Convergence of neuroinflammation across major neurotropic viral exposomes in AD and ADRD.

BACKGROUND: Alzheimer's disease (AD) and Alzheimer's disease-related dementias (ADRD) are multifactorial neurodegenerative disorders driven by complex interactions among genetic susceptibility, aging, and environmental exposures. Growing epidemiological and mechanistic evidence implicates neurotropic viral exposomes, defined as cumulative lifetime viral infections, as significant contributors to AD risk. Viral encephalitis and common viral infections, including herpes simplex virus type 1 (HSV-1), human immunodeficiency virus (HIV), cytomegalovirus (CMV), SARS-CoV-2, and influenza, have been associated with an increased incidence of AD/ADRD; however, the molecular mechanisms underlying these associations remain incompletely understood.

METHODS: A systematic literature review was conducted using PubMed, Web of Science, Scopus, and Google Scholar (1990-2025) to identify epidemiological, experimental, and mechanistic studies linking viral infections to AD-related pathology. Systems biology approaches were applied using Cytoscape, STRING, KEGG, WikiPathways, and Ingenuity Pathway Analysis to construct protein-protein interaction networks and identify convergent biological processes shared between AD and viral host-response pathways. Functional enrichment analyses focused on neuroinflammation, amyloid-β (Aβ) metabolism, tau pathology, autophagy, and blood-brain barrier (BBB) integrity.

RESULTS: Across diverse viral infections, strong convergence was observed in innate immune activation pathways, including microglial priming and NLRP3 inflammasome signaling, accompanied by chronic production of proinflammatory cytokines (IL-1β, TNF-α, IFN-γ). Multiple viruses modulated amyloidogenic APP processing, impaired Aβ clearance, promoted tau hyperphosphorylation, disrupted autophagy-lysosomal systems, and compromised BBB integrity. Systems-level analyses revealed overlapping signaling hubs, including NF-κB, MAPK, PI3K-Akt, and cGAS-STING that amplify neurodegenerative cascades, with effects most pronounced in genetically susceptible populations such as APOE4 carriers.

CONCLUSIONS: Collectively, current evidence supports a mechanistic link between viral exposomes and AD/ADRD mediated through convergent neuroinflammatory, and proteostatic pathways. Although viral infections alone are unlikely to be sufficient to cause AD, recurrent or persistent viral exposures may act as potent disease modifiers that accelerate neurodegenerative processes. Integrating viral biomarkers, genetic risk stratification, and systems biology approaches offers promising opportunities for early diagnosis, prevention, and development of mechanism-guided therapeutic strategies.