An Epigenetically Driven Mechanism Triggered by Viral and Bacterial RNA Regulates the IL-6 Levels in IgA Nephropathy

ABSTRACT

Background: Recently, the role of IL-6 in IgAN pathogenesis is becoming increasingly important. A possible hypothesis emerges from our recent work on genomewide DNA methylation screening in patients with IgAN, which identified, among other findings, a hypermethylated region comprising Vault 2-1 RNA (VTRNA2-1), a non-RNA coding also known as a precursor of miR-886 (pre-mi-RNA). Consistently, VTRNA2-1 expression was found downregulated in IgAN patients. Method(s) Total RNA were isolated from PBMCs of IgAN patients, transplanted IgAN patients (TP-IgAN), non-IgAN transplanted patients (TP) and healthy subjects (HS). VTRNA2-1, CREB, PKR and IL-6 were evaluated by RT-PCR and by ELISA. Poly (IC) and Pfizer-BioNTech COVID-19 COMIRNATY vaccine were used to transfect patient PBMCs. PKR inhibitor imoxin (C16) 1 muM was used to stimulate patient PBMCs. Result(s) Here we confirm that VTRNA2-1 is low expressed in IgAN subjects compared to HS and we found that also in TP-IgAN, compared to TP, the VTRNA2-1 transcript was expressed at level very low. We found that in IgAN patients with downregulated VTRNA2-1, PKR is overactivated, coherently with the role of the VTRNA2-1 that binds to PKR and inhibits its phosphorylation. The loss of the VTRNA2-1 natural restrain caused the activation of CREB by PKR, a classical cAMPinducible CRE-binding factor interacting with a region of the IL-6 promoter and leading to IL-6 production. We found higher CREB phosphorylation levels and IL-6 levels both in IgAN and in TP-IgAN patients. Since PKR is normally activated by bacterial and viral RNA, we hypothesized that these microorganisms can further activate the PKR/CREB/ IL-6 pathway leading to an excess of IL-6 production, explaining both the high levels of IL-6, both infection involvement in the disease, both cases of IgAN associated with COVID-19 infection and with COVID-19 RNA-vaccination. Both the RNA poly(IC) and the COVID-19 RNA-vaccine stimulation significantly increase the IL-6 levels in IgAN patient PBMCs. Conclusion(s) In conclusion, the discovery of the upregulated VTRNA2-1/PKR/ CREB/IL-6 pathway in IgAN patients may provide a new pathogenic mechanism in IgAN and may be useful for the development of novel therapeutic approaches, likely by modulating the VTRNA2-1 methylation level in IgAN patients.