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Molecular characterization of IgA1-receptor interactions implicated in IgA nephropathy

Gomes, Michelle Marie

Abstract Details

2009, PhD, University of Cincinnati, Medicine : Molecular Genetics, Biochemistry, and Microbiology.

IgA nephropathy (IgAN) is the most common form of glomerulonephritis, an inflammatory disease of the kidney and a leading cause of end-stage renal disease. It is characterized by deposits of IgA1-containing immune complexes in the glomerular mesangium, which result in the infiltration of inflammatory immune cells, mesangial cell proliferation and mesangial matrix expansion. The fundamental cause of these complexes is underglycosylation of the IgA1 antibody. The two IgA receptors involved in the pathogenesis of IgAN are FcαRI and the transferrin receptor (TfR). FcαRI has been implicated in the initial phase of the disease—generation of circulating soluble IgA1-immune complexes—whereas TfR is involved in the latter phase, the trapping of IgA1-immune complexes in the glomerular mesangium. The studies described herein were focused on determining the effects of IgA1 glycosylation on the IgA1-FcαRI and IgA1-TfR interactions. In addition, we have used lectins specific for the aberrantly glycosylated IgA1 hinge to lay the groundwork for developing a non-invasive method for the diagnosis of the disease from blood samples of IgAN patients. Such an approach would be useful, given that IgAN is currently diagnosed by kidney biopsy.

We carried out detailed biophysical studies on three IgA1 samples purified from human serum and recombinant IgA1-Fc and compared their binding to FcαRI. Our studies showed overlapping but distinct populations of N-glycan species between IgA1 samples; however, these IgA1 samples bound FcαRI with similar affinities. Complete removal of the N-glycan of IgA1 did not affect its binding to the receptor, suggesting that N-glycosylation of IgA1 was not important for the IgA1-FcαRI interaction. We further characterized this interaction using different N-glycosylation mutants of the receptor and found that receptor glycosylation has a minor effect. Taken together, these studies suggest that the N-glycans of both IgA1 and the receptor are unlikely to be involved in the pathogenesis of the disease. Interestingly, we observed that the IgA1 tailpiece was capable of modulating the stability of IgA1-FcαRI complexes, depending on whether it was free, as in monomeric IgA1, or tethered to the J-chain, as in dimeric IgA1. Dimeric IgA1-receptor complexes were more stable, and therefore, may be responsible for prolonged stimulation of inflammatory responses through FcαRI. Our studies on the IgA1-TfR interaction showed that IgA1 with underglycosylated O-glycans has a higher affinity for TfR, and the complexes formed are very stable. This is important, since IgAN patient IgA1 has underglycosylated O-glycans, and suggests that TfR may play an important role in the deposition of these complexes in the glomerular mesangium. Given that the aberrantly glycosylated IgA1 hinge is a marker for the disease, we developed a biosensor-based assay using two lectins, Helix aspersa agglutinin (HAA), and Helix pomatia agglutinin (HPA), that are specific for the IgAN glycan epitope (i.e., the GalNAc group). Our assay selectively recognized IgA1 secreted from immortalized B cell lines derived from circulation of IgAN patients with a higher affinity than IgA1 secreted from immortalized B cell lines derived from healthy controls. Thus, the lectin-based biosensor assay described could be developed for future diagnosis of IgAN.

Andrew Herr, PhD (Committee Chair)
Rhett Kovall, PhD (Committee Member)
Anil Menon, PhD (Committee Member)
Anil Dean, PhD (Committee Member)
Fred Finkelman, MD (Committee Member)
245 p.

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Citations

  • Gomes, M. M. (2009). Molecular characterization of IgA1-receptor interactions implicated in IgA nephropathy [Doctoral dissertation, University of Cincinnati]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1242938515

    APA Style (7th edition)

  • Gomes, Michelle. Molecular characterization of IgA1-receptor interactions implicated in IgA nephropathy. 2009. University of Cincinnati, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ucin1242938515.

    MLA Style (8th edition)

  • Gomes, Michelle. "Molecular characterization of IgA1-receptor interactions implicated in IgA nephropathy." Doctoral dissertation, University of Cincinnati, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1242938515

    Chicago Manual of Style (17th edition)