Muscle is increasingly being recognized as having the character of an endocrine organ. When muscles contract they release signaling molecules called myokines, which have various regulatory effects throughout the body and brain, affecting visceral fat, inflammation levels, and cognition. For example, here’s a quote from a recent paper “Skeletal muscle has emerged as a potent regulator of immune system function [and] might be the central integrator between sarcopenia and immune senescence in an aging biological system. Therapeutic approaches targeting skeletal muscle might be able to restore both muscle and immune system function.”1
Firstly, let’s define sarcopenia:
“Sarcopenia is a type of muscle loss (muscle atrophy) that occurs with aging and/or immobility. It is characterized by the degenerative loss of skeletal muscle mass, quality, and strength. The rate of muscle loss is dependent on exercise level, co-morbidities, nutrition and other factors. The muscle loss is related to changes in muscle synthesis signalling pathways. It is distinct from cachexia, in which muscle is degraded through cytokine-mediated degradation, although both conditions may co-exist. Sarcopenia is considered a component of frailty syndrome. Sarcopenia can lead to reduced quality of life, falls, fracture, and disability.”2
Back to the original article at the heart of the discussion. I simply want to highlight the main points.
1. Yes, we know that sarcopenia can result in a functional decline. (i.e. “increased risk of falls leading to fractures, disability and functional impairment, dysphagia, lower quality of life, and all-cause mortality.”) There is also a correlation with sarcopenia and risk of infection and/or pneumonia.
2. “Muscle is increasingly recognized as an organ with immune regulatory properties. As such, skeletal muscle cells modulate immune function by signalling through different soluble factors, cell surface molecules or cell-to-cell interactions.”
3. “Muscle is increasingly recognized as an endocrine organ producing and releasing cytokines and other peptides, which exert autocrine, paracrine and endocrine activity on numerous tissues. Consequently, these soluble factors are commonly termed myokines.” There are more than 300 potential myokines.
4. “As humans age, the immune system undergoes drastic changes. The umbrella term immune senescence is used to encompass these changes.” Aging is associated with pro-inflammatory molecules and studies suggest an impact of low-grade inflammation on muscle health. “Consequently, the muscle-immune system connection might be bidirectional: Chronic, low-grade inflammation induces muscle catabolism via pleiotropic mechanisms mediated by the inflammatory secretome. Concurrently, homeostasis of skeletal muscle is, in part, responsible for healthy immune function.”
5. “Exercise, a broad term summarizing physical activity with the goal of preserving or improving physical fitness, has already proven effective. In regard to sarcopenia, exercise has emerged as the most important and consistent treatment option, improving skeletal muscle metabolism and function. Importantly, physical activity has also been shown to support immune function in old age, specifically improving vaccine responses and reducing chronic inflammation.”
Exercise is huge determinant of healthy aging on a far bigger scale than we have previously understood. Naturally this has to transfer to our canine companions (as some of the information on the topics above are from animal studies as well as human). So, all in all, we need to advocate for keeping dogs active throughout their lifespan – for the sake of their entire body systems!
1. Nelke C, Dziewas R, Minnerup J, Meuth SG, Ruck T. Skeletal muscle as potential central link between sarcopenia and immune senescence. EBioMedicine. 2019 Nov;49:381-388.
2. Sarcopenia. https://en.wikipedia.org/wiki/Sarcopenia (accessed Sep 5, 2021)