed to induce ferroptotic priming or lipid peroxidation, consistent with its low metal composition. Together, these findings implicate metals as a shared driver linking diverse AirP exposures to amyloidogenic vulnerability and elevated AD risk.

The actin cytoskeleton is a fundamental and highly conserved structure that functions in diverse cellular processes, yet its direct contribution to organismal aging remains unclear. Here, we systematically interrogated how genetic and pharmacologic perturbations of actin structure and function influence lifespan and various hallmarks of aging in Caenorhabditis elegans. Whole-animal and tissue-specific knockdown of actin and key actin-binding proteins (ABPs)—arx-2 (Arp2/3), unc-60 (cofilin), and lev-11 (tropomyosin)—led to premature disruption of filament organization, reduced lifespan, and tissue-specific physiological defects. Actin dysfunction also displayed a more “aged” transcriptome using previously validated transcriptomics clocks, and broadly exacerbated many age-associated phenotypes, including mitochondrial dysfunction, lipid dysregulation, loss of proteostasis, impaired autophagy, and intestinal barrier failure. Pharmacological destabilization with Latrunculin A mirrored genetic knockdowns, while mild stabilization with Jasplakinolide modestly extended lifespan, emphasizing that optimal and finely tuned actin function is critical for healthy aging. Finally, analysis of human genome-wide association data revealed that common ACTB polymorphisms correlate with differences in age-related decline in gait speed, suggesting some links between aging and actin across organisms. Taken together, our results provide a comprehensive and publicly accessible resource that maps, for the first time, how changes in actin integrity correlate with diverse aging phenotypes across tissues. This descriptive framework is intended to enable future mechanistic discovery by offering a deep, unbiased dataset that can be integrated with emerging studies to define how actin dynamics can potentially influence aging.

Longevity-promoting interventions represent a promising strategy to mitigate brain aging and reduce Alzheimer's disease (AD) risk. The NIA Interventions Testing Program identified the weak estrogen 17α-estradiol (17αE2) as a compound that extends healthspan and lifespan in mice, with effects observed primarily in males. Our recent work demonstrated that 17αE2 healthspan benefits were modulated by human apolipoprotein E ( APOE ) genotype such that aging phenotypes were improved more strongly in middle-aged male mice with targeted-replacement of the AD-associated APOE4 allele compared to APOE3 , the risk neutral and most common APOE allele. Here, we tested whether APOE -dependent, AD-relevant benefits of 17αE2 observed in males extend to females. Specifically, we treated 12-month-old APOE3 and APOE4 targeted-replacement female mice for 6 months with chow containing 0 or 14.4ppm 17αE2. We find that relative to APOE3 , APOE4 genotype largely exhibits more robust systemic phenotypes associated with aging, including increased adiposity, impaired glucose tolerance, and reduced energy expenditure. Further, we observe that treatment with 17αE2 yields modest improvements in some outcomes, including decreased adiposity and increased lean mass, glucose tolerance, and energy expenditure, though significant benefits are found only in APOE4 females. In the CNS, we observed mixed effects of APOE genotype on behavioral performance and indices of brain aging, with APOE4 females performing worse in the Barnes Maze and having higher levels of the AD-related peptide soluble β-amyloid, but no APOE genotype differences in cortical lipid raft oxidative damage. In contrast to its systemic effects, 17αE2 did not significantly improve neural outcomes in APOE3 or APOE4 females. These findings address the impact of biological sex on established protective effects of a longevity-promoting intervention against APOE4 phenotypes, which have significant relevance to the prevention of age-related conditions including metabolic dysfunction, cognitive impairment and vulnerability to AD.

Suppression of insulin-like growth factor-1 (IGF-1) signaling extends mammalian life span and protects against a range of age-related diseases. Unexpectedly, we found that reduced IGF-1 signaling fails to extend the life span of mitochondrial mutator mice. Most of the longevity pathways that are normally initiated by IGF-1 suppression were either blocked or blunted in the mutator mice. These observations suggest that the prolongevity effects of IGF-1 suppression critically depend on the integrity of the mitochondrial genome, revealing an unexpected hierarchy in the pathways that control mammalian aging. Together, these findings deepen our understanding of the interactions between the hallmarks of aging and underscore the need for interventions that preserve the integrity of the mitochondrial genome.

