miR-519a-3p as a Novel Biomarker for Early Detection of Alzheimer’s Disease   

Alzheimer’s disease (AD) is a progressive neurodegenerative disorder and the most common cause of dementia, affecting millions of people worldwide. It is characterized by cognitive decline, memory loss, and changes in behavior and personality. Despite extensive research, early diagnosis of AD remains a significant challenge. Current diagnostic methods rely heavily on clinical evaluation and imaging techniques, which are often invasive, expensive, and typically confirm the disease only at symptomatic stages. Early detection, ideally at pre-symptomatic stages, is crucial for timely intervention and management, potentially slowing the progression of the disease. One of the primary neuropathological hallmarks of AD is the extracellular accumulation of β-amyloid (Aβ) plaques and intracellular neurofibrillary tangles (NFTs) composed of hyperphosphorylated tau protein. These pathological changes begin long before clinical symptoms appear, indicating a substantial preclinical phase during which early intervention could be most effective. However, identifying biomarkers that can detect AD during these asymptomatic stages remains a significant unmet need in the field. MicroRNAs (miRNAs) have emerged as promising candidates for biomarker development due to their stability in biofluids and their regulatory roles in gene expression. Dysregulation of specific miRNAs has been associated with various diseases, including AD. In particular, miR-519a-3p has been identified as a potential regulator of cellular prion protein (PrPC) expression, which is known to decrease as AD progresses. The cellular prion protein is implicated in several neurodegenerative processes, and its downregulation is thought to contribute to the pathogenesis of AD. To this end, new study, published in Biochimica et Biophysica Acta and conducted by Dayaneth Jácome, Tiziana Cotrufo, Pol Andrés-Benito, Laia Lidón, Eulàlia Martí, Isidre Ferrer, Professor José Antonio del Río, and Dr. Rosalina Gavín, investigated the critical need for early AD biomarkers. They explored the role of miR-519a-3p in the regulation of PrPC and to evaluate its potential as a biomarker for early stages of AD. The authors used in silico prediction to identify potential miRNAs that target the 3′ untranslated region (3’UTR) of the PRNP gene, which encodes PrPC. By cross-referencing data from miRWalk, miRanda, RNA22, and Targetscan databases, the researchers selected miR-519a-3p based on its reported overexpression in AD. This selection was crucial as it laid the groundwork for subsequent experimental validation. To validate miR-519a-3p’s targeting of PRNP, the researchers employed a dual-luciferase reporter assay. HEK293 cells were co-transfected with a reporter construct containing the 3’UTR of PRNP and miR-519a-3p mimic. The assay demonstrated a significant decrease in luciferase activity, confirming that miR-519a-3p binds to the PRNP 3’UTR and downregulates its expression. This experiment provided direct evidence of miR-519a-3p’s role in regulating PrPC at the post-transcriptional level. Next, the researchers used mimic technology to overexpress miR-519a-3p in CCF-STTG1 human astrocytoma cells, which naturally express high levels of PrPC. Western blot analysis revealed that overexpression of miR-519a-3p led to a significant reduction in PrPC protein levels (approximately 45% decrease) after 48 hours, while PRNP mRNA levels remained unchanged. This finding suggests that miR-519a-3p primarily exerts its regulatory effect through translational repression rather than mRNA degradation. To investigate miR-519a-3p’s expression in AD, the researchers analyzed postmortem hippocampal and frontal cortex samples from patients at different Braak stages of AD and compared them to samples from other neurodegenerative diseases (NDDs).  The authors found that RT-qPCR analysis of hippocampal samples to have significant upregulation of miR-519a-3p in AD patients across all Braak stages. Notably, miR-519a-3p levels were highest in early-stage AD (Braak I/II), indicating its potential as an early biomarker. In contrast, the expression of other miRNAs predicted to target PRNP, such as miR-409-3p, miR-410-3p, and miR-495-3p, did not show significant changes, underscoring the specificity of miR-519a-3p for AD. Further analysis of frontal cortex samples confirmed the upregulation of miR-519a-3p in AD patients. Importantly, miR-519a-3p levels were elevated even in asymptomatic individuals (Braak I/II), reinforcing its potential as a preclinical biomarker. The levels remained consistently higher in AD patients compared to non-AD tauopathies and synucleinopathies, demonstrating its specificity for AD. To ensure the specificity of miR-519a-3p for AD, the researchers compared its expression levels in samples from other neurodegenerative diseases, including corticobasal degeneration (CBD), glial globular tauopathy (GGT), Pick’s disease (PiD), Parkinson’s disease (PD), and PD-associated dementia (PDD). The analysis revealed no significant upregulation of miR-519a-3p in these conditions, highlighting its unique association with AD.

In conclusion, the authors demonstrated the upregulation of miR-519a-3p in the earliest stages of AD (Braak I/II) before the onset of clinical symptoms positions it as a promising biomarker for preclinical detection. Early diagnosis is critical for effective intervention, as it opens a window for therapeutic strategies that could delay or prevent the progression of cognitive decline. The miR-519a-3p is specifically upregulated in AD and not in other neurodegenerative diseases such as CBD, CGT,  PiD, and PD. This specificity is crucial for developing accurate diagnostic tools that can distinguish AD from other neurodegenerative conditions, reducing the risk of misdiagnosis. There is a potential development of a non-invasive blood test for early AD diagnosis based on miR-519a-3p levels. Current diagnostic methods such as cerebrospinal fluid analysis and positron emission tomography imaging are invasive, expensive, and not suitable for routine screening. A blood-based biomarker test would be a game-changer, making early diagnosis more accessible and feasible for large-scale screening. Moreover, detecting AD at the preclinical stage allows for earlier therapeutic interventions, which are more likely to be effective in slowing or preventing the progression of the disease. This could significantly improve patient outcomes and reduce the burden of AD on individuals, families, and healthcare systems.