Analysis of hepatic and retinal cell microRNAome during AAV infection reveals their diverse impact on viral transduction and cellular physiology.

Cellular microRNAs are known to modulate the life-cycle of different viruses. Surprisingly, very little data exists on AAV-induced changes to the cellular microRNAome in general and in hepatic and retinal cells, in particular. We reasoned that inducible microRNA in response to recombinant AAV infection may regulate immediate and long-lived cellular responses necessary for the cell's own survival as well as its ability to control several aspects of viral life-cycle. To study this, we performed a global small RNA sequencing analysis in Adeno-associated virus (AAV) serotypes 2 and 3 infected hepatic and retinal cell models. This screen identified multiple differentially expressed microRNAs, in AAV infected Huh-7 and ARPE-19 cells. Among these, one microRNA (miR-4488) was found to be significantly down regulated (-2.24 fold for AAV2 and -3.32 fold for ARPE-19) in AAV infected cells. An enrichment and pathway analysis of miR-4488 predicted its possible effects on gene targets involved in multiple biological processes including cell-cycle regulation, endoplasmic reticulum stress response and lipid-signalling pathways. Moreover, validation studies in miR-4488 mimic or sponge transfected cells revealed modulation of these target pathways in a cell-specific manner. Further studies demonstrated that overexpression of miR-4488, modestly increased gene expression (126-128%) from AAV2 and AAV3 vectors in Huh-7 cells whereas miR-4488 inhibition in ARPE-19 cells had a similar increase (142-158%) on AAV2 or AAV3 transduction. Our results highlight that recombinant AAV mediated microRNA expression is cell-type and serotype-specific and can target specific host cellular biological pathways.