Age-associated changes in gene expression in skeletal muscle of healthy individuals reflect accumulation of damage and compensatory adaptations to preserve tissue integrity. To characterize these changes, RNA was extracted and sequenced from muscle biopsies collected from 53 healthy individuals (22–83 years old) of the GESTALT study of the National Institute on Aging–NIH. Expression levels of 57,205 protein-coding and non-coding RNAs were studied as a function of aging by linear and negative binomial regression models. From both models, 1134 RNAs changed significantly with age. The most differentially abundant mRNAs encoded proteins implicated in several age-related processes, including cellular senescence, insulin signaling, and myogenesis. Specific mRNA isoforms that changed significantly with age in skeletal muscle were enriched for proteins involved in oxidative phosphorylation and adipogenesis. Our study establishes a detailed framework of the global transcriptome and mRNA isoforms that govern muscle damage and homeostasis with age.

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The allometric theory of metabolism predicts that the rate of biological aging is proportional to an organism’s size and metabolic rate (MR). Here we test this hypothesis in humans by generating longitudinal, multi-modal signatures of aging in primary human fibroblasts. Relative to metabolic rates in the human body, isolated cells exhibit markedly elevated MR and operate closer to their maximal energy production capacity. Accordingly, per-cell division, isolated cells display accelerated telomere shortening and increased rate of DNA methylation aging. Moreover, despite a marked reduction in division rate towards the end of life, mass-specific MR increases exponentially, reflecting hypermetabolism. We develop a theoretical-mathematical model that accounts for a partitioning of energetic costs related to both growth or maintenance, quantifying the potential origins of hypermetabolism in vitro, and with advancing age. Moreover, we define genome-wide molecular rescaling factors that confirm and quantify the systematic acceleration of molecular aging kinetics in cultured fibroblasts, and use this approach to show how metabolic and pharmacological manipulations that increase or decrease MR predictably accelerate or decelerate the rates of biological aging. The interconnected speedup of energetic and molecular dynamics across the lifespan of human cells has important theoretical and clinical implications for aging biology.

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