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BACKGROUND In Goodpasture’s disease, circulating autoantibodies bind to the noncollagenous-1 (NC1) domain of type IV collagen in the glomerular basement membrane (GBM). The specificity and molecular architecture of epitopes of tissue-bound autoantibodies are unknown. Alport’s post-transplantation nephritis, which is mediated by alloantibodies against the GBM, occurs after kidney transplantation in some patients with Alport’s syndrome. We compared the conformations of the antibody epitopes in Goodpasture’s disease and Alport’s post-transplantation nephritis with the intention of finding clues to the pathogenesis of anti-GBM glomerulonephritis. METHODS We used an enzyme-linked immunosorbent assay to determine the specificity of circulating autoantibodies and kidney-bound antibodies to NC1 domains. Circulating antibodies were analyzed in 57 patients with Goodpasture’s disease, and kidney-bound antibodies were analyzed in 14 patients with Goodpasture’s disease and 2 patients with Alport’s post-transplantation nephritis. The molecular architecture of key epitope regions was deduced with the use of chimeric molecules and a three-dimensional model of the α345NC1 hexamer. RESULTS In patients with Goodpasture’s disease, both autoantibodies to the α3NC1 monomer and antibodies to the α5NC1 monomer (and fewer to the α4NC1 monomer) were bound in the kidneys and lungs, indicating roles for the α3NC1 and α5NC1 monomers as autoantigens. High antibody titers at diagnosis of anti-GBM disease were associated with ultimate loss of renal function. The antibodies bound to distinct epitopes encompassing region EA in the α5NC1 monomer and regions EA and EB in the α3NC1 monomer, but they did not bind to the native cross-linked α345NC1 hexamer. In contrast, in patients with Alport’s post-transplantation nephritis, alloantibodies bound to the EA region of the α5NC1 subunit in the intact hexamer, and binding decreased on dissociation. CONCLUSIONS The development of Goodpasture’s disease may be considered an autoimmune “conformeropathy” that involves perturbation of the quaternary structure of the α345NC1 hexamer, inducing a pathogenic conformational change in the α3NC1 and α5NC1 subunits, which in turn elicits an autoimmune response. (Funded by the National Institute of Diabetes and Digestive and Kidney Diseases.)

Target-derived factors organize synaptogenesis by promoting differentiation of nerve terminals at synaptic sites. Several candidate organizing molecules have been identified based on their bioactivities in vitro, but little is known about their roles in vivo. Here, we show that three sets of organizers act sequentially to pattern motor nerve terminals: FGFs, beta2 laminins, and collagen alpha(IV) chains. FGFs of the 7/10/22 subfamily and broadly distributed collagen IV chains (alpha1/2) promote clustering of synaptic vesicles as nerve terminals form. beta2 laminins concentrated at synaptic sites are dispensable for embryonic development of nerve terminals but are required for their postnatal maturation. Synapse-specific collagen IV chains (alpha3-6) accumulate only after synapses are mature and are required for synaptic maintenance. Thus, multiple target-derived signals permit discrete control of the formation, maturation, and maintenance of presynaptic specializations.

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Laminin and type IV collagen composition of the glomerular basement membrane changes during glomerular development and maturation. Although it is known that both glomerular endothelial cells and podocytes produce different laminin isoforms at the appropriate stages of development, the cellular origins for the different type IV collagen heterotrimers that appear during development are unknown. Here, immunoelectron microscopy demonstrated that endothelial cells, mesangial cells, and podocytes of immature glomeruli synthesize collagen ␣1␣2␣1(IV). However, intracellular labeling revealed that podocytes, but not endothelial or mesangial cells, contain collagen ␣3␣4␣5(IV). To evaluate the origins of collagen IV further, we transplanted embryonic kidneys from Col4a3-null mutants (Alport mice) into kidneys of newborn, wildtype mice. Hybrid glomeruli within grafts containing numerous host-derived, wildtype endothelial cells never expressed collagen ␣3␣4␣5(IV). Finally, confocal microscopy of glomeruli from infant Alport mice that had been dually labeled with anti-collagen ␣5(IV) and the podocyte marker anti-GLEPP1 showed immunolabeling exclusively within podocytes. Together, these results indicate that collagen ␣3␣4␣5(IV) originates solely from podocytes; therefore, glomerular Alport disease is a genetic defect that manifests specifically within this cell type. Basement membranes are thin sheets of extracellular matrix that underlie epithelial cells, including the vascular endothelium, and surround all muscle cells, Schwann cells, and adipocytes. They are composed of polymers of laminin and type IV collagen, and also contain nidogen/entactin, and proteoglycans. During glomerulogenesis, a basement membrane beneath developing endothelial cells fuses with a separate basement membrane layer beneath differentiating podocytes, to produce the glomerular basement membrane (GBM) shared on opposing surfaces by both cell types. 1 Unlike most basement membranes in the body, the laminin and collagen IV composition of the GBM changes temporally as the glomerulus develops. 2 The earliest GBMs of comma-and S-shaped nephrons contain laminin ␣1␤1␥1 (laminin 111), whereas those at later developmental stages and in adulthood contain laminin ␣5␤2␥1 (laminin 521). 2,3 Previously, we showed by postfixation immunoelectron microscopy that both endothelial cells and podocytes synthesize laminin ␣1 and ␤1 initially, and both cells then undergo a laminin isoform switch and synthesize laminin ␣5 and ␤2 as glomeruli mature. 4 The mechanism and reason why laminin replacement occurs are unknown, but