Background/Purpose:

Originally considered primarily a B cell disorder, lupus pathogenicity has recently been linked to enhanced functions of neutrophils. The genetic analysis of the lupus prone NZM2410 mouse has identified a suppressor locus, Sle2c2, which confers resistance to spontaneous lupus in combination with NZM2410 susceptibility loci or in the chronic graft-vs.-host disease (cGVHD) induced model of SLE.  We have shown that Sle2c2 resistance is mediated by bone-marrow derived non-lymphoid cells. We hypothesize that a non-synonymous polymorphism in the granulocyte colony stimulating factor (G-CSF) receptor 3 (Csf3r) gene existing within Sle2c2 is responsible for providing protection. G-CSF is required for neutrophil granulopoiesis, mobilization and activation. We hypothesize that the defective G-CSF receptor is associated with lupus resistance by controlling the homeostasis of pro-inflammatory neutrophils. 

Methods:

We have investigated the role of G-CSF pathway in both cGVHD induced lupus in B6.Sle2c2 mice and spontaneous lupus in B6.Sle1.Sle2.Sle3 triple congenic (TC) strain (also carrying the Sle2c2 locus) as compared to B6 mice. The ability of G-CSFR to bind mouse biotinylated G-CSF was compared between B6.Sle2c2 and B6 splenocytes and analyzed by flow cytometry. Treatments with varying doses of rh-GCSF (Neulesta) were tested in reversing or enhancing the course of disease in cGVHD induced SLE (B6.Sle2c2), and spontaneous lupus (TC). The effects of Neulesta on immune cell activation markers were assessed by flow cytometry and by ELISA’s for antibodies against dsDNA and chromatin.  Gene expression analyses by real time PCR for neutrophil and G-CSF specific genes were also employed as an alternative mechanism for studying the downstream effects of GCSF-GCSFR pathway.

Results:

Neulesta treatments reversed cGVHD resistance in B6.Sle2c2 mice and increased anti-dsDNA IgG production in TC mice.  Dose-dependent effects were however observed with high doses of Neulasta having a protective effect in B6.TC mice. In vitro and in vivo experiments have shown a reduced binding of G-CSF on myeloid cells and a decreased mobilization of neutrophils in response to Neulesta treatment in B6.Sle2c2 mice compared to B6. Gene expression analyses have revealed a differential expression of G-CSFR-target genes between B6.Sle2c2 and B6 bone marrow cells and splenocytes in response to Neulesta. This included a lower expression of BAFF in B6.Sle2c2 splenocytes than in B6, suggesting that BAFF production by neutrophils may represent a mechanism by which G-CSF regulates systemic autoimmunity.

Conclusion:

Our results support the hypothesis that a G-CSF receptor with a defective binding for its ligand confers resistance to lupus. Future experiments aimed at elucidating the role of neutrophils as downstream effectors of the GCSF-GCSFR pathway will help in dissecting their pathogenic contribution to lupus. We predict that understanding the contribution of GCSFR axis towards SLE pathogenesis in mouse models of lupus will help us in identifying and designing potential and novel therapeutic targets for the disease.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/characterizing-the-role-of-the-granulocyte-colony-stimulating-factor-pathway-in-a-mouse-model-of-systemic-lupus-erythematosus/