Sex differences in metabolic aging of the brain: insights into female susceptibility to Alzheimer's disease

Metabolomics biomarkers of frailty: a longitudinal study of aging female and male mice

Frailty is an age-related geriatric syndrome. We performed a longitudinal study of aging female (n = 40) and male (n = 47) C57BL/6NIA mice, measured frailty index and derived metabolomics data from plasma. We identify age-related differentially abundant metabolites, determine frailty-related metabolites, and generate frailty features, both in the whole cohort and sex-stratified subgroups. Using the features, we perform an association study and build a metabolomics-based frailty clock. We find that frailty-related metabolites are enriched for amino acid metabolism and metabolism of cofactors and vitamins, include ergothioneine, tryptophan and alpha-ketoglutarate, and present sex dimorphism. We identify B vitamin metabolism related flavin-adenine dinucleotide and pyridoxate as female-specific frailty biomarkers, and lipid metabolism related sphingomyelins, glycerophosphoethanolamine and glycerophosphocholine as male-specific frailty biomarkers. These associations are confirmed in a validation cohort, with ergothioneine and perfluorooctanesulfonate identified as robust frailty biomarkers. Our results identify sex-specific metabolite frailty biomarkers, and shed light on potential mechanisms.

Unraveling sex differences in Alzheimer's disease and related endophenotypes with brain proteomes

INTRODUCTION

Sex differences exist in Alzheimer's disease (AD), but the underlying mechanisms remain unclear.

METHODS

We examined brain proteomes profiled from the dorsolateral prefrontal cortex of 770 donors (66.2% female).

RESULTS

Proteome-wide differential expression analysis in males and females jointly identified many significant proteins for AD dementia (n = 1228), amyloid beta (n = 1183), tangles (n = 1309), and global cognitive trajectory (n = 2325) at a false discovery rate of <0.05. Sex-stratified analyses also identified many proteins associated with AD or its endophenotypes. Finally, we found 10 proteins with significant sex-by-trait interactions, including one in AD clinical diagnosis (MARCKS), seven in cognitive trajectories (TOGARAM1, PLCD3, SLC22A5, MTFR1L, DCUN1D5, S100A12, and TRIM46), and two in cerebral pathologies (PANK4 and SOS1).

DISCUSSION

The 10 proteins with sex interaction in AD cover a range of functions likely relevant for AD pathogenesis, including estrogen response, inflammation, and mitochondrial biology, and their specific roles in AD ought to be studied. Future work should test their potential as sex-specific AD biomarkers.

HIGHLIGHTS

At the phenotypic level, we found sex differences in baseline cognitive performance, cognitive trajectories, and AD hallmark pathologies. Proteome-wide differential expression analyses identified many brain proteins associated with AD and its endophenotypes in either sex alone or when considered together. We found 10 brain proteins with significant sex interactions in AD and its endophenotypes, which could be investigated as potential sex-specific biomarkers of AD.

Evidence of cortical vascular impairments in early stage of Alzheimer's transgenic mice: Optical imaging

Alzheimer's disease (AD), a neurodegenerative disorder with progressive cognitive decline, remains clinically challenging with limited understanding of etiology and interventions. Clinical studies have reported vascular defects prior to other pathological manifestations of AD, leading to the "Vascular Hypothesis" for the disorder. However, in vivo assessments of cerebral vasculature in AD rodent models have been constrained by limited spatiotemporal resolution or field of view of conventional imaging. We herein employed two in vivo imaging technologies, Dual-Wavelength Imaging and Optical Coherence Doppler Tomography, to evaluate cerebrovascular reactivity (CVR) to vasoconstrictive cocaine and vasodilatory hypercapnia challenges and to detect resting 3D cerebral blood flow (CBF) in living transgenic AD mice at capillary resolution. Results showed that CVR to cocaine and hypercapnia was significantly attenuated in 7-10 months old AD mice vs controls, indicating reduced vascular flexibility and reactivity. Additionally, in the AD mice, arterial CBF velocities were slower and the microvascular density in cortex was decreased compared to controls. These results reveal significant vascular impairments including reduced CVR and resting CBF in early-staged AD mice. Hence, this cutting-edge in vivo optical imaging offers an innovative venue for detecting early neurovascular dysfunction in AD brain with translational potential.

Lifespan of male and female APP/PS1 and APPNL-F/NL-F mouse models of Alzheimer's disease

Alzheimer's disease (AD) disproportionately affects women, yet most preclinical research studies are male-centric. We performed lifespan analyses of male and female AD mouse models (APP/PS1 and APPNL-F/NL-F) and their shared genetic background control (C57BL/6). Survival curves support significant sex differences between genotypes. Minimal longevity revealed increased age in male APP/PS1, and decreased age in male APPNL-F/NL-F mice. Maximal longevity revealed an increased average age in males. Furthermore, median lifespan differed between sex and genotype. This study supports dimorphic survival in two mouse models of AD, emphasizing the need to examine mechanisms and treatments in both sexes.

Sexual dimorphisms in innate immune activation markers in predementia Alzheimer's disease

Females have an increased risk of developing Alzheimer's disease (AD). The innate immune system plays a key role in AD pathology, and sex differences in innate immune responses may contribute to differences in disease risk and progression. This study investigated sex differences in innate immune responses among participants without cerebrospinal fluid (CSF) determined amyloid pathology [A-; cognitively normal (CN), n = 83] and those with amyloid pathology (A+, n = 202), further stratified into preclinical (CN with A+, n = 72) and mild cognitive impairment (MCI with A+, n = 130). Participants were drawn from the Norwegian Dementia Disease Initiation cohort (n = 285). We measured plasma glial fibrillary acidic protein (GFAP) and CSF concentrations of nine innate immune markers: soluble triggering receptor expressed on myeloid cells 2 (sTREM2), monocyte chemoattractant protein 1 (MCP-1), fractalkine, chitinase 3-like 1 (YKL-40), clusterin, interferon gamma (IFN-γ), interleukin-6 (IL-6), IL-10, and IL-18. Linear regression was used, adjusted for multiple comparisons using the false discovery rate. In A+ cases (n = 202, females = 105), females had lower MCP-1 (P  < 0.01), IL-6 and IL-18 (both P  < 0.05) than males, while no sex differences were observed in A- cases (n = 83, females = 39). Among A+ participants, no sex differences were observed in CN cases (n = 72, females = 37), but females (n = 68) with MCI had lower MCP-1 and IL-6 (both P  < 0.05) than males (n = 62) with MCI. Moreover, A+ females exhibited stronger positive associations between sTREM2 and clusterin with CSF total tau (P < 0.001; P < 0.05) and Neurofilament light chain (P < 0.01; P < 0.01) than males. These findings suggest sex-specific differences in innate immune responses, which may contribute to disease progression in amyloid-positive individuals.

Metabolomics biomarkers of frailty: a longitudinal study of aging female and male mice

Frailty is an age-related geriatric syndrome, for which the mechanisms remain largely unknown. We performed a longitudinal study of aging female (n = 40) and male (n = 47) C57BL/6NIA mice, measured frailty index and derived metabolomics data from plasma samples. We identify differentially abundant metabolites related to aging, determine frailty related metabolites via a machine learning approach, and generate a union set of frailty features, both in the whole cohort and in sex-stratified subgroups. Using the features, we perform an association study and build a metabolomics-based frailty clock. We find that frailty related metabolites are enriched for amino acid metabolism and metabolism of cofactors and vitamins, include ergothioneine, tryptophan, and alpha-ketoglutarate, and present sex dimorphism. We identify B vitamin metabolism related flavin adenine dinucleotide and pyridoxate as female-specific frailty biomarkers, and lipid metabolism related sphingomyelins, glycerophosphoethanolamine and glycerophosphocholine as male-specific frailty biomarkers. These associations are confirmed in a validation cohort, with ergothioneine and perfluorooctanesulfonate identified as robust frailty biomarkers. In summary, our results identify sex-specific metabolite biomarkers of frailty in aging, and shed light on potential mechanisms involved in frailty.

APOE4 and infectious diseases jointly contribute to brain glucose hypometabolism, a biomarker of Alzheimer's pathology: New findings from the ADNI

BACKGROUND

Impaired brain glucose metabolism is a preclinical feature of neurodegenerative diseases such as Alzheimer's disease (AD). Infections may promote AD-related pathology. Therefore, we investigated the interplay between infections and APOE4, a strong genetic risk factor for AD.

METHODS

We analyzed data on 1,509 participants in the Alzheimer's Disease Neuroimaging Initiative (ADNI) database using multivariate linear regression models. The outcomes were rank-normalized hypometabolic convergence index (HCI), statistical regions of interest (SROI) for AD, and mild cognitive impairment (MCI). Marginal mean estimates for infections, stratified by APOE4 carrier status, were then computed.

