Angiotensin II stimulates DNA and protein synthesis in vascular smooth muscle cells from human arteries: role of extracellular signal-regulated kinases

Objective: This study investigates the growth effects and associated signaling pathways of angiotensin II (Ang II) in human vascular smooth muscle cells. Methods: Cultured vascular smooth muscle cells derived from resistance arteries (< 300 μm diameter) from subcutaneous gluteal biopsies of healthy subjects (n = 6) and human aortic vascular smooth muscle cells were used. Cells were studied between passages 3 and 6. Both 3H-thymidine and 3H-leucine incorporation were measured as indices of vascular smooth muscle cell hyperplasia (DNA synthesis) and cell hypertrophy (protein synthesis), respectively. Growth effects of Ang II (10-12 = 10-6 mol/l), in the absence and presence of 10-5 mol/l losartan (AT1 antagonist) and PD123319 (AT2 antagonist), were determined. Ang II-induced effects were compared to those of endothelin-1. To determine whether extracellular signal-regulated kinase (ERK)-dependent pathways play a role in Ang II-mediated growth, cells were pretreated with the selective ERK kinase (MEK) inhibitor, PD98059 (10-5 mol/l). ERK activation was determined by Western blot in the absence and presence of PD98059. Results: Ang II dose-dependently increased 3H-thymidine incorporation in cells from aorta (Emax = 276 ± 10.4% of control) and resistance arteries (Emax = 284 ± 5.1% of control). Ang II also stimulated 3H-leucine incorporation in cells from aorta (Emax = 162 ± 11.6 of control) and resistance arteries (Emax 175 ± 10% of control). Unlike Ang II, endothelin-1 failed to significantly alter cellular growth, except at high concentrations (> 10-7 mol/l), where it had a weak stimulatory effect. Losartan, but not PD123319, blocked Ang II-stimulated growth responses. Ang II significantly increased phosphorylation of ERK-1 and ERK-2, with maximum responses obtained at 5 min. PD98059 inhibited Ang II-stimulated ERK activity and abrogated agonist-induced DNA and protein synthesis. Losartan, but not PD123319 inhibited Ang II-induced phosphorylation of ERK-1 and ERK-2. Conclusions: Ang II stimulates both hyperplasia and hypertrophy in vascular smooth muscle cells from human arteries. These growth effects are mediated via Ang II receptors of the AT1 subtype that are linked to ERK-dependent signaling pathways.