ß-Amyloid peptides display protective activity against the human Alzheimer's disease-associated herpes simplex virus-1.

Amyloid plaques, the hallmark of Alzheimer's disease (AD), contain fibrillar ß-amyloid (Aß) 1-40 and 1-42 peptides. Herpes simplex virus 1 (HSV-1) has been implicated as a risk factor for AD and found to co-localize within amyloid plaques. Aß 1-40 and Aß 1-42 display anti-bacterial, anti-yeast and anti-viral activities. Here, fibroblast, epithelial and neuronal cell lines were exposed to Aß 1-40 or Aß 1-42 and challenged with HSV-1. Quantitative analysis revealed that Aß 1-40 and Aß 1-42 inhibited HSV-1 replication when added 2 h prior to or concomitantly with virus challenge, but not when added 2 or 6 h after virus addition. In contrast, Aß 1-40 and Aß 1-42 did not prevent replication of the non-enveloped human adenovirus. In comparison, antimicrobial peptide LL-37 prevented HSV-1 infection independently of its sequence of addition. Our findings showed also that Aß 1-40 and Aß 1-42 acted directly on HSV-1 in a cell-free system and prevented viral entry into cells. The sequence homology between Aß and a proximal transmembrane region of HSV-1 glycoprotein B suggested that Aß interference with HSV-1 replication could involve its insertion into the HSV-1 envelope. Our data suggest that Aß peptides represent a novel class of antimicrobial peptides that protect against neurotropic enveloped virus infections such as HSV-1. Overproduction of Aß peptide to protect against latent herpes viruses and eventually against other infections, may contribute to amyloid plaque formation, and partially explain why brain infections play a pathogenic role in the progression of the sporadic form of AD.

Alzheimer's disease plaques and tangles: cemeteries of a pyrrhic victory of the immune defence network against herpes simplex infection at the expense of complement and inflammation-mediated neuronal destruction.

Plaques and tangles are highly and significantly enriched in herpes simplex (HSV-1) binding proteins (by 11 and 15 fold respectively (P<4.47466E-39) and 132/341 (39%) of the known HSV-1 binding partners or associates are present in these structures. The classes involved include the majority (63-100%) of the known HSV-1 host protein carriers and receptors, 85-91% of the viral associated proteins involved in endocytosis, intracellular transport and exocytosis and 71% of the host proteins associated with the HSV-1 virion. The viral associated proteins found in plaques or tangles trace out a complete itinerary of the virus from entry to exocytosis and the virus also binds to plaque or tangle components involved in apoptosis, DNA transcription, translation initiation, protein chaperoning, the ubiquitin/proteasome system and the immune network. Along this route, the virus deletes mitochondrial DNA, as seen in Alzheimer's disease, sequesters the neuroprotective peptide, ADNP, and interferes with key proteins related to amyloid precursor protein processing and signalling as well as beta-amyloid processing, microtubule stability and tau phosphorylation, the core pathologies of Alzheimer's disease. Amyloid-containing plaques or neurofibrillary tangles also contain a large number of complement, acute phase and immune-related proteins, and the presence of these pathogen defence related classes along with HSV-1 binding proteins suggests that amyloid plaques and tangles represent cemeteries for a battle between the virus and the host's defence network. The presence of the complement membrane attack complex in Alzheimer's disease neurones suggests that complement mediated neuronal lysis may be a consequence of this struggle. HSV-1 infection is known to increase beta-amyloid deposition and tau phosphorylation and also results in cortical and hippocampal neuronal loss, cerebral shrinkage and memory deficits in mice. This survey supports the contention that herpes simplex viral infection contributes to Alzheimer's disease, in genetically predisposed individuals. Genetic conditioning effects are likely to be important, as all of the major risk promoting genes in Alzheimer's disease (apolipoprotein E, clusterin, complement receptor 1 and the phosphatidylinositol binding clathrin assembly protein PICALM), and many lesser susceptibility genes, are related to the herpes simplex life cycle. 33 susceptibility genes are related to the immune system. Vaccination or antiviral agents and immune suppressants should therefore perhaps be considered as viable therapeutic options, prior to, or in the early stages of Alzheimer's disease.

Herpes simplex virus type 1 DNA is located within Alzheimer's disease amyloid plaques.

The brains of Alzheimer's disease sufferers are characterized by amyloid plaques and neurofibrillary tangles. However, the cause(s) of these features and those of the disease are unknown, in sporadic cases. We previously showed that herpes simplex virus type 1 is a strong risk factor for Alzheimer's disease when in the brains of possessors of the type 4 allele of the apolipoprotein E gene (APOE-epsilon4), and that beta-amyloid, the main component of plaques, accumulates in herpes simplex virus type 1-infected cell cultures and mouse brain. The present study aimed to elucidate the relationship of the virus to plaques by determining their proximity in human brain sections. We used in situ polymerase chain reaction to detect herpes simplex virus type 1 DNA, and immunohistochemistry or thioflavin S staining to detect amyloid plaques. We discovered a striking localization of herpes simplex virus type 1 DNA within plaques: in Alzheimer's disease brains, 90% of the plaques contained the viral DNA and 72% of the DNA was associated with plaques; in aged normal brains, which contain amyloid plaques at a lower frequency, 80% of plaques contained herpes simplex virus type 1 DNA but only 24% of the viral DNA was plaque-associated (p < 0.001). We suggest that this is because in aged normal individuals, there is a lesser production and/or greater removal of beta-amyloid (Abeta), so that less of the viral DNA is seen to be associated with Abeta in the brain. Our present data, together with our finding of Abeta accumulation in herpes simplex virus type 1-infected cells and mouse brain, suggest that this virus is a major cause of amyloid plaques and hence probably a significant aetiological factor in Alzheimer's disease. They point to the usage of antiviral agents to treat the disease and possibly of vaccination to prevent it.

Herpes simplex virus infection causes cellular beta-amyloid accumulation and secretase upregulation.

It is uncertain whether environmental factors contribute to the formation of senile plaques and neurofibrillary tangles, the abnormal features that define the Alzheimer's disease (AD) brain. We previously proposed that herpes simplex virus type 1 (HSV1) is a strong risk factor for AD when it is present in the brains of people who possess the type 4 allele of the apolipoprotein E gene (APOE-epsilon4); however a direct biochemical link between viral infection and the development of the AD pathological features has never previously been examined. Here we show that infection of cultured neuronal and glial cells with HSV1 leads to a dramatic increase in the intracellular levels of beta-amyloid (Abeta) 1-40 and 1-42, whilst levels of amyloid precursor protein (APP) in cells decrease. Similarly, Abeta1-42 deposits are present in mouse brain after HSV1 infection. In the cultured cells the mechanism involves increased Abeta production, rather than merely greater retention of cellular Abeta, as levels of beta-site APP-cleaving enzyme (BACE-1) and of nicastrin, a component of gamma-secretase, both increase in HSV1-infected cells. These novel data show that HSV1 can directly contribute to the development of senile plaques.