RESULTS

Prior infections were associated with greater HCI [β = 0.15, 95% CI: 0.03, 0.27, p = 0.01]. The combined effects of infections and APOE4 carriers on HCI levels were significantly greater than either variable alone. Among APOE4 carriers, the estimated marginal mean was 0.62, rising to 0.77, with infections (p<0.001), indicating an interaction effect. Carriers with multiple infections showed greater hypometabolism (higher HCI), with an estimate of 0.44 (p = 0.01) compared to 0.11 (p = 0.08) for those with a single infection, revealing a dose-response relationship. The estimates for the association of infections with SROI AD and SROI MCI were β = -0.01 (p = 0.02) and β = -0.01 (p = 0.04), respectively.

CONCLUSION

Our findings suggest that infections and APOE4 jointly contribute to brain glucose hypometabolism and AD pathology, supporting a "multi-hit" mechanism in AD development.

Lifespan of male and female APP/PS1 and APPNL-F/NL-F mouse models of Alzheimer's disease

Alzheimer's disease (AD) disproportionately affects women, yet most preclinical research studies are male-centric. We performed lifespan analyses of male and female AD mouse models (APP/PS1 and APPNL-F/NL-F) and their shared genetic background control (C57BL/6). Survival curves support significant sex differences between within genotypes. Minimal longevity revealed increased age in male APP/PS1, and decreased age in APPNL-F/NL-F mice. Maximal longevity revealed an increased average age in males. Furthermore, median lifespan differed between sex and genotype. This study supports sexual dimorphic survival in two mouse models of AD, emphasizing the need to examine mechanisms and treatments in both sexes.

APOE4 and Infectious Diseases Jointly Contribute to Brain Glucose Hypometabolism, a Biomarker of Alzheimer's Pathology: New Findings from the ADNI

Background

Impaired brain glucose metabolism is a preclinical feature of neurodegenerative diseases such as Alzheimer's disease (AD). Infections may promote AD-related pathology. Therefore, we investigated the interplay between infections and APOE4, a strong genetic risk factor for AD.

Methods

We analyzed data on 1,509 participants in the Alzheimer's Disease Neuroimaging Initiative (ADNI) database using multivariate linear regression models. The outcomes were rank-normalized hypometabolic convergence index (HCI), statistical regions of interest (SROI) for AD, and mild cognitive impairment (MCI). Marginal mean estimates for infections, stratified by APOE4 carrier status, were then computed.

Results

Prior infections were associated with greater HCI [β=0.15, 95% CI: 0.03, 0.27, p=0.01]. The combined effects of infections and APOE4 carriers on HCI levels were significantly greater than either variable alone. Among APOE4 carriers, the estimated marginal mean was 0.62, rising to 0.77, with infections (p<0.001), indicating an interaction effect. Carriers with multiple infections showed greater hypometabolism (higher HCI), with an estimate of 0.44 (p=0.01) compared to 0.11 (p=0.08) for those with a single infection, revealing a dose-response relationship. The estimates for the association of infections with SROI AD and SROI MCI were β=-0.01 (p=0.02) and β=-0.01 (p=0.04), respectively.

Conclusion

Our findings suggest that infections and APOE4 jointly contribute to brain glucose hypometabolism and AD pathology, supporting a "multi-hit" mechanism in AD development.

Subcortical volume in middle-aged adults with fetal alcohol spectrum disorders

Studies of youth and young adults with prenatal alcohol exposure (PAE) have most consistently reported reduced volumes of the corpus callosum, cerebellum and subcortical structures. However, it is unknown whether this continues into middle adulthood or if individuals with PAE may experience premature volumetric decline with aging. Forty-eight individuals with fetal alcohol spectrum disorders (FASD) and 28 healthy comparison participants aged 30 to 65 participated in a 3T MRI session that resulted in usable T1-weighted and T2-weighted structural images. Primary analyses included volumetric measurements of the caudate, putamen, pallidum, cerebellum and corpus callosum using FreeSurfer software. Analyses were conducted examining both raw volumetric measurements and subcortical volumes adjusted for overall intracranial volume (ICV). Models tested for main effects of age, sex and group, as well as interactions of group with age and group with sex. We found the main effects for group; all regions were significantly smaller in participants with FASD for models using raw volumes (P's < 0.001) as well as for models using volumes adjusted for ICV (P's < 0.046). Although there were no significant interactions of group with age, females with FASD had smaller corpus callosum volumes relative to both healthy comparison females and males with FASD (P's < 0.001). As seen in children and adolescents, adults aged 30 to 65 with FASD showed reduced volumes of subcortical structures relative to healthy comparison adults, suggesting persistent impact of PAE. Moreover, the observed volumetric reduction of the corpus callosum in females with FASD could suggest more rapid degeneration, which may have implications for cognition as these individuals continue to age.

Human apolipoprotein E glycosylation and sialylation: from structure to function

Human apolipoprotein E (ApoE) was first identified as a polymorphic gene in the 1970s; however, the genetic association of ApoE genotypes with late-onset sporadic Alzheimer's disease (sAD) was only discovered 20 years later. Since then, intensive research has been undertaken to understand the molecular effects of ApoE in the development of sAD. Despite three decades' worth of effort and over 10,000 papers published, the greatest mystery in the ApoE field remains: human ApoE isoforms differ by only one or two amino acid residues; what is responsible for their significantly distinct roles in the etiology of sAD, with ApoE4 conferring the greatest genetic risk for sAD whereas ApoE2 providing exceptional neuroprotection against sAD. Emerging research starts to point to a novel and compelling hypothesis that the sialoglycans posttranslationally appended to human ApoE may serve as a critical structural modifier that alters the biology of ApoE, leading to the opposing impacts of ApoE isoforms on sAD and likely in the peripheral systems as well. ApoE has been shown to be posttranslationally glycosylated in a species-, tissue-, and cell-specific manner. Human ApoE, particularly in brain tissue and cerebrospinal fluid (CSF), is highly glycosylated, and the glycan chains are exclusively attached via an O-linkage to serine or threonine residues. Moreover, studies have indicated that human ApoE glycans undergo sialic acid modification or sialylation, a structural alteration found to be more prominent in ApoE derived from the brain and CSF than plasma. However, whether the sialylation modification of human ApoE has a biological role is largely unexplored. Our group recently first reported that the three major isoforms of human ApoE in the brain undergo varying degrees of sialylation, with ApoE2 exhibiting the most abundant sialic acid modification, whereas ApoE4 is the least sialylated. Our findings further indicate that the sialic acid moiety on human ApoE glycans may serve as a critical modulator of the interaction of ApoE with amyloid β (Aβ) and downstream Aβ pathogenesis, a prominent pathologic feature in AD. In this review, we seek to provide a comprehensive summary of this exciting and rapidly evolving area of ApoE research, including the current state of knowledge and opportunities for future exploration.

Brain-body mechanisms contribute to sexual dimorphism in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is the most common form of human motor neuron disease. It is characterized by the progressive degeneration of upper and lower motor neurons, leading to generalized motor weakness and, ultimately, respiratory paralysis and death within 3-5 years. The disease is shaped by genetics, age, sex and environmental stressors, but no cure or routine biomarkers exist for the disease. Male individuals have a higher propensity to develop ALS, and a different manifestation of the disease phenotype, than female individuals. However, the mechanisms underlying these sex differences remain a mystery. In this Review, we summarize the epidemiology of ALS, examine the sexually dimorphic presentation of the disease and highlight the genetic variants and molecular pathways that might contribute to sex differences in humans and animal models of ALS. We advance the idea that sexual dimorphism in ALS arises from the interactions between the CNS and peripheral organs, involving vascular, metabolic, endocrine, musculoskeletal and immune systems, which are strikingly different between male and female individuals. Finally, we review the response to treatments in ALS and discuss the potential to implement future personalized therapeutic strategies for the disease.

Aging, sex, metabolic and life experience factors: Contributions to neuro-inflammaging in Alzheimer's disease research

Alzheimer's disease (AD) is prevalent around the world, yet our understanding of the disease is still very limited. Recent work suggests that the cornerstone of AD may include the inflammation that accompanies it. Failure of a normal pro-inflammatory immune response to resolve may lead to persistent central inflammation that contributes to unsuccessful clearance of amyloid-beta plaques as they form, neuronal death, and ultimately cognitive decline. Individual metabolic, and dietary (lipid) profiles can differentially regulate this inflammatory process with aging, obesity, poor diet, early life stress and other inflammatory factors contributing to a greater risk of developing AD. Here, we integrate evidence for the interface between these factors, and how they contribute to a pro-inflammatory brain milieu. In particular, we discuss the importance of appropriate polyunsaturated fatty acids (PUFA) in the diet for the metabolism of specialised pro-resolving mediators (SPMs); raising the possibility for dietary strategies to improve AD outlook.

