Elucidating the mode-of-action of the human RNase 7 against α-herpesviruses and its impact on eczema herpeticum and severe herpes zoster

• Applicants: Dr. Katinka Döhner; Professor Dr. Jürgen Harder; Professor Dr. Thomas Werfel
• Subject Area: Dermatology
• Term: since 2017
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 364100506

Atopic dermatitis (AD) is one of the most common inflammatory skin diseases. Patients with AD are more susceptible to cutaneous viral infections and approximately 3% of AD patients have a history of eczema herpeticum (EH). EH is a disseminated herpes simplex virus (HSV) infection of the skin that, if left untreated, can progress to a potentially life-threatening systemic infection. The antimicrobial protein (AMP) RNase 7 (R7) is produced and secreted in high amounts by skin keratinocytes. In addition to its ribonuclease activity, R7 has potent antimicrobial and immunomodulatory activity, contributing to cutaneous defense. Our preliminary work indicates that R7 can protect human keratinocytes from HSV infection. This leads to the hypothesis that R7 plays an important role in the cutaneous antiviral defense against HSV infection. This project aims to investigate this hypothesis in detail. In the first mechanistic part of this project, we will analyze which steps in the HSV infection cycle are inhibited by R7, which domains of R7 are important for its antiviral activity, and whether R7 interacts directly with viral or cellular proteins. In the second functional part, we will use 2D and 3D skin models to study how different amounts of R7 and the ribonuclease inhibitor (RI) influence susceptibility to HSV infection and the expression of host and HSV genes. In preliminary work, we have shown that elevated levels of DNA and RI, as present on AD skin, inhibit the antibacterial activity of R7. Based on these findings, we now want to determine whether these factors also influence the antiviral effect of R7 against HSV. In the third clinical and translational part, we will examine whether R7 can also maintain its protective effect in the context of AD, especially in the presence of the AD-associated Th2 cytokines IL-4 and IL-13. Using keratinocytes from healthy volunteers and AD patients with and without EH, we will investigate how the genetic background of the keratinocytes affects the protective effect of R7. In addition, biopsies and skin washings will be used to investigate whether decreased expression and secretion of R7 or other AMPs, or increased expression of RI, is associated with EH in AD patients or with severe herpes zoster courses in the elderly. If AD patients at risk could be identified in advance, e.g. by measuring AMP concentrations in skin rinses, prophylactic measures could possibly be initiated to prevent severe disseminated HSV infections. Due to its antibacterial, antifungal and antiviral properties and its ability to reduce the secretion of Th2 cytokines, R7 is a promising candidate for the development of topical therapeutics for the supportive treatment of AD patients with EH.

• DFG Programme: Research Grants