HYALURONAN AND HYALURONECTIN PRODUCTION IN INJURED RAT THORACIC AORTA

The aim-of our study was to investigate the production of hyaluronan ( HA) by the intima-media during the sclerotic response to aortic injury with a catheter balloon in the rat. In addition we analyzed, for the first time in this model, the production of a glycoprotein (hyaluronec tin, HN) which binds specifically to HA. HA and HN were analyzed in co ntrol (D0); 14 (D14) and 28 (D28) days after injury using biochemical and immunohistochemical techniques. Intima-media DNA content and wet w eight increased significantly on D14 and declined on D28 (but remained significantly increased in comparison to controls). HA content (media n in D0 = 448 ng) increased significantly on D14 (2P < 0.04) and on D2 8 (2P < 0.02). HN content (median in D0 = 920 ng) increased significan tly on D14 (2P < 0.05) but decreased on D28 to return to the control l evel. On D0 the amount of HN was about 3 times higher than that of HA (median ratio HA/HN = 0.34). The ratio remained unchanged on D14 but s ignificantly increased on D28 (2P < 0.02). HPLC and Western blotting s howed no difference between HN extracted from normal aorta and HN extr acted from injured aorta at D14. Different isoforms of HN were present in both cases, ranging from 400 to 45 kDa. The HA increase on D14 and D28 was not related to a change in hyaluronidase activity of aortic t issue. Immunohistochemical analysis showed at D0 a small amount of HA around arterial smooth muscle cells (ASMC) in media, at D14 more HA wa s localized around and between ASMC in media and neointima but at D28 it was localized mainly near the vessel lumen. HN formed all the time (D0, D14 and D28) a continuous layer localized near the vessel lumen, In vitro studies showed that production of HA and HN was stimulated wh en ASMC proliferate and HA at high concentrations (1-100 mu g/ml) redu ced, in a dose dependent manner, ASMC growth. In conclusion our result s show that both neointima formation in vivo and ASMC proliferation in vitro correlated with increased HA and HN production. This suggests t hat HA and HN are probably involved in the Formation of neointima. On the other hand, the finding that HA continued to increase in the aorta when neointima decreased and that high concentrations of HA reduce AS MC proliferation in culture suggest that HA might be involved in the r egression of neointima.