Effect of exercise on kidney function, oxidative stress, and inflammation in type 2 diabetic KK-A(y) mice

Abstract

Exercise is recommended for the management of type 2 diabetes, but its effects on diabetic nephropathy (DN) are still unknown. We hypothesized that appropriate exercise improves early DN via attenuation of inflammation and oxidative damage. Type 2 diabetic KK-A(y) mice, a spontaneous DN model, underwent two different kinds of exercise (i.e., moderate and low intensity). Sedentary mice or those undergoing an exercise regimen causing no significant body weight loss were used. We examined the urinary excretion of albumin, number of podocytes and macrophages, renal expressions of HIF-1α and MCP-1, and biomarkers of oxidative stress such as urinary 8-OHdG and serum SOD. Exercise reduced urinary levels of albumin and also maintained the number of podocytes in the exercised KK-A(y) mice independently of improvements of overweight and hyperglycemia, although moderate-intensity exercise increased expression of HIF-1α. Sedentary KK-A(y) mice showed increased expression of MCP-1 and infiltration of macrophage, increased urinary 8-OhdG, and decreased serum SOD levels compared with exercised KK-A(y) mice. On the whole, low-intensity exercise attenuates progression of early DN without affecting marked renal ischemia. Reduction rates of urinary albumin and maintained podocyte numbers, with parallel improvements in oxidative damage and inflammation, are related to beneficial effects of exercise in diabetic kidney disease.

Figure 1

Change rate of urinary albumin from 12 to 20 weeks in KK-A ^y mice. Change rate of urinary albumin at 20 weeks of age divided by that at 12 weeks of age. Low-intensity exercised KK-A ^y mice had greater change rate of urinary albumin compared with sedentary mice. *P < 0.05.

Figure 2

HIF-1α staining intensity and staining in KK-A ^y mice with and without exercise at 20 weeks of age. HIF-1α staining intensity in moderate-intensity exercised KK-A ^y mice was significantly enhanced compared with that in the sedentary KK-A ^y mice, but these levels did not differ between sedentary and low-intensity exercised KK-A ^y mice. *P < 0.001. Representative HIF-1α staining in the renal cortex of sedentary KK (b, g), sedentary KK-A ^y (c, h), low-intensity exercised KK-A ^y (d, i), and moderate-intensity exercised KK-A ^y mice. (e, j) Staining (a, f) depicts the absence of primary antibody. Images (a–e) were taken at 40-fold magnification and images (f–j) were taken at 400-fold magnification. *P < 0.001.

Figure 3

Number of MCP-1 positive cells and staining in each mouse at 20 weeks of age. The number of MCP-1 positive cells in sedentary KK-A ^y mice was significantly greater compared with that in the exercised KK-A ^y mice and also sedentary KK mice. Representative MCP-1 staining in the renal cortex of sedentary KK (b), sedentary KK-A ^y (c), low-intensity exercised KK-A ^y (d), and moderate-intensity exercised KK-A ^y mice. (e) Staining (a) depicts the absence of primary antibody. Images were taken at 100-fold magnification. *P < 0.05^† P < 0.001.

Figure 4

Number of CD68 and CD204 positive cells and staining in each mouse at 20 weeks of age. Bar charts show CD68 and CD204 positive cells in the glomeruli and tubulointerstitial area of sedentary KK (b), sedentary KK-A ^y (c), low-intensity exercised KK-A ^y (d), and moderate-intensity exercised KK-A ^y mice. (e) The number of CD68 positive cells in glomeruli of sedentary KK-A ^y mice were significantly greater compared with that of sedentary KK mice, but it did not differ between sedentary and exercised KK-A ^y mice. The number of CD68 positive cells in glomeruli of sedentary KK-A ^y mice was significantly greater compared with that of sedentary KK mice and also low-intensity exercised KK-A ^y mice, but not moderate-intensity exercised KK-A ^y mice. The number of CD68 positive cells in the tubulointerstitial area of sedentary KK-A ^y mice was significantly greater compared with that of sedentary KK mice and also exercised KK-A ^y mice, but it did not differ between low- and moderate-intensity exercised KK-A ^y mice. The number of CD204 positive cells in tubulointerstitial area of sedentary KK-A ^y mice was significantly greater compared with that of sedentary KK mice, but it did not differ between sedentary and exercised KK-A ^y mice. *P < 0.05 ^† P < 0.01 ^‡ P < 0.001.

Figure 5

Renal expression of MCP-1 mRNA in the kidney at 20 weeks of age. The level of MCP-1 mRNA l in the sedentary KK-A ^y mice was significantly higher than that in exercised KK-A ^y mice and also sedentary KK mice. *P < 0.05 ^† P < 0.01.

Figure 6

Number of WT-1 positive cells and staining in each mouse at 20 weeks of age. WT-1 positive cells in exercised KK-A ^y mice were significantly maintained compared with those in the sedentary KK-A ^y mice and approached to those in KK mice. *P < 0.01 ^† P < 0.001. Representative WT-1 staining in the renal cortex of sedentary KK (a), sedentary KK-A ^y (b), low-intensity exercised KK-A ^y (c), and moderate-intensity exercised KK-A ^y mice. (d) Images were taken at 400-fold magnification.