Background/Purpose: SLE is primarily mediated by B cell dysregulation on a background of type I interferon (IFN) activation. This multi-faceted nature of immune defects in SLE has made it challenging to develop targeted therapies that are broadly effective. As a result, most patients rely on the broad effects of glucocorticoids, use of which contributes to adverse effects and irreversible organ damage. 

The intracellular protein glucocorticoid-induced leucine zipper (GILZ) mediates the anti-inflammatory effects of glucocorticoids but not the associated adverse effects. Increasing GILZ is a promising strategy to achieve the broad anti-inflammatory effects of glucocorticoids but without the adverse effects. Here, we investigated the potential of a pathway which modifies GILZ abundance to lead to a novel therapeutic approach in SLE.

Methods: We previously identified an E3 ubiquitin ligase of GILZ, “E3-X” (1). We characterised the effect of E3-X on the response to IFN or toll-like receptor (TLR) -4/7 activation in murine plasmacytoid dendritic cells (DCs), bone marrow-derived DCs, human A549 epithelial cells, and in a model of TLR7-stimulated peritoneal inflammation. In parallel, we studied the effect of E3-X on B cell activation and differentiation by flow cytometry, bulk RNA sequencing, proteomics and phosphoproteomics. Lastly, we examined the effect of E3-X deficiency in the Lyn^-/- model of SLE and mined publicly available gene expression datasets to characterise the clinical associations of E3-X in SLE.

Results: E3-X deficiency restored GILZ expression in human cell lines and mouse primary cells, and was associated with a 5-10 fold increase in the glucocorticoid sensitivity of IL-6, TNF, MCP-1 and IFN-signature expression. In plasmacytoid and bone marrow-derived DCs, E3-X deficiency resulted in diminished IFN signature expression, and reduced TNF and IL-6 production. Proteomic analysis revealed that E3-X deficiency significantly reduced IFN-stimulated protein expression. In vivo, E3-X deficiency was protective against TLR7-induced peritoneal inflammation, with marked suppression of IFN-signature gene expression, IL-6, IL-12, IL-23, IL-22 and MCP-1. B cells lacking E3-X demonstrated reduced capacity to proliferate and differentiate into plasma cells. Multi-omic analysis of murine E3-X^-/- B cells revealed reduced activation of multiple pathways, including AP-1, NFκB, MAPK-ERK and PI3K-Akt. In the Lyn^-/- model of SLE, E3-X^+/-/Lyn^-/-  mice exhibited ameliorated splenomegaly, autoantibody production and IFN- signature gene expression. In human SLE patients, E3-X was overexpressed compared to healthy controls, especially in IFN-high patients, and was positively correlated with SLEDAI-2K.

Conclusion: Disruption of a novel E3 ligase, E3-X, increased GILZ abundance and suppressed innate and adaptive immune mechanisms that are pathogenic in SLE, resulting in anti-inflammatory and glucocorticoid sparing effects. These findings support the development of therapies inhibiting E3-X for the treatment of SLE.

1. Miceli I, Sherlock R, Cheang I, D’Cruz A, Bennett T, et al. Creation of a glucocorticoid mimic: Targeting GILZ to bypass the metabolic adverse effects of glucocorticoids. Intern Med J. 2023;53(S1):5-57.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/a-novel-e3-ligase-of-gilz-validation-of-a-steroid-sparing-therapeutic-target-in-sle/