title: Podocyte injury caused by indoxyl sulfate, a uremic toxin and aryl-hydrocarbon receptor ligand.
abstract: Indoxyl sulfate is a uremic toxin and a ligand of the aryl-hydrocarbon receptor (AhR), a transcriptional regulator. Elevated serum indoxyl sulfate levels may contribute to progressive kidney disease and associated vascular disease. We asked whether indoxyl sulfate injures podocytes in vivo and in vitro. Mice exposed to indoxyl sulfate for 8 w exhibited prominent tubulointerstitial lesions with vascular damage. Indoxyl sulfate-exposed mice with microalbuminuria showed ischemic changes, while more severely affected mice showed increased mesangial matrix, segmental solidification, and mesangiolysis. In normal mouse kidneys, AhR was predominantly localized to the podocyte nuclei. In mice exposed to indoxyl sulfate for 2 h, isolated glomeruli manifested increased Cyp1a1 expression, indicating AhR activation. After 8 w of indoxyl sulfate, podocytes showed foot process effacement, cytoplasmic vacuoles, and a focal granular and wrinkled pattern of podocin and synaptopodin expression. Furthermore, vimentin and AhR expression in the glomerulus was increased in the indoxyl sulfate-exposed glomeruli compared to controls. Glomerular expression of characteristic podocyte mRNAs was decreased, including Actn4, Cd2ap, Myh9, Nphs1, Nphs2, Podxl, Synpo, and Wt1. In vitro, immortalized-mouse podocytes exhibited AhR nuclear translocation beginning 30 min after 1 mM indoxyl sulfate exposure, and there was increased phospho-Rac1/Cdc42 at 2 h. After exposure to indoxyl sulfate for 24 h, mouse podocytes exhibited a pro-inflammatory phenotype, perturbed actin cytoskeleton, decreased expression of podocyte-specific genes, and decreased cell viability. In immortalized human podocytes, indoxyl sulfate treatment caused cell injury, decreased mRNA expression of podocyte-specific proteins, as well as integrins, collagens, cytoskeletal proteins, and bone morphogenetic proteins, and increased cytokine and chemokine expression. We propose that basal levels of AhR activity regulate podocyte function under normal conditions, and that increased activation of podocyte AhR by indoxyl sulfate contributes to progressive glomerular injury.
authors.affiliation: Laboratory of Anatomy, Department of Biomedical Sciences, Graduate School of Veterinary Medicine, Hokkaido University, Hokkaido, Japan; Kidney Disease Section, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland, United States of America.
authors.forename: Osamu
authors.initials: O
authors.lastname: Ichii
authors.affiliation: Laboratory of Anatomy, Department of Biomedical Sciences, Graduate School of Veterinary Medicine, Hokkaido University, Hokkaido, Japan.
authors.forename: Saori
authors.initials: S
authors.lastname: Otsuka-Kanazawa
authors.affiliation: Laboratory of Anatomy, Department of Biomedical Sciences, Graduate School of Veterinary Medicine, Hokkaido University, Hokkaido, Japan; Section of Biological Safety Research, Chitose Laboratory, Japan Food Research Laboratories, Chitose, Japan.
authors.forename: Teppei
authors.initials: T
authors.lastname: Nakamura
authors.affiliation: Section of Biological Safety Research, Chitose Laboratory, Japan Food Research Laboratories, Chitose, Japan.
authors.forename: Masaaki
authors.initials: M
authors.lastname: Ueno
authors.affiliation: Laboratory of Anatomy, Department of Biomedical Sciences, Graduate School of Veterinary Medicine, Hokkaido University, Hokkaido, Japan.
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Kon
authors.affiliation: Microarray Core Facility, National Institute of Diabetes, Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland, United States of America.
authors.forename: Weiping
authors.initials: W
authors.lastname: Chen
authors.affiliation: Laboratory of Pathology, National Cancer Institute, National Institutes of Health, Bethesda, Maryland, United States of America.
authors.forename: Avi Z
authors.initials: AZ
authors.lastname: Rosenberg
authors.affiliation: Kidney Disease Section, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland, United States of America.
authors.forename: Jeffrey B
authors.initials: JB
authors.lastname: Kopp
mesh_terms: D000818:Animals; D007200:Indican / Q000378:metabolism / Q000633:toxicity*; D007668:Kidney / Q000098:blood supply / Q000187:drug effects; D008024:Ligands; D051379:Mice; D008810:Mice, Inbred C57BL; D050199:Podocytes / Q000187:drug effects*; D018336:Receptors, Aryl Hydrocarbon / Q000378:metabolism*
chemical_list: D008024:Ligands; D018336:Receptors, Aryl Hydrocarbon; D007200:Indican