title: Constitutive activation of the mTOR signaling pathway within the normal glomerulus.
abstract: Agents that target the activity of the mammalian target of rapamycin (mTOR) kinase in humans are associated with proteinuria. However, the mechanisms underlying mTOR activity and signaling within the kidney are poorly understood. In this study, we developed a sensitive immunofluorescence technique for the evaluation of activated pmTOR and its associated signals in situ. While we find that pmTOR is rarely expressed in normal non-renal tissues, we consistently find intense expression in glomeruli within normal mouse and human kidneys. Using double staining, we find that the expression of pmTOR co-localizes with nephrin in podocytes and expression appears minimal within other cell types in the glomerulus. In addition, we found that pmTOR was expressed on occasional renal tubular cells within mouse and human kidney specimens. We also evaluated mTOR signaling in magnetic bead-isolated glomeruli from normal mice and, by Western blot analysis, we confirmed function of the pathway in glomerular cells vs. interstitial cells. Furthermore, we found that the activity of the pathway as well as the expression of VEGF, a target of mTOR-induced signaling, were reduced within glomeruli of mice following treatment with rapamycin. Collectively, these findings demonstrate that the mTOR signaling pathway is constitutively hyperactive within podocytes. We suggest that pmTOR signaling functions to regulate glomerular homeostasis in part via the inducible expression of VEGF.
authors: The Transplantation Research Center, Division of Nephrology, Department of Medicine, Children's Hospital, and The Department of Pediatrics, Harvard Medical School, Boston, MA 02115, USA.
authors: Gearoid M
authors: GM
authors: McMahon
authors: Dipak
authors: D
authors: Datta
authors: Sarah
authors: S
authors: Bruneau
authors: Martin
authors: M
authors: Kann
authors: Myda
authors: M
authors: Khalid
authors: Jacqueline
authors: J
authors: Ho
authors: Tatsuichiro
authors: T
authors: Seto
authors: Jordan A
authors: JA
authors: Kreidberg
authors: Isaac E
authors: IE
authors: Stillman
authors: David M
authors: DM
authors: Briscoe
mesh_terms: D000818:Animals; D005455:Fluorescent Antibody Technique; D006706:Homeostasis; D006801:Humans; D007678:Kidney Glomerulus / Q000187:drug effects / Q000201:enzymology*; D000076222:Mechanistic Target of Rapamycin Complex 1; D008565:Membrane Proteins / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D046912:Multiprotein Complexes / Q000378:metabolism*; D050199:Podocytes / Q000201:enzymology; D015398:Signal Transduction; D020123:Sirolimus / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism*; D042461:Vascular Endothelial Growth Factor A / Q000096:biosynthesis
chemical_list: D008565:Membrane Proteins; D046912:Multiprotein Complexes; D042461:Vascular Endothelial Growth Factor A; C113267:nephrin; D000076222:Mechanistic Target of Rapamycin Complex 1; D058570:TOR Serine-Threonine Kinases; D020123:Sirolimus