Evidence for megalin-mediated proximal tubular uptake of L-FABP, a carrier of potentially nephrotoxic molecules.

Abstract

Liver-type fatty acid binding protein (L-FABP) binds with high affinity to hydrophobic molecules including free fatty acid, bile acid and bilirubin, which are potentially nephrotoxic, and is involved in their metabolism mainly in hepatocytes. L-FABP is released into the circulation, and patients with liver damage have an elevated plasma L-FABP level. L-FABP is also present in renal tubules; however, the precise localization of L-FABP and its potential role in the renal tubules are not known. In this study, we examined the cellular and subcellular localization of L-FABP in the rat kidney and tried to determine from where the L-FABP in kidney tissues had originated. Immunohistochemical studies of kidney sections localized L-FABP in the lysosomes of proximal tubule cells (PTC). In rats with carbon tetrachloride (CCl4)-induced acute liver injury, we detected high levels of L-FABP in the circulation and in the kidney compared with those in the control rat by immunoblotting, while reverse transcription-polymerase chain reaction showed that the level of L-FABP mRNA expression in the kidney of CCl4-treated rats was low and did not differ from that in the control rat. When 35S-L-FABP was intravenously administered to rats, the kidneys took up 35S-L-FABP more preferentially than the liver and heart, and histoautoradiography of kidney sections revealed that 35S-L-FABP was internalized via the apical domains of PTC. Quartz-crystal microbalance analysis revealed that L-FABP bound to megalin, a multiligand endocytotic receptor on PTC, in a Ca2+-dependent manner. Degradation assays using megalin-expressing rat yolk sac tumor-derived L2 cells demonstrated that megalin mediated the cellular uptake and catabolism of 125I-L-FABP. In conclusion, circulatory L-FABP was found to be filtered by glomeruli and internalized by PTC probably via megalin-mediated endocytosis. These results suggest a novel renal uptake pathway for L-FABP, a carrier of hydrophobic molecules, some of which may exert nephrotoxic effects.

• Authors: Yuko Oyama, Tetsuro Takeda, Hitomi Hama, Atsuhito Tanuma, Noriaki Iino, Kiyoko Sato, Ryohei Kaseda, Meilei Ma, Tadashi Yamamoto, Hiroshi Fujii, Junichiro J Kazama, Shoji Odani, Yoshio Terada, Kunihiro Mizuta, Fumitake Gejyo, Akihiko Saito
• Journal: Laboratory investigation; a journal of technical methods and pathology (Lab Invest) Vol. 85 Issue 4 Pg. 522-31 (Apr 2005) ISSN: 0023-6837 [Print] United States
• PMID: 15696188 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Carrier Proteins
• DNA Primers
• Fabp1 protein, rat
• Fatty Acid-Binding Proteins
• Low Density Lipoprotein Receptor-Related Protein-2

Topics

• Animals
• Base Sequence
• Carrier Proteins (biosynthesis, metabolism)
• DNA Primers
• Fatty Acid-Binding Proteins
• Immunohistochemistry
• Kidney Tubules, Proximal (drug effects, metabolism)
• Low Density Lipoprotein Receptor-Related Protein-2 (physiology)
• Male
• Rats
• Rats, Sprague-Dawley
• Reverse Transcriptase Polymerase Chain Reaction