Interaction between fibronectin, proteoglycans and lipoproteins.

The effect of purified human plasma fibronectin on LDL-GAG and LDL-PG complex formation was studied. Fibronectin added to LDL or to GAG or even to preformed LDL-GAG-Ca2+ complexes could inhibit complex formation and dissociated preformed complexes. Similar results were obtained with total serum instead of purified LDL: 1.2 mg fibronectin added to 1.0 mg LDL-cholesterol completely inhibited insoluble complex formation in the presence of Ca2+ between LDL and GAGs or LDL and PGs purified from aorta, whatever the order of mixing of the macromolecules. When fibronectin was added to preformed PG-LDL complexes however dissociation was less complete than with preformed LDL-GAG complexes (60% dissociation instead of 100% at similar concentration ratios). It appears therefore that the protein and GAG portions of PGs may not interact at the same sites of LDL and competition by fibronectin would be more efficient at the GAG binding site. Fibronectin could also dissociate LDL-heparin complexes formed on heparin-Sepharose affinity columns. As PG-LDL complexes were isolated from atherosclerotic plaques and fibronectin was also shown to increase in plaque area and exhibit opsonic-like functions, the above findings may well have physiopathological significance.