Multiple Herpes Simplex Virus-1 (HSV-1) reactivations induce neurodegenerative and oxidative damages in mouse brains

Introduction Several evidence support the role of oxidative stress in Alzheimer disease (AD) physiopathology, a neurodegenerative disorder characterized by the accumulation in the brain of β−amyloid peptides (Aβs) and neurofibrillary tangles (mainly composed by hyperphosphorylated tau), high level of oxidative stress markers and neuroinflammation (De Chiara et al, 2012, Piacentini et al, 2014). In particular, many redox proteomics studies on AD cerebral tissues led to the identification of oxidatively modified proteins that were consistent with biochemical or pathological alterations of the disease (Nunomura et al, 2001; Zhu et al, 2004; Smith et al, 2007; Droge et al, 2007). Interestingly, HSV-1, a neurotropic virus able to establish a lifelong latent infection in trigeminal ganglion followed by periodic reactivations, has been reported linked both to AD (Piacentini et al, 2015) and to oxidative stress conditions (Nucci et al, 2000; Palamara et al, 1995). Herein we design in vivo studies to investigate whether multiple HSV-1 reactivations induced in the brain the accumulation of oxidative stress hallmarks, particularly those correlated to AD Methods BALB/c mice were inoculated via snout abrasion with HSV-1, virus reactivation was periodically induced by thermal stress, and virus replication in the brain was verified through PCR and RT-PCR analysis of viral TK gene and ICP4 mRNA. These mice showed several signs of neurodegeneration (De Chiara et al 2017). Oxidative stress marker levels, i.e. 4-hydroxynonenal (HNE, marker of lipid peroxidation), 3-nitrotyrosine (3NT, marker of protein nytrosylation) and carbonylated proteins, were measured in brains of mice undergone multiple HSV-1 reactivations by dot-blot In addition, redox proteomic was used to identify those HNE-modified proteins mostly modulated by recurrent HSV-1 reactivations into the brain. Results Following several cycles of viral reactivation, we found in mouse brains: 1) increased levels of HNE, 3-NT, and protein carbonylation, indicating generalized conditions of oxidative stress; 2) thirteen HNE-modified proteins whose levels were significantly modulated in the cortex of HSV-1 infected mice compared to control mice. Interestingly, all these proteins are involved in important cellular processes, such as energy metabolism, protein folding, cell structure, and signal transduction, suggesting that their oxidative modification may affect brain physiology. Some of these proteins are reported to be significantly HNE-modified in AD brains compared to matched controls. Conclusion Overall, these data support the hypothesis that repeated HSV-1 reactivation into the brain may concur to neurodegeneration also inducing oxidative damages.