EMBRYONIC FIBRONECTIN ISOFORMS ARE SYNTHESIZED IN CRESCENTS IN EXPERIMENTAL AUTOIMMUNE GLOMERULONEPHRITIS

Crescents are a severe and stereotyped glomerular response to injury t hat occur in several forms of glomerulonephritis that progress to rena l failure The key pathogenetic step that leads to glomerular scarring is unknown, but fibronectin (FN), the clotting system, macrophages, an d proliferating parietal epithelial cells are known to participate. Th is study tons designed to determine whether FN is synthesized locally, and in what molecular isoform, and whether cytokines known to promote FN synthesis are present in the crescent. Rats immunized with bovine glomerular basement membrane develop cellular crescents by 14 days and fibrous crescents and glomerulosclerosis by 35 days, In situ hybridiz ation was performed with oligonucleotides specific for sequences commo n to all FN isoforms (total FN) or sequences specific for the alternat ively spliced segments (EIIIA, EIIIB, and V). Throughout the time peri od (14, 21, and 35 days) all crescents and glomerular tufts contained cells with strong ISH signals for total and V+ mRNA, with the stronges t signals present in large cellular crescents at tiny 21, lit contrast , EIIIA(+) and EIIIB(+) mRNAs showed maximal abundance within sclerosi ng crescents at 35 days, Protein deposition of EIIIA(+), EIIIB(+), and V+ FN isoforms was confirmed by immunofluorescence with segment-speci fic FN antibodies, Transforming growth factor-beta and interleukin-1 b eta both known to promote FN synthesis, were found in cellular crescen ts (days 14 and 21) and were still present, but greatly, diminished, i i, the sclerotic phase (day 35), In summary, EIIIA(-), EIIIB(-), and V + FN mRNA plasma isoforms predominate in cellular crescents, whereas h i the fibrosing stage, mainly, the oncofetal EIIIA(+), EIIIB(+), and V + isoforms are synthesized and accumulate.