Regulation of Vascular Smooth Muscle Cell Proliferation by Cyclooxygenase-2-Derived Prostanoids.
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 104 cells; p<0.001; control: 4.1 ± 0.3, TNF: 7.8 ± 0.4 x 104 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 (PGI2) 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 PGI2 levels also were significantly reduced by these inhibitors, suggesting a tight coupling of COX-2 to PGI2 synthesis in these cells. TNF and Ang II induced modest increases in vsmc TXA2 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 TXA2 synthesis was not affected. Despite the relatively small increases in TXA2 synthesis, the TXA2 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 TXA2 synthesis may contribute to vsmc hyperplasia in pathophysiological conditions associated with elevated levels of either TNF or Ang II. In contrast, PGI2 may contribute to a compensatory mechanism to limit the proliferative effects of cytokines such as TNF or vasoactive peptides such as Ang II.