Herpes simplex virus-type1 (HSV-1) impairs DNA repair in cortical neurons, causing accumulation of DNA damage and contributing to neurodegeneration

Several findings suggest that recurrent HSV-1 infections play a co-factorial role in Alzheimer's disease (AD). In particular, we have recently demonstrated that HSV-1 promotes intra-and extra-neuronal accumulation of beta amyloid pepdides. In addition, HSV-1 was reported to inhibit in epithelial cells the not homologous end joining (NHEJ) DNA repair pathway, targeting DNA-dependent protein kinase (DNA-PK) for proteasomal degradation. NHEJ pathway repairs double strand breaks (DBSs), the most dangerous form of DNA damage and relies on the DNA-PK complex. Emerging evidence indicate that unrepaired DSBs and deficiency in NHEJ are implicated in the progressive neuronal loss observed in AD. Aim of this study was to determine whether HSV-1 infections in neurons affect DNA repair system, particularly the NHEJ thus causing DNA damage accumulation and contributing to neurodegeneration. Methods HSV-1-infected rat cortical neurons were analyzed for: gammaH2AX (phosphorylated histone H2AX) accumulation by immunoflorescence and western blot analysis (wb); DNA damage characterization by Comet assays; DNA-PK complex expression levels by wb of cell lysates; NHEJ efficacy by an in vitro NHEJ assay. Results HSV-1 infection in cortical neurons causes accumulation of gammaH2AX, a sensitive marker of DNA damage within chromatin, in the neuronal genome in a time- and multiplicity of infection-dependent manner. Furthermore, comet assay results demonstrate the occurrence of DSBs following HSV-1 infection in neurons. Consistently, HSV-1 infection modulates DNA-PK complex protein levels and affects the efficacy of NHEJ pathway. Conclusions HSV may contribute to neurodegeneration though the impairment of NHEJ and the consequent accumulation of DNA damage.