Aim: 

Cadmium (Cd) is a well-known occupational and environmental hazard acting as a potent nephrotoxicant impairing the reabsorptive and secretory functions of renal proximal tubules. To gain insights into the mechanisms of Cd-induced albuminuria, we investigated the effects of Cd on the expression of Megalin and ClC5 chloride channels, two proteins that play a key role in the receptor-mediated endocytosis of albumin, using a porcine kidney cell line (LLC-PK1) as a proximal tubular cell model.

Methods: 

Real-Time PCR and immunoblotting analyses were carried out to evaluate the effect of 10 mM CdCl₂ on the expression and regulation of Megalin and ClC5 in LLC-PK1 cells. Albumin endocytosis assay and confocal microscopy were performed to study both the albumin uptake and subcellular localization of Megalin and ClC5 in Cd-treated cells.

Results: 

Cadmium treatment caused a significant and dose-dependent decrease of the mRNA and protein levels of both Megalin and ClC5. No changes were seen incubating LLC-PK1 cells with divalent heavy-metals such as ZnCl₂, MnCl₂, MgCl₂ and NiCl₂. Suggesting posttranscriptional regulation, treatment with the protein synthesis inhibitor cycloheximide abolished the expression of both proteins in Cd-challenged cells. Confocal microscopy confirmed the downregulation of Megalin and ClC5 and showed remarkable reduction of FITC-albumin uptake following Cd exposure.

Conclusions: 

Overall, our results show significant dysregulation of Megalin and ClC5 by cadmium. Our work in trying to understand the mechanism by which Cd impairs the reabsorption of protein in the renal proximal tubule will provide valuable insights into the mechanism of how this metal causes renal damage.