title: Isoflurane via TGF-beta1 release increases caveolae formation and organizes sphingosine kinase signaling in renal proximal tubules.
abstract: We previously showed that the inhalational anesthetic isoflurane protects against renal proximal tubule necrosis via isoflurane-mediated stimulation and translocation of sphingosine kinase-1 (SK1) with subsequent synthesis of sphingosine-1-phosphate (S1P) in renal proximal tubule cells (Kim M, Kim M, Kim N, D'Agati VD, Emala CW Sr, Lee HT. Am J Physiol Renal Physiol 293: F1827-F1835, 2007). We also demonstrated that the anti-necrotic and anti-inflammatory effect of isoflurane is due in part to phosphatidylserine (PS) externalization and subsequent release of transforming growth factor-beta1 (TGF-beta1) (Lee HT, Kim M, Kim J, Kim N, Emala CW. Am J Nephrol 27: 416-424, 2007). In this study, we tested the hypothesis that isoflurane, via TGF-beta1 release, increases caveolae formation in the buoyant fraction of the cell membrane of human renal proximal tubule (HK-2) cells to organize SK1 and S1P signaling. To detect SK1 protein in the caveolae/caveolin fractions, we overexpressed human SK1 in HK-2 cells (SK1-HK-2). SK1-HK-2 cells exposed to isoflurane increased caveolae/caveolin formation in the buoyant membrane fractions which contained key signaling intermediates involved in isoflurane-mediated renal tubule protection, including S1P, SK1, ERK MAPK, and TGF-beta1 receptors. Furthermore, treating SK1-HK-2 cells with recombinant TGF-beta1 or PS liposome mixture increased caveolae formation, mimicking the effects of isoflurane. Conversely, TGF-beta1-neutralizing antibody blocked the increase in caveolae formation induced by isoflurane in SK1-HK-2 cells. The increase in SK1 activity in the caveolae-enriched fractions from isoflurane-treated nonlentivirus-infected HK-2 cells, while smaller in magnitude, was qualitatively similar to that found in the SK1-HK-2 cell line. Finally, isoflurane also increased caveolae formation in the kidneys of TGF-beta1 +/+ mice but not in TGF-beta1 +/- mice (mice with reduced levels of TGF-beta1). Our study demonstrates that isoflurane organizes several key cytoprotective signaling intermediates including TGF-beta1 receptors, SK1 and ERK, within the caveolae fraction of the plasma membrane. Our findings may help to unravel the cellular signaling pathways of volatile anesthetic-mediated renal protection and lead to new therapeutic applications of inhalational anesthetics during the perioperative period.
authors.affiliation: Department of Anesthesiology, College of Physicians and Surgeons of Columbia University, 630 West 168th St., New York, NY 10032-3784, USA.
authors.forename: Joseph H
authors.initials: JH
authors.lastname: Song
authors.forename: Mihwa
authors.initials: M
authors.lastname: Kim
authors.forename: Sang Won
authors.initials: SW
authors.lastname: Park
authors.forename: Sean W C
authors.initials: SW
authors.lastname: Chen
authors.forename: Stuart M
authors.initials: SM
authors.lastname: Pitson
authors.forename: H Thomas
authors.initials: HT
authors.lastname: Lee
mesh_terms: D000818:Animals; D021941:Caveolae / Q000502:physiology*; D015971:Gene Expression Regulation, Enzymologic; D006801:Humans; D007530:Isoflurane / Q000494:pharmacology*; D007687:Kidney Tubules, Proximal / Q000166:cytology / Q000378:metabolism*; D051379:Mice; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D053773:Transforming Growth Factor beta1 / Q000378:metabolism*; D000099157:Sphingosine Kinase
chemical_list: D007530:Isoflurane; D017853:Phosphotransferases (Alcohol Group Acceptor); D053773:Transforming Growth Factor beta1; D000099157:Sphingosine Kinase