Background: The bulk of proteins filtered in the glomeruli are reabsorbed in the proximal tubule by endocytosis mediated by two multiligand receptors operating in concert, megalin and cubilin. Podocytes can also internalize protein and megalin; this was initially reported in rat proximal tubular and glomerular epithelial cells and has recently also been demonstrated in human podocytes. Cubilin, crucial for albumin reabsorption in the proximal tubule, has not been identified in glomerular epithelial cells.
Methods: In the present study, we used immunocytochemistry and reverse transcription-polymerase chain reaction on laser-captured glomeruli to demonstrate synthesis and expression of cubilin in rat and human glomeruli. In parallel experiments, the expression of cubilin was studied in cultured podocytes.
Results: This study identifies cubilin in rat and human glomeruli according to a pattern similar to that reported for megalin. Cubilin revealed a surface expression but also intracellular expression in the podocytes.
Conclusion: Our findings show that the podocytes display the two endocytic receptors which are responsible for the only documented process for protein reabsorption in proximal tubule cells.