Cyclooxygenase-2 inhibits tumor necrosis factor α-mediated apoptosis in renal glomerular mesangial cells

Abstract

Renal mesangial cell apoptosis is a crucial repair mechanism in glomerular nephritis (GN). These cells express receptors to tumor necrosis factor α (TNFα), a cytokine with proapoptotic properties implicated in the resolution of GN. Progression to proliferative GN is accompanied by cyclooxygenase-mediated formation of prostaglandins and inefficient apoptosis of mesangial cells. The aims of this study were to quantify TNFα-mediated apoptosis in renal mesangial cells and to determine whether expression of the inducible form of cyclooxygenase, cylooxygenase-2 (COX-2), inhibits this apoptosis. By 24 h significant levels of apoptosis were induced by TNFα (100 ng/ml) or etoposide control (100 μM), as shown by phosphatidylserine externalization, caspase-3 activation, development of a sub-G0/G1 region, and distinct chromatin condensation. Using adenoviral-mediated delivery of the COX-2 gene (AdCOX-2) apoptotic features were prevented from appearing in AdCOX-2 cells treated with TNFα, whereas etoposide-treated AdCOX-2 cells were not protected. Furthermore, COX-2 expression, induced by the vasoconstrictor peptide ET-1 or the cytokine interleukin-1β also inhibited TNFα-mediated but not etoposide-mediated apoptosis, to an extent, similar to adenoviral COX-2 infection. Selective COX-2 inhibition by NS-398 restored TNFα-mediated apoptosis. Prostaglandin (PG) E2 and PGI2 were shown to be the major prostaglandin metabolites in AdCOX-2 cells. The addition of PGE2 and PGI2 protected against TNFα-mediated apoptosis. These results demonstrate COX-2 anti-apoptotic activity via a death receptor route and suggest that selective COX-2 inhibition may augment TNFα apoptosis in chronic inflammatory conditions.