Impact of lifelong sedentary behavior on mitochondrial function of mice skeletal muscle

Abstract

This study investigated the impact of lifelong sedentariness on skeletal muscle mass and mitochondrial function. Thirty C57BL/6 strain mice (2 months) were randomly divided into three groups (young-Y; old sedentary-OS; old active-OA). Young animals were sacrificed after 1 week of quarantine, and OS and OA groups were individually placed into standard cages and in cages with running wheels, respectively, until sacrifice (25 months). Body weights and hind-limb skeletal muscle wet weights were obtained from all groups. Mitochondrial respiratory functional measures (i.e., state 3 and 4 respiration, respiratory control ratio, and ratio of nanomoles of ADP phosphorylated by nanomoles of O2 consumed [ADP/O]) and biochemical markers of oxidative damage (aconitase activity, protein carbonyl derivatives, sulfhydryl groups) were measured in isolated mitochondrial suspensions. Our results reveal that lifelong sedentary behavior has a negative impact on the age-related loss of skeletal muscle mass and on the isolated mitochondrial function of mixed skeletal muscle of mice, which is associated with an increased oxidative damage to mitochondrial biomolecules.

Figure 1.

Consecutive ADP stimulation test. See text for detailed description.

Figure 2.

Lifelong voluntary physical activity. Data points represent the daily average distance per day (km) (mean ± SD).

Figure 3.

Functional data obtained from skeletal muscle mitochondria isolated from young, old sedentary, and old active animals with complex I–linked substrates, pyruvate (5 mM), and malate (2 mM), in the consecutive ADP stimulation test. Data are mean ± SD of 10 separate experiments in young and old active animals and 8 separate experiments in old sedentary animals. State 3 and state 4 respiratory rates are expressed as nmol of O₂ consumed per minute per mitochondria (mit). RCR, respiratory control ratio; ADP/O, number of nanomoles of ADP phosphorylated by nanomoles of O₂ consumed per mitochondria. *Significantly different from young animals (p <. 05); **Significantly different from old active animals (p < .05); +Significantly different from first cycle (p < 0.05); and #Significantly different from first and second cycle (p < .05).

Figure 4.

Schematic representation of the assay IV (six ADP “cycles”) from the consecutive ADP-stimulation test in examples of one young, one old sedentary, and one old active animal.

Figure 5.

Acute biochemical alterations induced by the consecutive ADP stimulation test in skeletal muscle mitochondria isolated from young, old sedentary, and old active animals. Prestimulation (pre-) represents basal conditions; post- (3 ADP) and post- (6 ADP) represent the acute alterations induced by 3 and 6 ADP additions, respectively. Data are mean ± SD. Biochemical data represent ten experiments in young and old active animals and 8 separate experiments in old sedentary animals. Data from SH groups are expressed as nmol per mitochondria. Protein carbonyls and cytochrome c data are expressed as optical density arbitrary units. Protein carbonyl formation (blots) shows a representative pattern of anti-dinitrophenol–specific interaction with DNP for each group. Immediately below the cytochrome c histogram, the panel shows representative Western blots from each group and ADP stimulation test condition. *Significantly different from young animals (p < .05); **Significantly different from old active animals (p < .05); and +Significantly different from pre-stimulation (p < .05).