A high salt diet induces tubular damage associated with a pro-inflammatory and pro-fibrotic response in a hypertension-independent manner

Abstract

High salt diet (HSD), considered a public health problem worldwide, is associated with chronic degenerative diseases including renal diseases. However, little is known about the effects of HSD on renal function independently of the development of hypertension. To address the hypothesis that HSD induces renal injuries even without changes in blood pressure, BALB/c mice were fed for 7 days with chow with a high salt content (0.3–8%). Blood pressure did not change and there was a decrease in cortical (Na+ + K+)ATPase and NHE3 exchanger and an increase in renal fractional excretion of sodium. Positive correlations between Na+ intake or urinary sodium excretion with proteinuria were found. HSD did not change glomerular function and structure, but induced tubule-interstitial injury measured by an increase in collagen deposition, interstitial space and γ-GT activity, a marker of tubular injury. These effects were associated with a decrease in cortical albumin reabsorption and megalin expression. Similarly, the addition of NaCl 20 mM to the incubation medium of LLC-PK1 cells reduced megalin expression and albumin endocytosis indicating that HSD could have a direct effect on proximal tubule cells. Furthermore, tubule-interstitial injury was associated with pro-inflammatory and pro-fibrotic phenotypes with an increase in Th1 and Th17 phenotypes and a decrease in Tregs followed by increases in IL-6, -17, -10, TNF-α, IFN-γ and TGF-β. Our results reveal a complex network involved in renal injuries induced by HSD independently of changes in blood pressure. These findings strengthen the importance of restriction of salt intake for the general population even for salt-resistant individuals.