Excision of the endothelial blood-brain barrier insulin receptor does not alter spatial cognition in mice fed either a chow or high-fat diet

Insulin is transported across the blood-brain barrier (BBB) endothelium to regulate aspects of metabolism and cognition. Brain insulin resistance often results from high-fat diet (HFD) consumption and is thought to contribute to spatial cognition deficits. To target BBB insulin function, we used Cre-LoxP genetic excision of the insulin receptor (InsR) from endothelial cells in adult male mice. We hypothesized that this excision would impair spatial cognition, and that high-fat diet consumption would exacerbate these effects. Excision of the endothelial InsR did not impair performance in two spatial cognition tasks, the Y-Maze and Morris Water Maze, in tests held both before and after 14 weeks of access to high-fat (or chow control) diet. The HFD increased body weight gain and induced glucose intolerance but did not impair spatial cognition. Endothelial InsR excision tended to increase body weight and reduce sensitivity to peripheral insulin, but these metabolic effects were not associated with impairments to spatial cognition and did not interact with HFD exposure. Instead, all mice showed intact spatial cognitive performance regardless of whether they had been fed chow or a HFD, and whether the InsR had been excised or not. Overall, the results indicate that loss of the endothelial InsR does not impact spatial cognition, which is in line with pharmacological evidence that other mechanisms at the BBB facilitate insulin transport and allow it to exert its pro-cognitive effects.

Mechanisms of sex differences in Alzheimer's disease

Alzheimer's disease (AD) and the mechanisms underlying its etiology and progression are complex and multifactorial. The higher AD risk in women may serve as a clue to better understand these complicated processes. In this review, we examine aspects of AD that demonstrate sex-dependent effects and delve into the potential biological mechanisms responsible, compiling findings from advanced technologies such as single-cell RNA sequencing, metabolomics, and multi-omics analyses. We review evidence that sex hormones and sex chromosomes interact with various disease mechanisms during aging, encompassing inflammation, metabolism, and autophagy, leading to unique characteristics in disease progression between men and women.

Altered metabolism and DAM-signatures in female brains and microglia with aging

Despite Alzheimer's disease (AD) disproportionately affecting women, the mechanisms remain elusive. In AD, microglia undergo 'metabolic reprogramming', which contributes to microglial dysfunction and AD pathology. However, how sex and age contribute to metabolic reprogramming in microglia is understudied. Here, we use metabolic imaging, transcriptomics, and metabolic assays to probe age- and sex-associated changes in brain and microglial metabolism. Glycolytic and oxidative metabolism in the whole brain was determined using Fluorescence Lifetime Imaging Microscopy (FLIM). Young female brains appeared less glycolytic than male brains, but with aging, the female brain became 'male-like.' Transcriptomic analysis revealed increased expression of disease-associated microglia (DAM) genes (e.g., ApoE, Trem2, LPL), and genes involved in glycolysis and oxidative metabolism in microglia from aged females compared to males. To determine whether estrogen can alter the expression of these genes, BV-2 microglia-like cell lines, which abundantly express DAM genes, were supplemented with 17β-estradiol (E2). E2 supplementation resulted in reduced expression of DAM genes, reduced lipid and cholesterol transport, and substrate-dependent changes in glycolysis and oxidative metabolism. Consistent with the notion that E2 may suppress DAM-associated factors, LPL activity was elevated in the brains of aged female mice. Similarly, DAM gene and protein expression was higher in monocyte-derived microglia-like (MDMi) cells derived from middle-aged females compared to age-matched males and was responsive to E2 supplementation. FLIM analysis of MDMi from young and middle-aged females revealed reduced oxidative metabolism and FAD+ with age. Overall, our findings show that altered metabolism defines age-associated changes in female microglia and suggest that estrogen may inhibit the expression and activity of DAM-associated factors, which may contribute to increased AD risk, especially in post-menopausal women.

Long-term suboptimal dietary trace element supply does not affect trace element homeostasis in murine cerebellum

The ageing process is associated with alterations of systemic trace element (TE) homeostasis increasing the risk, e.g. neurodegenerative diseases. Here, the impact of long-term modulation of dietary intake of copper, iron, selenium, and zinc was investigated in murine cerebellum. Four- and 40-wk-old mice of both sexes were supplied with different amounts of those TEs for 26 wk. In an adequate supply group, TE concentrations were in accordance with recommendations for laboratory mice while suboptimally supplied animals received only limited amounts of copper, iron, selenium, and zinc. An additional age-adjusted group was fed selenium and zinc in amounts exceeding recommendations. Cerebellar TE concentrations were measured by inductively coupled plasma-tandem mass spectrometry. Furthermore, the expression of genes involved in TE transport, DNA damage response, and DNA repair as well as selected markers of genomic stability [8-oxoguanine, incision efficiency toward 8-oxoguanine, 5-hydroxyuracil, and apurinic/apyrimidinic sites and global DNA (hydroxy)methylation] were analysed. Ageing resulted in a mild increase of iron and copper concentrations in the cerebellum, which was most pronounced in the suboptimally supplied groups. Thus, TE changes in the cerebellum were predominantly driven by age and less by nutritional intervention. Interestingly, deviation from adequate TE supply resulted in higher manganese concentrations of female mice even though the manganese supply itself was not modulated. Parameters of genomic stability were neither affected by age, sex, nor diet. Overall, this study revealed that suboptimal dietary TE supply does not substantially affect TE homeostasis in the murine cerebellum.

Altered Metabolism and DAM-signatures in Female Brains and Microglia with Aging

Despite Alzheimer's disease (AD) disproportionately affecting women, the mechanisms remain elusive. In AD, microglia undergo 'metabolic reprogramming', which contributes to microglial dysfunction and AD pathology. However, how sex and age contribute to metabolic reprogramming in microglia is understudied. Here, we use metabolic imaging, transcriptomics, and metabolic assays to probe age-and sex-associated changes in brain and microglial metabolism. Glycolytic and oxidative metabolism in the whole brain was determined using Fluorescence Lifetime Imaging Microscopy (FLIM). Young female brains appeared less glycolytic than male brains, but with aging, the female brain became 'male-like.' Transcriptomic analysis revealed increased expression of disease-associated microglia (DAM) genes (e.g., ApoE, Trem2, LPL), and genes involved in glycolysis and oxidative metabolism in microglia from aged females compared to males. To determine whether estrogen can alter the expression of these genes, BV-2 microglia-like cell lines, which abundantly express DAM genes, were supplemented with 17β-estradiol (E2). E2 supplementation resulted in reduced expression of DAM genes, reduced lipid and cholesterol transport, and substrate-dependent changes in glycolysis and oxidative metabolism. Consistent with the notion that E2 may suppress DAM-associated factors, LPL activity was elevated in the brains of aged female mice. Similarly, DAM gene and protein expression was higher in monocyte-derived microglia-like (MDMi) cells derived from middle-aged females compared to age-matched males and was responsive to E2 supplementation. FLIM analysis of MDMi from young and middle-aged females revealed reduced oxidative metabolism and FAD+ with age. Overall, our findings show that altered metabolism defines age-associated changes in female microglia and suggest that estrogen may inhibit the expression and activity of DAM-associated factors, which may contribute to increased AD risk, especially in post-menopausal women.

Impairment of cerebral vascular reactivity and resting blood flow in early-staged transgenic AD mice: in vivo optical imaging studies

Background

Alzheimer's disease (AD) is a neurodegenerative disorder with progressive cognitive decline in aging individuals that poses a significant challenge to patients due to an incomplete understanding of its etiology and lack of effective interventions. While "the Amyloid Cascade Hypothesis," the abnormal accumulation of amyloid-β in the brain, has been the most prevalent theory for AD, mounting evidence from clinical and epidemiological studies suggest that defects in cerebral vessels and hypoperfusion appear prior to other pathological manifestations and might contribute to AD, leading to "the Vascular Hypothesis." However, assessment of structural and functional integrity of the cerebral vasculature in vivo in the brain from AD rodent models has been challenging owing to the limited spatiotemporal resolution of conventional imaging technologies.

Methods

We employed two in vivo imaging technologies, i.e., Dual-Wavelength Imaging (DWI) and Optical Coherence Tomography (OCT), to evaluate cerebrovascular reactivity (CVR; responsiveness of blood vessels to vasoconstriction as triggered by cocaine) in a relatively large field of view of the cortex in vivo, and 3D quantitative cerebrovascular blood flow (CBF) imaging in living transgenic AD mice at single vessel resolution.