BACKGROUND:Deferoxamine (DFO) and other iron chelators are clinically used for cancer and stroke. They may also be useful for Alzheimers disease (AD) to diminish iron from microbleeds. DFO may also stimulate antioxidant membrane repair which is impaired during AD. DFO, and other chelators do enter the brain despite some contrary reports. OBJECTIVE:Low dose, oral DFO was given in lab chow to wildtype (WT) C57BL/6 mice to evaluate potential impact on iron levels, iron-signaling and storage proteins, and amyloid precursor protein (APP) and processing enzymes. Young WT mice do not have microbleeds or disrupted blood-brain barrier of AD mice. METHODS:Iron was measured by MRI and chemically after two weeks of dietary DFO. Cerebral cortex was examined for changes in iron metabolism, antioxidant signaling, and APP processing by Western blot. RESULTS:DFO decreased brain iron by 18% (MRI) and decreased seven major proteins that mediate iron metabolism by at least 25%. The iron storage proteins ferritin light and heavy chain decreased by at least 30%. APP and secretase enzymes also decreased by 30%. CONCLUSIONS:WT mice respond to DFO with decreased APP, amyloid processing enzymes, and antioxidant repair. Potential DFO treatment for early-stage AD by DFO should consider the benefits of lowered APP and secretase enzymes.

Introduction: Air pollution derived from diesel exhaust has been linked with cognitive decline and cerebrovascular diseases. In previous studies, subacute diesel exhaust exposure has been shown to increase neurotoxicity and white matter damage; however, few studies have modeled the effects of air quality improvement. Our previous data from the same cohort showed persistent microglial activation (Iba-1) after an 8-week recovery period. The objective of this study was to further investigate the extent of recovery after neurotoxic diesel exhaust particulate (DEP) exposure. Methods: Female and male 8-week-old C57BL/6 mice were exposed to inhaled Filtered Air (FA) and DEP (NIST SRM 2975) at concentration of 100μg/m3. There were three arms in this study: 1) 8 weeks of FA or DEP exposure (n=16/group); 2) 8 weeks of FA or DEP exposure followed by 8 weeks of recovery (n=16/group); and 3) 16 weeks of FA or DEP exposure (n=16/group). Mice were humanely euthanized and brain hemispheres sectioned at 5 µm. Corpus callosum levels of C5 complement protein, C5a anaphylatoxin, 4-hydroxynonenal (4-HNE), 8-Oxo-2'-deoxyguanosine (8-OHDG), and degraded myelin basic protein (dMBP) were assayed via immunofluorescence. Results: The 8-week DEP group demonstrated increases in C5 (+39%), C5a (+45%), 4-HNE (+107%), 8-OHDG (+26%), and dMBP (+118%) in comparison to the 8-week FA group. The 8-week DEP recovery group demonstrated no significant elevation in C5, C5a, 4-HNE, and 8-OHDG in comparison to the 8-week FA recovery group. However, dMBP remained elevated (+87%) after in the 8-week DEP recovery group compared to the 8-week FA recovery group. The 16-week DEP group demonstrated increases in C5 (+44%), C5a (+58%), 4-HNE (+106%), 8-OHDG (+57%), and dMBP (+94%) in comparison to the 16-week FA group (p-values in Figure 1). Conclusions: DEP exposure results in increased oxidative stress, neuroinflammation, and myelin breakdown at 8 weeks and 16 weeks. Unlike neuroinflammation and oxidative stress that recovered, white matter damage showed a persistent effect after an 8-week washout period. Combined with our previous data on persistent microglia activation, this suggests that prolonged neuroimmune response may contribute to the white matter injury that persists several months after DEP exposure termination.

SummaryThe apolipoprotein ε4 allele (APOE4) is associated with decreased longevity, increased vulnerability to age-related declines, and disorders across multiple systems. Interventions that promote healthspan and lifespan represent a promising strategy to attenuate the development ofAPOE4-associated aging phenotypes. Here we studied the ability of the longevity-promoting intervention 17α-estradiol (17αE2) to protect against age-related impairments inAPOE4versus the predominantAPOE3genotype using early middle-aged mice with knock-in of humanAPOEalleles. Beginning at age 10 months, maleAPOE3orAPOE4mice were treated for 20 weeks with 17αE2 or vehicle then compared for indices of aging phenotypes body-wide. Across peripheral and neural measures,APOE4was associated with poorer outcomes. Notably, 17αE2 treatment improved outcomes in a genotype-dependent manner favoringAPOE4mice. These data demonstrate a positiveAPOE4bias in 17αE2-mediated healthspan actions, suggesting that longevity-promoting interventions may be useful in mitigating deleterious age-related risks associated withAPOE4genotype.

