We have identified a susceptibility locus for lupus-associated chronic glomerulonephritis using congenic mouse strains that replace segments of distal chromosome (Chr) 4 in the lupus-prone NZM2328 (NZM) strain with those from the nonobese diabetic (NOD) mouse. We designate the locus Cgnz2 (chronic glomerulonephritis NZM-2). In this application, we propose 1) to refine the localization of gene(s) on distal Chr 4 for which NOD alleles are protective and 2) to further characterize a prominent regional candidate gene, Runx3. Our preliminary data show that NZM congenic mice carrying NOD alleles across a 23 cM interval on Chr 4 are resistant to the development of lupus-like nephritis despite substantial deposition of both auto-antibodies and complement in glomeruli. Protection from renal disease is associated with a complex immunological phenotype previously seen only in mice homozygous for inactivating mutations in Runx3, a gene that maps to the congenic interval. Runx3 is a master transcriptional integrator of transforming growth factor 2 (TGF2) signaling and multiple other cell type-specific signaling pathways in hematopoietic lineages. In addition to regulating survival and expansion of CD8+ T cells after activation, it plays a critical role in the development and activity of both macrophages and dendritic cells. We propose 1) to determine whether any additional loci within the congenic interval encoding Runx3 contribute to the development of renal disease in this model, and 2) to test directly whether Runx3 expression from the NZM allele is specifically associated with susceptibility to chronic nephritis in lupus-prone NZM mice. For these studies, we will engineer selective replacement of the interval encoding wild-type NZM Runx3 expression in vivo using both introgression and transgenic approaches (Aim 1). Using these new mouse lines, we will identify the cell types required for determining susceptibility to renal disease through cell transfers (Aim 2). Finally, in Aim 3, we will identify the specific signaling pathways that are altered in the presence of NZM-derived Chr 4 segments, as well as the NZM Runx3 allele alone, in the cell type(s) identified in Aim 2. For these experiments, we will perform a focused analysis of signaling pathways and cytokine production in normal cell populations from the mouse strains developed for this project. Together, we expect these experiments to confirm the importance of Runx3 activity on disease development and to identify and characterize any additional regional susceptibility loci that contribute to protection from nephritis on the congenic strains.
The pathogenesis of chronic renal disease in systemic lupus erythematosus is still poorly understood. This project will identify specific genes that play a role in the progression of kidney damage once inflammation has been initiated by deposition of pro-inflammatory antigen-antibody complexes in the renal glomerulus. We expect that these studies will lead to improved understanding of the process and possibly will lead to novel therapeutic strategies for prevention of this devastating complication.