Results

Our results showed significantly impaired CVR and reduced CBF in basal state in transgenic AD mice compared to non-transgenic littermates in an early stage of AD progression. Changes in total hemoglobin (Δ[HbT]) in response to vasoconstriction were significantly attenuated in AD mice, especially in arteries and tissue, and the recovery time of Δ[HbT] after vasoconstriction was shorter for AD than WT in all types of vessels and cortical tissue, thereby indicating hypoperfusion and reduced vascular flexibility. Additionally, our 3D OCT images revealed that CBF velocities in arteries were slower and that the microvascular network was severely disrupted in the brain of AD mice.

Conclusions

These results suggest significant vascular impairment in basal CBF and dynamic CVR in the neurovascular network in a rodent model of AD at an early stage of the disease. These cutting-edge in vivo optical imaging tools offer an innovative venue for detecting early neurovascular dysfunction in relation to AD pathology and pave the way for clinical translation of early diagnosis and elucidation of AD pathogenesis in the future.

A small-molecule TLR4 antagonist reduced neuroinflammation in female E4FAD mice

BACKGROUND

APOE genotype is the greatest genetic risk factor for sporadic Alzheimer's disease (AD). APOE4 increases AD risk up to 12-fold compared to APOE3, an effect that is greater in females. Evidence suggests that one-way APOE could modulate AD risk and progression through neuroinflammation. Indeed, APOE4 is associated with higher glial activation and cytokine levels in AD patients and mice. Therefore, identifying pathways that contribute to APOE4-associated neuroinflammation is an important approach for understanding and treating AD. Human and in vivo evidence suggests that TLR4, one of the key receptors involved in the innate immune system, could be involved in APOE-modulated neuroinflammation. Consistent with that idea, we previously demonstrated that the TLR4 antagonist IAXO-101 can reduce LPS- and Aβ-induced cytokine secretion in APOE4 glial cultures. Therefore, the goal of this study was to advance these findings and determine whether IAXO-101 can modulate neuroinflammation, Aβ pathology, and behavior in mice that express APOE4.

METHODS

We used mice that express five familial AD mutations and human APOE3 (E3FAD) or APOE4 (E4FAD). Female and male E4FAD mice and female E3FAD mice were treated with vehicle or IAXO-101 in two treatment paradigms: prevention from 4 to 6 months of age or reversal from 6 to 7 months of age. Learning and memory were assessed by modified Morris water maze. Aβ deposition, fibrillar amyloid deposition, astrogliosis, and microgliosis were assessed by immunohistochemistry. Soluble levels of Aβ and apoE, insoluble levels of apoE and Aβ, and IL-1β were measured by ELISA.

RESULTS

IAXO-101 treatment resulted in lower Iba-1 coverage, lower number of reactive microglia, and improved memory in female E4FAD mice in both prevention and reversal paradigms. IAXO-101-treated male E4FAD mice also had lower Iba-1 coverage and reactivity in the RVS paradigm, but there was no effect on behavior. There was also no effect of IAXO-101 treatment on neuroinflammation and behavior in female E3FAD mice.

CONCLUSION

Our data supports that TLR4 is a potential mechanistic therapeutic target for modulating neuroinflammation and cognition in APOE4 females.

Sex differences in socioemotional behavior and changes in ventral hippocampal transcription across aging in C57Bl/6J mice

Socioemotional health is positively correlated with improved cognitive and physical aging. Despite known sex differences in socioemotional behaviors and the trajectory of aging, the interactive effects between sex and aging on socioemotional outcomes are poorly understood. We performed the most comprehensive assessment of sex differences in socioemotional behaviors in C57Bl/6J mice across aging to date. Compared to males, females exhibited decreased anxiety-like behavior and social preference but increased social recognition. With age, anxiety-like behavior, cued threat memory generalization, and social preference increased in both sexes. To investigate potential neural mechanisms underlying these behavioral changes, we analyzed transcriptional neuropathology markers in the ventral hippocampus and found age-related changes in genes related to activated microglia, angiogenesis, and cytokines. Sex differences emerged in the timing, direction, and magnitude of these changes, independent of reproductive senescence in aged females. Interestingly, female-specific upregulation of autophagy-related genes correlated with age-related behavioral changes selectively in females. These novel findings reveal critical sex differences in trajectories of ventral hippocampal aging that may contribute to sex- and age-related differences in socioemotional outcomes.

Sex differences in alpha-synucleinopathies: a systematic review

Background

Past research indicates a higher prevalence, incidence, and severe clinical manifestations of alpha-synucleinopathies in men, leading to a suggestion of neuroprotective properties of female sex hormones (especially estrogen). The potential pathomechanisms of any such effect on alpha-synucleinopathies, however, are far from understood. With that aim, we undertook to systematically review, and to critically assess, contemporary evidence on sex and gender differences in alpha-synucleinopathies using a bench-to-bedside approach.

Methods

In this systematic review, studies investigating sex and gender differences in alpha-synucleinopathies (Rapid Eye Movement (REM) Behavior Disorder (RBD), Parkinson's Disease (PD), Dementia with Lewy Bodies (DLB), Multiple System Atrophy (MSA)) from 2012 to 2022 were identified using electronic database searches of PubMed, Embase and Ovid.

Results

One hundred sixty-two studies were included; 5 RBD, 6 MSA, 20 DLB and 131 PD studies. Overall, there is conclusive evidence to suggest sex-and gender-specific manifestation in demographics, biomarkers, genetics, clinical features, interventions, and quality of life in alpha-synucleinopathies. Only limited data exists on the effects of distinct sex hormones, with majority of studies concentrating on estrogen and its speculated neuroprotective effects.

Conclusion

Future studies disentangling the underlying sex-specific mechanisms of alpha-synucleinopathies are urgently needed in order to enable novel sex-specific therapeutics.

Characterizing age- and sex-related differences in brain structure among middle-aged and older Hispanic/Latino adults in the study of Latinos- investigation of neurocognitive aging magnetic resonance imaging (SOL-INCA MRI)

Hispanic/Latino adults are a growing segment of the older U.S. population yet are underrepresented in brain aging research. We aimed to characterize brain aging among diverse Hispanic/Latino individuals. Hispanic/Latino individuals (unweighted n = 2273 ages 35-85 years; 56% female) from the Hispanic Community Health Study/Study of Latinos (HCHS/SOL) population-based study underwent magnetic resonance imaging (MRI) as part of the SOL- Investigation of Neurocognitive Aging MRI (SOL-INCA-MRI) ancillary study (2018-2022). We performed linear regressions to calculate age associations with brain volumes for each outcome (total (global) brain, hippocampal, lateral ventricle, total white matter hyperintensity (WMH), individual cortical lobar, and total cortical gray matter) and tested modification by sex. Older age was associated with smaller gray matter volumes and larger lateral ventricle and WMH volumes. Age-related differences in global brain volumes and gray matter volumes in specific regions (i.e., the hippocampus and temporal and occipital lobes) were less pronounced among women. Our findings warrant further investigation into sex-specific mechanisms of brain aging using longitudinal studies.

Sex differences in the progression of glucose metabolism dysfunction in Alzheimer's disease

Alzheimer's disease (AD) is a common neurodegenerative disease characterized by amyloid plaques and impaired brain metabolism. Because women have a higher prevalence of AD than men, sex differences are of great interest. Using cross-sectional and longitudinal data, we showed sex-dependent metabolic dysregulations in the brains of AD patients. Cohort 1 (South Korean, n = 181) underwent Pittsburgh compound B-PET, fluorodeoxyglucose-PET, magnetic resonance imaging, and blood biomarker (plasma tau and beta-amyloid 42 and 40) measurements at baseline and two-year follow-ups. Transcriptome analysis of data from Cohorts 2 and 3 (European, n = 78; Singaporean, n = 18) revealed sex differences in AD-related alterations in brain metabolism. In women (but not in men), all imaging indicators displayed consistent correlation curves with AD progression. At the two-year follow-up, clear brain metabolic impairment was revealed only in women, and the plasma beta-amyloid 42/40 ratio was a possible biomarker for brain metabolism in women. Furthermore, our transcriptome analysis revealed sex differences in transcriptomes and metabolism in the brains of AD patients as well as a molecular network of 25 female-specific glucose metabolic genes (FGGs). We discovered four key-attractor FGG genes (ALDOA, ENO2, PRKACB, and PPP2R5D) that were associated with amyloid/tau-related genes (APP, MAPT, BACE1, and BACE2). Furthermore, these genes successfully distinguished amyloid positivity in women. Understanding sex differences in the pathogenesis of AD and considering these differences will improve development of effective diagnostics and therapeutic treatments for AD.

