Background/Purpose:

Systemic Lupus Erythematosus (SLE) is a chronic autoimmune disease that affects women at a 9:1 ratio compared to men. Previous work in our laboratory showed that estrogen receptor alpha (ERα) deficient lupus prone mice have increased survival and less renal disease compared to wild type lupus prone mice. ERα deficient mice are protected from disease despite unaltered autoantibody levels and kidney IgG and C3 deposition. We hypothesize that ERα deficiency improves SLE by reducing the innate immune system’s ability to respond to immune activation. To study the innate immune response this research focuses on the role of ERa in plasmacytoid dendritic cells (pDC) and their Toll-like receptor (TLR) mediated production of type I interferon (IFN). 

Methods:

Bone marrow was harvested from WT and ERα deficient B6 and NZM2410 lupus prone mice. The bone marrow was cultured with IL-4 and GM-CSF or Flt3 ligand under estrogen free conditions to enrich for conventional DCs or pDCs respectively. After 8 days of culture, cells were stimulated with TLR 7 and 9 agonists or PBS control for 24 hours. The cells were stained for flow cytometry or RNA was extracted. pDCs were defined as CD11c⁺, PDCA1⁺, or SiglecH⁺ and an intraceullar IFNα stain was used to identify IFNα producing cells. qRT-PCR was used to measure the expression of the interferon signature genes ISG-15, CXCL-10, IRF7, MX-1, and IFNβ . Ex vivo experiments were preformed on bone marrow and spleens. Bone marrow and spleen single cell suspensions were stained for flow cytometry. pDCs were identified as B220⁺, SiglecH⁺, PDCA1⁺, and CD11c^int.

Results:

ERα deficiency significantly reduces TLR 7 and 9 ligand mediated expression of type I IFN signature genes in bone marrow derived DCs from lupus prone mice. Since pDCs produce large amounts of type I IFN, we investigated the impact of ERα on pDC development and IFNα production. When total bone marrow from healthy mice was cultured with Flt3L under estrogen free conditions, ERα deficiency significantly reduced the number of IFNα producing cells in response to TLR 7 and 9 ligands. ERα deficiency also significantly reduced the percent of pDCs obtained from estrogen free Flt3L cultures of bone marrow. Wild-type bone marrow yielded 25% (±1.3%) pDCs and ERα deficient bone marrow yielded 8% (±.63%) pDCs. Using the same culture conditions, a similar trend was seen in NZM 2410 and SLE1,3 mouse models. To determine if ERα deficiency alters pDC numbers in vivo, bone marrow and spleen pDC numbers are being investigated ex vivo. Preliminary data suggests ERα deficiency reduces the percent of pDCs in bone marrow while the percent and number of spleen pDCs remain unchanged. 

Conclusion:  

ERα deficiency reduces the TLR mediated type I IFN response in bone marrow derived dendritic cells from lupus prone mice under estrogen free conditions. The absence of ERα also reduces the percentage of IFNα producing cells and pDCs yielded in estrogen free bone marrow cultures. These findings suggest that the in vivo disease modulating effect of ERα is mediated via impacts on the development and response of pDCs.

ACR Meeting Abstracts - https://acrabstracts.org/abstract/absence-of-estrogen-receptor-alpha-reduces-the-number-and-function-of-bone-marrow-derived-plasmacytoid-dendritic-cells-in-lupus-prone-mice/