MicroRNA-mediated Attenuation of Inflammation in NZB/W Lupus Mice

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by the production and deposition of nuclear self-antigen-containing immune complexes. Epigenetic factors, including altered microRNA (miRNA) expression, may contribute to aberrant immune cell function in SLE. miRNAs are small, noncoding RNAs that bind to the 3’ untranslated region of target mRNAs resulting in post-transcriptional gene modulation. IL-6, an inflammatory cytokine overproduced by mesangial cells in SLE, contains a potential binding site for miR-let-7a. In order to examine if alterations in miR-let-7a expression can influence inflammatory mediator production in SLE, we isolated mesangial cell miRNAs from 8 and 32- week-old female New Zealand Black/White (NZB/W) mice. We found miR-let-7a expression was significantly increased in the mesangial cells of pre-diseased and actively diseased NZB/W mice compared to age-matched female New Zealand White (NZW) controls. Overexpression of miR-let-7a in vitro increased IL-6 production in LPS/IFN-γ-stimulated mesangial cells compared to the stimulated control. Due to the crucial role of miR-let-7a in cell division and inflammation, we investigated miR-let-7a-mediated proliferation and NFκB activation in J774A.1 macrophages and MES 13 mesangial cells in vitro. Cell proliferation, retinoblastoma protein (Rb) phosphorylation, and NFκB activation were increased in cells transfected with miR-let-7a and stimulated with LPS/IFN-γ. Expression and production of the cell cycle inhibitor E2F5 was decreased in stimulated cells overexpressing miR-let-7a. We found that the cell cycle promoter E2F2 and NFκB target the miR-let-7a promoter. Next we sought to determine alterations in iii specific disease-associated miRNAs in female NZB/W mice treated with hydroxychloroquine (HCQ) or prednisone (PRED) for 12 weeks beginning at 20 weeks-of-age. We found that treatment with HCQ or PRED induced unique changes to miRNA expression in multiple tissues. In order to identify specific miRNAs as disease-modifying agents and not merely disease correlates, further in vitro analyses confirmed HCQ or PRED-mediated inhibition of miRNAs is critical to alter the inflammatory response. Taken together, our results suggest that overexpression of miR-let-7a may contribute to hyperplasia and the proinflammatory response in SLE. Our studies indicate that lupus therapeutics may work, in part, by altering the expression of disease-associated miRNAs in immune cells and the urine.