The emerging role of circular RNAs in neurodegenerative diseases and viral infections.

Circular RNAs (circRNAs) represent a class of highly stable, covalently closed RNA molecules increasingly recognized as important regulators of brain aging and neurodegenerative disease. Growing evidence also implies circRNAs in viral infection, suggesting a potential intersection between viral neuropathogenesis and neurodegeneration. However, no studies have yet directly integrated circRNAs, neurotropic viral infections, and neurodegenerative disorders within a single mechanistic framework. To date, specific circRNAs have been linked to the progression of Alzheimer's disease and Parkinson's disease, where they regulate central pathological processes including amyloid-β clearance, neuroinflammation, synaptic plasticity, neuronal apoptosis, and oxidative stress. Moreover, it has been established that both host cells and viruses produce circRNAs during infection. Virus-derived circRNAs can enhance viral replication, promote immune evasion, and support latency. In contrast, host circRNAs contribute to antiviral defense by acting as microRNA sponges, interacting with viral proteins, or encoding peptides with antiviral activity, mechanisms particularly explored in viral oncogenesis. In this review, we will evaluate the most updated research evidence on the role of circRNAs in major neurodegenerative diseases and neurotropic viral infections. Considering the growing concern regarding the long-term neurological consequences of viral infections, including chronic neuroinflammation, viral reactivation, and post-viral syndromes, dysregulated circRNAs may represent a mechanistic link between viral infection and associated neurodegenerative processes. Finally, we will discuss future directions for identifying circRNAs-based biomarkers and developing circRNAs-targeted therapeutic strategies for age-related and virus-associated neurological disorders.