Abstract 102: Aldosterone Evokes Senescence-associated Secreting Phenotype And Subsequent Apoptosis In Proximal Tubular Cells

Abstract

We previously reported that aldosterone/mineralocorticoid receptor activation caused cell senescence via p21, a cell cycle regulator, -dependent pathway in proximal tubules of rat kidney and human proximal tubular cells. However, functional influences of cell senescent on the kidney are still unclear. In the present study, we hypothesized that aldosterone-induced cell senescence caused cell apoptosis by increasing the secretion of apoptotic factors (n=6 in all groups). Aldosterone increased senescent cells at day 3 and day 5 in human proximal tubular cells, and the changes were accompanied by the increase in p21 protein expression (day 3: 2.9±0.7 fold, day 5: 6.5±0.9 fold, p<0.05) and TNF-α mRNA (day 3: 2.3±0.3 fold, day 5: 2.4±0.6 fold, p<0.05). In addition, aldosterone also increased secretion of TNF-α into the culture medium compared with vehicle-treated group (day 3: 15.7±1.2 vs 7.2±1.6 pg/ml; day 5: 33.3±5.7 vs 11.8±2.3 pg/ml; p<0.05, respectively): gene silencing of p21 abolished these changes. Meanwhile, 3-day treatment with aldosterone showed no sign of cell apoptosis, which was evaluated by terminal nick end labeling (TUNEL) and annexin V/propidium iodide (PI) staining, and 5-day treatment with aldosterone increased cell apoptosis (TUNEL: aldosterone, 6.4±1.5%; vehicle, 0.6±0.3%; annexin V/PI: aldosterone, 5.8±0.8%; vehicle, 0.8±0.3%; p<0.05). Importantly, p21 siRNA and TNF-α neutralizing antibody abolished these aldosterone-induced apoptotic changes (TUNEL: 1.4±0.1 and 0.9±0.5%; annexin V/PI: 0.9±0.3 and 1.5±0.9%; respectively). These results indicate that aldosterone increases TNF-α synthesis and secretion in proximal tubular cells via p21/senescence-dependent pathway, and that the secreted TNF-α plays an important role as an autocrine/paracrine factor to mediate cell apoptosis, which may be involved in aldosterone-induced renal damage.