Evidence for increased protease activity secreted from cultured fibroblasts from patients with pseudoxanthoma...

Abnormal polyanion metabolism in cultured fibroblasts from patients with pseudoxanthoma elasticum (PXE) was studied by incubating normal and PXE fibroblasts in culture medium containing 35SO4 for 96 hr and measuring differences in secreted 35SO4-labelled proteoglycans (35S-PG). PXE medium contained less high molecular weight (MW) 35S-PG and more low MW 35S-labelled molecules than normal medium. Addition of diisopropylfluorophosphate (DFP), a serine protease inhibitor, to the media after the 96 hr incubation resulted in no change in the MW distribution of 35SO4-labelled molecules in normal media. However, DFP treated PXE medium contained significantly more high MW 35S-PG than either untreated PXE medium or DFP treated normal medium. High MW 35S-PG was isolated from PXE fibroblast culture medium and incubated with serum free medium from either normal or PXE fibroblast cultures. There was significantly more degradation of this 35S-PG to low MW 35S-labelled molecules by PXE medium than by normal medium. 32P-DFP, which binds to the active site of serine proteases, was added to serum free medium from normal and PXE cultures. The specific radioactivity of PXE medium was 4 times greater than that of normal medium. These lines of evidence are consistent with the hypothesis that a biochemical defect in cultured PXE fibroblasts is the increased secretion of a serine protease that can degrade sulfated proteoglycans.