Carbohydrate-supported mitochondrial respiration is maintained during short-term bed rest in healthy young adults

Abstract

Bed rest is common during hospitalization and has been shown to initiate skeletal muscle atrophy and impair metabolic function. Skeletal muscle mitochondria are dynamic organelles that adapt to changes in energy demand, and prolonged bed rest has been associated with impaired mitochondrial function in skeletal muscle. However, the effects of clinically relevant, short-term bed rest on the time course of mitochondrial respiratory adaptations remain unclear. We aimed to characterize the time course change in mass-specific carbohydrate-supported skeletal muscle mitochondrial respiration during short-term bed rest in healthy young adults. Twelve healthy, recreationally active young adults (7 females: age 20.6±1.7 years, BMI 21.4±1.6 kg/m2; 5 males: age 21.1±3.6 years, BMI 22.9±1.7 kg/m2) completed 5 days of diet-controlled bed rest. Skeletal muscle biopsies were collected from the vastus lateralis on days 0, 1, 3, and 5 of bed rest. Carbohydrate-supported mitochondrial respiration was measured in permeabilized skeletal muscle fibres using high-resolution respirometry (Oroboros Oxygraph-2K). We observed no significant changes in mass-specific maximal adenosine diphosphate (ADP)-stimulated Complex I- and Complex I+II-supported respiration across 5 days of bed rest (p=0.08). Moreover, bed rest had no effect on the apparent Km of ADP (day 0=392.7, day 1=382.6, day 3=351.3, day 5=379). These findings demonstrate that mass-specific carbohydrate-supported mitochondrial respiratory capacity and ADP sensitivity are maintained across 5 days of bed rest in healthy young adults. In contrast to mitochondrial impairments reported in response to longer periods of bed rest, these findings suggest that clinically relevant bed rest does not significantly impair mitochondrial respiration. This may indicate that mitochondrial respiratory dysfunction develops later than other physiological adaptations such as muscle atrophy and metabolic dysfunction, which have been reported following short-term bed rest. Further investigation integrating mitochondrial morphology with respiratory measurements is needed to characterize the structural mechanisms underlying early mitochondrial remodelling in short-term bed rest.Faculty Supervisor: Dr. Chris McGlory