Exercise regulation of adipose tissue

Abstract

Exercise training results in adaptations to numerous organ systems and offers protection against metabolic disorders including obesity and type 2 diabetes, and recent reports suggest that adipose tissue may play a role in these beneficial effects of exercise on overall health. Multiple studies have investigated the effects of exercise training on both white adipose tissue (WAT) and brown adipose tissue (BAT), as well as the induction of beige adipocytes. Studies from both rodents and humans show that there are exercise training-induced changes in WAT including decreased cell size and lipid content, and increased mitochondrial activity. In rodents, exercise training causes an increased beiging of WAT. Whether exercise training causes a beiging of human scWAT, as well as which factors contribute to the exercise-induced beiging of WAT are areas of current investigation. Studies investigating the effects of exercise training on BAT mass and function have yielded conflicting data, and hence, is another area of intensive investigation. This review will focus on studies aimed at elucidating the mechanisms regulating exercise training induced-adaptations to adipose tissue.

Exercise-induced adaptations to white and brown adipose tissue

“…Given that exercise also increases energy expenditure and heat production, it would not be surprising if BAT was downregulated with exercise to maintain body temperature. However, studies investigating the effects of exercise on BAT have yielded conflicting results (Stanford and Goodyear, 2016). In some studies, investigators have shown an increase in mitochondrial activity in rodent BAT (Ignacio et al, 2012;Yoshioka et al, 1989), whereas other studies have revealed a decrease in mitochondrial activity (Wu et al, 2014) and glucose uptake in BAT in exercise-trained humans (Vosselman et al, 2015;Motiani et al, 2017).…”

“…However, this mechanism does not make sense in the context of exercise-induced beiging because exercise increases heat production (Saugen and Vøllestad, 1995). Several hypotheses have been proposed as the underlying mechanism (Stanford and Goodyear, 2016), one of which is increased sympathetic innervation, which is known to occur in scWAT during exercise (Nedergaard et al, 2014;Ranallo and Rhodes, 1998). Other hypotheses focus on the exercisestimulated release of myokines, including irisin (Boström et al, 2012), myostatin (Feldman et al, 2006), meteorin-like 1 (Metrnl) (Rao et al, 2014), lactate (Carriere et al, 2014) and β-aminoisobutyric acid (BAIBA) (Roberts et al, 2014), as well as other secreted factors, including brain-derived neurotrophic factor (BDNF) (Cao et al, 2011).…”

“…There are also specific adaptations to each WAT depot, including adaptations to the structural lipidomic profile changes in scWAT (May et al, 2017) and the beiging of scWAT in rodents (Stanford et al, 2015a,b;Sutherland et al, 2009;Trevellin et al, 2014;Boström et al, 2012;Cao et al, 2011;Stanford and Goodyear, 2016) (Fig. 1).…”

“…It has been suggested that exercise-induced beiging of scWAT occurs because exercise decreases the adipocyte size and lipid content in scWAT, thus decreasing insulation of the body and necessitating heat production, resulting in the beiging of scWAT (Nedergaard et al, 2014;Stanford and Goodyear, 2016). This hypothesis presents a potential evolutionary significance; it is likely that foraging animals traveling great distances to find food would need a certain amount of plasticity in their adipose tissue to maintain body temperature and, thus, the ability to beige white adipocytes would be evolutionarily advantageous.…”

Is human white adipose tissue bright during exercise?

“…However, in some cytokines (e.g., IL-6 and TNF-a, among others) derived from adipose tissue or skeletal muscle, various nutrients and metabolites can induce browning (5,6). Although it seems reasonable to increase thermogenesis during cold exposure, it may seem counterintuitive to increase thermogenesis under conditions such as exercise and metabolic stress.…”