Background/Purpose:  Lupus nephritis is a major cause of death in both animal models and human patients.  Expression of Fli-1, a member of the Ets family of transcription factors, is implicated in the development of nephritis in murine models of SLE as well as human lupus nephritis.  The increased expression of Fli-1 is significantly associated with new or recurrent lupus nephritis in SLE patients with lupus nephritis compared with SLE without lupus nephritis.  Reducing the levels of Fli-1 in two lupus mouse strains significantly decreased renal disease with a profound decrease in infiltrating inflammatory cells and prolonged survival. IFN-gamma Inducible Protein (IP-10), also known as C-X-C motif chemokine 10 (CXCL10), is an inflammatory chemokine belonging to the CXC chemokine family.  Overexpression of CXCL10 is associated with clinical lupus nephritis.  CXCL10 is chemotactic for inflammatory cells including macrophages, monocytes and activated T and NK cells that express the CXCR3, a receptor for CXCL10.   Previous reports demonstrated that CXCR3+ cells are recruited into the inflamed kidneys in murine models of lupus and human patients.   In this study, we examined if Fli-1 impacts lupus nephritis by orchestrating CXCL10/CXCR3 Axis.

Methods: The expression of CXCL10 was measured in kidneys from Fli-1 knockout heterozygous MRL/lpr mice, a murine model of lupus (Fli1+/-; Fli-1 homozygous knockout is embryonic lethal), and wild-type (Fli1+/+) MRL/lpr mice.  A murine endothelial cell line, human renal glomerular endothelial cells (HRGEC), and human T cells were used in this study.  CXCL10 was measured using commercially available ELISA kits.  The specific Fli-1 siRNA was used to knock down the expression of Fli-1 in cells.

Results: CXCL10 protein concentration was significantly higher from kidney homogenates from wild-type MRL/lpr mice compared to the kidney homogenates from Fli-1+/- MRL/lpr mice at the age of 25 weeks (WT, 2,264±376 pg/mg vs Fli-1+/-,1322±129 pg/mg, N=11, p< 0.05).  CXCL-10 concentrations from mouse endothelial cells transfected with Fli-1 siRNA were significant lower compared to the cells transfected with control siRNA following stimulation with LPS (645.7± 167.1 pg/ml versus 336.2± 93.26 pg/ml at 6 hours, P< 0.001; and 1493.75± 392.35 pg/ml versus 540.01± 187.37 pg/ml at 24 hours, p< 0.001).  The CXCL10 concentrations in supernatant from HRGEC  transfected with Fli-1 siRNA and stimulated with LPS or TNF-α were significantly lower 6 and 24 hours post LPS or TNF-α stimulation compared to those transfected with control siRNA.  Fourteen putative Ets binding sites are identified within a 2900 bp region of the CXCL-10 promoter, and four sites in the promoter showed significant enrichment for Fli-1 specific antibodies compared to normal IgG controls by the chromatin immunoprecipitation (ChIP) assay.  We have demonstrated that mutation of the Fli-1 DNA binding domain led to a statistically significant reduction in activation from the CXCR3 promoter when compared to wild-type Fli-1 protein, and acetylation and phosphorylation of Fli-1 play a role in CXCR3 activity in T cell.

Conclusion: Together, the results implicate that one key factor in Fli-1’s impact on lupus nephritis is by modulating the CXCL10/CXCR3 Axis.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/transcription-factor-fli-1-impacts-lupus-nephritis-by-orchestrating-cxcl10-cxcr3-axis/