Exploring the aging process of cognitively healthy adults by analyzing cerebrospinal fluid metabolomics using liquid chromatography-tandem mass spectrometry

BACKGROUND

During biological aging, significant metabolic dysregulation in the central nervous system may lead to cognitive decline and neurodegeneration. However, the metabolomics of the aging process in cerebrospinal fluid (CSF) has not been thoroughly explored.

METHODS

In this cohort study of CSF metabolomics using liquid chromatography-mass spectrometry (LC-MS), fasting CSF samples collected from 92 cognitively unimpaired adults aged 20-87 years without obesity or diabetes were analyzed.

RESULTS

We identified 37 metabolites in these CSF samples with significant positive correlations with aging, including cysteine, pantothenic acid, 5-hydroxyindoleacetic acid (5-HIAA), aspartic acid, and glutamate; and two metabolites with negative correlations, asparagine and glycerophosphocholine. The combined alterations of asparagine, cysteine, glycerophosphocholine, pantothenic acid, sucrose, and 5-HIAA showed a superior correlation with aging (AUC = 0.982). These age-correlated changes in CSF metabolites might reflect blood-brain barrier breakdown, neuroinflammation, and mitochondrial dysfunction in the aging brain. We also found sex differences in CSF metabolites with higher levels of taurine and 5-HIAA in women using propensity-matched comparison.

CONCLUSIONS

Our LC-MS metabolomics of the aging process in a Taiwanese population revealed several significantly altered CSF metabolites during aging and between the sexes. These metabolic alterations in CSF might provide clues for healthy brain aging and deserve further exploration.

Molecular insights into sex-specific metabolic alterations in Alzheimer's mouse brain using multi-omics approach

BACKGROUND

Alzheimer's disease (AD) is a progressive neurodegenerative disorder that is characterized by altered cellular metabolism in the brain. Several of these alterations have been found to be exacerbated in females, known to be disproportionately affected by AD. We aimed to unravel metabolic alterations in AD at the metabolic pathway level and evaluate whether they are sex-specific through integrative metabolomic, lipidomic, and proteomic analysis of mouse brain tissue.

METHODS

We analyzed male and female triple-transgenic mouse whole brain tissue by untargeted mass spectrometry-based methods to obtain a molecular signature consisting of polar metabolite, complex lipid, and protein data. These data were analyzed using multi-omics factor analysis. Pathway-level alterations were identified through joint pathway enrichment analysis or by separately evaluating lipid ontology and known proteins related to lipid metabolism.

RESULTS

Our analysis revealed significant AD-associated and in part sex-specific alterations across the molecular signature. Sex-dependent alterations were identified in GABA synthesis, arginine biosynthesis, and in alanine, aspartate, and glutamate metabolism. AD-associated alterations involving lipids were also found in the fatty acid elongation pathway and lysophospholipid metabolism, with a significant sex-specific effect for the latter.

CONCLUSIONS

Through multi-omics analysis, we report AD-associated and sex-specific metabolic alterations in the AD brain involving lysophospholipid and amino acid metabolism. These findings contribute to the characterization of the AD phenotype at the molecular level while considering the effect of sex, an overlooked yet determinant metabolic variable.

Age-Related Oxidative Redox and Metabolic Changes Precede Intraneuronal Amyloid-β Accumulation and Plaque Deposition in a Transgenic Alzheimer's Disease Mouse Model

BACKGROUND

Many identified mechanisms could be upstream of the prominent amyloid-β (Aβ) plaques in Alzheimer's disease (AD).

OBJECTIVE

To profile the progression of pathology in AD.

METHODS

We monitored metabolic signaling, redox stress, intraneuronal amyloid-β (iAβ) accumulation, and extracellular plaque deposition in the brains of 3xTg-AD mice across the lifespan.

RESULTS

Intracellular accumulation of aggregated Aβ in the CA1 pyramidal cells at 9 months preceded extracellular plaques that first presented in the CA1 at 16 months of age. In biochemical assays, brain glutathione (GSH) declined with age in both 3xTg-AD and non-transgenic controls, but the decline was accelerated in 3xTg-AD brains from 2 to 4 months. The decline in GSH correlated exponentially with the rise in iAβ. Integrated metabolic signaling as the ratio of phospho-Akt (pAkt) to total Akt (tAkt) in the PI3kinase and mTOR pathway declined at 6, 9, and 12 months, before rising at 16 and 20 months. These pAkt/tAkt ratios correlated with both iAβ and GSH levels in a U-shaped relationship. Selective vulnerability of age-related AD-genotype-specific pAkt changes was greatest in the CA1 pyramidal cell layer. To demonstrate redox causation, iAβ accumulation was lowered in cultured middle-age adult 3xTg-AD neurons by treatment of the oxidized redox state in the neurons with exogenous cysteine.

CONCLUSION

The order of pathologic progression in the 3xTg-AD mouse was loss of GSH (oxidative redox shift) followed by a pAkt/tAkt metabolic shift in CA1, iAβ accumulation in CA1, and extracellular Aβ deposition. Upstream targets may prove strategically more effective for therapy before irreversible changes.

Effects of aging and long-term physical activity on mitochondrial physiology and redox state of the cortex and cerebellum of female rats

We investigated the effects of aging and long-term physical activity on markers of mitochondrial function and dynamics in the cortex and cerebellum of female rats. Additionally, we interrogated markers of oxidative damage and antioxidants. Thirty-four female Lewis rats were separated into three groups. A young group (YNG, n = 10) was euthanized at 6 months of age. Two other groups were aged to 15 months and included a physical activity group (MA-PA, n = 12) and a sedentary group (MA-SED, n = 12). There were no age effects for any of the variables investigated, except for SOD2 protein levels in the cortex (+6.5%, p = 0.012). Long-term physical activity increased mitochondrial complex IV activity in the cortex compared to YNG (+85%, p = 0.016) and MA-SED (+82%, p = 0.023) and decreased carbonyl levels in the cortex compared to YNG (-12.49%, p = 0.034). Our results suggest that the mitochondrial network and redox state of the brain of females may be more resilient to the aging process than initially thought. Further, voluntary wheel running had minimal beneficial effects on brain markers of oxidative damage and mitochondrial physiology.

Modeling CSF-1 receptor deficiency diseases - how close are we?

The role of colony-stimulating factor-1 receptor (CSF-1R) in macrophage and organismal development has been extensively studied in mouse. Within the last decade, mutations in the CSF1R have been shown to cause rare diseases of both pediatric (Brain Abnormalities, Neurodegeneration, and Dysosteosclerosis, OMIM #618476) and adult (CSF1R-related leukoencephalopathy, OMIM #221820) onset. Here we review the genetics, penetrance, and histopathological features of these diseases and discuss to what extent the animal models of Csf1r deficiency currently available provide systems in which to study the underlying mechanisms involved.

Biological underpinnings of sex differences in neurological disorders

The importance of sex differences in neurological disorders has been increasingly acknowledged in recent clinical and basic research studies, but the complex biology and genetics underlying sex-linked biological heterogeneity and its brain-to-body impact remained incompletely understood. Men and women differ substantially in their susceptibility to certain neurological diseases, in the severity of symptoms, prognosis as well as the nature and efficacy of their response to treatments. The detailed mechanisms underlying these differences, especially at the molecular level, are being addressed in many studies but leave a lot to be further revealed. Here, we provide an overview of recent advances in our understanding of how sex differences in the brain and brain-body signaling contribute to neurological disorders and further present some future prospects entailed in terms of diagnostics and therapeutics.

Retinal Aging in 3× Tg-AD Mice Model of Alzheimer's Disease

The retina, as part of the central nervous system (CNS), can be the perfect target for in vivo, in situ, and noninvasive neuropathology diagnosis and assessment of therapeutic efficacy. It has long been established that several age-related brain changes are more pronounced in Alzheimer's disease (AD). Nevertheless, in the retina such link is still under-explored. This study investigates the differences in the aging of the CNS through the retina of 3× Tg-AD and wild-type mice. A dedicated optical coherence tomograph imaged mice's retinas for 16 months. Two neural networks were developed to model independently each group's ages and were then applied to an independent set containing images from both groups. Our analysis shows a mean absolute error of 0.875±1.1 × 10⁻² and 1.112±1.4 × 10⁻² months, depending on training group. Our deep learning approach appears to be a reliable retinal OCT aging marker. We show that retina aging is distinct in the two classes: the presence of the three mutated human genes in the mouse genome has an impact on the aging of the retina. For mice over 4 months-old, transgenic mice consistently present a negative retina age-gap when compared to wild-type mice, regardless of training set. This appears to contradict AD observations in the brain. However, the ‘black-box” nature of deep-learning implies that one cannot infer reasoning. We can only speculate that some healthy age-dependent neural adaptations may be altered in transgenic animals.

