Abstract 12644: Aldosterone Activates Autophagy to Increase Vascular Smooth Muscle Cell Collagen Synthesis and Vascular Stiffness
Hyperaldosteronism is associated with vascular remodeling and increased arterial stiffness; however, the contribution of vascular smooth muscle cells to this response remains unknown. Accordingly, we treated human aortic smooth muscle cells (HASMC) with aldosterone (ALDO) (10−7 mol/L) for 72 h. ALDO induced endoplasmic reticulum (ER) stress in HASMC and increased expression of the ER stress markers GRP78, ATF6, p-IRE, and p-eIF2α; decreased ER Ca2+ levels by 24% (p<0.01); and increased cytosolic Ca2+ levels by 36% (p<0.01). ALDO-induced ER stress upregulated TGF-β expression by 3.8 ± 0.3-fold (p<0.01) and activated autophagy as demonstrated by an increase in beclin1 and LC3BI to LC3BII cleavage. This effect was associated with a 3.1 ± 0.2-fold (p<0.01) increase in collagen I expression. Coincubation with the ER stress inhibitor salubrinal (25 μmol/L) decreased TGF-β expression and autophagy. To demonstrate the role of autophagy in increased collagen I expression, HCSMC were transfected with beclin1 siRNA to decrease protein expression by 72%. In beclin1 siRNA-transfected cells, there was an 85% decrease (p<0.01) in collagen I protein expression compared to control-transfected cells with no effect on ER stress or TGF-β expression. Coincubation of ALDO-treated HASMC with imatinib mesylate (5 μmol/L), to inhibit TGF-β, decreased LC3BI to LC3BII cleavage by 79% (p<0.01) and collagen I protein levels by 89% (p<0.01). To confirm these findings in vivo, we infused C57Bl/6 mice with ALDO (50 μg/kg/d) or vehicle for 7 days. While there was no difference in blood pressure between treatment groups, pulse wave velocity was increased significantly in ALDO-infused mice (278. 3 ± 26.8 vs. 415.7 ± 12.2 cm/sec, p<0.01). Autophagy, demonstrated by LC3BII expression, was increased in aortas from ALDO-treated compared to vehicle-treated mice, and this was associated with a 3.4 ± 0.9-fold (p<0.01) increase in collagen I expression. Coadministration of imatinib mesylate (50 mg/kg/d) with ALDO decreased aorta collagen, autophagy, and pulse wave velocity. These data demonstrate that elevated levels of ALDO increase vascular collagen to increase vascular stiffness in the absence of hypertension through a mechanism that involves vascular smooth muscle cell autophagy.
- © 2010 by American Heart Association, Inc.