Effect of high salt diet on the renal medullary cyclooxygenase 2 expression / 中华肾脏病杂志

ABSTRACT

Objective To examine the effect and mechanism of high salt diet on the renal medullary cyclooxygenase 2 (COX2) expression and urinary sodium excretion. Methods Thirty male C57BL/6j mice were divided into four groups (1) normal salt diet group (0.4％NaCl, n=5); (2) high salt diet group (8％NaCl, n=5);(3) Bortezomib+normal salt diet group (n=10);(4) Bortezomib+high salt diet group (n=10). The different groups were pre-treated with saline or bortezomib ,followed by normal salt diet or high salt diet for three days. All the mice were maintained on metabolic cage at the last day and allowed free access to water. Twenty-four hours urine was collected. Body weight, urine volumes were documented. At the end of experiments, mice were sacrificed under anesthesia and the kidneys were harvested for Western blotting and immunohistochemistry. The transgenic mice carrying a luciferase reporter driven by an NF-κB response promoter, HIV long terminal repeat (LTR) (HLL mice) were used to explore the effect of high salt diet on renal medullary NF-κB activity. HLL mice were fed with normal salt diet or high salt diet for 3 days, after which renal medullary luciferase activity was determined using a commercial luciferase assay kit. Luciferase activity was quantified with a luminometer and adjusted for the total amount of proteins. The cellular location of NF-κB was examined using immunohistochemistry of NF-κB p65 staining. Results (1) Western blotting results showed high salt diet significantly increased the COX2 expression in the renal medulla of C57BL/6j mice (P﹤0.05). (2) High salt diet significantly increased NF-κB luciferase reporter activity in the HLL mice renal medullary tissues when compared to normal salt diet (P﹤0.05). The immunohistochemistry of NF-κB p65 showed the expression of NF-κB was mainly in the renal interstitial cells. (3) Western blotting results showed bortezomib inhibited the renal medullar COX2 expression induced by high salt diet (P﹤0.05). (4) Bortezomib decreased the urinary sodium excretion of high salt diet mice (P﹤0.05), but had no change on urine volume. Conclusions High salt diet induce renal medullary COX2 over-expression and activate the activation of NF-κB in renal medullary. Bortezmoib can inhibit the renal medullar COX2 expression induced by high salt diet. The NF-κB pathway activation may involve in the regulation of renal medullar COX2 expression by high salt diet.