Sex Differences in Alzheimer's Disease: Insights From the Multiomics Landscape

Alzheimer's disease (AD) has complex etiologies, and the impact of sex on AD varies over the course of disease development. The literature provides some evidence of sex-specific contributions to AD. However, molecular mechanisms of sex-biased differences in AD remain elusive. Multiomics data in tandem with systems biology approaches offer a new avenue to dissect sex-stratified molecular mechanisms of AD and to develop sex-specific diagnostic and therapeutic strategies for AD. Single-cell transcriptomic datasets and cell deconvolution of bulk tissue transcriptomic data provide additional insights into brain cell type-specific impact on sex-biased differences in AD. In this review, we summarize the impact of sex chromosomes and sex hormones on AD, the impact of sex-biased differences during AD development, and the interplay between sex and a major AD genetic risk factor, the APOE ε4 genotype, through the multiomics landscape. Several sex-biased molecular pathways such as neuroinflammation and bioenergetic metabolism have been identified. The importance of sex chromosome and sex hormones, as well as the associated pathways in AD pathogenesis, is further strengthened by findings from omics studies. Future research efforts should integrate the multiomics data from different brain regions and different cell types using systems biology approaches, and leverage the knowledge into a holistic examination of sex differences in AD. Advances in systems biology technologies and increasingly available large-scale multiomics datasets will facilitate future studies dissecting such complex signaling mechanisms to better understand AD pathogenesis in both sexes, with the ultimate goals of developing efficacious sex- and APOE-stratified preventive and therapeutic interventions for AD.

1H NMR metabolomic profiling of human cerebrospinal fluid in aging process

The molecular process of biological aging might be accompanied by significant metabolic derangement, especially in the central nervous system (CNS), since the brain has an enormous energy demand. However, the metabolic signature of the aging process in cerebrospinal fluid (CSF) has not been thoroughly investigated, especially in the Asian population. In this prospective cohort study on CSF metabolomics using proton nuclear magnetic resonance (NMR) spectroscopy, fasting CSF samples from 75 cognitively unimpaired patients aged 20-92 years without diabetes or obesity, undergoing spinal anesthesia for elective surgery were analyzed. Several metabolites in CSF samples were identified as having a significant association with the aging process in cerebral circulation; among the metabolites, the levels of alanine, citrate, creatinine, lactate, leucine, tyrosine, and valine significantly increased in old patients compared to those in young patients. The combined CSF metabolite alterations in citrate, lactate, leucine, tyrosine, and valine had a superior correlation with the aging process in all age groups. In conclusion, our pilot study of aging CSF metabolomics in the Taiwanese population presents significantly altered CSF metabolites with potential relevance to the aging process. These metabolic alterations in CSF samples might imply increasing anaerobic glycolysis, mitochondrial dysfunction, and decreasing glucose utilization in cerebral circulation in aged patients.

Towards developing a rhesus monkey model of early Alzheimer's disease focusing on women's health

Alzheimer's disease (AD) is the most common cause of elderly dementia, affecting nearly 50 million people worldwide, with two-thirds of the cases in the USA in women. Despite considerable investment, this prevalence is expected to increase further in the coming decades, based on the projected demographics of the population. Currently, most of the preclinical AD studies rely on transgenic mice carrying mutations associated with the early onset familiar form of AD, although the vast majority of cases are sporadic. A prevailing current hypothesis is that the cascade of events leading to AD starts with the accumulation of small soluble oligomers of the Aβ peptide (AβOs) that target and disrupt synapses. Taking advantage of the high translational power of rhesus monkeys due to their physiological and genetic similarities to humans, we recently developed a female rhesus monkey model of early AD pathogenesis based on exogenous administration AβOs. Here we review and discuss how soluble oligomers of Aβ can target vulnerable spines in the neocortex and hippocampus of female middle-aged monkeys and induce neuroinflammatory responses, similar to what is known to occur in the human brain. Developing a rhesus monkey model of early AD focusing on women's health is critical for the understanding of how hormonal changes during menopause transition affect brain health and ultimately may contribute to AD neurodegeneration.

Preventing Alzheimer's disease within reach by 2025: Targeted-risk-AD-prevention (TRAP) strategy

INTRODUCTION

Alzheimer's disease (AD) is a progressive neurodegenerative disease that currently affects 6.2 million people in the United States and is projected to impact 12.7 million worldwide in 2050 with no effective disease-modifying therapeutic or cure. In 2011 as part of the National Alzheimer's Project Act, the National Plan to Address Alzheimer's Disease was signed into law which proposed to effectively prevent AD by 2025, which is rapidly approaching. The preclinical phase of AD can begin 20 years prior to diagnosis, which provides an extended window for preventive measures that would exert a transformative impact on incidence and prevalence of AD.

METHODS

A novel combination of text-mining and natural language processing strategies to identify (1) AD risk factors, (2) therapeutics that can target risk factor pathways, and (3) studies supporting therapeutics in the PubMed database was conducted. To classify the literature relevant to AD preventive strategies, a relevance score (RS) based on STRING (search tool for the retrieval of interacting genes/proteins) score for protein-protein interactions and a confidence score (CS) on Bayesian inference were developed. To address mechanism of action, network analysis of protein targets for effective drugs was conducted. Collectively, the analytic approach, referred to as a targeted-risk-AD-prevention (TRAP) strategy, led to a ranked list of candidate therapeutics to reduce AD risk.

RESULTS

Based on TRAP mining of 9625 publications, 364 AD risk factors were identified. Based on risk factor indications, 629 Food and Drug Administration-approved drugs were identified. Computation of ranking scores enabled identification of 46 relevant high confidence (RS & CS > 0.7) drugs associated with reduced AD risk. Within these candidate therapeutics, 16 had more than one clinical study supporting AD risk reduction. Top-ranked therapeutics with high confidence emerged within lipid-lowering, anti-inflammatory, hormone, and metabolic-related drug classes.

DISCUSSION

Outcomes of our novel bioinformatic strategy support therapeutic targeting of biological mechanisms and pathways underlying relevant AD risk factors with high confidence. Early interventions that target pathways associated with increased risk of AD have the potential to support the goal of effectively preventing AD by 2025.

Exercise and estrogen: common pathways in Alzheimer's disease pathology

Alzheimer's disease (AD) is a neurodegenerative disease that is characterized by progressive declines in cognitive function. Current epidemiological data indicate significant sex-linked disparities, where females have a higher risk of developing AD compared with male counterparts. This disparity necessitates further investigations to uncover the pathological and molecular factors influencing these sex differences. Although the underlying pathways behind this observed disparity remain elusive, recent research points to menopausal estrogen loss as a potential factor. Estrogen holds a significant role in amyloid precursor protein (APP) processing and overall neuronal health through the regulation of brain-derived neurotrophic factor (BDNF), a factor that is also reduced in postmenopausal women. BDNF is a known contributor to neuronal health and its reduced expression is typically linked to AD disorders. Exercise is known to increase BDNF and may provide an accessible activity for postmenopausal women to reduce their risk of AD. This review aims to discuss the relationship between estrogen, exercise, and BDNF in AD pathology.

The piperine derivative HJ105 inhibits Aβ1-42-induced neuroinflammation and oxidative damage via the Keap1-Nrf2-TXNIP axis

BACKGROUND

Piperine is a great lead compound, as a phytopharmaceutical with reported neuroprotective effects in neurodegenerative diseases. HJ105, a piperine derivative with high affinity to Keap1 receptor, attracts increasing attention in Alzheimer's disease (AD) treatment.

PURPOSE

This work mainly aimed to study HJ105's therapeutic effects on Aβ_1-42-associated AD and the underpinning mechanisms.

METHODS

In the in vivo part, a rat model of AD was established by bilateral intra-hippocampal administration of aggregated Aβ_1-42, followed by a month of intragastric HJ105 or donepezil administration. Spatial and learning memories were detected by the Morris water maze assay, passive avoidance learning as well as Y-maze test. The morphology of hippocampal neurons was assessed by hematoxylin-eosin (H&E) staining. In addition, the amounts of the IL-1β and TNF-α were obtained with specific ELISA kits. More importantly, apoptosis-related proteins and factors involved in Nrf2/TXNIP/NLPR3 pathways were detected by Western blot, while the interaction between Keap1 and Nrf2 was assessed by co-immunoprecipitation. In the in vitro part, human neuroblastoma (SH-SY5Y) cells were applied to evaluate the role of HJ105 on Aβ_1-42-induced neuronal damage.

