Glomerular Binding Antibodies in Systemic Lupus Erythematosus. In: Kammer GM, Tsokos GC, editors. Lupus. Totowa: Humana Press; 1999. pp. 448-70. [DOI: 10.1007/978-1-59259-703-1_28]

The mouse and human Fli1 genes are similarly regulated by Ets factors in T cells

Fli1 is a member of the Ets family of transcription factors and is preferentially expressed in hematopoietic cell lineages. Its expression level is linked to the pathogenesis of lupus. In this study, we identified mechanisms involved in the transcriptional regulation of the mouse and human Fli1 promoters. We show that the Fli1 promoter is upregulated by Ets factors Ets1, Ets2, Fli1 and Elf1 either alone or in combination with GATA factors, but is inhibited by Tel. In vitro binding studies show that Elf1, Tel and Fli1 in T cells bind the three Ets-binding sites in the murine Fli1 proximal promoter. We identified transcription factor-binding sites in the human Fli1 promoter region that function in T cells in a similar manner to those in the mouse promoter. Furthermore, we show similar binding of Ets factors to the endogenous mouse and human Fli1 promoters in T cells and knocking down Ets1 results in an upregulation of Fli1 expression. Together, these results suggest that the human and mouse genes are regulated similarly and that Ets1 may be important in preventing the overexpression of Fli1 in T cells. This report lays the groundwork for identifying targets for manipulating Fli1 expression as a possible therapeutic approach.

Genetic interactions between susceptibility loci reveal epistatic pathogenic networks in murine lupus

Interactions between Sle1 and other susceptibility loci were required for disease development in the NZM2410 model of lupus. Sle1 corresponds to at least three subloci, Sle1a, Sle1b, and Sle1c, each of which independently causes loss of tolerance to chromatin, but displays a distinctive immune profile. We have used congenic strains to analyze the interactions between the Sle1 subloci and other lupus susceptibility loci using Y autoimmunity accelerator (Yaa) and Faslpr as sensitizing mutations. Sle1 coexpressed with either one of these single susceptibility alleles resulted in a highly penetrant nephritis, splenomegaly, production of nephrophilic antibodies, and increased expression of B- and T-cell activation markers. Here, we show that only Sle1b interacted with Yaa to produce these phenotypes, suggesting that Sle1b and Yaa belong to the same functional pathway. Interactions between the three Sle1 loci and lpr resulted in lymphocyte activation and lupus nephritis, but a significant mortality was observed only for the Sle1a.lpr combination. This suggests a major role for the FAS pathway in keeping in check the loss of tolerance mediated by the Sle1 loci, especially for Sle1a. Our results illustrate the complexity of interactions between susceptibility loci in polygenic diseases such as lupus and may explain the clinical heterogeneity of the disease.

Lessons from the NZM2410 model and related strains

SLE susceptibility requires the interplay of an unknown number of genes and equally unidentified triggering events. The past few years have seen significant advances in our understanding of SLE susceptibility through the genetic analysis of murine models. The NZM2410 strain, which is derived from the NZB/WF1 model has played a significant role in these advances. The main advantages presented by this strain over other models are the genetic homozygozity at all loci and an highly penetrant early onset lupus nephritis in both males and females, indicating that the strongest BWF1 susceptibility loci were retained in NZM2410. After identification of NZM2410 susceptibility loci via linkage analyses, congenic strains have been derived in order to convert a polygenic system into a series of monogenic traits. These congenic strains have been analyzed in an integrated process which has provided simultaneously 1) novel functional characterization of the Sle susceptibility loci, 2) high resolution genetic maps that will lead to the identification of the corresponding susceptibility genes by either candidate locus or positional cloning, and 3) insights into the mechanisms by which these loci interact to produce systemic autoimmunity with fatal end-organ damage.

Genetic reconstitution of systemic lupus erythematosus immunopathology with polycongenic murine strains

We previously produced three congenic strains carrying lupus susceptibility genes (Sle1-Sle3) from the lupus-prone NZM2410 mouse on the C57BL/6 background and characterized their component phenotypes. Sle1 mediates the loss of tolerance to nuclear antigens; Sle2 lowers the activation threshold of B cells; and Sle3 mediates a dysregulation of CD4(+) T cells. We have now created a collection of bi- and tricongenic strains with these intervals and assessed the autoimmune phenotypes they elicit in various combinations. Our results indicate that Sle1 is key for the development of fatal lupus. The combination of Sle1 with Sle2, Sle3, or the BXSB-derived autoimmune accelerating gene yaa results in the development of systemic autoimmunity with variably penetrant severe glomerulonephritis culminating in kidney failure. In contrast, two locus combinations of Sle2, Sle3, and yaa failed to mediate fatal disease. These results indicate that the loss of tolerance to chromatin mediated by Sle1 is essential for disease pathogenesis and identify the pathway occupied by Sle1 as a strategic target for therapeutic intervention in systemic lupus erythematosus. The coexpression of Sle1, Sle2, and Sle3 as a B6-triple congenic results in severe systemic autoimmunity and fully penetrant, fatal glomerulonephritis. These results demonstrate the fulfillment of the genetic equivalent of Koch's postulate, where susceptibility loci in a lupus-prone strain have been identified by a genome scan, isolated and functionally characterized by congenic dissection, and finally shown to mediate full disease expression when recombined in a normal genome.