Investigating the role of autophagy in herpes simplex encephalitis

Abstract

The role of autophagy in innate immunity has recently garnered attention from molecular biologists and pathologists alike. A growing number of reports suggest its anti-viral role in various infections, including Herpes simplex virus 1 (HSV1) which is the causative pathogen for herpes simplex encephalitis (HSE). Whilst studies have shown the non-redundant role of Toll-like receptor 3 (TLR3)-interferon (IFN) signalling pathway in HSV1 defence, the role of autophagy in HSV1 infection and HSE pathogenesis remains elusive. In this study, we characterised autophagy phenotypes in response to rapamycin, poly(I:C), c-di-GMP and HSV1 dsDNA stimulations as well as HSV1 infection, of human dermal fibroblasts derived from HSE patients harbouring mutations in components of the TLR3-IFN pathway – UNC93B1 (c.103del4), TLR3 (p.R867Q), TRIF (p.R141X), TRAF3 (p.R118W) and TBK1 (p.D50A and p.G159A). By using the autophagy marker LC3B, we established the HSV1-induced formation of two distinct autophagy phenotypes: cytoplasmic and perinuclear LC3B phenotypes. We correlated the former with the host protective autophagy response triggered early in HSV1 infection, which is TBK1-dependent but TLR3- and IFN-independent, and can be induced in neighbouring non-infected cells. Fibroblasts carrying the G159A mutation in TBK1 failed to induce LC3BII:I and reduce the autophagy adaptor p62 protein levels, suggesting a defect in autophagy response upon HSV1 infection. This impairment is reproducible by inhibiting TBK1 function using TBK1 inhibitor BX795 and depleting endogenous TBK1 in control fibroblasts. Furthermore, we demonstrated the cytoprotective nature of autophagy in HSV1 infection, whereby prior upregulation of autophagy by rapamycin in fibroblasts, led to enhanced cell viability following HSV1 infection.