Megalin mediates the uptake of angiotensin II in proximal tubule cells

Abstract

Background: Megalin and the Ang II type I receptor (AT1R) are coexpressed in the renal proximal tubule where megalin is involved in endocytosis and degradation of proteins that escape the glomerular barrier. Because Ang II uptake by AT1R-expressing BN/MSV cells (a non-renal cell line) is partially mediated by megalin, we tested if megalin mediates Ang II uptake in proximal tubule cells. Methods: Cultured proximal tubule cells (NRK-52E cells) were exposed to fluorescent Ang II for 4 hours (Alexa488-Ang II, 100 nM). Olmesartan (or Candesartan 10 μM) and anti-megalin antisera (or albumin 1 mg/mL) were used to block the AT1R and the megalin pathways respectively. Flow cytometry was used to measure single cell-associated fluorescence. Confocal or fluorescence microscope systems were used for image capturing and analysis. Results: In flow cytometry experiments, both anti-megalin antisera and AT1R blockers significantly reduced Ang II uptake (30% and 60% reductions respectively, p <0.05 vs. positive control). In imaging experiments, Ang II accumulated mostly in a perinuclear area and this accumulation was reduced by treatment with albumin, AT1R blockers or both. Conclusion: Megalin mediates Ang II uptake into proximal tubule cells in addition to the AT1R. Because megalin is responsible for the scavenging of proteins in the tubular fluid, megalin-mediated Ang II uptake might help to regulate intrarenal Ang II levels.