A sex-stratified analysis of neuroimmune gene expression signatures in Alzheimer's disease brains

Sex-specific modulation of FOLR1 and its cycle enzyme genes in Alzheimer's disease brain regions

Alzheimer's disease (AD) is the most common form of dementia, characterized by progressive cognitive and functional decline. Its incidence increases significantly with age and is more prevalent in women than men. We investigated the folate receptor alpha (FOLR1) gene expression levels in the central nervous system (CNS) of AD and non-demented healthy control (NDHC) subjects. Our cohort included 3,946 samples: 2,391 NDHC and 1,555 AD patients, stratified by brain region, age, and sex. Interestingly, a significant increase in FOLR1 expression was observed only in females with AD compared to NDHC females. Furthermore, we found that FOLR1 expression was differentially increased in the prefrontal cortex (PFC) and diencephalon (DIE) only in AD females. Moreover, in females, genes involved in the folic acid (FA) cycle that drives DNA synthesis were significantly modulated. In contrast, in males, downregulation of TYMS effectively blocks the completion of the cycle, thereby preventing downstream DNA synthesis. Tissue Transcriptome Deconvolution (TTD) analysis revealed astrocytes and endothelial cells associated with FOLR1 expression in both AD males and females. Gene Ontology analysis supported these findings, showing enrichment in processes aligned with these cell types. Positive correlations between brain FOLR1 expression and markers for astrocytes (glial fibrillary acidic protein) and endothelial cells (CD31) provided further validation. Our findings suggest a potential role for sex-dependent FOLR1 expression and its association with specific brain regions and cellular processes in AD.

Exploring SERPINA3 as a neuroinflammatory modulator in Alzheimer's disease with sex and regional brain variations

SERPINA3, a serine protease inhibitor, is strongly associated with neuroinflammation, a typical condition of AD. Its expression is linked to microglial and astrocytic markers, suggesting it plays a significant role in modulating neuroinflammatory responses. In this study, we examined the SERPINA3 expression levels, along with CHI3L1, in various brain regions of AD patients and non-demented healthy controls (NDHC). Nineteen microarray datasets were analyzed, with brain samples stratified by sex and age from areas including the prefrontal cortex, occipital lobe, and cerebellum. Results showed that SERPINA3 was significantly highly expressed in AD patients compared to NDHCs only in males. Sex-specific differences were observed only in NDHCs, where females had higher SERPINA3 levels than males. ROC analysis suggested that SERPINA3 could be a strong marker for distinguishing AD in males but not females. In NDHCs, SERPINA3 expression correlated more strongly with age than in AD patients. In brain regions, SERPINA3 expression in NDHC females was higher across multiple areas, while in AD patients, this difference was limited to the prefrontal cortex. The most significant differences between NDHC and AD patients were found in the occipital and prefrontal regions. Furthermore, we identified a potential nuclear localization for SERPINA3, supported by immunohistochemistry analysis from The Human Protein Atlas. Correlation with neuropathological traits, including Clinical Dementia Rating (CDR) and Braak Neurofibrillary Tangle Score, showed positive significant associations between SERPINA3 and CDR in AD patients. Performing a docking analysis, we revealed an interaction region between SERPINA3 and CHI3L1 proteins, suggesting a potential role in AD. Tissue transcriptomic deconvolution analysis indicated a significant overlap between SERPINA3 expression and microglial/astrocytic signatures, suggesting that SERPINA3 plays a key role in modulating neuroinflammation in AD.

