Background and objectives Several microRNAs are known to control the differentiation and function of B cells, that are considered key elements in the pathogenesis of systemic lupus erythematosus (SLE). However, a common miRNA signature has not emerged in SLE, since published data includes patients of variable ethnic background, type of disease and organ involvement. Moreover, published gene expression studies are often limited since they target only unfractionated, heterogeneous cell populations. Here, we aimed at identifying a miRNA-signature of purified B cells from renal and non renal severe (Bilag A) SLE patients of hispanic ethnic background, a population know to express severe disease.

Materials and methods Blood samples were obtained from healthy sex, age and ethnically matched controls (HC) with no history of autoimmune diseases and from SLE patients of chilean hispanic descent fulfilling SLICC and ACR criteria, with or without severe lupus nephritis (LN) (mean Bilag count respectively 17.8 and 16.8). Naive and memory B cells were sorted using CD27 surface marker. Total RNAs extraction, reverse transcription, and amplification steps were performed to fulfil quality and integrity criteria of the MIQE guidelines. The genome-wide miRNA expression study was perfomed using the TaqMan^® Human MicroRNA Array Cards v3.0 (Applied Biosystems). Data were normalised using ExpressionSuite software (Life technologies) and analysed using RT2 profiler PCR array data analysis version 3.5 (Qiagen).

Results TLDA analyses of naive and memory B cells from HC and 2 subsets of SLE patients revealed two categories of miRNA-based signatures. The first signature represents miRNAs with potential as diagnostic biomarkers : 11 miRNAs discriminating all SLE patients from HC, and 8 miARNs discriminating patient subsets (SLE versus SLE-LN). The second signature identifies 13 miRNAs with therapeutic potential in lupus. Clustering analyses of TLDA datasets evidenced that the main differences in miRNA expression profilings between SLE patients were between naive and memory B cells, independently of disease severity. In all cases, whether the miRNA was up or down-regulated in memory B cells as compared with naive B cells in HC, this difference was abolished in SLE patients. Among these, we found miR-223 that was previously reported as deregulated in SLE, as well as in other autoimmune disorders and B cell leukaemia. Array data were further validated on individual samples (n = 6).

Conclusions Overall, the present work identified two types of miRNA-based signatures in circulating B cells isolated from Chilean SLE patients, providing promising biomarkers in molecular diagnostics for disease severity as well as potential new targets for therapeutic intervention in SLE.

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