Alzheimer’s disease (AD) is associated with complex pathophysiology including synaptic dysregulation, compromised neurotrophic signaling, deficits in autophagic flux and neuroinflammation). Skeletal muscle regulates many brain functions relevant to aging, by activating the muscle-to-brain axis through the secretion of skeletal muscle originating factors (myokines) with cellular-modifying, neuro and geroprotective properties. Our group developed transgenic mice that overexpress the skeletal muscle human Transcription Factor EB (TFEB), a master regulator of lysosomal-to-nucleus signaling, resulting in enhanced proteostasis and neuroprotection in a Tau mouse model. However, the precise mechanisms remain unknown. Therefore, we further validated these effects in an AD amyloid β (Aβ) mouse model and investigated the underlying mechanism. We crossbred female 5xFAD mice, carrying 5 AD familial mutations, with transgenic mice that overexpress human TFEB to create 5xFAD;cTFEB;HSA-Cre (3FA) mice. At 4 and 8 months of age, we analyzed Aβ plaque accumulation through immunohistochemistry and conducted western blot analysis for multiple synaptic markers, growth factors, autophagic/lysosomal regulators, and myokines across the muscle-to-brain axis. We also performed a battery of neurocognitive tests (open field, the Barnes maze, and fear conditioning) at 8 months of age, when this model has previously been reported to demonstrate robust cognitive impairment. Skeletal muscle-targeted TFEB expression reduced Aβ plaque accumulation in cortices of 4-month-old female mice. Furthermore, muscle-TFEB expression altered synaptic-associated gene transcriptional signatures in hippocampi, and rescued behavioral deficits in 8-month-old female 5xFAD mice. Western blots of cortex from 8-month-old female 3FA mice confirmed a rescue of several synaptic markers including SNAP25, synaptophysin I, synaptotagmin I and PSD95, neurotrophic factors such as BDNF and autophagic/lysosomal regulators such as Cathepsin D and B, prosaposin (PSAP) and saposin C. Levels of PSAP (a recently identified exercise-responsive myokine) were also increased in skeletal muscle, plasma and cortices, suggesting that PSAP may act as a novel myokine involved in muscle-to-brain rescue mechanisms. scle, plasma and cortices of 8-month-old female mice, suggesting that PSAP may act as a novel myokine involved in muscle-to-brain rescue mechanisms. Skeletal muscle directly regulates CNS function and health in the 5xFAD model regulating synaptic integrity, neurotrophic signaling and autophagic flux, potentially through release of CNS-targeting myokines.

Increased brain iron is associated with sporadic Alzheimer Disease (AD) and Down Syndrome with AD (DSAD), which may involve iron from cerebral microhemorrhages (MBs). The prevalence of MBs is higher in DSAD, possibly from the triplication of the amyloid precursor protein on chromosome 21. Increased MB iron could cause oxidative damage through Fenton chemistry and subsequent lipid peroxidation. We hypothesize that iron and APP are intrinsically linked, and that triplication of APP would result in more tissue iron and lipid peroxidation than observed in sporadic AD. Prefrontal cortex and cerebellum of cognitively normal, AD, and DSAD( n  = 8/group) were examined for iron metabolism, antioxidant response, and amyloid peptides by immunoblot, inductively coupled mass spectrometry, and enzymatic assay. Iron was 2-fold higher in DSAD. Iron storage proteins and lipid peroxidation were increased in prefrontal cortex, but not in the cerebellum. The glutathione synthesis protein GCLM was decreased by 50% in both AD and DSAD. Activity of lipid raft GPx4, responsible for membrane repair, was decreased by at least 30% in AD and DSAD. These decreases in GPx4 activity were paralleled by reduced α-secretase activity while β-secretase activity increased. DSAD shows greater lipid peroxidation than AD consistent with greater MBs and iron load. DSAD also shares similar and more pronounced features of AD such as decreased protein levels of critical GSH producing enzyme GCLM and other protective mechanisms against lipid peroxidation. The extensive increase of iron and lipid peroxidation suggests their linkage to APP gene dosage. The impairment of these key mechanisms asserts ferroptosis as a key feature during AD.

