Upregulation and intrarenal redistribution of heat shock proteins 90α and 90β by low-sodium diet in the rat

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Abstract
Two genes encoding isoforms heat shock protein (Hsp) 90alpha and Hsp90beta constitute the Hsp90 subfamily. In addition to their role in regulating mineralocorticoid and glucocorticoid receptors, these proteins have been associated with nitric oxide production. However, little is known regarding Hsp90 isoform expression and regulation in kidney. In this study we characterized the expression and localization of Hsp90 isoforms and evaluated the influence of low-sodium intake on their expression and distribution in kidney by using reverse transcription-polymerase chain reaction, Western blot, and immunohistochemistry techniques. We found that Hsp90alpha and Hsp90beta were expressed abundantly in both the renal cortex and the medulla; however, Hsp90 isoform expression was higher in the medulla than in the cortex. Immunohistochemistry of Hsp90alpha and Hsp90beta showed intense staining in the apical membrane of proximal and distal tubules. In the outer cortex these proteins were localized intracytosolically, whereas in the inner renal medulla they were restricted mainly to the basolateral membrane. Expression of Hsp9alpha and Hsp90beta was upregulated in the renal cortex during sodium restriction. In addition, both proteins exhibited redistribution from the cytoplasm to the basolateral side in thick ascending limb cells when rats were fed with a low-salt diet. Our results showed that Hsp90alpha and Hsp90beta were expressed abundantly in renal tissue. Expression and localization patterns under normal and salt-restricted intake were different between the cortex and the medulla, suggesting that these proteins may be involved in different processes along the nephron. Hsp90alpha and Hsp90beta upregulation induced by a low-sodium diet together with redistribution in thick ascending limb cells suggests that Hsp90 plays a role in the modulation of sodium reabsorption under these circumstances.