Sex difference in biological change and mechanism of Alzheimer’s disease: from macro- to micro-landscape

Amyloid and Tau Pathology in Cognitively Unimpaired Individuals With a Parental History of Alzheimer Disease: Role of Sex and Parent's Sex

BACKGROUND AND OBJECTIVES

Female sex and a parental history of Alzheimer disease (AD), especially maternal, confer increased risk of AD. Associations between sex, or affected AD parent's sex, and biomarkers of AD are less clear. We examined whether sex or affected AD parent's sex influences (1) β-amyloid (Aβ) and tau burden/accumulation, (2) the association between Aβ and tau burden, and (3) brain and cognitive resilience to Aβ and tau burden.

METHODS

The sample included 243 participants from the Presymptomatic Evaluation of Experimental or Novel Treatments for AD cohort in Canada. All participants with [18F]-NAV4694 and [18F]-AV1451 PET and MRI were included. We examined (1) sex or affected AD parent's sex differences on regional Aβ and tau burden/accumulation; (2) 2-way interactions between sex, or affected AD parent's sex, and Aβ on tau burden; and (3) 3-way interactions between time, sex or affected AD parent's sex, and Aβ or tau deposition on hippocampal volume (brain resilience) and cognition (cognitive resilience) over time.

RESULTS

Participants (69.4% female) were aged 68.3 ± 5.1 years at their first PET scans. All were cognitively unimpaired at baseline. Longitudinal cognitive data were available for 242 participants (follow-up, 6.72 ± 2.38 years), including 238 (6.53 ± 2.48 years of follow-up) with MRI follow-ups and 115 (4.4 ± 0.6 years of follow-up) with PET follow-ups, and 71 developed mild cognitive impairment. Women showed greater tau deposition (standardized β = 0.13 ± 0.3) and showed a stronger association between global Aβ and tau deposition than men (standardized β = 0.79 ± 0.1). Individuals with an affected AD father showed stronger association between global Aβ and tau deposition than those with an affected AD mother (standardized β = 0.65 ± 0.1). Women showed less Aβ-associated hippocampal atrophy over time (standardized β = 0.24 ± 0.1).

DISCUSSION

Women and, surprisingly, individuals with a paternal history of AD seemed more vulnerable to the Aβ-related spread of tau, whereas women showed greater brain resilience to Aβ. Understanding sex-specific risk and resilience could allow more clinical trial precision and personalization. A major limitation included the reduced sample for the affected AD parent's sex analyses.

Sex- and dose-dependent catalase increase and its clinical impact in a benzoate dose-finding, randomized, double-blind, placebo-controlled trial for Alzheimer's disease

BACKGROUND

Sex differences in Alzheimer's disease (AD) are gaining increasing attention. Previously research has shown that sodium benzoate treatment can improve cognitive function in AD patients, particularly in the female patients; and 1000 mg/day of benzoate appears more efficacious than lower doses. Catalase is a crucial endogenous antioxidant; and deficiency of catalase is regarded to be related to the pathogenesis of AD. The current study aimed to explore the role of sex and benzoate dose in the change of catalase activity among benzoate-treated AD patients.

METHODS

This secondary analysis used data from a double-blind trial, in which 149 CE patients were randomized to receive placebo or one of three benzoate doses (500, 750, or 1000 mg/day) and measured with Alzheimer's disease assessment scale-cognitive subscale. Plasma catalase was assayed before and after treatment.

RESULTS

Benzoate treatment, particularly at 1000 mg/day, increased catalase among female patients, but not among male. The increases in the catalase activity among the benzoate-treated women were correlated with their cognitive improvements. In addition, higher baseline catalase activity was associated with more cognitive improvement after benzoate treatment among both female and male patients.

CONCLUSIONS

Supporting the oxidative stress theory and sex difference in AD, the finding suggest that sex (female) and benzoate dose co-determine catalase increase in benzoate-treated AD patients and the catalase increment contributes to cognitive improvement of benzoate-treated women.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT03752463.

Correlations between plasma markers and brain Aβ deposition across the AD continuum: Evidence from SILCODE

BACKGROUND

Previous studies have found that Alzheimer's disease (AD)-related plasma markers are associated with amyloid beta (Aβ) deposition, but the change of this association in different Aβ pathological stages remains unclear.

METHODS

Data were obtained from the SILCODE. According to the standardized uptake value ratio (SUVR) and Aβ stage classification, correlation analysis was performed among plasma biomarkers, and voxel/SUVR values in the regions of interest (ROI) and clinical scale information, respectively. Mediation analysis was used to study the possible pathways.

