Estrogen-regulated STAT1 activation promotes TLR8 expression to facilitate signaling via microRNA-21 in systemic lupus erythematosus.

Young NA, Valiente GR, Hampton JM, Wu LC, Burd CJ, Willis WL, Bruss M, Steigelman H, Gotsatsenko M, Amici SA, Severin M, Claverie LM, Guerau-de-Arellano M, Lovett-Racke A, Ardoin S, Jarjour WN
Clin Immunol 176 12-22 01/01/2017

Abstract

Recent studies implicate innate immunity to systemic lupus erythematosus (SLE) pathogenesis. Toll-like receptor (TLR)8 is estrogen-regulated and binds viral ssRNA to stimulate innate immune responses, but recent work indicates that microRNA (miR)-21 within extracellular vesicles (EVs) can also trigger this receptor. Our objective was to examine TLR8 expression/activation to better understand sex-biased responses involving TLR8 in SLE. Our data identify an estrogen response element that promotes STAT1 expression and demonstrate STAT1-dependent transcriptional activation of TLR8 with estrogen stimulation. In lieu of viral ssRNA activation, we explored EV-encapsulated miR-21 as an endogenous ligand and observed induction of both TLR8 and cytokine expression in vitro. Moreover, extracellular miR detection was found predominantly within EVs. Thus, just as a cytokine or chemokine, EV-encapsulated miR-21 can act as an inflammatory signaling molecule, or miRokine, by virtue of being an endogenous ligand of TLR8. Collectively, our data elucidates a novel innate inflammatory pathway in SLE.

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