We aimed to determine whether epidermal growth factor receptor (EGFR) inhibition, in addition to a peroxisome proliferator-activated receptor gamma (PPARγ) agonist, prevents high-glucose-induced proximal tubular fibrosis, inflammation, and sodium and water retention in human proximal tubule cells exposed to normal glucose; high glucose; high glucose with the PPARγ agonist pioglitazone or with the P-EGFR inhibitor, gefitinib; or high glucose with both pioglitazone and gefitinib. We have shown that high glucose increases AP-1 and NFκB binding activity, downstream phosphorylation of EGFR and Erk1/2, and fibronectin and collagen IV expression. Pioglitazone reversed these effects but upregulated NHE3 and AQP1 expression. Gefitinib inhibited high glucose induced fibronectin and collagen IV, and EGFR and Erk1/2 phosphorylation and reversed pioglitazone-induced increases in NHE3 and AQP1 expression. Our data suggests that combination of an EGFR inhibitor and a PPARγ agonist mitigates high-glucose-induced fibrosis and inflammation and reverses the upregulation of transporters and channels involved in sodium and water retention in human proximal tubule cells. Hence EGFR blockade may hold promise, not only in limiting tubulointerstitial pathology in diabetic nephropathy, but also in limiting the sodium and water retention observed in patients with diabetes and exacerbated by PPARγ agonists. 1. Introduction Cellular sodium and water transport are dysregulated in diabetes mellitus resulting in volume-mediated hypertension and cardiac complications. We have previously demonstrated that epidermal growth factor (EGF) and high-glucose-induced sodium reabsorption in proximal tubule cells by increasing the activity of the sodium hydrogen exchanger-3 (NHE3). This is dependent on EGFR signalling and downstream activation of serum and glucocorticoid-inducible kinase (Sgk-1) [1]. Enhanced expression and/or activity of the EGF receptor (EGFR) has previously been observed in the kidneys of diabetic animals [2] and tubular EGFR expression correlates with the extent of interstitial fibrosis [3]. Furthermore, the EGFR is activated/transactivated by multiple factors inherent in the diabetic milieu, including high glucose [4], angiotensin II (AngII) [5], and aldosterone [6], all of which have been implicated in the pathogenesis of diabetic nephropathy. Recent studies have supported the hypothesis that inhibition of the EGFR provides an attractive therapeutic target for the treatment of diabetic nephropathy [7]. Thiazolidinediones (TZDs) are synthetic peroxisome
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