Geroscience and pathology: a new frontier in understanding age-related diseases

Geroscience, a burgeoning discipline at the intersection of aging and disease, aims to unravel the intricate relationship between the aging process and pathogenesis of age-related diseases. This paper explores the pivotal role played by geroscience in reshaping our understanding of pathology, with a particular focus on age-related diseases. These diseases, spanning cardiovascular and cerebrovascular disorders, malignancies, and neurodegenerative conditions, significantly contribute to the morbidity and mortality of older individuals. We delve into the fundamental cellular and molecular mechanisms underpinning aging, including mitochondrial dysfunction and cellular senescence, and elucidate their profound implications for the pathogenesis of various age-related diseases. Emphasis is placed on the importance of assessing key biomarkers of aging and biological age within the realm of pathology. We also scrutinize the interplay between cellular senescence and cancer biology as a central area of focus, underscoring its paramount significance in contemporary pathological research. Moreover, we shed light on the integration of anti-aging interventions that target fundamental aging processes, such as senolytics, mitochondria-targeted treatments, and interventions that influence epigenetic regulation within the domain of pathology research. In conclusion, the integration of geroscience concepts into pathological research heralds a transformative paradigm shift in our understanding of disease pathogenesis and promises breakthroughs in disease prevention and treatment.

Identification of female-enriched and disease-associated microglia (FDAMic) contributes to sexual dimorphism in late-onset Alzheimer's disease

BACKGROUND

Late-onset Alzheimer's disease (LOAD) is the most common form of dementia; it disproportionally affects women in terms of both incidence rates and severity of progression. The cellular and molecular mechanisms underlying this clinical phenomenon remain elusive and ill-defined.

METHODS

In-depth analyses were performed with multiple human LOAD single-nucleus transcriptome datasets to thoroughly characterize cell populations in the cerebral cortex. ROSMAP bulk human brain tissue transcriptome and DNA methylome datasets were also included for validation. Detailed assessments of microglial cell subpopulations and their relevance to sex-biased changes at the tissue level were performed. Clinical trait associations, cell evolutionary trajectories, and transcription regulon analyses were conducted.

RESULTS

The relative numbers of functionally defective microglia were aberrantly increased uniquely among affected females. Substratification of the microglia into different subtypes according to their transcriptomic signatures identified a group of female-enriched and disease-associated microglia (FDAMic), the numbers of which were positively associated with disease severity. Phenotypically, these cells exhibit transcriptomic signatures that support active proliferation, MHC class II autoantigen presentation and amyloid-β binding, but they are also likely defective in phagocytosis. FDAMic are likely evolved from female activated response microglia (ARMic) with an APOE4 background and compromised estrogen receptor (ER) signaling that is deemed to be active among most subtypes of microglia.

CONCLUSION

This study offered important insights at both the cellular and molecular levels into how ER signaling affects microglial heterogeneity and function. FDAMic are associated with more advanced pathologies and severe trends of cognitive decline. Their emergence could, at least in part, explain the phenomenon of greater penetrance of the APOE4 genotype found in females. The biases of FDAMic emergence toward female sex and APOE4 status may also explain why hormone replacement therapy is more effective in APOE4 carriers. The pathologic nature of FDAMic suggests that selective modulations of these cells may help to regain brain neuroimmune homeostasis, serving as a new target for future drug development.

The Role of Methionine-Rich Diet in Unhealthy Cerebrovascular and Brain Aging: Mechanisms and Implications for Cognitive Impairment

As aging societies in the western world face a growing prevalence of vascular cognitive impairment and Alzheimer's disease (AD), understanding their underlying causes and associated risk factors becomes increasingly critical. A salient concern in the western dietary context is the high consumption of methionine-rich foods such as red meat. The present review delves into the impact of this methionine-heavy diet and the resultant hyperhomocysteinemia on accelerated cerebrovascular and brain aging, emphasizing their potential roles in cognitive impairment. Through a comprehensive exploration of existing evidence, a link between high methionine intake and hyperhomocysteinemia and oxidative stress, mitochondrial dysfunction, inflammation, and accelerated epigenetic aging is drawn. Moreover, the microvascular determinants of cognitive deterioration, including endothelial dysfunction, reduced cerebral blood flow, microvascular rarefaction, impaired neurovascular coupling, and blood-brain barrier (BBB) disruption, are explored. The mechanisms by which excessive methionine consumption and hyperhomocysteinemia might drive cerebromicrovascular and brain aging processes are elucidated. By presenting an intricate understanding of the relationships among methionine-rich diets, hyperhomocysteinemia, cerebrovascular and brain aging, and cognitive impairment, avenues for future research and potential therapeutic interventions are suggested.