Dietary methionine restriction enhances metabolic flexibility and increases uncoupled respiration in both fed and fasted states

Abstract

Dietary methionine restriction (MR) is a mimetic of chronic dietary restriction (DR) in the sense that MR increases rodent longevity, but without food restriction. We report here that MR also persistently increases total energy expenditure (EE) and limits fat deposition despite increasing weight-specific food consumption. In Fischer 344 (F344) rats consuming control or MR diets for 3, 9, and 20 mo, mean EE was 1.5-fold higher in MR vs. control rats, primarily due to higher EE during the night at all ages. The day-to-night transition produced a twofold higher heat increment of feeding (3.0 degrees C vs. 1.5 degrees C) in MR vs. controls and an exaggerated increase in respiratory quotient (RQ) to values greater than 1, indicative of the interconversion of glucose to lipid by de novo lipogenesis. The simultaneous inhibition of glucose utilization and shift to fat oxidation during the day was also more complete in MR (RQ approximately 0.75) vs. controls (RQ approximately 0.85). Dietary MR produced a rapid and persistent increase in uncoupling protein 1 expression in brown (BAT) and white adipose tissue (WAT) in conjunction with decreased leptin and increased adiponectin levels in serum, suggesting that remodeling of the metabolic and endocrine function of adipose tissue may have an important role in the overall increase in EE. We conclude that the hyperphagic response to dietary MR is matched to a coordinated increase in uncoupled respiration, suggesting the engagement of a nutrient-sensing mechanism, which compensates for limited methionine through integrated effects on energy homeostasis.

Fig. 1.

Postweaning responses of male Fischer 344 rats to dietary methionine restriction (MR) or 40% dietary restriction (DR). At 32 days of age, rats were randomly assigned to groups that would receive a control diet containing 0.86% methionine (control group), a diet with methionine restricted to 0.17% (MR), or a DR group that would receive the control diet at 60% of the consumption of the control group. Energy intake (A), body weight (B), relative adiposity (white adipose tissue, WAT) (C), and brown adipose tissue (BAT) UCP1 mRNA (F) were measured in separate cohorts of 8 rats per treatment per time point after 2, 4, and 8 wk on the respective diets. Plasma leptin and adiponectin (D) were measured in samples from the 8-wk time point, as were the mRNA levels for leptin, adiponectin, and UCP1 in the WAT and BAT tissues collected after 8 wk (E). EWAT, epididymal white adipose tissue; IWAT, inguinal white adipose tissue; RPWAT, retroperitoneal white adipose tissue. Response variables were analyzed by ANOVA. ^a,b,cMeans at each time point with letters that differ denote P < 0.05. E: *P < 0.05, significant difference for each gene and tissue compared with control group.

Fig. 2.

Energy expenditure (EE; A), respiratory quotient (B), and fat deposition (C) in male Fischer 344 rats after dietary methionine restriction (MR) or 40% dietary restriction (DR) for 3 mo. At 32 days of age, 8 rats per group were provided a control diet containing 0.86% methionine (control group), a diet with methionine restricted to 0.17% (MR), or the control diet restricted to 60% of the consumption of the control group. The rats were adapted to the calorimetry chambers for 24 h prior to measurement of O₂ consumption and CO₂ production at 45-min intervals for the following 3 days. Thereafter, fat pads were dissected and weighed, and EE and respiratory quotient were calculated as described in materials and methods. Average EE was calculated for each animal in each group for the period when lights were on (7 AM–7 PM), when lights were off (7 PM–7 AM), and averaged over both periods to assess total daily EE. FFM, fat-free mass; BW, body weight. These 3 variables and total fat pad weights were compared by ANOVA. ^a,b,cMeans with letters that differ denote P < 0.05.

Fig. 3.

Postweaning growth (A) and energy intake (B) of male Fischer 344 rats provided a control or methionine-restricted diet. At 32 days of age, rats were randomly assigned to receive a control diet containing 0.86% methionine (control group) or a diet with methionine restricted to 0.17% (MR). The diets were provided ad libitum, and cohorts (8–10 rats/cohort) of each group consumed their respective diets for 9 or 20 mo after weaning. Body weights were determined weekly, and food consumption was measured every other week.

Fig. 4.

Diurnal changes in energy expenditure, respiratory quotient, and UCP1 expression in BAT from male Fischer 344 rats consuming a control or methionine-restricted diet (MR) for 9 (4, A and B) or 20 mo (4, C and D). At 32 days of age, rats were randomly assigned to receive a control diet containing 0.86% methionine (control group) or a diet with methionine restricted to 0.17% (MR). The diets were provided ad libitum, and cohorts (8–10 rats/cohort) of each group consumed their respective diets for 9 or 20 mo after weaning. After 9 and 20 mo, rats from the respective control and MR cohorts were adapted to the calorimetry chambers for 24 h prior to measurement of O₂ consumption and CO₂ production at 30-min intervals for the following 3 days. Thereafter, body composition of each rat was determined by DEXA scanning as described in materials and methods and used to express EE per unit of fat-free mass. Average EE was calculated for each animal in each group for the period when lights were on (7 AM–7 PM), when lights were off (7 PM–7 AM), and averaged over both periods to assess total daily EE. The means were compared by ANOVA at each age (Table 1). UCP1 mRNA (E) and protein expression (F) were measured in BAT after 3 (experiment 2), 9, and 20 mo on the respective diets. The responses were compared by ANOVA. ^a,bMeans at each time point with letters that differ denote P < 0.05.

Fig. 5.

Energy intake (A), growth (B), fat deposition (C), and metabolic responses (D and E) of adult Fischer 344 rats to dietary methionine restriction. At 6 mo of age, rats were randomly assigned to receive a control diet containing 0.86% methionine (control group) or a diet with methionine restricted to 0.17% (MR). The diets were provided ad libitum. Food consumption, body weight, and body composition were measured weekly for the subsequent 26 wk. Thereafter, rats were adapted to the calorimetry chambers for 24 h prior to measurement of O₂ consumption and CO₂ production at 45-min intervals for the following 4 days. Body composition was determined by NMR using a Bruker Minispec and used to express energy expenditure per unit of fat-free mass as described in materials and methods. Average EE and RQ were calculated for each animal in each group for the period when lights were on (7 AM–7 PM), when lights were off (7 PM–7 AM), and averaged over both periods to assess total daily EE. Energy intake, body weight, adiposity, EE, and RQ were compared by one-way ANOVA at each time point as described in materials and methods. ^a,bLetters that differ denote P < 0.05.

Fig. 6.

Postweaning energy intake (A), growth (B), and adiposity (C) of male Osborne-Mendel rats weaned to a high-fat (60 kcal %), methionine-restricted diet. At 32 days of age, rats were randomly assigned to receive a high-fat (60 kcal %) control diet containing 0.86% methionine (control group) or the same high-fat diet with methionine restricted to 0.17% (MR). The composition of the formulated diets is described in the materials and methods, and the diets were provided ad libitum. Food consumption and body weight were measured at weekly intervals, and body composition was determined by DEXA scanning after 8, 16, and 28 wk on the respective diets. The variables were compared by one-way ANOVA at each time point. ^a,bMeans at each time point with letters that differ denote P < 0.05.