The Gut-Liver Axis in Hepatitis C Virus Infection: A Path Towards Altering the Natural History of Fibrosis Progression?

tRNA-Ser-UGA efficiently promotes the rapid release of duck hepatitis A virus from infected enterocytes and its remote dissemination to hepatocytes

Enterocytes are a necessary portal for fecal-oral transmission of viruses, including duck hepatitis A virus (DHAV), that act on the absorption of amino acids (AAs). We note that the rapid death of ducklings caused by DHAV is likely due to its rapid release from enterocytes. However, the underlying mechanism driving the release of DHAV remains poorly understood. Compared to infected fibroblasts, we found that DHAV-infected enterocytes triggered much more rapid viral release and induced swift and diverse remodeling of the mature tRNAome. Surprisingly, we found that tRNA-Ser-UGA in enterocytes was rapidly and specifically upregulated by DHAV infection and was highly correlated with serine decoding of DHAV, which is enriched with UCA codons. Overexpression of tRNA-Ser-UGA in enterocytes promoted rapid DHAV release, whereas overexpression of the cognate tRNA-Ser-GCU in enterocytes or the same tRNA in fibroblasts did not. In enterocytes, inhibition of serine charging of tRNA-Ser-UGA, transfection of a tRNAm-Ala-UGA backbone mutant or a tRNAm-Ser-UGA>CGA anticodon mutant decreased DHAV release. This finding suggests that tRNA-Ser-UGA plays a prominent role in DHAV release in infected enterocytes, which should be supported by efficient protein translation of the virus. Similarly, tRNA-Ser-UGA potently enhances DHAV protein synthesis, and the inhibition of charging of this tRNA or the transfection of the two mutants decreases DHAV protein synthesis. Phenotypically, the overexpression of tRNA-Ser-UGA in enterocytes further accelerates the spread of DHAV to hepatocytes. In conclusion, we revealed a novel tRNA-Ser-UGA that efficiently promotes the rapid release of DHAV by increasing serine decoding in infected enterocytes, thereby promoting remote cell-to-cell dissemination.

Intestinal Microbiota-A Promising Target for Antiviral Therapy?

The intestinal microbiota is thought to be an important biological barrier against enteric pathogens. Its depletion, however, also has curative effects against some viral infections, suggesting that different components of the intestinal microbiota can play both promoting and inhibitory roles depending on the type of viral infection. The two primary mechanisms by which the microbiota facilitates or inhibits viral invasion involve participation in the innate and adaptive immune responses and direct or indirect interaction with the virus, during which the abundance and composition of the intestinal microbiota might be changed by the virus. Oral administration of probiotics, faecal microbiota transplantation (FMT), and antibiotics are major therapeutic strategies for regulating intestinal microbiota balance. However, these three methods have shown limited curative effects in clinical trials. Therefore, the intestinal microbiota might represent a new and promising supplementary antiviral therapeutic target, and more efficient and safer methods for regulating the microbiota require deeper investigation. This review summarizes the latest research on the relationship among the intestinal microbiota, anti-viral immunity and viruses and the most commonly used methods for regulating the intestinal microbiota with the goal of providing new insight into the antiviral effects of the gut microbiota.