Introduction: Brain aging is a natural physiological process that results in cognitive declines, affecting memory, learning ability, and processing speed. It also increases the risk of neurodegenerative diseases such as Alzheimer’s disease (AD), which is characterized by brain atrophy and cell death due to β-amyloid (Aβ) plaques and neurofibrillary tangles (1,2) Neuroinflammation, mitochondrial dysfunction, and cellular senescence have been identified as major contributors to AD. Microglia, the primary innate immune cells in the brain, play a central role in this process (3). Also, the GAS–STING signaling pathway, which is responsible for detecting DNA, plays a significant role in chronic inflammation and functional decline associated with aging (4). Additionally Nicotinamide adenine dinucleotide (NAD+) is crucial for metabolism, mitochondrial function, and genome integrity. Studies indicate that NAD+ depletion may activate the cGAS-STING pathway, contributing to neuroinflammation and cellular senescence in Alzheimer's disease (AD)(3).
Methods: Given the importance of these processes in AD, the aim of this study is to identify differentially expressed genes (DEGs) that significantly contribute to the development of Alzheimer's disease. Raw microarray data from GSE135999, which includes 48 paired expression datasets from the brains of APP/PS1 AD mice and wild-type (WT) controls, were obtained from the GEO database. Analysis of these two groups was performed using the GEO2R tool, considering adj.p.value ≤ 0.05 and logFC ≥ 0.45. In this study, the STRING database was used to construct the PPI network, which was further analyzed using the Cytoscape application.The gene ITGAX was identified as a hub gene in this study, and further extensive studies were conducted on this gene
Results: ITGAX (Integrin subunit alpha X, also referred to as CD11c) is associated with immune functions, particularly the activation of microglia, and its expression is predominantly found in microglia within the brain, contributing to neuroinflammation in Alzheimer’s disease.(2) In one study, it also becomes significantly upregulated in aged mice, suggesting increased microglial activation and neuroinflammation associated with aging and neurodegenerative diseases like Alzheimer’s.(4) Additionally, ITGAX has been reported to play a common role between monocytes (blood myeloid cells) and microglia (brain myeloid cells).(5) To explore whether ITGAX plays a role in the cGAS-STING pathway, we used the STRING database to assess its interactions with key pathway genes, including CGAS, TMEM173 (STING1), IFNB1, and others. Our analysis revealed potential protein-protein interactions, suggesting that ITGAX may influence immune responses, particularly those regulated by the cGAS-STING pathway, which detects cytosolic DNA and initiates inflammatory responses. The interactions between ITGAX and genes like CXCL10 and IFNB1 indicate possible indirect regulatory roles in immune signaling and cytokine production.
Studies show that blocking the STING pathway reduces inflammation in aged human cells, peripheral organs, and the brain, leading to improved tissue function. Single-nucleus RNA sequencing of microglia in a cGAS gain-of-function mouse model demonstrates that cGAS activation promotes inflammatory microglial states, resulting in neurotoxicity, bystander cell inflammation, and cognitive decline. These findings establish cGAS-STING as a major driver of age-related inflammation and neurodegeneration, suggesting that inhibiting this pathway could be a promising therapeutic strategy to prevent neurodegenerative processes associated with aging.(4) Furthermore, lower NAD+ levels have been observed in various neurodegenerative diseases. In one study, brains of Alzheimer's disease (AD) mice exhibited reduced NAD+ levels and increased inflammation. Treatment with nicotinamide riboside (NR), a precursor to NAD+, reduced neuroinflammation, decreased DNA damage, and prevented cellular senescence. Scientists suggest that the beneficial effects of NR are partly mediated through the cGAS-STING pathway, as NR treatment reduced the DNA damage elevated in AD.(3)
Conclusion: Our study identifies ITGAX as a critical hub gene involved in neuroinflammation, particularly in the context of Alzheimer's disease. Given its presence in blood, ITGAX may hold potential as a biomarker, as increased expression could indicate heightened inflammatory activity and activation of the cGAS-STING pathway. The strong connection between ITGAX and key components of the cGAS-STING pathway suggests its role in modulating immune responses and contributing to age-related neurodegeneration. Furthermore, NAD+ depletion observed in AD and the beneficial effects of nicotinamide riboside (NR) in reducing inflammation through cGAS-STING inhibition highlight these pathways as promising therapeutic targets. Administering NAD+ supplements could potentially inhibit this pathway, offering a novel strategy to mitigate neuroinflammation and prevent neurodegenerative processes associated with AD and aging. Further research is needed to validate its clinical application.