Harnessing Muscle-specific Atrophy Susceptibility to Disentangle the Mechanisms of Disuse Atrophy in Human Skeletal Muscle Atrophy (iMOB)

Skeletal muscles host ~40% of all protein in the body. Muscles are not only crucial for locomotion but also represent the body's largest metabolically active tissue, glucose disposal site and fuel reservoir for other organs in pathological conditions (i.e., supply of amino acids to the liver for gluconeogenesis). Muscle atrophy is characterized by a reduction in cross sectional area (CSA) and length and occurs in many common illnesses (e.g. cancers (1), renal/heart failure, sepsis, genetic diseases, neurodegenerative disorders etc). It is also prevalent in situations of reduced neural input such as leg casting after fractures (2), bed-rest, spinal cord injury (3), space flight and chronic physical inactivity. Atrophy results in a loss of muscle power and strength (which is related to increased morbidity and mortality (4)) and reduced capacities for whole-body glucose storage and metabolism which causes insulin resistance. Strategies to oppose atrophy are limited but include mechanical loading (5) and the synergistic anabolic effects of nutrients. Although muscle atrophy is of great clinical importance, relatively little mechanistic research has been done in humans. Thus, the aim of this study is to assess the link between the variation in muscle physiological responses to disuse atrophy with variation in protein turnover and molecular-networks. This will not only provide new hypotheses for physiological regulation of human muscle and generate 'intervention targets' derived from clinically relevant human studies, it will also improve understanding of whether the response to disuse is altered with age and determine if mechanistic differences in atrophy resistant and atrophy sensitive muscles might explain inter-muscular variation in susceptibility to atrophy.

This study aims to define the molecular and metabolic mechanisms causing disuse atrophy in both young and older individuals and explore how and why some muscles are protected against it. The study will also assess temporal aspects of disuse atrophy (in younger individuals only) to explore the mechanistic basis for the more rapid atrophy observed in the early days of disuse.