Background/Purpose:

Systemic Lupus Erythematosus (SLE) is a devastating multi-organ autoimmune disease displaying an overwhelming female predilection. Estrogen (E2) influences gene expression by binding to estrogen receptors (ERα and ERβ) and a role for E2 has been proposed in SLE pathogenesis. Further, E2 has been shown to regulate Signal Transducer and Activator of Transcription (STAT) 1 and STAT4 function. Toll-Like Receptor 8 (TLR8) has also been implicated in SLE and is a potent inflammatory mediator.  The results of this study demonstrate the E2-mediated induction of STAT1 and STAT4 for the first time in primary human peripheral blood mononuclear cells (PBMCs) and mechanistically characterize the pathway that is operative in this induction.

Methods:

PBMCs isolated from SLE patients and healthy controls were treated with a physiological dose of E2.  Putative estrogen response elements (EREs) in the human genome were identified from ChIP-seq data of MCF-7 cells stimulated with E2 for one hour.  Radio-labeled probes corresponding to STAT1 DNA binding regions were used in EMSA analysis to examine DNA-protein complex formation in a human monocytic cell line (THP-1).  In the presence of E2, siRNA was used to block ERα or STAT1 expression in THP-1 cells lacking detectable IFNα expression.

Results:

Expression of STAT1 and STAT4 was elevated in PBMCs of SLE patients relative to age and sex-matched healthy controls. Moreover, E2 stimulation of freshly isolated human PBMCs significantly induced STAT1 and STAT4 expression.  Given that we have previously observed that TLR8 expression is higher in SLE and induced with E2 treatment, a bona fide STAT1 binding region located 24 kb from the 3’ end of the TRL8 gene was used in EMSA analysis to show that enhanced DNA-protein complex formation was induced by E2 stimulation.  Interestingly, STAT1 is located next to STAT4 and ChIP-seq data of cells stimulated with E2 revealed an intragenic ERE binding peak within the STAT1 locus, which suggests that E2 may be promoting the expression of both genes through this response element.  Using siRNA to explore E2 induction of STAT1 mechanistically, we demonstrate that this response is mediated through ERα.  Furthermore, siRNA blocking STAT1 significantly reduced TLR8 induction with E2 stimulation.

Conclusion:

E2 can stimulate the expression of STAT1 and STAT4 in PBMCs and potentially contribute to the pathogenesis observed in SLE due to their potent signal transducing effects over the immune system. STAT1 promotes TLR8 expression after E2 stimulation and an ERE near both STAT1 and STAT4 has been identified through ChIP analysis.  The identification of molecular targets to inhibit the TLR8 inflammatory pathway presents a significant therapeutic opportunity.  Collectively, our results indicate that STAT1 and STAT4 may contribute to the E2-mediated sex-bias observed in autoimmunity through ERα signaling and may potentially be ideal targets in future therapy to treat SLE.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/estrogen-induced-stat1-and-stat4-expression-is-estrogen-receptor-%ce%b1-dependent-and-ifn%ce%b1-independent-a-novel-mechanism-for-sex-bias-in-systemic-lupus-erythematosus-pathogenesis/