Receptor-mediated endocytosis in renal proximal tubule.
Proteins filtered in renal glomeruli are removed from the tubular fluid by endocytosis in the proximal tubule mediated by the two receptors megalin and cubilin. After endocytic uptake, the proteins are transferred to lysosomes for degradation, while the receptors are returned to the apical cell membrane by receptor recycling in dense apical tubules. In the renal proximal tubule, there is no significant transcellular transport of protein. The reabsorptive process is extremely efficient as evidenced by the virtual protein free urine in humans. The two receptors bind a variety of ligands. The process serves not only to remove the proteins from the ultrafiltrate but also to conserve a variety of essential substances such as vitamins and trace elements carried by plasma proteins. The endocytic apparatus is highly developed in the proximal tubule demonstrating the high capacity of the cells; however, under certain circumstances like diseases affecting the glomeruli, the system is overloaded resulting in proteinuria.
Christensen
Erik Ilsø
EI
Section of Cell Biology, Department of Anatomy, University of Aarhus, Wilh. Meyers Allé, Building 1234, 8000, Aarhus C, Denmark. eic@ana.au.dk
Verroust
Pierre J
PJ
Nielsen
Rikke
R
D000818:Animals; D004705:Endocytosis / Q000502:physiology*; D015870:Gene Expression; D006801:Humans; D007687:Kidney Tubules, Proximal / Q000502:physiology*; D008024:Ligands; D026561:Low Density Lipoprotein Receptor-Related Protein-2 / Q000502:physiology*; D008565:Membrane Proteins / Q000502:physiology*; D011956:Receptors, Cell Surface / Q000502:physiology*
C424167:Amn protein, mouse; D008024:Ligands; D026561:Low Density Lipoprotein Receptor-Related Protein-2; D008565:Membrane Proteins; D011956:Receptors, Cell Surface; C029486:intrinsic factor-cobalamin receptor