Glucocorticoids potently block tumour necrosis factor-α- and lipopolysaccharide-induced apoptotic cell death in bovine glomerular endothelial cells upstream of caspase 3 activation

1 Endothelial cell damage in glomeruli and kidney arterioles appears to play a pivotal role in glomerular inflammatory diseases. Glomerular endothelial cells, a specialized microvascular cell type involved in the regulation of glomerular ultrafiltration, die by apoptosis in response to tumour necrosis factor-alpha (TNF-alpha), TNF-alpha/basic fibroblast growth factor (bFGF), TNF-alpha/cycloheximide and bacterial lipopolysaccharide (LPS). Apoptotic cell death is characterized by extensive DNA cleavage, DNA ladder formation, and characteristic morphological alterations. 2 In search for apoptosis-preventing signals, we identified glucocorticoids as potent death preventing factors. Co-treatment of cells with 10 nM dexamethasone and TNF-alpha, TNF-alpha/bFGF, TNF-alpha/cycloheximide, or LPS blocked roughly 90% of apoptotic cell death in glomerular endothelial cells. 3 Similarly to dexamethasone (TNF-alpha- and LPS-induced apoptosis are prevented with IC50 values of 0.8 and 0.9 nM, respectively), other synthetic and natural forms of glucocorticoids, such as fluocinoione, prednisolone, hydrocortisone, and corticosterone potently inhibited cell death with IC50 values of 0.2, 6, 50 and 1000 nM, for TNF-alpha and 0.7, 8, 100 and 500 nM for LPS, respectively. 4 Apart from glucocorticoids, mineralocorticoids such as aldosterone also blocked TNF-alpha/LPS-induced apoptosis (IC50 similar to 500 nM for TNF-alpha and similar to 500 nM for LPS), whereas sex hormones, i.e. beta-estradiol and testosterone remained without effect. 5 The protective effect of glucocorticoids (and mineralocorticoids) required glucocorticoid receptor binding as it could be antagonized by the glucocorticoid receptor antagonist RU-486. Concerning TNF-alpha and LPS signal transduction, we found that dexamethasone efficiently prevented TNF-alpha- and LPS-induced activation of caspase-3-like proteases. Therefore, we postulate inhibitory mechanisms upstream of terminal death pathways.