ABSTRACTIron-mediated cell death (ferroptosis) is a proposed mechanism of Alzheimer’s disease (AD) pathology. While iron is essential for basic biological functions, its reactivity generates oxidants which contribute to cell damage and death. To further resolve mechanisms of iron-mediated toxicity in AD, we analyzed postmortem human brain and ApoEFAD mice. AD brains had decreased antioxidant enzymes, including those mediated by glutathione (GSH). Subcellular analyses of AD brains showed greater oxidative damage and lower antioxidant enzymes in lipid rafts, the site of amyloid processing, than in the non-raft membrane fraction. ApoE4 carriers had lower lipid raft yield with greater membrane oxidation. The hypothesized role of iron to AD pathology was tested in ApoEFAD mice by iron chelation with deferoxamine, which decreased fibrillar amyloid and lipid peroxidation, together with increased GSH-mediated antioxidants. These novel molecular pathways in iron mediated damage during AD.Graphical AbstractHypothesis: AD brain lipid peroxidation is driven by increased brain iron and decreased antioxidant defenses. Schema shows proteins that mediate iron metabolism in relation to lipid peroxidation (HNE) and antioxidant defenses in prefrontal cortex. AD-associated increase (red), decrease (blue), or no change (grey), relative to cognitively normal elderly controls. Aβ; amyloid beta, ALDH2; alcohol dehydrogenase, APP; amyloid precursor protein, DMT1; divalent metal transporter 1; FPN, ferroportin; FSP1, ferroptosis suppressor protein 1, which requires the quinol cycle to attenuate lipid peroxidation; FTH1, ferritin heavy chain; FTL; ferritin light chain; GCLC, glutathione cysteine ligase catalytic subunit; GCLM, glutathione cysteine ligase modulator; GPx4, glutathione peroxidase 4; GSH, glutathione; GSSG, glutathione disulfide; GSTA4, glutathione S-transferase A4; HMOX; heme oxygenase; IRP, iron regulatory protein; LAT1, large neutral amino acid transporter 1; LOOH, Lipid hydroperoxides; Nrf2, Nuclear factor erythroid 2-related factor 2; Prdx6, peroxiredoxin 6; TF, transferrin, TfR; Transferrin receptor; xCT, cysteine-glutamate antiporter.

Air pollution (AirP) increases the risk of accelerated cognitive decline, dementia, and behavioral disorders associated with oxidative damage in humans. These AirP responses are shared with rodent models. The underlying impact of AirP-mediated molecular changes on synapses remains unexplored. We examined synaptosomes extracted from cerebral cortex of mice chronically exposed to inhaled diesel exhaust particles (DEP) for 8 weeks. DEP selectively decreased postsynaptic proteins (PSD-95; p = 0.04, SAP97; p = 0.01) by at least 20 % and NMDA receptor subunits (GluN1; p = 0.03, N2A; p = 0.009, N2B; p = 0.01) by 15 %, without altering the evaluated pre-synaptic proteins. Antioxidant enzymes for oxidized phospholipid repair (GPx4; p = 0.015), iron metabolism (HMOX1; p = 0.04), and glutathione synthesis (GCLC; p = 0.008), which participate in mitigating ferroptosis, a form of cell death present in Alzheimer's disease, increased by at least 15 %. These findings suggest subcellular responses to AirP in glutamatergic synapses. Further analyses of the impact of AirP on synapses may consider protective mechanisms by antioxidant enzymes to enhance cognitive health at all ages.

Background Among the anthropoids, humans uniquely have apolipoprotein E (ApoE) isoforms that modulate Alzheimer's disease (AD) risk and accelerate aspects of brain aging. While chimpanzee and human ApoE4 share R112 and R158, the oldest chimps do not show symptoms of advanced AD. Another key structural difference is T61 in chimps instead of R61 found in humans predicted to be structurally similar to ApoE3.Objective Besides their impact on later life brain health, ApoE isoforms influence the development of brain regions relevant to AD. We explored the functional impact of ApoE isoforms produced by astrocytes on neuronal morphology and considered structural predictions for their differences.Methods Astrocyte conditioned media (ACM) was collected from primary astrocytes cultured from mice with targeted replacement of mouse ApoE with human ApoE3, ApoE4, or chimp. Neuron morphology was then examined in neonatal rat hippocampal neurons cultured in ACM. In vitro data was complemented by structural analysis of ApoE isoforms.Results ApoE-chimp ACM stimulated 30% more neurites per neuron than human ApoE ACM. In contrast, ACM from ApoE-chimp more closely resembled human ApoE4 than ApoE3, yielding 40% shorter neurites and spines. Structural modeling confirmed that chimpanzee ApoE differs from both ApoE4 than ApoE3, consistent with the predicted evolutionary trajectory.Conclusions Chimpanzee ApoE is structurally and functionally closer to ApoE4 than ApoE3 but still differs for neuronal development and protein folding. These findings provide insight into species-specific ApoE evolution, with implications for AD susceptibility and neuronal development.

