Project Summary Lupus nephritis is the kidney manifestation of the autoimmune disease systemic lupus erythematosus (SLE, lupus); 10% of those afflicted progress to end stage kidney disease. Lupus nephritis kidneys are characterized by a profound lymphocytic infiltrate and the degree of infiltrate, including B lymphocytes specifically, correlates with tissue damage and disease severity. Kidneys are also characterized by axial concentration gradients of sodium (Na+), up to 2-fold higher than serum. Thus the inimical kidney environment presents unique survival challenges for infiltrating lymphocytes that may shape their phenotype and function. The function of intrarenal B cells and the pathways they employ to adapt to the hostile kidney environment remain uncharacterized. My preliminary data demonstrate that B cells from lupus-prone mice exhibit enhanced survival when exposed to high Na+ ex vivo as compared to wildtype mice. This effect was mediated by high expression of sodium potassium ATPase (Na+-K+-ATPase, NKA), a key regulator of cellular ionic balance. I have also shown that kidney-infiltrating B cells in murine lupus adapted to elevated [Na+] and that the expression of in vivo NKA correlated with the ability of infiltrating B cells to persist in the kidney. Pharmacological inhibition of NKA and genetic knockout of the NKA g subunit, the latter not previously known to be expressed in B cells, resulted in reduced kidney B cell infiltration and amelioration of proteinuria. B cells in renal biopsies of SLE patients also expressed more NKA than intrarenal T cells, suggesting the same NKA-regulated B cell survival pathway is operative in human SLE nephritis. How Na+ affects cell death pathways and whether it regulates B cell function, such as antibody or cytokine production, is unknown. I hypothesize that Na+ modulates intrarenal B cell death pathways and function, dissection of which will augment understanding of lupus nephritis pathogenesis. In Aim 1, I will investigate death pathways that lupus versus healthy control B cells undergo when exposed to high Na+ ex vivo. In Aim 2, I will assess B cell function upon alteration of kidney Na+ environment in mice while in Aim 3 I will utilize in situ imaging to define the functional landscape of these pathogenic cells in human SLE nephritis biopsies. Together these studies will help identify kidney-specific targets for the treatment of SLE nephritis. The candidate for this award is a physician-scientist with dual expertise in nephrology and immunology. Her long-term goals are to be an independent academic researcher with a focus on autoimmune kidney disease and lymphocyte-ion interactions. This award would allow the candidate to receive exceptional mentorship from the departments of Immunobiology and Nephrology at Yale University School of Medicine, a premier research institution. A comprehensive career development plan with coursework in bioinformatics and statistics, acquisition of RNA hybridization an...