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.

RIVELLI JF; AMAIDEN MR; MONESTEROLO NE; PREVITALI G; SANTANDER VS; FERNANDEZ A; ARCE CA; CASALE CH

INTERNATIONAL JOURNAL OF BIOCHEMISTRY AND CELLULAR BIOLOGY

PERGAMON-ELSEVIER SCIENCE LTD

Lugar: Amsterdam; Año: 2012 vol. 44 p. 1203 - 1213

1357-2725

Our previous studies demonstrated that acetylated tubulin forms a complex with Na+,K+-ATPase andthereby inhibits its enzyme activity in cultured COS and CAD cells. The enzyme activity was restored bytreatment of cells with l-glutamate, which caused dissociation of the acetylated tubulin/Na+,K+-ATPasecomplex. Addition of glucose, but not elimination of glutamate, led to re-formation of the complex andinhibition of the Na+,K+-ATPase activity. The purpose of the present study was to elucidate the mechanismunderlying this effect of glucose. We found that exposure of cells to high glucose concentrationsinduced: (a) microtubule formation; (b) activation of aldose reductase by the microtubules; (c) associationof tubulin with membrane; (d) formation of the acetylated tubulin/Na+,K+-ATPase complex andconsequent inhibition of enzyme activity. Exposure of cells to sorbitol caused similar effects. Studies onerythrocytes from diabetic patients and on tissues containing insulin-insensitive glucose transportersgave similar results. Na+,K+-ATPase activity was >50% lower and membrane-associated tubulin contentwas >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 withNa+,K+-ATPase in erythrocyte membranes from diabetic patients. Based on these findings, we propose amechanism whereby glucose triggers a synergistic effect of tubulin and sorbitol, leading to activation ofaldose reductase, microtubule formation, and consequent Na+,K+-ATPase inhibition.