Background/Purpose: SLE is a disease that disproportionately affects females. The etiology of the sex bias in this disease is unclear. We previously showed that a functional knockout of estrogen receptor alpha (ERαKO) resulted in significantly reduced renal disease and increased survival in murine lupus. Subsequently, we demonstrated a role for ERα in modulating Toll-like receptor (TLR)-induced inflammation, partially explaining the protected phenotype. The mechanism of this effect, however, is not known. Dendritic cell development, which requires both estrogen and ERα is impacted, as is activation status and cytokine production.  Due to altered feedback loops, the hormonal milieu of ERα mutant mice is significantly different from WT.  ERαKO mice have hypergonadism and partial endocrine sex reversal (elevated estrogen and testosterone levels), and decreased prolactin levels.  These hormones may have immunomodulating effects in concert with other intact hormone receptors.  Therefore, we investigated the phenotype of the NZM/ERαKO mouse following ovariectomy (OVX) and estrogen pellet (to preserve a physiologic hormonal state). 

Methods: ERαKO and Ex3a (ERα null) strains were backcrossed onto the NZM2410 lupus-prone background.  Subsets of mice were ovariectomized (at 4 or 8 weeks).   Urine and blood were collected at 2-4 week intervals starting at 10 weeks, and mice were sacrificed at 32 weeks, or earlier if they had high proteinuria and >10% weight loss.   Bone marrow was isolated and cultured for 7 days with Flt3L to enrich for dendritic cells. Spleen and kidney cells were also isolated.  Flow cytometry was utilized to determine number of cDCs (CD11c+/CD11b+) and activated cDCs (CD11c+/CD11b+/MHCII+) from cultured BM-DCs, as well as from ex vivo spleen and kidney cells.

Results:  Survival at 32 weeks: NZM/ERαKO – OVX + E2: 8/8 (100%) vs. NZM/ERαKO – OVX: 5/9 (56%) vs. NZM/WT – OVX 8/14 (57%) vs. NZM/Ex3a 7/7 (100%) vs. NZM/Ex3a – OVX 3/6 (50%) vs. NZM/Ex3a – OVX + E2 5/8 (63%).  Proteinuria (dipstick) correlated with survival as did total and activated cDCs (BM-DCs) which were significantly reduced in NZM/ERαKO – OVX + E2 vs. both NZM/WT – OVX (p<0.001) and NZM/ERαKO – OVX (p<0.05). To date, analyzed numbers of activated cDCs from both spleen and kidney of NZM/ERαKO mice were also significantly reduced.

Conclusion:   Consistent with previous experiments, NZM/ERαKO mice were protected from lupus disease expression (no early deaths; no proteinuria at 32 weeks). This was only true if they were either unmanipulated, or both ovariectomized and E2-repleted. These mice had fewer inflammatory and activated cDCs from bone marrow, spleen and kidney, which correlated with increased survival in this group. The protective phenotype was lost after ovariectomy if no E2 pellet was administered, suggesting that the effect requires E2 in the system (despite the lack of a full length ERα). A protective effect was not observed in lupus-prone Ex3a mice (ERα-/-) that were OVX’ed and E2-repleted, suggesting that the A/B domain mutant in ERαKO mice potentially modulates disease in the presence of estrogen, rather than ERα deficiency alone being protective.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/decreased-inflammatory-dendritic-cells-in-lupus-prone-estrogen-receptor-alpha-knockout-er%ce%b1ko-mice-correlate-with-increased-survival/