Iron is implicated in Alzheimer’s disease (AD) and is bound to β-amyloid (Ab) plaques. AD brains have increased 4-hydroxynonenal (HNE) adducts, a lipid decomposition product bound to proteins originating from iron mediated lipid peroxidation. Increased brain iron may result from cerebral microbleeds which by nature are rich sources of iron. In EFAD aging, microbleeds arise before amyloid plaque formation, suggesting a role for microbleeds in plaque formation. We hypothesize that treatment with the iron chelator Deferoxamine (DFO) would reduce brain iron and attenuate oxidative damage from these microbleeds. 6-month female EFAD mice were treated with DFO (10mg/kg/day) by diet (2 weeks; n = 9) or intraperitoneal injection (1 week; n = 11) and compared to untreated (n = 8). Cerebral cortex was assayed for soluble Aβ peptides, insoluble Aβ fibrils, and HNE by dot blot. Antioxidants were measured by Western blot or GPx assay (Cayman Chemical). DFO in diet or by IP decreased insoluble fibrillar amyloid by 50% with corresponding 2-fold increases in soluble Aβ monomers Aβ40 and -42. DFO reduced HNE levels by 50%; nitrotyrosine, a non-iron dependent oxidation marker, remained unchanged. Protection from lipid oxidation is mediated by GPx4 or GSTA4, which DFO increased by 50%. These measures were complimented with 25% increases in total GPx activity by DFO. DFO solubilized fibrillar Aβ and increased Aβ monomers. Furthermore, DFO increased antioxidants critical to the protection against microbleed-induced oxidative damage. These findings are substantiated by the decrease in HNE. Future studies will examine combination therapy with Aβ monoclonal antibodies which may liberate bound iron from Aβ plaques.

An age-related decline in mitochondrial function is a multi-factorial hallmark of aging, driven partly by increased lipid hydroperoxide levels that impair mitochondrial respiration in skeletal muscle, leading to atrophy. Although pharmacological and genetic manipulations to counteract increased lipid hydroperoxide levels represent a promising strategy to treat sarcopenia, the mechanisms driving such phenotypes remain understudied. Peroxiredoxin 6 (Prdx6) is a multifunctional enzyme that contributes to peroxidized membrane repair via its phospholipid hydroperoxidase and phospholipase A2 activities. Here, we show decreased mitochondrial Prdx6 levels, increased mitochondrial lipid peroxidation, and dysregulated muscle bioenergetics in aged mice and muscle cells derived from older humans. Mechanistically, we found that Prdx6 supports optimal mitochondrial function and prevents mitochondrial fragmentation by limiting mitochondrial lipid peroxidation via its membrane remodeling activities. Our results suggest that age-related declines in mitochondrial Prdx6 contribute to dysregulated muscle bioenergetics, thereby opening the door to therapeutic modulation of Prdx6 to counteract diminished mitochondrial function in aging.

INTRODUCTION:Cerebral microbleeds (MBs) are associated with sporadic Alzheimer's disease (AD) and Down syndrome with AD (DSAD). Higher MB iron may cause iron-mediated lipid peroxidation. We hypothesize that amyloid deposition is linked to MB iron and that amyloid precursor protein (APP) triplication increases iron load and lipid peroxidation. METHODS:Prefrontal cortex and cerebellum of cognitively normal control (CTL), AD, and DSAD ApoE3,3 carriers were examined for proteins that mediated iron metabolism, antioxidant response, and amyloid processing in lipid rafts. RESULTS:Iron was twofold higher in DSAD than in CTL and AD. Iron storage proteins and lipid peroxidation were increased in the prefrontal cortex. The glutathione synthesis protein GCLM was decreased by 50% in both AD and DSAD. Activity of lipid raft GPx4, responsible for membrane repair, was decreased by at least 30% in AD and DSAD. DISCUSSION:DSAD shows greater lipid peroxidation than AD, consistent with greater MBs and iron load. HIGHLIGHTS:DSAD has increased ferroptotic-related changes compared to sporadic AD. Lipid rafts that process APP have a loss of protective antioxidant enzymes. Partial and mosaic trisomy lowers the amyloid and iron burden.

Age increases of brain amyloid plaques may be mediated by prior increase of soluble Aβ42. Here, we show that frontal cortex samples from brains of cognitively normal aging humans had progressively increased levels of soluble amyloid peptide Aβ40 throughout the lifespan. Aggregated amyloid fraction was subsequently obtained by formic acid, where Aβ42 showed increases only in humans over 90 years old when compared to those younger than 50. Similarly, aging wild-type mice without amyloid plaques had increases of both soluble Aβ40 and Aβ42, as previously shown in normal aging rats. Aging also alters secretase enzymes and processing of amyloid precursor protein (APP). Here, we isolate membrane domains known as lipid rafts, a site of APP cleavage. We found that lipid rafts isolated from mouse and human cerebral cortex showed age increases of β-secretase enzyme activity, while amyloidogenic secretase proteins levels BACE1 and PS1 decreased with age in mouse. Lipid rafts merit further study in aging and neurodegeneration.