Cellular source in ewes of prostaglandin-endoperoxide synthase-2 in uterine arteries following stimulation with lipopolysaccharide

Abstract

Prostaglandin-endoperoxide synthase (PTGS) (also known as cyclooxygenase) converts arachidonic acid into several prostaglandins, many of which have roles in vasodilation and vasoconstriction under normal and pathological conditions. There are two isoforms of PTGS: PTGS-1 and PTGS-2; PTGS-1 is constitutively expressed in many tissues and is believed to be involved in the homeostatic maintenance of the body. In contrast, PTGS-2 is believed to have a 'differentiative' role in the cells and is highly inducible during inflammation and in response to lipopolysaccharide (LPS). Endothelial cells as well as vascular smooth muscle cells can be a source of PTGS within the artery. The objective of this study was to determine the cell population(s) in uterine arteries that respond to LPS with an increase in PTGS-2 protein expression. Uterine arteries collected from ewes during the follicular (Day 0, Day 0 = estrus, n = 4) or luteal (Day 10, n = 4) phase were treated in vitro with LPS as intact artery segments, cut-open artery segments, or cut-open and denuded (endothelial cells absent) artery segments. After 24 h of LPS treatment, intact, cut-open, and denuded uterine artery segments were collected into homogenization buffer for determination of PTGS- 2 protein levels by Western blot analysis. The culture medium was collected and used for detection of 6-keto-prostaglandin F(1α) (6-keto-PGF(1α)), the stable metabolite of prostacyclin, using an enzyme immunoassay. In addition, the location of PTGS-2 after LPS treatment was analyzed by immunohistochemistry in intact artery segments. Denuded arteries (endothelium absent) did not show increases in PTGS-2 protein in the homogenates or 6- keto-PGF(1α) in the culture medium after LPS exposure. In contrast, cut uterine arteries responded to LPS stimulation with a significant increase in PTGS-2 protein in homogenates and 6-keto-PGF(1α) in culture medium. Immunohistochemical staining for PTGS-2 was associated with both endothelial cells and vascular smooth muscle cells. These results suggest that while both endothelial cells and vascular smooth muscle cells are associated with PTGS- 2, after LPS exposure it is the endothelial cells that are essential in uterine artery increases in PTGS-2 and prostacyclin in response to LPS stimulation.