Modulation of miRNome by HCMV and HHV-6 infection in human dermal fibroblasts: possible significance in systemic sclerosis

Background: Human cytomegalovirus (HCMV) and Human herpesvirus 6 (HHV-6) have been reportedly suggested as triggers of the onset and/or progression of many autoimmune diseases. Among them, we recently reported a possible involvement of both viruses in systemic sclerosis (SSc), a severe autoimmune disorder characterized by vasculopathy and multi-organ fibrosis. The etiology and pathogenesis of SSc are still largely unknown but virological and immunological observations support a role for these beta-herpesviruses. We recently observed a direct impact of HCMV and HHV-6 infection on the expression of cell factors associated with fibrosis at the cell microenvironment level. Since in SSc patients miRNA expression has been found deregulated at the tissue or blood level, here we aimed to investigate the impact of HCMV and HHV-6 infection on the miRNome of in vitro infected primary human dermal fibroblasts, which represent one of the main SSc target cells. Methods: Human primary dermal fibroblasts were infected in vitro with cell-free inocula of HCMV and HHV-6, and at different times post infection (0, 4, 7, 10, and 14 d.p.i.) were collected to extract RNA. The analysis was performed by Taqman arrays detecting and quantifying 754 miRNAs. Results: The miRNome analysis showed that both viruses significantly modulated miRNA expression in infected cells, with effects evident at both early and late times p.i.. PCA analysis showed a significantly different clusterization of miRNA at all time tested. Up to 106 miRNAs were up-regulated and 170 down-modulated by HCMV infection; HHV-6 infection up-regulated the expression of up to 117 miRNA and down-modulated 112 miRNAs. Several altered miRNAs belong to those already recognized for their key function in fibrosis; several other miRNAs appear potentially involved in the process leading to cell function impairment and apoptosis. Conclusion: HCMV and HHV-6 infection profoundly remodulate cell miRNome in human dermal fibroblasts, and the correlation between these in vitro results with in vivo observations is strongly suggestive of a role of HCMV and HHV-6 in the multistep pathogenesis of fibrosis in SSc.