HSV-1 Infection Triggers Alzheimer's Pathways and Cellular Senescence in Human Brain Models
New iPSC and cerebral organoid research shows HSV-1 directly activates neurodegeneration and senescence pathways, supporting the viral hypothesis of Alzheimer's disease.
Summary
Researchers infected human iPSC-derived neurons and 3D cerebral organoids with HSV-1 and tick-borne encephalitis virus to test whether viral infection triggers Alzheimer's-related changes. HSV-1 caused robust amyloid-beta clustering, activated neurodegeneration pathways, and induced a senescence-associated secretory profile — but only when extracellular amyloid peptides were already present. TBEV did not produce the same effects. Transcriptomic and proteomic analyses confirmed widespread HSV-1-driven molecular changes. Notably, familial Alzheimer's mutations in PSEN1/2 did not alter the acute infection response. Reanalysis of independent datasets supported the findings and showed a limited protective effect of the antiviral drug acyclovir. The results strengthen the Pathogen Infection Hypothesis and suggest antiviral vaccination may reduce Alzheimer's risk.
Detailed Summary
Alzheimer's disease (AD) affects tens of millions globally, yet its precise triggers remain poorly understood. The Pathogen Infection Hypothesis proposes that amyloid-beta (Aβ) functions as an antimicrobial peptide — a first-line brain defense that, when chronically activated by viral infection, may seed the plaques characteristic of AD. This study provides some of the most direct experimental evidence yet for this hypothesis using human-relevant cellular models, moving beyond animal or post-mortem tissue studies.
The research team at Masaryk University and collaborating Czech and NIH institutions used iPSC-derived 2D neuronal cultures and 3D cerebral organoids (COs) generated from both wild-type (WT) individuals and patients carrying familial AD mutations in PSEN1 or PSEN2. Two neurotropic viruses were tested: HSV-1 (herpes simplex virus type 1, a chronic neurotropic virus) and TBEV (tick-borne encephalitis virus, an acute neurotropic flavivirus). Organoids were infected at day 53 or day 93 of differentiation, with some pre-treated for seven days with synthetic Aβ40 or Aβ42 peptides (100 nM) prior to infection. Transcriptomic profiling used 3'mRNA sequencing (~10 million reads per sample) from six independent iPSC lines, and proteomic analysis characterized the secretome of infected organoids.
HSV-1 infection induced robust Aβ clustering in cerebral organoids, but this clustering was critically dependent on the presence of extracellular amyloid peptides — organoids pre-treated with synthetic Aβ40 or Aβ42 showed significantly greater plaque-like aggregation upon HSV-1 exposure compared to untreated controls. TBEV infection did not produce comparable Aβ clustering under any condition tested. ELISA quantification of secreted Aβ40 and Aβ42 at days 57 and 97 post-infection confirmed differential responses between the two viruses. These findings suggest that HSV-1's capacity to seed amyloid aggregation is not intrinsic to viral infection alone but requires a permissive amyloid environment.
Transcriptomic analysis revealed widespread HSV-1-induced gene expression changes, with significant enrichment of neurodegeneration-related pathways including ER stress, oxidative stress, synaptic dysfunction, and inflammatory signaling. Proteomic profiling of the conditioned secretome confirmed enrichment of senescence-associated secretory phenotype (SASP) markers, indicating that HSV-1 drives neurons and organoids into a senescent state. Importantly, PSEN1/2 mutations did not significantly alter the acute infection response at the transcriptomic or proteomic level, suggesting that the viral-induced AD-like cascade is largely independent of familial AD genetic background in the acute phase. Reanalysis of independent published datasets corroborated these findings and additionally revealed a limited but detectable protective effect of acyclovir treatment against HSV-1-induced molecular changes.
The study carries significant implications for AD prevention strategies. If viral infections — particularly HSV-1 reactivation — can trigger the molecular cascade leading to amyloid aggregation and neuronal senescence, then antiviral vaccination and prophylactic antiviral therapy represent actionable prevention targets. This aligns with recent population-level data showing that herpes zoster vaccination and influenza vaccination are associated with reduced AD incidence. A key caveat is that this is a preprint (bioRxiv), the models are acute infection systems that may not fully recapitulate chronic latent HSV-1 reactivation seen in aging humans, and the amyloid clustering required pre-existing extracellular Aβ, raising questions about the sequence of events in vivo.
Key Findings
- HSV-1 infection induced robust Aβ clustering in cerebral organoids, but only when organoids were pre-treated with 100 nM synthetic Aβ40 or Aβ42 for 7 days prior to infection — suggesting a permissive amyloid environment is required
- TBEV (tick-borne encephalitis virus) did not produce comparable Aβ aggregation under any tested condition, indicating the effect is HSV-1-specific rather than a general viral response
- Transcriptomic profiling (~10M reads/sample, 6 iPSC lines) revealed widespread HSV-1-induced activation of neurodegeneration-related pathways including ER stress, oxidative stress, and synaptic dysfunction
- Proteomic analysis of the organoid secretome confirmed enrichment of senescence-associated secretory phenotype (SASP) markers following HSV-1 infection, linking viral infection to cellular senescence in neurons
- PSEN1/2 familial AD mutations did not significantly alter the acute transcriptomic or proteomic response to either HSV-1 or TBEV infection, suggesting viral-induced AD pathology is largely genotype-independent in the acute phase
- Reanalysis of independent published datasets confirmed HSV-1-induced neurodegeneration signatures and revealed a limited protective effect of acyclovir against HSV-1-induced molecular changes in neuronal models
- Organoids infected at both day 53 and day 93 of differentiation showed infection-driven changes, with viral gene expression confirmed by qRT-PCR and absent in non-infected controls
Methodology
The study used iPSC-derived 2D NGN2-induced neurons (infected at day 17) and 3D cerebral organoids (infected at days 53 and 93) from 6 iPSC lines — 3 wild-type and 3 carrying PSEN1/2 familial AD mutations. HSV-1 (MOI 0.0001) and mCherry-TBEV (MOI 0.1) were applied for 30 minutes (2D) or 24 hours (3D), with 4–7 days post-infection follow-up. Molecular analyses included 3'mRNA sequencing (Lexogen QuantSeq, NextSeq 500, ~10M reads/sample), secretome proteomics, ELISA for Aβ40/42, qRT-PCR for viral genes, Western blot, and confocal immunohistochemistry with Imaris volumetric quantification. Statistical analyses were performed in R v4.4.2 and GraphPad Prism v9.
Study Limitations
This is a preprint and has not yet undergone peer review. The models use acute infection paradigms that may not fully replicate the chronic, latent-reactivation pattern of HSV-1 in aging human brains, potentially underestimating long-term effects. The finding that Aβ clustering requires pre-existing extracellular amyloid raises unresolved questions about the in vivo sequence of events — it is unclear whether viral infection alone can initiate amyloid deposition or only amplify existing pathology. No conflicts of interest were declared by the authors.
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