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Endocytosis provides a major alternative pathway for lysosomal biogenesis in kidney proximal tubular cells

Item Type:Article
Title:Endocytosis provides a major alternative pathway for lysosomal biogenesis in kidney proximal tubular cells
Creators Name:Nielsen, R., Courtoy, P.J., Jacobsen, C., Dom, G., Lima, W.R., Jadot, M., Willnow, T.E., Devuyst, O. and Christensen, E.I.
Abstract:Recruitment of acid hydrolases to lysosomes generally occurs by intracellular sorting based on recognition of a common mannose 6-phosphate signal in the transGolgi network and selective transport to late endosomes/lysosomes. Here we provide evidence for an alternative, efficient secretion-recapture pathway mediated by megalin and exemplified by cathepsin B in kidney proximal convoluted tubules (PCT). We found that in mouse kidneys with defective megalin expression [megalin knockout (KO)] or apical PCT trafficking (ClC-5 KO), the (pro)cathepsin B mRNA level was essentially preserved, but the protein content was greatly decreased and the enzyme was excreted in the urine as mannose 6-phosphate-devoid species. In polarized PCT-derived cells, purified cathepsin B was avidly and selectively taken up at the apical membrane, and uptake was abolished by the megalin competitor, receptor-associated protein. Direct interaction of cathepsin B with megalin was demonstrated by surface plasmon resonance. Procathepsin B was detected in normal mouse serum. Purified cathepsin B injected into mice was efficiently taken up by kidneys ( approximately 10% of injection) and targeted to lysosomes where it remained active, as shown by autoradiography and subcellular fractionation. A single cathepsin B injection into cathepsin B KO mice could reconstitute full lysosomal enzyme activity in the kidneys. These findings demonstrate a pathway whereby circulating lysosomal enzymes are continuously filtered in glomeruli, reabsorbed by megalin-mediated endocytosis, and transferred into lysosomes to exert their function, providing a major source of enzymes to PCT. These results also extend the significance of megalin in PCT and have several physiopathological and clinical implications
Keywords:Lysosomes, Mannose 6-phosphate, Megalin, Cathepsin B, Animals, Mice
Source:Proceedings of the National Academy of Sciences of the United States of America
Publisher:National Academy of Sciences
Page Range:5407-5412
Date:27 March 2007
Official Publication:https://doi.org/10.1073/pnas.0700330104
PubMed:View item in PubMed

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