Analysis and Potential Applications of miRNAs Related to Alzheimer’s Disease

Background and Research Motivation

Alzheimer’s Disease (AD) is a progressively worsening neurodegenerative disorder and the most common form of dementia among the elderly. The pathological features of AD in the brain primarily include senile plaques formed by the accumulation of β-amyloid (Aβ) and neurofibrillary tangles formed by hyperphosphorylated tau protein. Aβ is generated from the membrane-bound precursor protein APP (Amyloid Precursor Proteins) through cleavage by β- and γ-secretases. Its toxic molecular form, especially Aβ42, is considered the main neurotoxic component, inducing neuroinflammation, oxidative stress, synaptic dysfunction, and ultimately leading to neuronal loss. However, APP can also be sequentially cleaved by α- and γ-secretases to produce soluble APPα (sAPPα), which is believed to have neuroprotective effects, including promoting neurite outgrowth and neuronal survival. Therefore, balancing the generation and clearance of Aβ and its potential applications in AD treatment is a pressing challenge.

To address this issue, researchers have focused on microRNAs (miRNAs) that regulate the expression of key proteins. The aim of this study is to investigate the miRNA expression profiles in the plasma of AD patients compared to control groups, identify miRNAs related to AD pathology, validate their regulatory role on target proteins and mechanisms, and further explore their potential as therapeutic strategies.

Research Source

This study was collaboratively conducted by Chao Song, Shufang Li, and Yingren Mai from Jinan University and Guangzhou Medical University, among other research institutions. The paper was published in the 2024 issue of the Journal of Neuroinflammation.

Research Process

Research Subjects and Methods

The study used plasma samples from 11 AD patients and 14 age- and gender-matched cognitively normal individuals, conducting miRNA sequencing (miRNA-seq) to analyze their global expression profiles. The research included the following steps:

1. miRNA Expression Profile Analysis: Comprehensive global expression analysis was conducted on samples from AD patients and control groups using miRNA-seq to identify differentially expressed miRNAs (DEMs).
2. Experimental Validation: The effects of DEMs on AD pathology were further validated by in vivo and in vitro expression and knockdown of mir-140 and mir-122.
3. Protein Expression Detection: Molecular biology and immunohistochemistry techniques were used to detect the impact of miRNAs on target proteins such as ADAM10 and sAPPα.

Key Experiments and Techniques

• miRNA Sequencing and Data Analysis: miRNA sequencing libraries were constructed using the QIAseq miRNA Library Kit, and sequencing was performed on the Illumina NovaSeq 6000 system. Data analysis included sample cleanup, alignment, differential expression analysis, miRNA target gene prediction, and functional enrichment analysis.
• qRT-PCR Validation: Specific primers were used for quantitative real-time PCR validation of mir-140 and mir-122 expression in plasma and brain tissues.
• Protein Detection: Western blot analysis was used to detect the expression levels of key proteins like ADAM10 and sAPPα.
• Behavioral Tests: Cognitive function in mice was assessed using behavioral tests such as the Y-maze and Morris water maze.
• Functional Experiments and miRNA Target Validation: Including in vitro neuronal dendritic analysis, BV2 and HT22 cell co-culture experiments to evaluate phagocytosis capability using fluorescently labeled Aβ42 phagocytosis assays.

Research Results

miRNA Expression Profile Analysis and Validation

miRNA-seq identified 41 DEMs, with two significantly differentially expressed miRNAs—mir-140-3p and mir-122-5p—having potential functional roles in AD pathology. qRT-PCR validation showed significant upregulation of mir-140 and mir-122 in the plasma of AD patients and the brain tissues of APP/PS1 mice.

Regulatory Roles of mir-140 and mir-122 on ADAM10 and sAPPα

mir-140 and mir-122 target ADAM10 and influence non-amyloidogenic cleavage of APP. In vivo and in vitro experiments showed that overexpression of mir-140 and mir-122 in the mouse brain significantly downregulated ADAM10 and its product sAPPα, leading to cognitive decline. ATRCA (All-trans Retinoic Acid) treatment improved cognitive function by upregulating ADAM10 expression. Additionally, in HT22 cells, knockdown of endogenous mir-140/mir-122 significantly reduced Aβ production, indicating their therapeutic potential for AD.

Impact of mir-140 and mir-122 on Mouse Cognitive Function

AAV9-mediated overexpression of mir-140 and mir-122 induced cognitive impairment in both wild-type mice and APP/PS1 mice. ATRCA treatment restored the expression of ADAM10 and sAPPα, improving compromised cognitive function.

Effects of mir-140 and mir-122 on Microglial Activity

Further experiments showed that overexpression of mir-140 and mir-122 reduced microglial migration and phagocytosis of Aβ plaques, increased neuroinflammatory responses, and exacerbated neurodegeneration.

Conclusion and Significance

This study demonstrates that mir-140 and mir-122 play a crucial role in AD pathology by targeting ADAM10, inhibiting its expression, and reducing the production of the neuroprotective factor sAPPα. Modulation of these miRNAs’ expression could be a potential therapeutic strategy for AD.

• Scientific Value: The study reveals the mechanism by which two specific miRNAs influence AD pathology, providing the first systematic demonstration of how mir-140 and mir-122 regulate APP processing through the ADAM10 pathway.
• Application Value: Given the widespread role of miRNAs in gene expression regulation and their translational potential, the study’s results offer new targets and strategies for AD treatment.

Further research on this topic unveils significant innovations and findings, including the first systematic discovery and validation of the detailed mechanism by which mir-140 and mir-122 affect non-amyloidogenic cleavage of APP through ADAM10 in AD pathology, showcasing their potential as drug targets. Clinical application of these findings could revolutionize AD treatment strategies.