Regulation of Vascular Smooth Muscle Cell Proliferation by Cyclooxygenase-2-Derived Prostanoids.

Abstract

10 Tumor necrosis factor-alpha (TNF, 1 nM) and angiotensin II (Ang II, 100 nM) increased the DNA content of vascular smooth muscle cell (vsmc) derived from rat thoracic aorta (control: 3.7 ± 0.2, TNF: 5.7 ± 0.7, Ang II: 6.2 ± 0.5 arbitrary units; p<0.001). Cell number also increased in response to these molecules, indicative of a direct correlation between DNA content and cellular proliferation (control: 3.1 ± 0.1, Ang II: 4.4 ± 0.6 x 10 4 cells; p<0.001; control: 4.1 ± 0.3, TNF: 7.8 ± 0.4 x 10 4 cells; p<0.001). Increases in DNA content and cell number were preceded by increases in COX-2 mRNA accumulation and protein expression, and accumulation of COX-2 mRNA was prevented by pretreatment with losartan (1 μM) but not PD123319 (1 μM). COX-1 mRNA accumulation did not change after challenge with either TNF or Ang II for 0.5, 2, and 6 hr. Two different COX-2-selective inhibitors, NS-398 (0.1 μM) and nimesulide (1 μM) reduced TNF- and Ang II-mediated increases in DNA content and cell number by more than 95%. Prostacyclin (PGI 2 ) synthesis was increased approximately 3- and 8-fold, in response to TNF or Ang II, respectively, (control: 200 ± 35, TNF: 705 ± 28 pg 6-keto PGF1α/ml; p<0.001; control: 190 ± 45, Ang II: 1645 ± 120 pg 6-keto PGF1α/ml, p<0.001. These increases were completely inhibited by either NS-398 or nimesulide. Basal PGI 2 levels also were significantly reduced by these inhibitors, suggesting a tight coupling of COX-2 to PGI 2 synthesis in these cells. TNF and Ang II induced modest increases in vsmc TXA 2 synthesis (control: 33 ± 3, TNF: 49 ± 3, Ang II: 46 ± 6; p<0.001). The increases were abolished by NS-398 and nimesulide, although basal TXA 2 synthesis was not affected. Despite the relatively small increases in TXA 2 synthesis, the TXA 2 receptor antagonist, BMS 180,291 (1 μM) inhibited the proliferative response to Ang II and TNF by >95%. These data suggest that a COX-2-dependent increase in TXA 2 synthesis may contribute to vsmc hyperplasia in pathophysiological conditions associated with elevated levels of either TNF or Ang II. In contrast, PGI 2 may contribute to a compensatory mechanism to limit the proliferative effects of cytokines such as TNF or vasoactive peptides such as Ang II.