RESULTS

Treatment of HJ105 not only reversed memory impairment, but also protected neurons in the hippocampus by inhibiting Bax/Bcl2 ratio increase. HJ105 decreased TXNIP expression, suppressing NLRP3 inflammasome activation in the hippocampus, which in turn counteracted the upregulation of IL-1β and TNF-α. Notably, HJ105 exerted an inhibitory effect on Keap1-Nrf2 interaction and upregulated nuclear Nrf2, which conversely increased the expression levels of superoxide dismutase, catalase and glutathione peroxidase and downregulated malondialdehyde. Additionally, neurotoxicity induced by Aβ_1-42 in SH-SY5Y cells was alleviated by HJ105.

CONCLUSION

Overall, HJ105 exerts neuroprotective effects in SH-SY5Y cells induced by Aβ_1-42 as well as in experimental rats with AD by decreasing apoptosis, oxidative stress and neuroinflammation, partly via suppression of Keap1-Nrf2 complex generation. HJ105 might represent a promising compound for AD treatment.

Network Modeling Sex Differences in Brain Integrity and Metabolic Health

Hypothesis-driven studies have demonstrated that sex moderates many of the relationships between brain health and cardiometabolic disease, which impacts risk for later-life cognitive decline. In the present study, we sought to further our understanding of the associations between multiple markers of brain integrity and cardiovascular risk in a midlife sample of 266 individuals by using network analysis, a technique specifically designed to examine complex associations among multiple systems at once. Separate network models were constructed for male and female participants to investigate sex differences in the biomarkers of interest, selected based on evidence linking them with risk for late-life cognitive decline: all components of metabolic syndrome (obesity, hypertension, dyslipidemia, and hyperglycemia); neuroimaging-derived brain-predicted age minus chronological age; ratio of white matter hyperintensities to whole brain volume; seed-based resting state functional connectivity in the Default Mode Network, and ratios of N-acetyl aspartate, glutamate and myo-inositol to creatine, measured through proton magnetic resonance spectroscopy. Males had a sparse network (87.2% edges = 0) relative to females (69.2% edges = 0), indicating fewer relationships between measures of cardiometabolic risk and brain integrity. The edges in the female network provide meaningful information about potential mechanisms between brain integrity and cardiometabolic health. Additionally, Apolipoprotein ϵ4 (ApoE ϵ4) status and waist circumference emerged as central nodes in the female model. Our study demonstrates that network analysis is a promising technique for examining relationships between risk factors for cognitive decline in a midlife population and that investigating sex differences may help optimize risk prediction and tailor individualized treatments in the future.

Sex-specific Changes in Brain Estrogen Metabolism Induced by Acute Trimethyltin Exposure

BACKGROUND/AIM

In this study, we investigated sex-specific effects of acute exposure to trimethyltin, a known neurotoxicant on metabolic steroids.

MATERIALS AND METHODS

We administered intraperitoneally 2.3 mg/kg trimethyltin to 4-week-old male mice and measured the levels of metabolic steroids 24 h after treatment. We also measured mRNA and protein levels of cytochrome P450 1B1 using real-time polymerase chain reaction and western blotting.

RESULTS

Cortisol levels in the cortex increased in both sexes following acute trimethyltin exposure. The estradiol levels decreased, and the 4-hydroxyestradiol levels increased only in females. We also observed increased cytochrome P450 1B1 mRNA and protein levels only in the female cortex.

CONCLUSION

Acute trimethyltin exposure induces distinct sex-specific metabolic changes in the brain before significant sexual maturation.

A Negative Energy Balance Is Associated with Metabolic Dysfunctions in the Hypothalamus of a Humanized Preclinical Model of Alzheimer's Disease, the 5XFAD Mouse

Increasing evidence links metabolic disorders with neurodegenerative processes including Alzheimer’s disease (AD). Late AD is associated with amyloid (Aβ) plaque accumulation, neuroinflammation, and central insulin resistance. Here, a humanized AD model, the 5xFAD mouse model, was used to further explore food intake, energy expenditure, neuroinflammation, and neuroendocrine signaling in the hypothalamus. Experiments were performed on 6-month-old male and female full transgenic (Tg^5xFAD/5xFAD), heterozygous (Tg^5xFAD/-), and non-transgenic (Non-Tg) littermates. Although histological analysis showed absence of Aβ plaques in the hypothalamus of 5xFAD mice, this brain region displayed increased protein levels of GFAP and IBA1 in both Tg^5xFAD/- and Tg^5xFAD/5xFAD mice and increased expression of IL-1β in Tg^5xFAD/5xFAD mice, suggesting neuroinflammation. This condition was accompanied by decreased body weight, food intake, and energy expenditure in both Tg^5xFAD/- and Tg^5xFAD/5xFAD mice. Negative energy balance was associated with altered circulating levels of insulin, GLP-1, GIP, ghrelin, and resistin; decreased insulin and leptin hypothalamic signaling; dysregulation in main metabolic sensors (phosphorylated IRS1, STAT5, AMPK, mTOR, ERK2); and neuropeptides controlling energy balance (NPY, AgRP, orexin, MCH). These results suggest that glial activation and metabolic dysfunctions in the hypothalamus of a mouse model of AD likely result in negative energy balance, which may contribute to AD pathogenesis development.

Microglial heterogeneity in aging and Alzheimer's disease: Is sex relevant?

Neurodegenerative diseases and their associated cognitive decline are known to be more prevalent during aging. Recent evidence has uncovered the role of microglia, the immunocompetent cells of the brain, in dysfunctions linked to neurodegenerative diseases such as is Alzheimer's disease (AD). Similar to other pathologies, AD is shown to be sex-biased, with females being more at risk compared to males. While the mechanisms driving this prevalence are still unclear, emerging data suggest the sex differences present in microglia throughout life might lead to different responses of these cells in both health and disease. Furthermore, microglial cells have recently been recognized as a deeply heterogeneous population, with multiple subsets and/or phenotypes stemming from diverse parameters such as age, sex or state of health. Therefore, this review discusses microglial heterogeneity during aging in both basal conditions and AD with a focus on existing sex differences in this process.

Likelihood ratio statistics for gene set enrichment in Alzheimer's disease pathways

INTRODUCTION

The study of Alzheimer's disease (AD) has revealed biological pathways with implications for disease neuropathology and pathophysiology. These pathway-level effects may also be mediated by individual characteristics or covariates such as age or sex. Evaluation of AD biological pathways in the context of interactions with these covariates is critical to the understanding of AD as well as the development of model systems used to study the disease.

METHODS

Gene set enrichment methods are powerful tools used to interpret gene-level statistics at the level of biological pathways. We introduce a method for quantifying gene set enrichment using likelihood ratio-derived test statistics (gsLRT), which accounts for sample covariates like age and sex. We then use our method to test for age and sex interactions with protein expression levels in AD and to compare the pathway results between human and mouse species.

RESULTS

Our method, based on nested logistic regressions is competitive with the existing standard for gene set testing in the context of linear models and complex experimental design. The gene sets we identify as having a significant association with AD-both with and without additional covariate interactions-are validated by previous studies. Differences between gsLRT results on mouse and human datasets are observed.

DISCUSSION

Characterizing biological pathways involved in AD builds on the important work involving single gene drivers. Our gene set enrichment method finds pathways that are significantly related to AD while accounting for covariates that may be relevant to disease development. The method highlights commonalities and differences between human AD and mouse models, which may inform the development of higher fidelity models for the study of AD.

Sex differences in the blood-brain barrier and neurodegenerative diseases

The number of people diagnosed with neurodegenerative diseases is on the rise. Many of these diseases, including Alzheimer's disease, Parkinson's disease, multiple sclerosis, and motor neuron disease, demonstrate clear sexual dimorphisms. While sex as a biological variable must now be included in animal studies, sex is rarely included in in vitro models of human neurodegenerative disease. In this Review, we describe these sex-related differences in neurodegenerative diseases and the blood-brain barrier (BBB), whose dysfunction is linked to neurodegenerative disease development and progression. We explain potential mechanisms by which sex and sex hormones affect BBB integrity. Finally, we summarize current in vitro BBB bioengineered models and highlight their potential to study sex differences in BBB integrity and neurodegenerative disease.

