Abstract 3284: Differential Regulation of Myocardial Collagen Formation by Adenylyl Cyclase Subtypes in Cardiac Hypertrophy
Adenylyl cyclase type 5, when it is knocked out (AC5 KO) and type 6, when it is cardiac specific over-expressed transgenically (AC6 Tg) have both been reported to protect the heart in response to stress. If so, AC5 Tg and AC6 Tg should exert opposite effects, and microarrays of their gene profiles should provide insight into mechanisms mediating the opposing actions. Accordingly, RNA was extracted from AC5 and AC6 transgenic mice (Tg) and wild type (WT) hearts (n=5/group) and was hybridized to mouse microarrays (Gene Chip 430.2.0, Affymetrix, Santa Clara, CA). The results indicated that collagen genes were significantly downregulated in AC6 Tg mice compared with WT. Our hypothesis is that AC6 Tg, compared with AC5 Tg, would be protective in response to chronic pressure overload and that the effects on collagen and fibrosis would be opposite in these models.
Results of western blotting indicate that, at baseline, collagen I, which accounts for more than 80% of total collagen, was 5 fold greater in AC5 Tg (P<0.05), but 80% reduced in AC6 Tg vs. WT. Both AC5 and AC6 Tg mice were submitted to aortic banding for one week and were compared with WT. After 1 week banding, left ventricular (LV) function, as reflected by LV ejection fraction (LVEF), was reduced (p<0.05) in AC5 Tg mice (56±4 %) compared with WT (77±1%), but not in AC6 Tg (73±2 %). The level of collagen I was 6 fold higher in AC5 Tg mice (11.2±4.1unit) than in AC6 Tg mice (1.9±0.17 unit) (p<0.05) in response to pressure overload. Collagen content was confirmed with picric acid sirius red staining and was significantly higher (p<0.05) in AC5 Tg (7.3±1.4%) than in AC6 Tg at baseline (3.9±0.5%) and collagen content was still higher in AC5 Tg (13.4±1.2 %) than in AC6 Tg (7.4±1.7%) after banding, suggesting a pro-fibrotic role for AC5 Tg and an anti-fibrotic role for AC6 Tg during cardiac remodeling. Therefore, we conclude that there is a major difference in cardiac remodeling following pressure overload, due to opposite regulation of collagen and fibrosis in AC5 Tg vs AC6 Tg mice, which may explain the diametrically opposite responses to stress with cardiac overexpression of AC5 vs AC6.
This research has received full or partial funding support from the American Heart Association, National Center.