A pro‐proliferative endothelial cell phenotype occurs late in the course of inflammation

Abstract

We hypothesized that cytokine stimulation will result in an initial impairment of endothelial cell proliferation, followed by a pro‐proliferative phenotype mediated by elevated arginase expression. Bovine pulmonary artery endothelial cells (bPAEC) were treated with lipopolysaccharide and tumor necrosis factor‐α(L/T)or vehicle and harvested at 0, 1, 2, 4, 8, 24, 48, 72 and 96 h. Levels of mRNA were measured for iNOS, arginase I, arginase II, ornithine decarboxylase (ODC) and ornithine aminotransferase (OAT). iNOS mRNA in L/T treated cells was increased at 2 h and peaked by 24 h with a return to basal levels by 48 h. Conversely, arginase II mRNA expression was increased at 4 h and remained elevated throughout the experiment. Arginase I mRNA remained low in both control and L/T cells. The mRNA levels of ODC and OAT increased at 72 and 96 h in L/T cells. We measured PCNA expression and cells exposed to L/T showed significantly greater PCNA levels than did control cells after 96 h. Endothelial cells grown for 24 and 96 h in either L/T or vehicle were used in a proliferation assay, the number of viable L/T treated cells were lower in the 24 h treated cells and greater in the 96 h treated cells versus controls. Taken together, L/T treatment results in L‐arginine metabolism to NO early, followed by a shift to an arginase‐mediated metabolism of L‐arginine to ornithine resulting in cellular proliferation.