RESULTS

The proportion of cognitively normal (CN) and subjective cognitive decline (SCD) was the highest in stages A0 to 1, while in stages A2 to 4, the proportion of mild cognitive impairment (MCI) and AD increased. Plasma phosphorylated tau (p-tau)181 and glial fibrillary acidic protein (GFAP) levels were significantly lower in stage A0 compared to the later phases. Two pathways demonstrated fully mediated effects: positron emission tomography (PET) SUVR-plasma p-tau181-Mini-Mental State Examination (MMSE) and PET SUVR-plasma GFAP-MMSE.

DISCUSSION

This study demonstrated the role of plasma biomarkers in the early stage of AD, especially in SCD, from both the clinical diagnosis and Aβ stage dimensions.

HIGHLIGHTS

Plasma ptau181 and GFAP level serve as indicators of early Alzheimer's disease and the pathologic Aβ staging classification. A possible ceiling effect of GFAP was observed in the mid-to-late stages of the AD course. This study confirms the role of AD plasma markers in promoting Aβ deposition at an early stage, particularly in females with subjective cognitive decline(SCD). The overlapping brain regions of plasma p-tau181, GFAP, and neurofilament light for Aβ deposition in the brain in early AD were distributed across various regions, including the posterior cingulate gyrus, rectus gyrus, and inferior temporal gyrus.

Oligodendroglia-to-pericyte conversion after lipopolysaccharide exposure is gender-dependent

To investigate the sex-dependent differentiation of Sox10 cells and their response to pathological conditions such as lipopolysaccharide (LPS) exposure or ischemia, we utilized Sox10 Cre-ERT2, tdTomato mice. Tamoxifen administration induced the expression of red fluorescent protein (RFP) in these cells, facilitating their subsequent tracking and analysis after LPS injection and ischemia via immunofluorescence staining. Propidium iodide (PI) was injected to label necrotic cells following LPS administration. We found that the conversion of Sox10 cells to pericytes in female mice was significantly higher than in male mice, especially in those exposed to LPS. After LPS injection, the number of PI+ necrotic cells were significantly greater in females than in males. Moreover, RFP+ cells did not co-localize with glial fibrillary acidic protein (GFAP) or cluster of differentiation 11b (CD11b). Similarly, after brain ischemia, RFP+ cells did not express cluster of differentiation 13 (CD13), neuronal nuclei (NeuN), GFAP, or ionised calcium binding adaptor molecule 1 (Iba-1). These findings indicate that the conversion of Sox10 cells to pericytes following LPS exposure is sex-dependent, with neither male nor female groups showing differentiation into other cell types after LPS exposure or under ischemic conditions. The differences in LPS-induced necrosis of pericytes between sexes may explain the variations in the conversion of Sox10 cells to pericytes in both sexes.

Sex differences in the relationship between depression and Alzheimer's disease-mechanisms, genetics, and therapeutic opportunities

Depression and Alzheimer's disease (AD) are prevalent neuropsychiatric disorders with intriguing epidemiological overlaps. Their interrelation has recently garnered widespread attention. Empirical evidence indicates that depressive disorders significantly contribute to AD risk, and approximately a quarter of AD patients have comorbid major depressive disorder, which underscores the bidirectional link between AD and depression. A growing body of evidence substantiates pervasive sex differences in both AD and depression: both conditions exhibit a higher incidence among women than among men. However, the available literature on this topic is somewhat fragmented, with no comprehensive review that delineates sex disparities in the depression-AD correlation. In this review, we bridge these gaps by summarizing recent progress in understanding sex-based differences in mechanisms, genetics, and therapeutic prospects for depression and AD. Additionally, we outline key challenges in the field, holding potential for improving treatment precision and efficacy tailored to male and female patients' distinct needs.

The Granular Retrosplenial Cortex Is Necessary in Male Rats for Object-Location Associative Learning and Memory, But Not Spatial Working Memory or Visual Discrimination and Reversal, in the Touchscreen Operant Chamber

The retrosplenial cortex (RSC) is a hub of diverse afferent and efferent projections thought to be involved in associative learning. RSC shows early pathology in mild cognitive impairment and Alzheimer's disease (AD), which impairs associative learning. To understand and develop therapies for diseases such as AD, animal models are essential. Given the importance of human RSC in object-location associative learning and the success of object-location associative paradigms in human studies and in the clinic, it would be of considerable value to establish a translational model of object-location learning for the rodent. For this reason, we sought to test the role of RSC in object-location learning in male rats using the object-location paired-associates learning (PAL) touchscreen task. First, increased cFos immunoreactivity was observed in granular RSC following PAL training when compared with extended pretraining controls. Following this, RSC lesions following PAL acquisition were used to explore the necessity of the RSC in object-location associative learning and memory and two tasks involving only one modality: trial-unique nonmatching-to-location for spatial working memory and pairwise visual discrimination/reversal. RSC lesions impaired both memory for learned paired-associates and learning of new object-location associations but did not affect performance in either the spatial or visual single-modality tasks. These findings provide evidence that RSC is necessary for object-location learning and less so for learning and memory involving the individual modalities therein.

