Muscle also represents an energy repository and storehouse of amino acids and nitrogen which is liberated during states of acute infection, injury and starvation (6–8). Muscle-derived mechanical signals, secreted factors (known as “myokines”) (4), and exosomes (5) all exert substantial influence over adjacent tissues such as bone as well as distant tissues including liver, adipose and the pancreas. In addition to providing force production for respiration, eating and locomotion, skeletal muscle acts as an endocrine organ regulating whole body metabolism, glucose and lipid metabolism, inflammation, and even sleep and circadian rhythm (1–3). Skeletal muscle is a dynamic tissue comprising 40% of the total mass of a human body. What follows is an invited review summarizing a presentation by Teresa Zimmers in the Master Class Session of the 2018 Annual Meeting of the Shock Society. These approaches have utility for studies of myopenia, sarcopenia, cachexia, and acute muscle growth or atrophy in the setting of health or injury. In this invited review, we summarize techniques and methods to assess and manipulate muscle size and muscle mass in experimental systems, including cell culture and rodent models. Defining mechanisms of muscle growth regulation holds significant promise to find interventions that promote health and diminish morbidity and mortality after trauma, sepsis, inflammation, and other systemic insults. Muscle mass is highly plastic, appropriate to its role as reservoir, and subject to striking genetic control. In contrast, low muscle mass correlates with dysmetabolism, dysmobility, and poor survival. Overall, greater muscle mass is linked to greater insulin sensitivity and glucose disposal, strength, power, and longevity. As the primary reservoir for amino acids, skeletal muscle regulates whole-body protein and glucose metabolism by providing substrate for protein synthesis and supporting hepatic gluconeogenesis during illness and starvation. Beyond providing support and contraction, skeletal muscle also exerts essential roles in temperature regulation, metabolism, and overall health. Healthy muscle is essential for eating, posture, respiration, reproduction, and mobility, as well as for appropriate function of the senses including taste, vision, and hearing. Trauma, burn injury, sepsis, and ischemia lead to acute and chronic loss of skeletal muscle mass and function. The work cannot be changed in any way or used commercially without permission from the journal. This is an open access article distributed under the terms of the Creative Commons Attribution-Non Commercial-No Derivatives License 4.0 (CCBY-NC-ND), where it is permissible to download and share the work provided it is properly cited. The authors report no conflicts of interest. DHAJ was funded in part through the Adam Herbert Fellowship and the IU Simon Cancer Center Cancer Biology Training Program. JER was funded in part through an NIH training grant to Hal Broxmeyer (Grant T32 HL007910). This work was funded in part by grants to TAZ from the National Institutes of Health (Grants R01CA122596 and R01CA194593), the VA (Grant I01BX004177), the IU Simon Cancer Center, and the Lustgarten Foundation. ![]() Walnut Street, R3-C518, Indianapolis, IN 46202. Zimmers, PhD, HH Gregg Professor of Cancer Research, Professor of Surgery, 980 W. ∗∗Indiana University Simon Cancer Center, Indianapolis, IndianaĪddress reprint requests to Teresa A. ¶Indiana Center for Musculoskeletal Health, Indianapolis, Indiana Roudebush Veterans Administration Medical Center, Indianapolis, Indiana §Department of Otolaryngology-Head & Neck Surgery, Indiana University School of Medicine, Indianapolis, Indiana ‡Department of Anatomy, Cell Biology & Physiology, Indiana University School of Medicine, Indianapolis, Indiana †Department of Surgery, Indiana University School of Medicine, Indianapolis, Indiana ∗Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, Indiana
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