Effects of angiotensin II and aldosterone on collagen gene expression and protein turnover in cardiac fibroblasts

Earlier studies have demonstrated angiotensin II (AngII) and aldosterone (ALDO) each augment cultured adult rat cardiac fibroblast (CFb) collagen synthesis. Whether this involves type I collagen, the major structural protein of the myocardium, and represents a transcriptional event, is uncertain. Accordingly, the influence of AngII and ALDO on transcription and synthesis of fibrillar collagen and on collagenolytic activity was examined in cultured CFb maintained in serum-deprived media. Using concentrations for AngII (10(-7) M) or ALDO (10(-9) M), shown to influence collagen turnover in these cells, we found: a) total collagen synthesis was significantly (p < 0.05) increased (5.4 +/- 0.41 and 4.8 +/- 0.37 vs. control 3.1 +/- 0.55); b) type I collagen production (6590 +/- 710 and 6150 +/- 410 VS. control 4700 +/- 490 ng/mL) in the medium were significantly (p < 0.01) increased; c) type I collagen mRNA expression was also significantly (p < 0.01) increased by AngII (2.0 fold) and ALDO (1.8 fold) compared with control; d) AngII, but not ALDO, significantly (p < 0.05) decreased collagenolytic activity (0.5 fold) compared with control. Thus, AngII and ALDO each increase CFb type I collagen synthesis at the level of transcription and protein synthesis and AngII, but not ALDO, alters collagenolytic activity. Such hormonally mediated alterations in CFb collagen turnover may contribute to the adverse accumulation of fibrillar collagen found in the myocardium in various disease states, where circulating AngII and/or ALDO are increased.