Examining the effects of ovarian hormone loss and diet-induced obesity on Alzheimer's disease markers of amyloid-β production and degradation

After menopause, women experience declines in ovarian sex hormones, an event that has recently been associated with increased amyloid-β peptides, a main feature of Alzheimer's disease. Diet-induced insulin resistance also increases amyloid-β peptides; however, whether this process is exacerbated with ovarian sex hormone loss remains unknown. Female C57BL6/J mice received either bilateral ovariectomy (OVX; n = 20) or remained intact (n = 20) at 24 wk of age and were placed on either a low- or high-fat diet (LFD, n = 10 for OVX and intact; HFD, n = 10 for OVX and intact) for 10 wk. Independently, OVX led to increases in the amyloidogenic marker, soluble amyloid precursor protein β (sAPPβ). The HFD in combination with OVX led to lower insulin degrading enzyme (IDE) protein content and activity in the prefrontal cortex, indicative of decreased amyloid-β degradation; however, no differences in amyloid-β content were observed. Data from this study provide novel evidence of independent effects of peripheral insulin resistance and ovarian sex hormone loss in decreasing brain markers of amyloid-β degradation. Furthermore, findings indicate how the loss of ovarian sex hormones can promote the formation of amyloidogenic APP cleavage products, independent of diet-induced insulin resistance.NEW & NOTEWORTHY This study provides novel insight into the effect of peripheral insulin resistance and ovarian hormone loss in decreasing brain markers of amyloid-β degradation. Results demonstrate that ovarian hormone loss through ovariectomy increased the amyloidogenic marker, sAPPβ, while the high-fat diet in combination with ovariectomy led to lower IDE protein content and activity in the prefrontal cortex, indicative of decreased amyloid-β degradation. These original results provide important information for future targets in early AD pathogenesis.

Middle age as a turning point in mouse cerebral cortex energy and redox metabolism: Modulation by every-other-day fasting

Normal brain aging is accompanied by intensification of free radical processes and compromised bioenergetics. Caloric restriction is expected to counteract these changes but the underlying protective mechanisms remain poorly understood. The present work aimed to investigate the intensity of oxidative stress and energy metabolism in the cerebral cortex comparing mice of different ages as well as comparing mice given one of two regimens of food availability: ad libitum versus every-other-day fasting (EODF). Levels of oxidative stress markers, ketone bodies, glycolytic intermediates, mitochondrial respiration, and activities of antioxidant and glycolytic enzymes were assessed in cortex from 6-, 12- and 18-month old C57BL/6J mice. The greatest increase in oxidative stress markers and the sharpest decline in key glycolytic enzyme activities was observed in mice upon the transition from young (6 months) to middle (12 months) age, with smaller changes occurring upon transition to old-age (18 months). Brain mitochondrial respiration showed no significant changes with age. A decrease in the activities of key glycolytic enzymes was accompanied by an increase in the activity of glucose-6-phosphate dehydrogenase suggesting that during normal brain aging glucose metabolism is altered to lower glycolytic activity and increase dependence on the pentose-phosphate pathway. Interestingly, levels of ketone bodies and antioxidant capacity showed a greater decrease in the brain cortex of females as compared with males. The EODF regimen further suppressed glycolytic enzyme activities in the cortex of old mice, and partially enhanced oxygen consumption and respiratory control in the cortex of middle aged and old males. Thus, in the mammalian cortex the major aging-induced metabolic changes are already seen in middle age and are slightly alleviated by an intermittent fasting mode of feeding.

Adiposity-related insulin resistance and thickness of the cerebral cortex in middle-aged adults

The thickness of the cerebral cortex decreases with ageing. Recent research suggests that obesity and type 2 diabetes mellitus may accelerate this cortical thinning, and that obesity-related insulin resistance may be a shared mechanistic pathway. Ageing of the cerebral cortex demonstrates sex-specific trajectories, with a gradual shift towards accelerated thinning beginning in midlife. Here, we investigated whether adiposity-related insulin resistance is associated with lower thickness of the human cerebral cortex in a community-based sample of middle-aged adults. We studied 533 adult participants (36-65 years) from the Saguenay Youth Study. Adiposity was assessed with bioimpedance, and insulin resistance was evaluated from a fasting blood sample with the homeostatic model assessment of insulin resistance (HOMA-IR). Associations between adiposity-related insulin resistance (adiposity/IR) and cortical thickness were assessed with linear models, separately in males and females younger or older than 50 years. Potential biological underpinnings were investigated with virtual histology. Adiposity/IR was associated with lower cortical thickness in females older than 50 years but not in males or younger females. The strength of the association varied across the cerebral cortex, with regions of the lateral frontal and parietal cortices and the superior temporal cortex demonstrating most pronounced thinning. Based on virtual histology, adiposity/IR-related cortical thinning may involve neurones, astrocytes, oligodendrocytes and ependymal cells acting so that they lower the cortical potential for synaptogenesis, formation of dendritic spines, production of extracellular matrix and myelination. Adiposity-related insulin resistance is associated with lower cortical thickness in middle-aged women older than 50 years. This aspect of thinning may involve neuronal and glial cells in a way that lowers the capacity of the cerebral cortex for neuronal plasticity and maintenance of myelination.

Dynamic Neuroimmune Profile during Mid-life Aging in the Female Brain and Implications for Alzheimer Risk

Aging and endocrine transition states can significantly impact inflammation across organ systems. Neuroinflammation is well documented in Alzheimer disease (AD). Herein, we investigated neuroinflammation that emerges during mid-life aging, chronological and endocrinological, in the female brain as an early initiating mechanism driving AD risk later in life. Analyses were conducted in a translational rodent model of mid-life chronological and endocrinological aging followed by validation in transcriptomic profiles from women versus age-matched men. In the translational model, the neuroinflammatory profile of mid-life aging in females was endocrine and chronological state specific, dynamic, anatomically distributed, and persistent. Microarray dataset analyses of aging human hippocampus indicated a sex difference in neuroinflammatory profile in which women exhibited a profile comparable to the pattern discovered in our translational rodent model, whereas age-matched men exhibited a profile consistent with low neuroimmune activation. Translationally, these findings have implications for therapeutic interventions during mid-life to decrease late-onset AD risk.

Genistein inhibits amyloid peptide 25-35-induced neuronal death by modulating estrogen receptors, choline acetyltransferase and glutamate receptors

PURPOSE

To explore genistein, the most active component of soy isoflavones, on viability, expression of estrogen receptor (ER) subtypes, choline acetyltransferase (ChAT), and glutamate receptor subunits in amyloid peptide 25-35-induced hippocampal neurons, providing valuable data and basic information for neuroprotective effect of genistein in Aβ_25-35-induced neuronal injury.

METHODS

We established an in vitro model of Alzheimer's disease by exposing primary hippocampal neurons of newborn rats to amyloid peptide 25-35 (20 μM) for 24 h and observing the effects of genistein (10 μM, 3 h) on viability, expression of ER subtypes, ChAT, NMDA receptor subunit NR2B and AMPA receptor subunit GluR2 in Aβ_25-35-induced hippocampal neurons.

RESULTS

We found that amyloid peptide 25-35 exposure reduced the viability of hippocampal neurons. Meanwhile, amyloid peptide 25-35 exposure decreased the expression of ER subtypes, ChAT and GluR2, and increased the expression of NR2B. Genistein at least partially reversed the effects of amyloid peptide 25-35 in hippocampal neurons.

CONCLUSION

Genistein could increase the expression of ChAT as a consequence of activating estrogen receptor subtypes, modulating the expression of NR2B and GluR2, and thereby ameliorating the status of hippocampal neurons and exerting neuroprotective effects against amyloid peptide 25-35. Our data suggest that genistein might represent a potential cell-targeted therapy which could be a promising approach to treating AD.

Detection of Cerebrovascular Loss in the Normal Aging C57BL/6 Mouse Brain Using in vivo Contrast-Enhanced Magnetic Resonance Angiography

Microvascular rarefaction, or the decrease in vascular density, has been described in the cerebrovasculature of aging humans, rats, and, more recently, mice in the presence and absence of age-dependent diseases. Given the wide use of mice in modeling age-dependent human diseases of the cerebrovasculature, visualization, and quantification of the global murine cerebrovasculature is necessary for establishing the baseline changes that occur with aging. To provide in vivo whole-brain imaging of the cerebrovasculature in aging C57BL/6 mice longitudinally, contrast-enhanced magnetic resonance angiography (CE-MRA) was employed using a house-made gadolinium-bearing micellar blood pool agent. Enhancement in the vascular space permitted quantification of the detectable, or apparent, cerebral blood volume (aCBV), which was analyzed over 2 years of aging and compared to histological analysis of the cerebrovascular density. A significant loss in the aCBV was detected by CE-MRA over the aging period. Histological analysis via vessel-probing immunohistochemistry confirmed a significant loss in the cerebrovascular density over the same 2-year aging period, validating the CE-MRA findings. While these techniques use widely different methods of assessment and spatial resolutions, their comparable findings in detected vascular loss corroborate the growing body of literature describing vascular rarefaction aging. These findings suggest that such age-dependent changes can contribute to cerebrovascular and neurodegenerative diseases, which are modeled using wild-type and transgenic laboratory rodents.