Session Type: Abstract Submissions (ACR)
Background/Purpose: The Ets factor Fli1 is implicated as a key modulator of lupus disease expression. Over-expressing Fli1 in healthy mice, results in the development of an autoimmune kidney disease similar to that observed in lupus. Lowering the global levels of Fli1 in two lupus mouse models significantly improved kidney disease and prolonged survival. Lowering the levels of Fli1 in hematopoietic cells in MRL/lpr lupus mice resulted in significantly improved kidney disease. We recently demonstrated that lowering the global levels of Fli1 in the MRL/lpr lupus model has specific effects on T cells, including reducing their activation and IL-4 production when stimulated through the T cell receptor. We further showed that this was likely a result of decreased glycosphingolipid (GSL) metabolism, specifically decreased Neuraminidase1 (Neu1) expression and activity and decreased lactosylceramide (LacCer) in T cells. GSLs are a heterogeneous class of lipids in the sphingolipid family that play a role in the regulation of cellular processes. LacCer is a GSL to which sialic acid residues are added by ganglioside synthases to generate gangliosides in the GSL synthesis pathway. Sialic acids are then removed by NEUs from gangliosides in the GSL catabolic pathway. Lipids with distinct chain lengths are thought to possess distinct biological activities. We now demonstrate that lowering Fli1 levels significantly decreases the number of CXCR3+ T cells, T cell migration to the kidney and GSL metabolism in the kidney of MRL/lpr lupus prone mice.
Methods: Kidney and/or spleen were harvested from 11, 14 and 18 week-old MRL/lpr Fli1+/+ and Fli1+/- mice. Kidneys and/or T cells isolated from spleen by negative selection were analyzed by flow cytometry. Supercritical Fluid Chromatography coupled with tandem mass spectrometry was performed on kidney cortex homogenates. Gene expression was analyzed by real-time RTPCR on RNA isolated from kidney cortex. Matrix-assisted laser desorption/ionization-imaging mass spectrometry (MALDI-IMS) imaging and immunohistochemistry (IHC) for LacCer was performed on frozen kidney sections.
Results: LacCer levels, which are elevated in the kidneys of MRL/lpr mice compared to controls, are significantly reduced by 50% in age-matched MRL/lpr mice that are heterozygote for Fli1 (Fli1+/-). This reduction in LacCer expression is observed across the kidney using MALDI-IMS. Although Neu1 expression and NEU activity is decreased in T cells, their levels are unchanged in the kidney of Fli1+/- compared to Fli1+/+ MRL/lpr mice. The percentage of T cells expressing CXCR3 is significantly reduced by ~30% in Fli1+/- compared to Fli1+/+ MRL/lpr mice and the percentage and overall number of T cells in the kidney are significantly reduced by ~50%.
Conclusion: Our results demonstrate that one mechanism by which reducing Fli1 levels may be protective in lupus kidney disease is to decrease GSL metabolism in T cells, reducing T cell activation, production of IL-4, expression of CXCR3, a receptor shown to be important in T cell migration to the kidney in lupus, and migration to the kidney. This likely contributes to the decreased inflammation and GSL metabolism in the kidney and improved kidney disease of MRL/lpr Fli1+/- mice.
T. K. Nowling,
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ACR Meeting Abstracts - https://acrabstracts.org/abstract/the-role-of-fli1-in-lupus-t-cell-function-and-nephritis/