Downregulated miR‑29a promotes B cell overactivation by upregulating Crk‑like protein in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is an autoimmune disorder; however, the pathogenesis is not fully understood. Accumulating evidence suggested an important role of microRNAs (miRNA/miR) in autoimmunity. The present study aimed therefore to determine the miRNA expression patterns in the B cells from the peripheral blood of 66 patients with SLE and 10 healthy controls (HCs) by using an Affymetrix GeneChip® miRNA 2.0 array. In addition, next‑generation sequencing was used to obtain the peripheral blood mononuclear cell (PBMC) miRNA profiles from three patients with SLE and three HCs. Candidate miRNAs that were considered to contribute to the pathogenesis of SLE were obtained based on the intersection of miRNA profiles. The analysis revealed a significant downregulation in miR‑29a expression levels in B cells from patients with SLE, which was subsequently verified using reverse transcription‑quantitative PCR. Based on these results, the expression pattern of miR‑29a in SLE was further investigated and its role in the hyperactivity of B cells was determined. miR‑29a inhibitors and mimics were transfected into PBMCs obtained from HCs and patients with SLE, and an ELISA was used to demonstrate that miR‑29a inhibition increased the production of IgG. Bioinformatics analysis predicted Crk‑like protein (CRKL) as a target gene of miR‑29a in patients with SLE. Therefore, CRKL expression levels were compared between patients with SLE and HCs by using western blotting, and its direct transcriptional regulation by miR‑29a was determined using a dual‑luciferase reporter assay. Low expression levels of miR‑29a were revealed to upregulate the expression levels of CRKL in B cells, and the protein expression levels of CRKL in patients with SLE were significantly upregulated compared with the HCs. In conclusion, the results from the present study suggested that miR‑29a may affect IgG antibody secretion in B cells by regulating CRKL, thereby contributing to the development and progression of SLE, which offers a novel candidate target for treatment.