title: High glucose levels induce inhibition of Na,K-ATPase via stimulation of aldose reductase, formation of microtubules and formation of an acetylated tubulin/Na,K-ATPase complex.
abstract: Our previous studies demonstrated that acetylated tubulin forms a complex with Na(+),K(+)-ATPase and thereby inhibits its enzyme activity in cultured COS and CAD cells. The enzyme activity was restored by treatment of cells with l-glutamate, which caused dissociation of the acetylated tubulin/Na(+),K(+)-ATPase complex. Addition of glucose, but not elimination of glutamate, led to re-formation of the complex and inhibition of the Na(+),K(+)-ATPase activity. The purpose of the present study was to elucidate the mechanism underlying this effect of glucose. We found that exposure of cells to high glucose concentrations induced: (a) microtubule formation; (b) activation of aldose reductase by the microtubules; (c) association of tubulin with membrane; (d) formation of the acetylated tubulin/Na(+),K(+)-ATPase complex and consequent inhibition of enzyme activity. Exposure of cells to sorbitol caused similar effects. Studies on erythrocytes from diabetic patients and on tissues containing insulin-insensitive glucose transporters gave similar results. Na(+),K(+)-ATPase activity was >50% lower and membrane-associated tubulin content was >200% higher in erythrocyte membranes from diabetic patients as compared with normal subjects. Immunoprecipitation analysis showed that acetylated tubulin was a constituent of a complex with Na(+),K(+)-ATPase in erythrocyte membranes from diabetic patients. Based on these findings, we propose a mechanism whereby glucose triggers a synergistic effect of tubulin and sorbitol, leading to activation of aldose reductase, microtubule formation, and consequent Na(+),K(+)-ATPase inhibition.
authors.affiliation: Departamento de Biología Molecular, Facultad de Ciencias Exactas, Físico-Químicas y Naturales, Universidad Nacional de Río Cuarto, Río Cuarto, 5800 Córdoba, Argentina.
authors.forename: Juan F
authors.initials: JF
authors.lastname: Rivelli
authors.forename: Marina R
authors.initials: MR
authors.lastname: Amaiden
authors.forename: Noelia E
authors.initials: NE
authors.lastname: Monesterolo
authors.forename: Gabriela
authors.initials: G
authors.lastname: Previtali
authors.forename: Verónica S
authors.initials: VS
authors.lastname: Santander
authors.forename: Adriana
authors.initials: A
authors.lastname: Fernandez
authors.forename: Carlos A
authors.initials: CA
authors.lastname: Arce
authors.forename: Cesar H
authors.initials: CH
authors.lastname: Casale
mesh_terms: D000107:Acetylation; D000328:Adult; D000449:Aldehyde Reductase / Q000378:metabolism*; D000818:Animals; D001921:Brain / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D019556:COS Cells; D045744:Cell Line, Tumor; D002522:Chlorocebus aethiops; D003920:Diabetes Mellitus / Q000201:enzymology / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004910:Erythrocyte Membrane / Q000187:drug effects / Q000378:metabolism; D005260:Female; D005947:Glucose / Q000494:pharmacology*; D006801:Humans; D015151:Immunoblotting; D008297:Male; D018613:Microscopy, Confocal; D008870:Microtubules / Q000378:metabolism*; D008875:Middle Aged; D011485:Protein Binding / Q000187:drug effects; D051381:Rats; D017208:Rats, Wistar; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D013012:Sorbitol / Q000494:pharmacology; D014404:Tubulin / Q000378:metabolism* / Q000494:pharmacology
chemical_list: D014404:Tubulin; D013012:Sorbitol; D000449:Aldehyde Reductase; D000254:Sodium-Potassium-Exchanging ATPase; D005947:Glucose