COX-2 Up-regulation and vascular smooth muscle contractile hyperreactivity in spontaneous diabetic db/db mice

Objective: Abnormalities in vascular constriction and dilatation are associated with early diabetes and contribute to diabetic vascular complications. However, mechanisms underlying such vascular dysfunction remain to be fully elucidated. The current study tests the role of cyclooxygenase-2 (COX-2) in diabetic vascular smooth muscle dysfunction. Methods: Small mesenteric artery and aorta are isolated from type 2 diabetic db/db and control mice. Isometric contractions in response to serotonin, angiotensin II, phenylephrine and high potassium are determined in small spiral mesenteric arterial or aortic strips. COX-2 mRNA and protein levels are analyzed by using DNA microarray, real-time PCR and immunoblot. Results: Contractions induced by serotonin, angiotensin II, phenylephrine and high potassium are significantly higher in endothelium-denuded smooth muscle strips isolated from db/db mice than in those isolated from control mice. The contractile hyperreactivity is observed in aortic and third-order branch small mesenteric arterial smooth muscle strips. DNA microarray, real-time PCR and immunoblot analysis show that compared with control mice, COX-2 mRNA and protein are significantly increased in db/db mice aortic smooth muscle. The COX-2 up-regulation is temporally associated with the development of diabetes mellitus and vascular smooth muscle contractile hyperreactivity. Inhibition of COX-2 with NS-398 or SC-58125 partially-but significantly-alleviates agonist-induced but not potassium-induced contractile hyperreactivity. In addition, serum isolated from db/db mice induces COX-2 expression and increases thromboxane A₂ production in primary cultured vascular smooth muscle cells (VSMC). SQ-29548, a TP receptor antagonist, diminished the db/db mice vascular smooth muscle contractile hyperreactivity. Conclusions: COX-2 is up-regulated and contributes at least in part to the vascular smooth muscle contractile hyperreactivity in db/db mice.