*Article* **The Interplay between Transcriptional Factors and MicroRNAs as an Important Factor for Th17**/**Treg Balance in RA Patients**

**Tomasz Kmiołek 1, Ewa Rzeszotarska 1,\*, Anna Wajda 1, Ewa Walczuk 1, Ewa Kuca-Warnawin 2, Katarzyna Romanowska-Próchnicka 3,4, Barbara Stypinska 1, Dominik Majewski 5, Pawel Piotr Jagodzinski 6, Andrzej Pawlik <sup>7</sup> and Agnieszka Paradowska-Gorycka <sup>1</sup>**


Received: 5 August 2020; Accepted: 25 September 2020; Published: 28 September 2020

**Abstract:** MicroRNAs regulate gene expression of transcriptional factors, which influence Th17/Treg (regulatory T cells) balance, establishing the molecular mechanism of genetic and epigenetic regulation of Treg and Th17 cells is crucial for understanding rheumatoid arthritis (RA) pathogenesis. The study goal was to understand the potential impact of the selected microRNAs expression profiles on Treg/Th17 cells frequency, RA phenotype, the expression profile of selected microRNAs, and their correlation with the expression profiles of selected transcriptional factors: SOCS1, SMAD3, SMAD4, STAT3, STAT5 in RA; we used osteoarthritis (OA) and healthy controls (HCs) as controls. The study was conducted on 14 RA and 11 OA patients, and 15 HCs. Treg/Th17 frequency was established by flow cytometry. Gene expression analysis was estimated by qPCR. We noticed correlations in RA Th17 cells between miR-26 and SMAD3, STAT3, SOCS1; and miR-155 and STAT3—and in RA Treg cells between miR-26 and SOCS1; miR-31, -155 and SMAD3; and miR-155 and SMAD4. In RA Tregs, we found a negative correlation between miR-26, -126 and STAT5a. The expression level of miR-31 in Th17 cells from RA patients with DAS28 ≤ 5.1 is higher and that for miR-24 is greater in Tregs from patients with DAS28 > 5.1. MiR-146a in Tregs is higher in rheumatoid factor (RF) positive RA patients.

**Keywords:** rheumatoid arthritis (RA); Treg; Th17; gene expression; microRNA; transcriptional factor
