Corticosterone and Glucocorticoid Receptor in the Cortex of Rats during Aging-The Effects of Long-Term Food Restriction

Abstract

Numerous beneficial effects of food restriction on aging and age-related pathologies are well documented. It is also well-established that both short- and long-term food restriction regimens induce elevated circulating levels of glucocorticoids, stress-induced hormones produced by adrenal glands that can also exert deleterious effects on the brain. In the present study, we examined the effect of long-term food restriction on the glucocorticoid hormone/glucocorticoid receptor (GR) system in the cortex during aging, in 18- and 24-month-old rats. Corticosterone level was increased in the cortex of aged ad libitum-fed rats. Food restriction induced its further increase, accompanied with an increase in the level of 11β-hydroxysteroid dehydrogenase type 1. However, alterations in the level of GR phosphorylated at Ser²³² were not detected in animals on food restriction, in line with unaltered CDK5 level, the decrease of Hsp90, and an increase in a negative regulator of GR function, FKBP51. Moreover, our data revealed that reduced food intake prevented age-related increase in the levels of NFκB, gfap, and bax, confirming its anti-inflammatory and anti-apoptotic effects. Along with an increase in the levels of c-fos, our study provides additional evidences that food restriction affects cortical responsiveness to glucocorticoids during aging.

Keywords: 11β-HSD1; GRα isoforms; c-fos; food restriction; glucocorticoids; intermittent fasting.

Figure 1

The effect of food restriction on corticosterone and 11β-hydroxysteroid dehydrogenase 1 (11β-HSD1) levels in the rat cortex during aging. Basal tissue corticosterone concentration (A), relative 11β-HSD1 protein level (B), and 11β-HSD1 mRNA level (C) were determined in rats fed ad libitum (AL) (gray bars) or subjected to food restriction (FR) (black bars). Relative 11β-HSD1 protein and mRNA levels are presented as the mean ± SEM of fold changes relative to the values obtained in control, 6-month-old AL animals (n = 6). * p < 0.05 vs. 6-month-old rats; # p < 0.05 vs. age-matched AL rats.

Figure 2

The effect of food restriction on the levels of glucocorticoid and mineralocorticoid receptors in the rat cortex during aging. (A) Representative blot with full-length glucocorticoid receptor protein and shorter GRα protein isoforms (molecular weights indicated). Relative protein levels of the full-length glucocorticoid receptor (B), 70 kDa, 40 kDa, and 25 kDa GR isoforms additionally normalized to the values obtained in control (Ctrl.), 6-month-old animals presented as the line (C), GR mRNA (D), mineralocorticoid receptor (MR) mRNA (E), and GR phosphorylated at Ser²³² (pGR) (F) were determined in rats fed ad libitum (AL) (gray bars) or subjected to food restriction (FR) (black bars). (G) The level of GR phosphorylated at Ser²³² relative to the level of total GR. Data are presented as the mean ± SEM of fold changes relative to the values obtained in control, 6-month-old AL animals (n = 6). * p < 0.05 vs. 6-month-old rats; # p < 0.05 vs. age-matched AL rats.

Figure 3

The effect of food restriction on the levels of cyclin-dependent kinase 5 (CDK5), its activator, p35, Hsp90, and FKBP51 levels in the rat cortex during aging. Relative protein levels of the CDK5 (A), p35 (B), Hsp90 (C), and FKBP51 (D) were determined by Western blot analysis in rats fed ad libitum (AL) (gray bars) or subjected to food restriction (FR) (black bars). Data are presented as the mean ± SEM of fold changes relative to the values obtained in control, 6-month-old AL animals (n = 6). * p < 0.05 vs. 6-month-old rats; # p < 0.05 vs. age-matched AL rats.

Figure 4

The effect of food restriction on the neuronal inflammation and activity in the rat cortex during aging. The levels of gfap (A), bax (B), sgk-1 (E) and c-fos mRNAs (F) were determined by quantitative RT-PCR, while relative protein levels of ERK (C) and pERK (D) were determined by Western blot, in rats fed ad libitum (AL) (gray bars) or subjected to food restriction (FR) (black bars). Data are presented as the mean ± SEM of fold changes relative to the values obtained in control, 6-month-old AL animals (n = 6). * p < 0.05 vs. 6-month-old rats; # p < 0.05 vs. age-matched AL rats.

Figure 5

The effect of food restriction on the nuclear factor-kappa B (NFκB) abundance in the rat cortex during aging. Relative NFκB protein levels in the cytoplasmic fraction (A) and nuclear fraction (B) were determined in rats fed ad libitum (AL) (gray bars) or subjected to food restriction (FR) (black bars). Data are presented as the mean ± SEM of fold changes relative to the values obtained in control, 6-month-old AL animals (n = 6). * p < 0.05 vs. 6-month-old rats; # p < 0.05 vs. age-matched AL rats.