Mice with a DC-specific deletion of the transcriptional repressor B lymphocyte–induced maturation protein-1 (Blimp1) exhibit a lupus-like phenotype, secondary to enhanced DC production of IL-6. Here we explored further phenotypic changes in Blimp1-deficient DCs, the molecular mechanism underlying these changes, and their relevance to human disease. Blimp1-deficient DCs exhibited elevated expression of MHC II, and exposure to TLR agonists increased secretion of proinflammatory cytokines. This phenotype reflects enhanced expression of the microRNA let-7c, which is regulated by BLIMP1. Let-7c reciprocally inhibited Blimp1 and also blocked LPS-induced suppressor of cytokine signaling-1 (SOCS1) expression, contributing to the proinflammatory phenotype of Blimp1-deficient DCs. DCs from Blimp1 SLE-risk allele carriers exhibited analogous phenotypic changes, including decreased BLIMP1 expression, increased let-7c expression, and increased expression of proinflammatory cytokines. These results suggest that let-7c regulates DC phenotype and confirm the importance of BLIMP1 in maintaining tolerogenic DCs in both mice and humans.
Proinflammatory phenotype and increased let-7c in Blimp1-deficient DCs.
(A) Cytokines and chemokines were measured by protein array in supernatant from an overnight culture of splenic DCs purified from control or DCBlimp1ko mice in the presence or absence of LPS (1 μg/ml). Legend of individual proteins is provided in Supplemental Table 1. A pool of 2 mice was used for one blot. Representative pictures of 3 independent experiments. (B) Surface expression of MHC II was measured by flow cytometry and MFI was plotted. (Mean ± SEM of 4 independent experiments) (n = 8). (C) miRNA array was performed with RNAs from sorted splenic DCs from control and DCBlimp1ko mice. A representative plot from 2 independent arrays. Pool of 6 mice were used per group and per array. Expression of let-7c was measured by qPCR and relative expression level was calculated (right panel). Relative expression was calculated based on sno234 small RNA. Each dot represents an individual mouse, and the bar represents the mean. (D) BM-DCs were infected with lentivirus encoding either anti-Blimp1 or control siRNA with a GFP reporter gene. siRNA-transduced BM-DCs were sorted by expression of GFP, and total RNA was prepared. Expression of Blimp1 and let-7c was measured by qPCR, and relative expression was normalized to indicated housekeeping genes. Flow cytometry images for sorting are representative images from 3 independent experiments (upper panel). Graph depicts the mean ± SEM of 3 independent experiments (n = 6).