Age-associated molecular changes in the kidney in aged mice

Abstract

Background: Aging is a multifactorial process characterized by a progressive decline in physiological function. Decreased kidney function is associated with cardiovascular disease and mortality. Therefore, increasing our insight into kidney aging by understanding the anatomic, physiologic, and pathologic changes of aging in the kidney is important to prevent disastrous outcomes in elderly people.

Methods: Male two-, 12-, and 24-month-old C57/BL6 mice were used in this study. We measured histological change, oxidative stress, and aging-related protein expression in the kidneys.

Results: Twenty-four-month-old mice displayed increased albuminuria. Creatinine clearance decreased with aging, although this was not statistically significant. There were increases in mesangial volume and tubulointerstitial fibrosis in 24-month-old mice. There were also increases in F4/80 expression and in apoptosis detected by TUNEL assay. Urine isoprostane excretion increased with aging and SOD1 and SOD2 were decreased in 24-month-old mice. Oxidative stress may be mediated by a decrease in Sirt1, PGC-1α, ERR-1α, and PPARα expression. Klotho expression also decreased.

Conclusions: Our results demonstrate that Sirt1 was decreased with aging and may relate to changed target molecules including PGC-1α/ERR-1α signaling and PPARα. Klotho can also induce oxidative stress. Pharmacologically targeting these signaling molecules may reduce the pathologic changes of aging in the kidney.

Figure 1

Increased renal damage in aged mice. The 24 M group displayed higher 24 h albuminuria than other groups ((a) 16.5 ± 1.1 versus 41.5 ± 8.4, 65.5 ± 10.4; *P < 0.05 versus 2 M). Serum creatinine was increased in the 24 M group compared with the other groups ((b) 0.21 ± 0.008 versus 0.12 ± 0.009, 0.68 ± 0.15). Creatinine clearance was decreased in the 24 M group compared with the 12 M group ((c) 0.13 ± 0.004 versus 0.39 ± 0.04, 0.21 ± 0.05; *P < 0.05 versus 2 M). Values are shown as mean ± SE.

Figure 2

Renal histopathology of the glomerulus and tubulointerstitial areas. Representative images of PAS ((a) original magnification 400×) and Trichrome stain ((b) original magnification 200×) from renal tissue as indicated. Quantitative assessment of the areas of extracellular matrix in the glomerulus (c) and the tubulointerstitial fibrosis (d) from indicated groups. There was increased mesangial area expansion in the 24 M group compared with other groups (10.1 ± 1.19% versus 17.2 ± 2%, 36.3 ± 3.58%; **P < 0.01 versus 2 M), and significantly increased tubulointerstitial fibrosis in the 24 M group compared with other groups. (0.83 ± 0.11% versus 0.87 ± 0.07%, 15.9 ± 1.99%; **P < 0.01 versus 2 M). Values are shown as mean ± SE.

Figure 3

Immunohistochemistry for F4/80. Result of staining for F4/80-positive cells and quantitative analyses in the 2 M, 12 M, and 24 M groups ((a), original magnification 400×). There was a marked increase in the 24 M group compared with other groups (0.11 ± 0.06% versus 0.4 ± 0.11%, 2.5 ± 0.52%; **P < 0.01 versus 2 M). Values are shown as mean ± SE.

Figure 4

Increase in apoptotic cells in the glomerulus and tubules of the kidneys from the 24 M group. Representative pictures of TUNEL-positive mesangial cells ((a) original magnification 400×) in the glomerulus and cortical tubular areas for all the study groups. Quantitative analyses of the results are shown ((b) 0.27 ± 0.09% versus 0.53 ± 0.12%, 2.6 ± 0.63%; (c) 0.27 ± 0.09% versus 0.53 ± 0.12%, 2.8 ± 0.67%; **P < 0.01 versus 2 M). Values are shown as mean ± SE.

Figure 5

Intrarenal 24-h urinary 8-epi-prostaglandin F2α (isoprostane) concentrations in all the study groups. Quantitative analyses of the results are shown (7.4 ± 0.3% versus 19.4 ± 0.78%, 21.9 ± 1.9%; *P < 0.05 versus 2 M, **P < 0.01 versus 2 M). Values are shown as mean ± SE.

Figure 6

Representative Western blots of SOD1 and SOD2. Representative blots from the kidney are shown (a). The expression of SOD1 and SOD2 were decreased in the 24 M group compared with 2 M group and lower than 12 M group. Quantitative analyses of the results are shown (b, c). *P < 0.05 versus 2 M, **P < 0.01 versus 2 M.

Figure 7

Representative Western blots of SIRT1, PGC-1α, and ERR-1α. Representative blots from the kidney are shown. (a) Western blot analysis showed that aging markedly decreased SIRT1, PGC-1α, and ERR-1α protein levels in the 24 M group compared with other groups. Quantitative analyses of the results are shown (b–d). *P < 0.05 versus 2 M, **P < 0.01 versus 2 M.

Figure 8

Representative Western blots of PPARα and Klotho. Representative blots from the kidney are shown. (a) Western blot analysis showed that aging decreased PPARα and Klotho expression in the 24 M group compared with other groups. Quantitative analyses of the results are shown (b, c). **P < 0.01 versus 2 M.