Abstract
Human aging is characterized by both physical and physiological frailty. A key feature of frailty, sarcopenia is the age-associated decline in skeletal muscle mass, strength, and endurance that characterize even the healthy elderly. Increases in adiposity, particularly in visceral adipose tissue, are almost universal in aging individuals and can contribute to sarcopenia and insulin resistance by increasing levels of inflammatory cytokines known collectively as adipokines. Aging also is associated with declines in adaptive and innate immunity, known as immune senescence, which are risk factors for cancer and all-cause mortality. The cytokine interleukin-15 (IL-15) is highly expressed in skeletal muscle tissue and declines in aging rodent models. IL-15 inhibits fat deposition and insulin resistance, is anabolic for skeletal muscle in certain situations, and is required for the development and survival of natural killer (NK) lymphocytes. We review the effect that adipokines and myokines have on NK cells, with special emphasis on IL-15. We posit that increased adipokine and decreased IL-15 levels during aging constitute a common mechanism for sarcopenia, obesity, and immune senescence.
Highlights
AND PRELIMINARY OBSERVATIONSAn inevitable consequence of human and rodent aging is sarcopenia--loss of muscle mass [1]
Obesity, and declining immunity in aging, we speculated that these conditions are linked processes, which are controlled by adipose tissuederived and skeletal muscle-derived cytokines, known as adipokines and myokines, respectively (Figure 1)
We propose that the link between body composition and immunity in aging is due to increased expression of adipokines and decreased expression of myokines that affect the immune system
Summary
AND PRELIMINARY OBSERVATIONSAn inevitable consequence of human and rodent aging is sarcopenia--loss of muscle mass [1]. Obesity, and declining immunity in aging, we speculated that these conditions are linked processes, which are controlled by adipose tissuederived and skeletal muscle-derived cytokines, known as adipokines and myokines, respectively (Figure 1). Adipokine-producing cells include adipocytes themselves, as well as adipose tissue leukocytes.
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