Telomere length and micronuclei trajectories in APP/PS1 mouse model of Alzheimer's disease: Correlating with cognitive impairment and brain amyloidosis in a sexually dimorphic manner

Although studies have demonstrated that genome instability is accumulated in patients with Alzheimer's disease (AD), the specific types of genome instability linked to AD pathogenesis remain poorly understood. Here, we report the first characterization of the age- and sex-related trajectories of telomere length (TL) and micronuclei in APP/PS1 mice model and wild-type (WT) controls (C57BL/6). TL was measured in brain (prefrontal cortex, cerebellum, pituitary gland, and hippocampus), colon and skin, and MN was measured in bone marrow in 6- to 14-month-old mice. Variation in TL was attributable to tissue type, age, genotype and, to a lesser extent, sex. Compared to WT, APP/PS1 had a significantly shorter baseline TL across all examined tissues. TL was inversely associated with age in both genotypes and TL shortening was accelerated in brain of APP/PS1. Age-related increase of micronuclei was observed in both genotypes but was accelerated in APP/PS1. We integrated TL and micronuclei data with data on cognition performance and brain amyloidosis. TL and micronuclei were linearly correlated with cognition performance or Aβ40 and Aβ42 levels in both genotypes but to a greater extent in APP/PS1. These associations in APP/PS1 mice were dominantly driven by females. Together, our findings provide foundational knowledge to infer the TL and micronuclei trajectories in APP/PS1 mice during disease progression, and strongly support that TL attrition and micronucleation are tightly associated with AD pathogenesis in a female-biased manner.

Repurposing of Tibolone in Alzheimer's Disease

Alzheimer's disease (AD) is a debilitating neurodegenerative disease characterised by the accumulation of amyloid-beta and tau in the brain, leading to the progressive loss of memory and cognition. The causes of its pathogenesis are still not fully understood, but some risk factors, such as age, genetics, and hormones, may play a crucial role. Studies show that postmenopausal women have a higher risk of developing AD, possibly due to the decrease in hormone levels, especially oestrogen, which may be directly related to a reduction in the activity of oestrogen receptors, especially beta (ERβ), which favours a more hostile cellular environment, leading to mitochondrial dysfunction, mainly affecting key processes related to transport, metabolism, and oxidative phosphorylation. Given the influence of hormones on biological processes at the mitochondrial level, hormone therapies are of clinical interest to reduce the risk or delay the onset of symptoms associated with AD. One drug with such potential is tibolone, which is used in clinics to treat menopause-related symptoms. It can reduce amyloid burden and have benefits on mitochondrial integrity and dynamics. Many of its protective effects are mediated through steroid receptors and may also be related to neuroglobin, whose elevated levels have been shown to protect against neurological diseases. Its importance has increased exponentially due to its implication in the pathogenesis of AD. In this review, we discuss recent advances in tibolone, focusing on its mitochondrial-protective effects, and highlight how valuable this compound could be as a therapeutic alternative to mitigate the molecular pathways characteristic of AD.

Neuroimaging modalities in the detection of Alzheimer's disease-associated biomarkers

Alzheimer's disease (AD) is the most common cause of dementia. Neuropathological changes in AD patients occur up to 10-20 years before the emergence of clinical symptoms. Specific diagnosis and appropriate intervention strategies are crucial during the phase of mild cognitive impairment (MCI) and AD. The detection of biomarkers has emerged as a promising tool for tracking the efficacy of potential therapies, making an early disease diagnosis, and prejudging treatment prognosis. Specifically, multiple neuroimaging modalities, including magnetic resonance imaging (MRI), positron emission tomography, optical imaging, and single photon emission-computed tomography, have provided a few potential biomarkers for clinical application. The MRI modalities described in this review include structural MRI, functional MRI, diffusion tensor imaging, magnetic resonance spectroscopy, and arterial spin labelling. These techniques allow the detection of presymptomatic diagnostic biomarkers in the brains of cognitively normal elderly people and might also be used to monitor AD disease progression after the onset of clinical symptoms. This review highlights potential biomarkers, merits, and demerits of different neuroimaging modalities and their clinical value in MCI and AD patients. Further studies are necessary to explore more biomarkers and overcome the limitations of multiple neuroimaging modalities for inclusion in diagnostic criteria for AD.