Aberrant STAT3 activation and overproduction of IL-21 in systemic lupus erythematosus: role of miR-155 and miR-21 in target genes SOCS1, PTEN and PIAS3

Introduction SLE is a chronic autoimmune disease characterized by immune system dysregulation, including aberrant activation of B and T lymphocytes and overproduction of proinflammatory cytokines such as IL-21. Through the STAT3 signaling pathway, this cytokine plays a key role in SLE-promoting autoantibody production and immune imbalance. It has been reported that miRNAs, such as miR-155 and miR-21, could be overexpressed in SLE and contribute to the STAT3 pathway dysregulation. We aimed to analyze the association between miR-155 and miR-21 and the expression of SOCS1 , PTEN , PIAS3 , and IL21 in PBMC from SLE patients. Materials and methods PBMC isolation was performed by density gradient centrifugation using Histopaque-1077, culture overnight, and seeded at a concentration of 1x10 6 cells/mL in 24-well flat-bottom cell culture plates for subsequent stimulation with 0.5 μg/mL ionomycin and 2.5 μg/mL PMA. The expression levels of miR-155, miR-21, SOCS1, PTEN, PIAS3 , and IL21 were measured using the RT-qPCR technique. Western blotting determined the expression of SOCS1, PTEN, PIAS3, IL-21, and p-STAT3 proteins. IL-17A levels in cell culture supernatant were determined using ELISA to assess cell stimulation. Results Our results showed an increased expression of miR-155 and miR-21 in SLE patients compared to HC in both, stimulated and non-stimulated PBMC. The increased miR-155 and miR-21 expression were associated with a decreased gene expression of SOCS1 and PTEN . The IL21 expression was observed in stimulated PBMC with higher levels in SLE patients. These also showed lower expression of SOCS1, PTEN, and PIAS3, while levels of IL-21 were increased in total protein from PBMC, culture cell supernatants and plasma levels. Overall, p-STAT3 was increased in the PBMC of SLE patients. Finally, miR-21 inversely correlated with PIAS3 and PTEN and miR-155 with SOCS1. Discussion These findings highlight the association between miR-155 and miR-21 with target genes SOCS1, PTEN, and PIAS3, that may contribute to the aberrant activation of the STAT3 pathway and the overproduction of IL-21 in SLE patients.