Accumulating evidence suggests that
infections by herpesviruses might be closely linked to
Alzheimer's disease (AD). Pathological hallmarks of AD brains include
senile plaques induced by
amyloid β
peptide (Aβ) in the extracellular space and intracellular neurofibrillary tangles (NFTs) consisting of phosphorylated
tau protein. The prevailing hypothesis for the mechanism of AD is
amyloid cascade reaction. Recent studies revealed that
infections by herpesviruses induce the similar pathological hallmarks of AD, including Aβ production, phosphorylation of tau (P-tau), oxidative stress,
neuroinflammation, etc. Aβ
peptide is regarded as one of the
antimicrobial peptides, which inhibits HSV-1 replication. In the elderly, reactivation of herpesviruses might act as an initiator for
amyloid cascade reaction in vulnerable individuals, triggering the neurofibrillary formation of phosphorylated tau and inducing oxidative stress and
neuroinflammation, which can further contribute to the accumulation of Aβ and P-tau by impairing mitochondria and autophagosome. Epidemiological studies have shown AD susceptibility genes, such as APOE-ε4 allele, are highly linked to
infections by herpesviruses. Interestingly, anti-herpesviral
therapy significantly reduced the risk of AD in a large population study. Given that herpesviruses are arguably the most prevalent opportunistic pathogens and often reactivate in the elderly, it is reasonable to argue reactivation of herpesviruses might be major culprits for initiating AD in individuals carrying AD susceptibility genes. In this review, we summarize epidemiological and molecular evidence that support for a hypothesis of herpesviral
infections and antimicrobial protection in the development of AD, and discuss the implications for future prevention and treatment of the disease.