Endothelial cell induced modulation of cardiac fibroblast collagen metabolism

OBJECTIVE: The aim was to examine the influence of vascular endothelial cells on rat cardiac fibroblast collagen synthesis and collagenase activity under co-culture conditions, and to determine whether angiotensin II or aldosterone influence endothelial cell induced modulation of fibroblast collagen metabolism. METHODS: Bovine aortic endothelial cells were grown to confluence on microporous membrane inserts and then co-cultured with cardiac fibroblasts obtained from adult rats, previously grown to confluence in 35 mm dishes supplemented with 0.4% fetal bovine serum. Collagen synthesis was measured by 3H-proline incorporation. Experiments were also conducted under similar conditions to quantitate collagenase activity by zymography in conditioned medium from fibroblasts co-cultured with endothelial cells. RESULTS: After 48 h co-culture, there was a 1.9-fold increase in fibroblast collagen synthesis when compared to fibroblasts alone (p < 0.001). Aldosterone (10(-8) M) or angiotensin II (10(-7) M) added to endothelial cells did not increase fibroblast collagen synthesis over co-cultures alone. Neither the aldosterone receptor antagonist spironolactone (10(-8) M) nor type I (DuP 753, 10(-8) M) or type II (PD 123319, 10(-8) M) angiotensin II receptor antagonists altered fibroblast collagen synthesis in co-cultures. A significant increment in collagenase activity was observed in co-cultured fibroblasts relative to collagenase activity of fibroblasts alone. CONCLUSIONS: Endothelial cells modulate both cardiac fibroblast collagen synthesis and degradation. The nature of the responsible signal(s) remains to be defined, but does not appear to be mediated or regulated by angiotensin II or aldosterone.