Background/Purpose: MicroRNA-155(miR-155) has been shown to be a key regulator of B cell biology by PU.1 regulation. However, the role of miR-155 in the activation of B cells in Rheumatoid Arthritis(RA) has not been explored. This study aimed to investigate miR-155 expression in RA B cells and its association with B cell driven pathologies such as levels of antibodies against citrullinated peptides(ACPA) and follicular structures in the synovial tissues(ST).

Methods: 60 RA patients underwent ST biopsy. Based on immunostaining for CD68, CD21, CD3 and CD20 cells, ST samples were categorized as diffuse or with follicular pattern. MiR-155 expression in RA ST and synovial B cells was evaluated by in situ hybridization(ISH). B cells from peripheral blood(PB) and matched synovial fluid(SF) of RA and PB of healthy controls(HC) were isolated by CD19⁺micro-beads. IL-6 and BAFF levels in PB and SF were measured by ELISA. MiR-155 and PU.1 expression in B cells from PB and SF of RA; and in ST samples of osteoarthritis(OA) and RA patients was determined by qPCR. Finally, PB-derived B cells were cultured with or without IL-6(30ng/ml) or BAFF(20ng/ml) and miR-155 and PU.1 expression was assessed by qPCR.

Results: 29 out of 60 RA patients(49.2%) had follicular pattern in the ST biopsy. These patients were more likely ACPA positive compared to RA with a diffuse pattern(p=0.04). Moreover, ACPA plasma levels directly correlated with the synovial aggregate grade(r=0.39;p=0.01). IL -6 and BAFF levels were higher in SF than in PB of RA regardless of the synovial infiltrate pattern(p=0.001 for both). PB B-cells from ACPA positive RA showed higher miR-155 expression compared to ACPA negative RA(p=0.02) and HC(p=0.001). Furthermore, ISH showed that miR-155 was highly expressed in ST of follicular RA compared to diffuse RA(p=0.03). Double staining revealed that the majority of B cells within synovial follicular structures were miR-155 positive. qPCR  further confirmed  that miR-155 was significantly increased in ST of follicular RA compared to diffuse RA(p=0.03) and OA(p=0.03), respectively. Consistently, the expression of miR-155 target in B cells, PU.1 was found to be lower within synovial aggregates in RA. At the cellular level, miR-155 was highly expressed in PB-derived B-cells of RA compared to HC(p=0.0002). In addition, miR-155 was over-expressed in SF B-cells compared to matched PB B-cells(p=0.05) in RA. This was associated with reciprocal lower expression of PU.1 in SF-derived B-cells and within ST follicular structures compared to matched PB B-cells(p=0.001) and ST with a diffuse pattern, respectively. Finally, in vitrostimulation of HC B-cells with IL-6 and BAFF induced miR-155(p=0.04 and p=0.03) and decreased PU.1(p=0.01 and p=0.03) expression.

Conclusion: B-cells of RA show high expression of miR-155 that is associated with ACPA positivity, follicular synovial pattern and low expression of PU.1. IL-6 and BAFF that are significantly increased in the SF environment and induce miR-155 expression in B-cells in vitro are likely candidates for maintaining high levels of miR-155 in the synovial B cells. Thus, miR-155 may represent a key regulator of B-cells in RA patients.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/microrna-155pu-1-axis-as-an-epigenetic-regulator-of-b-cells-in-rheumatoid-arthritis/