Fibronectin mRNA and protein accumulation, distribution, and breakdown in rabbit anti-glomerular basement membrane...

Fibronectin is a multifunctional matrix protein which by immunofluorescence appears to be present in increased amounts during glomerular injury. To examine fibronectin metabolism in glomerular injury, an anti-glomerular basement membrane model that progresses to severe glomerular crescent formation, glomerulosclerosis, and interstitial fibrosis was used. Fibronectin was purified from rabbit plasma, and a monoclonal antibody raised against rabbit fibronectin was used for immunolocalization and quantitation of fibronectin protein. RNA and protein were extracted from isolated glomeruli and whole renal cortex at various times during progression of disease. At day 4, there was a 2.5-fold increase in fibronectin protein which by immunofluorescence appeared to be in the glomerular mesangial area. There was no increase in glomerular fibronectin mRNA at this time. This discrepancy is consistent with the conclusion that, at this early time point, the increased glomerular fibronectin comes predominantly from plasma. By day 7, glomerular fibronectin mRNA and extractable fibronectin protein were increased in association with bright immunofluorescence along the inner aspect of Bowman's capsule where early crescents were forming. Similarly, at day 14, crescents stained very brightly for fibronectin. These results are consistent with the conclusion that, at later time points, fibronectin is synthesized in glomeruli in association with cell division and crescent formation. Degradation of fibronectin in glomerular and cortical extracts was demonstrated under normal and nephritic conditions by finding fibronectin proteolytic fragmentation by Western blot.(ABSTRACT TRUNCATED AT 250 WORDS)