miRNAs: Promising Biomarkers for Alzheimer's Diagnosis and Treatment.

Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterized by amyloid-beta (Aβ) plaque deposition, neurofibrillary tangles of hyperphosphorylated tau protein, and chronic neuroinflammation, leading to synaptic dysfunction and cognitive decline. Current diagnostic methods rely on clinical symptoms and limited biomarkers, while available treatments only provide symptomatic relief without halting disease progression. MicroRNAs (miRNAs), small non-coding RNAs of 19-22 nucleotides, have emerged as crucial regulators of gene expression through post-transcriptional mechanisms and show distinct dysregulation patterns in AD patients' blood, cerebrospinal fluid (CSF), and brain tissues. Key miRNAs such as miR-132, miR-146a, miR-34a, and miR-125b demonstrate consistent alterations in expression levels, correlating with disease progression and offering potential as non-invasive diagnostic tools. This review comprehensively examines the dual role of miRNAs as diagnostic biomarkers and therapeutic targets for AD. We also provide an analysis of specific miRNA signatures in different biofluids (plasma, serum, CSF) and brain regions that correlate with disease stages, highlighting their potential for early and non-invasive diagnosis. Therapeutically, miRNAs modulate multiple AD-related pathways, including neuroinflammation via NF-κB signaling, Aβ production through BACE1 inhibition, and tau phosphorylation via GSK3β regulation. miRNAs also influence synaptic plasticity, mitochondrial function, and autophagy, presenting multifaceted opportunities for intervention. However, challenges, including miRNA heterogeneity, stability, and targeted delivery, remain critical impediments. Advances in nanocarriers, exosomal miRNAs, and viral vectors show promise in overcoming these obstacles, enabling precise miRNA modulation. In addition, we underscore the need for standardized protocols, further validation in clinical cohorts, and the development of cost-effective detection methods to translate miRNA-based approaches into practical diagnostics and therapies. By integrating miRNA biomarkers with existing diagnostic tools and exploring combinatorial therapeutic strategies, researchers can harness the potential of miRNAs to revolutionize AD intervention, paving the way for early detection and effective treatment of this devastating disease.