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Delayed apoptosis post-cadmium injury in renal proximal tubule epithelial cells
Lindsay J Stinson1, Alison J Darmon, Lina Dagnino
1Department of Pharmacology and Toxicology, University of Western Ontario, Child Health Research Institute, London, Ont, Canada.
Background:
Accumulation of the widespread environmental toxin cadmium (Cd) in the kidney results initially in proximal tubule dysfunction. Exposure to Cd has been previously shown to induce apoptosis in LLC-PK (Lily Laboratory Culture, Porcine Kidney) cells, which are a model of proximal tubule epithelium.
Hypothesis:
We postulated that modulation of the components of the apoptotic pathway triggered by Cd is amenable to therapeutic intervention.
Methods:
We subjected confluent LLC-PK cells grown on two-compartment filters and on plastic to Cd (1-50 microM). Apoptosis and changes in components of the apoptotic pathway were measured by immunocytochemical and immunoblot analysis during the period of exposure and following Cd withdrawal.
Results:
Insignificant apoptosis was seen during exposure to Cd and immediately after removal of this metal. Two waves of apoptosis were noted 6 and 48 h after the Cd was removed from the apical compartment. The apoptosis 48 h post-Cd exposure was accompanied by a decrease in cellular ATP levels and transepithelial resistance and preceded by an increase in p38 phosphorylation. Inhibition of p38 mitogen-activated protein kinase activity decreased the delayed apoptotic peak, without affecting the rate of recovery of the integrity of the renal epithelium. IGF-1 neither altered the delayed apoptosis nor facilitated the rate of recovery of the integrity of the renal epithelium.
Conclusion:
We demonstrate that following exposure to Cd, renal epithelial cells undergo significant apoptosis, which appears to involve p38 and is not amenable to IGF therapy.