This study examined the relationship between the expression of Ras guanyl nucleotide-releasing protein 3 (RasGRP3) and disease activity in systemic lupus erythematosus (SLE) and explored the possible mechanisms in MRL/lpr mice. We detected the expression of RasGRP3 in peripheral blood mononuclear cells (PBMCs) of SLE patients (n=26) and healthy controls (n=20) by employing RT-PCR and studied the association between the mRNA expression of RasGRP3 in PBMCs and the clinical findings. We also measured the protein level of RasGRP3 in PBMCs by Western blotting (n=10). In addition, we isolated the B cells from PBMCs with magnetic bead separation and determined the RasGRP3 expression by RT-PCR (n=10). Furthermore, we extracted spleen B cells from MRL/lpr mice and knocked down RasGRP3 by siRNA transfection to study the role of RasGRP3 in the pathway of B cell receptor (BCR) activation and the production of pro-inflammatory cytokines. Compared with healthy volunteers, the expression of RasGRP3 was significantly elevated in PBMCs and purified B cells from SLE patients. The mRNA expression of RasGRP3 in PBMCs was positively correlated with SLE disease activity index (SLEDAI). Moreover, silencing RasGRP3 could inhibit Akt and Erk1/2 activation in marginal zone (MZ) and follicular (FO) B cells of MRL/lpr mice. Additionally, the production of pro-inflammatory cytokines, such as interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α), was decreased whereas activation of caspase-3 cleavage was induced in vitro. In conclusion, over-expression of RasGRP3 is associated with disease activity and might be involved in the pathogenesis of SLE.
Keywords: B cell; MRL/lpr mice; RasGRP3; SLE disease activity index; Systemic lupus erythematosus.