Megalin-Mediated Endocytosis in the Kidney Proximal Tubule: Relevance to Regulation of the Renal Renin-Angiotensin System.

The kidney proximal tubule is a major target tissue of the renin-angiotensin system (RAS). Megalin is an endocytic multiligand receptor abundantly expressed in the proximal tubule where it drives reabsorption of peptides and proteins from the glomerular ultrafiltrate. All major RAS components are present in the kidney proximal tubules. Here, megalin drives endocytosis of angiotensinogen (AGT), prorenin, and renin, while angiotensin-converting enzyme is localised at the brush border of the proximal tubule cells. Intrarenal formation of the key RAS effector angiotensin II (ANG II) occurs, and liver-derived AGT appears to be the primary source. New studies further suggest that megalin-mediated reabsorption of liver-derived AGT contributes to renal ANG II levels and thereby may influence renal RAS activity. This mini-review presents the recent advances on RAS in the proximal tubule and the involvement of megalin in the uptake and regulation of local RAS and discusses the possibility that megalin is involved in blood pressure regulation.