Differences in mitochondrial efficiency between lines of mice divergently selected for heat loss1

Abstract

Divergent selection for heat loss was applied to lines of mice for 15 generations (G) in 3 replicates. Selection resumed at G42 and continued through G51 across all replicates. At the end of G51, differences in heat loss and feed intake per unit of BW were approximately 56 and 34%, respectively, between high heat loss (MH) and low heat loss (ML) lines, as a percentage of the control line (MC) mean. Rates of liver mitochondrial respiration states, degree of coupling, and mitochondrial efficiency were measured in G58 using a Clark-type oxygen electrode to investigate possible causes of underlying variation in maintenance requirements. Body composition, BW, liver weight, feed intake, and residual feed intake (RFI) were also measured or calculated. Results reported here represent data from 197 mature male mice from all replicates. There were no differences in BW (P = 0.91) between the selection lines. Selection had an effect on lean percentage (P = 0.02), with MH mice being leaner. Fat percentage differences between the selection lines tended toward significance (P = 0.13). Livers of MH mice were approximately 13% larger than livers of ML mice (P = 0.01). An effect of selection was observed (P < 0.01) in feed intake per unit BW, with MH mice consuming 29% more feed than ML mice in G58. Differences in state 2 and state 4 respiration rates were significant (P = 0.01), whereas state 3 rates approached significance (P = 0.06). Mitochondria of MH mice respired at a greater rate than mitochondria of ML mice in all states of respiration; ML mice had respiratory control ratios that were, on average, 8% greater than MH mice (P = 0.14). Although this difference only tended toward significance, we suspect a greater degree of coupling of mitochondrial processes exists in ML animals. Mice selected for reduced heat loss had ADP:oxygen ratios that were approximately 20% greater than MH mice (P = 0.03). Therefore, greater mitochondrial efficiency was expressed in the ML animals. Within a line-replicate, there was no correlation between ADP:O and feed intake per unit BW (P = 0.71). In addition, no correlation of ADP:O and RFI existed (P = 0.92). Although the selection lines differed in mitochondrial traits, including overall mitochondrial efficiency (ADP:oxygen), these differences were not a significant underlying cause of variation in feed intake per unit BW or in RFI estimates.

Selection for high and low oxygen consumption altered hepatic mitochondrial energy efficiency in mice

“…The digested materials are used as energy for production and basal maintenance. McDonald et al (2009) reported that this divergently selected line of mice at G58 differed in all states of mitochondrial respiration, although these differences were not a significant underlying cause of variation in feed intake per unit body weight (BW) or in residual feed intake. Genetic improvement to decrease the maintenance energy requirements should increase the energy proportion of energy partitioned into meat, milk or egg production, and decrease the feed cost.…”

“…The OC measurement reflects the basal metabolic rate more directly than does heat loss on the definition of a physiological calorie. McDonald et al (2009) and Murphy et al (2013) reported a difference in hepatic mitochondrial efficiency between lines of mice divergently selected for heat loss. We placed the mouse in the airtight container, including the carbon dioxide absorbent beforehand, and measured the amount of decompression for 5 min.…”

Effects of ad libitum and restricted feeding on early production performance and body composition of Yorkshire pigs selected for reduced residual feed intake

“…The main biological factors that contribute to variation in RFI have been partially quantified in mice (McDonald et al, 2009), poultry (Luiting, 1990) and beef cattle (Richardson and Herd, 2004). As reviewed by Herd and Arthur (2008), in beef cattle, approximately 73% of the variation in RFI is accounted by factors that include activity, feed intake patterns, behavior, stress, digestibility, protein turnover and tissue metabolism.…”

The biological control of voluntary exercise, spontaneous physical activity and daily energy expenditure in relation to obesity: human and rodent perspectives

“…Although direct and indirect calorimetry are seen as the most reliable and accurate methods for assessing energy expenditure (e.g. Ravussin et al, 1986;Joosen et al, 2005;McDonald et al, 2009), these techniques are not feasible for individuals moving about in their normal environment. Hence, DLW is considered the gold standard for capturing DEE in free-living populations (Speakman, 1997;Nagy, 2001;Nagy, 2005;Westerterp and Speakman, 2008).…”