Using RNA sequencing to examine age-dependent skeletal muscle transcriptome response to bed rest-induced atrophy, and age independent disuse-induced insulin resistance

Short-term bed rest is used to simulate muscle disuse in humans. In our previous reports, we found that 5d of bed rest induced a ~4% loss of skeletal muscle mass in OLD (60-79 y) but not YOUNG (18-28 y) subjects. Identifying muscle transcriptional events in response to bed rest and age-related differences will help identify therapeutic targets to offset muscle loss in vulnerable older adult populations. Skeletal muscle dysregulation during bed rest in the old may be driven by alterations in molecules related to fibrosis, inflammation, and cell adhesion. This information may aide in the development of mechanistic-based therapies to combat muscle atrophy during short-term disuse. Short-term muscle disuse is also characterized by skeletal muscle insulin resistance, though this response is divergent across subjects. The mechanisms regulating inactivity-induced insulin resistance between populations that are more or less susceptible to disuse-induced insulin resistance are not known, and delineated by age. High Susceptibility participants were uniquely characterized with muscle gene responses described by a decrease in pathways responsible for lipid uptake and oxidation, decreased capacity for triglyceride export (APOB), increased lipogenesis (i.e., PFKFB3, FASN), and increased amino acid export (SLC43A1). Overall design: RNA was isolated and sequenced from muscle biopsies obtained from the vastus lateralis of YOUNG (N=9) and OLD (N=18) men and women before and after five days of bed rest. Sequencing libraries (18 pM) were chemically denatured and applied to an Illumina TruSeq v3 single read flowcell using an Illumina cBot. Hybridized molecules were clonally amplified and annealed to sequencing primers with reagents from an Illumina TruSeq SR Cluster Kit v3-cBot-HS (GD-401-3001). Following transfer of the flowcell to an Illumina HiSeq 2500 instrument (HCS v2.0.12 and RTA v1.17.21.3), a 50 cycle single read sequence run was performed using TruSeq SBS v3 sequencing reagents (FC-401-3002). The design formula was constructed by following the section on group-specific condition effects, individuals nested within groups in the DESeq2 vignette.   The design included age + age:nested + age:time to test for differences in bed rest in old subjects, young subjects and the interaction, in this case if bed rest effects are different between the two age groups (where age is young or old, nested is patient number nested by age and time is pre- or post-bed rest). A similar design was used to determine susceptibility to disuse-induced insulin resistance, where “susceptibility” took the place of “age”.

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Mahmassani ZS, Reidy PT, McKenzie AI, Stubben C, Howard MT, Drummond MJ