Determination of structural features critical for nephritogenic properties of IgA1-containing immune complexes in IgA nephropathy - Immunoglobulin A nephropathy (IgAN) is a common primary glomerulonephritis with serious morbidity and mortality. Diagnosis of IgAN reduces the life expectancy by approximately a decade, and most IgAN patients develop kidney failure within 10-15 years from the diagnosis. With no cure for this chronic kidney disease, the patients require renal replacement therapy, i.e., dialysis or transplantation. Unfortunately, IgAN can recur after kidney transplantation, and can lead to graft failure. We have developed a pathogenesis model for IgAN based on the findings that most IgAN patients have immunologic defects that result in the generation of pathogenic immune complexes that deposit in the kidneys. These pathogenic immune complexes contain IgA1 with some O-glycans deficient in galactose (Gd-IgA1). Gd-IgA1 alone is not sufficient to induce IgAN. Elevated levels of Gd-IgA1 (an autoantigen) can induce Gd-IgA1-specific IgG autoantibodies. In the circulation of IgAN patients, Gd-IgA1 is bound by IgG autoantibodies, with additional proteins, such as complement C3, subsequently attached, resulting in the production of nephritogenic immune complexes. Our clinical studies with human kidney- biopsy specimens and data from experimental in vitro and in vivo models of IgAN support the nephritogenic role of C3-IgA-IgG immune complexes in the pathogenesis of IgAN. However, our understanding of the mechanisms involved in the formation of the nephritogenic immune complexes is limited. In this proposal, we have assembled a multidisciplinary team with combined expertise in biochemical, molecular, structural, and clinical studies to test a hypothesis that specific glycoforms of Gd-IgA1 are recognized by IgG autoantibodies to form nephritogenic immune complexes with C3 covalently attached to IgA and/or IgG. We will determine the pathogenic glycoforms of Gd-IgA1 that enable formation of pathogenic immune complexes (Aim 1, Gd-IgA1), define structural and functional requirements of IgG autoantibodies to effectively bind Gd-IgA1 to form immune complexes (Aim 2, IgG), and determine the structure and points of attachment of C3 to Gd-IgA1-containing nephritogenic immune complexes (Aim 3, C3). For the latter, we will assess whether Gd-IgA1 and/or IgG mimics can block formation of C3-Gd-IgA1-IgG immune complexes. In this new multi-PI grant application, we leverage our access to biospecimens from IgAN patients with opposite clinical phenotypes, glycoengineered systems to produce Gd- IgA1 with tailored glycan composition, new affinity purification system to isolate specific C3-Gd-IgA1-IgG complexes, and high-resolution structural biology techniques, to decipher how tripartite complexes of C3-Gd- IgA1-IgG are formed. Completion of the project will be a paradigm shift to the field of IgAN, as it would define principles that will aide in preventing formation of nephritogenic immune complexes and provide information for design of a disease-specific treatments that could lead to a cure for this chronic kidney disease.
