Herpes Simplex Virus type-1 infection induces synaptic dysfunction in cultured cortical neurons via GSK-3 activation and intraneuronal amyloid-β protein accumulation.

Roberto Piacentini,Claudio Grassi,Domenica Donatella Li Puma,Cristian Ripoli,Enrico Garaci,Maria Elena Marcocci,Anna Teresa Palamara,Giovanna De Chiara

doi:10.1038/srep15444

Abstract

Increasing evidence suggests that recurrent Herpes Simplex Virus type 1 (HSV-1) infection spreading to the CNS is a risk factor for Alzheimer’s Disease (AD) but the underlying mechanisms have not been fully elucidated yet. Here we demonstrate that in cultured mouse cortical neurons HSV-1 induced Ca2+-dependent activation of glycogen synthase kinase (GSK)-3. This event was critical for the HSV-1-dependent phosphorylation of amyloid precursor protein (APP) at Thr668 and the following intraneuronal accumulation of amyloid-β protein (Aβ). HSV-1-infected neurons also exhibited: i) significantly reduced expression of the presynaptic proteins synapsin-1 and synaptophysin; ii) depressed synaptic transmission. These effects depended on GSK-3 activation and intraneuronal accumulation of Aβ. In fact, either the selective GSK-3 inhibitor, SB216763, or a specific antibody recognizing Aβ (4G8) significantly counteracted the effects induced by HSV-1 at the synaptic level. Moreover, in neurons derived from APP KO mice and infected with HSV-1 Aβ accumulation was not found and synaptic protein expression was only slightly reduced when compared to wild-type infected neurons. These data further support our contention that HSV-1 infections spreading to the CNS may contribute to AD phenotype.

Highlights

Following HSV-1-induced phosphorylation at Thr[668], amyloid precursor protein (APP) is subjected to multiple cleavages by secretases (β and γ ) and caspases
Given that APP is substrate for several kinases including glycogen synthase kinase (GSK)-3, Jun N-terminus kinase (JNK) and Cyclin-dependent kinase 5 (Cdk-5), we studied their involvement in HSV-1-induced APP phosphorylation by adding specific kinase inhibitors to the culture medium of infected cells during the entire post-infection (p.i.) time
In this study we demonstrated that HSV-1 infection impairs synaptic function in cultured mouse cortical neurons through GSK-3 activation and intracellular accumulation of amyloid-β protein (Aβ)

Summary

Introduction

Following HSV-1-induced phosphorylation at Thr[668], APP is subjected to multiple cleavages by secretases (β and γ ) and caspases. It is known that Thr[668] of APP and its C-terminus fragment are substrate for the glycogen synthase kinase (GSK)-3, as well as for several other kinases including c-Jun N-terminus kinase (JNK) and Cyclin-dependent kinase 5 (Cdk-5)[9,10,11,12]. GSK-3 is markedly activated in the brains of AD mouse models[14,15] and patients[16]. This activation, obtained by either increased phosphorylation at Tyr residues (279 or 216 for α and β isoforms, respectively) or decreased phosphorylation at Ser sites (21α and 9β ), has been reported to mediate synaptic damage induced by Aβ 17. We report that HSV-1 infection markedly affects synaptic function via GSK-3-dependent intraneuronal accumulation of Aβ

Methods

Results

Conclusion