Antiviral activity of salivary microRNAs for ophthalmic herpes zoster

Ophthalmic herpes zoster is a common ocular infection caused by the varicella-zoster virus (VZV). Viral mRNA transcripts play a major role in the replicative cycle of the virus and current antiviral agents have little effect in preventing and treating the complications. Therapeutic use of saliva for certain painful ocular diseases such as ophthalmic herpes zoster is a well-known public practice in our region. We thought that antiviral activity of saliva may stem from salivary microvesicles and we aimed to look for molecules with antiviral activity in these vesicles. As a possible candidate for antiviral activity, salivary microvesicles contain at least 20 microRNAs (miRNAs), small noncoding RNAs, which suppress the translation of target mRNAs. miRNAs not only participate in maintenance of normal cell functions, but are also involved in host–virus interactions and limit the replication of certain virus types. Thus, miRNA gene therapy by targeting mRNAs required for VZV survival may find a niche in the treatment of ophthalmic herpes zoster. But, how could salivary microvesicles reach into the corneal cells to demonstrate their antiviral activity. We suggest that human salivary microvesicles can be effective carriers of miRNA for corneal cells, because they contain a molecular machinery for vesicle trafficking and fusion allowing them to be endocytosed by target cells. After binding to the plasma membrane, microvesicles seem to enter into the corneal cells through the clathrin-mediated endocytosis. In the cytosol, human salivary miRNAs base-pair with specific viral mRNAs and inhibit their translation, thus limiting the replication of the virus.